Process for the production of press compounds (BMC) from unhardened prepreg wastes

Abstract

A process for the recycling of wastes from webs or strands made of prepreg wastes comprising a first reactive resin, having the following steps: homogenization of prepreg wastes, dispersion of fillers and/or additives in a second reactive resin, mixing of the second resin, homogenized prepreg wastes and further processing of the mixture of resin, fillers and/or additives and prepreg wastes to produce molded workpieces.

Claims

1. A process for the recycling of wastes from webs or strands made of at least one of carbon fibers or glass fibers (prepreg wastes) respectively comprising reactive resin A, comprising: a) homogenizing webs or strands made of at least one of carbon fibers or glass fibers (prepreg wastes) respectively comprising a first reactive resin, where the prepreg wastes are comminuted, b) dispersing at least one of fillers or additives in a second reactive resin, c) mixing the second resin B, homogenized carbon fibers or glass fibers respectively comprising the first reactive resin, and optionally the at least one of fillers or additives, where the first and second reactive resins are mutually compatible or identical, and d) further processing the mixture of resin, fillers or additives, and prepreg wastes to produce molded workpieces.

2. The process according to claim 1, wherein the ratio by weight of the second resin to prepreg wastes is from 2:1 to 1:5.

3. The process according to claim 1, wherein the ratio by weight of the entirety of the fillers or additives to prepreg wastes is from 2:1 to 1:5.

4. The process according to claim 1, wherein the homogenization of the prepreg wastes is achieved with one of a guillotine, screw-type extruder, twin-screw extruder, injection-molding machine, dicer, portal-controlled ultrasound cutter, rotary cutter or rolling crusher.

5. The process according to claim 1, wherein the prepreg wastes are comminuted in a manner such that the fiber length is at most 50 mm.

6. The process according to claim 1, wherein the fillers or additives comprise at least one of CaCO3, talc powder, aluminum hydroxide or magnesium hydroxide, MgO talc powder, silica gel, pigments or silica.

7. The process according to any of the preceding claims, characterized in that a portion of the fillers and/or additives is added in step a).

8. The process according to claim 1, wherein the steps a) to d) take place in their alphabetic sequence.

9. The process according to claim 1, wherein the chronological separation between step c) and d) is at most 2 months.

10. The process according to claim 1, wherein step c) takes place at a temperature of at most 70 C.

11. The process according to claim 1, wherein step c) is carried out in one of a screw-type kneader, sigma kneader, wing kneader or high-speed mixer.

12. The process according to claim 1, wherein step e) takes place in one of the hot-press process or injection-molding process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The FIGURE shows a process flow diagram of the method of the invention with process variants.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The prepreg waste (1) collected must comprise as yet unhardened matrix resin. Materials that can be used are prepreg strips, mats, sections, and residues, which may be unidirectional or woven fabrics, single-ply or multiple-ply. Other requirements are fillers and/or additives (2) and resin B (3).

[0017] The prepreg waste is subjected to a homogenization step: homogenization is achieved either by cutting (4) or by shearing (5). In the case of homogenization by cutting (4), the prepreg waste is comminuted to produce strips or small fragments. A guillotine or a dicer can be used to achieve this. Another possible pretreatment method is homogenization by shearing (5). In the case of homogenization by shearing (5) the prepreg waste is, by way of example, extruded in a screw-type extruder or twin-screw extruder. The temperature here is set in such a way that no hardening of the matrix resin occurs. The resultant homogenized prepreg waste (7) can comprise short fibers of length from 5 to 20 mm, randomly orientated.

[0018] Resin B (3) and fillers and/or additives (2) can be introduced into the process in various ways. One possible method introduces resin B (3) and fillers and/or additives (2) into a mixing apparatus (d), (f) and disperses (6) the fillers and/or additives (2) in the resin B (3). A disperser disc or a dissolver can be used to achieve this. This produces the dispersion of resin B with fillers and/or additives (8). A second possible method introduces resin B (3) and fillers and/or additives (2) into a mixing apparatus (c), (e) into which the homogenized prepreg waste (7) is also introduced. In variants of both processes, a portion of the fillers and/or additives (2) is introduced into the apparatus (a) in which homogenization is achieved by cutting (4), or a portion of the fillers and/or additives (2) is introduced into the apparatus (b) in which homogenization is achieved by shearing (5).

[0019] Resin (3), fillers and/or additives (2), and also the homogenized prepreg waste (4) are fed into a mixing apparatus (9). As described, it is possible either to feed all three components directly or to add a dispersion (8) of fillers and/or additives (2) in resin (3). A particularly suitable mixing apparatus (9) is a twin-screw kneader. The nature of the resin must be such that it is compatible with the matrix of the prepreg waste. In particular, it is amenable to homogeneous mixing therewith and to successful hardening. Hexply M21E epoxy-resin-containing carbon prepregs from the company Hexcel, as used in aircraft construction, are by way of example compatible with the resins RTM6, M21 and DLS1791 which are likewise marketed by the company Hexcel. Additional resin is required to fill cavities in the randomly oriented fibers; these additional cavities can be attributable to the fact that the randomly oriented fibers comprise more cavities or require more space, and therefore absorb more resin than unidirectionally orientated fibers.

[0020] Particular fillers and/or additives (2) that can be used are flow improvers, for example CaCO3 (chalk or marble), preferably with particle size from 5 to 50 micrometers, and/or magnesium hydroxide or aluminum hydroxide, silica or silica gel; it is moreover possible to use release agents, pigments, stabilizers, catalysts and/or inhibitors.

[0021] Quantities that can be used, based on the final BMC products, are from 40 to 70% by weight of prepreg wastes, from 10 to 50% by weight of resin, from 10 to 30% by weight of flow improvers, up to 5% by weight of release agents, up to 10% by weight of pigments and/or up to 10% by weight of catalysts and/or inhibitors.

[0022] It can be advantageous to begin by charging resin (3) or resin dispersion (8) to the mixing apparatus (9), optionally mixing this with fillers and/or additives (2), and only then adding the homogenized prepreg wastes (7). The mixture is re-homogenized in the mixing apparatus (9), and after from 5 to 15 minutes recycled BMC (10) (reBMC) is obtained as intermediate product. This can then be further processed in the hot-press process (11) to produce workpieces.

[0023] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

KEY

[0024] (1) Prepreg waste [0025] (2) Fillers and/or additives [0026] (3) Resin B [0027] (4) Homogenization by cutting [0028] (5) Homogenization by shearing [0029] (6) Dispersion [0030] (7) Homogenized prepreg waste [0031] (8) Dispersion made of resin B with fillers and/or additives [0032] (9) Mixing apparatus [0033] (10) Recycled BMC [0034] (11) Further processing [0035] (a) Addition during homogenization by cutting [0036] (b) Addition during homogenization by shearing [0037] (c) Addition to the mixing apparatus [0038] (d) Addition with dispersion

EXAMPLES

Example 1: Production of reBMC with an Extruder

[0039] 500 kg of residues of offcut Hexcel Hexply M21E prepreg materialscomprising only resin and fiberwith no separating film or other foreign substances are charged to an extruder, which can be a single-screw or twin-screw extruder as desired. [0040] The material is comminuted in the extruder at about 70 rpm on a conveying screw (not a plastifying screw) with length about 1 m, L/D ratio >30 and maximal temperature 70 C. [0041] The prepreg is charged at the ingoing end of the screw; the following are added by way of another addition slot at about 1/3 of the length: Hexcel RTM6 resin (200 kg) and further fillers, e.g. Nabaltec Apyral 40 or Magnesia 7287 (300 kg). [0042] The remaining 2/3 of the screw length serves for mixing of the compound and homogenization of fiber length. [0043] The material is discharged at the outgoing end of the extruder. [0044] Finally, the material is consolidated in a press procedure in a heatable vertical press (platen press) in a divided mold (upper mold and lower mold) (cf. SMC/BMC) to produce the final component (press pressure from 120 to 140 bar, temperature 180 until material can be demolded).

Example 2: Production of reBMC with Cutter and Kneader

[0045] 500 kg of residues of offcut Hexcel Hexply M21E prepreg materials, without separating film or other foreign substances, are processed in a guillotine cutter, for example an N45 from the manufacturer Pierret, to produce a generally uniform fiber length: fiber length from 12 to 24 mm. For single-ply prepreg (e.g., roll residues) it is preferable to use a cutter. [0046] Hexcel RTM6 resin component and Nabaltec Apyral 40 or Magnesia 7287 fillers are then mixed in a Niemann Kreis-Dissolver (200 kg of resin and by way of example 300 kg of further fillers). The mixing of resin and fillers can also alternatively be achieved directly in the kneader, but the quality of the mixture is then poorer. [0047] Premixed resin and cut prepreg are charged to a sigma kneader and mixed at from 60 to 100 rpm for about 10 min. [0048] Finally, the material is consolidated in a press procedure in a heatable vertical press (platen press) in a divided mold (upper mold and lower mold) (cf. SMC/BMC) to produce the final component (press pressure from 120 to 140 bar, temperature 180 until material can be demolded).

Example 3: Production of reBMC with Extruder and Kneader

[0049] 500 kg of residues of offcut Hexcel Hexply M21E prepreg materials, without separating film or other foreign materials, are charged to an extruder, which can be a single-screw or twin-screw extruder, as desired, and are processed therein at about 70 rpm and at most 70 C. to produce a generally uniform fiber length (stochastical fiber length distribution around a value defined via these process parameters). [0050] Hexcel RTM6 resin component and Nabaltec Apyral 40 or Magnesia 7287 fillers are then mixed in a dissolver (for example Niemann Kreis-Dissolver) (200 kg of resin and by way of example 300 kg of further fillers). The mixing of resin and fillers can also alternatively be achieved directly in the kneader, but the quality of the mixture is then poorer. [0051] Premixed resin and cut prepreg are charged to a sigma kneader, for example K II 450 from the manufacturer Linden, and mixed at from 60 to 100 rpm for about 10 min. [0052] Finally, the material is consolidated in a press procedure in a heatable vertical press (platen press) in a divided mold (upper mold and lower mold) (cf. SMC/BMC) to produce the final component (press pressure from 120 to 140 bar, temperature 180 until material can be demolded).