JPH0129499B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to carbon fiber materials impregnated with thermosetting resin binders useful in the production of carbon-carbon composite materials. The use of boron in the production of carbon materials such as graphite from fillers such as graphite powder and graphitizable materials such as pitch or resins is known. The use of boron enhances the bonding of the material and the conversion of the material to graphite. It is also known in the art to use boron in making carbon-carbon composite materials consisting of carbon fiber materials, such as carbon cloth or graphite cloth, and thermoset resins. Examples of this type of composite material are:
Lec C. Ehrenreich, U.S. Patent No. 3,672,936 (1972
(June 27, 2016) as disclosed in the specification. This patent confirms that when a boron-containing compound is added to a resin-impregnated carbon fiber material prior to carbonization of the resin, there is some improvement in oxidation resistance as well as interlaminar tensile strength. Robert C. Shaffer, U.S. Pat. No. 4,101,354, discloses that if a boron-containing carbon-carbon composite material is heated to at least about 2150° C. during carbonization and graphitization, the interlaminar tensile strength of the composite material is significantly increased. and that at such temperatures, the tensile strength in the fiber direction of carbon fiber materials typically decreases substantially (this is clearly due to the complex due to the deterioration of the carbon fiber material) is disclosed. According to this patent, a significant reduction in the fiber direction tensile strength of carbon fiber materials is prevented by the use of a protective coating on the fibers. the protective coating includes a thermoset material;
The material is such that it remains flexible even after exposure to curing temperatures. Applying a coating to the fibers before adding the resin and boron-containing compounds;
harden. A resin and a boron-containing compound can then be added to at least partially cure the resin. Forming the laminate and heating the laminate to a temperature sufficient to carbonize and at least partially graphitize the resin significantly reduces the fiber-wise tensile strength of the carbon fiber material of the laminate. It was found that the interlaminar tensile strength was greatly improved. A protective resin coating on the fibers creates a barrier, resulting in an anisotropic composite even with high amounts of boron present in the matrix.
However, this barrier is insufficient to limit boron migration and the high coalescence temperature
When the temperature exceeds 2482°C, it is insufficient to maintain the anisotropy of the composite material. Above this coalescence temperature, high boron concentrations exhibit instability such that an isotropic composite is obtained or the composite becomes useless due to large fractures. According to the present invention, a mixture containing a refractory metal and a thermosetting resin is obtained. The resin is such that it remains flexible even after being exposed to curing temperatures. The metal can be in the form of particulate metal or finely dispersed metal or both metals. The metal can react with boron in the carbon ternary system at high temperatures. The carbon fiber material is coated with this mixture and the thermosetting resin is cured. The coated carbon fiber material is then re-impregnated with a second thermoset resin containing a boron compound and optionally a refractory metal capable of reacting with the boron to form a metal boride. For refractory metals within the first coating, if present, the metals can be in the form of particulate metals or finely dispersed metals or both metals. The second thermoset resin is at least partially cured and the plurality of fibrous material layers are then assembled to create a laminate. The laminate is heated to a temperature sufficient to carbonize and graphitize the thermoset resin. The obtained carbon-carbon composite material has better oxidation resistance than a composite material made without the presence of a heat-resistant metal in the thermosetting resin,
It has improved high temperature stability, higher density and improved interlaminar tensile strength. According to the present invention, a carbon fiber material is first coated with a flexible thermosetting resin that remains flexible even when cured. Thermosets contain refractory metals that can react with boron to form metal borides. The refractory metal can be finely dispersed within the resin (ie, the refractory metal is an integral part of the resin's molecular structure). Alternatively, the refractory metal can be a particulate metal, or both forms of metal can be used. By incorporating refractory metals into the resin in the form of reaction products of tungsten carbonyl and/or molybdenum carbonyl with pyrrolidine,
Thermosetting resins containing finely dispersed metals can be produced. Examples of such thermosetting resins include copolymers of furfuryl alcohol and polyester prepolymers that are reacted with complexes that are the reaction products of tungsten carbonyl and/or molybdenum carbonyl with pyrrolidine. was. Such copolymers are described by Robert
These copolymers can be used in the present invention as more fully disclosed in US Pat. No. 4,087,482 to C. Shaffer. Other thermoset polymers containing chemically bonded metals,
Polymers made by reacting complexes, which are the reaction products of tungsten carbonyl and/or molybdenum carbonyl with pyrrolidine, with monomers and prepolymers were described by Robert C.
Shaffer U.S. Patent Application No. 893,622 (filed April 5, 1978) and No. 36/084310 (October 1979)
These polymers can be used in the present invention. After resin production, the resin can be diluted with a suitable solvent, such as dimethylformamide, to a solids content of, for example, 70%. Carbon fiber materials that can be used in practicing the present invention can include carbon materials that are in the form of fibers or filaments or other shapes. Examples include fabrics such as carbon cloth or graphite cloth. As used herein, the term "carbon" is intended to include carbon in all its forms, including graphite. In a preferred embodiment of the invention, the first coating of flexible thermosetting resin includes, in addition to the finely dispersed refractory metal, a particulate refractory metal having a particle size of 5 to 50 microns. . Examples of such metals include niobium, tantalum, titanium (eg, as titanium dioxide), molybdenum, and tungsten. As the heat-resistant metal, one that converts into a stable boride in a ternary system with boron can be used. Preferably, about 50-90% of the total refractory metal content in the resin is particulate metal, with the remainder being finely dispersed metal. A first flexible coating is applied to the carbon fiber material using a suitable technique and cured.
One method that may be used is to remove excess coating material by dipping the carbon fiber material into an open container containing the coating material and then drawing the carbon fiber material through a pressure roll, after which the fibrous The coating is dried by suspending the material in air at ambient temperature to evaporate some of the solvent in the coating material. The coating material is then cured by placing the carbon fiber material in a circulating air oven to promote polymerization of the resin and to further remove the solvent. The solids content of the thermoset coating material is adjusted to produce a cured coating containing about 5 to 200 weight percent carbon fiber material. After application of the flexible coating, the carbon fiber material is re-impregnated with a second thermoset resin. This resin is partially cured or B stage. The resin can be the same as a flexible thermoset resin and, as described above, may contain suitable amounts of finely dispersed refractory metals or particulate refractory metals or both metals. It does not have to be included. The resin also contains a boron compound, the amount of boron being preferably balanced on a molecular basis with the amount of metal present in the overall system. The boron-containing compound is preferably amorphous boron. Impregnation and curing may be accomplished by any suitable method, such as by dipping the coated carbon fiber material into an open container containing a thermosetting resin containing boron and optionally a refractory metal. Excess material is removed by drawing the carbon fiber material between pressure rolls and the material is then dried by hanging it in air at ambient temperature to evaporate some of the solvent contained in the resin. do. The dried carbon fiber material is then processed to at least partially cure the thermoset resin, such as by placing the dried carbon fiber material in a circulating air oven to promote polymerization of the resin. The amount of amorphous boron incorporated into the resin is selected such that the amorphous boron comprises about 2-9% by volume of the laminate. The amount of metal contained in the boron-containing flexible thermoset and the boron-containing thermoset is in excess of the stoichiometric amount necessary to combine with the boron present. Preferably, it exists in Preferably, the total metal content of the laminate is about 75 to
100% by weight is present in the first flexible thermoset resin coating and the balance is present in the second thermoset resin coating. The resulting laminate is then consolidated, reinforced with a resin matrix, and further cured. According to one method of doing this, the laminate is prepared at high pressure and temperature for a time sufficient to impart a relatively high degree of adhesion of the fiber-resin matrix to the laminate and to the next step. The mold is placed in the conforming mold of an electrically heated corrugated press for a time sufficient to render it adequately self-supporting to maintain its shape and dimensions throughout processing. The laminate is then carbonized and preferably at least partially graphitized. This is, for example, 2320 ~
2870℃ temperature and about 35~211Kg/ ^cm2 (500~
This is done by heating under pressure (3000 psi). Carbonization and graphitization methods that can be used are described, for example, in Richard J. Larsen et al., US Pat. In the method described in the Larsen et al. patent application, the carbon-organic resin composite is first shaped by molding and at least partially precured. The composite material is then placed in an induction electric furnace where it is heated in a manner that substantially decomposes the resin rapidly but without delamination or other damage to the composite material.
Heat at a first rate to a temperature on the order of 538°C (1000°C). It is then heated until the composite material becomes substantially pliable and plastic, typically around 1927°C.
Continue heating at second rate at a temperature above (3500〓). Thereafter, the composite material is maintained at an elevated temperature, typically in excess of about 2760°C (5000°C), while continuing to apply high pressure to provide substantial reinforcement of the composite material. According to the continuous method, within a relatively short time,
Also, very dense laminate articles having substantially all carbon composition are produced without the need for sequential processing steps performed at different locations or using different pieces of equipment. The combination of refractory metals and boron in the composite material produces metal borides during thermal processing. Metal borides are considerably more stable at high temperatures than boron carbide. Thus, boron migration is limited, thereby preventing boron attack on the fibers and preventing fiber deterioration. Due to both boron and metal present in the laminate,
A synergistic effect on the interlaminar tensile strength of the final carbon-carbon composite is achieved. The following examples illustrate the invention. Example 1 50% by weight resin (Shaffer U.S. Pat. No. 4,087,482)
A grind was prepared containing 50% by weight of granular niobium (having a particle size of -325 mesh). The graphite fabric was immersed in an open container filled with grinding material. The solids content of the mill was adjusted to produce a coating consisting of approximately 175% by weight of the fabric. The fabric was pulled through pressure rolls to remove excess coating and hung to dry in air at ambient temperature. Then approximately 163℃ (325
The fabric was placed in an air circulation oven maintained at a temperature of 〓) for approximately 60 minutes. This temperature treatment cured the resin sufficiently to prevent intermixing with the resin of the second coating. Then 87% by weight of a resin prepared according to Example 1 of Shaffer U.S. Pat. No. 4,087,482 and 5% by weight of graphite fiber grinding.
and immersing the coated fabric in an open container holding a pulverized product consisting of 8% by weight of amorphous boron.
It was further impregnated. The initial weight of the fabric is about 120
Sufficient amount of grind was added to coat % by weight. The fabric was drawn between pressure rolls to remove excess resin and hung to dry in air at ambient temperature. The fabric was then placed in a circulating air oven for about 30 minutes at a temperature of about 163°C (325°) and then allowed to rise to a temperature of about 204°C (400°) for about 10 minutes. This temperature treatment progressed the resin to the B stage. The fully soaked fabric was then cut into pieces having selected dimensions and shapes and laid up into the desired shape. Integrate and strengthen laminates,
and approximately 70Kg/cm ² (1000psi) and 218℃ (428
The matrix material was further cured in the consistency mold of an electrically heated corrugated press for approximately 16 hours. It has been found that the length of time required for curing depends on various factors including the wall thickness and shape of the product. When removed from the press, the product had high fiber-matrix adhesion. The product was made properly self-supporting to maintain its shape and dimensions throughout further processing steps. Reference Example 1 The laminate obtained in Example 1 was heated under a pressure of about 70 to about 140 Kg/cm ² (1000 to 2000 psi) in a device heated to a temperature of about 2870°C (about 5200 〓) by induction heating. It was fully carbonized, further compressed, and turned into a graphite state. This step completed the conversion of the resin matrix, advanced graphite crystallinity and the formation of metal borides within the matrix. The interlaminar tensile strength and the tensile strength in the fiber direction of two different samples made according to this example were measured and were as follows.

[Table] X-ray diffraction of sample 1 shows that it is highly graphitic.
A graphite peak at 3.35 Å was shown, indicating that boron promoted graphitization. Further, X-ray analysis showed NbC, NbB ₂ and δ-WB, but B ₄ C was not found. These results indicate that the reaction between boron and the metal present is complete and that the molecular distance traveled by boron is large when high temperatures and pressures are applied. Example 2 A laminate was produced as described in Example 1. However, granular niobium was not used. Reference Example 2 Using the laminate produced in Example 2, Reference Example 1
A carbon-carbon composite material was produced in the same manner. However, a high coalescence temperature of 2316°C (4200°C) was not used. This composite material contained only finely dispersed tungsten and excess boron on a molecular basis, and did not contain any particulate metals. This composite material was found to have a fiber-wise tensile strength of 673 kg/cm ² (9572 psi) and an interlaminar tensile strength of 171 kg/cm ² (2432 psi). This interlaminar tensile strength is determined by Shaffer's U.S. Patent No. 4,164,601.
This was a considerable improvement over the carbon-carbon composites described in that patent, ie, composites that did not contain refractory metals. however,
Another carbon-carbon composite made in the same manner at a higher coalescence temperature of 2871°C (5200°C), but containing only finely dispersed tungsten, had a temperature of 181Kg/cm ² ( It exhibited a fiber direction tensile strength of 2583 psi) and an interlaminar tensile strength of 162 Kg/cm ² (2301 psi). These results indicate a decrease in tensile strength in the fiber direction, resulting in an isotropic composite. Example 3 A laminate containing particulate refractory metal as well as finely dispersed tungsten was prepared as described in Example 1 in order to maintain constant fiber identity and composite anisotropy. did. The particulate metal was added to a barrier placed on the fibers to block migrating boron. This additional metal protected the fibers, allowing them to create a stable composite material. The four metals used were tantalum, titanium as titanium dioxide, molybdenum, and tungsten, which were used in place of niobium in Example 1. Reference Example 3 Using the laminate obtained in Example 3, a carbon-carbon composite material was produced as described in Reference Example 1. The high coalescence temperature used to make each composite was approximately 2871°C (5200°C). The interlaminar tensile strength and fiber direction tensile strength were measured and found to be as follows.

[Table] It can be seen that the addition of particulate metal protected the fibers and produced a stable composite material. The tensile strength in the fiber direction for each of the above samples is approximately 2316℃
Composites manufactured at a high coalescence temperature of about 2871°C (5200°C), although lower than composites containing only finely dispersed tungsten.
〓) was significantly higher than that of a composite material manufactured at a high cohesion temperature and containing only finely dispersed tungsten. Analysis of the data obtained from the composites of Reference Examples 1, 2 and 3 shows that these composites had a change in fiber volume. In order to normalize the values obtained to those that a standard composite material could be expected to have at a standard fiber volume of 60%, the following chart is given.

[Table] Tensile strength * Without adding particulate metal.
The fibers in the chart above are approximately 2871℃ (5200〓)
For example, in the case of titanium dioxide, molybdenum and tungsten, the temperature is about 2316℃.
(4200〓) compared to the finely dispersed system. It is thus clear that the finely dispersed metal alone protects the fibers in the composite from boron, as long as the temperature does not exceed 2482°C, and that this protection does not extend to the metal-free flexible furfuryl resin, i.e.
This is seen to be superior to the resin disclosed in Shaffer US Pat. No. 4,164,601. Because composites made without metal particulates exhibit lower densities than composites made with metal particulates, fibers protected using finely dispersed metals provide important weight savings. It will be done. However, the purpose of the use of the metal particulates is to protect the fibers when higher coalescence temperatures are used, for example above 2482°C.

Claims (1)

[Claims] 1 a first portion surrounding the carbon fibers including a flexible thermosetting resin coating containing a refractory metal capable of reacting with boron to form a metal boride; and a second portion coated over the first portion, the carbon fiber material impregnated with a thermoset resin binder.