JP2013103355A - Image recording method, and set of ink and liquid composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image recording method that forms an image having high bleed prevention effect and high scratch resistance, and to provide a set of ink and a liquid composition.SOLUTION: The image recording method includes: a step for applying ink containing pigment dispersed by the action of an anionic group; and a step for applying the liquid composition facilitating instability of the dispersed state of the pigment in the ink to the recording medium. The liquid composition has pH buffering ability to the ink, wherein a pH thereof is between 5.1 and 6.5 inclusively, and includes a first acid having pKa lower than the pH and a second acid having pKa higher than the pH, wherein the content (mol) of the first acid in 100 g of the liquid composition is 1.0×10mmol or higher, and the content (mol) of the second acid in 100 g of the liquid composition is 1.1 times or more relative to the content (mol) of the first acid.

Description

  The present invention relates to an image recording method and a set of an ink and a liquid composition.

Conventionally, in an image recording method, a two-component reaction system using a liquid composition containing a pigment ink and a reagent that destabilizes the dispersion state of the pigment in the ink has been studied for the purpose of preventing bleeding of the image. Yes. Among these two-component reaction systems, an image recording method using an acid precipitation reaction (hereinafter referred to as “acid precipitation reaction system”) has been studied (Patent Documents 1 and 2). In the ink deposition reaction system, a pigment that is stably dispersed by an electrostatic repulsion between acid-dissociable anionic groups (for example, —COO ⁻ ) in an ink is mixed with an acidic liquid composition. Then, the anionic group becomes an acid type (for example, —COOH), and the dispersion state of the pigment collapses due to loss of electrostatic repulsion, and the pigment aggregates.

  Patent Document 1 discloses that the gloss uniformity of an image is improved and the stickiness of the image is improved by an image recording method using an ink containing a pigment and a liquid composition containing an organic acid as a reactant. Has been. Patent Document 2 discloses an ink containing a pigment dispersed with an anionic dispersant and a pH of 3.5 to 5.0 containing a pH buffer having a carboxyl group with a pKa of 3.7 to 6.5. It is disclosed that image quality is improved by an image recording method using a liquid composition.

JP 2010-069715 A JP 2007-084607 A

  However, as a result of investigations by the present inventors, the images obtained by the conventional acid precipitation reaction systems such as the image recording methods described in Patent Documents 1 and 2 are suppressed in abrasion, although bleeding is suppressed. It was low. Accordingly, an object of the present invention is to provide an image recording method of a two-component reaction system and a set of an ink and a liquid composition that achieve both high image blur suppression effect and image scratch resistance at a high level.

The above object is achieved by the present invention described below. That is, the image recording method according to the present invention destabilizes the dispersion state of the pigment in the ink, and the step of applying to the recording medium the ink containing the pigment dispersed by the action of the anionic group. An image recording method comprising a step of applying a liquid composition to the recording medium so as to at least partially overlap a region to which the ink is applied, wherein the liquid composition has a pH buffering ability for the ink. The liquid composition has a pH at 25 ° C. of not less than 5.1 and not more than 6.5, and the liquid composition has a first acid having a pKa less than the pH and a pKa higher than the pH. 2 acid, the content (mol) of the first acid in 100 g of the liquid composition is 1.0 × 10 ⁻² mmol or more, and the second in 100 g of the liquid composition. Acid content of The amount (mol) is 1.1 times or more with respect to the content (mol) of the first acid.

  According to the present invention, it is possible to provide an image recording method and a set of an ink and a liquid composition which have a high effect of suppressing bleeding of an image and high scratch resistance of the image.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments. The image recording method of the present invention includes a step of applying to a recording medium an ink containing a pigment dispersed by the action of an anionic group, and a liquid composition that destabilizes the dispersed state of the pigment in the ink Is applied to the recording medium so as to at least partially overlap with the region to which the ink is applied, wherein the liquid composition has a pH buffering ability for the ink, The liquid composition has a pH at 25 ° C. of 5.1 or more and 6.5 or less, and the liquid composition has a first acid having a pKa less than the pH and a second acid having a pKa higher than the pH. And the content (mol) of the first acid in 100 g of the liquid composition is 1.0 × 10 ⁻² mmol or more, and the second acid in 100 g of the liquid composition Content (mol) Is 1.1 times or more with respect to the content (mol) of the first acid. In the present invention, pH and pKa are values at 25 ° C.

  First, the inventors of the conventional acid deposition reaction system, such as the image recording methods described in Patent Documents 1 and 2, are able to suppress image bleeding but reduce the scratch resistance of the image. Study was carried out. In a general acid precipitation reaction system, the ink and the liquid composition are prepared so as to have high reactivity when the two liquids come into contact with each other. This is because, when the reactivity between the ink and the liquid composition is increased, the aggregation reaction of the pigment in the ink occurs quickly when the ink and the liquid composition are brought into contact with each other in the recording medium. Because. Specifically, as a method of increasing the reactivity between the ink and the liquid composition, a method of lowering the pH of the liquid composition or using a strong acid as a reactant is used. For example, in Patent Document 1, the pH of the liquid composition is 0.67 to 3.0, and in Patent Document 2, the pH of the liquid composition is 3.5 to 5.0. It is adjusted to be an acidic region.

  However, in the conventional acid precipitation reaction system in which the reactivity between the ink and the liquid composition is increased, the effect of suppressing image bleeding is increased. The subsequent aggregation reaction is hindered by the pigment aggregated. As a result, in the pigment layer of the image obtained, the portion formed by the initial contact between the ink and the liquid composition has a strong aggregation of the pigment, but as the distance from the portion, the aggregation of the pigment is increased. It becomes weak. Specifically, in the case where the liquid composition is applied prior to the ink, the portion formed by the initial contact of the ink with the liquid composition, that is, the lower portion of the pigment layer strongly aggregates, and the pigment The pigment agglomeration becomes weaker as it goes to the top of the layer. On the other hand, when the liquid composition is applied after the ink, similarly, the upper part of the pigment layer is strongly aggregated, and the aggregation of the pigment becomes weaker toward the lower part of the pigment layer. As described above, in the conventional acid precipitation reaction system in which the reactivity between the ink and the liquid composition is simply increased, the aggregation of the pigment does not occur uniformly. Therefore, when the stress is applied to the pigment layer surface, the stress is applied. Is not uniformly dispersed, the image becomes brittle, and the scratch resistance of the image is considered to be low.

  From the above, the present inventors can improve the scratch resistance of an image if the aggregation of the pigment occurs uniformly when the ink and the liquid composition are contacted in the acid precipitation reaction system. I thought that. The inventors have reached the technical idea of the present invention that “the reaction is controlled so that the pigments are uniformly aggregated”. Then, when the present inventors performed various examinations, it turned out that reaction can be controlled by the structure of this invention so that a pigment aggregates uniformly. This will be described in detail below.

  First, by setting the pH of the liquid composition to an acidic region close to neutrality (pH at 25 ° C. is not less than 5.1 and not more than 6.5), the pH change when the liquid composition comes into contact with the ink becomes gentle. I did it. However, if the pH of the liquid composition is simply set to an acidic region close to neutrality, when the ink and the liquid composition are brought into contact, the pH of the mixed solution of the two liquids becomes a neutral region. Aggregation reaction will not occur. Therefore, even if the ink and the liquid composition come into contact with each other, a liquid having a pH buffering action on the ink at a pH in the acidic region close to neutrality so that the pH of the mixed solution of the two liquids is maintained acidic. It is effective to use the composition. However, when the present inventors examined an image obtained using such a liquid composition and ink, although the scratch resistance of the image is improved, bleeding of the image may not be suppressed, Stable suppression of image bleeding and scratch resistance of the image could not be achieved stably. When the present inventors examined, it turned out that it is because it becomes difficult to cause aggregation of a pigment depending on the kind and combination of the acid used in a liquid composition.

  Therefore, the present inventors have further studied by paying attention to the pKa of the acid used in the liquid composition and the pH of the liquid composition. As a result, by containing each of the first acid having a pKa lower than the pH of the liquid composition and the second acid having a pKa higher than the pH of the liquid composition, it is possible to stably suppress image bleeding and image It was found that both the scratch resistance can be achieved. The present inventors consider that this mechanism is as follows.

  An acid having the pKa below the pH of the liquid composition having a pH of 5.1 or more and 6.5 or less (the first acid) is a strong acid and has a property of easily releasing protons. Due to protons released from the first acid, the acid dissociation type anionic group in which the pigment is dispersed becomes acid type, and the dispersion state of the pigment becomes unstable, so that the pigment aggregates. However, in the case where only the first acid having a pKa lower than the pH of the liquid composition is contained in the liquid composition, the pigment may not be aggregated if the protons are completely consumed. Therefore, by further containing an acid having the pKa higher than the pH of the liquid composition (the second acid), protons are supplied from the second acid having a high pKa to the first acid having a low pKa. For this reason, the aggregation reaction of the pigment by the protons released from the first acid occurs stably. As a result, in addition to the effect of improving the scratch resistance of the image, it is considered that the pigment aggregation reaction sufficiently occurs, and the effect of suppressing the bleeding of the image is improved to some extent.

Further investigation by the present inventors has revealed that when the first acid and the second acid are contained in the liquid composition at a specific content, the action of each of the above acids occurs particularly efficiently, and the image It has been found that the effect of suppressing bleeding and scratch resistance can be achieved at a high level. Specifically, the content (mol) of the first acid in 100 g of the liquid composition is 1.0 × 10 ⁻² mmol or more, and the content of the second acid in 100 g of the liquid composition. It is necessary that (mol) is 1.1 times or more with respect to the content (mol) of the first acid. When the content (mol) of the first acid in 100 g of the liquid composition is less than 1.0 × 10 ⁻² mmol, the absolute amount of protons attacking the anionic group of the pigment is small, and the pigment agglomeration reaction occurs. It does not occur sufficiently, and the effect of suppressing image bleeding is reduced. In addition, if the content (mol) of the second acid in 100 g of the liquid composition is less than 1.1 times the content (mol) of the first acid, The amount of protons supplied to the acid is not sufficient. Therefore, the aggregating action of the pigment due to the protons released from the first acid becomes unstable, and the effect of suppressing image bleeding is reduced. Further, according to the study by the present inventors, when the pH of the liquid composition is less than 5.1, the reactivity of the liquid composition is strong, the pigment does not aggregate uniformly, and the resulting image has low scratch resistance. I understood that. On the other hand, when the pH was higher than 6.5, the acidity was weak and the pigment agglomeration reaction did not occur sufficiently. In addition, when a liquid composition that does not have a pH buffering action at a pH in the acidic region close to neutrality (5.1 to 6.5) is used, as described above, The pH became neutral, and the pigment agglomeration reaction did not occur sufficiently, and bleeding was generated in the obtained image. Also, the scratch resistance of the image was low.

  As the above mechanism, the configurations of the present invention work synergistically to achieve the effects of the present invention that could not be obtained with a conventional acid precipitation reaction system.

[Image recording method]
In the present invention, examples of means for applying the liquid composition to the recording medium include an inkjet method and a coating method. Examples of the coating method include a roller coating method, a bar coating method, and a spray coating method. As the means for applying ink to the recording medium, an ink jet recording method is preferred in which recording is performed on the recording medium by ejecting ink from the ejection port of the recording head by an ink jet method in accordance with a recording signal. In particular, an ink jet recording method in which ink is ejected from the ejection port of the recording head by applying thermal energy to the ink is more preferable.

  The image recording method of the present invention includes a step (A) of applying ink to the recording medium and a step (B) of applying the liquid composition to the recording medium so as to overlap at least partly with the region to which the ink is applied. It has two steps. At this time, the step (B) may be performed after the step (A), or the step (A) may be performed after the step (B). Further, when the same process is performed twice or more, for example, the process (A) → the process (B) → the process (A) or the process (B) → the process (A) → the process (B) may be performed. In particular, it is more preferable to include the process of performing the step (A) after the step (B) because the effect of improving the scratch resistance and blurring suppression of the image is large.

[Set of ink and liquid composition]
The ink and liquid composition set of the present invention comprises an ink containing a pigment dispersed by the action of an anionic group, and a liquid composition that destabilizes the dispersion state of the pigment in the ink, The liquid composition has a pH buffering ability with respect to the ink, the pH of the liquid composition is 5.1 or more and 6.5 or less, and the liquid composition has a pKa of the pH or less. A first acid having a second acid having a pKa higher than the pH, and the content (mol) of the first acid in 100 g of the liquid composition is 1.0 × 10 ⁻² mmol or more. And the content (mol) of the second acid in 100 g of the liquid composition is 1.1 times or more with respect to the content (mol) of the first acid. To do. There is no particular limitation on the ink used in combination with the liquid composition as a set, and cyan ink, magenta ink, yellow ink, black ink, and the like can be used. The liquid composition and ink used for the image recording method and the ink and liquid composition set of the present invention will be described below.

(1) Liquid composition In the present invention, "a liquid composition having a pH buffering ability for ink" means a liquid composition whose pH does not substantially change even when mixed with ink used together. means. In the present invention, whether or not the liquid composition has a pH buffering ability with respect to ink can be determined by the following determination method. When the pH of the liquid composition to be used is P ₁ and the pH of the mixed solution obtained by mixing the liquid composition to be used and the ink to be used in equal mass is P ₂ , | P ₁ −P ₂ | ≦ 1. When 0 is satisfied, it is determined that the liquid composition has “pH buffering ability for ink”. In Examples described later, the pH of the liquid composition was measured using a pH meter F-21 (manufactured by Horiba, Ltd.).

In the present invention, the “liquid composition that destabilizes the dispersion state of the pigment in the ink” means the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) when the following determination method is performed. Means that the liquid composition is 1.3 or more. The determination method is as follows. First, the ink used is a laser diffraction / scattering particle size distribution measuring apparatus LA-950V2 (manufactured by Horiba Seisakusho), the refractive index of the sample is 1.5, the refractive index of the dispersion medium (water) is 1.333, and the number of repetitions is 15. The average particle size (volume-based average particle size D ₅₀ ) is measured under the conditions of the measurement, and this value is defined as D ₁ . Further, after mixing the ink with a liquid composition having a mass ratio of 0.5 times, D ₅₀ is measured in the same manner, and this value is defined as D ₂ . At this time, when the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) is 1.3 or more, the liquid composition is “a liquid composition that destabilizes the dispersion state of the pigment in the ink”. judge.

  In addition, the liquid composition used in the image recording method and the ink and liquid composition set of the present invention is preferably colorless, milky white, or white so as not to affect the image recorded with the ink. Therefore, the ratio of the maximum absorbance to the minimum absorbance (maximum absorbance / minimum absorbance) in the wavelength range of 400 nm to 800 nm, which is the wavelength range of visible light, is preferably 1.0 or more and 2.0 or less. This means that in the wavelength range of visible light, there is substantially no absorbance peak, or even if it has, the intensity of the peak is extremely small. Furthermore, in the present invention, the liquid composition preferably does not contain a coloring material. In the examples of the present invention described later, the above-described absorbance was measured with a Hitachi double beam spectrophotometer U-2900 (manufactured by Hitachi High-Technologies) using an undiluted liquid composition. At this time, the absorbance may be measured by diluting the liquid composition. This is because the values of the maximum absorbance and the minimum absorbance of the liquid composition are both proportional to the dilution factor, and the ratio of the maximum absorbance to the minimum absorbance (maximum absorbance / minimum absorbance) does not depend on the dilution factor.

  Further, the viscosity at 25 ° C. of the liquid composition is preferably 1.0 mPa · s or more and 10.0 mPa · s or less, and more preferably 2.0 mPa · s or more and 8.0 mPa · s or less. In the present invention, the viscosity of the liquid is a value measured under the condition of 50 rpm / min using a conical plate type rotational viscometer RE80L (manufactured by Toki Sangyo). Furthermore, the surface tension of the liquid composition used in the present invention is preferably 25.0 mN / m or more and 50.0 mN / m or less. The pH of the liquid composition is more preferably 5.1 or more and less than 6.0.

  Hereafter, each component which comprises the liquid composition used for the image recording method of this invention and the set of an ink and a liquid composition is each demonstrated.

<Acid>
The liquid composition used in the image recording method and the set of the ink and the liquid composition of the present invention includes two kinds of a first acid having a pKa lower than the pH of the liquid composition and a second acid having a pKa higher than the pH. Contains acid. What is necessary is just to select the acid used for a liquid composition in this invention from the acid generally used so that the requirements of this invention may be satisfy | filled.

Among acids, a divalent or higher acid has a plurality of pKas because it exhibits multiple stages of ionization derived from an acidic group of that valence. In this invention, when it has several pKa in this way, it shall treat as a different acid for every acid type (or salt type) corresponding to each pKa. Specifically, it is as follows. For example, maleic acid, a divalent acid, has two pKas (respectively pKa ₁ = 1.9 and pKa ₂ = 6.2) corresponding to two stages of ionization. Each of these two pKas corresponds to pKa ₁ is HOOC—CH ₂ CH ₂ —COOH and pKa ₂ is MOOC—CH ₂ CH ₂ —COOH, where M is an alkali metal, ammonium, or organic ammonium. ing. In the present invention, for convenience, the former is called maleic acid (2H type) and the latter is called maleic acid (1M1H type). When maleic acid is contained in the liquid composition, part of it is maleic acid (2H type) with a pKa of 1.9, and part of it is maleic acid (1M1H type) with a pKa of 6.2. When the pH of the liquid composition at this time is 6.0, maleic acid (2H type) is treated as the first acid, and maleic acid (1M1H type) is treated as the second acid. Table 1 shows typical acid types that can be used in the present invention and their pKa values. In addition, since pKa of the acid in 25 degreeC is a value intrinsic | native to each acid, what is necessary is just to refer to literature values about the acid which is not described in Table 1.

  In the present invention, since the pH of the liquid composition is in the range of 5.1 or more and 6.5 or less, examples of the first acid having a pKa less than or equal to the pH of the liquid composition include citric acid (1M2H type ), Tartaric acid (1M1H type), itaconic acid (2H type), β-alanine, malic acid (2H type), citric acid (3H type), tartaric acid (2H type), malonic acid (2H type), pyrophosphoric acid (1M3H) Type), glycine, phosphoric acid (3H type), maleic acid (2H type), sulfurous acid (2H type), ethyl phosphate (2H type), methyl phosphate (2H type), pyrophosphoric acid (4H type), taurine, Examples include glutaric acid (2H type). On the other hand, examples of the second acid having a pKa higher than the pH of the liquid composition include phosphoric acid (2M1H type), pyrophosphoric acid (3M1H type), sulfurous acid (1M1H type), phosphoric acid (1M2H type), and phosphoric acid. Examples include ethyl (1M1H type) and pyrophosphoric acid (2M2H type).

(Acid content)
In the present invention, as described above, the content (mol) of the first acid in 100 g of the liquid composition needs to be 1.0 × 10 ⁻² mmol or more. Furthermore, the content (mol) of the first acid in 100 g of the liquid composition is preferably 1.0 × 10 ⁻¹ mmol or more. Further, the content (mol) of the first acid in 100 g of the liquid composition is more preferably 8.6 × 10 mmol or less. If it is larger than 8.6 × 10 mmol, the amount of protons that attack the anionic group of the pigment is so large that the agglomeration reaction of the pigment occurs rapidly, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. is there.

The content (mol) of the second acid in 100 g of the liquid composition is preferably 7.5 × 10 mmol or more. Moreover, it is preferable that it is 2.0 * 10 < ² > mmol or less.

Further, the content (mol) of the second acid in 100 g of the liquid composition needs to be 1.1 times or more with respect to the content (mol) of the first acid. Furthermore, it is preferably 2.1 times or more. Further, the content (mol) of the second acid in 100 g of the liquid composition is more preferably 4.0 × 10 ³ times or less with respect to the content (mol) of the first acid. When the ratio is larger than 4.0 × 10 ³ times, the amount of protons that attack the anionic group of the pigment is smaller than the amount of protons supplied from the second acid to the first acid, so that the aggregation reaction of the pigment In some cases, the effect of suppressing bleeding of the image and improving the scratch resistance of the image cannot be sufficiently obtained.

In addition, the total content of the first acid and the second acid in 100 g of the liquid composition is preferably 5.0 × 10 mmol or more. When the total content of the first acid and the second acid is smaller than 5.0 × 10 mmol, the amount of acid contained in the liquid composition is small, the aggregating action of the pigment is weakened, and the image bleeding is improved. The effect may not be sufficiently obtained. In addition, the total content of the first acid and the second acid in 100 g of the liquid composition is preferably 2.2 × 10 ² mmol or less. If the total content of the first acid and the second acid is larger than 2.2 × 10 ² mmol, the acid may precipitate and stick in the apparatus. When the application method of the liquid composition is an ink jet method, the discharge stability of the liquid composition may not be sufficiently obtained.

  In the present invention, the content of the first acid having a pKa below the pH of the liquid composition (mol amount in 100 g of the liquid composition) and the content of the second acid having a pKa higher than the pH of the liquid composition ( The mol amount in 100 g of the liquid composition can be calculated by the following method.

The type of acid used in preparing the liquid composition is acid A (valence: x). At this time, the acid A has x pKas corresponding to each of the x-stage ionizations (respectively, pKa ₁ , pKa ₂ , pKa ₃ ... PKa _x ). An anion generated by the first stage ionization (acid dissociation constant: pKa ₁ ) of the acid A is A ⁻¹ , and an anion generated by the second stage ionization (acid dissociation constant: pKa ₂ ) is A ⁻² , the third stage When the anion generated by ionization (acid dissociation constant: pKa ₃ ) is A ⁻³ ,... X ionization (acid dissociation constant: pKa _x ) is A ^−x , the liquid composition 100 g mol of anion ^{a -n} generated by ionization of the n-stage in ^{([a -n])} can be calculated by the following equation. Incidentally, in the formula, W represents the addition amount of the preparation of acid A (wt%), M _A represents the molecular weight of the acid A. [H ⁺ ] is a hydrogen ion concentration in the liquid composition, and can be calculated from the pH of the liquid composition using a relational expression of pH = −log ₁₀ [H ⁺ ].

According to the above formula, the amount of mol of each anion in 100 g of the liquid composition is calculated, and the total amount of mol of the anion having a pKa below the pH of the liquid composition is “the first acid in 100 g of the liquid composition”. Content (mol) ". Further, the total amount of mols of anions having a pKa higher than the pH of the liquid composition is the “content (mol) of the second acid in 100 g of the liquid composition” in the present invention. In addition, about the method of analyzing the kind and addition amount (mass%) of an acid about a liquid composition whose component is unknown, it mentions later in the (analysis method of the kind of acid and addition amount).

(Analysis method of acid type and amount added)
About the liquid composition in which a component is unknown, the kind of acid contained and its addition amount (mass%) can be analyzed with the following method. First, the type of acid contained in the liquid composition and the amount added (% by mass) are liquid chromatograph mass spectrometry (LC / MS), nuclear magnetic resonance (NMR), and Fourier transform infrared spectrophotometry. It can be specified using a meter (FT-IR). Specifically, for a liquid composition containing a large number of components, after separating these components in the liquid chromatograph part (LC), what molecular weight components are contained in the mass spectrometer part (MS) Perform an analysis. Furthermore, about the isolate | separated each component, the kind of acid which a liquid composition contains can be specified by using NMR and FT-IR. If the type of acid contained in the liquid composition is specified, the amount added (% by mass) can be specified by obtaining a calibration curve for each of the specified acids. Specifically, a calibration curve is obtained by preparing samples of several levels for the acid whose type has been specified, and performing regression analysis on the relationship between the concentrations and the LC / MS output results. By using this calibration curve, it is possible to specify the concentration of each acid whose type is specified, that is, the addition amount (% by mass).

<Aqueous medium>
The liquid composition used in the present invention can use water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. The content (% by mass) of the water-soluble organic solvent in the liquid composition is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the liquid composition. Any conventionally used water-soluble organic solvent can be used. Examples thereof include alcohols, glycols, alkylene glycols having 2 to 6 carbon atoms in the alkylene group, polyethylene glycols, nitrogen-containing compounds, and sulfur-containing compounds. These water-soluble organic solvents can be used alone or in combination of two or more as required. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the liquid composition is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the liquid composition.

<Other ingredients>
In addition to the above-mentioned components, the liquid composition used in the present invention is a water-soluble solid solution at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. An organic compound may be contained. Furthermore, the liquid composition used in the present invention may be a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, a chelating agent, if necessary. And various additives such as resins.

(2) Ink The ink used for the image recording method and the set of the ink and the liquid composition of the present invention contains a pigment dispersed by the action of an anionic group. In the present invention, the pH of the ink is preferably 7.5 or more and 11.0 or less. Further, the pH of the ink is preferably 7.5 or more and 9.5 or less. Further, it is more preferable that the pH of the ink is 2.0 or more higher than the pH of the liquid composition. The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 10.0 mPa · s or less, and more preferably 2.0 mPa · s or more and 8.0 mPa · s or less. The surface tension of the ink used in the present invention is preferably 20.0 mN / m or more and 45.0 mN / m or less. Hereafter, each component which comprises the ink used for the image recording method of this invention and the set of an ink and a liquid composition is each demonstrated.

<Pigments dispersed by the action of anionic groups>
In the present invention, in order to disperse the pigment by the action of the anionic group, at least a part of the anionic group needs to be present as an acid dissociation type in the ink. Therefore, the acid dissociation constant pKa of the anionic group is required to be smaller than the pH of the ink. Furthermore, in the present invention, it is preferable that the pH of the ink is 7.0 or more and 11.0 or less, and the pKa of the anionic group is 4.0 or more and 5.0 or less.

  In the present invention, examples of the pigment that can be used in the ink include inorganic pigments such as carbon black and organic pigments, and any known pigment that can be used in the ink can be used. The content (% by mass) of the pigment in the ink is 0.1% by mass or more and 15.0% by mass or less, and further 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. It is preferable.

  In the present invention, as a method of dispersing a pigment by the action of an anionic group, a resin dispersion type pigment using a resin having an anionic group as a dispersing agent (a resin dispersing pigment or pigment using a resin dispersing agent having an anionic group) A microcapsule pigment in which the surface of the particle is coated with a resin having an anionic group, a resin-bonded self-dispersing pigment in which an organic group containing a resin having an anionic group is chemically bonded to the surface of the pigment particle), Examples include self-dispersion type pigments (self-dispersion pigments) in which an anionic group is bonded to the surface directly or through another atomic group. Of course, it is also possible to use pigments having different dispersion methods in combination.

  In the present invention, when the pigment used in the ink is a resin dispersion type pigment, a resin having an anionic group is used as a dispersant. Examples of the resin having an anionic group include an acrylic resin polymerized using a monomer having a carboxyl group such as acrylic acid or methacrylic acid; a urethane resin polymerized using a diol having an anionic group such as dimethylolpropionic acid. . In the present invention, when a resin dispersion type pigment is used, the resin preferably has both a hydrophilic part and a hydrophobic part. Moreover, it is preferable that the acid value of resin is 50 mgKOH / g or more and 300 mgKOH / g or less. Moreover, it is preferable that the polystyrene equivalent weight average molecular weight (Mw) obtained by GPC of resin is 1,000 or more and 15,000 or less. The resin content (% by mass) in the ink is 0.1% by mass or more and 10.0% by mass or less, and further 0.2% by mass or more and 4.0% by mass or less based on the total mass of the ink. It is preferable that In addition, the resin content (% by mass) in the ink is preferably 0.1 to 1.0 times by mass with respect to the pigment content (% by mass).

In the present invention, when the pigment used in the ink is a self-dispersing pigment, an anionic group is chemically bonded to the pigment surface directly or via another atomic group (-R-) Can be used. Examples of the anionic group include a COOM group, a SO ₃ M group, a PO ₃ HM group, a PO ₃ M ₂ group, a SO ₂ NH ₂ group, and a SO ₂ NHCOR group. In the above formula, M is a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Examples of the other atomic group (—R—) include an alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. In the present invention, if the dispersion state of the pigment in the ink is destabilized by the liquid composition, the amount of anionic groups in the ink and the amount of ink applied greatly affect the effect of the present invention. do not do.

<Aqueous medium and other components>
For the ink, water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. Furthermore, it is preferable that they are 3.0 mass% or more and 40.0 mass% or less. As the water-soluble organic solvent, the same water-soluble organic solvents as those which can be used in the liquid composition can be used. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The ink may be the same as the other components listed as usable in the liquid composition.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded.

[Preparation of liquid composition]
The following ingredients were mixed. The balance of ion-exchanged water is such that the total of all components constituting the liquid composition is 100.0% by mass.
-Acid See Table 2-Glycerin 5.0% by mass
Surfactant: Acetylenol E100 (manufactured by Kawaken Fine Chemicals) 1.0% by mass
-Preservative: Proxel GXL (Abyssia) 0.2% by mass
・ Ion exchange water balance

This was sufficiently stirred and dispersed, and filtered through a filter having a pore size of 3.0 μm (manufactured by Fujifilm) to prepare a liquid composition. Furthermore, the addition of 10 wt% aqueous solution of potassium hydroxide was appropriately prepared so that the pH in Table 2 (P _1). The measurement of pH _{(P 1)} of the liquid composition, using a pH meter F-21 (manufactured by Horiba), was carried out at 25 ° C.. About the liquid composition obtained above, the maximum absorbance A _max and the minimum absorbance A _min in the wavelength region of 400 nm to 800 nm were measured with a Hitachi double beam spectrophotometer U-2900, and the ratio A _max / A _min was calculated. As a result, all liquid compositions were 1.0 or more and 2.0 or less. Moreover, content X (mmol) of the 1st acid in liquid composition 100g and content Y (mmol) of the 2nd acid were computed by the above-mentioned method. Moreover, Y / X and X + Y were calculated from the obtained X and Y values.

[Preparation of ink]
<Preparation of pigment dispersion>
(Pigment dispersion A)
An anionic resin-dispersed carbon black dispersion using a vinyl alcohol-styrene-acrylic acid copolymer having an acid value of 100 mgKOH / g and a weight average molecular weight of 7,000 was prepared as a resin dispersant, and pigment dispersion A and did. The pigment dispersion A thus obtained had a pigment content of 15.0% by mass, a resin content of 7.5% by mass, and a volume average particle size of the pigment of 110 nm.

(Pigment dispersion B)
As a resin dispersant, an anionic resin-dispersed carbon black dispersion using a styrene-acrylic acid copolymer having an acid value of 150 mgKOH / g and a weight average molecular weight of 9,000 was prepared and designated as Pigment Dispersion B. The pigment dispersion B obtained had a pigment content of 15.0% by mass, a resin content of 4.0% by mass, and a volume average particle size of the pigment of 150 nm.

(Pigment dispersion C)
Cab-O-Jet200 (manufactured by Cabot), which is an anionic self-dispersing carbon black pigment having a sulfophenyl group bonded to the surface of carbon black, was used as pigment dispersion C (pigment content: 15.0 mass%). The volume average particle diameter of the pigment was 135 nm.

(Pigment dispersion D)
Further, water is added to Cab-O-Jet300 (manufactured by Cabot), which is an anionic self-dispersing carbon black pigment having a carboxylphenyl group bonded to the surface of carbon black, and pigment dispersion D (pigment content is 15.0 mass) %). The volume average particle diameter of the pigment was 130 nm.

<Preparation of resin fine particle dispersion>
Resin fine particles of glycidyl methacrylate-methacrylic acid having an acid value of 100 mgKOH / g, a weight average molecular weight of 8,000, and a volume average particle size of 150 nm were synthesized. A potassium hydroxide aqueous solution is added so that the neutralization rate of the anionic groups of the resin fine particles is 100% on a molar basis, and an appropriate amount of ion-exchanged water is further added to obtain a resin fine particle dispersion having a solid content of 30.0% by mass. It was.

<Preparation of ink>
The pigment dispersion and resin fine particle dispersion obtained above were mixed with the following composition. The balance of ion-exchanged water is such that the total of all components constituting the ink is 100.0% by mass.
Pigment dispersion (pigment content is 15.0% by mass) 20.0% by mass
・ Resin fine particle dispersion (resin content is 30.0 mass%) See Table 3. ・ Glycerin 5.0 mass%
・ 2-Pyrrolidone 10.0% by mass
-Polyethylene glycol (number average molecular weight: 600) 5.0% by mass
Surfactant: Acetylenol E100 (manufactured by Kawaken Fine Chemicals) 1.0% by mass
-Preservative: Proxel GXL (Abyssia) 0.2% by mass
・ Ion exchange water balance

  This was sufficiently stirred and dispersed, and filtered through a filter (manufactured by Fuji Film) having a pore size of 1.2 μm to prepare an ink. Furthermore, it prepared so that it might become pH shown in Table 3 by adding 10 mass% sulfuric acid aqueous solution or 10 mass% potassium hydroxide aqueous solution suitably. The pH of the ink was measured at 25 ° C. using a pH meter F-21 (Horiba Seisakusho).

[Evaluation]
Each of the liquid composition and the ink obtained above was filled in a cartridge, set as a set shown in Table 4, and mounted on an ink jet recording apparatus PIXUS Pro 9500 (manufactured by Canon). At this time, the ink was attached to the cyan position, and the liquid composition was attached to the photomagenta position. Then, the liquid composition was applied to an aurora coat (manufactured by Nippon Paper Industries Co., Ltd.) which is a recording medium, and then ink was applied in an overlapping manner on the area of the recording medium to which the liquid composition was applied. Then, an image (5 cm × 15 cm) having an ink recording duty of 100% and a liquid composition recording duty of 100% was created. The obtained images were stored at room temperature for 24 hours, and then evaluated as follows. The recording conditions were temperature: 23 ° C. and relative humidity: 55%. In the ink jet recording apparatus, the recording duty is 100% under the condition that 8 dots of 3.5 ng (nanogram) ink droplets are applied to a unit area of 1/600 inch × 1/600 inch with a resolution of 600 dpi × 600 dpi. It is defined as

(Confirmation of whether or not the liquid composition has pH buffering ability for ink)
The ink and liquid composition set in the combinations shown in Table 4 were mixed at an equal mass to obtain a mixed solution. The pH (P ₂ ) of this mixed solution was measured at 25 ° C. using a pH meter F-21 (manufactured by Horiba Seisakusho). Using this value (P ₂ ) and the pH (P ₁ ) of the liquid composition measured above, | P ₁ −P ₂ | was calculated. At this time, when | P ₁ −P ₂ | ≦ 1.0 was satisfied, it was determined that the liquid composition had a pH buffering ability for the ink. The evaluation criteria are as follows. In the evaluation criteria for the following evaluation items, OK was an acceptable level and NG was an unacceptable level. The evaluation results are shown in Table 4.
OK: | P ₁ −P ₂ | ≦ 1.0, and NG: | P ₁ −P ₂ |> 1.0, which was a liquid composition having a pH buffering ability with respect to the ink. The liquid composition has no pH buffering ability.

(Confirmation of whether the dispersion state of the pigment in the ink becomes unstable due to the liquid composition)
Using a laser diffraction / scattering particle size distribution analyzer LA-950V2 (manufactured by HORIBA, Ltd.), the ink was subjected to a refractive index of 1.5, a refractive index of the dispersion medium (water) of 1.333, and 15 repetitions. D ₅₀ was measured and this value was defined as D ₁ . Further, for the ink and liquid composition set in the combinations shown in Table 4, after mixing the ink with the liquid composition of 0.5 times the mass ratio, D ₅₀ was measured in the same manner, and this value was calculated as D ₂ It was. At this time, when the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) was 1.3 or more, it was determined that the dispersion state of the pigment in the ink was destabilized by the liquid composition. The evaluation criteria are as follows. In the evaluation criteria for the following evaluation items, OK was an acceptable level and NG was an unacceptable level. The evaluation results are shown in Table 4.
OK: D ₂ / D ₁ ≧ 1.3, and the dispersion state of the pigment in the ink is destabilized by the liquid composition. NG: D ₂ / D ₁ <1.3, and the liquid composition is in the ink. The dispersion state of the pigment was not destabilized.

(Image blur suppression)
By visually confirming the outline of the image obtained as described above, the suppression of bleeding of the image was evaluated. The evaluation criteria for image blur suppression are as follows. In the evaluation criteria for the following evaluation items, A to B are acceptable levels, and C is an unacceptable level. The evaluation results are shown in Table 4.
A: The outline of the image was not blurred. B: The outline of the image was slightly blurred, but the level was inconspicuous. C: The outline of the image was blurred.

(Image scratch resistance)
The scratch resistance of the image obtained above was evaluated according to JIS L 0849 as follows. Specifically, an image was placed on the curved surface of a Gakushin dyeing frictional fastness tester (manufactured by Yasuda Kikai Seisakusho), and an aurora coat, which was a recording medium used to produce the image, was fixed to the friction element. Then, a rubbing test was performed in which the fixed recording medium was rubbed back and forth 50 times with a load of 5.0 N. By visually comparing the images before and after the scratch test, the scratch resistance of the image was evaluated. The evaluation criteria for image scratch resistance are as follows. In the evaluation criteria for the following evaluation items, AA to B are acceptable levels, and C is an unacceptable level. The evaluation results are shown in Table 4.
AA: No scratches were observed in the image after the scratch test A: Almost no scratches were observed in the image after the scratch test B: Slight scratches were found in the image after the scratch test, but were conspicuous C: Scratches were observed in the image after the abrasion test.

Claims (4)

A step of applying an ink containing a pigment dispersed by the action of an anionic group to a recording medium, and a region where the ink is applied to a liquid composition that destabilizes the dispersion state of the pigment in the ink And an image recording method comprising a step of applying to the recording medium so as to overlap at least partly,
The liquid composition has a pH buffering capacity for the ink;
PH of the liquid composition at 25 ° C. is 5.1 or more and 6.5 or less,
The liquid composition comprises a first acid having a pKa below the pH and a second acid having a pKa higher than the pH;
The content (mol) of the first acid in 100 g of the liquid composition is 1.0 × 10 ⁻² mmol or more, and the content (mol) of the second acid in 100 g of the liquid composition. ) Is 1.1 times or more the content (mol) of the first acid.   The image recording method according to claim 1, wherein the content (mol) of the first acid in 100 g of the liquid composition is 8.6 × 10 mmol or less. 3. The content (mol) of the second acid in 100 g of the liquid composition is 4.0 × 10 ³ times or less with respect to the content (mol) of the first acid. The image recording method described in 1. A set of an ink and a liquid composition, comprising an ink containing a pigment dispersed by the action of an anionic group, and a liquid composition that destabilizes the dispersion state of the pigment in the ink,
The liquid composition has a pH buffering capacity for the ink;
PH of the liquid composition at 25 ° C. is 5.1 or more and 6.5 or less,
The liquid composition comprises a first acid having a pKa below the pH and a second acid having a pKa higher than the pH;
The content (mol) of the first acid in 100 g of the liquid composition is 1.0 × 10 ⁻² mmol or more, and the content (mol) of the second acid in 100 g of the liquid composition. ) Is 1.1 times or more with respect to the content (mol) of the first acid, a set of ink and liquid composition.