Inkjet recording method, inkjet recording device, and water-based ink

Abstract

The objective is to provide an inkjet recording method that offers excellent opacity and minimizes the reduction in opacity when water is present. [Solution] This is an inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles. The method comprises, in this order, an ink application step of applying the white aqueous ink to the recording medium, and a drying step of drying the recording medium to which the white aqueous ink has been applied. In the drying step, the recording medium is dried to melt the resin particles and form an ink film. The porosity in the ink film is 30% or more, and the water advance contact angle θ(°) of the ink film is 90° or more.

Description

Technical Field

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and an aqueous ink.

Background Art

[0002] In recent years, inkjet recording methods have come to be applied also in fields such as commercial printing. In fields such as commercial printing, white images may be recorded on recording media other than white, such as transparent films, translucent films, and colored papers. Some inks for recording white images use white pigments such as titanium oxide. Also, inks containing hollow particles or acrylic silicone resin particles, which have a small specific gravity of the material and are difficult to settle, have been proposed (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a result of investigations by the present inventors, it has been found that when water such as rain adheres to an image recorded using the inks described in Patent Documents 1 and 2, the water penetrates into the pores of the hollow particles forming the image, reducing light scattering and lowering the concealability of the image. White inks are used for package printing, posters, etc., but in any case, since there is a possibility that the recorded matter gets wet with water, the change in concealability is a major problem.

[0005] Therefore, an object of the present invention is to provide an inkjet recording method that can record images with excellent opacity and suppress the reduction in opacity when water adheres to them. Another object of the present invention is to provide an inkjet recording apparatus and a white aqueous ink for use in the above-mentioned inkjet recording method. [Means for solving the problem]

[0006] In other words, the present invention provides an inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles, comprising, in this order, an ink application step of applying the white aqueous ink to the recording medium, and a drying step of drying the recording medium to which the white aqueous ink has been applied, wherein in the drying step, the recording medium is dried to melt the resin particles and form an ink film, the porosity in the ink film is 30% or more, and the water advance contact angle θ(°) of the ink film is 90° or more. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an inkjet recording method that can record images with excellent opacity and suppress the reduction in opacity when water adheres to them. Furthermore, according to another embodiment of the present invention, it is possible to provide an inkjet recording apparatus and a white aqueous ink used in the inkjet recording method. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram illustrating one example of the image formation process. [Figure 2] This is a schematic diagram illustrating one example of the image formation process. [Figure 3] This is a schematic perspective view showing one embodiment of the inkjet recording apparatus of the present invention. [Figure 4] This is a schematic side view showing one embodiment of the inkjet recording apparatus of the present invention. [Figure 5] This is a schematic diagram showing a porous white ink film. [Modes for carrying out the invention]

[0009] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, the white aqueous ink and aqueous processing solution for inkjet printing may be simply referred to as "ink" and "processing solution." Unless otherwise specified, the physical properties are values ​​at room temperature (25°C) and normal pressure (1 atm).

[0010] As a result of their investigation, the present inventors found that by satisfying the following requirements, it is possible to achieve excellent opacity while suppressing the decrease in opacity when water adheres to the surface, leading to the present invention. Specifically, the inkjet recording method of the present invention is an inkjet recording method that records an image on a recording medium using a white aqueous ink containing particles and resin particles. The method comprises, in this order, an ink application step of applying the white aqueous ink to the recording medium and a drying step of drying the recording medium to which the white aqueous ink has been applied, wherein in the drying step the recording medium is dried and the resin particles are melted to form an ink film. The porosity in the ink film is 30% or more, and the water advance contact angle θ(°) of the ink film is 90° or more.

[0011] Figure 5 is a schematic diagram of a porous white ink film. 51 is the binder layer, and 52 is the pores (air). The method for forming the pores 52 is not limited; for example, an ink film can be formed using an ink containing hollow particles and the pores of the hollow particles can be utilized, or resin particles can be melted and absorbed into an inorganic particle layer, creating pores where the resin particles were located. The white porosity after white ink fixing is the ratio of the volume of pores 52 to the total volume of the ink film, including the binder layer 51 and the pores 52. Whiteness is achieved by the scattering of light at the interface between the binder layer and the pores. Therefore, to obtain high opacity, it is important to increase the scattering interface, that is, increase the pores, and the opacity of the ink film in a dry state (dry opacity) can be set to the desired level when the porosity in the ink film is 30% or more. If the porosity in the ink film is less than 30%, the desired opacity cannot be obtained because there are few interfaces where light is scattered.

[0012] When water comes into contact with the ink film, the water penetrates into the pores 52. Generally, because water has a higher refractive index than air, light scattering at the interface between the binder layer and water is reduced. As a result, it was found that the opacity (water-wetting opacity) of the ink film decreases after it comes into contact with water. In order to maintain high opacity even when water comes into contact with the ink film, it is necessary to reduce the number of paths through which water can penetrate the ink film. One possible solution is to reduce the porosity in the ink film, but as mentioned above, reducing the porosity in the ink film reduces the opacity in the dry state.

[0013] The conditions under which water entering the pores after contact with the ink film can be determined using the following Lucas Washburn equation (Equation (1) below). L is the penetration depth, r is the capillary diameter, γ is the surface tension, θ is the contact angle, η is the viscosity, and t is time. From this equation, it was found that even when the porosity of the ink film is high, increasing the contact angle of water on the ink film is effective in suppressing water penetration into the ink film. In this invention, the advancing contact angle is used as θ. The advancing contact angle is the contact angle when a liquid wets and spreads, and is known as an indicator of liquid removal ability, water repellency, and coating ability when liquid adheres to a surface. When the advancing contact angle of water on the ink film is 90 degrees or more, water that comes into contact with the ink film is repelled on the ink film and does not penetrate into the pores in the ink film. This suppresses the decrease in the water-wettability of the ink film even when the porosity of the ink film is high.

[0014]

number

[0015] <Inkjet recording method, inkjet recording device, and water-based white ink> The present invention relates to an inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles. The method comprises, in this order, an ink application step of applying the white aqueous ink to the recording medium, and a drying step of drying the recording medium to which the white aqueous ink has been applied. In the drying step, the recording medium is dried to melt the resin particles and form an ink film, characterized in that the porosity in the ink film is 30% or more, and the water advance contact angle θ(°) of the ink film is 90° or more.

[0016] The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method that records an image on a recording medium using a white aqueous ink containing particles and resin particles, and is an apparatus preferably used in the above recording method. In the present invention, it is not necessary to cure the image by irradiation with active energy rays or the like.

[0017] Furthermore, the aqueous ink of the present invention is an ink used in an inkjet recording method that records an image on a recording medium using a white aqueous ink containing particles and resin particles. It is an ink that is preferably used in the above-described recording method.

[0018] 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.

[0019] Figure 3 is a schematic perspective view showing one embodiment of the inkjet recording apparatus of the present invention. Figure 4 is a schematic side view showing one embodiment of the inkjet recording apparatus of the present invention. The recording apparatus of the embodiments shown in Figures 3 and 4 includes an inkjet type 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 is a thermal type recording head that imparts thermal energy to the ink by applying an electric pulse to an electrothermal conversion element and ejects the ink from the ejection port. Here, a recording head that ejects ink by the action of thermal energy is given as an example, but 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) for heating the aqueous ink ejected from the recording head. When a temperature control mechanism is provided, the heating temperature of the ink ejected from the recording head is preferably 35°C or more and 70°C or less.

[0020] Multi-pass recording is preferred, in which ink is applied to a unit area of ​​the recording medium by dividing the process into multiple relative scans between the recording head and the recording medium. In particular, it is preferable to apply white ink to a unit area by multiple relative scans. The unit area can be set to any area, such as one pixel or one band.

[0021] (Heating process for forming a porous ink film) The process may include a heating step in which the recording medium to which the ink has been applied is heated (heat treated). In the case of an ink that is a mixture of pigment particles and resin particles, the heating step heats the recording medium to which the ink has been applied to melt the resin particles in the ink. When the resin particles are dissolved, the melted resin penetrates into the gaps between the pigment particles, forming voids where the resin particles were and a binder layer of pigment particles and resin where the pigment particles were, thus forming a porous ink film.

[0022] In the heating process, the recording medium is heated to a temperature above the glass transition temperature or melting point of the resin particles in the ink in order to melt the resin particles. That is, heating temperature T H This refers to the glass transition temperature Tg or melting point T of the resin particles. M This can be set as appropriate depending on the circumstances. Here, if the resin particles are formed of crystalline resin, Tg and T M It has, but in that case, T M Heat to a temperature above T. Specifically, the heating temperature in the heating process is T H The heating temperature (°C) is preferably 70°C or higher, more preferably 80°C or higher, and particularly preferably 90°C or higher. While there is no particular upper limit to the heating temperature, it is preferably 200°C or lower from the viewpoint of the heat resistance temperature of the recording medium. H This refers to the maximum temperature of the recording medium surface during the heating process. It may also be interpreted as the set temperature of the heating means. The heating temperature can be measured using, for example, a contact thermometer that brings a thermocouple or the like into contact with the recording medium surface, or a non-contact infrared thermometer. In the embodiment described later, the temperature on the surface of the recording medium was measured using a non-contact infrared thermometer digital radiation temperature sensor FT-H20 (manufactured by Keyence) from a position 10 cm vertically upward from the surface of the recording medium.

[0023] By performing a heating process, the resin particles are melted, creating voids, and as a result, a porous ink film containing voids can be formed. The heating process may be performed alone or in combination with other processes. Examples of heating means for heating the recording medium include known heating means such as heaters, air blowing means such as dryers, and means combining these. Examples of heating means include the above-mentioned heating means, air blowing means, and means combining these. Examples of heating methods include applying heat from the side (back side) opposite to the recording surface (ink application surface) of the recording medium using a heater, applying warm air or hot air to the recording surface of the recording medium, and heating from the recording surface or back side using an infrared heater. A combination of these methods may also be used. Furthermore, heating may be performed by bringing a heated component into contact with the recording surface or back side of the recording medium. The duration of the heating process is not particularly limited as long as the resin particles can be melted. For example, when the heating process is performed by air blowing, the temperature of the air can be set to 80°C or higher and 120°C or lower.

[0024] In the recording apparatus shown in Figures 3 and 4, a heater 25 supported by a frame (not shown) is positioned 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 10 to which ink has been applied can be heated by the heater 25. Specific examples of the heater 25 include sheath heaters and halogen heaters. The heater 25 is covered by a heater cover 26. The heater cover 26 is a component that efficiently irradiates the recording medium 10 with the heat generated from the heater 25. Furthermore, the heater cover 26 also serves as a component that protects the heater 25. The recording medium 10 to which ink has been ejected from the recording head 22 is wound up by a take-up spool 27 to form a roll-shaped winding medium 24.

[0025] Prior to the heating step, it is preferable to further include a step of forming an ink film in which particles and resin particles are densely packed, as shown in Figure 1. By including such a step, it becomes possible to more reliably penetrate the voids between the molten resin particles, and it becomes easier to create an image containing voids as shown in Figure 2. That is, it is preferable that the inkjet recording method further includes at least one step selected from the group consisting of a reaction solution application step of applying an aqueous reaction solution containing a reactant that reacts with the ink to the recording medium, and a drying step of drying the liquid components on the recording medium. It is even more preferable to use these steps (reaction solution application step and drying step) in combination. When these steps are used in combination, it is particularly preferable to perform the drying step after the reaction solution application step. In other words, it is preferable to perform the steps in the order of reaction solution application step, ink application step, drying step, and heating step. Ink application may be performed in parallel with reaction solution application. When the reaction solution is applied to the recording medium, the particles and resin particles in the ink can be aggregated and densely packed. Details of the reaction solution will be described later. When blowing air onto the recording medium, it is preferable to blow air onto the surface (recording surface) of the recording medium from the viewpoint of drying efficiency.

[0026] The drying process can be performed to dry the liquid components on the surface of the recording medium. In this process, it is not necessary to completely dry the liquid components. Furthermore, while the liquid components on the recording medium will gradually dry even without the above process, performing the drying process accelerates the drying and efficiently brings the recording to the state shown in Figure 1. The drying process can be performed alone or in combination with other processes. The same heating means as in the heating process can be used in the drying process. Among these, blowing air is preferable from the viewpoint of efficiently drying the liquid components.

[0027] Since the drying process is carried out while the liquid component on the surface of the recording medium remains and is not sufficiently thickened, it is preferable not to increase the thermal energy applied to the recording medium too much from the viewpoint of suppressing the tendency to reach the state of FIG. 1. Specifically, it is preferable not to increase the heating temperature or heating time too much. For example, when drying by blowing air, the temperature of the blowing means (such as warm air) can be set so that the recording medium reaches a desired temperature, taking into account the conveying speed and the environmental temperature. Specifically, it is preferable to set the temperature of the air blown by the blowing means (such as warm air) to 60 ° C or lower, and more preferably 30 ° C or lower. The temperature of the air may be normal temperature (25 ° C). Here, as shown in FIG. 1, in order to reduce the liquid component without melting the resin particles and to make the particles and resin particles dense, it is preferable to heat at a temperature lower than the Tg or T M of the resin particles. Also, the wind speed is preferably 1 m / s or more and 100 m / s or less. The temperature of the air such as warm air can be measured using a K-type thermocouple thermometer. Specific measuring instruments include, for example, the product name "AD-5605H" (manufactured by A&D). If necessary, air may be blown against the back surface of the recording medium, but it is preferable to blow air against the front surface (the surface to which the ink is applied) of the recording medium. The distance from the device that blows air to the recording medium is preferably 5 mm or more and 50 mm or less.

[0028] (Recording medium) The type of the recording medium for recording an image is not particularly limited, and any recording medium may be used. Among them, since an ink capable of recording an image such as white with excellent concealment is used, it is preferable to use a recording medium other than white such as a transparent film, a translucent film, and colored paper. The "white" here refers to the same characteristics as the "white" of the ink described later. As the recording medium, it is preferable to use a non-absorbent recording medium. Here, the non-absorbent recording medium (difficult to non-absorbent recording medium) has a water absorption of 0 mL / m 1 / 2 from the start of contact to 30 msec in the Bristow method 2 or more and 10 mL / m 2The following are the recording media. The Bristow method is described in JAPAN TAPPI Paper and Pulp Test Method No. 51, "Test Method for Liquid Absorption of Paper and Paperboard". For inkjet recording media (glossy paper, matte paper, etc.) having a coating layer (ink-receiving layer) formed of inorganic particles, and for plain paper without a coating layer, the above water absorption amount is 10 mL / m². 2 It is a "highly absorbent recording medium" that exceeds [a certain limit].

[0029] As low-to-non-absorbent recording media, the following can be used: plastic films; recording media in which a plastic film is bonded to the recording surface of a substrate; and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Among these, plastic films are preferred, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred. In this specification, the term "recording media" refers to a recording media on which an image is recorded as a recording object, not a transfer medium.

[0030] (White water-based ink) The ink used in the recording method of the present invention is a white aqueous ink that forms a porous ink film with a porosity of 30% or more. The higher the porosity, the more interfaces there are between the pores and the binder layer, which can improve opacity. To obtain sufficient opacity, a porosity of 30% or more is necessary, and preferably between 40% and 50%. If it exceeds 50%, the interfaces between the pores and the binder layer decrease, and the opacity decreases.

[0031] Methods for forming porous ink films include using ink containing hollow particles to form an ink film and utilizing the pores of the hollow particles, and melting resin particles and absorbing them into an inorganic particle layer to create pores where the resin particles were located. The components that make up the ink will be explained in detail below.

[0032] [Method using hollow particles] White water-based ink can contain hollow particles and resin. The hollow particles in the formed ink film are filled with the liquid component of the ink (described later), and as the ink film is formed, the liquid component evaporates, creating voids. The resin fills the gaps between the hollow particles, forming a binder layer. The greater the difference in refractive index between the binder layer and the voids (air), the greater the scattering of light, thus achieving high opacity. Therefore, it is preferable that the resin is a material with a high refractive index. The refractive index of the binder layer can also be increased by mixing high refractive index particles (described later) into the ink. To suppress the intrusion of water into the voids, it is preferable to use silicone resin particles as the binder resin, or to apply a treatment solution containing hydrophobic components (described later) after the ink film is formed.

[0033] The size of the pores in hollow particles is defined by the porosity of the hollow particles. The porosity of hollow particles is an indicator of the size of the pores in the particles, and is obtained by dividing the measured specific gravity by the theoretical specific gravity. If the porosity of hollow particles is 50%, it means that 50% of the volume occupied by the hollow particles is void. Generally, the porosity of hollow particles is at most around 50%. In that case, in order to make the porosity 30% or more, it is preferable that the content (volume) of hollow particles be 1.5 times or more the volume of resin contained in the ink, and preferably between 2.0 times and 2.3 times.

[0034] [Method using colorless pigment particles and resin particles] White water-based inks can also contain colorless pigment particles and resin particles. A porous ink film with voids formed by the particles and resin particles is formed as follows.

[0035] Figures 1 and 2 are schematic diagrams illustrating an example of the image formation process. When ink is applied to the recording medium, as shown in Figure 1, the liquid component evaporates and the ink dries, forming an ink film in which particles 1 and resin particles 2 in the ink are densely packed. Subsequently, the temperature at which resin particles 2 melt (the glass transition temperature Tg (°C) or melting point T of the resin particles) is reached. MWhen the recording medium is heated to a temperature of (°C) or higher, as shown in Figure 2, the resin generated by the melting of the resin particles 2 penetrates into the voids between the particles 1. At the same time, voids 4 are formed where the resin particles 2 were located. As the resin penetrates into the voids between the particles 1, a binder layer 3, which is a mixture of particles 1 and resin, is formed. Here, the average primary particle diameter D of particle 1 P0 Since the (nm) is 150 nm or less, visible light is hardly scattered by particle 1. However, low refractive index air is present in the voids 4 formed by the melting of the resin particles. Therefore, the refractive index of voids 4 is considered to be relatively lower than that of binder layer 3. Under these conditions, incident light can be scattered due to the refractive index difference between binder layer 3 and voids 4. This allows for the recording of images with high opacity.

[0036] The higher the refractive index of the particles, the higher the refractive index of the binder layer; therefore, it is preferable to use particles with a high refractive index, as described later. To achieve a porosity of 30% or more, it is preferable to keep the particle volume 1.3 times or less the resin particle volume. More preferably, the particle volume is 0.25 times or more and 0.66 times or less the resin volume.

[0037] (Ink materials) [particle] The ink may contain particles. Since the particles become part of the material that makes up the binder layer, it is preferable that they have a high refractive index. These particles may be colorants or may be colorless, such as resin particles. In particular, since a white image is to be recorded, it is preferable to use colorless or white particles. The particle content (volume %) in the ink is preferably 1.5 volume% or more, based on the total volume of the ink. If the particle content is less than 1.5 volume%, when the resin particles described later melt, sufficient voids may not be formed for penetration, and the image opacity may not be sufficiently obtained. The particle content in the ink is preferably 5.0 volume% or less.

[0038] Particles are typically dispersed in ink in the form of secondary aggregates, which are aggregates of two or more primary particles. The average primary particle size D of the particles to be included in the ink. P0 The (nm) is 150 nm or less, preferably 50 nm or less. Average primary particle diameter D P0 The lower limit of (nm) is not particularly limited, but it is preferably 5 nm or greater. The particle diameter of the primary particles can be measured by observing the particles using a scanning electron microscope. The average primary particle diameter of the particles can be calculated as the average value of the particle diameters of multiple primary particles (e.g., 100 particles).

[0039] Particle volume-based cumulative 50% particle diameter D P The particle size (nm) is preferably 150 nm or less, and more preferably 5 nm to 100 nm. By using particles whose volume-based cumulative 50% particle diameter is within the above range, light scattering in the binder layer can be suppressed, contributing to an improvement in the refractive index of the binder layer.

[0040] In this specification, "cumulative 50% particle size by volume (D 50 The particle size distribution analyzer is defined as the diameter of the particle that reaches 50% of the total volume of the measured particles when accumulated from the smallest particle size side, and can be measured using a particle size distribution analyzer based on the dynamic light scattering method. For example, measurement conditions include SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: non-spherical. As for the particle size distribution analyzer, a particle size analyzer based on the dynamic light scattering method (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those described above.

[0041] The particles must not melt during the heating process that melts the resin particles. Specifically, the glass transition temperature Tg (°C) or melting point T of the particles must be specified. MThe temperature (°C) is equal to or greater than the temperature of the recording medium during the heating process, preferably 200°C or higher. The particles are preferably at least one selected from the group consisting of titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silicon dioxide, kaolin, clay, and second resin particles. The second resin particles are resin particles with a high melting point, separate from the aforementioned resin particles, and are preferably crosslinked resins, and more preferably crosslinked acrylic resins.

[0042] From the viewpoint of forming a binder with a high refractive index, it is preferable to use titanium dioxide, which has a relatively high refractive index, as particles. The refractive index of titanium dioxide is preferably 2.1 or higher, and more preferably 2.5 to 2.8. The surface of titanium dioxide may be coated with alumina or zirconia. Alternatively, the surface of titanium dioxide may be coated with inorganic oxides such as silica, zinc oxide, and zirconia; or organic substances such as polyols. By using titanium dioxide with a coated surface, it is expected that the photocatalytic activity will be suppressed and the dispersibility will be improved. There are three crystalline forms of titanium dioxide: rutile, anatase, and brookite. Among these, it is preferable to use rutile titanium dioxide, which has low photocatalytic activity. Industrial methods for producing titanium dioxide include the sulfuric acid method and the chlorine method. Titanium dioxide produced by either method can be used.

[0043] The titanium dioxide content (mass%) in the ink is preferably 5.0% to 45.0% by mass, and more preferably 7.0% to 38.0% by mass, based on the total mass of the ink. The average primary particle size D of the titanium dioxide contained in the ink. P0 The (nm) is preferably 50 nm or less, and more preferably 30 nm or less. Also, the cumulative 50% particle size D on a volume basis of titanium dioxide. P The (nm) is preferably 100 nm or less, and more preferably 5 nm or more and 50 nm or less.

[0044] Calcium carbonate particles can be cubic or spindle-shaped. Among these, cubic calcium carbonate with a uniform shape is preferred. Examples of calcium phosphate include monocalcium phosphate (Ca(H2PO4)2), dicalcium phosphate (CaHPO4), and tricalcium phosphate (Ca3(PO)2). Among these, apatite-type calcium phosphate is preferred, particularly hydroxyapatite (Ca 10 (PO6)(OH)2) is even more preferable.

[0045] Barium sulfate is broadly classified into extirpated barium sulfate and precipitated barium sulfate. Precipitated barium sulfate allows for control of particle size through synthesis conditions, enabling the production of barium sulfate with appropriate particle sizes. Zirconium oxide, also known as zirconia, is known as a highly tough ceramic. Pure zirconia is susceptible to degradation due to changes in its crystalline structure and volume with temperature fluctuations. Therefore, stabilized zirconia, which has volume changes suppressed by the addition of stabilizers, can be used.

[0046] For example, silicon dioxide synthesized by the Stober method can be used. The Stober method is a method in which the hydrolysis and polycondensation reaction of alkoxysilane, which is the silica source, proceeds in aqueous solutions of water, ethanol, and ammonia. By changing the concentrations of each reactant, it is possible to control the particle size of the resulting spherical particles.

[0047] Kaolin is a clay mineral containing multiple inorganic components. Specifically, it is a clay consisting of kaolinite, hydrated halloysite, and the crystalline structure of halloysite. In addition to the kaolin components, the clay also contains ilmenite, montmorillonite, and vermiculite. When using the above particles, it is preferable to use particles with high whiteness from the viewpoint of producing a white ink.

[0048] [Resin particles] The ink contains resin particles. The resin particle content (mass%) in the ink is preferably 2.5% to 17.0% by mass, and more preferably 2.5% to 14.0% by mass, based on the total mass of the ink. Furthermore, the resin particle content (volume%) in the ink is preferably 2.5% to 17.0% by volume, and more preferably 2.5% to 14.0% by volume, based on the total volume of the ink.

[0049] When forming a porous ink film by creating pores during the heating process, the size of the pores generally coincides with the size (particle diameter) of the resin particles. The size of the pores formed greatly affects the light scattering efficiency. Therefore, from the viewpoint of further improving the light scattering efficiency, the cumulative 50% particle diameter D based on the volume of the resin particles is considered. E The wavelength is preferably between 100 nm and 400 nm, and more preferably between 150 nm and 250 nm.

[0050] From the viewpoint of forming a binder with a high refractive index, it is preferable to use resin particles with a higher refractive index. Specifically, the refractive index of the resin particles is preferably 1.5 or higher, and more preferably 1.6 to 2.5.

[0051] Examples of resins that form resin particles include vinyl chloride resins, styrene resins, urethane resins, acrylic resins, polyester resins, and silicone resins. Using resin particles formed from resins other than those listed above can easily lead to unstable extrusion, resulting in insufficient image opacity. Details of the resins that make up the resin particles will be described later.

[0052] Glass transition temperature Tg (°C) and melting point T of resin particles M The temperature (°C) is preferably 100°C or lower, and more preferably 80°C or lower. Also, the glass transition temperature Tg (°C) and melting point T of the resin particles are also specified. MThe temperature (°C) is preferably 15°C or higher, and more preferably 25°C or higher. Glass transition temperature Tg (°C) and melting point T of the resin particles M The resin is prone to softening if the temperature (°C) is below 15°C. The glass transition temperature Tg (°C) and melting point T of the resin particles are also relevant. M (°C) can be measured using a differential scanning calorimeter (DSC).

[0053] In this specification, "resin particles" refers to resins that exist in an insoluble state in the aqueous medium of the ink, and more specifically, resins that can exist in the aqueous medium in a state in which particles whose particle size can be measured by dynamic light scattering are formed. In contrast, "water-soluble resin" refers to resins that exist in a dissolved state in the aqueous medium of the ink.

[0054] Whether a resin qualifies as "resin particles" can be determined according to the following method. First, a liquid containing the resin to be evaluated is prepared and diluted with pure water to a resin content of approximately 1.0% to prepare a sample. Then, the particle size of the resin in the sample is measured by dynamic light scattering. If particles with a particle size are measured, the resin is determined to be "resin particles" (i.e., a "water-dispersible resin"). On the other hand, if no particles with a particle size are measured, the resin is determined not to be "resin particles" (i.e., a "water-soluble resin"). The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 10 times, Measurement time: 120 seconds, Shape: Spherical, Refractive index: 1.5, Density: 1.0.

[0055] As a particle size distribution analyzer, a dynamic light scattering particle size analyzer (for example, product name "UPA-EX150," manufactured by Nikkiso) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those mentioned above.

[0056] The acid value of the resin constituting the resin particles is preferably 5 mg KOH / g or more and 100 mg KOH / g or less. 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 resin particles do not need to contain a colorant.

[0057] [resin] The ink may further contain resins other than particles and resin particles (other resins). The content (mass%) of resins (other resins) 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.

[0058] The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, i.e., as a resin dispersant or its auxiliary agent; or (ii) to improve various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. Furthermore, the resin is preferably a water-soluble resin that can dissolve in an aqueous medium.

[0059] [Composition of the resin] Examples of resins include acrylic resins, urethane resins, olefin resins, and silicone resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid and (meth)acrylate are even more preferred. Silicone resins are even more preferred because making the binder layer of the ink film hydrophobic can increase the advancing contact angle θ.

[0060] As for acrylic resins, those having hydrophilic units and hydrophobic units as constituent units are preferred. In particular, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one selected from the group consisting of monomers having aromatic rings and (meth)acrylic acid ester monomers are preferred. Especially preferred are resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene. Because these resins readily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

[0061] Hydrophilic units are units that have hydrophilic groups, such as anionic groups. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers that have hydrophilic groups. Specific examples of hydrophilic monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Cations that constitute salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. Hydrophobic units are units that do not have hydrophilic groups, such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups, such as anionic groups. Specific examples of hydrophobic monomers include monomers having aromatic rings, 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.

[0062] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[0063] Polyester resins are typically composed of units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. Examples of polyhydric alcohols that become units constituting polyester resins through reaction include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having aliphatic groups, polyhydric alcohols having aromatic groups, and sugar alcohols.

[0064] 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. Oligomers (low-molecular-weight polymers with a molecular weight of 1,000 or less) can also be used as polyhydric alcohols. It is preferable to use dihydric or trihydric polyhydric alcohols because it facilitates the adjustment of the weight-average molecular weight of the polyester resin.

[0065] Polycarboxylic acids that form units derived from polycarboxylic acids that constitute polyester resins through reactions include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acid structures include polycarboxylic acids having aliphatic groups, polycarboxylic acids having aromatic groups, and nitrogen-containing polycarboxylic acids. Examples of polycarboxylic acids include divalent carboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; trivalent carboxylic acids such as trimellitic acid; and tetravalent carboxylic acids such as ethylenediaminetetraacetic acid. Oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used as polycarboxylic acids. 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.

[0066] For silicone resin particles, an emulsion type with excellent dilution stability is preferred. An O / W type silicone emulsion can be obtained by emulsifying various silicone oils with an emulsifier. It is preferable to use a dimethyl type with low reactivity or a rubber type that forms a film upon drying. By incorporating silicone resin into the ink, the formed ink film can be made hydrophobic, and the advancing contact angle θ of water with respect to the ink film can be increased. The content V of silicone resin particles in the ink. SR (Volume %) represents the particle content in the ink. P It is preferable that the volume ratio to (volume %) is 0.3 times or more. The content of silicone resin in the ink is V. SR (by volume) represents the particle content in the ink. P By having a volume ratio of 0.3 times or more relative to (volume %), the advancing contact angle θ of water in the ink film can be further increased.

[0067] [Properties of the resin] The acid value of the water-soluble resin is preferably 100 mg KOH / g or more and 250 mg KOH / g or less. The weight-average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

[0068] [Aqueous medium] The ink used in the recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium which is water or 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 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The water-soluble organic solvent content (mass%) in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used.

[0069] [Physical properties of ink film] The forward contact angle θ of water in the ink film formed on the recording medium must be 90° or greater. A forward contact angle θ of 90° or greater repels water that comes into contact with the ink film, making it difficult for water to penetrate into the pores within the ink film. This suppresses a decrease in the water-wettability of the ink film, even when the porosity of the ink film is high. A forward contact angle θ of 100° or greater is even more preferable.

[0070] [Other ingredients] The ink may further contain water-soluble organic compounds that are solid at 25°C, such as urea and its derivatives, trimethylolpropane, and trimethylolethane. The content (by mass) of the water-soluble organic compounds in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink. In addition to the above components, the ink may also contain various other components as needed. Examples of other components include various additives such as surfactants, defoamers, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, mold inhibitors, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain the reactants included in the reaction solution.

[0071] [Ink properties] The ink is an aqueous ink for use in inkjet systems. 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. 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.

[0072] (Aqueous treatment solution) By applying a treatment solution containing hydrophobic components to the surface of the ink film after it has formed, the forward contact angle θ of water on the ink film can be increased. Hydrophobic components are mainly composed of nonpolar molecules and do not easily interact with polar water molecules. Therefore, the forward contact angle θ of water increases on an ink film to which hydrophobic components are attached. In particular, porous ink films have nanoscale surface irregularities due to their porosity, so the forward contact angle θ can be increased even further when the treatment solution is applied to the surface of the ink film.

[0073] Hydrophobic components are electrically neutral and contain many non-polar parts within the molecule, specifically those composed of hydrocarbon groups and siloxane bonds. As hydrophobic components, silicone oil is preferred because it possesses siloxane bonds surrounded by hydrophobic groups such as methyl groups, resulting in high hydrophobicity. The solubility parameter (SP value) of silicone oil is generally far from the SP value of water (23.4). For example, methyl hydrogen silicone oil (product name "KF-9901", manufactured by Shin-Etsu Chemical, SP value: 7.3) is an example. The molecular weight of the silicone oil is preferably 10,000 or less, more preferably 5,000 or less. A molecular weight of 10,000 or less suppresses the increase in viscosity of the processing solution, allowing the processing solution to follow the irregularities on the ink film surface and increase the water advance contact angle θ. Furthermore, methyl groups, phenyl groups, amino groups, polyether groups, and carboxyl groups are preferred as functional groups to be introduced into the silicone oil. Methyl groups have high hydrophobicity and are highly effective in increasing the water advance contact angle θ. Phenyl groups improve heat resistance and oxidation resistance, enhancing durability in high-temperature environments. Amino groups, polyether groups, and carboxyl groups are hydrophilic, making them easier to mix with water and apply using an inkjet recording device, as described later.

[0074] One method for applying the processing solution to the ink film is to apply silicone oil diluted with an organic solvent with a low SP value using a roller or similar device. Typical organic solvents include hexane (SP value 7.3), toluene (SP value 8.8), xylene (SP value 8.8), and benzene (SP value 9.2). The amount of silicone oil contained in the processing solution (mass %) is preferably 60% by mass or less, and more preferably 40% by mass or less, based on the total mass of the processing solution. By keeping the amount of silicone oil contained in the processing solution at 60% by mass or less, based on the total mass of the processing solution, the increase in viscosity of the processing solution is suppressed, making it easier to apply it uniformly to the recording medium.

[0075] Furthermore, as mentioned above, if a silicone oil has hydrophilic organic groups (amino groups, polyether groups, carboxyl groups) introduced into its molecular structure, it can be dispersed in water as a silicone emulsion and applied to a recording medium using an inkjet method. After applying the processing solution to the recording medium, drying the processing solution exposes the hydrophobic parts contained in the processing solution to the surface, thereby increasing the water advance contact angle θ of the ink film. When using an aqueous dispersion of silicone oil (silicone emulsion), the amount of silicone oil (mass%) contained in the processing solution is preferably 10% by mass or less based on the total mass of the processing solution. In particular, when applying the processing solution using an inkjet method, from the viewpoint of discharge performance, the amount of silicone oil (mass%) contained in the processing solution is preferably 5% by mass or less based on the total mass of the processing solution. When the amount of silicone oil (mass%) contained in the processing solution is 10% by mass or less based on the total mass of the processing solution, the processing solution can be discharged stably using an inkjet method, making it easier to uniformly apply it to the recording medium.

[0076] The hydrophobic component can be any component that can reduce the hydrophilicity of the ink film. The content (mass%) of the hydrophobic component in the processing solution is preferably 1.0% by mass or more and 50.0% by mass or less, based on the total mass of the processing solution. Other components of the processing solution can be the same as those used in the ink. However, it is preferable that the processing solution does not contain colorants so as not to affect the image recorded by the ink.

[0077] (Reaction solution) The recording method of the present invention preferably includes a reaction solution application step in which an aqueous reaction solution containing a reactant that reacts with aqueous ink is applied to a recording medium. In particular, it is preferable to have the reaction solution application step before the ink application step, or to perform the ink application step and the reaction solution application step in parallel. The components used in the reaction solution will be described in detail below.

[0078] [Reactive agent] The reaction solution reacts with the ink upon contact, causing the components in the ink (resins and components having anionic groups, such as self-dispersing pigments) to aggregate, and contains a reactant. Examples of reactants include organic acids, polyvalent metal salts, and cationic resins.

[0079] Examples of polyvalent metal ions 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 trivalent metal ions include the following. To include polyvalent metal ions in the reaction solution, a polyvalent metal salt (which may also be a hydrate) composed of a polyvalent metal ion bonded to an anion can be used. Examples of anions include Cl - , Br - , I - , - 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 -Examples of organic anions include the following. 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.

[0080] The reaction solution containing an organic acid has buffering capacity in the acidic range (pH less than 7.0, preferably pH 2.0 to 5.0), which efficiently converts the anionic groups of components present in the ink into acidic forms and aggregates them. Examples of organic acids include monocarboxylic acids and their salts such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furanic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and their salts or hydrogen salts 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 their salts or hydrogen salts such as citric acid and trimellitic acid; and tetracarboxylic acids and their salts or hydrogen salts such as pyromellitic acid. When using an organic acid as a reactant, the content (by mass) of the organic acid in the reaction solution is preferably 1.0% by mass or more and 50.0% by mass or less, based on the total mass of the reaction solution.

[0081] Examples of cationic resins include resins having the structure of primary to tertiary amines and resins having the structure of quaternary ammonium salts. Specifically, examples include resins having the structures of vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. To improve solubility in the reaction solution, cationic resins can be used in combination with acidic compounds, or cationic resins can be subjected to quaternization treatment. When a cationic resin is used as a reactant, the content (mass%) of the cationic resin in the reaction solution is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the reaction solution.

[0082] [Aqueous medium] The reaction solution is an aqueous reaction solution containing at least water as an aqueous medium. The aqueous medium used in the reaction solution may contain the aforementioned water-soluble organic solvent that can be incorporated into the ink.

[0083] [Other ingredients] The reaction solution may contain various other components as needed. Examples of other components include those similar to those mentioned above that can be included in the ink.

[0084] [Physical properties of the reaction solution] The reaction solution suitably used in the recording method of the present invention is an aqueous reaction solution applicable to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the reaction solution at 25°C is preferably 20 mN / m or more and 60 mN / m or less. The viscosity of the reaction solution at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction solution at 25°C is preferably 5.0 or more and 9.5 or less, and more preferably 6.0 or more and 9.0 or less. [Examples]

[0085] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components expressed in "parts" and "%" are based on mass. Hereinafter, particle dispersions will also be referred to as pigment dispersions.

[0086] <Measurement of physical properties> (porosity) A predetermined amount of white ink was applied to a PET film (product name "LLRPCF1372", manufactured by Sakurai) whose mass had been measured beforehand. After the PET film coated with white ink was thoroughly dried and its mass was measured, the mass of the white ink film was calculated by subtracting the mass of the PET film. The content (volume %) of particles and resin particles in the ink was also calculated, and the volume of the ink film was calculated from the sum of these. Next, an appropriate amount of ethanol was applied to the ink film and allowed to stand for 3 minutes to allow the organic solvent to fully penetrate the ink film. After that, the excess organic solvent was removed by lightly wiping the surface of the ink film. The mass of the ink film after ethanol penetration was measured, and the volume of ethanol that penetrated the ink film was calculated by subtracting the mass of the ink film before organic solvent penetration from the measured value and dividing by the density of ethanol. Finally, the porosity was calculated by dividing the volume of ethanol that penetrated the ink film by the sum of the volume of the ink film and the volume of the penetrated organic solvent.

[0087] (Water advance contact angle of the ink film) The advancing contact angle was measured using a contact angle meter (product name "Drop Master DMo-502WA", manufactured by Kyowa Interface Science). The expansion / contraction method was used for measurement. A water droplet dropped onto a white ink film was dispensed and aspirated using an automatic dispenser (product name "Single Dispenser System AD-301S", manufactured by Kyowa Interface Science), and the contact angle at the time of dispensing was measured and defined as the advancing contact angle.

[0088] (Hollow particle porosity) White ink was applied to a PET film (product name "LLRPCF1372", manufactured by Sakurai) and dried at 25°C. The dried white ink film was observed using a transmission electron microscope (product name "Talos F200E", manufactured by FEI), and the outer and inner diameters of the particles were measured. The porosity of the hollow particles was determined by dividing the volume obtained from the inner diameter by the volume obtained from the outer diameter.

[0089] <Particle preparation> The following particles were prepared. • Aqueous dispersion of particle 1 (product name "TTO-W-5", manufactured by Ishihara Sangyo, titanium dioxide aqueous dispersion, solid content 30%) • Aqueous dispersion of particle 2 (product name "ULTRA-E", manufactured by Lowpeak, hollow polymer dispersion, porosity of hollow particles 45%, solids content 30%).

[0090] <Preparation of resin particles> • Aqueous dispersion of resin particles 1 (product name "KM-2002-T2", manufactured by Shin-Etsu Chemical, aqueous dispersion of silicone resin particles, solid content 40%) • Aqueous dispersion of resin particles 2 (product name "Polon MF56", manufactured by Shin-Etsu Chemical, aqueous dispersion of silicone resin particles, solid content 40%) • Aqueous dispersion of resin particles 3 (product name "RKP-02", manufactured by Shin-Etsu Chemical, aqueous dispersion of silicone resin particles, solid content 40%) • Aqueous dispersion of resin particles 4 (product name "AE980", manufactured by E-Tech, aqueous dispersion of silicone resin particles, solid content 50%) • Aqueous dispersion of 5 resin particles (product name "SF860", manufactured by Daiichi Kogyo Seiyaku, aqueous dispersion of urethane resin particles, solid content 45%) • Aqueous dispersion of 6 resin particles (product name "MD2000", manufactured by Toyobo, aqueous dispersion of polyester resin particles, solid content 40%).

[0091] <Ink preparation> The components (in %) shown in the upper row of Tables 1 and 2 were mixed. Then, potassium hydroxide was added to adjust the pH to a range of 8 to 9. Each ink was prepared by pressure filtration through a 3.0 μm pore size microfilter (manufactured by Fujifilm). In Table 1, "Acetylenel E100" is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals.

[0092] [Table 1]

[0093] [Table 2]

[0094] <Preparation of reaction solution> A reaction solution was obtained by mixing 10.0 parts of magnesium sulfate heptahydrate, 2.0 parts of glycerin, 7.0 parts of ethylene glycol, 0.5 parts of a nonionic surfactant (product name "Acetylenel E100", manufactured by Kawaken Fine Chemicals), and 80.5 parts of deionized water.

[0095] <Preparation of the treatment solution> (Processing solution 1) Silicone oil (product name "KF-9901", manufactured by Shin-Etsu Chemical Co., Ltd.) was diluted to 40% by mass with isopropyl alcohol and used as treatment solution 1.

[0096] (Processing solution 2) Treatment solution 2 was prepared by mixing 10.0 parts of silicone emulsion, 2.0 parts of glycerin, 7.0 parts of ethylene glycol, 0.5 parts of nonionic surfactant (product name "Acetylenel E100", manufactured by Kawaken Fine Chemicals), and 80.5 parts of deionized water. As the silicone emulsion, product name "KM-2002-T-2" (manufactured by Shin-Etsu Chemicals, silicone oil content 40.0%) was used.

[0097] <Recording of images for evaluation> An inkjet recording device (product name "PIXUS PRO-10S", manufactured by Canon) equipped with a recording head that ejects liquid using thermal energy was prepared. The types of inks shown in Table 1 were filled into ink cartridges and set in the prepared inkjet recording device. In this embodiment, a solid image recording duty cycle of 100% is defined as recording an image with a resolution of 600 dpi x 600 dpi and 8 ink droplets with a mass of 3.5 ng per droplet applied to a unit area of ​​1 / 600 inch x 1 / 600 inch. Using this inkjet recording device, an image (50 mm x 50 mm) with a recording duty cycle of 400% was recorded on a recording medium by ejecting ink from the ejection port on the lower half of the longitudinal direction of the recording head. In parallel with the application of ink, a reaction solution was applied to the recording medium. The recording duty cycle of the reaction solution was set to 40%. As the recording medium, a PET film (product name "LLRPCF1372", manufactured by Sakurai, 30 msec from the start of contact in the Bristow method) was used. 1 / 2The amount of water absorbed up to this point is 0 mL / m². 2 More than 10mL / m 2 A sheet of paper cut to A4 size (within the following range) was used. The recording medium on which the image was recorded was then heated in a 100°C constant temperature bath for 1 minute to fix the image onto the recording medium.

[0098] In Table 5, in the embodiment where "1" is indicated in the "Method of applying processing solution" column, processing solution 1 was applied to the image fixed on the recording medium using a roller. In the embodiment where "2" is indicated in the "Method of applying processing solution" column, processing solution 2 was applied to the image fixed on the recording medium using an inkjet recording device (product name "PIXUS PRO-10S", manufactured by Canon).

[0099] <Rating> Each ink obtained as described above was evaluated for the following items. In this invention, "A" and "B" were considered acceptable levels, and "C" was considered an unacceptable level, according to the evaluation criteria for each item shown below. The evaluation results are shown in Table 3.

[0100] (Drying and concealing properties) For the examples and comparative examples where no processing solution was applied, the dry opacity of the images heat-treated using the method described above was evaluated. For the examples where the processing solution was applied, the recording medium was placed in a 100°C constant temperature bath for 1 minute after application of the processing solution, and then the dry opacity was evaluated. The opacity of the evaluation images was measured and calculated according to the method compliant with ISO 2471:2008, and the opacity of the images was evaluated. In ISO 2471:2008, the reflectance was measured by placing a white plate and a black plate on the back of the paper to be tested, and the opacity was calculated from the following formula (B). Hiding = (R0 / R ∞ ) × 100 ···(B) R0: Reflectance measured with a black board placed behind it. R ∞ Reflectance measured with a white board placed behind it. In accordance with the method described above, the opacity of images recorded using opacity test paper (manufactured by TP Giken, with inspection certificate from the Japan Paint Inspection Association) was measured and calculated, and the opacity of the images was evaluated according to the evaluation criteria shown below. A: The concealment level was 55% or higher. B: The concealment level was between 45% and 55%. C: The concealment level was less than 45%.

[0101] (Water-repellent properties) For the examples and comparative examples without the application of the processing solution, the image evaluation images, which had been heat-treated using the method described above, were immersed in 25°C water for 10 minutes. After that, the moisture was wiped off and the opacity was measured. For the examples with the application of the processing solution, after applying the processing solution, the recording medium was placed in a 100°C constant temperature bath for 1 minute for heat treatment, and then immersed in 25°C water for 10 minutes. After that, the moisture was wiped off and the opacity was measured. The opacity when wet was evaluated by calculating the difference between the dry opacity and the opacity after immersion in water. A: The difference between dry concealment and wet concealment was less than 10%. B: The difference between dry concealment and wet concealment was 10% or more but less than 15%. C: The difference between dry concealment and wet concealment was 15% or more.

[0102] [Table 3]

[0103] Furthermore, the disclosure of embodiments of the present invention includes the following methods and configurations.

[0104] (Method 1) An inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles, An ink application step of applying the white aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the white aqueous ink has been applied, In the drying step, the recording medium is dried to melt the resin particles and form an ink film. An inkjet recording method characterized in that the porosity in the ink film is 30% or more, and the advancing contact angle θ(°) of water in the ink film is 90° or more.

[0105] (Method 2) The inkjet recording method according to Method 1, wherein the forward contact angle θ(°) is 100° or more.

[0106] (Method 3) The resin particles include silicone resin particles, The inkjet recording method according to Method 1, wherein the content (volume %) of the resin particles in the white aqueous ink is 0.3 times or more in volume ratio to the content (volume %) of solids in the white aqueous ink.

[0107] (Method 4) The process further includes a step of applying a processing solution to the aforementioned ink film, The inkjet recording method according to Method 1, wherein the processing solution contains a hydrophobic component.

[0108] (Method 5) The inkjet recording method according to Method 4, wherein the hydrophobic component is silicone oil. (Method 6) The particles are titanium oxide, and the average primary particle diameter D of the titanium oxide is P0 The inkjet recording method according to Method 1, wherein (nm) is 150 nm or less.

[0109] (Composition 1) An inkjet recording apparatus used in an inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles, An ink application step of applying the white aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the white aqueous ink has been applied, In the drying step, the recording medium is dried to melt the resin particles and form an ink film. An inkjet recording apparatus characterized in that the porosity in the ink film is 30% or more, and the advancing contact angle θ(°) of water in the ink film is 90° or more.

[0110] (Configuration 2) A white aqueous ink used in an inkjet recording method that records an image on a recording medium using a white aqueous ink containing particles and resin particles, An ink application step of applying the white aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the white aqueous ink has been applied, In the drying step, the recording medium is dried to melt the resin particles and form an ink film. A white aqueous ink characterized in that the porosity in the ink film is 30% or more, and the advancing contact angle θ(°) of water in the ink film is 90° or more. [Explanation of symbols]

[0111] 1 Titanium Oxide 2 Resin particles 3. Binder (a mixture of resin and titanium dioxide) 4. Holes

Claims

1. An inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles, An ink application step of applying the white aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the white aqueous ink has been applied, In the drying step, the recording medium is dried to melt the resin particles and form an ink film. An inkjet recording method characterized in that the porosity in the ink film is 30% or more, and the advancing contact angle θ (°) of water in the ink film is 90° or more.

2. The inkjet recording method according to claim 1, wherein the forward contact angle θ (°) is 100° or more.

3. The resin particles include silicone resin particles, The inkjet recording method according to claim 1, wherein the content (volume %) of the resin particles contained in the white aqueous ink is 0.3 times or more in volume ratio to the content (volume %) of solids contained in the white aqueous ink.

4. The process further includes a step of applying an aqueous treatment solution to the ink film, The inkjet recording method according to claim 1, wherein the aqueous treatment solution contains a hydrophobic component.

5. The inkjet recording method according to claim 4, wherein the hydrophobic component is silicone oil.

6. The particles are titanium oxide, and the average primary particle diameter D of the titanium oxide is Ｐ０ The inkjet recording method according to claim 1, wherein the (nm) is 150 nm or less.

7. An inkjet recording apparatus used in an inkjet recording method for recording an image on a recording medium using a white aqueous ink containing particles and resin particles, An ink application step of applying the white aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the white aqueous ink has been applied, In the drying step, the recording medium is dried to melt the resin particles and form an ink film. An inkjet recording apparatus characterized in that the porosity in the ink film is 30% or more, and the advancing contact angle θ (°) of water in the ink film is 90° or more.

8. A white aqueous ink used in an inkjet recording method that records an image on a recording medium using a white aqueous ink containing particles and resin particles, An ink application step of applying the white aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the white aqueous ink has been applied, In the drying step, the recording medium is dried to melt the resin particles and form an ink film. A white aqueous ink characterized in that the porosity in the ink film is 30% or more, and the advancing contact angle θ (°) of water in the ink film is 90° or more.

Images