JP2018090698A - Ink set for inkjet recording, cartridge and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set capable of preventing the occurrence of an ink discharge failure.SOLUTION: There is provided an ink set for inkjet recording which comprises an aqueous ink and an aqueous cleaning solution. The aqueous cleaning solution contains a nonionic surfactant and a pH adjuster. The nonionic surfactant contains a first nonionic surfactant having an amino group in the molecule. The pH adjuster is an alkali metal salt. The pH of the aqueous ink is higher than the pH of the aqueous cleaning solution. The pH of the aqueous ink and the pH of the aqueous cleaning solution satisfy the following expressions (A) and (B): 0.50≤ΔpH≤1.0 Expression (A) and 8.0≤(the pH of the aqueous cleaning solution)≤9.0 Expression (B). In above Expression (A), ΔpH is represented by the following expression (C): ΔpH=(the pH of the aqueous ink)-(the pH of the aqueous cleaning solution) Expression (C).SELECTED DRAWING: None

Description

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

  For example, Patent Document 1 describes the following method as an image forming method using an inkjet method. First, ink jet recording ink (hereinafter sometimes simply referred to as “ink”) is ejected from the ejection surface of the recording head onto a recording medium. Next, maintenance liquid is supplied to the discharge surface.

JP2013-146964A

  As described above, in the image forming method using the ink jet method, ink is ejected from the ejection surface of the recording head onto the recording medium. More specifically, ink is ejected from each of a large number of ejection openings formed on the ejection surface toward the recording medium. For this reason, the ejection surface may be contaminated with ink. Here, in the water-based ink, the solvent component contained in the ink is easily evaporated as compared with the non-water-based ink. Therefore, since the water-based ink is easier to dry on the ejection surface than the non-aqueous ink, the water-based ink is easily fixed to the ejection surface.

  When the ink is fixed on the discharge surface, the fixed ink (hereinafter sometimes referred to as “fixed ink”) may block the discharge port. As a result, ink ejection failure occurs. For example, it becomes difficult to eject ink. Further, the ink is ejected in a direction different from the desired ejection direction. When ink ejection failure occurs, the image quality deteriorates. Therefore, it is required to prevent the occurrence of defective ink ejection.

  Incidentally, after the ink is ejected from the ejection surface of the recording head to the recording medium, a purge operation and a wiping operation are usually performed. Here, in the purge operation, the ink is pressurized and discharged from the ejection port. The wipe operation is performed after the purge operation. In the wiping operation, the discharge surface is wiped off. If the ink discharged by the purge operation (hereinafter sometimes referred to as “purge ink”) dissolves the fixed ink, the fixed ink is wiped from the ejection surface by the wipe operation. However, there are cases where the fixed ink is not sufficiently dissolved by the purge ink. In this case, as described in Patent Document 1, the discharge surface is cleaned using a maintenance liquid (cleaning liquid).

  Patent Document 1 describes the following. The maintenance liquid contains a surfactant having a specific chemical structure. This surfactant penetrates into the fixed ink and promotes the solubility of the fixed ink. Therefore, it is possible to provide a maintenance liquid having excellent solubility of the fixed ink.

  However, it has now been found that even when the surfactant contained in the maintenance liquid has the specific chemical structure described in Patent Document 1, it is not possible to prevent the occurrence of defective ink ejection. It has also been found that the occurrence of ink ejection failure cannot be prevented simply by changing the surfactant material.

  The present invention has been made in view of such circumstances, and provides an ink set capable of preventing the occurrence of defective ink ejection, and providing a cartridge including an ink set capable of preventing the occurrence of defective ink ejection; An object of the present invention is to provide an image forming method using an ink set capable of preventing the occurrence of defective ink ejection.

The ink set for inkjet recording according to the present invention includes a water-based ink and a water-based cleaning liquid. The aqueous cleaning liquid contains a nonionic surfactant and a pH adjuster. The nonionic surfactant contains a first nonionic surfactant having an amino group in the molecule. The pH adjuster is an alkali metal salt. The pH of the aqueous ink is higher than the pH of the aqueous cleaning liquid. The pH of the water-based ink and the pH of the water-based cleaning liquid satisfy the following formulas (A) and (B).
0.50 ≦ ΔpH ≦ 1.0 Formula (A)
8.0 ≦ (pH of the aqueous cleaning liquid) ≦ 9.0 Formula (B)
In the above formula (A), ΔpH is represented by the following formula (C).
ΔpH = (pH of the water-based ink) − (pH of the water-based cleaning liquid) Formula (C)

  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 aqueous cleaning liquid contains a nonionic surfactant and a pH adjuster. The nonionic surfactant contains a first nonionic surfactant having an amino group in the molecule. The pH adjuster is an alkali metal salt. The pH of the aqueous ink is higher than the pH of the aqueous cleaning liquid. The pH of the water-based ink and the pH of the water-based cleaning liquid satisfy the following formulas (A) and (B).
0.50 ≦ ΔpH ≦ 1.0 Formula (A)
8.0 ≦ (pH of the aqueous cleaning liquid) ≦ 9.0 Formula (B)
In the above formula (A), ΔpH is represented by the following formula (C).
ΔpH = (pH of the water-based ink) − (pH of the water-based cleaning liquid) Formula (C)

  According to the present invention, it is possible to prevent occurrence of defective ink ejection.

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 1 process of the image forming method concerning this invention. It is a figure explaining 1 process of the image forming method concerning 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. The measured value of the volume median diameter (D ₅₀ ) of the powder is a laser diffraction particle size distribution measuring device (“Zetasizer nano-ZS” manufactured by Malvern, Inc.) unless otherwise specified. It is the value measured using. 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”.

[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 aqueous cleaning liquid contains a nonionic surfactant and a pH adjuster. The nonionic surfactant contains a first nonionic surfactant having an amino group in the molecule. The pH adjuster is an alkali metal salt. The pH of the aqueous ink is higher than the pH of the aqueous cleaning liquid. The pH of the aqueous ink and the pH of the aqueous cleaning liquid satisfy the following formulas (A) and (B).
0.50 ≦ ΔpH ≦ 1.0 Formula (A)
8.0 ≦ (pH of aqueous cleaning solution) ≦ 9.0 Formula (B)
In the above formula (A), ΔpH is represented by the following formula (C).
ΔpH = (pH of aqueous ink) − (pH of aqueous cleaning liquid) Formula (C)
Here, “the pH of the water-based ink is higher than the pH of the aqueous cleaning solution” and that the formula (A) is satisfied are synonymous. Further, the pH of the water-based ink and the pH of the water-based cleaning liquid are each measured by the method described in Examples described later or a method analogous thereto.

  The ink set according to the present embodiment has the above configuration. If an image is formed using the ink set according to the present embodiment, an image can be formed without causing an ink ejection defect.

  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. The purge operation may be performed after the aqueous cleaning liquid is supplied to the discharge surface, or the aqueous cleaning liquid may be supplied to the discharge surface after the purge operation. Thereafter, a wiping operation is performed. Thus, in this embodiment, it is preferable that the water-based ink is discharged from the discharge surface of the recording head, and the aqueous cleaning liquid is preferably used for cleaning the discharge surface. Here, “cleaning the ejection surface” includes removing the fixed ink from the ejection surface. Below, for convenience of explanation, first, 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 easily forms 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. Here, the pigment particles preferably include a pigment core and a coating resin provided on the surface of the pigment core (see <Preferred configuration of water-based ink> above). Therefore, when the pigment particles are aggregated with each other, the coating resins existing on the surfaces of the different pigment cores are easily brought 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 why ink discharge failure can be prevented>
Next, the reason why it is possible to prevent the occurrence of defective ink ejection when image formation is performed using the ink set according to the present embodiment will be described in detail.

  In this embodiment, the aqueous cleaning liquid contains an alkali metal salt as a pH adjuster. Moreover, in this embodiment, Formula (A) and (B) are satisfy | filled. For these reasons, it is difficult to form fixed ink.

Specifically, as described in the above <fixed ink formation process>, when the water-based ink is dried on the ejection surface, the fixed ink is formed. However, it is considered that the aqueous cleaning liquid is often supplied to the ejection surface during the formation of the fixed ink. Here, as described in <Preferred configuration of water-based ink>, in the presence of a sufficient amount of an aqueous solvent, ionization tends to occur on the surface of the coating resin. Therefore, if the aqueous cleaning liquid is supplied to the ejection surface during the formation of the fixed ink, ionization tends to occur on the surface of the coating resin. For example, when the resin salt has a COONa group in the molecule, the surface of the coating resin is negatively charged (COO ⁻ ), and Na ⁺ adheres to the surface of the coating resin by electrical attraction.

  In the present embodiment, the aqueous cleaning liquid contains an alkali metal salt as a pH adjuster. Therefore, the pH adjuster is easily ionized into alkali metal ions and anions in the aqueous cleaning liquid. Therefore, when the aqueous cleaning liquid is supplied to the ejection surface during the formation of the fixed ink, not only the metal ions ionized from the resin salt but also the alkali metal ions ionized from the pH adjuster are electrically It adheres by attractive force.

  Here, the water-based ink often exhibits weak basicity. Therefore, if ΔpH is 0.50 or more and the pH of the water washing cleaning liquid is 8.0 or more, it is possible to prevent the pH of the aqueous cleaning liquid from becoming too low. Thereby, since the content of the pH adjusting agent in the aqueous cleaning liquid can be ensured, the amount of alkali metal ions ionized from the pH adjusting agent can be ensured. Therefore, the amount of alkali metal ions that can adhere to the surface of the coating resin can be secured. Therefore, a large electric repulsive force acts between the pigment particles.

  If a relatively large electric repulsive force acts between the pigment particles, the pigment particles are easily dispersed. As a result, the fixed ink is difficult to be formed (see <Fixed Ink Formation Process> above).

  Moreover, if ΔpH is 1.0 or less and the pH of the water washing cleaning liquid is 9.0 or less, it is possible to prevent the pH of the aqueous cleaning liquid from becoming too high. Thereby, it can prevent that the resin film which consists of coating resin is formed. This can also prevent the formation of fixed ink.

  Thus, in this embodiment, it is difficult to form fixed ink. Therefore, liquid (for example, aqueous cleaning liquid or purge ink) can enter between adjacent pigment particles.

  Furthermore, the aqueous cleaning liquid in the present embodiment contains a first nonionic surfactant. The present inventors have now examined the relationship between the surfactant material contained in the aqueous cleaning liquid and the prevention of ink ejection failure. As a result, the present inventors have found that if the aqueous cleaning liquid contains the first nonionic surfactant, it is easy to prevent the occurrence of ink ejection failure (see Evaluation 4 described later). As a reason why such a result is obtained, the present inventors consider the following. The first nonionic surfactant has an amino group in the molecule. Therefore, the first nonionic surfactant is more likely to enter between adjacent pigment particles as compared to other surfactants. Therefore, the aqueous cleaning liquid according to the present embodiment is easier to enter between adjacent pigment particles than the aqueous cleaning liquid containing a surfactant different from the first nonionic surfactant. Here, “other surfactant” and “surfactant different from the first nonionic surfactant” include a nonionic surfactant different from the first nonionic surfactant, respectively. , Cationic surfactants, anionic surfactants and amphoteric surfactants are included.

  Moreover, in the present embodiment, since the formula (A) is satisfied, the aqueous cleaning liquid exhibits high affinity for the aqueous ink. Therefore, the aqueous cleaning liquid has a high affinity for the purge ink. Further, as described above, the aqueous cleaning liquid according to the present embodiment easily enters between adjacent pigment particles. Accordingly, when the aqueous cleaning liquid is supplied to the ejection surface and the purge operation is performed, the purge ink easily enters between adjacent pigment particles together with the aqueous cleaning liquid.

  Thus, in this embodiment, the purge ink is likely to enter between adjacent pigment particles. 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 the occurrence of ink ejection failure.

  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.

[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, an image can be formed without causing ink ejection failure.

[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. In the image forming method according to the present embodiment, the discharge process, the supply process, the purge process, and the wipe process may be performed in this order, or the discharge process, the purge process, the supply process, and the wipe process are performed in this order. Also good. Preferably, the discharge process, the supply process, the purge process, and the wipe process are performed in this order. Each of the water-based ink and the water-based cleaning liquid is as described in the above [Ink set for inkjet recording according to this embodiment]. Therefore, an image can be formed without causing ink ejection failure.

  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.

  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. FIG. 2 is a diagram for explaining one process of the image forming method according to the present embodiment, and more specifically for explaining the supply process. FIG. 3 is a diagram for explaining another process of the image forming method according to the present embodiment, and more specifically for explaining a purge operation and a 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 descending 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 the 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 blade 92 removes the fixed ink. The image forming method according to the present embodiment has been described above with reference to FIGS. In the case where an image is formed on the recording medium S using the image forming apparatus 1 shown in FIG. 1, the discharge process, the purge process, the supply process, and the wipe process may be performed in this order.

  Hereinafter, the pH of the water-based ink, the example of the material of the water-based ink, the preferable method for manufacturing the water-based ink, the example of the material of the aqueous cleaning solution, and the preferable method of manufacturing the aqueous cleaning solution will be described in order.

[PH of water-based ink]
The pH of the water-based ink is preferably 8.5 or more and 10 or less. Thereby, it becomes easy to satisfy | fill Formula (A).

[Examples of water-based ink materials]
The aqueous ink preferably contains a pH adjuster. More preferably, the water-based ink contains a pH adjuster, a pigment dispersion, and an aqueous solvent. More preferably, the water-based ink contains a pH adjuster, 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.

<PH adjuster>
The aqueous ink preferably contains a pH adjuster. As a result, the pH of the water-based ink tends to be 8.5 or more and 10 or less. It is preferable to determine the content of the pH adjuster in the water-based ink so that the pH of the water-based ink is 8.5 or more and 10 or less.

  The pH adjuster is preferably an alkali metal salt. As a result, the pH adjuster is ionized into alkali metal ions and anions not only in the aqueous cleaning liquid but also in the aqueous ink. Therefore, alkali metal ions ionized from the pH adjusting agent contained in the water-based ink also adhere to the surface of the coating resin. Therefore, since the electric repulsion force acting between the pigment particles tends to increase, the aggregation of the pigment particles can be further prevented. Therefore, it becomes easier to remove the fixed ink from the ejection surface, and thus it is possible to further prevent the occurrence of ink ejection failure.

  The alkali metal salt is preferably an alkali metal hydroxide. More preferably, the alkali metal salt comprises at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide.

<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. 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.

  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-propanediol), 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% 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 to 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.). The other ink component is preferably a pH adjuster. More preferably, the other ink component contains a pH adjuster and an aqueous solvent. More preferably, a pH adjuster, an aqueous solvent, and component C are contained. 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 first nonionic surfactant and the pH adjuster.

  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. Therefore, it becomes easier for the aqueous cleaning liquid to enter between adjacent pigment particles.

<First nonionic surfactant>
The first nonionic surfactant is preferably, for example, polyoxyalkylene alkylamine or polyoxyethylene cumylphenyl ether. The polyoxyalkylene alkylamine preferably has a structure represented by the following formula (1-1). Examples of the polyoxyalkylene alkylamine include “Amate (registered trademark) 105A” manufactured by Kao Corporation, “Amate 320” manufactured by Kao Corporation, or “Puamyl (registered trademark) EP-300S manufactured by Sanyo Chemical Industries, Ltd. Can be used.

In the above formula (1-1), R ¹ represents a hydrocarbon group having 1 to 24 carbon atoms. Preferably, R ¹ represents an alkyl group or an alkenyl group having 1 to 24 carbon atoms. A ¹ O and A ² O each independently represent at least one of an oxyethylene group and an oxypropylene group. m1 and n1 each represents an integer of 0 or more, and represents an integer satisfying 1 ≦ (m1 + n1) ≦ 100. Preferably, m1 and n1 each represents an integer of 0 or more, and represents an integer satisfying 1 ≦ (m1 + n1) ≦ 40.

  The content of the first nonionic surfactant in the aqueous cleaning liquid is preferably 0.50% by mass or more and 20% by mass or less. Thereby, the quantity of the aqueous washing | cleaning liquid which permeates between adjacent pigment particles is securable. Therefore, the amount of purge ink that enters between adjacent pigment particles can be secured. When the aqueous cleaning liquid contains two or more kinds of first nonionic surfactants, the total content of the first nonionic surfactant in the aqueous cleaning liquid is 0.50% by mass or more and 20% by mass. The following is preferable.

  By the way, as the surfactant, in addition to the nonionic surfactant, a cationic surfactant, an anionic surfactant and an amphoteric surfactant are known. However, the aqueous cleaning liquid according to this embodiment contains a nonionic 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.

<PH adjuster>
The pH adjuster is an alkali metal salt. It is preferable to determine the content of the pH adjuster in the aqueous cleaning liquid so that the formulas (A) and (B) are satisfied.

  The alkali metal salt is preferably an alkali metal hydroxide. More preferably, the alkali metal salt comprises at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide.

[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 first nonionic surfactant and a pH adjusting agent) 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.

In evaluations 1 to 5, using the ink sets according to Examples and Comparative Examples, the wipeability of the fixed ink and the rate of change in the volume median diameter (D ₅₀ ) of the pigment particles were evaluated. In Evaluations 1 to 5, the method for producing the aqueous ink is common except for the configuration of the aqueous ink, and the method for producing the aqueous cleaning liquid is common except for the configuration of the aqueous cleaning solution. In the evaluations 1 to 5, the method for measuring the pH of the aqueous ink, the method for measuring the pH of the aqueous cleaning liquid, and the method for evaluating the ink set are common. Therefore, in the following, first, a part common in evaluations 1 to 5 among the production methods of the water-based ink, a part common in evaluations 1 to 5 among the production methods of the aqueous cleaning liquid, a method for measuring the pH of the water-based ink, A method for measuring the pH of the aqueous cleaning liquid and a method for evaluating the ink set will be described. Next, evaluation 1-5 is demonstrated in order.

[Parts common to evaluations 1 to 5 of the water-based ink production method]
<Method for Producing Pigment Dispersion Liquid L1>
Table 1 shows the configuration of the pigment dispersion L1 used in the production of the water-based ink. In Table 1, “resin A-Na” means resin A neutralized with an aqueous solution of sodium hydroxide (NaOH).

  Table 2 shows the configuration of the water-based ink. In Table 2, “EO adduct of acetylenic diol” means “Orphine E1010” manufactured by Nissin Chemical Industry Co., Ltd., and “EO” means ethylene oxide.

(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. The media-type disperser is adjusted so that the volume median diameter (D ₅₀ ) of the pigment particles falls within the range of 70 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. Thus, a pigment dispersion L1 was obtained.

Here, the volume median diameter (D ₅₀ ) of the pigment particles was measured using a laser diffraction particle size distribution measuring apparatus (“Zetasizer nano-ZS (Zetasizer Nano ZS)” manufactured by Malvern).

(Mixing of pigment dispersion L1 and other ink components)
The materials listed in Table 2 were placed in a beaker with the blending amounts listed in Table 2. 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, an aqueous ink was obtained. In addition, about the material of a pH adjuster, it shows by the below-mentioned evaluation 1-5. Further, “the blending amount of the pH adjusting agent is the adjusting amount (see Table 2)” means that the pH adjusting agent is blended so that the pH of the water-based ink becomes a value shown in each of Tables 4 to 7 and 9 below. Means that the amount has been adjusted.

[Parts common to evaluations 1 to 5 in the manufacturing method of the aqueous cleaning liquid]
Table 3 shows the configuration of the aqueous cleaning liquid.
Specifically, the materials described in Table 3 were put in a beaker with the blending amounts described 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. In this way, an aqueous cleaning solution was obtained. In addition, about the material of surfactant, the compounding quantity X of surfactant, and the material of a pH adjuster, it shows by the below-mentioned evaluation 1-5, respectively. Further, “the blending amount of the pH adjusting agent is the adjusting amount (see Table 3)” means that the pH of the aqueous cleaning liquid is blended so as to have the values shown in Tables 4 to 7 and 9 below. Means that the amount has been adjusted.

[Measurement Methods for Aqueous Ink pH and Aqueous Cleaning Liquid pH]
The pH of the aqueous ink and the pH of the aqueous cleaning liquid were each measured using a pH meter (“D-51” manufactured by Horiba, Ltd.).

[Evaluation method]
<Evaluation of wiping property of fixed ink>
According to the following method, the wiping property of the fixed ink was evaluated.
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.) equipped with a recording head (line head) was used. In the evaluation machine, the nozzle surface (the nozzle surface corresponds to the ejection surface of the recording head) has been cleaned, and therefore was not contaminated with ink.

  Next, 0.1 g of the sample (water-based ink in Examples and Comparative Examples) is placed on the tip of the blade of the evaluator, and the blade is placed in an environment at a temperature of about 25 ° C. and a humidity of about 60% RH for 10 minutes. Left to stand. Thereafter, the tip of the blade was wiped to the nozzle surface (outward wiping). As a result, an ink coating film was formed on the nozzle surface. The recording head on which the ink coating film was formed on the nozzle surface was allowed to stand for 4 days in an environment of a temperature of 40 ° C. and a humidity of 15% RH. Thereafter, a sheet (a cut product of “Bencot (registered trademark) M-3II” manufactured by Asahi Kasei Co., Ltd.) impregnated with 3 g of an aqueous cleaning solution (aqueous cleaning solution contained in the ink sets of Examples and Comparative Examples) The size was larger than the size of the nozzle surface), and the sheet was brought into contact with the nozzle surface for 30 seconds. After 1 minute had passed, the tip of the blade was wiped onto the nozzle surface (return wiping). And the ink wiping property was evaluated by visually confirming the presence or absence of ink stains on the nozzle surface.

  When ink stains were not confirmed on the nozzle surface, it was evaluated that the wiping property of the fixed ink was excellent (◯). When ink stains were confirmed on the nozzle surface, it was evaluated that the wiping property of the fixed ink was not excellent (x).

<Evaluation of change rate of volume median diameter of pigment particles>
First, using a laser diffraction particle size distribution measuring device (“Zetasizer nano-ZS” manufactured by Malvern, Inc.), the volume median diameter of pigment particles contained in aqueous ink in an environment at a temperature of 25 ° C. (D ₅₀ ) was measured. The volume median diameter (D ₅₀ ) of the pigment particles thus measured is described as “initial volume median diameter (D ₅₀ )”.

Next, a mixed liquid containing the aqueous ink and the aqueous cleaning liquid was placed in a container (capacity: 300 mL). In the mixed liquid, (aqueous ink) :( aqueous cleaning liquid) = 1: 300 (volume ratio). Next, the container was placed in a thermostatic bath whose temperature was set to 60 ° C. for 24 hours. Subsequently, the container was taken out from the thermostatic bath, and the container was allowed to stand until the temperature of the container contents dropped to 25 ° C. Thereafter, the volume median diameter (D ₅₀ ) of the pigment particles contained in the container was measured using a laser diffraction particle size distribution analyzer (“Zetasizer nano-ZS” manufactured by Malvern). The volume median diameter (D ₅₀ ) of the pigment particles thus measured is described as “volume median diameter after mixing (D ₅₀ )”.

The rate of change of the volume median diameter (D ₅₀ ) of the pigment particles was calculated using the following formula. When the change rate of the volume median diameter (D ₅₀ ) of the pigment particles was 1.05 or less, it was evaluated that the pigment particles were dispersed (◯). On the other hand, if the rate of change of the volume median diameter (D ₅₀ ) of the pigment particles is more than 1.05, it is evaluated that the pigment particles are aggregated (x).
Rate of change in volume median diameter (D ₅₀ ) of pigment particles = [volume median diameter after mixing (D ₅₀ )] / [initial volume median diameter (D ₅₀ )]

[Evaluation 1]
In Evaluation 1, ink sets S-1 to S-5 were evaluated. Table 4 shows the configurations and evaluation results of the ink sets S-1 to S-5.

In Table 4, the unit of the blending amount is mass%. The "rate of change" is measured value of the rate of change of the volume median diameter of the pigment particles (D ₅₀₎ and (upper), the volume median diameter of the pigment particles (D ₅₀₎ of the rate of change of the evaluation results (lower ).

  In the ink sets S-1 to S-5, ΔpH is different from each other. Specifically, the ink sets S-1 to S-5 had water-based inks I-1 to I-5 in order. Each pH of the water-based inks I-1 to I-5 was as shown in Table 4. In addition, each of the ink sets S-1 to S-5 had an aqueous cleaning liquid C-1. The pH of the aqueous cleaning liquid C-1 was 8.5.

  Each of the water-based inks I-1 to I-5 and the water-based cleaning liquid C-1 contained NaOH as a pH adjuster. In addition, the aqueous cleaning liquid C-1 contained a first nonionic surfactant (“Amate 320” manufactured by Kao Corporation) as a surfactant. In aqueous cleaning liquid C-1, the compounding amount X of the surfactant was 1.00% by mass.

[Evaluation 2]
In Evaluation 2, ink sets S-3 and S-6 to S-10 were evaluated. Table 5 shows the configurations and evaluation results of ink sets S-3 and S-6 to S-10.

In Table 5, the unit of the blending amount is mass%. The "rate of change" is measured value of the rate of change of the volume median diameter of the pigment particles (D ₅₀₎ and (upper), the volume median diameter of the pigment particles (D ₅₀₎ of the rate of change of the evaluation results (lower ).

  In the ink sets S-3 and S-6 to S-10, at least one of pH and ΔpH of the aqueous cleaning liquid is different from each other. Specifically, ink sets S-3 and S-6 to S-8 all had water-based ink I-3. The pH of the aqueous ink I-3 was 9.0. Ink sets S-3 and S-6 to S-8 had aqueous cleaning liquids C-1 to C-4 in this order. Each pH of the aqueous cleaning solutions C-1 to C-4 was as shown in Table 5.

  Ink sets S-9 and S-10 both had water-based ink I-5. The pH of the water-based ink I-5 was 10. Ink sets S-9 and S-10 had aqueous cleaning liquids C-4 and C-5 in this order. Each pH of the aqueous cleaning liquids C-4 and C-5 was as shown in Table 5.

  The water-based inks I-3 and I-5 and the water-based cleaning liquids C-1 to C-5 all contained NaOH as a pH adjuster. In addition, each of the aqueous cleaning liquids C-1 to C-5 contained a first nonionic surfactant (“Amate 320” manufactured by Kao Corporation) as a surfactant. In each of the aqueous cleaning liquids C-1 to C-5, the blending amount X of the surfactant was 1.00% by mass.

[Evaluation 3]
In Evaluation 3, ink sets S-3 and S-11 to S-16 were evaluated. Table 6 shows the configurations and evaluation results of the ink sets S-3 and S-11 to S-16.

In Table 6, the unit of the blending amount is mass%. “Amine” means triethanolamine. The "rate of change" is measured value of the rate of change of the volume median diameter of the pigment particles (D ₅₀₎ and (upper), the volume median diameter of the pigment particles (D ₅₀₎ of the rate of change of the evaluation results (lower ).

  In the ink sets S-3 and S-11 to S-16, at least one of the pH adjusting agent contained in the aqueous ink and the pH adjusting agent contained in the aqueous cleaning liquid is different from each other. Specifically, each of the water-based inks I-3 and I-6 to I-8 contained an alkali metal salt shown in Table 6 as a pH adjuster. On the other hand, the water-based ink I-9 contained triethanolamine as a pH adjuster. Moreover, each of the aqueous cleaning liquids C-1 and C-6 to C-8 contained an alkali metal salt shown in Table 6 as a pH adjuster. On the other hand, the aqueous cleaning liquid C-9 contained triethanolamine as a pH adjuster.

  The pH of each of the water-based inks I-3 and I-6 to I-9 was 9.0. Further, the pH values of the aqueous cleaning liquids C-1 and C-6 to C-9 were all 8.5. In addition, each of the aqueous cleaning liquids C-1 and C-6 to C-9 contained a first nonionic surfactant (“Amate 320” manufactured by Kao Corporation) as a surfactant. In each of the aqueous cleaning liquids C-1 and C-6 to C-9, the compounding amount X of the surfactant was 1.00% by mass.

[Evaluation 4]
In Evaluation 4, ink sets S-3 and S-17 to S-20 were evaluated. Table 7 shows the configurations and evaluation results of ink sets S-3 and S-17 to S-20.

In Table 7, the unit of the blending amount is mass%. “Xa”, “Xb”, “Xc”, “Xd”, and “Xe” are as shown in Table 8, respectively. The "rate of change" is measured value of the rate of change of the volume median diameter of the pigment particles (D ₅₀₎ and (upper), the volume median diameter of the pigment particles (D ₅₀₎ of the rate of change of the evaluation results (lower ).

  In the ink sets S-3 and S-17 to S-20, the surfactant materials contained in the aqueous cleaning liquid are different from each other. Specifically, the surfactants contained in each of the aqueous cleaning liquids C-1 and C-10 to C-13 were as shown in Table 8. Here, “Amate 105A” manufactured by Kao Corporation, “Amate 320” manufactured by Kao Corporation, and “Puamyl EP-300S” manufactured by Sanyo Chemical Industries, Ltd. all correspond to the first nonionic surfactant. . On the other hand, “Surfinol 465” manufactured by Nissin Chemical Industry Co., Ltd. contains an EO adduct of tetramethyldecynediol and does not correspond to the first nonionic surfactant. Further, “Emulgen 104P” manufactured by Kao Corporation contains polyoxyethylene lauryl ether and does not correspond to the first nonionic surfactant.

  The pH of the water-based ink I-3 was 9.0. Further, the pH values of the aqueous cleaning liquids C-1 and C-10 to C-13 were all 8.5. In addition, each of the water-based ink I-3 and the water-based cleaning liquids C-1 and C-10 to C-13 contained NaOH as a pH adjuster. In each of the aqueous cleaning liquids C-1 and C-10 to C-13, the compounding amount X of the surfactant was 1.00% by mass.

[Evaluation 5]
In Evaluation 5, ink sets S-3 and S-21 to S-23 were evaluated. Table 9 shows the configurations and evaluation results of the ink sets S-3 and S-21 to S-23.

In Table 9, the unit of the blending amount is mass%. The "rate of change" is measured value of the rate of change of the volume median diameter of the pigment particles (D ₅₀₎ and (upper), the volume median diameter of the pigment particles (D ₅₀₎ of the rate of change of the evaluation results (lower ).

  In the ink sets S-3 and S-21 to S-23, the compounding amounts X of the surfactants in the aqueous cleaning liquid are different from each other. In each of the aqueous cleaning liquids C-1 and C-14 to C-16, the blending amount X of the surfactant was as shown in Table 9.

  The pH of the water-based ink I-3 was 9.0. In addition, the pH values of the aqueous cleaning liquids C-1 and C-14 to C-16 were all 8.5. In addition, each of the water-based ink I-3 and the water-based cleaning liquids C-1 and C-14 to C-16 contained NaOH as a pH adjuster. In addition, each of the aqueous cleaning liquids C-1 and C-14 to C-16 contained a first nonionic surfactant (“Amate 105A” manufactured by Kao Corporation) as a surfactant.

  From the evaluations 1 to 5, the ink sets according to Examples 1 to 14 had the water-based ink and the water-based cleaning liquid. The aqueous cleaning liquid contained a nonionic surfactant and a pH adjuster. The nonionic surfactant contained a first nonionic surfactant having an amino group in the molecule. The pH adjuster was an alkali metal salt. The pH of the aqueous ink was higher than the pH of the aqueous cleaning liquid. The pH of the water-based ink and the pH of the water-based cleaning liquid satisfied the above formulas (A) and (B).

  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 aqueous cleaning liquid contains a nonionic surfactant and a pH adjuster,
The nonionic surfactant contains a first nonionic surfactant having an amino group in the molecule,
The pH adjuster is an alkali metal salt,
The pH of the aqueous ink is higher than the pH of the aqueous cleaning liquid,
The ink set for inkjet recording, wherein the pH of the water-based ink and the pH of the water-based cleaning liquid satisfy the following formulas (A) and (B).
0.50 ≦ ΔpH ≦ 1.0 Formula (A)
8.0 ≦ (pH of the aqueous cleaning liquid) ≦ 9.0 Formula (B)
In the above formula (A), ΔpH is represented by the following formula (C).
ΔpH = (pH of the water-based ink) − (pH of the water-based cleaning liquid) Formula (C) The ink set for inkjet recording according to claim 1, wherein the first nonionic surfactant is a polyoxyalkylene alkylamine having a structure represented by the following formula (1-1).

In the above formula (1-1), R ¹ represents a hydrocarbon group having 1 to 24 carbon atoms. A ¹ O and A ² O each independently represent at least one of an oxyethylene group and an oxypropylene group. m1 and n1 each represents an integer of 0 or more, and represents an integer satisfying 1 ≦ (m1 + n1) ≦ 100.   The ink set for inkjet recording according to claim 1 or 2, wherein the alkali metal salt includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide. 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. The water-based ink contains a pH adjuster,
The pH adjuster is an alkali metal salt,
The ink set for inkjet recording according to any one of claims 1 to 4, wherein the alkali metal salt includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide. 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 for storing the aqueous cleaning liquid of the ink set for ink jet 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 aqueous cleaning liquid contains a nonionic surfactant and a pH adjuster,
The nonionic surfactant contains a first nonionic surfactant having an amino group in the molecule,
The pH adjuster is an alkali metal salt,
The pH of the aqueous ink is higher than the pH of the aqueous cleaning liquid,
The image forming method, wherein the pH of the aqueous ink and the pH of the aqueous cleaning liquid satisfy the following formulas (A) and (B).
0.50 ≦ ΔpH ≦ 1.0 Formula (A)
8.0 ≦ (pH of the aqueous cleaning liquid) ≦ 9.0 Formula (B)
In the above formula (A), ΔpH is represented by the following formula (C).
ΔpH = (pH of the water-based ink) − (pH of the water-based cleaning liquid) Formula (C)

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