Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reactive liquid

Abstract

To provide an inkjet recording method that exhibits excellent effect in suppressing image irregularity and allows recording of an image with excellent water abrasion resistance.SOLUTION: The method comprises a step of applying an aqueous reactive liquid and an ink onto a low- to non-absorptive recording medium, and a step of heating the recording medium. The reactive liquid contains an acidic compound. The ink contains a pigment and resin particles having an anionic group content of 75 μmol / g to 600 μmol / g, with the resin particle content being 1.5 times or more the pigment content in mass ratio. In the ink, the content of a first water-soluble organic solvent having a vapor pressure of 3.1×10-5 kPa or less, and the content of a second water-soluble organic solvent having a dielectric constant of 28.0 or more and a vapor pressure of 4.0×10-3 kPa or less, are each 9.0 mass% or less. The heating temperature TF(°C) of the recording medium and the glass transition temperature TG(°C) of the resin particles satisfy the relation TF≥(TG-10).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and a set of an aqueous ink and an aqueous reaction liquid. [Background technology]

[0002] In recent years, inkjet recording methods have been increasingly used in the sign and display field, such as for recording posters and large advertisements. In this field, polyvinyl chloride sheets and polyethylene terephthalate (PET) sheets are often used as recording media due to their durability and cost. These recording media have no or almost no water-based ink absorbing layer on the recording surface, and are known as non-absorbent recording media (recording media that do not absorb water-based ink) or low-absorbent recording media (recording media that have low absorbency for water-based ink). There is a demand for an inkjet recording method that can record directly on these recording media.

[0003] In order to record an image with aqueous ink on the above-mentioned non-absorbent recording medium or low-absorbent recording medium (hereinafter collectively referred to as "non-absorbent recording medium"), it is necessary to thicken and fix the aqueous ink on the non-absorbent recording medium. Methods for this include thickening the ink by evaporating the water content of the ink on the non-absorbent recording medium, and rapidly thickening the ink on the recording medium by using a reaction liquid that aggregates the ink components. The former method is advantageous in terms of running costs because it does not require a reaction liquid, but it requires a slower recording speed to obtain a good image. Therefore, the latter method, which uses a reaction liquid, is being considered from the perspective of its superiority in productivity.

[0004] Previously, a recording method has been proposed in which a treatment liquid that aggregates ink components is brought into contact with the ink on a recording medium, ensuring high productivity even for recording media that have almost no ink absorption layer, and producing clear images with little bleeding (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-084102 [Patent Document 2] Japanese Patent Publication No. 2020-132802 [Patent Document 3] Japanese Patent Application Publication No. 2023-029244 Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors performed recording on a non-absorbent recording medium using the ink sets proposed in Patent Documents 1 to 3. As a result, it was found that when the ink sets proposed in Patent Documents 1 and 3 were used, the effect of suppressing image unevenness was obtained, but there was room for improvement in abrasion resistance when water was attached (hereinafter referred to as water abrasion resistance). Furthermore, when the ink set proposed in Patent Document 2 was used, the water abrasion resistance was better than when the ink set proposed in Patent Document 1 was used, but there was still room for improvement, and it was found that the effect of suppressing image unevenness was insufficient.

[0007] Therefore, an object of the present invention is to provide an inkjet recording method that is excellent in the effect of suppressing image unevenness and is capable of recording images that have excellent water abrasion resistance. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, the method comprising: a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium; an ink applying step of applying the aqueous ink so as to overlap at least a part of an area of the recording medium to which the aqueous reaction liquid is applied; and a heating step of heating the recording medium to which the aqueous ink and the aqueous reaction liquid have been applied at a predetermined temperature T F (°C), and the recording medium is heated to a temperature of 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 the reactant contains at least one acidic compound selected from the group consisting of organic acids and inorganic acids, the aqueous ink contains a pigment and resin particles dispersed by the action of anionic groups, the amount (μmol / g) of anionic groups in the resin particles is 75 μmol / g or more and 600 μmol / g or less, the content (mass%) of the resin particles is 1.5 times or more the mass ratio of the content (mass%) of the pigment, and the vapor pressure in the aqueous ink is 3.1×10 -5 The content (mass%) of the first water-soluble organic solvent of kPa or less is 9.0 mass% or less based on the total mass of the ink, and the ink has a relative dielectric constant of 28.0 or more and a vapor pressure of 4.0 x 10 -3 the content (mass %) of the second water-soluble organic solvent in the ink is 9.0 mass % or less based on the total mass of the ink, and the heating temperature T F (°C), and the glass transition temperature T G The inkjet recording method is characterized in that the temperature (° C.) satisfies the relationship of the following formula (1): T F ≧(T G -10) (1) [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an inkjet recording method that is excellent in the effect of suppressing image unevenness and is capable of recording images that have excellent water abrasion resistance. Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus used in the inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 2] 1 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience it will be expressed as "containing a salt." In addition, aqueous inkjet ink and reaction liquid may be simply referred to as "ink" and "reaction liquid." Physical property values are values at room temperature (25°C) unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0012] The present inventors first recorded solid images on non-absorbent recording media using the ink and reaction liquid proposed in Patent Document 2. As a result, because the ink did not penetrate non-absorbent recording media, the ink dots were prone to movement, i.e., the ink droplets met due to insufficient pinning, resulting in an uneven image with a mixture of dark and light areas. The present inventors believed that the ink's cohesion was insufficient, and attempted various methods to improve its cohesion. As a result, they discovered that the cohesion of ink is largely due to the cohesion of resin particles containing anionic groups, which are used to impart abrasion resistance, and that it is important to maintain the amount of anionic groups in the resin particles at 75 μmol / g or greater. The greater the amount of anionic groups in the resin particles, the greater the ionic repulsion in water, resulting in higher dispersion stability. However, compared to resin particles with fewer anionic groups due to their smaller hydrophobic portions, the dispersion stability is enhanced by water-soluble organic solvents, making them less susceptible to the solvation effect. Therefore, when recording an image, the reaction between the resin particles in the ink and the reactant in the reaction liquid occurs quickly, and the ink droplets aggregate before they begin to gather together, causing the ink to thicken, which is thought to suppress image unevenness.

[0013] When images were recorded using ink containing the above-mentioned resin particles with an anionic group content of 75 μmol / g or more and a pigment, it was found that image unevenness could be suppressed. However, when the water abrasion resistance of the image was checked by rubbing the image vigorously with a cloth moistened with water, it was found that the water abrasion resistance was significantly inferior to that of images recorded using ink containing resin particles with an anionic group content of less than 75 μmol / g. In other words, it was found that simply adjusting the amount of anionic groups in the resin particles was not enough to achieve both suppression of image unevenness and good water abrasion resistance.

[0014] Therefore, the inventors sought a means to improve water-rub resistance even when the amount of anionic groups in the resin particles was 75 μmol / g or greater. First, when images were observed after evaluating water-rub resistance, it was confirmed that only images recorded using inks containing resin particles with a high amount of anionic groups had partial collapse of the ink layer. The ink contains resin particles that are dispersed by the action of anionic groups. The resin particles penetrate between pigment particles to form a strong film, thereby improving water-rub resistance. When a polyvalent metal salt is used as a reactant in the reaction solution, the anionic groups on the resin particles react with the polyvalent metal ions derived from the polyvalent metal salt, and the anionic groups bond to the polyvalent metal ions. It is believed that when water is applied to the image, the ionic bonds slightly dissociate, increasing hydrophilicity. This tendency was also confirmed when a cationic resin was used as the reactant.

[0015] The inventors predicted that using an acidic inorganic or organic acid as a reactant would result in an acidic (H-type) anionic group with a lower degree of dissociation than when the anionic group is bonded to a polyvalent metal ion or a cationic resin, thereby reducing the hydrophilicity of the ink layer and improving water-rub resistance. As a result of their investigations, they found that when recording was performed using a reaction solution containing at least one acidic compound selected from organic and inorganic acids, image unevenness could be suppressed regardless of the type of water-soluble organic solvent contained in the ink. However, they found that water-rub resistance improved in some cases but not in others. When the inventors observed images in which water-rub resistance did not improve, they found that part of the ink layer had collapsed. The inventors hypothesized the reason why the reactivity of the acidic compound in the reaction solution differed depending on the type of water-soluble organic solvent contained in the ink as follows.

[0016] By ensuring that the amount of anionic groups in the resin particles contained in the ink is 75 μmol / g or more, the acidic compound (reactant in the reaction solution) reacts quickly with the resin particles in the ink, thickening the ink and suppressing image unevenness, as described above. Reaction of a certain proportion of the anionic groups in the resin particles results in aggregation of the resin particles and thickening of the ink; therefore, it is not necessary for all anionic groups on the resin particles to react. In contrast, to improve the water-abrasion resistance of the image, the hydrophilicity of the resin particles must be reduced; if a large number of unreacted anionic groups remain, the hydrophilicity of the resin particles is difficult to reduce. It is believed that a greater proportion of the anionic groups must react with the acidic compound than is necessary to achieve the effect of suppressing image unevenness. The inventors speculate that the difference in water-abrasion resistance of the image depending on the type of water-soluble organic solvent contained in the ink is due to the difference in the degree of reaction between the anionic groups of the resin particles in the ink and the acidic compound in the reaction solution. It was thought that the water-soluble organic solvent in the ink used when the image had low water abrasion resistance inhibited the reaction between the anionic groups of the resin particles in the ink and the acidic compound in the reaction liquid.

[0017] Next, the inventors investigated the relationship between the type of water-soluble organic solvent and water abrasion resistance, and found that the water-soluble organic solvent with a relative dielectric constant of 28.0 or more and a vapor pressure of 4.0 × 10 -3 It was found that if the ink contains a large amount of water-soluble organic solvent with a dielectric constant of 28.0 or more, the reaction with the reaction liquid is inhibited. Water-soluble organic solvents with a dielectric constant of 28.0 or more promote the dissociation of ions and exhibit a stabilizing effect. Such water-soluble organic solvents inhibit the reaction between the resin particles and the acidic compound. However, if the water-soluble organic solvent as described above evaporates during the drying process of the recording medium, such as by heating the recording medium to which the ink and reaction liquid have been applied, the reaction is less likely to be inhibited. Therefore, the vapor pressure of the water-soluble organic solvent is 4.0 x 10 -3 Therefore, the relative dielectric constant of the ink must be 28.0 or more and the vapor pressure must be 4.0 × 10 -3It was found that an image with good water abrasion resistance could be obtained if the content (mass %) of the water-soluble organic solvent at or below kPa was 9.0 mass % or less based on the total mass of the ink.

[0018] Furthermore, as a result of the investigations by the present inventors, it was found that the vapor pressure was 3.1 × 10 -5 It was found that water-soluble organic solvents with a vapor pressure of 3.1 × 10 kPa or less also contribute to the deterioration of the water abrasion resistance of images. -5 Water-soluble organic solvents with a vapor pressure of 3.1 × 10 kPa or less are difficult to evaporate even after a sufficient amount of time has passed, and tend to remain in the ink layer. If such water-soluble organic solvents remain in the ink layer, the hydrophilicity of the entire ink layer increases, and water abrasion resistance does not improve. In order to achieve the desired water abrasion resistance, the vapor pressure in the ink must be 3.1 × 10 -5 It was found that the content (mass %) of the water-soluble organic solvent at or below kPa should be 9.0 mass % or less based on the total mass of the ink.

[0019] The anionic groups of the resin particles are reacted with an acidic compound to convert them to the acid form (H form), causing them to aggregate, but there is an upper limit to the amount of anionic groups in the resin particles, which must be 600 μmol / g or less. If the amount of anionic groups in the resin particles is more than 600 μmol / g, it takes a long time for the anionic groups of the resin particles to react with the acidic compound, which means that unreacted anionic groups are likely to remain in the ink layer, preventing improvement in water abrasion resistance.

[0020] As described above, the reaction and aggregation of the acidic compound and the resin particles can suppress image unevenness, while unreacted anionic groups that have not reacted with the acidic compound remain in the ink layer. When the unreacted anionic groups come into contact with water, the unreacted anionic groups undergo ionic dissociation, causing the ink layer to collapse from the dissociated anionic groups, resulting in a decrease in water abrasion resistance. The present inventors have investigated the heating temperature T F (℃) and the glass transition temperature T G It has been found that the water scratch resistance of an image can be improved by satisfying the relationship of the following formula (1) between the temperature (° C.) and the temperature (° C.). T F≧(T G -10) (1)

[0021] When the relationship of the above formula (1) is satisfied, the resin particles of the ink melt when the recording medium is heated, filling the gaps between the ink dots and integrating the ink layers. This integration of the ink layers prevents water from penetrating into the ink layers, improving the water abrasion resistance of the image.

[0022] In addition, the content (mass %) of resin particles in the ink must be at least 1.5 times the mass ratio of the content (mass %) of pigment. As mentioned above, if there are voids in the ink layer, water will easily penetrate into the ink layer, and the anionic groups remaining in the ink layer will dissociate due to water, thereby reducing the water-scratch resistance of the image. When the content of resin particles in the ink is at least 1.5 times the content of pigment, the resin particles will fill the voids between the ink dots when melted by heating, effectively preventing water from penetrating into the ink layer. When the content of resin particles in the ink is less than 1.5 times the content of pigment, the resin particles will not be able to sufficiently fill the voids between the ink dots, preventing water from penetrating into the ink layer, and therefore preventing improved water-scratch resistance.

[0023] <Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reaction liquid> The inkjet recording method of the present invention is a method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid. This inkjet recording method includes a step of applying the aqueous reaction liquid to the recording medium (a reaction liquid application step) and a step of applying the aqueous ink to the recording medium so as to overlap at least a portion of the area on the recording medium to which the aqueous reaction liquid has been applied (an ink application step). This inkjet recording method also includes a step of heating the recording medium to which the aqueous ink and aqueous reaction liquid have been applied (a heating step).

[0024] The inkjet recording apparatus of the present invention is an apparatus used to record an image on a recording medium using an aqueous ink and an aqueous reaction liquid. It is also an apparatus suitable for use in the inkjet recording method described above. This inkjet recording apparatus includes a means for applying the aqueous reaction liquid to the recording medium (a reaction liquid applying means) and a means for applying the aqueous ink (an ink applying means) so as to overlap at least a portion of the area of the recording medium to which the aqueous reaction liquid is applied. The inkjet recording apparatus also includes a means for heating the recording medium to which the aqueous ink and the aqueous reaction liquid have been applied (a heating means). The inkjet recording method and inkjet recording apparatus of the present invention do not require curing the image by irradiation with actinic energy rays or the like.

[0025] The set of aqueous ink and aqueous reaction liquid of the present invention is used in an inkjet recording method in which an image is recorded on a recording medium using the aqueous ink and the aqueous reaction liquid, and is suitable for use in the inkjet recording method. The form of the set includes a set of multiple ink cartridges, each containing a plurality of inks (reaction liquids) independently, and an ink cartridge formed by combining multiple ink reservoirs, each containing a plurality of inks (reaction liquids). The set of the present invention is not limited to the above form and may be in any form as long as it is configured to allow the inks and reaction liquids to be used in combination.

[0026] The above recording medium is a recording medium that is measured 30 msec after contact with the Bristow method. 1 / 2 Water absorption up to 10mL / m 2The following recording medium (low-absorbency or non-absorbency recording medium) is used. The aqueous reaction liquid contains a reactant that reacts with the aqueous ink. The reactant contains at least one acidic compound selected from the group consisting of organic acids and inorganic acids. The aqueous ink also contains a pigment and resin particles that are dispersed by the action of anionic groups. The amount of anionic groups in the resin particles (μmol / g) is 75 μmol / g or more and 600 μmol / g or less. The content (mass%) of the resin particles is 1.5 times or more the mass ratio of the content (mass%) of the pigment. Furthermore, in the aqueous ink, a solvent having a vapor pressure of 3.1×10 -5 The content (mass %) of the first water-soluble organic solvent having a dielectric constant of 28.0 or more and a vapor pressure of 4.0×10 -3 The content (mass %) of the second water-soluble organic solvent in the ink is 9.0 mass % or less based on the total mass of the ink. F (℃), and the glass transition temperature T G (°C) satisfies the relationship of the following formula (1). T F ≧(T G -10) (1)

[0027] The inkjet recording method and inkjet recording apparatus (hereinafter also simply referred to as "recording method and recording apparatus") of the present invention will be described in detail below.

[0028] [Ink application process and reaction liquid application process] The recording method of the present invention includes a reaction liquid applying step of applying a reaction liquid to a recording medium, and an ink applying step of applying ink so as to overlap at least a portion of the area of the recording medium to which the reaction liquid is applied. An inkjet recording head is used as the ink applying means of the recording apparatus. The reaction liquid applying means of the recording apparatus can be an inkjet recording head or a means for applying the reaction liquid to the recording medium by a coating method using various coaters, rollers, or the like. In one embodiment of the recording method and recording apparatus, it is preferable to eject the ink and the reaction liquid from an inkjet recording head and apply them to the recording medium to record an image. Therefore, in one embodiment of the recording apparatus, it is preferable to use inkjet recording heads as the ink applying means and the reaction liquid applying means. An image may be recorded by ejecting the ink and the reaction liquid from separate recording heads, or by ejecting the ink and the reaction liquid from each of multiple ejection port arrays provided on a single recording element substrate.

[0029] FIG. 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. FIG. 2 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. As shown in FIGS. 1 and 2, the recording apparatus of this embodiment includes an inkjet recording head 22 that ejects ink. The recording head 22 is a recording head that ejects ink by the action of thermal energy. A recording head that ejects ink by the action of thermal energy applies thermal energy to the ink by applying an electric pulse to an electrothermal conversion element, causing the ink to be ejected from the ejection opening. While a recording head that ejects ink by the action of thermal energy has been described as an example here, a recording head that ejects ink by the action of mechanical energy may also be used. The recording head may be equipped with a mechanism (temperature control mechanism) that heats the aqueous ink ejected from the recording head. If a temperature control mechanism is provided, the temperature of the ink ejected from the recording head is preferably set to 35°C or higher and 70°C or lower.

[0030] [Heating process] In the recording method of the present invention, the recording medium to which the ink and the reaction liquid have been applied is heated to a predetermined temperature T F The method includes a heating step of heating (heat treatment) the recording medium to (°C). Heating the recording medium to which the ink and reaction liquid have been applied promotes the formation of a film of resin particles, making it possible to record an image with excellent water abrasion resistance.

[0031] Examples of the means for heating the recording medium include known heating means such as a heater, air blowing means using air blowing such as a dryer, and a combination of these. That is, the inkjet recording apparatus heats the recording medium to which the ink and the reaction liquid have been applied at a predetermined heating temperature T F The recording medium is provided with a mechanism (heating means) for heating to (°C). Examples of the heating means include the above-mentioned warming means, air blowing means, and a combination of these. Examples of the heat treatment method include a method of applying heat from the side opposite (backside of) the recording surface (ink application surface) of the recording medium using a heater, a method of blowing warm or hot air onto the recording surface of the recording medium, and a method of heating from the recording surface or backside using an infrared heater. A combination of these methods may also be used.

[0032] Since the scratch resistance of the image can be improved, the heating temperature T F The heating temperature T (°C) is preferably 50°C or higher and 90°C or lower. Here, the heating temperature of the recording medium to which the ink and reaction liquid have been applied can also be said to be the temperature of the recorded image or the temperature reached by heating the recording medium to which the ink and reaction liquid have been applied. The heating temperature T of the recording medium to which the ink and reaction liquid have been applied F The temperature (°C) may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined according to the type of ink and recording medium.

[0033] Heating temperature T of recording medium F (℃) and the glass transition temperature T G (℃) F -T G) is -10°C or higher and 0°C or higher (i.e., heating temperature T F is the T of the resin particles G It is more preferable that the difference (T F -T G ) is -10°C or higher, the resin particles are easily fused, and the effect of improving the water abrasion resistance of the image is obtained. F (℃) and the glass transition temperature T G (℃) F -T G ) is preferably +50°C or less, more preferably +30°C or less, and even more preferably +20°C or less.

[0034] The amount of heat ((W·h) / g) applied to the ink applied to the recording medium is preferably 2 (W·h) / g or more. By applying a heat amount of 2 (W·h) / g or more to the ink, the ink applied to the recording medium can be dried sufficiently, and the water abrasion resistance of the recorded image can be improved. The amount of heat ((W·h) / g) applied to the ink applied to the recording medium is preferably 10 (W·h) / g or less. The amount of heat applied to the ink can be measured as follows. First, the power A (W) applied to the heating means that heats the recording medium is measured. Also, the recording area B (m ) per unit time of the recording device is measured. 2 / h), and the ink consumption per unit area used for this printing, C (g / m 2 From these values, the amount of heat ((W·h) / g) applied to the ink applied to the recording medium is calculated based on the following formula (2). Amount of heat applied to ink applied to recording medium ((W·h) / g) =A(W) / B(m 2 / h) / C(g / m 2 ) ···(2)

[0035] In the recording device shown in FIGS. 1 and 2, a heater 25 supported by a frame (not shown) is disposed downstream in the sub-scanning direction A from the position where the recording head 22 reciprocates in the main scanning direction B. The recording medium 1 to which ink has been applied can be heated by the heater 25. Specific examples of the heater 25 include a sheath heater and a halogen heater. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 onto the recording medium 1. The heater cover 26 also serves as a member for protecting the heater 25. The recording medium 1 to which ink ejected from the recording head 22 has been applied is wound up by a take-up spool 27 to form a roll-shaped wound medium 24.

[0036] [Recording medium] In the recording method and recording device of the present invention, a low-absorbency or non-absorbent recording medium (low to non-absorbent recording medium) is used. The low-absorbency to non-absorbent recording medium is a recording medium that is measured by the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51, "Liquid Absorbency Test Method for Paper and Paperboard," and is measured within 30 msec from the start of contact. 1 / 2 Water absorption up to 10mL / m 2 That is, in the recording method and recording device of the present invention, the recording medium is a recording medium having a recording time of 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 0mL / m 2 More than 10mL / m 2 The following recording media are used. In this specification, a recording medium that satisfies the above-mentioned condition of water absorption amount is defined as a "low to non-absorbent recording medium." Inkjet recording media (glossy paper, matte paper, etc.) having a coating layer (ink receiving layer) formed of inorganic particles, and plain paper without a coating layer, have a water absorption amount of 10 mL / m or more. 2 It is an "absorbent recording medium" that exceeds

[0037] Examples of low to non-absorbent recording media that can be used include plastic films, recording media in which a plastic film is bonded to the recording surface of a substrate, and recording media in which an organic resin layer is provided on the recording surface of a substrate containing cellulose pulp. Of these, plastic films are preferred, and recording media in which an organic resin layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred.

[0038] When an ink containing resin particles is applied to a non-absorbent recording medium, components such as water and water-soluble organic solvents volatilize, concentrating the resin particles. This promotes fusion between the concentrated resin particles, improving the strength of the recorded image. In contrast, even when the ink is applied to a recording medium with high absorbency of liquid components (an absorbent recording medium), it is difficult to promote fusion between the resin particles, making it difficult to improve the strength of the image. Note that the recording medium in this specification does not refer to a transfer medium, but rather to a recording medium on which an image is recorded as a recorded product.

[0039] [Reaction solution] The recording method of the present invention includes a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to a recording medium. It is particularly preferred to have the reaction liquid application step before the ink application step, or to perform the ink application step and the reaction liquid application step in parallel. The components used in the reaction liquid are described in detail below.

[0040] [Reactant] The reaction liquid reacts with the ink upon contact with it, aggregating components in the ink (resins, self-dispersible pigments, and other components with anionic groups). The reaction liquid contains a reactant. The presence of the reactant destabilizes the state of the components with anionic groups in the ink when the ink and the reactant come into contact on the recording medium, promoting ink aggregation. Examples of the reactant include acid-type inorganic acids and organic acids. Specifically, the reactant contains at least one acidic compound selected from the group consisting of organic acids and inorganic acids. The content (mass %) of the acidic compound in the reaction liquid is preferably 0.10% by mass or more and 15.0% by mass or less, and more preferably 0.20% by mass or more and 10.0% by mass or less, based on the total mass of the reaction liquid. The content is particularly preferably 0.20% by mass or more and 5.0% by mass or less.

[0041] Inorganic acids readily dissociate in water, releasing protons and converting the anionic groups of the components present in the ink into the acid form, causing them to aggregate. Inorganic acids are also called mineral acids. Examples of inorganic acids include hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid. One or more of these acids can be used.

[0042] The organic acid-containing reaction solution has buffering properties in the acidic range (less than pH 7.0, preferably pH 2.0 to 5.0), thereby efficiently converting anionic groups present in the ink into the acid form and causing them to aggregate. Examples of organic acids include monocarboxylic acids and salts thereof, such as formic acid, acetic acid, propionic acid, butyric acid, pivalic acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrolecarboxylic acid, pyrrolidonecarboxylic acid, furancarboxylic acid, picolinic acid, nicotinic acid, thiophenecarboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and salts thereof, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and salts thereof, such as citric acid and trimellitic acid; and tetracarboxylic acids and salts thereof, such as pyromellitic acid. When an organic acid is used as a reactant, the content (mass %) of the organic acid in the reaction liquid is preferably 1.0 mass % or more and 50.0 mass % or less based on the total mass of the reaction liquid.

[0043] From the viewpoint of more easily increasing the water abrasion resistance of the image, organic acids are preferred among the acidic compounds. That is, the acidic compound in the aqueous reaction liquid is preferably an organic acid. Because organic acids have buffering ability, they react slowly with the anionic groups of the resin particles, and unreacted resin particles are less likely to remain.

[0044] Among organic acids, those with a pKa of 4.9 or less are preferred. In other words, the pKa of an organic acid is preferably 4.9 or less. pKa indicates the ease of dissociation of an acid proton, and is expressed as the negative common logarithm of the acid dissociation constant (Ka) (pKa=-log 10Ka). Here, if the organic acid has multiple pKas, it is designated as the first pKa. This is because the amount of acid dissociated in the reaction solution is largely determined by the first pKa. If the pKa of the organic acid is 4.9 or less, the effect of aggregating the resin particles is enhanced, and the effect of suppressing image unevenness is more easily achieved. Furthermore, if the resin particles are dispersed by the action of carboxylic acid groups, which are anionic groups, it is preferable to use an organic acid with a pKa of 2.8 or more. If the pKa of the organic acid is 2.8 or more, the effect of the above-mentioned gradual reaction of the organic acid is more easily achieved.

[0045] Furthermore, the pKa of the organic acid is preferably equal to or lower than the pKa of the anionic group of the resin particles in the ink. By having the pKa of the organic acid equal to or lower than the pKa of the anionic group of the resin particles, the reaction between the resin particles and the organic acid proceeds at a moderate rate, minimizing the proportion of unreacted resin particles, and further improving the water abrasion resistance of the image. Here, when the anionic group of the resin particles has multiple pKas, the reactivity with the organic acid is mostly contributed by the first acid dissociation constant, which can be considered as the first pKa (pKa1).

[0046] The reaction solution may contain a reactant (other reactant) other than the above-mentioned acidic compound. Examples of the other reactant include polyvalent metal salts and cationic resins. One or more of these can be used.

[0047] When the reactant further contains a polyvalent metal salt in addition to the acidic compound, it is preferable to use a polyvalent metal salt having a solubility in water at 20°C (g / 100mL) of 70.0g / 100mL or less from the viewpoint of further improving the effect of suppressing image unevenness and water abrasion resistance. Furthermore, when the reactant further contains a cationic resin in addition to the above-mentioned acidic compound, it is preferable to use a cationic resin having a cationic degree (meq / g) of 3 meq / g or more and 7 meq / g or less from the viewpoint of further improving the effect of suppressing image unevenness and water abrasion resistance.

[0048] The cationic degree (meq / g) of the cationic resin in this specification is a value at pH 7.0 defined by the colloid equivalent value using a polyvinyl potassium sulfate reagent. Specifically, it is measured by colloid titration using an automatic potentiometric titrator (trade name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) and a 1 / 400N (mol / L) polyvinyl potassium sulfate solution (trade name "N / 400 PVSK Solution", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the titration reagent. The cationic degree is then calculated using the formula: cationic degree (meq / g) = (titration volume (mL) of 1 / 400N polyvinyl potassium sulfate solution / 400) / (amount of cationic resin sample (g) × sample concentration (mass%)). The apparatus used to calculate the cationic degree is not limited to the above. The cationic degree (meq / g) of the cationic resin used in the examples below is a value measured by the above method.

[0049] Acidic compounds aggregate by converting the anionic groups in the ink into the acid form (H form), making them insoluble, so their ability as a flocculant is not very high.Reactants with multiple reactive sites per molecule, such as polyvalent metal ions in polyvalent metal salts and cationic resins, form three-dimensional entanglements (networks) of molecular chains when they react with resin particles, which tends to increase viscosity when aggregated.

[0050] Polyvalent metal salts and cationic resins enhance coagulation and are effective in suppressing image unevenness. Meanwhile, the reaction products of polyvalent metal salts or cationic resins with anionic groups on resin particles have higher solubility than the reaction products of acidic compounds with anionic groups on resin particles. Therefore, to achieve sufficiently high levels of both water resistance and abrasion resistance, it is preferable for the resin particles to react with both reactants. To this end, the solubility (g / 100 mL) of the polyvalent metal salt in water at 20°C is preferably 70.0 g / 100 mL or less. Furthermore, it is preferable for the cationic resin to have a cationic degree of 3 meq / g or more and 7 meq / g or less at pH 7.0, as defined by the colloidal equivalent value using a polyvinyl potassium sulfate reagent.

[0051] The higher the solubility of the polyvalent metal salt, the greater the dissociation in water and the faster the reaction rate tends to be. When a polyvalent metal salt is used as a reactant together with an acidic compound, a polyvalent metal salt having a solubility in water at 20°C of 70.0 g / 100 mL or less is used so that the resin particles also react with the acidic compound. Furthermore, from the viewpoint of the effect of suppressing image unevenness, the solubility of the polyvalent metal salt is preferably 3.0 g / 100 mL or more.

[0052] In cationic resins, the higher the cationic degree, the more reactive sites there are, and if the cationic degree is too high, the cationic resin tends to preferentially react with one resin particle, resulting in increased solubility. On the other hand, from the viewpoint of the effect of suppressing image unevenness, it is preferable that the cationic resin has a certain level of cationic degree. Therefore, when a cationic resin is used together with an acidic compound as a reactant, it is preferable to use a cationic resin having a cationic degree of 3 meq / g or more and 7 meq / g or less at pH 7.0.

[0053] Examples of polyvalent metal ions that constitute polyvalent metal salts include Ca. 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Sr 2+ , Ba 2+ , and Zn 2+ Divalent metal ions such as Fe 3+ , Cr 3+ , Y 3+ , and Al 3+ Examples of the trivalent metal ions include trivalent metal ions such as Cl. To add polyvalent metal ions to the reaction solution, a water-soluble polyvalent metal salt (which may be a hydrate) formed by combining a polyvalent metal ion with an anion can be used. Examples of the anion include Cl. - , Br - , I - , ClO - , ClO2 - , ClO3 - , ClO4 - , NO2 - , NO3 - , SO4 2- , CO3 2- , HCO3- , PO4 3- , HPO4 2- , and H2PO4 - Inorganic anions such as HCOO - , (COO - )2, COOH(COO - ), CH3COO - , C2H5COO - , CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - and other organic anions.

[0054] Examples of polyvalent metal salts having a solubility of 70.0 g / 100 mL or less in water at 20° C. include calcium lactate (3.1 g / 100 mL), calcium acetate (31.1 g / 100 mL), magnesium sulfate (26.9 g / 100 mL), aluminum chloride (46.0 g / 100 mL), magnesium acetate (53.4 g / 100 mL), and magnesium nitrate (69.0 g / 100 mL). The values in parentheses above represent the solubility (g / 100 mL) in water at 20° C.

[0055] From the viewpoint of easily achieving a balance between the reactivity of the anionic groups of the resin particles with the polyvalent metal salt and the reactivity of the anionic groups of the resin particles with the acidic compound, the polyvalent metal salt is preferably a divalent metal ion. Among them, magnesium ions (Mg 2+ ) is more preferred because the degree of dissociation of the ionic bond with the anionic group is not too high and the salt has excellent water abrasion resistance.

[0056] When polyvalent metal ions are used as reactants, the content (mass %) of the polyvalent metal salt in the reaction solution is preferably 1.0% by mass or more and 20.0% by mass or less, based on the total mass of the reaction solution. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass %) of the polyvalent metal salt" in the reaction solution refers to the "content (mass %) of the anhydrous polyvalent metal salt," excluding water as the hydrate. Furthermore, the content (mol) of the polyvalent metal salt in the aqueous reaction solution is preferably 0.60 to 10.0 times the molar ratio of the content (mol) of the acidic compound. By setting the molar ratio at 0.60 or more, the effect of suppressing image unevenness can be further improved. On the other hand, by setting the molar ratio at 10.0 or less, the water abrasion resistance of the image can be further improved.

[0057] Examples of cationic resins include resins having a primary, secondary, or tertiary amine structure and resins having a quaternary ammonium salt structure. Specific examples include resins having structures such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. To enhance solubility in the reaction solution, the cationic resin can be used in combination with an acidic compound or the cationic resin can be subjected to a quaternization treatment. When a cationic resin is further used as a reactant, the content (mass %) of the cationic resin in the reaction solution is preferably 0.10% by mass or more and 10.0% by mass or less, based on the total mass of the reaction solution.

[0058] The content (mass %) of the cationic resin in the aqueous reaction liquid is preferably 1.25 to 12.60 times the content (mass %) of the acidic compound. When the mass ratio is 1.25 or more, the proportion of the cationic resin increases, which facilitates the formation of a network between the resin particles, thereby further improving the effect of suppressing image unevenness. On the other hand, when the mass ratio is 12.60 or less, a certain proportion of the acidic compound relative to the cationic resin is ensured, which facilitates the effect of reducing the hydrophilicity of the ink layer, thereby further improving the water abrasion resistance of the image.

[0059] The weight-average molecular weight of the cationic resin is preferably 15,000 or less, and more preferably 10,000 or less. When the weight-average molecular weight of the cationic resin is 15,000 or less, the formation of an aggregation network with the resin particles is facilitated, and the effect of suppressing image unevenness can be further improved. The weight-average molecular weight of the cationic resin is preferably 1,000 or more. Here, the weight-average molecular weight of the cationic resin can be measured as a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0060] The cationic resin preferably has a quaternary amine structure as a cationic moiety. Compared with cationic resins that do not have a quaternary amine structure but have a primary to tertiary amine structure, cationic resins that have a quaternary amine structure are less likely to lose their cationic properties even when the pH is lowered by the addition of an acid, and therefore can have increased reactivity with resin particles.

[0061] [Aqueous medium] The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. Examples of the aqueous medium used in the reaction liquid include the same aqueous media as those described below that can be contained in the ink. The water content (mass %) in the reaction liquid is preferably 50.0 mass % or more, more preferably 60.0 mass % or more, and preferably 90.0 mass % or less, based on the total mass of the reaction liquid.

[0062] [Other ingredients] The reaction liquid may contain various other components as needed, including the same components as those that can be contained in the ink, which will be described later.

[0063] [Physical properties of reaction solution] The reaction liquid is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN / m or more and 60 mN / m or less. Furthermore, the viscosity of the reaction liquid at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction liquid at 25°C is preferably 1.7 or more and 7.0 or less, and more preferably 2.0 or more and 4.0 or less.

[0064] [ink] The recording method of the present invention includes an ink application step of applying an ink to a recording medium so as to overlap at least a portion of an area to which a reaction liquid is applied. The ink used in this recording method is an aqueous inkjet ink containing a pigment and resin particles dispersed by the action of anionic groups. Each component of the ink will be described in detail below.

[0065] [Pigments] The ink contains a pigment as a coloring material. The content (mass %) of the pigment in the ink is preferably 0.1% to 15.0% by mass, and more preferably 1.0% to 10.0% by mass, based on the total mass of the ink.

[0066] Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide, and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, etc. One type of pigment may be used alone, or two or more types may be used in combination.

[0067] Pigment dispersion methods include resin-dispersed pigments that use a resin (resin dispersant) as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface. Other methods include resin-bonded pigments in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microencapsulated pigments in which the pigment particle surface is coated with a resin or the like. It is also possible to combine pigments with different dispersion methods. Among these, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than resin-bonded pigments or microencapsulated pigments. In other words, it is preferable for the pigment to be dispersed by the action of a resin dispersant.

[0068] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of anionic groups. As the resin dispersant, a resin having anionic groups can be used, and it is preferable to use a resin such as those described below, especially a water-soluble resin. The content (mass %) of the pigment in the ink is preferably 0.3 to 10.0 times the mass ratio of the content of the resin dispersant.

[0069] Self-dispersing pigments can be used in which an anionic group such as a carboxylic acid group, sulfonic acid group, or phosphonic acid group is bonded to the surface of the pigment particle directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include alkali metal cations, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Furthermore, combinations of these groups may also be used.

[0070] [Resin particles] The ink contains resin particles dispersed by the action of anionic groups. When the ink contains resin particles dispersed by the action of anionic groups, they react with the reactant when they come into contact with the reaction liquid on the surface of the recording medium. As a result, the resin particles having anionic groups form large aggregates, which can suppress image unevenness and also provide the ink film strength required for water abrasion resistance.

[0071] The content (mass %) of resin particles in the ink must be at least 1.5 times the mass ratio of the pigment content (mass %). When the content of resin particles in the ink is at least 1.5 times the mass ratio of the pigment content, the resin particles melt when heated, filling the gaps between the ink dots and preventing water from penetrating into the ink layer. When the content of resin particles in the ink is less than 1.5 times the mass ratio of the pigment content, the resin particles cannot sufficiently fill the gaps between the ink dots, preventing water from penetrating into the ink layer and preventing improved water abrasion resistance. It is more preferable that the content (mass %) of resin particles in the ink be at least 1.7 times the mass ratio of the pigment content (mass %), and preferably no more than 40.0 times.

[0072] In this specification, "resin particles" refers to a resin that can be dispersed in an aqueous medium and exist in the aqueous medium in a state of having a particle size. Resin particles are resins that do not dissolve in the aqueous medium that constitutes the ink, and specifically, resins that can exist in the aqueous medium in a state of forming particles whose particle size can be measured by dynamic light scattering. Therefore, the resin particles exist in a state of being dispersed in the ink, i.e., in the state of a resin emulsion. Furthermore, these resin particles may encapsulate coloring materials (dyes, pigments, invisible coloring materials that develop color by fluorescence, etc.).

[0073] Whether a resin is a "resin particle" can be determined according to the following method. First, a liquid (resin solids content: 10% by mass) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. The particle size of the resin in the sample solution is measured by dynamic light scattering. If particles having a certain particle size are measured, the resin can be determined to be a "resin particle." A particle size analyzer (e.g., "UPA-EX150" manufactured by Nikkiso) can be used as a particle size distribution measurement device using dynamic light scattering. The measurement conditions can be, for example, Set Zero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above. The particle size is measured using neutralized resin to confirm that particles are formed even when the resin is sufficiently neutralized to make particle formation more difficult. Even under these conditions, the resin remains in particle form in the aqueous ink.

[0074] Examples of the resin constituting the resin particles include acrylic resins, urethane resins, olefin resins, and polyester resins, among which acrylic resins are preferred.

[0075] (acrylic resin) The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit as constituent units. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferred. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferred.

[0076] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium.

[0077] The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0078] (urethane resin) The urethane resin can be obtained by reacting, for example, polyisocyanate with a polyol. Alternatively, a chain extender may be further added to the urethane resin. Examples of the olefin resin include polyethylene and polypropylene.

[0079] (polyester resin) Polyester resins are resins composed of units derived from polyhydric alcohols and units derived from polycarboxylic acids. Examples of polyhydric alcohols that make up the polyhydric alcohol-derived units of polyester resins include dihydric, tetrahydric, and tetrahydric alcohols. Examples of polyhydric alcohol structures include polyhydric alcohols with aliphatic groups, polyhydric alcohols with aromatic groups, and sugar alcohols. Specific examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. Furthermore, oligomers (low-molecular polymers with a molecular weight of 1,000 or less) can also be used as polyhydric alcohols.

[0080] It is preferable to use dihydric or trihydric polyhydric alcohols because it is easy to adjust the weight-average molecular weight of the polyester resin. Also, from the viewpoint of structure, it is preferable to use polyhydric alcohols having an aliphatic group or polyhydric alcohols having an aromatic group. As the polyhydric alcohols having an aliphatic group, polyhydric alcohols having a linear or branched aliphatic group with 1 to 6 carbon atoms are more preferable.

[0081] Examples of the polycarboxylic acid that constitutes the polyester resin by reaction and that is derived from the polycarboxylic acid include divalent to tetravalent polycarboxylic acids. Examples of the structure of the polycarboxylic acid include polycarboxylic acids having an aliphatic group, polycarboxylic acids having an aromatic group, and nitrogen-containing polycarboxylic acids. Specific examples of the polycarboxylic acid include dicarboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; tricarboxylic acids such as trimellitic acid; and tetracarboxylic acids such as ethylenediaminetetraacetic acid. Furthermore, oligomers (low-molecular polymers having a molecular weight of 1,000 or less) can also be used as the polycarboxylic acid.

[0082] It is preferable to use divalent or trivalent polycarboxylic acids because it is easy to adjust the weight average molecular weight and acid value of the polyester resin. Also, from the viewpoint of structure, it is preferable to use carboxylic acids having an aromatic group or carboxylic acids having an aromatic group. In particular, it is preferable to use adipic acid, terephthalic acid, isophthalic acid, or trimellitic acid, and it is also preferable to use two or more of these in combination.

[0083] The anionic group is a group contained in a unit derived from the above-mentioned monomer, and examples thereof include a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group. The resin particles may be dispersed in the ink by the action of one or more of these anionic groups. Among these, the anionic group is preferably a carboxylic acid group. Since the carboxylic acid group has a lower degree of dissociation than other anionic groups such as a sulfonic acid group and a phosphonic acid group, it is easier to obtain an image with even better water abrasion resistance.

[0084] The content (mass %) of resin particles in the ink is preferably 2.0 mass % or more and 50.0 mass % or less, and more preferably 2.0 mass % or more and 20.0 mass % or less, based on the total mass of the ink.

[0085] (Method of producing resin particles) The resin particles can be produced by a conventional method such as emulsion polymerization, mini-emulsion polymerization, seed polymerization, or phase inversion emulsification. Among these, emulsion polymerization and seed polymerization are preferred because they can produce resin particles with a more uniform particle size. By using resin particles with a more uniform particle size, the ejection properties of the ink in an inkjet system can be further stabilized.

[0086] The weight-average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 3,000,000 or less, and more preferably 100,000 or more and 3,000,000 or less. The weight-average molecular weight of the resin constituting the resin particles can be measured as a polystyrene-equivalent value measured by gel permeation chromatography (GPC). The volume-average particle diameter (volume-based cumulative 50% particle diameter; D) of the resin particles measured by dynamic light scattering can also be measured. 50 The cumulative 50% particle diameter (D) in the volume-based particle size distribution of the resin particles is preferably 50 nm or more and 500 nm or less. 50 ) can be measured using the particle size distribution measuring device (for example, trade name "UPA-EX150" manufactured by Nikkiso) that uses the dynamic light scattering method described above.

[0087] (Thermal properties of resin particles) From the viewpoint of improving the adhesion and abrasion resistance of the image, the resin particles are heated to a temperature T F (℃) and the glass transition temperature T G (°C) must satisfy the relationship of the following formula (1). T F ≧(T G -10) (1)

[0088] The characteristic of the above formula (1) is the temperature T F (℃) is the thermal property required for sufficient film formation. Also, the glass transition temperature T GThe glass transition temperature T (°C) of the resin particles is preferably 0°C or higher and 100°C or lower, more preferably 30°C or higher, and even more preferably 90°C or lower. G When the glass transition temperature (°C) is 30°C or higher, the formed ink layer is moderately hard, and the water abrasion resistance can be further improved. The glass transition temperature (°C) of the resin particles can be measured using a differential scanning calorimeter (DSC). The glass transition temperature of the resin particles used in the examples was measured by DSC.

[0089] (Physical Properties) The amount of anionic groups in the resin particles (μmol / g) is 75 μmol / g or more and 600 μmol / g or less. In particular, the amount of anionic groups in the resin particles is preferably 95 μmol / g or more and 270 μmol / g or less. This value represents the density (in micromoles) of the anionic groups present in the resin particles per unit mass of the resin particles. Having the amount of anionic groups in the resin particles of 95 μmol / g or more can further improve the effect of suppressing image unevenness. On the other hand, having the amount of anionic groups in the resin particles of 270 μmol / g or less can further improve the water abrasion resistance of the image. Below, a method for extracting and analyzing resin particles from ink will be described, but similar analysis and verification can also be performed on resin particles extracted from an aqueous dispersion, etc.

[0090] (i) Extraction of resin particles Density gradient centrifugation can be used to separate and extract resin particles from ink containing them. Among density gradient centrifugation methods, density gradient sedimentation velocity separates and extracts resin particles based on the difference in sedimentation coefficient of the components. Also, among density gradient centrifugation methods, density gradient sedimentation equilibrium separates and extracts resin particles based on the difference in density of the components. Resin particles can be separated using this density gradient centrifugation method.

[0091] (ii) Measurement of the amount of anionic groups The amount of anionic groups in the resin particles can be determined by colloid titration using potential difference. In the examples described below, the amount of anionic groups in the resin particles (μmol / g) was measured by colloid titration using potential difference using an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). In this case, the pH of the resin particle dispersion during measurement was adjusted to 8 to 9, and methyl glycol chitosan was used as the titration reagent.

[0092] [Other resins] In addition to the resin particles described above that are dispersed by the action of anionic groups, the ink may contain other resins. Hereinafter, resins other than the resin particles described above that are dispersed by the action of anionic groups may be referred to simply as "resins." The content (mass %) of the resin in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0093] Resins can be added to inks (i) to stabilize the dispersion state of pigments, i.e., as a resin dispersant or its auxiliary. Resins can also be added to inks (ii) to improve various properties of the printed image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. Furthermore, the resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium, i.e., the resin particles described above. In this specification, the term "water-soluble resin" refers to a resin that can be dissolved in the aqueous medium that constitutes the ink. Specifically, it refers to a resin that can exist in an aqueous medium without forming particles whose particle size can be measured by dynamic light scattering.

[0094] (Resin Composition) Examples of the resin include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

[0095] The acrylic resin is preferably one having a hydrophilic unit and a hydrophobic unit as constituent units. Among these, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic ring and a (meth)acrylic acid ester-based monomer is preferred. A resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is particularly preferred. These resins are likely to interact with pigments, and can therefore be suitably used as resin dispersants for dispersing pigments.

[0096] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not having a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0097] The urethane resin can be obtained by, for example, reacting a polyisocyanate with a polyol. Alternatively, a chain extender may be further added to the urethane resin. Examples of the olefin resin include polyethylene and polypropylene.

[0098] (Resin properties) As used herein, the term "water-soluble resin" means that when the resin is neutralized with an alkali equivalent to its acid value, it exists in an aqueous medium in a state in which it does not form particles whose particle size can be measured by dynamic light scattering. Whether a resin is water-soluble or not can be determined according to the following method. First, a liquid (resin solids content: 10% by mass) containing the resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. When the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles having the particle size are measured, the resin can be determined to be water-soluble. The measurement conditions can be, for example, Set Zero: 30 seconds, measurement count: 3, and measurement time: 180 seconds. Furthermore, a particle size distribution measuring device such as a particle size analyzer using dynamic light scattering (e.g., the "UPA-EX150" product, manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring device and measuring conditions to be used are not limited to those described above.

[0099] The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 mgKOH / g or less. Herein, the acid value of the resin can be a value measured by a potentiometric titrator using a potassium hydroxide-methanol titrant. The weight-average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. Herein, the weight-average molecular weight of the resin can be measured as a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0100] [Wax particles] The ink may contain particles formed from wax (wax particles). By using ink containing wax particles, it is possible to record images with further improved abrasion resistance. In this specification, the term "wax" may refer to a composition containing components other than wax, or to wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a water-soluble resin. One type of wax may be used alone, or two or more types may be used in combination. The content (mass %) of wax particles in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total mass of the ink.

[0101] In a narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes but excludes oils and fats. In a broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method of the present invention, any wax in the broad sense can be used without particular limitation. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends thereof (blended waxes), and modified products thereof (modified waxes).

[0102] Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); plant waxes such as Japan wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). Blended waxes are mixtures of the above waxes. Modified waxes are those obtained by modifying the above waxes through oxidation, hydrogenation, alcohol modification, acrylic modification, urethane modification, or other such processes. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended versions thereof. Among these, a blend of multiple types of wax is more preferred, and a blend of petroleum wax and synthetic wax is particularly preferred.

[0103] The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (Melting Point Test Method) of JIS K2235:1991 (Petroleum Wax). For microcrystalline wax, petrolatum, and mixtures of multiple waxes, the test method described in 5.3.2 can be used for more accurate measurement. The melting point of the wax is easily affected by properties such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (linear chains have a high melting point, and branched chains have a lower melting point), crystallinity (the higher the crystallinity), and density (the higher the crystallinity). Therefore, by controlling these properties, a wax with the desired melting point can be obtained. The melting point of the wax in the ink can be measured, for example, by ultracentrifuging the ink, washing and drying the separated wax, and then measuring it in accordance with the above test method.

[0104] [Aqueous medium] The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 40.0% to 95.0% by mass, and more preferably 50.0% to 90.0% by mass, based on the total mass of the ink.

[0105] The water-soluble organic solvent can be any solvent that can be used in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents. A single water-soluble organic solvent may be used alone, or two or more may be used in combination. The content (mass %) of the water-soluble organic solvent in the ink is preferably 2.0% by mass or more and 50.0% by mass or less, and more preferably 3.0% by mass or more and 45.0% by mass or less, based on the total mass of the ink. The content of the water-soluble organic solvent in the ink may be 0% by mass. In other words, the ink may not contain a water-soluble organic solvent.

[0106] As mentioned above, in order to improve water abrasion resistance, the ink vapor pressure should be 3.1 × 10 -5 The content (mass %) of the first water-soluble organic solvent with a dielectric constant of 28.0 or more and a vapor pressure of 4.0×10 -3 The content (mass %) of the second water-soluble organic solvent having a dielectric constant of 0.0 kPa or less must be 9.0 mass % or less, based on the total mass of the ink. Preferably, the content (mass %) of the first water-soluble organic solvent is 3.0 mass % or less, based on the total mass of the ink, and the content (mass %) of the second water-soluble organic solvent is 3.0 mass % or less, based on the total mass of the ink. The contents of the first water-soluble organic solvent and the second water-soluble organic solvent in the ink may both be 0.0 mass %. In other words, the ink may be substantially free of the first water-soluble organic solvent and the second water-soluble organic solvent. Furthermore, the first water-soluble organic solvent may satisfy the requirements of the second water-soluble organic solvent. In other words, the first water-soluble organic solvent has a relative dielectric constant of 28.0 or more and a vapor pressure of 3.1 × 10 -5 kPa or less may also be used.

[0107] The "vapor pressure" in this specification is a value at 25°C and 1 atmosphere. Furthermore, the "dielectric constant" in this specification is a value measured at 25°C. The dielectric constant of a water-soluble organic solvent can be measured, for example, using a dielectric constant measuring instrument (trade name "BI-870", manufactured by Nippon Rufuto). The dielectric constants of the water-soluble organic solvents used in the examples described below are values measured by the above method.

[0108] Vapor pressure is 3.1 x 10 -5 The first water-soluble organic solvent with a viscosity of 0.1 kPa or less is, for example, triethanolamine (1.0 × 10 -6 ), polyethylene glycol with a number average molecular weight of 600 (1.0 × 10 -6 ), glycerin (3.1 × 10 -5 ), 1,2,6-hexanetriol (2.8 × 10 -6 ), 1-(2-hydroxyethyl)-2-pyrrolidone (2.0 × 10 -5 ), and trimethylolpropane (2.1 × 10 -5 The values in parentheses above are vapor pressures (kPa) at 25°C. Some first water-soluble organic solvents meet the definition of second water-soluble organic solvents.

[0109] A specific example of the second water-soluble organic solvent is glycerin (42.3 / 3.1×10 -5 ), 2-methylhexane-1,3-propanediol (28.3 / 2.8 × 10 -3 ), 1,4-butanediol (31.1 / 1.9×10 -3 ), trimethylolpropane (33.7 / 2.1 x 10 -5 ), diethylene glycol (31.7 / 6.0×10 -4 ), 3-methylsulfolane (29.0 / 9.4×10 -4 ), and 2-pyrrolidone (28.0 / 3.9 × 10 -3 ) are examples. The value in the parentheses above is the relative dielectric constant at 25°C on the left, and the vapor pressure (kPa) at 25°C on the right. Some second water-soluble organic solvents meet the definition of the first water-soluble organic solvent.

[0110] From the viewpoint of further improving the water abrasion resistance of the image, it is preferable that the ink further contains a third water-soluble organic solvent having a vapor pressure lower than that of water. A certain degree of ink fluidity is necessary for the diffusion of protons, but water has a very high vapor pressure, so it evaporates quickly and the fluidity of the ink is likely to decrease. Therefore, by adding a water-soluble organic solvent having a vapor pressure lower than that of water and not inhibiting the reaction to the ink, the resin particles can react evenly. Here, the third water-soluble organic solvent may be one of the first and second water-soluble organic solvents, or a water-soluble organic solvent having a vapor pressure of 4.0×10 -3 The third water-soluble organic solvent may be a water-soluble organic solvent having a vapor pressure of more than 1.0 kPa and lower than that of water. The vapor pressure of water at 25°C is 3.2 kPa. The content (mass %) of the third water-soluble organic solvent in the ink is preferably 1.0 mass % or more and 20.0 mass % or less, based on the total mass of the ink.

[0111] Among the third water-soluble organic solvents, 1,2-alkanediols are preferred for ensuring uniform reaction of the resin particles. 1,2-alkanediols function like surfactants because the hydrophilic hydroxyl groups are concentrated at the ends of the molecule. In other words, the hydrocarbon groups are easily solvated in the hydrophobic portions of the resin particles. This increases the fluidity around the resin particles, facilitating the reaction between the resin particles and the acidic compound, further improving water abrasion resistance. Examples of 1,2-alkanediols include 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol. One or more of these can be used.

[0112] Furthermore, when a 1,2-alkanediol is incorporated into the ink, the ratio of the anionic groups of the pigment (μmol / g) to the anionic groups of the resin particles (μmol / g) is preferably 2.0 times or more, from the viewpoint of further enhancing the water abrasion resistance of the image. When the anionic groups of the pigment are 2.0 times or more the anionic groups of the resin particles, the hydrophilicity of the pigment is enhanced. As described above, 1,2-alkanediols have a structure that easily solvates in hydrophobic portions, so they tend to preferentially solvate with the resin particles. This further enhances the fluidity around the resin particles. Furthermore, preferential solvation of the 1,2-alkanediol with the resin particles makes the pigment more susceptible to aggregation due to hydrophobic interactions. As a result, the pigments aggregate first, and then the resin particles form an ink layer, enveloping the pigment aggregates. Since pigments tend to have weaker film strength than resin particles, their presence between resin particles can reduce film strength. However, the resin particles enveloping the pigment aggregates reduces film strength. Furthermore, the ratio of the anionic groups in the pigment to the anionic groups in the resin particles is preferably 3.0 times or more, and more preferably 4.5 times or less. The amount of anionic groups in the pigment (μmol / g) can be determined by colloid titration, similar to the amount of anionic groups in the resin particles (μmol / g). In the examples described below, the amount of anionic groups in the pigment was measured in the same way as in the resin particles. Because the pigment has a different density from the resin particles, it can be separated by the ink density gradient centrifugation method described above.

[0113] [Other ingredients] The ink may contain various other components as needed. Examples of other components include various additives such as antifoaming agents, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and antireducing agents. However, it is preferable that the ink does not contain the reactants contained in the reaction liquid.

[0114] [Physical properties of ink] The ink is an aqueous ink used in inkjet printing. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less. Furthermore, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less. [Example]

[0115] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0116] <Preparation of cationic resin> Table 1 shows the details of cationic resins 1 to 5 used in preparing the reaction solution.

[0117] TIFF2025115370000001.tif80170

[0118] <Preparation of reaction solution> (Reaction mixtures 1 to 30) The components (unit: %) shown in Table 2 (Tables 2-1 to 2-5) were mixed and thoroughly stirred, followed by pressure filtration through a 3.0 μm pore size cellulose acetate filter (Advantec) to prepare each reaction solution. The MW (molecular weight) and pKa value are shown in parentheses to the right of the acidic compound names (succinic acid to nitric acid) shown in Table 2. The MW (molecular weight) and S (solubility in water at 20°C (g / 100 mL)) are shown in parentheses to the right of the polyvalent metal salts (magnesium sulfate heptahydrate to calcium chloride dihydrate) shown in Table 2. Furthermore, "BYK349" shown in Table 2 is the trade name of a silicone surfactant (manufactured by BYK Japan) (the same applies below).

[0119] TIFF2025115370000002.tif173170

[0120] TIFF2025115370000003.tif173170

[0121] TIFF2025115370000004.tif174170

[0122] TIFF2025115370000005.tif173170

[0123] TIFF2025115370000006.tif174170

[0124] (Reaction solution 31) The components shown below were mixed and thoroughly stirred, and then pressure filtered using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare reaction solution 31. Sodium sulfate heptahydrate: 20.0% 3-Methyl-1,3-butanediol: 5.0% Glycerin: 20.0% BYK349: 0.3% Ion-exchanged water: 54.7%

[0125] (Reaction solution 32) The components shown below were mixed and thoroughly stirred, and then pressure filtered using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare reaction solution 32. Acetic acid: 3.0% Dipropylene glycol dimethyl ether: 15.0% 2-pyrrolidone: 10.0% 1,2-Hexanediol: 1.0% Antifoaming agent (product name "Surfynol DF110D", manufactured by Nissin Chemical Industry Co., Ltd.): 0.1% Surfactant (product name "BYK-3455", manufactured by BYK): 0.8% Ion-exchanged water: 70.1%

[0126] (Reaction solution 33) The components shown below were mixed and thoroughly stirred, and then pressure filtered using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare reaction solution 33. Succinic acid: 2.0% N-(2-hydroxyethyl)-2-pyrrolidone: 15.0% 1,2-butanediol: 5.0% Surfactant (product name "NIKKOL BL-4.2", manufactured by Nikko Chemicals): 0.5% Ion-exchanged water: 77.5%

[0127] <Preparation of pigment dispersion> A styrene-ethyl acrylate-acrylic acid copolymer (Resin 1) with an acid value of 150 mgKOH / g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of Resin 1 were neutralized with potassium hydroxide in an amount equal to the acid value, followed by the addition of an appropriate amount of ion-exchanged water to prepare an aqueous solution of Resin 1 with a resin (solids) content of 20.0%. The pigment, Resin 1 aqueous solution, and ion-exchanged water were mixed in the amounts and types (units: parts) shown in Table 3 to obtain a mixture. The resulting mixture and 200 parts of 0.3 mm diameter zirconia beads were placed in a batch-type vertical sand mill (Imex) and dispersed for 5 hours with water cooling. After centrifuging to remove coarse particles, the mixture was pressure-filtered through a cellulose acetate filter (Advantec) with a pore size of 3.0 μm to prepare each pigment dispersion. The properties of each pigment dispersion are listed in the lower part of Table 3.

[0128] TIFF2025115370000007.tif82170

[0129] <Synthesis of resin particles> In a four-neck flask equipped with a stirrer, reflux condenser, and nitrogen gas inlet tube, 190.0 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. Separately, an emulsion was prepared by mixing the monomers (types and amounts, units: parts) shown in Table 4 (Tables 4-1 and 4-2) and 0.3 parts of a reactive surfactant. The "Blemmer PME-1000" shown in Table 4 is the trade name of methoxypolyethylene glycol monomethacrylate (number of ethylene oxide units: approximately 23) (manufactured by NOF Corp.). The reactive surfactant used was a nonionic surfactant, trade name "ADEKA REASOAP ER20" (manufactured by ADEKA, number of ethylene oxide units: 20). The prepared emulsion was added dropwise to the four-neck flask over 1 hour under a nitrogen atmosphere, and the polymerization reaction was carried out for 2 hours at 80°C with stirring. After cooling to 25°C, ion-exchanged water and an aqueous solution containing potassium hydroxide in an amount equimolar to the anionic groups of the resin particles were added to prepare an aqueous dispersion of each resin particle with a resin particle (solid content) content of 25.0%. The lower part of Table 4 shows the properties of each resin particle, including the glass transition temperature T measured by DSC. G (°C), the amount of anionic groups Ee (µmol / g), and pKa1 values are shown.

[0130] TIFF2025115370000008.tif77170

[0131] TIFF2025115370000009.tif77170

[0132] <Ink Preparation> (Ink 1-49) The components (unit: %) shown in the middle of Table 5 (Tables 5-1 to 5-6) were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each ink. The pigment dispersion and the aqueous dispersion of resin particles used were those with the numbers shown in the top of Table 5. The numbers in parentheses for the water-soluble organic solvents shown in Table 5 are the relative dielectric constant at 25°C on the left and the vapor pressure (unit: kPa) at 25°C on the right.

[0133] The lower part of Table 5 shows the content (%) of the first water-soluble organic solvent (abbreviated as "first solvent") and the second water-soluble organic solvent (abbreviated as "second solvent") in the ink, as well as the content (%) of the pigment and resin particles in the ink. Also shown are the amount of anionic groups (μmol / g) in the pigment and resin particles, and the ratio (times) of the amount of anionic groups in the pigment to the amount of anionic groups in the resin particles. The amount of these anionic groups was measured using the following method. Specifically, the ink was subjected to density gradient centrifugation at 50,000 rpm for 5 hours at 4°C, and the lower layer pigment dispersion and upper layer resin particles were removed. Acid was added to precipitate the mixture, which was then dried and measured using the colloid titration method using the aforementioned potential difference.

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[0135] TIFF2025115370000011.tif186170

[0136] TIFF2025115370000012.tif188170

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[0139] TIFF2025115370000015.tif180170

[0140] (Ink 50) The components shown below were mixed and thoroughly stirred, then pressure filtered through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec) to prepare Ink 50. The pigment content in Ink 50 was 5.0%, the resin particle 1 content was 6.0%, the first solvent content was 0.0%, and the second solvent content was 0.0%. The amount of anionic groups in the pigment, Ep, was 398 μmol / g, the amount of anionic groups in the resin particles, Ee, was 100 μmol / g, and the Ep / Ee ratio was 4.0. Pigment dispersion 8: 25.0% Resin particle 1 aqueous dispersion: 24.0% 3-Methyl-1,3-butanediol: 17.5% 1,2-butanediol: 10.0% BYK349: 0.5% Ion-exchanged water: 23.0%

[0141] (Ink 51) With reference to the description in Patent Document 2, an "St-Ac resin emulsion" was polymerized to obtain an aqueous dispersion of resin particles 16 with a resin particle content of 25.0%. The resin forming the resin particles was a copolymer of styrene / acrylic acid / methyl methacrylate / cyclohexyl methacrylate (mass ratio 75 / 0.5 / 0.5 / 14.5 / 10), and the glass transition temperature of the resin particles 16 was 99°C.

[0142] The components listed below were mixed and thoroughly stirred, then pressure filtered through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec) to prepare Ink 51. The pigment content in Ink 51 was 3.0%, the resin particle 16 content was 3.0%, the first solvent content was 0.0%, and the second solvent content was 14.5%. The amount of anionic groups in the pigment, Ep, was 663 μmol / g, the amount of anionic groups in the resin particles, Ee, was 70 μmol / g, and the Ep / Ee ratio was 9.5. Pigment dispersion 9: 15.0% Propylene glycol: 5.0% Dipropylene glycol dimethyl ether: 3.0% 2-pyrrolidone: 13.0% 1,2-Hexanediol: 2.0% Aqueous dispersion of resin particles 16: 12.0% Wax emulsion (product name "AQUACER507", wax particle content: 35.0%, manufactured by BYK): 8.6% Surfactant 1 (trade name "BYK-348", manufactured by BYK): 0.5% Surfactant 2 (product name "Olfine E1010", manufactured by Nissin Chemical Industry Co., Ltd.): 0.2% Antifoaming agent (product name "Surfynol DF110D", manufactured by Nissin Chemical Industry Co., Ltd.): 0.1% Ion-exchanged water: 40.6%

[0143] (Ink 52) A "pigment dispersion" was prepared with reference to the description in Patent Document 3, and pigment dispersion 10 was obtained, which had a pigment (carbon black) content of 30.0% and a resin content of 6.0%. Similarly, with reference to the description in Patent Document 3, "resin particles 2" were polymerized to obtain an aqueous dispersion of resin particles 17, which had a resin particle content of 25.0%. The resin forming the resin particles was a urethane-based resin, and the glass transition temperature of resin particles 17 was 64°C.

[0144] The components shown below were mixed and thoroughly stirred, then pressure filtered through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec) to prepare Ink 52. The pigment content in Ink 52 was 6.0%, the resin particle 17 content was 8.0%, the first solvent content was 0.0%, and the second solvent content was 14.5%. The amount of anionic groups in the pigment, Ep, was 634 μmol / g, the amount of anionic groups in the resin particles, Ee, was 125 μmol / g, and the Ep / Ee ratio was 5.1. Pigment dispersion 10: 20.0% Resin particle 17 water dispersion: 26.7% 1,2-butanediol: 20.0% Ion-exchanged water: 33.3%

[0145] <Evaluation> Each prepared reaction liquid and each ink was filled into a cartridge and set in an inkjet recording device (product name "imagePROGRAF PRO-2000", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. A heating device for drying the recording medium to which the reaction liquid and ink had been applied was incorporated into this recording device, located downstream of the recording head in the recording medium transport direction. The recording environment was a temperature of 25°C and a relative humidity of 50%. In this example, a recording duty of 100% was defined as an image recorded under conditions in which one drop of 4.0 ng of ink was applied to a unit area of 1 / 1,200 inch x 1 / 1,200 inch.

[0146] The reaction liquid and ink shown in Table 6 (Table 6-1 and Table 6-2) were prepared as a set. Then, the reaction liquid and the ink were applied to a recording medium in an overlapping manner with a recording duty of 15% and a recording duty of 50%, respectively, to record a 2 cm x 2 cm solid image. The recording medium was "Scotchcal Graphic Film IJ1220" (manufactured by 3M, material: polyvinyl chloride, 30 msec from the start of contact in the Bristow method). 1 / 2 Water absorption rate up to 0 mL / m 2 More than 10mL / m 2 The heating temperature T F (°C) was as shown in Table 6. However, in Comparative Example 15, heating was not performed using a heating device. F In the temperature (°C) column, "-" is entered. In this example, in the evaluation criteria for each item below, "AAA", "AA", "A" and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown on the right side of Table 6.

[0147] (Suppression of image unevenness) The obtained recorded matter was observed with a magnifying glass, and the suppression of image unevenness was evaluated according to the following evaluation criteria. A: No unevenness in the shading was observed in the image. B: Fine unevenness in the shade of less than 2 mm was observed in the image. C: Shading irregularities of 2 mm or more were observed in the image.

[0148] (Water abrasion resistance) The resulting print was subjected to an abrasion resistance test using a Gakushin-type testing machine (manufactured by Tester Sangyo) conforming to JIS L0849. Using this abrasion resistance tester, a rubbing test was conducted in which the surface of the printed image was rubbed 70 times with a load of 500 g using a white rubbing cloth (cotton) specified in JIS L0803, on which five 0.2 mL drops of water had been dropped. The number of times the image was rubbed during the rub test was counted until scraping occurred, and the image's water rub resistance was evaluated according to the evaluation criteria shown below. AAA: No image wear was observed after 40 round trips. AA: The image was scratched after 30 to 40 strokes. A: The image was scratched after 20 or more but less than 30 strokes. B: The image was scratched after 10 or more but less than 20 strokes. C: The image was scratched after less than 10 strokes.

[0149] TIFF2025115370000016.tif242170

[0150] TIFF2025115370000017.tif190170

[0151] The evaluation results for image unevenness for Examples 48, 52, 56, and 60 were all ranked "B", with Example 48 being relatively inferior.

Claims

1. 1. An inkjet recording method for recording an image on a recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, comprising: a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium; an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied; The recording medium to which the aqueous ink and the aqueous reaction liquid have been applied is heated to a predetermined heating temperature T Ｆ and a heating step of heating to (°C), 30 msec from the start of contact of the recording medium in the Bristow method １／２ Water absorption up to 10 mL / m ２ is as follows: the reactant contains at least one acidic compound selected from the group consisting of organic acids and inorganic acids, the aqueous ink contains a pigment and resin particles dispersed by the action of anionic groups; the amount (μmol / g) of anionic groups in the resin particles is 75 μmol / g or more and 600 μmol / g or less; the content (mass%) of the resin particles is 1.5 times or more the mass ratio of the content (mass%) of the pigment, In the aqueous ink, the vapor pressure is 3.1 × 10 －５ The content (mass %) of the first water-soluble organic solvent having a viscosity of 1000 kPa or less is 9.0 mass % or less based on the total mass of the ink, and the ink has a relative dielectric constant of 28.0 or more and a vapor pressure of 4.0×10 －３ the content (mass %) of the second water-soluble organic solvent having a viscosity of 0.1 kPa or less is 9.0 mass % or less based on the total mass of the ink, The heating temperature T Ｆ (°C), and the glass transition temperature T Ｇ (°C) satisfies the relationship of the following formula (1): T Ｆ ≧(T Ｇ -10) ・・・(1)

2. 2. The ink jet recording method according to claim 1, wherein the amount (μmol / g) of the anionic group in the resin particles is 95 μmol / g or more and 270 μmol / g or less.

3. the content (mass %) of the first water-soluble organic solvent in the aqueous ink is 3.0 mass % or less based on the total mass of the ink; and 2. The inkjet recording method according to claim 1, wherein the content (mass %) of the second water-soluble organic solvent in the aqueous ink is 3.0 mass % or less based on the total mass of the ink.

4. 2. The ink jet recording method according to claim 1, wherein the acidic compound in the aqueous reaction liquid is an organic acid.

5. 5. The ink jet recording method according to claim 4, wherein the organic acid has a pKa of 4.9 or less.

6. 5. The ink jet recording method according to claim 4, wherein the pKa of the organic acid is equal to or lower than the pKa of the anionic group of the resin particles.

7. The glass transition temperature T Ｇ 2. The ink jet recording method according to claim 1, wherein the temperature (°C) is 30°C or higher.

8. 2. The ink jet recording method according to claim 1, wherein the water-based ink further contains a third water-soluble organic solvent having a vapor pressure lower than that of water.

9. 9. The ink jet recording method according to claim 8, wherein the third water-soluble organic solvent contains a 1,2-alkanediol.

10. 10. The inkjet recording method according to claim 9, wherein the ratio of the amount (μmol / g) of the anionic groups of the pigment to the amount (μmol / g) of the anionic groups of the resin particles in the aqueous ink is 2.0 times or more.

11. the aqueous reaction liquid further contains a polyvalent metal salt, 2. The ink jet recording method according to claim 1, wherein the solubility (g / 100 mL) of the polyvalent metal salt in water at 20[deg.] C. is 70.0 g / 100 mL or less.

12. 12. The inkjet recording method according to claim 11, wherein the content (mol) of the polyvalent metal salt in the aqueous reaction liquid is 0.60 to 10.0 times the content (mol) of the acidic compound in terms of a molar ratio.

13. the aqueous reaction liquid further contains a cationic resin, 2. The ink jet recording method according to claim 1, wherein the cationic resin has a cationic degree (meq / g) of 3 meq / g or more and 7 meq / g or less.

14. 14. The inkjet recording method according to claim 13, wherein the content (mass%) of the cationic resin in the aqueous reaction liquid is 1.25 to 12.60 times the content (mass%) of the acidic compound in terms of a mass ratio.

15. An inkjet recording apparatus used to record an image on a recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, a reaction liquid applying means for applying the aqueous reaction liquid to the recording medium; an ink applying means for applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied; The recording medium to which the aqueous ink and the aqueous reaction liquid have been applied is heated to a predetermined heating temperature T Ｆ and a heating means for heating the temperature to (°C), 30 msec from the start of contact of the recording medium in the Bristow method １／２ Water absorption up to 10 mL / m ２ is as follows: the reactant contains at least one acidic compound selected from the group consisting of organic acids and inorganic acids, the aqueous ink contains a pigment and resin particles dispersed by the action of anionic groups; the amount (μmol / g) of anionic groups in the resin particles is 75 μmol / g or more and 600 μmol / g or less; the content (mass%) of the resin particles is 1.5 times or more the mass ratio of the content (mass%) of the pigment, In the aqueous ink, the vapor pressure is 3.1 × 10 －５ The content (mass %) of the first water-soluble organic solvent having a viscosity of 1000 kPa or less is 9.0 mass % or less based on the total mass of the ink, and the ink has a relative dielectric constant of 28.0 or more and a vapor pressure of 4.0×10 －３ the content (mass %) of the second water-soluble organic solvent having a viscosity of 0.1 kPa or less is 9.0 mass % or less based on the total mass of the ink, The heating temperature T Ｆ (°C), and the glass transition temperature T Ｇ (°C) satisfies the relationship of the following formula (1): T Ｆ ≧(T Ｇ -10) ・・・(1)

16. A set of an aqueous ink and an aqueous reaction liquid used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising: The inkjet recording method includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium, an ink applying step of applying the aqueous ink so as to overlap at least a part of an area of the recording medium to which the aqueous reaction liquid is applied, and a heating step of heating the recording medium to which the aqueous ink and the aqueous reaction liquid have been applied at a predetermined temperature T Ｆ and a heating step of heating to (°C), 30 msec from the start of contact of the recording medium in the Bristow method １／２ Water absorption up to 10 mL / m ２ is as follows: the reactant contains at least one acidic compound selected from the group consisting of organic acids and inorganic acids, the aqueous ink contains a pigment and resin particles dispersed by the action of anionic groups; the amount (μmol / g) of anionic groups in the resin particles is 75 μmol / g or more and 600 μmol / g or less; the content (mass%) of the resin particles is 1.5 times or more the mass ratio of the content (mass%) of the pigment, In the aqueous ink, the vapor pressure is 3.1 × 10 －５ The content (mass %) of the first water-soluble organic solvent having a viscosity of 1000 kPa or less is 9.0 mass % or less based on the total mass of the ink, and the ink has a relative dielectric constant of 28.0 or more and a vapor pressure of 4.0×10 －３ the content (mass %) of the second water-soluble organic solvent having a viscosity of 0.1 kPa or less is 9.0 mass % or less based on the total mass of the ink, The heating temperature T Ｆ (°C), and the glass transition temperature T Ｇ A set of an aqueous ink and an aqueous reaction liquid, characterized in that the temperature (°C) satisfies the relationship of the following formula (1): T Ｆ ≧(T Ｇ -10) ・・・(1)

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