MOLDED BODY AND PROCESS FOR PRODUCING THE SAME

Abstract

The invention relates to the use of a fibre-reinforced composite (K) in a thermoforming process. Moreover, a process for thermoforming a fibre-reinforced composite (K) to a molded body (M) is disclosed, the process comprising at least the following steps: (i) Providing a fibre-reinforced composite (K) as described herein; (ii) Heating the fibre-reinforced composite (K) to a temperature (T3) at which the at least one substantially amorphous matrix polymer composition (B) is substantially softened; (iii) Thermoforming the fibre-reinforced composition (K) in a mold at a mold surface temperature (T4) in order to obtain a molded body (M); (iv) Releasing the molded body (M) from the mold; wherein the mold surface temperature (T4) is 50 C.

Claims

1-15. (canceled)

16. A fibre-reinforced composite (K) comprising: (A) 50 wt.-%, based on the total weight of the fibre-reinforced composite (K), of at least one continuous fibrous reinforcement material; (B)<50 wt.-%, based on the total weight of the fibre-reinforced composite (K), of at least one substantially amorphous matrix polymer composition having a glass transition temperature (Tg) of at least 100 C. and a melt volume-flow rate (MVR (220/10) according to ISO 1133) of 10 to 90 mL/10 min, wherein the at least one matrix polymer composition (B) comprises: (B1) 60 to 80 wt.-%, based on the total weight of the matrix polymer composition (B), of at least one copolymer of styrene and/or -methyl styrene and acrylonitrile having a number average molecular weight Mn of 30,000 to 100,000 g/mol; and (B2) 20 to 40 wt.-%, based on the total weight of the matrix polymer composition (B), of at least one copolymer of styrene, acrylonitrile, maleic acid anhydride, and/or maleic acid and optionally monomers comprising further chemical functional groups which are appropriate to interact with the surface of the at least one continuous fibrous reinforcement material (A) having a number average molecular weight Mn of 30,000 to 100,000 g/mol; and (C) optional additives; wherein the fibre-reinforced composite (K) is used as a starting material in a thermoforming process for the preparation of a molded body (M).

17. A process for thermoforming a fibre-reinforced composite (K) to a molded body (M) wherein the process comprises at least the following steps: (i) providing a fibre-reinforced composite (K) comprising (A) 50 wt.-%, based on the total weight of the fibre-reinforced composite (K), of at least one continuous fibrous reinforcement material; (B)<50 wt.-%, based on the total weight of the fibre-reinforced composite (K), of at least one substantially amorphous matrix polymer composition having a glass transition temperature (Tg) of at least 100 C. and a melt volume-flow rate (MVR (220/10) according to ISO 1133) of 10 to 90 mL/10 min, wherein the at least one matrix polymer composition (B) comprises: (B1) 60 to 80 wt.-%, based on the total weight of the matrix polymer composition (B), of at least one copolymer of styrene and/or -methyl styrene and acrylonitrile having a number average molecular weight Mn of 30,000 to 100,000 g/mol; and (B2) 20 to 40 wt.-%, based on the total weight of the matrix polymer composition (B), of at least one copolymer of styrene, acrylonitrile, maleic anhydride, and/or maleic acid and optionally monomers comprising further chemical functional groups which are appropriate to interact with the surface of the at least one continuous fibrous reinforcement material (A) having a number average molecular weight Mn of 30,000 to 100,000 g/mol; and (C) optional additives; (ii) heating the fibre-reinforced composite (K) to a temperature (T3) at which the at least one substantially amorphous matrix polymer composition (B) is substantially softened; (iii) thermoforming the fibre-reinforced composition (K) in a mold at a mold surface temperature (T4) in order to obtain a molded body (M); and (iv) releasing the molded body (M) from the mold; wherein the mold surface temperature (T4) is 50 C.

18. The process according to claim 17, wherein the temperature (T3) is below the decomposition temperature of the at least one substantially amorphous matrix polymer composition (B).

19. The process according to claim 17, wherein the temperature (T3) is in the range of 200 C. and 280 C.

20. The process according to claim 17, wherein the mold surface temperature (T4) is below the glass transition temperature (Tg) of the at least one substantially amorphous matrix polymer composition (B).

21. The process according to claim 17, wherein the mold surface temperature (T4) is above or equal to the glass transition temperature (Tg) of the at least one substantially amorphous matrix polymer composition (B), above the glass transition temperature (Tg) of the at least one substantially amorphous matrix polymer composition (B).

22. The process according to claim 21, wherein the process comprises the following process steps: (i) providing a fibre-reinforced composite (K); (ii) heating the fibre-reinforced composite (K) to a temperature (T3) at which the at least one substantially amorphous matrix polymer composition (B) is substantially softened; (iii) (a) thermoforming the fibre-reinforced composition (K) in a mold at a first mold surface temperature (T4) in order to obtain a molded body (M); and (b) reducing the temperature of the mold surface to a second mold surface temperature (T5) below the glass transition temperature (Tg) of the least one substantially amorphous matrix polymer composition (B) in order to solidify at least the surface of the molded body (M); and (iv) releasing the molded body (M) from the mold; wherein the first mold surface temperature (T4) is at least 10 to 50 C. above the glass transition temperature (Tg) of the at least one substantially amorphous polymer composition (B) and the second mold surface temperature (T5) is at least 5 C. below the glass transition temperature (Tg) of the at least one substantially amorphous polymer composition (B).

23. The process according to claim 22, wherein the mold surface temperature (T4) is within the range of 130 C. and 210 C.

24. The process according to claim 17, wherein the glass transition temperature (Tg) of the at least one substantially amorphous matrix polymer composition (B) is in the range from 100 C. and 150 C.

25. The process according to claim 17, wherein the process further comprises a process step, wherein a film is applied to at least one surface of the fibre-reinforced composite (K).

26. The process according to claim 17, wherein the process further comprises a process step, wherein the molded body (M) is further processed by applying a coating and/or a print on at least one surface of the molded body (M).

27. The process according to claim 17, wherein the molded body (M) is a molded body (M) having carbon-fibre look and wherein no post-processing is required.

28. The process according to claim 17, wherein the process the thermoforming of the molded body (M) is carried out directly following the process for the preparation of the fibre-reinforced composite (K).

29. A molded body (M), optionally having carbon-fibre look, prepared by a thermoforming process according to claim 17.

30. The molded body (M) according to claim 29, wherein the molded body (M) is used for structural and/or aesthetic applications.

Description

FIGURES

[0271] FIG. 1a shows a photograph of a fracture surface obtained in a fatigue test made with a composite material comprising a polyamide matrix.

[0272] FIG. 1b shows an enlarged section from the photograph of FIG. 1a.

[0273] FIG. 2a shows a photograph of a fracture surface obtained in a fatigue test made with a composite material according to the invention.

[0274] FIG. 2b shows an enlarged section from the photograph of FIG. 2a.

[0275] FIG. 3a shows a molded body prepared in accordance with the invention at a mold surface temperature of 160 C.

[0276] FIG. 3b shows a molded body prepared in accordance with the invention at a mold surface temperature of 190 C.

[0277] FIG. 4a shows a molded body prepared from a composite material comprising a polyamide matrix at a mold surface temperature of 160 C.

[0278] FIG. 4b shows a molded body prepared from a composite material comprising a polyamide matrix at a mold surface temperature of 190 C.

[0279] FIG. 5a shows a molded body prepared with a mold surface temperature of a mold surface temperature of 80 C.

[0280] FIG. 5b shows a molded body prepared in accordance with the invention at a mold surface temperature of 160 C.

[0281] FIG. 5c shows a molded body prepared in accordance with the invention at a mold surface temperature of 190 C.

EXAMPLES

General Procedures

[0282] Weight average molecular weight and number average molecular weight are measured via gel permeation chromatography on standard columns with monodisperse polystyrene calibration standards.

[0283] Melt volume-flow rates (MVR (220/10) are determined according to ISO 1133.

[0284] Viscosity numbers (VN) are generally determined according to DIN 53726 at 25 C., using a solution of 0.5% by weight polymer in dimethylformamide (DMF).

[0285] Vicat softening temperatures are generally determined as VST/B/50 according to ISO 306.

[0286] Mold shrinkage is generally determined according to ISO 294-4.

[0287] Polymer density is generally determined according to ISO 1183.

Mechanical Properties of the Fibre-Reinforced Composites

[0288] The following experiments were carried out on an intermittent hot press which is capable of producing a fibre/film composite of polymer film, melt or powder, for the quasi-continuous production of fibre-reinforced thermoplastic semi-finished products, laminates and sandwich panels.

Technical Data for Melt Intermittent Hot Press are:

[0289] Board width: 660 mm
Laminate thickness: 0.2 to 9.0 mm
Laminate tolerances: max. 0.1 mm corresponding to semi-finished product
Sandwich plate thickness: max. 30 mm
Output: approx. 0.1-60 m/h, depending on quality and construction thickness
Nominal feed rate 5 m/h
Tool pressure: Pressing unit 5-25 bar, infinitely variable for minimum and maximum
tool size (optional)
Mold temperature control: 3 heating and 2 cooling zones
Tool temperature: up to 400 C.
Tool length: 1000 mm
Opening press: 0.5 to 200 mm
Preferred production direction: right to the left

Technical Data of the Melt Plastification:

[0290] Discontinuous melt application in the middle layer for the production of fibre-reinforced thermoplastics semi-finished products

Screw diameter: 35 mm
Max. Displacement: 192 cm.sup.3
Max. Screw speed: 350 rpm
Max. Discharge current: 108 cm.sup.3/s
Max. Discharge pressure: 2406 bar specific
with:
Melt volume: 22 ccm
Isobar=pressure-controlled pressing process
Isochor=volume controlled pressing process
T [ C.]=temperature of the temperature zones*
(*The press has 3 heating zones and 2 cooling zones, in the production direction)
P [bar]=pressure per cycle: isochorous 20
S [mm]=travel limit Press thickness: 1.1 mm
Temperature profile: (i) 210 to 245 C., therefore approx. 220 C. [0291] (ii) 300 to 325 C., therefore about 300 C. [0292] (iii) 270 to 320 C., therefore about 280 to 320 C. [0293] (iv) 160 to 180 C. [0294] (v) 80 C.
T [sec]=pressing time per cycle: 20-30 s

[0295] Construction/lamination: 6-layer structure with melt middle layer; Manufacturing Process: direct melt

Components

Continuous Fibrous Reinforcement Material (A)

[0296] A1: glass fibre twill fabric 2/2 with area weight=approx. 290 g/m.sup.2 (type: 011020800-1240, producer: Hexcel, obtained from Lange+Ritter).

[0297] A2: glass fibre twill fabric 2/2 with area weight=approx. 320 g/m.sup.2 (type: EC14-320-350; producer: PD Glasseide GmbH Oschatz).

[0298] A3: glass fibre non-woven fabric with surface area weight=approx. 50 g/m.sup.2 (type:

[0299] Evalith S5030, producer: Johns Manville Europe).

Matrix Polymer (B)

[0300] B1: Styrene/acrylonitrile (S/AN) copolymer having the composition 76% by weight of styrene (S) and 24% by weight of acrylonitrile (AN), Mw of 135,000 g/mol (measured by gel permeation chromatography on standard columns with monodisperse polystyrene calibration standards); MVR (220/10)) of 64 mL/10 min (determined according to ISO1133); viscosity number (determined in DMF according to DIN 53726) VN=64 g/ml.

[0301] B2: Styrene/acrylonitrile/maleic anhydride (S/AN/MSA) copolymer having the composition (wt.-%): 75/24/1; Concentration of functional groups: 1 wt.-% of MSA (98.1 g/mol) in 75 wt.-% of S (104.2 g/mol) and 25 wt.-% of AN (53.1 g/mol), Mw of 131.000 g/mol, Mn of 58.000-60.000 g/mol (measured by gel permeation chromatography on standard columns with monodisperse polystyrene calibration standards); MVR (220/10)) of 22 mL/10 min (determined according to ISO1133); viscosity number (determined in DMF according to DIN 53726) VN=80 g/ml.

[0302] B3: blend of B1 and B2 in a ratio B2:B1=1:2, concentration of functional groups: 0.33% by weight of MSA, MVR (220/10)) of 50 mL/10 min (determined according to ISO1133); viscosity number (determined in DMF according to DIN 53726) VN=65 g/ml.

[0303] B4: Styrene/acrylonitrile/maleic anhydride (S/AN/MSA) copolymer having the composition (wt.-%): 73.9/24/2.1; Concentration of functional groups: 2.1 wt.-% of MSA (98.1 g/mol) in 73.9 wt.-% of S (104.2 g/mol) and 24 wt.-% of AN (53.1 g/mol), Mw of 116,000 g/mol, Mn of 50.000-64.000 g/mol (measured by gel permeation chromatography on standard columns with monodisperse polystyrene calibration standards); MVR (220/10)) of 22 mL/10 min (determined according to ISO1133); viscosity number (determined in DMF according to DIN 53726) VN=80 g/ml.

[0304] PC(OD): easy-flowing, amorphous polycarbonate (optical grade for optical discs).

[0305] PA6: semi-crystalline, easy-flowing polyamide Durethan B30S.

[0306] The following fibre-reinforced composites were produced in order to investigate the E-modulus and the flexural strength, into which respective flat fibre material was introduced. The fibre composite materials produced each had a thickness of about 1.1 mm. For the preparation of the black samples, 2% by weight of carbon black was added to the polymer matrix.

TABLE-US-00001 TABLE 1 Design of the studied fibre-reinforced composites. Amount MSA in Fibre Example of glass matrix Thickness content No. Fabric Layup [g/m.sup.2] Matrix [wt.-%] [mm] [Vol.-%] Color 1 A3/4 A1/A3 1260 B3 0.33 1.09 45.33 black V1 A3/4 A1/A3 1260 B2 1.00 1.06 46.41 black V2 A3/4 A1/A3 1260 B2 1.00 1.09 45.22 transparent V3 A3/4 A2/A3 1380 PC(OD) 1.14 44.56 transparent V4 A3/4 A2/A3 1380 PA6 1.11 45.68 black

[0307] For the samples described in Table 1, the following mechanical properties were determined according to DIN EN ISO 14125.

TABLE-US-00002 TABLE 2 Mechanical properties of the studied fibre- reinforced composites according Table 1. E-Modulus Flexural strength Example No. [GPa] [MPa] 1 19.76 628.81 V1 21.96 675.92 V2 19.81 677.91 V3 23.36 377.97 V4 16.95 471.97

[0308] In summary, the fibre-reinforced composites according to the invention, in which the matrix polymer is formed from a blend of an S/AN copolymer and an S/AN/MSA copolymer, exhibit particularly high flexural strength and E-modulus compared to conventional fibre-reinforced composites having polycarbonate or polyamide matrices. Compared to polymer matrices comprising pure S/AN/MSA, the fibre composite materials according to the invention, are characterized by having a high melt-volume flow rate and a low viscosity number without having deteriorative effects on the mechanical properties. This combination was not achievable by pure S/AN/MSA copolymers. Example 1 and Comparative Examples V1 and V2 exhibit similar mechanical properties. However, the MVR (50 mL/10 min for Example 1 and 22 mL/10 min for Comparative Examples V1 and V2) as well as the viscosity numbers VN (65 g/mL for Example 1 and 80 g/mL Comparative Examples V1 and V2) attest to the better processability of the fibre-reinforced composites according to the invention.

[0309] In addition, the impact resistance or the penetration behavior (Dart test according to ISO 6603) was determined for the fibre-reinforced composite materials having the composite designs given in Table 3.

TABLE-US-00003 TABLE 3 Composite design of the studied fibre-reinforced composites for the dart test. Amount of MSA in Example glass matrix Thickness No. Fabric Layup [g/m.sup.2] Matrix [wt.-%] [mm] 2 A3/4 A2/A3 1380 B3 0.33 1.20 V5 A3/4 A2/A3 1380 B2 1.00 1.21 V6 A3/4 A2/A3 1380 B4 2.10 1.09 3 A3/4 A1/A3 1260 B3 0.33 1.09 V7 A3/4 A1/A3 1260 B2 1.00 1.07 V8 A3/4 A1/A3 1260 B4 2.10 1.07 V9 A3/4 A2/A3 1380 PC(OD) 1.2 V10 A3/4 A2/A3 1380 PA6 1.14

[0310] The measured experimental data are summarized in Table 4.

TABLE-US-00004 TABLE 4 Experimental data from the dart test according to ISO 6603. Fm Em Ep Example No. [N] [J] [J] 2 4725.13 9.56 14.47 V5 4760.84 10.24 15.77 V6 4649.99 9.29 14.29 3 3674.09 6.21 9.63 V7 3512.75 6.12 8.95 V8 3742.46 6.54 9.65 V9 5428.50 13.26 18.73 V10 3680.23 7.13 9.92

[0311] As can be seen from the above data, the fibre-reinforced composites according to the invention exhibit a high stability of Fm>3000 N which is comparable to known composite materials which have higher viscosities and are therefore more difficult to be processible and to obtain a sufficient impregnation.

[0312] Similar results were obtained for fibre-reinforced materials comprising fibrous reinforcement materials based on carbon fibres.

Visual Evaluation

[0313] All of the fibre composite materials produced could be produced in the form of a (large) planar composite material in a continuous process which could be cut to size without any problem (in laminable, transportable dimensions, such as 1 m0.6 m). In the case of transparent fibre composite materials, the embedded fibre material was precisely recognizable when viewed in the backlight. In the case of the fibre composite materials with (black) colored matrix, the embedded fibre material was not recognizable even with closer optical observation in the backlight.

Microscopic Evaluation

[0314] Defects (voids, incidence, etc.) were evaluated by means of reflected-light microscopy and surface quality by confocal laser scanning microscopy (LSM). A three-dimensional (3D) height survey (7.2 mm7.2 mm) of the local measuring range and a two-dimensional (2D) representation of the height differences were calculated by means of LSM after scaling and application of different profile filters. Measurement errors and a general warpage/skew position of the sample were compensated by the use of profile filters (noise filter). The 2D elevation profile of the image was transferred via an integrated software lines into line profiles and evaluated computer-supported.

[0315] Fibre-reinforced composites each having a layup according to Example 1 as well as Comparative Examples V1, V3 and V4 described in Table 1 were tested. For each example, nine test specimens were evaluated. The mean wave depth (Wd) and the average roughness (Rg) were determined and summarized in Table 5.

TABLE-US-00005 TABLE 5 Results of the LSM measurements. Example 1 V1 V3 V4 MW Wd [m] 4.573 4.827 11.745 12.323 MW Rg [m] 3.583 4.019 6.406 4.968

[0316] The mean wave depth (Wd) observed in Example 1 had a value of 4.573 m, thus being significantly lower than 10 m and more than 5% smaller than the mean wave depth (Wd) observed in Comparative Example V1. Composite materials comprising PA6 and PD (OD) matrices typically have mean wave depth (Wd) of >10 m. The determined average roughness (Rg) had a value of 3.583 m for Example 1 and is also significantly lower for fibre-composite materials according to the invention, e.g. more than 10% smaller than average roughness (Rg) observed in comparative Example V1.

[0317] Similar results were obtained for fibre-reinforced materials comprising fibrous reinforcement materials based on carbon fibres.

Tensile Tests and Compression Tests

[0318] Fibre-reinforced composites having a composite design similar to Example 1 were studied in Tensile Tests according to DIN EN ISO 527-4 in two directions (0 and 90). The test sample had a thickness of about 2 mm and the testing speed was 2 mm/min.

[0319] Fibre-reinforced composites having a composite design similar to Example 1 were also studied in Compression Tests according to DIN EN ISO 14126 in two directions (0 and 90). The test sample had a thickness of about 2 mm and the testing speed was 1 mm/min.

[0320] At least six samples were studied for each test and the mean values were calculated. The test results are summarized in Table 6.

TABLE-US-00006 TABLE 6 Experimental data form the Tensile Test and the Compression Test. 0 direction 90 direction Strength E-Modolus Strength E-Modolus Testing method [MPa] [GPa] [MPa] [GPa] Tensile Test 488.8 24.6 350.6 23.3 (DIN EN ISO 527-4) Compression 521.8 26.6 369.3 26.4 Test (DIN EN ISO 14126)

[0321] As can be seen from the above results, the E-modulus as well as the stability of the testing sample was higher in the compression tests than in the tensile test, i.e. the samples have a higher compressive strength than tensile strength in the 0 direction as well as in the 90 direction. This behavior is typically not observed for conventional fibre-reinforced thermoplastic composite materials. This specific property gives rise to improvements in applications wherein compression forces have to be compensated, e.g. in the protection against accidents.

Evaluation of the Fracture Surface

[0322] Fibre-reinforced composites were studied in Fatigue Tests in a 4-point bending test according to DIN EN ISO 14125 until fracture occurred.

[0323] As test samples, two plates of glass fibre-reinforced SAN-composites having a strength of 2 mm were grouted to a plate of 3.85 mm.

[0324] As a comparative sample, fibre-reinforced composites comprising a PA6 matrix having a strength of 4.45 mm were studied.

[0325] The fracture surfaces of the test samples were studied by microscopy and photographs were made. Photographs of the fracture surfaces are depicted in FIG. 1a, 1b and FIG. 2a, 2b, respectively.

[0326] The photographs were evaluated by visual methods.

[0327] As can be seen from FIG. 1a and FIG. 1b, the fracture surface of a sample comprising a polyamide matrix (PA6) exhibits numerous long reinforcement fibre endings, which protrude from the surface after fracture has occurred. This indicates an insufficient adhesion between the polymer matrix and the fibres within the fibre-reinforced material. It was determined by visual inspection of the photograph of FIG. 1b, that more than 10% of the reinforcement fibres protrude from the fracture surface with a length of at least 5 times the diameter of the respective fibre.

[0328] On the contrary, FIG. 2a and FIG. 2b reveal that the fibre-matrix adhesion is significantly higher in the fibre-reinforced composites (K) according to the present invention. As can be seen in the photographs, the reinforcement fibre endings at the fracture surface are short and protrude only very little from the surface. It was determined by visual inspection of the photograph of FIG. 2b, that less than 10% of the reinforcement fibres protrude from the fracture surface with a length of more than 5 times the diameter of the respective fibre.

Evaluation of the Molding Properties of the Fibre-Reinforced Composites

[0329] The preparation of molded bodies (M) from fibre-reinforced composites having a composite design similar to Example 1 were studied.

[0330] The deformation properties at temperatures of 125 C., 150 C. and 175 C. were evaluated in a study determining the bending deformation under gravity. A sample (size: approximately 151 mm50 mm1 mm) was mounted only on one side. The sample was subjected to the temperatures specified in Table 7 and the deformation was determined by comparing the deformation prior to the test (traverse 0) and after 10 min (traverse 1). Three samples were tested for each temperature. The values given in Table 7 are averaged.

TABLE-US-00007 TABLE 7 Deformation property evaluation at different temperatures. Example Temperature Traverse 0 Traverse 1 4 125 C. 1.2 mm 1.2 mm 5 150 C. 1.2 mm 12.5 mm 6 175 C. 1.2 mm 105.5 mm

[0331] As can be seen from the above data, no deformation occurs at a temperature of 125 C. Thus, this temperature is not sufficient in a process for the preparation of a molded body without application of pressure. On the contrary, sufficient deformation is observed at 150 C. and 175 C.

[0332] More importantly, no decomposition, degassing and/or dripping of the matrix material was observed. The characteristics were highly reproducible.

Preparation of Molded Bodies (M)

[0333] Molded bodies (M) were prepared from different fibre-reinforced composite materials using a forming press with IR emitter field having the following set-up:

Discontinuous Conversion of Fibre-Reinforced Thermoplastic Semi-Finished Products

[0334] Pressing force: 20 to
min./max. Pressure: 5/200 N/cm2
Working area: 350300 mm
Max. Press stroke: 300 mm
Close speed: 70 mm/s
Pressing speed: 8 mm/s
Opening speed: 130 mm/s
Temperature heating plates: 400 C.
Technical data of the forming tool:
Semi-finished dimensions: 190156 mm
Laminate thickness: 1.0 mm
Laminate tolerances: max. 0.05 mm corresponding to the semi-finished product
Oil temperature: up to 300 C.

[0335] Sample of fibre-reinforced composites of the size 190 mm156mm1.1 mm having the following lay-up were used:

TABLE-US-00008 TABLE 8 Composite design of the fibre-reinforced composites used for thermoforming studies. MSA in Example matrix No. Fabric Layup Matrix [wt.-%] Color 7 A3/4 A1/A3 B3 0.33% transparent 8 A3/4 A1/A3 B3 0.33% black 9 A3/4 A2/A3 B3 0.33% transparent 10 A3/4 A2/A3 B3 0.33% black V11 A3/4 A1/A3 B2 1 transparent V12 A3/4 A2/A3 PA6 black

[0336] Molded bodies were prepared with the process parameter given in Table 9.

TABLE-US-00009 TABLE 9 Thermoforming process parameter. SAN matrix (Ex. 7 to 10, PA6 matrix Parameter Comp. Ex. V11) (Comp. Ex. V12) Heating time 45 s both sides 45 s both sides (IR heating) Nominal temperature 240 C. 260 C. of the composite material Pressure 200 N/cm.sup.2 200 N/cm.sup.2 Cooling time 30 to 155 s 30 to 155 s (depending on (depending on mold surface mold surface temperature) temperature)

[0337] Molded bodies were prepared at mold surface temperatures of 160 C., 190 C. and 220 C. All molded bodies were processable. However, as can be seen from FIG. 3a and FIG. 3b, depicting molded bodies according to Example 10 prepared at 160 C. (FIG. 3a) and 190 C. (FIG. 3b), respectively, high quality molded bodies having smooth surfaces were obtained. By contrast, molded bodies prepared from Comparative Example V12 at 160 C. (FIG. 4a) and 190 C. (FIG. 4b), exhibit clearly inferior surface qualities. Thus, although the molded bodies according to the present invention were prepared at lower nominal temperatures of the composite material and thus in a process which demands less energy and less cycle time, the quality of the molded bodies is superior compared to conventional molded bodies having a polyamide matrix.

Variotherm Process

[0338] Molded bodies were prepared at in a variotherm process having a mold surface temperature of the thermoforming mold of 80 C., 160 C. and 190 C. As starting materials, the fibre-reinforced composites according to Example 1 and Comparative Example V8 were used. The composite of Comparative Example V8 was thermoformed with a surface temperature of the thermoforming device of 80 C. and a pressure of 200 N/cm.sup.2. The obtained molded body is depicted in FIG. 5a. The composite according to Example 1 was thermoformed with a surface temperature of the thermoforming device of 160 C. and 190 C. a pressure of 200 N/cm.sup.2, which is then cooled under pressure to a temperature of 80 C. The obtained molded body is depicted in FIG. 5b (prepared at 160 C.) and FIG. 5c (prepared at 190 C.). As can be seen from the photographs, the molded bodies obtained in the variotherm process exhibit high-quality surfaces. These may not be achieved in conventional processes. This effect may be attributed to the instant solidification of the surface of the heated fibre-reinforced composites if they are contacted with mold surfaces having a low temperature, e.g. a temperature as low as 80 C. The variotherm process allows thermoforming of the fibre-reinforced composite to a molded body (M) and thereafter cooling the surface of the molded body (M) under pressure in a controlled and fast manner without deterioration of the quality of the surface of the molded body. The cycle time is not significantly increased by the variotherm process and may further be improved by a variotherm process using an inductive heating device.