JP2020059275A - Inkjet recording method, and inkjet recording device - Google Patents

Abstract

To provide an inkjet recording method that can record an image while suppressing discharge deflection of ink even when ink containing a pigment is discharged from a recording head in which a plurality of recording element substrates are arranged.SOLUTION: An inkjet recording method records an image on a recording medium using an inkjet recording device that includes a recording head 51 in which a plurality of recording element substrates are arranged, and cleaning means 52 that wipes a discharge port surface. The cleaning means wipes the discharge port surface with a first wiper 53 to which a liquid for head is imparted, and then wipes the discharge port surface in a direction crossing a wiping direction 55 of a first wiper with a second wiper 54.SELECTED DRAWING: Figure 5

Description

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

  2. Description of the Related Art In recent years, an ink jet recording method has been used as a method for recording a business sentence including characters, diagrams, etc. on a recording medium such as plain paper. In such business applications, higher speed recording is required. In order to meet such a demand, a printing apparatus has been proposed which employs a so-called line head in which a plurality of printing element substrates are arranged to extend the array width of the ejection openings to the maximum width of the printing medium. In addition, an inkjet recording apparatus which is supposed to be used for business purposes is required to be able to record an image excellent in color development and robustness (resistance to light, ozone gas, water, etc.). In order to meet such a demand, an ink using a pigment as a coloring material (pigment ink) is often used.

  In order to record a high-quality image by the inkjet recording method, it is important to clean the surface (ejection port surface) of the recording head that ejects ink, on which the ejection port array is formed. A recording head is a device that ejects ink from a minute ejection port and directly applies the ink to a recording medium such as paper, but minute ink droplets (mist, etc.) other than the ink involved in recording are exposed to the atmosphere. It may drift. Minute ink droplets that are not involved in recording may adhere around the ejection openings of the recording head. If such unnecessary ink adheres to the periphery of the ejection port, the ejection direction of the ejected ink droplet may change, that is, the straightness of the ink droplet may be hindered.

  In order to solve such a problem, there is an inkjet recording apparatus that employs a so-called cleaning unit that wipes the ejection port surface of the recording head with a wiping member (wiper) formed of an elastic material such as rubber to remove foreign matter. Proposed. For example, a method of recovering a recording head has been proposed in which the ejection port surface is wiped in both forward and backward directions to suppress ink accumulation (Patent Document 1). Further, it has been proposed to supply a head liquid for cleaning the ejection port surface to perform wiping (Patent Document 2).

JP, 2016-087953, A JP, 2006-205713, A

  The pigment ink is obtained by dispersing a pigment, which is a solid coloring material, in a liquid medium by optionally using a dispersant together. Therefore, once attached to the ejection port surface, the adhered matter of the pigment ink is more difficult to remove by wiping than the adhered matter of the dye ink in which the coloring material is dissolved at the molecular level.

  The present inventors have examined wiping the ejection port surface of the recording head by the recovery method proposed in Japanese Patent Laid-Open No. 2004-242242. As a result, it was found that the adhered matter of the pigment ink could not be sufficiently removed even by wiping, and the pigment ink might be partially adhered to the ejection port surface. Further, it has been found that the fixed portion expands due to repeated wiping, and finally the fixed portion reaches the vicinity of the ejection port and is pulled by the fixed matter, so that the ejection direction of the ink tends to shift. Therefore, the application of the head liquid proposed in Patent Document 2 to the recovery method proposed in Patent Document 1 was also examined. However, even if the head liquid is used, it is not possible to sufficiently remove the adhered matter of the pigment ink.

  In the case of a recording head such as a line head in which multiple recording element substrates are arranged, it is easy for ink droplets to be left unwound on the steps of the joints of adjacent recording element substrates. The fixed part expands. That is, when an ink jet recording apparatus equipped with a recording head having a plurality of recording element substrates mounted thereon is used to record an image by ejecting pigment ink, conventional wiping should sufficiently suppress ink ejection deviation. Was difficult.

  Therefore, an object of the present invention is to print an image while suppressing ink ejection deviation even when ejecting ink containing a pigment from a recording head in which a plurality of recording element substrates are arranged. Another object of the present invention is to provide an inkjet recording method. Another object of the present invention is to provide an inkjet recording apparatus used in the inkjet recording method.

  The above object is achieved by the present invention described below. That is, according to the present invention, a recording head in which a plurality of recording element substrates having a plurality of ejection openings for ejecting an aqueous ink containing a pigment are arranged in a predetermined direction, An inkjet recording method for recording an image on a recording medium using an inkjet recording device comprising: a cleaning unit that wipes a surface of the recording element substrate on which the ejection port array is formed, the cleaning unit including: A step of wiping a surface on which the ejection port array is formed with a first wiper to which a head liquid is applied, and then wiping the surface with the second wiper in a direction intersecting a wiping direction of the first wiper. An inkjet recording method is provided.

  According to the present invention, it is possible to record an image while suppressing the occurrence of ink ejection deviation even when ejecting ink containing a pigment from a recording head in which a plurality of recording element substrates are arranged. A recording method can be provided. Further, according to the present invention, it is possible to provide an inkjet recording apparatus used in the inkjet recording method.

1 is a sectional view showing an embodiment of an inkjet recording device of the present invention. FIG. 3 is a schematic diagram showing an arrangement state of recording element substrates. FIG. 3 is a schematic diagram showing an arrangement state of recording element substrates. FIG. 3 is a schematic diagram showing an arrangement state of recording element substrates. FIG. 3 is a schematic diagram showing an example of a recording head and a cleaning unit that constitute the inkjet recording apparatus of the present invention. FIG. 3 is a schematic diagram showing an example of a positional relationship between a first wiper, a recording head, and a head liquid storage tank. It is a schematic diagram which shows the other example of the recording head and the cleaning means which comprise the inkjet recording device of this invention. FIG. 6 is a schematic diagram showing an example of a line head in which recording element substrates are arranged in an in-line form.

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

<Inkjet recording method>
FIG. 5 is a schematic diagram showing an example of a recording head and a cleaning unit that constitute the inkjet recording apparatus of the present invention. The inkjet recording method of the present invention is a method of recording an image on a recording medium using an inkjet recording apparatus including a recording head 51 and a cleaning unit 52 as shown in FIG. For simplicity, the recording element substrate is omitted in FIG. The recording head 51 is provided with a plurality of recording element substrates having an ejection port array configured by arranging a plurality of ejection ports for ejecting aqueous ink in a predetermined direction. The cleaning unit 52 is a unit that wipes the ejection port surface of the recording element substrate.

The inkjet recording method of the present invention has a wiping step. In the wiping process, first, the cleaning means 52 wipes the ejection port surface with the first wiper 53 to which the head liquid is applied. Thereafter, the ejection surface is wiped by the second wiper 54 in a direction intersecting with the wiping direction 55 of the first wiper (wiping direction 56 of the second wiper). As described above, by wiping with the second wiper, the ink droplets that cannot be completely removed by the wiping with the first wiper, among them, the ink droplets left at the joint (step) between the adjacent recording element substrates are effective. Can be removed selectively. Furthermore, as shown in FIG. 5, the second wiper 54 wipes in a direction intersecting the wiping direction 55 of the first wiper. That is, the angle D ₁ formed by the wiping direction 55 of the first wiper and the wiping direction 56 of the second wiper is more than 0 °.

  If the ejection port surface is wiped with only the first wiper, the ink is likely to be left behind on the step between the connecting portions of the adjacent recording element substrates. Further, the adhered matter spreads from the leftover ink to the vicinity of the ejection port, and ejection deviation easily occurs. Also, when wiping with the second wiper in a direction that does not intersect the wiping direction of the first wiper, the ink left behind in the joint is only stretched in the same or opposite direction and cannot be removed, causing ejection deviation. It will be easier.

In the inkjet recording method of the present invention, after wiping with the first wiper, wiping is performed with the second wiper in a direction intersecting the wiping direction of the first wiper. As a result, the ink left behind in the joint portion can be removed by scooping in different directions. The angle D ₁ between the wiping direction 55 of the first wiper and the wiping direction 56 of the second wiper is preferably 30 ° or more (FIG. 5). By wiping with the second wiper 54 so that the angle D ₁ is 30 ° or more, the ink left behind at the joint can be more effectively scooped and removed.

  The present inventors have found that by wiping with the first wiper to which the head liquid is applied, it is possible to prevent the pigment from sticking to the ejection port surface. The head liquid is supplied to the ink droplets on the ejection port surface by wiping with the first wiper to which the head liquid containing no pigment is applied. It is considered that this stabilizes the dispersed state of the pigment in the ink droplet and suppresses the fixation of the pigment ink. In order to apply the head liquid to the first wiper, for example, the configuration shown in FIG. 6 (a cross-sectional view of the recording head viewed from the lateral direction) can be adopted. That is, the first wiper 63, the recording head 61, and the head liquid storage tank 67 may be arranged so that the first wiper 63 contacts the head liquid storage tank 67 when the preceding wiping is completed. After the preceding wiping is completed, the first wiper 63 comes into contact with the head liquid storage tank 67, so that the head liquid adheres to the front side of the first wiper 63. When the first wiper 63 returns to the position shown in FIG. 6, the back side of the first wiper 63 contacts the recording head 61, so that the head liquid is kept attached to the front side. Then, at a desired timing, the ejection port surface is wiped with the first wiper 63 having the head liquid applied thereto.

  As described above, in the wiping step, the ejection port surface is wiped with the first wiper to which the head liquid is applied. As a result of examination, it was possible to remove the ink left in the joint portion to some extent by wiping with the second wiper after wiping with the first wiper to which the head liquid is not applied. However, since the head liquid was not used, part of the ink was not removed. Then, it was found that the pigment ink that could not be removed adheres to the ejection port surface, and the pigment ink further adheres from the adhered material as a starting point, so that ejection deviation occurs. When wiping with the first wiper to which the head liquid is not applied, the ink droplets are thinly stretched and the water is evaporated, so that the pigment is more easily fixed. Then, from the end of the wiping by the first wiper to the start of the wiping by the second wiper, the pigment ink begins to adhere to the ejection port surface. Since the fixed pigment ink loses fluidity, it cannot be removed even by wiping with the second wiper, and the fixed matter spreads.

(Recording head)
In general, in order to improve the printing speed, it is advantageous to widen the array width of the ejection openings in the print head (i.e. lengthen the ejection opening array). However, it is technically difficult to extend the ejection port array formed on one printing element substrate. Therefore, in the ink jet recording method of the present invention, a recording head in which a plurality of recording element substrates are arranged on the same plane and the ejection port array is substantially extended is used.

  A recording head mounted on an inkjet recording apparatus used in the inkjet recording method of the present invention has a plurality of ejection port arrays configured by arranging a plurality of ejection ports for ejecting a water-based ink containing a pigment in a predetermined direction. The recording element substrate of is arranged. 2 to 4 are schematic diagrams showing an arrangement state of the recording element substrate. As shown in FIG. 2, a plurality of recording element substrates 22 having an ejection port array 21 in which a plurality of ejection ports are arrayed in a predetermined direction are arranged in a direction (vertical direction) orthogonal to the array direction of the ejection ports. The recording head 23 can be used. In addition, as shown in FIG. 3, a plurality of recording element substrates 32 having ejection port arrays 31 may be arranged in a so-called zigzag pattern in the same direction (horizontal direction) as the arrangement direction of ejection ports to form a recording head 33. it can. Further, as shown in FIG. 4, a plurality of recording element substrates 42 having ejection port arrays 41 may be a recording head 43 arranged in a so-called in-line direction in the same direction (transverse direction) as the ejection port array direction. it can. Among them, as shown in FIGS. 3 and 4, a plurality of recording element substrates are arranged in a zigzag pattern or an in-line pattern, and the so-called line head, in which the array width of the ejection openings is extended to the maximum width of the recording medium, is used. Is preferable from the viewpoint of improving.

(Wiping with the first wiper)
The wiping direction of the first wiper is not particularly limited. For example, as shown in FIG. 5, the wiping direction 55 of the first wiper 53 can be a direction intersecting the longitudinal direction of the recording head 51. Further, as shown in FIG. 7, the wiping direction 75 of the first wiper 73 is a direction intersecting the lateral direction of the recording head 71, and the wiping direction 76 of the second wiper 74 is a direction intersecting the longitudinal direction of the recording head 71. Can also be For simplicity, the recording element substrate is omitted in FIG.

Among them, as shown in FIG. 5, it is preferable to wipe the ejection port surface with the first wiper 53 in a direction intersecting the longitudinal direction of the recording head 51. As shown in FIG. 7, when the wiping direction 75 of the first wiper is a direction intersecting the lateral direction of the recording head 71, the moving distance of the first wiper 73 is long, so that the head liquid application amount is uneven. It is easy to become. On the other hand, as shown in FIG. 5, when the wiping direction 55 of the first wiper is a direction intersecting the longitudinal direction of the recording head 51, the moving distance of the first wiper is short, so that the head liquid is more evenly distributed. It is suitable because it is easily applied. Further, it is preferable that the angle D ₂ formed by the wiping direction 55 of the first wiper and the longitudinal direction of the recording head 51 is 45 ° or more because the moving distance of the first wiper 53 becomes shorter.

  It is preferable that the first wiper is a blade-shaped wiper because it is easy to apply the head liquid. Further, it is preferable that the blade-shaped first wiper is brought into sliding contact with the ejection port surface for wiping. Examples of the material of the first wiper include a rubber material (urethane rubber) formed of urethane resin.

(Wiping with the second wiper)
Similar to the first wiper, a blade-shaped wiper can be used as the second wiper, and it is preferable that the blade-shaped second wiper is brought into sliding contact with the ejection port surface for wiping. Examples of the material of the second wiper include a rubber material (urethane rubber) formed of urethane resin. Further, the second wiper is preferably a suction wiper that sucks and wipes the ejection port surface. By sucking and wiping the ejection port surface with the suction wiper, it is possible to more efficiently scoop and remove the ink droplets left at the joint between the adjacent recording element substrates. Examples of the suction wiper for sucking and wiping the discharge port surface include, for example, a wipe unit having a suction nozzle for sucking and cleaning the discharge port surface, which is disclosed in Japanese Patent Laid-Open No. 2012-166374. it can. In this case, the suction nozzle can be shaped like a prism and its sidewall can be used as a blade-shaped wiper.

(Inkjet recording device)
FIG. 1 is a sectional view showing an embodiment of the inkjet recording apparatus of the present invention. In FIG. 1, x indicates the horizontal direction, y indicates the arrangement direction (depth direction) of the ejection openings of the recording head 8, and z indicates the vertical direction. The inkjet recording apparatus 1 of the embodiment shown in FIG. 1 is in a so-called standby state in which neither recording operation nor reading operation is performed.

  The inkjet recording apparatus 1 shown in FIG. 1 is a multi-function peripheral including a recording unit 2 and a scanner unit 3 and executes various processes relating to a recording operation and a reading operation individually or in cooperation with the recording unit 2 and the scanner unit 3. To do. The scanner unit 3 reads (scans) a document. The inkjet recording apparatus of the present invention may not have the scanner unit.

  In the recording unit 2, a first cassette 5A and a second cassette 5B for accommodating a cut sheet-shaped recording medium are detachably installed at the bottom of the housing 4 in the vertical direction. The first cassette 5A accommodates relatively small recording media up to A4 size in a flat stack. The second cassette 5B accommodates relatively large recording media up to A3 size in a flat stack. In the vicinity of the first cassette 5A, a first feeding unit 6A that separates and feeds the contained recording media one by one is provided. Similarly, a second feeding unit 6B is provided near the second cassette 5B. When the recording operation is performed, the recording medium is selectively fed from one of the cassettes.

  The transport roller 7, the discharge roller 12, the pinch roller 7a, the spur 7b, the guide 18, the inner guide 19, and the flapper 11 are transport mechanisms for guiding the recording medium in a predetermined direction. The transport roller 7 is a drive roller that is arranged on the upstream side and the downstream side of the recording head 8 and is driven by a transport motor (not shown). The pinch roller 7a is a driven roller that nips and rotates the recording medium together with the transport roller 7. The discharge roller 12 is a drive roller that is arranged on the downstream side of the transport roller 7 and is driven by a transport motor (not shown). The spur 7b nips and conveys the recording medium together with the conveying roller 7 and the discharge roller 12 arranged on the downstream side of the recording head 8.

  The guide 18 is provided on the conveyance path of the recording medium and guides the recording medium in a predetermined direction. The inner guide 19 is a member extending in the y direction and has a curved side surface, and guides the recording medium along the side surface. The flapper 11 is a member for switching the direction in which the recording medium is conveyed during the double-sided recording operation. The discharge tray 13 is a tray for stacking and holding the recording medium discharged by the discharge roller 12 after the recording operation is completed.

  The recording head 8 is a full-line type recording head, and a plurality of ejection openings for ejecting ink according to the recording data are arranged in a range that covers the width of the recording medium along the y direction. When the recording head 8 is at the standby position, the ejection port surface 8a of the recording head 8 is capped by the cap unit 10 as shown in FIG. When performing the recording operation, the orientation of the recording head 8 is changed so that the ejection port surface 8 a faces the platen 9. The platen 9 is composed of a flat plate extending in the y direction, and supports the recording medium from the back surface when the recording operation is performed by the recording head 8.

  The ink tank unit 14 contains four kinds of ink to be supplied to the recording head 8, respectively. The ink supply unit 15 is provided in the middle of the flow path connecting the ink tank unit 14 and the recording head 8, and adjusts the flow rate of the ink to the recording head 8 within an appropriate range. The maintenance unit 16 includes a cap unit 10 and a wiping unit 17, which are operated at a predetermined timing to perform a maintenance operation of the recording head 8.

  When the inkjet recording apparatus shown in FIG. 1 is used, first, the recording medium housed in the first cassette 5A or the second cassette 5B is conveyed in the apparatus, and the recording head 8 of the recording unit 2 records an image. The recording medium on which the image has been recorded is discharged to the discharge tray 13 with the surface on which the image is recorded (immediately before discharging) facing downward in the direction of gravity, that is, in the state of being turned upside down.

(Water-based ink)
The ink used in the inkjet recording method of the present invention is a water-based inkjet ink containing a pigment as a coloring material. Hereinafter, each component used in the ink will be described in detail.

[Pigment]
The coloring material contained in the ink is a pigment. The content (% by mass) of the pigment in the ink is preferably 0.5% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. Is more preferable.

  Specific examples of the pigment include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine and perinone.

  As a method for dispersing the pigment, a resin dispersed pigment using a resin as a dispersant, a self-dispersed pigment having a hydrophilic group bonded to the particle surface of the pigment, or the like can be used. Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, a microcapsule pigment in which the particle surface of the pigment is coated with a resin, or the like can be used.

  As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of the anionic group. As the resin dispersant, it is possible to use the resins described below, especially water-soluble resins. The content (% by mass) of the pigment in the ink is preferably 0.3 times or more and 10.0 times or less in terms of a mass ratio with respect to the content (% by mass) of the resin dispersant.

  As the self-dispersion pigment, one in which an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group is bonded directly to the particle surface of the pigment or through another atomic group (-R-) is used. be able to. The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be in a partially dissociated state or in a completely dissociated state. When the anionic group is a salt type, examples of the cation serving as a counter ion include an alkali metal cation, ammonium, organic ammonium and the like. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group and a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group. Group; ester group; ether group and the like. Moreover, the group which combined these groups may be sufficient.

[resin]
The ink may contain a resin. The content (% by mass) of the resin in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink. Is more preferable.

  The resin can be added to the ink to stabilize the dispersed state of the pigment (i), that is, as a resin dispersant or an auxiliary agent thereof. Further, (ii) it can be added to the ink in order to improve various characteristics of the recorded image. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium or resin particles that are dispersed in the aqueous medium. The resin particles do not need to include the coloring material.

In the present specification, "the resin is water-soluble" means that when the resin is neutralized with an acid equivalent to an alkali, the resin is aqueous in a state in which particles whose particle size can be measured by a dynamic light scattering method are not formed. Means being present in the medium. Whether or not the resin is water-soluble can be determined according to the method described below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali having an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by the dynamic light scattering method and no particle having the particle size is measured, it can be determined that the resin is water-soluble. The measurement conditions at this time can be set as follows, for example.
[Measurement condition]
SetZero: 30 seconds Number of measurements: 3 times Measurement time: 180 seconds

  As the particle size distribution measuring device, a particle size analyzer by a dynamic light scattering method (for example, trade name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring device and measuring conditions used are not limited to the above.

  The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 mgKOH / g or less. The acid value of the resin forming the resin particles is preferably 5 mgKOH / g or more and 100 mgKOH / g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. The weight average molecular weight of the resin forming the resin particles is preferably 1,000 or more and 2,000,000 or less. The volume average particle diameter of the resin particles measured by the dynamic light scattering method is preferably 50 nm or more and 500 nm or less.

  Examples of the resin include acrylic resin, urethane resin, and olefin resin. Among them, acrylic resins and urethane resins are preferable, and acrylic resins composed of a unit derived from (meth) acrylic acid or (meth) acrylate are more preferable.

  The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit as constituent units.

  The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, and other acidic monomers having a carboxylic acid group, and anions such as anhydrides and salts of these acidic monomers. And the like. Examples of the cation that constitutes the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium and organic ammonium. The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; methyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylic acid 2 Examples thereof include (meth) acrylic acid ester-based monomers such as ethylhexyl.

  Above all, an acrylic resin having a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth) acrylic acid ester-based monomer is preferable. In particular, an acrylic resin having a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from at least one of styrene and α-methylstyrene is preferable. Since these acrylic resins easily interact with the pigment, they can be suitably used as a resin dispersant for dispersing the pigment.

  The urethane resin can be obtained, for example, by reacting polyisocyanate and polyol. In addition, a chain extender may be further reacted. Examples of the olefin resin include polyethylene and polypropylene.

[Aqueous medium]
The ink used in the inkjet recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent (first water-soluble organic solvent described later). Deionized water or ion-exchanged water is preferably used as water. The content (% by mass) of water in the aqueous ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The content (mass%) of the first water-soluble organic solvent in the water-based ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink. As the first water-soluble organic solvent, any of those usable for ink jet inks such as alcohols, (poly) alkylene glycols, glycol ethers, nitrogen-containing compounds and sulfur-containing compounds can be used. . The first water-soluble organic solvent is preferably a mixture containing a water-soluble organic solvent having a lower dielectric constant than glycerin and glycerin.

[Other additives]
In addition to the above-mentioned components, the ink may contain various agents such as a defoaming agent, a surfactant, a pH adjusting agent, a viscosity adjusting agent, an anticorrosive agent, an antiseptic agent, an antifungal agent, an antioxidant and a reduction inhibitor. The additive may be included. In general, these additives have a considerably low content in the ink and have little direct effect on the fixation of the pigment ink on the ejection port surface. Therefore, in the present invention, these additives are not included in the "water-soluble organic solvent", and are not included in the calculation of the relative dielectric constant.

(Head liquid)
The head liquid applied to the first wiper preferably contains a water-soluble organic solvent (second water-soluble organic solvent). By using the head liquid containing the second water-soluble organic solvent, it is possible to more effectively avoid the decrease in the fluidity of the ink on the ejection port surface of the recording head. As the second water-soluble organic solvent, similar to the first water-soluble organic solvent, used for inkjet inks such as alcohols, (poly) alkylene glycols, glycol ethers, nitrogen-containing compounds and sulfur-containing compounds Any possible one can be used. Above all, it is preferable to use a water-soluble organic solvent having hydrophilicity equal to or higher than that of the first water-soluble organic solvent used for the ink, and it is more preferable to use glycerin because of its high relative dielectric constant. By using, as the second water-soluble organic solvent, a water-soluble organic solvent having hydrophilicity equal to or higher than that of the first water-soluble organic solvent, it is possible to further stabilize the dispersion state of the pigment in the ink droplet.

It can be said that a water-soluble organic solvent having a higher relative dielectric constant has a higher hydrophilicity. Therefore, the relative permittivity ε _h of the second water-soluble organic solvent contained in the head liquid and the relative permittivity ε _i of the first water-soluble organic solvent contained in the ink are such that ε _h ≧ ε _i It is preferable to satisfy the relationship. Each of ε _h and ε _i is preferably 25.0 or more and 45.0 or less.

When a plurality of types of water-soluble organic solvents are contained in the head liquid or ink, the whole of them is regarded as “(first or second) water-soluble organic solvent”, and the water in the head liquid or ink is treated. The relative dielectric constant of the organic solvent is calculated by a so-called weighted average method. For example, in the case of a liquid containing 30.0 parts by mass of a water-soluble organic solvent having a relative dielectric constant of 40.0 and 20.0 parts of a water-soluble organic solvent having a relative dielectric constant of 20.0, The relative permittivity can be calculated by the following formula.
(40.0 × 30.0 + 20.0 × 20.0) / (30.0 + 20.0) = 32.0

  As the water-soluble organic solvent contained in the water-based inkjet ink, one having a vapor pressure lower than that of water is usually used in consideration of reliability such as clogging of the ejection port. Therefore, evaporation of water from the ink droplets is progressing on the ejection port surface, and most of the liquid medium is a water-soluble organic solvent. Therefore, in the present invention, it is not necessary to consider the relative permittivity of water when calculating the relative permittivity. Similar to the ink, the relative permittivity of water is not considered for the head liquid.

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

Examples of the water-soluble organic solvent that is commonly used for water-based inks and is solid at 25 ° C. include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol having a number average molecular weight of 1,000. be able to. Here, the reason for obtaining the relative permittivity of the water-soluble organic solvent that is solid at 25 ° C. from the relative permittivity of the 50 mass% aqueous solution is as follows. Among the water-soluble organic solvents that are solid at 25 ° C., it is difficult to prepare a high-concentration aqueous solution having a concentration of more than 50% by mass, which may be a constituent component of the aqueous ink. On the other hand, in a low-concentration aqueous solution such as 10% by mass or less, the relative permittivity of water is dominant, and a reliable (effective) value of the relative permittivity of the water-soluble organic solvent cannot be obtained. Therefore, as a result of the investigations by the present inventors, it was possible to prepare an aqueous solution to be measured with most of the water-soluble organic solvents that are solid at 25 ° C. It has been found that the relative permittivity obtained also matches the effect of the present invention. For this reason, it was decided to use a 50 mass% aqueous solution. For a water-soluble organic solvent that is solid at 25 ° C and cannot be prepared as a 50% by mass aqueous solution due to its low solubility in water, use a saturated aqueous solution to calculate ε _sol and calculate according to the above The value of the relative dielectric constant is used for convenience.

  Water-soluble organic solvents that can be used in the ink and the head liquid include methyl alcohol (33.1), ethyl alcohol (23.8), n-propyl alcohol, isopropyl alcohol (18.3), n-butyl. Monohydric alcohols having 1 to 4 carbon atoms such as alcohol, sec-butyl alcohol and tert-butyl alcohol; 1,2-propanediol (28.8), 1,3-butanediol (30.0), 1, 4-butanediol (31.1), 1,5-pentanediol (27.0), 1,2-hexanediol (14.8), 1,6-hexanediol (7.1), 2-methyl- Dihydric alcohols such as 1,3-propanediol and 3-methyl-1,5-pentanediol (23.9); 1,2,6-hexanetriol ( 8.5), glycerin (42.3), trimethylolpropane (33.7), trimethylolethane and other polyhydric alcohols; ethylene glycol (40.4), diethylene glycol (31.7), triethylene glycol ( 22.7), alkylene glycols such as tetraethylene glycol, butylene glycol, hexylene glycol and thiodiglycol; diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether (9.8). ) And other glycol ethers; polyethylene glycol having a number average molecular weight of 600 (11.5), polyethylene glycol having a number average molecular weight of 1,000 (4.6), polypropylene glycol Polyalkylene glycols having a number average molecular weight of 200 to 1,000 such as; 2-pyrrolidone (28.8), N-methyl-2-pyrrolidone (32.0), 1,3-dimethyl-2-imidazolidinone , N-methylmorpholine, urea (110.3), ethyleneurea (49.7), triethanolamine (31.9) and other nitrogen-containing compounds; dimethyl sulfoxide (48.9), bis (2-hydroxyethyl) Sulfur-containing compounds such as sulfone); and the like. The numerical value in parentheses attached to the above water-soluble organic solvent is the relative dielectric constant of each water-soluble organic solvent at 25 ° C. As the water-soluble organic solvent, one having a vapor pressure at 25 ° C. lower than that of water is preferably used.

[Aqueous medium]
The head liquid used in the inkjet recording method of the present invention is preferably an aqueous liquid containing water as an aqueous medium. Suitably, the head liquid contains an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent (second water-soluble organic solvent). Deionized water or ion-exchanged water is preferably used as water. The content (% by mass) of water in the head liquid is preferably 1.0% by mass or more and 30.0% by mass or less based on the total mass of the head liquid. The content (mass%) of the second water-soluble organic solvent in the head liquid is preferably 70.0 mass% or more and 99.0 mass% or less based on the total mass of the head liquid.

[Other additives]
In addition to the above components, if necessary, in addition to the above components for the head liquid, a defoaming agent, a surfactant, a pH adjusting agent, a viscosity adjusting agent, an anticorrosive agent, an antiseptic agent, an antifungal agent, an antioxidant, a reduction inhibitor. Various additives may be contained. Generally, these additives have a considerably small content in the head liquid, and have little direct influence on the dispersed state of the pigment on the ejection port surface. Therefore, in the present invention, these additives are not included in the "water-soluble organic solvent", and are not included in the calculation of the relative dielectric constant. Since the head liquid is preferably colorless and transparent, it is preferable that the head liquid does not contain a coloring material.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. Regarding the component amounts, those described as “part” and “%” are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
A styrene / acrylic acid copolymer (composition (molar) ratio = 33: 67), which is a water-soluble resin, is neutralized with potassium hydroxide having an equimolar acid value and dissolved in ion-exchanged water to obtain a resin (solid content). An aqueous solution of a resin dispersant having a content of 2) of 20.0% was prepared. This water-soluble resin has a weight average molecular weight of 10,000 and an acid value of 200 mgKOH / g. A mixture of 15.0 parts of pigment (CI Pigment Red 122), 30.0 parts of an aqueous solution of a resin dispersant, and 55.0 parts of water was placed in a sand grinder and dispersed for 1 hour, followed by centrifugation. To remove coarse particles. After pressure filtration with a micro filter (manufactured by FUJIFILM) having a pore size of 3.0 μm, an appropriate amount of ion-exchanged water was added to obtain a pigment dispersion liquid 1. The pigment dispersion liquid 1 thus obtained had a pigment content of 10.0% and a resin dispersant content of 3.0%.

(Pigment dispersion 2)
The pigment is C.I. I. Pigment Dispersion Liquid 2 having a pigment content of 10.0% and a resin dispersant content of 6.0% are obtained by the same procedure as that for the Pigment Dispersion Liquid 1 described above except that the pigment dispersion liquid is changed to Pigment Yellow 74. It was

(Pigment dispersion 3)
The pigment is C.I. I. Pigment Blue 15: 3, except that the procedure is the same as that for Pigment Dispersion Liquid 1 described above, and Pigment Dispersion Liquid 3 has a pigment content of 10.0% and a resin dispersant content of 6.0%. Got

(Pigment dispersion 4)
20.0 g of carbon black, 10 mmol of 4-aminophthalic acid, and 200 mL of pure water were placed in a Silverson mixer and mixed for 30 minutes at room temperature and 6,000 rpm to obtain a mixture. To the obtained mixture, potassium nitrite (equimolar with 4-aminophthalic acid) dissolved in a small amount of water was slowly added and mixed. By this mixing, the temperature of the mixture reached 60 ° C. After reacting for 1 hour in this state, an aqueous potassium hydroxide solution was added to adjust the pH of the mixture to 10. After 30 minutes, 20 mL of pure water was added, and diafiltration was performed using a spectrum membrane to obtain a self-dispersion pigment. Water was added to the obtained self-dispersion pigment to obtain Pigment Dispersion Liquid 4 having a pigment content of 10.0%.

(Dye aqueous solution 1)
C. I. A 10.0% aqueous solution of Acid Red 249 was used as a dye aqueous solution 1.

<Preparation of ink>
The respective components (unit:%) shown in Table 1 were mixed, sufficiently stirred, and then pressure-filtered with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each ink. In Table 1, "acetylenol E100" is a trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The number average molecular weight of polyethylene glycol was 1,000. The numerical value in parentheses attached to the water-soluble organic solvent in Table 1 is the relative dielectric constant of the water-soluble organic solvent. The lower part of Table 1 shows the relative dielectric constant ε _i of the water-soluble organic solvent in the ink. The pH of the ink was adjusted using a 1 mol / L potassium hydroxide aqueous solution (indicated in Table 1 by including the amount of ion-exchanged water used).

<Preparation of head liquid>
The components shown in Table 2 (unit:%) were mixed and sufficiently stirred to prepare each head liquid. The number average molecular weight of polyethylene glycol was 1,000. The lower part of Table 2 shows the relative dielectric constant ε _h of the water-soluble organic solvent in the head liquid.

<Structure of recording head>
A recording head of the type that applies thermal energy to eject ink was prepared. The recording element substrate that constitutes the recording head has an ejection port array formed by arranging 512 ejection ports at an array density of 600 dpi. The mass of the ink droplet ejected from one ejection port is 4 ng. In the print head, as shown in FIG. 8, a plurality of print element substrates 92 are arranged in an inline form so that the end portions of adjacent print element substrates 92 overlap each other in the arrangement direction of the ejection ports to form a connecting portion. This is the line head 93. A single color ejection port array 91 is formed on the recording element substrate 92.

<Cleaning conditions>
Table 3 shows the cleaning conditions (conditions 1 to 8). The first wiper is capable of wiping the ejection port surface with the head liquid applied. The material of the “blade wiper” in Table 3 is urethane resin, and the thickness is 0.5 mm. The “suction wiper” in Table 3 is a wipe having a suction nozzle (side wall is blade-shaped) having the configuration shown in FIG. 9 of JP 2012-166374 A for suctioning and cleaning the discharge port surface. A unit was used.

<Evaluation>
(Discharged)
The inkjet recording device (FIG. 1) prepared according to the evaluation conditions shown in Table 4 was used. This inkjet recording apparatus is an apparatus in which a recording head is fixed to the apparatus and an image is recorded by one relative scanning of the recording head and the recording medium. After filling each of the prepared inks into the ink containing portion, the inks were sent to the recording head using a pump. In this embodiment, the print duty of an image printed under the condition that four 4 ng ink droplets are applied to a unit area of 1/600 inch × 1/600 inch is defined as 100%. The recording medium is conveyed at a speed of 8 inches / second, and a solid image measuring 18 cm in the longitudinal direction of the recording head × 2 cm in the paper feed direction and a pattern (nozzle check pattern) for confirming the ejection state from each ejection port are recorded. did.

  In addition, 30,000 images were recorded under the condition that cleaning is performed once for each image recorded. That is, cleaning was performed 30,000 times. As the recording medium, glossy paper (trade name "Glossy Gold GL-101", manufactured by Canon Inc.) was used. The recording conditions were a temperature of 15 ° C. and a relative humidity of 10%.

After recording 30,000 images (cleaning 30,000 times), the recorded nozzle check pattern was visually confirmed, and the discharge deviation was evaluated according to the following evaluation criteria. In the evaluation criteria shown below, "AA", "A", and "B" were set to acceptable levels, and "C" was set to an unacceptable level. Table 4 shows the evaluation results.
AA: Ink was normally ejected from all ejection ports.
A: Distortion occurred at the ejection openings of more than 0% and less than 5%.
B: Distortion occurred at 5% or more and less than 10% of the discharge ports.
C: Distortion occurred at 10% or more of the discharge ports.

1: Inkjet recording device 2: Recording unit 5A: First cassette 5B: Second cassette 7: Conveying roller 8: Recording head 13: Ejection tray 18: Guide 51: Recording head 52: Cleaning means 53: First wiper 54: First 2 wiper 55: wiping direction of first wiper 56: wiping direction of second wiper

Claims (8)

A recording head in which a plurality of recording element substrates each having a plurality of ejection openings for ejecting an aqueous ink containing a pigment are arranged in a predetermined direction, and the ejection openings of the recording element board. An inkjet recording method for recording an image on a recording medium using an inkjet recording device comprising: a cleaning unit that wipes a surface on which a row is formed,
A step of wiping the surface on which the ejection port array is formed by the cleaning means with a first wiper to which the head liquid is applied, and then wiping with a second wiper in a direction intersecting the wiping direction of the first wiper. An ink jet recording method comprising:   The inkjet recording method according to claim 1, wherein the first wiper wipes a surface on which the ejection port array is formed in a direction intersecting a longitudinal direction of the recording head. The water-based ink contains a first water-soluble organic solvent, the head liquid contains a second water-soluble organic solvent,
The inkjet recording according to claim 1 or 2, wherein a relative dielectric constant ε _h of the second water-soluble organic solvent and a relative dielectric constant ε _i of the first water-soluble organic solvent satisfy a relation of ε _h ≧ ε _i. Method.   The inkjet recording method according to claim 1, wherein the first wiper is a blade-shaped wiper.   The inkjet recording method according to claim 1, wherein the second wiper is a blade-shaped wiper.   The inkjet recording method according to claim 1, wherein the second wiper is a suction wiper that sucks and wipes a surface on which the ejection port array is formed.   The inkjet recording method according to claim 1, wherein the recording head is a line head. An inkjet recording apparatus used in the inkjet recording method according to claim 1,
A recording head in which a plurality of recording element substrates each having a plurality of ejection openings for ejecting an aqueous ink containing a pigment are arranged in a predetermined direction, and the ejection openings of the recording element board. Cleaning means for wiping the surface on which the rows are formed,
The cleaning means wipes the surface on which the ejection port array is formed with a first wiper to which the head liquid is applied, and then wipes the surface with the second wiper in a direction intersecting the wiping direction of the first wiper. An inkjet recording apparatus characterized by the following.

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