U.S. patent application number 11/317992 was filed with the patent office on 2006-07-06 for container assembly and method for humidity control.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Afshin Falsafi, Brian N. Holmes, Dong Wu.
Application Number | 20060144733 11/317992 |
Document ID | / |
Family ID | 36639125 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060144733 |
Kind Code |
A1 |
Wu; Dong ; et al. |
July 6, 2006 |
Container assembly and method for humidity control
Abstract
A container assembly has a material storage container defining a
sealed chamber therein. A quantity of moisture-sensitive material
is disposed in the chamber. The moisture-sensitive material has a
desired range of moisture content. A hydrated humidity control
substance is also disposed within the chamber, and the humidity
control substance is in humidity-transferable communication with
the chamber. The humidity control substance regulates a relative
humidity within the chamber in order to maintain a moisture content
of the moisture-sensitive material within the desired range of
moisture content.
Inventors: |
Wu; Dong; (Woodbury, MN)
; Holmes; Brian N.; (St. Paul, MN) ; Falsafi;
Afshin; (Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
36639125 |
Appl. No.: |
11/317992 |
Filed: |
December 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60640558 |
Dec 30, 2004 |
|
|
|
60640975 |
Jan 3, 2005 |
|
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Current U.S.
Class: |
206/368 |
Current CPC
Class: |
B65D 43/162 20130101;
B65D 81/266 20130101 |
Class at
Publication: |
206/368 |
International
Class: |
B65D 83/10 20060101
B65D083/10 |
Claims
1. A container assembly comprising: a container defining a sealed
chamber therein; a quantity of moisture-sensitive material for
healthcare use disposed in the chamber, wherein the
moisture-sensitive material has a desired range of moisture
content; and a hydrated humidity control substance, wherein the
humidity control substance is disposed within the chamber and is in
humidity-transferable communication with the chamber, and wherein
the humidity control substance regulates a relative humidity within
the chamber in order to maintain a moisture content of the
moisture-sensitive material within the desired range of moisture
content.
2. The container assembly of claim 1, wherein the humidity control
substance is a silica gel.
3. The container assembly of claim 2, wherein the silica gel is a
buffered silica gel.
4. The container assembly of claim 1, wherein the humidity control
substance has a preferred buffering range of between 10 percent to
about 100 percent relative humidity.
5. The container assembly of claim 4, wherein the humidity control
substance has a preferred buffering range of between 30 percent to
about 75 percent relative humidity.
6. The container assembly of claim 4, wherein the humidity control
substance has a preferred buffering range of between about 30
percent to about 60 percent relative humidity.
7. The container assembly of claim 1, wherein the
moisture-sensitive material is a dental material.
8. The container assembly of claim 7, wherein the dental material
is selected from a group consisting of glass ionomers, resin
modified glass ionomers, dental adhesives, orthodontic adhesives,
cements, restoratives, coatings, varnishes, sealants, and composite
crowns.
9. The container assembly of claim 7, wherein the
moisture-sensitive material is one or more capsules, each capsule
containing a dental composition therein.
10. The container assembly of claim 1, wherein the container can be
opened and is selectively resealable.
11. The container assembly of claim 1 wherein the container has a
single opening for access to the chamber therein, and wherein the
container has a cap for resealably covering the opening.
12. The container assembly of claim 11 wherein the cap is flexibly
attached to the container.
13. A method for controlling a relative humidity inside a
container, where the container is for retaining a
moisture-sensitive material for healthcare use, the method
comprising: hydrating a humidity control substance to a desired
moisture content; introducing the humidity control substance into a
chamber of the container in a humidity controlled environment;
introducing the moisture-sensitive material into the chamber of the
container in the humidity controlled environment; and sealing the
container.
14. The method of claim 13, wherein the step of hydrating
comprises: selecting a desired relative humidity of the chamber of
the container as a function of the moisture-sensitive material to
be stored in the chamber of the container; selecting a desired
moisture content of the humidity control substance as a function of
the desired relative humidity of the chamber of the container;
placing the humidity control substance in a constant humidity
environment, where the environment is set at the desired relative
humidity; removing the humidity control substance from the constant
humidity environment and placing the humidity control substance in
a sealed space; and testing a moisture content of the humidity
control substance to determine whether the humidity control
substance has the desired moisture content.
15. The method of claim 13 wherein, prior to introducing the
humidity control substance into the chamber of the container, an
amount of humidity control substance that should be used in the
container is determined by estimating a potential moisture loss
from the container.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/640,558, filed Dec. 30, 2004 and U.S.
Provisional Application No. 60/640,975 filed Jan. 3, 2005.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a container and method for
retaining a moisture-sensitive material. More specifically, the
present invention relates to a container that has a
moisture-sensitive material and a humidity control substance, where
the humidity control substance regulates a relative humidity within
a chamber of the container in order to help the moisture-sensitive
material maintain a desired range of moisture content.
[0003] Moisture-sensitive materials, such as pharmaceutical
products, are often stored in hermetically and waterproof
resealable containers. When opened for access to those materials,
however, there may be an exchange of moisture between the air
inside the container and the air outside the container. There may
also be an exchange of moisture between the air inside the
container and the air outside the container if there is an air leak
in the container. The exchange of moisture may adversely affect the
properties of the moisture-sensitive material stored in the
container. The quality of moisture-sensitive material may be
affected if the moisture level (also known as the "humidity level")
of the air inside the container falls below or rises above a
desired level, in part because the moisture content of the
moisture-sensitive material may change. For this and other reasons,
many manufacturers place an off-the-shelf humidity control
substance in the container to act as a desiccant and adsorb any
excess moisture from the air inside the container.
[0004] The desiccant may be any material that adsorbs moisture from
the air, such as, but not limited to wood, cotton, bentonite clay,
silica gel, montmorillonite clay, molecular sieve, calcium oxide,
calcium sulfate, glycerol, sorbitol, sodium PCA, or propylene
glycol. The desiccant may be used to help keep the air inside the
container at or below a desired moisture level by removing excess
moisture from the air inside the container.
[0005] The desiccant may be placed directly in a chamber of a
material storage container so that there is nothing separating the
desiccant substance from the moisture-sensitive material. However,
the desiccant is often packaged in a container ("inner container"
or "canister") that has holes in it or a membrane designed to allow
moisture into or out of the inner container and keep the desiccant
(often in particle form) from leaking out of the inner container.
The inner container may be formed of a rigid or non-rigid material.
The inner container is usually placed inside a chamber of the
material storage container, in order for the desiccant to be in
humidity transferable communication with the chamber (and hence,
the moisture-sensitive materials stored therein).
[0006] Off-the-shelf inner containers having a desiccant to adsorb
any excess moisture from the air inside the chamber of the material
storage container have been used. An "off-the-shelf" inner
container being an inner container containing a preset amount of
desiccant, where the desiccant has a preset moisture content. When
an off-the-shelf inner container is used, the manufacturer or
bottler of the moisture-sensitive material has little control over
the moisture level inside the chamber of the material storage
container, and the manufacturer or bottler can only maintain a
generally dry environment. This may be undesirable if the
moisture-sensitive material needs to be stored at a specific
moisture level in order to maintain its quality and/or if the
moisture-sensitive material is readily affected by a large change
in moisture level.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention is a container assembly for retaining
a moisture-sensitive material. The container assembly has a
container defining a sealed chamber. A humidity control substance
is disposed within the chamber of the container and is in
humidity-transferable communication with the chamber. The humidity
control substance regulates a relative humidity within the chamber
of the container in order to help the moisture-sensitive material
maintain a desired range of moisture content.
[0008] In one aspect, the present invention is a container assembly
including a container defining a sealed chamber therein, a quantity
of moisture-sensitive material for healthcare use disposed in the
chamber, the moisture-sensitive material having a desired range of
moisture content, and a hydrated humidity control substance
disposed within the chamber. The humidity control substance is in
humidity-transferable communication with the chamber and regulates
a relative humidity within the chamber in order to maintain a
moisture content of the moisture-sensitive material within the
desired range of moisture content.
[0009] In another aspect, the present invention is a method for
controlling a relative humidity inside a container for retaining a
moisture-sensitive material for healthcare use. The method includes
hydrating a humidity control substance to a desired moisture
content, introducing the humidity control substance into a chamber
of the container in a humidity controlled environment, introducing
the moisture-sensitive material into the chamber of the container
in the humidity controlled environment, and sealing the
container.
[0010] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The FIGURE and the detailed description that
follow more particularly exemplify illustrative embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will be further explained with
reference to FIG. 1, which is a perspective view of an exemplary
embodiment a container assembly in accordance with the present
invention.
[0012] While the above-identified FIGURE sets forth one embodiment
of the invention, other embodiments are also contemplated, as noted
in the discussion. In all cases, this disclosure presents the
invention by way of representation and not limitation. It should be
understood that numerous other modifications and embodiments can be
devised by those skilled in the art, which fall within the scope
and spirit of the principles of the invention.
DETAILED DESCRIPTION
[0013] The present invention is a container assembly having a
material storage container for retaining a moisture-sensitive
material, where a desired moisture level is controlled inside a
chamber of the container by a humidity control substance. The
humidity control substance regulates the moisture level inside the
chamber of the container (i.e., buffers changes in moisture level)
in order to maintain a moisture content of the moisture-sensitive
material within a desired range of moisture content. The
moisture-sensitive material may be any healthcare-related material,
including, but not limited to, pharmaceutical products, medical
products and devices, or dental materials or products, such as, but
not limited to one or more capsules containing a dental material
composition or dental materials, such as, but not limited to, glass
ionomers, resin modified glass ionomers, dental adhesives,
orthodontic adhesives, cements, restoratives, coatings, varnishes,
sealants, and/or composite crowns.
[0014] The moisture level or humidity level is often expressed in
terms of relative humidity ("RH"). Relative humidity may be defined
as the ratio of the water vapor density of the air to the
saturation water vapor density of the air, and is usually expressed
in percent.
[0015] Many moisture-sensitive materials contain moisture, and thus
have a moisture content. The moisture content is the weight of
water in a material expressed as a percentage of its dry weight. If
the moisture-sensitive material is hygroscopic, the moisture
content may differ depending upon the temperature and/or the RH of
the air surrounding the moisture-sensitive material. If the
temperature or the RH of the surrounding air changes, the moisture
content of the moisture-sensitive material may change so that it
will come into equilibrium with the new condition of the
surrounding air.
[0016] If the moisture content of the moisture-sensitive material
falls below a desired level, the properties and quality of the
moisture-sensitive material may be adversely affected. The present
invention addresses the problems that may arise with a change in
moisture content of a moisture-sensitive material due to a change
in RH of the air surrounding the moisture-sensitive material when
the moisture-sensitive material is stored in a material storage
container of a container assembly. The present invention allows
storage of moisture-sensitive materials in a material storage
container assembly that has a RH that remains within a desired
range.
[0017] If there is an exchange of air between a material storage
container and the air surrounding the container due to air leakage
or another reason, the RH inside a chamber of the material storage
container may increase or decrease, depending upon the RH of the
air surrounding the container. For example, if the RH inside the
chamber is lower than the RH surrounding the container and there is
an exchange of air, the RH inside the chamber may increase.
Similarly, if the RH inside the chamber is higher than the RH
surrounding the container and there is an exchange of air, the RH
inside the chamber may decrease. The amount of the increase or
decrease in RH inside the chamber of the container depends upon the
amount of air that is exchanged. The increase or decrease in RH
inside the chamber of the container may adversely affect the
quality and shelf-life of the moisture-sensitive material stored in
the chamber of the container because the moisture-sensitive
material within the chamber may gain or lose some moisture content
in order to remain in equilibrium with the RH of the air inside the
chamber.
[0018] It may be preferred to store moisture-sensitive material
(whether for shipping, storing, and/or during use), such as dental
capsules 18 of FIG. 1, in an environment having a stable RH in
order to limit the gain or loss of moisture content of the
moisture-sensitive material. In an exemplary embodiment of the
present invention, a stable RH is defined as a humidity level that
stays within 10% of the desired RH. However, a stable humidity
level may differ depending upon many variables, including the type
of moisture-sensitive material that is to be stored in the
container. A person skilled in the art may modify the desired
stable RH.
[0019] A humidity control substance may be used to regulate the RH
of the air inside the chamber in order to address the problems that
may be associated with the possible gain or loss of moisture
content of the moisture-sensitive material that arise with a change
in RH of the air inside the chamber. The humidity control substance
may be any material that adsorbs moisture from the air and/or any
hygroscopic ("water-pulling") material that promotes retention of
moisture, such as, but not limited to, wood, cotton, bentonite
clay, silica gel, montmorillonite clay, molecular sieve, calcium
oxide, calcium sulfate, glycerol, sorbitol, sodium PCA, or
propylene glycol. The humidity control substance may be used to
help the moisture-sensitive material maintain its moisture content
by either adding or subtracting moisture to the air inside the
container in order to maintain a stable RH. When the humidity
control substance subtracts moisture from the air inside the
container, it acts as a desiccant; when the humidity control
substance adds moisture to the air inside the container, it acts as
a humectant.
[0020] The humidity control substance buffers RH changes within a
container of a container assembly during shipping and storage of
the moisture-sensitive material. In this way, the humidity control
substance helps the moisture-sensitive material retain its moisture
content within a desired range of moisture content. By helping the
moisture-sensitive material retain its moisture content, the
humidity control substance may help the moisture-sensitive material
retain its properties as well as extend a shelf-life of the
moisture-sensitive material, even if the container is opened and
closed numerous times. A preferred buffering range for the humidity
control substance is a range between about 10% RH to about 100% RH.
A buffering range for a humidity control substance is the range of
RH for which the humidity control substance can buffer RH changes,
either by releasing moisture into the air inside the container or
by adsorbing moisture from the air inside the container. The
buffering range of a humidity control substance depends on the
buffering capacity, M.sub.H, at different RH values, and most
humidity control substances have an "optimum" RH range in which the
M.sub.H value is high. In order to provide effective RH control
("buffering effect"), it is preferred that the humidity control
substance have a high M.sub.H value over the desired RH range for
the particular moisture-sensitive material being stored. It is
preferred that a container assembly in accordance with the present
invention be used for storing moisture-sensitive materials that
should be stored at an RH between about 10% to about 100% RH. A
more preferred buffering range is about 30% RH to about 75% RH. A
most preferred buffering range is about 30% RH to about 60% RH.
[0021] The amount of humidity control substance that should be used
in the container assembly may be calculated by first estimating a
maximum expected amount of potential moisture loss (or a value
close to the maximum) that the humidity control substance needs to
compensate for. The maximum expected amount of potential moisture
loss is the maximum amount expected for the particular container in
the conditions in which the container assembly is reasonably
expected to be used. The amount of potential moisture loss
(W.sub.WATER) for the particular in the particular conditions is
calculated as a function of the moisture concentration (in grams
per pound of dry air) at the minimum tolerated RH inside the
container (C.sub.INSIDE), the moisture concentration (in grams per
pound of dry air) at the RH of the air surrounding the container
(C.sub.OUTSIDE), and the time the container assembly is reasonably
expected to be used to store the moisture-sensitive material (T).
Moisture concentration is measured as a function of the absolute
humidity of the air being measured. Both C.sub.INSIDE and
C.sub.OUTSIDE depend upon the temperature of the air inside and
outside the container, respectively. Similarly, the minimum
tolerated RH of the air inside the container also depends upon the
temperature inside the chamber of the container because moisture
level in the air is dependent on temperature.
[0022] The following formula may be used to calculate the potential
moisture loss that the humidity control substance may need to
compensate for: W.sub.WATER=K(C.sub.INSIDE-C.sub.OUTSIDE).times.T K
is the moisture transmission constant of a specific container, and
for the first exemplary embodiment, K is calculated as
8.2.times.10.sup.-6 (pound of dry air/day). Those skilled in the
art can calculate K for a container that is to be used in a
particular container assembly. It may not be possible to accurately
calculate the moisture concentration of the air surrounding the
container (C.sub.OUTSIDE) because the exact conditions in which the
container will be shipped, stored, and/or used may not be known.
However, for purposes of estimating the maximum (or near maximum)
potential moisture loss inside the chamber of the container,
C.sub.OUTSIDE may be estimated by estimating the RH and temperature
of the air outside the container at which the moisture content is
near the lowest possible moisture content at which the container
will be shipping, stored, and/or used.
[0023] After the potential moisture loss of the air inside the
chamber is calculated, the amount of humidity control substance
that should be used can be calculated using the following formula:
W.sub.HCS=(W.sub.WATER/[M.sub.H(RH.sub.START-RH.sub.END)])*1000.
[0024] W.sub.HCS is the quantity of the humidity control substance
(e.g., silica gel) that should be used in order to help maintain a
desired RH range in the chamber of the container, W.sub.WATER is
the amount of potential moisture loss inside the chamber that was
calculated using the formula discussed above, and M.sub.H, the
buffering capacity of a humidity control substance, which may
differ depending upon the type of humidity control substance used.
Specifically, M.sub.H is the average amount of water (in grams)
that is gained or lost by one kilogram (kg) of the humidity control
substance for each one percent change in RH. A M.sub.H value may
also depend upon the range of RH the humidity control substance is
regulating. For example, a regular density silica gel has a higher
M.sub.H when it is buffering a RH range having a maximum RH at or
below about 60% RH. RH.sub.START is the RH inside the chamber of
the container when the moisture-sensitive material is first placed
inside the chamber. RH.sub.END is the minimum tolerated RH the
moisture-sensitive material may be stored at before its quality is
affected.
[0025] Either before or after the amount of humidity control
substance that is required is calculated and measured out, the
humidity control substance may be hydrated (or "conditioned") to a
desired moisture content. The humidity control substance may be
hydrated prior to being introduced into the chamber of the
container. The proper moisture content of the humidity control
substance is usually a moisture content which will allow the
humidity control substance to maintain a RH of the air inside the
chamber of the container within a range of desired RH, which is
also, typically, the approximate range of RH at which the
moisture-sensitive material should be stored in order to maintain
its desired range of moisture content. The desired moisture content
of the humidity control substance will differ depending upon the
desired RH range and the buffering capacity of the humidity control
substance. In the present invention, the moisture content of the
humidity control substance may depend on the RH level at which it
is hydrated because different humidity control substances may
adsorb different quantities of moisture at the same RH level. If it
is known that the container assembly is going to be shipped,
stored, and/or otherwise used in a dry environment, the humidity
control substance should probably be hydrated to a moisture level
that will provide near the top of the desired RH range because it
is likely that the container will lose more moisture to the
surrounding air than if the container were shipped, stored, and/or
otherwise used in a more humid environment.
[0026] One method of hydrating the humidity control substance is by
placing the humidity control substance in a constant humidity
environment, such as a sealed room or oven, where the humidity of
the environment is set within the desired RH range. The humidity
control substance should be left in the constant humidity
environment long enough for the humidity control substance to
become sufficiently hydrated. After the humidity control substance
is removed from the constant humidity environment, its moisture
content may be measured or tested to ensure the humidity control
substance has been sufficiently hydrated. The moisture content of
the humidity control substance is measured by placing the humidity
control substance in a sealed space with a measuring instrument,
such as a hygrometer. If the humidity control substance is not
sufficiently hydrated, the hydrating process may be repeated; the
humidity control substance may be placed in the constant humidity
environment again and retested until the humidity control substance
has the correct moisture content. The resulting moisture content of
the humidity control substance will differ depending upon the type
of humidity control substance used because, as stated above,
different humidity control substances will adsorb different
quantities of moisture at the same RH level.
[0027] If a hydrated humidity control substance has a moisture
content that provides a higher than proper RH for the particular
container assembly, the humidity control substance may be dried,
such as by using an oven. If after the drying process, the humidity
control substance has a finite moisture content, i.e. it is not
"bone dry", it may still be considered "hydrated". In the present
invention, a "hydrated" humidity control substance is any humidity
control substance that has a moisture content that allows it to
buffer a RH range between about 10% RH to about 100% RH.
[0028] For moisture-sensitive materials that should be stored at
around 40%-60% RH, such as dental capsules 18 of FIG. 1, silica gel
is a preferred humidity control substance. The most optimum
buffering range for silica gel is between 40-60% RH. That is,
silica gel has relatively high M.sub.H at a RH between about 40% to
about 60%. Silica gel is a porous, granular, chemically inert,
amorphous form of silicon dioxide, which is capable of adsorbing
and desorbing water vapor in order to reach equilibrium with the
surrounding air. Furthermore, most silica gels have an infinite
life in terms of the ability to adsorb or desorb moisture, and may
be reconditioned and reused indefinitely. There are many different
types of silica gel that may be used in the present invention.
Those skilled in the art may select a silica gel based upon the
silica gel's buffering capacity, the type of container assembly,
and/or the type of moisture-sensitive material that is going to be
stored in the container assembly.
[0029] Different configurations of silica gel may be used for
purposes of regulating a RH in a container assembly. For example,
loose silica gel may be used in the container assembly, or the
silica gel may be contained in an inner container, such as a
flexible packet or a rigid container, which is then introduced into
a chamber of a container of the container assembly. If loose silica
gel is used, a membrane may be used to isolate the loose silica gel
from the moisture-sensitive material stored in the bottle. A rigid
container may be a tin or canister. The different configurations of
silica gel may also apply to all humidity control substances in
accordance with the present invention. In the present invention, a
preferred configuration of silica gel for use in a container
assembly for retaining moisture-sensitive materials that should be
stored at around 40%-60% RH is silica gel contained in a canister.
However, any other configuration may also be used.
[0030] Fungal growth may also be a concern when storing
moisture-sensitive materials in a humid environment Fungi generally
require at least 60%-65% RH for growth. Thus, the container
assembly of the present invention should not support fungal growth
as long as the RH in the chamber of the container remains lower
than about 60%.
[0031] FIG. 1 is a perspective view of an exemplary embodiment of a
container assembly in accordance with the present invention.
Container assembly 10 is formed of container 12, canister 14, and
cap 16. Container assembly 10 may be used for storing a
healthcare-related moisture-sensitive material, such as, but not
limited to a pharmaceutical product, medical product, medical
device, or dental product. Examples of dental products that may be
used in accord with the present invention include one or more
capsules containing a dental material composition, glass ionomers,
resin modified glass ionomers, dental adhesives, orthodontic
adhesives, cements, restoratives, coatings, varnishes, sealants,
and/or composite crowns. More particularly, the moisture-sensitive
material may be stored in chamber 13, which is defined by cap 16
and the bottom and side walls of container 12. In the embodiment
shown in FIG. 1, chamber 13 is sealed by cap 16.
[0032] Container 12 and canister 14 may be formed of any material
that does not react with the moisture-sensitive contents of chamber
13, such as, but not limited to, a plastic material or a glass
material. Container 12 and/or canister 14 may also be formed of a
transparent material (as shown for container 12 in FIG. 1).
Container 12 and canister 14 may also be formed of the same
material, but it is not required for the present invention.
Although container 12 is shown to be formed in a
cylindrically-shaped bottle, container 12 may be formed in any
other shape, such as, but not limited to, a square or rectangular
box.
[0033] A plurality of dental capsules 18 are stored in chamber 13
of container 12. An example of dental capsules 18 that may be
stored in the chamber of the container of the present invention is
3M ESPE Z100 MP Restorative System, available from 3M Company, St.
Paul, Minn., which is sold as nylon capsules containing dental
restorative filling material. Nylon capsules containing dental
restorative filling material should be stored at a RH within a
range of about 40% RH to about 60% RH. Although FIG. 1 shows a
plurality of dental capsules 18 stored in container assembly 10,
any type of healthcare-related moisture-sensitive material may be
used with the present invention, including pharmaceutical products,
medical products, medical devices, and other dental products (or
materials), such as, but not limited to, glass ionomers, resin
modified glass ionomers, dental adhesives, orthodontic adhesives,
cements, restoratives, coatings, varnishes, sealants, and/or
composite crowns. If a glass ionomer or resin modified glass
ionomer is stored in container 12, it is preferred that chamber 13
of container 12 have a RH in a range of about 70% to about 90%.
[0034] A humidity control substance may be stored in canister 14.
Canister 14 may also be known as an "inner container". Canister 14
of FIG. 1 is formed in a cylindrical shape. However, canister 14
may be any shape and/or size that minimizes interference with the
transfer of dental capsules 18 into or out of chamber 13 of
container 12. It may also be preferred to size canister 14 such
that it is not easily removable from container 12. In an alternate
embodiment, canister 14 may be formed of a flexible material, such
as in a pillow-shaped pouch.
[0035] The air inside chamber 13 may be set at a desired RH at the
time the moisture-sensitive material is deposited inside chamber
13. As container assembly 10 is used, the RH inside chamber 13 may
change, depending upon many factors, including how many times cap
16 is opened and closed, the amount of air that leaks through a
joint defined by cap 16 and container 12, and the RH of the air
outside of container 12. Even before container assembly 10 is
opened by a consumer, the RH of the air inside chamber 13 may
change. For example, if a seal is formed under cap 16 (such as a
foil layer) or over cap 16 after moisture-sensitive material is
"bottled" inside container 12 (where the seal is to be broken or
removed by the consumer when container assembly 10 reaches the
consumer), some moisture may still leak through the seal.
[0036] In general, if the RH of the air surrounding container 12 is
not the same as the RH inside chamber 13 and there is air leakage,
moisture may transfer between chamber 13 and the surrounding air.
Not only may air transfer through possible leaks in the joint
between cap 16 and container 12, air may also transfer when cap 16
is opened (through self-sealing flip-top 17 or otherwise), which
may cause the RH inside chamber 13 to increase or decrease beyond
the desired RH range. An increased or decreased RH inside chamber
13 may compromise the quality of dental capsules 18 contained in
chamber 13. The humidity control substance may be used to address
an excess or insufficient moisture problem by giving up moisture to
a drier atmosphere and absorbing moisture from a humid atmosphere.
More specifically, the humidity control substance inside canister
14 may be used to address an excess moisture problem by adsorbing
some or all of the excess moisture to regulate the RH inside
chamber 13 within a desired range. That is, if the RH in chamber 13
of container 12 exceeds a certain level, the humidity control
substance will adsorb the excess moisture. Similarly, the humidity
control substance may also release moisture into chamber 13 if the
RH inside chamber 13 falls below a desired RH range. In this way,
the humidity control substance may be used to help dental capsules
18 retain their moisture content by maintaining a desired range of
RH in chamber 13. In this way, the humidity control substance
buffers RH changes inside chamber 13.
[0037] A plurality of openings 15 in canister 14 provide a channel
for humidity transferable communication between the humidity
control substance and chamber 13. That is, openings 15 allow the
humidity control substance to either extract or input moisture into
chamber 13 of container 12. Openings 15 may be shaped such that the
humidity control substance (often in particle form) does not leak
from canister 14, or another mechanism may be provided to prevent
such leakage, such as a permeable membrane. It may be important to
keep substantially all of the humidity control substance sealed in
canister 14, because if the humidity control substance contacts
dental capsules 18 (or other moisture-sensitive material), the
quality of dental capsules 18 may be compromised. The humidity
control substance contained in canister 14 helps to keep the dental
capsules 18 fresher and may also extend a shelf-life of dental
capsules 18, even if container 12 is opened and closed numerous
times. The humidity control substance should be designed to
maintain the environment inside container 12 at the desired
moisture level for as long as container assembly 10 is reasonably
expected to be used to store the dental capsules 18.
[0038] Cap 16 provides a selectively resealable opening for access
to chamber 13. Cap 16 may be formed of any material that does not
react with the moisture-sensitive contents of chamber 13, such as,
but not limited to, a plastic material or a glass material. Cap 16
does not necessarily have to be formed of the same material as
container 12. In one embodiment, cap 16 has a flip top 17 that is
connected to main body 20 of cap 16 by flexible connection 22.
Flexible connection 22 may be any connection that allows flip top
17 to be opened and closed a plurality of times without breaking,
such as, but not limited to, a living hinge. Flip top 17 allows
container 12 to be selectively resealed once it has been opened.
When flip top 17 is lifted (as shown in FIG. 1), opening 24 is
exposed, and a consumer may extract dental capsules 18 contained in
chamber 13 of container 12 through opening 24. Flip top 17 allows a
user to easily access the contents of container 12 without removing
cap 16.
[0039] Cap 16 may be attached to container 12 by any method known
in the art. For example, cap 16 may be "popped" onto container 12
by an interference friction fit, or cap 16 may be a twist-on cap.
Although FIG. 1 shows container assembly 10 having cap 16 with flip
top 17, cap 16 may be any resealable mechanism. For example, cap 16
may just twist on without having a flip-top. However, a flip-top
arrangement may reduce the possibility of a consumer losing cap 16
because cap 16 does not have to be removed in order to access the
contents of container 12.
[0040] In the embodiment shown in FIG. 1, it is preferred that
dental capsules 18 containing a dental composite material be stored
in a container assembly having a RH range of about 30% RH to about
50% RH. Assuming one or more 3M ESPE Z100 MP Restorative System
capsules are stored in container 12, container 12 has a volume of
about 60 cubic centimeters, the RH outside container 12 is 15% at
25.degree. C., the minimum tolerated RH inside container 12 is 30%
at 25.degree. C., K for container 12 is 8.2.times.10.sup.-6 (pound
of dry air/day) and container 12 is reasonably expected to be used
for 180 days, the potential moisture loss of container 12 the
silica gel contained in canister 14 may need to compensate for
(W.sub.WATER) in order to store dental capsules 18 such that dental
capsules 18 retain a desired range of moisture content, is
calculated using the formula discussed above
(W.sub.WATER=K(C.sub.INSIDE-C.sub.OUTSIDE).times.T):
W.sub.WATER=[(8.2.times.10.sup.-6)(41.9 grams/pound of dry air-20.9
grams/pound of dry air)].times.180 days=0.031 grams
[0041] Using the amount of potential moisture loss, the quantity of
silica gel that should be used in order to help maintain a desired
RH range in chamber 13 of container 12 for can be calculated using
the following table (which is also discussed above):
W.sub.HCS=(W.sub.WATER/[M.sub.H(RH.sub.START-RH.sub.END)])*1000.
For purposes of the calculation, RH.sub.START is 50% RH, where
RH.sub.START is the RH inside chamber 13 of container 12 when
dental capsules 18 are introduced into chamber 13, and RH.sub.END
is 30% RH, where RH.sub.END is the minimum tolerated RH dental
capsules 18 may be stored at before their quality is affected.
[0042] The quantity of silica gel will differ depending upon
M.sub.H, the buffering capacity of the type of silica gel used. The
following table shows the minimum quantity of silica gel (which is
dried before hydration) needed for three different types of silica
gel having three different buffering capacities: TABLE-US-00001
TABLE 1 Quantity of Silica Gel Type of Silica Gel M.sub.H W.sub.HCS
(in grams) Type A 2.0 0.78 Type B 4.5 0.34 Type C 8.7 0.178
[0043] Either before or after the amount of silica gel that is
required is measured out, the silica gel may be hydrated if
necessary. As discussed above, the silica gel may be hydrated by
placing the silica gel in a constant humidity room set at a desired
RH.
[0044] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
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