JPH09216355A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to deal with the increase in size and decrease in cost of an ink jet head by using a ceramic board in which the surface flatness of the board provided with an ink channel is specified. SOLUTION: The ink jet head 1 comprises ink channel grooves 12 having a predetermined depth with a nozzle 11 at the end of a board 10 and formed at a predetermined pitch, and a common channel groove 13 formed to primarily preserve ink in communication with the grooves 12.... A diaphragm 14 made of nickel is adhered onto the board 10, and piezoelectric elements 15... are provided corresponding to the channels 12... on the diaphragm 14. As the board 10, a ceramic board having surface flatness Ra of 100nm or less is used. The ceramics can be obtained by pulverizing raw material to powder, then molding it and baking it to provide various shapes different from crystal silicon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet head, and more particularly to a substrate of the inkjet head.

[0002]

2. Description of the Related Art An ink jet recording apparatus has little vibration and noise at the time of recording and is easy to colorize. Therefore, it is used not only for a printer for outputting data of a digital processing device such as a computer but also for facsimile and copying. It is supposed to be. As such an ink jet recording apparatus, for example, an ink jet head is used which presses ink and ejects droplets of ink from an ejection port through an ink flow path provided on a substrate. There is a type in which high-speed, high-resolution, high-quality recording is performed by ejecting ink droplets onto a recording medium (those to which ink droplets adhere).

Here, the ink jet heads can be roughly classified into actuator elements for ejecting ink drops, those using a piezoelectric element, those using an electrostatic force, and those using a heating element. Among them, the one that uses an exothermic element to boil the ink in the vicinity of the element and eject the ink droplets by the force is a thermal ink jet (T
IJ).

In this thermal ink jet type ink jet head, the heating element is formed on the glass substrate, but a crystalline silicon wafer having a higher thermal conductivity is used as the element becomes higher in density and driven at a higher speed. It is designed to be used. Some ceramic substrates use a ceramic substrate, but the surface of the ceramic substrate is generally poor in flatness and cannot be used as it is as a substrate for forming a heating element of a thermal inkjet head. Therefore, for example, as described in JP-A-64-1553, the surface of the ceramics substrate excluding the heat-generating portion is covered with a grace layer (glass layer) having a thickness of 45 μm.

On the other hand, when the ink jet recording apparatus is classified according to the recording method, the ink jet head is mounted on the carriage, the carriage is moved and scanned in the main scanning direction, and the recording medium is conveyed in the sub scanning direction orthogonal to the main scanning direction. By doing so, a serial scan type recording apparatus for recording on a recording medium and an inkjet head having a length substantially the same as the width of the recording medium in the main scanning direction are used to convey the recording medium in the sub scanning direction. Is roughly classified into a line-type recording apparatus that performs recording without scanning.

The head structure of this line type recording apparatus uses a substrate having a width larger than the width of the recording medium, and JP-A-57-110450 and JP-A-5-110450.
As disclosed in Japanese Laid-Open Patent Publication No. 6-117682, there is one in which a plurality of small heads are connected to each other to make the head larger than the width of the recording medium. When connecting the latter small heads, it is difficult to connect them with high precision.
This causes an inconvenience of high manufacturing cost.

[0007]

As described above, in the thermal ink jet head, when the surface of the ceramic substrate is covered with the grace layer (glass layer) excluding the heat-generating portion, the heat-generating portion is dented. Therefore, it is difficult to use as an inkjet head, and the ink ejection method is limited, and it is more than tens of μ.
It is difficult and highly practical to form the heating element and its driving electrode pattern on the surface of the substrate having m steps, which is not practical.

Therefore, it is conceivable to use a conventional crystalline silicon wafer as a substrate. However, since the silicon wafer is round, a long and slender head is manufactured, especially like an ink jet head of a line type recording apparatus. In such a case, many parts are wasted, which is uneconomical, and it is not suitable for constructing an inkjet head of a line-type recording apparatus.

As described above, there is a problem that the substrate of the conventional ink jet head cannot cope with the increase in size and cost of the head.

The present invention has been made in view of the above points, and an object of the present invention is to provide an ink jet head which can cope with an increase in size and cost.

[0011]

In order to solve the above-mentioned problems, an ink-jet head according to a first aspect of the present invention applies ink pressure to ink droplets formed from an ejection port through an ink flow path provided on a substrate. In the ink jet head for discharging, the substrate was made of a ceramic substrate having a surface flatness of 100 nm or less.

According to a second aspect of the present invention, in the ink jet head according to the first aspect, the substrate has a thermal conductivity of 0.04 W / cmK or more.

According to a third aspect of the present invention, in the ink jet head according to the second aspect, the linear thermal expansion coefficient of the substrate is 3.0 × 10 ^-6 / K or more.

According to a fourth aspect of the present invention, there is provided an ink jet head according to any one of the first to third aspects, wherein a thin film made of a material different from a substrate material is formed on the surface of the substrate.

According to a fifth aspect of the present invention, in the ink jet head according to the fourth aspect, the thermal conductivity of the thin film is smaller than the thermal conductivity of the substrate.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a schematic perspective view of an essential part of an inkjet recording apparatus including an inkjet head according to a first embodiment of the present invention, FIG. 2 is a schematic plan view of the inkjet head, and FIG. 3 is a schematic sectional view of FIG.

In this ink jet recording apparatus, an ink jet head 1 having a large number of nozzles is finely moved in the left-right (horizontal) direction by a step motor 2 to convey a roller 3.
The recording paper 4 which is a recording medium in a direction orthogonal to the main scanning direction.
This is a line-type recording apparatus for recording a desired image on the recording paper 4 by ejecting ink droplets 5 from the nozzles of the inkjet head 1 while conveying the sheet.

The ink jet head 1 is shown in FIGS.
As shown in FIG. 3, the ink flow channel grooves 12 having a predetermined depth and having a nozzle 11 at the tip end are formed at a predetermined pitch on the substrate 10, and the ink flow channel grooves 12, 12 ... To form a common flow path groove 13 for primary storage, a diaphragm 14 made of nickel is adhered to the substrate 10, and the ink flow path grooves 12, 12 are formed on the diaphragm 14.
.. are provided correspondingly to the piezoelectric elements 15, 15.

Here, the substrate 10 has a surface flatness R
A ceramic substrate having a of 100 nm or less is used.
Ceramics are obtained by pulverizing raw materials, then molding and firing, and different from crystalline silicon, various shapes can be obtained. Raw materials include oxides such as alumina, zirconia, silicon dioxide, and zinc oxide, nitrides such as aluminum nitride, boron nitride, and silicon nitride, and carbides such as titanium carbide, boron carbide, and silicon carbide.
These raw materials use composites, not single substances,
Even if the same raw material is used, ceramics showing various characteristics can be obtained depending on the state of powder, molding conditions, and firing conditions.

Further, although ceramics generally have voids called pores, it is possible to obtain ceramics having almost no pores depending on the forming conditions. Therefore, a ceramic plate having a thickness of 1.5 mm and a size of 30 cm is manufactured by using various raw materials such as alumina, zirconia, silicon nitride, and silicon carbide. Among these, ceramics made of alumina as a raw material were obtained with almost no pores, and with flatness of 100 nm or less without polishing. Although there are some that exhibit high surface flatness even if they are fired as they are, the surface flatness of the ceramic plate can be significantly improved by polishing.

This polishing can be carried out by rotating a hub having a diamond paste in which water is dispersed at a high speed and bringing the hub into contact with a ceramic plate at a constant pressure. In this case, the surface flatness can be increased by using a paste having a small diamond grain size stepwise.
Further, the surface flatness of the ceramic plate can be controlled by the level of polishing, that is, the grain size of the diamond used. In addition, the surface flatness of the substrate is 10 at any place in the substrate by a stylus type film thickness measuring device.
It is represented by Ra when scanned at 0 μm.

Therefore, in the present embodiment, alumina is used as a raw material, with a pitch of 320 μm, a width of 40 μm and a depth of 30 μm.
The ceramic substrate 10 having the ink flow channel 12 and the common flow channel 13 for temporarily storing the ink was formed.
This is a non-polished ceramic material having a surface flatness of 80 nm, and the ink flow channel 12 is provided in a range of 215 μm. Then, the diaphragm 14 having a thickness of 0.2 mm is formed on the substrate 10.
A total of 67 so as to correspond to each flow channel 12.
The inkjet head 1 having the two piezoelectric elements 15 and having the nozzles 11 at a pitch of 320 μm was configured.

In the ink jet recording apparatus thus constructed, the ink jet head 1 having a nozzle pitch of 320 μm is stepped by the step motor 2 in steps of 32 μm in the direction orthogonal to the recording paper conveying direction, thereby achieving a recording dot density of 800 dpi. Images can be recorded. The ink jet head 1 can be moved minutely by using a piezoelectric element instead of the step motor.

Next, another embodiment of the present invention will be described with reference to FIGS. First, a substrate 20 made of ceramics is manufactured in the same manner as in the above embodiment, and the substrate 2
A 1 μm thick silicon dioxide layer was formed on the surface of No. 0 by the rf sputtering method. This silicon dioxide layer is called a heat storage layer for temporarily storing the heat generated in the heat generating element. By providing this heat storage layer, the heat generated in the heat generating element is efficiently transferred to the ink. can do.

Then, tantalum nitride is formed as a heating layer and an aluminum layer is formed as an electrode layer, and the heating element 21 and the electrode 22 are formed by photolithography and etching.
Was formed. Further, a hard carbon film (DLC film) was formed on the entire surface of the substrate by a plasma CVD method in order to prevent the electrode from being corroded by the ink. Here, the formed heating element 21 has a width of 215 μm and 5265 pieces (600 dp).
i).

After forming a flow path pattern of an ink flow path groove for ink discharge and a common flow path groove for ink replenishment on the substrate 20 having the heating element 21 formed thereon with a photosensitive resin having a thickness of 25 μm, A 0.2 mm thin glass plate was attached to manufacture a thermal inkjet head.

In this case, a thermal ink jet head was manufactured by using substrates having various surface flatness as the substrate 20, and the number of initial defective points and the number of defective points after continuous driving for 100 hours were measured. This measurement result is shown in FIG.
Is shown in

As can be seen from the figure, when the surface flatness Ra exceeds 100 nm, the number of bits of initial failure tends to increase. If Ra is greater than 80 nm, the number of defective points after continuous driving increases. Regarding the cause of this defect, most of the initial defects were film peeling of the heat storage layer, whereas the defect after continuous driving was damage to the heating element. The failure after continuous driving does not necessarily depend on the surface property of the substrate because it depends on the heating element material, configuration, use conditions, etc., but from the above results, Ra is preferably 100 nm or less, preferably It can be seen that the thickness is 80 nm or less.

Further, in the thermal ink jet head, since the heating element is used as the actuator element for ejecting ink, the temperature of the print head may rise during continuous recording and the quality of the recorded image may deteriorate. Therefore, a material having high thermal conductivity is preferable for the heating element supporting substrate.

Therefore, a thermal ink jet head was manufactured using the above-mentioned ceramic substrates having various thermal conductivities, and the temperature change of the print head during continuous driving was measured. The substrate supporting the heating element has a thickness of 7 mm.
It was measured by fixing it to an aluminum heat sink of mm with a silicone adhesive. The measurement result is shown in FIG.

As can be seen from the figure, when a substrate having a thermal conductivity of 0.04 W / cmK or more is used, the temperature of the substrate becomes constant after a certain period of time. When a substrate having a temperature of less than 0.04 W / cmK is used, the substrate temperature continues to rise as the driving time elapses. Therefore, when a ceramic substrate is used, by using a substrate having a thermal conductivity of 0.04 W / cmK or more, it is possible to prevent deterioration of recording quality due to an increase in substrate temperature during continuous recording.

Further, as described above, in the thermal ink jet head, a part of the heat generated in the heating element is radiated to the outside through the substrate to keep the substrate temperature during recording constant. In order to efficiently dissipate heat from the substrate, the substrate is adhered to a heat sink made of a material having higher thermal conductivity. Materials having high thermal conductivity include copper and aluminum, but since copper is inferior in workability and easily causes rust, aluminum is often used for the heat sink.

In this case, the heat sink material made of aluminum or copper has a large coefficient of thermal expansion (for example, aluminum is 23
It is about × 10 ⁻⁶ / K. ), The coefficient of thermal expansion of ceramic materials is smaller than that of metal materials. Therefore, if the difference in the coefficient of thermal expansion between the substrate and the heat sink is large, stress may occur between the substrate and the heat sink due to the temperature rise during recording, and the head may be deformed or the adhesive may peel off. It becomes remarkable as the size of the substrate increases.

Therefore, ceramic substrates having various coefficients of thermal expansion were prepared in the same manner as described above, and the width was set to 300 mm (73 mm).
A thermal inkjet head of 50 dots) was manufactured. Then, after bonding this head to an aluminum heat sink, a heat cycle test was conducted. The conditions for this test are 0 degrees and 30 degrees, considering the head temperature during recording.
Minutes → 70 degrees, 30 minutes → 0 degrees was set as 500 cycles. The test results are shown in Table 1.

[0035]

[Table 1]

As can be seen from Table 1, when the coefficient of linear thermal expansion of the ceramic substrate is smaller than 3.0 × 10 ^-6 / K, peeling is observed at the bonded portion, so the coefficient of linear thermal expansion is 3.0.
By using a ceramic substrate of × 10 ^-6 / K or more,
It is possible to prevent warping of the print head and separation from the heat sink during recording.

Next, still another embodiment of the present invention will be described with reference to FIG. In this embodiment, after the heat storage layer 23 made of the above-mentioned silicon dioxide layer is formed on the ceramic substrate 20, a 100 nm silicon nitride film is formed on the heat storage layer 23 by plasma CVD to form the protective film 24. It was formed.

That is, although ceramics are generally excellent in chemical resistance, some of them are corroded by acids or alkalis. Further, since tantalum nitride or a mixed material of tantalum and silicon dioxide used as a heating element is processed with an etching solution containing hydrofluoric acid, the ceramic substrate is damaged when the heating element is formed. In order to prevent this, pattern processing may be performed by dry etching, but dry etching has a disadvantage that the equipment cost is higher than that of wet etching and throughput is reduced.

Therefore, by forming the protective film 24 on the outermost surface of the substrate 20 as described above, damage to the substrate 20 can be prevented. When a silicon nitride film is used as the protective film 24, the silicon nitride film is also dissolved in the hydrofluoric nitric acid-based etching solution, but its etching rate is much slower than that of the silicon dioxide film used as the heat storage layer. It can exhibit the function as a protective film. The protective film may be formed only on the surface having the heat storage layer, or may be formed on the back surface of the substrate.

By forming the protective film in this manner, it is possible to pattern the heating element and the like without damaging the substrate surface even in hydrofluoric acid-based wet etching.

Further, in this case, as shown in FIG. 8, a protective layer 25 made of a material having a thermal conductivity smaller than that of the substrate material may be provided to serve both as the protective layer 24 and the heat storage layer 23. The protective layer 25 can be formed, for example, by forming a 1 μm thick zirconium oxide film by reactive sputtering on the surface of a ceramic substrate made of alumina as a raw material.

Since the thermal conductivity of this zirconium oxide is smaller than that of alumina ceramics by one digit or more,
Not only can it function as a protective film, but it can also function as a heat storage layer. By thus providing the protective film with the function of the heat storage layer, the manufacturing process can be simplified and the manufacturing cost can be reduced.

[0043]

As described above, according to the ink jet head of the first aspect, since the ceramic substrate having the surface flatness of 100 nm or less is used, the large size head having a recording width comparable to that of the recording medium can be inexpensively manufactured. You can get
The recording speed of the recording device can be improved.

According to the ink jet head of the second aspect, in the ink jet head of the first aspect, since the ceramic substrate having the thermal conductivity of 0.04 W / cmK or more is used, the heating element is used as the actuator element. It is possible to prevent the substrate temperature from increasing during continuous recording in the inkjet head and prevent deterioration of recording quality.

According to the ink jet head of the third aspect, in the ink jet head of the second aspect, since the ceramic substrate having the linear thermal expansion coefficient of 3.0 × 10 ⁻⁶ / K or more is used, the head at the time of recording is used. It is possible to prevent the warp and peeling from the heat sink.

According to the ink-jet head of the fourth aspect, in the ink-jet head according to any one of the first to third aspects, a thin film made of a material different from the substrate material is formed as a protective film on the surface of the substrate. The chemical resistance can be improved and the margin of the head manufacturing process can be widened.

According to the ink jet head of the fifth aspect, in the ink jet head of the fourth aspect, the thermal conductivity of the thin film is smaller than the thermal conductivity of the substrate. Therefore, the thin film functions as a protective film and a heat storage layer. Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an inkjet recording apparatus including an inkjet head according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of the inkjet head.

FIG. 3 is a schematic sectional view of the inkjet head.

FIG. 4 is an explanatory view showing a heating element pattern shape of an inkjet head according to another embodiment of the present invention.

FIG. 5 is a diagram showing the measurement results of the surface flatness of the ceramic substrate and the number of defective parts of the head.

FIG. 6 is a diagram showing the thermal conductivity of the ceramic substrate and the temperature change of the substrate temperature during continuous recording.

FIG. 7 is a schematic sectional view of an essential part of an inkjet head according to still another embodiment of the present invention.

8 is a schematic sectional view of an essential part for explaining another example of the embodiment of FIG.

[Explanation of symbols]

1 ... Inkjet head, 2 ... Step motor, 3 ...
Conveyor rollers, 4 ... Recording paper, 5 ... Ink droplets, 10, 20 ...
Substrate, 11 ... Nozzle, 12 ... Ink flow channel, 13 ... Common flow channel, 14 ... Vibration plate, 15 ... Piezoelectric element, 21 ... Heating element, 22 ... Electrode, 23 ... Heat storage layer, 24 ... Protective film , 25
… A protective film that doubles as a heat storage layer.

Claims (5)

[Claims] 1. In an ink jet head for pressurizing ink to eject ink droplets from an ejection port through an ink flow path provided on the substrate, the substrate is a ceramic substrate having a surface flatness of 100 nm or less. An inkjet head characterized in that. 2. The inkjet head according to claim 1, wherein the substrate has a thermal conductivity of 0.04 W / cmK or more. 3. The ink jet head according to claim 2, wherein the substrate has a coefficient of linear thermal expansion of 3.0 × 10 ⁻⁶ / K.
The above is an inkjet head. 4. The inkjet head according to any one of claims 1 to 3, wherein a thin film made of a material different from the substrate material is formed on the surface of the substrate. 5. The inkjet head according to claim 4, wherein the thermal conductivity of the thin film is smaller than the thermal conductivity of the substrate.