JP2007144362A - Method for manufacturing die head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a die head capable of solving the problem that a lip is mounted on an outside side face part and causes bleeding in a die coating method. <P>SOLUTION: The method for manufacturing a die head, which comprises an upstream side lip having an outside side face part, a slit side face part, and a tip end part; a downstream side lip having an outside side face part, a slit side face part, and a tip end part; and a slit part positioned between the upstream side lip and the downstream side lip, involves forming a water-repelling film on at least a portion of the outside side face parts except the slit side face parts and the tip end parts of the die head by plasm CVD method using a rare gas and raw material gases containing the water-repelling material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a die head for die coating and a method for manufacturing the same, mainly in fields requiring precise required quality such as optical members and electronics. More specifically, the present invention relates to a die head that does not cause various coating defects that occur in an extrusion die coating that continuously processes a long support that is continuously conveyed, and a method for manufacturing the same.

  As one of the methods of applying a coating solution to a desired film thickness on a continuous substrate that is continuously transported, the extrusion die coating method enables uniform and high-speed thin film coating. It is widely used as a precision coating method in various fields. In particular, it is a coating method that is attracting attention due to its characteristics in accordance with the recent demand for high-precision mass production in the optical member and electronics fields.

  In general, as shown in FIG. 1, the die coating method is performed at a constant speed while maintaining a uniform clearance gap between the die head 1 that discharges the coating liquid and the long support 2 that is continuously conveyed. A uniform coating film 4 can be formed. The coating liquid is a manifold 5 for spreading the coating liquid pushed out from a pump system that supplies the coating liquid (not shown) in the width direction, a slit portion 6 from which the coating liquid is pushed out, and discharging the coating liquid. A liquid puddle 12 called an application bead is formed through the lip portion and uniformly applied onto the support.

  In die coating, stabilization of the coating bead is the most important. For this stabilization measure, a decompression chamber 20 as shown in FIG. 2 is installed on the upstream side with respect to the flow direction of the support of the die head. Even if the body running speed is increased, a method for preventing the coating bead from collapsing by reducing the pressure on the upstream side is also performed.

  In the die coating method, as shown in FIG. 3, the die head 1 that discharges the coating liquid is disposed between the two rolls 15 and 16, and the coating is performed on the floating portion that does not have a roll behind the support. Is also done. By using this method, the clearance gap between the die head and the support can be brought close to the coating film thickness, and the effect of enabling high-speed thin film coating can be obtained.

  In the various die coating methods described above, the coating liquid discharged from the die head lip is configured to come into contact with only the surface parallel to the support at the tip of the lip. In many cases, the downstream lip climbs onto the outer side surface as shown in FIG. 1 and oozes out to the outer side surface of the upstream lip. If the downstream side lip climbs to the outer side surface, the coating liquid that accumulates on the surface will return to the coating surface irregularly, resulting in point defects, or the point-like climbing will grow greatly and continue. As a result, there were serious problems that caused a decrease in yield in continuous production. Moreover, even if the outer side surface portion of the upstream lip oozes out, the same phenomenon occurs, causing a problem.

  On the other hand, operation conditions such as appropriately adjusting the clearance gap between the die head and the support, or in the case of a system having a decompression chamber (see, for example, Patent Document 1), optimally adjusting the degree of decompression. In many cases, it is possible to find a condition that does not cause a run-up or seepage, but there are also cases where the characteristics of the coating liquid cannot find a condition that does not completely occur, which necessitates a major change in the coating liquid formulation. There was also a thing. In addition, by slightly changing the angle between the support and the die head, an operation to find out the conditions that do not occur is also performed, but adjusting the angle of the die head often significantly deteriorates the accuracy of the device, and causes another trouble. I was invited.

  In addition, by applying a water repellent treatment to the outer side surface of the upstream / downstream lip of the die head, it is possible to prevent the coating liquid from flowing out to the outer side surface of the upstream lip or the outer side surface of the downstream lip. However, due to poor adhesion between the water-repellent treatment agent and the die head and the durability of the water-repellent treatment agent, a portion with a weak water-repellent effect occurs partially due to the wiping operation and the lapse of time due to continuous application, On the contrary, there was a case where a coating streak was caused.

  In addition, by applying plating containing particles such as fluororesin to the outer side surfaces of the upstream and downstream lips of the die head, it is possible to provide a water repellent effect, but the flatness of the plating film surface and the edge portion are precise. It was mechanically difficult to process and often caused coating streaks.

Prior art documents are shown below.
JP 2003-53233 A

  An object of the present invention is to provide a method of manufacturing a die head capable of solving the problems of riding on the outer side surface portion of the lip and seepage in the die coating method as described above.

  The above object of the present invention is achieved by the following means.

  The invention according to claim 1 includes an upstream lip having an outer side surface portion, a slit side surface portion and a tip portion, an outer side surface portion, a downstream lip having a slit side surface portion and a tip portion, and an upstream lip and a downstream lip. A water repellent film is provided by a plasma CVD method using a source gas containing a dilution gas and a water repellent material on at least a part of the outer side surface portion excluding the slit side surface portion and the tip portion of the die head having a slit portion positioned therebetween. This is a method of manufacturing a die head.

  The invention according to claim 2 is the method of manufacturing a die head according to claim 1, wherein the plasma CVD method is performed within a pressure range of 15 to 150 kPa.

  The invention according to claim 3 is the method of manufacturing a die head according to claim 1 or 2, wherein the water repellent material contains a fluorine-containing organic silicon compound.

  The invention according to claim 4 is characterized in that the dilution gas is a gas selected from helium, argon, or nitrogen alone or mixed, and the ratio of the dilution gas in the whole is 90% or more. A method for producing a die head according to any one of the above.

  According to a fifth aspect of the present invention, the plasma CVD method includes: an upstream lip and a downstream side; and a counter electrode disposed opposite to an outer side surface portion of the upstream lip and the downstream lip and connected to a power source. The die head manufacturing method according to any one of claims 1 to 4, wherein a raw material gas containing a dilution gas and a water repellent material is supplied between the lip and the counter electrode and applied to the electrode. .

  The invention according to claim 6 is the die head manufacturing method according to any one of claims 1 to 5, wherein the counter electrode is a metal electrode coated with a dielectric.

  In a seventh aspect of the present invention, the distance between the outer side surface portions of the upstream lip and the downstream lip and the counter electrode is in the range of 0.05 mm to 20 mm. This is a method of manufacturing a die head.

  The invention according to claim 8 is characterized in that the opposite side of the counter electrode to the upstream lip and the downstream lip is similar in shape to the outer side surface of the upstream lip and the downstream lip. A die head manufacturing method according to any one of the above.

  The invention according to claim 9 is characterized in that the source gas containing the dilution gas and the water repellent material is supplied from the leading end side of the upstream lip and the downstream lip. It is a manufacturing method.

  The invention of claim 10 includes an upstream side lip having an outer side surface portion, a slit side surface portion and a tip portion, an outer side surface portion, a downstream lip having a slit side surface portion and a tip portion, and an upstream lip and a downstream lip. A die head having a slit portion positioned between, a counter electrode disposed opposite to the outer side surface of the upstream lip and the downstream lip and connected to a power source, and diluted between the upstream lip and the downstream lip and the counter electrode A die head surface treatment apparatus comprising gas supply means for supplying a source gas containing a gas and a water repellent material.

  The invention according to claim 11 is the die head surface treatment apparatus according to claim 10, wherein the counter electrode is a metal electrode coated with a dielectric.

  The invention according to claim 12 is the die head according to claim 10 or 11, wherein the distance between the outer side surface portions of the upstream lip and the downstream lip and the counter electrode is in the range of 0.05 to 20 mm. It is a surface treatment apparatus.

The invention of claim 13
The surface treatment of the die head according to any one of 10 to 12, wherein a side facing the upstream lip and the downstream lip of the counter electrode has a shape similar to the outer side surface portion of the upstream lip and the downstream lip. Device.

  According to the present invention, in the die coating method, it is possible to suppress the occurrence of run-up and seepage on the outer side surface portion of the lip, and it is possible to reduce the occurrence of coating stripes.

  In order to achieve the above-mentioned object, the present invention provides a plasma generated by applying an AC voltage between a counter electrode coated with a solid dielectric disposed opposite to a die head in a pressure atmosphere near atmospheric pressure. Thus, a water repellent film is provided on the die head surface. By using the plasma CVD method, a uniform film can be formed even on the curved shape portions of the outer side surface portions of the upstream and downstream lips of the die head. FIG. 4 is a cross-sectional view showing an outline of an embodiment of the die head manufacturing method of the present invention.

The die head used in the present invention has an upstream side lip having an outer side surface portion, a slit side surface portion and a tip portion, an outer side surface portion, a slit side surface portion and a tip portion.
Although a size, a shape, etc. are not specifically limited, Generally the width of the front-end | tip part of an upstream lip and a downstream lip is 0.1-2 mm, and the width | variety of a slit part is 0.05-1 mm. Further, the tip of the lip may have any shape shown in FIGS. 5 (a), (b), (c), and (d).
The present invention is characterized in that the water-repellent film is formed within a range of 1 to 5 mm from the tip of the outer side surface of the upstream / downstream lip. If it is in this range, it is possible to suppress the liquid from getting on the lip tip, coating stripes, and the like.

  The material of the die head is preferably a material that does not easily corrode. Examples of such a material include stainless steel and cemented carbide.

  The counter electrode used in the present invention is disposed so as to face the outer side surface portion of the upstream / downstream lip. A discharge treatment space is formed between the outer side surface portion of the upstream / downstream lip and the counter electrode, and a plasma CVD method is performed.

  The distance between the outer side surface of the upstream / downstream lip and the counter electrode is preferably in the range of 0.05 to 20 mm in consideration of stable discharge. Further, when helium is used as the dilution gas, it is preferably within a range of 0.5 to 5 mm, and when argon or nitrogen is used, it is preferably within a range of 0.5 to 2 mm.

  Moreover, it is preferable that the side which opposes the upstream lip and downstream lip of a counter electrode is similar to the outer side surface part of an upstream lip and a downstream lip. With such a shape, even if the die head has a complicated shape, the distance between the outer side surface portion of the upstream lip and the downstream lip and the counter electrode can be kept constant, and uniform discharge can be caused. Uniform processing can be performed.

  The counter electrode can be made of a metal material such as copper, silver, gold, titanium, aluminum, stainless steel, or brass, or an alloy conductor material. Moreover, what coated these metals and alloy conductor materials with the dielectric material can be used suitably.

  The solid dielectric layer disposed on the surface of the counter electrode is not particularly limited as long as it is a dielectric material such as a plastic material or a metal oxide film material. Particularly preferred are ceramic materials such as quartz, Pyrex (registered trademark), and alumina, and these materials are used in the form of a plate or deposited and sprayed on the electrode 51 surface. The thickness of these dielectric layers depends on the material and shape, but if they are too thick, a high voltage is required to generate plasma, and if they are too thin, they will break the dielectric layer and cause arc discharge. Therefore, a thickness of 0.3 to 5 mm is preferable.

  The water-repellent material used as the material for the water-repellent film may be any material that can dissociate in the plasma space and impart water repellency on the substrate surface, and examples thereof include organic silicon compounds and fluorine compounds. Among them, a fluorine-containing silicon compound having at least one silicon atom bonded to a reactive functional group is a particularly preferable material in order to obtain stronger adhesion to the object to be processed.

  Examples of the reactive functional group contained in the fluorine-containing silicon compound include a hydrolyzable group and a halogen atom. Specifically, examples of the hydrolyzable group include alkoxy groups such as methoxy group, ethoxy group, propoxy group and butoxy group; alkoxyalkoxy groups such as methoxymethoxy group, methoxyethoxy group and ethoxyethoxy group; allyloxy group and isopropenoxy group Alkenyloxy groups such as acetoxy group, propionyloxy group, butylcarbonyloxy group, benzoyloxy group, etc .; dimethyl ketoxime group, methyl ethyl ketoxime group, diethyl ketoxime group, cyclopentanoxime group, cyclohexanoxime group A ketoxime group such as N-methylamino group, N-ethylamino group, N-propylamino group, N-butylamino group, N, N-dimethylamino group, N, N-diethylamino group, N-cyclohexylamino group, etc. Amino group; N-methyl Acetamide group, N- ethyl acetamide group, an amido group such as N- methylbenzamide group; N, N- dimethylamino group, N, an amino group, such as N- diethylamino group and the like. Examples of the halogen atom include a chlorine atom, a bromine atom and an iodine atom. Of these, a methoxy group, an ethoxy group, and an isopropenoxy group are particularly preferable.

Specific examples of fluorine-containing silicon compounds having one or more silicon atoms bonded to these reactive functional groups include CF ₃ (CF ₂ ) p (CH ₂ ) qSi (OCH ₃ ) ₃ , CF ₃ (CF _{2) p (OC 3 F 6} ) qOCF 2 CF 2 CH 2 CH 2 (OCONH) (CH 3 O) 3, SiCH 2 CH 2 CH 2 OCH 2 CF 2 CF 2 O (CF 2 CF 2 CF 2 O) pCF _{2 CF 2 CH 2 OCH 2 CH} 2 CH 2 Si (OCH 3) 3, (CH 3 O) 2 CH 3 SiCH 2 CH 2 CH 2 OCH 2 CF 2 CF 2 O (CF 2 CF 2 CF 2 O) pCF 2 _{CF 2 CH 2 OCH 2 CH 2} CH 2 SiCH 3 (OCH 3) 2, (CH 3 O) 3 SiCH 2 CH 2 CH 2 OCH 2 CF 2 (OC 2 F 4) q _{(OCF 2) rOCF 2 CH 2} OCH 2 CH 2 CH 2 Si (OCH 3) 3, (CH 3 O) 2 CH 3 SiCH 2 CH 2 CH 2 OCH 2 CF 2 (OC 2 F 4) q (OCF 2) _{rOCF 2 CH 2 OCH 2 CH 2} CH 2 SiCH 3 (OCH 3) 2, (C 2 H 5 O) 3 SiCH 2 CH 2 CH 2 OCH 2 CF 2 (OC 2 F 4) q (OCF 2) rOCF 2 CH ₂ OCH ₂ CH ₂ CH ₂ Si (OC ₂ H ₅ ) ₃ , (CH ₃ O) ₃ SiCH ₂ C (═CH ₂ ) CH ₂ CH ₂ CH ₂ OCH ₂ CF ₂ CF ₂ O (CF ₂ CF ₂ CF _{2 O) pCF 2 CF 2 CH 2} OCH 2 CH 2 CH 2 (CH 2 =) CCH 2 Si (OCH 3) 3, (CH 3 O) 3 SiCH 2 C (= CH 2 _{) CH 2 CH 2 CH 2 OCH} 2 CF 2 (OC 2 F 4) q (OCF 2) rOCF 2 CH 2 OCH 2 CH 2 CH 2 (CH 2 =) CCH 2 Si (OCH 3) 3, (CH 3 O _{) 2 CH 3 SiCH 2 C (} = CH 2) CH 2 CH 2 CH 2 OCH 2 CF 2 (OC 2 F 4) q (OCF 2) rOCF 2 CH 2 OCH 2 CH 2 CH 2 (CH 2 =) CCH 2 SiCH _{3 (OCH 3) 2} and the like. However, it is an integer of p = 1-50, q = 1-50, r = 1-50, q + r = 10-100, and the repeating unit in a formula is random.

  These water-repellent materials are mainly liquid at normal temperature and pressure, and are vaporized by heating, pressurization, bubbling, etc., mixed with dilution gas, and sent to the discharge treatment space.

  As a dilution gas to be used, a gas selected from helium, argon and nitrogen is used alone or in combination. In addition to the dilution gas and the water repellent material, in some cases, a reactive gas such as air, oxygen, hydrogen, water vapor, carbon dioxide, hydrocarbon, and acetone may be mixed. However, the mixing ratio of the dilution gas needs to be 90% or more in order to improve discharge stability and maintain a highly reactive processing space.

  Next, an apparatus for providing a water repellent film on the die head surface in the present invention will be described. When processing the die head, the outside air needs to be a sealed space in consideration of environmental and human influences. In this way, as a configuration of the apparatus that cleanly fixes the die head in the discharge space and seals it with the outside, an apparatus configuration with an arrangement as shown in FIG. 4 can be considered, for example. However, the apparatus configuration of FIG. 4 is an example, and the present invention is not limited to this.

  For example, in the case of FIG. 4, as a material other than the electrode portion composed of the counter electrode 51 and the solid dielectric layer 52, the lip tip side wall surface 53, die head holding portion 55, gas supply port 58, gas exhaust port 59, etc. As long as it is a material that can insulate between the electrode portion and the die head 1, the shape and the material are not limited. If a conductive material is exposed to a portion in contact with the discharge space 57, an abnormal discharge occurs, so that only that point needs attention. For example, since the gas supply port 58 and the like are in contact with the processing space 57, it is necessary to select a material having high insulation and good workability. Specifically, acrylic, Teflon (registered trademark), and the like can be given. .

  When the die head 1 is installed, (1) sealing with the outside space and entry of processing gas, (2) preventing abnormal discharge, (3) from the viewpoint of protecting the lip portion, the die head 1 is used as a sealing material. 54 or the like is preferable. The material of the sealing material 54 may be an insulating material, and specific examples include Viton rubber and silicon rubber.

  The power source 56 used in the present invention may be an AC power source having a frequency of several kHz or more, and examples thereof include an AC pulse power source, an MF power source, and an RF power source. Preferably, a high frequency power source and a high frequency pulse power source of about 1 to 100 kHz that can easily perform impedance matching can be used. As a method of applying a voltage to the electrode 51, a method of applying an AC high frequency voltage by grounding either the die head 1 or the electrode 51 to the high voltage side and the ground can be considered.

  The higher the power output is and the longer the processing time is, the higher the temperature of the electrode head and the die head 1 as the object to be processed becomes. Therefore, it is preferable to process the electrode part and the die head in a constant temperature or cooled environment. The temperature is suitably in the range of 25 to 40 ° C. which prevents condensation and heating of the electrode. Examples of the cooling / constant temperature method include a general air cooling method and a water cooling method.

  The mixed dilution gas, the water repellent material and the reactive gas are supplied to the discharge treatment space. As the supply method, as shown by the arrows in FIG. 4, they are supplied from the tip side and away from the tip. It is good to flow in the direction.

  By processing from the front end side, it is possible to reliably perform processing near the front end close to the gas introduction means. That is, processing in the range of 1 to 5 mm can be reliably performed from the tip of the outer side surface portion of the upstream / downstream lip.

  The gas used to form these water-repellent films may be recovered by providing a gas exhaust port 59 on the wall surface or side surface facing the supply side. At that time, it is necessary to provide an exclusion device for the recovered gas.

  The treatment pressure in the discharge treatment space 57 is preferably treated at 15 to 150 kPa, which is under a pressure near atmospheric pressure. In particular, a pressure band of 90 to 105 kPa, which allows easy pressure adjustment, is preferable. The treatment under atmospheric pressure is simpler than the treatment under vacuum and the film formation rate is high.

  Since the counter electrode and the solid dielectric have a shape similar to the shape of the side surface of the lip portion of the die head that is the object to be processed, the counter electrode and the solid dielectric can be uniformly formed.

Next, a method for providing a water-repellent film on the surface of the die head in the present invention and the effects thereof will be described using examples.
As shown in FIG. 5, helium and heat-vaporized CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ are mixed in a weight ratio in a discharge treatment space 57 in which the die head 1 to be treated is installed and sealed. The mixture was supplied at a ratio of 99.8: 0.2. The water repellent material was vaporized using a liquid source vaporizer (Estec Co., Ltd.).
The counter electrode 51 and the solid dielectric layer 52 are made by spraying 1 mm of alumina ceramic on a titanium material. The distance between the die head and the electrode is 2 mm. The die head 1 was placed on the ground, and a voltage having a peak voltage of 10 kV was applied for 2 minutes.
Using the die head, continuous coating was performed with a coater apparatus. A polyethylene terephthalate film having a thickness of 75 μm was used as the support, a solvent-diluted acrylic resin having a viscosity of 10 mPa · s was used as the coating solution, and continuous coating at 3900 m was performed at a coating speed of 50 m / min. As a result, it was possible to stably produce good products without getting on or seeping out.
<Comparative example>
Under the above coating conditions, 3900 m of continuous coating was performed using a normal stainless steel die head that was not subjected to surface treatment. As a result, the run-up and the bleeding started from the time when the coating was performed for about 1000 m, and a coating streak that could be visually confirmed was generated, and a good product could not be obtained.

  The die head manufacturing method of the present invention requires high-precision quality, such as optical films, electronic substrates, food packaging materials, clothing packaging materials, etc., in the mass production field using the die coating method, stable production quality Is likely to contribute to cost reduction and higher accuracy.

It is sectional drawing which shows the outline of the conventional die coating system. In the conventional die coating system, it is sectional drawing which shows the outline of the apparatus which has a pressure reduction mechanism. It is sectional drawing which shows the outline of the system apply | coated to the floating support body part between two guide rolls in the conventional die coating system. It is sectional drawing which shows the outline of one Example of the manufacturing method of the die head of this invention. It is sectional drawing which shows the lip front-end | tip part shape of the die head conventionally used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Die head 2 Support body 3 Coating roll 4 Coating liquid 5 Manifold 6 Slit part 7 Upstream side lip 8 Downstream side lip 9 Tip part 10 Outer side surface part 11 Slit side side part 12 Application | coating bead 13 Riding | exuding 14 Outflow 15 Downstream guide roll 16 Upstream guide roll 20 Vacuum chamber 51 Counter electrode 52 Solid dielectric layer 53 Side wall surface of lip tip part 54 Sealing material 55 Die head holding part 56 High frequency power supply 57 Discharge treatment space 58 Gas supply port 59 Gas exhaust port

Claims (13)

  An upstream side lip having an outer side surface portion, a slit side surface portion and a tip portion, an outer side surface portion, a downstream lip having a slit side surface portion and a tip portion, and a slit portion positioned between the upstream lip and the downstream lip A die head characterized in that a water repellent film is provided by plasma CVD using a source gas containing a dilution gas and a water repellent material on at least a part of an outer side surface portion excluding a slit side surface portion and a tip portion of the die head. Production method.   2. The method of manufacturing a die head according to claim 1, wherein the plasma CVD method is performed within a pressure range of 15 to 150 kPa.   The method for manufacturing a die head according to claim 1, wherein the water repellent material contains a fluorine-containing organic silicon compound.   The die head according to any one of claims 1 to 3, wherein the dilution gas is a gas selected from helium, argon, and nitrogen alone or mixed, and the ratio of the dilution gas in the whole is 90% or more. Manufacturing method.   A counter electrode disposed opposite to the outer side surface of the upstream lip and the downstream lip and connected to a power source, wherein the plasma CVD method is provided between the upstream lip and the downstream lip and the counter electrode; 5. The method of manufacturing a die head according to claim 1, wherein a raw material gas containing a dilution gas and a water repellent material is supplied to the electrode and applied to the electrode.   The die head manufacturing method according to claim 1, wherein the counter electrode is a metal electrode coated with a dielectric.   The die head manufacturing method according to any one of claims 1 to 6, wherein a distance between the outer side surface portions of the upstream lip and the downstream lip and the counter electrode is in a range of 0.05 mm to 20 mm.   The die head according to any one of claims 1 to 7, wherein a side facing the upstream lip and the downstream lip of the counter electrode has a shape similar to an outer side surface portion of the upstream lip and the downstream lip. Production method.   9. The method of manufacturing a die head according to claim 5, wherein the source gas containing the dilution gas and the water repellent material is supplied from the leading end side of the upstream lip and the downstream lip.   An upstream side lip having an outer side surface portion, a slit side surface portion and a tip portion, an outer side surface portion, a downstream lip having a slit side surface portion and a tip portion, and a slit portion positioned between the upstream lip and the downstream lip A counter electrode disposed opposite to the outer side surface portion of the die lip, the upstream lip and the downstream lip and connected to a power source, and includes a dilution gas and a water repellent material between the upstream lip and the downstream lip and the counter electrode. A die head surface treatment apparatus comprising gas supply means for supplying a source gas.   The die head surface treatment apparatus according to claim 10, wherein the counter electrode is a metal electrode coated with a dielectric.   The die head surface treatment apparatus according to claim 10 or 11, wherein a distance between an outer side surface portion of the upstream lip and the downstream lip and a counter electrode is in a range of 0.05 to 20 mm.   The surface treatment of the die head according to any one of claims 10 to 12, wherein a side facing the upstream lip and the downstream lip of the counter electrode has a shape similar to an outer side surface portion of the upstream lip and the downstream lip. apparatus.