Inkjet recording method and inkjet recording apparatus

Abstract

To provide an ink jet recording method with high productivity, allowing the amount of ink in an ink storage portion to be easily checked from outside for a long time and allowing for mass recording of images.SOLUTION: The ink jet recording method includes the step of recording images, with use of an ink jet recording apparatus that includes aqueous ink and an ink storage portion. The ink storage portion composed of thermoplastic resin has a mechanism that allows the amount of water-based ink to be checked from outside, and an ink inlet port through which the aqueous ink can be injected. The water-based ink contains a pigment and a urethane resin. The urethane resin includes a unit derived from a polyisocyanate free of acid radicals, a unit derived from a polyol free of acid radicals, and a unit derived from a polyol having an acid radical.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus used therein. [Background technology]

[0002] In recent years, inkjet recording methods have been used to print business documents including characters and charts on recording media such as plain paper, and the frequency of use for such applications has increased dramatically. In such applications, a high level of color development is required for the recorded images. In order to meet such requirements, for example, aqueous pigment inks containing pigments as coloring materials have been widely used.

[0003] In addition, with the development of inkjet recording technology, it is required to improve the durability and reliability of inkjet recording devices so that they can withstand long-term use, and to increase the number of records that can be made to achieve high productivity. In order to improve productivity, for example, an inkjet recording device provided with a large-capacity main tank as an ink storage section has been proposed. Among large-capacity main tanks, ink injection type main tanks have been considered instead of conventional exchange type main tanks. Patent Document 1 discloses an inkjet recording device equipped with an ink injection type main tank to which pigment ink can be applied. The ink injection type main tank employs a method of injecting ink from an ink bottle into the main tank, for example. From the viewpoint of grasping the timing of ink injection when the ink amount decreases and adjusting the ink injection amount, it is required that the ink amount be visible from the outside of the main tank.

[0004] In the case of an inkjet recording device in which an ink injection type main tank is provided as an ink storage section, depending on the material of the main tank, a problem occurs in that the pigment gradually adheres to the inner surface of the main tank, making it difficult to visually check the amount of ink. In addition, for a large-capacity main tank, the same ink is used for a long period of time, so that the moisture in the ink evaporates over a long period of time and the pigment concentration increases. As a result, the amount of pigment adsorbed to the inner surface of the main tank increases due to hydrophobic interactions, and the visibility of the ink amount from the outside decreases. Furthermore, since the same main tank is used continuously in an injection type main tank instead of a replacement type, the visibility further decreases with longer use. In the case of dye ink, the above problem is less likely to occur. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-001391 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have studied the visibility of ink amount in the ink jet recording device proposed in Patent Document 1. As a result, they have found that there is room for improvement in visibility.

[0007] It is therefore an object of the present invention to provide an inkjet recording method which allows the amount of ink in an ink container to be easily and externally checked for a long period of time, and which is capable of recording a large amount of images, and which is excellent in productivity. It is also an object of the present invention to provide an inkjet recording apparatus for use in the inkjet recording method. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an inkjet recording method comprising a step of recording an image using an inkjet recording device equipped with an aqueous ink and an ink storage section for storing the aqueous ink, wherein the ink storage section is formed of a thermoplastic resin, and the ink storage section is equipped with a mechanism for visually checking the amount of the aqueous ink stored therein from outside the inkjet recording device, and an ink inlet for injecting the aqueous ink while the inkjet recording device is placed inside the inkjet recording device, and wherein the aqueous ink contains a pigment and a urethane resin, and the urethane resin contains a unit derived from a polyisocyanate that does not have an acid group, a unit derived from a polyol that does not have an acid group, and a unit derived from a polyol that has an acid group. Effect of the Invention

[0009] According to the present invention, it is possible to provide an inkjet recording method that allows the amount of ink in an ink storage section to be easily and visually confirmed from the outside for a long period of time, and that is capable of recording a large amount of images, and that is excellent in productivity. Also, according to the present invention, it is possible to provide an inkjet recording apparatus used in the inkjet recording method. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating an example of an ink supply system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. The "unit" of a resin means a repeating unit derived from one monomer. In addition, when "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0012] The inventors first prepared a main tank filled with a pigment ink that does not contain resin, and a main tank filled with a pigment ink that contains acrylic resin. They then examined the visibility of the ink amount in these main tanks from the outside (hereinafter, also referred to as "visibility (of the ink amount)"). As a result, it was found that the pigment ink containing acrylic resin has better visibility of the ink amount. The main tank is usually made of a thermoplastic resin. Therefore, the acrylic resin in the ink filled in the main tank undergoes hydrophobic interaction with the thermoplastic resin that constitutes the main tank, and is adsorbed to the inner surface of the main tank. This makes it difficult for the pigment in the ink to be adsorbed to the inner surface of the main tank, and it is considered that the visibility of the ink amount is improved. However, there is still room for improvement in visibility.

[0013] Next, the inventors investigated the visibility of the ink amount in a main tank filled with a pigment ink containing a urethane resin, and found that the visibility of the ink amount was significantly improved by using a urethane resin containing a unit derived from a polyisocyanate having no acid groups, a unit derived from a polyol having no acid groups, and a unit derived from a polyol having an acid group.

[0014] The urethane resin usually has a structure in which a unit derived from a polyol or polyamine and a unit derived from a polyisocyanate are arranged alternately via a urethane bond. The polyisocyanate is a compound that reacts with water, a hydroxyl group, and an amino group, while the portion other than the isocyanate group does not substantially contain a hydrophilic group such as an acid group or a hydroxyl group. Therefore, the unit derived from the polyisocyanate is a highly hydrophobic unit. In contrast, the unit derived from a polyol having an acid group is a highly hydrophilic unit because it has an acid group. That is, a hydrophilic part and a hydrophobic part exist in the molecule of the urethane resin. In addition, the unit derived from a polyol having no acid group has a high degree of freedom of the molecular chain. Therefore, it is considered that the urethane resin can exist in the ink in a state in which the hydrophobic part and the hydrophilic part are biased due to hydrophobic interaction.

[0015] In this way, the urethane resin has high surface activity because the hydrophobic and hydrophilic parts are separated in the ink and exist in a biased state, and it is considered that the urethane resin quickly orients itself at the interface between the ink and the inner surface of the main tank and exists in large amounts near the interface. Therefore, while the urethane resin is adsorbed to the inner surface of the main tank, the pigment is less likely to be adsorbed to the inner surface of the main tank, and the visibility of the ink amount is improved. In addition, the urethane resin has urethane bonds and urea bonds in its molecules. Since the urethane bonds and urea bonds form hydrogen bonds between molecules, an intermolecular force acts on the urethane resin adsorbed to the inner surface of the main tank. As a result, the urethane resin is considered to cover a wider area of ​​the inner surface of the main tank than other resins or surfactants. As a result, the pigment is less likely to be adsorbed to the inner surface of the main tank, and the visibility of the ink amount is improved.

[0016] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention includes a step of recording an image using an inkjet recording device including an aqueous ink and an ink storage section that stores the aqueous ink. The ink storage section of the inkjet recording device is formed of a thermoplastic resin. The ink storage section includes a mechanism that allows the amount of aqueous ink stored therein to be visually confirmed from the outside of the inkjet recording device, and an ink inlet through which the aqueous ink can be injected while the inkjet recording device is placed inside the inkjet recording device. The aqueous ink contains a pigment and a urethane resin, and the urethane resin includes a unit derived from a polyisocyanate that does not have an acid group, a unit derived from a polyol that does not have an acid group, and a unit derived from a polyol that has an acid group. The inkjet recording device of the present invention also includes an aqueous ink and an ink storage section that stores the aqueous ink. The ink storage section is formed of a thermoplastic resin. Furthermore, the ink storage section includes a mechanism that allows the amount of aqueous ink stored therein to be visually confirmed from the outside of the inkjet recording device, and an ink inlet through which the aqueous ink can be injected while the inkjet recording device is placed inside the inkjet recording device. The aqueous ink stored in the ink storage section includes a pigment and a urethane resin. The urethane resin contains a unit derived from a polyisocyanate having no acid groups, a unit derived from a polyol having no acid groups, and a unit derived from a polyol having an acid group.

[0017] (Inkjet recording device) FIG. 1 is a perspective view showing a schematic diagram of an embodiment of an inkjet recording apparatus of the present invention. The inkjet recording apparatus of this embodiment is a so-called serial type inkjet recording apparatus that performs a recording operation by reciprocating a recording head in an X direction (main scanning direction). A recording medium 101 is intermittently transported in a Y direction (sub-scanning direction) by a transport roller 107. A recording unit 102 mounted on a carriage 103 is reciprocally scanned in an X direction (main scanning direction) that is a direction perpendicular to the Y direction that is the transport direction of the recording medium 101. A recording operation is performed by transporting the recording medium 101 in the Y direction and reciprocating scanning of the recording unit 102 in the X direction. The recording unit 102 is composed of an inkjet type recording head 203 (FIG. 2) that ejects ink from a plurality of ejection ports, and a subtank 202 (FIG. 2) as a second ink storage section, and is mounted on the carriage 103. The carriage 103 is supported so as to be movable along a guide rail 105 arranged along the X direction, and is fixed to an endless belt 106 that moves in parallel with the guide rail 105. The endless belt 106 reciprocates due to the driving force of a motor, thereby causing the carriage 103 to scan back and forth in the X direction.

[0018] A main tank 201 (FIG. 2) serving as a first ink storage section is stored inside the main tank storage section 108. The main tank 201 stored in the main tank storage section 108 and a sub tank 202 of the recording unit 102 are connected by an ink supply tube 104. Ink is supplied from the main tank 201 to the sub tank 202 (FIG. 2) via the ink supply tube 104, and then ejected from the ejection opening of the recording head 203. The main tank 201, the ink supply tube 104, and the sub tank 202 can each be provided in numbers corresponding to the type of ink. It is preferable that the main tank 201 and the sub tank 202 are connected by the ink supply tube 104 without going through another ink storage section.

[0019] The main tank housing section 108 is provided with an ink inlet 109 for injecting ink into the main tank 201 from outside the inkjet recording device. When using the inkjet recording device for the first time or when the amount of ink is reduced, ink is injected from an ink bottle into the main tank placed inside the inkjet recording device. A user can open the ink inlet 210 and inject ink into the ink tank 201. In other words, the main tank is left inside the inkjet recording device and is not replaced itself. A window section 115 is formed on the side of the main tank housing section 108, which allows the inside of the main tank housing section 108 to be viewed. The main tank 201, which is an ink housing section, is housed inside the main tank housing section 108. The main tank 201 is a transparent or translucent container made of thermoplastic resin, and contains ink 110 inside. Therefore, the amount of ink 100 contained in the main tank 201 can be visually confirmed from outside the main tank 201 through the window portion 115 of the main tank containing portion 108 .

[0020] 2 is a schematic diagram showing an example of an ink supply system. Ink (shown by hatching) stored in a main tank 201 is supplied to a sub tank 202 via an ink supply tube 104, and then supplied to a print head 203. A gas introduction tube 204 serving as an air communication section is connected to the main tank 201. When printing is performed and ink is consumed, ink is supplied from the main tank 201 to the sub tank 202, and the ink in the main tank 201 decreases. Then, air is introduced into the main tank 201 from the gas introduction tube 204, one end of which is open to the atmosphere, so that the internal negative pressure for holding the ink is kept substantially constant in the ink supply system.

[0021] In order to increase the number of recordable sheets and thereby realize high productivity, it is preferable that the main tank 201 has a large maximum ink capacity V1 (mL). Specifically, the maximum ink capacity V1 (mL) of the main tank 201 is preferably 60 mL or more and 300 mL or less, and more preferably 100 mL or more and 250 mL or less. In addition, it is preferable that the initial ink filling amount of the main tank 201 is about 95% based on the maximum ink capacity.

[0022] It is also preferable that the subtank 202 has a large maximum ink capacity V2 (mL) in order to reduce the frequency of ink supply from the main tank 201 and to stably supply ink to the recording head 203. However, for example, assuming a serial system as shown in FIG. 1 in which the subtank 202 is mounted on the carriage 103, it is preferable that the maximum ink capacity V2 (mL) of the subtank 202 is not too large. In other words, if too much ink is stored in the subtank 202, the recording unit 102 becomes large, the moving speed of the carriage 103 decreases, and it becomes necessary to increase the strength of the endless belt 106 and the motor that move the carriage 103. Therefore, it is preferable that the maximum ink capacity V2 (mL) of the subtank 202 is 1 mL or more and 20 mL or less, and more preferably 2 mL or more and 10 mL or less.

[0023] The housings of the main tank 201 and the sub tank 202 are formed of thermoplastic resins such as polyester, polycarbonate, polyethylene, polypropylene, polystyrene, polyphenylene ether, and mixtures or modified versions of these. An ink absorber that generates negative pressure to retain ink may be provided inside the housing. Compressed fibers of polypropylene, urethane, or the like are preferable as the ink absorber. Also, ink may be stored directly inside the housing without providing an ink absorber.

[0024] The recording unit 102 is composed of a recording head 203 and a subtank 202. The subtank 202 may be attached to the recording unit 102, which is a head cartridge in which the recording head 203 is built, and the recording unit 102 with the subtank 202 attached may be attached to the carriage 103. Furthermore, the recording unit 102 integrally composed of the subtank 202 and the recording head 203 may be attached to the carriage 103. Among these, it is preferable to adopt a configuration in which the recording unit 102 with the subtank 202 attached is set in the carriage 103 as shown in Figures 1 and 2.

[0025] The ink ejection method of the recording head 203 may be a method of applying mechanical energy to the ink or a method of applying thermal energy to the ink. Among these, it is preferable to adopt a method of ejecting ink by applying thermal energy to the ink.

[0026] [Ink storage section] The housing of the main tank, which is the ink storage section, is made of a thermoplastic resin. The main tank made of a thermosetting resin is opaque and cloudy, so it is difficult to ensure sufficient visibility. On the other hand, transparent materials such as glass are not suitable because they are weak against impact. The thermoplastic resin is preferably at least one selected from the group consisting of polyester, polycarbonate, polyethylene, polypropylene, polystyrene, and polyphenylene ether. It may also be a composite resin of two or more of these thermoplastic resins. These thermoplastic resins have a hydrocarbon group or an aromatic group in their molecules. For this reason, they are likely to have hydrophobic interactions or CH / π interactions with the urethane resin in the ink filled in the main tank, so that the urethane resin is likely to be strongly adsorbed to the inner surface of the main tank, and the visibility of the ink amount can be further improved.

[0027] The thermoplastic resin constituting the main tank, which is the ink storage section, preferably has a haze value of 90 or less. If the haze value exceeds 90, the transparency of the main tank is particularly likely to be low, and the effect of improving the visibility of the ink amount may be reduced. The haze value is preferably 10 or more, and more preferably 50 or more. The transparency of the main tank can be adjusted by setting the crystallinity of the thermoplastic resin constituting the main tank. The haze value is an index indicating the degree of cloudiness, and is calculated based on the formula of scattered light / total light transmission x 100 (%), and the smaller the value, the higher the transparency. The haze value in this specification is a value measured on a sample with a thickness of 2 mm using a haze meter or the like. As the haze meter, a transmission haze meter turbidity meter (for example, the product name "NDH2000" (manufactured by Nippon Denshoku Industries Co., Ltd.)) or the like can be used.

[0028] The surface roughness Ra of the inner surface of the main tank, which is the ink storage section, is preferably 2.0 μm or less. If the surface roughness Ra of the inner surface of the main tank exceeds 2.0 μm, the unevenness is somewhat large, and the inner surface area of ​​the main tank that can come into contact with the pigment increases. For this reason, the pigment may be easily adsorbed to the inner surface of the main tank, and the effect of improving the visibility of the ink amount may decrease. The surface roughness Ra of the inner surface of the main tank is preferably 1.0 μm or more. The surface roughness Ra of the inner surface of the main tank can be adjusted by polishing processing or the like. The surface roughness Ra is an index indicating smoothness, and the smaller the numerical value, the smoother the surface. It can be measured as "average surface roughness Ra" in accordance with JIS 2001. A laser microscope (for example, product name "VK9700" (manufactured by Keyence)) or the like can be used to measure the surface roughness Ra.

[0029] (Recording process) The inkjet recording method of the present invention has a step of recording an image using the above-mentioned inkjet recording device (recording step). Specifically, in the recording step, ink discharged from the discharge port of a recording head is applied to a recording medium to record an image. Any recording medium may be used as the target for recording an image. In particular, it is preferable to use permeable paper such as a recording medium without a coating layer, such as plain paper or uncoated paper, and a recording medium with a coating layer, such as glossy paper or art paper. Other than using the above-mentioned inkjet recording device, the recording step may be a known one.

[0030] (Water-based ink) The inkjet recording method of the present invention includes a step of recording an image using an inkjet recording device equipped with an ink reservoir for accommodating a water-based ink. The water-based ink is an inkjet water-based ink that contains a pigment and a urethane resin. The composition of the ink will be described below.

[0031] [Colorant] A pigment is used as the coloring material. The content (mass%) of the pigment in the ink is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. Examples of pigment types include inorganic pigments such as carbon black, calcium carbonate, and titanium oxide; and organic pigments such as azo, phthalocyanine, and quinacridone. A dye may be used in combination for the purpose of color matching, etc.

[0032] The pigment dispersion method is not particularly limited. For example, resin-dispersed pigments dispersed with a resin dispersant, pigments dispersed with a surfactant, and microencapsulated pigments in which at least a part of the pigment particle surface is coated with a resin or the like can be used. Self-dispersed pigments in which a functional group containing a hydrophilic group such as an anionic group is bonded to the pigment particle surface, and pigments in which an organic group containing a polymer is chemically bonded to the pigment particle surface (resin-bonded self-dispersed pigments) can also be used. Pigments with different dispersion methods may be used in combination.

[0033] It is preferable to use a self-dispersing pigment having an ionic group amount of 0.20 mmol / g or more as the pigment. The urethane resin in the ink has a negative charge due to the acid group, and is considered to be adsorbed to the inner surface of the main tank. If the ionic group amount of the self-dispersing pigment is less than 0.20 mmol / g, the electrostatic repulsion force generated between the urethane resin adsorbed to the inner surface of the main tank becomes small. For this reason, the pigment may be easily adsorbed to the urethane resin adsorbed to the inner surface of the main tank, and the effect of improving the visibility of the ink amount may be reduced. It is preferable that the ionic group amount of the self-dispersing pigment is 2.00 mmol / g or less.

[0034] The amount of ionic groups in the self-dispersed pigment is expressed as the number of moles of ionic groups per unit mass of the self-dispersed pigment, and can be calculated from the amount of surface charge measured by colloid titration. In the examples described below, an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500) was used to measure the amount of surface charge of the self-dispersed pigment in the pigment dispersion by colloid titration using potential difference. More specifically, the pigment dispersion was diluted about 300 times (by mass) with pure water, and the pH was adjusted to about 10 with potassium hydroxide as necessary, and potentiometric titration was performed using 5 mmol / L methyl glycol chitosan as a titration reagent. It is of course possible to measure the amount of surface charge using a pigment extracted from the ink by an appropriate method.

[0035] The self-dispersing pigment may have an anionic group bonded to the particle surface of the pigment directly or via another atomic group (-R-). Examples of the anionic group include -COOM, -SO3M, and -PO3M2. Each M may independently include a hydrogen atom, an alkali metal, ammonium (NH4), or an organic ammonium. Examples of the other atomic group (-R-) may include an alkylene group, an arylene group, an amide group, a sulfonyl group, an imino group, a carbonyl group, an ester group, an ether group, or a group that combines these groups.

[0036] In addition, it is preferable to use a resin-dispersed pigment dispersed in the aqueous ink with a resin dispersant having an acid value of 50 mgKOH / g or more as the pigment. If the acid value of the resin dispersant is less than 50 mgKOH / g, the electrostatic repulsion force generated between the urethane resin adsorbed on the inner surface of the main tank is small. Therefore, the pigment may be easily adsorbed to the urethane resin adsorbed on the inner surface of the main tank, and the effect of improving the visibility of the ink amount may be reduced. The acid value of the resin dispersant is preferably 180 mgKOH / g or less. The degree of neutralization of the resin dispersant is preferably 0.70 times or more and 1.00 times or less in terms of a molar ratio to the acid group.

[0037] The resin dispersant usually contains a hydrophilic unit having an anionic group and a hydrophobic unit having no anionic group. The hydrophilic unit is a unit for ensuring affinity to an aqueous medium. The hydrophobic unit is a unit for adsorbing to the pigment particle surface by hydrophobic interaction. Examples of the resin-dispersed pigment include a type in which a resin dispersant is physically adsorbed to the pigment particle surface and dispersed, and a microcapsule pigment in which the pigment particle surface is coated with a resin dispersant. It is preferable that the resin dispersant is different from the urethane resin contained in the ink.

[0038] As the resin dispersant, it is preferable to use a water-soluble resin. In this specification, the term "water-soluble resin" means a resin that dissolves in an aqueous medium and can exist in the aqueous medium in a state where it does not form particles having a particle size. If the resin dispersant is water-dispersible (water-insoluble), the storage stability of the ink may be easily reduced.

[0039] Whether or not a resin is water-soluble can be determined according to the method shown below. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles having a particle size are measured, the resin can be determined to be water-soluble. As a particle size distribution measuring device, a particle size analyzer using dynamic light scattering (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used. The measurement conditions for the particle size can be, for example, as follows.

[0040] [Measurement conditions] SetZero: 30 seconds Number of measurements: 3 Measurement time: 180 seconds

[0041] As the resin dispersant, it is preferable to use a (meth)acrylic resin containing a hydrophilic unit having an anionic group and a hydrophobic unit not having an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a monomer having an anionic group. Specific examples of the monomer having an anionic group include monomers having a carboxy group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anhydrides and salts of these monomers, and the like. Examples of cations constituting the salts of monomers having an anionic group include lithium cations, sodium cations, potassium cations, ammonium cations, and organic ammonium cations.

[0042] The hydrophobic unit can be formed, for example, by polymerizing a monomer that does not have an anionic group. Specific examples of the monomer that does not have an anionic group include monomers having an aromatic group such as styrene, α-methylstyrene, benzyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole; and monomers having an aliphatic group such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso)propyl (meth)acrylate, (n-, iso-, and t-)butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0043] The volume average particle diameter of the pigment in the ink is preferably from 10 nm to 300 nm, and more preferably from 20 nm to 200 nm. The volume average particle diameter of the pigment can be measured, for example, using a particle size measuring device using a dynamic light scattering method.

[0044] [Urethane resin] The urethane resin contains a unit derived from a polyisocyanate having no acid group, a unit derived from a polyol having no acid group, and a unit derived from a polyol having an acid group. The urethane resin can be obtained by reacting a polyisocyanate having no acid group, a polyol having no acid group, and a polyol having an acid group. The urethane resin may be further reacted with a polyamine, a crosslinking agent, a chain extender, etc.

[0045] [Polyisocyanate] As the polyisocyanate, a polyisocyanate having no acid group is used. When a polyisocyanate having an acid group is used, the hydrophilicity of the molecular chain of the obtained urethane resin as a whole is improved and the hydrophobicity is reduced. For this reason, the urethane resin cannot have a structure in which the hydrophilic part and the hydrophobic part are separated. A urethane resin that does not have a structure in which the hydrophilic part and the hydrophobic part are separated is difficult to interact with the inner surface of the main tank due to hydrophobic interaction, and is therefore difficult to adsorb to the inner surface of the main tank. As a result, the pigment is adsorbed to the inner surface of the main tank, and the visibility of the ink amount cannot be improved. The ratio (mol %) of the unit derived from the polyisocyanate having no acid group in the urethane resin is preferably 10.0 mol % or more and 95.0 mol % or less, and more preferably 30.0 mol % or more and 70.0 mol % or less. In addition, it is particularly preferable that it is 40.0 mol % or more and 60.0 mol % or less.

[0046] The polyisocyanate preferably has a cyclic structure. Polyisocyanate having a cyclic structure has a low degree of freedom of the molecular chain, and therefore the hydrophobic structure of the hydrocarbon is dense. That is, polyisocyanate having no cyclic structure has a lower hydrophobicity than polyisocyanate having a cyclic structure. For this reason, urethane resin containing a unit derived from polyisocyanate having no cyclic structure has a low hydrophobicity, and may be difficult to adsorb to the inner surface of the main tank. As a result, the pigment may be easily adsorbed to the inner surface of the main tank, and the effect of improving the visibility of the ink amount may be reduced.

[0047] Polyisocyanates are compounds that have two or more isocyanate groups in their molecular structure. Examples of polyisocyanates that can be used include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of the aliphatic polyisocyanate include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0048] Specific examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

[0049] [Polyol] The polyol is a compound having two or more hydroxyl groups in its molecule. As the polyol, a polyol having no acid group and a polyol having an acid group are used. The ratio (mol%) of the unit derived from the polyol in the urethane resin is preferably 10.0 mol% or more and 95.0 mol% or less, more preferably 30.0 mol% or more and 70.0 mol% or less. In addition, it is particularly preferably 40.0 mol% or more and 60.0 mol% or less.

[0050] The unit derived from the polyol having an acid group has a lower degree of freedom of the molecular chain than the unit derived from the polyol having no acid group. Therefore, in a urethane resin containing only the unit derived from the polyol having an acid group as the unit derived from the polyol, the hydrophobic part and the hydrophilic part in the molecular structure are unlikely to exist in a biased state, and the resin is unlikely to be adsorbed to the inner surface of the main tank. Therefore, when a urethane resin containing only the unit derived from the polyol having an acid group as the unit derived from the polyol is used, the pigment is likely to be adsorbed to the inner surface of the main tank, and the visibility of the ink amount cannot be improved.

[0051] Examples of polyols without acid groups include long-chain polyols with a number average molecular weight of 450 to 4,000, such as polyether polyols, polyester polyols, and polycarbonate polyols. The number average molecular weight of the polyol without acid groups is preferably 1,000 or more. If the number average molecular weight of the polyol without acid groups is less than 1,000, the degree of freedom of the molecular chain is somewhat low, so that the urethane resin containing the unit derived from this polyol is somewhat difficult to adsorb to the inner surface of the main tank. This may cause the pigment to be easily adsorbed to the inner surface of the main tank, which may reduce the effect of improving the visibility of the ink amount.

[0052] Examples of polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly)alkylene glycol. Among them, (poly)alkylene glycols such as (poly)ethylene glycol, (poly)propylene glycol, (poly)tetramethylene glycol, and neopentyl glycol are preferred. Examples of polyester polyols include acid esters. Examples of polycarbonate polyols include polycarbonate polyols produced by known methods.

[0053] The polyol having no acid group is preferably a polyether polyol. The polyether polyol having no acid group has a flexible ether bond, and therefore has a higher degree of freedom of molecular chain than other polyols having no acid group. Therefore, the urethane resin containing a unit derived from the polyether polyol having no acid group is easily adsorbed to the inner surface of the main tank by hydrophobic interaction, and the pigment is more difficult to adsorb, so that the visibility of the ink amount can be further improved.

[0054] The ratio (mol %) of the units derived from a polyol having no acid group to the total amount of the units derived from a polyol in the urethane resin is preferably as follows: preferably from 1.0 mol % to 50.0 mol %, more preferably from 1.0 mol % to 30.0 mol %.

[0055] A urethane resin that contains only units derived from a polyol that does not have an acid group as units derived from a polyol has almost no hydrophilic portion, and therefore cannot exist in the ink with the hydrophobic portion and the hydrophilic portion biased. Therefore, such a urethane resin is unlikely to exist at the interface between the ink and the inner surface of the main tank, and is unlikely to be adsorbed onto the inner surface of the main tank. This makes it easy for the pigment to be adsorbed onto the inner surface of the main tank, and it is not possible to improve the visibility of the ink amount.

[0056] Examples of the acid group in the polyol having an acid group include a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group. Examples of the polyol having an acid group include dimethylolpropionic acid and dimethylolbutanoic acid. The urethane resin is preferably a water-soluble urethane resin containing a unit derived from the polyol having these acid groups. The acid group may form a salt. Examples of the cation forming the salt include ions of lithium, sodium, potassium, ammonium, and organic ammonium. In general, the urethane resin becomes water-soluble by neutralizing the acid group with a neutralizing agent such as hydroxide of an alkali metal (lithium, sodium, potassium, etc.) or aqueous ammonia.

[0057] The ratio (mol %) of the units derived from a polyol having an acid group to the total amount of the units derived from a polyol in the urethane resin is preferably as follows: preferably from 5.0 mol % to 50.0 mol %, and more preferably from 10.0 mol % to 50.0 mol %.

[0058] [Polyamine] Examples of polyamines include monoamines having multiple hydroxyl groups, such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines, such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; and trifunctional or higher polyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, and polyethylenepolyimine. For convenience, compounds having multiple hydroxyl groups and one "amino group, imino group" are also listed as "polyamines". The ratio (mol%) of the unit derived from polyamine in the urethane resin is preferably 10.0 mol% or less, and more preferably 5.0 mol% or less. The ratio (mol%) of the unit derived from polyamine in the urethane resin may be 0.0 mol%.

[0059] [Cross-linking agents, chain extenders] When synthesizing the urethane resin, a crosslinking agent or a chain extender can be used. The crosslinking agent is usually used when synthesizing a prepolymer. The chain extender is usually used when a prepolymer synthesized in advance is subjected to a chain extension reaction. The crosslinking agent or the chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. according to the purpose. A compound capable of crosslinking the urethane resin can also be used as the chain extender.

[0060] [Physical properties of urethane resin, etc.] The acid value of the urethane resin is preferably 50 mgKOH / g or more and 120 mgKOH / g or less. If the acid value of the urethane resin is less than 50 mgKOH / g, the hydrophobicity is somewhat strong, so that the hydrophobic portion and the hydrophilic portion may not be present in the ink in a biased state. Therefore, such a urethane resin may not be present at the interface between the ink and the inner surface of the main tank, and may not be adsorbed to the inner surface of the main tank. This may cause the pigment to be easily adsorbed to the inner surface of the main tank, and the effect of improving the visibility of the ink amount may be reduced. On the other hand, if the acid value of the urethane resin is more than 120 mgKOH / g, the content ratio of the unit derived from the polyol having an acid group is high and the degree of freedom of the molecular chain is somewhat low, so that the hydrophobic portion and the hydrophilic portion may not be present in the ink in a biased state. Therefore, such a urethane resin may not be adsorbed to the inner surface of the main tank, and the pigment may be easily adsorbed to the inner surface of the main tank, and the effect of improving the visibility of the ink amount may be reduced.

[0061] The acid value of the urethane resin can be measured by colloid titration using potential difference. The acid value of the urethane resin can be adjusted by appropriately changing the ratio of the unit derived from the polyol having an acid group and the ratio of the unit derived from the chain extender and the crosslinking agent.

[0062] The weight average molecular weight of the urethane resin is preferably 10,000 or more and 60,000 or less. If the weight average molecular weight of the urethane resin is less than 10,000, the number of units that can be adsorbed to the inner surface of the main tank contained in the urethane resin may be reduced. For this reason, the urethane resin may be less likely to be adsorbed to the inner surface of the main tank, and the pigment may be more likely to be adsorbed to the inner surface of the main tank, which may reduce the effect of improving the visibility of the ink amount. On the other hand, if the weight average molecular weight of the urethane resin is more than 60,000, the urethane resin may be somewhat less likely to be present at the interface between the ink and the inner surface of the main tank due to steric repulsion, and may be less likely to be adsorbed to the inner surface of the main tank. As a result, the pigment may be more likely to be adsorbed to the inner surface of the main tank, which may reduce the effect of improving the visibility of the ink amount. The weight average molecular weight of the urethane resin is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0063] The content (mass%) of the urethane resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The content (mass%) of the urethane resin in the ink is preferably 0.25 times or more and 1.00 times or less in mass ratio to the content (mass%) of the pigment. If the mass ratio is less than 0.25 times, the amount of urethane resin is relatively small relative to the pigment, so that the pigment is likely to be adsorbed to the inner surface of the main tank, and the effect of improving the visibility of the ink amount may be reduced. On the other hand, if the mass ratio is more than 1.00 times, the viscosity of the ink may increase excessively, and the ejection characteristics may be slightly reduced.

[0064] [Aqueous medium] The ink is an aqueous ink containing at least water as an aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water, it is preferable to use deionized water or ion-exchanged water. The content (mass%) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

[0065] [Other ingredients] The ink may further contain water-soluble organic compounds that are solid at 25° C., such as urea or its derivatives, trimethylolpropane, and trimethylolethane. The content (mass %) of the water-soluble organic compounds in the ink is preferably 0.1 mass % or more and 10.0 mass % or less, based on the total mass of the ink. In addition to the above components, the ink may contain various additives such as antifoaming agents, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors, as necessary.

[0066] [Ink properties] The pH, static surface tension, and viscosity of the ink at 25°C are preferably within the following ranges. The pH of the ink is preferably from 5.0 to 10.0, and more preferably from 7.0 to 9.5. The static surface tension of the ink is preferably from 30 mN / m to 50 mN / m. The viscosity of the ink is preferably from 2.0 mPa·s to 10.0 mPa·s. EXAMPLES

[0067] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples as long as it does not exceed the gist of the invention. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified. The acid value of the resin was measured by potentiometric titration using potassium hydroxide-methanol titrant. The weight average molecular weight of the resin is a value calculated in terms of polystyrene measured by gel permeation chromatography (GPC).

[0068] <Preparation of pigment dispersion> (Surface charge of self-dispersing pigment) The surface charge amount of the self-dispersed pigment in the pigment dispersion was measured by potentiometric titration using 5 mmol / L methyl glycol chitosan as a titration reagent, using an automatic potentiometric titrator equipped with a streaming potential titration unit (PCD-500). The automatic potentiometric titrator used was the product name "AT-510" (manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0069] (Pigment dispersions 1-4, 6-9) A solution of 50 g of concentrated hydrochloric acid dissolved in 55 g of water was cooled to 5°C, and in this state, the type and amount of treatment agent shown in Table 1 was added. The container containing this solution was placed in an ice bath, and while stirring to keep the temperature of the solution below 10°C, a solution obtained by dissolving sodium nitrite in the amount shown in Table 1 in 20.0 g of water at 5°C was added. After stirring for 15 minutes, 6.0 g of the pigment shown in Table 1 was added under stirring. The mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered with filter paper (product name "Standard Filter Paper No. 2", Advantec), the particles were thoroughly washed with water, and dried in an oven at 110°C. Thereafter, the sodium ions were replaced with potassium ions by ion exchange. An appropriate amount of ion-exchanged water was added to adjust the pigment content, and each pigment dispersion with a pigment content of 10.0% was obtained. The amount of ionic groups in the self-dispersing pigment is shown in Table 1.

[0070] (Pigment Dispersion 5) 500.0 parts of ion-exchanged water and 15.0 parts of carbon black (pigment) were mixed and stirred at 15,000 rpm for 30 minutes to pre-wet the pigment. 4,485 parts of ion-exchanged water were added and dispersed with a high-pressure homogenizer to obtain Dispersion A. The average particle size of the pigment in the obtained Dispersion A was 110 nm. The obtained Dispersion A was placed in a high-pressure container and pressurized to 3.0 MPa, and then ozone water with an ozone concentration of 100 ppm was introduced to oxidize the pigment to obtain Dispersion B. The pH of Dispersion B was adjusted to 10.0 using potassium hydroxide, and then an appropriate amount of ion-exchanged water was added to adjust the pigment content, obtaining Pigment Dispersion 5 with a pigment content of 10.0%.

[0071] The preparation conditions and properties of pigment dispersions 1 to 9 are shown in Table 1.

[0072] TIFF0007676248000001.tif130170

[0073] (Pigment dispersion 10~20) 15.0 parts of pigment, 30.0 parts of an aqueous solution of a dispersant (resin dispersant, weight average molecular weight: 10,000) shown in Table 2, and 55.0 parts of water were mixed, dispersed with a sand grinder for 1 hour, and then centrifuged to remove non-dispersed matter including coarse particles. As the aqueous solution of the resin dispersant, an aqueous solution with a resin content of 20.0% was used, which was obtained by neutralizing the resin (copolymer) shown in Table 1 with a 10% potassium hydroxide aqueous solution in an amount equimolar to the acid value and adding an appropriate amount of ion-exchanged water. After pressure filtration with a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm, an appropriate amount of ion-exchanged water was added to prepare pigment dispersions 10 to 20.

[0074] (Pigment Dispersion 21) 15.0 parts of carbon black (pigment), 15.0 parts of polyoxyethylene (EO number 12) lauryl ether ammonium sulfate (surfactant), 30.0 parts of ethylene glycol, 75.0 parts of ion-exchanged water, and 1.0 parts of diethanolamine (pH adjuster) were mixed. After thorough stirring, the mixture was dispersed using a three-roll mill. An appropriate amount of ion-exchanged water was further added and mixed and stirred, followed by centrifugation to remove coarse particles, to obtain pigment dispersion 21.

[0075] The preparation conditions and properties of pigment dispersions 10 to 21 are shown in Table 2.

[0076] TIFF0007676248000002.tif89170

[0077] <Preparation of dye aqueous solution> 10.0 parts of a dye (CI Food Black 2) was dissolved in 90.0 parts of ion-exchanged water to obtain an aqueous dye solution with a dye content of 10.0%.

[0078] <Synthesis of urethane resin> (Urethane resin 1-18, 20, 21) In a four-neck flask equipped with a stirrer, reflux condenser, nitrogen gas inlet tube, and thermometer, the type and amount of polyisocyanate and polyol not having an acid group (the number attached indicates the number average molecular weight) shown in Table 2 were placed. Furthermore, 300 parts of methyl ethyl ketone were placed and reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Next, dimethylolpropionic acid in the amount shown in Table 3 was added and reacted at 80°C. After cooling to 40°C, ion-exchanged water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer. Methyl ethyl ketone was distilled off by heating and reducing the pressure, and an aqueous solution of urethane resin with a resin content of 20.0% was obtained. The meanings of the abbreviations in Table 3 are as follows. IPDI: Isophorone diisocyanate TDI: Tolylene diisocyanate HDI: Hexamethylene diisocyanate PPG: Polypropylene glycol PC: Polycarbonate diol PCL: Polycaprolactone diol Isocyanate A: a compound represented by the following formula (1)

[0079] TIFF0007676248000003.tif41170

[0080] (Urethane Resin 19) Using "isocyanate A" as the polyisocyanate, an aqueous solution of urethane resin 19 precursor was obtained in the same manner as for the above-mentioned urethane resins 1 to 18, 20, and 21. A potassium hydroxide aqueous solution was added to the obtained aqueous solution of urethane resin 19 precursor, and the mixture was reacted at 80°C for 6 hours under a nitrogen gas atmosphere to hydrolyze the ester groups derived from isocyanate A to carboxylic acid groups. The mixture was heated and reduced pressure to distill off the ethanol, and an aqueous solution of urethane resin 19 with a resin content of 20.0% was obtained.

[0081] TIFF0007676248000004.tif177170

[0082] <Synthesis of acrylic resin> (Acrylic Resin 1) 93.4 parts of butanol was placed in a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. After heating to 110°C, a mixture of 101.5 parts of styrene, 38.5 parts of acrylic acid, 60.0 parts of methyl methacrylate, and 6 parts of a polymerization initiator (product name "V-601", Fujifilm Wako Pure Chemical Industries, Ltd.) was dropped over 2 hours to carry out a polymerization reaction. After reacting at 110°C for 3 hours, 0.6 parts of a polymerization initiator was further added, and the reaction was continued at 110°C for 1 hour to obtain a solution of dispersion resin 1. After cooling to room temperature, 37.1 parts of dimethylaminoethanol were added to neutralize, and 100 parts of water were further added. Butanol was distilled off by heating to 100°C or higher to perform azeotropy with water, and the concentration was adjusted. As a result, a liquid containing acrylic resin 1 with an acrylic resin 1 content of 20.0% was obtained. The acid value of the acrylic resin 1 was 120 mgKOH / g, and the weight average molecular weight was 12,000.

[0083] (Acrylic Resin 2) 30.0 parts of styrene, 30.0 parts of α-methylstyrene, 40.0 parts of benzyl methacrylate, 38.5 parts of acrylic acid, and 61.5 parts of methyl methacrylate were used as monomers. A liquid containing acrylic resin 2 with an acrylic resin 2 content of 20.0% was obtained by the same procedure as for acrylic resin 1 described above. The acid value of acrylic resin 2 was 120 mgKOH / g, and the weight average molecular weight was 12,000.

[0084] (Acrylic Resin 3) 80.8 parts of phenoxyethyl acrylate, 80.7 parts of phenoxyethyl methacrylate, and 38.5 parts of acrylic acid were used as polymerizable monomers. A liquid containing acrylic resin 3 with an acrylic resin content of 20.0% was obtained by the same procedure as for acrylic resin 1 described above. The acid value of acrylic resin 3 was 120 mgKOH / g, and the weight average molecular weight was 12,000.

[0085] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in Tables 4-1 to 4-6, thoroughly stirring, and then filtering under pressure with a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. In Tables 4-1 to 4-6, the numerical value attached to polyethylene glycol is the number average molecular weight, and "Acetylenol E100" is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals.

[0086] TIFF0007676248000005.tif117170

[0087] TIFF0007676248000006.tif117170

[0088] TIFF0007676248000007.tif116170

[0089] TIFF0007676248000008.tif117170

[0090] TIFF0007676248000009.tif116170

[0091] TIFF0007676248000010.tif130170

[0092] <Evaluation> An inkjet recording device was prepared that has the main components shown in Figure 1 and incorporates an ink supply system with the configuration shown in Figure 2. The characteristics of the main tank are shown in Table 5. The maximum ink capacity V1 of the main tank was 150 mL, and the maximum ink capacity V2 of the sub-tank was 5 mL. The haze value (thickness 2 mm) was adjusted by the crystallinity of the resin. The surface roughness (surface roughness Ra of the inner surface of the main tank) was adjusted by polishing the inner surface of the main tank. The sub-tank was made by directly bonding a recording element substrate equipped with a recording head that ejects ink by applying thermal energy to a housing made of polyphenylene ether (thermoplastic resin) without any other members in between.

[0093] TIFF0007676248000011.tif129170

[0094] (Ink volume visibility) The main tank and ink were combined as shown in Table 5, and the ink was poured into the main tank of the inkjet recording device. Using this inkjet recording device, a storage test was conducted in which the main tank was filled with 150 mL of ink and stored for two months in an environment of 60°C. After the storage test, the ink in the main tank was removed and 75 mL of ink was poured in again. Three minutes after the ink was poured in, the ink adhesion state, coloring state, and ink amount (liquid level height) in the part of the main tank corresponding to the difference between 150 mL and 75 mL were visually observed, and the visibility of the ink amount was evaluated according to the evaluation criteria shown below. The results are shown in Table 6. In the evaluation criteria shown below, "AAA", "AA", "A", and "B" were considered to be acceptable levels, and "C" and "D" were considered to be unacceptable levels. AAA: No ink adhesion or discoloration. The ink level was visible from the outside. AA: A small amount of ink was attached, but there was no coloring. The liquid level could be visually confirmed from the outside. A: There was no ink adhesion, but it was lightly colored. The ink level could be seen from the outside. B: A small amount of ink was attached and was lightly colored. The liquid level could be seen from the outside. C: There was a lot of ink attached, and although it was lighter than ink, it was still dark in color. It was difficult to visually check the liquid level from the outside. D: There was a lot of ink attached, and the color was as dark as the ink. It was difficult to visually confirm the height of the liquid level from the outside.

[0095] TIFF0007676248000012.tif206170

Claims

1. An inkjet recording method comprising a step of recording an image using an inkjet recording apparatus including a water-based ink and an ink reservoir that contains the water-based ink, The ink storage section is made of a thermoplastic resin, the ink container comprises a mechanism for visually checking an amount of the water-based ink contained therein from outside the inkjet recording apparatus, and an ink inlet through which the water-based ink can be injected while the ink container is placed inside the inkjet recording apparatus; the water-based ink contains a pigment and a urethane resin; The inkjet recording method according to claim 1, wherein the urethane resin contains a unit derived from a polyisocyanate having no acid group, a unit derived from a polyol having no acid group, and a unit derived from a polyol having an acid group.

2. 2. The ink-jet recording method according to claim 1, wherein the pigment is a self-dispersing pigment having an ionic group amount of 0.20 mmol / g or more.

3. The inkjet recording method described in claim 2, wherein the amount of ionic groups in the self-dispersing pigment is 2.00 mmol / g or less.

4. 2. The ink-jet recording method according to claim 1, wherein the pigment is a resin-dispersed pigment dispersed in the water-based ink with a resin dispersant having an acid value of 50 mgKOH / g or more.

5. The inkjet recording method according to claim 4, wherein the acid value of the resin dispersant is 180 mg KOH / g or less.

6. The ink jet recording method according to claim 1 , wherein the polyisocyanate has a cyclic structure.

7. 7. The ink jet recording method according to claim 1, wherein the polyol having no acid group has a number average molecular weight of 1,000 or more.

8. 8. The ink-jet recording method according to claim 1, wherein the polyol having no acid group is a polyether polyol.

9. The polyisocyanate having no acid group is a polyisocyanate having a cyclic structure, the polyol having no acid group is a (poly)alkylene glycol, 9. The ink jet recording method according to claim 1, wherein the polyol having an acid group is a polyol having a carboxylic acid group.

10. 10. The ink jet recording method according to claim 1, wherein the urethane resin has a weight average molecular weight of 10,000 or more and 60,000 or less.

11. The inkjet recording method according to any one of claims 1 to 10, wherein the acid value of the urethane resin is from 50 mgKOH / g to 120 mgKOH / g.

12. 12. The inkjet recording method according to claim 1, wherein the thermoplastic resin is at least one selected from the group consisting of polyester, polycarbonate, polyethylene, polypropylene, polystyrene, and polyphenylene ether.

13. The inkjet recording method according to any one of claims 1 to 12, wherein the thermoplastic resin has a haze value of 90 or less.

14. An inkjet recording method according to any one of claims 1 to 13, wherein the haze value of the thermoplastic resin is 10 or more.

15. The ink jet recording method according to any one of claims 1 to 14, wherein the surface roughness Ra of the inner surface of the ink containing section is 2.0 µm or less.

16. An inkjet recording method according to any one of claims 1 to 15, wherein the surface roughness Ra of the inner surface of the ink storage section is 1.0 μm or more.

17. An inkjet recording method described in any one of claims 1 to 16, wherein the content (mass %) of the pigment in the aqueous ink is 0.5 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

18. An inkjet recording method described in any one of claims 1 to 17, wherein the content (mass %) of the urethane resin in the aqueous ink is 0.1 mass % or more and 5.0 mass % or less, based on the total mass of the ink.

19. An inkjet recording method described in any one of claims 1 to 18, wherein the content (mass%) of urethane resin in the aqueous ink is 0.25 to 1.00 times the mass content (mass%) of the pigment.

20. An inkjet recording method described in any one of claims 1 to 19, wherein the inkjet recording device further comprises a second ink storage section mounted on the carriage, separate from the ink storage section as a first ink storage section.

21. The inkjet recording method according to claim 20, wherein the first ink storage section has a maximum ink storage volume V 1 (mL) of 60 mL or more and 300 mL or less.

22. The inkjet recording method according to claim 20, wherein the second ink storage section has a maximum ink storage volume V 2 (mL) of 1 mL or more and 20 mL or less.

23. An inkjet recording method described in any one of claims 20 to 22, wherein the first ink storage section and the second ink storage section are connected by an ink supply tube without passing through any other ink storage section.

24. An inkjet recording apparatus comprising: a water-based ink; and an ink storage section for storing the water-based ink, The ink storage section is made of a thermoplastic resin, the ink container comprises a mechanism for visually checking an amount of the water-based ink contained therein from outside the inkjet recording apparatus, and an ink inlet through which the water-based ink can be injected while the ink container is placed inside the inkjet recording apparatus; the water-based ink contains a pigment and a urethane resin; 11. An ink-jet recording apparatus, wherein the urethane resin contains a unit derived from a polyisocyanate having no acid group, a unit derived from a polyol having no acid group, and a unit derived from a polyol having an acid group.

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