1. Field of the Invention
The present invention relates to a liquid discharging head that discharges a liquid from plural discharge ports.
2. Description of the Related Art
It is advantageous to use a long liquid discharging head including an array of many discharge ports from which a liquid is discharged, in order to achieve high speed printing onto a recording medium. In particular, a full-line-type liquid discharge printing apparatus, which continuously feeds a recording medium and discharges ink for printing, uses a liquid discharging head including a long array of discharge ports having a length larger than the width of the recording medium. Such a liquid discharging head is typically configured by arranging relatively short print element substrates each including the discharge ports and heat-generating resistance elements that generate thermal energy in order to discharge the liquid from the discharge ports. This configuration enables the liquid discharging head including the long array of discharge ports to be readily provided at low cost. For the configuration of the arranged print element substrates, however, a difference in temperature that occurs in the interior of each print element substrate or among the print element substrates may cause a difference in the amount of discharged liquid. Accordingly, the difference in temperature that occurs in the interior of each print element substrate and the difference in temperature that occurs among the print element substrates need to be controlled so as to be restricted within a predetermined range.
As the liquid discharging head that performs such control, Japanese Patent Laid-Open No. 2011-240521 discloses a liquid discharging head in which each print element substrate is provided with a main channel through which a liquid is supplied and the liquid circulating through the main channel cools the print element substrates. In this liquid discharging head, heat generated by the heat-generating resistance elements when the liquid is discharged is divided into heat transferred to a support member that supports the print element substrates and heat transferred to the liquid. The heat transferred to the support member is transferred to the circulating liquid and the support member is thereby cooled. Thus, the heat generated in the print element substrates is successively transferred to the liquid via the support member, and an increase in the temperature of the print element substrates can be suppressed.
For current liquid discharge apparatuses, however, discharge frequency is further increased and the length of the liquid discharging head is further increased to achieve high speed printing and large size printing, and the number of discharges per unit time and a calorific value per unit time are likely to increase. Accordingly, the liquid discharging head disclosed in Japanese Patent Laid-Open No. 2011-240521 cannot sufficiently cool the print element substrates, and in some cases, it is difficult to restrict the difference in temperature in the interior of each print element substrate and the difference in temperature among the print element substrates to be within a predetermined range. In these cases, the amount of liquid discharged from the discharge ports in the interior of the liquid discharging head varies and this variation causes degradation in the quality of images. It is difficult to solve the problem of the variation in the amount of the discharged liquid by merely increasing the flow rate of the circulating liquid. It is known that even though the increase in the flow rate of the liquid may decrease the overall temperature of a liquid discharging head, there is almost no reduction in the difference in temperature among liquid discharging heads. Supposing a very large amount of liquid is circulated through the liquid discharging head, the difference in temperature among the liquid discharging heads can be reduced, but this needs a large pump, leading to an increase in the size of the liquid discharge apparatus and an increase in the production cost and running cost.
The present invention provides a liquid discharging head including a support member and plural print element substrates through which a liquid is discharged. The print element substrates are disposed on the support member and provided with the liquid through a liquid supply channel formed in the support member. The sectional area of the liquid supply channel at a position corresponding to each of the print element substrates is determined in accordance with an order in which the print element substrates are provided with the liquid.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An embodiment of a liquid discharging head according to the present invention will hereinafter be described in detail with reference to the drawings. The basic structure and the action of the liquid discharging head in the embodiment will be first described with reference to
As shown in
The support member 200 is made of silicon and formed into a rectangular parallelepiped. The size of the support member 200 in the longitudinal direction is longer than the width of the recording medium (length in the direction X perpendicular to the direction Y in which the recording medium is fed in the liquid discharge printing apparatus). The support member 200 secures the print element substrates 100 and supplies a liquid to the print element substrates 100. Liquid introduction ports 201 through which the liquid is supplied to the print element substrates are formed in the surface of the support member 200. A main channel 202 (liquid supply channel) that communicates with the liquid supplying member 400, which is described later, is formed in the interior of the support member 200 and the liquid is introduced into and discharged from the main channel 202 (see
Each print element substrate 100 includes a silicon substrate 101 and a discharge-port defining member 105 joined to the silicon substrate 101. Supply ports 102 are formed in the silicon substrate 101 along the longitudinal direction of the silicon substrate 101 (direction X in
Heat-generating resistance elements 103, which are energy-generating elements that generate energy used to discharge a liquid, are disposed on one surface of the silicon substrate 101 so as to face the respective discharge ports. The heat-generating resistance elements 103 are driven by a driving circuit of the liquid discharge printing apparatus, which is not shown, in order to generate thermal energy. This thermal energy results in film boiling of the liquid supplied to the interior of liquid passages 105a (see
The print element substrates 100 configured as above are arranged in a zigzag formation such that some print element substrates overlap each other when viewed in a direction perpendicular to the direction in which the recording medium is fed (direction Y). This arrangement enables a recording width of approximately 13 to 20 inches to be achieved in the embodiment.
The electric wiring component 300 supplies, to the print element substrates 100, driving signals and a driving power transferred from the liquid discharge apparatus. The electric wiring component 300 is provided with plural openings 301 in order to incorporate the print element substrates 100 and electrodes 302 (see
The liquid supplying member 400 connects a liquid storage member provided in the liquid discharge printing apparatus to the support member 200 and is made of a resin by injection molding. In the interior of the liquid supplying member 400, as shown in
Thus, the heat generated by the heat-generating resistance elements 103 of the liquid discharging head 1 is transferred to the liquid in the liquid passages 105a and the support member 200 that supports the print element substrates 100. The heat transferred to the support member 200 is transferred to the liquid flowing through the main channel 202 and the support member 200 is cooled. The liquid discharging head is maintained at an appropriate temperature when the heat is thus transferred. However, when the calorific value per unit time is large, e.g., when high speed printing is performed, the heat generated in the print element substrates cannot be sufficiently dissipated, and a difference in temperature occurs in the interior of each print element substrate 100 or a difference in temperature occurs among the print element substrates 100. In the liquid discharging head 1, such a difference in temperature causes a difference in the amount of liquid to be discharged, thereby causing a variation in the contrast of images to be printed.
The difference in temperature that occurs in each print element substrate will be described in more detail with reference to
The difference in temperature that occurs among the print element substrates 100 of the liquid discharging head 1 will be next described in more detail. In the circulating channel through which the liquid is supplied, the liquid has a relatively low temperature right after the liquid flows into the support member 200 from the liquid supplying member 400 (this liquid is referred to as a liquid on the upstream side below). For this reason, it is easy to cool a portion of the support member 200 and the print element substrates 100 that are located on the upstream side in the main channel 202 of the support member 200. In contrast, it is difficult to cool some of the print element substrates 100 that are located on the downstream side, because the temperature of the liquid is gradually increased due to the heat transferred from the other print element substrates 100 as the liquid flows to the downstream side of the main channel 202. The difference in temperature consequently occurs between the print element substrates 100 located on the upstream side and the print element substrates 100 located on the downstream side.
When the calorific value per unit time is increased due to increased recording speed, an increased length of the liquid discharging head, or other reasons, large differences in temperature occur in each print element substrate and among the print element substrates. These differences in temperature cannot be reduced by merely increasing the flow rate of the liquid in the liquid discharging head. In particular, the difference in temperature among the print element substrates is hardly reduced, although the increase in the flow rate of the liquid reduces the overall temperature. Supposing a very large amount of liquid is circulated, the difference in temperature can be reduced, but this requires that the liquid discharge apparatus be equipped with a large pump, leading to an increase in the size and the cost of the liquid discharge apparatus. In view of this, a first embodiment of the present invention has the features described below.
The features of the first embodiment of a liquid discharging head according to the present invention will be described with reference to
In the embodiment, a portion of the main channel 202, which is formed in the support member 200, that corresponds to each print element substrate 100 has a cross-sectional area (sectional area of the channel) that varies depending on the position of the portion of the main channel 202. More specifically, the portion of the main channel 202 that corresponds to each print element substrate 100 has a smaller sectional area as the portion is nearer to the most downstream position. The sectional area of the channel is determined in accordance with the height H (referred to as the height of the main channel below) of the upper surface (second inner surface) of the main channel from the bottom surface (first inner surface) of the main channel. Accordingly, the height of the main channel 202 at the positions corresponding to the print element substrates located on the upstream side is determined to be lower than the height of the main channel 202 on the downstream side. In other words, the sectional area of the main channel 202 at the positions corresponding to the print element substrates located on the downstream side is smaller than the sectional area of the main channel 202 at the positions corresponding to the print element substrates located on the upstream side. In an example shown in the figures, the relation H1≧H2≧H3≧H4 (H1>H4) holds, where the height H of the main channel 202 is denoted by H1, H2, H3, and H4 in order starting from the upstream side. As shown in
In contrast, when the height of the main channel formed in the support member is constant such as in the case of a liquid discharging head that is conventionally used, the temperature of the liquid gradually increases as the liquid flows from the downstream side to the upstream side of the main channel 202. Consequently, transfer of heat from a downstream portion of the beams 204 of the support member 200 to the liquid is more difficult than that from the other portions of the beams 204, and the temperature of the print element substrates 100 is increased at this portion. In the embodiment, however, the height of the main channel 202 at the position corresponding to each print element substrate is further reduced as the position is nearer to the most downstream position and the main channel 202 at this position has a smaller sectional area. Accordingly, the speed of the liquid flowing through the main channel 202 is further increased as the liquid flows to the downstream side, and the temperature of the liquid is inhibited from increasing. The amount of heat transferred from the beams 204 to the liquid is consequently increased compared with when the sectional area of the main channel 202 is constant, and the difference between the amount of heat transferred from the beams 204 on the upstream side to the liquid and the amount of heat transferred from the beams 204 on the downstream side to the liquid is reduced. Accordingly, in the embodiment, the difference in temperature among the print element substrates and the difference in temperature in each print element substrate can be reduced without circulating a very large amount of liquid with a large pump. The variation in the amount of liquid discharged from the discharge ports can thereby be reduced and the variation in the contrast of images to be printed can be reduced.
In the embodiment, the height H of the main channel 202 ranges approximately from 0.5 to 5 mm. The height of the main channel 202, however, can be determined optionally in accordance with the calorific value of the print element substrates 100, and the temperature and the flow rate of the circulating liquid. In the embodiment, the support member 200 is made of alumina formed by stacking green sheets. For this reason, the height is changed in a manner in which the section of the main channel 202 in the longitudinal direction is in the form of steps in this embodiment. However, when the support member is made of another material and by another method, the main channel may be formed so as to have a tapered section so that the height is continuously reduced from the upstream side to the downstream side.
A second embodiment of a liquid discharging head according to the present invention will be next described with reference to
In the liquid discharging head in the second embodiment, the distance between the upper surface (second inner surface) and the bottom surface (first inner surface) of the main channel 202 of the support member 200, that is, the height of the main channel 202 is constant. However, projections 203a to 203d extending toward the liquid introduction ports 201 are formed on the upper surface of the main channel 202 so as to face the central portion of the respective print element substrates 100. The distance h between the lower end of the projections 203a to 203d and the lower surface of the main channel varies. More specifically, the distance h between the lower surface of the main channel and the projections that face the print element substrates located on the downstream side is equal to or shorter than the distance h between the lower surface of the main channel and the projections that face the print element substrates located on the upstream side. In an example shown in the figures, the relation H>h1≧h2≧h3≧h4 (h1>h4) holds, where the height of the main channel 202 is denoted by H, and the distance between each projection 203 and each beam 204 is denoted by h1, h2, h3, and h4 in order starting from the upstream side. The symbol H represents the distance between the upper surface and the bottom surface of the main channel. In
Since the distances between the projections 203 and the beams 204 on the downstream side are smaller than on the upstream side, the difference T2 in temperature among the print element substrates 100 is reduced as in the first embodiment. The difference T2 in temperature shown in the figure represents a difference between the minimum temperature of the print element substrate located most upstream and the maximum temperature of the print element substrate located most downstream.
In this way, the variation in the amount of liquid discharged through the print element substrates is reduced, so that the variation in the contrast of images hardly occurs and the printing can be performed with a high quality, when the calorific value is increased due to high speed printing, or when the length of the liquid discharging head is further increased.
In the second embodiment, the distance H between the upper surface and the bottom surface of the main channel 202 (or the height) ranges approximately from 3 to 10 mm, and the distance h between the beams 204 and the print element substrates 100 ranges approximately from 0.5 to 5 mm. The values of H and h, however, can be determined optionally in accordance with the calorific value of the print element substrates 100, and the temperature and the flow rate of the circulating liquid as in the first embodiment.
As shown in
With this structure, the region at which the speed of the flowing liquid is increased due to the projections 203 spreads toward the downstream side, the maximum temperature of the print element substrates in the longitudinal direction can be further decreased, and the difference t2 in temperature in each print element substrate 100 can be further reduced.
A third embodiment of the present invention will be next described with reference to
In this embodiment, as shown in
The channel portion 220 may be made of alumina as in the second embodiment, or a resin having a low linear expansion coefficient. When a resin is used for the channel portion, it is possible not only to greatly reduce its cost but also to increase the degree of freedom of its shape that is to be formed, for example, such that the sides of each projection 223 are tapered to suppress gathered air bubbles as shown in
As shown in
A fourth embodiment of the present invention will be next described with reference to
The basic structure of the fourth embodiment is substantially the same as in the third embodiment except that, as shown in
Liquid introduction ports 231 through which a liquid is introduced into the print element substrates 100 are formed in the support portion 210. The support portion 210 is made of a material having a relatively low thermal conductivity such as borosilicate glass, zirconia, or a resin member with a thickness of approximately 0.5 to 3 mm. For this reason, in the fourth embodiment, it is difficult to transfer heat from the outer regions 101a to the support member 230, and the inner regions 101b come into direct contact with the liquid and thereby are efficiently cooled. Accordingly, as shown in
In the fourth embodiment, since no beam is provided within each of the liquid introduction ports 231, as shown in
In the fourth embodiment, since the inner regions 101b can be cooled with a high efficiency, the print element substrates can be maintained at a desired temperature, even when the flow rate of the circulating liquid is decreased in accordance with specifications required for the liquid discharging head. Accordingly, the size of a pump installed in the liquid discharge apparatus can be further reduced to downsize the liquid discharge apparatus.
In the embodiments, although the liquid discharging head used in the full-line-type liquid discharge printing apparatus has been described by way of example, the present invention can be applied to liquid discharging heads used in other recording-type liquid discharge printing apparatuses. For example, the present invention can be applied to a liquid discharging head used in a serial-type liquid discharge printing apparatus, in which a recording medium is intermittently fed and the liquid discharging head is moved in the direction perpendicular to the direction in which the recording medium is fed for recording.
In the embodiments, the sectional area of the liquid supply channel is increased in accordance with the order in which the recording elements are disposed in the direction in which the liquid flows through the main channel (liquid supply channel) formed in the support member that supports the print element substrates. The sectional area of the liquid supply channel, however, may be determined not in accordance with the order in which the recording elements are disposed but in accordance with positions at which the print element substrates are disposed, or frequency of use thereof, i.e., the amount of liquid discharged per unit time.
The liquid discharging head according to the present invention can reduce the difference in temperature in each print element substrate and the difference in temperature among the print element substrates without increasing the flow rate of the liquid circulating through the liquid discharging head.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-060852, filed Mar. 24, 2015, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2015-060852 | Mar 2015 | JP | national |