JP6882046B2 - 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. In addition, business documents often come into contact with and rub against other business documents, books, and stationery. Therefore, the ink used in such an application is required to be able to record an image having excellent scratch resistance.

Further, when an image of photographic image quality is recorded by an inkjet recording method, a pigment ink is often used from the viewpoint of enhancing the light resistance and water resistance of the image. It is known that in an image recorded on a recording medium using a pigment ink, a so-called bronze phenomenon in which light of a color different from the original color of the pigment is observed depending on the observation angle is likely to occur. The bronze phenomenon is a phenomenon that occurs because the refractive index of the pigment present on the recording medium on the particle surface has wavelength dependence. Then, from the viewpoint of improving the quality of the image recorded with the pigment ink, reduction of the bronze phenomenon (improvement of bronze resistance) is required. For the above technical problems, for example, an ink to which resin particles are added 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. 2011-074321 Japanese Unexamined Patent Publication No. 8-151544

As a result of the studies by the present inventors, even when the inks proposed in Patent Documents 1 and 2 are used, the scratch resistance of the image recorded on the recording medium such as plain paper and the recording medium such as coated paper are used. It turned out that it was difficult to achieve both the bronze resistance and the bronze resistance of the images recorded in.

Therefore, an object of the present invention is to provide a water-based ink capable of recording an image having excellent scratch resistance and bronze resistance. 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, wherein the pigment contains lipopolysaccharide .

According to the present invention, it is possible to provide a water-based ink capable of recording an image having excellent scratch resistance and bronze resistance. 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.).

An important feature of the ink of the present invention is that it contains a pigment containing a compound (hereinafter, also referred to as "polysaccharide compound") having a structure in which at least two structures represented by the general formula (1) are glycosidic bonded. Has. 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 investigated the reason why it is difficult to achieve both scratch resistance and bronze resistance of an image. In order to improve the scratch resistance of the image, it is considered necessary that the binding component such as resin is evenly present on the particle surface of the pigment. The ink proposed in Patent Document 1 contains pigments and resin particles. When the ink is applied to the recording medium, the liquid components evaporate and permeate, causing vigorous flow in the ink droplets. The pigment and the resin particles are dispersed independently of each other, and the flow causes bias in the ink droplets, resulting in impaired image uniformity. In addition, the bias of the resin particles also causes a bias in the scratch resistance of the image.

On the other hand, in order to suppress the bronze phenomenon, it is considered necessary to suppress the wavelength dependence of the refractive index on the particle surface of the pigment. In the case of the inks proposed in Patent Documents 1 and 2, since the resin and the pigment are likely to be unevenly distributed independently, it is difficult to suppress the bronze phenomenon. 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.

First, the present inventors examined the conditions under which the pigment is not biased even by the violent flow generated after the ink is applied to the recording medium. As a result, it was found that it is important to make the pigment and the recording medium interact uniformly. Next, the conditions for suppressing the wavelength dependence of the refractive index on the particle surface of the pigment were examined. As a result, it was found that it is important to make the particle surface of the pigment and the resin component interact uniformly. Then, it was found that it is necessary to use a pigment containing a polysaccharide compound in order to cause a uniform interaction between the pigment and the recording medium and a uniform interaction between the particle surface of the pigment and the resin component. did.

The present inventors speculate as follows about a mechanism capable of recording an image having excellent scratch resistance and bronze resistance by adopting the above configuration. When ink is applied to the recording medium, the evaporation and penetration of the liquid component increases the flow velocity of the liquid component outside the pigment. Therefore, according to Bernoulli's theorem (the principle of the aspirator), the polysaccharide compound contained in the pigment elutes from the pigment. The polysaccharide compound eluted from the pigment forms a hydrogen bond with the cellulose constituting the recording medium. As a result, the pigments are evenly distributed on the recording medium.

Further, since the evaporation and permeation of the liquid component in the ink applied to the recording medium occurs by the same mechanism as described above regardless of the type of the recording medium, the polysaccharide compound contained in the pigment elutes from the pigment. .. Therefore, when the resin is contained in the ink, the polysaccharide compound eluted from the pigment is hydrogen-bonded with a bond such as an ester bond, a urethane bond, an amide bond, or an ether bond that the resin usually has. As a result, the resin is evenly arranged on the recording medium, and the binder effect of the resin is uniformly exhibited. Further, the resin is evenly distributed on the surface of the pigment particles. Therefore, the wavelength dependence of the refractive index on the particle surface of the pigment is suppressed. It is considered that an image having excellent scratch resistance and bronze resistance is recorded by the occurrence of these actions.

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, whereby the polysaccharide compound, the recording medium and the resin are used. It is important to generate the interaction of.

<Water-based ink>
The ink of the present invention is a water-based ink for inkjet containing a pigment and a resin. 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 having a structure 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 glycosidic-bonded. 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 the ink contains a resin, the carboxylic acid group forms a hydrogen bond with a bond such as an ester bond, a urethane bond, an amide bond, or an ether bond that the resin usually has, so that the scratch resistance of the image can be further enhanced.

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 interaction between the eluted polysaccharide compound and the recording medium or resin is weakened, and the scratch resistance and bronze resistance 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. For this reason, the ejection stability may not be sufficiently obtained, the ink applied to the recording medium may be biased, and the scratch resistance of the image may not be sufficiently obtained.

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 resin interacts with the liberated polysaccharide compound in the ink, so that the interaction between the recording medium and the polysaccharide compound is less likely to occur, resulting in scratch resistance and scratch resistance. Bronze may not be obtained sufficiently. 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 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 easily adheres to the filter of the ink supply path. Become. 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 dispersion method is not particularly limited. For example, a resin-dispersed pigment using a resin as a dispersant, a self-dispersing pigment in which a hydrophilic group is bonded to the particle surface of the pigment, or the like can be used. Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the surface of the pigment particles, a microcapsule pigment in which the surface of the pigment particles is coated with a resin or the like can be used. The resin used as the dispersant for the pigment is preferably not crosslinked. Pigments having different dispersion methods may be used in combination for the ink. Among them, (i) a self-dispersing pigment in which an anionic group is bonded directly to the particle surface of the pigment or via another atomic group, or (ii) a resin as a dispersant is physically applied to the particle surface of the pigment. It is preferable to use a resin-dispersed pigment that is adsorbed and disperses the pigment by the action of this resin.

From the viewpoint of improving the optical density of the image, it is preferable to use the self-dispersing pigment of (i) above. In this case, since a resin for dispersing the pigment is basically unnecessary, the resin is used as an additive resin, not as a resin dispersant. Further, from the viewpoint of improving the scratch resistance and bronze resistance of the image, it is preferable to use the resin-dispersed pigment of the above (ii). When a resin (resin dispersant) is used to disperse the pigment, it is preferable that the ink contains a resin (additional resin) different from the resin dispersant. Then, it is preferable to hydrogen bond the polysaccharide compound as described above by utilizing the ester bond, urethane bond, amide bond, ether bond and other bonds of the added resin. The difference between the resin dispersant and the added resin means that at least one of the types of constituent units, their proportions, the acid value of the resin, and the physical property values such as the weight average molecular weight thereof is different. Although details will be described later, a small part of the resin dispersant and the added resin can be exchanged in the ink within the range of the general pH and surface tension of the water-based ink, but it can be ignored because it is a very small amount. Degree.

(Resin dispersant)
The ink of the present invention may contain a resin dispersant as a dispersant for dispersing the pigment in an aqueous medium. 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. Examples of the resin dispersant include acrylic resin, urethane resin, urea resin and the like. Of these, an acrylic resin is preferable, and an acrylic resin having a hydrophilic unit and a hydrophobic unit as constituent units is more preferable.

The hydrophilic unit is a unit having a hydrophilic group such as an acid group or a hydroxy group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include an acidic monomer having a carboxylic acid group such as (meth) acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anions such as anhydrides and salts of these acidic monomers. Sex Monomer; Monomer having a hydroxy group such as 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate; Ethylene such as methoxy (mono, di, tri, poly) ethylene glycol (meth) acrylate Monomers having an oxide group and the like can be mentioned. Examples of the cation constituting the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium and organic ammonium.

The hydrophobic unit is a unit that does not have a hydrophilic group such as an acid group or a hydroxy group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group such as an acid group or a hydroxy group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; ethyl (meth) acrylate, methyl (meth) acrylate, and (meth) acrylic acid ( Examples thereof include (meth) acrylic acid ester-based monomers such as iso) propyl, (meth) acrylic acid (n-, iso-, t-) butyl, and (meth) acrylic acid 2-ethylhexyl.

The resin dispersant preferably has a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from a monomer having an aliphatic group or an aromatic ring. Further, the resin dispersant preferably has a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from at least one monomer of styrene and α-methylstyrene. These resin dispersants are suitable because they are particularly prone to interaction with pigments.

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). 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. 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%. Above all, it is particularly preferable that it is 0.5% by mass or more and 1.0% by mass or less. The content (mass%) of the resin dispersant in the ink is preferably 0.05 times or more and 0.50 times or less, preferably 0.10 times, in terms of the mass ratio with respect to the pigment content (mass%). It is more preferably 0.30 times or more.

(resin)
The ink of the present invention contains a resin. The resin may be either a water-soluble resin soluble in an aqueous medium or a water-dispersible resin (water-insoluble resin) that may exist in a state of being dispersed in particles in the aqueous medium. As the resin, it is preferable to use a resin having at least one bond selected from the group consisting of an ester bond, a urethane bond, an amide bond, and an ether bond. Of these, it is preferable to use a resin having an ester bond or a urethane bond. Further, since the scratch resistance and bronze resistance of the image tend to be good, it is preferable to use at least one of urethane resin, block copolymer, and resin particles. Further, it is more preferable to use at least two kinds of urethane resin, block copolymer, and resin particles, and it is particularly preferable to use all three kinds. When a resin dispersant is used to disperse the pigment, the "resin" described in this item is an "additional resin". The content (mass%) of the resin in the ink is preferably 0.5% by mass or more and 20.0% by mass or less, and 1.0% by mass or more and 15.0% by mass or less, based on the total mass of the ink. Is more preferable. Above all, it is particularly preferable that it is 1.0% by mass or more and 10.0% by mass or less.

[Resin having an ester bond]
Examples of the ester bond include a carboxylic acid ester group, a sulfonic acid ester group, a phosphoric acid ester group, a phosphonic acid ester group, and the like, and a carboxylic acid ester group is preferable. A resin having a unit having an ester bond (preferably an acrylic resin) is referred to as a "resin having an ester bond". As the resin having an ester bond, a resin having a unit derived from (meth) acrylic acid ester can be preferably used. It is preferable to use a resin having a unit derived from the (meth) acrylic acid ester from the viewpoint that a wide variety of (meth) acrylic acid esters can be selected and physical properties such as molecular weight can be easily controlled.

Examples of the (meth) acrylate ester include an ester having a linear or branched alkyl chain having 1 to 12 carbon atoms such as methyl (meth) acrylate and 2-ethylhexyl (meth) acrylate; benzyl (meth) acrylate and the like. Ester having an aromatic ring; an ester having a cycloalkyl having 3 to 18 carbon atoms such as cyclohexyl (meth) acrylate; an ester having a hydroxy group such as 2-hydroxyethyl (meth) acrylate; N (meth) acrylate. , N-Esters with amino groups such as dimethylaminoethyl; Esters containing dimethylsiloxane structure (trade name "Silaplane" series (manufactured by JNC), etc.); Esters containing fluorine atoms (trade name "CHEMINOX" series (manufactured by Unimatec) ) Etc.); Known (meth) acrylate esters such as polyfunctional esters such as di (meth) acrylate ethylene can be used.

As the resin having an ester bond, a copolymer of a plurality of types of (meth) acrylic acid esters or a copolymer of a (meth) acrylic acid ester and a monomer other than the (meth) acrylic acid ester should be used. You can also. As the monomer other than the (meth) acrylic acid ester, any known monomer can be used. Among them, it is preferable to use an acid monomer from the viewpoint of imparting water solubility or water dispersibility to the resin.

Resins having an ester bond that can be used in water-based inks for inkjet are usually classified into random copolymers, block copolymers, and graft copolymers according to the arrangement of units. Further, it is classified into a water-soluble resin and a water-dispersible resin (resin particles) according to its hydrophilicity. As the resin having an ester bond, a block copolymer is preferable to a random copolymer or a graft copolymer. By using a block copolymer, when interacting with the pigment via the polysaccharide compound eluted from the pigment, the blocks having a high affinity with the particle surface of the pigment are selectively oriented to the particle surface of the pigment. It will be. As a result, the surface of the pigment particles is covered with the block copolymer to form a thin film, so that the occurrence of the bronze phenomenon can be suppressed more effectively. Further, the resin having an ester bond is preferably a water-dispersible resin (resin particles) rather than a water-soluble resin. When the resin particles are used, the resin particles having a large binder effect are arranged between the pigment particles when interacting with the pigment via the polysaccharide compound eluted from the pigment. As a result, the scratch resistance of the image can be further improved.

Classification by sequence of units and classification by hydrophilicity can overlap. In the present invention, it is preferable to use a resin having an ester bond classified as follows.
(1) Block copolymer, preferably water-soluble (2) Resin particles, preferably random copolymer (3) Other resins other than the above

[Block copolymer having an ester bond]
A block copolymer having a unit derived from a (meth) acrylic acid ester has a structure in which a plurality of blocks including a block composed of one or more kinds of (meth) acrylic acid esters are bonded. That is, a diblock copolymer, a triblock copolymer, and a multi-block copolymer in which a plurality of blocks including a block composed of one kind of (meth) acrylic acid ester are bonded can be used. Further, a block copolymer in which any block constituting these block copolymers is replaced with a block composed of two or more kinds of (meth) acrylic acid esters can be used. One block in a block copolymer can be composed of one type or two or more types of units. Among them, it is preferable to use a block copolymer in which one block is composed of only one type (only) unit.

Block copolymers can be synthesized by a living radical polymerization method, a living anion polymerization method, and a living polymerization method known as a living cationic polymerization method. Among them, it is preferable to synthesize a block copolymer by the living radical polymerization method from the viewpoint of compatibility with a wide variety of (meth) acrylic acid esters. As the living radical polymerization method, any known method such as NMP method, ATRP method, RAFT method, TERP method, SBRP method, BIRP method, CMRP method and RTCP method can be used.

In the living radical polymerization method, the polymerization rate of the first block is calculated from the concentration of the residual monomer measured by dry solid content or gas chromatography, and when the consumption of the monomer is confirmed, the second block is used. The monomers constituting the block are added to allow the polymerization reaction to proceed. As a result, a diblock copolymer in which the first block and the second block are bonded can be obtained. Further, by repeating the above operation a plurality of times, a block copolymer such as a triblock copolymer in which a plurality of blocks are bonded can be obtained.

The block copolymer preferably has a block having a carboxylic acid group. The carboxylic acid group in the block copolymer not only functions as a functional group that dissolves the block copolymer in the liquid medium of the ink, but also partially functions as a hydrogen-bonding site on the recording medium. Therefore, together with the unit derived from the (meth) acrylic acid ester, it can interact with the pigment via a recording medium or a polysaccharide compound to further improve the scratch resistance and bronze resistance of the image.

The content (mass%) of the block copolymer in the ink is preferably 0.05 times or more and 2.00 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. If the mass ratio is less than 0.05 times, since the amount of block copolymer is small with respect to the pigment, a sufficient binder effect may not be produced, and the scratch resistance of the image may not be sufficiently obtained. Further, the resin may not be able to cover the pigment uniformly, and the bronze resistance of the image may not be sufficiently obtained. On the other hand, when the mass ratio is more than 2.00 times, a block copolymer having a weak interaction with the polysaccharide compound eluted from the pigment is likely to exist. As a result, bias is likely to occur between the pigment and the block copolymer, and the scratch resistance and bronze resistance of the image may not be sufficiently obtained. The content (mass%) of the block copolymer in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and preferably 0.5% by mass or more and 2.5% by mass or less. More preferred.

The weight average molecular weight of the block copolymer is preferably 1,000 or more and 30,000 or less, and more preferably 5,000 or more and 20,000 or less. The weight average molecular weight of the block copolymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). The acid value of the block copolymer is preferably 100 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 120 mgKOH / g or more and 200 mgKOH / g or less. The volume average particle size of the block copolymer measured by the dynamic light scattering method is preferably 30 nm or less, and more preferably 15 nm or less. The volume average particle size may be 0 nm. That is, the block copolymer may be water-soluble rather than resin particles capable of forming particles showing a certain particle size when measured by a dynamic light scattering method.

[Resin particles having an ester bond]
A resin having a unit derived from a (meth) acrylic acid ester constituting the resin particles can be obtained by polymerizing one or more kinds of (meth) acrylic acid esters. It can also be obtained by phase inversion emulsification of a resin having a unit derived from a (meth) acrylic acid ester. The resin particles can be obtained by emulsion polymerization using a surfactant, miniemulsion polymerization, and soap-free polymerization using no surfactant. In emulsion polymerization and soap-free polymerization, resin particles composed of a plurality of resins can be prepared by appropriately changing the type and amount of monomers supplied during the polymerization reaction.

As the surfactant, an anionic surfactant, a nonionic surfactant, a cationic surfactant and the like can be used. Of these, anionic surfactants and nonionic surfactants are preferable. Further, a reactive surfactant having a vinyl group can also be used. Since the reactive surfactant binds to the resin particles by the polymerization reaction, it is preferable in that the surfactant is hard to be released.

The volume average particle diameter of the resin particles measured by the dynamic light scattering method is preferably more than 0 nm, more preferably more than 30 nm, and particularly preferably 50 nm or more and 300 nm or less. When the volume average particle diameter of the resin particles is less than 50 nm, the number of resin particles per unit mass becomes relatively large. For this reason, resin particles having a weak interaction with the polysaccharide compound eluted from the pigment are likely to exist, and the interaction state between the pigment and the resin particles is biased, resulting in scratch resistance and bronze resistance of the image. It may not be obtained sufficiently. On the other hand, if the volume average particle diameter of the resin particles is more than 300 nm, the ejection stability of the ink cannot be sufficiently obtained, and the application of the ink to the recording medium tends to be biased. Therefore, the scratch resistance of the image may not be sufficiently obtained.

The content (mass%) of the resin particles in the ink is preferably 0.10 times or more and 10.00 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. If the mass ratio is less than 0.10 times, since the amount of resin particles is small with respect to the pigment, a sufficient binder effect may not be produced, and the scratch resistance of the image may not be sufficiently obtained. Further, the resin particles may not be able to cover the pigment uniformly, and the bronze resistance of the image may not be sufficiently obtained. On the other hand, when the mass ratio is more than 10.00 times, resin particles having a weak interaction with the polysaccharide compound eluted from the pigment are likely to be present. As a result, bias is likely to occur between the pigment and the resin particles, and the scratch resistance and bronze resistance of the image may not be sufficiently obtained. The content (mass%) of the resin particles in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 0.5% by mass or more and 10.0% by mass or less. ..

The weight average molecular weight of the tetrahydrofuran-dissolved component of the resin particles is preferably 10,000 or more and 2,000,000 or less, and more preferably 50,000 or more and 500,000 or less. The weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). The tetrahydrofuran-dissolved component of the resin particles is a component contained in the filtrate after adding the resin to tetrahydrofuran so that its content is 1.0% by mass, stirring at a temperature of 25 ° C. for 1 hour, and then filtering with a filter. Is the "tetrahydrofuran-dissolved component". A filter having a pore size of about 0.45 μm can be used. Some of the resin particles do not have to be dissolved in tetrahydrofuran. The component dissolved in tetrahydrofuran is the non-crosslinked portion of the resin particles.

The glass transition temperature of the resin particles is preferably more than 0 ° C. and 200 ° C. or lower, and more preferably 10 ° C. or higher and 150 ° C. or lower. The glass transition temperature of the resin particles can be measured, for example, according to the method shown below. That is, after the resin taken out from the ink is dried at a temperature of 60 ° C., 2 mg is separated and sealed in an aluminum container to prepare a measurement sample. This measurement sample is subjected to thermal analysis using a differential scanning calorimetry (DSC) with the temperature program shown below. First, the temperature is raised to 200 ° C. at 10 ° C./min, and then the temperature is further lowered from 200 ° C. to −50 ° C. at 5 ° C./min. Next, thermal analysis is performed while raising the temperature from −50 ° C. to 200 ° C. at 10 ° C./min to measure the glass transition temperature. The glass transition temperature can be measured using a device such as a differential scanning calorimeter (trade name “DSC Q1000”, manufactured by TA instruments). Of course, the measuring device and the temperature program are not limited to the above.

The acid value of the resin particles is preferably 0 mgKOH / g or more and 150 mgKOH / g or less, more preferably 10 mgKOH / g or more and 100 mgKOH / g or less, and particularly preferably 10 mgKOH / g or more and 50 mgKOH / g or less. .. The resin particles may be either a random copolymer or a block copolymer, but are preferably a random copolymer.

[Other resins with ester bonds]
As the resin having an ester bond other than the block copolymer and the resin constituting the resin particles, a random copolymer or a graft copolymer can be used. The random copolymer can be synthesized by polymerizing one or more monomers containing (meth) acrylic acid ester in the presence of a polymerization initiator. Examples of the polymerization initiator include persulfates such as sodium persulfate; organic peroxides such as dicumyl peroxide; azo compounds such as 2,2'-azobis (2-methylbutyronitrile); and inorganic peroxides. Oxides and the like can be mentioned. In addition, a chain transfer agent can be used together with the polymerization initiator for controlling the molecular weight distribution and introducing the terminal functional group. Chain transfer agents include monofunctional thiols such as 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropionic acid, 6-mercaptohexanol, 4-acetamidobenzenethiol, 2- (2-mercaptoethoxy) ethanol, and dodecyl mercaptan. Can be mentioned. In addition, by using polyfunctional thiols such as 1,3-dimercaptopropanol, trimethylolpropane trithioglycolate, pentaerythritol tetrakisthiopropionate, and dipentaerythritol hexaxthiopropionate as chain transfer agents, stars can be used. Shaped resins can also be manufactured.

Examples of the method for synthesizing the graft copolymer include the following methods. Of these, the macromonomer method of (iii) is preferable from the viewpoint of ease of synthesis.
(I) A grafting-from method in which a monomer constituting a side chain is polymerized from a starting point of polymerization introduced into a polymer constituting the main chain.
(Ii) A polymer reaction method in which a polymer constituting a main chain and a polymer constituting a side chain are coupled to each other.
(Iii) Examples thereof include a macromonomer method in which a monomer constituting the main chain and a macromonomer constituting the side chain are copolymerized.

[Resin with urethane bond]
The urethane bond is a bond represented by −NH—C (= O) O−. A resin having a unit having a urethane bond is called a "resin having a urethane bond". A resin having a urethane bond (urethane resin) is, in a broad sense, a resin synthesized using polyisocyanate. The urethane resin is preferably a resin synthesized by using polyisocyanate and a polyol. If necessary, a urethane resin synthesized by using a cross-linking agent or a component such as a polyol or a polyamine as a chain extender is also preferable. The urethane resin synthesized using these components is mainly composed of two segments (hard segment and soft segment). The hard segment is composed of units derived from polyisocyanate, short-chain polyol (polyol having an acid group, etc.), polyamine, cross-linking agent, chain extender, etc., and is a segment that mainly contributes to the strength of urethane resin. .. On the other hand, the soft segment is composed of a unit derived from a long-chain polyol or the like, and is a segment that mainly contributes to the flexibility of the urethane resin.

As the polyisocyanate, a compound having two or more isocyanate groups can be used. Specific examples of the polyisocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and aromatic aliphatic polyisocyanates. Of these, aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate and isophorone diisocyanate are preferable. As the polyol, a compound having two or more hydroxy groups can be used. Specific examples of the polyol include a polyol having no acid group such as a polyester polyol, a polycarbonate polyol, and a polyether polyol; a polyol having an acid group; a polyhydroxypolyacetal; a polyhydroxypolyacrylate; a polyhydroxypolyacrylate; a polyhydroxypolythioether, etc. Can be mentioned. As the urethane resin, a urethane resin having a unit derived from a polyether polyol, a unit derived from a polyol having an acid group, or the like is preferable. The number average molecular weight of the units derived from the polyether polyol is preferably about 400 to 4,000. Further, the acid group contained in the polyol having an acid group is preferably a carboxylic acid group. Specific examples of the polyol having a carboxylic acid group include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid. As the chain extender, a compound having two or more hydroxy groups or amino groups in one molecule can be used.

The volume average particle size of the urethane resin measured by the dynamic light scattering method is preferably 15 nm or less. If the volume average particle size of the urethane resin is more than 15 nm, the ink ejection stability may not be sufficiently obtained. For this reason, the application of ink to the recording medium tends to be biased, and the scratch resistance of the image may not be sufficiently obtained. The volume average particle size of the urethane resin in the ink may be 0 nm. That is, the urethane resin may be water-soluble rather than resin particles capable of forming particles showing a certain particle size when measured by a dynamic light scattering method.

The content (mass%) of the urethane resin in the ink is preferably 0.05 times or more and 2.00 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. If the mass ratio is less than 0.05 times, the urethane resin is less than the pigment, so that a sufficient binder effect does not occur, and the scratch resistance of the image may not be sufficiently obtained. Further, the urethane resin may not be able to cover the pigment uniformly, and the bronze resistance of the image may not be sufficiently obtained. On the other hand, when the mass ratio is more than 2.00 times, a urethane resin having a weak interaction with the polysaccharide compound eluted from the pigment is likely to exist. As a result, bias is likely to occur between the pigment and the urethane resin, and the scratch resistance and bronze resistance of the image may not be sufficiently obtained. The content (mass%) of the urethane resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 2.5% by mass or less. ..

The weight average molecular weight of the urethane resin is preferably 3,000 or more and 50,000 or less, and more preferably 10,000 or more and 40,000 or less. The weight average molecular weight of the urethane resin is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). The acid value of the urethane resin is preferably 30 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 50 mgKOH / g or more and 150 mgKOH / g or less.

[Resin having an amide bond]
The amide bond is a bond represented by -C (= O) -NH-. A resin having a unit having an amide bond (preferably an acrylic resin) is called a "resin having an amide bond". As the resin having an amide bond, a polymer of an amide monomer having a vinyl group can be preferably used from the viewpoint that the arrangement of the amide bond in the resin can be easily controlled. Specific examples of the amide monomer having a vinyl group include (meth) acrylamide, N-vinylacetamide, and dimethylaminoethyl (meth) acrylate. The resin having an amide bond may be a copolymer of a plurality of types of amide monomers, or a copolymer of an amide monomer and a monomer other than the amide monomer. As the monomer other than the amide monomer, a known monomer can be used. As the monomer other than the amide monomer, it is preferable to use an acid monomer from the viewpoint of imparting water solubility or water dispersibility to the resin. In the present invention, for convenience, the content of a resin having an ester bond as well as an amide bond in its structure shall be calculated as "a resin having an amide bond".

[Resin having an ether bond]
The ether bond is a bond represented by −O−. A resin having a unit having an ether bond (preferably an acrylic resin) is referred to as a "resin having an ether bond". As the resin having an ether bond, a polymer of an ether monomer having a vinyl group or a resin having a unit having a polyether chain can be preferably used. It is preferable to use a polymer of an ether monomer having a vinyl group from the viewpoint that the arrangement of ether bonds in the resin can be easily controlled. Specific examples of the ether monomer having a vinyl group include ethyl vinyl ether, hydroxyethyl vinyl ether, methoxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, and phenoxyethyl (meth) acrylate. .. The resin having an ether bond may be a copolymer of a plurality of types of ether monomers or a copolymer of an ether monomer and a monomer other than the ether monomer. As the monomer other than the ether monomer, a known monomer can be used. As the monomer other than the ether monomer, it is preferable to use an acid monomer from the viewpoint of imparting water solubility or water dispersibility to the resin. In the present invention, for convenience, the content of a resin having an ester bond as well as an ether bond in its structure shall be calculated as "a resin having an ether bond".

[Neutralizer]
The resin contained in the ink of the present invention may be either a water-soluble resin or a water-dispersible resin. When the resin has an acid group, the acid group is preferably neutralized with a base. Examples of the base include ammonium; organic ammonium; alkali metal ions and the like. Neutralizing agents that can be used to neutralize acid groups with such bases include ammonia; N, N-dimethylethanolamine, N, N-diethylethanolamine, diethanolamine, triethanolamine, trimethylamine, triethylamine. Organic bases such as; inorganic bases such as potassium hydroxide, sodium hydroxide, lithium hydroxide; and the like.

[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 contains a resin dispersant and an additive resin, the resin dispersant and the additive resin can be separated according to the method shown below. 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 base material (matte, drawing paper, etc.) 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 canvas texture, 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.

<Manufacturing of pigments>
Each component shown in Table 3 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 dispersions I-1 to I-15 and I-17 to I-28)
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). As the resin (dispersant), a resin synthesized by the method described later was used. Then, an appropriate amount of ion-exchanged water was added to obtain each pigment dispersion.
-Pigments of the types shown in Table 4: 20.0 parts-Liquids of the types of resins shown in Table 4: 30.0 parts-Ion-exchanged water: 50.0 parts

(Pigment Dispersion Liquid I-16)
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-16 having a pigment content of 15.0%.

(Pigment Dispersion Liquid I-29)
A pigment dispersion liquid I-29 having a pigment content of 15.0% was obtained in the same manner as in the preparation of the pigment dispersion liquid I-16 except that the pigment 26 was used.

(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 Table 4.

(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 5, 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 5-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.

<Synthesis of resin>
(Resin R1-10)
Water-soluble resins R1-10, which are random copolymers having various bonds, were synthesized according to the procedure shown below. 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 6, 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. 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 meanings of the abbreviations in Table 6 are shown below.
St: Styrene nBA: n-Butyl acrylate PME200: Methoxypolyethylene glycol methacrylate (manufactured by NOF)
NVA: N-vinylacetamide 2-EHV: 2-ethylhexyl vinyl ether AA: Acrylic acid Polymerization initiator 1: Trade name "Percadox L-W75 (LS)" (manufactured by Kayaku Akzo, dibenzoyl peroxide, purity 75%) 5 Solution of 0.0 parts dissolved in 10.0 parts of isopropanol Polymerization initiator 2: Trade name "V-59" (manufactured by Wako Pure Chemical Industries, Ltd., 2,2'-azobis (2-methylbutyronitrile))
Chain transfer agent 1: A solution of 1.9 parts of 1-thioglycerol in 10.0 parts of isopropanol Chain transfer agent 2: Dipentaerythritol Hexakisthiopropionate 10.0 parts

(Resin G1-5)
Water-soluble resins G1 to 5, which are graft copolymers having an ester bond, were synthesized according to the procedure shown below. After putting 100.0 parts of methyl ethyl ketone in a flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer, the temperature was raised to 80 ° C. with stirring under a nitrogen atmosphere. A mixture of 3.0 parts of 3-mercaptopropionic acid and a mixture of 3.0 parts of 3-mercaptopropionic acid and 0.3 parts of a polymerization initiator dissolved in 10.0 parts of methyl ethyl ketone are prepared for the types and amounts of the monomers for macromonomers shown in Table 7. Got ready. As the polymerization initiator, 2,2'-azobis (2-methylbutyronitrile) (trade name "V-59", manufactured by Wako Pure Chemical Industries, Ltd.) was used. The prepared mixed solution and solution were added dropwise to the flask over 2 hours each while maintaining the temperature at 80 ° C. The internal temperature was maintained at 80 ° C., and the mixture was stirred for 4 hours to obtain a reaction product.

The obtained reaction product was put into methanol to precipitate a resin, which was then filtered and washed with water to obtain a prepolymer having a carboxylic acid group at the terminal. 20.0 parts of the obtained prepolymer was dissolved in 60.0 parts of N, N-dimethylacetamide, 6.2 parts of glycidyl methacrylate, 0.5 parts of N, N-dimethyldodecylamine, and hydroquinone (polymerization inhibitor). ) 0.1 part was added. The temperature was raised to 130 ° C. and the mixture was stirred for 6 hours to obtain a reaction product. The obtained reaction product was put into methanol to precipitate a resin, and then washed and dried with water to obtain a macromonomer having a weight average molecular weight of 2,000 having a methacryloyl group at the terminal.

After putting 200.0 parts of methyl ethyl ketone in a flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer, the temperature was raised to 80 ° C. with stirring under a nitrogen atmosphere. A mixture of 50.0 parts of the obtained macromonomer (solid content), the types and amounts of monomers shown in Table 7, and a solution of 2.0 parts of the polymerization initiator in 10.0 parts of methyl ethyl ketone were added. Got ready. As the polymerization initiator, 2,2'-azobis (2-methylbutyronitrile) (trade name "V-59", Wako Pure Chemical Industries, Ltd.) was used. The prepared mixed solution and solution were added dropwise to the flask over 2 hours each while maintaining the temperature at 80 ° C. After maintaining the internal temperature at 80 ° C. and stirring for 4 hours, 200.0 parts of a 2 mol / L potassium hydroxide ethanol solution was added, and methyl ethyl ketone was removed under reduced pressure.

1.0 part of trifluoroacetic acid was added and the mixture was stirred for 2 hours to hydrolyze the t-butyl group. 200.0 parts of 3 mol / L hydrochloric acid was added, and the precipitated resin was separated, washed with water and dried to obtain resins G1 to G5. 0.9 equivalents of potassium hydroxide and an appropriate amount of ion-exchanged water were added to the acid value of the obtained resin to obtain a liquid having a resin (solid content) content of 20.0%. The meanings of the abbreviations in Table 7 are shown below.
St: Styrene nBA: n-butyl acrylate tBA: t-butyl acrylate

(Resin B1-7)
According to the procedure shown below, water-soluble resins B1 to B7, which are block copolymers having an ester bond, were synthesized. The inside of a four-necked flask equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, and a reflux tube was replaced with nitrogen. In this flask, 100.0 parts of methyl ethyl ketone, a mixture of the monomers of the type and amount shown in Table 8 of the first block, 0.6 parts of ethyl 2-bromoisobutyrate, and 1.5 parts of tetramethylethylenediamine were placed. .. The temperature was raised to 40 ° C. and nitrogen was replaced for 30 minutes. After raising the temperature to 75 ° C. in a nitrogen atmosphere, 0.6 part of cuprous chloride was added to start the reaction. The solution was withdrawn at regular intervals, and the dry solid content in the solution was measured to calculate the polymerization rate. After confirming that the polymerization rate was 95% or more, a mixture of the monomers of the type and amount shown in Table 8 of the second block was added, and the reaction was continued.

After confirming that the final polymerization rate was 98%, 50.0 parts of methyl ethyl ketone was added, and the flask was cooled in a water bath to stop the reaction. The reaction product was filtered through activated alumina to remove the copper complex. The precipitate formed by adding the filtrate to a large amount of methanol was vacuum dried at 40 ° C. for 24 hours to obtain resins B1 to 7. 0.9 equivalents of potassium hydroxide and an appropriate amount of ion-exchanged water were added to the acid value of the resin to obtain a liquid having a resin (solid content) content of 20.0%.

(Resin B8)
A water-soluble resin B8, which is a block copolymer having an ester bond, was synthesized according to the procedure shown below. The inside of a four-necked flask equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, and a reflux tube was replaced with nitrogen. In this flask, 100.0 parts of methyl ethyl ketone, a mixture of the first block monomers of the type and amount shown in Table 8, 0.5 parts of cumyldithiobenzoate, and 0.1 parts of azobisisobutyronitrile I put it in. After nitrogen substitution at 25 ° C. for 30 minutes, the temperature was raised to 75 ° C. in a nitrogen atmosphere to start the reaction. The solution was withdrawn at regular intervals, and the dry solid content in the solution was measured to calculate the polymerization rate. After confirming that the polymerization rate was 95% or more, a mixture of the monomers of the type and amount shown in Table 8 of the second block was added, and the reaction was continued.

After confirming that the final polymerization rate was 98%, 50.0 parts of methyl ethyl ketone was added, and the flask was cooled in a water bath to stop the reaction. The reaction solution was added to a large amount of methanol, and the resulting precipitate was vacuum dried at 40 ° C. for 24 hours to obtain resin B8. 0.9 equivalents of potassium hydroxide and an appropriate amount of ion-exchanged water were added to the acid value of the resin to obtain a liquid having a resin (solid content) content of 20.0%. The meanings of the abbreviations in Table 8 are shown below.
St: Styrene BzMA: Benzyl methacrylate MMA: Methyl methacrylate HEMA: 2-Hydroxyethyl methacrylate MAA: Methacrylic acid

(Resin E1-17)
Resins E1 to 17, which are resins (resin particles) having an ester bond, were synthesized according to the procedure shown below. A mixture was obtained by mixing 150.0 parts of the surfactant, monomer, and ion-exchanged water shown in Table 9 with a homogenizer (trade name "T50D Ultratarax", manufactured by IKA). 50.0 parts of the mixture was placed in a flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer, and the temperature was raised to 90 ° C. with stirring under a nitrogen atmosphere. The balance of the mixture and the liquid in which 1.0 part of potassium persulfate was dissolved in 20.0 parts of ion-exchanged water were added dropwise over 2 hours. The internal temperature was maintained at 90 ° C., and the mixture was stirred for 2 hours to react to obtain a dispersion liquid containing resins E1 to 17. The pH of the obtained dispersion was adjusted to 8.5 using a 1 mol / L potassium hydroxide aqueous solution, and an appropriate amount of ion-exchanged water was added to increase the resin (solid content) content to 20.0%. Obtained a liquid that is. The glass transition temperatures of the resins E1 to 17 measured according to the above-mentioned method and the resins E18 and 19 obtained by the method described later were all in the range of 10 to 150 ° C. The meanings of the abbreviations in Table 9 are shown below.
MMA: Methyl methacrylate HEMA: 2-Hydroxyethyl methacrylate St: Styrene BzMA: Benzyl methacrylate CHMA: Cyclohexyl methacrylate FM-0711: Silaplane FM-0711 (trade name, manufactured by Chisso)
FAAC-6: 2- (Perfluorohexyl) ethyl acrylate (trade name, manufactured by Unimatec)
EGDMA: Ethylene Dimethacrylate Surfactant 1: Aqualon KH-10, Anionic Reactive Surfactant, Daiichi Kogyo Seiyaku Seisakusho 2: Adecaria Soap ER-20, Nonionic Reactive Surfactant, ADEKA Surfactant 3: Peletex 1225, Nonionic Surfactant, Miyoshi Oil and Fat Surfactant 4: FM-0711, Silicone One-Terminal Methacrylate, JNC Surfactant 5: FAAC-6, Acrylic Acid 2- (Perfluorohexyl) ethyl, made by Unimatec

(Resin E18 and 19)
Resins E18 and 19, which are resins (resin particles) having an ester bond, were synthesized according to the procedure shown below. A flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer was filled with 150.0 parts of ion-exchanged water and the first component of the type and amount shown in Table 10. After mixing the contents using a homogenizer (trade name "T50D Ultratarax", manufactured by IKA), the temperature was raised to 90 ° C. with stirring under a nitrogen atmosphere. A liquid prepared by dissolving 0.5 part of potassium persulfate in 5.0 parts of ion-exchanged water was added dropwise over 1 hour. Next, the second component of the type and amount shown in Table 10 and a liquid in which 0.5 part of potassium persulfate was dissolved in 5.0 parts of ion-exchanged water were added dropwise over 1 hour, respectively.

Regarding the resin E19, a third component of the type and amount shown in Table 10 and a liquid in which 0.5 part of potassium persulfate was dissolved in 5.0 parts of ion-exchanged water were further added dropwise over 1 hour. .. Then, the internal temperature was maintained at 90 ° C., and the mixture was stirred and reacted for 2 hours to obtain a dispersion liquid containing resins E18 and 19. The pH of the obtained dispersion was adjusted to 8.5 using a 1 mol / L potassium hydroxide aqueous solution, and an appropriate amount of ion-exchanged water was added to increase the resin (solid content) content to 20.0%. Obtained a liquid that is. The meanings of the abbreviations in Table 10 are shown below.
MMA: Methyl methacrylate EGDMA: Ethylene dimethacrylate MAA: Methacrylic acid Surfactant 1: Aqualon KH-10, anionic reactive surfactant (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)

(Resin U1-10)
Resins U1 to 10 having a urethane bond were synthesized according to the procedure shown below. Polyisocyanates and polyols of the types and amounts shown in Table 11 were placed in a flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer, and reacted at 100 ° C. for 2 hours under a nitrogen gas atmosphere. Next, the chain extender of the type and amount shown in Table 11, the polyol having an acid group, and 150.0 parts of methyl ethyl ketone were added, and while checking the residual ratio of the isocyanate group by FT-IR, until the desired residual ratio was reached. The reaction was carried out at 78 ° C. to obtain a reaction solution. After cooling the obtained reaction solution to 40 ° C., an appropriate amount of ion-exchanged water was added. Further, potassium hydroxide equivalent to the acid value was added while stirring at high speed with a homomixer. Methyl ethyl ketone was removed under reduced pressure to obtain a liquid having a resin (solid content) content of 20.0%. The meanings of the abbreviations in Table 11 are shown below.

IPDI: Isophorone diisocyanate H12MDI: 4,4'-dicyclohexylmethane diisocyanate HDI: Hexamethylene diisocyanate PES2000: Polyester polyol with a number average molecular weight of 2,000 T6002: Polyhexamethylene carbonate diol with a number average molecular weight of 2,000 (manufactured by Asahi Kasei Chemicals)
PPG2000: Polypropylene glycol with a number average molecular weight of 2,000 PTMG2000: Polytetramethylene glycol with a number average molecular weight of 2,000 PEG2000: Polyethylene glycol with a number average molecular weight of 2,000 EDA: Ethylenediamine NPG: Neopentyl glycol DMPA: Dimethylolpropionic acid

<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, the ink of Comparative Example 2 was prepared by adding 0.012% of a binding compound of peptidoglycan and lipopolysaccharide extracted by culturing Gram-negative bacteria (Escherichia coli) in addition to each component shown below. .. The characteristics of the prepared ink are shown in Tables 13-1 to 13-3.
-Pigment dispersions of the types shown in Tables 12-1 to 12-3: Amounts shown in Tables 12-1 to 12-3-Liquids containing resins of the types shown in Tables 12-1 to 12-3: Table 12-1 Amount shown in ~ 12-3 ・ Glycerin: 5.0%
-Triethylene glycol: 10.0%
-Acetyleneol E100: 0.1%
-Ion-exchanged water: The remaining amount of 100.0% of the total components

<Evaluation>
Each of the prepared inks was filled in an ink cartridge and set in an inkjet recording device (trade name "PIXUS Pro 9500", manufactured by Canon) that ejects ink from a recording head by the action of thermal 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, "AA", "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 Tables 14-1 to 14-3.

(Scratch resistance)
Using the above inkjet recording device, a solid image of 10 cm x 15 cm with a recording duty of 100% is recorded on a recording medium (plain paper, trade name "PB PAPER GF-500", manufactured by Canon) to obtain a recorded material. It was. 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. Of the evaluation results, "AA'" and "AA""are included in" AA "in the evaluation criteria shown below. However, it means that the evaluation is inferior in the order of "AA"->"AA'"->"AA"".
AA: There were no scratches on the image even after rubbing 30 times back and forth.
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.

(Bronze resistance)
Using the above inkjet recording device, a solid image of 10 cm x 15 cm with a recording duty of 100% is recorded on a recording medium (glossy paper, trade name "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon). I got a record. For the solid image portion of the obtained recorded material, a ^* ₄₅ and b ^* ₄₅ were measured according to the description in JP-A-2011-174046, and the formula B = (a ^* ₄₅ ² + b ^* ₄₅ ² ) ^0.5. The bronze value B was calculated according to the above. A variable-angle high-speed spectrophotometer (trade name "GCMS-3B type", manufactured by Murakami Color Technology Laboratory) was used for the measurement. The measurement conditions were a light source D65, a viewing angle of 2 degrees, an incident angle of 45 degrees, a reflection angle of 45 degrees, a tilt angle of 0 degrees, and an in-plane rotation angle of 0 degrees. Then, from the calculated bronze value B, the bronze resistance of the image was evaluated according to the evaluation criteria shown below. The smaller the bronze value B, the more the occurrence of the bronze phenomenon is suppressed.
AA: The bronze value B was less than 10.
A: The bronze value B was 10 or more and less than 15.
B: The bronze value B was 15 or more and less than 20.
C: The bronze value B was 20 or more.

Claims (20)

A water-based ink for inkjet that contains pigments and resins.
A water-based ink characterized in that the pigment contains lipopolysaccharide . The water-based ink according to claim 1, wherein the resin is a resin having at least one bond selected from the group consisting of an ester bond, a urethane bond, an amide bond, and an ether bond. The water-based ink according to claim 1 or 2 , 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 any one of claims 1 to 3 , 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 4 , wherein 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 5 , 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 6 , 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 7 , wherein the content (% by mass) of the resin is 0.5% by mass or more and 20.0% by mass or less based on the total mass of the ink. The water-based ink according to any one of claims 1 to 8 , wherein the resin has a unit derived from a (meth) acrylic acid ester. The water-based ink according to any one of claims 1 to 8 , wherein the resin contains at least one of a urethane resin, a block copolymer, and resin particles. The water-based ink according to claim 10 , wherein the volume average particle size of the urethane resin measured by a dynamic light scattering method is 15 nm or less. The water-based ink according to claim 10 or 11 , wherein the content (mass%) of the urethane resin is 0.05 times or more and 2.00 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. The water-based ink according to claim 10 , wherein the block copolymer has a block having a carboxylic acid group. The water-based ink according to claim 10 or 13 , wherein the content (mass%) of the block copolymer is 0.05 times or more and 2.00 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. .. The water-based ink according to claim 10 , wherein the volume average particle diameter of the resin particles measured by a dynamic light scattering method is 50 nm or more and 300 nm or less. The water-based ink according to claim 10 or 15 , wherein the content (mass%) of the resin particles is 0.10 times or more and 10.00 times or less in terms of the mass ratio with respect to the content (mass%) of the pigment. The water-based ink according to any one of claims 1 to 16 , wherein the pigment is a self-dispersing pigment in which an anionic group is bonded directly to the surface of the particles or via another atomic group. The water-based ink according to any one of claims 1 to 16 , wherein the pigment is dispersed by the action of a resin dispersant physically adsorbed on the surface of the particles. 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 18, 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 18.

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