JP6882047B2 - Water-based inks, ink cartridges, and inkjet recording methods - Google Patents

Description

The present invention relates to water-based inks, ink cartridges, and inkjet recording methods.

In recent years, the inkjet recording method has been used for recording business documents and the like using plain paper or the like as a recording medium, and the frequency of use thereof has increased remarkably. For applications such as recording business documents, it is important to record clear images at high speed. For this reason, inks used in such applications are required to have excellent optical density and to be able to record ruled lines without distortion.

In response to the above technical problems, for example, an ink for inkjet recording containing alginate, which thickens after being applied to a recording medium, has been proposed (see Patent Document 1). Further, in order to improve the ejection property in the inkjet recording method, an ink to which a polysaccharide is added has been proposed (see Patent Document 2).

Japanese Unexamined Patent Publication No. 8-283637 Japanese Unexamined Patent Publication No. 8-151544

As a result of the studies by the present inventors, it was confirmed that the optical density of the recorded image is improved by using the ink proposed in Patent Document 1. However, it was also confirmed that when a polysaccharide such as alginic acid is contained in the ink, various problems occur as the viscosity of the ink increases. For example, it has been confirmed that when ink is ejected again without performing a recovery operation after suspending ink ejection for a certain period of time, a phenomenon in which the ink ejection direction is bent, so-called "ejection twist" occurs. Further, it has been found that if a polysaccharide such as alginic acid is present in the ink in a free state, the polysaccharide may clog the filter of the ink supply path, and the ink supply failure to the recording head is likely to occur. Further, it was also found that the ink ejected in the ink proposed in Patent Document 2 was not suppressed. That is, with the conventionally proposed inks, it is difficult to improve the optical density of the image and suppress the ejection wrinkle at the same time.

Therefore, an object of the present invention is to provide a water-based ink capable of recording an image having a high optical density while suppressing ejection twist. Another object of the present invention is to provide an ink cartridge using the water-based ink and an inkjet recording method.

The above object is achieved by the following invention. That is, according to the present invention, there is provided a water-based ink for inkjet containing a pigment and a resin for dispersing the pigment, wherein the pigment contains lipopolysaccharide. To.

According to the present invention, it is possible to provide a water-based ink capable of recording an image having a high optical density while suppressing ejection twist. Further, according to the present invention, it is possible to provide an ink cartridge using this water-based ink and an inkjet recording method.

It is sectional drawing which shows typically one Embodiment of the ink cartridge of this invention. It is a figure which shows typically an example of the inkjet recording apparatus used in the inkjet recording method of this invention, (a) is the perspective view of the main part of the inkjet recording apparatus, (b) is the perspective view of the head cartridge.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt". Further, the water-based ink for inkjet may be simply referred to as "ink". Further, the "unit" related to the resin is the smallest repeating unit constituting the resin, and refers to a structure formed by (co) polymerization of one monomer. Unless otherwise specified, the physical characteristic values shall be values at room temperature (25 ° C.).

The ink of the present invention is characterized in that it contains a pigment containing a compound (hereinafter, also referred to as "polysaccharide compound") in which at least two structures represented by the general formula (1) form a glycosidic bond. Have. In the present specification, "pigment contains a compound" means that a plurality of primary particles of a pigment are aggregated to form secondary particles (aggregates of pigments) having pores inside the particles, and the inside of the pores is formed. Means that the compound is present in. Therefore, regardless of whether the compound is present in the ink in the form of primary particles or secondary particles, the compound existing in the state of being attached to the surface of the pigment particles in the form existing in the ink is "encapsulated in the pigment". It is not included in the concept of "compounds". Hereinafter, a compound other than the "compound contained in the pigment" may be referred to as a "compound existing in a free state".

The present inventors have confirmed that the optical density of a recorded image is improved by using an ink containing a pigment and a polysaccharide compound such as sodium alginate. However, it was confirmed that if the ruled lines were recorded without performing the recovery operation after the ink ejection was paused for about 2 seconds, the ruled lines would be distorted due to the ejection twist. This is because the ink rapidly thickens due to the addition of the polysaccharide compound and the evaporation of the liquid component from the ejection port, making it difficult to eject the ink normally, and the ejection direction bends, so that the ink is placed at the intended position of the recording medium. It is considered that this is because it became difficult to attach the ink.

The present inventors have studied an ink capable of improving the optical density while suppressing ejection twist. As a result, it has been found that the above-mentioned problems can be solved by using the polysaccharide compound in a pigment-encapsulated state instead of allowing it to exist in the ink in a free state. Since the polysaccharide compound existing in the free state in the ink has a high degree of steric freedom, it is easy to thicken the ink. On the other hand, the polysaccharide compound that exists in the state of being encapsulated in the pigment does not increase the steric degree of freedom in the ink. When the liquid component starts to evaporate from the discharge port, the polysaccharide compound contained in the pigment easily diffuses as the liquid component moves, but it is difficult to elute from the pigment. Therefore, it is considered that the ink is not rapidly thickened and the ejection twist is suppressed. It can be said that in the ink in which the polysaccharide compound is not contained in the pigment and exists in the ink in a free state, the polysaccharide compound is not incorporated into the pores of the secondary particles of the pigment. It is considered that this is due to the influence of steric hindrance of the polysaccharide compound.

On the other hand, when the ink is applied to the recording medium, much more liquid components evaporate than the ink evaporates from the ejection port, so that the polysaccharide compound is easily diffused. Since the polysaccharide compound has an affinity for hydrogen-bonding components such as cellulose constituting the recording medium, the ink is applied to the recording medium and the liquid component is reduced, so that the polysaccharide compound is extracted from the pigment. As a result, the polysaccharide compound exists in a free state, and the viscosity of the ink rapidly increases. Therefore, it is considered that the sinking of the pigment into the recording medium is suppressed and the optical density of the image is increased.

That is, in the present invention, the polysaccharide compound contained in the pigment in the ink is eluted from the pigment after the ink is applied to the recording medium, so that the viscosity of the ink is rapidly increased by the polysaccharide compound. It is important to prevent the pigment from sinking.

<Water-based ink>
The ink of the present invention is a water-based ink for inkjet containing a pigment and a resin (resin dispersant) for dispersing the pigment. Then, the pigment contains a compound (polysaccharide compound) in which at least two structures represented by the following general formula (1) are glycosidic bonded. Hereinafter, the components constituting the ink of the present invention, the physical characteristics of the ink, and the like will be described in detail.

(Polysaccharide compound)
The pigment used in the ink of the present invention contains a so-called polysaccharide compound in which at least two structures represented by the following general formula (1) are glycosidic bonded. The polysaccharide compound is preferably a compound in which at least two structures represented by the following general formula (1) are condensed between the hydroxy groups of each structure to form a glycosidic bond. Condensation between hydroxy groups is preferably in the form of dehydration condensation.

（前記一般式（１）中、Ｒ₁乃至Ｒ₆は、それぞれ独立に水素原子、メチル基、ホスホン酸基、−（ＣＨ₂）_x−ＯＨ、−（ＯＣＨ（ＣＨ₃））_y−ＣＯＯＨ、−ＮＨ（ＣＯＣＨ₂）_z−Ｈ、−ＯＣＯＣＨ₂ＣＨ（ＯＣＯＣＨ₂（ＯＨ）Ｃ₁₁Ｈ₂₂ＣＨ₃）Ｃ₁₀Ｈ₂₀ＣＨ₃、又は−ＮＨＣＯＣＨ₂ＣＨ（ＯＣ₁₁Ｈ₂₂ＣＨ₃）Ｃ₁₀Ｈ₂₀ＣＨ₃であるとともに、Ｒ₁及びＲ₂の少なくとも一方はヒドロキシ基である。ｘ、ｙ、及びｚは、それぞれ独立に０以上６以下の数である）

(In the general formula (1), R _{1 to} R ₆ are independently hydrogen atom, methyl group, phosphonic acid group, − (CH ₂ ) _x −OH, − (OCH (CH ₃ )) _y −COOH, respectively. -NH (COCH ₂ ) _z- H, -OCOCH ₂ CH (OCOCH ₂ (OH) C ₁₁ H ₂₂ CH ₃ ) C ₁₀ H ₂₀ CH ₃ , or -NHCOCH ₂ CH (OC ₁₁ H ₂₂ CH ₃ ) C ₁₀ H ₂₀ CH ₃ and _{at least one of R 1} and R ₂ is a hydroxy group. X, y, and z are independently numbers of 0 or more and 6 or less).

x, y, and z are independently numbers of 0 or more and 6 or less. As the group represented by − (CH ₂ ) _x −OH, −OH (hydroxy group), −CH ₂ −OH, − (CH ₂ ) ₂ −OH, − (CH ₂ ) ₃ −OH and the like are preferable; -OH (hydroxy group), -CH _2- OH and the like are more preferable. -(OCH (CH ₃ )) _{y As the} group represented by −COOH, −OCH (CH ₃ ) −COOH and the like are preferable. As the group represented by −NH (COCH ₂ ) _{z −H, −NHCOCH 3 and the} like are preferable.

Preferable examples of the structures represented by the general formula (1) include structures a to k shown in Table 1. Table 2 shows the relationship between the structure represented by the general formula (1) and the polysaccharide compound. For example, "xanthan gum" in Table 2 is a compound in which structures derived from glucose, mannose, and glucuronic acid are dehydrated and condensed between hydroxy groups of each structure to form a glycosidic bond. Of course, the present invention is not limited to the structural examples and polysaccharide compounds shown below as long as they are included in the structure of the general formula (1) and the definition of the compound.

The polysaccharide compound can be synthesized, for example, by polymerizing two or more compounds having a structure represented by the general formula (1) by a glycosylation reaction. Examples of the glycosylation reaction include an organic chemical glycosylation reaction and a glycosylation reaction using a glycosyltransferase.

Examples of the compound (monosaccharide) having the structure represented by the general formula (1) include ramnorse, glucose, galactose, mannose, glucuronic acid, xylose, glucosamine, N-acetylglucosamine, N-acetylgalactosamine, neuraminic acid, and N-. It is preferable to use at least one selected from the group consisting of acetylneuraminic acid, muramic acid, N-acetylmuramic acid, and lipid A. As the polysaccharide compound, it is preferable to use at least one selected from the group consisting of dextran, arabinoxylan, xanthan gum, guar gum, hyaluronic acid, gellan gum, ganglioside, peptidoglycan, and lipopolysaccharide.

The polysaccharide compound preferably has a carboxylic acid group. When a polysaccharide compound having a carboxylic acid group is used, the carboxylic acid group reacts with the filler contained in the recording medium or the cation contained as a constituent component of the ink receiving layer of the recording medium in contact with each other to form the polysaccharide compound. Gels. Therefore, the optical density of the image can be further increased.

The amount of the polysaccharide compound contained in the pigment is preferably 1 ppm or more and 4,500 ppm or less in terms of mass ratio with respect to the amount of the pigment. When the mass ratio is less than 1 ppm, the amount of the polysaccharide compound eluted from the pigment after the ink is applied to the recording medium is reduced. Therefore, the optical density of the image may not be sufficiently obtained. On the other hand, when the mass ratio is more than 4,500 ppm, the polysaccharide compound is likely to be eluted from the pigment when the ink is stored for a long period of time. Therefore, it may not be possible to sufficiently suppress the discharge twist.

The content (ppm) of the polysaccharide compound contained in the pigment is preferably 90% or more in terms of the mass ratio of the polysaccharide compound to the total content (ppm) in the ink. The total content (ppm) of the polysaccharide compound in the ink means the sum of the amount of the polysaccharide compound contained in the pigment and the amount of the polysaccharide compound present in the ink in a free state. That is, it is preferable that most of the polysaccharide compounds are contained in the pigment without being released in the ink. If the mass ratio is less than 90%, the amount of the polysaccharide compound existing in the free state becomes too large, so that the discharge wrinkle may not be sufficiently suppressed. The above mass ratio is preferably 100% or less.

The content (ppm) of the polysaccharide compound present in the free state in the ink is preferably 25 ppm or less based on the total mass of the ink. If the content of the polysaccharide compound present in the free state is more than 25 ppm, the viscosity of the ink increases when the liquid component evaporates, and the ejection stability may not be sufficiently obtained. The lower limit of the content of the polysaccharide compound existing in the free state may be 0 ppm.

The weight average molecular weight of the polysaccharide compound is preferably 20,000 or more and 2.2 million or less, and more preferably 20,000 or more and 2 million or less. The weight average molecular weight of the polysaccharide compound is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). When the weight average molecular weight of the polysaccharide compound is less than 20,000, the ink does not thicken so much even if the polysaccharide compound is eluted from the pigment, and the optical density of the image may not be improved so much. On the other hand, when the weight average molecular weight of the polysaccharide compound is more than 2.2 million, the rate at which the polysaccharide compound elutes from the pigment decreases. Therefore, the pigment tends to sink into the recording medium before the ink thickens, and the optical density of the image may not be improved so much. Further, when the weight average molecular weight of the polysaccharide compound is more than 2.2 million and the content of the polysaccharide compound present in the free state in the ink is more than 25 ppm, the polysaccharide compound adheres to the filter of the ink supply path. It will be easier to do. Therefore, the supply of ink to the recording head may easily decrease. The weight average molecular weight of the polysaccharide compound may be adjusted by a chemical treatment such as hydrolysis or a physical treatment such as ultrasonic irradiation.

[Analysis of polysaccharide compounds]
Hereinafter, a method for analyzing a polysaccharide compound in an ink will be described with an example. Whether or not the pigment contains a polysaccharide compound is determined by, for example, a phenol-sulfuric acid method, a colorimetric time analysis method (toxinometer method: color change correlation due to reaction with a specific substance), and a column for sugar analysis. It can be confirmed by the HPLC used. Hereinafter, an analysis method (toxinometer method) using a toxinometer, which is a simple method, will be described. The toxinometer method is an endotoxin measurement method capable of detecting all compounds including metabolites of microorganisms such as polysaccharides with high sensitivity.

First, a liquid A containing an appropriate amount of pigment is prepared. Then, the total amount a of the polysaccharide compound present in the liquid A is measured using a toxinometer. Then, the polysaccharide compound present in the liquid A in a free state is removed. Specifically, the liquid A is ultrafiltered using a hollow fiber membrane having a molecular weight cut-off of about 100 kDa, and separated into a liquid B containing a pigment and a filtrate. The presence or absence of polysaccharide compounds in the filtrate is confirmed by the phenol-sulfuric acid method, and if the filtrate discolors, ultrafiltration is repeated until the discoloration disappears. Then, a toxinometer is used to measure the total amount b of the polysaccharide compound present in the liquid B. The amount of the polysaccharide compound contained in the pigment corresponds to "b". In addition, the amount of the polysaccharide compound that was present in the liquid A in a free state corresponds to "ab". For example, when the value of "a" is larger than zero (0) and the value of "b" is zero (0), the polysaccharide compound is not contained in the pigment and exists in a free state in the liquid A. You will be doing.

The polysaccharide compound can be identified by liquid chromatography or the like. In order to identify the polysaccharide compound contained in the pigment, first, the pH of the liquid containing the pigment is made to be strongly alkaline at about 12.0, then the temperature is raised to about 80 ° C. and maintained for about 2 hours. This allows the polysaccharide compound to be eluted from the pigment. Next, the polysaccharide compound contained in the pigment can be identified by analyzing the filtrate containing the polysaccharide compound separated by ultrafiltration by liquid chromatography or the like. The pH of the liquid containing the pigment can be adjusted by using, for example, an aqueous solution of an alkali metal hydroxide such as potassium hydroxide. Further, ultrafiltration can be performed using a hollow fiber membrane having a molecular weight cut-off of about 70 kDa.

[Method of encapsulating polysaccharide compounds in pigments]
For example, the polysaccharide compound can be encapsulated in the pigment by carrying out the step (i) shown below. If the amount of the polysaccharide compound contained in the pigment becomes too large after the step (i) is carried out, the steps (ii) to (v) shown below are additionally carried out to be included in the pigment. The amount of polysaccharide compound to be produced can be adjusted. On the other hand, if the amount of the polysaccharide compound present in the free state becomes too large after the step (i) is carried out, at least one of the following steps (iii) to (v) is added and carried out. Then, the polysaccharide compound existing in the free state can be removed. If necessary, only a part of the steps (iii) to (v) may be carried out, or the order of the steps to be carried out may be changed as appropriate. Further, after the final step, a purification step may be added and carried out. Hereinafter, steps (i) to (v) will be described respectively.

-Step (i): The pigment is encapsulated with a polysaccharide compound.
-Step (ii): Desorbing the polysaccharide compound from the pigment.
-Step (iii): Of the components derived from the polysaccharide compound desorbed from the pigment, a component having a size smaller than that of the pigment is removed.
-Step (iv): Of the components derived from the polysaccharide compound desorbed from the pigment, a component having a size larger than that of the pigment is removed.
-Step (v): Removes the alkaline component or acid component used in step (ii).

<< Process (i) >>
In order to include the polysaccharide compound in the pigment, the polysaccharide compound itself may be used, or bacteria (gram-positive bacteria, gram-negative bacteria) that produce the polysaccharide compound by metabolism may be used. For example, a component containing a crude pigment and at least one of a polysaccharide compound and a fungus capable of producing a polysaccharide compound is kneaded and then refined. These steps can be carried out by ordinary treatments for refining the coarse pigment. Furthermore, the pigment can contain the polysaccharide compound by keeping the conditions for culturing the fungi, if necessary.

The crude pigment, the polysaccharide compound or fungus, and the liquid medium (water, organic solvent, mixed medium thereof) are kneaded to obtain a kneaded product. The resulting kneaded product has little fluidity. It is preferable to knead the obtained kneaded product under the condition that the solid content is about 80% by mass or more. By increasing the solid content, the viscosity of the kneaded product during kneading is maintained at an appropriately high level, and the share of the kneaded product increases. Therefore, it is possible to efficiently proceed with the pulverization of the crude pigment and the inclusion of the polysaccharide compound in the pigment. If the solid content of the kneaded product is less than 80% by mass, the viscosity of the kneaded product is low, so that the degree of crushing of the pigment may be slightly insufficient. In addition, it may not be possible to increase the efficiency of including the polysaccharide compound in the pigment. In order to stably maintain the high viscosity of the kneaded product, it is preferable to use a closed type kneader such as a twin-screw extrusion kneader.

When the polysaccharide compound itself is used, if the polysaccharide compound is in a non-crystalline state in advance, it can be easily dissolved in the liquid medium, so that it can be more efficiently encapsulated in the pigment by kneading. In addition, when fungi are used, the polysaccharide compound, which is a metabolite, is included in the pigment. Therefore, it is preferable to keep the kneaded product under the conditions for culturing the fungi. In this case, the kneaded product may be kept under culture conditions, or the kneaded product may be kept in a wet state such as a wet cake and then kept under culture conditions. The holding temperature is preferably 15 to 40 ° C., the relative humidity is preferably 20 to 30%, and the holding period is preferably 1 to 3 months. When fungi are used, the fungi after producing the polysaccharide compound become unnecessary, so that they are preferably inactivated. Examples of the treatment for inactivating the fungi include heat treatment; ozone treatment; treatment with a fungicide such as benzoisothiazolin-3-one, isothiazolinic acid, and imazalyl. After the step (i) is carried out, a usual dispersion treatment for dispersing the pigment can be carried out. Steps (ii) to (v) can be carried out regardless of whether or not the dispersion treatment is carried out. When at least one of the steps (ii) to (v) is carried out, the usual dispersion treatment for dispersing the pigment can be carried out following each step.

<< Process (ii) >>
Step (ii) is a step of desorbing the polysaccharide compound from the pigment. Step (ii) is carried out when the amount of the polysaccharide compound contained in the pigment is too large or when the amount of the polysaccharide compound present in the free state is too large. In the step (ii), the polysaccharide compound is desorbed from the pigment, and the desorbed polysaccharide compound is modified or hydrolyzed to facilitate the implementation of the step (iii) or the step (iv). The polysaccharide compound can be modified or hydrolyzed by alkali treatment or acid treatment. The polysaccharide compound usually exists in a state of retaining the hairpin loop structure. The polysaccharide compound whose hairpin loop structure is no longer retained due to denaturation becomes low in molecular weight and decreases in volume, or gels and increases in volume. In addition, when the polysaccharide compound is hydrolyzed, the molecular weight is reduced and the volume is reduced. Then, using the difference between the size of the pigment and the size of the component generated by the modification or hydrolysis of the polysaccharide compound, a step (iii) or a step (iv) is carried out to remove such a component.

In order to treat the polysaccharide compound with an alkali, for example, a liquid containing an alkaline component may be added to a liquid containing a pigment and mixed. In order to increase the efficiency of denaturation or hydrolysis of the polysaccharide compound, it is preferable to keep the pH of the mixed liquid as high as possible. Specifically, the pH of the mixed liquid is preferably 10.0 or higher, more preferably 12.0 or higher. The pH of the mixed liquid is preferably 13.5 or less. The mixed liquid is then heated to promote denaturation or hydrolysis of the polysaccharide compound. The temperature is preferably 60 ° C. or higher, and more preferably 80 ° C. or higher. The temperature is preferably 100 ° C. or lower.

The pKa of the polysaccharide compound is approximately 12.0 to 13.0. Therefore, when the pH of the liquid obtained by adding and mixing the liquid containing the alkaline component is 12.0, about half of the polysaccharide compound is in a dissociated state. For example, when heated to 80 ° C. or higher, pKa decreases, so that almost all of the polysaccharide compounds are dissociated. By holding in this state for a certain period of time, almost all of the polysaccharide compounds existing in the free state can be denatured or hydrolyzed. Further, if it is held in the above state for a longer period of time, the polysaccharide compound contained in the pigment can be desorbed and modified or hydrolyzed.

In order to treat the polysaccharide compound with an acid, for example, a liquid containing an acid component may be added to a liquid containing a pigment and mixed. In order to increase the efficiency of denaturation or hydrolysis of the polysaccharide compound, it is preferable to keep the pH of the mixed liquid as low as possible. Specifically, the pH of the mixed liquid is preferably 6.0 or less, and more preferably 4.0 or less. The pH of the mixed liquid is preferably 2.0 or higher. The mixed liquid is then heated to promote denaturation or hydrolysis of the polysaccharide compound. The temperature is preferably 40 ° C. or higher, and more preferably 60 ° C. or higher. The temperature is preferably 100 ° C. or lower.

In the case of acid treatment, hydrolysis is remarkably promoted by heating, so that the heating temperature can be set lower than in the case of alkaline treatment. However, since a general resin used as a dispersant for pigments has an anionic group, it is preferable to note that acid treatment may cause hydrolysis of the resin or precipitation by acid. The heating time for the alkali treatment and the acid treatment can be appropriately set according to the amount of the pigment used, the type of the stirring device, and the like. However, it is preferable that the time is set so that the pigment is sufficiently processed. Specifically, the heating time is preferably 5 to 240 minutes.

Examples of the alkaline component include hydroxides of alkali metals such as lithium, sodium and potassium; and hydroxides of alkaline earth metals such as strontium and barium. Examples of the acid component include inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid; and organic acids such as phthalic acid and methanesulfonic acid. An aqueous solution obtained by dissolving these alkaline components and acid components in water can be used. The content (mass%) of the alkaline component or acid component in the aqueous solution may be an amount capable of achieving a desired pH, and should be 0.1% by mass or more and 3.0% by mass or less based on the total mass of the aqueous solution. Is preferable. The mixing ratio of the pigment and the aqueous solution may be a ratio at which the pigment is sufficiently immersed in the aqueous solution. For example, the mass ratio is preferably pigment: aqueous solution = 1: 1 to 1:10.

<< Process (iii) >>
In the step (iii), among the components derived from the polysaccharide compound desorbed in the step (iii), a component having a size smaller than that of the pigment is removed from the liquid containing the pigment. Specifically, among the components derived from polysaccharide compounds, components having a size smaller than that of pigments can be removed by ultrafiltration, filter press, disc filter, centrifugation, or the like. For example, when the polysaccharide compound is treated so as to have a size of about 30 nm or less in the step (ii), a separation membrane having a pore size of 50 nm or less or a separation membrane having a molecular weight cut-off of 500 kDa or less, preferably 100 kDa or less may be used. it can. It is preferable that the pore size and the molecular weight cut-off of the separation membrane are not too large in order to avoid removing the resin used as the dispersant together with the components derived from the polysaccharide compound.

<< Process (iv) >>
In the step (iv), among the components derived from the polysaccharide compound desorbed from the pigment in the step (ii), a component having a size larger than that of the pigment is removed from the liquid containing the pigment. Specifically, among the components derived from the polysaccharide compound, a component having a size larger than that of the pigment can be removed by microfiltration or the like. As the filter medium, a filter paper, a membrane filter, a glass fiber filter and the like can be used.

<< Process (v) >>
In the step (v), the alkaline component or the acid component used in the above step (ii) is removed from the liquid containing the pigment. The removal method is not particularly limited, and a known method can be used. For example, the separation method such as ultrafiltration, filter press, disc filter, and centrifugation illustrated in the description of step (iii) may be performed once or more. In the case of centrifugation, the liquid to be treated is placed in a centrifuge tube for treatment, and the pigment is precipitated to remove the supernatant liquid. Then, a liquid such as water may be added and mixed with the precipitated pigment. In the case of ultrafiltration, the filtrate containing an alkaline component or an acid component is removed, and the same amount of water as the removed filtrate is added. By repeating these treatments as necessary, the alkaline component or the acid component is removed, and the pH of the liquid containing the pigment can be adjusted as appropriate. In addition to the above methods, a method using salt production by neutralization (a method of adding an acid component to a liquid containing a pigment and an alkaline component to remove the generated salt and appropriately adjusting the pH of the liquid) and ions A method of removing an alkaline component or an acid component using an exchange resin may be used.

(Pigment)
The ink of the present invention contains a pigment as a coloring material. Examples of the pigment include inorganic pigments such as carbon black and organic pigments known in the art. Of these, it is preferable to use carbon black or an organic pigment. The content (mass%) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. Is more preferable.

The pigment is dispersed in the ink by a resin dispersant which is a resin for dispersing the pigment. That is, the pigment used in the ink of the present invention is a resin-dispersed pigment dispersed in the ink by the action of the resin dispersant physically adsorbed on the particle surface.

(Resin dispersant)
As the resin dispersant, it is preferable to use a resin dispersant capable of dispersing the pigment in an aqueous medium by the action of an anionic group. Further, as the resin dispersant, it is preferable to use a resin having a unit having an aromatic group and a unit represented by the following general formula (2).

（前記一般式（２）中、Ｒ₁₀乃至Ｒ₁₃は、それぞれ独立に水素原子、炭素数１乃至８のアルキル基、炭素数４乃至８のシクロアルキル基、カルボン酸基、カルボン酸基が置換した炭素数１乃至５のアルキル基である。Ｒ₁₀乃至Ｒ₁₃のうち、少なくとも１つはカルボン酸基又はカルボン酸基が置換した炭素数１乃至５のアルキル基であり、残りは水素原子、炭素数１乃至８のアルキル基、又は炭素数４乃至８のシクロアルキル基である）

(In the general formula (2), R _{10 to} R ₁₃ are independently substituted with a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 4 to 8 carbon atoms, a carboxylic acid group, and a carboxylic acid group, respectively. Alkyl groups having 1 to 5 carbon atoms _{. At least one of R 10 to} R ₁₃ is a carboxylic acid group or an alkyl group having 1 to 5 carbon atoms substituted with a carboxylic acid group, and the rest are hydrogen atoms. An alkyl group having 1 to 8 carbon atoms or a cycloalkyl group having 4 to 8 carbon atoms)

[Unit with aromatic group]
A unit having an aromatic group (hereinafter, also referred to as an “aromatic group-containing unit”) is a unit that functions as a hydrophobic unit of a resin dispersant. More specifically, the aromatic group-containing unit is a unit that exhibits an action of physically adsorbing to the particle surface of the pigment by hydrophobic interaction. The aromatic group-containing unit is formed by (co) polymerizing a monomer having an aromatic group. Examples of the aromatic group in the aromatic group-containing unit include a phenyl group, a benzyl group, a tolyl group, an o-xylyl group, and a naphthyl group.

Specific examples of the monomer having an aromatic group include aromatic vinyl compounds such as styrene and α-methylstyrene; α, β- such as benzyl (meth) acrylate and 2-phenoxyethyl (meth) acrylate. Ester compounds of ethylenically unsaturated carboxylic acids and aromatic group-containing alkyl alcohols; α, β-ethylenically unsaturated carboxylic acids and aromatic group-containing alkyls such as benzyl (meth) acrylamide and 2-phenoxyethyl (meth) acrylamide. Amid compounds of amines; other compounds such as 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloxyethylphthalic acid and the like can be mentioned.

The proportion (mass%) of the aromatic group-containing unit in the resin dispersant is preferably 40% by mass or more and 80% by mass or less based on the total mass of the resin dispersant. If the above ratio is less than 40% by mass, since the number of hydrophobic units is small, the resin dispersant is difficult to be adsorbed on the particle surface of the pigment, and the storage stability of the ink may not be sufficiently obtained. On the other hand, if the above ratio exceeds 80% by mass, the hydrophobic interaction between the resin dispersants may become too strong. Therefore, the resin dispersant aggregates and the ink tends to thicken, and the performance of suppressing the ink ejection twist may be slightly deteriorated.

[Unit represented by general formula (2)]
Specific examples of the monomer represented by the general formula (2) by (co) polymerization are unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and fumaric acid; Derivatives such as unsaturated mono or dicarboxylic acid anhydrides; salts of these unsaturated mono or dicarboxylic acids and the like can be mentioned. Of these, acrylic acid and methacrylic acid are preferable. Examples of the cation forming the salt include alkali metal cations such as lithium, sodium and potassium; ammonium ions; organic ammonium ions and the like. Of these, sodium ions and potassium ions are preferable.

[Unit represented by general formula (3), unit represented by general formula (4)]
The resin dispersant preferably further has a unit represented by the following general formula (3) or a unit represented by the following general formula (4).

（前記一般式（３）中、Ｒ₁₄は、水素原子又はメチル基である。Ｒ₁₅は、炭素数１乃至１６のアルキル基、炭素数３乃至１０のシクロアルキル基、１乃至３級アミノ基で置換された炭素数１乃至６のアルキル基、炭素数１乃至６のアルキレン基と炭素数１乃至１０のフルオロアルキル基が結合した基、又は炭素数１乃至６のアルキレン基とシロキサン構造を有する基が結合した基である）

(In the general formula (3), R ₁₄ is a hydrogen atom or a methyl group. R ₁₅ is an alkyl group having 1 to 16 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and a primary to tertiary amino group. It has an alkyl group having 1 to 6 carbon atoms substituted with, a group in which an alkylene group having 1 to 6 carbon atoms and a fluoroalkyl group having 1 to 10 carbon atoms are bonded, or an alkylene group having 1 to 6 carbon atoms and a siloxane structure. The group is a bonded group)

（前記一般式（４）中、Ｒ₁₆は、水素原子又はメチル基である。Ｒ₁₇は、炭素数２乃至６のアルキレン基である。Ｒ₁₈は、水素原子、炭素数１乃至１８のアルキル基、又は炭素数３乃至１０のシクロアルキル基である。ｎは、１乃至１０の整数である）

(In the general formula (4), R ₁₆ is a hydrogen atom or a methyl group. R ₁₇ is an alkylene group having 2 to 6 _{carbon atoms. R 18} is a hydrogen atom and an alkyl having 1 to 18 carbon atoms. A group or a cycloalkyl group having 3 to 10 carbon atoms. N is an integer of 1 to 10).

When a resin dispersant having a unit represented by the general formula (3) or a unit represented by the general formula (4) is used, the dispersion stability of the pigment is enhanced, so that discharge twist can be suppressed more effectively. .. The present inventors speculate the reason why such an effect can be obtained as follows. In order to improve the dispersion stability of the pigment, it is advantageous to use a resin that easily adsorbs to the particle surface of the pigment and easily causes steric repulsion as a dispersant. The aromatic group-containing unit is adsorbed on the particle surface of the pigment by the hydrophobic interaction of the aromatic groups. However, the resin may be desorbed due to factors such as the composition of the ink and the storage temperature only by the hydrophobic interaction of the aromatic groups. On the other hand, the polysaccharide compound contained in the pigment has a very high hydrogen bonding property. In addition, the unit represented by the general formula (2) also has high hydrogen bonding properties. Further, the unit represented by the general formula (3) and the unit represented by the general formula (4) both have a hydrogen bond property because they have an ester bond. That is, between the polysaccharide compound and the unit represented by the general formula (2), the unit represented by the general formula (3), and the unit represented by the general formula (4) in the resin dispersant. By hydrogen bonding, the resin is strongly adsorbed on the surface of the pigment particles in combination with the hydrophobic interaction. It is considered that this effectively suppresses the desorption of the resin from the particle surface of the pigment and enhances the dispersion stability of the pigment.

Further, a resin having a unit represented by the general formula (2) and a unit represented by the general formula (3) or a unit represented by the general formula (4) is only easily adsorbed on the particle surface of the pigment. In addition, since steric repulsion is likely to occur, the dispersion stability of the pigment can be improved. For example, a resin having only an aromatic group-containing unit and a unit represented by the general formula (2) is rigid and lacks three-dimensional freedom. On the other hand, the resin further having the unit represented by the general formula (3) and the unit represented by the general formula (4) has a high degree of three-dimensional freedom. Therefore, even in a situation where the distance between the pigment particles is short, the aggregation of the pigment can be suppressed by the steric repulsion, and the dispersion stability can be improved.

Specific examples of the monomer that becomes the unit represented by the general formula (3) by (co) polymerization are ester compounds of (meth) acrylic acid and alkanol having 1 to 16 carbon atoms; (meth) acrylic acid and carbon. Ester compounds of cycloalkanols of number 3 to 10; ester compounds of alkanols having 1 to 6 carbon atoms substituted with (meth) acrylic acid and primary to tertiary amino groups; (meth) acrylic acid and ester compounds of 1 to 10 carbon atoms. Examples thereof include ester compounds of alkanol having 1 to 6 carbon atoms substituted with a fluoroalkyl group; ester compounds of (meth) acrylic acid and alkanol having 1 to 6 carbon atoms substituted with a group having a siloxane structure. The alkyl group moiety of the alkanol may be either a straight chain or a branched chain. Further, the alkanol and the cycloalkanol may have a substituent such as an alkyl group.

Examples of ester compounds of (meth) acrylic acid and alkanol having 1 to 16 carbon atoms include methyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, and (meth). ) Octyl acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, cetyl (meth) acrylate, -2-ethylhexyl (meth) acrylate and the like can be mentioned.

Examples of the ester compound of (meth) acrylic acid and cycloalkanol having 3 to 10 carbon atoms include cyclopropyl (meth) acrylic acid, cyclobutyl (meth) acrylic acid, cyclopentyl (meth) acrylic acid, cyclohexyl (meth) acrylic acid, and ( Cyclooctyl acrylate, (meth) cyclodecyl acrylate, isobornyl (meth) acrylate, norbornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, (meth) Dicyclopentenyloxylalkyl acrylate, adamantyl (meth) acrylate, tetrahydrofurfurfryl (meth) acrylate, γ-butyrolactone (meth) acrylate, piperidine (meth) acrylate, maleimide (meth) acrylate, (meth) Oxazoline acrylate and the like can be mentioned.

Examples of the ester compound of (meth) acrylic acid and alkanol having 1 to 6 carbon atoms substituted with 1 to tertiary amino groups include 2- (dimethylamino) ethyl acrylate, 3- (dimethylamino) propyl acrylate, and methacrylic acid. Examples thereof include 2- (dimethylamino) ethyl acid, 3- (dimethylamino) propyl methacrylate, 2- (diethylamino) ethyl methacrylate, 2- (diethylamino) propyl methacrylate and the like.

Examples of the ester compound of (meth) acrylic acid and an alkanol having 1 to 6 carbon atoms substituted with a fluoroalkyl group having 1 to 10 carbon atoms include a compound represented by the following general formula (3-1). ..

In the general formula (3-1), R ₂₃ is a hydrogen atom or a methyl group. R ₂₄ is a group represented by any of the following formulas.
(CH ₂ ) ₂ (CF ₂ ) ₁₀ F, (CH ₂ ) ₂ (CF ₂ ) ₈ F, (CH ₂ ) ₂ (CF ₂ ) ₆ F, CH ₂ (CF ₂ ) ₆ F, CH ₂ (CF ₂₎ ) ₇ F, CH ₂ (CF ₂ ) ₂ H, CH ₂ (CF ₂ CF ₂ ) ₂ H, CH ₂ (CF ₂ CF ₂ ) ₄ H, CH ₂ CF ₂ OCF ₂ CF ₂ OCF ₃ , CH ₂ CF ₂ O (CF ₂ CF ₂ O) ₃ CF ₃ , CH ₂ CF (CF ₃ ) OCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ F, CH ₂ CF (CF ₃ ) O (CF ₂ CF (CF ₃ )) O) ₂ (CF ₂ ) ₃ F, CH ₂ CH (OH) CH ₂ (CF ₂ ) ₆ CF (CF ₃ ) ₂ , CH ₂ CH (CH ₂ OH) CH ₂ (CF ₂ ) ₆ CF (CF ₃ ) ₂ , CH ₂ CH (OH) CH ₂ (CF ₂ ) ₁₀ F, CH ₂ CH (OH) CH ₂ (CF ₂ ) ₁₀ F, CH ₂ CH ₂ (CF ₂ CF ₂ ) ₃ CH ₂ CH ₂ OCOCH = CH ₂ , CH ₂ CH ₂ (CF ₂ CF ₂ ) ₃ CH ₂ CH ₂ OCOC (CH ₃ ) = CH ₂

Examples of the ester compound of (meth) acrylic acid and an alkanol having 1 to 6 carbon atoms substituted with a group having a siloxane structure include a compound represented by the following general formula (5). Examples of commercially available products of the compound represented by the following general formula (5) include Cyraplane FM-0711, FM-0721, FM-0725 (all manufactured by Chisso) and the like under the following trade names.

（前記一般式（５）中、Ｒ₁₉は、水素原子又はメチル基であり、Ｒ₂₀は、炭素数１乃至６のアルキレン基である。Ｒ₂₁は、それぞれ独立にメチル基又はフェニル基であり、Ｒ₂₂は、炭素数１乃至６のアルキル基炭素数６乃至１０のアリール基である。ｍは、１乃至１５０である）

(In the general formula (5), R ₁₉ is a hydrogen atom or a methyl group, R ₂₀ is an alkylene group having 1 to 6 carbon atoms, and R ₂₁ is an independently methyl group or a phenyl group. , R ₂₂ is an alkyl group having 1 to 6 carbon atoms and an aryl group having 6 to 10 carbon atoms. M is 1 to 150).

Among the above specific examples, cyclohexyl (meth) acrylate and tetrahydrofurfuryl (meth) acrylate are preferable as the monomers constituting the unit represented by the general formula (3).

Examples of the monomer constituting the unit represented by the general formula (4) include a hydroxy group-terminated mono (meth) acrylic acid ester, an alkyl group-terminated polyalkylene glycol mono (meth) acrylic acid ester, and the like. .. More specifically, mono (meth) acrylate polyethylene glycol, mono (meth) acrylate polypropylene glycol, (meth) acrylate methoxypolyethylene glycol, (meth) acrylate-lauroxy-polyethylene glycol, (meth) acrylate stearoxy- Examples thereof include polyethylene glycol.

[Physical characteristics of resin]
The acid value of the resin dispersant is preferably 80 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 200 mgKOH / g or less. When the acid value of the resin dispersant is less than 100 mgKOH / g, the hydrophobic interaction between the resins becomes strong, so that the resins tend to aggregate. For this reason, the viscosity of the ink becomes high, and the performance of suppressing ejection twist may be slightly lowered. On the other hand, when the acid value of the resin dispersant is more than 200 mgKOH / g, the number of hydrophobic units is reduced, and the resin is less likely to be adsorbed on the surface of the pigment particles. Therefore, the storage stability of the ink may not be sufficiently obtained.

The weight average molecular weight of the resin dispersant is preferably 1,000 or more and 30,000 or less, and more preferably 3,000 or more and 15,000 or less. The weight average molecular weight of the resin dispersant is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). If the weight average molecular weight of the resin dispersant is less than 3,000, it becomes difficult for the resin to be adsorbed on the particle surface of the pigment, and the storage stability of the ink may not be sufficiently obtained. On the other hand, when the weight average molecular weight of the resin dispersant is more than 15,000, the viscosity of the ink becomes high, and the performance of suppressing ejection twist may be slightly lowered.

The content (mass%) of the resin dispersant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.5% by mass or more and 2.0% by mass, based on the total mass of the ink. It is more preferably less than or equal to%. The content (mass%) of the resin dispersant in the ink is preferably 0.05 times or more and 0.50 times or less, and 0.10 times or more and 0 times, in terms of the mass ratio to the pigment content (mass%). It is more preferably .30 times or less. If the mass ratio is less than 0.05 times, the dispersion stability of the pigment is lowered, and the discharge wrinkle may not be sufficiently suppressed. On the other hand, if the mass ratio is more than 0.50 times, a part of the resin is likely to be separated from the particle surface of the pigment, and the optical density of the image may not be sufficiently obtained. It is considered that this is because the polysaccharide compound eluted from the pigment is taken into the desorbed resin when the ink is applied to the recording medium, and the increase in viscosity when the liquid component evaporates is suppressed. Be done.

[Method for synthesizing resin dispersant]
The resin dispersant can be synthesized by various conventionally known methods. When synthesizing the resin dispersant, a polymerization initiator and a chain transfer agent can be used.

Examples of the polymerization initiator include persulfates; organic peroxides such as dibenzoyl peroxide; azo compounds such as 2,2'-azobis (2-methylbutyronitrile); and inorganic peroxides. be able to. The amount (% by mass) of the polymerization initiator used is preferably 0.1% by mass or more and 10.0% by mass or less based on the total amount of the monomers.

As the chain transfer agent, a thiol-based chain transfer agent or the like can be used. The amount (% by mass) of the chain transfer agent used is preferably 2.0% by mass or more and 13.0% by mass or less based on the total amount of the monomers. When the amount of the chain transfer agent used is less than 2.0% by mass, the amount of sulfur atoms is smaller than that of the obtained resin dispersant. Therefore, the binding force due to the hydrogen bond with the polysaccharide compound tends to be weakened, and the storage stability of the ink may not be sufficiently obtained. On the other hand, when the amount of the chain transfer agent used is more than 13.0% by mass, the amount of sulfur atoms is larger than that of the obtained resin dispersant. For this reason, the binding force due to the hydrogen bond with the polysaccharide compound becomes strong, the viscosity of the ink tends to increase, and the performance of suppressing the ejection twist of the ink may be slightly deteriorated.

Examples of the thiol-based chain transfer agent include aromatic group-containing mercaptans; linear alkyl mercaptans; branched alkyl mercaptans; cyclic alkyl mercaptans such as 1-thioglycerol; and substituted alkyl mercaptans such as 1-thioglycerol.

It is also possible to use a trifunctional or higher functional thiol chain transfer agent such as an ester compound of a polyhydric alcohol and thioglycolic acid or thiopropionic acid, such as dipentaerythritol hexaxthiopropionate.

[Resin analysis method]
Physical properties such as the composition and molecular weight of the resin can be analyzed by a conventionally known method. Physical properties such as the composition and molecular weight of the resin can also be confirmed by analyzing the sediment and the supernatant obtained by centrifuging the ink containing the resin. Although it is possible to analyze in the state of ink, the accuracy of analysis can be further improved by using the extracted resin. Specifically, first, the resin is extracted from the liquid phase obtained by centrifuging the ink at 200,000 G for 30 minutes. Then, by analyzing the extracted resin using a pyrolysis gas chromatography / mass spectrometer (Py-GC / MS), the type of the unit constituting the resin can be confirmed. In addition, by quantitatively analyzing the extracted resin by nuclear magnetic resonance spectroscopy (NMR) or Fourier transform infrared spectrophotometer (FT-IR), the types, molecular weights, and contents of the monomers constituting the resin are contained. You can check the amount and so on. Further, when the resin is a block copolymer or a graft copolymer, the continuity of the units constituting the resin can be confirmed by using MALDI-TOF-MS. The acid value of the resin can be measured by the titration method. The type of acid group neutralizer in the resin can be identified by electrophoretic chromatography. The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the resin can be measured by gel permeation chromatography (GPC). The volume average particle size of the resin can be measured by a dynamic light scattering method.

When a certain ink further contains a resin (additional resin) different from the resin dispersant in addition to the resin dispersant, the resin dispersant and the added resin can be separated according to the method shown below. “The resin dispersant and the added resin are different” means that at least one of the physical property values such as the type of the constituent unit, the ratio of the constituent unit, the acid value, and the weight average molecular weight is different. Within the range of the general pH and surface tension of the water-based ink, a small part of the resin dispersant and the added resin can be exchanged in the ink, but it is negligible because it is a very small amount. As a premise, the resin dispersant and the added resin can be distinguished by the amount adsorbed on the pigment. That is, the resin that is more adsorbed by the pigment is the resin dispersant, and the other resins are the additive resins.

In theory, a plurality of resins existing in the system may be adsorbed and exchanged with each other. However, in the case of water-based ink for inkjet, the resin dispersant and the added resin are not substantially adsorbed and exchanged so as to be exchanged. This is because the additive resin is a component used with the expectation of actions such as image characteristics and reliability, and if the additive resin expected to have such actions is easily adsorbed and exchanged with the resin dispersant, the additive resin is used in the first place. Because there is no point in doing it.

The ink containing the pigment, the resin dispersant, and the added resin is centrifuged at 200,000 G for 30 minutes to separate the precipitate (including the pigment and the resin adsorbed on the pigment). The precipitate is washed with acid and dried thoroughly to give a dried product. The obtained dried product is added to an organic solvent such as tetrahydrofuran and stirred to elute the resin adsorbed on the pigment into the organic solvent to obtain a liquid. The obtained liquid is centrifuged at 5,000 G for 5 minutes to separate the pigment as a precipitate and the liquid component containing the resin in a state of being dissolved in an organic solvent. By drying the separated liquid components, the resin adsorbed on the pigment, that is, the resin dispersant can be obtained. On the other hand, the resin not adsorbed on the pigment is contained in the liquid phase obtained by centrifugation at 200,000 G for 30 minutes. A resin that has not been adsorbed on the pigment, that is, an added resin can be obtained by recovering the agglomerated resin by adding an acid or the like to the liquid phase, thoroughly washing with water, and then drying. Various characteristics of the resin dispersant and the added resin thus obtained can be known by applying the above-mentioned analysis method.

In the above method, a small amount of the other resin may be mixed as the "resin adsorbed on the pigment" and the "resin not adsorbed on the pigment". In this case, for example, the resin having the largest mass ratio among the "resins adsorbed on the pigment" can be regarded as the resin dispersant.

(Aqueous medium)
The ink of the present invention is a water-based ink containing at least water as an aqueous medium. The ink can contain an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent. As the water, it is preferable to use deionized water or ion-exchanged water. The water content (mass%) in the water-based ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

The water-soluble organic solvent is not particularly limited as long as it is water-soluble, and alcohol, polyhydric alcohol, polyglycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (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 additives)
The ink of the present invention may contain various kinds of surfactants, pH adjusters, rust preventives, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation promoters, chelating agents and the like, if necessary. Additives may be included.

Examples of the surfactant include anionic, cationic and nonionic surfactants. The content (mass%) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.1% by mass or more and 2.0% by mass, based on the total mass of the ink. It is more preferably less than or equal to%.

(Physical characteristics of ink)
The ink of the present invention is an ink for inkjet applied to an inkjet method. Therefore, it is preferable to appropriately control the physical property value. Specifically, the surface tension of the ink at 25 ° C. is preferably 10 mN / m or more and 60 mN / m or less, and more preferably 20 mN / m or more and 60 mN / m or less. Among them, it is preferably 30 mN / m or more and 50 mN / m or less, and particularly preferably 30 mN / m or more and 40 mN / m or less. The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 10.0 mPa · s or less, more preferably 1.0 mPa · s or more and 5.0 mPa · s or less, and 1.0 mPa. -It is particularly preferable that the content is s or more and 3.0 mPa · s or less. The pH of the ink at 25 ° C. is preferably 5.0 or more and 10.0 or less. Above all, it is preferably 6.0 or more and 8.5 or less.

(Ink manufacturing method)
The ink of the present invention can be obtained by a general method for producing an aqueous ink for inkjet, except that a pigment containing a polysaccharide compound is used. Specifically, the ink can be produced by carrying out (1) a step of preparing a pigment containing a polysaccharide compound and (2) a step of mixing an ink component containing the pigment. The step (1) above can be carried out according to the method of incorporating the polysaccharide compound described above into the pigment. Subsequent steps can be carried out in the same manner as a general method for producing a water-based ink for inkjet, and steps such as purification may be added if necessary.

<Ink cartridge>
The ink cartridge of the present invention includes an ink and an ink accommodating portion for accommodating the ink. The ink contained in the ink accommodating portion is the ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink accommodating portion for accommodating ink. The ink accommodating portion is composed of an ink accommodating chamber 14 and an absorber accommodating chamber 16, and these are communicated with each other through a communication port 18. Further, the absorber accommodating chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 contains the liquid ink 20, and the absorber storage chamber 16 contains the absorbers 22 and 24 that hold the ink in an impregnated state. The ink accommodating portion may not have an ink accommodating chamber for accommodating liquid ink, and may have a form in which the entire amount of ink contained is held by an absorber. Further, the ink accommodating portion may have a form in which the entire amount of ink is accommodating in a liquid state without having an absorber. Further, the ink cartridge may be in a form configured to have an ink accommodating portion and a recording head.

<Inkjet recording method>
The inkjet recording method of the present invention is a method of ejecting the ink of the present invention described above from an inkjet recording head to record an image on a recording medium. Examples of the method of ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of applying heat energy to the ink to eject the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be known.

FIG. 2 is a diagram schematically showing an example of an inkjet recording device used in the inkjet recording method of the present invention, (a) is a perspective view of a main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. Is. The inkjet recording device is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. The head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured so that the ink cartridge 42 is set. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by the conveying means (not shown), so that the image is recorded on the recording medium 32.

Any recording medium may be used for recording using the ink of the present invention, and it can be selected according to the purpose of use of the recorded material on which the image is recorded. For example, permeable paper such as plain paper and a recording medium having a coat layer can be mentioned. For example, plain paper suitable for obtaining images such as business documents can be used. In addition, the texture of the surface (matte, drawing paper, canvas) is used to express glossy paper suitable for obtaining glossy images with photographic image quality, paintings, photographs, and graphic images to the liking. Art paper that makes the best use of the ground tone, Japanese paper tone, etc. can be used. In particular, it is preferable to use a recording medium such as plain paper having no coat layer or a recording medium such as coated paper having a coat layer.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. It should be noted that those described as "parts" and "%" regarding the amount of components are based on mass unless otherwise specified.

<Synthesis of resin>
(Resin 1-12)
After putting 200.0 parts of isopropanol in a flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer, the temperature was raised to 85 ° C. with stirring under a nitrogen atmosphere. The mixture of monomers shown in Table 3, the liquid containing the polymerization initiator, and the chain transfer agent were each added dropwise to the flask over 2 hours while maintaining the temperature at 80 ° C. As the liquid containing the polymerization initiator, a solution prepared by dissolving 5.0 parts of the trade name "Percadox L-W75 (LS)" (manufactured by Kayaku Akzo, dibenzoyl peroxide, purity 75%) in 10.0 parts of isopropanol is used. Using. The internal temperature was maintained at 80 ° C. and the mixture was stirred for 4 hours to synthesize a resin. After adding 0.9 equivalents of potassium hydroxide and an appropriate amount of ion-exchanged water with respect to the acid value of the resin, isopropanol was removed under reduced pressure to make the resin (solid content) content 20.0%. I got a liquid. The resin thus obtained was used as a resin dispersant for dispersing the pigment. The meanings of the abbreviations in Table 3 are shown below.
St: Styrene BzMA: Benzyl methacrylate MMA: Methyl methacrylate nBA: n-butyl acrylate CHMA: Cyclohexyl methacrylate FM-0711: Silaplane FM-0711 (monomer represented by the general formula (5), manufactured by Chisso) )
FAAC-6: 2- (Perfluorohexyl) ethyl acrylate (trade name, manufactured by Unimatec)
EGDMA: ethylene dimethacrylate AA: acrylate MAA: methacrylic acid Chain transfer agent 1: 1-thioglycerol 1.9 parts dissolved in 10.0 parts of isopropanol Serial transfer agent 2: 1-hexanethiol 1.9 parts Chain transfer agent 3: A solution of 10.0 parts of dipentaerythritol hexaxthiopropionate in 10.0 parts of isopropanol.

<Manufacturing of pigments>
Each component shown in Table 4 was mixed and put into a twin-screw kneading extruder (trade name "TEM-26SX", manufactured by Toshiba Machine Co., Ltd.) and kneaded. After kneading the pigment, dimethyl sulfoxide was removed by washing to obtain pigments 1 to 26. The quinacridone solid solution is C.I. I. Pigment Red 122 and C.I. I. A solid solution pigment containing Pigment Violet 19.

Pigments 1 to 25 were analyzed using an endotoxin measurement system (trade name "Toxinometer ET6000, SLP reagent set", manufactured by Wako Pure Chemical Industries, Ltd.). As a result, it was confirmed that the polysaccharide compound was included in the pigment. Furthermore, the polysaccharide compound contained in the pigment was analyzed by HPLC equipped with a column for sugar analysis (trade name "Shim-pack SCR-101P, manufactured by Shimadzu Corporation). As a result, many used in the production of the pigment. It was confirmed that the same polysaccharide compound as the saccharide compound was included in the pigment. On the other hand, it was confirmed that the pigment 26 did not contain the polysaccharide compound.

<Preparation of pigment dispersion liquid>
(Pigment Dispersion Liquids I-1 to I-42)
Each component shown below was mixed and subjected to dispersion treatment at a treatment pressure of 245 MPa using a high-pressure homogenizer (trade name "Starburst", manufactured by Sugino Machine Limited). Then, an appropriate amount of ion-exchanged water was added to obtain each pigment dispersion.
-Pigments of the types shown in Tables 5-1 and 5-2: 20.0 parts-Liquids containing resins of the types shown in Tables 5-1 and 5-2: Amounts shown in Tables 5-1 and 5-2 (parts) )
-Ion-exchanged water: The remaining amount of 100.0 parts of the total components

(Pigment Dispersion Liquid I-43)
The solution obtained by dissolving 60 mmol of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and 8.28 mmol of 4-aminophthalic acid was added in this state. A container containing this solution was placed in an ice bath, and the solution obtained by dissolving 21.2 mmol of sodium nitrite in 9.0 g of water at 5 ° C. was added while keeping the temperature of the solution at 10 ° C. or lower with stirring. .. After stirring for 15 minutes, 6.0 g of Pigment 1 was added under stirring, and the mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered through a filter paper (trade name "Standard Filter Paper No. 2", manufactured by Advantech), the particles were thoroughly washed with water, and dried in an oven at 110 ° C. An appropriate amount of ion-exchanged water was added to adjust the pigment content to obtain a pigment dispersion liquid I-43 having a pigment content of 15.0%.

(Quantification of polysaccharide compounds)
Ion-exchanged water was added to the prepared pigment dispersion and diluted 2,500 times (based on mass). The content of the polysaccharide compound was quantified using an endotoxin measurement system (trade name "Toxinometer ET-6000", SLP reagent set, manufactured by Wako Pure Chemical Industries, Ltd.), and the mass ratio (ppm) to the pigment was calculated. Further, the prepared pigment dispersion was subjected to ultrafiltration by the diafiltration method using the ultrafiltration membrane shown below to remove the polysaccharide compound present in the pigment dispersion in a free state.
[Ultrafiltration membrane]
-Type: Modified Polyester Sulfone Hollow Fiber Module (trade name "MicroKross", manufactured by Spectrum Laboratories)
-Molecular weight cut-off: 100 kDa
・ Membrane area: 1600 cm ²
・ Inner diameter: 0.5 mm

Ion-exchanged water was added to the pigment dispersion after removing the polysaccharide compound existing in the liberated state, and the mixture was diluted 2,500 times (mass basis). The content of the polysaccharide compound was quantified using an endotoxin measurement system (trade name "Toxinometer ET-6000", SLP reagent set, manufactured by Wako Pure Chemical Industries, Ltd.). Then, from the comparison between the quantification result of the polysaccharide compound in the pigment dispersion liquid without ultrafiltration and the quantification result of the polysaccharide compound in the pigment dispersion liquid subjected to ultrafiltration, the amount contained in the pigment (Inclusive content) and the amount existing in the free state (free part) were calculated. The results are shown in Tables 5-1 and 5-2.

(Adjustment of the mass ratio of the amount of polysaccharide compound contained in the pigment to the amount of pigment)
The mass ratio of the amount of the polysaccharide compound contained in the pigment to the amount of the pigment was adjusted according to the procedure shown below.

(A) Step of desorbing the polysaccharide compound from the pigment Put 1 kg of the pigment dispersion to be treated in a glass beaker having a volume of 2 L, and add an appropriate amount of potassium hydroxide aqueous solution while stirring with a stirrer to bring the pH to 12.0. It was adjusted. The temperature was raised to the temperature shown in Table 6, and the mixture was stirred for about 10 minutes and then cooled to room temperature. As a result, the polysaccharide compound was eliminated from the pigment.

(B) A step of removing a component having a size smaller than that of the pigment among the components derived from the polysaccharide compound desorbed from the pigment The liquid after the above step (A) is subjected to the ultrafiltration shown below. Ultrafiltration was performed using a membrane by the diafiltration method.
[Ultrafiltration membrane]
-Type: Modified Polyester Sulfone Hollow Fiber Module (trade name "MicroKross", manufactured by Spectrum Laboratories)
-Molecular weight cut-off: Values shown in Table 6-Membrane area: 1600 cm ²
・ Inner diameter: 0.5 mm

(C) Step of removing the alkaline component used in the step (A) After continuing the above step (B), the pH of the liquid was adjusted to 9.0.

(D) Step of removing a component having a size larger than that of the pigment among the components derived from the polysaccharide compound desorbed from the pigment 22,000 G, 10 minutes for the liquid after performing the above step (C). The coarse particles of the pigment and the modified / gelled polysaccharide compound were removed by centrifugation under the above conditions.

(E) Step of removing the modified / gelled polysaccharide compound For the liquid after performing the above step (D), use a filter paper having a pore size of 0.45 μm (trade name “Ultipore GF-HV”, manufactured by Paul). The polysaccharide compound was removed by filtration to remove the modified / gelled polysaccharide compound.

(F) Calculation of mass ratio of amount of polysaccharide compound contained in pigment to amount of pigment Add ion-exchanged water to the liquid (pigment dispersion) after performing the above step (E) 2. It was diluted 500 times (based on mass). The content of the polysaccharide compound was quantified using an endotoxin measurement system (trade name "Toxinometer ET-6000", SLP reagent set, manufactured by Wako Pure Chemical Industries, Ltd.), and the mass ratio to the amount of pigment (inclusion P (inclusion P (inclusion P)). ppm)) was calculated.

Further, ion-exchanged water was added to the liquid (pigment dispersion liquid) after the above step (E), and the mixture was diluted 2,500 times (based on mass). Ultrafiltration was performed by the diafiltration method using the ultrafiltration membrane shown below to remove the polysaccharide compound present in the pigment dispersion in a free state.
[Ultrafiltration membrane]
-Type: Modified Polyester Sulfone Hollow Fiber Module (trade name "MicroKross", manufactured by Spectrum Laboratories)
-Molecular weight cut-off: 70 kDa
・ Membrane area: 1600 cm ²
・ Inner diameter: 0.5 mm

Ion-exchanged water was added to the pigment dispersion after removing the polysaccharide compound existing in the liberated state, and the mixture was diluted 2,500 times (mass basis). The content of the polysaccharide compound was quantified using an endotoxin measurement system (trade name "Toxinometer ET-6000", SLP reagent set, manufactured by Wako Pure Chemical Industries, Ltd.). Then, from the difference from the inclusion P (ppm), the amount of the polysaccharide compound present in the free state in the pigment dispersion and the mass ratio to the amount of the pigment (free F (ppm)) were calculated. Further, from the above results, a value of (P / (P + F)) × 100 was calculated.

<Ink preparation>
Each of the following components (unit:%) was mixed, sufficiently stirred, and then pressure-filtered with a microfilter (manufactured by Fujifilm) having a pore size of 2.5 μm to prepare each ink. However, for the ink of Comparative Example 2, instead of 31.9% of the ion-exchanged water, 0.036% of xanthan gum having a weight average molecular weight of 2 million and the remaining amount of ion-exchanged water having a total component of 100.0%. Was prepared using. The viscosity of the prepared ink was measured with an E-type viscometer (trade name "RE-80L", manufactured by Toki Sangyo). As a result, the viscosity of the ink of Example 28, which had the highest viscosity in Examples, was 2.8 mPa · s, and the viscosity of the ink of Comparative Example 3, which had the lowest viscosity in Comparative Examples, was 3.5 mPa · s.・ It was s.
-Pigment dispersions of the types shown in Table 7: 53.0%
・ Glycerin: 5.0%
-Triethylene glycol: 10.0%
-Acetyleneol E100: 0.1%
・ Ion-exchanged water: 31.9%

<Evaluation>
Each of the prepared inks was filled in an ink cartridge and set in an inkjet recording device that ejects ink from a recording head by the action of heat energy. In this embodiment, a solid image recorded by applying 28 ng of ink to a unit area of 1/600 inch × 1/600 inch is defined as “recording duty is 100%”. In the present invention, "A" and "B" are set to an acceptable level, and "C" is set to an unacceptable level in the evaluation criteria of each of the following items. The evaluation results are shown on the right side of Table 7.

(Optical density)
An image was recorded on a recording medium (plain paper, trade name "PB PAPER GF-500", manufactured by Canon) using an inkjet recording device (trade name "PIXUS MG5230", manufactured by Canon) according to the following conditions. First, after recording a solid image of 5 cm × 5 cm with a recording duty of 100%, a discharge pause time of 2 seconds is provided, and then a recovery operation (preliminary discharge and suction recovery) is not performed, and the width is equivalent to 3 dots. The ruled lines were recorded to obtain a recorded material. Then, using a spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth), the optical density of the solid image in the recorded material was measured under the conditions of light source: D50 and field of view: 2 °, and the optical density of the solid image in the recorded material was measured and used as the evaluation criteria shown below. Therefore, the optical density of the image was evaluated.
A: The optical density was 1.40 or more.
B: The optical density was 1.35 or more and less than 1.40.
C: The optical density was less than 1.35.

(Suppression of discharge twist)
The ruled lines in the recorded material used in the above evaluation of "optical density" were visually confirmed, and the suppression of ejection twist was evaluated according to the evaluation criteria shown below.
A: There was no deviation in the adhesion position of the dots, and it was a straight ruled line.
B: There was a deviation of about half a dot in the dot attachment position, but the ruled line was not distorted.
C: There was a deviation of about 1 dot in the adhesion position of the dots, or there was non-ejection of ink, and there was a place where the ruled line was distorted or faint.

(Scratch resistance)
Using an inkjet recording device, a solid image of 10 cm × 15 cm having a recording duty of 100% was recorded on a recording medium (plain paper, trade name “PB PAPER GF-500”, manufactured by Canon) to obtain a recorded material. As the inkjet recording device, the trade name "PIXUS Pro 9500" (manufactured by Canon) was used. The above recording medium was fixed as a friction element to a Gakushin dyeing friction fastness tester (manufactured by Yasuda Seiki Seisakusho), and under the condition of a load of 1.96 N, the solid image part of the obtained recorded material and the friction element were used. Was rubbed a predetermined number of times. Then, the solid image was visually confirmed, and the scratch resistance of the image was evaluated according to the evaluation criteria shown below.
A: There were scratches on the image after rubbing 20 round trips, but there were no scratches on the image after rubbing 10 round trips.
B: There were scratches on the image after rubbing 10 round trips, but there were no scratches after rubbing 5 round trips.
C: The image was scratched after rubbing 5 times.

Claims (12)

An inkjet water-based ink containing a pigment and a resin for dispersing the pigment.
A water-based ink characterized in that the pigment contains lipopolysaccharide . The water-based ink according to claim 1, wherein the lipopolysaccharide has a weight average molecular weight of 20,000 or more and 2.2 million or less. The water-based ink according to claim 1 or 2 , wherein the amount of the lipopolysaccharide contained in the pigment is 1 ppm or more and 4,500 ppm or less in terms of mass ratio with respect to the amount of the pigment. Any one of claims 1 to 3 in which the content (ppm) of the lipopolysaccharide contained in the pigment is 90% or more in terms of the mass ratio of the lipopolysaccharide to the total content (ppm) in the ink. The water-based ink described in. The water-based ink according to any one of claims 1 to 4 , wherein the content (ppm) of the lipopolysaccharide present in a free state is 25 ppm or less based on the total mass of the ink. The water-based ink according to any one of claims 1 to 5 , wherein the content (% by mass) of the pigment is 0.1% by mass or more and 15.0% by mass or less based on the total mass of the ink. The water-based ink according to any one of claims 1 to 6 , wherein the resin has a unit having an aromatic group and a unit represented by the following general formula (2).

(In the general formula (2), R _{10 to} R ₁₃ are independently substituted with a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 4 to 8 carbon atoms, a carboxylic acid group, and a carboxylic acid group, respectively. Alkyl groups having 1 to 5 carbon atoms _{. At least one of R 10 to} R ₁₃ is a carboxylic acid group or an alkyl group having 1 to 5 carbon atoms substituted with a carboxylic acid group, and the rest are hydrogen atoms. An alkyl group having 1 to 8 carbon atoms or a cycloalkyl group having 4 to 8 carbon atoms) The water-based ink according to claim 7 , wherein the resin further has a unit represented by the following general formula (3) or a unit represented by the following general formula (4).

(In the general formula (3), R ₁₄ is a hydrogen atom or a methyl group. R ₁₅ is an alkyl group having 1 to 16 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and a primary to tertiary amino group. It has an alkyl group having 1 to 6 carbon atoms substituted with, a group in which an alkylene group having 1 to 6 carbon atoms and a fluoroalkyl group having 1 to 10 carbon atoms are bonded, or an alkylene group having 1 to 6 carbon atoms and a siloxane structure. The group is a bonded group)

(In the general formula (4), R ₁₆ is a hydrogen atom or a methyl group. R ₁₇ is an alkylene group having 2 to 6 _{carbon atoms. R 18} is a hydrogen atom and an alkyl having 1 to 18 carbon atoms. A group or a cycloalkyl group having 3 to 10 carbon atoms) The invention according to any one of claims 1 to 8 , wherein the content (% by mass) of the resin is 0.05 times or more and 0.50 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. Water-based ink. The water-based ink according to any one of claims 1 to 9 , wherein the content (% by mass) of the resin is 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. An ink cartridge including an ink and an ink accommodating portion for accommodating the ink.
An ink cartridge according to any one of claims 1 to 10, wherein the ink is the water-based ink. An inkjet recording method in which ink is ejected from an inkjet recording head and an image is recorded on a recording medium.
The inkjet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 10.

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