Anti-spin-off coating for disc records

Magnetic recording media wherein the record surface is coated with an isocyanate lubricant (and, preferably, a supercoat of like lubricant), such lubrication being adapted to inhibit spin-off and like depletion, despite frequent head-contact, while exhibiting good durability, wear resistance and recording characteristics over extended life (computer applications).

This invention relates to lubricants for magnetic recording compositions 
(e.g., as coated on a rigid data disc or like substrate), and more 
particularly to such including an improved surface lubricant system 
adapted therefor. 
BACKGROUND, FEATURE OF INVENTION 
Workers in the art of making and using magnetic recording apparatus for 
data processing and the like are well aware that the media therefor often 
present serious wear problems, such as may foreshorten their useful life. 
For instance, with rigid magnetic recording disc surfaces which support a 
thin-film magnetic recording head (carried on a "slider") passing at 
relatively high speeds, the head is all too apt to problematically abrade 
both itself and the medium. 
A related problem is that of undesirably high friction between the disc and 
head (surfaces). To ameliorate abrasion, workers typically specify that a 
disc coating exhibit no more than a certain (maximum) coefficient of 
friction--this also reduces the force necessary to drive the disc past the 
head. To reduce friction and enhance wear, workers have resorted to 
various expedients such as "surface-(topical) lubricant" coatings on the 
disc's recording surface. 
This invention is also concerned with such surface lubricants, and with 
techniques for affixing the lubricants to such record surfaces, preferably 
by chemical bonding. 
Workers recognize the problems using such surface lubricants (on the 
surface of information carrying media such as magnetic recording discs and 
tapes). Such lubricants may be applied to a record surface, and held 
there, by purely mechanical means, for example, by capillary forces. 
Publications which illustrate physical retention of a lubricant on a solid 
surface include, for example, U.S. Pat. Nos. 4,188,434; 4,232,072 and 
4,268,556. In these patents, no chemical bond is taught between the 
surface lubricant and the underlying surface. 
According to the present invention, a prescribed isocyanate lubricant is 
applied to a record surface and cured there for a stable firmly-attached, 
chemically-bonded polymeric lubricant (contact disc with an 
isocyanate-terminated lube). 
Generally "surface lubricants" as here understood are chemically inert and 
thus exhibit little adherent interaction (such as hydrogen bonding or 
polar group interaction) with the record surface. Because of such loose 
adhesion when a record disc, as here understood, is rotated at high speed, 
the lubricant tends to migrate from the disc (e.g., adhesion forces being 
gradually overcome by the centrifugal force), and thus the lubricants are 
spun-off and depleted, with consequent likelihood of "head crash". 
According to the present invention, such lube depletion is inhibited by 
application of a thin film of isocyanate lubricant to the information 
carrying surface, this film being so chemically-bonded to the surface as 
to not be readily removed (e.g., by washing or rubbing with isopropanol). 
Record surfaces apt for this include, for example, magnetic discs, 
magnetic tapes, sound recording media and the like, especially certain 
compatible polymeric surfaces. 
Such lubricant coatings are particularly apt for polymeric magnetic record 
disc surfaces (e.g., of the type used in computer recording), especially 
where the relative head-medium velocity is very high, and the head is 
highly abrasive (cf. thin film heads) and consequent abrasion and reduced 
life of both head and media is quite likely. Thus, workers have resorted 
to various known "surface-lubricant" means for such disc coatings and like 
media (e.g., see the following U.S. Pat. Nos.: 3,490,946; 3,492,235; 
3,523,086; 4,431,702; 3,983,302; 3,837,912; 3,597,273; 4,446,193; also IBM 
TDB Vol. 26, #7B, p. 3778, December 1983; also article by Budinski in J. 
Vac. Sci. Technol. Vol. 12, #4, July-August 1975, pp. 786+; and article by 
Hamada, et al., J. Appl. Phys. 55(6), 15 March 1984, pp. 3775+. 
Depletion of surface lubricant on a spinning magnetic recording disc is 
believed primarily due to "spin-off" initiated by centrifugal forces. Some 
subsurface lubricant (within the body of the magnetic coating itself) is 
at times suggested as a potential reservoir for replenishing the surface 
lubricant so spun-off. 
Workers are aware of the "spin-off" problem and recognize that it commonly 
depletes surface lubricant prematurely inducing head-crash and system 
failure. A salient purpose of this disclosure is to inhibit such depletion 
by application and chemical bonding of an isocyanate-terminated (or 
acid-terminated) lubricant to a polymeric record surface, especially where 
the polymeric surface exhibits free, reactive groups (or can be induced 
so)--e.g., hydroxyl--which can chemically bond with the reactive isocyanate 
(or acid) groups, to yield urethane or ester bonds. 
A related object is to match this isocyanate lube with the characteristics 
of a lubricant supercoat thereon (e.g., significant mutual solubility and 
mutual molecular attraction plus substantial inter-diffusion) for improved 
adhesion thereof and synergistic co-lubrication. Thus, the two lube layers 
of like composition and structure can, together, act to inhibit depletion 
of the top lubricant layer. 
It is an object of this invention to address such problems and particularly 
to teach novel magnetic recording compositions including improved surface 
lubricant systems, especially for systems with rigid disc media and thin 
film heads. 
For instance, compared with a standard ferric oxide computer disc coating 
in a certain polymeric binder, a novel lube reactive coating system 
according to our invention applied as a scant undercoat for normal surface 
lube will reduce spin-off and like depletion, and enhance durability and 
operating life--to the surprise of workers! (e.g., because our undercoat 
material is conventionally viewed as a lubricant--thus we are improving 
adhesion of a lube coat by a lube under-coat!). Such a reactive lube 
undercoat will include isocyanate-terminations. They also, preferably, 
include fluorocarbon moieties (preferably fluoro-alkyls such as 
fluoro-ether polymers); further they are preferably super-coated with a 
fluorocarbon lube system of similar structure. For instance, a preferred 
reactive coating comprises a diisocyanate-terminated perfluoro-poly-ether 
which is very apt for use with a super-coat lube including fluoro-ether 
constituents (less preferably, the fluoro-version may be substituted for 
the perfluoropolyether, but will typically be less stable; for instance, 
where hydrogen replaces fluorine, it will be more likely to react 
adversely, change properties, offer a point of corrosive attack, etc.) 
Now workers have, of course, suggested fluorocarbon surface lubricants for 
magnetic recording surfaces. But such lubricants, in themselves and in 
general, are not necessarily effective in affording the kind of superior 
durability, stability and spin-off resistance we desire; also, in heavy 
concentrations they can badly impair magnetic performance (e.g., see U.S. 
Pat. No. 4,431,703). 
Some workers have suggested various organic (e.g., organo-fluorine) 
compounds as lubricants for rigid magnetic recording media (e.g., see U.S. 
Pat. No. 3,993,846, or U.S. Pat. No. 4,007,314, or U.S. Pat. No. 
4,131,717--or see U.S. Pat. No. 4,007,313 mentioning an 
organo-silicone-fluoride lubricant). 
The tendency now is to increase density of recording using very thin 
magnetic media films having highly polished surfaces and using recording 
heads which fly practicallly in contact with (if not actually 
sliding-over) these films. This calls for substantial improvements in 
surface lubrication for such high-density magnetic media, with lubricant 
layer specifications becoming very stringent. Such a lubricating layer 
should be as thin as possible (order of magnitude of several dozen .ANG. 
or more) and yet be very stable, long-lasting, effective and durable; it 
must not react with the record-binder lest it plasticize the record 
surface and, over all, it must not be removed or significantly depleted in 
use. 
Common "migratory" lubricants (which are added to the bulk of the record 
coating) are now suspect under such circumstances; e.g., their migration 
rate cannot be controlled with sufficient precision; hence they cannot 
assure a surface lube-coat which is sufficiently uniform. 
"Topic" or surface-applied lubricants (e.g., fluorocarbon oils) are now 
coming into favor for such media--indeed, in some cases, such as with thin 
film metallic media, workers feel there is no other conventional way to 
achieve superior surface lubrication. 
As a feature hereof, such media are surface-coated with a scant, 
well-bonded film: i.e., the (urethane) reaction product of the 
isocyanate-terminated polymer lubricant and the surface hydroxyls--(or the 
analogous ester product of the acid-terminated polymer). 
Fluorocarbon liquid films are generally known as useful to lubricate 
magnetic recording media (e.g., rigid discs of the Winchester type; cf. 
pp. 1073+of IEEE Transactions on Magnetics, Vol. MAG-18, No. 6, November 
1982). Such lubricants have desirable properties (oxidative and thermal 
stability, chemical inertness, wettability, viscosity range, etc.), but 
the mass of lubricant on the disc must be carefully controlled. If there 
is too little, head-wear is excessive and "crashes" can occur. If too much 
lubricant is applied, puddling and "stiction" of the head can occur; e.g., 
during "start-up". This can result in distortion of a head flexure and 
disc damage (and so can lead to a latent failure situation; cf. all the 
factors which cause "stiction" are not known, but excess lubricant seems 
to be a major contributing factor). 
General Aspects of Embodiments 
Certain salient features of our developments will come to mind upon review 
of this specification. 
For instance, we prefer to formulate our lubricant system to comprise an 
initial layer of isocyanate-terminated (and/or acid-terminated) polymer 
lubricant. Our lube systems are particularly apt as a surface-lube film 
for "in-contact" media (i.e., media characterized by continual, or 
periodic, frequent contact of a thin film head therewith--as distinguished 
from media which are seldom, if ever, so contacted; e.g., when the head 
usually "over-flys"). 
Such an "isocyanate-lube film" (or acid-terminated film) may be understood 
as a "reactive lubricant"; i.e., one with end-molecules that firmly attach 
themselves to the record surface (cf. polymeric recording surface of a 
magnetic record disc). To break such a bond and cause spin-off and 
depletion of the lube, energies of 128 to 84 k. cal/per molecule are seen 
as required. This is far greater than the mechanical forces developed on 
any spinning disc record. 
A "reactive lube" should have a characteristic "bonding molecular 
structure"; i.e., a carbon chain exhibiting lubricant properties, with one 
or several apt "reactive" terminal groups which are capable of further 
reaction. 
A preferred substrate record surface for our reactive lube film will be 
characterized by discrete surface molecules exhibiting, or capable of 
generating, reactive groups (especially hydroxyls) apt for reacting with 
acid or isocyanate terminations to form a "strong bond". Curing reactions 
which take place may also produce additional functional groups. For 
example, epoxy and/or phenolic binder resins used in recording embodiment 
coatings herein evidently contain such hydroxyl groups, or can readily be 
made to do so--as can most magnetic record binders. 
Typical structures for such an epoxy (Epon 1004) and phenolic (Methylon 
75108) are shown below (an E-P type binder): 
##STR1## 
In addition, the curing reaction of such binders can produce useful ester 
or esters, depending upon the resin and the relative rates of the various 
reactions. A related uncatalyzed reaction is shown in simplified form as: 
##STR2## 
Whereas a catalyzed reaction can yield an ether; as: 
##STR3## 
Thus, the unreacted binder resins produce such functional hydroxyl groups, 
as well as resins which are partially reacted or fully reacted 
(cross-linked). We have seen evidence of such hydroxyl groups, of such 
ester groups and of the disappearance of epoxy groups in instances like 
some embodiments herein 
A salient feature hereof is that the reaction of hydroxyl groups on the 
disc record-surface with isocyanate of our lube surface-coat yields a 
urethane bond at the surface of the disc, firmly adhering the 
isocyanate-lube on the magnetic recording coating. 
A particular preferred isocyanate which forms the basis of such a "reactive 
lube" according to this invention is produced from a "diol" (e.g., a 
fluoro-poly-ether-diol) and a di-isocyanate; to combine, and produce a 
short-chain fluoro-alkyl polymer that is di-isocyanate terminated, i.e., a 
"Disoc" as here understood. 
Workers will see that magnetic, in-contact digital recording surfaces may 
be enhanced and made more practical commercially (reasonably low 
depletion, high durability/life) by a mere coating with our novel 
"reactive-Disoc-lubricant" (or a related acid-terminated analog)--as the 
following Examples will show in some detail. 
One preferred embodiment involves the application and reaction of a 
fluorocarbon diisocyanate "reactive lube" with functional terminal 
hydroxyl groups on the magnetic recording surface to form a cross-linked 
surface layer with urethane bonding of the lube to the surface. The 
diisocyanate is preferably based on a fluorocarbon lube and materials 
which are available commercially; and can be readily prepared from 
available materials. The "reactive-lube" system and process described in 
this embodiment involves, in preferred forms: 
a) readily obtainable materials; 
b) specifically a diisocyanate-terminated and/or acid-terminated lube, 
particularly a fluorocarbon giving a stable "reactive-lube-undercoat" 
layer on record-surface, especially where this "under-coat" exhibits 
cross-linked fluorocarbon; 
c) reaction with functional (especially hydroxyl) groups on the disc 
surface, to be firmly bonded thereon; 
especially via urethane bonding and/or ester bonding between the record 
surface and the undercoat (readily induced; e.g., by heating an hour or so 
at about 100.degree. C.); 
d) controlled lube film thickness; 
e) an additional super-posed surface-lubricant layer applied which is 
mutually soluble in the."reactive undercoat", and so is better retained 
thereon; 
f) good wear characteristics; 
g) little or no appreciable depletion rate (spin-off); and 
h) easily applied; and with 
i) super-coat of surface-lubricant retained on under-coat via mutual 
solubility, etc.. 
The convenience and facile nature of such a lube-retention expedient will 
recommend itself to workers, e.g., as opposed to conventional relatively 
expensive/cumbersome expedients like surface-etching. 
While a number of chemical reactions can be used to bond such reactive 
layer lubricant molecules to a (disc) record surface, we believe our 
"reactive isocyanate" mode is best, considering material availability, 
reaction rate, stability of the reacted layer, and effectiveness. Other 
methods of attachment, such as esterfication, etherfication, etc. will 
prove more difficult to carry out and give products which are less stable. 
Our polymeric isocyanate lubricants may be synthesized from the 
corresponding materials as workers recognize. Preferred starting materials 
include fluorinated polymer lubricants such as poly(perfluoropropylene 
oxide) di-carboxylic acid, and poly(perfluoroethylene oxide) di-carboxylic 
acid. 
In a preferred form of the present invention, the mentioned layer of 
like-structure surface-lubricant is superposed atop the "reactive lube" 
under-layer, preferably retained there by inter-molecular attraction, by 
good inter-solubility and/or by inter-diffusion between the two layers 
(which thus have basically similar structures and, preferably, an 
identical "backbone". Spin-off and like depletion is thus inhibited, if 
not essentially eliminated. 
The invention will be better appreciated by workers upon consideration of 
the following detailed description of some preferred embodiments.

DESCRIPTION OF PREFERRED EMBODIMENTS 
General Description, Background 
Example I illustrates a magnetic (disc) recording substrate coated with a 
recording composition, and then a lube system formulated and applied 
according to principles of this invention. 
This, and other means discussed herein, will generally be understood as 
selected, formulated, and operating as presently known in the art, except 
where otherwise specified. And, except as otherwise specified, all 
materials, methods, and devices and apparatus herein will be understood as 
implemented by known expedients according to present good practice. 
A relatively conventional magnetic record polymeric coating will be 
understood as disposed on a rigid computer disc according to the 
invention, and modified to include a novel isocyanate-terminated lubricant 
layer. 
Following is a specific Example of such an isocyanate lube system 
embodiment used in the practice of the present invention. This composition 
is prepared to include the mentioned components in indicated 
concentrations, and to be applied, processed and used as indicated. 
Ex. I 
A magnetic disc record of the type coated with a polymeric magnetic 
recording film (magnetic oxide in polymeric epoxy-phenolic type binder 
(see E-P above) for Write/Read in-contact with slider) is presented for 
surface lubricant treatment according to the invention. The record surface 
is assumed to have been finally treated (e.g., polished, burnished, 
degreased and otherwise fully cleaned), except for surface lubrication and 
related steps. 
A fluorocarbon polymeric "reactive lubricant" exhibiting isocyanate end 
groups is prepared (cf. "Disoc" as above; e.g., molecular weight about 
2000) and is applied sparingly to the recording surface of the disc to 
give a scant, uniform, relatively continuous, minimum-thickness surface 
coating. After sufficient time, at operating temperature (e.g., can be 
heated to accelerate cure), to assure appropriate degree of cure 
(surface-bonding of binder hydroxyl, with reactive isocyanate end-groups 
and urethane-bond the record surface material), a "strip" step may be 
executed, removing unwanted, uncured material and further assuring a 
scant, uniform residue film left on the record surface. Alternatively and 
preferably in many cases, this "strip" is replaced by a "quench" whereby 
unreacted isocyanate terminations are inhibited from later reacting (e.g., 
by contact with an azeotropic mixture of Freon TF and alcohol). 
Preferably, the polymeric binder presents free, reactive (cf. OH--) groups 
apt for chemical bonding with the lube's isocyanate end-groups. Such 
reactive hydroxyl can be developed, as workers know, in many common binder 
polymer moieties, such as on the phenolic and the epoxy portions (e.g., 
cf. opening of epoxide ring). 
The reactive isocyanate groups are very reactive here; and may pick up 
unwanted contaminants like moisture --thus an inert atmosphere (e.g., 
N.sub.2 blanket) may be in order, e.g., until curing finished. 
The record may now be used, or, if one wishes to further assure optional 
surface lubrication, a compatible super-lubricant film may also be applied 
(e.g., preferably a like fluorocarbon lubricant). 
Workers will note that the scant isocyanate-lube reactive film (prefer 
40-90 .ANG.) seems to yield good lubricating characteristics of itself, 
and especially when supplemented with a like lubricant super-coated on the 
film. Spin-off and other lube depletion seems markedly inhibited. 
We assume (though it is not certain) that the record surface has 
essentially been modified by this isocyanate film, from the original 
relatively hydrophobic, highly polar surface to a "lower-energy" surface 
e.g., more compatible with a lube super-coat). Evidence of this is the 
fact that relatively little spin-off occurs. Such a coated record appears 
to exhibit superior lubricant characteristics over extended use; e.g., 
easily passing standard CSS (Contact Start-Stop) tests; e.g., 10-20 k. 
CSS. 
Of course, for increased toughness, load-bearing and durability, the 
isocyanate-lube will be prepared to exhibit moderate-to-high molecular 
weight (e.g., at least several thousand). Also, excess thickness will be 
avoided lest too much unreacted (unbonded) lube material remain and 
"soften" the lube film. 
Ex. II 
A record disc is lube coated as in Ex. I, with the isocyanate-lubricant 
comprising a pair of isocyanate end groups on a relatively short, low 
molecular weight fluoro-alkyl chain, being sponged on the recording 
surface uniformly in a Freon diluent (up to a few wt. % therein), and 
buffed or otherwise worked to spread more uniformly. Like results are 
obtained. 
Ex. III 
Ex. II is replicated with a di-isocyanate formed on a fluoro-ether polymer 
backbone. Like results are obtained. 
Ex. IV 
Ex. I is repeated, using a higher molecular weight isocyanate-terminated 
lube (e.g., 3-4000 or more) for the "reactive film" and no super-lubricant 
added on the reactive film--which will thus serve as the sole 
"surface-lubricant". This may be satisfactory for "light" service (e.g., 
only a few k.-CSS, or with a ferrite head, rather than a thin film head). 
Ex. V 
Ex. III is replicated, with a second layer ("top-layer") of surface 
lubricant superposed atop the di-isocyanate-terminated fluoro-ether 
reactive film. This "top layer" is of suitable thickness and similar 
structure to reactive film (e.g., fluoro-ether lube also). It will be seen 
as retained in place better than . conventionally (i.e., better than where 
no such "reactive film")--evidently because of the inter-molecular 
attraction, etc., between like layers, and because the underlying 
"reactive film" is so firmly bonded to the record surface. 
Ex. VI 
Ex. III is replicated, with the di-isocyanate-lube polymer prepared from a 
poly(perfluoro alkylene oxide) compound. Acceptable methods and materials 
for preparing such are known in the art; for example, some are disclosed 
in U.S. Pat. No. 3,810,874 and in U.S. Pat. No. 4,085,137, both 
incorporated herein. 
The so-developed isocyanate-terminated "reactive lube" is coated as in Ex. 
I-III, etc., on the recording surface and reacted there, then excess 
unreacted material stripped away. The isocyanate end-groups should 
eventually form urethane bonds with the free hydroxyl moieties in the 
(epoxy-phenolic) binder on the record surface. These chemical bonds are 
very strong and will resist all conceivable spin-off forces. The scant 
(e.g., several dozen .ANG.) isocyanate film left is then coated with a 
"surface-lubricant" readily soluble in the (isocyanate) reacted film. 
Preferably this surface-lube is a relative high m.w. perfluoropoly ether 
(Z-60, Z-25, based on polyethylene oxide types by Montedison, etc.); and 
will be mutually soluble, etc., in the reacted film (isocyanate) and so be 
better retained thereon and resist spin-off and like depletion. 
Results are satisfactory as above. 
Ex. VII 
Ex. VI is replicated, with a "Disoc" type perfluoro-polyether, 
isocyanate-terminated "reactive lube" film as described above, with the 
record surface including epoxy and phenolic binder polymers (e.g., as "EP 
Binder" described above). 
The "Disoc" is applied and heat-cured until about 80-95% reacted (e.g., 
about 100.degree.-110.degree. C. for about 90 min.) to yield urethane 
bonding--with excess unreacted unbonded Discoc then removed to yield a 
scant isocyanate-film of about 40-90 .ANG. (pref. 50-70 .ANG.) or, in any 
event, whatever it takes to form just one or several continuous, 
mono-molecular layers, if at all possible ("ideal thickness"). 
The results are satisfactory as before, with relatively little lube 
spin-off, no "stiction" or "head corrosion" problems and with good 
operational durability (e.g., passes 10-20 k.+Contact Start/Stop cycles). 
No toxicity or environmental problems will be seen [e.g., surprisingly, no 
water-uptake problems will be seen, and the so-lubed disc will give 
extended service even in high heat-humidity conditions]. 
Ex. VIII 
Ex. I is replicated, except that the reactive-film (fluorocarbon) lubricant 
is modified to include acid terminations appropriate for ester-bonding 
with the record surface (e.g., with reactive OH groups found, or induced 
therein--as can be done with virtually any current record binder). These 
acid terminations may be substituted for the isocyanate terminations, or 
supplemented thereto. 
Ex. IX 
Ex. VII is replicated, with the reactive film "Disoc" lube 
(isocyanate-terminated perfluoro poly ether) prepared as follows: 
1) A suitable form of carboxylic acid is mixed with a suitable 
di-isocyanate in a solvent therefor--preferably .alpha., .omega. 
terminated carboxylic acid in Freon TF (cf. about 50 ml. Freon tri-chloro 
tri-fluoro ethane) mixed with (an aliquot) 2, 4 toluene di-isocyanate. 
2) The mixture is stirred for about one hour; then the solvent evaporated, 
leaving a "Disoc" product: i.e., .alpha.,.omega. di-isocyanate of a 
perfluoro poly ethylene oxide polymer. 
[as workers recognize, a -polypropylene oxide Disoc analog may likewise be 
prepared and substituted here] 
3) The "Disoc" is applied to the medium surface e.g., diluted in suitable 
solvent, and cured, so a suitable number of urethane bonds form with the 
surface -OH groups. 
more particularly, this "Disoc" may be dissolved in Freon TF (0.5-2 wt. % 
strength) and applied via sponge applicator, or any like means, yielding 
as uniform a thickness as possible [e.g., initially 5-20 mg., 
corresponding to thickness of about 150-600 .ANG.] 
Alternatively, one may wipe-on, spin-on, spray-on or the like; and the 
Disoc may be otherwise diluted, or applied full strength. 
It is usually necessary to buff, or similarly "work" the rather viscous 
Disoc, to spread it more evenly across the record surface. 
3A) curing (decomposition to effect urethane bonding) may be done by any 
convenient practical method that yields the appropriate degree of urethane 
bonding with reasonable time and expense. We have found that heating 
(oven) for about 1.5 hours at about 100.degree.-120.degree. C. is 
satisfactory (e.g., 90-95% bonding by available isocyanate). 
since the isocyanate is so active, it may be advisable to screen-out 
unwanted reactants (e.g., moisture) with an inert atmosphere (e.g., 
N.sub.2 blanket) until the cure-period is concluded. 
4) Unreacted material (unbonded isocyanate, etc.) is preferably removed 
(e.g, washed off with Freon TF or like solvent). 
The remaining "reacted-lube" film (pref. 40-90 .ANG. thick, and uniform, 
continuous across record surface) will be found to be firmly bonded to the 
record surface (urethane bonds). 
The results are, otherwise, as before. 
Ex. X 
Use of Fomblin: 
Ex. IX is replicated with the reactive film "Disoc" lube comprising a 
"Fomblin-Z" material (supplied by Montefluos Co., Montedisen Group, Rome, 
Italy), the structure and characteristics given as follows: 
"Fomblin-Z" Disoc 
.alpha..omega.-perfluoropolyether-bis-carboxyamyde-tolylen-isocyanate 
NCO--C.sub.6 H.sub.3 (CH.sub.3)--HNCOCF.sub.2 --(C.sub.2 F.sub.4 O).sub.m 
--(CF.sub.2 O).sub.n --CH.sub.2 CONH--(CH.sub.3)C.sub.6 H.sub.3 --CON 
Typical Characteristics 
______________________________________ 
Solubility in Mek. 0.3-0.5% 
Average Molecular weight (NMR) 
2000 .+-. 400 
Ratio of groups C.sub.2 /C.sub.1 (NMR) 
0.7 .+-. 0.2 
Equivalent weight (amination) 
1100 .+-. 200 
Acidity in 100 g of product 
less than 5 acid 
millequivalent 
Specific gravity (20.degree. C.) 
1.62 kg/l 
Molecule length 82 A.degree. 
______________________________________ 
##STR4## 
Other suitable polyfluoroethers with active isocyanate end groups may be 
used; e.g., Krytox, a perfluoro-poly propylene oxide derivate (and cf. 
like perfluoro poly ethylene oxide derivatives). However, related fluoro 
polymers like tetrafluoro ethylene are unsuitable (e.g., having a long 
chain and no like active end groups). 
Processing is given above; however Table A below gives some preferred, more 
specific versions. 
TABLE A 
______________________________________ 
"Std. Disoc Treatment" 
______________________________________ 
After "standard" computer data rigid disc is coated with 
magnetic recording coat of mag. oxide, etc., in epoxy-phenolic 
binder, dried, etc., some preliminary steps are common, as: 
(A-1) Polish: 
record-surface polished to smooth 
(A-2A) Rebake: (e.g., in over) 
to oxidize surface, remove organics, raise melting 
point (vs "tacky-ness", binder-melt) 
(A-2B) Wash: 
clean-off oven rebake contaminants 
in many cases, steps 2A, 2B are eliminated 
(A-3A) Alcohol wipe: 
clean before burnish; e.g., with isopropyl alcohol 
(A-3B) Burnish: 
remove "peaks" on record-surface 
(A-3C) Degrease: 
remove alcohol residuals and any other residual 
contaminants 
(A-4A) Apply "Disoc" (reactive lube film) - see also 
Table B - sponge-on "Disoc" (auto. applicator, 
diluted in Freon TF - to about 20 mg. ( .sup..about. 600 
A.degree.) 
Buff-to-spread evenly; may need N.sub.2 blanket vs H.sub.2 O 
uptake; e.g., about 50-90 A.degree.; 60% reacted here 
(A-4B) Heat-to-react (e.g., in oven) 
Bake .sup..about. 1-2 hrs. @ 100-120.degree. C.; react to about 
90% 
(A-4C) Strip-away "Disoc" residue (Degrease) 
remove unreacted "Disoc"; e.g., Freon TF condensed 
on disc 
(A-5) Apply lube super-coat (e.g., 10-30 k m.w.) 
e.g., dip-coat Z-25 onto "reacted film" of "Disoc" 
DON'T disturb "reacted Disoc surface", 
leave wholly untreated, 
thereafter, perform normal "completion" steps; 
e.g., "glide", "wipe" and "certify". 
Results: 
(A) 
reduced spin-off: 
e.g., where control; spun @ 6000 rpm for 
1000 hrs.: 74 A.degree. .fwdarw. 40 A.degree. 
2000 hrs.: .fwdarw. 30 A.degree. or likely crash! 
vs Disoc-coat under super-lube: spun @ 6000 rpm 
1000-2000 hrs.: 74A.degree. .fwdarw. 72 A.degree. 
______________________________________ 
Further preferred process specifics for Disoc application are given in 
Table B as follows. 
TABLE B 
______________________________________ 
Apply "reactive lube" 
______________________________________ 
1. Apply sufficient "reactive lube" on disc surface. 
Preferred application mode: 
Conc. lube solution: 0.1-0.5% in diluent 
Flow rate: 5 ml/min. (from TF) 
Application time: 14-54 sec. 
2. Buff lube uniformly on surface to leave somewhat 
in excess of a mono-layer. 
Preferred Buff mode: 
Buff pressure: 100 psi-225 psi 
Buff speed: 400 rpm-900 rpm 
Buff time: 14 sec.-54 sec. 
______________________________________ 
Now, workers are aware of the concept of applying certain lubricants 
containing highly polar groups on recording media (e.g., see U.S. Pat. No. 
4,268,556) and of bonding a lubricant on a record surface by generating a 
highly reactive carbene which reacts with the surface in some manner 
(e.g., see U.S. Pat. No. 4,446,193 or U.S. Pat. No. 4,120,995). A related 
bonding of a telechelic polyether is suggested in U.S. Pat. No. 4,268,556 
(evidently depending upon loose molecular associations called "van der 
Walls forces", rather than discrete chemical bonds, though thermal 
stability and "spin-off" would be inferior to a more firmly chemically 
bonded system, and lubricity would probably be inferior too). 
U.S. Pat. No. 4,446,193 describes a chemically-reacted lube system. It 
involves a rather problematic synthesis of a diazoketone, and subsequent 
decomposition thereof to a carbene. The synthesis of the diazoketone is 
complicated; also purification of the product is a problem. In order to 
form the carbene intermediate, temperatures of ca., 200.degree. C. must be 
used; alternatively, U.V. exposure can be used, though U.V. absorption by 
a thin layer of diazoketone would likely be minor and thus inefficient. 
While the carbene can react with a record surface, it is difficult to 
determine the course of the reaction. The carbene can, in fact, react with 
itself, which would reduce its effectiveness. 
The '193 patent also states that carbenes can react with metal oxides but 
no specifics are given. It is, in fact, unknown whether the reaction with 
metal oxides produces a useful species. 
U.S. Pat. No. 4,120,995 teaches (chemically) bonding a lubricant to a 
substrate; as does European Patent No. 123707 (Nov. 7, 1984). This '707 
patent appears to use a fluorocarbon undercoat with silicon-bonding to the 
substrate (a bonding expedient somewhat different and less efficient than 
urethane bonding; also less stable, being apt for hydrolysis into Hcl, and 
presenting a serious risk of corrosion and toxicity). European '707 also 
seems to suggest the possibility of using a surface-lube overcoating, but 
employs fluorocarbon end-groups to retain this on a protective-film 
(analogous to our "undercoat"), seemingly a weaker, less stable retention 
mechanism. 
To recapitulate, our Examples describe an isocyanate-terminated (or 
acid-terminated) "reactive lube undercoat" to inhibit lube depletion 
(e.g., spin-off of a lube super-coat). This is done by applying and 
chemically-bonding such an undercoat on virtually any conventional 
polymeric magnetic recording surface susceptible of exhibiting appropriate 
functional groups to react with the isocyanate (or acid-) and produce 
strong bonding (e.g., this is true for essentially all polymer binders 
used with disc media of the type used to record high density digital data 
for high-speed data processing), with spin-off reduced. As described, this 
very thin undercoat should be well cured on the recording surface (with 
most uncured material removed). 
Subsequent application thereon of a relatively conventional like-structure, 
like-solubility surface-lube system (e.g., a fluoro-alkyl as described) is 
also very effective, yielding a novel, surprising "lube-on-lube" two-layer 
coating which is highly stable and resistant to spin-off depletion, and 
thus is superior for such high speed computer operation with a 
conventional TF head-"slider", etc. 
The isocyanate (or acid)-terminated "reactive lube" films of this invention 
will be seen to increase lubricant retention on magnetic disc coatings to 
give better wear characteristics and longer and more reliable product 
life. 
It will be understood that the preferred embodiments described herein are 
only exemplary, and that the invention is capable of many modifications 
and variations in construction, arrangement, and use without departing 
from the spirit of the invention. 
Further modifications of the invention are also possible. For example, the 
means and methods disclosed herein are also applicable for other like 
(in-contact, computer) recording media. Also, the present invention is 
applicable for providing a lubricant system in other analogous situations 
(such as for other "in-contact" media). 
The above examples of possible variations of the present invention are 
merely illustrative. Accordingly, the present invention is to be 
considered as including all possible modifications and variations coming 
within the scope of the invention as defined by the appended claims.