CA2111537A1

CA2111537A1 - Process and device for the comminution of plastics

Info

Publication number: CA2111537A1
Application number: CA002111537A
Authority: CA
Inventors: Joachim Wagner; Werner Rasshofer; Karl Peltzer
Original assignee: Individual
Current assignee: Bayer AG
Priority date: 1992-12-21
Filing date: 1993-12-15
Publication date: 1994-06-22
Also published as: DE4243282A1; JPH06218731A; KR940013812A; EP0603646A1

Abstract

PROCESS AND DEVICE FOR THE COMMINUTION OF PLASTICS
ABSTRACT OF THE DISCLOSURE
Plastic components can be comminuted particularly economically for the re-use of the material in that they are fed to a device which with two rollers form a roll gap. The roll gap comprises at least two roll gap sections with different gap widths. The rollers are being operated at different peripheral speeds, with specified shearing rates being maintained in the smallest gap width.

Description

h ' ' ~ i 0 7 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 Mo 3 985 Le A ?9 420-US/CA `

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 Mo3985 Le A 29 420-US/CA

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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 Mo3985 Le A 29 420-US/CA

) 7 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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:
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. . , , , , -, 3 7 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 Mo3985 Le A 29 420-US/CA

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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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~ . ) 3 7 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 Mo3985 Le A 29 420-US/CA

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i37 ; -8-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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Claims

1. 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 between two fixed rollers having a roll gap therebetween, the improvement wherein:
a) said roll gap comprises at least two roll gap sections with different gap widths, b) said rollers are operated at different peripheral speeds, c) a shearing rate of 0.0001 sec-1 to 100,000 sec-1 is maintained in the roll gap section with the smallest gap width.
d) the material to be comminuted is initially fed to the roll gap section with the largest gap width, and having passed through this section, is fed to the roll gap section with the next or smaller gap width, and e) the material to be comminuted has a minimum density of 0.005 g/cm3

2. The process of Claim 1, wherein in the roll section with the smallest gap width, a shearing rate of 100 sec-1 to 20,000 sec-1.

3. The process of Claim 1, wherein said rollers are operated at -20°C to 200°C.

4. The process of Claim 1, wherein the material to be comminuted is selected from the group consisting of chemically and/or physically cross-linked polyurethanes, polyureas and polyurethane ureas and mixtures, blends or composites composed of other materials with said cross-linked polyurethanes, polyureas and polyurethane ureas.

5. An device for comminuting plastic materials comprising two rollers which together form a roll gap, wherein said roll gap comprises at least two roll gap sections with different gap widths, wherein the roll gap section with the largest gap width is 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), and wherein adjacent roll gap sections are delimited from one another by walls.

6. The device of Claim 5, wherein said roll gap sections with different gap widths are formed by a roller comprising sections of different diameters, where the difference in diameter between said sections amounts to 0.01 mm to 10 mm.

7. The device of Claim 6, wherein one of said rollers comprises 2 to 10 sections with different diameters.

8. The device of Claim 6, wherein said roller with different diameters is symmetrically constructed along its length, the section with the smallest diameter being located in its center and the sections with the largest diameter being located at its ends.

9. The device of Claim 5, wherein the surfaces of the rollers possess a surface structure with an average surface roughness in accordance with DIN 4762 and 4768 in the range of 0.01 mm to 0.1 mm.

10. The device of Claim 5, wherein the surfaces of the rollers possess an average surface roughness of less than 0.01 mm.