Method of manufacturing a particle foam part

Abstract

The invention concerns a process and a device for producing a particle foam part. The method comprises the steps of feeding foam particles into a mould space of a mould, welding the foam particles in the mould space under application of a predetermined pressure, wherein the foam particles comprise a proportion of at least 10% by weight of recycled, shredded foam particles and the welding of the foam particles takes place by means of electromagnetic waves.

Claims

1. Method for producing a particle foam part, comprising the steps of feeding foam particles into a mould space of a mould, welding the foam particles in the mould space under application of a predetermined pressure, wherein the foam particles comprise a proportion of at least 10% by weight of recycled, shredded foam particles and the welding of the foam particles is effected by means of electromagnetic waves.

2. Method according to claim 1, characterized in that the proportion of recycled, shredded foam particles is at least 20% by weight and in particular at least 30% by weight or at least 50% by weight or at least 70% by weight.

3. Method according to claim 1, characterized in that the predetermined pressure in the mould space is at least 2 bar, in particular at least 3 bar and preferably at least 5 bar.

4. Method according to claim 1, characterized in that the foam particles are based on polystyrene (ePS), based on polypropylene (ePP), based on polyurethane (eTPU), based on polyether block amide (ePEBA), based on polylactate (PLA), based on polyamide (ePA), based on polybutylene terephthalate (ePBT), based on polyester ether elastomer (eTPEE) or based on polyethylene terephthalate (ePET). (of expandable thermoplastics)

5. Method according to claim 1, characterized in that a heat transfer medium is applied to the foam particles during welding by means of electromagnetic waves.

6. Method according to claim 5, characterized in that the heat transfer medium is a liquid, such as water.

7. Method according to claim 1, characterized in that the foam particles are welded by means of electromagnetic waves without the addition of a heat transfer medium.

8. Method according to claim 1, characterized in that recycled, shredded foam particles and non-recycled and non-shredded foam particles are mixed by means of a mixing device in a predetermined ratio and fed to the moulding tool.

9. Method according to claim 1, characterized in that recycled particle foam material is shredded and then fed to the mould space.

10. Method according to claim 1, characterized in that the particle foam part is made solely from foam particles.

11. Apparatus for producing a particle foam part comprising a mould defining a mould space, means for applying a predetermined pressure to foam particles in the mould space, and a generator for generating electromagnetic waves for welding the foam particles in the mould space, characterized in that a mixing device for mixing recycled, shredded foam particles and non-recycled and non-shredded foam particles and/or a shredding device for shredding foam material to be recycled is provided.

12. Apparatus for producing a particle foam part according to claim 11, comprising a mould defining a mould space, means for applying a predetermined pressure to foam particles in the mould space, and a generator for generating electromagnetic waves for welding the foam particles in the mould space, characterized in that a sorting device for sorting shredded foam particles is provided.

13. A method according to claim 1, wherein an apparatus for producing a particle foam part is used, wherein this apparatus comprises a mould defining a mould space, means for applying a predetermined pressure to foam particles in the mould space, and a generator for generating electromagnetic waves for welding the foam particles in the mould space, a mixing device for mixing recycled, shredded foam particles and non-recycled and non-shredded foam particles and/or a shredding device for shredding foam material to be recycled is provided and/or a sorting device for sorting shredded foam particles is provided.

14. Particle foam part, characterised in that it is produced by a method according to claim 1.

15. Apparatus for producing a particle foam part comprising a mould defining a mould space, means for applying a predetermined pressure to foam particles in the mould space, and a generator for generating electromagnetic waves for welding the foam particles in the mould space, characterized in that a sorting device for sorting shredded foam particles is provided.

Description

[0055] The invention is explained in more detail below using the drawings as examples. The drawings show schematically in:

[0056] FIG. 1 an apparatus for producing a particle foam part using recycled particle foam material in a block diagram.

[0057] The invention is explained below using an example of a device for producing particle foam parts (FIG. 1). Such devices are also referred to as moulding machine 1.

[0058] The automatic moulding machine 1 has at least one mould 2, which is formed from an upper mould half 3 and a lower mould half 4. Mould 2 defines a mould space (not shown) for receiving foam particles, which are welded in the mould space to form a particle foam part by adding heat.

[0059] Mould 2 is a so-called crack-gap mould, i.e. it is designed in such a way that the two mould halves 3, 4 can be moved apart a little to accommodate foam particles, and then compressed in the filled state by means of a press 5 to press the foam particles in the mould space.

[0060] The press 5 has a press table 6 with a support plate 7 and a press plunger 8 with a press plate 9. The press plunger 8 has a cylinder/piston unit 10 with which the press plate can be raised and lowered (double arrow 11).

[0061] Furthermore, a container 12 is provided for receiving particle foam parts to be recycled. The container 12 opens with its funnel-shaped and downwardly open underside into a shredding device 13. The shredding device 13 is designed for shredding particle foam parts which are shredded to foam particles with a predetermined size range. The shredded foam particles are unevenly shaped by the shredding process. The maximum expansion of these foam particles is usually in the range of at least 3 mm, especially at least 4 mm and up to a maximum of 10 mm or a maximum of 8 mm. The size of the shredded foam particles can, for example, be controlled by setting a distance between two shredder rollers.

[0062] The shredder unit 13 is connected to a sorting unit 15 via a line 14. Sorting devices for sorting foam particles are described in the German patent application DE 10 2019 127 708.6 which has not yet been published. Full reference is made to this patent application. With the sorting device 15 the shredded foam particles can be sorted according to predetermined criteria. One or more sorting criteria may be applied. Foam particles which do not meet the desired criteria are discharged via a discharge line 16 into a collection container 17.

[0063] The sorting device 15 is connected to a line 18 with a mixing device 19. Line 18 transports the recycled, shredded foam particles that meet the sorting criteria from sorting facility 15 to mixing facility 19. These foam particles form a regrind.

[0064] The mixing device is connected to a storage tank 20 via a line 21.

[0065] In pipes 14, 18 the foam particles are transported with a carrier gas. The carrier gas is usually air. This carrier gas can be pressurized with a pump 22. Pump 22 is connected to line 21 via branch line 23.

[0066] The storage container 20 is used to provide non-recycled foam particles. These are referred to as originate. The originate is fed to the mixing unit 19 via line 21.

[0067] At the mixing device 19 the regenerate and the originate are mixed together in a certain ratio. The mixing ratio is freely adjustable.

[0068] The mixing device 19 is connected to a line 24 with a filling injector 25, which opens at one of the two mould halves 3. In this example, the filling injector 25 leads to the upper half of the mould 3.

[0069] The filling injector is connected via a compressed air line 26 to a further pump 27, with which air under pressure can be supplied to the filling injector 25, which is referred to as filling air, with which the foam particles from the filling injector 25 are conveyed into the mould space of mould 2 and, if necessary, pressurised.

[0070] The support plate 7 is electrically conductive. It is preferably a metal plate. It can, for example, be made of steel or aluminium. The support plate 7 is connected with a coaxial cable 28 to a high frequency generator 29.

[0071] The high-frequency generator is designed to generate RF radiation. The high frequency generator is connected to an electrical earth 30.

[0072] The press plate 9 is also electrically conductive. It can also be a metal plate, especially an aluminium or steel plate, which is in turn connected to the electrical earth.

[0073] The support plate 7 and the press plate 9 thus form capacitor plates, between which a high-frequency field or RF radiation can be applied with the high-frequency generator 29.

[0074] The two mould halves 3, 4 are made of a material which is essentially transparent to RF radiation. This material is for example polytetrafluoroethylene (PTFE), polyethylene, especially UHMWPE or polyetherketone (PEEK).

[0075] Optionally, at one or more points on the lines 18, 21 and 24, a nozzle 31 may be provided to supply water or another fluid. The water may be supplied as liquid or steam.

[0076] The addition of fluid may be designed on the one hand to facilitate the movement of foam particles in the line. such foam particles have a tendency to clump together. If they are wetted on the surface with a fluid, e.g. water, then this tendency is reduced, and conveyance is more reliable. In addition, such fluid may be used as a heat transfer medium in the welding of foam particles. Certain plastic materials, e.g. polystyrene (ePS) and polypropylene (ePP), absorb electromagnetic radiation to only a limited extent. The heat transfer medium is able to absorb the electromagnetic radiation in the mould cavity and transfer it to the foam particles. If materials which, from the start, absorb electromagnetic radiation well are used, then the addition of a heat transfer medium is not necessary.

[0077] The following procedure can be carried out with this automatic moulding machine 1:

[0078] Particulate foam parts to be recycled are placed in the container 12 from where they are transported to the shredder 13. In the shredding facility 13 they are shredded to foam particles. The foam particles are shredded to a predetermined size, which is adjustable. This regrind is fed to the sorting device 15. With the sorting device 15, impurities or foam particles which do not meet predetermined criteria are sorted out. These criteria can be of various types, such as size, shape, colour, density. Magnetic particles can also be filtered out.

[0079] The regenerate prepared in this way is fed via line 18 to the mixing device 19, in which the regenerate can be mixed with the originate in a predetermined ratio. The mixing ratio can be set as desired. The share of originate can also be 0%.

[0080] The foam particles are fed from the mixing device 19 to the moulding tool 2. The carrier gas is pressurized by means of pumps 22, 27 so that the foam particles are fed under pressure into the mould space.

[0081] During the feeding of the foam particles the two mould halves 3, 4 are pulled apart. After the mould space is filled with foam particles, the two mould halves 3, 4 are pressed together a little by means of the press 5, which reduces the mould space and increases the pressure on the foam particles in the mould space.

[0082] The high-frequency generator 29 applies RF radiation to the pressurized foam particles so that the foam particles are heated and welded together.

[0083] The RF radiation heats the foam particles in the mold cavity and is heated from the inside out, as they either directly absorb the RF radiation or a heat transfer medium, such as water, is added to them, which absorbs the RF radiation and transfers it to the foam particles.

[0084] It is not necessary for steam to be supplied to the mould 2 from the outside to weld the foam particles together. Pressurizing the foam particles in the mould cavity does not impair the heat supply by electromagnetic radiation in any way.

[0085] The combination of electromagnetic radiation and the application of pressure to the foam particles in the mould space thus permits the welding of foam particles with a high proportion of regenerated material. Examples are explained in more detail below.

[0086] Within the scope of the invention, the above example can be modified in many different ways. For example, it is sufficient to provide only a pump or a press to apply pressure. It is not necessary to fill the foam particles with a pump under pressure and then compress the mould using the press. However, the combination of pressure filling by means of a pump and compression of the crack gap by means of a press allows a high pressure to be applied in the mould cavity.

[0087] In the context of the invention, it is also not necessary for the mould halves to be transparent to the electromagnetic waves. The mould halves can also be made of metal and act as capacitor plates themselves. If both mould halves are electrically conductive, however, they must be insulated from each other.

EXAMPLES

[0088] Plates with the dimensions 1000×500×60 mm (=30 litres) were produced. Both the originate and the regenerate were foam particles made of ePS. During filling, the tool was opened by a crack gap of 9 mm. The expanded volume of the mould chamber was 34.5 litres.

[0089] The foam particles were put under pressure by the moving together of the mould halves.

[0090] Plates were produced with a proportion of regrind of 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%.

[0091] Water was added as heat transfer medium. The amount of water was between 150 ml and 250 ml. The greater the amount of regenerate, the higher the amount of water added.

[0092] All plates could be welded. The surface of panels containing 70% or more regrind was slightly rougher and contained much more residual moisture, which remained in the open-pored foam particles of the regrind.

[0093] Sheets with up to 60% regrind fulfilled all quality requirements and are hardly distinguishable from sheets without regrind.

LIST OF REFERENCE NUMBERS

[0094] 1 automatic moulding machine [0095] 2 moulding tool [0096] 3 upper mould half [0097] 4 lower mould half [0098] 5 press [0099] 6 press table [0100] 7 support plate [0101] 8 press punch [0102] 9 press plate [0103] 10 cylinder/piston unit [0104] 11 double arrow [0105] 12 bins [0106] 13 shredding facility [0107] 14 line [0108] 15 sorting device [0109] 16 discharge line [0110] 17 collecting container [0111] 18 line [0112] 19 mixer [0113] 20 storage tank [0114] 21 line [0115] 22 pump [0116] 23 branch line [0117] 24 line [0118] 25 filling injector [0119] 26 pressure vessel [0120] 27 pump [0121] 28 coaxial cable [0122] 29 high-frequency generator [0123] 30 electrical earth [0124] 31 nozzle