EP3052302A1

EP3052302A1 - Method for making a highly finished surface article of an advanced composite material

Info

Publication number: EP3052302A1
Application number: EP13828926.9A
Authority: EP
Inventors: Paolo Canonico; Salvatore OMAGGIO; Davide BRIVIO
Original assignee: Composite Materials Italy SRL
Current assignee: Composite Materials Italy SRL
Priority date: 2013-10-04
Filing date: 2013-12-16
Publication date: 2016-08-10
Also published as: ITMI20131648A1; JP6241690B2; WO2015049550A1; JP2016535119A

Abstract

A method for making highly finished surface parts of an advanced composite material comprises the step of coupling a fibrous base material layer with a further layer impregnated by a resin system identical to or compatible with that used for making the part, and directly crosslinking the part made of the advanced composite material. The method is used for making motor vehicle body parts starting from a composite material, but can also be used in the nautical, sports and aeronautical fields. The method according to the present invention reduces or completely eliminates a visibility of reinforcement fibers on the surface of the article of manufacture thus made.

Description

METHOD FOR MAKING A HIGHLY FINISHED SURFACE ARTICLE OF AN ADVANCED COMPOSITE MATERIAL

BACKGROUND OF THE INVENTION

The present invention relates to a method for making a highly finished surface article of an advanced composite material and the advanced composite material article made thereby.

As is known, in the motor vehicle field, the motor vehicle components are conventionally classified based on their surface quality and, accordingly, on the aesthetic requirements they must meet.

Three motor vehicle classes are usually identified, that is the classes A, B and C.

The class A is related to the visible motor vehicle parts, such as, for example, motor vehicle bonnets .

The class B is also related to vehicle visible parts, but the aspect of which is not considered essential, such as, for example, the door opening recess.

The class C is related to the motor vehicle non-visible parts, such as, for example, the joints of the motor vehicle seats.

The surface quality is evaluated based on a human observation of images reflected from the motor vehicle body parts, under controlled illuminating conditions .

The class A surfaces are so designed as to provide an alignment between the bent and tangent lines, so as to give a perfect reflection quality. Moreover, the class A surfaces are free of undesirable waviness patterns and have a continuous bending in each direction.

This means that each point along a shared line has the same bending radius.

The main drawbacks of advanced composite materials for making class A motor vehicle body parts are the following:

- the presence of surface defects such as dottings and pores, which make the part unacceptable for surface portions of a motor vehicle;

- a possible delaminating ;

- the presence of joining lines;

- the presence of a visible surface waviness.

Thus, making class A surfaces starting from an advanced composite material can cause greater difficulties in comparison with conventional approaches.

This is due to the double nature of the part matrix and reinforcement therefor, which causes the product to have a number of variables much greater than that of the component materials, such as, for example, steel and aluminium.

Moreover, the reinforcement fibers may generate visible traces on the part surface, preventing the part from being used for class A finished surfaces.

In this connection it should be pointed out that the surface finishing level must be held constant for the whole motor vehicle life period.

In fact, the aesthetic details of the outer surfaces of motor vehicles must resist against ageing while remaining in contact with atmospheric agents and wet environments and, in addition, should also be nearly insensible to the effects of temperature and humidity sudden changes.

The making of motor vehicle parts of advanced composite materials, with high aesthetic properties, meeting the class A surface requirements, provides to use several custom designed additional solutions in the part molding and preparing steps.

The prior art approaches for achieving the above purpose depend on the motor vehicle parts to be made and the skill and making capability of the maker.

Further aspects are related to one or more of the hereinbelow mentioned items.

A use of one or more polymeric films to be arranged on the mold and spread in a laminating step and arranged between the mold surfaces, after having coated a separating film and a so-called "prepreg".

A spreading of the so-called "gelcoats" on the mold surface, which requires to use a further resin layer for covering the mold before laminating the prepreg to be fitted thereon.

A further machining of the molded piece or part: a further spreading of a primer, or a pre-smoothing operation, for eliminating possible surface defects or pores .

Thus, the method for making class A composite material parts further comprises one or more additional processing or machining steps performed by very long and complex operations, causing the making cost to greatly increase.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide such a method for making advanced composite material parts having a high surface finishing, which method is specifically designed for making motor vehicle body parts .

Within the scope of the above mentioned aim, a main object of the invention is to provide such a method adapted to make motor vehicle body parts having both a very high surface finishing and a very high size stability.

Another object of the present invention is to provide such an article or product, made by the inventive method, having both a very good impact resistance or resilience and a very good stiffness.

Yet another object of the present invention is to provide such a method allowing to make motor vehicle body parts at a much smaller cost than that of prior making systems and methods.

According to one aspect of the present invention, the above mentioned aim and objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by a method for making, by molding, a part coupled to two layers, in particular of a motor vehicle body, of an advanced composite material and having a high surface finishing, said method comprising coupling, by an impregnating hot-melt machine, a first layer of a fibrous base material and a second layer of a pre-impregnated coupled composite material, or prepreg, forming the outermost portion of said coupled part, that is that portion contacting the mold in the molding process and which, in a finished condition, has high surface finishing characteristics; said first layer being impregnated by an impregnating resin system identical to and compatible with that impregnating said second layer and being polymerized or cross-linked simultaneously with said second layer; said method comprising moreover the step of operating said impregnating hot-melt machine at an operating speed of 2-4 meters/min; said resin system consisting of a hot- melt epoxy resin forming from 40 to 65% of the weight of said coupled part.

The method according to the present invention is particularly useful for making motor vehicle body parts starting from a composite material, but it can also be used in the nautical, sports and aeronautical fields.

The method according to the present invention greatly reduces or fully eliminates the visibility of reinforcement fibers on the article surface.

The above aim and objects, as well as yet other objects which will become more apparent hereinafter, are also achieved by an advanced composite material product or article made by the inventive method.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will become more apparent hereinafter from the following detailed disclosure of a preferred, though not exclusive, embodiment of the invention, which is illustrated, by way of an indicative but not limitative example, in the accompanying drawings, where:

Figure 1 shows a table wherein temperatures, pressures, heating and cooling ramps of an autoclave cross-linking cycle, according to a first embodiment of the present invention, are shown;

Figure 2 is a diagram diagrammatically 3 002801

illustrating the operating steps shown in the table of Figure 1;

Figure 3 shows a further table indicating temperatures, pressures, heating and cooling ramps of an autoclave polymerizing or cross-linking cycle of a second embodiment of the present invention; and

Figure 4 is a further diagram diagrammatically showing the operating steps shown in the table of Figure 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The components of a composite material are separated by a well defined separating interface having a substantially zero thickness, each of said components having chemical-physical properties different from one another at a macroscopic and structural level.

More specifically, the individual components forming a composite material are herein called "the matrix" and "the reinforcement".

The coupling or joining of the above components or materials will provide a solid continuous material, adapted to transmit and redistribute the inner strains due to outer stresses.

The reinforcement material comprises a dispersed phase, which is variously dispersed through the matrix and is so designed as to provide the composite material with a target stiffness and mechanical strength.

More specifically, the composite materials used in the present invention are made of a reinforcement material consisting of a dispersed fibrous phase.

The fibers of said dispersed fibrous phase comprise solid and resistant bodies of an elongated shape, that is having a longitudinal dimension prevailing with respect to the cross dimension, and providing the composite material with the desired strength and stiffness.

The reinforcement material, in particular, may comprise, by way of an example:

- glass fibers;

- carbon fibers (consisting of graphitic carbon and amorphous carbon) ;

- ceramic fibers (for example silicon carbide or alumina) and aramidic fibers (such as Kevlar) ;

- basalt fibers.

To achieve the desired continuity and strength characteristics, the fibers are joined to form fiber beams, in the form of parallel fiber threads or of twined fibers.

The reinforcements used for preferred applications according to the present invention comprise the following materials:

- unidirectional reinforcements: fiber beams all arranged in the same direction;

multi-axial reinforcements: consisting of overlapped unidirectional reinforcements;

- fabrics: fibers woven therebetween.

The matrix comprises a homogeneous continuous phase operating as a filling material.

Such a material is at the start in the form of a viscous fluid, properly filling all the spaces and perfectly adhering to the fibers.

The matrix is subjected to a solidifying process providing the construction with stability and well defined geometric properties. The matrix types used for preferred applications according to the present invention mainly consist of polymeric matrix . composite materials, such as thermoplastic materials (such as Nylon and ABS) or thermosetting materials (such as epoxy resins) .

The joining of the resin to the reinforcement, consisting either of unidirectional, multiaxial fibers or woven fibers, may be performed during the component making, by conventional manual impregnating methods, or operating steps preceding the making of the piece.

The materials included in this second class are defined "preimpregnated" or "prepreg" materials.

The fibers forming the above materials are impregnated by an industrial process which, besides using a proper fiber amount, arranges the impregnating resins in an even manner.

The present invention also relates to a coupled preimpregnated (prepreg) material forming the outermost portion of the article to be made, that is that portion contacting the mold during the piece molding process and which, on the finished piece, will have high finishing surface characteristics.

The coupling is performed in the prepreg making method, and, accordingly, in impregnating said prepreg, and is related to the conventional support, consisting either of unidirectional, multiaxial fibers or woven fabrics, and a fibrous material layer, consisting either of a non-woven material, a felt material or any materials having similar characteristics.

In addition, said support and coupled layer can also comprise carbon, glass, aramidic fibers or any fibers used for making advanced composite materials. The making of said prepreg further comprises a short heating of pre-processed fibers, by heating ovens, so as to provide a first partial cross-linking of the matrix: this operating step provides the product with the reguired compactness while fully eliminating residual air bubbles and allowing the material to be further processed without altering its characteristics.

The fibrous material layer used in such an embodiment has the following characteristics:

- it comprises randomly arranged non-woven fibers having a fiber length from 6 to 12 mm;

- the fibers are bound by a PVA (polyvinyl alcohol) binder material;

- it is compatible with epoxy resin systems used in advanced composite materials;

- it is a flat and porous layer absorbing the resin in a very good manner;

- it has a layer weight typically ranging from 10 to 50 g/m².

The chosen material is impregnated by an epoxy resin system, modified by an addition of a proper amount of inert materials such as:

Phyllosilicates, a silicon, aluminium and potassium oxide mixture;

- Hollow glass microspheres having a maximum diameter of 30 micrometers.

The above characteristics make such an epoxy system an ideal one for aesthetic applications, since it has an increased resistance against ageing due to the temperature and humidity sudden changes.

Moreover, the use of inert materials provides a covering effect for the resin system with respect to the fabric, while minimizing the fiber surface projection, which would be an unacceptable phenomenon for class A finished surfaces.

Moreover, the subject system is compatible with other epoxy systems forming the remaining part of the article of manufacture.

Furthermore, the chosen . material allows to perform a standardized crosslinking operating cycle, for example in an autoclave, a vacuum bag and a hot press.

The finished surface of the part thus made has a very good surface quality, free of white spots, even after a processing in a water bath (two hours in boiling water or 30 days at room temperature) .

Moreover, the possibility of achieving class A motor vehicle body parts made of an advanced composite material, directly from the mold, provides further great advantages, for example a great reduction of manual machining time during the part layering and finishing operating steps.

In addition, the process is very simple, quick and inexpensive.

The coupling according to the present invention provides a direct connection to the prepreg used, while greatly reducing the machining time.

In fact, during the mold preparing step, it is not necessary to use a polymeric film to be arranged on the mold surface.

In addition, during the mold preparing step, it is not necessary to spread a gelcoat on the mold surface.

Downstream of the molding process, no further machining operation on the part, in addition to the conventional sanding and painting operations, is required.

The material and process must be accurately designed to provide the desired high surface finishing degree for the overall lifetime duration of the motor vehicle.

Besides solving the surface quality and finishing problem, the use of the above mentioned advanced composite material, owing to the optimization of its properties and making process, allows to further achieve a design flexibility which cannot be achieved in prior approaches using metal materials.

In particular, the advantages achieved comprise an optimization of the mechanical stress resistance, an optimum balancing of the stiffness and weight ratio, and an improved freedom in designing the motor vehicle body parts.

The above mentioned polymerizing/crosslinking cycle is a process in which the resin of the prepreg changes from a liquid to a solid status by applying heat .

Standard processing methods provide to perform the crosslinking cycle in an autoclave, a hot press or a vacuum bag.

The operating steps of each processing cycle will be briefly disclosed hereinbelow.

Polymerizing or crosslinking temperature and time

For each prepreg resin system, different crosslinking temperatures and times may be used.

The overall part, made of prepreg, and the related mold must be held at the crosslinking temperature for the time required by any resin system. The heating speed is a measurement of the time required for the part being made to achieve the polymerizing or crosslinking temperature.

This operating step is controlled by different parameters, such as, for example:

- the matrix viscosity;

- the matrix reaction time;

- the thickness of the part being made;

- the inertia and thermal conductivity of the mold.

The cooling speed or rate is so controlled as to prevent any sudden temperature changes from causing a mechanical stress within the composite material part. .

The operating steps defined for each different crosslinking cycle of each resin system, and related vacuum and pressure conditions must be either applied or removed.

The adequacy of this solution to the intended objects has been verified by means of evaluating parameters adopted for aesthetic finishing in a direct contact with atmospheric agents, in particular for aesthetic components on the motor vehicle outer surface, achieved by painting, in the motor vehicle color or with any desired chromatic effects, colors and aspects.

The parts made have been subjected to a further visual inspection at the end of the accelerated ageing procedures disclosed hereinbelow.

More specifically, the visual examination evaluates the aspect of the part under test: the requirements to be met provide that the examined part surface be a continuous and even one, free of surface and aesthetic defects.

The accelerated ageing procedures used a climatic chamber for the operating cycles here below:

- a humidity resistance:

- 20 cycles of 12 hours; each cycle providing to hold the temperature at 40°C and relative humidity at 98%;

- a resistance to the temperature variations:

- 20 cycles of 12 hours.

Each cycle comprises:

1) holding for 40 minutes at a temperature of 23°C and relative humidity of 30%;

2) switching to a temperature of 35°C in 90 minutes ;

3) holding for 60 minutes at a temperature of

35°C;

4) further switching to a temperature of 45 °C and a relative humidity of 80% in 80 minutes;

5) holding for 120 minutes at a temperature of 45°C and a relative humidity of 80%;

6) further switching to a temperature of 90°C and relative humidity of 30% in 30 minutes;

7) holding for 240 minutes at a temperature of 90°C and relative humidity of 30%;

8) further switching to a temperature of 23 °C and relative humidity of 30% in 60 minutes.

Downstream of the above disclosed procedures, no variations of the surface such as spots, blistering or any other alterations of aesthetic finishing have been observed.

Example 1

A coupled woven and non-woven carbon material and impregnating by a modified epoxy resin.

A carbon woven or fabric material: a 2x2 twill weave, with a weight from 180 to 400 g/m² (A) ;

A carbon non-woven material: a weight from 20 to 50 g/m² (B) ;

The epoxy resin characteristics were:

Volatile substances in the prepreg (%wt) <1

Resin density (g/cm³) 1.2

Tg (DSC)* ( ° C ) 135

TgE' (DMA)** (°C) 125

Peak Tg of Tan δ (DMA)** (°C) 146 * Dynamic scanning

** Fully cross-linked laminate

Temperature (°C) Gel time (min)

100 87

110 56

120 21

130 8.75

Resin contents: from 45% to 65% of the end weight of the overall coupled impregnated material.

Impregnating and coupling process

The impregnating process of the coupled material

A + B of this example is carried out by two different consecutive process stages, with an impregnating hot melt machine speed from 2 to 4 meters/min:

1 - impregnating the carbon fabric A (with a support function) : the amount of resin deposited on the support corresponds to an amount from 40% to 50% of the end weight of the impregnated fabric; the cylinder pressure being set from 2 to 6 bars;

2 - coupling the carbon non-woven material B to said support A and impregnating said non-woven material by an amount of impregnating resin, having the same composition as that used in the preceding stage or step, from 70% to 90% of the impregnated non-woven material weight; with a cylinder pressure set from 1 to 4 bars.

A possible laminating sequence suitable for using the solution disclosed in the previous example comprises:

1 - the woven/non-woven material coupling solution A + B made as above disclosed;

,2 - a carbon fabric or woven material B impregnated by an impregnating resin having a composition compatible with the previously disclosed one .

The method according to this exemplary embodiment comprises to make a motor vehicle body part as schematically disclosed hereinbelow, starting from the outside of the finished part, and accordingly from the mold surface:

1. [0°C]1 carbon non-woven material + carbon woven material (A + B)

2. [90°C]5 carbon woven material (B)

Suggested autoclave crosslinking operating cycle

A possible crosslinking cycle providing an efficient solution is disclosed hereinbelow.

This operating sequence depends on the resin system used and accordingly it is shown only by way of an indicative but not limitative example, since it is a peculiar characteristic of the epoxy resin used in the process herein disclosed.

The suggested process stages are disclosed in the Table of Figure 1, indicating the temperatures, pressures, heating and cooling ramps; to provide the best aesthetic yield on the mould contacting surface it is necessary to properly remove vacuum in case the crosslinking operating cycle is carried out in an autoclave .

The diagram of Figure 2 graphically shows the operating steps disclosed in the preceding Table.

Example 2

Unidirectional reinforcement (UD) and carbon non-woven coupled materials; an impregnating by a modified epoxy resin:

an unidirectional carbon reinforcement material: with a weight from 120 to 400 g/m² (C) ;

a carbon non-woven material: with a weight from 15 to 70 g/m² (D) ;

Characteristics of the epoxy resin:

Volatile substances in the prepreg (%wt) <1 Resin density (g/cm³) 1.23

Tg (DSC)* (°C) 181

TgE' (DMA)** (°C) 167

Peak Tg of Tan δ (DMA) (°C) 184

* Dynamic scanning

Fully cross-linked laminate

Temperature ( ° C) Gel time (min)

80 400

100 85

120 17

135 5.5

150 4

Resin contents: from 40% to 60% of the end weight of the overall coupled impregnated material. Impregnating and coupling process

The impregnating process for impregnating the coupled material C + B of this Example is carried out in two different following process stages, with a hot melting impregnating machine speed from 2 to 4 m/min:

1 - impregnating the unidirectional carbon reinforcement material C (with a support function) : the amount of resin deposited on the support corresponds to an amount from 30% to 40% of the end weight of the impregnated reinforcement material;

2 - coupling of the carbon non-woven material D to the preceding support C and impregnating thereof with an amount of resin of a composition identical to that used in the preceding step or stage, from 70% to 90% of the impregnated non-woven material weight.

A possible suggested laminating sequence

A possible laminating sequence herein suggested to be used in the solution of this Example provides to use :

1 - the UD/non-woven material coupling solution

C + D made as above disclosed;

2 - a carbon woven or fabric material, similar to the type B disclosed in Example 1, impregnated by a resin having a composition compatible with the preceding one .

The process comprises to make a motor vehicle body part as hereinbelow schematically disclosed, starting from the outside of the finished part, and accordingly from the mould surface:

1. [0°C]1 carbon non-woven material + UD reinforcement (C + D)

2. [90°C]4 carbon woven material (B) or, alternately:

1. [0°C]1 carbon non-woven material + UD reinforcement (C + D)

2. [90°C]2 carbon woven material (B)

3. [90°C]1 UD reinforcement material (C)

Suggested autoclave crosslinking cycle

This sequence is a characteristic one and strictly depends on the resin system used and accordingly it should be considered as an indicative and merely exemplary one, since it is a peculiar characteristic of the epoxy resin used in the process herein disclosed.

The suggested process stages are shown in the

Table of Figure 3, indicating temperatures, pressures, heating and cooling ramps; to provide the best aesthetic yield of the mould contacting surface, the vacuum removal should be carefully considered in case the crosslinking stage is carried out in an autoclave.

The diagram of Figure 4 graphically shows the passages disclosed in the preceding Table.

It has been found that the invention fully achieves the intended aim and objects.

In practicing the invention, the materials used, as well as the contingent size and shapes can be any, depending on requirements.

Claims

1. A method for making, by molding, a two-layer coupled part, in particular of a motor vehicle body, of an advanced composite material and with a high surface finishing, characterized in that said method comprises coupling, by a hot-melting impregnating machine, a fibrous material layer having the following characteristics :

- it is constituted by randomly arranged non-woven fibers having a fiber length from 6 to 12 mm;

- said fiber are bound by a PVA (polyvinyl alcohol) binder material;

- it is compatible with epoxy resin systems used for advanced composite materials;

- it is a flat and porous layer adapted to absorb the resin;

- it has a weight from 10 to 50 g/m².

2. A method for making, by molding, a two-layer coupled part, according to claim 1, characterized in that the chosen material is impregnated by an epoxy resin system as modified by an addition of an amount by weight of inert materials consisting of:

phyllosilicates, a silicon, aluminium and potassium oxide mixture;

- hollow glass microspheres having a maximum diameter of 30 micrometers.

3. A method for making, by molding, a two-layer coupled part, in particular of a motor vehicle body, of an advanced composite material, according to claim 1, characterized in that said second layer of coupled and pre-impregnated composite material or prepreg constitutes the outermost portion of the coupled part, that is the portion contacting the mould during the molding process and which, in a finished condition, comprises a highly finished surface; the first layer being impregnated by a resin system compatible with that impregnating the second layer and being cross-linked simultaneously with said second layer.

4. A method according to claim 1, characterized in. that said method comprises the step of using a hot- melt impregnating machine with an operating speed of 2-4 meters per minute; said resin being an epoxy and hot- melt- resin forming from 40 to 65% of the coupled part weight .

5. A method according to claim 1, characterized in that said first support layer comprises unidirectional, multi-axial fibers or woven materials, a felt material or any other material having like characteristics, said first support layer and said second coupled layer comprising carbon fibers, glass fibers, aramidic fibers or other fibers suitable for making advanced composite materials.

6. A method according to claim 1, characterized in that said support layer is a fibrous material layer constituted by non-woven fibers arranged in a random order compatible with said resin systems, said fibrous material layer being flat and porous and having a weight from 10 to 50 g/m².

7. A method according to claim 1, characterized in that said epoxy resin is a thermosetting resin.

8. A method according to claim 1, characterized in that said epoxy resin has the following characteristics : Volatile substances in the prepreg (%wt) <1

Resin density (g/cm³) 1.2

Tg (DSC)* (°C) 135

TgE' (DMA)** (°C) 125

Peak Tg of Tan δ (DMA)** (°C) 146 * Dynamic scanning

** Fully cross-linked laminate

Temperature (°C) Gel time (min)

100 87

110 56

120 21

130 8.75

Resin contents: from 45% to 65% of the end weight of the overall coupled part.

9. A method according to claim 1, characterized in that said epoxy resin has the following characteristics :

Volatile substances in the prepreg (%wt) <1

Resin density (g/cm³) 1.23

Tg (DSC)* (°C) 181

TgE' (DMA)** (°C) 167

Peak Tg of Tan δ (DMA)** (°C) 184

* Dynamic scanning

** Fully cross-linked laminate

Temperature ( ⁰C) Gel time (min)

80 400

100 85

120 17

135 5.5

150 4^ The contents of resin varying from 49% to 60% of the end weight of the overall coupled impregnated material .

10. A method according to claim 1, characterized in that said method comprises making a woven and non- woven carbon coupled material and impregnating said material by an epoxy resin modified by a carbon fabric having a 2x2 twill weave and a weight from 180 to 400 g/m² (A) , said carbon non-woven material having a weight from 20 to 50 g/m² (B) ;

the epoxy resin having the following characteristics:

Volatile substances in the prepreg (%wt) <1 Resin density (g/cm³)- 1.2 Tg (DSC)* (°C) 135

TgE' (DMA)** (°C) 125

Peak Tg of Tan δ (DMA)** (°C) 146

* Dynamic scanning

** Fully cross-linked laminate

Temperature (°C) Gel time (min)

100 87

110 56

120 21

130 8.75

The resin contents varying from 45% to 65% of the end weight of the overall impregnated coupling material .

11. A method according to claim 10, characterized in that said impregnating of said coupled material A + B is carried out by two different consecutive process stages with a hot-melt impregnating machine speed from 2 to 4 m/min:

2 - coupling the carbon non-woven material B to said support A and impregnating said non-woven material by an amount of resin, having the same composition as that used in the preceding stage or step, from 70% to 90% of the impregnated non-woven material weight; the cylinder pressure being set from 1 to 4 bars.

A possible laminating sequence providing to use:

2 - a carbon fabric or woven material B impregnated by a resin having a composition compatible with that previously disclosed.

12. A method for making a motor vehicle body part, according to claim 11, characterized in that said method provides to use, starting from an outside of the finished part, and accordingly from the mold surface:

1. a carbon non-woven material + a carbon woven material (A + B)

2. a carbon woven material (B)

wherein an autoclave crosslinking operating cycle is carried out and the method stages being shown in the Table of Figure 1, indicating temperatures,, pressures, heating and cooling ramps; the diagram of Figure 2 graphically showing the steps disclosed in the preceding Table .

13. A method according to claim 1, characterized in that said method provides to use an unidirectional (UD) reinforcement coupled material, a carbon non-woven material and a modified impregnating epoxy resin:

an unidirectional carbon reinforcement material: a weight from 120 to 400 g/m² (C) ;

a carbon non-woven material: a weight from_.15 to 70 g/m² (D) ;

Characteristics of the epoxy resin:

Volatile substances in the prepreg (%wt) <1 Resin density (g/cm³) 1.23

Tg (DSC)* (°C) 181

TgE' (DMA)** (°C) 167

Peak Tg of Tan δ (DMA)** (°C) 184

* Dynamic scanning

** Fully cross-linked laminate

Temperature (°C) Gel time (min)

80 400

100 85

120 17

135 5.5

150 4

with resin contents from 40% to 60% of the end weight of the overall coupled or laminated impregnated material.

14. A method according to claim 13, characterized in that said method provides to use an impregnating and coupling process wherein the coupled material C + D impregnating is carried out by two different consecutive process stages, with a holt-melt impregnating machine speed from 2 to 4 m/min:

1 - impregnating the unidirectional carbon reinforcement C (with a support function) : the amount of resin deposited on the support corresponding to an amount from 30% to 40% of the impregnated reinforcement end weight;

2 - coupling of the carbon non-woven material D to the support C and impregnating by an amount of resin, having a composition identical to that used in the preceding step, from 70% to 90% of the impregnated non- woven material weight.

15. A method according to claim 14, characterized in that said method further comprises a step of carrying out a laminating sequence using the solution disclosed in the present case, that is:

1 - the UD/non-woven material C + D coupling solution, made as above disclosed;

2 - a carbon woven material, being impregnated by a resin having a composition compatible with the preceding one.

16. A method according to claim 15, characterized in that said method further comprises the step of making a motor vehicle body part starting from the outside of the finished part and, accordingly, from the mould surface:

1. [0°C]1 carbon non-woven material + UD reinforcement (C + D)

2. [90°C]4 carbon woven material (B)

or, alternately:

1. [0°C]1 carbon non-woven material + UD reinforcement (C + D)

2. [90°C]2 carbon woven material (B)

3. [90°C]1 UD reinforcement (C) .

17. A method according to claim 16, characterized in that said method comprises an operating crosslinking cycle the stages of which are shown in the Table Of Figure 3, indicating temperatures, pressures, heating and cooling ramps; to provide an aesthetically improved surface contacting the mould, said method including a step of removing vacuum as the crosslinking cycle is carried out in an autoclave; the diagram of Figure 4 graphically showing the steps disclosed in said Table of Figure 3.