Inkjet recording method, inkjet recording apparatus, and aqueous ink

Abstract

Provided is an inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles. The present invention has an ink application step for applying an aqueous ink to a recording medium, and a heating step for heating the recording medium to which the aqueous ink is applied to a temperature equal to or higher than the glass transition temperature Tg (DEG C) or the melting point TM (DEG C) of the first resin particles and lower than the glass transition temperature Tg (DEG C) or the melting point TM (DEG C) of the particles, the average primary particle diameter DP0 (nm) of the particles is 150 nm or less, and the recording medium is heated in the heating step to melt the first resin particles and generate pores.

Description

Technical Field

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

[0002] In recent years, in the fields of commercial printing, white images are sometimes recorded on recording media other than white, such as transparent films, semi-transparent films, and colored paper. From the perspective of material stability and cost, ink used to record white images contains a white pigment, such as titanium oxide.

[0003] However, titanium oxide has a higher specific gravity than materials used for inks other than white. Consequently, the specific gravity difference with the solvent increases, and titanium oxide has the disadvantage of tending to settle in the ink. In particular, to enhance the concealment and whiteness of the recorded image, using titanium oxide with a larger particle size or increasing the titanium oxide content further increases the tendency for titanium oxide to settle. As an ink that can record images with excellent whiteness and easily redisperse even if the pigment settles, a white ink comprising rutile titanium oxide with an average particle size of 300 nm or greater and a urethane resin has been proposed (Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2013-60513 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] The settling velocity V of particles in ink can be calculated by the following formula (A) (Stokes equation):

[0009] V={g(ρ S -ρ)d 2} / 18μ(A)

[0010] d: particle size,

[0011] g: acceleration due to gravity,

[0012] ρ S : density of the particles,

[0013] ρ: density of the dispersion medium,

[0014] μ: Viscosity of the dispersion medium.

[0015] According to the Stokes equation, the sedimentation velocity V increases in proportion to the square of the particle size; that is, the larger the particle size, the easier it is for the particles to settle. Rutile titanium oxide has a higher specific gravity than other common materials used in inks and has a high sedimentation velocity. Therefore, in the white ink proposed in Patent Document 1, the titanium oxide used as a pigment tends to settle relatively slowly.

[0016] In contrast, images recorded with ink containing small-sized titanium oxide particles easily penetrate visible light without being scattered. Consequently, the scattering intensity decreases dramatically, and the image's contrast ratio tends to decrease. In other words, the particle settling velocity and the recorded image's contrast ratio are in a trade-off relationship.

[0017] Therefore, an object of the present disclosure is to provide an inkjet recording method that can record an image with excellent concealment while using an aqueous ink with excellent settling resistance. Another object of the present disclosure is to provide an inkjet recording apparatus and an aqueous ink for use in the inkjet recording method.

[0018] Solutions for solving problems

[0019] That is, according to the present disclosure, there is provided an inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, the method comprising an ink applying step of applying the aqueous ink to the recording medium and heating the recording medium to which the aqueous ink is applied to a temperature equal to or higher than the glass transition temperature Tg (° C.) or melting point Tg (° C.) of the first resin particles. M (℃) and less than the glass transition temperature Tg (℃) or melting point T M (°C) in the heating step, wherein the average primary particle size D of the particles P0 (nm) is 150 nm or less, and in the heating step, the recording medium is heated to melt the first resin particles and generate pores.

[0020] Advantageous Effects of the Invention

[0021] According to the present disclosure, an inkjet recording method can be provided that can record an image with excellent concealment while using an aqueous ink with excellent settling resistance. In addition, according to the present disclosure, an inkjet recording apparatus and an aqueous ink for use in the inkjet recording method can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] [ Figure 1 ] is a schematic diagram showing an example of an image forming process.

[0023] [ Figure 2 ] is a schematic diagram showing an example of an image forming process.

[0024] [ Figure 3] is an oblique view schematically showing an embodiment of the inkjet recording apparatus of the present disclosure.

[0025] [ Figure 4 ] is a side view schematically showing an embodiment of the inkjet recording apparatus of the present disclosure. DETAILED DESCRIPTION

[0026] The present disclosure will now be described in more detail with reference to preferred embodiments. In the present disclosure, when the compound is a salt, the salt is present as dissociated ions in the ink, but for convenience, it is expressed as "containing a salt." Furthermore, the aqueous ink and aqueous reaction liquid for inkjet printing may be simply referred to as "ink" and "reaction liquid." Unless otherwise specified, physical property values ​​are values ​​at room temperature (25°C).

[0027] The present inventors have studied an inkjet recording method that can record an image with excellent concealment properties while using an ink with excellent settling resistance. Consequently, they have discovered that by satisfying the following requirements (i) to (iv), an image with excellent concealment properties can be recorded while using an ink with excellent settling resistance, and have achieved the present disclosure.

[0028] (i) The method includes an ink applying step of applying ink to a recording medium and heating the recording medium to which the ink is applied to a temperature equal to or higher than the glass transition temperature Tg (° C.) or melting point Tg (° C.) of the first resin particles. M (℃) and less than the glass transition temperature Tg (℃) or melting point T M (°C) temperature of the heating step;

[0029] (ii) ink comprising particles and first resin particles;

[0030] (iii) Average primary particle size D of particles P0 (nm) is 150nm or less; and

[0031] (iv) In the heating step, the recording medium is heated to melt the first resin particles and generate pores.

[0032] Figure 1 and Figure 2 is a schematic diagram showing an example of an image forming process. Ink is applied to a recording medium, and then Figure 1 As shown, volatile components such as water and water-soluble organic solvent evaporate, and the ink dries to form an ink film in which the particles 1 in the ink and the first resin particles 2 are densely packed. Subsequently, the recording medium is heated to a temperature at which the first resin particles 2 melt (equal to or higher than the glass transition temperature Tg (° C.) or melting point Tg of the first resin particles). M (℃) temperature), then Figure 2As shown, the resin generated by melting the first resin particles 2 penetrates into the gaps between the individual particles 1. In addition, pores 4 are formed at the portions where the first resin particles 2 previously existed. Since the heating temperature in this case is lower than the glass transition temperature Tg (°C) or melting point T M (°C), it is inferred that the particles 1 do not melt. The resin penetrates into the gaps between the individual particles 1 to form a binder 3 made of a mixture of the particles 1 and the resin. Here, since the average primary particle size D of the particles 1 P0 (nm) is 150nm or less, so visible light is hardly scattered by the particles 1. However, air with a low refractive index is present in the pores 4 formed by the melting of the first resin particles. Therefore, it is assumed that the refractive index of the pores 4 is relatively low compared to the refractive index of the binder 3. In this case, due to the refractive index difference between the binder 3 and the pores 4, the incident light is scattered. Therefore, it is possible to record an image with high concealment without using components that easily settle, such as titanium oxide with a large particle size. As mentioned above, it is necessary to melt the first resin particles through a heating step. Therefore, when only a drying step is performed to evaporate the solvent (liquid component) on the surface of the recording medium after image recording, or when heating in the heating step is performed at a temperature lower than the temperature at which the first resin particles melt, it is inferred that the first resin particles do not melt. As a result, scattering due to the refractive index difference between the binder 3 and the pores 4 does not occur, and an image with high concealment cannot be recorded. In contrast, when heating in the heating step is performed at a temperature equal to or higher than the temperature at which the particles melt, not only the first resin particles but also the particles melt, and no pores are formed. As a result, the above-mentioned scattering does not occur, and an image with high concealment cannot be recorded.

[0033] As shown in the Stokes equation (Formula (A)), the smaller the particle size, the slower the sedimentation rate. Therefore, by using a particle with a relatively small particle size (i.e., an average primary particle size D of 150 nm or less), the particle size of the particle is reduced. P0 (nm)) of particles to reduce the sedimentation velocity, and an ink having excellent sedimentation resistance can be obtained. The details of the average primary particle size will be described later. If D P0 If the particle size (nm) is larger than 150nm, the concealment property is improved because visible light tends to be scattered. On the contrary, as shown in the Stokes equation, the sedimentation velocity increases and the sedimentation resistance cannot be obtained. If the particle size is enlarged, it is difficult to achieve the following when forming an image: Figure 1 The first resin particles are shown in a state uniformly distributed around the particles, and an image with high concealment cannot be recorded.

[0034] <Inkjet Recording Method, Inkjet Recording Apparatus, and Aqueous Ink>

[0035] The inkjet recording method disclosed herein is a method for recording an image by discharging aqueous ink from a recording head of an inkjet system to apply the ink to a recording medium. The inkjet recording method disclosed herein includes an ink applying step of applying the ink to the recording medium and a heating step of heating the recording medium to which the aqueous ink is applied to a predetermined temperature. In the heating step, the recording medium is heated to a temperature equal to or higher than the glass transition temperature Tg (°C) or the melting point Tg (°C) of the first resin particles. M (℃) and less than the glass transition temperature Tg (℃) or melting point T M The aqueous ink contains particles and first resin particles, and the average primary particle size D of the particles is P0 In the heating step, the recording medium is heated to melt the first resin particles and generate pores.

[0036] The inkjet recording apparatus disclosed herein is a device used in an inkjet recording method for recording an image by discharging aqueous ink from a recording head of an inkjet system and applying the ink to a recording medium. The inkjet recording apparatus disclosed herein is suitable for use in such a recording method. In the present disclosure, curing of the image by irradiation with active energy rays or the like is unnecessary.

[0037] The aqueous ink of the present disclosure is an ink used for an inkjet recording method of recording an image by discharging the aqueous ink from a recording head of an inkjet system and applying the ink to a recording medium, and is an ink suitable for use in the above-mentioned recording method.

[0038] The inkjet recording method and the inkjet recording apparatus (hereinafter also simply referred to as "recording method and recording apparatus") of the present disclosure will now be described in detail.

[0039] Figure 3 is an oblique view schematically showing one embodiment of the inkjet recording apparatus of the present disclosure. Figure 4 is a side view schematically showing one embodiment of the inkjet recording apparatus of the present disclosure. Figure 3 and Figure 4 The recording device of the illustrated embodiment includes a recording head 22 of an inkjet system for discharging ink. The recording head 22 is a recording head that ejects ink by the action of thermal energy. The recording head that ejects ink by the action of thermal energy is a recording head of a thermal system that applies thermal energy to the ink by applying an electric pulse to an electrothermal conversion element to allow the ink to be ejected from the ejection hole. Here, a recording head that ejects ink by the action of thermal energy is taken as an example, but a recording head that ejects ink by the action of mechanical energy may also be used. The recording head may include a mechanism (temperature control mechanism) for heating the aqueous ink ejected from the recording head. When the temperature control mechanism is included, the temperature of the ink ejected from the recording head is preferably controlled to be above 35°C and below 70°C.

[0040] Ink is preferably applied to a unit area of ​​the recording medium using multipath recording, where the recording head and the recording medium are scanned relative to each other multiple times. In particular, it is preferred that white ink and colored ink be applied to the unit area using different relative scans. This increases the time the inks spend in contact with each other, and tends to suppress mixing. The unit area can be set to any desired area, such as a single pixel or a single band.

[0041] (Heating step)

[0042] The recording method of the present disclosure includes a heating step (heating treatment) of heating a recording medium to which ink is applied. In the heating step, the recording medium to which ink is applied is heated to melt the first resin particles in the ink. Thus, an image including pores produced by the melting can be fixed to the recording medium. Volatile components (solvents) in the ink, such as water and water-soluble organic solvents, are evaporated by heating the recording medium to which ink is applied to form an ink film in which particles as solid components dispersed in the ink and first resin particles are closely packed. Subsequently, the heated first resin particles melt to form pores, and the resin produced by the melting of the first resin particles also penetrates into the gaps between the individual particles. Thus, a binder as a mixture of particles and resin is formed, and the image including pores therein can be fixed to the recording medium.

[0043] In the heating step, the recording medium is heated to a temperature equal to or higher than the glass transition temperature or melting point of the first resin particles and lower than the glass transition temperature Tg (° C.) or melting point Tg (° C.) of the particles. M (°C) to melt the first resin particles in the ink. That is, the heating temperature T H The first resin particles may be prepared according to their glass transition temperature Tg or melting point Tg. M and the glass transition temperature Tg (°C) or melting point T M (°C) is appropriately set. Here, the first resin particles made of a crystalline resin have Tg and T M , and in this case, the heating temperature is equal to or higher than the temperature T M The details of the crystalline resin will be described later. Specifically, the heating temperature T in the heating step is H The upper limit of the heating temperature is not particularly limited, but is preferably 200°C or lower from the viewpoint of the heat resistance temperature of the recording medium. H It refers to the maximum temperature of the recording medium surface during the heating step. Alternatively, it can be rephrased as the set temperature of the heating device. Heating temperature T HThe temperature of the recording medium surface can be measured using a contact thermometer or a non-contact infrared thermometer, for example, which is brought into contact with a thermocouple or the like. In the embodiment of the present disclosure, the temperature of the recording medium surface is measured at a position 10 cm vertically above the recording medium surface using a non-contact infrared thermometer digital radiation temperature sensor FT-H20 (manufactured by Keyence Corporation).

[0044] The first resin particles are melted by performing a heating step to produce holes, and as a result, an image including the holes can be recorded. The heating step can be performed once or multiple times. Examples of devices for heating the recording medium include known heating devices, such as heaters, air supply devices using air supply (such as dryers), and devices in combination thereof. Examples of heating devices include the above-mentioned heating devices, air supply devices, and devices in combination thereof. Examples of heating treatment methods include a method of providing heat from the opposite side (back side) of the recording surface (ink application surface) of the recording medium, a method of applying warm air or hot air to the recording surface of the recording medium, and a method of heating the recording surface or back side with an infrared heater. Alternatively, a combination of two or more of these methods can be adopted. In addition, heating can be performed by bringing a heating member into contact with the recording surface or back side of the recording medium. The time of the heating step is not particularly limited as long as the first resin particles can be melted. For example, when the heating step is performed by air supply, the temperature of the wind can be above 80°C and below 120°C.

[0045] exist Figure 3 and Figure 4 In the recording apparatus shown, a heater 25 supported by a frame (not shown) is provided at a position downstream in the sub-scanning direction A relative to the position where the recording head 22 reciprocates in the main scanning direction B. The recording medium 10 to which ink is applied can be heated by the heater 25. 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 effectively irradiating the recording medium 10 with the heat generated by the heater 25. In addition, the heater cover 26 is also a member for protecting the heater 25. The recording medium 10 to which ink ejected from the recording head 22 is applied is wound by a winding reel 27 to form a roll of the medium 24.

[0046] Preferably, before the heating step, Figure 1 As shown, the step of forming an ink film in which the particles and the first resin particles are closely packed is further included. By providing such a step, the molten first resin particles can be allowed to more surely penetrate into the gaps between the individual particles, and the image can more easily include holes, such as Figure 2As shown. That is, the inkjet recording method preferably further includes at least one step selected from the group consisting of: a reaction liquid applying step of applying an aqueous reaction liquid containing a reactant that reacts with the ink to the recording medium and a drying step of drying the liquid component on the recording medium. It is also preferred to perform these two steps (reaction liquid applying step and drying step). When these steps are adopted in combination, it is particularly preferred to perform the drying step after the reaction liquid applying step. That is, it is preferred to perform the reaction liquid applying step, the ink applying step, the drying step and the heating step in sequence. The ink application can be performed simultaneously with the application of the reaction liquid. The particles in the ink and the first resin particles can be aggregated and tightly stacked by applying the reaction liquid to the recording medium. The details of the reaction liquid will be described later. When air is supplied to the recording medium, from the viewpoint of drying efficiency, it is preferred to supply air to the surface (recording surface) of the recording medium.

[0047] A drying step may be performed to dry the liquid component (solvent) on the surface of the recording medium. Here, in the drying step, the liquid component does not need to be completely dried. Although the liquid component on the recording medium may be gradually dried without going through the above steps, drying can be accelerated by performing the drying step, and it can be effectively achieved. Figure 1 The drying step may be performed once or multiple times. In the drying step, the same heating device as in the heating step may be used. In particular, air blowing is preferred from the viewpoint of effectively drying the liquid component.

[0048] Since the drying step is performed in a state where the solvent remains on the surface of the recording medium and the viscosity is not sufficiently increased, the effect of suppressing the realization of Figure 1 From the perspective of the difficulty of the state shown, it is preferable that the heat energy applied to the recording medium is not too large. Specifically, it is preferable that the heating temperature and the heating time are not too large. For example, when drying by air supply, the temperature of the air supply device (such as hot air) can be set in consideration of the transmission speed and the ambient temperature so that the recording medium is heated to the desired temperature. Specifically, the temperature of the wind (such as hot air) blown by the air supply device is preferably set to below 60°C, and further preferably set to below 30°C. The temperature of the wind may be normal temperature (25°C). Here, as Figure 1 As shown, in order to achieve a close state of the particles and the first resin particles by reducing the liquid component without melting the first resin particles, the liquid component is preferably less than the Tg or Tg of the first resin particles. MIt is preferred to heat the recording medium at a temperature of 100°C. The wind speed is preferably 1 m / s or more and 100 m / s or less. A K-type thermocouple thermometer can be used to measure the temperature of wind such as hot wind. As a specific thermometer, for example, the trade name "AD-5605H" (manufactured by A&D Co., Ltd.) can be used. As needed, the wind can be applied to the back of the recording medium, but it is preferred to apply the wind to the front surface of the recording medium (to which ink is applied). The distance from the air supply device to the recording medium is preferably 5 mm or more and 50 mm or less.

[0049] (Recording Medium)

[0050] There is no particular limitation on the type of recording medium on which the image is recorded, and any recording medium can be used. In particular, since an ink that can record a white image excellent in concealment is used, it is preferable to use a recording medium other than white, such as a transparent film, a semi-transparent film, and colored paper. That is, the recording medium is preferably a non-absorbent recording medium. Here, a non-absorbent recording medium (low-absorbent to non-absorbent recording medium) is a medium that is recorded from the start of contact to 30 msec in the Bristow method. 1 / 2 The water absorption capacity is 0mL / m 2 Above 10mL / m 2 The following recording media. The Bristow method is described in the "Paper and Paperboard Liquid Absorption Test Method" of JAPANTAPPI Paper and Pulp Test Method No. 51. Recording media for inkjet recording (e.g., glossy paper and matte paper) including a coating layer (ink receiving layer) formed of inorganic particles and plain paper without a coating layer have a water absorption of more than 10 mL / m 2 "absorbent recording medium".

[0051] Examples of low- to non-absorbent recording media include: plastic films; recording media comprising a plastic film adhered to the recording surface of a substrate; and recording media comprising a resin coating provided on the recording surface of a substrate comprising cellulose pulp. Plastic films are particularly preferred, and recording media comprising a resin coating provided on the recording surface of a substrate comprising cellulose pulp are also preferred. The recording medium in this specification refers to the objective recording medium on which the image serving as the recording content is recorded, rather than a transfer medium.

[0052] (Water-based ink)

[0053] The ink used in the recording method of the present invention is an aqueous ink for inkjet, which contains particles and first resin particles. In particular, the ink is preferably a white ink. As white ink, an ink that does not have white color in the ink state but can record (form) a white image is also included. White refers to a color whose lightness (L*) and chroma (a*, b*) are respectively within the range of 70≤L*≤100, -4.5≤a*≤2, and -6≤b*≤2.5. The components constituting the ink will be described in detail below.

[0054] [Particles]

[0055] The ink contains particles. The particles may be a colored material, or may be a material without color, such as resin particles. In particular, since a white image is recorded, it is preferred to use colorless or white particles. Based on the total volume of the ink, the content (volume %) of the particles in the ink is preferably 1.5% by volume or more. If the content of the particles is less than 1.5% by volume, when the first resin particles described later are melted, gaps sufficient for penetration will not be formed, and the image may not have sufficient concealment. The content of the particles in the ink is preferably 5.0% by volume or less.

[0056] The particles are usually in a secondary aggregate state generated by the aggregation of two or more primary particles and are dispersed in the ink. The particles contained in the ink preferably have an average primary particle size D of 150 nm or less, preferably 50 nm or less. P0 (nm). Average primary particle size D P0 The lower limit of (nm) is not particularly limited, but is preferably 5 nm or more. The particle size of the primary particles of the particles can be measured by observing the particles using a scanning electron microscope. The average primary particle size of the particles can be calculated as the average value of the particle size of multiple primary particles (e.g., 100 individual particles).

[0057] The cumulative 50% particle size D of the particles based on volume P The particle size (nm) is preferably 150 nm or less, and more preferably 5 nm or more and 100 nm or less. By using particles having a cumulative 50% particle size based on volume within the above range, light scattering can be suppressed and light transmittance can be increased, and the sedimentation rate can be further reduced.

[0058] In this specification, the “50% cumulative particle size based on volume (D 50)" is a diameter of particles corresponding to 50% accumulation from the minimum particle size side based on the total volume of particles measured in the particle size cumulative curve, and can be measured by dynamic light scattering using a particle size distribution analyzer. Examples of measurement conditions include SetZero: 30 seconds, number of measurements: three times, measurement time: 180 seconds, and shape: non-spherical. As the particle size distribution analyzer, for example, a particle size analyzer by dynamic light scattering (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) can be used. The particle size distribution analyzer used and the measurement conditions are of course not limited thereto.

[0059] In the heating step for melting the first resin particles, the particles do not need to be melted. Specifically, the glass transition temperature Tg or melting point Tg of the particles is not necessarily the same as that of the first resin particles. M The temperature is equal to or higher than the temperature of the recording medium in the heating step, and is preferably 200° C. or higher. The particles are preferably at least one selected from the group consisting of titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silica, kaolin, clay, and second resin particles. The details of the second resin particles will be described later.

[0060] From the viewpoint of forming a binder with a high refractive index, it is preferred to use titanium oxide with a relatively high refractive index as particles. The refractive index of titanium oxide is preferably 2.1 or more, more preferably 2.5 or more and 2.8 or less. The surface of titanium oxide can be coated with aluminum oxide or zirconium dioxide. The surface of titanium oxide can be coated with inorganic oxides such as silica, zinc oxide and zirconium dioxide; or organic materials such as polyols. By using titanium oxide with a coated surface, suppression of photocatalytic function and improvement of dispersibility are expected. Titanium oxide includes three crystal types: rutile, anatase and brookite. In particular, rutile titanium oxide with low photocatalytic function is preferably used. Examples of industrial manufacturing methods of titanium oxide include sulfuric acid method and chlorine method. Titanium oxide manufactured by any manufacturing method can be used.

[0061] The content (mass %) of titanium oxide in the ink is preferably 5.0 mass % or more and 45.0 mass % or less, and more preferably 7.0 mass % or more and 38.0 mass % or less, based on the total mass of the ink. P0 The cumulative 50% particle size D of titanium oxide based on volume is preferably 50 nm or less, and more preferably 30 nm or less. P The thickness (nm) is preferably 100 nm or less, and more preferably 5 nm or more and 50 nm or less.

[0062] The particle shape of calcium carbonate is cubic or spindle-shaped. In particular, cubic calcium carbonate with a uniform shape is preferably used. Examples of calcium phosphate include first calcium phosphate (Ca(H2PO4)2), second calcium phosphate (CaHPO4) and third calcium phosphate (Ca3(PO)2). In particular, apatite-type calcium phosphate is preferred, and hydroxyapatite (Ca 10 (PO6)(OH)2) is further preferred.

[0063] Barium sulfate can be broadly divided into micronized barium sulfate and precipitated barium sulfate. The particle size of precipitated barium sulfate can be controlled by the synthesis conditions, allowing barium sulfate with an appropriate particle size to be obtained. Zirconia, also known as zirconium dioxide, is known as a ceramic with high toughness. Pure zirconium dioxide changes its crystal structure with temperature, and this change also causes volume changes, which can easily lead to degradation. Therefore, stabilized zirconium dioxide containing a stabilizer to suppress volume changes can be used.

[0064] As silicon dioxide, for example, silicon oxide synthesized by the Stober method can be used. The Stober method is a method in which alkoxysilane, a source of silica, undergoes a hydrolysis-polycondensation reaction in a water-ethanol-ammonia solution. The particle size of the resulting spherical particles can be controlled by varying the concentrations of the reactants.

[0065] Kaolin is a clay mineral containing multiple inorganic components. Specifically, kaolin is a clay composed of kaolinite, hydrated halloysite, and a halloysite crystal structure. In addition to kaolin components, clay also includes illuminite, montmorillonite, and vermiculite. When using the above particles, from the perspective of producing white ink, it is preferred to use particles with high whiteness.

[0066] [Resin particles]

[0067] The ink contains first resin particles. A close contact state between the particles and the first resin particles is formed by evaporation of a solvent in the ink applied to the recording medium. Then, the first resin particles are melted by a heating step to generate pores. The content (mass %) of the first resin particles in the ink is preferably 2.5% by mass or more and 17.0% by mass or less based on the total mass of the ink, and more preferably 2.5% by mass or more and 14.0% by mass or less. In addition, the content (volume %) of the first resin particles in the ink is preferably 2.5% by volume or more and 17.0% by volume or less based on the total volume of the ink, and more preferably 2.5% by volume or more and 14.0% by volume or less.

[0068] The size of the pores formed in the heating step is roughly the same as the size (particle diameter) of the first resin particles. The size of the pores formed highly affects the efficiency of light scattering. Therefore, from the viewpoint of further improving the light scattering efficiency, the cumulative 50% particle diameter D of the first resin particles based on volume is E It is preferably from 100 nm to 400 nm, and more preferably from 150 nm to 250 nm.

[0069] Whether the first resin particles melt in the heating step can be easily determined by, for example, cutting the recording medium on which the image is recorded before and after the heating step and observing them with a scanning electron microscope, etc. Alternatively, the particle size of the first resin particles in the image before the heating step is measured, and when the difference between the pore size of the image after the heating step and the particle size of the first resin particles is small (for example, within 10%), it can be judged that the first resin particles melt to generate pores.

[0070] From the viewpoint of forming a binder having a high refractive index, it is preferable to use first resin particles having a relatively high refractive index. Specifically, the refractive index of the first resin particles is preferably 1.5 or more, and more preferably 1.6 or more and 2.5 or less.

[0071] In the ink, the volume ratio of the content (volume %) of the first resin particles to the content (volume %) of the particles is preferably 1.3 times or more and 5.0 times or less, and further preferably 2.0 times or more and 4.0 times or less. When the volume ratio is greater than 5.0 times, the amount of fusion of the individual first resin particles tends to increase, and it is difficult to form holes of the desired size. As a result, the concealment of the image may be insufficient. In addition, the refractive index of the binder composed of the molten first resin particles and the particles may be small, and the efficiency of light scattering and the concealment rate may tend to decrease. On the contrary, when the above-mentioned mass ratio is less than 1.3 times, the amount of holes formed is reduced, and an image with a sufficient concealment rate may not be obtained.

[0072] When the particles are titanium oxide, the mass ratio of the content (mass %) of the first resin particles to the content (mass %) of titanium oxide in the ink is preferably 0.30 times or more and 1.0 times or less, and more preferably 0.40 times or more and 0.60 times or less.

[0073] The content (volume %) of the first resin particles in the ink corresponds to the volume occupied by the first resin particles in the ink. Therefore, when the first resin particles include pores or internal voids, the volume occupied by the first resin particles in the ink is a value including the pores and internal voids. Since the first resin particles are directly replaced by pores, the apparent density of the first resin particles is preferably 0.8 g / cm 3 If the apparent density is less than 0.8g / cm 3If the binder is too low, it will be difficult to generate enough resin to fill the gaps between the particles, the refractive index of the binder will be small, and the light scattering efficiency and concealment rate may be insufficient. The amount of resin in the binder will be reduced, and the intensity of the image may be insufficient.

[0074] The apparent density of the first resin particles can be measured, for example, according to the following procedure. First, a 30 cm 3 The first resin particles fill a 100-cm 3 The measuring flask is filled with the first resin particles and the mass of the filled first resin particles is measured. Next, the measuring flask filled with the first resin particles is filled with isopropyl alcohol up to the mark line. The mass of the isopropyl alcohol added to the measuring flask is accurately measured, and the apparent density (g / cm) of the first resin particles can be calculated using the following formula (X): 3 ). In the examples described later, the apparent density of the first resin particles is measured and calculated by the above method. Alternatively, the apparent density can also be measured using a Le Chatelier specific gravity meter according to JIS Z 8807.

[0075] The apparent density of the first resin particles (g / cm 3 )=A / (100-B) / C (X)

[0076] A: mass of the first resin particle (g);

[0077] B: mass of isopropyl alcohol (g); and

[0078] C: Specific gravity of isopropyl alcohol at 25°C.

[0079] Examples of the resin forming the first resin particles include vinyl chloride resins, styrene resins, urethane resins, acrylic resins, and polyester resins. In particular, acrylic resins, polyester resins, and urethane resins are preferred from the perspective of inkjet performance. If first resin particles formed from resins other than those listed above are used, the jetting tends to be unstable, and the resulting image may not have sufficient concealment. In particular, acrylic resins are preferred, and acrylic resins containing units derived from styrene are even more preferred. The details of the resins forming the resin particles will be described later.

[0080] If the first resin particles are melted before the heating step is performed, mixing of the particles and the resin does not proceed quickly, or individual first resin particles fuse with each other, and it may be slightly difficult to form the desired pores. When the desired pores are not formed, the efficiency of light scattering decreases, and the concealment rate may tend to decrease. Therefore, it is preferred to use resin particles that are substantially infusible at room temperature (25°C). Specifically, it is preferred that (i) the glass transition temperature Tg (°C) of the first resin particles is 25°C or higher, or (ii) the melting point Tg (°C) of the first resin particles is 25°C or higher. M (° C.) is 25° C. or higher and the resin constituting the first resin particles is a crystalline resin.

[0081] Tg and T of the first resin particles M The upper limits of Tg and Tg are not particularly limited, but both are preferably 100°C or lower, and more preferably 80°C or lower. The Tg and Tg of the first resin particles can be measured using a differential scanning calorimeter (DSC). M .

[0082] The term "resin particles" in this specification refers to a resin that is present in an undissolved state in the aqueous medium of the ink, and more specifically, a resin that is present in the aqueous medium in the form of particles whose particle size can be measured by dynamic light scattering. In contrast, the term "water-soluble resin" refers to a resin that is present in a dissolved state in the aqueous medium of the ink.

[0083] Whether a certain resin corresponds to "resin particles" can be judged according to the method shown below. A liquid containing the resin to be judged is provided and diluted with pure water so that the content of the resin is about 1.0% to prepare a sample. When the particle size of the resin in the sample is measured by a dynamic light scattering method, if particles with a particle size are detected, the resin is judged to be "resin particles" (i.e., it is a "water-dispersible resin"). On the contrary, if particles with a particle size are not detected, the resin is judged not to be "resin particles" (i.e., it is 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: true sphere, refractive index: 1.5, and density: 1.0.

[0084] As the particle size distribution analyzer, a particle size analyzer by a dynamic light scattering method (for example, trade name “UPA-EX150” manufactured by Nikkiso Co., Ltd.) can be used. The particle size distribution analyzer used and the measurement conditions are of course not limited to the above.

[0085] Whether the resin constituting the resin particles is an amorphous resin or a crystalline resin can be determined by measuring the crystallinity using a differential scanning calorimeter. When no melting peak is observed by the differential scanning calorimeter, it can be determined that it is an amorphous resin. On the contrary, when a melting peak is observed, it can be determined that it is a crystalline resin. When the resin is a crystalline resin, the crystallinity can also be determined based on the ratio of the heat of fusion determined by the peak area to the heat of fusion of a perfect crystal with a crystallinity of 100% determined by theoretical calculation.

[0086] The acid value of the resin constituting the first 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 first resin particles is preferably 1,000 or more and 3,000,000 or less, more preferably 100,000 or more and 3,000,000 or less. The first resin particles do not need to contain a color material therein.

[0087] As described above, the first resin particles are melted by heating, and the resulting resin fills the voids between the individual particles. Thus, pores are generated. Therefore, the properties of the first resin particles as an elastomer, particularly the loss elastic modulus associated with viscosity, affect the ease with which pores are generated. The resin generated by melting fills the voids between the individual particles, thereby generating pores. Therefore, the properties of the first resin particles as an elastomer, particularly the loss elastic modulus associated with viscosity, affect the ease with which the voids are filled, that is, the ease with which desired pores are generated. Therefore, the loss elastic modulus of the resin at high temperatures is important. This loss elastic modulus varies depending on the temperature. For example, the loss elastic modulus of the first resin particles at 80°C is preferably 1.0×10 7 Pa or less, more preferably 3.3×10 5 Below Pa.

[0088] As particles, the glass transition temperature Tg (°C) or the melting point T M (°C) are higher than the glass transition temperature Tg (°C) or melting point Tg (°C) of the first resin particles. M (°C) of the second resin particles. As the resin constituting the second resin particles, the same resin as that constituting the first resin particles can be used. In particular, the resin constituting the second resin particles is preferably a cross-linked resin, more preferably a cross-linked acrylic resin.

[0089] [Resin]

[0090] The ink may further contain a resin (optional resin) other than the first resin particles. The content (mass %) of the resin (optional 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.

[0091] The resin may be added to the ink to (i) stabilize the dispersion of the pigment, i.e., to serve as a resin dispersant or an auxiliary agent thereof. Furthermore, the resin may be added to the ink to (ii) improve the properties of the recorded image. Examples of the resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin is preferably a water-soluble resin that is soluble in an aqueous medium.

[0092] [Resin composition]

[0093] Examples of the resin include acrylic resins, urethane resins, and olefin resins. In particular, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are further preferred.

[0094] Acrylic resins preferably have hydrophilic and hydrophobic units as structural units. In particular, the resin preferably includes a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one member selected from the group consisting of monomers having an aromatic ring and (meth)acrylate monomers. In particular, preferred resins include a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic acid derived from at least one member selected from the group consisting of styrene and α-methylstyrene. These resins tend to interact with pigments and can therefore be suitably used as resin dispersants for dispersing pigments.

[0095] The hydrophilic unit is a unit including a hydrophilic group such as an anionic group. The hydrophilic unit can be formed by, for example, polymerizing a hydrophilic monomer including a hydrophilic group. Examples of hydrophilic monomers containing hydrophilic groups include acidic monomers containing 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. Examples of cations constituting the salts of the acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not including a hydrophilic group such as an anionic group. The hydrophobic unit can be formed by, for example, polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; and (meth) acrylate monomers such as methyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

[0096] Urethane resins can be obtained by, for example, reacting polyisocyanate and polyol. A chain extender may be further reacted. Examples of olefin resins include polyethylene and polypropylene.

[0097] Polyester resins are generally composed of units derived from polyols and units derived from polycarboxylic acids. Examples of polyols obtained by reacting units derived from polyols constituting polyester resins include divalent to tetravalent polyols. Examples of polyols include polyols containing aliphatic groups, polyols containing aromatic groups, and sugar alcohols. Examples of polyols include diols such as ethylene glycol (1,2-ethylene glycol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzene glycol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); triols such as glycerol, trimethylolethane, and trimethylolpropane; and tetraols such as pentaerythritol. As polyols, oligomers (low molecular weight polymers having a molecular weight of 1,000 or less) may also be used. Since the weight average molecular weight of the polyester resin can be easily adjusted, it is preferred to use divalent or trivalent polyols.

[0098] The example of the polycarboxylic acid of the unit derived from the polycarboxylic acid constituting the polyester resin obtained by the reaction includes dibasic to tetrabasic polycarboxylic acids. The example of the structure of the polycarboxylic acid includes polycarboxylic acids containing aliphatic groups, polycarboxylic acids containing aromatic groups and nitrogen-containing polycarboxylic acids. The example of the polycarboxylic acid includes dicarboxylic acids, such as glutamic 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. As the polycarboxylic acid, oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used. Since the weight average molecular weight and acid value of the polyester resin can be easily adjusted, it is preferred to use dibasic or tribasic polycarboxylic acids.

[0099] [Resin properties]

[0100] 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.

[0101] [Aqueous medium]

[0102] 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 water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As water, deionized water or ion-exchanged water may be preferably used. The content (mass %) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any solvent that can be used for inkjet inks may be used, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds.

[0103] [Other components]

[0104] The ink may also contain a water-soluble organic compound that is solid at 25°C, such as urea or its derivatives, trimethylolpropane and trimethylolethane. The content (mass %) of the water-soluble organic compound 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. As needed, in addition to the above components, the ink may also contain other components. Examples of other components include various additives, such as surfactants, defoamers, pH regulators, viscosity modifiers, rust inhibitors, preservatives, antifungal agents, antioxidants and reduction inhibitors. However, the ink preferably does not contain the reactants contained in the reaction liquid.

[0105] [Physical properties of ink]

[0106] The ink is aqueous ink applied to the inkjet system. Therefore, from a reliability perspective, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the ink at 25°C is preferably 20 mN / m or higher and 60 mN / m or lower. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or higher and 10.0 mPa·s or lower. The pH of the ink at 25°C is preferably 7.0 or higher and 9.5 or lower, and more preferably 8.0 or higher and 9.5 or lower.

[0107] (Reaction solution)

[0108] The recording method of the present disclosure preferably includes a reaction liquid applying step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to the recording medium. In particular, the reaction liquid applying step is preferably performed before or simultaneously with the ink applying step. The components used in the reaction liquid will be described in detail below.

[0109] [Reactants]

[0110] The reaction liquid is brought into contact with the ink and reacts to aggregate the components in the ink (resin and component including anionic groups, such as self-dispersible pigment) and contain reactants. Examples of reactants include organic acids, polyvalent metal salts, and cationic resins.

[0111] Examples of polyvalent metal ions include divalent metal ions such as Ca 2+ 、Cu 2+ 、Ni 2+ Mg 2+ 、Sr 2+ 、Ba 2+ and Zn 2+ ; and trivalent metal ions such as Fe 3+ Cr 3+ 、Y 3+ and Al 3+In order to obtain a reaction solution containing polyvalent metal ions, a polyvalent metal salt (which may be a hydrate) composed of bonding polyvalent metal ions and anions may be used. Examples of anions include inorganic anions such as Cl - Br - , I - , ClO - 、ClO2 - 、ClO3 - 、ClO4 - 、NO2 - 、NO3 - 、SO4 2- 、CO3 2- 、HCO3 - PO4 3- 、HPO4 2- and H2PO4 - ; and organic anions such as HCOO - 、(COO-)2、COOH(COO - ), CH3COO - 、C2H5COO - 、CH3CH(OH)COO - 、C2H4(COO - )2、C6H5COO - 、C6H4(COO - )2 and CH3SO3 - When a polyvalent metal ion is used as a reactant, the content (mass %) of the polyvalent metal ion in the reaction solution is preferably 1.0 mass % or more and 20.0 mass % or less based on the total mass of the reaction solution in terms of the polyvalent metal salt. 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.

[0112] The reaction solution containing organic acid has buffering capacity in acidic region (pH is less than 7.0, preferably pH is 2.0 to 5.0), thereby effectively making the anionic group of the component present in ink be acid type to aggregate. The example of organic acid includes monocarboxylic acid and its salt such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid and coumaric acid; Dicarboxylic acid and its salt and hydrogen salt 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 acid and its salt and hydrogen salt such as citric acid and trimellitic acid; With tetracarboxylic acid and its salt and hydrogen salt such as pyromellitic acid. When using organic acid as reactant, the content (mass %) of organic acid in reaction solution is preferably 1.0 mass % or more and 50.0 mass % or less based on the gross mass of reaction solution.

[0113] The example of cationic resin comprises the resin with the structure of primary amine to tertiary amine and the resin with the structure of quaternary ammonium salt.Specifically, the example of cationic resin comprises the resin with the structure such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride and alkylamine-epichlorohydrin condensation products.In order to increase the solubility in reaction solution, cationic resin and acidic compound can be used in combination or cationic resin is carried out quaternization.When using cationic resin as reactant, in reaction solution, the content (mass %) of cationic resin is preferably more than 0.1 mass % and below 10.0 mass % based on the gross mass of reaction solution.

[0114] [Aqueous medium]

[0115] The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. The aqueous medium used in the reaction liquid may contain the water-soluble organic solvent that can be contained in the ink.

[0116] [Other components]

[0117] The reaction liquid may contain other components as needed. Examples of other components include the same components as those described above that may be contained in the ink.

[0118] [Physical properties of reaction solution]

[0119] The reaction liquid suitable for the recording method of the present disclosure is an aqueous reaction liquid used in an inkjet system. Therefore, from the perspective of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN / m or more and 60 mN / m or less. 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 5.0 or more and 9.5 or less, and more preferably 6.0 or more and 9.0 or less.

[0120] Example

[0121] The present disclosure will now be described in more detail with reference to Examples and Comparative Examples, but the present disclosure is not limited in any way by the following Examples without exceeding the scope of the present disclosure. Unless otherwise specified, the amounts of components expressed as "parts" and "%" are by mass. Hereinafter, the dispersion of particles is also referred to as a pigment dispersion.

[0122] <Measurement of Physical Property Values>

[0123] (Average primary particle size and cumulative 50% particle size based on volume)

[0124] The sample was photographed at 100,000 times magnification using a scanning electron microscope (trade name: "S-4700", manufactured by Hitachi High Tech Corporation). The diameters of 100 circles circumscribed with the primary particles were measured, and the average value thereof was calculated. The calculated average value was defined as the average primary particle diameter D of the particles. P0 The volume-based cumulative 50% particle diameter D of the particles was measured by a dynamic light scattering method using a particle size analyzer (trade name: "UPA-EX150", manufactured by Nikkiso Co., Ltd.) P The volume-based cumulative 50% particle size D of the resin particles was also measured using the above-mentioned particle size analyzer. E .

[0125] (Glass transition temperature and melting point of resin particles)

[0126] The glass transition temperature (Tg) and melting point (Tg) of the resin particles were measured using a differential scanning calorimeter (DSC). M. Specifically, resin particles (2 mg) obtained by drying and curing a liquid containing resin particles at 60°C were placed in and sealed in an aluminum container to prepare a sample for measurement. The prepared sample was thermally analyzed using a differential scanning calorimeter (trade name: "DSC-2500", manufactured by TA Instruments) according to the temperature program shown below. The glass transition temperature of the resin particles in this specification is defined as follows. That is, in the heating curve (horizontal axis: temperature, vertical axis: heat) of the following temperature program (3), the temperature at the intersection of a straight line passing through two points in the curve on the low temperature side and extending to the high temperature side and a tangent drawn at a point where the gradient of the step-like change in the curve is the largest is determined. The temperature thus determined is defined as "the glass transition temperature Tg of the resin particles". With regard to crystalline resins, the peak top of the endothermic peak of the heating curve is defined as "the melting point Tg of the resin particles". M ”.

[0127] [Temperature program]:

[0128] (1) Raise the temperature from 20°C to 200°C at a rate of 10°C / min;

[0129] (2) decreasing the temperature from 200°C to -50°C at a rate of 5°C / min; and

[0130] (3) The temperature was increased from -50°C to 200°C at a rate of 10°C / min.

[0131] (Loss modulus of resin pellets)

[0132] The loss elastic modulus of the resin particles is measured according to the method shown below. About 10 g of an aqueous dispersion of the resin particles is added dropwise to a fluororesin plate and placed in a vacuum dryer (trade name: "ADP300", manufactured by Yamato Scientific Co., Ltd.). The sample for measurement is prepared by vacuum drying at 80°C for 30 minutes. The prepared sample is compressed while increasing the temperature, and the loss elastic modulus is measured using a viscoelasticity measuring device (trade name: "Rheogel-E4000", manufactured by UBM). The measurement conditions are set as a measuring fixture: compression fixture φ20, strain wave shape: sine wave, excitation state: continuous excitation, fundamental frequency: 1 Hz, strain control: constant at 3 μm, starting temperature: -20°C, step temperature: 2°C, end temperature: 80°C and heating rate: 5°C / min.

[0133] (Density of particles)

[0134] The density of the particles was measured by the Gay-Lussac pycnometer (density meter) method according to JIS Z 8807. The density of the resin particles was also measured by the same method.

[0135] <Preparation of Particles (Pigment Dispersion)>

[0136] The particles shown in Table 1 (Particles 1 to 14) were provided, and Pigment Dispersions 1 to 14 were prepared using the provided particles.

[0137] Regarding particles 1 to 3, 7, and 10, the particle content was adjusted to 30.0% by adding an appropriate amount of ion-exchanged water or evaporating the liquid component to obtain pigment dispersions 1 to 3, 7, and 10. Regarding particles 4 to 6, 8, and 9, 10.0 parts of each particle, 0.8 parts of an acrylic dispersant (trade name: "DISPER BYK-154", manufactured by BYK Chemie GmbH), and 100 parts of 0.1-mm zirconium dioxide beads were dispersed using a bead mill for 6 hours. The zirconium dioxide beads were removed by filtration, and an appropriate amount of ion-exchanged water was added to the filtrate as needed to obtain pigment dispersions 4 to 6, 8, and 9.

[0138] Tetraethyl orthosilicate (6.3 g) was dissolved in a mixed solvent of ethanol (75.0 g), methanol (25.0 g) and ion-exchanged water (18.0 g) to obtain a solution. 28% aqueous ammonia (2.2 g) was added to the obtained solution, followed by stirring at 25° C. for 24 hours to obtain a pigment dispersion 11. In addition to adjusting the time of the dispersion treatment so as to achieve the D shown in Table 1, the following steps were repeated: P Pigment dispersion 12 was obtained in the same manner as pigment dispersion 4 except for the above conditions (nm).

[0139] Each (30.0 parts) of titanium oxide (particles 13 and 14), potassium hydroxide (0.45 parts), ion-exchanged water (69.55 parts) and 0.1-mm zirconium dioxide beads (100 parts) were mixed and dispersed using a bead mill. The zirconium dioxide beads were removed by filtration, and an appropriate amount of ion-exchanged water was added to the filtrate as needed to obtain pigment dispersions 13 and 14. The time of the dispersion treatment was adjusted so that the D values ​​shown in Table 1 were achieved. P (nm).

[0140] The pigment dispersion was appropriately adjusted to achieve a particle content of 30.0%. In Table 1, particles 4 and 12 are cubic calcium carbonate. Particle 5 is hydroxyapatite, a type of calcium phosphate. Particle 7 is stabilized zirconium dioxide containing a stabilizer. In Table 1, the refractive index of each titanium oxide is 2.5 to 2.8. The refractive index of particles other than titanium oxide is 1.5 to 2.2.

[0141] [Table 1]

[0142]

[0143] <Preparation of Resin Pellets>

[0144] Aqueous dispersions of the resin particles shown in Table 2 were prepared. In Table 2, the content of the resin particles in each aqueous dispersion of the resin particles is shown in the column "Content of Resin Particles (%)." Aqueous dispersions of Resin Particles 2 and Resin Particles 3 were prepared by the following methods, respectively.

[0145] (Aqueous dispersion of resin particles)

[0146] Sebacic acid (300 g) and 1,6-hexanediol (170 g) were mixed and heated to 190° C. over 1 hour while stirring. Tetrabutyl orthotitanate (0.01 g) was added thereto, and then the internal temperature was raised to 240° C. over 6 hours to carry out polymerization while distilling off the generated water to obtain a crystalline polyester resin. The melting point T of the obtained polyester resin was 240° C. M The obtained polyester resin (50g) was placed in a 300mL four-necked flask equipped with a nitrogen inlet tube, a stirrer and a thermocouple. Methyl ethyl ketone (50g) was added thereto, and then heated to 40°C under a nitrogen stream to dissolve the polyester resin. Triethylamine (1.2g) was further added thereto, the mixture was stirred for 1 hour, and then ion exchange water (106g) was added dropwise thereto at a rate of 7.5g / min, and the mixture was stirred for 30 minutes. Subsequently, the methyl ethyl ketone was removed under reduced pressure to obtain an aqueous dispersion of resin particles 2 containing 30.0% resin particles. The cumulative 50% particle size D of the resin particles 2 measured by the above-mentioned equipment based on volume E It is 190nm.

[0147] (Aqueous dispersion of resin particles 3)

[0148] Sebacic acid (300 g) and 1,6-hexanediol (170 g) were mixed and heated to 190° C. over 1 hour while stirring. Tetrabutyl orthotitanate (0.01 g) was added thereto, and then the internal temperature was raised to 240° C. over 6 hours to perform polymerization while distilling off the generated water to obtain a crystalline polyester resin. The melting point T of the obtained polyester resin was 240° C. M The obtained polyester resin (50g) was placed in a 300mL four-necked flask equipped with a nitrogen inlet tube, a stirrer and a thermocouple. Methyl ethyl ketone (50g) was added thereto, and then heated to 40°C under a nitrogen stream to dissolve the polyester resin. Triethylamine (1.0g) was further added thereto, and the mixture was stirred for 1 hour, and then ion exchange water (106g) was added dropwise thereto at a rate of 7.5g / min, and the mixture was stirred for 30 minutes. Subsequently, the methyl ethyl ketone was removed under reduced pressure to obtain an aqueous dispersion of resin particles 3 containing 30.0% resin particles. The cumulative 50% particle size D of the resin particles 3 measured by the above-mentioned equipment based on volume E It is 230nm.

[0149] [Table 2]

[0150]

[0151] (Resin particles 15 to 17)

[0152] The resin particles 15 to 17 shown below were provided. The density and apparent density of the resin particles 15 to 17 were both 1.0 g / cm 3 .

[0153] Resin particles 15: styrene acrylic resin (trade name: "VINYBLAN 2685", manufactured by Nissin Chemical Industry Co., Ltd., amorphous, average particle size: 210 nm, Tg: 50° C., resin particle content: 30.0%);

[0154] - Resin particles 16: styrene acrylic resin (trade name: "Joncryl 450", manufactured by Johnson Polymer LLC, amorphous, average particle size: 90 nm, Tg: 16° ​​C., resin particle content: 42.0%); and

[0155] - Resin particles 17: styrene acrylic resin (trade name: "WEM-3000", manufactured by Taisei Fine Chemical Co., Ltd., amorphous, average particle size: 300 nm, Tg: 98° C., resin particle content: 33.0%)

[0156] <Preparation of Emulsion>

[0157] (Lotion 1)

[0158] A fluorine-based nonionic surfactant (0.3 parts, trade name: "Capstone FS-31", manufactured by DuPont deNemours, Inc.) was dissolved in ion-exchanged water (10.0 parts). Perfluorohexane (4.0 parts) was added thereto, and dispersion treatment was performed for 4 minutes using an ultrasonic disperser with a duty cycle of 50% to obtain Emulsion 1 of an O / W type emulsion.

[0159] <Ink Preparation>

[0160] The components shown in the upper column of Table 3-1 to Table 3-3 (unit: %) were mixed separately. Potassium hydroxide was added thereto to adjust the pH to within the range of 8 to 9. The resulting solution was pressure filtered through a microfilter (manufactured by FUJIFILM Corporation) having a pore size of 3.0 μm to prepare each ink. In Table 3-1 to Table 3-3, "Acetylenol E100" is a trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals Co., Ltd. The characteristics of the prepared ink are shown in the lower column of Table 3-1 to Table 3-3. As shown in Table 3-3, ink 38 was prepared using resin particles 16 and 17 in amounts of 8.3 parts and 10.7 parts, respectively.

[0161] [Table 3-1]

[0162]

[0163] [Table 3-2]

[0164]

[0165] [Table 3-3]

[0166]

[0167] <Preparation of Reaction Solution>

[0168] (Reaction solution 1)

[0169] Magnesium sulfate heptahydrate (10.0 parts), glycerin (2.0 parts), ethylene glycol (7.0 parts), a nonionic surfactant (0.5 parts, trade name "Acetylenol E100", manufactured by Kawaken Fine Chemicals Co., Ltd.) and ion-exchanged water were mixed to obtain a reaction liquid 1. The amount of the ion-exchanged water was appropriately controlled so that the total amount of the components was 100.0 parts.

[0170] (Reaction solution 2)

[0171] A cationic resin (37.0 parts), glycerin (2.0 parts), ethylene glycol (7.0 parts), Acetylenol E100 (0.5 parts) and ion-exchanged water (53.5 parts) were mixed to obtain a reaction liquid 2. The cationic resin used was trade name "UNISENCE FPA100L" (manufactured by SENKA Corporation, cationic resin content: 27.0%).

[0172] (Reaction solution 3)

[0173] Succinic acid (10.0 parts), glycerin (2.0 parts), ethylene glycol (7.0 parts), Acetylenol E100 (0.5 parts), and ion-exchanged water (81.5 parts) were mixed to obtain a reaction liquid 3.

[0174] <Evaluation>

[0175] The obtained ink was evaluated for the following items. In the present disclosure, in the evaluation criteria of the items shown below, "AA", "A", and "B" are defined as acceptable levels, and "C" is defined as an unacceptable level. The evaluation results are shown on the right side of Table 4.

[0176] (Recording of images for evaluation)

[0177] An inkjet recording apparatus (trade name "PIXUSPRO-10S", manufactured by CANON KABUSHIKI KAISHA) equipped with a recording head that ejects liquid by the action of thermal energy is provided. The ink shown on the left side of Table 4 is filled in an ink cartridge and set in the provided inkjet recording apparatus. In this embodiment, the recording duty of a solid image recorded under the following conditions is defined as 100%: eight ink droplets each having a mass of 3.5 ng per droplet are applied to a unit area of ​​1 / 600 inch × 1 / 600 inch at a resolution of 600 dpi × 600 dpi. Using this inkjet recording apparatus, an image (50 mm × 50 mm) of a recording duty of 400% is recorded on a recording medium by discharging ink from the ejection hole in the lower half of the recording head in the length direction. The recording medium used is a PET film cut into A4 size (trade name "LLRPCF1372", manufactured by Sakurai Co., Ltd., in the Bristow method, from the start of contact to 30 msec 1 / 2 The water absorption capacity is 0mL / m 2 Above 10mL / m 2 within the following range).

[0178] In Table 4, in the embodiment where the reaction liquid applying step "exists", the ink cartridge is filled with each reaction liquid shown in Table 4, and the ink and reaction liquid are applied to the recording medium at the same time. The recording duty of the reaction liquid is adjusted to 40%. The reaction liquid with the number shown in the column of the reaction liquid applying step is used. In Table 4, in the embodiment where the drying step "exists", the recording medium is conveyed to a length corresponding to half of the length of the recording head, and then the image is dried by blowing hot air at 25°C for 5 minutes. The temperature of the hot air is the temperature at the hot air outlet measured using a mold surface sensor (trade name "MF-OK", manufactured by ToaElectric Inc.).

[0179] Subsequently, in the example of the heating step "1" in Table 4, the recording medium having the image recorded thereon was heat-treated in a thermostatic chamber at 100°C for 5 minutes to fix the image to the recording medium. The heating temperature at this time is T H In the embodiment of the heating step "2", the image is fixed to the recording medium in the same manner as in the above-mentioned heating step "1", except that the temperature of the constant temperature chamber is set to 80°C. The heating temperature T at this time is H 70° C. or higher and lower than 80° C. Heating by the thermostatic chamber corresponds to heating the recording surface and the back surface with an infrared heater. In Examples 21, 37, and 38, the ink and the reaction liquid were applied simultaneously, and the drying step and the heating step were performed in sequence.

[0180] In the embodiment of the heating step "3", the recording medium is conveyed by a length corresponding to half of the length of the recording head, and then the image is dried by blowing hot air at 90°C at a wind speed of 11 m / s for 1 minute. The heating temperature at this time is T H is about 90°C. In the embodiment of the heating step "4", the recording medium is conveyed by a length corresponding to half of the length of the recording head, and then the image is dried by blowing hot air at 110°C at a wind speed of 15 m / s for 10 seconds. The heating temperature T at this time is H is about 90°C.

[0181] (Pore Formation)

[0182] Whether the resin particles melted and whether pores were generated was determined by the following method. A portion of the recording medium to which the ink was applied was cut before and after the heating step, and the cross-section was observed using a scanning electron microscope. When resin particles were observed in the cross-section before the heating step, the particle size was measured. When pores were observed in the cross-section after the heating step, the pore size was measured. When the difference between the measured pore size and the particle size of the resin particles was 10% or less, the resin particles were determined to have melted and generated pores during the heating step. The results of this evaluation are shown in the "Pore Formation" column in Table 4.

[0183] (concealment)

[0184] The concealment rate of the recorded image used for evaluation was measured and calculated according to the method in accordance with ISO 2471:2008, and the concealment property of the image was evaluated. The ink prepared in each example was a white ink. In ISO 2471:2008, the paper used for testing is backed with a white plate or a black plate to measure the reflectivity of each, and the concealment rate is calculated by the following formula (B):

[0185] Concealment rate = (R0 / R ∞ )×100 (B)

[0186] R0: reflectivity measured when backed with a black board; and

[0187] R ∞ : Reflectance measured when backed with a white plate.

[0188] In this embodiment, according to this method, the concealment rate of the recorded image was measured and calculated using concealment rate test paper (manufactured by TP Giken Co., Ltd. and certified by the Japan Paint Inspection and Testing Association). The concealment of each image was evaluated by the following evaluation criteria:

[0189] AA: Concealment rate is above 60%;

[0190] A: The concealment rate is above 55% and less than 60%;

[0191] B: Concealment rate is greater than 45% and less than 55%; and

[0192] C: Concealment rate is less than 45%.

[0193] (Resistance to sedimentation)

[0194] The prepared ink was placed in a cylindrical sample container to a height of 24 mm and placed in an environment at 25° C. for 1 week. The thickness (mm) of the transparent portion of the supernatant after placement was measured, and the ink's sedimentation resistance was evaluated according to the evaluation criteria shown below:

[0195] A: The thickness of the transparent part of the supernatant is less than 2 mm;

[0196] B: The thickness of the transparent portion of the supernatant is greater than 2 mm and less than 10 mm; and

[0197] C: The thickness of the transparent portion of the supernatant is greater than 10 mm.

[0198] [Table 4]

[0199]

[0200] The evaluation results for image concealment in Examples 25 and 26 were the same as those in Examples 4 to 6, which were "A," but Examples 4 to 6 were superior in this property. The evaluation results for image concealment in Example 29 were the same as those in Examples 27 and 28, which were "B," but Examples 27 and 28 were superior in this property. The evaluation results for image concealment in Example 31 were the same as those in Example 32, which were "A," but Example 32 was superior in this property.

[0201] The present disclosure is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Therefore, in order to disclose the scope of the present disclosure, the following claims are attached.

[0202] This application claims the benefit of Japanese Patent Application No. 2023-084008, filed May 22, 2023, and Japanese Patent Application No. 2024-062310, filed April 8, 2024, which are hereby incorporated by reference herein in their entirety.

[0203] Description of Reference Numerals

[0204] 1 pellet

[0205] 2. First resin particles

[0206] 3. Adhesive

[0207] 4 holes

Claims

1. An inkjet recording method for recording an image on a recording medium using an aqueous ink comprising particles and first resin particles, the method comprising: an ink applying step of applying the aqueous ink to the recording medium; and The recording medium to which the aqueous ink is applied is heated to a temperature equal to or higher than the glass transition temperature Tg (° C.) or melting point Tg (° C.) of the first resin particles. M (°C) and less than the glass transition temperature Tg (°C) or melting point Tg of the particles M (°C) temperature, wherein The average primary particle size D of the particles P0 (nm) is less than 150nm, and In the heating step, the recording medium is heated to melt the first resin particles and generate pores.

2. The inkjet recording method according to claim 1, wherein The cumulative 50% volume-based particle size D of the first resin particles E (nm) is greater than or equal to 100 nm and less than or equal to 400 nm.

3. The inkjet recording method according to claim 1, wherein In the aqueous ink, a volume ratio of a content (volume %) of the first resin particles to a content (volume %) of the particles is 1.3 times or more and 5.0 times or less.

4. The inkjet recording method according to claim 1, wherein The glass transition temperature Tg (° C.) of the first resin particles is 25° C. or higher.

5. The inkjet recording method according to claim 1, wherein The melting point T of the first resin particles M (℃) is 25℃ or above, and The resin constituting the first resin particles is a crystalline resin.

6. The inkjet recording method according to claim 1, wherein The loss elastic modulus of the first resin particles at 80°C is 1.2×10 7 Below Pa.

7. The inkjet recording method according to claim 1, wherein The loss elastic modulus of the first resin particles at 80°C is 3.3×10 5 Below Pa. 8 . The inkjet recording method according to claim 1 , wherein the resin constituting the first resin particles includes at least one selected from the group consisting of acrylic resins, polyester resins, and urethane resins.

9. The inkjet recording method according to claim 1, wherein The apparent density of the first resin particles is 0.8 g / cm 3 above.

10. The inkjet recording method according to claim 1, wherein the cumulative 50% particle size D of the particles based on volume is P (nm) is less than 150nm.

11. The inkjet recording method according to claim 1, wherein the particles include at least one selected from the group consisting of titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silicon dioxide, kaolin, clay, and second resin particles.

12. The inkjet recording method according to claim 1, wherein The particles comprise titanium oxide; and In the aqueous ink, a mass ratio of the content (mass %) of the first resin particles to the content (mass %) of the titanium oxide is 0.30 times or more and 1.0 times or less.

13. The inkjet recording method according to claim 12, wherein the cumulative 50% particle size D of the titanium oxide based on volume is P (nm) is less than 100nm. 14 . The inkjet recording method according to claim 1 , wherein in the aqueous ink, the content (volume %) of the particles is 1.5 volume % or more based on the total volume of the ink.

15. The inkjet recording method according to any one of claims 1 to 13, wherein The heating temperature T in the heating step H (℃) is 80℃ or above.

16. The inkjet recording method according to any one of claims 1 to 13, further comprising at least one step selected from the group consisting of: a reaction liquid applying step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to the recording medium, and a drying step of drying the liquid component on the recording medium.

17. The inkjet recording method according to any one of claims 1 to 13, wherein The aqueous ink is white ink.

18. An inkjet recording apparatus for use in an inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, the inkjet recording apparatus comprising: an ink applying device for applying the aqueous ink to the recording medium; and A heating device for heating the recording medium to which the aqueous ink is applied to a temperature equal to or higher than the glass transition temperature Tg (° C.) or the melting point Tg (° C.) of the first resin particles. M (°C) and less than the glass transition temperature Tg (°C) or melting point Tg of the particles M (℃) temperature, where The average primary particle size D of the particles P0 (nm) is less than 150nm, and The heating device is a device for heating the recording medium to melt the first resin particles and generate pores.

19. An aqueous ink for use in an inkjet recording method for recording an image on a recording medium using an aqueous ink comprising particles and first resin particles, wherein The inkjet recording method comprises: an ink applying step of applying the aqueous ink to the recording medium, and The recording medium to which the aqueous ink is applied is heated to a temperature equal to or higher than the glass transition temperature Tg (° C.) or melting point Tg (° C.) of the first resin particles. M (°C) and less than the glass transition temperature Tg (°C) or melting point Tg of the particles M (°C) temperature of the heating step; The average primary particle size D of the particles P0 (nm) is less than 150nm; and In the heating step, the recording medium is heated to melt the first resin particles and generate pores.

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