U.S. patent application number 11/515076 was filed with the patent office on 2008-03-27 for heat sealing pressure monitoring system.
This patent application is currently assigned to Bausch & Lomb Incorporated. Invention is credited to Trevor O'Neill.
Application Number | 20080072550 11/515076 |
Document ID | / |
Family ID | 39223431 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080072550 |
Kind Code |
A1 |
O'Neill; Trevor |
March 27, 2008 |
Heat sealing pressure monitoring system
Abstract
The method provides for monitoring pressure applied by a heat
sealing tool. The heat sealing tool seals a lidstock to the flange
of a rigid polymeric container with a well containing a contact
lens and an aqueous storage solution. The flange includes an upper
sealing surface and a lower surface. The tool includes a first
plate adapted to contact the lower surface of the flange and a
second plate adapted to press the lidstock against the sealing
surface of the flange.
Inventors: |
O'Neill; Trevor; (Waterford,
IE) |
Correspondence
Address: |
Bausch & Lomb Incorporated
One Bausch & Lomb Place
Rochester
NY
14604-2701
US
|
Assignee: |
Bausch & Lomb
Incorporated
|
Family ID: |
39223431 |
Appl. No.: |
11/515076 |
Filed: |
September 1, 2006 |
Current U.S.
Class: |
53/478 |
Current CPC
Class: |
B29C 66/8748 20130101;
B29L 2031/7164 20130101; B29C 66/542 20130101; B29C 66/81422
20130101; B29C 66/131 20130101; B29C 66/112 20130101; B29C 66/81423
20130101; B29C 66/9241 20130101; B29C 66/9674 20130101; B65B 51/14
20130101; B29C 66/81431 20130101; B29C 66/8322 20130101; B29C
66/9231 20130101; B29C 66/92211 20130101; B29C 66/7234 20130101;
B29C 65/18 20130101; B29C 66/8161 20130101; B29C 66/72321 20130101;
B29C 66/849 20130101 |
Class at
Publication: |
53/478 |
International
Class: |
B65B 51/10 20060101
B65B051/10 |
Claims
1. A method comprising monitoring pressure applied by a heat
sealing tool, wherein said heat sealing tool seals a lidstock to a
rigid polymeric container comprising a well containing a contact
lens and a storage solution, and a flange with an upper sealing
surface and a lower surface, wherein the tool comprises a first
plate adapted to contact the lower surface of the flange and a
second plate adapted to press the lidstock against the sealing
surface of the flange.
2. The method according to claim 1, wherein the first plate
elevates the container and the second plate is heated.
3. The method according to claim 2, wherein the first plate is in
connection with a pressure transducer that measures pressure
applied by the first and second plates to the container flange and
lidstock.
4. The method according to claim 3, wherein the pressure transducer
is connected to a controller.
5. The method according to claim 1, wherein the second plate is
curved with an identical curvature as the sealing surface of the
flange.
6. The method according to claim 1, wherein the first plate is
curved with substantially the same curvature as the lower surface
of the flange.
7. The method according to claim 1, further comprising setting off
an alarm if the monitored pressure is not within a predetermined
range during the heat sealing operation.
Description
FIELD OF THE INVENTION
[0001] The invention relates to heat sealing tools for sealing
lidstock to plastic containers to form sealed packages,
particularly disposable packages for contact lenses known as
blister packages. Especially, this invention relates to monitoring
the pressure applied in sealing lidstock to such plastic
containers.
BACKGROUND OF THE INVENTION
[0002] Soft hydrogel contact lenses have been increasing in
popularity ever since they were first introduced in the 1970's.
Such contact lenses are conventionally packaged in the hydrated
state and in a storage solution. Many contact lenses are packaged,
along with the aqueous storage solution, in a disposable blister
package typically formed from a rigid polymer. Examples of blister
packages can be seen in U.S. Pat. Nos. 4,691,820; 5,524,419;
5,578,331, 5,649,410, 5,722,536 and 6,082,533. The base of a
blister package can either be part of the original contact lens
mould or a separately moulded base, typically formed from a rigid
polymer. In the above mentioned package types, the base that
contains the contact lens and any aqueous storage solution, is
sealed by a flexible lidstock. This lidstock is typically a
laminated foil which can be pulled back by a user to access the
lens contained in the base. Typically, this lidstock is sealed to
the area surrounding the portion of the base containing the contact
lens. This sealing area of the base has typically been a
substantially flat surface area, or a raised flattened annular
surface as seen, for example, in U.S. Pat. No. 5,722,536.
SUMMARY OF THE INVENTION
[0003] The sealing tool for sealing the lidstock to the flange of a
plastic container typically has a lower face which supports the
container directly below the flange, and an upper face which
presses the lidstock against the surface sealing surface of the
flange of the package, supported by the lower face which is in
contact with the lower surface of the flange of the package.
Typically, the upper face is heated in order to provide a seal by
melting a thermoplastic basal layer of the lidstock to the sealing
surface of the flange.
[0004] This invention provides a method of monitoring the pressure
applied to an individual blister package during heat sealing of
lidstock to the flange of the package.
[0005] The sealing tools may have flat faces where they contact the
lidstock and lower surfaces of the flange of the package for
sealing. Alternately, and according to preferred embodiments, the
sealing tool may have curved faces, for example, with substantially
the same curvature as the sealing surface of the flange of the
package.
[0006] The invention will now be further described, by way of
example only, with reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows an exploded view of a tool according to the
invention with a sealed blister pack between the plates of the
tool. The curvature of the surfaces has been exaggerated for
purposes of illustration.
[0008] The lower first plate 1 of the tool has a recess 2 in the
first face 8 to accommodate well 7 of the blister pack as sealing
takes place. The lidstock 5 is in contact with the upper sealing
surface of the flange 4 of blister pack 6. The first face 8 is
curved with the same curvature as the lower surface of the flange
4. The second face 9 of the upper second plate 3 of the tool is
curved with the same curvature as the upper sealing surface of the
flange 4.
[0009] Accordingly, lower first part I of the tool serves to
elevate the blister pack so that the lidstock 5 contacts the second
face 9 of upper second part 3. Lower first part 1 includes a servo
driven block 10 to elevate the blister pack. This lower first part
1 further includes spring 11 and pressure transducer 12. Pressure
transducer 12 is connected to a controller, shown schematically as
13, so that pressure the applied pressure, detected by transducer,
can be monitored. If desired, the controller 13 may be further
connected to a display so that an operator can observe real-time
operation of the heat sealing unit.
[0010] It may be desired to heat seal several blister packs
concurrently, with the blister packs arranged in an array. However,
when this is done, it is preferred that the heat sealer for each
blister pack is monitored individually.
Detailed Description of Preferred Embodiments
[0011] According to preferred embodiments of this invention, the
blister package has the form of a rigid polymeric container
comprising a well and a flange. The flange has a curved upper
sealing surface and a lower surface. The heat sealing tool
comprises a first plate adapted to contact the lower surface of the
flange and a second plate adapted to press the lidstock against the
sealing surface of the flange, wherein the second plate is curved
with substantially the same curvature as the sealing surface of the
flange. Preferably, the first plate is also curved with
substantially the same curvature as the lower surface of the
flange, as illustrated schematically in FIG. 1. Ideally the second
plate is curved with an identical curvature as the sealing surface
of the flange and the first plate is curved with an identical
curvature as the lower surface of the flange.
[0012] By providing the second plate with substantially the same
curvature as the curved sealing surface of the flange, when the
second plate comes into contact with the lidstock to press the
lidstock against the sealing surface of the flange, substantially
uniform contact time and contact pressure will be delivered over
the sealing surface of the flange, leading to greater uniformity in
the strength of the seal over the entire flange. This uniformity
may be further improved by providing the first plate with
substantially the same curvature as the lower surface of the
flange, such that as the plates are squeezed together sandwiching
the lidstock and the flange, substantially uniform pressure is
applied over the entire sealing surface of the flange over the
entire time span of the sealing process.
[0013] Suitably, in use, the first plate is not heated and is at
ambient temperature, while the second plate is heated to a suitable
temperature such that a hermetic seal is formed by heat transmitted
through the lidstock when the plates are brought together to
sandwich the lidstock and flange.
[0014] The lidstock is suitably a laminated foil with a basal layer
which melts to form a seal when heated in contact with the sealing
surface of the flange. Preferably, the upper layer of the laminated
foil is a surface upon which printing may be carried out. A
suitable upper layer is a metal foil such as aluminium foil.
[0015] The container is suitably moulded from a rigid polymer, for
example a thermoplastic polymer such as polypropylene or
polystyrene. The container comprises a well for holding a soft
contact lens immersed in an aqueous, storage solution, and has a
flange around the well to which the lidstock is sealed to form the
sealed package. The flange may simply be the top surface of the
package itself, or may be in the form of a raised area surrounding
the well and provided on the top surface of the package. The
sealing surface of the flange may be all or part of the upper
surface of the flange, provided the sealing surface surrounds the
well such that when a seal is made, the contents of the well are
hermetically sealed. The nature of the moulding process can lead to
the top surface of the package and hence the flange, and the
sealing surface of the flange, having a concave or a convex upper
surface. This may arise from uneven shrinkage of the polymer
forming the container during the moulding process to form the
well.
[0016] Where the container starts as a flat sheet of polymer and
then is moulded simply to form a well, leaving the remaining
surface as the flange of the well, the upper sealing surface of the
flange and the lower surface of the flange will be endowed with the
same curvature as a result of the uneven tensions set up in the
moulding process, but with the upper surface being concave and the
lower surface convex or vice versa.
[0017] In order to better control the strength of the seal made by
heat sealing tools according the invention, it is preferred the
tools are calibrated such that when the first and second plates are
brought together to sandwich the lidstock and the flange of the
container, the force applied is controlled within a preferred
range. Such a calibration may be achieved by means of pressure or
displacement readings on the plates, and associated calculation
formulae. However, a preferred method is to use a strain sensing
load cell (such as a semiconductor load cell) mounted into a
replica blister package with the surface of the load cell at the
same position as the sealing surface of the blister package to be
used with the tool of the invention. The replica blister package is
mounted onto the first plate and then the first and second plates
are brought together to their normal sealing position and the
applied force shown by a display monitor connected to the load
cell. The normal sealing position may then be adjusted and set to
give the required sealing force as shown by the display.
[0018] The method of the present invention is directed not to such
calibration operations, but to monitoring the pressure applied to
individual blister packs and their lidstock during the heat sealing
process. In other words, the method of this invention allows for
monitoring the heat sealing process to ensure that the desired,
proper pressure, determined initially by calibration, was applied
in sealing a blister package. It will be appreciated that the heat
sealing unit is used to sequentially seal multiple blister packs.
Over time, a heat seal unit may fail to apply this desired, proper
pressure, whereas this invention allows for ensuring that the
desired pressure was applied. And because the container includes a
sterile storage solution, it is important that a hermetic seal is
obtained for each package.
[0019] This invention provides several practical applications. As
an example, the controller may be programmed to set off an alarm if
a pressure within a predetermined range was not applied during the
heat sealing operation. Accordingly, such an alarm serves to alert
an operator to check integrity of the heat seal applied to that
package and/or to confirm whether maintenance of the heat sealing
unit is required.
* * * * *