JP2622895B2 - Bar application method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photographic photosensitive material such as a photographic film and a photographic paper, a photoengraving material, a magnetic recording material such as a magnetic recording tape, a pressure-sensitive recording paper, and a heat-sensitive recording paper. For example, a liquid coating composition is applied to a long flexible support (hereinafter, referred to as a web) and a non-continuous substrate such as a semiconductor wafer, a printed circuit board, and a glass substrate that are continuously running in the production of a recording material. A bar coating method.

[Conventional technology]

The coating liquid is supplied such that a liquid pool is formed immediately before the contact portion of the support that is running while being in contact with the rotating bar,
In the bar coating method in which the bar is used to apply the coating solution to the support, it is sometimes necessary to make the coating width narrower than the width of the support. For example, in a web-like support, to prevent the applied liquid from spreading from the side of the web and to stain a pass roll to be touched after coating, or to hold a part of the substrate for transporting the substrate after coating on a discontinuous substrate. And so on. For this purpose, the bar diameter at both ends of the bar is made smaller than that at the center (referred to as a stepped bar) and the bar contacts the support only inside the width of the support,
It is possible to provide uncoated portions on both sides of the support.

However, when the coating is performed by such a method, there is a problem that a coating thick film portion is generated at both ends in the width direction of the coating surface, which causes a delay in drying and a reduction in the effective width of the product.

As a method for solving this problem, JP-A-60-225669 and JP-A-63-63158 disclose providing a blade for scraping a coating liquid on both sides of a coating roll. . Each of these methods has a certain effect in improving the thick coating at both ends of the coating width, but is not always sufficient. On the other hand, Japanese Patent Application Laid-Open No. Sho 62-7467 discloses that a means for sucking excess liquid is provided along the end face of the coating bar, and this method is superior to the former two in preventing thick coating. If the suction port is not very close to the end face of the bar, the effect is small, so it is difficult to install, or depending on the properties of the liquid, the suction port is liable to be clogged by the dried coating liquid when used for a long time depending on the properties of the liquid. There was a problem.

[Problems to be solved by the invention]

In a bar coating method of providing an uncoated portion on both sides of a support, an object is to provide a method in which it is relatively easy to improve a coated thick film portion generated at both ends in the width direction, and the effect is maintained for a long time. I do.

[Means for solving the problem]

As a result of analyzing the reason why the above-mentioned problem occurs, a part of the liquid in the liquid pool formed immediately before the contact portion between the bar and the support (primary side) protrudes from the end of the bar, and the end surface of the bar and the support The cause was found to be a bypass to the secondary side over a corner made on the surface. It has been found that this problem can be solved by blowing air toward the end of the bar or the contact portion between the bar and the support at the end surface. The present invention has been made based on the above findings.

That is, according to the present invention, the coating liquid is supplied such that a liquid pool is formed immediately before the contact portion of the support running while contacting the rotating bar, and the coating liquid is applied to the support by the bar. In the bar coating method, the bar diameter at both ends of the bar is made thinner than that at the center, so that uncoated portions are provided on both sides of the support, and the contact portion between the bar and the support in the coating portion is provided. A bar coating method characterized by blowing air to an end.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view showing a bar coating method of the present invention, showing a case of coating on a discontinuous substrate, and FIG. 2 is an enlarged sectional view of the bar coating apparatus of FIG.

The bar 2 is horizontally and rotatably supported by a bar support member 6 over the entire length or a part thereof, and one end of the bar 2 is connected to a rotation driving unit (not shown).

The bar support member 6 is surrounded by the weir members 5 and 5 ′, and the coating liquid 3 supplied from the liquid supply port 4 provided in a part of the weir member 5 is used for the coating between the bar support member 6 and the weir member 5. The liquid storage unit 8 is formed between them. In addition, an air blowing nozzle 21 for blowing air toward an end of a contact portion between the bar and the support in the application section is provided.
Air and nitrogen are blown out from here to send out the wind.

The substrate 1 to be coated includes a pass roll 14 and a pressing roll.
By 15, the substrate 1 is conveyed horizontally so that the lower surface of the substrate 1 contacts the vertex of the bar 2 in the rotation direction of the bar 2.

FIG. 2 shows that the rotating bar 2 is moved from the liquid storage section 8 to the coating liquid 3.
To transfer the coating liquid 3 to the lower surface of the substrate 1 via the liquid reservoir 9 formed at the contact point with the lower surface of the substrate 1 and simultaneously scrape off the metered liquid (by the action of the bar 2). The state in which the coating film 7 is formed is shown.

In the present invention, in order to perform the coating uniformly, it is important that the substrate 1 and the bar 2 adhere to each other over the entire width.
In the case of the method shown in FIG. 1, a method in which the substrate 1 is transported by the pass roll 14 and the pressing roll 15 is shown. In this scheme,
It is desirable to use an edge roll as the pass roll 14 so as to make contact with the lower surface of the substrate 1 as little as possible. Press roll
It is preferable that the substrate 15 be provided with an elastic body such as rubber on the surface so that the substrate 1 and the stepped bar 16 are in close contact over the entire width.

In the present invention, as shown in FIG. 3, a bar having a smaller diameter at both ends of the bar than that at the center is used. By doing so, the width of the coating surface of the coating bar is smaller than the width of the support. In the present invention, as long as uncoated portions are formed at both ends of the bar, the difference between the bar diameters at both ends and the center of the bar can be arbitrary, but 1.5 m
It is preferable to make it thinner than m.

In the present invention, such a coating bar is used,
The thick coating portions formed at both ends in the width direction of the support are improved by using an air blowing nozzle. This embodiment will be described in detail with reference to FIG.

In FIG. 4, the wind blown from the nozzle 21 is blown toward the contact portion between the bar and the support at the bar end face.
The air blowing action according to the present invention suppresses the liquid in the primary liquid pool from spreading to the end of the bar. It suppresses the liquid protruding outside from the end of the primary side bar, and discharges the protruded liquid to the secondary side. Escape to the bar end face without bypassing. The operation in the embodiment shown in FIG. 4 is as follows. In order to enhance the effect in particular, and to prevent the film surface after coating from being disturbed by wind, the secondary side rather than blowing air at right angles toward the bar end surface. It is better to incline slightly from to the primary side. The tilt angle is 0-60 °, preferably,
It should be 15-45 ゜. Further, it is better that the blowing nozzle is thinner, and the inner diameter is 2 mm or less, preferably 1 mm or less. The tip of the nozzle is preferably as close as possible to the end face of the bar as long as the coating liquid does not adhere to the nozzle. Actually, the tip is 15 to 20 mm, preferably 2 to 10 mm. These (small inner diameter and nozzle position) are preferable because they effectively draw out the action of the wind with a small amount of air, and the air spreads and does not cause scattering of the liquid or disturbance of the coating surface. The wind speed needs to be appropriately adjusted depending on the coating conditions (coating liquid viscosity, coating speed, etc.).
It is better to be in the range of sec. It is of course possible to use a pipe as the blow-out nozzle in the present invention. However, in order to improve operability and reproducibility of position setting, a block 22 having an internal hole as shown in FIG. It is desirable that the position can be set with good reproducibility. In order to enhance the effect of the present invention, it is desirable that the end face of the bar has a substantially concentric depression. This is to make it easier for the liquid blown by the wind to escape to the end face of the bar (that is, to enhance the effect of the action). According to this method, since the liquid does not pass through the nozzle, clogging of the nozzle does not occur, and the wind outlet does not need to be in close contact with the end face of the bar. .

FIG. 6 shows another embodiment of the present invention. In the figure, the end of the bar is provided with a blade 23 that contacts a part of the surface of the bar as disclosed in JP-A-60-225669,
At the end of the bar, the wire groove is crushed over a fixed width (preferably 2 to 15 mm). This enhances the scraping effect of the liquid on the bar surface by the blade, and serves to suppress the formation of a liquid pool on the primary side of the bar. As a method of crushing the groove of the wire, a method of filling grooves with solder,
Known methods, such as a method in which the rod diameter of a predetermined portion is twice as large as the wire diameter of the wire wound portion in advance, and a method in which a groove is not cut only in a predetermined portion by using a groove bar instead of a wire bar. Can be used. In the embodiment of FIG. 6 according to the present invention, a nozzle 21 is further provided at the end of the bar, and air is blown toward a contact portion between the bar and the support. In this figure, when there is no air blowing, the blade installation part at the end of the bar has very little or no coating on the primary side immediately after the start of application of the support, or is not applied at all. The coating liquid is pushed to the end of the bar by capillary action from the liquid pool on the primary side, and the liquid eventually turns around the end face of the bar to generate thick coating. The action of the wind in this drawing is an effect of preventing the liquid in the primary pool at the center of the bar from spreading to the end of the bar, and corresponds to the above-described action. In order to enhance the effect of the wind in this method, it is considered good to blow the wind from the outside to the inside. However, if the wind is blown in such a direction, the liquid in the primary liquid pool will be disturbed. It was found that the coating surface was easily disturbed. Therefore, it is desirable that the direction of the wind is slightly outward from the direction perpendicular to the bar. More specifically, 10 ゜ to 70 ゜, more specifically
30 ゜ to 60 ゜ is desirable. The blowing nozzle is preferably narrow as in FIG. 4, and the inner diameter is preferably 2 mm or less, more preferably 1 mm or less. Similarly, the position at the tip of the nozzle is preferably as close as possible to the end face of the bar as long as the coating liquid does not adhere to the nozzle, and in practice, it is 1 to 10 mm, preferably 1.5 to 5 mm. The wind speed also needs to be appropriately adjusted according to the application conditions as in FIG. 4, but is preferably in the range of 5 to 30 m / sec.

The material of the bar 2 used in the present invention is preferably a metal (especially stainless steel) in terms of strength and chemical resistance in many cases, but is not limited thereto, and a wire bar wrapped with a plastic fiber such as nylon, Rubber or plastic fluted bars are also used.

As the wire bar, a wrapping bar in which the outer peripheral surface of the wound wire is polished flat to increase the contact area with the substrate 1 can also be used.

The diameter of the bar 2 is 6.0 to 30.0 mm, more preferably 6.0 to 20.0 mm.
The range of mm is good, and if it is larger than this, the coating film tends to have uneven vertical stripes, and if it is smaller than this, production becomes difficult.

When the bar 2 is a wire bar, the range of the wire diameter is preferably 0.05 to 1.0 m in order to obtain a good coated surface state.
m, more preferably in the range of 0.05 to 0.7 mm.

The selection of the bar shape based on these findings, the wet coating amount can be applied stably from the thin layer coating of 4 cc / m ² to about 70 cc / m ² approximately thick film coating.

The web or substrate applied in the present invention is not particularly limited, for example, paper, plastic film, resin-coated paper, metal plate, glass plate and the like, the thickness of which is not limited, but is about 0.1 to 10 mm. It is preferably used.

The size of the substrate 1 in the present invention is not particularly limited.
In general, in the case of a glass substrate, the flatness of the surface tends to deteriorate as the size increases. However, by using an elastic body provided on the surface of the holding roll 15 shown in FIG. It has been confirmed that even a square glass plate with a thickness of 2 mm) can be applied sufficiently uniformly. The shape of the substrate 1 can be satisfactorily applied in any of a square shape and a circular shape.
The shape is not particularly limited.

Various liquids can be applied to a continuous or discontinuous substrate by the method of the present invention. The composition and physical properties of the coating solution are not particularly limited, but those having a viscosity of 100 cp or less, particularly 50 cp or less, are preferably applied.

A color filter can be suitably manufactured by the method of the present invention. Normally, when a color image is handled in an imaging device or a display device, the wavelength of visible light is usually divided and taken out, photoelectrically converted, and electrical energy is converted into light through the steps of amplification, transport, and amplification. , And a method of assembling and displaying color light is performed. Generally, B is set for each pixel which is the minimum unit representing the image density.
(Blue), G (Green), and R (Red) are divided into three wavelengths, and an imaging device that does not emit light or a display device such as a liquid crystal television needs a filter therefor. I'm calling

A photosensitive composition colored by a pigment used in the production of a color filter is a photopolymerization composition comprising an addition-polymerizable unsaturated monomer, a photopolymerization initiator, and a binder disclosed in U.S. Patent No. 3,549,367. Photosensitive cross-linkable photopolymers having an unsaturated double bond residue in the main chain or side chain of the photosensitive photosensitive composition and the polymer are useful.

The addition-polymerizable unsaturated monomer in the photopolymerizable photosensitive composition is a compound having at least one addition-polymerizable ethylenically unsaturated group and having a boiling point of 100 ° C. or more at normal pressure.
For example, monofunctional acrylates and methacrylates such as polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, and phenoxyethyl (meth) acrylate; polyethylene glycol di (meth) acrylate, trimethylolethanetri (meth) Acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, hexanediol (meth) acrylate, mermethylolpropane tri (acryloyloxy) Propyl) ether, tri (acryloyloxyethyl) isocyanurate, polyfunctional alcohols such as glycerin and trimethylolethane. After adding ethylene oxide or propylene oxide to call (meth) those acrylated, JP-B-48-41708, JP-B 50-6034
Urethane acrylates described in JP-A-51-37193, JP-A-48-64183,
Polyfunctional acrylates and methacrylates such as polyester acrylates described in JP-A-9-43191 and JP-B-52-30490, and epoxy acrylates which are reaction products of epoxy resin and (meth) acrylic acid. I can do it. In addition, Journal of the Adhesion Society of Japan Vol. 20, No.
Those described as photocurable monomers and oligomers on pages 7,300 to 308 can also be used. Used amount is 5-50Wt
% (Hereinafter abbreviated as%), preferably 10 to 40%.

As the photopolymerization initiator, vicinal polyketo aldonyl compounds disclosed in U.S. Pat.No. 2,367,660, α-carbonyl compounds disclosed in U.S. Pat.Nos. 2,367,661 and 2,367,670, U.S. Pat. No. 2,
Acyloin ethers disclosed in 448,828, α disclosed in U.S. Pat.No. 2,722,512
-Hydrocarbon substituted aromatic acyloin compounds, polynuclear quinone compounds disclosed in U.S. Pat.Nos. 3,046,127 and 2,951,758, triallylamidazole dimer disclosed in U.S. Pat.
/ p-Aminophenyl ketone combination, JP-B-51-48516
Benzothiazole compound / trihalomethyl-s-triazine compound disclosed in Japanese Patent Application No.
No. 186238, a photosensitive s-triazine compound described in U.S. Pat.No. 4,239,850, a trihalomethyl-s-triazine-based compound disclosed in U.S. Pat.
Oxadiazole compounds described in the specification of 4,212,976 are exemplified. The amount used is about 0.2-20 in solid content ratio
%, Preferably 0.5 to 15%.

The binder is preferably a linear organic high molecular polymer compatible with the monomer, soluble in an organic solvent, and developable with a weak alkaline aqueous solution. As such a linear organic high molecular polymer, a polymer having a carboxylic acid in a side chain, for example, JP-A-59-44615, JP-B-54-34327,
JP-B-58-12577, JP-B-54-25957, JP-A-59-53
No. 836, methacrylic acid copolymers, acrylic acid copolymers, itaconic acid copolymers, crotonic acid copolymers, maleic acid copolymers, and the like described in JP-A-59-71048. There are esterified maleic acid copolymers and the like, as well as acidic cellulose derivatives having a carboxylic acid in the side chain. In addition, those obtained by adding an acid anhydride to a polymer having a hydroxyl group are also useful. Among these, a benzyl (meth) acrylate / (meth) acrylic acid copolymer and a multi-component copolymer with benzyl (meth) acrylate / (meth) acrylic acid / and other monomers are particularly preferable. In addition, polyvinyl pyrrolidone, polyethylene oxide, polyvinyl alcohol, and the like are also useful as the water-soluble polymer. In order to increase the strength of the cured film, alcohol-soluble nylon and polyether of 2,2-bis- (4-hydroxyphenyl) -propane and epichlorohydrin are also useful. These polymers can be mixed in any amount, but if it exceeds 90%, it does not give favorable results in terms of the strength of the formed image and the like. Preferably it is 30-85%.

In addition to the above, it is preferable to further add a thermal polymerization inhibitor, for example, hydroquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol, t-butylcatechol, benzoquinone, 4,4 '-Thiobis (3-methyl-6-t-butylphenol), 2,
2'-methylenebis (4-methyl-6-t-butylphenol), 2-mercaptobenzimidazole and the like are useful.

Usually, an appropriate amount of a thermal polymerization inhibitor is added to commercially available monomers.

As the photocrosslinkable photopolymer, for example,
Polyester compounds disclosed in -96696, British Patent Nos. 1,112,277, 1,313,390 and 1,341,004
No. 1,377,747, JP-A-55-23941, and the like, and the like.

Useful organic solvents for the photosensitive composition include glycol ether methyl cellosolve, ethyl cellosolve, propyl cellosolve, propylene glycol methyl ether,
Propylene glycol ethyl ether, propylene glycol propyl ether and their acetates, namely methyl cellosolve acetate, ethyl cellosolve acetate, propyl cellosolve acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate are useful. In the case of acetic ester, amyl acetate, butyl acetate, propyl acetate, and ethyl acetate; in the case of ketone, methyl isobutyl ketone, methyl ethyl ketone, acetone, and cyclohexanone; Ethyl and the like are useful, and each alkyl group may be a linear or branched isomer.

Solution concentrations can be utilized in the range of 3-70%, with a more preferred range being 15-50%.

Coloring materials, for example, azo, anthraquinone, xanthene, quinacridone, indigo, dioxazine, indanthrone, isoindolinone, phthalocyanine, triphenylmethane, nitroso, perylene, Isoindoline pigments are useful, for example, phthalocyanine blue (CI Pigment Blue 15: 6
Or CI Pigment Blue 15: 3: for example, Lionol Blue ES manufactured by Toyo Ink Mfg. Co., Ltd., Chromo Blue A3R manufactured by Ciba Geigy, or phthalocyanine green (CI
Pigment Green 7, 36, or CI Pigment Green 37: for example, Lionol Green 2YS manufactured by Toyo Ink Mfg. Co., Ltd., perylene pigment (CI Pigment Red 155, anthraquinone pigment (CI Pigment Red 1)
77: For example, Lionogen Red GD manufactured by Toyo Ink Mfg. Co., Ltd., and Chromophthal Red BRN manufactured by Ciba Geigy)
And CI Pigment Yellow 83, CI Pigment Yellow 154: For example, Lionogen Yellow 3G and CI Pigment Bio Red 23 manufactured by Toyo Ink Manufacturing Co., Ltd .: For example, Toyo Ink Manufacturing Co., Ltd. ) Is particularly preferred. The coloring material is dispersed in the photocurable photosensitive composition to produce a colored photosensitive composition.

The ratio of the pigment in the photosensitive layer is 5 to 90 in terms of solid content.
%, More preferably 10 to 60%.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to the coating method of this invention, the thickness of the coating thick film part which arises in the width direction both ends of a support body can be made thin, and the thickness of a coating film can be made uniform. Therefore, according to the method of the present invention, a coated web or substrate can be produced very efficiently.

Therefore, according to the present invention, a photographic photosensitive material such as a photographic film and a photographic paper, a photoengraving material, a magnetic recording material such as a magnetic recording tape, a pressure-sensitive recording paper, and a heat-sensitive recording paper can be efficiently manufactured.
In addition, in the application of a photoresist for a photomask used in the production of a semiconductor wafer or the production thereof, a solder resist for a printed circuit board, or a glass substrate, it is possible to apply evenly to a large-sized substrate or a substrate of an arbitrary shape. Further, there is provided an economically excellent coating method in which the loss of the coating liquid is small.

In addition, when the method of the present invention is applied to a method for producing a color filter, a colored solution of the photosensitive composition can be applied to a large area without unevenness.

Therefore, according to the method of the present invention, a liquid crystal color display, a liquid crystal color television, a color image pickup tube, a color image sensor and the like can be easily manufactured at low cost.

 Next, the present invention will be described with reference to examples.

〔Example〕

Example 1 Using a bar coating device shown in FIG. 1, a size of 45 cm × 45 c
A photoresist solution was applied on a glass substrate having a thickness of 1.1 mm and a thickness of 1.1 mm. For the bar 2, a stainless wire having a diameter of 0.175 mm was wound around a stainless steel having a diameter of 12 mm, and an end face having a concentric hollow formed at an angle of 45 ° as shown in FIG. 5 was selected.
The height of the step was 2 mm. The transport speed of the substrate and the rotation speed of the wire bar were all 3 m / min.

At this time, as shown in FIG. 4, air was blown from a nozzle toward a contact portion between the bar and the glass plate at the end face of the bar. The blowing nozzle was a pipe having an inner diameter of 0.9 mm, the blowing direction was inclined by 45 ° from the secondary side to the primary side, and the tip of the nozzle was set so as to be about 5 mm away from the bar end face. The wind speed was set so that the wind speed was 15 m / sec at the nozzle outlet. Thick coating as shown in FIG. 8 also occurred at both ends in the width direction of the coating surface, but the maximum thickness b at the coating edge portion was about three times the average thickness a at the central portion and within 5% of the average thickness. Distance 1 for entering has been improved to about 10mm.

Example 2 Using a bar in which a wire groove was crushed by solder with a width of 5 mm at an edge portion, and as shown in FIG. 6, a contact portion of a bar and a glass plate at an end portion of the bar while contacting a blade over a bar edge portion of 10 mm. Wind was blown from the nozzle toward. The blow-out nozzle is a 0.9 mm inside diameter pipe, the blow-out direction is 45 ° outward, and the tip of the nozzle is approximately
It was set to be 2.5mm apart. Wind speed is 15m / s at nozzle exit
The air volume was set to be ec. The other conditions are the same as in the first embodiment. As a result of the application as described above, thick coating as shown in FIG. 8 also occurred at both ends in the width direction of the coating surface, but the maximum thickness b at the coating edge portion was approximately equal to the average thickness a at the central portion. The distance 1 for doubling and falling within 5% of the average film thickness was improved to about 5 mm.

Comparative Example 1 As shown in FIG. 7, coating was performed in the same manner as in Example 1 except that a method in which no measure was taken on the edge portion was used. Thick coating occurred as shown, and the maximum film thickness b at the coating edge portion was about 5 times the average film thickness a at the central portion, and the distance 1 for entering within 5% of the average film thickness was about 25 mm.

Comparative Example 2 Coating was performed in the same manner as in Example 1 except that a bar in which the wire groove was crushed by solder with a width of 5 mm at the edge portion was used, and as shown in FIG. About 30 mm from the tip of the substrate due to the bar surface liquid scraping effect of the blade
No thick coating occurs at both ends in the width direction of the coating surface, but thereafter thick coating occurs gradually, and after 50 mm from the front end of the substrate, the maximum film thickness b at the coating edge portion is about the central portion average film thickness a. 4 times, distance 1 to enter within 5% of average film thickness is about 15
mm.

[Brief description of the drawings]

FIG. 1 is a schematic view of a bar coating method of the present invention, and FIG.
3 is a perspective view of a stepped bar, FIG. 4 is a sectional view of another form of a stepped bar, FIG.
FIG. 6 and FIG. 6 are schematic diagrams showing a coating method of the present invention, FIG. 7 and FIG. 9 are diagrams showing a coating method for comparison, and FIG. 8 shows a film thickness distribution formed by coating. DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... bar, 3 ... coating liquid, 4 ... liquid supply hole, 5 ... dam member, 6 ... bar support member, 7 ... coating film, 8 ... liquid storage part, 9 …… Reservoir, 10 …… Bar application device, 14 …… Pass roll, 15 …… Press roll, 16 …… Stepped bar, 21 …… Blow-off nozzle, 22 …… Blow-off block, 23… Blade.

Continuation of the front page (72) Inventor Hiroshi Matsuoka 1005 Koizono, Ayase-shi, Kanagawa Prefecture Inside of Fuji Micro Graphics Co., Ltd. , A)

Claims (3)

(57) [Claims] An application liquid is supplied so that a liquid pool is formed immediately before a contact portion of a support running while contacting a rotating bar, and the coating liquid is applied to the support by the bar. In the bar coating method, uncoated portions are provided on both sides of the support by making the bar diameters at both ends of the bar smaller than those at the center, and the end of the contact portion between the bar and the support in the coated portion is provided. A bar coating method characterized by blowing air to a part. 2. Blades are provided at both ends of the effective coating width of the coating bar so as to be in contact with a part of the surface of the bar. 2. The method according to claim 1, wherein the number of the bars is reduced. 3. The bar coating method according to claim 1, wherein both end faces of the coating bar have substantially concentric depressions.