JP2018100341A - Ink set for ink-jet recording, cartridge and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set capable of maintaining a discharge performance of aqueous ink even after uncapping action.SOLUTION: An ink set has aqueous ink and aqueous cleaning liquid. The aqueous ink and the aqueous cleaning liquid contain a deliquescent agent, respectively. The content of the deliquescent agent in the aqueous ink is 0.10 mass% or more and 7.0 mass% or less. The content of the deliquescent agent in the aqueous cleaning liquid is 0.10 mass% or more and 10 mass% or less. The aqueous cleaning liquid further contains an ampholytic surfactant.SELECTED DRAWING: None

Description

  The present invention relates to an ink set for inkjet recording, a cartridge, and an image forming method.

  An image forming method using an ink jet method is known (see, for example, Patent Document 1). The ink composition described in Patent Document 1 contains a pigment, water, a polymerizable compound having an acrylamide structure, a polymerization initiator, and a sugar alcohol having a predetermined SP value.

JP 2013-53173 A

  In an image forming method using an inkjet method, ink is ejected from a ejection surface of a recording head onto a recording medium. A large number of nozzles are formed in the recording head, and each of the nozzles opens at the discharge surface. Therefore, the ink is ejected from the nozzle opening (ejection port) to the recording medium.

  When ink is ejected from the ejection port to the recording medium, the ejection surface may be contaminated with ink, and as a result, the ink may dry on the ejection surface and adhere to the ejection surface. If the cleaning liquid is supplied to the discharge surface, the purge operation, and the wipe operation are performed, the fixed ink (hereinafter sometimes referred to as “fixed ink”) can be removed from the discharge surface. Thereby, it is possible to prevent the fixed ink from blocking the discharge port. Therefore, it is possible to prevent a decrease in ink ejection performance. For example, it is possible to prevent ink from becoming difficult to be ejected. Further, it is possible to prevent ink from being ejected in a direction different from the desired ejection direction. The “purge operation” means an operation of pressurizing and discharging ink from the ejection port. Hereinafter, the ink discharged by the purge operation may be referred to as “purge ink”. The “wipe operation” means an operation of wiping the ejection surface, and is performed after the purge operation.

  When ink is not ejected for a long period (for example, one week or more), the capping operation is performed after the wiping operation. “Cap operation” means an operation of sealing the discharge port. If the capping operation is performed, the discharge port is sealed, so that the ink in the nozzle can be prevented from drying. Thereby, it is possible to prevent clogging from occurring in the nozzle. Therefore, when ink ejection is resumed after an operation for releasing the sealed state of the ejection port (hereinafter referred to as “uncapping operation”), image formation can be performed without causing a decrease in ink ejection performance. .

  However, if unwiped ink remains in the wiping operation, the ink may dry and thicken on the ejection surface. If the cap operation is performed in a state where thickened ink (hereinafter sometimes referred to as “thickened ink”) is present on the ejection surface, the thickened ink may impede the sealing of the ejection port. When the sealing of the discharge port is hindered, the ink in the nozzle is easily dried, and the nozzle may be clogged. Therefore, when an attempt is made to resume ink ejection after the uncapping operation, the ink ejection performance may deteriorate.

  The present invention has been made in view of the above circumstances, and provides an ink set capable of maintaining the water-based ink ejection performance even after the uncapping operation, and can maintain the water-based ink ejection performance after the uncapping operation. An object of the present invention is to provide a simple cartridge and to provide an image forming method using an ink set capable of maintaining the discharge performance of water-based ink even after an uncapping operation.

  The ink set for inkjet recording according to the present invention includes a water-based ink and a water-based cleaning liquid. The water-based ink and the water-based cleaning liquid each contain a deliquescent agent. The content of the deliquescent agent in the water-based ink is 0.10% by mass or more and 7.0% by mass or less. The content of the deliquescent agent in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less. The aqueous cleaning liquid further contains an amphoteric surfactant.

  The cartridge according to the present invention stores a first tank that stores the water-based ink included in the ink set for ink-jet recording having the above-described configuration, and a second tank that stores the water-based cleaning liquid included in the ink set for ink-jet recording having the above-described configuration. And a tank.

  An image forming method according to the present invention includes a discharge step of discharging a water-based ink from a discharge surface of a recording head onto a recording medium, a supply step of supplying an aqueous cleaning liquid to the discharge surface, and pressurizing the water-based ink. A purge step of discharging from the discharge surface, and a wiping step of wiping the discharge surface. The supply process and the purge process are each performed after the ejection process and before the wiping process. The water-based ink and the water-based cleaning liquid each contain a deliquescent agent. The content of the deliquescent agent in the water-based ink is 0.10% by mass or more and 7.0% by mass or less. The content of the deliquescent agent in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less. The aqueous cleaning liquid further contains an amphoteric surfactant.

  According to the present invention, the water-based ink ejection performance can be maintained even after the uncapping operation.

1 is a diagram illustrating an example of a configuration of an image forming apparatus used in an image forming method according to the present invention. It is a figure explaining the image forming method which concerns on this invention. It is a figure explaining the image forming method which concerns on this invention.

An embodiment of the present invention will be described. In addition, the evaluation result (a value indicating the shape or physical properties) of the powder is the number average of the values measured for a considerable number of particles unless otherwise specified. Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is a value measured using a laser diffraction type particle size distribution measuring device (“Zetasizer Nano ZS” manufactured by Malvern) unless otherwise specified. It is. Here, the powder is, for example, a pigment dispersion described later.

  In addition, a compound and a derivative thereof may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”.

  Also, “the ability to maintain water-based ink ejection performance even after the uncapping operation” means that the water-based ink ejection performance after the uncapping operation is that of the water-based ink before the uncapping operation (more specifically, before the capping operation) This means that it is possible to prevent the discharge performance from deteriorating.

  In addition, when distinguishing the deliquescent agent contained in the water-based ink and the deliquescent agent contained in the aqueous cleaning liquid, the “deliquescent agent contained in the aqueous ink” is described as “first deliquescent agent” and the “aqueous cleaning liquid contains The “deliquescent agent” is referred to as “second deliquescent agent”. When the deliquescent agent contained in the water-based ink and the deliquescent agent contained in the aqueous cleaning liquid are not distinguished, they are simply described as “deliquescent agent”.

[Ink set for inkjet recording according to this embodiment]
The ink set for inkjet recording according to the present embodiment (hereinafter sometimes simply referred to as “ink set”) includes a water-based ink and a water-based cleaning liquid. The water-based ink and the water-based cleaning liquid each contain a deliquescent agent. The content of the deliquescent agent (first deliquescent agent) in the water-based ink is 0.10% by mass or more and 7.0% by mass or less. The content of the deliquescent agent (second deliquescent agent) in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less. The aqueous cleaning liquid further contains an amphoteric surfactant. If image formation is performed using the ink set according to the present embodiment, the water-based ink ejection performance can be maintained even after the uncapping operation.

  Examples of a method for forming an image using the ink set according to the present embodiment include the following methods. Specifically, first, the water-based ink included in the ink set is ejected from the ejection surface of the recording head (the recording head included in the inkjet recording apparatus) onto the recording medium. Next, the aqueous cleaning liquid of the ink set is supplied to the ejection surface, and a purge operation is performed. Subsequently, a wiping operation is performed.

  When water-based ink is not discharged over a long period of time, it is preferable to perform a capping operation after the wiping operation. When the discharge of water-based ink is resumed after the capping operation, the uncapping operation is performed. Preferably, preliminary wiping is performed after the uncapping operation, and then the discharge of the water-based ink is resumed. The “preliminary wipe” is a kind of wipe operation, and means a wipe operation that is performed after the uncapping operation and before the re-ejection of the water-based ink. Below, for convenience of explanation, a preferable configuration of the water-based ink and a formation process of the fixed ink will be described in order.

<Preferred configuration of water-based ink>
The aqueous ink preferably has an aqueous solvent and a pigment dispersion. A pigment dispersion means a composition in which a plurality of pigment particles are dispersed in an aqueous medium. Each of the pigment particles preferably includes a pigment core containing a pigment and a coating resin provided on the surface of the pigment core.

In the water-based ink, the pigment particles are dispersed with each other. Specifically, in many cases, a resin salt is used as the coating resin. Here, the resin salt has a functional group capable of ionization in the molecule, for example, a COONa group in the molecule. The aqueous ink contains a sufficient amount of an aqueous solvent. Therefore, ionization is likely to occur on the surface of the coating resin. Therefore, an electric double layer is formed on the surface of the coating resin. For example, when a resin salt having a COONa group in the molecule is used as the coating resin, the surface of the coating resin is negatively charged (COO ⁻ ), and Na ⁺ adheres to the surface of the coating resin by electrical attraction. Since the electric double layer is thus formed on the surface of the coating resin, the pigment particles repel each other electrically. As a result, the pigment particles are dispersed with each other.

<Fixed ink formation process>
It is considered that the fixing ink is formed by the following process.
When water-based ink is discharged from the discharge surface of the recording head onto the recording medium, the water-based ink may adhere to the discharge surface. When the water-based ink adheres to the ejection surface, the water-based ink is dried due to contact between the water-based ink and air. When the water-based ink is dried, the coating resin tends to form a film.

  Specifically, when the water-based ink is not dried, it is considered that the water-based ink contains a sufficient amount of the water-based solvent. Therefore, ionization tends to occur on the surface of the coating resin (see <Preferred configuration of water-based ink> above).

  However, when the water-based ink is dried, the content of the water-based solvent in the water-based ink decreases, so that ionization hardly occurs on the surface of the coating resin. Thereby, the pigment particles are less likely to be electrically repelled, and the pigment particles are likely to aggregate with each other. When the pigment particles are aggregated with each other, the coating resins present on the surfaces of the different pigment cores are likely to come into contact with each other. As a result, a film made of a coating resin (hereinafter referred to as “resin film”) is easily formed. As described above, when the water-based ink is dried, the aggregate of the pigment core is covered with the resin film. In this way, a fixed ink is formed.

<Reason for obtaining the desired effect>
Subsequently, items that can be considered as reasons why a predetermined effect is obtained when image formation is performed using the ink set according to the present embodiment will be described. Here, the “predetermined effect” includes an effect that the water-based ink ejection performance can be maintained even after the uncapping operation.

  As described in the above <fixed ink formation process>, the surface of the fixed ink is formed of a resin film. Here, the resin film is made of a coating resin, and a resin salt is often used as the coating resin. Therefore, when the fixed ink comes into contact with a liquid containing an aqueous solvent (for example, an aqueous cleaning liquid or purge ink), ionization is likely to occur on the surface of the fixed ink, and the surface of the fixed ink is likely to be negatively charged. Further, if ionization is likely to occur on the surface of the fixed ink, the surface of the fixed ink is likely to exhibit hydrophilicity.

  In the ink set according to the present embodiment, the aqueous cleaning liquid contains an amphoteric surfactant. Amphoteric surfactants exhibit the properties of cationic surfactants in acidic liquids and the properties of anionic surfactants in basic liquids. Here, the water-based ink generally exhibits weak basicity. Therefore, when the fixing ink and the aqueous cleaning liquid come into contact with each other, the obtained solution tends to show weak basicity. Therefore, when the aqueous cleaning liquid is supplied to the ejection surface of the recording head, the amphoteric surfactant tends to exhibit the properties of an anionic surfactant.

  Anionic surfactants are easily ionized in an aqueous solvent. When the anionic surfactant is ionized in an aqueous solvent, the hydrophobic group is easily negatively charged and the hydrophilic group is easily positively charged. For this reason, when the aqueous cleaning liquid is supplied to the discharge surface, in the amphoteric surfactant, the hydrophobic group tends to be negatively charged, and the hydrophilic group tends to be positively charged. Further, as described above, when the aqueous cleaning liquid is supplied to the ejection surface, the surface of the fixed ink tends to be negatively charged. For these reasons, when the aqueous cleaning liquid is supplied to the ejection surface, an electric attractive force is likely to act between the surface of the fixed ink and the hydrophilic group of the amphoteric surfactant.

  Further, as described above, when the aqueous cleaning liquid is supplied to the ejection surface, the surface of the fixed ink tends to show hydrophilicity. On the other hand, the discharge surface generally tends to exhibit hydrophobicity. Therefore, when the aqueous cleaning liquid is supplied to the ejection surface, among the amphoteric surfactants, the hydrophilic group shows affinity (hydrophilic interaction) with the surface of the fixed ink, and the hydrophobic group has affinity with the ejection surface ( Shows hydrophobic interactions).

  In summary, when the aqueous cleaning liquid is supplied to the ejection surface, the hydrophilic group of the amphoteric surfactant tends to exhibit affinity for the surface of the fixed ink due to the electric attractive force and the hydrophilic interaction. Further, the hydrophobic group of the amphoteric surfactant tends to show affinity for the ejection surface due to hydrophobic interaction. For these reasons, the amphoteric surfactant can exist stably between the fixed ink and the ejection surface. Here, the amphoteric surfactant is contained in the aqueous cleaning liquid. Therefore, if the amphoteric surfactant can stably exist between the fixed ink and the discharge surface, the aqueous cleaning liquid is more likely to exist between the fixed ink and the discharge surface than the surface of the fixed ink. Therefore, the aqueous cleaning liquid supplied to the ejection surface is likely to enter between the fixed ink and the ejection surface from the surface of the fixed ink.

  In the ink set according to the present embodiment, the aqueous cleaning liquid contains the second deliquescent agent. Here, since the ink set according to the present embodiment has water-based ink, the purge ink is water-based ink. Therefore, when the aqueous cleaning liquid is supplied to the ejection surface and the purge operation is performed, the purge ink is easily absorbed by the aqueous cleaning liquid (more specifically, the second deliquescent agent). Therefore, when the aqueous cleaning liquid enters between the fixed ink and the ejection surface from the surface of the fixed ink, the purge ink absorbed by the aqueous cleaning liquid (specifically, the purge ink absorbed by the second deliquescent agent) is fixed. Easily enters between the fixed ink and the ejection surface.

  In the ink set according to this embodiment, the water-based ink contains the first deliquescent agent. Here, the fixed ink is formed by drying the water-based ink. Therefore, when the water-based ink contains the first deliquescent agent, the fixed ink also contains the first deliquescent agent. Thus, when the aqueous cleaning liquid is supplied to the ejection surface and the purge operation is performed, the purge ink is easily absorbed by the fixed ink (more specifically, the first deliquescent agent contained in the fixed ink). Also by this, the purge ink can easily enter between the fixed ink surface and the ejection surface from the fixed ink surface.

  As described above, in this embodiment, the purge ink easily enters from the surface of the fixed ink to the space between the fixed ink and the ejection surface. Thus, when the aqueous cleaning liquid is supplied to the ejection surface and the purge operation is performed, the fixed ink is easily dissolved in the purge ink. Therefore, when the wiping operation is performed after the aqueous cleaning liquid is supplied to the ejection surface and the purge operation is performed, the fixed ink can be removed from the ejection surface. Accordingly, it is possible to prevent a decrease in the water-based ink ejection performance.

  If the fixed ink can be removed from the ejection surface by the wiping operation, the ejection opening can be sealed by performing the cap operation. Thereby, even if it is a case where a water-based ink is not discharged over a long period of time, it can prevent that the water-based ink in a nozzle dries. If the water-based ink in the nozzle can be prevented from drying, clogging at the nozzle can be prevented. Therefore, the water-based ink ejection performance can be maintained even after the uncapping operation.

  In addition, in the ink set according to the present embodiment, the water-based ink contains the first deliquescent agent. Thereby, even if wiping residue of water-based ink occurs in the wiping operation, it is possible to prevent the ink ejection performance from being lowered. Specifically, since the water-based ink in the present embodiment contains the first deliquescent agent, the unwiped ink also contains the first deliquescent agent. Therefore, if the uncapping operation is performed, the unwiped ink absorbs moisture in the air and liquefies. If the remaining ink is liquefied, the remaining ink can be removed by performing preliminary wiping. This can also prevent the water-based ink ejection performance from being lowered after the uncapping operation.

  Moreover, in the ink set according to the present embodiment, not only the water-based ink but also the water-based cleaning liquid contains a deliquescent agent. Thereby, even if the wiping residue of the aqueous cleaning liquid occurs together with the wiping residue of the aqueous ink in the wiping operation, it is possible to prevent the ink discharge performance from being deteriorated. Specifically, since the aqueous cleaning liquid in the present embodiment contains the second deliquescent agent, the unwiped cleaning liquid also contains the second deliquescent agent. Therefore, if the uncapping operation is performed, not only the remaining ink but also the remaining cleaning liquid absorbs moisture in the air and liquefies. If the unwiped ink and the uncleaned cleaning liquid are liquefied, they can be removed by performing preliminary wiping. Further, if the unwiped ink and the uncleaned cleaning liquid are liquefied, the unwiped ink and the uncleaned cleaning liquid can be easily removed as compared with the case where only the aqueous ink of the aqueous ink and the aqueous cleaning liquid contains the deliquescent agent. This can also prevent the water-based ink ejection performance from being lowered after the uncapping operation. Hereinafter, the deliquescent agent and the amphoteric surfactant will be described in order.

<Deliquescent agent>
The deliquescent agent is preferably at least one of sorbitol, trimethylolpropane, and 1,3-bis (2-hydroxyethyl) -5,5-dimethyl-2,4-imidazolidinedione. The first and second deliquescent agents may be the same or different from each other.

  Thus, the deliquescent agent has no charge and is not a polysaccharide. Therefore, the water-based ink ejection performance is easily maintained even after the uncapping operation.

  Specifically, as described above in <Preferred configuration of water-based ink>, an electric double layer is formed on the surface of the pigment particles. Therefore, when a material having an electric charge is used as the first deliquescent agent, an electric attractive force may be generated between the first deliquescent agent and the pigment particles. When such water-based ink is dried on the ejection surface of the recording head, the first deliquescent agent is likely to be present on the surface of the pigment particles or the aggregate of the pigment particles. Therefore, the first deliquescent agent is unlikely to exist on the surface of the fixed ink. As a result, the purge ink is less likely to be absorbed by the fixed ink, so that it is difficult for the purge ink to enter between the fixed ink and the ejection surface. However, since the first deliquescent agent has no electric charge, it is possible to prevent the occurrence of such a problem.

  Further, when the fixed ink comes into contact with a liquid containing an aqueous solvent (for example, an aqueous cleaning liquid), ionization tends to occur on the surface of the fixed ink. Therefore, when a material having a charge is used as the second deliquescent agent, an electric attractive force may be generated between the second deliquescent agent and the surface of the fixed ink. Therefore, the second deliquescent agent is likely to be present on the surface of the fixed ink. Therefore, even if the purge ink is absorbed by the second deliquescent agent, it is difficult for the purge ink to enter between the fixed ink and the ejection surface. However, since the second deliquescent agent has no electric charge, it is possible to prevent the occurrence of such a problem.

  Polysaccharide means a multi-polymer of monosaccharides, for example starch or glycogen. Therefore, the viscosity of the polysaccharide is higher than the viscosity of the deliquescent agent. Therefore, even if the wiping operation or the preliminary wiping is performed, the polysaccharide may remain on the discharge surface without being wiped off. However, since the deliquescent agent is not a polysaccharide, the occurrence of such problems can be prevented.

  In addition, when a polysaccharide is used as the second deliquescent agent, the viscosity of the aqueous cleaning liquid is increased, so that the aqueous cleaning liquid does not easily enter between the fixed ink and the ejection surface. Therefore, it becomes difficult for the purge ink to enter between the fixed ink and the ejection surface. However, since the second deliquescent agent is not a polysaccharide, the occurrence of such problems can be prevented.

  The content of the first deliquescent agent in the water-based ink is 0.10% by mass or more and 7.0% by mass or less. If the content of the first deliquescent agent in the water-based ink is 0.10% by mass or more, it is possible to ensure the amount of penetration of the purge ink (see, for example, Comparative Examples 2, 4 and 5 described later). If the content of the first deliquescent agent in the water-based ink is 7.0% by mass or less, it is possible to prevent a decrease in the intermittent discharge performance of the water-based ink (see, for example, Comparative Examples 15, 16, and 18 described later). Preferably, the content of the first deliquescent agent in the water-based ink is 0.50% by mass or more and 5.0% by mass or less. Here, “intermittent discharge performance of water-based ink” means discharge performance of water-based ink when water-based ink is discharged intermittently without performing a cap operation. For example, the intermittent discharge performance of water-based ink is the discharge performance of water-based ink when water-based ink is discharged at intervals of several hours.

  When the water-based ink contains two or more deliquescent agents, the total amount of the deliquescent agent in the water-based ink is 0.10% by mass or more and 7.0% by mass or less. Preferably, the total amount of the deliquescent agent in the water-based ink is 0.50% by mass or more and 5.0% by mass or less.

  The content of the second deliquescent agent in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less. If the content of the second deliquescent agent in the aqueous cleaning liquid is 0.10% by mass or more, the amount of purge ink absorbed by the aqueous cleaning liquid can be secured, so that the amount of penetration of purge ink can be secured (for example, Comparative Example 6 described later). , 8 and 12). If the content of the second deliquescent agent in the aqueous cleaning liquid is 10% by mass or less, it is possible to prevent the second deliquescent agent from being precipitated in the aqueous cleaning liquid (see, for example, Comparative Examples 7, 9, and 13 described later). Preferably, the content of the second deliquescent agent in the aqueous cleaning liquid is 0.50% by mass or more and 7.0% by mass or less. In addition, when an aqueous cleaning liquid contains 2 or more types of deliquescent agents, the sum total of the content of a deliquescent agent in an aqueous cleaning liquid is 0.10 mass% or more and 10 mass% or less. Preferably, the total content of the deliquescent agent in the aqueous cleaning liquid is 0.50% by mass or more and 7.0% by mass or less.

<Amphoteric surfactant>
The amphoteric surfactant is preferably at least one of lauryl dimethylamine oxide, lauryl dimethylaminoacetic acid betaine, coconut oil fatty acid amidopropyl betaine, and octanoic acid amidopropyl betaine. Since such amphoteric surfactants are readily available, an aqueous cleaning solution can be easily prepared. Therefore, the ink set according to the present embodiment can be easily provided.

  The content of the amphoteric surfactant in the aqueous cleaning liquid is preferably 0.10% by mass or more. If the content of the amphoteric surfactant in the aqueous cleaning liquid is 0.10% by mass or more, the intrusion amount of the aqueous cleaning liquid is easily ensured, so that the intrusion amount of the purge ink is easily secured (see, for example, Comparative Example 10 described later). . More preferably, the content of the amphoteric surfactant in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less. If the content of the amphoteric surfactant in the aqueous cleaning liquid is 10% by mass or less, the content of other materials excluding the amphoteric surfactant is easily ensured in the aqueous cleaning liquid. More preferably, the content of the amphoteric surfactant in the aqueous cleaning liquid is 0.10% by mass or more and 5.0% by mass or less.

  When the aqueous cleaning liquid contains two or more amphoteric surfactants, the total content of amphoteric surfactants in the aqueous cleaning liquid is preferably 0.10% by mass or more. More preferably, the total content of amphoteric surfactants in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less. More preferably, the total content of amphoteric surfactants in the aqueous cleaning liquid is 0.10% by mass or more and 5.0% by mass or less.

  By the way, as the surfactant, an anionic surfactant, a cationic surfactant, and a nonionic surfactant are known separately from the amphoteric surfactant. However, the aqueous cleaning liquid in this embodiment contains an amphoteric surfactant among a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic surfactant. Thereby, the foamability of the aqueous cleaning liquid can be kept low. In addition, an aqueous cleaning liquid that is less harmful to the human body can be provided. Further, it is considered that the amphoteric surfactant not only exhibits affinity due to hydrophilic interaction but also exhibits affinity due to electrical interaction with the fixed ink. Therefore, an aqueous cleaning liquid containing an amphoteric surfactant is more likely to enter between the fixed ink surface and the ejection surface than an aqueous cleaning liquid containing another surfactant. Therefore, the water-based ink ejection performance is easily maintained even after the uncapping operation (see, for example, Comparative Example 11 described later). Here, the other surfactant means a surfactant excluding the amphoteric surfactant. Other surfactants include, for example, anionic surfactants, cationic surfactants, and nonionic surfactants.

[Cartridge according to this embodiment]
The cartridge according to the present embodiment includes the ink set according to the present embodiment, a first tank that stores aqueous ink, and a second tank that stores aqueous cleaning liquid. Accordingly, if the cartridge according to the present embodiment is loaded into the ink jet recording apparatus, image formation using the ink set according to the present embodiment can be easily performed. Therefore, the water-based ink ejection performance can be maintained even after the uncapping operation.

[Image Forming Method According to the Present Embodiment]
The image forming method according to the present embodiment includes a discharge process, a supply process, a purge process, and a wipe process. In the ejection step, water-based ink is ejected from the ejection surface of the recording head onto the recording medium. In the supplying step, the aqueous cleaning liquid is supplied to the discharge surface. In the purge process, a purge operation is performed. More specifically, water-based ink (purge ink) is pressurized and discharged from the ejection surface. In the wiping process, a wiping operation is performed. More specifically, the discharge surface is wiped off. The supply process and the purge process are each performed after the discharge process and before the wiping process. More specifically, the supply process may be performed before the purge process, may be performed after the purge process, or may be performed simultaneously with the purge process.

  The water-based ink and the water-based cleaning liquid to be used are as described above in [Ink set for inkjet recording according to this embodiment]. Therefore, the water-based ink ejection performance can be maintained even after the uncapping operation.

  If image formation is performed using the ink jet recording apparatus loaded with the water-based ink in the present embodiment, the discharge process, the purge process, and the wipe process can be performed.

  As described above, in the supplying step, the aqueous cleaning liquid according to the present embodiment is supplied to the ejection surface. Examples of the supply method of the aqueous cleaning liquid include discharge of the aqueous cleaning liquid by an ink jet method, application of the aqueous cleaning liquid using a roller, or spraying of the aqueous cleaning liquid.

  In the image forming method according to the present embodiment, an image may be formed by loading the cartridge according to the present embodiment into an ink jet recording apparatus, or an image is formed using separately prepared aqueous ink and aqueous cleaning liquid. May be.

[One Example of Image Forming Method According to this Embodiment]
Hereinafter, an example of the image forming method according to the present embodiment will be specifically described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration of an image forming apparatus used in the image forming method according to the present embodiment. 2 and 3 are diagrams for explaining an image forming method according to the present embodiment. More specifically, FIG. 2 is a diagram for explaining a supply process. FIG. 3 is a diagram for explaining the purge operation and the wipe operation. Here, the X axis, the Y axis, and the Z axis shown in FIGS. 1 to 3 are orthogonal to each other. 2 and 3 are views of the main part of the image forming apparatus 1 shown in FIG. 1 as viewed from the side.

  First, the configuration of the image forming apparatus 1 shown in FIG. 1 will be described. The image forming apparatus 1 shown in FIG. 1 includes a paper feed unit 3, a recording head 4, a liquid storage unit 5, a paper transport unit 7, a discharge unit 8, and a maintenance unit 9.

  The paper feed unit 3 includes a paper feed cassette 31 and a paper feed roller 32a. A plurality of recording media (for example, copy sheets) S are stored in the paper feed cassette 31 in a stacked state.

  As shown in FIGS. 2 and 3, the recording head 4 is formed with a nozzle 41, an ink inlet 43, and an ink outlet 45. The recording head 4 has an ejection surface 47. The nozzle 41 is open at the discharge surface 47 and discharges water-based ink toward the recording medium S (see FIG. 1). The water-based ink is stored in the first tank 52 (see FIG. 1). The water-based ink flows from the first tank 52 through the ink inlet 43 to the recording head 4, and flows out of the recording head 4 through the ink outlet 45.

  As shown in FIG. 1, a cartridge 51 is provided in the liquid storage unit 5. The cartridge 51 is detachably attached to the image forming apparatus 1. The cartridge 51 includes an ink set according to the present embodiment, a first tank 52, and a second tank 53. The first tank 52 stores the water-based ink in the present embodiment. The second tank 53 stores the aqueous cleaning liquid in the present embodiment.

  The paper transport unit 7 includes a first transport unit 71 and a second transport unit 72. The discharge unit 8 has a discharge tray 81.

  The maintenance unit 9 has a sponge 91 and a blade 92. Each of the sponge 91 and the blade 92 is movable between a position facing the discharge surface 47 (see FIGS. 2 and 3) and a position facing the second transport unit 72 (position shown in FIG. 1). is there. As shown in FIG. 2, the sponge 91 is movable along each of the ascending direction D1 and the descending direction D2. The sponge 91 is impregnated with an aqueous cleaning liquid. The aqueous cleaning liquid is stored in the second tank 53 (see FIG. 1) and is supplied from the second tank 53 to the sponge 91. As shown in FIG. 3, the blade 92 is movable along each of an ascending direction D1, a descending direction D2, and a wiping direction D3. Here, the “rising direction D1” means a direction approaching the ejection surface 47 along the Z-axis direction. The “downward direction D2” means a direction away from the ejection surface 47 along the Z-axis direction. The “wiping direction D3” means a direction along the ejection surface 47.

  When the image forming apparatus 1 shown in FIG. 1 is used to form an image on the recording medium S, first, the paper feeding roller 32a takes out the recording medium S stored in the paper feeding cassette 31 one by one from the top. Then, the taken-out recording medium S is sent to the first transport unit 71. When the recording medium S reaches a position facing the ejection surface 47 (see FIG. 2), the water-based ink is ejected from the ejection surface 47 (more specifically, the opening of the nozzle 41) to the recording medium S (ejection process). . Thereafter, the recording medium S is sent to the second transport unit 72 and discharged to the discharge tray 81.

  In the ejection process, water-based ink may adhere to the ejection surface 47. When the water-based ink adheres to the ejection surface 47, a fixed ink (not shown) is formed due to the contact between the water-based ink and air. Therefore, a supply process, a purge process, and a wipe process are performed after the discharge process.

  The supplying process will be described with reference to FIG. In the supplying step, first, the sponge 91 is impregnated with the aqueous cleaning liquid. Next, after the sponge 91 has moved to a position (position shown in FIG. 2) facing the discharge surface 47, it moves along the rising direction D <b> 1 and is pressed against the discharge surface 47. At this time, it is preferable that the state in which the sponge 91 is pressed against the discharge surface 47 (hereinafter referred to as “the pressed state of the sponge 91”) is maintained for a predetermined time. Further, the operation of moving the sponge 91 along the upward direction D1 and the operation of moving the sponge 91 along the downward direction D2 may be repeated while the pressed state of the sponge 91 is maintained. Further, the sponge 91 may move in the direction along the ejection surface 47 (direction along the X-axis direction shown in FIG. 2) while the pressed state of the sponge 91 is maintained.

  When the predetermined time has elapsed, the sponge 91 moves along the descending direction D2, and the pressed state of the sponge 91 is released. Thereby, a supply process is complete | finished. A purge process is performed after a supply process.

  The purge process will be described with reference to FIG. In the purge process, a purge operation is performed. In the purge operation, the recording head 4 performs a purge process. Thereby, the purge ink Nf is forcibly discharged from the ejection surface 47 (more specifically, the opening of the nozzle 41). A wiping process is performed after the purging process.

  The wiping process will be described with reference to FIG. In the wiping process, a wiping operation is performed. In the wiping operation, the blade 92 moves to a position facing the discharge surface 47 (position shown in FIG. 3), then moves along the rising direction D <b> 1 and is pressed against the discharge surface 47. Then, the blade 92 moves in the direction along the discharge surface 47 (wiping direction D3 shown in FIG. 3) while the state where the blade 92 is pressed against the discharge surface 47 is maintained. Thereby, the fixed ink is removed.

  When water-based ink is not discharged over a long period of time, a capping operation is performed after the wiping process. In the cap operation, the discharge surface 47 is covered with a rubber cap (not shown). Thereby, the opening of the nozzle 41 is sealed.

  When the discharge of water-based ink is resumed after the capping operation, the uncapping operation is performed. In the uncapping operation, the rubber cap is removed from the discharge surface 47. Thereby, the sealing state of the opening of the nozzle 41 is released. Then, after performing a preliminary wipe, a discharge process is performed. In the preliminary wiping, the blade 92 moves in the direction along the ejection surface 47 (wiping direction D3 shown in FIG. 3), similarly to the wiping operation shown in FIG. The example of the image forming method according to the present embodiment has been described above with reference to FIGS.

  Hereinafter, an example of a water-based ink material, a preferable method of manufacturing a water-based ink, an example of a material of an aqueous cleaning liquid, and a preferable method of manufacturing an aqueous cleaning liquid will be described in order.

[Examples of water-based ink materials]
As described above, the water-based ink contains the first deliquescent agent. The first deliquescent agent is as described above in <Deliquescent Agent>. The water-based ink is preferably ejected from the ejection surface of the recording head.

  Preferably, the water-based ink contains a first deliquescent agent, a pigment dispersion, and an aqueous solvent. More preferably, the aqueous ink contains a first deliquescent agent, a pigment dispersion, an aqueous solvent, and component C. Component C preferably contains at least one of a surfactant, a dissolution stabilizer, a humectant, and a penetrant.

<Pigment dispersion>
The pigment dispersion includes a plurality of pigment particles. Each of the pigment particles includes a pigment core and a coating resin.

(Pigment core)
The pigment core contains a pigment. As the pigment, for example, a yellow pigment, an orange pigment, a red pigment, a blue pigment, a purple pigment, or a black pigment can be used. Examples of yellow pigments include C.I. I. Pigment yellow 74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, or 193. Examples of the orange pigment include C.I. I. Pigment orange 34, 36, 43, 61, 63, or 71. Examples of red pigments include C.I. I. Pigment red 122 or 202. Quinacridone / magenta (PR122) may be used as the red pigment. Examples of blue pigments include C.I. I. Pigment Blue 15 or 15: 3. Examples of purple pigments include C.I. I. And CI Pigment Violet 19, 23, or 33. Examples of black pigments include C.I. I. And CI Pigment Black 7. Carbon black may be used as the black pigment.

  The content of the pigment core in the water-based ink is preferably 4% by mass or more and 8% by mass or less. When the content of the pigment core in the water-based ink is 4% by mass or more, an image having a desired image density is easily obtained. If the content of the pigment core in the water-based ink is 8% by mass or less, the fluidity of the water-based ink is easily secured. This also makes it easy to obtain an image having a desired image density. Further, the permeability of the water-based ink to the recording medium is easily ensured.

The volume median diameter (D ₅₀ ) of the pigment core is preferably 30.0 nm or more and 200 nm or less. This improves the color density, hue, or stability of the water-based ink. More preferably, the volume median diameter (D ₅₀ ) of the pigment core is 70.0 nm or more and 130 nm or less.

(Coating resin)
The coating resin is provided on the surface of the pigment core. The coating resin preferably has an anionic property, for example, styrene-acrylic acid resin, styrene-maleic acid copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, and vinyl. It is preferably at least one of naphthalene-maleic acid copolymers. More preferably, the coating resin is a styrene-acrylic acid resin. If the coating resin is a styrene-acrylic acid resin, pigment particles can be easily produced. Further, the dispersibility of the pigment core can be enhanced.

  The styrene-acrylic acid resin is a resin including a unit derived from styrene and a unit derived from acrylic acid, methacrylic acid, an acrylic ester, or a methacrylic ester. Preferably, the styrene-acrylic acid resin is a copolymer of styrene, acrylic acid, and alkyl acrylate, a copolymer of styrene, methacrylic acid, alkyl methacrylate, and alkyl acrylate, styrene and acrylic acid. A copolymer of styrene, maleic acid and alkyl acrylate, a copolymer of styrene and methacrylic acid, and a copolymer of styrene and alkyl methacrylate. is there. More preferably, the styrene-acrylic acid resin is a copolymer of styrene, methacrylic acid, a methacrylic acid alkyl ester, and an acrylic acid alkyl ester. More specifically, the styrene-acrylic acid resin is a copolymer of styrene, methacrylic acid, methyl methacrylate, and butyl acrylate.

  The content of the coating resin is preferably 15.0 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the pigment core. If the content of the coating resin is too small, there may be a case where the recording medium after the image formation is exposed. On the other hand, if the content of the coating resin is excessive, a desired image density may not be obtained.

<Aqueous solvent>
The aqueous solvent preferably contains water, more preferably ion-exchanged water. The water content in the water-based ink is preferably 20% by mass or more and 70% by mass or less. Thereby, the water-based ink which has a suitable viscosity can be provided.

  For example, the aqueous solvent preferably contains ion-exchanged water, glycerin and / or glycol, and alcohol and / or glycol ether. If the water-based ink contains glycerin and / or glycol, the water-based ink can be further prevented from drying. If the water-based ink contains alcohol and / or glycol ether, the permeability of the water-based ink to the recording medium can be improved.

  Examples of the glycol ether include diethylene glycol monoethyl ether, triethylene glycol mononormal butyl ether, triethylene glycol monoisobutyl ether, triethylene glycol monoisopropyl ether, and diethylene glycol mononormal butyl ether.

<Surfactant>
If the water-based ink contains a surfactant, the wettability of the water-based ink with respect to the recording medium is improved. The surfactant contained in the water-based ink is preferably a nonionic surfactant. The content of the nonionic surfactant in the water-based ink is preferably 0.050% by mass or more and 2.0% by mass or less. Thereby, the image density is improved while suppressing the offset of the image.

  The nonionic surfactant contained in the water-based ink is preferably an acetylene glycol surfactant, and more specifically “Olfin (registered trademark) E1010” manufactured by Nissin Chemical Industry Co., Ltd.

<Dissolution stabilizer>
If the water-based ink contains a dissolution stabilizer, the components contained in the water-based ink are easily compatible, so that the dissolved state of the water-based ink can be stabilized. The dissolution stabilizer is preferably at least one of 2-pyrrolidone, N-methyl-2-pyrrolidone, and γ-butyrolacton. The content of the dissolution stabilizer in the water-based ink is preferably 1.0% by mass or more and 20% by mass or less, and more preferably 3.0% by mass or more and 15% by mass or less.

<Humectant>
If the water-based ink contains a humectant, the volatilization of the liquid component from the water-based ink can be suppressed, so that the viscosity of the water-based ink can be stabilized. The humectant is preferably at least one of polyalkylene glycols, alkylene glycols, and glycerin. The polyalkylene glycol is preferably polyethylene glycol or polypropylene glycol. Alkylene glycols include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, trimethylene glycol (1,3-propylene glycol), triethylene glycol, tripropylene glycol, 1,2,6-hexanetriol, thiol Diglycol, 1,3-butanediol, or 1,5-pentanediol is preferred. The content of the humectant in the water-based ink is preferably 2.0% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less.

<Penetration agent>
If the water-based ink contains a penetrant, the penetrability of the water-based ink into the recording medium is improved. The penetrant is preferably 1,2-hexylene glycol, 1,2-octanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, At least one of triethylene glycol monobutyl ether and diethylene glycol monobutyl ether. The content of the penetrant in the aqueous ink is preferably 0.50% by mass or more and 20% by mass or less.

[Preferred production method of water-based ink]
A preferred method for producing a water-based ink includes a step of preparing a pigment dispersion and a step of mixing the pigment dispersion with other ink components.

<Pigment dispersion preparation process>
First, a coating resin is synthesized. Specifically, a monomer or prepolymer capable of synthesizing a coating resin by polymerization and a polymerization initiator are added to a predetermined solvent, and the mixture is heated to reflux at a predetermined temperature. In this way, the coating resin is synthesized. More specifically, styrene, (meth) acrylic acid, (meth) acrylic acid alkyl ester, and a polymerization initiator are added to a mixed solution of isopropyl alcohol and methyl ethyl ketone, and the mixture is heated to reflux at 70 ° C. Thereby, a styrene-acrylic acid resin is synthesized.

  Next, the synthesized resin, the pigment core, and the aqueous solvent are kneaded using a media-type disperser. In this way, a pigment dispersion containing a large number of pigment particles is obtained. By changing the particle diameter (for example, bead diameter) of the media used in the media type disperser, the degree of dispersion of the pigment particles, the amount of resin released from the pigment particles in the pigment dispersion, or the particle diameter of the pigment particles can be adjusted. . For example, the smaller the particle diameter of the media, the smaller the particle diameter of the pigment particles.

<Mixing process of pigment dispersion and other ink components>
The obtained pigment dispersion is mixed with other ink components. It is preferable to mix the pigment dispersion and the other ink components using a stirrer (for example, “Three-One Motor (registered trademark) BL-600” manufactured by Shinto Kagaku Co., Ltd.). Examples of other ink components include a first deliquescent agent. Preferably, the other ink component contains a first deliquescent agent and an aqueous solvent. More preferably, the other ink component contains a first deliquescent agent, an aqueous solvent, and component C. Component C preferably contains at least one of a surfactant, a dissolution stabilizer, a humectant, and a penetrant. After mixing the pigment dispersion and the other ink components, filtration is performed as necessary. In this way, an aqueous ink is obtained.

[Examples of materials for aqueous cleaning liquid]
As described above, the aqueous cleaning liquid contains the second deliquescent agent and the amphoteric surfactant. The second deliquescent agent is as described above in <Deliquescent Agent>. The amphoteric surfactant is as described above in <Amphoteric surfactant>. The aqueous cleaning liquid is preferably used for cleaning the ejection surface of the recording head. Further, the aqueous cleaning liquid can be used not only for cleaning the ejection surface but also for cleaning the blade used in the wiping operation or cleaning the transport roller.

  Preferably, the aqueous cleaning liquid further contains at least one of the aqueous solvent described in <Aqueous solvent> and the dissolution stabilizer described in <Solution stabilizer>. Thereby, in the water-based ink and the water-based cleaning liquid, at least one material of the water-based solvent and the dissolution stabilizer is the same or similar to each other. Therefore, the affinity between the aqueous cleaning liquid and the aqueous ink can be increased. Here, the fixed ink is formed by drying the water-based ink. Therefore, if the affinity between the aqueous cleaning liquid and the water-based ink can be increased, the affinity between the aqueous cleaning liquid and the fixed ink can be increased. Therefore, it becomes easier to enter the aqueous cleaning liquid.

[Preferred production method of aqueous cleaning liquid]
A preferred method for producing an aqueous cleaning liquid includes a step of uniformly mixing materials (for example, a second deliquescent agent and an amphoteric surfactant) in a predetermined blending amount. The materials are preferably mixed using a stirrer (for example, “Three-One Motor BL-600” manufactured by Shinto Kagaku Co., Ltd.).

  Examples of the present invention will be described. Note that the evaluation result (a value indicating the shape or physical properties) of the powder containing a plurality of particles is the number average of the values measured for a considerable number of particles unless otherwise specified. In the evaluation in which an error occurs, a considerable number of measurement values with which the error is sufficiently small are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

  Using the ink sets S-1 to S-33 according to Examples and Comparative Examples, the water-based ink ejection performance after the uncapping operation, the water-based ink intermittent ejection performance, and the presence or absence of sorbitol precipitation in the aqueous cleaning liquid evaluated. Table 1 shows the configurations of the ink sets S-1 to S-23. Table 2 shows the configurations of the ink sets S-24 to S-33.

  Below, first, the manufacturing method of a water-based ink and the manufacturing method of an aqueous cleaning liquid are demonstrated in order. Next, an ink set evaluation method and evaluation results will be described in order.

[Method for producing water-based ink]
Table 3 shows the configurations of the water-based inks I-1 to I-5. Each of the water-based inks I-1 to I-5 included a cyan-based water-based ink, a yellow-based water-based ink, a magenta-based water-based ink, and a black-based water-based ink. Hereinafter, a method for producing a cyan water-based ink will be mainly described. In addition, when not describing the color of water-based ink, it describes only as "water-based ink".

  In Table 3, “EO adduct of acetylenic diol” means “Olfin E1010” manufactured by Nissin Chemical Industry Co., Ltd., and “EO” means ethylene oxide. “Ether” means triethylene glycol mononormal butyl ether. Further, “the blending amount of ion-exchanged water is an adjustment amount” and “the blending amount of glycerin is an adjustment amount” means that the viscosity of each of the water-based inks I-1 to I-5 at 25 ° C. It means that the blending amount of ion-exchanged water and the blending amount of glycerin were adjusted to 6.0 ± 0.20. The viscosity of each of the water-based inks I-1 to I-5 was measured in accordance with the method described in “JIS Z 8803: 2011 (liquid viscosity measurement method)”. The composition of “pigment dispersion L1” is as shown in Table 4.

  In Table 4, “resin A-Na” means resin A neutralized with an aqueous solution of sodium hydroxide (NaOH). The cyan water-based ink contained 40.0% by mass of the pigment dispersion L1 (see Table 3). Here, the pigment dispersion L1 contained 15.0% by mass of a cyan pigment (see Table 4). Therefore, the cyan aqueous ink contained 6.00% by mass of a cyan pigment.

<Method for Producing Pigment Dispersion Liquid L1>
(Synthesis of Resin A)
First, resin A was synthesized. Specifically, a stirrer, a nitrogen introducing tube, a condenser (stirrer), and a dropping funnel were set in a four-necked flask (capacity 1000 mL). The flask was then charged with 100 g isopropyl alcohol and 300 g methyl ethyl ketone. The flask was heated to reflux at 70 ° C. while bubbling nitrogen through the contents.

  Also 40.0 g styrene, 10.0 g methacrylic acid, 40.0 g methyl methacrylate, 10.0 g butyl acrylate, 0.400 g azobisisobutyronitrile (AIBN, polymerization initiated) The monomer solution was obtained. The monomer solution was added dropwise to the flask over about 2 hours in a state heated to reflux at 70 ° C. After the dropwise addition, the mixture was further refluxed at 70 ° C. for 6 hours.

  A solution containing 0.200 g of AIBN and methyl ethyl ketone was added dropwise to the flask over 15 minutes. After the dropwise addition, the mixture was further refluxed at 70 ° C. for 5 hours. Thus, Resin A (styrene-acrylic acid resin) was obtained. In the obtained resin A, the mass average molecular weight (Mw) was 20000, and the acid value was 100 mgKOH / g.

Here, the mass average molecular weight Mw of the resin A was measured under the following conditions using gel filtration chromatography (“HLC-8020GPC” manufactured by Tosoh Corporation).
Column: “TSKgel SuperMultipore HZ-H” manufactured by Tosoh Corporation (semi-micro column of 4.6 mm ID × 15 cm)
Number of columns: 3 Eluent: Tetrahydrofuran Flow rate: 0.35 mL / min Sample injection volume: 10 μL
Measurement temperature: 40 ° C
Detector: IR detector In addition, a calibration curve is F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000 from TSKgel standard polystyrene made from Tosoh Corporation. 7 types and n-propylbenzene were selected.

  The acid value of the resin A is described in “JIS (Japanese Industrial Standard) K0070-1992 (acid acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponified test method for chemical products)”. Required in accordance with the method.

(Preparation of pigment dispersion L1)
Next, using the synthesized resin A, a pigment dispersion L1 was prepared. Specifically, 6.00% by mass of Resin A and 15.0% by mass of phthalocyanine were added to a vessel (capacity 0.6 L) of a media-type disperser (“Dynomill” manufactured by Willy et Bacofen (WAB)). Blue 15: 3 (“Lionol (registered trademark) Blue FG-7330” manufactured by Toyo Ink Co., Ltd.), 0.500% by mass of 1,2-octanediol, and ion-exchanged water (remaining amount) were added.

  Further, an aqueous sodium hydroxide solution necessary for neutralizing the resin A was added to the vessel. Here, an aqueous NaOH solution was added to the vessel so that the pH of the vessel content was 8. More specifically, an aqueous NaOH solution having a mass 1.1 times the neutralization equivalent was added to the vessel. The mass of Na to be added to the vessel was added to the mass of Resin A. The mass of water contained in the NaOH aqueous solution and the mass of water generated by the neutralization reaction were added to the mass of ion-exchanged water.

The vessel was filled with media (zirconia beads having a diameter of 0.5 mm) so that the filling amount was 70% by volume with respect to the vessel capacity. Media type dispersion so that the volume median diameter (D ₅₀ ) of pigment particles falls within the range of 70.0 nm or more and 130 nm or less while water-cooling the vessel under conditions where the temperature is 10 ° C. and the peripheral speed is 8 m / sec. The vessel contents were kneaded using a machine. Thus, a pigment dispersion L1 was obtained.

Here, the volume median diameter (D ₅₀ ) of the pigment particles is a value measured using a laser diffraction particle size distribution analyzer (“Zeta Sizer Nano ZS” manufactured by Malvern).

<Mixing of pigment dispersion L1 and other ink components>
The materials listed in Table 3 were placed in a beaker with the blending amounts listed in Table 3. Using a stirrer (“Three-One Motor BL-600” manufactured by Shinto Kagaku Co., Ltd.), the contents of the beaker were stirred at a rotation speed of 400 rpm to uniformly mix the contents of the beaker. The liquid mixture obtained using a filter (pore size 5 μm) was filtered to remove foreign substances and coarse particles contained in the liquid mixture. In this way, a cyan-based aqueous ink was obtained.

  A yellow aqueous ink was produced according to the cyan aqueous ink production method except for the following points. Specifically, a pigment dispersion L1 was produced using a yellow pigment (more specifically, CI Pigment Yellow 74) as a pigment and a blending amount of the yellow pigment being 16.3% by mass. Using the obtained pigment dispersion L1, a yellow-based aqueous ink was produced.

  The yellow aqueous ink contained 40.0% by mass of the pigment dispersion L1 (see Table 3). Here, the pigment dispersion L1 contained 16.3 mass% of a yellow pigment. For this reason, the yellow aqueous ink contained 6.50% by mass of a yellow pigment.

  A magenta water-based ink was manufactured according to the cyan water-based ink manufacturing method except for the following points. Specifically, a magenta pigment (more specifically, quinacridone magenta (PR122)) was used as the pigment, and the pigment dispersion L1 was produced with the blending amount of the magenta pigment being 20.0% by mass. A magenta water-based ink was manufactured using the obtained pigment dispersion L1.

  The magenta water-based ink contained 40.0% by mass of the pigment dispersion L1 (see Table 3). Here, the pigment dispersion L1 contained 20.0% by mass of a magenta pigment. Therefore, the magenta water-based ink contains 8.00% by mass of a magenta pigment.

  A black aqueous ink was produced according to the cyan aqueous ink production method except for the following points. Specifically, a black pigment (more specifically, carbon black) was used as the pigment, and the pigment dispersion L1 was produced with the blending amount of the black pigment being 20.0% by mass. A black water-based ink was produced using the obtained pigment dispersion L1.

  The black aqueous ink contained 40.0% by mass of the pigment dispersion L1 (see Table 3). Here, the pigment dispersion L1 contained 20.0% by mass of a black pigment. Therefore, the black aqueous ink contained 8.00% by mass of a black pigment.

[Method for producing aqueous cleaning liquid]
Table 5 shows the configurations of the aqueous cleaning liquids C-01 to C-05. Table 6 shows the configurations of the aqueous cleaning liquids C-11 to C-14. Table 7 shows the configurations of the aqueous cleaning liquids C-21 to C-24.

  In Tables 5 to 7, “the blending amount of ion-exchanged water is an adjustment amount” and “the blending amount of 1,3-propylene glycol is an adjustment amount” are the viscosity of an aqueous cleaning liquid at 25 ° C. Means that the blending amount of ion-exchanged water and the blending amount of 1,3-propylene glycol were adjusted so as to be 15 ± 2.0. The viscosity of each of the aqueous cleaning liquids was measured in accordance with the method described in “JIS Z 8803: 2011 (liquid viscosity measuring method)”. Further, the surfactants a to e are as shown in Table 8.

  The materials described in Tables 5 to 7 were put in a beaker with the blending amounts described in Tables 5 to 7. Using a stirrer (“Three-One Motor BL-600” manufactured by Shinto Kagaku Co., Ltd.), the contents of the beaker were stirred at a rotation speed of 400 rpm to uniformly mix the contents of the beaker. In this way, aqueous cleaning liquids C-01 to C-05, C-11 to C-14, and C-21 to C-24 were obtained.

[Evaluation method of ink set]
<Water-based ink ejection performance after uncapping operation>
The water-based ink ejection performance after the uncapping operation was evaluated according to the following method.
Specifically, first, an evaluation machine was prepared. As an evaluation machine, an inkjet recording apparatus (prototype evaluation machine manufactured by Kyocera Document Solutions Co., Ltd.) provided with four recording heads (each line head) was used. Each of the recording heads has a resolution of 360 dpi (= 180 dpi × 2 rows), 512 nozzles (= 256 × 2 rows), a droplet amount of 14 pL, and a driving frequency of 12.8 kHz (manufactured by Konica Minolta, Inc.). Met. The recording heads were arranged at an interval of 20 mm so that the longitudinal direction thereof was orthogonal to the paper transport direction. The four recording heads were filled with water-based inks having different colors (water-based inks included in the ink sets of Examples and Comparative Examples). Also, the nozzle surface was washed and therefore was not contaminated with aqueous ink.

  Next, in the evaluation machine, a purge operation, an aqueous cleaning liquid supply, and a wipe operation were performed. Specifically, first, each of the four recording heads performed a purge process (purge operation). In addition, the size of the cut product and the cut product of “Bencot (registered trademark) M-3II” manufactured by Asahi Kasei Co., Ltd., impregnated with 3 g of the aqueous cleaning solution (the aqueous cleaning solution of the ink sets of Examples and Comparative Examples). Was larger than the size of the nozzle surface). The sheet was brought into contact with the nozzle surfaces of each of the four recording heads for 30 seconds (supply of aqueous cleaning liquid). Next, the tip of the blade included in the evaluator was wiped on each nozzle surface of the four recording heads (wiping operation). This series of operations (hereinafter referred to as “maintenance operation”) was performed 600 times.

  Subsequently, a capping operation was performed. In the capping operation, each nozzle surface of the four recording heads was covered with a rubber cap. Thereby, the opening of the nozzle was sealed. With the nozzle opening sealed, the evaluator was allowed to stand for 1 week in a normal temperature and normal humidity environment (more specifically, an environment having a temperature of 25 ° C. and a humidity of 60% RH). Thereafter, an uncapping operation was performed. In the uncapping operation, the rubber caps were removed from the nozzle surfaces of the four recording heads. Thereby, the sealing state of the nozzle opening was released.

Subsequently, a maintenance operation was performed until water-based ink was normally ejected from all nozzles of the four recording heads. Here, “water-based ink is normally ejected” means that the water-based ink is ejected in a desired ejection direction without difficulty. Then, the number of maintenance operations required until water-based ink is normally ejected (hereinafter simply referred to as “the number of maintenance operations”) is counted to evaluate the water-based ink ejection performance after the uncapping operation. did.
Good (○): The maintenance operation is performed once. Poor (×): The maintenance operation is performed twice or more.

<Intermittent ejection performance of water-based ink>
In accordance with the method shown below, the intermittent discharge performance of water-based ink was evaluated.
Specifically, first, an evaluator was prepared according to the method described in <Water-based ink ejection performance after uncapping operation>. In addition, the evaluation machine was adjusted so that the amount of water-based ink ejected from the recording head was 11 pL per ink drop.

Next, using an evaluator, in the environment of a temperature of 25 ° C. and a humidity of 60% RH, one recording sheet (“C ² ” manufactured by Fuji Xerox Co., Ltd., A4 size plain paper) in the conveyance direction rear end One dot row was formed. More specifically, one drop of water-based ink was ejected from all nozzles of the four recording heads with respect to the rear end in the conveyance direction of one recording sheet. At this time, the recording sheet was conveyed so that the longitudinal direction of the recording sheet was perpendicular to the conveying direction of the recording sheet. And the presence or absence of disorder of a dot row was confirmed visually, and the intermittent discharge performance of water-based ink was evaluated.
Good (O): Disturbance was not confirmed in the dot row. Poor (X): Disturbance was confirmed in the dot row.

<Presence or absence of sorbitol precipitation in aqueous cleaning solution>
First, the aqueous cleaning liquid was allowed to stand for 1 week in an environment of a temperature of 32.5 ° C. and a humidity of 10% RH. And the presence or absence of precipitation of sorbitol in an aqueous washing | cleaning liquid was confirmed visually.
Good (◯): No sorbitol precipitation was confirmed. Bad (×): sorbitol precipitation was confirmed.

[Ink set evaluation results]
Tables 9 and 10 show the evaluation results of the ink set. In Tables 9 and 10, evaluation A shows the evaluation result of the water-based ink ejection performance after the uncapping operation. Evaluation B shows the evaluation result of the intermittent discharge performance of water-based ink. Evaluation C shows the results of evaluating the presence or absence of sorbitol precipitation in the aqueous cleaning solution.

[Discussion]
The ink sets according to Examples 1 to 15 had water-based ink and water-based cleaning liquid. Specifically, the water-based ink and the water-based cleaning liquid each contained sorbitol. The content of sorbitol in the water-based ink was 0.10% by mass or more and 7.0% by mass or less. The content of sorbitol in the aqueous cleaning solution was 0.10% by mass or more and 10% by mass or less. The aqueous cleaning solution further contained an amphoteric surfactant. As a result, the water-based ink ejection performance was maintained even after the uncapping operation. Moreover, the fall of the intermittent discharge performance of water-based ink was prevented. Furthermore, it was possible to prevent sorbitol from being precipitated in the aqueous cleaning solution.

  The present inventors have confirmed the following. Specifically, when at least one of trimethylolpropane and 1,3-bis (2-hydroxyethyl) -5,5-dimethyl-2,4-imidazolidinedione is used instead of sorbitol, Also, the results showing the same tendency as the results described in Table 9 and Table 10 were obtained.

  The ink set according to the present invention can be used for forming an image in a color printer, for example.

4 Recording head 47 Discharge surface 51 Cartridge 52 First tank 53 Second tank S Recording medium

Claims (7)

Having water-based ink and water-based cleaning liquid,
The water-based ink and the water-based cleaning liquid each contain a deliquescent agent,
The content of the deliquescent agent in the water-based ink is 0.10% by mass or more and 7.0% by mass or less,
The content of the deliquescent agent in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less,
The aqueous cleaning liquid is an ink set for inkjet recording, further containing an amphoteric surfactant.   The inkjet recording ink according to claim 1, wherein the amphoteric surfactant is at least one of lauryl dimethylamine oxide, lauryl dimethylaminoacetic acid betaine, coconut oil fatty acid amidopropyl betaine, and octanoic acid amidopropyl betaine. set.   The ink set for inkjet recording according to claim 1 or 2, wherein the content of the amphoteric surfactant in the aqueous cleaning liquid is 0.10% by mass or more.   The deliquescent agent contained in the aqueous ink and the deliquescent agent contained in the aqueous cleaning liquid are each independently sorbitol, trimethylolpropane, and 1,3-bis (2-hydroxyethyl) -5,5- The ink set for inkjet recording according to any one of claims 1 to 3, which is at least one of dimethyl-2,4-imidazolidinedione. The water-based ink is ejected from the ejection surface of the recording head,
The ink set for inkjet recording according to claim 1, wherein the aqueous cleaning liquid is used for cleaning the ejection surface. A first tank that contains the water-based ink included in the ink set for inkjet recording according to any one of claims 1 to 5;
A second tank that contains the aqueous cleaning liquid of the ink set for inkjet recording according to any one of claims 1 to 5;
Including the cartridge. A discharge step of discharging the water-based ink from the discharge surface of the recording head to the recording medium;
A supply step of supplying an aqueous cleaning liquid to the discharge surface;
A purge step of pressurizing and discharging the water-based ink from the ejection surface;
A wiping step of wiping the discharge surface;
Including
The supply step and the purge step are each performed after the discharge step and before the wipe step,
The water-based ink and the water-based cleaning liquid each contain a deliquescent agent,
The content of the deliquescent agent in the water-based ink is 0.10% by mass or more and 7.0% by mass or less,
The content of the deliquescent agent in the aqueous cleaning liquid is 0.10% by mass or more and 10% by mass or less,
The image forming method, wherein the aqueous cleaning liquid further contains an amphoteric surfactant.

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