Note: Descriptions are shown in the official language in which they were submitted.
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SELF-LUBRICATING MAGNETIC RECORDING DISKETTE
This invention concerns a magnetic recording medium
of the type that is called the diskette which comprises a
flexible magnetic recording disk contained in an envelope
to which is attached a wiping fabric in facing relationship
to the disk. An early form of the diskette is disclosed in
U. S. patent No. 3,668,658.
Diskettes are widely used as storage media for
digital data. Virtually error-free performance is expected.
The aforementioned patent No. 3,668,658 showed that error-
free performance could be enhanced by continuously wipingthe disk with a porous, low-friction, anti-static dusting
fabric. To prolong the life of the disk by minimizing wear
as the disk moves ln contact with a magnetic recording head,
the disk has been provided with various lubricants. Never-
theless, there has been a continuing demand for longer disk
life, some users insisting that the disk should withstand
one million passes of continuous contact with the head along
a single track without a signal dropout and even asking for
four million error-free passes or more.
The present invention significantly advances the
diskette art by greatly prolonging the useful life of the t
disk. This is accomplished by applying to the wiping fabric
a dilute solution of a highly fluorinated alkyl polyether
having a viscosity index (ASTM D 2270) of about 10-130 and
then evaporating the solvent. Particularly preferred are
highly fluorinated ethyl polyethers having the repeated unit
-CF2-CF2-0-
and propyl polyethers having the repeating unit
-CF-CF2-0-
~ 30 CF3
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105~ 6
such as -
CF3-cF2-cF2-o~cF-cF2-o~cFH-cF3
- CF3 n
and the dimer thereof:
~ _ ~ 1 3~ ~
~CF3 CF2 C 2 -CF-CF2-O~ t :i
~ _CF3 ~ In /2
where n is an integer providing a viscosity index (ASTM D 2270)
of about 10-130.
The highly fluorinated alkyl polyether is prefer- ~ ~ -
ably applied by drawing long lengths of the fabric continu-
ously through a bath containing about 0.1 to 1.0 part of
the polyether per 100 parts of a solvent such as CC12FCClF2.
A lesser proportion of the polyether in the solution tends to
15 result in insufficient deposit of the polyether on the fabric ~ -
whereas higher proportions of the polyether are considered
less economical. Adequate impregnation is achieved when the
fabric is advanced at a rate such that the fabric is immersed
for about 1 to 20 seconds. Normally, the solvent evaporates
in air at ordinary room temperatures within one minute after
the fabric is withdrawn from the bath. Desirably, the dried
fabric contains 1-20 parts by weight of the polyether per
100 parts by weight of the fabric. Lesser amounts do not
provide error-free performance for periods as long as do
amounts within that range, whereas greater amounts are
considered to be unnecessary and expensive and may produce
an esthetically undesirable visual pattern on the disk.
The wiping fabric should be a nonwoven, porous,
tissue-like material of synthetic fibers which are insoluble
in solvents for fluorocarbon polymers. Preferably the fabric
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is made from two fibers, one of which is employed at a
relatively low proportion and initially has a lower soften-
ing point than the other and is partially fused durlng
fabrication to act as an adhesive ~oining the higher-
softening fibers into a coherent fabric of the type general-
ly disclosed in U. S. patent No. 2,676,128. A preferred
fabric consists of 80 parts by weight of rayon fibers and 20
parts by weight of polypropylene fibers which bond the rayon
fibers together. The weight of the fabric may be 10-100
(preferably 20-45) grams per square meter. Fabric having a
weight below that range may be unduly fragile whereas a
heavler fabric would tend to be too thick to meet current
industry specifications for the diskette.
The single figure of the drawing is & perspective
vlew of a diskette, cut away to show details.
In the drawing, a magnetic recordlng disk 10 is
positioned within a flexible, shape-retaining plastic envelope
12. A porous, nonwoven, tissue-like fabric 14 attached to
the inner walls of the envelope is impregnated with highly
fluorinated alkyl polyether lubricant (not shown).
In use, the disk 10 is rotatively driven at its
central opening 16 while the envelope remains stationary,
and a magnetic recording head (not shown) contacts the
rotating disk through either of the identical oval apertures
18 in each of the side walls of the envelope. As the disk
10 rotates, it lightly contacts the fabric 14, and the poly-
ether lubricant gradually transfers to the surface of the
disk to provide continuous lubrication between the head
and the disk.
lV~7~96
Exa ple
A diskette as illustrated in the drawing was pre-
pared using a nonwoven wiping fabric consisting of 80 parts
by weight of rayon fibers of approximately 1.5 denier and
20 parts by weight of polypropylene fibers of approximately
1.5 denler which have been fused together to afford integrity
to the fabric. The weight of the fabric was about 36 grams
per square meter.
The fabric was immersed for 15 seconds into a
solution of approximately one part by weight of a solute
comprising a highly fluorinated propyl polyether (viz.,
"Krytox" 143AZ) in 100 parts by weight of the solvent
CC12FCClF2 (viz., "Freon" 113). It ls believed that part
of the solute was a telomer of F2C=CF2. The vlscosity lndex
(ASTM D 2270) of the solute was 23, its density at 24C was
1.86 g/ml and its boiling point range at 0.8 mm Hg was 143-
185C. Within 45 seconds after being withdrawn from the
bath, the solvent had substantially evaporated in air at
room temperature. Solvent extraction indicated the presence
of 11 parts b~ weight of the solute Per 100 parts by weight
of the fabric.
The treated fabric was cut to shape and attached
to the envelope material at areas ad~acent the openings and
edges and at intermediate areas by a single pass of a roll
having knurled sections of about 3 mm in width which had
been preheated to 175C. The envelope material was a film
of a copolymer of about 90 parts by weight of vinyl chloride
and 10 parts b~ weight of vinyl acetate containing about 10%
carbon particles and having a matte surface. The temperature
of the knurl roll was sufficient to fuse the fabric to the
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vinyl fllm without observable change in the overall porosity
of the fabric. Attempts to remove the fabric resulted in its
delamination at the fused areas.
The magnetic recording disk was of conventional
construction, having a backing of biaxiall~-oriented poly-
ethylene terephthalate film 0.08 mm in thickness and a 0.003
mm coating of acicular gamma-Fe203 particles in binder on each
surface. The coatings were polished to a surface roughness
not exceeding oOo8 micrometer. The envelope and fabric
were folded and two edges were heat-sealed followed by
insertion of the disk and sealing of the third ~dge to pro-
vlde a permanent enclosure for the disk as shown in the t
drawing.
This dlskette was tested by rotatln~ the disk ln
contact with a magnetic recording head along a sin~le track
continuously except for periodic tests for dropouts. A drop-
out was not detected after two million passes, at which
point the test was discontinued. An otherwise identical
diskette except for omission of the lubricant showed a drop-
out withln 160,000 passes.
