JP2002172785A - Electrostatic ink jet recorder and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic ink jet recorder in which an ink ejection opening is not clogged easily even when an aqueous ink is used and an ink drop is formed stably even if ink is flown continuously. SOLUTION: The recorder 1 comprises an ink jet head 2 comprising an ink chamber 6 containing ink 4, a plurality of ink ejection openings 8 communicating with the ink chamber, and control electrodes 20 disposed in the vicinity of respective ink ejection opening; and a back face electrode 16 disposed oppositely to the ink ejection openings of the head. By applying voltages to the back face electrode and the control electrode, ink is flown through the ink ejection opening toward the back face electrode to adhere to a recording medium 30. The ink is an aqueous ink comprising water, a pigment and a resin wherein the pigment and/or the resin has an anionic hydrophilic group in the molecule. The voltages being applied to the back face electrode and the control electrode are set to have potentials lower than that of ink in the ink chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electrostatic ink jet recording apparatus and method for performing recording by flying ink using electrostatic force.

[0002]

2. Description of the Related Art Conventionally, electric charges are injected into conductive ink,
There is known an electrostatic ink jet recording apparatus that causes an electric field to act on the ink to fly the ink toward a recording medium, thereby forming an image on the recording medium.

As such a conventional ink jet recording apparatus, an ink chamber containing ink, a plurality of ink ejection ports communicating with the ink chamber and connected to the atmosphere, and a control electrode arranged near each ink ejection port are provided. Some have an ink jet head provided and a back electrode arranged opposite to an ink ejection port of the ink jet head.
The ink chamber is always filled with ink.By applying a predetermined voltage to the back electrode, the ink in the ink chamber is urged toward the back electrode by electrostatic force, and an ink meniscus is formed at each ink ejection port. It is formed. In this state, by applying a predetermined voltage to a predetermined control electrode,
An electrostatic force is applied to the ink meniscus formed at the ink ejection port corresponding to the predetermined control electrode to cause the ink droplet to fly from the ink ejection port and adhere to the recording medium conveyed to the area facing the inkjet head. .

[0004]

In the ink jet recording apparatus having the above-mentioned structure, it is possible to use either oil-based ink or water-based ink. However, with the oil-based ink, when performing image formation on plain paper, ink bleeding or so-called show-through, in which ink that is not sufficiently dried on the paper adheres to another paper laminated thereon, occurs. Because of the possibility, it is difficult to perform high-speed printing and double-sided printing on plain paper. Also, because an organic solvent is used,
There are also problems with odor and safety. On the other hand, when an image is formed using water-based ink, there is no problem with odor or safety, but the ink ejection port is clogged or ink droplets are not formed stably when ink is continuously ejected. was there.

[0005] Aqueous ink is composed mainly of water and compounds such as coloring materials, resins, additives, and water-soluble organic solvents. These compounds are in a state of being dissolved or dispersed in water,
For that purpose, a substance having high hydrophilicity is selected. In general, hydrophilicity can be imparted by including an ionic group such as an anion or a cation in the molecule, or by bonding a molecule having a hydroxyl group and / or an ether bond. The present inventors have found that when a pigment is used as a coloring material, the highly hydrophilic substance receives electrostatic force due to an electric field formed by applying a voltage to the control electrode, and gathers at the tip of the ink meniscus to aggregate. Therefore, it is considered that the ink droplets are not stably formed because the density in the ink meniscus is not uniform even if the ink ejection port is clogged or does not occur.

Therefore, the present invention provides an electrostatic ink jet recording apparatus and a method in which ink ejection ports are hardly clogged even when aqueous ink is used, and ink droplets are formed stably even when ink is continuously ejected. The purpose is to do.

[0007]

In order to achieve the above object, an electrostatic ink jet recording apparatus according to the present invention comprises: an ink chamber for containing ink; a plurality of ink ejection ports communicating with the ink chamber; The inkjet head includes an inkjet head having a control electrode arranged near the ejection port, and a back electrode arranged to face the ink ejection port of the inkjet head. By applying a voltage to at least one of the control electrode and the back electrode, the ink flies in a direction from the ink chamber to the back electrode via the ink discharge port, and adheres to a recording medium between the inkjet head and the back electrode. Let it.

When an aqueous ink comprising at least water, a pigment, and a resin and the pigment and / or the resin has an anionic hydrophilic group in a molecule is used, the ink is applied to at least one of the control electrode and the back electrode. The voltage is set such that the potentials of the control electrode and the back electrode are lower than the potential of the ink in the ink chamber. Also, as ink,
When an aqueous ink comprising at least water, a pigment, and a resin, and the pigment and / or the resin has a cationic hydrophilic group in a molecule, a voltage applied to at least one of the control electrode and the back electrode is controlled by the control electrode. And the potential of the back electrode is set to be higher than the potential of the ink in the ink chamber.

According to the electrostatic ink jet recording method of the present invention, there is provided a step of preparing an ink jet head having an ink chamber which communicates with a plurality of ink ejection ports and contains ink, and the step of preparing an ink chamber sandwiching the ink ejection ports. Electrically energizing the ink in the ink chamber to the opposite side to cause the ink to fly through the ink ejection port, thereby attaching the ink to the recording medium facing the ink ejection port of the inkjet head.

When an aqueous ink comprising at least water, a pigment, and a resin, and the pigment and / or the resin has an anionic hydrophilic group in a molecule is used, the ink in the ink chamber is electrically energized. For this purpose, the electric field is generated such that its direction is substantially the same as the direction in which the ink is ejected. Further, when an aqueous ink composed of at least water, a pigment, and a resin, and the pigment and / or the resin has a cationic hydrophilic group in a molecule is used, the ink in the ink chamber is electrically energized. Then, an electric field is generated such that the direction is substantially opposite to the direction in which the ink is ejected.

In the present application, the term “direction of the electric field” is defined as a direction from a positive charge to a negative charge.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic partial sectional view of an ink jet recording apparatus according to the present invention. The recording apparatus 1 includes an inkjet head 2
(Hereinafter, referred to as a “head”). The head 2 has an ink chamber 6 for storing the aqueous ink 4 and a plurality of ink chambers 6 having a predetermined shape (for example, a cylindrical shape) communicating with the ink chamber 6. Are formed (two in the figure for simplicity). The ink chamber 6 is fluidly connected to an ink cartridge 12 via a pipe 10 so that the ink chamber 6 is always filled with the ink 4. Above the drawing of the head 2, a back electrode 16 is provided at a predetermined distance from the ink ejection surface of the head 2 (the outlet of the ink ejection port 8). The back electrode 16 has a first bias power supply 1
8 is connected so that a predetermined negative voltage V _B (for example, a bias voltage of −3000 V) can be applied.

The water-based ink 4 of the present embodiment has at least
It consists of water, pigment, and resin, and the pigment and / or resin is in the molecule.
Is an aqueous ink having an anionic hydrophilic group. this
The hydrophilic group is, for example, -COOM, -SO_ThreeM, -PO_Three
HM, -SO_TwoNH_Two, -SO _TwoNHCOR (M; hydrogen,
Alkali metal, ammonium, or organic ammonium,
R; having an alkali group having 1 to 12 carbon atoms and a substituent
Phenyl group or naphthyl which may have a substituent
At least one anionic hydrophilicity selected from
Group. The aqueous ink used in the present invention will be described later.
explain in detail.

A ring-shaped control electrode 20 is provided on the surface or inside of the head 2 on the side of the back electrode 16 so as to surround each ink ejection port 8. These control electrodes 20 are supplied with a predetermined negative pulse voltage Vp (for example,-
(300-500 V). A ring-shaped ejection electrode 24 is provided near the entrance of each ink ejection port 8 so as to surround the entrance of each ejection port 8. Each ejection electrode 24 is in contact with the ink 4 in the ink chamber 6, and
It is set to a constant potential (grounded in the example in the figure).

The magnitude of the bias voltage V _B is such that the ink 4 contained in the ink chamber 6 is attracted toward the back electrode 16 by an electric field formed between the ink 4 and the back electrode 16 due to a potential difference between the ink 4 and the back electrode 16. Then, a meniscus is formed in the ink discharge port 8, but the suction force alone is adjusted so that the ink is not separated from the ink 4 in the ink chamber 6 as droplets and does not fly. The magnitude of the pulse voltage Vp is such that, when a predetermined voltage is applied to the back electrode 16 to form a meniscus, the magnitude of the electric field formed between the back electrode 16 and the control electrode 20 and the ink meniscus is Is set to a value sufficient to separate and fly from the ink 4 in the ink chamber 6 as a droplet. In order to form an ink meniscus, the control electrode 20 may be set to a constant potential (for example, -100 V) during non-printing.

More specifically, when the aqueous ink 4 having a pigment and / or a resin having an anionic hydrophilic group is used as in this embodiment, the voltage is applied to the back electrode 16 and the control electrode 20. Of the back electrode 16 and the control electrode 20 are set lower than the potential of the ejection electrode 24 (that is, the direction of the electric field is from the ejection electrode 24 side to the back electrode 16 side).

According to these configurations, a part of the ink is separated from the ink 4 in the ink chamber 6 by applying the negative pulse voltage Vp to the desired control electrode 20 with the ink meniscus formed. Then, the ink droplets fly as ink droplets 28 from the ink discharge ports 8 corresponding to the desired control electrodes 20. The ink droplet 28 further includes the control electrode 20 and the back electrode 1.
6 flies straight toward the recording medium 30 conveyed between the head 2 and the back electrode 16 due to the electric field formed between them due to the potential difference between the recording medium 30 and the recording medium 30 and adheres to the recording medium 30 to form an image.

By the way, unlike the present embodiment, when the potentials of the back electrode 16 and the control electrode 20 are set higher than the potential of the ejection electrode 24 in a state where a voltage is applied to the back electrode 16 and the control electrode 20. (That is, the direction of the electric field is a direction from the back electrode 16 side toward the ejection electrode 20 side.) The pigment and / or resin having an anionic hydrophilic group in the ink 4 collects at the tip of the ink meniscus. Agglomerates and the ink discharge port 8 is easily clogged. Further, even if the ink ejection port 8 is not clogged, the ink droplets are not stably formed because the density in the ink meniscus becomes uneven. As a result, uniform dots are not formed on the recording medium 30.

On the other hand, in the present embodiment, the pigment and / or resin having an anionic hydrophilic group in the ink 4 is dispersed in the ink 4 without gathering at the tip of the ink meniscus (that is, in the ink meniscus). Is uniform), and the ink droplets are formed stably even if the ink is continuously ejected without clogging the ink discharge port 8. As a result, uniform dots are formed on the recording medium 30.

(Second Embodiment) The aqueous ink of the present embodiment is composed of at least water, a pigment, and a resin.
Alternatively, the resin is an aqueous ink having a cationic hydrophilic group in the molecule. This hydrophilic group is, for example, at least one cationic hydrophilic group selected from quaternary ammonium and tertiary amine.

Referring to FIG. 1, in this embodiment,
The pole 16 has a predetermined positive polarity voltage V _B(For example, +300
(A bias voltage of 0 V). Ma
The control electrode 20 has a predetermined positive polarity according to image information.
Pulse voltage Vp (for example, +300 to 500 V) is applied
I can do it. Further, each ejection electrode 24 is
It is set to a constant potential (for example, grounded).

According to this configuration, the pigment and / or resin having a cationic hydrophilic group in the ink 4 is dispersed in the ink 4 without being collected at the tip of the ink meniscus (that is, the concentration in the ink meniscus is reduced). (Uniform), and the ink droplets are stably formed even if the ink is continuously ejected without clogging the ink discharge port 8.

(Overall Configuration and Operation of Inkjet Recording Apparatus) FIG.
1 shows a perspective view of one embodiment. This recording device 100
A pair of vertically extending support walls 102a, 102b facing each other at a predetermined interval;
And an intermediate wall 103 extending in the vertical direction and provided in a space sandwiched between the two. On the outer side of the space between the support wall 102b and the intermediate wall 103 on the right side of the drawing, a paper feed tray 10 for storing a sheet (paper) S to be printed by the recording apparatus 100 is provided.
The sheet S stored in the paper feed tray 104 is supplied to the space.

A first guide rail 106 extending in the horizontal direction is supported by the pair of support walls 102a and 102b. A second guide rail 107 extending in the horizontal direction is provided on the opposite side of the paper feed tray 104 with the first guide rail 106 interposed therebetween. These guide rails 10
A carriage 110 on which an inkjet head 108 is mounted is movably supported by 6 and 107. The head 108 is connected via a film-shaped wiring board 109 to a drive circuit (not shown) for applying a predetermined voltage to a control electrode (not shown, which corresponds to the control electrode 20 in FIG. 1). On the carriage 110, ink cartridges 111 of black, yellow, magenta, and cyan are also provided.
B, 111Y, 111M, and 111C are detachably mounted. These ink cartridges supply ink to the head 108 via a manifold (not shown). A scanning mechanism 112 for reciprocating the carriage 110 along the guide rails 106 and 107 includes a pair of pulleys 114a and 114b supported near the support walls 102a and 102b, and the pulleys 114a and 114b.
A belt 116 wound around 14b and a motor 118 for rotating one of the pulleys 114b in the forward and reverse directions are provided. A carriage 110 is connected to a part of the belt 116.

Between the intermediate wall 103 and the support wall 102b, the sheet S conveyed from the paper feed tray 104
A paper feed roller 122 that folds back by 0 ° and conveys in the direction of arrow 121 (transport direction), and a pressing roller 124 that contacts the paper feed roller 122 and presses the sheet S against the paper feed roller 122, is orthogonal to the transport direction 121 And is rotatably supported by the intermediate wall 103 and the support wall 102b.

The paper feed roller 122 is a metal roller, for example, and can apply a predetermined voltage, and as a result, functions as a back electrode. The paper feed roller 122 is also drivingly connected to a motor (not shown).
2 rotates to convey the sheet S in the direction of arrow 121. The paper feed roller 122 can be manually rotated by a user.

The paper feed roller 122 further includes a head 1
08 while the head 108 moves with the carriage 110, the ink ejection surface of the head 108 (the outlet of the ink ejection port of the head) is substantially spaced from the outer peripheral surface of the paper feed roller 122. I try to keep it.
Although not shown in the figure, the ink ejection orifice array including a plurality of ink ejection orifices is arranged in the vertical direction for the black, yellow, magenta, and cyan inks (scanning mechanism 112).
(In the direction perpendicular to the direction in which the head 108 moves). The number of the ink ejection port array may be one or plural for each color.

Between the first guide rail 106 and the second guide rail 107, these guide rails 106,
A belt-like timing slit 1 in the form of a film in parallel with 107
26 are provided. One end of the timing slit 126 is fixed to the support wall 102b on the right side in the drawing, and the other end is connected to a hook 128 provided on the wall of the support wall 102a on the left side in the drawing.
The timing slit 126 is locked under an appropriate tensile force.

As shown in detail in FIG. 3, the timing slit 126 is formed by forming a large number of transparent portions 130 and non-transparent portions 132 having a predetermined width alternately in the longitudinal direction. The carriage 110 has a timing slit 12
A light-emitting element and a light-receiving element (both not shown) are arranged with 6 interposed therebetween. Transparent part 1 between light emitting element and light receiving element
When 30 is present, the light receiving element receives light from the light emitting element. Non-transparent portion 13 between light emitting element and light receiving element
When 2 exists, the light receiving element does not receive light from the light emitting element. Therefore, the position of the carriage 110 can be obtained based on the signal output from the light receiving element while the carriage 110 moves in the horizontal direction.
Specifically, for example, when the light receiving element outputs a “HIGH” signal when receiving light from the light emitting element and outputs a “LOW” signal when not receiving light from the light emitting element,
By counting the “HIGH” signal output intermittently, the position of the carriage 110 from a predetermined position (for example, a standby position during non-printing) can be calculated.

A cap 134 is provided between the intermediate wall 103 and the support wall 102a to protect the head 108 when the ink jet recording apparatus 100 is not used for a long time. The cap 134 can be moved between a position where the head 108 is sealed and a position where the head 108 is separated from the head 108 in a state where the carriage 110 is arranged at a standby position facing the cap 134. The cap 134 is disposed on a surface facing the ink ejection surface of the head 108 at the standby position at a position that communicates with a negative pressure applying unit (not shown) and that corresponds to the plurality of ink ejection ports of the head 108. A plurality of suction ports (not shown) are provided to suck air bubbles and defective ink from the ink discharge ports of the head 108 via the suction ports.

At the time of printing by the recording apparatus 100 having the above-described configuration, the user holds the leading end of the sheet S from the sheet feeding tray 104 against the sheet feeding roller 122 and
By rotating the sheet S manually, the sheet S is moved to the intermediate wall 1.
It is guided between the support wall 03 and the support wall 102b. Subsequently, the user turns back the sheet S by about 180 ° and presses the pressing roller 12.
4 and a paper feed tray 122, thereby pressing the sheet S against the outer peripheral surface of the paper feed roller 122, and causing the sheet S and the ink ejection surface of the head 108 to move in the horizontal direction by the scanning mechanism 112 during printing. Make the intervals constant.

In this state, the sheet S is conveyed in the direction of arrow 121 by rotating the sheet feeding roller 122 based on the driving of a motor (not shown).

In synchronization with the movement of the sheet S, the carriage 1
The guide rail 10 is rotated by the rotation of the belt 116.
The ink is ejected from the head 108 to the portion of the sheet S that reciprocates along the sheets 6 and 107 and moves on the sheet feeding roller 122 to perform printing. The control of the ejection of the ink is performed by a drive circuit connected to the control electrode applying a voltage to a predetermined control electrode according to the position of the carriage 110. The printed sheet S is discharged onto the paper feed tray 104 again.

At the time of non-printing, especially when printing is not performed for a long time, the carriage 110 moves to the standby position, where the head 108 is sealed by the cap 134 and the head 10 is closed.
8 is prevented from drying. If necessary, the negative pressure applying means sucks bubbles or defective ink from the ink ejection ports of the head 108, so that the head 108 can normally eject ink at the next printing.

The recording apparatus 100 shown in FIG. 2 uses a serial type ink jet head. However, the plurality of ink ejection ports for each color are set in the sheet conveyance direction (arrow 1 in FIG. 2) at the same density as the image resolution to be printed.
It is more preferable to form an image without moving the head by using a line-type inkjet head arranged so as to cover at least the printing width of the printing area of the sheet in a direction orthogonal to (21). . The reason is that in the line type ink jet head, the distance between the sheet and the ink ejection surface of the head is easily made constant, and thus the electric field for ejecting ink can be formed stably.

(Aqueous Ink) As the water-soluble and / or water-dispersible pigment in the embodiment of the present invention, the following organic and inorganic pigments can be used. For example, azo, phthalocyanine, anthraquinone, quinacridone, dioxazine, indigo, thioindigo,
Organic pigments such as perylene, aniline black, azomethine, and rhodamine B lake; and inorganic pigments such as carbon black, titanium oxide, calcium carbonate, barium sulfate, talc, and kaolin. The colorant concentration in the ink is preferably in the range of 3 to 20% by weight based on the total amount of the ink. Specifically, C.I. I Pigment Yellow 1, 2, 3, 13, 1
6, 83, 93, 95, etc. as magenta pigments such as C.I. I Pigment Red 5, 7, 12, 48, 57, 112, 1
22 as a cyan pigment; I Pigment Blue 1,
2, 3, 15: 3, 16 and the like.

In order to disperse these pigments in water, if a water-soluble and / or water-dispersible resin having a weight average molecular weight of about 500 to 200,000 called a dispersant is used, these pigments are stably dispersed in water. be able to. As described above, the water-soluble and / or water-dispersible compound used as the dispersant exhibits any of anionic, cationic, nonionic, and amphoteric properties, and these can be used as appropriate. The amount of the dispersant added is preferably in the range of 0.5 wt% to 100 wt% based on the weight of the pigment.

Further, by adding a hydrophilic group as a functional group directly to the pigment, a self-dispersible pigment which can stably disperse the pigment in water without using a dispersant can be used. Good. Examples of the hydrophilic group include those having a metal salt and / or an organic salt formed by using an anionic group or a cationic group as a functional group, those having a zwitterionic group, and those having a nonionic group having high affinity for water. One is commonly used. Further, it is also possible to use a coloring material in which a pigment and / or a dye is encapsulated in the resin having the ionic group and microencapsulated.

The anionic water-soluble / water-dispersible resin has an anionic group such as a sulfonic acid group, a carboxylic acid group and a phosphoric acid group as a functional group, and contains a metal such as K, Na, Mg, Ca and / or the like. Alternatively, it is a resin that forms a salt with ammonia, amines, and alkanolamines and becomes water-soluble / water-dispersible. Specifically, carboxymethyl cellulose,
Cellulose derivatives such as viscose, natural polymers such as alginic acid, gum arabic, tragacanth gum, and lignin sulfonic acid; starch derivatives such as phosphate starch and carboxymethyl starch salt; polyacrylic acid, polymethacrylic acid, polyvinyl sulfate, and polyvinyl sulfone Acid, condensed naphthalene sulfonic acid, ethylene-acrylic acid copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, acrylic ester-acrylic acid copolymer, acrylic ester, methacrylic acid copolymer Styrene-itaconic acid copolymer, itaconic acid ester-itaconic acid copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-methacrylic acid copolymer, vinylnaphthalene-itaconic acid copolymer, phenol resin and A copolymer of Rukido, epoxy, polyester, there is a water-dispersible resin or a water-soluble resin of urethane or the like, the addition of increased less water-dispersible resin of viscosity preferred for the amount added.

In addition, the ink for electrostatic ink jet recording according to the present invention includes aqueous inks and conventionally known additives such as humectants such as polyhydric alcohols, fungicides, chelating agents, defoamers and the like. Can be added. Examples of humectants include methanol, ethanol, propanol, butanol, ethylene glycol, diethylene glycol,
Triethylene glycol, propylene glycol, dipropylene glycol, glycerin, diglycerin, d-
Compounds such as sorbitol, pentaerythritol, trimethylolpropane, and the like. It is preferable that these humectants are added in the range of 2.5 to 40% by weight in the ink composition.

(Experiment 1) The present inventors used the anionic ink shown below to print 3 million dots from each ink ejection port on plain paper by the ink jet recording apparatus of FIG. 1 under the following conditions. (Example 1, Comparative Example 1). Then, "nozzle clogging" was evaluated.

Setting conditions Gap between ink discharge surface of head and back electrode: 500
μm Ink ejection port (nozzle): circular section with a diameter of 50 μm (Example 1) Back electrode: Apply a bias voltage of -3.0 kV Ejection electrode: Set to GND Control electrode Non-printing: Apply a bias voltage of -100 V At the time of printing: Applying a pulse voltage of -300 V at 2 kHz (Comparative Example 1) Back electrode: Applying a bias voltage of +3.0 kV Discharge electrode: Set to GND Control electrode At the time of non-printing: Applying a bias voltage of +100 V At the time of printing: 2 kHz Apply + 300V pulse voltage with

Evaluation items: Nozzle clogging When printing 3 million dots from each nozzle on plain paper, ○: 3 million dots can be output from all nozzles without any problem.
There is no difference in dot diameter between immediately after printing and before printing. Δ: 3,000,000 dots can be output from all nozzles without any problem. However, there is a difference in dot diameter between immediately after printing and before printing ×: at least partly. Cannot output 3 million dots from the nozzle

Aqueous Ink Used in Experiments and Method for Producing the Ink Aqueous Ink A 300 g of commercially available acidic carbon black (Raven 1060; manufactured by Columbian Carbon Co., Ltd.) was thoroughly stirred and mixed in 1000 ml of distilled water, and hypochlorous acid was added. 450 g of soda was added dropwise and stirred at 100 ° C. for 12 hours. The resulting slurry was filtered through filter paper, washed with sufficient distilled water,
The solution was redispersed in 1 L of distilled water and desalted with a reverse osmosis membrane until the conductivity reached 0.15 μS. The obtained carbon black dispersion was concentrated by a rotary evaporator until the carbon black concentration became 30% by weight to obtain an anionic carbon black aqueous dispersion. Then, 12, 5 parts by weight of the thus obtained anionic self-dispersible carbon black pigment, 25.0 parts by weight of glycerin, 5.0 parts by weight of sorbitol, a nonionic surfactant (Nonipol 40; manufactured by Sanyo Chemical Industries, Ltd.) After mixing and stirring 1.0 part by weight and 56.5 parts by weight of distilled water in a beaker, the mixture was filtered through a 1.0 μm membrane filter (manufactured by Advantech) to remove dust and coarse particles, thereby obtaining ink A. Obtained.

Aqueous ink B 12, 5 parts by weight of anionic self-dispersible carbon black pigment used for preparation of aqueous ink A, acrylic resin emulsion (AN198; manufactured by Dainippon Ink and Chemicals)
0 parts by weight, glycerin 25.0 parts by weight, sorbitol 5.0 parts by weight, a nonionic surfactant (Nonipol 4
0; manufactured by Sanyo Chemical Co., Ltd.) and 54.5 parts by weight of distilled water were mixed and stirred in a beaker, and then filtered through a 1.0 μm membrane filter (manufactured by Advantech) to remove dust and coarse particles. After removal, ink B was obtained.

Aqueous ink C 12.5 parts by weight of carbon black pigment (Printex 35; manufactured by Degussa), pigment dispersant (styrene-α-methylstyrene-acrylic acid / triethanolamine neutralization: weight average molecular weight 12500, acid value 120) ) (John Krill 62 / manufactured by Johnson Polymer Co.) 4.0 parts by weight, 30.0 parts by weight of glycerin, 0.5 part by weight of a surfactant, and 52.0 parts by weight of distilled water were mixed and stirred, and then mixed with a bead mill. 6
The pigment was dispersed over time to obtain ink C.

Aqueous ink D 12.5 parts by weight of carbon black pigment (Printex 35; manufactured by Degussa), pigment dispersant (styrene-α-methylstyrene-acrylic acid / triethanolamine neutralization: weight average molecular weight 12500, acid value 120) ) (John Krill 62 / manufactured by Johnson Polymer) 5.0 parts by weight, 30.0 parts by weight of glycerin, 0.5 part by weight of a surfactant, and 51.0 parts by weight of distilled water were mixed and stirred, and then mixed with a bead mill. 6
After the pigment was dispersed for a time, coarse particles were removed with a 1.0 μm membrane filter to obtain ink D.

Aqueous ink E 10.0 parts by weight of copper phthalocyanine pigment (FG7330; manufactured by Toyo Ink), pigment dispersant (styrene-α-methylstyrene-acrylic acid / triethanolamine neutralization: weight average molecular weight 12500, acid value) 120) 4.0 parts by weight (John Krill 62 / manufactured by Johnson Polymer), 30.0 parts by weight of glycerin, 0.5 part by weight of a surfactant, and 54.5 parts by weight of distilled water were mixed and stirred, and then mixed with a bead mill. 6
The pigment was dispersed for a time, and then coarse particles were removed with a 1.0 μm membrane filter to obtain ink E.

Aqueous ink F Quinacridone magenta pigment (Super Agent)
a R; Dainippon Ink and Chemicals, Inc. 10.0 parts by weight, a pigment dispersant (styrene-α-methylstyrene-acrylic acid /
Triethanolamine neutralization: weight average molecular weight 1250
0, acid value 120) (John Krill 62 / manufactured by Johnson Polymer) 4.0 parts by weight, glycerin 30.0 parts by weight, surfactant 0.5 part by weight, and distilled water 54.5 parts by weight were mixed and stirred. Thereafter, the pigment was dispersed in a bead mill for 6 hours,
Thereafter, coarse particles were removed with a 1.0 μm membrane filter to obtain ink F.

Aqueous ink G Chromofine Yellow pigment (5930; manufactured by Dainichi Seika)
10.0 parts by weight, pigment dispersant (styrene-α-methylstyrene-acrylic acid / triethanolamine neutralization: weight average molecular weight 12500, acid value 120) (Joncryl 62)
4.0 parts by weight, glycerin 30.0 parts by weight, surfactant 0.5 part by weight, distilled water 5
After mixing and stirring 4.5 parts by weight, the pigment was dispersed in a bead mill for 6 hours, and then coarse particles were removed with a 1.0 μm membrane filter to obtain ink G.

The experimental results are shown in the following table.

As shown in the table, when using aqueous inks A and B having pigments having anionic hydrophilic groups and aqueous inks C to G having resins having anionic hydrophilic groups, the back electrode was used during printing. In addition, by setting the potential of the control electrode to be lower than the potential of the ejection electrode, the ink droplets can be formed stably without causing clogging of the nozzles and continuously flying ink.

(Experiment 2) Using the cationic ink shown below, each ink was discharged onto recording paper by the ink jet recording apparatus of FIG. 1 under the same conditions as in Experiment 1 except for the voltages applied to the back electrode and the control electrode. Printing of 3 million dots was performed from the exit (Example 2, Comparative Example 2). And the above-mentioned "nozzle clogging" was evaluated.

Setting conditions (Example 2) Back electrode: +3.0 kV bias voltage applied Ejection electrode: set to GND Control electrode Non-printing: +100 V bias voltage applied Printing: 2 kHz +300 V pulse voltage applied (Comparative Example 2) Back electrode: -3.0 kV bias voltage applied Discharge electrode: set to GND Control electrode Non-printing: -100 V bias voltage applied Printing: 2 kHz -300 V pulse voltage applied Aqueous Ink Used and Method for Producing the Ink Aqueous Ink H 10.0 g of commercially available carbon black (Printex; manufactured by Degussa) and 3.06 g of 3-amino-N-ethylpyridinium bromide are sufficiently dissolved in 72 g of water. After mixing
1.62 g of nitric acid was added dropwise thereto, and the mixture was stirred at 70 ° C.
Further, a solution obtained by dissolving 1.07 g of sodium nitrite in 5 g of water was added and stirred for 2 hours. The obtained slurry was filtered with filter paper, washed with sufficient distilled water, redispersed in 3000 ml of distilled water, and desalted with a reverse osmosis membrane until the electric conductivity reached 0.15 μS. The obtained carbon black dispersion was concentrated by a rotary evaporator until the carbon black concentration became 30% by weight to obtain a cationic carbon black aqueous dispersion. And the cationic self-dispersion type carbon black pigment 1 thus obtained is obtained.
2, 5 parts by weight, glycerin 25.0 parts by weight, sorbitol 5.0 parts by weight, a nonionic surfactant (Nonipol 4
0; manufactured by Sanyo Chemical Co., Ltd.) and 56.5 parts by weight of distilled water were mixed and stirred in a beaker, and then filtered through a 1.0 μm membrane filter (manufactured by Advantech) to remove dust and coarse particles. Thus, ink H was obtained.

Aqueous Ink I 12, 5 parts by weight of a cationic self-dispersible carbon black pigment used for preparing aqueous ink H, polyallylamine / hydrochloride (PAA-HCl-3L; manufactured by Nitto Boseki) 2.0
Parts by weight, glycerin 25.0 parts by weight, sorbitol 5.
0 parts by weight, 1.0 part by weight of nonionic surfactant (Nonipol 40; manufactured by Sanyo Chemical Co., Ltd.) and 54.5 parts by weight of distilled water were mixed and stirred in a beaker, and then a 1.0 μm membrane filter (manufactured by Advantech) ) To remove dust and coarse particles to obtain ink I.

The experimental results are shown in the following table.

As shown in the table, when the aqueous inks H and I each having a pigment having a cationic hydrophilic group are used, the potential of the back electrode and the control electrode is set to be higher than the potential of the ejection electrode during printing. In addition, the ink droplets can be stably formed even if the ink is continuously flown without clogging the nozzles.

[0058]

According to the present invention, the direction of the electric field generated to fly ink is set so that the ionic groups in the aqueous ink do not aggregate at the tip of the ink meniscus formed at the ink discharge port. Accordingly, the ink droplets are stably formed even when the ink is continuously ejected without clogging the ink discharge ports, and therefore, a high-quality image can be formed on the recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic partial sectional view showing an electrostatic ink jet recording apparatus according to the present invention.

FIG. 2 is a perspective view showing an embodiment of an electrostatic ink jet recording apparatus according to the present invention.

FIG. 3 is an enlarged front view of a timing slit provided in the recording apparatus of FIG. 2;

[Explanation of symbols]

1: inkjet recording device, 4: ink, 6: ink chamber, 8: ink ejection port, 16: back electrode, 20: control electrode, 24: ejection electrode, 30: recording medium, 100: inkjet recording device, 108: inkjet head.

Claims (6)

[Claims] 1. An ink jet head comprising: an ink chamber for accommodating ink; a plurality of ink ejection ports communicating with the ink chambers; and a control electrode disposed in the vicinity of each ink ejection port. A back electrode disposed oppositely, and applying a voltage to at least one of the control electrode and the back electrode to cause the ink to fly in a direction from the ink chamber toward the back electrode via the ink discharge port, thereby forming an ink jet head. An electrostatic ink jet recording apparatus that is attached to a recording medium between a substrate and a back electrode, wherein the ink comprises at least water, a pigment, and a resin, and the pigment and / or the resin have an anionic hydrophilic group in a molecule. A voltage applied to at least one of the control electrode and the back electrode is such that the potential of the control electrode and the back electrode is Recording apparatus characterized by being set to be lower than the potential of the ink in the click chamber. 2. An ink jet head comprising: an ink chamber for accommodating ink; a plurality of ink ejection ports communicating with the ink chambers; and control electrodes disposed near each of the ink ejection ports. To apply ink to the ink chamber so that the ink in the ink chamber flies to the opposite side of the ink chamber across the ink ejection port,
Thus, in an electrostatic ink jet recording apparatus that adheres to a recording medium facing an ink ejection port of an ink jet head, the ink comprises at least water, a pigment, and a resin, and the pigment and / or the resin have an anionic property in a molecule. An aqueous ink having a hydrophilic group, wherein the voltage applied to the control electrode is set so that the potential of the control electrode is lower than the potential of the ink in the ink chamber. A step of preparing an ink jet head having an ink chamber which communicates with a plurality of ink ejection ports and contains ink; and electrically connects the ink in the ink chamber to a side opposite to the ink chamber with the ink ejection port interposed therebetween. And causing the ink to fly through the ink ejection port, thereby attaching the ink to a recording medium facing the ink ejection port of the inkjet head. An aqueous ink comprising at least water, a pigment, and a resin, wherein the pigment and / or the resin has an anionic hydrophilic group in a molecule. In order to electrically energize the ink in the ink chamber, an electric field is applied. Wherein the direction is generated so as to be substantially the same as the direction in which the ink is ejected. 4. An ink jet head comprising: an ink chamber for accommodating ink; a plurality of ink ejection ports communicating with the ink chambers; and a control electrode disposed in the vicinity of each ink ejection port. A back electrode disposed oppositely, and applying a voltage to at least one of the control electrode and the back electrode to cause the ink to fly in a direction from the ink chamber toward the back electrode via the ink discharge port, thereby forming an ink jet head. An electrostatic ink jet recording apparatus that is attached to a recording medium between a substrate and a back electrode, wherein the ink comprises at least water, a pigment, and a resin, and the pigment and / or the resin has a cationic hydrophilic group in a molecule. A voltage applied to at least one of the control electrode and the back electrode is such that the potential of the control electrode and the back electrode is Recording apparatus characterized by being set to be higher than the potential of the ink in the click chamber. 5. An ink jet head comprising: an ink chamber for storing ink; a plurality of ink ejection ports communicating with the ink chambers; and control electrodes disposed near each of the ink ejection ports. To apply ink to the ink chamber so that the ink in the ink chamber flies to the opposite side of the ink chamber across the ink ejection port,
Thus, in an electrostatic ink jet recording apparatus that adheres to a recording medium facing an ink ejection port of an ink jet head, the ink comprises at least water, a pigment, and a resin, and the pigment and / or the resin have a cationic property in a molecule. A recording apparatus, comprising a water-based ink having a hydrophilic group, wherein the voltage applied to the control electrode is set so that the potential of the control electrode is higher than the potential of the ink in the ink chamber. 6. A step of preparing an ink jet head having an ink chamber which communicates with a plurality of ink discharge ports and stores ink, and electrically connects ink in the ink chamber to a side opposite to the ink chamber with the ink discharge ports interposed therebetween. And causing the ink to fly through the ink ejection port, thereby attaching the ink to a recording medium facing the ink ejection port of the inkjet head. An aqueous ink comprising at least water, a pigment, and a resin, wherein the pigment and / or the resin has a cationic hydrophilic group in a molecule. In order to electrically energize the ink in the ink chamber, an electric field is applied. The recording method is such that the direction is substantially opposite to the direction in which ink is ejected.