JP2012229308A - Ink, inkjet recording method, and ink cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ink containing a self-dispersible pigment, good in water resistance of images obtained, and suppressed in jet twist caused by ink deposition on the jet port face.SOLUTION: The pigment ink for inkjet use comprises: a self-dispersible pigment having a surface electric charge level of ≤0.20 mmol/g, determined by colloidal titration; a compound represented by general formula (1): CFSOM (wherein, n is 4 to 6; and M is an alkali metal atom); water; and a water-soluble organic solvent.

Description

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

  Conventionally, pigments excellent in fastness such as water resistance and light resistance have been widely used as color materials for printing inks. In ink-jet inks as well, studies have been actively conducted on the use of pigments as ink coloring materials with the aim of further improving the fastness of images obtained. By the way, in order to use a pigment as a coloring material for an inkjet aqueous ink, it is important to stably disperse the pigment in an aqueous medium. Generally, in order to disperse the pigment in the aqueous medium, a dispersant, for example, a resin dispersant is used. Such a resin dispersant is a water-soluble resin having a hydrophilic group for stably dispersing a pigment in an aqueous medium and a hydrophobic group for physically adsorbing on the surface of pigment particles that are hydrophobic. . An image obtained with an ink containing such a resin-dispersed pigment can exhibit good water resistance when recorded on a recording medium, particularly plain paper, due to the presence of the resin dispersant.

  In addition, in order to stably form a high-quality image by the ink jet recording method, it is important to eject ink as a stable droplet from a fine ejection port of the recording head. Specifically, for example, it is important for stable ink jet recording that the ink does not dry and solidify at the ejection port of the recording head. However, the inkjet ink in which the pigment is dispersed in the aqueous medium by the resin dispersant as described above has a problem in this respect. That is, in the ink as described above, it is considered that there is a considerable amount of the resin dispersant present in a dissolved state in the ink without adsorbing on the surface of the pigment particles. Therefore, there are cases where such a resin dispersant is likely to be clogged by adhering to the discharge port of the recording head.

  Various methods for improving the reliability of the pigment ink have been proposed for the problems described above (see Patent Documents 1 and 2). Specifically, an ink is disclosed that uses a self-dispersing pigment as a colorant that can be dispersed stably without using a dispersant by introducing a hydrophilic group on the surface of carbon black particles.

  On the other hand, in an ink using a resin-dispersed pigment (see Patent Document 3), a surface on which a discharge port of a recording head is formed (hereinafter referred to as a discharge port surface) by containing a nonionic surfactant. Improves ejection misalignment due to ink adhering to the ink.

JP-A-8-3498 Japanese Patent Laid-Open No. 10-195360 JP 2009-7556 A

  In an ink using a self-dispersing pigment as a coloring material, when the amount of hydrophilic groups introduced into the surface of the pigment particles is small, the reason for this will be described in detail later, but there may be a case where ejection misalignment occurs. On the other hand, if the introduction amount of the hydrophilic group on the surface of the pigment particle is too large, the ink hardly adheres to the discharge port surface of the recording head, but the water resistance of plain paper is hardly exhibited under specific conditions. It became clear that there was a problem.

  Conventionally, attempts have been made to improve the ejection deviation caused by the ink adhering to the ejection port surface of the recording head. However, all of these are studies on ink containing resin, and as a result of such studies, the ink composition should be devised. Thus, the discharge deviation is reduced. According to these ink compositions, the ink containing the resin-dispersed pigment showed an effect of reducing the discharge deviation, but it was found that when the above composition was applied to the ink containing the self-dispersed pigment, the water resistance was lowered. It was.

  As described above, Patent Literature 3 describes that an ink contains a nonionic surfactant. When a nonionic surfactant as described in Patent Document 3 is added to a self-dispersing pigment, particularly an ink containing a self-dispersing pigment with a small amount of hydrophilic group introduced, hydrophilicity on the surface of the pigment particles is added. The surfactant is adsorbed on the exposed portion not covered with the sex group. As a result, the dispersion state of the self-dispersing pigment becomes a more stable direction. For this reason, there may arise problems such as color developability, which is realized by reducing the amount of hydrophilic group introduced in the self-dispersing pigment, and that water resistance in plain paper is difficult to develop under specific conditions. It was revealed.

  Accordingly, an object of the present invention is to provide an ink jet ink that has good water resistance of an image obtained and that suppresses occurrence of ejection deviation due to adhesion of ink to the ejection port surface in an ink containing a self-dispersing pigment. To provide ink. Another object of the present invention is to provide an ink cartridge and an ink jet recording method capable of stably obtaining an image excellent in water resistance when plain paper or the like is used as a recording medium by using the ink. There is to do.

The above object is achieved by the present invention described below. That is, the inkjet ink according to the present invention includes a self-dispersing pigment having a surface charge amount of 0.20 mmol / g or less obtained by colloid titration, a compound represented by the following general formula (1), water, and a water-soluble organic compound. It contains a solvent.
C _n F _{(2n + 1)} SO ₃ M (1)
(In general formula (1), n is a number from 4 to 6, and M is an alkali metal.)

  According to the present invention, in an ink containing a self-dispersing pigment, an ink for ink jet in which water resistance of an obtained image is good and occurrence of ejection deviation due to adhesion of ink to the ejection port surface is suppressed. Can be provided. Further, according to another embodiment of the present invention, an ink cartridge and an ink jet recording method that can stably obtain an image excellent in water resistance by using the ink are provided.

FIG. 3 is a perspective view illustrating a configuration example of a recording head. It is a disassembled perspective view which shows the example of 1 structure of a head unit. FIG. 5 is a perspective view showing a partially broken structure near a discharge port array for one color ink.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments. First, the background to the present invention will be described.
As described above, when ink containing a self-dispersing pigment with a small amount of hydrophilic groups introduced onto the surface of pigment particles is used in an ink jet recording system, ejection deviation may occur. On the other hand, if an ink containing a self-dispersing pigment with a large amount of hydrophilic groups introduced to the surface of the pigment particles is used, the ink hardly adheres to the discharge port surface of the recording head. It becomes difficult to develop water resistance. These mechanisms will be described in detail.

  A self-dispersing pigment with a small amount of hydrophilic group introduced to the surface of the pigment particle has many exposed portions of the surface of the pigment particle not covered with the hydrophilic group. Since the surface of the pigment particles is hydrophobic, the exposed surface of the hydrophobic pigment particles adheres to the discharge port surface of the recording head, and the state of the discharge port surface becomes non-uniform. Ink is likely to adhere to the ejection port surface in such a state, and the ejected ink droplets are pulled by the adhered ink, and the ejection direction of the ink is deviated. On the other hand, since the surface of the pigment particle is covered with the hydrophilic group in the self-dispersing pigment having a large amount of introduction of the hydrophilic group to the surface of the pigment particle, the surface of the hydrophobic pigment particle is difficult to be exposed. It becomes difficult to adhere to the discharge port surface, and it is difficult to cause a discharge twist. However, if most of the surface of the pigment particles are covered with hydrophilic groups, the affinity for water becomes too strong, so even if the pigment has excellent water resistance, it is difficult to exhibit water resistance under certain conditions. I found out that As a result of the study by the present inventors, it is clear that the environment in which water resistance is hardly developed is a low humidity environment (relative humidity of about 10%), particularly a low temperature and low humidity environment (temperature of about 15 ° C., relative humidity of about 10%). It became. The present inventors presume the mechanism that makes it difficult for water resistance to develop in a low-temperature, low-humidity environment as follows.

  In an environment of normal temperature and humidity (temperature of about 25 ° C., relative humidity of about 50%), the recording medium (plain paper) absorbs moisture in the air, so that the surface of the recording medium is weak due to the absorbed moisture. Also exhibits hydrophilicity. For this reason, the water and the water-soluble organic solvent contained in the applied ink are easily adapted to the surface of the recording medium exhibiting weak hydrophilicity and penetrate into the inside of the recording medium. On the other hand, it is considered that a pigment having a lower hydrophilicity than water and a water-soluble organic solvent remains near the surface of the recording medium. Thus, the pigment is present near the surface of the recording medium, and water and the water-soluble organic solvent are present inside the recording medium. Therefore, in the recording medium, the pigment, water, and the water-soluble organic solvent Are considered to exist at separate positions.

  On the other hand, in a recording medium placed in a low humidity environment, moisture is completely removed from the surface and inside thereof, so that the fibers constituting the recording medium are considered to exhibit weak hydrophobicity. For this reason, moisture and water-soluble organic solvents in the ink become difficult to adapt not only to the inside of the recording medium but also to the inside, so that the penetration is slow, and the pigment, water, and the water-soluble organic solvent remain in the vicinity of the surface of the recording medium. It is considered a thing. Thereafter, water evaporates in a low-humidity environment, but since many water-soluble organic solvents used for ink jet ink have a lower vapor pressure than water, they continue to exist around the pigment without evaporating. For this reason, it is considered that when water is poured on the image immediately after recording, the pigment flows out together with the water-soluble organic solvent, so that the water resistance is hardly exhibited.

  Patent Document 3 describes that a nonionic surfactant is added to ink in order to reduce ejection deviation. However, when such a nonionic surfactant is added to an ink containing a self-dispersing pigment with a small amount of introduced hydrophilic groups, the nonionic surfactant is added to the surface of the pigment particles not covered with the hydrophilic groups. The agent is adsorbed. As a result, the dispersion state of the self-dispersing pigment is further stabilized, and the color developability and water resistance immediately after recording, which have been achieved by the self-dispersing pigment with a reduced amount of hydrophilic groups introduced, are reduced.

  As a result of studies by the present inventors, a self-dispersing pigment having a surface charge amount determined by colloid titration of 0.20 mmol / g or less, a specific perfluoroalkyl sulfonate, water, and a water-soluble organic solvent. The present invention has been found to contain the ink of the present invention. As a result, it is possible to provide an ink suitable for an ink jet recording method, in which the obtained image has good water resistance and the occurrence of ejection deviation due to ink adhesion to the ejection port surface is reduced. About the reason why the ink of the present invention has such characteristics, the present inventors presume as follows.

  First, the mechanism for suppressing the ejection deviation is considered as follows. The self-dispersing pigment contained in the ink of the present invention, which is defined by the surface charge amount determined by colloid titration being 0.20 mmol / g or less, has a small amount of hydrophilic group introduced. Hydrophobic groups of perfluoroalkyl sulfonate are adsorbed on the hydrophobic part to which the hydrophilic groups are not bonded on the surface of such pigment particles, and the pigment is absorbed by the hydrophilic group or the perfluoroalkyl sulfonate. The surface of the particles is covered. For this reason, it becomes possible to suppress the adhesion of the pigment to the discharge port surface of the recording head. Here, when the carbon number of the perfluoroalkyl sulfonate, that is, n in the general formula (1) to be described later is 3 or less, adsorption to the pigment hardly occurs, so that the pigment easily adheres to the discharge port surface. It is impossible to suppress the occurrence of ejection deviation. On the other hand, when the carbon chain of the perfluoroalkyl sulfonate, that is, n is 7 or more, the perfluoroalkyl sulfonate is too hydrophobic. For this reason, the perfluoroalkyl sulfonate itself is likely to adhere to the discharge port surface, and it is considered that discharge deviation occurs.

  The mechanism for improving the water resistance of the image is considered as follows. The perfluoroalkyl sulfonate has a compact molecular structure including a perfluoroalkyl group that is a hydrophobic group exhibiting strong water repellency and a sulfonate that is a strong hydrophilic group. In an ink containing water or a water-soluble organic solvent, the perfluoroalkyl sulfonate is oriented so that the perfluoroalkyl group is on the surface of the pigment particles and the sulfonate is on the outside. On the ejection port surface of the recording head, the water-soluble organic solvent exists even when the water in the ink evaporates, and the above-described orientation state is maintained, so that the adhesion of the pigment to the ejection port surface is suppressed. On the other hand, since the evaporation of water and the penetration of the water-soluble organic solvent into the recording medium occur after the ink is applied to the recording medium, the pigment and the water-soluble organic solvent are separated from each other. It will be exposed to the air. In that case, the perfluoroalkyl group oriented on the surface of the pigment particle is oriented outward and away from the surface of the pigment particle. For this reason, it is considered that the water resistance of the image is developed by exposing the surface of the pigment particles.

<Ink>
The ink-jet ink of the present invention contains a specific self-dispersing pigment and a specific perfluoroalkyl sulfonate. Other than that, the configuration may be the same as that of the conventional ink. Below, each component which comprises the ink concerning this invention is demonstrated.

(Self-dispersing pigment)
The color material used in the ink of the present invention is a pigment. The kind of pigment that can be used in the present invention is not particularly limited, and any known inorganic pigment or organic pigment can be used. Specific examples include inorganic pigments such as calcium carbonate, titanium oxide, and carbon black, and organic pigments such as phthalocyanine and quinacdrine.

  In the ink of the present invention, the pigment needs to be a self-dispersing pigment having a surface charge obtained by colloid titration of 0.20 mmol / g or less. That is, the hydrophilic group is chemically bonded to the surface of the pigment particle directly or via another atomic group, and the amount of the hydrophilic group per 1 g of the pigment shown as the surface charge amount determined by colloid titration. Is required to be 0.20 mmol / g or less. By using 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 self-dispersing pigment, if the introduction amount of the hydrophilic group on the surface of the pigment particle is too large, the water resistance of the image is lowered due to the reason described above. Therefore, the surface charge obtained by colloid titration needs to be 0.20 mmol / g or less. Conversely, if the amount of hydrophilic group introduced is reduced, the effect of improving the color development due to the introduction of the hydrophilic group tends to be somewhat difficult to obtain, but the water resistance of the image is improved. The surface charge amount to be obtained is preferably 0.10 mmol / g or more.

  The surface charge amount of the self-dispersing pigment required in the present invention is measured by a colloid titration method. In the Example mentioned later, it measured using the potentiometric automatic titration apparatus AT-510 (made by Kyoto Electronics Industry) equipped with the streaming potential titration unit (PCD-500). Further, the surface charge amount of the self-dispersed pigment in the pigment dispersion was measured by potentiometric titration using methyl glycol chitosan as a titration reagent.

On the surface of the pigment particles, the hydrophilic groups are chemically bonded directly or through another atomic group, for _{example, -COOM, -SO 3 M, -PO} 3 HM, -PO 3 M 2 ( General M in the formula represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium). The other atomic group (—R—) includes 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 sulfonic acid group, an amino group, Examples include a carbonyl group, an ester group, and an ether group. Moreover, the group etc. which combined these groups are mentioned. Examples of the alkali metal represented as M include Li, Na, K, and the like. When the hydrophilic group forms a salt, the form of the salt in the ink may be in any dissociated state or all dissociated state.

  The content (% by mass) of the self-dispersing pigment in the ink is 0.1% by mass or more and 15.0% by mass or less, and further 0.2% by mass or more and 10.0% by mass or less based on the total mass of the ink. It is preferable. The ink may contain other colorants such as known dyes in addition to the self-dispersing pigment.

  The self-dispersing pigment used in the present invention may be a self-dispersing pigment that has been subjected to surface oxidation treatment, and can be used as long as the surface charge obtained by colloid titration is 0.20 mmol / g or less. . Examples of such self-dispersed pigments include those obtained by methods such as oxidation with sodium hypochlorite, ozone treatment in water, and ozone treatment, followed by wet oxidation with an oxidizing agent and modification of the particle surface. It is done. In the present invention, other dispersion type pigments (resin dispersion pigments, microcapsule pigments, resin-bonded self-dispersion pigments, etc.) may be used in combination as long as the effects of the present invention are obtained.

(Compound represented by the general formula (1))
The ink of the present invention contains a compound represented by the following general formula (1) (perfluoroalkyl sulfonate). M in the general formula (1) is an alkali metal, and specific examples thereof include lithium, sodium, and potassium. The content (% by mass) of the compound represented by the general formula (1) in the ink is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink. The form of the perfluoroalkyl acid salt in the ink may be in a state where a part thereof is dissociated or a state where all of it is dissociated.

C _n F _{(2n + 1)} SO ₃ M (1)
(In general formula (1), n is a number from 4 to 6, and M is an alkali metal.)

  As a result of the study by the present inventors, the content (% by mass) of the compound represented by the general formula (1) in the ink is 0.5% by mass or more and 3.0% by mass or less based on the total mass of the ink. It turned out that it is more preferable. In the case where the content is within the above range, when water in the ink adhering to the ejection port surface evaporates, the ink droplet evaporates in a shape close to a perfect circle. The fact that the ink droplets evaporate in a shape close to a perfect circle indicates that the ink is well repelled on the ejection port surface and no adhesion has occurred.

  On the other hand, if the content of the compound represented by the general formula (1) exceeds 3.0% by mass, the content is too much, so that it is more than the perfluoroalkyl sulfonate necessary for covering the surface of the pigment particles. Is present as a salt in the ink. Since the amount of the salt is too large, the electrolyte concentration increases as the water evaporates from the ink adhering to the discharge port surface, causing the pigment to aggregate. Since the aggregates are randomly attached to the ejection port surface, the shape of the droplet when the ink is evaporated becomes irregular. In addition, the pigment in the agglomerates generated as a result of the evaporation of ink on the ejection port surface has a water-soluble organic solvent around it even after the water has evaporated, so The fluoroalkyl sulfonate is present in an adsorbed form as before moisture evaporation. Therefore, both the pigment and the pigment aggregate exist in a state where the surface is hydrophilic and the adhesion to the discharge port surface is very weak, so the droplets are distorted, but the discharge deviation does not occur it is conceivable that.

  In addition, when the content of the compound represented by the general formula (1) is less than 0.5% by mass, the surface of the pigment particles is not sufficiently covered, so that the ink is effectively repelled on the discharge port surface. May not be obtained. However, since the perfluoroalkylsulfonic acid salt is adsorbed on the hydrophobic portion of the pigment particle surface, although not so much, the hydrophobic portion of the pigment and the discharge port surface do not come into direct contact with each other. For this reason, since the pigment has weak adhesion to the discharge port surface, the droplets are distorted, but it is considered that no discharge deviation occurs.

(Aqueous medium)
The ink of the present invention contains an aqueous medium composed of water and a water-soluble organic solvent. As water, deionized water or ion exchange water is preferably used. The content (% by mass) of water in the ink is preferably 30.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. By including an appropriate amount of water in the ink, it is possible to obtain an ink that has an appropriate viscosity to enable stable ejection by the ink jet method and in which clogging in the recording head is suppressed. Moreover, as a water-soluble organic solvent, all the well-known things generally used for the ink for inkjets can be used, and 1 type, or 2 or more types of water-soluble organic solvents can be used. Specifically, monohydric or polyhydric alcohols, alkylene glycols having an alkylene group having about 1 to 4 carbon atoms, polyethylene glycols having a number average molecular weight of about 200 to 2,000, glycol ethers, nitrogen-containing compounds Examples thereof include compounds. In the present invention, it is particularly preferable to use a water-soluble organic solvent having a vapor pressure higher than that of water at room temperature (25 ° C.). The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

(Other ingredients)
In addition to the above components, the ink of the present invention may contain a water-soluble organic compound that is solid at room temperature, such as nitrogen-containing compounds such as urea and ethyleneurea, trimethylolethane, and trimethylolpropane, if necessary. . In addition to the above components, various kinds of surfactants, pH adjusters, antifoaming agents, rust inhibitors, antiseptics, antifungal agents, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, etc. An additive may be contained.

(Total cation concentration)
Further, according to the study by the present inventors, it has been found that the total cation concentration in the ink is preferably less than 0.10 mmol / L. When the total cation concentration is 0.10 mmol / L or more, as the water in the ink adhering to the ejection port surface evaporates, the electrolyte concentration increases, which may cause pigment aggregation. In some cases, the aggregates randomly adhere to the discharge port surface, resulting in an irregular shape of the droplet when the ink evaporates. The agglomerates generated as a result of the evaporation of ink on the surface of the ejection port are free of perfluoroalkyl sulfonate on the surface of the pigment particles due to the presence of a water-soluble organic solvent around the water after the evaporation of water. Exists in the form of adsorbed in the same manner as before the evaporation of moisture. Therefore, both the pigment and the pigment aggregate exist in a state where the surface is hydrophilic and the adhesion to the discharge port surface is very weak, so the droplets are distorted, but the discharge deviation does not occur it is conceivable that.

<Ink cartridge>
The ink cartridge of the present invention includes an ink storage portion that stores ink, and the ink storage portion stores the ink of the present invention described above. As for the structure of the ink cartridge, the ink storage portion includes an ink storage chamber that stores liquid ink and a negative pressure generation member storage chamber that stores a negative pressure generation member that holds the ink therein by a negative pressure. Things. Alternatively, the ink cartridge may be an ink container that does not have an ink storage chamber for storing liquid ink and is configured to hold the entire storage capacity by a negative pressure generating member. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a recording medium by ejecting the ink of the present invention described above with an ink jet recording head. Examples of a 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 recording method that utilizes thermal energy. . Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

  FIG. 1 is a perspective view illustrating a configuration example of a recording head, and FIG. 2 is an exploded perspective view illustrating a configuration example of a head unit that is a component of the recording head.

  As illustrated in FIG. 1, the recording head 1 includes a head unit 400 having an ejection port array that ejects ink, and an ink cartridge 410 that stores ink and supplies ink to the head unit 400. In the recording head 1, the ejection port array provided in the head unit 400 faces the recording medium, and the arrangement direction thereof coincides with a direction different from the main scanning direction (for example, the sub-scanning direction that is the recording medium conveyance direction). Mounted on the carriage. The number of sets corresponding to the type of ink to be used can be provided for the set of ejection port arrays and ink cartridges 410. In the illustrated example, six sets are provided corresponding to six colors (for example, black (Bk), cyan (C), magenta (M), yellow (Y), light cyan (LC), and light magenta (LM)). . In the recording head 1 shown here, ink cartridges 410 independent for each color are prepared, and each is detachable from the head unit 400.

As shown in FIG. 2, the head unit 400 includes a recording element substrate 420, a first plate 430, an electric wiring substrate 440, a second plate 450, a cartridge holder 460, an ink flow path 461, and a flow path forming member 470. Has been. A recording element substrate 420 having an ejection port array for each color ink is bonded and fixed on a first plate 430 made of aluminum oxide (Al ₂ O ₃ ) or the like. Here, ink is attached to the recording element substrate 420. An ink supply port 431 for supplying the ink is formed. Further, a second plate 450 having an opening is bonded and fixed to the first plate 430. The second plate 450 holds the electrical wiring board 440 so that the electrical wiring board 440 for applying an electrical signal for ejecting ink and the recording element board 420 are electrically connected. On the other hand, a flow path forming member 470 is ultrasonically welded to the cartridge holder 460 that detachably holds the ink cartridge 410, thereby forming an ink flow path (not shown) extending from the ink cartridge 410 to the first plate 430.

  FIG. 3 is a perspective view showing a partially broken structure in the vicinity of the ejection port array for one color ink in the recording element substrate shown in FIG. In FIG. 3, reference numeral 421 denotes a heating element (heater) that generates thermal energy that causes film boiling in the ink in response to energization as energy used to eject the ink. On the base 423 on which the heater 421 is mounted, a temperature sensor 428 for detecting the temperature of the head unit 400 and a sub heater (not shown) for keeping the head or ink in accordance with the detected temperature are provided. . Reference numeral 422 denotes an ejection port, 424 denotes an ink supply port, and 426 denotes an ink flow path wall. Reference numeral 425 denotes a plate on which discharge ports 422 are formed facing each heater, and is disposed on the substrate 423 via a resin coating layer 427. Further, the surface of the plate 425 facing the recording medium, that is, the discharge port surface may be subjected to water repellent treatment.

  When the ink of the present invention is used, the surface characteristics of the discharge port surface of the plate 425 are preferably water repellent. Since the ejection port surface of the recording head is water-repellent, ejection deviation due to adhesion of ink to the ejection port surface is more effectively suppressed. In order to make the discharge port surface of the recording head water repellent, for example, the plate 425 may be made of a water repellent material. As the water repellent material, various materials such as polyolefin, silicon and fluorine are preferably used. Furthermore, in order to more effectively suppress the ejection deviation due to the ink adhering to the ejection port surface, it is preferable that the surface characteristics of the ejection port surface be oil repellency. In order to make the ejection port surface of the recording head oil-repellent, for example, the plate 425 may be made of an oil-repellent material. As the oil repellent material, a fluorine-based material is preferably used.

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

<Preparation of pigment dispersion>
(Surface charge of self-dispersing pigment)
First, a method for measuring the surface charge amount of the self-dispersing pigment will be described. Using a potentiometric automatic titration apparatus AT-510 (manufactured by Kyoto Denshi Kogyo Co., Ltd.) equipped with a streaming potential titration unit (PCD-500), the potentiometric titration using methyl glycol chitosan as a titration reagent allows The surface charge amount was measured.

(Pigment dispersion A)
To a solution of 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water, 0.8 g of p-aminobenzoic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 0.9 g of sodium nitrite was added to 9 g of water at 5 ° C. The dissolved solution was added. After the solution was further stirred for 15 minutes, 9 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. After the obtained slurry was filtered with a filter paper (standard filter paper No. 2; manufactured by Advantech), the particles were sufficiently washed with water and dried in an oven at 110 ° C., and a —C ₆ H ₄ —COONa group was formed on the surface of the pigment particles. Self-dispersing pigment A in which is bound was prepared. Pigment dispersion B was prepared by adding water to the obtained self-dispersion pigment A and dispersing the pigment so that the pigment content was 10.0%. The surface charge obtained by colloid titration of self-dispersing pigment A was 0.16 mmol / g.

(Pigment dispersion B)
To a solution of 5 g of concentrated hydrochloric acid dissolved in 5.5 g of water, 1.55 g of p-aminobenzoic acid was added while being cooled to 5 ° C. Next, the solution containing the solution is placed in an ice bath and the solution is stirred so that the solution is always kept at 10 ° C. or lower, and 1.8 g of sodium nitrite is added to 9 g of water at 5 ° C. The dissolved solution was added. After stirring this solution for another 15 minutes, 6 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. After the obtained slurry was filtered with a filter paper (standard filter paper No. 2; manufactured by Advantech), the particles were sufficiently washed with water and dried in an oven at 110 ° C., and a —C ₆ H ₄ —COONa group was formed on the surface of the pigment particles. Self-dispersing pigment B in which Pigment dispersion B was prepared by adding water to the obtained self-dispersion pigment B and dispersing the pigment so that the pigment content was 10.0%. The amount of surface charge obtained by colloid titration of the self-dispersing pigment B was 0.21 mmol / g.

(Pigment dispersion C)
10 g of pigment (CI Pigment Red 122) and 4.0 g of sulfanilic acid were mixed. The container containing the mixture was placed in a 70 ° C. water bath. To this mixture, a solution of 1.68 g sodium nitrite in 74.32 g water was added under stirring. Further, hydrochloric acid was added to adjust the pH of the slurry to 2, and the mixture was stirred at 70 ° C. for 1 hour. Thereafter, the particles were dried to prepare self-dispersed pigment C in which —C ₆ H ₄ —SO ₃ Na groups were bonded to the surface of the pigment particles. Pigment dispersion C was prepared by adding water to the obtained self-dispersion pigment C and dispersing the pigment so that the pigment content was 10.0%. The surface charge determined by colloid titration of self-dispersing pigment C was 0.15 mmol / g.

(Pigment dispersion D)
7 g of pigment, 7 mmol of ((4-aminobenzoylamino) -methane-1,1-diyl) bisphosphonic acid monosodium salt, 20 mmol of nitric acid, and 200 mL of pure water were mixed. At this time, examples of the pigment include C.I. I. Pigment Yellow 74 was used, and the mixture was mixed at 6,000 rpm at room temperature using a Silverson mixer (manufactured by Silverson). 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 mixture was reacted for 1 hour in this state. Thereafter, the pH of the mixture was adjusted to 10 using an aqueous sodium hydroxide solution. After 30 minutes, 20 mL of pure water was added, diafiltration was performed using a spectrum membrane, and water was added to disperse the pigment so that the pigment content was 10.0%. Prepared. In this way, the self-dispersing pigment D in which the ((4-aminobenzoylamino) -methane-1,1-diyl) bisphosphonic acid group in which the counter ion is sodium is bonded to the surface of the pigment particle is dispersed in water. Pigment dispersion D in a fresh state was obtained. The amount of surface charge obtained by colloid titration of self-dispersing pigment D was 0.11 mmol / g.

(Pigment dispersion E)
15 g of pigment (CI Pigment Blue 15: 3) and 4.0 g of sulfanilic acid were mixed. The container containing the mixture was placed in a 70 ° C. water bath. To this mixture, a solution of 1.68 g sodium nitrite in 74.32 g water was added under stirring. Further, hydrochloric acid was added to adjust the pH of the slurry to 2, and the mixture was stirred at 70 ° C. for 1 hour. Thereafter, the particles were dried to prepare self-dispersed pigment E in which —C ₆ H ₄ —SO ₃ Na groups were bonded to the surface of the pigment particles. Pigment dispersion E was prepared by adding water to the obtained self-dispersion pigment E and dispersing the pigment so that the pigment content was 10.0%. The amount of surface charge obtained by colloid titration of self-dispersion pigment E was 0.19 mmol / g.

<Synthesis of Compound Represented by General Formula (1)>
(Compound 1: Sodium perfluorooctane sulfonate)
In a three-necked flask, 60 g of perfluorooctyl iodide, 50 g of sodium bisulfite, 100 mL of dimethylformamide, and 100 mL of water were added, and the temperature was adjusted to 70 ° C. by heating, followed by stirring for 3 hours. After completion of the reaction, the solvent was distilled off under reduced pressure, and the resulting crystals were extracted with acetone. After concentrating the extracted solution, 320 g of 5% sulfuric acid aqueous solution and 80 mL of 35% hydrogen peroxide solution were added and stirred at room temperature for 5 hours. Thereafter, the aqueous layer was washed with hexane, adjusted to pH 7 with an aqueous sodium hydroxide solution, and concentrated. The obtained crystals were extracted with acetone. Then, the acetone solution was concentrated to obtain sodium perfluorooctane sulfonate (Compound 1).

(Compound 2: Sodium perfluorohexane sulfonate)
In the synthesis of Compound 1, sodium perfluorohexanesulfonate (Compound 2) was obtained by the same procedure as Compound 1 except that perfluorohexyl iodide was used instead of perfluorooctyl iodide.

(Compound 3: Sodium perfluorobutane sulfonate)
In the synthesis of Compound 1, sodium perfluorobutanesulfonate (Compound 3) was obtained by the same procedure as Compound 1 except that perfluorobutyl iodide was used instead of perfluorooctyl iodide.

(Compound 4: sodium perfluoroethanesulfonate)
In the synthesis of Compound 1, sodium perfluoroethanesulfonate (Compound 4) was obtained by the same procedure as Compound 1 except that perfluoroethyl iodide was used instead of perfluorooctyl iodide.

<Preparation of ink>
Each component (unit: part) shown in the upper part of Table 1 was mixed and sufficiently stirred, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each ink. Acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.) and NIKKOL BC20 (manufactured by Nikko Chemical Co., Ltd.) are nonionic surfactants, and polyethylene glycol having a number average molecular weight of 600 was used.

  The lower part of Table 1 shows the value of the total cation concentration (mol / L) in the ink. The total cation concentration was calculated as the sum of the cation concentration derived from the pigment and the cation concentration derived from other components. The cation concentration derived from the pigment is a value calculated from the surface charge determined by colloid titration and the pigment content in the ink. Further, the cation concentration derived from other components is a value calculated on the assumption that all of the used compounds are ionically dissociated. From these values, the value calculated by setting the specific gravity of the ink to 1 was taken as the total cation concentration in the ink.

Hereinafter, taking the ink of Example 1 as an example, the calculation method of the total cation concentration (mol / L) in the ink will be described. For the preparation of the ink of Example 1, a pigment dispersion A containing a self-dispersing pigment having a surface charge amount of 0.16 mmol / g determined by colloid titration and a pigment content of 10.0% was added to 50. 0 parts were used. Therefore, the amount of the cation derived from the pigment is 10.0 (g) of the ink, the amount of the pigment dispersion A used is 50.0 parts, the pigment content is 10.0 (%), the surface charge, and the specific gravity of the ink is 1. From the amount of 0.16 (mmol / g), it is determined as follows.
1000 (g) x 50 parts (0.5) x 10.0% x 0.16 (mmol / g) = 8 mmol
Therefore, the cation concentration derived from the pigment in the ink is 0.008 (mol / L).
In addition, the cation concentration derived from other components may be determined by considering compound 3 because the only ion-dissociating component contained in the ink of Example 1 is compound 3 (sodium perfluorobutanesulfonate). Compound 3 has a molecular weight of 322.10 and a use amount of 2.5 parts. Assuming that all of the added compound 3 is ionically dissociated, the amount of cations derived from the other compounds is 2.5 parts by weight of compound 3 in 1 L (1,000 g) of ink, assuming that the specific gravity of the ink is 1. The molecular weight of 322.10 is determined as follows.
1000 (g) x 2.5 parts (0.025) /322.10 = 0.078 mol
Therefore, the cation concentration derived from other components in the ink is 0.078 mol / L.
From these values, the total cation concentration in the ink becomes a pigment-derived cation concentration of 0.008 (mol / L) + the cation concentration of other components of 0.078 (mol / L) = 0.086 mol / L. .

<Evaluation>
Each of the inks obtained above was filled in an ink cartridge, and the following evaluation was performed using an ink jet recording apparatus PIXUS 850i (manufactured by Canon). The recording apparatus has a resolution of 600 dpi × 600 dpi, and applies an ink droplet having a discharge amount of 30 ng per droplet to a unit area of 1/600 inch × 1/600 inch. The recording duty is defined as 100%. In the present invention, according to the evaluation criteria for each item, AA and A are acceptable levels, and B is an unacceptable level. The evaluation results are shown in Table 2.
(Dischargeability)
The evaluation of dischargeability was performed as follows in an environment of a temperature of 25 ° C. and a relative humidity of 50%. An ink cartridge was mounted at the yellow ink position of the recording apparatus. After recording 10 A4 size solid images with a recording duty of 50% on plain paper (PB PAPER GF-500; manufactured by Canon), a PIXUS 850i nozzle check pattern was recorded, and the ejection port of the recording head The state of the surface was observed with a microscope.
AA: The ink droplets on the ejection port surface are almost perfect circles, and the nozzle check pattern is not disturbed.
A: The ink droplets on the ejection port surface are not perfect circles, but the ink is repelled and the nozzle check pattern is not disturbed.
B: The ink droplets on the discharge port surface are distorted, wet with ink, and the nozzle check pattern is disturbed.

(water resistant)
The water resistance was evaluated as follows. Using a recording medium (plain paper) that has been blended in a low-temperature, low-humidity environment (temperature: 15 ° C, relative humidity: 10%) for one night or longer and mounting the ink cartridge at the black ink position of the recording device under the same temperature and humidity conditions did. And on 4 types of plain paper (GF-500, SW-101, Office 70 [above, made by Canon], XEROX 4200 (made by Xerox)), a solid image of 5 mm in length and 150 mm in width with a recording duty of 100%. Recorded. One day after recording, 1 mL of pure water was dropped by a micropipette from the direction perpendicular to the long side of the solid image with the paper standing upright, and the image was visually checked for bleeding.
A: There is no bleeding of the image on all the recording media.
B: Image blur is observed on some recording media.

1: Recording head 400: Head unit 410: Ink cartridge 420: Recording element substrate 421: Heating element (heater)
422: discharge port 423: base 424: ink supply port 425: discharge port plate 426: ink flow path wall 427: coating layer 428: temperature sensor 430: first plate 431: ink supply port 440: electrical wiring board 450: first 2 plate 460: cartridge holder 461: ink flow path 470: flow path forming member

Claims (5)

A self-dispersing pigment having a surface charge obtained by colloid titration of 0.20 mmol / g or less, a compound represented by the following general formula (1), water, and a water-soluble organic solvent, ink.
C _n F _{(2n + 1)} SO ₃ M (1)
(In general formula (1), n is a number from 4 to 6, and M is an alkali metal.)   The content (% by mass) of the compound represented by the general formula (1) in the ink is 0.5% by mass or more and 3.0% by mass or less based on the total mass of the ink. ink.   The ink according to claim 1 or 2, wherein the total cation concentration in the ink is less than 0.10 mmol / L.   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 for recording an image on a recording medium by ejecting ink from an inkjet recording head, wherein the ink is the ink according to any one of claims 1 to 3. Inkjet recording method.

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