U.S. patent application number 15/381967 was filed with the patent office on 2018-01-25 for process for the production of press compounds (bmc) from unhardened prepreg wastes.
The applicant listed for this patent is Airbus Operations GmbH. Invention is credited to Tassilo Witte.
Application Number | 20180022887 15/381967 |
Document ID | / |
Family ID | 57609712 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180022887 |
Kind Code |
A9 |
Witte; Tassilo |
January 25, 2018 |
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.
Inventors: |
Witte; Tassilo; (Hamburg,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Airbus Operations GmbH |
Hamburg |
|
DE |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20170174860 A1 |
June 22, 2017 |
|
|
Family ID: |
57609712 |
Appl. No.: |
15/381967 |
Filed: |
December 16, 2016 |
Current U.S.
Class: |
524/433 |
Current CPC
Class: |
B29K 2105/246 20130101;
B29C 48/92 20190201; B29K 2709/08 20130101; C08J 2300/30 20130101;
B29B 17/0412 20130101; Y02W 30/62 20150501; B29K 2105/08 20130101;
B29B 17/0026 20130101; C08J 5/24 20130101; B29C 70/00 20130101;
B29K 2707/04 20130101; C08K 7/06 20130101; C08K 7/14 20130101; B29B
17/0042 20130101; B29C 2948/92704 20190201; B29C 43/02 20130101;
C08K 2003/222 20130101; B29C 2948/92876 20190201; B29C 48/2886
20190201; B29C 48/288 20190201; C08J 11/06 20130101; C08K 2003/2227
20130101; B29K 2105/0872 20130101; B29K 2101/10 20130101; B29B
17/00 20130101; Y02W 30/625 20150501; C08K 3/22 20130101; B29C
48/022 20190201; B29K 2105/26 20130101 |
International
Class: |
C08J 11/06 20060101
C08J011/06; C08K 3/22 20060101 C08K003/22; C08J 5/24 20060101
C08J005/24; C08K 7/06 20060101 C08K007/06; C08K 7/14 20060101
C08K007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2015 |
DE |
10 2015 122 308.2 |
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.degree. 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
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of the German patent
application No. 102015122308.2 filed on Dec. 18, 2015, the entire
disclosures of which are incorporated herein by way of
reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates to a process for the recycling of
material comprising unhardened prepreg wastes to produce
fiber-containing press compounds (BMC).
[0003] Prepregs are fiber products in sheet form or in strand form
which comprise glass fibers or carbon fibers and which have been
treated with reactive resin. Resin used can be epoxy resin. The
epoxy resins used are formulated in such a way that they harden at
a particular temperature. Epoxy resins used in aircraft
construction mostly harden at 180.degree. C.; curing temperatures
of the epoxy resins used in other technical sectors are usually
different, mostly being significantly lower. Because the reactive
resin of the prepregs has limited shelf life, it can be necessary
to cool prepregs during storage. After a particular period of
exposure of these prepregs to higher temperatures (for example room
temperature) they are subject to usage limitations, because the
resin has already reacted to an unacceptable extent, and cures. It
is naturally desirable that this material that has exceeded its
shelf life is recycled. Carbon prepregs in particular are,
moreover, very expensive.
[0004] Lay-up procedures, for example AFP processes or ATL
processes (automated fiber placement, automated tape laying)
moreover produce offcut material. On the prepreg rolls there can,
moreover, be prepreg residues that cannot be used for lay-up (roll
ends). The final cutting-to-size of a workpiece prior to hardening
can also produce single- or multilayer wastes.
[0005] Fiber-containing press compounds are composed of short glass
fibers or short carbon fibers and a matrix resin, and are known as
bulk molding compounds (BMC). BMC can be processed in the hot-press
process. For this, the BMC is inserted centrally into a heated,
divided mold. Closure leads to distribution of the BMC within the
mold cavity. BMC can also be processed by injection molding.
[0006] BMC can be composed of a mixture of from 10 to 35% of resin,
from 10 to 50% of fibers and from 0 to 70% of fillers and/or
additives.
[0007] Production of BMC from prepreg wastes can begin with removal
of the resin, for example by pyrolysis. The resin-free fibers can
then be comminuted and mixed with fresh resin, fillers and
additives.
[0008] DE 19514543 C1 discloses a process for the reclamation and
recycling of offcut material wastes from webs made of resin that is
still reactive, where the offcut material wastes are chopped in a
particular way, the viscosity of the resin is reduced by heating or
addition of solvent, and mechanical shear stress is used to produce
a mixture of separated fibers and resin which is then used as raw
material for further processing.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to recycle offcut
wastes of prepreg material made of unhardened prepregs without
first removing the resin. The person skilled in the art could not
have anticipated what has now been found: that the disadvantages of
the prior art are eliminated by a process for the recycling of
wastes from webs or strands made of carbon fibers and/or glass
fibers (prepreg wastes) respectively comprising reactive resin A,
characterized by the following steps:
[0010] a) homogenization of webs or strands made of carbon fibers
and/or glass fibers (prepreg wastes) respectively comprising
reactive resin A, where the prepreg wastes are comminuted,
[0011] b) dispersion of fillers and/or additives in reactive resin
B,
[0012] c) mixing of resin B, homogenized carbon fibers and/or glass
fibers respectively comprising reactive resin A, and optionally of
fillers and/or additives, where the reactive resins A and B are
mutually compatible or identical,
[0013] d) further processing of the mixture of resin, fillers
and/or additives and prepreg wastes to produce molded workpieces.
Prepreg wastes can thus be recycled to produce fiber-containing
press compounds without any requirement for prior separation of the
fibers from the resin. The process of the invention permits easy
handling of the tacky prepreg wastes, processing of large
quantities of the waste materials, and indeed in specific cases
continuous recycling, and finally the re-use of these wastes as raw
material.
[0014] For clarification, it should be noted that it is difficult
to draw a clear distinction between the terms "fillers" and
"additives." For the purposes of the invention, therefore, the term
"fillers and/or additives" is used with the intention of
encompassing all such additions without differentiating between
fillers and additives. The fillers and/or additives can in
particular be incorporated successfully into the resin B by using a
disperser disc, and it is also advantageous here that the resultant
mixture exhibits homogeneous dispersion of the fillers and/or
additives, can be produced without agglomerates, and is heated to
70.degree. C. via introduction of mechanical energy, with resultant
improved flow properties. A particularly elegant homogenization
method of the process of the invention uses an enclosed space in
which conveying action and shear action, for example provided by a
screw, allow both comminution and mixing of the prepreg wastes. The
ratio by weight of resin B to prepreg wastes is preferably from 2:1
to 1:5, particularly preferably from 1:1 to 1:2. The ratio by
weight of the entirety of fillers and/or additives to prepreg
wastes is preferably from 2:1 to 1:5, particularly preferably from
1:1 to 1:2. Formulations that have proved successful comprise, in
each case based on the compound, from 1/3 to 1/2 of prepreg wastes,
from 1/3 to 1/4 of resin B and from 1/3 to 1/4 of the fillers
and/or additives. It is moreover preferable that the homogenization
of the prepreg wastes is achieved with a guillotine, screw-type
extruder, twin-screw extruder, injection-molding machine, dicer,
portal-controlled ultrasound cutter, rotary cutter or rolling
crusher. In the case of unidirectional fibers, the guillotine here
is oriented in such a way that its blade is in essence
perpendicular to the fiber direction. In the case of multiaxial
laid scrims, there can be a rotary cutter orthogonal to the
guillotine, in order that fibers oriented in essence parallel to
the guillotine blade are likewise comminuted. The guillotine can be
of the type seen at (http://www.pierret.com/de/produits/coupeuses/)
(a copy of which is filed herewith). If a screw-type extruder,
twin-screw extruder or injection-molding machine is used, the
following operating parameters must be selected and balanced with
respect to one another in such a way that the shear forces arising
in the composition made of resin A and fibers comminute the fibers
to the desired dimensions: screw geometry, rotation rate and
conveying length. When a dicer is used, the dimensions of the
comminuted fibers can be determined very easily via the dimensions
of the grid. A portal-controlled ultrasound cutter is usually part
of an AFP system. In the AFP procedure the laid-up fibers are thus
cut to the desired length dimension. The unwanted parts of the
fibers beyond the desired length can likewise be chopped in a
manner that makes them directly suitable for use in a process of
the invention. This type of cutter can also be operated
independently of an AFP system. Rotary cutters can be used in
machinery, or else manually. Rolling crushers can be successful in
comminuting the prepreg wastes when the wastes are brittle.
Brittleness can generally be increased, and the comminution
procedure can thus be facilitated, by using cooled prepreg wastes,
for example by adding a coolant that evaporates to leave no residue
(liquid nitrogen, dry ice) to the homogenization apparatus. This is
not possible when extruders and injection-molding machines are
used. Another possibility is prior cooling of the prepreg wastes to
temperatures below -18.degree. C. The fiber length is
advantageously selected in such a way that the flow properties of
the resultant product are appropriate for the component to be
produced: longer fibers provide greater stability to a component;
shorter fibers permit better flow of the press compound and thus
production of geometries with greater complexity. It is preferable
to comminute the prepreg wastes in such a way that the fiber length
is at most 50 mm, preferably from 6 to 30 mm, particularly
preferably from 10 to 24 mm; 95% of the fibers by mass here are
intended to be within the stated range. When a screw-type extruder,
twin-screw extruder or injection-molding machine is used, the
scattering range can be controlled via the following operating
parameters: screw geometry, rotation rate and conveying length. It
is preferable that the fillers and/or additives comprise CaCO3,
preferably marble, talc powder, aluminum hydroxide or magnesium
hydroxide, MgO, silica gel, pigments and/or silica. Aluminum
hydroxide is also termed aluminum trihydrate, and has
flame-retardant effect. Very particular preference is given to talc
powder and aluminum trihydrate. It is moreover particularly
preferable that a portion of the fillers and/or additives is added
in step a). This reduces the tackiness of the prepreg wastes that
have been homogenized and are to be homogenized. It is preferable
that 10% of all of the fillers and/or additives to be added are
added in step a). It is moreover particularly preferable that the
steps a) to d) are carried out in their alphabetic sequence. It is
moreover particularly preferable that the chronological separation
between step c) and d) is at most 2 months. The shelf life of the
reBMC product of the invention at -18.degree. C. is up to 2 months.
It is moreover particularly preferable that step c) takes place at
a temperature of at most 80.degree. C., preferably at most
60.degree. C. This avoids any significant hardening of the resin,
because that requires at least 160.degree. C. and is usually
achieved at 180.degree. C. If the process of the invention is
intended for prepreg wastes which cure at lower temperatures, a
temperature sufficiently different from this temperature must be
maintained during the steps a), b) and c) which involve thermal
stress. It is moreover particularly preferable that step c) is
carried out in a screw-type kneader, sigma kneader, wing kneader or
high-speed mixer. The mixing procedure is usually carried out
batchwise for from 5 to 15 minutes, preferably from 10 to 15
minutes. There are known continuous compounding processes for the
production of BMC, and these can likewise be used for the purposes
of the process of the invention. It is moreover particularly
preferable that step e) takes place in the hot-press process or
injection-molding process.
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
[0038] [0039] 500 kg of residues of offcut Hexcel Hexply M21E
prepreg materials--comprising only resin and fiber--with 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.degree. 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.degree. until material can be
demolded).
Example 2: Production of reBMC with Cutter and Kneader
[0044] [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.degree. until
material can be demolded).
Example 3: Production of reBMC with Extruder and Kneader
[0048] [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.degree. 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.degree. until
material can be demolded).
* * * * *
References