Note: Descriptions are shown in the official language in which they were submitted.
~221059
Case V-5203
INFUSION BAG
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 slotted holes
or openings therein.
0 Thermoplastic films such as polyethylene and polypro-
pylene are common packaging materials. ~ultilayer films of
various types are also quite common packaging materials. The
films are generally non-porous and impervious to water and other
inert li~uids. 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. 4,233,367; 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, gar-
dening and farming to prevent growth of weeds while permi~tingmoisture 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.
~7
~ZZ~59
-- 2 --
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. Depending
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 plastic film is disclosed in U.S. 3,054,148. Perforations
are generally round, oval, pentagonal or hexagonal.
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 joining
the 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 develooed. The bags are usually constructed of filter paper
or some other type of porous material such as cloth or the like.
~22~59
-- 3 --
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.S~ 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
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. British Patent 2,053,668 discloses a tea bag having
2n a 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,
e.g., polyester, or woven or non-woven fabric of natural or
synthetic origin.
12;~1059
-- 4 --
A percolatable porous bag constructed of a blend of
individualized 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
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
permeability thereof. When placed in a water containing vessel
such as a cup or pot, the bags tend to float since the fibrous
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
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
the pores or openings must be of such size that migration of the
lZ210~9
-- 5 --
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 infus;`on begins to take place within
a few seconds and be completed within a few minutes. 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.
~ore 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 fil~ forming resin, the vacuum perforated coextruded
dual layer thermoplastic film having about 1800 to 4200 uniform
substantially rectangularly shaped perforations or holes per
square inch of film, the substantially rectangularly shaped
perforations or holes having been formed by vacuum perforation
of the thermoplastic film, said substantially rectangularly
shaped vacuum formed perforations or holes being about 1 mil to
about 4 mils across the minor axis, the vacuum formed perfora-
tions 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 coextruded 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 co-
extruded thermoplastic film having a porosity of about 100 to
about 500 cubic feet per minute.
dal/~
~2~5~
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 oE
Fig. 1;
Fig. 5 is an enlarged top view of a portion of the
thermoplastic film of which the embodiment of ~ig. 1 is
constructed: and,
Fig. 6 is a view similar to that of Fig. 5 illustrating
an alternate embodiment of the film of the invention.
Referring now to the drawings, an infusion bag of the
present invention is illustrated gen_rally at 10. The bag or
packet 10 is constructed of a rectangular strip of a perforated
plastic film 11 which is described in more detail hereinafter.
The strip of film 11 is folded at 12, sealed at edges 13 and 14
and filled with a particulated 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 seen 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
lZ2~059
-- 7 --
layer 22 of a somewhat less heat resistant film forming
thermoplastic resin, such as polyethylene, polyester,
polycarbonate or nylon, with polyethylene being preferred. The
film ll has a multiplicity of fine slots or rectangularly-shaped
capillaries 23 which are of a somewhat tapered construction,
being more or less in the form of a truncated box.
The slots 23 are illustrated in alternate rows in a
uniform, pre-determined pattern and represent an ideally shaped
slot. The slots are rectangularly shaped with somewhat rounded
ends. In actual construction, they may have slight bulges at
their center. The slots are of such a size that particulate
matter is inhibited from passing therethrough. The size of the
slot can be adjusted by changing either the major axis or the
minor axis. By changing the minor axis, the slot can control
the size particulate matter that can be passed or sifted through
the film. By changing either the major axis or the minor axis,
the liquid infusion rate can be controlled. It is important
that the slots be sufficiently large in size and in sufficient
number to provide a desired rate of liquid infusion and yet be
sufficiently small in size to prevent the migration of particles
therethrough such as the particulated product P.
A perforated thermoplastic film 31 is illustrated in
Fig. 6 which has slots 33 which are arranged in somewhat diagonal
lines. It can be appreciated that the slots can be arranged in
a variety of patterns as desired.
~L2Z~059
In the packaging of an item such as tea, a preerred
slot size is from one to four mils across the minor axis, with a
size of two to four mils being most preferred. The major axis
is four to 10 mils across, with about four to six mils being
preferred. The film has a thickness of 0.25 mil to two mils and
about 500 slots per square inch or more. From 1800 to 4200
slots per square inch are preferred, with about 2900 slots per
square inch being most preferred. The porosity of the film is
100 to 500 cubic feet per minute (CFM).
The outer layer of the coaxial or coextruded perforated
thermoplastic film of the bag is preferably a heat resiskant
polyester film having a melting temperature of 425F to 600F
witb 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
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 be kept below about 260F. It
~Z2:1~5~
can be appreciated that 2articular polyolefin resins or other
film forming resins may have higher or lower melting tempera-
tures; however, it is essential that a melting temperature dif-
ferential 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 2referred. The melting temperature of 180F to 250F
of the somewhat less heat resistant polyethylene film layer
provides the necessary melting temperature differential.
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
sealers, hot wires, hot air or other suitable apparatuses or
techniques.
For the packaging of a typical commercial tea for brew-
ing, a perforated thermoplastic film suitable for constructing
the infusion bag is a coextruded polypropylene/polyethylene slot
perforated thermoplastic film formed from a high density poly-
~221059
-- 10 --
ethylene resin and a polypropylene resin. The resins are odor-
less 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 bag and thus accelerates the infusion process.
Although a coextruded multilayer polyester/polyethylene
film is preferred, other combinations of multilayer films are
suitable. ~sing the following designations:
Polypropylene PP
Polyethylene PE
Crystalline polyester 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 ~/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 and the inner sealant layer.
With some resins, it may be necessary to provide multi-
layer films of more than two layers. ~or example, a triple layer
~Z~059
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 desired
or permitted.
The film has a dry surface and has no tendency to stick,
0 cling or ~block~.
In the construction of infusion bags, the male surface
of the film is on the inside of the bag.
The invention is illustrated in its simplest form, and
as a typical smal~ size infusion bag for the packaging of in-
dividual servings of tea for brewing. Larger size packages,such as those customarily used in the food services industry can
also be constructed. Such larger bags can be similarly con-
structed or 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 configurations as
desired. Rectangularly shaped packages are generally more suit-
able for boxing or other type of group packaging and can usually
be more easily fabricated.
The infusion bags of the present invention have excel-
lent wet strength and will not deteriorate in boiling water.
12ZlOS9
- 12 -
The bags themselves are odorless and tasteless and do not impart
any foreign taste to the item being packaged. They are, in
effect, substantially inert.
Unlike bags constructed of fibrous materials, the poro-
sity of the bags of this invention is unaffected by the brewingprocess. The slots 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
0 flotation of the bag and slows the brewing process.
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
items such as tobacco, snuff and the like. The bags may be used
for packaging of any items in which infusion of liquids 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
the appended claims without departing from the spirit of the
invention.
