Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVENTION
1. Field of the Invention
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This invention relates to a method of cleaning a
magnetic head for flexible discs and cleaning sheets and
cleaning ~ackets for cleaning such magnetic heads.
2. Descri~tion of the Prior Art
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In recent years, video recorders for slow motion
images or still images for television have been developed as
one type of video recording system.
In magnetic recording systems for memory use, magnetic
disc systems, magnetic tape systems, cassette tape systems and
the like, are in use. Magnetic disc systems have hlgh recording
density and are easily used, but are expensive. Magnetic tapes
take up much space and cannot be easily used as compared with
magnetic discs and the like. Cassette tape sys*ems are compact
and easily used, but their recording capacity is not satis-
factory and their reliability is low. ~ ~
Accordingly, flexible systems possessing the advantages
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of the above systems, i.e., high recording density, com-
pactness and ease of handling have recently come in-to useO
In general, when a magnetic recording medium i5 used
in magnetic recording for a long time while in contact with a
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magnetic head, the magnetic recording layer is partially
scraped off onto the magnetic head or a very small amount of
lubricant or the like which is present in or on the magnetic
recording layer accumulates on the magnetic head, resulting
in a lowering of output.
Problems of partial wear of the magnetic recording
layer and accumulation of lubricant can be solved by improvements
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1 in the m~gnetic reco~ding layer.
However, since magnetic recording is performed by
slidlng the magnetic recording layer across the magnetic head,
it is very difficul-t to make a magnetic recordiny layer so
strong as to completely resist wear.
Therefore, as long as conventional magnetic recording
mediums and magnetic recording systems are used, it is necessary
to periodically clean the magnetic head in some suitable fashion.
In flexible disc systems, since most of the magnetic
heads are located in the innermost part of ~he apparatus, one
problem is that the magnetic head cannot easily be cleaned by
merely using a cloth impregnated with a liquid cleaner or
the like, as in the case of conventional tape recorders for
open reels, cassettes, home video recorders and broadcast
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video recorders.
,
~ Furthermore, while cleaning tapes for such magnetic
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heads are conveniently used, such tapes comprise,-e.g., a ~-~
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polyester base which has applied thereto an abrasive such as
fused alumlna, silicon carbide, chromium sesquioxide (Cr203)
or corundum in a binder. Although a part of the magnetic
recording layer and the accumulation of the lubricant can be
scraped~off the magnetic head by this methodt the ma~netic
head per se is disadvantageously abra~ed. This defect is also
found in applying this method to heads for vi~eo magnetic
sheets.
This invention provides a cleaning sheet ~or over-
coming the aforesaid inconveniences and defects, which enables
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the cleanina of a magnetic head in a very short time without ~ -
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wearing it away. -~ ~
3~ SU~RY OF THE IN~ENTION ~ -;
One object of this invention is to provide a method of
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1 cleaning a magnetic head for flexible discs which cleans the
magnetic head in a short time without head wear and further ~`
provides a cleaning sheet and a cleaning jacket used in said
method.
The object of this invention can be accomplished by
cleaning a magnetic head for flexible discs using a cleaning
sheet having a coating composed of a fibrous material which is
provided on one or both sides of a base sheet, e.g., using an
adhesive or thermocompression bonding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures l and 2 are sectional vlews showing cleaning
sheets of this invention.
Figure 3 is a plane view of a cleaning shee~ of thls
invention.
Figure 4 is a plane view of the cleaning sheet shown --
in Figures l to 3 as inserted in a container.
Figures 5(a), (b) and ~c) are sectional views of such -;
cleanlng sheets.
~ Figures 6 and 7 are sectional views of cleaning
jackets of this invention as used. -~
Figures 8 and 9 are views showing preparing cleaning
sheets of this invention.
~ Figure 10 lS a graph showing the relationship between
the rotation rate (at 360 r.p.m.) of a conventional cleaning -
jacket or the cleaning jacket of this invention and -the depth
of wear of the magnetic head. --
Figure 11 is a view showing preparing cleaning sheets ;- -
of this invention.
Figure 12 is a sectional view of the preferred cleaning
sheet.
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1 Figure 13 is a graph showing the relationship between
rotation time (at 3,600 r.p.m.) of the cleaning sheet and the
depth of wear (,um) of the magnetic head.
DETAILED DESCRIPTION OF THE INVENTION
Flexible base sheets which can be used in this invention
include sheets of high molecular weight compounds, i.e., a resin
or plastic film as such as commonly called, such as polyvinyl
chloride, polycarbonate, acrylonitrile-styrene copolymers,
ABS resin, polyester, glass-fiber-filled polyester resins or -
cellulose derlvatives, cardboard, metallic sheets such as -
aluminum or copper, and the like. The thickness of the base is ~
preferably about 10 !um to about 1 mm, whlch can be selec~ed ~-
depending upon the use of the apparatus.
In additlon, the base sheet may have a magnetic
recording layer or an antistatic layer provided on one side or - -
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both sides thereof, for example, as disclosed in U.S. Patents
3,476,596 and 3,2~3,066. In this case, the coating composed
of a fibrous material of this invention is provided on one ;~
side or both sides on such layers.
Fibrous materials which can be used in this invention
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are essentially textiles in nature and include nonwoven
materials, synthetic leathers, leathers, woven mat rials of
synthetic fibers, woven materials of natural fibers and ~;
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Japanese paper. The thickness of the fibrous materials is ~
about 20 to about 1,000 ~m, preferably 30 to lOO pm. -
The nonwoven materials are fabric-like products
which are made by arranging fibers such as acetate, nylon or
polyester in a web or mat form by a conventional method and ~ -
then bonding the fibers to each other using an adhesive such
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as a natural latex, a synthetic latex or such in combination
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1 with a urea resin or a melamine resin adhesive, or by
utilizing the adhesive force of the fibers themselves, e.g.,
with polyethylenes, polypropylenes and polyamides. Of the
synthetic latices, acrylonitrile - butadiene copolymers and
acrylonitrile are preferred, with synthetics of a molecular
weight of about 800 to abou-t 10,000 being most preferred.
In addition, other nonwoven materials, e.g., those
which are made through fusion bonding can also be used, e.g.,
polyesters, polystyrenes and polyvinyl acetate, usually a
temperature of about 70 to 250C being used for the bonding.
Many of the nonwoven materials disclosed above are
commercially available nonwoven closes, e.g., Vilene H-8103
(polyethylene terephthalate fiber), Vilene BX10, Vilene ~3000,
Vilene #4000 (produced by Japan Vilene Co., Ltd.), Nippon Cloth
~1500, Nippon Cloth #1600 (produced by Nippon Cloth Industries
Co., Ltd )), as are fibers of copolymers of polyethylene tere-
phthalate (60 mol%) and rayon (40 mol%) bonded using styrene-
butadiene rubber as an adhesive and formed into a sheet.
The woven materials of synthetic fibers are those
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made from synthetic fibers of high molecular welght, e.g.,
polyamides such as nylon-6, nylon-6,6 or nylon-6,10; polyesters ~ -
such as polyethylene terephthalate or polyethylene naphthalate;
polyurethanes produced by reacting hydrazine, diamine or a
diol with a prepolymer formed by reacting a polyester or
polyether with a diisocyanate; polyolefins such as polyethy:lene
or polypropylene; polystyrene; polyvinyl chloride; poly-
vinylidene chloride; polyfluoroethylene; polyacrylonitrile;
polyvinyl alcohol; etc.
The woven materials of natural fibers are those made ;
from protein fibers such as wool or silk; cellulose fibers such
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as cotton or hemp; etc.
The Japanese papers are those made from natural fibers,
cellulose fibers being preferred, using bast fibers as a raw
material, digesting the ~ibers to make single fibers and
then making a paper therefrom. The bast fibers consist of
celluloses about 3 to 50 mm long by about 0.01 to 0.08 mm wide.
Examples of such are flax, hemp, jute, ramie, kozo, mitsumata
and gampi. Of these fibers, kozo, mitsumata and gampl are
preferred.
The above fibrous materials are laminated on a base
sheet using an adhesive or by thermocompression bonding,
typically at about 1 Kg/cm2 to about 25 Kg/cm2 and at about
70C to about 150C for about 1 to about 30 min., or the like.
In this case, it has been found that a fibrous material -
impregnated wi~h a silicone oil, fluoro-oil or the like is very -
useful for preventing a magnetic head from later becoming
dirty. Typically impregnation is by spraying after adhering
the fibers to the base sheet using about 0.5 to about 10 wt%
of the oil based on the fibrous material weight.
The aforesaid adhesives used in this invention i~clude
natural latexes, synthetic latexes and such late~es in com- -
bination with a urea or melamlne resin adhesive, a synthetic -
rubber a polyester, a vinyl ace~ate resin, a butyral resin, ~
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an acrylate resin, a vinyl chloride resin, a polyamide, a ;~
reclaimed rubber, starch, dextrin, glue, gum arabic , caseinO
polyvinyl alcohol, polyacrylamide, carboxymethyl cellulose, ;
rosins, wax, paraffin, epoxy resins, isocyanate resins, phenyl
resins, furan resins, nitrocellulosé, etc. Preferred are
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those resins which have a softening point of about 30 to about --
150C, most preferably 50 to 120C, and a molecular weight of
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1 about 1,000 to about 100,000. They are conveniently applied
with a spray-gun, brush, blade, spatula, etc.
Examples of conveniently used adhesives are copolymers
of vinyl chloride and vinyl acetate (about 30 to 90 wt~
vinyl acetate), copolymers of ethylene and vinyl acetate (about
30 to 90 wt~ vinyl acetate), terpene resins, copolymers of
acrylonitrile and butadiene (about 20 to 40 wt% acrylonitrile)
liner polyesters (copolymers of ethyleneglycol and tere-
phthalic acid at a 3:2 to a 2:3 molar ratio, respectively)
and polyamide terpolymer (for example, caprolactam (20 to
80 wt%): lauryollactam (5 to 70 wt%): ~-c-methyl caprolactam
(5 to 60 wt%).
In the case of laminating the fibrous material on the
base sheet by thermocompression bonding, the fibrous material
or at least a portion of the constituents of the fibrous
material, e.g., an adhesive for the fibrous or ~e-base sheet,
must be a thermoplastic resin. Preferably, both the fibrous
material and base sheet comprise or are made of a thermo-
plastic resin.
2~ Preferred of such ther~oplastic resins have a softening
point of 150C or less, an a~erage molecular weight of about
10,000 to about 200,000 and a polymerization degree of about
200 to about 500, e.g., polypropylene-vinyl chloride, copolymers,
.
ABS resins, vinyl chloride vinyl acetate copolymers, vinyl
chloride-vinylidene chloride copolymers, vinyl chloride-
acrylonitrile copolymers, acrylate-acrylonitrile copolymers,
acrylate-vinylidene chloride copolymers, acrylate-styrene
copolymers, methacrylate-acrylonitrile copolymers~ methacry-
late-vinylidene chloride copolymers, methacrylate-styrene
copol~mers, urethane elas~omers, polyamides, etc.
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Referring to the method of using the cleaning sheet for
a magnetic head according to this invention~ in the case of
video magnetic sheets, a cleaning sheet which has been prepared
by laminating a fibrous material onto a base sheet and punching
out the same to specified shape and dimensions is inserted so
as to contact, while sliding, the head surface with the fibrous
material on the cleaning sheet. When sliding con-tact is effected
for several seconds to several ten seconds, typically about 3
to about 20 seconds, with 8 seconds being used in the Examples,
1C output which has been lowered due to dirt on the magnetic head
can be recovered to almost 100~ of its original state.
Using the cleaning sheet prepared as above, dirt left
after cleaning is avoided, while the magnetic head is not worn
at all and variations in output are not observed, and, thus, very -
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satisfactory results are obtained.
The constitutions of the cleaning sheet and the cleaning
jacket of this invention described hereinbefore will be explained
with reference to the accompanying drawings. In the drawings,
like numerals are utilized to identify like elements.
Figure 1 is a cross-sectional view of a cleaning shee~
having a cleaning layer provided on one~ide thereof, in which
there is shown a cleaning la~er (of a nonwoven material) 1 and
a suppor~ 2.
Figure 2 is a cross-sectional view of a cleaning sheet
having cleaning layers provided on both sides thereof, in which
those parts denoted by numerals 1 and 2 are the same as in
Figure 1.
Figure 3 is a upper plan view of the cleaning sheet
shown in Figure 1 or 2, in which there is shown the cleaning ~ `
30 layer l, a bearing aperture 4, and an aperture 5 for an index `
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hole. Aperture 5 may be omitted where light selectors are not
used.
Figure 4 is a plan view of a container (jacket) .in
which the cleaning sheet shown in Figures 1 to 3 is inserted,
wherein there is shown the cleaning layer 1, a container 3, an
aperture 6 which is larger than the bearing apertuxe 4 of the
cleaning sheet, an aperture 7 which is larger than the aperture
for the light selector and an aperture 8 for a recording and
reproducing head. Aperture 7 may be omitted where light selectors
are not used. Moreover, in the case of a cleaning sheet as
shown in Figure 2, apertures 6, 7 and 8 must be provided on both
sides o~ the container 3, but for the cleaning sheet as shown in
Figure 1, apertures 6, 7 and 8 can be provided only on the one
side provided with the cleaning layer 1.
Figure 5(a), (b) and (c) are cross-sectional views of
the cleaning sheets shown in Figures 1 to 3 as inserted in a
container. Figure 5(a) shows a cleaning sheet having cleaning
layers on both sides thereof, and Figures 5(b) and (cj show a
cleaning sheet having a cleaning layer on one side thereof, ~
wherein those parts denoted by numerals 1 to 8 are the same as
in Figures 1 to 4, and numeral 14 shows a sheet fixing hub
(which simply supports the sheet). Moreover, in order to improve
the rotation of the sheet, the inner surface of the container
;~ ~jacket) can be subjected to a lubrication treatment by attaching,
e.g., a synthetic paper or a nonwoven material impregnated
with a silicone resin, Tèflo ~or a silicone oil thereto.
The following description relates to the cleaning
jacket of this invention for use with a magnetlc head for ~lexible
discs, as shown in Figures 1 to 5, as mounted in a recorder for
30 ~lexlble discs. -
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1 Figure 6 shows a jacket containing a cleaning sheet
having cleaning layers on both sides thereof as shown in Figure 2
and Figures 5(a) and (b), wherein there is shown a cleaning
layer l, a support sheet 2, a container 3, an idler 9, a driving
motor for rotation lO, a recording and reproducing head ll, a
load pad 12 to insure good contact with the head and a light
selector 13.
Figure 7 shows a jacket containing a cleaning sheet
having a cleaning layer on one side thereof as shown in Figure l
and Figure 5(c), wherein there is shown a cleaning layer l, a
support 2, a container 3, an idler 9 a driving motor for rotation
lO, a recording and reproducing head ll, and a sheet fixing hub 14.
When the cleaning jacket of this invention is mounted
in a recorder for flexible discs as shown in Figures 6 and 7
and then used in the same manner as in the case of magnetic discs,
the recording and reproducing head 11 and the cleaning layer 1 are
contacted with each other while sliding, thus cleaning the
recording and reproducing head. Such sliding contact for several
seconds to several ten seconds can bring about almos~ a 100%
recovery of the output which has been lowered due to dirt
accumulation on the magnetic head, t~pically a mixture of
ferromagnetic powder, binder and other additives.
The following examples further illustrate this invention.
It will be apparent to one skilled in the art that components,
ratios of amounts, sequence of operations, and the like, shown
in the examples can be changed without departing from the spirit
and scope o this invention, and this invention is not limited
to the following exa~ples.
EXAMPLE_l
As illustrated in Figure 8, a polyvinyl chloride sheet
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2 (50 ~m thick, 25 cm x 25 cm square; the molecular weight of
the polyvinyl chloride sheet is not overly important and a con-
centional PVC was used. The molecular weight is usually 10,000
to 200,000, corresponding to a polymerization degree of 200 to
2,000) and two nonwoven materials. 1 of 70~m thick (Vilene H 8103
polyethylene terephthalate fiber made by Japan Vilene Co., Ltd.)
were put between two press plates (stainless steel plates) 15.
The assembly thus obtained was laminated using a hot pressing
machine 16 under the following conditions: pressure of 2Kg/cm2,
temperature of 120C, time of 10 minutes~ and then allowed to
cool to room temperature. The press plates lS were then peeled
off~ A polyvinyl chloride sheet which was laminated with the non~
woven materials 1 on both sides thereof was thus obtained.
The cleaning sheet thus obtained was punched out to
a doughnut-like sheet (see Figure 3) of an outer diameter of
200 + O.5 mm and an inner diameter of 25.4 ~ O.05 mm using a
punching machine for magnetic sheets. The doughnut-like sheet
was assembled in a jacket as shown in ~igures 4 and 5(a) to
make a cleaning jacket for use with a magnetic head for
2~ ~lexible discs.
EXAMPLE 2
As illustrated in Figure 9, a polyvinyl chloride
sheet 2 (50 ~m thick, 25 cm x 25 cm square as in Example 1) `~
and a nonwoven material. 1 of 70~m thickness (Vilene H 8103,
polyethylene terephthalate fiber made by Japan Vilene Co.,
~td.3 were put between press plates (stainless steel plates) 15
At this time, mesh 17 was put between the nonwoven material 1
and the press plate 15 (in this example the mesh was steel;
the size of the mesh is generally about 1 mm to about 10 mm, -
~ -
preferably 1 mm to 5 mm, while the diameter of the steel wire~
is 0.2 mm to 5 mm, preferably 0.5 to 2 mm)O
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1 The assembly thus o~tained was laminated using a hot
pressing machine 16 under the following conditions; pressure
of 2 Kg/cm2, temperature of 120C, time of 10 minutes, and then
allowed to cool to room temperature. The press plates 15 and
the mesh plate 17 were peeled off. A polyvinyl chloride sheet
which was laminated with the nonwoven material 1 on one
side thereof was thus obtained.
The cleaning sheet thus obtained was punched out in
the same manner as in Example 1 (see Figure 3). The doughnut-
like sheet thus obtained was assembled in a jacket as shown inFigures 4 and 5(b) to make a cleaning jacket for use with a
magnetic head for flexible discs, which comprised a cleaning
sheet of an outer diameter of 200 + 0.5 mm and an inner diameter
of 25.4 -~ 0.05 mm inserted in the container.
Comparative Ex~le 1
The followin~ composition was coated on a polyvinyl
chloride sheet of 50 ~m thickness so as to provide a film
thickness of 10 ~m and then dried at 80C for 2 min. to prepare
a cleaning sheet havin~ an abrasive layer.
parts by wei~ht
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Cr2O3 (abrasive of 10,000 mesh) 100
Epoxy resin ~epoxy equivalent
450 to 500j molecular weight
900, melting point 64 to 74C) 30
Polyamide resin (condensation
- product of a poly-fatty acid and
a diamine; amin~ value 300, avexage
molecular weight 2500) 30
Vinyl chloride - vinyl acetate
copolymer (VC : VAC = 87 : 13
Wt4; polymerization degree 500) 40
;. - .:.
Methyl ethyl kekone 500
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1 The cleaning sheet thus obtained was punched out to
the same dimensions as in Example 1, and then assembled in the
same jac~et as in Example 1. The jacket was set in a recorder
for flexible discs, and the cleaning sheet was contacted with a
magnetic head and rotated at 360 r.p.m. with a pressure of
about 2 g to about 100 g to clean the magnetic head. The
cleaning effect was the same as those obtained in Examples 1
and 2 (the cleaning jackets in which the fibrous material of
this invention was used under the same conditions). However,
the head was remarkably worn away on repeated use, and, there-
fore, the cleaning jac~et of this Comparative Example was
unacceptable.
The relationship between rotation time (min) of the
sheet and depth of wear ~m) of the magnetic head using the
cleaning jackets of the above Examples and Comparative Example
is shown in Figure 10.
From the results shown in Figure 10, it is apparent
that when the cleaning jacket of the Comparative Example in
which an abrasive layer was used and when the cleaning jackets
of Examples 1 and 2 in which the fi~rous material of this
invention was used were respectively contacted with a magnetic
head and then rotated, the cleaning jacket in which the abrasive
layer was used apparently caused, at the end of several ten
minutes, more remarkable head wear. Thus, it was confirmed
that the cleaning jacket of this invention is superior.
In addition, the cleaning jacket prepared in the
manner as illustrated in Figure 9 (i.e., of Example 2) is superior
in cleaning effect to one prepared in the manner as illustrated ~ j-
in Figure 8, i.e., cleaning effects are improved due to ~-
irregularities ~surface roughness) provided by the mesh.
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E~YAMPLE 3
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As is illustrated in Figure 11, a polyvinyl chloride
sheet 2 as in Example 1 (50 ~m thick, 25 cm x 25 cm square) and
a nonwoven material l of 70 ~m thickness (Vilene H 8103,
polyethylene terephthalate fiber made hy Japan Vilene Co., Ltd.)
were put between two press plates ~sta;nless steel plates) 15.
The assembly thus obtained was treated using a hot pressing
machine 16 under the following conditions: pressure of 2 Xg/cm2,
temperature of 120C r time 7 minutes, and then allowed to cool
to room temperature. The press plates 15 were then peeled
off. A polyvinyl chloride sheet which was laminated with the
nonwoven materia:L 1 was thus obtained.
The cleaning sheet thus obtained ~a section of which
is shown in Figure 12~ was punched out to a doughnut-like -
sheet of an outer diameter of 200 + O.S mm and an inner diameter
of 25.4 -~ 0~05 mm using a punching machine for magnetic sheets,
...
thus making a cleaning sheet for use with a magnetic head for
video magnetic sheets.
EXAMPLE 4
0
As illustrated in Figure 9,~a polyvinyl chloride sheet
2 (50 pm thick, 25 cm ~ 25 cm square; the molecular weight of ~ -
the polyvinyl chloride sheet is not overly important, and a
. . .
conventional PVC was used. The molecular weight is usually
.. .. ..
10,000 to 200,000, corresponding to a polymerization degree of ~ -
.
~ 200 to 2,000) and a nonwoven material 1 of 70 ~m thickness
,. . .
(Vilen~ H ~103, polyethylene terephthalate fiber made by Japan
Vilene Co., Ltd.) were put between press plates (stainless
steel plates) 15. At this time, a mesh 17 as in Example 2 was
put between the nonwoven material 1 and the press plate 15.
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1 The assembly thus o~tained was treated using a hot
pressing machine under the following conditions: pressure of 2
Kg/cm2, temperature of 120C, tlme of 7 minutes, and then allow to
cool to room temperature. The press plates 15 and the mesh
plate 17 were then peeled off. A polyvinyl chloride sheet
which was laminated with the nonwoven material was thus
obtained.
The cleaning sheet thus obtained was punched out in
the same manner as in Example 3 to make a cleaning sheet of an
outer diameter of 200 ~ 0.5 mm and an inner diameter 25.4 +
0.05 mm for use with a magnetic head for vîdeo magnetic sheets.
Comparative Exam~
The following composition was coated on a polyvinyl
chloride sheet of 50 pm thickness so as to provide a film thick- -
ness of 10 pm and then dr;ed to prepare a cleanlng sheet
having an abrasive layer.
parts by weight
Cr2O3 ~abrasive of 10,000 mesh) 100
Epoxy resin ~epoxy equ;valent
450 to 500, molecular weighO
900, melting point 64 to 74 C) 30
Polyamide resin (condensation
product of a poly-fatty acid
and a diamine; amine value 300,
average molecular welght 2500) 30
Vinyl chloride - vinyl acetate
copolymer (VC : V~C - 87 : 13
wt%; polymerization degree 5003 40
Methyl ethyl ketone 500
The cleaning sheet was punched out to the same dimensions
as in Example 3, then set in a recorder for magnetic sheets,
and contacted with a magnetic head and rotated at 3,600 r.p.m.
3n at a pressure of from about 1 g to about 100 g for cleaning the
15 -
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1 magnetlc head. As a result, the cleaning effect was the same
as those obtained in Examples 3 and 4 ~the cleaning sheets in
which the fibrous material of this invention was used at the
same conditions). However, the head was remarkably worn away
on repeated use, and therefore, the cleaning sheet of khis
Comparative Example was unaccepta~le.
The relationship between rotation time (min) of the
cleaning sheet and depth of wear ~m) of the magnetic head
using the cleaning sheets of Examples 3 and 4 and Comparative
Example 2 is shown in Figure 13~
From the results shown in Figure 13, it is apparent
that when the cleaning sheet of Comparative Example 2 (in which
the abrasive layer was used) and the cleaning sheets of Examples
3 and 4 (in which the fibrous material of this invention was
used) were respectively contacted with a magnetic head and
rotated, the cleaning sheet having the abrasive layer,at the
end of several ten minutes, caused remarkable wear of the
head. Thus, it was confirmed that the cleaning sheet of this :
invention is superior thereto.
While the invention has been described in detail and
with reference to specific embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
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