Cover-gasket assembly for hard disk device

A cover-gasket assembly for a hard disk device which comprises a gasket applied to a predetermined position of a cover for the hard disk device, wherein the gasket is formed essentially of a cured product of a fluorosilicone rubber composition. The assembly is particularly excellent in sealing property against permeation of water vapor, and can be used extremely effectively for hard disk devices for handy office-automation apparatuses such as laptop or pocket-size personal computers, word processors and the like which are expected to be used under various temperature and humidity conditions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cover-gasket assembly obtained by direct 
formation and adhesion of a rubber gasket onto a cover member for a hard 
disk device. 
2. Description of the Prior Art 
A hard disk device generally comprises hard disks, namely, disks of an 
aluminum alloy or the like coated with a magnetic material which are 
enclosed in a sealed container, and magnetic heads each disposed close to 
the disk, with an about 0.1- to 0.5-.mu.m gap therebetween, for recording 
and reproduction of information into and from the disks. 
If dust is generated in the sealed container or comes into the container 
from the outside, therefore, magnetic surfaces of the disks or the 
magnetic heads can be broken. In order to obviate such troubles, an air 
circulator comprising a high performance filter is installed in the sealed 
container to catch dust, whether generated internally or coming from the 
outside, thereby keeping clean air inside the container. 
For preventing the penetration of dust or the like from the outside of the 
sealed container, however, any gap between a cover and a body of the 
container must be sealed with a gasket. Therefore, it is necessary for the 
gasket to have both cleanness such that the gasket itself does not 
generate dust or the like, and sealing properties sufficient for 
preventing the external penetration of dust or the like. 
As the known gasket of this type, there have hitherto been gasket members 
molded from, or die-cut from a molded sheet of, neoprene rubber, urethane 
rubber, silicone rubber, nitrile-butadiene rubber or the like, and gasket 
members die-cut from foam sheets of these rubbers, polyolefin (e.g., 
polyethylene) or the like. 
In use of these conventional gaskets for constructing a cover-gasket 
assembly, it has been a common practice to store the gasket with a release 
paper attached thereto through a pressure sensitive adhesive and 
thereafter adhere the gasket to a predetermined position of a cover member 
for a hard disk device by removing the release paper, or to adhere the 
gasket to the cover member with an adhesive. The use of a pressure 
sensitive adhesive or an adhesive has been the cause of such troubles as 
staining of the cover for the hard disk device, generation of dust inside 
the hard disk device, and the like. 
In addition, accurate positioning in adhering the gasket member to a 
predetermined position of joint between the cover member and the container 
body of a hard disk device is extremely difficult to accomplish and 
requires skill, leading to higher manufacturing costs of cover-gasket 
assemblies. 
Furthermore, production of the die-cut gaskets needs cutting dies, and 
inevitably generates waste sheets (cutting wastes) which cannot be 
utilized. Thus, there arise an added increase in production cost and 
difficulties associated with disposal of waste sheets. 
The molded gaskets, on the other hand, not only need molds for the 
production thereof, leading to high production costs, but also have the 
disadvantage that an unsatisfactory deflashing upon molding will cause 
generation of dust in the hard disk device. 
In consideration of the above, the present inventors have made a proposal 
to apply a liquid addition-curable type silicone rubber composition, as a 
gasket, directly to a joint portion of a cover for a hard disk device 
(Refer to U.S. Pat. No. 4,950,521 and U.S. Pat. No. 5,147,691). According 
to the proposal, the gasket is formed without using a pressure sensitive 
adhesive, an adhesive or the like; therefore, the problem of generation of 
dust inside the hard disk device can be obviated effectively. In addition, 
neither a cutting die nor a mold is used for obtaining the gasket, which 
is advantageous economically and offers freedom from the generation of 
cutting wastes, flashes or the like. Thus, the gasket according to the 
proposal is highly advantageous over the conventional gaskets. 
However, in recent years there is a trend toward the use of hard disks with 
a sputtered magnetic film thereon and, in addition, the head-disk gaps 
have come to be set extremely narrow. As a result, there have been an 
increasing number of cases where troubles at head-disk gaps are caused not 
only by dust but also by bleedings, bloomings or condensates of volatile 
components coming out of the gasket material or the like. Of common gasket 
materials, silicone rubber is said to be the least liable to cause these 
troubles. Even in the case of silicone rubber gaskets, however, ordinary 
cured products of silicone rubber have the problem that low molecular 
weight siloxanes contained in the silicone rubber are evaporated and 
diffused in the hard disk device and are thereafter recondensed in 
head-disk gaps, leading to insufficient floating of the head above the 
disk surface and, eventually, to such troubles as head crash and 
destruction of magnetic disk surfaces. 
Besides, silicone rubbers have comparatively high moisture permeability 
coefficients on the order of 100 g.mm/m.sup.2.24 hr, and are 
unsatisfactory as to sealing properties against permeation of water vapor. 
Therefore, use of a silicone rubber gasket for a cover of a hard disk 
device restricts the environments in which the hard disk device can be 
used. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a 
cover-gasket assembly for a hard disk device comprising a gasket which 
shows evaporation of extremely small amounts of low molecular weight 
substances and has good sealing properties against permeation of water 
vapor, and a method of producing the same. 
It is another object of the present invention to provide a method of 
producing a cover-gasket assembly for a hard disk device without using a 
pressure sensitive adhesive, an adhesive, a cutting-die, a mold or the 
like. 
According to the present invention, there is provided a cover-gasket 
assembly for a hard disk device which comprises a gasket applied to a 
predetermined position of a cover for the hard disk device, wherein said 
gasket is formed of a cured product of a fluorosilicone rubber 
composition. 
The cover-gasket assembly according to the present invention is 
particularly excellent in sealing properties against permeation of water 
vapor, and can be used extremely effectively for hard disk devices for 
handy office-automation apparatuses such as laptop or pocket-size personal 
computers, word processors and the like which are expected to be used 
under various temperature and humidity conditions. 
In addition, according to the invention, it is possible to form a gasket by 
the FIPG (Formed In Place Gasket) method, that is to say, without needing 
a mold or a cutting die. Thus, according to the invention, the 
cover-gasket assembly can be mass-produced extremely advantageously on an 
economic basis. Moreover, the method according to the invention does not 
need an adhesion step, so that generation of dust arising from use of a 
pressure sensitive adhesive or an adhesive can be obviated effectively.

DETAILED DESCRIPTION OF THE INVENTION 
Fluorosilicone Rubber Composition 
In the present invention, a fluorosilisone rubber composition is used as a 
gasket material. That is, the gasket is formed of a cured product of the 
composition. The cured product generally has a low coefficient of moisture 
permeability of 40 g.mm/m.sup.2.24 hr or below, normally from 10 to 40 
g.mm/m.sup.2.24 hr, and hence good sealing properties against permeation 
of water vapor. Accordingly, a hard disk device comprising the 
cover-gasket assembly of the present invention can be used without special 
restrictions as to environmental conditions. 
As the fluorosilicone rubber composition, fluorosilicone rubber 
compositions of any curing type, for example, so-called addition-curing 
type or condensation-curing type, can be used, provided the compositions 
have a favorable moisture permeability coefficient. Among the usable 
fluorosilicone rubber compositions, particularly preferred are those 
curable compositions comprising (a) a fluorine-containing 
diorganopolysiloxane, (b) a filler, and (c) a curing agent. 
(a) Fluorine-Containing Diorganopolysiloxane 
The fluorine-containing diorganopolysiloxanes include, for example, the 
compounds having the following general formula (1): 
##STR1## 
wherein R.sup.1 and R.sup.2 may be the same or different from each other 
and are each an unsubstituted or substituted monovalent hydrocarbon group 
which does not have aliphatic unsaturated bonds, 
R.sup.3 is a monovalent aliphatic unsaturated hydrocarbon group, 
R.sup.4 is a divalent hydrocarbon group having no aliphatic unsaturated 
bonds or is a group represented by the following general formula (2): 
EQU --R.sup.5 --O--R.sup.6 -- (2) 
(wherein R.sup.5 and R.sup.6 are each a divalent hydrocarbon group having 
no aliphatic unsaturated bonds), 
Rf is a perfluoroalkyl group or a perfluoroalkyl ether group, 
X is a hydrogen atom or a group represented by the following general 
formula (3): 
##STR2## 
(wherein R.sup.7 may be same or different from each other and are each an 
unsubstituted or substituted monovalent hydrocarbon group), 
l and m are each an integer of 1 or above, and 
n is an integer of 0 or above. 
In the general formula (1), preferable examples of the unsubstituted or 
substituted monovalent hydrocarbon groups R.sup.1 and R.sup.2 are those 
having from 1 to 8 carbon atoms. More specific examples include alkyl 
groups such as methyl, ethyl, isopropyl, butyl, and the like; cycloalkyl 
groups such as cyclohexyl, cyclopentyl, and the like; aryl groups such as 
phenyl, tolyl, xylyl, and the like; aralkyl groups such as benzyl, 
phenylethyl, and the like; halogenated hydrocarbon groups such as 
chloromethyl, chloropropyl, chlorocyclohexyl, 3,3,3-trifluoropropyl, and 
the like; cyanohydrocarbon groups such as 2-cyanoethyl, and the like. 
Among these, particularly preferred in the present invention are methyl, 
ethyl, phenyl and 3,3,3-trifluoropropyl groups. 
The monovalent aliphatic unsaturated hydrocarbon group R.sup.3 includes, 
for example, vinyl, allyl, ethynyl, and the like groups, of which 
particularly preferred is the vinyl group. 
The divalent group R.sup.4 located intermediately between a silicon atom 
and the fluorine-containing organic group Rf is a divalent hydrocarbon 
group not having a aliphatic unsaturated bond or a group having an ether 
linkage which is represented by the above general formula (2). Specific 
examples of the group R.sup.4 include --CH.sub.2 --, --CH.sub.2 CH.sub.2 
--, --CH.sub.2 CH.sub.2 CH.sub.2 --, --(CH.sub.2).sub.6 --, 
--(CH(CH.sub.3)CH.sub.2).sub.2 --, --CH.sub.2 --O--CH.sub.2 --, --CH.sub.2 
CH.sub.2 CH.sub.2 --O--CH.sub.2 --, --CH.sub.2 --O--CH.sub.2 CH.sub.2 
CH.sub.2 --, --Y--, --CH.sub.2 --O--CH.sub.2 --Y--, (wherein Y is a 
p-phenylene group), and the like, of which particularly preferred are 
--CH.sub.2 CH.sub.2 --, --CH.sub.2 CH.sub.2 CH.sub.2 --, and --CH.sub.2 
CH.sub.2 CH.sub.2 --O--CH.sub.2 --. 
The fluorine-containing organic group Rf is a perfluoroalkyl group or a 
perfluoroalkyl ether group. The perfluoroalkyl groups which can be used 
include, for example, those having the following general formula (4): 
EQU C.sub.p F.sub.2p+1 -- (4) 
wherein p is an integer from 4 to 10, preferable examples including those 
having the general formula (4) wherein p is 6, 8 or 10. 
On the other hand, preferable perfluoroalkyl ether groups for use as the 
fluorine-containing organic group Rf include those having from 5 to 15 
carbon atoms, most preferable examples including 
C.sub.3 F.sub.7 OCF(CF.sub.3)--, 
C.sub.3 F.sub.7 OCF(CF.sub.3)CF.sub.2 OCF(CF.sub.3)--, 
C.sub.2 F.sub.5 OCF.sub.2 CF.sub.2 --, 
C.sub.3 F.sub.7 OCF(CF.sub.3)CF.sub.2 OCF.sub.2 --, 
C.sub.3 F.sub.7 OCF(CF.sub.3)CF.sub.2 OCF.sub.2 CF.sub.2 --, 
and the like. 
In the general formula (1), X is a hydrogen atom or a group represented by 
the above general formula (3). In the general formula (3), namely, 
EQU --Si(R.sup.7).sub.3 (3) 
(wherein R.sup.7 may be the same or different from each other and are each 
an unsubstituted or substituted monovalent hydrocarbon group), the group 
R.sup.7 includes, for example, the monovalent hydrocarbon groups not 
having an aliphatic unsaturated bond which are mentioned above for 
R.sup.1, and alkenyl groups such as vinyl, allyl, hexenyl, and the like. 
In the present invention, particularly preferred examples of X include 
hydrogen atom, (CH.sub.3).sub.3 Si--, (CH.sub.2 .dbd.CH) (CH.sub.3).sub.2 
Si--, and the like. 
In the general formula (1) above, l is an integer of 1 or above, 
preferably, an integer from 100 to 10,000, and n is an integer of 0 or 
above. 
It is preferable that m/(l+m+n) has a value in the range from 1/50 to 1/3. 
In the fluorine-containing diorganopolysiloxane as above, aliphatic 
unsaturated groups such as vinyl or the like are not necessarily contained 
in the structural units, as is understood from the value of n in the 
general formula (1). Such unsaturated group is needed only where curing is 
accomplished through addition reaction; namely, such unsaturated group is 
not necessary where curing is carried out by use of an organic peroxide. 
The fluorine-containing diorganopolysiloxane is preferably a liquid 
material having a viscosity at 25.degree. C. in the range from 100 to 
10,000,000. Such fluorine-containing diorganopolysiloxanes can be used 
either singly or in combination of two or more. These fluorine-containing 
diorganopolysiloxanes can be produced by a method which is known per se. 
In the present invention, fluorine-containing diorganopolysiloxanes 
deprived of volatile components by a treatment at a temperature of 
100.degree. C. or above and a reduced pressure of 10.sup.-1 mmHg or below, 
or by extraction with solvent or the like, are preferably used. 
Particularly preferred for use in the invention are those 
fluorine-containing diorganopolysiloxanes in which the content of cyclic 
polysiloxanes with a molecular weight of 3,000 or below is 0.01% by weight 
or below, preferably 0.005% by weight or below. 
(b) Filler 
As a filler in the composition according to the present invention, various 
fillers ordinarily used in general silicone rubber compositions can be 
used suitably. For example, reinforcing fillers such as fumed silica, 
precipitated silica, carbon powder, titanium dioxide, aluminum oxide, 
ground quartz, talc, sericite, bentonite, and the like, fibrous fillers 
such as asbestos, glass fibers, organic fibers, and the like can be used. 
These fillers are generally compounded preferably in an amount of from 10 
to 300 parts by weight, more preferably from 20 to 200 parts by weight, 
per 100 parts by weight of the diorganopolysiloxane of component (a). If 
the amount of the fillers is less than 10 parts by weight, a satisfactory 
reinforcing effect is not obtainable. If the amount exceeds 300 parts by 
weight, on the other hand, mechanical strength of the cured product 
obtained may be lowered. 
(c) Curing Agent 
As the curing agent compounded in the fluorosilicone rubber composition for 
use in the present invention, organic peroxides and 
organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen 
atoms in their molecule can be used. 
As the organic peroxide, a variety of organic peroxides conventionally used 
for so-called organic-peroxide crosslinking can be used. Specific examples 
of the usable organic peroxides include benzoyl peroxide, 
2,4-dichlorobenzoyl peroxide, 4-monochlorobenzoyl peroxide, dicumyl 
peroxide, tert-butyl benzoate, tert-butyl peroxide, 
2,5-dimethyl-2,5-bis(tert-butyl peroxy)hexane, cumyl-tert-butyl peroxide, 
and the like. These may be used either singly or in combination of two or 
more. The organic peroxides are generally used preferably in an amount of 
from 0.2 to 5 parts by weight per 100 parts by weight of the component 
(a). 
The above-described organohydrogenpolysiloxane is used for forming a cured 
product by addition reaction, particularly where the diorganopolysiloxane 
of the component (a) has an aliphatic unsaturated group. That is, the 
cured product is formed through addition of SiH groups in the 
organohydrogenpolysiloxane to the aliphatic unsaturated groups in the 
component (a). 
As the organohydrogenpolysiloxane, any one of organohydrogenpolysiloxanes 
having at least two silicon-bonded hydrogen atoms their molecule can be 
used. Particularly, the compounds having the following formulas (c-1) to 
(c-4): 
##STR3## 
(wherein in the above formulas, R.sup.2, R.sup.4 and Rf are the same as 
defined above, s and t are each an integer of 0 or above, and u is an 
integer of 2 or above), and copolymers comprised of (CH.sub.3).sub.2 
HSiO.sub.0.5 units and SiO.sub.2 units are used preferably. 
Generally, these organohydrogenpolysiloxanes preferably have a viscosity at 
25.degree. C. of 1,000 cSt or below. 
The organohydrogenpolysiloxanes are generally used preferably in an amount 
such that the number of the SiH groups is at least one, more preferably 
from 1 to 5, per one aliphatic unsaturated hydrocarbon group (R.sup.3 in 
the general formula (1)) in the component (a). 
In the present invention, furthermore, where an organohydrogenpolysiloxane 
is used as the curing agent, a platinum group metal catalyst is used as a 
curing catalyst. Such catalysts include platinum catalysts, palladium 
catalysts, and rhodium catalysts. Particularly, platinum catalysts, for 
example, platinum black, chloroplatinic acid, complexes of chloroplatinic 
acid with an olefin (e.g., ethylene), alcohol, ether, aldehyde, 
vinylsilane, vinylsiloxane or the like, catalysts comprising platinum 
powder supported on an alumina, silica, asbestos or other carrier, and the 
like are used preferably. These curing catalysts are generally used 
preferably in an amount of from 1 to 500 ppm, particularly from 5 to 20 
ppm, in terms of platinum group metal based on the component (a). 
Other Components 
Into the fluorosilicone rubber composition comprising the above-described 
components (a) to (c), various additives which are known per se can be 
compound, provided that they do not produce bad effects on the moisture 
permeation resistance of the cured product obtained from the composition. 
For instance, dispersing agents such as diphenylsilanediol, 
hydroxyl-endblocked low-molecular-weight dimethylpolysiloxanes, 
hexamethyldisilazane and the like, thermal resistance improving agents 
such as ferrous oxide, ferric oxide, cerium oxide, iron octylate and the 
like, coloring agents such as pigments, and the like can be compounded, as 
required. 
Besides, in order to further enhance the adhesion between the 
fluorosilicone rubber composition used in the present invention and the 
cover member, adhesion aids such as the compounds having the following 
formulas: 
##STR4## 
(wherein in the above formulas, e, f, g, h, i and j are each a positive 
integer) can be compounded in the composition, as required. These adhesion 
aids generally are used preferably in an amount of from 0.01 to 5 parts by 
weight per 100 parts by weight of the component (a). 
The fluorosilicone rubber composition used in the present invention can be 
prepared easily by uniformly mixing necessary components described above. 
In general, however, in order to ensure that the composition retains its 
as-applied shape after application to a cover member, it is preferable to 
control the viscosity of the composition at 25.degree. C. to within the 
range from 100 to 10,000,000 cSt by regulating the amounts of the 
components in the above-described respective ranges. Besides, for reducing 
stress loads on the cover member attached to a predetermined container, it 
is preferable to regulate the amount of the curing agent compounded in the 
composition so that the cured product of the composition has a hardness Hs 
(measured on a Type A spring hardness tester according to JIS K 6301) in 
the range from 10 to 60. It is also preferable that the cured composition 
is so conditioned that the content of cyclic polysiloxanes with a 
molecular weight of 3,000 or below is 0.01% by weight or below, more 
preferably 0.005% by weight or below. 
Production of Cover-Gasket Assembly 
The cover-gasket assembly for a hard disk device according to the present 
invention is produced by applying the above-described fluorosilicone 
rubber composition to a predetermined position of a cover for the hard 
disk device and then curing the composition. 
The fluorosilicone rubber composition used in the present invention can be 
conveyed by a pump, and the application and curing of the composition, for 
instance, can be carried out by an FIPG (Formed In Place Gasket) method, 
in which a combination of a coating robot, a feed pump and a dispenser is 
used. That is, according to the FIPG method, the fluorosilicone rubber 
composition is supplied to a predetermined position by the feed pump, is 
then ejected onto a cover member by the dispenser and, simultaneously, 
applied by the coating robot in accordance with a preliminarily stored 
pattern, and is cured to form a gasket. 
The gasket formed in this manner can be made to have a semi-circular, flat 
or other cross-sectional shape, by controlling suitably the ejection 
conditions for the rubber composition. 
According to the method, the position at which the gasket is formed can be 
set with extremely high accuracy. 
The curing of the composition is carried out quickly by heating or the 
like, as required. After the cure, if necessary, a cleaning treatment such 
as washing with water, cleaning with air stream, drying and the like is 
carried out. 
The cover-gasket assembly thus obtained is united to a hard disk container 
by fastening with screws or the like, whereby a hard disk device is 
produced. Because the cured product constituting the gasket has an 
appropriate hardness, stresses exerted on the cover are reduced 
effectively. 
In addition, the gasket has an extremely low coefficient of moisture 
permeability and, hence, good sealing properties against permeation of 
water vapor. 
EXAMPLES 
Examples of the present invention will now be described below, in which 
"parts" means "parts by weight". 
Composition Example 1 
One hundred (100) parts of a fluorosilicone oil having the following 
formula: 
##STR5## 
0.5 part of 2,4-dichlorobenzoyl peroxide (curing agent), 30 parts of 
trimethoxysiloxyl-treated fumed silica (reinforcing agent), 0.5 part of 
carbon black (coloring agent) and 1.0 part of cerium dioxide (thermal 
resistance improving agent) were mixed uniformly, to prepare a 
fluorosilicone rubber composition having a viscosity at 25.degree. C. of 
800,000 cSt. 
The composition, after cured at 150.degree. C. for 60 minutes, had general 
physical properties and a moisture permeability coefficient as shown in 
Table 1. 
Measurements of the general properties of the cured product were carried 
out according to JIS K 6301, and measurement of moisture permeability 
coefficient was carried out according to the condition B (temperature: 
40.degree..+-.0.5.degree. C.; relative humidity: 90.+-.2%) of JIS Z 0208. 
Composition Example 2 
One hundred (100) parts of a fluorosilicone rubber having the following 
formula: 
##STR6## 
0.5 part of an alcoholic 2 wt. % solution of chloroplatinic acid (curing 
catalyst), 15 parts of trimethoxysiloxyl-treated fumed silica (reinforcing 
agent), 0.5 part of carbon black (coloring agent), and 0.7 part of cerium 
dioxide (thermal resistance improving agent) were mixed uniformly, to 
prepare a fluorosilicone rubber composition having a viscosity at 
25.degree. C. of 1,000,000 cSt. 
The composition, after cured at 150.degree. C. for 60 minutes, had general 
properties and a moisture permeability coefficient as shown in Table 1. 
TABLE 1 
______________________________________ 
Properties of Composition 
Composition 
cured product Example 1 Example 2 
______________________________________ 
General properties: 
Hardness 50 25 
Elongation (%) 300 350 
Tensile strength (kg/cm.sup.2) 
48 37 
Tear strength (kg/cm.sup.2) 
9 7 
Moisture permeabiliy 
30 35 
coefficient (g .multidot. mm/m.sup.2 .multidot. 24 hr) 
______________________________________ 
Hardness measurement was carried out on a Type A spring hardness tester 
according to JIS K 6301. 
EXAMPLE 1 
Using an FIPG machine equipped with a coating robot (produced by Yasukawa 
Denki Seisakusho K.K., product code: K10S), a feed pump (produced by 
Hyoshin Sobi K.K., product code: 3NTL-08/Mark II) and a dispenser (Hyoshin 
Sobi K.K., product code 4NDP-04), the fluorosilicone composition prepared 
in the above Composition Example 1 was applied, in accordance with a 
preliminarily stored pattern, to an aluminum top cover whose surface had 
been coated with an epoxy resin by cationic electrode-position coating. 
The coating by the FIPG machine was carried out under the conditions of a 
dispenser nozzle inside diameter of 1.69 mm, a dispenser rotor revolution 
frequency of 30 rpm, a coating rate of 200 cm/min, and a dispenser nozzle 
height (from the cover surface) of 2.20 mm. 
After the coating operation was over, the composition was cured by 
maintaining it in a hot-air dryer at 150.degree. C. for 60 min. 
After the curing was completed, the cover was taken out of the dryer and 
was cooled to room temperature, whereby a gasket having a semi-circular 
cross-sectional profile 1.50 mm in height and 2.00 mm in width was formed. 
A perspective view of the cover-gasket assembly thus obtained is shown in 
FIG. 1, together with a cross-sectional view of the gasket. 
In the cover-gasket assembly, the gasket formed was adhered to the cover 
satisfactorily firmly. 
The cover-gasket assembly was washed with purified water conditioned by use 
of a 0.5 .mu.m filter to have an electric conductivity of 10 .mu.S or 
below, and was air dried in a room having a cleanliness of 100 (0.3 
.mu.m). Subsequently, while maintaining this cleanliness, the cover-gasket 
assembly was united to a hard disk container, thereby fabricating a hard 
disk device. 
The hard disk device thus obtained was excellent in cleanness. When the 
atmosphere inside the device was pressurized to 100 mmH.sub.2 O and the 
internal pressure was measured after a lapse of time of 1 min, the 
pressure value was 99 mmH.sub.2 O, indicating good sealing performance of 
the device. 
EXAMPLE 2 
Using the same FIPG machine as in Example 1, the fluorosilicone composition 
prepared in Composition Example 2 was applied to an aluminum top cover 
equivalent to that used in Example 1. The coating operation was carried 
out under the conditions of a dispenser nozzle inside diameter of 1.30 mm, 
a dispenser rotor revolution frequency of 25 rpm, a coating rate of 100 
cm/min, and a dispenser nozzle height (from the cover surface) of 1.0 mm. 
After the coating was over, the composition was cured in a hot-air dryer at 
160.degree. C. for 60 min. 
After completion of the curing, the cover was taken out of the dryer and 
cooled to room temperature, whereby a gasket having a flat-top 
cross-sectional profile 1.0 mm in height and 1.5 mm in width was formed. A 
perspective view of the cover-gasket assembly thus obtained is shown in 
FIG. 2, together with a cross-sectional view of the gasket. 
In the cover-gasket assembly, the gasket formed was found in satisfactorily 
firm adhesion to the cover. 
When the cover-gasket assembly was washed in the same manner as in Example 
1 and a hard disk device was fabricated using the assembly, the hard disk 
device obtained was also excellent in cleanness and sealing performance.