EP2231378A1

EP2231378A1 - Article or layer made of a fiber reinforced composite material and injection molding method of production thereof

Info

Publication number: EP2231378A1
Application number: EP08856464A
Authority: EP
Inventors: Klaus Müller; Klaus Klemm
Original assignee: Basell Poliolefine Italia SRL
Current assignee: Basell Poliolefine Italia SRL
Priority date: 2007-12-05
Filing date: 2008-12-04
Publication date: 2010-09-29
Also published as: WO2009071290A1

Abstract

The present invention relates to an article or layer made of a composite material comprising a plastic material reinforced with fibers, said article or layer comprising at least one segment of a predominantly two-dimensional structure with a first and a second surface and a basis thickness of the segment and at least one of the surfaces of the segment shows a surface profile with dents or knobs or dents and knobs, wherein the surface with the surface profile has a continuous basis surface, in which the dents are impressed or of which the knobs stick out, and the basis thickness of the segment is the distance between the basis surface of the surface with the surface profile and the other surface, if only one surface has a surface profile, or the basis thickness of the segment is the distance between both basis surfaces, if both surfaces have a surface profile, wherein in case of dents the distance between the surface in the area of the dent and the other surface, if only one surface has a surface profile, or the other basis surface is at least 10% less than the basis thickness and in case of knobs the distance between the surface in the area of the knob and the other surface if only one surface has a surface profile, or the other basis surface is at least 10% more and at the most 200% more than the basis thickness; and wherein at least 10% of the surface with the surface profile are knobs or dents. Furthermore, the present invention provides layered composite materials comprising such layers, methods of producing such articles or layers and the use of the articles or layered composite materials as as component or part of a component produced by or for the automotive industry or as component or part of a component of a household appliance.

Description

Article or layer made of a fiber reinforced composite material and injection molding method of production thereof

The invention relates to the field of articles or layers made of composite materials, in particular to composite materials comprising a plastic material reinforced with fibers, in which the articles or layers may be prepared by injection molding the plastic fiber-reinforced material, and in which the resulting articles or layers exhibits strength and fracture characteristics that are reduced in anisotropy. The invention further relates to methods of production of such articles or layers by injection molding.

lsotropy of strength and fracture-resisting characteristics may be introduced into composite materials by specifically orienting the fibers in different directions. This technique is particularly effective with large molded structures in which woven or unwoven sheets of relatively long fibers may be oriented to resist particular stress patterns to which the structure may be expected to be subjected.

However, such techniques are inapplicable to methods of producing fiber-reinforced articles by injection molding: the fluidity requirements that are placed upon the injected material by such technique necessitate the use of fibers which are not aggregated and which are also of restricted length.

The injection molding process imposes sheer effects and flow stresses upon an injected fiber- reinforced plastic material which introduce a very substantial orientation of the fibers in the direction of flow of the plastic material. These flow-related fiber orienting influences are much stronger than any randomizing influences upon fiber orientation, such as turbulence, that may be inherently associated with the process. The reinforcing fibers therefore remain similarly oriented in the injection molded composite material: in consequence the ability of the composite material to resist fracture parallel to this orientation of the fibers is greatly reduced in comparison to its ability to resist fracture perpendicular to this orientation. This characteristic of anisotropy in strength can be a severe disadvantage of such injection molded composite materials, particularly where such materials are used to manufacture components subject to mechanical stresses repetitively or for extended durations.

Consequently, there remains a need in the art for methods of injection molding plastic materials reinforced with fibers to form articles which possess strength and fracture characteristics that are reduced in anisotropy or even substantially isotropic, and do not exhibit a weakness or propensity to fracture in any particular direction. However, it should be possible to maintain economically important criteria, such as straightforward manufacturing processes, cost-effective production of the products and use of materials customarily and widely available in the market. The present invention addresses this need existing in the art, and is applicable to injection molding methods using those plastic materials reinforced with fibers generally employed in the art. However, contrary to the standard procedure in the art, the present invention ensures that during the injection step the flow of fiber-reinforced plastic material is modified in a controlled manner, thereby causing the fibers to become oriented in a multiplicity of directions.

The present inventors have surprisingly and unexpectedly observed that by imposing a surface profile upon one or both surfaces of a predominantly two-dimensional structure of fiber-reinforced plastic material during injection molding, so that thickness variations are introduced into the structure as it is being formed, a significant improvement in mechanical properties can be achieved. In particular, the resulting two-dimensional structure of fiber-reinforced plastic material has a greatly improved ability to withstand both mechanical stress and fracture propagation imposed in a direction parallel to that of the direction of flow of the material during its formation by injection.

Thus the present invention provides articles or layers of improved strength, and a method of manufacturing them by injection molding. The articles or layers are made of a composite material comprising a plastic material reinforced with fibers, said article or layer comprising at least one segment of a predominantly two-dimensional structure with a first and a second surface and a basis thickness of the segment and at least one of the surfaces of the segment shows a surface profile with dents or knobs or dents and knobs, wherein the surface with the surface profile has a continuous basis surface, in which the dents are impressed or of which the knobs stick out, and the basis thickness of the segment is the distance between the basis surface of the surface with the surface profile and the other surface, if only one surface has a surface profile, or the basis thickness of the segment is the distance between both basis surfaces, if both surfaces have a surface profile, wherein in case of dents the distance between the surface in the area of the dent and the other surface, if only one surface has a surface profile, or the other basis surface is at least 10% less than the basis thickness and in case of knobs the distance between the surface in the area of the knob and the other surface, if only one surface has a surface profile, or the other basis surface is at least 10% more and at the most 200% more than the basis thickness; and wherein at least 10% of the surface with the surface profile are knobs or dents.

Furthermore, the present invention provides layered composite materials comprising such layers, methods of producing such articles or layers and the use of the articles or layered composite materials as component or part of a component produced by or for the automotive industry or as component or part of a component of a household appliance.

The features and advantages of the present invention can be better understood via the following description and the accompanying drawings. Figure 1 shows a suds container constructed of plastic comprising a plurality of segments of a predominantly two-dimensional structure.

Figure 2 illustrates a segment of the invention in plan view. Hexagons (2) represent dents in the continuous basis surface (1). It is assumed that the second surface is plane without a surface profile. Sections A-B and C-D through the segment are illustrated, indicating inter alia the surface profile of the first surface. The sections show that the distance between the surface in the area of the dents and the second surface is about 33% less than the basis thickness. About 17% of the surface with the surface profile are hexagonal dents (2).

Figure 3 illustrates a segment of the invention in plan view. Hexagons (3) represent knobs in the continuous basis surface (1). It is assumed that the second surface is plane without a surface profile. Sections A-B and C-D through the segment are illustrated, indicating inter alia the surface profile of the first surface. The sections show that the distance between the surface in the area of the knobs and the second surface is about 50% more than the basis thickness. About 47% of the surface with the surface profile are hexagonal knobs (3).

Figure 4 demonstrates a surface profile of the present invention with knobs (3) of circular shape. About 54% of the surface with the surface profile are knobs (3).

Figure 5 demonstrates a surface profile of the present invention with knobs (3) of octagonal shape. About 53% of the surface with the surface profile are knobs (3).

Figure 6 demonstrates a surface profile of the present invention with knobs (3) of triangular shape. About 43% of the surface with the surface profile are knobs (3).

Figure 7 demonstrates a surface profile of the present invention with knobs (3) of a rectangular shape with rounded corners. About 40% of the surface with the surface profile are knobs (3).

Figure 8 demonstrates a surface profile of the present invention with knobs (3) of V-shape.

Figure 9 illustrates a segment of the invention in plan view. Hexagons (3) and (3¹) represent knobs of different height in the continuous basis surface (1). It is assumed that the second surface is plane without a surface profile. Sections A-B, C-D and E-F through the segment are illustrated, indicating inter alia the surface profile of the first surface. The sections show that the distance between the surface in the area of the knobs (3) and the second surface is about 33% more than the basis thickness and the distance between the surface in the area of the knobs (3¹) and the second surface is about 80% more than the basis thickness. Figure 10 illustrates a segment of the invention in plan view. Hexagons (2) and (2¹) represent dents of different depth in the continuous basis surface (1). It is assumed that the second surface is plane without a surface profile. Sections A-B and C-D through the segment are illustrated, indicating inter alia the surface profile of the first surface. The sections show that the distance between the surface in the area of the dents (2) and the second surface is about 25% less than the basis thickness and the distance between the surface in the area of the knobs (2') and the second surface is about 45% less than the basis thickness.

Figure 11 shows the surface profile of Figure 4 in enlarges scale with dents (4) and (5) of circular structure. Arrow (6) indicates the general direction of the melt flow. Dotted arrows (7) indicate the direction of the melt flow in the region of dent (5). Continuous strokes (8) demonstrate the orientation of the fibers after the solidification of the melt in vicinity of dent (5).

The customary construction of a molded plastic component - as for example, a component of a suds container constructed of plastic - provides even, smooth-sided, partly ribbed structures that are often omega-form in cross-section to improve rigidity (see for example Figure 1). That means, such articles have frequently segments, which have a predominantly two-dimensional structure. Such construction principles may also be used for plastic components for use in a variety of machines such as household appliances (e.g. drums of a washing machine or spin-dryer), for components of industrial tools or industrial products such as those used or produced by the automotive industry. The construction principle can be combined with the use of plastic materials reinforced with either mineral products or glass fibers: the plastic material frequently being reinforced polypropylene, as disclosed for example in WO 01/44556 A1.

By using this form of construction with polypropylene reinforced with short glass fibers, the short glass fibers orient themselves more or less uniformly in an orientation conforming to the direction of flow of the plastic material as it flows into and through the mold during injection molding. This can lead to the resulting article having significantly different mechanical properties when measured 'along' (i.e. parallel to) versus 'across' (i.e. perpendicular to) the direction of this flow. The stiffness and rigidity properties of the resulting fiber-reinforced material, e.g. polypropylene, across this direction of flow do not exceed those of the equivalent mineral-reinforced material. This in turn limits the uses of short glass fiber reinforced polypropylene for thin-walled molded parts. An application of polypropylene reinforced with short glass fibers for the production of suds containers, which are optimized for rigidity - and therefore also for costs, has not been possible because the strength and rigidity enhancing potential of glass fibers reinforcement could not fully been tapped.

The invention particularly concerns the arrangement of the surface structure, especially in form of a surface profile, and the thickness distribution of articles or layers molded from fiber-reinforced plastic, and methods of manufacturing such articles or layers by injection molding. The invention permits and facilitates the use of plastic material reinforced with short fibers, for example short glass fibers, in circumstances in which the use of such fibers would otherwise not be possible or appropriate due to the directional dependency of the mechanical properties of such plastic materials when conventionally manufactured. The invention therefore allows fibers, such as short fibers, and particularly short glass fibers, to replace other reinforcing materials which are currently in use and which do not exhibit such directionally dependent properties: such as minerals, e.g. talc or chalk.

The article or layer of the present invention is made of a composite material comprising a plastic material which is reinforced with fibers. In preferred embodiments of the invention the plastic material is a thermoplastic polymer. Examples of advantageously usable thermoplastic polymers are polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polysulfones, polyetherketones, polyesters, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) or polyalkylene naphthalate, polycycloolefins, polyacrylates, polymethacrylates, such as polymethylmethacrylate (PMMA), polyamides (PA), such as poly- epsilon-caprolactam or polyhexamethyleneadipamide or polyhexamethylene sebacamide, polycarbonate (PC), polyurethanes, polyacetals, such as polyoxymethylene (POM), polystyrene (PS), acrylonitrile/butadiene/styrol copolymer (ABS), liquid crystal polymer (LCP), e.g. liquid crystal copolyester, or polyphenylene sulfide (PPS). It is also possible to use mixtures of such thermoplastic polymers as plastic material of the present invention.

Homopolymers and copolymers are in principle suitable as thermoplastic polymers. Copolymers of propylene and ethylene or of ethylene or propylene and other olefins having 4 to 10 carbon atoms, or co- or terpolymers of styrene and smaller proportions of butadiene, alpha- methylstyrene, acrylonitrile, vinylcarbazole or esters of acrylic or methacrylic or itaconic acid are particularly worthy of mention in the context. The plastic material may also comprise said thermoplastic polymers in recycled form in amounts of up to 60% by weight, based on the total weight of the plastic material reinforced with fibers for improving the cost-efficiency of its production.

According to the invention, the term polyoxymethylene (POM) is understood as meaning homopolymers as well as copolymers of aldehydes, such as formaldehyde or acetaldehyde, but preferably of cyclic acetals. For POM, it is characteristic that repeating carbon-oxygen bonds always typify the appearance of the molecular chain. If polyester is to be used for the present invention, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) are preferred. Both are high-molecular-weight esterification products of terephthalic acid and, respectively, ethylene glycol and butylene glycol. Suitable copolymers of styrene are in particular copolymers comprising up to 45% by weight, preferably comprising up to 20% by weight, of acrylonitrile incorporated in the form of polymerized units. Further terpolymers of styrene comprise up to 35% by weight, in particular up to 20% by weight, of acrylonitrile incorporated in the form of polymerized units and up to 35% by weight, preferably up to 30% by weight, of butadiene.

Preferably the plastic material comprises a polyolefin, such as polyethylene or polypropylene, of which polypropylene is particularly preferred. According to the invention, polypropylene is understood as meaning homopolymers as well as copolymers of propylene. Suitable copolymers of propylene comprise up to 50% by weight of further monomers copolymerizable with propylene, such as 1 -olefins having 2 or 4 to 8 carbon atoms. If required, two or more comonomers may also be used. Suitable copolymers are preferably random copolymers but may also be block copolymers.

The polymerization for the preparation of PP can usually be effected under a pressure in the range from 1 to 100 bar (from 0.1 to 10 MPa) in suspension or in the gas phase and in the presence of a Ziegler-Natta catalyst system. Those catalyst systems which, in addition to a titanium-containing solid component, also comprise cocatalysts in the form of organic aluminum compounds and electron donor compounds are preferred.

Ziegler-Natta catalyst systems comprise as a rule a titanium-containing solid component, in particular halides or alcoholates of trivalent or tetravalent titanium, and also a halogen-containing magnesium compound, inorganic oxides, such as silica gel, as support material and electron donor compounds. In particular, carboxylic acid derivatives or ketones, ethers, alcohols or organosilicon compounds may be mentioned as electron donor compounds.

The titanium-containing solid component can be prepared by known processes for example as described in EP 0 761 696 Al

Cocatalysts suitable for the Ziegler-Natta catalyst systems are, in addition to trialkylaluminium, also those compounds in which an alkyl group is replaced by an alkoxy group or by a halogen atom, such as chlorine or bromine. The alkyl groups may be identical or different. Linear or branched alkyl groups are also suitable. Trialkylaluminium compounds whose alkyl groups comprise 1 to 8 carbon atoms, for example triethylaluminium, triisobutylaluminium, trioctylaluminium or methyhdiethylaluminium or mixtures thereof, are preferably used according to the invention.

The preparation of PP can however also be effected in the presence of a metallocene as a catalyst. Metallocenes are to be understood as meaning complex compounds having a layer structure and comprising metals from the subgroups of the Periodic Table of the Elements plus organic, preferably aromatic, ligands. For their use for the preparation of PP, the metallocene complexes are expediently applied to a support material. The inorganic oxides which are used for the preparation of the titanium-containing solid component in Ziegler-Natta catalysts have also proven to be useful as support material.

Metallocenes usually used comprise, as a central atom, titanium, zirconium or hafnium, of which zirconium is preferred. The central atom is linked via a pi bond to at least one pi system which is embodied by a cyclopentadienyl group. The cyclopentadienyl group is equipped in the vast majority of cases with additional substituents, by means of which the activity of the catalyst can be controlled. Preferred metallocenes comprise central atoms which are bonded via two identical or different pi bonds to two pi systems which may simultaneously also be part of corresponding heteroaromatic systems.

In principle, any compound, which can convert the neutral metallocene into a cation and can stabilize it, is suitable as a cocatalyst for the metallocene. In addition, the cocatalyst or the anion formed from it should not undergo any further reactions with the metallocenium cation formed, which is stated in EP 0 427 697. The preferably used cocatalyst is an aluminium compound and/or a boron compound. A preferably used cocatalyst is an aluminium compound, such as alumoxane and/or an alkylaluminium.

The plastic material of the present invention is reinforced with fibers. The reinforcing fibers may be selected from glass fibers and carbon fibers, preferably being short fibers of up to 4 mm in length, preferably less than 2 mm and more preferably of 1 mm or less; they are preferably short glass fibers. The fibers may also be coated glass fibers. The content of fibers is from 1 to 60% by weight, preferably from 5 to 50% by weight, particularly preferably from 10 to 40% by weight, based on the weight of the reinforced plastic material.

The plastic material reinforced with fibers may comprise further reinforcing fillers. Examples are barium sulfate, magnesium hydroxide, talc having a mean particle size in the range from 0.1 to 10 μm, measured according to DIN 66 115, wood, flax, chalk, glass beads or mixtures of these. In addition, the lower substrate layer may comprise further additives, such as light stabilizers, UV stabilizers and heat stabilizers, pigments, carbon blacks, lubricants and processing aids, flame retardants, blowing agents and the like, in respectively advantageous amounts.

The invention refers to segments of an article or to layers within an article which have a predominantly two-dimensional structure wherein the two-dimensional segment of the article may of course also form the whole article. According to the present invention, at least one of the two surfaces of such a predominantly two-dimensional structure has a surface profile with dents or knobs or dents and knobs. Such a surface with a surface profile of the present invention has a continuous basis surface in which dents are impressed or of which knobs stick out. The basis thickness of the segment of the predominantly two-dimensional structure is the distance between the continuous basis surface of the surface with the surface profile and the other surface, if only one surface has a surface profile, or it is the distance between both basis surfaces, if both surfaces have a surface profile. In a preferred embodiment only one of the surfaces of the segment shows a surface profile.

In case the surface with the surface profile possesses dents, the distance between the surface in the area of the dents and the other surface, if only one surface has a surface profile, or between the surface in the area of the dents and the other basis surface, if both surfaces have a surface profile, is at least 10% less than the basis thickness. Preferably this distance is less than 20%, more preferably less than 25% and even more preferably less than 30% of the basis thickness. However, usually this distance is at the most 80% less than the basis thickness, preferably at the most 60% less than the basis thickness and more preferably at the most 55% less than the basis thickness. Most preferred for this distance is a range of from 30% to 50% less than the basis thickness.

In case the surface with the surface profile possesses knobs, the distance between the surface in the area of the knobs and the other surface, if only one surface has a surface profile, or between the surface in the area of the knobs and the other basis surface, if both surfaces have a surface profile, is at least 10% more and at the most 200% more than the basis thickness. Preferably the distance is from 17.6% to 150% and more preferably from 25% to 81.8% more than the basis thickness. Most preferred for this distance is a range of from 40% to 70% more than the basis thickness.

For a surface with the surface profile of the present invention at least 10%, preferably at least 20% of the surface are knobs or dents. In preferred embodiments knobs or dents constitute from 25% to 75%, more preferably from 30% to 70%, even more preferably from 35% to 65%, yet more preferably from 40% to 60%, and most preferably from 45% to 55% of the surface with the surface profile.

All combinations of ranges of the distance between the surface in the area of the dents or knobs and the other surface or basis surface with ranges of the proportion of knobs or dents on the surface with the surface profile, as each of these parameters is disclosed hereinabove, are specifically contemplated as being encompassed by the invention.

The dents or knobs may optionally be geometrically shaped. Figure 2 shows a surface with surface profile wherein the continuous basis surface (1) has dents (2), which have in this case a hexagonal structure. Figure 3 displays in contrast a surface with surface profile wherein the continuous basis surface (1 ) has knobs (3), which have in this case also a hexagonal structure. In general there is no limit to the shape of the dents or knobs. Figures 4 to 6 display examples for knobs (3), which are of circular, octagonal or triangular shape. The knobs shown in Figure 7 and 8 are rectangular with rounded corners or in a V-shape. Normally the dents or knobs are located on the surface in a repetitive pattern.

The surface with surface profile may have more than one type of dents or knobs. The dents or knobs may differ in shape. They may however also differ in depth or height, that means for dents that the distance between the surface in the area of the dents and the other surface or the other basis surface may be different for different types of dents and that means for knobs that the distance between the surface in the area of the knobs and the other surface or the other basis surface may be different for different types of knobs. Figure 9 shows an example of a surface profile with two types of hexagonal knobs with different height and Figure 10 shows an example of a surface profile with two types of hexagonal dents with different depth.

The dents and knobs may have shapes with sharp angles or with geometric forms in which the angles are rounded. Although rounded structures may provide better mechanical properties because of a reduced notching effect which may be preferable, the constraints of mold manufacture, which allow easier preparation of molds with sharp etches, suggest that in practice it may be preferable from the economic perspective to use distinctly angular shapes.

In addition to the thickness variations caused by the knobs and dents there may exist a further texture of the surface on a smaller scale, resulting e.g. in a grained structure. This texture may be present both in the regions of the continuous basis surface and in the areas of the dents or the knobs. The thickness variations caused by the texture of the surface are however less than that caused by the knobs or dents, often much less than that caused by the knobs or dents, and are normally at the most 5% of the basis thickness. In a preferred embodiment the surface in the regions of the continuous basis surface and in the areas of the dents or the knobs is flat without a surface texture, i.e. without additional surface variations beside those coming from the dents or knobs.

In a preferred embodiment of the present invention the segment of a predominantly two- dimensional structure is exclusively formed by the composite material comprising the plastic material reinforced with fibers.

In a further preferred embodiment of the present invention the composite material comprising the plastic material reinforced with fibers forms only a layer of the segment of a predominantly two- dimensional structure. Preferably this layer is the support layer of a layered composite material. Such layers are known in the art and are for example described in EP 1 060 877 A2 or EP 1 126 069 A2. The layered composite material has usually a total thickness of from 1 to 100 mm and at least 80% of the total thickness of the layered composite material are contributed by the support layer. Preferably the layered composite material comprises in addition to the support layer an intermediate layer arranged thereupon, and a heat-cured layer applied to the intermediate layer.

The intermediate layer is usually made from a thermoplastic, preferably from the thermoplastic also used as component of the support layer. The intermediate layer is in particular a thin film or else a thin nonwoven web of a thickness from 0.001 to 1.0 mm, in particular from 0.005 to 0.3 mm. Another possibility for an intermediate layer is a resin-saturated nonwoven or a resin- saturated film made from a thermoplastic. Resins used for this are in particular acrylate resins, phenolic resins, urea resins or melamine resins.

The layered composite material may additionally also have a decorative layer arranged on the intermediate layer, between the intermediate layer and the heat-cured layer. The decorative layer may be composed of a plastic which has an embossment or coloration, or both combined, or may be a ready-to-use laminate. However, the decorative layer may also be composed of paper or of a fabric or of metal or of a paper-like or fabric-like or metal-like or wood-like material. The decorative layer may also have been resinified with acrylic resins, phenolic resins, urea resins or melamine resins.

The heat-cured layer arranged upon the decorative layer, or upon the intermediate layer if no decorative layer is present, is preferably composed of a thermoset plastic, for example of a paper saturated with acrylic resin, with phenolic resin, with melamine resin or with urea resin, crosslinked by exposure to pressure or heat during the production of the layered composite material.

In a preferred embodiment the whole surface of the surface with the surface profile of the segment of a predominantly two-dimensional structure is covered with the additional layers of the layered composite material. That means, also the area of the dents and knobs is covered with the additional layers of the layered composite material and consequently all layers of the layered composite material have a surface profile.

In a further preferred embodiment all or some of the other layers of the layered composite material, that means those layers which are not the support layer, form a template for preparing the surface profile. Those other layers have cavities which are filled with the composite material comprising the plastic material reinforced with fibers during the injection molding of the support layer and consequently the resulting support layer has a surface profile according to the present invention while the outer surface of the layered composite material, preferably formed by the heat- cured layer, does not exhibit a surface profile. The article comprising the segment of a predominantly two-dimensional structure of the present invention or the layered composite material comprising the layer of the present invention can be used as component or part of a component of a machine, preferably a household appliance, especially selected from the group consisting of washing machines, clothes dryers, dish-washers, refrigerators, freezers, stoves, ovens, air-conditioners and exhaust systems. The article or layered composite material may also be used as an industrial component, for example a component produced by or for the automotive industry like a front end carrier or a spare wheel cover.

The present invention also provides a method of producing such an article or layer by injection molding a plastic material comprising reinforcing fibers. The method comprises the steps of

(a) injecting a plastic material reinforced with fibers into a mold comprising an interior cavity and at least one surface with a surface profile which is shaped complementary to that of the desired segment of the article or layer and (b) subsequently allowing said plastic material reinforced with fibers to solidify.

In a state of the art injection molding process for predominantly two-dimensional parts with common surfaces without dent or knobs, the melt flows more or less in parallel from the injection point to the opposite side of the mold. Since in plastic material reinforced with fibers the fibers are predominantly oriented in the direction of flow, a more or less parallel orientation of the fibers is obtained in articles prepared by such state of the art injection molding processes. In contrast, if the injection molding is carried out according to the present invention, the parallel orientation of the fibers is significantly reduced. Figure 11 demonstrates in diagrammatic form such flow of the melt during injection molding. Figure 11 shows a surface profile with dents (4) and (5) of circular structure. Arrow (6) indicates the direction of the melt flow. If the melt approaches dent (5), where the thickness of the mold is reduced, the melt is caused to circumvent the region of the dent, resulting in the vicinity of dent (5) in an arrangement of the fibers, which is predominantly concentric with the boundary of the dent. Thereafter the region of the dent is filled by the melt as demonstrated by the dotted arrows (7) and in this way arriving there in a predominantly radial arrangement of the fibers. Over all, a quite non-uniform orientation of the fibers throughout the entire molded article is achieved resulting in much better mechanical properties.

It may by preferable that the dents or knobs are shaped in a way that they are of greater dimension across the direction of flow of plastic material than they are in the direction of flow. This could lead to greater cross-current formation within the regions of dents or knobs, resulting in greater unevenness of fiber distribution within the molded segment. The structure of the knobs displayed in Figure 7 is an example for such an arrangement, if the melt flow occurs from the top of the picture to the bottom. The preparation of the articles of the present invention is normally carried out by injection molding the plastic material reinforced with fibers into a cavity, which has at least one surface with a surface profile, which is directly implemented into the mold surface. However, in one embodiment of the present invention, the mold as such has no surface profile and the surface profile is introduced by templates, which are placed into the mold and the knobs, or in case of a surface profile with dents the basis surface, are formed in the cavities of these templates. Such templates may be prepared for example from metal sheets or plates. It is then possible to remove the template from the article after the article has cooled and the template can subsequently be reused.

The template can also be formed by a laminate structure with cavities wherein after injecting the plastic material reinforced with fibers the additional layers are firmly bonded to the plastic material and the cavities of the additional layers are filled with plastic material reinforced with fibers, in this way forming the dents or knobs of the support layer. The outer surface may accordingly be a flat surface. The cavities of the template made of laminate structures may go through all additional layers. Such a structure may be prepared for example by punching the additional layers. In such a case the surface profile of the inventive support layer can only have knobs. If only the layers in vicinity to the support layer have cavities and the whole layered structure of the template is held together by a continuous outer layer it is possible to form a surface profile of the support layer with both knobs and dents. It is self-evident that the thickness of the layers with cavities, and accordingly also the whole ensemble of additional layers, is sufficient to create a surface profile with the required thickness variances of the present invention.

The present invention permits a further method of manufacture, in which the part is injection molded with at least one profiled surfaces of the invention by using a prepared or prefabricated laminate as at least one surface of the mold: this prepared laminate possess a surface complementary to that of the formed layer with the surface profile. After the molded product is removed from the injection apparatus, the prepared laminate remains bound to the molded layer to form a laminated composite material.

Claims

1. An article or layer made of a composite material comprising a plastic material reinforced with fibers, said article or layer comprising at least one segment of a predominantly two- dimensional structure with a first and a second surface and a basis thickness of the segment and at least one of the surfaces of the segment shows a surface profile with dents or knobs or dents and knobs,

wherein the surface with the surface profile has a continuous basis surface, in which the dents are impressed or of which the knobs stick out, and the basis thickness of the segment is the distance between the basis surface of the surface with the surface profile and the other surface, if only one surface has a surface profile, or the basis thickness of the segment is the distance between both basis surfaces, if both surfaces have a surface profile,

wherein in case of dents the distance between the surface in the area of the dent and the other surface, if only one surface has a surface profile, or the other basis surface is at least 10% less than the basis thickness and in case of knobs the distance between the surface in the area of the knob and the other surface if only one surface has a surface profile, or the other basis surface is at least 10% more and at the most 200% more than the basis thickness; and

wherein at least 10% of the surface with the surface profile are knobs or dents.

2. An article or layer according to claim 1 , wherein only one of the surfaces of the segment has a surface profile.

3. An article or layer according to claim 1 or 2, wherein the basis surfaces or, if only one of the surfaces has a surface profile, the base surface and the opposite surface are planes which are substantially parallel.

4. An article or layer according to any one of claims 1 - 3, wherein the plastic material is a thermoplastic polymer selected from the group consisting of polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polysulfones, polyetherketones, polyesters, polycycloolefins, polyacrylates, polymethacrylates, polyamides (PA), polycarbonate (PC), polyurethanes, polyacetals, polystyrene (PS), acrylonitrile/butadiene/styrol copolymer (ABS), liquid crystal polymer (LCP), and polyphenylene sulfide (PPS), or is a mixture of these.

5. An article or layer according to any one of claims 1 - 4, wherein the plastic material is a homopolymer of propylene or a copolymer of propylene with up to 50% by weight of further monomers copolymerizable with propylene.

6. An article or layer according to any one of claims 1 - 5, wherein the fibers are glass fibers.

7. An article or layer according to any one of claims 1 - 6, wherein the fibers are short fibers, ranging in length up to 4 mm.

8. An article according to any one of claims 1 - 7, wherein the segment of a predominantly two-dimensional structure is exclusively formed by the composite material comprising a plastic material reinforced with fibers.

9. A layer according to any one of claims 1 - 7, wherein the segment of a predominantly two- dimensional structure is the support layer of a layered composite material.

10. A layer according to claim 9, wherein the segment of a predominantly two-dimensional structure is the support layer of a layered composite material further comprising an intermediate layer arranged upon the support layer, a heat-cured layer and optionally a decorative layer arranged on the intermediate layer, between the intermediate layer and the heat-cured layer.

11. A layered composite material comprising a layer according to claim 9 or 10.

12. A method of producing an article or layer according to any one of claims 1 - 10, comprising the steps of

a) injecting a plastic material reinforced with fibers is into a mold comprising an interior cavity and at least one surface with a surface profile, which is shaped complementary to that of the desired segment of the article or layer, and

b) subsequently allowing the plastic material reinforced with fibers to solidify.

13. A method according to claims 12, wherein the surface profile complementary to that of the desired segment of the article or layer is brought into the cavity by a template, which is introduced into the mold.

14. A method according to claims 13, wherein the template is a layered structure with cavities and the product obtained after allowing the plastic material reinforced with fibers to solidify is a layered composite material according to claim 11.

15. A method according to claims 12, wherein a prepared or prefabricated laminate, which possesses a surface profile complementary to that of the desired segment of the layer, is introduced into the mold and after steps (a) and (b) a layered composite material according to claim 11 is obtained.

16. Use of an article as claimed in claim 8 or an layered composite material as claimed in claim 12 as component or part of a component produced by or for the automotive industry or as component or part of a component of a household appliance selected from the group consisting of washing machines, clothes dryers, dish-washers, refrigerators, freezers, stoves, ovens, air-conditioners and exhaust systems.