JP5328108B2 - Aqueous ink, ink jet recording method, ink cartridge, recording unit, and ink jet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-based ink containing a pigment, but generating no clogging caused by drying of the ink at a nozzle tip and expressing high levels of discharge stability recently required to the ink. <P>SOLUTION: The water-based ink comprises at least water, a water-soluble organic solvent and carbon black particles and contains the carbon black having &ge;0.5 &mu;m particle size. In the water-based ink, the rate of volume of the carbon black particles having &ge;0.2 &mu;m to &lt;0.5 &mu;m particle size is &le;0.3% based on the sum total volume of all carbon black particles in the ink, the number of carbon black particles having &ge;0.5 &mu;m to &lt;5.0 &mu;m particle size is &le;1.0&times;10<SP>7</SP>per 1 mL, and the average particle size of the carbon black particles is 0.06-0.130 &mu;m. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an aqueous ink, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus.

  In recent years, the development of pigment inks using pigments as coloring materials has been energetically advanced as inks for ink jets used in ink jet recording apparatuses. However, in the pigment ink, the particle diameter increases due to the aggregation of the particles over time, or the precipitation of the pigment particles occurs according to Stokes' law. As a result, ink with a high pigment concentration and an increased pigment particle size (hereinafter referred to as sedimented ink) accumulates in the lower part of the ink cartridge. May not be sufficient.

  In particular, in recent years, the following have been performed to obtain a clear image with little blurring at the boundary between the black ink and the color ink, and combined with these effects, the ink ejection stability has been improved. Keeping is getting harder than ever. In other words, for the purpose of forming a clear image, etc., a dispersion containing carbon black with high quick drying properties is used as a coloring material, and the ink flow path of the recording head is miniaturized in order to reduce ink droplets. And so on.

  In order to solve the above-described problem of ejection stability, the following means have been proposed. For example, it has been proposed to redisperse the precipitated ink by placing balls or beads in an ink cartridge (see Patent Document 1). In addition, there is a proposal relating to an ink cartridge that includes storage means for storing data for determining the settling speed of pigment or the like in ink, and controls the stirring operation in accordance with the data in the storage means (see Patent Document 2).

There is also a proposal for an ink cartridge that incorporates at least one of the following three ideas (see Patent Document 3).
(1) A configuration that suppresses the mixing of precipitated ink into the pigment ink to be supplied (precipitated ink supply suppression structure).
(2) A configuration that suppresses the generation (or accumulation) of precipitated ink (precipitated ink generation suppression structure).
(3) A configuration (precipitation ink elimination promoting structure) that can be eliminated by initial supply after the sedimentation ink is stored.

Further, the following proposals have been made to solve the problem of sedimentation ink. There is a proposal for an ink jet black ink that can obtain a good black image density in a short drying time and has less blur between the black image portion and the color image portion when the recording time difference between the black ink and the color ink is short (patent) Reference 4). Specifically, the volume average particle size of the dispersed particles in the ink is 85 nm or more and 115 nm or less, and among the dispersed particles contained in the ink, the volume of the particles is in the range of 0.5 μm or more and 1.0 μm or less. Is 0.001% or more and 0.03% or less with respect to the volume of the ink. In addition, in order to obtain an ink having excellent stability over time as an inkjet ink, it has been proposed that the following parameters are preferable (see Patent Document 5). That is, the particle size distribution of about 10 nm or more and 300 nm or less, or the number of accumulators with less than 10 ¹⁰ particles exceeding 0.5 μm per mL of dispersion (solid content: 15%) is 50% per week at 25 ° C. It has been mentioned that it has stability that does not change until it exceeds.

JP-A-4-169269 JP 2003-311993 A Japanese Patent No. 3384379 JP 2004-10632 A Special table 2003-513138 gazette

  According to the study by the present inventors, even when an ink cartridge satisfying the configurations of Patent Documents 1 to 3 described above is used, clogging occurs at the ink flow path or the nozzle tip, and ejection stability cannot be obtained. It has been found that such a problem occurs. The reason for this is that, in the above-described invention, although the above-described invention has an effect of delaying the progress of the sedimentation phenomenon of the pigment particles in the pigment ink, the ink has a function of essentially preventing the pigment particles from sedimenting. I think that is because it is not. Further, as described in Patent Document 3, the sedimentation ink in the ink cartridge can be eliminated by the initial supply after storage, so that the sedimentation ink can be eliminated. However, this method is not preferable in this respect because a large amount of wasted ink that is not used for recording is generated.

  In addition, the present inventors prepared inks satisfying the configurations of Patent Documents 4 and 5 and examined them. As a result, it has been found that these inks are clogged at the ink flow path and the nozzle tip, and the ejection stability cannot be obtained sufficiently. The reason for this is that, by specifying the volume and the number of particles having an average particle size or particle size of 0.5 μm or more, the performance for the technical level that has been conventionally required can be sufficiently satisfied. This is thought to be because the required technical level cannot be fully met. That is, the technical level required in recent years has become very strict, and it is considered that the conventional technology as described above has not yet achieved high performance corresponding to the technology.

  Accordingly, the present inventors have analyzed the causes and mechanisms that cannot satisfy the strict technical level required in recent years even when using conventional inks, and as a result, have come to the following idea. That is, since the number and volume of particles having a particle diameter of 0.5 μm or more are a very small ratio with respect to the entire ink, in the inventions described in Patent Documents 4 and 5, with respect to the entire image of the particle size distribution, I thought it was because only a small part was specified.

  Patent Document 5 described above relates to an inkjet ink having a stability in which the number and volume of particles having a particle diameter of 0.5 μm or more do not change until storage exceeds 50% in one week when stored at a temperature of 25 ° C. There is. However, the change in the longer period is not specified, and it cannot be said that it has sufficient performance for the high level of ejection stability required in recent years.

  Accordingly, an object of the present invention is to provide a water-based ink that prevents clogging due to drying of ink at the nozzle tip, which is a problem of the prior art, and can obtain a high level of ejection stability that has been required in recent years. Another object of the present invention is to provide an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus using such aqueous ink.

The above object is achieved by the present invention described below. That is , the water- based ink according to the present invention contains water , a water-soluble organic solvent, and carbon black particles, and the carbon black particles include carbon black particles having a particle diameter of 0.5 μm or more. The ratio of the volume of the carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm is 0.3% or less with respect to the total volume of all the carbon black particles in the water-based ink, The number of carbon black particles having a particle size of 0.5 μm or more and less than 5.0 μm is 1.0 × 10 ⁷ or less per mL of the water-based ink, and the average value of the particle size of the carbon black particles is 0.060 μm. It is characterized by being not less than 0.130 μm.

  In addition, an ink jet recording method according to another embodiment of the present invention is characterized in that, in the ink jet recording method in which ink is ejected by an ink jet method, the aqueous ink is used as the ink.

  An ink cartridge according to another embodiment of the present invention is an ink cartridge including an ink storage portion for storing ink, wherein the water-based ink is stored in the ink storage portion.

  According to another embodiment of the present invention, there is provided a recording unit comprising an ink storage portion for storing ink and a recording head for discharging ink, wherein the water-based ink is provided in the ink storage portion. Is housed.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus including an ink containing portion for containing ink and a recording head for ejecting ink. It is characterized by containing water-based ink.

  ADVANTAGE OF THE INVENTION According to this invention, although it is an ink containing the carbon black which is a pigment, there is no clogging by the drying of the ink at a nozzle tip, and the water-based ink excellent in discharge stability can be provided. In another embodiment of the present invention, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus that are excellent in ejection stability are provided by using the water-based ink having the above-described excellent characteristics.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. In the ink, carbon black exists in a primary particle state composed of one particle or in a structure state in which a plurality of the primary particles are aggregated. In the present invention, “carbon black” and “carbon black particles” refer to carbon black particles in a state of being present in ink regardless of the state of presence of the aforementioned particles. In the following description, the carbon black particles may be simply referred to as “particles”. In the following description, “the ratio occupied by the volume of the particles” refers to the ratio to the total volume of all the particles in the ink unless otherwise specified. Further, the “particle diameter” in the present invention is a “volume-based particle diameter”. Specifically, the particle diameter of the carbon black particles is a standard sample (spherical) of styrene latex having the same volume as the carbon black particles. It means the particle diameter obtained by converting to the particle diameter.

  In contrast to the conventional techniques as described above, the present inventors have studied a pigment ink containing carbon black particles for the purpose of satisfying the strict technical level required in recent years. As a result, the particle size distribution in a region not considered in the prior art, that is, the particle size distribution of 0.2 μm or more and less than 0.5 μm, which is intermediate between the average value of the particle size distribution and 0.5 μm or more, is specified. I found out that it was important. Specifically, by using a water-based ink having the following configuration (hereinafter sometimes simply referred to as “ink”), the above-described problems can be solved, and clogging due to drying of the ink at the nozzle tip is prevented, It has been found that a high level of ejection stability required in recent years can be obtained.

[Water-based ink]
In the water-based ink of the present invention, the water-based ink contains at least water, a water-soluble organic solvent, and carbon black particles, and the carbon black particles include carbon black particles having a particle diameter of 0.5 μm or more. The proportion of the volume of the carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm is 0.3% or less with respect to the total volume of all the carbon black particles in the water-based ink. The number of carbon black particles having a particle size of 0.5 μm or more and less than 5.0 μm is 1.0 × 10 ⁷ or less per mL of the water-based ink, and the average value of the particle size of the carbon black particles is 0.060 μm or more and 0 .130 μm or less.

  The carbon black particles having a particle diameter of 0.5 μm or more are present in a certain proportion in the ink when using the ink preparation method or the carbon black dispersion method that is usually performed. On the other hand, in order to reduce the possibility of heteroaggregation described in detail below, substantially eliminating carbon black particles having a particle size of 0.5 μm or more from the ink has the effect of the present invention. It can be said that it is not efficient in obtaining. In the present invention, in order to obtain an ink excellent in ejection stability without being clogged due to drying of the ink at the nozzle tip while being an ink containing carbon black, the particle size distribution of carbon black particles described below, etc. It is characterized by prescribing the characteristics of

(Percentage occupied by the volume of carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm)
As described above, according to the study by the present inventors, the volume of particles having a particle diameter of 0.5 μm or more is a very small ratio. For this reason, only by specifying the number of particles having a particle diameter of 0.5 μm or more and the volume of the particles, the technical level of ink that has been required in recent years (reducing the ink flow path to finer ink droplets). Response) cannot be satisfied. For this reason, it is very important to define the particle size distribution in a smaller region.

  As a result of the inventors paying attention to the above viewpoint, the ratio of the volume of particles having a particle diameter of 0.2 μm or more among particles having a particle diameter of less than 0.5 μm greatly affects the discharge performance. Found to affect. In other words, it was confirmed that the ratio of the volume of particles having a particle diameter of less than 0.2 μm in the particle diameter region having a particle diameter of less than 0.5 μm does not significantly affect the discharge performance. Therefore, the present inventors have studied the relationship between the proportion of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm and the ejection performance. As a result, when the proportion of the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm exceeds 0.3% with respect to the total volume of all the particles in the ink, the following problems occur: I found out that Specifically, it was found that clogging due to ink drying at the nozzle tip is likely to occur and the ejection stability may be significantly reduced, especially when using a recording head with a finer ink flow path. It was.

  The present inventors consider that the above-described reason is that heteroaggregation is likely to occur in which coarse particles are entangled with fine particles existing around them. That is, the presence of hetero-aggregated particles tends to lead to sedimentation of the particles in the ink cartridge. As a result, clogging at the ink flow path and the nozzle tip is likely to occur due to the high concentration of the precipitated ink generated in the lower part of the ink cartridge. Further, when the ink cartridge is left for a long time with the ink cartridge mounted on the recording head, the hetero-aggregation easily occurs similarly due to the influence of water evaporation, which causes clogging at the ink flow path and the nozzle tip.

  Here, a comparison between the above-described phenomenon and an adverse effect due to the presence of particles having a particle diameter of 0.5 μm or more described in the prior arts (Patent Documents 4 and 5) described above will be described below. In pigment inks that require good dispersibility, the volume of particles having a particle size of 0.2 μm or more and less than 0.5 μm as defined in the present invention is compared with the volume of particles having a particle size of 0.5 μm or more. Overwhelmingly large (about 50 times or more). For this reason, the possibility of the heteroaggregation described above is very high. Accordingly, the number and volume of heteroaggregates by particles having a particle diameter of 0.2 μm or more and less than 0.5 μm are overwhelmingly larger than those of heteroaggregated particles by particles having a particle diameter of 0.5 μm or more. . As a result, ink sedimentation inside the ink cartridge, or clogging at the ink flow path and nozzle tip when the ink cartridge is left attached for a long time with the recording cartridge mounted, is caused by particles having a specific particle diameter. It is thought that it is greatly influenced by the proportion of volume. In particular, it is considered that the particle size in the ink is greatly influenced by the proportion of the volume of the particles in the region of 0.2 μm or more and less than 0.5 μm.

  Furthermore, it is considered that particles once heteroaggregated continue to change from an unstable state to a stabilized state. Therefore, even if the problem does not occur so much in the initial stage, it is considered that the problem described above is more likely to occur when the storage is performed with time, particularly at a high temperature.

  Therefore, in the present invention, first, the proportion of the volume of the carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm is 0.3% with respect to the total volume of all the carbon black particles in the ink. % Or less. As described above, when the ratio of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm exceeds 0.3% with respect to the total volume of all particles in the ink, ejection stability May decrease.

The proportion of the volume of particles having a particle size of 0.2 μm or more and less than 0.5 μm can be measured using, for example, a dynamic light scattering type particle size distribution measuring device (UPA150EX; manufactured by Nikkiso). Of course, the present invention is not limited to this. The measurement conditions are preferably as follows.
-Particle size distribution measuring device: UPA150EX (manufactured by Nikkiso)
・ Setzero: 10 s or more and 120 s or less ・ Measurement time: 30 s or more and 300 s or less ・ Number of measurements: 1 or more and 5 or less

(Number of carbon black particles having a particle size of 0.5 μm or more and less than 5.0 μm)
In the present invention, the number of carbon black particles having a particle size of 0.5 μm or more and less than 5.0 μm is required to be 1 × 10 ⁷ or less per 1 mL of ink. As a result of the study by the present inventors, when the number of particles having a particle diameter of 0.5 μm or more and less than 5.0 μm exceeds 1 × 10 ⁷ per mL of ink, the heteroaggregation described above occurs more easily. I found it easier. That is, the ink sedimentation phenomenon inside the ink cartridge and clogging at the ink flow path and the nozzle tip when stored for a long time with the ink cartridge mounted on the recording head are more likely to occur. However, as described above, excellent ejection stability can be obtained if the number of particles having a particle diameter in the ink of 0.5 μm or more and less than 5.0 μm is 1 × 10 ⁷ or less per 1 mL of ink. it can.

  The number of particles having a particle size of 0.5 μm or more and less than 5.0 μm can be measured, for example, using a number counting type particle size distribution measuring apparatus (Accusizer780APS; manufactured by Particle Sizing System). The above-described apparatus detects scattered light of each particle having a particle diameter of 0.5 μm or more passing through the measurement unit (sensing zone), and converts the particle diameter from the intensity of the signal. Of course, the present invention is not limited to this.

(Average value of particle size of carbon black particles)
Furthermore, in the present invention, it is necessary that the average value of the carbon black particle diameter is 0.060 μm or more and 0.130 μm or less. When the average value of the particle diameter exceeds 0.130 μm, the discharge stability may be greatly reduced. On the other hand, when the average value of the particle diameter is less than 0.060 μm, the specific surface area of the carbon black is increased, and the dispersion stability may be lowered. In this case, particularly when the ink is stored for a long period of time, the ratio of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm tends to increase, which is not preferable.

In addition, the average value of the particle diameter in the present invention is d ₅₀ (average value of volume-based particle diameter = volume average particle diameter). The average value of particle diameters (d ₅₀ ; volume average particle diameter) can be measured using, for example, a dynamic light scattering type particle size distribution measuring apparatus (UPA-150; manufactured by Nikkiso). Of course, the present invention is not limited to this. The measurement conditions are preferably as follows.
-Particle size distribution measuring device: UPA150EX (manufactured by Nikkiso)
・ Setzero: 10 s to 120 s ・ Measurement time: 30 s to 300 s ・ Number of measurements: 1 to 5 times

(Change rate of the proportion of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm)
In the present invention, it is more preferable to satisfy the following requirements. That is, the ratio (A) of the volume of the carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm is 0.3% or less with respect to the total volume of all the carbon black particles in the ink. The ratio (B) of the volume of the carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm in the ink after storage where the ink was stored at a temperature of 60 ° C. for 1 month is the ink after storage It is 0.3% or less with respect to the sum total of the volume of all the carbon black particle | grains in inside, and the said (A) and said (B) satisfy | fill the relationship of (B) / (A) <1.7. preferable.

  The above-mentioned requirements mean the following two things. First, the proportion of the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm in each ink before and after storage for 1 month at a temperature of 60 ° C. It means 0.3% or less with respect to the total volume of the particles. Second, the rate of change (increase rate) of the volume of particles having a particle size of 0.2 μm or more and less than 0.5 μm is less than 70% before and after the ink is stored at a temperature of 60 ° C. for one month. Means.

  The storage test in which the ink is stored at a temperature of 60 ° C. for one month is an accelerated test that is assumed to correspond to a period and temperature at which a general user uses the ink, and is assumed to be stored at room temperature for approximately one year. Ink that satisfies the above requirements, even if it is stored at room temperature for about one year, the proportion of the volume of particles having a particle size of 0.2 μm or more and less than 0.5 μm is the total volume of all particles in the ink. On the other hand, it means that 0.3% or less is maintained. That is, when the ink satisfies the above-described requirements, it is possible to maintain excellent ejection stability over a period in which a general user uses the ink.

  The rate of change in the proportion of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm before and after storage for 1 month at a temperature of 60 ° C. can be verified by the following method. First, for the ink to be verified, the ratio of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm is measured. This is the ratio (A) occupied by the volume of particles having a particle size of 0.2 μm or more and less than 0.5 μm before storage. Further, the same ink as described above is put in a container with an appropriate capacity and sealed, and stored at a temperature of 60 ° C. for one month. Thereafter, after the ink is returned to room temperature and stirred, the ratio of the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm to the ink is measured. This is the ratio (B) occupied by the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm after storage. By comparing the ratio (A) before storage and the ratio (B) after storage thus obtained, the rate of change between before and after storage can be obtained.

  In the present invention, as described above, it is particularly preferable that (A) and (B) satisfy the relationship (B) / (A) <1.7. The rate of change of the proportion of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm before and after storage at a temperature of 60 ° C. for 1 month was 70% or more. If B) / (A) ≧ 1.7, the ejection stability may be significantly reduced, especially over time.

[Each component constituting water-based ink]
As long as the water-based ink of the present invention satisfies the above-mentioned characteristics with respect to the particle size distribution of the carbon black particles, the characteristics of the raw materials to be used are not particularly defined, and the configuration is the same as that of the conventional water-based ink. Can do. Below, each component which comprises the water-based ink of this invention is demonstrated concretely, respectively.

<Carbon black dispersion>
The water-based ink of the present invention contains at least water, a water-soluble organic solvent, and carbon black particles. Hereinafter, a carbon black dispersion (sometimes referred to as a pigment dispersion) used for ink preparation will be described. The carbon black dispersion used in the water-based ink of the present invention is not particularly limited with respect to the characteristics of the raw materials used as long as each of the characteristics described above is satisfied. For example, the carbon black dispersion method may be a self-dispersion type carbon black dispersion or a polymer dispersion type (resin dispersion type) carbon black dispersion.

  Here, the self-dispersing carbon black dispersion is a carbon black that can be dispersed in an aqueous medium by carbon black itself without containing a dispersant such as a surfactant or a polymer dispersant. Refers to a carbon black dispersion. A polymer dispersion type (resin dispersion type) carbon black dispersion is a carbon black that can be dispersed in an aqueous medium by dispersing the carbon black using a dispersant such as a surfactant or a polymer dispersant. The carbon black dispersion used as a raw material.

(Self-dispersing carbon black)
For the self-dispersing carbon black dispersion, carbon black having at least one ionic group bonded to the surface directly or through another atomic group is used. As long as this condition is satisfied, there is no particular limitation, and the following self-dispersing carbon black can be used. For example, carbon black in which a compound having an ionic group is bonded to the surface using a diazo coupling method, carbon black in which an ionic group is introduced to the surface by surface oxidation treatment such as sodium hypochlorite or ozone treatment in water, etc. Is mentioned. These carbon blacks can be used alone or in combination of two or more.

In particular, it is preferable to use a self-dispersing carbon black in which at least one selected from the group consisting of —COOM, —SO ₃ M, and —PO ₃ HM is chemically bonded using a diazo coupling method. (M in the formula represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium). The functional group described above may be directly bonded to the surface of the carbon black particle, or may be chemically bonded through another atomic group. Examples of the other atomic group include an alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Such a self-dispersing carbon black is described in, for example, pamphlet of WO 97/47699. In the present invention, among the above ionic groups, it is particularly preferable to use a pigment in which —COOM is chemically bonded to the surface of the carbon black particle directly or via another atomic group.

(Polymer dispersion type (resin dispersion type) carbon black)
Any surfactant or polymer dispersant used for the polymer-dispersed carbon black can be used as long as it has water solubility. When a water-soluble resin is used as the polymer dispersant, the weight average molecular weight is preferably 1,000 or more and 100,000 or less, more preferably 3,000 or more and 25,000 or less. The acid value of the water-soluble resin is preferably 30 mgKOH / g or more and 400 mgKOH / g or less, more preferably 50 mgKOH / g or more and 250 mgKOH / g or less.

  The polymer dispersant suitable for the present invention is a co-polymer composed of at least two monomers (at least one of which is a hydrophilic monomer) selected from the following hydrophobic monomers, nonionic monomers, and hydrophilic monomers. A coalescence or a salt thereof is exemplified. The copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer.

  Examples of the hydrophobic monomer include the following. Acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylic acid-n-propyl, acrylic acid-n-butyl, acrylic acid-t-butyl, and benzyl acrylate. Methacrylate monomers such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylic acid-n-propyl, methacrylic acid-n- (or -t-) butyl, isobutyl methacrylate, tridecyl methacrylate, benzyl methacrylate . Styrene monomers such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tert-butylstyrene. Itaconic acid ester monomers such as benzyl itaconate. Maleate ester monomers such as dimethyl maleate. Fumarate ester monomers such as dimethyl fumarate. Acrylonitrile, methacrylonitrile, vinyl acetate, etc.

  As the hydrophilic monomer, a monomer having an anionic group or a monomer having a nonionic group can be suitably used. Specifically, examples of the monomer having an anionic group include the following. Monomers having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid, and salts thereof. Monomers having a sulfonic acid group such as styrene sulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-ethyl sulfonate, ethyl methacrylic acid-2-ethyl sulfonate, and butyl acrylamide sulfonic acid, and salts thereof. Monomers having a phosphonic acid group such as ethyl methacrylate-2-phosphonate and acrylic acid-2-ethyl phosphonate. Among these, it is particularly preferable to use acrylic acid or methacrylic acid.

  Examples of the monomer having a nonionic group include the following. Monomers having simultaneously a radically polymerizable unsaturated bond and a hydroxyl group showing strong hydrophilicity in the structure such as hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and the like. Monomers containing alkylene oxide groups such as methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, and polypropylene glycol (meth) acrylate. In addition, various known or novel oligomers, macromonomers and the like.

  Among the above, copolymers of styrene or benzyl methacrylate and acrylic acid or methacrylic acid can be suitably used because they can be polymerized relatively easily and have excellent ejection stability. In the present invention, it is particularly preferable to use a resin containing styrene and acrylic acid as monomers as a dispersant. Of course, the present invention is not limited to this. These dispersants are preferably used as a state in which they are neutralized with a base such as sodium hydroxide, potassium hydroxide, ammonia, dimethylethanolamine and dissolved in water (alkali-soluble resin).

  The content (% by mass) of the water-soluble resin used as the pigment dispersant listed above is preferably in the range of 0.1% by mass to 10.0% by mass based on the total mass of the ink. The ratio of the pigment content and the water-soluble resin content in the ink is within the range of pigment content / water-soluble resin content = 95/5 to 40/60, that is, 0.67 to 19 The following range is preferable.

  As a method for dispersing the polymer dispersion type (resin dispersion type) carbon black in water, a dispersion method used in preparing a conventional pigment ink can be used. For example, a disperser such as a paint shaker, a sand mill, a bead mill, an agitator mill, and a three roll mill, a high-pressure homogenizer such as a microfluidizer, a nanomizer, and an optimizer, an ultrasonic disperser, and the like can be given. In the present invention, any dispersion method generally used for preparing a pigment dispersion can be used without any limitation.

Among the above, a bead mill is most preferably used from the viewpoints of simplicity and dispersion stability. The operating conditions of the bead mill are not particularly specified, but the following conditions are preferable.
・ Bead filling rate: 50% or more and 90% or less, further 70% or more and 85% or less ・ Bead diameter: 0.05 mm or more and 1 mm or less, further 0.1 mm or more and 0.9 mm or less ・ Rotation speed: 300 rpm or more and 5,000 rpm In the following, further 1,000 to 2,000 rpm, dispersion time: 0.1 to 24 hours, further 1 to 10 hours

(Carbon black)
As the carbon black used for preparing the above-described carbon black dispersion, for example, carbon black such as furnace black, lamp black, acetylene black, channel black and the like can be used. Specifically, for example, the following commercially available products can be used.

Ray Van: 7000, 5750, 5250, 5000 ULTRA, 3500, 2000, 1500, 1250, 1200, 1190 ULTRA-II, 1170, 1255 (above Colombia). Black Pearls L, 880; Legal: 400R, 330R, 660R; Mogul L; Monak: 700, 800, 880, 900, 1000, 1100, 1300, 1400, 2000; Vulcan XC-72R (above, manufactured by Cabot). Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170; Printex: 35, 55, 60, 65, 70, 80, 90, U, V, 140U, 140V; Special Black: 6, 5 4A, 4 (made by Degussa). No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical).

However, the present invention is not limited to these, and any conventionally known carbon black can be used. Carbon black newly prepared for the present invention can also be used. Among the above-mentioned carbon blacks, it is preferable to use those having specific surface area and DBP oil absorption having the following characteristics from the viewpoint of dispersibility of pigments and ink jet suitability. That is, the specific surface area of the carbon black is preferably 40 m ² / g or more and less than 600 m ² / g. The DBP oil absorption amount of carbon black is preferably 50 mL / 100 g or more and less than 200 mL / 100 g, and more preferably 50 mL / 100 g or more and less than 125 mL / 100 g. The content (% by mass) of carbon black in the ink is from 0.1% by mass to 15.0% by mass, and further from 1.0% by mass to 10.0% by mass, based on the total mass of the ink. It is preferable.

<Aqueous medium>
In the ink of the present invention, a mixed solvent of water and a water-soluble organic solvent is used. It is preferable to use deionized water as the water. The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. Moreover, a water-soluble organic solvent is not specifically limited, For example, the following can be used. These water-soluble organic solvents may be used alone or in combination of two or more. The content (% by mass) of the water-soluble organic solvent in the ink is 3.0% by mass or more and 60.0% by mass or less, and further 5.0% by mass or more and 45.0% by mass based on the total mass of the ink. The following is preferable.

Specific examples of water-soluble organic solvents that can be used in the ink of the present invention are given below.
Polyhydric alcohols such as ethylene glycol, glycerin, diethylene glycol, propylene glycol, triethylene glycol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2,6-hexanetriol; Trimethylolpropane. Polyethylene glycols having an average molecular weight of 200 to 2,000, specifically, an average molecular weight of 200, 400, 600, 1,000, and 2,000. Nitrogen-containing solvents such as 2-pyrrolidone. Sugars such as glucose and galactose.

  In the present invention, it is particularly preferable to use a water-soluble organic solvent that does not substantially solvate with respect to carbon black in order to improve the high image density and bleeding performance with color ink. In other words, even when the water-based ink of the present invention contains a water-soluble organic solvent that does not substantially solvate with respect to carbon black, it hardly affects the storage stability and ejection stability. The fact that the water-soluble organic solvent is not substantially solvated with respect to the carbon black can be determined by dispersing the carbon black in the water-soluble organic solvent. Specifically, the water-soluble organic solvent to be judged is added to the pulverized carbon black obtained by pulverizing carbon black which has been sufficiently dried and evaporated by placing the ink in a petri dish or the like, for 1 hour. Allow to stand after stirring to the extent. About this liquid, the presence or absence of solid-liquid phase separation is judged visually. At this time, it can be judged that the solid-liquid phase separation has occurred that the water-soluble organic solvent does not substantially solvate with respect to the carbon black.

  Specific examples of the water-soluble organic solvent that does not substantially solvate with respect to carbon black include the following. For example, polyethylene glycol, 1,5-pentanediol, 1,4-pentanediol, 1,2,6-hexanetriol, 2-pyrrolidone having an average molecular weight of 200 to 600, particularly 200, 400, and 600 Etc. These water-soluble organic solvents can be used alone or in combination of two or more. The content (% by mass) of these water-soluble organic solvents is preferably 1.0% by mass or more and 15.0% by mass or less based on the total mass of the ink. In addition, the content (% by mass) of the water-soluble organic solvent that does not substantially solvate with respect to the carbon black is 10.0% based on the content (% by mass) of all the water-soluble organic solvents in the ink. % Or more and 80.0% by mass or less is preferable. When the content of the water-soluble organic solvent that does not substantially solvate with respect to carbon black is less than 10.0% by mass, high image density and bleeding performance may not be sufficiently obtained. Exceeding this may result in insufficient ink storage stability. Further, the ratio of the content (mass%) of carbon black in the ink to the content (mass%) of a water-soluble organic solvent that does not substantially solvate with respect to carbon black is 0.2 times or more. It is preferably 0 times or less. That is, the value of (content of carbon black / content of water-soluble organic solvent that does not substantially solvate with respect to carbon black) is preferably 0.2 times or more and 3.0 times or less. If the ratio is less than 0.2 times, ink storage stability may not be sufficiently obtained, and if it exceeds 3.0 times, high image density and bleeding performance may not be sufficiently obtained. .

<Other ingredients>
In addition to the above-described components, the ink of the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, and chelation as necessary. You may contain various additives, such as an agent. Further, by using an ink containing a polymer or the like, the scratch resistance and marker resistance of the image can be improved. In particular, a nonionic polymer having no ionic group has little influence on the reliability of the ink and can be suitably used.

<Ink preparation method>
The carbon black dispersion used in the preparation of the water-based ink and the preparation of the water-based ink are purified by centrifugation, filtration, etc. in order to obtain a water-based ink satisfying the particle size distribution of the carbon black particles as described above. The method is preferably used. The purification method that can be used in the present invention is not limited by any method as long as it is a method generally used for color materials. For purification of the carbon black dispersion, it is particularly preferable to remove coarse particles with a centrifuge. Moreover, it is particularly preferable to purify the water-based ink by pressure filtration with a filter. In particular, in order to satisfy the characteristics such as the particle size distribution of the carbon black particles as described above, the ink is filtered using a filter having a pore size (pore size) of 1.5 μm or less when purifying the water-based ink. Is preferred. Of course, the present invention is not limited to these purification methods, and the structure of the present invention is satisfied as long as the characteristics such as the particle size distribution of the carbon black particles described above are satisfied.

<Color ink>
The water-based ink of the present invention may be used for forming an image as a water-based ink set in combination with another ink jet ink (color ink). The configuration of the color ink will be described below.

  In the present invention, any of the conventionally known water-based color inks for inkjet can be used. However, the color ink preferably contains at least water, a water-soluble organic solvent, and a coloring material. Examples of the color material of the color ink include water-soluble dyes, and it is particularly preferable to use a water-soluble dye having an anionic group as a solubilizing group. The color tone of the color ink used in the present invention can be appropriately selected from, for example, cyan, magenta, yellow, red, green, blue and orange.

  In addition to the above, a dye having a solubilizing group such as a carboxyl group, an oil-soluble dye, or a pigment can be used for the color material of the color ink that can be used in the present invention.

  As the aqueous medium and other additives used in producing the color ink that can be used in the present invention, the same water-based inks as described above can be used.

<Ink physical properties>
The water-based ink of the present invention having the configuration described above and the color ink that can be used together with the ink preferably have characteristics that allow good ejection from the recording head. For this reason, from the viewpoint of ejectability from the recording head, the viscosity of the ink is 1 mPa · s to 15 mPa · s, further 1 mPa · s to 5 mPa · s, and the surface tension is 25 mN / m to 50 mN / m. Preferably there is.

[Inkjet recording method, ink cartridge, recording unit, and inkjet recording apparatus]
The water-based ink of the present invention is effectively used as an ink used in a recording unit including an ink jet discharge type recording head and an ink containing portion. The usage form of the water-based ink of the present invention and the water-based ink set in which the ink is combined is not limited to this, and may be an ink cartridge containing these inks, or an ink for filling an ink cartridge or the like. Is also effective. In particular, the water-based ink of the present invention has an excellent effect in a bubble jet (registered trademark) type recording head and an ink jet recording apparatus among ink jet methods.

  Typical configurations and principles of bubble jet (registered trademark) type recording heads and inkjet recording apparatuses are disclosed in, for example, US Pat. Nos. 4,723,129 and 4,740,796. Those which are carried out using the basic principles that are described are preferred. This method can be applied to both a so-called on-demand type and a continuous type. In particular, it is effective to apply the water-based ink of the present invention to an on-demand type recording head or an ink jet recording apparatus. In the case of the on-demand type, at least one of the electrothermal transducers arranged corresponding to the sheet or liquid path holding the ink gives a rapid temperature rise corresponding to the recorded information and exceeding the nucleate boiling. Apply drive signal. As a result, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the recording head. As a result, this drive signal is in one-to-one correspondence and bubbles in the ink can be formed. Then, ink is ejected through the ejection port by the growth and contraction of the bubbles to form at least one droplet. It is more preferable that the drive signal has a pulse shape, because the bubble growth and contraction is performed immediately and appropriately, and thus ink discharge with particularly excellent responsiveness can be achieved. As this pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by adopting the conditions described in US Pat. No. 4,313,124, which is an invention relating to the rate of temperature increase of the heat acting surface.

  The water-based ink of the present invention has a configuration in which the recording head has a combination of a discharge port, a liquid path, and an electrothermal transducer (linear liquid flow path or right-angle liquid flow path) as disclosed in the above-mentioned specifications. It is effective to apply In addition to this, it is effective to apply the water-based ink of the present invention even in the case where the heat acting portion is arranged in a bent region. The above configuration is disclosed in US Pat. No. 4,558,333 and US Pat. No. 4,459,600. In addition, the present invention also applies to a recording head having a configuration in which a common discharge port is used as a discharge portion of an electrothermal transducer for a plurality of electrothermal transducers (Japanese Patent Laid-Open No. 59-123670, etc.). It is effective to apply water-based ink. Furthermore, the water-based ink of the present invention can also be applied to a full-line type recording head having a length corresponding to the maximum recording medium width that can be recorded by the ink jet recording apparatus. Such a configuration may be either a configuration satisfying the length or a configuration as a single recording head formed integrally by combining a plurality of recording heads as disclosed in the above specification. The water-based ink of the present invention can exhibit the above-described effects more effectively when applied to these.

  The application of the water-based ink of the present invention is not limited to the above, and is also effective when used in the following ink jet recording apparatus. For example, a replaceable chip type recording head that can be electrically connected to the recording apparatus main body and supplied with ink from the recording apparatus main body by being mounted on the ink jet recording apparatus main body can be used. Alternatively, a cartridge type recording head provided integrally with the recording head can be used. In addition, the ink jet recording apparatus to which the water-based ink of the present invention is applied has a configuration in which recovery means for the recording head, preliminary auxiliary means, etc. are added. This is preferable. These recovery means include a capping means for the recording head, a cleaning means, a pressure or suction means, an electrothermal converter, a preheating means using a heating element different from this, or a combination thereof, and a discharge different from recording. There is a preliminary discharge mode for performing.

  An example of the ink jet recording apparatus will be described below. First, FIG. 1 and FIG. 2 show an example of the configuration of a recording head that is a main part of an ink jet recording apparatus using thermal energy. FIG. 1 is a cross-sectional view of the recording head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along the line AB of FIG. The recording head 13 includes a member having an ink flow path (nozzle) 14 and a heating element substrate 15. The heating element substrate 15 includes a protective layer 16, electrodes 17-1 and 17-2, a heating resistor layer 18, a heat storage layer 19, and a substrate 20.

  When pulsed electric signals are applied to the electrodes 17-1 and 17-2 of the recording head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. Will occur. Then, the meniscus 23 protrudes due to the pressure of the bubbles, and the ink 21 is ejected as an ink droplet 24 from the ejection port 22 of the nozzle 14 toward the recording medium 25.

  FIG. 3 is an external view of an example of a multi-head in which a large number of recording heads shown in FIG. 1 are arranged. The multi-head includes a glass plate 27 having multi-nozzles 26 and a recording head 28 similar to that shown in FIG.

  FIG. 4 is a perspective view showing an example of an ink jet recording apparatus incorporating a recording head. The blade 61 is a wiping member, one end of which is held by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65 and is held in a form protruding in the moving path of the recording head 65.

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

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

  Reference numeral 51 denotes a paper feeding unit for inserting a recording medium, and 52 denotes a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the ejection port surface of the recording head 65 and discharged to a paper discharge unit having a paper discharge roller 53 as recording progresses. When recording by the recording head 65 is completed and the recording head returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. Yes. In this way, the ejection port of the recording head 65 is wiped.

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

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

  The recording head and the ink cartridge are not limited to separate units, and as shown in FIG. 6, a unit in which the recording head and the ink cartridge are integrated can be suitably used. In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink storage unit that stores ink, for example, an ink absorber is stored, and a recording head unit in which the ink in the ink absorber has a plurality of ejection openings. 71 is ejected as ink droplets. Alternatively, a structure in which the ink container is an ink bag with a spring or the like inside without using an ink absorber may be used. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  Next, an ink jet recording apparatus using mechanical energy will be described. A nozzle forming substrate having a plurality of nozzles, a pressure generating element composed of a piezoelectric material and a conductive material, and ink that fills the surroundings of the pressure generating element are provided. The pressure generating element is displaced by an applied voltage, and ink droplets are ejected from ejection ports. It has a feature of having a recording head. FIG. 7 is a schematic diagram showing an example of the configuration of the recording head. The recording head includes an ink flow path 80 communicating with an ink chamber, an orifice plate 81, a vibration plate 82 that applies pressure to ink, a piezoelectric element 83 that is bonded to the vibration plate 82 and is displaced by an electric signal, the orifice plate 81, and the vibration plate. It is comprised with the board | substrate 84 which supports and fixes 82 etc. The distortion stress generated by applying a pulsed voltage to the piezoelectric element 83 deforms the vibration plate bonded to the piezoelectric element 83 and pressurizes the ink in the ink flow path 80, thereby causing the discharge port of the orifice plate 81 to discharge. Ink droplets are ejected from 85. Such a recording head can be used by being incorporated in an ink jet recording apparatus similar to that shown in FIG.

  Next, an Example and a comparative example are given and this invention is demonstrated concretely. The present invention is not limited by the following examples unless it exceeds the gist. In the text, “part” or “%” is based on mass unless otherwise specified.

[Preparation of pigment dispersion]
Pigment dispersions 1 to 14 were prepared by the method described below. As the carbon black, Black Pearls 880 (trade name; manufactured by Cabot) having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was used.

(Preparation of pigment dispersion 1)
To a solution of 5 g of concentrated hydrochloric acid dissolved in 10 g of water, 1.6 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 at 10 ° C. or less, and 1.8 g of sodium nitrite was dissolved in 20 g of water at 5 ° C. The solution was added. After stirring this solution for another 15 minutes, 10 g of carbon black was added with stirring. Thereafter, the mixture was further stirred for 30 minutes. After the obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), the particles were sufficiently washed with water and dried in an oven at 105 ° C. to prepare self-dispersing carbon black 1 did.

Further, water was added to the self-dispersing carbon black 1 obtained above and dispersed so that the pigment concentration was 15% by mass, thereby preparing a dispersion. The obtained dispersion was centrifuged using a high-speed cooling centrifuge CR21G (manufactured by Hitachi Koki Co., Ltd.) at 5,000 rpm for 10 minutes to remove aggregated components. Then, pressure filtration was performed with a filter having a pore size of 0.7 μm (47 mm diameter, FR70 filter; manufactured by Fuji Film) to obtain Pigment Dispersion Liquid 1. By the above method, a pigment dispersion 1 was obtained in a state where self-dispersing carbon black 1 (pigment 1) in which —C ₆ H ₄ —COONa group was introduced was dispersed in water on the surface of carbon black particles. . The pigment concentration of the obtained pigment dispersion 1 was 15% by mass.

(Preparation of pigment dispersions 2 to 6)
Concentrated hydrochloric acid, p-aminobenzoic acid, and the amount of sodium nitrite added, and the type of filter used for purification were changed to those shown in Table 1 below, in the same manner as in pigment dispersion 1, 6 was prepared. The pigment concentrations of the obtained pigment dispersions 2 to 6 were all 15% by mass. Table 1 also shows data regarding the pigment dispersion 1. In Table 1, the types of filters are as follows. FR70 (pore size 0.7 μm, 47 mm diameter, trade name: FR70 filter; manufactured by Fuji Film). HDCII 2.5 μm (pore size 2.5 μm, 47 mm diameter, trade name: HDCII 2.5 μm; manufactured by Pall).

(Preparation of pigment dispersion 7)
First, a styrene-acrylic acid copolymer [copolymerization ratio: styrene / acrylic acid = 75/25 (mass ratio), weight average molecular weight (Mw): 10,000] as a dispersant was prepared according to a conventional method. Then, the styrene-acrylic acid copolymer, water, and potassium hydroxide equivalent to the acid value of the copolymer are mixed, stirred at 80 ° C., and 20 mass of the styrene-acrylic acid copolymer. % Aqueous solution was prepared. Next, 15 parts of carbon black, 30 parts of a 20% by weight aqueous solution of the above styrene-acrylic acid copolymer (6 parts in terms of solid content), and 55 parts of water are mixed and dispersed as described below. went. For the dispersion treatment, a bead mill (trade name: Minicer, capacity: 0.6 L, manufactured by Ashizawa Finetech Co., Ltd.) was used. It went on condition of. Further, the dispersion obtained above was centrifuged using a high-speed cooling centrifuge CR21G (manufactured by Hitachi Koki Co., Ltd.) at 5,000 rpm for 30 minutes to remove agglomerated components. Then, pressure filtration was performed with a filter having a pore size of 0.7 μm (47 mm diameter, FR70 filter; manufactured by Fuji Film) to obtain Pigment Dispersion Liquid 7. By the above method, a pigment dispersion liquid 7 in which the resin-dispersed carbon black 7 (pigment 7) was dispersed in water was obtained. The pigment dispersion 7 thus obtained had a pigment concentration of 15% by mass.

(Preparation of pigment dispersions 8-14)
Pigment dispersions 8 to 14 were prepared in the same manner as pigment dispersion 7 except that the operating conditions of the copolymer and bead mill and the type of filter used for purification were changed to those shown in Table 2 below. The pigment concentrations of the obtained pigment dispersions 8 to 14 were all 15% by mass. Table 2 also shows data on the pigment dispersion 7. The types of filters in Table 2-2 are as follows. FR70 (pore size 0.7 μm, 47 mm diameter, trade name: FR70 filter; manufactured by Fuji Film). HDCII 1.2 μm (pore size 1.2 μm, 47 mm diameter, trade name: HDCII 1.2 μm; manufactured by Pall).

[Determination of water-soluble organic solvent that does not substantially solvate to carbon black]
Whether or not each water-soluble organic solvent used for ink preparation is a water-soluble organic solvent that does not substantially solvate with respect to carbon black was determined by the following procedure. 10 g of each of the pigment dispersions obtained above was placed in a petri dish having an inner diameter of 5 cm and dried in an oven at a temperature of 60 ° C. for one day to evaporate the water. Then, the pulverized product of carbon black was obtained by pulverizing with a mortar. 0.5 g of the pulverized carbon black obtained was weighed into a beaker, 10 g of the water-soluble organic solvent to be determined was added, stirred for 1 hour with a stirrer, and allowed to stand for 1 hour. About this liquid, the presence or absence of solid-liquid phase separation was confirmed visually. At this time, the water-soluble organic solvent in which the solid-liquid phase separation has occurred is not substantially solvated with respect to the carbon black, and the water-soluble organic solvent in which the solid-liquid phase separation has not occurred with respect to the carbon black. And solvated. The results of determining the water-soluble organic solvent that does not substantially solvate the carbon black in each pigment dispersion are shown in Table 3 below. In Table 3, a water-soluble organic solvent that does not substantially solvate with respect to carbon black is indicated by ◯, and a water-soluble organic solvent that is solvated is indicated by ×.

[Preparation of ink]
Eighteen types of inks were prepared using the pigment dispersions obtained above and the components shown below. The ink was prepared by mixing the components shown in Tables 4 and 5 below, stirring for 1 hour, and then pressure-filtering with the filters shown in the lower part of Tables 4 and 5 below. ~ 18 were obtained.

[Ink characteristics]
About the inks 1-18 obtained above, the physical property was measured with the following method, respectively. The obtained results are shown in Tables 6 and 7.

(Percentage occupied by the volume of particles having a particle size of 0.2 μm or more and less than 0.5 μm, and an average value of the particle size)
The ratio of the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm and the average value of the particle diameter (volume average particle diameter d) for a liquid obtained by diluting each ink 500 times (by mass) with pure water ₅₀ ). For the measurement, a particle size distribution measuring device (UPA150EX; manufactured by Nikkiso) was used. The measurement conditions are as shown below.

[Measurement condition]
・ Setzero: 30s
・ Measurement time: 120s
-Number of measurements: 3 times-Particle refractive index: 1.8
・ Solvent: Water ・ Filter: Standard
・ Sensitivity: Standard

(Number of particles having a particle diameter of 0.5 μm or more and less than 5.0 μm)
The number of particles having a particle diameter of 0.5 μm or more and less than 5.0 μm was measured for a liquid obtained by diluting each ink 40 times (by mass) with pure water. Then, from the obtained value, the number of particles having a particle diameter of 0.5 μm or more and less than 5.0 μm per 1 mL of ink was determined. For the measurement, a particle size distribution measuring device (Accusizer780APS; manufactured by Particle Sizing System) was used. The measurement conditions are as shown below.

[Measurement condition]
・ Measurement time: 60s
・ Number of channels: 128
・ Flow rate: 60 mL / min ・ Sample LOOP capacity: 1 mL
・ First stage dilution ratio: 30 times ・ Second stage dilution ratio: 40 times

(Change rate of the proportion of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm due to storage)
Measure the ratio [%] of the volume of particles whose particle diameter is 0.2 μm or more and less than 0.5 μm before and after storage for 1 month at a temperature of 60 ° C. by the following method. The performance of the ink was compared by calculating the rate of change later. The obtained results are shown in Table 8 and Table 9.

  First, for each ink, the ratio of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm was measured. This was defined as the ratio (A) occupied by the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm before storage. Further, 100 g of each ink was put in a Teflon (registered trademark) container and sealed, and the container was stored in an oven at a temperature of 60 ° C. for one month. Thereafter, the container was removed from the oven, the ink was returned to room temperature, and the ink in the container was uniformly stirred. About the ink after this preservation | save, the ratio for which the particle | grain volume whose particle diameter is 0.2 micrometer or more and less than 0.5 micrometer occupies was measured. This was defined as the ratio (B) occupied by the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm after storage. The measurement apparatus and measurement conditions were the same as the measurement of the proportion of the volume of particles having a particle diameter of 0.2 μm or more and less than 0.5 μm performed as described above. By comparing the ratio (A) before storage and the ratio (B) after storage obtained in this way, the rate of change between (B) / (A) before and after storage. Value). It shows that as the change rate (value of (B) / (A)) is larger, the stable state of the ink is not maintained over time, that is, the ejection stability is likely to be lowered.

[Evaluation of ejection stability]
For each ink, the ejection stability before and after storage for 1 month at a temperature of 60 ° C. was evaluated by the following method. For the evaluation of ejection stability, each of the inks obtained above (referred to as “before storage”) and the inks stored at a temperature of 60 ° C. for one month (referred to as “after storage”) The discharge stability was evaluated. The ink after storage was prepared in the same manner as that used for the evaluation of the rate of change in the proportion of the volume of the particles having a particle diameter of 0.2 μm or more and less than 0.5 μm. Each ink before and after storage was mounted on an inkjet recording apparatus PIXUS850i (manufactured by Canon), and 1,000 characters were continuously recorded on an A4 size recording medium (Office Planner; manufactured by Canon). The obtained recorded matter was visually observed, and the ejection stability was evaluated according to the following evaluation criteria. Table 10 shows the obtained results. As shown in Table 10, it was confirmed that when the inks of the examples of the present invention were used, the ejection stability was superior to that when the inks of the comparative examples were used.

[Evaluation criteria]
AAA: 1,000 sheets can be recorded, and there is no difference in the state of streaks, unevenness, and twist when comparing the first and 1,000th recorded matter.
AA: 1,000 sheets can be recorded, and there is no difference in streak, unevenness, and twist when comparing the first and 500th recorded matter, but the 1,000th recording There are slight streaks, irregularities and twists in the objects.
A: 1,000 sheets can be recorded, and the 500th recorded matter has slight streaks, unevenness, and twisting, but the 500th and 1,000th recorded items are compared. There is no difference in the state of streak, unevenness and twist.
B: 1,000 sheets can be recorded, and the 500th recorded matter has considerably streaks, unevenness, and twist, and the 500th to 1,000th recorded matter has streaks and unevenness. , Yole's condition gradually worsens.
C: One sheet can be recorded, but streaks, unevenness, and twisting are poor, and 500 sheets cannot be recorded.

FIG. 2 is a longitudinal sectional view of a recording head. It is a cross-sectional view of the recording head. FIG. 2 is a perspective view of a recording head in which the recording head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a schematic diagram illustrating an example of a configuration of a recording head.

Explanation of symbols

13: recording head 14: nozzle 15: heating element substrate 16: protective layer 17-1, 17-2: electrode 18: heating resistor layer 19: heat storage layer 20: substrate 21: ink 22: discharge port 23: meniscus 24: Ink droplet 25: recording medium 26: multi-nozzle 27: glass plate 28: recording head 40: ink bag 42: stopper 44: ink absorber 45: ink cartridge 51: paper feed unit 52: paper feed roller 53: paper discharge roller 61 : Blade 62: Cap 63: Ink absorber 64: Ejection recovery unit 65: Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 70: Recording unit 71: Recording head 72: Air communication port 80: Ink flow path 81: Orifice plate 82: Vibration plate 83: Piezoelectric element 84: Substrate 85: Discharge port

Claims (6)

In an aqueous ink containing water, a water-soluble organic solvent, and carbon black particles, and the carbon black particles include carbon black particles having a particle diameter of 0.5 μm or more.
The proportion of the volume of the carbon black particles having a particle diameter of 0.2 μm or more and less than 0.5 μm is 0.3% or less with respect to the total volume of all the carbon black particles in the water-based ink,
The number of carbon black particles having a particle diameter of 0.5 μm or more and less than 5.0 μm is 1.0 × 10 ⁷ or less per mL of the water-based ink,
An aqueous ink, wherein the average value of the particle diameter of the carbon black particles is 0.060 μm or more and 0.130 μm or less. The water-based ink according to claim 1, wherein the carbon black particles are self-dispersing carbon black particles. An ink jet recording method for discharging ink by an ink jet method, wherein the water-based ink according to claim 1 or 2 is used as the ink. An ink cartridge comprising an ink containing portion for containing ink, wherein the water containing ink according to claim 1 or 2 is contained in the ink containing portion. A recording unit comprising an ink containing portion for containing ink and a recording head for ejecting ink, wherein the water containing ink according to claim 1 or 2 is contained in the ink containing portion. To record unit. An ink jet recording apparatus comprising an ink containing portion for containing ink and a recording head for ejecting ink, wherein the water containing ink according to claim 1 or 2 is contained in the ink containing portion. An inkjet recording apparatus.

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