Note: Descriptions are shown in the official language in which they were submitted.
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Additives for Processing Plastics
Field of the Invention
This invention relates to additives for the processing of plastics, the
additives being present in a granular supply form, characterized in that the
granules are present in the form of spherical to cylindrical granules with a
length-to-diameter ratio of 1:1 to 3:1. The invention also relates to
compositions containing such granules for the processing of plastics and to
the use of the granules as auxiliaries for the processing of plastics.
Prior Art
Plastics are polymers which consist structurally of molecule chains
with numerous, almost infinitely recurring structural elements and which
differ in their physical properties from low molecular weight compounds.
Thus, polymers have high tensile strengths and elasticity, for example, by
comparison with low molecular weight compounds.
In the course of industrial processing, suitable additives are
incorporated in polymerized plastic melts to facilitate their further
processing and their intended application. In this way, basic polymers can
be adapted to meet individual requirements in regard to the required
properties.
Additives for plastics are available in various supply forms. For solid
compounds, the simplest supply form is the powder. Unfortunately,
powder can cake too easily and leads to dust emissions during processing.
Compression of the powder in a granulator gives rodlet granules.
Although the dust component is small, processing problems can be caused
by the poorer handling behavior of such granules and the dust present.
For some additives which have a high meltable component, pellets or
flakes are available as supply forms. For production, the particular product
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is melted and then cooled down on cooled flaking rollers or belts. Pellets
are dust-free and may readily be incorporated in the plastic. However,
thermally labile or reactive compounds cannot be flaked or pelleted.
Description of the Invention
The problem addressed by the present invention was to provide
additives for the processing of plastics which would be easy to handle and
which could readily be incorporated in thermoplastics.
It has now been found that extruded plastic additives can be
converted by spheronizing, such as "marumerizing", into a substantially
spherical or cylindrical shape. Granules thus shaped ("beads") on the one
hand afford the advantage of easy handling and freedom from dust; on the
other hand, they can readily be incorporated during the processing of
thermoplastics, i.e. dispersed in the plastics.
The additive beads thus produced are eminently suitable as a supply
form for plastic additives, more particularly for stabilizer and/or lubricant
compounds for the processing of PVC, for example those based on
calcium/zinc and on lead.
The present invention relates to additives for the processing of
plastics, the additives being present in a granular supply form,
characterized in that the granules are present in the form of spherical or
cylindrical granules with a length-to-diameter ratio of 1:1 to 3:1.
With regard to the length-to-diameter ratio, attention is drawn to the
following: the additives granules according to the invention assume the
form of bodies of rotation (i.e. they may also be graphically referred to as
"beads"). The length of the longitudinal axis of the beads is termed the
"length" while the maximum diameter of the beads (as measured
perpendicularly of the longitudinal axis) is termed the "diameter". In cases
where the length-to-diameter ratio is 1:1, the beads are spheres. In the
process described hereinafter for producing the additive granules, the bead
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form is obtained by virtue of the fact that, after extrusion and chopping up
of the extruded strands at the granulation head with multiple-bore dies,
cylindrical particles are initially obtained and are then rounded off at their
ends in spheronizing machines.
The supply form according to the invention for the plastic additives
combines several favorable applicational properties which are not found in
this number in conventional supply forms, such as powders or pellets. For
experimental proof, reference is made to the Examples. As mentioned
above, these positive applicational properties include excellent transport
behavior and the absence of dust - both properties which guarantee
excellent handling behavior. In addition, the supply form according to the
invention opens up extensive possibilities in regard to the "range of
formulation". By this is meant that the beads according to the invention
may contain not just one additive, but also several additives irrespective of
whether these additives are - for instance - thermally labile, infusible or
substantially infusible, represent otherwise difficult-to-handle polymers,
etc.
The positive applicational properties mentioned remain intact even when
the formulation range of the beads according to the invention is broad, i.e.
when several different additives, including thermally labile and otherwise
difficult-to-handle additives, are present in the beads.
According to the invention, the plastics may be selected basically
as required from the thermoplastics known to the relevant expert. The
following are examples of suitable plastics:
~ homopolymers of an a-olefin containing two to eight carbon atoms,
copolymers of two corresponding a-olefins, preferably copolymers of
ethylene, ethylene homopolymers, such as HDPE (high-density
polyethylene), LDPE (low-density polyethylene), VLDPE (very low
density polyethylene), LLDPE (linear low-density polyethylene), MDPE
(medium-density polyethylene), UHMPE (ultra-high-molecular
polyethylene), VPE (crosslinked polyethylene), HPPE (high-pressure
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polyethylene), isotactic polypropylene, syndiotactic polypropylene,
Metallocen-catalyzed polypropylene, high-impact polypropylene,
random copolymers based on ethylene and propylene, block
copolymers based on ethylene and propylene, homopolymers based
on 1-butylene, 1-pentylene, 1-hexylene, 1-octylene, isobutylene, 2-
methyl-1-butylene, 3-methyl-1-pentylene, 4-methyl-1-pentylene, 2,3-
dimethyl-1-butylene, 2-ethyl-1-butylene and mixtures thereof.
~ copolymers of ethylene with 1-butylene, 1-hexylene, 1-octylene and 4-
methyl-1-pentylene.
~ ethylene/vinyl acetate copolymers, ethylene/ethyl acetate copolymers,
ethylene/acrylic acid copolymers and mixtures thereof.
~ ethylene/propylene rubber (EPDM), including diene-modified types
(EPR), styrene/butadiene/styrene copolymers (SBS),
styrene/ethylene/butylene/styrene copolymers (SEBS) and mixtures
thereof.
~ halogen-containing plastics, more particularly homopolymers of vinyl
compounds, for example vinyl chloride.
According to the invention, the additives may be selected basically
as required from the additives known to the relevant expert for the
processing of thermoplastics. Examples of suitable additives are antistatic
agents, antifogging agents, antioxidants, UV stabilizers, coupling agents,
calendering aids, mold release agents, lubricants, release agents, slip
agents, plasticizers, perfumes, flame retardants, fillers and agents for
increasing thermal stability (heat stabilizers).
So far as the terms "lubricants" and "release agents" are concerned,
attention is drawn to the following: in the standard language of the expert,
release agents are products which reduce the frictional resistances
primarily between the polymer melt and the steel surface of the machine
used for molding; the effect of reducing the frictional resistance is that the
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melt pressure of the melt is reduced. By contrast, lubricants act
predominantly in the polymer melt and reduce the internal frictional forces
so that, even with high filler contents, the melt retains good plastic flow
which is important for filling the mold.
In one embodiment of the invention, calcium salts and/or
magnesium salts and/or aluminium salts and/or zinc salts solid or liquid at
20°C selected from
a) calcium salts of saturated or unsaturated, linear or branched
monocarboxylic acids containing 6 to 36 carbon atoms,
b) calcium salts of unsubstituted or C~~-alkyl-substituted benzoic acid,
c) zinc salts of saturated or unsaturated, linear or branched
monocarboxylic acids containing 6 to 36 carbon atoms,
d) magnesium salts of saturated or unsaturated, linear or branched
monocarboxylic acids containing 6 to 36 carbon atoms,
e) magnesium salts of saturated or unsaturated dicarboxylic acids
containing 6 to 10 carbon atoms,
f) aluminium salts of saturated or unsaturated, linear or branched
monocarboxylic acids containing 6 to 36 carbon atoms
are used as lubricants or release agents.
The above-mentioned calcium, magnesium, zinc and aluminium
salts may be used both individually and in admixture with one another.
Other lubricants or release agents which may be used individually or
in combination with one another are the relevant substances known from
the prior art. Compounds of the following types are preferably used:
hydrocarbon waxes which melt at temperatures of 70 to 130°C, oxidized
polyethylene waxes, free fatty acids containing 8 to 22 carbon atoms and
branched-chain isomers thereof, for example stearic acid or even
hydroxystearic acid, a-olefins, wax esters, i.e. esters of relatively long-
chain monocarboxylic acids and monoalcohols, primary and secondary,
saturated and unsaturated higher alcohols preferably containing 16 to 44
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carbon atoms in the molecule, ethylenediamine stearate, montanic acid
esters of diols, for example of ethanediol, butane-1,3-diol and glycerol,
mixtures of such montanic acid esters with nonesterified montanic acids,
partial esters of fatty acids containing 8 to 22 carbon atoms and polyols
containing 2 to 6 carbon atoms and 2 to 6 hydroxyl groups which contain
on average at least one free polyol hydroxyl group per molecule. Also
suitable are the mixed esters described in DE-C-19 07 768 with hydroxyl or
acid values of 0 to 6 of aliphatic, cycloaliphatic or aromatic dicarboxylic
acids containing 2 to 22 carbon atoms in the molecule, aliphatic polyols
containing 2 to 6 hydroxyl groups in the molecule and aliphatic
monocarboxylic acids containing 12 to 30 carbon atoms in the molecule.
Examples of these mixed esters are mixed esters of malefic acid/penta-
erythritol/behenic acid, mixed esters of adipic acid/pentaerythritol/oleic
acid
and mixed esters of adipic acid/pentaerythritol/stearic acid. According to
the invention, corresponding lubricants or release agents may be used both
individually and in combination with one another and also in combination
with the above-mentioned calcium, magnesium or aluminium salts.
In one embodiment of the invention, compounds selected from the
group consisting of talcum, kaolin, chalk and the like, are used as fillers.
In another embodiment of the invention, compounds selected from
the group consisting of calcium and/or zinc soaps, antioxidants, cationic
layer compounds, for example hydrotalcites or modified hydrotalcites,
zeolites, are used as heat stabilizers.
As known to the expert, additives used in the processing of plastics
may be classified not only in regard to their function but also in regard to
their chemical structure. From the structure perspective, too, the additives
according to the invention are not subject to any restrictions. It is pointed
out in this connection that compounds belonging to a certain class, i.e.
compounds which may be structurally assigned to the same class, often
perform not just one but two or more functions in practice. For example,
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calcium or zinc soaps - as described above - may act as lubricants and/or
release agents but may also be used to improve thermal stability, for
example in the processing of polyvinyl chloride (PVC).
The additive granules ("beads") according to the invention are
generally produced as follows: a composition containing plastic additives,
more particularly a composition consisting solely of plastic additives, is
introduced into a single-screw or twin-screw extruder. Twin-screw
kneader/extruders (twin-screw co-rotating or contra-rotating extruders) are
preferred, an extrusion pressure of 15 to 100 bar and more particularly in
the range from 25 to 60 bar preferably being established. Basically, the
temperature in the extruder is not critical although extrusion is preferably
carried out at 20 to 110°C. The extruders used are provided with
granulation heads equipped in particular with multiple-bore extrusion dies.
The effect of this is that the melt is extruded into fine strands which, after
leaving the die, are converted into cylindrical granules by means of a
chopping blade. Multiple bore dies with bores between 0.8 and 5 mm and
more particularly between 1.5 and 2.5 mm in diameter are preferably used.
The chopping temperature is preferably adjusted to a value of 30 to
110°C
and more preferably to a value of 40 to 80°C. These granules are then
spheronized continuously or in batches in conventional spheronizers. The
spheronizing temperature is adjusted so that the granules have sufficient
plasticity. The preferred spheronizing temperature is between 20 and
110°C. Relevant spheronizing techniques, especially marumerizing, are
known to the expert. Reference is made by way of example in this
connection to the disclosure of German patent DE-C-12 94 351
"Vorrichtung zur Herstellung von kugelformigen Kornern aus feuchten,
vorgeformten Teilchen (arrangement for the production of spherical
granules from moist preformed particles)" which describes a spheronizer
with a rotating bottom disk, the required degree of spheronizing being
adjustable by variation of the residence time of the granules in the
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spheronizer and/or the rotational speed of the disk. According to the
invention, any commercially available spheronizers may be used.
In one embodiment, the still plastic additive granules initially formed
may be impregnated with other active substances before, during or after
spheronizing. These other active substances may be, for example,
particularly heat-sensitive plastic additives. In one particularly preferred
embodiment, the additive granules according to the invention are surface-
powdered with one or more compounds. Organic active substances,
inorganic active substances and release agents, which may be used
individually or in combination with one another, are particularly suitable for
this purpose. Zeolites and cationic layer lattice compounds, for example
hydrotalcites or modified hydrotalcites, are most particularly suitable. The
compounds used for powdering are used in particular in quantities of 0.01
to 5% by weight, based on the additive granules (beads). Powdering is
preferably carried out at the same time as spheronizing.
As already mentioned, the plastic additive granules ("beads")
according to the invention are present in the form of spherical or cylindrical
granules with a length-to-diameter ratio of 1:1 to 3:1. In one important
embodiment, particle size and particle shape are uniform. The preferred
particle form is spherical. Preferred particle sizes are in the range from 0.5
to 5 mm sphere diameter and more particularly in the range from 0.8 to 3
mm. The constituents of these spheres may correspond in type and
quantity to standard formulations for plastic additive compositions.
In another embodiment, the additive granules according to the
invention may be recycled. By this is meant that they may be reused
together with other substances in the first process step for producing the
additive granules - extrusion.
The present invention also relates to compositions for the
processing of plastics containing additives for the processing of plastics,
characterized in that the compositions are present in a granular supply form
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and in that the granules are present in the form of spherical or cylindrical
granules with a length-to-diameter ratio of 1:1 to 3:1.
The present invention also relates to the use of granules as
auxiliaries for the processing of plastics, characterized in that the granules
consist of one or more typical plastic additives and are present in the form
of spherical or cylindrical granules with a length-to-diameter ratio of 1:1 to
3:1.
The present invention also relates to a process for the production of
plastics, characterized in that powder-form and/or granular thermoplastic
homopolymers and/or copolymers are subjected to molding, more
particularly extrusion, injection molding or film blowing, together with the
additive granules according to the invention. Any of the machines known
to the relevant expert may be used, the various commercially available
single- and twin-screw extruders being particularly suitable for extrusion.
Examples
1. Materials
For the following tests, a commercially available powder-form Ca/Zn
stabilizer ("Stabilox CZ 2697", Henkel, Dusseldorf) was processed
~ to rodlet granules (= additive granules intended for comparison) and
~ to spheronized beads (= additives granules according to the invention).
2. Production of the materials
2.1. Rodlet granules
A CPM granulator (pressing temperature 30°C) was used to produce
the rodlet granules. The rodlets obtained had a diameter of 3 mm and a
length of about 5 mm.
2.2. Beads
The additive granules according to the invention were produced as
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follows: powder-form Stabilox CZ 2697 was continuously added to a twin-
screw kneader (Werner & Pfleiderer type ZSK 35 extruder = twin-screw
kneader/co-rotating extruder; screw diameter = 25 mm; L/D = 12) of which
the housing, including the granulation head of the extruder, was heated to
50°C. The screw speed was 160 r.p.m., the extrusion pressure 42 bar and
the specific energy input 0.017 kWh/kp. The melt was extruded through
the extruder head multiple-bore die to form fine strands which, after leaving
the die, were size-reduced to cylindrical granules by a chopping blade (hot-
chopping granulation head with a 47-bore die (bore diameter 2 mm); twin-
bladed cutter; chopping temperature 50°C; blade speed 2650 r.p.m.). The
granules collecting from the extruder/granulator were spheronized in a
commercially available spheronizer of the Marumerizer type (Schliiter RM
400 Spheronizer - spheronizing conditions: rotational speed 320 r.p.m.;
residence time 30 s). In the spheronizer, the granules were powdered with
3% by weight - based on the Stabilox CZ 2697 used - of Sasil A 40
(Vllessalith P, Degussa AG). The granules were then sieved through a 2.5
mm sieve, about 10% of oversize granules (agglomerates) being removed.
The additive granules obtained ("beads") were substantially spherical.
3. Performance tests
3.1. Determination of abrasion
Quantities of 50 g of the rodlet-like and the bead-like Ca/Zn stabilizer
(produced as described above in 2.1. and 2.2.) were subjected to
mechanical stressing in a Retsch sieve analyzer and the abrasion was
determined. The following parameters were adjusted: time 5 mins.,
vibration amplitude 1 mm, mesh width of test sieve: 0.315 mm.
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Abrasion
Supply Form Abrasion [g] Abrasion (gJ
Rodlet granules 0.23 0.46
2.1.
Beads 2.2. 0.02 0.04
As can be seen from the Table, the beads showed considerably
lower abrasion. This is of great importance from the applicational
perspective.
3.2. Determination of flowability
To determine flowability, quantities of 96 g of the rodlet granules 2.1.
and the beads 2.2. were introduced into a funnel closed at its lower end,
the outlet was opened and the outflow time was measured. The funnel
(polyethylene powder funnel with an upper diameter of 105 mm) had the
following dimensions: diameter of outlet: 23 mm, length of outlet: 23 mm).
Flowability
Supply form Outflow time
(s]
Rodlet granules 2.6 / 3.2 /
2.8
Beads 1.5 / 1.4 /
1.4
The outflow times were measured three times.
As can be seen from the Table, the outflow time was significantly
shorter for the beads according to the invention than for the rodlet
granules. In practice, this means that flowability is considerably improved,
thus ensuring higher feed rates.
3.3 Use in PVC formulations
The performance properties of powder, rodlet granules and beads
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were compared using the Ca/Zn stabilizer Stabilox CZ 2697. To this end,
the individual supply forms were processed with polyvinyl chloride (PVC,
"Evipol SH 6830" = commercially available suspension PVC) in a Herschel
mixer to form a dry blend (quantity of material: 3 kg, heating to
120°C,
subsequent cooling)
Formulations
81 82 B3
EVIPOL SH 6830 100 100 100
Stabilox CZ 2697 (powder 1.) 3.35 - -
Stabilox CZ 2697 (rodlet granules - 3.35 -
2.1.)
Stabilox CZ 2697 (beads 2.2.) - - 3.35
Figures in Table = parts by weight
Formulations B1 to B3 (dry blends) were tested first for sieve residue
and bulk density:
Sieve residue and bulk density
Sieve residue [ >0.5Bulk density
mm]
Formulation 0.09 621
B1
Formulation 0.12 617
B2
Formulation 0.07 614
B3
Sieve residue: expressed in g based on 200 g of dry blend
Bulk density: expressed in g/I
Explanation of the determination of the sieve residue: as an
indicator of the degree of dispersion during mixing, 200 g of the dry blend
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were sieved through a 0.5 mm mesh sieve. All the particles above 0.5 mm
in size remain in the sieve in this test. This is known as the sieve residue.
The dry blends were then extruded to a flat strip in a Weber twin-
screw extruder. The extrusion parameters were as follows: screw speed
20 r.p.m., machine load 42, temperature 180°C. The strip had a
thickness
of 1.5 mm and a width of 25 mm.
The color of the strips was determined immediately after their
production (so-called initial color) using the L*,a*,b* method known to the
expert (cf. DIN 6174, CIELAB 1976). The b* value indicates the position on
the blue/yellow axis. Normally, the b* value is also called the yellow value.
A commercially available instrument known as a "Micro Color" (Dr. Lange)
was used for the measurements. The color values are set out in the
following Table. Another parameter determined was how long it took the
test strips to turn black in color during heat treatment in a "thermo-oven"
(cf.
DIN 5033). To this end, the strips were heated at 180°C in a
thermo-oven,
being briefly removed from the oven every 15 minutes for visual
examination. The time in minutes which the strips took to turn black is
termed "long-term stability". The test results are set out in the following
Table.
Heat stability
Yellow Long term stability (=
value end of
b* after stability after)
0 mins.
75 mins.
Formulation 15 34 90 mins
B1
Formulation 15 35 90 mins.
B2
Formulation 15 35 90 mins.
B3
Overall, it was found that the strip which had been produced using
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the beads according to the invention (formulation B3) was as heat-stable as
the strips which had been produced using powder or rodlet granules
(formulations B1 and B2). Accordingly, the above-mentioned performance-
related advantages of the additive granules according to the invention
("beads"), i.e. in particular less dust, better flowability, greater
formulation
flexibility, have no adverse effects on their ability to heat-stabilize PVC.
