JPH02139243A - Inkjet head - Google Patents

Abstract

PURPOSE:To obtain an ink feed apparatus which is high in reliability and stability without leaking an ink by providing an ink retaining means having a narrow gap into which said ink is retained by the capillary action, a nozzle forming member having one or more nozzle openings, a pressure generating means for generating a pressure assuring flying in the form of ink drops and a filter means placed within said ink retaining means. CONSTITUTION:When a selective electric signal is applied to a vibrator 24, a piezoelectric element shrinks by the piezoelectric effect, whereas a foil member which is high in rigidity is restricted to change its size. Accordingly, the vibrator is deformed and shifted to the side of a nozzle plate 21, whereby a pressure is generated at a very small gap between the vibrator 24 and nozzle plate 21. Consequently, ink drops are discharged by this pressure. At this time, the volume of a hot melt ink is greatly changed when the ink changes its phase, making it impossible to avoid generation of air bubbles inside an ink retaining means. However, a filter 40 placed inside the ink retaining means can play a role as an air trap, so that the air bubbles can be prevented from entering the vicinity of the pressure generating means subsequent to the consumption of the ink 32.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording apparatus such as a printer that flies ink droplets to form an ink image on a medium such as recording paper, and a recording method therefor. The present invention relates to the configuration of an inkjet printer head.

[Prior Art] A conventional inkjet head has a structure in which liquid ink stored in an ink cartridge is passed through a flexible tubular member and a filter means installed within the tubular member without coming into contact with outside air. A method of supplying liquid ink near a pressure generating means, and a method of supplying liquid ink stored in an ink cartridge into a sub-tank connected to the pressure generating means, and supplying the ink to an inkjet head through a filter means installed in the sub-tank. Are known.

[Problems to be Solved by the Invention] In the inkjet head of the above-mentioned prior art, the ink in the tubular member is supplied to the vicinity of the pressure generating means without contacting the outside air through the flexible tubular member. Because it is affected by the acceleration and deceleration of the carriage on which the head is mounted, the ink pressure near the pressure generating means fluctuates, making it impossible to obtain good ink droplet ejection characteristics.Furthermore, since the ink is isolated from the outside air, it is difficult to obtain good ink droplet ejection characteristics. This method has the problem that a highly reliable inkjet head cannot be obtained due to the strong influence of the generated air bubbles.

In addition, because the distance between the filter means and the ink droplet ejection means is relatively large, new molten matter may be deposited or bubbles may be generated in the ink along that path, which may cause nozzle clogging or the inability to eject ink droplets. It has the problem of becoming.

In addition, with the method of supplying into a sub-tank connected to a pressure generating means, if the inkjet head is placed in an unexpected situation such as being placed upside down, liquefied ink may leak, seriously affecting the entire device. Furthermore, since the ink level within the sub-tank varies greatly, the filter means is exposed to the air and the ink supply path is cut off, making it impossible to eject ink droplets.

The purpose of the present invention is to solve these problems, to provide easy operations such as ink replenishment, high operability, simple configuration, and easy miniaturization of the device. The object of the present invention is to provide a highly reliable and safe ink supply device that can eject ink droplets even if the ink droplets are not leaked.

Another object of the present invention is to provide a highly reliable ink supply device that is not affected by acceleration or deceleration of a carriage and has good ink droplet ejection characteristics.

Another object of the present invention is to provide an inkjet head having good ink droplet ejection characteristics without the generation of precipitation or bubbles between the pressure generating means and the filter means.

[Means for Solving the Problems] An inkjet head of the present invention includes a casing disposed to face a recording medium, and an ink holder disposed within the casing and having a narrow gap for retaining ink by capillary action. a nozzle forming member forming a part of the ink holding means and having at least one or more nozzle openings disposed to face the recording medium; and a nozzle forming member disposed within the ink holding means and having at least one nozzle opening. The apparatus is characterized by comprising a pressure generating means for generating a pressure that allows the ink near the opening to fly as ink droplets, and a filter means installed within the ink holding means.

Note that the ink is in a solid state at room temperature, and the housing may be provided with at least one heat source.

Note that the capillary force generated at the nozzle opening may be configured to be larger than the capillary force generated at the filter means.

[Function] In the above configuration of the present invention, since the filter means is installed in the ink holding means having a narrow gap, the ink can only be supplied to the pressure generating means by passing through the filter means without running out of ink. Moreover, since the pressure generating means and the filter means are located close to each other, air bubbles, dust, etc. are not generated.

[Example] Next, the present invention will be explained based on an example. FIG. 1 is a perspective view of a printer showing an embodiment of the present invention. In the figure, a recording paper 10, which is a recording medium, is wound around a platen 11 and pressed by a feed roller shaft 12. Guide shaft 1
An inkjet head (hereinafter referred to as head) 16 is mounted on a carriage 15 guided by 3.14 and movable in a direction parallel to the platen axis.

The head 16 has a plurality of nozzles that can independently control the ejection of ink droplets, and is scanned in the platen axis direction to selectively eject ink droplets from the nozzles to form an ink image on the recording paper 10. The recording paper 10 is conveyed in the sub-scanning direction perpendicular to the scanning direction by rotation of the platen 11, and printing is performed on the recording paper surface.

Inside the device, there is an ink supply device 1 on the side of the head scanning start position.
8 and an ink container 19 for storing ink (not shown) is attached.

FIG. 2(a) is a sectional view of a head showing an embodiment of the present invention. The container-shaped housing 20 is made of metal materials such as aluminum and SUS, and polysulfone, polyacetal, and ABS.
The recording paper 10, which is a recording medium wound around the platen 11, is placed so that the opening 35 on one side faces the recording paper 10, which is a recording medium wound around the platen 11. On the back of the opening 35,
A housing includes a nozzle plate 21 which is a nozzle forming member in which a required number of nozzle openings 22 are arranged in a row in the platen axis direction, a spacer 23, a vibrator 24 which is a pressure generating means, an electric wiring 25, and an elastic member 26 having rubber elasticity. 20. The vibrator 24 is made of a laminated layer of a piezoelectric element and a foil member such as Ni or SUS to have bimetal-like flexibility, and one end is connected to the rigidity of the housing 20 and the elastic member 26.
Due to the rubber elasticity of the nozzle plate 21 and spacer 2
3, it has a cantilever structure with a fixed end that is clamped under a constant pressure and the other end as a free end. The free end of the vibrator 24 is placed opposite the nozzle opening 22 formed in the nozzle plate 21, and in particular, the small gap between the nozzle plate 21 and the vibrator 24 is managed with high precision by the spacer 23.

The ink holding means is constructed by arranging the housing 20, the nozzle plate 21, and the plate-like members 29, 30, 31 to face each other with a required narrow gap of 2 mm or less in between. includes a vibrator 24 which is a pressure generating means.The narrow gap formed by the plate members 29, 30, and 31 is controlled to be substantially parallel by a gap regulating member (not shown). The gap lies in this device, which is configured so that the level L of the ink 32 is always located below the axis of the nozzle opening 22, as will be described later. In order to prevent the ink 32 from leaking, it needs to be below a certain set value determined by the head shape, the physical properties of the ink, and the surface tension.More specifically,
In two plate members in the atmosphere that face each other through a certain narrow gap and are installed parallel to the direction of gravity, liquid stably flows between the two plate members within a certain range of the direction of gravity. Retained. This is because the weight acting on the liquid and the surface tension generated at the contact surface between the liquid and the plate member are balanced. The present invention applies this principle to the head, and the narrow gap can exist in the head shape, that is, the ink holding means, so that the above principle can be applied no matter what position the head is placed in. At the maximum distance, it is necessary to set the gap below such that the weight of the ink 32 and the surface tension generated on the contact surface with other members are balanced. Further, the narrow gap allows the ink in the ink holding means to be pulled up to above the nozzle opening 22, and at the same time, the carriage 1
The gap must be small enough to suppress fluctuations in the ink surface during the movement of the ink. It must have such a narrow gap that it can respond sufficiently without running out of ink even when the ink 32 is ejected at a high frequency, and without causing a shortage of supply even when the ink 32 is ejected at a high frequency. Further, an ink level detection device 34 is provided inside the ink holding means, and when the level L reaches a certain set value or less and is detected by this ink level detection device 34, the upper part of the container-shaped housing 20 is Attached lid 2 that can be opened and closed as appropriate
8 is opened, and ink is supplied to the ink receiver section 33 from an ink storage tank (not shown).

Here, the volume of the supplied ink is such that the level L does not exceed the axis of the nozzle opening 22.

A filter 40, which is a filter means, is installed inside the pressure generating means so as to be in contact with the end surfaces of the plate members 29, 30, 31. The filter 40 has at least one side of 10
The filter 40 is made of stainless steel, nylon fiber mesh of 0 μm or less, and electroformed nickel.In particular, the flow path resistance of the filter 40 is such that the ink 32 supplied from the ink receiver section 33 is in the process of reaching the pressure generating means. It is necessary to set it so that it does not become a factor that significantly reduces the supply capacity of 32. More specifically, the filter 40
Adjust by the mesh shape and aperture ratio. Further, since the filter 40 is provided so as to be in direct contact with the end portions of the plate-like members 29, 30, 31,
When the ink 32 sandwiched between the narrow gaps 1 moves in the direction of the pressure generating means, it has the effect of facilitating the movement of the ink 32 from one narrow gap to another and enabling smoother supply of the ink 32. . FIG. 2(b) is an embodiment for explaining another installation location of the filter means, and for the sake of simplicity, the housing 20, plate-like members 29, 30, 31, and nozzle plate are shown in FIG. 2(a). 21 is a cross-sectional view showing only 21. FIG. The filter 41 is provided near the pressure generating means, and since the distance from the filter 41 to the pressure generating means is short, it can be said that the head is particularly resistant to precipitates and bubbles. Further, the filter 42 is a filter means having a function as an ink holding means similar to the plate member 29, 30.degree. 31, and it is possible to use not only one filter but also a plurality of filters. In this case, it is possible to set the area of the filter 42 to be large, and since the aperture ratio is large, the flow path resistance during the process of supplying the ink 32 is extremely small, and the volumetric efficiency inside the ink holding means is improved, so that the ink 32 It has the effect of having a large capacity.

By the way, the capillary force caused by the surface tension generated in the filter means is preferably set to be lower than the capillary force generated at the nozzle opening 22. If the head is designed in this way, the ink holding means It becomes possible to use all of the ink 32 held inside, and a highly reliable head with good ink consumption efficiency and no deterioration of the quality of the remaining ink can be realized.

Next, the operation will be explained. Ink 32 is supplied to the vibrator 24 and the vicinity of the nozzle plate 21 to fill it.

The ink droplet ejection operation will be explained. When a selective electric signal is applied to the vibrator 24, the piezoelectric element contracts due to the piezoelectric effect, while the dimensional change of the foil member with high interstitiality is restricted, and as a result, the vibrator 24 is deformed and displaced toward the nozzle plate 21.
Pressure is generated in the minute gap between the vibrator 24 and the nozzle plate 21. This pressure causes ink droplets to be ejected. Here, in the head based on the above-mentioned ejection principle, as long as there are no air bubbles in the gap between the vibrator 24 and the nozzle plate 21, ink droplet ejection failure due to air bubbles will not occur. When used in combination with an ink supply device that has a structure that allows air bubbles to escape, as shown in
It is possible to provide an extremely reliable head that is completely unaffected by air bubbles existing in the ink holding means.Nineth, the ink level detection device 34 inside the head detects that the amount of ink remaining in the head is below a predetermined amount. When this is detected, an ink replenishment request is output. The ink 32 supplied to the ink receiver section 33 is quickly sucked in and held by the capillary force in the narrow gap, and the ink level L rises. By the way, the capillary force generated in the narrow gap
Since the capillary force generated at 2 is stronger, the ink 32 is gradually consumed as the ink droplet is ejected, and as a result, the ink level L falls.

Furthermore, an open portion 36 that is open to the atmosphere is provided above the nozzle opening 22. It becomes possible to release air bubbles generated in the vicinity of the vibrator 23 through the open portion 36.

Incidentally, it is desirable that the volume of the ink 32 supplied is small enough not to overflow from within the ink holding means.

The reason for this is that if the ink overflows from inside the ink holding means, the ink will leak when the head is placed in an inverted position or the like.

In this embodiment, the ink is supplied to the upper part of the ink holding means, but the present invention does not limit the supply position; it may be supplied from the side or lower part of the ink holding means due to constraints in the inkjet printer configuration. is also possible.

Further, in this embodiment, a plate member 29 is used as the ink holding means.
．． Although the laminated structure of 30.31 and the gap of the casing 20 were used, other examples include a structure made of a foam member having a plurality of continuous micro-cavities inside, a structure made of a plurality of micro-diameter tubes, etc. It is.

On the other hand, a case will be explained in which a hot melt ink which is in a solid state at room temperature is used. In FIG. 2(a), a heater 27 serving as a heat source is installed on the casing 20 on the back side of the pressure generating means. In the embodiment, only one heater 27 is shown, but the present invention does not limit the number of heaters 27 and the installation location, and it is possible to set a plurality of heaters 27 at appropriate locations in consideration of thermal efficiency. . In addition, the plate member 29
．． 30.31 and the gap regulating member (not shown) are thermally connected to the housing 2.
0, and the thermal energy generated by the heater 27 is quickly conducted and used for heating and melting the ink 32 and maintaining its temperature.

Further, when the heater 27 is used, the housing 20 is preferably made of a metal material with excellent thermal conductivity such as aluminum or stainless steel.

In this embodiment, the area of the ink holding means in contact with each unit volume of ink is large, and the head is downsized, so it takes a long time from when the power is turned on until the ink 32 reaches the reference temperature and printing is possible. This has the effect of shortening the time. In particular, since solid ink 32 at room temperature is supplied when ink is supplied, the ink temperature in the vicinity of the pressure generating means may drop over time, causing an increase in ink viscosity and preventing good ink droplet ejection. However, in this embodiment, the ink 32 is first supplied to the plate members 29.30.31, so the heat capacity and good thermal conductivity from the heat source of the plate members 29.3o and 31 are It plays the role of an interference material and has the effect of not causing a large temperature change to the ink 32 near the pressure generating means. Further, it is desirable that the filter 40 used in this embodiment is made of metal. This is because it has good thermal conductivity and can quickly function as a filter when the power is turned on. By the way, since hot melt ink undergoes a large volume change during phase transformation, the generation of bubbles inside the ink holding means is unavoidable. However, in the method of installing the filter 40 within the ink retaining means of the present invention, the filter 40 plays the role of an air trap, making it possible to prevent air bubbles from entering the vicinity of the pressure generating means as the ink 32 is consumed. Furthermore, if the filter 40 is installed in a narrow gap like the filter 41 in FIG. 2(b), and installed not horizontally but diagonally, it is possible to restrict the flow of air bubbles within the ink holding means. Therefore, air bubbles can be eliminated without changing the flow direction of the ink 32, and the ink 32 can be efficiently supplied.
It is possible to realize a head that is not affected by air bubbles, has high reliability, and has excellent ink droplet ejection characteristics.

[Effects of the Invention] As described above, according to the above structure of the present invention, the amount of ink stored in the head is small, and therefore the head and carriage can be made smaller.Furthermore, since the carriage is small, the amount of ink required for this movement is reduced. It has the advantage that it requires less power, has a simple device configuration, and can be made smaller. Further, since the ink is quickly consumed, there is an effect that the characteristics of the ink do not deteriorate. Furthermore, since the distance from the filter means to the pressure generation means is short, the probability of new bubbles and precipitates being generated after being removed by the filter is low, and the pressure generation means for air bubbles existing in the ink holding means is low. It is possible to prevent the inkjet head from approaching the vicinity, and has the effect of realizing a highly reliable inkjet head. In addition, since the filter means is included in the ink holding means, no matter what position the head is placed in, the ink passes through the filter and is ejected as ink droplets, making it possible to realize a highly reliable inkjet head. It is.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an inkjet printer showing one embodiment of the present invention. FIG. 2(a) is a sectional view of an inkjet head showing an embodiment of the present invention. FIG. 2(b) is also a sectional view of an inkjet head showing an embodiment of the present invention. 29.3 Inkjet head housing nozzle plate nozzle opening oscillator o131 Plate member ink 1.42 Filter and above Applicant Seiko Epson Co., Ltd. agent Patent attorney Kizobe Suzuki and 1 other person 24 Toshiko 27 Heater Fig. 2

Claims (3)

[Claims] (1) a housing disposed to face a recording medium; an ink retaining means disposed within the housing having a narrow gap for retaining ink through capillary action; forming a part of the ink retaining means; a nozzle forming member having at least one or more nozzle openings disposed to face the recording medium; and a nozzle forming member disposed within the ink holding means and capable of flying as ink droplets to the ink near the nozzle openings. An inkjet head comprising: a pressure generating means for generating a pressure; and a filter means installed within the ink holding means. (2) Claim 1, wherein the ink is in a solid state at room temperature, and the housing is provided with at least one heat source.
Inkjet head as described. (3) The inkjet head according to claim 1 or 2, characterized in that the capillary force generated at the nozzle opening is larger than the capillary force generated at the filter means.