A transparent enclosure having an internal cavity divided into
two portions, the first of which is designed to accept and hermetically
seal a container. The second is designed to accept and hold a mixture
of a desiccant and a humidity sensitive color indicator. The first
and second portions of the cavity are separated by a barrier wall
which contains a filter in the central area of the wall. The filter
comprises a porous area in the barrier wall and is formed of a wicking
polymer that conducts the humidity within the container to the desiccant
and humidity sensitive color indicator, drying the contents of the
container and causing the color indicator to provide a visual indication
of the humidity within the container. The peripheral surface of
the barrier wall is designed to engage and seal the barrier wall
within the cavity in order to physically isolate the contents of
the container from the desiccant, while providing a means by which
the moisture within the container may be extracted by the desiccant.
Having described our invention, we claim:
1. A desiccant cap for a container, comprising:
(a) a transparent, substantially nonporous plastic enclosure means
having a generally cylindrical cavity with a closed end, the cavity
being formed about a reference axis of revolution, and the cavity
being partially threaded internally begining about its open end
to accept and seal an opening in the container having mating external
threads, the threads within the cavity extending into the cavity,
but terminating before reaching the closed end of the cavity,
(b) a mixture of desiccant and a humidity sensitive color indicator
placed within the cavity adjacent the closed end beyond the termination
of the threads, the color indicator being visible through the enclosure
walls to indicate the humidity level within the cavity and container,
(c) a shoulder extending inwardly of and completely about the periphery
of the cavity wall adjacent the termination of the threads, the
shoulder providing a bearing surface positioned adjacent the termination
of the threads, generally orthogonal to the reference axis of revolution,
and facing the open end of the cavity, and
(d) a generally disc shaped barrier means with a diameter generally
equal to that of the cavity, the barrier means formed of a wicking
polymer and having a central area filter containing fine through
pores, the barrier means being positioned within the cavity abutting
and sealed to the bearing surface of the shoulder to separate the
mixture of desiccant and humidity sensitive color indicator from
the container and its contents, while permitting water vapor from
the container to pass through the pores to maintain a dry atmosphere
within the container and actuate the color indicator to indicate
the level of humidity absorbed from the container, the extraction
of water vapor from the container through the pores being aided
by the characteristic of the wicking polymer.
2. Apparatus as claimed in claim 1 wherein the barrier means further
(a) threads about the periphery of the barrier means to mate with
the threads within the cavity,
(b) slot means, located on one side of the barrier means, the slot
means having two side walls spaced apart for accepting a tool between
the walls to drive the barrier means on the threads in the cavity,
the pressure developed in threading the barrier means against the
shoulder providing a seal between the barrier means and the shoulder.
3. Apparatus as claimed in claim 2 wherein the slot means includes
a taper in the side walls of the slot which widens the slot with
depth to accept tools that enable pick up and threading of the barrier
4. Apparatus as claimed in claim 1 wherein the barrier means includes
a projection on one side adjacent to and extending about the entire
periphery of the barrier means, the projection including blind pores
to provide a more compliant area than the unpored area of the barrier
means to aid in sealing the container within the cavity.
5. Apparatus as claimed in claims 1 or 4 wherein the barrier means
includes in the area abutting the shoulder, a plurality of blind
pores to provide a more compliant area than the unpored area of
the barrier means to aid in sealing the barrier means to the shoulder.
The present invention pertains to means for dehumidification of
containers and, more particularly, to container caps incorporating
2. Prior Art
There are many and varied applications for desiccant caps intended
to provide a low humidity atmosphere within an associated container.
Materials requiring such protection include pharmaceuticals, seeds,
food and machinery. The need for a reliable cap can be exemplified
by the effect of moisture on special seeds, such as ornamental cactus
seed. A relatively small bottle of these seeds may cost as much
as $500. A short period of exposure to a moist atmosphere results
in the sprouting and eventual destruction of the seeds. Damage is
similarly incurred with many expensive pharmaceuticals when exposed
to a humid atmosphere for a relatively short period of time.
A number of desiccant caps, bags and cartridges have been designed
to overcome these problems as indicated by U.S. Pat. Nos. 1425790
1637656 1655248 2317882 2446361 2487620 2548168
2676078 3820309 and 3990872. The cap devices usually include
a preforated metal holder for a desiccant which is either held together
by a binder, such as asbestos, or separated from the container by
a fibreglass sheet. In some cases the fibreglass is eliminated and
only the preforated shield is used to isolate the desiccant from
the container contents.
The results of these approaches has been inadequate. The dehumidification
is short lived and the desiccant and carcenogenic materials, such
as asbestos and fibreglass comingle with the container contents.
The contents are often food and pharmaceuticals, making the use
of such devices a serious health and product liability problem.
Attempts to avoid the use of desiccant caps by way of hermetically
sealed caps embodying no desiccant have been found to be unsatisfactory.
Such caps rarely provide a true hermetic seal. Even where a hermetic
seal is achieved initially, the cap backs off over a period of time
due to expansions and contractions of the cap caused by normal variations
in ambient temperature.
In a number of prior art devices which use desiccants, an indication
of the state of the desiccant cannot be determined by visual inspection,
or if visual inspection is possible, the cap must be removed to
make the inspection, resulting in detrimental exposure of the contents
Some of the more sophistocated and expensive reusable caps do have
humidity indicators which may be observed without opening the container,
but they generally require that each individual container be picked
up in order to observe the condition of the desiccant through the
top of the cap, making it impractical to carry out a rapid determination
of the state of humidity during shelf life.
Important disadvantages of prior art desiccator caps include high
cost and the inability to have the state of the humidity rapidly
determined while in storage. The inability to inspect rapidly generally
increases the cost of storage, and where the cap must be opened
for inspection, the storage life of the contents is appreciably
shortened. The high cost of prior art devices is primarily due to
the many machining operations required to produce the caps. In some
cases, the expense is justified where the caps are intended for
reuse. However, reuse is not practical for pharmaceuticals because
of the possibility of contamination.
A prior art, low cost substitute designed to overcome the cost
problem is the desiccant bar or cartridge which is simply inserted
in the container along with the pharmaceuticals. Unfortunately,
the bag or cartridge provide no indication of the humidity within
the container and the humidity reducing capacity of such devices
is limited. Where large bags or cartridges are used to extend useful
life, they reduce the holding capacity of the container in proportion
to their size. In addition, near sighted people have swollowed the
pill sized desiccants, mistaking them for medication contained in
similar sized capsules. As reported in the May 1980 issue of the
Journal of the American Medical Association desiccants that are
mistaken for capsules containing medication and are swollowed, result
in gastrointestinal obstructions, requiring surgical removal in
a number of cases.
It is an object of the present invention to provide a cap containing
a desiccant and an indicator of moisture content which may be viewed
while in shelf storage to provide a rapid determination of the state
of humidity within an associated container without the need to individually
remove each container for inspection.
It is an object of the present invention to provide a desiccant
containing cap which aids in the extraction of moisture from a container
by incorperating a filter between the desiccant and the contents
of the container that is fabricated from a wicking polymer.
It is an object of the present invention to speed production, reduce
component cost as well as overall cost of a desiccant cap, by incorperating
a self gasketing filter.
It is an object of the present invention to provide a low cost
desiccator cap that permits disposal after use to avoid contamination
The present invention comprises a substantially nonporous, transparent
plastic enclosure having a cavity divided into two portions. The
first portion is designed to accept and hermetically seal a container,
while the second portion is designed to accept and hold a mixture
of a desiccant and a humidity sensitive indicator. The two portions
are separated by a barrier wall containing a porous filter fabricated
from a wicking polymer. The filter passes moisture within the container
to the desiccant for absorption, but isolates the desiccant and
color indicator from the container contents.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional, side elevation view of a first embodiment
of the invention illustrating the position of the filter and barrier
wall which separates the color indicator and desiccant from the
contents of the container.
FIG. 2 is a top view of the cap showing the position of the desiccant
and the color indicator within the cap.
FIG. 3 is a top view of the filter and the barrier wall.
FIG. 4A is a side elevation view of a barrier wall and filter which
includes threads at its periphery for securing the filter within
FIG. 4B is a side elevation view of a barrier wall and filter embodiment
designed for direct insertion within a cap without threading.
FIG. 4C is a side elevation view of a barrier wall design for direct
bonding to the enclosure and for use with an external gasket.
FIG. 5A is a bottom view of a barrier wall embodiment having slots
in the peripheral projection for automatic insertion.
FIG. 5B is a side elevation view of the barrier wall of FIG. 5A
showing a taper in the slot side walls.
FIG. 5C is an enlarged view of the slot shown in FIG. 5B with an
automatic tool positioned within the slot.
FIG. 5D is a side elevation view of the tool shown in FIG. 5C with
the pawls positioned for insertion.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 the present invention is shown to comprise
a transparent, nonporous cap enclosure 101 with a closed ended
generally cylindrical cavity 109 formed about a reference axis
of revolution of the cap enclosure. A mixture of a humidity sensitive
color indicator and a desiccant 103 (typically silica gel) are
positioned adjacent the closed end of the cavity. The mixture of
the desiccant and color indicator are separated from the contents
of an associated container, such as container 105 by means of a
disc shaped barrier wall and filter 102 which extends across the
opening of the cavity 109. The cap is typically attached to the
container by securing means, such as internal threads 104 which
extend from the open end a portion of the distance towards the closed
The barrier wall is connected about its periphery to a bearing
surface 110 on a shoulder 113 located on the inner walls of the
cavity to completely seal the desiccant and indicator in the cavity.
The bearing surface is positioned generally orthogonal to the axis
of revolution of the cavity. The centrally located filter area 106
contains a number of fine pores which will not pass the humidity
indicator or the contents of the container, preventing comingling
of the container contents with the desiccant; however, the moisture
content within the atmosphere in the container may pass through
the filter pores in the barrier wall to the desiccant, where it
is absorbed, maintaining the container at low humidity.
The color indicator is also exposed to the moisture content within
the container by way of the filter pores and by virtue of its contact
with the desiccant. Since the entire cap enclosure is transparent,
the color indicator can be seen through various portions of the
cap, including the sides and top. In view of this feature, the state
of humidity within the container can be ascertained visually at
a distance, eliminating the need to pick up each individual container,
or open the container, as was required by the prior art. This feature
is especially advantageous when used with products placed in inventory
by means of shelf storage, a primary inventory system for pharmaceuticals.
Although the containers may be stored several units deep on a shelf,
the state of humidity may be ascertained for all the units on the
shelf at a glance because of the relatively large area of the cap
and the ability to see the color indicator from a wide range of
The cap is preferably fabricated from a transparent, nonporous
plastic which is either suitable for injection or thermocompression
molding. FIG. 2 is a top view of a cap 201 showing the desiccant
and color indicator 103 through the transparent top of the cap.
The desiccant and color indicator 103 can be seen to be bounded
by the inner contour 202 of the cap side wall. Formation of the
cap enclosure to provide the features shown in FIG. 2 by these methods
of manufacturing reduce the cost over prior art machining processes
by a factor of ten or more. The barrier wall in a preferred embodiment
is fabricated from a wicking polymer which not only passes a humid
atmosphere through pores, but also aids the process by means of
its wicking property which aids in drawing the moisture through
The plastic barrier wall is flexible and deforms slightly to accept
and fill the imperfections on the lip of the container mouth, providing
a hermetic seal without the use of O-rings; however, a plastic O-ring
may be added to further improve the sealing process as desired.
The ability of the barrier wall to function as its own gasket is
an important advantage in high volume production because the time
required for insertion as well as the added cost of an O-ring is
eliminated. To enhance the ability of the barrier wall to function
as its own gasket, an alternative embodiment includes an O-ring
like projection 107 on one side of the wall. Although not shown,
a second O-ring like projection may be added to the opposite side
to provide gasketing on either side of the barrier wall. The resiliency,
compliance, and compressibility of the O-ring like projection, or
of the barrier wall itself may be increased over that of the basic
plastic used to form the wall by means of blind pores which do not
pass through the wall. There is no added cost in producing the blind
pores because they are produced at the same time and in the same
manner as the pores in the filter area 106. Similarly, blind pores
are also produced in the area 108 located directly on the opposite
side of the barrier wall from the O-ring like projection to provide
a compressible area abutting the bearing surface 110 on shoulder
113 in order to provide an improved seal between the barrier wall
and the cap. The seal between the barrier and the container as well
as the seal between the barrier and the cap reduce the amount of
moisture entering the system from outside, thereby extending the
life of the desiccant.
In the embodiment of FIG. 1 the periphery of the barrier includes
threads 112 which engage the threads 111 located on the inside walls
of the cavity 107. In the production process, described in more
detail below, the desiccant and the humidity sensitive color indicator
are first deposited in the closed end of the cavity and then the
barrier wall is threaded into place against the bearing surface
110 sealing the desiccant and color indicator within the cavity.
In the use of the desiccant cap, the container 105 is threaded into
the cavity on the same threads 111 securing the cap to the container.
In this process, the pressure applied by the container on the barrier
wall is transmitted through the wall against the bearing surface
110 further improving the seal between the barrier wall and the
There are a number of embodiments of the barrier wall that function
satisfactorily in the present invention, three of which are illustrated
in FIGS. 3 and 4. FIG. 3 illustrates the basic filter and barrier
wall 301 in plan view, while FIG. 4A illustrates a threaded type
similar to that shown in FIG. 1. In the embodiment of FIG. 4A, the
threads are used to secure the barrier wall in place against the
bearing surface 110 as described above. The break away view of FIG.
4A also illustrates the O-ring like projection 107 and a raised
area 401 within the O-ring projection containing the porous, centrally
located filter area 106.
In one low cost production process for the present invention, the
enclosures are formed automatically by standard injection or thermo-compression
molding techniques. The cap cavity receives a measured deposit of
desiccant and humidity sensitive color indicator. The barrier wall
is then inserted and attached to the cavity walls to complete the
fabrication of the cap. All of the fabrication and assembly steps
are automated to drastically reduce cost over prior art processes
where the individual components were generally separately machined
and then individually assembled. The cost savings of these processes
permits the caps to be used only once and then discarded, a decided
advantage for pharmaceuticals, where repetitive use must be avoided
to prevent contamination.
In the above described low cost production process, barrier walls
of the type shown in FIG. 4B (threadless type 402) or 4C (threadless
and projectionless type 403) are used to avoid threading. These
walls are simply dropped in position against the bearing surface
and bonded in place by means of a chemical bonding agent such as
epoxy cement or by fusing the barrier wall to the bearing surface
by means such as RF heating.
Although the threaded embodiment of FIG. 4A is not as readily adaptable
to high volume production as the embodiment shown in FIGS. 4B and
4C, it may be adapted for medium to high volume production through
the use of special tooling in conjunction with a slot 501 in the
projection 107 as shown in FIG. 5A. In low volume production, this
slot is driven by conventional tools to thread the barrier wall
into the enclosure cavity. In high volume production, this slot
is used to pick up, position and drive the wall into position by
a special tool shown in FIGS. 5C and 5D.
The cross section of the slot is shown in FIG. 5B to have tapered
sided walls 502 which are positioned to widen the slot with depth.
This configuration of the slot permits either conventional tools
or special tools to thread the barrier wall into position.
One type of special tool, shown in FIG. 5C, comprises a drive shaft
503 a first and a second pawl 504 and 505 pivoting respectively
about detent pins 506 and 507 which pass through shaft 503.
In the operation of this special tool, the pawls are first positioned
close together as shown in FIG. 5D. The pawls are held in this position
by a second set of detents, not shown. The tool tip is first placed
in position in the slot, where the tips of the pawls contact the
bottom of the slot and then the pawls are driven outward into the
position shown in FIG. 5C, where they are held by a second set of
detents, not shown. In the position of FIG. 5C, the pawls may be
used to aid in picking up the barrier wall and thread it into place
in the enclosure cavity. Where no threads are used, the slot design
remains useful in picking up and placing the barrier wall in the
cavity. The pawls revert to the position shown in FIG. 5D when withdrawn
from the slot.
An alternative tool configuration, not shown, contains conforming
wedge shaped tips which are slideably positioned into the slots
from the side, as for example from the region over the filter area
106 shown in FIG. 5A.