JPH0237299B2 - KIROKUHETSUDO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a recording head applied to a so-called inkjet recording method, and more specifically, an inlet side end having an ejection orifice for ejecting liquid, a pressure generating section, and an inlet for supplying liquid to the pressure generating section. Department,
The present invention relates to a recording head that is equipped with an electromechanical transducer and is applied to a recording method that performs recording by forming flying droplets. In particular, the present invention is directed to relatively liquid droplets in which the ejection of droplets of a recording liquid called ink from an ejection orifice is controlled by an electrical input signal applied to the electromechanical transducer. Discharge pressure is small,
drop on demand
This invention relates to a recording head applied to a type of inkjet recording method. Examples of recording heads applicable to the drop-on-demand type inkjet recording method include those described in publications such as USP 3,683,212 and USP 3,832,579. This type of recording head is a cylindrical member made of, for example, glass, with one end tapered and provided with an ejection orifice of a predetermined diameter. An electromechanical transducer is fixedly attached to the exterior, and an electrical pulse signal is applied to the transducer to change its inner diameter in a pulse manner, and the actuation force is applied to at least a portion of the cylindrical member. When the pressure is transmitted to the liquid (ink) in the pressure generating part consisting of the wall surface,
It cannot be denied that there is a decrease in transmission efficiency and transmission speed. Therefore, if an electrical pulse signal is applied continuously and the pulse repetition application frequency is increased, satellites may be generated or the direction of droplet flight may be divided into two, making it difficult to maintain uniform droplets. It was observed that droplets became difficult to form under the same condition, irregularity of droplet flying speed occurred, and droplet generation efficiency decreased, making it impossible to expect stable recording and high quality. There were cases where recorded images could not be obtained. In addition, when a recording head like the one described above is mounted on the main body of the device and recording is performed by reciprocating scanning printing operation, such as in a serial printer, it is necessary to avoid the effects of vibration during return or acceleration of scanning movement. As a result, the droplets may not be ejected smoothly, the flying direction of the ejected droplets may not be stable, or the size of the ejected droplets may vary, resulting in a reduction in print quality. Furthermore, the influence of such reciprocating scanning of the recording head becomes greater as the recording head is moved at higher speeds, and in particular,
Shock to the head during return causes unnecessary droplet ejection or liquid leakage from the ejection orifice, and many efforts have been made to prevent shock during return. Furthermore, in order to drive the electro-mechanical transducer with low voltage, conventional recording heads have one tip of the electro-mechanical transducer installed on the outer surface of the cylindrical member connected to the ejection orifice. Efforts have been made to install the recording head as close as possible, but although it is true that droplets are ejected at a low voltage in such conventional recording heads, the droplet ejection frequency is increased, that is, the droplet ejection frequency is increased to When attempting to perform high-speed recording by increasing the frequency of droplet ejection, the stable droplet ejection voltage range (called voltage margin) tends to become narrower, and the tolerance range for drive voltage fluctuations becomes narrower. It was causing some inconvenience at the top. Therefore, the minimum voltage for stable droplet ejection (threshold voltage
It is desirable to have a recording head that has a low voltage (Vth) and a wide stable droplet ejection voltage range even if the droplet ejection frequency is increased. The present invention has been developed in view of the above-mentioned points, and the present invention has been made in consideration of the above-mentioned points.
The purpose of the present invention is to provide a recording head that is suitable for use in on-demand type devices, and is particularly designed to prevent external vibrations to the head as described above, especially when recording by scanning the head back and forth at high speed. Provides a recording head that is not easily affected by vibration or movement acceleration during return, reduces pressure loss to ink passing through the pressure generating section, and can perform stable, accurate, and reliable recording at all times. The purpose is to do. Separately, the acting force caused by the sudden pulse-like inner diameter change of the cylindrical electromechanical transducer is transmitted to the liquid in the pressure generating part with high efficiency to effectively generate droplets, and the threshold voltage Vth is increased. Another object of the present invention is to provide a recording head that can sufficiently respond to high-frequency electrical pulse signals with a wide voltage margin and eject droplets stably. The recording head of the present invention includes an ejection orifice for ejecting liquid, a pressure generating section connected to the ejection orifice having a deformable wall surface, and an inlet side end for supplying liquid to the pressure generating section. a cylindrical member having a section, an electromechanical transducer layer coupled to the pressure generating section of the cylindrical member, an inner electrode provided on a surface of the layer on the pressure generating section side, and an inner electrode coupled to the pressure generating section of the cylindrical member; A recording head comprising a cylindrical electromechanical transducer having outer electrodes disposed opposite to each other, wherein a folded portion of the inner electrode to the outer electrode is provided on the ejection orifice side. characterized by something. The recording head of the present invention, which has these characteristics, can stably eject droplets and obtain high-quality prints even when recording by scanning back and forth at high speed, and the droplet ejection frequency range is higher than that of conventional ones. The Vth
It exhibits effects such as being able to follow electrical pulse signals of low frequency and high frequency sufficiently quickly, and being able to eject droplets sufficiently stable against external vibrations. The present invention will be explained below with reference to the drawings. FIG. 1 is a partially cutaway schematic explanatory view schematically showing the structure of an example of a preferred embodiment of the recording head of the present invention. The recording head 1 shown in FIG. 1 has a hydrodynamically substantially smooth and deformable inner wall surface, and is made of a material having relatively high hardness, such as hard or soft glass, quartz glass, or metal such as stainless steel. , a cylindrical member 2 made of ceramics, etc., and the cylindrical member 2
It is equipped with a cylindrical electrical/mechanical transducer element 3 fixed to the outer periphery of the transducer. The cylindrical member 2 is usually
An inlet side end 5 having an inlet 4 for liquid supplied from a liquid supply tank (not shown) provided separately from the recording head through a supply pipe provided as necessary; A liquid ejecting part 7 having a discharging orifice 6 at its tip for discharging the liquid in the shaped member 2, and an inlet side end 5.
and a pressure generating section 8 located between the liquid ejecting section 7 and the liquid ejecting section 7. The circular cross section of the pressure generating part 8 is approximately constant over the entire length of the pressure generating part 8, and the circular cross section of the liquid injection part 7 gradually decreases from the pressure generating part 8 side, and at the end, the liquid ejecting part 7 is discharged. An orifice 6 is formed. The inlet side end portion 5 has a circular cross section that is equal to or approximately equal to the circular cross section of the pressure generating portion 8 over the entire length, and an inlet port 4 is formed at the end thereof. - Located outside the area surrounded by the mechanical transducer 3. The electro-mechanical transducer 3 surrounds the pressure generating section 8, and is designed to prevent blockage and pressure from the electro-mechanical transducer 3 so as to effectively supply pulsed pressure waves to the liquid in the pressure generating section 8. It is tightly attached and fixed to the outer circumferential surface of the cylindrical member 2, for example by press-fitting or by gluing, so as to minimize acoustic energy loss at the interface with the generating part 8. In the recording head 1 of the present invention, the non-functional part (dead zone) L ₂ of the electro-mechanical transducer 3 is arranged on the ejection orifice 6 side, and the electro-mechanical transducer 3 is fixed to the cylindrical member 2. Ru. That is, in the recording head shown in FIG. 1, a cylindrical electro-mechanical transducer element 3, the structure of which is schematically shown as a partial cross-sectional view in FIG. 2, is used. The conversion element 3 is electrically
An inner electrode 10 is provided on the circular side surface of the mechanical transducer layer 9, and an outer electrode 11 is provided on the outer surface.
is folded back at one end of the electromechanical converter layer 9, and a part thereof is pulled out outside the converter layer 9 so as to be separated from the outer electrode 11 by the electrically insulating region 14, and the lead electrode 12 It is devised to facilitate the installation of the depletion zone L2 and to form a depletion zone _L2 , thereby producing the following effects. 13 is a lead electrode of the outer electrode 11. Now, when the electromechanical transducer 3 having the structure shown in FIG. 2 is energized through the lead electrodes 12 and 13, in the area (functional part) _L1 where the inner electrode 10 and the outer electrode 11 face each other, Although the electrical/mechanical conversion function works, the function does not work in the region where the inner electrode 10 and its lead-out portion face each other, that is, the dead zone _L2 . In the present invention, the electromechanical transducer 3 having such a structure is installed in a dead zone as shown in FIG.
It is firmly attached to the cylindrical member 2 so that L ₂ is disposed on the discharge orifice 6 side. By arranging the dead zone L ₂ of the electro-mechanical transducer 3 on the side of the discharge orifice 6 in this way, the liquid ejection part 7 is clamped and is protected against external vibrations and the drive of the electro-mechanical transducer 3. The liquid ejecting section 7 is no longer affected by the accompanying vibrations, and droplet ejection becomes extremely stable. Furthermore, even if there is a certain distance from the ejection orifice 6 to the tip of the functional part _L1 of the conversion element 3, the stable liquid ejection region extends to the low voltage side, and even if the droplet ejection frequency is increased, the droplet remains stable. The ejection area is almost never pinched. In addition, even if the thickness of the cylindrical member 2 is made thinner so that the action of the electromechanical transducer 3 is applied to the liquid in the pressure generating part 8 as effectively as possible, the above characteristics will not be lost. There isn't. In the present invention, the structure of the recording head is designed as described above, but in order to further improve the effect, it is important to add the following design conditions. It was discovered by the following people. That is, the length of the functional part of the electromechanical conversion element 3
The electromechanical transducer 3 is designed and manufactured so that the relationship between L ₁ and the length L ₂ of the non-functional portion satisfies L ₁ /L ₂ ≧1. Also, the length of the functional part of the electrical/mechanical conversion element 3 is
L ₁ [mm], average inner diameter d [mm], average wall thickness t [mm]
Therefore, the object of the present invention can often be more effectively achieved by designing and manufacturing the electromechanical conversion element 3 so as to satisfy the condition L ₁ /dt≧20 [mm ^-1 ]. It is clear from the experimental results that. The present invention will be described below with reference to Examples. Example 1 The presence or absence of a non-functional part of an electromechanical transducer and its position were investigated. 1) Electrical/mechanical conversion element... Cylindrical piezoelectric element Γ Lead zirconate titanate Γ Outer diameter 1.0 mm, Inner diameter 0.7 mm, Total length 10 mm 2) Nozzle... Made of hard glass Γ Outer diameter 0.65 mm, Inner diameter 0.55 mm, Total length 15mm 3) Liquid injection part...Length = 1.2mm 4) Ink used...Water + polyhydric alcohol + dye 5) L ₁ (functional part) = 7.5mm L ₂ = (non-functional part) = 2.5
mm The results are shown in Table 1 and Figure 3. In the figure, the area between the solid line and the dotted line is the area where ink droplets are stably ejected. Also, those marked with ○ and ● are the heads of the present invention,
The head marked with △ and ▲ is the comparative head 1 in which the functional part of the electromechanical transducer is placed adjacent to the liquid ejection part, contrary to the head of the present invention, and the head marked with □ and ■ is the shape of the head of the present invention. These are the measurement results of comparative head 2 which has no non-functional parts. Here, 〇, △, and □ indicate threshold values, and ●, ▲, and ■ indicate unstable ejection occurrence values. Table 1 below shows the results of measuring the droplet ejection stability while varying the drive frequency when each of the above heads was scanned at right angles to the droplet ejection direction. However, as the drive voltage, the center voltage of the stable ejection region in FIG. 3 was used for each head. Also, the scanning speed for each head is set at a frequency of 1 [K
10 cm/sec for frequency 2 [KHz], 20 for frequency 2 [KHz]
cm/sec, and in the case of a frequency of 5 [KHz], the rate was 50 cm/sec. It is clear from Table 1 and FIG. 3 that the head of the present invention has the best droplet ejection performance.

[Table] Example 2 The relationship between L ₁ /L ₂ and stable ejection of droplets was determined. The head specifications were basically the same as in Example 1, but the length of the cylindrical member was set to be +5 mm to the total length (L ₁ +L ₂ ) of the electromechanical conversion element. The position of L ₂ took the form shown in FIG. The results are shown in Figure 4. From the results shown in FIG. 4, it is recognized that satisfying the relationship L ₁ /L ₂ ≧1 is more advantageous for discharge performance. In FIG. 4, ◯ indicates good ejection, △ indicates weak ejection force, and × indicates poor ejection. Example 3 The length L ₁ [mm] of the functional part of a cylindrical piezoelectric element (electrical/mechanical transducer element) and the length L ₂ of the non-functional part are kept constant, and the inner diameter d [mm] and inner thickness of the element are The discharge performance of the head was evaluated when changing t [mm]. The head specifications are basically the same as in the first embodiment. The results are shown in Table 2. From Table 2, L ₁ /dt≧20
It is recognized that satisfying the relationship [mm ^-1 ] is more advantageous for discharge performance.

[Table] ○...Good discharge △...Discharge force not strong but well within practical range ×...Failure to discharge

[Brief explanation of drawings]

FIG. 1 is a schematic partially broken cross-sectional schematic explanatory diagram showing an outline of one preferred embodiment of the recording head of the present invention, and FIG. FIGS. 3 and 4 are graphs showing the results of the respective examples. 1... Recording head, 2... Cylindrical member, 3... Electricity.
Mechanical conversion element, 5... Inlet side end, 7... Liquid injection part, 8... Pressure generation part.

Claims (1)

[Claims] 1. A cylindrical cylinder having a discharge orifice for discharging liquid, a pressure generating part having a deformable wall surface and connected to the discharge orifice, and an inlet side end for supplying liquid to the pressure generating part. a member, an electromechanical transducer layer, an inner electrode coupled to the pressure generating portion of the cylindrical member, and an inner electrode provided on a surface of the layer facing the pressure generating portion, and facing each other with the layer interposed therebetween. A recording head comprising a cylindrical electromechanical transducer having an outer electrode, characterized in that a folded portion of the inner electrode toward the outer electrode is provided on the ejection orifice side. recording head.