JP2017057360A - Aqueous ink, recording device, and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink suppressing generation of impact unevenness when initially recording to a recording medium dried under a predetermined condition.SOLUTION: There is provided an aqueous ink containing a coloring agent, a polymer particle, and a solvent containing water and an aqueous organic solvent and having a relation between the number Nc1 of coarse grain with grain diameter of 0.5 μm or more in the aqueous ink after weight loss when mass is reduced by 60% by evaporation of the solvent and the number Ni1 of coarse grain with grain diameter of 0.5 μm or more before weight loss satisfying the formula: 1≤Nc1/Ni1≤50.SELECTED DRAWING: None

Description

  The present invention relates to a water-based ink, a recording apparatus, and a recording method.

For example, Patent Document 1 states that “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 rate of 30 to 50% and the water evaporation rate of 30 Ink for ink jet recording, in which the average particle diameter of the colorant in the ink is up to twice the initial average particle diameter.
Patent Document 2 states that “the colored fine particles have a quaternized carboxyl group on the surface thereof and a volume average particle size of 0.5 μm or less in the re-dispersed liquid of the dry ink. A jet ink in which the increase rate of the volume average particle diameter of the colored fine particles is 50% or less has been proposed.
Further, Patent Document 3 proposes “an inkjet ink containing a pigment dispersion in which the total number of coarse particles having a particle diameter of 0.5 μm or more is 1,000,000 / 5 μL or less”.

JP 2006-077232 A JP 2007-146167 A JP 2010-261028 A

The above-mentioned "increase rate of viscosity is 10 or less up to a water evaporation rate of 30%, and the viscosity increase rate exceeds 500 between 30 to 50% of the water evaporation rate. Ink-jet recording ink in which the average particle size of the colorant is less than or equal to twice the initial average particle size. ”The ejection state from nozzles that are not used frequently becomes unstable (= landing unevenness), and image defects in the printed matter It may become.

  The problem of the present invention is that 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 rate of 30 to 50% and the water evaporation rate of up to 30%. The occurrence of uneven landing is suppressed when recording is first performed on a recording medium dried under a predetermined condition, as compared with an inkjet recording ink in which the average particle diameter of the colorant in the ink is twice or less the initial average particle diameter. It is to provide a water-based ink.

  The above problem is solved by the following means.

The invention according to claim 1
A colorant, polymer particles, and a solvent containing water and an aqueous organic solvent,
The number Nc1 of coarse particles having a particle diameter of 0.5 μm or more in the water-based ink after weight reduction after reducing the mass by 60% by evaporation of the solvent, and the number Ni1 of coarse particles having a particle diameter of 0.5 μm or more in the water-based ink before weight reduction Is a water-based ink satisfying the formula: 1 ≦ Nc1 / Ni1 ≦ 50.

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

The invention according to claim 3
The aqueous ink according to claim 1 or 2, further comprising a pigment dispersant containing a pigment as a colorant and having an acid value of 70 mgKOH / g or more and 200 mgKOH / g or less.

The invention according to claim 4
A recording apparatus comprising the discharge head for containing the water-based ink according to claim 1 and discharging the water-based ink onto a surface of a recording medium.

The invention according to claim 5
A first discharge in which the discharge head stores the first water-based ink as the water-based ink according to any one of claims 1 to 3 and discharges the first water-based ink first onto the surface of the recording medium. Head,
5. The apparatus according to claim 4, further comprising: a second discharge head that contains a second water-based ink and discharges the second water-based ink onto the surface of the recording medium after the discharge of the first water-based ink by the first discharge head. The recording device described.

The invention according to claim 6
A first discharge head that contains a first aqueous ink and discharges the first aqueous ink onto the surface of a recording medium;
A drying device for drying the first water-based ink ejected on the surface of the recording medium by the first ejection head;
The water-based ink according to any one of claims 1 to 3 is accommodated as a second water-based ink, and after the first water-based ink is dried by the drying device, the second water-based ink is placed on the back surface of the recording medium. A second discharge head for discharging;
A recording apparatus.

The invention according to claim 7 provides:
The second discharge head is a third discharge head that contains a third water-based ink as the second water-based ink and discharges the third water-based ink first on the back surface of the recording medium;
7. The apparatus according to claim 6, further comprising: a fourth discharge head that contains a fourth water-based ink and discharges the fourth water-based ink onto the back surface of the recording medium after the third water-based ink is discharged by the third discharge head. The recording device described.

The invention according to claim 8 provides:
A recording method comprising a discharge step of discharging the water-based ink according to any one of claims 1 to 3 onto a surface of a recording medium by an discharge head.

The invention according to claim 9 is:
4. The first ejection of the first water-based ink as the water-based ink according to any one of claims 1 to 3 first on the surface of the recording medium by the first ejection head as the ejection head in the ejection step. Discharge process,
9. The recording method according to claim 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 ejection of the first aqueous ink by the first ejection head. .

The invention according to claim 10 is:
A first discharge step of discharging the first aqueous ink onto the surface of the recording medium by the first discharge head;
A drying step of drying the first water-based ink ejected on the surface of the recording medium in the first ejection step;
After the first aqueous ink is dried by the drying step, the second ink ejects the aqueous ink according to any one of claims 1 to 3 to the back surface of the recording medium as a second aqueous ink by a second ejection head. A discharge process;
A recording method.

The invention according to claim 11 is:
The second discharge step is a third discharge step of first discharging a third water-based ink as the second water-based ink onto the back surface of the recording medium by a third discharge head as the second discharge head;
The recording method according to claim 10, further comprising a fourth discharge step of discharging the fourth aqueous ink onto the back surface of the recording medium by the fourth discharge head after the discharge of the third water-based ink by the third discharge head. .

  According to the first, second, or third aspect of the invention, 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 rate of 30 to 50%. First, recording is performed on a recording medium dried under a predetermined condition as compared with an inkjet recording ink in which the average particle diameter of the colorant in the ink having a water evaporation rate of up to 30% is not more than twice the initial average particle diameter. In some cases, a water-based ink that suppresses the occurrence of uneven landing is provided.

According to the fourth aspect of the present invention, the rate of increase in viscosity is 10 or less up to a water evaporation rate of 30%, and the rate of increase in viscosity exceeds 500 between 30% and 50% of the water evaporation rate. When recording for the first time on a recording medium dried under predetermined conditions, compared to the case where an ink for ink jet recording in which the average particle size of the colorant in the ink up to 30% is not more than twice the initial average particle size is applied. A recording apparatus that suppresses the occurrence of uneven landing of water-based ink is provided.
According to the fifth aspect of the present invention, the rate of increase in viscosity is 10 or less up to a water evaporation rate of 30%, and the rate of increase in viscosity exceeds 500 between 30% and 50% of the water evaporation rate. When recording on a dry recording medium, compared to the case where an ink for inkjet recording in which the average particle size of the colorant in the ink up to 30% is less than twice the initial average particle size is applied as the first aqueous ink, There is provided a recording apparatus that suppresses uneven landing of a first water-based ink that is first ejected on the surface of a recording medium under predetermined conditions.

According to the invention of claim 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 rate of 30 to 50%, Compared to the case where an ink for inkjet recording in which the average particle diameter of the colorant in the ink having a water evaporation rate of up to 30% is less than twice the initial average particle diameter is applied as the second water-based ink, recording is performed on both surfaces of the recording medium. In this case, there is provided a recording apparatus that suppresses landing unevenness 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 device under a predetermined condition.
According to the seventh aspect of the present invention, the rate of increase in viscosity is 10 or less up to a water evaporation rate of 30%, and the rate of increase in viscosity exceeds 500 between 30% and 50% of the water evaporation rate. When recording on both sides of the recording medium, compared with the case where the ink for inkjet recording in which the average particle diameter of the colorant in the ink up to 30% is less than twice the initial average particle diameter is applied as the third aqueous ink, There is provided a recording apparatus that suppresses uneven landing of the third aqueous ink that is first ejected on the back surface of the recording medium dried by drying the first aqueous ink by a drying apparatus under a predetermined condition.

According to the eighth aspect of the present invention, the rate of increase in viscosity is 10 or less up to a water evaporation rate of 30%, and the rate of increase in viscosity exceeds 500 between 30% and 50% of the water evaporation rate. When recording for the first time on a recording medium dried under predetermined conditions, compared to the case where an ink for ink jet recording in which the average particle size of the colorant in the ink up to 30% is not more than twice the initial average particle size is applied. Also provided is a recording method for suppressing the occurrence of uneven landing of water-based ink.
According to the ninth aspect of the present invention, the rate of increase in viscosity is 10 or less up to a water evaporation rate of 30%, and the rate of increase in viscosity exceeds 500 between 30% and 50% of the water evaporation rate. Compared to the case where an inkjet recording ink having an average particle diameter of up to 30% of the colorant in the ink that is not more than twice the initial average particle diameter is applied as the first aqueous ink, the recording medium is dried under predetermined conditions. A recording method is provided that suppresses uneven landing of the first water-based ink that is first ejected onto the surface of the recording medium when recording.

According to the invention according to claim 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 rate of 30 to 50%, Compared to the case where an ink for inkjet recording in which the average particle diameter of the colorant in the ink having a water evaporation rate of up to 30% is less than twice the initial average particle diameter is applied as the second water-based ink, recording is performed on both surfaces of the recording medium. In this case, a recording method for suppressing landing unevenness of the second water-based ink ejected on the back surface of the recording medium dried by drying the first water-based ink by a drying process under a predetermined condition is provided.
According to the invention of claim 11, the rate of increase in viscosity is 10 or less up to a water evaporation rate of 30%, and the rate of increase in viscosity exceeds 500 between 30% and 50% of the water evaporation rate. When recording on both sides of the recording medium, compared with the case where the ink for inkjet recording in which the average particle diameter of the colorant in the ink up to 30% is less than twice the initial average particle diameter is applied as the third aqueous ink, A recording method is provided that suppresses uneven landing of the third water-based ink that is first ejected on the back surface of the recording medium that has been dried by drying the first water-based ink by a drying process under a predetermined condition.

1 is a schematic configuration diagram illustrating a recording apparatus according to an embodiment.

  Embodiments that are examples of the present invention will be described below.

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

Here, when recording is first performed on a recording medium dried under a predetermined condition (for example, a sheet having a water content of 3% or less), the periphery of the ejection surface of the ejection head is easily dried due to moisture absorption of the recording medium. When the periphery of the discharge surface of the discharge head dries, drying proceeds from the meniscus surface in the nozzle of the discharge head (the curved surface created by the surface of the water-based ink), and when water-based ink is concentrated in the nozzle of the discharge head, it is more water-based than water. The proportion of organic solvent is increased. For this reason, the dispersibility of the colorant (pigment) or polymer particles is lowered, the colorant (pigment) or polymer particles are aggregated, and the number of coarse particles tends 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 the periphery of the nozzle edge, and the adhered coarse particles serve as nuclei to grow particles. Then, the coarse particles having grown particles hinder the discharge of the water-based ink, and the discharge amount may be reduced or the discharge directionality may be deteriorated. For this reason, uneven landing may occur. In particular, due to moisture absorption of the dried recording medium, the solvent of the water-based ink rapidly evaporates in the nozzles of the discharge head, and the mass of the water-based ink may be reduced by nearly 60%, and landing unevenness is likely to occur.
In addition, when the discharge amount of water-based ink decreases and landing unevenness occurs, it becomes difficult to fill up the gap between adjacent dots, and for example, it appears as a white stripe in the image. Further, when the discharge directionality of the water-based ink deteriorates and landing unevenness occurs, the gap between the adjacent dots becomes difficult to be filled and at the same time, the overlap between the adjacent dots increases, and for example, it appears as a black streak in the image.

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

For this reason, in the water-based ink according to the present embodiment, occurrence of uneven landing is suppressed when recording is first performed on a recording medium dried under a predetermined condition. Note that the drying of the recording medium under a predetermined condition indicates drying by the “drying drum and hot air blower” at the set temperature described in “Details of the recording apparatus” in [Example]. However, even when the recording medium is dried under conditions other than the predetermined conditions, occurrence of uneven landing is suppressed.
Further, in the water-based ink according to the present embodiment, since the coarse particle growth around the nozzle inner wall surface of the ejection head and the periphery of the nozzle is suppressed, the generation of latency is also suppressed. Here, latency refers to the amount of ink ejected next when the next ejection is carried out after a period of time after ejection of the aqueous ink, or the landing position of the next ejected aqueous ink on the recording medium. This indicates a discharge failure that lands at a position shifted from the planned position.
In addition, when using a plurality of colors of water-based ink 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 ejected first. This is because the water content of the recording medium is increased by the discharge of the first water-based ink, and the drying of the water-based ink in the nozzles of the discharge head that discharges the water-based ink after the first water-based ink is eased. .

Also, when recording on both sides of the recording medium, water-based ink is discharged onto the surface (front surface) of the recording medium, and then the water-based ink is heated and dried, and further water-based ink is discharged onto the back surface of the recording medium. . In this case, the drying of the water-based ink ejected on the surface (front surface) of the recording medium brings the recording medium into a dry state in which the moisture content is particularly reduced. For this reason, in the nozzles of the ejection head that ejects the water-based ink onto the back surface of the recording medium, the water-based ink evaporates remarkably and landing unevenness tends to occur. However, when the water-based ink according to the present embodiment is applied as the water-based ink ejected on the back surface of the recording medium, the water-based ink ejected on the surface (front surface) of the recording medium when recording on both surfaces of the recording medium. By drying, landing unevenness of the water-based ink discharged on the back surface of the excessively dried recording medium is suppressed.
Even when a plurality of colors of water-based ink are used for recording on the back surface of the recording medium, it is preferable to apply the water-based ink according to this embodiment to at least the water-based ink ejected first. This is because, as described above, the water content of the recording medium is increased by the first water-based ink discharge, and the drying of the water-based ink in the nozzles of the discharge head that discharges the water-based ink after the first water-based ink is eased. It is to be done.

In the ink according to the present embodiment, the relationship between the coarse particle number Nc1 during concentration of the water-based ink and the initial coarse particle number Ni1 preferably satisfies the formula: 1 ≦ Nc1 / Ni1 ≦ 30 from the viewpoint of suppressing landing unevenness. More preferably, the formula: 1 ≦ Nc1 / Ni1 ≦ 10 is satisfied.
In addition, as a method of adjusting the coarse particle number Nc1 at the time of concentration of the water-based ink, for example, 1) A method of setting the glass transition temperature Tg of the polymer particles to 40 ° C. or more and 90 ° C. or less (the glass transition temperature Tg of the polymer particles is 2) A method in which the acid value of the pigment dispersant is 70 mg KOH / g or more and 200 mg KOH / g or less (if the acid value of the pigment dispersant is lowered, the concentration Nc1 tends to decrease during concentration) 3) A method for selecting the type of surfactant (for example, when a surfactant having a small HLB value is selected, the number of coarse particles Nc1 tends to decrease). Is mentioned. And Nc1 / Ni1 is adjusted using these methods.

Further, the initial coarse particle number Ni1 of the water-based ink is preferably 10 ¹⁰ particles / ml or less, more preferably 10 ⁹ particles / ml or less, from the viewpoint of suppressing landing unevenness.
On the other hand, the number Nc1 of coarse particles at the time of concentration of the water-based ink is preferably 10 ¹⁰ particles / ml or less, more preferably 10 ⁹ particles / ml or less from the viewpoint of suppressing uneven landing.

Here, the method for reducing the mass of water-based ink by evaporation of the solvent by 60% is as follows. The target aqueous ink 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 aqueous ink solvent in the container is evaporated until the aqueous ink solvent is reduced by 60% with respect to the mass of the total aqueous ink. That is, the solvent is evaporated until the mass of the water-based ink becomes 40% of the mass of the water-based ink before the weight reduction.
The number of coarse particles in the water-based ink is set to 0.5 μm or less with a lower limit particle size of 0.5 μm using an Accusizer 780APS (manufactured by PS), and a particle size of 0.5 μm or more per 1 ml of ink is counted. Calculated by measuring the total number of particles.
The number of coarse particles at the time of concentration of the water-based ink is calculated with respect to the diluted ink obtained by adding pure water to the water-based ink after the weight reduction until the mass of the water-based ink before the weight reduction is reached, and is calculated by converting the dilution rate. .

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

  The aqueous ink according to this embodiment contains a colorant, polymer particles, and a solvent containing water and an aqueous organic solvent.

(Coloring agent)
First, the colorant will be described.
As the colorant, those according to the water-based ink having the target hue may be used, and specific examples thereof include pigments. Examples of the pigment include organic pigments and inorganic pigments.

  Specific examples of black pigments (black pigments) include Raven7000, Raven5750, Raven5250, Raven5000 ULTRAII, Raven3500, Raven2000, Raven1500, Raven1250, Raven1200, Raven1190, Raven1190, Raven1190, Raven1190 ) Regal 400R, Regal 330R, Regal 660R, Mogul L, Black Pearls L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Mon rch 1400 (above Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S150, Color Black S160, Color Black S160, Color Black S160, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black S150 , Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Orion Engineered Carbons) 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like, but are 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. It is not limited.
Specific examples of the magenta color pigment 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 yellow pigments include C.I. I. Pigment Yellow-1, -2, -3, -12, -13, -14, -16, -17, -73, -74, -75, -83, -93, -95, -97, -98, -114, -128, -129, -138, -151, -154, -180, and the like, but are not limited thereto.

  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 a polymer dispersant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant.

The acid value of the pigment dispersant is preferably 70 mgKOH / g or more and 200 mgKOH / g or less, more preferably 100 mgKOH / g or more and 200 mgKOH / g or less from the viewpoint of reducing the number of coarse particles Nc1 during concentration and suppressing uneven landing. .
The acid value is measured according to JIS K0070 and using a neutralization titration method. That is, an appropriate amount of a sample is taken, 100 ml of a solvent (diethyl ether / ethanol mixed solution) and a few drops of an indicator (phenolphthalein solution) are added, and shaken sufficiently until the sample is completely dissolved in a water bath. This is titrated with a 0.1 mol / l potassium hydroxide ethanol solution, and the end point is when a light red color of the indicator lasts 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 the 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 addition polymers of monomers having an α, β-ethylenically unsaturated group. By 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. A homopolymer of a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group is also used.

  Monomers having an α, β-ethylenically unsaturated group having a hydrophilic group include monomers having a carboxyl group, a sulfonic acid group, a hydroxyl group, a phosphoric acid group, such as 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, methacryloxyethyl phosphate, bis Examples include methacryloxyethyl phosphate, methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, and diethylene glycol dimethacrylate.

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

  Examples of preferred copolymers as the polymer dispersant include styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene- Maleic acid copolymer, vinyl naphthalene-methacrylic acid copolymer, vinyl naphthalene-acrylic acid copolymer, alkyl acrylate ester-acrylic acid copolymer, alkyl methacrylate ester-methacrylic acid copolymer, styrene-methacrylic acid Alkyl ester-methacrylic acid copolymer, styrene-alkyl acrylate ester-acrylic acid copolymer, styrene-phenyl methacrylate-methacrylic acid copolymer, styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, or these Examples of salt It is. Moreover, you may copolymerize the monomer which has a polyoxyethylene group and a hydroxyl group with these polymers.

  The weight average molecular weight of the polymer dispersant is preferably, for example, 2000 or more and 50000 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 generally stated, but it is preferably 0.1% by mass or more and 100% by mass or less based on the pigment.

Examples of the pigment include pigments that are self-dispersed in water (hereinafter referred to as self-dispersing pigments).
The self-dispersing pigment refers to a pigment that has a water-solubilizing group on the pigment surface and disperses in water without the presence of a polymer dispersant. The self-dispersing pigment can be obtained, for example, by subjecting the pigment to surface modification treatment such as acid / base treatment, coupling agent treatment, polymer graft treatment, plasma treatment, oxidation / reduction treatment, and the like.

  As self-dispersing pigments, in addition to pigments that have been surface-modified to the above pigments, Cab-o-jet-200, Cab-o-jet-300, Cab-o-jet-400 manufactured by Cabot Corporation. 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 -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., etc. Examples include dispersed pigments.

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

Here, examples of the pigment include a pigment coated with a resin. This is called a microcapsule pigment, and there are commercially available microcapsule pigments such as those manufactured by DIC and Toyo Ink. In addition, it is not restricted to a commercially available microcapsule pigment, You may use the microcapsule pigment produced according to the objective.
Examples of the pigment also include a resin dispersion type pigment in which a polymer compound is physically adsorbed or chemically bonded to the pigment.
In addition to black, cyan, magenta, and yellow, the pigments include specific color pigments such as red, green, blue, brown, and white, metallic luster pigments such as gold and silver, and colorless or light-colored constitutions. Examples include pigments and plastic pigments.
Examples of the pigment include particles in which silica, alumina, polymer beads or the like are used as a core, and a dye or pigment is fixed on the surface thereof, an insoluble lake of the dye, a colored emulsion, a colored latex, or the like.

  As colorants, in addition to pigments, hydrophilic anionic dyes, direct dyes, cationic dyes, reactive dyes, dyes such as polymer dyes and oil-soluble dyes, wax powders colored with dyes, resin powders, Or an emulsion, a fluorescent dye, a fluorescent pigment, etc. are mentioned.

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

  The content (concentration) of the colorant is, for example, preferably from 1% by mass to 25% by mass and more preferably from 2% by mass to 20% by mass with respect to the aqueous ink.

(Polymer particles)
The polymer particles will be described.
The polymer particles are a component that improves 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 components different from the polymer dispersant described above.

Examples of the polymer particles include styrene-acrylic acid copolymer, styrene-acrylic acid-sodium acrylate copolymer, styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, and acrylate copolymer. And particles (latex particles) such as polyurethane, polyester, silicon-acrylic acid copolymer, and acrylic-modified fluororesin.
Examples of the polymer particles include core / shell type polymer particles having different compositions at the center and outer edge of the particles.

The polymer particles may be dispersed in an aqueous ink using an emulsifier, or may be dispersed in an aqueous ink without using an emulsifier.
As an emulsifier, a polymer having a hydrophilic group such as a surfactant, a sulfonic acid group, or a carboxyl group (for example, a polymer having a hydrophilic group grafted thereto, a hydrophilic monomer 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 glossiness and scratch resistance of the image.
The volume average particle diameter of the polymer particles is measured with a Microtrac UPA particle size analyzer UPA-UT151 (manufactured by Microtrac). The measurement is performed by placing 1000-fold diluted aqueous ink in a measurement cell. As the input value at the time of measurement, the viscosity of the aqueous ink diluent is used as the viscosity, and the refractive index of the polymer particles is used as the particle refractive index.

The glass transition temperature of the polymer particles is preferably 40 ° C. or higher and 90 ° C. or lower, 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 landing unevenness. 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 image scratch resistance.
The glass transition temperature of the polymer particles is determined from the DSC curve obtained by differential scanning calorimetry (DSC). More specifically, the method for determining the glass transition temperature in JIS K7121-1987 “Method for Measuring Plastic Transition Temperature”. It is calculated | required by description of "extrapolated glass transition start temperature".

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

(water)
Explain about water.
As water, ion-exchanged water, ultrapure water, distilled water, and ultrafiltered water are particularly preferable from the viewpoint of preventing contamination of impurities or generation of microorganisms.

  For example, the water content is 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 aqueous 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, and sulfur-containing solvents. 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, and glycerin. .

  Examples of 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 include ethylene oxide adducts.

Examples of the nitrogen-containing solvent include pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 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.

  1 mass% or more and 60 mass% or less are preferable with respect to water, and, as for content of an aqueous organic solvent, 1 mass% or more and 40 mass% or less are more preferable.

(Surfactant)
The surfactant will be described.
The water-based ink preferably contains, for example, a surfactant having an HLB (hydrophilic-lipophilic balance) of 14 or less as a surfactant. It is easy to adjust the surface tension of the water-based ink by adjusting the amount of the surfactant having an HLB of 14 or less, or by using a plurality of surfactants having different HLB.

The HLB (hydrophilic group / hydrophobic group balance “Hydrophile-Lipophile Balance”) is defined by the following formula (Griffin method).
・ HLB = 20 × (sum of formula weight 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 to 30). A compound having an integer)
Examples of commercially available products of ethylene oxide adducts of acetylene glycol (the values in parentheses indicate catalog values of HLB) include, for example, Olphine E1004 (7-9), Olphine E1010 (13-14), Olphine EXP. 4001 (8-11), Olfine EXP. 4123 (11-14), Olfine EXP. 4300 (10-13), Surfinol 104H (4), Surfinol 420 (4), Surfinol 440 (4), Dinol 604 (8) [Nippon Chemical Industry Co., Ltd.] and the like.

The polyether-modified silicone is, for example, a compound in which a polyether group is bonded to a silicone chain (polysiloxane main chain) in a graft form or a block form. 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 form or randomly.
As commercial products of polyether-modified silicone (the numbers in parentheses indicate catalog values of HLB), Silface SAG002 (12), Silface SAG503A (11), Silface SAG005 (7) [more, Nissin Chemical Industry Co., Ltd.].

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

Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, sulfuric acid of higher alcohol ether. 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, dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, monobutylbiphenylsulfonate, dibutylphenylphenol A disulfonate is preferable.

Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, poly Examples thereof include oxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, alkyl alkanol amide, polyethylene glycol polypropylene glycol block copolymer, acetylene glycol and the like.
Among these, nonionic surfactants include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Oxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, polyethylene glycol polypropylene glycol block copolymer, and acetylene glycol are preferred.

  Other nonionic surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Agents; biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin; and the like.

  The hydrophilic / hydrophobic balance (HLB) of other surfactants is preferably in the range of 3 to 20, for example, in consideration of solubility.

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

  The total surfactant content is preferably from 0.1% by weight to 10% by weight, more preferably from 0.1% by weight to 5% by weight, and more preferably from 0.2% by weight to 3% by weight, based on the aqueous ink. A mass% or less is more preferable.

(Other additives)
Other additives will be described.
The water-based ink may contain other additives.
Other additives include ink ejection improvers (polyethyleneimine, polyamines, polyvinylpyrrolidone, polyethylene glycol, ethylcellulose, carboxymethylcellulose, etc.), conductivity / pH adjusters (potassium hydroxide, sodium hydroxide, lithium hydroxide) Etc.), reactive diluents, penetrants, pH buffers, antioxidants, fungicides, viscosity modifiers, conducting agents, chelating agents, ultraviolet absorbers, infrared absorbers, etc. Is mentioned.

(Physical properties of water-based ink)
The preferred physical properties of the water-based ink will be described.
The pH of the water-based ink is preferably in the range of 4 to 10, more preferably in the range of 5 to 9.
Here, the pH of the water-based ink has a temperature of 23 ± 0.5 ° C. and a humidity of 55 ± 5% RP. H. Under the environment, a 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 to 0.5 S / m (preferably in the range of 0.01 S / m to 0.25 S / m, more preferably in the range of 0.01 S / m to 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 any of black ink, cyan ink, magenta ink, yellow ink, and intermediate color inks other than these colors, for example.
Further, the water-based ink according to the present embodiment may be used as an ink set that includes at least one kind of the water-based ink (preferably all of the water-based ink according to the present embodiment).

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

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

In the recording apparatus according to the first embodiment, the ejection head stores 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. And a second ejection head that contains the second aqueous ink and that ejects the second aqueous ink onto the surface of the recording medium after ejection of the first aqueous ink by the first ejection head. Good. That is, the recording apparatus may include a plurality of ejection heads that eject each of the water-based inks of a plurality of colors.
On the other hand, in the recording method according to the first embodiment, in the first discharge step, the first water-based ink as the water-based ink according to the present embodiment is first discharged onto the surface of the recording medium. It may be a discharge step, and may further include a second discharge step of discharging the second aqueous ink onto the surface of the recording medium by the second discharge head after the discharge of the first aqueous ink by the first discharge head. . In other words, the recording method may include an ejection step for ejecting each of the water-based inks of a plurality of colors.

In these forms, the water-based ink according to the present embodiment is applied as the first water-based ink that is first ejected onto the surface of the recording medium.
In these forms, in particular, due to moisture absorption of the dried recording medium, the periphery of the first ejection head that first ejects the first aqueous ink onto the surface of the recording medium is dried, and the first aqueous water in the nozzles of the first ejection head. Ink drying becomes prominent 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 that is first ejected on the surface of the recording medium, occurrence of uneven landing is suppressed.
On the other hand, as the second water-based ink ejected on 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 water-based ink discharge causes the water content of the recording medium to increase, and the drying of the second water-based ink in the nozzles of the second discharge 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.

  Note that the second discharge head that discharges the second water-based ink onto the surface of the recording medium may include a plurality of discharge heads that discharge each of the water-based inks of a plurality of colors. The aqueous ink according to the present embodiment may be applied as the second aqueous ink.

  In the recording apparatus and the recording method according to the first embodiment, the number of coarse particles Ncn at the time of concentration of the second aqueous ink (the number of coarse particles Ncn of the second aqueous ink after the weight is reduced by 60% by evaporation of the solvent) and the initial value. The ratio (Ncn / Nin) to the coarse particle number Nin (the coarse particle number Nin before weight reduction) is greater than the ratio (Nc1 / Ni1) between the coarse particle number Nc1 during concentration of the first aqueous ink and the initial coarse particle number Ni1. Big is good. 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. Thereby, 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. As described above, since the drying of the second water-based ink in the nozzles of the second ejection head is alleviated, even if the ratio (Ncn / Nin) is increased, the landing unevenness is increased in order to improve the image fixability. This is because the occurrence of this is suppressed.

  In the recording apparatus and the recording method according to the first embodiment, only one side of the recording medium may be recorded, or recording is performed on both sides of the recording medium by a mechanism that reverses the recording medium after recording on one side. Form may be sufficient.

(Second Embodiment)
The recording apparatus according to the second embodiment contains a first discharge head that contains a first aqueous ink and discharges the first aqueous ink onto the surface of the recording medium, and a first discharge head that is discharged onto the surface of the recording medium by the first discharge head. (1) A drying device that dries the water-based ink, and the water-based ink according to the above-described embodiment as the second water-based ink are accommodated. A second ejection head.
In the recording apparatus according to the second embodiment, a first discharge step of discharging the first aqueous ink onto the surface of the recording medium by the first discharge head, and the first aqueous ink discharged onto the surface of the recording medium through the first discharge step. And a second discharge step of discharging the second aqueous ink onto the back surface of the recording medium by the second discharge head after the first aqueous ink is dried by the drying device (second embodiment). Recording method) is realized.
That is, the recording apparatus and the recording method according to the second embodiment are an embodiment in which recording is performed on both sides of the recording medium by the ejection heads for each side. The aqueous ink according to the present embodiment is applied as the second aqueous ink. Note that the water-based ink according to the present embodiment may be applied as the first water-based ink.

  In the recording apparatus and the recording method according to the second embodiment, after the first aqueous ink is dried, the second aqueous ink is ejected to the back surface of the recording medium. In the reduced dry state, the evaporation of the second water-based ink becomes remarkable in the nozzles 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 on the back surface of the recording medium, the recording medium is excessively dried by the drying of the first water-based ink when recording on both surfaces of the recording medium. The landing unevenness of the second water-based ink discharged on the back surface of the ink is suppressed.

In the recording apparatus according to the second embodiment, the second ejection head stores the third aqueous ink as the second aqueous ink (the aqueous ink according to the present embodiment), and the third aqueous ink is first placed on the back surface of the recording medium. A fourth ejection head that contains the fourth aqueous ink and ejects the fourth aqueous ink onto the back surface of the recording medium after ejection of the third aqueous ink by the third ejection head. Furthermore, the form which it has may be sufficient. That is, the recording apparatus may include a plurality of ejection heads that eject each of the water-based inks of a plurality of colors.
On the other hand, in the recording method according to the second embodiment, the second discharge step records the third water-based ink as the second water-based ink (water-based ink according to the present embodiment) by the third discharge head as the second discharge head. A third ejection step of first ejecting on the back surface of the medium, and after ejecting the third aqueous ink by the third ejection head, ejecting the fourth aqueous ink to the back surface of the recording medium by the fourth ejection head. The form which further has four discharge processes may be sufficient. 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.

In these forms, the water-based ink according to the present embodiment is applied as the third water-based ink that is first ejected on the back surface of the recording medium.
In the case of these forms, in particular, the periphery of the third ejection head that first ejects the third aqueous ink onto the back surface of the recording medium is dried due to the moisture absorption of the excessively dried recording medium due to the drying of the third aqueous ink. Drying of the third water-based ink in the nozzles of the three-ejection head becomes significant, and landing unevenness is likely to occur. However, by applying the water-based ink according to the present embodiment as the third water-based ink that is first ejected to the back surface of the recording medium, occurrence of uneven landing is suppressed.
On the other hand, as the fourth water-based ink ejected on 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 water-based ink discharge causes the water content of the recording medium to increase, and the drying of the fourth water-based ink in the nozzles of the fourth discharge head is alleviated. However, the water-based ink according to the present embodiment is preferably applied to the fourth water-based ink in terms of suppressing the occurrence of uneven landing.

  Note that the fourth discharge head that discharges the fourth water-based ink onto the back surface of the recording medium may also include a plurality of discharge heads that discharge each of the water-based inks of a plurality of colors. The water-based ink according to the present embodiment may be applied as the fourth water-based ink.

  In the recording apparatus and the recording method according to the second embodiment, the number of coarse particles Ncn at the time of concentration of the fourth aqueous ink (the number of coarse particles Ncn of the fourth aqueous ink after the weight is reduced by 60% by evaporation of the solvent) and the initial value. The ratio (Ncn / Nin) to the coarse particle number Nin (the coarse particle number Nin before weight reduction) is greater than the ratio (Nc1 / Ni1) between the coarse particle number Nc1 during concentration of the third aqueous ink and the initial coarse particle number Ni1. Big is good. 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. Thereby, when recording on a dry recording medium, it is possible to secure the fixability of the image with the fourth water-based ink while suppressing the occurrence of uneven landing. As described above, since the drying of the fourth water-based ink in the nozzles of the fourth ejection head is alleviated, even if the ratio (Ncn / Nin) is increased, the landing unevenness is improved in order to improve the image fixability. This is because the occurrence of this is suppressed.

  Hereinafter, an example of a recording apparatus according to the present embodiment will be described with reference to the drawings. In the following description, discharging water-based ink (to a target area) onto a recording medium may be referred to as “image formation” or “forming an image”. The process of discharging, drying, and fixing is sometimes referred to as “recording”, “image recording”, or “recording an image”.

FIG. 1 is a schematic configuration diagram illustrating a recording apparatus according to the present embodiment.
The recording apparatus 100 according to the present embodiment includes an image recording unit 10 that records an image on a recording medium P, a preprocessing unit 20 that stores a recording medium P that is supplied to the image recording unit 10, and a preprocessing unit 20. And a buffer unit 30 for adjusting the conveyance amount of the recording medium P supplied to the image recording unit 10. The buffer unit 30 is disposed between the image recording unit 10 and the preprocessing unit 20.

  Further, the recording apparatus 100 adjusts the post-processing unit 40 that accommodates the recording medium P that is discharged from the image recording unit 10, the conveyance amount of the recording medium P that is discharged from the image recording unit 10 to the post-processing unit 40, and the like. And a buffer unit 50. The buffer unit 50 is disposed between the image recording unit 10 and the post-processing unit 40.

  Further, the recording apparatus 100 includes a cooling unit 60 that is disposed between the image recording unit 10 and the buffer unit 50 and cools the recording medium P carried out of the image recording unit 10.

  The image recording unit 10 includes, for example, a roll member (not shown) that guides the recording medium P along the conveyance path R of the recording medium P, and the surface of the recording medium P that is conveyed along the conveyance path R of the recording medium P. First, an image is formed on the surface of the recording medium P by the discharge head (first discharge head) 12A for discharging water-based ink (water-based ink droplets) to the surface, and the discharge head 12B for the first time. The second image formation is performed on the back surface of the recording medium P after the image formation.

The ejection heads 12A and 12B have, for example, an effective recording area (arrangement area of nozzles that eject water-based ink) equal to or greater than the width of the recording medium P (the length in a direction intersecting (for example, orthogonal to) the conveyance direction of the recording medium P). This 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. The ejection heads 12A and 12B move in the width direction of the recording medium P to eject aqueous ink (so-called carriage system). ).

  The discharge heads 12A and 12B may be a so-called thermal system that discharges water-based ink droplets by heat, or may be a so-called piezoelectric method that discharges water-based ink droplets by pressure. Things apply.

  The discharge heads 12A and 12B are, for example, discharge heads 12KA and 12KB that form a K (black) image by discharging aqueous ink onto the recording medium P, and discharge heads 12YA and 12YA that form a Y (yellow) color image. 12YB, discharge heads 12MA and 12MB for forming M (magenta) color images, and discharge heads 12CA and 12CB for forming C (cyan) color images, respectively. 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 conveyance direction of the recording medium P (hereinafter simply referred to as “paper conveyance direction”). (Which may be described) from the upstream side to the downstream side so as to face the recording medium P. In the description of the ejection head, when K, Y, M, and C are not distinguished, the symbols K, Y, M, and C are omitted.

  The ejection heads 12KA, 12YA, 12MA, 12CA, 12KB, 12YB, 12MB, and 12CB are connected to ink cartridges (not shown) of respective colors that are attached to and detached from the recording apparatus 100 through supply tubes (not shown). Ink of each color is supplied from the cartridge to the respective ejection heads 12KA, 12YA, 12MA, 12CA, 12KB, 12YB, 12MB, and 12CB.

  The ejection heads 12A and 12B are not limited to the form in which the four ejection heads corresponding to each of the four colors are arranged, and depending on the purpose, four or more corresponding to each of four or more colors including other intermediate colors. The form which has arrange | positioned the discharge head may be sufficient.

Here, as the ejection heads 12A and 12B, for example, a low-resolution ejection head (e.g., a 600 dpi ejection head) that ejects aqueous ink in an ink droplet amount range of 1 pl to 15 pl, and an ink droplet amount range of less than 10 pl. Any of high-resolution ejection heads (e.g., 1200 dpi ejection head) that ejects water-based ink may be used. Further, as the ejection heads 12A and 12B, both a low-resolution ejection head and a high-resolution ejection head may be provided.
The amount of ink droplets from the ejection heads 12A and 12B is in the range of the maximum droplet amount of water-based ink. In addition, dpi means “dot per inch”.

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

In the image recording unit 10, for example, the back surface of the recording medium P is wound downstream of the ejection head 12 </ b> A in the paper conveyance direction, and the image on the surface of the recording medium is rotated while being driven in contact with the recording medium P. A drying drum 14A (an example of a drying device) that dries (ink) is disposed.
Similarly, for example, the surface of the recording medium P is wound around the image recording unit 10 on the downstream side in the paper conveyance direction with respect to the ejection head 12B, and recording is performed while being driven to rotate in contact with the recording medium P. A drying drum 14B (an example of a drying device) for drying an image (ink) on the back surface of the medium is disposed.
A transport roller 18 that contacts the surface of the recording medium P is disposed downstream of the drying drum 14A in the paper transport direction and upstream of the discharge head 12B in the paper transport direction.

  Inside the drying drums 14A and 14B, a heating source (for example, a halogen heater or the like: not shown) is incorporated. The drying drum 14A dries the image (ink) on the surface of the recording medium P when heated by the heating source, and the drying drum 14B dries the image (ink) on the back surface of the recording medium P due to heating by the heating source.

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

When using the drying apparatus which performs the above-mentioned heat drying, it is preferable that the drying conditions are as follows.
That is, for example, the temperature of the heating source of the drying drum and the temperature of the hot air blowing device are 40 ° C. or higher and 120 ° C. or lower from the viewpoint of speeding up drying of the water-based ink and suppressing deformation of the recording medium P. The range is preferably 60 ° C. or higher and 100 ° C. or lower.
This drying temperature condition may be the same or different between the drying drum 14A and the drying drum 14B, and between the hot air blowing device 16A and the hot air blowing device 16B.

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

  The image recording unit 10 includes a near-infrared heater (not shown) for drying an image (ink) on the underlayer of the recording medium P, a laser, on the downstream side in the paper transport direction with respect to the ejection heads 12A and 12B. Other drying apparatuses such as an irradiation apparatus may be arranged. Other drying devices such as a near infrared heater and a laser irradiation device may be arranged in place of at least one of the drying drums 14A and 14B and the hot air blowing devices 16A and 16B, or the drying drums 14A and 14B and the warm air You may arrange | position in addition to the wind blower 16A, 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. The supply roll 20A is rotatably supported by a frame member (not shown).

  In the buffer unit 30, for example, a first pass roller 30A, a dancer roller 30B, and a second pass roller 30C are arranged along the paper conveyance direction. The dancer roller 30B moves up and down in FIG. 1 to adjust the tension of the recording medium P conveyed to the image recording unit 10 and the conveyance amount of the recording medium P.

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

  In the buffer unit 50, for example, a first pass roller 50A, a dancer roller 50B, and a second pass roller 50C are arranged along the paper conveyance direction. The dancer roller 50B moves up and down in FIG. 1 to adjust the tension of the recording medium P discharged to the post-processing unit 40 and the conveyance amount of the recording medium P.

  The cooling unit 60 is provided with a plurality of cooling rollers 60A. The recording medium P is cooled by conveying the recording medium P between the plurality of cooling rollers 60A.

  Here, the recording speed in the recording apparatus 100, that is, the conveyance speed of the recording medium is not particularly limited. However, the recording apparatus 100 includes a drying device that dries the water-based ink discharged onto the recording medium. It may be.

Next, an operation (recording method) by the recording apparatus 100 will be described.
In the recording apparatus 100 according to the present embodiment, first, the recording medium P is transported from the supply roll 20 </ b> A 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 the ejection heads 12 </ b> A onto the surface of the recording medium P. Thereafter, the image (ink) on the surface of the recording medium P is dried from the back surface side of the recording medium P (the surface opposite to the ink ejection surface from the ejection head 12A) by the drying drum 14A. Then, the ink (image) ejected on the surface of the recording medium P is dried from the surface side of the recording medium P (the ink ejection surface side from the ejection head 12A) by the hot air blower 16A. That is, the water-based ink discharged on the surface of the recording medium P is dried by the drying drum 14A and the hot air blowing device 16A.
Then, the image recorded on the surface of the recording medium P is brought into contact with the conveying roller 18 so that the recording medium P is neutralized through the image.
Subsequently, in the image recording unit 10, water-based ink is ejected from the ejection heads 12 </ b> B to the back surface of the recording medium P. Thereafter, the image (ink) on the back surface of the recording medium P is dried from the front surface side of the recording medium P (the surface opposite to the ink discharge surface from the discharge head 12B) by the drying drum 14B. Then, the ink (image) ejected on the back surface of the recording medium P is dried from the back surface side (ink ejection surface side from the ejection head 12B) of the recording medium P by the hot air blower 16B. That is, the water-based ink discharged on the back surface of the recording medium P is dried by the drying drum 14B and the hot air blowing device 16B.
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 having an image recorded on the surface by the winding roll 40A.

Through the above steps, images of water-based ink are recorded on both sides of the recording medium P.
Note that the recording medium P having the image recorded as described above is cut into a target size through a cutting step.

  The recording apparatus 100 has been described with respect to the configuration including the ejection head 12A that ejects aqueous ink onto the surface of the recording medium P and the ejection head 12B that ejects aqueous ink onto the back surface of the recording medium P. I can't. For example, the recording apparatus 100 does not include the ejection head 12B, and after the water-based ink is ejected onto the surface of the sheet as the recording medium P of the paper sheet by the ejection head 12A, the recording medium P is reversed by a mechanism that reverses the recording medium P. The configuration may be such that water-based ink is ejected to the back surface of the recording medium P by the ejection head 12A again.

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

  In the recording apparatus 100, the method of ejecting aqueous ink onto a roll-shaped recording medium P (so-called continuous paper) and recording an image after drying has been described. A system may be used in which an image is recorded by discharging ink and drying.

  It is needless to say that the above-described embodiment is not limited to the embodiment and is realized within a range satisfying the requirements of the present invention.

  EXAMPLES 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 Corporation, particle size 120 nm, glass transition temperature 40 ° C.): 2% by mass (solid content)
・ Glycerin: 10% by mass
・ Diethylene glycol: 10% by mass
Surfactant (Olfin E1010, manufactured by Nissin Chemical Industry Co., Ltd.): 0.5% by mass
Surfactant (Surfinol 104PG-50, manufactured by Nissin Chemical Industry): 0.5% by mass
Product: 1% by mass
-Ion-exchange water: remainder After mixing the said composition, it filtered with a 5 micrometer filter, and obtained black ink K1.

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

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

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

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

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

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

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

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

<Preparation of magenta ink M>
(Magenta ink M1-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-Y8)
Instead of carbon black, C.I. I. Yellow inks Y1 to Y8 were obtained in the same manner as the black inks K1 to K8, except that Pigment Yellow 128 was used.

  The coarse particle characteristics (number of coarse particles during concentration, initial number of coarse particles) of each ink are listed in Table 1. Since the inks of the respective colors having the same composition other than the colorant have the same coarse particle characteristics, they are collectively shown.

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

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

  Then, the prepared black aqueous ink was filled in a black ink cartridge of the recording apparatus. The following evaluation was performed using this recording apparatus.

(Evaluation of uneven landing)
Using the above recording apparatus, black ink is ejected from the black ejection head 12KA (600 dpi piezo head (maximum ink droplet amount 11 pl)) on the surface of the recording medium to form a halftone chart with 80% coverage. Then, the halftone chart formed on the surface of the recording medium was dried by the drying drum 14A and the sending drying device 16A.
Next, black ink is ejected from the black ejection head 12KB (600 dpi piezo head (maximum ink droplet amount 11 pl)) onto the back surface of the recording medium dried by recording on the surface of the recording medium, and the halftone with 80% coverage A 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 sending drying device 16B. Thereafter, cooling was performed by the cooling roller 60A.
And the halftone chart formed in the back surface of the recording medium was observed visually, and landing unevenness was evaluated. The evaluation criteria are as follows.
-Evaluation criteria-
G1 (◯): No streaks G2 (Δ): Some streaks G3 (×): Conspicuous streaks G4 (xx): There are streaks due to missing nozzles.

(Evaluation of latency)
Using the above recording apparatus, black ink is ejected from the black ejection head 12KA (600 dpi piezo head (maximum ink droplet amount 11 pl)) on the surface of the recording medium to form a halftone chart with 80% coverage. Then, the halftone chart formed on the surface of the recording medium was dried by the drying drum 14A and the sending drying device 16A.
Next, 5 pl of black ink is ejected from the black ejection head 12 KB (600 dpi piezo head (maximum ink droplet amount 11 pl)) onto the back surface of the recording medium dried by recording on the surface of the recording medium. After a pause of 0.36 seconds from the ink ejection, the landing position deviation when the black ink was next ejected was measured. The ink ejection pause period is adjusted according to the recording speed and the length of the non-ejection portion (the area where no image is formed, that is, the non-image portion) (length in the conveyance direction of the recording medium).
Specifically, when a 1-dot line recorded immediately after recording a solid image is used as a reference, after recording a solid image, 1 dot recorded immediately after a non-image portion of about 12 inches is formed in the conveyance direction of the recording medium. Measure how much the distance from the line (1 dot line recorded after 0.36 second pause) is different from the length of the non-image part corresponding to the pause period of 0.36 second, and land this The amount of positional deviation 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 (×): Deviation amount of landing position exceeds 43μm

(Evaluation of fixability)
Fixability was evaluated as follows.
Using the above recording apparatus, black ink is ejected from the black ejection head 12KA (600 dpi piezo head (maximum ink droplet amount 11 pl)) on the surface of the 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 sending drying device 16A.
Next, NIJ70 paper was placed on a solid chart, a load of 20 N / cm was applied from above, and the ink was slid to measure the density of the ink transferred to the NIJ70 paper.
The evaluation criteria are as follows.
-Evaluation criteria-
G1 (◎): 0.01 or less G2 (◯): 0.01 to 0.02 or less G3 (Δ): 0.02 to less than 0.03 G4 (×): 0.03 or more

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

  The details of each example are listed in Tables 1 to 3 below. In Tables 1 to 4, “Nc1” represents the number of coarse particles during concentration of each ink, and “Ni1” represents the initial number of coarse particles of each ink.

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

10 Image recording units 12A, 12KA, 12YA, 12MA, 12CA Discharge heads 12B, 12KB, 12YB, 12MB, 12CB Discharge heads 14A Dry drum 14B Dry drum 16A Hot air blower 16B Hot air blower 20 Pretreatment unit 20A Supply roll 30 Buffer unit 30A First pass roller 30B Dancer roller 30C Second pass roller 40 Post-processing unit 40A Take-up roll 50 Buffer unit 50A First pass roller 50B Dancer roller 50C Second pass roller 60 Cooling unit 60A Cooling roller 100 Recording device P Recording medium R Conveyance path

Claims (11)

A colorant, polymer particles, and a solvent containing water and an aqueous organic solvent,
The number Nc1 of coarse particles having a particle diameter of 0.5 μm or more in the water-based ink after weight reduction after reducing the mass by 60% by evaporation of the solvent, and the number Ni1 of coarse particles having a particle diameter of 0.5 μm or more in the water-based ink before weight reduction Is a water-based ink satisfying the formula: 1 ≦ Nc1 / Ni1 ≦ 50.   The water-based ink according to claim 1, wherein the polymer particles have a glass transition temperature of 40 ° C. or higher and 90 ° C. or lower.   The aqueous ink according to claim 1 or 2, further comprising a pigment dispersant containing a pigment as a colorant and having an acid value of 70 mgKOH / g or more and 200 mgKOH / g or less.   A recording apparatus comprising the discharge head for containing the water-based ink according to claim 1 and discharging the water-based ink onto a surface of a recording medium. A first discharge in which the discharge head stores the first water-based ink as the water-based ink according to any one of claims 1 to 3 and discharges the first water-based ink first onto the surface of the recording medium. Head,
5. The apparatus according to claim 4, further comprising: a second discharge head that contains a second water-based ink and discharges the second water-based ink onto the surface of the recording medium after the discharge of the first water-based ink by the first discharge head. The recording device described. A first discharge head that contains a first aqueous ink and discharges the first aqueous ink onto the surface of a recording medium;
A drying device for drying the first water-based ink ejected on the surface of the recording medium by the first ejection head;
The water-based ink according to any one of claims 1 to 3 is accommodated as a second water-based ink, and after the first water-based ink is dried by the drying device, the second water-based ink is placed on the back surface of the recording medium. A second discharge head for discharging;
A recording apparatus. The second discharge head is a third discharge head that contains a third water-based ink as the second water-based ink and discharges the third water-based ink first on the back surface of the recording medium;
7. The apparatus according to claim 6, further comprising: a fourth discharge head that contains a fourth water-based ink and discharges the fourth water-based ink onto the back surface of the recording medium after the third water-based ink is discharged by the third discharge head. The recording device described.   A recording method comprising a discharge step of discharging the water-based ink according to any one of claims 1 to 3 onto a surface of a recording medium by an discharge head. 4. The first ejection of the first water-based ink as the water-based ink according to any one of claims 1 to 3 first on the surface of the recording medium by the first ejection head as the ejection head in the ejection step. Discharge process,
9. The recording method according to claim 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 ejection of the first aqueous ink by the first ejection head. . A first discharge step of discharging the first aqueous ink onto the surface of the recording medium by the first discharge head;
A drying step of drying the first water-based ink ejected on the surface of the recording medium in the first ejection step;
After the first aqueous ink is dried by the drying step, the second ink ejects the aqueous ink according to any one of claims 1 to 3 to the back surface of the recording medium as a second aqueous ink by a second ejection head. A discharge process;
A recording method. The second discharge step is a third discharge step of first discharging a third water-based ink as the second water-based ink onto the back surface of the recording medium by a third discharge head as the second discharge head;
The recording method according to claim 10, further comprising a fourth discharge step of discharging the fourth aqueous ink onto the back surface of the recording medium by the fourth discharge head after the discharge of the third water-based ink by the third discharge head. .