Stock material or miscellaneous articles – Sheet including cover or casing – Foamed or expanded material encased
Reexamination Certificate
1996-04-08
2001-06-26
Davis, Jenna (Department: 1771)
Stock material or miscellaneous articles
Sheet including cover or casing
Foamed or expanded material encased
C428S076000, C428S220000, C428S354000
Reexamination Certificate
active
06251493
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a one-piece vibration attenuating article that has a non-tacky film covering enclosing all or a significant portion of the surface of a vibration attenuating material, wherein at least a portion of the vibration attenuating material's surface covered by the film covering is a three dimensional surface. The articles can be used in numerous applications where vibration or shock attenuation is required, including, but not limited to, disk drive applications, automotive applications, and electronics applications.
BACKGROUND OF THE INVENTION
Vibrations and/or shocks can excite resonant frequencies in structures. Damping and/or isolation can be used to reduce the vibration and shock effects.
Applications where vibration and shock control are particularly important include disk drive applications, actuator voice coil motor applications, computer shock isolation applications, car applications, shock isolator applications for drawers or doors, and the like.
As a specific example, resonant vibrations or shocks in a disk drive can be caused by the read-write actuator voice coil motor assembly. An actuator is used in a disk drive to very quickly and precisely position the read/write element over the data track of a spinning disk. The actuator voice-coil motor design most often used to position the transducer can often generate vibrations that lead to excessive acoustical noise that is irritating to users of the disk drive. These vibrations can also impair the positioning or stability of the read-write transducer over the desired data track, thus reducing the drive's performance.
FIG. 1
illustrates a partial exploded view of a disk drive with only a few key features shown for clarity.
FIG. 1
shows top cover
2
, a bottom cover
4
, and a top magnetic plate of the voice coil motor
6
. A damper which would be used to damp vibrations within the disk drive could be positioned on the top magnetic plate of the voice coil motor
6
. The damper location is indicated as
8
. A more detailed description of a disk drive and actuator voice coil motor is found in U.S. Pat. No. 5,224,000.
One method of damping such an actuator is to use a damper which is a die cut part of damping material that is placed in key areas which experience vibration to add damping to the actuator motor assembly. (See
FIG. 2
where the die cut part of damping material is represented by
10
, the top cover of the disk drive is
2
, and the top magnetic plate of the voice coil motor is
6
.) Typically, the damper is placed between a portion of the motor assembly and an outer surface, such as the drive's cover or base. Known dampers often use a damping material with a tacky surface associated with the polymer that can make their use difficult.
Known die cut dampers are typically from 0.025 mm (1 mil) thick to over 3.81 mm (150 mils) thick. These die cut dampers have essentially flat top and bottom surfaces and straight die cut side edges that are essentially perpendicular to the top and bottom surfaces of the damper. The vibration damper may optionally have a polymeric film layer, for example, a die cut piece of polyester or polyethylene film, attached to the damper with a pressure sensitive adhesive. The add on polymeric film covers only the top portion of the flat top damper. This polymeric film layer can be the same size as the damper top surface area or extend past the top surface edges. (See
FIGS. 2
a
and
2
b,
respectively. In
FIG. 2
a
the polyethylene film is
16
, the pressure sensitive adhesive is
14
, the damping material is
12
, the disk drive cover is
2
, and the top magnetic plate of the voice coil motor is
6
. In
FIG. 2
b
the polyethylene film is
22
, the pressure sensitive adhesive is
20
, the damping material is
18
, the disk drive cover is
2
, and the top magnetic plate of the voice coil motor is
6
.) Neither the surface of the film in contact with the damper, nor the damper surface with which the film is in contact, is three dimensional. The films do not offer any significant damping benefit as compared to the damping material and the main benefit the film does provide is to provide a tack-free surface on a single flat surface of the damper that will not bond to other surfaces it contacts.
Two-piece “damping” constructions that use a damper and a separate die cut film part have been used in disk drive systems where a damper (a die cut section of damping polymer) has a film (a polyethylene polymeric film with a pressure sensitive adhesive on one side) attached to a surface opposite from that which the damper is placed on, such that when the drive is assembled, the damper and film are in contact (See
FIG. 2
c,
wherein the polyethylene polymeric film is
26
, the pressure sensitive adhesive is
28
, the damping polymer is
24
, the top cover of the disk drive is
2
, and the top magnetic plate of the voice coil motor is
6
). The film provides a surface to which the damper will have a fairly weak bond so that the drive can be easily opened and reworked. The surface of this film in contact with the damper is not three dimensional, nor does it contact a three dimensional surface of the damper.
SUMMARY OF THE INVENTION
These known dampers provide for significant reductions in acoustical noise as well as vibration levels. However, problems with these known dampers include the inability to use low Tg damping materials effectively because they may be tacky at room temperature or at disk drive use temperatures. Additional problems with the current dampers include poor outgassing, difficulty in dimensional control, etc. These and other problems are expanded upon in detail hereafter:
1) Known dampers not used in conjunction with a polymeric film attached opposite the dampers (See
FIG. 2
) can build a strong bond to the surfaces they come into contact with (such as such as the cover or base surface of a drive). This makes reworking of the drive difficult as the drive may be difficult to reopen due to the strong bond which may have been formed.
2) A damper that has a film attachment coextensive with the top surface of the damper, can experience “blooming” whereby the damping polymer expands past the edge of the film during use creating a situation where the damping polymer can still create a significant bond in an undesired location. When compressed into position, the damping polymer expands around the film allowing a bond to form to an undesired surface (See
FIG. 2
d
wherein the polymeric film is
30
, the pressure sensitive adhesive is
32
, and the damping polymer is
34
). Using thicker films to limit this is not practical for thick dampers and could make the dampers difficult and more costly to manufacture.
3) Dampers with a polymeric film (such as a polyester film) extended over the edges of the damper (See
FIG. 2
b
) are difficult to handle and costly to manufacture as the larger film is die cut and attached via pressure sensitive adhesive to the damper or the damper is pre-cut and subsequently attached via pressure sensitive adhesive to the film.
4) Dampers that use a separate film die cut part attached to an opposite surface in the drive (to prevent high degree of bonding) prior to assembly of the drive require an additional part to manufacture and apply to the drive (See
FIG. 2
c
).
5) Often low Tg damping materials have a tacky surface associated with the damping material, unless a sufficient degree of crosslinking is present in the polymer to render them tack-free. The polymers that have been rendered tack-free by high levels of crosslinking (greater than or equal to about 0.5%) have a higher rubbery region modulus than a similar polymer not so highly crosslinked. The mechanical strength of the damping polymer may also be reduced due to the high level of crosslinking.
These highly crosslinked tack-free polymers will not stress relax as quickly or to as low a level as less highly crosslinked damping polymers. This retention of stress in highly crosslinked polymers is detrimental in applications where the damper is ini
Johnson Gordon G.
Jung Michael A.
Landin Donald T.
McCutcheon Jeffrey W.
3M Innovative Properties Company
Davis Jenna
Trussell James J.
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