JP2024076990A - Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and reaction liquid - Google Patents

Abstract

The present invention provides an inkjet recording method that is resistant to blocking and winding damage even when the recording medium after image recording is wound into a roll, and is capable of recording high-quality images without unevenness.
[Solution] This is an inkjet recording method for recording an image on a roll-shaped recording medium 1100 using an aqueous ink and an aqueous reaction liquid. The method includes a reaction liquid applying step of applying a reaction liquid to the recording medium 1100, an ink applying step of applying an aqueous ink to the recording medium 1100, a drying step of applying hot air to dry the aqueous ink so that the surface temperature of the recording medium 1100 becomes 70° C. or higher, a cooling step of lowering the surface temperature of the recording medium 1100 by 20° C. or higher 5 seconds after the drying step is completed, and a winding step of winding up the cooled recording medium 1100 into a roll.
[Selected Figure] Figure 1A

Description

The present invention relates to an inkjet recording method, an inkjet recording device, and a set of an aqueous ink and a reaction liquid.

In recent years, the use of inkjet recording devices at high speed in the fields of label printing and package printing has been considered. In these fields, in order to produce a large amount of recorded material in a short time, a method is adopted in which a roll-shaped recording medium is unwound and transported, while ink is applied in one relative scan (one pass) between the recording head and the recording medium to record an image. There is also a demand for recording images on recording media that have low ink absorption, such as art paper with a thin coating layer (low-absorbency recording medium), and on recording media that do not substantially absorb ink, such as plastic film (non-absorbency recording medium). From the standpoint of environmental and safety considerations, the use of aqueous inks containing pigments as coloring materials is being considered.

Until now, it has been possible to record high-resolution images on recording media with high ink absorption (absorbent recording media) such as plain paper by using aqueous inks. In contrast, ink does not easily penetrate low-absorbency recording media or non-permeable recording media, so the next ink adheres to the recording medium before the previous ink adheres to the recording medium. As a result, ink droplets tend to coalesce and cause bleeding and unevenness, making it difficult to improve the quality of the resulting image. To solve this problem, for example, a pretreatment liquid has been proposed that contains a polyvalent metal salt, which is a component that causes the pigments and solids in the ink to aggregate and thicken the ink (Patent Document 1).

In addition, images recorded by the above method are formed by fixing the pigment to the surface of the recording medium, and are therefore easily scratched by rubbing the surface. For this reason, improving the scratch resistance of images recorded with pigment inks is generally considered to be an issue. In order to improve the scratch resistance of recorded images, for example, an ink set has been proposed that includes a reaction liquid containing polyvalent metal ions that aggregate the pigment in the ink, and an ink containing resin particles (Patent Document 2).

Water-based inkjet inks usually contain water and water-soluble organic solvents such as alcohol as liquid components, with more than half of the liquid components being water. If these liquid components remain in the recorded image, the scratch resistance of the image decreases and the image is more likely to stick to other parts that come into contact with it, a phenomenon known as blocking, which can cause problems such as damage to the image. For this reason, in the fields of label printing and package printing, in order to solve these problems, it is common to carry out a drying process in which the ink applied to the recording medium is heated and dried.

JP 2018-134853 A JP 2020-104487 A

The inventors recorded an image on a rolled non-absorbent recording medium by applying the pretreatment liquid and ink proposed in Patent Documents 1 and 2 in one relative scan (one pass) with the recording head. Then, when the recording medium after image recording was stored for a certain period of time in a rolled-up state, blocking occurred, in which the recording surface and the recording medium stuck together, and it was found that the recorded image was easily damaged. In addition to damage caused by blocking, it was also found that storing the recording medium in a rolled-up state caused damage to the image that looked like it had been rubbed (scratches). It was also found that the quality of the image was reduced due to deformation, such as warping, of the recording medium.

Therefore, an object of the present invention is to provide an inkjet recording method that is less likely to cause blocking or wound tightening scratches, even when the recording medium after image recording is wound into a roll, and that can record high-quality images with reduced unevenness and warping. Another object of the present invention is to provide an inkjet recording device and a set of aqueous ink and reaction liquid to be used in this inkjet recording method.

That is, according to the present invention, there is provided an inkjet recording method for recording an image on a roll-shaped recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, the inkjet recording method comprising a reaction liquid application step of applying the reaction liquid to the recording medium, an ink application step of applying the aqueous ink to the recording medium so as to overlap at least a portion of the area of the recording medium to which the reaction liquid has been applied, a drying step of applying hot air to dry the aqueous ink so that the surface temperature of the recording medium becomes 70°C or higher, a cooling step of reducing the surface temperature of the recording medium by 20°C or more 5 seconds after the drying step is completed, and a winding step of winding up the cooled recording medium into a roll.

According to the present invention, it is possible to provide an inkjet recording method that is less likely to cause blocking or wound tightening scratches, even when the recording medium after image recording is wound into a roll, and that is capable of recording high-quality images with reduced unevenness and warping. In addition, according to the present invention, it is possible to provide an inkjet recording device used in this inkjet recording method, and a set of an aqueous ink and a reaction liquid.

FIG. 1 is a schematic diagram illustrating an embodiment of an inkjet recording apparatus of the present invention. FIG. 4 is a schematic diagram showing another embodiment of the inkjet recording apparatus of the present invention. FIG. 4 is a schematic diagram showing another embodiment of the inkjet recording apparatus of the present invention. FIG. 1 is a schematic diagram illustrating an example of an inkjet recording apparatus. FIG. 4 is a schematic diagram showing another embodiment of the inkjet recording apparatus of the present invention. FIG. 4 is a schematic diagram showing another embodiment of the inkjet recording apparatus of the present invention. FIG. 2 is a perspective view showing an example of a liquid application device. FIG. 2 is a cross-sectional perspective view showing an example of a discharge element substrate. FIG. 2 is a schematic diagram showing an example of a liquid supply system. FIG. 13 is a schematic diagram showing another example of the heating unit.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, the aqueous ink and reaction liquid for inkjet printing may be simply referred to as "ink" and "reaction liquid." Unless otherwise specified, the physical property values are values at room temperature (25°C) and normal pressure (1 atm). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

Conventionally, inkjet recording methods using aqueous inks use inks containing resin particles, and the resin particles are softened by heat such as drying, forming a film, thereby improving the scratch resistance of the image. However, because aqueous inks contain a large amount of water, which has a large latent heat, they need to be heated to a higher temperature in order to dry. If the recording medium is in a high temperature state and the resin particles and other components in the image are softened when the recording medium is wound into a roll, there is a problem that blocking is likely to occur. On the other hand, if the heating temperature during drying is low, liquid components are likely to remain in the image, and the remaining liquid components soften the resin particles and other components. Furthermore, blocking is likely to occur because the image is not fixed sufficiently.

In addition, when the image is heated and dried, the recording medium expands due to the heat. If the recording medium is wound up in an expanded state, it will radiate heat after winding and shrink, generating a particularly large stress in the winding direction, causing the recording medium wound into a roll to be further tightened. On the other hand, when a reaction liquid is used, the ink attached to the recording medium quickly thickens, making it difficult to level the ink dots and making the image more prone to unevenness. In addition, most of the reactants in the reaction liquid are consumed by reacting with the components in the ink to form salts, but some of the reactants remain unreacted. The inventors' studies have revealed that the unreacted reactants are scattered in the image and in the non-recording parts of the recording medium to which only the reaction liquid has been applied, and precipitate over time. It has been found that the precipitated reactants come into contact with the unevenness of the image surface and the back surface of the recording medium, and damage the image surface and the back surface of the recording medium due to the aforementioned tightening of the roll, thereby reducing the quality of the image. When an image is recorded using only ink without using a reaction liquid, the ink does not rapidly aggregate, making it difficult for unevenness to form in the image and preventing blocking problems, but the recorded image is prone to unevenness.

In addition, when a transparent film is used as the recording medium, the reactant precipitates in the non-recording areas of the recording medium to which only the reaction liquid has been applied, as described above, and the transparency of the recording medium is easily impaired. Furthermore, if a recording medium that has been heated and dried is left in a heated state for a long period of time, it is likely to warp or become deformed. This is thought to be because the recording medium softens when heated, the tension applied during transportation differs depending on the location, and natural heat dissipation also differs depending on the location.

Under these circumstances, the present inventors have investigated a method for recording a high-quality image with reduced unevenness and warping, without blocking or winding damage, even when the recording medium after image recording is wound into a roll. As a result, they have found that such problems can be solved by the following configuration, and have arrived at the present invention. That is, the inkjet recording method of the present invention is a recording method for recording an image on a roll-shaped recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink. The inkjet recording method of the present invention has a reaction liquid application process, an ink application process, a drying process, a cooling process, and a winding process. In the drying process, hot air is applied to dry the aqueous ink so that the surface temperature of the recording medium is 70°C or higher. Then, in the cooling process, the surface temperature of the recording medium is reduced by 20°C or more 5 seconds after the end of the drying process.

By heating the recording medium so that its surface temperature reaches a high temperature of 70°C or higher, it is possible to efficiently remove liquid components such as water, which have a large latent heat, and to prevent blocking from occurring. In addition, by drying the recording medium with hot air, it is possible to blow away and remove the reactant that has precipitated in the non-recording areas of the recording medium. This makes it possible to prevent damage to the image surface and the back surface of the recording medium caused by tight rolling, and also prevents the transparency of the recording medium from being impaired, even when a transparent film is used as the recording medium.

The recording medium, which has become hot during the drying process, is cooled during the cooling process, and the expansion of the recording medium is reduced when the recording medium is wound into a roll, thereby preventing damage caused by tight winding. Furthermore, by lowering the surface temperature of the recording medium by 20°C or more 5 seconds after the end of the drying process, that is, by cooling a specified recording medium in a short period of time, deformation of the recording medium can be prevented.

<Inkjet recording method and inkjet recording apparatus>
The inkjet recording method of the present invention (hereinafter, also simply referred to as "recording method") is a method for recording an image on a roll-shaped recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink. The recording method of the present invention includes a reaction liquid application step, an ink application step, a drying step, a cooling step, and a winding step. The reaction liquid application step is a step of applying a reaction liquid to the recording medium. The ink application step is a step of applying an aqueous ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the reaction liquid has been applied. The drying step is a step of drying the aqueous ink by applying hot air to the recording medium so that the surface temperature of the recording medium becomes 70°C or higher. The cooling step is a step of lowering the surface temperature of the recording medium by 20°C or more 5 seconds after the end of the drying step. And the winding step is a step of winding the cooled recording medium into a roll.

The inkjet recording apparatus of the present invention (hereinafter, also simply referred to as the "recording apparatus") is an apparatus used in an inkjet recording method in which an image is recorded on a roll-shaped recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink. The recording apparatus of the present invention has a reaction liquid applying means, an ink applying means, a drying means, a cooling means, and a winding means. The reaction liquid applying means is a means for applying a reaction liquid to the recording medium. The ink applying means is a means for applying an aqueous ink to the recording medium so as to overlap at least a part of the area of the recording medium to which the reaction liquid has been applied. The drying means is a means for drying the aqueous ink by applying hot air so that the surface temperature of the recording medium becomes 70°C or higher. The cooling means is a means for lowering the surface temperature of the recording medium by 20°C or more 5 seconds after the end of the drying process. And the winding means is a means for winding up the cooled recording medium into a roll.

The set of aqueous ink and reaction liquid of the present invention is a set of aqueous ink and reaction liquid used in an inkjet recording method in which an image is recorded on a roll-shaped recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink. The inkjet recording method in which the set of aqueous ink and reaction liquid of the present invention is used has a reaction liquid application step, an ink application step, a drying step, a cooling step, and a winding step. The reaction liquid application step is a step of applying a reaction liquid to the recording medium. The ink application step is a step of applying an aqueous ink to the recording medium so as to overlap at least a part of the area of the recording medium to which the reaction liquid has been applied. The drying step is a step of drying the aqueous ink by applying hot air so that the surface temperature of the recording medium becomes 70°C or higher. The cooling step is a step of lowering the surface temperature of the recording medium by 20°C or more 5 seconds after the end of the drying step. And the winding step is a step of winding the cooled recording medium into a roll.

(Inkjet recording device)
The inkjet recording apparatus will be described in detail below with reference to the drawings. Fig. 1A is a schematic diagram showing one embodiment of the inkjet recording apparatus of the present invention. The inkjet recording apparatus of this embodiment is an inkjet recording apparatus that records an image on a recording medium using ink and a reaction liquid containing a reactant that reacts with the ink. The X direction, Y direction, and Z direction respectively indicate the width direction (total length direction), depth direction, and height direction of the inkjet recording apparatus. The recording medium is transported in the X direction.

The inkjet recording device of the embodiment shown in FIG. 1A is configured with a recording unit 1000, a heating unit 2000, a fixing unit 3000, a cooling unit 4000, a bending unit 5000, and a winding unit 6000. In the recording unit 1000, various liquids are applied by a liquid application device 1200 to a roll-shaped recording medium 1100 transported from a paper feeder 1400 by a transport member 1300. In the heating unit 2000, the liquid applied to the recording medium 1100 is heated by a heating device 2100, and volatile components such as moisture in the liquid are evaporated and dried. In the fixing unit 3000, a 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. The recording medium 1100 is then cooled by the cooling members 4100 and 4200 of the cooling unit 4000. The recording medium 1000 on which the image is recorded is transported in the winding section 6000 while being supported by the transport member 6100, and then wound up by the winding device 6200.

Any recording medium may be used as the recording medium 1100. For example, recording media that have ink absorption (permeability) such as recording media without a coating layer, such as plain paper, uncoated paper, and synthetic paper, and recording media with a coating layer, such as printing paper, glossy paper, and art paper, may be used. In addition, recording media that do not have permeability, such as films or sheets made of resin materials such as polyvinyl chloride (PVC) and polyethylene terephthalate (PET), may be used.

The recording method of the present invention is suitable as a method for recording an image on a rolled recording medium that is non-ink absorbing or low-ink absorbing. In this specification, the term "non-ink absorbing recording medium" refers to a recording medium having a water absorption amount of less than 5 mL/ ^m2 from the start of contact to 30 msec ^1/2 in the Bristow method. In addition, in this specification, the term "low ink absorbing recording medium" refers to a recording medium having a water absorption amount of 5 mL/ ^m2 or more and 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. In the case of an ink absorbing recording medium such as plain paper having a water absorption amount of more than 10 mL/ ^m2 from the start of contact to 30 msec ^1/2 in the Bristow method, air flows in from the outside even when the recording medium is wound into a roll. Therefore, the inside of the gaps in the recording medium is less likely to become negative pressure, and the problem of blocking is less likely to occur.

Examples of low ink-absorbent recording media having a water absorption of 5 mL/m ² or more and 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method include recording media having a thin coating layer such as art paper, fine coated paper, medium coated paper, fine light coated paper, medium light coated paper, lightly coated paper, and cast coated paper. Examples of non-ink-absorbent recording media having a water absorption of less than 5 mL/m ² from the start of contact to 30 msec ^1/2 in the Bristow method include synthetic films made of polymer compounds such as polyethylene, polyethylene terephthalate, polypropylene, and polyvinyl chloride; paper coated with these polymer compounds; glass; metal; ceramics, etc. As the recording media, it is preferable to use non-ink-absorbent recording media having a water absorption of less than 5 mL/m ² from the start of contact to 30 msec ^1/2 in the Bristow method. Among these, it is particularly preferable to use a film or sheet made of at least one material selected from the group consisting of polyethylene, polypropylene, nylon, polyethylene terephthalate, polyvinyl chloride, and metal.

As the non-ink-absorbing recording medium, films and sheets in which the content of polymer compounds such as polyethylene terephthalate, nylon, polyethylene, and polypropylene is 50% by mass or more based on the total mass of the recording medium are preferred. Of these, films and sheets in which the content of polyethylene terephthalate or nylon is 70% by mass or more based on the total mass of the recording medium are even more preferred. These non-ink-absorbing recording media are preferred because they expand less with temperature changes than general paper substrates that have ink absorption, and deformation can be suppressed even when a heating process is performed.

[Recording section]
The recording unit 1000 includes a liquid applying device 1200. The liquid applying device 1200 includes a reaction liquid applying device 1201 and an ink applying device 1202. The reaction liquid applying device 1201 shown in FIG. 1 is an example of a unit using an inkjet type ejection head. In addition, the reaction liquid applying device may be configured using a gravure coater, an offset coater, a die coater, a blade coater, or the like. The reaction liquid may be applied by the reaction liquid applying device 1201 either before or after the 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 the ink is applied. As the ink applying device 1202, an inkjet type ejection head (recording head) is used. The ejection method of the ejection head as the liquid applying device 1200 can be exemplified by a method of ejecting liquid by generating film boiling in the liquid by an electrothermal converter to form bubbles, and a method of ejecting liquid by an electromechanical converter.

The liquid application device 1200 is a line head extending in the Y direction, with ejection ports arranged in a range that covers the image recording area of the widest usable recording medium. The ejection head has an ejection port surface 1207 (Figure 3) on which ejection ports are formed below it (on the recording medium 1100 side), and the ejection port surface faces the recording medium 1100 at a very small distance of about a few millimeters.

A plurality of ink applicators 1202 may be provided to apply ink of each color to the recording medium 1100. For example, when recording images of each color using yellow ink, magenta ink, cyan ink, and black ink, four ink applicators 1202 ejecting the above four types of ink are arranged in the X direction. Hereinafter, the ink and reaction liquid may be collectively referred to as "liquid."

Figure 2 is a perspective view showing an example of a liquid application device. The liquid application device 1200 shown in Figure 2 is a line head, and multiple ejection element substrates 1203 each having an ejection port array are arranged in a straight line. Multiple ejection port arrays are arranged on the ejection element substrate 1203.

Figure 3 is a cross-sectional perspective view showing an example of an ejection element substrate. The ejection element substrate 1203 shown in Figure 3 includes an ejection port forming member 1206 with an ejection port 1204 opened, and a substrate 1205 with an ejection element (not shown). The ejection port forming member 1206 and the substrate 1205 are laminated to form a first flow path 1208 and a second flow path 1209 through which liquid flows. The first flow path 1208 is a region from an inlet 1212 through which liquid flows from an inflow path 1210 to a portion between the ejection port 1204 and the ejection element (Figure 4, liquid chamber 1508). The second flow path 1209 is a region from a portion between the ejection port 1204 and the ejection element (Figure 4, liquid chamber 1508) to an outlet 1213 through which liquid flows out to an outlet path 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, liquid can flow from the high-pressure side to the low-pressure side (in the direction of the arrow in FIG. 3). The liquid that passes through the inlet 1210 and the inlet 1212 enters the first flow path 1208. Then, the liquid that passes through the portion between the outlet 1204 and the ejection element (liquid chamber 1508 in FIG. 4) flows through the second flow path 1209 and the outlet 1213 to the outlet 1211.

[Supply system]
FIG. 4 is a schematic diagram showing an example of a supply system for liquid such as ink. The supply unit 1500 of the liquid application device 1200 shown in FIG. 4 is configured to include 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 connected to a main tank 1504, which is a liquid storage unit, has an air communication port (not shown) and can discharge air bubbles mixed in the liquid to the outside of the circulation system. The sub tank 1503 is also connected to a refill pump 1506. The liquid is consumed in the liquid application device 1200 by discharging (discharging) the liquid from the discharge port for image recording, suction recovery, etc. The refill pump 1506 transfers the liquid corresponding to the consumed amount from the main tank 1504 to the sub tank 1503.

The first circulation pump (high pressure side) 1501 and the first circulation pump (low pressure side) 1502 flow the liquid in the liquid application device 1200 that flows out from the connection part (inlet part) 1507 to the sub tank 1503. It is preferable to use a volumetric pump having 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 volumetric pumps include a tube pump, a gear pump, a diaphragm pump, and a syringe pump. When the ejection 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 channel 1514 toward the common outlet channel 1515.

The negative pressure control unit 1509 has two pressure adjustment mechanisms with different control pressures. The pressure adjustment mechanism (high pressure side) 1510 and the pressure adjustment mechanism (low pressure side) 1511 are connected to a common inlet 1514 and a common outlet 1515 in the ejection element substrate 1203 via a supply unit 1513 provided with a filter 1512 for removing foreign matter from the liquid. The ejection element substrate 1203 is provided with the common inlet 1514, the common outlet 1515, and the inlet 1210 and outlet 1211 that communicate with the liquid chamber 1508, which is a portion between the ejection port 1204 and the ejection element (not shown). Since the inlet 1210 and the outlet 1211 are connected to the common inlet 1514 and the common outlet 1515, respectively, a flow (arrow in FIG. 4) occurs in which a part of the liquid flows from the common inlet 1514 through the inside of the liquid chamber 1508 to the common outlet 1515. The arrows in Figure 4 indicate the flow of liquid inside the liquid chamber 1508. That is, as shown in Figure 3, the liquid in the first flow path 1208 flows into the second flow path 1209 via the gap between the ejection port 1204 and the ejection element.

As shown in FIG. 4, a pressure adjustment mechanism (high pressure side) 1510 is connected to the common inlet channel 1514, and a pressure adjustment mechanism (low pressure side) 1511 is connected to the common outlet channel 1515, so that a pressure difference occurs between the inlet 1212 (FIG. 3) communicating with the inlet channel 1210 and the outlet 1213 (FIG. 3) communicating with the outlet channel 1211. When liquid is caused to flow by the pressure difference between the inlet 1212 and the outlet 1213, it is preferable to control the flow rate (mm/s) of the liquid to be 0.1 mm/s or more and 10.0 mm/s or less.

[Transport system]
As shown in FIG. 1, the recording unit 1000 is configured to include a liquid applying device 1200 and a conveying member 1300 that conveys the recording medium 1100. The liquid applying device 1200 applies a reaction liquid and ink to a desired position of the recording medium 1100 conveyed by the conveying member 1300. Each liquid applying device receives an image signal of recording data and applies the necessary reaction liquid and ink to each position. FIG. 1 shows the conveying member 1300 in the form of a conveying belt, but a spur, a conveying cylinder, or the like may be used as long as it has the function of conveying the recording medium 1100. In order to improve the conveying accuracy, a material that can fix the recording medium 1100 can be used as the conveying member 1300. Specifically, a method of providing a hole in the conveying member 1300 and fixing the recording medium 1100 by sucking from the back side, a method of forming the conveying member 1300 from an appropriate material and fixing the recording medium 1100 by electrostatic adsorption, etc. can be mentioned.

The conveying speed (recording speed) of the recording medium is preferably 1 m/min to 200 m/min, more preferably 5 m/min to 100 m/min. If the recording speed is less than 5 m/min, the time interval between the application of the reaction liquid and the ink becomes long. Therefore, before the ink and the reaction liquid come into contact on the recording medium, the dots of liquid previously applied to the recording medium are likely to move, which makes the image more likely to become uneven, and the effect of improving uniformity may not be fully achieved. On the other hand, if the recording speed is more than 100 m/min, the time to bend the recording medium becomes short. Therefore, the unevenness of the image cannot be fully smoothed, and the effect of further improving blocking resistance may not be fully achieved.

[Bend]
The bending section 5000 is provided between the recording section 1000 and the heating section 2000, and includes a transport roller 5100 for transporting the roll-shaped recording medium 1100 to which the reaction liquid and ink have been applied. The transport roller 5100 allows the recording medium 1100 to be transported while being bent. When the recording medium 1100 in a state in which the liquid components remain immediately after the reaction liquid and ink have been applied is bent, the unevenness of the image is smoothed out so that the image flows in the bending direction. This makes it possible to effectively suppress blocking that is likely to occur after the recording medium 1100 is wound up. When the recording medium 1100 in a state in which the liquid components in the image have evaporated is bent, the image has low fluidity, so that the unevenness of the image cannot be effectively smoothed out, and the effect of further improving blocking resistance may not be sufficiently obtained. For this reason, it is preferable to install the bending section 5000 between the recording section 1000 and the heating section 2000.

At the bending portion 5000, it is preferable to bend the recording medium 1100 so that the recording surface (surface on which an image is recorded) faces outward. By bending the recording surface outward (mountain folding), the image stretches, so that the unevenness of the image can be more effectively smoothed out, and the blocking resistance can be further improved. As shown in Figures 1B and 1F, when bending the recording medium 1100 so that the recording surface faces inward (valley folding), it is preferable to provide a member such as a transport roller 5200 at the position where the recording medium 1100 is bent. This makes it possible to bend the recording medium 1100 with the transport roller 5200 in contact with the surface of the image, so that the unevenness of the image can be smoothed out and the blocking resistance can be improved. However, if the recording medium 1100 is bent with a large amount of liquid remaining in the image, the image is more likely to be transferred to the transport roller 5200, and the recorded image may be more likely to be damaged.

At the bending portion 5000, it is preferable to bend the recording medium 1100 at a bending angle α of 80° or more. In this specification, the "bending angle" of the recording medium is a positive angle (+α (°)) when the recording surface is bent outward, and a negative angle (-α (°)) when the recording surface is bent inward. By bending the recording medium at a bending angle of 80° or more, it is possible to effectively smooth out the unevenness of the image and further improve blocking resistance. The bending angle α is preferably 100° or less, and more preferably 90° or less.

At the bending portion 5000, it is preferable to bend the recording medium 1100 to a bending radius of 20 cm or less. By setting the bending radius to 20 cm or less, it is possible to bend the recording medium at a sharper angle, so that the unevenness of the image can be effectively smoothed out and the blocking resistance can be further improved. The bending radius is preferably 5 cm or more, and more preferably 10 cm or more. The bending radius can be set, for example, by the radius of curvature of the transport roller 5100.

When applying liquids such as reaction liquid and ink to the recording medium 1100, it is preferable not to substantially heat the recording medium 1100. Specifically, it is preferable not to substantially heat the recording medium at the application position of the reaction liquid and ink. Heating the recording medium promotes evaporation of liquid components from ink droplets attached to the recording medium 1100, increasing the fluidity of the ink, and it may become difficult to sufficiently smooth out the unevenness of the image even if the recording medium 1100 is bent at the bending portion 5000. As a result, the effect of further improving blocking resistance may not be sufficiently obtained.

[Heating section]
1, the heating section 2000 is configured to include a heating device 2100 and a transport member 2200. The recording medium 1100, to which a reaction liquid and ink have been applied and an image has been recorded, is heated by the heating device 2100 while being transported by the transport member 2200, thereby evaporating and drying the liquid components of the image. This makes it possible to effectively suppress deformation (cockling and curling) of the recording medium 1100.

The heating device 2100 may have any configuration as long as it can dry the ink by blowing hot air so that the surface temperature of the recording medium 1100 reaches or exceeds a predetermined temperature, and various conventional devices such as hot air dryers and heaters can be used. Among these, the use of non-contact heaters such as electric heating wires and infrared heaters is preferable from the standpoint of safety and energy efficiency. Furthermore, the drying efficiency can be easily improved by using a mechanism that incorporates a fan to spray heated gas onto the recording medium 1100 and blows hot air.

Regarding the heating method, the recording medium 1100 may be heated from the side to which the reaction liquid and ink are applied (recording surface (front side)), from the back side, or from both sides. The transport member 2200 may be provided with a heating function. In particular, it is preferable to apply hot air to the surface of the recording medium with the surface to which the reaction liquid and ink are applied (the surface of the recording medium) facing downward, as this can further prevent the occurrence of tightening scratches. The reason for this is presumably that the unevenness formed in the image can be reduced compared to when the recording medium is transported and dried with the surface facing in a direction other than downward, due to the way in which moisture evaporates and the resistance of the hot air.

While FIG. 1 shows a conveying member 2200 using a conveying belt, a spur, conveying drum, or the like may also be used as long as it has the function of conveying 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 conveyed while being in close contact with the conveying member 2200 by blowing air from the heating unit 2000, or to have a mechanism for fixing the recording medium to the conveying member 2200. Specifically, examples of the method include a method of providing holes in the conveying member 2200 and fixing the recording medium 1100 by suction from the back side, or a method of forming the conveying member 2200 from an appropriate material and fixing the recording medium 1100 by electrostatic adsorption.

The heating temperature is preferably set so as to quickly evaporate the liquid components and not to over-dry the recording medium 1100 in order to suppress deformation of the recording medium. Taking into account the conveying speed and the environmental temperature, the ink is dried by blowing hot air so that the surface temperature of the recording medium is 70° C. or higher, preferably 70° C. or higher and 110° C. or lower. The surface temperature of the recording medium can be measured by either a contact or non-contact method. In particular, it is preferable to use a non-contact infrared radiation thermometer to measure the surface temperature of the recording medium from the surface (recording surface) side. In addition, the wind speed of the hot air blown onto the recording medium is preferably 1 m/s or higher and 100 m/s or lower. The temperature of the wind such as the warm air can be measured using a K-type thermocouple thermometer. A specific example of a measuring device is the product name "AD-5605H" (manufactured by A&D).

Figure 6 is a schematic diagram showing another example of a heating unit. Here, the differences from the heating unit shown in Figure 1 and described above will be explained. The heating unit 2000 shown in Figure 6 includes a first heating device 2101 and a second heating device 2102, and a first conveying member 2201 and a second conveying member 2202 arranged opposite the first heating device 2101 and the second heating device 2102, respectively.

The first conveying member 2201 does not have a mechanism for sucking and fixing the recording medium 1100. The recording medium 1100 is then pressed against the first conveying member 2201 by the hot air of the first heating device 2101, and conveyed. This allows the recording medium 1100 to be transferred with high precision from the conveying member 1300 (FIG. 1) to the first conveying member 2201, and from the first conveying member 2201 to the second conveying member 2202. Furthermore, it is possible to reduce conveying deviations caused by slight differences in the conveying speeds of the conveying member 1300 (FIG. 1) and the first conveying member 2201. On the other hand, a conveying belt with holes that can pass gas is used as the second conveying member 2202, and the recording medium 1100 is conveyed while being fixed to the second conveying member 2202 by a suction mechanism (not shown).

Air knives 2300 are disposed between the transport member 1300 (FIG. 1) and the first transport member 2201, between the first transport member 2201 and the second transport member 2202, and downstream of the second transport member 2202. The air pressure from the air knife 2300 prevents the leading edge of the transported recording medium 1100 from floating up. This makes it possible to prevent the leading edge of the recording medium 1100 from colliding with the first heating device 2101, the second heating device 2102, etc., and to suppress transport failures.

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 and the hot air speeds of the first heating device 2101 and the second heating device 2102 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 necessary.

[Fuser unit]
As shown in FIG. 1A, the fixing section 3000 includes a transport roller 3100. The transport roller 3100 transports the recording medium 1100, and the transport roller 3100 contacts the image on the recording medium 1100, and the image can be fixed to the recording medium 1100 by the contact pressure. That is, after the heating step, it is preferable to further have a fixing step of applying pressure to the recording surface to fix the image. The pressure applied to the recording surface of the recording medium (contact pressure of the transport roller) is preferably 10 Pa or more and 1,000 Pa or less, more preferably 10 Pa or more and 500 Pa or less, and particularly preferably 10 Pa or more and 100 Pa or less. In particular, it is particularly preferable to set the pressure to 30 Pa or more, since it can effectively smooth out the unevenness of the image and further improve the blocking resistance. In addition, the time required for the recording medium to pass through the transport roller (nip time) is preferably 0.01 seconds or more and 5.0 seconds or less.

[Cooling section]
The cooling section 4000 is configured to include a cooling member 4100 and a conveying member 4200 (FIG. 1). The cooling section 4000 cools the recording medium 1100, which has passed through the heating section 2000 and the fixing section 3000 and has become hot. The cooling member 4100 may 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 them, blowing unheated gas is preferable in terms of safety and energy efficiency. In addition, if a fan is built in to inject gas onto the recording medium 1100 and a mechanism for blowing air is used, it is easy to increase the cooling efficiency. Furthermore, it is preferable that the cooling section 4000 blows air onto the front and back surfaces of the recording medium 1100 to lower the surface temperature of the recording medium 1100. In this way, deformation of the recording medium can be more effectively suppressed.

In the cooling section 4000, the surface temperature of the recording medium is cooled by 20°C or more, preferably 25°C or more, 5 seconds after the drying process in the heating section 2000 is completed. The surface temperature is preferably reduced by 80°C or less, more preferably 60°C or less. The temperature of the recording medium after being cooled in the cooling section is preferably 20°C or more, more preferably 50°C or less, more preferably 40°C or less. By keeping the temperature within this range, the occurrence of tightening scratches can be further suppressed. In addition, the temperature of the cooling means can be set so that the image on the recording medium is at the desired temperature, taking into account the conveying speed and the environmental temperature. Specifically, the temperature of the cooling means (such as air blowing) is preferably 20°C or more and 50°C or less, more preferably 20°C or more and 40°C or less. When cooling the recording medium 1100 by blowing gas, the wind speed is preferably 1 m/s or more and 100 m/s or less. By setting these conditions, it is possible to further suppress deformation and image sticking (blocking) of the recording medium 1100 that is wound into a roll in the winding unit 6000 described below.

[Winding section]
The recording medium 1100 after the image recording is accommodated in the winding section 6000 (FIG. 1). After the image is recorded, the recording medium 1100 passes through the cooling section 4000, is transported by the transport member 6100, and is finally accommodated in the recording medium accommodation section 6200 in a rolled-up state. It is preferable to wind the recording medium 1100 with the recording surface of the recording medium 1100 facing outward. When the recording medium 1100 is wound with the recording surface facing outward, the image on the recording surface stretches, so that unevenness in the image is more effectively smoothed out, and blocking resistance can be further improved.

(Recording method)
In the recording method of the present invention, while conveying a roll-shaped recording medium, ink and a reaction liquid are applied to the recording medium to record an image. When the reaction liquid is discharged from an inkjet recording head and applied to the recording medium, the amount of the reaction liquid applied to the recording medium is preferably 8.0 mg/ ^inch2 or less. Moreover, it is more preferably 4.0 mg/inch2 or ^less , and particularly preferably 0.1 mg/ ^inch2 or more. By setting the amount of the reaction liquid applied within the above range, the energy load in the drying process can be reduced. It is preferable that the amount of the reaction liquid applied to the recording medium is appropriately adjusted according to the amount of the ink applied. Moreover, it is preferable that the amount of the ink applied to the recording medium is 15.0 mg/ ^inch2 or less, and it is also preferable that it is 0.1 mg/ ^inch2 or more. By setting the amount of the ink applied to the recording medium within the above range, the energy load in the drying process can be reduced.

Because the reaction liquid is a component used to fix the ink to the recording medium, it is preferable to control the ratio of the reaction liquid to the ink to be applied within an appropriate range in order to record a more uniform and high-quality image. Specifically, the amount of reaction liquid applied to the recording medium is preferably 0.08 to 0.40 times the mass ratio of the amount of ink applied to the recording medium. By setting the above ratio to 0.08 or more, blocking resistance can be further improved. In addition, by setting the above mass ratio to 0.40 or less, the uniformity of the recorded image can be further improved.

<Reaction solution>
The recording method of the present invention includes a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to a recording medium. Each component of the reaction liquid will be described in detail below.

[Reactants]
The reaction liquid reacts with the ink by contacting with the ink, and aggregates the components in the ink (components having anionic groups such as resins, surfactants, and self-dispersing pigments), and contains a reaction agent. When the ink and the reaction agent come into contact with each other on the recording medium, the presence of the reaction agent can destabilize the state of the components having anionic groups in the ink, and promote the aggregation of the ink. Examples of the reaction agent include cationic components such as polyvalent metal ions and cationic resins, and organic acids. The reaction agent may be used alone or in combination of two or more. Among them, it is preferable to use cationic components such as polyvalent metal ions and cationic resins as the reaction agent, because they are unlikely to corrode the storage stability of the reaction liquid and the components of the inkjet recording device. In particular, polyvalent metal ions are preferable because they have good reactivity and excellent image characteristics. Among the reaction agents, polyvalent metal ions and cationic resins are more likely to damage the image surface and the back surface of the recording medium due to tight winding when unreacted reaction agents are precipitated, compared to organic acids. However, by satisfying the drying and cooling steps specified in the present invention, the occurrence of scratches due to tight winding can be suppressed even in the case where polyvalent metal ions or cationic resins are used.

Examples of polyvalent metal ions constituting the polyvalent metal salt include divalent metal ions such as Ca2 ⁺ , Cu2 ⁺ , Ni2 ⁺ , Mg2 ⁺ , Sr2 ⁺ , Ba2 ⁺ , and Zn2 ⁺ , and trivalent metal ions such as Fe3 ⁺ , Cr3 ⁺ , Y3 ⁺ , and Al3 ⁺ . In order to incorporate polyvalent metal ions into the reaction solution, a water-soluble polyvalent metal salt (which may be a hydrate) formed by combining a polyvalent metal ion with an anion can be used. Examples of the anion include inorganic anions such as Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ ; and organic anions such as HCOO ⁻ , (COO ⁻ ) ₂ , COOH(COO ⁻ ), CH ₃ COO ⁻ , CH ₃ CH(OH)COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , and CH ₃ SO ₃ ^{− .}

The water solubility of the polyvalent metal salt at 20°C is preferably 1% by mass or more and 50% by mass or less, and more preferably 8% by mass or more and 30% by mass or less. If the water solubility of the polyvalent metal salt is too low, the amount of polyvalent metal ions in the reaction solution is too small, and the ink may become weakly cohesive, resulting in a decrease in the uniformity of the solid image. On the other hand, if the water solubility of the polyvalent metal salt is too high, the image may easily absorb moisture in the air. As a result, the blocking resistance may be easily decreased, and the friction coefficient of the image surface may increase, making it easier for scratches to occur due to tightening. In addition, the polyvalent metal salt may not precipitate easily even when dried, and the reactant may not be completely removed even when air is blown. In this specification, the "water solubility at 20°C" is defined as the mass (g) of the anhydrous compound contained in 100 g of a saturated solution at a temperature of 20°C/100 (g) x 100 (mass%). For example, "water solubility of 1% by mass at 20°C" means that the amount dissolved in 100 g of water at a temperature of 20°C is 1 g.

Among polyvalent metal salts formed by combining polyvalent metal ions and anions, magnesium sulfate is preferred. When magnesium sulfate is used as the polyvalent metal salt, the aggregation rate of the pigment and resin particles in the ink can be easily controlled by adjusting the content in the reaction liquid and the amount of the reaction liquid applied. This makes it possible to reduce unevenness on the surface of the recorded image, and further suppresses the occurrence of scratches due to tightening of the winding. In addition, even when a transparent film is used as the recording medium, loss of transparency of the recording medium can be effectively suppressed.

When polyvalent metal ions are used as the reactant, the content (mass%) of polyvalent metal salt in the reaction solution is preferably 1.0% by mass or more and 20.0% 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 reaction solution. In this specification, the "content (mass%) of polyvalent metal salt" in the reaction solution when the polyvalent metal salt is a hydrate means the "content (mass%) of anhydrous polyvalent metal salt" excluding water as a hydrate. If the content of polyvalent metal salt in the reaction solution is too high, the amount of precipitation of the reactant in the non-recording part of the recording medium may become excessively large. For this reason, the image may be easily scratched by rubbing against the back side of the wound recording medium, and wound-tightening scratches may easily occur. In addition, when a transparent film is used as the recording medium, the transparency of the recording medium may be easily reduced.

The reaction liquid containing an organic acid has a buffering ability in the acidic range (less than pH 7.0, preferably pH 2.0 to 5.0), and thus efficiently converts the anionic groups of the components present in the ink into the acid form and causes them to aggregate. 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, furan carboxylic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and their salts and 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 and hydrogen salts, such as citric acid and trimellitic acid; and tetracarboxylic acids and their salts and hydrogen salts, such as pyromellitic acid. When an organic acid is used as a reactant, the content (mass %) of the organic acid in the reaction solution is preferably 1.0 mass % or more and 50.0 mass % or less based on the total mass of the reaction solution.

Examples of cationic resins include resins having a primary to tertiary amine structure and resins having a quaternary ammonium salt structure. Specific examples include resins having structures such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. In order to increase the solubility in the reaction solution, the cationic resin can be used in combination with an acidic compound or the cationic resin can be subjected to a quaternization treatment. When a cationic resin is used as a reactant, the content (mass %) of the cationic resin in the reaction solution is preferably 0.1 mass % or more and 10.0 mass % or less based on the total mass of the reaction solution.

[Aqueous medium]
The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. The reaction liquid can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of the water-soluble organic solvent in the reaction liquid is preferably 20.0 mass% or less, more preferably 5.0 mass% or less, and particularly preferably 1.0 mass% or less, based on the total mass of the reaction liquid. Among them, it is particularly preferable that the reaction liquid does not contain a water-soluble organic solvent. By reducing the content of the water-soluble organic solvent in the reaction liquid, the water-soluble organic solvent can be dried and quickly evaporated in the non-recording part where only the reaction liquid is applied. As a result, it is possible to promote the precipitation of the reactant, and the removal of the reactant by blowing air becomes even easier.

The boiling point of the water-soluble organic solvent is preferably 250°C or less, and more preferably 230°C or less. By using a water-soluble organic solvent with a boiling point of 250°C or less, it is possible to evaporate more quickly by heating, further reducing the amount of water-soluble organic solvent remaining in the image, and further improving the blocking resistance of the image. In addition, it is possible to promote the precipitation of the reactant in the non-recording area where only the reaction liquid is applied, making it easier to remove the reactant by blowing air. Therefore, even if a transparent film is used as the recording medium, it is possible to effectively suppress the transparency of the recording medium from being impaired. The boiling point of the water-soluble organic solvent is preferably 150°C or more. In particular, when using a water-soluble organic solvent with a boiling point of more than 250°C, especially more than 230°C, it is preferable to reduce the content. In particular, it is preferable that the reaction liquid does not contain a water-soluble organic solvent with a boiling point of more than 250°C, especially more than 230°C.

Specific examples of preferred water-soluble organic solvents include ethylene glycol (boiling point 197°C), 1,2-propanediol (boiling point 188°C), 1,3-propanediol (boiling point 210°C), 1,2-butanediol (boiling point 193°C), 1,3-butanediol (boiling point: 208°C), 1,4-butanediol (boiling point 230°C), 1,3-butanediol (boiling point 182°C), 1,2-pentanediol (boiling point 206°C), 1,2-hexanediol (boiling point 223°C), 2-methyl-1,3-propanediol ( Examples include diethylene glycol monomethyl ether (boiling point 194°C), diethylene glycol monoethyl ether (boiling point 202°C), diethylene glycol monoisopropyl ether (boiling point 207°C), diethylene glycol monoisobutyl ether (boiling point 229°C), diethylene glycol monobutyl ether (boiling point 230°C), 1,5-pentanediol (boiling point 242°C), diethylene glycol (boiling point 245°C), and 2-pyrrolidone (boiling point 245°C).

In addition, the moisture absorption rate of the water-soluble organic solvent is preferably 60% or less. By using a water-soluble organic solvent with a moisture absorption rate of 60% or less, the water-soluble organic solvent in the reaction solution can be evaporated more quickly by hot air drying, and the removability of the precipitated reactant can be further improved. Therefore, even when a transparent film is used as a recording medium, the transparency of the recording medium can be effectively prevented from being impaired. In addition, if the moisture absorption rate of the water-soluble organic solvent remaining in the image is low, the blocking resistance of the image can be further improved. The moisture absorption rate of the water-soluble organic solvent can be measured and calculated by the following procedure. First, 2 g of the water-soluble organic solvent is placed in a petri dish with an outer diameter of 31 mm and a height of 15 mm, and left to stand for 24 hours in an environment at a temperature of 30° C. and a humidity of 80%. Next, the mass (x (g)) of the water-soluble organic solvent after standing is measured, and the moisture absorption rate (%) can be calculated from the following formula (1).
Moisture absorption rate (%) = {(x-2)/2} x 100 ... (1)

When the reaction liquid contains a water-soluble organic solvent, it is preferable to use a water-soluble organic solvent that has a boiling point that is not too high and a low moisture absorption rate in order to prevent liquid components (water and water-soluble organic solvent) from remaining on the recording medium as much as possible. For this reason, it is preferable to use a water-soluble organic solvent that satisfies both the above-mentioned conditions of a boiling point of 250° C. or less (preferably 230° C. or less) and a moisture absorption rate of 60% or less. In particular, even if the water-soluble organic solvent has the above-mentioned boiling point and moisture absorption rate characteristics, it is preferable to reduce the content. This can further improve the blocking resistance of the image, and can effectively prevent the transparency of the recording medium from being impaired even when a transparent film is used as the recording medium. The content (mass %) of the water-soluble organic solvent in the reaction liquid that has a boiling point of 230° C. or less and a moisture absorption rate of 60% or less is preferably 20.0 mass % or less based on the total mass of the reaction liquid. In particular, the content is more preferably 5.0 mass % or less, and particularly preferably 1.0 mass % or less.

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

[Properties of reaction solution]
The reaction liquid is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property value. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN/m or more and 60 mN/m or less. Since bending the recording medium makes it possible to more uniformly level the unevenness of the image and further improve the blocking resistance, it is more preferable that the surface tension of the reaction liquid is 39 mN/m or less. The surface tension of the reaction liquid can be measured by a plate method. In addition, the viscosity of the reaction liquid at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The viscosity of the reaction liquid can be measured by a rotational viscometer. The pH of the reaction liquid at 25°C is preferably 5.0 to 9.5, more preferably 6.0 to 9.0.

<Ink>
The ink used in the recording method of the present invention is preferably a water-based ink for ink-jet recording containing a coloring material. Each component of the ink will be described in detail below.

[Colorant]
The ink preferably contains a coloring material. A pigment or a dye can be used as the coloring material. The content (mass %) of the coloring material in the ink is preferably 0.5 mass % or more and 15.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

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

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

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

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

It is preferable to use a dye having an anionic group. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes. A single type of dye may be used alone, or two or more types may be used in combination. The coloring material is preferably a pigment, and more preferably a resin-dispersed pigment or a self-dispersed pigment.

[resin]
The ink can contain a resin. By using an ink containing a resin, an image with improved abrasion resistance can be recorded. The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary, or (ii) to improve various properties of the recorded image.

The content (mass %) of the resin in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink. Examples of the form of the resin include block copolymers, random copolymers, graft copolymers, and combinations of these. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. One type of resin may be used alone, or two or more types may be used in combination.

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

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as constituent units is preferable. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferable. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of styrene and α-methylstyrene is preferable. These resins are easily interacted with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

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

Urethane-based resins can be obtained, for example, by reacting polyisocyanate with polyol. They may also be obtained by further reacting with a chain extender. Examples of olefin-based resins include polyethylene and polypropylene.

[Resin properties]
In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which no particles whose particle size can be measured by a dynamic light scattering method are formed. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if no particles having a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. In addition, as a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above.

The acid value of the water-soluble resin is preferably 100 mgKOH/g or more and 250 mgKOH/g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

The acid value of the resin constituting the resin particles is preferably 5 mgKOH/g or more and 100 mgKOH/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, more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D ₅₀ ) 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 particles that is integrated from the small particle diameter side and is 50% based on 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 ink preferably contains resin particles. The resin particles are heated and softened, which increases the strength of the image, further improving the blocking resistance of the image and reducing the unevenness of the image layer formed by the pigment. This makes it possible to reduce the unevenness of the surface of the recorded image, and more effectively suppresses the occurrence of wound tightening scratches. The content (mass%) of the resin particles in the ink is preferably 5.0 mass% or more and 20.0 mass% or less, based on the total mass of the ink. If the content of the resin particles is less than 5.0 mass%, the strength of the image may decrease and wound tightening scratches may easily occur. On the other hand, if the content of the resin particles is more than 20.0 mass%, the ejection stability of the ink may decrease slightly. In order to further improve the blocking resistance of the image, the glass transition temperature of the resin particles is preferably 40°C or more, and is preferably equal to or lower than the surface temperature of the recording medium heated in the drying process. Specifically, the glass transition temperature of the resin particles is preferably 120°C or less, and more preferably 100°C or less. The glass transition temperature (°C) of the resin particles can be measured using a differential scanning calorimeter (DSC).

[Wax particles]
The ink may contain particles (wax particles) formed of wax. By using an ink containing wax particles, an image with further improved abrasion resistance can be recorded. In this specification, the wax may be a composition containing components other than wax, or the wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a resin. The wax may be used alone or in combination of two or more kinds. The content (mass %) of the wax particles in the ink is preferably 0.1 mass % or more and 10.0 mass % or less, and more preferably 1.0 mass % or more and 5.0 mass % or less, based on the total mass of the ink.

In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high melting point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends of these (blended waxes), and modified products of these (modified waxes).

Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Among these, a blend of multiple types of wax is more preferable, and a blend of petroleum-based wax and synthetic wax is especially preferable.

The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if the chain is straight, and the lower the melting point if the chain is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the crystallinity, the higher the melting point). Therefore, by controlling these characteristics, it is possible to obtain a wax having a desired melting point. The melting point of the wax in the ink can be measured in accordance with the above test method, for example, after the ink is subjected to ultracentrifugation, the wax separated is washed and dried.

[Aqueous medium]
The ink used in the recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, the content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 2.0 mass% or more and 40.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, can be used. The water-soluble organic solvent may be used alone or in combination of two or more.

The boiling point of the water-soluble organic solvent is preferably 250°C or less, and more preferably 230°C or less. By using a water-soluble organic solvent whose boiling point is 250°C or less, it can be evaporated more quickly by heating. If the boiling point of the water-soluble organic solvent is over 250°C, the water-soluble organic solvent is more likely to remain in the formed image and is more likely to absorb moisture from the air. As a result, blocking is more likely to occur, the friction coefficient of the image surface may increase, and winding scratches may be more likely to occur.

[Other ingredients]
The ink may contain various other components as necessary. Examples of other components include various additives such as defoamers, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain a reactant to be contained in the reaction liquid.

[Ink properties]
The ink is an aqueous ink applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property value. Specifically, the surface tension of the ink at 25°C is preferably 20 mN/m or more and 60 mN/m or less. Since bending the recording medium makes it possible to more uniformly level the unevenness of the image and further improve the blocking resistance, it is more preferable that the surface tension of the ink is 39 mN/m or less. The surface tension of the ink can be measured by a plate method. In addition, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. Since bending the recording medium makes it possible to more uniformly level the unevenness of the image and further improve the blocking resistance, it is more preferable that the viscosity of the ink is 7.0 mPa·s or less. The viscosity of the ink can be measured by a rotational viscometer. The pH of the ink at 25°C is preferably 7.0 to 9.5, more preferably 8.0 to 9.5.

In the recording method of the present invention using the reaction liquid and ink, the reaction liquid and the ink come into contact with each other on the recording medium and thicken, and an image is recorded. Since the viscosity of the mixture of the ink and the reaction liquid affects the image to be recorded, it is preferable to set the viscosity of this mixture within an appropriate range. The viscosity of the mixture changes depending on the mass ratio when the ink and the reaction liquid are mixed. In the present invention, it is preferable to use the reaction liquid at a ratio within the range of 0.08 parts by mass to 0.40 parts by mass per 1.00 parts by mass of ink. Furthermore, it is preferable that the ratio of the viscosity (mPa·s) at 25°C of the mixture obtained by mixing 1.00 parts by mass of ink and the reaction liquid within the range of 0.08 parts by mass to 0.40 parts by mass of ink to the viscosity (mPa·s) at 25°C of the ink is 10 times or more and 100 times or less. By setting the above ratio to 10 times or more, the uniformity of the recorded image can be further improved. Furthermore, by setting the above ratio to 100 times or less, it is possible to more uniformly smooth out the unevenness of the image by bending the recording medium, thereby further improving blocking resistance.

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 to the following examples as long as it does not deviate from the gist of the invention. Unless otherwise specified, the terms "parts" and "%" used to describe the amounts of components are based on mass.

<Preparation of reaction solution>
The components (unit: %) shown in the upper part of Tables 1-1 and 1-2 were mixed and thoroughly stirred, and then pressure filtered using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each reaction liquid. In Tables 1-1 and 1-2, "Sharol DC902P" is the trade name of a cationic resin manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and "Acetylenol E100" is the trade name of a surfactant manufactured by Kawaken Fine Chemical Co., Ltd. The properties of the reaction liquid are shown in the lower part of Tables 1-1 and 1-2. The surface tension of the reaction liquid was measured using an automatic surface tensiometer (trade name "DY-300", manufactured by Kyowa Interface Science Co., Ltd.).

<Preparation of Pigment Dispersion>
(Pigment Dispersion 1)
A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) with an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide in an amount equimolar to the acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solid content) content of 20.0%. 15.0 parts of pigment (carbon black), 22.5 parts of the aqueous solution of resin 1, and 62.5 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of zirconia beads with a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 5 hours while cooling with water. After removing coarse particles by centrifugation, the mixture was pressure-filtered with a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare a pigment dispersion 1 with a pigment content of 15.0% and a resin dispersant (resin 1) content of 4.5%.

(Pigment Dispersion 2)
A pigment dispersion 2 having a pigment content of 15.0% and a resin dispersant (resin 1) content of 4.5% was prepared in the same manner as in the pigment dispersion 1 described above, except that the pigment was changed to C.I. Pigment Blue 15:3.

(Pigment Dispersion 3)
A pigment dispersion 3 having a pigment content of 15.0% and a resin dispersant (resin 1) content of 4.5% was prepared in the same manner as in the pigment dispersion 1 described above, except that the pigment was changed to C.I. Pigment Red 122.

(Pigment Dispersion 4)
A pigment dispersion 4 having a pigment content of 15.0% and a resin dispersant (resin 1) content of 4.5% was prepared in the same manner as in the pigment dispersion 1 described above, except that the pigment was changed to C.I. Pigment Yellow 74.

(Pigment Dispersion 5)
A solution of 5.0 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5°C, and 1.8 g of 4-aminophthalic acid was added. The container containing this solution was placed in an ice bath, and while stirring to maintain the temperature of the solution at 10°C or less, a solution obtained by dissolving 0.9 g of sodium nitrite in 9.0 g of 5°C ion-exchanged water was added. After stirring for 15 minutes, 6.0 g of carbon black was added under stirring, and the mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered with filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), and the particles were thoroughly washed with water and dried in an oven at 110°C. Thereafter, sodium ions were replaced with potassium ions by ion exchange to obtain a self-dispersing pigment in which -C ₆ H ₃ -(COOK) ₂ groups were bonded to the surface of the carbon black particles. An appropriate amount of water was added to adjust the pigment content, and a pigment dispersion liquid 5 with a pigment content of 15.0% was obtained.

<Preparation of Resin Particles>
In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 74.0 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, a predetermined amount of 2-ethylhexyl methacrylate, methacrylic acid, and 0.3 parts of a reactive surfactant (trade name "ADEKA REASOAP ER-20", manufactured by ADEKA) were mixed to prepare an emulsion. The amounts of 2-ethylhexyl methacrylate and methacrylic acid used were adjusted so that the glass transition temperatures of resin particles 1 to 3 were 70 ° C., 40 ° C., and 35 ° C., respectively. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and a polymerization reaction was carried out for 2 hours while stirring at 80 ° C. 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 each resin particle having a resin particle (solid content) content of 40.0%.

<Ink Preparation>
The components (unit: %) shown in the upper rows of Tables 2-1 and 2-2 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each ink. In Tables 2-1 and 2-2, "Acetylenol E100" is the trade name of a surfactant manufactured by Kawaken Fine Chemicals. The lower rows of Tables 2-1 and 2-2 show the properties of the ink. The surface tension of the ink was measured using an automatic surface tensiometer (trade name "DY-300", manufactured by Kyowa Interface Science).

<Preparing the recording medium>
The recording media used were the following five types of rolled recording media and recording media cut into a specified size from the rolled recording media. The PET film and PP film were both label papers integrated with release paper.
Recording medium 1 (non-absorbent): PET film, product name "PETWH50 PAT8LK", manufactured by Lintec, water absorption amount less than 2.5 mL/ ^m2 Recording medium 2 (absorbent): wood-free paper, product name "55 PW 8k", manufactured by Lintec, water absorption amount 10.2 mL/ ^m2
Recording medium 3 (low absorbency): Art paper, product name "Gloss PW8k", manufactured by Lintec, water absorption amount 5.5 mL/ ^m2
Recording medium 4 (non-absorbent): PP film, product name "OPP50C PAT1E8LK", manufactured by Lintec, water absorption amount less than 2.5 mL/ ^m2 Recording medium 5 (non-absorbent): Aluminum, product name "Aluminum Tantai 50 PAT1 8EA", manufactured by Lintec, water absorption amount less than 2.5 mL/ ^m2 Recording medium 6: Recording medium 1 cut to A4 size

<Evaluation>
The reaction liquid and ink in the combinations shown in Tables 5-1 to 5-3 were used as sets. The reaction liquid and ink constituting the set were measured for viscosity of the mixed liquid in the following procedure, and the ratio of the viscosity of the mixed liquid to the viscosity of the ink was calculated. First, the reaction liquid and the ink were mixed at the "mixed mass ratio (times) of reaction liquid/ink" shown in Table 4, and stirred for 1 minute to prepare a mixed liquid. Next, the viscosity (mPa·s) of the prepared mixed liquid was measured using an E-type viscometer (product name "RE80-L", manufactured by Toki Sangyo Co., Ltd.) in which antifreeze is circulated through a tube in a thermostatic bath set at 25°C. Furthermore, the ratio value (mixed viscosity ratio (times)) to the viscosity (mPa·s) of the corresponding ink at 25°C was calculated. The results are shown in Tables 5-1 to 5-3. The reaction liquid and ink constituting the set were filled in the reaction liquid application device 1201 and the ink application device 1202 of an inkjet recording device having the configuration shown in Table 3, respectively. In these inkjet recording devices, an image recorded under conditions in which one ink droplet of 3.0 ng is applied to a unit area of 1/1,200 inch×1/1,200 inch is defined as having a recording duty of 100%.

Using the inkjet recording device having the above configuration, two types of solid images shown below were recorded on the recording medium while conveying the recording medium according to the recording conditions shown in Table 4 and the evaluation conditions shown in Tables 5-1 to 5-3. The above two types of images were repeatedly recorded on 1,000 m of the recording medium with an interval of 1 cm in the conveying direction, and then the recording medium was wound up in a roll at a tension of 15 MPa in the winding section. The wound roll-shaped recording medium was stored for 24 hours under tension at a temperature of 23° C. and a relative humidity of 50%. After storage, the tension of the wound recording medium was released, and the recording medium was taken out at a position 500 m from the wound end, and the following items were evaluated. In the present invention, the evaluation criteria for each of the following items were set to "AA", "A", and "B" as acceptable levels, and "C" as unacceptable levels. The evaluation results are shown in Table 6.
A 15 cm x 15 cm solid image with a reaction liquid printing duty of 25% and an ink printing duty of 100%. A 15 cm x 15 cm solid image with only reaction liquid applied at a printing duty of 25%.

In Examples 14 and 72, an inkjet recording device was used that had a cooling section that contacted a water-cooled cooling roll. In Example 20 and Reference Examples 1 and 2, an inkjet recording device was used that heat-dries the recording medium with the recording surface facing up, as shown in FIG. 1D. In Comparative Examples 2 and 4 to 11, an image was recorded with the cooling function of the cooling member turned off. In Comparative Example 2, an image was recorded with the function of the heating device turned off. In Comparative Example 12, after an image was recorded with the cooling function of the cooling member turned off, the conveying distance was adjusted so that the recording medium would reach a predetermined temperature by natural heat dissipation while passing through the heating device and being wound up. For this reason, it took more than 5 seconds from the end of the drying process to cool to 35°C.

In Reference Example 1, a recording medium cut to a predetermined size was used, and an image was recorded on 1,000 m of recording medium in the same manner as in Example 1. The recording medium was then discharged in a stacked manner in a discharge section (not shown). A load was applied to the stacked recordings so that a force equivalent to 15 MPa, which is the tension of the roll paper, was applied, and the stacked recordings were stored for 24 hours under conditions of a temperature of 23° C. and a relative humidity of 50%, and the recordings at a position where half the number of recordings were recorded were evaluated as described below. In Reference Example 2, after the reaction liquid and ink were applied to the recording medium, the recording medium was transported in the reverse direction, and when it passed the recording section, it was transported in the forward direction again, and the reaction liquid and ink were applied again. This operation was repeated a total of two times, and the reaction liquid and ink were applied three times in total, and multi-pass recording was performed so that the total amount of reaction liquid applied was 8% duty and the total amount of ink applied was 100% duty. In Reference Example 2, the time required to perform the same amount of recording as in Example 1 was very long.

(Blocking resistance)
At a position 500 m from the leading end of the wound film, the image and the condition of the back surface of the recording medium with which the image had been in contact were visually observed, and the blocking resistance was evaluated according to the following evaluation criteria.
AA: The image was not damaged.
A: Peeling of more than 0% but less than 1% was observed on an area basis in the image, but no ink was attached to the back side of the recording medium.
B: Peeling of 1% or more and less than 5% on an area basis was observed in the image, and ink was attached to the back surface of the recording medium.
C: Peeling of 5% or more in terms of area was observed in the image, and ink was attached to the back surface of the recording medium.

(Wrapping damage)
An image taken at a position 500 m from the leading end of the wound cable was observed using a 50x magnifying glass, and the occurrence of tightening scratches was evaluated according to the following evaluation criteria.
AA: No scratches were observed even using a 50x magnifying glass.
A: No scratches were observed with the naked eye, but linear scratches were observed using a 50x magnifying glass.
B: Linear scratches were visually observed only in a part of the image.
C: Linear scratches were visually observed over the entire image.

(Warping of recording media)
The recording medium was cut out to A4 size from a position 500 mm from the leading edge of the roll, and placed flat on a flat surface with the recorded image facing up. The amount of lift of each of the four sides from the flat surface was measured under conditions of a temperature of 23° C. and a humidity of 50%, and the warpage of the recording medium was evaluated according to the following evaluation criteria.
A: The maximum floating amount was less than 1 cm.
B: The maximum floating amount was 1 cm or more and less than 3 cm.
C: The maximum floating amount was 3 cm or more.

(Uniformity)
The recording medium was cut out to A4 size from a position 500 mm from the leading end of the roll, and the image recorded using a scanner under the conditions of mode: professional, resolution: 300 dpi, and color: 24 bit was captured. As the scanner, a product name "OFFIRIO ES-10000G" (manufactured by Seiko Epson) was used. Using image/photo editing software (product name "Adobe Photoshop (registered trademark)", manufactured by Adobe), a range of 200 pixels x 200 pixels of the captured image was copied, pasted into a new clipboard (200 pixels x 200 pixels), and converted to grayscale. Then, the standard deviation obtained from the histogram was obtained, and the uniformity of the image was evaluated according to the evaluation criteria shown below. The smaller the standard deviation, the better the uniformity of the solid image.
A: The standard deviation was less than 3.0.
B: The standard deviation was 3.0 or more and less than 4.0.
C: The standard deviation was 4.0 or more.

(Transparency of non-recorded areas)
The transparency of the non-recorded portion was evaluated for the recorded matter using the PET film and the PP film. The release paper of the non-recorded portion of the recorded matter (the area where only the reaction liquid was applied) and the film on which no recording was performed were peeled off, and the non-recorded portion was attached to a black paper (product name "FSPG Color B Dark", manufactured by Daio Paper Corporation) without touching the measurement portion. The lightness L ^* in the L ^* a ^* b ^* color system was measured using a fluorescent spectrodensitometer (product name "FD-7", manufactured by Konica Minolta). Then, the difference in lightness L ^* between the area where only the reaction liquid was applied and the film on which no recording was performed was obtained, and the transparency of the non-recorded portion was evaluated according to the evaluation criteria shown below.
The difference in AA:L ^* was less than 2.0.
A: The difference in L ^* was 2.0 or more and less than 3.0.
The difference in B:L ^* was 3.0 or more and less than 4.0.
The difference in C:L ^* was 4.0 or more.

Claims (21)

1. An inkjet recording method for recording an image on a roll-shaped recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying step of applying the reaction liquid to the recording medium;
an ink applying step of applying the water-based ink to the recording medium so as to overlap at least a portion of an area of the recording medium to which the reaction liquid has been applied;
a drying step of drying the water-based ink by blowing hot air onto the recording medium so that the surface temperature of the recording medium becomes 70° C. or higher;
a cooling step of lowering the surface temperature of the recording medium by 20° C. or more 5 seconds after the completion of the drying step;
and a winding step of winding the cooled recording medium into a roll. The inkjet recording method according to claim 1, wherein in the drying step, hot air is applied to the surface of the recording medium while the surface of the recording medium is facing downward. The inkjet recording method according to claim 1, wherein in the cooling step, air is blown onto the front and back surfaces of the recording medium to lower the surface temperature of the recording medium. The inkjet recording method according to claim 1, wherein in the winding step, the recording medium is wound up with the recording surface of the recording medium facing outward. The inkjet recording method according to claim 1, further comprising a bending step of bending the recording medium between the reaction liquid application step and the ink application step and the drying step. The inkjet recording method according to claim 5, wherein in the bending step, the recording medium is bent so that the recording surface of the recording medium faces outward. The inkjet recording method according to claim 5, wherein the recording medium is bent at a bending angle of 80° or more in the bending step. The inkjet recording method according to claim 5, wherein in the bending step, the recording medium is bent to a bending radius of 20 cm or less. The inkjet recording method according to claim 1, further comprising a fixing step of applying pressure to the recording surface of the recording medium to fix the image after the drying step. The inkjet recording method according to claim 9, wherein the pressure applied to the recording surface of the recording medium in the fixing step is 30 Pa or more. The inkjet recording method according to claim 1, wherein the reaction liquid contains a polyvalent metal salt whose water solubility at 20°C is 8% by mass or more and 30% by mass or less. The inkjet recording method according to claim 11, wherein the content (mass %) of the polyvalent metal salt in the reaction liquid is 10.0 mass % or less based on the total mass of the reaction liquid. The inkjet recording method according to claim 11, wherein the polyvalent metal salt is magnesium sulfate. The inkjet recording method according to claim 1, wherein the reaction liquid contains a water-soluble organic solvent having a boiling point of 250°C or less. The inkjet recording method according to claim 14, wherein the moisture absorption rate of the water-soluble organic solvent is 60% or less. The inkjet recording method according to claim 1, wherein the water-based ink contains a water-soluble organic solvent having a boiling point of 250°C or less. The inkjet recording method according to claim 1, wherein the ratio of the viscosity (mPa·s) at 25°C of the mixed liquid obtained by mixing 1.00 parts by mass of the aqueous ink and 0.08 parts by mass or more and 0.40 parts by mass or less of the reaction liquid to the viscosity (mPa·s) of the aqueous ink at 25°C is 10 times or more and 100 times or less. The inkjet recording method according to claim 1, wherein the surface tension of the aqueous ink and the reaction liquid is 39 mN/m or less. The inkjet recording method according to claim 1, wherein the recording medium is a film or sheet made of at least one material selected from the group consisting of polyethylene, polypropylene, nylon, polyethylene terephthalate, polyvinyl chloride, and metal. An inkjet recording apparatus for use in an inkjet recording method for recording an image on a roll-shaped recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying means for applying the reaction liquid to the recording medium;
an ink applying means for applying the water-based ink to the recording medium so as to overlap at least a portion of an area of the recording medium to which the reaction liquid has been applied;
a drying means for drying the water-based ink by blowing hot air onto the recording medium so that the surface temperature of the recording medium becomes 70° C. or higher;
a cooling means for lowering the surface temperature of the recording medium by 20° C. or more 5 seconds after the completion of the drying process;
and a winding means for winding up the cooled recording medium into a roll. A set of an aqueous ink and a reaction liquid used in an inkjet recording method for recording an image on a roll-shaped recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising:
The inkjet recording method comprises:
a reaction liquid applying step of applying the reaction liquid to the recording medium;
an ink applying step of applying the water-based ink to the recording medium so as to overlap at least a portion of an area of the recording medium to which the reaction liquid has been applied;
a drying step of drying the water-based ink by blowing hot air onto the recording medium so that the surface temperature of the recording medium becomes 70° C. or higher;
a cooling step of lowering the surface temperature of the recording medium by 20° C. or more 5 seconds after the completion of the drying step;
and a winding step of winding up the cooled recording medium into a roll.

Images