DE112016004611T5 - Overmolded carbon fiber structures with adjusted void content and uses thereof - Google Patents

Abstract

Summary: The present invention relates to novel carbon composites having very high directional properties which are higher in the direction of the UD carbon layer, and with improved potential for failure over full carbon fibers and standard composite fibers. Further, the invention relates to a method of making these carbon composites with a new overmolded thermoplastic composition, the overmolded thermoplastic composition, methods of making same, and articles made from these carbon composites.

Description

Field of the invention

The present invention relates to carbon fiber composites (CF composites) for use in composite structures, e.g. for automotive, industrial, consumer or aerospace applications.

Background of the invention

With the aim of replacing metal components for weight and cost savings while achieving comparable or superior mechanical performance, structures based on composites and comprising a polymer matrix containing a fibrous material have been developed.

For applications with high requirements, e.g. Structural components for automotive and aerospace applications, composites are desirable due to a unique combination of light weight, high strength and temperature resistance.

However, in fiberglass composites, there are limitations in stiffness and weight specific stiffness to metallic materials such as e.g. Steel and aluminum have been found. In order to achieve the required stiffness of the components, the use of fiberglass composites requires extended design space which, unfortunately, is often not available depending on the type of component.

On the other hand, because of the high fiber modulus, carbon composites have excellent weight specific properties, and can take the place of metal with significant weight savings when using carbon fiber composites for mass applications, e.g. However, in the motor vehicle and consumer electronics sectors, cost-effectiveness has come to the fore.

Efficient composite structures can be made with thermosetting resins or thermoplastics as polymer matrix. In addition to the cost of the carbon fiber material used in the final component, two issues are important in terms of reducing the cost of manufacturing carbon fiber composites.

The first question is fast cycle times in the manufacture of components. Thermoplastic-based composite structures have several advantages over thermoset-based composite structures; This includes in particular the possibility of re-forming or reprocessing by the application of heat and pressure. In component manufacturing, cycle time is limited by heat transfer in the stamping or injection molding process, where molten thermoplastics are molded in cycle times typically less than 60 seconds. In addition, less time is required to produce the thermoplastic composite structures than is the case with thermoset composites because the curing step does not require time to initiate the crosslinking reaction, which requires additional processing lines for higher production volumes, and also has greater reuse potential ,

The second question is the ratio of the starting material to the material used in the final molded part, with a 1: 1 ratio being the ideal case. Become a textile based carbon fiber architectures, e.g. Tissue or multiaxial scrims are used, and when the unattached master from the final component to the parent material is not straight but curved, waste accumulates, which is costly even when reused in different lower-performance material derivatives.

Thus, a thermoplastic carbon fiber composite system is desirable for fast cycle times and high production volumes, which also limits the waste or trim volume of wide fabric fabrics.

Another requirement that is common to many structures in many industries, e.g. In the automotive industry, the carbon fiber thermoplastic structure is not only stiff in normal use, but also absorbs significant amounts of energy in a crash or failure, resulting in either other components of the structure or the occupants associated therewith or goods are protected.

It is generally known that carbon fiber composites can absorb large amounts of energy on impact, especially in axial impacts, where the delamination of the carbon fibers from the matrix resin and the large interface areas involved can absorb large amounts of energy.

Applications used in crash situations often need to follow a desired force-displacement curve, limiting intrusion while avoiding a high force peak and catastrophic failure of the component. Rather, it requires a controlled response so that the molded part builds up a resistance at given penetration without significant failure against the force to a desired force peak followed by progressive damage and a significant increase in energy absorption.

It has been found that in fully impregnated carbon fiber nylon bars overmoulded with standard glass fiber nylon resins, as an example of structures in automotive, consumer electronics and other components of this type, the load builds up to catastrophic failure in trials.

A well-known assumption is that for high stiffness and good mechanical properties overall, low void content, preferably below 2%, is desirable in carbon fiber structures. To achieve this, it is known to use fully impregnated carbon ribbon with less than 2% voids of raw material of the structure, or to use partially impregnated carbon ribbon, which is then preconsolidated in a second step after incorporation to reduce voids content to about 2% or so less to reduce. These methods are both associated with high costs.

The challenge, therefore, is to provide structures with a stiffness comparable to that of the fully impregnated carbon fiber nylon beams, allowing them to achieve similar peak load at a lower cost and improved energy absorption properties. Higher energy absorption properties are advantageous in order to maintain high forces for larger displacements, in particular to allow a load control and an adapted rupture of the component.

Summary of the invention

An object of the present invention is to provide a carbon fiber-based composite which has high stiffness and yet high energy absorption capacity and high elongation at break.

Another object of the present invention is to provide a carbon fiber based composite article having high energy absorption capacity and high elongation at break.

It is advantageous to provide a carbon fiber-based composite and articles made therefrom which are economical to manufacture.

It is advantageous to provide a carbon fiber based composite and articles made therefrom in which the scraping volume is reduced.

It is advantageous to provide a carbon fiber-based composite, as well as articles made therefrom, which have consistent and reliable properties.

The objectives of this invention have been achieved by providing the method of claim 1, the composite of claim 22, the overmouldable thermoplastic of claim 35 and the manufacturing method thereof of claim 20.

1. (i) Vorsehen von mindestens zwei Schichten aus unidirektionalem (UD) Kohlefaserband, wobei das UD-Kohlefaserband unidirektionale Kohlefasern umfasst, die in einen Thermoplasten imprägniert sind, wobei das Faser-Harz-Verhältnis im Bereich von 50 % bis 70 % liegt und der anfängliche Hohlraumgehalt vor dem Stapeln 2 % übersteigt;
2. (ii) Stapeln der mindestens zwei Schichten aus UD-Kohlefaserband in einer diagonalen Anordnung in Bezug aufeinander;
3. (iii) Anwenden von Wärme bei einer zum Schmelzen des Thermoplasten geeigneten Temperatur;
4. (iv) Kühlen der erwärmten gestapelten Schichten unter Druck, um die Verbundstruktur zu härten,

wobei die erwärmten gestapelten Schichten mit einer Thermoplast-Faser-Zusammensetzung umspritzt werden, wobei die Thermoplast-Faser-Zusammensetzung ein Glasfasermaterial, ein Kohlefasermaterial und ein Polyamidharz umfasst.Disclosed herein is a method of making a carbon fiber composite structure comprising:

1. (i) providing at least two layers of unidirectional (UD) carbon fiber tape, the UD carbon fiber tape comprising unidirectional carbon fibers impregnated in a thermoplastic, wherein the fiber to resin ratio is in the range of 50% to 70% and the initial one Void content before stacking exceeds 2%;
2. (ii) stacking the at least two layers of UD carbon fiber ribbon in a diagonal arrangement with respect to each other;
3. (iii) applying heat at a temperature suitable for melting the thermoplastic;
4. (iv) cooling the heated stacked layers under pressure to cure the composite structure,

wherein the heated stacked layers are overmolded with a thermoplastic-fiber composition, the thermoplastic-fiber composition comprising a glass fiber material, a carbon fiber material, and a polyamide resin.

Experimental data suggest that composites according to the invention, in which the unidirectional CF bundles are already pre-impregnated with the thermoplastic in the form of a UD-CF tape, wherein the UD-CF tape layers are stacked according to the invention with respect to each other in a diagonal arrangement, and wherein the resulting stack of carbon fiber layers has a void content greater than 2%, the overmolding of such a stack with a resin according to the invention surprisingly results in a composite having not only a stiffness and peak load comparable to those of a preconsolidated carbon fiber material but also one preconsolidated Carbon fiber material has significantly increased peak load energy and energy to significant failure.

The invention thus relates to the unexpected findings of new carbon composites with excellent elongation at break and load retention at strains that significantly exceed the maximum peak force. These composites with these improved properties find practical application where high stiffness and high energy absorption are required, e.g. Impact protection in automotive and other applications. Contrary to expectations, it has been found that the use of unidirectional carbon fiber ribbons (UD carbon fiber ribbons), which consist of long or continuous UD carbon fiber strands, with a thermoplastic (eg in a continuous pultrusion or other band production process, in particular one or double-sided melt coating, Wire coating, fiber encapsulation by resin, reactive thermoplastic impregnation and powder impregnation (the aim being to impregnate an impregnated carbon dioxide / polyamide UD tape)) in the formation of a carbon fiber composite wherein the void content exceeds 2% in conjunction with an overmolding resin according to the invention, which is modified for efficient heating during encapsulation of the outer prepreg carbon layers, increased energy absorption at equivalent stiffness against the use of pre-impregnated carbon fiber layers with geri Another void content as a starting material during stacking and thermoforming or another Umspritzharz leads. The stacking of the CF layers to form laminates, as well as the thermoforming process after stacking the layers may together use standard techniques (e.g., with laminators, double belt presses, continuous forming, etc.).

The properties of the composite according to the invention are particularly unexpected since it consists of UD tapes with cavity contents after tape production of more than 2%, e.g. a void content of about 4 to 12%, or about 6 to 8%, while having high stiffness and good overall mechanical properties. These properties make it possible to use UD tapes that are less expensive to manufacture and are capable of being directly stamped into a shell structure with a heater, press, and mold without the need for fully impregnated tape or another preconsolidation step.

Surprisingly, the stiffness and peak load equivalent to low voids carbon fiber material and the gain in peak power that can be observed in the carbon fiber composite of the present invention while providing a composite at a lower cost than standard carbon fibers.

Further objects and advantageous aspects of the invention can be found as well as the patent claims and the following detailed description and the accompanying drawings.

list of figures

• 1 Figure 3 shows beams (A & B) molded from a flat composite sheet according to embodiments of the invention and from comparative material which were then overmoulded with short fiber filled resin and the mechanical properties (flexure test bed) tests described in Example 1 from a laminate board of a composite according to the invention over a comparison composite (C & D). Also shown is the specific geometry of the a composite produced according to the invention beams (E & F & G). The generic beam structure has a length of 730 mm (B), a top rib thickness of 2 mm, a width of 140 mm (B), a laminate cup thickness of 1.5 mm, which is encapsulated with 1.5 mm encapsulated polymer (G), with a height of 15 mm, 30 mm and 50 mm in the different steps (F). The width-depth-length ratio of the beam is 9.3: 4.7: 2.8 as examples of structures of this type. 1 also shows the details of the bending test, in particular span and loader radius (C & D).
• 2 shows the comparative method with preconsolidation step used for Comparative Examples C1 and C2. A: Provide a UD tape as manufactured; B: Diagonal arrangement and spot welding of UD tape; C: preconsolidation process of the diagonally arranged bands; D: preconsolidated, diagonally arranged UD band; E: punched, diagonally arranged UD band; F: Overmoulded, stamped, diagonally arranged UD band.
• 3 shows the process according to the invention used for the examples without Vorkonsolidierungsschritt. A: Provide a UD tape as manufactured; B: Diagonal arrangement and spot welding of UD tape; C: punched, diagonally arranged UD band; D: Overmoulded, stamped, diagonally arranged UD band.
• 4 Fig. 12 is a schematic representation of Comparative Method (A) used for Comparative Examples C1 and C2 with preconsolidating step, and Example of Conditions of Method of Invention (without Preconsolidating Step) (B).
• 5 Figure 4 is a schematic representation of the conditions used in the comparative process for preparing Comparative Examples C1 and C2 with preconsolidation step (left) and the process of the invention (without preconsolidation step) (right).
• 6 shows the results achieved in Example 1 when stacking 10 layers with a thickness of 2 mm and a stacking arrangement of [0/0/90/0/0] s; the preheat profile being shown at 300 ° C in (A), die temperature = 140 ° C, time under pressure = 38s at 40 bar pressure. A: Preheating conditions and number of steps (each under PID pyrometer control) for B, C, D and void content B: Microgram of the stamped composite without preconsolidation C: Microgram of pre-consolidated UD tape without punching D: Microgram of preconsolidated UD tape with punching ,
• 7 Figure 4 shows the micrographic results and void contents achieved in Example 1, wherein diagonally arranged UD tape has been die-cut, either with or without a prior preconsolidation step, and then overmoulded with a comparative resin and the resin composition of the invention. A: Diagonal UD tape structure. which has been punched bent without prior Vorkonsolidierung and then overmoulded with Umspritzharz; B: structure of the diagonally arranged UD tape, which has been preconsolidated into a flat plate and then punched, followed by overmoulding with overmolding resin 1; C: structure of the diagonally arranged UD tape, which has been preconsolidated to a flat plate and then punched, followed by overmoulding with overmolding resin 2; D: Structure of the diagonally arranged UD strip, which has been punch-bent without prior preconsolidation and subsequently overmoulded with encapsulation resin 2.
• 8th shows the micrographic results and void contents achieved in Example 1; the overall structure is shown, a first detail enlargement of an example section and a second detail enlargement of the fiber agglomerations and local resinous areas and the locations where cavities are located in the structure; wherein diagonally arranged UD tape has been punch-bent with either (A) or without (B) prior preconsolidation and the resulting stamped and bent part subsequently overmoulded with the resin composition of the present invention; A: Structure of the diagonally arranged UD strip, which has been punch-bent with prior preconsolidation and then overmoulded with encapsulating resin 2, wherein the shallower and wider agglomerations of UD fibers with smaller resin-rich areas and an overall more homogeneous microstructure can be seen; B: Structure of the diagonally arranged UD tape without prior preconsolidation, which has been punched and subsequently overmoulded with overmolding resin 2, where agglomerations of UD fibers contain voids at the center of the agglomeration and the shape of the agglomeration is more square than A, and where the UD Fiber agglomerations are spaced with wider resinous areas than A and thus have a less homogeneous microstructure.
• 9 Figure 3 shows the micrographic results and void contents of the UD tape produced by pultrusion prior to any subsequent thermal processing steps (and thus preconsolidation, stamping or overmolding, as described in detail elsewhere herein), with the UD fiber agglomerations centering on cavities Contain agglomeration and the shape of the agglomeration is rather square or circular than flat and rectangular as in the 8A , and wherein the void content in the fabricated state over the entire width of the tape is 6 to 8% (ROI is called "region of interest").
• 10 FIG. 12 shows photographs of the exemplary beam structure made from diagonally arranged UD punched ribbon (with or without prior preconsolidation) which was then overmoulded with a coating resin, the beam following 3-point bending tests. FIG 1 C and D the light image shows the possibility of error of the bar and the diagonally arranged UD band; A: Diagonally arranged UD tape, which has been punched bent without prior preconsolidation and then overmoulded with encapsulating resin 1 (OM1), wherein the UD fibers are broken with a strand-like behavior, which leads to the in 8B corresponds to carbon fiber agglomerations shown; B: Diagonal UD tape preconsolidated into a flat plate and then punched, followed by overmolding with the overmolding resin 1 (OM1), the diagonally arranged UD tape due to the in 8A showed a more homogeneous microstructure, suffered a shear failure without strand-like breakage; C: Diagonally arranged UD tape, which has been punch-bent without prior preconsolidation and then overmoulded with encapsulating resin 2 (OM2), wherein the UD fibers are broken with a strand-like behavior, which results in the UD band 8 B corresponds to carbon fiber agglomerations shown, and wherein the combination of OM2 and omitted Vorkonsolidierung allows tearing of the three load application points; D: Diagonally arranged UD tape, which has been preconsolidated to a flat plate and then punched, followed by overmolding with the overmolding resin 2, the diagonally arranged UD tape due to the in 8 A shown more homogeneous microstructure, a shear failure without strand-like breakage has suffered.

Detailed description of embodiments of the invention

As used herein, "fiber" is defined as a macroscopically homogeneous body having a high length / width ratio across its cross-sectional area perpendicular to its length. The cross section of the fiber may have any shape, but is typically round or oval.

The basis weight of the fibrous layer refers to the weight of the dry fibrous layer per unit area. The filament count of a fiber cable is useful to define a cable gauge of the carbon fiber. Frequently occurring sizes are in particular 12,000 (12k) filaments per cable or 50,000 (50k) filaments per cable.

As used herein, the term resin prepreg impregnated unidirectional carbon ribbon is well known to those skilled in the art; this can be made by melt pultrusion, powder or film impregnation, reactive impregnation or many other methods. The resin is distributed over the entire cross section of the belt instead of forming or surrounding an agglomeration or coating on the outside of the carbon fibers. The voids that may be present in the structure are then randomized rather than distributed in a preferred area where there is an intentional lack of resin or impregnation.

As used herein, "impregnated" means that the resin composition flows into the voids of the fibrous material. Quality and extent of impregnation may e.g. evaluated and measured by determining the void content.

The void content can be measured as described in the examples.

In preparing the UD carbon fiber used in the invention, the resin for preimpregnating in the form of a conventional resin composition such as PA66 or PA66 / 6 (75:25 mixing ratio) may be applied to the UD carbon fiber, and the resin composition may be applied to the fiber materials by conventional means, eg, powder coating, reactive thermoplastic impregnation, film lamination, extrusion coating or a combination of two or more thereof, with the proviso that the resin composition is applied to at least a portion of the surface of the composite structure. In the case of extrusion coating, the polymer can be applied with a pultrusion die, with resin applied to both sides of the fiber material and using impregnation pins, if necessary; Optionally, an internal convergence matrix can also be used; alternatively, a one-sided coating carrier may be used wherein molten resin is extruded via a die onto the fibrous material, preferably in a distributed form, the fibrous material being carried on a curved surface to drive the resin into the fibrous material. A round or flattened wire coating mat can also be used. in case of a Powder coating process is applied to the UD carbon fiber produced by conventional milling process polymer powder. The powder may be applied to the UD carbon fiber by scattering, trickling, spraying, thermal or flame spraying, extrusion, printing or fluid bed coating techniques. On the fiber material more powder layers can be applied. Optionally, the powder coating process may further comprise a step consisting in post-sintering the powder to the fiber material. This is followed by a thermal pressing of the powder-coated fiber materials with optional preheating of the powder-coated fiber materials outside of the pressurized area. Rheology additives, heat stabilizers and black pigmentation can be used as adjuncts to the thermoplastics used to make the UD-CF layer. Further polymers which are suitable for the production of the UD-CF layers used in connection with the invention are, in particular, polypropylene, thermoplastics, polyphenylene sulfide and various nylon grades and mixtures, as described below.

Polyamide resins useful in the preparation of the UD-CF layers used in the invention are condensation products of at least one dicarboxylic acid and at least one diamine and / or at least one aminocarboxylic acid and / or ring-opening polymerization products of at least one cyclic lactam. The polyamide resins are selected from the fully aliphatic polyamide resins, the partly aromatic polyamide resins and mixtures thereof. The term "partially aromatic" describes polyamide resins containing at least some aromatic carboxylic acid monomers and aliphatic diamine monomers as opposed to "fully aliphatic" which describes polyamide resins containing aliphatic carboxylic acid monomer (s) and aliphatic diamine monomer (s). include.

Fully aliphatic polyamide resins are prepared from aliphatic and alicyclic monomers such as e.g. Diamines, dicarboxylic acids, lactams, aminocarboxylic acids, and their reactive equivalents formed. A suitable aminocarboxylic acid is e.g. 11-Aminododecandisäure. In the context of the present invention, the term "fully aliphatic polyamide resin" refers to copolymers derived from two or more monomers of this type and blends of at least two fully aliphatic polyamide resins. Linear, branched and cyclic monomers can be used. Star polymers can also be used.

Carboxylic acid monomers useful in the preparation of fully aliphatic polyamide resins include, in particular, aliphatic carboxylic acids, e.g. Adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9), sebacic acid (C10), dodecanedioic acid (C12) and tetradecanedioic acid (C14) are, but are not limited to. Among the useful diamines include u.a. those having at least four carbon atoms, in particular tetramethylenediamine, hexamethylenediamine, octamethylenediamine, decamethylenediamine, 2-methylpentamethylenediamine, 2-ethyltetramethylenediamine, 2-methyloctamethylenediamine; Trimethylhexamethylenediamine and / or mixtures thereof. As suitable examples of fully aliphatic polyamide resins may be mentioned in particular: PA6; PA6.6; PA4,6; PA6,10; PA6,12; PA6,14; P6,13; PA 6,15; PA6,16; PA11; PA 12; PA10; PA 9.12; PA9,13; PA9,14; PA9,15; PA6,16; PA9,36; PA10,10; PA10,12; PA10,13; PA10,14; PA12,10; PA12,12; PA12,13; PA12,14 and copolymers and mixtures thereof.

Partially aromatic polyamide resins are homo-, co-, ter- or higher polymers, wherein at least a part of the acid monomers is selected from at least one aromatic carboxylic acid. The at least one aromatic carboxylic acid may be terephthalic acid or mixtures of terephthalic acid and at least one other carboxylic acid, for example, isophthalic acid, substituted phthalic acid such as 2-methyl terephthalic acid and unsubstituted or substituted isomers of naphthalene dicarboxylic acid, wherein the carboxylic acid component preferably contains at least 55 mole% terephthalic acid the mole percentage on the carboxylic acid mixture). Preferably, the at least one aromatic carboxylic acid is selected from terephthalic acid, isophthalic acid and mixtures thereof; The at least one carboxylic acid is particularly preferably mixtures of terephthalic acid and isophthalic acid, the mixture preferably containing at least 55 mol% of terephthalic acid. Furthermore, the at least one carboxylic acid with at least one aliphatic carboxylic acid such as adipic acid; pimelic; suberic; azelaic acid; Sebacic acid and dodecanedioic acid; Adipic acid is preferred. The mixture of terephthalic acid and adipic acid contained in the at least one carboxylic acid mixture of the partly aromatic polyamide resin particularly preferably contains at least 25 mol% of terephthalic acid. Partially aromatic polyamide resins comprise at least one diamine which can be selected from the diamines having at least 4 carbon atoms, in particular tetramethylenediamine, hexamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 2-methylpentamethylenediamine, 2-ethyltetramethylenediamine, 2-methyloctamethylenediamine; Trimethylhexamethylenediamine, bis (p-aminocyclohexyl) methane; m-xylylenediamine; p-xylylenediamine and / or mixtures thereof. As suitable examples of partly aromatic polyamide resins are in particular called poly (hexamethylene terephthalamide) (polyamide 6, T), poly (nonamethylene terephthalamide) (polyamide 9, T), poly (decamethylene terephthalamide) (polyamide 10, T), poly (dodecamethylene terephthalamide) (polyamide 12, T), hexamethylene adipamide / hexamethylene terephthalamide Copolyamide (polyamide 6, T / 6,6), hexamethylene terephthalamide / hexamethylene isophthalamide (6, T / 6, I), poly (m-xylylene adipamide) (polyamide MXD, 6), hexamethylene adipamide / hexamethylene terephthalamide copolyamide (polyamide 6, T / 6 , 6), hexamethylene terephthalamide / 2-methylpentamethylene terephthalamide copolyamide (polyamide 6, T / D, T), hexamethylene adipamide / hexamethylene terephthalamide / hexamethylene isophthalamide copolyamide (polyamide 6,6 / 6, T / 6.1); Poly (caprolactam-hexamethylene terephthalamide) (polyamide 6/6, T) as well as copolymers and blends thereof, in particular PA6, T; PA6, T / 6,6, PA6, T / 6, I; PAMXD, 6; PA6, T / D, T and copolymers and mixtures thereof.

In a particular aspect, the fiber to resin mass ratio in the UD tape used in making the stack is in the range of 50% to 70% fiber with an initial void content before stacking that exceeds 2%. The preparation of the UD tapes to achieve such a void content is usually done by known methods if no preconsolidation step is carried out.

As used herein, "fibrous material" means a material which is any suitable mat, tissue or sheet form known to those skilled in the art. The fibers or strands used to form the fibrous material are crosslinked (ie, at least one strand contacts at least one other strand or fiber to form a continuous material), or are in contact with each other to form a continuous mat, continuous web or a similar structure. The fibrous material may be made of glass or carbon fibers, mineral fibers such as e.g. Basalt, kevlar or aramid, or mixtures thereof. Carbon fibers give particularly good results. The fibrous material comprising carbon fibers used in the thermoplastic-fiber composition of the present invention comprises oriented fibrous structures. Examples of aligned fiber structures are: unidirectional (UD) fiber strands, bidirectional strands, multidirectional strands, multiaxial textiles. Textiles can be selected from fabrics, knits, braids, and combinations thereof. The oriented fiber structure may further comprise elements of nonwoven structures (e.g., mats, felts, fabrics, webs, virgin fibers) and combinations thereof.

In accordance with an advantageous embodiment, the stack of fiber layers prior to encapsulation comprises 2 to 26 layers of pre-impregnated UD carbon fiber tape, e.g. 2-20, 2-10, 2-8. In one embodiment, a stack of 8 layers of UD carbon fiber tape is used to form a part, with the stack giving a thickness of about 1.5 to 1.6 mm it is the material thickness required to fill the mold cavity of this part.

In one embodiment, the initial void content of the UD carbon fiber tape prior to stacking is between about 4 and 12%, e.g. 6 to 8% (41).

Depending on the component (42) different stacking sequences (ply angles) can be selected, eg unidirectional stacks, balanced and symmetric stacks, eg with balanced biaxial orientation, biaxial directional distortion, quasi-isotropic orientation and directional isotropic orientation with off-axis UD layers, such as 90/0/0/0] s, [45/0 / -45 / 0] s, [90/0/90/0] s, [90/45/0 / -45] s, and where the 45 ° Position can be replaced by an arbitrarily selected angle, which is selected according to the requirements of the respective component. In one particular aspect, the angle between the fibers of one of two diagonally stacked layers is between 0 and 90 degrees relative to the other.

In a particular aspect, an optional step of spot welding the UD tapes within the stacked layers (42) using various means such as ultrasonic spot welding, vibration welding, and thermal spot welding, since bonding the UD tape layers prior to heating (iii) (possibly with pre-consolidation after spot welding and before heating) facilitates processing of the material as it is being formed. The welds formed between two or more plies are intended to provide a stack of UD plies that can be manipulated manually or by automated means when the stack is below the melting point of the polymer without losing the orientations of the plies or UD plaits are still discernible as discrete layers, since no melting of the entire structure has taken place to form a homogeneous mass in which all layers are fused into a cohesive whole.

According to another specific embodiment, the stacked UD tape layers (42) in step (iii) above the melting point of the polymer of the UD band (43) heated; then there will be pressure used to bond the UD carbon fiber ribbon layers in a homogeneous structure, followed by crystallization and cooling under pressure (44) , and to shape the composite prior to injection molding. The cooled part may optionally be trimmed (46) in step (iv), and prior to overmolding, the part is heated (47) to bond the thermoplastic fiber overmold composition (48a) to assist, and repeated cooling under pressure (iv ').

A description of a stamping bending process (44) is found in Example 1. Typical heating temperatures for stacking layers of UD carbon fiber tape comprising PA66-6 as the impregnating resin are 290 to 300 ° C (heat treatment), and the die used in the punch press becomes 120 - 160 ° C warmed. The warmed material must be transferred quickly, ideally in less than 10 seconds, so that it is still far enough above the melting point when pressurized to allow consolidation across the part. Typical pressures which are used in the molding of components for the multilayered UD structure are from 20 to 200 bar, preferably from 40 to 100 bar.

According to a concrete embodiment, the void content of the stacked layers (42) before punching (44) advantageously maintained above 2%, but typically between about 4 and 8%.

Alternatively, the stacked UD carbon fiber tape layers may be heated above the melting point by means of an inductively heated tool disposed in a molding press, with only the tool surface being heated; thus allowing pressure to be applied in the molten state and cooling the tool while maintaining pressure, followed by removal of the molded UD preform. The stamped structure is then reheated (47) prior to the overmolding step (48a) is subjected to the overmolding resin composition of the present invention.

From a concrete aspect, the heated stacked layers can (43) under pressure (eg, by over-compression or over-molding) with the thermoplastic-fiber composition, either before the cooling step (iv) of the one-step process (45b) or after warming up the cured composite structure produced in step (v) in a 2-stage process (48a) ,

In a concrete aspect, the pressure applied to the stacked layers in the cooling step is about 10 to about 150 bar.

According to a specific embodiment, the overmolding of the thermoplastic-fiber overmold composition takes place at a temperature which exceeds the melting point of the composition, typically at 290 to 300 ° C for PA66, which is adjusted according to the quality of the polyamide actually employed, resulting in Injection molding of polyamide resins is generally known and is regulated by the injection molding apparatus used, the example provided by the company Engel, and wherein the temperature of the injection molding tool is maintained at a temperature which depends on the quality of the respective polymer and in the preparation of the component to be molded, e.g. adjusted at PA66 at 100 to 120 ° C.

In particular, the cured composite in the case of a method according to the invention, in which the encapsulation following a warm-up (47) the cured composite structure resulting from step (iv) slightly below its melting point (47) , eg 180-230 ° C at PA66-6, warmed and then rapidly placed in an overmoulding tool placed in a molding press in which the thermoplastic-fiber overmolding composition according to the invention is applied under pressure to the heated stacked UD layers (overmolding process). (48a) ,

According to an advantageous embodiment, the steps of applying heat and pressure to the stacked layers (step (iii)) and overmolding the thermoplastic-fiber composition of the invention onto the heated stacked layers are part of a single thermal forming step in which the resin is made from the UD carbon fiber layers are melted through the entire stacked layers (eg in an oven immediately inside a transfer tool) and the molten thermoplastic fiber composition of the invention is over-injected onto the heated stacked layers. The heated UD carbon fiber ribbon layers are pressed together by the pressure of the overmolding resin while being sprayed directly onto the punch, resulting in several heating phases and the cost of the equipment associated therewith, and more specifically, a punch bending step (44) can be omitted.

In an alternative aspect, to achieve a single thermal forming step as described above, the heat treating step may be by pre-heating the stacked UD carbon fiber ribbon layers in a furnace above the melting point using an extruder in parallel to form the dry fiber and matrix resin components the resin-fiber overmolding composition or pellets of premixed fiber and resin components according to the invention of the resin-fiber overmolding composition according to the invention, which are then extruded by means of a die into a melt or charge. The molten mass is then transported with the stacked UD-carbon fiber tape layers preferably by a robot in a steel mold, which is mounted in a vertical hydraulic press, such as the known equipment of the Fa. Dieffenbacher, in which the stacked UD carbon fiber tape layers are pressed together and the The UD is overmolded (48b) and the part is cooled under pressure (45b).

According to a concrete embodiment, the void content of the stacked layers (42) before overmolding (48b) advantageously maintained above 2%, but typically between about 4 and 8%, eg, about 6 to about 8%.

In a further specific aspect, in preparing the composite structure of the present invention, the overmolding step is carried out in a period of time that is a function of the thickness of the overmolding resin, typically in a period of less than 2 minutes.

In a further specific aspect, in the method according to the invention the overmolding step is carried out in a period of less than 2 minutes at mold temperatures of about 120 to about 160 ° C and pressures of more than between about 200 and 1000 bar.

Concretely, the over-molded stacked layers (45b and 45a2) are cooled under pressure to cure the composite structure, with a cooling time in the mold typically of 7 - 10 s / mm overmold thickness and preferably less than 1 minute cycle time for use in mass production wherein the temperature of the mold is 100 ° C to about 160 ° C, eg between 100 and 120 ° C, and injection pressures of 500 bar for the corresponding packaging of the nylon materials are known to be required.

In one aspect, the UD layers of the composite structure may be used as a material covering most of the component to provide overall stiffening, or for use as streaks or local patches where stiffening is required only in local areas.

In yet another specific aspect, a composite structure is provided which can be produced by a method according to the invention.

According to one embodiment, the composite structure may comprise a plurality of UD carbon fiber ribbon layers.

According to an advantageous embodiment, the composite structure may have 2 to 26 layers, e.g. 2 to 20, 2 to 10, 2 to 8, UD carbon fiber tape.

According to an advantageous embodiment, the composite structure may comprise between 4 and 8 UD carbon fiber ribbon layers.

According to one embodiment, a composite structure according to the invention has a resin / UD carbon fiber ratio in the range of 0.3 to 0.5% by weight.

According to one embodiment, a composite structure according to the invention is provided, wherein the overmolded thermoplastic-fiber composition is injection-molded over.

According to another embodiment, a composite structure according to the preceding claim, wherein the resin composition has a melting point of between about 220 and 280 ° C, in particular 250 - 275 ° C.

According to one embodiment, each impregnated UD carbon fiber ribbon layer in a composite material according to the invention or used in a method according to the invention has a basis weight which exceeds 100 g / m ² and falls below 1000 g / m ² , in particular between 200 and 500 g / m ² .

In another specific aspect, the resin composition of the present invention used in the UD tape (Table 1) differs from the overmolding resin, and is selected to have a melt viscosity of between 10 Pa.s and 300 Pa.s at 290 ° C. preferably 10 to 75 Pa.s at 290 ° C and in the shear rate range of 40 to 5000 reciprocal seconds, which is also applicable to shear rates of 10 - 40 reciprocal seconds. The rheology of the mixtures was measured using a Kayeness capillary rheometer from Dynisco. Dry pellets from the samples were melted in the rheometer barrel at the test temperature. The capillary used was a die of 0.762 mm diameter, 15.24 mm in length. The velocity of the piston driving the capillary flow was varied during the measurement, and a force transducer was used to calculate apparent melt viscosity as a function of shear rate.

According to one embodiment of the invention, the thermoplastic overmolding composition according to the invention comprises between 25% by weight and 70% by weight (typically between 35 and 70% or between 30 and 60%, eg 30 to 50% by weight or 30 to 45% by weight) a mixture of the polyamide resins PA 66 / PA6, wherein the weight ratio between the two polyamides between 40 wt.% And 100 wt.% Based on PA66. According to another embodiment, the thermoplastic overmolding composition according to the invention comprises 42% of a mixture of the polyamide resins PA66 / PA6 (60:40).

In a specific embodiment, the thermoplastic overmolding composition is a resin composition comprising a composition according to Table 2.

The fibrous material used in the composition of the thermoplastic overmolding resin composition is preferably discontinuous, however, according to some embodiments of the invention, the glass and / or carbon fiber material used may also be a woven or nonwoven material.

The amount of thermoplastic coating resin provided in the injection-molding step may advantageously be for the whole part, or depending on the partial area, if different partial areas comprise encapsulating resin in different amounts or thicknesses on or around the UD band, e.g. between no locally applied extrusion coating resin and a heavy, thick coating resin layer on both sides of the UD tape, so that in the respective region of the composite structure or over the entire part the coating resin a weight ratio to the total weight of the component (UD carbon tape plus extrusion resin) between 0% ( when the overmolding resin composition is applied only to partial areas) and 100% (when a local overmolding feature is entirely made of overmolding resin and no UD carbon tape is present in the portion of the part where UD tape reinforcement is not required).

According to one specific embodiment, the average component-related weight ratio of the composite structure to the extrusion resin is 20-80%. In the exemplary beam structure, the overmolding resin / composite structure mass ratio is between 2: 1 and 2.6: 1, which is a function of the cavity of the overmold tool relative to the strength of the UD-band composite structure.

The amount of fibrous material of glass fibers provided in the thermoplastic encapsulation composition according to the invention is preferably selected such that the mass fraction of the glass in the total mass fraction in the encapsulating polymer is between 25 and 70%, and preferably between 25 and 40% by weight, with a further concrete Embodiment of Table 2 is shown.

According to one embodiment, the carbon fiber content provided in the thermoplastic overmolding composition according to the invention is preferably chosen such that the mass fraction of the carbon fibers in the total mass fraction of the overmolding polymer is between 10 and 70%, and preferably between 10 and 25% by weight, whereby a further concrete embodiment Table 2 is shown.

The polyamide resin composition may further comprise at least one common additive, particularly, but not limited to, UV light stabilizers, flame retardants, anti-caking agents, lubricants, antistatic agents, dyes (especially dyes, pigments, carbon black, etc.), nucleating agents, crystallization promoters, and other processing aids and mixtures thereof known in the polymer blend art.

Fillers, modifiers and other ingredients described above may be in the known amounts and forms, especially in the form of so-called nanomaterials, where at least one of the dimensions of the particles is in the range of 1 to 1000 nm.

Preferably, any additives used in the polyamide resin composition are thoroughly dispersed in the polyamide resin. For combining the polyamide resins and additives of the present invention, any melt mixing method can be used. For example, the polyamide resins and additives may be added to a melt mixer, eg, a single or twin screw extruder, a blender, a single or twin screw kneader, or a Banbury mixer, all at once in a single step or stepwise, followed by melt blending. In the stepwise addition of the polyamide resins and other additives, a portion of the polyamide resin and / or additives is first added and subjected to the melt blending process, with the remaining polyamide resins and additives subsequently added and further melt blended to yield a thoroughly blended or homogeneous composition ,

According to another embodiment, the thermoplastic-fiber overmolding composition of the present invention comprises: a glass fiber material, a carbon fiber material, and a polyamide resin.

In a particular aspect, the thermoplastic-fiber overmolding composition of the present invention further comprises an agent for improving the viscosity and wettability, e.g. Dodecanedioic acid (DDDA). According to one specific embodiment, the resin composition of the invention comprises about 0.3 to 2% DDDA (e.g., 0.5 to about 1.8%).

According to another embodiment, a viscosity and wettability improver of lysine, alanine, pentaerythritol and H ₂ O may be chosen.

In a specific aspect, the thermoplastic-fiber overmolding composition according to the invention further comprises a toughening agent for increasing the ductility of the thermoplastic overmolding composition according to the invention. According to one specific embodiment, a toughener comprises ethylene / propylene / hexadiene terpolymer grafted with between 5% and 0.1% maleic anhydride, e.g. between 4 and 0.5% or between 3 and 1%, e.g. between 3 and 4%, e.g. 2.1%.

In a further aspect, polymeric tougheners may also comprise: (a) a copolymer of ethylene, glycidyl (meth) acrylate and optionally at least one (meth) acrylate ester, (b) an ethylene / alpha-olefin or ethylene / alpha-olefin / diene - (EPDM) copolymer, grafted with an unsaturated carboxylic anhydride such as Maleic anhydride. Type Fusabond / TRX, (c) a copolymer of ethylene, 2-isocyanatoethyl (meth) acrylate and optionally at least one (meth) acrylate ester, (d) a copolymer of ethylene and acrylic acid reacted with a Zn, Li, Mg or Mn compound to form the corresponding ionomer.

In one specific embodiment, an impact modifier comprises an ethylene alpha olefin copolymer containing about 95-50 wt% polymerized ethylene and about 5 to 50 wt% of at least one polymerized alpha olefin containing from 3 to about 20 carbon atoms.

According to one specific embodiment, the impact modifier further comprises a copolymer of ethylene, propylene and a diene grafted (or copolymerized) with from 0.1 to 3% by weight of a dicarboxylic acid.

In a concrete aspect, the glass fiber content in the overmolding resin composition of the invention is between 25 and 70% by weight, preferably between 25 and 40% by weight, e.g. 30% by weight.

In a specific aspect, the carbon fiber material content in the thermoplastic-fiber overmolding composition of the invention is between 10% and 70% by weight, preferably between 10 and 25% by weight, e.g. 15% by weight.

In a specific aspect there is provided a thermoplastic fiber composition comprising from 25 to 70% by weight of a blend of PA66 / PA6, from 0.3 to 2% by weight viscosity and wettability improver, from 1 to 10% by weight impact modifier, 1 to 5% toughener, 25 to 70% by weight of glass fibers and 10 to 70% by weight of carbon fibers.

The resin composition of the present invention may be applied to stacked UD carbon fiber ribbons in the form of a melt or film made by known conventional extrusion techniques, e.g. Blown film extrusion, cast film extrusion, and cast sheet extrusion, onto at least one layer of the fiber materials, e.g. be applied by coating.

• - Eine deutlich reduzierte Viskosität gegenüber vergleichbaren gehärteten Umspritzharzen (z.B. Zytel 75CG45) unter Spritzgussbedingungen, was ein ausgezeichnetes Fließ- und Werkzeugfüllverhalten ergibt;
• - Eine mit nicht gehärteten Umspritzharzen vergleichbare Viskosität unter Spritzgussbedingungen, was ein mit herkömmlichen Harzen vergleichbares Füllverhalten ergibt;
• - Gute Benetzbarkeit am Verbundstoff beim Spritzgussverfahren infolge der modifizierten Viskosität;
• - Hohe Steifheit, Festigkeit und Duktilität des umspritzen Verbundstoffs gegenüber anderen Harzen (niedrige Steifheit).

In a specific aspect of the invention, the thermoplastic overmolding composition according to the invention has advantageous properties, inter alia:

• A significantly reduced viscosity compared to comparable cured overmolding resins (eg Zytel 75CG45) under injection molding conditions, resulting in excellent flow and tooling performance;
• A viscosity comparable to non-cured overmolding resins under injection molding conditions, giving a filling behavior comparable to conventional resins;
• Good wettability on the composite in the injection molding process due to the modified viscosity;
• High stiffness, strength and ductility of the overmolding composite over other resins (low stiffness).

According to a specific embodiment, the article produced from the composition according to the invention is a bar.

According to another specific embodiment, the article is a component comprising a reinforcing layer of the composite according to the invention.

Depending on the end use, the composite structure may be formed into a desired geometry or configuration.

A method of molding the composite structure of the present invention comprises a step of forming the composite structure after fabrication and optionally preconsolidating the diagonal UD tape layer (42) , Shaping of the composite structure may be accomplished by compression molding, stamping, or any method utilizing heat and / or pressure, with compression molding and stamping being preferred. Preferably, pressure is applied by means of a hydraulic molding press. In press molding or stamping, the composite structure is heated with heating means to a temperature above the melting point of the resin composition and into a forming means such as a molding press containing a mold having a cavity in the shape of the final desired geometry, which is formed into a desired configuration and thereafter taken out of the press after being cooled to a temperature below the melting point of the resin composition. Such a molding process can also be carried out by continuous compression molding.

The composite structures according to the invention are characterized by very high directional properties in UD carbon fiber direction (higher than, for example, a biaxially balanced carbon fiber twill weave), while in the transverse direction the properties of the UD are much lower, which is advantageous when layering the UD carbon fiber tapes in the UD stack in order to achieve suitable properties for an application with a mixture of properties in normal and transverse directions. Such layer structures may include combinations of layers at 0 °, 90 ° and intermediate angles such as 45 °, 60 ° or 80 ° or at another angle between 0 and 90 °; in order to avoid distortion in these structures, it is desirable that the laminate stack be both balanced and symmetrical about the neutral axis. Examples of examples of a 2 mm strip structure with a thickness of 0.18-0.2 mm include: a UD stack [0] ₁₀ , quasi-isotropic stack [0/90 / ± 45/0] s, a directional stack [0 / 0/90/0/0] s; as further examples may be mentioned in a 1.5 mm thick stack of 8 layers of 0.18-0.2 mm thickness as in the exemplary beam structure: [90/0/0/0] s, [45/0 / -] 45/0] s, [90/0/90/0] s and [90/45/0 / -45] s.

In any event, it is desirable that the void content of the stacked UD tape (42) upon incorporation into the final overmold component exceed 2% by various intermediate processes as described above, typically 4 to 12% or about 6 to 8%.

Forming panels of these composite structures into a beam portion representative of a variety of automotive, consumer electronics, industrial or other components of this type clearly demonstrates the advantages as demonstrated in the examples below.

Because of their advantageous properties, the composite structures according to the invention can be used in numerous applications, e.g. Components for automobiles, trucks, commercial aircraft, aerospace, rail, home appliances, computer hardware, portable electronics, recreational and sports equipment, machine components, buildings, photovoltaic or mechanical devices.

Particular examples of automotive applications include: seat components and frames, hood mounts, engine mounts, suspension arms and girders, spare wheel wells, chassis reinforcements, floor panels, front modules, steering column frames, instrument panels, door systems, body panels (eg, horizontal body panels and door panels), tailgates, hardtop -Frame structures, convertible roof frame structures, roof structures, hoods, gearbox and power distribution components housings, oil sumps, airbag containers, internal vehicle impact structures, engine mounts, dashboards, stop rails, pedestrian protection beams, firewalls, parcel shelters, bulkheads, pressure vessels such as refrigerant cylinders, fire extinguishers and vessels for truck air brake systems, battery holders for hybrid electric / electric vehicles, control arms and control arms for vehicle suspensions, anti-roll bars, leaf springs, vehicle wheels, rockers for campers and motorcycles, mudguards, Roof frame and tank flaps.

Examples of household appliances are in particular washing machines, dryers, refrigerators, air conditioning and heating systems. Examples of recreational and sports equipment include inline skate components, baseball bats, hockey sticks, ski and snowboard bindings, rucksacks and frames for backpacks and bicycle frames. As examples of machine components may be mentioned in particular: electrical / electronic components such. Housing for portable electronics, televisions, screens and computers.

EXAMPLES

Example 1: Example of a finished product made from a composite according to the invention and a composite according to the comparative examples

To compare the performance of a beam of a composite according to the invention with a beam of a composite according to the comparative examples, the following experiments were carried out.

Generic bar structures were molded from a composite panel and used to investigate mechanical properties, particularly tear strength, flexibility or stiffness, displacement to peak load, and subsequent load and displacement development after peak load until failure of the beam structure. A series of bars were prepared as described below with the materials listed in Table 1. Table 1 Overmolding resin (hybrid glass-carbon overmolding resin) OM1 (comparison) PA66 GF 50 BK HS resin (Vizilon ™) commercially available, 50% by weight glass reinforced PA66, heat stabilized and black pigmented overmolding resin OM2 (resin according to the invention) As described in Table 2 carbon fiber Unidirectional (UD) carbon fiber tape (CF tape) CF UD tape 0.19 mm thick, resin 73.15% PA66 DuPont Zytel® FE310036 / 24.72% Ultramid B27 PA6 / 1.5% rheology modifier and heat stabilizer (dipentaerythritol) / 0.63% carbon black (United States 31878F1), 48% Vf carbon fiber type 12kToray T-700) → Void content 6 - 8% produced by pultrusion

In another aspect, the resin used in the CF UD tape of Table 1 has a melt viscosity of 10 to 75 Pa.s at 290 ° C and a shear rate range of 40 to 5000 reciprocal seconds, and the overmolding resin OM2 of Table 2 has a Melt viscosity of 90 Pa.s at 2000 s-1 to 720 Pa.s at 50 s ^-1 at 290 ° C.

Production of the diagonally arranged UD band

Components were coated with a Fiberforge UD band deposition cell ( US 6,607,626 . US 6,939,423 . US 8,007,894 . US 8,048,253 . US 8,168,029 ), wherein the UD tapes were arranged diagonally by passing the end of a tape reel over a CNC controlled table, each piece of UD tape being positioned accordingly, which is then cut automatically and then ultrasonically onto the tape Underlying UD tape layer was spot welded, which could be in the same or a different orientation, so that the UD tape layers were brought into an 8-layer structure. The stacking order was [90/0/90/0] s, where "90" and "0" represent the angle formed between the fiber axis and the UD tape layers in the stack (expressed in degrees).

• - Zunächst wurde diagonal angeordnetes UD-Band mit 6 - 8 % Hohlraumgehalt unmittelbar ohne zusätzliche Schmelzverbindung oder Vorkonsolidierung verwendet, wie es in den Beispielen E1 und E2 gemacht wurde.
• - Zweitens wurde diagonal angeordnetes UD-Band mit 6 - 8 % Hohlraumgehalt einem Vorkonsolidierungsschritt unterzogen, um eine Schmelzverbindung der UD-Bandschichten miteinander vorzunehmen und den Hohlraumgehalt unter 2 % zu reduzieren (6C), wie es in den Vergleichsbeispielen C1 und C2 gemacht wurde.

For comparison purposes, diagonally arranged UD tape made using the Fiberforge process was considered in the manufacture of the exemplary beam parts in two ways.

• Firstly, diagonally arranged UD tape with 6-8% void content was used immediately without additional fusing or preconsolidation, as was done in Examples E1 and E2.
• Secondly, a diagonally arranged 6 to 8% void UD tape was subjected to a preconsolidation step to fuse the UD tape layers together and reduce void content below 2% ( 6C ), as was done in Comparative Examples C1 and C2.

In Comparative Examples C1 and C2, the preconsolidation step involved fusion bonding and additional void reduction below 2% of the stacked UD tape layers using a hot / cold press after the UD tapes were positioned and locally spot welded together (hot side at 280 ° C, cold side) 180 ° C, pressure hot side 1.7 bar, cold side 12 bar, residence time at temperature under pressure 350 - 400 s hot side, 60 s cold side).

2 and 3 show the method of the comparative examples (with the preconsolidation step for reducing the void content) and the method of the invention using UD tape layers each comprising high voids UD tapes.

Void content was measured according to ISO7822 1990 (en) method C, statistical counting. Samples were prepared for optical microscopy by embedding in Strues acrylic cold embedding and polishing to produce a clear contrast between fiber, resin and voids. Images were taken with an X-Y-Z automatic X-Y stage Olympus light microscope to acquire multiple images of the sample. An area of full thickness and 15-25 mm in length was imaged with sufficient resolution to detect voids both within the bundles and between the bundles. The cavities were then counted to a binary image by segmenting the grayscale image with all features except the cavities removed and the cavity area automatically counted with the "Analysis" software.

Production of Exemplary Beam Structure

Beams were made from the diagonal UD tape made in accordance with the above description either in unconsolidated or preconsolidated form, with the combinations of overmolding resin and laminate shown in Table 4. The produced laminate was then cut to the dimensions of the beam tool with a 6-axis robotic KMT waterjet cutter.

Example E2 corresponds to bars made with unconsolidated CF UD tape layers overmoulded with a resin of the invention (OM2), while example E1 corresponds to bars containing unconsolidated (un-con) CF UD tape layers were produced which were overmolded with a comparative resin (OM1). Comparative examples C1 and C2 correspond to bars which were produced with preconsolidated (pre-con) diagonal CF UD tape layers, which were in each case encapsulated with a comparative resin (OM1) or a resin (OM2) according to the invention.

The generic bar structure is in 1 having a length of 730 mm (B), a top rib thickness of 2 mm, a width of 140 mm (B), a laminate cup thickness of 1.5 mm, overmolded with 1.5 mm overmolded polymer (G) , having a height of 15 mm, 30 mm and 50 mm in the different steps (F) on ( 1E, F , G). The width-depth-length ratio of the beam is 9.3: 4.7: 2.8 as examples of structures of this type.

4 Figure 3 is a schematic representation of the most important steps of a process according to one embodiment of the invention (B) versus a process with preconsolidating step (A) used in the comparative examples. As in 4 As shown, the inventive method used comprises two Forming steps, wherein after the warming of the cured composite structure produced in step (iv), this is overmolded with the composition according to the invention ( 4B , Left).

(41)

Vorsehen eines aus UD-Kohlefasern und einem Thermoplasten bestehenden UD-Bandes;

(42)

diagonales Anordnen des UD-Bandes und lokales Zusammenfügen der Schichten, z.B. durch Punktschweißen;

(43)

Heizen der nicht konsolidierten UD-Schichten, z.B. mit Infrarotstrahlung, oberhalb des Schmelzpunktes des Thermoplasten;

(44)

Stanzbiegen der erwärmten UD-Schichten

(45a1)

Kühlen unter Druck;

(46)

Optionales Zuschneiden der erwärmten, stanzgebogenen, gekühlten UD-Schichten;

(47)

Erwärmen der ausgestanzten UD-Schichten leicht unterhalb des Schmelzpunktes des Thermoplasten;

(48a)

Umspritzen mit der erfindungsgemäßen Umspritzharzzusammensetzung;

(45a2)

Kühlen unter Druck;

(49)

Isolieren des Endbauteils. Alternativ kann das Verfahren folgenden Schritten folgen:

(41)

Vorsehen eines aus UD-Kohlefasern und einem Thermoplasten bestehenden UD-Bandes;

(42)

diagonales Anordnen des UD-Bandes und lokales Zusammenfügen der Schichten, z.B. durch Punktschweißen;

(43)

Heizen der nicht konsolidierten UD-Schichten, z.B. mit Infrarotstrahlung, oberhalb des Schmelzpunktes des Thermoplasten;

(48b)

Überspritzen mit der erfindungsgemäßen Umspritzharzzusammensetzung;

(45b)

Kühlen unter Druck;

(49)

Isolieren des Endbauteils.

In this example, the procedure may follow these steps:

(41)

Providing a UD tape made of UD carbon fibers and a thermoplastic;

(42)

diagonal placement of the UD tape and local assembly of the layers, eg by spot welding;

(43)

Heating the non-consolidated UD layers, eg with infrared radiation, above the melting point of the thermoplastic;

(44)

Punch bending of the heated UD layers

(45a1)

Cooling under pressure;

(46)

Optional cutting of the heated, punched, cooled UD layers;

(47)

Heating the punched out UD layers slightly below the melting point of the thermoplastic;

(48a)

Overmolding with the coating resin composition of the invention;

(45a2)

Cooling under pressure;

(49)

Isolate the end component. Alternatively, the process may follow the following steps:

(41)

Providing a UD tape made of UD carbon fibers and a thermoplastic;

(42)

diagonal placement of the UD tape and local assembly of the layers, eg by spot welding;

(43)

Heating the non-consolidated UD layers, eg with infrared radiation, above the melting point of the thermoplastic;

(48b)

Overmolding with the overmolding resin composition of the invention;

(45b)

Cooling under pressure;

(49)

Isolate the end component.

In the following example, the shaping process comprises two main steps, as illustrated in more detail in FIG. 5 (example of a method according to the invention on the right and comparison method on the left):

Forming step 1:

Composite panels were cut to a size of 890 x 340 mm to fit the mold. The die-bending die tool consisted of a 1.5 mm continuous cavity steel tool tempered with a pressure pot heater / condenser so that a desired temperature could be maintained, using 140 ° C in these tests, which was adapted to the polymer composition used. The tool is guided by index bolts and shoulder blocks, which is generally known to ensure precise guidance of the tool when closing. The mold was placed in a vertical hydraulic press with under-cheek hydraulics and quick hydraulic saliva to ensure rapid closure and rapid pressure build-up. The plate materials were placed in a blank holder mounted on an electric power servo slide. The sled loaded the materials into a fast-acting medium wave infrared oven by heating the diagonally arranged UD band above the melting point of the UD band (43), ie at about 290-300 ° C, with the temperature Pyrometers was regulated. To ensure that the UD tape stacks were sufficiently melted, a residence time of 5 to 30 seconds at 290-300 ° C was used (plot of step (iii)). The carriage was then programmed to move quickly out of the IR oven to above the steel die, with the transfer time from leaving the oven to closing the press typically being 8 seconds (44). For 30 seconds, a force of 1800 kN was applied which gave a pressure of 100-150 bar for consolidation, crystallization and cooling under pressure (45a1) to ensure (representation of step (iv)) before the tool was opened and the punched part was removed. An alternative to using the blank holder and carriage is to use pick-and-place robots, eg 6-axis robots, and needle grippers. The punched out Shell structure was then removed from the mold and cut to the shape of the second phase overmold tool (46).

Forming step 2:

The punched-out shell structure was then placed in an overmold cell comprising conveyors, a 6-axis robotic vacuum robot, a forced convection heater (Reinhardt), an Engel 700T injection press, and an injection mold. The punched composite panel, which was the structural insert of the beam tool, was heated in the heating furnace to 220-230 ° C (warming up) (47) before being rapidly transferred by the robot to the open overmoulding tool. The transfer times were typically 13 s. Insulating resin compositions (composition of the invention or comparative composition) were then used and overmolded (48a) onto the punched insert such that adhesive bonding or healing (healing) occurred between the two polyamide compositions so that the molten overmold polymer melts would be at a small pitch of the stacked UD tapes into it, and while both materials cool in the overmold tool, the polymer of the stacked UD ribbons recrystallizes through the interface to give an integral part (45a2), as in FIG 7A shown. An injection pressure rating of 500 bar was used with a temperature of the injection tool of 120 ° C and a holding time of 30 seconds, which is typical for the usual field for injection molding of polyamide resins. A delayed injection was used to move the weld line away from the center of the bar with the 4-hot runner injection point control system. The overmolded bar was then removed from the mold and packaged in a dry pouch to maintain the moisture level when molded prior to testing.

Umspritzharzzusammensetzung

An overmolding resin according to the invention was coated with a 40 mm screw compound compounder and side feeders with a barrel temperature of 280 ° C., a die pressure of 19 bar, a screw speed of 300 rpm at a throughput of 120 kg / h as a mixture of nylon PA66 / 6 and dodecanedioic acid (DDDA) as a chain splitting agent to reduce viscosity and increase wettability. In addition, a toughener was added via the side feed of the mixture, a toughener after US 6,756,443 named DuPont Fusabond TRX-301 ™ copolymer, which is a polymer comprising maleic anhydride modified ethylene propylene diene monomer (EPDM) available from EI DuPont de Nemours and Company of Wilmington, Delaware, USA. Further, an impact modifier was added, namely ethylene-octene copolymer (Engage® 8180, consisting of 72% by weight of ethylene and 28% by weight of Dow Chemical Co., Midland, MI, USA). Fiber material in the form of a mixture of carbon and glass fibers was further added via the side feed and the resulting composition was cut from strands into pellets suitable for the injection molding process. The composition of the resulting coating resin according to the invention (OM2) is shown in Table 2 below. Table 2 Nature of the ingredient component % glass fiber PPG 3660 E-glass fiber, PPG 30 Viscosity & Wettability Improver DDDA 0.5 polyamide resin PA66 (DuPont Zytel 101®) 23,02 polyamide resin PA66 (DuPont Zytel 101 PWD500, ground Zytel® 101 with average particle size of 500 μm) 2 polyamide resin PA6 (BASF Ultramid B3) 17 carbon fiber Zoltek PX33CF333 48 15 impact modifiers Ethylene-octene copolymer (Engage® 8180 consisting of 72% by weight of ethylene and 28% by weight of Dow Chemical Co., Midland, MI, USA). 5.64 toughener Ethylene / propylene / hexadiene terpolymer grafted with 2.1% maleic anhydride (DuPont Fusabond TRX-301®) 3.75 Nature of the ingredient component % soot Soot AM ER 38395C1 2.44 heat stabilizer 7: 1: 1 HS tri-blend 0.4 Nucleating & Lubricant Calcium salt of long-chain linear carboxylic acids Clariant Licomont CaV102® 0.25 100

The properties of the encapsulating resin (OM2) according to the invention were compared to Zytel 75CG45 (contains no DDDA) tested according to the ISO standards listed in Table 3 at 23 ° C in the fresh state (DAM) and are below in Table 3 as the average of 5 samples shown. It can be seen that the stiffness and strength of OM2 were slightly increased and changes in elongation at break and unnotched Charpy within the standard deviation were noted. Table 3 tensile Properties OM2 Zytel 75CG45 Tensile modulus [MPa] ISO 527 17'396 16'702 Std. 202 288 Breaking strength [MPa] ISO 527 192.7 175.3 Std. 1.4 0.9 Elongation at break [%] ISO 527 3.2 3.4 Std. 0.1 0.2 Uncorked CHARPY value [kJ / m2] ISO 179 / 1eU 81.5 83.8 Std. 3.5 6.6 Multiaxial puncture Strength [N] ISO 6602-3 892.9 944.8 Energy [J] ISO 6602-3 0.3 3

By modifying the overmolding resin to reduce viscosity, increased wetting could be achieved at the interface. Table 4 compares the overmolding resin (OM2) according to the invention with the same composition without DDDA (Zytel 75CG45) and the glass filled comparative overmolding resin with lower stiffness, since it contains only glass fibers (Zytel 70G50HSLA BK039B, OM1). Table 4 sample Shear rate [1 / s] Viscosity [Pa-s] OM1 Zytel 70G50HSLA BK039B 50.0 498.3 100.0 375.9 250.0 255.6 500.0 183.6 750.0 157.6 1000.0 139.7 2000.0 103.0 Zytel 75CG45 50.0 2136.0 100.0 1540.8 250.0 822.0 500.0 547.3 750.0 416.1 1000.0 350.4 2000.0 223.2 sample Shear rate [1 / s] Viscosity [Pa-s] OM2 50.0 719.8 100.0 536.7 250.0 277.7 500.0 196.1 750.0 147.7 1000.0 129.4 2000.0 93.6

It can be seen that the elongation at break is greater than 3% while maintaining a tensile modulus of 17 GPa to yield a tough but stiff overmolding material, while maintaining the lower viscosity of a conventional overmolding resin such as that shown in FIG. OM 1 Zytel 70G50HSLA BK039B, which contains no DDDA to maintain.

Tests on the exemplary beam structure

To demonstrate the advantages of composite structures using the example of the beam structure, the beams were tested in a mechanics laboratory according to the following sequence of steps, as in 1C and 1D shown.

The bars were tested on a servohydraulic universal testing machine from Instron with an extended test bench. Solid steel beams were made and the beams were fixed to the backing plates with 6 x steel bolts at each end, which were tightened with a snap. A force was applied to the center of the beam with a 37mm radius loading nose. The test carriers had a radius of 4 mm and the span was 452 mm. The tests were performed at 23 ° C and the samples were DAM. The test speed was 0.2 in / min. Three replicates were made for each of Examples C1, C2, E1, E2, with the average results shown in Table 5 below (VC is void content, as measured above). Table 5 Ex. Treatment diagonally arranged UD band OM resin Peak load (kN) Shift at peak load (mm) Energy up to peak load (J) Shift in case of failure (mm) Energy to failure (J) Compliance before turning point (kN / mm) C1 pre-con OM2 25.9 44.1 593.9 52.4 762.3 1.20 C2 pre-con OM1 20.9 36.8 401.8 37.3 410.7 1.27 E1 un-con OM2 23.9 54.7 775.9 87.9 1469.2 1.22 E2 un-con OM1 23.1 36.8 434.1 38.1 461.8 1:33

It can be seen that the preconsolidation step, which reduced the void content of the UD tape below 2%, did not increase the compliance of the beam, which was 1.20 kN / mm for C1 and 1.22 for E1 (both overmoulded with resin OM2) and 1.27 kN / mm for C2 and 1.33 for E2 (both overmoulded with resin OM1). The peak power was slightly higher at C1 than at E1, while between C2 and E2 the peak power of the unconsolidated material was slightly higher. Consequently, the unconsolidated UD band may be considered equivalent to the pre-consolidated UD band from the viewpoint of component stiffness and peak load, which is a surprising finding.

It can also be seen that the combination of unconsolidated UD band and OM2 resulted in increases in peak load energy, which was determined by integrating the area under the force-displacement curve. The OM2 overmoulded C1 (pre-consolidated) had an energy up to peak load of 594 J, which was less than the energy to peak load of the same resin overmolded, non-pre-consolidated E1 (776 J). Surprisingly, the desired increase in peak load energy was not observed using either the OM1 overmolded consolidated UD tape (C2) or the OM1 overmolded unconsolidated UD tape (E1); this requires the use of OM2 and unconsolidated UD tape. It should be noted that the unexpected significant improvements in the properties of the beams not only in the energy to peak load, but v.a. (which is desirable) at the energy to failure of the bar occur. There was a 2-fold increase in energy to failure of the beam achieved by the new combination of unconsolidated UD tape and OM2 resin. Specifically, E1 with unconsolidated UD band and OM2 had energy at beam failures of 1469 J, i. Almost twice the energy at beam failures at C1, where pre-consolidated UD band and OM2 resin were observed (762 J).

The same unconsolidated UD tape has no such improvement in energy to beam failure when overmoulded with a comparative resin (OM1) as Comparative Example E2 using unconsolidated UD tape and OM1 resin and energy at beam failures of 462 J, which corresponds to Comparative Example C2 with preconsolidated UD tape and OM1 resin (411 J).

These results support the beneficial effects of the unconsolidated UD band and OM2 combination in achieving energy doubling to bar failure with equivalent stiffness and peak beam strength.

In this experiment, conventional glass fiber joists typically break in the middle of the beam, causing catastrophic failure when the glass laminate in the middle of the beam fails. This leads to a sudden load drop. Carbon fiber laminate beams, while stiffer, fail in the same manner with central catastrophic failure.

On the other hand, the beams made of laminates of the present invention have a conventional UD CF band beam of equivalent peak load and stiffness, exhibiting a significant increase in energy absorption and displacement to failure against the preconsolidated UD CF tape beams.

Furthermore, the inventive method results in materials with increased stiffness compared to conventional cured glass fiber compositions (eg WO 2004 / 022652A1 ).

Thus, the methods and materials of the invention offer the possibility of reducing the overall manufacturing cost of the carbon fiber components (by avoiding pre-consolidation prior to conversion into the final component) and thereby achieve the desired crash performance.

Another characteristic of the results of the bending tests is the void content in the area of the UD band of the overmolded beam (in 7 and 8th shown) as well as the possibility of error of the area of the UD band of the bar of 10 , It can be seen that the increased energy absorption with the combination of non-pre-consolidated UD tape and overmoulding with OM2 resin is due to the composite's microstructure and resulting failure mode, which together lead to a surprising increase in energy absorption.

In the 9 It can also be seen that the UD tape as fabricated has a voids content of 6-8%, with the voids occurring within local carbon fiber agglomerations and not within the resinous regions between the carbon fiber bundles. This is due to the difficulty of impregnating the interior of the bundles with high local fiber volume (low permeability) and the relatively high viscosity of the resin (over other fluids).

In the comparative example, the preconsolidation achieves a reduction in void content by additional heat and pressure treatment to produce a homogeneous plate. 6A and C show that its flat UD belt plate, which has been preconsolidated and not stamped, has a voids content below 2%. UD tape stamped into a flat plate after IR heating but without preconsolidation step has a voids content of 6 - 9% ( 6A and B). In a preconsolidated sample, which has also been warmed up and punched (Figures A and D), the void content is also below 2%, ie the heating and punching process carried out does not increase void content. In the comparative example, it is well known that its preconsolidation for lowering the initial void content increases the rupture strength, for example, in tensile strength tests against void-filled samples, while it is also desirable for cost-reduction to omit this phase, as is the case with the present invention.

7 Figure 3 shows the micrographic results and void contents achieved in Example 1, wherein diagonally arranged UD tape has been punch-bent either with or without a prior preconsolidation step and subsequently overmoulded with a comparative resin or the resin composition of the invention. The differences are in 8th to recognize in more detail; this shows the overall structure, a first detail enlargement of an example section and a second, more detailed enlargement of the fiber agglomerations and the local resinous areas as well as the locations of the cavities in the structure. At C1, the diagonally arranged UD tape was die-cut with prior preconsolidation and then overmoulded with overmolding resin 2 (C), with the shallower and wider agglomerations of UD fibers (0.2 to 1 mm) with smaller resinous regions (0.1 0.2 mm) and an overall more homogeneous microstructure can be seen ( 8A ). In contrast, shows 8B a microgram of E1, wherein diagonally arranged UD tape which has not been preconsolidated to a flat plate and then punched, followed by overmoulding with the overmolding resin 2, wherein UD fiber agglomerations (0.1 to 0.6 mm) internal cavities in the middle of the agglomeration and the shape of the agglomeration in 8A Rather square or circular than rectilinear or ellipsoid, and where the UD fiber agglomerations are spaced apart by wider resin rich regions of much smaller fiber fraction (0.1 to 0.4 mm) than C1 and thus have a less homogeneous microstructure overall.

Thus, the improved energy absorption in the tests, without sacrificing component stiffness, is achieved by a less homogeneous microstructure with increased void content in the center of the local carbon fiber agglomerations with resinous regions between these agglomerations when used with the tough, less viscous overmolding resin OM2.

It should be noted that void content after punch bending in non-preconsolidated UD is 6 - 9% ( 6B but was reduced to less than 3% after overinflation due to the pressures applied during overspraying and heating of the punched UD tape insert prior to overspraying.

The microstructure after 8B gives a change in the possibility of error as observed in the bar tests and in 10 is shown. For preconsolidated bars with OM1 and OM2 (C2 and C2 of the 10B and D ), the diagonal UD tape has failed due to shearing force in the sidewall, stress in the flange and compression in the base without string-like fracture due to the more homogeneous microstructure. For non-preconsolidated bars with OM1 and OM2 (E2 and E1 in 10A and C ), the diagonally arranged UD bands with strand-like behavior and delaminations between the UD band layers are refracted over a much wider fracture surface, which forms the agglomerations of the 8B equivalent. If not preconsolidated, punched out UD is then overmolded with OM2, the UD fibers are again broken with an even more recognizable strand-like behavior, the agglomerations of 8B with breaking through the three load introduction points (E1 in 10C ).

Thus, the improved energy absorption in the tests, without sacrificing component stiffness, is achieved by having a less homogeneous but controlled microstructure with increased void content in the center of the local carbon fiber agglomerations with resinous regions between these agglomerations when combined with the tough, less viscous overmolding resin OM2 which results in strand-like failure of the UD tape layers with delamination between UD tape layers with stress domain rupture and force retention in flexure due to higher displacements.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6607626 [0103]
• US 6939423 [0103]
• US 8007894 [0103]
• US8048253 [0103]
• US 8168029 [0103]
• US Pat. No. 6756443 [0116]
• ER 38395 C1 [0116]
• WO 2004/022652 A1 [0128]

Claims (35)

A method of making a carbon fiber composite structure comprising: (i) providing at least two layers of unidirectional (UD) carbon fiber tape, the UD carbon fiber tape comprising unidirectional carbon fibers impregnated in a thermoplastic, wherein the fiber to resin ratio is in the range of 50% to 70% and the initial one Void content before stacking exceeds 2%; (ii) stacking the at least two layers of UD carbon fiber ribbon in a diagonal arrangement with respect to each other; (iii) applying heat at a temperature suitable for melting the thermoplastic; (iv) cooling the heated stacked layers under pressure to cure the composite structure, wherein the heated stacked layers are overmolded with a thermoplastic-fiber composition, the thermoplastic-fiber composition comprising a glass fiber material, a carbon fiber material, and a polyamide resin. Method according to Claim 1 wherein the overmolding composition comprises a viscosity and wettability improver. A method according to the preceding claim, wherein the viscosity and wettability improver comprises dodecanedioic acid (DDDA). Method according to one of the preceding claims, wherein the overmolding composition comprises a toughener and / or an impact modifier. A process according to the preceding claim, wherein the toughener comprises an ethylene / propylene / hexadiene terpolymer grafted with between 5% and 0.1% maleic anhydride. A method according to any one of the preceding claims wherein the fiberglass content in the overmold composition is between 25 and 70 weight percent. A method according to any one of the preceding claims, wherein the carbon fiber content in the overmold composition is between 10% and 70% by weight. A method according to any one of the preceding claims, wherein the thermoplastic in the overmolding composition is a blend of polyamide resin PA66 / PA6 between 35 and 70% by weight. A method according to the preceding claim, wherein the mixture comprises a PA66 / PA6 content of between 90 and 10% by weight. A method of making a carbon fiber composite structure comprising: Providing at least two layers of UD carbon fiber tape and stacking these layers in a diagonal arrangement; Overmolding the heated stacked layers with a molten thermoplastic overmolding resin composition to ensure cure between the two thermoplastics and then cooling the stacked layers under pressure to cure the thermoplastic to form the composite structure, the UD carbon fiber ribbons UD- Carbon fibers which are pre-impregnated with a thermal load and have an initial void content exceeding 2% before stacking; and wherein the thermoplastic overmolding resin composition comprises: between 25 and 70% by weight of glass fiber material; between 10 and 70% by weight of carbon fiber material; between 25 and 70% by weight of polyamide resin mixture PA66 / PA6; between 0.3 and 2% by weight of viscosity and wettability improvers, e.g. dodecanedioic; a toughener such as ethylene / propylene / hexadiene terpolymer grafted with 3 to 4% maleic anhydride. Method according to one of the preceding claims, wherein the layer stack before injection molding comprises 2 to 26 layers UD carbon fiber tape. A method according to any one of the preceding claims, wherein the angle between the fibers of one of two diagonally stacked layers is between 0 and 90 ° relative to the other. Method according to one of the preceding claims, wherein the void content is between 4 and 8%. A method according to the preceding claim, wherein the void content is between 6 and 8%. The method of any one of the preceding claims, wherein the heat treatment applied to the stacked layers is at a temperature of about 290 to about 300 ° C. A method according to any preceding claim, wherein the pressure applied to the stacked layers in the cooling step is from about 10 to about 150 bars. The method of any one of the preceding claims, wherein the overmolding step is carried out in a period of less than 2 minutes at temperatures of from about 120 to about 160 ° C and pressures greater than about 200 to 1000 bar. A method according to any one of the preceding claims, wherein each resin impregnated UD carbon fiber ribbon layer has a basis weight of 200 to 500 g / m ² . A method of making a thermoplastic composition comprising the steps of: (a) providing a blend by melt mixing the polyamide resins PA66 / PA6, wherein the weight ratio between the two polyamides comprises between 40 and 100 weight percent PA66, in combination with a viscosity and wettability Improver chosen from the following group: dodecanedioic acid, lysine, alanine, pentaerythritol and H ₂ O; (b) adding an ethylene / propylene / hexadiene terpolymer grafted with 3 to 4% maleic anhydride as toughening agent to the mixture of step (a) (c) adding a mixture of carbon fiber and glass fiber material to the mixture of step (b) such that the resulting blend to 25 and 70 wt.% PA66 / PA6, 0.3 and 2 wt.% Viscosity and Wettability Improver, 1 and 5 wt.% Toughener, 25 and 70 wt.% Glass Fiber and 10 and 70 wt.% Contains carbon fibers. Composite structure obtained in a process according to any one of the preceding claims. A carbon fiber composite structure comprising at least two stacked layers of UD carbon fiber in a diagonal array impregnated with a thermoplastic and an overmolded thermoplastic fiber composition, said composition comprising a glass fiber material, a carbon fiber material and a polyamide resin, said void content the stacked UD carbon fiber layers is between 3 and 10%. A composite structure according to any one of the preceding claims, wherein the ratio of resin to UD carbon fiber is in the range of 0.3 to 0.5% by weight. A composite structure according to any one of the preceding claims wherein the overmolded thermoplastic fiber composition is overmolded by injection. A composite structure according to any one of the preceding claims, wherein the void content is between 4 and 8%. A composite structure according to any one of the preceding claims, wherein the overmolded thermoplastic fiber composition comprises glass fiber material. A composite structure according to any one of the preceding claims, wherein the overmolded thermoplastic fiber composition comprises carbon fiber material. A composite structure according to any one of the preceding claims, wherein the overmolded thermoplastic fiber composition comprises a blend of the polyamide resins PA66 / PA6. A composite structure according to any one of the preceding claims, wherein the thermoplastic fiber overmold composition comprises a viscosity and wettability improver selected from the group consisting of dodecanedioic acid, lysine, alanine, pentaerythritol and H ₂ O. A composite structure according to any one of the preceding claims, wherein the thermoplastic fiber overmold composition comprises a toughening agent, e.g. a grafted with 3 to 4% maleic anhydride ethylene / propylene / hexadiene terpolymer. A composite structure according to any one of the preceding claims, wherein the resin composition has a melt viscosity at 290 ° C between 10 and 400 Pa.s, in particular between 10 and 75 Pa.s. A composite structure according to any one of the preceding claims, wherein the resin composition has a melting point of between about 220 and 280 ° C, especially 250-275 ° C. A composite structure according to any one of the preceding claims comprising 2 to 26 UD carbon fiber ribbon layers. A composite structure according to any one of the preceding claims, wherein each carbon fiber layer has a basis weight of between 200 and 500 g / m ² . A thermoplastic resin composition comprising 25 to 70% by weight of a mixture of PA66 / PA6, 0.3 to 2% by weight of viscosity and wettability improver, 1 to 5% by weight toughener, 25 to 70% by weight of glass fiber and 10 to 70% by weight of carbon fiber. An article made from or comprising the composite structure according to any one of the preceding claims.

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