JP2006008899A - Ink set, inkjet recording method, ink cartridge, recording unit, inkjet recording apparatus, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set simplified in color ink composition, high in OD (optical density), for forming images with color mixing (bleeding) effectively controlled along boundaries between images different in color from each other. <P>SOLUTION: The ink set contains at least water, colorants, and a water-soluble organic solvent, and has several water-based inks different in color from each other. The colorant contained in at least one of the water-based inks is a self-dispersion type colorant wherein at least one ionic group combines with a colorant particulate surface directly or through another atomic group. At least one colorant of the water-based inks contains at least one kind of a water-soluble organic solvent which is a poor solvent relative to the self-dispersion type colorant. The poor solvent does not solvate with the self-dispersion type colorant at all or in effect, and the ionic group does not ionically dissociate at all or in effect in the poor solvent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink set comprising water, a water-soluble organic solvent and a water-based ink containing a pigment. More specifically, the present invention relates to a recording apparatus using an ink jet recording method, and further, an ink jet recording method (an image forming method or a recording method). It is related with the ink set suitable for.

  Conventionally, an ink containing a pigment as a colorant (pigment ink) is known to give an image having excellent fastness such as water resistance and light resistance. In recent years, when the optical density of an image formed with such an ink is further improved, and when color image recording in which different color areas are adjacent to each other is performed, the color mixture ( Various techniques have been proposed for the purpose of effectively suppressing bleeding.

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 forcibly aggregated on the surface of the recording medium, thereby suppressing the penetration of the pigment into the recording medium. A high image with suppressed bleeding is obtained.
JP 2000-198955 A JP 2000-63719 A

  However, it is preferable that the constituent components of the ink be simplified, and in general, by controlling the basic components forming the water-based ink, for example, appropriate design and combination of a coloring material, a water-soluble organic solvent, and the like, It has been desired to form a high-quality image similar to the above.

  Therefore, the object of the present invention is to simplify the components of the ink in the pigment ink and eliminate the dependence on external factors as much as possible, thereby suppressing the adverse effects caused by the combined action and the like, and the OD (optical density) is reduced. An object of the present invention is to provide an ink set capable of obtaining an image in which color mixing at the boundary portion of each color image is suppressed when color image recording is performed in which regions of different colors are adjacent to each other.

  Another object of the present invention is to provide an ink jet recording method capable of forming a high quality image with high OD and suppressed bleeding by using such an ink set.

  Another object of the present invention is to provide an ink cartridge, a recording unit, and an ink jet recording apparatus that can be suitably used in the above recording method.

  Another object of the present invention is to effectively suppress color mixing (bleeding) at the boundary between color images when color image recording is performed in which different color areas are adjacent to plain paper. An object is to provide an image forming method.

  The above object is achieved by the present invention described below. That is, the present invention relates to an ink set comprising at least one of water, a color material, and a water-soluble organic solvent, and comprising a plurality of water-based inks having different colors, and the color material contained in at least one of the water-based inks is pigment particles. A self-dispersing pigment having at least one ionic group bonded to the surface directly or through another atomic group, and at least one color of each aqueous ink becomes a poor solvent for the self-dispersing pigment Contains at least one water-soluble organic solvent, the poor solvent is not completely or substantially solvated with respect to the self-dispersing pigment, and the ionic group is completely or substantially in the poor solvent. It has the relationship which does not ion-dissociate.

  According to the present invention, when an OD (optical density) is high in a pigment ink and an image recording in which different color areas are adjacent to each other is performed, color mixing (bleeding) at the boundary portion of each color image is effectively suppressed. An ink set can be provided. In addition, according to the present invention, by using such an ink set, an ink that can be suitably used for an ink jet recording method capable of forming a high-quality image with high OD and suppressed bleeding, and the above recording method. A cartridge, a recording unit, and an ink jet recording apparatus can be provided. Furthermore, according to the present invention, when color image recording in which different color areas are adjacent to each other on plain paper is performed, image formation that can effectively suppress color mixing (bleed) at the boundary between the color images. Can provide a method.

  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. Although the details of the definition will be described later, when a pigment having at least one ionic group bonded to the pigment particle surface directly or through another atomic group is used as a coloring material, the above-mentioned for the water-soluble organic solvent is used. A pigment having good dispersion stability is used as a good solvent, and a pigment having a poor dispersion stability is used as a poor solvent.

  A feature of the present invention is that it focuses on a combination of a coloring material, which is a basic component constituting water-based ink, and a water-soluble organic solvent, and at least one ionic group is directly or other atomic group on the pigment particle surface as the coloring material. A water-soluble organic solvent having a function to disperse the self-dispersing pigment using the self-dispersing pigment bonded through the above-mentioned self-dispersing pigment exhibits the behavior as the poor solvent described above. In addition, the self-dispersing pigment and the water-soluble organic solvent are configured so as to have the specific relationship described above. By using an ink set in which such water-based ink is combined, an image with reduced bleeding can be obtained even on plain paper that has conventionally had various problems in image formation with water-based ink, and an image with a high OD. Is obtained. In addition, by using such an ink set, high-speed printing and downsizing of the recording apparatus can be achieved, and further, it is excellent in robustness, can realize a higher image density, and can form a high-quality image with reduced bleeding. It has been found that a remarkable effect of being possible is obtained, and the present invention has been achieved.

  The ink set according to the present invention is an ink set using a combination of water-based inks of different colors containing at least water, a water-soluble organic solvent, and a coloring material, and the coloring material has at least one ionic group on the pigment particle surface. Is a self-dispersing pigment bonded directly or through another atomic group, and at least one color of each water-based ink is at least one water-soluble organic solvent that is a poor solvent for the self-dispersing pigment And the poor solvent does not completely or substantially solvate with respect to the self-dispersing pigment, and the ionic group does not completely or substantially ion dissociate in the poor solvent. It is characterized by. When such an ink set is in an ink state, water, a water-soluble organic solvent containing a poor solvent for the self-dispersing pigment, and a self-dispersing pigment are mixed at a predetermined ratio, so that the dispersed state of the pigment is maintained. Yes.

  Although the reason why such an effect is obtained by the present invention is not clear, the present inventors presume as follows. Generally, when an image is formed with a water-based ink on a recording paper such as plain paper, it is necessary to leave the color material on the paper more efficiently in order to realize an excellent printing density and printing quality. In addition, when performing color image recording in which areas of different colors are adjacent to each other, in order to obtain an image in which color mixing (bleeding) at the boundary portion of each color image is suppressed, the adjacent region of the color material at the boundary portion It is necessary to control the outflow to

  That is, as shown in FIG. 10A, when the ink droplet 101 of the present invention is printed on the recording medium 100, for example, on plain paper, the ink starts from the moment when the ink lands on the recording medium. The ratio of water, water-soluble organic solvent, and coloring material changes. That is, as the ink is fixed on the recording medium after the ink droplets have landed on the surface of the recording medium, the water-soluble organic solvent in the ink takes the initiative to penetrate into the recording medium as the water evaporates. it is conceivable that.

  In this case, it is considered that the concentration of the water-soluble organic solvent is higher in the penetrating liquid outer peripheral portion 103 than in the central portion 102 of the dots shown in FIG. As a result, the ratio of the water-soluble organic solvent to the coloring material in the penetrating liquid outer peripheral portion 103 rapidly increases, and when the constituent components of the water-soluble organic solvent contain what becomes a poor solvent for the coloring material, Alternatively, when a material that does not substantially solvate the colorant and does not substantially ionically dissociate the ionic group of the colorant is contained, the dispersion of the colorant becomes unstable, and the colorant aggregates or disperses. Destruction occurs and begins to precipitate.

  Then, as shown in FIG. 10C, the coloring material 104 deposited by aggregation or dispersion failure makes it as if a bank is formed on the outer edge portion of the dot. Subsequently, the evaporation and penetration of moisture and water-soluble organic solvent proceed in the center of the dot, and the color material is sequentially deposited to form the final dot 105 (FIG. 10 (d)).

  In the image formed by the above-described process, in the initial stage after the ink has landed on the recording medium, the penetration depth and the extent of the color material penetration into the recording medium are determined. As a result, the OD (optical density) is high and bleed is effectively suppressed.

[Determination of good and poor solvents]
Under the assumed mechanism as described above, the good solvent and the poor solvent used in the present invention are determined depending on whether or not the dispersion state of the pigment can be maintained well. Therefore, in the preparation of the water-based ink used in the ink set according to the present invention, when selecting a good solvent and a poor solvent, it is preferable to observe the stability of the dispersion state of the pigment to be used and obtain the result. And the present inventors examined various reference | standards of the determination of the good solvent and poor solvent which bring about the effect of this invention in relation to the effect of this invention. As a result, the pigment particle size when the pigment dispersion containing about 50% by mass of the solvent to be determined and containing the pigment used in the ink in a dispersed state is stored at 60 ° C. for 48 hours, A solvent that does not contain the solvent to be judged or contains a small amount and that is increased compared to the pigment particle size of the pigment dispersion containing the pigment used in the ink in a dispersed state is regarded as a poor solvent, and the solvent to be judged Consistency with the effect of the present invention is defined as a good solvent that does not contain or is contained in a small amount, and is defined as a good solvent that is the same or reduced as the pigment dispersion containing the pigment used in the ink in a dispersed state. I found something very good.

More specifically, it was determined by the following method whether the solvent used for the specific pigment is a good solvent or a poor solvent. First, the following two pigment dispersions A and B are prepared.
Pigment dispersion A: Pigment dispersion having a composition in which the concentration of the water-soluble organic solvent to be determined is 50% by mass, the concentration of the pigment is 5% by mass, and the concentration of water is 45% by mass. Pigment dispersion B: The concentration of the pigment 5% by mass of a pigment dispersion containing no water-soluble organic solvent

  Next, after the pigment dispersion A was stored at 60 ° C. for 48 hours and then cooled to room temperature, the pigment particle size of the pigment dispersion A was measured using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). And measured. Similarly, the pigment particle size of the pigment dispersion B was measured using the concentrated particle size analyzer. Then, when the pigment particle diameters of the pigment dispersion liquid A and the pigment dispersion liquid B are the particle diameter (A) and the particle diameter (B), the determination target is determined according to the following definition from the relationship between these values. As a water-soluble organic solvent, a good solvent and a poor solvent were distinguished. When the particle size (A) is larger than the particle size (B), the water-soluble organic solvent as the determination target is the poor solvent, and the particle size (A) is the same as the particle size (B) or the particle size (A ) Was smaller than the particle size (B), the water-soluble organic solvent as the determination target was defined as a good solvent. When the ink having the configuration of the present invention was prepared using the good solvent and the poor solvent determined as described above, it was confirmed that the excellent effects as described above could be obtained.

[Definition of solvation and ion dissociation]
Next, a water-soluble organic solvent does not completely or substantially solvate a pigment in which at least one ionic group is bonded to the pigment particle surface directly or through another atomic group, The phenomenon that the ionic group of the pigment does not completely or substantially cause ionic dissociation in the water-soluble organic solvent will be described.

One factor that disperses pigment particles is electrostatic repulsion resulting from ion dissociation. In a pigment in which at least one ionic group is bonded to the surface of the pigment particle directly or via another atomic group, the ionic group causes ionic dissociation in the medium, resulting in charging of the pigment particle, resulting in The electrostatic repulsion force is one factor for dispersing the pigment particles in the medium. One of the indicators of this ion dissociation may be an attractive force between ions in the medium. When two charges q ₁ and q ₂ having different polarities are placed at a distance r in a medium having a relative permittivity ε _r to a vacuum permittivity ε ₀ , the attractive force F acting on the two charges is ,

It is known that

It is considered that the above formula 1 is also applied to an ionic group bonded to the pigment particle surface, and when the attractive force F is increased, the distance between the ion and the counter ion is shortened or the ions are completely separated from each other. As a result of ionic bonding, the charge amount of the pigment particles is reduced or the electric double layer is compressed, so that the electrostatic repulsion is weakened and the dispersion of the pigment particles becomes unstable. From the above formula 1, when using a water-soluble organic solvent having a small relative dielectric constant ε _r with respect to the vacuum dielectric constant ε ₀ , the interatomic attractive force of the ionic group bonded to the pigment particle surface increases, It is clear that the ionic groups of the coloring material are not substantially ion dissociated in the water-soluble organic solvent, and the dispersibility of the pigment particles due to electrostatic repulsion is reduced. The _value of the relative permittivity ε _r of the water-soluble organic solvent in the present invention relative to the vacuum permittivity ε ₀ at room temperature (for example, 25 ° C.) is preferably 35 or less, more preferably 30 or less.

  However, it has been difficult to explain the dispersibility of the pigment only by the degree of dissociation of the ionic group with respect to the solvent.

  Therefore, the present inventors paid attention to the solvation of the medium with respect to the pigment as another factor affecting the dispersion of the pigment particles. The solvation in the present invention is the affinity between the pigment and the solvent, and depends on how much the pigment has a portion having an affinity for the medium. As an example of the part having affinity with the medium, there is a pigment particle surface part to which no ionic group is bonded. For example, when the group having an ionic group is bonded to the pigment particle surface at a high density, the exposed area of the pigment particle surface portion having affinity with the medium is reduced, and the pigment particle surface is covered at a higher density. It is presumed that the synergistic effect with the influence of steric hindrance by the ionic group makes the medium difficult to solvate with respect to the pigment, and the dispersibility of the pigment decreases.

  When a combination of a pigment and a water-soluble organic solvent is applied to water-based ink so that dispersion due to electrostatic repulsion resulting from ionic dissociation of the ionic group and dispersion due to solvation with respect to the pigment of the medium do not occur completely or substantially Since an image is formed on the recording medium by the process described above, a high-quality image with a high OD (optical density) and effectively suppressed bleeding can be obtained.

  Below, the water-soluble organic solvent does not completely or substantially solvate with respect to the pigment, and the ionic group of the pigment does not completely or substantially ion dissociate in the water-soluble organic solvent. An example of a method for determining that is not dispersed in a water-soluble organic solvent will be described.

  First, a pigment is prepared in a state where the ionic group of the pigment having at least one ionic group bonded to the pigment particle surface directly or through another atomic group is not ionically dissociated. In the process of preparing the pigment, if there is something that meets the above conditions, use it, and if it is in the form of a pigment dispersion or ink dispersed by ionic dissociation, components other than the pigment such as the medium are washed or evaporated. A solid state pigment in which the ionic group is not ionically dissociated is prepared. Specifically, ultrafiltration, centrifugal separation, drying under reduced pressure and high temperature environment, and the like are effective. The obtained pigment is desirably pulverized into a powder form with a mortar or the like.

  Next, the pulverized product of the pigment obtained as described above is added to various water-soluble organic solvents at a concentration of 0.05% by mass and stirred for about 1 hour. At this point, there is also a combination of a pigment and a water-soluble organic solvent in which a clear solid-liquid phase separation can be visually confirmed. These combinations resulting in solid-liquid phase separation are such that the water-soluble organic solvent does not completely or substantially solvate the pigment, and the ionic group of the pigment is completely or substantially in the water-soluble organic solvent. Therefore, it can be determined that the pigment does not dissociate substantially and the pigment does not disperse in the water-soluble organic solvent.

  Further, the determination is performed as follows in order to ensure the determination. In order to precipitate the pigment that is not substantially dispersed in the water-soluble organic solvent to some extent, the mixture of the pigment and the water-soluble organic solvent is allowed to stand. The standing condition at this time depends on the viscosity of the solvent and the like, but as a guideline, it is about 100 hours at room temperature. Thereafter, the upper 50 mass% of the liquid phase is gently collected, and the collected liquid phase is filtered for the purpose of removing floating coarse particles. The pore size of the microfilter used for the filtration is determined depending on the particle size of the pigment, and as a guide, about 10 times the average particle size of the pigment in the aqueous dispersion can be mentioned. Then, the pigment concentration contained in the obtained filtrate (coloring material solvent dispersion) is measured.

  An example of a method for measuring the pigment concentration is measurement by absorbance. Specifically, the measurement is performed as follows. Absorbance at a certain wavelength (for example, 550 nm for a black pigment) by adding a predetermined amount of pure water to a water dispersion of a color material in which a color material of a known concentration (Ck% by mass) is dispersed in water and diluting to a predetermined magnification. Measure. The measured value of absorbance is defined as (ABS1). Next, the colorant solvent dispersion whose concentration is to be determined is diluted with pure water at the same magnification as described above, and the absorbance at the same wavelength as before is measured. The measured value of absorbance is defined as (ABS2). As a result, the color material concentration in the color material solvent dispersion is calculated by the following equation.

  Using the ratio of the color material concentration in the color material solvent dispersion liquid obtained as described above and the initial color material concentration (0.05% by mass in the above example) in the mixture of the color material and the water-soluble organic solvent. The colorant solvent dispersion rate (%) is defined as follows.

  For the color material solvent dispersion obtained as described above, for example, very small, such as 16 or less, preferably 10 or less, more preferably 5 or less, the color material is substantially dispersed in the water-soluble organic solvent. The water-soluble organic solvent is not completely or substantially solvated with respect to the coloring material, and the ionic group of the coloring material is completely or substantially ionically dissociated in the water-soluble organic solvent. It is thought that it is not.

  In addition to the determination method described above, a method for determining that the pigment is a pigment that is not completely or substantially solvated with the water-soluble organic solvent, or that the ionic group of the pigment is completely in the water-soluble organic solvent. Alternatively, an example of a method for determining that ions are not substantially dissociated will be described.

  The first is an example of a method for determining that a pigment is a pigment that does not completely or substantially solvate with a water-soluble organic solvent. This is a measure of how much surfactant is adsorbed to the pigment. This makes it possible to make a determination. As described above, the degree of solvation depends on how much the pigment has a part having affinity with a medium such as a water-soluble organic solvent, and the amount of the part is the amount of the surfactant adsorbed. It can be said that there is a correlation. In other words, in a pigment that substantially solvates with a medium such as a water-soluble organic solvent, the above-mentioned affinity portion is large or large, and the adsorption amount of the surfactant is also large. On the other hand, in a pigment that does not completely or substantially solvate with a medium such as a water-soluble organic solvent, the above-mentioned affinity portion is small or small, and the adsorption amount of the surfactant is very small.

  Surfactant has the characteristic that the surface tension of the liquid changes remarkably depending on its concentration. Therefore, measurement of surface tension is effective as one index for estimating how much surfactant is adsorbed to the pigment. It is considered a means. For example, when comparing the surface tension of an aqueous solution containing a surfactant with a certain concentration and the surface tension of a liquid consisting of the surfactant with the same concentration, a pigment with a certain concentration, and water, the surfactant is compared to the pigment. In the case of hardly adsorbing, since the effective concentration of the surfactant that contributes to the reduction of the surface tension is almost the same in both liquids, the surface tension of the liquid is also almost the same. Conversely, when the amount of surfactant adsorbed on the pigment is large, the effective concentration of the surfactant is reduced in the liquid containing the pigment, and therefore the degree of decrease in surface tension compared to the surfactant aqueous solution not containing the pigment. Becomes smaller. In other words, unless the pigment has the effect of significantly reducing the surface tension of the liquid, the surface tension of the aqueous solution containing a certain concentration of surfactant, and a liquid composed of the surfactant of the same concentration, the pigment of a certain concentration, and water. It is possible to estimate how much the surfactant is adsorbed to the pigment from the difference in surface tension between the two.

  Specifically, first, a liquid (liquid 1) composed of a surfactant and water and having a surfactant concentration of 2 mmol / kg, the surfactant, a pigment and water, and the surfactant concentration is 2 mmol. A liquid (Liquid 2) having a pigment concentration of 5 mass% is prepared. The surfactant is not particularly limited as long as the surface tension of the liquid is remarkably changed depending on the concentration thereof, and those having the above (liquid 1) having a surface tension of 50 mN / m or less are preferable. Examples of the surfactant preferably used include those having a structure represented by the following structural formula (1) or structural formula (2).

  When preparing the above (Liquid 2), when collecting the pigment from the ink form, remove components other than the pigment as much as possible by using ultrafiltration, centrifugation, drying under reduced pressure and high temperature environment, etc. It is preferable to keep. If a large amount of components other than pigments, such as solvents, surfactants, and additives contained in the ink, remain, the surface tension of the liquid will change due to these components, and the degree of adsorption of the surfactant to the pigments will increase. This is because there is a possibility that an accurate determination result cannot be obtained. It is preferable that the surface tension of a liquid composed of a pigment collected from ink and water and having a pigment concentration of 5% by mass is 65 mN / m or more.

  After sufficiently stirring (Liquid 1) and (Liquid 2) prepared by the above procedure, each surface tension is measured. When the surface tension of (Liquid 1) is A (mN / m) and the surface tension of (Liquid 2) is B (mN / m), the relationship of B−A ≦ 10, preferably B−A ≦ 5 is satisfied. It is determined that the surfactant is not completely or substantially adsorbed to the pigment, and such a pigment is a pigment that does not completely or substantially solvate with a medium such as a water-soluble organic solvent. It is determined.

  Next, an example of a method for determining that the ionic group of the pigment is not completely or substantially ionically dissociated in the water-soluble organic solvent will be described. For example, such determination can be made by electrophoretic measurement of particles or observation of zeta potential. When dissociation of an ionic group of a pigment occurs in a water-soluble organic solvent, the pigment is charged, so that in the presence of an electric field, movement in a specific direction according to its polarity, so-called electrophoresis occurs. In addition, the charged pigment that causes such electrophoresis has a certain value or more as the absolute value of the zeta potential in the water-soluble organic solvent. Conversely, in spite of having an ionic group, the presence of an electric field causes complete or substantially no movement in a specific direction, that is, complete or substantially no electrophoresis occurs, A pigment having a (very) small value as an absolute value of zeta potential is not completely or substantially charged in the water-soluble organic solvent, that is, the ionic group of the pigment is completely or substantially uncharged. It is thought that ion dissociation has not occurred.

  Specifically, first, the pigment or the ink containing the pigment is diluted with various water-soluble organic solvents. When ink containing pigments is used, components other than pigments such as water and media are also included in the diluted solution, but since the dilution is performed to a very thin concentration, the effect of these is It can be regarded that the interaction between the water-soluble organic solvent present in a large excess and the pigment is dominant.

  Using this dilute solution, a microscopic zeta potential measuring device (trade name: ZEECOM; manufactured by Microtech Nichion Co., Ltd.) capable of observing the actual movement of particles, the particles are completely or substantially in a specific direction when a voltage is applied. The ionic group of the pigment is the water-soluble organic solvent when it is determined that it does not migrate and is not completely or substantially electrophoretic, or when the absolute value of the measured zeta potential is (very) small Judgment is not complete or substantially ion dissociation.

  By the way, in the case of forming a color image in which different color areas are adjacent to each other on plain paper, if the ink set according to the present invention is used, as described above, the water-based ink of each color is formed on the paper surface. It is considered that the aggregation or dispersion destruction of the coloring material that progresses proceeds relatively quickly as compared with other inks.

  In the image forming method of the present invention, after forming an image with an ink of a certain color constituting the ink set of the present invention, more preferably, an ink of a certain color is applied by forming an image with an ink of a different color. After scanning, at least one scan or more is passed, and then scanning is performed to apply ink of a different color, so that even if multiple colors of ink come into contact with each other, mixed color bleeding does not occur on the paper surface, and bleed Can be effectively suppressed. In other words, only by performing image formation with different color inks with a time difference, a method of performing multi-pass printing that requires printing time to complete printing by a plurality of scans, or a separate recovery system for each color that is reactive to each other. The above-described excellent effect can be obtained without requiring a method for increasing the size of the device.

  The water-based ink used in the ink set according to the present invention is characterized in that the water-soluble organic solvent in the ink component has the above-described configuration in relation to the pigment to be used. The configuration may be the same as that of the water-based ink. Hereinafter, the aqueous medium, the color material, and other components constituting the ink of the present invention will be described.

<Aqueous medium>
First, the aqueous medium in which the pigment is dispersed will be described. The water-based ink used in the ink set according to the present invention includes a mixed solvent of water and a water-soluble organic solvent. When the water-soluble organic solvent is selected, the self-dispersion type used first is the method described above. It is necessary to discriminate between a good solvent and a poor solvent for the pigment, and based on the determination result, thereafter, it is necessary to prepare an ink so as to contain at least one kind of poor solvent. In order to exhibit the effects of the present invention more remarkably, it is particularly preferable that all the colors of the water-based ink used in the ink set contain a poor solvent.

  The water-soluble organic solvent is not particularly limited as long as it satisfies the above conditions, as determined by the method described above. Of course, the poor solvent alone can be used as a mixture of two or more types, It can also be used in combination with a good solvent for the color material. When the good solvent is contained, the ratio X: Y is 1: 2 or less when the total amount (% by mass) of the good solvent in the ink is X and the total amount (% by mass) of the poor solvent in the ink is Y. It is preferable to adjust the type and content of the water-soluble organic solvent constituting the ink so as to satisfy the above range. The ratio X: Y = 1: 2 or less means that when Y is 2, Y is 0 or more and 30 or less.

  In the present invention, the content of the water-soluble organic solvent is 1 to 50% by mass, preferably 5 to 30% by mass with respect to the total mass of the ink. Furthermore, the effect of the present invention is more remarkably exhibited in the form of a water-based ink in which the total amount of the poor solvent in the ink is contained twice or more by mass ratio with respect to the color material. In addition, as water, it is preferable to use deionized water, and it is preferable that content of water is 50-95 mass% with respect to the total mass of ink.

  Furthermore, when the black ink is contained in the aqueous ink used in the ink set according to the present invention, the amount (% by mass) of the total poor solvent in the black ink is equal to the total poor solvent in each of the other aqueous inks used in the ink set. When the amount is smaller than the amount (% by mass), the effect of the present invention is more remarkably exhibited.

<Color material>
Next, the coloring material constituting the water-based ink used in the ink set according to the present invention will be described. As the coloring material constituting the water-based ink of the present invention, a self-dispersing pigment in which at least one ionic group is bonded to the pigment particle surface directly or through another atomic group is used. As long as this condition is satisfied, there is no particular limitation, but in particular, a self-dispersing pigment in which a compound having an ionic group is bonded to the pigment particle surface using a diazo coupling method can be suitably used. These self-dispersing pigments can be used alone or in combination of two or more.

In particular, using a diazo coupling method, from the group consisting of —COOM1, —SO ₃ M1 and —PO ₃ H (M1) ₂ (wherein M1 represents a hydrogen atom, an alkali metal, ammonium or organic ammonium). A self-dispersing pigment in which at least one selected is bonded to the pigment particle surface directly or via another atomic group can be suitably used. 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. Although such a pigment is described in, for example, a patent document (WO97 / 476993), a detailed relationship between the pigment and the water-soluble organic solvent is not described. Among the above ionic groups, a pigment in which —COOM1 is bonded directly to the pigment particle surface or via another atomic group can be used more suitably because it is relatively easy to exhibit water resistance.

Further, more specifically, _-C 6 _H 4 -COOM1 group or _-C 6 _H 3 on the pigment particle surface - _{(COOM1) 2} group (M1 in the formula is a hydrogen atom, an alkali metal, ammonium or organic ammonium Can be suitably used, and particularly those having a —C ₆ H ₃ — (COOM1) ₂ group introduced can exhibit favorable effects in the constitution of the present invention.

Regarding the introduction amount of the -C ₆ H ₄ -COOM1 group or -C ₆ H _3- (COOM1) ₂ group onto the surface of the pigment particle, the amount of introduction per unit surface area of the pigment particle is larger. A preferable effect is exhibited. As described above, this is considered to be because the degree of solvation of the water-soluble organic solvent with respect to the pigment decreases due to steric hindrance or the like as the ionic group increases.

  The pigment that can be used in the aqueous ink of the present invention is not particularly limited, and any of those listed below can be used.

  Carbon black is suitable as the pigment used in the black ink. For example, 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 (above, Ki Bot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U , Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (above, manufactured by Degussa), No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. Commercial products such as 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical) can be used. Carbon black newly prepared for the present invention can also be used. However, the present invention is not limited to these, and any conventionally known carbon black can be used. Further, the material is not limited to carbon black, and magnetic fine particles such as magnetite and ferrite, titanium black, and the like may be used as the 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, and soluble azo pigments such as ritole red, heliobordeaux, pigment scarlet, and permanent red 2B. Derivatives from vat dyes such as alizarin, indanthrone, thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, and perylene pigments such as perylene red and perylene scarlet , Isoindolinone yellow, isoindolinone pigments such as isoindolinone orange, benzimidazolone yellow, benzimidazolone orange, benzimidazolone red Imidazolone pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, indigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel Azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet and the like can be mentioned. Of course, it is not limited to these, Other organic pigments may be used.

Moreover, when the organic pigment which can be used by this invention is shown by a color index (CI) number, the following are mentioned, for example.
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. can be exemplified. In the present invention, the pigment content is 0.1 to 15% by mass, preferably 1 to 10% by mass, based on the total mass of the ink.

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

  Further, the ink used in the aqueous ink set according to the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, and a reduction inhibitor, as necessary, in addition to the above components. Various additives such as an agent, an evaporation accelerator and a chelating agent may be contained. Moreover, it is also possible to improve abrasion resistance and marker resistance by containing a polymer etc. as needed. In particular, a nonionic polymer having no ionic group has little influence on the reliability of the ink and can be suitably used.

  It is preferable that the ink used in the present invention composed of the constituents described above has a characteristic that it can be discharged well from an ink jet recording head. For this reason, from the viewpoint of ejectability from the 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 or more, and a viscosity of 1 to 5 mPa · s. The surface tension is preferably 25 to 50 mN / m.

<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 recording is performed on plain paper by an ink jet recording method using an ink set in which water-based inks of different colors are combined. When forming an image in which the images are adjacent to each other, after performing scanning that applies ink of a certain color to form an image, scanning that applies ink of a different color to the region where the image is formed is performed It is characterized by that. A specific method will be described below.

  In the image forming method of the present invention, it is preferable to use a recording head in which ink ejection port arrays for ejecting ink of each color are arranged shifted in the sub-scanning direction. FIG. 8 shows an example of a recording head that can be used when performing the recording method of the present invention. In FIG. 8, first, the black print data is scanned on a recording medium such as plain paper by one-pass printing by scanning the print head in the horizontal direction (main scanning direction) using the black ink ejection port array. Form. Next, the recording medium is transported in the vertical direction (sub-scanning direction) in the figure by the distance of the black ink ejection port array, and the cyan ink ejection port array is moved in the forward scanning process of the next print head. Then, the cyan ink image is formed in the one-pass printing in the area formed with the black ink. At this time, the black ink ejection port array simultaneously performs image formation in the next region. Similarly, image formation with magenta ink and yellow ink is sequentially performed. By repeating this, black and color mixed image formation is performed.

  FIG. 9 shows another example of a recording head that can be used when carrying out the recording method of the present invention. In the illustrated recording head, as shown in the drawing, a distance corresponding to one paper feed amount a 'is placed between the portion a of the black ink ejection port array and the portion b of the cyan ink. For this reason, the recording head having such a configuration causes an extra time difference for one print scan in a reciprocating period from the formation of a black image to the formation of a color image. The same applies to magenta and yellow. Therefore, the recording head illustrated in FIG. 9 has a more advantageous configuration for preventing bleeding between colors than the configuration shown in FIG. Although the image forming method of the present invention has been described above, the form of the recording head that can be used in the method of the present invention is not limited to FIGS. 8 and 9.

  In addition, as the order of the color of the ink applied to the recording medium, it is preferable that the ink is applied in order from the one with the lower lightness, for example, the black ink, from the viewpoint of advantageous for preventing bleeding.

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

  When a pulsed electric signal is applied to the electrodes 17-1 and 17-2 of the head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. The pressure causes the meniscus 23 to protrude, and the ink 21 is ejected through the ink nozzles 14 of the head to form ink droplets 24 from the ejection orifices 22 and fly toward the recording medium 25.

  FIG. 3 shows an external view of an example of a multi-head in which a large number of heads shown in FIG. 1 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

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

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

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

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

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

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

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

  Next, as a preferable example of an ink jet recording apparatus using mechanical energy, a nozzle forming substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material disposed opposite to the nozzles, and the pressure An on-demand ink jet recording head that includes ink that fills the periphery of the generating element, displaces the pressure generating element by an applied voltage, and discharges a small droplet of ink from a nozzle can be exemplified. An example of the configuration of a recording head which is a main part of the recording apparatus is shown in FIG. The head includes an ink flow path 80 communicating with an ink chamber (not shown), an orifice plate 81 for ejecting ink droplets of a desired volume, a vibration plate 82 that directly applies pressure to ink, and the vibration plate 82. And a substrate 84 for supporting and fixing the orifice plate 81, the diaphragm 82 and the like. The ink flow path 80 is formed of a photosensitive resin or the like, the orifice plate 81 is formed with a discharge port 85 by drilling or the like by electroforming or pressing a metal such as stainless steel or nickel, and the diaphragm 82 is made of stainless steel. The piezoelectric element 83 is formed of a dielectric material such as barium titanate or PZT. The recording head configured as described above applies a pulsed voltage to the piezoelectric element 83 to generate a distortion stress, and the energy deforms the vibration plate bonded to the piezoelectric element 83, so that the ink in the ink flow path 80 is obtained. Is pressed vertically and ink droplets (not shown) are ejected from the ejection ports 85 of the orifice plate 81 to perform recording. Such a recording head is used by being incorporated in an ink jet recording apparatus similar to that shown in FIG. The detailed operation of the ink jet recording apparatus can be performed in the same manner as described above.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited by the following Example, unless the summary is exceeded. In the text, “parts” and “%” are based on mass unless otherwise specified.

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

When the ionic group density of the self-dispersing carbon black A prepared above was measured, it was 3.1 μmol / m ² . The ionic group density used here was measured by measuring the sodium ion concentration in the black pigment dispersion A prepared above using an ion meter (manufactured by Toa DKK), and using the value, self-dispersing carbon black Converted to the ionic group density of A.

(Preparation of black pigment dispersion B)
To a solution of 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water, 0.7 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing this solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 0.9 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 10 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare self-dispersing carbon black B. Further, water was added to the self-dispersing carbon black B obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a black pigment dispersion B was obtained in a state where self-dispersing carbon black B in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of the carbon black particles was dispersed in water.

When the ionic group density of the self-dispersing carbon black B prepared above was measured by the same method as that for the self-dispersing carbon black A, it was 1.4 μmol / m ² .

(Preparation of Cyan Pigment Dispersion A)
To a solution prepared by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After stirring this solution for another 15 minutes, 5 g of Pigment Blue 15: 3 was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing cyan pigment A. Further, water was added to the self-dispersing cyan pigment A obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a cyan pigment dispersion A was obtained in which a self-dispersing cyan pigment A in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of cyan pigment particles was dispersed in water.

(Preparation of Cyan Pigment Dispersion B)
To a solution of 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water, 0.7 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing this solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 0.9 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. This solution was stirred for an additional 15 minutes, and then 15 g of Pigment Blue 15: 3 was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing cyan pigment B. Further, water was added to the self-dispersing cyan pigment B obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a cyan pigment dispersion B was obtained in which a self-dispersing cyan pigment B in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of the cyan pigment particles was dispersed in water.

(Preparation of magenta pigment dispersion A)
To a solution prepared by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 5 g of Pigment Red 122 was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing magenta pigment A. Further, water was added to the self-dispersing magenta pigment A obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a magenta pigment dispersion A was obtained in which a self-dispersing magenta pigment A in which -C ₆ H _3- (COONa) ₂ groups were introduced on the surface of magenta pigment particles was dispersed in water.

(Preparation of magenta pigment dispersion B)
To a solution of 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water, 0.7 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing this solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 0.9 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 15 g of Pigment Red 122 was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing magenta pigment B. Furthermore, water was added to the self-dispersing magenta pigment B obtained above to disperse the pigment so that the pigment concentration would be 10% by mass to prepare a dispersion. By the above method, a magenta pigment dispersion B was obtained in which a self-dispersing magenta pigment B in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of magenta pigment particles was dispersed in water.

(Preparation of yellow pigment dispersion A)
To a solution prepared by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 5 g of Pigment Yellow 74 was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing yellow pigment A. Further, water was added to the self-dispersing yellow pigment A obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a yellow pigment dispersion A was obtained in which a self-dispersing yellow pigment A in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of yellow pigment particles was dispersed in water.

(Preparation of yellow pigment dispersion B)
To a solution of 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water, 0.7 g of 4-aminophthalic acid was added while being cooled to 5 ° C. Next, the container containing this solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 0.9 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 15 g of Pigment Yellow 74 was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare a self-dispersing yellow pigment B. Further, water was added to the self-dispersing yellow pigment B obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a yellow pigment dispersion B was obtained in which a self-dispersing yellow pigment B in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of the yellow pigment particles was dispersed in water.

[Method for determining dispersibility of pigment in water-soluble organic solvent]
A combination of a pigment constituting a water-based ink used in the ink set according to the present invention and a water-soluble organic solvent, that is, the water-soluble organic solvent does not completely or substantially solvate the pigment, and pigment particles In determining a combination in which the ionic group on the surface does not completely or substantially ion dissociate with respect to the water-soluble organic solvent, that is, a combination in which it can be determined that the pigment is not substantially dispersed in the water-soluble organic solvent. The following experiment was conducted.

  The combination of the pigment obtained by the above-described method and various water-soluble organic solvents will be described by taking self-dispersing carbon blacks A and B as examples. In the process of preparing the pigment dispersion described above, the self-dispersed carbon blacks A and B obtained after being dried in an oven at 110 ° C. were each pulverized in powder form with a mortar or the like. Each of these pigments was added to various water-soluble organic solvents to be studied so that the pigment concentration was 0.05% by mass, stirred for about 1 hour, and observed. There were some combinations of pigments and water-soluble organic solvents whose liquid phase separation could be visually confirmed. In this combination, the water-soluble organic solvent is not completely or substantially solvated with respect to the pigment, and the ionic groups on the surface of the carbon black particles are not ionically dissociated in the water-soluble organic solvent. It can be determined that the pigment is not dispersed in the water-soluble organic solvent.

  Furthermore, the following measurement was performed and the combination which can be judged that a pigment did not disperse | distribute with respect to a water-soluble organic solvent substantially was determined quantitatively. First, the mixture of each pigment and each water-soluble organic solvent described above was allowed to stand at room temperature for about 100 hours, and then the upper 50% of the liquid phase was collected and filtered using a microfilter having a pore size of 1.2 μm. And about the obtained filtrate (coloring material solvent dispersion liquid), the coloring material density | concentration contained in a filtrate was measured with the following method. In addition, the following method is an example of a measuring method, and this invention is not limited to this.

  The colorant concentration of the filtrate was measured by the following method by absorptiometry. First, the absorbance at a certain wavelength (for example, 550 nm in the case of a black pigment) is obtained by adding a predetermined amount of pure water to a color material dispersion obtained by dispersing a color material having a known concentration (Ck mass%) in water and diluting the color material at a predetermined magnification. taking measurement. The measured value of absorbance is defined as (ABS1). Next, the colorant solvent dispersion (filtrate) for which the colorant concentration is to be obtained is diluted with pure water at the same magnification as described above, and the absorbance at the same wavelength as before is measured. ). As a result, the color material concentration in the color material solvent dispersion (filtrate) is calculated by the following equation.

  The color material concentration in the color material solvent dispersion (filtrate) obtained as described above and the initial color material concentration (initially set concentration in the mixture of the color material and the water-soluble organic solvent. The above example) Then, using a ratio of 0.05% by mass), the dispersion ratio (hereinafter referred to as color material solvent dispersion ratio) (%) of a specific color material with respect to a specific water-soluble organic solvent was defined as follows.

  The values of the colorant solvent dispersion obtained by the above measurement and the visual confirmation results of the solid-liquid phase separation described above are shown in Table 1 below. In the table, black pigments A and B are self-dispersing carbon blacks A and B.

  From the results shown in Table 1 above, since solid-liquid phase separation occurs in the combination of black pigment A and polyethylene glycol 600, the water-soluble organic solvent does not completely or substantially solvate the pigment, Further, it can be determined that the ionic group of the pigment is not completely or substantially ion-dissociated in the water-soluble organic solvent, and the pigment is not substantially dispersed in the water-soluble organic solvent.

  Further, in addition to the above determination, each pigment used above is determined to be a pigment that does not completely or substantially solvate with the water-soluble organic solvent of interest, and further, the ionicity of the pigment particle surface The determination that the ionic dissociation was not completely or substantially with respect to the target water-soluble organic solvent was made by each method described below.

  Specifically, first, a liquid (liquid 1) comprising a surfactant having a structure represented by the following structural formula (1) or structural formula (2) and water, and having a surfactant concentration of 2 mmol / kg, Various liquids (liquid 2) comprising the surfactant, pigment (any one of pigments A to D) and water, having a surfactant concentration of 2 mmol / kg and a pigment concentration of 5% by mass were prepared. . (Liquid 1) and (Liquid 2) were prepared by mixing each component and stirring for about 30 minutes under normal temperature conditions.

  The surface tension at room temperature (25 ° C.) of the liquid in which the black pigments A and B were added and the pigment concentration in water was 5% by mass was measured. m), and it was confirmed that the black pigments A and B themselves have no effect of reducing the surface tension of the liquid.

  Table 2 shows the surface tension measurement results A and B for (Liquid 1) and (Liquid 2) at room temperature, and the difference B-A in the surface tension between (Liquid 2) and (Liquid 1). It was.

  As is clear from the results in Table 2 above, in the black pigment A, the difference B−A between the surface tension B of (Liquid 2) and the surface tension A of (Liquid 1) is compared with that of the black pigment B. A small value was shown. This means that in the black pigment A, the effective concentration of the surfactant that contributes to the reduction of the surface tension of the liquid is substantially equal regardless of the presence or absence of the pigment. That is, it is determined that the surfactant is not completely or substantially adsorbed with respect to the black pigment A. For the reason described above, the black pigment A is completely or substantially a solvent with a medium such as a water-soluble organic solvent. It can be determined that the pigment is not compatible.

  The same determination was made for yellow pigments A and B, magenta pigments A and B, and cyan pigments A and B. As a result, yellow pigment A, magenta pigment A, and cyan pigment A were completely or substantially in combination with a medium such as a water-soluble organic solvent. Was determined to be a non-solvated pigment.

  Subsequently, for a pigment that does not completely or substantially solvate with the medium such as the water-soluble organic solvent, the ionic group of the pigment does not completely or substantially ion dissociate with respect to the water-soluble organic solvent. The determination was performed by the following method. The black pigment A will be described as an example.

  Specifically, first, the black pigment A is diluted with various water-soluble organic solvents so as to have a very thin concentration, thereby preparing an evaluation liquid. As a standard for dilution, the level is such that each particle can be sufficiently recognized by a microscopic zeta potential measuring device described later. When a voltage is applied to the evaluation liquid prepared as described above using a microscopic zeta potential measuring device (trade name: ZEECOM; manufactured by Microtech / Nichion) that can actually observe the movement of particles. Observe whether or not moves in a specific direction.

  As a result of the above observation, clear electrophoresis was confirmed in an evaluation liquid using glycerin or the like as a water-soluble organic solvent, whereas in an evaluation liquid using a water-soluble organic solvent such as polyethylene glycol 600, etc. The movement of the particles in a specific direction is not confirmed, and it can be determined that the electrophoresis does not substantially occur. That is, in such a water-soluble organic solvent, it can be determined that the ionic groups on the surface of the pigment particles of the black pigment A are not completely or substantially ionically dissociated in the water-soluble organic solvent for the reasons described above.

  Similar determinations were made for yellow pigment A, magenta pigment A, and cyan pigment A, which are pigments that are not completely or substantially solvated with a medium such as a water-soluble organic solvent. It was determined that the ionic group on the pigment particle surface of Pigment A did not completely or substantially ion dissociate in a water-soluble organic solvent such as polyethylene glycol 600.

[Method for verifying ink with unknown composition]
It is also possible to identify whether or not the ink (solvent verification ink) constituting the ink set having an unknown composition is the object of the present invention by using the determination method described above. The verification method will be described below.

  Specifically, first, the type and content of the water-soluble organic solvent contained in (solvent verification ink) are identified. For example, (solvent verification ink) diluted to a predetermined concentration with methanol is included in (solvent verification ink) by analyzing it using GC / MS (trade name: TRACE DSQ; manufactured by ThermoQuest). Identify the type of water-soluble organic solvent.

  Subsequently, the pigment component is collected from (solvent verification ink). At this time, it is preferable to remove components other than the pigment, for example, a solvent, a surfactant and an additive contained in the ink as much as possible. An example of a means for separating a pigment and a component other than the pigment is as follows. First, (solvent verification ink) is diluted about 10 times with pure water, and an ultrafiltration device (trade name: Centramate Low Volume; manufactured by PALL) Then, ultrafiltration is performed using a filter having a molecular weight cut off of 300,000 until the liquid amount becomes the original amount, and water-soluble components other than the pigment are separated from the system together with the filtrate. By repeating this process several times, a liquid mainly composed of pigment and pure water can be obtained. As a guideline for the number of repetitions of the above-mentioned process, water-soluble components other than pigments, for example, solvents, surfactants, additives, etc. contained in the ink are hardly contained in the filtrate. preferable.

  Next, after drying the liquid obtained as described above and a liquid containing water as a main component (for example, in an environment of 60 ° C.) to remove water, the powder is pulverized in a mortar or the like, and the pigment is used as the main component. To prepare a powder. If necessary, the powder can be dried (for example, for 24 hours) in a reduced pressure and high temperature (for example, 100 ° C.) environment to remove components other than the pigment remaining in a trace amount. By the above series of operations, a pigment extracted from (solvent verification ink) can be obtained.

  Then, using the pigment extracted from the (solvent verification ink) and the water-soluble organic solvent contained in the (solvent verification ink) identified by the above-described method, a test according to the determination method described above was performed. Then, it is determined whether or not the ink whose composition is unknown (solvent verification ink) is the object of the present invention.

  As a result of performing the above operations and determinations on the inks constituting the ink sets of Examples and Comparative Examples to be described later, an appropriate determination result was obtained. It was confirmed that the above-described operation and determination method are effective in identifying whether the verification ink) is an object of the present invention.

<Preparation of ink>
Using each of the water-soluble organic solvents examined above and the pigment dispersion of each color, the components listed in Tables 3 to 6 were mixed, dissolved or dispersed with sufficient stirring, and then a microfilter having a pore size of 3.0 μm. Each color ink was prepared by pressure filtration with Fuji Film. Tables 3, 4, 5 and 6 show the compositions (mass%) of black, cyan, magenta and yellow inks, respectively.

（＊）商品名：アセチレノールＥ−１００

(*) Product name: Acetylenol E-100

<Examples 1 and 2 and Comparative Examples 1 and 2>
The inks of the respective colors prepared above were combined as shown in Table 7 below to obtain ink sets of Examples 1 and 2 and Comparative Examples 1 and 2.

<Evaluation>
The following evaluations were performed using the ink sets of Examples 1 and 2 and Comparative Examples 1 and 2. The obtained evaluation results are shown in Table 8.

1. Printing density Each ink set of Examples 1 and 2 and Comparative Examples 1 and 2 and an ink jet recording apparatus having an on-demand type multi-recording head that discharges ink by applying thermal energy to the ink according to a recording signal Using a modified version of BJ F600 (manufactured by Canon), perform the following character printing on plain paper for copying A to E, including a solid portion of 2cm x 2cm. It was measured. The printer driver selected the default mode. The setting conditions for the default mode are shown below.
Paper type: Plain paper Print quality: Standard Color adjustment: Automatic

Using the print density obtained as a result of the measurement as described above, the evaluation was made according to the following criteria.
Black ink ○: The average print density of 5 papers is 1.4 or more. X: The average print density of 5 papers is less than 1.4. Cyan, magenta, yellow ink ○: The average print density of 5 papers is 1. 1 or more ×: The average print density of 5 papers is less than 1.1 In the above-described image output test, the following copy papers were used.
A: Canon, PPC paper NSK
B: Canon PPC paper NDK
C: Xerox PPC paper 4024
D: manufactured by Fox River, PPC paper prober bond E: manufactured by Neuzidora, PPC paper for Canon Bleed resistance Using the above ink sets and the above-described ink jet recording apparatus, solid portions of black and color (yellow, magenta, cyan) are printed adjacent to each other, and the degree of bleeding at the boundary portion of each color is visually observed. And evaluated according to the following criteria. The plain paper used here was Canon PB-Paper (NSK paper).
AA: The bleed cannot be visually recognized. A: The bleed is hardly noticeable. B: Although the bleed is present, the level is practically no problem. C: The bleed is not clear.

It is a longitudinal cross-sectional view of an inkjet recording device head. It is a vertical and horizontal view of an inkjet recording device head. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is a figure for demonstrating typically a mode when the ink droplet concerning this invention landed on the surface of a recording medium.

Explanation of symbols

13 Head 14 Ink Nozzle 15 Heating Element Substrate 16 Protective Layer 17-1, 17-2 Electrode 18 Heating Resistor Layer 19 Heat Storage Layer 20 Substrate 21 Ink 22 Discharge Orifice (Micropore)
23 Meniscus 24 Ink Droplet 25 Recording Medium 26 Multi Nozzle 27 Glass Plate 28 Heating Head 40 Ink Bag 42 Plug 44 Ink Absorber 45 Ink Cartridge 51 Paper Feeder 52 Paper Feed Roller 53 Paper Discharge Roller 61 Blade 62 Cap 63 Ink Absorber 64 Ejection recovery part 65 Recording head 66 Carriage 67 Guide shaft 68 Motor 69 Belt 70 Recording unit 71 Head part 72 Atmospheric communication port 80 Ink flow path 81 Orifice plate 82 Vibration plate 83 Piezoelectric element 84 Substrate 85 Ejection port 100 Recording medium 101 Ink droplet 102 dot central part 103 permeation liquid outer peripheral part 104 deposited color material 105 final dot

Claims (18)

  In an ink set including at least water, a coloring material, and a water-soluble organic solvent and having a plurality of water-based inks having different colors, the coloring material contained in at least one of the water-based inks has at least one ion on the pigment particle surface. A self-dispersing pigment in which a functional group is bonded directly or through another atomic group, and at least one color of each water-based ink contains at least a water-soluble organic solvent that is a poor solvent for the self-dispersing pigment. 1 type, the poor solvent is not completely or substantially solvated with respect to the self-dispersing pigment, and the ionic group is not completely or substantially ionically dissociated in the poor solvent. An ink set comprising:   In an ink set using a combination of water-based inks of different colors containing at least water, a coloring material and a water-soluble organic solvent, the coloring material has at least one ionic group directly or other atomic group on the pigment particle surface. The water-soluble organic solvent contained in at least one color of each water-based ink is composed only of a water-soluble organic solvent that is a poor solvent for the self-dispersing pigment. The poor solvent does not completely or substantially solvate with the self-dispersing pigment, and the ionic group does not completely or substantially ion dissociate in the poor solvent. Characteristic ink set.   The water-based ink constituting the ink set contains a water-soluble organic solvent that is a poor solvent for the self-dispersing pigment in a mass ratio of at least twice that of the self-dispersing pigment. The ink set according to 2. The ionic group is selected from the group consisting of —COOM1, —SO ₂ M1 and —PO ₂ H (M1) ₂ (wherein M1 represents any one of a hydrogen atom, an alkali metal, ammonium and organic ammonium). The ink set according to any one of claims 1 to 3.   The said other atomic group is selected from the group which consists of a C1-C12 alkylene group, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Ink set.   The water-based ink constituting the ink set is a water-based ink having at least two different colors selected from black, cyan, magenta, yellow, red, blue, and green. Ink set.   The ink set according to any one of claims 1 to 6, wherein at least one of the water-based inks constituting the ink set is a black ink.   The ink set according to claim 7, wherein the black ink contains carbon black in which at least one ionic group is bonded to the pigment particle surface directly or through another atomic group.   The ink set according to claim 1, wherein the ink set is for inkjet.   An ink jet recording method comprising a step of discharging the ink set according to claim 9 by an ink jet recording method.   An ink cartridge containing the ink set according to claim 1.   A recording unit comprising: an ink storage unit that stores the ink set according to claim 1; and an ink jet head that discharges the ink.   An ink jet recording apparatus comprising: an ink containing portion containing the ink set according to any one of claims 1 to 9; and an ink jet head for discharging the ink.   An image forming method for recording on plain paper by an ink jet recording method using an ink set in which water-based inks of different colors are combined, wherein the ink set according to any one of claims 1 to 9 is used as the ink set. And an image forming method for forming an image in which images formed with water-based inks of different colors are adjacent to each other.   The image forming method according to claim 14, wherein after an image is formed by performing scanning for applying an ink of a certain color, scanning for applying an ink of a different color is performed on a region where the image is formed.   16. The image forming method according to claim 14 or 15, wherein after performing a scan for applying a certain color of ink, a scan for applying an ink of a different color is performed after a gap of at least one scan.   The ink application is performed using a recording head in which an ejection port array for a certain color of ink and an ejection port array for an ink of a different color are arranged to be shifted in the sub-scanning direction. The image forming method according to item.   The image forming method according to any one of claims 14 to 17, wherein the image formation in a certain region starts from a scan for applying black ink.

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