Ink storing device

Details Ink storing device Ink storing device

2002-12-03

2004-10-19

Vo, Anh T. N. (Department: 2861)

Incremental printing of symbolic information

Ink jet

Fluid or fluid source handling means

Reexamination Certificate

active

06805436

ABSTRACT:

This application claims priority from Japanese Patent Application No. 2002-000169 filed Jan. 4, 2002, which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid reserving or storing device or reservoir that can reserve or store a liquid.
2. Description of the Related Art
For ink-jet printing apparatuses, a large number of means have been proposed and put to practical use which supply ink to an ink-jet print head from which the ink can be ejected.
The capillary force of nozzles in the ink-jet print head is utilized to supply ink to the ink-jet print head. Accordingly, the external force of pressurizing means, such as a pump, is not required. Thus, except for special cases, it is unnecessary to have a mechanism that delivers ink under pressure from an ink supply tank to the ink-jet print head. On the other hand, to continuously eject ink droplets stably through the nozzles in the ink-jet print head, the ink must be subjected to a very weak negative pressure of 100 to 2,000 Pa. This has been important in designing an ink-jet printing apparatus.
A classical ink supply method is known which is used for, for example, an ink-jet printing apparatus of a serial scan type such as the one shown in FIG.
1
.
The printing apparatus in this example sequentially prints an image on a sheet
17
as a printing medium by alternately performing a printing operation of ejecting ink from an ink-jet print head
12
on the basis of image data while moving a carriage
11
with the mounted the ink-jet print head
12
in a main scanning direction shown by arrow A, and a transporting operation of transporting the sheet
17
in a sub-scanning direction shown by arrow B and crossing the main scanning direction. Reference numeral
15
denotes a guide shaft that guides the carriage
11
so as to be movable in the main scanning direction. Reference numeral
16
denotes a platen roller. Reference
18
denotes a cap that can cap a nozzle portion (ink ejection port portion) of the print head
12
. The print head
12
can execute a recovery process for allowing ink to be ejected properly, by (preliminarily) ejecting ink that does not contribute to image printing, into the cap
18
. Further, a suction recovery process can be executed to allow ink to be ejected properly, by introducing negative pressure into the cap
18
capping the print head
12
to suction ink out from an ink ejection port.
A configuration of the print head
12
can be employed which includes an electrothermal converter used to eject ink droplets through the ink ejection port. That is, the electrothermal converter generates heat to cause film boiling, so that the resulting bubbling energy is utilized to eject ink droplets through the ink ejection port.
A method of supplying ink in such a printing apparatus comprises supplying ink from an ink reserving or storing device
13
such as an ink bag through a tube
14
to the print head
12
mounted on the carriage
11
as shown in FIG.
1
. With this method, to exert negative pressure on ink supplied to the print head
12
, the ink reserving device
13
is arranged on a surface located several centimeters lower than the gravitational height (also referred to as a “head”) of the print head
12
. Thus, the method of exerting negative pressure using the head difference can be achieved inexpensively using a very simple structure. However, the installation site of the printing apparatus is limited to a flat place such as a desk, or the printing apparatus must be high in order to ensure the head difference. To solve these problems, many attempts have been made to provide the ink reserving device
13
with negative pressure generating mechanism.
FIGS. 2 and 3
illustrate a different conventional example of a negative pressure generating mechanism provided in the ink reserving device.
The negative pressure generating mechanism in
FIG. 2
is provided with a metal spring
22
or the like in a flexible bag
21
in which ink is housed. The spring expands the bag
21
in the vertical directions of
FIG. 2
, shown by the arrows, to generate negative pressure in the ink
23
in the bag
21
. Reference numeral
24
denotes an outlet from which the ink
23
is supplied from the bag
21
to the print head. On the other hand, the negative pressure mechanism in
FIG. 3
is provided in a pressure regulating valve
31
in a case
30
that houses the bag
21
to control the air pressure in an outer area
32
around the bag
21
. Thus, negative pressure is exerted on the ink
22
in the bag
21
. That is, the pressure regulating valve
31
performs opening and closing operations so as to maintain a predetermined negative pressure in the outer area
32
. When the pressure regulating valve
31
is opened, external air flows into the case
30
.
However, a large number of parts are required by the negative pressure generating mechanisms that generate negative pressure in the flexible bag
21
as shown in
FIGS. 2 and 3
. This increases costs. Further, it is technically difficult to generate a negative pressure of the order of several hundred Pa. Furthermore, the presence of such a negative pressure generating mechanism may degrade the capability of storing available ink. Moreover, the thin bag
21
does not hinder passing of gas sufficiently, so that the open air may enter the bag
21
to expand it or evaporate the ink. Thus, many problems must be solved before the negative pressure generating mechanism can be added to the ink reserving method that uses the bag, while maintaining its reliability.
FIG. 4
is a sectional view of an ink reserving device that uses a sponge method, a presently popular ink reserving method. A sponge-like porous member (ink absorber)
41
can reserve ink on the basis of its own capillary force and can exert an appropriate negative pressure on ink when having a properly selected density. Reference numerals
40
,
42
, and
43
denote a case, an air intake port, and an ink outlet, respectively. Such a reserving method involves a very simple structure and allows the ink absorber
41
to be manufactured inexpensively by using a commercially available sponge-like porous member. Further, the size of the ink reserving device can be reduced, and the predetermined negative pressure can be generated regardless of changes in its position during operation.
However, general methods of manufacturing a sponge-like porous member do not provide a sufficiently dense porous member. Accordingly, the porous member must be compressed to some degree before use. This causes ink to be used inefficiently, so that the ink reserving device can generally be filled with ink only up to 70% of the volume of the sponge-like porous member. Further, it is difficult to arrange the sponge-like porous member uniformly in the ink reserving device. The nonuniform arrangement of the porous member may cause the ink to be used inefficiently. Further, a part of the ink-jet printing apparatus which contacts with ink is commonly composed of metal such as stainless steel or resin such as polypropylene, polyethylene, or a fluorine resin. When this metal or resin contacts with the ink, a very small amount of decomposed material or additive may dissolve. Many commercially available porous members are composed of a urethane resin and are thus relatively chemically unstable. In recent years, more chemically stable sponge-like porous members made of polypropylene have been employed. However, the sponge-like porous member contacts with ink over a large area and may thus chemically react to the ink or may be eluted into it. As a result, a large amount of product may affect the nozzles in the print head. On the other hand, various types of ink are used in order to enhance the applicability of the ink-jet printing apparatus. However, since the chemical stability of the sponge-like porous member is critical, it has been unavoidable to take proper measures such as changing the formation of the ink to improve its chemical stability, while sacrificing its physical properties.
FIG

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