Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-06-16
2001-09-11
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S045000, C347S044000
Reexamination Certificate
active
06286933
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording head that forms images on a medium by enabling ink or other liquid to fly onto the medium.
2. Related Background Art
For the ink jet recording, ink or other liquid is caused to fly onto a medium for the formation of images. More specifically, it is arranged to discharge liquid from the discharge ports of an ink jet head as shown in FIG.
10
.
FIG. 10
is a front view which shows the recording device substrate of a side shooting type ink jet head.
In
FIG. 10
, reference numeral
1
designates a plurality of ink discharge ports arranged on the recording substrate for discharging ink; and
2
, an orifice plate. An ink supply opening
3
is open substantially in the center of the recording element substrate on which the discharge ports are arranged to supply ink to the discharge ports.
This opening is usually made by means of sandblasting, anisotropic etching, laser processing, or the like.
FIG. 11
is a cross-sectional view taken along line
11
—
11
in FIG.
10
. In
FIG. 11
, reference numeral
5
designates an electrothermal converting element; and
6
, a nozzle portion that retains ink to be discharged by means of bubbling caused by heat generated by the electrothermal converting element
5
.
The discharge ports are usually in a state of being exposed to the outside air. As a result, liquid in the nozzles is evaporated from the discharge ports, thus causing the viscosity of liquid in the nozzle portion to rise. In some cases, the phenomenon may take place that hinders the regular discharges of ink droplets.
FIG. 12
is a view which shows this phenomenon conceptually. The portion in the interior of a discharge port, which is indicated by slanted lines in
FIG. 12
, represents the state where the evaporating component in ink has been evaporated.
Here, on the portion indicated by the slanted lines, the viscosity has risen due to the fact that the density of the non-volatile component of a solvent or the like becomes more densified mainly because water is evaporated. Also, the ratio of colorant, such as dyes contained in ink, has increased in ink. (Hereinafter, ink in such state is referred to as viscosity-increased ink.)
When ink becomes viscosity-increased, the volume of ink discharge is reduced, the shooting accuracy is lowered, and the disabled discharges may take place, among some other drawbacks. Particularly, if the temperature and/or humidity of the environment of outside air is low, this phenomenon becomes more conspicuous.
Also, the increasing of density of dyes in the nozzle portion tends to higher density of prints at the start of printing, causing the unevenness thereof. Also, it has been found that the longer the interval between the last and current discharges, the more the evaporation is advanced, presenting these drawbacks more conspicuously.
Therefore, as means conventionally adopted, ink is discharged onto the region other than the recording area before printing or in printing, (which is hereinafter referred to as predischarge). The execution of the predischarges prevents these drawbacks from taking place in operation, because the ink whose water content has been evaporated to make it viscosity-increased is discharged from the nozzle portion beforehand.
Here, however, the frequent predischarges result in the increased amount of ink consumption, leading to the higher running costs.
Also, it is required to increase the capacity of the waste ink absorbing member for storing predischarged ink in an ink jet printer, which necessitates to make the size of the printer larger with the inevitable increase of costs.
Also, fundamentally, the volume of the nozzle portion of the ink jet head currently in use should become smaller as it is required to print images in higher resolution by use of smaller liquid droplets. As a result, the ratio of viscosity-increased ink contained in ink to be discharged tends to become larger. Here, it is known that once such smaller droplets are exposed to the outside air, the discharges are subjected more easily to the instability than the larger liquid droplets used conventionally.
In accordance with the conventional examples described above, the evaporation makes rapid progress in the ink jet head that discharges smaller droplets. This phenomenon may bring about the deviation in the shooting accuracy, the reduction of discharge volume, and the disabled discharges as well in some cases.
Also, with the attention given to a single discharge port, the longer the interval between the last and current discharges, the more the evaporation is advanced to aggravate the problems described above.
SUMMARY OF THE INVENTION
With a view to solving the problems described above, the present invention is designed. It is an object of the invention to provide an ink jet head capable of preventing its unstable discharges by suppressing the evaporation from its discharge ports, and also, capable of minimizing the increase of running costs and others by making the time intervals as long as possible before any unstable discharges may take place. The ink jet head is also made capable of preventing the density from being densified more for the prints at the start of printing, which may result from evaporation from discharge ports.
In order to achieve the object described above, an ink jet head is structured as given below in accordance with the present invention.
In other words, an ink jet head, which is provided with an orifice plate having a plurality of discharge ports being open thereto, comprises evaporation suppressing grooves in the vicinity of the discharge ports.
For the ink jet head of the present invention, the interior of the evaporation suppressing grooves is made hydrophilic to the orifice plate thereof.
Also, for the ink jet head of the present invention, there are provided an orifice plate having a plurality of discharge ports open thereto, and a groove on the circumference of the array of the discharge ports. Then, evaporation suppressing grooves are formed in the vicinity of the discharge ports. For this ink jet head, the hydrophilicity of the surface of the evaporation suppressing grooves is higher than that of the orifice plate, and also, the hydrophilicity of the surface of the evaporation suppressing grooves is made higher still than that of the orifice plate, and then, the hydrophilicity of the surface of the evaporation suppressing grooves is higher than that of the aforesaid groove.
Also, for the ink jet head of the present invention, slope is provided on the end portion of the sectional configuration of each evaporation suppressing groove.
Also, for the ink jet head of the present invention, there are provided an orifice plate having a plurality of discharge ports open thereto, and a groove on the circumference of the array of the discharge ports. Then, evaporation suppressing grooves are formed in the vicinity of the discharge ports. For this ink jet head, the hydrophilicity of the surface of the evaporation suppressing grooves is made higher than that of the orifice plate. Here, the evaporation suppressing grooves are not connected with the aforesaid groove.
Also, for the ink jet head of the present invention, the water-repellency is relatively high on the orifice plate as the distance from the evaporation suppressing grooves becomes greater. In this case, the ratio of area covered by the water-repellent material on the orifice plate is made greater in order to heighten the water-repellency relatively as the distance from the evaporation suppressing grooves becomes larger on the orifice plate.
Also, for the ink jet head of the present invention, each end portion of the evaporation suppressing grooves, which is caused to abut upon first when operating the wiper, is formed at an acute angle, while the end portion thereof, which is then caused to abut upon later, is formed to be vertical or at an obtuse angle with respect to the end configurations of the evaporation suppressing grooves.
REFERENCES:
patent: 4994825 (1991-02-01), S
Akama Yuichiro
Inoue Takashi
Kaneko Mineo
Mizutani Michinari
Murakami Shuichi
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Shah M
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