Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR CONTINUOUSLY PREPARING THERMO-CROSSLINKABLE AND/OR
THERMOPLASTIC ELASTOMER BLENDS
TECHNICAL FIELD
This invention relates to a method for continuously pre-
paring thermo-crosslinkable and/or thermoplastic elastomer
blends.
"Thermoplastic elastomers (TPE)" is the generally accept-
ed designation for materials in which the elastomeric phases
(as soft component) are embedded in plastic material (as hard
component). Depending on the nature of this embedding one dis-
tingishes between block copolymers and polyblends.
,
Furthermore, the thermoplastic elastomers may be classi-
fied as follows:
1 Types having ~igh hardness
1.1 Copolyesters
1.2 Polyether block amides
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2 Types having low hardness
2.1 Thermoplastic polyurethanes (TPU)
2.1.1 Polyetherurethanes
2.1.2 Polyesterurethanes
2.2 Thermoplastic polyolefins (TPO)
2.2.1 Ethylene-propylene diene elastomer/polypropylene
(EPDM/PP)
2.2.2 Acrylonitrile-butadiene copolymer/polypropylene
(NBR/PP)
2~3 Styrene block copolymers
2.3.1 Styrene-butadiene-styrene triblock copolymer
(SBS~ : .
2.3.2 Styrene-ethylene/butylene-styrene triblock co
polymer (SEBS~.
BACXGROUND OF THE INVENTION
So far, the preparation of thermo-crosslinkable and/or
thermoplastic elastomer blends, in particular o~ vulcanizable
rubber blends, was generally effected, either:
(a) on a two-roll calender;
or preferably
(b) in an internal mixer.
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In variant (a), the calender comprised two parallel, hor-
izontally mounted heatable and coolable hollow rolls. For car-
rying out mixing, the crude rubber was put onto the rolls in
the form of coarse pieces, and was worked until a smooth sheet
was obtained. Thereafter, the processing and vulcanization ad-
juvants were batchwisely added, and the rolled sheet were re-
peatedly homogenized by cutting and finally cooled with water
in order to prevent them from prematurely vulcaniælng.
Th2 internal mixer according to variant (b) comprised a
closed mixing chamber and two heatable and coolable mixing pad-
dles arranged in said mixing chamber. This feature did provide,
it is true, a higher mixing speed and a more intensive mixing
effect than variant (a). However, due to the applied speed of
rotation, the crude rubber blend in the internal mixer was so
strongly heated that no crosslinking reagents could be added.
Therefore, it was often necessary either
- to arrange a calender downstream of said internal mixer and
to add sulfur and accelerators to the crude blend removed
from the internal mixer on said calender only;
or alternatively
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- to prepare a preblend without sulfur and accelerator in a
first mixing passage through said interior mixer, and there-
after to prepare the final blend with addition of sulfur and
accelerator in a second mixing passage through said interior
mixer.
Besides the effectiveness of the mixing aggregate, the
order and the moment of addition of the adjuvants have a deci-
sive influence on the elastomer ~uality. Thus, it was necessary
to first add difficultly mixable plasticizers which do not ini-
tiate crosslinking, and to add vulcanizing agents at the end
only.
So far, the attempts for achieving a continuous mixing in
mixing extruders failed for the abovementioned compulsion of
observing this order. Calculations show that a spindle length
of the order of 40-D would be necessary (D being the spindle
diameter). This is technically difficult to realize and econom-
ically unattractive.
Furthermore, the use of plasticized elastomers or the ad-
dition of large q~lantities of plasticizers was critical since
the shearing forces produceable in the mixture were no longer
sufficient for a regular mixing.
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OBJECTS OF THE INVENTION
It is a primary object of the present invention is to
provide a method for continuously preparing thermo-crosslink-
able and/or thermoplastic elastomer blends which avoids the
abovementioned disadvantages of the prior art.
It is a further object of the invention to provide a
method for continuously preparing thermo~crosslinkable and/or
thermoplastic elastomer blends, in particular of vulcanizable
rubbPr blends, which allows using simple mixers or mixing ex-
truders.
SUMMARY OF THE INVENTION
To meet these and other objects, the present invention
provides a method for continuously preparing thermo-crosslink-
able and/or thPrmoplastic elastomer blends by mixing the pow-
dered or granulated elastomer with plasticizer oil and other
additives, said method comprising the steps of:
(a) continuously premixing said elastomer in a premixer with at
least part of said plasticizer oil, and optionally with at
least part of said other additives, to form a preblend in
which said elastomer is decomposed and said additives are
embedded in the polymer matrix;
and thereafter
(b) continuously completing the mixing of said premix, and op-
tionally o~ the remainder of said additives in a mixing ex~
truder.
In the method according to the invention, said premixer
of said first step ~a) has the function of decomposing the
elastomer to such an extent that a mixing with the adjuvants
becomes possible. Thus a large part of the total mixing process
is e~fected in said premixer, whereas the function of said mix-
ing extruder is reduced to a simple aftermixing. This was most
surprising to a person skilled in the art~
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In applying the method according to the invention, all
known groups of adjuvants can be used, that is to say:
1 Crosslinking systems, in particular vulcanization agents.
2 Fillers, namely:
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2.1 Active fillers which result :in a decisive improvement of
the mechanical properties, particularly of the tensile
strength and the abrasion resistance, such as: types of
active black carbon, aluminium and calcium silicate, and
zinc oxide; or
2.2 Inactive fillers which do not result in a quantitative
improvement of the vulcanized goods, for example calcium
and magnesium carbonate, kaolin, barite, kieselguhr, and
various clays;
2.3 For elastomers which are not filled with carbon black:
dyes, namely:
2.3.1 Inorganic pigments, for example lithopone, titani-
um dioxide, iron oxide, and chrome oxide green; or
2.3.2 Organic dyes, for example azo, alizarin and
phthalocyanine dyes.
3 Plasticizers for improving the processing properties, the
elasticity, and the cold-behavior, namely:
3.1 For non-polar or weakly polar crude rubber types (for
example natural rubber (NR), styrene-butadiene copoly-
mers (SBR~, polybutadiene (BR), isobutylene-isoprene co-
polymers (IIR)): mineral oil products.
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3.2 For more polar types (for example acrylonitrile-buta-
diene copolymer (NBR) and polychlorobutadiene (CR)):
phthalates (for example dibut:yl and dioctylphthalate),
phosphoric esters (for example tricresyl phosphate), and
aromatic mineral oils.
3.3 Further processing adjuvants, for exampie factices (i.e
vegetable oils treated with sulfur or sulfur chlori~e),
lanoline, soft paraffin, soft polyethylene, bitumen, and
pitch.
4 Age protectors for improving the resistance of the finished
vulcanized good against oxygen, the action of light, and dy-
namic strain, namely:
4.1 For protecting elastomers the macromolecules of which
contain double bonds against oxygen and ozone: antioxi-
dants, for example amines and phenols;
4.2 Screening agents, in particular paraffinic substances,
for example ceresin and ozocerite;
4.3 For retarding the hydrolysis of elastomers having the
'endency to hydrolyze (for example polyurethane elasto-
mers (PU) and ethylene-vinylacetate copolymers (EVA):
polycarbodiimine.
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Other adjuvants, namely:
5.1 Agant for influencing the st-ickiness, namely:
5.1.1 Agents for reducing the undesired adherence of the
crude rubber during its processing, for example
paraffin, lanoline, stearic acid and its salts;
5.1.2 Agents for improving the stickiness of the crude
rubber during its assembly, ~or example colophoni-
um, coumarone resins, alkylphenol acetylene con-
densates, as well as low-molecular polyethylenes.
5.2 Adhesives which are necessary for manufacturing firm
joints between elastomers and metals, as well as com-
pound materials with ~abrics, for example in the tire
production and for conveyor belts, namely:
5.2.1 For manufacturing metallic compound materials: for
example cobalt naphthenate, recorcin resin, as
well as increased quantities of sulfur;
5.2.2 For manufacturing textile compound materials: for
example styrene-butadiene-vinylpyridine terpoly-
mers in combination with resorcinol formaldehyde
resins and special isocyanates.
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5.3 Foaming agents for the manufacturing of porous vulcaniz-
ed goods, for example sulfohydrazides (such as benzene-
sul*ohydrazide), nitroso compounds (such as dinitroso-
pentamethylenetetramine and am- monium carbonateO
As a general rule, the adjuvants can be used with the
commercial grain sizes in the my-range. Their use in paste form
provides the possibility of refining them, in particular to
pulverize, to disperse or to degas them. This makes it possible
to use coarse-grinded and therefore less expensive adjuvants,
for example blacX carbons.
In carrying out the method of the invention, at least
part of said plasticizer oil and at least part of said other
additives may be converted into one or several pastes which are
introduced into said premixer of said first step (a).
If pastes are to be prepared from said adjuvants, it is
obviously necessary that the quantity of liquid adjuvants, and
in particular of plasticizer oil r be high enough.
A single paste may be produced ~rom all additives, said
single paste being then introduced into said premixer of said
first step (a).
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Alternatively, said additives may be shar~d for preparingseveral pastes, preferably two pastes, which are then intro-
duced into said premixer of said first step (a), either sepa-
rately or after being mixed together.
If said adjuvants are to be converted into a paste or
pastes, respectively, the quantity of liquid ingredients, in
particular that of the plasticizer oil, should obviously be
high enough for allowing the effective forming of a paste or of
pastes, respectively.
Preferably, groups of adjuvants which remain unchanged
for different applications are combined into one paste. For ex~
ample, when working with two pastes, one of them may colour-
neutral and the other paste may be coloured. In this way it is
possible to use the colour-neutral paste for the manufacturing
of differently coloured elastomer mixtures, so that only the
coloured paske is to be adapked to the desired colouring.
Said single paste or said pastes, respectively, may be
refined before being introduced into said premixer of said
first step (a), in particular by pulverization, by dispersing,
or by degasification.
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Since homogenous mixing of the various ingredients is the
easier the quantities of the various adjuvants are equal, it is
advisable to prepare first a prepaste of those adjuvants which
are needed in relatively small quantities only, and t~ mix said
prepaste with the other pasta or pastes, respectively, before
mixing it with the elastomer.
Alternatively, part of the additives, which are in pow
dered form, may be directly introduced into said premixer of
said first step (a) and/or part of the additives, which are in
powdered or paste form, may be directly introduced into said
mixing extruder of said second step (b). The latter is particu-
larly useful if mixtures, for example tire mixtures, are to be
prepared in which the quantity of plasticizer is relatively
small as compared with that of the the fillers.
Preferably, a continuously working high speed turbomixer
is used as premixer, said turbomixer working for example at
2000 r.p.m (revolutions per minute), and in particular a annu-
lar zone mixer. As it is generally known, this mixing device
has a shaft provided with teeth which rotates with high speed
inside a smooth tllbe. Thereby, a turbulent annular zone is pro-
duced near the wall of the tube. The decomposition of the elas-
tomer and its mixing with the other ingredients is essentially
effected exclusively in this zone, due to the high ~rictional
forces produced by said turbulence.
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The method according to the invention may be used for
preparing crosslinkable and/or thermoplastic elastomer blends
form all crosslinkable or thermoplastic elastomers, and in par-
ticular from:
- natural rubber tNR),
- synthetic cis-1,4-polyisoprene (IR),
- cis-1,4-polybutadiene (BR),
- styrene-butadiene copolymer (SBR),
- acrylonitrile-butadiene copolymers (NBR),
- poly-2-chlorobutadiene (CR),
- isobutylene-isoprene copolymers (IIR),
- ethylene-propylene-dien terpolymers (EPDM),
- ethylene propylene copolymers (EPM),
- ethylene-vinylacetate copolymers (EVA),
- polyurethane elastomers (PU),
- polysulfide elastomer (PSR),
- polyacrylate elastomers (AR),
- polyepichlorohydrin elastomers (CHR),
- sulfochlorinated polyethylene (CSM),
- fluorocarbon elastomers (FE),
- silicone elastomers (SIR),
- 1,5-trans-polypentenamers (TPR),
- ethylene-proyplene-dien elastomer/polyproylene polyblend
(EPDM/PP),
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- acrylonitrile-butadien copolymer/polypropylene polyblend
(NBR/PP),
- styrene-butadiene-styrene triblock copolymer (SBS),
- styrene-ethylene/butaylene-styrene triblock copolymer (SEBS).
For preparing commercial semifinished products, the re-
sulting mixture is preferably continuously pelleted after the
mixing procedure. Preferably, the obtained pellets, depending
of the intended use, are either immediately :
- continuously heated in order to vulcanize or crosslink them,
respectively;
or
- continuously cooled in order to prevent them from vulcaniza-
tion or crosslinking, respectively.
Alternatively, the elastomer mixture coming out from the
mixing extruder may be directly subject to its final shaping
procedure, for example in an extruder or on a calender.
The method according to the invention shows a number of
outstanding advantages, as compared with the status of the art,
namely:
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The admixing of the adjuvants is extremely simple and ener-
gy-saving.
The mixing extruder necessary for completing the mixing pro-
cedure, i.e. an Pxtruder comprising a mixing zone, can be of
simple and light construction, due to the fact that only a
low speed of rotation, for example 100 r.p.m. (revolutions
per minute), is necessary. A spindle length of 12 D to
18D is quite sufficient. Such mixing extruders have a
very high throughput, as compared with the vulcanization
devices according to the status of the art.
At the same time, the mixing is extremely energy-saving,
since the elastomer is already present in the form of a pow-
der or a granulate and does not need to be rendered flowable
or kneadable by the application of heat. Accordingly, the
mechanical overdimensioning of the mixing device, which was
so far necessary, is dropped.
The present problem of a subsequent treatment owing to bub-
ble formation does no longer exist, a short degasification
segment being just sufficient. A typical mixing extruder
may, for example, comprise the following se~ments:
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- Addition of materials (premix ~ eventual powders): 2-D
- Mixing: ~ D
- Degasification: 4-D
- Mixing: 4-D
- Total length: 14-D
The elastomers used can - per se - be unplasticized. This
not only facilitates their pulverization or granulation, re-
spectively, but also avoids the situation where, due to in-
sufficient shearing forces, an effective mixing is no longer
possible.
From the point of view of industrial hygiene, it is impor-
tant that a dust-free working is possible both at the pre-
mixer and at the mixing extruder.
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PREPARATION OF THE BLENDS FOR EX~MPLES 1 TO 3
Three vulcanizable rubber blends were prepared form the
following ingredients in the manner described hereafter. The
"parts" referred to are parts by weight.
No. Component Parts Parts
1 BUNA AP 447 1) 100.0
2 Zinc oxide RS 5.0
3.1 Stearic acid 1.0
3.2 Stearic acid 1.0 :
3 Total stearic acid 2.0
4 Chalk . 250.0
5.1 Paraffinic/naphthenic mineral oil70.0
5.2 Paraffinic/naphthenic mineral oil10.0
5 Total paraffinic/naphthenic mineral oil 80.0
6 Iron oxide red 6.0
7 Sulfur 7.0
8 W LCACIT CZ 2) 1.0
9 W LCACIT LDA 3) 1.0
10 W LCACIT Thiuram 4) 0.4
Total 452.4
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1) EPDM = ethylene-propylene-dien terpolymer -
grain size smaller than 10 mm
2) CPS = benzodiacetyl-2-cyclohexyl sulfenamide
3) ZDEC = zinc N diethyl thiocarbamate
4) TMTB = tetramethyl thiuramdisulfide
EXAMPLE 1
All adjuvants (Nos. 2, 3, 4, 5, 6, 7, 8, 9 and 10) were
mixed to from one single paste. This paste/ if desired after
homogenization, was premixed with the elastomer (No. 1) in an
annular zone mixer, the elastomer thereby being decomposed. The
resulting premix was then introduced into the material feed
sector of a mixing extruder.
EXAMPLE 2
The adjuvants Nos. 2, 3.1, 4, 5.1, 7, 8, 9 and 10 were
mixed to form a colour-neutral paste, and the adjuvants Nos.
3.2, 5.2 and 6 were mixed to form a coloured paste. These
pastes, if desired after homogenization, were premixed with the
elastomer (No. 1) in an annular zone mixer, the elastomer
thereby being decomposed. The resulting premix was then intro~
duced into the material feed sector of a mixing extruder.
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EXAMPLE 3
The adjuvants Nos. 2, 3, 7, 8, 9 and 10 were premixed to
form a prepaste, and the adjuvants Nos. 4, 5 and 6 were mixed
to form a main paste. Then, the two pastes were combined. The
comhined sinqle paste, if desired after homogenization, was
premixed with the elastomer (No. 1) in an annular zone mixer,
the elastomer thereby being decomposed. The resulting premix
was then introduced into the material feed sector of a mixing
extruder.
EXAMPLE 4
A typical tire mixture was prepared from the following
ingredients, the "parts" referred to being again parts by
weight:
100 parts rubber
parts plasticizer oil
60 to 80 parts carbon.black
8 to 10 parts other adjuvants (including sulfur).
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The rubber, the plasticizer o:il and the other adjuvants
were continuously premixed in an annular zone mixer rotating at
2000 r.p.m. (revolutions per minute~. The resulting blend and
the carbon black were then introduced into a vulcanization ex-
truder. There, the elastomer blend was completed.
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