JP2022022108A - Inkjet recording method and inkjet recording device - Google Patents

Abstract

To provide an inkjet recording method that has excellent ink discharge stability and can record a high-quality image with high productivity while using an inkjet recording device with a sub-tank.SOLUTION: An inkjet recording method records an image using an inkjet recording device that includes: aqueous ink; a first ink storage part for storing the aqueous ink; a second ink storage part for storing the aqueous ink without impregnating the ink into an absorber; and a recording head, where an ink flow channel is constituted through the second ink storage part to the inside of the recording head to supply the aqueous ink, a filter for sectioning an upstream side and a downstream side is disposed in the middle of the ink flow channel, a value of a ratio (A/B) of volume A (mL) of an upstream side of the ink flow channel to volume B (mL) of a downstream side of the ink flow channel is 5 or more and the aqueous ink contains a coloring material, a nonionic surfactant and a first water-soluble organic solvent with a relative dielectric constant of 30.0 or less.SELECTED DRAWING: None

Description

The present invention relates to an inkjet recording method and an inkjet recording device used thereof.

According to the inkjet recording method, it is possible to record images such as photographs and documents on various recording media. Further, various inks according to a purpose have been proposed, such as an ink suitable for recording an image of photographic image quality on glossy paper and an ink suitable for recording a document or the like on plain paper.

In recent years, an inkjet recording method has been used for printing business sentences including characters and charts on a recording medium such as plain paper, and the frequency of use for such purposes has increased remarkably. And, in order to record a larger amount of documents, there is a strong demand from the market for increasing the capacity of the ink tank. Furthermore, it is also required to be able to record documents at a higher speed than before. Under such circumstances, an inkjet recording device including a main tank capable of accommodating a large amount of ink, a recording unit connected to the main tank by a tube, and a recording unit in which a recording head and a sub tank are integrally formed has been proposed. (Patent Document 1). Further, a recording unit in which a sub tank and a recording head are connected via a filter has been proposed (Patent Document 2).

Japanese Unexamined Patent Publication No. 2017-001391 Japanese Unexamined Patent Publication No. 2003-08714

The present inventor has studied the inkjet recording method and the configuration of the inkjet recording apparatus necessary for increasing productivity. Specifically, it has been considered to adopt a system in which ink is supplied from the main tank to a recording unit in which a sub tank and a recording head are connected via a filter as described in Patent Document 2. As a result, it was found that by adopting such a system, the time required for filling the ink and recovering the ejection state by suction is shortened, and the productivity is improved. However, depending on the configuration of the sub-tank and the recording head, when the recording head is continuously reciprocated in the main scanning direction to record an image, it becomes difficult for ink to be ejected normally, and the obtained image tends to be blurred. It has been found.

Therefore, an object of the present invention is to provide an inkjet recording method capable of recording a high-quality image with high productivity and excellent ink ejection stability while using an inkjet recording apparatus provided with a sub-tank. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method.

That is, according to the present invention, the water-based ink, the first ink accommodating portion accommodating the water-based ink, the first ink accommodating portion and the first ink accommodating portion are connected via a tube, and the water-based ink is not impregnated into the absorber. Ink including a second ink accommodating portion and a recording head connected to the second ink accommodating portion and formed with a discharge port for ejecting the water-based ink supplied from the second ink accommodating portion. It is an inkjet recording method comprising a step of applying the water-based ink ejected from the ejection port to a recording medium and recording an image by using a recording device, wherein the second ink accommodating portion and the recording head are used for these. An ink flow path to which the water-based ink is supplied is configured inside, and a filter for partitioning the upstream side and the downstream side of the ink flow path is arranged in the middle of the ink flow path, and the said. The value of the ratio (A / B) of the volume A (mL) on the upstream side of the ink flow path to the volume B (mL) on the downstream side of the ink flow path is 5 or more, and the water-based ink is a coloring material. , A nonionic surfactant, and a first water-soluble organic solvent having a specific dielectric constant of 30.0 or less, and the ink-ink recording device is a device that reciprocally scans the recording head to record the image. An inkjet recording method comprising the above is provided.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an inkjet recording method capable of recording a high-quality image with high productivity and excellent ink ejection stability while using an inkjet recording apparatus provided with a sub tank. Further, according to the present invention, it is possible to provide an inkjet recording apparatus used in this inkjet recording method.

It is a perspective view which shows typically one Embodiment of the inkjet recording apparatus of this invention. It is a schematic diagram schematically showing an example of an ink supply system.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt". Further, the water-based ink for inkjet may be simply referred to as "ink". The physical characteristic values are values at room temperature (25 ° C.) unless otherwise specified.

The present inventors first examined a configuration for recording images at high speed over a long period of time. In order to record an image for a long period of time, it is effective to use a recording device having a first ink accommodating portion (main tank) and a second ink accommodating portion (sub tank) connected to each other by a tube. By using such a recording device, the time required for filling the ink and recovering the ejection state by suction is shortened, and the productivity is improved. Further, in order to record an image at a higher speed, it is important to reduce the flow resistance of the ink in the sub tank and improve the flow velocity of the ink. That is, it is important to use a sub-tank that does not have a negative pressure generation mechanism such as an absorber that hinders the flow of ink. Examples of such a sub-tank include a container having a hollow inside (ink storage portion).

If the recording device is miniaturized, restrictions on the installation location can be reduced, and the user can be provided with usage methods suitable for various environments and situations. Therefore, the present inventors have studied the miniaturization of the recording device. As a result, by reducing the volume of the ink flow path on the downstream side (recording head side) of the filter arranged between the sub tank and the recording head, the size of the recording head can be reduced and the recording device can be miniaturized. I found. However, when an image is recorded by continuously reciprocating the recording head in the main scanning direction using a recording device having the above configuration, it becomes difficult for ink to be ejected normally and blurring occurs in the obtained image. It turned out that new issues such as the existence of

It is presumed that the above problems occur by the following mechanism. The ink filled in the ink flow path such as a recording head usually contains bubbles or dissolved gas that can become bubbles. These are generated or mixed in the ink due to, for example, various recovery operations, ink flow, and outgas from the member, and repeatedly generated and disappeared in the ink supplied from the ink flow path. The bubbles existing in the ink in the ink flow path move in the ink flow path due to the fluctuation of the ink generated when the recording head is serially driven, and adhere to the filter provided between the sub tank and the recording head. Since the bubbles adhering to the filter have an effect such as reducing the ink flow rate, it is considered that the ink flow rate may not be appropriate and the image may be blurred. The problem of reduced ink ejection stability has not occurred when a recording unit having a certain volume of ink flow path on the downstream side of the filter, as described in Patent Document 2, is used. However, in this case, since the size of the recording unit becomes large, it is difficult to reduce the size of the recording device.

The present inventors have investigated a method for solving the above-mentioned problems caused by the movement of bubbles in the ink as the ink fluctuates. As a result, they have found that this problem can be solved by using an ink containing a nonionic surfactant and a water-soluble organic solvent having a relative permittivity of 30.0 or less, and have reached the present invention. The present inventors speculate on the mechanism obtained by using an ink containing a nonionic surfactant and a water-soluble organic solvent having a relative permittivity of 30.0 or less as follows.

A water-soluble organic solvent having a relative permittivity of 30.0 or less has a hydrophobic property. In the ink, the shape of the foam is maintained by orienting the surfactant around the hydrophobic gas. When the ink around the bubble has hydrophobic properties, the hydrophobic part of the surfactant present at the interface of the bubble tends to orient not only on the gas side but also on the ink side with hydrophobic properties. .. As a result, it is believed that the surfactant moves away from the foam. That is, by incorporating a nonionic surfactant and a water-soluble organic solvent having a relative permittivity of 30.0 or less in the ink, the surfactant existing at the interface of the foam is separated from the foam, so that the shape of the foam It is thought that the bubbles cannot be maintained and the bubbles are likely to burst and disappear. Therefore, even when bubbles move in the ink flow path due to the shaking of the ink and adhere to the filter, a nonionic surfactant and a water-soluble organic solvent having a relative permittivity of 30.0 or less are used as the ink. By including it, the bubbles burst and easily disappear. As a result, bubbles that affect the flow rate of the ink are reduced, so that the ink is ejected without delay and it is considered that blurring is less likely to occur in the recorded image.

<Inkjet recording method and inkjet recording device>
The inkjet recording method of the present invention includes a water-based ink, a first ink accommodating portion for accommodating water-based ink, a second ink accommodating portion for accommodating water-based ink, and a recording head having an ejection port for ejecting water-based ink. Use an inkjet recording device equipped with. The second ink accommodating portion is a member that is connected to the first ink accommodating portion via a tube and accommodates the water-based ink without impregnating the absorber. The recording head is connected to the second ink accommodating portion. The inkjet recording method of the present invention includes a step of applying the water-based ink ejected from the ejection port of the recording head to the recording medium to record an image. Further, in the inkjet recording apparatus of the present invention, a recording in which a water-based ink, a first ink accommodating portion for accommodating the water-based ink, a second ink accommodating portion for accommodating the water-based ink, and an ejection port for ejecting the water-based ink are formed. It is equipped with a head. The inkjet recording device of the present invention is a device that scans the recording head back and forth to record an image.

(Inkjet recording device)
FIG. 1 is a perspective view schematically showing an embodiment of the inkjet recording apparatus of the present invention. The inkjet recording device of the present embodiment is a so-called serial type inkjet recording device that performs a recording operation by reciprocating the recording head in the X direction (main scanning direction). The recording medium 101 is intermittently conveyed in the Y direction (sub-scanning direction) by the conveying roller 107. The recording unit 102 mounted on the carriage 103 is reciprocally scanned in the X direction (main scanning direction), which is a direction orthogonal to the Y direction, which is the transport direction of the recording medium 101. The recording operation is performed by the transfer of the recording medium 101 in the Y direction and the reciprocating scanning of the recording unit 102 in the X direction. The recording unit 102 includes an inkjet recording head 203 (FIG. 2) that ejects the supplied ink from a plurality of ejection ports, and a sub tank 202 (FIG. 2) as a second ink accommodating portion, and is formed on the carriage 103. It will be installed. The carriage 103 is movably supported 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 the motor, whereby the carriage 103 is reciprocated in the X direction.

Inside the main tank accommodating portion 108, the main tank 201 (FIG. 2) as the first ink accommodating portion is accommodating. The main tank 201 housed in the main tank accommodating portion 108 and the sub tank 202 of the recording unit 102 are connected to each other via the ink supply tube 104. The ink is supplied from the main tank 201 to the sub tank 202 (FIG. 2) via the ink supply tube 104, and then discharged from the discharge port of the recording head 203. The main tank 201, the ink supply tube 104, and the sub tank 202 can all be provided in a number 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 interposing other ink accommodating portions.

The main tank accommodating portion 108 is provided with an ink injection port 210 for injecting ink into the main tank 201 from the outside of the inkjet recording device. When the inkjet recording device is used for the first time or when the amount of ink is reduced, ink is injected from an ink bottle into the main tank mounted inside the inkjet recording device. The user can open the ink injection port 210 and inject ink into the ink tank 201. That is, the main tank is stationary inside the inkjet recording device and is not itself replaced.

FIG. 2 is a schematic diagram schematically showing an example of an ink supply system. The ink contained in the main tank 201 (indicated by hatching) is supplied to the sub tank 202 via the ink supply tube 104, and then passes through the filter 215 and is supplied to the recording head 203. A gas introduction tube 204 as an atmospheric communication portion is connected to the main tank 201. When the recording is performed and the ink is consumed, the ink is supplied from the main tank 201 to the sub tank 202, and the ink in the main tank 201 is reduced. Then, the air is introduced into the main tank 201 from the gas introduction tube 204 whose one end is open to the atmosphere, so that the internal negative pressure for holding the ink is kept substantially constant in the ink supply system. ..

In the main tank 201, it is preferable to increase the maximum ink capacity V ₁ (mL) in order to realize high productivity by increasing the number of recordable sheets. Specifically, the maximum ink capacity V ₁ (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. Further, the initial ink filling amount of the main tank 201 is preferably up to about 95% based on the maximum ink capacity.

In the sub tank 202 as well, in order to reduce the frequency of ink supply from the main tank 201 and to stably supply ink to the recording head 203, it is preferable to increase the maximum ink capacity V ₂ (mL). .. However, for example, assuming a form in which the sub tank 202 is mounted on the carriage 103 as a serial system as shown in FIG. 1, it is preferable that the maximum ink capacity V ₂ (mL) of the sub tank 202 is not too large. That is, when too much ink is stored in the sub tank 202, the recording unit 102 becomes large, the moving speed of the carriage 103 decreases, and the strength of the endless belt 106 for moving the carriage 103 and the motor increases. Needs arise. Therefore, the maximum ink capacity V ₂ (mL) of the sub tank 202 is preferably 1 mL or more and 20 mL or less, and more preferably 2 mL or more and 10 mL or less. Here, the volume A on the upstream side of the ink flow path (volume on the upstream side of the filter in the ink flow path) and the volume B on the downstream side of the ink flow path (volume on the downstream side of the filter in the ink flow path). _Is shown as the maximum ink capacity V2 of the sub tank.

The housings of the main tank 201 and the sub tank 202 are made of polyester, polycarbonate, polyethylene, polypropylene, polystyrene, polyphenylene ether, and a thermoplastic resin such as a mixture or a modification thereof. From the viewpoint of realizing high-speed recording, an absorber for impregnating and accommodating ink is not arranged in the sub tank 202, and the ink is directly stored inside the housing constituting the sub tank 202.

The recording unit 102 includes a recording head 203 and a sub tank 202. The sub-tank 202 may be mounted on the recording unit 102, which is a head cartridge in which the recording head 203 is incorporated, and the recording unit 102 on which the sub-tank 202 is mounted may be mounted on the carriage 103. Further, the recording unit 102 integrally composed of the sub tank 202 and the recording head 203 may be mounted on the carriage 103. Above all, as shown in FIGS. 1 and 2, it is preferable to adopt a form in which the recording unit 102 equipped with the sub tank 202 is set on the carriage 103.

Examples of the ink ejection method of the recording head 203 include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. Above all, it is preferable to adopt a method of applying heat energy to the ink to eject the ink.

As shown in FIG. 2, the inkjet recording apparatus of this embodiment includes a recording unit 102 including a sub tank 202 as a second ink accommodating unit and a recording head 203. Inside the sub-tank 202 and the recording head 203 constituting the recording unit 102, an ink flow path for supplying ink is configured so as to communicate from the upstream end of the sub-tank 202 to the downstream end which is the ink ejection port of the recording head 203. ing. A filter 215 that separates the upstream side and the downstream side of the ink flow path is arranged in the middle of the ink flow path. In the inkjet recording apparatus of the present embodiment, the value (A / B) of the ratio (A / B) of the volume A (mL) on the upstream side of the ink flow path to the volume B (mL) on the downstream side of the ink flow path is 5 or more. .. The volume of the ink flow path inside the sub tank (second ink accommodating portion) 202 and the recording head 203 is designed so that the A / B value is 5 or more, and the arrangement location of the filter 215 is adjusted. Therefore, the height of the recording head 203 can be lowered. This makes it possible to make the inkjet recording device smaller. The value of the ratio (A / B) of the volume A (mL) to the volume B (mL) is preferably 5 or more and 50 or less, and more preferably 5 or more and 40 or less.

The inkjet recording method of the present invention includes a step of applying ink ejected from the ejection port of a recording head to a recording medium to record an image. As described above, the inkjet recording method of the present invention uses an inkjet recording device that is small in size but has excellent ink ejection stability, so that images can be recorded with high productivity. Specifically, the moving speed of the recording head when recording an image can be preferably 30 inches / sec or more, more preferably 35 inches / sec or more. The moving speed is preferably 70 inches / sec or less. Further, it is preferable to apply ink to the unit area of the recording medium by one relative scanning between the recording head and the recording medium to record an image. The unit area can be set as an arbitrary area such as one pixel or one band.

Any recording medium may be used as the recording medium for recording the image. Among them, it is preferable to use a recording medium having no coated layer such as plain paper or uncoated paper, and a paper having permeability such as a recording medium having a coated layer such as glossy paper or art paper.

(Water-based ink)
The inkjet recording method of the present invention includes a step of applying water-based ink ejected from a ejection port of a recording head to a recording medium to record an image. The water-based ink contains a coloring material, a nonionic surfactant, and a first water-soluble organic solvent having a relative permittivity of 30.0 or less. Hereinafter, the components constituting the ink and the like will be described.

[Color material]
As the coloring material, pigments and dyes can be used. The content (mass%) of the coloring material in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 10.0% by mass, based on the total mass of the ink. The following is more preferable.

When a pigment is used as the coloring material, the dispersion method of the pigment is not particularly limited. For example, a resin-dispersed pigment dispersed with a resin dispersant, a pigment dispersed with a surfactant, a microcapsule pigment in which at least a part of the particle surface of the pigment is coated with a resin or the like can be used. In addition, a self-dispersing pigment in which a functional group containing a hydrophilic group such as an anionic group is bonded to the particle surface of the pigment, or a pigment in which an organic group containing a polymer is chemically bonded to the particle surface of the pigment (resin bond). A type of self-dispersing pigment) or the like can also be used. Further, pigments having different dispersion methods may be used in combination. Among them, a self-dispersed pigment in which a functional group containing a hydrophilic group such as an anionic group is bonded to the particle surface of the pigment, and a resin-dispersed pigment dispersed in a resin dispersant are preferable. It is more preferable to use a water-soluble resin as the resin dispersant. In particular, as the color material for black ink, a self-dispersing pigment in which a functional group containing an anionic group is bonded to the surface of carbon black particles is preferable, and as the color material for color ink, a water-soluble resin is used as a resin dispersant. A resin-dispersed pigment in which an organic pigment is dispersed is preferable.

Examples of the pigment include inorganic pigments such as carbon black; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolenone, imidazolone, diketopyrrolopyrrole, and dioxazine. These pigments can be used alone or in combination of two or more.

Examples of the dye include a direct dye, an acid dye, a basic dye, a disperse dye, and an edible dye. Among them, it is preferable to use a dye having an anionic group. Specific examples of the dye skeleton include azo, triphenylmethane, phthalocyanine, azaphthalocyanine, xanthene, anthrapyridone and the like.

[Surfactant]
The ink contains a surfactant, including a nonionic surfactant. Examples of the nonionic surfactant include various surfactants such as hydrocarbon-based, fluorine-based, and silicone-based surfactants. The nonionic surfactant is preferably at least one of a hydrocarbon-based surfactant and a fluorine-based surfactant. By using an ink containing at least one of a hydrocarbon-based surfactant and a fluorine-based surfactant, bubbles in the ink are more likely to disappear, and the ejection stability of the ink can be further improved.

Examples of the hydrocarbon-based nonionic surfactant include polyoxyethylene alkyl ethers, ethylene oxide adducts of acetylene glycol, polyethylene glycol polypropylene glycol block copolymers, and ethylene oxide adducts of polyhydric alcohols. Examples of the fluorine-based nonionic surfactant include a perfluoroalkylethylene oxide adduct. Examples of the silicone-based nonionic surfactant include a polyether-modified siloxane compound and the like. In particular, it is preferable to use both a hydrocarbon-based nonionic surfactant and a fluorine-based nonionic surfactant. When these are used in combination, it is preferable that the content of the hydrocarbon-based nonionic surfactant is higher than the content of the fluorine-based nonionic surfactant.

The HLB value of the nonionic surfactant is preferably 8.0 or more, and more preferably 10.0 or more and 18.5 or less. When the HLB value of the nonionic surfactant is less than 8.0, the effect of eliminating bubbles is low, and the effect of improving the ejection stability of the ink may be reduced. The "HLB value" of the nonionic surfactant in the present specification is a value obtained by the Griffin method.

The ink can further contain various surfactants (other surfactants) other than the nonionic surfactant. Examples of other surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants and the like. Further, the other surfactant may be a hydrocarbon-based surfactant, a fluorine-based surfactant, a silicone-based surfactant, or the like.

The content (% by mass) of the surfactant (total of nonionic surfactant and other surfactants) in the ink is 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. It is preferably 0.2% by mass or more and 1.5% by mass or less.

[resin]
The ink can contain a resin. The resin can be added to the ink in order to (i) stabilize the dispersed state of the pigment, that is, as a resin dispersant or an auxiliary thereof. Further, (ii) it can be added to the ink in order to improve various characteristics of the recorded image. The state of the resin in the ink may be a state of being dissolved in an aqueous medium or a state of being dispersed as resin particles in the aqueous medium. The term "resin is water-soluble" as used herein means that when the resin is neutralized with an acid value and an equivalent amount of alkali, particles whose particle size can be measured by a measuring method such as a dynamic light scattering method are not formed. Means that. The content (% by mass) of the resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, preferably 0.1% by mass or more and 3.0% by mass or less, based on the total mass of the ink. Is more preferable.

Examples of the resin include acrylic resin, polyester resin, urethane resin, urea resin, polysaccharides, and polypeptides. Of these, acrylic resin and urethane resin are preferable from the viewpoint of ejection characteristics from the ejection port of the recording head. However, since the resin component such as resin particles tends to retain air bubbles, it is preferable not to contain too much in the ink.

The anionic group of the water-soluble resin may form a salt. Examples of the cation forming the salt include alkali metal cations such as lithium, sodium and potassium; ammonium ^ions (NH ₄₊ ); and organic ammonium cations such as dimethylamine and triethanolamine. The acid value of the resin is preferably 40 mgKOH / g or more and 300 mgKOH / g or less.

[Aqueous medium]
The ink is a water-based ink containing at least water as a water-based medium. Further, the ink contains a first water-soluble organic solvent having a relative permittivity of 30.0 or less. That is, the ink can contain an aqueous medium which is a mixed solvent of water and the first water-soluble organic solvent. By using an ink containing both a first water-soluble organic solvent and a nonionic surfactant, as described above, it is possible to effectively eliminate bubbles generated in the ink, and the ejection stability of the ink can be improved. Can be improved.

The first water-soluble organic solvent may be any water-soluble organic solvent having a relative permittivity of 30.0 or less. Specifically, any of alcohols, (poly) alkylene glycols, glycol ethers, nitrogen-containing compounds, sulfur-containing compounds and the like that can be used for ink for inkjet can be used. Examples of the first water-soluble organic solvent include 1,3-butanediol (30.0), 1,2-propanediol (28.8), 1,2,6-hexanetriol (28.5), and 2 -Methyl-1,3-propanediol (28.3), 2-pyrrolidone (28.0), 1,5-pentanediol (27.0), 3-methyl-1,3-butanediol (24.0) ), 3-Methyl-1,5-pentanediol (23.9), 1- (hydroxymethyl) -5,5-dimethylhydantin (23.7), triethylene glycol (22.7), 1,2- Butanediol (22.2), tetraethylene glycol (20.8), dipropylene glycol (19.7), polyethylene glycol with a number average molecular weight of 200 (18.9), 2-ethyl-1,3-hexanediol ( 18.5), 1,2-hexanediol (14.8), propylene glycol monomethyl ether (12.4), polyethylene glycol with a number average molecular weight of 600 (11.4), diethylene glycol monobutyl ether (11.0), tri Ethethylene glycol monobutyl ether (9.8), ethylene glycol monobutyl ether (9.4), tetraethylene glycol monobutyl ether (9.4), tripropylene glycol monomethyl ether (8.5), 1,6-hexanediol (7) 1. 1), polyethylene glycol (4.6) having a number average molecular weight of 1,000, and the like can be mentioned. The numerical value in parentheses attached to each water-soluble organic solvent is the relative permittivity of each water-soluble organic solvent at 25 ° C. The relative permittivity of the first water-soluble organic solvent is preferably 3.0 or more. Further, as the first water-soluble organic solvent, one having a lower vapor pressure than water is preferable. Among them, the first water-soluble organic solvent includes 1,3-butanediol, 2-pyrrolidone, 3-methyl-1,5-pentanediol, triethylene glycol, 1,2-hexanediol, and triethylene glycol monobutyl ether. Is preferred, and triethylene glycol is even more preferred. The content (% by mass) of the first 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.

The relative permittivity of the water-soluble organic solvent can be measured using a dielectric constant meter (for example, trade name "BI-870", manufactured by BROOKHAVEN INSTRUMENTS CORPORATION, etc.) under the condition of a frequency of 10 kHz. The relative permittivity of the water-soluble organic solvent solid at 25 ° C. is a value calculated from the following formula (1) by measuring the relative permittivity of a 50% by mass aqueous solution. Normally, the "water-soluble organic solvent" refers to a liquid, but in the present invention, a water-soluble organic solvent that is solid at 25 ° C. (normal temperature) is also included.
ε _sol = 2ε _50% -ε _water ... (1)
ε _sol : Relative permittivity of solid water-soluble organic solvent at 25 ° C ε _50% : Relative permittivity of 50% by mass aqueous solution of solid water-soluble organic solvent at 25 ° C ε _water : Relative permittivity of water

Examples of the water-soluble organic solvent that is general-purpose for water-based inks and solid at 25 ° C. include 1,6-hexanediol, trimethylolpropane, ethyleneurea, urea, and polyethylene glycol having a number average molecular weight of 1,000. be able to. Here, the reason for obtaining the relative permittivity of the water-soluble organic solvent solid at 25 ° C. from the relative permittivity of the 50% by mass aqueous solution is as follows. Among the water-soluble organic solvents that are solid at 25 ° C., some that can be constituents of water-based inks make it difficult to prepare a high-concentration aqueous solution of more than 50% by mass. On the other hand, in a low-concentration aqueous solution having a concentration of 10% by mass or less, the relative permittivity of water becomes dominant, and it is not possible to obtain a probable (effective) relative permittivity value of the water-soluble organic solvent. Therefore, as a result of studies by the present inventors, it is possible to prepare an aqueous solution to be measured with most of the water-soluble organic solvents solid at 25 ° C. that can be used for ink, and it is determined. It was found that the relative permittivity to be obtained is also consistent with the effect of the present invention. For this reason, we decided to use a 50% by mass aqueous solution. For water-soluble organic solvents that are solid at 25 ° C and whose solubility in water is low, a 50% by mass aqueous solution cannot be prepared, use an aqueous solution with a saturated concentration and calculate according to the above-mentioned ε _sol . The value of the relative permittivity is used for convenience.

The ink may further contain a water-soluble organic solvent (other water-soluble organic solvent) other than the above-mentioned first water-soluble organic solvent. As the other water-soluble organic solvent, any of alcohols, (poly) alkylene glycols, glycol ethers, nitrogen-containing compounds, sulfur-containing compounds and the like that can be used for ink for inkjet can be used. .. Examples of other water-soluble organic solvents include urea (110.3), ethylene urea (49.7), dimethyl sulfoxide (48.9), glycerin (42.3), γ-butyrolactone (41.9), and the like. Ethylene glycol (40.4), 1- (2-hydroxyethyl) -2-pyrrolidone (37.6), trimethylolpropane (33.7), N-methyl-2-pyrrolidone (32.0), triethanol Examples thereof include amine (31.9), diethylene glycol (31.7), and 1,4-butanediol (31.1). The relative permittivity of the other water-soluble organic solvent is preferably 150.0 or less. Further, as the other water-soluble organic solvent, a solvent having a lower vapor pressure than water is preferable. The numerical value in parentheses attached to each water-soluble organic solvent is the relative permittivity of each water-soluble organic solvent at 25 ° C.

The content (% by mass) of the water-soluble organic solvent (total of the first water-soluble organic solvent and other water-soluble organic solvents) in the ink is 3.0% by mass or more and 50.0% by mass based on the total mass of the ink. % Or less is preferable. The content (% by mass) of the first water-soluble organic solvent in the ink is preferably 1.0% by mass or more and 20.0% by mass or less, and 2.5% by mass or more and 15 by mass, based on the total mass of the ink. It is more preferably 0.0% by mass or less. The content (% by mass) of the first water-soluble organic solvent in the ink is preferably 5.0 times or more in terms of the mass ratio with respect to the content (mass%) of the nonionic surfactant. It is more preferably 0 times or more and 50.0 times or less. By setting the above mass ratio to 5.0 times or more, it becomes possible to effectively disturb the orientation of the nonionic surfactant, and the bubbles in the ink are more effectively eliminated, so that the ink ejection stability is achieved. Can be further improved.

As the water, it is preferable to use deionized water or ion-exchanged water. The content (% by 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.

[Other ingredients]
In addition to the above components, the ink contains various additives such as a pH adjuster, a viscosity regulator, a rust inhibitor, a preservative, a fungicide, an antioxidant, and an antioxidant, if necessary. May be good. In general, these additives have a considerably low content in the ink and have little direct effect on the action utilized in the present invention. Therefore, in the present invention, these additives are not included in the "water-soluble organic solvent" and are not included in the calculation of the relative permittivity.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. Unless otherwise specified, those described as "parts" and "%" regarding the amount of components are based on mass.

<Preparation of pigment dispersion>
(Pigment dispersion liquid 1)
A solution prepared by dissolving 70.6 mmol of concentrated hydrochloric acid in 5.5 g of water was cooled to a temperature of 5 ° C., and 9.8 mmol of 4-aminophthalic acid was added. The container containing this solution was placed in an ice bath and the solution was stirred to keep the solution at 10 ° C. or lower at all times. To this was added a solution prepared by dissolving 24.9 mmol of sodium nitrite in 9.0 g of water at 5 ° C. After stirring for another 15 minutes, 6.0 g of the pigment was added under stirring. As the pigment, carbon black (trade name "Black Pearls 880", manufactured by Cabot) was used. Then, the mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered through a filter paper (trade name "Standard Filter Paper No. 2", manufactured by Advantech), washed thoroughly with water, and dried in an oven at 110 ° C. to obtain a self-dispersed pigment. The content of the pigment was adjusted using ion-exchanged water to obtain a pigment dispersion liquid 1. The pigment dispersion 1 contained a self-dispersed pigment in which a phthalic acid group whose counter ion was a sodium ion was bonded to the particle surface, and the content of the pigment was 10.0%.

(Pigment dispersion liquid 2)
The type of pigment is C.I. I. The pigment dispersion liquid 2 was obtained in the same procedure as the pigment dispersion liquid 1 described above except that the pigment red 122 was changed. The pigment dispersion 2 contained a self-dispersed pigment in which a phthalic acid group whose counter ion was a sodium ion was bonded to the particle surface, and the content of the pigment was 10.0%.

(Pigment dispersion liquid 3)
The type of pigment is C.I. I. The pigment dispersion liquid 3 was obtained in the same procedure as the pigment dispersion liquid 1 described above, except that the pigment blue was changed to 15: 3. The pigment dispersion 3 contained a self-dispersed pigment in which a phthalic acid group whose counter ion was a sodium ion was bonded to the particle surface, and the content of the pigment was 10.0%.

(Pigment dispersion liquid 4)
A mixture was obtained by mixing 10.0 parts of the pigment, 20.0 parts of an aqueous solution of the resin dispersant (resin (solid content) content 20.0%), and 70.0 parts of ion-exchanged water. As the pigment, carbon black (trade name "Black Pearls 880", manufactured by Cabot) was used. As the aqueous solution of the resin dispersant, water having a neutralization equivalent of 1 with respect to the acid value of a styrene-acrylic acid copolymer (weight average molecular weight 10,000, acid value 200 mgKOH / g), which is a water-soluble resin. The one dissolved in ion-exchanged water using sodium oxide was used. The obtained mixture was dispersed for 3 hours using a batch type vertical sand mill, and then pressure-filtered with a microfilter (manufactured by Fujifilm) having a pore size of 1.2 μm. Next, ion-exchanged water was added to adjust the pigment content to obtain a pigment dispersion liquid 4. The pigment dispersion liquid 4 contained a pigment dispersed with a water-soluble resin (resin dispersant), and the content of the pigment was 10.0% and the content of the water-soluble resin was 4.0%. ..

(Pigment dispersion liquid 5)
The type of pigment is C.I. I. The pigment dispersion liquid 5 was obtained in the same procedure as the pigment dispersion liquid 4 described above, except that the pigment red 122 was changed. The pigment dispersion liquid 5 contained a pigment dispersed with a water-soluble resin (resin dispersant), and the content of the pigment was 10.0% and the content of the water-soluble resin was 4.0%. ..

(Pigment dispersion liquid 6)
The type of pigment is C.I. I. The pigment dispersion liquid 6 was obtained in the same procedure as the pigment dispersion liquid 4 described above except that the pigment yellow 74 was changed. The pigment dispersion liquid 6 contained a pigment dispersed with a water-soluble resin (resin dispersant), and the content of the pigment was 10.0% and the content of the water-soluble resin was 4.0%. ..

(Pigment dispersion liquid 7)
The type of pigment is C.I. I. A pigment dispersion 7 was obtained in the same procedure as the pigment dispersion 4 described above, except that the pigment blue was changed to 15: 3. The pigment dispersion 7 contained a pigment dispersed with a water-soluble resin (resin dispersant), and the content of the pigment was 10.0% and the content of the water-soluble resin was 4.0%. ..

<Preparation of aqueous dye solution>
A commercially available aqueous dye solution containing a dye (trade name "Project Fast Black 2", manufactured by FUJIFILM) was prepared. The dye content of the prepared dye aqueous solution was adjusted to obtain a dye aqueous solution. The content of the dye in the aqueous dye solution was 10.0%.

<Preparation of surfactant>
The surfactants shown in Table 1 were prepared.

<Ink preparation>
Each component (unit:%) shown in the upper part of Tables 2-1 to 2-3 is mixed, sufficiently stirred, and then pressure-filtered with a microfilter (manufactured by FUJIFILM) having a pore size of 3.0 μm. Ink was prepared. In Tables 2-1 to 2-3, the numerical values in parentheses attached to the water-soluble organic solvent are the values of the relative permittivity of each water-soluble organic solvent at 25 ° C. The characteristics of the prepared ink are shown in the lower part of Tables 2-1 to 2-3.

<Evaluation>
An inkjet recording apparatus having the configuration of the main part shown in FIG. 1 and incorporating the ink supply system having the configuration shown in FIG. 2 was prepared. This recording device is a serial type recording device in which a recording head 203 is incorporated and a recording unit 102 equipped with a sub tank 202 is mounted on a carriage 103. As the tube (ink supply tube 104) connecting the main tank 201 and the sub tank 202, a tube having an inner diameter of 2 mm and an outer diameter of 4 mm, which was formed of a styrene-based thermoplastic elastomer, was used. The maximum ink capacity V ₁ of the main tank was 150 mL, and the maximum ink capacity V ₂ of the sub tank was the values shown in Tables 3-1 and 3-2. In Reference Example 1, an inkjet recording device of a type that does not have a first ink accommodating portion (main tank) and accommodates ink only in a second ink accommodating portion integrally formed with a recording head is used. Other than Reference Example 2, as the sub-tank, a tank in which the absorber was not arranged inside the housing made of the thermoplastic resin was used, and in Reference Example 2, a sub-tank in which the absorber was arranged was used. Further, in Reference Example 3, a line head was used instead of the recording head 203 (serial recording head) shown in FIGS. 1 and 2.

(Ink ejection stability)
The prepared ink was injected into the main tank of the above-mentioned inkjet recording apparatus, and the ink was supplied to the sub tank and the recording head. After that, a solid image with a recording duty of 50% was recorded on the entire surface of A4 size PPC paper (trade name "GF-500", manufactured by Canon). Details of the evaluation conditions are shown in Tables 3-1 and 3-2. In this embodiment, the recording duty of a solid image recorded under the condition that two drops of ink having a mass of 5 ng per drop are applied to a unit area of 1/600 inch × 1/600 inch is defined as 100%. .. The recorded solid pattern was visually confirmed, and the ink ejection property was evaluated according to the evaluation criteria shown below. In the evaluation criteria shown below, "AA", "A", and "B" were set as acceptable levels, and "C" was set as an unacceptable level. The evaluation results are shown in Tables 3-1 and 3-2.
AA: Solid images were recorded evenly.
A: Unevenness was observed at the edges of the solid image.
B: Unevenness was observed in about half of the solid image.
C: Unevenness was observed in the entire solid image.

The throughput of Example 32 was lower than that of Example 33, and that of Example 35 was lower than that of Example 1. In addition, Examples 36 and 37 had lower throughput as compared with all other Examples. In Reference Example 1, since an inkjet recording device having no first ink accommodating portion (main tank) was used, a large amount of images could not be recorded. In Reference Examples 2 to 4, since an inkjet recording device provided with a sub-tank provided with an absorber inside thereof was used, images could not be recorded at high speed under good ejection stability conditions, and the throughput decreased. Since the inkjet recording device used in Reference Example 5 was a recording device provided with a line head as a recording head, the recording device was large. In Reference Example 6, since a sub-tank without a filter inside was used, non-discharge due to foreign matter such as dust was likely to occur. Since the recording head used in Reference Examples 7 to 10 was large, the recording device was also quite large.

Claims (7)

The water-based ink, the first ink accommodating portion for accommodating the water-based ink, and the second ink accommodating portion connected to the first ink accommodating portion via a tube and accommodating the water-based ink without impregnating the absorber. An inkjet recording device provided with a recording head connected to the second ink accommodating portion and formed with an ejection port for ejecting the water-based ink supplied from the second ink accommodating portion is used. An inkjet recording method comprising a step of applying the water-based ink ejected from an outlet to a recording medium to record an image.
The second ink accommodating portion and the recording head form an ink flow path to which the water-based ink is supplied, and a filter for partitioning the upstream side and the downstream side of the ink flow path is the ink. The value (A / B) of the ratio (A / B) of the volume A (mL) on the upstream side of the ink flow path to the volume B (mL) on the downstream side of the ink flow path, which is arranged in the middle of the flow path. Is 5 or more,
The water-based ink contains a coloring material, a nonionic surfactant, and a first water-soluble organic solvent having a relative permittivity of 30.0 or less.
An inkjet recording method, wherein the inkjet recording device is a device that scans the recording head back and forth to record the image. The inkjet recording method according to claim 1, wherein the content (% by mass) of the first water-soluble organic solvent is 5.0 times or more in terms of the mass ratio to the content (mass%) of the nonionic surfactant. .. The inkjet recording method according to claim 1 or 2, wherein the HLB value of the nonionic surfactant is 8.0 or more. The inkjet recording method according to any one of claims 1 to 3, wherein the nonionic surfactant is at least one of a hydrocarbon-based surfactant and a fluorine-based surfactant. The inkjet recording method according to any one of claims 1 to 4, wherein the moving speed of the recording head during the reciprocating scan is 30 inches / sec or more. The inkjet recording according to any one of claims 1 to 5, wherein the water-based ink is applied to a unit area of the recording medium and the image is recorded by one relative scanning between the recording head and the recording medium. Method. The water-based ink, the first ink accommodating portion for accommodating the water-based ink, and the second ink accommodating portion connected to the first ink accommodating portion via a tube and accommodating the water-based ink without impregnating the absorber. An inkjet recording apparatus including a recording head connected to the second ink accommodating portion and formed with a discharge port for ejecting the water-based ink supplied from the second ink accommodating portion.
The second ink accommodating portion and the recording head form an ink flow path to which the water-based ink is supplied, and a filter for partitioning the upstream side and the downstream side of the ink flow path is the ink. The value (A / B) of the ratio (A / B) of the volume A (mL) on the upstream side of the ink flow path to the volume B (mL) on the downstream side of the ink flow path, which is arranged in the middle of the flow path. Is 5 or more,
The water-based ink contains a coloring material, a nonionic surfactant, and a first water-soluble organic solvent having a relative permittivity of 30.0 or less.
An inkjet recording apparatus characterized by being an apparatus for recording an image by reciprocating scanning the recording head.

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