JP2021154614A - Maintenance method and recording device - Google Patents

Abstract

To achieve continuous printing stability in an inkjet recording device for discharging an aqueous ink composition using a continuous multistage structure head.SOLUTION: An inkjet recording device discharges an aqueous ink composition containing water and resin particles from a nozzle of an inkjet head having a continuous multistage structure 121 in its inner wall, and performs recording on a heated recording medium, and can achieve continuous printing stability by a maintenance method including a wiping step of wiping a nozzle surface of the inkjet head using an absorptive wiping member 21.SELECTED DRAWING: Figure 4

Description

The present invention relates to a maintenance method and a recording device.

The inkjet recording method is a relatively simple device that can record high-definition images, and is rapidly developing in various fields. Among them, various studies have been made on discharge stability and the like. For example, in Patent Document 1, for the purpose of improving continuous printing stability when placed in a high temperature environment, the viscosity at 20 ° C. is 2 mPa · s or more and 7 mPa · s or less, and the yield value at 20 ° C. is 0. Disclosed are water-based ink compositions that are less than .2 mPa and have a yield value of less than 0.8 mPa at 20 ° C. when the water is evaporated by 25%.

JP-A-2018-002778

As a discharge head capable of increasing the arrangement density of the nozzle holes and realizing high-speed high image quality, there is a discharge head in which a concave-convex shape is repeatedly formed on a side wall surface near the nozzle outlet. A structure in which such an uneven shape is repeatedly formed is also called a scallop structure or a continuous multi-stage structure.

When an inkjet head having such a structure is used to attach ink to a heated recording medium for recording, the continuous print stability is impaired, which is not yet sufficient.

The present invention is a maintenance method for an inkjet recording device that records on a recording medium. The inkjet recording device includes an inkjet head, ejects an aqueous ink composition from a nozzle of the inkjet head, and heats the recording medium. The inkjet head has a nozzle having a continuous multi-stage structure on the inner wall, and has a wiping step of wiping the nozzle surface of the inkjet head with an absorbent wiping member. The water-based ink composition is a maintenance method containing water and resin particles.

The present invention includes an inkjet head that ejects an aqueous ink composition containing water and resin particles, a wiping mechanism that wipes the nozzle surface of the inkjet head with an absorbent wiping member, and a heating mechanism that heats a recording medium. The inkjet head is a recording device having a continuous multi-stage structure on the inner wall of the nozzle.

It is sectional drawing which shows an example of the inkjet head of this embodiment. It is the schematic which shows an example of the wiping process of the maintenance method of this embodiment. It is a schematic cross-sectional view which shows the nozzle which has a continuous multistage structure on the inner wall. It is a conceptual diagram which shows that the deposit is removed by maintenance from the nozzle which has a continuous multi-stage structure on the inner wall. It is a perspective view which shows an example of the inkjet recording apparatus of this embodiment.

Hereinafter, embodiments of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary, but the present invention is not limited thereto, and a gist thereof. Various deformations are possible within the range that does not deviate from. In the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the positional relationship such as up, down, left, and right shall be based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown.

1. 1. Maintenance method The maintenance method of the present embodiment is a maintenance method of an inkjet recording device that records on a heated recording medium, and the inkjet recording device ejects an aqueous ink composition from a nozzle having a continuous multi-stage structure on an inner wall. It includes an inkjet head, has a wiping step of wiping the nozzle surface of the inkjet head with an absorbent wiping member, and the water-based ink composition contains water and resin particles.

In recent years, in order to realize a high array density and a large number of nozzles, a discharge head having a continuous multi-stage structure on a side wall surface has been used. In a nozzle having such a continuous multi-stage structure, since the surface area inside the nozzle hole is large, the ink dries inside the nozzle hole when the meniscus is drawn in during ejection, and the water-based ink composition is applied to the continuous multi-stage structure portion. Solids can adhere and gradually accumulate. When such accumulation occurs, the discharge direction may be deviated or the discharge may be defective. In particular, in an aqueous ink composition containing a resin, such deposition is likely to occur. Further, even when recording is performed on a heated recording medium, the water-based ink composition is more likely to be dried due to the nozzle receiving heat, and accumulation is likely to occur.

On the other hand, in the present embodiment, in order to eliminate such accumulation of the water-based ink composition in the nozzle, the nozzle surface of the inkjet head is wiped with an absorbent wiping member, thereby performing continuous multi-stage. The water-based ink composition deposited on the structural portion can be removed. Further, in the maintenance method of the present embodiment, it is possible to eliminate the accumulation in the nozzle and at the same time remove the water-based ink composition adhering (fixed) to the nozzle surface.

Normally, such wiping is to clean the nozzle surface, so it is considered that it is not related to the removal of the water-based ink composition deposited on the continuous multi-stage structure inside the nozzle. It is thought that. In the maintenance method of the present embodiment, an absorbent wiping member is used. As a result, it is considered that the absorbent wiping member absorbs and removes the water-based ink composition on the nozzle surface and also absorbs the water-based ink composition in the nozzle, so that the deposits in the nozzle are also removed. However, the reason for removing the deposits in the nozzle is not limited to the above.

1.1. Inkjet Head The inkjet recording device that is the target of the maintenance method of the present embodiment includes an inkjet head that ejects a water-based ink composition from a nozzle having a continuous multi-stage structure on the inner wall, and records on a heated recording medium. Is to do. Specifically, recording is performed by ejecting and adhering ink to a heated recording medium.
First, an inkjet head having a continuous multi-stage structure will be described.

FIG. 1 shows a cross-sectional view of the inkjet head. The inkjet head 11 includes a nozzle plate 112 having a plurality of nozzles 111 on a surface facing the recording medium (adhesion target), a plurality of pressure chambers 114 communicating with each of the plurality of nozzles 111 formed on the nozzle plate 112, and a plurality of pressure chambers 114. It includes a pressurizing unit 115 that changes the volume of each of the plurality of pressure chambers 114, and an ink supply chamber 116 that supplies ink to the plurality of pressure chambers 114. In the present embodiment, the nozzle surface 12 refers to a surface including the surface of the nozzle plate 112. The nozzle surface is also called a nozzle forming surface.

Examples of the pressurizing unit 115 include a piezo method in which ink is discharged by the driving pressure of a piezoelectric element and a thermal method in which ink is discharged by bubbles generated by heating the ink. An inkjet head that uses the piezo method is called a piezo head, and an inkjet head that uses the thermal method is also called a thermal head.

The nozzle plate 112 is a plate material in which a plurality of nozzles 111 for ejecting ink are provided in a row. In order to improve the resolution of the water-based ink composition adhered to the recorded material, it is necessary to arrange the nozzles 111 at a high density on the nozzle plate 112 to increase the number of nozzles. As a method for manufacturing such a high-density inkjet head, a method of forming through holes at a high density by, for example, a Bosch process is known for a silicon wafer on which a nozzle is formed.

In the Bosch process, a through hole is formed by alternately and repeatedly etching the silicon wafer in the thickness direction and protecting the etching side wall many times. The through hole formed in this way, that is, the nozzle has a continuous multi-stage structure on the inner wall.

An example of such a continuous multi-stage structure of the inner wall of the nozzle is shown in FIG. Assuming that the nozzle is a cylindrical space, it is a side view of the cylindrical cross section. Circular steps along the circle of the cylinder are formed continuously on the inner surface of the cylinder in the direction of the cylinder.
The continuous multi-stage structure 121 refers to an uneven shape in which the side wall of the nozzle is formed in the direction in which ink passes through the nozzle when the cross section of the nozzle is viewed. Such a concave-convex shape has, for example, a shape in which a concave portion 122 curved toward the inner wall side and a convex portion 123 serving as a boundary of the curved portion are repeated. In the figure, the unevenness of the continuous multi-stage structure is shown in an enlarged manner.

Such a continuous multi-stage structure 121 can also be defined by the depth a of the concave portion and the distance b between the adjacent convex portions. When there are a plurality of convex portions or concave portions, the depth a of the concave portions and the distance b between the convex portions can be represented by the average value of the depths of the concave portions and the average value of the distances between the convex portions.

The depth a of the recess is preferably 1.0 μm or less. It is more preferably 0.01 μm or more and 1.0 μm or less, more preferably 0.015 μm or more and 0.5 μm or less, and further preferably 0.02 μm or more and 0.3 μm or less. Particularly preferably, it is 0.02 to 0.15 μm.
On the other hand, the distance b between the adjacent convex portions is preferably 1.0 μm or less. It is more preferably 0.3 μm or more and 1.0 μm or less, more preferably 0.4 μm or more and 0.8 μm or less, and further preferably 0.45 μm or more and 0.7 μm or less. When the depth a of the concave portion and the distance b between the convex portions are within the above ranges, the water-based ink composition deposited in the continuous multi-stage structure tends to be more easily removed.

Further, the ratio b / a of the distance b between the adjacent convex portions of the continuous multi-stage structure to the depth a of the concave portion of the continuous multi-stage structure is preferably 1.0 to 25, more preferably 1.5 to 20. It is more preferably 2.0 to 15, and particularly preferably 3.0 to 10. When the ratio b / a is 1.0 or more, the depth a is shallow and the distance b is long, so that it is difficult for the water-based ink composition to be deposited in the continuous multi-stage structure, and the deposited water-based ink composition is more removed. It tends to be easier to do. Further, when the ratio b / a is 25 or less, the water-based ink composition is likely to be deposited on the continuous multi-stage structure, which makes the present invention particularly useful.
The thickness of the nozzle plate, which is the substrate on which the nozzle of the inkjet head is formed, is not limited, but is preferably 20 μm or more, more preferably 20 to 300 μm, further preferably 40 to 100 μm, and particularly preferably 45 to 80 μm.
The nozzle diameter is not limited, but is preferably 5 to 50 μm or more, more preferably 10 to 40 μm, still more preferably 15 to 30 μm.

1.2. Heating Mechanism The inkjet recording device that is the target of the maintenance method of the present embodiment may have a heating mechanism for heating the recording medium during recording. Such a heating mechanism is not particularly limited, and examples thereof include a platen heater, a preheater, an IR heater, and a blower fan (warm air heater). When the recording medium is heated in the step of adhering the ink composition, it may be heated by using a heating mechanism. As a result, excellent image quality can be obtained.

1.3. Wiping step The wiping step is a step of wiping the nozzle surface of the inkjet head with an absorbent wiping member. The wiping method is not particularly limited, but for example, while moving the wiping member or the nozzle forming surface so as to press the wiping member against the nozzle surface and move the wiping member relatively in the direction along the nozzle surface. Can be wiped.

FIG. 2 shows a schematic cross-sectional view showing a state in which the wiping member (cloth wiper) is brought into contact with the nozzle forming surface of the inkjet head. FIG. 2 is a diagram showing a state in which the wiping member 21 is pressed against the nozzle forming surface 12 of the inkjet head 11 in the direction of the arrow F1. Further, FIG. 4 shows a conceptual diagram showing that deposits are removed by maintenance from a nozzle having a continuous multi-stage structure on the inner wall. By wiping the nozzle forming surface 113 with the absorbent wiping member 21, the ink in the nozzle is absorbed by the wiping member 21 and sucked from the nozzle. At this time, it is presumed that the deposit 118 generated on the inner wall of the nozzle also exerts a force to be discharged together with the ink, and the deposit 118 is removed from the inner wall of the nozzle in the direction of the arrow. On the other hand, if the absorbent wiping member 21 is not used for wiping, it is presumed that the deposits are not removed and accumulate on the inner wall of the nozzle, which gradually sticks and becomes difficult to remove, and the landing position shift gradually increases. do. 117 indicates the ink absorbed by the wiping member.

The wiping direction is not particularly limited, but it is preferable to wipe in the direction along the nozzle row. As a result, it is possible to prevent the portion of the wiping member that is in contact with one nozzle row from coming into contact with the other nozzle row and contaminating the nozzle surface 12.

The pressing load of the absorbing member 21 against the nozzle forming surface 12 is preferably 8 gf / cm or more. On the other hand, it is preferably 300 gf / cm or less. Furthermore, it is preferably 8 to 300 gf / cm, more preferably 15 to 200 gf / cm, and even more preferably 25 to 100 gf / cm. Particularly preferably, it is 30 to 50 gf / cm.
When the load is 8 gf / cm or more, the ink wiping property of the nozzle forming surface is excellent, and the deposits in the nozzle can be removed more effectively. Further, when the load is 300 gf / cm or less, the storage stability of the liquid repellent film formed on the nozzle forming surface is further excellent. The load referred to here is a value obtained by dividing the contact length from the total load applied to the inkjet head 11 (that is, the average linear pressure). Further, the contact length is the contact length in the longitudinal direction between the inkjet head 11 and the absorbing member 21, and includes the length when the nozzle plate cover and the absorbing member are in contact with each other.

13.1. Wiping member The wiping member is not particularly limited as long as it absorbs liquid, and a sponge, a woven fabric, a non-woven fabric, or the like can be used. The absorbency means that the maintenance liquid, the ink composition, and the like can be absorbed. Here, when the wiping member is a woven cloth or a non-woven fabric, the constituent fibers thereof are not particularly limited, and examples thereof include natural fibers such as cellulose fibers and synthetic fibers such as polyester fibers. Of these, natural fibers are preferable, and cellulose fibers are more preferable. Both polyester fibers and cellulose fibers tend to have excellent detergency. Further, since the cellulose fibers are swollen by water, the fibers are softened by the maintenance liquid, and the wear of the water-repellent film on the nozzle forming surface can be further reduced. In addition, since foreign matter enters the gaps between the swollen cellulose fibers, the detergency tends to be further improved.

The wiping member shown in FIG. 2 is a long cloth, and the wiping member 21 before use is sent out from the first roll 22, and the used wiping member 21 is wound up from the second roll 23. As a result, the nozzle forming surface 12 can be brought into contact with the new wiping member 21 before use. Therefore, it is possible to prevent the nozzle forming surface 12 from being recontaminated by the ink composition that has permeated the used wiping member 21 by recontacting the used wiping member 21 with the nozzle forming surface 12.

1.3.2. In the maintenance liquid wiping step, wiping may be performed using the maintenance liquid. The maintenance liquid may be used by impregnating the wiping member with the wiping member, or may be used by adhering to the nozzle surface. The components contained in the maintenance liquid are not particularly limited, and examples thereof include water, organic solvents, pH adjusters, and the like.

1.3.2.1. As the water maintenance liquid, water, a water-based composition, or the like is preferable.
The maintenance liquid preferably contains 50% by mass or more of water with respect to the total mass. Further, it is more preferable to contain 70% by mass or more of water, and it is particularly preferable to contain 80% by mass or more of water. As a result, the permeability of the wiping member is improved, and foreign matter is easily taken into the wiping member. Therefore, in addition to the improvement of the cleanability of the nozzle surface, the removal property of the deposit in the nozzle tends to be further improved. Further, when the water content is within the above range, the components of the solidified water-based ink composition tend to be easily redispersed and easily removed.

From the above viewpoint, the content of water in the maintenance liquid is preferably 85% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass. The water content in the maintenance liquid is 100% by mass or less, preferably 99% by mass or less, more preferably 98.5% by mass or less, and further preferably 98% by mass or less. When the water content of the maintenance liquid is equal to or higher than the above range, foreign matter is more easily taken into the wiping member, and the cleaning property tends to be better.

When the water content of the maintenance liquid is less than the above range, for example, when the maintenance liquid contains an organic solvent less than a predetermined amount than the maintenance liquid which is all water, the removal property of foreign matter on the nozzle forming surface is excellent and cleaning is performed. The sex tends to improve.

1.3.2.2. Organic solvent From the above viewpoint, the maintenance liquid preferably contains an organic solvent. This tends to further improve the detergency. The organic solvent is not particularly limited, but for example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol. , 1,2-Hexanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol monoethyl ether, methanol, ethanol and other organic solvents that are miscible with water. Examples thereof include organic solvents that may be contained in the water-based ink composition described later.

Among the organic solvents, polyols, glycol ethers, and alkanediols having 5 or more carbon atoms are particularly excellent and preferable in the above respects.
The alkanediol having 5 or more carbon atoms preferably has 5 to 10 carbon atoms, and more preferably 6 to 8 carbon atoms. The alkanediols having 5 or more carbon atoms are not particularly limited, and are, for example, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-hexanediol. Heptanediol, 2-ethyl-1,3-hexanediol, 2,2-dimethyl-1,3-propanediol, 2,2-dimethyl-1,3-hexanediol, 3-methyl-1,5-pentanediol And so on. Of these, 1,2-alkanediol is preferable, and 1,2-pentanediol and 1,2-hexanediol are more preferable.
Glycol ether is an etherified product of alkylene glycol or a condensate of alkylene glycol hydroxyl groups condensed between molecules. In the case of a condensate, the number of condensations is preferably 2 to 6, more preferably 2 to 4. In the alkylene glycol and its condensate, the alkylene may be linear or branched, preferably having 1 to 7 carbon atoms, and more preferably 2 to 5 carbon atoms. As the ether of glycol ether, alkyl ether is preferable. The alkyl group of the alkyl ether preferably has 1 to 5 carbon atoms, more preferably 1 to 4 carbon atoms. The glycol ether may be glycol monoether or glycol diether, and glycol monoether is preferable.
Examples of the glycol ether include those that may be contained in the ink described later.

Polyols are also preferable because they have excellent detergency. Examples of the polyols include alkane polyols having 4 or less carbon atoms and condensates of alkane polyols having 4 or less carbon atoms in which hydroxyl groups are condensed between molecules. These carbon numbers are preferably 2 to 3. In the case of a condensate, the number of condensations is preferably 2-4. Polyols have 2 or more hydroxyl groups in the molecule, preferably 2 to 4.
Glycol ethers, polyols, and alkanediols having 5 or more carbon atoms may be used alone or in combination of two or more.

The content of the organic solvent is preferably 20% by mass or less with respect to the total mass of the maintenance liquid. The lower limit of the content of the organic solvent is 0% by mass or more, that is, it does not have to be contained. Furthermore, the content of the organic solvent is preferably 0.5 to 20% by mass, more preferably 1.0 to 10% by mass, and even more preferably 1.0 to 5.0% by mass. , Particularly preferably 1.0 to 3.0% by mass. When the content of the organic solvent is equal to or higher than the above range, the organic solvent permeates into the nozzle forming surface or the foreign matter stuck in the nozzle, swells or dissolves the foreign matter, and makes it easier to remove the foreign matter. Detergency tends to be improved. Further, when the content of the organic solvent is not more than the above range, it tends to be possible to suppress the decrease in absorption of the maintenance liquid into the wiping member due to the relative decrease in the water content.

Among the organic solvents, polyols, glycol ethers, and alkanediols having 5 or more carbon atoms are preferable in the above points, and the contents thereof may be in the above range.
In particular, glycol ether and alkanediol having 5 or more carbon atoms are more preferable in the above points, and the content thereof may be in the above range.

1.3.2.2. pH regulator The maintenance solution may contain a pH regulator. As the pH adjuster, it is possible to easily adjust the pH value of the water-based ink composition. The pH adjuster is not particularly limited, but is, for example, an inorganic acid (for example, sulfuric acid, hydrochloric acid, nitrate, etc.), an inorganic base (for example, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), and an organic base (for example, lithium hydroxide, sodium hydroxide, ammonia, etc.). Examples thereof include triethanolamine, diethanolamine, monoethanolamine, triisopropanolamine), organic acids (for example, adipic acid, citric acid, succinic acid, etc.). Of these, organic bases are preferable, and triethanolamine and triisopropanolamine are more preferable. The pH adjuster may be used alone or in combination of two or more.

The content of the pH adjuster is preferably 0.01 to 2% by mass, more preferably 0.05 to 1% by mass, and even more preferably 0.05 to 0, based on the total mass of the maintenance liquid. It is 5.5% by mass.

1.3.2.4. Surfactant The maintenance liquid may further contain a surfactant. The surfactant is not particularly limited, and examples thereof include an acetylene glycol-based surfactant, a fluorine-based surfactant, and a silicone-based surfactant.

The acetylene glycol-based surfactant is not particularly limited, and is, for example, 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5. Selected from alkylene oxide adducts of decin-4,7-diol and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol and 2,4-dimethyl-5-decyne-4-ol. One or more is preferable. Commercially available products of acetylene glycol-based surfactants are not particularly limited, but for example, E series such as Orfin 104 series and Orfin E1010 (trade name, manufactured by Air Products Japan, Inc.), Surfinol 465. And Surfinol 61 (trade name, manufactured by Nissin Chemical Industry CO., Ltd.). The acetylene glycol-based surfactant may be used alone or in combination of two or more.

The fluorosurfactant is not particularly limited, and is, for example, perfluoroalkyl sulfonate, perfluoroalkyl carboxylic acid salt, perfluoroalkyl phosphate ester, perfluoroalkyl ethylene oxide adduct, perfluoroalkyl betaine, per. Fluoroalkylamine oxide compounds can be mentioned. Commercially available products of fluorine-based surfactants are not particularly limited, but for example, S-144, S-145 (trade name, manufactured by Asahi Glass Co., Ltd.); FC-170C, FC-430, Florard-FC4430 (the above products). Name, manufactured by Sumitomo 3M Co., Ltd .; FSO, FSO-100, FSN, FSN-100, FS-300 (trade name, manufactured by DuPont); FT-250, 251 (trade name, manufactured by Neos Co., Ltd.), etc. Can be mentioned. The fluorine-based surfactant may be used alone or in combination of two or more.

Examples of the silicone-based surfactant include polysiloxane-based compounds and polyether-modified organosiloxanes. The commercially available silicone-based surfactant is not particularly limited, but specifically, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK. -348, BYK-349 (trade name, manufactured by Big Chemie Japan Co., Ltd.), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640 , KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) and the like. The silicone-based surfactant may be used alone or in combination of two or more.

When a surfactant is contained, the content thereof is preferably 0.1 to 3.0% by mass with respect to the total mass of the maintenance liquid. The surfactant is more preferably 0.1 to 2.0% by mass, still more preferably 0.3 to 1.0% by mass.

On the other hand, since the maintenance liquid contains a surfactant, the contact angle with respect to the nozzle forming surface is lowered, so that the maintenance liquid containing foreign matter or the like is spread on the nozzle forming surface, and the cleaning property may be deteriorated. .. From this point of view, it is preferable that the surfactant is not contained or is contained as little as possible, or the content is small. In this case, the content of the surfactant is preferably 3.0% by mass or less, more preferably 1.0% by mass or less, still more preferably 0.5% by mass, based on the total mass of the maintenance liquid. % Or less, more preferably 0.1% by mass or less, still more preferably 0.05% by mass or less, and particularly preferably 0.01% by mass or less. The lower limit is 0% by mass or more. Further, the lower limit is preferably not more than the detection limit.

The fact that the content of a certain component of the composition is XX% by mass or less with respect to the total mass of the composition is also referred to as the composition does not contain the component in excess of XX% by mass. It means that the composition does not have to contain the component, and may contain the component as long as it does not exceed XX% by mass.

1.3.2.5. Surface tension The surface tension of the maintenance liquid is preferably 20 mN / m or more, and more preferably 45 mN / m or more. Further, it is more preferably 50 mN / m or more, further preferably 55 mN / m or more, and particularly preferably 60 mN / m or more. When the surface tension of the maintenance liquid is 20 mN / m or more, foreign matter is taken into the droplet-shaped maintenance liquid, and the foreign matter is further absorbed by the wiping member, so that the cleaning property tends to be further improved. The surface tension of the maintenance liquid is preferably 80 mN / m or less, more preferably 75 mN / m or less, and further preferably 73 mN / m or less. When the surface tension of the maintenance liquid is 80 mN / m or less, the wet area of the nozzle forming surface per maintenance liquid is improved, and the detergency tends to be further improved.

The surface tension of the maintenance liquid can be adjusted by adjusting the amount and type of the organic solvent contained in the maintenance liquid and the presence or absence of the use of a surfactant. Further, the surface tension of the maintenance liquid can be measured by the method described in Examples.

1.4. Adhesion Step of Maintenance Liquid The maintenance method of the present embodiment may further include an adhesion step of adhering the maintenance liquid to the nozzle surface or the wiping member. The method of adhering the maintenance liquid to the nozzle forming surface or the wiping member is not particularly limited, but for example, the maintenance liquid is adhered to the nozzle forming surface or the wiping member by injecting, dropping, or applying (coating) the maintenance liquid. A method of impregnating the maintenance liquid with a wiping member and the like can be mentioned. As a result, the nozzle forming surface is wiped by the wiping member in the presence of the maintenance liquid.

For example, in FIG. 2, the maintenance liquid 31 can be adhered to the first roll 22 on which the wiping member 21 before use is wound by the first jet 24. Alternatively, the maintenance liquid 31 may be attached to the wiping member 21 by adhering the first roll 22 around which the wiping member before use is wound to the pool 26 of the maintenance liquid 31. ..

The position where the maintenance liquid adheres to the wiping member 21 in the stage before reaching the nozzle forming surface 12 is not limited to the position in FIG. 2, and the wiping before use is sent from the first roll 22 in the direction of arrow F2. The maintenance liquid 31 may be attached to the member 21 at an arbitrary stage before reaching the nozzle forming surface 12. For example, the position may be closer to the nozzle forming surface 12. For example, it may be the position immediately before the roller that presses the wiping member 21 in the direction of the arrow F1. Further, the maintenance liquid 31 can be adhered to the nozzle forming surface 12 by the second injector 25.

The maintenance method of the present embodiment does not have to include an adhesion step of adhering the maintenance liquid to the nozzle forming surface or the wiping member. In this case, maintenance may be performed using a wiping member to which the maintenance liquid is attached in advance.

The bonding step for adhering the maintenance liquid to the nozzle forming surface or the wiping member is not limited to the one using the adhering mechanism such as the injector or the pool (immersion machine), and can be changed as appropriate. For example, as the adhesion mechanism, a dropping machine, a coating machine, or the like can also be used.

In the adhesion process, the amount of the maintenance liquid attached is the amount of the maintenance liquid attached to the wiping member or the nozzle forming surface. The adhesion amount is the amount of maintenance liquid used when performing maintenance once, and is the amount of maintenance liquid used per nozzle row that ejects one (one type) ink composition.

The amount of the maintenance liquid adhered is preferably 0.1 g or more, more preferably 0.3 g or more, and further preferably 0.5 g or more. On the other hand, the amount of adhesion is preferably 5 g or less, more preferably 3.0 g or less, and further preferably 1.0 g or less. In this case, the detergency is more excellent and the waste of the maintenance liquid can be reduced, which is preferable.
The amount of the maintenance liquid adhered is the amount of the maintenance liquid adhered when the wiping process is performed once, and is the amount of the maintenance liquid adhered to one ink nozzle row.

1.5. Water-based ink composition The water-based ink composition used in the inkjet recording apparatus, which is the target of the maintenance method of the present embodiment, contains water and resin particles. If necessary, an organic solvent, a pigment, a wax, an antifoaming agent, a surfactant, a pH adjuster and the like may be contained. In the present embodiment, the "aqueous system" refers to a composition containing water as one of the main solvent components. Specifically, it refers to a composition in which the content of water with respect to the total mass of the composition is approximately 40% by mass or more. Hereinafter, each component will be described in detail.

1.5.1. The content of water and water is preferably 40% by mass or more with respect to the total amount of the water-based ink composition. Further, it is preferably 40 to 99% by mass, more preferably 50 to 90% by mass, more preferably 60 to 80% by mass, and further preferably 65 to 70% by mass. When the water content is in the above range or more, the amount of VOC (volatile organic compound) emitted tends to be smaller, and the drying property of the water-based ink composition by blowing air tends to be further improved.

1.5.2. Resin particles Resin particles may be dispersed in the form of an emulsion or suspension. By using such a resin, a recorded material having more excellent abrasion resistance tends to be obtained. In particular, it tends to contribute to the improvement of the bondability (rubbing resistance) between the recording medium and the water-based ink coating film.
On the other hand, when the ink contains a large amount of resin particles, the resin particles are likely to be formed as deposits in a continuous multi-stage structure.

The resin constituting the resin particles is not particularly limited, and for example, acrylic resin, vinyl acetate resin, vinyl chloride resin, butadiene resin, styrene resin, polyester resin, crosslinked acrylic resin, crosslinked styrene resin, benzoguanamine resin, phenol resin, and the like. Examples thereof include silicone resins, epoxy resins, urethane resins, paraffin resins, fluororesins, and water-soluble resins, and copolymers in which the monomers constituting these resins are combined. The copolymer is not particularly limited, and examples thereof include styrene butadiene resin and styrene acrylic resin. Further, as the resin, a polymer latex containing these resins can be used. For example, a polymer latex containing fine particles of an acrylic resin, a styrene acrylic resin, a styrene resin, a crosslinked acrylic resin, and a crosslinked styrene resin can be mentioned. The resin may be used alone or in combination of two or more. In particular, it is preferable that the resin particles contained in the water-based ink composition of the present embodiment contain at least one of an acrylic resin, a urethane resin, or a polyester resin.
The above-mentioned acrylic resin is a polymer obtained by at least polymerizing an acrylic monomer, and also includes a copolymer polymer of the acrylic monomer and another monomer. Examples of the acrylic monomer include (meth) acrylate and (meth) acrylic acid. Examples of other monomers include vinyl monomers and the like, and examples thereof include styrene.
The urethane-based resin is a resin obtained by urethane polymerization of a polyisocyanate compound and a polyol compound.

The content of the resin particles is preferably 0.5% by mass or more, more preferably 1% by mass or more, based on the total amount of the water-based ink composition. Further, it is preferably 2.0% by mass or more, more preferably 3.0 to 15.0% by mass, more preferably 4.0 to 10.0% by mass, still more preferably 3.0. ~ 8.0% by mass. When the resin content is in the above range or more, the abrasion resistance is more excellent, but the present invention is particularly useful because deposits are likely to be formed in the continuous multi-stage structure. When the resin content is less than or equal to the above range, the suppression of landing position deviation is more excellent.

1.5.3. Organic Solvent The organic solvent contained in the aqueous ink composition is not particularly limited, and is, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, and diethylene glycol. Monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monobutyl ether, 1-methyl-1-methoxybutanol, 3-methoxy-3-methylbutanol, propylene glycol Monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol mono Glycol monoethers such as butyl ether and tetraethylene glycol monobutyl ether; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol ethyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, di Glycoldiethers such as propylene glycol diethyl ether and tripropylene glycol dimethyl ether; nitrogen-containing solvents such as 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone; glycerin; ethylene glycol, diethylene glycol and triethylene glycol , Propropylene glycol, dipropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,4-butanediol, 1,5-pentanediol, Glycols such as 1,6-hexanediol; methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, 2-butanol, tert- Alcohols such as butanol, iso-butanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol can be mentioned.
Examples of the nitrogen-containing solvent include cyclic amides and acyclic amides. Examples of the cyclic amide include the above-mentioned pyrrolidones. Examples of the acyclic amide include N, N-dialkyl-alkyl amide and the like. Examples of the N, N-dialkyl-alkylamide include N, N-dialkyl-alkoxyalkylamide.
Among the organic solvents, the organic solvent which may be contained in the above-mentioned maintenance liquid is preferable. Further, nitrogen-containing solvents, polyols, glycol ethers, and alkanediols having 5 or more carbon atoms are preferable.
Further, among them, propylene glycol, 2-pyrrolidone, 1,2-hexanediol, glycerin and the like are preferable. The organic solvent may be used alone or in combination of two or more.

The content of the organic solvent is preferably 1% by mass or more, more preferably 1 to 45% by mass, based on the total amount of the water-based ink composition. Further, it is preferably 10 to 45% by mass, more preferably 15 to 40% by mass, and further preferably 20 to 35% by mass. When the standard boiling point of the organic solvent is within the above range, the deviation of the landing position is more suppressed, and the discharge stability tends to be further improved.

The organic solvent having a standard boiling point of more than 280 ° C. is preferably not contained in an amount of more than 2.0% by mass, more preferably not more than 1.0% by mass, based on the total amount of the aqueous ink composition. It is more preferable that the content does not exceed 0.5% by mass, and it is particularly preferable that the content does not exceed 0.1% by mass. The lower limit of the content of the organic solvent having a standard boiling point of more than 280 ° C. is 0% by mass or more. Not containing more than XX% by mass means that it may or may not be contained if it does not exceed.
When the content of such an organic solvent is within the above range, the drying property of the ink tends to be improved, and the image quality and scratch resistance of the obtained recorded matter tend to be further improved.

1.5.4. Pigments The pigments are not particularly limited, but are, for example, carbon blacks such as furnace black, lamp black, acetylene black and channel black (CI pigment black 7), inorganic pigments such as iron oxide and titanium oxide; quinacridone-based pigments. Pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanslon pigments, flavanthron pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments , Kinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments, magenta pigments, and organic pigments such as azo pigments. The pigment may be used alone or in combination of two or more.

The content of the pigment is preferably 0.5% by mass or more, more preferably 0.5 to 20% by mass, based on the total amount of the water-based ink composition. Further, it is preferably 2.0% by mass or more, more preferably 3.0 to 18% by mass, and further preferably 5.0 to 10% by mass. When the content of the pigment is not more than the above range, the solidification of the aqueous ink composition is more suppressed, and the ejection stability tends to be further improved. Further, when the content of the pigment is equal to or more than the above range, the optical density of the obtained recorded matter tends to be further improved. The content of the pigment means the solid content, and when the pigment is mixed with the water-based ink composition in the form of a pigment dispersion liquid, it means the solid content.

1.5.5. Wax Wax may be one that dissolves in an aqueous ink composition or one that disperses in the form of an emulsion.

Such wax is not particularly limited, and examples thereof include ester wax, paraffin wax, olefin wax, or a mixture thereof of a higher fatty acid and a higher monohydric alcohol or a dihydric alcohol (preferably a monohydric alcohol). .. Among these, olefin wax is preferable, and polyethylene wax is more preferable.

The wax content is preferably 0.1 to 3.0% by mass, preferably 0.3 to 2.0% by mass, preferably 0.3 to 0.3% by mass, based on the total amount of the water-based ink composition. It is 1.0% by mass. When the wax content is 0.1% by mass or more, the abrasion resistance tends to be further improved as described above. Further, when the wax content is 3.0% by mass or less, the viscosity of the ink tends to decrease and the ejection stability tends to be excellent.

1.5.6. Defoaming agent The defoaming agent is not particularly limited, and examples thereof include a silicone-based defoaming agent, a polyether-based defoaming agent, a fatty acid ester-based defoaming agent, and an acetylene glycol-based defoaming agent. Commercially available antifoaming agents include BYK-011, BYK-012, BYK-017, BYK-018, BYK-019, BYK-020, BYK-021, BYK-022, BYK-023, BYK-024, BYK. -025, BYK-028, BYK-038, BYK-044, BYK-080A, BYK-094, BYK-1610, BYK-1615, BYK-1650, BYK-1730, BYK-1770 (trade names, Big Chemie Japan) DF37, DF110D, DF58, DF75, DF220, MD-20, Envilogem AD01 (all of the above are trade names, manufactured by Nissin Chemical Industry Co., Ltd.). .. The defoaming agent may be used alone or in combination of two or more.

The content of the defoaming agent is preferably 0.03 to 0.7% by mass, more preferably 0.05 to 0.5% by mass, still more preferably, based on the total amount of the water-based ink composition. It is 0.08 to 0.3% by mass.

1.5.7. Surfactant The surfactant is not particularly limited, and examples thereof include the same ones as those exemplified in the above maintenance liquid. The content of the surfactant is preferably 0.3 to 3.0% by mass, more preferably 0.5 to 2.0% by mass, still more preferably, based on the total amount of the water-based ink composition. Is 0.8 to 1.5% by mass.

1.5.8. pH adjuster The water-based ink composition may contain a pH adjuster. The pH adjuster can facilitate the adjustment of the pH value of the water-based ink composition.

The pH adjuster is not particularly limited, but is, for example, an inorganic acid (for example, sulfuric acid, hydrochloric acid, nitrate, etc.), an inorganic base (for example, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), and an organic base (for example, lithium hydroxide, sodium hydroxide, ammonia, etc.). Examples thereof include triethanolamine, diethanolamine, monoethanolamine, tripropanolamine), organic acids (for example, adipic acid, citric acid, succinic acid, etc.). The pH adjuster may be used alone or in combination of two or more.

The content of the pH adjuster is preferably 0.1% by mass or less, more preferably 0.05 to 0.1% by mass, still more preferably, based on the total amount of the water-based ink composition. Is 0.01 to 0.1% by mass.
The surface tension of the ink composition is preferably 15 _{mN / m or more, and more preferably 17 to} 40 mN / m or more. It is more preferably 20 _to 30 mN / m or more, and more preferably 22 to 25 mN / m or more. Further, the above-mentioned maintenance liquid preferably has a higher surface tension than the ink composition, and more preferably 10 mN / m or more.
It is more preferably 20 to 50 mN / m higher. In this case, the detergency tends to be further improved. The method of adjusting and measuring the surface tension of the ink can be carried out in the same manner as in the maintenance liquid.

1.6. Heating Step The recording apparatus of the present embodiment records by a recording method having a heating step of heating the recording medium in the step of adhering the water-based ink composition to the recording medium. That is, recording is performed by a recording method in which the water-based ink composition is adhered to a heated recording medium. This is a step of quickly heating the ink that has landed on the recording medium and rapidly accelerating the drying. The step of heating the recording medium in the step of adhering the ink composition is also referred to as a primary heating step or a primary drying step.
The heating step is not particularly limited, but for example, the heating function as described above is used. Platen heaters, hot air heaters, IR heaters, pre-heaters and the like can be mentioned.

By heating the recording medium in the step of adhering the water-based ink composition, the volatile components of the water-based ink composition adhering to the recording medium are likely to volatilize, and the image quality of the obtained recorded material tends to be further improved. It is in.

When the recording medium is heated in the step of adhering the water-based ink composition, the surface temperature of the recording medium in the step is preferably 50 ° C. or lower, more preferably 45 ° C. or lower, and more preferably 45 ° C. or lower. It is 40 ° C. or lower, more preferably 38 ° C. or lower, more preferably 35 ° C. or lower, and further preferably 20 to 35 ° C.
On the other hand, the surface temperature of the recording medium is preferably 15 ° C. or higher, more preferably 20 ° C. or higher, more preferably 25 ° C. or higher, still more preferably 30 ° C. or higher, and even more preferably 32 ° C. or higher. Is.
When the temperature is above the above range, the image quality is more excellent, and when the temperature is below the above range, the reduction of the ink landing position deviation, the nozzle surface wiping property, and the like are more excellent and preferable.
The surface temperature of the recording medium is the surface temperature of the recording medium at the position where the inkjet head faces the recording medium during recording, and is the maximum temperature during recording.

The recording method includes a secondary drying step (secondary heating step) in which the recording medium is further heated to sufficiently dry the ink on the downstream side of the platen in the transport direction of the recording medium after the ink adhesion step is completed. You may. The surface temperature of the recording medium in the secondary drying step is preferably 60 ° C. or higher, more preferably 70 to 120 ° C.

1.7. Recording medium The recording medium used in the present embodiment is not particularly limited, and examples thereof include an absorbent recording medium and a low-absorbent or non-absorbent recording medium. Of these, it is preferable to use a low-absorption or non-absorbent recording medium. In particular, it is preferable to use a non-absorbent recording medium.

The absorbent recording medium is not particularly limited, but for example, plain paper such as electrophotographic paper having high ink permeability, inkjet paper (an ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol (PVA)). ), Polyvinylpyrrolidone (PVP), and other ink-absorbing layers made of hydrophilic polymers). Alternatively, fabrics and the like can also be mentioned.

Examples of the low-absorbency recording medium include art paper, coated paper, cast paper, and the like used for general offset printing having relatively low ink permeability. These are also referred to as coated paper because a coating layer having a relatively low ink permeability is provided on a base material such as paper. The coating layer is a layer made of a resin, an inorganic compound, etc., which has low water absorption, and has low ink absorption.

The non-absorbent recording medium is not particularly limited, and is, for example, a film or plate of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; iron, silver, copper, and aluminum. Plates of metals such as; or metal plates and plastic films manufactured by vapor deposition of these various metals, plates of alloys such as stainless steel and true cast; polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate on a paper base material. Examples thereof include a recording medium in which a plastic film such as (PET), polycarbonate, polystyrene, or polyurethane is adhered (coated).

2. Inkjet recording device The inkjet recording device of the present embodiment includes an inkjet head that ejects a water-based ink composition containing water and a resin, a wiping mechanism that wipes the nozzle surface of the inkjet head with an absorbent wiping member, and recording. The inkjet head includes a heating mechanism for heating the medium, and the inkjet head has a continuous multi-stage structure on the inner wall of the nozzle. Further, the recording device is maintained by the above-mentioned maintenance method.

As an example of the inkjet recording apparatus used in the maintenance method of the present embodiment, FIG. 5 shows a perspective view of a serial printer. As shown in FIG. 5, the serial printer 200 includes a transport unit 220 and a recording unit 230. The transport unit 220 transports the recording medium F supplied to the serial printer to the recording unit 230, and discharges the recording medium after recording to the outside of the serial printer. Specifically, the transport unit 220 has each feed roller and transports the fed recording medium F in the sub-scanning directions T1 and T2.

Further, the recording unit 230 has an inkjet head 11 that ejects the composition to the recording medium F sent from the transport unit 220, a carriage 234 on which the composition is ejected, and a carriage 234 in the main scanning direction S1 of the recording medium F. A carriage moving mechanism 235 for moving to S2 is provided.
The inkjet recording device may further include a wiping member as shown in FIG. 2 and a maintenance liquid adhering mechanism. In this case, a control unit (not shown) of the inkjet recording device controls the wiping member and the maintenance liquid adhering mechanism to perform the wiping step and the maintenance liquid adhering step.
The inkjet recording device in the example of FIG. 5 is an example of a serial printer, but the inkjet recording device may be a line printer in which the inkjet head is a line head.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

1. 1. Adjustment of water-based ink composition 1.1. Preparation of pigment dispersion liquid St-Ac acid copolymer (methacrylic acid / butyl acrylate / styrene / hydroxyethyl acrylate = 25/50/15/10, copolymerized at a mass ratio. Weight average molecular weight 7000, acid value 150 mgKOH / g) 40 parts by mass was put into a mixed solution of 7 parts by mass of potassium hydroxide and 53 parts by mass of water, and heated with stirring at 80 ° C. to prepare an aqueous resin solution. 20 parts by mass of the pigment (PB15: 3), 10 parts by mass of the above resin aqueous solution, and 70 parts by mass of the ion-exchanged water were mixed and dispersed using a zirconia bead mill to obtain a pigment dispersion liquid.

Each component was put into a mixture tank so as to have the composition shown in Table 1, mixed and stirred, and further filtered through a 5 μm membrane filter to obtain an aqueous ink composition of each example. The numerical values of each component shown in each example in the table represent mass% unless otherwise specified. Further, in the table, the numerical value of the pigment dispersion liquid represents the mass% of the solid content.

The abbreviations and product ingredients used in Table 1 are as follows.
〔Organic solvent〕
-Propylene glycol (boiling point 188 ° C)
2-Pyrrolidone (boiling point 245 ° C)
1,2-Hexanediol (boiling point 223 ° C)
-Glycerin (boiling point 290 ° C)
[Pigment dispersion]
・ PB15: 3
[Resin particles]
・ John Krill 631 (Acrylic resin particles, BASF Japan Ltd.)
・ Takelac W-6010 (urethane resin particles, Mitsui Chemicals, Inc.)
〔wax〕
・ AQUACER539 (polyethylene wax, Big Chemie Japan Co., Ltd.)
[Defoamer]
・ Surfinol DF110D (acetylene diol-based surfactant, Nissin Chemical Industry Co., Ltd.)
[Surfactant]
・ BYK348 (Silicone-based surfactant, Big Chemie Japan Co., Ltd.)
[PH regulator]
・ Triethanolamine

1.2. Preparation of maintenance liquid The maintenance liquids of each example were obtained by putting each component in a tank for mixture, mixing and stirring, and further filtering with a 5 μm membrane filter so as to have the composition shown in Table 2.

The abbreviations and product ingredients used in Table 2 are as follows.
〔Organic solvent〕
-Propylene glycol-1,2-hexanediol-3-methoxy-3-methylbutanol [surfactant]
・ BYK348 (Silicone-based surfactant, Big Chemie Japan Co., Ltd.)
[PH regulator]
・ Triethanolamine

1.3. Surface Tension The surface tension shown in Table 1 was measured by the Wilhelmy method using an automatic tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.). Specifically, when the platinum plate was wet with the ink composition or the maintenance liquid in an environment of 25 ° C., the force of pulling the platinum plate into the ink was measured. The surface tension of the inks in Table 2 was also measured in the same manner, and all the inks were 24.0 mN / m.

2. Inkjet recording device As the inkjet recording device, a serial type SC-S40650 (manufactured by Seiko Epson Corporation) was modified and used. A secondary drying heater for drying the ink or the like on the recording medium was attached downstream of the inkjet head.

なお、参考例２〜５については、いずれも連続多段構造を有しないインクジェットヘッドを用いた。参考例２及び４の「非スキャロップ１」とは、ステンレス製のノズルプレートにパンチで穴を打ち、ノズルを形成したものであり、スキャロップ形状を有しないノズルを備えるインクジェットヘッドを意味する。また、参考例３及び５の「非スキャロップ２」とは、他ヘッド１と同様にしてノズルを形成したものであるが、パンチ穴の直径をノズル内で変えることで、ノズル側壁の、ノズルプレート厚み方向の約中央に、ノズル直径方向に０．２μｍの段差を１段設けたインクジェットヘッドとしたものであり、スキャロップ形状を有しないノズルを備えるインクジェットヘッドを意味する。 Further, the nozzle plate, which is a silicon substrate, was subjected to a multi-step dry etching process by the BOSCH method to form a continuous multi-step structure, which was used for the inkjet head. Inkjet heads having different ratios b / a of distances b between adjacent convex portions with respect to the depth a of the concave portions were prepared. The ratio b / a is shown in Table 3 below. The a and b of each inkjet head were as follows. For each inkjet head, the thickness of the nozzle plate was 50 μm, and the nozzle diameter was about 20 μm.

For Reference Examples 2 to 5, an inkjet head having no continuous multi-stage structure was used. The “non-scallop 1” in Reference Examples 2 and 4 means an inkjet head having a nozzle formed by punching a hole in a stainless steel nozzle plate and having no scallop shape. Further, the "non-scallop 2" of Reference Examples 3 and 5 is a nozzle formed in the same manner as the other head 1, but by changing the diameter of the punch hole in the nozzle, the nozzle plate on the side wall of the nozzle is formed. It is an inkjet head provided with one step of 0.2 μm in the nozzle diameter direction at about the center in the thickness direction, and means an inkjet head provided with a nozzle having no scallop shape.

Further, in Table 4 below, as the maintenance method, the following W1 and W2 were used as the cloth wipers made of cloth as the absorbent wiping member.
W1: Type of cloth Benlyse (cellulose fiber, Asahi Kasei Corporation).
W2: Type of cloth Toraysee (polyester fiber, Toray Industries, Inc.).
In addition, a rubber wiper made of silicone rubber was prepared as a non-absorbent wiping member. Other maintenance methods described in the table are as follows.
Rubber wiper: Wipe off with a rubber wiper.
FL + rubber wiper: Flushing was performed and then wiped with a rubber wiper.
Suction + rubber wiper: Suction was performed, and then wiped with a rubber wiper.
In flushing, 1000 drops of ink were ejected from the nozzle row to the ink receiver per nozzle. For suction, 2 g of ink was sucked from the nozzle row and discharged.
For wiping with each wiping member, wiping was performed once in a direction in which the nozzle surface was perpendicular to the direction of the nozzle row.

In Table 4 below, when the maintenance liquid was used in the wiping step, the amount of the maintenance liquid adhered (g) was shown as the amount per ink (1 nozzle row).
The recording test was conducted as follows.
The inkjet recording apparatus was filled with a water-based ink composition, and a solid pattern was recorded on a recording medium. As the recording conditions, the conditions shown in Table 4 were used for each example. The recording resolution of the solid pattern was 720 × 1440 dpi, the amount of ink adhered was 12 mg / inch2, the number of scans was 8, and the recording medium was Oraget-3169G (model number, vinyl chloride film, Orafor Japan Co., Ltd.).
In the example with the primary heating step, the recording medium was heated with a platen heater, and the surface temperature of the recording medium in the ink adhesion step was taken as the value in the table. The secondary drying temperature by the secondary heater after the ink adhesion step was set to 90 ° C. The surface temperature of the recording medium in each step was determined by measuring the temperature of the recording medium with a thermocouple.

3. 3. Evaluation method 3.1. Misalignment of landing position of water-based ink composition Recording was carried out continuously for 2 hours under the above-mentioned recording test conditions. Then, under the conditions shown in Table 4, maintenance was performed to wipe the nozzle surface with the wiping member. This was set as one set, and then recording and maintenance were repeated again. This was repeated until the total recording time reached 100 hours. This is how the recording and maintenance was completed. Then, nozzle check patterns were created and compared at the initial stage before recording and after recording for 100 hours, respectively, and the deviation of the landing position was confirmed. When creating the nozzle check pattern, the nozzle surface was wiped clean so that the ink composition did not adhere to the nozzle surface so that there was no influence of flight bending due to dirt on the nozzle surface.

(Evaluation criteria)
AA: A deviation of less than 1/3 of the distance between nozzles is observed.
A: A deviation of 1/3 or more and less than 2/3 of the distance between nozzles is observed.
B: A deviation of 2/3 or more and less than 3/3 of the distance between nozzles is observed.
C: A deviation of 3/3 or more of the distance between nozzles is observed.

3.2. Solid image quality A solid image was printed on a recording medium under the conditions of the recording test. The printing conditions were the conditions shown in Table 4. The image quality of the image was visually confirmed, and the solid image quality was judged according to the following evaluation criteria.
(Evaluation judgment)
AA: The ink is uniform in the pattern, and uneven shading is not observed.
A: Some uneven concentration is observed.
B: Some uneven density is observed, and the edges of the pattern are not slightly straight.
C: The edges of the pattern are not fairly straight.

3.3. Wipingability Under the conditions of the recording test, a solid image was printed on a recording medium for 2 hours continuously. After that, maintenance was performed under the conditions shown in Table 4. After maintenance, the wiping property of the nozzle surface was visually confirmed.
(Evaluation judgment)
AA: No ink adhesion is observed on the nozzle surface.
A: No ink adhesion was observed on the nozzle surface, but when observed with a loupe, adhesion of solid content of the water-based ink composition was confirmed.
B: Some ink residue is observed on the nozzle surface.
C: A considerable amount of ink residue is observed on the nozzle surface.

3.4. A solid image was printed on a recording medium under the conditions of the abrasion resistance recording test. The printing conditions were the conditions described in the evaluation in Table 4. The obtained solid image was left at room temperature for 30 minutes, and then the solid image printing portion was cut into a rectangle of 30 × 150 mm. The degree of ink peeling when the recording surface of the obtained sample was rubbed 30 times with a Gakushin type friction resistance tester (load 500 g) using a plain weave cloth was visually confirmed, and the scratch resistance was determined according to the following evaluation criteria. The sex was judged.
(Evaluation criteria)
AA: There is no ink transfer to the plain weave cloth, and there is no peeling of the ink coating film.
A: Some ink is transferred to the plain weave cloth, but the ink coating film does not peel off.
B: Part of the ink is transferred to the plain weave cloth, and the ink coating film is slightly peeled off.
C: The ink coating film is remarkably peeled off, or the base material itself is torn.

3. 3. Evaluation Results Table 4 shows the configuration of the inkjet recording device used in each example, each condition of the water-based ink composition and the maintenance liquid, and the evaluation results.
In each of the examples in which the nozzle surface of the nozzle having a continuous multi-stage structure of the recording device, which was recorded by a recording method in which ink adheres to a heated recording medium, was wiped with an absorbent wiping member, landed. The position shift suppression and image quality were excellent. On the other hand, in the comparative examples in which this was not the case, either the landing position shift suppression or the image quality was inferior.

From Examples 1, 7 and 8, the higher the surface temperature of the recording medium at the time of ink adhesion, the better the image quality, and the lower the surface temperature, the better the suppression of landing position shift.
From Examples 1 to 3, it was considered that the smaller the content of the resin particles contained in the ink, the better the landing position shift, and the resin particles were related to the landing position shift. In addition, the larger the amount, the better the abrasion resistance.

From Examples 1, 10 and 11, the larger the ratio (b / a) of the continuous multi-stage structure of the nozzle, the better the suppression of the landing position shift.

From Examples 1, 14 to 21, an excellent landing position was obtained regardless of whether the maintenance liquid was used or not when wiping with the wiping member, but depending on the type of maintenance liquid, the landing position deviation was suppressed or the nozzle surface was wiped off. The sex was better.

From Comparative Examples 1 and 2, wiping using a non-absorbent wiping member was inferior in suppressing the landing position shift. These wipes were inferior in wiping the nozzle surface because they did not absorb ink, but in the evaluation of landing misalignment, the nozzle surface was wiped clean so that there was no effect, but the landing misalignment was suppressed. inferior. Further, in Comparative Example 2, although the ink of the nozzle was discharged by flushing, the suppression of the landing position shift was inferior. From this, it is presumed that in the embodiment, the suppression of the landing position shift was excellent by wiping with the absorbent wiping member.

From Comparative Examples 3 and 4, when the recording medium was not heated when the ink adhered, the suppression of the landing position shift was excellent. If heating is not performed, it is presumed that deposits are unlikely to occur in the first place and the problem of landing position shift does not occur. However, in Comparative Examples 3 and 4, since heating was not performed, another problem that the image quality was clearly inferior occurred.

From Reference Example 1, the displacement of the landing position could be suppressed by performing suction cleaning in which the ink of the nozzle is discharged by suction. However, suction cleaning has the disadvantages that a large amount of ink is wasted due to suction and that suction takes time and maintenance time is required. Moreover, the wiping property of the nozzle surface was inferior.
From Reference Examples 2 to 5, it was found that when a nozzle having no continuous multi-stage structure is used, the problem of deposits derived from the continuous multi-stage structure and the problem of landing position shift due to the problem do not occur in the first place.
Although not described in the table, an ink was prepared in the same manner except that the ink A did not contain resin particles, and the ink was evaluated in the same manner as in Comparative Example 1, and the ink landed. The misalignment was AA and the abrasion resistance was C. From this, it is presumed that the inclusion of the resin particles in the ink provides excellent abrasion resistance, but causes a problem of landing position deviation.

11 ... Inkjet head, 12 ... Nozzle forming surface, 21 ... Wiping member, 22 ... 1st roll, 23 ... 2nd roll, 24 ... 1st injector, 25 ... 2nd injector, 26 ... Pool, 31 ... Maintenance liquid , 111 ... Nozzle hole, 112 ... Nozzle plate, 114 ... Pressure chamber, 115 ... Pressurized part, 116 ... Ink supply chamber, 117 ... Ink absorbed by the wiping member, 118 ... Deposit, 121 ... Continuous multi-stage structure, 122 ... Concave, 123 ... Convex, 200 ... Serial printer, 220 ... Transport, 230 ... Recording, 234 ... Carriage, 235 ... Carriage moving mechanism

Claims (15)

It is a maintenance method for an inkjet recording device that records on a recording medium.
The inkjet recording apparatus includes an inkjet head, ejects a water-based ink composition from a nozzle of the inkjet head, attaches the water-based ink composition to a heated recording medium, and records the ink.
The inkjet head has a nozzle having a continuous multi-stage structure on the inner wall.
The water-based ink composition contains water and resin particles.
A wiping step of wiping the nozzle surface of the inkjet head with an absorbent wiping member is provided.
Maintenance method. The content of the resin particles is 3.0% by mass or more with respect to the total amount of the water-based ink composition.
The maintenance method according to claim 1. The ratio b / a of the distance b between the adjacent convex portions of the continuous multi-stage structure to the depth a of the concave portion of the continuous multi-stage structure is 1.0 to 25.
The maintenance method according to claim 1 or 2. The wiping member contains cellulose fibers.
The maintenance method according to any one of claims 1 to 3. The continuous multi-stage structure is manufactured by alternately and repeatedly etching the silicon wafer in the thickness direction and protecting the etching side wall many times.
The maintenance method according to any one of claims 1 to 4. The water-based ink composition does not contain an organic solvent having a standard boiling point of more than 280 ° C. in an amount of more than 2.0% by mass based on the total amount of the water-based ink composition.
The maintenance method according to any one of claims 1 to 5. The surface temperature of the heated recording medium is 45 ° C. or lower.
The maintenance method according to any one of claims 1 to 6. The recording medium is a low absorption recording medium or a non-absorption recording medium.
The maintenance method according to any one of claims 1 to 7. In the wiping step, wiping is performed using a maintenance liquid.
The maintenance method according to any one of claims 1 to 8. The maintenance liquid contains water and
The content of the water is 80% by mass or more with respect to the total amount of the maintenance liquid.
The maintenance method according to claim 9. The maintenance liquid contains an organic solvent and contains
The content of the organic solvent is 0.5 to 20% by mass with respect to the total amount of the maintenance liquid.
The maintenance method according to claim 9 or 10. The organic solvent contained in the maintenance liquid contains glycol ether or an alkane diol having 5 or more carbon atoms.
The maintenance method according to claim 11. A step of adhering the maintenance liquid to the nozzle surface or the wiping member is further provided.
The maintenance method according to any one of claims 9 to 12. The maintenance liquid does not contain a surfactant in an amount of more than 0.01% by mass based on the total mass of the maintenance liquid.
The maintenance method according to any one of claims 9 to 13. An inkjet head that ejects a water-based ink composition containing water and resin particles,
A wiping mechanism that wipes the nozzle surface of the inkjet head with an absorbent wiping member,
It is equipped with a heating mechanism that heats the recording medium.
The inkjet head has a continuous multi-stage structure on the inner wall of the nozzle.
Perform maintenance by the maintenance method according to any one of claims 1 to 14.
Recording device.

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