JP4396192B2 - Inkjet recording head - Google Patents

Description

  The present invention relates to an ink jet recording head that can dissipate drive heat generated during ink ejection with a simple structure and can eliminate problems caused by a decrease in ink viscosity that occurs during high speed drive.

  Conventionally, an actuator substrate is formed by forming a number of grooves in a polarized piezoelectric element, and a cover plate is bonded to the upper surface of the actuator substrate to form a number of pressure generating chambers partitioned by the piezoelectric element. A so-called shear mode type in which an electric field is applied to the piezoelectric elements between adjacent pressure generating chambers to deform the piezoelectric elements so that ink in the pressure generating chambers is ejected from nozzle holes formed in the nozzle plate. Inkjet recording heads (hereinafter also referred to as Shear mode heads) are known.

  Since this shear mode head forms an ink channel serving as an ink groove in the piezoelectric element, when the piezoelectric element generates heat by driving, the heat is transmitted to the ink and the ink is heated. When the ink temperature rises due to heating, the viscosity decreases and the discharge speed increases, causing the landing position to deviate from the target position and causing a significant decrease in image quality.

  For this reason, in the shear mode head, if the heat dissipation measures are not taken positively or if the heat dissipation measures are insufficient, the heat generated in the piezoelectric element will not escape and heat will be transferred to the ink. Decreases, the ink droplet ejection speed increases, and a landing error occurs on a recording medium moving at a constant speed, thereby degrading the image.

  This phenomenon of heat generation has a sensitive effect on the image. For example, when a 20 pl ink droplet is continuously ejected at 17 kHz for 2 seconds at a driving voltage of 20 V, specifically, the end of the wide recording medium is end-to-end. When the distance is about 1350 mm and the carriage is reciprocated at a speed of about 600 mm / sec, and printing is performed at the time of forward movement and backward movement, the printing is finished when discharging is performed for about 2 seconds at the time of forward movement. The image density rises by 0.1 m / sec or more, and the image density changes by 0.01 or more. This is because the head generates heat and this heat is transmitted to the ink, resulting in a decrease in the viscosity of the ink.

  When switching from forward movement to backward movement, the temperature of the head falls while printing is stopped, and the carriage moves in the reverse direction. When the printing starts and ends, the image density is 0.01 or more. Change. Although the density difference of 0.01 is slight, since this density difference appears side by side at the same location, it is possible to detect that there is density unevenness with the naked eye at both the left and right ends of the wide image. In order to prevent such a density difference from being detected with the naked eye, it is necessary to suppress an increase in ejection speed due to heat generated by the head to less than 0.1 m / sec and a density change to less than 0.01 during continuous ejection for 2 seconds. is there.

  The extent to which the discharge speed increases due to the increase in ink temperature is different between low-viscosity ink and high-viscosity ink. For example, a high-viscosity ink of 10 cp at room temperature has a discharge speed of 0.3 m / sec when the temperature of 1 ° C. rises. It is known to increase. Therefore, when printing a wide recording medium from end to end in full, the temperature rise of the ink in the head must be suppressed to within 0.3 ° C. If ejection continues for a long time, heat accumulates in the piezoelectric element and is transferred to the ink, causing the ink temperature to rise gradually. Normally, the head is equipped with a thermistor, and the drive voltage is changed by detecting the ink temperature. However, since there is a time delay of about 10 seconds in the response, the temperature rise that occurs in 10 seconds or less during the printing of one line is at a minimum. I can not cope.

  It is expected that the head temperature rises due to continuous ejection for about 2 seconds for one scan of a wide recording medium, but in order to prevent the temperature rise occurring in this short time, the heat dissipation of the head is improved, The best countermeasure is to prevent heat generated by the piezoelectric element from flowing to the ink side.

  2. Description of the Related Art Conventionally, in an ink jet recording head, a technology (Patent Document 1) in which a drive circuit IC is incorporated inside a ceramic substrate having good thermal conductivity and insulation, and heat generated by the IC is radiated by a ceramic plate (Patent Document 1) or high thermal conductivity. A technique (Patent Document 2) is known in which a heating element is bonded to a substrate with a film adhesive tape having high thermal conductivity.

  However, in order to dissipate the heat of the piezoelectric element, it is not sufficient to configure the member in contact with the piezoelectric element with a member having high thermal conductivity, and the following problems cannot be solved.

  That is, since the discharge amount and frequency of the shear mode head are determined by the length of the ink flow path, the length of the ink channel needs to be 5 mm or less in order to discharge micro droplets at high frequency. For this reason, it is necessary to grind a groove in a piezoelectric element having a length of several centimeters, form an electrode, adhere a cover plate so as to cover the upper surface of the ink channel, and then cut the ink channel so as to have a predetermined length. . At this time, if the physical properties of the piezoelectric element and the cover plate differ greatly, for example, if ceramics that are harder than the piezoelectric element are used for the cover plate, if the cutting conditions are set according to the hard material, the piezoelectric element that is a soft material will be excessively ground. As a result, the groove serving as the ink channel is greatly shaved. Also, if the cutting conditions are matched to the soft piezoelectric element, the hard cover plate cannot be cut cleanly. A nozzle plate on which nozzles for ejecting ink are bonded is attached to the cut surface. If the cut surface is uneven, the nozzle plate will not be smooth, and the direction of ink droplets ejected from the nozzles will not be smooth. There is a problem of bending.

  For this reason, it is necessary to bond the nozzle plate after polishing and smoothing the cut surface of the piezoelectric element, but the polishing is time-consuming and troublesome, and there is a problem that the ink flow path is clogged or dirty during polishing. .

  PZT, which is exclusively used as a piezoelectric element, has a Young's modulus of about 50 GPa and is low as a ceramic. A smooth grinding surface can be obtained by grinding with a diamond cutter, but ceramics other than piezoelectric elements, such as alumina, have a Young's modulus. Since it is as high as 300 to 400 GPa, a material obtained by bonding PZT and alumina is difficult to cut and a smooth cut surface cannot be obtained. Therefore, it is necessary to polish the cut surface for a longer time.

  It is desirable to use the same material as the piezoelectric element for the cover plate, because it is not necessary to consider thermal expansion, and it can be cut with a clean cut surface. For example, a piezoelectric element made of PZT has a thermal conductivity of 1.5. Since it is as low as ˜2 W / mK, the heat generated inside the piezoelectric element is difficult to escape. For this reason, if the same material as that of the piezoelectric element is used for the cover plate, the ink channel is surrounded by a material having poor thermal conductivity, and the heat generated inside the piezoelectric element cannot be escaped. Will rise.

In addition, in a shear mode head, a technique is known in which a ceramic having a high thermal conductivity is used for a cover plate that covers the upper surface of an ink channel formed in a piezoelectric element and is bonded with an adhesive having a high thermal conductivity ( Patent Document 3) does not mention anything about the problems seen during the above-described cutting process.
Japanese Patent Laid-Open No. 10-217454 JP 2001-150680 A JP 2000-135788 A

  Unlike the above-described conventional technology, the present invention uses a material having a higher thermal conductivity than the piezoelectric element as the cover plate material to improve heat dissipation, and uses a material having a linear expansion coefficient close to that of the piezoelectric element to manufacture the head. It is an object of the present invention to provide a highly reliable ink jet recording head that can prevent distortion and peeling of the head during and during use, and that does not require polishing of the cut surface of the adhesive between the cover plate and the piezoelectric element. .

  The above problems are solved by the following inventions.

1. A partition wall that partitions a plurality of ink flow paths and at least a part of which is formed of a piezoelectric element; an upper wall that closes an upper surface of the ink flow path along an arrangement direction of the plurality of ink flow paths; while have a tubular ink flow path formed by the bottom wall which closes a lower surface, have a top plate provided so as to surround the nozzle plate surface almost same plane of the nozzle plate, the piezoelectric element An ink jet recording head that discharges ink in the ink flow path from a nozzle hole formed in the nozzle plate by deformation of the at least one of the upper wall and the lower wall , wherein the thermal conductivity is higher than that of the piezoelectric element. Ri is higher AlN-BN der, the top plate, the higher thermal conductivity than AlN-BN, the ink jet recording head, characterized in that said are AlN-BN and thermally coupled.

2. A partition wall that partitions a plurality of ink flow paths, an upper wall that closes an upper surface of the ink flow path along an arrangement direction of the plurality of ink flow paths, and a lower wall that closes a lower surface of the ink flow path has a tubular ink flow path, the upper wall, ceiling at least a portion of the lower wall is provided so as to surround the nozzle plate Rutotomoni formed by a piezoelectric element, a surface substantially coplanar nozzle plate has a plate, said an ink jet recording head for discharging ink of the ink flow path due to the deformation of the piezoelectric element from the nozzle holes formed in the nozzle plate, the top wall, at least a portion of the lower wall, the piezoelectric element Ri high a l N -BN der thermal conductivity than said top plate, characterized in that it is a high thermal conductivity, thermally coupled with said AlN-BN than the AlN-BN Inkjet Doo recording head.

3. An ink jet recording head according to claim 1, characterized in that the said AlN-BN piezoelectric device is bonded with an epoxy adhesive containing aluminum nitride, alumina or silica.

4). The partition wall is formed in the AlN-BN, claim 2, characterized in that the said AlN-BN piezoelectric elements are bonded with an epoxy adhesive containing aluminum nitride, alumina or silica Inkjet recording head.

5). The inkjet recording head according to claim 3 or 4, wherein a film thickness of the adhesive between the AlN-BN and the piezoelectric element is 5 to 10 µm.

6). 6. The ink jet recording head according to claim 1, wherein the AlN-BN and the top plate are bonded with an epoxy adhesive containing Ag particles.

7). The film thickness of the adhesive between the top plate and the AlN-BN is an ink jet recording head according to claim 6, characterized in that the 50 ~ 70 [mu] m.

8). The ink jet recording head according to claim 1, wherein the top plate is a support body attached to a casing of a carriage.

9. The ink jet recording head according to claim 8, wherein the top plate is thermally coupled to the carriage .

10. The ink jet recording apparatus according to claim 1, wherein any one of aluminum, brass, copper, and aluminum die cast is used for the top plate.

11. The inkjet recording head according to claim 1, wherein the top plate has a thickness of 1.0 mm to 10.0 mm .

  According to the present invention, a highly reliable inkjet that has excellent heat dissipation effects, does not cause density unevenness, does not cause distortion or peeling, and does not require polishing of the cut surface of the adhesive between the cover plate and the piezoelectric element. A recording head can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The ink jet recording head of the present invention can take two modes: an aspect in which at least a part of the partition wall is configured by a piezoelectric element, and an aspect in which at least a part of the upper wall and the lower wall are configured by a piezoelectric element.

  First, an ink jet recording head having an aspect in which at least a part of the partition wall is constituted by a piezoelectric element will be described.

  FIG. 1 is a longitudinal sectional view showing an example of an ink jet recording head according to the present invention, and FIG. 2 is a sectional view of the recording head taken along line II-II in FIG.

  1 and 2, H is a recording head, 1 is an actuator substrate as a partition wall, 2 is a nozzle plate, 3 is a nozzle hole, 4 is an ink channel as a pressure generation chamber (ink channel), and 5 is a side wall (partition wall). ), 6 is a cover plate as an upper wall, 7 is a manifold, and 8 is an FPC (flexible printed circuit board).

  Note that the recording head H shown in the present embodiment is symmetrical in the vertical direction with respect to the center line indicated by the alternate long and short dash line in FIG. It is configured. Thereby, it is possible to double the number of nozzles and double the nozzle density without changing the head width.

  The actuator substrate 1 is composed of two piezoelectric elements 1a and 1b having different polarization directions, which are bonded to each other with an adhesive, and a plurality of groove-shaped ink channels 4 are all formed from the upper piezoelectric element 1a by a diamond blade or the like. The same shape is cut in parallel so that adjacent ink channels 4 are delimited by side walls 5 polarized in the direction of the arrows.

  Further, the ink channel 4 is a shallow groove that gradually becomes shallower from the deep groove portion 4a toward the ink channel inlet side (right side in FIG. 1) from the deep groove portion 4a on the ink channel outlet side (left side in FIG. 1) of the actuator substrate 1. And a groove 4b.

The piezoelectric material used for the piezoelectric elements 1a and 1b is not particularly limited as long as it causes a change in shape when a voltage is applied. A known material may be used, and a substrate made of an organic material may be used. A substrate made of a piezoelectric non-metallic material is preferable, and the substrate made of the piezoelectric non-metallic material is, for example, a ceramic substrate formed through a process such as molding or firing, or formed without requiring molding or firing. There are substrates. Examples of the organic material include organic polymers and hybrid materials of organic polymers and inorganic materials.

As the ceramic substrate, there are PZT (PbZrO ₃ -PbTiO ₃ ) and third component added PZT. As the third component, Pb (Mg _1/3 Nb _2/3 ) O ₃ , Pb (Mn _1/3 Sb _{2 / 3} ) O ₃ , Pb (Co _1/3 Nb _2/3 ) O _{3, and the} like, and further, BaTiO ₃ , ZnO, LiNbO ₃ , LiTaO _{3, and the} like can be used.

Moreover, as a board | substrate formed without requiring shaping | molding and baking, it can form by the sol-gel method, laminated substrate coating, etc., for example. According to the solgale method, the sol is prepared by adding water, an acid or an alkali to a homogeneous solution having a predetermined chemical composition to cause a chemical change such as hydrolysis. Further, by applying a treatment such as evaporation of the solvent or cooling, a sol in which the precursor of the target composition or the precursor of the nonmetallic inorganic fine particles is dispersed can be prepared and used as a substrate. A compound having a uniform chemical composition can be obtained, including the addition of a small amount of a different element, and a metal salt or metal alkoxide soluble in water such as sodium silicate is generally used as a starting material. A compound represented by the formula M (OR) n, which is easily hydrolyzed because the OR group has a strong basicity, and is converted into a metal oxide or a hydrate thereof through a condensation process like an organic polymer. .

  In addition, as a laminated substrate coating, there is a method of vapor deposition from the gas phase, and there are two methods for producing a ceramic substrate from the gas phase: a vapor deposition method by physical means and a production method by chemical reaction of the gas phase or the substrate surface. Further, physical vapor deposition (PVD) is subdivided into vacuum vapor deposition, sputtering, ion plating, etc., and chemical methods include gas phase chemical reaction (CVD), plasma CVD, etc. is there. The vacuum deposition method as physical vapor deposition (PVD) is a method in which a target substance is heated and evaporated in a vacuum, and the vapor is deposited on a substrate. A sputtering method is a high energy particle on a target substance (target). This is a method that utilizes a sputtering phenomenon in which atoms and molecules on the target surface exchange momentum with the colliding particles and are repelled from the surface. The ion plating method is a method of performing vapor deposition in an ionized gas atmosphere. In the CVD method, a compound containing atoms, molecules, or ions constituting the film is put into a gas phase state, and then introduced into a reaction part with an appropriate carrier gas, and the film is formed by reacting or precipitating on a heated substrate. Form. In the plasma CVD method, a gas phase state is generated by plasma energy, and a film is deposited by a gas phase chemical reaction in a relatively low temperature range from 400 ° C. to 500 ° C.

On the upper surface of the actuator substrate 1, a cover plate 6 is bonded via an adhesive so as to cover the deep groove portion 4 a over the entire ink channel 4, and the ink channel 4 is formed on the shallow groove portion 4 b of each ink channel 4. An ink inlet 4c to the inside is formed, and the manifold 7 is bonded via an adhesive so as to cover the ink inlet 4c. Further, the nozzle plate 2 in which the nozzle holes 3 are opened is bonded to the front end surface of the actuator substrate 1 to which the cover plate 6 is bonded via an adhesive.

  In each ink channel 4, a metal electrode 9 is formed from both side surfaces to the bottom surface, and the metal electrode 9 extends to the rear side upper surface 1c of the actuator substrate 1 through the shallow groove portion 4b. An FPC 8 is bonded to each metal electrode 9 via an ACF (anisotropic conductive film) 10 on the rear-side upper surface 1c, and each metal electrode 9 passes through an electrode 8a formed on the back surface of the FPC 8 from a drive circuit (not shown). By applying a driving voltage to the metal electrode 9, the side wall 5 is sheared and deformed, and ink in the ink channel 4 is ejected from the nozzle hole 3 formed in the nozzle plate 2 by the pressure at the time of deformation.

  As the metal used for the metal electrode 9, platinum, gold, silver, copper, aluminum, palladium, nickel, tantalum, and titanium can be used. In particular, from the viewpoint of electrical characteristics and workability, gold, aluminum, copper Nickel is preferable and is formed by plating, vapor deposition, or sputtering. In particular, it is preferable to form by electroless plating. Since the piezoelectric element is composed of particles having a particle size of about several μm, the surface thereof is rough. For example, even when an electrode is formed by oblique vapor deposition using aluminum, a uniform electrode cannot be formed, and the driving voltage increases. Tend. On the other hand, in the electroless plating, the metal is uniformly deposited along the base, so that the driving voltage can be lowered as compared with the case of vapor deposition. Nickel is preferred for this electroless plating.

In the present invention, the cover plate 6 in direct contact with the actuator substrate 1 has higher thermal conductivity than the piezoelectric elements 1a and 1b, and the linear expansion coefficient (Lc) of the cover plate 6 and the linear expansion coefficient of the piezoelectric elements 1a and 1b. (Lp) is made of machinable ceramics satisfying the condition of | Lc−Lp | ≦ 5 × 10 ⁻⁶ / ° C., and the cover plate 6
A top plate 11 having a higher thermal conductivity than that is provided.

By using a material having higher thermal conductivity than the piezoelectric elements 1a and 1b for the cover plate 6, the heat generated in the piezoelectric elements 1a and 1b can be released to the cover plate 6 side, and the ink in the ink channel 4 can be released. Temperature rise can be suppressed. For example, when PZT is used for the piezoelectric elements 1a and 1b, since the thermal conductivity of PZT is 1.5 to 2 W / mK, a machinable ceramic having a higher thermal conductivity is used. The thermal conductivity is preferably 5 W / mK or more higher than the piezoelectric element 1, more preferably 10 W / mK or more, and most preferably 50 W / mK or more.

  Machinable ceramics are generally referred to as free-cutting ceramics and are ceramics that are easy to machine. In general, ceramics have extremely poor processability, and even if expensive diamond cutters are used, machining efficiency is extremely poor and machining costs are high. However, machinable ceramics are machine tools and tools for ordinary metal working. Can be processed.

  Machinable ceramics include mica glass ceramics and aluminum nitride with countless microcracks inside. The former has a structure in which microcrystals of fluorinated mica are deposited three-dimensionally in a vitreous matrix, and when the cutting edge of a cutting tool breaks through this ceramic, the mica crystals are preferentially broken and cracked. Stops only on that part and releases fine chips. Specific examples include “Macor” manufactured by Corning Glass Works and “Photovale II” manufactured by Sumikin Ceramics Co., Ltd.

  The latter is particularly preferable because it is an infinite number of fine cracks inside, is excellent in workability, and has a sufficiently high thermal conductivity. In particular, aluminum nitride-boron nitride having an Al component ratio of 70% or more (Molar ratio of Al is 70% or more and B is less than 30%) is preferable. Specifically, AlN-BN (aluminum nitride-boron nitride) manufactured by Sumikin Ceramics Co., Ltd. and “Shape Msoft” manufactured by Tokuyama Co., Ltd. may be mentioned.

Further, “Forsterite” manufactured by Kyocera Corporation is available as MgO · SiO ₂ -based mica ceramics.

The machinable ceramic used for the cover plate 6 has a condition that the linear expansion coefficient (Lc) is equal to the linear expansion coefficient (Lp) of the piezoelectric elements 1a and 1b and | Lc−Lp | ≦ 5 × 10 ⁻⁶ / ° C. It is necessary to satisfy. That is, it is preferably close to the linear expansion coefficient of the piezoelectric elements 1a and 1b. The reason is that when the cover plate 6 is bonded to the actuator substrate 1 formed of the piezoelectric elements 1a and 1b, a thermosetting adhesive is used, but the linear expansion coefficient of the cover plate 6 is that of the piezoelectric elements 1a and 1b. This is because if it is far from it, there is a problem that distortion occurs during cooling or separation occurs between materials.

In addition, by satisfying the above conditions, it is possible to suppress a situation in which the same distortion or peeling as described above occurs between the piezoelectric elements 1a and 1b and the actuator substrate 1. Preferably, the condition of | Lc−Lp | ≦ 3 × 10 ⁻⁶ / ° C. is satisfied.

  In addition, when some thermal conductivity (W) and linear expansion coefficient (Lc) of the machinable ceramic illustrated above are shown, AlN-BN manufactured by Sumikin Ceramics Co., Ltd .: W = 90, Lc = 4.9. (Sharp Msoft) manufactured by Tokuyama Corporation: W = 90, Lc = 4.4, “Photovale II” manufactured by Sumikin Ceramics Co., Ltd .: W = 19.5, Lc = 1.4, “Forsterite” manufactured by Kyocera Corporation: W = 7.8, Lc = 10.5. These have higher thermal conductivity than the PZT (W = 1.5, Lp = 5) preferably used as the piezoelectric element 1, and the linear expansion coefficient satisfies the above conditions.

A top plate 11 having a higher thermal conductivity than that of the cover plate 6 is bonded to the cover plate 6 via an adhesive 12. The top plate 11 functions as a support for attaching the actuator substrate 1 to which the cover plate 6 is bonded to the housing 13 of the carriage (not shown) of the recording apparatus, and is substantially flush with the surface of the nozzle plate 2. By doing so, it functions as a member that serves as a guide when wiping the surface of the nozzle plate 2.

  By configuring the top plate 11 with a member having a higher thermal conductivity than the cover plate 6, the heat inside the piezoelectric elements 1a and 1b is released to the cover plate 6 having a higher thermal conductivity than the piezoelectric elements 1a and 1b. Furthermore, by letting the cover plate 6 escape to the top plate 11 having higher thermal conductivity, the top plate 11 can function as a so-called heat sink. For this reason, it is preferable that the top plate 11 has a sufficiently larger area than the cover plate 6, and a wider contact area is preferable because the thermal resistance is small and the heat capacity is large. For example, the thickness along the length direction of the ink channel 4 in the contact surface direction is preferably 1.0 to 10.0 mm. When the top plate 11 functions as a heat sink, the heat in the ink channel 4 transmitted through the cover plate 6 can be released to the top plate 11 used as the heat sink, so that the cooling effect can be enhanced. In addition, the fact that the top plate 11 used as a heat sink is thermally coupled to the carriage is also effective in enhancing the cooling effect.

  The material of the top plate 11 may be any material that has a higher thermal conductivity than the cover plate 6, and is aluminum (thermal conductivity W = 236 W / mK), brass (W = 106), copper (W = 403), aluminum Die casting (W = 90) is preferably used. Among these, aluminum is most preferable in terms of workability and cost.

In order to efficiently release the heat generated in the piezoelectric elements 1a and 1b to the top plate 11 through the cover plate 6, it is preferable that the adhesive 12 for bonding the two also has a high thermal conductivity. From this viewpoint, it is preferable to add Ag (silver) particles to the epoxy adhesive to the adhesive 12 that bonds the cover plate 6 and the top plate 11. Epoxy adhesives have extremely poor thermal conductivity (0.1 to 0.3 W / mK), but by adding Ag, the thermal conductivity of the adhesive 12 is improved to 3 to 5 W / mK. In general, when the thickness of a material having thermal conductivity k (W / mK) is L (m) and the area is A (m ² ), the heat transfer resistance Rc of the material is Rc = L / k · A (K / W), it is preferable to make L as small as possible and A as large as possible.

  For this reason, a thinner film thickness of the adhesive 12 is preferable because the thermal resistance becomes smaller. In addition, the surface of the top plate 11 is preferably rough in order to enhance the heat dissipation effect. However, if bubbles are present in the adhesive layer, the thermal conductivity of air is extremely poor. The film thickness of the adhesive 12 between the plates 6 is preferably 50 to 70 μm.

The adhesive 14 interposed between the cover plate 6 and the actuator substrate 1 also preferably has a high thermal conductivity. Since this is in contact with the metal electrode 9 and electrical insulation is required, it is preferable to add fine particles of AlN, alumina or silica having high thermal conductivity to the epoxy adhesive. Epoxy adhesives have extremely poor thermal conductivity (0.1 to 0.3 W).
/ MK) is improved by adding ceramic particles having high thermal conductivity such as aluminum nitride (AlN), alumina or silica (0.5 to 1.0 W / mK in the case of AlN), and an actuator. The heat of the substrate 1 can be effectively radiated to the cover plate 6 side. The thickness of the adhesive between the cover plate 6 and the actuator substrate 1 is preferably 5 to 10 μm. If it is thinner than 5 μm, bubbles easily enter the adhesive layer, and if it is thicker than 10 μm, the deformation efficiency of the ink channel 4 decreases.

The roughness of each substrate surface is important when the cover plate 6 and the actuator substrate 1 are bonded. From this point of view, when the cover plate 6 is made of Photoveel II, the adhesive penetrates into the microvoids in the substrate, and the adhesive layer thickness after curing cannot be maintained sufficiently, resulting in weak adhesive strength. Similarly, when it is made of Al ₂ O ₃ or PZT, it is difficult to assemble, and it is difficult to obtain optimum bonding conditions. On the other hand, when the cover plate 6 is made of AlN-BN, AlN-BN has a dense structure with few microvoids, high Young's modulus, and high hardness. Functions as an agent layer. Therefore, when the cover plate 6 is made of AlN-BN, the assemblability is good and the production stability is excellent.

In the present invention, the cover plate 6 preferably has a low dielectric constant (ε). The reason is that the lower the dielectric constant, the smaller the electric field leakage from the piezoelectric elements 1a and 1b, and the lower the drive voltage. If the drive voltage is lowered, heat generation of the piezoelectric elements 1a and 1b can be suppressed. Specifically, the dielectric constant (ε) is 100 or less, preferably 10 or less. For example, in the above AlN-BN manufactured by Sumikin Ceramics Co., Ltd., ε = 7.1, in “Photovale II” manufactured by Sumikin Ceramics Co., Ltd., ε = ˜6, and “Follow” manufactured by Kyocera Corporation. For “Stellite”, ε = 6.8. This is extremely low compared to the dielectric constant of PZT being 2000 to 4000.

The cover plate 6 preferably has a higher bending strength, specifically 100 MPa or more, more preferably 200 MPa or more. The reason is that, when the actuator substrate 1 is deformed, the smaller the bending of the cover plate 6, the better the ejection efficiency. For example, the bending strength of AlN-BN manufactured by Sumikin Ceramics Co., Ltd. is 294MP.
a, The bending strength of “Photoveel II” manufactured by Sumikin Ceramics Co., Ltd. is 440 MPa. If the bending strength is less than 100 MPa, the discharge efficiency is lowered and the drive voltage is increased, which is not preferable.

  Furthermore, the cover plate 6 preferably has a Young's modulus of 50 to 200 GPa. Since the Young's modulus of the piezoelectric elements 1a and 1b is about 50 GPa, if it is higher than 50 GPa, the piezoelectric elements 1a and 1b are not easily affected by the deformation, and the discharge efficiency is improved. However, when it becomes higher than 200 GPa, the machinability of the cover plate 6 is lost, and the cutting property is inferior.

  The Vickers hardness of the cover plate 6 is preferably 5.0 GPa or less. If it exceeds 5.0 GPa, the grindability will deteriorate and it will not be possible to cut cleanly. Or the life of the diamond cutter is shortened.

The nozzle plate 2 also preferably has a higher thermal conductivity than the piezoelectric elements 1a and 1b. That is, since the nozzle plate 2 is bonded to the front end surfaces of the actuator substrate 1 and the cover plate 6, the piezoelectric conductivity of the nozzle plate 2 is made higher than that of the piezoelectric elements 1a and 1b, so that the piezoelectric elements 1a and 1b The internal heat generation can be radiated from the nozzle plate 2 in addition to the heat radiated from the cover plate 6.

The nozzle plate 2 may be made of any material having higher thermal conductivity than the piezoelectric elements 1a and 1b. However, resin is generally not preferable because it has lower thermal conductivity than the piezoelectric element. Therefore, the material of the nozzle plate 2 is preferably a metal. For example, since the thermal conductivity of stainless steel is 15 W / mK, compared with the case where the thermal conductivity of polyimide resin generally used as a nozzle plate material is about 0.1 to 0.2 W / mK, the heat dissipation effect is improved. Can be increased. Among these, Kovar or 42 alloy having a linear expansion coefficient close to that of the actuator substrate 1 is preferable.

  In the above description, the ink jet recording head having the structure in which the cover plate 6 is provided as the upper wall of the actuator substrate 4 provided as the partition wall has been described as an example. However, as the lower wall of the actuator substrate 4 provided as the partition wall. An inkjet recording head having a configuration in which the cover plate 6 is provided and an inkjet recording head having a configuration in which the cover plate 6 is provided as the upper wall and the lower wall of the actuator substrate 4 provided as a partition are also included in the present invention.

  Next, an ink jet recording head according to an embodiment of the present invention in which at least a part of the upper wall and the lower wall is constituted by piezoelectric elements will be described.

  FIG. 3 is a sectional view showing another example of the ink jet recording head according to the present invention.

  In FIG. 3, reference numeral 20 denotes an ink flow path, which is divided into a plurality of partitions by a plurality of partition walls 22. Further, the ink flow path 20 is formed in a cylindrical shape by closing the upper surface with a piezoelectric element 21 as an upper wall and closing the lower surface with a lower wall 23.

  In the ink jet recording head of this aspect, ink is ejected in the direction perpendicular to the paper surface by applying a voltage between the electrode 24 and the electrode 25 provided on both surfaces of the piezoelectric element 21. For the lower wall 23 of the ink jet recording head of this mode, the same material as that of the cover plate 6 of the above mode can be used. A heat sink is preferably thermally coupled to the lower wall 23. For this reason, it is preferable that the heat sink has a sufficiently larger area than the lower wall 23, and a larger contact area is preferable because a thermal resistance is small and a heat capacity is increased. For example, the thickness along the length direction of the ink flow path 20 in the contact surface direction is preferably 1.0 to 10.0 mm.

  As the material of the heat sink, the same material as that of the top plate 11 can be used.

  In order to efficiently release the heat generated in the piezoelectric element 21 to the heat sink via the partition wall 22 and the lower wall 23, the adhesive bonding the lower wall 23 and the heat sink must also have a high thermal conductivity. preferable. From this point of view, the same adhesive as the adhesive 12 can be used as an adhesive for bonding the two.

  For this reason, since the thermal resistance becomes small, the one where the film thickness of the adhesive agent between a heat sink and the lower wall 23 becomes thin is preferable. The surface of the heat sink is preferably rough in order to enhance the heat dissipation effect. However, if bubbles are present in the adhesive layer, the thermal conductivity of air is extremely poor. It is preferable that the film thickness of the adhesive in between is 50-70 micrometers.

  The heat sink bonded to the lower wall is preferably provided on a carriage (not shown) on which the recording head is mounted. When the heat sink is provided on the carriage, it is not necessary to provide a heat sink for each recording head, so that the assemblability is good. When the recording head is replaced, it is not necessary to replace the heat sink at the same time. In addition, it is preferable that the heat sink and the carriage are thermally coupled, because a cooling effect for efficiently releasing generated heat is improved.

  In the present invention, it is preferable that the partition wall 22 is also made of the same material as that of the cover plate 6 and is bonded to the piezoelectric element 21 using the same adhesive as the adhesive 14.

  The thickness of the adhesive between the partition wall 22 and the piezoelectric element 21 is preferably 5 to 10 μm. When the thickness is less than 5 μm, bubbles easily enter the adhesive layer, and when the thickness is greater than 10 μm, the deformation efficiency of the piezoelectric element 21 decreases.

Example 1
Using a diamond cutter on a polarized piezoelectric element (“H5D” manufactured by Sumitomo Metals Co., Ltd., thermal conductivity W = 1.5 W / mK, linear expansion coefficient = 5 × 10 ⁻⁶ / ° C.), a width of 80 μm serving as an ink channel An actuator substrate was formed by providing 768 grooves having a depth of 200 μm and a length of 6 cm, and a nickel electrode was formed on the side wall in the ink channel by electroless plating.

Aluminum nitride (AlN-BN) manufactured by Sumikin Ceramics & Quartz Co., Ltd. (thermal conductivity W = 90.0 W / mK, linear expansion coefficient = 4.9 ×) is a machinable ceramic with high thermal conductivity. The cover plate made of 10 ⁻⁶ / ° C. was bonded with a highly thermally conductive epoxy adhesive containing AlN particles (film thickness: 10 μm, W = 1.0 W / mK).

The obtained adhesive is cut with a diamond cutter to make the ink channel length 2.5 mm, and then the polyimide resin nozzle plate and manifold are bonded with a room temperature curable adhesive to connect to each electrode. The FPC was connected as follows. An aluminum top plate (thickness: 1 mm) was adhered to the upper surface of the cover plate with an epoxy adhesive (A film thickness 50 μm, W = 3.0 W / mK) containing Ag particles.

  The recording head configured as described above was mounted on a carriage and continuously discharged for 2 seconds, and the speed of ink droplets at the start and end of discharge and the density of the printed image were measured.

Example 2
Example 1 was the same as Example 1 except that a normal epoxy adhesive (W = 0.3 W / mK) not containing heat conductive particles was used as the adhesive.

Example 3
Example except that electrode is made of aluminum, ordinary epoxy adhesive (W = 0.3W / mK) not containing heat conductive particles is used as adhesive, and stainless steel is used for nozzle plate. 1 was the same.

Example 4
The electrode is made of aluminum, and the cover plate is made of mica ceramic machinable ceramics, “Photoveel II” (W = 19.5 W / mK) manufactured by Sumikin Ceramics & Quartz, Inc., containing thermally conductive particles It was the same as Example 1 except that it was bonded with a normal epoxy adhesive (W = 0.3 W / mK) and stainless steel was used as the nozzle plate.

Comparative Example 1
Except for using an alumina ceramic substrate (thermal conductivity W = 33 W / mK) for the cover plate and using an ordinary epoxy adhesive (W = 0.3 W / mK) that does not contain thermal conductive particles as the adhesive. The same as Example 1.

Comparative Example 2
A depolarized piezoelectric element (PZT: thermal conductivity W = 1.5 W / mK) is used for the cover plate, and engineering plastic PEI (polyetherimide: thermal conductivity W = 0.1 W / mK) is used for the top plate. ) And an ordinary epoxy adhesive (W = 0.3 W / mK) that does not contain thermally conductive particles was used as the adhesive.

  In the image quality evaluation, the obtained image was visually confirmed, and the image quality was evaluated according to the following criteria. The results are shown in Table 1.

A: There was no printing unevenness and it was very clear.
B: Printing unevenness was not noticeable and clear.
C: Some printing unevenness was noticeable, and the image quality was slightly deteriorated.
D: Printing unevenness was conspicuous and the image quality was poor.

  The head productivity (assembling property) was evaluated according to the following criteria.

A: Productivity such as processability and adhesiveness was good.
C: Productivity, such as workability and adhesiveness, was slightly inferior.

  In Table 1, an adhesive 1 is an adhesive between the top plate and the cover plate, and an adhesive 2 is an adhesive between the cover plate and the piezoelectric element.

  In Example 1, when printing about 1350 mm from end to end of a large-sized recording medium over about 2 seconds, the increase in print density due to head heat generation was 0.005, and printing unevenness could not be confirmed. Further, in this recording head, when the length of the ink channel was cut and aligned using a diamond cutter, the cut surface was clean and polishing was unnecessary.

  In Example 2, since an adhesive having poor thermal conductivity was used, the density difference was slightly larger than that in Example 1, but it could not be detected with the naked eye, and there was no problem in image quality.

  In Example 3, since aluminum was used for the electrodes, the drive voltage was higher and the density difference was slightly larger than that in Example 1, but it was hardly detectable with the naked eye and there was no problem with image quality.

  In Example 4, since the cover plate was slightly inferior in thermal conductivity to that in Example 1, the difference in density was large, but it was hardly detectable with the naked eye, and there was no problem in image quality.

In Comparative Example 1, since Al ₂ O ₃ having poor workability was used for the cover plate, when the lengths of the piezoelectric elements were aligned, the cut surface was rough and had to be polished. Further, since the thermal conductivity of Al ₂ O ₃ is poorer than that of AlN-BN, the density difference is considerably large, the density difference is detected with the naked eye, and the deterioration of the image quality is conspicuous.

  In Comparative Example 2, PZT having poor thermal conductivity was used for the cover plate, and PEI having poor thermal conductivity was used for the top plate, so the density difference was further deteriorated. The productivity (assembly) of the head is excellent in Examples 1 to 3 in which the machinable ceramics AlN-BN is used for the cover plate, and the other examples are slightly inferior.

1 is a longitudinal sectional view showing an example of an ink jet recording head according to the present invention. Sectional view when cut along line II-II in FIG. Sectional drawing which shows another example of the inkjet recording head which concerns on this invention.

Explanation of symbols

1: Actuator substrate 1a, 1b: Piezoelectric element 2: Nozzle plate 3: Nozzle hole 4: Ink channel 5: Side wall (partition wall)
6: Cover plate 7: Manifold 8: FPC
9: Metal electrode 10: ACF
11: Top plate 12: Adhesive 13: Housing 14: Adhesive 20: Ink flow path 21: Piezoelectric element 22: Partition wall 23: Lower wall 24: Electrode 25: Electrode

Claims (11)

A partition wall that partitions a plurality of ink flow paths and at least a part of which is formed of a piezoelectric element; an upper wall that closes an upper surface of the ink flow path along an arrangement direction of the plurality of ink flow paths; while have a tubular ink flow path formed by the bottom wall which closes a lower surface, have a top plate provided so as to surround the nozzle plate surface almost same plane of the nozzle plate, the piezoelectric element An ink jet recording head that discharges ink in the ink flow path from a nozzle hole formed in the nozzle plate by the deformation of
The upper wall, at least a portion of the lower wall, Ri higher AlN-BN der thermal conductivity than the piezoelectric element,
The ink jet recording head , wherein the top plate has higher thermal conductivity than the AlN-BN and is thermally coupled to the AlN-BN . A partition wall that partitions a plurality of ink flow paths, an upper wall that closes an upper surface of the ink flow path along an arrangement direction of the plurality of ink flow paths, and a lower wall that closes a lower surface of the ink flow path has a tubular ink flow path, the upper wall, ceiling at least a portion of the lower wall is provided so as to surround the nozzle plate Rutotomoni formed by a piezoelectric element, a surface substantially coplanar nozzle plate has a plate, an ink jet recording head for discharging ink from a nozzle hole formed in the nozzle plate of the ink flow path by deformation of the piezoelectric element,
The upper wall, at least a portion of the lower wall, Ri high A l N -BN der thermal conductivity than the piezoelectric element,
The ink jet recording head , wherein the top plate has higher thermal conductivity than the AlN-BN and is thermally coupled to the AlN-BN . An ink jet recording head according to claim 1, characterized in that the said AlN-BN piezoelectric device is bonded with an epoxy adhesive containing aluminum nitride, alumina or silica. The partition wall is formed in the AlN-BN, claim 2, characterized in that the said AlN-BN piezoelectric elements are bonded with an epoxy adhesive containing aluminum nitride, alumina or silica Inkjet recording head. The inkjet recording head according to claim 3 or 4, wherein a film thickness of the adhesive between the AlN-BN and the piezoelectric element is 5 to 10 µm. 6. The ink jet recording head according to claim 1, wherein the AlN-BN and the top plate are bonded with an epoxy adhesive containing Ag particles. The film thickness of the adhesive between the top plate and the AlN-BN is an ink jet recording head according to claim 6, characterized in that the 50 ~ 70 [mu] m. The ink jet recording head according to claim 1, wherein the top plate is a support body attached to a casing of a carriage. The ink jet recording head according to claim 8, wherein the top plate is thermally coupled to the carriage . The ink jet recording apparatus according to claim 1, wherein any one of aluminum, brass, copper, and aluminum die cast is used for the top plate. The inkjet recording head according to claim 1, wherein the top plate has a thickness of 1.0 mm to 10.0 mm.

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