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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a coating apparatus for coating a flexible
support made of plastic film, paper, metal foil or the like (hereinafter
referred to as "a web" when applicable) with a coating solution such as a
photographing photosensitive solution, magnetic solution, surface
protective solution or the like.
Examples of a coating apparatus for coating a web with a coating solution
include a roll type coating apparatus, bead type coating apparatus, slide
coat type coating apparatus, bar coater type coating apparatus, or
extrusion type coating apparatus. In each of these coating apparatuses,
the widthwise dimension of the apparatus is larger than the width of the
web, and the width of the coating part of the apparatus is smaller than
the width of the web. As a result, uncoated regions are formed along the
two edges of the web. With this arrangement, there is eliminated the
difficulties of the coating solution flowing over to the rear side of the
web during coating, or, if the web meanders, the coating solution being
jetted past the edges of the web.
In the case of a bar coater or extrusion type coating apparatus in which
the coating head is held close to the web and the coating solution is
applied onto the web from a widthwise-extending slit in the coating head,
coating width regulating boards are fitted in the two ends of the slit to
prevent the coating solution from moving sideward. (See, for example,
Japanese Unexamined Published Patent Application Nos. 257263/1986 and
257268/1986.) This will be described more concretely.
In the case of an extrusion type coating apparatus as shown in FIG. 4, the
coating head 22 is larger in width than the web 20 being coated. The
coating head 22 has a back edge 24 and a doctor edge 23 between which is
defined a slot 26 through which is discharged a coating solution over the
web in the widthwise direction. The slot 26 is communicated with a
solution pool formed inside the coating head 22. The solution pool has
openings at both ends which are closed with shield boards 28 provided at
both ends of the coating head 22. A coating solution supplying inlet 27 is
formed through one of the shield boards 28, thus supplying the coating
solution into the solution pool. The coating solution thus supplied is
discharged through the slot 26 under a pressure uniform in the widthwise
direction of the slot 26. A pair of coating width regulating boards 25 are
fitted in the slot 26 at both ends to determine the coating width and to
prevent the coating solution from flowing sidewardly. The coating width of
the coating solution applied onto the web 20 can be controlled by
adjusting the distance between the coating width regulating boards 25.
The coating width regulating boards 25 are made of a synthetic resin
material such as TEFLON (polytetrafluoroethylene) resin so that they can
be formed readily and installed accurately. If the coating width
regulating boards 25 were made of a metallic material, it would be
necessary to polish their end faces and make the boards flush with the end
faces of the back edge 24 and the doctor edge 23. It is, however, rather
difficult to make the end face of such regulating boards flush with those
of the back edge and the doctor edge, and it is also difficult to install
the regulating boards with high accuracy.
The coating width regulating boards 25 made of synthetic resin material can
be installed accurately due to the fact that they can be cut readily.
Resin boards whose thickness is equal to the gap of the slot 26 are
selected for formation of the coating width regulating boards. To install
the boards, the resin boards thus Selected are fitted in the slot 26 in
such a manner that they protrude from the end portions of the slot 26, and
then the protrusions are cut along the end faces of the back edge 24 and
the doctor edge 23. The resultant end faces of the coating width
regulating boards 25 are thus easily made accurately flush with those of
the back edge and the doctor edge.
However, when an extrusion type coating head with coating width regulating
boards of synthetic resin is used for a long time to coat a web with a
coating solution, the border lines between the coated region of the web
and the uncoated regions along the edges of the web tend to become wavy,
or the coating solution applied to the web becomes thicker along the
border lines.
The inventors have conducted intensive research on these problems, and have
found that the difficulty is due to the fact that the inner edges of the
coating width regulating boards used to regulate the coating width tend to
wear during coating or to suffer deformation when the coating head is
cleaned, or the end edges of the coating width regulating boards of
synthetic resin machined are not sufficiently sharp. In such cases, the
coating solution tends to leak at the coating width regulating boards.
Furthermore, the inventors have found that, in the case where the web is a
resin sheet, dust has a tendency to accumulate on the web due to static
electricity generated by the contact of the coating width regulating
boards with the part of the web to be coated with the coating solution,
the dust thus accumulated pushes up both edge portions of the resin sheet,
and thus the thickness of the coated layer in those regions is increased.
Accordingly, an object of the present invention is to eliminate the
above-described difficulties accompanying a conventional coating
apparatus. More specifically, an object of the invention is to provide a
coating apparatus with excellent coating width regulating members capable
of forming a coated layer which is free from the difficulties that the
coating solution applied onto a web is wavy and not uniform in thickness.
SUMMARY OF THE INVENTION
The foregoing and other objects of the invention have been achieved by the
provision of an extrusion type coating apparatus having a coating head
with a back edge end face and a doctor edge end face set close to a
flexible support which is continuously run and with which a coating
solution is applied to the flexible support, in which, according to the
invention, the inner edge of each of a pair of coating width regulating
members made of a metallic material and which are arranged in the slot of
the coating head at respective ends thereof are formed to have a radius of
curvature between 0.5 mm and 0.001 mm, the downstream edge of the end face
of each coating width regulating member is continuous with the upstream
edge of the doctor edge end face, and the upstream edge of the end face of
each coating width regulating member is abutted against the inner wall of
a back edge forming the coating head with the distance between the slot
forming edge of the back edge end face and the upstream edge of the end
face of the coating width regulating member set to half or less of the gap
of the slot.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing an extrusion type coating head of a
coating apparatus constructed in accordance with a preferred embodiment of
the invention;
FIG. 2 is a sectional view showing a part of the extrusion type coating
head of FIG. 1;
FIG. 3 is a sectional view taken along a line III--III in FIG. 1; and
FIG. 4 is a top view of an extrusion type coating head of a conventional
coating apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a perspective view of an extrusion type coating head 1 in a
coating apparatus constructed in accordance with a preferred embodiment of
the present invention.
The width of the coating head 1 is larger than the width of a web 20. The
coating head 1 includes a doctor edge 2 and a back edge 3 between which is
defined a slot 4 through which is discharged a coating solution over the
width of the web 20. The doctor edge 2 and the back edge 3 have a doctor
edge end face 14 and a back edge end face 13 at their respective ends
which are set close to the web 20. The slot 4 is communicated with a
solution pool 6 formed inside the coating head 1. The solution pool 6 has
openings at both ends which are closed with a pair of shield boards 5. A
coating solution supplying inlet 9 through which the coating solution is
supplied into the solution pool 6 is formed through one of the shield
boards 5. The coating solution thus supplied is discharged through the
slot 4 under a pressure uniform in the widthwise direction of the latter.
A pair of coating width regulating boards 7 are fitted in the slot 4 at
both ends to resist the flow of the coating solution thereby to determine
the width of a coated layer 21 formed on the web.
The coating width regulating boards 7 are rectangular plates of cemented
carbide material, and their surfaces are polished to less than 1-S (J.I.S.
code B 0601) in surface roughness. In particular, the inner edge 8 of each
of the coating width regulating boards 7 is polished so that the radius of
curvature (r) between 0.5 mm and 0.001 mm (see FIG. 2). If the radius of
curvature (r) is less than 0.001 mm., the edge portion may be
substantially deformed and/or cause undesirable static electricity.
When the coating width regulating boards 7 are inserted into the slot 4 at
both ends as shown in FIG. 3, they are fixedly positioned in such a manner
that the downstream edge 12 of the end face of each coating width
regulating board 7 meets the upstream edge 15 of the doctor edge end face
14, and the end face of the coating width regulating board 7 is continuous
with the doctor edge end face 14. It is not always necessary that the
upstream edge 11 of the end face of the coating width regulating board 7
meet the slot forming edge 10 (downstream edge) of the back edge end face
13; that is, all that is necessary for the upstream edge 11 of the end
face of the coating width regulating board 7 is that it abut the inner
wall of the back edge 3 with the distance C between the upstream edge 11
and the slot forming edge 10 of the back edge 3 being not more than half
of the gap width B of the slot 4. That is, it is unnecessary to make the
end faces of the coating width regulating boards 7 flush with the back
edge end face 13 with high accuracy. Hence, even if the coating width
regulating boards 7 are made of a metallic material, the coating head can
be fabricated with ease.
Thus, according to the invention, the alignment of the end face of the
coating width regulating boards 7 with the back edge end face 13 is
simplified, which makes it possible to employ coating width regulating
boards 7 made of a metallic material. The edges of the width regulating
boards of a metallic material can be much higher in machining accuracy
than those the conventional boards made of synthetic resin. Therefore,
even if the coating head is used for a long time, the edges of the coating
width regulating boards will not wear appreciably and little or no
deformation will occur when, for instance, the coating head is cleaned.
As described above, the coating width regulating boards 7 are made of a
metallic material, which is of course high in conductivity. Hence, very
little static electricity is generated by the contact of the coating width
regulating boards with the part of the web which is to be coated with the
coating solution, and accordingly the accumulation of dust in the those
regions is prevented.
The coating head according to the invention is not limited to that which
has been described above; that is, the technical concept of the invention
may be applied to a variety of different types of coating heads used to
form a coated layer uniform in thickness on a web.
In the extrusion type coating apparatus according to the invention, the
inner edges of the coating width regulating members made of a metallic
material arranged in the slot of the coating head at both ends thereof is
formed to have a radius of curvature of 0.5 mm or less. The end face of
the coating head is formed by the back edge end face and the doctor edge
end face, and the downstream edge of the end face of each coating width
regulating member is continuous with the upstream edge of the doctor edge
end face, while the upstream edge of the end face of each coating width
regulating member is abutted against the inner wall of a back edge forming
the coating head with the distance between the slot forming edge of the
back edge end face and the upstream edge of the end face of the coating
width regulating member set to half or less of the gap width of the slot.
With this arrangement, the alignment of the end face of the coating width
regulating boards with the back edge end face 13 is simplified, which
makes it possible to employ coating width regulating boards made of a
metallic material. The edges of the width regulating boards made of a
metallic material can be much higher in machining accuracy than those the
conventional boards made of synthetic resin. Furthermore, the inner edge
of each of the coating width regulating members is formed so as to have a
radius of curvature of 0.5 mm or less, which eliminates the difficulty
that, when the web is coated with the coating solution, the border lines
of the coated region and the uncoated regions along both edges of the web
become wavy.
In the coating apparatus of the invention, because the coating width
regulating boards are made of a metallic material high in electrical
conductivity, very little static electricity is generated by the contact
of the coating width regulating boards with the uncoated regions of the
web. This eliminates the difficulty of dust accumulating on the uncoated
regions of the web and pushing both edge portions of the web to thereby
make the coated layer nonuniform in thickness.
Thus, the coating apparatus according to the invention has excellent
coating width regulating members capable of forming a coated layer which
is free from the difficulties of the coating solution applied onto a web
being wavy and nonuniform in thickness.
As conducive to a full understanding of the effects of the invention,
specific examples thereof will be described.
EXAMPLES OF THE INVENTION
Example 1
A methyl ethyl ketone solution of vinyl chloride-vinyl acetate copolymer
(copolymerization ratio 71:29, and polymerization degree 700) was prepared
as a coating solution. A plurality of extrusion type coating heads as
shown in FIG. 1 were used to form coated layers on the webs. These coating
heads had respective slot widths B of 0.1 mm, 0.3 mm, 0.8 mm and 2.0 mm.
Coated layers were formed on webs using each of these coating heads.
In each of the coating heads, the radius of curvature of the curved part of
the doctor edge end face 14 was 5 mm. The web employed was a polyethylene
terephthalate film 15 .mu.m in thickness and 300 mm in width.
The coating width regulating boards 7 to be fitted in the slots 4 of the
coating heads were made of cemented carbide, and polished to 1-S or less
in surface roughness. The coating width regulating boards 7 fitted in the
above-described coating heads were machined to have respective radii of
curvature (r) of their inner edges of 0.1 mm, 0.3 mm, 0.5 mm, 0.7 mm and
1.0 mm. In this operation, in each of the coating heads, the end face of
the coating width regulating board, the doctor edge end face 14, and the
back edge end face 13 were continuous to and flush with one another.
The presence or absence of the wavy border line phenomenon or nonuniform
thickness phenomenon, as might occur along the border lines between the
two edges in the widthwise direction of the coated layer formed on the web
under the coating conditions specified in the following Table 1, were
detected, and the results of detection are as indicated in Table 2 below.
TABLE 1
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Coating solution 0.05 to 1 poise with a
viscosity shear rate of 1000 sec.sup.-1
Coating rate 5 to 30 cc/m.sup.2
Coating speed 100 to 800 m/min
Coating part tension
15 to 30 kgw/m
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The coating solution viscosity was adjusted by suitably changing the
density of the vinyl chloride-vinyl acetate copolymer.
TABLE 2
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Radius of curvature (r)
of inner edge of coating
width regulating board
(mm)
0.1 0.3 0.5 0.7 1.0
______________________________________
Slot distance B
0.1 .smallcircle.
.smallcircle.
X X X
(mm) 0.3 .smallcircle.
.smallcircle.
.smallcircle.
X X
0.8 .smallcircle.
.smallcircle.
.smallcircle.
X X
2.0 .smallcircle.
.smallcircle.
.smallcircle.
X X
______________________________________
In Table 2, the mark "O" indicates the case where neither the wavy border
line phenomenon nor the nonuniform thickness phenomenon was detected with
the coating conditions varied within the ranges specified in Table 1, and
the mark "X" indicates the case where the wavy border line phenomenon or
nonuniform thickness phenomenon was detected with the coating conditions
changed within the ranges specified in Table 1.
Example 2
A methyl ethyl ketone solution of vinyl chloride-vinyl acetate copolymer
(copolymerization ratio 71:29, and polymerization degree 700) was prepared
as a coating solution. A plurality of extrusion type coating heads as
shown in FIG. 1 which were 0.1 mm, 0.3 mm, 0.8 mm and. 2.0 mm in slot gap
width B, respectively, were used to form coated layers.
In each of the coating heads, the radius of curvature of the curved part of
the doctor edge end face 14 was 5 mm. The web employed was a polyethylene
terephthalate film 15 .mu.m in thickness and 300 mm in width.
The coating width regulating boards 7 fitted in the slots 4 of the coating
heads were made of cemented carbide, and were polished to 1-S or less in
surface roughness. The coating width regulating boards 7 were machined to
have inner edges having a radius of curvature (r) of 0.02 mm. In this
operation, the coating width regulating boards were set in the coating
head with the downstream edge 12 of each of the coating width regulating
boards meeting with the upstream edge of the doctor edge end face, and the
upstream edges 11 of the coating width regulating board abutting against
the inner walls of the back edge with the distances between the slot
forming edges 10 of the back edge end faces and the upstream edges 11 set
to 1/10, 3/10, 1/2, 7/10, and 9/10 of the slot distances B described
above.
The presence or absence of the wavy border line phenomenon or nonuniform
thickness phenomenon was detected along the border lines between the two
edges and in the widthwise direction of the coated layer formed on the web
for each of the coating heads and the uncoated region of the web. The
results of detection are as indicated in Table 3 below.
TABLE 3
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Distance C (mm)/Slot distance B (mm)
1/10 3/10 1/2 7/10 9/10
______________________________________
Slot distance
0.1 .smallcircle.
.smallcircle.
.smallcircle.
X X
B (mm) 0.3 .smallcircle.
.smallcircle.
.smallcircle.
X X
0.8 .smallcircle.
.smallcircle.
X X X
2.0 .smallcircle.
X X X X
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In Table 3, the mark "O" indicates the case where neither the wavy border
line phenomenon nor the nonuniform thickness phenomenon was detected with
the coating conditions varied within the ranges specified in Table 1, and
the mark "X" indicates the case where the wavy border line phenomenon or
nonuniform thickness phenomenon was detected with the coating conditions
varied within the ranges specified in Table 1.
As is apparent from Table 2, in the case where the coated layer was formed
with a coating head in which the radius of curvature of the inner edges of
the coating width regulating boards was set to 0.5 mm or less, the wavy
border line phenomenon and the nonuniform thickness phenomenon are
substantially prevented.
As is seen from Table 3, it is not always necessary for the upstream edge
of the coating width regulating board to meet the slot forming edge of the
back edge end face. That is, if the coating head is designed so that the
upstream edge of the coating width regulating board abuts the inner wall
of the back edge at a distance from the slot forming edge which is about
half the slot width or less, then an excellent coating can be formed which
is free from the wavy border line phenomenon or the nonuniform thickness
phenomenon along the two edges in the widthwise direction of the coated
layer.
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