JP7707359B2 - Inkjet recording method - Google Patents

Description

The present invention relates to an inkjet recording method .

The inkjet recording method allows images to be recorded on various recording media. In recent years, inkjet recording devices equipped with ink cartridges in which a recording head is built into an ink storage section that contains water-based ink have become widespread, with the aim of simplifying and miniaturizing the device configuration and shortening the preparation time until initial use. In addition, in the business field, inkjet recording methods are also used when recording text, including text and colored diagrams, on recording media such as plain paper. In such applications, there is an increasing need for inks that contain resins, which are less susceptible to image distortion due to uneven ejection and can record images that are excellent in water resistance and abrasion resistance.

A method is known that employs a cleaning means using a cleaning liquid to prevent the occurrence of irregular ejection, which is one of the causes of image distortion. In addition, an inkjet recording device has been proposed that is equipped with a sheet-like wiping member with voids that can efficiently remove ink that has adhered to the ejection port surface (Patent Document 1).

JP 2020-128031 A

The inventors prepared an inkjet recording device equipped with an ink cartridge incorporating a recording head and a means for wiping the nozzle surface of the recording head. They then investigated the use of aqueous ink containing organic pigments and resin to record an image from the recording head of this inkjet recording device, and found that irregular ejection was likely to occur immediately after the device began to be used for the first time. Conventionally, irregular ejection occurred after a certain amount of ink had been ejected or when the device was used again after a period of non-use, so irregular ejection immediately after the start of initial use is a problem caused by a different cause than conventional irregular ejection. Furthermore, when dye ink or ink not containing resin was used, it was found that irregular ejection did not occur immediately after the start of initial use.

Furthermore, when aqueous ink containing organic pigments and resins was ejected from a recording head that was not integrated with the ink storage section, it was found that no irregular ejection occurred immediately after the start of initial use. In other words, it was found that irregular ejection that occurs immediately after the start of initial use is an issue that arises when an image is recorded by ejecting aqueous ink containing organic pigments and resins from the recording head of an ink cartridge in which the recording head is built.

Therefore, an object of the present invention is to provide an inkjet recording method capable of recording images with excellent water resistance and abrasion resistance while suppressing the occurrence of irregular ejection immediately after the start of initial use. Another object of the present invention is to provide an inkjet recording device for use in this inkjet recording method.

That is, according to the present invention, there is provided an inkjet recording method that uses an inkjet recording device comprising: an aqueous ink containing an organic pigment and a resin; an ink storage section that stores the aqueous ink; a recording head incorporated in the ink storage section that has an ejection port surface formed with ejection ports for ejecting the aqueous ink supplied from the ink storage section; and a wiping means that wipes the ejection port surface, and that includes a step of applying the aqueous ink ejected from the ejection port to a recording medium to record an image, wherein a protective tape having an adhesive layer formed from an adhesive that is peeled off when used is attached to the ejection port surface of the recording head, and the peeling direction of the protective tape and the wiping direction of the ejection port surface by the wiping means are approximately perpendicular or opposite to each other .

According to the present invention, it is possible to provide an inkjet recording method capable of recording images with excellent water resistance and abrasion resistance while suppressing the occurrence of irregular ejection immediately after the start of initial use. In addition, according to the present invention, it is possible to provide an inkjet recording device used in this inkjet recording method.

1A and 1B are diagrams illustrating an ink jet recording apparatus according to an embodiment of the present invention, in which FIG. 1A is a perspective view and FIG. 1B is a perspective view showing a state in which a cover member is open. 1 is a perspective view showing a schematic internal structure of an inkjet recording apparatus according to an embodiment of the present invention; FIG. 2 is a perspective view illustrating an example of a recording unit. 1A and 1B are diagrams each showing a schematic view of an example of a recording unit, in which FIG. 1A is a perspective view and FIG.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing salt". In addition, water-based ink for inkjet may be simply referred to as "ink". Physical property values are values at room temperature (25°C) unless otherwise specified. Regarding the peeling direction of the protective tape, the wiping direction of the ejection port surface, and the arrangement direction of the ejection port array, when these are "approximately parallel", "approximately the same direction", and "approximately opposite directions", they may be described as "parallel", "same direction", and "opposite directions" respectively, with "approximately" omitted.

The inventors prepared an ink cartridge in which a recording head is incorporated in an ink storage section having an ejection port surface where ejection ports for ejecting ink are formed. Then, using the prepared ink cartridge, they analyzed the ejection irregularities that occur when ink containing an organic pigment and a resin is ejected from the recording head immediately after peeling off the protective tape and opening the package. Ink cartridges in which an ink storage section and a recording head are integrally formed are usually stored in a state where a protective tape having an adhesive layer is attached to the ejection port surface of the recording head to suppress evaporation of the ink, and the ejection port is blocked. Then, when the ink cartridge is used for the first time (at the start of initial use), the ink cartridge packed in a sealed container is opened, the protective tape is peeled off, and the ink cartridge is mounted on a recording device to start recording an image. However, when the protective tape is peeled off, a part of the adhesive forming the adhesive layer may remain attached to the ejection port surface, and it was found that the remaining adhesive causes the ejection irregularities of the ink.

However, it was found that when dye ink or organic pigment ink that does not contain resin is used, irregular ejection does not occur even when adhesive is attached to the ejection port surface of the recording head. When the ejection port surface of the recording head where irregular ink ejection occurred was observed after the attached protective tape was peeled off, adhesive residue was confirmed. In addition, the contact angle of the ejection port surface with various inks before the protective tape was attached, and the contact angle of the ejection port surface with various inks after the protective tape was attached and peeled off were measured. As a result, it was found that the contact angle with the ink containing resin was uniquely different before and after the protective tape was attached. In other words, it is thought that the ejection port surface with adhesive attached is more easily wetted by the ink containing resin, causing irregular ejection.

When using a recording unit in which an ink storage section is set in a head cartridge equipped with a recording head, there is no need to suppress the evaporation of ink from the ejection ports, which is necessary in ink cartridges in which a recording head is built into the ink storage section. Therefore, when using a recording unit in which an ink storage section is set in a head cartridge equipped with a recording head, ink ejection irregularities caused by residual adhesive do not occur.

The inventors checked the state of the ejection port surface by setting the peeling direction of the protective tape and the wiping direction of the ejection port surface by the wiping means to the same direction. As a result, unlike when the directions cross or are reversed, it was found that the remaining adhesive was not sufficiently removed, making it difficult to suppress the occurrence of irregular ejection of ink. Furthermore, the inventors investigated the material of the wiper, which is one of the wiping means, and the composition of the cleaning liquid used for wiping. For example, when a sheet-like wiping member having voids was used, the efficiency of removing the remaining adhesive was improved, and it was possible to suppress the occurrence of irregular ejection of ink immediately after the start of initial use. However, it was found that the ejection port surface was easily deteriorated, such as the water-repellent material constituting the ejection port surface being easily scraped off, and that irregular ejection of ink was easily caused by long-term use. In addition, when wiping was performed using a cleaning liquid containing a large amount of "good solvents" such as solvents with good moisturizing properties that can improve the resolubility of ink, it was found that the effect of removing the remaining adhesive was weak. In addition, when wiping was performed using a cleaning solution that contained a large amount of a "poor solvent," such as a solvent that has good solubility for the substance, the efficiency of removing the remaining adhesive improved, but it was found that the ink was more likely to aggregate, which could lead to non-ejection or irregular ejection.

The inventors further investigated the wiping conditions of the ejection port surface and the composition of the ink. As a result, they discovered that by using the composition shown below, it is possible to suppress the occurrence of ejection irregularities immediately after the start of initial use, while recording images with excellent water resistance and abrasion resistance, which are required for business documents, etc.

That is, in the inkjet recording method of the present invention, an inkjet recording device is used that includes an ink containing an organic pigment and a resin, an ink storage section that stores the ink, and a recording head built into the ink storage section. The recording head has an ejection port surface in which ejection ports are formed for ejecting ink supplied from the ink storage section. The inkjet recording device further includes a wiping means that wipes the ejection port surface. A protective tape having an adhesive layer formed of an adhesive is attached to the ejection port surface of the recording head in order to suppress evaporation of ink from the ejection ports, and this protective tape is peeled off when the inkjet recording device is used for the first time. The peeling direction of the protective tape and the wiping direction of the ejection port surface by the wiping means intersect or are opposite directions.

When the protective tape is peeled off from the nozzle surface of the recording head, part of the adhesive that forms the adhesive layer of the protective tape remains on the nozzle surface in a "fluffy state". Therefore, it is believed that by making the direction in which the protective tape is peeled off and the direction in which the nozzle surface is wiped by the wiping means cross or are opposite directions, the adhesive that remains in a fluffy state can be efficiently removed. This makes it possible to suppress the occurrence of irregular ink ejection immediately after the start of initial use.

<Inkjet recording method and inkjet recording apparatus>
The inkjet recording method of the present invention is a recording method using an inkjet recording device including ink, an ink storage section for storing the ink, a recording head, and a wiping means for wiping the nozzle surface of the recording head. The ink contains an organic pigment and a resin. The recording head is a recording head incorporated in the ink storage section, and has a nozzle surface in which nozzles for ejecting ink supplied from the ink storage section are formed. The inkjet recording method of the present invention includes a step of applying ink ejected from the nozzles of the recording head to a recording medium to record an image. A protective tape having an adhesive layer formed of an adhesive, which is peeled off when used, is attached to the nozzle surface of the recording head. The peeling direction of the protective tape and the wiping direction of the nozzle surface by the wiping means intersect or are opposite directions.

The inkjet recording device of the present invention comprises ink, an ink storage section that stores the ink, a recording head, and a wiping means that wipes the nozzle surface of the recording head. The ink contains an organic pigment and a resin. The recording head is a recording head incorporated in the ink storage section, and has a nozzle surface in which nozzles that eject ink supplied from the ink storage section are formed. A protective tape having an adhesive layer formed of an adhesive, which is peeled off when used, is attached to the nozzle surface of the recording head. The peeling direction of the protective tape and the wiping direction of the nozzle surface by the wiping means intersect or are opposite directions.

(Inkjet recording device)
FIG. 1 is a diagram showing an embodiment of an inkjet recording device of the present invention, in which (a) is a perspective view and (b) is a perspective view with a cover member open. As shown in FIG. 1, the inkjet recording device 1 of this embodiment has an exterior 2 and a cover member 3 provided on the upper surface of the exterior 2. The cover member 3 is a member that can be opened and closed in the vertical direction, and the inside of the inkjet recording device 1 can be seen by opening it in the upward direction. The inkjet recording device 1 has a shape of a substantially rectangular parallelepiped and is provided with a paper feed tray 4 at the rear. (b) shows a state in which the paper feed tray 4 is extended from the exterior 2. For simplicity, FIGS. 1 and 2 show a device equipped with ink of one color, but the type of ink and the number of inks are not limited to those shown in FIGS. 1 and 2.

2 is a perspective view showing a schematic internal structure of an embodiment of an inkjet recording device of the present invention. The inkjet recording device 1 of the embodiment shown in FIG. 2 has a paper feed tray 4 on the rear side of the exterior. A recording medium such as paper is placed in the paper feed tray 4. A recording unit 8 is placed inside the inkjet recording device 1. A recording head is provided under the recording unit 8. The recording unit 8 ejects ink from the nozzles of the recording head while moving back and forth in the y direction in FIG. 2. The recording medium placed on the paper feed tray 4 is sent forward in the x direction by the paper feed roller 5 and the transport roller 6, and reaches and is supported by the platen 7. The recording medium supported by the platen 7 is placed in a position facing the recording head, and in this state, ink is ejected from the recording head onto the recording medium. The ejected ink adheres to the recording medium, and an image is recorded on the recording medium. The inkjet recording device 1 further has a cap 9 at the home position that abuts against an area including the nozzle surface of the recording head and covers the nozzles. When the recording unit 8 is in the home position, the wiper 20 wipes the nozzle surface of the recording head 1.

Figure 3 is a perspective view showing a schematic example of a recording unit (ink cartridge). As shown in Figure 3, the recording unit 8 has an ink storage section 10, which is a housing made of a material such as a thermoplastic resin, and a recording head 11 built into the ink storage section 10. That is, the recording head 11 is formed integrally with the ink storage section 10. The ink storage section 10 contains ink containing an organic pigment and a resin. The recording head 11 has an ejection port surface 30 in which an ejection port for ejecting ink supplied from the ink storage section 10 is formed. A protective tape 50 having an adhesive layer formed of an adhesive, which is peeled off at the time of initial use of the ink cartridge, is attached to the ejection port surface 30 of the recording head 11. The peeling direction of the protective tape 50 can be regulated, for example, as follows. A tab 40 is provided as a non-adhesive portion that is not adhered to the recording head at the end of the peeling tape along the peeling direction. This makes it easier to peel off the protective tape from the tab 40 in the longitudinal direction of the protective tape, and the peeling direction can be regulated. In order to more simply and reliably regulate the peeling direction, it is preferable that no non-adhesive portion is provided in the direction intersecting the peeling direction. It is also preferable that the peeling direction of the protective tape 50 is a direction intersecting the arrangement direction of the nozzle array of the recording head 11. In particular, as shown in FIG. 3, it is even more preferable that the peeling direction of the protective tape 50 is X-X' and the arrangement direction of the nozzle array of the recording head 11 is Y-Y'. The configuration and peeling direction of the protective tape are not limited to those shown in FIG. 3.

The ink ejection method of the recording head can be a method in which mechanical energy generated by a piezoelectric element or the like is applied to the ink to eject it, or a method in which thermal energy generated by an electrothermal converter (heater) or the like is applied to the ink to eject it. Either ink ejection method can be used.

The protective tape is a member used to prevent evaporable components in the ink, such as water, from evaporating from the nozzle of the recording head. The protective tape has an adhesive layer formed of an adhesive. Examples of adhesives include acrylic adhesives, silicone adhesives, and ethylene vinyl acetate (EVA), with acrylic adhesives and silicone adhesives being preferred, and silicone adhesives being more preferred. When a silicone adhesive is used, the adhesive is less likely to be deteriorated by the ink, even at a pH (alkaline) that is common for water-based inks for inkjet printing, compared to when other adhesives such as acrylic adhesives are used. For this reason, adhesive residue is less likely to be left behind, making it easier to prevent ejection irregularities. The adhesive layer is formed on the surface of, for example, a sheet-like or film-like substrate. Resin materials such as polyethylene terephthalate (PET) can be used as the substrate.

The inkjet recording device is equipped with a wiping means for wiping the discharge port surface of the recording head. As described above, the peeling direction of the protective tape and the wiping direction of the discharge port surface by the wiping means intersect or are opposite directions. When the directions intersect, the angle between the peeling direction and the wiping direction can be any angle other than 0°. In particular, it is preferable that the peeling direction and the wiping direction are approximately perpendicular to each other. When the directions are opposite, the angle between the peeling direction and the wiping direction is substantially 0°. It is particularly preferable that the peeling direction of the protective tape and the wiping direction of the discharge port surface by the wiping means are intersecting directions. It is also particularly preferable that the wiping direction of the discharge port surface by the wiping means and the arrangement direction of the discharge port row are approximately parallel, and that these directions intersect with the peeling direction of the protective tape. For example, a wiper that can slide in contact with the discharge port surface can be used as the wiping means. The shape of the wiper is preferably blade-shaped. By using a blade-shaped wiper, the wiping ability of the discharge port surface can be further improved. The wiper is preferably made of a material having rubber elasticity. For example, the wiper may be made of a rubber material (urethane rubber) made of urethane resin.

The thickness of the wiper is preferably 0.4 mm or more and 1.1 mm or less. If the thickness of the wiper is less than 0.4 mm, the efficiency of removing adhesive adhering to the nozzle surface may be slightly reduced. On the other hand, if the thickness of the wiper is more than 1.1 mm, it may be more likely to damage the nozzle surface of the recording head, and irregular ejection may be more likely to occur after long-term use.

The wiper movement speed during wiping is preferably 15 mm/s or more and 130 mm/s or less. If the wiper movement speed is less than 15 mm/s, the nozzle surface of the recording head may be easily damaged, and irregular ejection may be somewhat more likely to occur after prolonged use. On the other hand, if the wiper movement speed exceeds 130 mm/s, the efficiency of removing adhesive adhering to the nozzle surface may be somewhat reduced.

Figure 4 is a diagram showing an example of a recording unit, (a) is a perspective view, and (b) is a perspective view in an exploded state. The recording unit 8 shown in Figure 4 has an ink storage section 10, which is a housing, and a recording head 11. The recording head 11 is attached to the ink storage section 10 without any other members. The ink storage section 10 is a housing made of a material such as a thermoplastic resin, and is therefore lightweight. Furthermore, the recording head 11 is attached to the ink storage section 10 without any other members such as a heat sink, so the entire recording unit 8 is made smaller and lighter. By using such a recording unit 8, the entire inkjet recording device can be made smaller and lighter. Examples of heat sinks include those made of materials such as metal oxides such as alumina. There is no need to interpose other members such as a heat sink between the ink storage section 10 and the recording head 11. However, an adhesive layer formed of an adhesive or the like for fixing the recording head 11 to the ink storage section 10 may be present.

The recording head 11 is provided with a number of ejection ports for ejecting ink, and energy generating elements for generating thermal energy for ejecting ink. The energy generating elements can be driven, for example, by power supplied through the electrical wiring member 14. The energy generating elements are elements that generate thermal energy, and the action of the generated thermal energy can cause ink to be ejected from the ejection ports.

The recording head 11 has an ejection port surface in which an ejection port array made up of multiple ejection ports is arranged on the same recording element substrate. The ejection port array is preferably arranged in a direction (sub-scanning direction) that is approximately perpendicular to the direction of reciprocating movement of the recording unit (main scanning direction). Multiple ejection port arrays may be arranged on the recording element substrate. In this case, it is possible to eject multiple inks with one recording unit, and the entire inkjet recording device can be made smaller.

Sponge-like ink absorbers 12a-12c are stored inside the ink storage section 10. Filters 13a-13c are also arranged below the ink storage section 10 in the direction of gravity. By using the capillary force of the sponge-like ink absorbers 12a-12c to generate negative pressure, it is possible to prevent ink from leaking out of the ejection ports. In addition, by arranging the filters 13a-13c, it is possible to prevent fine foreign matter such as dust from entering the ejection ports.

The recording head preferably has a heating means for heating the ink in the recording head. The heating means may be any means capable of heating the ink in the recording head to a temperature equal to or higher than the cloud point of the surfactant in the ink. Examples of such heating means include a heater for adjusting the ink temperature that is arranged in contact with the recording head, and a heater for ink ejection. To heat the ink using a heater for ink ejection, for example, it is sufficient to repeatedly pass a current that is not strong enough to eject the ink. The ink temperature in the recording head is preferably heated to a temperature between 40°C and 70°C.

Examples of the material of the ejection port surface of the recording element substrate constituting the recording head 11 include resin materials such as epoxy resin. Using a recording head with an ejection port surface formed of a resin material that has been treated to be water repellent is preferable because it makes it easier to suppress deterioration of ejection characteristics due to ink adhering to the ejection port surface. In particular, this makes it easier to peel off the protective tape and makes it even more difficult for adhesive to remain on the ejection port surface. In addition, adhesive remaining on the ejection port surface can be more easily removed by wiping.

The discharge port surface of the recording head is preferably treated to be water-repellent. Methods for treating the discharge port surface to be water-repellent include a method of applying a water-repellent material by spraying, etc., and a method of attaching a water-repellent material by vacuum deposition or plasma polymerization. The water repellency of the discharge port surface can be evaluated by measuring the contact angle with water. If the contact angle with water is 70° or more, it can be determined to be "water-repellent," and it is preferable that the contact angle with water is 90° or more. The contact angle with water can be measured using pure water (ion-exchanged water) and a general contact angle meter. Examples of contact angle meters include an automatic contact angle measuring machine (product name "CA-W", manufactured by Kyowa Interface Science).

Examples of water-repellent materials for the water-repellent treatment of the discharge port surface include compounds of fluororesins. The water-repellent surface is preferably formed as a uniform resin film made of these materials, and this resin film preferably does not contain metals such as nickel. Examples of fluororesins include polytetrafluoroethylene resins and fluororesins having a cyclic structure. Examples of 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, and modified resins thereof, can also be mentioned. In addition, compounds containing silicon atoms and silicone-based resins may also be used as water-repellent materials. Among these, it is preferable to use a hydrolyzable silane compound having a fluoroalkyl group and a condensate of a hydrolyzable silane compound having a cationic polymerizable group, since a high level of water repellency can be obtained. In addition, examples of silicone-based resins obtained by curing this condensate by irradiation of active energy rays such as ultraviolet rays can also be mentioned. The hydrolyzable silane compound has a hydrolyzable group such as an alkoxy group in its molecular structure. Examples of the cationic polymerizable group include a cyclic ether group and a cyclic vinyl ether group.

(Water-based ink)
The inkjet recording method of the present invention includes a step of recording an image by applying the ink containing an organic pigment and a resin to a recording medium by ejecting the ink from an ejection orifice.

[Colorant]
The coloring material of the ink is an organic pigment (hereinafter, simply referred to as "pigment"). Examples of the pigment include an azo pigment, a phthalocyanine pigment, a quinacridone pigment, an isoindolinone pigment, an imidazolone pigment, a diketopyrrolopyrrole pigment, a dioxazine pigment, and a perinone pigment.

The content (mass %) of organic pigment in the aqueous ink is preferably 0.5% to 10.0% by mass, based on the total mass of the ink, and more preferably 1.0% to 8.0% by mass.

Examples of pigment dispersion methods include resin-dispersed pigments, which use a resin (resin dispersant) as a dispersant, and self-dispersed pigments, in which hydrophilic groups are bonded to the pigment particle surface. In addition, resin-bonded pigments, in which organic groups containing resin are chemically bonded to the pigment particle surface, and microencapsulated pigments, in which the surface of pigment particles is coated with a resin or the like, can also be used.

As a 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 anionic groups. As the resin dispersant, a resin as described below, particularly a water-soluble resin, can be used. The content (mass %) of the resin dispersant in the aqueous ink is preferably 0.1 to 0.6 times the mass ratio of the content (mass %) of the organic pigment. If the mass ratio is more than 0.6 times, the scratch resistance of the image tends to improve, but the ejection irregularity tends to occur easily immediately after the start of initial use.

As the self-dispersing pigment, a pigment having an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group bonded directly or via another atomic group (-R-) to the particle surface of the pigment can be used. The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium. 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 or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. The pigment may also be a group that is a combination of these groups.

[resin]
The ink contains a resin. The content (mass%) of the resin in the aqueous ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink. The content (mass%) of the resin in the aqueous ink is preferably 0.1 times or more and 1.0 times or less, and more preferably 0.1 times or more and 0.6 times or less, in terms of mass ratio to the content (mass%) of the organic pigment. This content of the resin is a value including a dispersant for dispersing the pigment.

The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, (ii) to improve various characteristics of the recorded image. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations of these. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. Of these, water-soluble resins are preferred, and the water-soluble resin is preferably a resin dispersant for dispersing the pigment.

Examples of resins include acrylic resins, polyester resins, urethane resins, urea resins, polysaccharides, and polypeptides. Among these, acrylic resins are preferred from the viewpoint of ejection characteristics from the ejection ports of the recording head. Acrylic resins are preferred that have as their constituent units a unit having an anionic group and a unit not having an anionic group. Acrylic resins are resins that have units derived from acrylic monomers such as (meth)acrylic acid and (meth)acrylate. Examples of the form of acrylic resins include random copolymers, block copolymers, graft copolymers, and combinations of these.

Examples of monomers that become units that constitute acrylic resins upon polymerization include monomers that have an anionic group and monomers that do not have an anionic group. Usually, monomers that have an anionic group become hydrophilic units upon polymerization, and monomers that do not have an anionic group become hydrophobic units upon polymerization.

Examples of monomers having an anionic group include monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anhydrides and salts of these monomers; and the like. Examples of cations constituting the salts of monomers having an anionic group include lithium cations, sodium cations, potassium cations, ammonium cations, and organic ammonium cations.

Examples of monomers that do not have an anionic group include monomers that have an aromatic group, such as styrene, α-methylstyrene, benzyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole; and (meth)acrylic acid esters, such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso)propyl (meth)acrylate, (n-, iso-, and t-)butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

Among these, acrylic resins 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 monomer are preferred. In particular, acrylic resins having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of styrene and α-methylstyrene are preferred. These acrylic resins easily interact with pigments, making them suitable as resin dispersants for dispersing pigments in aqueous media.

Urethane resins can be obtained, for example, by reacting polyisocyanate with polyol. They may also be obtained by further reacting with a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[Aqueous medium]
The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. The ink preferably contains a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inkjet inks, such as alcohols, glycols, glycol ethers, and nitrogen-containing compounds, can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink, and more preferably 15.0 mass% or more and 30.0 mass% or less based on the total mass of the ink.

The ink preferably contains at least one water-soluble organic solvent selected from the group consisting of compounds having a cyclic amide structure, alkanediols, and amine compounds, and more preferably contains at least two water-soluble organic solvents. By using ink containing these water-soluble organic solvents, it is possible to further suppress uneven ejection immediately after the start of initial use. An example of a compound having a cyclic amide structure is 1-(2-hydroxyethyl)-2-pyrrolidone. Alkanediols are compounds in which two hydroxy groups are substituted on a saturated hydrocarbon chain having about 2 to 8 carbon atoms, and examples of such compounds include 1,2-hexanediol, 1,5-pentanediol, and 1,6-hexanediol. An example of an amine compound is triethanolamine.

[Surfactant]
The ink preferably further contains a surfactant. It is particularly preferable that the ink contains a surfactant having a cloud point. The inkjet recording method of the present invention further includes a step of heating the ink in the recording head to a temperature equal to or higher than the cloud point of the surfactant by a heating means, and then wiping the discharge port surface by a wiping means. This enables so-called "cloud point cleaning", which can further improve the efficiency of removing the adhesive attached to the discharge port surface, and can further suppress discharge irregularities immediately after the start of initial use. The cloud point of a surfactant refers to the temperature at which a solute (nonionic surfactant) and water separate when an aqueous solution of a nonionic surfactant is heated, and the aqueous solution begins to cloud, and is specified as 1047 in JIS K 3211:1990. In the examples described below, the temperature at which a 1.0 mass% aqueous solution of the surfactant begins to cloud when heated was measured.

Examples of surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants. Of these, it is preferable to use nonionic surfactants such as acetylene glycol surfactants and polyoxyethylene alkyl ethers. The content (mass %) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink, and more preferably 0.1% by mass or more and 2.0% by mass or less. Of these, it is particularly preferable that the content is 0.1% by mass or more and 1.0% by mass or less.

[Other ingredients]
The ink may further contain various additives, such as an antifoaming agent, a pH adjuster, a viscosity adjuster, an antirust agent, an antiseptic, an antifungal agent, an antioxidant, and an antireducing agent, as required.

[Ink properties]
The ink is a water-based ink applied to an inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the ink at 25° C. is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25° C. is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. The terms "parts" and "%" used to describe the amounts of components are by weight unless otherwise specified.

<Preparation of Pigment Dispersion>
(Pigment Dispersion 1)
A styrene-acrylic acid copolymer (water-soluble resin) having an acid value of 120 mgKOH/g and a weight average molecular weight of 10,000 was neutralized with potassium hydroxide in an amount equimolar to the acid value. A mixture was obtained by mixing 10.0 parts of C.I. Pigment Blue 15:3, 3.0 parts of the neutralized styrene-acrylic acid copolymer (solid content), and 85.0 parts of ion-exchanged water. The mixture obtained was dispersed for 1 hour using a sand grinder, and then centrifuged to remove coarse particles. The mixture was then filtered under pressure with a microfilter (manufactured by Fujifilm) having a pore size of 3.0 μm to obtain a pigment dispersion 1 in which C.I. Pigment Blue 15:3 was dispersed in water by the resin. The pigment content in the pigment dispersion 1 was 15.0%, and the resin (resin dispersant) content was 4.5%.

(Pigment Dispersion 2)
Pigment dispersion 2 was obtained in the same manner as in the above-mentioned pigment dispersion 1, except that C.I. Pigment Red 122 was used instead of C.I. Pigment Blue 15:3. The pigment content in pigment dispersion 2 was 15.0%, and the resin (resin dispersant) content was 4.5%.

(Pigment Dispersion 3)
Pigment dispersion 3 was obtained in the same manner as in the above-mentioned pigment dispersion 1, except that C.I. Pigment Blue 15:3 was replaced with C.I. Pigment Yellow 74. The pigment content in pigment dispersion 3 was 15.0%, and the resin dispersant content was 4.5%.

(Pigment Dispersion 4)
A commercially available pigment dispersion containing a self-dispersing pigment in which the pigment type is an organic pigment (C.I. Pigment Blue 15:4) (product name "CAB-O-JET250C", manufactured by Cabot Corporation, pigment content 15.0%) was used as pigment dispersion 4.

(Pigment Dispersion 5)
Pigment Dispersion 5 was obtained in the same manner as in the above-described Pigment Dispersion 1, except that an inorganic pigment (carbon black) was used instead of C.I. Pigment Blue 15:3. The pigment content in Pigment Dispersion 5 was 15.0%, and the resin dispersant content was 4.5%.

(Pigment Dispersion 6)
A commercially available pigment dispersion containing a self-dispersing pigment in which the pigment type is an inorganic pigment (carbon black) (product name "CAB-O-JET300", manufactured by Cabot Corporation, pigment content 15.0%) was used as pigment dispersion 6.

<Preparation of Dye Aqueous Solution>
C.I. Direct Blue 199 was dissolved in water to obtain an aqueous dye solution having a C.I. Direct Blue 199 content of 15.0%.

<Preparation of acrylic resin>
Styrene 81.0 parts and acrylic acid 19.0 parts were copolymerized according to a conventional method to synthesize an acrylic resin (water-soluble resin). The carboxylic acid group in the acrylic resin was neutralized with potassium hydroxide in an amount equivalent to the acid value of the acrylic resin to dissolve the resin, and then an appropriate amount of pure water was added to obtain an aqueous solution of the acrylic resin with a resin content of 20.0%. The acid value of the acrylic resin was 148 mgKOH/g, and the weight average molecular weight of the acrylic resin measured by gel permeation chromatography was 10,000.

<Ink Preparation>
Each ink was prepared by mixing the components (unit: %) shown in the upper rows of Tables 1-1 and 1-2, thoroughly stirring the mixture, and then filtering under pressure using a polypropylene filter (manufactured by Pall) having a pore size of 2.5 μm. In Tables 1-1 and 1-2, "Surfynol 465" is the trade name of an ethylene oxide adduct of acetylene glycol (manufactured by Air Products, number of moles of ethylene oxide groups added: 10). The cloud point of "Surfynol 465", measured on a 1.0% aqueous solution, was 55° C.

<Configuration of Recording Unit (Ink Cartridge)>
A recording unit (ink cartridge) was prepared in which a recording head, which ejects ink by applying thermal energy as shown in FIG. 3, was directly attached to an ink storage unit 10 without a heat sink. The recording head used had an ejection port surface made of epoxy resin and treated with a water repellent agent. The water repellent agent was a resin obtained by hardening a condensate of a hydrolyzable silane compound having a fluoroalkyl group (a compound having a fluoromethyl group and a methoxy group) and a hydrolyzable silane compound having a cationic polymerizable group (a compound having an epoxy group and an ethoxy group). The contact angle of the water repellent treated ejection port surface with water, measured using an automatic contact angle measuring device (product name "CA-W", manufactured by Kyowa Interface Science Co., Ltd.), was 90° or more. A protective tape 50 was attached to the ejection port surface 30 of the recording heads of recording units 1 to 4. A protective tape was not attached to the ejection port surface of the recording head of recording unit 5, and the ejection port surface was covered with a protective cap that can be covered in a sealed state. The peeling direction of the protective tape 50 ("X→X'", "Y'→Y", or "Y→Y'" in FIG. 3) is shown in Table 2. The recording element substrate constituting the recording head has an ejection port array in the YY' direction, in which 384 ejection ports are arranged at an array density of 600 dpi. The mass of the ink droplet ejected from one ejection port is 5.5 ng.

<Evaluation>
(Inkjet recording device)
As an inkjet recording apparatus, a product name "PIXUS TS5130S" (manufactured by Canon) was prepared. A blade-shaped wiper (thickness 1.0 mm) made of urethane resin, which is a wiping means for wiping the discharge port surface, and a recording unit shown in Table 3 were incorporated into the prepared inkjet recording apparatus. Then, wiping was controlled to be performed at a speed of 20 mm/s in the Y→Y' direction shown in FIG. 3. In this embodiment, the recording duty of a solid image recorded under the condition that two ink droplets with a mass of 5.5 ng per droplet are applied to a unit area of 1/600 inch×1/600 inch is defined as 100%. In the present invention, in the evaluation criteria for each item shown below, "AAA", "AA", "A" and "B" were defined as acceptable levels, and "C" was defined as unacceptable levels. The evaluation results are shown in Table 3.

(Discharge distortion)
Each ink shown in Table 3 was filled into the ink storage section of the recording unit shown in Table 3. In order to prevent the ink from evaporating through the member forming the ink storage section, the obtained recording head was placed in a polypropylene container and sealed by heat welding a polyethylene terephthalate film. This container was placed in a thermostatic chamber at a temperature of 60° C. and a relative humidity of 20% and stored for one month. The recording head was stored and used in order to evaluate irregular ejection under more severe conditions. A recovery operation including wiping was performed on the recording head after storage. During the recovery operation, the ink was heated to the temperature shown in Table 3. Thereafter, a nozzle check pattern of PIXUS TS5130S was recorded to check whether irregular ejection of ink occurred. If irregular ejection occurred, a recovery operation was performed and the nozzle check pattern was recorded again. The recovery operation and recording of the nozzle check pattern were repeatedly performed until the ink ejection state from all ejection ports became normal. The number of recovery operations required until the ink ejection state from all the ejection ports returned to normal was then measured, and ejection irregularities immediately after the start of initial use were evaluated according to the following evaluation criteria.
AAA: After one recovery operation, irregular ejection no longer occurred, and ink did not adhere to the ejection port surface.
AA: The irregular ejection did not occur after one recovery operation, but ink was still attached to the ejection port surface.
A: The uneven ejection did not occur after two recovery operations.
B: The uneven ejection did not occur after three recovery operations.
C: Irregular ejection occurred even after three recovery operations.

(Image characteristics)
Using the above-mentioned inkjet recording device, a 2 cm x 2 cm solid image with a recording duty of 100% was recorded on each of the following recording media 1 and 2. The recording conditions were a temperature of 25°C and a relative humidity of 50%. After the recorded solid image was left in an environment of a temperature of 25°C and a relative humidity of 50% for one day, the "water resistance" and "abrasion resistance" of the image were evaluated according to the procedures described below, and the image characteristics were evaluated according to the evaluation criteria described below.
[Recording medium]
Recording medium 1: Plain paper (product name "CS-680", manufactured by Canon)
Recording medium 2: Glossy paper (product name "Glossy Gold", manufactured by Canon)
[Image characteristics]
A: Both the "water resistance" and the "abrasion resistance" were rated "a" or "b".
C: At least one of the "water resistance" and the "abrasion resistance" was rated "c".

[water resistance]
After the recording medium 1 (plain paper) on which a solid image was recorded was immersed in pure water, the solid image was visually observed and the water resistance of the image was evaluated according to the following evaluation criteria.
a: No bleeding of coloring material was observed.
b: Bleeding of coloring material was observed, but at a level that was not problematic.
c: Problematic level of bleeding of coloring material was observed.

[Abrasion resistance]
Silbon paper (3 cm x 3 cm) and a weight (360 g) were placed on a solid image recorded on recording medium 2 (glossy paper). With the weight placed on it, the Silbon paper was moved once over the solid image, and the condition of the solid image was then visually confirmed, and the scratch resistance of the image was evaluated according to the following evaluation criteria.
A: No scraping was observed in the image.
b: Scraping was observed in the image, but the base was not visible.
c: Scraping was confirmed in the image, and the base was visible.

The evaluation results for irregular discharge in both Example 1 and Example 14 were AAA rank, but Example 1 was relatively better than Example 14.

The disclosure of this embodiment includes the following methods and configurations.
(Method 1) An inkjet recording apparatus is used, the inkjet recording apparatus comprising: an ink storage section for storing the water-based ink; a recording head incorporated in the ink storage section, the recording head having an ejection port surface formed with ejection ports for ejecting the water-based ink supplied from the ink storage section; and a wiping means for wiping the ejection port surface;
An inkjet recording method comprising a step of applying the water-based ink ejected from the ejection orifice to a recording medium to record an image,
a protective tape having an adhesive layer formed of an adhesive, the adhesive layer being peeled off when the recording head is used, is attached to the ejection port surface of the recording head;
11. The ink jet recording method according to claim 10, wherein a direction in which the protective tape is peeled off and a direction in which the wiping means wipes the ejection port surface are intersecting or opposite to each other.
(Method 2) The ink-jet recording method according to Method 1, wherein the resin is a water-soluble resin.
(Method 3) The inkjet recording method according to Method 1 or 2, wherein the content (mass %) of the organic pigment in the aqueous ink is 0.5 mass % or more and 10.0 mass % or less based on the total mass of the ink.
(Method 4) The inkjet recording method according to any one of Methods 1 to 3, wherein the content (mass %) of the resin in the aqueous ink is from 0.1 mass % to 20.0 mass % based on the total mass of the ink.
(Method 5) An inkjet recording method described in any one of Methods 1 to 4, wherein the content (mass %) of the resin in the aqueous ink is 0.1 to 0.6 times the content (mass %) of the organic pigment in terms of mass ratio.
(Method 6) The inkjet recording method according to any one of Methods 1 to 5, wherein the aqueous ink further contains at least one water-soluble organic solvent selected from the group consisting of compounds having a cyclic amide structure, alkanediols, and amine compounds.
(Method 7) The inkjet recording method according to any one of Methods 1 to 5, wherein the aqueous ink further contains at least two water-soluble organic solvents selected from the group consisting of compounds having a cyclic amide structure, alkanediols, and amine compounds.
(Method 8) The inkjet recording method according to any one of Methods 1 to 7, wherein the adhesive is a silicone-based adhesive.
(Method 9) The ink jet recording method according to any one of Methods 1 to 8, wherein a peeling direction of the protective tape and a wiping direction of the ejection port surface by the wiping means intersect.
(Method 10) An inkjet recording method described in any one of Methods 1 to 9, wherein the wiping direction of the nozzle surface by the wiping means and the arrangement direction of an nozzle array composed of a plurality of the nozzles on the nozzle surface are approximately parallel to each other.
(Method 11) The ink jet recording method according to any one of Methods 1 to 10, wherein the wiping means is a blade-shaped wiper.
(Method 12) The ink jet recording method according to Method 11, wherein the wiper is made of a rubber material formed from a urethane resin.
(Method 13) The ink jet recording method according to Method 11 or 12, wherein the wiper has a thickness of 0.4 mm or more and 1.1 mm or less.
(Method 14) The ink jet recording method according to any one of Methods 1 to 13, wherein the moving speed of the wiping means when wiping the ejection port surface with the wiping means is 15 mm/s or more and 130 mm/s or less.
(Method 15) The recording head has a heating means for heating the water-based ink in the recording head,
The water-based ink further contains a surfactant,
15. The inkjet recording method according to any one of Methods 1 to 14, further comprising a step of heating the aqueous ink in the recording head to a temperature equal to or higher than the cloud point of the surfactant by the heating means, and then wiping the ejection port surface by the wiping means.
(Configuration 1) An inkjet recording apparatus comprising: an aqueous ink containing an organic pigment and a resin; an ink container for containing the aqueous ink; a recording head incorporated in the ink container, the recording head having an ejection port surface formed with ejection ports for ejecting the aqueous ink supplied from the ink container; and a wiping device for wiping the ejection port surface,
a protective tape having an adhesive layer formed of an adhesive, the adhesive layer being peeled off when the recording head is used, is attached to the ejection port surface of the recording head;
11. An ink jet recording apparatus, comprising: a peeling direction of the protective tape and a wiping direction of the ejection port surface by the wiping means, the peeling direction being intersecting or opposite to each other.

Claims (15)

using an ink jet recording apparatus comprising: an aqueous ink containing an organic pigment and a resin; an ink storage section for storing the aqueous ink; a recording head incorporated in the ink storage section, the recording head having an ejection port surface formed with ejection ports for ejecting the aqueous ink supplied from the ink storage section; and a wiping means for wiping the ejection port surface;
An inkjet recording method comprising a step of applying the water-based ink ejected from the ejection orifice to a recording medium to record an image,
a protective tape having an adhesive layer formed of an adhesive, the adhesive layer being peeled off when the recording head is used, is attached to the ejection port surface of the recording head;
2. The ink jet recording method according to claim 1, wherein a direction in which the protective tape is peeled off and a direction in which the wiping means wipes the ejection port surface are substantially perpendicular to each other or opposite to each other. The inkjet recording method according to claim 1, wherein the resin is a water-soluble resin. The inkjet recording method according to claim 1, wherein the content (mass %) of the organic pigment in the aqueous ink is 0.5 mass % or more and 10.0 mass % or less based on the total mass of the ink. The inkjet recording method according to claim 1, wherein the content (mass %) of the resin in the aqueous ink is 0.1 mass % or more and 20.0 mass % or less based on the total mass of the ink. The inkjet recording method according to claim 1, wherein the content (mass%) of the resin in the aqueous ink is 0.1 to 0.6 times the content (mass%) of the organic pigment in terms of mass ratio. The inkjet recording method according to claim 1, wherein the aqueous ink further contains at least one water-soluble organic solvent selected from the group consisting of compounds having a cyclic amide structure, alkanediols, and amine compounds. The inkjet recording method according to claim 1, wherein the aqueous ink further contains at least two water-soluble organic solvents selected from the group consisting of compounds having a cyclic amide structure, alkanediols, and amine compounds. The inkjet recording method according to claim 1, wherein the adhesive is a silicone-based adhesive. The inkjet recording method according to claim 1, wherein the direction in which the protective tape is peeled off and the direction in which the wiping means wipes the ejection port surface intersect. The inkjet recording method according to claim 1, wherein the wiping direction of the nozzle surface by the wiping means is approximately parallel to the arrangement direction of the nozzle array composed of the plurality of nozzles on the nozzle surface. The inkjet recording method according to claim 1, wherein the wiping means is a blade-shaped wiper. The inkjet recording method according to claim 11, wherein the wiper is made of a rubber material formed from a urethane resin. The inkjet recording method according to claim 11, wherein the thickness of the wiper is 0.4 mm or more and 1.1 mm or less. The inkjet recording method according to claim 1, wherein the moving speed of the wiping means when wiping the ejection port surface is 15 mm/s or more and 130 mm/s or less. the recording head has a heating means for heating the water-based ink in the recording head,
The water-based ink further contains a surfactant,
15. The inkjet recording method according to claim 1, further comprising a step of wiping the ejection port surface with the wiping means after heating the aqueous ink in the recording head to a temperature equal to or higher than the cloud point of the surfactant with the heating means.