Note: Descriptions are shown in the official language in which they were submitted.
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Polymeric, partially crystalline thermoplastic material with a nanoscale
nucleating went and highly transparent mouldings produced therefrom
The present invention relates to a polymeric, partially crystalline
thermoplastic
material which contains particles having a nucleating action of a size of less
than 100
nm nanoscale nucleating agents in dispersed form. Mouldings produced therefrom
are distinguished by excellent transparency combined with elevated gloss
together
with elevated dimensional stability and hardness. The present invention
accordingly
also provides mouldings, in particular films, which are produced in zones or
in their
entirety using the material according to the invention as the sole constituent
or as a
blend component. Advantages in comparison with polymeric materials containing
conventional nucleating agents reside in the extremely fine-grained and highly
crystalline crystal structure which may be established and, in particular, the
accompanying transparency. The nucleating agent itself has no influence upon
transparency.
Nucleating agents for polymeric, partially crystalline thermoplastic materials
are of
considerable significance. They bring about an elevated nucleation rate and
thus a
speed of crystallisation which, over a wide temperature, i.e. supercooling,
range, is
distinctly raised in comparison with non-nucleated systems. As a consequence,
in
conventional industrial cooling processes from the melt, they give rise to a
high
degree of crystallinity. This is explained, using polyamide 6 and the
nucleating
agents talcum and kaolin by way of example, in Kohan (ed.), Nylon Plastics
Handbook, Hanser Publishers, Munich, 1995.
Applicational advantages of nucleated polymeric materials reside in increased
rigidity and hardness due to the crystalline fractions combined with greater
toughness, abrasion resistance and surface hardness and, due to the fine
crystalline
structure obtained even with conventional nucleating agents, in appreciably
improved
transparency and increased gloss of the mouldings produced therefrom, in
~r~,~ ss ;~3
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comparison with non-nucleated polymeric materials. Due to the rapid and
extensive
crystallisation which occurs during cooling from the melt, crystallisation in
the
moulding is very largely complete after the shaping process. In contrast, in
non-
nucleated systems, cooling which is excessively rapid relative to the speed of
crystallisation may give rise to a metastable state, which results in post-
crystallisation
of the moulding over a relatively long period after the shaping process. As a
result of
the reduction in specific volume of the polymer which accompanies
crystallisation,
this gives rise to post-shrinkage of the corresponding moulding. This is in
principle
undesirable. Moreover, faster production rates may be achieved in many shaping
processes, such as for example injection moulding, with more rapidly
crystallising
moulding compositions.
It is prior art to used nucleating systems, in particular in the form of
dispersed, finely
divided inorganic solid particles. WO 8802763 in particular mentions in this
connection talcum, mica, kaolin and, secondarily, substances such as asbestos,
aluminium, silicates, silver bromide, graphite, molybdenum disulfide, lithium
fluoride, sodium phenylphosphinate, magnesium oxide, mercury bromide, mercury
chloride, cadmium acetate, lead acetate, silver chloride, diatomaceous earth
and the
like. The stated systems are added in concentrations between one thousandth of
a
percent and one percent, relative to the total weight of the nucleated
polymer.
In addition to the solid particles which act as crystallisation nuclei,
plasticising
substances are frequently added to the polymer. In this manner, the glass
transition
temperature of the polymer may be reduced and the temperature range over which
crystal growth may still occur around the nuclei is extended downwards to
lower
temperatures. While this indeed does not give rise to a more fine-grained
structure
than without the addition of such substances, it does result in an overall
higher
degree of crystallinity at an identical spherulite count. Suitable substances
are, for
example, polymers with a molecular weight which imparts a waxy consistency to
the
polymer. Polyolefins, polyoxides, polysulfides and/or fatty acid derivatives,
in
particular fatty acid amides, may be used.
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In the case of polyamide, for example, talcum is predominantly used as a
nucleating
agent. The size of the particles used is here in the range from approx. 1 to S
pm with
typical polyamide loading rates ranging from one thousandth to approx. one
tenth of
S one weight percent. Higher filling rates than this prove inadvisable for
various
reasons. Accordingly, above a content of approx. 1000 ppm, it is not possible
to
bring about any further acceleration of crystallisation, but instead the
particles
themselves greatly increase haze due to their size and refractive index, which
differs
from that of the polymeric matrix. A fatty acid amide, in particular
ethylenebisstearamide, is frequently added as a plasticising component for the
purpose described above. Nucleation may be improved by surface modification of
the particles, for example with citric acid.
It has also been known for a relatively long period to add very fine solid
particles of a
size of below one micrometre to polymeric matrices and, in particular,
polyamides.
Such systems are primarily used to increase mechanical rigidity, gas barrier
properties and heat resistance and to reduce the cycle time in, for example,
injection
moulding, flammability or moisture absorption in hydrophilic systems. Systems
which, unlike the above-stated nucleated polyamides, retain their transparency
despite a higher rate of addition of the nanoscale particles, have also been
described.
Nanoscale fillers having a nucleating action or the benefits thereof have,
however,
not been described in the literature.
EP 358 415 describes a moulding composition comprising a polyamide resin with
a
phyllosilicate uniformly dispersed therein, wherein the individual layers of
the
phyllosilicates may exhibit thicknesses of around 1 nm and side lengths of up
to 1
pm. As a result of suitable maceration, the layers are separately present in
the
polyamide matrix and are spaced apart by approx. 10 nm. Mouldings, such as for
example films, produced with this material made from polyamide 6 as the base
polymer are characterised by significantly increased oxygen barrier properties
and
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rigidity in comparison with those made from pure polyamide 6. To the same
extent,
toughness falls appreciably. Surface slip properties are improved. The
transparency
of single layer amorphously quenched flat films and of water-cooled blown
films
with the structure polyamide mixture/coupling agent/PE-LD is unchanged
relative to
pure polyamide 6.
WO 9304118 and WO 9311190 and WO 9304117 disclose polymer nanocomposites
which likewise comprise lamellar particles of a thickness of a few nanometres.
In
particular, composites made from PA 6 and montmorillonite or from PA 6 and
silicates are described. These materials may be converted into films. The
advantages
of such films in comparison with those without nanoscale particles are higher
rigidity, greater wet strength, better dimensional stability, higher gas
barrier
properties and lower water absorption. The effect of the added particles upon
transparency is not described.
EP 810 259 also describes a polyamide moulding composition comprising
nanodisperse fillers. The burner action desired therein for the polyamide may
be
improved by the addition of sufficiently finely divided oxides, oxyhydrates or
carbonates. The particles preferably have a diameter of less than 100 nm. The
patent
also describes multilayer films comprising at least one layer made from this
moulding composition, wherein the stated intention for using said moulding
compositions is always to improve oxygen barrier properties. However, the
optical
properties of the films made therefrom are impaired in comparison with the
system
without the additive.
WO 980346 also describes the use of nanodisperse fillers for improving the
burner
properties of polyesters. Such a polymer comprising a fraction of between 0.1
and
10% of lamellar mineral dispersed therein with a particle thickness of below
100 nm
is distinguished by elevated oxygen barrier properties and strength while
retaining
transparency and is suitable, for example, for the production of packaging
films.
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In the light of the prior art, the object arises of providing a melt-
processable,
polymeric, partially crystalline material which may be processed using typical
industrial shaping processes to yield a moulding, which exhibits very good
transparency, elevated gloss, elevated rigidity and toughness, elevated
hardness and
abrasion resistance and, once shaped, exhibits only slight post-shrinkage.
This has been achieved according to the invention by the provision of a
material
made from a partially crystalline polymer comprising a phase of inorganic
solid
particles dispersed therein, which material is characterised in that the
extent of the
particles in at least one direction freely selectable for each particle is, on
a number-
weighted average of all particles, less than 100 nm.
According to the invention, the materials according to the invention may be
produced
from a partially crystalline polymer comprising a phase of inorganic solid
particles
1 S dispersed therein in that the polymer containing inorganic solid particles
and
optionally further conventional additives is melted in an extruder and the
completely
molten polymer is then cooled at a cooling rate of between 30° and
40°C per minute,
wherein crystalline structures are obtained.
The nanoscale particles may preferably be incorporated into the partially
crystalline
polymer using conventional processes used to disperse solids in polymers.
A material according to the invention is preferably obtainable by melting the
polymer
containing inorganic solid particles in an extruder and cooling the completely
molten
polymer at a cooling rate of between 30° and 40°C per minute.
The partially crystalline polymer may be any desired crystallisable polymer.
Ideally
suitable polymers are those which are selected from the group of polymers
comprising polyamide, polyethylene, ethylene-based copolymers, polypropylene,
propylene-based copolymers, polyvinyl chloride, polyacetals, polyketones,
polyesters
and copolyesters and polyurethane. Partially crystalline polymers which may
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preferably be used comprise polyamide in the form of aliphatic or aromatic
homo-
and copolyamides and the mixtures thereof, in particular polyamide 6,
polyamide 10,
polyamide 12, polyamide 66, polyamide 610, polyamide 6I, polyamide 612,
polyamide 6/66, polyamide 6I/6T, polyamide MXD6, polyamide 6/6I, polyamide
6/6T, polyamide 6/IPDI and copolyamides or mixtures thereof.
The advantages of the invention are particularly pronounced if very small
nanoscale
particles are selected.
The size of the particles is thus preferably less than SO nm, still more
preferably less
than 10 nm in at least one direction freely selectable for each particle on a
number-
weighted average of all particles.
The solid nanoscale particles preferably have an approximately spherical
shape, but
may also be lamellar or of a unidirectionally extensive form. Amorphous
particles
may also be used. Agglomerates of such particles may also be used.
The solid nanoscale particles may have a modified surface enabling increased
affinity
towards the surrounding polymer.
Suitable quantities of the solid nanoscale particles to be added are between
10 and
10000 ppm, preferably between 100 and 5000 ppm, relative to the total weight
of the
material. It was surprising in this connection that even at elevated contents
of
nanoscale particles in the material, the achievable transparency and
achievable gloss
of mouldings produced therefrom are not impaired.
Apart from the solid nanoscale particles, the material may also contain
further
conventionally used additives in conventional quantities. Examples are
lubricants,
stabilisers, processing auxiliaries, antiblocking agents, fillers, dyes and
the like. It is
particularly suitable to add macromolecular substances which, before addition,
are in
a waxy state at room temperature.
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The material according to the invention may be melt processed to yield
mouldings, in
particular films. These mouldings may contain the material in zones or
throughout; in
the zones containing the material, they may consist of the material alone or
as a
S mixture of two or more different materials according to the invention with
further
polymers or other materials.
Using the material according to the invention, it is possible to provide a
material
which, in typical industrial shaping processes from the melt, gives rise to
highly
crystalline mouldings which exhibit not only elevated rigidity, hardness and
abrasion
resistance but also elevated toughness. While the cooling rate does indeed in
principle here have an influence upon the action of the nanoscale particles,
any action
discernible in the moulding only occurs at cooling rates of greater than
200°C/s.
It was not to be expected that the mouldings should additionally exhibit
outstanding
transparency and gloss properties.
The mouldings which may be produced from this material are fiu~thermore also
distinguished by surprisingly low shrinkage after the shaping process.
The material according to the invention may in particular readily be processed
to
yield flexible films. The present invention accordingly also provides films
comprising one or more layers containing at least one such material alone or
in a
mixture.
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Examples
Single layer flat films were made from polyamide using the process typical for
this
purpose. The moulding composition was melted in an extruder and cast through a
S slot die onto a temperature-controlled, rotating casting roll. The casting
roll had a
diameter of 1100 mm, wherein the film contacted the casting roll over an angle
of
190°. The tangential velocity of the surface of the casting roll was 30
m/min. The
. resultant films have a thickness of 50 pm.
Comparative Example 1
A polyamide 6 film was produced at a casting roll temperature of
30°C. The
polyamide 6 used has a crystallite melting point of 22U°C and a
relative viscosity in
98% sulfuric acid of 3.6. It contains 600 ppm of ethylenebisstearamide and is
I S nucleated with approx. 150 ppm of talcum.
Comparative Example 2
The film from Comparative Example 1 was produced at a casting roll temperature
of
100°C. All other conditions are the same as in Comparative Example 1.
Example 3
Using the production conditions as in Comparative Example 2, a film was
produced
from polyamide 6 with 0.2 wt.% of montmorillonite. The montmorillonite is
dispersed in the polyamide in macerated form, where it forms lamellar units of
a
thickness of approx. 1 nm with a characteristic diameter of approx. 100 to
1000 nm.
The polyamide contains no further nucleating agent.
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Example 4
Finn from Example 3 produced with a casting roll temperature of
30°C as in
Comparative Example 1.
Example 5
Film from Example 3 with a montmorillonite content of 0.4%.
Comparative Example 6
Film from Comparative Example 2 with a polyamide 6 as in Comparative Example
2, but containing no talcum.
I S The following measurements were made on the Examples according to the
invention
and Comparative Examples which were produced.
- Tensile modulus to DIN EN ISO 527 in the longitudinal direction of the film
as a measure of rigidity in a test atmosphere of 23°C and 0% relative
humidity in a period of between 24 and 36 hours after production of the film.
- Flex crack resistance as a measure of film toughness. Flex crack resistance
is
measured at a temperature of 23°C and relative humidity of 0% by
rolling up
a specimen in a single layer to form a cylinder of length 198 mm and
circumference 280 mm and fastening it at both ends in suitably shaped
clamps. The free length of the cylinder formed by the film between the
clamps is 192 mm. While being simultaneously rotated by 440° around the
axis of symmetry which describes the cylinder, the clamps are brought to a
distance of 40 mm apart for a predetermined number of cycles and at a
frequency of 35 cycles per minute. The films to be tested are previously kept
for 3 days in an atmosphere of 23°C and 0% relative atmospheric
humidity.
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The number of cracks which occur in the film after the predetermined number
of strokes may be determined by wetting the film on one side with ammonia
solution while the other side of the film is simultaneously in contact with a
sheet of blueprint paper. The number of blue/black spots on the blueprint
paper caused by ammonia which are discernible after 15 minutes is deemed to
be the number of flex cracks in the tested portion of film. The value is here
obtained as an average of the individual values from two test specimens.
Film shrinkage after heat treatment in water at 121 °C for 30
minutes. The
change in length in both longitudinal and transverse direction of a square
piece of film of an edge length of 100 mm was determined at 23°C and 0%
relative humidity by measurement before and after heat treatment and a
shrinkage value per unit area was calculated from these measurements.
- Haze to ASTM D 1003.
- Gloss on the casting roll side of the film at an angle of 20° to DIN
67 530.
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The results are shown in Table 6 below:
Feature (unit) Example
(Ex.)
or
Comparative
Example
(CEx.)
CEx. CEx. Ex. Ex. Ex. CEx.
1 2 3 4 S 6
Gloss 155 121 163 166 164 105
(gloss units)
Haze (%) 0.4 7.5 0.7 0.5 0.5 12.3
Number of holes 1 8.5 2 1.5 3 11.5
after
250 strokes
Modulus of elasticity630 1490 1610 1530 1720 1450
(MPa)
Shrinkage (%) 9.3 3.4 2.3 2.7 2.0 4.6
Properties of the Examples according to the invention and Comparative Examples
