JP2012031350A - Ink, ink cartridge, inkjet recording method, and inkjet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink that strikes a balance between ink reliability excellent in recovery from fixation in a recording head, in which the ink is prevented from being accumulated in a cap, and image characteristics excellent in image density and bleeding resistance.SOLUTION: The ink contains a self-dispersing pigment, a salt, and a water-soluble organic compound. The self-dispersing pigment is such that a functional group containing a phosphonic acid group is bonded to a particle surface, wherein the introduction amount of the functional group is 0.34 to 0.40 mmol/g. The salt is configured by making a cation selected from an alkali metal ion, an ammonium ion, and an organic ammonium ion bond to an anion selected from a halide ion and the like. The value obtained by multiplying the concentration of the anion of the salt by the valence of the anion, in the ink, is 0.01-0.04 mol/L. The water-soluble organic compound contains an ethylene urea, wherein the content of the ethylene urea is 22-50 mass% based on the total content of the water-soluble organic compound in the ink.

Description

  The present invention relates to an inkjet ink, an ink cartridge, an inkjet recording method, and an inkjet recording apparatus.

  In recent years, inks used in ink jet recording methods have been required to further improve image density and bleeding resistance in recorded images. Among recording media for recording images, there are various types of plain paper having different ink permeability, and the difference affects the image characteristics. In particular, a recording medium having high ink permeability tends to lower the image density and tends to reduce bleeding resistance. In recent years when the inkjet recording method has been widely used, it is required that the recorded image has a high level of the above performances regardless of the type of recording medium including such a highly permeable recording medium. Has been.

  In response to the above requirements, based on the calcium index value, which is an index of reactivity with calcium, an image density is increased by an ink containing a self-dispersing pigment in which a functional group highly reactive with calcium is bonded to the pigment particle surface. There is a proposal for improving the above (see Patent Document 1). There is also a proposal for improving image density and bleeding resistance by using an ink containing a salt and a self-dispersing pigment having a functional group such as a carboxy group bonded to the pigment particle surface (see Patent Documents 2 and 3). . Patent Document 3 describes that the image density of a recorded image can be further increased by further increasing the density of functional groups on the surface of the pigment particles.

Special table 2009-515007 JP 2000-198955 A Japanese Patent No. 4273104

  As described above, the inventors of the present invention have made various studies to improve image characteristics such as image density and bleeding resistance with respect to ink-jet ink. As a result, it has been recognized that it is necessary to satisfy sufficiently excellent characteristics. For example, by using the self-dispersing pigment described in Patent Document 1 mentioned above, improvement in image density is expected to some extent, but there is still room for improvement in bleeding resistance, and in addition, the type of recording medium However, it was found that an excellent image density could not be given. Therefore, when the self-dispersing pigment described in Patent Document 1 is used, the present inventors include a salt for promoting aggregation of the pigment in the ink in order to satisfy the above characteristics, The study proceeded focusing on the types and contents of organic compounds. However, it has been found that when such a self-dispersing pigment is used, the fixing and recovering properties of the ink in the recording head may deteriorate depending on the type and content of the salt or water-soluble organic compound used in combination. Further, it has been found that the reliability of ink staying in a cap provided in the ink jet recording apparatus for covering the recording head becomes insufficient. Further, in the inks described in Patent Documents 2 and 3, the ink storage stability and the reliability such as ink retention in the cap are at a level with no problem, but the image density needs to be further improved. I also understood that. Hereinafter, the cap for covering the recording head provided in the ink jet recording apparatus is simply referred to as “cap”.

  Accordingly, an object of the present invention is to provide a novel ink that can achieve both ink reliability and image characteristics. In other words, ink that suppresses stagnation of ink in the cap and has excellent reliability in fixing and fixing ink in the recording head and image characteristics that can record an image having excellent image density and bleeding resistance can be achieved. Is to provide. Another object of the present invention is to provide an ink cartridge, an ink jet recording method, and an ink cartridge that can ensure the reliability by using the ink and can stably obtain an image having excellent image density and bleeding resistance. It is to provide an ink jet recording apparatus.

The above object is achieved by the present invention described below. That is, the ink according to the present invention is an inkjet ink containing a self-dispersing pigment, a salt, and a water-soluble organic compound, and the self-dispersing pigment has a functional group containing at least a phosphonic acid group bonded to the particle surface. The amount of the functional group bonded to the self-dispersing pigment is 0.34 mmol / g or more and 0.40 mmol / g or less, and the salt is an alkali metal ion or ammonium ion. And at least one cation selected from the group consisting of organic ammonium ions, and Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ are combined with at least one anion selected from the group consisting of The value of anion concentration × anion valence is 0.01 mol / L or more and 0.04 mol / L or less, the water-soluble organic compound contains ethylene urea, and the content of ethylene urea in the ink is It is characterized by being 22 mass% or more and 50 mass% or less with respect to the total content of the water-soluble organic compound therein.

  According to the present invention, it is possible to provide a novel ink that can achieve both ink reliability and image characteristics. That is, according to the ink of the present invention, the retention of the ink in the cap is suppressed, the reliability that the ink fixing and recovering property in the recording head is excellent, and the image characteristics that the image having excellent image density and bleeding resistance can be recorded. It becomes possible to achieve both. Further, according to another embodiment of the present invention, by using the ink, the reliability is ensured, and an image excellent in image density and bleeding resistance can be stably obtained. Ink cartridge, ink jet recording A method and an inkjet recording apparatus are provided.

It is a schematic diagram which shows the cleaning part of an inkjet recording device.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention. In the following description, ink jet ink may be simply abbreviated as “ink”. A pigment having a phosphonic acid group in the structure of the functional group may be referred to as a “phosphonic acid type self-dispersing pigment”.

  According to the study by the present inventors, when the phosphonic acid type self-dispersing pigment is used as an ink coloring material, the fixing property of the ink in the recording head depends on the pH of the ink and the water-soluble organic compound or salt in the ink. It turned out to be easily affected. This is because the phosphonic acid group in the structure of the pigment has a plurality of pKas, and they exist within the general pH range of the ink. This is because it becomes sensitive to water-soluble organic compounds and salts. Here, in the recording head to which the ink is fixed, the pigment is also aggregated. Therefore, in order to recover the adhesion, it is necessary to disperse the aggregated pigment once again. For this reason, the fixing recovery property of the ink containing the phosphonic acid type self-dispersing pigment in the recording head is also easily affected by the ink composition such as pH.

  As a result of the study, the inventors have studied that the ink composition described later suppresses the retention of the ink in the cap, has an excellent fixing recovery property of the ink in the recording head, and has an image with excellent image density and bleeding resistance. As a result, the present invention was found. The ink of the present invention capable of obtaining such effects contains a pigment having a functional group containing at least a phosphonic acid group bonded to the particle surface, a specific salt, and a water-soluble organic compound containing ethylene urea. It is characterized by that. The amount of the functional group bonded to the self-dispersing pigment is 0.34 mmol / g or more and 0.40 mmol / g or less, and the salt anion concentration × anion valence value in the ink is 0. It is necessary to be 0.01 mol / L or more and 0.04 mol / L or less. Furthermore, the ink of the present invention requires that the content of ethylene urea in the ink is 22% by mass or more and 50% by mass or less with respect to the total content of the water-soluble organic compounds in the ink.

  The present inventors presume the reason why the above-described effect can be obtained by the configuration of the present invention as follows. First, the following points are considered regarding the suppression of ink retention in the cap. As described above, the ink containing the phosphonic acid type self-dispersing pigment is easily affected by the ink composition, and is also easily affected by environmental factors. For example, if the ink composition changes due to evaporation of the ink or the pH of the ink decreases, the dissociation state of the phosphonic acid groups on the particle surface changes, and the dispersion of the phosphonic acid-type self-dispersing pigment is reduced as the surface charge decreases Stability is reduced. Further, as a result of the study by the present inventors, it has been found that if the amount of the functional group bonded to the self-dispersing pigment is too large, the ink stays in the cap.

  It is considered that the aggregation of the phosphonic acid type self-dispersing pigment is alleviated by using ethylene urea as the water-soluble organic compound contained in the ink for such a phosphonic acid group. In other words, due to its molecular structure, ethylene urea aggregates phosphonic acid-type self-dispersed pigments while maintaining excellent image characteristics due to complex factors such as being easily present between pigments and acting as a moisturizing agent. It is thought to ease. According to the study by the present inventors, even when other water-soluble organic compounds were added to such ethylene urea, the same excellent effects as when ethylene urea was added could not be obtained. . For example, diethylene glycol has a dielectric constant value of 50% aqueous solution close to that of ethylene urea. Trimethylolpropane is also a humectant, and the dielectric constant of a 50% aqueous solution is close to that of ethylene urea. However, even if these are used instead of ethylene urea, an effect comparable to that obtained when ethylene urea is used, in particular, an effect of suppressing ink retention in the cap cannot be obtained. Also, for example, when glycerin is used instead of ethylene urea, it is difficult to achieve both excellent image characteristics and a high level of both the retention of ink retention in the cap and the recovery of ink fixation in the recording head. Met. Furthermore, as a result of the study by the present inventors, it has been found that an ink containing ethylene urea can suppress the degree to which the pH decreases even when stored for a long period of time. This is considered to have contributed greatly to suppressing the retention in the cap of the ink containing the phosphonic acid type self-dispersing pigment.

  Next, pigment aggregation will be considered. In order to improve the image characteristics, it is important to promote the aggregation of the pigment. On the other hand, to suppress the retention of the ink in the cap, it is important to reduce the aggregation of the pigment. That is, improvement in image characteristics and suppression of ink retention in the cap are in a trade-off relationship in terms of pigment aggregation. Aggregation of the pigment in the recording medium is caused by solid-liquid separation promoted by a salt in the ink, a water-soluble organic compound having low affinity for the pigment, and the like after the ink is applied to the recording medium. Further, it is also caused by evaporation of moisture or the like in the ink after the ink is applied to the recording medium, and further by interaction between phosphonic acid contained in the functional group and calcium contained in the recording medium. On the other hand, in order to suppress the retention of the ink in the cap, there is no calcium that causes the interaction as described above, and the aggregation of the pigment in a state where the ink contains a certain amount of moisture is suppressed. That's fine. In other words, these two phenomena are the promotion / relaxation of pigment aggregation when the ink states are different, and therefore, in the ink of the present invention having the above-described configuration, both the image characteristics and the suppression of ink retention in the cap are compatible. It is thought that it was made.

  In the present invention, the self-dispersing pigment constituting the ink needs to have an introduction amount of a functional group bonded to the pigment particle surface of 0.34 mmol / g or more and 0.40 mmol / g or less. When the introduction amount of the functional group is less than 0.34 mmol / g, the fixing property of fixing the ink in the recording head cannot be obtained. On the other hand, when the amount exceeds 0.40 mmol / g, the retention of the ink in the cap cannot be suppressed. In the case of a conventional self-dispersing pigment to which an ionic group such as a carboxylic acid group is bonded, which is not a phosphonic acid type self-dispersing pigment, as discussed in Patent Document 3 described above, the amount of functional groups introduced The image density is improved by further increasing the image quality. This is because the effect of steric hindrance due to the functional group and the affinity with the water-soluble organic solvent in the ink is reduced by reducing the area of the pigment particle surface where the functional group is not bonded. This is because the water-soluble organic solvent can be made difficult to solvate. Further, according to the study by the present inventors, the conventional self-dispersing pigment did not cause ink retention in the cap even if the amount of the functional group introduced was increased for the purpose of improving the image density.

  In the phosphonic acid type self-dispersing pigment, as described above, the phosphonic acid group has a plurality of pKa, which are present in the general pH range of the ink. For this reason, if the introduction amount of the functional group bonded to the self-dispersing pigment is too large, the retention of the ink in the cap may not be suppressed even if ethylene urea is used. In addition, if the amount of the functional group bonded to the self-dispersing pigment is too small, it becomes sensitive to impurities such as ethylenediamine derived from ethylene urea used as a constituent material of the ink, and the fixing recovery property in the recording head is not good. May be sufficient.

  Further, according to the study by the present inventors, in view of the effect, the content of ethylene urea in the ink of the present invention is 22% by mass with respect to the total content of water-soluble organic compounds in the ink. It is required to be 50% by mass or more. When this ratio is less than 22% by mass or exceeds 50% by mass, bleeding resistance cannot be obtained. In particular, unless ethylene urea is used, ink retention in the cap cannot be suppressed. This ratio is assumed to be rounded off to the first decimal place.

The ink of the present invention stipulates that the value of the salt anion concentration in the ink × the value of the valence of the anion must be within a specific range. The reason for paying attention to the value of the anion concentration × the valence of the anion will be described.
Self-dispersing pigments in which an ionic group is bonded to the pigment particle surface generally have a counter ion, which may be the same species as the salt cation added to the ink. Furthermore, the concentration of the counter ion of the self-dispersing pigment in which the ionic group is bonded to the surface of the pigment particle may vary depending on the pH of the ink in the case of the phosphonic acid type self-dispersing pigment. Therefore, by paying attention to the value of the salt anion concentration × anion valence, it is possible to more accurately grasp the relationship between the image characteristics and the ink reliability. For this reason, in the ink of the present invention, the provision that the value of the salt anion concentration × anion valence in the ink is within a specific range is adopted to ensure the manifestation of the effect. The value of the salt anion concentration × anion valence corresponds to a so-called normality. In the ink of the present invention, the value of the salt anion concentration × anion valence in the ink of the present invention needs to be 0.01 mol / L or more and 0.04 mol / L or less. If this value is less than 0.01 mol / L, image characteristics cannot be obtained, and if it exceeds 0.04 mol / L, the ink stays in the cap even if ethylene urea is contained so as to satisfy the above relationship. Can not be suppressed. In the present invention, the value of the salt anion concentration × anion valence in the ink is particularly preferably 0.01 mol / L or more and 0.02 mol / L or less.

<Ink>
Hereinafter, the components constituting the ink of the present invention and the physical properties of the ink will be described in detail.
(Pigment)
Examples of the pigment include organic pigments and inorganic pigments such as carbon black, and any of those usable for ink jet inks can be used. In addition to pigments, dyes may be used in combination for purposes such as toning. In the present invention, a black ink using carbon black as a pigment is particularly preferable. The pigment content (% by mass) in the ink is 0.1% by mass or more and 15.0% by mass or less, and further 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. Is preferred.

  The pigment used in the ink of the present invention is a self-dispersing pigment in which a functional group containing at least a phosphonic acid group is bonded to the pigment particle surface. By using such a self-dispersing pigment, it is not necessary to add a dispersant for dispersing the pigment in the ink, or the amount of the dispersant added can be reduced.

In the ink, the phosphonic acid group —PO (O [M ₁ ]) ₂ may be either partially dissociated or dissociated. That is, a phosphonic acid group, -PO ₃ H ₂ (acid ^{_{form), - PO 3 H - M}} 1 + ( monobasic salt), and any ^{_{-PO 3 2- (M 1 +)}} 2 ( dibasic salt) It can take the form. Here, M ₁ is independently at least one selected from the group consisting of alkali metals, ammonium, and organic ammonium. In the present invention, the functional group preferably contains two phosphonic acid groups. It is of course possible to improve the image density by using a monophosphonic acid type self-dispersing pigment, but more preferably, a higher image density can be obtained by using a bisphosphonic acid type self-dispersing pigment. Use of a trisphosphonic acid type self-dispersing pigment is not preferable because sufficient fixing and recovering properties of ink in the recording head may not be obtained.

It is also preferred that the phosphonic acid group is at the end of the functional group, that is, there is another atomic group between the pigment particle surface and the phosphonic acid group.
Examples of the other atomic group (—R—) include a linear or branched alkylene group having 1 to 12 carbon atoms, an arylene group such as a phenylene group or a naphthylene group, an amide group, a sulfone group, an amino group, a carbonyl group, Examples include an ester group and an ether group. Moreover, the group etc. which combined these groups are mentioned. Furthermore, the other atomic group includes at least one of the alkylene group and the arylene group, and a group having a hydrogen bond (amide group, sulfone group, amino group, carbonyl group, ester group, ether group). It is particularly preferable to include it. In the present invention, it is particularly preferred that the functional group contains —C ₆ H ₅ —CONH— (benzamide structure).

In the present invention, it is more preferable that the functional group bonded to the pigment particle surface contains a structure of -CQ (PO ₃ [M ₁ ] ₂ ) ₂ . Here, Q in the formula is any one of a hydrogen atom, R, OR, SR, and NR ₂ , and each R independently represents any of a hydrogen atom, an alkyl group, an acyl group, an aralkyl group, and an aryl group. It is. When R is a group containing a carbon atom, the number of carbon atoms contained in the group is preferably 1 to 18. Specifically, the alkyl group includes a methyl group, an ethyl group, the acyl group includes an acetyl group, a benzoyl group, the aralkyl group includes a benzyl group, the aryl group includes a phenyl group, a naphthyl group, and the like. . M ₁ is independently at least one selected from the group consisting of a hydrogen atom, an alkali metal, ammonium, and organic ammonium. In the present invention, it is particularly preferable that a functional group containing a structure of —CQ (PO ₃ [M ₁ ] ₂ ) ₂ in which Q is a hydrogen atom is bonded to the pigment particle surface, and M ₁ is ammonium. It is more preferable that

[Amount of functional group introduced]
In the ink of the present invention, as described above, the amount of the functional group bonded to the self-dispersing pigment needs to be 0.34 mmol / g or more and 0.40 mmol / g or less. The unit of the functional group introduction amount is the number of millimoles of functional group per 1 g of pigment solid content.

  The amount of the functional group introduced into the self-dispersing pigment used in the present invention can be measured by quantifying phosphorus ions as follows. Specifically, first, a liquid A is prepared by diluting the pigment dispersion with pure water so that the content of the pigment (solid content) is about 0.03% by mass. Further, ultracentrifugation is performed on the pigment dispersion at 5 ° C. under conditions of 80,000 rpm for 15 hours, and the supernatant liquid from which the pigment has been removed is collected, and this is diluted about 80 times with pure water. To prepare solution B. About the obtained A liquid and B liquid, an ICP emission-spectral-analysis apparatus etc. each performs fixed quantity of phosphorus ion, From the difference of the amount of phosphorus ions calculated | required from a measured value about these A liquid and B liquid, the quantity of a phosphonic acid group is calculated | required. Can be calculated. The amount of functional group introduced into the pigment is the amount of phosphonic acid groups / n (n is the number of phosphonic acid groups contained in one functional group, 1 for mono, 2 for bis, 3 for tris) Can be calculated. Here, when the number of phosphonic acid groups contained in the functional group is unknown, it can be known by analyzing the structure by NMR or the like. In the above, the method of measuring using a pigment dispersion was described, but it can be measured in the same manner using ink, and of course, the method of measuring the amount of functional group introduction is not limited to the above. Absent.

(Salt composed of a combination of a cation and an anion)
The ink of the present invention contains a salt formed by combining a cation and an anion. The cation is at least one selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions. Further, the anions include Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO _3. ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO It must be at least one selected from the group consisting of ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ . The form of the salt in the ink may be in a state in which a part thereof is dissociated or in a state in which all is dissociated. By using such a salt, it is possible to achieve both high ink reliability and image characteristics.

Examples of the salt formed by combining a cation and an anion that can be used in the ink of the present invention include the following. For example, (M ₂ ) Cl, (M ₂ ) Br, (M ₂ ) I, (M ₂ ) ClO, (M ₂ ) ClO ₂ , (M ₂ ) ClO ₃ , (M ₂ ) ClO ₄ , (M ₂ ) NO ₂ , (M ₂ ) NO ₃ , (M ₂ ) ₂ SO ₄ , (M ₂ ) ₂ CO ₃ , (M ₂ ) HCO ₃ , HCOO (M ₂ ), (COOM ₂ ) ₂ , COOH (COOM ₂ ), CH ₃ COOM ₂ , C ₂ H ₄ (COOM ₂ ) ₂ , C ₆ H ₅ COOM ₂ , C ₆ H ₄ (COOM ₂ ) ₂ , (M ₂ ) ₃ PO ₄ , (M ₂ ) ₂ HPO ₄ , (M ₂ ) H ₂ PO ₄ may be mentioned. The M ₂ is at least one selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions. Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions.

In the present invention, the salt is C ₆ H ₄ (COO (Na)) ₂ , C ₆ H ₄ (COO (K)) ₂ , C ₆ H ₄ (COO (NH ₄ )) ₂ , and (NH ₄ ). More preferably, it is at least one selected from the group consisting of ₂ SO ₄ . Furthermore, the salt is at least one selected from the group consisting of C ₆ H ₄ (COO (K)) ₂ , C ₆ H ₄ (COO (NH ₄ )) ₂ , and (NH ₄ ) ₂ SO _4. It is particularly preferred. These salts are preferable because the ink stays in the cap more easily. In the present invention, it is particularly preferable to use a salt having a solubility in 100 mL of water of 10 g or more at 25 ° C. When a salt having a solubility of less than 10 g such as potassium hydrogen oxalate is used, the salt may precipitate as the ink in the cap evaporates, and the ink retention in the cap may not be sufficiently suppressed.

  As described above, the ink of the present invention requires that the value of the salt anion concentration × anion valence in the ink be 0.01 mol / L or more and 0.04 mol / L or less. As described above, this unit corresponds to a so-called normality. When the ink contains a plurality of types of salts, the salt anion concentration × anion valence value is obtained for each salt, and the sum is considered as the value specified in the present invention. Although different depending on the molecular weight of the salt, the content (% by mass) of the salt in the ink is preferably 0.05% by mass or more and 2.0% by mass or less based on the total mass of the ink. If the content is less than 0.05% by mass, the image density and bleeding resistance of a highly permeable recording medium may not be compatible at a high level. If the content exceeds 2.0% by mass, the ink in the recording head may not be compatible. In some cases, fixing recovery properties may not be obtained.

(Aqueous medium)
The ink of the present invention can contain an aqueous medium that is a mixed solvent of water and a water-soluble organic compound, but it must contain at least ethylene urea as the water-soluble organic compound. Furthermore, in the present invention, the content of ethylene urea in the ink needs to be 22% by mass or more and 50% by mass or less with respect to the total content of the water-soluble organic compounds in the ink. Further, the content (% by mass) of ethylene urea is 3.0% by mass or more and 20.0% by mass or less, and further 4.0% by mass or more and 13.0% by mass or less based on the total mass of the ink. Is preferred.

  As the water-soluble organic compound, in addition to ethylene urea, any of those usable for ink jet inks such as alcohols, glycols, glycol ethers and other nitrogen-containing compounds can be used. Moreover, these water-soluble organic compounds can contain 1 type, or 2 or more types in an ink. In the present invention, in addition to ethylene urea, at least one water-soluble organic compound selected from the group consisting of glycerin, 2-pyrrolidone, trimethylolpropane, and triethylene glycol is particularly used as the water-soluble organic compound. preferable. The water-soluble organic compound that serves as the denominator when calculating the proportion of ethylene urea in the total content of the water-soluble organic compound defined in the present invention includes various additives as described below and those described above. It does not contain salt. Moreover, it is preferable to use deionized water as water. The content (% by mass) of the water-soluble organic compound in the ink is preferably 3.0% by mass or more and 30.0% by mass or less based on the total mass of the ink. The water content (% by mass) in the ink is preferably 40.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

(Other additives)
In the ink of the present invention, various kinds of surfactants, resins, pH adjusters, antifoaming agents, rust preventives, antiseptics, antifungal agents, antioxidants, anti-reducing agents, chelating agents, etc. These additives may be included.

  In the present invention, for example, an acetylene glycol-based, fluorine-based, silicone-based, or polyoxyethylene alkyl ether-based surfactant is preferably included in the ink. The content (% by mass) of the surfactant in the ink is preferably 0.05% by mass or more and 2.0% by mass or less based on the total mass of the ink.

(Ink physical properties)
The ink of the present invention preferably has a dynamic surface tension of 40 mN / m or more at 25 ° C. and a lifetime of 50 milliseconds, and more preferably 45 mN / m or more. By satisfying such characteristics, the pigment can be present particularly efficiently on the surface of the recording medium, and a higher image density can be obtained. In the present invention, the maximum bubble pressure method is employed for measuring the dynamic surface tension of the ink. In this method, the surface tension is obtained by measuring the maximum pressure required to release bubbles pushed out from the tip of a probe (thin tube) immersed in the liquid to be measured. Further, in the present invention, “lifetime” means the maximum bubble pressure (bubble curvature) after a new surface is formed after the bubbles are released when bubbles are formed from the tip of the probe in the maximum bubble pressure measurement. Time when the radius and the radius of the probe tip are equal).

  In order for the ink of the present invention to satisfy the above-described dynamic surface tension characteristics, it is particularly preferable to use polyoxyethylene alkyl ether among the surfactants listed above. Furthermore, the polyoxyethylene alkyl ether used preferably has an HLB value determined by the Griffin method of 13 to 20 and an alkyl group having 12 to 20 carbon atoms. The content (% by mass) of the polyoxyethylene alkyl ether in the ink is 0.05% by mass or more and 2.0% by mass or less, and further 0.05% by mass or more and 1.0% by mass based on the total mass of the ink. It is preferable that it is below mass%.

<Ink cartridge>
The ink cartridge of the present invention has an ink storage portion for storing ink, and the ink storage portion stores the ink of the present invention described above. The ink cartridge has a structure in which the ink storage portion stores a negative pressure generation member storage chamber that stores a negative pressure generation member that is held in a state of being impregnated with negative pressure, and ink that is not impregnated by the negative pressure generation member. What is comprised by the ink storage chamber to accommodate is mentioned. Or, it does not have an ink storage chamber as described above, and holds the entire amount of ink impregnated with a negative pressure generating member, or does not have a negative pressure generating member and does not impregnate the entire amount of ink with a negative pressure generating member. It is good also as an ink accommodating part of the structure accommodated in a state. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method and inkjet recording apparatus>
The inkjet recording method of the present invention includes a step of recording an image on a recording medium by discharging from an ejection port of an inkjet recording head, and a step of covering the ejection port of the recording head with a cap. Further, the ink jet recording apparatus of the present invention includes an ink containing portion for containing ink, means for ejecting ink from an ejection port of an ink jet recording head, and recording an image on a recording medium, and a cap covering the ejection port of the recording head Are provided. Examples of the method for ejecting ink include a method for imparting mechanical energy to the ink and a method for imparting thermal energy to the ink. In the present invention, it is particularly preferable to employ an ink jet method that utilizes thermal energy. Except for using the ink of the present invention, the steps of the ink jet recording method and the means that can be provided in the ink jet recording apparatus may be known ones.

  Hereinafter, a configuration for covering the ejection port of the recording head in the inkjet recording method and the inkjet recording apparatus of the present invention will be described. In the following description, for the sake of simplicity, the discharge port is described as (1) discharge port. Usually, an inkjet recording apparatus is provided with a plurality of discharge ports for discharging one ink to form a discharge port array. To do. When a plurality of types of ink are used, ejection port arrays are provided according to the number of inks. In the present invention, it is particularly preferable to use a color ink whose coloring material is a dye as an ink for combining with the ink of the present invention described above (a black ink whose coloring material is a pigment).

  FIG. 1 is a schematic diagram illustrating a cleaning unit of an ink jet recording apparatus. The cleaning unit covers the ejection port by bringing the cap M5010 into contact with the surface of the recording head (not shown) having the ejection port, thereby suppressing ink evaporation. More specifically, capping is performed by raising the cap holder M5060 by a vertically movable mechanism (not shown) and bringing the cap M5010 into contact with the surface of the recording head having the ejection port with an appropriate adhesion force. When the pump M5000 is operated in the capped state, a negative pressure is generated between the surface having the ejection port and the cap M5010, ink is sucked from the ejection port, and the recording head is cleaned. Further, the ink is fixed to the recording head by discharging ink (preliminary discharge) to the suction chambers M5020 and M5030, or by sucking ink existing on the cap M5010 with the cap M5010 opened. And other harmful effects. An ink absorbing member or the like may be provided inside the suction chamber.

  As described above, FIG. 1 shows a configuration in which the suction chamber formed by the peripheral wall portion M5040 is divided into two suction chambers M5020 and M5030 having the same volume at the partition wall M5050. However, the volumes of these suction chambers may be different from each other, and may be constituted by one suction chamber without having a partition wall. Furthermore, it is good also as a structure which covers each discharge port row | line | column which discharges multiple types of ink collectively with one cap, or may provide a cap for each discharge port row | line | column which discharges multiple types of ink.

  Next, the present invention will be specifically described with reference to Examples, Reference Examples, and Comparative Examples. The present invention is not limited by the following examples unless it exceeds the gist. In the text, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
(Amount of pigment functional group introduced)
First, a method for measuring the amount of functional group introduced into the pigment will be described. A liquid A is prepared by diluting the pigment dispersion with pure water so that the content of the pigment to be measured is about 0.03%. Further, ultracentrifugation was performed on the pigment dispersion at 80 ° C. for 15 hours at 5 ° C., and the supernatant liquid from which the phosphonic acid-type self-dispersing pigment was removed was collected. B liquid was prepared by diluting to about twice. About the liquid A and B of the measurement sample obtained as described above, phosphorus ions were quantified using an ICP emission spectroscopic analyzer (SPS5100; manufactured by SII Nanotechnology). Then, the amount of phosphonic acid groups is obtained from the difference in the amount of phosphorus ions in the obtained liquid A and liquid B, and divided by the number of phosphonic acid groups contained in one functional group, thereby calculating the functional group introduction amount into the pigment. did.

(Pigment dispersion 1)
20 g (solid content) of carbon black, 10 mmol of ((4-aminobenzoylamino) -methane-1,1-diyl) bisphosphonic acid monosodium salt (treatment agent), 20 mmol of nitric acid, and 200 mL of pure water were mixed. did. At this time, carbon black having a specific surface area of 220 m ² / g and DBP oil absorption of 105 mL / 100 g was used, and mixing was performed at 6,000 rpm at room temperature using a Silverson mixer. After 30 minutes, 20 mmol of sodium nitrite dissolved in a small amount of water was slowly added to the mixture. By this mixing, the temperature of the mixture reached 60 ° C., and the reaction was performed in this state for 1 hour. Thereafter, the pH of the mixture was adjusted to 10 using an aqueous sodium hydroxide solution. After 30 minutes, 20 mL of pure water is added, diafiltration is performed using a spectrum membrane, and then sodium ions are replaced with ammonium ions by an ion exchange method, so that the pigment content becomes 10.0%. Thus, a dispersion was obtained. In this way, the self-dispersed pigment having the ((4-aminobenzoylamino) -methane-1,1-diyl) bisphosphonic acid group whose counter ion is ammonium is dispersed in water on the pigment particle surface. A pigment dispersion 1 in a wet state was obtained. The amount of functional groups introduced to the pigment surface was 0.34 mmol / g.

(Pigment dispersion 2)
Sodium (4- (4-aminobenzenesulfonylamino) -1-hydroxybutane-1,1-diyl) bisphosphonate was synthesized using sodium alendronate. At this time, a monosodium salt of (4-amino-1-hydroxybutane-1,1-diyl) bisphosphonic acid (manufactured by Zentiva) was used as the alendronate sodium. Using a 500 mL beaker, 34 g (104 mmol) of alendronate was added to 150 mL of pure water, and the pH of the liquid was adjusted to 11 using concentrated aqueous sodium hydroxide solution and dissolved. To this, 25 g (110 mmol) of nitrophenylsulfonyl chloride dissolved in 100 mL of tetrahydrofuran was added dropwise. At this time, an aqueous sodium hydroxide solution was further added to keep the pH of the liquid at 10-11. After the addition was completed, the liquid was further stirred at room temperature for 2 hours. Thereafter, tetrahydrofuran was evaporated in a vacuum, and the pH of the liquid was adjusted to 4 to precipitate a solid. After cooling at 4 ° C. overnight, the solid was filtered, washed with pure water, and dried to give (4- (4-aminobenzenesulfonylamino) -1-hydroxybutane-1,1-diyl). Sodium bisphosphonate was obtained.

20 g (solid content) of carbon black, 10 mmol of sodium (4- (4-aminobenzenesulfonylamino) -1-hydroxybutane-1,1-diyl) bisphosphonate (treatment agent) obtained above, 20 mmol of nitric acid, And 200 mL of pure water were mixed. At this time, carbon black having a specific surface area of 220 m ² / g and DBP oil absorption of 105 mL / 100 g was used, and mixing was performed at 6,000 rpm at room temperature using a Silverson mixer. After 30 minutes, 20 mmol of sodium nitrite dissolved in a small amount of water was slowly added to the mixture. By this mixing, the temperature of the mixture reached 60 ° C., and the reaction was performed in this state for 1 hour. Thereafter, the pH of the mixture was adjusted to 10 using an aqueous sodium hydroxide solution. After 30 minutes, 20 mL of pure water is added, diafiltration is performed using a spectrum membrane, and then sodium ions are replaced with ammonium ions by an ion exchange method, so that the pigment content becomes 10.0%. Thus, a dispersion was obtained. Thus, the self-dispersion in which the counter ion is ammonium ((4- (4-aminobenzenesulfonylamino) -1-hydroxybutane-1,1-diyl) bisphosphonic acid group is bonded to the pigment particle surface. A pigment dispersion 2 was obtained in a state where the pigment was dispersed in water, and the amount of functional groups introduced was 0.34 mmol / g.

(Pigment dispersion 3)
A pigment dispersion 3 was obtained in the same manner as in the preparation of the pigment dispersion 1, except that the amount of the treatment agent used was changed from 10 mmol to 12 mmol. The amount of functional group introduced was 0.40 mmol / g.

(Pigment dispersion 4)
A pigment dispersion 4 was obtained in the same manner as in the preparation of the pigment dispersion 1, except that the amount of the treatment agent used was changed from 10 mmol to 9 mmol. The amount of functional group introduced was 0.32 mmol / g.

(Pigment dispersion 5)
A pigment dispersion 5 was obtained in the same manner as in the preparation of the pigment dispersion 1, except that the amount of the treating agent used was changed from 10 mmol to 13 mmol. The amount of functional group introduced was 0.42 mmol / g.

(Pigment dispersion 6)
A dispersion was prepared in the same procedure as for Pigment Dispersion 1 except that the amount and type of the treating agent used in the preparation of Pigment Dispersion 1 were changed to 7 mmol of 4-aminobenzylphosphonic acid. At this time, a 4-aminobenzylphosphonic acid manufactured by Sigma-Aldrich was used. Further, sodium ions are replaced with potassium ions by an ion exchange method, and —C ₆ H ₄ — (PO (OK) ₂ ) groups are bonded to the surface of the pigment particles by the same procedure as in the pigment dispersion 1. A pigment dispersion 6 in which the self-dispersed pigment was dispersed in water was obtained. The amount of functional group introduced was 0.35 mmol / g.

(Pigment dispersion 7)
In the preparation of the pigment dispersion 1, the counter ion is potassium ((4-aminobenzoylamino) -methane- on the pigment particle surface in the same manner except that sodium ions are replaced with potassium ions by an ion exchange method. A pigment dispersion 7 was obtained in which the self-dispersed pigment to which the 1,1-diyl) bisphosphonic acid group was bonded was dispersed in water. The amount of functional group introduced was 0.34 mmol / g.

(Pigment dispersion 8)
To a solution prepared by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-aminophthalic acid (treatment agent) was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution at 10 ° C. or lower, and 2.2 g of potassium nitrite was dissolved in 9 g of water at 5 ° C. Solution was added. After stirring this solution for another 15 minutes, 6 g (solid content) of carbon black (specific surface area 220 m ² / g, DBP oil absorption 105 mL / 100 g) was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and the particles were sufficiently cooled with water and dried in an oven at 110 ° C. Water was added thereto to obtain a dispersion so that the pigment content was 10.0%. In this way, a pigment dispersion 8 was obtained in which a self-dispersed pigment having —C ₆ H ₃ — (COOK) ₂ groups bonded to the surface of the pigment particles was dispersed in water. The potassium ion concentration in this pigment dispersion 8 was measured using an ion meter (manufactured by DKK), and the amount of functional groups introduced to the pigment surface determined by conversion from the obtained potassium ion concentration was 0.68 mmol. / G.

<Preparation of ink>
Each component (unit:%) shown in the upper part of Table 1 was mixed and stirred sufficiently, and then pressure filtration was performed with a polypropylene filter (made by Pole) having a pore size of 2.5 μm to prepare each ink. . “NIKKOL BL-9EX” in Table 1 is a polyoxyethylene lauryl ether manufactured by Nikko Chemicals, and is a surfactant having an HLB value of 14.5 determined by the Griffin method and an added mole number of ethylene oxide groups of 9. is there. “Surfinol 465” in Table 1 is an ethylene oxide adduct of acetylene glycol manufactured by Air Products, and is a surfactant having an addition mole number of ethylene oxide groups of 10.
The lower part of Table 1 also shows the characteristics of each ink. Further, for each ink, the dynamic surface tension at 25 ° C. was measured using a Bubble Pressure Tensiometer BP2 MK2 (manufactured by Kruss) using a maximum bubble pressure method. Table 1 shows that the dynamic surface tension at a lifetime of 50 msec is 40 mN / m or more as A and that the dynamic surface tension is less than 40 mN / m as B.
In Table 1, “salt anion concentration × anion valence [mol / L]” means “salt anion concentration × anion valence value [mol / L] = anion use amount / molecular weight × valence”. Calculated from number × 10.

<Evaluation of ink>
(Image density)
The ink cartridge filled with each ink obtained above was set in an ink jet recording apparatus (PIXUS MP480; manufactured by Canon Inc.) equipped with a recording head that ejects ink by thermal energy. In the above-described ink jet recording apparatus, the resolution is 600 dpi × 600 dpi, and the condition is that one ink droplet having a mass per droplet of 25 ng ± 10% is applied to a unit area of 1/600 dpi × 1/600 dpi. The recorded image is defined as having a recording duty of 100%. A solid image (2 cm × 2 cm / 1 line) having a recording duty of 100% was recorded on the following three types of recording media (plain paper). As a recording medium, GF-500, Canon Extra Multifunctional Paper (manufactured by Canon Inc.), and Bright White Inkjet Paper (manufactured by Hured Packard) were used. One day after recording, a reflection densitometer (Macbeth RD-918; manufactured by Macbeth) was used to measure the image density of solid images on three types of recording media, and the image density was evaluated based on the average value and the minimum value. It was. The evaluation criteria are as follows. The results are shown in Table 2. In the present invention, according to the following evaluation criteria, A is acceptable and B and C are unacceptable.
A: The average value was 1.5 or more, and the minimum value was 1.3 or more.
B: The average value was 1.4 or more and less than 1.5, and the minimum value was 1.3 or more.
C: The minimum value was less than 1.3.

(Bleeding resistance)
Using each ink (black ink) obtained above and yellow ink of BC-71 color (manufactured by Canon), the bleeding resistance of the image was evaluated as follows. The BC-71 yellow ink is a color ink containing a dye as a coloring material. An ink cartridge filled with ink of each color was set in an ink jet recording apparatus PIXUS MP450 (trade name; manufactured by Canon Inc.) equipped with a recording head that ejects ink by thermal energy. In the ink jet recording apparatus described above, the resolution is 600 dpi × 600 dpi, and black ink applies one drop of ink with a mass per drop of 30 ng ± 10% to a unit area of 1/600 dpi × 1/600 dpi. In addition, an image recorded under the condition of applying two ink droplets having a mass per droplet of 5.5 ng ± 10% for the color ink is defined as a recording duty of 100%. A black solid image (2 cm × 2 cm) having a recording duty of 100% and a yellow solid image (2 cm × 2 cm) having a recording duty of 70% are recorded on the recording medium (GF-500; manufactured by Canon). Adjacent images were recorded. And the obtained image was confirmed visually and the bleeding resistance was evaluated. The evaluation criteria are as follows. The results are shown in Table 2. In the present invention, AA and A are acceptable levels and B and C are unacceptable levels according to the following evaluation criteria.
AA: Bleeding could not be confirmed.
A: Although bleeding occurred, it was hardly noticeable.
B: Bleeding occurred considerably.
C: Bleeding occurred so that the boundary between the two color images was not recognized.

(Inhibition of ink retention in the cap)
Each ink obtained above was put in an open container, and liquids (concentrated ink) evaporated by 10% by mass were prepared. Using the obtained concentrated ink, the same ink jet recording apparatus as that used in the above evaluation of the image density was used, and the recording duty was 7% on an A4 size recording medium in an environment of temperature 30 ° C. and humidity 10% RH. A black solid image of 2,000 was recorded every 4 minutes. When performing this recording, 0.21 mg ± 10% of ink is preliminarily ejected to the cap before recording, and as a cleaning operation, a cap that covers the ejection port of the recording head is applied once per 100 sheets. Thus, 0.1 g ± 30% of ink is sucked. After 2,000 sheets were recorded, the evaluation result was D for the ink remaining in the cap. For ink that did not retain ink in the cap at the time when 2,000 sheets were recorded, the above-mentioned recording was further added for 1,000 sheets, and the state of the cap at that time was visually confirmed, It was evaluated whether ink retention was suppressed. With respect to the ink whose evaluation result based on the following evaluation criteria was rank B, the above-mentioned record was further added for 2,000 sheets, and the evaluation result was A or more. For inks with an evaluation result of A or more, 2,000 sheets of the above-mentioned recording were further added, and ink with stagnation in the cap when 7,000 sheets were recorded was evaluated as A. For those that did not stay, the evaluation result was AA. That is, the evaluation criteria are as follows. The results are shown in Table 2. In the present invention, AA, A and B are acceptable levels, and C and D are unacceptable levels. In addition, the evaluation was performed using the concentrated ink because the ink retention in the cap is evaluated under more severe conditions, and the ink of the present invention has sufficiently excellent performance in terms of suppressing the retention in the cap. This is to confirm.
AA: After recording for 7,000 sheets, no ink stayed in the cap.
A: After recording for 5,000 sheets, no ink stayed in the cap.
B: After recording for 3,000 sheets, no ink stayed in the cap.
C: After recording for 3,000 sheets, ink stayed in the cap.
D: After recording for 2,000 sheets, ink remained in the cap.

(Adhesive recovery)
Each of the inks obtained above was put in an open container, and a liquid (concentrated ink) evaporated by 20% by mass was prepared. The obtained ink cartridge containing the concentrated ink was mounted on the recording head of the same ink jet recording apparatus as that used in the above image density evaluation, and left in an environment of temperature 30 ° C. and humidity 10% RH for 3 days. . Thereafter, the recording head was mounted on the same ink jet recording apparatus as described above, and the nozzle check pattern of PIXUS MP480 was recorded. The obtained nozzle check pattern was visually confirmed, and with respect to the ink that was not normally recorded, a cleaning operation was performed until normal recording was performed, and the fixation recovery property was evaluated. The evaluation criteria are as follows. The results are shown in Table 2. In the present invention, A and B are acceptable levels and C is not acceptable according to the following evaluation criteria. In addition, the evaluation was performed using the concentrated ink in order to confirm that the ink of the present invention has a sufficiently excellent performance in terms of the fixing recovery property by evaluating the fixing recovery property under more severe conditions. is there.
A: Recording could be performed normally without performing a cleaning operation or with a single cleaning operation.
B: Recording was successfully performed by two cleaning operations.
C: Three or more cleaning operations were required until normal recording could be performed.

  The image density of Example 24 was slightly inferior to that of Example 1, and the image density of Example 15 was slightly inferior to that of Example 2. In addition to the inks used in the above examples, inks using salts of various anions specified in the present invention were also evaluated in the same manner as in Example 5. Specifically, the same evaluation as above was performed except that the anion of the salt in Example 5 was different. As a result, almost the same result as in Example 5 was obtained for any anion salt.

Claims (6)

An inkjet ink containing a self-dispersing pigment, a salt, and a water-soluble organic compound,
The self-dispersing pigment is a pigment in which a functional group containing at least a phosphonic acid group is bonded to the particle surface, and the amount of the functional group bonded to the self-dispersing pigment is 0.34 mmol / g or more 0.40 mmol / g or less,
The salt is at least one cation selected from the group consisting of alkali metal ions, ammonium ions, and organic ammonium ions, and Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO _4. ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , HCOO ⁻ , (COO ⁻ ) ₂ , COOH (COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₄ (COO ^- ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ^−. The anion concentration of the salt in the ink × the value of the valence of the anion is 0.01 mol / L or more and 0.04 mol / L or less,
The water-soluble organic compound contains ethylene urea, and the content of the ethylene urea in the ink is 22% by mass to 50% by mass with respect to the total content of the water-soluble organic compound in the ink. Characteristic ink.   The ink of claim 1, wherein the functional group comprises at least two phosphonic acid groups.   The ink according to claim 1 or 2, wherein the solubility of the salt in 100 mL of water is 10 g or more at 25 ° C.   An ink cartridge having an ink storage portion for storing ink, wherein the ink stored in the ink storage portion is the ink according to any one of claims 1 to 3.   An inkjet recording method comprising: a step of recording an image on a recording medium by ejecting ink from an ejection port of an inkjet recording head; and a step of covering the ejection port of the recording head with a cap, wherein the ink includes: An ink jet recording method comprising the ink according to any one of claims 1 to 3.   An ink jet recording apparatus comprising: an ink containing portion for containing ink; means for ejecting ink from an ejection port of an ink jet recording head to record an image on a recording medium; and a cap covering the ejection port of the recording head. An ink jet recording apparatus, wherein the ink is the ink according to any one of claims 1 to 3.

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