Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND DEVICE FOR THE COMMINUTION OF PLASTICS
BACKGROUND OF THE INVENTION
The present invention relates to a process and a device for the
comminution, and in particular pulverization, of plastics or of materials,
composites or mixtures and blends containing plastics, between two fixed
rolls which form a roll gap~
Most methods of recycling plastics comprise a comminution stage.
Thé costs of the comminution stage constitute an important economic
factor in terms of the process and are thus critical as to whether the
socially desirable re-use of used plastics is at all viable.
It is generally known to comminute materials in a roll gap.
Between cylindrical rolls only one roll gap is provided which serves as
grinding device. A plurality of roll arrangements in the form of cascades
are very costly. In addition, it is not possibie to supply a relatively large
quantity of grinding stock simultaneously to the rolls, as excess grinding
stock is immediately ejected laterally past the rolls. The known
measures involve a relatively long grinding process using cost-intensive
devices.
The object of the present invention was the development of a
process and device whereby the comminution process can be carried out
favorably in terms of costs and at high speed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of an apparatus according to the present
invention.
Figure 2 is a side view of the apparatus of Figure 1.
DESCRIPTION OF THE INVENTION
The invention is directed to an improved process for the
comminution of plastics or of materials, composites, or mixtures or blends
containing plastics comprising passing the material to be comminuted
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be~ween two fixed rollers having a roll gap therebetween. The
improvement resides in:
a) using a roll gap comprising at least two roll gap sections
with different gap widths,
b) operating the rolls at different peripheral speeds,
c) maintaining in the roll gap section with the smallest gap
width a shearing rate of 0.0001 sec'~ to 100,000 secl,
d) initially feeding the materials to ~e comminuted to the roll
gap section with the largest gap width, and having passed
through this section, feeding said materials to the roll gap
section with the next or smaller gap width, and
e) using materials to be comminuted with a minimum density
o~ 0.005 g/cm3
In this way it is ensured that objects consisting of plastics or of
15 materials, composites or mixtures and blends containing plastics can be
comminuted, and in particular pulverized, favorably in terms of costs and
at high speed. By the use of a roll gap having at least two sections with
different gap widths, the space requirement of the device required for the
implementation of the process can be reduced to a minimum, and the
20 transport paths between the individual grinding stages can be kept small.
The operation of the rolls at different peripheral speeds results not only in
the crushing of the materials but also in an additional tearing effect. The
new process is thus also highly suitable for elastic materials of low
density. Operation at a shearing rate within the above stated range in
25 the roll gap with the smallest gap width optimizes this effect. It is
optionally possible to dispense with sieving or separation for the
elimination of excessively coarse grinding stock between the individual
grinding stages or when the last grinding stage has been passed
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through~ The rolls can rotate in the same direction or in opposite
directions~ Adjustment of the roll gap during the grinding process in the
event of successively finer grinding stock is unnecessary. As a result the
costs of the device are substantially reduced.
Mainly a shearing rate of 100 sec I to 20,000 sec '~ and preferably
~i,000 sec' to 10,000 sec' is maintained in the section of the roll gap
with the smallest width. A shearing rate within these ranges promotes
the comminution.
In accordance with another preferred embodiment of the process,
the rolls are operated at -20C to 200C, preferably at 0C to 100C,
particularly preferably at 10C to 80C. Corresponding temperatur~
regulation of the rolls, adapted to the materials to be comminuted,
favorably influences the grinding effect.
Suitable plastics to be comminuted are mainly chemically and/or
physically cross-linked polyurethanes, polyureas or polyurethane ureas or
mixtures, blends or composites composed of other materials with these
physically cross-linked polyurethanes, polyureas and polyurethane ureas.
Also suitable are ABS and ABS-blends with other plastics, PVC
and PVC-blends with other plastics, SMA, polyamide or polyamide blends
with other thermoplastic materials, polyolefins or polyolefin blends with
other thermoplastic materials, particulariy preferably polypropylene resins
or polystyrene resins. Cross-linked rubbers can also be used.
The described plastics can also be further modified. Thus, they
can contain conventional mineral or organic fillers or strengthening
materials Tn fibrous, planar or other forms and in a continuous or discrete
structure. They can contain conventional processing aids or agènts for
improving mechanical, surface or ageing properties. The described
plastics can also be lacquered or have been subjected to another type of
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surface modification by currentless or electrolytic metallization or plating,
surface etching~ plasma treatment, and the like
Particularly preferred are thermoplastic or thermosetting
polyurethanes, polyurethane ureas or pol~ureas, such as described for
5 example in the "Kunststoff Handbuch" (Plastics Handbook), Vol~ 7,
"Polyurethanes", published by Carl HanserVerlag, MunichNienna, 1st
Edition 1966 and 2nd Edition 1983~ Such polyurethanes, polyurethane-
ureas or polyureas possess a density exceeding 0~005 g/cm3 and are
used for example for the production of bumpers, roof linings, hat holders,
10 boot linings, door inner linings, head supports, seats, dashboards,
consoles, in energy-absorbent foams and the like.
Also preferred are composites or mixtures of these thermoplastic
or thermosetting polyurethanes, polyurethane-ureas or polyureas with
materials such as are used in the production of composite bodies, these
16 materials consisting for example of glass mats, textiles, plastic sheets,
foam sheets, wooden components or cellulose materials.
The powder produced according to the present invention is
suitable as a starting material for many different types of recycling
techniques:
a) thermoplastics can be supplied in powder form to a
conventional thermoplastic processing plant, in which they
can be processed and blended relatively simply;
b) polyurethanes can be used advantageously in this powder
form 1) in chemolytical processes, such as for example
glycolysis, alcoholysis, aminolysis and hydrolysis, 2) for
extrusion and injection molding processing (this applies in
particular to lacquered starting material) and 3) as a filler
material; and 3) for thermal treatment processes.
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The device of the present invention broadly comprises two rollers
gap which form a roll gap therebetween~ The novelty of the invention
resides in a the roll gap having at least two roll gap sections of different
gap widths, where the roll gap section with the largest gap width is
5 associated at its input end with a material feeding station and its output
end is coupled to the input end of the roll gap section with the next or
smaller gap width by a material feedback path, adjacent roll gap sections
being delimited from one another by walls.
The device is extremely compact and requires only two rolls.
10 Consequently, the drive problems are also simplified and adjustment of a
roll during the grinding process in the event of successively smaller
grinding stock is unnecessary.
Preferably the sections with different gap widths are formed by a
roll comprising corresponding sections of different diameter, where the
15 difference in diameter between these sections amounts to 0.01 mm to 10
mm, preferably 0.05 mm to 1 mm, particula~y preferably 0.1 to 0.5 mm.
The individual diameters of the rolls are dimensioned such that the
grinding process can be carried out with the largest possible throughput
and with the highest possible degree of fineness of the product. The
20 overall length of the roll section with th~ larger roll diameter is generallygreater than the overall length of the roll section with the next smaller
diameter. The precise length ratios are adjusted such that the sections
of the gap with different widths facilitate identical mass throughputs. The
product ground in one gap section can be transported, without sieving or
25 separation, via a conveyor to the next gap section in order to be more
finely ground therein. Conveyors suitable for this purpose include bucket
conveyors or scraper conveyors.
In accordance with a special embodiment of the device, one of the
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rollers comprises 2 to 10, preferably 2 to 5, particularly preferably 2 to 4
sections of different diameter.
Preferably the roll with different diameters is symmetrically
constructed along its length, the section with the smallest diameter being
5 located in the center and the sections with the largest diameters being
located at the ends~ln this way symmetrical loading of the rolls is
achieved.
It is also possible for both of the rolls to comprise sections of
different diameter in order to achieve the desired different gap widths.
10 Such a construction is naturally more costly.
Preferably the surfaces of the rolls possess a structure with an
average surface roughness in accordance v~ith DIN 4762 and 4768 in the
range of 0.01 mm to 0.1 mm, preferably to 0.05 mm.
Alternatively, the surfaces of the rolls are smooth, i.e. they
15 possess an average surface roughness of less than 0.0~ mm. The choice
of the surface properties of the rolls is of particular significance in terms
of the introduction of the material into the roll gap and for the grinding
effect.
Clearly, the individual roll sections can possess different surface
20 properties.
Finally, temperature-regulatable rolls are also advantageous.
The new device and the ground stock produced with the
assistance of said device offer a large number of advantages. All kinds
of plastics with highly differing densities can be commonly processed.
25 Very soft, comminuted plastics of low density can be processed in the
same way as arbitrary mixtures of thermoplastics with thermosetting
plastics and materials and arbitrary mixtures of brittle and elastic or soft-
elastic materials.
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It is particularly advantageous that it is now possible to process by
injection molding mixtures of thermoplastics and thermosetting plastics
which could not previously be injection molded on account of too coarse
a thermosetting plastic constituent or which now possess improved
5 properties as the particles are now very effectively bound into the
thermoplastic matrix because of their small size and good distribution~
The new device permits the production of particularly fine-particled
powders~ The construction of the new device is simple and favorable in
terms of costs and the grinding process is more effective.
The new process is economical, with the result that many
recycling or reprocessing measures based on powder or granulates can
thus gain commercial significance. Substantially all plastics can be
comminuted. Plastics in any desired combination can be comminuted
togethen Plastics, in all forms, of a frictionally connected or only partially
15 frictionally connected composites can be comminuted together. Plastics,
in all forms, of a mixture or blend can be comminuted together. Plastics
in any form of a mixture, blend or composite can be comminuted together
with various non-plastics, such as, e.g., wood, glass, ceramic or metal.
Depending upon the size of the components to be comminuted,
20 preliminary comminution may be necessary to enable the materials to be
picked up by the roll gap.
In the drawings the new device is illustrated schematically, in the
form of an exemplary embodiment and will be explained in detail in the
following.
The device comprises two rollers 1, 2 which form a roll gap 3 with
one another and can be driven at different peripheral speeds by a drive
means (not shown) via a gear (not shown). The roller 1 has a diameter
of 600 mm. The roller 2 comprises two symmetrically arranged outer
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sections 4, 5 having diameters of 600 mnn, thus conresponding to that of
the roll 1, and a central section 6 having a diameter of 599.5 mm.
Corresponding to the sections 4, 5, 6 of the roll 2, the roll gap 3
comprises roll gap sections 7, 8, 9~ The roll gap sections 7, 8 have gap
widths of 200 ~m; the roll gap section 9 has a gap width of 700 ,um.
Above the roll gap section 9, a fee~er funnel 10 (Fig. 2) is arranged as
3 material feeding station. Walls 11 delimit the roll gap section 9 in relation
to the roll gap sections 7, 8. Below the roll gap section 9 is arranged a
t collecting funnel 12 with a star wheel 13. Below this star wheel 13,syrnmetrically arranged material feedback paths 14, 15 not shown in
detail and having the form of mechanical conveyors lead upwards and
open into the feeding funnels 16, 17 (Fig. 2) arranged above the roll gap
sections 7, 8. Walls 18, 19 laterally delimit the roll gap sections 7, 8.
Below the roll gap sections 7, 8 is arranged a collecting and discharging
system 20 for the ground stock.
The diameter of the roll sections 4 and 5 of the roller 2 need not
be identical to the diameter of the roller 1. The roller 1 can readily
possess a larger or smaller diameter in order to achieve different
peripheral speeds at the same rotational speed. The operation of such a
device with different roll diameters is additionally possible at different
rotational speeds~ The only factor of importance is that a sufficient
shearing rate should be achieved in the gap sections.
Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood that such
detail is solely for that purpose and that variations can be made therein
by those skilled in the art without departing from the spirit and scope of
the invention except as it may be limited by the claims.
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