Heat sealable tea bag paper and process of producing same
Tea bag abstract
The tea bag paper comprises a first phase of natural fibers in
a weight percentage of from 60% to 85%, and a second phase of heat-sealable
synthetic fibers with the remainder of the weight percentage of
from 15% to 40%. The second phase penetrates the first phase in
such a way that both sides of the paper are adapted to be heat-sealed,
with the unit area weight of the paper being between 10 and 15 g/m.sup.2.
The tea bag paper exhibits enhanced tea diffusion, and may be processed
on special high-speed automatic tea packing machines, because it
is heat-sealable on either side thereof.
Tea bag claims
1. A process of producing a tea bag paper, comprising the steps
depositing an aqueous suspension of natural fibers having a stock
density of less than 0.1% on a paper machinewire or screen in order
to form a first layer, the first layer having first and second sides
and forming 60-85 weight % of the tea bag paper;
depositing a second layer comprising heat-sealing thermoplastic
synthetic fibers forming 15-40 weight % of the tea bag paper on
the first side of the first layer;
dewatering the first and second layers so that said layers merge
together and said second layer penetrates said first layer to the
extent that said synthetic fibers exist on both first and second
sides of said first layer;
melting said synthetic fibers in a subsequent drying process and
reconsolidating said synthetic fibers in such a way that they cover
said natural fibers when being reconsolidated;
whereby said tea bag paper is heat-sealing on both sides and the
weight of said tea bag paper is between 10 and 15 g/m.sup.2.
2. A process according to claim 1, wherein said permeation of said
first and second layers is intensified by a rigorous dewatering.
3. The process of claim 1, further comprising the step of forming
said tea bag paper into a tea bag.
4. The process of claim 1 wherein said heat-sealing thermoplastic
synthetic fibers comprise polyethylene, polypropylene, or a copolymer
of vinyl chloride and vinyl acetate.
Tea bag description
The present invention relates to a tea bag paper, comprising a
first phase of natural fibers and a second phase of heat-sealing
synthetic fibers. Furthermore, the present invention relates to
a process of producing such a tea bag paper, and a tea bag made
from said paper.
Heat-sealable tea bag papers are known which have a unit area weight
of at least 16 g/m.sup.2, and which may be processed into tea bags
on high-speed automatic packing machines at a rate of up to 4,000
units per minute. Normally, these tea bag papers consist of about
75% of natural fibers and about 25% of heat-sealing synthetic materials.
European patent specification 00 39 686 describes a multi-phase
heat-sealing fibrous material and the process of producing same.
In this multi-phase material, portions of a high tea diffusion and
such of a low tea diffusion are provided alternately. This is obtained
in that the portions of high tea diffusion have a substantially
smaller proportion (percentage) of heat-sealing fibers than the
portions of lower diffusion. Apart from the complex process described
in said publication, the weight of the tea bag is relatively high
with 16.5 g/m.sup.2. Further, owing to the irregular distribution
of the heat-sealing fibers for defining portions of high and low
diffusion, there is the risk that upon sealing of the tea bag, its
seams are less resistant in boiling water than the seams of a bag
which has been formed from a paper having a continuously uniform
German patent specification 2,147,322 describes the production
of a heat-sealable paper having a weight of between 14 to 17 g/m.sup.2,
and in which the heat-sealable fibers or particles are concentrated
preferably to one side of the paper surface. However, if the heat-sealable
layer is provided preferably on one side of the paper only, and
this layer is then fused during the drying process on the paper-making
machine, this-layer closes or blocks the porous base layer, thereby
preventing good diffusion of tea.
German patent specification 1,546,330 describes a process in which
the thermoplastic fibers and the non heat sealable fibers are deposited
in common in an aqueous suspension on the wire of a papermaking
machine. Owing to the characteristic of the lower density of the
thermoplastic fibers formed of polypropylene, a different proportion
of polypropylene fibers is deposited or precipitated on the opposite
surfaces of the paper formed. Accordingly, the drawbacks mentioned
above with respect to one-sidedly sealable papers similarly apply
to this process. Described is this process for a paper of a weight
of 17 g/m.sup.2.
Moreover, there are known heat-sealable tea bag papers having a
so-called open structure in which openings of various sizes and
shapes are formed in the paper by various methods. This structure
is intended to provide improved tea diffusion, which is not readily
obtained, however. At any rate, this open structure of the paper
greatly limits the use of the tea bag paper, as an excessive amount
of dust-like material would pass through the paper. All of these
so-called open papers are being produced in a weight class of above
A feature common to all of these conventional heat-sealable tea
bag papers is that these papers, due to their relatively high unit
area weight and the high proportion or content of synthetic fibers,
show a tea diffusion inferior to that of the conventional light-weight,
not heat-sealable materials having a weight of about 12 g/m.sup.2.
However, these conventional tea bag papers, consisting of a single
phase, can be processed on packing machines only with a relatively
complex folding process, and only at a rate per unit of time of
about 230 bags/minute.
It is the object of the present invention to provide a light-weight
heat-sealable tea bag paper which has a substantially enhanced tea
diffusion compared to conventional heat-sealable papers, and which
may be processed on high-speed tea bag producing machines calling
particularly for double-sided sealing of the paper. Further, the
invention contemplates to provide a process for the production of
such a tea bag paper.
According to the present invention, this object is solved by a
tea bag paper in which the first phase of a weight percentage of
from 60 to 85% is penetrated by the second phase having the remainder
of the weight percentage of from 15 to 40%, in such a way that both
sides of the paper are heat-sealable, with the weight per unit area
of the paper being between 10 and 15 g/m.sup.2, preferably 12 g/m.sup.2.
According to a preferred embodiment, the first phase comprises natural
fibers having a weight per unit area of from 8.5 to 9.7 g/m.sup.2,
and the second phase comprises synthetic fibers having a weight
per unit area of from 3.1 to 4.0 g/m.sup.2.
Regarding the process of production, the object of the invention
is solved in that in one step an aqueous suspension of the natural
fibers having a stock density of less than 0.1% is deposited on
the wire (or screen) of a papermaking machine to form a first layer;
that in a second step the heat-sealable synthetic fibers are deposited
from an aqueous suspension onto the first layer in a way to penetrate
the first layer; and that the tea bag paper is obtained from said
two layers by dewatering and drying in accordance with conventional
methods. Here, the penetration of the two layers can be particularly
intensified by rigorous dewatering.
Well-known natural fibers, such as hemp, Manila hemp, jute, sisal
and others, as well as long-fiber wood pulp may be used for the
first layer. Preferred materials for the second layer of heat-sealable
fibers are polyethylene, polypropylene or copolymers of vinyl chloride
and vinyl acetate.
In the production operation, the synthetic heat-sealing fibers
of the second phase penetrate the first phase, to enclose or cover
the natural fibers in a molten state during the drying process on
the papermaking machine. These fibers thereby expose the necessary
pores in the material. Thus, tea diffusion is not impaired in the
material according to the invention. Furthermore, the material according
to the invention can be heat-sealed on both sides, and this feature
is likewise ensured by the penetration of the second phase through
the not heat-sealing first phase.
Below, the invention is described in greater detail in an exemplary
embodiment with reference to the drawings, wherein:
FIG. 1a through 1c is a general, roughly schematical illustration
of the various steps in the formation of the tea bag paper according
to the invention from natural fibers and synthetic fibers; and
FIG. 2 illustrates, likewise in a roughly schematical form, the
structure of a system for carrying out the process according to
FIG. 1 shows in schematical illustration the formation of the tea
bag paper according to the invention. FIG. 1a) illustrates the formation
of a first fibrous layer of natural fibers 1, and the formation
of a second fibrous layer of synthetic, heat-sealable fibers 2.
As shown, the second layer containing the fibers 2 is formed by
depositing this layer above the second layer formed of the natural
fibers 1. In the drawing, for distinction the natural fibers 1 are
hatched horizontally, while the synthetic fibers 2 are hatched approximately
FIG. 1b) shows how penetration of the two layers is obtained by
the above-mentioned rigorous dewatering of the two layers, especially
of the second layer containing the fibers 2, such that the synthetic
fibers 2 come to lie between the natural fibers 1, to extend between
the natural fibers 1 from the upper side of the first layer to the
bottom side thereof.
In a further production step, the layers 1 and 2 penetrating each
other are dried and thereby heated in such a manner that the synthetic
fibers 2 melt and, upon solidification, wrap around the fibers 1
so that these fibers are enclosed or covered at least partially.
In this way, the final tea bag paper becomes heat-sealable on both
sides thereof (FIG. 1c)).
FIG. 2 illustrates the basic structure of a papermaking machine
which may be used for producing a tea bag paper according to the
invention. First, a suspension "A" is prepared from ground
natural fibers and water, and another suspension "B" is
prepared from the partially ground Synthetic fibers and water. These
two suspensions A and B are supplied from the respective reservoirs
3 and 4 to the papermaking machine through the so-called head box
(or breast box). The papermaking machine comprises essentially a
rotating wire (screen) 5 which travels across a plurality of dewatering
chambers 6, 7 and 8.
Through suitable pipelines and pump devices (not illustrated),
suspension A is deposited on wire 5 above the first two dewatering
chambers 6, and water is sucked off through chambers 6 and a dewatering
pipe a. In this way, a first fibrous layer of natural fibers 1 is
formed on the moving wire 5. When the wire 5 is advanced to a position
above the dewatering chambers 7, the second suspension B is supplied,
thereby to deposit a second layer of synthetic fibers onto the first
layer above the dewatering chambers 7. In this stage, dewatering
takes place through dewatering pipe b. Upon further movement of
the wire 5 supporting the two superposed fibrous layers, rigorous
dewatering is effected above dewatering chambers 8, whereby the
two layers are caused to penetrate each other. By correspondingly
controlling the dewatering effect, a higher or lesser degree of
penetration may be obtained.
The thus formed material 9 of natural fibers and synthetic fibers
is removed from the wire and transferred to a drying stage. Such
drying may be effected in various ways. For example, by contact
drying or flow-through drying. Corresponding drying elements are
indicated in a roughly schematical way by elements 10. FIG. 2 (drying
station) illustrates three drying cylinders 10 through which the
paper web formed is dried by the contact method. However, it is
also practicable to cause the paper web formed to travel across
one single cylinder, and dry it by hot air, without the web contacting
this cylinder. Heating of the dual-layer fibrous material results
in melting or fusing of the synthetic fibers 2 contained in the
compound layer 9. In solidification at the outlet end of the drying
station, the synthetic fibers enclose or cover the natural fibers
at least partially, such that tea bag paper wound onto a reel 11
is heat-sealable on either side thereof.
The improved characteristics or properties of the tea bag paper
according to the invention may be demonstrated below in an Example
in comparison with conventional materials. A tea bag paper (sample
A) according to the invention was compared with a conventional heat-sealable
tea bag paper (sample B) and a conventional, not heat-sealable tea
bag paper (sample C). The below characteristics were determined
for these three materials:
TABLE ______________________________________ A B C ______________________________________
Unit area weight (g/m.sup.2) 12.2 16.5 12.3 Time of initial 8.9
11.8 9.7 development of color (seconds) Tea diffusion factor 1.71
3.59 1.86 (or product) (density .times. air resistance) ______________________________________
Sample A is according to the invention; Sample B is a conventional
heatsealable tea bag paper; Sample C is a not heatsealable tea bag
Explanations with respect to the Table:
Time of initial development of color
Tea bags of precisely the same configuration were formed from the
different papers according to Sample A, Sample B and Sample C, which
bags were filled with precisely the same quantity of normal tea.
The quantity was about 5 g/bag. Upon immersion of the separate tea
bags into boiling water, the period of time was determined until
the first or initial color streaks appeared. This period of time
is a measure of how fast the flavor-giving and coloring constituents
of the tea are extracted from the tea bags made of the different
Tea diffusion factor (product)
Whereas the above-mentioned period of time for the initial development
of color is determined in an experimental method, the tea diffusion
factor is a mathematical value. Minimum raw density and high porosity
(low air resistance) define the rate at which tea extraction from
a bag takes place. Accordingly, when the product of raw density
and air resistance is as small as possible, the prior conditions
for good tea extraction or tea diffusion exist.
The raw density is the well-known quotient of unit area weight
and thickness. Air resistance is specified in seconds and determined
by measuring the period of time in which a given volume of air flows
through a defined surface area of the paper to be tested (compare
also Gurley measurement).
As is clear from the above Table, both the time of initial development
of color (coloration) and the tea diffusion factor are optimum with
Sample A, i.e. the material according to the invention. Accordingly,
this material shows a tea diffusion being as good as that of the
conventional not heat-sealable papers, or being even slightly better
than the tea diffusion of these latter papers; however, the material
of the invention may be processed on special high-speed automatic
tea packing machines.