BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to an ink jet apparatus that prints by ejecting ink
droplets under pressure from nozzles.
2. Description of the Related Art
[0002] Traditional impact printers are now being replaced with non-impact printers, and
the market of the non-impact printers is being expanded. One known kind of non-impact
printers is an ink jet printer simple in principle and that can easily effect multi-scale
or color printing. Of all of the types of ink jet printers, a drop-on-demand type
ink jet printer capable of jetting ink droplets at a required time during printing
has rapidly spread owing to its good jetting efficiency and its low running cost.
[0003] Typical examples of such drop-on-demand type ink jet printers, are a Kaiser type
disclosed in Japanese Patent Publication No. Sho 53-12138 and a thermal jet type disclosed
in Japanese Patent Publication No. Sho 61-59914, for example. However, the former
is hard to reduce in size, and the latter is required to have a high heat resistance
of ink because the ink undergoes a high temperature. Thus, both types have very severe
problems in application.
[0004] To solve the above problems, there has been a newly proposed shear mode type disclosed
in U.S. Patent No. 4,887,100, for example.
[0005] Fig. 16 shows a shear mode type ink jet apparatus 1 in the prior art. As shown in
Fig. 16, the ink jet apparatus 1 is constructed of a piezoelectric ceramics plate
2, a cover plate 10, a nozzle plate 14, and a substrate 41.
[0006] The piezoelectric ceramics plate 2 is provided with a plurality of grooves 3 by grinding
with use of a diamond blade or the like. Accordingly, a plurality of side walls 6
extend along the grooves 3 in such a manner that each side wall 6 is formed between
adjacent ones of the grooves 3. Each side wall 6 is polarized in a direction indicated
by an arrow 5. All the grooves 3 have the same depth, and they are parallel to each
other. The depth of each groove 3 is gradually reduced as it approaches a rear end
surface 15 of the piezoelectric ceramics plate 2 to form a shallow groove 7 near the
rear end surface 15. A pair of metal electrodes 8 are formed on opposed side surfaces
of each groove 3 at an upper half portion thereof by sputtering or the like. Further,
a metal electrode 9 is formed on opposed side surfaces and a bottom surface of each
shallow groove 7 by sputtering or the like. The pair of metal electrodes 8 formed
on the opposed side surfaces of each groove 3 are connected with the metal electrode
9 formed on the opposed side surfaces and the bottom surface of the corresponding
shallow groove 7 contiguous to the groove 3.
[0007] The cover plate 10 is formed of a ceramics material, a resin material, etc. The cover
plate 10 is provided with an ink inlet hole 16 and a manifold 18 communicating with
the ink inlet hole 16 by grinding, cutting, etc. The lower surface of the cover plate
10, on which the manifold 18 is formed, is bonded to the upper surface of the piezoelectric
ceramics plate 2 on which the grooves 3 are formed by an epoxy adhesive 20 (see Fig.
18). Accordingly, a plurality of individual ink chambers 4 functioning as ink channels
(see Fig. 18) are defined by the grooves 3 of the piezoelectric ceramics plate 2 and
the lower surface of the cover plate 10 to be transversely equally spaced from each
other. As shown in Fig. 18, each ink chamber 4 is rectangular in vertical section,
and it is filled with ink in operation.
[0008] As shown in Fig. 16, the nozzle plate 14 is bonded to the front end surface of the
assembly of the piezoelectric ceramics plate 2 and the cover plate 10. The nozzle
plate 14 is provided with a plurality of nozzles 12 at laterally spaced positions
corresponding to the front end positions of the ink chambers 4. The nozzle plate 14
is formed of a plastic material such as polyalkylene terephthalate (e.g., polyethylene
terephthalate), polyimide, polyetherimide, polyetherketone, polyethersulfone, polycarbonate,
or cellulose acetate.
[0009] The substrate 41 is bonded to the lower surface of the piezoelectric ceramics plate
2 on the opposite side of the cover plate 10 by an adhesive such as an epoxy adhesive.
A plurality of individual conductor film patterns 42 are formed on the substrate 41
at transversely spaced positions corresponding to the rear end positions of the ink
chambers 4. Each conductor film pattern 42 is connected through a conductor wire 43
to the metal electrode 9 formed on the bottom surface of the shallow groove 7 in the
corresponding ink chamber 4 by wire bonding.
[0010] Fig. 17 shows a schematic diagram of a control section for controlling the ink jet
apparatus 1. As shown in Fig. 17, the conductor film patterns 42 formed on the substrate
41 are individually connected to an LSI chip 51. Also connected to the LSI chip 51
are a clock line 52, a data line 53, a voltage line 54, and a ground line 55. The
LSI chip 51 determines from which nozzle 12 the ink droplets are to be jetted according
to data appearing on the data dine 53 on the basis of continuous clock pulses supplied
from the clock line 52. Then, according to the result of determination, the LSI chip
51 applies a voltage V of the voltage line 54 to the conductor film pattern 42 connected
to the metal electrode 8 in the ink chamber 4 to be driven. Further, the LSI chip
51 applies a zero volt of the ground line 55 to the other conductor film patterns
42 connected to the metal electrodes 8 in the other ink chambers 4 not to be driven.
[0011] The operation of the ink jet apparatus 1 is described with reference to Figs. 18
and 19. When the LSI chip 51 determines that the ink droplets are to be jetted from
the nozzle 12 corresponding to the ink chamber 4b as one of the ink chambers 4 of
the ink jet apparatus 1 according to given data, a positive driving voltage V is applied
to the metal electrodes 8e and 8f and the metal electrodes 8d and 8g are grounded.
As shown in Fig. 19, a driving electric field in a direction indicated by an arrow
13b is generated in the side wall 6b, and a driving electric field in a direction
indicated by an arrow 13c is generated in the side wall 6c. As the directions indicated
by the arrows 13b and 13c of the driving electric fields are perpendicular to the
direction indicated by the arrow 5 of polarization of the piezoelectric ceramics plate
2, the side walls 6b and 6c are rapidly deformed inwardly of the ink chamber 4b by
a piezoelectric thickness shear effect. This deformation of the side walls 6b and
6c reduces the volume of the ink chamber 4b to rapidly increase the pressure of the
ink filled in the ink chamber 4b and thereby generate a pressure wave. As a result,
the ink droplets are jetted from the nozzle 12 (see Fig. 19) communicating with the
ink chamber 4b.
[0012] When the application of the driving voltage V is stopped, the side walls 6b and 6c
gradually restore their original positions before deformation (see Fig. 18), and the
pressure of the ink contained in the ink chamber 4b is therefore gradually decreased.
Then, additional ink is supplied from an ink tank (not shown) through the ink inlet
hole 16 (see Fig. 16) and the manifold 18 (see Fig. 16) into the ink chamber 4b.
[0013] Referring to Fig. 14 for explanatory purposes, which is a sectional side view of
the ink jet apparatus according to the invention, when the pressure in each ink chamber
4 is increased to jet the ink droplets, the ink is forced from the corresponding nozzle
12 simultaneously, the ink reversely flows from the manifold 18 into the ink inlet
hole 15. As a result, the pressure near the manifold 18 is rapidly reduced to generate
a negative pressure wave. When this negative pressure wave reaches the nozzle 12,
the ink jet from the nozzle 12 is stopped. The shorter the distance y between the
front side surface of the manifold 18 and the inner surface of the nozzle plate 14,
the shorter the time of reach of the negative pressure wave to the nozzle 12. Accordingly,
when the distance y is reduced, the ink jet from the nozzle 12 is quickly stopped
to result in a reduction in volume of ink droplets, causing a deterioration in print
quality. On the other hand, when the distance y is largely increased, to cope with
the above problem, the distance x between the front side surface of the manifold 18
and the rear end surface of each ink chamber 4 becomes very small. Accordingly, the
ink flow from the manifold 18 into each ink chamber 4 becomes difficult, so that a
necessary amount of ink cannot be supplied to each ink chamber 4. As a result, the
volume of ink droplets is reduced to cause deterioration in print quality.
SUMMARY OF THE INVENTION
[0014] It is a primary object of the present invention to provide an ink jet apparatus that
can maintain a pressure necessary for jetting ink droplets for a relatively long period
of time and can smoothly introduce ink from the manifold into each ink chamber, thereby
improving a print quality.
[0015] According to the present invention, an ink jet apparatus includes a plurality of
ink chambers each having a front end and a rear end. A manifold is provided to introduce
ink into each of the ink chambers and has a front side surface on a side near the
front end of the each ink chamber. A nozzle is provided at the front end of each ink
chamber. The ink is jetted from the nozzle by applying a pressure to the ink contained
in each ink chamber. The improvement of this invention is that a position of the manifold
is such that a distance between the front side surface of the manifold and the rear
end of the each ink chamber is set to 0.2mm or more, and a distance between the front
side surface of the manifold and the nozzle is set to 3mm or more.
[0016] Preferably, the distance between the front side surface of the manifold and the nozzle
comprises a distance between the front side surface of the manifold and an opening
of the nozzle on a side exposed to the ink chamber.
[0017] In the ink jet apparatus off the present invention having the above construction,
pressure necessary for jetting ink droplets can be maintained for a relatively long
period of time. A flow resistance to the ink flowing from the manifold into each ink
chamber can be reduced.
[0018] As described above, the distance between the front side surface of the manifold and
the nozzle is set so that the pressure near the nozzle can be maintained for a necessary
period of time upon jetting of the ink, thereby ensuring a sufficient volume of ink
droplets to be jetted. Accordingly, print quality is improved. Further, since a necessary
amount of ink is supplied to each ink chamber, the volume of ink droplets to be jetted
can be made into a desired value, thereby improving print quality.
[0019] Other objects and features of the invention will be more fully understood from the
following detailed description and appended claims when taken with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
Fig. 1A is an enlarged partial sectional view of a principle part of an ink jet apparatus
in a preferred embodiment according to the present invention, showing the size of
an ink inlet hole;
Fig. 1B is a partial cross section taken along the line I-I in Fig. 1A;
Fig. 2 is a graph showing the relation between the diameter of the ink inlet hole
and a Reynolds number;
Fig. 3A is an enlarged partial sectional view similar to Fig. 1A, showing the depth
of a manifold;
Fig. 3B is a partial cross section taken along the line III-III in Fig. 3A;
Fig. 4 is a graph showing the relation between the depth of the manifold and the central
speed of a jet;
Fig. 5A is a view similar to Fig. 1A, showing the sectional area of the manifold and
the total sectional area of ink chambers;
Fig. 5B is a cross section taken along the line V-V in Fig. 5A;
Fig. 6 is a graph showing the relation between the sectional area of a channel and
a pressure loss;
Fig. 7 is a graph showing the relation between the ratio of the sectional area of
the manifold to the total sectional area of the ink chambers and a pressure loss;
Fig. 8 is a schematic partial sectional view similar to Fig. 1B, showing the depth
of each ink chamber and the thickness of a cover plate;
Fig. 9 is a graph showing the relation between the product of the depth of each ink
chamber and the thickness of the cover plate and the flying speed of ink droplets;
Fig. 10A is a partial sectional view similar to Fig. 1B, showing when the bonded surface
of the cover plate is smooth;
Fig. 10B is a partial sectional view similar to Fig. 10A, showing when the bonded
surface of the cover plate is rough;
Fig. 11 is a graph showing the relation between the surface roughness of the cover
plate and the volume of ink droplets;
Fig. 12A is a partial sectional view similar to Fig. 10A, showing the condition where
an adhesive for bonding a piezoelectric ceramics plate and the cover plate is heated
to be hardened when a coefficient of linear expansion of the piezoelectric ceramics
plate is different from that of the cover plate;
Fig. 12B is a partial sectional view similar to Fig. 12A, showing the condition where
the adhesive heated to be hardened is returned to ordinary temperature;
Fig. 13 is a table showing the result of an endurance test when various materials
are used for the piezoelectric ceramics plate and the cover plate of the ink jet apparatus;
Fig. 14 is an enlarged partial sectional view similar to Fig. 1A, showing the position
of the manifold relative to each ink chamber;
Fig. 15 is a graph showing the relation between the position of the manifold and the
volume of ink droplets;
Fig. 16 is a partially cutaway perspective view of a shear mode type ink jet apparatus
in the prior art;
Fig. 17 is a schematic diagram of a control section of the ink jet apparatus shown
in Fig. 16;
Fig. 18 is a partial sectional view of the ink jet apparatus shown in Fig. 16; and
Fig. 19 is a partial sectional view similar to Fig. 18, showing the operation of the
ink jet apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] A preferred embodiment of the present invention is described referring to the drawings,
in which the same members as those shown in Figs. 16 to 19 are denoted by the same
reference numerals, and the explanation thereof will be omitted.
[0022] Figs. 1A and 1B are enlarged views of an ink inlet hole 16 and a manifold 18 in the
preferred embodiment. Specifically, Fig. 1A is a cross section taken from the side
of an ink jet apparatus 1, and Fig. 1B is a cross section taken along the line I-I
in Fig. 1A.
[0023] As shown in Fig. 1B, the ink jet apparatus 1 includes a piezoelectric ceramics plate
2 and a cover plate 10. The piezoelectric ceramics plate 2 has a plurality of grooves
3 and a plurality of side walls 6 partitioning the grooves 3. The cover plate 10 has
the ink inlet hole 16 and the manifold 18. The piezoelectric ceramics plate 2 and
the cover plate 10 are bonded together by an adhesive 20 to thereby define a plurality
of ink chambers 4 as ink channels.
[0024] As shown by an arrow 30 in Fig. 1A, ink is supplied from an ink tank (not shown)
through an ink supply tube (not shown) into the ink inlet hole 16 having a diameter
d. Then, the ink is supplied from the ink inlet hole 16 through the manifold 18 into
each ink chamber 4. Since the manifold 18 has a sectional area larger than that of
the ink inlet hole 16 as shown, the ink flowing from the ink inlet hole 16 into the
manifold 18 is jetted therein. Accordingly, the ink undergoes a divergent flow loss
due to rapid enlargement of a channel. A total flow loss occurring in the ink flowing
from the ink inlet hole 16 into the manifold 18 varies according to the state the
ink is jetted in. When the ink is jetted in a state of laminar flow, the total flow
loss is equal to the divergent flow loss. When the ink is jetted in a state of turbulent
flow, the total flow loss is equal to the sum of the divergent flow loss and a turbulent
flow loss.
[0025] To reduce the total flow loss and obtain a stable flow of the ink, excluding any
small fluctuations, the jet state must be kept in the laminar flow state. To obtain
the laminar flow state, it is known that a Reynolds number Re, which is an important
parameter deciding the flow state of a fluid, must be reduced to about 30 or less
(see for example,
Dynamics of Viscous Fluid, Takefumi Ikui and Masahiro Inoue, p. 206, Rikogaku-sha). The Reynolds number Re
is expressed as

, where u represents the velocity of the ink flowing from the ink inlet hole 16; d
represents the diameter of the ink inlet hole 16; and ν represents the coefficient
of kinematic viscosity of the ink. If the consumption of the ink per unit time is
fixed, the velocity u is in inverse proportion to the square of the diameter d of
the ink inlet hole 16. The Reynolds number Re is, therefore, in inverse proportion
to the diameter d of the ink inlet hole 16, as shown in Fig. 2.
[0026] In this preferred embodiment, the maximum consumption of the ink per unit time was
set so that ink droplets in a volume of 40pl were simultaneously jetted from 25 nozzles
at a frequency of 5kHz. A value of 10cps of pigment ink containing tripropylene glycol
monomethylether (TPM) as a base at ordinary temperature was used as the coefficient
of kinematic viscosity ν of the ink. Then, the diameter d of the ink inlet hole 16
was varied to obtain the Reynolds number Re. The relation shown by a solid curve 32
in Fig. 2 was obtained as the result.
[0027] The Reynolds number Re is influenced not only by the diameter d of the ink inlet
hole 16 but also by the consumption of the ink per unit time and the coefficient of
kinematic viscosity ν of the ink. The consumption of the ink per unit time cannot
be reduced because a printing speed and clearness must be maintained. The coefficient
of kinematic viscosity ν of the ink cannot be largely increased due to the need for
stability of the jet of ink droplets. In particular, it is desired to prevent generation
of unduly small ink droplets called satellites. Accordingly, there is a possibility
that the relation between the Reynolds number Re and the diameter d of the ink inlet
hole 16 may shift upwards as shown by a broken line 34 in Fig. 2 according to a change
in printing speed or ink viscosity. However, there is no possibility that the relation
may shift downwards from the solid line 32 calculated by using a minimum printing
speed and a minimum ink viscosity.
[0028] Using the relation shown by the solid line 32 in Fig. 2, the larger the diameter
d of the ink inlet hole 16, the less likely the jet state will become the turbulent
flow state. As is apparent from Fig. 2, the diameter d of the ink inlet hole 16 must
be set to 0.2mm or more to reduce the Reynolds number Re to 30 or less.
[0029] As mentioned above, the jet state of the ink flowing from the ink inlet hole 16 into
the manifold 18 can be made into a laminar flow state by setting the diameter d of
the ink inlet hole 16 to 0.2 mm or more. Accordingly, the total flow loss occurring
in the ink flowing from the ink inlet hole 16 into the manifold 18 becomes the divergent
flow loss, so that the total flow loss can be minimized, resulting in no turbulence
of the ink flow in the manifold 18. Accordingly, the pressure of the ink in the manifold
18 becomes constant, and the pressure of the ink in each ink chamber 4 therefore becomes
constant. As a result, the volume and the flying speed of ink droplets to be jetted
become constant, thereby improving print quality. Further, since a desired amount
of ink is supplied to each ink chamber 4, the volume of ink droplets to be jetted
becomes a desired amount, thereby improving a print quality.
[0030] In this preferred embodiment, the size of the ink inlet hole 16 having a circular
shape is decided to reduce the Reynolds number Re to 30 or less. When the ink inlet
hole 16 is rectangular, elliptical, etc., the Reynolds number Re that will not cause
a turbulent flow of ink may be obtained by carrying out a test to decide the size
of the ink inlet hole 16.
[0031] In the ink jet apparatus 1 of this preferred embodiment, the ratio of pressure generated
in each ink chamber 4 to driving voltage applied to each electrode 8 is large. Further,
the ink flow into each ink chamber 4 is stable, and a resistance to the ink flow is
small. Accordingly, a high pressure can be generated in each ink chamber 4 by applying
a low driving voltage, and ink droplets can be jetted with a speed and a volume sufficient
to form print images. According to the ink jet apparatus 1 of this preferred embodiment,
ink droplets can be stably jetted with a speed of about 3 to 8m/sec and a volume of
about 30 to 90pl by applying a low driving voltage of about 20 to 50 volts. Thus,
a driving circuit can be manufactured at a low cost with a small size. The ink jet
apparatus 1 as a whole can therefore be manufactured at a low cost with a small size.
[0032] Now, the depth of the manifold 18 is described referring to Fig. 3a. As shown by
an arrow 30 in Fig. 3a, ink is supplied from an ink tank (not shown) through an ink
supply tube (not shown) into the ink inlet hole 16. Then, the ink is supplied from
the ink inlet hole 16 through the manifold 18 into each ink chamber 4. At this time,
the ink in the manifold 18 flows, as shown by arrows 31 in Fig. 3B, into each ink
chamber 4. Since ink chambers 4a and 4b directly face the ink inlet hole 16, the ink
pressures in the ink chambers 4a and 4b are changed by the jet of the ink flowing
from the ink inlet hole 16.
[0033] Fig. 4 shows a change in central speed of the ink jet when the ink flows from the
ink inlet hole 16 through the manifold 18 into the ink chambers 4a and 4b directly
facing the ink inlet hole 16. In Fig. 4, the axis of the abscissa represents the depth
h of the manifold 18, and the axis of the ordinate represents the central speed of
the jet. In this preferred embodiment, a test was carried out using three values of
the diameter d of the ink inlet hole 16 and setting a maximum ink consumption so that
ink droplets in a volume of 40pl were simultaneously jetted from 20 nozzles at a frequency
of 5kHz. Solid lines 35, 36, and 37 shown in Fig. 4 correspond to the diameter d of
the ink inlet hole 16 set to 0.7, 1.0, and 1.4mm, respectively.
[0034] As is apparent from Fig. 4, when the depth h of the manifold 18 is zero, the central
speed u of the ink jet flowing from the ink inlet hole 16 is maximum in each case.
As well known, the central speed u of the ink jet is in inverse proportion to the
square of the diameter d of the ink inlet hole 16. The central speed u relatively
rapidly decreases with an increase in depth h from zero. When the depth h becomes
about 0.2mm or more, especially, 0.3mm or more, the central speed in becomes sufficiently
small in each case. Even when the depth h is further increased, the central speed
u hardly decreases in each case. Further, as far as the diameter d of the ink inlet
hole 16 is 0.2mm or more, a tendency similar to that shown in Fig. 4 is exhibited.
[0035] The flow velocity of the jet is proportional to the ink consumption per unit time,
which varies according to a print pattern. Accordingly, unless the depth h of the
manifold 18 is set to a value enough to diminish the influence of the ink jet flowing
from the ink inlet hole 16, the ink pressures in the ink chambers 4a and 4b directly
facing the ink inlet hole 16 would vary according to the print pattern, causing instability
of jetting of the ink droplets.
[0036] Consequently, in the ink jet apparatus 1 of this preferred embodiment, the depth
h of the manifold 18 for distributing the ink flowing from the inlet hole 16 to each
ink chamber 4 is set to 0.2mm or more, preferably 0.3mm or more.
[0037] Because the depth h of the manifold 18 is set to 0.2 mm or more, preferably 0.3mm
or more, the ink flow into each ink chamber becomes stable and uniform. Accordingly,
the pressure generated in each ink chamber 4 upon application of a driving voltage
to each electrode 8 becomes constant, and ink droplets can be jetted with a speed
and a volume sufficient to form print images. According to the ink jet apparatus 1
of this preferred embodiment, ink droplets can be stably and uniformly jetted with
a speed of about 3 to 8m/sec and a volume of about 30 to 90pl by applying a driving
voltage of about 20 to 50 volts. Further, since the ink flow into each ink chamber
4 is stable and uniform, it is not necessary to provide a function for correcting
the ink flow in the driving circuit. Thus, the driving circuit can be simplified and
made compact. The ink jet apparatus 1 can therefore be stabilized and manufactured
at a low cost with a small size.
[0038] The relation between the sectional area of the manifold 18 and the total sectional
area of the ink chambers 4 is described referring to Fig. 5A. In this description,
the sectional area of the manifold 18 means the area of a cross section perpendicular
to the longitudinal direction of the manifold 18, and the total sectional area of
the ink chambers 4 means the total areas of the cross sections perpendicular to the
longitudinal directions of all of the ink chambers 4.
[0039] As shown by an arrow 30 in Fig. 5A, ink is supplied from an ink tank (not shown)
through an ink supply tube (not shown) into the ink inlet hole 16. Then, the ink is
supplied from the ink inlet hole 16 through the manifold 18 into each ink chamber
4. At this time, the ink in the manifold 18 flows as shown by arrows 31 in Fig. 5B
into each ink chamber 4.
[0040] The manifold 18 is a rectangular channel having a sectional area

as shown. Each ink chamber 4 is a rectangular channel having a sectional area

as shown. When the ink flows in these channels, it undergoes a flow resistance. In
general, a flow resistance increases proportionally to the length of a channel and
rapidly decreases with a decrease in sectional area of the channel. When the channel
has a rectangular cross section as in the manifold 18 and each ink chamber 4, the
flow resistance to the ink in a unit length of the channel is in substantially inverse
proportion to the square of the sectional area of the channel, as shown in Fig. 6.
This is true provided that the aspect ratio of the channel is kept substantially constant
when the cross section of the channel changes in size. However, when the height and
the width of the rectangular cross section are greatly different from each other,
the relation shown in Fig. 6 is not obtained. Assuming that the height and the width
of the rectangular cross section in both the manifold 18 and each ink chamber 4 are
not greatly different from each other, the relation between the sectional area of
the cross section and the flow resistance in both the manifold 18 and each ink chamber
4 shows a tendency similar to that shown in Fig. 6.
[0041] The ink flowing from the ink inlet hole 16 undergoes a flow resistance in the manifold
18 and a flow resistance in each ink chamber 4 until the ink reaches each nozzle (not
shown). In other words, the total flow resistance to the ink is the sum of the flow
resistance in the manifold 18 and the flow resistance in all of the ink chambers 4.
As shown in Fig. 5B, a flow distance from the ink inlet hole 16 to an ink chamber
4c is larger than a flow distance from the ink inlet hole 16 to an ink chamber 4a,
for example. Therefore, the flow resistance to the ink that will flow into the ink
chamber 4c becomes larger than the flow resistance to the ink that will flow into
the ink chamber 4a. Further, the ink that will flow into another ink chamber 4 more
distant from the ink inlet hole 16 than the ink chamber 4c undergoes a larger flow
resistance.
[0042] To make the ink flow into each ink chamber 4 uniform, the manifold 18 is designed
in such a manner that the flow resistance in the manifold 18 becomes uniform regardless
of the position of each ink chamber 4. Alternatively, the manifold 18 is designed
to have a sectional area such that the flow resistance in the manifold 18 is insignificant
compared with the flow resistance in each ink chamber 4. The former method is impractical
in general because the shape and the forming of the manifold 18 are complicated. Accordingly,
the latter method will now be described.
[0043] Fig. 7 shows a change in total flow resistance to the ink in this preferred embodiment,
in which the axis of abscissa represents a sectional area ratio S1/SA between the
manifold 18 and all the ink chambers 4. The sectional area SA of all of the ink chambers
4 is equal to the product of the sectional area S2 of each ink chamber 4 and the number
of all of the ink chambers 4. In a test according to this preferred embodiment, the
maximum ink consumption per unit time was set so that ink droplets in a volume of
40pl were simultaneously jetted from 50 nozzles at a frequency of 2.5kHz. A value
of 10cps of pigment ink containing tripropylene glycol monomethylether (TPM) as a
base at ordinary temperature was used as the coefficient of kinematic viscosity ν
of the ink. The dimensions of each ink chamber 4 were the height H of 400µm, the width
b of 80µm, and the length of 12mm.
[0044] In Fig. 7, a solid line 38 is a curve showing the total flow resistance to the ink,
and a broken line 39 is a line showing the flow resistance in the ink chambers 4 only
with no flow resistance in the manifold 18. As is apparent from Fig. 7, the total
flow resistance rapidly increases on the left side of the sectional area ratio S1/SA
with respect to a boundary value of about 1, that is, it rapidly increases with a
decrease in sectional area ratio S1/SA from about 1. Further, when the sectional area
ratio S1/SA increases from about 1, the total flow resistance rapidly approaches the
flow resistance in the ink chambers 4 only as shown by the broken line 39. In other
words, when the sectional area ratio S1/SA decreases from 1, the flow resistance in
the manifold 18 rapidly increases; while, when the sectional area S1/SA increases
from 1, the flow resistance in the manifold 18 rapidly decreases.
[0045] Accordingly, the sectional area ratio S1/SA needs to be set to 1 or more to reduce
the flow resistance in the manifold 18. Further, in an ink jet apparatus having a
structure like that of this preferred embodiment, there is no possibility that the
inks in the adjacent ink chambers 4 will be simultaneously jetted. Accordingly, the
total sectional area of all of the ink chambers 4 becomes half in reality. Even considering
this fact, the sectional area ratio S1/SA needs to be set to 0.5 or more.
[0046] Thus, the increase in the sectional area ratio S1/SA is necessary for a reduction
in flow resistance in the manifold 18. However, when the sectional area ratio S1/SA
becomes about 5 or more, the flow resistance in the manifold 18 is greatly reduced
to 1% or less of the flow resistance in the ink chambers 4, which is substantially
insignificant. Accordingly, an increase in sectional area ratio S1/SA from about 5
merely causes enlargement of the ink jet apparatus 1 and is hardly effective for the
reduction in the total flow resistance. Thus, it is reasonable to set the sectional
area ratio S1/SA to a value up to 5 from the viewpoints of a reduction in size and
cost of the ink jet apparatus 1.
[0047] In the test according to this preferred embodiment, the dimensions of each ink chamber
4 were set to 400µm in height H, 80µm in width b, and 12mm in length. However, even
when the dimensions of each ink chamber 4 are changed, the above preferable sectional
area ratio S1/SA is unchanged. That is, as shown in Fig. 7, the curve 38 showing a
pressure loss is merely expanded or contracted in a vertical direction on the basis
of the axis of abscissa as shown by a broken line 38a or 38b.
[0048] Consequently, in the ink jet apparatus 1 of this preferred embodiment, the sectional
area of the manifold 18 for distributing the ink having flowed from the ink inlet
hole 16 into each ink chamber 4 is set to about 0.5 to 5 times the total sectional
area of all of the ink chambers 4.
[0049] Because the sectional area of the manifold 18 is set to about 0.5 to 5 times the
total sectional area of all the ink chambers 4, the ink is substantially uniformly
distributed through the manifold 18 into each ink chamber 4 with a low flow resistance.
Accordingly, the ink can be smoothly introduced into each ink chamber 4, and a high
pressure can be generated in each ink chamber 4 by applying a low driving voltage.
Thus, ink droplets are jetted with a sufficient speed and a uniform volume to form
print images. According to the ink jet apparatus 1 of this preferred embodiment, ink
droplets can be stably jetted with a speed of about 3 to 8m/sec and a volume of about
30 to 90pl by applying a low driving voltage of about 20 to 50 volts. Thus, a driving
circuit can be manufactured at a low cost with a small size. The ink jet apparatus
1 as a whole can therefore be manufactured at a low cost with a small size.
[0050] Now, the depth of each groove 3 forming each ink chamber 4 and the thickness of the
cover plate 10 is described referring to Fig. 8 which is a sectional view of a part
of the ink jet apparatus 1 showing the shapes of the grooves 3, the side walls 6,
the metal electrodes 8, and the cover plate 10. Reference character b represents the
width of each groove 3 formed on the piezoelectric ceramics plate 2, and reference
character H represents the depth of each groove 3. As each metal electrode 8 is formed
on the upper half portion of each side wall 6, the length from the upper end to the
lower end of each metal electrode 8 becomes half of the depth H of each groove 3,
that is, becomes H/2. Further, reference character k represents the thickness of the
cover plate 10 made of the same material as that of the piezoelectric ceramics plate
2.
[0051] The relation between the depth H of each groove 3 forming each ink chamber 4 and
the thickness k of the cover plate 10 was examined to obtain a flying speed of ink
droplets necessary for stable printing.
[0052] In a test according to this preferred embodiment, three kinds of piezoelectric ceramics
plates 2 having different groove depths H of 0.2, 0.4, and 0.6mm were used. In each
piezoelectric ceramics plate 2, the width of each side wall 6 was set to 80µm, and
the width b of each groove 3 was set to 80µm. Lead zirconate titanate (PZT) piezoelectric
ceramics were used as the materials of the piezoelectric ceramics plate 2 and the
cover plate 10. An aluminum film having a thickness of about 1µm formed by vacuum
deposition was used as each metal electrode 8, and an epoxy adhesive was used as the
adhesive 20. Further, four kinds of cover plates 10 having different thicknesses k
of 0.25, 0.5, 1, and 2mm were used. Thus, twelve kinds of ink jet apparatus 1 were
totally prepared by using the three kinds of piezoelectric ceramics plate 2 and the
four kinds of cover plates 10 in combination. Further, pigment ink containing tripropylene
glycol monomethylether (TPM) as a base was used as the ink, and a driving voltage
to be applied to each metal electrode 8 was set to 40 volts. The flying speed of ink
droplets was calculated by emitting light from a light emitting diode in synchronism
with a driving voltage pulse to form a still image of the droplets and shifting a
timing of the light emission to the driving voltage pulse to obtain a travel of the
still image of the ink droplets.
[0053] The flying speeds of ink droplets in the various kinds of ink jet apparatus 1 prepared
above were measured. The result of measurement is shown in Fig. 9, in which the axis
of abscissa represents the product H x k of the depth H of each groove 3 and the thickness
k of the cover plate 10 and the axis of ordinate represents the flying speed of ink
droplets. In Fig. 9, solid lines 40, 42, and 44 correspond to the ink jet apparatuses
1 having the depths H of 0.2, 0.4, and 0.6mm, respectively.
[0054] As is apparent from Fig. 9, the larger the depth H of each groove 3, the larger the
flying speed of droplets. In each of the solid lines 40, 42, and 44, the flying speed
rapidly decreases when the product H x k becomes about 0.2 or less. The reason for
such a rapid decrease is that when the adjacent side walls 6 are deformed as shown
by broken lines in Fig. 8 at the time of jetting of the ink, the cover plate 10 is
minutely deformed as shown by broken lines in Fig. 8. The larger the rate of the deformation
of the cover plate 10 to the volume of each ink chamber 4, the smaller the increase
in pressure in each ink chamber 4, resulting in a reduction in flying speed of droplets.
To reduce the rate of the deformation of the cover plate 10 to the volume of each
ink chamber 4, it is necessary to either enlarge the depth H of each groove 3 or enlarge
the thickness k of the cover plate 10. Accordingly, it is sufficient to enlarge the
product H x k. As is apparent from Fig. 9, it is preferable to set the product H x
k to 0.2 or more, so as not to rapidly decrease the flying speed of ink droplets.
[0055] While the width of each side wall 6 was set to 80µm in the above test according to
this preferred embodiment, a tendency similar to that shown in Fig. 9 is exhibited
even when the width of each side wall 6 varies from the above value.
[0056] Further, while the width b of each groove 3 was set to 80µm in the above test, a
tendency similar to that shown in Fig. 9 is exhibited when the width b of each groove
3 is about 80µm.
[0057] Consequently, in the ink jet apparatus 1 according to this preferred embodiment,
the product of the depth of each groove 3 and the thickness of the cover plate 10
is set to 0.2 (mm x mm) or more.
[0058] Because the product of the depth of each groove 3 and the thickness of the cover
plate 10 is set to 0.2 (mm x mm) or more, the deformation of the cover plate 10 due
to the deformation of the side walls 6 can be prevented as much as possible. Accordingly,
the ratio of the pressure generated in each ink chamber 4 to the driving voltage to
be applied to each metal electrode 8 can be increased. Accordingly, a high pressure
can be generated in each ink chamber 4 by applying a low driving voltage, and ink
droplets can be jetted with a speed and a volume enough to form print images. According
to the ink jet apparatus 1 of this preferred embodiment, ink droplets can be jetted
with a speed of about 3 to 8m/sec and a volume of about 30 to 90pl by applying a low
driving voltage of about 20 to 50 volts. Thus, a driving circuit can be manufactured
at a low cost with a small size. The ink jet apparatus 1 as a whole can therefore
be manufactured at a low cost with a small size.
[0059] The influence of the surface roughness of the cover plate 10 to ink jet characteristics
is described referring to Fig. 10A. As shown, each side wall 6 is integral at a lower
end thereof with the piezoelectric ceramics plate 2, and an upper end of each side
wall 6 is bonded to the cover plate 10 by the adhesive 20. When the surface of the
cover plate 10 is smooth, a very thin film of the adhesive 20 is formed between each
side wall 6 and the cover plate 10, and a bonded portion formed by the adhesive 20
has a high rigidity. On the other hand, when the surface of the cover plate 10 is
rough, a large amount of the adhesive 20 is interposed between each side wall 6 and
the cover plate 10 as shown in Fig. 10B to cause a low rigidity of the bonded portion.
As a result, the pressure generated in each ink chamber 4 upon jetting of ink droplets
cannot be sufficiently increased, so that a desired volume of the ink droplets cannot
be obtained.
[0060] The volume of ink droplets jetted was measured by using the cover plates 10 having
different surface roughnesses.
[0061] In the ink jet apparatus 1 used in this test, the width W of each side wall 6 was
set to 80µm, the depth H of each groove 3 equal to the height of each side wall 6
was set to 400µm, and the width b of each groove 3 was set to 80µm. Lead zirconate
titanate (PZT) piezoelectric ceramics were used as the materials of the piezoelectric
ceramics plate 2 and each cover plate 10. An aluminum film having a thickness of about
1µm formed by vapor deposition was used as each metal electrode 8. Further, an epoxy
adhesive was used as the adhesive 20. The thickness k of each cover plate 10 was set
to 1mm, and the surface roughness of the surface to be bonded to each side wall 6
was changed from 1 to 8µm. Further, to eliminate any influences other than the influence
of the surface roughness, the adhesive 20 was applied uniformly and thinly in all
the cover plates 10 having the different surface roughnesses. The volume of ink droplets
was calculated by measuring the weight of a predetermined number of the ink droplets
with use of a high-precision analysis balance and by using the weight thus measured
and the density of the ink.
[0062] As is apparent from Fig. 11, when the surface roughness of the cover plate 10 is
3µm or less, the volume of the ink droplets is maximum and substantially constant.
In comparison with this, when the surface roughness increases to about 4µm, the volume
of the ink droplets decreases about 10%. Further, when the surface roughness increases
to about 5µm or more, the volume of the ink droplets decreases 20% or more, causing
a remarkable reduction in formation efficiency of the ink droplets.
[0063] Another jet test using the ink jet apparatus 1 having any dimensions other than the
above dimensions was carried out. As the result of this test, an absolute amount of
the volume of ink droplets changes, but a manner of change due to the surface roughness
of the cover plate 10 is similar to that shown in Fig. 11.
[0064] Further, even when any adhesive (e.g., phenol adhesive) other than the epoxy adhesive
is used, a tendency similar to that shown in Fig. 11 is exhibited.
[0065] Consequently, in the ink jet apparatus 1 according to this preferred embodiment,
the surface roughness of the cover plate 10 is set to 5µm or less, preferably 3µm
or less.
[0066] Because the surface roughness of the cover plate 10 is set to 5µm or less, preferably
3µm or less, the ratio of the pressure generated in each ink chamber 4 to the driving
voltage applied to each metal electrode 8 is large. Accordingly, a high pressure can
be generated in each ink chamber 4 by applying a low driving voltage, and ink droplets
can be jetted with a speed and a volume enough to form print images. According to
the ink jet apparatus 1 of this preferred embodiment, ink droplets can be jetted with
a speed of about 3 to 8m/sec and a volume of about 30 to 90pl, which depends on the
length of each ink chamber 4, by applying a low driving voltage of about 20 to 50
volts. Thus, a driving circuit can be manufactured at a low cost with a small size.
The ink jet apparatus 1 as a whole can therefore be manufactured at a low cost with
a small size.
[0067] The influence of a difference in material between the piezoelectric ceramics plate
2 and the cover plate 10 to the endurance of the ink jet apparatus 1 is described
referring to Fig. 12A. As shown, the piezoelectric ceramics plate 2 of the ink jet
apparatus 1 is formed with a plurality of grooves 3 each forming an ink chamber 4
and with a plurality of side walls 6 partitioning the grooves 3. The width b of each
groove 3 is set to 80µm, and the depth H of each groove 3 is set to 400µm. The width
W of each side wall 6 is set to 80µm. The upper end surface of each side wall 6 is
bonded to the cover plate 10 by an adhesive 20. A thermosetting adhesive such as an
epoxy adhesive is used as the adhesive 20. The adhesive 20 is hardened by heating
up to about 160°C. The thickness of the cover plate 10 is set to 1mm.
[0068] In the ink jet apparatus 1 as mentioned above, the material of the piezoelectric
ceramics plate 2 is not necessarily the same as the material of the cover plate 10.
Accordingly, when the material of the piezoelectric ceramics plate 2 has a coefficient
of linear expansion different from that of the material of the cover plate 10, the
deformation of both members becomes nonuniform when the temperature of the adhesive
20 after being hardened by heating is returned to ordinary temperature. As a result,
even when each side wall 6 is bonded to the cover plate 10 at about 160°C in such
a manner that the adjacent side walls 6 are parallel to each other as shown in Fig.
12A, the side walls 6 are deformed after reaching ordinary temperatures as shown in
Fig. 12B, a residual stress is generated in each side wall 6 and the adhesive 20 reducing
the strength of a bonded portion, in particular.
[0069] In general, the magnitude of the residual stress is dependent upon not only a difference
in coefficient of linear expansion but also an elastic modulus (Young's modulus) of
material. In the ink jet apparatus 1 of this preferred embodiment, however, the cover
plate 10 is sufficiently thick as compared with each side wall 6. Thus, the influence
caused by a change in Young's modulus due to a difference in material of the cover
plate 10 is substantially insignificant.
[0070] Then, the influence of the above phenomenon to the life of the ink jet apparatus
1 was examined. By using three kinds of lead zirconate titanate (PZT) piezoelectric
ceramics having three coefficients of linear expansion of 1, 2, and 4ppm/°C, three
kinds of piezoelectric ceramics plates 2 having different coefficients of linear expansion
were prepared. Further, three kinds of cover plates 10 having the same materials as
those of the above piezoelectric ceramics plates 2 were prepared. Additionally, three
kinds of cover plates 10 made of magnesia (MgO), zirconia (ZrO
2), and alumina (Al
2O
3) were prepared. Thus, six kinds of cover plates 10 having different coefficients
of linear expansion were totally prepared.
[0071] By using the various kinds of piezoelectric ceramics plates 2 and the various kinds
of cover plates 10 mentioned above, various ink jet apparatuses 1 were prepared. Then,
driving pulses at a voltage level of 40 volts continued to be applied at a frequency
of 8kHz to each ink jet apparatus 1. At this time, the number of times of the applied
driving pulses was measured until the jet function of each ink jet apparatus 1 was
reduced to a degree such that ink droplets could not be formed.
[0072] The result of measurement is shown in Fig. 13. As is apparent from Fig. 13, when
the difference in coefficient of linear expansion between the piezoelectric ceramics
plate 2 and the cover plate 10 is 6.0ppm/°C or less, the life of the ink jet apparatus
1 is 30 x 10
8 times. In contrast, when the difference in coefficient of linear expansion becomes
8.5ppm/°C, the life decreases to 20 x 10
8 times. Further, when the difference in coefficients of linear expansion becomes larger,
the life decreases more remarkably.
[0073] While an epoxy adhesive is used as the adhesive 20 in this preferred embodiment,
any other thermosetting adhesives such as a phenol adhesive may be used. Also in these
cases, a tendency similar to that shown in Fig. 13 is exhibited.
[0074] Consequently, in the ink jet apparatus 1 of this preferred embodiment, the difference
in coefficients of linear expansion between the piezoelectric ceramics plate 2 and
the cover plate 10 is set to 8.5ppm/°C or less, preferably 6.0ppm/°C or less.
[0075] Because the difference in coefficients of linear expansion between the piezoelectric
ceramics plate 2 and the cover plate 10 is set to 8.5ppm/°C or less, preferably 6.0ppm/°C
or less, the jet life of the ink jet apparatus 1 becomes at least about 20 x 10
8 times, preferably 30 x 10
8 times which is sufficient in practical use. Accordingly, the ink jet apparatus 1
can be sufficiently applied to not only printing of character images but also printing
of graphics images requiring a great frequency of jets of ink. Accordingly, the number
of replacements of the ink jet apparatus 1 in a printer can be reduced, and the reliability
of the printer can be improved.
[0076] The relative positional relationship between each ink chamber 4 and the manifold
18 is described referring to Fig. 14 which shows a cross section of the ink jet apparatus
1 as viewed from one side thereof. As shown by an arrow 30 in Fig. 14, ink is supplied
from an ink tank (not shown) through an ink supply tube (not shown) into the ink inlet
hole 16. Then, the ink is supplied from the ink inlet hole 16 through the manifold
18 into each ink chamber 4. In a test using the ink jet apparatus 1, lead zirconate
titanate (PZT) piezoelectric ceramics were used as the materials of the piezoelectric
ceramics plate 2 and the cover plate 10. To examine a change in volume of ink droplets
due to a change in relative positional relationship between the manifold 18 and each
ink chamber 4, various ink jet apparatuses 1 were prepared having different distances
x from the front side surface of the manifold 18 to the rear end surface of each ink
chamber 4. However, in each ink jet apparatus 1, the full length L of each ink chamber
4 was set to 17mm. Further, in each ink jet apparatus 1, the depth h of the manifold
18 was set to 0.5mm, and the width w of the manifold 18 was set to 5mm. The volume
of ink droplets was calculated by measuring the weight of a predetermined number of
the ink droplets jetted with use of a high-precision analysis balance and by using
the weight thus measured and the density of the ink.
[0077] Using the above various ink jet apparatuses 1 having different relative positional
relationship between the manifold 18 and each ink chamber 4, the volume of ink droplets
jetted from each ink jet apparatus 1 was measured. The result of measurement is shown
in Fig. 15, in which the axis of abscissa represents the distance x between the front
side surface of the manifold 18 and the rear end surface of each ink chamber 4, and
the axis of ordinate represents the volume of ink droplets. As is apparent from Fig.
15, when the distance x ranges between 1mm and 6mm, the volume of ink droplets reaches
a maximum value of 60pl, which is kept substantially constant.
[0078] When the distance x becomes 1mm or less, the volume of ink droplets rapidly decreases.
Further, when the distance x decreases to about 0.2mm, the ink cannot be jetted. That
is, x = 1 means that the distance of overlap between the manifold 18 and each ink
chamber 4 is equal to 1mm, and a decrease in the distance x down from 1mm causes the
ink flow into each ink chamber 4 to become rapidly hard.
[0079] On the other hand, when the distance x becomes 6mm or more, the volume of ink droplets
does not decrease as rapidly. This is due to the fact that an increase in the distance
x results in an approach of the manifold 18 to a nozzle plate 14, that is, the distance
y between the front side surface of the manifold 18 and the inner surface of the nozzle
plate 14. When the pressure in each ink chamber 4 is increased to jet the ink droplets
from a nozzle 12 formed through the nozzle plate 14, the ink in each ink chamber 4
is forced from the nozzle 12. Simultaneously, it reversely flows from the manifold
18 into the ink inlet hole 16. As a result, the pressure near the manifold 18 is rapidly
reduced to generate a negative pressure wave. When this negative pressure wave reaches
the nozzle 12, the ink jet from the nozzle 12 is stopped. The shorter the distance
y, the shorter the time of reach of the negative pressure wave to the nozzle 12. Accordingly,
when the distance y is reduced, the ink jet from the nozzle 12 is quickly stopped
to result in a reduction in the volume of ink droplets.
[0080] As is apparent from Fig. 15, when the distance x becomes about 11mm (

), the volume of ink droplets becomes about 30pl, i.e., half of the maximum value.
Further, when the distance x increases up to 14mm (y = 3mm) or more, the ink droplets
cannot be jetted. While the volume of ink droplets may be adjusted more or less by
controlling the applied driving pulse, the relative positional relationship between
the manifold 18 and each ink chamber 4 must be defined so that the distance x is set
to 0.2mm or more and the distance y is set to 3mm or more, preferably 6mm or more.
[0081] While the depth h and the width w of the manifold 18 were set to 0.5mm and 5mm, respectively,
in the above test, a tendency similar to that shown in Fig. 15 is exhibited even when
the dimensions of the manifold 18 vary from the above values.
[0082] Further, while the full length L of each ink chamber 4 was set to 17mm in the above
test, a tendency similar to that shown in Fig. 15 is exhibited even when the full
length L varies from 17mm.
[0083] Consequently, in the ink jet apparatus 1 according to this preferred embodiment,
the position of the manifold 18 to be formed in the cover plate 10 relative to each
ink chamber 4 is such that the distance between the front side surface of the manifold
18 and the rear end surface of each ink chamber 4 is set to 0.2mm or more. Also, the
distance between the front side surface of the manifold 18 and the inner surface of
the nozzle plate 14 is set to 3mm or more, preferably 6mm or more.
[0084] Because the distance between the front side surface of the manifold 18 and the rear
end surface of each ink chamber 4 is set to 0.2mm or more and the distance between
the front side surface of the manifold 18 and the inner surface of the nozzle plate
14 is set to 3mm or more, preferably 6mm or more, the ink droplets can be efficiently
jetted and the ink can be smoothly supplied to each ink chamber 4. Accordingly, the
ink droplets can be jetted with a speed and a volume sufficient to form print images.
According to the ink jet apparatus 1 of this preferred embodiment, ink droplets can
be jetted with a speed of about 3 to 8m/sec and a volume of about 30 to 90pl by applying
a low driving voltage of about 20 to 50 volts. Thus, a driving circuit can be manufactured
at a low cost with a small size. The ink jet apparatus 1 as a whole can therefore
be manufactured at a low cost with a small size.
[0085] It is to be noted that the present invention is not limited to the preferred embodiment
described above, but various modifications may be made without departing from the
scope of the present invention.
[0086] For example, while the ink jet apparatus 1 of the preferred embodiment is of a shear
mode type, such that the ink in each ink chamber 4 is jetted by the shear mode deformation
of each side wall 6 made of piezoelectric ceramics, the ink jet apparatus according
to the present invention may be another type, such as a Kaiser type or a thermal jet
type as mentioned previously.
1. An ink jet printing apparatus comprising:
a plate (2) with a plurality of longitudinally extending upstanding walls (6) defining
parallel ink chambers (4), each of said ink chambers (4) having a front end and a
rear end;
a nozzle assembly (14) coupled to said plate (2) at said front end of said ink chambers
(4) and having nozzles (12) formed therein, said nozzles (12) being aligned with said
ink chambers (4); and
a cover (10) coupled to said plate (2) and closing said ink chambers (4), said cover
(10) including an ink manifold (18) having a front side and a rear side and being
in communication with said ink chambers (4) and including an ink inlet (16) in said
manifold (18) for introducing ink into said manifold (18);
wherein a distance between said front side of said manifold (18) and said rear
end of said ink chambers (4) is in the range of 0.2mm to 6mm and a distance between
said front side of said manifold (18) and said front end of said ink chambers (4)
at said nozzle (12) is at least 3mm.
2. An ink jet printing apparatus according to claim 1 wherein said distance between said
front side of said manifold (18) and said front end of said ink chambers (4) at said
nozzle (12) is at least 6mm.
3. An ink jet printing apparatus comprising:
a plate (2) with a plurality of longitudinally extending upstanding walls (6) defining
parallel ink chambers (4), each of said ink chambers (4) having a front end and a
rear end;
a nozzle assembly (14) coupled to said plate (2) at said front end of said ink chambers
(4) and having nozzles (12) formed therein, said nozzles (12) being aligned with said
ink chambers (4); and
a cover (10) coupled to said plate (2) and closing said ink chambers (4), said cover
(10) including an ink manifold (18) having a front side and a rear side and being
in communication with said ink chambers (4) and including an ink inlet (16) in said
manifold (18) for introducing ink into said manifold (18);
wherein each of said ink chambers (4) has a depth and said cover (10) has a thickness,
and wherein said depth times said thickness is 0.2mm
2 or more, which suppresses deformation of said cover (10).
4. An ink jet printing apparatus comprising:
a plate (2) with a plurality of longitudinally extending upstanding walls (6) defining
parallel ink chambers (4), each of said ink chambers having a front end and a rear
end;
a nozzle assembly (14) coupled to said plate (2) at said front end of said ink chambers
(4) and having nozzles (12) formed therein, said nozzles (12) being aligned with said
ink chambers (4); and
a cover (10) coupled to said plate (12) and closing said ink chambers (4), said cover
(10) including an ink manifold (18) having a front side and a rear side and being
in communication with said ink chambers (4) and including an ink inlet (16) in said
manifold (18) for introducing ink into said manifold (18);
wherein said cover (10) has a surface that faces said plate (2) and said surface
has a roughness of 5µm or less.
5. An ink jet printing apparatus according to claim 4 wherein said surface has a roughness
of 3µm or less.
6. An ink jet printing apparatus comprising:
a plate (2) with a plurality of longitudinally extending upstanding walls (6) defining
parallel ink chambers (4), each of said ink chambers having a front end and a rear
end;
a nozzle assembly (14) coupled to said plate (2) at said front end of said ink chambers
(4) and having nozzles (12) formed therein, said nozzles (12) being aligned with said
ink chambers (4); and
a cover (10) coupled to said plate (2) and closing said ink chambers (4), said cover
(10) including an ink manifold (18) having a front side and a rear side and being
in communication with said ink chambers (4) and including an ink inlet in said manifold
(18) for introducing ink into said manifold (18);
wherein said ink inlet (12) is sized to create a laminar flow of ink into said
manifold.
7. An ink jet printing apparatus comprising:
a plate (2) with a plurality of longitudinally extending upstanding walls (6) defining
parallel ink chambers (4), each of said ink chambers (4) having a front end and a
rear end;
a nozzle assembly (14) coupled to said plate (2) at said front end of said ink chambers
(4) and having nozzles (12) formed therein, said nozzles (12) being aligned with said
ink chambers (4); and
a cover (10) coupled to said plate (2) and closing said ink chambers (4), said cover
(10) including an ink manifold (18) having a front side and a rear side and being
in communication with said ink chambers (4) and including an ink inlet (16) in said
manifold (18) for introducing ink into said manifold (18);
wherein each of said ink chambers (4) has a cross-sectional area and said manifold
(18) has a cross-sectional area, and wherein the cross-sectional area of said manifold
(18) is at least 0.5 times the cross-sectional area of all of said ink chambers (4)
combined.
8. An ink jet printing apparatus according to claim 7, wherein the cross-sectional area
of said manifold (18) is at most 5 times the cross-sectional area of all of said ink
chambers (4) combined.
9. An ink jet printing apparatus comprising:
a plate (2) with a plurality of longitudinally extending upstanding walls (6) defining
parallel ink chambers (4), each of said ink chambers (4) having a front end and a
rear end;
a nozzle assembly (14) coupled to said plate (2) at said front end of said ink chambers
(4) and having nozzles (12) formed therein, said nozzles (12) being aligned with said
ink chambers (4); and
a cover (10) coupled to said plate (2) and closing said ink chambers (4), said cover
(10) including an ink manifold (18) having a front side and a rear side and being
in communication with said ink chambers (4) and including an ink inlet (16) in said
manifold (18) for introducing ink into said manifold (18);
wherein said manifold (18) has a depth that allows ink to flow into said ink chambers
(4) without a change in pressure.
10. An ink jet printing apparatus according to any preceding claim except claim 7 or 8
wherein each of said ink chambers (4) has a cross-sectional area and said manifold
(18) has a cross-sectional area, and wherein the cross-sectional area of said manifold
(18) is in a range of 0.5 to 5 times the cross-sectional area of all of said ink chambers
(4) combined.
11. An ink jet printing apparatus according to any preceding claim except claim 3 or claim
10 when dependent on claim 3 wherein each of said ink chambers (4) has a depth and
said cover (10) has a thickness, and wherein said depth times said thickness is 0.2mm2 or more, which suppresses deformation of said cover.
12. An ink jet printing apparatus according to any preceding claim except claim 4 or 5
or claim 10 or 11 when dependent on claim 4 or 5 wherein said cover has a surface
that faces said plate (2) and said surface has a roughness of 5µm or less, preferably
3µm or less.
13. An ink jet printing apparatus according to any preceding claim wherein said ink inlet
(16) has a diameter of at least 0.2mm.
14. An ink jet printing apparatus according to any preceding claim wherein said manifold
(18) has a depth of at least 0.2mm.
15. An ink jet printing apparatus according to claim 14 wherein said manifold (18) has
a depth of at least 0.3mm.
16. An ink jet printing apparatus according to any preceding claim wherein said plate
(2) and said cover (10) are bonded together with thermosetting adhesive.