JP2013022794A - Liquid droplet discharge head, and recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid droplet discharge head and a recording device which can reduce inclusion of air bubbles by optimizing an advance contact angle and a retreat contact angle of an inner wall surface of a nozzle with respect to a liquid material to stably discharge and increase a speed.SOLUTION: In the liquid droplet discharge head for discharging the liquid material from the nozzle 13, the inner wall surface of the nozzle 13 has the advance contact angle of 50° or less and the retreat contact angle of 90° or more with respect to the liquid material. The recording device includes the liquid droplet discharge head and records by landing the liquid material discharged from the nozzle 13 on a recorded material.

Description

  The present invention relates to a droplet discharge head and a recording apparatus, and more particularly to a droplet discharge head capable of reducing bubble entrainment during a discharge operation of a liquid from a nozzle and enabling stable discharge, and a recording apparatus equipped with the droplet discharge head.

  As a droplet discharge head that discharges a liquid material from a nozzle, an ink jet head that uses ink as the liquid material and discharges the ink as fine ink droplets from the nozzle is generally known.

  The inkjet head fills the ink in the nozzle, applies a positive pressure, pushes the ink out of the pressure chamber, then applies a negative pressure to the ink and pulls it back into the nozzle, tearing out the extruded ink column, Ink droplets are discharged from At this time, the meniscus is drawn deeply into the nozzle, and this negative pressure fills the nozzle with new ink to prepare for the next discharge. When the negative pressure is reversed and becomes a positive pressure, the meniscus is pushed out again and moves in the nozzle outlet direction.

  Since the pressure applied to eject ink in this way remains in the pressure chamber and vibrates after ejecting ink, the ink pressure in the nozzle fluctuates and the meniscus vibrates. This vibration is repeated several times and gradually attenuates to enable the next discharge. Also, depending on the ink ejection method of the head, when ink is ejected from one pressure chamber, the ejection pressure is also transmitted to the adjacent pressure chamber, and the meniscus vibrates.

  When a positive pressure is applied to the ink in the nozzle due to this pressure fluctuation, the meniscus may jump out of the nozzle. The meniscus that has jumped out of the nozzle is drawn into the nozzle at the next negative pressure. However, particularly when ink is ejected continuously, the meniscus may jump out too much. It was found that the meniscus that protrudes greatly causes bubbles to be trapped in the nozzle due to meniscus vibration, resulting in unstable ejection. When bubbles are entrained and air bubbles enter the ink, the bubbles absorb the pressure fluctuations of the pressure that propagates through the ink. Insufficient energy causes a decrease in ink discharge amount and discharge speed. Further, when the discharge energy is insufficient due to entrainment of bubbles, there is a problem that ink is not discharged from the nozzle even when pressure is applied.

  In particular, in the case of a shear mode type ink jet head in which a partition between adjacent pressure chambers is an actuator and ink in the pressure chamber is ejected from a nozzle by a deformation operation of the partition, the pressure chambers are adjacent to each other via a common partition. Therefore, it is greatly affected by the meniscus vibration generated by the discharge of the adjacent pressure chamber. Therefore, such a meniscus jump-out and bubble entrainment due to meniscus vibration are likely to occur.

  As a result of intensive analysis on the cause of bubble entrainment, the present inventor has found that the dynamic wettability of the inner wall surface on the discharge port side of the nozzle is important. A simulation result showing the behavior of the meniscus is shown in FIG. In the figure, 300 is a nozzle and 400 is ink. The ink 400 forms a meniscus 401 near the discharge port at the right end of the nozzle 300 in the figure.

  The meniscus 401 that has jumped out of the nozzle 300 due to meniscus vibration starts to be drawn into the nozzle 300 due to negative pressure (FIG. 6A). However, the ink 400 to be drawn into the nozzle 300 has a frictional resistance between the portion contacting the inner wall surface 301 of the nozzle 300 and the inner wall surface 301, so that the ink 400 is in the center near the axis of the nozzle 300. A speed difference is generated between the ink 400 and the meniscus 401b in contact with the inner wall surface 301 with a delay compared to the meniscus 401a in the center of the nozzle 300 (FIGS. 6B and 6C). . Thereafter, when a positive pressure is applied to the nozzle 300 and the meniscus 401 is pushed out, the meniscus 401b in contact with the inner wall surface 301 is pushed out before being drawn into the nozzle 300 at that timing, whereby the center of the nozzle 300 is pushed. Part of the meniscus 401a is encased, and the bubble 500 is caught inside (FIG. 6D).

  As a result of intensive studies by the present inventors, such a bubble entrainment phenomenon was not observed for the case where the advancing contact angle with respect to the ink on the inner wall surface of the nozzle was small and the receding contact angle was large. From this, it was found that the advancing contact angle and the receding contact angle with respect to the ink on the inner wall surface of the nozzle are greatly related to bubble entrainment.

  In general, an angle formed by a stationary droplet with a solid surface is called an equilibrium contact angle θe or simply a contact angle θ. When the stationary droplet shown in FIG. 7 (a) is moved by applying an external force in the direction indicated by the arrow as shown in FIG. 7 (b), the equilibrium contact angle disappears, and the forward contact angle θa and the backward contact angle disappear. The contact angle θr appears. The advancing contact angle θa is a contact angle that appears when a droplet is advanced, and is a contact angle with respect to a solid surface that is not yet wet with the liquid. The receding contact angle θr is a contact angle that appears when the liquid is receded, and is a contact angle with respect to a solid surface that has already been wetted by the liquid.

  θ is a contact angle indicated by a stationary droplet, and indicates whether the liquid is likely to wet the solid surface. Since a liquid having a large θ does not easily wet the solid surface, the contact area is small and the liquid surface easily moves on the solid surface. However, when the liquid droplet starts to move, the advancing contact angle θa and the receding contact angle θr appear. Is not influenced by θ, but is influenced by θa and θr. Normally, it can be assumed that θa≈θ, so that the mobility of the droplet can be estimated by only the value of θ, but the meniscus vibration in the nozzle is a motion that repeats pushing (forward) and pulling (retracting) from the nozzle. Therefore, when considering the bubble entrainment phenomenon, not only the value of the advancing contact angle θa for the liquid on the inner wall surface of the nozzle but also the value of the receding contact angle θr is important.

  In addition, since the bubble entrainment phenomenon is caused by a speed difference between the ink in the center of the nozzle and the ink in contact with the inner wall surface of the nozzle, the low-viscosity ink in which the speed difference increases becomes more conspicuous. I understood.

  Conventionally, there are Patent Documents 1 to 4 as technologies that focus on the advancing contact angle and the receding contact angle of the inner wall surface on the nozzle outlet side in order to perform good and stable ejection of the droplet ejection head.

  In Patent Document 1, an in-nozzle liquid-repellent film is formed on the inner wall surface of the nozzle, and the forward contact angle with respect to the liquid to be discharged is set to 50 ° to 90 ° on the discharge port side of the in-nozzle liquid-repellent film. It is described that by setting the contact angle to 25 ° or less, the end of the meniscus is approximately the same position every time, thereby improving the ejection stability.

  However, there is no mention of reducing bubble entrainment by defining the advancing contact angle and the receding contact angle. According to the knowledge of the present inventor, it has been found that the entrainment of bubbles cannot be reduced even if the forward contact angle and the backward contact angle of the inner wall surface on the discharge port side of the nozzle are defined as described above. That is, in order not to entrain bubbles, the meniscus must return quickly when returning to the inside of the pressure chamber, so that water repellency is required. In this case, the receding contact angle needs to be 90 ° or more. For this reason, when the receding contact angle is 25 ° or less as in Patent Document 1, the return speed of the ink in contact with the inner wall surface of the nozzle is slowed, so that the meniscus returns slowly and air bubbles are easily involved. Also, since the forward contact angle is relatively large, not only the ejection performance during extrusion becomes unstable, but also the inner wall surface of the nozzle becomes difficult to wet when pushing out the meniscus, and this time, bubbles are trapped in the gap with the inner wall surface during extrusion. It did not help at all to reduce entrainment of bubbles.

  Furthermore, because the advancing contact angle is larger than the receding contact angle, the meniscus is still not pushed out smoothly, resulting in a large variation in droplet volume in terms of discharge characteristics, which cannot be used in actual use. Met.

  In Patent Document 2, an in-nozzle lyophobic film in which the difference between the receding contact angle and the advancing contact angle with respect to the liquid to be ejected is large is formed in the vicinity of the ejection port on the inner wall surface of the nozzle, and the advancing contact angle. As a specific example of this, it is described that 60 ° is a specific example of the receding contact angle, 20 ° is a specific example of the receding contact angle, and the difference between the two is 40 °.

  However, no mention is made here of preventing bubble entrainment by defining the advancing contact angle and the receding contact angle, and according to what the present inventor has confirmed through experiments, the entrainment of bubbles is still avoided. It was found that it cannot be reduced. That is, in order to prevent entrainment of bubbles, the forward contact angle must be small in order to increase the receding contact angle so that the meniscus can quickly return to the pressure chamber while obtaining stable characteristics during discharge. Because it will not be. For this purpose, the relationship of the receding contact angle> the advancing contact angle is particularly important. However, the technique described in Patent Document 2 has a configuration opposite to this, and reduces the entrainment of bubbles, In addition, stable discharge characteristics cannot be obtained.

  In Patent Document 3, an in-nozzle liquid-repellent film is formed on the inner wall surface of the nozzle, the forward contact angle of the liquid-repellent film in the nozzle with respect to the liquid to be ejected is 50 ° or more and 90 ° or less, and the receding contact angle is 25. It is stated that it is less than °. However, this technique has the same configuration as that of Patent Document 1, and consequently, entrainment of bubbles cannot be reduced, and stable discharge characteristics cannot be obtained.

  Patent Document 4 describes that the advancing contact angle with respect to the nozzle surface is 65 ° or more, the receding contact angle is 55 ° or more, and the difference between the advancing contact angle and the receding contact angle is 20 ° or less.

  However, this technique has a problem of preventing stable sticking to the nozzle surface even with water-based ink containing a particulate colorant by regulating the advancing contact angle and the receding contact angle. There is no mention of reducing entrainment. This technique discloses that the advancing contact angle and the receding contact angle are obtained by further defining the physical properties (surface tension) of the ink. Since the receding contact angle is small and easy to get wet, entrainment of bubbles cannot be reduced.

JP 2005-40979 A JP 2005-7654 A Japanese Patent Laying-Open No. 2005-40978 JP 2003-277651 A

  Accordingly, the present invention can reduce the entrainment of bubbles by optimizing the advancing contact angle and the receding contact angle with respect to the liquid on the inner wall surface of the nozzle, thereby enabling stable ejection and increasing the speed. It is an object to provide a droplet discharge head and a recording apparatus that can be used.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

1. In the droplet discharge head for discharging a liquid material from a nozzle, the inner wall surface of the nozzle has a forward contact angle with respect to the liquid material of 50 ° or less and a backward contact angle of 90 ° or more. Discharge head.
2. The angle obtained by subtracting the advancing contact angle from the receding contact angle is 60 ° or more. The droplet discharge head described.
3. The liquid has a viscosity of less than 6 cp. Or 2. The droplet discharge head described.
4). A large number of pressure chambers to which the liquid material is supplied are arranged in parallel, and a partition between adjacent pressure chambers is configured by an actuator that deforms in response to an applied voltage. 1. The share mode head that discharges the liquid material from the nozzle. 2. Or 3. The droplet discharge head described.
5. 1 above. ~ 4. A recording apparatus comprising the droplet discharge head according to any one of the above, and performing recording by landing a liquid material discharged from the nozzle on a recording material.

  According to the present invention, it is possible to provide a droplet discharge head and a recording apparatus that can reduce the entrainment of bubbles in a nozzle, perform stable discharge, and increase the speed.

(A) is a schematic perspective view showing an example of a shear mode type droplet discharge head, and (b) is a cross-sectional view. The figure which shows an example of the production method of a nozzle plate The figure for explaining the production method of the nozzle plate The figure which shows schematic structure of a recording device Plan view of nozzle plate in embodiment Diagram for explaining the behavior of a conventional meniscus A diagram for explaining the advancing contact angle and the receding contact angle

  The droplet discharge head in the present invention may be any one that discharges a liquid material from a nozzle, and its specific structure is not limited.

  For example, a large number of pressure chambers (channels) formed in a groove shape and a large number of partition walls are alternately arranged side by side, and at least a part of the partition walls is formed of a piezoelectric material, so that the partition walls respond to an applied voltage. The actuator is operated in a deformed manner, and a liquid is ejected from the nozzle by applying a pressure to the liquid material in the pressure chamber by a deforming operation of the partition wall, and a diaphragm is provided on one wall surface of the pressure chamber containing the liquid material. The piezoelectric material is laminated on the vibration plate, and the piezoelectric material is mechanically deformed to vibrate the vibration plate, thereby applying pressure to the liquid in the pressure chamber and discharging droplets from the nozzle. An electrothermal conversion element is disposed in a pressure chamber containing a discharge head and a liquid material, bubbles are generated by heating the liquid material by energization of the electrothermal conversion element, and the liquid material in the pressure chamber is formed by the bursting action of the bubbles. And applying a force, there is the liquid droplet ejection head or the like of the structure to be discharged from the nozzle, the present invention is applicable to any droplet discharge head.

  Among these, a droplet discharge head (shear mode type droplet discharge head) of a type in which pressure chambers and partition walls are alternately arranged in parallel and the partition walls are deformed in response to an applied voltage is used as an adjacent pressure. Since the chambers are adjacent to each other through a common partition wall, the chambers are easily affected by meniscus vibrations generated by the discharge operation of the adjacent pressure chambers, and the meniscus jumps out and bubbles are easily generated due to the meniscus vibrations. Therefore, it is preferable because a remarkable effect can be obtained by applying the present invention.

  In the present invention, the inner wall surface of the nozzle has an advancing contact angle with respect to the liquid material of 50 ° or less and a receding contact angle of 90 ° or more.

  In the present invention, when the advancing contact angle with respect to the liquid material on the inner wall surface of this nozzle is 50 ° or less, the wettability of the inner wall surface with respect to the liquid material is good, and the meniscus in contact with the inner wall surface is smoothly pushed out. It is possible to reduce entrainment of bubbles during extrusion. In addition, since the extrusion is smooth, variation in the amount of droplets can be suppressed, ejection can be stabilized, and speed can be increased.

  Further, when the receding contact angle is 90 ° or more, the meniscus in contact with the inner wall surface of the nozzle can quickly return into the nozzle, and the speed difference from the meniscus located at the center (axis) of the nozzle can be reduced. . For this reason, it is possible to reduce the entrainment of bubbles due to the difference in speed between the meniscuses of the ink in contact with the inner wall surface of the nozzle and the ink located in the central portion of the nozzle.

  The position of the meniscus due to the meniscus vibration in the nozzle that causes entrainment of bubbles is exclusively on the discharge port side in the nozzle, that is, on the outlet side from which the liquid material is discharged. The portion of the inner wall surface of the nozzle need not necessarily be the entire surface of the inner wall surface, but may be at least on the discharge port side of the inner wall surface.

  In the present invention, when the angle obtained by subtracting the advancing contact angle from the receding contact angle is 60 ° or more, the effect of stabilizing the ejection and the effect of reducing the entrainment of bubbles as described above can be remarkably exhibited.

  The liquid material that can be used in the present invention is not particularly limited as long as it can be ejected as droplets from a nozzle of a droplet ejection head. For example, in addition to ink for image formation, a color filter for a liquid crystal panel, a manufacturing device for a semiconductor device, Examples include functional liquids used in various industrial applications.

  In particular, a low-viscosity liquid having a viscosity of less than 6 cp (viscosity at 25 ° C.) is likely to have large meniscus fluctuations, and as a result, air bubbles are easily involved. Therefore, it is preferable because a remarkable effect can be obtained by applying the present invention.

  Next, the present invention will be further described with reference to the drawings for a specific droplet discharge head.

  FIG. 1 shows an example of a share mode type droplet discharge head as a droplet discharge head. FIG. 1A is a perspective view thereof and FIG. 1B is a sectional view thereof.

  In the droplet discharge head 1 shown in FIG. 1, 11 is an ink tube, 12 is a nozzle plate, 13 is a nozzle, 14 is a cover plate, 15 is an ink supply port, 16 is a channel substrate, and 17 is a partition. A channel 18 serving as a pressure chamber is formed by the partition wall 17, the cover plate 14, and the channel substrate 16.

  Each partition wall 17 is formed by an upper wall portion 17a and a lower wall portion 17b made of a piezoelectric material such as PZT whose polarization directions are opposite to each other. However, the piezoelectric material may be only a portion indicated by reference numeral 17a, for example. It suffices if it is at least part of the partition wall 17. The partition walls 17 are alternately arranged in parallel with the channels 18 so that the one partition wall 17 is shared by the adjacent channels 18 and 18. One end of each channel 18 is connected to a nozzle 13 provided at a position corresponding to each channel 18 in the nozzle plate 12, and the other end is connected to an ink tank (not shown) by an ink tube 11 through an ink supply port 15. .

  An electrode (not shown) is formed on the surface of the partition wall 17 facing the channel 18. By applying a predetermined drive voltage to the electrode, the partition wall 17 is deformed into a U-shape, and the ink tube 11 is moved. A pressure for discharging is applied to the liquid material supplied into the channel 18 through the nozzle 18, and the liquid material in the channel 18 is discharged as droplets from the nozzle 13.

  In this droplet discharge head 1, the advancing contact angle with respect to the liquid on the inner wall surface of the nozzle 13 provided in the nozzle plate 12 corresponding to each channel 18 is set to 50 ° or less and the receding contact angle is set to 90 ° or less. As a specific method for making the inner wall surface of the nozzle 13 have such an advancing contact angle and a receding contact angle with respect to the liquid material, in general, the inner wall surface of the nozzle 13, particularly in the vicinity of the discharge port on the inner wall surface, is generally used. The film can be formed by forming a film in which the contact angle to the liquid is appropriately adjusted.

  The method for adjusting the contact angle by the film, that is, the method for adjusting the advancing contact angle and the receding contact angle of the liquid material that contacts the inner wall surface is by applying energy to a part of the liquid repellent film formed on the inner wall surface of the nozzle. , By changing its liquid repellency.

  That is, the nozzle plate 12 is made of a lyophilic resin such as polyimide, for example, and a liquid repellent film 121 is provided on one side (FIG. 2A), and a desired nozzle is provided on the opposite side of the liquid repellent film 121. After applying a mask having a pattern, the nozzle 13 is perforated using, for example, an excimer laser (oscillation wavelength: 248 nm, pulse width: 150 nsec) (FIG. 2B).

  As the liquid repellent film 121, an organic solvent soluble and applicable fluoropolymer, silicon resin, or the like can be preferably used. An alternating copolymer of fluoroolefin and vinyl ether (FEVE, manufactured by Asahi Glass Co., Ltd .; Lumiflon, Dainippon Ink, Inc.), which improves the solubility in a solvent by reducing the crystallinity of the perfluoropolymer and simultaneously introduces a crosslinkable group Fluonate, manufactured by Central Glass Co., Ltd .; Cephral Coat, manufactured by Daikin Co., Ltd .; C-1, etc.), amorphous, liquid-repellent and solvent-soluble perfluorocyclopolymer (manufactured by Asahi Glass Co., Ltd.) Cytop, manufactured by Dupont; Teflon AF, etc.), a polymer having a perfluoro group in the side chain (manufactured by Asahi Glass Co., Ltd .; Asahi Guard AG series, etc.), room temperature curable silicone resin, room temperature curable organic modified silicone resin, Silicon hard coat material, silane coupling agent, fluoroalkylsilane, etc. (manufactured by Toray Dow Corning Silicone; SR24 0,2411,2107,2115, Toshiba Silicone Co., Ltd. fluoroalkyl silane; can be exemplified TSL-8233,8257, etc.).

  Since the liquid repellent film 121 on the surface of the nozzle plate 12 is rubbed by a wiper, paper, cloth, etc., durability is required. In order to strongly bond the liquid repellents and adhere strongly to the nozzle plate 12, a liquid repellent having a hydroxyl group or a carboxyl group is adopted and crosslinked with an isocyanate curing agent or an epoxy curing agent, or reacted with moisture in the air. Then, a silicon compound having a silanol group that crosslinks may be employed.

  After forming the nozzle 13, the inside of the nozzle 13 is once again subjected to surface treatment by dipping or the like on the inner wall surface of the nozzle 13 using the same liquid repellent treatment compound as described above, thereby forming the in-nozzle liquid repellent film 122. Provided (FIG. 2C).

  Then, in order to change the liquid repellency of the liquid repellency film 122 in the nozzle, the inside of the nozzle 13 is made from the side opposite to the discharge port side of the nozzle 13 using, for example, an excimer laser (oscillation wavelength: 248 nm, pulse width: 150 nsec). Exposure. On the liquid repellent film 121 side of the nozzle plate 12, a reflecting plate 20 having fine irregularities is provided on the surface, and the inner wall surface of the nozzle 13 is exposed by reflection and interference due to the irregularities of the reflecting plate 20, and the nozzle A strongly exposed portion and a weakly exposed portion are formed on the inner liquid repellent film 122 (FIG. 2D).

  The reflection plate 20 can be formed of a metal plate such as aluminum or stainless steel having a concavo-convex pattern comparable to the wavelength of the laser beam used (for example, 248 nm).

  As such a reflection plate 20, a laser resonator mirror in which a dielectric film is coated on a concave substrate or a parallel flat substrate can be obtained and used. In the present invention, as the concave / convex pattern, a mirror designed so that the pattern of the exposed portion and the non-exposed portion is a predetermined pattern, for example, about 0.2 μm and 0.4 μm, respectively, is used as the following interference pattern.

  In the nozzle 13, interference occurs between the incident light of the excimer laser light and the reflected light from the reflection mirror, and an interference fringe (interference pattern) is generated. Then, the in-nozzle lyophobic film 122 is exposed by the interference fringes. In other words, in the in-nozzle lyophobic film 122, ring-shaped exposed portions and non-exposed portions are alternately formed at a pitch of about 0.2 μm / 0.4 μm due to interference fringes.

  In this way, by forming the strong exposure part (exposure part) and the weak exposure part (non-exposure part) on the in-nozzle liquid repellent film 122, The allyl group is destroyed by excimer laser light, and oxygen in the atmosphere is taken in, whereby the liquid repellency is reduced or destroyed, and finally a lyophilic region is formed. On the other hand, since the weakly exposed portion is originally formed by a liquid repellent treatment, it becomes a liquid repellent region.

  Further, the liquid repellent film 122 in the nozzle is selected to have a contact angle of 90 ° to 120 °, and the area ratio between the strong exposure portion and the weak exposure portion is adjusted, and as a result, the inner wall surface of the nozzle 13 advances. The contact angle and the receding contact angle can be adjusted. As a result, the difference between the receding contact angle and the advancing contact angle can also be controlled.

  As described above, the lyophilic region by the strongly exposed portion of the liquid repellent film 122 in the nozzle 12 and the lyophobic region by the weakly exposed portion are alternately provided on the inner wall surface of the nozzle 12, and a large number of strongly exposed portions are provided in an area ratio. The contact angle can be reduced and the contact angle when retreating can be reduced.

  As a specific method for adjusting the area ratio between the strong exposure portion and the weak exposure portion so that the advancing contact angle is 50 ° or less and the receding contact angle is 90 ° or more, for example, as described above, the reflector 20 It is possible to adjust by increasing the number of the strongly exposed portions to be less than the weakly exposed portions by giving a certain regularity to the unevenness, for example, by devising the area ratio, the pitch, and the like.

  In addition, by increasing the pitch of the strongly exposed part / weakly exposed part from 0.4 μm / 0.2 μm to, for example, 0.6 μm / 0.2 μm pitch, the advancing contact angle, the contact between the hydrophilic part and the hydrophobic part As a result, the advancing contact angle is increased, but the receding contact angle can be adjusted appropriately.

  Further, for example, by forming the in-nozzle liquid repellent film 122 using a material having a large contact angle, which is an original property of the hydrophobic portion, the moving contact speed is increased and the advancing contact angle is kept unchanged, and the receding contact angle is increased. Thus, the present invention can be obtained.

  As another method of forming the inner wall surface of the nozzle 13 so that the forward contact angle is 50 ° or less and the backward contact angle is 90 ° or more, the above-described method is performed without forming a liquid repellent film on the inner wall surface of the nozzle 13. An advancing contact angle and a receding contact angle can also be obtained.

  In that case, a nozzle plate 12 such as polyimide, polysulfone, polyethersulfone or the like that has a contact angle of liquid with respect to the liquid material, that is, a contact angle with water of 50 ° or more is selected. Use with.

  If the nozzle 13 is formed on the nozzle plate 12 using such a material, the inner wall surface of the nozzle 13 becomes liquid repellent even if the process of forming the liquid repellent film in advance on the inner wall surface of the nozzle 13 is omitted. When the inner wall surface of the nozzle 13 is irradiated with laser light using the reflector 20 in the same manner as in FIG. 2D, lyophilic functional groups such as —OH and —COOH are formed on the inner wall surface of the nozzle 13. Further, the surface of the inner wall surface is roughened, and the contact angle can be reduced to about 0 ° to 10 °. At the same time, by adjusting the interference pattern by the same method as described above, a lyophilic region and a liquid repellent region can be formed on the inner wall surface of the nozzle 13 as a result.

  In particular, if the number of times of laser irradiation is increased, minute irregularities can be formed on the inner wall surface of the nozzle 13, and the shape effect due to these irregularities causes partial liquid repellency to be expressed partially equivalent to the so-called Cassie contact angle, A region where the contact angle exceeds 90 ° can be formed, and as a result, the advancing contact angle and the receding contact angle of the inner wall surface of the nozzle 13 can be adjusted.

  When a resin is used for the nozzle plate 12, it is preferably a polyimide resin, and Dupont; Kapton, Ube Industries, Ltd .; Ubilex, etc. are excellent in dimensional stability, ink resistance, and heat resistance. In addition, the nozzle plate 12 can also be produced using a silicon plate or the like.

  As another method for defining the advancing contact angle and the receding contact angle of the inner wall surface of the nozzle 13, it is possible to control the region covering the inner wall surface of the nozzle 13 by plasma polymerization.

  For example, plasma polymerization of silicon resin is performed, and a plasma polymerization film is formed on the inner wall surface of the nozzle 13 in the same manner as in FIG. The plasma polymerized film has a main chain composed of —Si— and has a carbon-containing group such as an alkyl group or an allyl group as a side chain, and thus becomes a liquid repellent film exhibiting liquid repellency.

Thereafter, as in FIG. 2D, a reflection plate 20 is provided, and laser light is irradiated from the side opposite to the discharge port side into the nozzle 13 in the presence of oxygen using an excimer laser (oscillation wavelength: 248 nm) for reflection. The plasma polymerization film is reflected by the plate 20 and exposed in an irregular pattern to form a strong exposure portion and a weak exposure portion. Then, in the strongly exposed portion, the alkyl group or allyl group which is a side chain in the plasma polymerized film is destroyed by laser light, and oxygen in the atmosphere is introduced, thereby forming lyophilic SiO ₂ . It becomes a lyophilic region. On the other hand, the weakly exposed portion becomes a lyophobic region due to relatively little lyophilicity or no lyophilicity, resulting in the formation of irregular lyophilic and lyophobic regions. it can.

  When a plasma polymerized film is formed on the inner wall surface of the nozzle 13, an ultrashort pulse laser beam is irradiated into the nozzle 13 from the side opposite to the discharge port side in the presence of oxygen, and the plasma polymerized film is formed with this ultrashort pulse laser beam. You may make it expose. Since the plasma polymerized film is exposed with an ultra-short pulse laser beam, the resulting plasma polymerized film is exposed non-uniformly by being exposed instantaneously with a large energy, thereby causing the plasma polymerized film to have a weakly exposed part and a weakly exposed part. An exposed portion is formed. Then, as described above, the plasma polymerized film has both a lyophilic region and a liquid repellent region, and as a result, the advancing contact angle and the receding contact angle of the inner wall surface of the nozzle 13 are adjusted. The

  When irradiating laser light into the nozzle 13, as shown in FIG. 3, a condensing lens 1002 is disposed between the laser light source 1001 and the nozzle 13, and the condensing lens 1002 condenses the nozzle 13. It is preferable. Reference numeral 1003 denotes an optical lens system that causes laser light oscillated from the laser light source 1001 to enter the condenser lens 1002 in parallel. In this way, by condensing the laser beam into the nozzle 13 by the condenser lens 1002, the exposure efficiency can be increased, and the exposure time can be shortened and the exposure degree can be improved.

  As another method for adjusting the advancing contact angle and the receding contact angle of the inner wall surface of the nozzle 13, when the nozzle plate 12 is manufactured, the nozzle plate forming material itself is made of a liquid repellent material and a lyophilic material. The nozzle plate 12 can also be manufactured by using two kinds of materials and laminating them by vapor deposition, coating, or the like to form a so-called laminated nozzle plate, and then drilling the nozzle 13. At this time, since the layer of the liquid repellent material and the layer of the lyophilic material are exposed on the inner wall surface of the nozzle 13, the lyophilic region and the liquid repellent property can be obtained simply by processing the nozzle 13 with laser light. The advancing contact angle and the receding contact angle can be adjusted by adjusting the thickness of each layer.

  For example, when the liquid repellent material layer is 0.5 μm, the lyophilic material layer is 0.5 μm, and these layers are alternately laminated one by one, the advancing contact angle is 30 ° and the receding contact angle is 100 °. We were able to.

  Next, an example of a recording apparatus according to the present invention is shown in FIG.

  FIG. 4 is a diagram illustrating a schematic configuration of a recording apparatus that forms an image on a recording material. In the recording apparatus 200, the recording material P is sandwiched between a pair of conveyance rollers 201 and is further rotated by a conveyance motor 202. It is conveyed in the Y direction in the figure by a driven conveyance roller 203.

  The droplet discharge head 1 is provided between the transport roller 203 and the transport roller pair 201 so as to face the recording surface PS of the recording material P. The droplet discharge head 1 is substantially the same as the conveyance direction (sub-scanning direction) of the recording material P by a driving unit (not shown) along the guide rail 204 spanned across the width direction of the recording material P. The nozzle 205 is mounted on a carriage 205 provided so as to be able to reciprocate along the XX ′ direction (main scanning direction) orthogonal to the recording surface PS of the recording material P. It is electrically connected to a drive signal generator (not shown) via a flexi cable 206.

  The droplet discharge head 1 scans and moves the recording surface PS of the recording material P in the XX ′ direction as the carriage 205 moves in the main scanning direction, and discharges droplets from the nozzles during the scanning movement. By doing so, a desired inkjet image is formed.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.
Example 1
<Liquid repellency treatment of nozzle plate>
The following liquid repellent compound was applied to a thickness of 0.1 μm by spin coating on one side of a 120 μm-thick polyimide plate (manufactured by Ube Industries Co., Ltd .; Upilex). A liquid repellent film was formed by heat treatment for a period of time.

C ₈ F ₁₇ CH ₂ CH ₂ Si (OCH ₃ ) ₃ 1 part by weight Si (OC ₂ H ₅ ) ₄ 10 parts by weight γ-glycidoxypropyltrimethoxysilane 1 part by weight Methanol 38 parts by weight Water 30 parts by weight Acetic acid 20 Parts by weight

  Next, an excimer laser (oscillation wavelength: 248 nm, pulse width: 150 nsec) is irradiated from the side where the liquid repellent film is not formed, and a diameter of 40 μm, a taper angle of 30 °, and a length of 50 μm are obtained so as to be 180 dpi. 64 step-shaped nozzles were produced.

  Furthermore, a circular mask that covers a portion that is five times the nozzle diameter centered on the center of the nozzle is hung on the surface provided with the liquid repellent film to protect the periphery of the discharge port, and then the excimer laser is irradiated in the same manner to repel the liquid. By removing the film, a lyophilic region 31 and a lyophobic region 32 were formed on the discharge side surface as shown in FIG.

  After that, the surface of the nozzle plate on which the liquid repellent film is formed is masked, and the liquid repellent compound is dipped and applied again to form a liquid repellent film (thickness 0.5 μm) on the inner wall surface of the nozzle. did

  Next, in the same manner as in FIG. 2 (d), a reflective plate having fine irregularities is brought into close contact with the surface on the discharge port side, and an excimer laser (oscillation wavelength: 248 nm) is applied in the presence of oxygen in the nozzle. Irradiation along the axial direction of As a result, interference occurs between the incident light of the excimer laser light and the reflected light from the reflecting plate in the nozzle, and an interference fringe pattern is generated. The liquid repellent film on the inner wall surface of the nozzle has a strong exposure portion and a weak exposure portion. And are formed.

  The strongly exposed portion becomes a lyophilic region showing lyophilicity by introduction of oxygen, while the weakly exposed portion becomes a lyophobic region showing original lyophobic property. These were formed by the interference fringes so that the ring-shaped strong exposure portions and the weak exposure portions were alternately arranged at a pitch of 0.3 μm along the nozzle axis direction.

(Measurement of contact angle)
The receding contact angle and the advancing contact angle are called dynamic contact angles. For example, (1) Wilhelmy method, (2) expansion contraction method, (3) fall-down method, etc. are known. In the following measurement method, as a solid sample, the same lyophilic region and repellent area as the liquid repellent film in the nozzle are used on the surface of a plate piece made of the same material as the nozzle plate for producing the nozzle. A liquid-repellent film provided with a liquid region is used.

  In the present invention, the falling method (3) is used unless otherwise specified. This is a method in which a fixed amount of a liquid sample is placed on the surface of a solid sample to be measured from the tip of an injection needle or a glass capillary, the surface of the solid sample is tilted at an angle, and measurement is performed immediately before sliding.

  In actual measurement, as a droplet amount, an ink droplet of about 15 pl was placed on the solid sample, and then the solid sample was gradually tilted, and the state was photographed and observed. Then, the advancing contact angle θa and the receding contact angle θr were calculated and measured from the image when the ink droplet moved about 1 μm.

(Discharge characteristics)
Using the obtained nozzle plate, a shear mode type droplet discharge head similar to that shown in FIG. 1 was prepared, and ink having a viscosity of 5.7 cp and a surface tension of 40 dyn / cm at 25 ° C. was supplied, and continuously at 7.2 kHz. Discharged. During discharge, the discharge was interrupted occasionally, and the nozzle plate surface was observed and wiped. The discharge amount was measured using a precision balance, and the average discharge amount per ink drop was determined. At the same time, the discharge state was observed using an optical microscope, the discharge speed was gradually increased from 3 m / sec, and the discharge amount fluctuation and the discharge state were evaluated according to the following criteria. The results are shown in Table 1.

(Double-circle): It discharged without a problem to the discharge speed of 10 m / sec, and the discharge amount fluctuation | variation was less than 5%.
A: The ink was discharged without any problem up to a discharge speed of 8 m / sec, and the discharge amount fluctuation was 5% or more and less than 10%.
(Triangle | delta): The bending generate | occur | produced at the discharge speed of less than 8 m / sec, or discharge amount fluctuation | variation exceeded 10% and was less than 15%.
X: Discharge amount fluctuation exceeded 15%.

(Bubble entrainment)
Poor ejection from a nozzle due to bubble entrainment after continuous ejection for 1 hour from the number of nozzles of 1/3 or more of all nozzles of the droplet ejection head (a phenomenon in which ink droplets are not ejected from the nozzle even when driven) The occurrence of “nozzle missing”) was observed. The occurrence of missing nozzles was evaluated by observing whether or not ink droplets were ejected from the nozzles according to driving by high-speed video shooting, and was evaluated according to the following criteria. The results are shown in Table 1.

◎: No nozzle missing ○: No nozzle missing within 3 nozzles ×: Nozzle missing over 4 nozzles

(Examples 2-5, Comparative Examples 1-3)
The same method as in Example 1 except that the concentration of the liquid repellent film in the nozzle, the pitch and intensity of the laser processing interference pattern were changed to the forward contact angle and the backward contact angle shown in Table 1, respectively. It was evaluated by.

  As shown in Table 1, when the advancing contact angle of the liquid repellent film provided on the inner wall of the nozzle is 50 ° or less and the receding contact angle is 90 ° or more, the nozzle missing is within 3 nozzles, Entrainment is at an acceptable level and ejection characteristics are at an acceptable level. In particular, in Example 1, Example 2, Example 4, and Example 5 in which the value obtained by subtracting the advancing contact angle from the receding contact angle is 60% or more, the variation in the ejection amount is less than 10% and the ejection characteristics are good. is there. Further, in Example 4 where the value obtained by subtracting the advancing contact angle from the receding contact angle was 85 °, nozzle missing was not observed at all, and particularly good results were obtained in terms of bubble entrainment and discharge characteristics.

  On the other hand, in the comparative examples, the nozzle missing was 4 nozzles or more. In Comparative Example 1, a phenomenon (referred to as ejection bending) in which the landing position is shifted due to a change in the ejection direction of the ink droplets occurred.

1: Liquid droplet ejection head 11: Ink tube 12: Nozzle plate 121: Liquid repellent film 122: Liquid repellent film in nozzle 13: Nozzle 14: Cover plate 15: Ink supply port 16: Channel substrate 17: Partition 17a: Upper wall portion 17b: Lower wall portion 18: Channel 20: Reflecting plate 200: Recording device 201: Conveying roller pair 202: Conveying motor 203: Conveying roller 204: Guide rail 205: Carriage 206: Flexi cable P: Recording material PS: Recording surface

Claims (5)

  In the droplet discharge head for discharging a liquid material from a nozzle, the inner wall surface of the nozzle has a forward contact angle with respect to the liquid material of 50 ° or less and a backward contact angle of 90 ° or more. Discharge head.   The droplet discharge head according to claim 1, wherein an angle obtained by subtracting the advancing contact angle from the receding contact angle is 60 ° or more.   The droplet discharge head according to claim 1, wherein the liquid has a viscosity of less than 6 cp.   A large number of pressure chambers to which the liquid material is supplied are arranged in parallel, and a partition between adjacent pressure chambers is configured by an actuator that deforms in response to an applied voltage. 4. The droplet discharge head according to claim 1, wherein the liquid discharge head is a share mode type head that discharges the liquid material from the nozzle. A recording apparatus comprising the droplet discharge head according to claim 1, wherein recording is performed by landing a liquid material discharged from the nozzle on a recording material.

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