Patent Publication Number: US-6986916-B2

Title: Coating apparatus and method for applying coating solution on web

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and a method thereof for applying a coating solution on a continuous base (hereinafter web) with a solution in slide bead method for producing photographic film, photographic paper, photosensitive printing material, medical photosensitive material, micro film, magnetic recording tape, adhesive tape, pressure sensitive recording paper, thermosensitive recording paper, off-set printing material, film for liquid crystal display, and the like. 
     2. Description Related to the Prior Art 
     In a coating apparatus for applying a coating solution on a web in a slide bead method, a method for regulating a form of edges of the coating solution are disclosed in Japanese Patent Laid-Open Publications No. 55-84577, 10-128212, 10-151397, 10-165870, and 10-165872. In the method disclosed in the publications, a thickness of a coating layer at the edge is regularized by forming the best shape of an edge plate for regularizing a width of the solution on a slide surface, by blowing an air blow to the edge, and inserting a slot to the edges and the like. 
     However, the above mentioned coating apparatus has complex structure for which fine adjustments are necessary. When the coating apparatus is renewed, a difference of accuracy between the coating apparatuses causes to prevent from being in the best condition. 
     A method for solving the problem is disclosed in Japanese Patent No. 3-71185 and Japanese Patent Laid-Open Publication 7-502685. However, the coating apparatus described in the former publication often causes a defect of the edges of bead. Further an operation of the coating apparatus described in the latter publication is not so easy as to make a positional adjustment of an edge plate with a hopper edge guide device, and the determination of position of the edge plate is hard. 
     Further as shown in  FIG. 21 , when a height Dg of a side perpendicular wall  101  of an edge plate  100  is made to be less than the minimum thickness Db of bead of a coating solution, a flow of the solution  117  cannot be regulated only by the side perpendicular wall  101  at a minimum thickness position Dr of bead. Accordingly, a vena contracta is generated at the minimum thickness position Dr of the bead, the thickness at the edges of the coating solution becomes large, which causes the defect in drying. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a coating apparatus having a simple structure for which adjustments are easily carried out. 
     Another object of the present invention is to provide a coating apparatus with which a difference in a distribution of applying a coating solution on a web is not so large that a defect in drying may not occur. 
     Still another object of the present invention is to provide a method of applying a coating solution on a continuously feeding web with a coating apparatus, in which adjustments of the coating apparatus are easily carried out. 
     Still another object of the present invention is to provide a method of applying a coating solution on a continuously feeding web with a coating apparatus, in which a difference in a distribution of applying a coating solution on the web is not so large that a defect in drying may not occur. When Db is a minimum thickness of bead at vena contracta and Ds is an upper limit of a height of said regulation portion, then Db and Ds are represented as follows,
 
 Db ( m )=1.03 ×h   1 −1.50 ×he×U   −1/3 +12800 ×he   2   ×U 
 
 Ds ( m )={3 ×η×q /(ρ× g ×sin α)} 1/3 
 
     Herein,
         h 1  is a distance between said web and a lip of said die, whose unit is “m”;   he is a thickness of said coating layer formed on said web, whose unit is “m”;   U is a feeding velocity of said web, whose unit is “m/s”;   η is an averaged viscosity of solution flowing on said slide surface at a share rate, whose unit is “m·Pa·s”;   q is a total amount of said coating solution in a predetermined width, whose unit is “m 3 /(m·sec)”;   ρ is an averaged density of said solution, whose unit is “kg/m 3 ”;   g is an acceleration of gravity, and   α is an angle of slide surface.       

     Further, a height of the regulate portion Dg may satisfy a condition 0.15 mm≦Dg≦5 mm. On the uppermost of the regulate portion is formed a side inclination portion which is inclined to the slide surface. 
     Otherwise, the edge member has a front end portion provided so as to be parallel to a tangent line at a lowest position of applying the coating solution on the web. A height of the end portion is lower than 0.6 mm. Further on the uppermost of the front end portion is formed a front inclination portion which is inclined to the slide surface. 
     In a method for coating a coating solution, a coating solution is applied on a web with a coating apparatus of slide bead type that has an edge member provided for regulating a width of the coating solution flowing on a slide surface. The regulate portion is provided to be perpendicular to the slide surface, and an edge of the regulate portion contacts to the slide surface. A height Dg of the regulate portion satisfies a condition Db≦Dg≦Ds, in which Db and Ds is represented as follows:
 
 Db ( m )=1.03 ×h   1 −1.50 ×he×U   −1/3 +12800 ×he   2   ×U 
 
 Ds ( m )={3×η× q /(ρ× g ×sin α)} 1/3 .
 
     Herein,
         h 1  is a distance between said web and a lip of said die,   he is a thickness of said coating layer formed on said web,   U is a feeding velocity of said web,   η is an averaged viscosity of solution flowing on said slide surface at a share rate,   q is a total amount of said coating solution in a predetermined width,   ρ is an averaged density of said solution,   g is an acceleration of gravity, and   α is an angle of slide surface.       

     Further, a height of the regulation portion Dg may satisfy a condition 0.15 mm≦Dg≦5 mm. 
     Otherwise, the edge plate includes an end portion provided so as to be parallel to a tangent line at a lowest position of applying the coating solution on the web. A height of the end portion is lower than 0.6 mm. 
     The edge member may be constructed of a plate body and an end block attached to the plate body. In this case, it is preferable that the end block is fixed to the plate body with screws. 
     According to the invention, as the edge member of the coating apparatus is formed so as to satisfy the above conditions, the adjustments of the coating apparatus is easily made, and the difference in a distribution of applying a coating solution on a web is not large that a defect in drying may not occur. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become easily understood by one of ordinary skill in the art when the following detailed description would be read in connection with the accompanying drawings. 
         FIG. 1  is a side view of a coating apparatus in a situation of forming a coating layer of a coating solution on a web; 
         FIG. 2  is an enlarged perspective view of an edge plate of the coating apparatus; 
         FIG. 3  is a plan view of the edge plate in  FIG. 2 ; 
         FIG. 4  is a sectional view of the coating apparatus, which illustrates a positional relation to the web and a back-up roller for feeding the web; 
         FIG. 5  is a sectional view of the coating apparatus, which illustrates an adequate shape of the edge plate; 
         FIG. 6  is an explanatory view illustrating a shape of a bead formed of the coating solution when in applied on the web; 
         FIG. 7  is an enlarged view illustrating a front part of another embodiment of the coating apparatus of the present invention; 
         FIG. 8  is a diagrammatic view illustrating an inadequate positional relation between the edge plate and the die; 
         FIG. 9  is a graph illustrating a relation between a minimum thickness of bead and a thickness of the coating layer; 
         FIG. 10  is a graph illustrating a relation between a minimum thickness position of bead and the thickness of the coating layer; 
         FIG. 11  is a diagrammatic view of a third embodiment of the coating apparatus of the present invention; 
         FIG. 12  is a diagrammatic view illustrating an inadequate positional relation between the edge plate and the web; 
         FIG. 13A  is a side view of another embodiment of the edge plate; 
         FIG. 13B  is a side view the same as  FIG. 13A , which illustrates a situation of attachment of an end block to a plate body of the edge plate; 
         FIG. 13C  is a sectional view of  FIG. 13A , which illustrates a situation that the end block and the plate body is fixed by a screw; 
         FIG. 14  is a side view of a third embodiment of the edge plate; 
         FIG. 15  is a side view of a forth embodiment of the edge plate; 
         FIG. 16  is a plan view of a top of the coating apparatus of the present invention; 
         FIG. 17  is a vertical sectional view of the coating apparatus; 
         FIG. 18  is an exploded sectional view of the edge plate and the die; 
         FIG. 19  is a sectional view of another embodiment of the die; 
         FIG. 20  is a sectional view of a third embodiment of the die; 
         FIG. 21  is a sectional view illustrating a front part of a coating apparatus of a prior art. 
     
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     As shown in  FIG. 1 , a coating apparatus  10  includes a die  11 , an edge plate  12  having a front inclination  21 , and a back-up roller  16  for supporting a web  15 . When the back-up roller  16  rotates in a direction R 1 , the web  15  is fed in a feeding direction L 1 . A coating solution  17  having three solution elements (see,  FIG. 17 ) flows out from the lip  14  formed on an end of the die  11 . Then the coating solution  17  forms a bead  18  to reach the web  15 , and is dried in natural seasoning on the web  15  to form a coating layer  19  constructed with lowest, middle and uppermost sub-layers  19   a ,  19   b ,  19   c  on the web  15 . 
     Note that the temperature of the web  15  is adjusted by a temperature adjustment device  80  before applied with the coating solution  17 , such that the temperature may be 30–40° C. when receiving the coating solution  17 . 
     The feeding velocity U of the web  15  is between 1–6 m/s, preferably. Further the die  11  includes a vacuum chamber  81  for sucking or aspirating an air below the bead  18 , such that the pressure Pb below the bead  18  becomes smaller than the normal pressure P 0  above the bead  18 . Note that a difference P 0 –Pb is preferable to be between 300 and 1000 Pa, particularly between 400 and 700 Pa. 
     The web  15  coated with the coating layer  19  is fed to a drying section (not shown) by a feed roller  82 . In the drying section, the solvent in the coating layer  19  evaporates and dries to form a product. 
     [Web] 
     The web  15  is for example, a paper, a plastic film, a resin coated paper, a synthesized paper and the like. However the web is not restricted in them. Materials of the plastic film are for example polyolefine (polyethylene, polypropyrene, and the like), and vinyl polymer (vinyl acetate, polyvinylchloride, polystyrene and the like). Further, there are polyamide (nylon-66, nylon-6 and the like), polyester (polyethylene terephthalate, polyethylene-2,6-naphthalate, and the like), polycarbonate, and cellulose acetate (cellulosetriacetate (hereinafter TAC), cellulose diacetate and the like). Preferably, under-layer of gelatin and the like is formed on a surface of the web  15 . In this case the coating solution is smoothly and effectively applied on the web  15 . As a resin for the resin coated paper, the polyolefine, such as polyolefine is usually used. However, it is not restricted. 
     [Coating Solution] 
     There are a lot of types of the coating solution used for the present invention. For example, in producing a photosensitive material, the coating solution is used for forming a photosensitive emulsion layer, a under layer, a protective layer, a back layer and the like. Further the coating solution may be used, which forms the adhesive layer, coloring layer, anticorrosion layer, and the like. It is preferable the coating solution contains a water soluble binder or an organic binder. Particularly, the main component of the coating solution is gelatin, latex, polyvinylalchohol, styrene butadiene rubber, and the like, and especially gelatin. However, the coating solution of the present invention is not restricted in it. 
     [Coating Apparatus] 
     In  FIG. 2 , the edge plate  12  is provided on a slide face  13  of the die  11  such that an end face  20  having a height Dg and the lip  14  of the die  11  form the same face. The edge plate  12  has a perpendicular wall  22  having a height Dg, an inclined wall  23  and an upper wall  24 . The edge plate  12  is provided also in another edge of the die  11 , whose illustration is omitted. The coating solution  17  flows in a space formed by the slide surface  13 , the perpendicular wall  22  and the inclined wall  23 . The upper wall  24  prevents the coating solution  17  from overflowing. Note that the form of the end portion  22   a  of the perpendicular wall  22  may have a complex form. Accordingly, the form of the end portion is not restricted in that of the figure. Further, as shown in  FIG. 3 , an angular between the inclined wall  23  and the slide surface  13  is set in range of 45–75°. 
     In  FIG. 4 , it is preferable that a distance h 1  between the lip  11  and the web  15  set in a 200–300 μm, as the coating solution  17  is applied so as to have a constant thickness on the web  15 . It is especially preferable that the end face  20  is formed to be parallel to a tangent line  25  drawn at a lowest position (hereinafter contact position)  25   a  where the coating solution  17  contacts to the web  15 . However the angle of the tangent line  25  to the end face  20  may be charged between −30° and +30°. An angle D 2  between the front inclination  21  and the slide surface  13  is set to 35–60°. Thus the applying of the coating solution  17  is made adequately. Note that the  FIG. 4  illustrates a situation in which the coating solution  17  is not applied. However, the position of the coating solution  17  is shown by the chain double-dashed line for easy understanding. 
     In the coating solution has a surface tension to make the size of a surface of the coating solution minimum. The tension causes the vena contracta in the coating solution, and is at the maximum in the bead. The reason is as follows:
     (1) before reaching the web, the coating solution leaves the edge plates which has been regulated the coating solution;   (2) as the coating solution is extended in a lengthwise direction in the bead, the vena contracta is generated not only in a direction of thickness but also in a widthwise direction;   (3) the extending causes to decrease the density of the surface active agent on a surface and to increase the surface tension for minimizing the size of the surface of the coating solution. The vena contracta in the coating solution  17  enlarges the thickness of the edge of the bead  18 , which causes a defect in drying.   

     As shown in  FIG. 5 , a position at which the thickness of the coating liquid  17  becomes minimum on the slide surface  13  is determined as a minimum thickness position Dr by vena contracta. The height Dg of the perpendicular wall  22  of the edge plate  12  is larger than a minimum thickness Db of the bead  18 . As the flow of the coating solution  17  is regularized by the perpendicular wall  22 , the bead  18  that is caused by the vena contracta is hardly deformed. Thus a thickness “he” of the coating layer  19  on the web  15  becomes constant. Note that the lowest, middle and uppermost sub-layers  19   a – 19   c  in the coating layer  19  are omitted in  FIG. 5  and the following figures for easiness of understanding. 
     In order to make the coating of the solution  17  adequately, it is preferable to satisfy the condition Df≦Db. Further, it is preferable the height Df of the end face  20  satisfies the condition 0 mm&lt;Df≦0.6 mm. However, the height Df is not restricted in this condition. 
     The minimum thickness Db of the bead  18  can be calculated. As shown in  FIG. 6 , an angle α is that between the slide surface  13  and a horizontal line. An upper meniscus  18   a  of the bead  18  is an arc whose radius of curvature is R. A center of the arc is determined as a point O, which is represented as (0,0) in X-Y Cartesian coordinate. A point F is an end of the upper meniscus  18   a . Then the distance between the point F and the point O is the radius R of curvature. Hens &amp; Boiy “Chemical Engeneering Science Vol. 41, P. 1827–1831 (1986)” discloses the following formular:
 
 R= 2 ×he×{σ /(η× U )} 1/3 ,  (1)
 
herein he is the thickness (mm), σ is a surface tension, η is a average of viscosity (mPa·S) of coating solution at a share rate in flowing on the slide surface, and U is a feed velocity (m/s) of the web  15 . Further, the line O-F is extended toward the web  15  and the extended line reaches the web  15  at a point A. The point A is represented as (−R−he,0). Note that the radius of the back-up roller is much larger than the radius R of the bead  18   a  and the thickness he. Accordingly, part of the periphery illustrated in  FIG. 6  can be regarded as a perpendicular line.
 
     At a point B, a lower meniscus  18   b  of the bead  18  contacts to the web  15  in  FIG. 6 . The point B is represented as (−R−he, Yb) in the Cartesian coordinate. The length Yb is a distance between the point A and the point B, and known as an expulsion thickness which is a length necessary for the coating solution  17  to form on the web  15  the coating layer  19  having the thickness he. The Publication of J. Hens &amp; L. Boiy “Chemical Engeneering Science Vol. 41, P. 1827–1831 (1986)” discloses that the following formula is satisfied after a theory of boundary layer of Sakiadis:
 
 Yb= 0.383×(ρ× U×he   2 /η).  (2)
 
     At point C, the coating solution  17  leaves the uppermost of the lip  14 . A line B-C between the point B and the point C reaches the horizontal line at an angular β. Accordingly, the point C is represented as (−R−he+h 1 , −Yb−h 1 ×tan β) in the Cartesian coordinate. 
     A line O-Dr is perpendicular to the slide surface  13 , and crosses with an upper meniscus  18   a  of the bead  18  at a point E. Accordingly, the length of a line Dr-E is determined as a minimum thickness Db of the bead  18 , and a length from a front end of the slide surface to the minimum thickness position Dr of bead is determined as the length Lr of a line C-Dr. The minimum thickness position Dr of bead is represented as (Dx, Dy) in Cartesian coordinate, and Dx and Dy are calculated as follows. 
     If the point C is represent as (Cx, Cy), the formula of the line C-Dr is:
 
 Y= tan α×( x−Cx )+ Cy.   (3)
 
According to the line O-Dr:
 
tan α=− x/y , therefore:
 
 y=−x /tan α.  (4)
 
The formula (3) and (4) are solved according to (x, y):
 
 x= sin α×cos α×( Cx ×sin α/cos α− Cy )= Dy   (5)
 
when the above formula (5) is solved according to y:
 
 y =−cos 2 α×( Cx ×sin α/cos α− Cy )= Dy   (6)
 
Herein, in order to obtain formulae representing Dx and Dy, the coordinate of Cx and Cy are used:
 
( Cx,Cy )=( −R−he+h   1 ,− Yb−h   1 ×tan β).  (7)
 
As “R” and “Yb” can be diminished from the formula (7) and (1),
 
Cx and Cy are represented as follows.
 
 Cx=h   1   −he×[ 1+2×{σ/(η× U )} 1/3 ]  (8)
 
 Cy=− 0.383×(ρ× U×he   2 /η)− h× tan β  (9)
 
     As shown in  FIG. 6 , a formula Db=r−R is satisfied. Further, a formula of a circle whose radius is r and whose central point is (Dx,Dy) is as follows.
 
 r= ( Dx   2   +Dy   2 ) 1/2   (10)
 
 Db= ( Dx   2   +Dy   2 ) 1/2   −R   (11)
 
     In order to solve according to Dx 2 +Dy 2 , the formula (10) is solved from the formula (5) and (6) as follows:
 
 Dx   2   +Dy   2 =cos 2  α×( Cx ×sin α/cos α −Cy ) 2   (12)
 
From the formula (11) and (13):
 
 Db=Cx ×sin α− Cy ×sin α− R   (13)
 
     From the formula (8), (9) and (13):
 
 Db = (sin α+tan β×cos α)× h   1 −sin α× he− 2×(sin α+1)×(ρ/η) 1/3   ×he×U   −1/3 +0.383×cos α×(ρ/η)× he   2   ×U   (14)
 
     Further, considering the following conditions:
 
 b   1 =(sin α+tan β×cos α)
 
 b   2 =−sin α
 
 b   3 =−2×(sin α+1)×(σ/η) 1/3 
 
 b   4 =0.383×cos α×(ρ/η)
 
the formula (14) is represented with use of b 1 –b 4  as follows:
 
 Db=b   1   ×h   1 − b   2   ×he−b   3 × he×U   −1/3   +b   4   ×he   2   ×U   (15)
 
     In the formula (14), regions of value of α, β, σ, ρ, η are as follows:
     α (inclination angle of slide surface)=0°–30°   β (contact angle)=50°   σ (surface tension)=20–70 mN/m   ρ (averaged density of coating solution)=100 kg/m 3      η (averaged viscosity of coating solution at share rate)=30–50 mPa·s
 
Note that the value of the contact angle β is reported in “AIChE Spring meeting (1988)” by Katagiri. In the condition of β=50°, the coating solution is applied on the web stably.
   

     b 1 –b 4  has the following values when in using the value of α, β, σ, ρ and η: 
     b 1 =0 to 1.03 
     b 2 =−0.5 to (−0) 
     b 3 =−4 to (−1.5) 
     b 4 =6634 to 12767 
     Considering the significant digit,
 
 b   1 =1.03,  b   2 =−0(=0),  b   3 =−1.50,  b   4 =12800,
 
     then,
 
 Db= 1.03 ×h   1 −1.50 ×he×U   −1/3 +12800 ×he   2   ×U   (16)
 
     When the minimum thickness Db of the perpendicular wall  22  is enough large, the contraction is prevented. However, when the minimum thickness Db is too large, the thickness of the coating layer  19  on the web  15  becomes inconstant in the widthwise direction. The reason therefor is that the boundary layer of Blasius develops more on the slide surface. In order to prevent it, it is preferable that almost of the coating solution flows in lower part of a top of the perpendicular wall  22  on the slide face  13 . 
     An upper limit Ds of the height Dg of the perpendicular wall  22  is calculated from the following formula shown in “Transport Phenomena (Willey; 1960) P. 35–40” by R. B. Bird et al.
 
 Ds ( m )={3 ×η×q /(ρ× g ×sin α)} 1/3   (17)
 
herein, η is averaged viscosity of the coating solution at sharing rate when in flowing on the slide surface, q is a total amount of the flowing coating solution for a predetermined width, ρ is a averaged density of coating solution, and g is the acceleration of gravity.
 
     Now, the minimum thickness position Dr of bead is calculated. According to the formula cos α=(Dx−Cx)/Lr:
 
 Lr= ( Dx−Cx )/cos α  (21)
 
The formula 5 is put into Dx of the formula (21), then
 
 Lr ={sin α×cos α×( Cx× sin α/cos α− Cy )− Cx }/cos α  (22)
 
therefore,
 
 Lr=−Cx× cos α− Cy ×sin α  (23)
 
The formulae (8) and (9) are put into Cx and Cy of the formula (23) respectively, then
 
 Lr =−cos α[ h   1   −he×{ 1+2(σ/(η× U )) 1/3 }]−sin α×{−0.383×(ρ× U×he   2 /η)− h   1 ×tan β}  (24)
 
     The formula (24) is transformed as follows:
 
 Lr= (−cos α+sin α×tan β)× h   1 +cos α× he+ 2×cos α×(σ/η× U ) 1/3   ×he×U   −1/3 +0.383×sin α(ρ/η)× U×he   2   (25)
 
herein h 1  is the distance between the web and the die, he is the thickness of the coating layer, and U is a moving velocity of the web.
 
     When the following substitutions are used;
 
 r   1 =(−cos α+sin α×tan β)
 
r 2 =cos α
 
 r   3 =2×cos α×(σ/η) 1/3 
 
 r   4 =0.383×sin α×(ρ×η)
 
then the formula (25) is transformed as follows:
 
 Lr=r   1   ×h   1   +r   2   ×he+r   3   ×he×U   −1/3   +r   4   ×U×he   2   (26)
 
     Further, regions of value of α, β, σ, ρ, η are as follows in the formulae representing r 1  to r 4 :
     α (inclination angle of slide surface)=0° to 30°   β (contact angle)=50°   σ (surface tension)=20 to 70 mN/m   ρ (averaged density of coating solution)=1000 kg/m 3      η (averaged viscosity of coating solution at share rate)=30 to 50 mPa·s   r 1  to r 4  have the following values when in using the value of α, β, σ, ρ and η:   r 1 =−1.0 to −0.27   r 2 =0.87 to 1.0   r 3 =−2.5 to (−1.3)   r 4 =0 to 5319   

     Considering the significant digit of the above values, the formula (26) is:
 
 Lr=− 0.270 ×h   1 +1.00 ×he− 1.30 ×he×U   −1/3 +5320 ×U×he   2   (27)
 
     The tensional rate of surface of the coating solution is the highest at the minimum thickness position Dr of bead where the distance between the upper meniscus and the slide surface is the smallest. Accordingly, the substitutive force of the upper meniscus of the bead tense to the edge plate is most effectively applied at the minimum thickness position Dr of bead. Thereafter, when reaching the web, the coating solution is tensed furthermore. However, the tensional rate is lower than at the minimum thickness position Dr of bead. Accordingly, it is necessary for preventing the contraction that the minimum thickness Db of bead is smaller than the height Dg, and that the edge plate is provided at the minimum thickness position Dr of bead. Therefore, it is required to satisfy the following condition:
 
Db≦Dg≦Ds  (31)
 
     The coating solution is applied without generating contraction by using the edge plate which satisfies the condition of the formula (31). 
     When the condition of the formula (31) is satisfied, the end face  20  of the edge plate  12  may be retracted from the lip  14  of the die  11 . In  FIG. 7 , there is a distance De between the end face  20  and the lip  14 . The distance De and the length Lr have a relation De≦Lr. 
     As shown in  FIG. 8 , the distance De between the lip  14  and an end surface  103  of an edge plate  102  is larger than the length Lr. In this case, a perpendicular face  104  is not provided at the minimum thickness position Dr. Accordingly, the contraction causes a deformation of a bead  105 , which makes hard to form a coating layer  106  at a constant thickness. 
       FIG. 9  illustrates a relation between the thickness he of the coating layer and the minimum thickness Db of bead according to several feeding velocities U of the web. Note that the distance h 1  between the web and the lip of the die is set to 200 μm. In order to form the coating layer having a constant thickness, the minimum thickness Db of bead must be larger when in applying at the larger feeding velocity U of the web, and therefore the larger amount of the coating solution is supplied. The minimum thickness Db of bead is usually more than about 0.2 mm. The conditions for calculating the upper limit Ds of the height of the perpendicular wall  22  are as follows: 
     The averaged viscosity η of coating solution at the share rate in flowing on the slide surface is 30 (mPa·S), a total amount q of the flowing coating solution for a predetermined width is 0.001 {m 3 /(m×sec)}, the angle α of the slide surface is 15°, the averaged density ρ of coating solution is 1000 (kg/m 3 ), the acceleration of gravity is 9.8 (m/sec 2 ). 
     When these values are put into the formula (17), the upper limit Ds is 1.5 mm. Accordingly, the height Dg of the perpendicular wall can be 0.15 mm≦Dg≦5 mm, preferably 0.2 mm≦Dg≦1.5 mm. However, in the present invention, the height Dg of the perpendicular wall is not restricted in the region of value. 
       FIG. 10  illustrates a relation between the thickness he of the coating layer and the length Lr from the lip to the minimum thickness position Dr of bead according to several feeding velocities U of the web. Note that the distance h 1  between the web and the lip of the die is set to 200 μm. In order to form the coating layer with a constant thickness, the length Lr must be larger when in applying at the larger feeding velocity U of the web. 
     In  FIG. 11 , the end face  20  of the edge plate  12  is positioned closer to the web  15  than the lip  14 . In this embodiment, the perpendicular wall satisfies at the minimum thickness position Dr of bead the condition Db≦Dg. Accordingly, the coating layer  19  is formed to have a constant thickness. Otherwise, as shown in  FIG. 12 , the end face  20  is positioned too close to the web  15 . In this case, the end surface  20  often contacts to the web  15 . In the present invention, it is preferable that a nearest interval L 1  between the end surface  20  to the web  15  may be L 1 ≧100 μm. 
     As the fine processing is made on an inner side in a forward part of the edge plate, the forward part is easily broken. As shown in  FIG. 13A , the edge plate  12  is constituted of a plate body  12   a  and a removable end block  12   b . As shown in  FIG. 13B , the end block  12   b  has the perpendicular wall  22 , the inclined wall  23  and the upper wall  24 . When the end block  12   b  is broken, another end block  12  may be attached to the plate body  12   a . Further, it is preferable that a length of the end block  12   b  is 10–50 mm. However, the length is not restricted in it. As shown in  FIG. 13C , the end block  12   b  is fixed with a screw  28  to the plate body  12   a . Note that although the number of the screw  28  illustrated in  FIG. 13C  is only one, plural screws may be used for fixing the end block  12   b  to the plate body more strongly. 
     In  FIG. 14 , the edge plate  30  is constructed of a plate body  30   a  and an end block  30   b . The end block  30   b  has a front inclination  32 , an inclined wall  33  and a perpendicular wall  34 . An upper wall  35  is provided only with the plate body  30   a . Further, as shown in  FIG. 15 , an end block  36   b  of an end plate  36  has only a part  38   b  of an inclination  38 , a part  39   b  of an inclined face  29 , and a perpendicular wall  40 . In this case, the inclination  38  is separated into a part  38   a  and the part  38   b  of the inclination  38 , and the inclination face  39  is separated into a part  39   a  and the part  39   b . As illustrated in the above figures, there are several types of the end blocks having several shapes. 
     In  FIG. 16 , a top of the edge plate  12  has a width L 5 , and a heartwood  26  fills a retraction formed on a top of each edge plate  12 . Screw holes  11   a  are formed in the heartwood  26 . As shown in  FIG. 17 , screw holes  12   c  are formed in the plate body  12   a , so as to be positionarily corresponding to the screw holes  11   a . When a screw  50  is inserted through the heartwood  26  into the screw holes  12   c  and  11   a , the edge plate  12  is fixed to the die  11 . Thus the distribution of the coating solution becomes adequate, which causes to prevent the damage of the web or a disorder of the edge of the coating layer. Accordingly, the coating solution is stably applied on the web. Further, it is preferable to fix the edge plate  12  from an inner side with the screw  50 . Thus the position of the plate  12  is fixed on the die  11  accurately. 
     Considering heat deformation, it is preferable to form the screw  50  with the same material as the die  11 . The material may be metal such as stainless and the like, polymers such as fluoride resin, acetal resin, acryl resin, and another nonmetals. Further, the number of the screw  50  for fixing the edge plate  12  on the die  11  is not restricted in four, which is shown in  FIG. 17 . A method for fixing the die  11  and the edge plate  12  is not restricted in using the screw  50 , and may be one of the methods for fixing that are already known. 
     The material for forming the edge plate  12  is not especially restricted. However, it is preferable that the perpendicular wall  22  and the inclined wall  23  are formed of a nonmetal such as polymers, in order to prevent the corrosion. It is especially preferable to use the fluoride resin which is excellent in a anticorrosion. 
     Note that the die  11  has three manifolds  55   a ,  55   b ,  55   c  connected with the slits  41 . Three solution elements  19   a ,  19   b ,  19   c  of the coating solution  17  are filled in the manifolds  55   a – 55   c , respectively. 
     As shown in  FIG. 18 , the heartwood  26  is positioned to have a length L 3  from an outer surface and a length L 4  from a bottom of the edge plate  12 . It is preferable that the length L 3  is more than 1 mm, and the length L 4  is more than 3 mm, with consideration of strength of the edge plate  12 . However, the shape of the heartwood  26  is not restricted in that of this figure. It is preferable that the heartwood  26  is made of stainless although other metal is used. Further, nonmetal may be used. As the nonmetal, there is the engineering plastic (for example, polycarbonate and the like) that has an excellent strength. 
     Preferably the width L 5  is 20 to 100 mm. When the width L 5  is less than 20 mm, it is hard to fit the heartwood  26  in the edge plate  12 . However the width L 5  is not restricted in this description. 
     Note that the shape of the perpendicular wall  22  is not restricted in the above embodiment. Further, a coating apparatus  60  illustrated in  FIG. 19  may be used in the present invention. In the coating apparatus  60 , an edge plate  62  is attached to a die  61  (the screws are omitted in  FIG. 19 ). The edge plate  62  has a perpendicular wall  62   a , an inclined wall  62   b  and an upper wall  62   c . On a slide surface  63  are formed three slits  67 ,  68 ,  69  which are connected with manifolds  64 ,  65 ,  66 , respectively. Further, the slide surface drops at each of the slits  67 – 69 . In the coating apparatus  60 , the height Dg of the perpendicular wall  62  satisfies the condition Db≦Dg≦Ds. 
     Also a coating apparatus  70  illustrated in  FIG. 20  may be used in the present invention. In the coating apparatus  70 , an edge plate  72  is attached to a die  71  (the screws are omitted in  FIG. 20 ). The edge plate  72  has a perpendicular wall  72   a , an inclined wall  72   b  and an upper wall  72   c . The perpendicular wall  72   a  is formed so as to become wider in downstream. In the coating apparatus  70 , the height Dg of the perpendicular wall  72  satisfies the condition Db≦Dg≦Ds. 
     EXAMPLES 
     In followings, examples of the present invention are described. However, the present invention is not restricted in them. 
     &lt;Experiment 1&gt; 
     In Experiment 1, there are examples 1–9 and comparisons 1 and 2, in which respective conditions are determined when in applying the coating solution. At first, an explanation about the example 1 is made in detail. In explanations about examples 2–9 and the comparisons 1 and 2, the same is omitted. 
     Example 1 
     The first to third solution elements of the coating solution were prepared for forming the lowest, middle and uppermost sub-layer, respectively. The first solution element contained gelatin (4%), and the viscosity thereof was 80 mpa·s, and the amount of coating was 20 ml/m 2 . The second solution element contained gelatin (8%), and the viscosity thereof was 150 mpPa·s, and the amount of coating was 100 ml/m 2 . The third solution element contained gelatin (6%), and the viscosity thereof was 40 mPa·s, and the amount of coating was 10 ml/m 2 . The viscosity of each of the three solution elements was adjusted by adding the polyvinyl sulfonic acid. A dyne was added into the second solution element for the middle sub-layer, and thickness of the coating layer formed on the web was evaluated from an optical density. An aerosol OT was added in the third solution element for the uppermost sub-layer, to adjust the surface tension to 27×10 −3  (N/m). 
     In order to apply the above coating solution on the web, the coating apparatus  10  illustrated in  FIG. 1  was used. Thus three sub-layers  19   a – 19   c  were formed on the web simultaneously in a slide bead method. According to the edge plate  12 , the angle D 1  of the inclined wall  22  was 45°, the angle D 2  of the front inclination  21  is 60°, and the height Dg of the perpendicular wall is 0.6 mm. The angle α of the slide surface  13  was 15°. The end face  20  protrudes from the lip  14  of the die  11 , and the distance De between the end face  20  and the lip  14  was 0.07 mm (=70 μm), as shown in  FIG. 3 . Further, the difference (P 0 −P b ) of pressures between the upper and lower meniscuses of the bead was 490 Pa, and the temperature of the surface of the web  15  was 36° C. 
     The velocity of coating of the coating solution was 2 m/s. The temperature of the coating the coating solution was 35° C. Thereby the averaged density ρ of the coating solution was 1000 kg/m 3 . The total flowing amount q of the coating solution in a predetermined width was 3×10 −4  m 3 /(m×sec). The viscosity η of the coating solution at the share rate on the slide surface was 100 mPa·s. The upper limit Ds of the height Dg of the perpendicular wall  22  was calculated from these conditions of ρ, q, η, the angle α of the slide surface and the acceleration g (m/sec 2 ) of gravity, to be 3.288 mm. 
     Note that a TAC was used as the web  15 . According to the coating condition, the moving velocity U of the web was 2 m/sec, the distance h 1  between the lip and the web was 0.20 mm. The thickness he of the coating layer  19  was 0.15 mm. The minimum thickness Db of bead was calculated by putting these values of U, h 1  and he into the formulae (15) and (16). The minimum thickness Db of bead was 0.181 mm. 
     The thickness of coating layer of each sample film was measured at a position 10 mm from edges. The thickness at the position was compared with the thickness at the middle position in the widthwise direction of the sample film. In the experiment 1, the difference of the thickness between at the position and the middle position was less than 1%. Further, conditions in the edges of the coating layer were checked with eyes. The result thereof was “good”. 
     Examples 2–9 and Comparisons 1 and 2 
     In Examples 2–9 and Comparisons 1 and 2, some conditions is changed. 
     The conditions of Examples 1–9 and Comparisons 1 and 2 are shown in Tables 1–4 for easily understanding. In table 1 and 4, the distance De between the end face and the lip of the die has a negative value when the end face protrudes from the lip as shown in  FIG. 11 . 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 FORM OF EDGE PLATE 
                 De 
                 P 0 –P b   
                 T 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 α (°) 
                 D1 (°) 
                 D2 (°) 
                 Dg (mm) 
                 (mm) 
                 (Pa) 
                 (° C.) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 E1 
                 15 
                 60 
                 45 
                 0.6 
                 −0.07 
                 490 
                 36 
               
               
                 E2 
                 15 
                 60 
                 45 
                 0.6 
                 −0.07 
                 588 
                 42 
               
               
                 E3 
                 15 
                 60 
                 45 
                 0.6 
                 −0.07 
                 686 
                 30 
               
               
                 E4 
                 15 
                 60 
                 35 
                 1 
                 −0.07 
                 343 
                 30 
               
               
                 E5 
                 15 
                 60 
                 45 
                 0.6 
                 −0.07 
                 686 
                 30 
               
               
                 E6 
                 15 
                 60 
                 45 
                 0.6 
                 0.1 
                 686 
                 30 
               
               
                 E7 
                 15 
                 60 
                 45 
                 0.6 
                 −0.07 
                 588 
                 35 
               
               
                 E8 
                 10 
                 60 
                 75 
                 0.5 
                 0.05 
                 882 
                 30 
               
               
                 E9 
                 20 
                 60 
                 75 
                 0.5 
                 0.05 
                 882 
                 30 
               
               
                 C1 
                 15 
                 60 
                 45 
                 5 
                 −0.07 
                 588 
                 42 
               
               
                 C2 
                 15 
                 60 
                 45 
                 0.1 
                 −0.07 
                 686 
                 30 
               
               
                   
               
               
                 α: Angle of slide surface 13 
               
               
                 D1: Angle of inclined wall 23 
               
               
                 D2: Angle of front inclination 21 
               
               
                 Dg: Height of perpendicular wall 22 
               
               
                 De: Distance between end face 20 and lip 14 
               
               
                 P 0 –P b : Difference of pressure in bead 
               
               
                 T: Temperature of web 15 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 ρ 
                 Q 
                 η 
                 Ds 
               
               
                   
                 (kg/m 3 ) 
                 {m 3 /(m × sec)} 
                 (mPa · s) 
                 (mm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 E1 
                 1000 
                   3 × 10 −4   
                 100 
                 3.288 
               
               
                 E2 
                 1000 
                   3 × 10 −4   
                 50 
                 2.610 
               
               
                 E3 
                 1000 
                 2.77 × 10 −4   
                 200 
                 4.032 
               
               
                 E4 
                 1000 
                 1.35 × 10 −4   
                 20 
                 1.474 
               
               
                 E5 
                 1000 
                 2.77 × 10 −4   
                 200 
                 4.032 
               
               
                 E6 
                 1000 
                 2.77 × 10 −4   
                 200 
                 4.032 
               
               
                 E7 
                 1000 
                 3.03 × 10 −4   
                 140 
                 3.692 
               
               
                 E8 
                 1000 
                  3.2 × 10 −4   
                 70 
                 3.407 
               
               
                 E9 
                 1000 
                  3.2 × 10 −4   
                 70 
                 2.718 
               
               
                 C1 
                 1000 
                   3 × 10 −4   
                 50 
                 2.610 
               
               
                 C2 
                 1000 
                 2.77 × 10 −4   
                 200 
                 4.032 
               
               
                   
               
               
                 ρ: Averaged density of coating solution 
               
               
                 Q: Total amount of flowing coating solution in predetermined width 
               
               
                 η: Averaged viscosity of coating solution at share rate 
               
               
                 Ds: Upper limit of height of perpendicular wall 22 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                   
                   
                 SHAPE OF 
                   
                   
               
               
                   
                 COATING CONDITION 
                   
                 BEAD 
                   
                 RESULT 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 U 
                 He 
                 H1 
                 Db 
                 Lr 
                 Difference 
                   
               
               
                   
                 (m/sec) 
                 (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
                 of thickness 
                 Est. 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 E1 
                 2 
                 0.15 
                 0.20 
                 0.181 
                 0.181 
                 Less than 1% 
                 P 
               
               
                 E2 
                 3 
                 0.10 
                 0.20 
                 0.458 
                 0.115 
                 Less than 1% 
                 P 
               
               
                 E3 
                 1.67 
                 0.17 
                 0.20 
                 0.582 
                 0.174 
                 Less than 1% 
                 P 
               
               
                 E4 
                 1 
                 0.14 
                 0.20 
                 0.236 
                 0.002 
                 Less than 1% 
                 P 
               
               
                 E5 
                 1.67 
                 0.17 
                 0.21 
                 0.593 
                 0.172 
                 Less than 1% 
                 P 
               
               
                 E6 
                 1.67 
                 0.17 
                 0.21 
                 0.593 
                 0.172 
                 Less than 1% 
                 P 
               
               
                 E7 
                 2.33 
                 0.13 
                 0.20 
                 0.562 
                 0.158 
                 Less than 1% 
                 P 
               
               
                 E8 
                 4 
                 0.08 
                 0.20 
                 0.457 
                 0.097 
                 Less than 2% 
                 P 
               
               
                 E9 
                 4 
                 0.08 
                 0.20 
                 0.457 
                 0.097 
                 Less than 2% 
                 P 
               
               
                 C1 
                 3 
                 0.10 
                 0.20 
                 0.485 
                 0.115 
                 0% 
                 N 
               
               
                 C2 
                 1.67 
                 0.17 
                 0.20 
                 0.582 
                 0.174 
                 Less than 1% 
                 N 
               
               
                   
               
               
                 U: Feeding velocity 
               
               
                 He: Thickness of coating layer 19 
               
               
                 H1: Distance between web 15 and lip 14 of die 11 
               
               
                 Db: Minimum thickness of bead 
               
               
                 Lr: Length from lip to minimum thickness position 
               
               
                 Est: Estimation 
               
            
           
         
       
     
     In Table 3, the estimation was positive or good (describes as “P”) when the coating layer is formed on the web without problem, and was negative (describes as “N”) when the coating layer is formed on the web with problem. 
     Table 4 teaches the relation between the estimation in Table 3 and conditions of Db, Dg and Ds in Tables 1–3. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Db (mm) 
                 Dg (mm) 
                 Ds (mm) 
                 Est. 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 E1 
                 0.181 
                 0.6 
                 3.228 
                 P 
               
               
                 E2 
                 0.485 
                 0.6 
                 2.610 
                 P 
               
               
                 E3 
                 0.582 
                 0.6 
                 4.032 
                 P 
               
               
                 E4 
                 0.236 
                 1 
                 1.474 
                 P 
               
               
                 E5 
                 0.593 
                 0.6 
                 4.032 
                 P 
               
               
                 E6 
                 0.593 
                 0.6 
                 4.032 
                 P 
               
               
                 E7 
                 0.562 
                 0.6 
                 3.692 
                 P 
               
               
                 E8 
                 0.457 
                 0.5 
                 3.407 
                 P 
               
               
                 E9 
                 0.457 
                 0.5 
                 2.718 
                 P 
               
               
                 C1 
                 0.485 
                 5 
                 2.610 
                 N 
               
               
                 C2 
                 0.582 
                 0.1 
                 4.032 
                 N 
               
               
                   
               
            
           
         
       
     
     When the condition Db≦Dg≦Ds was satisfied, the estimation of the coating layer formed on the web is positive. 
     &lt;Experiment 2&gt; 
     In Experiment 2, the edge plate was attached to the die (Example 10), and the end block is changed (Example 11). However, a method of attachment of the edge plate to the die and that of change of the end block were not restricted in the following Examples 10 and 11. 
     Example 10 
     As shown in  FIG. 18 , the hardwood  26  was fit in the retraction formed on the top of the edge plate  12 . The hardwood  26  and the edge plate  12  were formed of stainless and fluoride resin. According to the position of the hardwood  26 , the length L 3  from the outer surface was 10 mm, and the length L 4  from the bottom of the edge plate  12  was 2 mm. Further, the width L 5  of a top of the edge plate  12  was 50 mm. The screws were tightened to fix the edge plate on the die at a predetermined position, such that there may be no space between the edge plate and the die. Thereby the end of the edge plate  12  was moved only for 100 mm. Then the coating of the coating solution was carried out, the edge plate did not touch the web, and the coating solution was applied on the web, stably. This experiment was repeated three times, and the position of the edge plate is observed with a magnifier. The edge plate was attached at the almost same position on the die. 
     [Comparison 3] 
     The edge plate is formed of fluoride resin only. The screws were tightened to fix the edge plate on the die at a predetermined position, such that there may be no space between the edge plate and the die. Thereby the end of the edge plate moves for 500 μm forwards. Then the coating of the coating solution was carried out, the edge plate touched and damaged the web. Further, an forward end of the edge plate is broken. 
     [Experiment 11] 
     The edge plate used in Experiment 11 had the plate body  12   a  and the end block  12   b  as illustrated in  FIG. 13B . The length L 2  of the end block  12   b  was set to 40 mm. It took about 30 minutes to change the end block  12   b  to the same one. However, it takes about a month for changing the plate body  12   a  to the same one, as the other plate body  12   a  must be produced for changing. 
     Various changes and modifications are possible in the present invention and may be understood to be within the present invention.