JPH02258352A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To enable a temperature gradient generated in an ink contained in a common liquid chamber to be constantly controlled in a common liquid chamber to be constantly controlled to within an allowable range by forming the common liquid chamber in such a shape that the sectional area thereof as viewed in the array direction of a plurality of ejecting parts varies with the distance along the direction from a part at which an ink-supplying port communicates with the chamber. CONSTITUTION:A common liquid chamber 3 has such a shape that the sectional area as viewed in the array direction of ejecting ports increases gradually with the distance from a supplying port 6A. That is, the internal volume of the chamber 3 corresponding to each of ink passages increases with the distance from the supplying port 6A. This shape ensures that heat tending to generate a temperature gradient in an ink is released due to the ink volume varied correspondingly to the gradient, resulting in a substantially uniform temperature distribution. Consequently, it is possible to record with a density uniform along the direction of a recording width S.

Description

[Detailed Description of the Invention] [Field of Application in Industry] The present invention relates to an inkjet recording head, and more specifically, the present invention relates to an inkjet recording head, and more specifically, an inkjet recording head comprising a plurality of ejection ports and a common liquid chamber for supplying ink ejected from the plurality of ejection ports. It relates to an inkjet recording head.

[Prior Art] Conventionally, inkjet recording heads have been those that eject ink droplets by generating a pressure change in a liquid path by deforming a piezoelectric element, for example, or those that are provided with a pair of electrodes and ejected ink droplets by an electric field between the electrodes. One that electrostatically attracts and ejects droplets, and another that generates air bubbles in the ink by rapidly generating heat from a thermal energy generating element placed in the liquid path to eject ink droplets. Various proposals have been made.

Among these, the method of ejecting ink using thermal energy is a particularly effective method because it is easy to mount ejection ports, thermal energy generating elements, etc. in high density, and high-speed recording is possible. It can be said.

In addition, the recording heads used in recording equipment include serial types that record while moving in a fixed direction on a recording medium such as recording paper, and ejection ports and ejection energy that correspond to the width of the recording medium in this direction. A line type in which generating elements are arranged is known, but the line type is advantageous from the viewpoint of high-speed recording.

FIGS. 7(^) and 7(8) are a schematic top sectional view and a schematic side sectional view, respectively, showing a conventional example of a line type inkjet recording head. Here, 1 is the recording head,
Reference numeral 3 indicates a common liquid chamber within the recording head 1, and reference numeral 2 indicates an orifice serving as an ink ejection port provided on the ink ejection surface. A plurality of these orifices 2 are arranged across the width of the recording medium that is conveyed facing the recording head, and a heating element 5 made of an electrothermal transducer is provided in a liquid path 4 that communicates with each orifice 2. By selectively driving the ink, ink is ejected and recording is performed.

FIG. 8 is a block diagram showing an ink supply system provided in the inkjet recording apparatus for supplying ink to the recording head shown in FIG. Ink supply tank, 16
is a main tank for replenishing the supply tank 15 with ink. Ink is supplied from the supply tank 15 to the common liquid chamber 3 of the recording head 1 through the supply pipe 8, and when replenishing ink, the ink is supplied from the main tank 16 in one direction. Ink can be replenished into the supply tank 15 by the recovery pump 14 via the replenishment rectifier valve 11 . Further, 10 is a one-way recovery rectifier valve used during a recovery operation to restore the ejection function of the recording head 1, 9 is a circulation pipe in which the recovery rectifier valve 10 is interposed, and 12 is a circulation pipe in which the recovery rectifier valve 10 is interposed. The electromagnetic valve 13 interposed in the first supply pipe 8 described above is an air vent valve disposed in the supply tank 15.

In the recording head 1 and its ink supply system and recovery system configured as described above, when recording is performed, the solenoid valve 12
is kept open, and the common liquid chamber 3 is replenished with ink from the supply tank 15 due to the surface tension of the ink. In addition, during a recovery operation performed to remove air bubbles remaining in the common liquid chamber 3 and the supply system and to cool the recording head 1, the recovery pump 14 is driven and new ink is supplied to the common liquid chamber 3 through the circulation pipe 9. The ink can be returned to the supply tank 15 from the common liquid chamber 3 via the first supply pipe 8 and circulated. Furthermore, during initial filling to remove ink clogging and fill ink into liquid channels, etc., the ink is force-fed to the common liquid chamber 3 via the circulation pipe 9 by the pump 14 with the solenoid valve 12 closed, and air bubbles are removed. Ink is discharged from orifice 2
It can be discharged from

[Problems to be Solved by the Invention] However, in particular, in the conventional line-type inkjet recording head as described above, high-density recording such as solid recording that drives all heating elements and high-speed recording by high-frequency driving of the heating elements are not possible. When carrying out this method, the excess heat generated from the heating element may not be sufficiently radiated by the ejected ink or the heat radiated through each part of the recording head. Furthermore, the print head and ink are also heated by the heat generated from the driver for driving the heat generating elements. This thermal energy accumulates in the recording head and ink during long-term recording. As a result, such heat accumulation causes a temperature gradient in the ink within the common liquid chamber.

To explain this phenomenon with reference to Figures 9 (^) to (C), in the case of ink in the common liquid chamber of a recording head as shown in Figure 9 (B), the amount of ink in the ink as recording progresses. Due to heat accumulation and the like, the ink temperature near the center of the recording head is highest. On the other hand, the temperature of the ink supplied from the supply pipe 8 is influenced by the ambient temperature of the device and is therefore lower than the temperature of the ink in the head. These two main factors cause the temperature gradient of the ink in the common liquid chamber to change as shown in the figure. The result will be as shown in C). As a result, a difference occurs in the viscosity of the ink within the common liquid chamber, and the ink droplet ejected from the ejection port on the right side in the figure, where the temperature is higher, becomes larger. As a result, as shown in (A) of the same figure, the recorded image is darker on the right side than on the left side with respect to the entire recording width S, and the recording quality is impaired due to imbalance in image density. Put it away.

Furthermore, this tendency can be seen, for example, when the number of discharge ports arranged is 128.
The more the number of ejection openings increases (256), the more noticeable this becomes, and especially in the case of a line-type recording head that ejects ejection using bubbles generated by thermal energy, this tendency becomes even more pronounced as the number of ejection ports increases to several tens.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide an inkjet recording head that is controlled so that the temperature gradient occurring in the ink in the common liquid chamber is always within an allowable range. Our goal is to provide the following.

[Means for Solving the Fi Problem] To this end, the present invention includes a plurality of ejection portions for ejecting ink, and a plurality of ejection portions provided for supplying ink to the ejection portions in response to ink ejection from each of the ejection portions. In an inkjet recording head that includes a common liquid chamber and an ink supply port that communicates with the common liquid chamber and supplies ink to the common liquid chamber,
The common liquid chamber is characterized in that it has a shape in which the cross-sectional area in the direction in which the plurality of ejection portions are arranged changes depending on the distance from the portion where the ink supply ports communicate with each other in the direction in which the plurality of ejection portions are arranged.

[Function] According to the above configuration, the shape of the common liquid chamber can be changed according to the temperature gradient that may occur in the ink in the common liquid chamber. It is possible to increase the volume of a portion of the common liquid chamber where heat tends to concentrate, which promotes heat dissipation from the nail into the ink, and makes it possible to suppress temperature gradients occurring in the ink.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic perspective view of an inkjet recording head showing an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a line-type recording head in which a plurality of ejection ports (hereinafter referred to as orifices) 2 are arranged corresponding to the width of the recording medium.
Moving a recording medium (not shown) relative to the recording head 1,
Recording is performed by ejecting ink from the orifice 2 facing the recording medium in response to this movement.

Reference numeral 3 denotes a common liquid chamber arranged to supply ink to each of the ink liquid paths 4 communicating with the orifice 2, and a common liquid chamber 3 is provided in the liquid path 4 to generate thermal energy for ejecting the ink. The illustrated heating element is provided. These heating elements, ink liquid path 4, and orifice 2 constitute an ink ejection section. 6^ is a supply port provided at one end of the common liquid chamber 3 for supplying ink to the common liquid chamber 3 during recording, and 2 is provided at the other end of the common liquid chamber 3 for use during ejection recovery processing. This is a second feed port for feeding ink from a supply tank, which will be described later, when circulating ink to the common liquid chamber 3, etc.

As shown in the figure, the common liquid chamber 3 has a shape in which the cross-sectional area increases from the supply port 6^ to the supply port 6B, and in this example, the cross-sectional area increases as the shape expands in the ink ejection direction. ing.

FIG. 2 is a block diagram showing an ink supply system and circulation system for the recording head 1 configured as described above. Elements similar to those shown in FIG. 8 are designated by the same reference numerals, and their explanations will be omitted. Here, 8 is a supply pipe that supplies ink from the tank 15 to the recording head 1, and 9 is a second supply pipe that supplies ink to the common liquid chamber 3 of the head 1 during ink circulation. An on-off valve 9 such as a solenoid valve 14 is provided.

In the above configuration, the temperature of the recording head 1 increases as recording progresses due to heat generated by the heating elements for ejecting ink. In particular, when recording by ejecting ink from all ejection ports or when performing high-speed recording using high frequency drive,
As described above, the heat generated from the large number of heat generating elements cannot be completely radiated by the ejected ink and heat radiation through various parts of the print head, and is stored in the print head, causing a temperature gradient in the ink in the common liquid chamber.

On the other hand, as shown in FIG. 3 (It), the liquid chamber shape of the common liquid chamber 3 is such that the cross-sectional area gradually increases as it moves away from the supply port 6^ in the ejection port array direction. The volume of the common liquid chamber 3 corresponding to each liquid path increases as the distance from the supply port 6^ increases. As a result, the heat that causes a temperature gradient in the ink is dissipated by the ink volume corresponding to this gradient, as shown in Figure 3 (
A substantially uniform temperature distribution is obtained as shown in C). As a result, it becomes possible to perform recording with uniform density in the direction of the recording width S, as shown in FIG.

FIG. 4 is a schematic perspective view of a recording head showing another embodiment of the present invention, and as shown in the figure, the shape of the common liquid chamber 3 of this embodiment is such that the dimension in the direction perpendicular to the ejection direction is the supply port. The cross-sectional area is increased by increasing the distance from 6^.

In each of the above embodiments, the case where there is one ink supply port has been explained, but when there are two ink supply ports as shown in FIG. The cross-sectional area increases as the distance from the respective supply ports 6c and 6D increases. This maximizes the volume of the common liquid chamber corresponding to the center of the discharge port array.

FIG. 6 shows a modification of the embodiment shown in FIG. 5, in which the dimensions of the common liquid chamber 3 in the direction perpendicular to the ink discharge direction are increased as the distance from the respective supply ports 6C and 6D increases.

As described above, the increase rate of the cross-sectional area of the common liquid chamber shape in all the examples is the pitch of the array of heating elements.

It varies depending on the number, drive frequency, etc., and the optimal one for each head type is determined in advance through experiments or the like. Therefore, according to the common liquid chamber 3 whose shape is optimally determined, the ink capacity is larger in the part where heat is more likely to concentrate in the common liquid chamber. It becomes possible to suppress temperature gradients that may occur in the ink.

In each of the above embodiments, the ink supply port is disposed at the end of the common liquid chamber, but the ink supply port may be disposed at any position as required. The cross-sectional area of the common liquid chamber at the portion where the mouth is disposed may be minimized, and the cross-sectional area may be increased toward other portions.

Furthermore, although the above embodiments have been described with respect to a line-type recording head, the application of the present invention is not necessarily limited to this, and even in a serial-type recording head, a large number of ejection ports are arranged. If so, the application of the present invention will be effective.

Furthermore, although the ejection energy generating element for ejecting ink is particularly effective when using a heating element,
The invention is not limited thereto, and the present invention can also be applied to a recording head of a type that ejects ink using strain energy using, for example, a piezoelectric element.

[Effects of the Invention] As is clear from the above description, according to the present invention, the shape of the common liquid chamber can be changed in accordance with the temperature gradient that may occur in the ink in the common liquid chamber. Accordingly, it is possible to increase the volume of the area in the common liquid chamber where the heat emitted from the ink ejecting section etc. tends to concentrate, thereby promoting heat dissipation into the ink and suppressing the temperature gradient that occurs in the ink. It becomes possible.

As a result, changes in the size of formed ink droplets are suppressed, and differences in recording density on the recording medium can be eliminated. Moreover, it is possible to provide an inkjet recording head that has a simple structure, is inexpensive, and is especially suitable for line type.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of an inkjet recording head showing an embodiment of the present invention, FIG. 2 is a block diagram showing an ink supply system for supplying ink to the recording head shown in FIG. 1, and FIG. Figure (^),
(B) and (C) are a schematic top view of the recording medium and a schematic diagram of the recording head, respectively, for explaining the relationship between the ink temperature distribution in the common liquid chamber of the recording head shown in FIG. 1 and the recording density. A top view and a diagram of temperature distribution, FIGS. 4 to 6 are schematic perspective views of inkjet recording heads showing other embodiments of the present invention, and FIGS. 7(^) and (B) are inkjet recording FIG. 8 is a block diagram showing an ink supply system for supplying ink to the recording head shown in FIG. 7; FIG. (A)
, (B) and (C) are a schematic top view of the recording medium and a schematic diagram of the recording head, respectively, for explaining the relationship between the ink temperature distribution in the common liquid chamber of the recording head shown in FIG. 7 and the recording density. FIG. DESCRIPTION OF SYMBOLS 1... Recording head, 2... Orifice, 3... Common liquid chamber, 4... Ink liquid path, 6^, 6C, 6D... Ink supply port. Figure Figure

Claims (1)

[Scope of Claims] 1) A plurality of ejection sections for ejecting ink, a common liquid chamber provided for supplying ink to the ejection sections in response to ink ejection from each of the ejection sections, and communicates with the common liquid chamber,
In an inkjet recording head comprising an ink supply port for supplying ink to the common liquid chamber, the common liquid chamber has a distance from a portion where the ink supply ports communicate in a direction in which the plurality of ejection units are arranged. An inkjet recording head characterized in that it has a shape whose cross-sectional area in the direction changes depending on the direction. 2) The shape in which the cross-sectional area changes is a shape in which the cross-sectional area increases. 3) The shape in which the cross-sectional area changes is characterized in that each of the plurality of ink supply ports communicates with each other. 2. The inkjet recording head according to claim 1, wherein the cross-sectional area increases in accordance with the distance from the ink supply port, and the cross-sectional area is maximized between each of the ink supply ports. 4) Claim 1, wherein the ejection unit has an ink ejection port, an ink liquid path communicating with the ink ejection port and the common liquid chamber, and a heating element disposed in the ink liquid path. The inkjet recording head according to any one of items 3 to 3. 5) The inkjet according to any one of claims 1 to 4, wherein the plurality of ejection units are arranged in accordance with the width of a recording medium that is conveyed opposite to the ejection units. recording head.