JP2006045520A - Cyan ink and ink set - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water base ink which can be used even by a little ink drop amount to have a sufficiently large area factor, can provide a highly concentrated image, and is excellent in storage stability; and an ink set which allows employment of a plurality of the water base inks to form an image with abrasion resistance improved. <P>SOLUTION: The cyan ink comprises water, a water-insoluble dyestuff, and a plurality of water-soluble organic solvents containing a good solvent and a poor solvent for the water-insoluble dyestuff, and is applied for an ink set holding a plurality of water base inks, wherein the cyan ink has a B/A value of within a specific range which is a ratio of the good solvent to the poor solvent, the poor solvent being a water-soluble organic solvent having the maximum Ka value among a plurality of Ka values of the water-soluble organic solvents, and the B/A value satisfying a specific relationship with a B/A value of any other water base ink than the cyan inks held in the ink set. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cyan ink containing a water-insoluble colorant and an ink set having the cyan ink, and more particularly to a cyan ink suitable for an ink jet recording system.

  Conventionally, it has been known that an ink containing a water-insoluble colorant such as a pigment (pigment ink) as a colorant gives an image excellent in fastness such as water resistance and light resistance. In recent years, various techniques have been proposed for the purpose of further improving the image density of an image formed with such ink.

  For example, it has been proposed to further improve the image density by using an ink containing self-dispersing carbon black and a specific salt (see, for example, Patent Document 1). Also, an ink for inkjet recording which is a composition containing pigment, polymer fine particles, a water-soluble organic solvent and water, and a polyvalent metal salt-containing aqueous solution are attached to a recording medium, and the ink composition and the polyvalent metal salt aqueous solution There is a proposal of a technique for forming a high-quality image by reacting (see, for example, Patent Document 2). In any of these techniques, the pigment existing in a dispersed state in the ink is forced to aggregate on the surface of the recording medium, thereby suppressing the penetration of the pigment into the recording medium. I get a high image.

Further, since the pigment ink aggregates the pigment on the recording medium, the pigment tends to remain on the surface of the recording medium. In particular, when printing is performed using pigment ink that does not contain resin or the like on plain paper, the pigment particles themselves remain on the surface of the recording medium, so that even after a sufficient amount of time has elapsed after printing, the image is strengthened. Dirt may form when rubbed.
JP 2000-198955 A JP 2000-63719 A

  However, according to the study by the present inventors, in the above-described technique, since the pigment particles are aggregated on the recording medium, the surface of the recording medium is coated with a color material as compared with the volume of the ink droplet. It has been found that the area (so-called area factor) that can be produced may not be sufficient. This means that the amount of applied ink required to obtain the same image density is larger in the above-described technology than in a pigment ink in which a conventional pigment is dispersed with a polymer dispersant or the like. There was room for improvement in this regard. There is also a method for obtaining a large area factor even with a small volume of ink droplets by increasing the permeability of the ink to the recording medium. However, when the ink permeability is increased, the ink permeates not only on the surface of the recording medium but also in the depth direction of the recording medium, and a sufficient image density may not be obtained.

  The present inventors have pursued the advantages and disadvantages of each conventional ink and analyzed the characteristics of the image itself. As a result, the higher the concentration of the color material in the ink, the more excess color material exists on the surface of the recording medium, or dots that have a visually dispersed shape are formed. As a result, it has been found that useless coloring materials that are not involved in color development are generated.

  In addition, the present inventors have used other inks to remove the printed portion and the white background caused by rubbing the secondary color image portion formed using cyan ink such as green and blue with a finger or the like. Faced with the problem that it may be more conspicuous than the image portion such as the secondary color formed in this way, it has been recognized that further improvement is necessary.

The present inventors have found that an image superior to the conventional one can be formed by solving at least one of the above technical problems. The problems found by the inventors are listed below. The present invention solves at least one of the following problems.
(1) When the pigment present in a dispersed state in the ink is forcibly agglomerated on the surface of the recording medium, the surface of the recording medium can be coated with a color material as compared with the volume of the ink droplets. The area (so-called area factor) may not be sufficient. Therefore, the problem is that the amount of ink applied necessary to obtain the same image density increases.
(2) When increasing the permeability of the ink, the ink penetrates not only in the surface of the recording medium but also in the thickness direction of the recording medium, and the color material is distributed at a high concentration near the surface of the recording medium. The problem of not being able to achieve high image density.

  Accordingly, an object of the present invention is to provide a cyan ink having a sufficiently large area factor and a high image density even with a small amount of ink droplets, and having excellent storage stability. is there.

  Another object of the present invention is to form an image by using a plurality of inks having a sufficiently large area factor and capable of obtaining an image having a high image density even with a small ink droplet amount. An object of the present invention is to provide a cyan ink capable of improving the scratch resistance in the case of the above.

  Another object of the present invention is to provide an ink set that has a sufficiently large area factor even with a small amount of ink droplets, can provide an image with high image density, and is excellent in storage stability. It is in.

  The above object is achieved by the present invention described below.

That is, the cyan ink according to the present invention contains at least water, a water-insoluble colorant, a plurality of water-soluble organic solvents including a good solvent for the water-insoluble colorant and a poor solvent for the water-insoluble colorant, In a cyan ink applied to an ink set having four types of water-based inks, cyan ink, magenta ink, yellow ink, and black ink, the content (% by mass) of a good solvent contained in the cyan ink is A ₁ , When the content (% by mass) of the poor solvent is B ₁ , B ₁ / A ₁ is 0.5 or more and 3.0 or less, and the water-soluble organic solvents are obtained by the Bristow method. A water-soluble organic solvent exhibiting the maximum Ka value among the respective Ka values is the poor solvent, and a good solubility contained in any aqueous ink other than the cyan ink included in the ink set. When the content (mass%) of the medium is A and the content (mass%) of the poor solvent is B, the following formula (I) is satisfied.

(B ₁ / A ₁ ) / (B / A) <1 (I)
The ink set according to the present invention includes a plurality of water-soluble organic materials including the cyan ink having the above-described configuration, and at least water, a water-insoluble colorant, a good solvent for the water-insoluble colorant, and a poor solvent for the water-insoluble colorant. It has four types of water-based inks, magenta ink, yellow ink, and black ink, each containing a solvent.

The cyan ink according to the present invention contains at least water, a water-insoluble colorant, a plurality of water-soluble organic solvents including a good solvent for the water-insoluble colorant and a poor solvent for the water-insoluble colorant. Cyan ink applied to an image forming apparatus using cyan ink, magenta ink, and yellow ink,
When the content (% by mass) of the good solvent contained in the cyan ink is A ₁ and the content (% by mass) of the poor solvent is B ₁ , B ₁ / A ₁ is 0.5 or more and 3.0. The water-soluble organic solvent that shows the maximum Ka value among the Ka values of the plurality of water-soluble organic solvents obtained by the Bristow method is the poor solvent, and is included in the image forming apparatus. When the content (% by mass) of the good solvent and B (% by mass) of the poor solvent contained in any aqueous ink other than the applied cyan ink is B, the following formula (I) is satisfied. It is characterized by that.

(B ₁ / A ₁ ) / (B / A) <1 (I)
The technical gist of the present invention is conceptually summarized. In the water-based ink containing at least water, a water-insoluble colorant, and a plurality of water-soluble organic solvents, the plurality of water-soluble organic solvents are the water-insoluble colorant. A water-soluble organic solvent having a maximum Ka value among the Ka values of each of the plurality of water-soluble organic solvents, which is a good solvent for the water-soluble material and a poor solvent for the water-insoluble colorant, and is determined by the Bristow method. A poor solvent, and the poor solvent penetrates into the recording medium prior to the good solvent, and the water-insoluble colorant aggregates in the liquid medium rich in the good solvent on the recording medium surface side. It is a cyan ink characterized by assisting.

  With this configuration, there is an effect that the ink does not need to contain a large amount of wasted color material that is not involved in the image density due to being diffused in the recording medium as in the case of conventional water-based ink. can get. In addition, the image can be in an ideal state. That is, a large amount of color material does not exist on the recording surface of the recording medium, and at the same time, the color material does not reach the surface opposite to the recording surface inside the recording medium (double-sided recording is possible). As a result, a uniform image having a high image density can be formed on the recording surface side of the recording medium.

  Further, another technical gist of the present invention is conceptually summarized. In the cyan ink used when forming an image using a plurality of inks, the ratio of the poor solvent to the good solvent in the cyan ink is different from that of the cyan ink. The cyan ink is characterized by being relatively lower than the ratio of the poor solvent to the good solvent in the ink.

  With this configuration, when an image is formed using a plurality of inks, the water-insoluble color material in the cyan ink existing on the recording surface of the recording medium is relatively less than the water-insoluble color material of other inks. Scratch resistance in an image of a secondary color such as a secondary color can be improved.

  According to the present invention, it is possible to provide a cyan ink having a sufficiently large area factor and a high image density even with a small amount of ink droplets and having excellent storage stability. According to another embodiment of the present invention, a plurality of inks having a sufficiently large area factor and a characteristic capable of obtaining an image with a high image density even with a small ink droplet amount are used. A cyan ink capable of improving the scratch resistance when forming an image can be provided. According to another embodiment of the present invention, an ink set having a sufficiently large area factor and a high image density can be obtained even with a small amount of ink droplets, and further excellent in storage stability. Can be provided.

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

  First, the poor solvent and the good solvent in the present invention will be described. The details of the definition will be described later. Regardless of the dispersion method of the water-insoluble color material used as the color material, the water-insoluble color material having a good dispersion stability with respect to the water-soluble organic solvent is regarded as a good solvent, and the bad one. Is a poor solvent.

  The water-based ink according to the present invention is characterized by focusing on the water-soluble organic solvent contained in the ink together with the water-insoluble colorant, and the water-insoluble colorant having the function of dissolving or dispersing the water-insoluble colorant. The materials are classified into those exhibiting the behavior as the poor solvent and those exhibiting the behavior as the good solvent, and the ratio (B / A) of the poor solvent to the good solvent in the ink is in a specific range. The ink is designed so that it is adjusted to the inside. Another feature of the ink according to the present invention is that each of a plurality of water-soluble organic solvents obtained by the Bristow method, in addition to the above-described specific configuration of the water-soluble organic solvent (the measurement method will be described later). The water-soluble organic solvent showing the maximum Ka value is a poor solvent.

  As a result, the dispersion stability of the water-insoluble colorant in the ink is very excellent, and at the same time a sufficiently large area factor even when the amount of ink droplets is small when printed on a recording medium, particularly plain paper. In addition, an image having a high image density and an excellent storage stability can be obtained.

[Image formation mechanism]
Here, an example of the mechanism of image formation in the present invention will be described. When the water-based ink according to the present invention is printed on a recording medium, particularly plain paper, it is considered that it is possible to provide a very excellent print density and print quality for the reasons described below.

  That is, as shown in FIG. 8A, when the ink droplet 1301 according to the present invention is printed on the recording medium 1300, for example, on plain paper, the ink starts from the moment when the ink lands on the recording medium. The ratio of the good solvent and the poor solvent to the water, the water-insoluble color material, and the water-insoluble color material changes. That is, as shown in FIGS. 8B and 8C, after the ink droplet 1301 has landed on the surface of the recording medium 1300, as the ink is fixed on the recording medium, the ink first evaporates with water. It is considered that the poor solvent 1307 having a high Ka value among the water-soluble organic solvents therein diffuses closer to a perfect circle near the recording medium surface than the good solvent having a low Ka value, thereby forming ink dots.

  FIGS. 8B to 8D are schematic views showing the state of ink from when the ink lands on the recording medium 1300 until it is fixed later. When attention is paid to the spreading state of the ink dots in this case, it is considered that the concentration of the poor solvent is higher in the outer periphery 1302 of the dot in the contact portion between the ink and the paper than in the central portion 1303 of the dot. As a result, ink dots diffuse near the recording medium surface in a shape close to a perfect circle, and in the process of diffusion, the concentration of the poor solvent 1307 rapidly increases with respect to the water-insoluble colorant. Along with this, the dispersion of the water-insoluble colorant is suddenly destabilized, and the water-insoluble colorant aggregates or breaks down. At this time, the surface of the recording medium diffuses while taking a nearly circular border (see FIG. 8B), and the water-insoluble colorant 1304 stays on the surface of the recording medium 1300. It looks as if a bank of water-insoluble colorant has been formed. In this way, it is considered that the dots of the water-insoluble color material are formed in a perfect circle and are fixed on the surface of the recording medium in that state (see FIG. 8C). At this point, the dot formation of the water-insoluble colorant is completed, but the water-soluble organic solvent and the water 1306 in the ink spread radially while further diffusing. In other words, the water-soluble organic solvent and the water 1306 diffuse near the surface of the recording medium even after forming the dots of the water-insoluble colorant. Subsequently, due to evaporation and penetration of the water-soluble organic solvent in the good solvent-rich central portion 1303, the water-insoluble colorant is also deposited in this portion to form dots 1305 (see FIG. 8D). An image formed by the process as described above has a sufficiently large area factor even with a small amount of ink droplets, a high image density, and a high-quality image in which bleeding is effectively suppressed.

  Next, the present inventors apply the water-based ink having the above-described configuration to water-based inks other than cyan ink, that is, magenta ink, yellow ink, and black ink, thereby making the color ink more than conventional ink sets. We thought that an image with excellent balance could be obtained. Therefore, the present inventors examined various performances required for an image formed on plain paper or the like by changing the ratio of the good solvent and the poor solvent for each color. As a result, it was confirmed that the color balance of the obtained image is improved by applying the above-described configuration of the water-based ink to the water-based ink other than the cyan ink, that is, the magenta ink, the yellow ink, and the black ink. It was.

  Cyan ink generally has low brightness. For this reason, even if the amount of the water-insoluble colorant present on the surface of the recording medium is the same, the image obtained using cyan ink is more resistant than the image obtained using magenta ink or yellow ink. Abrasion feels bad. As a result, an image obtained using cyan ink may seem to have a seemingly deteriorated scratch resistance compared to other colors. Therefore, as a result of investigations by the present inventors, by reducing the ratio (B / A) of the poor solvent to the good solvent in the cyan ink relative to other colors, secondary colors such as green and blue are obtained. It has been confirmed that it is possible to reduce image shaving and white background stains that occur when an image printed in color is rubbed. Note that, as described above, the scratch resistance that appears to be deteriorated is referred to as “poor scratch resistance” in the present invention. Further, the apparent improvement in scratch resistance is referred to as “improving scratch resistance” in the present invention.

  The inventor presumes the reason why the above effect is obtained as follows. Here, the mechanism by which the above effect is obtained will be described with reference to FIGS. FIGS. 9A to 9D and FIGS. 10A to 10D are processes for forming an image of a secondary color (here, blue) using cyan ink and another ink (here, magenta ink). 3 is a diagram schematically illustrating a process in which an image is formed after ink droplets are applied to a recording medium such as plain paper. FIG. 9 shows that the (B / A) value of cyan ink is smaller than the (B / A) value of other ink (magenta ink in this case), and FIG. 10 shows that the (B / A) value of cyan ink is other ink. Each case is greater than the (B / A) value of (here magenta ink).

  The penetration process of ink into the recording medium in FIGS. 9 and 10 is basically the same mechanism as described above with reference to FIG. As the (B / A) value of the cyan ink is larger than the (B / A) value of the other inks, the water-insoluble colorant in the cyan ink tends to precipitate more on the surface layer of the recording medium. I understand that. For example, as shown in FIG. 9, when the (B / A) value of cyan ink is relatively smaller than the (B / A) value of other ink (here, magenta ink), the water in the cyan ink It is considered that the ratio of the insoluble color material existing at the position submerged in the depth direction of the recording medium is larger than that of the water insoluble color material in the magenta ink. On the other hand, as shown in FIG. 10, when the (B / A) value of the cyan ink is relatively larger than the (B / A) value of the other ink (magenta ink here), the water in the cyan ink It is considered that the proportion of the insoluble color material existing in the vicinity of the surface of the recording medium is larger than that of the water insoluble color material in the magenta ink. Further, by taking into account the difference in the time for each ink ejection and the ratio of the poor solvent and the good solvent in the ink mixed on the recording medium, the water-insoluble colorant in the cyan ink is replaced with another ink (here, magenta). In comparison with the water-insoluble colorant in the ink), it can be present at a position submerged in the depth direction of the recording medium. In particular, when the (B / A) value of cyan ink is lower than 1.0 and the (B / A) value of other ink (here, magenta ink) is larger than 2.5, other ink ( When an image is formed by applying cyan ink to a recording medium later than magenta ink here, an image is formed using cyan ink and other ink (here magenta ink) that do not satisfy the relational expression (I) of the present invention. Compared to the case of forming, the scratch resistance can be greatly improved.

  Further, the two types of images obtained by setting the (B / A) value of the cyan ink and the (B / A) value of the other ink (magenta ink in this case) as described above are rubbed with a finger to remove the scratch resistance. The degree of sex was confirmed. As a result, the more water-insoluble colorant in the cyan ink is present near the surface of the recording medium, that is, the state as shown in FIG. It turned out that the dirt tends to stand out.

  The present inventors have examined the relationship between the characteristics of the color material and the scratch resistance. As a result, in a secondary color image or the like that tends to increase the amount of applied ink, a water-insoluble color material with low brightness is used for the recording medium. It has been found that the greater the presence in the vicinity of the surface, the more apparent the scratch resistance tends to be felt. In the above description, magenta ink is used as an example of ink that forms a secondary color in combination with cyan ink, but the present invention is not limited to this.

  In addition, when forming a multi-order color image using a plurality of inks, the order of applying ink to the recording medium sinks in the depth direction of the recording medium if the ink with lower lightness is applied earlier. Since most of the water-insoluble colorant can be present at the recessed position, the scratch resistance can be further improved.

[Determination of good and poor solvents]
Under the assumption mechanism as described above, whether the good solvent and the poor solvent used in the present invention can maintain the dispersion state of the water-insoluble colorant satisfactorily, that is, the water-insoluble colorant or the water-insoluble colorant. And a substance that contributes to the dispersion (such as a dispersant or a surfactant described later). Therefore, in the preparation of the water-based ink according to the present invention, when a good solvent and a poor solvent are selected, it is preferable to observe the stability of the dispersion state of the water-insoluble color material to be used and obtain the result. And as a result of various studies on the criteria for determining good and poor solvents that bring about the effects of the present invention in relation to the effects of the present invention, the present inventors have found that the following determination methods are effective. I found out.

  First, a water-insoluble colorant dispersion liquid containing 50% by mass of a water-soluble organic solvent to be determined and 45% by mass of water and containing 5% by mass of a water-insoluble colorant used in the ink in a dispersed state is prepared. When the prepared dispersion was stored at 60 ° C. for 48 hours, the water-insoluble colorant in the liquid had an average particle diameter of 5% by mass of the water-insoluble colorant prepared separately and 95% by mass of water. What is increased compared to the average particle size of the water-insoluble colorant in the aqueous dispersion contained is a poor solvent, and the average particle size of the water-insoluble colorant in the dispersion is the same or decreased. Was defined as a good solvent.

  More specifically, the following method was used to determine whether the water-soluble organic solvent used was a good solvent or a poor solvent for a certain insoluble colorant. First, the following two types of dispersions are prepared: a dispersion A of a water-insoluble colorant and an aqueous dispersion B of the water-insoluble colorant, which contain the water-soluble organic solvent to be judged.

  Dispersion A: The concentration of the water-soluble organic solvent to be determined is 50% by mass, the concentration of the water-insoluble colorant (if a substance that contributes to its dispersion is used, it contributes to the water-insoluble colorant and its dispersion A water-insoluble colorant dispersion having a composition in which the concentration of the total amount with the substance is 5% by mass and the concentration of water is 45% by mass.

  Water dispersion B: The concentration of the water-insoluble colorant (if a substance that contributes to the dispersion is used, the total amount of the water-insoluble colorant and the substance that contributes to the dispersion) is 5% by weight, water An aqueous dispersion of a water-insoluble colorant having a composition of 95% by mass.

Next, the dispersion A was stored at 60 ° C. for 48 hours and then cooled to room temperature, and the average particle size of the water-insoluble colorant of dispersion A was measured using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). ) And the like. In addition, the aqueous dispersion B was measured for the average particle size of the water-insoluble colorant in a state where it was not warmed and stored using a concentrated particle size analyzer in the same manner as described above. Then, when the average particle size values of the respective water-insoluble colorants in the dispersion A and the water dispersion B are defined as the particle size (A) and the particle size (B), these values may be determined according to the following definitions. A distinction was made between solvents and poor solvents.
-Poor solvent: In the above, when the particle size (A) was larger than the particle size (B), the water-soluble organic solvent to be determined was defined as a poor solvent.
-Good solvent: When the particle size (A) is the same as the particle size (B) or when the particle size (A) is smaller than the particle size (B), the water-soluble organic solvent to be determined is defined as the good solvent did.

  Thus, when the ink which has the structure of this invention was prepared using the determined good solvent and poor solvent in the ratio mentioned later, it has confirmed that the above outstanding effects were acquired.

[Ka value of water-soluble organic solvent]
In the present invention, in addition to the above-described specific configuration of the water-soluble organic solvent, the water-soluble organic solvent having the maximum Ka value among the Ka values of each of the plurality of water-soluble organic solvents obtained by the Bristow method is In the case of a poor solvent, the above-described image formation mechanism can be exhibited.

Here, the Ka value obtained by the Bristow method will be described. This value is used as a measure for the penetrability of the liquid into the recording medium. Hereinafter, the ink will be described as an example. 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. 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).

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

[Water-based ink]
The cyan ink according to the present invention requires the water-soluble organic solvent in the ink component to have the above-described configuration in relation to the water-insoluble colorant to be used. A configuration similar to that of ink may be used. Below, each component which comprises the water-based ink of this invention is demonstrated.

  The magenta ink, the yellow ink, and the black ink each contain water, a water-insoluble color material, a plurality of water-soluble organic solvents including a good solvent for the water-insoluble color material and a poor solvent for the water-insoluble color material. There is no particular limitation as long as it is a material, but it is preferable to have the same configuration as that of cyan ink except for the items described below according to hue.

<Aqueous medium>
The aqueous medium constituting the aqueous ink according to the present invention will be described. The aqueous medium is a mixed solvent of water and a water-soluble organic solvent. In the cyan ink of the present invention, the water-soluble organic solvent is discriminated as a good solvent and a poor solvent for the water-insoluble colorant by the method described above. Based on the determination result, the Bristow method is further performed so that at least the good solvent and the poor solvent are mixed in the water-based ink, and the content of each water-soluble organic solvent is within the range defined in the present invention. A water-soluble organic solvent is selected from among a plurality of water-soluble organic solvents determined by the formula (1) so that the water-soluble organic solvent exhibiting the maximum Ka value becomes a poor solvent, and an ink is prepared as appropriate. It will be necessary.

  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 Alcohols such as glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol 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. Moreover, it is preferable to use deionized water.

  In the cyan ink of the present invention, a water-soluble organic solvent is selected so that a water-soluble organic solvent having at least a good solvent and a poor solvent and having a maximum Ka value becomes a poor solvent. The content (% by mass) of the good solvent is A (the total content is indicated when multiple good solvents are used), and the content (% by mass) of the poor solvent is B (multiple poor solvents). When it is used, it means that the total content is adjusted) so that B / A is 0.5 or more and 3.0 or less. In the preferred form of the cyan ink of the present invention, the B / A is preferably 0.5 or more and 1.0 or less, and more preferably B / A is 0.6 or more and 1.0 or less. .

Here, the relationship between the ratio B / A of the poor solvent to the good solvent in the cyan ink and the ratio B / A of the poor solvent to the good solvent in the water-based ink of other colors included in the ink set will be described. When the ratio of the poor solvent and the good solvent in the cyan ink of the present invention is B ₁ / A ₁ , the following equation (B / A value for any aqueous ink other than the cyan ink included in the ink set) It satisfies I). The following formula (I) means that the cyan ink of the present invention has the smallest B / A value among the water-based inks included in the ink set.

(B ₁ / A ₁ ) / (B / A) <1 (I)
In a preferred embodiment of the present invention, it is particularly preferable that the following formula (I ′) is satisfied.

(B ₁ / A ₁ ) / (B / A) <0.6 (I ′)
According to the detailed study by the present inventors, when the content of the good solvent contained in the water-based ink is large, the water-based ink is excellent in storage stability, but is particularly high when the recording medium is plain paper. It is difficult to obtain image density. Conversely, when the content of the good solvent contained in the water-based ink is small, a high image density can be obtained, but the storage stability of the water-based ink may be insufficient.

  On the other hand, if the ratio of the good solvent to the poor solvent in the water-soluble organic solvent in the ink is controlled as described above, it is possible to achieve both the storage stability of the water-based ink and the realization of a high image density. It becomes possible. Furthermore, as described above, when determining each water-soluble organic solvent to be contained in the ink, the Ka value obtained by the Bristow method, which is a measure representing the permeability to the recording medium, is controlled. Thus, even with a small amount of ink droplets, it is possible to achieve an effect that could not be obtained in the past, such that it has a sufficiently large area factor and can realize a high image density.

  In the magenta ink, yellow ink, and black ink other than the cyan ink included in the ink set of the present invention, at least a good solvent and a poor solvent are mixed, and a water-soluble organic solvent that maximizes the Ka value is poor. It is preferable to select a water-soluble organic solvent so as to be a solvent. Further, when the content (mass%) of the good solvent is B and the content (mass%) of the poor solvent is B with respect to the total mass of each water-based ink, B / A is 0.5 or more and 3.0 or less. It is preferable that B / A is 0.5 or more and 1.0 or less, and it is particularly preferable that B / A is 0.6 or more and 1.0 or less.

Here, the relationship between the ratio B / A of the poor solvent to the good solvent in the magenta ink, the yellow ink, and the black ink and the ratio B / A of the poor solvent to the good solvent in the water-based ink of other colors included in the ink set. Will be described. The B / A value for magenta ink is B ₂ / A ₂ , the B / A value for yellow ink is B ₃ / A ₃ , and the B / A value for black ink is B ₄ / A ₄ . At this time, it is preferable that the following formula is satisfied in each color of water-based ink.
Magenta ink 0.6 ≦ (B ₂ / A ₂ ) / (B / A) <1.8 (II)
Yellow ink 0.6 ≦ (B ₃ / A ₃ ) / (B / A) <1.8 (III)
Black ink 0.6 ≦ (B ₄ / A ₄ ) / (B / A) <1.8 (IV)
In the above formulas (II) to (IV), B / A is a ratio B / A of a poor solvent and a good solvent contained in any aqueous ink other than the aqueous ink included in the ink set. That is, it is preferable to fill any of the water sets other than the water-based ink included in the ink set. In each of the above formulas (II) to (IV), the leftmost value 0.6 is particularly preferably 0.8. In each of the above formulas (II) to (IV), the value 1.8 on the rightmost side is particularly preferably 1.3.

Furthermore, according to the study by the present inventors, the Ka value in the water-based 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 preferably adjusted so that, furthermore, it is preferable to adjust so as to 0.2mL · m ^-2 · msec ^-1/2 or more 1.5mL · m ^-2 · msec less than ^-1/2. In other words, if the aqueous ink has a Ka value of less than 1.5 mL · m ⁻² · msec ^−1/2 , solid-liquid separation can be achieved at an early stage in the process of penetration of the aqueous ink into the recording medium. This makes it possible to form a high-quality image with very little bleeding.

  The content of the water-soluble organic solvent in the aqueous ink according to the present invention 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 ink, and more preferably 10% by mass to 35%. It is preferable to set it as the range of the mass%. Further, the water content (% by mass) in the water-based ink is preferably in the range of 50% by mass to 95% by mass with respect to the total mass of the ink, and more preferably in the range of 60% by mass to 95% by mass. It is preferable to do.

  Further, in the water-based ink according to the present invention, when the content (% by mass) of the poor solvent is 4% by mass or more based on the total mass of the ink, from the viewpoint of achieving both high image density and ink storage stability. More preferred. In addition, the content (% by mass) of the poor solvent is preferably 37.5% by mass or less, and more preferably 5% by mass to 20% by mass with respect to the total mass of the ink.

<Water-insoluble colorant>
The water-insoluble color material constituting the water-based ink according to the present invention will be described. Any water-insoluble colorant constituting the water-based ink of the present invention can be used regardless of its dispersion method. Among these, it is particularly preferable to use a pigment. Specifically, the pigment may be, for example, a so-called resin dispersion type pigment (resin dispersion type pigment) using a dispersant or a surfactant, a surfactant dispersion type pigment, or the pigment itself. A microcapsule-type pigment that has improved dispersibility and can be dispersed without using a dispersant, a so-called self-dispersion type pigment (self-dispersion type pigment) in which a hydrophilic group is introduced on the surface of pigment particles, Furthermore, a modified pigment (polymer-bonded self-dispersing pigment) in which an organic group containing a polymer is chemically bonded to the surface of the pigment particle can be used. Of course, these pigments having different dispersion methods can also be used in combination.

  The water-insoluble colorant of the present invention is in a state where the water-insoluble colorant is dispersed in an aqueous medium, such as the resin-dispersed pigment, self-dispersed pigment, and polymer-bonded self-dispersed pigment described above. That is, it goes without saying that the good solvent and the poor solvent for the water-insoluble colorant of the present invention indicate the good solvent and the poor solvent for the resin-dispersed pigment, self-dispersed pigment, polymer-bonded self-dispersed pigment, and the like. It is. Hereinafter, the water-insoluble coloring material that can be used in the present invention will be described.

  In the water-based ink of the present invention, the content (% by mass) of the water-insoluble colorant is preferably 0.1% by mass to 15.0% by mass with respect to the total mass of the ink. It is preferable that it is mass%-10.0 mass%.

(Pigment)
The pigment that can be used in the water-based ink according to the present invention is not particularly limited, and any of those listed below can be used.

  Carbon black is suitable for the pigment used in the black ink. For example, any carbon black such as furnace black, lamp black, acetylene black, and channel black can be used. Specifically, for example, Raven 7000, Rayvan 5750, Rayvan 5250, Rayvan 5000ULTRA, Rayvan 3500, Rayvan 2000, Rayvan 1500, Rayvan 1250, Rayvan 1200, Rayvan 1190ULTRA-II, Rayvan 1170, Rayvan 1255 (and above) 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 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 pigment particles used other than black ink include various organic pigment particles. Specific examples of the organic pigment include 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, 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 Dazolone 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.

Moreover, the organic pigment that can be used in the present invention is represented by the color index (CI) number, and examples thereof include the following.
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. (resin dispersed pigments)
As described above, a resin-dispersed pigment using a dispersant can be used as the water-insoluble colorant that can be used in the aqueous ink according to the present invention. In this case, a compound such as a surfactant or a resin dispersant for dispersing the hydrophobic pigment as listed above is required.

  The surfactant is preferably an anionic surfactant or a nonionic surfactant. Specific examples of the anionic surfactant include fatty acid salt, alkyl sulfate ester salt, alkylbenzene sulfonate salt, alkyl naphthalene sulfonate salt, dialkyl sulfosuccinate salt, alkyl phosphate ester salt, naphthalene sulfonate formalin condensate, polyoxyethylene Examples thereof include alkyl sulfate salts and substituted derivatives thereof. Specific examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin fatty acid. Examples thereof include esters, oxyethyleneoxypropylene block polymers, and substituted derivatives thereof.

  Specific examples of the resin dispersant include styrene and derivatives thereof, vinyl naphthalene and derivatives thereof, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acid, acrylic acid and derivatives thereof, maleic acid and derivatives thereof, and itaconic acid. And a derivative thereof, fumaric acid and a derivative thereof, vinyl acetate, vinyl alcohol, vinyl pyrrolidone, acrylamide, and a derivative thereof, and the like (including at least one of which is a hydrophilic monomer). Examples thereof include block copolymers, random copolymers, graft copolymers, and salts thereof. Furthermore, a block copolymer and a random copolymer can be used in combination.

(Microcapsule type pigment)
As described above, the water-insoluble colorant that can be used in the water-based ink according to the present invention uses a microcapsule type pigment obtained by coating a water-insoluble colorant with an organic polymer to form a microcapsule. Can do. Examples of the method of encapsulating a water-insoluble colorant with organic polymers to form microcapsules include a chemical production method, a physical production method, a physicochemical method, and a mechanical production method. Specifically, interfacial polymerization method, in-situ polymerization method, submerged cured coating method, coacervation (phase separation) method, submerged drying method, melt dispersion cooling method, air suspension coating method, spray drying method , Acid precipitation method, phase inversion emulsification method and the like.

  Specific examples of organic polymers used as the material constituting the wall membrane material of the microcapsule include, for example, polyamide, polyurethane, polyester, polyurea, epoxy resin, polycarbonate, urea resin, melamine resin, phenol resin, polysaccharide, Gelatin, gum arabic, dextran, casein, protein, natural rubber, carboxypolymethylene, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, cellulose, ethyl cellulose, methyl cellulose, nitrocellulose, hydroxyethyl cellulose, cellulose acetate , Polyethylene, polystyrene, polymer or copolymer of (meth) acrylic acid, polymer or copolymer of (meth) acrylic acid ester, (meth) acrylic acid- (meth) a Acrylic acid ester copolymer, styrene - (meth) acrylic acid copolymer, styrene - maleic acid copolymer, sodium alginate, fatty acids, paraffin, beeswax, water wax, hardened beef tallow, carnauba wax, albumin and the like. Among these, organic polymers having an anionic group such as a carboxylic acid group or a sulfonic acid group are preferable. Specific examples of the nonionic organic polymer include, for example, polyvinyl alcohol, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, methoxypolyethylene glycol monomethacrylate or their (co) polymer, and 2-oxazoline cationic ring-opening weight. Examples include coalescence. In particular, a completely saponified polyvinyl alcohol is particularly preferable because it has low water solubility and is easily dissolved by hot water but not easily dissolved by cold water.

  When the phase inversion method or the acid precipitation method is selected as the microencapsulation method, an anionic organic polymer is used as the organic polymer constituting the wall membrane material of the microcapsule.

  The phase inversion method is a composite or composite of an anionic organic polymer having self-dispersibility or solubility in water and a colorant such as a self-dispersible organic pigment or self-dispersible carbon black, or self A mixture of a colorant such as a dispersible organic pigment or self-dispersing carbon black, a curing agent, and an anionic organic polymer is used as an organic solvent phase, and water is added to the organic solvent phase or the organic solvent is submerged in water. In this method, a solvent phase is introduced and microencapsulation is performed while self-dispersion (phase inversion emulsification) is performed. In the phase inversion method, the organic solvent phase can also be produced by mixing a water-soluble organic solvent or additive used in the ink. In particular, from the viewpoint that an ink dispersion can be directly produced, it is preferable to mix an aqueous ink medium.

  In the acid precipitation method, a part or all of anionic groups of organic polymers containing anionic groups are neutralized with a basic compound, and water-based with a coloring material such as self-dispersing organic pigment or self-dispersing carbon black. A water-containing cake is obtained by a production method comprising a step of kneading in a medium and a step of neutralizing or acidifying an acidic compound to precipitate an anionic group-containing organic polymer and fixing it to a pigment. And it is the method of microencapsulating the said water-containing cake by neutralizing a part or all of anionic group using a basic compound. By an acid precipitation method, an anionic microencapsulated pigment which is fine and contains a large amount of pigment can be produced.

  Specific examples of the organic solvent used for microencapsulation as described above include, for example, alkyl alcohols such as methanol, ethanol, propanol, and butanol; aromatic hydrocarbons such as benzol, toluol, and xylol. Esters such as methyl acetate, ethyl acetate and butyl acetate; chlorinated hydrocarbons such as chloroform and ethylene dichloride; ketones such as acetone and methyl isobutyl ketone; ethers such as tetrahydrofuran and dioxane; methyl cellosolve and butyl cellosolve And cellosolves.

  The microcapsules prepared by the above method are once separated from these organic solvents by centrifugation or filtration, and then stirred and redispersed with water and the necessary solvent to obtain the desired microcapsule type pigment. It can also be. The average particle diameter of the microcapsule type pigment obtained by the above method is preferably 50 nm to 180 nm.

(Self-dispersing pigment)
As described above, the water-insoluble colorant that can be used in the water-based ink according to the present invention uses a self-dispersing pigment that increases the dispersibility of the pigment itself and is dispersible without using a dispersant or the like. be able to. The self-dispersing pigment preferably has a hydrophilic group chemically bonded to the pigment particle surface directly or via another atomic group. For example, the hydrophilic group introduced into the pigment particle surface is —COOM1, —SO ₃ M1 and —PO ₃ H (M1) ₂ (wherein M1 represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. And the like selected from the group consisting of Furthermore, those in which the other atomic group is an alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted naphthylene group can be preferably used. In addition, a method of oxidizing carbon black with sodium hypochlorite, a method of oxidizing carbon black by ozone treatment in water, and a method of modifying the carbon black surface by wet oxidation with an oxidizing agent after ozone treatment A self-dispersing pigment of the surface oxidation treatment type obtained by the above method can also be suitably used.

(Polymer-bonded self-dispersing pigment)
As described above, the water-insoluble colorant that can be used in the water-based ink according to the present invention is a polymer-bonded self-dispersing pigment that increases the dispersibility of the pigment itself and is dispersible without using a dispersant or the like. Can be used. The polymer-bonded self-dispersing pigment is a reaction between a functional group chemically bonded to the pigment surface directly or through another atomic group, and a copolymer of an ionic monomer and a hydrophobic monomer. It is preferable to use a thing containing a thing. This can appropriately change the copolymerization ratio of the ionic monomer and hydrophobic monomer, which is a material for forming the copolymer used when modifying the surface, and thereby the hydrophilicity of the modified pigment. This is because can be adjusted appropriately. Moreover, since the kind of ionic monomer and hydrophobic monomer to be used, and the combination of both can be changed as appropriate, various properties can be imparted to the pigment surface.

(Functional group)
The functional group of the polymer-bonded self-dispersing pigment is chemically bonded to the pigment surface directly or through another atomic group. The functional group is for constituting an organic group by reaction with a copolymer described later, and the type of the functional group is selected in relation to the functional group carried by the copolymer. In consideration of the fact that the pigment is dispersed in an aqueous medium, the reaction between the functional group and the copolymer is preferably a reaction that generates a bond that does not cause hydrolysis, for example, an amide bond. . For this purpose, the functional group can be an amino group, and the copolymer can be introduced onto the pigment particle surface via an amide bond by carrying a carboxyl group on the copolymer. Alternatively, the copolymer can be introduced to the pigment particle surface via an amide bond in the same manner as described above by converting the functional group to a carboxyl group and supporting the amino group on the copolymer.

  Here, the functional group chemically bonded to the pigment surface may be bonded directly to the pigment surface, or may be bonded to the pigment surface via another atomic group. However, when a copolymer having a relatively large molecular weight is introduced onto the pigment surface, the functional group is preferably introduced onto the pigment surface via another atomic group in order to avoid steric hindrance between the copolymers. The other atomic groups are not particularly limited as long as they are polyvalent elements or organic groups. However, for the reasons described above, for example, a divalent organic residue is preferably used from the viewpoint of controlling the distance of the functional group from the pigment surface. Specific examples of the divalent organic residue include an alkylene group and an arylene group (phenylene group).

  More specifically, for example, in the examples described later, the pigment is reacted with aminophenyl (2-sulfoethyl) sulfone to introduce an aminophenyl (2-sulfoethyl) sulfone group on the pigment surface. An amino group as a functional group is introduced by reacting an amino group of hexamine with an aminophenyl (2-sulfoethyl) sulfone group. In this case, the amino group is chemically bonded to the pigment surface via an atomic group containing a phenyl (2-sulfoethyl) group. Of course, the present invention is not limited to this.

[Copolymer]
As the copolymer of the ionic monomer and the hydrophobic monomer, for example, an anionic copolymer having an anionic property or a cationic copolymer having a cationic property is preferable.

  Examples of the anionic copolymer include a copolymer of a hydrophobic monomer and an anionic monomer, or a salt thereof.

  Specific examples of the hydrophobic monomer include methacrylic acid alkyl esters such as styrene, vinyl naphthalene, and methyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p. -Acrylic acid alkyl esters such as tolyl methacrylate, sorbyl methacrylate and methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate and sorbyl acrylate. Specific examples of the anionic monomer include acrylic acid, methacrylic acid, maleic acid and the like. Of course, the present invention is not limited to this.

  The anionic copolymer of an anionic monomer and a hydrophobic monomer is at least two of any one selected from the hydrophobic monomers listed above and at least one selected from the anionic monomers listed above It consists of the above monomers. Examples of the anionic copolymer include a block copolymer, a random copolymer, a graft copolymer, or a salt thereof.

  Such an anionic copolymer preferably has an acid value in the range of 100 to 500, and preferably has a variation in acid value within 20% of the average acid value. If the acid value is higher than the above range, the hydrophilicity of the pigment surface becomes too high, so that the water and solvent in the ink after printing stays on the pigment surface, and the development of scratch resistance after printing on the recording medium. May be slow. On the other hand, when the acid value is lower than the above range, the hydrophilicity of the pigment surface becomes too low, and it may be difficult to stably disperse the pigment in the ink.

  In addition, examples of the salt of the anionic copolymer described above include ammonium salts, alkylamine salts, alkanolamine salts, and the like, in addition to alkali metal salts such as sodium, lithium, and potassium. Moreover, these can be used individually or in combination of multiple suitably.

  Next, examples of the cationic copolymer include a copolymer of a hydrophobic monomer and a cationic monomer, or a salt thereof.

  As the hydrophobic monomer, the monomers listed above can be used. Specific examples of the cationic monomer include allylamine, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, N-vinylcarbazole, Examples include methacrylamide, acrylamide and dimethylacrylamide. Of course, the present invention is not limited to this.

  The anionic copolymer of the cationic monomer and the hydrophobic monomer is at least two of any one selected from the hydrophobic monomers listed above and at least one selected from the cationic monomers listed above. It consists of the above monomers. Examples of the cationic copolymer include a block copolymer, a random copolymer, a graft copolymer, and salts thereof.

  Such a cationic copolymer preferably has an amine value in the range of 100 to 500, and preferably has a variation in amine value within 20% of the average amine value. The amine value is a value expressed in mg of KOH by neutralizing 1 g of the sample and corresponding to the acid value.

  Examples of the above-mentioned cationic copolymer salt include acetic acid, hydrochloric acid, nitric acid and the like. Moreover, these can be used individually or in combination of multiple suitably.

  The anionic or cationic copolymer described above preferably has a weight average molecular weight (Mw) in the range of 1,000 to 20,000, and more preferably in the range of 3,000 to 20,000. Are preferred. Moreover, the polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of the cationic copolymer segment is preferably 3 or less. The mass of such an anionic or cationic copolymer is 5% or more and 40% or less with respect to the mass of pigment particles whose surface is modified by the copolymer in the ink. It is preferable. In addition, when the polydispersity of the copolymer is large, the molecular weight distribution of the copolymer becomes wide, and the above-described properties based on the molecular weight of the copolymer are difficult to be expressed. Are more preferable.

  Next, taking carbon black as an example, a method for modifying the pigment by chemically bonding an organic group to the pigment particle surface will be described. The method that can be used in this case is to introduce a functional group on the surface of the pigment particle or a functional group on the surface of the pigment particle, and bond a copolymer composed of an ionic monomer and a hydrophobic monomer to these functional groups. As long as it is a method of chemically bonding the copolymer to the pigment particle surface, any method that is usually used may be used, and there is no particular limitation.

  As a specific example of such a method, for example, the following method can be used. A method in which polyethyleneimine or the like is introduced on the surface of pigment particles such as carbon black, and a copolymer composed of an ionic monomer and a hydrophobic monomer having an amino group at its terminal functional group is bonded by a diazonium reaction, carbon Methods such as a method of bonding a copolymer having an amino group and a carboxyl group in the molecule to the surface of pigment particles such as black by a diazonium reaction can be used. The most typical example of this other method is disclosed in WO 01/51566 A1.

In the above-described method, for example, when an anionic copolymer is chemically bonded to the surface of the carbon black particles, the following three steps are included.
First step: A step of adding an aminophenyl (2-sulfoethyl) sulfone group (APSES) to carbon black by a diazonium reaction.
Second step: A step of adding polyethyleneimine or pentaethylenehexamine (PEHA) to carbon black subjected to APSES treatment.
Third step; a step of attaching a copolymer of a hydrophobic monomer and an ionic monomer having a carboxyl group.

  In the second step, the phenyl (2-sulfoethyl) sulfone group chemically bonded to the carbon black surface in the first step is reacted with the amino group of APSES to chemically react with the carbon black surface. An amino group as a functional group formed by bonding is introduced. In the third step, for example, a part of the carboxyl group of the ionic monomer portion of the copolymer is reacted with an amino group to form an amide bond, thereby forming the copolymer on the surface of carbon black. In addition, a copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group which is a residue of APSES and a residue of PEHA.

Further, in the above-described method, for example, when the cationic copolymer is chemically bonded to the surface of the carbon black particles, the following two steps are included.
First step: A step of adding an aminophenyl (2-sulfoethyl) sulfone group (APSES) to carbon black by a diazonium reaction.
-2nd process; The process of attaching the copolymer of a hydrophobic monomer and a cationic monomer.

  In the first step, a sulfone group is introduced as a functional group chemically bonded to the carbon black surface. In the second step, for example, a part of the amino group of the ionic monomer portion of the copolymer is reacted with a sulfone group (nucleophilic substitution), and the copolymer is placed on the surface of carbon black. A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group which is a residue of APSES.

<Other ingredients>
The water-based ink according to the present invention may use a moisturizing solid content such as urea, urea derivative, trimethylolpropane, trimethylolethane or the like as an ink component in addition to the above-described components in order to maintain the moisture retention. The content of the moisturizing solid content in the aqueous ink, such as urea, urea derivative, and trimethylolpropane, is generally 0.1% by mass to 20.0% by mass, and more preferably 3.0% by mass with respect to the total mass of the ink. The range of% -10.0 mass% is preferable.

  Furthermore, in addition to the above-described components, the water-based ink according to the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, and an evaporation as necessary. Various additives such as an accelerator and a chelating agent may be contained.

  It is preferable to add a nonionic surfactant to the water-based ink according to the present invention in order to adjust the surface tension and improve the discharge property. Specific examples of the nonionic surfactant include compounds having any one of the following structural formulas (1) to (4).

  In the structural formula (1), R is preferably a linear or branched alkyl group having 8 to 21 carbon atoms, and n is an integer of 5 to 40. Moreover, the mixture of 2 or more types of compounds from which the value of R and / or n differs can also be used.

  In the structural formula (2), R is preferably a linear or branched alkyl group having 8 to 21 carbon atoms, and n is an integer of 5 to 40. Moreover, the mixture of 2 or more types of compounds from which the value of R and / or n differs can also be used.

  In the structural formula (3), m is preferably an integer of 1 to 10, and n is preferably an integer of 1 to 10. Note that m represents the number of ethylene oxide units, and n represents the number of propylene oxide units, which may be any of a block copolymer, an alternating copolymer, and a random copolymer. A mixture of two or more compounds having different values of m and / or n can also be used.

  In the structural formula (4), m is preferably an integer of 1 to 10, and n is preferably an integer of 1 to 10. A mixture of two or more compounds having different values of m and / or n can also be used.

  The content of the compound having any one of the structural formulas (1) to (4) in the aqueous ink is in the range of 0.05% by mass to 5% by mass with respect to the total mass of the aqueous ink, and Is preferably 0.1% by mass to 2% by mass.

<Ink physical properties>
It is preferable that the water-based ink used in the present invention, which is composed of the constituents described above, has a characteristic that can be satisfactorily discharged from the ink jet recording head. From the viewpoint of ejection from an ink jet recording head, the ink characteristics are, for example, a viscosity of 1 to 15 mPa · s, a surface tension of 25 mN / m (dyne / cm) or more, and a viscosity of 1 to 5 mPa · s. s, and the surface tension is preferably 25 to 50 mN / m (dyne / cm).

[Ink set]
The cyan ink of the present invention includes magenta ink and yellow ink each containing water, a water-insoluble color material, a plurality of water-soluble organic solvents including a good solvent for the water-insoluble color material and a poor solvent for the water-insoluble color material. And an ink set having four types of water-based inks in combination with black ink.

  The ink set referred to in the present invention may be in any of the following forms as long as a plurality of inks are combined. For example, an ink tank having a structure in which a tank containing cyan ink, magenta ink, yellow ink, and black ink is integrated, or an ink set including an ink tank with a head thereof, or cyan ink, magenta ink, yellow ink Can be attached to and removed from the recording device. And an ink set having a structure as described above. In any case, in the present invention, the characteristics of the ink alone of the present invention are specified relative to other inks used (in the recording apparatus or as an ink tank). However, the present invention is not limited to this, and any modification may be possible.

[Inkjet recording method, recording unit, cartridge, and inkjet recording apparatus]
FIG. 1 shows an example of an ink jet recording apparatus. In FIG. 1, 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 this example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, 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 a discharge recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the discharge port surface. In addition, a recovery unit that restores the original ink ejection performance of the recording head by sucking the ink etc. located at each ink ejection port of the recording head by a pump (not shown) through the cap is doing.

  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 discharge port surface of the recording head 65, and is discharged to a paper discharge portion provided with a paper discharge roller 53 as recording progresses. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port of the recording head 65 is wiped.

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

[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 for recording on a recording medium such as plain paper by an ink jet recording method. When forming an image in which the image formed by the color ink is adjacent to the image, the image is formed by performing a scan for applying the black ink, and then the color ink is applied to the region where the image is formed. Scanning is performed. A specific method will be described below.

  FIG. 2 is an example of a recording head used when carrying out the image forming method according to the present invention. As shown in FIG. 2, the recording head has 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. 2, when forming only a black image, 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. 2 is 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 conveyed 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 discharge port array is used. A color image is formed on the recording medium by one-pass printing in the image area formed by the portion a of the black ink discharge 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. 3 shows another example of a recording head that can be used in the present invention. In FIG. 3, as in the case of FIG. 2, the black ink uses the a portion of the black ink ejection port array, and the C, M, and Y color inks use the b portion corresponding to the entire area of the color ink ejection 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. 4 shows another example of a recording head that can be used in the present invention. Also in FIG. 4, as in the case of FIG. 2, 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. 4, a distance of one paper feed amount a ′ is placed between the portion a of the black ink ejection port array and the portion b 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. 4 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. 5 shows another example of a recording head that can be used in the present invention. In the case of using a recording head in which the black ink ejection port array and the color ink ejection port array are arranged in a line 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. 6 shows another example of a recording head that can be used in the present invention. In the recording head shown in FIG. 6, the color ink ejection port arrays are arranged in cyan ink (C1, C2) and magenta ink (in order to make the color ink ejection order 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.

  In the recording head corresponding to bidirectional printing as shown in FIG. 6, as in the recording head described in FIG. 4, the a portion of the black ink ejection port array and the b portion of the color ink ejection port array The distance between the paper feed amount a ′ is one (see FIG. 7), and once 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.

[recoding media]
As the recording medium used for forming an image using the water-based ink of the present invention, any recording medium can be used as long as recording is performed by applying ink. In particular, in the present invention, plain paper, a recording medium having a coating layer for receiving water-based ink on at least one surface, and the like are preferably used. Of course, the present invention is not limited to this.

  Examples of the recording medium having a coating layer for receiving aqueous ink include recording media having a coating layer for receiving aqueous ink on at least one surface containing at least a hydrophilic polymer and / or an inorganic porous material. When an image is formed on a medium, a particularly excellent effect is exhibited. The recording medium having a coating layer that receives the water-based ink includes the surface state, the thickness of the coating layer, the size of the pores that absorb the water-based ink, the difference in the material constituting the ink absorption layer, and the type of the substrate. There are a wide variety of things. For example, strong glossy paper and glossy film having a high surface gloss, fine glossy paper or semi-glossy paper whose surface gloss is adjusted by processing, matte paper with no gloss, and a very small amount of coated paper with few coating layers.

  The recording medium used for ink jet recording is variously selected according to the purpose. For example, glossy paper for obtaining an image having glossiness similar to that of silver salt photographic printing paper, paintings and photographs, and graphic images are preferred. Art paper that makes use of the texture of the base material (drawing paper tone, canvas tone, Japanese paper tone, etc.) is used for expression.

  Conventionally known substances can be used as the hydrophilic polymer constituting the coating layer of the recording medium. For example, starch, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, alginic acid, gelatin, polyvinyl alcohol, polyvinyl acetal, polyethylene oxide, sodium polyacrylate, cross-linked polyacrylic acid, polyvinyl methyl ether, polystyrene sulfonic acid, quaternary Examples thereof include polyvinyl pyridine, polyacrylamide, polyvinyl pyrrolidone, polyamine, aqueous urethane resin, water-soluble acrylic resin, water-soluble epoxy compound, and water-soluble polyester. In addition, modified products of the above polymers, for example, ion-modified products such as cation-modified polyvinyl alcohol and cation-modified polyvinyl pyrrolidone can be used as appropriate. Furthermore, examples of the inorganic porous material used for constituting the ink receiving layer of the recording medium include silica gel, alumina, zeolite, and porous glass.

  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 and reaction solution]
(Preparation of black pigment dispersion)
10 parts by weight of sodium hydroxide containing 10 parts by weight of styrene-acrylic acid copolymer having a specific surface area of 210 m ² / g and a DBP oil absorption of 74 ml / 100 g, an acid value of 200 and a weight average molecular weight of 10,000. 20 parts of the aqueous solution neutralized with the aqueous solution and 70 parts of ion-exchanged water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the obtained dispersion, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare a resin-dispersed black pigment. Further, water was added to the resin-dispersed black pigment obtained above to disperse the pigment concentration to 10% by mass to prepare a dispersion. A black pigment dispersion was obtained by the above method.

(Preparation of cyan pigment dispersion)
An aqueous solution of 10 parts of a pigment (CI Pigment Blue 15: 3), neutralized with a 10% by weight sodium hydroxide aqueous solution of a styrene-acrylic acid copolymer having an acid value of 200 and a weight average molecular weight of 10,000. 20 parts and 70 parts of ion-exchanged water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the obtained dispersion, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare a resin-dispersed cyan pigment. Furthermore, water was added to the resin-dispersed cyan pigment obtained above to disperse the pigment concentration to 10% by mass, thereby preparing a dispersion. By the above method, a cyan pigment dispersion was obtained.

(Preparation of magenta pigment dispersion)
10 parts of a pigment (CI Pigment Red 122), 20 parts of an aqueous solution obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 200 and a weight average molecular weight of 10,000 with a 10% by mass aqueous sodium hydroxide solution Then, 70 parts of ion-exchanged water was mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the obtained dispersion, followed by pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare a resin-dispersed magenta pigment. Furthermore, water was added to the resin-dispersed magenta pigment obtained above to disperse the pigment concentration to 10% by mass, thereby preparing a dispersion. By the above method, a magenta pigment dispersion was obtained.

(Preparation of yellow pigment dispersion)
10 parts of pigment (CI Pigment Yellow 74), 20 parts of an aqueous solution obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 200 and a weight average molecular weight of 10,000 with a 10% by mass aqueous sodium hydroxide solution Then, 70 parts of ion-exchanged water was mixed and dispersed for 3 hours using a batch type vertical sand mill. The obtained dispersion was centrifuged to remove coarse particles, and then pressure filtered through a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare a resin-dispersed yellow pigment. Further, water was added to the resin-dispersed yellow pigment obtained above to disperse the pigment concentration to 10% by mass, thereby preparing a dispersion. By the above method, a yellow pigment dispersion was obtained.

[Determination of good and poor solvents for water-soluble organic solvents]
In order to select a water-soluble organic solvent that acts as a good solvent or a poor solvent for the pigment in the pigment dispersion, the following experiment was conducted. First, an aqueous solution having a solid content concentration of 10% by mass of the pigment dispersion of each color obtained above was prepared, and using this and each water-soluble organic solvent, dispersion for determination of good solvent / poor solvent with the following blending ratio Liquid A and determination aqueous dispersion B were prepared.

(Dispersion A for determination)
-50 parts by weight of 10% by weight solids concentration of pigment dispersion for each color-50 parts of each water-soluble organic solvent listed in Table 1 (Water dispersion B for determination)
・ 50 parts aqueous solution of 10% solids concentration of pigment dispersion of each color ・ 50 parts of pure water (Judgment method)
Next, 10 g of the dispersion liquid A for determining good and poor solvents prepared as described above is placed in a transparent glass lidded sample bottle, capped, and then sufficiently stirred. For 48 hours. Thereafter, using the dispersion taken out from the oven as a measurement sample, the average particle size of the pigment in the dispersion was measured using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). The average particle size of the pigment in the dispersion liquid for determination A after storage at 60 ° C. for 48 hours (average particle size of the pigment measured without dilution) was used. On the other hand, the determination aqueous dispersion B was not stored with warming, and the average particle size of the pigment in the dispersion was measured using a concentrated particle size analyzer in the same manner as described above. Then, the water-soluble organic solvent in which the average particle size of the pigment in the determination dispersion A and the determination aqueous dispersion B is larger than that of the determination aqueous dispersion B is determined as a poor solvent, and determination is made. A water-soluble organic solvent in which the average particle diameter of the dispersion liquid A was equal to or less than that of the determination aqueous dispersion liquid B was determined as a good solvent.

[Measurement of Ka value for water-soluble organic solvent]
First, in measuring the Ka value of each water-soluble organic solvent, a dye aqueous solution having a composition shown below and having a dye concentration of 0.5% by mass was prepared. The reason why such an aqueous dye solution is used is to visualize a colorless and transparent sample by coloring it to facilitate measurement of the Ka value.
Water-soluble dye C.I. I. Direct Blue 199 0.5 part / pure water 99.5 parts Next, a colored water-soluble organic solvent having the composition shown below is prepared by the 0.5% by mass dye aqueous solution and each water-soluble organic solvent to be measured. Each 20% aqueous solution was prepared.
80 parts of the 0.5% by weight dye aqueous solution 20 parts of the water-soluble organic solvent described in Table 1 20% by weight aqueous solution of each of the water-soluble organic solvents prepared above was used as a sample for measurement. (Product name: Dynamic permeability test apparatus S; manufactured by Toyo Seiki Seisakusho) was used to determine the Ka values of 20% by mass aqueous solutions of each water-soluble organic solvent by the Bristow method.

[Judgment and measurement results]
About the water-soluble organic solvent that can be used in the ink measured as described above, it is a good or poor solvent for the black pigment dispersion, cyan pigment dispersion, magenta pigment dispersion, and yellow pigment dispersion. Table 1 shows the results of the determination and the measurement results of the Ka value in a 20% by mass aqueous solution of each water-soluble organic solvent. In the table, o and x represent a good solvent and a poor solvent, respectively.

[Preparation of ink]
(Examples 1-4)
The components shown in Tables 2 to 5 below were mixed and sufficiently stirred, followed by pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm. An ink set was prepared. B / A in the table is a value of B / A when the content (% by mass) of the good solvent in each water-based ink is A and the content (% by mass) of the poor solvent is B. In the preparation of the water-based ink of the examples, the B / A value was adjusted to be 0.5 or more and 3.0 or less, and among the water-based inks included in the ink set, the B / A of cyan ink was used. It adjusted so that the value of might become the minimum.

(Reference Examples 1 and 2)
After mixing each component shown in Table 6 and Table 7 and stirring sufficiently, pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm, and each of the water-based inks of Reference Examples 1 and 2 and An ink set was prepared. B / A in the table is a value of B / A when the content (% by mass) of the good solvent in each water-based ink is A and the content (% by mass) of the poor solvent is B. In preparing the water-based inks of the examples, the B / A value was adjusted to be 0.5 or more and 3.0 or less.

(Comparative Examples 1-3)
The components shown in Tables 8 to 10 below were mixed and sufficiently stirred, and then subjected to pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm. An ink set was prepared. B / A in the table is a value of B / A when the content (% by mass) of the good solvent in each water-based ink is A and the content (% by mass) of the poor solvent is B.

[Evaluation 1: Image density]
Using the inks of Examples 1 to 3, Reference Examples 1 and 2 and Comparative Examples 1 to 3 prepared above, recorded matter was prepared. For the production of the recorded matter, a modified machine of an ink-jet recording apparatus PIXUS950i (manufactured by Canon) having an on-demand type multi-recording head that discharges ink by applying thermal energy to the ink according to a recording signal was used. . Specifically, characters including a solid portion of 2 cm × 2 cm were printed on the following recording medium to prepare a recorded matter. The obtained recorded matter was allowed to stand for 1 day, and then the image density of the solid portion was measured. For the measurement of the image density, a reflection densitometer (trade name: Macbeth RD-918; manufactured by Macbeth) was used. The image density evaluation criteria are as follows. The evaluation results are shown in Table 11.

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 The following plain paper was used as the recording medium.
・ PPC paper PB Paper (Canon)
・ PPC paper SC250C (Canon)
・ PPC paper 4200 (manufactured by Xerox)
・ PPC paper 4024 (Xerox)
・ High white paper SW-101 (Canon)
(Evaluation criteria)
AA: A sufficient image density can be obtained with all papers.

  A: Although sufficient image density cannot be obtained with some papers, there is no problem in actual use.

  B: A sufficient image density cannot be obtained with some paper.

  C: A sufficient image density cannot be obtained with all papers.

[Evaluation 2: Storage stability]
Each of the inks of Examples 1 to 4, Reference Examples 1 and 2, and Comparative Examples 1 to 3 prepared above was put in a shot bottle, sealed, and stored in an oven at 60 ° C. for 2 weeks, and the state of the ink was observed. . The evaluation criteria for storage stability are as follows. The evaluation results are shown in Table 11.

(Evaluation criteria)
A: The color material is uniformly and stably dispersed in the ink.

  B: The ink has changed to a gel, or the upper part of the ink is transparent, or the ink is clearly thickened.

[Evaluation 3: Scratch resistance]
Of the ink sets of Examples 1 to 4, Reference Examples 1 and 2 and Comparative Examples 1 to 3 prepared above, a secondary color image is formed by combining three inks, cyan ink, magenta ink, and yellow ink. A recorded matter on which was printed was prepared. For the production of the recorded matter, a modified machine of an inkjet recording apparatus BJF930 (manufactured by Canon) having an on-demand type multi-recording head that discharges ink by applying thermal energy to the ink according to a recording signal was used. . Specifically, solid images of green and blue were printed at 1 inch × 0.5 inch on a recording medium (PPC paper PB Paper; manufactured by Canon). At the time of printing, low-lightness ink, that is, cyan ink was applied to the recording medium before other inks. Further, the ratio of the applied amount of each ink was set to 1: 1, 2: 1, and 1: 2, and the applied amount of ink was set to 14.4 g / m ² . The obtained recorded matter was allowed to stand for 10 minutes, and then a sylbon paper and a weight having a surface pressure of 40 g / cm ² were placed on the solid image of the printed matter, and the recording medium and the sylbon paper were rubbed together. Thereafter, the Sylbon paper and the weight were removed, and the solid image was stained and transferred to a white background by visual observation. The evaluation criteria for scratch resistance are as follows. The evaluation results are shown in Table 11.

(Evaluation criteria)
AA: The green image and the blue image are free from white background stains and solid portions.

  A: On either the green image or the blue image, the white background is slightly stained or the solid portion is slightly scraped.

  B: On either the green image or the blue image, the white background portion and the solid portion are slightly scraped, but there is no problem in actual use.

  C: Both the green image and the blue image show dirt on the white background and shaving of the solid part.

It is a schematic perspective view which shows an example of an inkjet recording device. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. It is explanatory drawing for demonstrating typically the state when the droplet of the water-based ink of this invention has landed on the recording medium (plain paper) surface, (a) The state before landing, (b) The state immediately after landing, (C) A state in which dots are being formed, and (d) a state in which dots are formed. It is explanatory drawing for demonstrating typically a mode when forming a secondary color by cyan ink (thing with a small B / A value) and magenta ink, (a) State before landing, (b) Landing A state immediately after, (c) a state in which dots are being formed, and (d) a state in which dots are formed are shown. It is explanatory drawing for demonstrating typically a mode when forming a secondary color with cyan ink (thing with a large B / A value) and magenta ink, (a) The state before landing, (b) Landing A state immediately after, (c) a state in which dots are being formed, and (d) a state in which dots are formed are shown.

Explanation of symbols

51: Paper feeding unit 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 1300: Recording medium 1301: Ink droplet 1302: Dot periphery 1303: Dot center 1304: Water-insoluble colorant 1305: Dot 1306: Water-soluble organic solvent and water 1307: Poor solvent 1308: Cyan ink 1309: Water-soluble organic solvent in cyan ink 1310: Water-insoluble colorant in cyan ink 1311: Magenta ink 1312: Water-soluble organic solvent in magenta ink 1313: Water-insoluble colorant in magenta ink 1314: Surface of recording medium

Claims (5)

A cyan ink, a magenta ink, a yellow ink, each containing at least water, a water-insoluble colorant, a plurality of water-soluble organic solvents including a good solvent for the water-insoluble colorant and a poor solvent for the water-insoluble colorant, and In cyan ink applied to an ink set having four types of water-based inks of black ink,
When the content (% by mass) of the good solvent contained in the cyan ink is A ₁ and the content (% by mass) of the poor solvent is B ₁ , B ₁ / A ₁ is 0.5 or more and 3.0. And
And the water-soluble organic solvent which shows the maximum Ka value among the Ka values of each of the plurality of water-soluble organic solvents obtained by the Bristow method is the poor solvent,
Further, when the content (mass%) of the good solvent and B (mass%) of the poor solvent contained in any aqueous ink other than the cyan ink included in the ink set is B, the following formula Cyan ink characterized by satisfying (I).
(B ₁ / A ₁ ) / (B / A) <1 (I) The cyan ink according to claim 1, wherein the cyan ink satisfies the following formula (I ′).
(B ₁ / A ₁ ) / (B / A) <0.6 (I ′)   3. The cyan ink according to claim 1, wherein the content (% by mass) of the poor solvent contained in the cyan ink is 4% by mass or more based on the total mass of the cyan ink. The cyan ink according to any one of claims 1 to 3,
A magenta ink, a yellow ink, and a black ink, each containing at least water, a water-insoluble colorant, a plurality of water-soluble organic solvents including a good solvent for the water-insoluble colorant and a poor solvent for the water-insoluble colorant,
An ink set comprising the following four types of water-based inks. Cyan ink, magenta ink, and yellow ink each containing at least a plurality of water-soluble organic solvents including water, a water-insoluble color material, a good solvent for the water-insoluble color material, and a poor solvent for the water-insoluble color material Cyan ink applied to an image forming apparatus using
When the content (% by mass) of the good solvent contained in the cyan ink is A ₁ and the content (% by mass) of the poor solvent is B ₁ , B ₁ / A ₁ is 0.5 or more and 3.0. And
And the water-soluble organic solvent which shows the maximum Ka value among the Ka values of each of the plurality of water-soluble organic solvents obtained by the Bristow method is the poor solvent,
In addition, when the content (mass%) of the good solvent contained in any aqueous ink other than the cyan ink applied to the image forming apparatus is A and the content (mass%) of the poor solvent is B, A cyan ink satisfying the following formula (I):
(B ₁ / A ₁ ) / (B / A) <1 (I)

Images