Inkjet recording method, inkjet recording device, and set of aqueous ink and reaction solution.

Abstract

The present invention provides an inkjet recording method that enables the recording of highly color-reproduced images on a non-absorbent recording medium and the recording of images with suppressed edge unevenness on a low-absorbent recording medium when recording images using a single-pass method. [Solution] An inkjet recording method that uses an aqueous reaction solution containing an aqueous ink and a reactant that reacts with the aqueous ink to record an image on a low to non-absorbent recording medium in a single pass, with the time from the application of the reaction solution to the application of the aqueous ink being 1800 ms or less. The reaction solution contains at least two types of nonionic surfactants having an HLB value in the range of 4 to 16, and the difference between the highest and lowest HLB values ​​of the at least two types of nonionic surfactants is 1 or more. The aqueous ink contains resin particles. Surface tension γ of the aqueous ink at 25°C. i and the surface tension γ of the reaction solution r The difference (γ i -γ r ) is 9 mN / m or less.

Description

Technical Field

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and a set of a water-based ink and a reaction liquid.

Background Art

[0002] In recent years, inkjet recording methods have attracted attention in the commercial printing field and the industrial printing field, such as poster, wallpaper and label printing, because they can reduce environmental load and support small-lot printing that meets the needs of individual customers. In the commercial printing field and the industrial printing field, high-definition images on various recording media are required. As an example of recording media, it is required to record images on recording media with low water-based ink absorbency or recording media that hardly absorb water-based inks. Examples of the recording media with low water-based ink absorbency (hereinafter also referred to as "low-absorbency recording media") include recording media having a coat layer such as art paper and coated paper. In addition, examples of the recording media that hardly absorb water-based inks (hereinafter also referred to as "non-absorbency recording media") include plastic films.

[0003] From the viewpoints of environmental friendliness and safety, use of water-based inks containing pigments (hereinafter also referred to as "pigment inks") has been studied. Heretofore, high-definition image quality has been obtained using pigment inks on recording media that easily absorb water-based inks, such as plain paper and other recording media without a coat layer. On the other hand, for low-absorbency recording media and non-absorbency recording media, the applied ink droplets hardly permeate into the recording media, so adjacent ink droplets are applied while the ink is hardly fixed by permeation. As a result, the ink droplets coalesce with each other to cause bleeding and unevenness, making it difficult to obtain high-definition image quality.

[0004] To solve the above problems, a reaction liquid (also referred to as a treatment liquid) containing a polyvalent metal salt that reacts with components such as pigments in the ink to cause aggregation and thickening has been used (see Patent Literatures 1, 2 and 3).

[0005] On the other hand, inkjet recording devices used in commercial and industrial printing fields are required to improve productivity for the convenience of customers. While a drying process is essential for fixing water-based inks on non-absorbent and low-absorbent recording media, applying a large amount of reaction solution and ink to achieve high color vibrancy results in a longer drying time, leading to decreased productivity. Therefore, there is a need for an inkjet recording method that can achieve high color vibrancy with a small amount of ink. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-076960 [Patent Document 2] Japanese Patent Publication No. 2021-017005 [Patent Document 3] Japanese Patent Publication No. 2019-142068 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, with the increasing speed of recording, methods for applying ink to recording media in a so-called one-pass manner to record images are being considered in order to produce large quantities of recorded material in a short time. The one-pass method is a method in which liquid such as ink or reaction solution is applied to a unit area of ​​the recording media in a single relative scan between the recording head and the recording media. A single relative scan between the recording head and the recording media includes, for example, a method in which the recording media is transported in a direction intersecting the arrangement direction of the recording head nozzles, and an image is recorded using a line head that can record an image across the entire width of the recording media in a single scan. In one-pass recording, an image is recorded in a unit area of ​​the recording media with only one relative scan between the recording head and the recording media. The unit area can be set as any area such as "1 pixel".

[0008] The inventors performed one-pass recording on non-absorbent and low-absorbent recording media using the reaction solution and ink proposed in Patent Documents 1, 2, and 3. As a result, it was found that when the reaction solution was applied to the recording media before the ink, and then the ink was applied to the recording media in a one-pass manner to record an image, the inventors' desired level of high color development with a small amount of ink was not achieved on the non-absorbent recording media. Furthermore, it was found that on the low-absorbent recording media, a phenomenon occurred in which the color at the edges of solid areas of an image became darker than the color at the center (hereinafter referred to as "image edge unevenness").

[0009] Therefore, an object of the present invention is to provide an inkjet recording method that enables the recording of highly color-developed images on a non-absorbent recording medium and the recording of images with suppressed unevenness at the image edges on a low-absorbent recording medium when recording images in a single pass. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method, as well as a set of aqueous ink and reaction solution. [Means for solving the problem]

[0010] In other words, according to the present invention, an aqueous reaction solution containing an aqueous ink and a reagent that reacts with the aqueous ink is used in the Bristow method from the start of contact to 30 ms. 1 / 2 Up to 10 mL / m² of water absorption capacity 2 An inkjet recording method for recording an image on a recording medium, wherein the aqueous ink and the reaction solution are applied to a unit area such that the time from when the reaction solution is applied to the recording medium until when the aqueous ink is applied to the recording medium is 1800 ms or less, and the application is performed in a single relative scan between an inkjet ejection head and the recording medium, wherein the reaction solution contains a surfactant, and the surfactant includes at least two types of nonionic surfactants having an HLB value in the range of 4 to 16, and the difference between the highest HLB value and the lowest HLB value of the at least two types of nonionic surfactants is 1 or more, and the aqueous ink contains resin particles, and the surface tension γ of the aqueous ink at 25°C is iand the surface tension γ of the reaction solution r The difference (γ i -γ r An inkjet recording method is provided, characterized in that the coefficient of force is 9 mN / m or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an inkjet recording method that enables the recording of highly color-reproduced images on a non-absorbent recording medium and the recording of images with suppressed unevenness at the image edges on a low-absorbent recording medium when recording images in a single pass. Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus used in this inkjet recording method, as well as a set of aqueous ink and reaction solution. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram illustrating the estimated state of surfactants in a reaction solution applied to a non-absorbent recording medium. [Figure 2] This is another schematic diagram illustrating the estimated state of surfactants in a reaction solution applied to a non-absorbent recording medium. [Figure 3] This is a schematic diagram showing one embodiment of the inkjet recording apparatus of the present invention. [Figure 4] This is a perspective view showing an example of a liquid dispensing device. [Figure 5] This is a cross-sectional perspective view showing an example of an ejection element substrate. [Figure 6] This is a schematic diagram showing an example of a liquid supply system. [Figure 7] This is a schematic diagram showing another example of a heating section. [Figure 8] This is a schematic diagram showing another example of the fixing section. [Modes for carrying out the invention]

[0013] The present invention will be further described in detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, the aqueous ink and reaction solution for inkjet printing may be simply referred to as "ink" and "reaction solution." Unless otherwise specified, the physical properties are given at room temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (50% relative humidity). Furthermore, with respect to resins, "unit" means the unit structure corresponding to one monomer unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively. Also, the unit "ms" means milliseconds.

[0014] The inventors of this invention have been studying how to achieve high color development even with a small amount of ink when recording an image on a non-absorbent recording medium using an inkjet recording device in a single pass method by applying the reaction solution and ink in that order.

[0015] In single-pass recording, the image of a unit area must be recorded in a single relative scan between the recording head and the recording medium. Therefore, compared to multi-pass recording, which records the image by applying the reaction solution or ink to the recording medium in multiple stages, single-pass recording cannot overlap the dot arrangement in multiple passes, which leads to problems such as white spots in the image and reduced color reproduction.

[0016] First, to reduce the white areas in the image, we thought that wetting and spreading the ink would be effective, so we created an ink with reduced surface tension and recorded an image. As a result, we obtained some effect, but it was insufficient to meet the level required by the inventors.

[0017] Therefore, in order to clarify the mechanism by which white spots occur, the process of applying the reaction solution and ink to the recording medium was observed. As a result, it was found that the behavior of the ink differed between the parts of the recording medium to which the reaction solution was applied (reaction solution coated parts) and the parts to which the reaction solution was not applied (uncoated parts). In the reaction solution coated parts, when ink is applied, it aggregates at the point of contact with the reaction solution. On the other hand, in the uncoated parts of the reaction solution, when ink is applied, it cannot aggregate at that point and merges with other ink dots. In other words, it was found that in the uncoated parts of the reaction solution, ink dots disappear in the places where ink dots should have been placed, resulting in white spots in the image. Therefore, the inventors have clarified that to achieve high color development, it is more effective to wet and spread the reaction solution over the entire surface of the recording area of ​​the recording medium than to wet and spread the ink.

[0018] One specific method for wetting the entire recording area of ​​a recording medium is to apply a large amount of the reaction solution. However, this increases the drying load on the recorded material, leading to a decrease in productivity. Therefore, there is a need for a reaction solution with low liquid-interface energy and solid-liquid-interface energy that can efficiently wet the entire recording area even with a small amount of solution.

[0019] Next, the inventors focused on surfactants in the reaction solution and investigated methods to efficiently reduce both the liquid interface energy and the solid-liquid interface energy. After examining various surfactants, it was found that using at least two nonionic surfactants with an HLB value difference of 1 or more and an HLB value between 4 and 16 is effective in efficiently reducing the liquid interface energy and the solid-liquid interface energy. The estimated mechanism by which images with high color development were obtained on non-absorbent recording media by using a reaction solution containing at least two of the above nonionic surfactants is described below with reference to Figures 1 and 2.

[0020] Figure 1 is a schematic diagram illustrating the estimated state of nonionic surfactants in reaction solution L applied to a non-absorbent recording medium M from the perspective of HLB values. Figure 1(a) is a schematic diagram of the case where nonionic surfactant H1 with an HLB value of 4 to 16 is used, Figure 1(b) is a schematic diagram of the case where nonionic surfactant H2 with an HLB value of less than 4 is used, and Figure 1(c) is a schematic diagram of the case where nonionic surfactant H3 with an HLB value greater than 16 is used. Furthermore, Figure 2 is a schematic diagram illustrating the estimated state of nonionic surfactants in reaction solution L applied to a non-absorbent recording medium M from the perspective of the difference in HLB values. Figure 2(a) is a schematic diagram of the case where one type of nonionic surfactant H1 with an HLB value of 4 to 16 is used. Figure 2(b) is a schematic diagram of the case where two types of nonionic surfactants H11 and H12 with an HLB value difference of 1 or more and an HLB value of 4 to 16 are used. Figure 2(c) is a schematic diagram showing the case where two nonionic surfactants, H13 and H14, have an HLB value difference of less than 1 and an HLB value between 4 and 16.

[0021] First, to lower the liquid interface energy, it is effective to use a nonionic surfactant H1 with an HLB value between 4 and 16 (Figures 1(a) and 2(a)). If the HLB value is less than 4, the solubility of the nonionic surfactant H2 is low, making it more likely to form micelles in the solution and thus less likely to act on the interface (Figure 1(b)). Also, if the HLB value is greater than 16, the solubility of the nonionic surfactant H3 is high, and it is thought that it dissolves in the solution and thus less likely to act on the interface (Figure 1(c)).

[0022] Furthermore, it has been found that using at least two nonionic surfactants H11 and H12 having an HLB value difference of 1 or more is effective for simultaneously reducing the solid-liquid interfacial energy (Fig. 2(b)). The present inventors consider the reason as follows. The other different nonionic surfactant H12 having a different HLB value penetrates between the molecules of the one same-type nonionic surfactant H11, so that the intermolecular distance between the same-type nonionic surfactant H11 molecules increases. It is considered that this makes it easy to obtain the effect that the nonionic surfactant molecules are arranged at the interface to reduce the solid-liquid interfacial energy (Fig. 2(b)). In contrast, when the difference between the HLB values of the two nonionic surfactants H13 and H14 is less than 1, the nonionic surfactants are compatible with each other and are less likely to be oriented at the interface, so it is considered difficult to obtain the effect of reducing the solid-liquid interfacial energy (Fig. 2(c)). Therefore, the reaction liquid contains at least two nonionic surfactants in which the difference between the highest HLB value and the lowest HLB value is 1 or more, and the HLB values are in the range of 4 to 16. By using this reaction liquid, the present inventors have found a means for developing high color developability even with a small applied amount of the reaction liquid on a non-absorbing recording medium.

[0023] On the other hand, in the fields of commercial printing and industrial printing, recording of images not only on non-absorbing recording media but also on various recording media is required. One example thereof is a low-absorbency recording medium. It has been clarified that when a reaction liquid having low liquid interfacial energy and low solid-liquid interfacial energy is used on a low-absorbency recording medium, unevenness occurs at the edge of an image. This is considered to be a result of the difference in surface tension between the reaction liquid and the ink increasing due to the lowered surface tension of the reaction liquid, which makes convection of the ink on the surface of the recording medium more likely to occur. Accordingly, the surface tension of the ink is lowered, and the surface tension γ of the ink i and the surface tension γ of the reaction liquid r difference between (γ i -γ r ) is set to 9 mN / m or less, the occurrence of convection is suppressed, and even when a reaction liquid with reduced surface tension is used, the occurrence of unevenness at the image edge can be suppressed.

[0024] The unevenness at the edges of the image described above is a phenomenon that occurs specifically when a low-absorption recording medium is used as the recording medium. In the case of ordinary paper, which is a recording medium in which ink and reaction solution penetrate relatively quickly, the reaction solution penetrates rapidly immediately after being applied to the recording medium. Subsequently, the ink applied to the recording medium comes into contact with the reaction solution and then aggregates, while the pigment and aqueous medium also penetrate into the recording medium. As a result, there is no convection of ink on the surface of the recording medium, and there is almost no movement of pigment, so an image with suppressed unevenness is obtained. On the other hand, in the case of non-absorbent recording mediums in which ink and reaction solution are hardly absorbed, the reaction solution hardly penetrates. As a result, the reaction solution and ink come into sufficient contact on the surface of the non-absorbent recording medium, and the viscosity of the ink increases sufficiently, so convection of ink is less likely to occur, and unevenness at the edges of the image is less likely to occur.

[0025] <Inkjet recording method, inkjet recording device, and set of water-based ink and reaction solution> The present invention's inkjet recording method (hereinafter also simply referred to as "recording method") records an image by applying ink and reaction solution to a unit area of ​​a recording medium using an inkjet ejection head, and performing this in a single relative scan between the ejection head and the recording medium. At this time, the time from when the reaction solution is applied to the recording medium until the aqueous ink is applied to the recording medium is 1800 ms or less. This inkjet recording method may include a reaction solution application step of applying the reaction solution to the recording medium, and an ink application step of applying ink to the recording medium so as to overlap at least a portion of the area on the recording medium to which the reaction solution is applied. The reaction solution contains a surfactant. The surfactant includes at least two nonionic surfactants with HLB values ​​in the range of 4 to 16, and the difference between the highest and lowest HLB values ​​of the at least two nonionic surfactants is 1 or more. The aqueous ink also contains resin particles. Furthermore, the surface tension γ of the aqueous ink at 25°C is... i and the surface tension γ of the reaction solution r The difference (γ i -γ r The pressure is 9 mN / m or less. The recording medium is subjected to the Bristow method from the start of contact for 30 ms. 1 / 2The amount of water absorbed up to 10 mL / m² is 2 The recording medium is as follows:

[0026] Furthermore, the inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which aqueous ink and reaction solution are ejected from an inkjet ejection head and applied to a recording medium to record an image. It is an apparatus that is suitably used in the above recording method. In the inkjet recording method and inkjet recording apparatus of the present invention, it is not necessary to cure the image by irradiation with active energy rays or the like.

[0027] The aqueous ink and reaction solution set of the present invention is a set used in an inkjet recording method in which an image is recorded on a recording medium by ejecting an aqueous ink and an aqueous reaction solution containing a reactant that reacts with the aqueous ink from an ejection head. It is a set that is suitably used in the above recording method. The form of the set includes a set of multiple ink cartridges, each independently containing multiple inks (reaction solutions), and an ink cartridge formed by combining multiple ink storage sections, each containing multiple inks (reaction solutions). The set of the present invention is not limited to the above form, but may take any form as long as it is configured to allow the ink and reaction solution to be used in combination.

[0028] (Inkjet recording device) The details of the inkjet recording device will be described below with reference to the drawings. Figure 3 is a schematic diagram showing one embodiment of the inkjet recording device of the present invention. The inkjet recording device of this embodiment is an inkjet recording device that records an image on a recording medium 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 device, respectively. The recording medium is transported in the X direction.

[0029] The inkjet recording apparatus 100 of the embodiment shown in Figure 3 is configured to include a recording unit 1000, a heating unit 2000, a fixing unit 3000, a cooling unit 4000, a reversing unit 5000, and a paper discharge unit 6000. In the recording unit 1000, various liquids are applied to the recording medium 1100, which has been transported from the paper feed device 1400 by the transport member 1300, by the liquid application device 1200. In the heating unit 2000, the liquid applied to the recording medium 1100 is heated by the heating device 2100 to evaporate volatile components such as water in the liquid and dry it. In the fixing unit 3000, the fixing member 3100 is brought into contact with the area of ​​the recording medium 1100 to which the liquid has been applied and heated to promote the fixing of the image to the recording medium 1100. After that, the recording medium 1100 is cooled by the cooling member 4100 of the cooling unit 4000. When recording an image on the reverse side following the front side (recording side), the recording medium 1100 is first inverted by the inversion device 5100 of the inversion unit 5000. Then, after the image is recorded on the reverse side in the same manner as on the front side, it is transported by the transport member 6100 of the paper discharge unit 6000 and loaded into the recording medium storage unit 6200.

[0030] [Records Department] The recording unit 1000 includes a liquid application device 1200. The liquid application device 1200 is composed of a reaction liquid application device 1201 and an ink application device 1202. The reaction liquid application device 1201 uses an inkjet type ejection head. The application of the reaction liquid by the reaction liquid application device 1201 can be done either before or after ink application, as long as it can come into contact with the ink on the recording medium 1100. However, in order to record high-quality images on various recording media with different liquid absorption characteristics, it is preferable to apply the reaction liquid before ink application. The ink application device 1202 uses an inkjet type ejection head (recording head). The ejection method of the ejection head as the liquid application device 1200 can include a method in which a film boiling is generated in the liquid using an electro-thermal converter to form bubbles and eject the liquid, or a method in which a liquid is ejected using an electro-mechanical converter. Among these, it is preferable to use an ejection head that ejects liquid by the action of thermal energy. Such an ejection head is also called a thermal head.

[0031] In the recording method of the present invention, the time from when the reaction solution is applied to the recording medium until the ink is applied to the recording medium is 1800 ms or less. When the time from when the reaction solution is applied to the recording medium until the ink is applied is 1800 ms or less, it becomes easier to suppress unevenness at the edges of the image on low-absorption recording media, and it becomes easier to obtain images with high color development on non-absorption recording media. For the same reason, the time from when the reaction solution is applied to the recording medium until the ink is applied to the recording medium is preferably 550 ms or less, and more preferably 500 ms or less. On the other hand, the time from when the reaction solution is applied to the recording medium until the ink is applied to the recording medium is preferably 40 ms or more, and more preferably 50 ms or more. After the reaction solution is applied to a non-absorption recording medium, it spreads over time. Therefore, a longer time from when the reaction solution is applied until the ink is applied is advantageous for color development because the coverage rate of the reaction solution increases. If the time between the application of the reaction solution to the recording medium and the application of the ink is 50 ms or more, it becomes easier to obtain images with even higher color development on non-absorbent recording media.

[0032] The liquid dispensing device 1200 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 1207 (Figure 5) with discharge ports formed below it (towards the recording medium 1100), and the discharge port surface faces the recording medium 1100 at a very small distance of a few millimeters.

[0033] Multiple ink dispensers 1202 may be provided to dispense each color of ink onto the recording medium 1100. For example, when recording color images using yellow ink, magenta ink, cyan ink, and black ink, four ink dispensers 1202, each dispensing one of the four types of ink, are arranged in a line in the X direction. Hereinafter, the ink and reaction solution may be collectively referred to as "liquid".

[0034] Figure 4 is a perspective view showing an example of a liquid dispensing device. The liquid dispensing device 1200 shown in Figure 4 is a line head, and multiple discharge element substrates 1203, each provided with a row of discharge ports, are arranged in a straight line. Multiple rows of discharge ports are arranged on the discharge element substrate 1203.

[0035] Figure 5 is a cross-sectional perspective view showing an example of a discharge element substrate. The discharge element substrate 1203 shown in Figure 5 comprises a discharge port forming member 1206 with an opening for a discharge port 1204, and a substrate 1205 on which a discharge element (not shown) is disposed. By stacking the discharge port forming member 1206 and the substrate 1205, a first flow path 1208 and a second flow path 1209 through which liquid flows are formed. The first flow path 1208 is the region from the inlet 1212, through which liquid flows in from the inlet passage 1210, to the portion between the discharge port 1204 and the discharge element (Figure 6, liquid chamber 1508). The second flow path 1209 is the region from the portion between the discharge port 1204 and the discharge element (Figure 6, liquid chamber 1508) to the outlet 1213 through which liquid flows out to the outlet passage 1211. For example, by creating a pressure difference between the inlet 1212 and the outlet 1213, such as a high-pressure inlet 1212 and a low-pressure outlet 1213, the liquid can be made to flow from the high-pressure area to the low-pressure area (in the direction of the arrow in Figure 5). The liquid that has passed through the inlet passage 1210 and the inlet 1212 enters the first flow path 1208. Then, the liquid that has passed through the section between the discharge port 1204 and the discharge element (Figure 6, liquid chamber 1508) flows through the second flow path 1209 and the outlet 1213 to the outlet passage 1211.

[0036] [Supply system] Figure 6 is a schematic diagram showing an example of a liquid supply system, such as ink. The supply unit 1500 of the liquid supply device 1200 shown in Figure 6 is composed of a first circulation pump (high pressure side) 1501, a first circulation pump (low pressure side) 1502, a sub-tank 1503, and a second circulation pump 1505. The sub-tank 1503, which is connected to the main tank 1504, the liquid storage unit, has an atmospheric communication port (not shown), making it possible to discharge air bubbles mixed in the liquid to the outside of the circulation system. The sub-tank 1503 is also connected to a replenishment pump 1506. Liquid is consumed by the liquid supply device 1200 by discharging (discharging) the liquid from the discharge port, such as for image recording or suction recovery. The replenishment pump 1506 transfers liquid corresponding to the amount consumed from the main tank 1504 to the sub-tank 1503.

[0037] The first circulation pump (high pressure side) 1501 and the first circulation pump (low pressure side) 1502 move the liquid in the liquid supply device 1200, which has been discharged from the connection part (inlet part) 1507, to the sub-tank 1503. It is preferable to use positive displacement pumps with a quantitative liquid delivery capacity as the first circulation pump (high pressure side) 1501, the first circulation pump (low pressure side) 1502, and the second circulation pump 1505. Examples of such positive displacement pumps include tube pumps, gear pumps, diaphragm pumps, and syringe pumps. When the discharge element substrate 1203 is driven, the first circulation pump (high pressure side) 1501 and the first circulation pump (low pressure side) 1502 can cause the liquid to flow from the common inlet passage 1514 towards the common outlet passage 1515.

[0038] The negative pressure control unit 1509 is equipped with two pressure adjustment mechanisms, each with a different control pressure. The pressure adjustment mechanism (high pressure side) 1510 and the pressure adjustment mechanism (low pressure side) 1511 are connected to a common inlet passage 1514 and a common outlet passage 1515 in the discharge element substrate 1203, respectively, via a supply unit 1513 equipped with a filter 1512 that removes foreign matter from the liquid. The discharge element substrate 1203 is provided with a common inlet passage 1514, a common outlet passage 1515, and inlet passages 1210 and 1211 that communicate with the liquid chamber 1508, which is the part between the discharge port 1204 and the discharge element (not shown). Since the inlet passage 1210 and 1211 communicate with the common inlet passage 1514 and the common outlet passage 1515, respectively, a flow occurs in which a portion of the liquid flows from the common inlet passage 1514 through the inside of the liquid chamber 1508 to the common outlet passage 1515 (arrow in Figure 6). The arrows in Figure 5 indicate the flow of liquid inside the liquid chamber 1508. That is, as shown in Figure 5, the liquid in the first channel 1208 flows through the outlet 1204 and the discharge element to the second channel 1209.

[0039] As shown in Figure 6, a pressure regulating mechanism (high pressure side) 1510 is connected to the common inlet passage 1514, and a pressure regulating mechanism (low pressure side) 1511 is connected to the common outlet passage 1515, so a pressure difference is created between the inlet passage 1210 and the outlet passage 1211. As a result, a pressure difference is also created between the inlet 1212 (Figure 5) which communicates with the inlet passage 1210 and the outlet 1213 (Figure 5) which communicates with the outlet passage 1211. When a liquid is flowed by the pressure difference between the inlet 1212 and the outlet 1213, it is preferable to control the liquid flow velocity (mm / s) to be between 0.1 mm / s and 10.0 mm / s.

[0040] [Conveyor System] As shown in Figure 3, the recording unit 1000 is configured to include a liquid application device 1200 and a transport member 1300 for transporting the recording medium 1100. The liquid application device 1200 applies reaction liquid and ink to desired positions on the recording medium 1100 transported by the transport member 1300. Each liquid application device receives an image signal of the recorded data and applies the necessary reaction liquid and ink to each position. Figure 3 shows the transport member 1300 in the form of a transport belt, but spurs, transport cylinders, etc., may be used as long as they have the function of transporting the recording medium 1100. To improve transport accuracy, the transport member 1300 can be made of a material that can fix the recording medium 1100 in place. Specifically, methods include providing holes in the transport member 1300 and fixing the recording medium 1100 by suction from the back side, or forming the transport member 1300 of an appropriate material and fixing the recording medium 1100 by electrostatic attraction.

[0041] [Heating section] As shown in Figure 3, the heating unit 2000 is configured to include a heating device 2100 and a transport member 2200. The recording medium 1100, to which the reaction liquid and ink have been applied and an image has been recorded, is transported by the transport member 2200 and heated by the heating device 2100 to evaporate the liquid component of the image and dry it. Preferably, between the ink application step and the fixing step, there is further a drying step in which the ink-applied recording medium is heated non-contact to dry the ink. Having such a drying step makes it possible to effectively suppress deformation (cockling and curling) of the recording medium 1100.

[0042] The heating device 2100 can have any configuration as long as it can heat the recording medium 1100, and various conventionally known devices such as hot air dryers and heaters can be used. In particular, 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 1100 and using a mechanism to send hot air, drying efficiency can be easily increased and image unevenness can be more easily suppressed.

[0043] Regarding the heating method, the recording medium 1100 may be heated from the side where the reaction solution and ink are applied (the recording surface (front)), from the back side, or from both sides. The transport member 2200 may also be provided with a heating function. Figure 3 shows a transport member 2200 using a transport belt, but spurs, transport cylinders, etc., may be used as long as they have the function of transporting the recording medium 1100. From the viewpoint of suppressing deformation of the recording medium 1100 due to heating, it is preferable to have a configuration in which the recording medium 1100 is transported while being in close contact with the transport member 2200 by blowing air from the heating unit 2000, or to provide a mechanism for fixing the recording medium to the transport member 2200. Specifically, examples include a method of providing holes in the transport member 2200 and fixing the recording medium 1100 by suction from the back side, or a method of forming the transport member 2200 with an appropriate material and fixing the recording medium 1100 by electrostatic attraction.

[0044] The heating temperature should be set so as not to over-dry the recording medium 1100, while rapidly evaporating the liquid components and suppressing deformation of the recording medium 1100. The temperature of the drying means can be set so that the recording medium reaches the desired temperature, taking into account the transport speed and ambient temperature. Specifically, the temperature of the drying means (such as hot air) is preferably 40°C to 100°C, and more preferably 60°C to 80°C. When heating the recording medium 1100 by blowing heated gas, the wind speed is preferably 1 m / s to 100 m / s. The temperature of the wind, such as hot air, can be measured using a K-type thermocouple thermometer. A specific measuring instrument could be, for example, the product name "AD-5605H" (manufactured by A&D).

[0045] (drying process) Figure 7 is a schematic diagram showing another example of the heating section. Here, we will explain the differences between this section and Figure 3 and the heating section described above. The heating section 2000 shown in Figure 7 comprises a first heating device 2101 and a second heating device 2102, and a first conveying member 2201 and a second conveying member 2202, which are arranged opposite to the first heating device 2101 and the second heating device 2102, respectively.

[0046] The first transport member 2201 does not have a mechanism for suctioning and fixing the recording medium 1100. Instead, the recording medium 1100 is pressed against the first transport member 2201 by the hot air from the first heating device 2101, thereby transporting the recording medium 1100. This allows for accurate transfer of the recording medium 1100 from the transport member 1300 (Figure 3) to the first transport member 2201, and from the first transport member 2201 to the second transport member 2202. Furthermore, slight differences in the transport speeds of the transport member 1300 (Figure 3) and the first transport member 2201 can be reduced. On the other hand, the second transport member 2202 utilizes a transport belt with holes that allow gas to pass through, and transports the recording medium 1100 while fixing it to the second transport member 2202 by a suction mechanism (not shown).

[0047] Air knives 2300 are positioned between the transport member 1300 (Figure 3) and the first transport member 2201, between the first transport member 2201 and the second transport member 2202, and between the second transport member 2202 and the transport member 3200 (Figure 3). The air pressure from the air knives 2300 suppresses the lifting of the leading edge of the transported recording medium 1100. This prevents the leading edge of the recording medium 1100 from colliding with the first heating device 2101, the second heating device 2102, and the fixing member 3100 (Figure 3), thereby suppressing transport defects.

[0048] The first heating device 2101 and the second heating device 2102 can have the same configuration as the heating device 2100 described above. The temperatures of the first heating device 2101 and the second heating device 2102, and the airflow velocity when heating by blowing heated gas, may be the same or different. In addition, heating may be performed from the first conveying member 2201 and the second conveying member 2202 as needed.

[0049] [Fixing section] As shown in Figure 3, the fixing unit 3000 is a contact-type heating and pressurizing mechanism having a fixing member 3100 as a fixing belt such as an endless belt and a transport member 3200. In the fixing unit 3000, the transport member 3200 transports the recording medium 1100, and the fixing member 3100 is brought into contact with the recording medium 1100 under pressure, heating the liquid such as reaction solution or ink applied to the recording medium 1100. This allows the image to be fixed to the recording medium 1100. After the image is recorded on the recording medium 1100, the liquid components of the reaction solution or ink penetrate the recording medium 1100 or evaporate after passing through the heating unit 2000, and then are fixed in the fixing unit 3000 to complete the image. By heating and pressurizing the recording medium 1100 while it is sandwiched between the fixing member 3100 and the transport member 3200, the image on the recording medium 1100 and the fixing member 3100 come into close contact, and the image is fixed to the recording medium 1100. By using a liquid such as ink containing resin particles and colorants, the resin particles soften and form a film mainly by heating in the fixing unit 3000, and the colorants can be bonded onto the recording medium 1100.

[0050] One method for heating the fixing member 3100 is to install a heat source, such as a halogen heater, inside the roller that drives the fixing member 3100 as a fixing belt. Another method is to install a heat source, such as an infrared heater, in a location separate from the fixing member 3100. Furthermore, these methods may be combined. The transport member 3200 may also be heated as needed. The temperature of the fixing member 3100 can be set so that the surface of the recording medium reaches a desired temperature, taking into account the transport speed and ambient temperature. Specifically, it is preferable to set the temperature of the fixing member 3100 to 50°C or more and 120°C or less, and more preferably to 60°C or more and 110°C or less. The temperature of the contact-type heating and pressing mechanism (fixing member 3100) and the surface temperature of the recording medium immediately after passing through the contact-type heating and pressing mechanism can both be measured using a radiation thermometer. The radiation thermometer should be installed near the end (terminal) of the contact-type heating and pressing mechanism. A specific example of a radiation thermometer is the product name "Radiation Thermometer IT-545S" (manufactured by Horiba, Ltd.).

[0051] When the ink contains resin particles, setting the temperature of the fixing member 3100 to a temperature above the glass transition temperature of the resin particles in the ink softens the resin particles, making it easier to form a film and improving the scratch resistance of the image. When the ink contains wax particles, it is preferable to set the temperature of the fixing member 3100 to a temperature lower than the melting point of the wax constituting the wax particles. This makes it easier for the wax, whose melting is suppressed, to remain on the surface of the image, improving the scratch resistance of the image.

[0052] The nip pressure of the fixing member 3100 and the transport member 3200, that is, the pressure applied to the recording medium when it passes through the contact-type heating and pressurizing mechanism, is preferably 10 Pa or more and 1,000 Pa or less, more preferably 10 Pa or more and 500 Pa or less. It is also particularly preferably 10 Pa or more and 400 Pa or less. The time required for the recording medium to pass through the contact-type heating and pressurizing mechanism (nip time) is preferably 0.25 seconds or more and 5.0 seconds or less, more preferably 0.5 seconds or more and 4.0 seconds or less, and particularly preferably 1.0 second or more and 3.0 seconds or less.

[0053] Figure 8 is a schematic diagram showing another example of a fixing unit. Here, we will explain the differences between this unit and the fixing unit described in Figure 3 and above. The fixing unit 3000 shown in Figure 8 is a contact-type heating and pressurizing mechanism comprising a plurality of fixing rollers 3101 and a plurality of transport members 3201 positioned opposite these fixing rollers 3101. The image is fixed to the recording medium by passing the recording medium 1100, to which a liquid such as ink has been applied, between the fixing rollers 3101 and the transport members 3201. The degree of image fixing to the recording medium can be adjusted by controlling the number of fixing rollers 3101 and transport members 3201, the nip time of the recording medium caused by them, the temperature, and the pressure.

[0054] [Cooling section] The cooling unit 4000 is comprised of a cooling element 4100 and a transport element 4200 (Figure 3). The cooling unit 4000 cools the recording medium 1100, which has become hot after passing through the heating unit 2000 and the fixing unit 3000. The cooling element 4100 can have any configuration as long as it can cool the recording medium 1100, and methods such as air cooling and water cooling can be used. Among these, blowing an unheated gas is preferable from the standpoint of safety and energy efficiency. Furthermore, using a mechanism that incorporates a fan to blow gas onto the recording medium 1100 makes it easier to improve cooling efficiency. The temperature of the cooling means can be set so that the image on the recording medium reaches the desired temperature, taking into account the transport speed and ambient temperature. Specifically, it is preferable to set the temperature of the cooling means (such as blowing air) to 20°C or more and 60°C or less, and more preferably to 25°C or more and 50°C or less. When cooling by blowing gas, it is preferable to set the wind speed to 1 m / s or more and 100 m / s or less. By implementing these conditions, deformation of the recording media 1100 and image sticking (blocking) of the data loaded in the paper output section 6000, which will be described later, can be suppressed.

[0055] [Reversal section] When performing double-sided recording, the recording medium 1100 is inverted using the inversion unit 5000 (Figure 3). The recording medium 1100, with the image recorded on its recording surface (front), passes through the cooling unit 4000, then branches off and is transported, and inverted by the inversion device 5100. The inverted recording medium 1100 is then transported to the paper feed device 1400 of the recording unit 1000 with liquid applied to its back surface (the side opposite to the recording surface (front)).

[0056] [Paper output section] After image recording, the recording medium 1100 is placed in the paper discharge unit 6000 (Figure 3). After single-sided or double-sided recording is performed, the recording medium 1100 passes through the cooling unit 4000, is transported by the transport member 6100, and is finally placed in the recording medium storage unit 6200 in a stacked state. Two or more recording medium storage units 6200 may be provided to accommodate different recording materials, for example.

[0057] (Recording medium) The recording method and recording apparatus of the present invention use a low-absorbency or non-absorbency recording medium (low to non-absorbency recording medium). That is, in the Bristow method, from the start of contact to 30ms 1 / 2 Up to 10 mL / m² of water absorption capacity 2 The following recording media are used. In this disclosure, a low absorption recording media is defined as a recording medium that is used from the start of contact for 30ms in the Bristow method. 1 / 2 Up to 4 mL / m² of water absorption capacity 2 More than 10mL / m 2 The following recording media are defined. Furthermore, a non-absorbent recording medium is defined as a recording medium from the start of contact for 30ms in the Bristow method. 1 / 2 Up to 4 mL / m² of water absorption capacity 2 Recording media are defined as those with a water absorption capacity of less than 10 mL / m². The Bristow method is described in JAPAN TAPPI Paper and Pulp Test Method No. 51, "Test Method for Liquid Absorption of Paper and Paperboard". Recording media for inkjet recording (glossy paper, matte paper, etc.) that have a coating layer (ink-receiving layer) made of inorganic particles, and plain paper that does not have a coating layer, have a water absorption capacity of 10 mL / m². 2 It is an absorbent recording medium that exceeds [a certain limit].

[0058] 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 side 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.

[0059] When ink containing resin particles is applied to a non-absorbent recording medium, components such as water and water-soluble organic solvents evaporate, concentrating the resin particles. This promotes the fusion of the concentrated resin particles, improving the intensity of the recorded image. In contrast, when ink is applied to a recording medium with high liquid absorption, the fusion of the resin particles is not easily promoted, and the image intensity does not improve. In this specification, "recording medium" refers to a recording medium on which an image is recorded, not a transfer medium.

[0060] (Reaction solution) The recording method of the present invention may include 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 in which aqueous ink is applied to the recording medium. The components used in the reaction solution will be described in detail below.

[0061] [Reactive agent] The reaction solution reacts with the ink upon contact, causing the components in the ink (components with anionic groups, such as resins, surfactants, and self-dispersing pigments) to aggregate, and contains a reactant. The presence of the reactant destabilizes the state of the components with anionic groups in the ink when the ink and reactant come into contact on the recording medium, thereby promoting ink aggregation. Examples of reactants include polyvalent metal ions, cationic components such as cationic resins, and organic acids. The reactant may be used alone or in combination of two or more types.

[0062] Examples of polyvalent metal ions that make up polyvalent metal salts include Ca 2+ Cu 2+ Ni 2+ Mg 2+ Sr 2+ Ba 2+ , and Zn 2+ Divalent metal ions such as Fe 3+ , Cr 3+ , Y 3+ , and Al 3+ Examples of trivalent metal ions include the following. To include polyvalent metal ions in the reaction solution, a water-soluble polyvalent metal salt (which may also be a hydrate) composed of a polyvalent metal ion and an anion can be used. Examples of anions include Cl - , Br - , I - , - ClO2 - ClO3 - ClO4 - NO2 -NO3 - SO4 2- CO3 2- , HCO3 - , PO4 3- HPO4 2- , and H2PO4 - Inorganic anions such as HCOO - , (COO - )2, COOH(COO - ), CH3COO - C2H5COO - CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - Examples of organic anions include:

[0063] When polyvalent metal ions are used as a reactant, the content (mass%) of the polyvalent metal salt in the reaction solution is preferably 1.0% by mass or more and 20.0% by mass or less, based on the total mass of the reaction solution. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass%) of polyvalent metal salt" in the reaction solution means the "content (mass%) of the anhydrous polyvalent metal salt," excluding water as the hydrate.

[0064] 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.

[0065] The reaction solution containing organic acids 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.

[0066] [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 a water-soluble organic solvent, as described later, which can be incorporated into the ink. The water content (mass%) in the reaction solution is preferably 65.0% by mass or more and 98.0% by mass or less, and more preferably 70.0% by mass or more and 95.0% by mass or less, based on the total mass of the reaction solution.

[0067] Examples of water-soluble organic solvents that can be suitably included in the reaction solution include alkanediols such as 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; amino acids such as β-alanine and trimethylglycine; sulfonyl compounds such as bis(2-hydroxyethyl)sulfone; alkylene glycols such as triethylene glycol, tetraethylene glycol, tripropylene glycol, and polyethylene glycol with a number average molecular weight of about 200 to 1,000; and sugars such as sorbitol. One or more of these can be included in the reaction solution. When a water-soluble organic solvent is included in the reaction solution, the content (mass%) of the water-soluble organic solvent in the reaction solution is preferably 0.5% by mass or more and 30.0% by mass or less, and more preferably 1.0% by mass or more and 25.0% by mass or less, based on the total mass of the reaction solution.

[0068] The water-soluble organic solvents described above have the effect of lowering the surface tension of the liquid immediately after it is applied to the recording medium, that is, immediately after the interface is formed. In this disclosure, as a method for simulating the surface tension of the reaction solution immediately after the interface is formed, a method of measuring the surface tension of a reaction solution with a composition in which the surfactant is replaced with water is used. At this time, the inventors have found that it is preferable for the surface tension of the liquid in which the surfactant of the reaction solution is replaced with water to be 60 mN / m or higher at 25°C. When the surface tension of the liquid in which the surfactant of the reaction solution is replaced with water is 60 mN / m or higher at 25°C, the reaction solution immediately after it is applied to the recording medium becomes less likely to penetrate the recording medium, and unevenness at the image edges of low-absorption recording media is further suppressed. The surface tension of the liquid in which the surfactant of the reaction solution is replaced with water is the value of the surface tension of the liquid prepared by mixing the components of the reaction solution excluding the surfactant. The surface tension of the liquid in which the surfactant of the reaction solution is replaced with water at 25°C is the static surface tension measured by the platinum plate method. Furthermore, at 25°C, the surface tension of the reaction solution obtained by replacing the surfactant with water can be adjusted to a range of 60 mN / m or more by adjusting the type and amount of water-soluble organic solvent.

[0069] [Surfactants] The reaction solution contains a nonionic surfactant. A surfactant is a molecule having a hydrophobic part and a hydrophilic part, and significantly reduces the static surface tension of a liquid. The surfactant included in the reaction solution contains at least two nonionic surfactants with HLB values ​​in the range of 4 to 16, and the difference between the highest and lowest HLB values ​​of these at least two nonionic surfactants is 1 or more. Furthermore, it is preferable that the upper limit of the difference in HLB values ​​of these at least two nonionic surfactants is 12 or less. From the viewpoint of making it easier to record images with even higher color development on a non-absorbent recording medium, it is preferable that all of the above at least two nonionic surfactants have HLB values ​​in the range of 8 to 16.

[0070] In this specification, the "HLB value" of nonionic surfactants is a value determined by the Griffin method, and is calculated based on the formula: HLB value = 20 × (formula weight of hydrophilic group of surfactant) / (molecular weight of surfactant). The HLB value determined by the Griffin method is a physical property value that represents the degree of hydrophilicity or lipophilicity of nonionic surfactants, and takes a value of 0 to 20. A smaller HLB value indicates higher lipophilicity, and a larger HLB value indicates higher hydrophilicity.

[0071] Examples of surfactants include hydrocarbon surfactants, fluorinated surfactants, and silicone surfactants. Examples of hydrocarbon surfactants include acetylene glycol ethylene oxide adducts, polyethylene glycol alkyl ethers, and polyoxyethylene polyoxypropylene block polymers. Examples of fluorinated surfactants include perfluoroalkyl ethylene oxide adducts. Examples of silicone surfactants include polyether-modified siloxane compounds.

[0072] In particular, the reaction solution preferably contains a hydrocarbon-based surfactant and a silicone-based surfactant. The presence of a hydrocarbon-based surfactant and a silicone-based surfactant in the reaction solution further enhances the color development of images on non-absorbent recording media. From this viewpoint, it is more preferable that at least two nonionic surfactants, the difference between the highest HLB value and the lowest HLB value being 1 or more, and having an HLB value in the range of 4 to 16, include a silicone-based surfactant and a hydrocarbon-based surfactant. Furthermore, it is even more preferable that the above at least two nonionic surfactants are a combination of a silicone-based surfactant and a hydrocarbon-based surfactant. In addition, it is preferable that the above at least two nonionic surfactants in the reaction solution include a first nonionic surfactant and a second nonionic surfactant, and that the mass ratio of the content of the first nonionic surfactant to the content of the second nonionic surfactant in the reaction solution is 1 / 5 or more and 5 / 1 or less. In other words, it is preferable that the mass ratio of the content of one of the above at least two types of nonionic surfactants (first nonionic surfactant) to the content of the other nonionic surfactant (second nonionic surfactant) is 0.2 or more and 5.0 or less. By setting the mass ratio of the content of the above at least two types of nonionic surfactants in the reaction solution to 1 / 5 or more and 5 / 1 or less, it becomes easier to obtain the effect of lowering the solid-liquid interface energy between the reaction solution and the recording medium, and the color development of images on non-absorbent recording media becomes easier to obtain. Furthermore, if the reaction solution contains three or more types of nonionic surfactants, it is preferable that the mass ratio of the content of at least two of those nonionic surfactants is 1 / 5 or more and 5 / 1 or less. In this case, it is even more preferable that the mass ratio of the content of two types of nonionic surfactants in all combinations of the three or more types of nonionic surfactants is 1 / 5 or more and 5 / 1 or less.

[0073] The reaction solution may further contain various surfactants other than nonionic surfactants with an HLB value of 4 to 16 (other surfactants). Examples of other surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Furthermore, the other surfactants may be hydrocarbon surfactants, fluorine-based surfactants, silicone-based surfactants, etc., with HLB values ​​outside the above range. The total content (mass%) of surfactants (nonionic surfactants and other surfactants) in the reaction solution is preferably 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the reaction solution. Furthermore, the proportion of the content of at least two of the above-mentioned surfactants in the total surfactant content of the reaction solution is preferably 80.0% by mass or more and 100.0% by mass or less, and more preferably 90.0% by mass or more and 100.0% by mass or less.

[0074] [Other ingredients] The reaction solution may contain various other components as needed. Examples of other components include those similar to those described later that can be included in the ink.

[0075] [Surface tension of the reaction solution] The reaction solution is an aqueous reaction solution applied to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension γ of the reaction solution at 25°C. r The surface tension of the reaction solution is preferably 20 mN / m or more and 60 mN / m or less, and more preferably 30 mN / m or less. When the surface tension of the reaction solution at 25°C is 30 mN / m or less, the reaction solution spreads easily on the recording medium, and the coverage of the reaction solution on the recording medium tends to be high, making it easier to obtain sufficient color development. The surface tension of the reaction solution can be measured at 25°C using the platinum plate method.

[0076] [Other physical properties of the reaction solution] The viscosity of the reaction solution at 25°C is preferably between 1.0 mPa·s and 10.0 mPa·s. The pH of the reaction solution at 25°C is preferably between 5.0 and 9.5, and more preferably between 6.0 and 9.0.

[0077] (ink) The ink used in the recording method of the present invention is an inkjet-compatible water-based ink. The components of the ink will be described in detail below.

[0078] [Colorants] The ink preferably contains a colorant. Pigments and dyes can be used as the colorant. In particular, the ink preferably contains a pigment. The colorant content (mass%) in the ink is preferably 0.1% 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 total mass of the ink.

[0079] Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, and dioxazine. Pigments may be used individually or in combination of two or more.

[0080] As for the dispersion method of the pigment, resin-dispersed pigments using a resin as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with resin or the like can be used. It is also possible to use a combination of pigments with different dispersion methods from among these. In particular, it is preferable to use resin-dispersed pigments in which the resin as a dispersant is physically adsorbed to the surface of the pigment particles, rather than resin-bonded pigments or microcapsule pigments.

[0081] For the resin dispersant used to disperse the pigment in an aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium through the action of anionic groups. As the resin dispersant, a resin having anionic groups can be used, and it is more preferable to use a resin such as those described later, and among them, a water-soluble resin. The pigment content (mass%) in the ink is preferably 0.3 times or more and 10.0 times or less by mass ratio to the resin dispersant content.

[0082] Self-dispersing pigments can be those in which anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are bonded directly to the particle surface of the pigment or via other atomic groups (-R-). The anionic group may be either acidic or salt-type, and if it is salt-type, it may be in a partially dissociated state or a fully dissociated state. When the anionic group is salt-type, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium. Specific examples of other atomic groups (-R-) include linear or branched alkylene groups with 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Combinations of these groups may also be used.

[0083] It is preferable to use dyes that have anionic groups. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone. Dyes may be used individually or in combination of two or more. The colorant is preferably a pigment, and more preferably a resin-dispersed pigment or a self-dispersing pigment.

[0084] [Resin particles] The ink contains resin particles. When the ink contains resin particles, it becomes easier for the ink to thicken upon contact with the reaction solution, which helps to suppress unevenness at the image edges on low-absorption recording media. Examples of resins that make up the resin particles include acrylic resins, urethane resins, olefin resins, and polyester resins.

[0085] The resin particle content (mass%) in the ink is preferably 0.1% to 15.0% by mass, and more preferably 1.0% to 10.0% by mass, based on the total mass of the ink. The resin particle content (mass%) in the aqueous ink is preferably 1.5 times or more, more preferably 1.7 times or more, and preferably 10.0 times or less, relative to the pigment content (mass%). When the mass ratio of the resin particle content to the pigment content in the ink is 1.5 times or more, the ink in contact with the reaction solution tends to thicken more easily, further suppressing unevenness at the image edges on low-absorption recording media. The resin particles exist in the ink in a dispersed state, i.e., in the form of a resin emulsion. It is preferable that the resin particles do not contain colorants.

[0086] In this specification, "resin particles" refers to resins that do not dissolve in the aqueous medium that constitutes the ink, and specifically means 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. On the other hand, "water-soluble resin" refers to resins that can dissolve in the aqueous medium that constitutes the ink, and specifically means resins that can exist in the aqueous medium in a state in which particles whose particle size can not be measured by dynamic light scattering are not formed. "Resin particles" can also be rephrased as "water-dispersible resin (water-insoluble resin)".

[0087] The acid value of the resin constituting the resin particles is preferably 5 mg KOH / g or more and 100 mg KOH / g or less. The weight-average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 3,000,000 or less, and more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D50) of the resin particles measured by dynamic light scattering is preferably 50 nm or more and 500 nm or less. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particle that, when accumulated from the smallest particle diameter side, is 50% of the total volume of the measured particles in the particle diameter integration curve. The volume-based cumulative 50% particle diameter of the resin particles can be measured using the dynamic light scattering particle size analyzer and measurement conditions described above. The glass transition temperature of the resin particles is preferably 40°C or more and 120°C or less, and more preferably 50°C or more and 100°C or less. The glass transition temperature (°C) of resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not need to contain colorants.

[0088] [Other resins] Ink can contain resins other than the resin particles mentioned above. By using resin-containing ink, it is possible to record images with improved scratch resistance. Resins can be added to ink (i) to stabilize the dispersion state of pigments, i.e., as a resin dispersant or its auxiliary agent. They can also be added to ink (ii) to improve various properties of the recorded image.

[0089] The resin content (mass%) in the ink is preferably 0.1% to 20.0% by mass, and more preferably 0.5% to 15.0% by mass, based on the total mass of the ink. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can dissolve in an aqueous medium, and may be used alone or in combination of two or more types.

[0090] [Composition of the resin] Examples of resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid and (meth)acrylate are even more preferred.

[0091] 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 monomer selected from the group consisting of monomers having an aromatic ring and (meth)acrylic acid ester monomers are preferred. In particular, 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 are preferred. Because these resins readily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

[0092] 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.

[0093] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[0094] [Properties of the resin] In this specification, "water-soluble resin" means that when the resin is neutralized with an amount of alkali equivalent to its acid value, it exists in an aqueous medium without forming particles whose particle size can be measured by dynamic light scattering. Whether or not a resin is water-soluble can be determined by the following method. First, prepare a liquid containing the resin (resin solids content: 10% by mass) neutralized with an alkali equivalent to its acid value (such as sodium hydroxide or potassium hydroxide). Next, prepare a sample solution by diluting the prepared liquid 10 times (by volume) with pure water. Furthermore, if no particles with a specific particle size are detected when the particle size of the resin in the sample solution is measured by dynamic light scattering, the resin can be determined to be water-soluble. For example, the measurement conditions can be: SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds. A particle size analyzer using dynamic light scattering (for example, product name "UPA-EX150," manufactured by Nikkiso) can be used as the particle size distribution analyzer. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those described above.

[0095] 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.

[0096] [Aqueous medium] The ink 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 (by mass) in the aqueous ink is preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink.

[0097] Furthermore, the content (by mass) of water-soluble organic solvents in the aqueous ink is preferably 3.0% by mass or more and 45.0% 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 solvents, and sulfur-containing solvents, can be used. One type of water-soluble organic solvent may be used alone, or two or more types may be used in combination.

[0098] [Other ingredients] The ink may contain various other components as needed. Examples of other components include various additives such as defoamers, surfactants, pH adjusters, viscosity modifiers, rust inhibitors, preservatives, fungicides, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain the reagents included in the reaction solution.

[0099] [Ink surface tension] The ink is an aqueous ink used 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 32 mN / m or less, and more preferably 28 mN / m or less. A surface tension of 28 mN / m or less at 25°C increases the wettability of the ink, making it easier to obtain images with higher color development. The surface tension of the ink at 25°C is preferably 18 mN / m or more. The surface tension of the ink can be measured at 25°C using the platinum plate method.

[0100] [Other physical properties of ink] The viscosity of the ink at 25°C is preferably between 1.0 mPa·s and 10.0 mPa·s. The pH of the ink at 25°C is preferably between 7.0 and 9.5, and more preferably between 8.0 and 9.5.

[0101] <Relationship between the surface tension of the reaction solution and the surface tension of the ink> Surface tension γ of water-based ink at 25°C i and the surface tension γ of the reaction solution r The difference (γ i -γ r The surface tension of the ink is γ ≤ 9 mN / m. When the difference between the surface tension of the ink and the surface tension of the reaction solution exceeds 9 mN / m, ink convection is more likely to occur on the surface of the recording medium, causing unevenness at the edges of the image in low absorption recording media. From the viewpoint of further suppressing unevenness at the edges of the image in low absorption recording media, the surface tension of the ink γ i and the surface tension γ of the reaction solution r The difference (γ i-γ r ) is preferably 5 mN / m or less.

[0102] <Average particle size of particles when the reaction solution and ink are mixed> This disclosure uses a method for simulating the reactivity caused by contact between the reaction solution and the ink by measuring the average particle size of particles in a mixture when the reaction solution and ink are mixed in a mass ratio of 1:1. The particles in the mixture when the reaction solution and ink are mixed in a mass ratio of 1:1 are aggregates of components in the ink that are formed by contact between the ink and the reaction solution. Preferably, the average particle size of the particles in the mixture when the reaction solution and ink are mixed in a mass ratio of 1:1 is 7 μm or more. When the above average particle size is 7 μm or more, ink droplets applied adjacent to the reaction solution are less likely to flow towards the reaction solution, thus increasing the effect of suppressing the granularity of the image. Furthermore, it is even more preferable that the average particle size of the particles in the mixture when the reaction solution and ink are mixed in a mass ratio of 1:1 is 15 μm or more and 40 μm or less. When the above average particle size is 15 μm or more, the occurrence of ink convection on the surface of the recording medium is suppressed, which not only suppresses the granularity of the image but also suppresses the occurrence of unevenness at the edges of the image. On the other hand, when the average particle size is 40 μm or less, the effect of suppressing the graininess of the image is enhanced while maintaining the spread of the ink dots. Also, when the average particle size is 40 μm or less, the ink that comes into contact with the reaction solution aggregates in a state where it is somewhat wetted and spread out, so white spots and crack-like irregularities in the image are less likely to occur, improving color development. The average particle size can be measured using a laser diffraction particle size distribution analyzer with a sample of a mixture of the reaction solution and ink mixed in a mass ratio of 1:1.

[0103] The average particle size of particles in a mixture when a reaction solution and ink are mixed in a mass ratio of 1:1 can be adjusted by, for example, the content and type of reactant contained in the reaction solution; the content, molecular weight, and cationicity of cationic resins that can be used as reactants; and the valency of organic acids that can be used as reactants. Furthermore, if the reaction solution is kept constant to a predetermined composition, the average particle size can also be adjusted by the ink used in combination with the reaction solution. For example, if the ink contains a self-dispersing pigment, the average particle size can be adjusted by the density of anionic groups such as carboxylic acid groups that are directly or via other atomic groups bonded to the surface of the pigment particles. Also, if the ink contains a resin-dispersed pigment, the average particle size can be adjusted by the acid value and content of the resin dispersant used. Furthermore, if the ink contains resin particles or water-soluble resins, the average particle size can also be adjusted by the acid value and content of the resin particles and the water-soluble resin. In addition, the average particle size can also be adjusted by surfactants. Means for increasing the average particle size include, for example, increasing the density of anionic groups such as carboxylic acid groups in self-dispersing pigments, increasing the acid value of resin dispersants in resin-dispersed pigments, or increasing the acid value of resin particles or water-soluble resins. [Examples]

[0104] 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.

[0105] <Preparation of reaction solution> Each component (unit: %) shown in the upper row of Table 1 (Tables 1-1 and 1-2) was mixed and thoroughly stirred, then pressure filtered through a 3.0 μm pore size cellulose acetate filter (Advantec) to prepare each reaction solution. In Table 1, "silicone-based surfactants" are surfactants having the chemical structure of formula (1) below. Silicone-based surfactant 1 is a nonionic surfactant with x = 11 in formula (1) and an HLB value of 11. Silicone-based surfactant 2 is a nonionic surfactant with x = 12 in formula (1) and an HLB value of 12. "Hydrogen-based surfactants" are shown in Table 2. These hydrocarbon-based surfactants are nonionic surfactants. "Proxel GXL(S)" is the trade name of a preservative manufactured by Arch Chemicals. When the reaction solution contains three types of nonionic surfactants, the "Difference in HLB values ​​of two types of surfactants" in Table 1 indicates the difference between the highest and lowest HLB values ​​of the three types of nonionic surfactants. Furthermore, the "mass ratio of the content of the two types of surfactants" in Table 1 in the above case represents the value when the mass ratio of the content of the two types of nonionic surfactants is the largest among the three types of nonionic surfactants.

[0106] At 25°C, the surface tension of the reaction solution was measured by mixing and stirring all components except the surfactants listed in Table 1 (silicone-based surfactants and hydrocarbon-based surfactants). The surface tension of the reaction solution was measured by mixing and stirring all components listed in Table 1. The surface tension values ​​are those measured using the platinum plate method with an automatic surface tensimeter (DY-300 model; manufactured by Kyowa Interface Science).

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[0111] <Preparation of Pigment Dispersion> (Pigment dispersion) A styrene-ethyl acrylate-acrylic acid copolymer (Resin 1) with an acid value of 150 mg KOH / g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of Resin 1 were neutralized with potassium hydroxide equimolar to its acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of Resin 1 with a resin (solids) content of 20.0%. 15.0 parts of pigment (CI Pigment Red 122), 30.0 parts of the aqueous solution of Resin 1, and 55.0 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of 0.3 mm diameter zirconia beads were placed in a batch-type vertical sand mill (manufactured by AIMEX) and dispersed for 5 hours while cooling with water. After removing coarse particles by centrifugation, the mixture was pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare a pigment dispersion with a pigment content of 15.0% and a resin dispersant (Resin 1) content of 6.0%.

[0112] <Manufacturing of resin particles> (Resin particles) In a four-necked flask equipped with a stirrer, reflux condenser, and nitrogen gas inlet tube, 74.0 parts of deionized water and 0.2 parts of potassium persulfate were mixed. An emulsion was then prepared by mixing 24.0 parts of ethyl methacrylate, 1.5 parts of methacrylic acid, and 0.3 parts of a reactive surfactant. The reactive surfactant used was "ADEKA Soap ER20" (manufactured by ADEKA, nonionic surfactant, 20 moles of ethylene oxide groups added). Under a nitrogen atmosphere, the prepared emulsion was added dropwise to the above four-necked flask over 1 hour, and the polymerization reaction was carried out at 80°C with stirring for 2 hours. After cooling to 25°C, ion-exchanged water and an aqueous solution containing potassium hydroxide equimolar to the acid value of the resin particles were added to prepare an aqueous dispersion of resin particles 1 with a resin particle (solid content) of 40.0%.

[0113] <Preparation of aqueous solutions of water-soluble resins> (Aqueous solution of water-soluble resin) A styrene-ethyl acrylate-acrylic acid copolymer (Resin 1) with the same acid value of 150 mg KOH / g and weight-average molecular weight of 8,000 as used in the preparation of the pigment dispersion described above was prepared. 20.0 parts of Resin 1 were neutralized with potassium hydroxide equimolar to its acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of Resin 1 with a resin (solids) content of 20.0%.

[0114] <Ink preparation> Each ink was prepared by mixing the components (in %) shown in the upper part of Table 3 (Tables 3-1 and 3-2), stirring thoroughly, and then pressure filtering through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec). "Acetylenel E60" shown in Table 3 is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals, as also shown in Table 2. "NIKKOL BO-50V" is the trade name of a nonionic surfactant (polyoxyethylene oleyl ether) manufactured by Nikko Chemicals. "Silicone-based surfactant 1" is a nonionic surfactant in which x in formula (1) is 11 and the HLB value is 11, as described above. It is a surfactant having the chemical structure x=11 and HLB=11 in formula (1). The surface tension of the inks shown in the lower part of Table 3 was measured by measuring the surface tension of the sample prepared by mixing all the components shown in Table 3 and stirring. The surface tension values ​​shown are those measured using an automatic surface tension meter (DY-300 model; manufactured by Kyowa Interface Science Co., Ltd.) and the platinum plate method. Furthermore, the "B / P value (times)" shown in the lower section of Table 3 represents the mass ratio of the resin particle content B in the ink to the pigment content P in the ink.

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[0117] <Measurement of physical properties> (Average particle size when mixed) The average particle size of particles in the mixture obtained by mixing the reaction solution and ink used in the following examples and comparative examples in a 1:1 (mass ratio) was measured as follows. First, the reaction solution was added to the ink in the above mass ratio to obtain the mixture. Then, the mixture was stirred for 90 seconds at a setting of 2.5 using a magnetic stirrer (product name "HS-360", manufactured by AS ONE), and the average particle size was measured. A laser diffraction particle size analyzer (product name "SALD-2300", manufactured by Shimadzu Corporation) was used to measure the average particle size.

[0118] <Recording medium> The following recording media 1-3 were prepared. • Recording medium 1: Product name "PETWH50 PAT 1 9K" (Lintec, material: PET, 30ms from the start of contact in the Bristow method) 1 / 2 The amount of water absorbed up to this point is 0 mL / m². 2 More than 3mL / m 2 (Within the following range) • Recording medium 2: Product name "Art PW8E Shiro" (Lintec, 30ms from the start of contact in the Bristow method) 1 / 2 The amount of water absorbed up to 4 mL / m² is 4 mL / m². 2 More than 10mL / m 2 (Within the following range) • Recording medium 3: Product name "High-quality 55PW8K Blue" (Lintec, 30ms from the start of contact in the Bristow method) 1 / 2 The water absorption capacity up to 10 mL / m² is 10 mL / m². 2 (It is super)

[0119] <Rating> Table 4 (Tables 4-1 and 4-2) shows the recording conditions. The types of reaction solutions and inks shown on the left side of Table 4 were combined to form reaction solution and ink sets. The reaction solutions and inks constituting these sets were filled into the reaction solution dispenser 1201 and ink dispenser 1202 of the inkjet recording device 100 having the configuration shown in Figure 3. Using this inkjet recording device 100, images were recorded under the evaluation conditions shown in Table 4. Specifically, the reaction solution and ink were applied to the recording medium in this order in a single pass, and then 80°C hot air from the heating device 2100 was applied to the recording medium to dry the image, and the images used for each evaluation were recorded. In the inkjet recording device 100 used in this embodiment, an image recorded under the condition of applying one 4.0 ng drop of ink to a unit area of ​​1 / 1200 inch × 1 / 1200 inch is defined as having a recording duty cycle of 100%. The "time difference between reaction solution and ink application (ms)" shown in Table 4 is the time from when the reaction solution is applied to the recording medium until the ink is applied to the recording medium. In this invention, "AA," "A," and "B" were defined as acceptable levels, and "C" as an unacceptable level in the evaluation criteria for each item below. The evaluation results are shown on the right side of Table 4.

[0120] (Color development) A reaction solution (recording duty cycle of 20%) and ink (in 10% increments within the range of recording duty cycles from 40% to 110%) were applied to recording medium 1 in this order, and a grayscale image was recorded. The recorded grayscale image was analyzed using a fluorescence spectrophotometer (product name "FD-7", manufactured by Konica Minolta) with a light source D50, field of view of 2 degrees, incident angle of 45 degrees, and reflection angle of 0 degrees, according to the L standards defined by the CIE (International Commission on Illumination). * a * b * L in color systems * a * , b * The following was measured. From the obtained measurements, the saturation (C * The following formula was used to calculate the value. In Reference Examples 1 and 2, as shown in Table 4, recording medium 3 was used instead of recording medium 1 to evaluate the color development. C * ={(a * ) 2 +(b * )2} 1 / 2 C * The required ink application amount (μg / cm 2 ) to obtain an image with a value of 75 was used as a basis, and the color developability of the image was evaluated according to the evaluation criteria shown below. A: The required ink application amount was less than 500 μg / cm 2 . B: The required ink application amount was 500 μg / cm 2 or more and less than 720 μg / cm 2 . C: The required ink application amount was 720 μg / cm 2 or more.

[0121] (Unevenness at image edge) A reaction liquid (recording duty 24%) and an ink (recording duty 160%) were applied in this order to recording medium 2 to record an image. Regarding the recorded image, the unevenness at the image edge was evaluated according to the evaluation criteria shown below from a distance where the unevenness at the image edge can be visually recognized. Note that in Reference Examples 1 and 2, as described in Table 4-2, recording medium 3 was used instead of recording medium 2 to perform the evaluation of unevenness at the image edge. AA: Unevenness was not visually recognized at a distance of 30 cm from the recorded matter. A: Unevenness was visually recognized at a distance of 30 cm from the recorded matter, but the unevenness was not visually recognized at a distance of 40 cm. B: Unevenness was visually recognized at a distance of 40 cm from the recorded matter, but the unevenness was not visually recognized at a distance of 50 cm. C: Unevenness was visually recognized even at a distance of 50 cm from the recorded matter.

[0122] (Graininess) The image recorded in the above evaluation of unevenness at the image edge was observed from distances of 20 cm, 30 cm and 50 cm, and the graininess of the image was evaluated according to the evaluation criteria shown below. Note that in Reference Examples 1 and 2, as described in Table 4-2, recording medium 3 was used instead of recording medium 2 to perform the graininess evaluation. AA: Even when observed from a distance of 20 cm, roughness caused by graininess was not observed, and the image could be viewed as uniform. A: When observed from a distance of 20 cm, roughness due to granularity was observed, but when observed from a distance of 30 cm, roughness due to granularity was not observed, and it appeared uniform. B: When observed from a distance of 50 cm, no roughness due to granularity was observed and the surface appeared uniform. However, when observed from a distance of 30 cm, roughness due to granularity was observed.

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Claims

1. Using an aqueous reaction solution containing an aqueous ink and a reagent that reacts with the aqueous ink, the Bristow method was used for 30 ms from the start of contact. １／２ Up to 10 mL / m² of water absorption capacity ２ An inkjet recording method for recording an image on a recording medium, wherein the application of the aqueous ink and the reaction solution to a unit area is performed in a single relative scan between an inkjet ejection head and the recording medium, wherein the time from when the reaction solution is applied to the recording medium until when the aqueous ink is applied to the recording medium is 1800 ms or less, and the application is performed in a single relative scan between the inkjet ejection head and the recording medium. The reaction solution contains a surfactant, The surfactant comprises at least two nonionic surfactants having an HLB value in the range of 4 to 16. Among the at least two nonionic surfactants mentioned above, the difference between the highest HLB value and the lowest HLB value is 1 or more. The aforementioned water-based ink contains resin particles, The surface tension γ of the aqueous ink at 25°C ｉ and the surface tension γ of the reaction solution ｒ The difference (γ ｉ -γ ｒ An inkjet recording method characterized in that the coefficient of gravity is 9 mN / m or less.

2. The surface tension γ of the reaction solution at 25°C ｒ The inkjet recording method according to claim 1, wherein the density is 30 mN / m or less.

3. The surface tension γ of the aqueous ink at 25°C ｉ The inkjet recording method according to claim 1, wherein the density is 28 mN / m or less.

4. The inkjet recording method according to claim 1, wherein the at least two nonionic surfactants include a silicone-based surfactant and a hydrocarbon-based surfactant.

5. The inkjet recording method according to claim 1, wherein at least two types of nonionic surfactants all have an HLB value in the range of 8 to 16.

6. The inkjet recording method according to claim 1, wherein the at least two nonionic surfactants in the reaction solution include a first nonionic surfactant and a second nonionic surfactant, and the mass ratio of the content of the first nonionic surfactant to the content of the second nonionic surfactant is 1 / 5 or more and 5 / 1 or less.

7. The inkjet recording method according to claim 1, wherein the surface tension of the liquid obtained by replacing the surfactant in the reaction solution with water at 25°C is 60 mN / m or more.

8. The surface tension γ of the aqueous ink at 25°C ｉ and the surface tension γ of the reaction liquid ｒ difference therebetween (γ ｉ −γ ｒ ) is 5 mN / m or less, the inkjet recording method according to claim 1.

9. The aforementioned aqueous ink further contains a pigment, The inkjet recording method according to claim 1, wherein the content (mass%) of the resin particles in the aqueous ink is 1.5 times or more by mass ratio to the content (mass%) of the pigment.

10. The inkjet recording method according to claim 1, wherein the time from when the reaction solution is applied to the recording medium until when the aqueous ink is applied to the recording medium is 50 ms or more.

11. The inkjet recording method according to claim 1, wherein the time from when the reaction solution is applied to the recording medium until when the aqueous ink is applied to the recording medium is 500 ms or less.

12. The inkjet recording method according to claim 1, wherein the average particle size of the particles in the mixture when the reaction solution and the aqueous ink are mixed in a mass ratio of 1:1 is 7 μm or more.

13. The inkjet recording method according to claim 1, wherein the average particle size of the particles in the mixture when the reaction solution and the aqueous ink are mixed in a mass ratio of 1:1 is 15 μm or more and 40 μm or less.

14. Using an aqueous reaction solution containing an aqueous ink and a reagent that reacts with the aqueous ink, the Bristow method was used for 30 ms from the start of contact. １／２ Up to 10 mL / m² of water absorption capacity ２ An inkjet recording apparatus used in an inkjet recording method for recording an image, wherein the application of the aqueous ink and the reaction solution to a unit area of ​​a recording medium is performed in a single relative scan between an inkjet ejection head and the recording medium, wherein the time from when the reaction solution is applied to the recording medium until when the aqueous ink is applied to the recording medium is 1800 ms or less, and the application is performed in a single relative scan between the inkjet ejection head and the recording medium. The reaction solution contains a surfactant, The surfactant comprises at least two nonionic surfactants having an HLB value in the range of 4 to 16. In the above-mentioned at least two types of nonionic surfactants, the difference between the highest HLB value and the lowest HLB value of the nonionic surfactant is 1 or more. The aforementioned water-based ink contains resin particles, The surface tension γ of the aqueous ink at 25°C ｉ and the surface tension γ of the reaction solution ｒ The difference (γ ｉ -γ ｒ An inkjet recording apparatus characterized in that the coefficient of gravity is 9 mN / m or less.

15. Using an aqueous reaction solution containing an aqueous ink and a reagent that reacts with the aqueous ink, the Bristow method was used for 30 ms from the start of contact. １／２ Up to 10 mL / m² of water absorption capacity ２ A set of aqueous ink and reaction solution used in an inkjet recording method for recording an image on a recording medium, wherein the application of the aqueous ink and the reaction solution to a unit area is performed in a single relative scan between an inkjet ejection head and the recording medium, the time from when the reaction solution is applied to the recording medium until the aqueous ink is applied to the recording medium is 1800 ms or less, and the application is performed in a single relative scan between the inkjet ejection head and the recording medium. The reaction solution contains a surfactant, The surfactant comprises at least two nonionic surfactants having an HLB value in the range of 4 to 16. In the above-mentioned at least two types of nonionic surfactants, the difference between the highest HLB value and the lowest HLB value of the nonionic surfactant is 1 or more. The aforementioned water-based ink contains resin particles, The surface tension γ of the aqueous ink at 25°C ｉ and the surface tension γ of the reaction solution ｒ The difference (γ ｉ -γ ｒ A set of water-based ink and reaction solution characterized in that the ) is 9 mN / m or less.

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