Note: Descriptions are shown in the official language in which they were submitted.
PF 70547
Process for producing clingfilms
Description
The present invention relates to a process for producing clingfilms by using
biodegradable polyesters obtainable via polycondensation of:
i) from 65 to 80 mol%, based on components i to ii, of one or more
dicarboxylic
acid derivatives or dicarboxylic acids selected from the group consisting of:
succinic acid, adipic acid, sebacic acid, azelaic acid, and brassylic acid;
ii) from 35 to 20 mol%, based on components i to ii, of a terephthalic acid
derivative;
iii) from 98 to 102 mol%, based on components i to ii, of a C2-Ca-alkylenediol
or C2-
C6-oxyalkylenediol;
iv) from 0.1 to 2% by weight, based on the polymer obtainable from components
i to
iii, of at least trifunctional crosslinking agent or at least difunctional
chain
extender.
The invention further relates to a process for producing clingfilms by using
polymer
components a) and b):
a) from 5 to 95% by weight of a biodegradable polyester according to claim I
and
b) from 95 to 5% by weight of an aliphatic-aromatic polyester obtainable via
polycondensation of:
i) from 40 to 60 mol%, based on components i to ii, of one or more
dicarboxylic acid derivatives or dicarboxylic acids selected from the group
consisting of: succinic acid, adipic acid, sebacic acid, azelaic acid, and
brassylic acid;
ii) from 60 to 40 mol%, based on components i to ii, of a terephthalic acid
derivative;
iii) from 98 to 102 mol%, based on components i to ii, of a C2-C8-alkylenediol
or C2-C6-oxyalkylenediol;
iv) from 0 to 2% by weight, based on the polymer obtainable from components
i to iii, of at least trifunctional crosslinking agent or difunctional chain
extender.
PF 70547
2
The invention also relates to a process for producing clingfilms by using
polymer
components a), b), and c):
a) from 10 to 40% by weight of a biodegradable polyester according to claim I
and
b) from 89 to 46% by weight of an aliphatic-aromatic polyester obtainable via
polycondensation of:
i) from 40 to 70 mol%, based on components i to ii, of one or more
dicarboxylic acid derivatives or dicarboxylic acids selected from the group
consisting of: succinic acid, adipic acid, sebacic acid, azelaic acid, and
brassylic acid;
ii) from 60 to 30 mol%, based on components i to ii, of a terephthalic acid
derivative;
iii) from 98 to 102 mol%, based on components i to ii, of a C2-Ca-alkylenediol
or C2-C6-oxyalkylenediol;
iv) from 0 to 2% by weight, based on the polymer obtainable from components
i to iii, of at least trifunctional crosslinking agent or difunctional chain
extender;
c) from 1 to 14% by weight of one or more polymers selected from the group
consisting of: polylactic acid, polycaprolactone, polyhydroxyalkanoate,
polyalkylene carbonate, chitosan, and gluten, and one or more polyesters based
on aliphatic diols and on aliphatic dicarboxylic acids -
and
from 0 to 2% by weight of a compatibilizer.
WO-A 92/09654 describes linear aliphatic-aromatic polyesters which are
biodegradable. WO-A 96/15173 describes crosslinked, biodegradable polyesters.
The
polyesters described have relatively high terephthalic acid content and are
not always
entirely satisfactory in terms of their film properties - in particular their
elastic behavior,
which is of great importance for clingfilm.
It was accordingly an object of the present invention to provide a process for
producing
clingfilms.
PF 70547
3
Surprisingly, the polyesters described in the introduction, which have very
narrowly
defined terephthalic acid content and narrowly defined crosslinking agent
content have
very good suitability for clingfilm.
Preference is given to biodegradable polyesters having the following
constituents:
Component i is preferably adipic acid and/or sebacic acid.
Component iii), the diol, is preferably 1,4-butanediol.
Component iv), the crosslinking agent, is preferably glycerol.
The polyesters described are generally synthesized in a two-stage reaction
cascade
(see W009/127555 and W009/127556). The dicarboxylic acid derivatives are first
reacted together with the diol (for example 1,4-butanediol) as in the
synthesis
examples, in the presence of a transesterification catalyst, to give a
prepolyester. The
intrinsic viscosity (IV) of said prepolyester is generally from 50 to 100 mUg,
preferably
from 60 to 90 mUg. Catalysts used are usually zinc catalysts, aluminum
catalysts, and
in particular titanium catalysts. An advantage of titanium catalysts, such as
tetra(isopropyl) orthotitanate and in particular tetrabutyl orthotitanate
(TBOT) in
comparison with the tin catalysts, antimony catalysts, cobalt catalysts, and
lead
catalysts often used in the literature, an example being tin dioctanoate, is
lower toxicity
of any residual amounts of the catalyst, or downstream product from the
catalyst, that
remain within the product.
The polyesters of the invention are then optionally chain-extended by the
processes
described in WO 96/15173 and EP-A 488 617. By way of example, chain extenders
vib), such as diisocyanates or epoxy-containing polymethacrylates, are used in
a chain-
extension reaction with the prepolyester to give a polyester with IV of from
60 to
450 mUg, preferably from 80 to 250 mUg.
A mixture of the dicarboxylic acids is generally first condensed in the
presence of an
excess of diol, together with the catalyst. The melt of the resultant
prepolyester is
usually then condensed at an internal temperature of from 200 to 250 C within
a period
of from 3 to 6 hours at reduced pressure, with distillation to remove the diol
liberated,
until the desired viscosity has been achieved at an intrinsic viscosity (IV)
of from 60 to
450 mUg and preferably from 80 to 250 mUg.
It is particular preferable that the polyesters of the invention are produced
by the
continuous process described in WO 09/127556. The abovementioned intrinsic
viscosity ranges serve merely as guidance for preferred process variants and
do not
restrict the subject matter of the present application.
PF 70547
4
Alongside the continuous process described above, a batch process can also be
used
to produce the polyesters of the invention. For this, the aliphatic and the
aromatic
dicarboxylic acid derivative, the diol, and a branching agent are mixed in any
desired
sequence of addition and condensed to give a prepolyester. The process can be
adjusted to give a polyester with the desired intrinsic viscosity, optionally
with the help
of a chain extender.
The abovementioned processes can give by way of example polybutylene
terephthalate succinates, polybutylene terephthalate azelates, polybutylene
terephthalate brassylates, and in particular polybutylene terephthalate
adipates and
polybutylene terephthalate sebacates, having an acid number measured to
DIN EN 12634 which is smaller than 1.0 mg KOH/g and having an intrinsic
viscosity
which is greater than 130 mUg, and also having an MVR to ISO 1133 which is
smaller
than 6 cm3/10 min (190 C, 2.16 kg weight). Said products are of particular
interest for
film applications.
Sebacic acid, azelaic acid, and brassylic acid (i) are obtainable from
renewable raw
materials, in particular from vegetable oils, e.g. castor oil.
The amount of terephthalic acid ii used is from 20 to 35 mol%, based on the
acid
components i and ii.
Terephthalic acid and the aliphatic dicarboxylic acid can be used either in
the form of
free acid or in the form of ester-forming derivatives. Particular ester-
forming derivatives
that may be mentioned are the di-C,-C6-alkyl esters, such as dimethyl,
diethyl, di-n-
propyl, diisopropyl, di-n-butyl, diisobutyl, di-tert-butyl, di-n-pentyl,
diisopentyl, or di-n-
hexyl esters. It is equally possible to use anhydrides of the dicarboxylic
acids.
The dicarboxylic acids or ester-forming derivatives thereof can be used
individually or
in the form of a mixture here.
1,4-Butanediol is equally accessible from renewable raw materials. WO
09/024294
discloses a biotechnological process for producing 1,4-butanediol by starting
from
various carbohydrates and using Pasteurellaceae microorganisms.
At the start of the polymerization reaction, the ratio of the diol (component
iii) to the
acids (components i and ii) is generally set at from 1.0 to 2.5 : 1 and
preferably from
1.3 to 2.2: 1 (diol: diacids). Excess amounts of diol are drawn off during the
polymerization reaction, so as to obtain an approximately equimolar ratio at
the end of
the polymerization reaction. Approximately equimolar means a diol/diacid ratio
of from
0.98 to 1.02:1.
PF 70547
The polyesters mentioned can comprise hydroxy and/or carboxy end groups in any
desired ratio. The semiaromatic polyesters mentioned can also be end-group-
modified.
By way of example, therefore, OH end groups can be acid-modified by reaction
with
5 phthalic acid, phthalic anhydride, trimellitic acid, trimellitic anhydride,
pyromellitic acid,
or pyromellitic anhydride. Preference is given to polyesters having acid
numbers
smaller than 1.5 mg KOH/g.
Use is generally made of a crosslinking agent iva and optionally also of a
chain
extender ivb selected from the group consisting of: a polyfunctional
isocyanate,
isocyanurate, oxazoline, epoxide, carboxylic anhydride, an at least
trifunctional alcohol,
or an at least trifunctional carboxylic acid. Chain extenders ivb that can be
used are
polyfunctional and in particular difunctional isocyanates, isocyanurates,
oxazolines,
carboxylic anhydride, or epoxides. The concentration generally used of the
crosslinking
agents iva) is from 0.1 to 2% by weight, preferably from 0.2 to 1.5% by
weight, and with
particular preference from 0.3 to 1 % by weight, based on the polymer
obtainable from
components i to iii. The concentration generally used of the chain extenders
ivb) is from
0.01 to 2% by weight, preferably from 0.1 to 1 % by weight, and with
particular
preference from 0.35 to 2% by weight, based on the total weight of components
i to iii.
Chain extenders, and also alcohols or carboxylic acid derivatives having at
least three
functional groups, can also be regarded as crosslinking agents. Particularly
preferred
components have from 3 to 6 functional groups. By way of example, mention may
be
made of: tartaric acid, citric acid, malic acid; trimethylolpropane,
trimethylolethane;
pentaerythritol; polyethertriols and glycerol, trimesic acid, trimellitic
acid, trimellitic
anhydride, pyromellitic acid, and pyromellitic dianhydride. Preference is
given to polyols
such as trimethylolpropane, pentaerythritol, and in particular glycerol. By
means of
components iv it is possible to construct biodegradable polyesters that are
pseudoplastic. The rheological behavior of the melts improves; the
biodegradable
polyesters are easier to process, for example easier to draw to give films by
the melt-
solidification process. The compounds iv reduce viscosity under shear, i.e.
viscosity is
reduced under load.
It is generally useful to add the crosslinking (at least trifunctional)
compounds at a
relatively early juncture within the polymerization reaction.
Suitable bifunctional chain extenders are aromatic diisocyanates and in
particular
aliphatic diisocyanates, especially linear or branched alkylene diisocyanates,
or
cycloalkylene diisocyanates having from 2 to 20 carbon atoms, preferably from
3 to 12
carbon atoms, e.g. hexamethylene 1,6-diisocyanate, isophorone diisocyanate, or
methylenebis(4-isocyanatocyclohexane). Particularly preferred aliphatic
diisocyanates
are isophorone diisocyanate and in particular hexamethylene 1,6-diisocyanate.
PF 70547
6
The number-average molar mass (Mn) of the polyesters of the invention is
generally in
the range from 5000 to 100 000 g/mol, in particular in the range from 10 000
to
60 000 g/mol, preferably in the range from 15 000 to 38 000 g/mol, their
weight-
average molecular mass (Mw) being from 30 000 to 300 000 g/mol, preferably
from
60 000 to 200 000 g/mol, and their Mw/Mn ratio being from 1 to 15, preferably
from 2 to
8. Intrinsic viscosity is from 30 to 450 mUg, preferably from 50 to 400 mUg,
and with
particular preference from 80 to 250 mUg (measured in o-dichlorobenzene/phenol
(ratio by weight 50/50)). The melting point is in the range from 85 to 150 C,
preferably
in the range from 95 to 140 C.
In one preferred embodiment, from 1 to 80% by weight, based on the total
weight of
components i to iv, of an organic filler is added, selected from the group
consisting of:
native or plastified starch, natural fibers, wood flour, comminuted cork,
ground bark, nut
shells, ground press cake (vegetable-oil refining), dried production residues
from the
fermentation or distillation of drinks, such as beer or fermented nonalcoholic
drinks
(e.g. Bionade), wine, or sake, and/or of an inorganic filler selected from the
group
consisting of: chalk, graphite, gypsum, conductive carbon black, iron oxide,
calcium
chloride, dolomite, kaolin, silicon dioxide (quartz), sodium carbonate,
titanium dioxide,
silicate, wollastonite, mica, montmorillonites, talc, glass fibers, and
mineral fibers.
Starch and amylose can be native, i.e. not thermoplastified or
thermoplastified with
plasticizers, such as glycerol or sorbitol (EP-A 539 541, EP-A 575 349, EP 652
910).
Examples of natural fibers are cellulose fibers, hemp fibers, sisal, kenaf,
jute, flax,
abacca, coconut fiber, or else regenerated cellulose fibers (rayon), e.g.
Cordenka
fibers.
Preferred fibrous fillers that may be mentioned are glass fibers, carbon
fibers, aramid
fibers, potassium titanate fibers, and natural fibers, particular preference
being given to
glass fibers in the form of E glass. These can be used in the form of rovings
or in
particular in the form of chopped glass in the forms commercially available.
The
diameter of said fibers is generally from 3 to 30 pm, preferably from 6 to 20
pm, and
particularly preferably from 8 to 15 pm. The length of the fibers within the
compounding
material is generally from 20 pm to 1000 pm, preferably from 180 to 500 pm,
and
particularly preferably form 200 to 400 pm.
The fibrous fillers can, for example, have been surface-pretreated with a
silane
compound in order to improve compatibility with the thermoplastic.
The biodegradable polyesters and, respectively, polyester mixtures can
comprise other
ingredients that are known to the person skilled in the art but that are not
essential to
PF 70547
7
the invention. Examples are the additives usually used in plastics technology,
e.g.
stabilizers; nucleating agents; neutralizing agents; lubricants and release
agents, such
as stearates (in particular calcium stearate); plasticizers, such as citric
esters (in
particular tributyl acetylcitrate), glycerol esters, such as
triacetylglycerol, or ethylene
glycol derivatives, surfactants, such as polysorbates, palmitates, or
laureates; waxes,
such as beeswax or beeswax esters; antistatic agents, UV absorbers; UV
stabilizers;
antifogging agents, or dyes. The concentrations used of the additives are from
0 to 5%
by weight, in particular from 0.1 to 2% by weight, based on the polyesters of
the
invention. The polyesters of the invention can comprise from 0.1 to 10% by
weight of
plasticizers.
The biodegradable polyesters according to claim 1 are often tacky. If the
polyesters are
intended for use alone rather than as part of a blend, it is useful to add
additives,
particular examples being lubricants and release agents, so that processing of
the
polyesters to give films is problem-free.
Particular lubricants or mold-release agents (component e) that have proven
successful are hydrocarbons, fatty alcohols, higher carboxylic acids, metal
salts of
higher carboxylic acids, e.g. calcium stearate or zinc stearate, fatty acid
amides, such
as erucamide, and waxes, e.g. paraffin waxes, beeswax, or montan waxes.
Preferred
lubricants are erucamide and/or waxes, and particularly preferably
combinations of
these lubricants. Preferred waxes are beeswax and ester waxes, in particular
glycerol
monostearate, or dimethylsiloxane, or polydimethylsiloxane, e.g. Belsil DM
from
Wacker.
The amount added of component e is generally from 0.05 to 5.0% by weight and
preferably from 0.1 to 2.0% by weight, based on the biodegradable polyester.
One preferred formulation of the biodegradable polyester comprises:
a) from 99.9 to 98% by weight of an aliphatic-aromatic polyester obtainable
via
polycondensation of:
i) from 65 to 80 mol%, based on components i to ii, of one or more
dicarboxylic acid derivatives or dicarboxylic acids selected from the group
consisting of: succinic acid, adipic acid, sebacic acid, azelaic acid, and
brassylic acid;
ii) from 35 to 20 mol%, based on components i to ii, of a terephthalic acid
derivative;
PF 70547
8
iv) from 98 to 102 mol%, based on components i to ii, of a C2-Ca-alkylenediol
or C2-C6-oxyalkylenediol;
iv) from 0.1 to 2% by weight, based on the polymer obtainable from
components i to iii, of at least trifunctional crosslinking agent or
difunctional
chain extender, and
b) from 0.1 to 2% by weight of a lubricant or release agent.
Preference is further given to clingfilms comprising the abovementioned
formulations.
The abovementioned formulations and biodegradable polyester mixtures of the
invention can be produced from the individual components by known processes
(EP 792 309 and US 5,883,199). By way of example, all of the components of the
mixture can be mixed and reacted in one step in mixing apparatuses known to
the
person skilled in the art, examples being kneaders or extruders, at elevated
temperatures, for example from 120 C to 250 C.
Typical polyester mixtures for clingfilm production comprise:
a) from 5 to 95% by weight, preferably from 10 to 40% by weight, and
particularly
preferably from 25 to 35% by weight, of a biodegradable polyester according to
claim 1 and
b) from 95 to 50% by weight, preferably from 90 to 60% by weight, and
particularly
preferably from 75 to 65% by weight, of an aliphatic-aromatic polyester
obtainable via polycondensation of:
i) from 40 to 60 mol%, based on components i to ii, of one or more
dicarboxylic acid derivatives or dicarboxylic acids selected from the group
consisting of: succinic acid, adipic acid, sebacic acid, azelaic acid, and
brassylic acid;
ii) from 60 to 40 mol%, based on components i to ii, of a terephthalic acid
derivative;
iii) from 98 to 102 mol%, based on components i to ii, of a C2-C8-alkylenediol
or C2-C6-oxyalkylenediol;
iv) from 0 to 2% by weight, based on the polymer obtainable from
components i to iii, of at least trifunctional crosslinking agent or
difunctional
chain extender.
PF 70547
9
The following polymer mixtures are moreover suitable for producing clingfilms:
a) from 10 to 40% by weight, preferably from 20 to 30% by weight, of a
biodegradable polyester according to claim 1, and
b) from 89 to 46% by weight of an aliphatic-aromatic polyester obtainable via
polycondensation of:
i) from 40 to 70 mol%, based on components i to ii, of one or more
dicarboxylic acid derivatives or dicarboxylic acids selected from the group
consisting of: succinic acid, adipic acid, sebacic acid, azelaic acid, and
brassylic acid;
ii) from 60 to 30 mol%, based on components i to ii, of a terephthalic acid
derivative;
v) from 98 to 102 mol%, based on components i to ii, of a C2-C8-alkylenediol
or C2-C6-oxyalkylenediol;
vi) from 0 to 2% by weight, based on the polymer obtainable from components
i to iii, of at least trifunctional crosslinking agent or difunctional chain
extender;
c) from 1 to 14% by weight, preferably from 1 to 10% by weight, of one or more
polymers selected from the group consisting of: polylactic acid,
polycaprolactone,
polyhydroxyalkanoate, polyalkylene carbonate, chitosan, and gluten, and one or
more polyesters based on aliphatic diols and on aliphatic dicarboxylic acids -
and
from 0 to 2% by weight of a compatibilizer.
The excellent recovery behavior of the abovementioned polyester mixtures
comprising
components a) and b) and, respectively, a), b), and c) makes them suitable as
clingfilms.
It is preferable that the polymer mixtures in turn comprise from 0.05 to 2% by
weight of
a compatibilizer. Preferred compatibilizers are carboxylic anhydrides, such as
maleic
anhydride, and in particular the styrene-, acrylic-ester-, and/or methacrylic-
ester-based
copolymers described above that comprise epoxy groups. The units bearing epoxy
groups are preferably glycidyl (meth)acrylates. Copolymers of the
abovementioned
type containing epoxy groups are marketed by way of example by BASF Resins
B.V.
PF 70547
with trademark Joncryl ADR. By way of example, Joncryl ADR 4368 is
particularly
suitable as compatibilizer.
Polylactic acid is suitable by way of example as biodegradable polyester
(component
5 b). It is preferable to use polylactic acid with the following property
profile:
= melt volume rate (MVR for 190 C and 2.16 kg to ISO 1133) or from 0.5 to
30 ml/10 minutes, preferably from 2 to 18 mV10 minutes
= melting point below 240 C
= glass transition temperature (Tg) above 55 C
10 = water content smaller than 1000 ppm
= residual monomer content (lactide) smaller than 0.3%
= molecular weight greater than 80 000 daltons.
Examples of preferred polylactic acids are NatureWorks 3001, 3051, 3251,
4020,
4032, or 4042D (polylactic acid from NatureWorks or NL-Naarden and USA
Blair/Nebraska).
Polyhydroxyalkanoates are primarily poly-4-hydroxybutyrates and poly-3-
hydroxybutyrates, and the term also comprises copolyesters of the
abovementioned
hydroxybutyrates with 3-hydroxyvalerates or 3-hydroxyhexanoate. Poly-3-hydroxy-
butyrate-co-4-hydroxybutyrates are in particular known from Metabolix. They
are
marketed with trademark Mirel . Poly-3-hydroxybutyrate-co-3-hydroxyhexanoates
are
known from P&G or Kaneka. Poly-3-hydroxybutyrates are marketed by way of
example
by PHB Industrial with trademark Biocycle and by Tianan as Enmat .
The molecular weight Mw of the polyhydroxyalkanoates is generally from 100 000
to
1 000 000 and preferably from 300 000 to 600 000.
Polycaprolactone is marketed as Placcel by Daicel.
Polyalkylene carbonates are in particular polyethylene carbonate and
polypropylene
carbonate.
The expression semiaromatic (aliphatic-aromatic) polyesters based on aliphatic
diols
and on aliphatic/aromatic dicarboxylic acids (component c) also covers
polyester
derivatives such as polyetheresters, polyesteramides, or polyetheresteramides.
Among
the suitable semiaromatic polyesters are linear non-chain-extended polyesters
(WO 92/09654). Particularly suitable constituents in a mixture are
aliphatic/aromatic
polyesters made of butanediol, terephthalic acid, and of aliphatic C6-C,8
dicarboxylic
acids, such as adipic acid, sorbic acid, azelaic acid, sebacic acid, and
brassylic acid
(for example as described in WO 2006/097353 to 56). Preference is given to
chain-
extended and/or branched semiaromatic polyesters. The latter are known from
the
PF 70547
11
following specifications mentioned in the introduction: WO 96/15173 to 15176,
21689 to
21692, 25446, 25448, or WO 98/12242, and these are expressly incorporated
herein
by way of reference. It is equally possible to use a mixture of various
semiaromatic
polyesters. Particular semiaromatic polyesters are products such as Ecoflex
(BASF
SE), Eastar Bio, and Origo-Bi (Novamont). In comparison with the
biodegradable
polyesters of claim 1, they have relatively high terephthalic acid content
(aromatic
dicarboxylic acid).
For the purposes of the present invention, a substance or a substance mixture
complies with the "biodegradable" feature if said substance or the substance
mixture
has a percentage degree of biodegradation of at least 90% to DIN EN 13432.
Biodegradation generally leads to decomposition of the polyesters or polyester
mixtures in an appropriate and demonstrable period of time. The degradation
can take
place by an enzymatic, hydrolytic, or oxidative route, and/or via exposure to
electromagnetic radiation, such as UV radiation, and can mostly be brought
about
predominantly via exposure to microorganisms, such as bacteria, yeasts, fungi,
and
algae. Biodegradability can be quantified by way of example by mixing
polyester with
compost and storing it for a particular period. By way of example, in DIN EN
13432,
C02-free air is passed through ripened compost during the composting process,
and
the compost is subjected to a defined temperature profile. Biodegradability
here is
defined as a percentage degree of biodegradation, by taking the ratio of the
net amount
of CO2 released from the specimen (after subtraction of the amount of CO2
released by
the compost without specimen) to the maximum amount of CO2 that can be
released
from the specimen (calculated from the carbon content of the specimen).
Biodegradable polyesters or biodegradable polyester mixtures generally exhibit
marked
signs of degradation after just a few days of composting, examples being
fungal
growth, cracking, and perforation.
Other methods of determining biodegradability are described by way of example
in
ASTM D 5338 and ASTM D 6400-4.
The clingfilms (freshness-retention films) are generally produced within the
thickness
range from 10 to 25 pm. The usual production process is blown-film extrusion
in one
layer in the form of monofilm. The chill-roll extrusion process has also
become
established as a process for coextruded freshness-retention films.
Most of the clingfilms available hitherto within the market are mainly
composed of PVC,
plasticizer (e.g. from 20 to 30% of dioctyl phthalate) and antifogging
additives, which
reduce the amount of condensation on the film during temperature changes.
= P F 70547
12
Clingfilms based on LDPE have also become established, but require a cling
additive
(polyisobutylene). Clingfilms made of PE also comprise antifogging additives.
One specific clingfilm variant comprises a styrene/butadiene copolymer
(Styroflex)
which has excellent capability for recovery after deformation. These films are
produced
with 3 layers. The external layers comprise an ethylene-vinyl acetate equipped
with
antifogging additives. The middle layer comprises the styrene/butadiene
copolymer that
provides the strength, the extensibility, and the capability for recovery.
Clingfilms are used for packaging fruit and vegetables, and also fresh meat,
bones, and
fish. The requirements profile applicable to these is as follows:
1. extrudability on specific blown-film plants:
a. bubble stability at 10 pm
b. MFR (190 C, 2.16 kg) in the range from 0.3 to 4 g/10 min.
2. Transparency
3. Capability for recovery after deformation (hysteresis)
4. Strength to prevent slippage of the contents of the package
5. Puncture resistance
6. Ease of cutting perpendicularly to the direction of extrusion
7. Antifogging effect between room temperature and 0 C in cold storage
8. Weldability on the packing line or for manual packing
Traditional PVC film serves as comparison:
Films made of biodegradability polyester according to claim 1 have good film
properties
and can give very good results in drawing down to 10 pm. The level of
mechanical
properties is high, examples being strength values longitudinally and
perpendicularly
with respect to the direction of extrusion, and puncture resistance.
Blown films produced from said polyesters exhibit highly elastomeric behavior.
The pre-
breaking strengths achieved by the films are higher than those for PVC. It is
therefore
useful to modify the stiffness-toughness ratio by using branching agents and
to reduce
the terephthalic acid content for clingfilms.
Clingfilms produced from said polyesters can also be equipped with antifogging
additives. The transparency of these clingfilms is sufficient for most
applications.
However, they are not quite as transparent as PVC and in this respect they
differ from
traditional PVC.
The improved hysteresis (capability for recovery after deformation) of
clingfilms of the
invention is particularly impressive.
= PF 70547
13
The clingfilms of the invention are also easier to cut, without tearing
longitudinally with
respect to the direction of extrusion, since the marked anisotropy of the film
is reduced
with lower terephthalic acid content and a higher degree of branching.
The level of weldability of the clingfilms of the invention is similar to that
of PVC or PE.
Measurements of performance characteristics:
The molecular weights Mn and Mw of the semiaromatic polyesters were determined
to
DIN 55672-1 with eluent hexafluoroisopropanol (HFIP) + 0.05% by weight of
potassium
trifluoroacetate; narrowly distributed polymethyl methacrylate standards were
used for
calibration. Intrinsic viscosities were determined to DIN 53728 part 3,
January 3, 1985,
capillary viscosimetry. An M-II micro-Ubbelohde viscometer was used. The
solvent
used was the following mixture: phenol/o-dichlorobenzene in a ratio by weight
of 50/50.
The hysteresis test was carried out at 23 C to DIN 53835 on films of thickness
60 pm.
The film was first stressed at a rate of 120 mm/min. Once 50% tensile strain
had been
reached, the load was removed, with no waiting time. A waiting time of 5
minutes then
followed. The second cycle then followed, using 100% tensile strain at the
peak.
The degradation rates of the biodegradable polyester mixtures and of the
mixtures
produced for comparison were determined as follows:
The biodegradable polyester mixtures and the mixtures produced for comparison
were
pressed at a 190 C, in each case to produce films of thickness 30 pm. Each of
these
films was cut into square pieces with edge lengths of 2 x 5 cm. The weight of
each of
these pieces of film was determined and defined as "100% by weight". The
pieces of
film were heated to 58 C in an oven for a period of 4 weeks in a plastics jar
filled with
moistened compost. At weekly intervals the residual weight of each piece of
film was
measured and converted to % by weight (based on the weight defined as "100% by
weight" determined at the start of the experiment.
Starting materials
Polyester Al
A polybutylene terephthalate adipate produced as follows: 110.1 g of dimethyl
terephthalate (27 mol%), 224 g of adipic acid (73 mol%), 246 g of 1,4-
butanediol
(130 mol%), and 0.34 ml of glycerol (0.1% by weight, based on the polymer)
were
mixed together with 0.37 ml of tetrabutyl orthotitanate (TBOT), the molar
ratio of
alcohol components to acid component being 1.30. The reaction mixture was
heated to
a temperature of 210 C and kept at said temperature for 2 h. The temperature
was
then increased to 240 C and the system was subjected to stepwise evacuation.
The
PF 70547
14
excess of dihydroxy compound was removed by distillation under a vacuum below
1 mbar over a period of 3 h. The melting point of the resultant polyester Al
was 60 C
and its IV was 156 ml/g.
Polyester A2
A polybutylene terephthalate adipate produced as follows: 583.3 g of dimethyl
terephthalate (27 mol%), 1280.2 g of adipic acid (73 mol%), 1405.9 g of 1,4-
butanediol
(130 mol%), and 37 ml of glycerol (1.5% by weight, based on the polymer) were
mixed
together with 1 g of tetrabutyl orthotitanate (TBOT), the molar ratio of
alcohol
components to acid component being 1.30. The reaction mixture was heated to a
temperature of 210 C and kept at said temperature for 2 h. The temperature was
then
increased to 240 C and the system was subjected to stepwise evacuation. The
excess
of dihydroxy compound was removed by distillation under a vacuum below 1 mbar
over
a period of 3 h. The melting point of the resultant polyester A2 was 60 C and
its IV was
146 ml/g.
Polyester A3
A polybutylene terephthalate adipate produced as follows: 697.7 g of
terephthalic acid
(35 mol%), 1139.9 g of adipic acid (65 mol%), 1405.9 g of 1,4-butanediol (130
mol%),
and 37.3 ml of glycerol (1.5% by weight, based on the polymer) were mixed
together
with 2.12 ml of tetrabutyl orthotitanate (TBOT), the molar ratio of alcohol
components to
acid component being 1.30. The reaction mixture was heated to a temperature of
210 C and kept at said temperature for 2 h. The temperature was then increased
to
240 C and the system was subjected to stepwise evacuation. The excess of
dihydroxy
compound was removed by distillation under a vacuum below 1 mbar over a period
of
2 h. The melting point of the resultant polyester A3 was 80 C (broad) and its
IV was
191 ml/g.
Polyester A4
A polybutylene terephthalate adipate produced as follows: 726.8 g of
terephthalic acid
(35 mol%), 1187.4 g of adipic acid (65 mol%), 1464.5 g of 1,4-butanediol (130
mol%),
and 372.06 ml of glycerol (0.1 % by weight, based on the polymer) were mixed
together
with 2.21 ml of tetrabutyl orthotitanate (TBOT), the molar ratio of alcohol
components to
acid component being 1.30. The reaction mixture was heated to a temperature of
210 C and kept at said temperature for 2 h. The temperature was then increased
to
240 C and the system was subjected to stepwise evacuation. The excess of
dihydroxy
compound was removed by distillation under a vacuum below 1 mbar over a period
of
3 h. The melting point of the resultant polyester A4 was 80 C and its IV was
157 ml/g.
Polyester 131
A polybutylene terephthalate adipate produced as follows: 87.3 kg of dimethyl
terephthalate (44 mol%), 80.3 kg of adipic acid (56 moi%), 117 kg of 1,4-
butanediol,
PF 70547
and 0.2 kg of glycerol (0.1 % by weight, based on the polymer) were mixed
together
with 0.028 kg of tetrabutyl orthotitanate (TBOT), the molar ratio of alcohol
components
to acid component being 1.30. The reaction mixture was heated to a temperature
of
180 C and reacted for 6 h at this temperature. The temperature was then
increased to
5 240 C and excess dihydroxy compound was removed by distillation in vacuo
over a
period of 3 h. 0.9 kg of hexamethylene diisocyanate were then slowly metered
in within
a period of 1 h at 240 C. The melting point of the resultant polyester 131 was
119 C, its
molar mass (Me) was 23 000 g/mol, and its molar mass (Mw) was 130 000 g/mol.
10 Polyester C1
NatureWorks 4042D polylactic acid
Compatibilizer D1
Joncryl ADR 4368CS
Examples:
Polyesters Al, A3, and A4, and comparative example B1, were processed in the
heated press to give pressed films FA1; FA3, FA4, and comparative film F131,
and
subjected to a hysteresis test.
Production of pressed films
2.5 g of polyester was distributed within the frame (60 m, 20 x 20 cm). The
frames
were placed in the press. The polymer was then heated to a temperature of 160
C and
10 min at said temperature. The plates of the press were then brought into
contact with
the polymer films and a pressure up to 200 bar was applied stepwise. After 2
min, the
plates of the press were cooled to RT and the pressure was removed from the
plates.
Hysteresis test
The hysteresis test was carried out at 23 C to DIN 53835 on films of thickness
60 m.
First, the films were cut to dimensions of 4 mm * 25 mm. These pieces of film
were
then stressed at a rate of 120 mm/min. Once 50% tensile strain had been
reached, the
load was removed, with no waiting time (first measurement of recovery
capability). A
waiting time of 6 minutes then followed. The second cycle then followed, using
100%
tensile strain at the peak.
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16
Specimen Thickness Recovery after 50% tensile Recovery after 100% tensile
( m) strain (1st measurement) strain (2nd measurement)
FA1 60 83% 63%
FA3 65 74% 62%
FA4 65 68% 56%
FB1 60 44% 34%
The measurements show that the films composed of a polyester having low
terephthalic acid content, for example FA1, exhibit higher recovery capability
than the
comparative film FB1. There was a further increase in the recovery capability
of films
having high content of crosslinking agent (FA3 in comparison with FA4).
