JP4612793B2 - Inkjet recording method - Google Patents

Description

  The present invention relates to a water-based ink containing a water-insoluble colorant, and more particularly to a recording method and a recording apparatus using an inkjet recording method, and further to a water-based ink suitable for an image forming method.

  2. Description of the Related Art Conventionally, it is known that an image having excellent fastness such as water resistance and light resistance can be obtained by using a water-insoluble colorant as a colorant, for example, an ink containing a pigment (pigment ink). In recent years, various techniques have been proposed for the purpose of further improving the optical density of an image formed with such an ink. For example, a technique has been proposed that achieves a further improvement in 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-containing aqueous solution are attached to a recording medium, and the ink composition and the polyvalent metal aqueous solution There is a proposal of a technique for forming a high-quality image by reacting (see, for example, Patent Document 2). In these techniques, in any case, the pigment present 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, An image having a higher density than that obtained with a conventional pigment ink is obtained.

  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 compared to the volume of the ink droplets. It has been found that the area (so-called area factor) that can be performed 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 technique than in the case of a conventional pigment ink in which a pigment is dispersed with a polymer dispersant or the like. There is room for improvement in this regard. In addition, there is 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 is not limited to the surface of the recording medium. In some cases, the ink penetrates into the interior and a sufficient image density cannot be obtained.

JP 2000-198955 A JP 2000-63719 A

  The present inventors have pursued the advantages and disadvantages of each conventional ink and analyzed the characteristics of the image itself. As the concentration of the coloring material in the ink increases, more coloring material exists on the surface of the recording medium. In other words, it has been found that dots having visually varied shapes are formed, and that a desired color material cannot be effectively used in the recording medium and is used wastefully. The present inventors have found that an image superior to the conventional one can be formed by solving at least one of these 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, and in this case, there is a problem that the amount of ink applied necessary to obtain the same image density increases.
(2) When the permeability of the ink is increased, the ink penetrates not only in the surface of the recording medium but also in the thickness direction of the recording medium. The problem that the color material cannot be distributed by density and high image density cannot be achieved.

  Accordingly, an object of the present invention is to obtain an image having a sufficiently large area factor and a high OD (image density) even with a small amount of ink droplets in the pigment ink. The object is to provide a water-based ink having excellent properties. Another object of the present invention is to provide an ink jet recording method capable of forming a high-quality image with a high OD with a small ink application amount by using such an ink. 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 perform color mixing at the boundary between black ink and color ink areas without causing feathering when color image recording is performed in which different color areas are adjacent to plain paper. An object of the present invention is to provide an image forming method capable of effectively suppressing (bleed).

  Further, the technical gist of the present invention is conceptually summarized. In a water-based ink containing water, a plurality of different types of water-soluble organic solvents, and a water-insoluble colorant, the plurality of water-soluble organic solvents are used. A poor solvent for the water-insoluble colorant to be used, and a poor solvent for the water-insoluble colorant to be used, wherein each of the plurality of water-soluble organic solvents has a Ka value determined by the Bristow method. The poor solvent exhibiting the maximum Ka value diffuses in a form close to a perfect circle in the vicinity of the recording medium surface prior to the good solvent, and the water-insoluble organic solvent in the diffusion process The water-based ink is characterized by assisting the aggregation of the color material. With this configuration, in addition to the advantage that it is not necessary to include a large amount of color material in the ink that cannot be consumed by being diffused in the recording medium as in the prior art, and is wasted, it is ideal for the image itself. In other words, there is no color material on the surface of the recording medium, and at the same time, the recording medium does not reach the back side (both sides can be recorded). A high density image can be formed in a uniform state on the surface side in the recording medium.

The above object is achieved by the present invention described below. That is, an ink jet recording method according to an embodiment of the present invention, the step of discharging with an inkjet method of water soluble ink on a recording medium at least having an ink jet recording method, the aqueous ink, water, different kinds of a plurality and a water-soluble organic solvent, containing a water-insoluble colorant, a water-soluble organic solvent wherein the plurality of the good solvent for the water-insoluble colorant, a plurality of poor solvent for the water-insoluble colorant, the the good solvent in the total amount of the ink (mass%) a, the total amount of the poor solvent (mass%) in the case of the B in the ink, a: B is 10: 5 over 7: 9 is within the range , selected from the group at least one poor solvent for said plurality of consisting of diethylene glycol, polyethylene glycol and 2-pyrrolidone, water-insoluble colorant, a resin dispersion pigment, microcapsule Fee, hydrophilic group selected from the group consisting of self-dispersion pigment and polymer-bonded self-dispersion pigment is bonded through another atomic group to the pigment particle surface, the recording medium is, the more water-soluble organic each of the solvent, when comparing the Ka value determined by the Bristow method, a water-soluble organic solvent showing the Ka value of the maximum is characterized in that it is a plain paper such that the poor solvent.

  The present invention provides a water-based ink that can obtain an image having a sufficiently large area factor and a high OD (reflection density) even with a small amount of ink droplets in the pigment ink. Further, according to the present invention, by using such an ink, it can be suitably used for the ink jet recording method capable of forming a high quality image with a high OD even with a small ink application amount, and the above recording method. An ink cartridge, a recording unit, and an ink jet recording apparatus can be provided. Furthermore, according to the present invention, when performing color image recording in which different color areas are adjacent to each other on plain paper, color mixing (bleeding at the boundary between black ink and color ink areas does not occur without causing feathering). ) Can be effectively suppressed.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. First, the poor solvent and the good solvent used in this specification will be described. The details of the definition will be described later. Regardless of the dispersion method of the water-insoluble colorant, the water-insoluble colorant with good dispersion stability in the water-soluble organic solvent is a good solvent, and the poor one is a poor solvent. . A feature of the present invention is that it focuses on a water-soluble organic solvent contained in a water-based ink together with a water-insoluble colorant, and a water-soluble organic solvent having a function of dissolving or dispersing the water-insoluble colorant is used for the colorant. It is classified into those showing the behavior as the above poor solvent and those showing the behavior as a good solvent, and adjusted so that the ratio of the poor solvent to the good solvent in the aqueous ink is within a specific range. It is in the point which designed the ink. By adopting such a configuration, an image with reduced feathering and bleeding can be obtained even on plain paper, which has conventionally had various problems in image formation with water-based ink. Even if the amount is small, an ink having a sufficiently large area factor and capable of forming an image with a high OD can be obtained. Also, by using such ink, high-speed printing, downsizing of the recording device, cost reduction including consumables can be achieved, and it is excellent in robustness, can realize higher printing density, and form high-quality images. It has been found that a remarkable effect is obtained that it is possible to achieve the above, and the present invention has been achieved.

  Although the reason why such an effect is obtained by the present invention is not clear, the present inventors presume as follows. In general, when an image is formed with a water-based ink on recording paper such as plain paper, it is necessary to leave the color material on the paper more efficiently in order to achieve excellent print density and print quality. is there. As a method therefor, there is a method of obtaining an excellent print density and print quality by attaching a pigment ink to a recording paper after attaching a reaction liquid to a recording medium. In addition, there is a method that achieves both the storage stability of the ink and the achievement of a high print density by using a special dispersant. However, according to the study by the present inventors, it is difficult to obtain a sufficient print density even by these methods, and in particular, even with a small amount of ink droplets, it has a sufficiently large area factor and high print quality. The concentration could not be obtained.

  The water-based ink according to the present invention includes at least water, a water-insoluble color material, and a plurality of different types of water-soluble organic solvents, and as the water-soluble organic solvent, a good solvent for the water-insoluble color material, And a poor solvent for the water-insoluble colorant. When such a water-based ink is in an ink state, water, a water-soluble organic solvent containing a good solvent and a poor solvent for a water-insoluble colorant, and a water-insoluble colorant are mixed at a predetermined ratio, and water-insoluble pigments and the like are mixed. The storage stability of the coloring material is maintained.

  When such a water-based ink according to the present invention is printed on a recording medium, particularly plain paper, it is possible to provide a very excellent print density and print quality for the reasons described below. It is considered to be. That is, as shown in FIG. 14A, when the ink droplet 1301 according to the present invention is printed on a recording medium 1300, for example, plain paper, after landing on the ink recording medium, The ratio of water, the good and poor solvents of the water-insoluble colorant, and the water-insoluble colorant in the ink changes. That is, as shown in FIGS. 14A and 14B, 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 water first evaporates. Of the water-soluble organic solvents in the ink, the poor solvent 1307 having a high Ka value diffuses in a shape closer to a perfect circle near the recording medium surface than the good solvent having a low Ka value, and ink dots are formed. it is conceivable that.

  14B to 14D are schematic views showing the state of ink from when the ink lands on the recording medium 1300 until it is fixed later. Focusing on 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 dots in the contact portion between the ink and the paper than in the center portion 1303 of the dots. As a result, the ink dots diffuse near the recording medium surface in a shape close to a perfect circle, and in the process of spreading, the concentration of the poor solvent 1307 rapidly increases with respect to the water-insoluble colorant. Along with this, the water-insoluble color material becomes unstable, causing the color material to aggregate or disperse, and as a result, diffuses while taking a near-circumferential border in the vicinity of the paper surface (see FIG. 14B). The insoluble color material 1304 stays in the vicinity of the surface of the recording medium 1300, and it looks as if a water-insoluble color material bank is formed on the outer edge portion of the dot. 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 paper surface in that state (see FIG. 14C). At this point, the dot formation of the water-insoluble colorant is completed, but the water-soluble organic solvent and water in the ink spread radially while further diffusing. That is, even after the formation of the dots of the water-insoluble colorant, water and the water-soluble organic solvent diffuse near the recording medium surface. Subsequently, due to evaporation and permeation 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 that form an image (see FIG. 14D). ). The ink image formed by the process as described above has a sufficiently large area factor and a high print density even with a small amount of ink droplets, and the occurrence of feathering is sufficiently reduced. High quality.

  Under the assumption 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 water-insoluble colorant can be maintained well. That is, it is determined in relation to the water-insoluble colorant or its dispersant. Therefore, in the preparation of the ink according to the present invention, when a good solvent and a poor solvent are selected, it is preferable to observe the degree of stability of the dispersion state of the water-insoluble colorant 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 particle diameter in the liquid when the pigment dispersion containing about 50% by mass of the solvent to be determined and containing the water-insoluble colorant used in the ink in a dispersed state is stored at 60 ° C. for 48 hours. However, it is determined that the poor solvent does not contain the solvent to be judged or contains a small amount and is increased compared to the particle size of the pigment dispersion containing the water-insoluble colorant used in the ink in a dispersed state. The present invention is defined when a good solvent is defined as a pigment dispersion that does not contain or is contained in a small amount of the solvent to be used, and that is the same or reduced as the pigment dispersion containing the water-insoluble colorant used in the ink in a dispersed state. It was found that the consistency with the effect was extremely good.

More specifically, it was determined by the following method whether the solvent used for the specific water-insoluble colorant is a good solvent or a poor solvent. First, the following two water-insoluble colorant dispersions A and B are prepared.
A: The concentration of the water-soluble organic solvent to be determined is 50% by mass, the concentration of the water-insoluble colorant, or the total amount of the water-insoluble colorant and the substance contributing to the dispersion is 5% by mass, and the concentration of water is A water-insoluble colorant dispersion having a composition of 45% by mass;
B: An aqueous dispersion of a water-insoluble color material that does not contain a water-soluble organic solvent and has a concentration of 5% by mass of the total amount of the water-insoluble color material and substances that contribute to its dispersion.

  Next, the dispersion A was stored at 60 ° C. for 48 hours and then cooled to room temperature, and the particle size of the dispersion A was measured using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.), etc. It measured using. Similarly, the particle size of the aqueous dispersion B was measured using the concentrated particle size analyzer. And when each particle size value of the dispersion A and the water dispersion B is defined as a particle size (A) and a particle size (B), these values are classified into a good solvent and a poor solvent according to the following definitions. Determined. Thus, when the ink which has the structure of this invention was prepared using the determined good solvent and poor solvent, it has confirmed that the above outstanding effects could be acquired. In the above description, when the particle size (A) is larger than the particle size (B), the good solvent and the poor solvent use the water-soluble organic solvent as the determination target as the poor solvent, and the particle size (A) and the particle size (B ) Or when the particle size (A) is smaller than the particle size (B), the water-soluble organic solvent as the determination target is defined as a good solvent.

  The water-based ink according to the present invention may have the same configuration as that of a conventional water-based ink containing a water-insoluble colorant except that the water-soluble organic solvent has the specific configuration described above. That is, the first feature of the water-based ink according to the present invention includes at least water, a plurality of water-soluble organic solvents, and a water-insoluble colorant. The water-soluble organic solvent is determined by the determination method described above. Each of a plurality of different types of water-soluble organic solvents comprising at least one water-soluble organic solvent that is a good solvent and at least one water-soluble organic solvent that is a poor solvent. When the required Ka values are compared, the water-soluble organic solvent having 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 even with a small amount of ink droplets when printed on a recording medium, particularly plain paper. It is possible to form an image that has a factor and has a high print density and provides a very good print quality.

Here, the Ka value obtained by the Bristow method will be described. This value is used as a measure representing the penetrability of the ink into the recording medium. Taking the ink liquid as a reference example, when the ink permeability is expressed by the ink amount V per 1 m ² , the ink is applied to the recording medium after a predetermined time t has elapsed since the ink droplet was ejected. The permeation amount V (mL / m ² = μm) is expressed by the Bristow equation shown below.
V = Vr + Ka (t−tw) ^1/2

  Here, immediately after the ink droplets adhere to the surface of the recording medium, the ink is mostly absorbed in the uneven portion of the surface of the recording medium (the roughness portion of the surface of the recording medium). It hardly penetrates into the medium. The time between them is the contact time (tw), and the amount of ink absorbed in the concavo-convex portion of the recording medium at the contact time is Vr. Then, when the contact time is exceeded after the ink is deposited, the amount of penetration into the recording medium increases by a time proportional to the time that exceeds the contact time, that is, (t-tw) to the power of 1/2. . Ka is a proportional coefficient of this increase, and indicates a value corresponding to the penetration rate. The Ka value can be measured using a Bristow method dynamic liquid permeability tester (for example, trade name: Dynamic permeability tester S; manufactured by Toyo Seiki Seisakusho).

  Furthermore, the water-based ink according to the present invention has a ratio of A: B [in the ink, where A is the total amount (% by mass) of the good solvent in the ink and B is the total amount (% by mass) of the poor solvent in the ink. Total good solvent amount (% by mass): Total amount of poor solvent (% by mass) in the ink] is adjusted to be in the range of 10: 5 or more and 10:30 or less. The “total amount” indicates, for example, the sum of all types of solvents when there are plural types of solvents as good solvents. “A: B ratio is 10: 5 or more and 10:30 or less” means that when A is 10, B is 5 or more and 30 or less.

  Furthermore, in another embodiment of the present invention, in a water-based ink containing water, a plurality of different types of water-soluble organic solvents, and a water-insoluble colorant, the plurality of water-soluble organic solvents contain the water-insoluble color. When the Ka value obtained by the Bristow method of each of the good solvent for the material and the poor solvent for the water-insoluble colorant and each of the plurality of water-soluble organic solvents is compared, the maximum Ka is obtained. Examples thereof include water-based inks in which the water-soluble organic solvent exhibiting a value is a poor solvent, and the ink adhesion behavior to plain paper is as follows.

  The water-based ink according to the present invention having the above-described configuration exhibits the following behavior different from that of the conventional ink when the ink is fixed to plain paper. Even when a color image is recorded that has a sufficiently large area factor and has a high OD (reflection density), and that has different color areas adjacent to plain paper. It has been found that the effect of suppressing feathering can be obtained. In other words, it is possible to determine whether or not the ink according to the present invention has the above-described remarkable effects by measuring the behavior of the ink when the ink is fixed on plain paper by the following method. is there.

  The behavior of water-based ink with respect to plain paper is as follows. First, a needle with a needle diameter of 28G (inner diameter: 0.18 mm, outer diameter: 0.36 mm) is used, and the tip of the needle is placed at a height of 4 mm from the plain paper surface. Then, the target ink is dropped from there. Thereafter, the ink is fixed. Then, the diameter of the ink dot immediately after landing of the ink on the plain paper is measured, the measured value is defined as dI, the maximum diameter of the ink spread after the ink is fixed on the plain paper is measured, and the measured value is expressed as dS. And the maximum diameter of the spread of the water-insoluble colorant in the ink after the ink is fixed on plain paper is measured, and the measured value is defined as dC. In the water-based ink according to the present invention, a relationship of dC <dI <dS (Formula 1) is established between the measured values obtained as described above. Further, after the ink is fixed on plain paper by ink jet recording, the existing depth of the water-insoluble colorant on the plain paper is less than 30 μm.

  What is expressed by the above (Formula 1) is the maximum spread of the water-insoluble colorant in the ink shown in FIG. 14C with respect to the ink dot diameter dI immediately after landing shown in FIG. 14B. The diameter dC is dC <dI, and the relationship with the maximum ink spread diameter dS after fixing the ink onto the recording medium shown in FIG. 14D is expressed by dC <dI <dS. It shows that.

  In view of the configuration of the water-based ink according to the present invention, this relational expression shows that after the ink droplet is applied to the recording medium, the coloring material becomes a perfect circle near the recording medium surface by a poor solvent having a high Ka value. This means that the water and water-soluble organic solvent in the ink spread in a radial manner while being diffused further near the surface of the recording medium after being diffused and fixed in a close form. The fixing process of water and water-soluble organic solvent onto the recording medium indicates that water and the water-soluble organic solvent diffuse in the recording medium after the water-insoluble coloring material is fixed. . Further, the presence depth of the water-insoluble colorant after fixing on the recording medium is less than 30 μm, which means that the surface of the recording medium is effectively covered after the water-insoluble colorant is applied to the recording medium. It means that

  On the other hand, when the behavior of conventional water-based ink is measured on plain paper in the same manner, the maximum diameter dC of the spread of the water-insoluble colorant after the ink is fixed on the plain paper is the ink landing on the plain paper. The diameter dI of the ink dot immediately after the printing is greater than dI <dC <dS, and the boundary between the water-insoluble colorant and the water and water-soluble organic solvent spreading around the water-soluble colorant is the present invention. As compared with the water-based ink, the ink becomes unclear. This is because when water and water-soluble organic solvent diffuse in the recording medium after the ink has landed on plain paper, the water-insoluble color material spreads together, and the color material effectively spreads the paper surface. It cannot be covered and the outline of the color material is not a perfect circle, indicating that the print quality is unclear. Even when the relationship between the maximum diameter dS of the ink spread after fixing the ink on the recording medium satisfies the relationship dC <dI <dS, the presence depth of the water-insoluble colorant after fixing is sufficient. When the thickness is 30 μm or more, the water-insoluble color material penetrates not only in the vicinity of the surface of the paper but also in the depth direction of the paper, and in this case, the color material does not effectively cover the paper.

  In the present invention, when ink droplets are applied to plain paper as a recording medium, the ink dot diameter dI immediately after the ink has landed on the plain paper, the maximum diameter dS of the ink spread after fixing the ink on the plain paper, The maximum diameter dC of the spread of the water-insoluble colorant in the ink after fixing the ink on plain paper was measured by the following methods.

  First, a small amount of a water-soluble dye that is soluble in a water-soluble organic solvent contained in the ink and has a hue different from that of the water-insoluble colorant that is a constituent of the ink is added to the ink to be measured. By using ink, the maximum diameter dS of the spread of the ink component after fixing on plain paper can be measured visually. In other words, plain paper after the water-insoluble colorant in the ink is fixed by adding a small amount of a water-soluble dye that is soluble in the water-soluble organic solvent and has a hue different from that of the water-insoluble colorant. The spreading state of the water and the water-soluble organic solvent diffusing into it becomes visible by the presence of the water-soluble dye added to the ink.

  The ink dot diameter dI immediately after landing of the ink on the plain paper when the ink droplet is applied to the plain paper is determined using a contact angle meter (Face CONACT-ANGLEMETER CA-P) manufactured by Kyowa Interface Science Co., Ltd. Measured. Specifically, using a needle with a needle diameter of 28G (inner diameter: 0.18 mm, outer diameter: 0.36 mm), ink is dropped onto plain paper from a height where the distance between the needle tip and the plain paper surface is 4 mm. The diameter of the ink droplet after dropping was measured by reading with a scale of a contact angle meter. In other words, the read value was the ink dot diameter dI immediately after the ink landed on plain paper.

  Furthermore, the maximum diameter dS of the ink spread after fixing the ink on the plain paper and the maximum diameter dC of the spread of the water-insoluble colorant in the ink after fixing the ink on the plain paper are measured under the conditions described above. After the ink dots dropped on the plain paper are allowed to stand for 6 hours or more and the ink droplets are stabilized, the maximum linear length of the ink dots is measured, and the value is taken as the maximum diameter dC. The maximum diameter dS of the ink spread after fixing to the ink was determined by measuring the maximum linear length of the hue spread of the water-soluble dye having a hue different from that of the water-insoluble colorant in the ink. Further, the maximum diameter dC of the spread of the water-insoluble colorant in the ink after the ink is fixed on the plain paper is determined by measuring the maximum linear length of the spread of the hue of the water-insoluble colorant contained in the ink. Asked.

Further, the depth of the water-insoluble colorant after fixing the ink on plain paper was determined by cutting the printed portion of plain paper after printing the ink with an ink jet printer and observing the cross section under a microscope.
In order to make the ink dots in such a shape, when A is the total amount (% by mass) of the good solvent in the ink and B is the total amount (% by mass) of the poor solvent in the ink, A: B Ratio [total amount of good solvent in ink (% by mass): total amount of poor solvent in ink (% by mass)] of 10: 5 or more and 10:30 or less, and further 10: 5 or more and 10:10 or less. It is preferable to adjust so that it may become in the range, especially 10: 6 or more and 10:10 or less.

The water-based ink according to the present invention is a water-soluble organic material having a maximum Ka value when comparing the Ka values obtained by the Bristow method for each of a plurality of different types of water-soluble organic solvents contained in the ink. The solvent is a poor solvent. Further, according to the study by the present inventors, the Ka value of the ink is less than 1.5 (ml / m ² / msec ^1/2 ) in order to further improve the quality of the formed recorded image. Preferably, the Ka value is 0.2 (ml / m ² / msec ^1/2 ) or more and less than 1.5 (ml / m ² / msec ^1/2 ). It is preferable to do so. In other words, if the ink is configured to have 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 ink penetrating into the recording medium. As a result, it is possible to form a high-quality image with very little feathering. Further, by setting the Ka value of the ink to 0.2 (ml / m ² / msec ^1/2 ) or more, more preferable fixability can be obtained.

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

  By the way, in the case of forming an image in which black and color inks are mixed on plain paper, if the water-based ink according to the present invention is used as the black ink, as described above, the black ink is used on the paper. It is considered that the aggregation or dispersion destruction of the constituting color material proceeds relatively quickly as compared with other inks. In the image forming method according to the present invention, the aqueous ink according to the present invention is used for the black ink, and the image formation with the color ink is performed after the black ink image is formed, and more preferably, scanning for applying the black ink is performed. Later, at least one scan or more later, the scanning is performed to apply the color ink, and even if it comes into contact with the color ink, black and mixed color bleeding on the paper surface does not occur, and the bleeding property Excellent image formation is possible. That is, a method for performing multi-pass printing that requires printing time to complete printing by scanning a plurality of times only by performing image formation with black ink and color ink with a time difference, and a recovery system with black and color ink. The above-described excellent effects can be obtained without requiring a method for increasing the size of the device such as separate devices.

  Further, when the water-based ink according to the present invention is used, the color material in the ink remains efficiently on the recording medium for the reason described above, so that the ink less than the conventional ink discharge amount (droplet volume). This makes it possible to print with high density. Furthermore, since printing can be performed with a small amount of ink, effects such as cost reduction in image formation and a faster fixing time than conventional ink can be expected.

  The water-based ink 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 water-insoluble colorant to be used. A configuration similar to that of ink may be used. Below, each component which comprises the ink of this invention is demonstrated. First, the aqueous medium in which the water-insoluble color material is dispersed will be described.

<Aqueous medium>
The water-based ink according to the present invention includes water and a mixed solvent with a water-soluble organic solvent, and the water-soluble organic solvent can be selected from those listed below. In the present invention, when selecting a water-soluble organic solvent, first, in the method described above, first, a good solvent and a poor solvent for the water-insoluble colorant to be used are determined, and based on the determination result, The water-soluble organic solvent is selected and blended appropriately so that at least the good solvent and the poor solvent are mixed, and the content of each water-soluble organic solvent is within the range specified in the present invention. It is necessary to prepare.

  Specific examples of the water-soluble organic solvent include those having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol. Alkyl 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; Propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, etc. Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms; 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. As the water, it is desirable to use deionized water.

  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 to 50% by mass with respect to the total mass of the ink. The amount of water contained in the ink is preferably in the range of 50 to 95% by mass with respect to the total mass of the ink.

  In a preferred embodiment of the present invention, when the total amount (% by mass) of the good solvent in the ink is A and the total amount (% by mass) of the poor solvent in the ink is B, the ratio A: B is 10: 5 or more and 10 : The ratio A: B is more preferably in the range of 10: 5 to 10:10, more preferably the ratio A: B is in the range of 10: 6 to 10:10, so that it is in the range of 30 or less. The type and content of the water-soluble organic solvent constituting the water-based ink are adjusted so as to be within the range of 10 or less.

  According to the detailed study by the present inventors, when the ratio of the good solvent contained in the water-based ink is larger than the above range, the storage stability is excellent, but it is difficult to obtain a high print density, and vice versa. When the ratio of the good solvent is less than the above range, a high printing density can be obtained, but the storage stability 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 ink and the realization of a high print density. It becomes. Furthermore, as described above, in the present invention, when determining each water-soluble organic solvent to be contained in the ink, a measure representing the permeability to the recording medium possessed by each water-soluble organic solvent to be contained. By controlling the Ka value obtained by the Bristow method, it is impossible to obtain in the past that a sufficiently large area factor can be achieved even with a small amount of ink droplets and a high printing density can be realized. To achieve the desired effect.

  The storage stability of the ink is generally the stability of the ink in a form without water evaporation, and the realization of a high print density is achieved by the solvent on the paper surface in the ink dot formation when the ink lands on the paper. This is a phenomenon of pigment aggregation accompanying spreading.

  Another effect of using a poor solvent and a good solvent in the ink is not only a combination of storage stability and realization of a high print density, but also a certain degree of pigment aggregation when water in the ink evaporates. There is also an effect that it can be suppressed. Specifically, when ink droplets adhere to the nozzle surface of the recording head, the color material concentration in the ink increases due to evaporation of the ink. At this time, since the poor solvent and the good solvent coexist in the ink, the aggregation of the pigment can be suppressed to some extent by the good solvent effect. Thus, by including a good solvent in the ink, the aggregation of the pigment on the nozzle surface of the recording head is suppressed, so that an improvement in reliability in the recovery operation of the recording head can be expected.

<Water-insoluble colorant>
Next, the water-insoluble colorant constituting the water-based ink according to the present invention will be described. Regardless of the dispersion method, the water-insoluble color material constituting the water-based ink according to the present invention is, for example, a resin dispersion type pigment (resin dispersion type pigment) using a dispersant or an activator, or an activator dispersion type. It may be a pigment or a self-dispersing microcapsule-type pigment that has improved the dispersibility of the water-insoluble colorant itself and that can be dispersed without using a dispersant, or a hydrophilic group introduced on the surface of pigment particles Type pigments (self-dispersing pigments), and furthermore, modified pigments (polymer-bonding self-dispersing pigments) in which organic groups containing polymers are chemically bonded to the surface of pigment particles are used. it can. Of course, these pigments having different dispersion methods can also be used in combination. The ratio of the water-insoluble colorant to the total amount of ink is 0.1 to 15% by mass, more preferably 1 to 10% by mass. Hereinafter, these pigments that can be used in the present invention will be described.

[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 as 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, Ray Van 5750, Ray Van 5250, Ray Van 5000 ULTRA, Ray Van 3500, Ray Van 2000, Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA-II, Ray Van 1170, Ray Van 1255 (above, Colombia), Black Pearls L, Legal 400R, Legal 330R, Legal 660R, Mogul L, Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000, Monak 1100, Monak 1300, Monak 1400, Monak 2000, Valcan XC-72R (above, 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 (above, manufactured by Mitsubishi Chemical Corporation) 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.

  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.

  The organic pigment that can be used in the present invention is represented by a color index (CI) number. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153, 154, 166, 168, 180, 185, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 71, 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, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, C.I. I. Examples thereof include CI Pigment Brown 23, 25, 26, and the like.

[Resin dispersion type pigment]
As described above, as the water-insoluble colorant contained in the water-based ink according to the present invention, resin-dispersed pigments using a dispersant can also be used. A compound for dispersing such a hydrophobic pigment is required. As such a thing, what is called a dispersing agent, surfactant, resin dispersing agent, etc. can be used. The dispersant or surfactant is not particularly limited, but among them, anionic and nonionic ones can be preferably used. For example, as anionic compounds, fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensates, polyoxyethylene alkyls Sulfuric acid ester salts and substituted derivatives thereof; nonionic compounds such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxy Examples thereof include ethylene alkylamine, glycerin fatty acid ester, oxyethyleneoxypropylene block polymer, and substituted derivatives thereof. Resin dispersants include styrene and its derivatives, vinyl naphthalene and its derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its A block copolymer comprising at least two monomers (of which at least one is a hydrophilic monomer) selected from derivatives, fumaric acid and derivatives thereof, vinyl acetate, vinyl alcohol, vinyl pyrrolidone, acrylamide, and derivatives thereof. Examples thereof include a polymer, a random copolymer, a graft copolymer, and salts thereof.

[Microcapsule type pigment]
As the water-insoluble colorant contained in the water-based ink according to the present invention, as described above, a microcapsule type pigment formed by coating a water-insoluble colorant with an organic polymer to form a microcapsule is used. You can also Examples of a method for coating 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.

  Examples of organic polymers used as the material constituting the wall membrane material of the microcapsule include 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, (meth) acrylic acid polymer or copolymer, (meth) acrylic acid ester polymer or copolymer, (meth) acrylic acid- (meth) acrylic acid Le 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 can be used. Examples of the nonionic organic polymer include polyvinyl alcohol, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, methoxypolyethylene glycol monomethacrylate or their (co) polymer, and 2-oxazoline cationic ring-opening polymer. Can be mentioned. In particular, a completely saponified product of polyvinyl alcohol is particularly preferable because it has low water solubility and is easily dissolved in hot water but difficult to dissolve in cold water.

  When the phase inversion method or the acid precipitation method is selected as the microencapsulation method, anionic organic polymers are used as the organic polymers constituting the wall membrane material of the microcapsules. 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 microencapsulated while self-dispersing (phase inversion emulsification). In the above phase inversion method, there is no problem even if the organic solvent phase is produced by mixing a water-soluble organic solvent or additive used in the ink. In particular, it is more preferable to mix an ink liquid medium because a dispersion liquid for ink can be directly produced.

  On the other hand, in the acid precipitation method, a part or all of the anionic group of the anionic group-containing organic polymer is neutralized with a basic compound, and a colorant such as a self-dispersing organic pigment or self-dispersing carbon black; A water-containing cake obtained by a production method comprising a step of kneading in an aqueous medium and a step of neutralizing and acidifying an acidic compound to precipitate an anionic group-containing organic polymer and fixing the pigment to a pigment, This is a method of microencapsulation by neutralizing part or all of an anionic group using a compound. By doing in this way, the anionic microencapsulated pigment which is fine and contains many pigments can be manufactured.

  Examples of the solvent used for microencapsulation as described above include alkyl alcohols such as methanol, ethanol, propanol and butanol; aromatic hydrocarbons such as benzol, toluol and xylol; methyl acetate Esters such as 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; Cellosolves such as methyl cellosolve and butyl cellosolve Etc. The microcapsules prepared by the above method are separated once from these solvents by centrifugation or filtration, and this is stirred and redispersed with water and the necessary solvent to obtain the desired microcapsule type pigment and You can also The average particle size of the microencapsulated pigment obtained by the above method is preferably 50 nm to 180 nm.

[Self-dispersing pigment]
As described above, the water-insoluble colorant contained in the water-based ink according to the present invention is a self-dispersible material that has improved dispersibility of the water-insoluble colorant itself and can be dispersed without using a dispersant or the like. It is also possible to use a type of pigment. Examples of the self-dispersing pigment include those in which a hydrophilic group is chemically bonded to the pigment particle surface directly or through another atomic group. For example, the hydrophilic group introduced into the pigment particle surface, -COOM1, -SO ₃ M1 and _{-PO 3 H (M1) 2 (} M1 in the formula 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 contained in the water-based ink according to the present invention is a polymer bond that has improved the dispersibility of the water-insoluble colorant itself and can be dispersed without using a dispersant or the like. Self-dispersing pigments can also be used. This polymer-bonded self-dispersing pigment that does not use a dispersant is a co-polymerization of a functional group that is chemically bonded to the surface of the pigment directly or through another atomic group and an ionic monomer and a hydrophobic monomer. It is preferable to use the one containing the reaction product of the coalescence. That is, if a material having such a structure is used, the copolymerization ratio between the ionic monomer and the hydrophobic monomer, which is a material for forming a copolymer used for modifying the surface, can be appropriately changed. This is preferable because the hydrophilicity of the modified pigment can be appropriately adjusted. Moreover, since the kind of ionic monomer and hydrophobic monomer to be used, and a combination of both can be appropriately changed, various characteristics can be imparted to the pigment surface, which is also preferable from this point.

(Functional group)
The functional group in 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. The The reaction between the functional group and the copolymer is a reaction that generates a bond that does not cause hydrolysis, for example, an amide bond, considering that the pigment is dispersed in an aqueous medium. It is preferable that By making the functional group an amino group and supporting the carboxyl group on the copolymer, the copolymer can be introduced to the pigment particle surface via an amide bond. Similarly, the copolymer can be introduced to the pigment particle surface via an amide bond 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 via another atomic group. However, when a copolymer having a relatively large molecular weight is introduced to the pigment surface, it is preferable to introduce a functional group to the pigment surface via another atomic group in order to avoid steric hindrance between the copolymers. Here, the other atomic groups are not particularly limited as long as they are polyvalent elements or organic groups. However, from the viewpoint of controlling the distance of the functional group from the pigment surface, for example, a divalent organic residue is preferably used. 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, it can be said that the amino group is chemically bonded to the pigment surface via an atomic group containing a phenyl (2-sulfoethyl) group.

(Copolymer of polymer-bonded self-dispersing pigment)
As the copolymer composed 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 preferably used.

  Examples of the anionic copolymer include a copolymer composed of a hydrophobic monomer and an anionic monomer, or a salt thereof. Typical hydrophobic monomers used at this time include the following monomers, but the present invention is not limited to these. For example, methacrylic acid alkyl esters such as styrene, vinyl naphthalene, methyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate Alkyl acrylates such as methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate and sorbyl acrylate.

  Examples of the anionic monomer used above include the following monomers, but the present invention is not limited thereto. For example, acrylic acid, methacrylic acid, maleic acid and the like can be mentioned.

  As an anionic copolymer comprising an anionic monomer and a hydrophobic monomer as an embodiment of the copolymer used in the present invention, any one selected from the above-mentioned hydrophobic monomers, And at least one monomer selected from the anionic monomers listed above. The copolymer includes a block copolymer, a random copolymer, a graft copolymer, or a salt thereof.

  The acid value of such an anionic copolymer is preferably in the range of 100 to 500, and it is preferable to use an acid value whose variation in acid value is within 20% of the average acid value. By setting the acid value of the copolymer within such a range, the hydrophilicity of the pigment surface is too high, the water and solvent in the ink after printing stays on the pigment surface, and the ink after printing on the recording medium. It is possible to effectively suppress the slow expression of the marker resistance. In addition, it is possible to effectively suppress the fact that the hydrophilicity of the pigment surface is too low and the pigment is difficult to stably disperse in the ink.

  Examples of the salt include alkali metal salts such as sodium, lithium, and potassium, ammonium salts, alkylamine salts, alkanolamine salts, and the like, and these can be used alone or in combination of several kinds.

  Next, a cationic copolymer comprising a cationic monomer and a hydrophobic monomer as another embodiment of the copolymer used in the present invention will be described. Examples of the cationic copolymer include copolymers composed of the following hydrophobic monomers and cationic monomers, or salts thereof. As the hydrophobic monomer, the monomers listed above can be used.

  Examples of the cationic monomer include allylamine, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, N-vinylcarbazole, methacrylamide, Acrylamide, dimethylacrylamide, and the like can be used.

  The cationic copolymer is a block copolymer, a random copolymer, a graft copolymer comprising at least two monomers including a hydrophobic monomer selected from the above monomers and a cationic monomer, or these And the like. In particular, the cationic copolymer having an amine value in the range of 100 to 500 is preferable, and the variation of the amine value is preferably within 20% of the average amine value. The amine value is expressed in mg of KOH equivalent to hydrochloric acid required to neutralize 1 g of the sample. The salt includes acetic acid, hydrochloric acid, nitric acid and the like, and these can be used alone or in appropriate combination of several kinds.

  As the anionic or cationic copolymer described above, those having a weight average molecular weight (Mw) in the range of 1,000 to 20,000 can be preferably used, and further 3,000 to 20,000. The thing of the range of can be used preferably. In addition, it is preferable to use a cationic copolymer segment having a polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of 3 or less. The content of such a cationic copolymer in the ink is preferably 5% by mass or more and 40% by mass or less with respect to pigment particles surface-modified with the copolymer. . As for the polydispersity of the copolymer, when the polydispersity 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. The molecular weight distribution of the copolymer is preferably uniform.

  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. As a method that can be used in this case, a functional group on the surface of the pigment particle or a functional group is introduced on the surface of the pigment particle, and a copolymer composed of an ionic monomer and a hydrophobic monomer is bonded 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 such a method, the following method etc. can be used, for example.

  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 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. As the other, the most typical example 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.
1st process; The process 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, by reacting a part of the carboxyl group of the ionic monomer portion of the copolymer with an amino group to form an amide bond, the copolymer is formed on the surface of carbon black, APSES. A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group that is a residue of the above 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. Through 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), the copolymer is placed on the surface of carbon black, and the APSES A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group as a residue.

[Water-soluble resin adsorption type self-dispersion pigment]
As described above, a resin-dispersed pigment, a microcapsule-type pigment, a self-dispersed pigment, or a polymer-bonded self-dispersed pigment is used as the water-insoluble colorant contained in the aqueous ink according to the present invention. In addition to these, pigments added with a water-soluble resin can also be used. This will be described below.

In the present invention, the water-soluble resin is adsorbed to the self-dispersing pigment in the system in which the water-soluble resin is added to the pigment as listed above, and the water-soluble resin is added to the self-dispersing pigment. Water-soluble resin adsorbing self-dispersing pigments in the form can also be used.
The water-soluble resin adsorption type self-dispersing pigment can be prepared by adding a water-soluble resin to the self-dispersing pigment dispersion described above and stirring and mixing. Below, the preferable example of a water-soluble resin adsorption type self-dispersion pigment is given.

As the self-dispersing pigment used in the water-soluble resin-adsorptive self-dispersing pigment that can be used in the present invention, a hydrophilic group is chemically bonded to the pigment particle surface directly or through another atomic group. Things. For example, the hydrophilic group introduced into the pigment particle surface, -COOM1, -SO ₃ M1 and _{-PO 3 H (M1) 2 (} M1 in the formula 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 by ozone treatment in water, a method of modifying the carbon black surface by wet oxidation with an oxidizing agent after ozone treatment, etc. A surface-oxidation-type self-dispersion type pigment can be suitably used. As for the self-dispersing pigment that can be used when forming the water-soluble resin adsorbing self-dispersing pigment used in the present invention, it is desirable that the alkali-soluble polymer is adsorbed at a certain ratio. If the surface of the self-dispersing pigment is modified to the limit by the carboxylation or the like, the adsorption of the alkali-soluble polymer to the pigment particles becomes practically zero. Conversely, if the surface modification is too small, it is difficult to obtain the effect of the modification. Therefore, as a measure of the degree of surface modification, the surface carboxyl group content is set within the range of 0.1 to 0.5 mmol / g.

  The water-soluble resin that can be used in forming the water-soluble resin adsorption type self-dispersing pigment used in the present invention includes a hydrophobic monomer and a copolymer composed of an anionic monomer, a hydrophobic monomer and a nonionic monomer, Examples thereof include a copolymer made of an anionic monomer, or a salt thereof. Typical hydrophobic monomers used at this time include the following monomers, but the present invention is not limited to these. For example, methacrylic acid alkyl esters such as styrene, vinyl naphthalene, methyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate Alkyl acrylates such as methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate and sorbyl acrylate. Nonionic monomers include the following monomers, but the present invention is not limited to these. Examples thereof include hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, alkoxy polyethylene glycol (meth) acrylate, and silicone macromer. Examples of the anionic monomer used above include the following monomers, but the present invention is not limited thereto. For example, acrylic acid, methacrylic acid, maleic acid and the like can be mentioned. The copolymer includes a block copolymer, a random copolymer, a graft copolymer, or a salt thereof.

  The acid value of the anionic copolymer used above is preferably in the range of 100 to 500, and the acid value variation is preferably within 20% of the average acid value. Examples of the salt include alkali metal salts such as sodium, lithium, and potassium, ammonium salts, alkylamine salts, alkanolamine salts, and the like, and these can be used alone or in combination of several kinds. As the anionic copolymer described above, those having a weight average molecular weight (Mw) in the range of 1,000 to 20,000 can be preferably used, and more preferably in the range of 3,000 to 20,000. A thing can preferably be used.

  The adsorption of the pigment and the water-soluble resin described in the present invention means adsorption by van der Waals force or intermolecular force. As a means for adsorption, a sufficient effect can be obtained by ordinary stirring of the pigment and the alkali-soluble polymer. However, there is no problem even if a disperser that takes a high share is used for adsorption. In order to examine the adsorptivity of the alkali-soluble polymer to the self-dispersing pigment, evaluation by surface tension is simple. For example, the surface tension when a water-soluble resin is added to 1% by mass of the self-dispersing pigment is measured (the amount of alkali-soluble polymer vs. γ in a system containing 1% by mass of the self-dispersing pigment). : Plot A). On the other hand, the surface tension of the aqueous solution containing only the water-soluble resin is measured (the amount of water-soluble resin vs. γ: referred to as plot B). By comparing plot A and plot B and examining how much the concentration of water-soluble resin differs between plot A and plot B to reach any surface tension, the approximate amount of water-soluble resin adsorbed can be estimated. Is possible.

<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. In general, the content of moisturizing solids such as urea, urea derivatives, and trimethylolpropane in the ink is preferably in the range of 0.1 to 20.0% by mass, more preferably in the range of the ink. It is the range of 3.0-10.0 mass%.

  Furthermore, in addition to the above components, the 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 accelerator as necessary. Various additives such as chelating agents may be contained.

（但し、上記構造式（１）中、Ｒはアルキル基を表し、ｎは整数を表す。）

（但し、上記構造式（２）中、Ｒはアルキル基を表し、ｎは整数を表す。）

（但し、上記構造式（３）中、Ｒは水素原子又はアルキル基を表し、ｍ及びｎは、夫々整数を表す。）

（但し、上記構造式（４）中、ｍ及びｎは、夫々整数を表わす。） As the surfactant used in the present invention, a compound having any one of the following structural formulas (1) to (4) is preferable.

(In the structural formula (1), R represents an alkyl group, and n represents an integer.)

(In the structural formula (2), R represents an alkyl group, and n represents an integer.)

(In the structural formula (3), R represents a hydrogen atom or an alkyl group, and m and n each represents an integer.)

(In the structural formula (4), m and n each represent an integer.)

<< Image Forming Method Using the Ink >>
An image forming method according to the present invention is an inkjet recording method in which recording is performed on plain paper using black ink and at least one aqueous color ink, and the aqueous ink having the above-described configuration is applied to the black ink. And when forming an image in which an image formed by the black ink and an image formed by the color ink are adjacent to each other, after forming the image by performing a scan to which the black ink is applied, Scanning for applying color ink to a region where an image is formed is performed.

<Color ink to be used in combination>
Here, the color ink used in combination with the black ink in the present invention will be described. In the image forming method according to the present invention, any conventionally known water-based color ink for ink jet recording can be used. Examples of the color material of the color ink include water-soluble dyes, and it is particularly preferable to use a water-soluble dye having an anionic group as a solubilizing group. The color ink used in the present invention can be appropriately selected from, for example, cyan, magenta, yellow, red, green, blue and orange.

  The water-soluble dye having an anionic group used in the present invention is not particularly limited as long as it is a water-soluble acidic dye, a direct dye, or a reactive dye described in the color index (COLOUR INDEX). Even if the dye is not described in the color index, there is no particular limitation as long as it has an anionic group, for example, a sulfone group. These dyes are used in the ink in an amount of 1 to 10% by mass, preferably 1 to 5% by mass.

Specific examples of the dye include the following.
C. I. Direct yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 98, 100, 110
C. I. Direct Red: 2, 4, 9, 11, 20, 23, 24, 31, 39, 46, 62, 75, 79, 80, 83, 89, 95, 197, 201, 218, 220, 224, 225, 226 227, 228, 230
C. I. Direct blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226
C. I. Acid Yellow: 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99
C. I. Acid Red: 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 94, 106, 114, 115, 133, 134 145, 158, 198, 249, 265, 289
C. I. Acid Blue: 1, 7, 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 100, 102, 104, 117, 127, 138, 158, 161

In addition to the above, the color material of the color ink that can be used in the present invention includes the following 1. ~ 3. Can be mentioned. These color materials are preferable because many of them exhibit excellent water resistance when applied to a recording medium.
1. 1. A dye having a carboxyl group as a solubilizing group 2. Oil-soluble dyes Pigment

The oil-soluble dye is not particularly limited as long as it is described in the color index (COOLUR INDEX). Even if it is a new dye not described in the color index, there is no particular limitation. Specific examples include the following. These dyes are preferably used in the ink in an amount of 1 to 10% by mass, more preferably 1 to 5% by mass.
C. I. Solvent blue: 33, 38, 42, 45, 53, 65, 67, 70, 104, 114, 115, 135
C. I. Solvent Red: 25, 31, 86, 92, 97, 118, 132, 160, 186, 187, 219
C. I. Solvent yellow: 1, 49, 62, 74, 79, 82, 83, 89, 90, 120, 121, 151, 153, 154

  When a pigment is used as the color material of the color ink used in the present invention, the amount of the pigment is 1 to 20% by mass, preferably 2 to 12% by mass, based on the total mass of the ink. Use within the range. Examples of color organic pigments that can be used in the present invention include the following.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 2, C.I. I. Pigment Yellow 3, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 16, C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 83, C.I. I. Pigment Yellow 128 and the like.

  Examples of pigments used in magenta ink include C.I. I. Pigment Red 5, C.I. I. Pigment Red 7, C.I. I. Pigment Red 12, C.I. I. Pigment Red 48 (Ca), C.I. I. Pigment Red 48 (Mn), C.I. I. Pigment Red 57 (Ca), C.I. I. Pigment Red ll2, C.I. I. Pigment Red 122 and the like.

  Examples of pigments used for cyan ink include C.I. I. Pigment Blue 1, C.I. I. Pigment Blue 2, C.I. I. Pigment Blue 3, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 16 and C.I. I. Pigment Blue 22, C.I. I. Vat Blue 4, C.I. I. Vat Blue 6 etc. are mentioned. However, it is not limited to these. In addition to the above, a pigment newly produced for the present invention can of course be used.

  In addition, when a pigment is used, any dispersing agent for dispersing the pigment in the ink can be used as long as it is a water-soluble resin, but the weight average molecular weight is 1,000 to 30. In the range of 3,000, more preferably in the range of 3,000 to 15,000. Specific examples of such dispersants include styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, acrylic acid derivatives, maleic acid, and the like. , At least two monomers selected from maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, vinyl acetate, vinylpyrrolidone, acrylamide, and derivatives thereof (of which at least one is hydrophilic) Monomer), a random copolymer, a graft copolymer, or a salt thereof. Alternatively, natural resins such as rosin, shellac and starch can be preferably used. These resins are soluble in an aqueous solution in which a base is dissolved, and are alkali-soluble resins. In addition, it is preferable to contain the water-soluble resin used as these pigment dispersants in the range of 0.1 to 5% by mass with respect to the total mass of the ink.

  A suitable aqueous liquid medium in the color ink used in the present invention is water or a mixed solvent of water and a water-soluble organic solvent. The water is not general water containing various ions but ion-exchanged water ( Preference is given to using deionized water). Examples of the water-soluble organic solvent used by mixing with water include carbon atoms of 1 such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and the like. Alkyl alcohols of -4; amides such as dimethylformamide and dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; Ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol Alkylene glycols having 2 to 6 carbon atoms, such as coal; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of monohydric alcohols; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred.

  The content of the water-soluble organic solvent as described above in the color ink is generally in the range of 3 to 50% by mass, preferably in the range of 3 to 40% by mass with respect to the total mass of the ink. The water content used is in the range of 10 to 90% by mass, preferably 30 to 80% by mass, based on the total mass of the ink. In addition to the above-mentioned components, the color ink used in the present invention is appropriately added with a surfactant, an antifoaming agent, a preservative, etc. in order to obtain an ink having a desired physical property value as necessary. Can be added.

  It is preferable that the black and color inks used in the present invention composed of the components as described above have characteristics that allow them to be discharged well from an inkjet 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. Further, particularly when black ink and color ink are used in combination, it is more preferable that the surface tension of the color ink is lower than the surface tension of the black ink. Specifically, the black ink is 35 to 50 mN / m and the color ink is 25 to 35 mN / m.

<Image forming method>
The image forming method according to the present invention will be described below with specific examples. In the image forming method of the present invention, the aqueous ink according to the present invention having the above-described configuration is used as the black ink, and the image is formed by the black ink and the color ink as described above. When forming an image that is adjacent to an image, after performing scanning that applies black ink to form an image, scanning that applies color ink to a region where the image is formed is performed. . Hereinafter, a specific method will be described.

  FIG. 8 is an example of a recording head used when carrying out the image forming method according to the present invention. As shown in FIG. 8, the recording head includes an ejection port array (Bk) for ejecting black ink, and three colors of cyan (C), magenta (M), and yellow (Y) as color inks. And an ejection port array for ejecting each of the inks. In the image forming method of the present invention, when a color image is formed, a recording head in which a black ejection port array for ejecting black ink and a color ejection port array for color ink are shifted in the sub-scanning direction. Is preferably used. For this reason, for example, when forming an image using the recording head shown in FIG. 8, in the case of black-only image formation, the entire discharge port array for black is used, and color mixed with black and color. When forming an image, it is preferable to use the portion a in the drawing for black, and use the portion b in the drawing for C, M, and Y. Hereinafter, the case of forming an image in which black and color are mixed will be described in more detail with reference to FIG.

  In FIG. 8, first, black image data is recorded on plain paper or the like 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 discharge port array. Form on the medium. Next, the recording medium is transported by a distance a in the vertical direction (sub-scanning direction) in the drawing, and in the process of the forward direction of the main scanning of the next print head, the portion of the color ejection port array b is used. A color image is formed by one-pass printing in the area where the image is formed in the black row a. At this time, the black discharge port array a simultaneously forms an image in the next area. By repeating this process, black and color mixed images are formed.

  FIG. 9 shows another example of a recording head that can be used when carrying out the image forming method according to the present invention. In FIG. 9, as in FIG. 8, the portion a in the discharge port row is used for black, and the portion b in the drawing corresponding to the entire region of the discharge port row is used for C, M, and Y. In the same manner as described above with reference to FIG. 8, a black and color mixed image is formed.

  FIG. 10 shows another example of a recording head that can be used when carrying out the image forming method according to the present invention. Also in FIG. 10, as in the case of FIG. 8, for black, the portion a in the drawing of the ejection port array is used, and for C, M, and Y, b in the diagram corresponding to the entire region of the color ejection port array. Using this part, black and color mixed images will be formed. In the recording head illustrated in FIG. 10, as shown in the drawing, a distance corresponding to the paper feed amount a 'for one time is provided between the portion a of the black discharge port array and the portion b of the collar. 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. Therefore, the recording head illustrated in FIG. 10 has a more advantageous configuration for bleeding between black and color than the configuration shown in FIG.

  FIG. 11 shows another example of a recording head that can be used when performing the image forming method according to the present invention. Even when a recording head in which black and color discharge port arrays are arranged in a line in this order in the paper feed direction is used, a color image is formed after a black image is formed according to the paper feed. Will be.

  FIG. 12 shows another example of a recording head that can be used when carrying out the image forming method according to the present invention. In the recording head shown in FIG. 12, the color ejection port arrays are cyan (C1, C2) and magenta (M1, M2) so that the order of color ink ejection is the same in the forward scanning and the backward scanning. ) And yellow (Y1, Y2), two rows each, being provided symmetrically in the main scanning direction. As a result, bidirectional printing is possible even in the formation of black and color mixed images. In this case, the black a portion is used to first form a black image in the forward direction of the main scanning of the print head, and then the recording medium is conveyed by the distance a, and then the main print head is moved. In the process in the backward direction of scanning, a color image is formed by one-pass printing in the region where the image is formed in the above-described black a row using the portion of the color ejection port row b. At this time, the black image of the next region is simultaneously formed in the black a portion. By repeating this process, black and color mixed images are formed.

  Of course, in the bidirectional print head as shown in FIG. 12, as described above, the black and color nozzles are arranged so that an interval of one scan is provided between the black and color image formations. A more advantageous configuration may be used (see FIG. 13). 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.

[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 a head configuration 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 bonding a heating element substrate 15 to a glass, ceramic, silicon or plastic plate having a flow path (nozzle) 14 through which ink passes. The heating element substrate 15 includes a protective layer 16 formed of silicon oxide, silicon nitride, silicon carbide, etc., electrodes 17-1 and 17-2 formed of aluminum, gold, aluminum-copper alloy, 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 nozzle 14 of the head, becomes an ink droplet 24 from the ejection orifice 22, and flies toward the recording medium 25. FIG. 3 shows an external view of an example of a multi-head in which a large number of heads shown in FIG. 1 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating this head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in the 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 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 that has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface on which the discharge ports are arranged. It is a carriage for moving. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area by the recording head 65 and its adjacent area can be moved.

  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 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. It is preferable for the present invention to use polyurethane as the material of the ink absorber. Alternatively, a structure may be used in which the ink container is an ink bag with a spring or the like inside without using an ink absorber. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  Next, 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 indicating and fixing the orifice plate 81, the diaphragm 82 and the like.

  In FIG. 7, an ink flow path 80 is formed of a photosensitive resin or the like, an orifice plate 81 has a discharge port 85 formed by electroforming or punching a metal such as stainless steel or nickel, and the vibration plate 82 is The piezoelectric element 83 is formed of a dielectric material such as barium titanate or PZT. The piezoelectric element 83 is formed of a metal film such as stainless steel, nickel, or titanium and a highly elastic resin film. 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 , a reference example, and a comparative example are given and this invention is demonstrated more concretely, unless the summary is exceeded, this invention is not limited by the following Example. In the text, “parts” and “%” are based on mass unless otherwise specified.

(Preparation of pigment dispersion 1)
10 parts of a 10% sodium hydroxide neutralized aqueous solution of 10 parts of carbon black having a specific surface area of 210 m ² / g and DBP oil absorption of 74 ml / 100 g and a styrene-acrylic acid copolymer having an acid value of 200 and a weight average molecular weight of 10,000. Furthermore, after mixing 70 parts of ion-exchanged water and dispersing for 1 hour using a sand grinder, coarse particles are removed by centrifugation, and pressure filtration is performed with a micro filter (made by Fuji Film) having a pore size of 3.0 μm. Thus, a pigment dispersion 1 containing a resin-dispersed pigment was obtained. The physical properties of the obtained pigment dispersion 1 were a solid content of 10%, pH = 10.0, and an average particle size of 120 nm.

(Preparation of pigment dispersion 2)
After mixing 10 g of carbon black with a specific surface area of 230 m ² / g and DBP oil absorption of 70 ml / 100 g and 3.41 g of p-amino-N-benzoic acid in 72 g of water, 1.62 g of nitric acid was added thereto. The solution was added dropwise and stirred at 70 ° C. Several minutes later, a solution of 1.07 g of sodium nitrite dissolved in 5 g of water was added, and the mixture was further stirred for 1 hour. The obtained slurry was Toyo Filter Paper No. After filtering through 2 (manufactured by Advantis), the pigment particles were sufficiently washed with water and dried in an oven at 90 ° C., water was added to the pigment to prepare a pigment aqueous solution having a pigment concentration of 10%. By the above-described method, Pigment Dispersion Liquid 2 was obtained in which an anionically charged self-dispersing carbon black having a hydrophilic group bonded thereto via a phenyl group was dispersed on the surface.

The ionic group density of the self-dispersing carbon black produced above was measured as follows and found to be 1.3 μmol / m ² . As a measuring method, an ion meter (manufactured by DKK) was used to measure the sodium ion concentration, and the ionic group density was converted from the value. By the above method, Pigment Dispersion Liquid 2 in which self-dispersing carbon black having —C ₆ H ₄ —COONa group introduced was dispersed on the surface of carbon black was obtained.

(Preparation of pigment dispersion 3)
500 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 112 ml / 100 g, 45 g of aminophenyl (2-sulfoethyl) sulfone (APSES), and 900 g of distilled water are charged into the reactor, and the temperature is maintained at 55 ° C. Stir at 300 RPM for 20 minutes. Thereafter, 40 g of 25% sodium nitrite was added dropwise for 15 minutes, and 50 g of distilled water was further added. Then, it was made to react for 2 hours, keeping at 60 degreeC. And the obtained reaction material was taken out, diluting with distilled water, and it adjusted to the density | concentration from which solid content will be 15%. Thereafter, a centrifugal separation treatment and a purification treatment for removing impurities were performed. This prepared dispersion was a dispersion in which the above-described APSES functional group was bonded to carbon black. This dispersion is designated as A1.

  Next, in order to determine the number of moles of functional groups bonded to the carbon black in the dispersion A1, Na ions in the dispersion are measured with a probe-type sodium electrode, and the obtained value is calculated per carbon black powder. In conversion, the number of moles of the functional group bonded to the carbon black was determined. Next, the previously prepared dispersion A1 having a solid content of 15% was dropped into a pentaethylenehexamine (PEHA) solution. At this time, the PEHA solution was kept at room temperature with vigorous stirring, and the dispersion A1 was added dropwise over 1 hour. The PEHA concentration at this time was 1 to 10 times the number of moles of Na ions measured previously, and the amount of the solution was the same as that of the dispersion A1. Furthermore, this mixture was stirred for 18 to 48 hours, and then a purification treatment for removing impurities was performed. Finally, a dispersion having a solid content of 10% bonded with pentaethylenehexamine (PEHA) was obtained. This dispersion is designated as B1.

  Next, a styrene-acrylic acid resin as a copolymer was prepared as follows. First, 190 g of a styrene-acrylic acid resin having a weight average molecular weight of 8,000, an acid value of 140, and a polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of 1.5 was weighed, and 1,800 g was measured. Of distilled water was added, NaOH necessary for neutralizing the resin was added, and the mixture was stirred and dissolved to prepare a styrene-acrylic acid resin aqueous solution. Next, 500 g of the previously prepared dispersion B1 having a solid content of 10% was dropped into the styrene-acrylic acid resin aqueous solution while stirring. Further, the mixture of B1 and a styrene-acrylic resin aqueous solution was transferred to a Pyrex (registered trademark) evaporating dish, heated at 150 ° C. for 15 hours to evaporate, and then the evaporated and dried product was cooled to room temperature.

  Subsequently, this evaporated and dried product was dispersed in NaOH-added distilled water adjusted to pH = 9.0 using a disperser, and 1.0 M NaOH was further added with stirring to adjust the pH to 10-11. did. Thereafter, desalting, purification for removing impurities, and removal of coarse particles were performed to obtain pigment dispersion 3. Regarding the physical properties of the obtained pigment dispersion 3, the solid content was 10%, the pH was 10.1, and the average particle size was 130 nm. The following shows a synthesis scheme of a polymer-bonded self-dispersing pigment that is contained in the pigment dispersion 3 described above and in which an organic group is chemically bonded to the surface of carbon black particles.

[Method for determining good and poor solvents of water-soluble organic solvent used]
In order to select a good solvent and a poor solvent for the pigment in the pigment dispersion, or the pigment and the dispersant, the following experiment was conducted. First, a 10% solid concentration aqueous solution of the pigment dispersions 1 to 3 was prepared, and a dispersion for determining good and poor solvents was prepared using the aqueous solution with the following blending ratio.
(Compounding ratio of dispersion for determining good and poor solvents)
-10% solid concentration aqueous solution of each pigment dispersion: 50 parts-Each water-soluble organic solvent listed in Table 1: 50 parts

(Judgment method)
Next, 10 g of the good solvent / poor solvent determination dispersion prepared as described above was placed in a transparent glass lidded sample bottle, capped, and then sufficiently stirred, which was placed in an oven at 60 ° C. Allowed to stand for 48 hours. Then, using the dispersion liquid taken out from the oven at 60 ° C. as a measurement sample, the particle size of the water-insoluble colorant in the liquid was measured using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). This was taken as the stock solution particle size (particle size measured without dilution) of the dispersion for determining good and poor solvents after heating at 60 ° C. for 48 hours. On the other hand, as a reference, a pigment water dispersion with the same solid content concentration as the dispersion for determination of good solvent and poor solvent, that is, determination comparison of good solvent and poor solvent with the same amount of water added instead of water-soluble organic solvent A pigment aqueous dispersion was prepared, and the particle size of the water-insoluble colorant in the liquid was measured with a concentrated particle size analyzer in the same manner as described above, without performing warm storage. Then, the stock solution particle size of the obtained dispersion for determination is compared with the particle size of the aqueous dispersion of the reference, and the stock solution particle size of the dispersion after warming storage at 60 ° C. for 48 hours is the water dispersion of the reference. What is larger than the liquid stock particle size of the liquid is judged to be a poor solvent, and the raw liquid particle size of the dispersion after heating at 60 ° C. for 48 hours is the same or smaller than that of the aqueous dispersion of the reference. Was determined as a good solvent.

[Ka value measurement method for each water-soluble organic solvent]
First, a dye aqueous solution with a dye concentration of 0.5% having the following composition was prepared so that the Ka value of each water-soluble organic solvent could be easily measured.
Water-soluble dye C.I. I. Direct Blue 199
0.5 part pure water 99.5 parts

Then, using this 0.5% aqueous dye solution, a 20% aqueous solution of a colored water-soluble organic solvent was prepared using each water-soluble organic solvent to be measured at the following blending ratio.
80 parts of the above 0.5% dye aqueous solution 20 parts of the water-soluble organic solvent listed in Table 1

  A 20% aqueous solution of each water-soluble organic solvent prepared above was used as a measurement sample, and a dynamic permeability test apparatus S (trade name) manufactured by Toyo Seiki Seisakusho was used. Each Ka value was determined.

<< Judgment and measurement results >>
About each water-soluble organic solvent which can be used for the ink measured as described above, the result of determining whether it is a good solvent or a poor solvent with respect to the pigment dispersions 1 to 3, and each water-soluble organic solvent Table 1 shows the measurement results of the Ka value in a 20% aqueous solution. The polyethylene glycol derivative in Table 1 is a derivative having the structure shown below and having a molecular weight of about 1,000.

<Example 4 and Reference Examples 1-3, 5 >
Using each of the water-soluble organic solvents investigated above and the pigment dispersions 1 to 3, the components described in Table 2 were mixed, dissolved or dispersed with sufficient stirring, and then a microfilter (pore size: 3.0 μm) The inks of Example 4 and Reference Examples 1 to 3 and 5 were prepared by pressure filtration with Fuji Film. At this time, when A is the total amount (% by mass) of the good solvent in the ink and B is the total amount (% by mass) of the poor solvent in the ink, A: B is in the range of 10: 5 to 10:30. When the Ka value of the 20% aqueous solution of the good solvent for the water-insoluble colorant determined by the Bristow method is compared with the Ka value of each of the plurality of water-soluble organic solvents determined by the Bristow method, Was prepared such that the largest water-soluble organic solvent was a poor solvent.

<Verification of ink according to Example 4>
The ink prepared in Example 4 was assumed to have an unknown composition, and it was verified by the following method that the ink was an object of the present invention. According to this verification method, even if the composition is an unknown ink, it can be easily confirmed whether or not the ink is an object of the present invention.

  The type and amount of the organic solvent contained in the ink can be identified using, for example, GC / MS (trade name: TRACE DSQ; manufactured by ThermoQuest). Specifically, for example, 1 g of the ink of Example 4 was collected, and a sample diluted with methanol was analyzed using the GC / MS. As a result, first, the presence of glycerin, diethylene glycol, and polyethylene glycol 600 was confirmed. Next, it is necessary to determine whether these three types of solvents are good solvents or poor solvents. In the determination method for the good solvent and the poor solvent described above, a dispersion liquid in which a water-insoluble colorant is dispersed in the solvent and water is prepared. It is necessary to extract a water-insoluble colorant and a dispersant from the water. However, in this case, it cannot be denied that the water-insoluble colorant and the dispersant may be altered during the extraction process.

  On the other hand, the present inventors are a determination method of a good solvent and a poor solvent using the ink itself of Example 4, and the result matches the determination method of the good solvent and the poor solvent described above. Various investigations were made on how to do this. As a result, the following method was found to be suitable as a verification method. First, the following three types of ink dilutions were prepared by adding the same amount of the above three types of water-soluble organic solvents to be judged to 100 parts of the ink of Example 4, and using these liquids. Judgment was made. That is, three types of ink dilutions having the composition shown in Table 3 (indicated as Verification Examples 1 to 3 in Table 3) in which the amount of the water-soluble organic solvent to be judged was about 50% by mass were prepared. Next, with respect to those which were heated and stored at 60 ° C. for 48 hours, a water-insoluble colorant was obtained using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). The particle size was measured. On the other hand, the particle size of the water-insoluble colorant was also measured for unstored ink that was not warmed. When the measured particle size after warm storage is larger than the measured particle size of the unstored ink, the particle size is the same as or decreased with the poor solvent. In the case of being a good solvent, the poor solvent and the good solvent were determined in accordance with the criteria for the good solvent. In Table 3, the viscosity (cP) value of the solvent used as a measurement condition for the stock solution particle size is also shown. This viscosity is a value measured with an E type viscometer (VISCONIC ED type manufactured by Tokyo Keiki Co., Ltd.).

  In Table 4, the pigment stock solution particle size in the ink of Example 4 (unstored) measured as described above, and the liquids of Verification Examples 1 to 3 (60 ° C., 48 hours, after warm storage) The stock solution particle size of the pigment inside was shown. The measured value of the particle size of the verification example is compared with the particle size of the ink of Example 4, and when the particle size is increased, it is good when the particle size is the same or decreased with the poor solvent. Determination as a solvent was performed.

  As shown in Table 4, in the result of the determination method of the good solvent and the poor solvent using the verification example sample obtained by diluting the actual ink, glycerin is the same as the determination method shown in Table 1 above. (Used in Verification Example 1) was a good solvent, diethylene glycol (used in Verification Example 2), and polyethylene glycol 600 (used in Verification Example 3) was a poor solvent, and it was confirmed that the results were consistent. Accordingly, a method of determining whether the solvent used in the ink is a good solvent or a poor solvent for the color material in the ink from the actual ink described above is effective. It was confirmed that there was. Therefore, the determination method using the sample diluted with the ink described above can be effectively used as the determination method for the good solvent and the poor solvent in the present invention.

<Comparative Examples 1-17>
(Preparation of ink)
Using each of the water-soluble organic solvents investigated above and the pigment dispersions 1 to 3, the components described in Tables 5-1 to 5-3 were mixed and dissolved or dispersed with sufficient stirring. The ink was subjected to pressure filtration with a 0 μm microfilter (Fuji Film) to prepare inks of Comparative Examples 1-17.

<Image characteristic evaluation>
An on-demand type multi-recording head that ejects ink by applying thermal energy to the ink in accordance with a recording signal using each of the inks of Example 4, Reference Examples 1 to 5, and Comparative Examples 1 to 17 An inkjet recording apparatus BJS-700 (manufactured by Canon Inc.) having the following characteristics was modified and evaluated as follows. The evaluation results obtained are shown in Table 6 for Examples and Reference Examples , and in Table 7 for Comparative Examples.

1. Printing density Using the above inks and the ink jet recording apparatus described above, character printing including a solid portion of 2 cm × 2 cm is performed on the following copy plain papers A to E, and a solid portion of 2 cm × 2 cm one day after printing is printed. The print density was measured. The printer driver was operated in the default mode. The setting conditions for the default mode are shown below. Further, the ejection amount per dot of ink is within 30 ng ± 10%.
-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.
A: The average print density of 5 papers is 1.4 or higher, and the print density of paper with the lowest print density is 1.25 or higher.
(Triangle | delta): The average of the printing density of 5 papers is 1.4 or more, and the printing density in the paper of the lowest printing density is less than 1.25.
X: The average of the printing density of 5 papers is less than 1.4.

In the image output test, the following copy paper was used.
A: PPC paper NSK manufactured by Canon Inc.
B: PPC paper NDK manufactured by Canon Inc.
C: Xerox Co., Ltd., PPC paper 4024
D: PPC paper prober bond, manufactured by Fox River Co., Ltd. E: PPC paper for Canon, manufactured by Neuzidora Co., Ltd.

2. Print density with small ink amount The print density with small ink dots is measured in the same manner as the print density evaluation method described in 1 above, except that the discharge amount per dot of ink is in the range of 24 ng ± 10%. Evaluation based on the criteria.

<Storage stability evaluation>
Each ink of Example 4, Reference Examples 1 to 3, and Comparative Examples 1 to 17 was put into a shot bottle, sealed, put into a 60 ° C. oven, taken out after 2 weeks, and the ink state at that time The storage stability was evaluated according to the following criteria. The obtained evaluation results are shown in Table 6 for Examples and Reference Examples , and in Table 7 for Comparative Examples.
○: The color material in the ink is stably and uniformly dispersed.
X: The ink is changed into a gel or the upper part of the ink is transparent. Or it is clearly thickened.

<Measurement of ink landing on plain paper>
(Preparation of inks for reference and comparative examples for ink landing measurement)
Using the pigment dispersion 2 was mixed the ingredients listed in Table 8 were dissolved or dispersed by thoroughly stirring, then pressure filtered at a pore size of 3.0μm microfilter (product of Fuji Photo Film Co., Ltd.), Reference Example 6, And each ink of Comparative Examples 18-20 was prepared. In preparing the inks of the reference examples and comparative examples for ink landing measurement, the water-soluble dye C.I. I. Direct Blue 199 is added, which is for visualizing and observing the extent of ink spreading after the ink is fixed on the recording medium. The surface tension of these inks is shown in Table 8. The surface tension was measured using a surface tension meter CBVP-A3 manufactured by Kyowa Interface Science at a measurement temperature of 25.0 ± 0.5 ° C. using a 10 mm × 24 mm platinum plate 10 mm × 24 mm.

<Dot diameter measurement>
When ink droplets are applied to plain paper, the ink dot diameter dI immediately after the ink has landed on the plain paper, the maximum ink spread diameter dS after fixing the ink on the print medium, and the ink to the print medium The maximum diameter dC of the spread of the water-insoluble colorant in the ink after fixing, and the existing depth of the water-insoluble colorant after fixing the ink on plain paper were measured by the following method. First, the ink dot diameter dI immediately after landing of the ink on plain paper was determined using a contact angle meter (Face CONACT-ANGLEMETER CA-P) manufactured by Kyowa Interface Science Co., Ltd., with a needle diameter of 28 G (inner diameter: 0.18 mm, outer diameter: 0). .36 mm) needle, ink was dropped onto plain paper from a height of 4 mm between the tip of the needle and the plain paper surface, and the diameter of the dropped ink drop was read with a contact angle meter. This value was taken as the ink dot diameter dI immediately after the ink recording medium landed. The plain paper used in this example is PB-Paper (NSK paper) manufactured by Canon.

  The maximum diameter dS of the ink spread after fixing the ink on the recording medium and the maximum diameter dC of the spread of the water-insoluble colorant in the ink after fixing the ink on the recording medium are measured by the above conditions. The ink dots were allowed to stand for 6 hours or more, and after the ink droplets were stabilized, the maximum linear length of the ink dots was measured and the value was taken as the maximum diameter. The maximum diameter dS of the ink spread after fixing of the ink on the recording medium is the water-soluble dye C.I. I. The maximum diameter dC of the water-insoluble colorant in the ink after fixing the ink to the recording medium is determined by measuring the maximum linear length of the cyan hue spread of Direct Blue 199. The maximum linear length of the black spread was measured. Further, when the maximum diameter dC of the spread of the water-insoluble colorant in these inks was obtained, the black dot shape of the pigment in the ink was also observed.

<Measurement of depth of water-insoluble colorant>
The presence depth of the water-insoluble colorant was measured from the ink compositions of Reference Example 6 and Comparative Examples 18 to 20 using the water-soluble dye C.I. I. Except for Direct Blue 199, an ink prepared by adding water to that extent was prepared and filtered under the same conditions. Using these inks, an ink jet recording apparatus BJS-700 (manufactured by Canon Inc.) having an on-demand type multi-recording head that discharges ink by applying thermal energy to the ink according to a recording signal, Printing was performed on PB-Paper (NSK paper) manufactured by Canon under the same conditions as those for the printing density evaluation. After printing, after the ink was fixed, the print part was cut from the back side of the print using a razor, the cut cross section was observed with a microscope, and the thickness (depth) of the water-insoluble colorant in the cross section of the paper was measured. From the obtained measurement results, evaluation was performed according to the following evaluation criteria. The obtained evaluation results and the measured values of the maximum diameter dC of the spread of the water-insoluble colorant in the ink after fixing the ink on the recording medium are shown in Table 9.

[Evaluation criteria]
(Dot diameter relational expression)
○: satisfying the relationship of dC <dI <dS.
X: Not satisfying the relationship of dC <dI <dS.

(Dot shape of water-insoluble colorant)
1: Visual observation from above the paper surface ○: The dot shape of the water-insoluble colorant is a perfect circle and the edge is sharp.
X: The dot shape of the water-insoluble colorant is not a perfect circle, and the edge is blurred.
2: Visual observation from the lateral direction of the paper surface ○: The dots of the water-insoluble color material are present at almost the same height as the paper surface.
X: Dots of water-insoluble colorant are clearly raised on the paper surface.

(Depth of water-insoluble colorant)
○: Less than 30 μm ×: 30 μm or more

FIG. 15 is a schematic view from above of a fixed image of dots formed in the above measurement. FIG. 16 is a schematic diagram of a micrograph used for measuring the thickness (depth) of the water-insoluble colorant in the cross section of the paper. As shown in FIG. 15 and Table 9, when the inks of Reference Example 6 and Comparative Example 18 were used, the water-insoluble color material formed a perfect circle, but Comparative Example 18 was a water-insoluble color. Since the material is swelled on the paper surface and the paper surface is covered with more than the required amount of water-insoluble color material, the reference example 6 is compared with the comparative example 18 in comparison with the surface of the paper. It shows that the color material stays effectively in the vicinity. On the other hand, when the ink of Comparative Example 19 was used, the water-insoluble color material spreads unevenly, forming dots, and spreading not only to the surface of the paper but also to the depth of the paper. It was confirmed that it was not used effectively. Further, when the ink of Comparative Example 20 was used, as shown in FIG. 15, the water-insoluble colorant formed a perfect circle, but the inkjet recording apparatus BJS-700 ( As can be seen from the cross section of the print section using Canon Inc.), the color material spreads not only to the surface of the paper but also to the depth of the paper. In this case, the color material is not used effectively. I was able to confirm.

Further, as can be seen from the value of the maximum diameter dC of the spread of the water-insoluble colorant shown in Table 9, the poor solvent and the good solvent of Reference Example 6 are better than the ink containing only the poor solvent of Comparative Example 18 as a solvent. In the case of an ink in which water coexists appropriately, the spread of the water-insoluble colorant is increased. For this reason, the pigment ink, which is one of the objects of the present invention, achieves an image having a sufficiently large area factor and a high OD (reflection density) even with a small ink droplet amount. It has been confirmed that. In addition, from the ink compositions of Reference Example 6 and Comparative Example 18, the acetylene glycol EO adduct, which is a surfactant, was removed, and inks containing no surfactant were prepared correspondingly. Under the same conditions as the landing measurements on the plain paper performed with the inks of Reference Example 6 and Comparative Example 18, the dot diameter measurement with the ink containing no surfactant and the presence depth of the water-insoluble colorant were measured. went. As a result, in the inks without these surfactants, although the fixing time after landing is slower than when the surfactants are used, the poor solvent is better than the ink containing only the poor solvent as a solvent. In the case of the ink in which the solvent appropriately coexists, the spread of the water-insoluble colorant becomes larger, and the same relationship as in the case of the ink using the surfactant is obtained.

[Test on color mixture (bleed)]
<Examples 10 and 15 and Reference Examples 7 to 9, 11 to 14, 16 >
Using the ink of Example 4 and Reference Examples 1 to 3 and 5 described above as the black ink, image formation was performed in combination with the color ink. The color inks (three colors of cyan, magenta, and yellow) used at this time were prepared as follows.

(Cyan ink production)
The components shown below were mixed, sufficiently stirred and dissolved, and then pressure filtered through a micro filter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare a cyan ink.
・ DBL (Direct Blue) 199 3.5 parts ・ Glycerin 7.5 parts ・ Diethylene glycol 7.5 parts ・ Acetylenol E-100 1.0 part ・ Pure water 80.5 parts

(Production of magenta ink)
A cyan ink was prepared in the same manner as the cyan ink with the following components.
・ AR (Acid Red) 289 2.5 parts ・ Glycerin 7.5 parts ・ Diethylene glycol 7.5 parts ・ Acetylenol E-100 1.0 part ・ Pure water 81.5 parts

(Production of yellow ink)
A yellow ink was prepared in the same manner with the following components.
・ DY (direct yellow) 86 2.5 parts ・ Glycerin 7.5 parts ・ Diethylene glycol 7.5 parts ・ Acetylenol E-100 1.0 part ・ Pure water 81.5 parts

<Evaluation>
Using the black inks of Example 4 and Reference Examples 1 to 3 and 5 and the color inks prepared as described above, the combinations shown in Table 10 below, as shown in FIG. 9 or FIG. Further, printing evaluation was performed using an inkjet recording apparatus having an on-demand type multi-recording head that discharges ink by applying thermal energy to the ink in accordance with a recording signal. The obtained evaluation results are shown in Table 11.

(Bleedability)
Solid portions of black and color (yellow, magenta, cyan) are printed adjacent to each other by the recording method shown in FIGS. 9 and 10, and the degree of bleeding at the boundary between black and color is visually observed. Evaluation based on the criteria. The plain paper used here was Canon PB-Paper (NSK paper). The evaluation results are shown in Table 11.
AA: Bleeding cannot be visually recognized.
A: Bleeding is hardly noticeable.
B: Although bleeding is occurring, the level is substantially free of problems.
C: Breeding so that the color boundary line is not clear.

  As an application example of the present invention, there is an aqueous ink that can obtain an image having a sufficiently large area factor and a high OD (reflection density) even with a small amount of ink droplets in the pigment ink. Further, as an application example of the present invention, by using such an ink, an ink jet recording method capable of forming a high-quality image with a high OD even with a small ink application amount, and the above-described recording method are preferably used. Ink cartridges, recording units, and inkjet recording apparatuses that can be used. Furthermore, as an application example of the present invention, when color image recording in which different color areas are adjacent to each other on plain paper is performed, color mixing at the boundary between the black ink and color ink areas does not occur without causing feathering. Examples thereof include an image forming method capable of effectively suppressing (bleed).

It is a longitudinal cross-sectional view of an inkjet recording device head. It is a vertical and horizontal view of an inkjet recording device head. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. FIG. 6 is an explanatory diagram for schematically explaining a state when an ink droplet according to the present invention has landed on the surface of a recording medium. It is a schematic diagram showing the difference in the spread state of the ink after fixing the ink on plain paper in the reference example and the comparative example. It is a schematic diagram showing the difference in the presence state of the color material in the depth direction after fixing the ink on plain paper in the reference example and the comparative example.

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: Heat generating 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: Discharge recovery unit 65: Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 70: Recording unit 71: Head unit 72: Air Communication port 80: Ink channel 81: Orifice plate 82: Vibration plate 83: Piezoelectric element 84: Substrate 85: Ejection port 1300: Recording medium 1301: Ink droplet 1302: Dot periphery 1303: Dot center 1304: Water-insoluble colorant 1305: Dot 1306: Water-soluble solvent 1307: Poor solvent

Claims (3)

The step of discharging with an inkjet method of water soluble ink on a recording medium at least having an ink jet recording method,
The water-based ink contains water, a plurality of different types of water-soluble organic solvents, and a water-insoluble colorant,
The plurality of water-soluble organic solvents are a good solvent for the water-insoluble colorant and a plurality of poor solvents for the water-insoluble colorant, wherein the total amount (% by mass) of the good solvent in the ink is A, the ink When the total amount (% by mass) of the poor solvent is B, A: B is in the range of 10: 5 to 7: 9,
At least one of the plurality of poor solvents is selected from the group consisting of diethylene glycol, polyethylene glycol and 2-pyrrolidone;
The water-insoluble colorant comprises a resin-dispersed pigment, a microcapsule-type pigment, a self-dispersed pigment in which a hydrophilic group is bonded to the pigment particle surface via another atomic group, and a polymer-bonded self-dispersed pigment. Chosen by
The recording medium is plain paper in which the water-soluble organic solvent exhibiting the maximum Ka value becomes a poor solvent when comparing the Ka values obtained by the Bristow method for each of the plurality of water-soluble organic solvents. An inkjet recording method characterized by the above. The water-insoluble colorant, an ink jet recording method according to claim 1 including mosquitoes over carbon black. The hydrophilic group is from —COOM1, —SO ₃ M1, and —PO ₃ H (M1) ₂ (wherein M1 represents any one of a hydrogen atom, an alkali metal, ammonium, and organic ammonium). The inkjet recording method according to claim 1 or 2, which is selected from the group consisting of :

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