Patent Number: 
Section: description

The invention will now be illustrated by some examples, without however being limited to the compositions shown in the examples. A resin mixture based on a vinyl ester (Atlac XP 810, DSM Composite Resins, Zwolle, the Netherlands) with the following composition was prepared: The amount of resin mixture was split in 2 parts, and, using a doctor blade, spread to form a resin film on 2 polyethylenelpolyamide carrier films. The split, continuous carbon fibre bundles with a styrene-soluble binder (K value 80, split into 10 packages of 8K on average) from 14 bobbins were introduced into the chopper while spaced 4 cm apart above the bottom resin layer. The carbon fibre bundles were cut with rotating blades into packages of filaments approximately 2.5 cm long. On the bottom resin layer a 2D-randomly distributed and homogeneous fibre bed with a width of 50 cm was obtained. Next, the second resin layer was applied onto the fibre bed, after which the fibre material was impregnated with the resin mixture in a compacting unit. The sheet-shaped resin composition thus obtained was subsequently coiled. A carbon fibre loading of 52% by weight was achieved. Good wetting of the 8K packages with the resin mixture was distinctly visible up to the individual filaments. Thickening of the compound obtained took place in 10 days, after which the resin composition was moulded into a flat sheet using a mould coverage of 40%. A homogeneously black-coloured sheet was the result. Test specimens were sawn from the flat sheet obtained, and these were subsequently subjected to a bending test and an ILSS test. Results of bending test (ISO 178): Flexural modulus 33 GPa Flexural strength 500 MPa Results of ILSS test (ASTM 2344): 68 MPa The density of the material obtained was 1.39 g/cm3. Using the same resin mixture as in Example I and the same split, continuous carbon fibre bundle, a compound was made containing 25% by weight of carbon fibres with a length of approximately 2.5 cm. After thickening for 12 days a number of flat sheets were moulded with a mould coverage of 40% and with the following thicknesses 1.4 mm, 2.8 mm and 5.8 mm. The shielding efficiency was measured in accordance with ASTM 4935 in the frequency range between 30 MHz and 1 GHz. The shielding curves have a smooth profile across a wide frequency range. A number of characteristic values of these curves are shown in the table. Using the resin mixture of Example I, carbon fibre bundles from 14 bobbins with an unsplit 24K carbon fibre bundle were chopped to a length of approximately 2.5 cm above the bottom resin bed. The fibre bundles were spaced 4 cm apart as in Example I. Instead of a homogeneous fibre bed over a width of 50 cm, what was now obtained were rather 14 xe2x80x9cridgesxe2x80x9d of fibre material, in between which were areas where scarcely any fibre bundles were to be found. A carbon fibre loading of 48% by weight was achieved. To avoid such areas, the distance between the bundles in the chopper had to be reduced. Only when the bundles were spaced 1.5 cm apart could a homogeneous fibre distribution be achieved (the width of the SMC obtained then was approx. 20 cm). However, impregnation of this 20 cm wide fibre bed was found to be not well possible, as appeared from the high proportion of dry fibre bundles that were still present after the compacting unit. Using the resin mixture of Example I, split, continuous carbon fibre bundles with a non-styrene-soluble binder (48K, split into 7 packages of 7K on average) from 14 bobbins were cut to a length of approximately 2.5 cm. Under identical conditions to those in Example I, a 50 cm wide C-SMC was thus made with a carbon fibre loading of 52% by weight. After the compound had thickened for 10 days, a flat sheet was moulded using a mould coverage of 40%, from which a number of test bars were sawn for a bending test. On the surface of the flat sheet (and the test bars) areas were clearly perceptible where there were scarcely any carbon fibres (light-yellow in colour). As a result the strength of the material was relatively low. The results of the bending test according to ISO 178 were: Flexural strength: 200 MPaxc2x140 MPa Flexural modulus: 31 GPa. The ILSS (ASTM 2344) was 59 MPa. A resin mixture based on maleate resin (Palapreg 0423-N-2, DSM Composite Resins) was prepared, with the following composition: The amount of resin mixture was divided into 2 parts and, using a doctor knife, spread out to form a 30-cm wide resin film on 2 calender rolls. The split, continuous carbon fibre bundles with a styrene-soluble binder (K value 80, split into 10 packages of on average 8K) from 8 bobbins were introduced into the chopper above the calender gap while being spaced 4 cm apart. The carbon fibre bundles were cut with rotating knives into filament packages of approximately 2.5 cm length. The chopped fibres fell randomly distributed onto the resin layers on the rolls after which the fibre material together with the resin mixture passed through the gap between the 2 rolls and was impregnated with the resin mixture. The bulk resin composition thus obtained was removed from the rolls by means of scrapers and packed. A carbon fibre loading of 17% by weight was achieved. Good wetting of the 8K packages with the resin mixture was distinctly visible up to the individual filaments. Thickening of the obtained compound took place in 7 days, after which the resin composition was moulded into a flat sheet. A homogeneously dark-grey coloured sheet was the result. From the flat sheet obtained test specimens were sawn, which were subsequently subjected to a bending test. Results of bending test (ISO 178): Flexural modulus 20 GPa Flexural strength 200 MPa The density of the material obtained was 1.79 g/cm3. Using the resin mixture of Example III, carbon fibre bundles from 8 bobbins with a non-split 24K carbon fibre bundle were now cut above the calender to a length of approximately 2.5 cm. The distance between the fibre bundles was 4 cm, as in Example III. Instead of a homogeneous fibre distribution over a width of 30 cm, now rather 8 xe2x80x9cstripesxe2x80x9d of fibre material were obtained, with in between them areas where scarcely any fibre bundles were to be found. A carbon fibre loading of 16% by weight was achieved. To avoid the formation of such areas with and without fibre bundles, the distance between the bundles in the chopper had to be reduced. When the bundle spacing was smaller than 1.5 cm a more homogeneous fibre distribution could be achieved, but impregnation of the fibres was found to be not well possible, which appeared from the large proportion of dry fibre bundles that were still present in the bulk compound obtained. Example I was repeated without any LPA being present. The resin mixture used had the following composition: The same compounding procedure and split, continuous carbon fibre bundles as in Example I were applied. A carbon fibre loading of 52% by weight was achieved. Good wetting of the 8K packages with the resin mixture was distinctly visible up to the individual filaments. Thickening of the compound obtained took place in 10 days, after which the resin composition was moulded into a flat sheet using a mould coverage of 40%. A homogeneously black-coloured sheet was the result. Test specimens were sawn from the flat sheet obtained, and these were subsequently subjected to a bending test and an ILSS test. Results of bending test (ISO 178): Flexural modulus 33 gpa flexural strength 530 mpa Results of ILSS test (ASTM 2344): 68 mpa