A desiccant stopper suitable for use with a bottle of pills or
the like, which stopper is of a thermoplastics material and is in
the form of a pot at least one end face of which is made from a
fibrous fabric sheet of a plastic material attached around its periphery
to either the body of the pot or to a lid for the pot body, and
wherein the attachment is effected by the sheet being embedded within
the material of the body or lid, or both. It also proposes two methods
by which such a structure can be manufactured, one involving holding
the sheet in place while the body or lid material is injection-molded
around it, the other involving sonic fusion of the body/lid material
around the sheet.
1. A method for the production of a stopper suitable for use with
a bottle of pills or the like, which stopper is of a thermoplastics
material and is in the form of a pot at least one end face of which
is made from a fibrous fabric sheet of a plastics material attached
by fusion around its periphery to either the body of the pot or
to a lid for the pot body, in which method the fibrous fabric sheet
is held in place between the stopper body and the lid, and these
two are then fused together so that on cooling and solidifying they
form a solid, integral plastic supporting frame around the sheet
2. A method according to claim 1 in which the lid/body join is
effected by sonic welding.
3. A method according to claim 1 or 2 in which the stopper has
two membranes, one at either end.
4. A method according to claim 1 2 or 3 in which the stopper is
suitable for use with a bottle of pills or the like.
5. A stopper whenever made by a method as claimed in any of the
 This invention relates to desiccant stoppers, and concerns
in particular stoppers, in the nature of small plugs, that fit into
the tops of bottles, such as pill bottles, and absorb any free moisture
in the bottle so as to prevent the pills from being damaged thereby.
 Desiccant stoppers are used to control the moisture or odour
vapour levels of air, within a sealed container, such as a bottle,
jar, bag or box, and to control the closed atmosphere to the benefit
of sensitive products such as pharmaceuticals packaged within.
 Desiccant stoppers are produced in a number of sizes and
types relevant to the size and nature of the container and the content
to be protected. They must be non-toxic, resistant to water, strong,
sterile, and able to provide a microbial barrier.
 A desiccant stopper can be constructed in a number of ways,
but in the main they follow a similar pattern; they comprise a suitably-sized
capsule, rather like a small pot or jar, as the desiccant holder,
and after this has been filled with the chosen desiccant it is capped
with either a porous-type material wad (such as a thin disc of cardboard)
crimped into place, or capped with a moulded plastic lid with cast-in
 Dependant upon their end use, desiccant stoppers can be
filled with a wide variety of desiccant-material content. In the
event that they are required to control moisture, suitable absorbent
materials are silica-gel, or molecular sieve, while for the control
of odours, granulated carbon, is used. In some instances, a mixture
of each of the mentioned materials will be formulated, and there
are a number of proprietary brands of admixtures on the market.
 A most important part of any desiccant stopper is the porous
membrane section, which allows ingress of the moisture or odour
vapours to the desiccant within. In many instances, manufacturers
use materials which have not been specifically designed for such
membrane use, and adapt materials which are well below the required
performance levels. The ideal membrane should be designed to promote
optimum permeability, but should also control the escape of fine
particles from the sealed container (many desiccant materials used
are of inconsistent particle size, and the very smallest of the
particles will escape given the opportunity to do so--such as through
the inevitable gaps round the edge of a crimped cardboard disk seal).
A further requirement is the need to use a sterile material which
will not support bacterial penetration or growth. In addition to
these qualities the membrane must be strong mechanically, and must
remain so during performance.
 Some problems experienced with the use of desiccant stoppers
relate to the efficiency of the product in use. The injection-moulded
plastic used either for the capsule container or for the lid is
not permeable to vapours and odours, and will prevent the vapours
or odours from reaching the desiccant chemical, in the best method
or shortest period of time. Plastic injection moulded lids with
small perforations supposedly to allow vapour ingress are in fact
poor in performance, and can be subject to flashing (flashing when
present will partially or completely block the holes). Likewise,
the low efficiency of some wadding materials is such that their
permeability for vapours or odours, whilst being acceptable, are
not optimum. Consequently, the total efficiency potential of the
desiccant is impaired by the nature of the container construction
and the wad material being used.
 A good mechanical strength for the desiccant stopper is
imperative, for damage suffered to the container will allow the
content to escape, and cause contamination to the packaged contents.
And in fact desiccant materials will escape through poor seals or
perforations in plastic parts, even without mechanical damage. The
use of wadding, crimped into place to produce a good seal at the
outset, is often undone if the desiccant stopper has been subjected
to careless handling during transportation or by the packaging filling
 Crimping plastic materials often results in the plastic
attempting to recover to the original shape prior to the new crimped
form, the resultant relaxation produces poor seal properties.
 The present invention proposes a new idea--a stopper in
which the "wadding" is a porous plastics material that
forms the end face of the stopper itself, the wadding being embedded
around its periphery within the stopper material. It also proposes
a particular method by which such a structure can reliably be manufactured.
 There are nowadays available, breathable plastic materials--olefinic
materials, such as polyethylene--which are manufactured using non-moulding
techniques. Specifically, by using spinning methods of manufacture,
the finished form of the material is as a fabric sheet, of predetermined
thickness, when the multiple strands that are employed to compose
the matrix overall overlay each other in an ordered manner. This
creates a sheet which is apparently solid but which is in fact porous
because of the micro spaces which exist between the layered spun
fibres. The performance of this type of material is very suitable
for use as a permeable wad for desiccant stoppers due to the superb
transfer of moisture and odour vapours through the membrane. The
microporosity of the material controls dust emission, biological
control is inherent due to the nature of the olefin materials from
which the membrane is made, and the high tear strength and puncture
resistance promotes high mechanical strength, and resistance to
 In one aspect, therefore, the invention provides a stopper
suitable for use with a bottle of pills or the like, which stopper
is of a thermoplastics material and in the form of a pot at least
one end face of which is made from a fibrous fabric sheet of a plastics
material attached around its periphery to either the body of the
pot or to a lid for the pot body, and wherein the attachment is
effected by the sheet being embedded within the material of the
body or lid, or both.
 In a second aspect, the invention provides a first method
for the production of such a stopper, in which method the stopper
body or lid is injection-moulded, and the fibrous fabric sheet is
held in place as this injection-moulding is effected, so that it
is totally captured at its outer edges by being overmoulded by the
injected plastic which, as it cools, solidifies and forms a solid,
integral plastic supporting frame around the sheet embedded therein.
 In an alternative second aspect, the invention provides
a second method for the production of such a stopper, in which method
the fibrous fabric sheet is held in place between the stopper body
and the lid, and these two are then fused together so that on cooling
and solidifying they form a solid, integral plastic supporting frame
around the sheet embedded therein.
 The term "embedded" as used herein means that
the material of the body and/or lid is not merely attached to either
side of the fibrous sheet but actually extends integrally through
it--as will clearly be the case if it has been injection-moulded
around the sheet, or if it has been fused (so as to flow) together
from either side of the sheet.
 The stopper is pot-like--that is, it is in the shape of
a small container (perhaps 0.75 in [2 cm] across, and 0.188 in [1
cm] deep) for holding in use the desiccant (or other) material contained
by the stopper. The stopper can be of any convenient cross-section,
but a tubular section is generally most suitable, fitting into most
containers of pills or the like.
 The stopper ends up as a one-piece object, but for manufacturing
purposes it is formed from at least two pieces, namely having a
body portion and a lid (or cap) portion that fit sealingly together
(starting from three-pieces--an open-ended central ring portion,
with a cap at each end--is also be possible). The porous membrane
can be integrally formed in either the body or the cap portion (or
even in both cap portions), or between the two. The pieces can be
joined sealingly together, to make a closed stopper, in any convenient
manner. For example, they can be joined by an interference press
fit, a snap-over ridge fit, by sonic welding or friction welding,
or even by adhesive, or a screw fix.
 The flat bottom surface of the body portion, and the flat
top surface of the (or each) lid/cap portion, provide the two end
faces of the stopper; one or both of these is made from the fibrous
fabric sheet of plastics material fused sealingly around its periphery
to the main/side parts--the wall portions--of the body or lid appropriately.
 Obviously, the material from which the main parts of the
stopper body/lid are made and the material from which the fabric
sheet is made must be such that they can be welded/fused--that is
to say, caused to flow into each other so as to adhere very tightly
(and even to intermingle so as to become integral). This is perhaps
easiest if the two materials are the general type of material, and
specifically if they are in fact the same material. Such a material
is that known as Perfecseal HBD 1059B TYVEK, manufactured by Dupont.
 Dupont produce a range of materials under the Trademark
TYVEK, each of which have specific end uses. Many of the products
from this range are suitable for the purposes which are here described.
 Another suitable material is that available under the name
TEIJIN, and manufactured by Unisel.
 The principal purposes of these types of materials are as
breathable fabric membranes used to construct bags or sachets, or
to cover plastic or foil tray-like containers, to which they are
fastened using conventional heat sealing techniques. For best results
a large area of contact is required between the two materials which
are to be joined.
 The use of a TYVEK-type material as the wadding medium has
many advantages beyond the capabilities of paper-based wadding,
as the available literature on the product describes, but there
are problems in the application of the product when using normal
 Paper-based wads are available in varying grades of board,
surface finish, and thickness. They are usually at least 0.65 mm
thick, when used in small diameter desiccant stoppers (typically
12 mm diameter), and proportionately thicker as diameters increase,
and they are stiff in structure. The manufacturing process is similar
to that of producing cardboard, but with a fine paper finish for
cosmetic reasons. The thickness of the chosen board is important,
as it contributes to the structural strength of the finished product.
When crimped into place, the wad forms one end of the finished desiccant
stopper, where it is the moisture- or odour-permeable window to
the capsule. It is also the mechanical end of the desiccant stopper
 Now, TYVEK-type materials are generally very much thinner
in comparison to paper-based wad materials, and whilst immensely
strong are also extremely flexible. Unfortunately, these features
do not allow a simple substitution of TYVEK-type material for a
card wad as the flexibility of the material lacks the required mechanical
strength found in the latter. In addition these types of material
are relatively thin--typically 0.15 mm thick--and they do not compress
to a sufficient depth to allow the crimped edge of the plastic to
embed into the membrane and anchor if firmly (this is an important
requirement of crimping). To be mechanically effective, TYVEK-type
materials need to be anchored to the container wall in a completely
 TYVEK-type materials are also available with an adhesive
coating, to facilitate a heat-sealing join to a suitable substrate,
but the strength of the seal is directly related to the two surface
areas being brought together. If that surface area of sealing is
extremely small, then the integrity of the seal is suspect.
 The invention proposes two production methods either of
which allows the satisfactory formation of a desiccant stopper which
employs the rigidity of a plastic injection-moulded capsule for
the body of the unit, and the simultaneous moulding in-situ of a
suitable--most preferably TYVEK-type--material membrane at one or
at both ends of the plastic body to allow the ingress of either
moisture or odour vapours through the membrane to the encapsulated
desiccant materials contained within. In one method the membrane
is held in place as the stopper body or lid is being injection-moulded;
the membrane is totally captured at its outer edges by being overmoulded
by the injected plastic which, as it cools, solidifies and forms
a solid plastic supporting frame around the membrane. In the other
method the membrane is held in place between the stopper body and
the lid, and these two are then fused together so that on cooling
and solidifying they form a solid, integral plastic supporting frame
around the sheet embedded therein. This fusing is most conveniently
carried out by a sonic welding process (described in more detail
 More specifically, then, the invention provides a first
method of making a desiccant stopper of the invention by injection
moulding of the main stopper parts, in which method:
 the fibrous fabric sheet material membrane to be the end
wall of the main part is held in place in the mould at the appropriate
position relative to where the walls of the main part--which may
be either the body portion or the lid portion--will be formed; and
 thereafter the walls are injection-moulded, whereby the
membrane is totally captured at its outer edges by being overmoulded
by the injected plastic which, whilst still liquid, forms around
the membrane edges, and, as it cools, solidifies and forms a solid
plastic frame around, above or below the membrane.
 Also more specifically, the invention provides a second
method of making a desiccant stopper of the invention by fusion
of the main stopper parts, in which method:
 the fibrous fabric sheet material membrane to be the end
wall of the main part is held in place between the body portion
and the lid portion; and
 these two are then fused together by sonic welding so that
on cooling and solidifying they form a solid, integral plastic supporting
frame around the sheet embedded therein.
 This second method relies upon the technique of sonic--that
is to say, "ultrasonic"--welding of thermoplastic parts
to fuse the body and lid parts together, embedding the membrane
therewithin. This technique is now described in more detail.
 The principle of ultrasonic assembly involves the use of
high-frequency mechanical vibrations transmitted through thermoplastic
parts to generate a frictional heat build-up at an interface. The
effect of the vibrations causes intense friction between separate
but touching parts, causing the materials to heat and melt and weld
 This vibrational movement is effected by a vibrating component
called a "sonotrode", which is applied at right angles
to the surface of a part to be welded. The latter starts to vibrate
throughout due to a series of stationary waves, with a maximum amplitude
in the area of contact of the two parts to be joined.
 After cooling, which is rapid, a solid homogeneous weld
results between the two parts of the assembly.
 The frequency of vibration of the sonotrode is in the order
of 20 kHz, which is outside the limit of perception by the human
ear. For this reason, this assembly process is called ultrasonic
 The success of this technique depends entirely on the ability
of the materials to propagate vibrations without damping them; excellent
results can be obtained with suitable thermoplastic rigid materials
with a high modulus of elasticity. The method permits the welding
of objects of very complex design with a sonotrode which is very
simple in form.
 The stiffness of the polymer to be welded will influence
its ability to transmit the ultrasonic energy to the joint interface.
Generally the stiffer a material the better its transmission capability.
It is usually not possible to weld materials of different types
by ultrasonics, due to the differences in fusion temperature. If
the macromolecular structure is not the same for both materials,
it will prevent interpenetration.
 As specifically applied in the alternative method of the
invention, the following points should be borne in mind when using
 1. The cap/lid is to be welded to the body, and while this
could be butt weld it is preferred to chamfer each abutting face
in a matching manner, to form a larger weld surface. Specifically,
the edge of the side wall of the cap(s) is moulded to a form recommended
as a correct interface profile for ultrasonic welding.
 2. The edge of the side wall of the body is correspondingly
moulded to a form recommended as a correct interface profile for
ultrasonic welding, but also incorporates a section which, when
the two plastic components (body & cap) are placed together
with the TYVEK type material also in place, acts as a snap fit to
temporarily secure the components together, with the underside of
the cap in close proximity with the uppermost side of the top edge
of the inserted profiled wall of the plastic body.
 3. When a membrane window is required at both ends of the
stopper, the process described is repeated at the opposite end of
the container, which is moulded to suit.
 4. It is normally most convenient to assemble the stopper
one end at a time, in an upright position, with the end cap placed
on top at the time of assembly and ultrasonic welding.
 5. Once correctly positioned, with the membrane held therebetween,
the body/lid mouldings are ultrasonically welded together to form
an integrally-joined capsule. The or each porous membrane is encapsulated
within the previously separate components, held in place by the
weld between the body and the relevant cap or end.
 In these ways the fabric sheet--the TYVEK-type material--is
embedded around its periphery within the material forming the stopper
body/lid combination. In the first method it is embedded within
to the injection-moulded plastic, for at the injection pressures
at which the plastic is introduced the plastic penetrates the sheet
so that around its edges the membrane is fully incorporated within,
and fully supported by, the moulding. In the second method the material
of the body and lid portions fuses together--each flows into and
intermingles with the other to form an integral whole. In each case
the membrane is thus presented as a window to the stopper container's
body or lid portion, and thus in use allows unimpeded ingress by
moisture or odour vapours. Moreover, reinforced as it is by the
plastic frame in which it is totally suspended, the membrane acts
as a structural form securing the contents of the stopper from loss
 As can be inferred from what has been said above, there
is a choice of TYVEK-type material membrane at one or more positions
on the desiccant stopper. Typically the position of a single membrane
could be at the end of a stopper, whilst a stopper with two membranes
could have them situated one at either end (the purpose of two membranes
would be to allow a faster ingress of vapours).
 And as also noted above, in the case of a stopper with one
membrane only, it will be seen that there is a requirement for two
parts. One is the body portion--the receptacle into which the desiccant
is placed, while the other is the lid portion. Either may carry
the membrane as its end wall, but usually it is more convenient
to use the lid for this.
 When two membranes are required within a single desiccant
stopper the unit can be constructed in a variety of ways. One preferred
way is to manufacture the main body of the stopper of a size sufficient
to accommodate the total volume of the required fill, and with the
membrane integrally moulded into the base of that container. The
fill content is then added, and the lid, incorporating a second
moulded-in membrane, attached by whatever means thought suitable.
 A second preferred way would be to manufacture the unit
in three or more parts, comprising two separate cap/lid-like end
parts and one (or more) central body part open at both ends. The
end parts--each identical in manufacture--incorporate the moulded-in
membrane, and each resemble a lid. Assembly of each end part to
the central body part then builds the container, into which the
fill content is placed before attachment of the second lid end to
complete the structure.
 Where the several parts of the stopper--the body and one
or more end cap/lid--are manufactured separately (and then joined
together) it is of course possible to give them different colours.
This may be used, if wished, for identification purposes--to indicate,
perhaps, either what is inside the stopper (what desiccant is used)
or what the stopper is to be employed with (what materials or articles
it can be utilised to keep dry, say).
 Embodiments of the invention are now described, though by
way of illustration only, with reference to the accompanying diagrammatic
Drawings (the Drawings are based on cylindrical and circular designs,
but other shapes are also suitable for moulding) in which:
 FIG. 1--shows a section through a desiccant stopper of the
 FIGS. 2a & B--show general views of the moulding equipment
(in the open and the closed states) needed to make the lid of FIG.
 FIG. 3--shows a detail of the moulding equipment of FIG.
2 in the closed state; and
 FIG. 4--shows a diagrammatic version of part of FIG. 3.
 FIG. 1 is almost self-explanatory. It shows a section through
a desiccant stopper (generally 11) of the invention. The stopper
is of circular section, and thus is like a small pot.
 The stopper has a main body portion (12) and a lid portion
(13), and the top (as viewed) surface of the lid 13 is a "window"
(14) made of a porous fibrous fabric sheet material sealed (at 15)
all around its edge into the top edge of the lid's wall, and so
effective integral therewith.
 The lid 13 and body 12 are shaped (at 16) to be a snap fit.
And when they are to be joined by a sonic welding technique their
shape is also adjusted to be suitable for that method.
 FIGS. 2a & B show general views of the moulding equipment
(in the open and the closed states) needed to make the lid of FIG.
1. The mould (generally 21) is in three portions--a centre part
(22), a top part (23: to the left as viewed) and a bottom part (24:
to the right as viewed). The top part 23 also contains a punch (26)
while the centre part 22 contains the punch cavity, and fed off
a reel and though centre part is a web of membrane material (27).
As the mould closes so the punch cuts out a small disc of membrane
material, and carries it forward (to the right) into position ready
to be fused with the lid plastic.
 The centre portion 22 and the bottom portion 24 together
make the volume defining the lid to be moulded. Once the mould is
closed, the plastic is injected thereinto to make the lid, and as
it does so it fuses to the membrane disc.
 The working parts of the punch and mould are shown in more
detail in FIGS. 3 and 4.
 The moulding method and cycle is now discussed in more detail.
 The mould is designed to produce the complete item in one
operation. The size of the mould is determined by the size of the
individual component required, but it is normal to manufacturer
a mould with multiple cavities, to produce volume and lessen production
costs. However, for the purpose of this application a single cavity
mould is illustrated, to explain the cycle.
 The requirement is to produce a moulding in plastic, which
has as part of its construction, a previously separate membrane.
At the start of the cycle, the membrane (3141) is inserted into
the mould cavity, and securely positioned. Whilst held in place,
the plastic is formed around the exposed edges of the membrane at
the time of injection, creating a frame (3242: cross-hatched in
FIG. 4) which securely anchors the edges only, leaving the centre
of the membrane fabric exposed at the time of ejection.
 The preferred method of insertion of the membrane, is to
produce the membrane wad from reeled sheet form 27 during the moulding
cycle, and to position the wad immediately after cutting.
 During a standard method of injection moulding the moulding
tool is made in a number of parts 222324 which open and close
during the cycle. For the purpose of this explanation the mould
tool will be considered to have three separate sections which, combined,
will constitute one mould tool. During the open part of the cycle
the mould sections will separate to allow the cycle to begin.
 The membrane material is available in reel form cut to choice
of width. The reel is mounted adjacent to, but separate from the
mould tool. The end of the reel length is passed through the centre
section 22 of the three part mould, and wound onto the second (scrap)
reel which is positioned to receive the web as it is passed through.
The material on the feed reel is indexed to feed the correct length
of material through the mould, and to ensure that waste is kept
to a minimum.
 The mould is closed in a predetermined way, assisted mechanically
or hydraulically if required. During the closing part of the cycle,
the web of membrane material is clamped securely between two metal
plates. Each of the plates have a number of aligned holes, which
are centred to the cavity/cavities of the mould. The holes described
are sized to the required wad size.
 When the mould is closed, a metal sleeve pin (3343), correspondent
in diameter to the size of the wad to be cut, and also to the size
of the two metal plates' holes described above, is pushed forward,
through the plates, and also through the web of membrane material
which is trapped within. This forward action produces the necessary
wad cleanly cut from the web and pushed forward into the cavity
in one single motion. Situated within the sleeve pin is a spring-loaded
solid pin (3444), water-cooled to protect the membrane from heat
damage, which travels forward to a distance further than the sleeve
pin, to pinion the wad to the rear wall of the cavity. The rear
wall of the cavity houses a water gallery to assist in the cooling,
and protection of the wad during the plastic injection process.
 The sleeve pin 3343 and the internal solid pin 3444 both
stay forward during the injection process, and form the core to
the moulding which is produced around their form.
 After a period of cooling the mould opens to the greatest
extent. The two pins are withdrawn from the cavity, pulling the
moulding clear and ejecting as the snatch on the inside of the moulding
is released. The two pins continue to travel backwards to the full
extent of their back stroke, clear of the membrane material, through
which they had been positioned during the mould closed portion of
 The membrane material is now indexed forward from the reel
and the cycle is repeated as the mould closes again.
 The scrap reel takes up the waste produced from each subsequent