Apparatus for removing foreign matter from flexible support

An apparatus for removing foreign matter from a flexible support such as a photographic film or magnetic tape. After applying a solvent to the surface of the support from which the foreign matter is to be removed, the support is passed over at least two parallel adjacent plates which extend widthwise perpendicular to the direction of movement of the support, with the plates being located relative to the support at a position before the solvent evaporates. The edge surface of the downstream one of the two plates is provided with a cutting edge at the upstream side thereof. The cutting edge forms a gap with the surface sufficiently small that the foreign matter to be removed cannot enter the gap. Further, the gap is large enough to leave solvent film in a thickness of at least 0.2 microns after passing the two plates.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for removing foreign matter 
from the surface of a flexible support. 
The term "support" as used herein is intended to mean a flexible 
belt-shaped support made of plastic film several centimeters to several 
meters in width, more than several tens of meters in length, and several 
microns to several hundred of microns in thickness. Examples of the 
material of the belt include polyethylene terephthalate, 
polyethylene-2.6-naphthalate, cellulose diacetate, cellulose triacetate, 
cellulose acetate propionate, polyvinyl chloride, polyvinylidene chloride, 
polycarbonate, polyimide, and polyamide; pieces of paper on which is 
deposited a layer formed of .alpha.-polyolefins having two ten carbons 
such as polyethylene, polypropylene and ethylene-butane copolymer; metal 
foils of aluminum, copper, and tin; and belt-shaped supports which are 
prepared by preliminarily treating the surfaces of the above-described 
various belt-shaped supports. 
The support is coated with one or more solutions such as a photosensitive 
solution, magnetic solution, surface protecting solution, charge 
preventing solution and smoothing solution according to the application. 
The support thus coated is dried and cut to desired dimensions to provide 
a desired product. Typical products are various photographic films, pieces 
of photographic paper and rolls of magnetic tape. 
The following methods of removing foreign matter from the surface of such a 
support are well known in the art. In a first method, a piece of unwoven 
cloth or a blade is abutted against the support in a suitable manner to 
remove foreign matter from the support. In a second method, clean air is 
blown across the belt-shaped support at high speed to remove the foreign 
matter from the support, and the foreign matter thus removed is directed 
to a suction hole provided near the support. These methods are of a "dry" 
type. In contrast to these dry type methods, "wet" type methods are also 
known in the art. In one of the wet type methods, a belt-shaped support is 
conveyed into a cleaning solution tank where foreign matter is removed 
from the support by ultrasonic vibration. In another method, after a 
cleaning solution is applied to the support, air is blown across the 
support at high speed (see Japanese Patent Application Publication No. 
13020/1974). 
These methods all involve particular problems. For instance, the method of 
removing foreign matter with a piece of cloth or a blade suffers from a 
difficulty that the support can be scratched by the cloth or blade, or is 
electrostatically charged by friction. In the case where unwoven cloth is 
used to remove the foreign matter, fibers of the unwoven cloth may fall 
onto the surface of the support and stick to the support. 
The method of removing foreign matter by applying air at high speed is 
effective in removing foreign matter of relatively large size, more than 
about 20 or 30 microns; however it is not effective in removing foreign 
matter of relatively small size or foreign matter adhering strongly to the 
support. The wet-type foreign matter removing method described above is 
disadvantageous in that an apparatus for practicing the method is 
considerably large in size. Moreover, when foreign matter is removed from 
a support which is running at high speed, a large quantity of mist is 
generated which tends to stick not only to the surrounding equipment, but 
also to the support from which the foreign matter has been removed. 
Accordingly, an object of the invention is to provide an apparatus for 
removing foreign matter from the surface of a support in which the 
above-mentioned difficulties accompanying a conventional method have been 
eliminated. 
SUMMARY OF THE INVENTION 
The foregoing object and other objects of the invention have been achieved 
by the provision of an apparatus for removing foreign matter from a 
flexible support in which, after a necessary amount of solvent is applied 
to a flexible support to the surface of which foreign matter to be removed 
adheres, the surface is passed over at least two plates arranged in the 
direction of movement of the support and positioned relative to the 
support before the solvent evaporates, the two plates being defined by the 
following conditions: 
(1) the two plates are adjacent to each other and parallel to each other, 
and extend along the widthwise direction of the support, 
(2) each of the two plates has a surface which confronts the support, the 
surface being longer than the width of the support in the widthwise 
direction of the support and shorter in the direction or movement. 
(3) at least the surface of the plate provided on the downstream side in 
the direction of movement of the support, which confronts the support, is 
sharply cut by an adjacent surface thereof to have a cutting edge at the 
upstream end thereof, 
(4) at least the surface of the plate provided on the upstream side in the 
direction of movement of the support and the support have a gap 
therebetween, the gap being sufficiently small at the upstream end thereof 
that the foreign matter to be removed cannot enter the gap, and 
(5) the gap is large enough to leave a solvent film of a thickness of at 
least 0.2 microns on the support which has passed through the plates. 
The earlier-described conventional method in which the blade is used is the 
more effective of the conventional techniques in removing foreign matter 
from a support. However, the method is not practical because in a dry 
state the support is liable to be scratched, as described above, and 
foreign matter removed may stick to the edge of the blade due to static 
electricity. On the other hand, in the method of the invention, after a 
solvent film is formed on the support, the foreign matter is removed 
together with the solvent film. Accordingly, in the method of the 
invnetion, there is little likelihood that the support will be scratched 
due to the lubricating action of the solvent film, and very little static 
electricity is induced in the support for the same reason. Since the 
foreign matter is scraped together wtih the solvent film as described 
above, the foreign matter scraped off with the blade will not stick to the 
edge of blade. That is, such matter is dispersed in the solvent film, 
leaving the edge of the blade as the solvent film falls away from the 
blade. In order to remove the conditions (1) through (5) are essential.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will now be described in detail with reference to FIGS. 1 
through 3. FIG. 1 shows the overall arrangement of an apparatus of the 
invention. As shown in FIG. 1, a flexible support 2 to which foreign 
matter 1 has adhered is moved along rollers 4 and 5 by a support conveying 
device after a solvent film 3 has been coated thereon. A plate 6 provided 
on the upstream side and a plate 7 provided on the downstream side are 
positioned between the rollers 4 and 5 in such a manner that they are 
parallel to each other and extend across the support. The plates 6 and 7 
meet the support 2 at a position before the solvent film 3 evaporates so 
as to remove a part or almost all of the solvent film 3. In this 
operation, the foreign matter 1 adhering to the support is also removed 
therefrom together with the solvent film 3, dispersed in dropping solvent 
passes through slot 8, and finally discharged out of the system through a 
solvent receiving pan 9. 
FIG. 2 shows the plates in more detail. The upstream plate 6 and the 
downstream plate 7 are arranged adjacent to each other as described above. 
Of these plates, only the downstream plate 7 is absolutely necessary to 
remove foreign matter from the support. However, addition of the upstream 
plate 6 immediately before the downstream plate 7 provides an advantage in 
that the gap between the support 2 and the upper edge 11 of the plate 7 
which confronts the support 2 is made uniform in the widthwise direction. 
In the case where the solvent film 3 is removed using the downstream plate 
7 alone, it is difficult to reduce longitudinal crease-shaped 
irregularities between the roller 4 and the plate 7. This is especially 
difficult in the case of a very thin support such as photographic film or 
magnetic tape. If the gap is not uniform because of the presence of 
longitudinal crease-shaped iregularities, it is impossible to uniformly 
remove the foreign matter from the support, and the gap between the plate 
and the support may become small locally, as a result of which the support 
can be scratched. 
On the other hand, using two plates as in the case of the invention, the 
support will have no longitudinal crease-shaped irregularities between the 
two plates. That is, the support is made flat between the two plates. 
Accordingly, the gap at the upstream edge of the downstream plate is 
uniform in the widthwise direction. 
In order to make the gap uniform, it is desirable that the distance between 
the upstream plate 6 and the downstream plate 7 be 20 mm or less. However, 
it is essential that the distance be long enough to allow the dropping 
solvent, which has been scraped by the upstream edge of the downstream 
plate 7, to smoothly flow down the downstream plate. It is preferable that 
this distance be determined experimentally because there are many factors 
such as layout and preliminary scraping which must be taken into account. 
The upstream plate 6 and the downstream plate 7 have surfaces 10 and 11, 
respectively, each of which is longer than the width of the support in the 
widthwise direction of the support and shorter in the direction of 
running. Each of the surfaces 10 and 11 may be a flat surface or a curved 
surface, or it may be made up of flat surfaces, or a flat surface and a 
curved surface. In order for the support 2 to run stably and the foreign 
matter to be removed over the width of the support, it is essential that 
the length of the plates 6 and 7 be longer than the width of the support 
2. 
If the plates are made longer in the direction of running, that is, if the 
surfaces 10 and 11 are increased in width, an increase in friction 
results. Accordingly, the widths of the surfaces 10 and 11 should be as 
small as possible. However, the surfaces should not be too short because, 
if the plates have knife edges, where the plates meet the support, the 
surface pressures will be excessively high. The length of the edge should 
be 0.5 to 20 mm, preferably 1 to 15 mm. In FIG. 2, the surface 11 of the 
downstream plate 7, which confronts the support 2, is cut sharply by the 
adjacent surface so that the upstream end thereof is similar to a cutting 
edge. In order to finally remove substantially all of the foreign matter, 
it is essential that the gap between the support 2 and the upstream edge 
of the downstream plate 7 be uniform, as described above, so that the 
foreign matter cannot enter the gap between the plate 7 and the support. 
In order to effectively satisfy these requirements, the surface 11 of the 
plate 7 which confronts the support should be sharply cut by the adjacent 
surface, thereby making the upstream end of the surface similar to a 
cutting edge. Accordingly, the foreign matter 1, after striking the 
adjacent surface, drops together with the dropping solvent through slot 8. 
In order to improve this effect, it is preferable that the angle .alpha. 
which is formed between the surface 11 of the downstream plate 7 and the 
adjacent surface, on the upstream side, of the plate 7 be 120 degrees or 
less. If the angle is larger than 120 degrees, then the foreign matter is 
liable to enter the gap. For the same reason, the gap between the support 
and the upstream edge of the plate surface 11 is made smaller. Since the 
foreign matter is blocked by the upstream edge, the allowable gap depends 
on the size of foreign matter to be removed. However, if the gap is made 
excessively small, then the support 2 will be scratched. In order to 
eliminate this difficulty, it is necesary to leave a solvent film at least 
0.2 microns in thickness on the support 2 afer passing the downstream 
plate 7 and to maintain the gap large enough to form the solvent film. 
FIG. 3 shows one preferred embodiment of the invention. The upstream end of 
the surface 10 of the upstream plate 6, which confronts the support 2, is 
also formed into a sharp cutting edge. The support 2 is run substantially 
in the direction of a tangent to the surface 10. In this operation, the 
foreign matter 1 together with the solvent film 3 is scraped off by the 
upstream plate 6 and the downstream plate 7. As illustrated in FIG. 3 a 
slot 8' is formed upstream of plate 6. Relatively large foreign matter is 
blocked by the upstream edge of plate 6 and passes into the slot 8' for 
discharge. Relatively smaller matter 1 passes over plate 6 and is scraped 
off by plate 7 for discharge through slot 8. Surface 10 of plate 6 has a 
radius of curvature R.sub.1 and angle .alpha. (see FIG. 4) between the 
vertical face and the tangential line with support 2. Accordingly, the 
embodiment of FIG. 3 is capable of more completely removing foreign matter 
than that of FIG. 2. The embodiment in FIG. 3 is effective especially in 
removing large foreign matter which may cause serious problems. 
It is desirable that the surfaces 10 and 11 of the plates 6 and 7 which 
confront the support 2 have little roughness and that they be as straight 
as possible in the widthwise direction of the support 2. In order to 
improve the durability of the plates 6 and 7, it is preferable that the 
end portions of the plates 6 and 7 be made of metal or ceramic, preferably 
cemented carbide or hard ceramic. 
Fundamentally, any solvent which forms a liquid film stably on the support 
can be employed in the process of the invention and it is not necessary 
for the solvent to dissolve the foreign matter. However, it goes without 
saying that the solvent should not adversely affect the surface of the 
support. Whether or not the scraped solvent is recycled or whether a step 
of thermal evaporation is employed after the above-described operation 
should be suitable determined in accordance with the application at hand. 
The above-described method of the invention has eliminated the difficulties 
accompanying the conventional method and can be used to very effectively 
remove foreign matter from a support without adversely affecting the 
quality of the surface of the support. 
EXAMPLE 
The invention will now be further described with reference to a specific 
example. The plates used were as depicted in FIG. 4. As indicated in FIG. 
4, the surface 10 of the upstream plate 6 had a radius of curvature 
R.sub.1 =10 mm and an edge angle .alpha.=110 degrees at the upstream end, 
and the surface 11 of the downstream plate 7 had a radius of curvature 
R.sub.2 =5 mm and an edge angle .alpha.=90 degreees at the upstream end. 
The support was arranged so as to be run substantially tangent to the 
plate surfaces. Other conditions were as follows: 
Support: 
material--Polyethylene terephthalate 
thickness--20 microns 
width--500 mm 
Solvent: xylole 
The above-described foreign matter removing device was employed in a 
magnetic tape coating process. The support was run at a speed of 30 m/min. 
After being coated with xylole by a roll coater, the support passed 
through the foreign matter removing device, and then the solvent was 
completely removed by a hot air type solvent evaporating unit 5 m in 
length. Thereafter, a coating device 21 as shown in FIG. 5 was used to 
apply a magnetic solution 22 to the support 23 in thicknesses of 10, 20 
and 30 microns in accordance with a method disclosed in Japanese Laid-Open 
Patent Application No. 84771/1982, after which the coating were checked 
for coating defects. The term "coating defects" as herein used includes 
pin-hole-shaped or stripe-shaped coating defects where no coating is 
formed, and coating defects in which the coating thickness is not more 
than 50% of the desired value. When stripe-shaped coating defects occured 
successively over about a hundred meters of the support, the operation of 
coating the support with the magnetic solution was stopped once. 
Thereafter, the coating operation was carried out again, and the coating 
was checked for coating defects. The coating defects were detected by a 
defect detecting device before the coated support was wound, and the 
frequency of occurrence of pin-hole-shaped coating defects and the 
frequency of occurrence of stripe-shaped coating defects were determined. 
As a comparison example, under the same conditions as those in the 
above-described example, a magnetic layer was formed on a support by a 
coating from which no foreign matter was removed. The frequency of 
occurrence of coating defects of the product was checked in the same 
manner. The coating magnetic solution used in the above-described 
experiments was prepared by thoroughly mixing components as indicated in 
Table 1 below in a ball mill, and the resultant mixture was added to epoxy 
resin (epoxy equivalent 500) or 30 parts by weight and uniformly mixed and 
dispersed to again the coating mgnetic solution. 
TABLE 1 
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.gamma.-Fe.sub.2 O.sub.3 powder (needle-shaped 
300 parts by weight 
particles having an average 
major diameter 0.5 microns and 
a coercive force of 320 Oe) 
Vinyl chloride - vinyl acetate 
30 parts by weight 
copolymer (copolymerization 
ratio 87:13, polymerization 
degree 400) 
Electrically conductive carbon 
20 parts by weight 
Polyamide resin (amine value 300) 
15 parts by weight 
Lecithin 6 parts by weight 
Silicon oil (dimethyl polysiloxane) 
3 parts by weight 
Xylole 300 parts by weight 
Methly isobutyl ketone 
300 parts by weight 
n-butanol 100 parts by weight 
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The balanced viscosity of the coating magnetic solution thus prepared was 
measured with a Shimazu rheometer model no. RM-1 manufactured by Shimazu 
Seisakusho Company of Japan and found to be 8 poise with a shear rate of 
10 sec.sup.-1, and 1 poise with a shear rate of 500 sec.sup.1. 
For each of the above-described three different thicknesses of magnetic 
film formed on the support, ten rolls, each 4000 m long, were tested for 
coating defects. The results of test are indicated in the following Table 
2. Each entry in Table 2 represents the average frequency of occurrence of 
coating defects per roll. 
TABLE 2 
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Liquid-phase magnetic 
Layer thickness 
10 20 30 
microns microns microns 
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Foreign matter 
Stripes 0 0 0 
removed Pin holes 
0.6 0 0 
Foreign matter 
Stripes 4.8 1.9 0.4 
not removed 
Pin holes 
35.3 14.6 2.2 
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