Note: Descriptions are shown in the official language in which they were submitted.
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Heat-sealable filter material containing biodegradable polymers
This invention relates to a filter material consisting of at least one ply of
natural fibres
and at least a second ply of heat-sealable synthetic material, which is
biodegradable.
EP-A 0 380 127 A2 describes, for example, a heat-sealable tea bag paper and
the
process for the production thereof, wherein the heat-sealing phase contains
polyethy-
lene and/or polypropylene and/or a copolymer of vinyl chloride and vinyl
acetate and
the basis weight of this material is between 10 and 15 g/m2.
EP-A 656 224 (application number 94 107 709.1) describes a filter material, in
par-
ocular for the production of tea bags and coffee bags or filters, having a
basis weight
of between 8 and 40 g/m'~, in which the heat-sealing ply consists of plastic
fibres,
preferably polypropylene or polyethylene, which are laid in the heated state
onto the
first ply consisting of natural fibres.
German application DE-A 2 147 321 (US priority 23.09.70, US 74 722) describes
a
thermoplastic, heat-sealable composition consisting of a polyolefin powder
(polyethylene or polypropylene) which is embedded in a matrix material of
vinyl
chloride/vinyl acei:ate copolymer. This material is also used to provide a
heat-sealable
finish on a fibrous material produced using papermaking techniques.
All these stated filter materials require a content of at least 20 to 30 wt.%
of thermo-
plastic material, relative to the total basis weight of the filter material,
in order to pro-
duce a filter bag b:y heat sealing.
It is known that used filter materials, for example tea bags, coffee bags or
also other
filters are disposed Of on a compost heap or in the biowaste bin. After a
certain period
of time, which is dependent upon further parameters such as temperai:ure,
atmospheric
humidity, microorganisms etc., the natural fibre component of the filter bag
has de-
composed and biodegraded, while the thermoplastic network of polymer fibres re-
mains and reduces the quality of the compost.
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On the other hand, it is not possible to separate the natural fibre component
from the
thermoplastic, nor-biodegradable polymer, i.e. the used filter bag would have
to be
classed as non-reutilisable waste (grey bin).
S
The object of the invention is accordingly to provide a completely
biodegradable,
heat-sealable filter material which is compostable, so constituting the most
favourable
solution both environmentally and economically. It is also intended to
describe proc-
esses for the production of such filter materials.
The present invention provides a filter material consisting of an at least two-
ply
structure, wherein at least one ply contains natural fibres and one ply
biodegradable,
thermoplastic fibres, wherein the thermoplastic fibres are selected from the
group
comprising aliphatic or partially aromatic polyesteramides, aliphatic or
partially aro-
matic polyesters, .aliphatic or partially aromatic polyesterurethanes,
aliphatic or ali-
phatic-aromatic polyestercz~rbonates.
Thermoplastic fibres may both be applied onto the ply of natural fibres in an
operation
on the papermaking machine and laid onto this paper ply of natural fibres in
the
heated state using a melt-blowing process and be fused both with themselves
and with
the paper ply.
The first ply of tile filter material generally has a basis weight of between
8 and
40 g/m2, preferably of 10 to 20 g/m2 and air permeability of 300 to
40001/m2~sec
(DIN 53 887), preferably of 500 to 30001/m2~sec.
The second layer of the filter material preferably has a basis weight of 1 to
15 g/m2,
preferably of 1.5 to 10 g/rri ~.
The first ply of the: filter material made from natural fibres is preferably
provided with
wet strength.
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The filter material is used, for example, for the production of tea bags,
coffee bags or
tea or coffee filter:..
The filter material may be produced in the following manner:
In a first stage, an aqueous suspension of the natural fibres is applied onto
a paper-
making machine wire and, in a second stage, the heat-sealable, biodegradable
polymer
fibres are laid onto the natural fibre layer in such a manner that they
partially penetrate
the natural fibre layer, wherein interpenetration of the two layers may be
adjusted by
the degree of dewatering on the wire. Known natural fibres, such as hemp,
manilla,
jute, sisal and others, as well as long-fibre woodpulp, are used for the first
layer and
produced on a papermakinf; machine in a manner lrnown per se.
According to the i.nventior.~, a biodegradable, thermoplastic polymer in fibre
form is
used for the second layer, which polymer is selected from the group comprising
ali-
phatic or partially .aromatic polyesteramides, aliphatic or partially aromatic
polyesters,
aliphatic or partially aromatic polyesterurethanes, aliphatic or aliphatic-
aromatic poly-
estercarbonates.
Biodegradable andl compostable polymers which may be considered are aliphatic
or
partially aromatic polyesters, thermoplastic aliphatic or partially aromatic
polyester-
urethanes, aliphatic or aliphatic-aromatic polyestercarbonates, aliphatic or
partially
aromatic polyester.amides.
The following polymers are; suitable:
aliphatic or partially aromatic polyesters prepared from
A) aliphatic bifimction,al alcohols, preferably linear C2 to C,o dialcohols,
such as
for example ethanediol, butanediol, hexanediol or particularly preferably bu-
tanediol and/or optionally cycloaliphatic bifimctional alcohols, preferably
having 5 or 6 C atoms in the cycloaliphatic ring, such as for example cyclo-
hexanedimethanol, and/or, partially or entirely instead of the diols,
monomeric
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or oligome:ric polyols based on ethylene glycol, propylene glycol, tetrahy-
drofuran or copolyrr~ers thereof having molecular weights of up to 4000, pref
erably of up to 1000, and/or optionally small quantities of branched bifunc-
tional alcohols, prei:erably C3-C~2 allcyldiols, such as for example neopentyl
glycol, and additionally optionally small quantities of more highly functional
alcohols, such as for example 1,2,3-propanetriol or trimethylolpropane and
from aliphatic bifunctional acids, preferably Cz-CIZ alkyldicarboxylic acids,
such as for example and preferably succinic acid, adipic acid and/or
optionally
aromatic bifunctional acids, such as for example terephthalic acid,
isophthalic
acid, naphthalenedicarboxylic acid and additionally optionally small
quantities
of more highly functional acids, such as for example trimellitic acid or
B) from acid- and alcohol-functionalised units, preferably having 2 to 12 C
atoms
in the alkyl chain, fir example hydroxybutyric acid, hydroxyvaleric acid, lac-
tic acid or the derivatives thereof, for example s-caprolactone or dilactide,
or a mixture and/or a copolymer prepared from A and B,
wherein the aromatic acids constitute a fraction of no more than 50 wt.%,
relative to
all the acids.
Aliphatic or partially aromatic polyesterurethanes prepared from
C) aliphatic bifunctional alcohols, preferably linear C2 to Clo dialcohols,
such as
for example ethanediol, butanediol, hexanediol, particularly preferably bu-
tanediol and/or optionally cycloaliphatic bifunetional alcohols, preferably
having a C',5 or C6 cycloaliphatic ring, such as for example cyclohexanedi-
methanol, and/or, partially or entirely instead of the diols, monomeric or oli-
gomeric polyols based on ethylene glycol, propylene glycol, tetrahydrofuran
or copolymers thereof having molecular weights of up to 4000, preferably of
up to 1000, andlor optionally small quantities of branched bifunctional alco-
hols, preferably C3-C12 alkyldiols, such as for example neopentyl glycol, and
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additionally optionally small quantities of more highly functional alcohols,
preferably C3-C~Z ;alkylpolyols, such as for example 1,2,3-propanetriol or
trimethylolpropane and from aliphatic bifimctional acids, preferably C2-C,2 al-
kyldicarbo:cylic acids, such as for example and preferably, succinic acid,
S adipic acid., and/or optionally aromatic bifimctional acids, such as for
example
terephthalic; acid, is~ophthalic acid, napthalenedicarboxylic acid and
addition-
ally optionally small quantities of more highly functional acids, such as for
ex-
ample trimellitic acid, or
D) from acid- and alcohol-functionalised units, for example having 2 to 12 C
at-
oms, for e~;ample hydroxybutyric acid, hydroxyvaleric acid, lactic acid or the
derivatives thereof, for example s-caprolactone or dilactide,
or a mixture and/o:r a copolymer prepared from C and D,
wherein the aromzvtic acids constitute a fraction of no more than 50 wt.%,
relative to
all the acids;
E) from the rc;action product of C and/or D with aliphatic and/or
cycloaliphatic
bifunctional and additionally optionally more highly functional isocyanates,
preferably having 1. to 12 C atoms or 5 to 8 C atoms in the case of cyclo-
aliphatic isocyanates, for example tetramethylene diisocyanate, hexamethylene
diisocyanate, isophorone diisocyanate, optionally additionally with linear
and/or brmched and/or cycloaliphatic bifunctional and/or more highly fiulc-
tional alcolrlols, preferably C3-C12 allcyldiols or allcylpolyols or 5 to 8 C
atoms
in the case of cycloaliphatic alcohols, for example ethanediol, hexanediol, bu-
tanediol, cyclohexanedimethanol, and/or optionally additionally with linear
and/or bra~iched an.d/or cycloaliphatic bifimctional and/or more highly func-
tional amines and/or aminoalcohols preferably having 2 to 12 C atoms in the
alkyl chair, for example ethylenediamine or aminoethanol, and/or optionally
further modified amines or alcohols, such as for example ethylenediamino-
ethanesulphonic acid, as the free acid or as a salt,
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wherein the ester fraction C) and/or D) amounts to at least 75 wt.%, relative
to the
sum of C), D) and E).
Aliphatic or aliphatic-aromatic polyestercarbonates prepared from
F) aliphatic bifunctional alcohois, preferably linear CZ to C,o dialcohols,
such as
for example ethanediol, butanediol, hexanediol or particularly preferably bu-
tanediol and/or optionally cycloaliphatic bifunctional alcohols, preferably
having S to 8 C atoms in the cycloaliphatic ring, such as for example cyclo-
hexanedim~~thanol, and/or, partially or entirely instead of the diols,
monomeric
or oligome:ric poly~ols based on ethylene glycol, propylene glycol, tetrahy-
drofuran or copolymers thereof having molecular weights of up to 4000, pref
erably of up to 1OC10, and/or optionally small quantities of branched bifunc-
tional alcohols, preferably with C2-C12 alkyldicarboxylic acids, such as for
ex-
ample neopentyl-glycol, and additionally optionally small quantities of more
highly functional alcohols, such as for example 1,2,3-propanetriol or
trimethylolpropane and from aliphatic bifunctional acids, such as for example
and preferably, succinic acid, adipic acid, and/or optionally aromatic bifunc-
tional acids, such a~ for example terephthalic acid, isophthalic acid,
napthale-
nedicarboxylic acid and additionally optionally small quantities of more
highly
functional ;acids, such as for example trimellitic acid, or
G) from acid- and alcohol-functionalised units, for example having 2 to 12 C
at-
oms in the alkyl chain, for example hydroxybutyric acid, hydroxyvaleric acid,
lactic acid ~or the derivatives thereof, for example s-caprolactone or
dilactide,
or a mixture and/or a copolymer prepared from F and G,
wherein the aromatic acids constitute a fraction of no more than 50 wt.%,
relative to
all the acids,
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H) a carbonate; fraction which is produced from aromatic bifunctional phenols,
preferably bispheno:l A, and carbonate donors, for example phosgene,
or
a carbonate: fraction which is produced from aliphatic carbonic acid esters or
the derivatives thereof, such as for example chlorocarbonic acid esters or ali
phatic carboxylic acids or the derivatives thereof, such as for example salts
and
carbonate donors, for example phosgene, wherein
the ester fraction F') and/or G) amounts to at least 70 wt.%, relative to the
sum of F),
G) and H).
Aliphatic or partially aromatic polyesteramides prepared from
I) aliphatic bifunctional alcohols, preferably linear C2 to Coo dialcohols,
such as
for example ethanediol, butanediol, hexanediol, particularly preferably bu-
tanediol and/or optionally cycloaliphatic bifunctional alcohols, preferably
having 5 to 8 C atoms, such as for example cyclohexanedimethanol, and/or,
partially or entirely instead of the diols, monomeric or oligomeric polyols
based on ethylene glycol, propylene glycol, tetrahydrofuran or copolymers
thereof having molecular weights of up to 4000, preferably of up to 1000,
and/or opti~~nally small quantities of branched bifunctional alcohols, prefera-
bly C3-C12 alkyldiol.s, such as for example neopentyl glycol, and additionally
optionally small quantities of more highly functional alcohols, preferably C3-
C~2 alkylpolyols, such as for example 1,2,3-propanetriol, trimethylolpropane
and from aliphatic bifunctional acids, preferably having 2 to 12 C atoms in
the
alkyl chain, such :as for example and preferably succinic acid, adipic acid
and/or optionally aromatic bifunctional acids, such as for example
terephthalic
acid, isophthalic acid, naphthalenedicarboxylic acid and additionally option-
ally small quantities of more highly functional acids, such as for example
trimellitic acid or
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K) from acid- ~~.nd alcohol-functionalised units, preferably having 2 to 12 C
atoms
in the carbon chain, for example hydroxybutyric acid, hydroxyvaleric acid,
lactic acid or the derivatives thereof, for example s-caprolactone or
dilactide,
or a mixture and/or a copolymer prepared from I) and K),
wherein the aromatic acids constitute a fraction of no more than 50 wt.%,
relative to
all the acids,
L) an amide fraction prepared from aliphatic and/or cycloaliphatic
bifunctional
and/or optionally small quantities of branched bifunctional amines, with
linear
aliphatic C; to Clo cliamines being preferred, and additionally optionally
small
quantities of more highly functional amines, the amines preferably being hex-
amethylenediamine, isophoronediamine and particularly preferably hex-
amethylenediamine, and from linear and/or cycloaliphatic bifunctional acids,
preferably having 2 to 12 C atoms in the alkyl chain or a CS or C6 ring in the
case of cyc:loaliphatic acids, preferably adipic acid, and/or optionally small
quantities of branched bifunctional andlor optionally aromatic bifunctional
acids, such. as for example terephthalic acid, isophthalic acid, napthalene-
dicarboxylic acid and additionally optionally small quantities of more highly
functional acids, preferably having 2 to 10 C atoms, or
M) from an annide fraction prepared from acid- and amine-functionalised units,
preferably having 4 to 20 C atoms in the cycloaliphatic chain, preferably
w-laurolactam, s-caprolactam, particularly preferably s-caprolactam,
or a mixture prepared from L) and M) as the amide fraction, wherein
the ester fraction I) and/or K) amounts to at least 30 wt.%, relative to the
sum of I),
K), L) and M), wiith the fraction by weight of the ester structures preferably
amount-
ing to 30 to 70 wt.'%, and the fraction of the amide structures to 70 to 30
wt.%.
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During the production pro<;ess, the synthetic biodegradable heat-sealing
fibres of the
second ply partiallly penetrate the first ply and, during the drying process
on the pa-
permaking machine, in a molten state enclose the natural fibres. The pores
necessary
for filtration are kept clear during this operation.
The invention is illustrated below by means of the drawings.
Figure 1 shows a general, broadly diagrammatic representation of the various
stages
in the formation e~f the filter material according to the invention from
natural fibres
and synthetic fibres.
Figure 1 shows a diagrammatic representation of the formation of the filter
material
according to the invention. Figure 1 a) shows the formation of a first fibre
layer from
natural fibres 1 anal the formation of a second fibre layer from synthetic,
biodegrad-
1 S able, heat-sealable- fibres 2. The second layer is thus formed using the
fibres 2 by
deposition on top of tho first layer, which is formed by the natural fibres 1.
For the
purposes of differentiation in the drawing, the natural fibres 1 are shown
with horizon-
tal hatching, while the s~mthetic fibres 2 are shown with approximately
vertical
hatching.
Figure lb) shows how, by means of the stated dewatering of the two layers, in
particu-
lar the second layer containing the fibres 2, partial interpenetration of the
two layers is
achieved, the synthetic fibres 2 passing between the natural fibres 1.
In a fiirther production stage, the partially interpenetrating layers 1 and 2
are dried,
during which operation they are heated in such a manner that the synthetic
fibres 2
melt and, after resolidification, lie around the fibres 1 in such a manner
that these lat-
ter fibres are at least partially enclosed. The filter material has thus
become heat-
sealable (figure lc).
Figure 2 shows the essential structure of a papermaking machine, as may be
used for
the production of a filter material according to the invention. First of all,
a suspension
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"A" is prepared from the ground natural fibres and water, while a suspension
"B" is
also prepared from the partially ground synthetic fibres and water.
These two suspen:cions A and B are transferred from their individual tanks (3
and 4)
into the papermaking machine via the so-called head box. This essentially
comprises a
circulating wire (5), which is conveyed through a number of dewatelzng
chambers (6,
7 and 8).
By means of suitable pipework and pumping apparatus, which are not shown in
any
further detail, suspension A,, on the wire 5, is passed through the first two
dewatering
chambers 6, wherein the water is drawn off by the chambers 6 and the
dewatering
line. This results in the formation of a first fibre layer of natural fibres 1
on the mov-
ing wire 5. As the wire 5 moves onwards through the dewatering chambers 7, the
sec-
ond suspension B is introduced, wherein the second layer of synthetic fibres
is depos-
ited on the first layer in the dewatering chambers 7. Dewatering proceeds by
means of
the dewatering line. As the wire 5 bearing the two superposed fibre layers
moves on-
wards through the dewatering chambers 8, further dewatering is performed, as a
result
of which the two layers partially interpenetrate. The degree of
interpenetration may be
increased or reduced by appropriate adjustment of the dewatering.
The material 9, which has now been formed from natural fibres and synthetic
fibres, is
removed from the wire and dried. Drying may proceed in various manners, for
exam-
ple by contact drying or by through-flow drying.
The units 10 give only a general diagrammatic indication of suitable drying
units.
Figure 2 shows three drying cylinders 10, by means of which the formed paper
web is
dried by the contact' process. It is, however, also practicable to pass the
formed paper
web over only on<; cylinder and to dry it with hot air without the web lying
on this
cylinder.
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Heating of the two-layer fibre material causes the synthetic fibres 2 in the
mixed layer
9 to melt. After resolidification on leaving the drying apparatus, the
synthetic fibres at
least partially enclose the natural fibres and the heat-sealable filter
material is wound
onto a reel 11.
A second production process for a biodegradable, heat-sealable filter material
is per-
formed as follows:
If the biodegradable polymer is in pellet form, it may be shaped into fibres
using the
melt-blowing process and deposited while still hot and tacky onto a substrate,
for ex-
ample a paper made from n;3tural fibres.
This is a prior art process. but the essentials of the process shown in figure
3 are
nonetheless briefly described below:
The dried pellets 12 are conveyed into an extruder 13, in which they are
melted and
heated to the temperature required for fibre formation. This heated polymer
melt then
passes into the M)=s spinneret 14. This spinneret has a large number of small
orifices
through which the polymer melt is pressed and drawn into fibres. A strong
stream of
air is directed onto these fibres 1 S immediately below the spinneret, the
fibres are
stretched further, torn into varying lengths and deposited onto a substrate,
for example
a paper 16, which lies upon a suction roll 17. Since these fibres are still in
a hot, tacky
state, they adhere to the natural fibres of the paper. Once cool, the material
is wound
on the winder 18. Typical diameters of these melt-blown fibres are between 2
and
7 pm. Figure 3 is a diagrammatic representation of the melt-blowing process.
