JP2006076039A - Inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus with a nozzle which can stably form particles without being affected by fluid resonance, even if a sonic speed in ink is changed by a change in temperature. <P>SOLUTION: The nozzle of the inkjet recording apparatus comprises an orifice for emitting a jet of ink, an exciting means for exciting the ink, and at least three stepped ink channels with mutually different cylindrical diametral holes for guiding the ink to the orifice, are connected together. In the nozzle of the inkjet recording apparatus, the exciting means is arranged in such a manner as to be positioned on the outer peripheral part of the stepped ink channel, and the lengths of the at least three ink channels different in the inside diameter are set shortest on the side of the orifice, so that this short part can be separated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus that performs printing by ejecting ink continuously from nozzles.

  A continuous inkjet recording device that ejects ink continuously from a nozzle, charges ink droplets in the middle of flight, and deflects the ink droplets with an electric field for printing. Numbers and symbols are printed on a metal can or plastic surface. It is widely used as a device to perform. Conventionally, as shown in Patent Document 1, pressurized ink is supplied to the ink chambers of the nozzles of the ink jet recording apparatus, and the inks are vibrated using vibration amplification by fluid resonance of the ink chambers. It is known that ink is made to fly from an orifice present at the end of a chamber.

JP-A-5-254117

  In the above prior art, the nozzle drive frequency (80 kHz) is set between two fluid resonance frequencies (70 kHz and 90 kHz). By vibrating the ink chamber with the piezoelectric element at this driving frequency, the ink flying from the orifice is made into particles.

  However, the speed of sound in ink generally used in an ink jet recording apparatus is 1200 to 1400 m / s at room temperature, but varies depending on the temperature. In the temperature range of 0 to 45 ° C., which is the operating temperature range of the ink jet recording apparatus, the speed of sound in the ink changes by about ± 10% with respect to the normal temperature. Since the fluid resonance frequency in the ink flow path is proportional to the sound velocity, the fluid resonance frequency also changes by about ± 10% when the sound velocity changes. Therefore, the two fluid resonance frequencies change in the range of 70 ± 7 kHz and 90 ± 9 kHz. For this reason, the amplification factor of vibration at a driving frequency of 80 kHz varies greatly with temperature, and there is a problem that particle formation becomes unstable. In order to reduce this instability, if the two fluid resonance frequencies are greatly separated from the nozzle drive frequency, a sufficient amplification factor cannot be obtained. Therefore, it is necessary to increase the amplitude of the piezoelectric element. There was a problem that an increase in size and an increase in input voltage were essential.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ink jet recording apparatus having a nozzle capable of forming stable particles without being affected by fluid resonance even when the speed of sound in ink changes due to temperature change. It is.

  In order to achieve the above object, an ink jet having an orifice for ejecting ink, a vibration means for vibrating ink, and a stepped ink flow path in which three or more cylindrical holes having different inner diameters for guiding ink to the orifice are connected. In the nozzle of the recording apparatus, the vibration means is arranged so as to be on the outer periphery of the stepped ink flow path. The lengths of the three or more ink flow paths having different inner diameters are configured such that the short side can be separated so that the short side can be separated. Further, when the separation part is joined to form the nozzle, a rubber seal member is provided inside the separation part in order to prevent ink leakage from the connection part of the ink flow path. In addition, three or more flow paths having different inner diameters are configured such that the inner diameters become smaller toward the orifice.

  According to the present invention, since the mechanical resonance frequency of the ink flow path is close to the drive frequency for vibrating the piezoelectric element that is the vibration means, the vibration of the piezoelectric element can be efficiently transmitted to the ink. Therefore, the piezoelectric element can be made small, and the nozzle can be miniaturized. Also, by making the fluid resonance frequency of the ink flow path higher than the nozzle drive frequency, stable particle formation is possible without being affected by fluid resonance even if the sound velocity in the ink changes due to temperature changes. There is an effect. Further, since a part of the ink flow path can be separated, there is an effect that it is easy to clean when the orifice at the end of the ink flow path is clogged. Furthermore, there is an effect that the dimensional accuracy at the time of manufacturing the orifice at the nozzle tip is improved.

Embodiments of the present invention will be described below with reference to the drawings.
First, FIG. 6 shows an overview of the ink jet recording apparatus.

  Inside the main body 100, there are a control system of the printing apparatus and an ink circulation system, and maintenance work can be performed by opening and closing the door 105. A cable 103 extends from the main body 100. The cable 103 includes a pipe for sending ink from the main body 100 to the print head 101, a pipe for collecting ink from the print head 101 to the main body 100, and a wiring for sending an electric signal to the print head 101. Further, the main body 100 is provided with a touch panel type liquid crystal panel 104 for a user to input print contents, print specifications, and the like. The liquid crystal panel 104 displays the control contents of the recording device, the operating status, and the like. The print head 101 is made of stainless steel, and a printing unit that creates ink particles and controls the flying of the ink particles is housed therein. The ink particles created inside the print head 101 are ejected from an opening 102 provided on the bottom surface and adhere to a recording medium (not shown) to form an image.

  Next, the internal configuration of the main body 100 will be described with reference to FIG.

  On the upper part of the main body 100, electrical parts such as the control board 109 are arranged. Further, circulation system control parts such as the electromagnetic valve 108 and the pump unit 106 are disposed in the lower part 110 of the main body, and an ink container 1 that stores ink to be supplied to the nozzles is housed in the vicinity thereof. The door 105 can be opened and closed, the ink container can be pulled out to the door 105 side, and maintenance work such as ink supply and disposal can be easily performed.

  Next, a schematic configuration of the ink circulation system and the printing unit of the ink jet recording apparatus will be described with reference to FIG.

  The ink supply path 21 includes an ink container 1 that contains ink, a supply pump 2 that pumps ink, a pressure regulating valve 3 that adjusts the ink pressure, a pressure gauge 4 that displays the pressure of the supplied ink, and a filter 5 that catches foreign matter in the ink. The ink is supplied to the nozzle 6. The nozzle 6 has a piezoelectric element. By applying a sine wave of about 70 kHz to the piezoelectric element, ink is ejected from an orifice existing at the end of the nozzle 6 and is divided into ink particles during flight. A recording signal source (not shown) is connected to the charging electrode 7, and by applying a recording signal voltage to the charging electrode 7, the ink particles 8 ejected regularly from the nozzle 6 are charged. Since the upper deflection electrode 9 is connected to a high voltage source (not shown) and the lower deflection electrode 10 is grounded, an electrostatic field is formed between the upper deflection electrode 9 and the lower deflection electrode 10. The charged ink particles 8 are deflected according to the charge amount of the charged ink particles 8 while passing through the electrostatic field, and adhere to a recording medium (not shown) to form an image.

  The ink collection path 22 includes a gutter 11, a filter 12, and a collection pump 14. The ink particles 8 that are not charged by the charging electrode 7 and are not deflected while passing through the electrostatic field are collected by the gutter 11, and ink is collected. It can be returned to the container 1 and reused.

  Next, the nozzle 6 of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a nozzle 6 of the present invention. The nozzle 6 includes a body 30, a piezoelectric element 29 disposed on the outer periphery of the body 30, a protective cover 32, and a joint 27 disposed at one end of the body 30. The body 30 can be divided into a body 30a and a body 30b. This divided portion is configured to be divided at a boundary portion having a different diameter of the ink flow path provided inside. A joint 27 for connecting to the ink supply pipe from the filter 5 is joined to the body 30 with an adhesive. The protective cover 32 is fixed to the body 30 with screws 33. The hole 34 provided in the protective cover 32 is a lead wire outlet for supplying a signal to the piezoelectric element 29.

  Ink is supplied from the joint 27 to the body 30, passes through the ink flow paths 37, 38, and 39 that gradually decrease in diameter in three stages inside the body 30, and is ejected from the orifice 31 ahead. The material of the body 30 is stainless steel, and the ink flow path whose diameter gradually decreases in three stages is manufactured by drilling. The body 30 is divided at the boundary between the flow path 38 and the flow path 39. Therefore, after drilling the flow path 39 on the orifice 31 side, the orifice 31 ahead is manufactured by pressing. The reason for providing the flow paths 37, 38, and 39 having a reduced diameter in three stages will be described later.

  Here, a manufacturing method of the orifice 31 will be described with reference to FIG.

  After the cylindrical ink channel 39 is manufactured by drilling, tapered portions 80 and 82 are formed. This taper angle is about 120 °, the same as the drill tip angle. Thereafter, by pressing using a punch having the same shape at the tip of the orifice, the tapered portion 80 is eliminated, and the tapered portion 81 and the orifice 31 having a diameter of about 65 μm are formed along the shape of the tip of the punch.

  Next, the piezoelectric element 29 will be described in detail with reference to FIG. The piezoelectric element 29 has a cylindrical shape, and electrodes are provided on the inner and outer surfaces. The inner surface electrode 51 of the piezoelectric element 29 is provided on the entire inner surface of the cylindrical portion and the end surface of the piezoelectric element 29. That is, the piezoelectric element 29 is provided so as to surround the outer surface side. An outer surface electrode 52 is provided on the outer surface of the piezoelectric element 29 so that an electrodeless portion 54 can be formed to maintain electrical insulation with the inner surface electrode 51. In the piezoelectric element 29, the inner electrode 51 is adhesively bonded to the body 30 so that the vibration of the piezoelectric element 29 can be efficiently transmitted to the body 30. Since the inner surface electrode 51 of the piezoelectric element 29 is in contact with the body 30, conduction between the body 30 and the inner surface electrode 51 can be ensured. For this reason, the piezoelectric element 29 can be vibrated by connecting a transmitter that generates a sinusoidal electric signal to the outer electrode 52 and the body 30.

  FIG. 4 is a detailed view of the body 30. The bodies 30a and 30b have a cylindrical shape with a combined length L0, and ink channels 37 and 38 having lengths L1 and L2 are formed inside the body 30a. The flow path 37 is formed by inserting and bonding a joint 27 having a predetermined length so that the length is L1. An ink flow path 39 having a length L3 is formed inside the body 30b. Further, the outer diameter of the body 30 a is set according to the inner diameter of the piezoelectric element 29 provided at the root portion 60.

Here, when the body 30 (the combined body of the body 30a and the body 30b) is vibrated by applying a high-frequency voltage to the piezoelectric element 29, how the vibration is transmitted to the ink flowing in the body will be described. The vibration in the voltage range that can be applied to the piezoelectric element 29 is very small and insufficient for particle formation. Therefore, the body 30 is configured to amplify the vibration so that the axial resonance frequency f _b (mechanical resonance) is in the vicinity of the nozzle drive frequency f _n . The axial resonance frequency f _b can be obtained by the following equation.

f _b = nV _b / 4 (L + k ₁ )
Here, n is an integer value determined by a resonance mode, L is the length of the body 30, the V _b are those sound velocity in the body 30, k ₁ is determined experimentally by the correction factor. In this embodiment, the material is stainless steel, and V _b = 5000 m / s. The optimum driving frequency f _{n of the} nozzle is almost determined by the orifice diameter (the hole diameter in this embodiment is Φ0.065 mm), and in this embodiment, f _n = 70 kHz. The length of L that makes f _{n the} calculated primary resonance frequency f _b (n = 1) is about 22 mm. However, since the primary resonance frequency actually changes depending on the shape of the joint, it is appropriate. The length of L is in the range of about 22 to 26 mm. Thereby, the vibration of the piezoelectric element 31 is amplified by the body 30, and the ink is vibrated, so that efficient particle formation is possible.

  Next, the ink flow path of the body 30 will be described. One end of the body 30 is processed with an orifice 31 (hole diameter Φ0.065 mm) through which the orifice ejects ink.

  Each of the ink flow paths 37, 38, and 39 has a stepped structure with different inner diameters. That is, the inner diameter becomes smaller as going to the orifice 31 side. This is because a fluid resonance close to the drive frequency is not generated by increasing the fluid resonance frequency generated in the ink flow path. The fluid resonance frequency of the ink flow path is obtained by the following equation.

f _r = nV _i / 4 (l + k ₂ )
Here, n is an integer value determined by the resonance mode, V _i is the speed of sound in the ink, l is the length of the ink flow path, and k ₂ is a correction coefficient. Since the orifice diameter is sufficiently smaller than the hole diameter of the ink flow path 39, the boundary condition of one end closing and one end opening is taken, n = 1 in the primary mode, n = 3 in the second mode, and n = 3 in the third mode. 5 Further, since the ink flow paths 37 and 38 are boundary conditions with both ends open, n = 2 in the primary mode, n = 4 in the secondary mode, and n = 6 in the tertiary mode. In general, the speed of sound in ink is 1200 to 1400 m / s at room temperature, but the speed of sound in ink varies depending on the temperature. The amount of change is about ± 10% at 0 to 45 ° C., which is the operating temperature range of the ink jet recording apparatus. Therefore, in this embodiment, in order to prevent the particle formation from being affected by fluid resonance, the flow path length l is set so that the fluid resonance frequency is sufficiently higher than the driving frequency. Specifically, the diameter of the flow path was divided into three or more stages, and each flow path length l was set to be shorter than ½ of the flow path length L. This flow path length l becomes L1, L2, and L3 in FIG. By setting in this way, the fluid resonance frequency of the ink flowing through each flow path can be made higher than the drive frequency. Here, the length of the ink flow path 39 is shorter than the length of the ink flow paths 37 and 38 so that the fluid resonance frequency is higher than that of the other ink flow paths 37 and 38. This is because the fluid resonance characteristic of the ink flow path 39 closest to the orifice 31 affects the particle formation.

  With the above configuration, vibration amplification using mechanical resonance with little change with respect to temperature can be obtained without being affected by fluid resonance that has a large change with respect to temperature, so that stable particle formation is possible. Become.

  By the way, when printing is performed using a nozzle as shown in FIG. 1, the orifice 31 may be clogged due to the high volatility of the ink solvent. In addition, fine particles that could not be removed by the filter in the ink circulation path may be clogged. In such a case, the nozzle is removed from the ink jet recording apparatus, immersed in a solvent, and cleaned by ultrasonic cleaning. When the length of the nozzle is long, it often takes time to clean the inside of the nozzle by ultrasonic cleaning. When the body having the shape shown in FIG. 4 is manufactured, the length of the punch for processing required for manufacturing the orifice 31 at the tip of the flow path 39 by press processing is as follows. It is a length obtained by adding the length of L0 which is 30 to the length attached to the press machine. The length is about 35 mm, and the production accuracy of the punch itself is problematic. In addition, since a minute hole is present at the end of a long punch, there is a problem that the punch is easily damaged. Therefore, as shown in FIG. 2, the structure capable of separating the body 30 into the bodies 30 a and 30 b can facilitate cleaning, improve the processing accuracy of the orifice 31, and extend the life of the press punch. be able to. The structure of the separation part will be described with reference to FIG.

  FIG. 2 is an enlarged view of the nozzle tip in FIG. The bodies 30a and 30b are separate members and are structured to be joined by screws 50. A rubber plate or packing, which is a seal member 40, or an O-ring is attached to the boundary between the flow path 38 and the flow path 39 so as to prevent leakage of ink flowing from the flow path 38 to the flow path 39.

  As described above, in an ink jet recording apparatus that records ink droplets ejected from the tip of a nozzle by deflecting them onto a surface to be recorded, the nozzle portion is formed in a cylindrical shape, and the cylinder is also formed on the outer diameter side. A vibrating portion made of a piezoelectric element having a shape is provided so that the diameter of the ink flow path inside the nozzle changes in three stages, the diameter decreases toward the ejection hole side, and the second stage at the tip. The third stage (tip portion) where the diameter of the flow path changes can be divided, so that it is possible to facilitate the manufacture of the nosle and the maintenance easily.

It is sectional drawing of the nozzle which is one Example of this invention. It is sectional drawing of the front-end | tip part of the nozzle which is one Example of this invention. It is sectional drawing of the orifice vicinity in the front-end | tip of the nozzle which is one Example of this invention. It is sectional drawing of the body used for the nozzle which is one Example of this invention. It is sectional drawing of the piezoelectric element used for the nozzle which is one Example of this invention. It is a general-view figure of an inkjet recording device It is a figure which shows the inside of the main body of an inkjet recording device. It is a figure explaining the mode of the ink circulation in an inkjet recording device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ink container, 2 ... Pump, 6 ... Nozzle, 7 ... Charging electrode, 8 ... Ink particle, 9 ... Deflection electrode, 11 ... Gutter, 27 ... Joint, 29 ... Piezoelectric element, 30 ... Body, 31 ... Orifice

Claims (5)

In an inkjet recording apparatus having an orifice for ejecting ink, an ink flow path for guiding ink to the orifice, and a vibration means for applying vibration to the ink,
The vibration means is disposed on the outer periphery of the ink flow path, and the ink flow path has a stepped structure in which three or more cylindrical holes having different inner diameters are connected, and the ink flow path has a stepped portion having a different inner diameter. An ink jet recording apparatus that can be divided at positions. The inkjet recording apparatus according to claim 1, wherein
2. An ink jet recording apparatus, comprising: an ink channel continuous with the orifice; and a boundary between the ink channel and a channel having a different inner diameter. The inkjet recording apparatus according to claim 1 or 2,
2. An ink jet recording apparatus according to claim 1, wherein the diameter of the ink flow path decreases as the diameter approaches the orifice. The inkjet recording apparatus according to claim 2,
An ink jet recording apparatus, wherein the divided ink flow paths are coupled by screws. 5. The ink jet recording apparatus according to claim 4, wherein an ink leakage preventing member is provided at a boundary between the divided ink flow path coupling portions.

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