JP2009166278A - Inkjet head and image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head which can inhibit the growth of deposits near nozzle holes even when using an UV-curing ink containing many metal ions as impurities without using special pigments or purifying pigments, and an image recording method using this head. <P>SOLUTION: In the inkjet head of piezo system, the piezo electrode is insulated, and the front or rear surface of a nozzle plate has an electric conductivity while the surface potential of this electric conductivity being maintained in a ground potential or a plus potential as the feature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezo-type inkjet head and an image recording method, and more particularly to the emission stability of UV ink.

  An image forming method using an inkjet method using UV curable ink has attracted attention. This is because the adaptability to various image receiving media is high. For example, even an ink-absorbing medium can record an image on a plastic surface or a metal surface that does not absorb ink. It is.

  A piezo-type DOD (Drop On Demand) head has been generally used as an inkjet head used for UV curable ink.

  UV curable inks are broadly classified into radical polymerization types and cationic polymerization types. At present, radical polymerization types are the mainstream, or radical polymerization type inks have low electrical conductivity, and are inkjet heads that are not insulated by piezo electrodes. It can be used.

  However, since the other cationic polymerization type UV curable ink contains a photoacid generator such as an ionic triarylsulfonium salt as an initiator species, the ink has a slight electrical conductivity. For this reason, if the electrode for driving the PZT element, which is a piezoelectric element, is not insulated, the contacted ink may cause electrophoresis or electrochemical reaction.

  In order to prevent these phenomena, electrode insulation is the most effective.

  However, it has been found by the present inventors that even if the electrodes are insulated, long-term output stability may be hindered.

  When a cationic polymerization type UV curable ink is ejected from an inkjet head for a long period of time, a precipitate containing alkali metal ions may be generated in the vicinity of the nozzle hole. Cause clogging.

  This precipitation phenomenon is specific to a combination of (a) ink with a large amount of impurities of alkali metal ions, (b) UV light leaks to the nozzle emission surface, and (c) nozzle that emits ink. I found out. It was found that precipitates grew on the meniscus surface at the nozzle outlet.

  It is presumed that when alkali metal ions are localized on the meniscus surface of the nozzle and are irradiated with UV light, anion species are generated and a metal salt insoluble in the ink is generated.

  On the other hand, due to the insulation of the electrodes, there is a problem that electric charge remains in the ink and impairs the emission stability, and the pressure contact chamber, the fluid resistance portion, the ink contact portion of the common flow channel chamber and the nozzle plate Disclosed is a method of obtaining an output stability by providing an electric conductive layer on the entire surface of the bonding surface and the insulating film of the diaphragm so as to provide an electric shielding property to prevent the flow of liquid due to the electrolysis and electrophoresis of the ink. (See Patent Document 1). However, Patent Document 1 does not describe the surface of the nozzle plate or the nozzle holes.

On the other hand, in order to form a highly accurate nozzle hole, a method of forming a nozzle plate with a metal using an electrolytic plating method is disclosed (for example, see Patent Document 2). The use of an electrically conductive metal nozzle plate as described herein is a well known technique.
JP 2004-66571 A JP 7-329304 A

  The object of the present invention is to suppress precipitate growth near the nozzle holes even when using a UV curable ink containing a large amount of alkali metal ions as impurities without using a special pigment or purifying the pigment, An inkjet head capable of obtaining long-term stable emission and an image recording method using the same are provided.

  In the present invention, by providing an electrically conductive layer on the entire surface of the nozzle plate and setting the potential of the electrically conductive layer to the ground level, alkali metal ions contained in the ink are localized at the meniscus interface. It was found that long-term emission stability can be obtained by preventing the formation of precipitates made of alkali metal salts by preventing the above.

  Furthermore, it has been found that precipitation can be effectively suppressed by positively charging to a positive potential.

  That is, the said subject was able to be solved with the following structures.

  1. In a piezo-type ink jet head, the piezo electrode is insulated, the front or back surface of the nozzle plate has electrical conductivity, and the surface potential of the electrical conductivity is maintained at a ground potential or a positive potential. Inkjet head.

  2. 2. The ink jet head as described in 1 above, wherein the method for imparting electrical conductivity is an electrically conductive layer.

  3. 3. The inkjet head as described in 2 above, wherein an electrically conductive layer is provided on the inner surface of the orifice of the nozzle hole and is electrically connected to either the front surface or the back surface of the nozzle plate.

  4). An image recording method using a UV curable ink using the inkjet head according to any one of 1 to 3, wherein the UV curable ink contains 10 ppm or more of a compound containing an alkali metal ion, An image recording method characterized by curing using UV light.

  According to the present invention, in an ink jet recording method using a cationic polymerization type UV curable ink, it has been possible to prevent contamination and precipitation in the vicinity of a nozzle hole and maintain stable emission stability over a long period of time.

  Hereinafter, the present invention will be described in detail.

  A piezoelectric inkjet head used in the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of the main configuration showing an example of a commonly used piezo ink jet head.

  In FIG. 1, the ink jet head 1 includes an ink chamber 16 formed by a PZT element 15, a cover plate 14, a back plate 18, and a nozzle plate 20, and a manifold 13, an ink supply tube 11, and the like are connected and held in the ink jet head casing. Has been. The ink supplied in the direction of the arrow is held in the ink chamber 16 and is discharged as an ink droplet 17 from the nozzle hole 10 by applying a charge to the PZT element.

  FIG. 2 is a further exploded perspective view of the inkjet head. Each member is the same as in FIG.

  FIG. 3 is a view showing a nozzle plate according to the present invention, FIG. 3 (a) is a front view of the nozzle plate, and FIG. 3 (b) is a sectional view thereof.

  The nozzle plate has a front surface (atmosphere surface) 21 and a back surface (ink contact surface) 22 on the atmosphere side, and an orifice surface 23 that forms a nozzle hole therethrough.

  As shown in FIG. 3B, the nozzle hole has a tapered structure in which the liquid contact surface is usually wide and the atmosphere side is narrow, and the nozzle plate 20 has a large number of nozzle holes 10.

  FIG. 4 is an enlarged view showing a portion of the nozzle hole portion surrounded by a circle in FIG. 3 where the electrically conductive layer of the present invention is formed.

  In the present invention, when an image is formed using a UV curable inkjet ink having a low quality level and containing a large amount of alkali metals as impurities, precipitates containing alkali metals are formed on the orifice surface, and the straightness of the ink is improved. They found the problem of inhibiting and eventually causing clogging, and found a solution.

  That is, the present invention is a problem peculiar to the cationic polymerization type UV curable ink jet ink, and as described above, it is a phenomenon in which precipitates are generated only in the driven nozzle, and the nozzle hole irradiated with UV light. The precipitate is composed of a substance containing a large amount of alkali metals.

  From these phenomena, the inventors have made various studies and made hypotheses and verified them, but the cause has not been clarified yet. However, it has been found that the formation of precipitates can be effectively prevented by forming an electrically conductive layer on the front side or the back side of the nozzle plate and setting the potential to the ground level and further to the + side.

  Furthermore, in the present invention, the formation of precipitates can be prevented more effectively by forming an electrically conductive layer on the orifice surface and joining and short-circuiting the electrically conductive film on the front or back side. I found it.

  A preferred embodiment of the nozzle plate of the present invention will be described with reference to FIG.

  The nozzle plate 30 in FIG. 4 (a) has an electrically conductive layer 31 formed on the front surface side, FIG. 4 (b) has an electrically conductive layer 33 formed on the back surface side, and FIG. In FIG. 4D, an electrically conductive layer 35 is also formed on the orifice surface and is electrically connected to the electrically conductive layer 31 on the front surface side. FIG. The thing short-circuited with the conductive layer 33 is shown.

  Further, FIG. 4E shows an electrically conductive layer formed on all surfaces of the nozzle plate, the front surface side, the back surface side, and the orifice surface.

  As a method for producing a piezo ink jet head used in the present invention, it can be produced based on JP-A-2002-103629.

  Further, if the liquid contact surface (ink flow path and PZT drive electrode) of the ink liquid is not insulated, the electrophoresis and electrochemical reaction occur in the ink, so that the insulation of the electrode is essential.

  As a method for insulating the wetted surface of the ink, it can be produced with reference to Japanese Patent Application Laid-Open Nos. 2002-103629 and 2004-66571.

  The nozzle plate used in the present invention is a conductive metal nozzle plate as a whole even if an electrically conductive layer is formed on the front surface, back surface or orifice surface of a non-conductive nozzle plate substrate. May be.

  As a nozzle plate base material, various things, such as a metal plate and a resin film, can be used, for example. In the present invention, a resin film is preferable, and examples thereof include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), synthetic resins such as polyimide resins, aromatic polyamide resins, and polysulfone resins. . As for the thickness of a nozzle plate base material, about 60-100 micrometers is preferable.

  As a material for forming the electrically conductive layer, an inorganic or organic conductive material can be used. As the inorganic conductive material, a metal or metal oxide conductive material can be used, such as aluminum, nickel, gold, silver, platinum, palladium, titanium, carbon, titanium nitride, indium oxide, tin oxide, ITO, etc. These conductive materials can be mentioned. Further, as the organic conductive material, for example, a π-electron conjugated conductive polymer such as polyacetylene, polyparaphenylene, polythiophene, polypyrrole, polyaniline, and polyacene can be used to form an electrically conductive layer by coating with a solvent or the like. it can.

  As a method of forming these conductive materials as an electrically conductive layer, a method such as a plasma method, a sputtering method, a vacuum deposition method, an ion plating method, a CVD method, or a conductive material is applied to the surface of the nozzle plate substrate. Various methods such as a method of coating by dissolving or dispersing in a solvent, a method of electrolysis or electroless plating, a method of forming and attaching a foil, a method of transferring after forming a conductive layer on the surface of another substrate Can be used.

  A method of forming the nozzle hole after forming the electroconductive layer on the substrate may be used, even after forming the nozzle hole in advance and then forming the electroconductive layer.

  Examples of the method of forming the electrically conductive layer only on the front surface or the back surface of the nozzle plate include a method of forming the nozzle hole after forming the electrically conductive layer on one surface of the substrate. The orifice surface of the nozzle hole In the case of forming the electrically conductive layer, after forming the nozzle holes in advance, the plate is immersed in a solution in which the conductive material is dissolved to form the electrically conductive layer on the entire surface and the nozzle hole orifice surface. When forming a nozzle plate having nozzle holes by forming an electrically conductive layer on the surface of the mold having projections that form nozzle holes and forming the nozzle holes, the orifice surface and the substrate surface are also formed. The method of transferring and forming an electroconductive layer can be mentioned.

  The thickness of the electrically conductive film is preferably several tens nm to several hundreds nm.

  The potential of the formed electrically conductive layer needs to be zero V or higher, and is preferably a positive potential. By setting the potential to be positive, it is possible to effectively prevent localization of alkali metal ions on the meniscus surface. The positive potential is preferably 0.01 to 10 V, and more preferably 0.01 to 2 V. This is because when the voltage is 10 V or higher, the ink undergoes electrophoresis when energization occurs in the flow path including the head due to some accident.

  The most preferable configuration is a configuration having an electrically conductive layer from the front and back surfaces of the nozzle plate to the inside of the orifice, and applying a potential of 0.01 to 2V.

  Various methods can be used as the power supply device for applying a positive potential. FIG. 5 shows an example of the power supply device used in the present invention.

  5 forms a circuit in which a variable resistance of 100 kΩ and a fixed resistance of 1 kΩ are connected in series to a 2 V battery, and terminals A and B are taken out as shown in FIG. The meter is connected. By changing the variable resistance from 100 kΩ to 0, a voltage of 0.01 to 2 V can be generated between the terminals.

  By connecting the terminal B to the surface of the nozzle plate having the electrically conductive layer on the surface of the present invention and dropping the terminal A to the ground, a positive potential can be generated and maintained in the nozzle plate.

  Further, the nozzle plate preferably used in the present invention has a structure in which only the surface of the nozzle plate is further provided with a water-repellent layer, or water repellency is provided by eutectoid plating of a fluorine compound and Ni. It should be noted that the inside of the orifice is preferably not given water repellency.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these descriptions.

<< Production of inkjet head >>
<Preparation of nozzle plate 1>
A surface on which an electrically conductive layer is formed using an excimer laser after forming an electrically conductive layer of ITO (film thickness: 20 nm) on one surface of a polyimide film having a thickness of 50 μm by an atmospheric pressure plasma method As a result, a nozzle plate 1 having a plurality of nozzle holes with an air surface diameter of 18 μm and an ink contact surface diameter of 20 μm was obtained (see FIG. 4A).

<PZT element>
A PZT element is formed by joining two PZT piezoelectric material substrates that are deformed by applying an electric field up and down using an epoxy adhesive or the like with their polarization directions opposite to each other. By using a known grinding machine such as a disk-shaped grindstone (dicing blade), a plurality of rows of grooves parallel to each other at a predetermined pitch are formed, whereby channels and partition walls are alternately formed. After providing the drive electrode in each ink channel, the ink wetted part formed an insulating film by parylene conformal coating.

<Assembly of inkjet head>
In addition to the PZT element and nozzle plate 1 produced above, the following materials were prepared.

Tube: Teflon (registered trademark)
Manifold: Nylon Cover plate: Ceramics The ink jet head 1 was manufactured by assembling and bonding these materials.

  Between the ink tank (not shown) and the nozzle plate, the ink contact surface was an insulating member except for the nozzle plate.

  The surface (atmosphere surface) of the nozzle plate was grounded to make the potential 0V.

Examples 2-5 and comparisons 1-4
In Example 1, each ink jet head was produced in the same manner as the ink jet head 1 except that the nozzle plate shown in Table 1 was used instead of the nozzle plate 1 used.

  In Comparative Examples 1 and 2, the same inkjet head as in Example 1 was used.

  As the nozzle plate without the electrically conductive layer of Comparative Examples 3 and 4, a polyimide film having a thickness of 50 μm was used as it was, and nozzle holes were formed.

  In Example 4, an ITO film was formed on the nozzle plate (base material on which nozzle holes were formed) of Comparative Example 3 by the atmospheric pressure plasma method from the ink contact side, and an ITO film was also formed on the orifice surface.

  In Example 5, an ITO film was also formed from the surface of the nozzle plate of Example 4 by the atmospheric pressure plasma method, and an ITO film was also formed on the front and back surfaces and the orifice surface.

  Using each inkjet head, the electric potential of the electrically conductive surface from the front surface or back surface (ink contact surface) to the orifice surface of the nozzle plate is 0 V (ground earth) or 0.01 V to 0.2 V (power supply device shown in FIG. 5) Was used).

[Outgoing evaluation]
The UVIJ printer (manufactured by Konica Minolta HIJ) incorporating the inkjet head produced above was used to evaluate the long-term emission stability of the cationic UV ink.

  In the long-term emission stability evaluation, the UV lamp was turned on and UV leakage light was irradiated on the nozzle plate surface.

<UV curable ink>
As the ink, two kinds of cationic polymerizable UV curable inks having different alkali metal amounts were evaluated.

Ink A: Alkali metal (total amount of Na, Ca and Mg) is 200 ppm
Ink B: Alkali metal (total amount of Na, Ca, Mg) is 30 ppm
<Evaluation method>
Long-term emission stability ◎: No emission bending occurs even if emitted for 30 days or more, and no deposit is seen in the nozzle hole ○: Even if emitted for 30 days or more, the emission curve is slight, and there is a deposit in the nozzle hole Δ: Almost no emission bend when emitted for 7 days, but almost no deposit is observed in the nozzle hole, no exit bend occurs after 30 days of emission, and a little deposit is seen in the nozzle hole X: The emission curve starts to appear after the emission for 1 day, the emission curve becomes remarkable after the emission for 7 days, and a large amount of precipitates are observed in the nozzle holes.

  As can be seen from the table, it can be seen that deposition on the nozzle holes can be effectively prevented by forming an electrically conductive layer on the back or surface of the nozzle plate and controlling the potential to a positive potential of 0 or more. Moreover, it turns out that it has the further outstanding effect by forming the electrically conductive layer continuous on the surface of a nozzle plate, and an orifice surface.

  In addition, when the deposit seen by (triangle | delta) and x was analyzed, the alkali metal salt was detected. By using this head, it can be seen that even when ink containing a large amount of impurities made of an alkali metal is used, it is possible to suppress emission defects associated with UV leakage light.

It is a schematic cross section of a piezo-type inkjet head. It is a disassembled perspective view of a piezo-type inkjet head. It is sectional drawing of the nozzle plate which concerns on this invention. It is an expanded sectional view of the nozzle hole part of the nozzle plate which has an electroconductive layer of this invention. It is a figure which shows an example of the power supply device used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 10 Nozzle hole 11 Ink supply tube 13 Manifold 14 Cover plate 15 PZT element 17 Ink droplet 18 Back plate 20, 30 Nozzle plate 21 Nozzle plate surface (atmosphere surface)
22 Back side of nozzle plate (ink contact surface)
23 Orifice surface 31, 33, 35 Electrically conductive layer

Claims (4)

In a piezo-type ink jet head, the piezo electrode is insulated, the front or back surface of the nozzle plate has electrical conductivity, and the surface potential of the electrical conductivity is maintained at a ground potential or a positive potential. Inkjet head. The inkjet head according to claim 1, wherein the method for imparting electrical conductivity is an electrically conductive layer. The inkjet head according to claim 2, further comprising an electrically conductive layer on an inner surface of the orifice of the nozzle hole, wherein the electrically conductive layer is electrically connected to either the front surface or the back surface of the nozzle plate. An image recording method using a UV curable ink using the inkjet head according to claim 1, wherein the UV curable ink contains 10 ppm or more of a compound containing an alkali metal ion. An image recording method comprising curing using UV light.

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