U.S. patent application number 14/238516 was filed with the patent office on 2014-10-16 for solidified fiber bundles.
This patent application is currently assigned to SGL CARBON SE. The applicant listed for this patent is Rudi Beck, Florian Gojny, Frank Kochems, Konrad Maier. Invention is credited to Rudi Beck, Florian Gojny, Frank Kochems, Konrad Maier.
Application Number | 20140309365 14/238516 |
Document ID | / |
Family ID | 47595553 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140309365 |
Kind Code |
A1 |
Beck; Rudi ; et al. |
October 16, 2014 |
SOLIDIFIED FIBER BUNDLES
Abstract
A method for producing solidified fiber bundles includes
applying a melt or solution to a carrier web forming a viscous
coating, applying parallel filaments under tension to the carrier
web, and pressing the filaments into the viscous coating, forming
an impregnate. The coating is partially solidified until a
plastically deformable state of the impregnate is obtained by
vaporizing the solvent, thermal curing and/or cooling. The
impregnate is rolled onto a winding core to form a roll while
maintaining a winding tension of the filaments in the impregnate.
The outer roll is fixed on the winding core by a sleeve and/or by
adhesive tape. The impregnate is solidified by vaporizing the
solvent, thermal curing and/or cooling. The solidified impregnate
is divided up to form solidified fiber bundles. A pressure produced
by the winding tension of the filaments in the impregnate is
exerted on the roll.
Inventors: |
Beck; Rudi;
(Moenchsdeggingen, DE) ; Gojny; Florian;
(Kelkheim, DE) ; Kochems; Frank; (Binswangen,
DE) ; Maier; Konrad; (Kaisheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Beck; Rudi
Gojny; Florian
Kochems; Frank
Maier; Konrad |
Moenchsdeggingen
Kelkheim
Binswangen
Kaisheim |
|
DE
DE
DE
DE |
|
|
Assignee: |
SGL CARBON SE
WIESBADEN
DE
|
Family ID: |
47595553 |
Appl. No.: |
14/238516 |
Filed: |
August 10, 2012 |
PCT Filed: |
August 10, 2012 |
PCT NO: |
PCT/EP2012/065683 |
371 Date: |
June 18, 2014 |
Current U.S.
Class: |
524/594 ;
427/177; 428/377 |
Current CPC
Class: |
C04B 2235/524 20130101;
C04B 35/6269 20130101; C04B 35/806 20130101; C04B 2235/5244
20130101; C04B 2235/5256 20130101; C04B 2235/526 20130101; C04B
2235/5248 20130101; D04H 3/04 20130101; B29L 2009/005 20130101;
C04B 2235/5264 20130101; B29K 2061/00 20130101; C04B 35/589
20130101; B29C 70/504 20130101; D04H 3/02 20130101; D04H 3/12
20130101; C04B 2235/428 20130101; C04B 2235/483 20130101; C04B
2235/486 20130101; B29B 15/122 20130101; C04B 35/83 20130101; Y10T
428/2936 20150115; B29C 70/82 20130101; C04B 35/573 20130101; D04H
3/002 20130101; C04B 2235/616 20130101; B29K 2307/04 20130101 |
Class at
Publication: |
524/594 ;
427/177; 428/377 |
International
Class: |
B29C 70/82 20060101
B29C070/82; D04H 3/12 20060101 D04H003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 2011 |
DE |
102011080917.1 |
Aug 19, 2011 |
DE |
102011081263.6 |
Claims
1-16. (canceled)
17. A method for producing solidified fiber bundles, which
comprises the steps of: a) applying a melt or solution to a
sheet-shaped carrier layer, thereby forming a viscous coating; b)
applying parallel filaments under tension to the sheet-shaped
carrier layer having the viscous coating; c) pressing the filaments
into the viscous coating, thereby forming an impregnate; d) rolling
the impregnate onto a winding core to form a roll while maintaining
a winding tension of the filaments in the impregnate; e)
solidifying the impregnate by at least one of vaporizing a solvent,
thermal curing and cooling resulting in a solidified impregnate,
wherein a pressure produced by the winding tension of the filaments
in the impregnate is exerted on the roll during a performance of
step e); and f) dividing up the solidified impregnate for forming
the solidified fiber bundles.
18. The method according to claim 17, wherein the melt is a melt of
a thermoplastic plastic, a thermosetting synthetic resin, a pitch
and/or a sugar.
19. The method according to claim 17, wherein the solution is a
solution of a thermoplastic plastic, a thermosetting synthetic
resin, a phenolic resin, a pitch and/or a sugar.
20. The method according to claim 17, which further comprises
dividing the impregnate into strips before performing the rolling
step by cutting parallel to a filament direction with a cutting
device.
21. The method according to claim 17, which further comprises
dividing the solidified impregnate into sub-rolls by cutting
parallel to a filament direction with a cutting device before
performing step f).
22. The method according to claim 17, which further comprises
covering the impregnate with a top cover immediately after
performing step c).
23. The method according to claim 17, wherein the filaments contain
carbon filaments.
24. The method according to claim 17, which further comprises:
providing the solution or the melt as a solution or melt of an
organic substance in step a); and treating the solidified fiber
bundles at a temperature from 750.degree. C. to 1300.degree. C. in
an absence of oxidizing agents after step f), thereby converting at
least some of the organic substance into carbon.
25. The method according to claim 17, which further comprises:
partially solidifying the viscous coating after step c) until a
plastically deformable state of the impregnate is obtained by
vaporizing the solvent, thermal curing and/or cooling, wherein the
vaporizing, the thermal curing and/or the cooling are only
performed to an extent that a plastically deformable state is
maintained, wherein a force is exerted directly or indirectly on
the impregnate by a pressure application device during or after
solidification of the viscous coating; fixing the roll on the
winding core after step d) by at least one sleeve and/or at least
one adhesive tape; dividing up the solidified impregnate in step f)
in parallel and perpendicularly to the direction of the filaments
for forming the solidified fiber bundles.
26. A solidified fiber bundle, comprising: a solid matrix being a
solidified viscous coating formed from a melt or a solution; and
parallel filaments under tension disposed and pressed in said
viscous coating thereby forming an impregnate, said impregnate
rolled onto a winding core forming a roll while maintaining a
winding tension of said filaments in said impregnate, said
impregnate being solidified by at least one of vaporizing a
solvent, thermal curing or cooling resulting in a solidified
impregnate, wherein a pressure produced by the winding tension of
said filaments in said impregnate is exerted on said roll, said
solidified impregnate being divided up and forming the solidified
fiber bundles.
27. The solidified fiber bundle according to claim 26, wherein the
solidified fiber bundle has a width, measured as an average of a
larger spatial extension in each case of the solidified fiber
bundle perpendicular to an average vector in a direction of a
lengthwise extension of the solidified fiber bundle between 0.1 mm
and 20 mm, and a length of the solidified fiber bundle, measured as
an average of a spatial extension of the solidified fiber bundle
parallel to an average vector in a direction of longitudinal
extension of the filaments in the solidified fiber bundle is
between 2 mm and 50 mm.
28. The solidified fiber bundle according to claim 26, wherein the
solidified fiber bundle has a thickness, measured as an average of
a respective smaller spatial extension of the solidified fiber
bundle perpendicular to an average vector in a longitudinal
direction of an alignment of said filaments in the solidified fiber
bundle is between 0.05 mm and 2 mm.
29. The solidified fiber bundle according to claim 27, wherein:
said width is between 0.5 mm and 3 mm; and said length is between 3
mm and 20 mm.
30. The solidified fiber bundle according to claim 28, wherein said
thickness is between 0.1 mm and 0.5 mm.
31. A method for producing reinforced synthetic resins, which
comprises the steps of: producing solidified fiber bundles by the
sub-steps of: applying a melt or solution to a sheet-shaped carrier
layer, thereby forming a viscous coating; applying parallel
filaments under tension to the sheet-shaped carrier layer having
the viscous coating; pressing the filaments into the viscous
coating, thereby forming an impregnate; rolling the impregnate onto
a winding core to form a roll while maintaining a winding tension
of the filaments in the impregnate; solidifying the impregnate by
at least one of vaporizing the solvent, thermal curing or cooling
resulting in a solidified impregnate, wherein a pressure produced
by the winding tension of the filaments in the impregnate is
exerted on the roll during a performance of the solidifying step);
and dividing up the solidified impregnate for forming the
solidified fiber bundles; providing the solidified fiber bundles as
a reinforcing agent for a synthetic resin selected from the group
consisting of thermoplastic synthetic resins and thermosetting
synthetic resins.
32. The method according to claim 31, which further comprises
treating the synthetic resin reinforced with the solidified fiber
bundles at a temperature from 750.degree. C. to 1300.degree. C. in
an absence of oxidizing agents, wherein at least some of the
synthetic resin is converted into carbon by carbonization.
33. A molded body, comprising: solidified fiber bundles each
containing a solid matrix being a solidified viscous coating formed
from a melt or a solution and parallel filaments under tension
disposed and pressed in said viscous coating thereby forming an
impregnate, said impregnate rolled onto a winding core forming a
roll while maintaining a winding tension of said filaments in said
impregnate, said impregnate being solidified by vaporizing a
solvent, thermal curing and/or cooling resulting in a solidified
impregnate, wherein a pressure produced by the winding tension of
said filaments in said impregnate is exerted on said roll, said
solidified impregnate being divided up and forming said solidified
fiber bundles; and a synthetic resin, selected from the group
consisting of thermoplastics synthetic resins and thermosetting
synthetic resins, and reinforced with said solidified fiber
bundles, the molded body being treated to a temperature of
750.degree. C. to 1300.degree. C. in an absence of oxidizing
agents, wherein at least some of said synthetic resin being
converted into carbon by carbonization resulting in a carbonized
molded body, and by infiltrating said carbonized molded body with
liquid or gaseous carbide-forming elements, above a melting or
vaporization temperature thereof, thereby forming carbides of said
carbide-forming elements.
34. A production process, which comprises the steps of: providing
solidified fiber bundles each containing a solid matrix being a
solidified viscous coating formed from a melt or a solution and
parallel carbon filaments under tension disposed and pressed in the
viscous coating thereby forming an impregnate, the impregnate being
rolled onto a winding core forming a roll while maintaining a
winding tension of the carbon filaments in the impregnate, the
impregnate being solidified by vaporizing the solvent, thermal
curing and/or cooling resulting in a solidified impregnate, wherein
a pressure produced by the winding tension of the carbon filaments
in the impregnate is exerted on the roll, the solidified impregnate
being divided up and forming the solidified fiber bundles; and
providing the solidified fiber bundles as a reinforcing agent in
mixtures having thermosetting resins with at least one additional
ingredient selected from the group consisting of pitches and
particulate carbon.
35. The process according to claim 34, which further comprises:
processing the mixtures provided with the reinforcing agent to form
molded bodies; and treating the molded bodies at a temperature from
750.degree. C. to 1300.degree. C. in an absence of oxidizing
agents, wherein at least some of the thermosetting resins and the
pitches is converted into carbon by carbonization.
Description
[0001] The invention relates to solidified fiber bundles, a
production method therefor and use thereof in the manufacture of
composite materials.
[0002] Polymer-bonded fiber fabrics produced by impregnating a
thread of yarn by drawing said yarn thread through a bath
containing a resin solution or molten resin (of a thermosetting or
heat-curable polymer), or a thermoplastic, and subsequently
compressing the impregnated yarn thread and cutting the flattened
yarn thread in the lengthwise and crosswise directions are known
from European Patent Application No. 1 645 671 A1.
[0003] In this process, with appropriate cutting equipment it is
possible to ensure a high degree of uniformity in terms of the
length (measured as the average spatial extension of the fiber
bundles parallel to the average vector in the direction of the
lengthwise extension of the fibers in the fiber bundle in question)
and the width (measured as the average of the larger spatial
extension in each case of the fiber bundles perpendicular to the
average vector in the direction of the lengthwise extension of the
fibers in the fiber bundle in question) of the fiber bundles
created during the cutting steps. However, in the tests that led to
the present invention, it was discovered that the fiber bundles
created in this way tend to disintegrate in a subsequent mixing
process for producing fiber-reinforced plastics or fiber-reinforced
resins, and although the length of the fiber bundles changes little
or not at all, the width thereof, that is to say their extension
perpendicular to the direction of the fibers, shrinks
significantly. This disintegration occurs not only when they are
mixed with particulate solids such as thermoplastics, thermosetting
resins, filler materials, but also with liquid resins or pitches,
and also with any of said solid and liquid substances in any
combination, and is particularly pronounced when they are mixed
with solids in the powder form.
[0004] In view of the above, the object was to produce such
solidified fiber bundles having improved strength in such manner
that they disintegrate only insignificantly or not at all when
mixed with the aforementioned substances. A further object was to
suggest a production method that enables such solidified fiber
bundles to be manufactured efficiently and inexpensively. Yet
another object may be considered to be to improve the positioning
requirements to which the impregnated precursor materials of the
fiber bundles are subject, so that in particular their positioning
may require less space.
[0005] These objects were solved with a continuous process for
manufacturing solidified fiber bundles comprising the steps of
[0006] a) applying a melt or solution to a sheet-like carrier
layer, thereby forming a viscous coating, [0007] b) applying
parallel filaments under tension to said carrier layer coated in
this way, [0008] c) pressing the filaments into the viscous
coating, thereby forming an impregnate, [0009] d) optionally,
partially solidifying the coating until a plastically deformable
state of the impregnate is obtained by at least one of the steps
comprising vaporizing the solvent, thermal curing and cooling,
wherein these steps are only performed to the extent that a
plastically deformable state is maintained, wherein in particular a
force is exerted directly or indirectly on the impregnate by at
least one pressure application device during or after
solidification of the coating, [0010] e) rolling the impregnate
onto a winding core to form a roll while maintaining a winding
tension of the filaments in the impregnate, [0011] f) optionally,
fixing the roll on the winding core by means of at least one sleeve
and/or at least one adhesive tape, [0012] g) solidifying the
impregnate by at least one of the steps comprising vaporising the
solvent, thermal curing and cooling, and [0013] h) dividing up the
solidified impregnate, in particular in parallel and
perpendicularly to the direction of the filaments to form
solidified fiber bundles, [0014] wherein a pressure produced by the
winding tension of the filaments in the impregnate is exerted on
the roll during the performance of step g).
[0015] The stated objects were further solved by solidified fiber
bundles that are obtainable by the application of such a
method.
[0016] Here and in the following, the term impregnate is understood
to mean an arrangement of filaments or fibers of which at least
some have undergone impregnation. Accordingly, complete
impregnation for the purposes of complete coating of the filaments
or fibers is not necessary.
[0017] In detail, the method according to the invention involves
first applying a melt or solution, preferably a polymer melt or a
polymer solution to a sheet-like carrier layer, preferably a film
or a paper web, in the form of a viscous coating, wherein the mass
of the applied substance per unit of area is preferably 80
g/m.sup.2 to 400 g/m.sup.2, particularly preferably 100 g/m.sup.2
to 200 g/m.sup.2. If a melt is used, such melt is preferably of a
thermosetting plastic or of a thermosetting synthetic resin or of a
pitch or of a sugar. If a solution is used, such a solution is
preferably of a thermosetting plastic or of a thermosetting
synthetic resin or of a pitch or of a sugar.
[0018] Filaments arranged parallel with each other, possibly
enclosed in a fabric, are deposited under tension on said carrier
layer coated in this manner, for example by a warping device, and
the filaments are subsequently pressed into the viscous coating,
and thus bonded therewith, for example by passing between a pair of
calendar rolls. If the coating material is a synthetic resin, that
is to say a duroplast, said coating material is at least partly
cured, optionally in a heating device by vaporisation of the
solvent and/or by a crosslinking reaction of the duroplast, during
the subsequent passage of the multilayered structure, consisting of
a carrier layer with a coating in which filaments arranged parallel
to each other and aligned in the direction of transport are
embedded in a melt or a viscous solution. In a preferred variant,
after exiting the heating a top cover may be added on the side
opposite the carrier layer side before a second pair of rollers,
which top cover adheres to the coating, which is normally still
deformable and viscous, that is to say still suitable for
impregnation. The bonded filament layer thus created, which may be
covered or uncovered, and is applied to the carrier layer, may then
preferably be advanced over a cooling table. Then, it may either be
rolled up directly onto a winding core, or preferably first cut
into narrower individual webs in the lengthwise direction of the
filaments in a cutting device, that is to say divided up according
to the desired width of the fiber bundles that are to be produced.
In both cases, the webs are then wound onto winding cores or reels.
Cardboard tubes, having a diameter of 300 mm for example, are
preferably used as the winding cores. In this case, the filaments
retain a predefined winding tension, which further helps to hold
the webs together in the winding. The winding tension is created
due to the fact that a tension is applied to the fiber bundles
during the winding process, that is to say the fiber bundles are
wound onto the winding cores under tension. The winding tension is
also supported by the strength of the impregnate, which results
from the tension that is applied to the filaments while they are
deposited under tension on the coated carrier layer to create the
impregnate.
[0019] The division according to the desired width of the fiber
bundles may be carried out either before or not until after a
fixing step, which is described as optional, and before or also
after a curing step, which will be described in the following. In
the latter case, the entire filament layer bonded with the carrier
layer is rolled up at full width.
[0020] If the bonded filament layer applied to the carrier layer is
divided before the optional fixing step and/or the curing step, the
top cover is preferably placed thereon after said dividing step, in
which case it has an overhang of at least 1 mm, preferably at least
2 mm, and particularly at least 5 mm, on each side of the carrier
layer over the width of the partial web. In this case, winding is
carried out in such manner that the side of the partial web with
the top cover faces inward, that is to say towards the reel
body.
[0021] According to the experiments carried out as part of the
present invention, the method step which then follows, in which the
windings thus created are optionally fixed and solidified, results
in improved stability of the fiber bundles. The carrier layer with
the coated filament layer, that is to say the impregnate (hereafter
also referred to as "prepreg") is wound onto the reels or winding
cores at the desired length, optionally fixed with a sleeve or with
thermally resistant adhesive tape, and if thermoplastics or other
meltable substances are used, is cooled to below the melting
temperature thereof, or if thermosetting, duroplastic substances
are used, it is transported into a heating device to cure the
thermosetting layer, in which case the suitable temperature range
and required dwell time may be adjusted depending on the type and
mass of the synthetic resin or duroplast. If a furnace is used, the
heating device for curing is preferably operated in recirculated
air mode, other heating options, such as microwave heating,
infrared heating or induction heating for conductive carbon
filaments, may also be used. The curing conditions such as
temperature and dwell time are normally dependent on the mass of
the material to be cured, the energy input from the heating device,
and the chemical composition (reactivity) of the thermosetting
substance. Of course, a continuous operating mode, with a
continuous pass furnace for example, is also possible here.
[0022] The critical feature in this context is that pressure must
be exerted on the winding that is to be hardened, during curing (in
the case of duroplasts) or during cooling (in the case of
thermoplasts). This pressure is created by the winding tension of
the filaments in the impregnate, and according to a preferred
embodiment is maintained by fixing the windings with a sleeve or
adhesive tape. In the case of carbon filaments that are bonded with
synthetic resins, that is to say duroplasts, the force exerted on
the windings is preferably in the order of 10 N to 1500 N,
particularly preferably 100 N to 1000 N, most preferably 450 N to
800 N. For a reel having a length of 500 mm and a core diameter of
300 mm, this corresponds to a pressure on the outside surface of
0.5 kPa to 2 kPa. In order to achieve the adhesion between the
filaments and the matrix necessary to enable further processing, it
is essential that pressure of this magnitude be maintained. In
particular, the winding tension must be selected such that at least
a pressure of 0.5 kPa, preferably at least 1.0 kPa is created.
[0023] If duroplasts or mixtures containing duroplasts are used,
raising the temperature in the heating device causes said materials
to soften, and the winding tension created by the force described
in the preceding sets a flowing process in motion, which further
improves the evenness of the impregnation and wetting of the
filaments with the impregnating agent. This homogeneous structure
is fixed by the subsequent curing.
[0024] If the filaments are bonded with thermoplasts or other
meltable substances, such as pitches, it is sufficient to cool and
solidify them, also with pressure on the winding. It has been
discovered that mixtures containing a percentage by mass of at
least 30% of a thermosetting, that is to say a duroplastic
substance, can be cured by the effect of heat It has been
discovered that mixtures can be cured by the effect of heat,
although the lower limit depends on the type of the duroplast and
of the other substances contained in the mixture. For example,
mixtures of phenolic resins and pitches having a mass percentage of
at least 30% phenolic resins are also thermosettable, although
curing agents are added in the case of novolaks, something that is
not necessary when phenol-resol resins are used.
[0025] According to one of the embodiments described in the
preceding, filament strips are produced using said windings (cured
or hardened by cooling) by lengthwise cutting, that is to say
parallel to the alignment of the filaments, or filament strips are
unrolled from the reels or windings, and in both cases the
solidified filament strips are then forwarded to a transverse
cutting device, in which they are cut to the desired length
(perpendicularly to the direction of the filaments), and so form
the desired fiber bundles.
[0026] After curing, the process webs, that is to say the papers of
films serving as the carrier layer or top cover, may be removed
from the cured, bonded filament layers by rewinding, as was done in
the following application example. In this way, the carrier layers
and top covers can be recycled or downcycled. Alternatively, the
carrier layers and top covers may be removed in the following
process step during further processing. If the carrier layer and
top cover are divided together with the cured prepreg, they can
also be left in the product as aggregate.
[0027] The width of the filament strips, obtained by dividing in
the lengthwise direction--that is the direct of the filament
alignment--, is between 0.1 mm and up to 20 mm, and is preferably
in the range from 0.5 mm to 3 mm. Cutting to size in the transverse
direction, that is to say perpendicularly to the direction of the
filaments or fibers, is carried out in a cutting and/or punching
process, and yields the desired, solidified fiber bundles. The
length thereof may be in a range for example from 2 mm to 50 mm,
and is preferably from 3 mm to 20 mm.
[0028] As usual, the term filaments is used to denote endless
(i.e., the length of which is only limited by the capacity of the
reels) single strands or multiple parallel strands; in this
context, the term fibers is used to denote single or multiple
mainly parallel strands having limited length, wherein in the case
of synthetically produced fibers the lengths are usually determined
by a cutting process.
[0029] After the solidified windings have been cooled and cut,
hard, that is to say dimensionally stable, bonded fiber layers
remain, referred to as cured prepregs. The length and width of
these cured prepreg cut lengths are defined by the cutting
operations during the manufacture thereof.
[0030] These solidified fiber bundles comprise fibers aligned in
parallel, embedded in a solid matrix, particularly a thermoplast or
synthetic resin matrix, wherein the matrix is solidified by cooling
to below the melting or glass transition temperatures (for
thermoplasts) or by curing (for synthetic resins or
duroplasts).
[0031] Due to the solidification and the rolling up onto a winding
core, the solidified, impregnated fiber layers also have a
curvature, which in turn causes curvature in the solidified fiber
bundles. Accordingly, the solidified fiber bundles may also have a
curvature that is discernible with the naked eye, in some cases
even when they have been unrolled from the winding body and cut or
stamped. This curvature may be reduced or even eliminated entirely
by a subsequent smoothing process, carried out for example with a
smoothing device integrated in a cutting device, or by mechanical
stretching after unrolling from the winding.
[0032] Solidified fiber bundles of such kind may be used preferably
for producing fiber-reinforced ceramic materials, particularly for
producing C/SiC materials, which today are used particularly for
brake and clutch discs. Other applications include reinforcing
elements in synthetic carbon materials, for electrodes in smelting
furnaces for example, or in electrolysis applications, for
reinforcing concrete or in the reinforcement of materials for
antiballistic protection equipment.
[0033] These solidified fiber bundles are notable for the following
properties: [0034] very low fluctuations in the mass per unit area
and mass percentage per unit area of the fibers, also in the resin
content and the low crack formation over the full width thereof,
[0035] mass percentage per unit area of the fibers in the fiber
bundles is in the range from 50 g/m2 up to 800 g/m2, preferably
from 100 g/m2 to 350 g/m2, and particularly from 200 g/m2 to 300
g/m2, [0036] the resin content can be adjusted with an accuracy of
.+-.3%, and not more than .+-.5%, with a mass percentage of 40%
synthetic resin and a mass percentage per unit area of 400 g/m2 for
the impregnate; without the step of curing under tension, the
fluctuation range is .+-.15%, [0037] improved flowability in the
cut state: during measured delivery via shaking channels, no
clustering or clumping occurs, the shaking angle is about one half
smaller than prepreg cut lengths with the same length and width
distribution but which are manufactured without the step of curing
under tension, [0038] lower mass percentage of dusts, less than 1%,
particularly fine dusts and aerosols, during cutting and in the cut
state, [0039] high cutting/shearing strength (cross-sectional
splitting force) within the impregnated and solidified prepreg cut
sections or fiber bundles, from 70 MPa to 150 MPa in the solidified
and cured state (with bundles according to the prior art, as
represented by patent application EP 1 645 671 A1, values from only
about 35 MPa to about 55 MPa were achieved) [0040] uniform
impregnation of the fiber bundles, resulting in a high tapped
density, in the case of carbon filaments bonded with phenolic
resin, tapped density values are achievable that are 20% to 25%
higher than without the step of curing under tension.
[0041] Raw materials for the fiber bundles according to the
invention may preferably be filaments made from carbon, ceramic
materials such as silicon carbide, silicon nitride, silicon
carbonitride, silicon boron carbonitride, which are obtainable in
known manner by pyrolysis of silicon-organic polymers, from
aromatic polyamides (aramides), from thermotropic liquid
crystalline polymers, particularly aromatic copolyesters on a
hydroxybenzoic acid or hydroxynaphthoic acid basis, from glass and
even thin metal wires. Particularly preferred are filaments made
from carbon. The material for the bonding agent or the matrix is
preferably a polymer, which may be thermosetting or thermoplastic.
It is also possible to use low-molecular organic substances, which
are applied as a melt like thermoplasts and lend sufficient
strength to the fiber bundles in the cooled state, such as for
example pitches and/or sugars. The "preceramic" polymers are also
usable, stabilising the fiber bundles in the cured state, and
which, when used, cause the fiber bundles to be converted to a
ceramic phase by thermal treatment after cutting and incorporation
in a material, such polymers particularly including polysilazanes,
polyborosilazanes, polycarbosilazanes, and polyborocarbosilazanes,
which can be converted to silicon nitride, silicon boronitride,
silicon carbonitride, and silicon borocarbonitride. These
reinforcing fibers are aligned parallel within the fiber bundles
and are present in a matrix of polymers (for example phenolic,
epoxy, cyanate ester, polyester, vinyl ester, benzoxazine resin or
mixtures of such resins, which contain a percentage by mass of at
least 10% of one of the cited components), or thermoplastic
materials (e.g., pitches, polyimides, polyetherimides, polyamides,
polyketones), the preceramic polymers cited previously, carbon or
ceramic materials (for example CSiC, that is to say carbon-fiber
reinforced silicon carbide). In addition, the polymers listed
previously may also contain fillers such as carbon blacks,
graphites or nanoparticles (for example carbon nanotubes, carbon
nanofibers). A viscous solution of a phenolic resin is particularly
preferred for use as the bonding agent.
[0042] The fiber bundles produced in this manner may also be used
to strengthen thermoplastic or thermosetting plastics, the fiber
bundles preferably being mixed with powders or a granulate of the
plastics concerned as the matrix material and then being reshaped
by compressing for example. The fiber bundles according to the
invention may also be mixed with the matrix material in a kneader
(for example a Z-arm kneader with intermittent operation) or in a
worm extruder (extruder with continuous operation), possible with
the addition of the fillers cited in the preceding. The addition of
the solidified fiber bundles according to the invention results in
considerable improvement to the strength and rigidity of the
moulded parts manufactured therefrom.
[0043] A plant that is suitable for the method for producing the
solidified fiber bundles according to the invention is represented
diagrammatically in FIG. 1. In this drawing:
[0044] FIG. 1 shows a plant for producing the windings that
according to the invention are rolled up while under tension, and
are solidified by thermal curing (in the case of thermosetting
binders) of by cooling (in the case of thermoplastic binders, i.e.,
binders that soften with heat) with the application of traction and
the pressure generated thereby.
[0045] In detail, a warping device is designated by 10, and from
said warping device a warp of parallel filaments issues in a
uniform layer thickness over the entire width of the warp and
passes over a roll pair 11 and 12. A carrier layer 20 comes from an
unwinding unit--not shown in further detail--and passes over a
pressure roller 23 to a roll pair 21, 22. The outer surfaces of
rolls 21, 22 define a narrow gap, the thickness of which may be
altered by shifting the axes of these two rolls relative to one
another, wherein a bonding agent in liquid form is poured between
the two rolls from above. In this context, the viscosity of the
bonding agent is selected such that it is able to be applied
through the gap between the rolls, and the binding agent does not
run off of the carrier layer, simply forming a coat thereon. In a
preferred embodiment, the two rolls 21 and 22 can be heated, so
that a constant viscosity of the binding agent may be assured via a
regulating device with continuous viscosity measurement and
temperature control. When the two rolls are counter-rotated with
respect to one another, an even film of the bonding agent is spread
over the carrier layer from above. In a preferred embodiment, roll
22 is not rotated and roll 21 is rotated in such manner that the
outer surface thereof that is close to the carrier layer rotates in
the opposite direction to the transport direction of the carrier
layer. In this way, it is possible to apply a film of bonding agent
to the carrier layer as evenly as possible. The filament warp is
pressed into the bonding agent layer on the carrier layer 20 by
roll 12. In a particular embodiment, after this step a further web
from a roll 30 may be spread as a top cover over the filament warp
impregnated with bonding agent from above via a deflection roller
31. Then, the "impregnate" consisting of carrier layer 20 and the
filament warp soaked with the bonding agent, possibly with the
applied top cover drawn from roll 30 is guided through a heating
device, for example a heating table 40 as shown here, with surface
contact with the impregnate from below, that is to say the side of
the carrier layer, or an infrared heater from above, or in a hot
air tunnel with lengthwise or transverse airflow, is smoothed from
top to bottom with pressure by preferably at least one roll pair 50
and 51 (shown in FIG. 1 as three roll pairs 50 and 51, 52 and 53,
and 54 and 55), the at least one roll pair preferably being
designed so as to be heatable as well, then optionally through a
cooling apparatus, represented here as a cooling table 60, guided
between rolls 70 and 71 that are implemented as the main drive, and
through a apparatus 72 for measuring the mass per unit of area, and
finally rolled up on a wind-up reel 80. Normally, the winding
device is constructed with wind-up reel 80 in such manner that
reels can be changed automatically, thus enabling the system to
continue operating without interruption.
[0046] It is preferred to use a solution or a melt of an organic
substance in step a), and the solidified fiber bundles are treated
at a temperature from 750.degree. C. to 1300.degree. C. in the
absence of oxidising agents after step h), thereby converting at
least some of the organic substance into carbon. In this way, fiber
bundles may be produced that, when filaments of carbon are used,
consist of porous carbon reinforced with carbon fibers. Suitable
fibers are then obtained by cutting (dividing) the filaments
perpendicularly to the direction of the filaments.
[0047] The solidified fiber bundles produced according to the
invention are preferably used as reinforcing elements for
thermoplastic materials or for thermosetting resins. Such
thermoplastics or thermosetting synthetic resins reinforced with
the solidified carbon fiber bundles produced according to the
invention may be treated at a temperature of 750.degree. C. to
1300.degree. C. in the absence of oxidising agents, in which case
at least a part of the thermoplastic materials or thermosetting
synthetic resins is converted to carbon by carbonisation. If
moulded bodies from such thermoplastics or thermosetting synthetic
resins reinforced with the solidified carbon fiber bundles produced
according to the invention are treated at a temperature from
750.degree. C. to 1300.degree. C. in the absence of oxidising
agents, wherein at least a part of the thermoplastic materials or
thermosetting synthetic resins is converted to carbon by
carbonisation, and the carbonised moulded bodies obtained thereby
are subsequently treated by infiltration with liquid or gas-phase,
carbide-forming elements above the melting or vaporisation
temperature thereof to form carbides of such elements, moulded
bodies are produced that contain carbon fibers as reinforcing
elements, and of which the matrix contains carbides of the elements
used for infiltration, possibly as well as unconverted residues of
the carbon formed by the carbonisation and/or of the elements used
for infiltration. If silicon is used as a carbide-forming element,
moulded bodies made from CSiC are obtained, that is to say made
from silicon carbide reinforced with carbon fibers, the matrix of
which also still contains residues of unconverted carbon and/or
unconverted silicon.
[0048] It is particularly advantageous to use mixtures of
thermosetting synthetic resins with at least one further component
selected from pitches and particulate carbon as the bonding
agent.
[0049] The invention will be explained in greater detail in the
following example. The method described comprises several substeps,
which together yield the fiber bundles according to the
invention.
1 Production of Prepregs
[0050] A unidirectional prepreg was produced, wherein first a
liquid phenol-resol resin (percentage by mass of substances that
are non-volatile for 60 minutes at 135.degree. C., approximately
71%, viscosity determined according to Hoppler at 20.degree. C. in
accordance with ISO 9371: 750 mPa s, .COPYRGT.Norsophen 1203,
Hexion Specialty Chemicals) was applied to a web of paper coated
with silicon and having a width of 1100 mm serving as the carrier
layer. The mass per unit of area of the carrier layer was 90
g/m.sup.2, the thickness of the coated paper was 0.07 mm. The resin
application quantity was adjusted such that a resin mass per unit
of area of 190 g/m.sup.2 with a variation margin of up to .+-.3%
was created in the prepreg. Spatially spread 50 k carbon filaments
(.COPYRGT.Sigrafil C30 T050 EPY, SGL Carbon SE, approximately
50,000 filaments per bundle) with a single filament thickness of
about 7 .mu.m were added all at once at a distance of 1800 mm after
the resin application, and the addition of the carbon filaments
caused the mass per unit of area to rise by 285 g/m.sup.2 (with the
same variation margin of .+-.3%). The filament layer impregnated
with resin on the carrier layer was approximately 1020 mm wide.
[0051] The material was prepolymerised with a line speed of 3.2
m/min in a furnace with heating table and full surface contact at
180.degree. C., wherein the viscosity was lowered by the raised
temperature to the extent that the resin penetrated the filament
stands.
[0052] After passing through the heating apparatus, the compacting
and compression steps followed in a roll pair functioning as a
calendar, thus forming a bead of the resin in front of the roll
gap, which rendered the prepreg more even and enabled the resin to
penetrate the filament structure. In this context, the heated rolls
were set to a temperature of 100.degree. C.
[0053] In this case, it had proven beneficial to delay the
application of the top cover until after the heating table was
passed, but before passing through the first roll pair, functioning
as a calender, because this allowed solvents and other volatile
substances to escape from the filament web impregnated with resin.
The same silicon-coated paper was used for the top cover as for the
carrier layer. The pressure applied by the roll pair was set to 9.8
kN by adjusting the pressing force. In this way, an even resin bead
was created, and therewith also a homogeneous, visibly closed
prepreg.
[0054] In another experiment, it was found that the selection of a
defined roller gap, in this case 0.52 mm, and minor adjustment of
the mass per unit of area by altering the roller gap with a maximum
pressing force of 39.2 kN on the spacers of the gap calendar roll
adjustment results in more even mass distribution of the
prepreg.
[0055] The impregnate consisting of top cover, prepreg and carrier
layer was then passed over a cooling table that had been set to
30.degree. C., with the selected line speed, this caused the
impregnate to cool to a temperature of about 41.degree. C. in the
core.
[0056] The impregnate was guided to the winding apparatus via a
further roll pair which functions as that main drive unit, and the
cited low variations in the mass per quantity unit were achieved
through continuous measurement of the area weight coupled with the
operating mode of the calender and of the resin application
system.
[0057] The impregnate was rolled up onto cardboard cylinders having
an external diameter of 300 mm as the winding core and with a
tractive force of 600 N. The winding core was changed after every
150 m of winding length; the completed windings were fixed by
banding with thermally stable adhesive tape and then removed and
placed in storage with a manipulation arm.
[0058] The mass content of (precured) resin in the finished
impregnate was 41.5%, with a mass percentage of 5.5% volatile
components.
2 Curing the Impregnate
[0059] Four such rolls were each arranged in a frame of 2.times.2
slots, and dried and hardened together in a circulating air oven.
The following temperature programme was maintained:
[0060] Heat up from room temperature (23.degree. C.) to 180.degree.
C. with a heating rate of 6.degree. C./min,
[0061] Maintain at 180.degree. C. for 150 min,
[0062] Cool down from 180.degree. C. to 40.degree. C. within 60
min
[0063] On these cured impregnates, a residual moisture
corresponding to a mass percentage of about 2.8% was measured.
3 Cutting and Stamping
[0064] The cured impregnates were rewound, so that the top cover,
carrier layer and the cured prepreg were rolled up separately from
each other. Then, the rolls with the cured prepregs were cut into
sub-rolls with a width of 40 mm with a rotating knife on a roll
cutting machine. As a result of the "displacement cut" used to
divide the partial rolls, the mass percentage of material lost in
this work step was less than 0.2%.
[0065] The cured prepreg strips thus obtained were cut in a
stamping apparatus into solidified fiber bundles called "rods", 90%
of which were within the specified parameters for length and width,
in this case with a width between 0.8 mm and 1.1 mm, and with
length between 9.0 mm and 13.5 mm. These percentages of
specification-conforming values for length and width of the rods
under identical stamping conditions are 9% better for length and
17% better for width than the polymer bonded fiber fabrics produced
according to patent application EP 1 645 671 A1.
[0066] The rods obtained were dispensed in metered quantities via
vibrating troughs and hoppers without problems or clogging.
[0067] The cutting/shearing strength was measured on rods having
dimensions 50 mm.times.100 mm, and was in the order of 121 MPa. The
cutting/shearing strength is about 110% greater than that of the
polymer bonded fiber fabrics produced according to patent
application EP 1 645 671 A1.
[0068] Compared with the polymer-bonded fiber fabrics produced
according to application EP 1 645 671 A1, the total area of
unimpregnated portions in the cross section between individual
filaments in the rods produced according to the present invention
is at least 20% lower than in the rods having the same dimensions.
This was verified by imaging analysis of pictures of sections
through said rods that had been captured with a light microscope
and enlarged with and electron microscope.
[0069] Further comparative experiments were conducted on rods
according to the example of this application and rods according to
application EP 1 645 671 A1, and the rods were treated at
900.degree. C. in the absence of oxidising agents until constant
weight was reached, wherein the cured phenolic resin (used
identically in both cases) was converted into a porous carbon
matrix. The porosities of the rods were compared, and the porosity
of the carbonised rods according to the present invention was
measured at 28%, the porosity in the rods according to application
EP 1 645 671 A1 was found to be 45%. The greater the density of the
resin matrix, the less the measured porosity is after
carbonisation. This also shows on a quantitative scale that the
method according to the present invention results in the better
impregnation.
REFERENCE SIGNS
[0070] 10 Fiber feed [0071] 11, 12 Deflection rollers [0072] 20
Carrier layer [0073] 21 Application roller [0074] 22 Fixed roller
[0075] 23 Deflection roller for carrier layer [0076] 30 Top cover
[0077] 31 Deflection roller for top cover [0078] 40 Heating table
[0079] 50, 51, 52, 53, 54, 55 Roller set [0080] 60 Cooling table
[0081] 70, 71 Take-up rollers (main drive) [0082] 72 Mass per area
quantity unit measurement device [0083] 80 Winding
* * * * *