Patent Grant
7066582
1. Technical Field of the Invention
The present invention relates to a method for producing an organic insulating coating such as a protective coating for electrodes in ink chambers of an ink-jet printhead, and further to an ink-jet printhead produced according to the method.
2. Description of Related Art
In place of impact printers, there has been a rapid diffusion of non-impact printers suitable for color and multiple-tone printing such as ink-jet printers. In particular drop-on-demand printers, which eject ink droplets only when needed to print on media, are popular because of their improved printing efficiency and low production and running costs. Most of the drop-on-demand printers today are using a Kyser method utilizing piezoelectric elements or a thermal ink-jet method.
In the Kyser-type printers, however, printheads are difficult to miniaturize and nozzle density thereof is difficult to increase. In the thermal ink-jet printers, although a high nozzle density is obtainable, since the energy of bubbles produced in ink by heating the ink with a heater is used to eject ink droplets, high ink durability is required, long life of the heater is hard to obtain, and power consumption is high.
To solve the foregoing problems, there has been proposed an ink-jet method according to which shear mode deformation of a piezoelectric material is utilized to eject ink. More specifically, an electric field perpendicular to a poling field of the piezoelectric material is applied to electrodes provided on sidewalls of an ink chamber made of the piezoelectric material to deform the sidewalls in shear mode, so that a pressure wave generated by the deformation is utilized to eject ink droplets through nozzle orifices. This method can realize a higher nozzle density, lower power consumption, and a higher drive frequency.
Illustrated in
Rear bottom edges of the ink chambers 16 are formed into an arc of a circle having radius of a dicing blade used to cut the grooves 4. The dicing blade is used to cut shallow grooves 6 as electrode lead parts for electrical conduction with the exterior. The electrodes 5 in the shallow grooves 6 are connected to external electrodes 8, for example on a flexible substrate, at rear ends of the shallow grooves 6.
Used as an insulating coating for preventing the electrodes 5 from contacting the ink is a poly-p-xylylene (known as parylene: “parylene” is a trademark of Nihon Parylene Kabushikikaisha) coating. The poly-p-xylylene coating is made from di-p-xylylene by CVD (chemical vapor deposition) method. Specifically, di-p-xylylene dimer is vaporized and then pyrolyzed to form stable monomeric diradical p-xylylene. The monomer simultaneously absorbs and polymerizes on a substrate to form a high-molecular-weight thin film. Hereinafter referred to as parylene N or poly-p-xylylene is the reaction product of di-p-xylylene dimer as dimeric p-xylylene, and referred to as parylene C or poly-monochloro-p-xylylene is the reaction product of di-p-xylylene dimer as dimeric monochloro-substituted p-xylylene.
Since the poly-p-xylylene coating is chemically stable and less susceptible to damage in an environment where the coating is exposed, the coating maintains constant insulating properties. Also, since the poly-p-xylylene coating is formed at room temperature by vapor phase epitaxy, it is possible to form an uniform insulating coating of the poly-p-xylylene over a substrate whose properties are degraded by heat or whose surface has a complex shape, without thermally damaging the substrate.
However, when the poly-p-xylylene coating is in use as the insulating coating for electrodes in ink chambers of an ink-jet printhead, there occurs a problem as described below.
Although it is possible to form an uniform coating of the poly-p-xylylene in ink chambers of ink-jet printheads having a complex shape, piezoelectric materials such as PZT used in the ink-jet printheads are sintered ceramics, and surfaces on which electrodes are to be formed attains a pear-skin finish with microscopic concavities and convexities because ceramic particles fall out of the surfaces when grooves are cut in there. When a parylene coating is formed over such a pear-skin-finished base, macroscopically a uniform coating is obtained. However, the parylene coating grown with the concavities and convexities of the base reflected has microscopic flaws (pinholes).
Since aqueous ink is an electrolyte solution with a very high electrical conductance in comparison with oil-based ink, if there is a pinhole through an insulating coating separating an electrode and the aqueous ink in an ink chamber, the electrode is electrically conducted with another electrode in an adjacent ink chamber through the ink infiltrating through the pinhole, so that electrolyte corrosion of the electrodes occurs. This causes ink-jet printhead reliability problems such as fluctuations in ink-ejecting properties during operation of an ink-jet printhead and inferiority in ink ejection in the ink-jet printhead caused by breaking of electrode wires. These problems also occur in an organic insulating coating formed over another kind of substrate such as a semiconductor.
To solve the problems, Japanese Laid-open Patent Publication No. 2001-96754 discloses a method for improving insulating properties of a parylene coating, by which after the parylene coating is formed polyimide resin is electrodeposited selectively over a pinhole and then sintered at 80° C. for 24 hours. According to the method, however, equipment is required for the electrodeposition of polyimide resin, thereby increasing production costs. Also, it is necessary to sinter the polyimide resin for a long time, so that production throughput is decreased.
On the other hand, Japanese Laid-open Patent Publication H11-309856 discloses a method for improving insulating properties of parylene coatings, by which coatings of two kinds of parylene having different structures are layered with plasma treatment performed to a lower parylene coating. According to the method, however, vacuum equipment is required for the plasma treatment, thereby increasing production costs.
An object of the present invention is to provide a method for producing an organic insulating coating which prevents electrolytic corrosion of electrodes by improving insulating properties of the organic insulating coating separating the electrodes from an electrolyte solution, as well as to provide an ink-jet printhead having stable ink-ejecting properties ensured by utilizing the method for producing the organic insulating coating.
The present invention includes:
In this configuration, an organic insulating coating includes at least the two layers of the first organic coating which is formed on the substrate and the second organic coating which is formed on the first coating, with at least either one of the first organic coating and the second organic coating treated with heat. Consequently occurrence of pinholes is prevented in either one of the two layers of organic coatings, such that insulating properties of the organic insulating coating is improved.
The present invention further includes:
In this configuration, the protective coating for the electrodes in the ink chambers of an ink-jet printhead includes two or more layers of the organic coatings with at least one of the layers treated with heat. The configuration ensures that the electrodes formed in the ink chambers to be filled with ink are insulated from the ink by the organic coating in which occurrence of pinholes is prevented.
Then, as shown in
Finally, the second parylene coating 202 is formed on the first parylene coating 201 treated with heat, as shown in
In sample #1 the organic insulating coating 200 is formed according to the method of the embodiment of the present invention as shown in
In comparison sample #2, a parylene coating of thickness 4 μm is formed on the glass substrate 301 having the Cu coating 302.
In comparison sample #3, a parylene coating of thickness 4 μm is formed on the glass substrate 301 having the Cu coating 302 and then processed with heat at 100° C. in the atmosphere for two hours.
In comparison sample #4, a parylene coating of thickness 4 μm is formed on a SiO2 coating of thickness 1 μm formed on the glass substrate 301 having the Cu coating 302.
In comparison sample #5, a parylene coating of thickness 8 μm is formed on the glass substrate 301 having the Cu coating 302.
In comparison sample #6, a parylene coating of thickness 2 μm is formed on a parylene coating of thickness 2 μm formed on the glass substrate 301 having the Cu coating 302.
In the comparison samples #2 to #6, etching caused by one or more pinholes is observed on the Cu coating 302 within 24 hours. Illustrated in
The comparison samples #2 and #5 show that merely increasing the thickness of a parylene coating is less effective in preventing the etching caused by pinholes.
The comparison sample #6 shows that merely forming two layers of parylene coatings of total thickness 4 μm is less effective in preventing the etching caused by pinholes.
The comparison sample #3 shows that heat treatment after the two layers of parylene coatings are formed is less effective.
The comparison sample #4 shows that the layers of the SiO2 coating of thickness 1 μm and the parylene coating of thickness 4 μm are less effective in preventing the etching caused by pinholes.
In the sample #1, by contrast, no pinhole is spotted in an observation after 24 hours, nor after 120 hours. Specifically, two layers of parylene coatings of thickness 4 μm with a lower coating treated with heat at 100° C. for two hours after being formed prevent the electrolytic corrosion of the Cu coating caused by pinholes, thereby increasing the insulating properties of the parylene coating.
In the sample #15 where the first coating 201 is treated at 250° C., the coating 201 is detached from the Cu coating 302, structurally destroyed. In the samples #11 to #14 where the first coatings 201 are treated at temperatures of 200° C. and below, by contrast, the detachment of the coatings 201 is not observed.
Regarding the insulating properties, however, etching of the Cu coating 302 caused by two pinholes is observed after a lapse of 120 hours in the sample #14 where the heat treatment is performed at 200° C. Also, the etching by three pinholes is observed after a lapse of 24 hours in the sample #12 where the heat treatment is performed at 60° C. The sample #6 where the heat treatment is performed at 150° C., by contrast, has no etching observable after a lapse of 120 hours, as in the case of the sample #1, and proves to have good insulating properties.
These results show that effective temperature range for the heat treatment of the first parylene coating 201 is between its glass transition point (87 to 97° C.) and its melting point (250° C.), preferably at and below 150° C. within the range.
When an organic insulating coating is formed as a protective coating for electrodes in ink chambers in an ink-jet printhead using mainly aqueous ink, the coating is required to have water-resisting property for keeping the electrodes and the aqueous ink insulated as well as gas impermeability for preventing permeation of gases including water vapor, it being considered that air is mixed in the aqueous ink and the heated ink is vaporized.
There are two variations of parylene: parylene C and parylene N. The parylene C has a high level of gas (including water vapor) impermeability, and the parylene N has high water resistance. The problem is how the parylene C and the parylene N should be used for an organic insulating coating as the protective coating for electrodes in ink chambers in an ink-jet printhead.
In sample #21, a parylene-C coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, to be treated with heat at 120° C. in the atmosphere for two hours, and then a parylene-N coating of thickness 2 μm is formed on the parylene-C coating.
In comparison sample #22, a parylene-C coating of thickness 4 μm is formed on the glass substrate 301 having the Cu coating 302.
In comparison sample #23, a parylene-N coating of thickness 4 μm is formed on the glass substrate 301 having the Cu coating 302.
In comparison sample #24, a parylene-C coating of thickness 4 μm is formed on the glass substrate 301 having the Cu coating 302 and then treated with heat at 100° C. in the atmosphere for two hours.
In comparison sample #25, a parylene-N coating of thickness 4 μm is formed on the glass substrate 301 having the Cu coating 302 and then treated with heat at 100° C. in the atmosphere for two hours.
In comparison sample #26, a parylene-C coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, and then another parylene-C coating of thickness 2 μm is formed on the initial parylene-C coating.
In comparison sample #27, a parylene-N coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, and then a parylene-N coating of thickness 2 μm is formed on the parylene-C coating.
In comparison sample #28, a parylene-C coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, to be treated with heat at 120° C. in the atmosphere for two hours, and then a parylene-C coating of thickness 2 μm is formed on the initial parylene-C coating.
In comparison sample #29, a parylene-N coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, to be treated with heat at 120° C. in the atmosphere for two hours, and then another parylene-N coating of thickness 2 μm is formed on the initial parylene-N coating.
In comparison sample #30, a parylene-C coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, and then a parylene-N coating of thickness 2 μm is formed on the parylene-C coating.
In comparison sample #31, a parylene-N coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, and then a parylene-C coating of thickness 2 μm is formed on the parylene-N coating.
In comparison sample #32, a parylene-N coating of thickness 2 μm is formed on the glass substrate 301 having the Cu coating 302, to be treated with heat at 120° C. in the atmosphere for two hours, and then a parylene-C coating of thickness 2 μm is formed on the parylene-N coating.
Etching caused by more than one pinhole is observed in the comparison samples #22 to #27 within 24 hours, in the samples #29, #31, and #32 within 120 hours, and in the samples #28 and #30 within 250 hours.
The samples #22 and #23 show that etching occurs in the parylene coatings within 24 hours if additional treatment is not performed to the coatings when they are formed and that such coatings do not display effective insulating properties in ink with a high electric conductivity.
The samples #24 and #25 show that heat treatment performed after the parylene coatings are formed is less effective in preventing etching caused by pinholes.
The samples #26 and #27 show that merely forming two layers of parylene coatings of total thickness 4 μm is less effective in preventing etching caused by pinholes.
In the samples #28 and #29, pinhole(s) is not observed until a lapse of 120 hours since heat treatment acts more effectively, if not sufficiently effectively, than in the samples #26 and #27. The fact indicates that even if the heat treatment is performed, merely forming two layers of the same kind of parylene coating is less effective in preventing the etching.
Pinholes are not observed in the sample #31 until a lapse of 120 hours, and in the sample 30 until a lapse of 250 hours. The results show that the two layers formed of two different kinds of parylene coatings of parylene C and parylene N are effective in preventing the etching.
In the sample #32, pinholes are not observed until a lapse of 250 hours. In comparison with the result of the sample #31, this result shows that the two layers of two different kinds of parylene coatings of parylene C and parylene N and the heat treatment of the parylene-N coating act effectively.
In the sample #21, no pinhole is observed after a lapse of 285 hours. This result shows that electrolytic corrosion of the Cu coating 302 caused by pinhole(s) is prevented by treating the parylene-C coating with heat at 120° C. in the atmosphere for two hours after the parylene-C coating is formed and then forming the parylene-N coating on the parylene-C coating, so that insulating properties of the parylene coatings are improved.
The base member 101 has a plurality of grooves 104 to serve as ink chambers cut therein by rotation of a diamond cutting wheel (dicing blade). The grooves 104 are formed with sidewalls 103 therebetween so as to be parallel to each other and all of the same depth. The grooves 104 are of depth about 300 μm, width about 70 μm, and pitch about 140 μm. Metal electrodes 105 are formed on upper surfaces, and upper-half portions of both side surfaces, of the sidewalls 103. Used for the electrodes 105 is metal such as aluminum, nickel, copper, or gold.
Metal electrodes formed on the upper surfaces of the sidewalls 103 concurrently with formation of the metal electrodes 105 on the upper-half portions of the both side surfaces of the sidewalls 103 are removed by lapping, or by lifting off resist coatings which are attached to cutting surfaces of the base member 101 before the grooves 104 are cut therein.
The base member 101 provided with the metal electrodes 105 has an applying groove 168 cut therein in a direction perpendicular to a direction of ink channels by rotation of a diamond cutting wheel 130, as shown in
The conductive member 126 is first poured into the applying groove 168 and then penetrates into the grooves 104 by the effect of capillary phenomenon. Thus the conductive member 126 is not applied to the upper surfaces of the sidewalls 103. When the conductive member 126 is solidified, accordingly, it is possible to bear down on a surface of the base member 101 on which the conductive member 126 is applied (hereinafter referred to as the applied surface), with a flat plate or the like so as to prevent the base member 101 from bending because of the solidification of the conductive member 126. Also, it is unnecessary to remove the conducting member 126 from the upper surfaces of the sidewalls 103 by lapping or the like. In a practical production process, a plurality of the dispensers is arranged above the applying groove 168.
Concurrently with bearing down on the applied surface of the base member 101 with a flat plate or the like, the conductive member 126 is heated with a device (not shown) to be solidified. Used as the conductive member 126 is gold, silver, or copper paste including epoxy resin components, or, gold or nickel plating solution.
As illustrated in
The substrate 141 with conductor patterns respectively formed thereon at corresponding positions to those of the respective ink channels is connected to the conductive member 126 formed at an edge 115 of the base member 101. The substrate 141 and the conductive member 126 are joined with an anisotropic conductive adhesive, or connected by insertion of bumps formed on the conductor patterns into the conductive member 126.
Next, as illustrated in
After the parylene coating 201 is formed in the ink-jet printhead 100, heat treatment is performed to the printhead 100 in an oven at 100° C. for two hours. As described earlier, the base member 101 is made of the poled PZT. A temperature at which the PZT is depoled, namely the Curie temperature of the PZT (hereinafter referred to merely as the Curie temperature), is 250° C. and heating is normally allowed up to half the Curie temperature in Celsius scale. Therefore the heat treatment at 100° C. does not present any problem in producing the ink-jet printhead 100.
Then, the second parylene coating 202 is formed to have a thickness of 2 μm. In the ink-jet printhead 100 according to the present embodiment, the second parylene coating 202 in the ink channels has a thickness of 1.7 μm or more. As a result formed in the ink channels of the ink-jet printhead 100 is the organic insulating coating 200 of sample #1 as shown in
A surface of the second parylene coating 202 is now etched with a plasma processing device (not shown), so that polar groups are arranged on the surface, thereby improving affinity for water molecules of the parylene coating 202: the surface of the second parylene coating 202 is hydrophilized. When ink is filled in an ink-jet printhead having a complicated internal constitution as described later, accordingly, there is a reduced risk of air bubbles remaining on an inner coating surface and being trapped inside the ink-jet printhead. Air bubbles existing in an ink-jet printhead, by their expansion and contraction, decrease pressure fluctuation in the ink chambers to be used to eject ink, thereby causing the respective ink chambers to have varied ink-ejecting properties. In addition, since all the component parts are hydrophilized in the hydrophilizing process by the plasma processing, the etching of the surface of the parylene coating 202 is preferably performed prior to a nozzle-joining process so as not to decrease water-repellent properties of a water-repellent coating formed on nozzles. Furthermore, although in the present embodiment the plasma processing is used to hydrophilize the surface of the second parylene coating 202, the hydrophilizing process may be performed by an alternative method such as of applying hydrophilic resin.
Next, as illustrated in
With the arrangement as described above, in each of the ink chambers 116, the electrodes 105 which are respectively formed on two mutually-facing lateral surfaces of the two sidewalls 103 which form the instant ink chamber 116 are electrically connected to the conductive member 126. Therefore, a voltage, when applied to the conductive member 126, is applied through the conductive member 126 simultaneously to the electrodes 105 formed on the two mutually-facing lateral surfaces. At the same time the sidewalls 103 serving as the two lateral surfaces of the instant ink chamber 116 are deformed toward the interior of the ink chamber 116, such that ink droplets are ejected through the nozzle orifices 110.
Formed as samples for comparison purpose are: an ink-jet printhead 100′ (not shown) using an organic insulating coating having a similar constitution to that of the comparison sample #2 as shown in
On these ink-jet printheads 100, 100′, and 100″, durability tests are conducted by continuous ink ejecting. In the tests, an ink of conductivity 19.85 S/m is used and the continuous ink-ejecting operation is performed by inputting a drive signal of voltage 30 V and frequency 120 kHz. After 101o times of ink ejection, change in ink ejection speed, and the number of ink chambers that do not eject ink are examined in each of the ink-jet printheads.
The test results are as follows. In the ink-jet printhead 100, although the ink ejection speed decreases in all the ink chambers by three percent with respect to its initial speed value, there are no ink chambers observed that show a decrease in the ink ejection speed by more than 10 percent, or that do not eject ink. In the ink-jet printhead 100′, however, the ink ejection speed decreases by more than ten percent in 17 ink chambers, and two ink chambers do not eject ink. In the ink-jet printhead 100″, the ink ejection speed already decreases by more than 10 percent in 23 ink chambers when the durability test starts.
These results show that although the heat treatment to the first parylene coating is necessary for stable ink ejection, the treatment, when performed at a temperature (150° C.) beyond half the Curie temperature (125° C.), has a negative effect of the PZT being depoled, thereby preventing the stable ink ejection. Therefore, the experimental results as shown in
In the foregoing embodiment the organic insulating coating 200 includes the two layers of parylene coatings. However, it goes without saying that the more the number of parylene coating layers, and the more the number of times the heat treatment is performed between the parylene coating layers, the higher insulating properties to be obtained become. The organic insulating coating may include more than three layers of parylene coatings.
Although a piezoelectric ink-jet printhead is described in the foregoing embodiment, the present invention is not limited to the specific embodiment as described above, but is applicable to electrostatic or thermal ink-jet printheads for which insulation between electrical circuit parts and ink is required. The present invention is also applicable to other semiconductor parts which are required to remain insulated from an electrolyte solution.
According to the present invention the following advantages can be obtained.
The organic insulating coating includes at least two layers of the first organic coating formed on the substrate and the second organic coating formed on the first coating. At least either one of the first and second organic coatings is treated with heat, such that occurrence of pinholes is prevented in at least either one of the two organic coatings. Thus the insulating properties of the organic insulating coating are improved.
At least either one of the first and second organic coatings is treated with heat at a temperature between its glass transition point and its melting point, such that at least either one of the two layered organic coatings become a uniform, flawless coating with insulating properties, thereby preventing the occurrence of pinholes. Thus the insulating coating is improved.
At least either one of the first and second organic coatings is treated with heat at a temperature between its glass transition point and half the Curie temperature. Consequently, even if a substrate on which the coatings are formed has piezoelectric properties, the piezoelectric properties are not impaired by the heat treatment and thus the substrate can be used without a problem.
The heat treatment to the organic coating, performed in the atmosphere, can be performed in a normal environment. Consequently a device for providing a particular environment is unnecessary, and thereby production costs can be reduced.
At least two layers of the organic coatings are formed by the deposition of organic materials. As a result a device for performing such a process as an electrodeposition process is unnecessary, and thereby production costs can be reduced.
The protective coat for the electrodes in the ink chambers of the ink-jet printhead includes two and more layers of the organic coatings with at least one of the layer treated with heat. This ensures that the electrodes formed in the ink chambers to be filled with ink are insulated from the ink by the organic coating that has improved insulating properties with occurrence of pinholes prevented therein, thereby allowing stable ink ejection to be maintained.
The protective coat for the electrodes in the ink chambers of the ink-jet printhead is formed of an organic coating including mainly poly-p-xylylene. This ensures that the electrodes formed in the ink chambers to be filled with ink are insulated from the ink by the organic coating that is chemically stable and less susceptible to damage in an environment where the coating is exposed. Also, since the poly-p-xylylene coating can be formed at room temperature by vapor phase epitaxy, it is possible to form an uniform protective coating of the poly-p-xylylene over a substrate whose properties are degraded at high temperatures or whose surface has a complex shape, without thermally damaging the substrate.
The protective coat for the electrodes in the ink chambers of the ink-jet printhead is formed of an organic coating including mainly parylene C that has gas impermeability for preventing permeation of gases including water vapor. This ensures that the electrodes remain insulated from the ink without deterioration of the protective coat even when the ink in the ink channels is vaporized by heat or when air is in the ink channels.
The protective coat for the electrodes in the ink chambers of the ink-jet printhead is formed of: an organic coating including mainly parylene C that has high gas impermeability for preventing permeation of gases including water vapor; and an organic coating including mainly parylene N that has high water resistance. This ensures that the electrodes remain insulated from aqueous ink without deterioration of the protective coat even when the ink in the ink channels is vaporized by heat or when air is in the ink channels.
The protective coat for the electrodes in the ink chambers of the ink-jet printhead is formed of two layers of organic coatings: an organic coating in contact with the electrodes, including mainly parylene C that has high gas impermeability for preventing permeation of gases including water vapor; and an organic coating in contact with ink, including mainly parylene N that has high water resistance. This allows the electrodes to be protected from aqueous ink by the organic coating with high water resistance and from vaporized ink or air mixed in ink by the organic coating with high gas (including water vapor) impermeability.
Of the two layers of organic coatings forming the protective coating for the electrodes in the ink chambers of the ink-jet printhead, the upper-layer coating, namely the second organic coating, has a hydrophilized surface. This ensures a smooth flow of aqueous ink into the ink chambers by contact with the hydrophilic organic coating.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2002-234772 | Aug 2002 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5248998 | Ochiai et al. | Sep 1993 | A |
| 6176571 | Kishima et al. | Jan 2001 | B1 |
| 6715860 | Watanabe | Apr 2004 | B1 |
| 6733113 | Yoshizawa et al. | May 2004 | B1 |
| 6802596 | Higuchi et al. | Oct 2004 | B1 |
| Number | Date | Country |
|---|---|---|
| 11-309856 | Nov 1999 | JP |
| 2000-71451 | Mar 2000 | JP |
| 2001-096754 | Apr 2001 | JP |
| 2002-210967 | Jul 2002 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20040032466 A1 | Feb 2004 | US |
