WO2016069670A1

WO2016069670A1 - Fiber-reinforced composite preform

Info

Publication number: WO2016069670A1
Application number: PCT/US2015/057682
Authority: WO
Inventors: David R. Hartman
Original assignee: Ocv Intellectual Capital, Llc
Priority date: 2014-10-29
Filing date: 2015-10-28
Publication date: 2016-05-06

Abstract

A fiber-reinforced preform is provided that includes a woven reinforcing fabric having a top surface and a bottom surface. The woven reinforcing fabric is formed of continuous glass fibers woven in a balanced weave pattern. The fiber-reinforced preform further includes a first thermoplastic film layer laminated across the top surface of the woven reinforcing fabric and a second thermoplastic film layer laminated across the bottom surface of the woven reinforcing fabric. The fiber-reinforced preform has a thickness of less than about 3 mm and a surface flatness of less than 2 mm.

Description

FIBER-REINFORCED COMPOSITE PREFORM

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No. 62/069,920, filed on October 29, 2014, the entire disclosure of which is incorporated by reference.

BACKGROUND

[0002] Plastic composites are often incorporated into materials because of their advantageous combination of properties, including light weight, high strength to weight ratio, and ease and versatility of construction. These materials find many uses, for example, as a housing for electronic equipment.

[0003] Housings for electrical equipment, such as casings for computers, cell phones, and other portable electronics, are often made out of plastic composite materials, since plastic composites are strong and have good shielding properties. To increase the strength and durability of these materials, the plastic composite materials may be reinforced with structural fibers, such as glass and/or carbon.

[0004] Conventional composite preform materials have been formed using an injection molding process in which chopped fiber strands are mixed with a polymeric resin and supplied to a compression or injection molding machine to form a fiber reinforced composite perform. The chopped fiber strands are mixed with powder, regrind, or pellets of a thermoplastic polymer resin in an extruder. The fiber/resin mixture is then fed directly into an injection molding machine, or, alternatively, the fiber/resin mixture may be formed into pellets. The dry fiber strand resin dispersion pellets may then be fed to a molding machine and formed into a molded composite article having a substantially homogeneous dispersion of glass fiber strands throughout the composite article.

[0005] Conventional composite preform materials have also been formed by assembling a plurality of sheets of fiber reinforcement material in a mold having a desired product shape. The mold is filled with a thermosetting or thermoplastic resin material that is then cured or caused to harden, thereby taking the form of the mold. The fiber reinforcement material may be pre-impregnated with the thermoplastic or thermosetting resin and then placed in the mold. In this case, the filled mold can then be placed in a vacuum or subject to thermal compression until the resin cures or hardens.

[0006] U.S. Patent No. 8,562,886 discloses a composite laminate formed from a plurality of stacked preimpregnated sheets and a scrim located on the exterior surface of the laminate. The scrim comprises substantially parallel or woven carbon or glass.

[0007] However, there is an increasing push towards miniaturization of products and particularly electronic products. Electronic companies are driven by demands for smaller and lighter components, while maintaining desirable physical and mechanical properties.

SUMMARY

[0008] In accordance with various aspects of the general inventive concepts, a fiber- reinforced preform is provided. The fiber-reinforced preform includes a woven reinforcing fabric having a top surface and a bottom surface, the woven reinforcing fabric being formed of continuous glass fibers woven in a balanced weave pattern. The fiber reinforced preform further includes a first thermoplastic film layer laminated across the top surface of the woven reinforcing fabric and a second thermoplastic film layer laminated across the bottom surface of the woven reinforcing fabric. In some exemplary embodiments, the fiber-reinforced preform has a thickness of less than about 3 mm and a surface flatness of less than about 2 mm.

[0009] In accordance with some exemplary aspects, the thermoplastic film layers comprise at least one of polycarbonate, polyamide, and a polycarbonate/ABS blend.

[0010] In accordance with some exemplary aspects, the glass fibers are coated with a sizing composition comprising an epoxy film former and a compatibilizer. The compatibilizer comprises a polyol having at least three hydroxyl groups and has functional groups that are reactive with polycarbonate and/or polyamide.

[0011] Various exemplary aspects of the general inventive concepts further include at least one additional woven reinforcing fabric, with each of the additional woven reinforcing fabrics having a top surface and bottom surface laminated with a thermoplastic film layer. Each of the woven reinforcing fabrics is layered in a top- up/bottom-up configuration.

[0012] In some exemplary embodiments, the fiber-reinforced preform has a thickness of 1.1 mm or less. In some exemplary embodiments, the fiber-reinforced preform has a thickness of 0.5 mm or less. In some exemplary embodiments, the fiber-reinforced preform has a surface flatness of 1 mm or less and a tensile strength of at least 50 Ksi and a tensile modulus of at least 2.3 Msi.

[0013] In accordance with some exemplary aspects of the general inventive concepts, a composite article is disclosed. The composite article includes at least one composite preform comprising a woven reinforcing fabric having a top surface and a bottom surface and being formed of continuous glass fibers woven in a balanced weave pattern. The composite preform further includes a first thermoplastic layer laminated across the top surface of the woven reinforcing fabric and a second thermoplastic layer laminated across the bottom surface of the woven reinforcing fabric. The fiber-reinforced preform has a thickness of less than about 3 mm and a surface flatness of less than about 2 mm. The composite article further includes a thermoplastic molding material.

[0014] In some exemplary embodiments, the glass fibers are coated with a sizing composition comprising an epoxy film former and a compatibilizer.

[0015] In some exemplary embodiments, the composite article is radio wave transparent and is capable of providing EMI shielding upon the addition of a conductive material, such as carbon. In some exemplary embodiments, the composite article is a housing for enclosing a plurality of electronic components.

[0016] In accordance with further exemplary aspects of the general inventive concepts, a method of making a fiber-reinforced preform is provided. The method includes providing at least one woven reinforcing fabric having a top surface and a bottom surface being formed of continuous glass fibers woven in a balanced weave pattern. The method further includes laminating a first thermoplastic film layer to the top surface of the woven reinforcing fabric and laminating a second thermoplastic film layer to the bottom surface of the woven reinforcing layer, wherein the woven reinforcing fabric and thermoplastic film layers are compression molded to provide a fiber-reinforced preform having a thickness of less than 3 mm and a surface flatness of less than 2 mm.

[0017] Additional features and advantages will be set forth in part in the description that follows, and in part may be apparent from the description, or may be learned by practice of the embodiments disclosed herein. The objects and advantages of the embodiments disclosed herein will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing summary and the following detailed description are examples and are explanatory only and are not restrictive of the disclosure herein or as otherwise claimed. DESCRIPTION OF THE DRAWINGS

[0018] Embodiments of the disclosure will be apparent from the more particular description of certain exemplary embodiments provided below and as illustrated in the accompanying drawings.

[0019] Figure 1 graphically illustrates a flexural test in accordance with ASTM-D-790 that compares E-glass polycarbonate composites with epoxy laminates.

[0020] Figure 2 graphically illustrates a flexural test in accordance with ASTM-D-790 that compares conventional epoxy laminates to the inventive composite preforms disclosed herein.

DETAILED DESCRIPTION

[0021] While the general inventive concepts are susceptible of embodiment in many different forms, there are shown in the drawings and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the general inventive concepts. Accordingly, the general inventive concepts are not intended to be limited to the specific embodiments illustrated herein.

[0022] Unless otherwise defined, the terms used herein have the same meaning as commonly understood by one of ordinary skill in the art encompassing the general inventive concepts. The terminology used herein is for describing exemplary embodiments of the general inventive concepts only and is not intended to be limiting of the general inventive concepts. As used in the description of the general inventive concepts and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0023] The present invention relates to a fiber reinforced composite preform that achieves a reduced weight and thickness while also having improved strength, dimensional stability, and flatness.

[0024] The fiber reinforced composite includes at least one type of fiber reinforcement material. The fiber reinforcement material may include any type of fiber suitable for providing structural reinforcement as well as good thermal properties to a resulting preform. The reinforcement fibers may be any type of organic, inorganic, or natural fibers. In some exemplary embodiments, the reinforcement fibers are made from any one or more of glass, carbon, aramid, polyesters, polyolefins, nylons, aramids, poly(phenylene sulfide), silicon carbide (SiC), boron nitride, and the like. In some exemplary embodiments, the reinforcement fibers are formed of any of glass, carbon, and aramid fibers. In some exemplary embodiments, the reinforcement fibers comprise a hybrid of multiple types of fibers.

[0025] Glass fibers are commonly used as the reinforcement material in polymer matrices because glass fibers provide dimensional stability as they do not shrink or stretch in response to changing atmospheric conditions, such as changing temperature. In addition, glass fibers have high tensile strength, heat resistance, moisture resistance, and high thermal conductivity. The glass fibers may be formed from any type of glass suitable for a particular application and/or desired product specifications, including conventional glasses. Non-exclusive examples of glass fibers include S-type glass fibers, A-type glass fibers, C-type glass fibers, G-type glass fibers, E-type glass fibers, E-CR-type glass fibers (e.g., Advantex® glass fibers commercially available from Owens Corning), R-type glass fibers, wool glass fibers, biosoluble glass fibers, and combinations thereof, which may be used as the reinforcing fibers. In some exemplary embodiments, the reinforcing fibers are formed of S-glass.

[0026] Typically, glass fibers are formed by attenuating streams of a molten glass material through orifices in a bushing or the like. An aqueous sizing composition containing a film forming polymer, a coupling agent, and a lubricant is typically applied to the fibers after they are drawn from the bushing to protect the fibers from breakage during subsequent processing and to improve the compatibility of the fibers with the matrix resins that are to be reinforced.

[0027] The film former holds individual filaments together to aid in the formation of the fibers and protects the filaments from damage caused by abrasion. Acceptable film formers include, for example, polyvinyl acetates, polyurethanes, modified polyolefins, polyesters, epoxies, and mixtures thereof. In some exemplary embodiments, the film former comprises an epoxy film former.

[0028] The sizing composition may further include at least one coupling agent, such as a silane coupling agent. Silane coupling agents function to enhance the adhesion of the film forming polymers to the glass fibers and to reduce the level of fuzz, or broken fiber filaments, during subsequent processing. Examples of silane coupling agents, which may be used in the present size composition, may be characterized by the functional groups amino, epoxy, vinyl, methacryloxy, azido, ureido, and isocyanato.

[0029] Non-limiting examples of suitable epoxy silane coupling agents include a glycidoxy polymethylenetrialkoxysilane such as 3 -glycidoxy-1 -propyl -trimethoxysilane, 201

an acryloxy or methacrylyloxypolymethylenetrialkoysilane such as 3-methacrylyloxy-l- propyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane (A-187), γ- methacryloxypropyltrimethoxysilane (A- 174), a-chloropropyltrimethoxysilane (KBM- 703) a-glycidoxypropylmethyldiethoxysilane (A-2287), and vinyl-tris-(2- methoxyethoxy)silane (A- 172). In various exemplary embodiments, the epoxy silane coupling agent is γ-glycidoxypropyltrimethoxysilane (A-187). The silane coupling agent may be present in the size composition in an amount of from 5% to 20% by weight solids, or from amount of from 7% to 10% by weight solids.

[0030] Additionally, the sizing composition may also contain at least one lubricant. The lubricant(s) may be non- ionic, cationic, anionic, or a combination thereof. The non-ionic lubricant in the sizing composition acts as a "wet lubricant" and provides additional protection to the fibers during the filament winding process. In addition, the non-ionic lubricant helps to reduce the occurrence of fuzz. Examples of suitable non-ionic lubricants include PEG 200 Monolaurate, PEG 400 Monooleate, and PEG 600 Monooleate. Other non-limiting examples include a polyalkylene glycol fatty acid such as PEG 600 Monostearate, PEG 400 Monostearate, and PEG 600 Monolaurate. The non- ionic lubricant may be present in the size composition in an amount from 10% to 30% by weight solids, or from 15% to 25% by weight solids.

[0031] In addition to the non-ionic lubricant, the sizing composition may also contain at least one cationic lubricant. The cationic lubricant aids in the reduction of interfilament abrasion. Examples of suitable cationic lubricants include, but are not limited to, a polyethyleneimine polyamide salt and a stearic ethanolamide. The amount of cationic lubricant present in the size composition may be an amount sufficient to provide a level of the active lubricant that will form a coating with low fuzz development. In at least one exemplary embodiment, the cationic lubricant is present in the size composition in an amount from 0.01 % to 5.0% by weight solids, or from 1 .0% to 3.0% by weight solids.

[0032] In addition, the size composition may optionally include at least one pH adjusting agent, such as acetic acid, citric acid, sulfuric acid, or phosphoric acid to adjust the pH level of the composition. The pH may be adjusted depending on the intended application or to facilitate the compatibility of the ingredients of the size composition. The sizing composition may have a pH of from 3.0 to 7.0, or from 3.5 to 4.5. The pH adjusting agent may be included in any amount to reach a desired pH, such as from 0.25% to 5% by weight solids, or from 0.5% to 2% by weight solids. [0033] Additional additives may be included in the sizing compositions, depending on the intended application. Such additives include, for example, anti-statics, wetting agents, and antioxidants

[0034] Once the sizing composition has been applied, the sized fibers may be gathered into separate strands and wound to produce a glass fiber package. The glass fiber package may then be heated to remove excess water. Multiple dried glass fiber packages may be consolidated and wound onto a spool referred to as a roving doff or package. The roving package is composed of a glass strand with multiple bundles of glass fibers.

[0035] In some exemplary embodiments, the glass fiber bundles are used to form reinforcement sheet material. Any suitable unidirectional or multidirectional reinforcement sheet materials can be employed. The general inventive concepts contemplate that such unidirectional or multidirectional reinforcement sheet materials may include, for example, non-woven mats, chopped strand mats, continuous fiber mats, woven fabrics, and the like. In some exemplary embodiments, the reinforcement sheet material comprises a woven reinforcing fabric formed of continuous glass fibers. Conventional fabrics are made by weaving bundles of fibers, or yarns, in two substantially perpendicular directions (warp and weft). The entire fabric may be made of a single material, or different materials can be used in each layer for a hybrid fabric. Although the reinforcement sheet material shall be referred to herein as a woven glass fabric, it is to be understood that alternative reinforcement sheet materials may be used.

[0036] In some exemplary embodiments, the woven glass fabric has a weave pattern consisting of a basket weave or a "plain" weave, where each yarn alternatingly passes over one then under one of the crossing yarns. The basket weave is a symmetric over- under style weave. In other exemplary embodiments, the weave pattern may be a twill weave, in which each yarn alternatingly passes over two yarns and then under two yarns. The twill weave typically has a different angle than the basket weave. In some exemplary embodiments the twill weave consists of a 45° twill pattern to reduce any warp in the machine direction. The weave pattern may also be a satin weave, wherein each yarn passes over three or more cross yarns and then passes over one. In some exemplary embodiments, each of the warp yarns and weft yarns are substantially free of twist and in other exemplary embodiments each of the warp yarns and weft yarns are completely free of twist.

[0037] In some exemplary embodiments, the woven glass fabric has a balanced woven fabric pattern, meaning that the fabric has the same thickness and content in the 0° and 90° directions. A balanced woven fabric pattern may be obtained when the glass yarns in the two woven construction directions, that is, warp and weft, are made from the same denier material and contain the same count of yarns of equal size, strength, and spacing. These yarns are then woven together to form a balanced weave patterned fabric, which also fortuitously results in a balanced modulus of elasticity in the warp and weft direction. Modulus of elasticity, in this usage, is the quotient of stress induced in a material divided by the strain resulting from that stress.

[0038] In some exemplary embodiments, the woven glass fabric is formed using a very fine weave by reducing the glass tex (bundle size). In some exemplary embodiments, the glass tex ranges from about 20 to about 300 tex, or about 60 to about 170 tex. Reducing the glass tex allows for a very fine, high density weave, which increases the glass content in a fabric while reducing the fabric's overall thickness.

[0039] The number of ends/inch (warp yarns) and the number of picks/inch (weft yarns) of a woven glass fabric defines the structure of the fabric and is expressed as W x F. The structure of the woven glass fabric utilized in the present inventive concepts balances good coverage with also allowing resin through the fabric for fast wetting. In some exemplary embodiments, the woven glass fabric construction is balanced, in that the number of warp yarns is the same as the number of weft yarns. In some exemplary embodiments, the structure of the fabric is 24 x 24. In some exemplary embodiments, the woven glass fabric construction is 28 x 28. Balancing the weft yarns with the warp yarns helps ensure the ends of the fabric do not curl.

[0040] In some exemplary embodiments, the woven fabric is free or substantially free of contamination, skew, dropped ends, and distortion.

[0041] The woven glass fabric may be laminated with a polymeric matrix material to form a composite preform, also known as a laminate. In the production of the composite preform, the woven glass fabric is consolidated with the polymeric matrix material. The polymeric matrix material to be used in forming the composite laminate may comprise any thermoplastic or thermoset material desired for a particular application. In some exemplary embodiments, the thermoplastic material comprises one or more of polycarbonate, polyamide, and acrylonitrile butadiene styrene (ABS). In some exemplary embodiments, the thermoplastic material comprises polycarbonate. In some exemplary embodiments, the thermoplastic comprises a polycarbonate/ABS blend. One benefit of using polycarbonate or a polycarbonate blend is that it exhibits clear transparency, high impact strength, and a high glass transition temperature. Thus, preforms formed with polycarbonate and glass have very desirable aesthetics. The composite preform will be described herein as a thermoplastic preform, although it should be understood that the preform may alternatively be formed using a thermoset material.

[0042] To form the inventive thermoplastic preform, at least one thermoplastic film is at least partially melted into the woven glass fabric under increased heat and pressure to wet the glass fibers and impregnate the woven fabric with the thermoplastic material, in a process called compression molding. During the compression molding consolidation process, it is desirable that the woven glass fabric contact or be fully "wet" with thermoplastic material. By creating a balanced weave, as described above, the glass fibers are able to wet more evenly, which leads to a low flatness tolerance.

[0043] In some exemplary embodiments, the thermoplastic preforms comprise one or more layered woven glass fabrics (known as "plies") and one or more layers of thermoplastic film. For instance, one or more of the woven fabrics may be "sandwiched" and compression molded between two layers of thermoplastic film. In some exemplary embodiments, the thermoplastic preform comprises one woven glass fabric ply with a thermoplastic film layer laminated to the top and bottom of the sheet. In some exemplary embodiments, the thermoplastic preform comprises two woven glass fabric plies each with a thermoplastic film laminated to the top and bottom of the fabric. In some exemplary embodiments, the thermoplastic preform comprises three or more woven glass fabric plies each with a thermoplastic film laminated to the top and bottom of each fabric ply.

[0044] It is generally inherent in a weaving process for at least some yarns to become crimped, which may cause stress points in preforms and subsequently affect a fabric's strength and stiffness. To minimize these residual stresses, the woven fabrics may be layered in a top-up/bottom-up fashion, which helps to minimize warpage and residual stresses. This top-up/bottom-up configuration causes a "mirror effect" by reversing the location of any residual stresses in layered woven fabrics and ensures that any built in stresses in the fabric are not perpetuated throughout the preform, but rather are neutralized around the midpoint of the laminate. Therefore, a single point in the fabric is not unduly stressed compared to other points in the fabric.

[0045] In some exemplary embodiments, the thermoplastic preform is a thin-walled preform. To achieve a thin structure while maintaining sufficient strength, the inventive thermoplastic preform has an increased amount of glass and a decreased amount of thermoplastic material. In some exemplary embodiments, the thermoplastic preform has a glass content between about 40 and 75 weight percent. In some exemplary embodiments, the thermoplastic preform has a thickness of about 3.0 mm or less, or about 1.2 mm or less, or about 1.1 mm or less, and particularly about 0.5 mm or less. In some exemplary embodiments, the thermoplastic preform has a thickness of about 0.1 to about 0.5 mm.

[0046] The thickness of the thermoplastic preform may also depend on the number of fabric plies making up the composite. In some exemplary embodiments, a 2-ply preform has a thickness of about 0.2 mm to about 0.4 mm. In some exemplary embodiments, a 3- ply preform has a thickness of about 0.4 mm to about 0.5 mm. A thin thermoplastic preform allows for improved transparency, while maintaining sufficient strength to withstand further processing, such as forming a molded structure by injection molding.

[0047] As the demand for electronic miniaturization continues to increase, manufacturers are requiring suppliers to reduce the functional weight of the material to meet the increasing demands. In some exemplary embodiments, the thermoplastic preform is lightweight, with an areal weight of less than 1000 gsm, or from 500 gsm to 900 gsm.

[0048] In some exemplary embodiments, the thermoplastic preform demonstrates improved dimensional stability during temperature variations and minimal shrinking during consolidation. In some exemplary embodiments, this improved dimensional stability is due at least in part to the reduced coefficients of thermal expansion ("CTE") of the glass fibers. The low CTE of glass helps to reduce warpage by lowering the overall CTE of the glass/thermoplastic mixture. By eliminating warpage during consolidation, the thermoplastic preform may be formed having a surface flatness of less than about 2 mm, or less than about 1 mm. In some exemplary embodiments, the thermoplastic preform has a 2-ply flatness of about 0.5 mm to 1.0 mm, or less than or equal to 0.7 mm. In some exemplary embodiments, a 3-piy thermoplastic preform has a surface flatness of 1.0 mm to 1.7 mm, or less than or equal to 1.5 mm.

[0049] As mentioned above, the ability for the glass fibers to fully "wet" in the polymeric matrix material is very important in the formation of both the composite laminate and in the formation of a final molded part, as it may impact the occurrence of warpage and the physical and surface characteristics of the final molded part. For example, poor wetting may result in low composite strengths and surface defects in the final molded part. The ability for reinforcement fibers, particularly glass fibers to wet depends heavily on the compatibility of the polymeric film former in the sizing composition coated on the fibers with the matrix material. For example, sizing compositions that contain epoxy film formers are compatible with and demonstrate sufficient wetting in an epoxy matrix material.

[0050] In some exemplary embodiments, the glass fibers forming the woven fabric were coated with a sizing composition that includes an epoxy film former. Thus, in order to provide wetting compatibility with a thermoplastic matrix material, such as polycarbonate, the sizing composition further includes a compatibilizer. In some exemplary embodiments, the compatibilizer helps with cohesion of the film former on the glass fibers, aids in drying the sized fibers, and also contains functional groups the make the sizing composition compatible with the polycarbonate resin. In some exemplary embodiments, the compatibilizer comprises a polyol having at least three hydroxyl groups. In some exemplary embodiments, the compatibilizer is a polyol with four hydroxyl groups. The compatibilizer has high functionality with at least one of polycarbonate and polyamide (nylon). The compatibilizer may be present in the sizing composition in an amount from about 0.5% to about 10.0% by weight solids, or from about 1.0 % to about 3.0 % by weight solids.

[0051] The thermoplastic preform, while having a very thin, light, and flat structure, also demonstrates improved performance properties. For instance, the thermoplastic preform disclosed herein has a flexural modulus of at least 2.5 Msi, or at least 2.8 Msi and a tensile modulus of at least 2.3 Msi, or at least 2.5 Msi. In some exemplary embodiments, the thermoplastic preform has both a flexural modulus and a tensile modulus of at least 3.0 Msi. The thermoplastic preform further has a tensile strength of at least 50 Ksi, or at least 60 Ksiand a flexural strength of at least 65 Ksi, or at least 75 Ksi. In some exemplary embodiments, the thermoplastic preform has both a tensile strength and a flexural strength greater than 80 Ksi.

[0052] Additionally, in some exemplary embodiments, the thermoplastic preform has a high tensile strain to failure percentage, such as greater than 2.5%. In some exemplary embodiments, the thermoplastic preforms achieve a tensile strength to failure percentage of greater than 3%.

[0053] In some exemplary embodiments, the thermoplastic preforms are configured such that they pass UL 94 HB flammability standard for external components and V0 for internal components. The UL 94 test is a burning test that classifies materials based on a material's burning characteristics after a test specimen has been exposed to a specified test flame. An HB flame rating indicates that the material was tested in a horizontal position and found to burn at a rate less than a specified maximum. The vertical rating V0 indicates that the material was tested in a vertical position and self-extinguished within a specified time after the ignition source was removed.

[0054] The thermoplastic preforms may be utilized to form molded parts, including housings for electrical equipment, such as structural antenna for electromagnetic compatibility (EMC) casings, accessory covers, and the like. In some exemplary embodiments, the composite preforms may be inserted into a mold structure including any accessory structure(s) to be included, such as an antenna or glass, etc., and a molding material is overmolded around the accessory part. In some exemplary embodiments, the molding material comprises a thermoset or thermoplastic molding material. In some exemplary embodiments, the molding material comprises a thermoplastic material, such as polycarbonate, nylon, polyethylene, and polystyrene. In some exemplary embodiments, the molded exterior components are UV light stable and meets color specifications. In some exemplary embodiments, the molded exterior components are temperature resistant to temperatures of at least 80 °C. In some exemplary embodiments, the molded exterior is formed of polycarbonate and is temperature resistant up to about 260 °C for 2 minutes.

[0055] To ensure efficient OEM assembly of products, the thermoplastic preform must be compatible with, and properly adhere to, other materials used therein, such as metal, glass, and the like. For instance, a polycarbonate preform, formed as described herein, allows excellent secondary adhesion with metal, since glass and metal have similar CTEs for good molding tolerance and adhesion performance. The improved secondary adhesion further comes from the surface tension and the high stability due to the high glass transition temperatures of polycarbonate (roughly 150 °C). Accordingly, as the over- molding process occurs, the temperature gets close to the glass transition temperature, but not so close that the polycarbonate begins to flow.

[0056] As mentioned above, the inventive composite preforms may be used to form electronic housings, such as for one or more antenna. In some instances the housings may contain 12 or more antennae. Therefore, the composite preforms should be both radio transparent and, in some locations, radio wave shielding, to ensure the composites are protected from interference both internally and with other sources. To provide shielding functionality, the composites may be filled with conductive materials, such as carbon fibers, carbon nanotubes, simple carbon particles, and the like.

EXAMPLES

[0057] As shown in Table 1, below, the physical properties of traditional epoxy laminates reinforced with H-glass (Samples 1-2B), polycarbonate laminates reinforced with various plies of E-glass fabric reinforcement (Samples 3-8), and polycarbonate preforms reinforced with S-glass fabrics formed in accordance with the present invention (Samples 9-13), are compared.

Table 1

[0058] As shown in Table 1, the epoxy H-glass laminate had a thickness greater than 1.0 mm and demonstrated a high areal weight of 1294.8 gsm. However, sample 1, having a cross- ply epoxy sandwich configuration, demonstrated more resilience and less damage during an ASTM-D-790 Flexural Test, which forced bending failure, than the multiple ply epoxy fabrics in Samples 2A and 2B, which indicates the importance of the cross-ply sandwich configuration. (See, Figure 1).

[0059] Samples 3-8, consisting of cross-ply sandwich preforms of polycarbonate and various plies of E-glass fabric were thinner than the epoxy laminates in Samples 1-2B by about half. However, the preforms were not able to achieve a flatness of less than 7 mm, which indicates an issue with warpage.

[0060] Samples 9-13 illustrate thermoplastic preforms formed in accordance with the present invention having a cross-ply sandwich configuration with S-glass fabric and polycarbonate. The inventive preforms demonstrate excellent flatness at very low thicknesses (0.25 mm to 0.48 mm) and low weight (less than 1000 gsm).

[0061] As shown in Table 2, various mechanical properties for Samples 9-13 are detailed. Particularly, each sample demonstrated a flexural modulus greater than 2.5 Msi and a tensile strain to failure greater than 2.5%. Accordingly, the thermoplastic preforms formed as outlined herein achieve a very thin, light structure, while maintaining excellent flatness and desirable mechanical properties.

Table 2

[0062] Figure 2 illustrates the improved bending stiffness of S-glass polycarbonate preforms thicknesses between 0.25 mm and 0.5 mm with good resilience and lower damage, as compared to preforms formed with epoxy or with conventional, non-sandwich structures.

[0063] As shown in Table 3, the improved physical and mechanical properties of inventive compression molded thermoplastic preforms (sandwich structure with S-glass fabric and polycarbonate) disclosed herein compared to a conventional injection molded short fiber (both Advantex® and S-glass) preform. As shown below, the inventive compression molded polycarbonate preforms demonstrated a higher tensile strength (at least 60.1 Ksi), and tensile modulus (at least 2.5 Msi) than the conventional injection molded preforms (less than 20.5 Ksi tensile strength and less than 2.21 Msi tensile modulus). The inventive preforms additionally demonstrated a higher flexural strength (at least 65.0 Ksi) and flexural modulus (at least 2.6 Msi), as compared to the conventional injection molded preforms (less than 25.5 Ksi flexural strength and less than 1.9 Msi flexural modulus).

Table 3

[0064] Although only a few embodiments of this invention have been described above, it should be appreciated that many modifications can be made without departing from the spirit and scope of the general inventive concepts. All such modifications are intended to be included within the scope of the general inventive concepts, which are to be limited only by the following claim.

Claims

1. A fiber-reinforced preform comprising:

a woven reinforcing fabric having a top surface and a bottom surface, said woven reinforcing fabric being formed of continuous glass fibers woven in a balanced weave pattern;

a first thermoplastic film layer laminated on the top surface of said woven reinforcing fabric; and

a second thermoplastic film layer laminated on the bottom surface of said woven reinforcing fabric,

wherein said fiber-reinforced preform has a thickness of no greater than 3 mm and a surface flatness of no greater than 2 mm.

2. The fiber-reinforced preform of claim 1, wherein the thermoplastic film layers comprise at least one of polycarbonate, polyamide, and a polycarbonate/ ABS blend.

3. The fiber-reinforced preform of claim 1, wherein the glass fibers are selected from the group consisting of S-glass fiber, H-glass fiber, and E-CR glass fiber.

4. The fiber-reinforced preform of claim 1, wherein said glass fibers are S-glass fibers.

5. The fiber-reinforced preform of claim 1, wherein said glass fibers are coated with a sizing composition comprising an epoxy film former and a compatibilizer.

6. The fiber-reinforced preform of claim 5, wherein said compatibilizer comprises a polyol having at least three hydroxyl groups.

7. The fiber-reinforced preform of claim 1, further including at least one additional woven reinforcing fabric,

wherein each of said additional woven reinforcing fabric has a top surface and bottom surface laminated with a thermoplastic film layer, and wherein each additional woven reinforcing fabric is layered in a top-up/bottom-up configuration.

8. The fiber-reinforced preform of claim 7, wherein said fiber-reinforced preform comprises three of said additional woven reinforcing fabric layers.

9. The fiber-reinforced preform of claim 1, wherein said fiber-reinforced preform has a thickness of 1.1 mm or less.

10. The fiber-reinforced preform of claim 8, wherein said fiber-reinforced preform has a thickness of 0.5 mm or less.

11. The fiber-reinforced preform of claim 1, wherein said fiber-reinforced preform has a surface flatness of 1 mm or less.

12. The fiber-reinforced preform of claim 1, wherein said fiber-reinforced preform has a tensile strength of at least 50 Ksi.

13. The fiber-reinforced preform of claim 1, wherein said fiber-reinforced preform has a tensile modulus of at least 2.3 Msi.

14. The fiber-reinforced preform of claim 1, wherein said fiber-reinforced preform has a tensile-strain-to-failure percentage of greater than 2.5%.

15. A composite article comprising:

a fiber-reinforced preform comprising:

a first thermoplastic layer laminated across the top surface of said woven reinforcing fabric; and a second thermoplastic layer laminated across the bottom surface of said woven reinforcing fabric,

wherein said fiber-reinforced preform has a thickness of no greater than 3 mm and a surface flatness of no greater than 2 mm; and

a molding material, said molding material comprising a thermoplastic molding material.

16. The composite article of claim 14, wherein the thermoplastic film layers comprise at least one of polycarbonate, polyamide, and a polycarbonate/ABS blend.

17. The composite article of claim 14, wherein the glass fibers are selected from the group consisting of S-glass fibers, H-glass fibers, and E-CR glass fibers.

18. The composite article of claim 14, wherein said glass fibers are S-glass fibers.

19. The composite article of claim 14, wherein said glass fibers are coated a sizing composition comprising an epoxy film former and compatibilizer.

20. The composite article claim 18, wherein the fiber-reinforced composite article is transparent to radio waves and shields against electromagnetic interference.

21. The composite article of claim 14, wherein the fiber-reinforced composite article is a housing for enclosing a plurality of electronic components.

22. The composite article of claim 14, wherein the fiber-reinforced preform has a thickness less than 1.0 mm.

23. The composite article of claim 14, wherein the fiber-reinforced preform has a thickness between 0.2 mm and 0.5 mm.

24. A method of making a fiber-reinforced preform, the method comprising: providing at least one woven reinforcing fabric, said woven reinforcing fabric having a top surface and a bottom surface and being formed of continuous glass fibers woven in a balanced weave pattern;

laminating a first thermoplastic film layer to said top surface of said woven reinforcing fabric;

laminating a second thermoplastic film layer to said bottom surface of said woven reinforcing layer,

wherein said layered woven reinforcing fabric and thermoplastic film layers are compression molded to provide a fiber-reinforced preform having a thickness of less than 3 mm and a surface flatness of less than 2 mm.