Note: Descriptions are shown in the official language in which they were submitted.
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Case V-5193
INFUSION ~AG
The present invention is directed to infusion bags,
especially tea bags and the like, and more particularly to an
infusion bag constructed of a non-woven, fiber-free, perforated
thermoplastic film.
The invention is particularly concerned with an infusion
bag constructed of a coextruded multilayer perforated thermo-
plastic film having a plurality of uniform minute holes or
openings therein.
Thermoplastic films such as polyethylene and polypro-
pylene are common packaging materials. Multilayer films of
various types are also quite common packaging materials. The
films are generally non-porous and impervious to water and other
inert liquids. At least one of the layers of film has strong
adhesive qualities. Examples of such multilayer films may be
seen in U.S. 4,254,169; U.S. 4,239,826; U.S. g,233,367; U.S.
3,908,070; U.S. 3,423,231; U.S. 2,817,124 and U.S. 2,817,123.
Perforated thermoplastic films have many useful applica-
tions, including packaging of food products such as cheese,
gardening and farming to prevent growth of weeds while permitting
moisture to be transmitted through the film to the soil beneath
and for making absorptive structures such as disposable diapers,
for example, see U.S. 3,814,101.
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Perforation of thermoplastic films is generally achieved
by vacuum perforation of thin plastic films which involves the
extrusion of molten polymeric materials such as polyethylene
through a slot die. The hot melt web of film exiting the die
impinges on a form through which a vacuum is drawn causing the
film web to be perforated and holes formed therein. ~epending
upon the form used, films can be produced which have as few as
50 holes per square inch or which have thousands of holes per
square inch. One of the earlier methods for vacuum perforation
of plactic film is disclosed in U.S. 3,054,148.
Infusion-type tea bags are usually rectangular packets
or sachets made from single or multiple pieces of paper folded
in half and crimped or otherwise sealed along the edges. In
another type, a single strip of paper is folded twice longitu-
dinally to form an inner centrally disposed double fold joiningthe two meeting edges. In a type of flow-through tea bag, a
triple transverse fold intermediate the length of the folded
strip forms two pockets which are partially filled with tea
before the open ends thereof are folded over and stapled to a
strand of string usually having a tag on the end thereof.
Over the years, a wide variety of infusion packets or
bags, usually for containing tea for subsequent brewing, have
been developed. The bags are usually constructed of filter paper
or some other type of porous material such as cloth or the like.
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An infusion packet having two oppositely disposed,
rigidly separated pockets of tea joined together by two tapering
end portions which form a narrow, triangular shaped porous cup
is shown in U.S. 3,597,222.
U.SO 3,653,913 discloses an infusion bag made from a
rectangular strip of porous fibrous material, the longitudinal
margins of which are folded together so as to form a longitudinal
joint consisting of three layers which are knurled together.
The tube is divided by a transverse bend so as to form a pair of
chambers for holding an infusible substance, and the opposite
ends of the tube are connected to each other so as to close the
bag.
An early type of tea bag or tea ball wherein the bag is
a triangularly-shaped pocket formed from a rectangular strip of
15 perforated aluminum foil is described in U.S. 1,581,578.
Other types of filter paper tea bags or the like with a
variety of handles are illustrated in U.S. 2,328,017; U.S.
2,359,292, U.S. 3,566,573; U.S. 4,153,153; and Great Britain
2,087,350. The British patent discloses a tea ba~ having a
20 somewhat accordion fold.
Infusion bags with positioning means and flotation means
are disclosed in U.S. 3,797,642 and U.S. 3,809,215, respectively.
The tea bags themselves may be made of various materials inclu-
ding paper, plastics such as nylon, perforated plastic film,
25 e.g., polyester, or woven or non-woven fabric of natural or
synthetic origin.
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A percolatable porous bag constructed of a blend of
individuali~ed textile or cellulosic fiber and a small amount of
thermoplastic fiber is disclosed in Canadian patent 802,720.
Various degrees of success have been achieved with the
5 foregoing infusion bags, with paper of fibrous bags presently
dominating the market place. One of the problems with paper
bags is lack of wet strength. This is even more of a problem
with the larger bags for tea brewing commonly used by the food
service industries.
Another problem with fibrous or paper bags is that as
they become wet, the fibers expand or swell. Such expansion or
swelling closes the openings in the bag material and removes the
perm~ability thereof. When placed in a water containing vessel
such as a cup or pot, the bags tend to float since the films
structure is so closed or porosity so diminished that air is
trapped inside the bag.
An infusion bag for items such as tea, coffee or similar
food products for brewing must have a number of qualities. It
must have an inability to impart a taste factor to the liquid
20 product after brewing. In effect, it must be substantially odor-
less and tasteless. It must also be sufficiently strong to con-
tain the brewing product in boiling water, e.g., in the steeping
of tea, coffee, and similar liquid beverages. The bag must also
be porous enough to permit liquid diffusion therethrough, but
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the pores or openings must be of such size that migration of the
beverage material therethrough is inhibited, both when the bag
is dry and when the bag has been immersed in a liquid. It is
also important that infusion begins to take place within a few
seconds. It is further desirable that a sachet, such as a tea
sachet, retain sufficient stability that it can be compressed
after brewing is completed without destruction of the container.
The present invention provides an infusion bag or sachet
which meets all of these requirements.
More particularly, the present invention provides an
infusion bag for particulated or granular products such as tea
and coffee constructed of a vacuum perforated coextruded dual
layer thermoplastic film having a base thickness of about 0.25
mil to~2 mils and having an outer heat resistant layer of film
forming resin, and a less heat resistant inner sealant layer
of film forming resin, the vacuum perforated coextruded dual
layer thermoplastic fllm having about 1800 to 4200 uniform
perforations or holes per square inch of film,the perforations
or holes-having been formed by vacuum perforation of the thermo-
plastic film, the vacuum formed perforations or holes being
about 2 mils to about 10 mils in diameter or across the major
axis, the vacuum formed perforations or holes of the vacuum
perforated coextruded dual layer thermoplastic film being
tapered capillaries, with the larger capillary opening being in
the outer heat resistant layer of the vacuum perforated co-
extruded dual layer thermoplastic film and the smaller capillary
opening being in the inner less heat resistant layer of the
vacuum perforated coextruded dual layer thermoplastic film, and
the vacuum perforated dual layer coextruded thermoplastic film
having a porosity of about 100 to about 500 cubic feet per minute.
jrc:
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Fig. 1 is a top plan view of one embodiment of the
invention;
Fig. 2 is a side view of the embodiment of Fig. l;
Fig. 3 is an end view of the embodiment of Fig. l;
Fig. 4 is an enlarged sectional view across line
4-4 of Fig. l; and
Fig. 5 is an enlarged top view of a portion of the
thermoplastic film of which the embodiment of Fig. 1 is
constructed.
Referring now to the drawings, an infusion bag of
the pxesent invention is illustrated generally at 10.
The bag or packet 10 is constructed of a rectangular strip
of a perforated plastic film 11 which is described in
more de~tail hereinafter. The strip of film 11 is folded
at 12, sealed at edges 13 and 14 and filled with a part-
iculated product P which can be seen through the film 11.
After the product P is inserted in the sachet 10, the edge
15 is sealed, thereby encasing the product P within the
bag 10.
As best been in Figs. 4 and 5, the infusion bag 10 is
constructed of a coextruded multilayer thermoplastic film 11
comprising an outer layer 21 of a heat resistant film forming
thermoplastic resin such as polyester, polyolefin, polycarbonate
or nylon with polyester being preferred, and an inner sealant
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layer 22 of a somewhat less heat resistant film forming thermo-
plastic resin, such as polyethylene, polyester, polycarbonate or
nylon with polyethylene being preferred. The film 11 has a
multiplicity of fine holes or capillaries 23 which are of a
somewhat tapered construction, being more or less in the form of
a truncated cone. Tapered holes help to speed infusion. The
somewhat cone shape of the holes effectively channels liquid
into the bag and into contact with the particles contained
therein.
For simplicity of illustration, the holes or openings
are shown as being circular or round. It can be appreciated
that the openings may be of any desired shape such as oval, pen-
tagonal, hexagonal or other geometric configuration. It is
important that the holes be uniform and that they be sufficiently
large in size and number to provide adequate infusion and be
sufficiently small in size to prevent the migration of particles
therethrough such as the particulated product P.
In the packaging of an item such as tea, a preferred
hole size is from two to 10 mils, in diameter or across the
opening, with a size of three to four mils being most pre-
ferred. The film has a base thickness of 0.25 mil to two mils
and 500 holes per square inch or more. From 1800 to 4200 holes
per square inch are preferred, with about 2900 holes per square
inch being most preferred. The porosity of the film is 50 to
500 cubic feet per minute (CFM).
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The outer layer of the coaxial or coextruded perforated
thermoplastic film of the bag is preferably a heat resistant
polyester film having a melting temperature of 425F to 600F
with about 525F being most preferred. The inner sealant layer
of the coextruded perforated thermoplastic film of the bag is
preferably a somewhat less heat resistant polyethylene film
having a melting temperature of 180F to 250F with 220F being
most preferred. The use of an outer polyester layer enables a
sealing/melting temperature differential of about 150F to be
0 obtained. The film has a desired seal strength of 3/4 lb. per
inch width.
A temperature of about 240F is required to melt the
polyethylene film for sealing. To prevent sticking of the outer
layer of thermoplastic film to the steel jaws of the sealing
device or heat sealing machine, it is important that the melting
temperature of the polyethylene inner layer be kept below about
260~F. It can be appreciated that particular polyolefin resins
or other film forming resins may have higher or lower melting
temperatures; however, it is essential that a melting temperature
differential be obtained between each layer to achieve the
desired seal without a deleterious effect on the film.
For example, a heat resistant polypropylene film layer
has a melting temperature of 230F to 350F with about 320F
being preferred. The melting temperature of 180F to 250F of
the somewhat less heat resistant polyethylene film layer
provides the necessary melting temperature differential.
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The edges of the film are heat sealed to complete the
package. The melting temperature of the outer layer of the bag
must be sufficiently high to prevent the film from sticking to
the sealant jaws. The melting temperature of the inner sealant
layer of the bag must be less than the melting temperature of
the outer layer.
The edges of the bags may be readily heat sealed using
standard sealing and automatic bag making machines. The edges
may also be effectively sealed with use of impulse or band type
0 sealers, hot wires, hot air or other suitable sealing apparatuses
or techniques.
For the packaging of a typical commercial tea-for brew-
ing, a VisQueen~ Vispore~ film identified as X-6040 is especially
suitable for constructing the infusion bag. The film is a coex-
truded polypropylene/polyethylene perforated thermoplastic filmformed from a high density polyethylene resin and a polypropylene
resin. The resins are odorless and tasteless and approved for
food packaging.
The female side or surface of the thermoplastic film to
be on the outside of the bag is also preferably flame or corona
discharge treated. Such treatment enhances the flow of water
into the oag and thus accelerates the infusion process.
Although a coextruded multilayer polyester/polyethylene
film is preferred, other combinations of multilayer films are
suitable. Using the following designations:
* Trade Mark
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Polypropylene PP
Polyethylene PE
Crystalline polysster CPE
~ Amorphous polyester APE
Polycarbonate PC
Nylon N
some examples of other suitable multilayer films are as follows:
PP/PE PC/PE N/PP
CPE/PP PC/PP N/PE
CPE/APE PC/APE N/APE
It can readily be appreciated that other film forming
resins can be used providing they can be effectively perforated
and provided that there is an adequate melt differential between
the outer layer of the bag and the inner sealant layer of the
bag.
With some resins, it may be necessary or desirable to
provide multilayer films of more than two layers. For example,
a triple layer film is suitable. Regardless of the number of
layers of film, it is essential that the melting temperature
differential be maintained between the outer layer of the bag
and the inner sealant layer of the bag. The layers of a sheet
of film must also, of course, not be subject to separation or
delamination.
The film is preferably clear in color, but may be manu-
factured in its natural color or a variety of colors as desiredor permitted.
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The film has a dry surface and has no tendency to stick,
cling or ~block~.
In the construction of infusion bags, the male side of
the film is on the inside of the bag.
The invention is illustrated in its simplest form, and
as a typical small size infusion bag for the packaging of indivi
dual servings of tea for brewing. Larger size packages, such as
those customarily used in the food services industry can also be
constructed. Such bags are constructed of two rectangular strips
of film and sealed on all four edges. The bags or packages of
the invention can be constructed in other geometrical configura-
tions as desired. Rectangularly shaped packages are generally
more suitable for boxing or other type of group packaging and
can usually be more easily fabricated.
~5 The infusion bags of the present invention have excel-
lent wet strength and will not deteriorate in boiling water.
The bags themselves are odorless and tasteless and do not impart
any foreign taste to the item being packaged. They are, in ef-
fect, substantially inert.
Unlike bags constructed of fibrous materials, the poro-
sity of the bags of this invention is unaffected by the brewing
process. The holes or openings in the thermoplastic film remain
unchanged when submerged in water and the porosity of the film
remains constant. The infusion bag of the invention is also not
as prone to entrap air as a bag of fibrous material. Entrapped
air causes flotation of the bag and slows the brewing process.
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Although the invention is particularly suitable for the
packaging of tea, it can be used for packaging of other types of
finely ground or particulated food products such as coffee and
grits. The bags of the invention are also suitable for packaging
5 items such as tobacco, snuff and the like. The bags may be used
for packaging of any items in which infusion is desired.
The foregoing disclosure and description of the inven-
tion is illustrative and explanatory thereof and various changes
in the illustrated construction may be made within the scope of
0 the appended claims without departing from the spirit of the
invention.
