FIELD OF THE INVENTION AND RELATED ART
[0001] The present invention relates to an ink jet recording head substrate and an ink jet
recording head having the same.
[0002] A recording head used in an ink jet recording system generally comprises a plurality
of fine ejection outlets (orifices) for ejecting ink, ink passages communicating with
the orifices, a common chamber for supplying ink to the respective ink passages and
ejection energy generating elements disposed corresponding to the ink passages.
[0003] In order to dispose the plural, particularly a great number of orifices with high
positional precision, the following manufacturing method is known, for example. The
number of grooves for constituting the ink passages are formed on a substrate with
photosensitive resin. Another substrate (top plate) is bonded on the groove-formed
surface to provide the ink passages, by which the number of orifices are disposed
with good positional precision.
[0004] It is known that means is provided on the substrate for permitting to display identification
of each of the energy generating elements (electrothermal transducer) in order to
facilitate quality control and observation of the change after inspection and repair
during the manufacturing step or after the manufacturing of the ink jet recording
head substrate and the ink jet recording head using the substrate wherein the number,
particularly the great number of electrothermal transducer are disposed on a supporting
member, corresponding to orifices.
[0005] For example, as shown in Figure 1, reference electrodes having a cut corner 3-1 are
provided at regular intervals (every 16 electrodes, in Figure 1), by which each of
the electrothermal transducers can be identified.
[0006] As another method, as shown in Figure 2, numericals giving representative identification
numbers (reference numbers) are written at predetermined positions during a photolithographic
process.
[0007] However, the method shown in Figure 1 involves a problem that when the great number
of electrothermal transducers are disposed at a high density, it is not easy to correctly
and quickly know the place of a reference number electrode, so that the correct inspection
is not possible in a short time.
[0008] The method shown in Figure 2 involves the problem that there is a limit to the reduction
of the size of the numerical, and therefore, it is not suitable to the electrothermal
transducers disposed at a high density.
[0009] When, for example, the heat generating resistor are disposed at a density higher
than 400 dpi (dot per inch), and when the numericals are reduced correspondingly,
the numericals are not easily read when they are observed by the operator's eyes through
an enlarging optical system or when they are automatically read using a CCD (charge
coupled device) camera, an optical microscope and a computer.
[0010] The recording head manufactured through the process described above may be inspected
after the manufacturing at the orifice and the portions therearound to inspect the
ink ejection or the like.
[0011] The inspection is carried out for each of the orifices. If some trouble is discovered,
the ejection energy generating element corresponding to the orifice is energized to
eject the ink, and the ink ejection and the ink dot deposited on the recording medium
are inspected further in detail. In addition, the trouble orifice is identified to
take some measure thereto, as the case may be.
[0012] When the orifice is identified in the observation thereof, there are following problems.
[0013] In the observation of the orifices, they are counted from one end, and therefore,
the orifice is erroneously identified. In addition, it takes long period to identify
it, with the result that the cost for the inspection process is increased.
[0014] US Patent 4,740,800 discloses liquid jet recording head comprising: a plurality of
discharge ports through which liquid is discharged; a plurality of electro-thermal
converting elements, each provided correspondingly to each discharge port and generating
thermal energy used for discharging said liquid, the electro-thermal converting elements
having a heat resistive layer provided on a substrate and an electrically, conductive
layer for forming at least one set of electrodes electrically connected to the heat
resistive layer; and a dummy heater provided adjacent to a group of plural elements
of the heat resistive layer.
SUMMARY OF THE INVENTION
[0015] According to the present invention an ink jet recording head substrate, comprising
a supporting member, a plurality of electrothermal transducers having heat generating
elements, and electrodes electrically connected thereto; and identification marks
for easy identification of each of said electrothermal transducers, is characterized
in that said identification mark comprises an information code representing a binary
coded decimal number and being located adjacent the electrothermal transducers.
[0016] The identification mark used in this embodiment indicates the number by dot arrangement
in a predetermined area, and therefore is easily formed in a small area, and in addition,
is easily read in the observation and the automatic inspection. The identification
mark can be easily formed at the correct position by a simple process step change,
for example, by adding a pattern for the formation of the identification mark to the
exposure pattern when the pattern is formed using the photolithography for the electrode
and the heat generating resistor constituting the electrothermal transducer, for example.
[0017] However, the material for forming the identification mark and the method for the
formation are not limited to the above, and various methods are usable.
[0018] When the identification mark is formed using an electrode layer and a heat generating
resistance layer, it will suffice if the materials of such layers have different refraction
indexes.
[0019] According to an aspect of the present invention, the marks are provided for every
predetermined number of ejection outlets on the ejection surface where the plural
ejection outlets are aligned, by which the position of the ejection outlet can be
counted on the basis of the mark, so that the ejection outlet can be identified easily.
[0020] By forming the mark during the manufacturing process for the ink passages and the
ink ejection outlets in the recording head manufacturing process, the positional relation
with the ejection outlet can be correct, and in addition, the ink ejection is not
influenced by the provision of the marks. How the invention may be carried out will
now be described by way of example only and with reference to the accompanying drawings
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figures 1 and 2 are top plan views of conventional substrates in a background art.
[0022] Figure 3 is a top plan view of a major part of the ink jet recording head substrate
according to an embodiment of the present invention.
[0023] Figure 4A is a part sectional view taken along a line B-B of Figure 3.
[0024] Figure 4B is a part sectional view taken along a line A-A of Figure 3.
[0025] Figures 5A - 5F are top plan views of an example of an identification mark.
[0026] Figure 6A is a perspective view of an ink jet recording head including the substrate
of Figure 3.
[0027] Figure 6B is a part sectional view taken along an ink passage of the recording head
of Figure 6A.
[0028] Figures 7 and 9 are top plan views illustrating another example of arrangements of
the identification marks.
[0029] Figures 8A - 8F and Figures 10A - 10D are top plan views of other examples of the
identification marks.
[0030] Figure 11 is a top plan view illustrating another example of the identification mark
arrangement.
[0031] Figure 12 is a perspective view of an ink jet recording head according to another
embodiment of the present invention.
[0032] Figures 13A - 13E are perspective view illustrating an example of ink jet recording
head manufacturing.
[0033] Figure 14 is a perspective view of an ink jet recording head according to a further
embodiment of the present invention.
[0034] Figure 15 is a somewhat schematic perspective view illustrating a major part of an
ink jet apparatus provided with the ink jet recording head according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The preferred embodiments of the present invention will be described in conjunction
with the accompanying drawings.
Embodiment 1
[0036] As shown in Figures 3, 4A and 4B, the ink jet recording head substrates in this embodiment
includes a supporting member 1, on which a great number of electrothermal transducers
are disposed at a desired density. Each of the electrothermal transducers includes
a heat generating resistor 2a and electrodes 3a and 3b electrically connected to the
heat generating resistor 2a, wherein the heat generating resistor 2a is constituted
by a heat generating resistor layer 2 between electrode layers to constitute a heat
generating portion for generating heat by electric power supply. Identification marks
4 representing identification numbers are formed above (adjacent one side of the substrate)
for representative electrothermal transducers.
[0037] As shown in Figures 4A and 4B, the identification mark 4 is constituted by projection
dots 4-1 provided by the electrode layer on the lower layer 4-2 constituting the heat
generating resistance layer, correspondingly to the identification number.
[0038] Since the heat generating resistance layer and the electrode layer have different
refractive indexes, the dots 4-1 are discriminated on the lower layer 4-2.
[0039] As shown in Figures 5A - 5F, the top line of the identification mark 4 as seen from
the above (the line (5)) represents the number of tens, and the bottom line (the line
(6)) represents the number of units. The columns (1) - (4) represents the number in
the binary system, wherein the digit increases from (1) column to (4) column. The
presence of the dot 4-1 in the columns (1) - (4) represents "1" in the binary system,
whereas the absence thereof represents "0" in the binary system.
[0040] For example, the identification mark in Figure 5A represents "0001" in the units,
and "0001" in the tens, and therefore, it represents "11" in the decimal system.
[0041] In the identification mark of Figure 5B, the number of units is "0010" in the binary
system, and the number of tens is "0010" in the binary system, and therefore, it represents
"22" in the decimal system.
[0042] Similarly, Figures 5C - 5F represent "44", "88", "34" and "51", respectively.
[0043] The identification mark 4 can be formed when the electrothermal transducers are formed
by patterning the heat generating resistor layer and the electrode layer laminated
on the supporting member 1. This is done by remaining the proper portions of the layers
on the supporting member as a predetermined configuration of the lower layer 4-2 and
as the dots 4-1 at the predetermined positions on the lower layer.
[0044] When the heat generating resistor layer and the electrode layer are patterned using
the photolithographic process, the identification marks can be formed simultaneously
with the formation of the electrothermal transducer simply adding the identification
mark forming pattern into the exposure mask.
[0045] The supporting member 1, the heat generating resistor 2A and the electrodes 3A and
3B may be made of material ordinarily used.
[0046] The configuration of the identification mark 4, more particularly, the configurations
of the dots 4-1 and the lower layer 4-2 are not limited to those illustrated in the
Figures, but may be in various forms. For example, the dot 4-1 may be in the form
of a circle or the like.
[0047] On the substrate having the structure described above, ink passages and ejection
outlets or the like are formed corresponding to the heat generating resistors 2a through
a usual method which will be described hereinafter, by which an ink jet recording
head having the structure shown in Figures 6A and 6B, for example, can be provided.
[0048] The materials of various parts of the ink jet recording head may be those ordinarily
used.
[0049] By the provision of the identification marks described above, the correct identification
number of each of the electrothermal transducer can be known quickly without difficulty
during the inspection after the power supply test for the substrate or during the
inspection after the printing test for the ink jet recording head.
[0050] An ink jet recording head having the structure shown in Figures 6A and 6B has actually
been manufactured through the process which will be described hereinafter. The identification
number has easily been known for each of the electrothermal transducers by observation
through metallurgical or through a stereoscopic microscope into the ink passage 9
from the ejection outlet 8 side.
[0051] The substrate 1 is a silicon plate having a surface layer of SiO₂ provided by heat
oxidation (layer thickness is 2.75 microns). On the supporting member 1, HfB₂ layer
having a layer thickness of 0.13 micron is formed as the heat generating resistor
layer by bias sputtering, and on the HfB₂ layer, an Al layer having a layer thickness
of 0.55 micron is laminated as the electrode layer 3 by the bias sputtering.
[0052] By the patterning process using the photolithographic technique, the electrode 3a
and 3b (line width of 26 microns), the heat generating resistor layer 2a (100 microns
x 20 microns with a pitch of 63.5 microns) and identification marks 4 (14 microns
x 28 microns of the lower layer 4-2 and 7 microns x 7 microns of the dot 4-1) are
formed by remaining the layers on the supporting member 1 in the configuration shown
in Figures 3, 4A and 4B.
[0053] At least on those portions of the electrodes 3a and 3b and the heat generating resistor
2a which will be right below the ink passage or the ink chamber, a protection layer
of SiO₂ having a thickness of 1.9 microns by bias sputtering.
[0054] Using the photolithographic process, the walls constituting the ink passages 9 and
the ink chamber (not shown) is formed by a cured layer of epoxy resin. A top plate
6 is bonded thereto to provide the ink jet recording head having the structure shown
in Figures 6A and 6B.
Embodiment 2
[0055] As shown in Figures 7, 8A - 8F, three digit decimal numbers can be represented by
adding a line (5) representing the number of hundreds. It will be understood that
Figures 8A - 8F represent "1", "64", "128", "448", "834" and "906". It will be understood
that a larger numbers can be represented by increasing the number of lines for the
dots 4-1.
Embodiment 3
[0056] The identification mark shown in Figures 9, 10A - 10D is constituted by two mark
elements each having two lines, thus providing in total four lines to represents the
numbers of hundreds. As will be understood, Figures 10A - 10D represent "1", "1822",
"1280" and "4736".
[0057] When the identification mark shown in Figure 9 is used, the two identification marks
may be formed over a plurality of electrothermal transducers, depending on the density
of the electrothermal transducers. In this case, by cutting a corner of the electrode
to provide the pattern 11, it can be made clear which electrothermal transducer corresponds
to the identification mark.
Embodiment 4
[0058] In the foregoing embodiments 1 - 3, the direction in which the ink is supplied in
the ink passage to the position corresponding to the heat generating resistor is substantially
the same as the direction in which the ink is ejected through the ejection outlet.
If the directions are different, for example, if the directions form right angles,
the identification mark 4 may be disposed at a position shown in Figure 11, for example.
Embodiment 5
[0059] Referring to Figure 12, a further embodiment will be described. Figure 12 is a perspective
view of an ink jet recording head of a so-called full line type manufactured by a
manufacturing method according to an embodiment of the present invention. The recording
head is provided with not less than 3000 orifices through which ink is ejected to
perform the recording.
[0060] A substrate 31 is provided with electrothermal transducer elements for producing
energy for ejecting the ink and function elements or the like for driving the electrothermal
transducer element. The substrate is made of a silicon wafer. Designated by a reference
numeral 32 is a layer of material curable by active energy radiation which will constitute
ink passages. A top plate 33 is made of glass. Ejection or discharging outlets (orifices)
34 are effective to form ink droplets. An ink supply port 35 functions to supply ink
to the recording head from an ink container. Grooves 36 are formed at a pitch of 10
orifices. The grooves function as orifice identification marks. By counting the orifices
on the basis of the mark, an orifice can be identified by smaller number of counting
operations.
[0061] Figures 13A - 13E are perspective views illustrating various manufacturing steps
for manufacturing the ink jet recording head of Figure 12, according to an embodiment
of the present invention. Referring to this Figure, the manufacturing method for the
recording head will be described.
[0062] Figure 13A illustrates the substrate provided with the ejection energy generating
elements 37. The ejection energy generating elements 37 are disposed at the portions
corresponding to the portions at which the ink passages will be formed. As the material
for the substrate 31, glass silicon wafer or the like are usable. As for the ejection
energy generating element 37, a piezoelectric element or a heat generating element
may be used, for example. In this embodiment, the substrate is made of silicon wafer,
and the element 37 is an electrothermal transducer element.
[0063] The substrate 31 is provided with function elements and electrode wiring (not shown)
for driving the electrothermal transducer element 37.
[0064] As shown in Figure 13B, a dissolvable and removable solid layer 38 is formed on the
substrate 31 in the pattern of the liquid passages and in the pattern corresponding
to the common liquid chamber communicating with all the liquid passages and in the
pattern of grooves adjacent to the orifices for each of 10 orifices.
[0065] The material of the solid layer 38 is of a positive type photoresist material containing
as major components naphthoquinonediazide derivative and orthocrezolenovolak resin
or a positive type dry film photoresist material.
[0066] The pattern of the solid layer 38 is formed by the photolithographic technology,
for example, to a thickness of 20 - 100 microns with the passage width of 20 - 100
microns. The material of the solid layer 38 will suffice if it can be dissolved and
removed by solvent after the formation of the pattern. The other chemical properties
are not limited. The positive chemical reaction may be of any type. The formation
of the solid layer 38 at the portions corresponding to the common chamber is not inevitable.
The formation thereof may be selected depending on the heads and the subsequent processing
steps.
[0067] As shown in Figure 13C, the side 31 having the solid layer 38 is coated with a material
32 curable by active energy radiation. The material 32 constitutes the walls of the
liquid passages, and therefore, it is preferable that the material exhibits good bonding
property with the substrate, sufficient mechanical strength and good chemical resistance.
The curable material 32 does not easily dissolve the solid layer 38 when it is applied
on the solid layer 38.
[0068] Figure 13D is a perspective view of a top plate having a recess 39 which will constitute
the common chamber. On the top side of the top plate 33, an ink supply port 35 is
formed. The material of the top plate 33 may be, for example, metal, glass, plastic
resin, ceramic material or the like. The recess 39 and the ink supply port 35 may
be formed through a process suitable for the material selected.
[0069] Subsequently, as shown in Figure 13E, the top side of the curable material 32 shown
in Figure 13C is bonded with the top plate 33 shown in Figure 13D. Thereafter, the
portions which will constitute the common liquid chamber is masked, and the active
energy radiation is applied thereto. After the application, it is developed with developing
liquid.
[0070] In the bonding, it is preferable that the surfaces bonded together is not warped,
but it is not inevitably necessary that the surfaces are smooth. They may be physically
or chemically treated for the improvement in the bonding property therebetween.
[0071] Then, the side of the bonded assembly in which the orifices are formed is cut, abraded
to provide a correct predetermined distance between the ejection energy generating
elements 37 and the orifices 35. The side is finished into a smooth orifice surface
(ejection surface). Next, the metallizing treatment or the like such as ink repelling
treatment or metal evaporation. When the abrading or other processing is carried out,
the passages and grooves for each ten orifices are filled with the solid layer 38,
and therefore, the abrading or other processes do not influence the internal walls
of the liquid passage. If necessary or desired, the other portions may be cut. If
not necessary, the abrading and the other processing may not be performed. For the
cutting operations, a precision cutting device for manufacturing semiconductor devices
is preferably used.
[0072] In order to provide the grooves or slot for each of ten orifices and the liquid passages,
the filling solid layer 38 is dissolved and removed, and the inside is cleaned. In
this manner, the liquid passages are formed and the grooves are formed in the orifice
surface.
[0073] In the dissolving, removing and the cleaning steps for the solid layer 38, it is
dipped in an organic solvent in a ultrasonic wave cleaning bath, by which the processing
can be completed quickly.
[0074] The above-described abrading step, the other treating step and the solid layer 38
dissolving and removing step may be performed before the top plate 33 is bonded. By
the method described in the foregoing according to the present invention, an ink jet
recording head shown in Figure 12 may be provided.
Embodiment 6
[0075] Figure 14 is a perspective view of a full line type recording head manufactured by
the manufacturing method described in the foregoing embodiment.
[0076] In this embodiment, the numbers of the grooves 36 for each 10 orifices, for each
100 orifices and for each 1000 orifices are different to facilitate identification
of an orifice. By this, the orifice can be identified quickly.
[0077] According to this embodiment, the correct identification number of each of the electrothermal
transducer may be known by eyes quickly using the identification mark representing
the identification of the electrothermal transducers, which can be easily read.
[0078] The discrimination of the identification number can be carried out automatically.
if a binary representation, a CCD camera, an optical microscope or a computer or the
like which constitute an automatic reading device.
[0079] Accordingly, the efficiency of the identification of the electrothermal transducers
during various inspections can be increased.
[0080] The identification mark according to this embodiment can be made at the same time
as and by the same material as the electrothermal transducers. In addition, the area
occupied by the identification mark can be very easily reduced, as compared with the
case where figures are written. Therefore, it can meet the high density of the thermal
electrotransducers.
[0081] In addition, according to another aspect of the present invention, a mark in the
form of a groove or grooves is provided for each predetermined number of ejection
outlets on the ejection orifice surface where the plural ejection outlets are disposed,
by which the position of an ejection outlet may be counted on the basis of the mark,
so that an ejection outlet can be identified.
[0082] In addition, by forming the mark during the manufacturing process for forming the
ink ejection outlets and the ink liquid in the recording head manufacturing process,
the positional relation with the ejection outlet can be made correct, and the ink
ejection is not adversely affected by the provision of the marks.
[0083] Accordingly, an ejection outlet can be identified quickly during the ejection outlet
inspecting operation, for example. Therefore, the time required for the inspection
can be reduced.
[0084] Figure 15 is a somewhat schematic perspective view of an ink jet recording apparatus
provided with the ink jet recording head according to an embodiment of the present
invention. In Figure 15, the apparatus includes the ink jet recording head 230. In
the ejection surface 231 of the ink jet head 230, ejection outlets (not shown) are
formed over the entire width of the recording region for a recording material (not
shown). In this example, the ink is ejected downwardly through the ejection outlets.
The recording material is supplied to the conveyer belt 265 by unshown means, and
is conveyed by the movement of the conveyer belt 265 driven by the conveying roller
264.
[0085] The apparatus further comprises an ejection recovery system 215, and an ink absorbing
material 261. To the absorbing material 261, the ink is ejected by the ink jet head
232 (preliminary ejection), the ejection trouble is prevented. A blade 260 is effective
to wipe the ejection side surface 231 of the head. In order for the blade 260 to continuously
wipe the plural ejection outlets in the ejection side surface 231, it is driven by
a motor 262 along the guide shaft 263.
[0086] The present invention is particularly suitable to an ink jet recording head of a
type wherein electrothermal transducers generating thermal energy for the ejection
of the ink are provided for plural ejection outlets (for example, not less than 1000
outlets and further not less than 2000 outlets) covering the entire recording region
for the recording material. The reason for this is that with the increase of the number
of the electrothermal transducers and the ejection outlets, the tendency of arising
the problems described in conjunction with the background art increases.
[0087] The present invention provides excellent effects particularly in a recording head,
recording device of a bubble jet recording system among the ink jet recording systems.
[0088] As to the ink ejection principle, the one disclosed in U.S. Patents Nos. 4,723,129
and 4,740,796 is preferred. This system is applicable to either of the so-called on-demand
type and the continuous type. Particularly, the on-demand type is preferable because
in that type, by applying at least one driving signal which gives rapid temperature
rise exceeding the nuclear boiling, corresponding to the recording information supplied
to the electrothermal transducers arranged corresponding to the sheets or the liquid
passages containing liquid (ink), heat energy is generated by the electrothermal transducers
to produce film boiling at the heating surface of the recording head, and consequently
a bubble is formed in the liquid (ink), corresponding to each of the driving signals.
[0089] By ejecting or discharging the liquid (ink) through an opening for discharging by
growth and shrinkage of the bubble at least one droplet is formed. By making the driving
signals into pulse shapes, growth and shrinkage of the bubble can be effected instantaneously
adequately to accomplish more preferable discharging of the liquid (ink) particularly
excellent in response characteristics. As the driving signals of such pulse shape,
those as disclosed in U.S. Patents Nos. 4,463,359 and 4,345,262 are suitable. Further
excellent recording can be performed by employment of the conditions disclosed in
U.S. Patent No. 4,313,124 relating to the temperature rising rate of the heating surface.
[0090] As to the construction of the recording head and the combination of the ejection
orifices, liquid passages the electrothermal transducers (linear liquid passage or
right angle liquid passage), the disclosure of the U.S. Patents Nos. 4,558,333 and
4,459,600 disclosing the construction in which the heating portion is arranged in
the flexed region is incorporated in the present invention. In addition, the present
invention can be also advantageously practiced using the structure disclosed in Japanese
Laid-Open Application No. 123670/1984 disclosing a slit common to a plurality of electrotransducers
as the discharging portions of the transducer or Japanese Laid-Open Patent Application
No. 138461/1984 disclosing an opening for absorbing pressure wave of thermal energy
corresponding to the discharging portion.
[0091] Further, as the recording head of the full line type having a length corresponding
to the maximum recording width for a maximum usable recording medium, either the construction
which satisfies its length by combination of a plurality of recording heads or the
construction of one recording head may be used, and the present invention provides
the corresponding effect.
[0092] In addition, the present invention is effective for a recording head of the freely
exchangeable chip type which enables electric connection to the main device or supply
of ink from the main device by being mounted on the main device, or for the case by
use of a recording head of the cartridge type provided integrally on the recording
head itself.
[0093] Also, addition of a restoration means for the recording head, a preliminary auxiliary
means, or the like provided as the construction of the recording device of the present
invention is preferable, because the effect of the present invention can be further
stabilized. Specific examples of these may include, for the recording head, capping
means, cleaning means, pressurizing or aspiration means, electrothermal transducers
or another heating element or preliminary heating means according to a combination
of them and it is also effective for performing stable recording operation to perform
preliminary mode which performs discharging the liquid for not performing the recording
operation.
[0094] Further, as the recording mode of the recording device, the present invention is
extremely effective for not only the recording mode only of a primary stream color
such as black or the like, but also a device equipped with at least one of plural
different colors or full-color by color mixing, whether the recording head may be
either integrally constructed or combined in plural number.
[0095] In the embodiment of the present invention described in the foregoing, liquid ink
is taken. However, the present invention is applicable to ink which is solid or softened
in the room temperature, since in the ink jet recording apparatus described above,
the ink is heated to and maintained at a temperature not less than 30 degrees and
not more than 70 degrees to provide stabilized ink viscosity so as to place it in
a stabilized ejection region. Therefore, the present invention is applicable to any
ink if it is in liquid state when the recording signal is applied. In addition, the
present invention is applicable to the ink liquefied by application of the thermal
energy, even if it starts to solidify at the time reaching the recording material,
wherein the temperature rise by the thermal energy is positively prevented by causing
the energy to be consumed for the phase change from the solid state to the liquid
state of the ink, or wherein the ink may be such that it is solidified to prevent
evaporation. In these cases, the ink may be retained in the form of liquid or solid
material in recess or through holes of porous sheet, which is faced to the electrothermal
transducers. In this embodiment, the present invention is most advantageous when the
above-described film boiling is used.
[0096] While the invention has been described with reference to the structures disclosed
herein, it is not confined to the details set forth and this application is intended
to cover such modifications or changes as may come within the scope of the following
claims.