DE1923622C3 - Use of carbon fibers to reinforce plastics - Google Patents

Description

and the use of such carbon fibers as The invention consists in the use of

Reinforcement embedding in matrix synthetic resins, where carbon fibers are obtained from a polyacrylonitrile poly- hirch composite materials of high strength and other fibers or copolymers in fiber form due to more advantageous properties, two-stage heat treatment is obtained at worldind known. In particular, the polyacrylonitrile is first heated in eir.er acidic Patent 1,430,803 the production of carbon-containing atmosphere to a temperature in cloth fibers of high strength by Wärmcbehand- range of 150 to 300 ° C and from the French rather then in development of Polyacrylonitrile fibers are known in which 50 an inert atmosphere to a temperature in the polyacrylonitrile fibers are first heated at 200 to 250 ° C range from 900 to 1200 ° C, exposed to an oxidizing atmosphere and to reinforce plastics.

finally the fibers under non-oxidizing layers. The invention provides the surprising finding

conditions above 1000 ° C are carbonized. It is based on the fact that a very good _{bond strength can be achieved in order to achieve particularly good properties of the 55} if the temperature of the crwähn-Külllenstoffasermaterials is after the carbonization final graphitization heat treatment heat treatment above 1000 ° C or a widening step This final graphitization heat treatment with tempering heat treatment can be completely omitted, temperatures above 2000 ° C are provided, whereby those properties, especially high values of strength and elasticity, which depend on the strength of the composite, are achieved can be achieved between the module. In the French fiber material and the carrier resin depend, quite tentschrift 1430 803 is also considerably improved on the use, while the other properties of such carbon fibers as reinforcing materials retain values which are intended for polyester, epoxy and other carriers Uses more than sufficient. If synthetic resins, in which the synthetic fibers are embedded, this is a certain reduction in the value of the tet, pointed out. Young's module brings with it, it retains

_{It is also known that the quality of such materials has a value v} which is above the value of comparable materials due to the incorporation of carbon fibers in the carrier and the improvement in the torsion resistance.

i 923 622

and flexural strength has the effect that the material obtained in this way is specially tailored to the needs and requirements of, for example, aircraft engine superstructures. This applies to »Onders for fan blades and the like, for which the low weight and high value of the Yoimgschen Modules make such composite materials attractive, but with a view to bird impact and aerodynamic requirements good flexural and bond strength is required.

This finding, which supports the invention, that by restricting the treatment temperatures to below the high graphitization temperatures, a substantial improvement in the bond strength between the reinforcing fibers and the carrier plastic and, as a result, a substantial improvement in the various material properties mentioned, can be achieved, was unexpected and surprising to the person skilled in the art . Because, as already mentioned, for the production of such composite materials it was obvious to proceed in such a way that the individual reinforcing fibers are obtained as such with optimal properties (with regard to tensile strength and modulus of elasticity), since this at the same time led to the expectation of optimal properties for the composite material as a whole . It was unexpected that a manufacturing procedure which does not accept the optimal properties of the individual fibers (namely the less than optimal values of the modulus of elasticity and tensile strength) would result in a significantly higher strength of the bond between the reinforcement fibers and the carrier plastic and, as a result, significant improvements the material properties of the composite material as such.

Preferably, after the second process step, the fibers are applied in film form, and these foils are then applied to form the composite material.

The carrier resin can be applied to the fibers before they are laid out to form films, wherein the foils are then partially cured to facilitate handling; the partially Cured foils are then placed on top, compacted and finally to form the composite fully cured.

The films can be impregnated with the carrier resin by spraying or immersion.

An epoxy novolac resin in Compound with a boron trifluoride-containing latent catalytically active hardener used will. Alternatively, different ones can be used depending on those desired for the finished composite Properties other resin systems can also be used.

In the following examples, materials that are produced by the method according to the invention are compared with similar materials that have been subjected to "graphitization" and therefore do not correspond to the present invention.

For the material produced according to the invention, the fiber material was produced in such a way that a fiber made of Courtellee polyacrylonitrile (PAN) copolymer of 1Vt denier is wound onto a frame, the PAN is pre-oxidized in air at a temperature of 220 ° C. for 7 hours and then heating the fiber in an inert atmosphere to a temperature of 1000 ° C for a period of about 4 hours

The fiber obtained is cut from the frame for the production of material foils; the foils are then coated with a solution of epoxy novolac resin (in the specific example described, CIBA LY 558 was used) with a latent catalytically active boron trifluoride hardener (in the specific example, Shell Chemicals BF ₃ x 400

ίο used) sprayed. The films thus obtained were dried and partially cured by heating to a temperature of 80 ° C. in air to facilitate handling.

For the production of objects from the foils

and especially for the production of the test specimens required for testing the material properties of this material , several resin-impregnated foils are placed on top of one another until the required thickness is reached, so that all fibers

ao run in parallel; Then the stacked foils are compacted in a press with a pressure of a few 28 kg / cm ⁵ and at the same time heated to 165 ° C. for 10 minutes; then the foils are removed from the press and post-cured in an oven four Stuis the long at 180 ^J C to completely harden the resin. The cured object is then processed, if necessary, to produce the required test specimen or to shape it in some other way.

To produce the comparative material not designed according to the invention, from assumed the same output fiber wound on a frame in the same way. the Fiber was then processed in a manner similar to that described above.

3s wrote, heat treated, but it was in In this case, after the "carbonization" which took place at 1000 "C, it was placed in a boiling temperature oven and graphitized in an inert atmosphere for about 5 hours at 1750 ° C. Then became

4ü the fiber removed from the oven and in exactly processed into objects in the same way as described above for the material according to the invention.

The results of the aforementioned tests on material test items are given below. In the tables below, material A means the material produced according to the invention, while material B is the material not produced according to the invention. It should be noted that in all cases the fiber content is given in percent by volume; this volume fraction depends mainly on the spacing of the fibers in the foils that are placed on top of one another to produce the objects; the material properties show a dependency on this volume fraction. Table 1 shows a comparison of the “ short beam shear strength” of the materials. To obtain these results, a standard test specimen with the dimensions (16.5 ± 0.25 mm) x (6.35 ± 0.127 mm) x (1.524 ± 0.025 mm) was placed on two rollers with a diameter of 0.635 cm, which were arranged at a distance of 1.525 cm arranged and under the action of a similar one equally spaced between these rollers

6s roller deformed. The arrangement was made that the fibers lay in the direction of the longitudinal axis of the test specimen. There is general agreement about the fact that the breaking strength from such a

Test can be related to the interlaminar shear strength, and for materials of the In the type in question, this gives a good indication of the bond strength between the fibers and the carrier or matrix material.

Table I.
Small bar shear strength (in kg / cm ² )

Material A Material A Material B Material B 55% fiber 67 'It fiber 50 »/« fiber 60 «/ ο fiber 613.01 323.38 224.25 140.00 420.04 331.11 201.05 153.25 423.48 331.82 231.28 153.95 485.98 335.33 198.24 165.20 589.18 334.62 215.11 170.12 586.37 337.44 233.39 171.53 583.70 338.14 221.44 172.23 550.37 352.90 232.69 174.34 575.68 366.26 233.3t / 185.59 500.53 373.29 234.80 620.74 376.10 224.96 586.09 397.19 224.25 400.00 409.84 428.12 435.86 450.62 471.01 496.69

Material A Material B 65 · / · fiber 60 »/. Fiber 92.13 · 10 « 61.42 · 10 « 93, ^ · 10 * 62.52 · 10 « 96.86 · ΙΟ « 64.10 · 10 « 99.69 · 10 * 65.36 · 10 * 103.47 · 10 * 67.72 · 10 * 103.79 · 10 ² 68.04 · 10 « 100.80 · 10 * 72.45 · 10 * 76.38 · 10 «

Here, too, is again in the case of the invention Material A an increase of about 50% determine; the fiber volume fractions are; .was different, but practically negligible because the Scatter in any production of materials likely to cover the difference of 5% would.

Table TII shows the values of Young's modulus (= modulus of elasticity) along the fiber direction compared with each other, as they result when measuring with standard tensile tests, but rather Minimum values for certain special fiber proportions.

Table III

Minimum normal values of the modulus of elasticity
(in kg / cm ² )

As can be seen, the values for material A according to the invention are about three times as good as that for material B, which is an indication that the bond strength is significantly improved could. It can also be seen that the values vary considerably as a function of the fiber volume fraction change and that this change is different between the two materials. In the Indeed, it can be assumed that the material according to the invention has an optimal fiber volume, which is significantly different from the optimal fiber volume fraction of material B.

Tables concerns the final flexural strength of the materials, measured on a rod with the dimensions 11.4 x 1.27 x 0.51 cm (span-depth ratio = 20) in a three-point bending test with a distance of 10 cm between the centers. the The direction of the fibers runs in the same direction along the longitudinal axis of the rod.

Table II
Final flexural strength (in kg / cm ² )

Material A

Material F

64% fiber 1.209-10 ⁶
67 »/ o fiber 1.237 x 10β
72% fiber 1.315 x 10 °

6O ° / o fiber 1,582 -10 «

With regard to this special property, material A is not quite as good as material B; However, as explained at the outset, it has been found that this does not exist for many practical applications is particularly noteworthy Abiall and considerably through the improvement of other properties is outweighed. (It should be emphasized that it is necessary because of the anisotropy of the material, respectively specify a direction for the property in question.)

Table IV again shows minimum normal values for final tensile strength, according to conventional ones Procedure measured.

Table IV

40 60 ° / o Final Tensile strength (in 60 0/0 kg / cm ² ) 102 Material A Material B 45 Fiber 110.25 • 10 ² Fiber 126

Accordingly, the material of the invention shows a slight reduction in ultimate tensile strength.

Table V shows typical values as obtained using standard conventional test methods for Young's modulus (elastic modulus) was determined in a direction transverse to the fibers.

Table V

Modulus of elasticity in the transverse direction (in kp / cm ² )

Material A

65% fiber 9.84 -KH

Material B

60 «/ 0 fiber 4.92 -

Here, the improved bond strength through the improvement of this property points in the direction of across the fibers by a factor of 2.

Table VI relates to the torsional modulus of the materials, again according to the conventional state; rdver-

drive measured. The table shows typical values for this parameter.

Table Vl
Torsional modulus (in kg / cm ² )

Material Λ

7% fiber 6.046-16 »
72 Vo fiber 6,327- K) ¹

Material B

57 "ο fiber 4,639- K) ¹ 58 ¹ Vo fiber 4,639- K) ¹ 63 ¹ Vo fiber 5,272! () '

You can see that there is a significant improvement (up to 5 () "/ o) with regard to this material property is achieved, which is very important in items such as blades for gas turbine engines is what torsional forces have to withstand, not only as a result of centrifugal and aerodynamic Compressive forces occur, but also and to an increased extent as a result of bird impact loads, which can be many times greater than the causes mentioned above.

It is clear from the results reported above that the use of the inventive Material brings about a significant improvement in the overall properties. Of course In the test tests reported above, the carrier resin was the same in all cases and it could other resins can readily be used. It would then also be

training of the process according to the invention better Properties to be expected than would otherwise be achieved with the same resin system. Λ1 Obviously applicable resins include epoxy resins, polyimide resins and other resins ii Question, depending on the required properties, wii For example, shelf life, ease of manufacture, etc.

Since the fiber material of the VVerkstolfe Λ or FJ cii

ίο specific gravity of 1.75 or 1.80g / cm ^{: l} bc sits, composite materials produced using the relevant materials with the same fiber volume fraction differ in their specific weight in the same ratio as the specific gravity of the fibers.

It follows that the specific properties of a composite material with fibers from fiction according to type Λ can be further improved.

In fact, the improvements achieved by the invention are not limited to those above reported results. Preliminary tests show that both the pressure and impact resistance improved by about 50 ", 0 using the invention will.

The results not reported relate to Fibers that do not have any surface treatment to improve the adhesion between the carrier and experienced the fibers. Of course: can be used in connection with the present invention to further improve the properties of the composite, methods such as for example surface etching application linden

Claims (4)

Composite materials obtained from synthetic resins, in particular, their shear and torsional strength, which is useful for a wide range of 1. Use of carbon fibers, which are essential for a polyacrylonitrile polymer or -copoly- 5 of the production of the composite material achievable meren in fiber form through a two-stage War- composite strength between the embedded fusion treatment, in which the reinforcing fibers and the Matnx synthetic resin from, polyacrylonitrile fiber initially in an acid-hangs. Until now, achieving prepared zufnedenstelstoffhaltigen atmosphere to a temperature in the lender values of these bond strength with the verBereich of 150 heated to 300 ° C and then _iC fügbaren carbon materials difficulties, and in an inert atmosphere to a temperature, there have been various ways of solving this proim range of 900 are heated up to 1200 ° C, investigated blems. for reinforcing plastics. In this context it should be noted that 2. Use according to claim 1, characterized ge according to the previous ideas of the professional world as indicates that the carbon fibers are designed for the i _S prerequisite for achieving optimal self-embedding in the carrier plastic in film form shafts of the composite material for the manufacture of the. individual carbon fibers with maximum values 3. Use according to claim 1, characterized in that the strength and the modulus of elasticity are viewed indicates that the carbon fibers were after. The decisive factor for this, in turn, was for Application of synthetic resin in the form of a film made * o the production of high-strength carbon fibers is a drop first, the synthetic resin in a so-called »graphitization« process Foil is partially cured and the pyrolysis is viewed after the actual pyrolysis, partially cured foils for the formation of the fiber in which the fiber is reinforced to a temperature in the fiber Layered plastic body is heated from 1500 ° C upwards. In agreement and then cured to the end. 25 The mood hereby is in the aforementioned French 4. Use according to one of the previous zösischen patent 1 430 803 to achieve the claims, characterized in that an epoxy novolac resin with values of the strength and the modulus of elasticity mentioned the boron trifluoride as latently catalytically acting as a particularly high quality carbon fibers with high carrier plastic Graphitization heat treatment above hardener is used. 30 2000 ⁿ C provided. The object of the invention is to create a fiber-reinforced composite material of the type mentioned at the beginning made of embedded in a synthetic resin, carbon fibers obtained by carbonization of synthetic fibers 35 are based on the due The invention relates to the production of a perfect, previously achievable composite carbon fiber-reinforced plastic molded strength between the reinforcing fibers and the lower use of heat treatment carrier or matrix resin in generally good • crystalline polyacrylonitrile polymers or copolymers especially good values in properties of shear and carbon fibers obtained in fiber form. 40 has torsional strength, which is necessary for various The manufacture of high stress applications by pyrolysis charring is essential * are carbon fibers obtained from synthetic fibers.