JP7187231B2 - Inkjet recording method and inkjet recording apparatus - Google Patents

Description

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

2. Description of the Related Art In recent years, inkjet recording apparatuses are increasingly being used in the fields of commercial printing and office printing. In the fields of commercial printing and office printing, miniaturization of inkjet recording apparatuses is required. In order to reduce the size of the apparatus, it has been studied to shorten the conveying distance of the recording medium by using a recording head in which the ejection port surface of the recording head is arranged at an angle with respect to the direction of gravity (see Patent Document 1). ). Furthermore, the use of a plurality of printheads corresponding to a plurality of inks such as cyan, magenta, yellow, and black is being studied (see Japanese Patent Application Laid-Open No. 2002-200013).

JP-A-2005-342982

In order to reduce the size of the apparatus, the present inventors have proposed using a print head having a plurality of ejection port arrays for ejecting a plurality of inks instead of using a plurality of print heads corresponding to a plurality of inks. did. Investigation was carried out using a print head having a plurality of ejection port arrays for ejecting a plurality of inks while the ejection port surface of the print head is inclined with respect to the direction of gravity. As a result, it has been found that when ink is ejected from the recording head and the ink adhering to the ejection port surface is removed by a cleaning member, color mixture may occur in the image to be recorded thereafter.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing mixed colors of an image even if ink adhering to an orifice surface inclined with respect to the direction of gravity and having a plurality of orifice arrays for ejecting a plurality of inks is removed by a cleaning member. An object of the present invention is to provide an ink jet recording method capable of suppressing the Another object of the present invention is to provide an inkjet recording apparatus using the inkjet recording method.

In the present invention, a first ink and a second ink, which are water-based inks containing a pigment; a recording head arranged adjacent to each other in order from the top to the bottom, and arranged such that at least a part of the first ejection port array and the second ejection port array overlap in the conveying direction of the recording medium; An inkjet recording method using an inkjet recording apparatus comprising a cleaning member for cleaning an ejection port surface on which the first ejection port array and the second ejection port array are formed, wherein a recording step of recording an image on a recording medium by ejecting the water-based ink from the recording head arranged to form an angle of 0° or more and less than 90°; and a cleaning step of cleaning the ejection port surface. The second ink contains a resin, and the content (% by mass) of the resin in the second ink is 0.5% by mass or more and 10.0% by mass based on the total mass of the ink. % by mass or less, and the content of the resin in the second ink is higher than the content of the resin in the first ink.

Further, according to the present invention, a first ink and a second ink, which are water-based inks containing a pigment; a recording head arranged adjacent to the bottom in order from the bottom, and arranged so that at least a part of the first ejection port array and the second ejection port array overlap in the conveying direction of the recording medium; An inkjet recording apparatus comprising: a cleaning member for cleaning an ejection port surface of a head on which the first ejection port array and the second ejection port array are formed, wherein an angle between the ejection port surface and the direction of gravity is 0. The water-based ink is ejected from the recording head arranged so as to be at an angle of 90° or more to record an image on a recording medium, the ejection port surface is cleaned, and the second ink is a resin. and the content (% by mass) of the resin in the second ink is 0.5% by mass or more and 10.0% by mass or less based on the total mass of the ink, and The present invention relates to an inkjet recording apparatus, wherein the content of the resin is greater than the content of the resin in the first ink.

According to the present invention, even if the cleaning member removes the ink adhering to the ejection port surface having a plurality of ejection port arrays for ejecting a plurality of inks, the color mixture of the image is suppressed. It is possible to provide an inkjet recording method and an inkjet recording apparatus that can

3A and 3B are diagrams showing the relationship between the ejection port surface of the recording head and the direction of gravity, FIG. is about 45°, and (c) is a view showing the case where the angle formed is 0°. 1A and 1B are diagrams schematically showing an example of a recording head, FIG. 1A being a schematic diagram of a recording element substrate, and FIG. 1B being a perspective view of the recording head; 1A and 1B are diagrams schematically showing an example of a line head, in which (a) is a schematic diagram of a line head in which recording element substrates are arranged in a zigzag pattern (non-adjacent arrangement) in the arrangement direction of a plurality of ejection port arrays; 1 is a schematic diagram of a line head in which recording element substrates are linearly arranged (adjacently arranged). FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of an inkjet recording device typically, (a) is sectional drawing of the whole apparatus, (b) is an enlarged view of the periphery of a recording head. It is a sectional view showing an example of a cleaning device typically.

Hereinafter, embodiments of the present invention will be described in detail. In the present invention, hereinafter, water-based ink may be referred to as "ink". Various physical property values are values at a temperature of 25° C. unless otherwise specified. "(Meth)acrylic acid" and "(meth)acrylate" shall mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

1A and 1B are diagrams showing the relationship between the ejection port surface of the print head and the direction of gravity. FIG. is a diagram showing the case where the angle formed is approximately 45°, and (c) is a diagram showing the case where the formed angle is 0°. In FIG. 1, .theta. indicates the angle formed by the ejection port surface 8a of the recording head 8 and the direction of gravity (arrow G in FIG. 1). In a general inkjet recording method, as shown in FIG. 1A, from a recording head in which the angle between the ejection port surface of the recording head and the direction of gravity is 90°, that is, the ejection port surface is substantially perpendicular to the direction of gravity. An image is recorded by ejecting ink. However, in the ink jet recording method of the present invention, the angle between the ejection port surface of the recording head and the direction of gravity is 0° or more and less than 90°, that is, the ejection port surface is arranged at an angle with respect to the direction of gravity. Eject to record an image. As shown in FIG. 1C, the angle formed by the ejection port surface of the recording head and the direction of gravity may be 0°, that is, the ejection port surface may be substantially horizontal with respect to the direction of gravity.

When repeating image recording by removing ink adhering to an ejection port surface inclined with respect to the direction of gravity and having a plurality of ejection port arrays for ejecting a plurality of inks with a cleaning member, the recording is performed after that. It has been found that color mixing occurs in the resulting image. The reason is as follows.

When an image is printed, small ink droplets (hereinafter referred to as "mist") generated accompanying the main ink droplets increase, and the mist tends to adhere to the periphery of the ejection port. Therefore, the ink to be ejected next may be pulled by the ink adhering to the periphery of the ejection port, and the ink may be ejected unevenly. Therefore, it is necessary to use a cleaning member to remove the ink adhering to the periphery of the ejection port.

When the ink contains a pigment, the pigment agglomerates around the ejection port as the liquid component in the mist adhering around the ejection port evaporates. When the ejection port surface is cleaned to remove the aggregated pigment, the aggregated pigment scrapes the ejection port surface as if it were abrasive by the cleaning member, which tends to cause unevenness around the ejection port. When ink ejection and cleaning are repeated, unevenness is more likely to occur around the ejection port, and ink tends to adhere to the periphery of the ejection port.

The phenomenon that ink tends to adhere to the periphery of the ejection port also occurs in a normal ink jet recording method in which an image is recorded by ejecting ink from a recording head whose ejection port surface is perpendicular to the direction of gravity. In that case, no ink color mixing occurred. Color mixture of inks is a problem that occurs when an image is printed using a print head in which the ejection port surface of the print head is inclined with respect to the direction of gravity.

Here, as an example, as shown in FIG. 1B, description will be made focusing on adjacent ejection port arrays I and II of a print head having an ejection port surface on which four ejection port arrays I to IV are formed. The ejection port groups forming each ejection port array are arranged substantially perpendicular to the conveying direction of the recording medium (arrow A in FIG. 1B). The recording medium is conveyed in the direction of arrow A, and ink is ejected onto the recording medium in the order of ejection port arrays I and II.

When an image is printed using a print head in which the ejection port surface of the print head is tilted with respect to the direction of gravity, the particles adhere toward the direction of the ejection port array I around the ejection ports forming the ejection port array II. A force in the direction of gravity is applied to the ink. As a result, ink tends to accumulate toward the direction of the ejection port array I around the ejection ports that constitute the ejection port array II. When images are printed continuously, ink further accumulates in the direction of the ejection opening array I around the ejection openings forming the ejection opening array II. Then, the meniscus of the ink formed at the ejection openings of the ejection opening array II is destroyed, the ink overflows, and the ink ejected from the ejection opening array II drips along the ejection opening surface. Enter I. As a result, the inks ejected from the ejection port array I are mixed in color, resulting in color mixture in the printed image.

Furthermore, in a print head in which the ejection port array I and the ejection port array II are at least partially overlapped in the print medium conveying direction, the ink ejected from the ejection port array II tends to enter the ejection port array I. . As a result, the inks ejected from the ejection port array I are mixed in color, resulting in color mixture in the printed image.

In order to suppress color mixture in an image, the inventors paid attention to the relationship between the amount of resin in ink ejected from two adjacent ejection port arrays. When the ejection port array that ejects ink with a high resin content is arranged at the top in the direction of gravity, even if the liquid component in the mist adhering to the periphery of the upper ejection port array evaporates, the resin remains around the pigment. will exist. Therefore, aggregation of the pigment is suppressed. Even if the ejection port surface is cleaned, the ejection port surface is less likely to be scraped by the aggregated pigment, so that unevenness is less likely to occur around the ejection port, and ink is less likely to adhere to the periphery of the ejection port. As a result, ink is less likely to enter the lower ejection port array in the direction of gravity, so color mixing of ink is less likely to occur, and color mixing in a printed image can also be suppressed. On the other hand, when the ejection port array that ejects ink with a small resin content is arranged at the top in the direction of gravity, when the liquid component in the mist adhering to the periphery of the upper ejection port array evaporates, the resin surrounds the pigment. Hard to exist. Therefore, aggregation of the pigment is promoted. When the ejection port surface is cleaned, the aggregated pigment tends to scrape the ejection port surface, so that unevenness tends to occur around the ejection port, and ink tends to adhere to the periphery of the ejection port. As a result, since ink tends to enter the lower ejection port array, color mixing of ink becomes severe, and color mixing in a printed image cannot be suppressed. In other words, by locating the ejection port array that ejects ink having a relatively high resin content at the top in the direction of gravity, it is possible to suppress color mixture in the image.

<Inkjet recording method>
In the recording head used in the present invention, the first ejection port array and the second ejection port array for ejecting the first ink and the second ink are arranged adjacent to each other in order from the bottom in the direction of gravity. Furthermore, the resin content in the second ink is greater than the resin content in the first ink. Even when the print head has a plurality of ejection port arrays (third ejection port array and fourth ejection port array), it is possible to satisfy the relationship of the resin content in the ink ejected from each of the adjacent ejection port arrays. preferable. As a result, color mixture in the image can be suppressed.

Also, the first ink and the second ink may have different hues or may have the same hue. If the first ink and the second ink have different hues, the color mixture in the recorded image is likely to be conspicuous. Even in such a case, the configuration of the present invention can suppress the color mixture in the image. The hue of the first ink and the second ink can be selected from black, cyan, magenta, yellow, and the like. In the case of different hues, the first ink and the second ink are preferably a combination of two inks selected from the group consisting of black ink, cyan ink, magenta ink, and yellow ink. When the hues are the same, the first ink and the second ink have a relationship of dark ink and light ink. The combination of the first ink and the second ink is a dark ink having a black hue (black ink), a light ink having a black hue (gray ink), a dark ink having a cyan hue (cyan ink), and a cyan hue. and a dark ink having a magenta hue (magenta ink) and a light ink having a magenta hue (light magenta ink). .

<Inkjet recording device>
2 to 4, the X direction indicates the horizontal direction, the Y direction indicates the depth direction of the inkjet recording apparatus, and the Z direction indicates the vertical direction.

FIGS. 2A and 2B are diagrams schematically showing an example of a printhead, where FIG. 2A is a schematic diagram of a print element substrate, and FIG. 2B is a perspective view of the printhead. The print head has an ejection port surface on which a plurality of ejection port arrays for ejecting a plurality of inks are formed. In particular, as shown in FIG. 2, it is preferable to use a print head having one print element substrate on which a plurality of ejection port arrays are arranged. FIG. 2(a) shows a recording element substrate H1110 having four ejection port arrays (100a to 100d) arranged in the Y direction. The ejection port surface of the printhead is the surface on which the printing element substrate H1110 having the ejection port array is provided. The recording element substrate may have a plurality of ejection port arrays. For example, when one recording element substrate has four ejection port arrays, four types of ink such as cyan, magenta, yellow, and black (CMYK) are ejected from the four ejection port arrays.

The distance (mm) between an ejection port array configured with ejection ports for ejecting a certain ink and an ejection port array configured with ejection ports for ejecting another ink is 0.1 mm or more and 1.5 mm or less. , and more preferably 0.1 mm or more and 1.0 mm or less. More preferably, the distance is 0.3 mm or more and 1.0 mm or less. Here, the distance between the ejection port arrays is the distance between a straight line connecting the centers of the ejection ports that eject a certain ink and a straight line connecting the centers of the ejection ports that eject another ink. That is. When there are a plurality of ejection port arrays that eject one type of ink, the distance between the ejection port arrays refers to the ejection port array that is the closest in the X direction and is composed of ejection ports that eject a certain ink. , is the distance between ejection port arrays composed of ejection ports for ejecting different inks.

If the distance between the ejection port arrays is short, the ejection port arrays can be arranged densely, so that a higher quality image can be printed. The problem of color mixture occurs remarkably. Even in such a case, color mixture of an image can be suppressed by adopting the configuration of the present invention.

The long diameter (μm) passing through the center of the ejection port of the print head is preferably 10 μm or more and 50 μm or less. Furthermore, the ejection amount (ng) per ink droplet ejected from the print head is preferably 8.0 ng or less. If the ejection amount exceeds 8.0 ng, the ink tends to overflow when ejected, and the amount of mist tends to increase. As a result, the inks tend to mix colors, and the color mixing of the image may not be sufficiently suppressed. More preferably, the discharge amount (ng) is 2.0 ng or more.

FIG. 2B shows a print head 8 having one print element substrate H1110. The recording head may have one recording element substrate, or may have a plurality of recording element substrates. When using a print head having a plurality of print element substrates, a print head in which a plurality of print element substrates are arranged along the Y direction in FIG. is preferred. When using a printhead having a plurality of printing element substrates, it is preferable to arrange the plurality of printing element substrates so that the ejection openings overlap in the conveying direction of the printing medium. As a result, although black streaks and white spots can be suppressed in the joints between the recording element substrates, overlapping the ejection ports makes it easy for ink to mix from one ejection port to another. The problem of color mixture in the recorded image remarkably arises. Even in such a case, color mixture of an image can be suppressed by adopting the configuration of the present invention.

3A and 3B are schematic diagrams of a line head. FIG. 3A is a schematic diagram of a line head in which recording element substrates are arranged in a staggered manner (non-adjacent arrangement) in the arrangement direction of a plurality of ejection port rows, and FIG. 3B is a schematic diagram of a line head. 1 is a schematic diagram of a line head in which recording element substrates are linearly arranged (adjacently arranged); FIG. In FIG. 3, a plurality of recording element substrates H1110 are arranged on a support substrate. In order to reduce the size of the apparatus and suppress an increase in the length of the line head in the X direction in FIG. , it is preferable to use line heads arranged adjacently. That is, it is preferable to use a line head in which a plurality of recording element substrates H1110 are arranged linearly. Furthermore, the shape of the recording element substrate may be parallelogram, rectangle, trapezoid, or other shapes, but the parallelogram is preferable.

Methods for ejecting ink include a method of applying mechanical energy to ink, a method of applying thermal energy to ink, and the like. Among them, the method of ejecting ink is preferably a method of applying thermal energy to the ink.

4A and 4B are diagrams schematically showing an example of an inkjet recording apparatus, in which FIG. 4A is a cross-sectional view of the entire apparatus, and FIG. 4B is an enlarged view around the recording head. As shown in FIG. 4, in order to reduce the size of the apparatus, an inkjet printer that can record an image with a single recording head capable of ejecting multiple types of ink instead of recording images with multiple recording heads corresponding to multiple types of ink. A recording device is preferably used. When ink is ejected to record an image, as shown in FIG. 4, the angle formed by the ejection port surface 8a of the recording head 8 and the direction of gravity is 0° or more and less than 90°, and is tilted with respect to the direction of gravity. An image is recorded by ejecting ink from the recording head 8 .

When printing an image by ejecting ink, the difference between the angle between the recording medium S and the direction of gravity and the angle between the ejection port surface 8a of the recording head 8 and the direction of gravity should be ±5° or less. It is preferably 0°, more preferably 0°. That is, the difference between the distance between the ejection openings forming the ejection opening array I and the recording medium S and the distance between the ejection openings forming the ejection opening array IV and the recording medium S is ±1 mm or less. Preferably, it is more preferably 0 mm. Here, the distance between the ejection port and the recording medium S is the distance between the center of the ejection port and the position where the line intersects the recording medium when a line is extended from the center of the ejection port in the direction of gravity. It's about. In this way, by setting the transport direction of the recording medium when recording an image to the above conditions, the transport distance of the recording medium in the X direction is also shortened, and the size of the apparatus can be reduced. In order to shorten the conveying distance of the recording medium in the X direction, the angle formed by the ejection port surface of the recording head and the direction of gravity is preferably 10° or more and 80° or less, and preferably 30° or more and 60° or less. is more preferred.

An ejection port surface 8 a of the recording head 8 faces the platen 9 . In FIG. 4, the plane of the platen 9 is tilted at about 45° with respect to the direction of gravity, and the ejection port surface 8a of the recording head 8 is also tilted at about 45° with respect to the direction of gravity so that the distance from the platen 9 is kept constant. 45° tilted. When the inkjet recording apparatus is not performing a recording operation, the angle formed by the ejection port surface 8a of the recording head 8 and the direction of gravity is 90°.

Further, the conveying path of the recording medium when recording an image will be described. In FIG. 4B, the recording medium S is guided by the first guide 10, and the leading edge position of the recording medium S is detected by the paper sensor 11. As shown in FIG. The recording medium S is conveyed toward a recording area P between the recording head 8 and the platen 9 while being sandwiched between a first conveying roller 12 and a first pinch roller 13 constituted by a spring-biased spur or the like. be. In the print area P, ink is ejected toward the print medium S from a plurality of ejection port arrays (I to IV) of the print head 8 . The back surface of the recording medium S in the area to which ink is applied is supported by the platen 9, and the distance between the ejection port surface 8a and the recording medium S is kept constant. The recording medium S to which ink has been applied is conveyed by being guided by the second guide 16 while being nipped between the second conveying roller 14 and the second pinch roller 15 . The conveying direction of the recording medium when recording an image may be the direction opposite to the direction shown in FIG. 4(b), but is preferably the direction shown in FIG. 4(b). That is, the first ejection port array (ejection port array I) arranged on the upstream side in the recording medium transport direction is the second ejection port array (ejection port array I) disposed on the downstream side in the recording medium transport direction. It is preferably arranged below II) in the direction of gravity. Further, it is preferable that the direction in which the recording medium is conveyed when recording an image is a direction that intersects with the direction in which the ejection port arrays I to IV are arranged.

FIG. 5 is a cross-sectional view schematically showing an example of a cleaning device. This cleaning device has a wiper which is a member for cleaning the ejection port surface 8 a of the recording head 8 . A wiper 17 formed of an elastic member such as rubber is fixed to a wiper holder 18, and the wiper holder 18 moves in the left-right direction in the drawing (a direction intersecting with the arrangement direction of the ejection port arrays I to IV of the recording head). It is possible. As shown in FIG. 5, when the ejection port face is cleaned in the direction intersecting the ejection port arrays I to IV of the print head, the print head is tilted with respect to the direction of gravity. It tends to occur in any direction. As a result, color mixture of ink from one ejection port to another ejection port is likely to occur, so that a problem of color mixture in a printed image remarkably arises. Even in such a case, color mixture of an image can be suppressed by adopting the configuration of the present invention.

The home position is the position where the recording head stands by when no image is recorded. When cleaning the ejection port surface 8a, after moving the recording head 8 to the home position, the wiper holder 18 is moved in the direction of the arrow in FIG. In this case, when the wiper 17 slides against the ejection port surface 8a of the recording head 8, some wipers are bent greatly so that the side portions come into contact with each other, while others are bent slightly so that the tip portion comes into contact with the wiper 17. Some are As a cleaning device, as shown in FIG. 5, a device that wipes the ejection port surface with a wiper or the like, or a device that cleans the ejection port surface by pressing a cloth or a porous member, etc., can be used. Among others, it is preferable to use a device that wipes the discharge port surface with a wiper or the like. It is preferable to perform this cleaning operation at least after the conditions for ink to adhere to the ejection port surface are met. For example, the cleaning operation can be performed at a timing such as after a suction recovery operation performed to eliminate clogging of the ejection port or after printing an image.

In order to suppress variations in the ink ejection amount, it is preferable to preheat the ink before ejecting the ink based on the image data. This preheating is heating by a heating element present in the vicinity of the recording element for ejecting ink. Heating the ink tends to lower the viscosity of the ink, so that the ink ejected from the ejection port tends to drip along the ejection port surface, and the ink tends to mix colors. As a result, the problem of color mixture in the recorded image remarkably arises. Even in such a case, color mixture of an image can be suppressed by adopting the configuration of the present invention.

Furthermore, it is preferable that the ejection port surface of the recording head is water repellent. As a result, the contact angle between the ink adhering to the periphery of the ejection port and the ejection port surface becomes large, so that the ink droplets tend to be grainy. Therefore, it is difficult for the ink to drip along the ejection port surface in the direction of gravity, and color mixture in the image can be further suppressed.

A method of applying a water-repellent material by spraying, a method of attaching a water-repellent material by vacuum deposition or plasma polymerization, or the like can be selected as a method for water-repellent treatment of the ejection port surface. The water repellency of the formed ejection port surface can be specified by measuring the contact angle of water droplets on the surface of the member. When the contact angle of water is 70 degrees or more, it can be said to have water repellency, and the case where the contact angle of water is 90 degrees or more is preferable. The contact angle with water can be measured using pure water (ion-exchanged water) using a general contact angle meter. Examples of such a contact angle meter include an automatic contact angle measuring machine (CA-W, manufactured by Kyowa Interface Science).

As the water-repellent material, for example, a fluororesin compound is preferably used. In particular, it is preferable that the water-repellent surface is formed as a uniform resin film made of a fluororesin compound, and it is preferable that this resin film does not contain a metal such as nickel. Examples of fluororesin compounds include polytetrafluoroethylene resins and fluororesins having a cyclic structure. Specifically, Polyflon PTFE (manufactured by Daikin Industries), Teflon (registered trademark) PTFE (manufactured by DuPont), Cytop (manufactured by Asahi Glass), and the like can be mentioned. Furthermore, other resins containing fluorine atoms, such as fluorinated epoxy resins, fluorinated polyimide resins, fluorinated polyamide resins, fluorinated acrylic resins, fluorinated urethane resins, fluorinated siloxane resins, modified resins thereof, etc. can be used. A compound containing a silicon atom or a silicone-based resin may also be used as the water-repellent material.

Among them, a condensate of a hydrolyzable silane compound having a fluoroalkyl group and a hydrolyzable silane compound having a cationically polymerizable group is used as the water-repellent material, since high water repellency and durability can be obtained. is preferred. A resin obtained by curing this condensate by irradiation with active energy rays such as ultraviolet rays may also be used. These hydrolyzable silane compounds have hydrolyzable groups in their molecular structures. An alkoxy group can be mentioned as a hydrolyzable group. Moreover, a cyclic ether group, a cyclic vinyl ether group, etc. can be mentioned as a cationic polymerizable group.

The inkjet recording apparatus may include means for applying a reaction liquid containing a reaction agent for aggregating the coloring material in the ink to the recording medium. Examples of means for applying the reaction liquid to the recording medium include means for applying the reaction liquid to the recording medium with a roller or the like, and means for ejecting the reaction liquid from an inkjet type recording head. The ink jet recording apparatus of the present invention does not need to be provided with an energy beam irradiation means.

<Ink>
Each component constituting the ink used in the present invention will be described in detail below. The ink used in the present invention may not contain a compound that polymerizes upon exposure to energy rays.

(pigment)
The ink contains pigments. The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 11.0% by mass or less based on the total mass of the ink. is more preferable.

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

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

Of the two adjacent ejection port arrays, the ejection port array that ejects the ink containing carbon black is preferably positioned lower in the direction of gravity. Carbon black has a well-developed structure compared to other pigments. Therefore, when agglomerated carbon black adheres to the periphery of the ejection port, unevenness is likely to occur around the ejection port, and ink tends to adhere. If the ejection port row that ejects the ink containing carbon black is arranged above the two adjacent ejection port rows in the direction of gravity, the ink enters the lower ejection port row in the direction of gravity, resulting in serious color mixing of the inks. Therefore, it may not be possible to sufficiently suppress color mixture in an image. Therefore, by arranging the ejection port array that ejects the ink containing carbon black at the bottom of the two adjacent ejection port arrays in the direction of gravity, even if the ink drips along the ejection port surface, another It is difficult to get into the outlet row. As a result, the inks are less likely to mix colors, and the color mixing of the image can be further suppressed. It is more preferable that the ejection port array for ejecting the ink containing carbon black is positioned at the bottom in the direction of gravity.

(resin)
Among the plurality of inks ejected from each ejection port array (first ejection port array to fourth ejection port array), one type of ink contains a resin. Moreover, it is preferable that each ink among the plurality of inks contains a resin. As a result, aggregation of the pigment can be suppressed around any of the ejection ports, so that the inks are less likely to mix, and the color mixing of the image can be further suppressed.

The resin can be added to the ink for the following reasons: (i) it stabilizes the dispersed state of the pigment, i.e., it serves as a resin dispersant or its auxiliary, and (ii) it improves various characteristics of the recorded image. Forms of the resin include block copolymers, random copolymers, graft copolymers, combinations thereof, and the like. Moreover, the resin may be dissolved in the aqueous medium as a water-soluble resin, or may be dispersed as resin particles in the aqueous medium. The resin particles do not need to contain a coloring material. Among them, the resin is preferably a water-soluble resin.

In the present invention, the resin being water-soluble means that when the resin is neutralized with an alkali equivalent to the acid value, it does not form particles whose particle size can be measured by a dynamic light scattering method. do. 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 acid value equivalent alkali (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10-fold (by volume) 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, it can be determined that the resin is water-soluble if particles having a particle size are not measured. The measurement conditions at this time can be set to, for example, SetZero: 30 seconds, the number of measurements: 3, and the measurement time: 180 seconds. As a particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, UPA-EX150, manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and measurement conditions to be used are not limited to those described above.

Examples of resins include acrylic resins, urethane resins, and olefin resins. Among them, the resin is preferably an acrylic resin.

The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit as structural units. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer of styrene and α-methylstyrene is preferred. Since these resins easily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

A hydrophilic unit is a unit having a hydrophilic group such as an anionic group. A hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having hydrophilic groups include acidic monomers having carboxylic acid groups such as (meth)acrylic acid, itaconic acid, maleic acid and fumaric acid, and anions such as anhydrides and salts of these acidic monomers. organic monomers, and the like. Examples of cations constituting salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium and organic ammonium. A hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. A hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; methyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylic acid 2 - (meth)acrylic acid ester monomers such as ethylhexyl.

The urethane resin can be obtained, for example, by reacting polyisocyanate and polyol. Moreover, what made the chain extension agent further react may be used. Examples of olefinic resins include polyethylene and polypropylene.

The resin is preferably used as a resin dispersant for dispersing the pigment. Whether or not the resin is a resin dispersant can be determined according to the method shown below. First, a liquid obtained by concentrating or diluting the ink so that the solid content in the ink is about 10% by mass is centrifuged at 12,000 rpm for 1 hour. As a result, since the liquid layer contains resin and the like that do not contribute to the dispersion of the pigment, the sedimented component containing the pigment is recovered. At this time, the resin contained as a main component in the sedimentation component containing the pigment is a resin (resin dispersant) that contributes to the dispersion of the pigment, and the resin contained as a main component in the liquid layer is a resin that does not contribute to the dispersion of the pigment. is.

The resin content (% by mass) in the ink is preferably 0.5% by mass or more and 10.0% by mass or less, and 0.5% by mass or more and 8.0% by mass or less, based on the total mass of the ink. More preferably, it is 2.0% by mass or more and 8.0% by mass or less. When a resin dispersant is used as the resin, the content (% by mass) of the coloring material is preferably 2.0 times or more and 10.0 times or less as a mass ratio with respect to the content (% by mass) of the resin dispersant. .

(First water-soluble organic solvent)
The ink preferably contains a first water-soluble organic solvent having a dielectric constant of 20.0 or higher. By suppressing aggregation of the pigment and reducing unevenness around the ejection port, ink is less likely to accumulate around the ejection port, and ink is less likely to drip along the ejection port surface. As a result, it is possible to suppress the color mixture of the inks and further suppress the color mixture of the image. The dielectric constant of the first water-soluble organic solvent is more preferably 40.0 or more, and even more preferably 45.0 or less. The vapor pressure of the first water-soluble organic solvent at a temperature of 25°C is preferably lower than that of water.

The dielectric constant of the water-soluble organic solvent can be measured at 10 kHz using a dielectric constant meter (eg, BI-870, manufactured by BROOKHAVEN INSTRUMENTS CORPORATION). The dielectric constant of a solid water-soluble organic solvent at a temperature of 25° C. can be calculated from the following formula (1) by measuring the dielectric constant of a 50.0% by mass aqueous solution.

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 50.0 mass % aqueous solution of solid water-soluble organic solvent at temperature 25° C. ε _water : Relative permittivity of water The reason for calculating the dielectric constant of a solid water-soluble organic solvent at a temperature of 25° C. from the dielectric constant of a 50.0 mass % aqueous solution is as follows. Among water-soluble organic solvents that are solid at a temperature of 25° C., there are those that are difficult to prepare as high-concentration aqueous solutions exceeding 50.0% by mass, among those that can be used as constituents of ink. On the other hand, in a low-concentration aqueous solution of 10.0% by mass or less, the relative dielectric constant of water becomes dominant, and it is difficult to obtain a probable (effective) value of the relative dielectric constant of the water-soluble organic solvent. Therefore, as a result of investigation by the present inventors, most of the water-soluble organic solvents that are solid at a temperature of 25 ° C. used for ink can prepare an aqueous solution to be measured, and the calculated dielectric constant is It has been found to be consistent with the effects of the present invention. For the above reasons, in the present invention, the dielectric constant of a solid water-soluble organic solvent at a temperature of 25° C. is calculated from the dielectric constant of a 50.0% by mass aqueous solution and used. Even if the water-soluble organic solvent is solid at a temperature of 25 ° C., the solubility in water is low, and for a solvent that cannot be prepared into a 50.0% by mass aqueous solution, an aqueous solution with a saturated concentration is used to calculate the above ε _sol . The relative permittivity value calculated according to the case is used for convenience.

Specific examples of the first water-soluble organic solvent include monohydric alcohols having 1 to 4 carbon atoms such as methyl alcohol (33.1) and ethyl alcohol (23.8); 1,2-propanediol (28. 8), 1,3-butanediol (30.0), 1,4-butanediol (31.1), 1,5-pentanediol (27.0), 3-methyl-1,5-pentanediol ( 23.9) and other dihydric alcohols; 1,2,6-hexanetriol (28.5), glycerin (42.3), trimethylolpropane (33.7) and other polyhydric alcohols; ethylene glycol ( 40.4), diethylene glycol (31.7), triethylene glycol (22.7), alkylene glycols such as tetraethylene glycol (20.8); 2-pyrrolidone (28.8), N-methyl-2- Nitrogen-containing compounds such as pyrrolidone (32.0), urea (110.3), ethylene urea (49.7), triethanolamine (31.9); sulfur-containing compounds such as dimethylsulfoxide (48.9) is mentioned.

The content (% by mass) of the first water-soluble organic solvent is preferably at least 1.5 times the content (% by mass) of the pigment as a mass ratio (times). When the ratio is 1.5 times or more, the first water-soluble organic solvent is larger than the pigment, so aggregation of the pigment can be suppressed. Even if the ejection port surface is cleaned, the ejection port surface is less likely to be scraped by the pigment. This makes it difficult for the inks to mix, and further suppresses the color mixing of the image to be recorded thereafter. The ratio is preferably 10.0 times or less. In addition, the content (% by mass) of the first water-soluble organic solvent in the ink with a high resin content is the mass ratio (times) to the content (% by mass) of the pigment in the ink with a high resin content. , 2.5 times or more. When the ratio is 2.5 times or more, it is possible to further suppress the aggregation of the pigment around the ejection port located above in the direction of gravity. This makes it difficult for the inks to mix, and further suppresses the color mixing of the image to be recorded thereafter. The ratio is preferably 10.0 times or less.

The mass ratio of the resin content to the pigment content in the ink with a high resin content is greater than the mass ratio of the resin content to the pigment content in the ink with a low resin content. preferable. Furthermore, the mass ratio of the content of the first water-soluble organic solvent to the content of the pigment in the ink having a high resin content is the first water-soluble organic solvent content to the content of the pigment in the ink having a low resin content. It is preferably larger than the mass ratio of the content of the organic solvent.

(aqueous medium)
The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As water, it is preferable to use deionized water or ion-exchanged water. The water content (% by mass) in the water-based ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

As the water-soluble organic solvent, a water-soluble organic solvent other than the first water-soluble organic solvent (another water-soluble organic solvent) can be used in combination. Other water-soluble organic solvents are not particularly limited as long as they are water-soluble, and alcohols, glycols, glycol ethers, nitrogen-containing compounds, and the like can be used. In addition, one or more of other water-soluble organic solvents can be contained in the ink. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. This content is a value including the first water-soluble organic solvent. The content (mass%) of the first water-soluble organic solvent is a mass ratio (times) to the total content (mass%) of the water-soluble organic solvent, and is 0.4 times or more and 1.0 times or less. preferable. The ratio is more preferably 0.5 times or more and 1.0 times or less, and further preferably 0.5 times or more and 0.8 times or less.

Specific examples of water-soluble organic solvents include the following, including the specific water-soluble organic solvents mentioned above (the numbers in parentheses represent the dielectric constant at a temperature of 25°C). 1 to 4 carbon atoms such as methyl alcohol (33.1), ethyl alcohol (23.8), n-propyl alcohol, isopropyl alcohol (18.3), n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol The following monohydric alcohols; 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-1,3-propanediol, 3-methyl-1,5-pentanediol Dihydric alcohols such as (23.9); Polyhydric alcohols such as 1,2,6-hexanetriol (28.5), glycerin (42.3), trimethylolpropane (33.7), trimethylolethane Alkylene glycols such as ethylene glycol (40.4), diethylene glycol (31.7), triethylene glycol (22.7), tetraethylene glycol, butylene glycol, hexylene glycol, thiodiglycol; diethylene glycol monomethyl ether, Glycol ethers such as diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether (9.8); .6) Polyalkylene glycols having a number average molecular weight of 200 or more and 1,000 or less such as polypropylene glycol; 2-pyrrolidone (28.8), N-methyl-2-pyrrolidone (32.0), 1,3-dimethyl -Nitrogen-containing compounds such as 2-imidazolidinone, N-methylmorpholine, urea (110.3), ethylene urea (49.7), triethanolamine (31.9); dimethyl sulfoxide (48.9), Sulfur-containing compounds such as bis(2-hydroxyethylsulfone) can be mentioned. The water-soluble organic solvent contained in the ink preferably has a dielectric constant of 3.0 or more and a vapor pressure lower than that of water at a temperature of 25°C.

(Other additives)
Various additives such as surfactants, pH adjusters, antifoaming agents, rust inhibitors, antiseptics, antifungal agents, antioxidants, reduction inhibitors, chelating agents, and resins are added to the ink as necessary. agents may be included. These additives generally have a considerably low content in the ink and have little influence on the effects of the present invention. Therefore, in the present invention, these additives are not included in the "water-soluble organic solvent" and are not subject to the calculation of the dielectric constant. The surfactant content (% by mass) is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.2% by mass or more and 3.0% by mass or less, based on the total mass of the ink. It is even more preferable to have A nonionic surfactant is preferably used as the surfactant.

(physical properties)
In order to suppress color mixture of ink, it is important that the ink does not easily adhere around the ejection port when the ink is ejected. Therefore, since the time required from ink bubbling to ejection is several milliseconds, attention was focused on the dynamic surface tension of ink at 10 milliseconds as an extremely short life time that can be measured with high accuracy. The dynamic surface tension (mN/m) of the ink at a lifetime of 10 ms is preferably 35 mN/m or more.

When the dynamic surface tension is less than 35 mN/m, the tension that reduces the surface area of the ink surface is less likely to act, and when the ink is ejected, the ink tends to adhere around the ejection port. As a result, the ink ejected from the ejection port tends to run down along the ejection port surface, resulting in color mixture of the inks, which may not sufficiently suppress the color mixture of the image to be printed. The dynamic surface tension is preferably 48 mN/m or less.

The dynamic surface tension of ink is measured by the maximum bubble pressure method. In this method, a probe (capillary tube) is immersed in the liquid to be measured, and the surface tension is determined by measuring the maximum pressure required to release the bubble pushed out from the tip of the probe. In addition, the life time is the time when a bubble is formed from the tip of the probe, and the time when a new surface is formed after the bubble leaves and the maximum bubble pressure (the radius of curvature of the bubble and the radius of the tip of the probe are equal). means the time until

Furthermore, the static surface tension (mN/m) of the ink is preferably 30 mN/m or more and 40 mN/m or less. The static surface tension of ink is measured by the Wilhelmy method (plate method). The surface tension value can be appropriately adjusted depending on the type and amount of surfactant.

The viscosity of the ink at a temperature of 25° C. is preferably 1.0 mPa·s or more and 15.0 mPa·s or less.

EXAMPLES The present invention will be described in more detail below with reference to examples, comparative examples, and reference examples, but the present invention is not limited by the following examples as long as it does not exceed the scope of the invention. Note that "parts" and "%" regarding component amounts are based on mass unless otherwise specified.

(Pigment dispersion liquid 1)
To a solution of 5.0 g of concentrated hydrochloric acid dissolved in 5.5 g of water was added 1.6 g of 4-amino-1,2-benzenedicarboxylic acid at a temperature of 5°C. A solution of 1.8 g of sodium nitrite dissolved in 9.0 g of water was added to the solution obtained above while stirring in an ice bath in order to maintain the temperature at 10° C. or lower. After stirring for 15 minutes, 6.0 g of carbon black having a specific surface area of 220 m ² /g and a DBP oil absorption of 105 mL/100 g was added and mixed. After further stirring for 15 minutes, the resulting slurry was filtered through a filter paper (standard filter paper No. 2, manufactured by Advantech), the carbon black was thoroughly washed with water, and dried in an oven at a temperature of 110°C. Water was added to the obtained carbon black to prepare a pigment dispersion 1 (pigment dispersion liquid 1) in which a self-dispersing pigment having —C ₆ H ₃ —(COONa) ₂ groups bonded to the carbon black particle surface was dispersed in water. content of 10.0%) was obtained. After that, using an ion exchange method, sodium ions in the pigment dispersion were replaced with potassium ions.

(Pigment dispersion liquid 2)
12.0 parts of pigment, 24.0 parts of resin-containing liquid, and 64.0 parts of deionized water were mixed. As a pigment, C.I. I. Pigment Blue 15:3 (Hostaperm Blue B2G, manufactured by Clariant) was used. As a liquid containing resin, a styrene-acrylic acid copolymer (Joncryl 680, manufactured by BASF) is neutralized with an aqueous potassium hydroxide solution of 0.85 equivalent to the acid value of the copolymer, and the resin content is was 20.0%. This mixture was dispersed for 3 hours while being cooled with water using a batch-type vertical sand mill (manufactured by Imex) filled with 85.0 parts of zirconia beads having a particle size of 0.3 mm. Thereafter, this dispersion liquid was subjected to centrifugal separation to remove coarse particles, and pressure filtration was performed using a cellulose acetate filter (manufactured by Advantech) having a pore size of 3.0 μm. Pigment Dispersion 2 (pigment content: 10.0%, resin content: 4.0%) in which the pigment was dispersed in water by the resin was obtained by the above method.

(Pigment dispersion liquid 3)
In the preparation of Pigment Dispersion Liquid 2, the type of pigment was C.I. I. Pigment Red 202 and C.I. I. It was changed to a solid solution of Pigment Violet 19 (Cromophtal Jet Magenta 2BC, manufactured by Ciba). Pigment Dispersion 3 (pigment content: 10.0%, resin content: 4.0%) was obtained in the same manner as Pigment Dispersion 2 except for the above.

(Pigment dispersion liquid 4)
In the preparation of Pigment Dispersion Liquid 2, the type of pigment was C.I. I. It was changed to Pigment Yellow 74 (Hansa yellow 5GXB, manufactured by Clariant). Pigment dispersion 4 (pigment content: 10.0%, resin content: 4.0%) was obtained in the same manner as pigment dispersion 2 except for the above.

(Pigment dispersion liquid 5)
20.0 g of pigment, 1.6 mmol of treating agent, 8.0 mmol of nitric acid, and 200.0 mL of water were mixed. As a pigment, C.I. I. Pigment Blue 15:3 (Hostaperm Blue B2G, manufactured by Clariant) was used, and p-aminophthalic acid was used as a treating agent. Mixing was performed using a Silverson mixer under conditions of a temperature of 25° C., 6,000 rpm, and 30 minutes. An aqueous solution of 8.0 mmol of potassium nitrite dissolved in a small amount of water was slowly added to the resulting mixture. The temperature of the mixture reached 60° C. with the addition of the aqueous solution. At a temperature of 60° C., the mixture was allowed to react for 1 hour. After that, the pH of the mixture was adjusted to 10 using a 1.0 mol/L potassium hydroxide aqueous solution. After 30 minutes, 20.0 mL of water was added to the mixture, and low-molecular substances were removed and desalted using a spectrum membrane. Further, the mixture was diluted with water to obtain a pigment dispersion 5 (pigment content: 10.0%) containing a self-dispersing pigment. Pigment Dispersion 5 contained a self-dispersing pigment with —C ₆ H ₃ —(COOK) ₂ groups attached to the particle surface.

(Pigment dispersion liquid 6)
In the preparation of Pigment Dispersion Liquid 5, the type of pigment was C.I. I. Pigment Red 202 and C.I. I. It was changed to a solid solution of Pigment Violet 19 (Cromophtal Jet Magenta 2BC, manufactured by Ciba). Furthermore, the amount of the treating agent was changed to 4.0 mmol. Pigment Dispersion 6 (pigment content: 10.0%) was obtained in the same manner as Pigment Dispersion 5 except for the above. Pigment Dispersion 6 contained a self-dispersing pigment with —C ₆ H ₃ —(COOK) ₂ groups attached to the particle surface.

<Liquid containing dye>
C. I. A dye-containing liquid containing Direct Blue 199 (dye content 10.0%) was obtained.

<Preparation of liquid containing resin>
(liquid containing resin 1)
100.0 parts of ethylene glycol monobutyl ether was added to a four-necked flask equipped with a stirrer, nitrogen inlet, reflux condenser, and thermometer. The temperature was raised to 110° C. under a nitrogen atmosphere while stirring. A liquid obtained by mixing 39.5 parts of styrene, 40.0 parts of methyl methacrylate, and 20.5 parts of acrylic acid, and 1.3 parts of a polymerization initiator were dropped into the flask over 3 hours. The polymerization initiator used here is t-butyl peroxide. After that, aging was performed for 2 hours, ethylene glycol monobutyl ether was removed under reduced pressure, and a solid resin 1 was obtained. Potassium hydroxide equivalent to the acid value and an appropriate amount of ion-exchanged water are added to this solid resin, neutralized and dissolved at a temperature of 80 ° C. Resin 1 whose content of Resin 1 is 20.0% A liquid containing Resin 1 was an acrylic resin and a random copolymer.

(liquid containing resin 2)
31.6 parts of polypropylene glycol having a number average molecular weight of 2,000 was dissolved in methyl ethyl ketone with stirring. Then, 46.9 parts of isophorone diisocyanate and 21.5 parts of dimethylolpropionic acid were added and reacted at a temperature of 75° C. for 1 hour to obtain a prepolymer solution. The obtained prepolymer solution was cooled to a temperature of 60° C., and an aqueous potassium hydroxide solution was added to neutralize the acid groups. After that, the mixture was cooled to 40° C., ion-exchanged water was added, and emulsified by high-speed stirring with a homomixer. After emulsification, 2.1 parts of a chain extender was added, and a chain extension reaction was carried out at a temperature of 30°C for 12 hours. When the presence of isocyanate groups was no longer confirmed by a Fourier transform infrared spectrophotometer (FT-IR), the solution was heated under reduced pressure to remove methyl ethyl ketone, and the content of Resin 2 was 20.0%. A liquid containing resin 2 was obtained. Resin 2 was a urethane resin and a random copolymer.

(liquid containing resin 3)
100.0 parts of ethylene glycol monobutyl ether was added to a four-necked flask equipped with a stirrer, nitrogen inlet, reflux condenser, and thermometer. The temperature was raised to 110° C. under a nitrogen atmosphere while stirring. A liquid obtained by mixing 80.0 parts of styrene, 20.0 parts of polyethylene glycol (20.0 mol added) acrylate, and 1.3 parts of a polymerization initiator were dropped into the flask over 3 hours. The polymerization initiator used here is t-butyl peroxide. After that, aging was performed for 2 hours, ethylene glycol monobutyl ether was removed under reduced pressure, and a solid resin 3 was obtained. An appropriate amount of ion-exchanged water was added to this solid resin and dissolved at a temperature of 80° C. to obtain a liquid containing resin 3 in which the content of resin 3 was 20.0%. Resin 3 was a nonionic resin and a random copolymer.

(liquid containing resin 4)
After purging a four-necked flask equipped with a stirring device, a nitrogen inlet tube, a reflux condenser, and a thermometer, 100.0 parts of dimethylformamide, 0.5 parts of pentamethyldiethylenetriamine, 5.2 parts of styrene, an initiator 0.5 mmol of chloroethylbenzene as a is added. The mixture was heated with stirring, and when the temperature reached 80° C., 0.1 part of copper(I) chloride was added to initiate polymerization to synthesize a hydrophobic unit composed of styrene. Further, 4.3 parts of trimethylsilylacrylic acid was added and polymerized while monitoring using column chromatography, and when the polymerization was completed, 2.6 parts of n-butyl acrylate was further added and polymerized. After termination of the polymerization, the carboxy group of trimethylsilyl acrylic acid was hydrolyzed with sodium hydroxide and an aqueous methanol solution to convert it to carboxylic acid. To this solution, 2.8 g of 35.0% hydrochloric acid aqueous solution was added, stirred at room temperature for 10 minutes, filtered, and washed with pure water three times to obtain a solid resin 4. The resulting resin 4 was dissolved in tetrahydrofuran, and potassium hydroxide was added to the solution so that the anionic groups of the resin were neutralized by 80%. Furthermore, after adding an appropriate amount of ion-exchanged water and stirring, tetrahydrofuran was removed under reduced pressure to obtain a liquid containing resin 4 with a content of resin 4 of 20.0%.

Hydrolysis of the carboxyl group of trimethylsilylacrylic acid was confirmed from the presence of a peak in the chemical shift of the carboxyl group by proton nuclear magnetic resonance spectroscopy. Resin 4 was an acrylic resin and a block copolymer. When the components constituting each block were analyzed by proton nuclear magnetic resonance spectroscopy, they were found to be 52.4% styrene, 21.8% acrylic acid, and 25.8% n-butyl acrylate.

(liquid containing resin 5)
In a four-necked flask equipped with a stirrer, nitrogen inlet, reflux condenser, and thermometer, 0.3 parts of sodium lauryl sulfate, 20.8 parts of 2-ethylhexyl acrylate, 62.4 parts of methyl methacrylate, and 16 parts of methacrylic acid were added. .8 parts were added. Into this flask, 10.0 parts of a 5% aqueous solution of potassium persulfate was added dropwise over 3 hours. After that, aging was performed for 2 hours, and an appropriate amount of deionized water was added to obtain a liquid containing resin 5 in which the content of resin 5 was 20.0%.

Resins 1-4 were water-soluble resins and Resin 5 was resin particles. Whether the resin is water-soluble or particulate can be determined according to the method described below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an acid value equivalent alkali (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10-fold (by volume) 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, it can be determined that the resin is water-soluble if particles having a particle size are not measured. If particles with a particle size are measured, the resin can be determined to be resin particles. The measurement conditions at this time were SetZero: 30 seconds, the number of measurements: 3, and the measurement time: 180 seconds. In the examples, a dynamic light scattering particle size analyzer (UPA-EX150, manufactured by Nikkiso Co., Ltd.) was used as the particle size distribution analyzer.

<Ink preparation>
Each component described in Table 1 was mixed and thoroughly stirred. Thereafter, pressure filtration was performed with a cellulose acetate filter (manufactured by Advantec) having a pore size of 1.2 μm to prepare an ink. Acetylenol E100 is a nonionic surfactant manufactured by Kawaken Fine Chemicals. The numbers attached to polyethylene glycol represent the number average molecular weight. The relative permittivity of the water-soluble organic solvent shown in parentheses is a value obtained at a frequency of 10 kHz using a permittivity meter (BI-870, manufactured by BROOKHAVEN INSTRUMENTS CORPORATION).

<Evaluation>
In the present invention, according to the following evaluation criteria, AA, A, or B was defined as an acceptable level, and C was defined as an unacceptable level. Evaluation results are shown in Table 3. Using the inkjet recording apparatus having the configuration shown in FIG. 4, ink was mounted on a recording head having one recording element substrate. As recording heads, recording heads 1 to 5 shown in Table 2 were used.

In Table 2, the ejection port arrays of the recording element substrate correspond to the ejection port arrays I to IV shown in FIG. The print element substrates of print heads 1 to 3 and 5 have overlapping ejection port arrays in the print medium transport direction, but the print element substrate of print head 4 has an ejection port array in the print medium transport direction. are not duplicated. Further, although the recording head 2 has the ejection port arrays I to III, ink is not ejected from the ejection port array II.

The print heads 1 to 5 had 1024 ejection ports per ejection port array, and the density of the ejection ports per ejection port array was 600 dpi. The length (μm) passing through the center of the ejection port was 20 μm, and the distance (mm) between adjacent ejection port rows was 0.7 mm. Further, the ejection port surface of the recording head is water-repellent treated with a condensate of a hydrolyzable silane compound having a fluoroalkyl group and a hydrolyzable silane compound having a cationic polymerizable group.

In this embodiment, an image printed under the condition that three 5.0 ng ink droplets are applied to a unit area of 1/600 inch×1/600 inch is defined as having a print duty of 100%. The conveying speed was 15 inches/second. When the recording medium is conveyed in the direction from ejection port array I to ejection port array II (“I→II” in Table 3), the recording medium is conveyed from bottom to top in the direction of gravity when printing an image. . When the recording medium is conveyed from ejection port array II to ejection port array I (“II→I” in Table 3), the recording medium is conveyed from top to bottom in the direction of gravity when printing an image. .

(Mixed colors in image)
Except for Reference Examples 4 and 5, the cleaning device shown in FIG. 5 was used to wipe the ejection port surface. The wiper material is rubber. When the wiper was in sliding contact with the ejection port surface of the recording head, the wiper was greatly bent and abutted at its side, and the contact pressure on the ejection port surface was 1N. The ejection port surface was wiped from the ejection port rows I to IV at a wiper speed of 80 mm/sec.

First, using each ink, a monochromatic solid image (approximately 3 cm in the conveying direction of the printing medium×approximately 4 cm in the depth direction of the apparatus) with a printing duty of 100% was printed. The obtained image was designated as image 1 for evaluation. Then, after stopping recording for 1 hour, the ejection port surface was wiped once. Then, using each ink, a solid image of multiple colors (approximately 17 cm in the conveying direction of the printing medium×approximately in the depth direction of the apparatus) is obtained so that the printing duty of each ink is uniform and the total printing duty of the inks is 100%. 4 cm) was continuously recorded on 50 sheets. After repeating a series of operations of resting, cleaning, and continuous printing a predetermined number of times, each ink is used again to produce a monochrome solid image with a printing duty of 100% (approximately 3 cm in the conveying direction of the printing medium×the depth of the apparatus). 4 cm) was recorded. The obtained image was used as image 2 for evaluation. Plain paper (PPC paper PB Paper, manufactured by Canon Inc.) was used as the recording medium. In Reference Examples 4 and 5, wiping of the ejection port surface was not performed.

Evaluation image 1 and evaluation image 2 were visually observed to evaluate whether or not color mixture occurred in evaluation image 2 .
AA: No color mixture occurred in evaluation image 2 even after repeating a series of operations 10,000 times A: Color mixture occurred in evaluation image 2 when a series of operations was repeated 8,000 times or more and less than 10,000 times B: When the series of operations is repeated 6,000 times or more and less than 8,000 times, color mixture occurs in the evaluation image 2. C: When the series of operations is repeated less than 6,000 times, the evaluation image 2 Color mixing occurred.

As Reference Example 10, an image was recorded using an inkjet recording apparatus having two recording heads corresponding to black ink 9 and cyan ink 8 in order from the upstream side in the conveying direction of the recording medium. An image was recorded in the same manner as in Comparative Example 3 except that two recording heads were used.

As Reference Example 11, an image was recorded using an inkjet recording apparatus having two recording heads corresponding to black ink 1 and cyan ink 1 in order from the upstream side in the conveying direction of the recording medium. An image was recorded in the same manner as in Example 1, except that two recording heads were used.

Claims (20)

A first ink and a second ink, which are water-based inks containing a pigment; a first ejection port row for ejecting the first ink and a second ejection port row for ejecting the second ink are adjacent to each other in order from the bottom in the gravitational direction. a recording head arranged such that at least a part of the first ejection port array and the second ejection port array overlap in a conveying direction of the recording medium; and the first ejection of the recording head An inkjet recording method using an inkjet recording apparatus comprising: a cleaning member for cleaning an ejection port surface on which the outlet array and the second ejection port array are formed,
a recording step of recording an image on a recording medium by ejecting the water-based ink from the recording head arranged so that the angle between the ejection port surface and the direction of gravity is 0° or more and less than 90°; Having a cleaning step of cleaning the surface,
The second ink contains a resin, and the content (% by mass) of the resin in the second ink is 0.5% by mass or more and 10.0% by mass or less based on the total mass of the ink. and
An inkjet recording method, wherein the content of the resin in the second ink is greater than the content of the resin in the first ink. 2. The inkjet recording method according to claim 1, wherein the angle formed by the ejection port surface of the recording head and the direction of gravity is 10[deg.] or more and 80[deg.] or less. 2. The inkjet recording method according to claim 1, wherein the angle formed by the ejection port surface of the recording head and the direction of gravity is 30[deg.] or more and 60[deg.] or less. 4. The inkjet recording method according to claim 1, wherein the recording head comprises one recording element substrate on which the first ejection port array and the second ejection port array are arranged. 5. The inkjet recording method according to claim 4, wherein said recording head comprises a plurality of said recording element substrates. 6. The inkjet recording method according to claim 5, wherein the plurality of recording element substrates provided in the recording head are arranged adjacent to each other in the direction in which the first ejection port array and the second ejection port array are arranged. The inkjet recording method according to any one of claims 1 to 6, wherein the recording medium is conveyed in a direction from the first ejection port array toward the second ejection port array. The inkjet recording method according to any one of claims 1 to 7, wherein the first ink and the second ink have hues different from each other. The inkjet recording method according to any one of claims 1 to 8, wherein the pigment in the first ink contains carbon black. The inkjet recording method according to any one of claims 1 to 9, wherein the resin contained in the second ink contains an acrylic resin. The inkjet recording method according to any one of claims 1 to 10, wherein the first ink contains a resin . 12. The inkjet recording method according to any one of claims 1 to 11, wherein both the first ink and the second ink contain a first water-soluble organic solvent having a dielectric constant of 20.0 or more. 13. The inkjet recording method according to claim 12, wherein the dielectric constant of the first water-soluble organic solvent is 45.0 or less. 14. The ink jet recording method according to any one of claims 1 to 13, wherein the ejection port surface of the recording head is water repellent. 7. The ink jet recording method according to any one of claims 4 to 6, wherein the shape of the recording element substrate is a parallelogram, a rectangle, or a trapezoid. 7. The ink jet recording method according to claim 4 , wherein the shape of the recording element substrate is a parallelogram. 17. The inkjet recording method according to any one of claims 1 to 16, wherein the recording head is a line head. The inkjet recording method according to any one of Claims 1 to 17, wherein the cleaning member is a wiper. 19. The inkjet recording method according to claim 18, wherein the wiper moves in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array. A first ink and a second ink, which are water-based inks containing a pigment; a first ejection port row for ejecting the first ink and a second ejection port row for ejecting the second ink are adjacent to each other in order from the bottom in the gravitational direction. a recording head arranged such that at least a part of the first ejection port array and the second ejection port array overlap in a conveying direction of the recording medium; and the first ejection of the recording head An inkjet recording apparatus comprising: a cleaning member for cleaning an ejection port surface on which the outlet array and the second ejection port array are formed,
recording an image on a recording medium by ejecting the water-based ink from the recording head arranged so that the angle between the ejection port surface and the direction of gravity is 0° or more and less than 90°;
cleaning the ejection port surface;
The second ink contains a resin, and the content (% by mass) of the resin in the second ink is 0.5% by mass or more and 10.0% by mass or less based on the total mass of the ink. and
An inkjet recording apparatus, wherein the content of the resin in the second ink is greater than the content of the resin in the first ink.

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