U.S. patent application number 12/138390 was filed with the patent office on 2008-12-18 for nozzle plate and the method of manufacturing the same.
This patent application is currently assigned to BROTHER KOGYO KABUSHIKI KAISHA. Invention is credited to Hikaru Nakamoto.
Application Number | 20080309717 12/138390 |
Document ID | / |
Family ID | 40131878 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080309717 |
Kind Code |
A1 |
Nakamoto; Hikaru |
December 18, 2008 |
NOZZLE PLATE AND THE METHOD OF MANUFACTURING THE SAME
Abstract
A nozzle plate has a nozzle hole for ejecting liquid, which
penetrates in a thickness direction of the nozzle plate. An
ejection face of the nozzle plate having an ejection opening of the
nozzle hole is covered with a water-repellent coat having a through
hole communicating with the nozzle hole. The through hole has a
straight portion and a diameter expansion portion. The straight
portion is contiguous to the nozzle hole and having the same
diameter as the ejection opening. The diameter expansion portion is
provided to interpose the straight portion with the nozzle hole and
gradually expanding so that a part thereof farther from the
straight portion has a larger diameter than a part thereof closer
to the straight portion.
Inventors: |
Nakamoto; Hikaru;
(Inuyama-shi, JP) |
Correspondence
Address: |
BAKER BOTTS LLP;C/O INTELLECTUAL PROPERTY DEPARTMENT
THE WARNER, SUITE 1300, 1299 PENNSYLVANIA AVE, NW
WASHINGTON
DC
20004-2400
US
|
Assignee: |
BROTHER KOGYO KABUSHIKI
KAISHA
Nagoya-shi
JP
|
Family ID: |
40131878 |
Appl. No.: |
12/138390 |
Filed: |
June 12, 2008 |
Current U.S.
Class: |
347/45 |
Current CPC
Class: |
B41J 2/1606 20130101;
B41J 2/1433 20130101; B41J 2/1643 20130101; B41J 2/1625 20130101;
B41J 2/162 20130101 |
Class at
Publication: |
347/45 |
International
Class: |
B41J 2/135 20060101
B41J002/135 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 2007 |
JP |
2007154875 |
Claims
1. A nozzle plate having a nozzle hole for ejecting liquid, which
penetrates in a thickness direction of the nozzle plate, wherein:
an ejection face of the nozzle plate having an ejection opening of
the nozzle hole is covered with a water-repellent coat having a
through hole communicating with the nozzle hole; and the through
hole has a straight portion and a diameter expansion portion, the
straight portion being contiguous to the nozzle hole and having the
same diameter as the ejection opening, the diameter expansion
portion being provided to interpose the straight portion with the
nozzle hole and gradually expanding so that a part thereof farther
from the straight portion has a larger diameter than a part thereof
closer to the straight portion.
2. The nozzle plate according to claim 1, wherein a circumference
of the diameter expansion portion is curved so as to protrude
towards a central axis of the through hole.
3. The nozzle plate according to claim 1, wherein an axial
direction length of the diameter expansion portion is 0.1 .mu.m or
more but 0.5 .mu.m or less.
4. The nozzle plate according to claim 1, wherein the nozzle plate
is made of stainless steel, and a nickel coat thinner than the
water-repellent coat is formed between the ejection face and the
water-repellent coat.
5. The nozzle plate according to claim 1, wherein the
water-repellent coat has a first surface where the straight portion
is open and a second surface where the diameter expansion portion
is open, the first surface extending parallel to the ejection face,
the second surface extending parallel to the first surface and
being distant from the first surface along the central axis of the
through hole.
6. A method of manufacturing a nozzle plate having a nozzle hole,
comprising the steps of; (a) forming the nozzle hole penetrating
through an opaque conductive plate which becomes the nozzle plate,
in a thickness direction of the conductive plate; (b) covering,
with light-curable resin, a first surface of the conductive plate
which surface has one opening of the nozzle hole to become an
ejection opening, and supplying the light-curable resin into an
area inside the nozzle hole contiguous to the one opening; (c)
forming a cured resin portion from the light-curable resin by
applying, to the conductive plate, light directed from a second
surface of the conductive plate having the other opening of the
nozzle hole to the first surface of the same so as to cure a part
of the light-curable resin inside the nozzle hole and another part
of the light-curable resin outside the nozzle hole, the another
part overlapping the one opening in a direction from the second
surface to the first surface; (d) eliminating an uncured portion of
the light-curable resin after the step of (c); (e) forming a
water-repellent coat by electroplating using the curable resin as a
mask, after the step of (d); and (f) eliminating the cured resin
portion after the step of (e), wherein in the step of (e), a
current density is adjusted so that the through hole, on the
water-repellent coat, communicating with the nozzle hole has a
straight portion and a diameter expansion portion, the straight
portion being contiguous to the nozzle hole and having the same
diameter as the ejection opening, the diameter expansion portion
being provided to interpose the straight portion with the nozzle
hole and gradually expanding so that a part thereof farther from
the straight portion has a larger diameter than a part thereof
closer to the straight portion.
7. The method of manufacturing the nozzle plate according to claim
6, wherein: the conductive plate is made of stainless steel; the
method further includes a step of (g) forming a nickel coat thinner
than the water-repellent coat on the first surface of the
conductive plate, before the step of (e); and in the step of (e)
the water-repellent coat is formed on the nickel coat.
8. The method of manufacturing the nozzle plate according to claim
7, wherein, in the step of (g), the nickel coat is formed by
electroplating.
9. The method of manufacturing a nozzle plate according to claim 6,
wherein the current density is 0.5 A/dm.sup.2 or higher but 2
A/dm.sup.2 or lower.
10. The method of manufacturing the nozzle plate according to claim
6, wherein, in the step of (e), the water-repellent coat is formed
by electroplating with a first current density and then with a
second current density which is lower than the first and is 0.5
A/dm.sup.2 or higher but 2 A/dm.sup.2 or lower.
11. The method of manufacturing the nozzle plate according to claim
6, wherein, in the step of (e), the water-repellent coat is formed
so as to have a third surface where the straight portion is open
and a fourth surface where the diameter expansion portion is open,
the third surface extending parallel to the ejection face, the
fourth surface extending parallel to the third surface and being
distant from the third surface along the central axis of the
through hole.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese Patent
Application No. 2007-154875, which was filed on Jun. 12, 2007, the
disclosure of which is herein incorporated by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a nozzle plate having a
nozzle hole which ejects liquid and a manufacturing method thereof.
The present invention especially relates to a nozzle plate whose
ejection face has a water-repellent coat formed by electroplating,
and a manufacturing method of the same.
[0004] 2. Description of Related Art
[0005] An ink-jet head includes a nozzle plate having a plurality
of nozzle holes through which ink droplets are ejected towards a
recording medium. There is known a technique to prevent ink deposit
near ejection openings of the nozzle holes, which are formed on an
ejection face of the nozzle plate, and thus stabilize the ejection
direction of ink droplets, by means of a water-repellent coat
formed through electroplating on the ejection face (Refer to
Japanese Unexamined Patent Publication No. 2002-219808). The
publication suggests that a dispersion electrode be positioned near
the ejection openings, and that the electric potential of the
dispersion electrode be set equal to that of the nozzle plate
during the electroplating, in order to homogenize the current
density to prevent unevenness in the thickness of the
water-repellent coat near the ejection opening, thereby forming the
water-repellent coat with an even thickness.
SUMMARY OF THE INVENTION
[0006] According to the above publication, however, the
water-repellent coat has a corner near each of the ejection
opening. This may lead to the following problem. When wiping the
ejection face of the nozzle plate with a wiper made of an elastic
material such as rubber, foreign matters wiped off by the wiper
during the wiping may adhere to the corner of the water-repellent
coat. Moreover, there is a problem that the water-repellent coat is
damaged by the wiper contacting the corner. The adhesion of the
foreign matters or the damage caused by them leads variation in the
ejection direction of ink droplets, consequently deteriorating the
printing quality.
[0007] The object of the present invention is to provide a nozzle
plate which is capable of preventing a disturbance of droplet
ejection caused by adhesion of foreign matters to, or the damage to
the water-repellent coat during wiping, and a manufacturing method
of the same.
[0008] According to a first aspect of the present invention, there
is provided a nozzle plate having a nozzle hole for ejecting
liquid, which penetrates in a thickness direction of the nozzle
plate. An ejection face of the nozzle plate having an ejection
opening of the nozzle hole is covered with a water-repellent coat
having a through hole communicating with the nozzle hole. The
through hole has a straight portion and a diameter expansion
portion. The straight portion is contiguous to the nozzle hole and
has the same diameter as the ejection opening. The diameter
expansion portion is provided to interpose the straight portion
with the nozzle hole and gradually expands so that a part thereof
farther from the straight portion has a larger diameter than a part
thereof closer to the straight portion.
[0009] In the first aspect, foreign matters are likely to adhere to
a part corresponding to the diameter expansion portion during
wiping, rather than a part corresponding to the straight portion of
the water-repellent coat. Thus, droplet ejection is less likely
disturbed. Moreover, since the through hole has a diameter
expansion portion near an exit thereof, wiper-caused damage to the
water-repellent coat is avoided. Hence, the above structure
prevents droplet ejection from being disturbed by the adhesion of
foreign matters to the ejection opening or damage to the
water-repellent coat during wiping.
[0010] In addition, since the through hole has the diameter
expansion portion near the exit thereof, it is possible to prevent
the wiper from being damaged by contacting the area near the exit
of the through hole during wiping.
[0011] There is a possibility of the following problems taking
place, if the through hole of the water-repellent coat does not
have a straight portion, that is, in case the through hole has only
a diameter expansion portion. Namely, the area near the exit of the
through hole more likely forms an asymmetrical shape. This may
cause a curvature in the droplet ejection direction. Moreover, this
may cause re-ejection of droplet, since a vibration center of the
meniscus is lead to be closer to the ejection face of the nozzle
plate and thus vibration takes place after ejection of ink.
[0012] On the other hand, according to the above structure, since
the through hole of the water-repellent coat has a straight
portion, the shape of around the exit of the through hole can
easily be symmetrical, so that the direction of droplet ejection is
stabilized, and the vibration center of the meniscus becomes
relatively far from the ejection face of the nozzle plate. Thus,
re-ejection of a droplet as described above is prevented.
[0013] In addition, capillarity occurs at the straight portion
having water repellency. Therefore, a tail of a droplet is pulled
back, forming a new meniscus immediately after droplet ejection,
thus allowing the next ejection in a short period of time.
[0014] Moreover, the water-repellent coat having a straight portion
is thicker than a structure having only the diameter expansion
portion. This contributes to an increased durability of the
water-repellent coat. Thus, stable ink ejection can be continued
for a long period of time.
[0015] According to a second aspect of the present invention, there
is provided a method of manufacturing a nozzle plate having a
nozzle hole, comprising the steps of; (a) forming the nozzle hole
penetrating through an opaque conductive plate which becomes the
nozzle plate, in a thickness direction of the conductive plate; (b)
covering, with light-curable resin, a first surface of the
conductive plate which surface has one opening of the nozzle hole
to become an ejection opening, and supplying the light-curable
resin into an area inside the nozzle hole contiguous to the one
opening; (c) forming a cured resin portion from the light-curable
resin by applying, to the conductive plate, light directed from a
second surface of the conductive plate having the other opening of
the nozzle hole to the first surface of the same so as to cure a
part of the light-curable resin inside the nozzle hole and another
part of the light-curable resin outside the nozzle hole, the
another part overlapping the one opening in a direction from the
second surface to the first surface; (d) eliminating an uncured
portion of the light-curable resin after the step of (c); (e)
forming a water-repellent coat by electroplating using the curable
resin as a mask, after the step of (d); and (f) eliminating the
cured resin portion after the step of (e). In the step of (e), a
current density is adjusted so that the through hole, on the
water-repellent coat, communicating with the nozzle hole has a
straight portion and a diameter expansion portion, the straight
portion being contiguous to the nozzle hole and having the same
diameter as the ejection opening, the diameter expansion portion
being provided to interpose the straight portion with the nozzle
hole and gradually expanding so that a part thereof farther from
the straight portion has a larger diameter than a part thereof
closer to the same.
[0016] In the second aspect, simply adjusting the current density
of electroplating enables manufacturing of a nozzle plate whose
water-repellent coat is provided with a through hole having the
straight portion and the diameter expansion portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Other and further objects, features and advantages of the
invention will appear more fully from the following description
taken in connection with the accompanying drawings in which:
[0018] FIG. 1 is a cross sectional view of a nozzle plate according
to an embodiment of the present invention.
[0019] FIG. 2 is an explanatory diagram showing a manufacturing
method of the nozzle plate, where (a), (b), (c), (d), (e), (f)
respectively show a light-curable resin supplying step, a curing
step, an uncured portion eliminating step, a nickel coat forming
step, a water-repellent coat forming step, and a curable resin
eliminating step.
[0020] FIG. 3 is a graph showing the relation of the current
density of electroplating and the axial direction length of the
diameter expansion portion in the water-repellent coat forming
step.
[0021] FIG. 4 is a graph showing the relation of the axial
direction length of the diameter expansion portion and a hole-edge
foreign matter deposit ratio.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The following describes a preferred embodiment of the
present invention with reference to the drawings. The following
embodiment deals with an application of the present invention to a
nozzle plate positioned to an ink-jet head.
[0023] First, the structure of a nozzle plate P according to the
present embodiment will be described with reference to FIG. 1. The
nozzle plate P has a substrate 1 made of stainless steel having a
thickness of substantially 70 .mu.m. The substrate 1 has a nozzle
hole 2 which ejects ink formed through in a thickness
direction.
[0024] The nozzle hole 2 is symmetrical to a central axis O, and
includes a column portion 2b and a truncated cone portion 2a. The
column portion 2b has a cylindrical circumference and opens towards
the ejection face 1a of the substrate 1. The truncated cone portion
2a has a truncated cone shaped circumference and opens at the
bottom towards a back surface 1b, which is the opposite side to the
ejection face 1a of the substrate 1. The column portion 2b has a
diameter d of substantially 20 to 30 .mu.m. The top of the
truncated cone portion 2a has the same diameter as that of the
column portion 2b and is connected to the column portion 2b. The
opening formed by the column portion 2b towards the ejection face
la serves as an ejection opening 2c where ink is ejected. The
ejection opening 2c has the smallest diameter within the nozzle
hole 2.
[0025] The ejection face la is covered with a nickel coat 6 as an
interface layer, and a water repellent coat 3 is formed on the
nickel coat 6. The water-repellent coat 3 is made by nickel plating
containing a fluorine-based macromolecular material such as
polytetrafluoroethylene or the like, and has a thickness of
substantially 1.5 .mu.m. The nickel coat 6 does not contain a
fluorine-based macromolecular material, and has a thickness of
substantially 0.1 .mu.m.
[0026] The nickel coat 6 and the water-repellent coat 3
respectively have through holes 6a and 3a which share the central
axis O with the nozzle hole 2, and communicate with the nozzle hole
2. The ejection opening 2c of the nozzle hole 2, or an inner wall
of the column portion 2b are not obturated by the nickel coat 6 or
the water-repellent coat 3. To the contrary, areas other than the
ejection opening 2c of the ejection face 1a are covered with the
nickel coat 6 and the water-repellent coat 3.
[0027] The through hole 3a of the water-repellent coat 3 includes a
straight portion 3c and a diameter expansion portion 3b. The
straight portion 3c is contiguous to the nozzle hole 2 and has the
same diameter d as the ejection opening 2c. The diameter expansion
portion 3b is provided to interpose the straight portion 3c with
the nozzle hole 2, and gradually expands so that a part thereof
farther from the straight portion 3c has a larger diameter than a
part thereof closer to the straight portion 3c. The diameter
expansion portion 3b has a circumference curved so as to protrude
towards the central axis O of the through hole 3a, where the axial
direction length x along the central axis O is 0.1 .mu.m or more
but 0.5 .mu.m or less. The water-repellent coat 3 has a lower
surface 3x where the straight portion 3c is open and an upper
surface 3y where the diameter expansion portion 3b is open. The
lower surface 3x extends parallel to the ejection face 1a. The
upper surface 3y extends parallel to the lower surface 3x and is
distant from the lower surface 3x along the axis O. The through
hole 6a of the nickel coat 6 has the same diameter d as the
ejection opening 2c, that is, the same diameter d as the straight
portion 3c. Thus, a cylindrical airspace having the diameter d is
formed from the column portion 2b to the straight portion 3c.
[0028] As mentioned above, according to the nozzle plate P of the
present embodiment, foreign matters are likely to adhere to apart
corresponding to the diameter expansion portion 3b, i.e., adhere to
the boundary of the upper surface 3y and the diameter expansion
portion 3b, during wiping, rather than a part corresponding to the
straight portion 3c of the water-repellent coat 3. Thus, ink
ejection is less likely disturbed. Moreover, since the through hole
3a has the diameter expansion portion 3b near the exit thereof, the
wiper-caused damage to the water-repellent coat 3 is avoided.
Hence, the structure of the present embodiment prevents ink
ejection from being disturbed by the adhesion of foreign matters to
the ejection opening 2c or damage to the water-repellent coat 3
during wiping.
[0029] In addition, since the through hole 3a has the diameter
expansion portion 3b near the exit thereof, it is possible to
prevent the wiper from being damaged by contacting the area near
the exit of the through hole 3a during wiping.
[0030] There is a possibility of the following problems taking
place, if the through hole 3a of the water-repellent coat 3 does
not have the straight portion 3c, that is, in case the through hole
3a has only the diameter expansion portion 3b. Namely, the area
near the exit of the through hole 3a more likely forms an
asymmetrical shape. This may cause a curvature in the droplet
ejection direction. Moreover, this may cause re-ejection of
droplet, since a vibration center of the meniscus is lead to be
closer to the ejection face la of the nozzle plate P and thus
vibration takes place after ejection of ink.
[0031] On the other hand, the through hole 3a of the
water-repellent coat 3 having a straight portion 3c as in the
present embodiment brings about the following advantages. Namely,
the area near the exit of the through hole 3a can easily form a
symmetrical shape. This stabilizes the ink ejection direction.
Moreover, since the vibration center of the meniscus is relatively
far from the ejection face 1a of the nozzle plate P, the above
mentioned re-ejection of ink is prevented.
[0032] In addition, capillarity occurs at the straight portion 3c
having water repellency. Therefore, a tail of ink is pulled back,
forming a new meniscus immediately after ink ejection, thus
allowing the next ejection in a short period of time.
[0033] Moreover, the water-repellent coat 3 having the straight
portion 3c is thicker than a structure having only the diameter
expansion portion 3b. This contributes to an increased durability
of the water-repellent coat 3. Thus, stable ink ejection can be
continued for a long period of time.
[0034] In addition, the circumference of the diameter expansion
portion 3b curves so as to protrude towards the central axis O of
the through hole 3a. Thus, a part corresponding to the diameter
expansion portion 3b, a part corresponding to the straight portion
3c, and the outer surface of the water-repellent coat 3 can be
respectively connected smoothly. Thus, the above structure can
further restrain the damage by the wiper to the water-repellent
coat 3 and the wiper itself during wiping.
[0035] As described below, if the axial direction length x of the
diameter expansion portion 3b is less than 0.1 .mu.m, the boundary
of the upper surface 3y and the diameter expansion portion 3b
becomes too close to the ejection opening 2c in a plan view. If the
axial direction length x of the diameter expansion portion 3b is
0.1 .mu.m, for example, the above boundary is placed substantially
1 .mu.m distant from the circumference of the ejection opening 2c
in a plan view. If the axial direction length x of the diameter
expansion portion 3b is 0.5 .mu.m the boundary is placed
substantially 7 to 8 .mu.m distant from the circumference of the
ejection opening 2c in a plan view. Therefore, taking the sizes and
the shapes of foreign matters inconsideration, if the axial
direction length x of the diameter expansion portion 3b is less
than 0.1 .mu.m, there will be a higher possibility of foreign
matters adhering to the part corresponding to the straight portion
3c of the water-repellent coat during wiping, and the ink ejection
is more conspicuously disturbed by the adherence of foreign
matters.
[0036] If the axial direction length x exceeds 0.5 .mu.m, it is
necessary to decrease the current density of the electroplating in
the water-repellent coat forming step. Thus, it takes longer to
form a water-repellent coat. If it takes longer to form a
water-repellent coat, a below-mentioned curable resin 5 immersed
into a plating solution may swell. The curable resin 5 defines a
diameter of the straight portion 3c of the water-repellent coat 3.
Accordingly, the swelling of the curable resin 5 may cause
unevenness in the diameter of the straight portion 3c.
[0037] In view of that, the thickness of the water-repellent coat 3
is limited to about 1.5 .mu.m, and the axial direction length x of
the diameter expansion portion 3b is set to 0.1 .mu.m or more but
0.5 .mu.m or less, as in the present embodiment. That way, it is
possible to prevent the ink ejection from being disturbed by the
adherence of foreign matters, and to shorten the manufacturing
time.
[0038] Here, when the axial direction length x of the diameter
expansion portion 3b is 0.5 .mu.m, the production time is as short
as substantially twenty minutes. Thus, the straight portion 3c will
not at all be formed with an uneven diameter.
[0039] Moreover, the substrate 1 is made of stainless steel, and
the nickel coat 6 thinner than the water-repellent coat 3 is formed
between the substrate 1 and the water-repellent coat 3. Therefore,
the adhesivity of the water-repellent coat 3 to the substrate 1
increases.
[0040] Next, the manufacturing method of the nozzle plate P with
reference to FIG. 2 is described.
[0041] First, by carrying out a pressing to form the truncated cone
portion 2a and the column portion 2b, the nozzle hole 2 is formed
to a substrate 1 (nozzle hole forming step). If the pressing
generates a protrusion such as a burr to the ejection face 1a,
grinding and polishing is carried out to eliminate the protrusion.
The nozzle hole 2 may be formed by etching.
[0042] Thereafter, as shown in FIG. 2(a), a film of a light-curable
resin 4 serving as a resist is heated and crimped at the same time
to the ejection face 1a of the substrate 1 with a use of a roller
or the like. The ejection face 1a is covered with the light-curable
resin 4, while adjusting the heating temperature, the pressure, the
speed of the roller, or the like. Then, a predetermined amount of
the light-curable resin 4 is supplied to the leading end area of
the column portion 2b of the nozzle hole 2 (light-curable resin
supplying step). Note that if the heating temperature is too high,
such as a case where the temperature is far beyond the glass
transition point, the light-curable resin 4 begins to show
liquidity, and the ejection face 1a therefore cannot be coated with
the light-curable resin 4 having a necessary film thickness (for
example, substantially 15 .mu.m). To the contrary, if the heating
temperature is too low, the film does not soften so that the
necessary amount of light-curable resin 4 cannot be supplied to the
leading end area of the column portion 2b.
[0043] In view of that, the heating temperature is set, for
example, at the glass transition point where the light-curable
resin 4 begins to show a soft rubber-like characteristic.
[0044] Note that, the heating temperature is preferably set within
the range of 80.degree. C. to 100.degree.; however, the temperature
is not limited to this range.
[0045] Moreover, to easily supply a necessary amount of the
light-curable resin 4 to the leading end area of the column portion
2b, the thickness t of the light-curable resin 4 is preferably
equal to or smaller than the diameter d of the column portion
2b.
[0046] Then, as shown in FIG. 2(b), ultraviolet light emitted in a
direction from the back-surface 1b of the substrate 1 towards the
ejection face 1a is applied to the substrate 1 in order to
partially cure the light-curable resin 4 (curing step).
[0047] A part of the light-curable resin 4 inside the nozzle hole 2
and another part of the light-curable resin 4 outside the nozzle
hole 2 which overlaps the ejection opening 2c in the direction from
the back-surface 1b to the ejection face 1a are cured by the light
passing through the nozzle hole 2. Hence, a cylinder-shaped curable
resin 5 is formed. The substrate 1 where the nozzle hole 2 is
formed functions as a mask during the irradiance of ultraviolet
light. Thus, the diameter of the curable resin 5 is substantially
the same as that of the ejection opening 2c at any point along the
axial direction. Here, the light exposure is adjusted in order to
prevent the light-curable resin 4 from curing outwardly from nearby
the ejection opening 2c in the radial direction of the nozzle hole
2.
[0048] Thereafter, an uncured portion of the light-curable resin 4
on the ejection face 1a, that is a section other than the curable
resin 5, is eliminated with a developer such as an alkaline
developer containing 1%-Na.sub.2CO.sub.3 (uncured portion
eliminating step). Thus, as shown in FIG. 2(c), cured resin 5 is
left protruded from the ejection face 1a. In the present
embodiment, the protrusion distance of the curable resin 5 from the
ejection face la is substantially 15 .mu.m, and is greater than the
total thickness of later formed nickel coat 6 and water-repellent
coat 3.
[0049] Then, electroplating is carried out with the curable resin 5
left unremoved, so as to form a nickel coat 6 of substantially 0.1
.mu.m in thickness on the ejection face 1a (nickel coat forming
step). Note that the curable resin 5 functions as a mask against
the plating coat. In this step, as shown in FIG. 2(d), the nickel
coat 6 is not formed on a nonmetal curable resin 5, but selectively
grows on the conductive substrate 1. Note that the curable resin 5
is left protruded from the upper surface of the nickel coat 6.
[0050] Afterwards, as shown in FIG. 2(e), a water-repellent coat 3
is formed on the nickel coat 6 by electroplating, using the curable
resin 5 as a mask (water-repellent coat forming step) In this step,
the current density of the electroplating is adjusted so that,
where a position which is a distance x (see FIG. 1) away from the
upper surface 3y of the water-repellent coat 3 is a reference
position, the inner circumference of the water-repellent coat 3
below the reference position contacts the curable resin 5, while
the inner circumference above the reference position does not
contact the curable resin 5 but gradually distances from the
curable resin 5 in such a manner that a part of the inner
circumference farther from the ejection face 1a is farther
distanced from the curable resin 5 than a part of the inner
circumference closer to the ejection face 1a. In other words, the
current density is adjusted so as to form in the water-repellent
coat 3, the through-hole 3a having the straight portion 3c and the
diameter expansion 3b. More specifically, the current density of
the electroplating is 0.5 A/dm.sup.2 or higher but 2 A/dm.sup.2 or
lower.
[0051] The current density of 0.5 A/dm.sup.2 produces a
water-repellent coat 3 with the diameter expansion portion 3b
having an axial direction length x of substantially 0.5 .mu.m. The
current density of 2 A/dm.sup.2 produces a water-repellent coat 3
with the diameter expansion portion 3b having an axial direction
length x of substantially 0.1 .mu.m. The plating time to form a
water-repellent coat 3 is substantially 20 minutes when the current
density is 0.5 A/dm.sup.2, and is substantially 5 minutes when the
current density is 2 A/dm.sup.2. In either case, a water-repellent
coat 3 having a total thickness of substantially 1.5 .mu.m is
formed. Note that the temperature of the plating solution is
substantially 50.degree. C.
[0052] After the formation of the water-repellent coat 3 through
the above method, a release agent which is 3%-NaOH or the like is
used to melt the curable resin 5 and eliminate it from the
substrate 1 (curable resin eliminating step). Thus, as shown in
FIG. 2(f), there is completed a nozzle plate P where the ejection
opening 2c of the nozzle hole 2 is open via the through hole 6a of
the nickel coat 6 and the through hole 3a of the water-repellent
coat 3.
[0053] As mentioned above, according to the method of the present
embodiment for manufacturing a nozzle plate P, simply adjusting the
current density of electroplating enables manufacturing of a nozzle
plate P whose water-repellent coat 3 is provided with a through
hole 3a having the straight portion 3c and the diameter expansion
portion 3b.
[0054] In addition, the substrate 1 is made of stainless steel, and
a nickel coat forming step is carried out prior to the
water-repellent coat forming step, to form a nickel coat 6 thinner
than the water-repellent coat 3 on the ejection face 1a of the
substrate 1. Then, through the water-repellent coat formation step
the water-repellent coat 3 is formed on the nickel coat 6. That way
the adhesivity of the water-repellent coat 3 to the substrate 1
increases.
[0055] The nickel coat 6 may be formed by electroless plating;
however, in this case, it is necessary to prepare a production
equipment for nickel coat 6 formation, aside from the production
equipment for water-repellent coat formation. When the nickel coat
6 is formed by the same electroplating for forming the
water-repellent coat 3 as in the present embodiment, it is possible
to simplify the production equipments and avoid complication of
steps since the production equipments other than the plating
solutions can be shared.
[0056] As described below, if the current density of the
electroplating in the water-repellent coat forming step is 2
A/dm.sup.2 or higher, the axial direction length x of the diameter
expansion portion 3b decreases. This increases the possibility of
the adhesion of foreign matters to the part corresponding to the
straight portion 3c of the water-repellent coat 3 during wiping.
Consequently, the interference of ink ejection due to the adhesion
of foreign matters becomes conspicuous. Moreover, formation of the
water-repellent coat takes a long time, if the current density is
lower than 0.5 A/dm.sup.2. The formation taking a long time may
cause unevenness in the diameter of the straight portion 3c.
[0057] In view of that, the current density of the electroplating
in the water-repellent coat forming step is set at 0.5 A/dm.sup.2
or higher but 2 A/dm.sup.2 or lower as in the present embodiment.
That way, it is possible to prevent the ink ejection from being
disturbed by the adherence of foreign matters, and to shorten the
manufacturing time.
[0058] Next, an exemplary variation of the manufacturing method
according to the present embodiment is described. The below
exemplary variation is the same as the method described in the
foregoing embodiment except the water-repellent coat forming step.
That is, only the water-repellent coat forming step is carried out
in a different manner from the above.
[0059] More specifically, in the water-repellent coat forming step,
electroplating is carried out first at a current density of 4
A/dm.sup.2 or higher, and then, another electroplating is carried
out at a current density of 0.5 A/dm.sup.2 or higher but 2
A/dm.sup.2 or lower. In this case, electroplating is carried out at
a current density of 4 A/dm.sup.2 or higher in the beginning of the
water-repellent forming step. This forms the most part of the
thickness of the water-repellent coat 3, including the straight
portion 3c. Then, with an application of a current density lower
than that of the beginning of the step, the diameter expansion
portion 3b is formed.
[0060] According to the exemplary variation, most part of the
thickness of the water-repellent coat 3 can be formed in a
relatively short period of time at the beginning of the step. Thus,
the time taken for forming the entire water-repellent coat 3 is
reduced. This is particularly effective for forming a thicker
water-repellent coat 3. In addition, the current density applied
afterwards is set at 0.5 A/dm.sup.2 or higher but 2 A/dm.sup.2 or
lower. That way, it is possible to prevent the ink ejection from
being disturbed by the adherence of foreign matters, and to shorten
the manufacturing time.
[0061] Next, the following describes an experiment conducted on the
current density of the electroplating in the water-repellent coat
forming step. In the experiment used was a substrate 1 of 70 .mu.m
in thickness which is made of SUS 430 and has a nozzle hole 2
having a column portion 2b whose diameter d is 20 .mu.m.
Thereafter, the light-curable resin 4 was crimped, while heating
the same, to an ejection face 1a of the substrate 1. Then, the
ejection face 1a was covered with the light-curable resin 4 of
substantially 15 .mu.m in thickness, and a predetermined amount of
the light-curable resin 4 was supplied to the leading end area of
the column portion 2b of the nozzle hole 2. Afterwards, the curable
resin 5 was formed by partially curing the light-curable resin 4 by
applying ultraviolet light. After eliminating the uncured portion
of the light-curable resin 4, the nickel coat 6 having a thickness
of 0.1 .mu.m was formed on the ejection face 1a by electroplating.
Then, the current density of the electroplating in the
water-repellent coat forming step was changed. Then, the resulting
axial direction length x of the diameter expansion portion 3b in
the water-repellent coat 3, and the resulting foreign matter
deposit ratio, i.e., a hole-edge foreign matter deposit ratio, to
the part corresponding to the straight portion 3c during wiping,
were examined. The thickness of the water-repellent coat 3 was set
to 1.5 .mu.m.
[0062] Note that the hole-edge foreign matter deposit ratio is a
ratio of the number of nozzle holes 2 where foreign matters adhered
to the part corresponding to the straight portion 3c by wiping, to
the total number of nozzle holes 2. Hereinafter, the hole-edge
foreign matter deposit ratio is called simply as the "ratio".
[0063] FIG. 3 is a graph showing the relation of the current
density of the electroplating and the axial direction length x of
the diameter expansion portion 3b in the water-repellent coat
forming step. FIG. 4 is a graph showing the relation of the axial
direction length x of the diameter expansion portion 3b and the
ratio.
[0064] As shown in FIG. 3, when the current density is 0.5
A/dm.sup.2, the axial direction length x of the diameter expansion
portion 3b is 0.5 .mu.m, and the ratio is substantially 3%. The
axial direction length x of the diameter expansion portion 3b
decreases with an increase in the current density, and is
substantially 0.03 .mu.m when the current density is 4 A/dm.sup.2.
If the current density exceeds 4 A/dm.sup.2, the axial direction
length x of the diameter expansion portion 3b is predicted to be
asymptotic to 0 .mu.m. Moreover, as shown in FIG. 4, the ratio
increases when the axial direction length x of the diameter
expansion portion 3b decreases. Once the axial direction length x
of the diameter expansion portion 3b falls below 0.1 .mu.m, the
ratio rapidly increases with a decrease in the length. When the
axial direction length x of the diameter expansion portion 3b is
substantially 0.03 .mu.m, i.e., when the current density is 4
A/dm.sup.2, the ratio is 50%. If the axial direction length x of
the diameter expansion portion 3b falls below 0.03 .mu.m, i.e., if
the current density exceeds 4 A/dm.sup.2, the ratio is predicted to
be asymptotic to a high-rate exceeding 50%.
[0065] Thus, it is found that, with an increase in the current
density, the axial direction length x of the diameter expansion
portion 3b decreases and the hole-edge foreign matter deposit rate
increases.
[0066] It is understood by FIG. 4 that the longer the axial
direction length x of the diameter expansion portion 3b, the more
difficult it becomes for foreign matters to adhere to the part
corresponding to the straight portion 3c during wiping. Moreover,
it is understood that when the axial direction length x of the
diameter expansion portion 3b approaches 0, that is when the
diameter expansion portion 3b barely exists and the through hole 3a
is formed only with the straight portion 3c, foreign matters adhere
more easily to the section corresponding to the straight portion 3c
during wiping.
[0067] In short, it is understood that the diameter expansion
portion 3b contributes to the prevention of adhesion of foreign
matters to the part corresponding to the straight portion 3c.
[0068] If foreign matters adhere to the part corresponding to the
straight portion 3c, the ink ejection from the nozzle hole 2 is
disturbed by foreign matters, causing variation in the direction of
ink ejection, thus deteriorating the printing quality. In view of
that, it is important to form the diameter expansion portion 3b so
as to highly contribute to the prevention of foreign matter
adhesion. Moreover, the diameter expansion portion 3b preferably
maintains a high contribution to the prevention of foreign matter
adhesion, even when the manufacturing condition changes more or
less. As seen in FIG. 4, the ratio rapidly increases with a
decrease in the axial direction length x of the diameter expansion
portion 3b, once the length falls below 0.1 .mu.m. When the axial
direction length x of the diameter expansion portion 3b is 0.1
.mu.m or more, the change in the ratio to the change in the axial
direction length x of the diameter expansion portion 3b becomes
smaller, and the ratio becomes lower than substantially 20%
constantly.
[0069] According to FIG. 3, in order to form the water-repellent
coat 3 with the axial direction length x of the diameter expansion
portion 3b of 0.1 .mu.m or more, current density should be set as 2
A/dm.sup.2 or lower. On the other hand, it is necessary to consider
manufacturing time and evenness in the diameter of the straight
portion 3c. Therefore, the current density is preferably set to at
least the value where the water-repellent coat 3 having the axial
direction length x of the diameter expansion portion 3b of 0.5
.mu.m is formed, i.e., the value of 0.5 A/dm.sup.2.
[0070] Accordingly, in the water-repellent coat formation step, the
current density of the electroplating is preferably set at 0.5
A/dm.sup.2 or higher but 2 A/dm.sup.2 or lower so that the axial
direction length x of the diameter expansion portion 3 is 0.1 .mu.m
or more but 0.5 .mu.m or less.
[0071] In the experiment, the axial direction length x of the
diameter expansion portion 3b and the broadening of the diameter
expansion portion 3b from the straight portion 3c were both
measured with a non-contact surface roughness measure (More
specifically, a non-contact three-dimensional surface
formation/roughness measure made by Zygo: New View 5032).
[0072] Note that the substrate 1 of the nozzle plate P is not
limited to one made of stainless steel, and maybe one made of a
different material.
[0073] The formation of the nickel coat 6 is not limited to
electroplating, and other methods such as non-electroplating or the
like are possible.
[0074] The present invention is not limited to a structure in which
a nickel coat 6 is formed between the ejection face 1a and the
water-repellent coat 3. For example, instead of the nickel coat 6,
the ejection face 1a and the water-repellent coat 3 may interpose a
chrome plating coat, a copper plating coat, a lamination of several
plating films, or the like. Alternatively, the water-repellent coat
3 may be directly formed on the ejection face la with no layer
interposed therebetween.
[0075] The circumference of the diameter expansion portion 3b does
not have to be curved so as to protrude towards the central axis O
of the through hole 3a.
[0076] To prevent ink ejection from being disturbed by the adhesion
of foreign matters, and to shorten the manufacturing time, the
axial direction length x of the diameter expansion portion 3b is
preferably 0.1 .mu.m or more but 0.5 .mu.m or less; however, the
range of the axial direction length x is not limited to this.
Especially, the axial direction length x of the diameter expansion
portion 3b, when it exceeds 0.5 .mu.m, is preferably in a range
where the diameter of the straight portion 3c is unlikely
uniformed.
[0077] To prevent ink ejection from being disturbed by the adhesion
of foreign matters, and to shorten the manufacturing time, the
current density of the electroplating in the water-repellent coat
forming step is preferably 0.5 A/dm.sup.2 or higher but 2
A/dm.sup.2 or lower; however, the range of the current density is
not limited to the this. For example, the current density may be
0.5 A/dm.sup.2 or lower, for the reason that the ratio is reduced
as much as possible. In this case, however, a caution is required
to avoid unevenness in the diameter of the straight portion 3c.
This limits the amount of manufacturing time extendable.
[0078] The light applied to the substrate 1 in the curing step
advances in a direction from the back-surface 1 of the substrate 1
towards the ejection face la; however, it can advance in a
direction other than the above direction, as long as the light
includes a component directed in the above direction.
[0079] In the curing step, the curing of the curable resin 5 does
not have to be completely cured, and may be half-cured. Doing so
will leave adhesiveness in curable resin 5, since cure reaction is
not completed. With this adhesiveness, it is less likely that the
curable resin 5 falls due to vibration and shock in the later
steps.
[0080] The nozzle plate and the manufacturing method thereof are
applicable to ink-jet heads and various types of other
equipments.
[0081] While this invention has been described in conjunction with
the specific embodiments outlined above, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, the preferred embodiments of
the invention as set forth above are intended to be illustrative,
not limiting. Various changes may be made without departing from
the spirit and scope of the invention as defined in the following
claims.
* * * * *