WO1999038683A1

WO1999038683A1 - Composite panels with class a surfaces

Info

Publication number: WO1999038683A1
Application number: PCT/US1999/001710
Authority: WO
Inventors: Gerald Warren Minato; Mark David Thiede-Smet; Brian Curtis Roundtree; Jon Petter Bakken; Blaine Mattison; Richard Matt Okarski
Original assignee: Hexcel Corporation
Priority date: 1998-01-28
Filing date: 1999-01-28
Publication date: 1999-08-05

Abstract

The invention provides composite structural panels, including consolidated layers of reinforcing material embedded in a resin matrix, with at least one Class A surface, and methods for producing these panels. In an important feature of the invention, a layer underlying the Class A surface is a non-woven veil (or a film overlying the veil) that is of a type drapeable over a contoured surface before consolidation into the laminate. The veil reduces or eliminates print-through of the underlying reinforcement to the surface. The optional film over the veil reduces pin hole defects in the surface and promotes paint adhesion. In certain embodiments, where stiffness is required, the panels include a central core layer. Methods of making the panels are also disclosed. The structural panels are significantly stronger than prior art panels, eliminating the need for stiffeners on undersurfaces of the panels for most applications.

Description

-1-

COMPOSITE PANELS WITH CLASS A SURFACES

This application is a continuation-in-part of U.S. Patent Application Serial No. 09/015,028, filed January 28, 1998.

Field of the Invention The invention relates to laminated composite panels made up of layers of reinforcement in a resin matrix, that have a "Class A" surface so that they may be used in a variety of applications including contoured panels in automobiles, aircraft, and the like.

Background of the Invention In the recent years demand for lightweight vehicles that offer the potential for increased fuel efficiency has excited interest in the use of reinforced polymer composites as a substitute for metal, such as steel. To date, polymer composites have not lived up to expectations and have significant disadvantages. For example, to meet the desired "Class A" surface finish (as molded), the glass-reinforcement of composite panels is kept to below about 20 wt%, and the glass fibers are not oriented. But, low fiber content and lack of orientation result in low modulus ("stiffness") and low strength composites. To improve modulus to meet performance goals, the composite must either be made thicker (which offsets the weight reduction expected) or must be reinforced with stiffeners applied to the "B" side (non-cosmetic surface). Adding stiffeners increases the complexity, and hence the expense, of making the panels.

The prior art efforts to make vehicle panels usually focused on ABS (alkyl benzene styreπe) or other thermoplastic polymer-based composite with added stiffeners. Such panels are heavy, lack low temperature durability, and exhibit poor "paintability" (paint adhesion).

There is an identified need for lightweight structural panels of such strength that they do not require stiffeners, that have at least one Class A surface, that are relatively easily and quickly fabricated, and that may be readily painted in a variety of colors, so that they are suitable for use in applications requiring a good surface finish, for example body panels and fairings for motor vehicles.

Summary of the Invention The invention provides lightweight structural panels with Class A surfaces, and methods for producing these panels. The panels are suitable for use in vehicles, such as automobiles, trucks, boats, railway cars, and the like, where it is desired to have a lightweight structural panel with a cosmetically smooth surface to which a paint can be tightly adhered. The laminated panels of the invention can be made in a range of thicknesses and strengths to accommodate a wide variety of applications. Moreover, proper selection of laminate components, in particular the proportion and type of reinforcement, eliminates the need for stiffeners on undersurfaces of the panels, for most applications.

The panel laminate structure has several layers. Proceeding sequentially from the Class A surface, a first layer underlies the surface. This layer is either a film, or a veil. Generally, when the layer is a film, it overlies the veil, which is the second layer. In certain embodiments, the film is not needed, and the veil is the first layer. In certain other embodiments, the veil is not required. This veil, which assists in preventing print-through of underlying reinforcement, is of a type that is drapeable over a contoured surface, before it is consolidated into the laminate. Moreover, the veil is comprised of non-woven fibers and, before consolidation, it is able to absorb liquid resin. Underlying the veil is at least one reinforcing layer of reinforcing fibers. Preferably, this layer of reinforcing fibers has a unidirectional fiber orientation. Other reinforcing layers may underlay this layer. In certain embodiments, the central layer of the laminate is a core of a material that is compressible, before consolidation. The optional film which overlies the veil may be selected from "dry films" and "wet films," as defined herein. The film reduces pin-holing of the laminate's surface, improves paint adhesion, and reduces the amount of release agent needed in the mold in the laminate consolidation process. The dry films are selected from commercially available sheets of thermoplastic or thermosetting polymer or composite. The wet films are gelcoats applied to the mold surface, matched to the resin matrix.

The preferred laminate is symmetrical in the sense that layers on each side are duplicated on the other side, except for the veil (and film, if one is present) which is only on the side(s) requiring a Class A finish.

The veil, reinforcing layers, and the central core (if one is present), are embedded in a resinous matrix that also forms the Class A surface. The matrix is a mixture of a thermosetting resin and optionally a relatively high proportion of an organic and/or inorganic filler, or mixture of fillers. In certain embodiments, these fillers, in combination with the veil layer, play an important role in preventing print- through of the underlying reinforcing layers of the composite on the panel surface. This facilitates the forming of a smooth Class A surface.

The structural panels of the invention may be prepared with a resin matrix selected from any one or more of a wide variety of thermosetting resins. Among the useful thermosetting resins are epoxy resins, phenolic resins, polyester, vinyl ester, polyvinyl ester, polyimide, modified acrylic, polyurethane, bismaleimide, and the like, and hybrids of these.

In another aspect of the composite panels of the invention, the composite includes a high proportion of reinforcing fiber, which provides an improved strength to thickness ratio relative to prior art composite panels. Thus, for example, stiffeners are not needed to make panels suited for automotive applications. It is preferred that the reinforcing layers of the laminated panels be located as near to the outer surfaces of the laminate as possible for maximum strength and stiffness.

The invention also provides methods of making the laminated structural panels. In one embodiment, the method includes sequentially laying down each layer and wetting the layer with liquid resin before laying down the next layer. The core layer, if one is used, may not be wetted. Preferably, the last reinforcing layer underlying the veil has a unidirectional ply. A resin mixture, preferably including a relatively high proportion of opaque filler, is applied to the last reinforcement layer laid down . A drapeable veil is laid down over the resin- wetted last reinforcement layer, and the resin mixture is then applied over the veil. Optionally, a film is then laid down over the wetted veil. The final layer added, whether veil or film, faces the surface where the Class A surface will be formed after consolidation. Consolidation under heat and pressure produces a structural panel with a Class A surface on the side adjacent the veil (or optional film). Importantly, in accordance with the invention, this Class A surface is achieved directly through consolidation, and without further surface modifying treatment, such as abrasion, blasting (using particulates or water), surface filling, or another technique. Thus, significant cost savings over the prior art are achieved. In an alternative embodiment of the method, all the reinforcing layers and central core layer to be consolidated are laid down, with the veil (or film) as the topmost layer. Then a resin mixture, preferably including a relatively high proportion of opaque filler, is applied before consolidation.

The invention also provides a "stratified cure" method of regulating the relative gellation or cure sequence of resin- wetted layers during consolidation of a composite panel which results in production out-of-mold of a composite laminate panel with a Class-A surface. In accordance with the invention, the rate of cure of a resin is accomplished by a selection of cure agents, or adjusting the reactivity of the resin before application to a specific layer of the layup construction to be consolidated. By an appropriate selection of relative cure rates or sequence, the less reactive layers will remain more moldable to fill any surface or interlaminar deviations that may arise after the layers wetting with the more reactive resin have gelled or cured. Resins with varying characteristics can be used in any panel layer. These include: gelcoats, resins with conductive fillers, and foamed resins. Controlling resin reactivity and cure rate can also be accomplished by varying the temperatures of the press molds (dies). For example if there are two mold halves of different temperatures, the hotter mold half will accelerate the resin cure rate closest to its surface while the cooler mold surface will impede the resin cure rate adjacent to its surface. For press molds with two halves, the preferred temperature difference range is from 10 - 55°C.

The resin matrix may include several additives, including electrical conductors, and resin charge modifiers. Preferably, the resin contains additives that dissipate any electrical charge after a panel has been cured to facilitate the adhesion of paint to the consolidated panel. Brief Description of the Drawings

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: FIGURE 1 is a schematic end view of a panel, with layers exploded for ease of description, in accordance with the invention;

FIGURE 2 is an end view of an alternative embodiment of a panel in accordance with the invention, with layers exploded for ease of description; FIGURE 3 is a simplified process flow diagram illustrating process steps in an embodiment of the method of the invention;

FIGURE 4 is a schematic cross section through an edge of a mold for forming panels showing a seal for drawing a vacuum on the mold and a peripheral knife edge to size the panels; FIGURE 5 is a schematic cross section through an edge of a mold containing layers for consolidating into a laminate, showing knife edges for cutting laminates to size;

FIGURE 6 is a schematic exploded end view of a structural panel constructed in accordance with the present invention; FIGURE 7 is an environmental view of a press used to construct a structural panel in accordance with the present invention, with the press shown in cross section for clarity;

FIGURE 8 is a cross-sectional end view of a press used to construct a structural panel in accordance with the present invention, with the press shown in the open position;

FIGURE 9 is a cross-sectional end view of a press used to construct a structural panel in accordance with the present invention, with the press shown in the partially closed position; and

FIGURE 10 is a cross-sectional end view of a press used to construct a structural panel in accordance with the present invention, with the press shown in the compressed position.

Detailed Description of the Preferred Embodiment In accordance with the invention, there are provided structural panels, and methods of making these panels, that have a Class A surface finish on at least one side. The surface finish is obtained directly out-of-mold without requiring subsequent abrasive surface modifying treatments or surface filling techniques. The structural panels are significantly stronger (i.e., higher strength to thickness ratio, flexural modulus) than panels previously made in the automotive industry. As a result of the improved strength, stiffeners are not needed where prior art panels for the same application needed stiffeners. Also, the composites are of lighter weight for equivalent strength since strength to weight ratio is increased.

The term "symmetrical" as used in the specification and claims with reference to a laminate or layup means that the stack of reinforcing layers on one side of the center of the laminate and their orientation is duplicated on the other side. The term is used to describe such layups or laminates even if only one side has a surface veil and/or a film layer.

The term "layer" with reference to reinforcing layers includes a single physical layer of reinforcement, whether or not these are individually of "multi-layer" construction, such as a bidirectional or multiaxial layer of reinforcement.

The Class A surface of the panels of the invention is achieved by the use of the "surface veil," and an optional film overlying the veil, that is added to the side of the layup where the Class A surface is to be formed. This veil (and film) mask the underlying reinforcing layers, and thereby minimize "print-through" of these layers to the surface. The veil also holds resin at the laminate surface (when no film is present) to assist in forming the surface gloss.

The veil may be selected from non-woven mat or felt able to absorb resin and compressible to absorb mild irregularities in surfaces against which it is pressed. The veil may be made of polyester fibers, glass fibers, carbon fibers, aramid fibers, cotton fibers, mixtures of these fibers and any other fiber that can withstand the consolidation temperature. The surface veil is preferably selected from materials that have an areal weight of about 60 to about 500g/m², more preferably about 100 to about 300g/m² and most preferably about 140g/m². Clearly, the thickness of the veil will depend on the coarseness of the underlying reinforcement, and the need to prevent print-through of this coarse weave. For this reason, it is preferred that the veil be underlaid with a unidirectional fiber layer.

In certain embodiments, the surface veil may be overlaid with a film. The film may be selected from the "dry films," and the "wet films." The purpose of the film is to reduce or eliminate pin-holing of the laminate surface, and to assist paint adherence to the surface. The film also reduces the amount of release agent that must be added to the mold for ready release of the laminate from the mold.

The preferred "dry films" of the invention include TEDLAR® (product of DuPont of Delaware), and other thermoplastic, thermosetting, or elastomeric films, such as PAINT ON A ROLL® (product of Avery Denison); and other commercially available films. Preferably, the film has a thickness in the range 0.001 to .125 inches. -7-

The "wet" films are selected from resinous coatings or gelcoats. The resinous coatings and gelcoats may be applied to either the surface of the mold or to the reinforcements. The gelcoats may be selected from any gelcoat that is compatible with the resin matrix of the panel. The reinforcing layers that are useful in the composite panels of the invention include a wide variety of commercially available reinforcing layers. Reinforcing layers may be selected for a particular purpose, depending upon the type of panel being produced. Thus, while layers that comprise plies with unidirectional fibers are preferred, multiaxial materials are also useful, especially in larger panels. Furthermore, non-woven materials may also be used as "reinforcing layers." In accordance with the invention, the type of reinforcing layers selected depends upon several factors, including for example, the load to which the panel will be subjected, and cost factors. Thus, a reinforcing layer may include unidirectional fibers, and could comprise a multiaxial ply, depending upon the application. In certain structural laminates, the proportion of reinforcement may be in the range 60-65 wt%, based on the weight of the laminated panel.

The composite panels of the invention optionally include a central, compressible core for certain applications. Preferably, the core is of a non-woven fleece material that is at least somewhat compressible under molding conditions to aid the panel in conforming to the shape of the mold during consolidation. The core may be made from a wide variety of non- woven, compressible material including, for example, glass fiber, polyester fiber, carbon fiber and the like, and mixtures of materials.

With regard to the organic polymers useful in forming the matrix of the composite panels of the invention, these polymers may be selected from thermosetting polymers, such as the epoxy resins, phenolic resins, polyester, vinyl ester, polyvinylester, polyimide, modified acrylic, polyurethane, bismaleimide, and the like, and hybrids of these. Additives including fillers (both reinforcing and nonreinforcing), low-profile agents to reduce resin shrinkage, mold-release agents, surfactants, thickening agents, foaming agents, flame retardants, pigments, diluents and electrical conductors to dissipate electrostatic charge, may be added to the resin(s). Preferably, the polymer/additive combination is selected to minimize shrinkage, thereby reducing the likelihood of print-through and facilitating the production of a Class A surface. An important additive to the resin or resin mixture is an agent that dissipates residual charge on the consolidated panel to facilitate the electrostatic application of paint coatings. Examples of these electrically conductive additives include carbon black and powdered metals.

While it is possible to make the laminates of the invention without addition of fillers to the resin, addition of fillers is preferred for several reasons. Fillers reduce the amount of resin needed thereby reducing costs. Fillers also assist in masking underlying reinforcement from the surface. Therefore, for laminates with reinforcing layers that are not smooth and unidirectional, addition of a high proportion of filler, in the range of about 20 to about 45 vol. % (of the resin) is preferred.

The following tables illustrate exemplary ranges of resin additives that are useful in the invention:

Example 1

Resin Ingredients Range (voIume%) useful preferred

Resin/Hardener 55-100 77.9

Wood Flour Filler 0-30 18.0

Talc Powder Filler 0-45 3.4

Hi-Sil 233 (thixotropic additive) 0-12 0.7

Total 100

Example 2

Resin System Ingredients Range (vt tlume %) useful preferred

Resin/Hardener 50-100 81

Talc (powder filler) 0-45 6

Glass Balloons 0-50 11.4

Hi-Sil 233 (thixotropic additive) 0-12 1.6

Total 100

The useful cure temperature range may be between, but not limited to 50°C-200°C. The preferred range is between 60°C-150°C.

The accompanying FIGURES are illustrative of preferred embodiments of the invention, and do not limit the scope of the invention. Instead, they are intended to -9-

enhance the understanding of the invention as described herein, and as claimed herebelow.

FIGURE 1 is a schematic, simplified, not-to-scale, end view of a layup for a structural panel in accordance with the invention. As shown, the layup 10 is made up of a number of layers. In this embodiment the central layer 12 is a compressible core. The layup 10 is "symmetrical" in the sense that the layers on either side of the core 12 are identical in both composition and orientation. However, in this embodiment only one side has a drapeable veil 14 to screen any print-through of underlying layers. This side is the "A" side. For purposes of this description, the layup 10 illustrated in FIGURE 1 is "symmetrical except for the veil on the A side." On either side of the central core 12 is a weft ply 16 of unidirectional fibers oriented in the 90° direction. Adjacent to, and outside of, each of the 90° plies 16, is a warp unidirectional ply 18, with fibers oriented in the 0° direction. Finally, on the A side only, is a veil or mat 14 of compressible fibrous material. The layered structure of FIGURE 1 is consolidated in a press equipped with smooth mold surfaces to produce a structural panel having a Class A surface on the A side, as explained below with reference to methods of the invention.

FIGURE 2 shows a layup identical to that of FIGURE 1, except for the addition of a "dry" film 20 overlying the veil 14. In an important aspect of the invention, the flexural strength of the structural panels are at least about 270 MPa, and preferably in the range from about 350 to about 700 MPa, even without the addition of added-on stiffeners, or molded-on stiffeners. This represents a significant advance over the prior art where such strength properties could only be obtained with the addition of stiffeners. This important property is the direct result of the use of a high proportion of reinforcing material in the invention, as compared to prior art structural panels, while maintaining a Class A surface without print-through and without requiring subsequent abrasive or other surface treatments to improve surface smoothness.

The methods of preparing the structural panels of the invention may be practiced with commercially-available equipment, or with equipment customized for greater automation.

In certain preferred embodiments, the method of the invention includes a stratified cure process that uses a variety of curing agents, specific to layers of the laminate, to control the cure time of the resin and matrix resin flow at that layer. The purpose of stratified cure of the resin(s) is to produce out-of-mold composite -10-

laminate panels with a Class-A surface. The process includes the elimination of surface pinholes and surface print-through of materials. "Pinholes" on the surface are primarily caused resin curing around gas bubbles entrapped between the composite and the molded surface. "Print-through" on the surface of a composite panel is a defect that is primarily caused by the use of materials with unlike properties which have differences in shrinkage during either the curing or cool down processes, materials with like properties can cause print-through or some surface defects by having thickness changes within the part. That is, upon curing or cool down the thicker areas shrink more than the thinner areas. Depending on the construction of the composite panel controlling the cure rates and use of resin characteristics varies, materials that are, for example, coarsely constructed such as knitted, woven or material that have gaps typically would cause surface print-through.

For an example, depending on the engineering requirements a composite panel may be constructed of five sequentially stacked layers with layer 4 closest to the veil layer, layer 5. The panel may be produced by the following method of curing the resin:

Layer 1 - This layer may consist of a reinforcement. If the material is of a coarsely constructed reinforcement then the resin gellation or cure should occur before layer 4. Layer 2 - when this layer contains a non-woven core and is used as a buffer then the resin gellation or cure should occur before layer 1. this layer may also contain foamed resin to lessen panel weight and/or cost. This layer may also be a reinforcement. If the material is of a coarsely constructed reinforcement then resin gellation or cure should occur before layer 4. Layer 3 - This layer consists of a reinforcement. If the material is of a coarsely constructed reinforcement then resin gellation or cure should occur before layer 4.

Layer 4 - If resin cure of this layer is first, then the layer provides the benefit of a buffer that eliminates or reduces print-through on this surface. If the resin cure for this layer is delayed until after the cure of other layers then the laminate can be remolded by further compaction in the pressing process by adding more pressure to create a resin flow. This will remold the surface to fill in defects of previously gelled or cured layers.

Layer 4 may be the Class-A surface layer, if the fifth layer is not used. Layer 4 incorporates a surface veil that eliminates print-through produced by materials or -11-

reinforcements in layers 1, 2, or 3. If reinforcements in layers 1, 2, and 3 consist of finely constructed materials or reinforcements including unidirectional plies, then layers 1-4 and 5 may be cured simultaneously as an option. Layer 5 may be substituted for by applying a gelcoat enhances mold surface wetout and eliminates surface pinholes.

Layer 5 - This layer may be the Class-A surface layer and may include a surface film, sheeting or gelcoat and/or resin modifiers to reduce the risk of producing a pinholed surface. If a pigmented surface film or sheeting has been used, no further paint application is needed. In one embodiment of the method of the invention, illustrated in FIGURE 3, a resin mixture is pre-prepared by the steps in box 50. Thus, in this particular case, epoxy resin is combined with the predetermined proportion of filler in a mixer. The combined resin and filler mixture, in liquid form, is then pumped from the mixer to resin mixture holding tanks. From these holding tanks, the resin mixture is pumped, under manual or electronic control, to the dispensing head of a resin mixture dispenser to apply the resin to layers of the layup to be consolidated into the panel. Other methods of resin mixture preparation and application may also be useful.

The illustrative example of a layup to be consolidated is prepared by first cutting a reinforcing ply, such as a glass fiber or carbon fiber ply, to the required size and shape in step 52. Then, resin is applied 54 to the laid down cut fiber ply, in a proportion of from about 30 to about 95 wt % resin, based on the total volume of resin, filler and fiber of the cured laminate, and depending upon the nature of the resin and the type of fiber. Next, a second ply is cut in step 56 to form a second layer that is laid over the first layer. In step 58, resin mixture is applied to the second fiber ply. In this manner, several fiber plies of various orientations may be laid down, one after the other and wetted with applied resin mixture. If the layup includes a central mat core, in step 60 a mat core is cut and laid down over the previously laid down and wetted layers that will ultimately form the "B" side of the panel. In step 62, resin mixture is then applied to the mat core. Thereafter, a third layer is cut and laid on the mat 64, resin mixture is applied to this layer 66. A fourth layer is cut 68 and laid on top of the resin wetted third layer, and the fourth layer is in turn is wetted with the resin mixture 70.

While the foregoing describes a layup consisting of a central mat core with two layers of oriented fiber plies on either side, clearly more plies can be laid up on each side of the central core to produce a symmetrical layup, or a nonsymmetrical -12-

layup, as required for the particular application. As pointed out before, the last reinforcing layer that underlies the veil, preferably has a ply of unidirectional fibers.

In step 72, a surface veil is cut from a drapeable material and laid over the layup. Clearly, the surface veil could also be the first layer that is laid down. Either way, this would ensure that the surface veil is immediately adjacent the surface that is to have the Class A surface finish. Resin is then applied 74 to the cut surface veil. Optionally, a film may then be applied over the veil. The entire layup is transferred to a press where it is consolidated 76 under heat and pressure into a laminate.

While planar laminates and panels may be produced in accordance with the invention, the invention is particularly useful and advantageous for making contoured panels. Prior art methods, on the other hand, experience great difficulty in producing contoured panels, especially with a Class A surface finish. Clearly, in accordance with the invention, a layup having a first surface veil (or film) as the top layer, and another surface veil (or film) as the bottom layer, can be consolidated into a panel with Class A surfaces on both sides.

Temperature and pressure of consolidation are dependent on the nature of the resin used. Preferably, the consolidated panel is removed from the press while the part is still hot, and is removed with vacuum chucks on the "B" side, assisted with air ejectors on the "A" side. Preferably, the "A" side of the hot panel is not touched during the entire operation, to preserve surface finish. Thereafter, a water jet may be used to trim the part to size, and the edges may be deburred. Thus, a final structural panel with Class A surface is produced without need for further surface modifying treatments.

In order to minimize voids and pinholes in the laminate and surface air bubbles, the invention provides a method of vacuum molding the panels of the invention. In accordance with this aspect of the invention, the mold is modified as shown in FIGURE 4 so that it may be partially closed while a vacuum is drawn on its contents. When the vacuum has been pulled, the mold can be completely closed and the laminate consolidated. FIGURE 4 illustrates a seal plate 30 with elastomeric seals 36 that engage the top mold half 32 prior to full closure of the mold. This allows a vacuum to be created in the mold cavity 33 around the material charge 34 by evacuating the air through the tube 35. The mold then closes further and compresses the material charge.

In a further aspect of the invention, the mold may be fitted with knife edges for cutting the molded laminate to size and shape desired, as shown in FIGURE 5. •13-

The top mold half 40 and the bottom mold half 41 are shown compressing the material charge 42. Two hardened cutting blades, one stationary 43 and one moving 44 cut off the material hanging out the mold. This results in a molded part which does not require trimming after the part is removed from the mold.

In a further embodiment of the method of the invention, the reinforcing layers (and optional core) are first consolidated to produce an unfinished panel. Thereafter, the veil is applied to the side of the laminate on which a Class A surface is desired. Optionally, a film is applied over the veil. The layup is then consolidated to form the Class A surface on the panel. In accordance with this embodiment of the method of the invention, the materials that provide structural strength to the panel are molded twice, while the materials that provide the Class A surface are only molded once. Optionally, the veil may be molded first and then consolidated with the reinforcing layers.

The following examples are intended to illustrate specific embodiments of the invention, and are not intended to limit the invention as described herein and as claimed herebelow.

Examples Example 1

A layup was prepared, in accordance with FIGURE 2. Each of the layers were as follows in sequence, from the center:

Layer Type Number

12 340 gram per square meter (gsm) polyester core PI 000 from Paltex Inc.

16 Two plies 160 gsm unidirectional carbon from HEXCEL Fabrics

18 Two plies 160 gsm unidirectional carbon from HEXCEL Fabrics

14 130 gsm glass/polyester mat (veil) TECHMAT™ from BGF Industries

20 Film of TEDLAR TPD 20BE5 from DuPont

The resin mixture utilized is as follows:

Composition Weight

Refcoa R5200 epoxy resin from Composite Materials, Inc. 5,911 grams

-14-

Refcoa H595 hardener from Composite Materials, Inc. 1182 grams

Talc MP 70-22 from Barretts Minerals, Inc. 766 grams

Wood flour 14010 from American Wood Fibers of Scholfield 784 grams

Hi-Sil 233 from PPG Industries 115 grams

The resin was applied at the following rates for each layer, from the B-side to the A-side:

Layer 18: 290 gsm (mixture of R5200 and H595 only, without Talc, flour and Hi-Sil)

Layer 16 690 gsm (using above-described resin mixture)

Layer 12 1730 gsm (using the above-described resin mixture)

Layer 16 O gsm

Layer 18 830 gsm (using the above-described resin mixture)

Layer 14 1450 gsm (using the above-described resin mixture) The resin- wetted layup was then placed in a mold which was closed slowly

(approximately 20 seconds for the last 1 cm of closure) and was cured at a temperature of 82° C for the B-side mold, and 71° C for the A-side of the mold. The panel was cured for 15 minutes.

The resulting panel was painted and evaluated by the surface evaluation expert of a major automotive company and determined to be production-acceptable Class-A. Example 2

A panel with a Class-A surface was produced as follows, from the following layup, commencing on the "B" side:

^■15-

Dry Materials for Layup:

Layer Number Type

1 & 2 Product: TECHMAT™ of BGF Industries, Inc. Composition: Non Woven Glass/Polyester 80% Fiberglass, 20% Polyester Approximate Areal Weight 305g/m²

3 & 4 Product: P1000™ ofPaltex, Inc. Composition: Non Woven Polyester Approximate Areal Weight: 340 g/m²

5 & 6 Product: TECHMAT™ of BGF Industries, Inc. Composition Non Woven Glass/Polyester 80% Fiberglass, 20% Polyester Approximate Areal Weight 305g/m²

7 Product: ISF2000™ of Rexhamn/3M Composition: Thermoplastic Film

Thickness: 0.021 inches

Resin Batch Ingredients: gms.

Ciba, GY6010™, Epoxy Resin 192.4

Harwick Chemical Co., Stan- white 400™, Calcium Carbonate 59.3

PPG Industries, Hi-Sil 233™ 13.2

3M, B38/4000™Glass Bubbles 10.1

Total 275.0

Epoxy hardeners for Resin

1. Shell Chemical Co., Epi Cure 3200

2. Shell Chemical Co., Epi Cure 3234 -16-

Primary Equipment

Press: Dake 150 Ton Heated Press

Platens: Upper: 25" x 25" x 1 " thick, steel, 16 rms finish

Lower: 25" x 25" x 1" thick, steel, 2-6 rms finish Dielectrometer: Micromet Instruments, Inc., Model Eumetric 100a

The press platens were preheated to 180°F (82°C) and the materials for the layers 1-7 were cut into 17 inch squares. For each of layers 1-6, a batch of resin was premixed. 43.7 grams of hardener No. 1 was added to each of 4 batches of the resin, which were then applied to each of layers 1-4. 24.8 grams of hardener No. 2 was added to each of the remaining two batches, which were each then applied to layers 5 and 6.

Film layer number 7 was placed onto the lower press platen, and the edges secured with the tape. The remaining layers were stacked in decreasing number sequence on top of layer 7. To ensure complete material wetout with the resin, the press was initially slowly closed to a part thickness of 0.25 inches. While the resin in layers 5 and 6 were still flowable, and during the time of onset of gellation or cure of layers 1-4, the press was closed to a final part thickness of 0.23 inches. The cure was monitored by the dielectrometer instrument. The part was molded for about 12 minutes. Upon inspection of the panel produced by the above method, it was found to have a Class-A surface finish.

Referring now to FIGURE 6, another alternate embodiment of a laminate structural panel 120 will now be described in greater detail. The structural panel 120 is substantially identical in construction and materials as that described above for the preferred embodiment, with the most notable exception being a lack of a veil. The structural panel 120 includes a bottom reinforcement layer 122, a reinforcement layer 124, an optional core 126, first and second multi-layer reinforcements 128 and

130 and a film layer 132. The bottom reinforcement layer 122 is bonded to the reinforcement layer 124 by a layer of resin 134. The reinforcement layer 124 is bonded to the core 126 only at predetermined contact positions by a layer of resin 136. In this alternate embodiment, the core 126 includes a partial layer of reinforcement 138a-138d disposed at the sides of the core 126. As a result, an increased amount of resin 136 is applied in the areas of the reinforcement layer 124 that are in contact with the partial layers of reinforcements 138a-138d. Although it is preferred that the partial layers of •17-

reinforcement 138a-138d are disposed at the sides of the core 126, other locations, such as a continuous layer of reinforcements, are also within the scope of the present invention. Additionally, while the inclusion of the partial layers of reinforcements 138a-138d is preferred, such reinforcements are not required and, therefore, a structural panel 120 without the reinforcements 138a-138d is also within the scope of the invention.

The core 126 is bonded to the first multi-layer reinforcement 128 by an application of resin 140 only at predetermined contact positions, as described above for the resin layer 136. The first multi-layer reinforcement 128 includes preassembled upper and lower reinforcement layers 142 and 144. The second multi-layer reinforcement 130 also includes preassembled upper and lower reinforcement layers 142 and 144. The first and second multi-layer reinforcements 128 and 130 are bonded together by a layer of resin 152. Although it is preferred that the structural panel 120 includes two multi-layer reinforcements, 128 and 130, more or fewer multi-layer reinforcements are also within the scope of the present invention.

As discussed above for the preferred embodiment of the structural panel, the structural panel 120 may include the film layer 132. The film layer 132 may be selected from the same "dry films," and "wet films" described above. The preferred dry film 132 may be bonded to the structural panel by a layer of resin 154.

The following non-limiting example is intended only to illustrate a specific embodiment of structural panel constructed in accordance with the present invention.

Example Example 1

A layup was prepared, in accordance with FIGURE 6. Each of the layers were as follows in sequence, from the bottom:

Layer Type Number

122 285 gsm carbon woven fabric (43377) from Hexcel Fabrics

124 285 gsm carbon woven fabric (43377) from Hexcel Fabrics

138 carbon woven unidirectional fabric (G1078) from Hexcel Fabrics

126 polyurethane foam 4.5 pounds per cubic foot(pcf) (6704.5) from

General Plastics -18-

Layer Type Number

144 160 gsm carbon unidirectional tape from Hexcel Fabrics

132 Film of TEDLAR TPD20B5from DuPont

The resin-wetted layup is then placed in a mold that is closed slowly by the molding process, as is described in greater detail below. The layup is then cured at a temperature of 63 °C for both the A-side and B-side of the mold. The panel then is cured for 35 minutes.

The resin mixture utilized is as follows:

Composition Weight

Refcoa R5200 epoxy resin from Composite Materials, Inc. 5860 grams

Refcoa H595 hardener from Composite Materials, Inc. 1084 grams

Talc MP 70-22 from Barrets Minerals, Inc. 1265 grams

Glass Balloons from 3M 308 grams

Hi-Sil 233 from PPG Industries 238 grams

Layer Resin Weight Description

Layer 134 590 gsm Using above-described resin mixture

Layer 136 415 gsm Using above described resin mixture and 800 gsm contacting layers 138a and 138b

Layer 140 400 gsm Using above described resin mixture

Layer 152 550 gsm Using above described resin mixture

Layer 154 420 gsm Using above described resin mixture

Referring now to FIGURES 7-10, another method of preparing structural panels in accordance with the present invention will now be discussed in greater detail. As briefly noted above, for the purpose of reducing void content and surface -19-

air bubbles, a vacuum may be achieved in the press around the material charge prior to compressing the material charge.

As may be best seen by referring to FIGURES 7 and 8, a commercially available press 220 includes upper and lower platens 222 and 224. Attached to opposing surfaces of the upper and lower platens 222 and 224, in a manner well- known in the art, is an upper mold 226 and a lower mold 228, respectively. Opposing surfaces of the upper and lower molds 226 and 228 may be configured for a variety of contours or shapes. A material charge 229 is removably disposed between the upper and lower molds 226 and 228 on a clamping frame 230 by well- known clamps 232a and 232b. The clamping frame 230 is disposed between the upper and lower molds 226 and 228 on a well-known support structure 234.

Additionally, the clamping frame 230 is indexed between the upper and lower molds 226 and 228 by a tooling ball and cap fixture 236, as is well-known in the art.

As may be best seen by referring to FIGURE 9, the press 220 includes a vacuum chamber 238. The vacuum chamber 238 includes a rectangularly shaped upper C channel 240 defining the upper vacuum chamber, a rectangularly shaped lower C channel 242, an elastomeric vacuum seal 244 housed within a housing 245 and a vacuum seal surface 246. The vacuum seal 244 is rigidly fastened to the lower edge of the upper C channel 240 by well-known fasteners, such as rivets or screws, extending through the lower edge of the C channel 240 and into the vacuum seal housing 245. The vacuum seal surface 246 is a substantially planar member that extends along the upper edge of the lower C channel 242. The vacuum seal surface 246 is sized to be sealing received within the vacuum seal housing 245 and against the vacuum seal 244, as is described in greater detail below. Operation of the press 220 may be best understood by referring to

FIGURES 8-10. As seen in FIGURE 8, the material charge 229 is disposed between the upper and lower molds 226 and 228 and indexed therebetween on the support structure 234. The lower mold 228 is driven upwards until the seal surface 246 is received within the seal housing 245 and engages the vacuum seal 244, as seen in FIGURE 9. After the seal surface 246 is sealingly received against the vacuum seal 244, the vacuum chamber 238 is evacuated by a tube 250 and well-known evacuation means (not shown). The tube 250 extends through the lower C channel 242 and is sealed therein by a well-known seal (not shown). Preferably, the vacuum chamber 238 is evacuated above 28 inches of mercury. Although a vacuum -20-

above 28 inches of mercury is preferred, other levels are also within the scope of the present invention.

As the vacuum chamber 238 is being evacuated, the process begins a dwell period. During the dwell period, heat is transferred from the upper and lower molds 226 and 228 to the material charge 229. The heat transfer causes the resins to become less viscous and fill voids within the material charge 229, thereby drawing out pockets of air. The dwell period may last between, but is not limited to, 0-60 seconds. After the dwell period, the upper and lower molds 226 and 228 continue to compress the material charge 229, at a useful rate range of .0001-1 inches per second, preferably at a rate of .01 -.02 inches per second. The compression step continues until the lower mold 228 reaches a predetermined distance. As a result, the material charge 229 has fewer imperfections due to entrapped air and results in a panel that is lightweight, strong and does not include a veil.

While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

Claims

-21-The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A laminated structural panel comprising a composite with a Class A surface finish on at least one side, the composite comprising in sequential order, at least the following layers from the at least one side having a Class A surface:

(a) a veil underlying the at least one side with Class A finish, the veil drapeable over a contoured surface before consolidation into the laminate, the veil able to absorb liquid resin before consolidation; and

(b) at least one reinforcing layer underlying the veil; wherein the veil and the at least one reinforcing layer are embedded in a cured resin matrix, a resinous surface of the resin matrix over the veil forming the Class A surface of the structural panel.

2. The panel of Claim 1, wherein the at least one reinforcing layer comprises unidirectional fibers.

3. The panel of Claim 2, further comprising a central core of a material that was compressible before consolidation into the panel.

4. The panel of Claim 3, wherein the laminate is symmetrical around the central core, except for the veil directly adjacent to, and underlying, the at least one Class A surface.

5. The panel of Claim 1, wherein the resin of the resin matrix is selected from the group of thermosetting resins consisting of polyester, vinyl ester, epoxy, phenolic, polyimide, modified acrylic resin, polyurethane bismaleimide, polyvinyl ester, and mixtures including these resins.

6. The panel of Claim 1, wherein the veil comprises fibers selected from the group consisting of polyester fibers, glass fibers, aramid fibers, cotton fibers, carbon fibers and high density polyethylene fibers.

7. The panel of Claim 1, further comprising a film overlying the veil, the film interposed between the veil and the Class A surface.

8. The panel of Claim 1, further comprising a hardened gel coat overlying the veil. -22-

9. The panel of Claim 1, further comprising an electrically conductive filler to facilitate adherence of a pigmented coating to the surface.

10. The panel of Claim 1, wherein the panel has a flexural strength of at least 270 MPa, without attachment of stiffeners to a side opposite the at least one side with the Class A surface finish.

11. The panel of Claim 1, wherein fiber reinforcement comprises from about 60 wt% to about 65 wt% based on the mass of the panel.

12. A method of making a laminated structural panel with Class A surface on at least one side thereof, the method comprising sequentially:

(a) laying down a first reinforcing layer comprising parallel fibers;

(b) applying a liquid resin mixture to the first layer;

(c) laying down a second reinforcing layer;

(d) applying liquid resin to the second layer;

(e) laying down a veil, the veil drapeable to conform to a contoured shape before consolidation;

(f) applying a resin mixture to the veil; and

(g) consolidating the layers under applied heat and pressure into a panel with a Class A outer surface adjacent the veil, the Class A surface substantially free of print-through of underlying reinforcing layers and the Class A surface produced through consolidation without subsequent abrasive surface treatment and surface filling.

13. The method of Claim 12, further comprising laying down a core layer, the core layer surrounded on each side by a reinforcing layer.

14. The method of Claim 12, comprising coating a surface of a mold, wherein the step of consolidating is carried out, with a gelcoat.

15. The method of Claim 12, wherein steps (e) and (f) precede step (a).

16. The method of Claim 12, further comprising, before consolidating, laying down a film over the drapeable veil.

17. The method of Claim 13, further comprising, before consolidating, laying down a film over the drapeable veil. -23-

18. The method of Claim 13, wherein the consolidating is between mold halves, one of the mold halves at a temperature between 10 and 55°C hotter than the other half.

19. The method of Claim 12 wherein the consolidating comprises applying heat and pressure in a mold under a partial vacuum.

20. The method of Claim 12, further comprising cutting layers to a predetermined size in a mold equipped with knife edges when the mold is closed for the step of consolidating the layers.

21. The method of Claim 12, wherein the consolidating comprises a first step comprising consolidating reinforcing layers and another step comprising consolidating the veil to the consolidated reinforcing layers.

22. The method of Claim 12, wherein the consolidating comprises a first step comprising consolidating the veil, and another step comprising consolidating the reinforcing layers to the consolidated veil.

23. A method of making a laminated panel with a Class A surface on at least one side thereof, the method comprising:

(a) laying down a layered structure comprising: (i) a reinforcing layer; and

(ii) a veil layer, the layer drapeable over a contoured surface before consolidation;

(b) applying a first liquid resin; and a second liquid resin, the second resin curing faster than the first resin; and

(c) consolidating the layered structure with the applied resin mixture under heat and pressure into a panel with a Class A surface adjacent the veil, the Class A surface substantially free of print-through of reinforcing layers and the Class A surface produced without abrasive surface treatment and without surface filling.

24. The method of Claims 23, comprising laying down a film over the veil layer before the step of consolidating. -24-

25. The method of Claim 23, further comprising applying a gelcoat to a surface of a mold wherein the step of consolidating is to be carried out, the surface adjacent the veil layer in the mold during the consolidating.

26. The method of Claim 23, wherein the applying of a first and second liquid resin comprises applying a mixture of the resins.

27. The method of Claim 23, wherein the consolidating comprises a first step comprising consolidating reinforcing layers and another step comprising consolidating the veil to the consolidated reinforcing layers.

28. The method of Claim 23, wherein the consolidating comprises a first step comprising consolidating the veil, and another step comprising consolidating the reinforcing layers to the consolidated veil.

29. A laminated structural panel comprising a composite with a Class A surface finish on at least one side of the panel, the composite comprising:

(a) at least one reinforcing layer underlying the Class A surface, the reinforcing layer being embedded in a cured resin matrix, a resinous surface of the resin matrix forming the Class A surface of the structural panel, wherein the Class A surface is substantially free of print through of the underlying reinforcing layer.

30. The structural panel of Claim 29, further comprising a layer of film interposed between the Class A surface and the reinforcing layer.

31. The structural panel of Claim 29, further comprising a hardened gel coat overlying the reinforcing layer.

32. The structural panel of Claim 29, wherein the resin of the resin matrix is selected from the group of thermosetting resins consisting of polyester, vinyl ester, epoxy, phenolic, polyimide, modified acrylic resin, polyurethane bismaleimide, polyvinyl ester, and mixtures including these resins.

33. The structural panel of Claim 29, further comprising at least one layer of foam. -25-

34. The structural panel of Claim 33, wherein the core includes a reinforcement layer located at predetermined positions on the core.

35. The structural panel of Claim 33, further comprising a layer of film interposed between the core and the Class A surface.

36. A method of making a laminated structural panel with a Class A surface on at least one side of the structural panel, the method comprising the steps of:

(a) laying down a first reinforcing layer;

(b) applying a liquid resin layer to the first reinforcing layer;

(c) laying down a second reinforcing layer to the resin layer;

(d) applying a resin mixture to the second reinforcing layer; and (d) consolidating the layers under applied heat and pressure into a panel with a Class A outer surface, the Class A surface being substantially free of print-through of underlying reinforcing layers and the Class A surface produced through consolidation without subsequent abrasive surface treatment and surface filling.

37. The method of Claim 36, further comprising the step of laying down a core layer between the first and second reinforcing layer before consolidating the layers.

38. The method of Claim 36, further comprising the step of coating a surface of a mold with a gelcoat before consolidating the layers.

39. The method of Claim 36, further comprising the step of laying down a film over the second reinforcing layer before consolidating the layers.

40. The method of Claim 37, further comprising the step of laying down a film over the second reinforcing layer before consolidating the layers.

41. The method of Claim 36, wherein the step of consolidating the layers further comprises the step of applying a partial vacuum during the application of heat and pressure. -26-

42. A method of making a laminated structural panel with a Class A surface on at least one side of the structural panel, the method comprising the steps of:

(a) placing a layered structure between upper and lower platens of a press;

(b) closing the upper and lower platens to form a vacuum chamber therebetween;

(c) evacuating the vacuum chamber while compressing the platens together to draw entrapped air within the layered structure;

(d) transferring heat from the platens to the layered structure for a predetermined amount of time; and

(e) continue compressing layered structure at a predetermined speed until platens reach a predetermined compression position.