JP6808923B2 - Water-based ink, recording device, and recording method - Google Patents

Description

The present invention relates to water-based inks, recording devices, and recording methods.

For example, Patent Document 1 states that "the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate is 30. The average particle size of the colorant in the ink up to% is twice or less the initial average particle size. ”Is proposed.
Further, Patent Document 2 states that "colored fine particles have a quaternized carboxyl group on the surface thereof and have a volume average particle size of 0.5 μm or less, and are contained in a redispersion liquid of dry ink. A jet ink in which the increase rate of the volume average particle size of the colored fine particles is 50% or less. ”Has been proposed.
Further, Patent Document 3 proposes "an inkjet ink containing a pigment dispersion having a total number of coarse particles having a particle diameter of 0.5 μm or more of 1 million / 5 μL or less."

Japanese Unexamined Patent Publication No. 2006-07732 JP-A-2007-146167 Japanese Unexamined Patent Publication No. 2010-261028

Above, "The viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the ink has a water evaporation rate of up to 30%. Ink for inkjet recording, in which the average particle size of the colorant is less than twice the initial average particle size. ”, The ejection state from nozzles that are rarely used becomes unstable (= uneven landing), and image defects in printed matter. May be.

The subject of the present invention is that the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate is up to 30%. Compared to an inkjet recording ink in which the average particle size of the colorant in the ink is twice or less the initial average particle size, the occurrence of uneven landing is suppressed when first recording on a recording medium dried under predetermined conditions. The purpose is to provide a water-based ink.

The above problem is solved by the following means.

The invention according to < 1 > is
It contains a colorant, polymer particles, and a solvent containing water and an aqueous organic solvent.
The number of coarse particles Nc1 having a particle size of 0.5 μm or more in the water-based ink after weight loss by reducing the mass by 60% by evaporation of the solvent, and the number of coarse particles Ni1 having a particle size of 0.5 μm or more in the water-based ink before weight loss. A water-based ink that satisfies the formula: 1 ≦ Nc1 / Ni1 ≦ 50.

The invention according to < 2 > is
The water-based ink according to < 1 > , wherein the glass transition temperature of the polymer particles is 40 ° C. or higher and 90 ° C. or lower.

The invention according to < 3 > is
The water-based ink according to < 1 > or < 2 > , which contains a pigment as a colorant and further contains a pigment dispersant having an acid value of 70 mgKOH / g or more and 200 mgKOH / g or less.

The invention according to < 4 > is
A recording device having an ejection head that accommodates the water-based ink according to any one of < 1 > to < 3 > and ejects the water-based ink onto the surface of a recording medium.

The invention according to < 5 > is
The first ejection head accommodates the first aqueous ink as the aqueous ink according to any one of < 1 > to < 3 > , and first ejects the first aqueous ink onto the surface of the recording medium. Is the head
< 4 > further has a second ejection head that accommodates the second aqueous ink and ejects the second aqueous ink onto the surface of the recording medium after the ejection of the first aqueous ink by the first ejection head. The recording device described.

The invention according to < 6 > is
A first ejection head that accommodates the first aqueous ink and ejects the first aqueous ink onto the surface of the recording medium.
A drying device that dries the first water-based ink ejected onto the surface of the recording medium by the first ejection head, and a drying device.
The water-based ink according to any one of < 1 > to < 3 > is contained as the second water-based ink, and after the first water-based ink is dried by the drying device, the second water-based ink is applied to the back surface of the recording medium. The second discharge head to discharge and
A recording device having.

The invention according to < 7 > is
The second ejection head is a third ejection head that stores the third aqueous ink as the second aqueous ink and first ejects the third aqueous ink to the back surface of the recording medium.
< 6 > further has a fourth ejection head that accommodates the fourth aqueous ink and ejects the fourth aqueous ink to the back surface of the recording medium after the ejection of the third aqueous ink by the third ejection head. The recording device described.

The invention according to < 8 > is
A recording method comprising a ejection step of ejecting the water-based ink according to any one of < 1 > to < 3 > onto the surface of a recording medium by an ejection head.

The invention according to < 9 > is
In the ejection step, the first ejection head as the ejection head first ejects the first aqueous ink as the aqueous ink according to any one of < 1 > to < 3 > onto the surface of the recording medium. It is a discharge process,
The recording method according to < 8 > , further comprising a second ejection step of ejecting the second aqueous ink onto the surface of the recording medium by the second ejection head after the ejection of the first aqueous ink by the first ejection head. ..

The invention according to < 10 > is
The first ejection step of ejecting the first water-based ink onto the surface of the recording medium by the first ejection head
A drying step of drying the first water-based ink discharged onto the surface of the recording medium by the first ejection step, and a drying step.
After the first water-based ink is dried by the drying step, the second water-based ink according to any one of < 1 > to < 3 > is discharged as the second water-based ink to the back surface of the recording medium by the second ejection head. Discharge process and
Recording method having.

The invention according to < 11 > is
The second ejection step is a third ejection step in which the third ejection head as the second ejection head first ejects the third aqueous ink as the second aqueous ink onto the back surface of the recording medium.
The recording method according to < 10 > , further comprising a fourth ejection step of ejecting the fourth aqueous ink to the back surface of the recording medium by the fourth ejection head after the ejection of the third aqueous ink by the third ejection head. ..

According to the invention according to < 1 > , < 2 > , or < 3 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, and the viscosity increase rate is 500 between the water evaporation rates of 30 to 50%. Compared to inkjet recording ink, which has a point exceeding the above and the average particle size of the colorant in the ink up to a water evaporation rate of up to 30% is twice or less the initial average particle size, the recording medium is dried under predetermined conditions. When recording for the first time, a water-based ink that suppresses the occurrence of uneven landing is provided.

According to the invention according to < 4 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate. When first recording on a recording medium dried under predetermined conditions, compared to the case where an inkjet recording ink in which the average particle size of the colorant in the ink up to 30% is twice or less the initial average particle size is applied. , A recording device for suppressing the occurrence of uneven landing of water-based ink is provided.
According to the invention according to < 5 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate. When recording on a dry recording medium, compared to the case where an inkjet recording ink in which the average particle size of the colorant in the ink up to 30% is twice or less the initial average particle size is applied as the first water-based ink, Provided is a recording device that suppresses uneven landing of the first water-based ink that is first ejected onto the surface of a recording medium under predetermined conditions.

According to the invention according to the invention of < 6 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, and the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%. Recording is performed on both sides of the recording medium as compared with the case where the average particle size of the colorant in the ink having a water evaporation rate of up to 30% is twice or less the initial average particle size as the second water-based ink. At that time, there is provided a recording device that suppresses uneven landing of the second water-based ink discharged to the back surface of the recording medium dried by drying the first water-based ink by the drying device under predetermined conditions.
According to the invention according to < 7 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate. When recording on both sides of the recording medium, compared to the case where the average particle size of the colorant in the ink up to 30% is twice or less the initial average particle size as the third water-based ink. Provided is a recording device that suppresses uneven landing of the third water-based ink that is first ejected onto the back surface of the recording medium that has been dried by drying the first water-based ink with a drying device under predetermined conditions.

According to the invention according to < 8 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate. When first recording on a recording medium dried under predetermined conditions, compared to the case where an inkjet recording ink in which the average particle size of the colorant in the ink up to 30% is twice or less the initial average particle size is applied. , A recording method for suppressing the occurrence of uneven landing of water-based ink is provided.
According to the invention according to < 9 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate. Compared to the case where an inkjet recording ink in which the average particle size of the colorant in the ink up to 30% is twice or less the initial average particle size is applied as the first aqueous ink, the recording medium is dried under predetermined conditions. Provided is a recording method for suppressing uneven landing of the first water-based ink first ejected onto the surface of a recording medium during recording.

According to the invention according to the invention of < 10 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, and the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%. Recording is performed on both sides of the recording medium as compared with the case where the average particle size of the colorant in the ink having a water evaporation rate of up to 30% is twice or less the initial average particle size as the second water-based ink. At that time, there is provided a recording method for suppressing uneven landing of the second water-based ink discharged on the back surface of the recording medium dried by drying the first water-based ink by a drying step under predetermined conditions.
According to the invention according to < 11 > , the viscosity increase rate is 10 or less up to a water evaporation rate of 30%, the viscosity increase rate exceeds 500 between the water evaporation rates of 30 to 50%, and the water evaporation rate. When recording on both sides of the recording medium, compared to the case where the average particle size of the colorant in the ink up to 30% is twice or less the initial average particle size as the third water-based ink. Provided is a recording method for suppressing uneven landing of a third water-based ink that is first ejected onto the back surface of a recording medium that has been dried by drying the first water-based ink in a drying step under predetermined conditions.

It is a schematic block diagram which shows the recording apparatus which concerns on this embodiment.

Hereinafter, embodiments that are an example of the present invention will be described.

The water-based ink according to the present embodiment contains a colorant, polymer particles, and a solvent containing water and an aqueous organic solvent. Then, the number of coarse particles Nc1 having a particle size of 0.5 μm or more (hereinafter, also referred to as “the number of coarse particles at the time of concentration Nc1”) in the water-based ink after the weight loss by 60% weight reduction by evaporation of the solvent and the water-based ink before the weight loss. The relationship with the number of coarse grains Ni1 having a particle size of 0.5 μm or more (hereinafter, also referred to as “initial number of coarse grains Ni1”) satisfies the formula: 1 ≦ Nc1 / Ni1 ≦ 50. Hereinafter, the number of coarse grains is referred to as "the number of coarse grains".

Here, when first recording is performed on a recording medium dried under predetermined conditions (for example, paper having a water content of 3% or less), the moisture absorption of the recording medium makes it easier for the periphery of the discharge surface of the discharge head to dry. When the periphery of the discharge surface of the discharge head dries, drying proceeds from the menicas surface (curved surface created by the surface of the water-based ink) in the nozzle of the discharge head, and when the water-based ink concentrates in the nozzle of the discharge head, it is more water-based than water. The ratio of organic solvent increases. Therefore, the dispersibility of the colorant (pigment) or the polymer particles is lowered, the colorant (pigment) or the polymer particles are aggregated, and the number of coarse particles is likely to increase. When the number of coarse particles increases, coarse particles adhere to the inner wall surface of the nozzle of the discharge head and around the edge of the nozzle, and the adhered coarse particles become nuclei and grow particles. Then, the coarse particles in which the particles have grown interfere with the ejection of the water-based ink, which may reduce the ejection amount or deteriorate the ejection direction. Therefore, uneven landing may occur. In particular, due to the moisture absorption of the dry recording medium, the solvent of the water-based ink evaporates rapidly in the nozzle of the ejection head, and the mass of the water-based ink may be reduced by nearly 60%, so that uneven landing is likely to occur.
When the ejection amount of the water-based ink decreases and uneven landing occurs, it becomes difficult to fill the gap between the adjacent dots, and for example, it appears as a white streak in the image. Further, when the ejection direction of the water-based ink deteriorates and uneven landing occurs, it becomes difficult to fill the gap between the adjacent dots and the overlap with the adjacent dots increases, and for example, black streaks appear in the image.

Therefore, in the water-based ink according to the present embodiment, the relationship between the number of coarse grains Nc1 during concentration of the water-based ink and the initial number of coarse grains Ni1 is set to satisfy the formula: 1 ≦ Nc1 / Ni1 ≦ 50, and when the water-based ink is concentrated. The amount of change between the number of coarse grains Nc1 and the initial number of coarse grains Ni1 is reduced. That is, when the water-based ink is concentrated (dried) by evaporation of the solvent, the generation of coarse particles is suppressed. As a result, even when the mass of the water-based ink is reduced by nearly 60% due to the moisture absorption of the dry recording medium, excessive coarse particles of the water-based ink are suppressed in the nozzle of the ejection head, and the inner wall surface of the nozzle of the ejection head and The growth of coarse particles around the edge of the nozzle is suppressed, and the ejection property of water-based ink is ensured.

Therefore, in the water-based ink according to the present embodiment, the occurrence of uneven landing is suppressed when first recording on a recording medium dried under predetermined conditions. The drying of the recording medium under a predetermined condition means drying by the "drying drum and warm air blower" at the set temperature described in "Details of the recording device" in [Example]. However, even when the recording medium is dried under conditions other than these predetermined conditions, the occurrence of uneven landing is suppressed.
Further, in the water-based ink according to the present embodiment, the generation of coarse particles is suppressed on the inner wall surface of the nozzle of the ejection head and around the edge of the nozzle, so that the occurrence of latency is also suppressed. Here, the latency means that the amount of the next ejected ink decreases or the landing position of the next ejected water-based ink on the recording medium is changed when the next ejection is performed after a lapse of time after the ejection of the water-based ink. Indicates a discharge defect that lands at a position deviated from the planned position.
When a plurality of colors of water-based inks are used for recording on a recording medium, it is preferable to apply the water-based ink according to the present embodiment to at least the water-based ink to be ejected first. This is because the water content of the recording medium is increased by the first ejection of the water-based ink, and the drying of the aqueous ink in the nozzle of the ejection head that ejects the aqueous ink after the first ejected water-based ink is alleviated. ..

When recording is performed on both sides of the recording medium, the water-based ink is ejected onto the front surface (front surface) of the recording medium, and then the water-based ink is heated and dried, and then the water-based ink is further ejected onto the back surface of the recording medium. .. In this case, the water-based ink ejected onto the surface (front surface) of the recording medium is dried, so that the recording medium is in a dry state in which the water content is particularly reduced. Therefore, in the nozzle of the ejection head that ejects the water-based ink to the back surface of the recording medium, the evaporation of the water-based ink becomes remarkable, and uneven landing is likely to occur. However, when the water-based ink according to the present embodiment is applied as the water-based ink ejected to the back surface of the recording medium, the water-based ink ejected to the front surface (front surface) of the recording medium when recording on both sides of the recording medium By drying, it suppresses uneven landing of water-based ink ejected to the back surface of an excessively dried recording medium.
Even when a plurality of colors of water-based inks are used for recording on the back surface of the recording medium, it is preferable to apply the water-based inks according to the present embodiment to at least the water-based inks to be ejected first. This is because, as described above, the water content of the recording medium is increased by the first ejection of the water-based ink, and the drying of the aqueous ink in the nozzle of the ejection head that ejects the aqueous ink after the first ejected water-based ink is also alleviated. This is because it is done.

In the ink according to the present embodiment, the relationship between the number of coarse grains Nc1 at the time of concentration of the water-based ink and the initial number of coarse grains Ni1 preferably satisfies the formula: 1 ≦ Nc1 / Ni1 ≦ 30 from the viewpoint of suppressing uneven landing. , Formula: 1 ≦ Nc1 / Ni1 ≦ 10 is more preferable.
As a method for adjusting the number of coarse particles Nc1 when the water-based ink is concentrated, for example, 1) a method of setting the glass transition temperature Tg of the polymer particles to 40 ° C. or higher and 90 ° C. or lower (glass transition temperature Tg of the polymer particles). If it is increased, the number of coarse particles Nc1 at the time of concentration tends to decrease.) 2) A method of adjusting the acid value of the pigment dispersant to 70 mgKOH / g or more and 200 mgKOH / g or less (If the acid value of the pigment dispersant is decreased, the acid value of the pigment dispersant tends to decrease during concentration. Coarse grain number Nc1 tends to decrease) 3) Method of selecting the type of surfactant (For example, if a surfactant having a small HLB value is selected, the coarse grain number Nc1 tends to decrease during concentration) Can be mentioned. Then, Nc1 / Ni1 is adjusted by using these methods.

The initial coarse number Ni1 aqueous ink, from the point of suppressing the landing unevenness, preferably ^{10 10} / ml or less, more preferably 10 ⁹ / ml.
On the other hand, concentrated at coarse speed Nc1 of water-based ink, from the point of suppressing the landing unevenness, preferably ^{10 10} / ml or less, more preferably 10 ⁹ / ml.

Here, the method for reducing the mass of the water-based ink by 60% by evaporation of the solvent is as follows. The water-based ink of interest is contained in a glass container, and this container is placed on a hot plate. Then, the temperature of the hot plate is set to 40 ° C., and the solvent of the water-based ink in the container is evaporated until the solvent of the water-based ink is reduced by 60% with respect to the mass of the total water-based ink. That is, the solvent is evaporated until the mass of the water-based ink is 40% of the mass of the water-based ink before weight loss.
Then, for the number of various coarse particles of the water-based ink, the lower limit particle size is set to 0.5 μm using Accuser 780 APS (manufactured by PSS), the particles are counted, and the particle size per 1 ml of ink is 0.5 μm or more. Calculated by measuring the total number of particles.
The number of coarse grains at the time of concentration of the water-based ink is calculated by measuring the diluted ink obtained by adding pure water to the water-based ink after the weight loss until the mass of the water-based ink before the weight loss is reached, and converting the dilution ratio. ..

Hereinafter, the details of the water-based ink according to the present embodiment will be described.

The water-based ink according to the present embodiment contains a colorant, polymer particles, and a solvent containing water and an aqueous organic solvent.

(Colorant)
First, the colorant will be described.
As the colorant, one corresponding to the water-based ink having the desired hue may be used, and specific examples thereof include pigments. Examples of pigments include organic pigments and inorganic pigments.

Specific examples of the black pigment (black pigment) include Raven7000, Raven5750, Raven5250, Raven5000 ULTRAII, Raven 3500, Raven2000, Raven1500, Raven1250, Raven1200, Raven1250, Raven1200, Raven1190, Raven1190, Raven1190, Raven1190, Raven1190, Raven1190, Raven ) Regal400R, Regal330R, Regal660R, Mogul L, Black Pearls L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1300, Monarch 1300, Monarch 1300, Monarch 1300, Monarch 1300, FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex35, PrintMax U, PrintXV, PrintBlack, Print Special Black4 (all manufactured by Orion Engineered Carbons), No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, No. 2300, MCF-88, MA600, MA7, MA8, MA100 (all manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned, but the present invention is not limited thereto.

Specific examples of the cyan pigment include C.I. I. Pigment Blue-1, -2, -3, -15, -15: 1, -15: 2, -15: 3, -15: 4, -16, -22, -60 and the like. Not limited.
Specific examples of magenta color pigments include C.I. I. Pigment Red-5, -7, -12, -48, -48: 1, -57, -112, -122, -123, -146, -168, -177, -184, -202, C.I. I. Pigment Violet-19 and the like, but are not limited thereto.
Specific examples of the yellow pigment include C.I. I. Pigment Yellow-1, -2, -3, -12, -13, -14, -16, -17, -73, -74, -75, -83, -93, -95, -97, -98, Examples thereof include, but are not limited to, -114, -128, -129, -138, -151, -154, and -180.

Here, when a pigment is used as the colorant, it is preferable to use a pigment dispersant together. Examples of the pigment dispersant used include polymer dispersants, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and the like.

The acid value of the pigment dispersant is preferably 70 mgKOH / g or more and 200 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 200 mgKOH / g or less, from the viewpoint of reducing the number of coarse grains Nc1 during concentration and suppressing uneven landing. ..
The acid value is measured according to JIS K0070 and measured by a neutralization titration method. That is, an appropriate amount of the sample is separated, 100 ml of a solvent (diethyl ether / ethanol mixed solution) and a few drops of an indicator (phenolphthalein solution) are added, and the sample is shaken sufficiently on a water bath until the sample is completely dissolved. This is titrated with a 0.1 mol / l potassium hydroxide ethanol solution, and the end point is when the light red color of the indicator continues for 30 seconds. When the acid value is A, the sample amount is S (g), the 0.1 mol / l potassium hydroxide ethanol solution used for titration is B (ml), and f is the factor of the 0.1 mol / l potassium hydroxide ethanol solution. , A = (B × f × 5.611) / S.

As the polymer dispersant, a polymer having a hydrophilic structure portion and a hydrophobic structure portion is preferably used. As the polymer having a hydrophilic structure part and a hydrophobic structure part, for example, a condensation polymer and an addition polymer are used. Examples of the condensation polymer include known polyester dispersants. Examples of the addition polymer include a monomer addition polymer having an α, β-ethylenically unsaturated group. A high target is achieved by combining and copolymerizing a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group and a monomer having an α, β-ethylenically unsaturated group having a hydrophobic group. A molecular dispersant is obtained. Further, a homopolymer of a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group is also used.

Examples of the monomer having an α, β-ethylenic unsaturated group having a hydrophilic group include a monomer having a carboxyl group, a sulfonic acid group, a hydroxyl group, a phosphoric acid group and the like, for example, acrylic acid, methacrylic acid and croton. Acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, metharoxyethyl phosphate, bis Examples thereof include methacryloxyethyl phosphate, methacrylooxyethylphenyl acid phosphate, ethylene glycol dimethacrylate, and diethylene glycol dimethacrylate.

Examples of the monomer having an α, β-ethylenic unsaturated group having a hydrophobic group include styrene derivatives such as styrene, α-methylstyrene and vinyltoluene, vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives and acrylic acid alkyl esters. , Methacrylate alkyl ester, methacrylate phenyl ester, methacrylate cycloalkyl ester, crotonic acid alkyl ester, itaconic acid dialkyl ester, maleic acid dialkyl ester and the like.

Examples of preferable copolymers as polymer dispersants include styrene-styrene sulfonic acid copolymers, styrene-maleic acid copolymers, styrene-methacrylic acid copolymers, styrene-acrylic acid copolymers, and vinylnaphthalene-. Maleic acid copolymer, vinylnaphthalene-methacrylic acid copolymer, vinylnaphthalene-acrylic acid copolymer, acrylic acid alkyl ester-acrylic acid copolymer, methacrylate alkyl ester-methacrylic acid copolymer, styrene-methacrylic acid Alkyl ester-methacrylic acid copolymer, styrene-acrylic acid alkyl ester-acrylic acid copolymer, styrene-methacrylic acid phenyl ester-methacrylic acid copolymer, styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, or these. Salt and the like. Further, these polymers may be copolymerized with a monomer having a polyoxyethylene group and a hydroxyl group.

The weight average molecular weight of the polymer dispersant is, for example, 2,000 or more and 50,000 or less.

These polymer dispersants may be used alone or in combination of two or more. The content of the polymer dispersant varies greatly depending on the pigment and cannot be unequivocally determined, but it is preferably 0.1% by mass or more and 100% by mass or less with respect to the pigment.

Examples of the pigment include a pigment that self-disperses in water (hereinafter referred to as a self-dispersing pigment).
The self-dispersing pigment refers to a pigment having a solubilizing group for water on the surface of the pigment and dispersing in water even in the absence of a polymer dispersant. The self-dispersing pigment can be obtained, for example, by subjecting the pigment to surface modification treatments such as acid / base treatment, coupling agent treatment, polymer graft treatment, plasma treatment, and oxidation / reduction treatment.

As the self-dispersing pigment, in addition to the pigment obtained by subjecting the above pigment to a surface modification treatment, Cab-o-jet-200, Cab-o-jet-300, and Cab-o-jet-400 manufactured by Cabot Co., Ltd. , IJX-157, IJX-253, IJX-266, IJX-273, IJX-444, IJX-55, Cab-o-jet-250C, Cab-o-jet-260M, Cab-o-jet-270Y, Cab Commercially available self such as -o-jet-450C, Cab-o-jet-465M, Cab-o-jet-470Y, Cab-o-jet-480M, Microjet Black CW-1, CW-2 manufactured by Orient Chemical Co., Ltd. Dispersed pigments and the like can also be mentioned.

The self-dispersing pigment is preferably a pigment having at least a sulfonic acid, a sulfonate, a carboxylic acid, or a carboxylic acid salt as a functional group on the surface thereof. More preferably, it is a pigment having at least a carboxylic acid or a carboxylic acid salt as a functional group on the surface.

Here, examples of the pigment include pigments coated with a resin. This is called a microcapsule pigment, and there are commercially available microcapsule pigments manufactured by DIC Corporation, Toyo Ink Corporation, and the like. The microcapsule pigment is not limited to the commercially available microcapsule pigment, and a microcapsule pigment produced according to the purpose may be used.
Further, examples of the pigment include a resin-dispersed pigment in which a polymer compound is physically adsorbed or chemically bonded to the pigment.
In addition, as pigments, in addition to the three primary color pigments of black, cyan, magenta, and yellow, specific color pigments such as red, green, blue, brown, and white, metallic glossy pigments such as gold and silver, and colorless or light-colored constitutions. Pigments, plastic pigments and the like can also be mentioned.
Further, examples of the pigment include particles in which silica, alumina, or a polymer bead is used as a core and a dye or pigment is fixed on the surface thereof, an insoluble rake of the dye, a colored emulsion, a colored latex, and the like.

Coloring agents include, in addition to pigments, hydrophilic anionic dyes, direct dyes, cationic dyes, reactive dyes, polymer dyes and other dyes such as oil-soluble dyes, wax powders colored with dyes, resin powders, etc. Alternatively, emulsions, fluorescent dyes, fluorescent pigments and the like can also be mentioned.

The volume average particle size of the colorant is, for example, 10 nm or more and 1000 nm or less.
The volume average particle size of the colorant means the particle size of the colorant itself, or, when an additive such as a dispersant is attached to the colorant, the particle size to which the additive is attached.
The volume average particle size is measured by the Microtrac UPA particle size analyzer UPA-UT151 (manufactured by Microtrac). The measurement is performed by putting a 1000-fold diluted water-based ink into a measurement cell. As the input value at the time of measurement, the viscosity of the aqueous ink diluent is used for the viscosity, and the refractive index of the colorant is used for the particle refractive index.

The content (concentration) of the colorant is, for example, preferably 1% by mass or more and 25% by mass or less, and more preferably 2% by mass or more and 20% by mass or less with respect to the water-based ink.

(Polymer particles)
The polymer particles will be described.
The polymer particles are components that enhance the fixability of an image with a water-based ink on a recording medium.
The polymer particles are obtained by granulating a polymer compound and are different components from the above-mentioned polymer dispersant.

Examples of the polymer particles include styrene-acrylic acid copolymer, styrene-acrylic acid-sodium acrylate copolymer, styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, and acrylic acid ester copolymer. , Polyurethane, polyester, silicon-acrylic acid copolymer, acrylic-modified fluororesin and other particles (latex particles).
Examples of the polymer particles include core-shell type polymer particles having different compositions at the central portion and the outer edge portion of the particles.

The polymer particles may be dispersed in the water-based ink using an emulsifier, or may be dispersed in the water-based ink without using an emulsifier.
Examples of the emulsifier include a polymer having a hydrophilic group such as a surfactant, a sulfonic acid group, and a carboxyl group (for example, a polymer having a hydrophilic group graft-bonded, a monomer having hydrophilicity, and a hydrophobic portion. Polymers obtained from monomers).

The volume average particle size of the polymer particles is preferably 10 nm or more and 300 nm or less, more preferably 10 nm or more and 200 nm or less, from the viewpoint of image glossiness and scratch resistance.
The volume average particle size of the polymer particles is measured by the Microtrac UPA particle size analyzer UPA-UT151 (manufactured by Microtrac). The measurement is performed by putting a 1000-fold diluted water-based ink into a measurement cell. As the input value at the time of measurement, the viscosity of the aqueous ink diluent is used for the viscosity, and the refractive index of the polymer particles is used for the particle refractive index.

The glass transition temperature of the polymer particles is preferably 40 ° C. or higher and 90 ° C. or lower, and more preferably 70 ° C. or higher and 90 ° C. or lower, from the viewpoint of reducing the number of coarse particles Nc1 during concentration and suppressing uneven landing. On the other hand, the glass transition temperature of the polymer particles is preferably −20 ° C. or higher and 80 ° C. or lower, more preferably −10 ° C. or higher and 60 ° C. or lower, from the viewpoint of scratch resistance of the image.
The glass transition temperature of polymer particles can be determined from the DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, the method for determining the glass transition temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics". It is determined by the described "external glass transition start temperature".

The content of the polymer particles is preferably 0.1% by mass or more and 10% by mass or less, preferably 0.5% by mass, based on the water-based ink, from the viewpoint of enhancing the fixability of the image, ejection stability, and film forming property. More preferably 5% by mass or less.

(water)
Explain water.
Preferable examples of water include ion-exchanged water, ultrapure water, distilled water, and ultrafiltered water from the viewpoint of preventing contamination of impurities or generation of microorganisms.

The water content is, for example, preferably 10% by mass or more and 95% by mass or less, and more preferably 30% by mass or more and 90% by mass or less with respect to the water-based ink.

(Aqueous organic solvent)
The aqueous organic solvent will be described.
Examples of the aqueous organic solvent include polyhydric alcohols, polyhydric alcohol derivatives, nitrogen-containing solvents, alcohols, sulfur-containing solvents and the like. Other examples of the aqueous organic solvent include propylene carbonate and ethylene carbonate.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol, glycerin and the like. ..

Polyhydric alcohol derivatives include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and diglycerin. Examples thereof include ethylene oxide adducts.

Examples of the nitrogen-containing solvent include pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, triethanolamine and the like.
Examples of the alcohol include ethanol, isopropyl alcohol, butyl alcohol, benzyl alcohol and the like.
Examples of the sulfur-containing solvent include thiodiethanol, thiodiglycerol, sulfolane, dimethyl sulfoxide and the like.

The aqueous organic solvent may be used alone or in combination of two or more.

The content of the aqueous organic solvent is preferably 1% by mass or more and 60% by mass or less, and more preferably 1% by mass or more and 40% by mass or less with respect to water.

(Surfactant)
The surfactant will be described.
The water-based ink preferably contains, for example, a surfactant having an HLB (hydrophilic group / hydrophobic group balance "Hydrofil-Lipophile Barance") of 14 or less as a surfactant. By adjusting the amount of the surfactant having an HLB of 14 or less, or by using a plurality of types of surfactants having different HLBs, it becomes easy to adjust the surface tension of the water-based ink.

The HLB (hydrophilic / hydrophobic group balance “Hydrophile-Lipophile Balance”) is defined by the following formula (Griffin method).
・ HLB = 20 × (sum of formulas of hydrophilic part / molecular weight)

Examples of such a surfactant include at least one selected from the group consisting of an ethylene oxide adduct of acetylene glycol and a polyether-modified silicone.

The ethylene oxide adduct of acetylene glycol is, for example, an −O- (CH ₂ CH ₂ O) _n− H structure in which ethylene oxide is added to at least one hydroxyl group of acetylene glycol (for example, n is 1 or more and 30 or less. A compound with (indicating an integer),
Examples of commercially available acetylene glycol ethylene oxide adducts (numbers in parentheses indicate HLB catalog values) include Orphine E1004 (7-9), Orphine E1010 (13-14), and Orphine EXP. 4001 (8-11), Orfin EXP. 4123 (11-14), Orfin EXP. Examples thereof include 4300 (10 to 13), surfinol 104H (4), surfinol 420 (4), surfinol 440 (4), dinol 604 (8) [above, Nissin Chemical Industry Co., Ltd.].

The polyether-modified silicone is, for example, a compound in which a polyether group is bonded in a graft shape to a silicone chain (polysiloxane main chain), or a compound in which a polyether group is bonded in a block shape. Examples of the polyether group include a polyoxyethylene group and a polyoxypropylene group. The polyether group may be, for example, a polyoxyalkylene group in which an oxyethylene group and an oxypropylene group are added in a block shape or at random.
Commercially available products of polyether-modified silicone (the values in parentheses indicate the HLB catalog values) include Silface SAG002 (12), Silface SAG503A (11), and Silface SAG005 (7) [above, Nisshin. Chemical Industry Co., Ltd.] and the like.

As the water-based ink, other surfactants other than the ethylene oxide adduct of acetylene glycol and the polyether-modified silicone may be used.
Examples of other surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants and the like, preferably anionic surfactants and nonionic surfactants. is there.

Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenyl sulfonates, alkylnaphthalene sulfonates, higher fatty acid salts, higher fatty acid ester sulfates, higher fatty acid ester sulfonates, and higher alcohol ether sulfates. Examples thereof include ester salts and sulfonates, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates and the like.
Among these, as anionic surfactants, dodecylbenzene sulfonate, isopropylnaphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, monobutylbiphenylsulfonate, dibutylphenylphenol Disulfonate or the like is preferable.

Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, and poly. Examples thereof include oxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, alkyl alkanolamide, polyethylene glycol polypropylene glycol block copolymer, and acetylene glycol.
Among these, examples of the nonionic surfactant include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, and poly. Oxyethylene sorbitan fatty acid ester, fatty acid alcoholylamide, polyethylene glycol polypropylene glycol block copolymer, and acetylene glycol are preferable.

Other nonionic surfactants include silicone-based surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylic acid salts, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Agents; biosurfactants such as spicrysporic acid, ramnolipide, lysolecithin; and the like.

The hydrophilic / hydrophobic balance (HLB) of other surfactants is preferably in the range of 3 or more and 20 or less in consideration of solubility and the like.

The surfactant may be used alone or in combination of two or more.

The total content of the surfactant is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and 0.2% by mass or more and 3% by mass with respect to the water-based ink. More preferably, it is by mass or less.

(Other additives)
Other additives will be described.
The water-based ink may contain other additives.
Other additives include ink ejection improvers (polyethylene imine, polyamines, polyvinylpyrrolidone, polyethylene glycol, ethyl cellulose, carboxymethyl cellulose, etc.) and conductivity / pH regulators (potassium hydroxide, sodium hydroxide, lithium hydroxide). Alkali metal compounds such as), reactive diluting solvent, penetrant, pH buffer, antioxidant, antifungal agent, viscosity regulator, conductive agent, chelating agent, ultraviolet absorber, infrared absorber, etc. Can be mentioned.

(Physical characteristics of water-based ink)
Suitable physical properties of the water-based ink will be described.
The pH of the water-based ink is preferably in the range of 4 or more and 10 or less, and more preferably in the range of 5 or more and 9 or less.
Here, the pH of the water-based ink is 23 ± 0.5 ° C. for temperature and 55 ± 5% R. for humidity. H. In an environment, the value measured by a pH / conductivity meter (MPC227 manufactured by METTLER TOLEDO) is adopted.

The conductivity of the water-based ink is, for example, in the range of 0.01 S / m or more and 0.5 S / m or less (preferably in the range of 0.01 S / m or more and 0.25 S / m or less, more preferably 0.01 S / m or more and 0). .20 S / m or less range).
The conductivity is measured by MPC227 (pH / Conductivity Meter, manufactured by METTLER TOLEDO).

(Use)
Here, the water-based ink according to the present embodiment may be, for example, any of black ink, cyan ink, magenta ink, yellow ink, and intermediate color ink other than these colors.
Further, the water-based ink according to the present embodiment may be used as an ink set containing at least one such water-based ink (preferably all of the water-based ink according to the present embodiment).

[Recording device / Recording method]
Hereinafter, the recording device and the recording method according to the present embodiment will be described.

(First Embodiment)
The recording device according to the first embodiment is a recording device having a discharge head that stores water-based ink and discharges the water-based ink onto the surface of a recording medium. In the recording apparatus according to the first embodiment, a recording method having a ejection step of ejecting water-based ink onto the surface of a recording medium by an ejection head (recording method according to the first embodiment) is realized. Then, as the water-based ink, the water-based ink according to the present embodiment is applied.
In the recording device (recording method) according to the first embodiment, as described above, by applying the water-based ink according to the present embodiment as the water-based ink, uneven landing occurs when recording on a dry recording medium. Is suppressed.

In the recording device according to the first embodiment, the ejection head accommodates the first aqueous ink as the aqueous ink according to the present embodiment, and first ejects the first aqueous ink onto the surface of the recording medium. Even in a form having a second ejection head that accommodates the second aqueous ink and ejects the second aqueous ink to the surface of the recording medium after the ejection of the first aqueous ink by the first ejection head. Good. That is, the recording device may have a plurality of ejection heads for ejecting each of the water-based inks of a plurality of colors.
On the other hand, in the recording method according to the first embodiment, the ejection step first ejects the first aqueous ink as the aqueous ink according to the present embodiment to the surface of the recording medium by the first ejection head as the ejection head. This is a ejection step, and may further include a second ejection step of ejecting the second aqueous ink to the surface of the recording medium by the second ejection head after the ejection of the first aqueous ink by the first ejection head. .. That is, the recording method may include a ejection step of ejecting each of the water-based inks of a plurality of colors.

Then, in the case of these forms, the water-based ink according to the present embodiment is applied as the first water-based ink to be first ejected to the surface of the recording medium.
In the case of these forms, in particular, the moisture absorption of the dried recording medium dries the periphery of the first ejection head that first ejects the first aqueous ink onto the surface of the recording medium, and the first aqueous solution in the nozzle of the first ejection head is dried. The ink dries significantly, and uneven landing is likely to occur. However, by applying the water-based ink according to the present embodiment as the first water-based ink to be first ejected to the surface of the recording medium, the occurrence of uneven landing can be suppressed.
On the other hand, as the second water-based ink to be ejected to the surface of the recording medium after the first water-based ink, a water-based ink other than the water-based ink according to the present embodiment may be applied. This is because, as described above, the first ejection of the first water-based ink increases the water content of the recording medium, and the drying of the second aqueous ink in the nozzle of the second ejection head is alleviated. However, the water-based ink according to the present embodiment may be applied to the second water-based ink in terms of suppressing the occurrence of uneven landing.

As the second ejection head for ejecting the second water-based ink to the surface of the recording medium, a plurality of ejection heads for ejecting each of the water-based inks of a plurality of colors may be provided. Then, as the second water-based ink, the water-based ink according to the present embodiment may be applied.

In the recording apparatus and recording method according to the first embodiment, the number of coarse grains of the second water-based ink at the time of concentration Ncn (the number of coarse grains of the second water-based ink after weight loss by reducing the mass by 60% by evaporation of the solvent) and the initial stage. The ratio (Ncn / Nin) to the number of coarse grains Nin (the number of coarse grains before weight loss Nin) is larger than the ratio (Nc1 / Ni1) of the number of coarse grains Nc1 at the time of concentration of the first aqueous ink to the initial number of coarse grains Ni1. It should be big. For example, the ratio (Ncn / Nin) may be 3 or more and 50 or less, and the ratio (Nc1 / Ni1) may be 1 or more and less than 10. As a result, when recording on a dry recording medium, it is possible to secure the fixability of the image by the second water-based ink while suppressing the occurrence of uneven landing. This is because, as described above, the drying of the second water-based ink in the nozzle of the second ejection head is alleviated, and therefore, in order to improve the fixability of the image, even if the ratio (Ncn / Nin) is increased, the impact unevenness is achieved. This is because the occurrence of

The recording device and recording method according to the first embodiment may be in the form of recording only on one side of the recording medium, or recording on both sides of the recording medium by a mechanism for reversing the recording medium after recording on one side. It may be in the form.

(Second Embodiment)
The recording apparatus according to the second embodiment has a first ejection head that accommodates the first water-based ink and ejects the first aqueous ink onto the surface of the recording medium, and a first ejection head that ejects the first aqueous ink onto the surface of the recording medium. 1 A drying device for drying the water-based ink and the water-based ink according to the present embodiment as the second water-based ink are stored, and after the first water-based ink is dried by the drying device, the second water-based ink is ejected to the back surface of the recording medium. It has a second discharge head.
In the recording apparatus according to the second embodiment, the first ejection step of ejecting the first water-based ink to the surface of the recording medium by the first ejection head and the first aqueous ink ejected to the surface of the recording medium by the first ejection step. A recording method having a drying step of drying the ink and a second ejection step of ejecting the second aqueous ink to the back surface of the recording medium by the second ejection head after the first aqueous ink is dried by the drying apparatus (second embodiment). (Recording method according to) is realized.
That is, the recording device and the recording method according to the second embodiment are in the form of recording on both sides of the recording medium by the ejection heads for each surface. Then, as the second water-based ink, the water-based ink according to the present embodiment is applied. As the first water-based ink, the water-based ink according to the present embodiment may be applied.

In the recording apparatus and recording method according to the second embodiment, after the first water-based ink is dried, the second water-based ink is ejected to the back surface of the recording medium. Therefore, the recording medium has a particularly high water content due to the drying of the first water-based ink. In the reduced dry state, the evaporation of the second water-based ink becomes remarkable in the nozzle of the second ejection head, and uneven landing is likely to occur. However, when the water-based ink according to the present embodiment is applied as the second water-based ink to be ejected to the back surface of the recording medium, the recording medium is excessively dried due to the drying of the first water-based ink when recording on both sides of the recording medium. Suppresses uneven landing of the second water-based ink discharged on the back surface of the ink.

In the recording device according to the second embodiment, the second ejection head stores the third water-based ink as the second water-based ink (the water-based ink according to the present embodiment), and the third water-based ink is first placed on the back surface of the recording medium. A third ejection head that ejects the fourth water-based ink to the back surface of the recording medium, and ejects the fourth aqueous ink to the back surface of the recording medium after the third aqueous ink is ejected by the third ejection head. Further, it may have a form. That is, the recording device may have a plurality of ejection heads for ejecting each of the water-based inks of a plurality of colors.
On the other hand, in the recording method according to the second embodiment, in the second ejection step, the third aqueous ink is recorded as the second aqueous ink (the aqueous ink according to the present embodiment) by the third ejection head as the second ejection head. This is the third ejection step of first ejecting to the back surface of the medium, and the fourth aqueous ink is ejected to the back surface of the recording medium by the fourth ejection head after the ejection of the third aqueous ink by the third ejection head. 4 The form may further include a discharge step. That is, the recording method may include a plurality of ejection steps for ejecting each of the water-based inks of a plurality of colors.

Then, in the case of these forms, the water-based ink according to the present embodiment is applied as the third water-based ink to be first ejected to the back surface of the recording medium.
In the case of these forms, in particular, due to the drying of the third water-based ink, the moisture absorption of the excessively dried recording medium dries the periphery of the third ejection head that first ejects the third water-based ink to the back surface of the recording medium. 3 The dryness of the third water-based ink in the nozzle of the ejection head becomes remarkable, and uneven landing is likely to occur. However, by applying the water-based ink according to the present embodiment as the third water-based ink to be first ejected to the back surface of the recording medium, the occurrence of uneven landing can be suppressed.
On the other hand, as the fourth water-based ink to be ejected to the back surface of the recording medium after the third water-based ink, a water-based ink other than the water-based ink according to the present embodiment may be applied. This is because, as described above, the first ejection of the third water-based ink increases the water content of the recording medium, and the drying of the fourth aqueous ink in the nozzle of the fourth ejection head is alleviated. However, the water-based ink according to the present embodiment may be applied to the fourth water-based ink in order to suppress the occurrence of uneven landing.

The fourth ejection head that ejects the fourth water-based ink to the back surface of the recording medium may also have a plurality of ejection heads that eject each of the water-based inks of a plurality of colors. Then, as the fourth water-based ink, the water-based ink according to the present embodiment may be applied.

In the recording apparatus and recording method according to the second embodiment, the number of coarse grains at the time of concentration of the fourth water-based ink Ncn (the number of coarse grains of the fourth water-based ink after weight loss by reducing the mass by 60% by evaporation of the solvent) and the initial stage. The ratio (Ncn / Nin) to the number of coarse grains Nin (the number of coarse grains before weight loss Nin) is larger than the ratio (Nc1 / Ni1) of the number of coarse grains Nc1 at the time of concentration of the third aqueous ink to the initial number of coarse grains Ni1. It should be big. For example, the ratio (Ncn / Nin) may be 3 or more and 50 or less, and the ratio (Nc1 / Ni1) may be 1 or more and less than 10. As a result, when recording on a dry recording medium, it is possible to secure the fixability of the image by the fourth water-based ink while suppressing the occurrence of uneven landing. This is because, as described above, the drying of the fourth water-based ink in the nozzle of the fourth ejection head is alleviated, and therefore, in order to improve the fixability of the image, even if the ratio (Ncn / Nin) is increased, the impact unevenness This is because the occurrence of

Hereinafter, an example of the recording device according to the present embodiment will be described with reference to the drawings. In the following description, ejecting water-based ink (to a target region) to a recording medium may be referred to as "image formation" or "image formation", and the water-based ink to a recording medium. It is sometimes referred to as "recording", "image recording", or "recording an image" that the ink is discharged, dried, and fixed.

FIG. 1 is a schematic configuration diagram showing a recording device according to the present embodiment.
The recording device 100 according to the present embodiment is composed of an image recording unit 10 that records an image on the recording medium P, a preprocessing unit 20 that houses the recording medium P supplied to the image recording unit 10, and the preprocessing unit 20. A buffer unit 30 for adjusting the amount of transport of the recording medium P supplied to the image recording unit 10 is provided. The buffer unit 30 is arranged between the image recording unit 10 and the preprocessing unit 20.

Further, the recording device 100 adjusts the post-processing unit 40 accommodating the recording medium P discharged from the image recording unit 10 and the amount of the recording medium P discharged from the image recording unit 10 to the post-processing unit 40. It includes a buffer unit 50 and. The buffer unit 50 is arranged between the image recording unit 10 and the post-processing unit 40.

Further, the recording device 100 includes a cooling unit 60 which is arranged between the image recording unit 10 and the buffer unit 50 and cools the recording medium P carried out from the image recording unit 10.

The image recording unit 10 includes, for example, a roll member (reference numeral omitted) that guides the recording medium P along the transport path R of the recording medium P, and the surface of the recording medium P that is conveyed along the transport path R of the recording medium P. The ejection head (first ejection head) 12A for ejecting water-based ink (droplets of water-based ink) and the ejection head 12A form the first image on the surface of the recording medium P, and the ejection head 12B performs the first image formation. A second image formation is performed on the back surface of the recording medium P after the image formation.

In the ejection heads 12A and 12B, for example, the effective recording area (the area where the nozzles for ejecting water-based ink) is equal to or larger than the width of the recording medium P (the length in the direction intersecting (for example, orthogonal to) the conveying direction of the recording medium P). It is a long recording head.
The ejection heads 12A and 12B are not limited to this, and are ejection heads that are shorter than the width of the recording medium P and move in the width direction of the recording medium P to eject water-based ink (so-called carriage method). ) May be the discharge head.

The ejection heads 12A and 12B may be a so-called thermal method in which droplets of water-based ink are ejected by heat, or may be a so-called piezoelectric method in which droplets of water-based ink are ejected by pressure. Things apply.

The ejection heads 12A and 12B include, for example, the ejection heads 12KA and 12KB that eject water-based ink onto the recording medium P to form a K (black) color image, and the ejection heads 12YA and 12YA that form a Y (yellow) color image. It has 12YB, discharge heads 12MA and 12MB for forming an M (magenta) color image, and discharge heads 12CA and 12CB for forming a C (cyan) color image, respectively. Then, the ejection heads 12KA and 12KB, the ejection heads 12YA and 12YB, the ejection heads 12MA and 12MB, and the ejection heads 12CA and 12CB are in this order in the conveying direction of the recording medium P (hereinafter, simply referred to as "paper conveying direction"). (May be described), they are arranged from the upstream side to the downstream side so as to face the recording medium P. When K, Y, M, and C are not distinguished in the notation of the discharge head, K, Y, M, and C attached to the reference numerals are omitted.

The ejection heads 12KA, 12YA, 12MA, 12CA, 12KB, 12YB, 12MB, and 12CB are connected to and from the recording device 100 through ink cartridges (not shown) and supply pipes (not shown) of each color, respectively. Ink of each color is supplied from the cartridge to each ejection head 12KA, 12YA, 12MA, 12CA, 12KB, 12YB, 12MB, 12CB.

The discharge heads 12A and 12B are not limited to the form in which the four discharge heads corresponding to each of the above four colors are arranged, and four or more discharge heads 12A and 12B corresponding to each of the four or more colors including other intermediate colors are added according to the purpose. The discharge head may be arranged.

Here, the ejection heads 12A and 12B include, for example, a low-resolution ejection head (for example, a 600 dpi ejection head) that ejects water-based ink in the range of ink droplet amount lpl or more and 15 pl or less, and an ink droplet amount of less than 10 pl. It may be any of high-resolution ejection heads (for example, 1200 dpi ejection heads) that eject water-based ink. Further, as the discharge heads 12A and 12B, both a discharge head for low resolution and a discharge head for high resolution may be provided.
The amount of ink droplets from the ejection heads 12A and 12B is in the range of the maximum amount of water-based ink droplets. In addition, dpi means "dot per inch".

Here, the discharge head 12A corresponds to an example of the discharge head of the recording device and the recording method according to the first embodiment, or an example of the first discharge head of the recording device and the recording method according to the second embodiment. The discharge head 12AK corresponds to an example of the first discharge head of the recording device and recording method according to the first embodiment. The discharge heads 12YA, 12MA, and 12CA correspond to an example of the second discharge head of the recording device and recording method according to the first embodiment.
On the other hand, the discharge head 12B corresponds to an example of the second discharge head of the recording device and recording method according to the second embodiment. The discharge head 12BK corresponds to an example of the third discharge head of the recording device and recording method according to the second embodiment. The discharge heads 12YB, 12MB, and 12CB correspond to an example of the fourth discharge head of the recording device and recording method according to the second embodiment.

For example, the back surface of the recording medium P is wound around the image recording unit 10 on the downstream side in the paper transport direction with respect to the ejection head 12A, and the image of the front surface of the recording medium is imaged while being driven to rotate in contact with the recording medium P. A drying drum 14A (an example of a drying device) for drying (ink) is arranged.
Similarly, the image recording unit 10 is wound with, for example, the surface of the recording medium P on the downstream side in the paper transport direction with respect to the ejection head 12B, and records while contacting the recording medium P and rotating in a driven manner. A drying drum 14B (an example of a drying device) for drying an image (ink) on the back surface of the medium is arranged.
A transport roller 18 that comes into contact with the surface of the recording medium P is arranged on the downstream side of the drying drum 14A in the paper transport direction and on the upstream side of the discharge head 12B in the paper transport direction.

A heating source (for example, a halogen heater or the like: not shown) is built in the drying drums 14A and 14B. The drying drum 14A dries the image (ink) of the front surface of the recording medium P by heating with a heating source, and the drying drum 14B dries the image (ink) of the back surface of the recording medium P by heating with a heating source.

Around the drying drums 14A and 14B, warm air blowers 16A and 16B (an example of the drying device) for drying the image (ink) on the recording medium P are arranged, respectively. The image (ink) of the surface of the recording medium P wound around the drying drum 14A by the warm air from the warm air blower 16A is wound around the drying drum 14B by the warm air from the warm air blower 16B. The image (ink) on the back surface of the recording medium P is dried.

When a drying device that performs heat drying as described above is used, the drying conditions are preferably as follows.
That is, for example, the temperature of the heating source of the drying drum and the temperature of the warm air of the hot air blower are 40 ° C. or higher and 120 ° C. or lower from the viewpoint of accelerating the drying of the water-based ink and suppressing the deformation of the recording medium P. The range is preferably in the range of 60 ° C. or higher and 100 ° C. or lower.
The drying temperature conditions may be the same for the drying drum 14A and the drying drum 14B, and may be the same for the hot air blower 16A and the warm air blower 16B, or may be different.

Here, the drying device in the image recording unit 10 has the same configuration for the front surface of the recording medium P (drying drum 14A, warm air blower 16A) and for the back surface of the recording medium P (drying drum 14B, warm air blower 16B). However, the configuration is not limited to this, and different configurations may be used.

The image recording unit 10 has a near-infrared heater (not shown) and a laser on the downstream side of the ejection heads 12A and 12B in the paper transport direction to dry the image (ink) on the base layer of the recording medium P. Other drying devices such as an irradiation device may be arranged. Other drying devices such as near-infrared heaters and laser irradiators may be arranged in place of at least one of the drying drums 14A and 14B and the hot air blower 16A and 16B, or the drying drums 14A and 14B and the temperature. It may be arranged in addition to the air blowers 16A and 16B.

The preprocessing unit 20 includes a supply roll 20A around which a recording medium P supplied to the image recording unit 10 is wound, and the supply roll 20A is rotatably supported by a frame member (not shown).

In the buffer unit 30, for example, the first pass roller 30A, the dancer roller 30B, and the second pass roller 30C are arranged along the paper transport direction. The dancer roller 30B adjusts the tension of the recording medium P conveyed to the image recording unit 10 and the amount of the recording medium P conveyed by moving up and down in FIG.

The post-processing unit 40 includes a winding roll 40A as an example of a conveying unit that winds the recording medium P on which an image is recorded. The take-up roll 40A rotates by receiving a rotational force from a motor (not shown), so that the recording medium P is conveyed along the transfer path R.

In the buffer unit 50, for example, the first pass roller 50A, the dancer roller 50B, and the second pass roller 50C are arranged along the paper transport direction. The dancer roller 50B adjusts the tension of the recording medium P discharged to the post-processing unit 40 and the amount of the recording medium P conveyed by moving up and down in FIG.

A plurality of cooling rollers 60A are arranged in the cooling unit 60. The recording medium P is cooled by transporting the recording medium P between the plurality of cooling rollers 60A.

Here, the recording speed in the recording device 100, that is, the transport speed of the recording medium is not particularly limited, but is as high as 10 m / min or more because the drying device for drying the water-based ink ejected to the recording medium is provided. It may be.

Next, the operation (recording method) by the recording device 100 will be described.
In the recording device 100 according to the present embodiment, first, the recording medium P is conveyed from the supply roll 20A of the preprocessing unit 20 to the image recording unit 10 through the buffer unit 50.
Next, in the image recording unit 10, water-based ink is ejected from each ejection head 12A to the surface of the recording medium P. Then, the image (ink) on the front surface of the recording medium P is dried by the drying drum 14A from the back surface side of the recording medium P (the surface opposite to the ink ejection surface from the ejection head 12A). Then, the warm air blower 16A dries the ink (image) ejected on the surface of the recording medium P from the surface side of the recording medium P (the ink ejection surface side from the ejection head 12A). That is, the drying drum 14A and the warm air blower 16A dry the water-based ink discharged on the surface of the recording medium P.
Then, the image recorded on the surface of the recording medium P comes into contact with the transport roller 18 to eliminate static electricity from the recording medium P through the image.
Subsequently, in the image recording unit 10, water-based ink is ejected from each ejection head 12B to the back surface of the recording medium P. Then, the image (ink) on the back surface of the recording medium P is dried by the drying drum 14B from the front surface side of the recording medium P (the surface opposite to the ink ejection surface from the ejection head 12B). Then, the warm air blower 16B dries the ink (image) ejected to the back surface of the recording medium P from the back surface side (ink ejection surface side from the ejection head 12B) of the recording medium P. That is, the drying drum 14B and the warm air blower 16B dry the water-based ink discharged on the back surface of the recording medium P.
Next, in the cooling unit 60, the recording medium P on which the image is recorded is cooled by the cooling roller 60A.
Next, through the buffer unit 50, the post-processing unit 40 winds up the recording medium P on which the image is recorded on the surface by the winding roll 40A.

Through the above steps, an image with water-based ink is recorded on both sides of the recording medium P.
The recording medium P including the image recorded as described above is cut to a target size through a cutting step.

The recording device 100 has described a configuration including an ejection head 12A for ejecting water-based ink on the front surface of the recording medium P and an ejection head 12B for ejecting water-based ink on the back surface of the recording medium P, respectively. I can't. For example, the recording device 100 does not include the ejection head 12B, and after ejecting water-based ink onto the surface of the sheet of paper as the recording medium P of the leaf paper by the ejection head 12A, the recording medium P is inverted by a mechanism for inverting the recording medium P. Again, the ejection head 12A may be configured to eject the water-based ink onto the back surface of the recording medium P.

In the recording device 100, a method of directly ejecting water-based ink droplets onto the surface of the recording medium P by the ejection heads 12A and 12B has been described, but the present invention is not limited to this, and for example, the water-based ink droplets are ejected onto the intermediate transfer body. Later, a method may be used in which droplets of the water-based ink on the intermediate transfer body are transferred to the recording medium P.
Further, the recording device 100 includes a recording device (drying drum 14A, warm air blower 16A) for the front surface of the discharge head 14A and the recording medium P, and a recording device (drying drum 14A) for the back surface of the discharge head 14B and the recording medium P. 14B, warm air blower 16B) were all in the same image recording unit 10, but the configuration is not limited to this. For example, the recording device 100 has two image recording units, one of which is provided with a discharge head 14A and a recording device (drying drum 14A, warm air blower 16A) for the surface of the recording medium P, and the other is a discharge head. A recording device (drying drum 14B, warm air blower 16B) for the back surface of the recording medium P and 14B may be provided.

Further, in the recording device 100, a method of ejecting water-based ink onto a roll-shaped recording medium P (so-called continuous paper) and recording an image after drying has been described. For example, the recording device 100 is water-based on a sheet of paper of a target size. A method of ejecting ink, drying the ink, and recording an image may be used.

It goes without saying that the above-described embodiment is not limited to that embodiment and is realized within a range that satisfies the requirements of the present invention.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Preparation of black ink K>
(Black ink K1)
・ Carbon black: 5% by mass
-Acrylic dispersion resin: 2.5% by mass (pigment dispersant: acid value = 150 mgKOH)
-Acrylic emulsion (polymer particles, W-4627: manufactured by Toyochem, particle diameter 120 nm, glass transition temperature 40 ° C.): 2% by mass (solid content)
・ Glycerin: 10% by mass
・ Diethylene glycol: 10% by mass
-Surfactant (Orfin E1010, manufactured by Nissin Chemical Industry Co., Ltd.): 0.5% by mass
-Surfactant (Surfinol 104PG-50, manufactured by Nissin Chemical Industry Co., Ltd.): 0.5% by mass
Made): 1% by mass
-Ion-exchanged water: balance After mixing the above composition, filtration was performed with a 5 μm filter to obtain black ink K1.

(Black ink K2)
Black ink K2 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 100 mgKOH.

(Black ink K3)
Black ink K3 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 50 mgKOH.

(Black ink K4)
Black ink K4 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 10 mgKOH.

(Black ink K5)
Black ink K5 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 70 mgKOH.

(Black ink K6)
Black ink K6 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 80 mgKOH.

(Black ink K7)
Black ink K7 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 120 mgKOH.

(Black ink K8)
Black ink K8 was obtained in the same manner as black ink K1 except that the acid value of the pigment dispersant was 30 mgKOH.

<Preparation of cyan ink C>
(Cyan inks C1 to C8)
Instead of carbon black, C.I. I. Cyan inks C1 to C8 were obtained in the same manner as black inks K1 to K8 except that Pigment Blue 15: 3 was used.

<Preparation of magenta ink M>
(Magenta Ink M1 to M8)
Instead of carbon black, C.I. I. Magenta inks M1 to M8 were obtained in the same manner as the black inks K1 to K8 except that Pigment Red 122 was used.

<Preparation of yellow ink Y>
(Yellow ink Y1 to Y8)
Instead of carbon black, C.I. I. Yellow inks Y1 to Y8 were obtained in the same manner as black inks K1 to K8 except that Pigment Yellow 128 was used.

The coarse grain characteristics (number of coarse grains at concentration, number of initial coarse grains) of each ink are listed in Table 1. Inks of each color having the same composition other than the colorant have the same coarse grain characteristics, and are therefore shown together.

<Examples A1 to A5, Comparative Examples A1 to A3>
(Preparation of recording device)
With the same configuration as shown in FIG. 1, double-sided printing is possible, and the ejection heads 12A (12KA, 12YA, 12MA, 12CA) and 12B (12KB, 12YB, 12MB, 12CB) for ejecting each water-based ink are used. A recording device equipped with a 600 dpi piezo head (maximum ink droplet amount 11 pl) was prepared. The recording device ejects black (K), yellow (Y), magenta (M), and cyan (C) water-based inks in this order on both the front and back surfaces of the recording medium to perform image recording.
Further, Next-IJ 70 (continuous paper, manufactured by Nippon Paper Industries) was used as the recording medium P of this recording device.

Here, the details of the recording device are as follows.
-Details of recording device-
-Recording speed (recording medium transport speed): 100 m / min
-Set temperature of the drying drums (drying drums 14A, 14B): 100 ° C.
-Set temperature of the warm air blower (warm air blower 16A, 16B): 100 ° C

Then, the prepared black water-based ink was filled in the black ink cartridge of the recording device. The following evaluation was performed using this recording device.

(Evaluation of uneven landing)
Using the above recording device, black ink is ejected from a black ejection head 12KA (600 dpi piezo head (maximum ink droplet amount 11pl)) onto the surface of a recording medium to form a halftone chart with 80% coverage. , The halftone chart formed on the surface of the recording medium was dried by the drying drum 14A and the feeding drying device 16A.
Next, black ink is ejected from a black ejection head 12KB (600 dpi piezo head (maximum ink droplet amount 11pl)) to the back surface of the recording medium dried by recording on the front surface of the recording medium, and halftone with 80% coverage. The chart was formed, and the halftone chart formed on the back surface of the recording medium was dried by the drying drum 14B and the feeding drying device 16B. Then, cooling was carried out by a cooling roller 60A.
Then, the halftone chart formed on the back surface of the recording medium was visually observed to evaluate the uneven landing. The evaluation criteria are as follows.
-Evaluation criteria-
G1 (○): No streaks G2 (Δ): Slight streaks G3 (×): Prominent streaks G4 (XX): Streaks due to nozzle omission.

(Evaluation of latency)
Using the above recording device, black ink is ejected from a black ejection head 12KA (600 dpi piezo head (maximum ink droplet amount 11pl)) onto the surface of a recording medium to form a halftone chart with 80% coverage. , The halftone chart formed on the surface of the recording medium was dried by the drying drum 14A and the feeding drying device 16A.
Next, 5 pl of black ink is ejected from a black ejection head 12KB (600 dpi piezo head (maximum ink droplet amount 11 pl)) to the back surface of the recording medium dried by recording on the front surface of the recording medium, and the previous black ink is ejected. After a pause of 0.36 seconds from the ink ejection, the landing position deviation was measured when the black ink was ejected next time. The ink ejection pause period is adjusted according to the recording speed and the length of the non-ejection portion (the region where the image is not formed, that is, the non-image portion) (the length in the transport direction of the recording medium).
Specifically, when the 1-dot line recorded immediately after recording the solid image is used as a reference, the 1-dot recorded immediately after recording the solid image and leaving a non-image portion of about 12 inches in the transport direction of the recording medium. Measure how much the distance from the line (1 dot line recorded after a pause of 0.36 seconds) deviates from the length of the non-image part corresponding to the pause period of 0.36 seconds, and land this. The amount of misalignment was used. The evaluation criteria for the deviation of the landing position are as follows.
-Evaluation criteria-
G1 (◎): Landing position deviation amount is 22 μm or less G2 (○): Landing position deviation amount exceeds 22 μm and 32 μm or less G3 (Δ): Landing position deviation amount exceeds 32 μm and 43 μm or less G4 (×): The amount of deviation of the landing position exceeds 43 μm

(Evaluation of fixability)
The fixability was evaluated as follows.
Using the above recording device, black ink is ejected from a black ejection head 12KA (600 dpi piezo head (maximum ink droplet amount 11pl)) onto the surface of a recording medium to form a solid chart with 100% coverage. The halftone chart formed on the surface of the recording medium was dried by the drying drum 14A and the feeding drying device 16A.
Next, NIJ70 paper was placed on a solid chart, a load of 20 N / cm was applied from above, and the paper was slid to measure the density of the ink transferred to NIJ70 paper.
The evaluation criteria are as follows.
-Evaluation criteria-
G1 (◎): 0.01 or less G2 (○): 0.01 or more and 0.02 or less G3 (△): 0.02 or more and less than 0.03 G4 (×): 0.03 or more

<Examples B1 to B4, Comparative Examples C1 to C5>
A recording device similar to that of Example A1 was prepared, and the prepared water-based inks of each color were filled in the ink cartridges for each color of the recording device according to Tables 2 and 3. Using this recording device, landing unevenness, latency, and fixability were evaluated using water-based inks of each color in the same manner as in Example 1.

The details of each example are listed below in Tables 1 to 3. In Tables 1 to 4, "Nc1" indicates the number of coarse grains at the time of concentration of each ink, and "Ni1" indicates the initial number of coarse grains of each ink.

From the above results, it can be seen that the black inks of Examples A1 to A5 are less likely to cause uneven landing when recorded on a dry recording medium than the black inks of Comparative Examples. It can also be seen that the black inks of Examples A1 to A5 also suppress the occurrence of latency.
In particular, from Examples B1 to B4 and Examples C1 to C4, it can be seen that uneven landing is likely to occur in the black ink first ejected to the back surface of the dried recording medium. Then, in Examples B1 to B5, it can be seen that the occurrence of uneven landing is suppressed in the black ink first ejected to the back surface of the dried recording medium. It can also be seen that in Examples B1 to B5, the occurrence of latency is also suppressed.
It can be seen that the occurrence of uneven landing is alleviated in the inks of other colors ejected after the black ink.

10 Image recording unit 12A, 12KA, 12YA, 12MA, 12CA Discharge head 12B, 12KB, 12YB, 12MB, 12CB Discharge head 14A Dry drum 14B Dry drum 16A Warm air blower 16B Warm air blower 20 Pretreatment unit 20A Supply roll 30 Buffer unit 30A 1st pass roller 30B Dancer roller 30C 2nd pass roller 40 Post-processing unit 40A Winding roll 50 Buffer unit 50A 1st pass roller 50B Dancer roller 50C 2nd pass roller 60 Cooling unit 60A Cooling roller 100 Recording device P Recording medium R Conveyance path

Claims (10)

A pigment as a colorant, a pigment dispersant having an acid value of 70 mgKOH / g or more and 200 mgKOH / g or less, polymer particles having a volume average particle size of 10 nm or more and 300 nm or less and containing no colorant, and two or more kinds of surfactants. It contains an ethylene oxide adduct of acetylene glycol, water, and a solvent containing two or more polyhydric alcohols as an aqueous organic solvent.
The number of coarse particles Nc1 having a particle size of 0.5 μm or more in the water-based ink after weight loss with the mass reduced by 60% by evaporation of the solvent, and the number Ni1 of coarse particles having a particle size of 0.5 μm or more in the water-based ink before weight loss. The relationship satisfies the equation: 1 ≦ Nc1 / Ni1 ≦ 6 .
The number of coarse particles Nc1 having a particle size of 0.5 μm or more in the water-based ink after weight loss is 1045 × 10 ⁶ pieces / ml or more and 10 ¹⁰ pieces / ml or less .
The number of coarse particles with a particle size of 0.5 μm or more in the water-based ink before weight loss Ni1 is 308 × 10 ⁶ pieces / ml or more and 10 ¹⁰ pieces / ml or less.
The content of the pigment dispersant is 0.1% by mass or more and 100% by mass or less with respect to the pigment.
The content of the polymer particles is 0.1% by mass or more and 10% by mass or less with respect to the water-based ink.
The total content of the two or more kinds of polyhydric alcohols is 1% by mass or more and 60% by mass or less with respect to water.
The total content of the ethylene oxide adducts of the two or more acetylene glycols is 0.1% by mass or more and 10% by mass or less with respect to the water-based ink.
Water-based ink. The water-based ink according to claim 1, wherein the glass transition temperature of the polymer particles is 40 ° C. or higher and 90 ° C. or lower. A recording device having a discharge head that accommodates the water-based ink according to claim 1 or 2, and discharges the water-based ink onto the surface of a recording medium. The ejection head is a first ejection head that contains the first aqueous ink as the aqueous ink according to claim 1 or 2, and first ejects the first aqueous ink onto the surface of the recording medium.
3. The third aspect of the present invention further comprises a second ejection head that accommodates the second aqueous ink and ejects the second aqueous ink onto the surface of the recording medium after the ejection of the first aqueous ink by the first ejection head. The recording device described. A first ejection head that accommodates the first aqueous ink and ejects the first aqueous ink onto the surface of the recording medium.
A drying device that dries the first water-based ink ejected onto the surface of the recording medium by the first ejection head, and a drying device.
Second ejection in which the aqueous ink according to claim 1 or 2 is contained as the second aqueous ink, and after the first aqueous ink is dried by the drying device, the second aqueous ink is ejected to the back surface of the recording medium. With the head
A recording device having. The second ejection head is a third ejection head that stores the third aqueous ink as the second aqueous ink and first ejects the third aqueous ink to the back surface of the recording medium.
5. The fifth aspect of the present invention further comprises a fourth ejection head that accommodates the fourth aqueous ink and ejects the fourth aqueous ink to the back surface of the recording medium after the ejection of the third aqueous ink by the third ejection head. The recording device described. A recording method comprising a ejection step of ejecting the water-based ink according to claim 1 or 2 onto the surface of a recording medium by an ejection head. The ejection step is the first ejection step of first ejecting the first aqueous ink as the aqueous ink according to claim 1 or 2 to the surface of the recording medium by the first ejection head as the ejection head.
The recording method according to claim 7, further comprising a second ejection step of ejecting the second aqueous ink onto the surface of the recording medium by the second ejection head after the ejection of the first aqueous ink by the first ejection head. .. The first ejection step of ejecting the first water-based ink onto the surface of the recording medium by the first ejection head
A drying step of drying the first water-based ink discharged onto the surface of the recording medium by the first ejection step, and a drying step.
A second ejection step of ejecting the aqueous ink according to claim 1 or 2 as a second aqueous ink to the back surface of the recording medium by the second ejection head after the first aqueous ink is dried by the drying step.
Recording method having. The second ejection step is a third ejection step in which the third ejection head as the second ejection head first ejects the third aqueous ink as the second aqueous ink onto the back surface of the recording medium.
The recording method according to claim 9, further comprising a fourth ejection step of ejecting the fourth aqueous ink to the back surface of the recording medium by the fourth ejection head after the ejection of the third aqueous ink by the third ejection head. ..