DE102014200510B4 - Ceramic composites based on thermoplastically processable, rapidly cross-linkable precursors for CFRP and CMC production - Google Patents

Abstract

Process for the preparation of ceramic matrix composites, wherein the following steps are carried out:
a) Preparation of a thermoplastic fiber-plastic composite with a fiber reinforcement and a thermoplastic multicomponent prepolymer with the substeps:
i. Preparation of a base polymer from phenol-based polymers, preferably novolaks, or mixtures thereof with furfuryl components, wherein the thermoplastic matrix material has a toughness of 100 Pa * s to 500 Pa * s,
ii. Preparation of a crosslinker / moderator mixture of a crosslinker of b-naphthol, resorcinol and phloroglucin and a moderator of a xylenol mixture,
iii. Preparation of the multicomponent prepolymer by mixing the base polymer with the crosslinker / moderator mixture in a cold grinding process,
b) preparing a chain-extension catalyst by linking a poly-cresol having functional groups at the chain ends, which subsequently crosslink with the multicomponent prepolymer;
c) mixing the multi-component prepolymer with the chain-extension catalyst,
d) shaping the thermoplastic fiber-plastic composite, wherein a chain extension reaction begins, but without the crosslinking by injection molding, or
Reactive compounding which starts a chain extension reaction, but without crosslinking and subsequent injection molding,
e) conversion of the thermoplastic fiber-plastic composite into a thermosetting fiber-plastic composite material by heating immediately after the injection molding process,
f) conversion of the matrix polymer to matrix carbon and production of the fiber-reinforced carbon (C / C) to produce the CMC.

Description

• • Herstellung eines duroplastischen Faserverbundwerkstoffs (CFK)
• • Umsetzung des Matrixpolymers zu Matrixkohlestoff unter Bildung eines charakteristischen Rissnetzwerks durch Pyrolyse (C/C)
• • Infiltration des Risssystems mit flüssigen Silicium, unter Bildung von SiC im rissnahen Bereich (C/C-SiC)

Ceramic matrix composites have advantageous properties over conventional monolithic ceramics, such as improved fracture toughness, good temperature, wear and corrosion resistance. They are particularly suitable as mechanically strong components in the space industry and industrial furnace construction. In addition, they are for tribological applications, such. B. in brake discs, predestined. The methods of preparation differ depending on the matrix material and the reinforcing component selected and may be enhanced by liquid phase infiltration, such as. By polymer infiltration and pyrolysis (PIP), liquid silicon infiltration (LSI), or chemical vapor infiltration (CVI). A precursor of the ceramic matrix composite (CMC) may be an infiltratable fiber preform or a suitable polymer with or without reinforcing components. Advantages of the LSI process compared to the other methods are the relatively short process times. The LSI process essentially consists of a 3-stage process:

• • Production of a thermosetting fiber composite material (CFRP)
• Implementation of the matrix polymer into matrix carbon to form a characteristic crack network through pyrolysis (C / C)
• Infiltration of the cracking system with liquid silicon, forming SiC in the crack region (C / C-SiC)

Such a method is in the US 7,186,360 B2 in which the unidirectional reinforcing fibers are coated with a polymer and subsequently incorporated into a resin matrix. Subsequently, the fibers and the surrounding matrix material are carbonized by the action of heat. The carbonization leaves a carbon skeleton and fiber reinforcement. Volume shrinkage of the matrix creates channels. In these channels liquid silicon is passed, which converts in the channel walls to silicon carbide.

DE 28 26 114 C1 discloses a process for producing a carbon fiber reinforced carbon in which cured novolac fibers are embedded in a phenolic resin and then formed into the desired shape. The resin with the fibers is then cured. This is followed by firing at a defined heating rate at a temperature above 800.degree.

DE 10 2004 043 985 A1 describes a method for producing a silicon carbide ceramic material in which a porous preform is produced from a starting material of cellulose-containing powder and carbon short fibers, which is then converted by pyrolysis into an open-pore carbon body. This is further converted by infiltration of silicon-containing materials in a carbide ceramics.

In the production of the CFRP state, the validation of the precursors takes place empirically or semiempirically in practice. In addition to a high carbon yield to produce the matrix carbon, the chemical conversion behavior as well as the formation of a suitable shrinkage crack network and a suitable pore structure in the matrix are also important. Both thermoplastic precursors, such as pitches and thermosetting-crosslinkable precursors, such as phenolic and furan resin prepolymers, are used. The disadvantage of these crosslinkable systems is their uneconomic handling and processability. Especially for large-scale production processes of CMCs, a time-consuming autoclave process is required for their cross-linking to the CFRP state. Peche, however, are highly viscous to solid residues of tar distillation from a versatile mixture of predominantly crosslinked and uncrosslinked polycyclic aromatics and heterocyclic compounds and phenols. The molecular weight of the mixture is nonspecific. At higher temperatures, various polymerization and degradation reactions take place. As a product is at about 400 - 500 ° C, a kind of metaformstabiler pitch coke before, which can be graphitized at temperatures up to 3000 ° C. Despite some behaviors that can also be assigned to thermoplastics, pitches, especially when heated, do not show the behavior of classic thermoplastic polymers which simulate the general plastic molding compounds and thermoplastic molding compositions of polymer mixtures DIN 16780 such as DIN EN ISO 472 are assigned. Pitches can be used as impregnation in preforms by a hot isostatic pressure infiltration and carbonization process.

It can thus be stated that the known processes for the preparation of CMCs are complex and not very economical. If it were possible to apply known processes for the processing of fiber composites to CMC production, this situation would improve considerably. A significant contribution could be made to be able to use known shaping technologies. In particular Processes for molding thermoplastic polymer-based composites are known, widely used and inexpensive.

Thermoplastic polymers consist of a multiplicity of defined, identical or different monomer units. These repeating units, depending on their type, number of constitution, configuration and conformation, define a non-branched or hardly branched, intermolecularly uncrosslinked strand which macroscopically exhibits a defined thermoplastic behavior due to secondary intermolecular interactions. A significant disadvantage of these polymers, however, is their poor suitability as carbon precursors because of their deliquescence upon elevation of temperature (Eyerer, P .: Elsner, P. Hirth, T .: Plastics and Their Properties.) 6th edition Berlin, Heidelberg, New York: Springer Publisher, 2005).

It is therefore the task of proposing a process suitable for large-scale production, which allows the use of conventional thermoplastic processing methods in the production of ceramic matrix composites (CMC ceramic matrix composite) or carbon fiber reinforced carbon (CFC- carbon fiber reinforced carbon).

According to the invention the object is achieved by the method according to claim 1. Advantageous developments of the method are disclosed in the dependent claims.

• • Erzeugung komplexer Geometrien,
• • endkonturnahe Herstellung,
• • breites Spektrum an Schussgrößen und -gewichten,
• • hohe Reproduzierbarkeit,
• • kurze Prozesszeiten,
• • Vollautomatisierbarkeit,
• • Großserientauglichkeit sowie eine
• • Kostenreduktion.

The process of the invention provides to improve the CFRP process step in the CMC production route by means of innovative carbon precursors capable of processing by conventional thermoplastic processing techniques such as injection molding and the requirements imposed on a suitable carbon precursor be fulfilled. This process is highly productive and close to the production line. This allows a significant cost reduction in the technological process. The invention offers the following advantages in CFRP production compared to previous processing methods such as hand lamination, RTM or RIM processes:

• • creation of complex geometries,
• • near net shape production,
• • wide range of shot sizes and weights,
• • high reproducibility,
• • short process times,
• • fully automatable,
• • Mass production suitability as well as a
• • Cost reduction.

The innovative carbon precursors are realized by thermoplastically formable plastics, which crosslink at higher temperatures than in the original molding. In this way, it is possible to give the plastics by methods of thermoplastic processing near-net shape and to give these thermoplastics in an immediately subsequent heating step thermosetting properties. For this purpose usable plastics must be suitable for the subsequent stages of CMC production as carbon precursor.

According to the invention, phenol-based thermoplastically processable, postcrosslinking precursors are used for CMC production. Phenol resin prepolymers are well suited as starting material for the preparation of carbon-based CMCs due to their high carbon yield. Particularly preferred for carrying out the process according to the invention are furfuryl alcohol derivatives having weight fractions of 10 to 50% by weight, preferably 25 to 50% by weight, and novolaks having percentages by weight of 70 to 98% by weight, preferably 80 to 95% by weight, and and combinations of both are used. Novolacs are phenolic resins which are synthesized from phenol and formaldehyde in a ratio of phenol to formaldehyde> 1. They are previously by means of complex thermoset injection molding, z. B. processed to bulk molding compounds (BMCs). However, they crosslink very slowly over several hours (Eyerer, P. Elsner, P., Hirth, T .: Plastics and their properties, 6th Ed Berlin, Heidelberg, New York: Springer Verlag, 2005).

In order to process thermoplastically processable precursors such as conventional thermoplastics, the precursors with a sufficiently large number of repeating units (molecular weights the starting materials in the range 200-5000 g / mol, molecular weights of the chain-extended thermoplastics in the range of 50,000-300,000 g / mol), which gives them rheologically suitable flow properties in the range of 10 - 500 Pa * s for the processing window in reactive injection molding. The uncrosslinked or partially precrosslinked phenol prepolymer contains a defined number of specific reaction sites. The crosslinking of the individual regions can be carried out on the phenol-based components, preferably in the ortho and para positions of the phenol groups, which do not yet react in the region of the processing window of the injection molding process, directly after the injection molding process, preferably in the same shaping tool.

Through the integration of the formaldehyde-equivalent crosslinker system, preferably trioxane or hexamethyltetramine, the polymer described in its special composition is crosslinked in a predetermined temperature-pressure range to form thermosets. By variable chain lengths due to a chain extension catalyst, the polymer can be adjusted specifically to the injection molding process. The crosslinking takes place independently after the injection molding process at a high reaction rate (t <5 min) directly in the injection mold at a temperature of 150-300 ° C., more preferably 150-250 ° C. The crosslinking temperature is always below the decomposition temperature of the polymer, which is about 300 ° C for said polymer. Thereafter, there is a geometrically defined, dimensionally stable molded part as a precursor for the subsequent pyrolysis. The polymer may be pure, as a blend, in the filled or unfilled state.

The injection molding processing is preferably carried out on conventional injection molding machines with screw conveyors, which advantageously produce low shear heat. The plasticizing cylinder is equipped with a fluid temperature, the cylinder temperatures preferably realized in the range of 60 to 150 ° C.

In the subsequent step, the pyrolysis of the molding in an inert gas, preferably argon or in vacuo in the temperature range between 300 ° C and 1200 ° C, preferably between 300 ° C and 980 ° C. The product is a suitable infiltratable preform for a subsequent liquid phase infiltration process, preferably for polymer infiltration and pyrolysis (PIP) or liquid silicon infiltration (LSI), or chemical vapor infiltration (CVI).

First preferred procedure

Phenol is melted and with a formaldehyde-furfuryl alcohol solution of 80-90 mol%, preferably 82-86 mol% of the amount of phenol used and with oxalic acid 0.5-1.5 mol%, preferably 0.8 to 1.2 mol%. of the phenol used and mixed in a suitable stirred tank reactor, preferably in a stirred autoclave at a moderate shear rate (depending on the mixer type). The reaction mixture is 0.5 - 3 hours, preferably 1 to 2 hours at 80 - 100 ° C, preferably at 90 - 99 ° C tempered. Subsequently, water and unreacted constituents are removed by a suitable vacuum, preferably directly in the stirred autoclave. The product is the phenol-based polymer with a molecular weight distribution of 500-5000 g / mol. Subsequently, the solidified phenol-based polymer is comminuted, preferably by cold painting, to make it free-flowing and pourable for further processing.

The phenol-based polymer is fed to a single-screw compounding extruder, preferably in a highly wear-resistant twin-screw compounding extruder, as powder or granules, preferably as granules. There are reinforcing materials such as carbon, silicon and silicon carbide in fiber form with diameters of 3 - 25 .mu.m, preferably 5-12 .mu.m and / or particles with 0.1 - 500 .mu.m supplied, wherein the supplied fiber lengths are from 1 mm. Furthermore, endless fibers are fed directly to the twin-screw extruder in the area of the feed zone or metering zone. Carbon fibers with variable volume fractions of 0-85% by volume, preferably 40-80% by volume, are preferably fed to the phenol-based polymer as filler. The parameters of the shear rate and zone tempering must be set depending on the process and the machine. The compounded, extruded, reinforced phenol-based polymer strand passes through a cooling section in air or a liquid cooling medium depending on the temperature. Subsequently, the granulation takes place in a wear-resistant cutting unit. The granules serve as starting material for a subsequent injection molding process. The parameters of injection molding, such as injection pressure, dynamic pressure, holding pressure, zone tempering, etc., are largely determined by the molding to be molded and its molding composition and geometry, and depending on the molded part to be determined via parameter and mold filling studies or mold filling simulations.

The granulate particles are melted with a formaldehyde equivalent, preferably hexamethyltetramine, triazine at 0.5 to 20 wt .-%, preferably 1.5 to 5 wt .-%, in the screw of an injection molding machine in the temperature range between 80 - 140 ° C and homogenized , The injection pressure, dynamic pressure, holding pressure and the respective zone temperature control are decisively dependent on the molded part to be molded and its molding compound and geometry and must be determined beforehand to achieve a stable reproducible injection molding process by parameter and mold filling studies or mold filling simulations. The injection takes place analogously to conventional thermoplastics in one or more mold cavities, which image the molding.

Vernetzungsprinzip phenolbasierter Polymere durch FormaldehydäquivalenteThereafter, the thermoplastic melt is not cooled to the thermoplastic molding by a tool cooling. In the tool inner wall of the mold cavity are dynamic temperature control based on resistance heaters, fluid temperature or other known from the prior art method by which the thermoplastic melt can be further heated. When a temperature of 220-290 ° C. is exceeded, the thermoplastic cross-links through the crosslinker system to a spatially crosslinked thermosetting plastic molded part while applying a variably adjustable cavity pressure, which must be determined simulatively and experimentally before the series process.

Crosslinking principle of phenol-based polymers with formaldehyde equivalents

The crosslinked and cured component can then be removed from the mold and transported out of the machine.

In a subsequent process, the pyrolysis of the molded article takes place in a special recipient under argon, at atmospheric pressure, at a temperature-time regime from room temperature to 400 ° C at about 1.5 K / min and a molded part-dependent holding time of 30 - 720 min. This is followed by a further rise in temperature from 400 to 600 ° C with about 0.5 K / min and a molded part-dependent holding time of 30 - 720 min. Finally, the temperature rises from 600 to 1200 ° C with approx. 2 K / min and molding-dependent holding time of 30 - 720 min. At a wall thicknesses of z. B. 3 mm, a respective holding time of 60 minutes is preferred. The end product is a carbon fiber reinforced carbon preform. Optionally, further heat treatments are preferably above 1200 ° C under vacuum or inert gas, preferably in argon possible, the holding times during pyrolysis are largely determined by the component wall thickness, the inert gas used and the process pressure.

In the pyrolysis process versatile routes can be recreated. Depending on the type of temperature control, the protective gas or pressure specific crack networks can be generated. In this regard, there are a variety of possibilities in the art. The temperature-time profile used here was derived from the mass degradation behavior from the thermogravimetric study of the phenolic polymer

Second preferred procedure

The process according to the invention provides for the production of composites from plastic-based molding compositions by mixing a multicomponent prepolymer (MKV) with a chain-lengthening catalyst (KV).

• Komponente A: enthält das Basispolymer (auf Novolake-Basis), den Vernetzer und einen Moderator,
• Komponente B: enthält den Kettenverlängerungskatalysator (Polykresol) und einen Moderator.

According to the invention, the melt-processable mixture is produced by the mixture of two components:

• Component A: contains the base polymer (novolak-based), the crosslinker and a moderator,
• Component B: contains the chain extension catalyst (polycresol) and a moderator.

The moderators of components A and B need not be identical and serve to prevent or largely avoid too early crosslinking reactions. More preferably, a moderator is added to both the base polymer and the chain extension catalyst. In a preferred embodiment, no moderator is added to component B.

A chain extension reaction produces a high molecular weight thermoplastic molding compound upon mixing the MKV with the KV and results in its volume contraction. The material shrinkage is compensated by desserts of material. The mixture is carried out by methods of the prior art. It is particularly preferably realized by a reactive compounding process with or without an upstream cold grinding process or by a reactive injection molding process. When using the upstream reactive compounding is a free-flowing high molecular weight thermoplastic granules, which can be further processed in a conventional thermoplastic injection molding to form parts. After injection molding, the high molar thermoplastic molding compound crosslinks in a subsequent process due to heat input to the thermoset molding. The reaction shrinkage is minimized compared to the curing of conventional phenolic resins. The crosslinking takes place in the same tool in which the molding process took place (see 1 ).

In a preferred subsequent step, the pyrolysis of the molding is carried out in an inert gas, preferably argon or in vacuo in the temperature range between 300 ° C and 1200 ° C, preferably between 300 ° C and 980 ° C. The product is a suitable infiltratable preform for a subsequent infiltration process, preferably for polymer infiltration and pyrolysis (PIP) or liquid silicon infiltration (LSI), or chemical vapor infiltration (CVI).

Particularly preferred procedure:

The preferred procedure is the preparation of the multi-component prepolymer (MKV), which consists of the steps of preparation of the base polymer and preparation of the crosslinker / moderator mixture. Furthermore, the preparation of the chain extension catalyst (KV) takes place. These components are then mixed, forming a thermoplastic under volume contraction. In a further step, the crosslinking to a thermoset molding occurs. The products are preferably used as starting material for CMC production.

Preparation of the multicomponent prepolymer (MKV)

The multicomponent prepolymer (MKV) is blended from the base polymer and the crosslinker / moderator / accelerator mixture via a cold milling process. It is possible to introduce additives, such as reinforcing and fillers and additives in the mixing process. This is followed by a drying process. The product is available as a powder or granules.

a. Preparation of the base polymer

The base polymer is a phenol novolac. For this purpose, phenol is melted and treated with a formaldehyde furfuryl alcohol and oxalic acid and then tempered and degassed and ground.

b. Preparation of the crosslinker / moderator mixture

The crosslinker consists of a mixture of b-naphthol (inert), resorcinol and phloroglucinol (reactive) in the desired ratio. The addition of a moderator of a xylenol mixture is necessary to retard the intermolecular movements of the reactants and thus determine the reactivity. This makes it possible subsequently to control a crosslinking reaction. The crosslinker / moderator mixture thus produced allows a defined effectiveness of the crosslinker in the crosslinking. The variants of the composition of the crosslinker / moderator mixture are shown in Table 1. Table 1: Composition of the crosslinker / moderator mixture Reactivity depending on the proportions Proportion of crosslinker (% by weight) based on total weight Share moderator (wt .-%) based on total weight Ratio (Networker / Moderator) β-naphthol resorcinol phloroglucinol Σ 2.6 3.4 3.5 Σ xylenol 1 none 80 - - 80 - - 20 20 (4: 1) 2 none - low 50 30 - 80 - 10 10 20 (4: 1) 3 moderate 30 40 10 80 - 15 5 20 (4: 1) 4 moderate - high - 40 40 80 10 5 5 20 (4: 1) 5 high - 15 65 80 20 - - - (4: 1)

In addition to temperature, the accelerator affects the rate of crosslinking. The accelerator is mixed at -10 ° C and added to the crosslinker / moderator mixture according to Table 2 below. Table 2: Composition of the crosslinker / moderator / accelerator mixture Reactivity depending on the proportions Proportions of crosslinker / moderator mixture (A) and accelerator (B) [% by weight] A B Share: crosslinker / moderator mixture Share: accelerator relationship B1 B2 B3 B4 Σ [% by weight] (FROM) 1 none 100 - - - - 0 (1) 2 none - low 98 - - 2 - 2 (49: 1) 3 moderate 94 2 - 2 - 4 (23.5: 1) 4 moderate - high 95 - 5 - - 5 (19: 1) 5 high 92 - - 1 7 8th (11.5: 1) accelerator Chemical name B1 1,3,5-triazine B2 1,3,5,7-tetraazaadamantane (hexamethyltetramine) B3 1,4-cyclohexyl B4 3-isocyanatomethyl-3,5,5-trimethyl

Preparation of the Chain Extending Catalyst (KV)

The chain extension catalyst is chained from a defined molecular weight polycresol. At each end of the chain there are functional groups that can network with the MKV afterwards. For this purpose, poly (4-vinyl) phenol is mixed with a formaldehyde solution and with oxalic acid in solution. In a further step, 2-methylphenol, 2,4,6-trihydroxyacetophenone and 1,3,5-triaminobenzene are admixed and polycondensed under pressure. This is followed by disproportionation under ethanolic KOH solution and addition of 4-hydroxytoluene. Finally, the neutralization and the removal of residual products in a vacuum. Finally, the product is ground to powder.

Mixing the components

The multicomponent prepolymer and the chain extension catalyst are homogenized either by a 2-component injection molding process or by cold milling with a subsequent compounding process. The functional groups of the MKV react with the functional groups of the KV and form polymer chains.

a. 2-component injection molding

The MPV and the KV are melted in separate plasticizing units and injected separately into the cavity by means of two-component injection molding through two nozzles close to each other. The mixing process triggers the chain extension reaction in the molding compound, with a static holding pressure compensating for the volume contraction in the cavity. The product is a high molecular weight thermoplastic molding material.

b. Cold grinding / blending /

The mixing process can alternatively be done by 2-component injection molding by cold milling with or without subsequent compounding. In cold grinding, the MPV is homogenized with the KV. It is recommended that the subsequent melting of the molding compound in a compounding extruder, wherein the chain extension reaction of the molding composition is triggered. Subsequently, a high molecular weight thermoplastic molding strand is removed in a water bath and processed in a cutting unit to granules. Finally, the drying of the granules takes place. In another conventional thermoplastic injection molding process, the granules in the plasticizing unit are melted and injected into the cavity. A volume contraction as described in Method 3a is not present in its original magnitude. The product is a high molecular weight thermoplastic molding material.

Crosslinking reaction in the cavity

The crosslinking reaction follows immediately after the process steps 3a or 3b, wherein in the cavity of the tool is a high molecular weight thermoplastic molding composition. Based on ceramic heating elements in the mold cavity wall, heating takes place after the holding pressure phase at 200-260 ° C. Due to the reaction kinetics, this local heating causes the steric blockade of the crosslinker by the moderator, since xylenol is only released at max. 203 - 226 ° C becomes inactive. A self-sustained exothermic crosslinking reaction occurs to form a thermoset molding. Due to the volume contraction described in method step 3, a moderate effect occurs during crosslinking. This advantage has an effect on the better dimensional stability of the products compared to the processing of conventional phenol novolak-based thermosets. Finally, the removal of the thermosetting molding from the tool for further processing.

CMC production

In the subsequent step, the pyrolysis of the molding is carried out in an inert gas, preferably argon or in vacuo in the temperature range between 300-1200 ° C. The product is a suitable carbon matrix composite material that can be further processed into a subsequent infiltration process to form a CMC.

First embodiment:

Phenol is melted and admixed with a formaldehyde-furfuryl alcohol solution of 83 mol% of the amount of phenol used and with oxalic acid 1.22 mol% of the phenol used and mixed in a stirred autoclave. The reaction mixture is heated at 93-96 ° C for 1.5 hours. Then, water and unreacted ingredients are removed by a suitable vacuum directly in the stirred autoclave. The product is the phenol-based polymer with a molecular weight distribution of 500-5000 g / mol. Subsequently, the solidified phenol polymer is comminuted by Kaltmalen, in order to make it free-flowing and pourable for further processing.

The phenol-based polymer is fed to a twin-screw compounding extruder as granules. Carbon and silicon carbide are added in fiber form as reinforcing materials with diameters of 5 - 12 microns or, with the supplied fiber lengths from 1 mm. The twin-screw extruder In the area of the feed zone or metering zone, continuous fibers are also supplied directly. These are carbon fibers with 50% by volume, which are fed to the phenol-based polymer as a filler. The parameters of the shear rate and zone tempering must be set depending on the process and the machine. The compounded, extruded reinforced phenol-based polymer strand passes through a cooling section in air or a liquid cooling medium depending on the temperature. Subsequently, the granulations are carried out in a wear-resistant cutting unit. The granules serve as starting material for the subsequent injection molding process.

The granulate particles are melted with a formaldehyde equivalent, here hexamethyltetramine 3.5 wt .-%, in the screw of the injection molding machine in the temperature range between 100 - 120 ° C and homogenized. The injection pressure, back pressure, holding pressure and the respective zone temperature control are set according to the molded part to be molded and its molding compound and geometry. They were previously determined by parameter and form filling studies or mold filling simulations. The injection takes place analogously to conventional thermoplastics in one or more mold cavities, which image the molding.

Thereafter, the thermoplastic melt is further heated by means of located in the tool inner wall of the mold cavity dynamic temperature control based on resistance heaters. When a temperature of 220-290 ° C. is exceeded, the thermoplastic cross-links through the crosslinker system to a spatially crosslinked thermosetting plastic molded part while applying a variably adjustable cavity pressure, which must be determined simulatively and experimentally before the series process

The cross-linked and cured component is then automatically demoulded and transported out of the machine.

In a subsequent process, the pyrolysis of the molding takes place in a special recipient under argon, at atmospheric pressure, at a temperature-time regime from room temperature to 400 ° C at 1.5 K / min and a molding-dependent retention time of 60 min. This is followed by a further increase in temperature from 400 to 600 ° C at 0.5 K / min and a molded part-dependent holding time of 60 min. Finally, a temperature rise of 600 to 1200 ° C with 2 K / min and molding-dependent retention time of 60 min. The mentioned respective holding times of 60 minutes result from the wall thickness of the molded part of 3 mm. The end product is a carbon fiber reinforced carbon preform.

Second embodiment:

C-precursor A (average reactivity, filler HTA C-fibers, production by 2-K injection molding)

Preparation of the multicomponent prepolymer (MKV)

The multicomponent prepolymer (MKV) is mixed from the base polymer and the crosslinker / moderator / accelerator mixture via a cold grinding process at a temperature of about -10 ° C and a shear rate of 0.1 - 20 1 / s until a powdery Granules present. The pulverulent intermediate product is then introduced with HTA-type carbon fibers in a compounding process and enriched at an average temperature of 110 ° C. and up to a fiber volume content of 40% by volume. This is followed by a drying process at a temperature of 40 ° C and a relative humidity of <20% for 30 min.

Preparation of the base polymer

Phenol is melted and admixed with a formaldehyde-furfuryl alcohol solution of 80-90 mol% of the amount of phenol used and with oxalic acid 1.1 mol% of the phenol used and in a stirred autoclave at a shear rate of 0.1-5 s ^-1 mixed. The reaction mixture is heated for 0.5-4 h between 80 and 100 ° C. Then, water and unused educts are removed by a suitable vacuum directly from the stirred autoclave. The product is the base polymer with a molecular weight distribution of 1500 to 5000 g / mol. Subsequently, the solidified mass is comminuted by cold milling to granules to make it trickle and pourable for further processing.

Preparation of the crosslinker / moderator mixture

The crosslinker / moderator mixture preferably consists of the composition according to Table 3 below. It is homogenized in a stirred autoclave with a shear rate between 0.5-20 s ^-1 and a temperature-time program (80-120 ° C., 1 h) , Table 3: Composition of the crosslinker / moderator mixture Reactivity depending on the proportions Proportion of crosslinker (% by weight) based on total weight Share moderator (wt .-%) based on total weight Ratio (Networker / Moderator) β-naphthol resorcinol phloroglucinol Σ 2.6 3.4 3.5 Σ xylenol moderate 30 40 10 80 - 15 5 20 (4: 1)

In addition to temperature, the accelerator affects the rate of crosslinking. The accelerator is mixed at -10 ° C and added to the crosslinker / moderator mixture according to Table 4 below. Table 4: Composition of the crosslinker / moderator / accelerator mixture Reactivity depending on the proportions Proportions of crosslinker / moderator mixture (A) and accelerator (B) [% by weight] A B Proportion of: Share: accelerator relationship Crosslinker / moderator mixture B1 B2 B3 B4 Σ [% by weight] (FROM) moderate 94 2 - 2 - 4 (23.5: 1) accelerator Chemical name B1 1,3,5-triazine B2 1,3,5,7-tetraazaadamantane (hexamethyltetramine) B3 1,4-cyclohexyl B4 3-isocyanatomethyl-3,5,5-trimethyl

Preparation of the Chain Extending Catalyst (KV)

This is done by chaining poly (4-vinyl) phenol to a polymer with a defined molar mass (500-2500 g / mol). At the ends of each chain are functional groups that can subsequently crosslink with phenolic novolacs. For the synthesis, phenol is melted and admixed with a formaldehyde solution of 80-90 mol%, the amount of phenol used and oxalic acid 1.1 mol .-% of the phenol used in a stirred autoclave at a shear rate of 0.1-5 s ^-1 mixed. The reaction mixture is heated at 55 ° C for 1 hour. In a further step, in proportion to 64.5% by weight of the solution produced, 32.4% by weight of 2-methylphenol, 0.4% by weight of 2,4,6-trihydroxyacetophenone and also 0.6% by weight 1,3,5-triaminobenzene mixed. The stirring time in a stirred tank reactor is <20 min, at a pressure of 5.0 bar. Subsequently, 0.1% by weight of ethanolic 1N KOH solution and 2% by weight of 4-hydroxytoluene are mixed in. Finally, the neutralization and the removal of residual products. The product is a polycresol with reactive end groups and a molecular weight distribution of 500 - 2500 g / mol. Finally, the fluffy mass, preferably by cold milling, with the addition of 2-6 wt .-% magnesium or calcium stearate and 20 wt .-% 3.5 xylenol (as moderator) homogenized at room temperature. The product is available as a highly viscous powder.

Mix the components by 2-component injection molding

In the example, the MKV filled with C fibers and the KV are homogenized by a conventional 2-component injection molding process. The components are melted in separate plasticizing units. In addition to the generated shear heat, the respective injection cylinders are heated to approx. 80 ° C-120 ° C preheated. The mold filling takes place at the same time by two close to each other separate nozzles in the cavity. The parameters of the mold filling process are significantly dependent on the geometry and the shot weight of the molded part to be produced. The mixing process triggers the chain extension reaction in the molding compound, causing it to shrink in volume by up to 10%. A static pressure compensates for the volume contraction in the cavity. The product is a high molecular weight thermoplastic molding composition having a molecular weight distribution in the range of 50,000 - 300,000 g / mol.

Crosslinking reactions in the cavity

Based on ceramic heating elements in the mold cavity wall, heating to 200-260 ° C. takes place immediately after the holding pressure phase. Due to the reaction kinetics, this local heating causes the steric blockade of the crosslinker by the moderator, since xylenol is only released at max. 203 - 226 ° C becomes inactive. It enters a self-sustaining exothermic crosslinking reaction to form a geometrically defined, dimensionally stable thermoset molding. The crosslinking takes place at high reaction rate (t <5 min) directly in the injection mold at a temperature of 180 ° C - 300 ° C, more preferably 200 ° C - 250 ° C. The crosslinking temperature is always below the decomposition temperature of the polymer, which is about 300 ° C for said polymer. Due to the volume contraction described in method step 3, a moderate effect occurs during crosslinking. This advantage has an effect on the better dimensional stability of the products compared to the processing of conventional phenol novolak-based thermosets. Finally, the removal of the thermosetting molding from the tool for further processing.

CMC production

The pyrolysis process produces the C / C composite. Versatile routes can be recreated. Depending on the type of temperature control, the protective gas or pressure specific crack networks can be generated. In this regard, there are a variety of possibilities in the art. The temperature-time profile used here was derived from the mass degradation behavior from the thermogravimetric analysis of the carbon precursor. The pyrolysis of the molding is done under argon, at atmospheric pressure, at a temperature-time regime from room temperature to 400 ° C at about 1.5 K / min and a molding-dependent retention time of 30 - 720 min. This is followed by a further rise in temperature from 400 to 600 ° C with about 0.5 K / min and a molded part-dependent holding time of 30 - 720 min. Finally, the temperature rises from 600 to 1200 ° C with approx. 2 K / min and molding-dependent holding time of 30 - 720 min. At a wall thicknesses of z. B. 3 mm, a respective holding time of 60 minutes is preferred. The end product is a carbon fiber reinforced carbon preform. Optionally, further heat treatments are preferably above 1200 ° C under vacuum or inert gas, preferably in argon possible, the holding times during pyrolysis are largely determined by the component wall thickness, the inert gas used and the process pressure.

In a follow-up process, the C / C composite, preferably for polymer infiltration and pyrolysis (PIP) or liquid silicon infiltration (LSI), or chemical vapor infiltration (CVI) is further processed. The general procedure is known from the prior art.

Third embodiment:

C-Precursor B (high reactivity, filler HTA C-fibers, production by cold milling, compounding and injection molding)

Preparation of the multicomponent prepolymer (MKV)

The multi-component prepolymer (MKV) is mixed from the base polymer and the crosslinker / moderator / accelerator mixture via a cold grinding process at a temperature of about -10 ° C and a shear rate of 0.1 -20 1 / s until a powdery Granules present. This is followed by a drying process at a temperature of 40 ° C and a relative humidity of <20% for 30 min.

The preparation of the base polymer is identical to the procedure of the previous example.

Preparation of the crosslinker / moderator mixture

The crosslinker / moderator mixture preferably consists of the composition according to the following table. It is homogenized in a stirred autoclave at a shear rate between 0.5 and 20 s ^-1 and a temperature-time program (80-100 ° C., 0.5 h). Table 5: Composition of the crosslinker / moderator mixture Reactivity depending on the proportions Proportion of crosslinker (% by weight) based on total weight Share moderator (wt .-%) based on total weight Ratio (Networker / Moderator) b-naphthol resorcinol phloroglucinol Σ 2.6 3.4 3.5 Σ xylenol high - 15 65 80 20 - - - (4: 1)

The accelerator is mixed at -10 ° C and added to the crosslinker / moderator mixture according to Table 6 below. Table 6: Composition of crosslinker / moderator / accelerator mixture Reactivity depending on the proportions Proportions of crosslinker / moderator mixture (A) and accelerator (B) [% by weight] A B Ratio (A: B) Share: crosslinker / moderator mixture Share: accelerator B1 B2 B3 B4 Σ [% by weight] high 92 - - 1 7 8th (11.5: 1) accelerator Chemical name B1 1,3,5-triazine B2 1,3,5,7-tetraazaadamantane (hexamethyltetramine) B3 1,4-cyclohexyl B4 3-isocyanatomethyl-3,5,5-trimethyl

The preparation of the chain extension catalyst is identical to the procedure of the previous example.

Mixing of components Cold painting and subsequent compounding

The MKV and the KV are homogenized to powder at a temperature of -10 ° C at a shear rate of 0.5 - 10 s ^-1 . The powder mixture is melted in a conventional compounding extruder at a temperature of about 80-120 ° C. During homogenization, the chain extension reaction starts from the molding material. A C-fiber roving 3K HTA is fed to a side channel in the vicinity of the shaping die in such a way that a total mass throughput of 0.1 kg / min (depending on the installation) sets a fiber volume content of about 40% by volume. As a product, a thermoplastic molded strand is drawn off in a water bath and processed into granules in a cutting unit. Finally, the drying of the granules is carried out at a temperature of 40-60 ° C for 1 h, preferably at 55 ° C and a relative humidity of <20%.

Additional fillers may preferably be particles and / or fibers consisting of carbon, silicon, molybdenum, tungsten, tantalum, niobium, titanium, carbides, borides, nitrides, oxides, carbonates or intermetallic phases.

injection molding

In a subsequent process, the granules produced in FIG. 3 are further processed into a shaped part by means of a conventional injection molding process. The injection molding processing is preferably carried out on conventional injection molding machines with screw conveyors, which advantageously produce low shear heat. The plasticizing cylinder is equipped with a fluid temperature, the cylinder temperatures preferably realized in the range of 60 to 150 ° C. The mean temperature in the plasticizing unit may be 100-130 ° C. The parameters of the mold filling process are significantly dependent on the geometry and the shot weight of the molded part to be produced.

Networking, CMC production

The process characteristics of the subsequent processes can be identical to the procedure of the previous example.

characters

The 1 shows the second preferred embodiment of the method according to the invention in the overview: Stage of CFRP production in the CMC production: mixing of the components by compounding or injection molding. Chain extension reaction by chain extension catalyst. Final crosslinking of the molding compound by crosslinker.

Claims (7)

Process for the preparation of ceramic matrix composites, wherein the following steps are carried out: a) Preparation of a thermoplastic fiber-plastic composite with a fiber reinforcement and a thermoplastic multicomponent prepolymer with the substeps: i. Preparation of a base polymer from phenol-based polymers, preferably novolaks, or mixtures thereof with furfuryl components, wherein the thermoplastic matrix material has a toughness of 100 Pa * s to 500 Pa * s, ii. Preparation of a crosslinker / moderator mixture of a crosslinker of b-naphthol, resorcinol and phloroglucin and a moderator of a xylenol mixture, iii. Preparation of the multicomponent prepolymer by mixing the base polymer with the crosslinker / moderator mixture in a cold grinding process, b) preparing a chain-extension catalyst by linking a poly-cresol having functional groups at the chain ends, which subsequently crosslink with the multicomponent prepolymer; c) mixing the multi-component prepolymer with the chain-extension catalyst, d) shaping the thermoplastic fiber-plastic composite, wherein a chain extension reaction begins, but without the crosslinking by injection molding, or Reactive compounding which starts a chain extension reaction, but without crosslinking and subsequent injection molding, e) conversion of the thermoplastic fiber-plastic composite into a thermosetting fiber-plastic composite material by heating immediately after the injection molding process, f) conversion of the matrix polymer to matrix carbon and production of the fiber-reinforced carbon (C / C) to produce the CMC. Method according to Claim 1 , characterized in that the thermoplastic fiber-plastic composite material after step a) is filled or unfilled and present with or without additives. Method according to one of the preceding claims, characterized in that step c) and step d) take place simultaneously in a shaping tool for the thermoplastic processing. Method according to one of the preceding claims, characterized in that step e) takes place in the same shaping tool in which the injection molding process was carried out. Method according to one of the preceding claims, characterized in that the further processing after step f) is carried out as a pyrolysis to form a characteristic crack network for a C / C. Method according to one of the preceding claims, characterized in that the further processing after step f) is carried out as infiltration of the crack system by means of Si-based systems to form SiC and / or its further compounds in the crack region. Method according to Claim 6 , characterized in that the further compounds comprise SiCN, SiBCN or SiCO.

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