JP3424690B2 - Droplet ejector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid droplet ejecting apparatus. [0002] Hitherto, as a droplet ejecting apparatus using a piezoelectric ceramic element, for example, a drop-on-demand type droplet ejecting apparatus has been proposed. This is to change the volume in the ink flow path, eject the ink in the ink flow path from the nozzle when the volume decreases, and introduce the ink into the ink flow path from the ink supply port when the volume increases. It is. Then, desired characters and images are formed by ejecting ink from an ejection device at a predetermined position in accordance with the print data. [0003] Such a droplet ejecting apparatus is disclosed in, for example, JP-A-63-247051 and JP-A-63-252.
750 and JP-A-2-150355. Hereinafter, a schematic configuration of the droplet ejecting apparatus will be described. As shown in FIG. 3, the ink jet printer head 1 includes a piezoelectric ceramic plate 2, a cover plate 3, a nozzle plate 31, and a substrate 41. The piezoelectric ceramic plate 2 has a plurality of grooves 8 cut by a thin disk-shaped diamond blade or the like. The side wall 11 serving as the side surface of the groove 8 is polarized in the direction of the arrow 5. The grooves 8 are of the same depth and are parallel. The depth of each of the grooves 8 gradually becomes shallower toward the one end face 15 of the piezoelectric ceramic plate 2, and a shallow groove 16 is formed near the one end face 15. And on the inner surface of the groove 8,
Metal electrodes 13 are formed on the upper half of both side surfaces by sputtering or the like. Also, on the inner surface of the shallow groove 16,
Metal electrodes 9 are formed on the side and bottom surfaces by sputtering or the like. As a result, the metal electrodes 13 formed on both sides of the groove 8 are replaced with the metal electrodes 9 formed in the shallow groove 16.
Are linked by Next, the cover plate 3 is formed of a ceramic material or a resin material. Then, on the cover plate 3, by grinding or cutting, or the like,
An ink inlet 21 and a manifold 22 are formed. Then, the surface of the piezoelectric ceramic plate 2 on the processing side of the groove 8 and the surface of the cover plate 3 on the processing side of the manifold 22 are bonded with an adhesive 4 such as an epoxy-based adhesive (see FIG. 6). Accordingly, the ink jet printer head 1 has a plurality of ink flow paths 12 (FIG. 6) that cover the upper surface of the groove 8 and are spaced apart from each other in the horizontal direction. As shown in FIG. 6, the ink flow path 12 has an elongated shape with a rectangular cross section, and all the ink flow paths 12 are filled with ink. As shown in FIG. 3, each ink flow path 1 is provided on the end faces of the piezoelectric ceramic plate 2 and the cover plate 3.
The nozzle plate 31 provided with the nozzle 32 at a position corresponding to the position 2 is adhered by an adhesive 33 such as an epoxy type (see FIG. 4). This nozzle plate 31
Is formed of a plastic such as polyalkylene (eg, ethylene) terephthalate, polyimide, polyetherimide, polyetherketone, polyethersulfone, polycarbonate, or cellulose acetate. A substrate 41 is bonded to the surface of the piezoelectric ceramic plate 2 opposite to the processing side of the groove 8 with an adhesive (not shown) such as an epoxy resin. The conductive layer pattern 42 is formed on the substrate 41 at a position corresponding to the position of each ink flow path 12. The conductive layer pattern 42 and the metal electrode 9 on the bottom surface of the shallow groove 16 are connected by a conductive wire 43 by known wire bonding or the like. Next, the configuration of the control unit will be described with reference to FIG. 5 which shows a block diagram of the control unit. The conductive layer patterns 42 formed on the substrate 41 are individually connected to the LSI chip 51. Further, the clock line 52, the data line 53, the voltage line 54 and the ground line 55 are also LS.
It is connected to the I chip 51. The LSI chip 51
Based on the continuous clock pulse supplied from the clock line 52, it is determined which nozzle 32 should eject the ink droplet according to the data appearing on the data line 53. Then, the voltage V of the voltage line 54 is applied to the pattern 42 of the conductive layer that is connected to the metal electrode 13 in the ink flow path 12 to be driven. Further, a voltage of 0 V of the ground line 55 is applied to the conductive layer pattern 42 that is connected to the metal electrode 13 other than the ink flow path 12 to be driven. Next, the operation of the ink jet printer head 1 will be described with reference to FIGS. LSI chip 5
1 determines that ink is to be ejected from the ink flow path 12b of the inkjet printer head 1 according to required data. Then, a positive drive voltage V is applied to the metal electrodes 13e and 13f, and the metal electrodes 13d and 13g are grounded. As shown in FIG. 6, an arrow 14 is provided on the side wall 11b.
A driving electric field in the direction b is generated, and an arrow 14
A driving electric field in the direction of c is generated. Then, since the driving electric field directions 14b and 14c are orthogonal to the polarization direction 5,
The side walls 11b and 11c are formed by the piezoelectric thickness-shear effect.
In this case, the ink flow path 12b is rapidly deformed toward the inside. Due to this deformation, the volume of the ink flow path 12b decreases, the ink pressure rapidly increases, a pressure wave is generated, and ink droplets are ejected from the nozzle 32 (FIG. 3) communicating with the ink flow path 12b. When the application of the driving voltage V is stopped,
Since the side walls 11b and 11c gradually return to the positions before deformation (see FIG. 5), the ink pressure in the ink flow path 12b gradually decreases. Then, ink is supplied from the ink supply port 21 (FIG. 6) into the ink flow path 12b through the manifold 22 (FIG. 6). However, in the above-described conventional droplet ejecting apparatus, the ink droplets are ejected by changing the volume of the ink flow path 12 by deforming the side wall 11 due to the piezoelectric thickness-shear effect. There is enough ink flow path 12
Requires a change in volume. For this purpose, the elasticity of the adhesive 33 that bonds the nozzle plate 31 to the piezoelectric ceramic plate 2 and the cover plate 3 in FIG. That is, if the elasticity of the adhesive 33 is small, that is, the rigidity is large, the end face of the side wall 11 and the nozzle plate 31
Is fixed, the volume change of the ink flow path 12 due to the piezoelectric thickness-shear effect of the side wall 11 is not sufficiently performed, which affects the ejection of the ink droplet, and the desired ejection speed of the ink droplet cannot be obtained, There has been a problem that ink droplets are not ejected. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to provide a droplet ejecting apparatus capable of constantly and stably ejecting ink droplets. In order to achieve this object, according to the present invention, there is provided a flow path member having an ink flow path having an open end between a plurality of side walls; A nozzle plate adhered to an end of a side wall of the path member with an adhesive and having a nozzle formed so as to communicate with the ink flow path, wherein the volume of the ink flow path is changed by deformation of the side wall of the ink flow path. In a droplet ejecting apparatus that ejects the ink filled in the ink flow path from the nozzle at an injection speed of 1 m / s or more , the nozzle plate is bonded to an end of a side wall of the flow path member. Value obtained by dividing the Young's modulus of the adhesive for the adhesive by the thickness of the adhesive layer of the adhesive is 1 × 10 ⁶ kg / m
characterized in that m ³ or less. In the droplet ejecting apparatus of the present invention having the above structure, the value obtained by dividing the Young's modulus of the adhesive for bonding the nozzle plate by the thickness of the bonding layer is 1 × 10 ⁶ kg / mm. ³
By performing the following, the volume change of the ink flow path due to the deformation of the side wall is obtained by a predetermined change amount , and the ejection speed is 1 m / s or more.
You injection. The present invention will be described below in detail with reference to the drawings. For convenience, the same parts and equivalent parts as those in the conventional example are denoted by the same reference numerals, and detailed description thereof is omitted. The adhesive 4 for bonding the upper surface of the side wall 11 of the piezoelectric ceramic plate 2 to the cover plate 3 will be described. As described above, when the Young's modulus of the adhesive 4 is small, or the adhesive layer of the adhesive 4 is thick, and the elasticity of the adhesive layer of the adhesive 4 is large, that is, the rigidity is small, as shown in FIG. Since the adhesive 4 is deformed in the direction opposite to the direction in which the side wall 11 is deformed, a sufficient change in volume of the ink flow path 12 cannot be obtained. Therefore, an experiment was conducted using a plurality of epoxy adhesives 4 having different Young's moduli (after curing) to change the thickness of the adhesive layer, and to eject ink droplets from the ink jet printer head 1 for each of them. The adhesive 4 used in the experiment is important in Young's modulus after curing, and other properties do not need to be considered in this experiment. FIG. 1 shows the results of the experiment. The thickness of the adhesive layer of the adhesive 4 in the experiment was measured with a microscope. Inkjet printer head 1
The evaluation was performed by measuring the ejection speed of the ink droplets because the ejection speed of the ink droplets is proportional to the change in the volume of the ink flow path 12. Here, the ejection speed of ink droplets and the stability of ink ejection will be described based on experimental experience. First, when the ejection speed is less than 1 m / s, the ink is not ejected (the ink droplets are not separated), or even if it is ejected, the ink is moved to a desired position due to an air flow between the nozzle 32 and the paper. Drops do not adhere and the printing quality deteriorates. Therefore, in order to commercialize the droplet ejection device, the ejection speed needs to be at least 1 m / s or more. Further, the influence of the ink jetting speed on the droplet jetting device is as follows. First, when the nozzle shape is non-uniform or dust or ink adheres to the vicinity of the nozzle, a low ejection speed affects the straightness of the ink. Further, in the carriage scanning type droplet ejecting apparatus, the air movement between the nozzle 32 and the sheet becomes strong due to the movement of the carriage, and when the ejection speed is low, a shift tends to occur at the ink landing point. This is more noticeable when the carriage movement speed is increased for high-speed printing or when the distance between the nozzle and the platen is increased so that printing can be performed on thick paper. Therefore, in consideration of the above several conditions, the injection speed is preferably 3 m / s or more, and the injection speed is 5 m / s in order to realize stable injection.
Above, stable injection can be realized even if all the above conditions are considered. Based on these facts, the evaluation of the ink jet printer head 1 shown in FIG. 1 is based on the assumption that the ejection speed of the ink droplets is 5 m / s or more, 3 to 5 m / s, 1 to 3 m / s.
s and less than 1 m / s. As can be seen from FIG. 1, the ejection speed of the ink droplets is 5 m / s or more in the region above the straight line L3, and the ejection speed is 3 to 5 m / s in the region between the straight lines L3 and L2. Injection speed in the region between 1 and 3 m /
s, the injection speed is less than 1 m / s in the region below the straight line L1. Here, the inclination of the straight lines L1, L2, L3 is a value obtained by dividing the Young's modulus of the adhesive 4 by the thickness of the adhesive 4.
This value is 5 × 10 ³ kg / mm ³ , 5 × 10 ⁴ kg
/ Mm ³ , 1.2 × 10 ⁵ kg / mm ³ . Therefore, the value obtained by dividing the Young's modulus of the adhesive 4 by the thickness of the adhesive 4 is 5 × 10 ³ kg / mm ³ or more, preferably 5 × 10 ⁴ k.
g / mm ³ or more, more preferably 1.2 × 10 ⁵ kg /
If it is not less than ³ mm, stable ejection of ink droplets can be performed. Here, from the above results, it is preferable that the thickness of the adhesive layer is thinner as the rigidity increases, but it is preferable that the thickness is sufficient to completely join the cover plate 3 and the upper surface of the side wall 11. There are also technical limitations for doing so. Therefore, when the thickness of the adhesive layer is increased to some extent, an adhesive having a large Young's modulus may be used in accordance with the required injection speed. As described above, the value obtained by dividing the Young's modulus of the adhesive 4 for bonding the upper surface of the side wall 11 of the piezoelectric ceramic plate 2 to the cover plate 3 by the thickness of the adhesive 4 is 5 × 10 ³ kg / kg. mm ³ or more, preferably 5 × 10 ⁴ k
g / mm ³ or more, more preferably 1.2 × 10 ⁵ kg /
If the material and thickness of the adhesive are selected so as to be not less than ³ mm, a sufficient change in volume of the ink flow path 12 can be obtained by deformation of the side wall 11 due to the piezoelectric thickness-shear effect, and stable ejection of ink droplets Done. Next, the adhesive 33 (see FIG. 4) for bonding the nozzle plate 31 to the end surfaces of the piezoelectric ceramic plate 2 and the cover plate 3 will be described. As shown in FIG. 4, the adhesive 33 is applied to the side wall 11.
The adhesive 33 is formed between the nozzle plate 31 and the ink flow path 12 (FIG. 6), which is formed between the end surface of the piezoelectric ceramic plate 2 including the nozzle plate 31 and the nozzle 32. Not. Generally, a resin or a metal material is used for the nozzle plate 31 in consideration of the formation of the nozzle 32 and the like, and the nozzle plate 31 has a different linear expansion coefficient from the piezoelectric ceramic plate 2 using a ceramic material. Therefore, the piezoelectric ceramic plate 2 and the nozzle plate 3
The adhesive 33 that adheres to the first and second nozzles needs to have a certain degree of elasticity in order to buffer the difference between the linear expansion coefficient of the piezoelectric ceramic plate 2 and the linear expansion coefficient of the nozzle plate 31.
If the elasticity of the adhesive 33 is small, that is, the rigidity is large, the end face of the side wall 11 and the nozzle plate 31 are fixed, and the volume change of the ink flow channel 12 due to the piezoelectric thickness-shear effect of the side wall 11 is sufficiently performed. Not affect ink droplet ejection. Therefore, the thickness of the adhesive layer was changed by using a plurality of epoxy adhesives 33 having different Young's moduli (after curing), and an ink droplet ejection experiment of the ink jet printer head 1 was performed for each of them. The adhesive 33 used in the experiment is important in Young's modulus after curing, and other properties do not need to be considered in this experiment. The evaluation of the ink jet printer head 1 was performed by measuring the ejection speed of ink droplets. The ejection speed of the ink droplets is 5 m / s or more, 3 to 5 m / s, and 1 to 3 m / s for the reason described above.
s and less than 1 m / s. The thickness of the adhesive 33 was measured by a microscope after the inkjet printer head 1 was cut in the direction of the ink flow path 12 after the ejection experiment. FIG. 2 shows the results of the experiment. Figure 2 shows the Young's modulus
Use four different adhesives and change the thickness of the adhesive layer
Nozzle plate 3 and piezoelectric ceramic plate
2 to produce an inkjet printer head,
Results of measuring ink droplet ejection speed for each head
Is expressed in relation to the Young's modulus and thickness of the adhesive.
You. As can be seen from FIG. 2, the ejection speed of the ink droplets is 5 m / s or more in the region below the straight line M3, and the ejection speed is 3 to 5 m / s in the region between the straight lines M3 and M2. Injection speed in the region between 1 and 3 m /
s, the injection speed is less than 1 m / s in the region above the straight line M1. Here, the inclination of the straight lines M1, M2, M3 is a value obtained by dividing the Young's modulus of the adhesive 33 by the thickness of the adhesive 33, and this value is 1 × 10 ⁶ kg / mm ³ , 5 × 10 ⁵
kg / mm ³ , 3 × 10 ⁵ kg / mm ³ . Therefore, the value obtained by dividing the Young's modulus of the adhesive 33 by the thickness of the adhesive 33 is 1 × 10 ⁶ kg / mm ³ or less, preferably 5 × 10 ⁶ kg / mm ³ or less.
⁵ kg / mm ³ or less, more preferably 3 × ¹⁰ 5 kg /
If it is not more than ³ mm, stable ejection of ink droplets can be performed. As described above, the value obtained by dividing the Young's modulus of the adhesive 33 for bonding the nozzle plate 31 to the end surfaces of the piezoelectric ceramic plate 2 and the cover plate 3 by the thickness of the adhesive 33 is 1 × 10 ⁶ kg. / Mm ³ or less, preferably 5 × 10 ⁵ kg / mm ³ or less, more preferably ³ × 10 ⁵ kg / mm ³ or less.
If the material and the thickness of the adhesive are selected so as to be 10 ⁵ kg / mm ³ or less, the side wall 11 due to the piezoelectric thickness-slip effect can be obtained.
Due to this deformation, a sufficient change in volume of the ink flow path 12 is obtained, and stable ejection of ink droplets is performed. Based on the above experimental results, the ink jet printer head 1 according to the present embodiment was prepared, and printing was attempted as a carriage scanning type droplet ejecting apparatus.
The specification of the droplet ejecting apparatus is that the carriage moving speed is 0.635 m / s, and the distance between the nozzle and the paper surface is 1.
5 mm. When the ink jet printer head 1 is manufactured, if the material and the bonding process of the adhesive 4 for bonding the cover plate 3 to the piezoelectric ceramic plate 2 and the adhesive 33 for bonding the nozzle plate 31 are different. Since this leads to waste of manufacturing costs and manufacturing time, in the present embodiment, the bonding is performed in the same bonding step using an adhesive of the same material. Accordingly, the Young's modulus and the thickness of the adhesive become equal, and therefore it is necessary to set the Young's modulus and the thickness so as to satisfy both of the above two experimental results. From the above experimental results, the most preferable relationship between the Young's modulus and the thickness is that the value obtained by dividing the Young's modulus by the thickness is 1.2 × 10 ⁵ kg / mm ³ or more and 3 × 10 ⁵ kg / m 3.
m ³ is equal to or less than. Therefore, in this embodiment, the Young's modulus is 73
Using an adhesive of 0 kg / mm ² , the thickness of the adhesive is 3 μm
And The value obtained by dividing the Young's modulus in this case by the thickness is 2.
Since it is 43 × 10 ⁵ kg / mm ³ , both conditions can be satisfied. The print sample produced by the ink jet printer head 1 produced as described above, when printed as a droplet ejecting apparatus, was evaluated with a focus on the deviation of the ink landing point. Has been confirmed. Although an epoxy adhesive is used in this embodiment, an acrylic or phenol adhesive may be used. As is apparent from the above description, in the liquid droplet ejecting apparatus of the present invention, the adhesive for bonding the end of the flow path member forming the ink flow path to the nozzle plate is used. The value obtained by dividing the Young's modulus by the thickness of the adhesive layer is 1 × 10 ⁶ kg / m
m ³ than to below, sufficient volume change of the ink flow path is obtained by the deformation of the side walls, it can be performed by <br/> stable ink injection at 1 m / s or more ejection velocity. It is also effective when there is a difference in linear expansion coefficient between the flow path member and the nozzle plate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the Young's modulus of an adhesive for bonding a piezoelectric ceramic plate and a cover plate and the thickness of an adhesive layer in one embodiment of the present invention. FIG. 2 is a graph showing a relationship between a Young's modulus of an adhesive for bonding a piezoelectric ceramic plate and a nozzle plate and a thickness of an adhesive layer in the embodiment. FIG. 3 is a perspective view illustrating a configuration of the ink jet printer head according to the embodiment and the related art. FIG. 4 is a cross-sectional view of the ink jet printer head according to the embodiment and the related art, which is cut in a flow direction of an ink flow path. FIG. 5 is an explanatory diagram showing a control unit of the ink jet printer head of the embodiment and the prior art. FIG. 6 is a sectional view showing a configuration of the ink jet printer head according to the embodiment and the prior art. FIG. 7 is an explanatory view showing an operation state of the ink jet printer head according to the embodiment and the prior art. FIG. 8 is an explanatory view showing a state of the adhesive layer when the piezoelectric thickness-shear effect of the side wall is obtained when the elasticity of the adhesive layer between the side wall and the cover plate of the inkjet printer head is large. [Description of Signs] 2 Piezoelectric ceramic plate 11 Side wall 12 Ink channel 31 Nozzle plate 33 Adhesive

Continuation of front page       (56) References JP-A-4-348949 (JP, A)                 JP-A-4-282254 (JP, A)                 JP-A-4-357037 (JP, A)                 JP-A-5-345417 (JP, A)                 Hikaru 4-132949 (JP, U)

Claims (1)

(57) Claims: 1. A flow path member having an ink flow path having an open end formed between a plurality of side walls, and an adhesive bonded to an end of the side wall of the flow path member with an adhesive. A nozzle plate having nozzles formed therein so as to communicate with the ink flow path, wherein the side wall of the ink flow path is deformed to change the volume of the ink flow path, and the ink flow path is filled. A droplet ejecting apparatus for ejecting the ink from the nozzle at an ejection speed of 1 m / s or more , wherein a Young's modulus of an adhesive for adhering the nozzle plate to an end of a side wall of the flow path member is determined by the adhesive. Wherein the value obtained by dividing by the thickness of the adhesive layer is 1 × 10 ⁶ kg / mm ³ or less.