US20120301695A1

US20120301695A1 - Method of producing a 3d textile structure and semi-finished fiber product made of fiber composites

Info

Publication number: US20120301695A1
Application number: US13/487,867
Authority: US
Inventors: Florian H. Gojny; Heide Gommel; Thomas Putz; Tobias Schmidt
Original assignee: SGL Carbon SE
Current assignee: SGL Carbon SE
Priority date: 2009-12-04
Filing date: 2012-06-04
Publication date: 2012-11-29
Also published as: EP2507039A1; WO2011067390A1; DE102009047491A1; CA2782718A1

Abstract

A three-dimensional (3D) textile structure with contours that are matched to the 3D textile structure is formed by folding a 2D textile structure. The three-dimensional textile structure has a areal weight of 100-5000 g/m². A semi-finished three-dimensional fiber product is formed by infiltrating the 3D textile structure with thermosetting and/or thermoplastic resins and cured to form the three-dimensional semi-finished fiber product. The semi-finished product is then usable to produce leaf springs or profiles for the aerospace field, for the automobile field, for wind energy, and for sports articles.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, under 35 U.S.C. §120, of copending international application PCT/EP2010/068875, filed Dec. 3, 2010, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2009 047 491.9, filed Dec. 4, 2009; the prior applications are herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for producing a 3D textile structure and a semi-finished fiber product made of fiber composites and the use thereof.
In order to produce composite materials, fibers can be used in the form of woven or non-woven textile structures and in the form of individual, loose fibers. Use of woven fabrics has the advantages that fibers can be introduced in large quantities and with a comparatively uniform distribution in the composite material. In addition, the use of a woven fabric has the advantage that the fibers are present in bound form in the woven fabric and usually do not require any further fastening to one another. It is a disadvantage however that the production of a woven fabric is associated with high costs, in particular if sensitive or difficult-to-weave fibers are used.
Compared to woven fabrics, fiber scrims have the advantage that these can usually be manufactured far more cost-effectively. At the same time, however, fiber scrims have only a very poor cohesion which makes any processing of fiber scrims, particularly on an industrial scale, very difficult. In order to improve the cohesion of fiber scrims, for example, fiber layers can be adhesively bonded, linked or woven by hot-melting binding threads or interconnected by needling.
However, joining fiber layers by needling only results in fiber scrims capable of withstanding comparatively low loading while joining by adhesive bonding or by using hot-melting binding threads brings with it the risk that at higher temperatures cohesion of the fiber scrim is no longer given in sufficient strength since the adhesive or the hot-melting binding threads melt or decompose.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method of producing a 3D textile structure and semi-finished fiber product made of fiber composites which overcome various disadvantages of the heretofore-known devices and methods of this general type and which provides for an improved method that makes it easier to produce three-dimensional semi-finished fiber products made of fiber composites and in which the individual starting material components of the composite material, i.e. the fiber material component, the matrix material component and the fastener components are matched to one another.
In other words, it is an object of the invention to provide a method for producing a 3D textile structure (three-dimensional semi-finished fiber product, preform) having contours matched to the 3D textile structure by folding a 2D textile structure.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a 3D textile structure, the method comprises providing a 2D textile structure and forming the 3D textile structure having contours matched to the 3D textile structure by folding the 2D textile structure.
In a preferred embodiment of the invention, the contours are tracks and/or knitting patterns. The structure is preferably folded in a concertina manner.
The 2D textile structure has fold-assisting gaps which make it easier to construct the semi-finished fiber product to the shape close to the final contour.
It is preferred for the 2D textile structure to be selected from the group consisting of scrim, woven fabric, networks, knitwear, felts, nonwovens, combinations of the same and other two-dimensional structures.
According to the invention, the 2D textile structures may consist of glass fibers, carbon fibers, aramid fibers, ceramic fibers, other polymer fibers, metal fibers or mixtures of the aforesaid fibers.
In accordance with a preferred embodiment of the invention, at least one fiber layer consists of more than 70 wt. %, preferably more than 87 wt. %, particularly preferably more than 98 wt. % of fibers, selected from carbon fibers, precursor fibers of carbon fibers, ceramic fibers and mixtures thereof, relative to the total weight of the particular fiber layer.
Advantageously, the textile structure consists of at least 50% of fibers in the principal direction of loading of the three-dimensional semi-finished fiber product to be produced.
It is particularly advantageous if the textile structure is coated and/or impregnated with a matrix system or with several matrix systems. The content of the matrix system for coating and/or impregnating the two-dimensional textile structure is at least 0% to 70%.
In accordance with an additional feature of the invention, the textile structure contains soluble polymers.
In accordance with another feature of the invention, the textile structure can be transformed into a three-dimensional semi-finished fiber products by applying of chemical, physical and/or mechanical strengthening methods.
With the above and other objects in view there is also provided, in accordance with the invention, a three-dimensional textile structure having a weight per unit area of 100-5000 g/m², preferably 500-2300 g/m², which can be obtained by a method according to one or more of the preceding claims.
The weight per unit area may be locally adapted by reducing or increasing the amount of fiber in the two-dimensional fiber structure or by a separate process step.
The three-dimensional semi-finished fiber product may be infiltrated and cured with thermosetting and/or thermoplastic resins.
In a preferred implementation, the three-dimensional semi-finished fiber products as described herein are used to produce leaf springs or profiles for the aerospace field, for the automobile field, for wind energy, and/or sports articles.
In accordance with a concomitant feature of the invention, the two dimensional structure is already adapted to the shape of the three-dimensional semi-finished fiber product close to the final contour.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in production of a 3D textile structure and semi-finished fiber product made of fiber composites, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows the folding of scrims in 2D structures; and

FIG. 2 shows the folding of scrims in 3D structures.

DETAILED DESCRIPTION OF THE INVENTION

The figures of the drawing show in an explanatory and non-restrictive manner a fiber-scrim reinforced composite material according to the invention and a plurality of fiber scrims produced as intermediate products during the process according to the invention.
A 2D structure comes about in a woven fabric by the crossing of warp and weft threads at right angles. In a scrim a 2D structure is achieved by one or more fiber layers being arranged one above the other with different fiber orientation and interconnected by means of a warp thread system.
The folding is particularly preferably accomplished in a concertina manner as a result of which the textile semi-finished product is achieved. In so doing, the 2D structure is in each case folded into itself by means of the inserted fold contours so that the same side of the product always meets. A zigzag fold is thus produced similar to a concertina.
It is further particularly preferred that the 2D textile structure has fold-assisting gaps which make it easier to construct the semi-finished fiber product to the shape close to the final contour.
The preferred textile structure is selected from the group consisting of scrim, woven fabric, networks, knitwear, felts, nonwovens, combinations of the same and other two-dimensional structures (e.g., films).
The scrim is optionally coated with a binder so that after the folding process, a stabilized preform such as a leaf spring, for example, is obtained by a thermal forming process.
The textile structure preferably consists of glass fibers, carbon fibers, aramid fibers, ceramic fibers, other polymer fibers (e.g. polyester, HD polyethylene or polyamides), metal fibers or mixtures of the foregoing fibers.
The term “carbon fiber” as used within the framework of the present specification comprises any carbon fiber which was manufactured starting from a carbon-containing starting material fiber, for example, a polyacrylonitrile-based fiber, a polyacetylene-based fiber, a polyphenylene-based fiber, a pitch-based fiber or a cellulose-based fiber, where this term can in particular comprise fibers having a carbon content of more than 75 wt. %, preferably more than 85 wt. %, preferably more than 92 wt. %, in each case relative to the total weight of the fiber.
Manufacturing methods for polyacrylonitrile fibers, pre-oxidized polyacrylonitrile fibers and carbon fibers manufactured from these are described, for example, in the publication by E. Fizter, L. M. Manocha, “Carbon Reinforcements and Carbon/Carbon Composites”, Springer Verlag, Berlin, 1998, ISBN 3-540-62933-5, p. 10-24 and in the patent documents U.S. Pat. No. 4,001,382, U.S. Pat. No. 6,326,451, EP 0 384 299 B1 and U.S. Pat. No. 6,054,214.
Methods for manufacturing phenol resin fibers and the manufacture of binding threads from these threads are known to those of skill in the pertinent art. In addition, such methods are described, for example, in German published patent applications DE 2 308 827 and DE 2 328 313.
For example, oxide and/or non-oxide fibers based on one or more compounds comprising at least one, preferably at least two, of the elements carbon, silicon, boron, titanium, zirconium, tungsten, aluminum and nitrogen, can be used as ceramic fibers, for example, for fiber layers.
The term “fiber layer” as used in the present application comprises any layer or ply of fibers of any materials or material mixtures. A fiber layer can in particular comprise a unidirectional layer or setting layer, that is a fiber layer which, for example, comprises a plurality of filaments or yarns which usually extend parallel or substantially parallel in one direction. This can be accomplished, for example, by spreading out a cable or an arbitrary parallel arrangement of filaments or yarns. In addition, the term fiber layer also comprises fiber layers having an arbitrary arrangement or arbitrary profile of filaments or fiber sections of shorter length, for example, a nonwoven layer. In particular, the fiber layers can also have different length and/or width dimensions or a different shape.
Preferably the ceramic fibers consist completely or of at least 90 wt. % relative to the total weight of the ceramic fibers of compounds comprising at least two of the elements carbon (C), silicon (Si), boron (B), titanium (Ti), zirconium (Zr), tungsten (W), aluminum (Al) and nitrogen (N).
In particular, ceramic fibers can be used in which the sum of the content of C, Si, B, N, Al, Zr, Ti, W is more than 50 wt. %, preferably more than 83 wt. %, preferably more than 85 wt. %, in particular more than 95 wt. % of the total weight of the ceramic fibers, where the content of one or more of C, Si, B, N, Al, Zr, Ti, W can be 0 wt. %.
For example, fibers, in particular fibers highly resistant to elevated temperatures, based on Si, C, B, N, Al or compounds thereof (where these fibers are designated, for example, in German patent DE 197 11 829 C1 as “Si/C/B/N fibers”) and in particular ceramic fibers based on compounds comprising at least two of these elements are used. Such fibers are described, for example in German patent DE 197 11 829 C1.
Ceramic fibers can comprise, for example, at least one compound selected from aluminum oxide, zirconium oxide, SiNC, SiBNC, SiC, B₄C, BN, Si₃N₄, TiC, WC and mixtures thereof, or can consist completely of this or of at least 90 wt. %, preferably of at least 93 wt. % in relation to the total weight of fibers. In particular, ceramic fibers can comprise basalt fibers and/or glass fibers or a mixture hereof with other ceramic fibers.
The contours are particularly preferably tracks and/or knitting patterns which allow the intended folding. This is accomplished by omitting one or more fiber yarns in each case in the 0° direction or by splitting the textile by modifying the connecting knitting threads.
As a result of the scrim according to the invention having tracks introduced in the longitudinal and/or transverse direction, the folding is in particular made possible in the case of heavy scrims.
A single fiber layer or unidirectional layer can have an area-related weight in the range of, for example, 50 g/m²to 500 g/m², preferably in a range of 150 g/m²to 2000 g/m². Depending on the desired end product, it can be particularly preferred to select one or more fiber layers or unidirectional layers having an area-related weight of at least 305 g/m².
When using carbon fibers and/or precursor fibers, both fibers which were obtained starting from polyacrylonitrile but also starting from pitch or phenol resin fibers yielded a fiber layer having a very good mechanical loading capacity.
The diameter of the filaments of at least one fiber layer or unidirectional layer, preferably of all fiber layers or unidirectional layers, can lie in a range of, for example, from 6 to 8 μm.
At least one fiber layer preferably consists of more than 70 wt. %, further preferably more than 87 wt. %, particularly preferably more than 98 wt. % of fibers, selected from carbon fibers, precursor fibers of carbon fibers, ceramic fibers and mixtures thereof, relative to the total weight of the particular fiber layer.
In addition to carbon fibers, their precursor fibers and ceramic fibers, the fiber layers can comprise any fibers which a person skilled in the art can select on the basis of his general technical knowledge and the teaching of the present invention.
The textile structure preferably consists of at least 50% of fibers in the principal direction of loading of the three-dimensional semi-finished fiber product to be produced.
The two-dimensional textile structure is preferably coated and/or impregnated with a matrix system or with several matrix systems (liquid/solid) after knitting.
The content of the matrix system for coating and/or impregnating the two-dimensional textile structure is preferably at least 0% to 70%. The textile structure preferably contains soluble polymers (e.g. PVA, polyphenoxy).
The textile structure can be transformed into a three-dimensional semi-finished fiber product (preform) by applying chemical, physical (chemical reaction, pressure and/or temperature) and/or mechanical strengthening methods (sewing, needling).
The two-dimensional (quasi two-dimensional) textile structure having a weight per unit area of 100-5000 g/m², preferably 500-2300 g/m², can be obtained by a method according to one or more of the preceding claims.
The weight per unit area is preferably locally adapted by reducing or increasing the amount of fiber in the two-dimensional (quasi-two-dimensional) fiber structure or by a separate process step.
The three-dimensional semi-finished fiber product can be infiltrated and cured with thermosetting and/or thermoplastic resins.
Fiber scrims having very advantageous properties can be obtained, for example, if at least one fiber layer, in particular a unidirectional layer, preferably all the fiber layers, have a number of filaments which lies in the range of 0.5 K (500 filaments) to 500 K (500,000 filaments). Preferably, the number of filaments of a fiber layer or unidirectional layer lies in a range of 1 K (1000 filaments) to 400 K (400,000 filaments), preferably in a range of 12 K (12,000 filaments) to 60 K (60,000 filaments).
Fiber scrims having advantageous material properties and comparatively low manufacturing costs can further be obtained if one or more fiber layers, in particular unidirectional layers are used, which comprises polymer fibers, in particular organic polymer fibers, or mixtures thereof. In some applications, it can also prove advantageous to use polyacrylonitrile-based fibers, viscose-based fibers, to produce at least one fiber layer. One, two, three or more of the fiber layers can, for example, consist completely or of at least 80 wt. % of polyacrylonitrile fibers and/or viscose fibers relative to the total weight of fibers in the fiber layer.
Fiber scrims having different material properties can be obtained by producing fiber scrims comprising two, three, four, five, six, seven, eight or arbitrarily more fiber layers and/or unidirectional layers. In order to achieve highly loadable material it can be advantageous if one unidirectional layer extends in a different longitudinal direction from the unidirectional layer located in each case above and/or below this unidirectional layer. Preferably all the unidirectional layers in a fiber scrim extend in a respectively different longitudinal direction. it can be advantageous here if at least the longitudinal direction of one unidirectional layer forms an angle of at least 30°, preferably at least 45°, preferably at least 60°, in particular 85-90° to the longitudinal direction of at least one following unidirectional layer.
If the unidirectional layers each have different longitudinal directions from one another, biaxial fiber scrims are obtained when using two unidirectional layers, triaxial fiber scrims are obtained when using three unidirectional layers, quadraxial fiber scrims are obtained when using four unidirectional layers.
Preferably when using two or more unidirectional layers, the two or more other unidirectional layers are arranged in such a manner that their respective longitudinal directions form angles having opposite signs to the 0° direction, where the magnitude of the angles can be the same (and the angles can, for example, be +60°/−60° or) +45°/−45° or different or their respective longitudinal directions to the 0° direction are at angles of 0° and 90°.
Preferably a 0/90 scrim is produced on a scrim machine, in which at least 90% of the fibers, particularly preferably 95% of the fibers are disposed in the 0° direction. The width and the fiber weight per unit area of the scrim according to the invention is determined by the fiber titer (fiber tester) used, the layer structure provided, the resulting number of layers and their width.
It is a surprising advantage of the method according to the invention that the total width of a, for example, fast-running scrim machine can be used. This is, for example also a particular advantage compared with ribbon looms.
Resins which are particularly suitable for impregnating fiber scrims are, for example, phenol resins, epoxide resins, benzoxane resins, cyanate ester resins, polyester/vinyl ester resins, furan resins, polyamide resins, polyimide resins, polyacrylate resins, derivatives therefrom and mixtures thereof.
In addition, inorganic impregnating agents can be used for impregnating the fiber scrim, where, for example, liquid silicon, SiC precursor polymers, in particular silazanes, SiC precursor oligomers and mixtures thereof are particularly suitable for impregnating the fiber scrim.
The term “SiC precursor polymer” as used within the framework of the present specification describes any compound having a molecular mass of more than about 300 g/mol which comprises silicon, as well as carbon and/or nitrogen and for example, can have a content of 10 to 99 wt. % of Si, relative to the total weight of the compound. The term “SiC precursor oligomer” as used within the framework of the present invention describes any compound which comprises silicon, as well as carbon and/or nitrogen, which has at least two silicon atoms and has a molecular mass of up to and including about 300 g/mol, and for example, can have a content of 10 to 99 wt. % of Si, relative to the total weight of the compound. Preferably a SiC precursor polymer or a SiC precursor polymer is at least partially converted into SiC when heated to a temperature of more than 150° C. in an inert atmosphere.
When impregnating fiber scrims, for example, very good results can be obtained by using at least one compound selected from the group consisting of oligosilazanes, polysilazanes, oligocarbosilazanes, polycarbosilazanes, oligosilanes, polysilanes, oligoborocarbosilazanes, polyborocarbosilazanes, methyl-oligosiloxanes, methyl-polysiloxanes, oligocarbosilanes, polycarbosilanes, oligoborosilazanes, polyborosilazanes, oligo(dialkyl)silicones, poly(dialkyl)silicones, oligosiloxanes, polysiloxanes, for example poly(dialkyl)siloxanes, such as poly(dimethyl)siloxanes, for example, poly(diaryl)siloxanes, such as poly(diphenyl)siloxanes, for example, poly(monoalkyl-monoaryl)siloxanes, such as poly(monomethyl-monophenyl)siloxanes, derivatives thereof and mixtures thereof. The terms oligosilazanes, oligocarbosilazanes, oligosilanes, oligoborocarbosilazanes, methyl-oligosiloxanes, oligocarbosilanes, oligoborosilazanes, oligo(dialkyl)silicones, oligosiloxanes, etc. comprise any oligomer coming under the term, which is constructed from at least two monomer units, that is, any oligomer beginning with one dimer as far as compounds having a molecular weight up to an including about 300 g/mol.
The terms polysilazanes, polycarbosilazanes, polysilanes, polyborocarbosilazanes, methyl-polysiloxanes, polycarbosilanes, polyborosilazanes, poly(dialkyl)silicones, polysiloxanes, etc. comprise any polymer falling under the term that has a molecular weight of more than about 300 g/mol.
A fiber scrim can additionally be impregnated with inorganic impregnating agents and also with resins, preferably synthetic resins. For example, neighboring sections of a fiber scrim can be impregnated with one or more inorganic impregnating agents and/or with one of more resins. For example, an impregnation can additionally be accomplished in several layers or in a sequence of impregnating processes using one or more inorganic impregnating agents and/or using one or more resins and/or an impregnation can be made using mixtures of one or more inorganic impregnating agents and resins. The choice of curing conditions takes into account the requirements of the selected impregnating agent.
The curing of the impregnated fiber scrim can take place in a curing temperature range of at least 40° C., at a curing temperature in the range of 50 to 260° C., preferably 80 to 200° C. The curing can preferably take place before commencement of and/or at least during a subperiod of the curing time under pressure, for example, by pressing at least one surface section of at least one surface of the impregnated fiber scrim with a pressing tool. The curing time can, for example, be at least 1 minute, preferably between 10 minutes and 8 hours, preferably between 15 minutes and 3 hours. The curing time under pressure can, for example, be in a range of at least 1 minute, preferably between 10 minutes and 8 hours, preferably between 15 minutes and 3 hours. The pressing pressure can, for example, be at least 0.01 MPa, preferably 0.01 MPa to 100 MPa.
The content of resin and/or inorganic impregnating agents, relative to the total weight of the non-impregnated fiber scrim, can lie in a range of 5 to 85 wt. %, preferably of 25 to 65 wt. %, particularly preferably of 30 to 45 wt. %.
The fiber scrim can, for example, be impregnated as far as saturation of the fiber scrim. In particular, liquid resins or molten resins (“hot melt resin”) can be used, which can for example comprise phenol resins.
The curing and impregnation can be carried out using any method known for this to the person skilled in the art. Very advantageous results can be obtained if the impregnation is carried out by dipping in a dipping bath or by means of a film transfer method. For example, these process steps can be carried out continuously, that is, the woven fabric can, for example, be unrolled from a roll, passed through one or more furnaces having a suitable temperature and atmosphere such as, for example, 400° C. or more in an inert atmosphere and then passed further through a resin bath and/or a bath containing inorganic impregnating agent, and/or roll calendars and/or another impregnating device. A curing can then take place, where a composite material is obtained whose matrix is reinforced by a fiber scrim, for example, a carbon fiber scrim. The curing process step can be carried out both continuously and discontinuously. The cured resin and/or the cured inorganic impregnating agent fulfils several functions in the composite material obtained after the curing. Firstly, the resin makes connections between the cables and threads of the fiber scrim and fixes their position in the woven fabric. Depending on the application of the composite material, the fiber scrim can be embedded in a matrix comprising cured resin and/or inorganic impregnating agent, completely or in sections and/or it can be covered with a film of resin and/or inorganic impregnating agent merely covering individual fibers, completely or in sections and/or it can be free of resin in sections. The cured binder additionally effects a mechanical reinforcement of the fiber scrim.
After the curing and/or pressing, a fiber-scrim-reinforced composite material or a fiber-scrim-reinforced composite material product can be obtained.
A fiber-scrim-reinforced composite material product within the framework of the present application designates a partially or preferably completely cured fiber-scrim-reinforced composite material which has optionally been subject to further processing steps, for example, cutting to size, shape cutting etc. Within the framework of the present application a cured fiber-scrim-reinforced composite material is also designated as green body.
Optionally, the partially or completely cured fiber-scrim-reinforced composite material, even without an interposed step of obtaining, or the partially or completely cured fiber-scrim-reinforced composite material product can undergo further process steps such as, inter alia, a thermal treatment, for example, for carbonizing or graphitizing or an extensive heating and/or pressing.
A thermal treatment can be carried out in a first temperature range (frequently also designated as “carbonization”) and can, for example, be carried out by heating with the exclusion of oxidizing substances, i.e. either in an inert atmosphere, in protective gas or by enveloping the material to be combusted with a substance acting as a getter, which binds oxidizing media, especially oxygen, at a temperature or in a temperature range from about 800° C. to about 1250° C., preferably from 850° C. to 950° C., in particular from 880° C. to 920° C. The thermal treatment in the first temperature range can take place during a time interval of, for example, at least 30 minutes, preferably of at least 8 hours, in particular from 30 minutes to 96 hours. Any method known to the person skilled in the art can be used for the thermal treatment in a first temperature range (“carbonization”) within the framework of the teaching of the present invention, for example, a solid phase pyrolysis. In order to achieve a good coke yield, a heating-up phase can be executed first, for example, with a comparatively small temperature gradient in the range from 300 to 600° C. at a maximum of 4° C. per hour or coking is carried out under pressure. The final temperature in this process step cannot exceed, for example, 1250° C.
Both a completely and also an only partially cured fiber-scrim-reinforced composite material can be subjected to the thermal treatment in a first temperature range.
After the thermal treatment in the first temperature range, a composite material is obtained whose matrix comprises carbon and is reinforced with a carbon fiber woven fabric (“carbon fiber reinforced carbon”, CFC).
Alternatively to the thermal treatment in a first temperature range or additionally to this, in particular after this, a thermal treatment can be carried out in a second temperature range (frequently also designated as “graphitization”). The thermal treatment in a second temperature range (“graphitization”) can be carried out by any method known for this to the person skilled in the art. In particular, heating can be carried out in an inert atmosphere at a temperature in the range from about 1251° C. to 3000° C., preferably from 1800° C. to 2200° C. during a time interval of, for example, at least about 30 minutes, preferably of at least 8 hours, in particular from 30 minutes to 96 hours.
During a thermal treatment in the first and/or second temperature range, the resin layer shrinks as a result of the weight loss due to the cleaving of volatile components. The composite material obtained after the thermal treatment is characterized by a high temperature resistance.
After the thermal treatment of the fiber-scrim-reinforced composite material or composite material product, a thermally treatment fiber-scrim-reinforced composite material or composite material product can be obtained. Optionally the composite material obtained after one or more thermal treatments in a first and/or second temperature range, in particular a composite material comprising fiber-scrim-reinforced carbon can be additionally subjected once or several times to an after-treatment, in particular an after-treatment in which the composite material is impregnated at least once, in particular is impregnated with a carbonizable agent, and/or is subjected at least one again to a thermal treatment in a first and/or second temperature range (which is usually designated as after burn). The post-compaction, in particular the steps of impregnation and thermal treatment, can fundamentally be carried out by any method known for this to the person skilled in the art within the framework of the teaching of the present invention. The term post-compaction as used within the framework of the present invention designates any treatment of a material or workpiece which results in a maintaining of or increase in the density of the treated material or workpiece. Advantageously an increase in the density can be accomplished by such aftertreatment. The impregnation and the thermal treatment can particularly advantageously be carried out under the conditions explained hereinbefore and hereinafter. The so-called vacuum pressure method can be used, for example, for the impregnation.
All substances known for an impregnation of parts comprising carbon or consisting thereof, can be used as impregnating agents, for example, substances having a coke yield of more than 30 weight percent, for example, synthetic resins, in particular thermosetting resins or pitches and derivatives derived therefrom as well as mixtures or resins and pitches and/or pitch derivatives. In particular, phenol resins of the novolak or resol type, furan resins or impregnating pitches can be used. A thermal treatment in a first and/or second temperature range as defined previously following the impregnation, so-called after-burning, is carried out with the exclusion of oxidising substances, in particular in an inert atmosphere.
Prior to and/or after the thermal treatment in a first and/or second temperature range, a heating or cooling of, for example, 8 to 10 hours, for example to room temperature (20° C.) can be carried out. Example and preferred time intervals and temperature ranges for a thermal treatment in a first and/or second temperature range are explained in detail hereinbefore. In this process step one or several carbon shells should be applied to the already existing shell and after the first carbonization step, cracks and pores still present in the first shell should be closed. Depending on the intended protective effect for the fibers, this impregnation and after-burning process can take place several times, preferably once to three times.
It can be advantageous for optimisation of the composite material in specific applications if a first thermal treatment in a first temperature range in which carbonization can take place is followed by a thermal treatment in a second temperature range in an inert atmosphere in which graphitization takes place. However, the execution of such a measure is merely optional. Usually the end temperature of 3000° C., in particular 2400° C., is not exceeded during graphitisation.
It is preferable to work at temperatures from 1800 to 2200° C. All known graphitization processes can be used for this step.
The post-compaction described hereinbefore which comprises firstly an impregnation and then a burning process can be repeated once or several times.
The number of post-compactions to be carried out is dependent on the desired target density of the carbon fiber-reinforced carbon ceramic and can be carried out once or several times, for example, twice, three times or four times or more, preferably in a directly successive manner. Preferably the steps of impregnation and subsequent burning are each carried out three times. After post-compaction, densities for example of 1.30-1.60 g/cm³, preferably of 1.30-1.55 g/cm³can be achieved.
Furthermore, the composite material comprising fiber-scrim-reinforced carbon obtained after one or more thermal treatments and/or post-compacted as explained hereinbefore can optionally be provided with a gas phase coating by the CVD method (CVD=chemical vapor deposition) or by the CVI method (CVI=chemical vapor infiltration) with protective layers of high-melting substances such as pyrocarbon, TiC, TiN or SiC. Any CVD/CVI method known to a person skilled in the art can be used within the framework of the preceding invention. CVD/CVI methods are, for example, taught in the document DE 39 33 039 A1 or in the publication E. Fitzer et. al., Chemie-Ingenieur-Technik 57, No. 9, p. 737-746 (1985).
In addition, the composite material comprising fiber-scrim-reinforced carbon obtained after a thermal treatment in a first and/or second temperature range and/or post-compacted as explained hereinbefore and/or additionally coated by the CVD method or by the CVI method can be subjected to siliconizing. Such a process is described for example in the publication E. Fitzer et. al., Chemie-Ingenieur-Technik 57, No. 9, p. 737-746 (1985).
Siliconization can be carried out within the framework of the present invention by any method known to a person skilled in the art. Composite materials of particularly high quality can be obtained, for example, if the siliconization is carried out in the temperature range from 1450° C. to 2200° C., preferably in the temperature range from 1650° C. to 1750° C. in an inert atmosphere. In particular it is possible to work in the temperature range from 1650° C. to 1750° C. in vacuum. After reaching the siliconization temperature, the time interval for infiltration and reacting to give SiC can be at least 10 minutes, for example, 10 minutes to 1 hour.
In the case of siliconization without using vacuum, siliconization can be carried out in particular at temperatures from 2100° C. to 2200° C. in an inert atmosphere. The total of infiltration and reaction time also during a siliconization without using vacuum can be at least 10 minutes, for example, between 10 minutes and one hour.
Advantageously the previously described siliconizations can be carried out using the so-called wick technique. In this case, the bodies to be siliconized lie on porous highly absorbent carbon bodies in relation to the silicon, whose lower part stands in liquid silicon. The silicon then rises through this wick body into the bodies to be siliconized without the latter having a direct connection with the silicon bath.
The previously explained steps of post-compaction, in particular by impregnation and optional, subsequent thermal treatment in a first and/or second temperature range, siliconization and gas-phase coating can each be repeated once or several times and combined with one another in any sequence.
Composite materials having particularly high quality can be obtained, for example, if, following the step of curing and optionally pressing the impregnated fiber scrim and a thermal treatment in a first temperature range in which carbonization can take place, the previously described steps of impregnation and thermal treatment in a first and/or second temperature range through which post-compaction can be achieved, are executed at least once, preferably once to three times, preferably three times.
Optionally a siliconization or a gas-phase coating or a siliconization followed by a gas-phase coating can then additionally be carried out. The gas-phase coating can in particular be carried out with carbon or carbon-comprising mixtures, by means of a CVD or CVI process, as described hereinbefore.
The three-dimensional semi-finished fiber product is preferably used for leaf springs or profiles (e.g. T profiles or stringers) for the aerospace field, for the automobile field, for wind energy and sports articles as a result of the low weight, the high flexibility and loading capacity.
The textile structure is preferably already adapted or machined (e.g. contour machining or cutouts) in the two-dimensional (quasi two-dimensional) textile structure to the shape of the three-dimensional semi-finished fiber product close to the final contour.

Claims

1. A method for producing a 3D textile structure, the method which comprises providing a 2D textile structure and forming the 3D textile structure having contours matched to the 3D textile structure by folding the 2D textile structure.

2. The method according to claim 1, wherein the contours are one or both of tracks or knitting patterns.

3. The method according to claim 1, wherein the folding step comprises folding in a concertina manner.

4. The method according to claim 1, which comprises forming the 2D textile structure with fold-assisting gaps to assist constructing the semi-finished fiber product to the shape close to the final contour.

5. The method according to claim 1, wherein the 2D textile structure is selected from the group consisting of scrim, woven fabric, networks, knitwear, felts, nonwovens, and combinations thereof.

6. The method according to claim 1, wherein the 2D textile structures are selected from the group consisting of glass fibers, carbon fibers, aramid fibers, ceramic fibers, polymer fibers, metal fibers or mixtures and combinations thereof.

7. The method according to claim 6, wherein at least one fiber layer consists of more than 70 wt. % of fibers selected from carbon fibers, precursor fibers of carbon fibers, ceramic fibers and mixtures thereof, relative to a total weight of the respective fiber layer.

8. The method according to claim 7, wherein the at least one fiber layer consists of more than 87 wt. % of the selected fibers.

9. The method according to claim 8, wherein the at least one fiber layer consists of more than 98 wt. % of the selected fibers.

10. The method according to claim 1, wherein the textile structure consists of at least 50% of fibers in a principal direction of loading of the three-dimensional semi-finished fiber product to be produced.

11. The method according to claim 1, which comprises coating or impregnating the textile structure with a matrix system or with a plurality of matrix systems.

12. The method according to claim 11, wherein a content of the matrix system for coating and/or impregnating the two-dimensional textile structure ranges from 0% to 70%.

13. The method according to claim 11, wherein the textile structure contains soluble polymers.

14. The method according to claim 1, which comprises transforming the textile structure into a three-dimensional semi-finished fiber product by applying strengthening methods selected from the group of chemical, physical, and mechanical strengthening methods.

15. A three-dimensional textile structure, comprising a 3D structure formed from a 2D textile structure having contours matched to the 3D textile structure by folding the 2D textile, wherein the 3D structure has a weight per unit area of 100-5000 g/m².

16. The three-dimensional textile structure according to claim 15, wherein the weight of the 3D structure is 500-2300 g/m².

17. The three-dimensional textile structure according to claim 15, wherein the weight per unit area is locally adapted by selectively reducing or increasing an amount of fiber in the two-dimensional fiber structure or by a separate process step.

18. A semi-finished three-dimensional fiber product, comprising a 3D structure manufactured by the method according to claim 1, infiltrated with thermosetting and/or thermoplastic resins and cured to form the three-dimensional semi-finished fiber product.

19. The semi-finished three-dimensional fiber product according to claim 15 configured for producing leaf springs or profiles for the aerospace field, for the automobile field, for wind energy, and for sports articles.

20. The three-dimensional textile structure according to claim 15, wherein the two dimensional structure is already adapted to the shape of the three-dimensional semi-finished fiber product close to the final contour.