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

Abstract

This invention provides an inkjet recording method that offers excellent opacity and suppresses the reduction in opacity when liquids such as water come into contact with it. [Solution] An inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, comprising an ink application step of applying the aqueous ink to the recording medium, and the recording medium to which the aqueous ink has been applied is subjected to the glass transition temperature Tg of the first resin particles. R (°C) or melting point Tm R (°C) or higher, and the glass transition temperature Tg of the particles. P (°C) or melting point Tm P The process includes a heating step of heating to a temperature below (°C), and the aqueous ink contains a compound in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms, and the average primary particle diameter of the particles is D P The (nm) is 150 nm or less, and in the heating process, the recording medium is heated to melt the first resin particles and create voids.

Description

[Technical Field]

[0001] This invention relates to an inkjet recording method, an inkjet recording apparatus, and an aqueous ink. [Background technology]

[0002] In recent years, inkjet recording methods have been used in fields such as commercial printing to record white images on non-white recording media such as transparent films, translucent films, and colored paper. Some inks used to record white images utilize white pigments such as titanium dioxide. In addition, inks containing hollow particles that have a low specific gravity and are less prone to settling have been proposed (see Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-194847 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Our investigations have revealed that when water, such as rain, adheres to an image recorded using the inks described in Patent Documents 1 and 2, water penetrates the pores of the hollow particles that form the image, reducing light scattering and decreasing the image's opacity. In particular, when attempting to increase the number of pores to improve image opacity, water penetrates more easily, and the opacity tends to decrease when water adheres to the image. White ink is used in applications such as package printing and posters, and in both cases, the recorded material may get wet, so changes in opacity are a major issue. Furthermore, for images used in applications such as package printing and posters, liquid varnish is sometimes applied to improve scratch resistance. Even if varnish penetrates the pores, the opacity rate changes.

[0005] Therefore, an object of the present invention is to provide an inkjet recording method that, when using an aqueous ink with excellent sedimentation resistance, can record an image with excellent opacity and suppressed reduction in opacity when liquids such as water adhere to it. Another object of the present invention is to provide an inkjet recording apparatus and a white aqueous ink to be used in the above-mentioned inkjet recording method. [Means for solving the problem]

[0006] In other words, according to the present invention, an inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, comprising: an ink application step of applying the aqueous ink to the recording medium; and the recording medium to which the aqueous ink has been applied, the glass transition temperature Tg of the first resin particles. R (°C) or melting point Tm R (°C) or higher, and the glass transition temperature Tg of the particles. P (°C) or melting point Tm P The process includes a heating step of heating to a temperature below (°C), wherein the aqueous ink contains a compound in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms, and the average primary particle diameter of the particles is D P An inkjet recording method is provided, characterized in that the (nm) is 150 nm or less, and in the heating step, the recording medium is heated to melt the first resin particles and create voids. [Effects of the Invention]

[0007] According to the present invention, when using an aqueous ink with excellent sedimentation resistance, it is possible to provide an inkjet recording method that can record images with excellent opacity and suppress the reduction in opacity when liquids such as water adhere to them. Furthermore, according to another embodiment of the present invention, an inkjet recording apparatus and an aqueous ink used in the above-mentioned inkjet recording method can be provided. [Brief explanation of the drawing]

[0008] [Figure 1]It is a schematic diagram for explaining an example of an image formation process. [Figure 2] It is a schematic diagram for explaining an example of an image formation process. [Figure 3] It is a perspective view schematically showing an embodiment of the inkjet recording apparatus of the present invention. [Figure 4] It is a side view schematically showing an embodiment of the inkjet recording apparatus of the present invention [Figure 5] It is a side view schematically showing an embodiment of the inkjet recording apparatus of the present invention.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described in more detail by giving preferred embodiments. In the present invention, when the compound is a salt, although the salt dissociates into ions in the ink, for convenience, it is expressed as "containing a salt". In addition, the aqueous ink and aqueous reaction solution for inkjet may be simply described as "ink" and "reaction solution". Physical property values are values at normal temperature (25 ° C) and normal pressure (1 atm) unless otherwise specified.

[0010] The present inventors have studied an inkjet recording method capable of recording an image that is excellent in concealability (dry concealability) in a dried state of the image and is less likely to have a decrease in concealability (water-wetting concealability) when water adheres to the image when using an aqueous ink excellent in sedimentation resistance. As a result, it has been found that recording becomes possible by satisfying the requirements (i) to (v). (i) An ink application step of applying ink to a recording medium, and heating the recording medium to which the ink has been applied to a temperature equal to or higher than the glass transition temperature Tg R (° C) or melting point Tm R (° C), and lower than the glass transition temperature Tg P (° C) or melting point Tm P (° C), having a heating step (ii) The aqueous ink contains particles and first resin particles (iii) The aqueous ink further contains a compound in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. (iv) Mean primary particle size D of the particles P (nm) is 150nm or less (v) In the heating step, the recording medium is heated to melt the first resin particles and create voids.

[0011] 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, volatile components such as water and water-soluble organic solvents evaporate, forming an ink film in which particles 1 and first resin particles 2 are densely packed. Subsequently, the glass transition temperature Tg of the first resin particles 2 melts. R (°C) or melting point Tm R 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 first resin particles 2 penetrates into the voids between the particles 1. At the same time, voids 5 are formed where the first resin particles 2 were located. The heating temperature at this time is equal to the glass transition temperature Tg of the particles. P (°C) or melting point Tm P Since the temperature is below (°C), it is considered that particle 1 does not melt. The resin produced by the melting of the first resin particles permeates into the voids between particle 1, forming a binder 4 which is a mixture of particle 1 and melted particles. Here, the average primary particle diameter D of particle 1 P 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 5 formed by the melting of the first resin particles. Therefore, the refractive index of voids 5 is considered to be relatively lower than that of binder 4. Under these conditions, incident light can be scattered due to the difference in refractive index between binder 4 and voids 5. Therefore, it is possible to record highly opaque images without using components that tend to settle, such as titanium dioxide with large particle sizes.

[0012] As described above, it is necessary to melt the first resin particles through the heating process. For example, if only a drying process is performed to evaporate the liquid component on the surface of the recording medium after image recording, or if the heating process is performed at a temperature lower than the melting temperature of the first resin particles, the first resin particles are unlikely to melt. As a result, scattering due to the refractive index difference between the binder 4 and the voids 5 does not occur, and it is not possible to record images with high opacity. Furthermore, if the heating process is performed at a temperature higher than the melting temperature of the particles, not only the first resin particles but also the particles themselves will melt, and no voids will be formed. As a result, the above-mentioned scattering does not occur, and it is not possible to record images with high opacity.

[0013] Furthermore, as shown by Stokes' equation (Equation (A)), the smaller the particle size, the slower the sedimentation velocity. Therefore, the mean primary particle size D P By using particles with a relatively small particle size of 150 nm or less (nm), the sedimentation rate is slowed, resulting in an ink with excellent sedimentation resistance. Details regarding the average primary particle size will be described later. D P When the (nm) is greater than 150 nm, scattering of visible light is more likely to occur, improving opacity, but as shown in Stokes' equation, the settling velocity increases, and settling resistance cannot be obtained. Also, when the particles are large, it is difficult for the first resin particles to be uniformly distributed around the particles during image formation, as shown in Figure 1, and highly opaque images cannot be recorded.

[0014] By incorporating a compound in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms (hereinafter sometimes simply referred to as "compound") into the ink, the decrease in opacity (water-wettability) when liquids such as water adhere to the ink can be suppressed. As described above, during the process of evaporation of the liquid component of the ink, compound 3 orients its hydrophobic surface toward the air at the gas-liquid interface of the ink, and a hydrophobic film is formed on the image surface. If compound 3 is not present, liquid adhering to the image penetrates into the pores, reducing light scattering and thus decreasing water-wettability. Furthermore, if the chain hydrocarbon of compound 3 has 7 or fewer carbon atoms, the hydrophobic surface of compound 3 cannot orient itself toward the gas-liquid interface during the ink film formation process, and a hydrophobic film is not formed on the image surface. Therefore, the penetration of liquid into the pores in the ink film cannot be suppressed, and water-wettability decreases.

[0015] <Inkjet recording method, inkjet recording device, and water-based ink> The present invention relates to an inkjet recording method that records an image by ejecting aqueous ink from an inkjet recording head and applying it to a recording medium. The present invention relates to an ink application step of applying aqueous ink to a recording medium and a heating step of heating the recording medium to which the aqueous ink has been applied to a predetermined temperature. In the heating step, the glass transition temperature Tg of the first resin particles R (°C) or melting point Tm R (°C) or higher, and the glass transition temperature Tg of the particles. P (°C) or melting point Tm P Heat to a temperature below (°C). The ink contains particles and first resin particles, and the average primary particle diameter of the particles is D P The (nm) is 150 nm or less. The ink further contains a compound in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. Then, in the heating process, the recording medium is heated to melt the first resin particles and create voids.

[0016] The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which aqueous ink is ejected from an inkjet recording head and applied to a recording medium to record an image, and is an apparatus suitably used in the above-described 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 in which aqueous ink is ejected from an inkjet recording head and applied to a recording medium to record an image. It is an ink that is preferably used in the above-described recording method.

[0018] The inkjet recording method and inkjet recording apparatus of the present invention (hereinafter also simply referred to as "recording method and recording apparatus") will be described in detail below.

[0019] Figure 3 is a schematic diagram showing one embodiment of the inkjet recording apparatus of the present invention. The inkjet recording apparatus 100 in the form shown in Figure 3 is an inkjet recording apparatus that records an image on a recording medium wound in a roll shape using a reaction liquid containing a reactant that reacts with ink and ink. The X, Y, and Z directions represent the width (overall length), depth, and height directions of the inkjet recording apparatus, respectively. The recording medium is transported in the X direction.

[0020] The inkjet recording apparatus 100 of the embodiment shown in Figure 3 is configured to include a recording unit 1100, a drying unit 2000, a heating unit 2300, and a paper discharge unit 4000. In the recording unit 1100, a long recording medium 1000, supported by a transport member 1300 and transported from a paper feed device 1400, is coated with various liquids, including ink, by a liquid application device 1101 to form an image. In the drying unit 2000, the recording medium 1000 is transported along a transport member 2200 while maintaining tension, and the liquid applied to the recording medium is blown by a drying unit 2100 to evaporate the liquid components in the ink and dry it (drying process). In the heating unit 2300, the recording medium 1000 is transported along a second transport member 2500 while maintaining tension, and the liquid applied to the recording medium is heated by a heating device 2400. This evaporates the liquid components in the ink and melts the first resin particles to form pores. Although not shown in Figure 3, after the drying section 2000 and the heating section 2300, a cooling section for cooling the recording medium 1000 and a recording section for performing color recording may be provided in addition to the recording section 1100.

[0021] The recording medium 1000 on which the image is recorded is transported in the winding (paper discharge) section 4000 while being supported by the support member 4100, and then wound onto the winding device 4200. The recording device shown in Figure 4 is a configuration in which an image is recorded on a roll-shaped recording medium, but the recording medium is not limited to a roll shape; a sheet-shaped recording medium can also be used by changing the recording medium transport method and the paper discharge device.

[0022] [Records Department] The recording unit consists of a recording unit 1100 that dispenses a liquid containing ink. The recording unit 1100 has a liquid dispensing device 1101. The liquid dispensing device 1101 is configured to include a reaction liquid dispensing device 1102 and an ink dispensing device 1103. The reaction liquid dispensing device 1102 shown in Figure 4 is an example of a unit using an inkjet ejection head. In addition, a gravure coater, offset coater, die coater, blade coater, etc., may be used to configure the reaction liquid dispensing device. The dispensing of the reaction liquid by the reaction liquid dispensing device 1102 may be done either before or after ink dispensing, as long as it can come into contact with the ink on the recording medium 1000. However, in order to record high-quality images on various recording media with different liquid absorption characteristics, it is preferable to dispensing the reaction liquid before ink dispensing. An inkjet ejection head (recording head) is used as the ink dispensing device 1103. The discharge method of the discharge head of the liquid dispensing device 1101 can include a method in which liquid is discharged by generating film boiling in the liquid using an electro-thermal converter and forming bubbles, or a method in which liquid is discharged using an electro-mechanical converter.

[0023] The liquid dispensing device 1101 is a line head extending in the Y direction, with discharge ports arranged to cover the image recording area of ​​the maximum usable width of the recording medium. The discharge head has a discharge port surface with discharge ports formed below it (towards the recording medium 1000), and the discharge port surface faces the recording medium 1000 at a distance of only a few millimeters. Hereinafter, the ink and reaction solution may be collectively referred to as "liquid".

[0024] The inkjet recording method preferably further comprises at least one step selected from the group consisting of a reaction solution application step, in which an aqueous reaction solution containing a reactant that reacts with the ink is applied to the recording medium, and a drying step, in which the liquid components on the recording medium are dried. 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 in the ink and the first resin particles can be aggregated and densely packed. Details of the reaction solution will be described later.

[0025] [Conveyor System] As shown in Figure 3, the recording unit 1100 is configured to include a liquid application device 1101 and a transport member 1300 for transporting the recording medium 1000. The liquid application device 1101 applies reaction liquid and ink to desired positions on the recording medium 1000 being transported by the transport member 1300. The reaction liquid application device 1102 and the ink application device 1103 receive the image signal of the recorded data and apply the necessary reaction liquid and ink to each position. When the recording medium 1000 is in sheet form, the transport member 1300 can be one that can fix and transport the recording medium 1000. Specifically, examples include using a transport belt, spurs, or transport cylinder, providing holes in the transport member 1300, and fixing the recording medium 1000 by suction from the back side, or forming the transport member 1000 from an appropriate material and fixing the recording medium 1100 by electrostatic attraction.

[0026] [Drying section] To form a hydrophobic film on an image surface using a compound in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms, it is preferable to have a drying step to evaporate the liquid component prior to the heating step. The drying step forms an ink film in which particles and first resin particles are densely packed. By including such a step, it becomes possible to more reliably penetrate the voids between the molten first resin particles, and it becomes easier to create an image containing voids as shown in Figure 2.

[0027] As shown in Figure 4, the drying process is configured such that the drying unit 2000 includes a drying device 2100 and a transport member 2200. The recording medium 1000, to which the reaction liquid and ink have been applied and an image has been recorded, is transported by the transport member 2200 and dried by the drying device 2100, thereby evaporating the liquid components in the ink. Here, it is not necessary to completely dry the liquid components in the drying process. In addition, the liquid components on the recording medium will gradually dry even without going through the above process, but by performing the drying process, drying is accelerated and the state shown in Figure 2 can be efficiently achieved. The drying device 2100 can have any configuration as long as it can dry the recording medium 1000, and various conventionally known devices such as blower generators and heaters can be used.

[0028] Furthermore, in order to improve drying efficiency, when heating is performed in the drying section 2000 by the drying device 2100, the drying temperature T D It is preferable to heat the ink at a temperature below the glass transition temperature or melting point of the resin particles, as described later, so as not to melt the first resin particles in the ink. That is, the drying temperature T D The glass transition temperature Tg of resin particles R or melting point Tm R It is preferable to set it appropriately according to the following. Specifically, the drying temperature T in the drying section 2000. D The heating temperature (°C) is preferably less than 70°C, more preferably 30°C or higher, and particularly preferably 40°C or higher. D This refers to the maximum temperature of the recording medium surface during the drying process. Heating temperature T DThis can be measured, for example, using a contact thermometer that brings a thermocouple or similar device into contact with the surface of the recording medium, or a non-contact infrared thermometer.

[0029] [Heating section] As shown in Figure 3, the heating unit 2300 is configured to include a heating device 2400 and a transport member 2500. The recording medium 1000, to which the reaction liquid and ink have been applied, is heated while being transported by the transport member 2500. This causes the liquid components in the ink to evaporate and the resin particles to melt, forming pores.

[0030] The heating device 2400 can have any configuration as long as it can heat the recording medium 1000, and various conventionally known devices such as hot air dryers and heaters can be used. Among these, the use of non-contact heaters such as electric heating wires and infrared heaters is preferable from the standpoint of safety and energy efficiency. Furthermore, by incorporating a fan to spray the heated gas onto the recording medium 1000 and using a mechanism to send hot air, it is easy to improve drying efficiency in addition to heating. Regarding the heating method, the recording medium 1000 may be heated from the side to which the reaction liquid and ink are applied (recording surface (front)), from the back side, or from both sides. The transport member 2500 may also be equipped with a heating function.

[0031] Heating temperature T H This refers to the maximum temperature of the recording medium surface during the drying process. Heating temperature T H The temperature can be measured, for example, using 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.

[0032] Figure 2 shows the heating temperature T. H (°C) is the glass transition temperature Tg of the first resin particle. R or melting point Tm RThis is a schematic diagram illustrating an example of the image formation process under the above conditions. The heating temperature TH (°C) is the glass transition temperature Tg of the resin particles. R or melting point Tm R By doing so, an image containing voids created by the melting of the first resin particles can be fixed onto the recording medium.

[0033] Heating temperature T H The temperature (°C) is preferably set so as not to overheat, in order to melt the first resin particles and form voids while suppressing deformation of the recording medium 1000. The temperature of the heating means can be set so that the recording medium reaches the desired temperature, taking into account the transport speed and ambient temperature.

[0034] Heating temperature T H (°C) represents the glass transition temperature Tg of the resin particles. R or melting point Tm R It is preferable to set these appropriately according to the following. Here, if the first resin particles are a crystalline resin, the glass transition temperature Tg (°C) and melting point T M Since it has (°C), in order to melt the first resin particles, melting point T M It is preferable to heat to a temperature above (°C). Details of the crystalline resin will be described later. Specifically, the heating temperature T in the first drying section 2000. H The heating temperature (°C) is preferably 70°C or higher, more preferably 80°C or higher, and particularly preferably 90°C or higher. H (°C) is preferably 200°C or less from the viewpoint of the heat resistance temperature of the recording medium.

[0035] [Paper output section] After image recording, the recording medium 1000 is stored in the paper discharge unit 4000 (Figure 4). After recording is performed in the recording unit 1100, the recording medium 1000, having passed through the drying unit 2000 and the heating unit 2300, is transported by the transport member 6100. The recording medium 1100 is finally stored in a rolled state by the paper discharge device 4200. Two or more winding and paper discharge devices 4200 may be provided to accommodate different recording materials, for example.

[0036] Figure 4 is a schematic perspective view showing another embodiment of the inkjet of the present invention, different from that shown in Figure 3. Figure 5 is a side view of Figure 5. The recording device of the embodiment shown in Figures 4 and 5 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 higher and 70°C or lower.

[0037] The inkjet recording apparatus shown in Figure 4 can perform so-called multi-pass recording, in which ink is applied to a unit area of ​​the recording medium by multiple relative scans between the recording head and the recording medium. The unit area can be set to any area, such as one pixel or one band. When recording an image using an ink of a different color in addition to the ink containing particles and first resin particles (white ink), it is preferable to apply the white ink and the different colored ink using different relative scans.

[0038] A drying device 28 is provided upstream or downstream of the transport direction of the recording medium 10, which intersects with the main scanning direction scanned by the recording head 22. This drying process does not require drying all of the liquid components of the ink. Furthermore, while the liquid components on the recording medium will gradually dry even without the drying process, performing the drying process accelerates drying, efficiently reaching the state shown in Figures 1 and 2. The drying device 28 can have any configuration as long as it can dry the liquid components of the first ink on the recording medium 10, and various conventionally known devices such as blowers and heaters can be used. Drying temperature T by the drying device 28 HBy setting the heating temperature (°C) to 80°C or lower, even in a recording device where the recording head 22 and the drying device 28 are positioned close to each other, a decrease in ejection performance due to drying of ink near the ejection port of the recording head can be suppressed. H (°C) is preferably 50°C or higher, and more preferably 70°C or higher.

[0039] In the recording apparatus shown in Figures 4 and 5, 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 is heated by the heater 25. Examples of heaters 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.

[0040] After applying the ink, the liquid components in the ink can be further evaporated and dried using the heater 25. Furthermore, the glass transition temperature Tg of the first resin particles can be controlled during the drying process. R (°C) or melting point Tm R When heated above (°C), as illustrated in Figure 3, the resin generated by the melting of the first resin particles 4 penetrates the voids between the inorganic material particles. This forms a binder 3, which is a mixture of inorganic material particles and resin, and allows an image containing voids 4 to be fixed onto a recording medium.

[0041] The recording medium 10, to which ink ejected from the recording head 22 has been applied, is wound up by the take-up spool 27 to form a roll-shaped winding medium 24. The recording apparatus shown in Figures 4 and 5 is an apparatus for recording images on a roll-shaped recording medium, but the recording medium is not limited to a roll shape. By changing the recording medium transport method and the paper discharge device, a sheet-shaped recording medium can also be used.

[0042] (Recording medium) The type of recording medium used to record the image is not particularly limited, and any recording medium may be used. In particular, since an ink capable of recording images, such as white ink with excellent opacity, is used, it is preferable to use a recording medium other than white, such as transparent film, translucent film, or colored paper. Here, "white" refers to the same characteristics as the "white" ink described later. As the recording medium, it is preferable to use a non-absorbent recording medium. Here, a non-absorbent recording medium (low to non-absorbent recording medium) is used in the Bristow method from the start of contact for 30 msec. 1 / 2 Water absorption up to 0 mL / m² 2 More than 10mL / m 2 The 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].

[0043] 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.

[0044] (Water-based ink) The ink used in the recording method of the present invention is an aqueous inkjet ink containing particles and first resin particles. Among these, a white ink is preferred. Here, "white ink" includes inks that, even if they do not appear white in their ink state, can record (form) a white image. White refers to CIEL * a * b* Lightness (L) in a color system * ) and chromaticity (a * , b * ) but 70≦L * ≤100, -4.5 ≤a * ≤2.0, -6.0 ≤b * This refers to values ​​within the range of ≤2.5. The components that make up the ink will be explained in detail below.

[0045] [particle] The ink contains particles. Since the particles become part of the material that makes up the binder layer, it is preferable that they are particles with a high refractive index. These particles may be colorants, or they may be colorless, such as resin particles. In particular, when recording a white image, 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 first 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. Furthermore, the particle content (mass %) in the ink is preferably 5.0 mass% to 45.0 mass%, and more preferably 5.0 mass% to 40.0 mass%, based on the total mass of the ink.

[0046] Particles are typically dispersed in ink in the form of secondary particles, which are aggregates of two or more primary particles. The average primary particle diameter D of the particles. P0 The particle size (nm) must be 150 nm or less, and more preferably 50 nm or less. The average primary particle diameter of the particles is preferably 5 nm or more. The average primary particle diameter of the particles can be calculated by measuring the particle diameter of about 100 primary particles using a scanning electron microscope and taking the average value.

[0047] The particles must not melt during the heating process that melts the resin particles. Specifically, the glass transition temperature (Tg) of the particles must be... P (°C) or melting point Tm P(°C) is above the temperature 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. Details of the second resin particles will be described later.

[0048] 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.

[0049] 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 materials such as polyols. Using titanium dioxide with a coated surface is expected to suppress photocatalytic activity and improve dispersibility. Titanium dioxide exists in three crystalline forms: 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.

[0050] The titanium dioxide content (mass%) in the ink is preferably 5.0% to 55.0% by mass, and more preferably 20.0% to 50.0% by mass, based on the total mass of the ink. The average primary particle size D of the titanium dioxide contained in the ink. P The (nm) wavelength is preferably 50 nm or less, and more preferably 30 nm or less.

[0051] Calcium carbonate particles can be cubic or spindle-shaped. Of 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). Of these, apatite-type calcium phosphate is preferred, particularly hydroxyapatite (Ca 10 (PO6)(OH)2) is even more preferable.

[0052] 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.

[0053] Silicon dioxide can be synthesized, for example, by the Stober method. 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.

[0054] Kaolin is a clay mineral containing multiple inorganic components. Specifically, it is a clay composed of kaolinite, hydrated halloysite, and the crystalline structure of halloysite. In addition to the kaolin components, clay also contains ilmenite, montmorillonite, vermiculite, etc. When using the above particles to make a white ink, it is preferable to use particles with high whiteness.

[0055] The second resin particles are different from the first resin particles and must not melt during the drying process that melts the first resin particles. Therefore, the glass transition temperature Tg of the particles is important. P(°C) or melting point Tm P (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Rd The temperature must be higher than (°C). The second resin particles only need to satisfy this condition, and the resin forming the resin particles can be selected from the same materials as those used for the first resin particles, as described later. In particular, it is preferable that the resin particles be formed from a crosslinked resin, and it is even more preferable that the resin particles be formed from a crosslinked acrylic resin.

[0056] One method for dispersing particles is to apply energy (mechanical or thermal) to a liquid medium containing the particles to disperse them. Furthermore, from the viewpoint of stably maintaining the dispersed state of the particles, it is preferable to use a dispersant. For example, for particles with a low isoelectric point and a negative surface charge in an aqueous medium, such as dry silica, it is preferable to use a cationic resin as the dispersant. For particles with a positive surface charge, such as alumina hydrate, it is preferable to use an acid as the dispersant. In addition, the dispersant can also be physically adsorbed onto the surface of the particles for dispersion. Dispersants are preferable because they can effectively suppress particle aggregation due to intermolecular electrical repulsion and steric hindrance. Dispersants can be appropriately selected according to the characteristics of the particles, such as acids, alkalis, and polymer resins. The amount of dispersant is preferably 0.5% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the amount of particles. If the amount of dispersant is less than 0.5% by mass, the dispersibility of the particles may become unstable and cause aggregation. If the amount is 15.0% by mass or more, the amount of dispersant will be excessive, which may conversely destabilize the dispersibility of the particles.

[0057] [First resin particles] The ink contains first resin particles. As the solvent in the ink applied to the recording medium evaporates, the particles and the first resin particles become closely adhered to each other. Then, the first resin particles melt during the heating process, creating voids. 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, and more preferably 2.5% by mass or more and 14.0% by mass or less, based on the total mass of the ink. Furthermore, 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, and more preferably 2.5% by volume or more and 14.0% by volume or less, based on the total volume of the ink.

[0058] The pores formed during the heating process are created by melting the first resin particles. Therefore, the size of the formed pores is greatly influenced by the particle size of the first resin particles. On the other hand, the light scattering efficiency is also greatly influenced by the size of the formed pores. For this reason, from the viewpoint of further improving the light scattering efficiency, the cumulative 50% particle diameter D50 of the first resin particles is determined based on volume. R The wavelength is preferably between 80 nm and 400 nm, and more preferably between 150 nm and 250 nm.

[0059] Whether the first resin particles have melted due to the heating process can be easily determined, for example, by cutting a recording medium on which images before and after the heating process have been recorded and observing it with a scanning electron microscope. If, in the image after the heating process, the spherical first resin particles have disappeared and holes approximately the same size as the first resin particles or where particles are connected and linked to each other are observed, it can be simply determined that the first resin particles have melted and voids have been created.

[0060] In the heating process, the following methods can be used to determine whether the first resin particles have been melted by heating the recording medium and thus voids have been created. First, the recording medium on which the image is recorded is cut, and the cut surface is observed with a scanning electron microscope. Then, the observed image is binarized, and the proportion of the black image originating from voids to the entire image is calculated. The area ratio of voids in the image obtained by this method is preferably 10% or more from the viewpoint of scattering efficiency. More preferably, it is between 20% and 60%. If the area ratio of voids is less than 20%, the scattering efficiency decreases because there are substantially few voids in the film, and the opacity of the obtained image decreases. Furthermore, if the area ratio of voids is less than 20%, because there are relatively few voids in the film, even when a small amount of liquid such as water is applied, the voids may be filled with liquid, which may reduce the water-wetting opacity. On the other hand, if the area ratio of voids is 60% or more, the volume through which liquid such as water permeates is too large, which may reduce the water-wetting opacity.

[0061] From the viewpoint of forming a binder with a high refractive index, it is preferable to use first resin particles with a higher refractive index. Specifically, the refractive index of the first resin particles is preferably 1.5 or higher, and more preferably 1.6 to 2.5.

[0062] In the ink, the content (volume %) of first resin particles is preferably 1.3 to 5.0 times the total particle content (volume %), and more preferably 1.8 to 4.0 times. If the above volume ratio exceeds 5.0 times, the amount of fusion between first resin particles tends to increase, making it difficult to form voids of the desired size. As a result, sufficient image opacity may not be obtained. In addition, the refractive index of the binder composed of the molten first resin particles decreases, which can easily reduce light scattering efficiency and opacity. On the other hand, if the above mass ratio is less than 1.3 times, the amount of voids formed decreases, and sufficient image opacity may not be obtained.

[0063] Examples of resins that form the first resin particles include vinyl chloride resins, styrene resins, urethane resins, acrylic resins, and polyester resins. Among these, acrylic resins, polyester resins, and urethane resins are preferred from the viewpoint of inkjet properties. If first resin particles formed from resins other than those mentioned above are used, ejection tends to be unstable, and as a result, sufficient image opacity may not be obtained. Among these, acrylic resins are preferred, and acrylic resins having units derived from styrene are even more preferred. Details of the resins constituting the first resin particles will be described later. The acrylic resin may be a homopolymer formed from only one type of monomer unit, or a copolymer formed from multiple types of monomer units. The resin that forms the first resin can be appropriately selected from the same resin compositions as those for "other resins" described later.

[0064] It is preferable that the first resin particles maintain their shape and remain unmelted until the heating process is performed. If the first resin particles melt before the heating process, the mixing of the particles and the resin may not proceed quickly, or the first resin particles may fuse together, making it somewhat difficult to form the desired pores. If the desired pores are not formed, the light scattering efficiency may decrease, and the opacity may tend to decrease. Therefore, it is preferable that the first resin particles do not substantially fuse together at room temperature (25°C). Specifically, it is preferable that (i) the glass transition temperature Tg (°C) of the first resin particles is 25°C or higher; or (ii) the melting point Tm (°C) of the first resin particles is 25°C or higher, and the resin constituting the first resin particles is a crystalline resin.

[0065] Glass transition temperature Tg of the first resin particle R (°C) and melting point Tm R The temperature (°C) is preferably 100°C or lower, and more preferably 80°C or lower. The glass transition temperature Tg of the first resin particles. R (°C) and melting point Tm R (°C) can be measured using a differential scanning calorimeter (DSC).

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Whether the resin forming the first resin particles is amorphous or crystalline can be determined by measuring the degree of crystallinity of the resin using a differential scanning calorimeter. Resins in which no melting peak is observed with a differential scanning calorimeter are determined to be amorphous. Resins in which a melting peak is observed are determined to be crystalline. In the case of crystalline resins, the heat of fusion can be calculated from the peak area, and the degree of crystallinity can be determined from the ratio of this heat of fusion to the heat of fusion of a perfect crystal with 100% crystallinity, which is determined from theoretical calculations.

[0070] 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, and more preferably 100,000 or more and 3,000,000 or less. The first resin particles do not need to contain a colorant.

[0071] As mentioned above, the first resin particles melt upon heating, and the resulting resin enters the voids between the particles. As a result, voids are created. Therefore, the viscoelastic properties of the first resin particles, particularly the loss modulus related to viscosity, affect how easily voids are formed. Voids are created when the resin produced by melting enters the voids between the particles. Therefore, the viscoelastic properties of the first resin particles, particularly the loss modulus related to viscosity, affect how easily the resin enters the voids, that is, how easily the desired voids are formed. Thus, the loss modulus of the resin at high temperatures is important. This loss modulus changes with temperature. For example, the loss modulus of the first resin particles at 80°C is 1.0 × 10⁻⁶. 7 It is preferable that it is less than or equal to Pa, 3.3 × 10 5 It is even more preferable that it be Pa or less.

[0072] [Compound] The ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. As the liquid component evaporates, the compound orients its hydrophobic surface towards the air at the liquid-gas interface of the ink, forming a hydrophobic film on the ink surface. If the anionic group substituted on the chain hydrocarbon is a carboxylic acid group, the total number of carbon atoms, including the carboxylic acid group, must be 8 or more.

[0073] Examples of anionic groups include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups. Among these, the use of carboxylic acid groups is preferred. Compounds substituted with carboxylic acid groups are preferred because they have a good balance between solubility in the aqueous medium constituting the ink and orientation of the compound on the image surface, and because resolubility is easily suppressed when liquids such as water adhere to the image. Furthermore, it is preferable that the counterion of the carboxylic acid group contains an alkali metal ion.

[0074] If the number of carbon atoms in the chain hydrocarbon is 7 or less, it is difficult to orient the hydrophobic surface toward the air at the gas-liquid interface of the ink, and a hydrophobic film cannot be formed on the image surface. As a result, when liquids such as water adhere to the image, water enters the pores, reducing the opacity. It is even more preferable that the number of carbon atoms in the chain hydrocarbon is between 12 and 18. If the number of carbon atoms is too long, the solubility of the compound in the ink decreases, which may cause the compound to precipitate near the ejection port of the recording head during continuous recording, reducing the ejection stability.

[0075] In the aqueous ink, the compound content (mass%) is preferably 0.1% to 3.0% by mass, and more preferably 0.5% to 2.00% by mass, based on the total mass of the ink. If the content is less than 0.1% by mass, a sufficiently hydrophobic film cannot be formed on the ink film surface, and if the content exceeds 3.0% by mass, it may not dissolve sufficiently in the ink, which may reduce the ejection stability during continuous recording.

[0076] Examples of counterions for the anionic group of a compound include hydrogen atoms, ammonium ions, organic amine ions, and alkali metal ions. Alkali metal ions are preferred because they offer a good balance between solubility in the aqueous medium that constitutes the ink and orientation of the compound to the image surface, and because their re-solubility is easily suppressed when liquids such as water adhere to the image.

[0077] [resin] The ink may further contain resins other than 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.

[0078] 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.

[0079] [Composition of the resin] Examples of resins include acrylic resins, urethane resins, olefin resins, and polyester 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.

[0080] 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.

[0081] 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.

[0082] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting with a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] [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.

[0087] [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.

[0088] The boiling point of the water-soluble organic solvent is preferably 250°C or lower, more preferably 230°C or lower. By setting the boiling point to 250°C or lower, the water-soluble organic solvent evaporates rapidly during the drying and heating processes.

[0089] When the boiling point of a water-soluble organic solvent exceeds 250°C, the organic solvent tends to remain in the ink during the drying process as volatile components such as water and water-soluble organic solvents evaporate. In this invention, as shown in Figures 1 and 2, the difference in refractive index between the binder 3 and the pores 4 causes light scattering, resulting in high opacity. Therefore, if a large amount of organic solvent remains in the pores after drying, the refractive index of the pores decreases, which tends to reduce the opacity of the resulting image.

[0090] Water-soluble organic solvents that can assist in the dissolution of compounds in which a hydroxyl group or anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms in an aqueous medium are preferred. Examples of such solvents include alcohols, with primary or secondary alcohols being preferred, and secondary alcohols being even more preferred. Among secondary alcohols, 1,2-alkanediols having 5 or more carbon atoms are particularly preferred, as they have a long alkyl moiety and the hydroxyl group is located at the alkyl terminal, resulting in a polarized structure. Hereinafter, 1,2-alkanediols having 5 or more carbon atoms may be referred to as "first water-soluble organic solvents".

[0091] If the number of carbon atoms in the 1,2-alkanediol is less than 5, its ability to aid in the dissolution of the compound is low, and the compound may precipitate from the ink before it can orient itself on the image surface, making it difficult to sufficiently improve the water-wettability. It is preferable that the number of carbon atoms be 8 or less.

[0092] The content (mass%) of the first water-soluble organic solvent 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. Furthermore, the content (mass%) of the first water-soluble organic solvent in the ink is preferably 1.0 times or more in mass ratio to the content (mass%) of the compound. If the mass ratio is less than 1.0 times, the ability to help dissolve the compound is low, and the compound may precipitate from the ink before it can orient itself on the image surface, making it impossible to sufficiently improve the water-wettability. Among 1,2-alkanediols with 5 or more carbon atoms, 1,2-pentanediol and 1,2-hexanediol are preferred because they have a high ability to help dissolve the compound and are also preferred in terms of the evaporation rate of the water-soluble organic solvent. Note that among 1,2-alkanediols, those with a large number of carbon atoms include those that are solid at 25°C, but for convenience in this specification they are treated as "water-soluble organic solvents".

[0093] [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.

[0094] [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.

[0095] (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.

[0096] [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.

[0097] 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+ . To incorporate polyvalent metal ions into the reaction solution, polyvalent metal salts (which may be hydrates) composed of the combination of polyvalent metal ions and anions can 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 using polyvalent metal ions as a reactant, the content (mass %) of the polyvalent metal salt in the reaction solution, based on the total mass of the reaction solution, is preferably 1.0 mass % or more and 40.0 mass % or less.

[0098] 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.

[0099] 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.

[0100] [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.

[0101] [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.

[0102] [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]

[0103] 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 indicated in "parts" and "%" are based on mass.

[0104] <Measurement of physical properties> (Average primary particle diameter, cumulative 50% particle diameter based on volume) A scanning electron microscope (product name "S-4700," manufactured by Hitachi High-Tech) was used to image the sample at a magnification of 100,000x. The diameter of 100 circles circumscribing the primary particles was then measured, and the average value was calculated. The average value was then used to determine the average primary particle diameter D of the particles. P Furthermore, a particle size analyzer using dynamic light scattering (product name "UPA-EX150", manufactured by Nikkiso) was used to determine the cumulative 50% particle size D50 based on particle volume. P The following was measured: Volume-based cumulative 50% particle diameter D50 of resin particles. R The above-mentioned particle size measuring device was also used for measurement.

[0105] (Glass transition temperature, melting point) The glass transition temperature (Tg) and melting point (Tm) of particles and resin particles were measured using a differential scanning calorimeter (DSC). A sample for measuring the "glass transition temperature in a dry state" was prepared by drying an aqueous dispersion of resin particles at 60°C, obtaining 2 mg of resin particles, placing them in an aluminum container, and sealing it. Thermal analysis was performed on the prepared sample using a differential scanning calorimeter (product name "DSC-2500", manufactured by TA instruments) according to the temperature program shown below. In this specification, the glass transition temperature of resin particles is defined as follows: Specifically, the temperature at the intersection of a straight line extending from two points on the low-temperature side of the heating curve (horizontal axis: temperature, vertical axis: heat) in the following temperature program (4) or (5) to the high-temperature side, and a tangent line drawn at the point where the slope of the step-like change in the curve is maximum, is determined. The temperature thus determined was defined as the "glass transition temperature of the resin particles." Glass transition temperature (Tg) of resin particles in a dry state R (°C) was calculated from the measurement results of the second cycle after running the temperature program for two cycles. Furthermore, for crystalline resins, the peak top of the endothermic peak in the above heating curve was defined as the "melting point Tm of the resin particles". R The melting point of the particles was determined as follows: The melting point of the particles was measured using the same method as in the temperature programs (1) to (4) below, except that the upper temperature limit of (4) was changed, and the peak top of the endothermic peak in the heating curve was defined as the "melting point Tm of the particles". P " he said. [Temperature Program]: (1) Heat from -40°C to 200°C at a rate of 10°C / min. (2) Hold at 200°C for 5 minutes (3) Cooling from 200°C to -40°C at a rate of 10°C / min (4) Heat from -40°C to 200°C at a rate of 10°C / min. (5) Increase the temperature from -40°C to 150°C at a rate of 10°C / min.

[0106] (Particle density) The density of particles ρ was determined using the Gay-Lussac type pycnometer method in accordance with JIS Z 8807. P The density was measured. The density of the resin particles was also measured using the same method.

[0107] <Particle preparation> Inorganic particles were prepared or synthesized using the following procedure. The properties of the obtained inorganic particles are shown in Table 1.

[0108] (particle 1) An appropriate amount of deionized water was added to the types of particles shown in Table 1 to obtain an aqueous dispersion of particle 1.

[0109] (particle 2) A mixture of 30.0 parts of the type of particles (titanium dioxide) shown in Table 1, 0.45 parts of potassium hydroxide, 69.55 parts of deionized water, and 100 parts of 0.1 mm zirconia beads was prepared. This mixture was dispersed using a batch-type bead mill (product name "Easy Nano RMBII", manufactured by AIMEX). An appropriate amount of deionized water was added to obtain an aqueous dispersion of particle 2.

[0110] [Table 1]

[0111] <Preparation of resin particles> Aqueous dispersions of the types of resin particles shown in Table 2 were prepared. In Table 2, the resin particle content in each aqueous dispersion is indicated in the "Resin Particle Content (%)" column. Furthermore, the aqueous dispersions of resin particle 1 and resin particle 2 were prepared according to the methods described below.

[0112] (Resin particle 1) A solution was prepared by mixing 0.2 parts potassium persulfate and 74.0 parts deionized water. An emulsion was also prepared by mixing 1.5 parts acrylic acid, 2.5 parts 2-ethylhexyl acrylate, 30.0 parts methyl methacrylate, 5.0 parts styrene, and 0.3 parts reactive surfactant. The reactive surfactant used was "ADEKA Soap ER20" (manufactured by ADEKA, nonionic surfactant, 20 ethylene oxide units). Under a nitrogen atmosphere, the emulsion was added dropwise to the solution over 1 hour, polymerized with stirring at 80°C, and then stirred for a further 2 hours. After cooling to room temperature, deionized water and potassium hydroxide aqueous solution were added, and the solid content was adjusted with deionized water to obtain an aqueous dispersion of resin particles 1 with the characteristics shown in Table 2.

[0113] (Resin particles 2) As the aqueous dispersion of the second resin particles, an aqueous dispersion of polyurethane resin particles (product name "Superflex 300", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used.

[0114] [Table 2]

[0115] <Ink preparation> The components (in %) shown in the upper section of Tables 3 and 4 were mixed. Potassium hydroxide was added to adjust the pH to a range of 7-9. Each ink was prepared by pressure filtration through a 3.0 μm pore size microfilter (manufactured by Fujifilm). In Tables 3 and 4, Surfinol 465 is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Nisshin Chemical Industry Co., Ltd. The properties of each ink are shown in the lower section of Tables 3 and 4.

[0116] [Table 3]

[0117] [Table 4]

[0118] <Preparation of reaction solution> 20.0 parts of magnesium sulfate heptahydrate, 20.0 parts of 1,2-butanediol, 0.5 parts of nonionic surfactant (product name "Surfinol 465", manufactured by Nisshin Chemical Industry Co., Ltd.), and 59.5 parts of deionized water were mixed and thoroughly stirred. Then, the mixture was pressure filtered through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec) to prepare the reaction solution.

[0119] <Rating> Each ink obtained as described above was evaluated for the following items. In this invention, "AA," "A," and "B" were considered acceptable levels in the evaluation criteria shown below, and "C" was considered an unacceptable level. The evaluation results are shown in Table 5.

[0120] (Recording of images for evaluation) Each ink and reaction solution shown in Table 5 was used as a set, and evaluation images (solid images) were recorded under the following conditions. In this example, a solid image recorded at a resolution of 600 dpi × 600 dpi, with 8 ink droplets having a mass of 3.5 ng per droplet applied to a unit area of ​​1 / 600 inch × 1 / 600 inch, is defined as having a recording duty cycle of 100%. Using this inkjet recording device, a solid image (50 mm × 50 mm) with a reaction solution recording duty cycle of 40% and an ink recording duty cycle of 400% was recorded on a recording medium. The recording medium was PET film (product name "Ultra-Transparent PET Film GIY-0305", manufactured by Lintec, 30 msec from the start of contact in the Bristow method). 1 / 2 The amount of water absorbed up to V0 is 0 g / m³. 2 More than 10g / m 2 (The following range was used)

[0121] • Recording device 1: An inkjet recording device 100 having the configuration shown in Figure 3 had an ink cartridge filled with reaction solution set in the reaction solution dispenser 1102 and an ink cartridge filled with ink set in the ink dispenser 1103. Image recording was performed using a single-pass method in which the reaction solution and ink were applied to a unit area in a single relative scan between the recording head and the recording medium using the discharge port in the longitudinal center of the recording head. In the examples and comparative examples where "Yes" was indicated in the "Drying process" column, the first drying unit 2000 was used to dry the recording medium for 1 minute so that the surface temperature reached 80°C. After that, the heating unit 2300 was used to heat the recording medium for 1 minute so that the surface temperature reached the temperature indicated in the "Heating process temperature" column.

[0122] • Recording device 2: An inkjet recording device having the configuration shown in Figure 4 was fitted with ink cartridges filled with reaction solution and ink, respectively. Image recording was performed using a multi-pass method in which the reaction solution and ink were applied to a unit area by multiple relative scans of the recording head and the recording medium using all the ejection ports of the recording head. In the examples and comparative examples where "Yes" was indicated in the "Drying process" column, the recording medium was dried for 1 minute using a drying device 28 located below the head scanning unit so that its surface temperature reached 80°C. After that, the recording medium was heated for 1 minute using a heater 25 so that its surface temperature reached the temperature indicated in the "Heating process temperature" column.

[0123] (Sinking resistance) The prepared ink was placed in a cylindrical sample container to a height of 24 mm and left in an environment of 25°C for one week. The thickness (mm) of the transparent supernatant after the period was measured, and the ink's resistance to sedimentation was evaluated according to the evaluation criteria shown below. A: The thickness of the clear supernatant was 10 mm or less. C: The thickness of the clear supernatant was over 10 mm.

[0124] (Drying and concealing properties) For the evaluation images recorded using the method described above, the dry opacity was measured and calculated according to the method compliant with ISO 2471:2008, and the dry opacity of the images was evaluated. According to ISO 2471:2008, the reflectance is measured by placing a white board and a black board on the back of the paper being tested, and the dry opacity is calculated from the following formula (B). Dry opacity = (R0 / R∞) × 100 ... (B) (R0: Reflectance measured with a black board behind it, R∞: Reflectance measured with a white board behind it).

[0125] In this example, 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 in accordance with this method. The opacity of the images was then evaluated according to the evaluation criteria shown below. AA: The concealment level was 60% or higher. A: The concealment level was between 55% and 60%. B: The concealment level was between 45% and 55%. C: The concealment level was less than 45%.

[0126] (Water-repellent properties) The recorded evaluation images were immersed in 25°C water and immediately removed. The water on the image surface was wiped off, and the wet opacity was measured using the same method as for dry opacity. The wet opacity was evaluated by calculating the difference between the opacity before immersion and the wet opacity after immersion. AA: The difference between dry opacity and wet opacity was less than 5%. A: The difference between dry concealment and wet concealment was between 5% and 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.

[0127] (Discharge stability) For the inks shown in Table 5, all examples and comparative examples were evaluated using recording device 1. A solid image (50 mm x 50 mm) with an ink recording duty cycle of 400% was recorded 20 times consecutively on the same recording medium, with a 10 mm interval in the direction of transport of the recording medium. The recorded solid image was visually checked, and if any recording was missing, a cleaning operation (suction recovery operation) was performed. The ink ejection stability was then evaluated according to the following evaluation criteria. A: The record was kept without any gaps until the very end. B: A gap occurred in the recording midway through, but it was recovered through a cleaning operation.

[0128] [Table 5]

[0129] Furthermore, the disclosure of embodiments of the present invention includes the following methods and configurations.

[0130] (Method 1) An inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, An ink application step of applying the aqueous ink to the recording medium, The recording medium to which the aqueous ink is applied is subjected to the glass transition temperature Tg of the first resin particles. R (°C) or melting point Tm R (°C) or higher, and the glass transition temperature Tg of the particles. P (°C) or melting point Tm P It includes a heating step of heating to a temperature below (°C), The aqueous ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. The average primary particle diameter D of the aforementioned particles P (nm) is 150nm or less, An inkjet recording method characterized in that, in the heating step, the recording medium is heated to melt the first resin particles and create voids.

[0131] (Method 2) The inkjet recording method according to Method 1, wherein the number of carbon atoms in the compound is 12 or more and 18 or less.

[0132] (Method 3) The inkjet recording method according to method 1 or 2, wherein the content (by mass) of the compound in the aqueous ink is 1.0% by mass or more, based on the total mass of the ink.

[0133] (Method 4) The inkjet recording method according to any one of methods 1 to 3, wherein the compound has a carboxylic acid group.

[0134] (Method 5) The inkjet recording method according to method 4, wherein the counterion of the carboxylic acid group comprises an alkali metal ion.

[0135] (Method 6) The aqueous ink contains a water-soluble organic solvent which includes a first water-soluble organic solvent, and the first water-soluble organic solvent contains a 1,2-alkanediol having 5 or more carbon atoms. The inkjet recording method according to any one of methods 1 to 5, wherein the content (mass%) of the first water-soluble organic solvent in the aqueous ink is 1.0 times or more in mass ratio to the content (mass%) of the compound.

[0136] (Method 7) The inkjet recording method according to method 6, wherein the first water-soluble organic solvent is 1,2-pentanediol or 1,2-hexanediol.

[0137] (Composition 1) An inkjet recording apparatus used in an inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, The recording medium to which the aqueous ink is applied is subjected to the glass transition temperature Tg of the first resin particles. R (°C) or melting point Tm R (°C) or higher, and the glass transition temperature Tg of the particles.P (°C) or melting point Tm P It includes a heating step of heating to a temperature below (°C), The aqueous ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. The average primary particle diameter D of the aforementioned particles P (nm) is 150nm or less, An inkjet recording apparatus characterized in that, in the heating step, the recording medium is heated to melt the first resin particles and create voids.

[0138] (Configuration 2) An aqueous ink used 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 method includes an ink application step of applying the aqueous ink to the recording medium, The recording medium to which the aqueous ink is applied is subjected to the glass transition temperature Tg of the first resin particles. R (°C) or melting point Tm R (°C) or higher, and the glass transition temperature Tg of the particles. P (°C) or melting point Tm P It includes a heating step of heating to a temperature below (°C), The aqueous ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. The average primary particle diameter D of the aforementioned particles P (nm) is 150nm or less, A water-based ink characterized in that, in the heating step, the recording medium is heated to melt the first resin particles and create voids. [Explanation of symbols]

[0139] 1 particle 2 First resin particle 3 compounds 5. Holes

Claims

1. An inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, An ink application step of applying the aqueous ink to the recording medium, The recording medium to which the aqueous ink is applied is subjected to the glass transition temperature Tg of the first resin particles. Ｒ (°C) or melting point Tm Ｒ (°C) or higher, and the glass transition temperature Tg of the particles. Ｐ (°C) or melting point Tm Ｐ It includes a heating step of heating to a temperature below (°C), The aqueous ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. The average primary particle diameter D of the aforementioned particles Ｐ (nm) is 150 nm or less, An inkjet recording method characterized in that, in the heating step, the recording medium is heated to melt the first resin particles and create voids.

2. The inkjet recording method according to claim 1, wherein the number of carbon atoms in the compound is 12 or more and 18 or less.

3. The inkjet recording method according to claim 1, wherein the content (by mass) of the compound in the aqueous ink is 1.0% by mass or more, based on the total mass of the ink.

4. The inkjet recording method according to claim 1, wherein the compound has a carboxylic acid group.

5. The inkjet recording method according to claim 4, wherein the counterion of the carboxylic acid group comprises an alkali metal ion.

6. The aqueous ink contains a water-soluble organic solvent which includes a first water-soluble organic solvent, and the first water-soluble organic solvent contains a 1,2-alkanediol having 5 or more carbon atoms. The inkjet recording method according to claim 1, wherein the content (mass%) of the first water-soluble organic solvent in the aqueous ink is 1.0 times or more by mass ratio to the content (mass%) of the compound.

7. The inkjet recording method according to claim 6, wherein the first water-soluble organic solvent is 1,2-pentanediol or 1,2-hexanediol.

8. An inkjet recording apparatus used in an inkjet recording method for recording an image on a recording medium using an aqueous ink containing particles and first resin particles, heating the recording medium to which the aqueous ink has been applied to a temperature that is equal to or higher than the glass transition temperature Tg Ｒ (°C) or the melting point Tm Ｒ (°C) of the first resin particles, and lower than the glass transition temperature Tg Ｐ (°C) or the melting point Tm Ｐ (°C) of the particles; and a heating step The aqueous ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. The average primary particle diameter D of the aforementioned particles Ｐ (nm) is 150 nm or less, An inkjet recording apparatus characterized in that, in the heating step, the recording medium is heated to melt the first resin particles and create voids.

9. An aqueous ink used 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 method includes an ink application step of applying the aqueous ink to the recording medium, The recording medium to which the aqueous ink is applied is subjected to the glass transition temperature Tg of the first resin particles. Ｒ (°C) or melting point Tm Ｒ (°C) or higher, and the glass transition temperature Tg of the particles. Ｐ (°C) or melting point Tm Ｐ It includes a heating step of heating to a temperature below (°C), The aqueous ink contains a compound in which a hydroxyl group or an anionic group is substituted on a chain hydrocarbon having 8 or more carbon atoms. The average primary particle diameter D of the aforementioned particles Ｐ (nm) is 150 nm or less, A water-based ink characterized in that, in the heating step, the recording medium is heated to melt the first resin particles and create voids.

Images