WO2008137952A2

WO2008137952A2 - Microparticle breather layer for use in composite part manufacture

Info

Publication number: WO2008137952A2
Application number: PCT/US2008/062944
Authority: WO
Inventors: Mchael D. Kipp; Dilworth L. Pugh; Michael D. Ridges; William T. Mccarvill
Original assignee: America Consulting Technology & Research, Inc.
Priority date: 2007-05-07
Filing date: 2008-05-07
Publication date: 2008-11-13
Also published as: WO2008137952A3

Abstract

A breather material for use within a negative pressure environment (e.g., for use with a vacuum bag in the manufacture of composite articles), wherein the breather material comprises, at least in part, a plurality of microparticles, such as cenospheres as obtained from the byproduct fly ash, as well as a binder that operates to adhere the microparticles together.

Description

MLCROPARTICLE BREATHER LAYER FOR USE IN COMPOSITE PART MANUFACTURE

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Serial No. 60/928,148, filed May 7, 2007, and entitled, "Microp article Breather Layer for Use in Composite Part Manufacture," which is incorporated by reference in its entirety herein. FIELD OF THE INVENTION

The present invention relates generally to composite part manufacture, and more particularly to a breather material for use in the manufacture of composite parts or articles.

BACKGROUND OF THE INVENTION AND RELATED ART Fiber reinforced resin composite articles are fabricated using one of two basic techniques - a "dry" lay-up process and a "wet" lay-up process. In a "dry"^'lay-up process, fiber forms that have been pre-wetted with resin, forming a "pre-preg" structure, are laid up against a mold to provide the proper shape. The process is "dry" because no new resin is introduced to the fiber forms after the material has been laid up against the mold. On the other hand, in a "wet" lay-up process, a dry fiber reinforcement material, otherwise known as a preform, is laid up on a mold and sprayed, brushed, or otherwise coated or "wetted" with the resin. If the resin employed is of the thermoset type, the composite article may then cured at an elevated temperature in an autoclave to form the fiber reinforced plastic structure. In other techniques the resin and the composite article may be designed to cure at ambient temperature.

Composite manufacturing methods can be further distinguished by their use of either closed mold or open mold processes. A common manufacturing method using a closed mold process is the resin transfer molding process (hereinafter "RTM") process. RTM is a version of the "wet" lay-up process in which a continuous strand^' mat or fiber preform is positioned on an open female mold or tool. A rigid, cooperatively shaped male mold is mated to the female mold and the sealing edges of the two are pressed together, creating a cavity of fixed dimensions which encloses the fiber preform. A catalyzed resin mix is thereafter pumped into the cavity formed between the two mold surfaces. After a suitable curing cycle, the part is removed from the mold. Closed mold methods such as RTM offer several advantages and can be cost effective when molding relatively small articles. Because a closed mold is rigid and easily sealed, the resin can be injected under pressure at one end while at the same time employing a vacuum to remove air from the sealed cavity at the other. Removing air before the resin is introduced reduces the possibly of air pockets and resin voids in the composite matrix and results in a stronger finished product. Another advantage of the closed mold is that as a closed system, all emissions of hazardous fumes can easily be controlled. Yet another benefit is the minimal set-up time. Indeed, the mold can be used again immediately after the resin is cured and the previous part removed. Finally, because both halves of the closed mold provide rigid, smooth surfaces, the final composite product has a quality surface finish on both sides. Unfortunately, because of the high cost of matched metal dies and high tonnage presses, parts produced with closed molds are generally limited in size and geometry.

As a consequence, most large composite articles, such as boat hulls, are currently manufactured using open molds and a "wet" lay-up process. These methods generally involve positioning a mat of fiber reinforcement material in a single open mold cavity and spraying or flow coating the fiber material with a liquid curable resin. A variation of this method involves chopping fiberglass in front of the resin spray stream, depositing the curable resin and the fiber reinforcements simultaneously in the open mold. A significant drawback to these "wet" open mold methods of fabrication is the release of large amounts of hazardous air pollutants (hereinafter "HAPs") into the surrounding atmosphere, which is a matter of great concern both to the Environmental Protection Agency (EPA) and the Occupational Safety and Health Agency (OSHA).

A solution for reducing HAPs, which is well known in the art, is to enclose the open mold and the fiber reinforcement material within an impermeable liner or vacuum bag during application of the resin. This method is formally known as Vacuum Assisted Resin Transfer Molding (hereinafter "VARTM"), but is more commonly referred to as an "infusion" process. Utilizing a vacuum bag allows manufacturers of composite articles to form such articles on an open mold, while at the same time eliminating the need for matching metal dies and high tonnage presses.

In VARTM processing, the dry fiber mat, or 'preform', is applied over a mold surface to form a lay-up of fiber reinforcement material of desired thickness. Resin injection ports and vacuum suction ports are installed at selected locations around the preform lay-up, and a flexible, gas impervious sheet, liner, membrane, film, or bag (hereinafter "bag") is placed over the entire assembly. The edges of the bag are clamped or sealed around the periphery of the mold to form a sealed vacuum envelope surrounding the preform lay-up. A vacuum source is placed in pneumatic or fluid communication with the space between the open mold and the bag and is used to draw a vacuum and to create a negative pressure within the sealed vacuum envelope. Resin is then introduced, or 'infused', into the. interior of the vacuum bag after and during the application of negative pressure. Under ideal circumstances, the induced negative pressure serves to cause the vacuum bag to pressurize the article, and thus shape the article to the mold, to draw the resin through the fiber mat, to completely "wet" the fiber, and to remove any air that might cause the formation of voids within the completed article. The negative pressure is maintained while the wetted fiber is pressed and cured against the mold to form the fiber reinforced composite structure or part having the desired shape. Once the composite part is fully cured, the bag is normally removed from the molded article and discarded as waste.

The use of an impermeable bag offers a significant advantage as HAPs generated from resin transfer are greatly reduced. However, it also creates a host of new manufacturing difficulties which, in turn must be overcome. One ongoing concern is the potential formation of air pockets or voids in the composite part that can result in both structural deficiencies and reduced aesthetics. As the bag is normally a thin, flat sheet laid upon the fiber preform, which is in turn laid up against the contoured surface of the open mold, the bag must be carefully folded or cut and taped to conform to the shape of the finished part. Any location where the bag is folded, wrinkled or bunched together creates the potential for a pocket of air, gas, or vapor to form between the bag and the fiber preform. Additionally, wrinkles can also form on the surface of the bag during setup, which allow excess resin to accumulate between the bag and the fiber preform, permanently transferring the impression of the wrinkle to the surface of the completed composite part. Although slowing down the evacuation process can reduce the occurrence of air pockets and wrinkles, it also results in reduced production rates, and therefore increased costs.

Any taped seam in the bag also creates the potential for a pinhole leak, which will cause air to be introduced into the resin stream. This problem causes a quality issue commonly called "bubble trails." Such defects that are not corrected during the molding process require costly reworking. Moreover, if the bag is of inadequate thickness, the induced negative pressure may draw portions of the bag film down into the intricacies in the fiber preform to partially block the flow of the resin. This phenomenon may require additional flow time to allow the affected area to be filled from another direction, and may also result in a structural defect caused by incomplete wetting of the fiber preform by the resin.

The method of properly installing traditional vacuum bags is labor-intensive, especially for very large structures, such as boat hulls. Trained technicians must accurately lay the bag over the contoured surface of the open mold and fiber preform, and attention must be taken when taping and sealing the outer edges of the bag against the sealing surfaces around the periphery of the open mold. Special care is required when installing the resin injection and vacuum suction ports to properly tape and seal the holes in the bag. Furthermore, additional up-front effort must also be spent assembling resin supply and vacuum suction manifolds which connect to the injection and vacuum ports. These piping systems are normally disposable as they become clogged with the resin after each use and must be discarded.

In the typical VARTM process every step in assembling the vacuum bag must be duplicated each time a part is built. It is recognized that it is costly to discard the completed vacuum bag after each use, but as the bag film must be thin and flexible in order to be applied in the first place, it lacks the structural integrity to withstand removal, cleaning and repositioning without tearing. Therefore, the expensive process of manually assembling the vacuum bag by laying down the bag film, attaching the injection and vacuum ports, and sealing the periphery of the bag against the open mold must be repeated for each new composite structure which is to be built using the resin infusion process.

A similar problem exists with the bags used in the traditional vacuum bagging process, which has long been used in industry to fabricate laminated articles comprised of composite materials that are adhesively bonded together. To make a composite or laminated article, a few thin layers of "pre-preg" fiber reinforcement material are stacked upon the forming surface portion of an open mold. A flexible gas impervious vacuum bag, similar to the one discussed above, is then placed over the composite or laminated article. A double-sided sealing tape, such as chromium tape, is continuously applied between the bag and the periphery of the open mold. Thus, a volume defined by the bag and the open mold is sealed off.

A vacuum source is placed in pneumatic or fluid communication with the space between the forming tool and the bag and is used to create a negative pressure in the sealed off volume. The creating of the negative pressure performs several functions. First, the bag is firmly pressed against the pre-preg fiber material laid up on the open mold, thereby forming the materials to the shape of open mold. The vacuum also draws out any pockets of air which were left trapped between the layers of pre-preg material, consolidating the layers into a tighter laminate structure. Moreover, in the same process the vacuum "debulks" the composite part by removing the excess resin initially added to the pre-pregs to ensure the fiber reinforcement material was complete wetted. What is left is a few layers of a tight composite, laminate structure which may be further built up to produce a light-weight, high-strength laminated article that is capable of being used as an aircraft component. When the vacuum induces an internal collapse of the bag against the prepreg fiber reinforcement, the bag can restrict the resin from freely flowing through the fiber reinforcement. This has a tendency to trap pockets of air and other vapors between the bag and the composite structure. To counteract this problem, a breather material (often used with a permeable release film) is often positioned between the prepreg lay-up and the inside of bag. The breather material stops the bag from completely collapsing on the lay-up and allows for all excess air and gas to escape the consolidating structure. The breather/bleeder material may be two layers placed one on top the other, or may also be a single layer that performs both functions.

A breather material is an important component of the composite part manufacturing process. In effect, a traditional breather material functions to provide a series of fluid flow paths over the laminate or fiber lay-up to permit the evacuation or escape of air, reactants, moisture and volatiles within the vacuum bag enclosure throughout the cure cycle when a vacuum or negative pressure is applied to the vacuum bag enclosure. It is important to remove such reactants and volatiles to prevent gas build- up and voids that can cause very high internal pressures.

The breather material further functions to ensure uniform vacuum pressure across the component by reducing or eliminating the likelihood of air pockets within the vacuum bag enclosure. Through the use of a breather material, high pressure differentials between the pressurizing means and the composite part may be maintained. To achieve this, the breather material is intended to be in direct contact or communication with the negative pressure ports in order to properly evacuate air and other gasses or fluids, and to reduce the pressure within the vacuum bag enclosure. A breather material may also provide a dual function as a bleeder material to absorb excess resin present in some fiber lay-ups. Traditionally, a bleeder material functions to provide an absorption area within a porous membrane material so that excess resin may be absorbed from the prepreg member during the vacuum process. When negative or vacuum pressure is applied to vacuum bag the prepreg member secretes excess resin material, which is then absorbed by the bleeder layer. Many skilled in the art have referred to the breather material as a breather/bleeder material or layer. However, these may indeed be separate components (e.g., a bleeder material and a separate breather material) or they may be the same material.

Various different types and/or constructions of breather material (or breather/bleeder material) are available on the market. The selection of these will largely depend upon the environments in which they will be used (e.g., taking into consideration such things as the magnitude of temperature and pressure within the vacuum bag). Conventional breather/bleeder materials are generally comprised of a porous or fibrous material, such as a felt type material. The material is typically about 1 mm to about 10 mm in thickness and more preferably about 3 mm to about 5 mm. The most common type of breather material comprises a non- woven polyester, nylon or synthetic cloth.

Conventional fabric or other types of breathers are problematic in that they are difficult to apply, as well as to adequately cover the needed areas. Without proper installation, pockets of gasses and other volatiles can get trapped between the vacuum bag and the fiber lay-up, thus leading to part inaccuracies and inconsistencies. Fabric breathers are also time consuming to properly place, which increases the overall time of part manufacture.

Cenospheres are part of the "fly ash" byproduct generated in coal burning plants. Billions of tons of coal is burned annually in many plants worldwide to generate electricity, and as a result, over 100 million tons of coal or fly ash is produced. Only a small percentage of the total amount is used, with the rest being disposed of mainly in landfills. Increasing cost and heightened regulations are making the disposal of fly ash an undesirable option. Fly ash is the fine powder formed from the mineral matter in coal, consisting of the noncombustible matter in coal plus a small amount of carbon that remains from incomplete combustion. It is called "fly" ash because it is transported from the combustion chamber by exhaust gases. Fly ash is generally light tan in color and consists mostly of different sized glassy spheres, the cenospheres. Properties of fly ash vary significantly with coal composition and plant operating conditions. Fly ash has found its way into a variety of applications in different industries, particularly in the building and construction industries.

SUMMARY OF THE INVENTION In light of the problems and deficiencies inherent in the prior art, the present invention seeks to overcome these by providing a flowable breather material, wherein the breather material comprises, at least in part, a plurality of microparticles, such as cenospheres obtained from the byproduct fly ash, or synthetically manufactured microparticles, such as Extendospheres™, as well as a binder that operates to adhere the microparticles together.

In accordance with the invention as embodied and broadly described herein, the present invention resides in a method for fabricating a composite article comprising preparing a fiber lay-up about a working surface; providing a breather material operable with the fiber lay-up, the breather material comprising a plurality of microparticles having a generally spherical shape, and a binder configured to adhere the plurality of microparticles together to form a plurality of voids that define a plurality of fluid passages; initiating a negative pressure to cause gasses to move through the plurality of voids in the breather; and curing the fiber lay-up to form the composite article.

The present invention also resides in a system for fabricating a composite article comprising a working surface; a fiber lay-up supported about the working surface and comprising a plurality of fiber reinforcing members; an impermeable member adapted to facilitate formation of a negative pressure environment about the fiber lay-up and the working surface; a breather operable with the fiber lay-up and the working surface, the breather comprising a plurality of microparticles, and a binder configured to adhere the plurality of microparticles together to form a plurality of voids that define a plurality of fluid passages, the breather facilitating evacuation of gasses and volatiles from the negative pressure environment during fabrication of the composite article. The present invention further resides in a method for forming a breather material operable about a surface within a negative pressure environment to facilitate evacuation of gasses, the method comprising obtaining a plurality of microparticles; obtaining a binder; interspersing and suspending the plurality of microparticles in the binder to form a flowable mixture; and curing the flowable mixture to cause the microparticles to adhere together to form the breather material.

The present invention still further resides in a breather material for facilitating the flow of gasses, the breather material comprising a plurality of microparticles having a generally spherical shape; and a binder configured to adhere the plurality of microparticles together to form a plurality of voids that define a plurality of fluid passages, the breather being adapted to facilitate selective fluid flow within a negative pressure environment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings merely depict exemplary embodiments of the present invention they are, therefore, not to be considered limiting of its scope. It will be readily appreciated that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Nonetheless, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1 illustrates an exploded, cross-sectional view of the components within a vacuum bagging process, and utilizing an spray-on breather in accordance with one exemplary embodiment of the present invention. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following detailed description of exemplary embodiments of the invention makes reference to the accompanying drawings, which form a part hereof and in which are shown, by way of illustration, exemplary embodiments in which the invention may be practiced. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.

The following detailed description and exemplary embodiments of the invention will be best understood by reference to the accompanying drawings, wherein the elements and features of the invention are designated by numerals throughout.

The present invention describes a breather formulated from a plurality of microparticles and a binder that is intended to replace conventional or traditional breather products, namely those formed from a cloth or fabric material. The present invention also describes a method and system for providing or forming such a breather, and a method for facilitating the selective evacuation of air from a negative pressure environment. In general, the breather of the present invention comprises a plurality of microparticles that are bound or adhered together by a binder to create and define a plurality of voids, which facilitate the flow of fluids or gasses therethrough upon application of the breather (which may be formulated to be flowable) to a surface, such as within a negative pressure environment (e.g., within a VARTM or vacuum bag process). The created voids are intended to be in fluid communication with one another so as to facilitate the flow of fluid or airflow across the breather, no matter its size. The microparticles are interspersed and suspended in a composition, comprising the binder, that preferably has a degree of flowability to allow the composition and the microparticles suspended therein to flow. This is primarily for pumping and application or dispensing purposes, such as for facilitating spraying or brushing on of the breather. The flowable mixture may comprise other components or constituents, such as a foaming agent or surfactant, a water soluble polymer, and others. The present invention breather may also be formulated and configured to comprise flexible sheets that may be applied in a similar manner as conventional breathers formed from cloth or fabric material.

The present invention breather provides several significant advantages over prior related breather products, and particularly fabric-based breathers, some of which are recited here and throughout the following more detailed description. First, the present invention breather provides a high degree of breathability. This is in large part due to the voids created by adhering the microparticles together. Second, the present invention breather, namely its composition or makeup, can be manipulated to achieve different performance characteristics. For example, it is possible to control the porosity to achieve any level desired. This is critical in many applications, namely composite part manufacture where the transmittal of volatiles and air contributes to a more reliable and predictable part. It is contemplated that the porosity of the present invention breather will be at least as good as current fabric-based materials. Third, the breather may be both flexible and semi-rigid. Indeed, the breathe can be formulated to comprise a flowable, pumpable mixture that can be applied using a spray or brush applicator, or a flexible, semi-rigid sheet. Fourth, the breather provides enhanced thermal insulation properties as the microparticles are hollow. Fifth, the breather provides enhanced filtering abilities as the size of the voids may be modified as needed in creating a breather for a specific composite part. Sixth, the breather may be efficiently applied to hard to reach areas of a fiber lay-up, particularly when using a flowable, sprayable formulation.

Each of the above-recited advantages will be apparent in light of the detailed description set forth below, with reference to the accompanying drawings. These advantages are not meant to be limiting in any way. Indeed, one skilled in the art will appreciate that other advantages may be realized, other than those specifically recited herein, upon practicing the present invention.

For purposes of discussion and interpretation of the claims as set forth herein, the term "breather" or "breather material" or "breather/bleeder," as used herein, shall be understood to mean a porous material or product designed to provide a plurality of fluid pathways to facilitate flow of such fluids. In a fiber lay-up, the breather is intended to facilitate airflow between the vacuum film layer and the fiber lay-up, thus facilitating the passage of air, volatiles, or other fluids or gasses, as well as any resins. The breather may also function as a bleeder in some applications.

The term "microparticle," as used herein, shall be understood to mean any naturally occurring or manufactured or synthetic particle having an outer surface, and in some cases, a hollow interior. Generally, the microparticles referred to herein comprise a spherical or substantially spherical geometry having a hollow interior. Other types of microparticles may include those made from wood, ground rubber, ground up plastic, sawdust, etc. An exemplary type of microparticle comprises cenospheres, which are the small microspheres found in the byproduct fly ash from coal burning plants.

MICROPARTICLES The present invention breather material incorporates and utilizes a plurality of microparticles combined with one or more other components, such as a binder, to form a flowable mixture having a matrix of microparticles adhered together to form a plurality of voids. The microparticles contemplated for use herein may comprise many different sizes, shapes, etc. Although not limited to this, the microparticles used in the present invention breather materials will generally have a size ranging between 100 and 1500 microns, and preferably between 200 and 800 microns. The size of the microparticles will depend upon the application and the performance characteristics desired, However, the particles should not be too large so as to cause any binder disposed thereon to run off or to not be effective. The size of the microparticles will function to influence the size of the voids, as well as the flowability of the mixture.

In one exemplary embodiment, the microparticles comprise hollow, inert, lightweight naturally occurring glass or synthetic structures that are substantially spherical in geometry. A hollow interior is preferred as this will reduce the weight of the utility material, as well as provide good insulating properties.

In one aspect of this embodiment, the microparticles may comprise the naturally occurring hollow, inert glass microspheres obtained from a fly ash byproduct, which microspheres are often referred to as cenospheres, as discussed above. These cenospheres may be separated from the other byproduct components present in the fly ash and further processed, such as to clean and separate these into desired size ranges. Cenospheres are comprised primarily of silica and alumina, and have a hollow interior that is filled with air and/or other gasses. They possess many desirable properties, such as a crush strength between 3000 and 5000 psi, low specific gravity and are able to endure extremely high temperatures (above 1800° F). Although they are substantially spherical in overall shape, many are not true spheres, as many are fragmented, or comprise unsmooth surfaces caused by additional silica and/or alumina.

In another aspect, the microparticles may comprise hollow, spherical structures manufactured from a synthetic material. One particular type of synthetic microparticle is sold under the trademark Extendospheres™, which are manufactured and sold by PQ Corporation. The advantage with having a synthetic material is the uniformity between microparticles, thus making their behavior more predictable. However, these advantages may not be significant enough to justify their use, as synthetic microparticles are extremely expensive. The use of naturally occurring microparticles over synthetic ones to form a utility material may depend on several different factors, such as the intended application, and/or the desired performance properties or characteristics. In some applications, naturally occurring microparticles may be preferred while in others a synthetic type may be more desirable.

Other types of microparticles may be comprised of thermosets, thermoplastics, glass, cross-linked rubber, etc. Microparticles must be able withstand the high cure temperatures. Those skilled in the art will recognize other microparticles that may be used in a given breather material. BINDER

The present invention further comprises a binder operable to adhere the microparticles together, and to facilitate the porous matrix formation of the microparticles in a flowable or sheet-like structure. The binder may be caused to adhere the microparticles together, wherein the binder is allowed to dry if water based, or cured in a high temperature environment if non-water based. In another aspect, the binder may be cross-linked, wherein the binder and the microparticles are physically bonded. Whether the binder is cross-linked or not may depend on the desired type of breather material to be formed, and the intended application.

The binder is designed to breath efficiently early in the part cure cycle, as well as to retain some permeability throughout the part cure cycle. The binder, however, should retain at least some degree of breathability at all times. In addition, the binder is intended to comprise some degree of temperature resistance, but this does not necessarily mean that its needs to be configured to withstand the highest cure temperatures. The binder must also adhere the microparticles together without clogging the created voids, and long enough during the part cure cycle to evacuate air and volatiles. The binder should also provide some degree of ductility or flexibility so as it goes through stresses and strains of curing it does not crack or break.

The ratio of binder to microparticles may vary greatly depending upon the breather material to be formed. A higher ratio of binder to microparticles will result in a breather material that is more dense than a utility material with a smaller ratio. Indeed, a smaller ratio of binder to microparticles will result in a more porous breather material. The porosity of the breather is also affected by the size of the microparticles. The amount of binder may depend upon the intended type of breather and the needed requirements, but in most cases, enough binder will be used to adhere the niicroparticles together while also preserving, or even optimizing, the voids between the microparticles to optimize the porosity of the breather material.

The present invention contemplates the use of many different types of binders, again depending upon the desired type of breather material to be formed, the desired state (e.g., flowable or formed or sheet like) and the intended application. Different binders may be selected as part of the composition to contribute to the makeup of the resulting utility material and to help provide the utility material with certain physical and performance properties. Both water-based (aqueous) and non-water-based (non-aqueous) binders are contemplated for use. Any one of these may be used alone or in combination with another binder. Examples of general binder categories include, but are not limited to, thermoplastics, epoxy resins, curatives, urethanes, thermosets, silicones, and others.

One particular exemplary type of binder may be a latex, water-based or aqueous binder present in the breather product in an amount between 5 and 20 percent by weight. This type of binder is particularly useful in forming a sprayable or spray-on type of breather utilizing microparticles, but the breather may also be formed into flexible, semirigid sheets using a latex binder. The water-based binder may be combined with a foaming agent or surfactant to provide additional functionality, such as increased flowability. The binder may be introduced and interspersed with the microparticles through a foaming process. One particular example of a latex binder is ethylene vinyl acetate (water-based binder) sold under the trademark Airflex™ (e.g., Airflex 420), which is manufactured and sold by Airproducts, Inc. This particular binder may be used to produce flowable compositions, as well as flexible or semi-rigid compositions. The Airflex™ product further includes a water soluble polymer (WSR 301), namely a polyethylene oxide.

Other exemplary specific types of binders may comprise sodium silicates in one form or another, with the sodium silicate combining with an ethylene vinyl acetate copolymer in a operable ratio. As combined with the microparticles, the preferred composition contains between 400 g and 600 g of microparticles, mixed with between 600 g and 800 g of sodium silicate, and between 200 g and 300 g of ethylene vinyl acetate. Of course, other ranges are possible, depending upon the application. For example, it may be desirable to have between 200 g and 1500 g of sodium silicate or other binder mixed with between 300 and 800 g of microparticles, mixed with between 200 g and 400 g of ethylene vinyl acetate copolymer.

Any binder used may be used may be used alone or in conjunction with another binder type to provide different characteristics to the breather material that may be better suited for some applications, hi addition, binders may be used with different sized microparticles. With appropriate binders or combinations of binders, as well as appropriate microparticle sizes, it is possible to achieve a proper and/or desired balance between structure and functionality or porosity, and to achieve needed end performance characteristics. For example, certain types of binders, or more binder quantities, may provide the breather material with increased strength, but may decrease the porosity of the breather material.

FOAMING AGENT/SURFACTANT

The present invention further contemplates the use of a foaming agent or surfactant within the composition and mixed with the microparticles and binder constituents making up the breather material. The foaming agent may be added to achieve breather materials with lower densities, to more easily facilitate the flowability of the breather material composition, to stabilize the mixture, etc. With use of a foaming agent, the microparticles may be suspended for easy transport, storage and/or application. The foaming agent provides for more easy and efficient pumping and spraying or dispensing, thus allowing all of the constituents of the mixture to be more easily pumped and sprayed.

Examples of suitable surfactants or foaming agents include, but are not limited to, anionic foaming agents, such as Steol™ FS406 or Bio-terge™ AS40, sodium alkyl ether sulfate, sodium olefin sulfonate and others. With respect to a foaming process, once ingredients are combined, they are whipped or agitated to introduce air into the mixture, and then dried. Mechanical agitation or compressed air may be used to physically introduce air into the mixture and to create the foaming process. The foaming process effectively causes the microparticles to be supported in a much more separated position with respect to one another as compared to a non-foamed composition. With the presence of the foam, the microparticles suspended and are able to dry in more dispersed configurations. In another aspect, the suspension of the microparticles due to the presence of the foaming agents may also function to make certain compositions more flowable or pumpable. WATER SOLUBLE POLYMER

The present invention further contemplates use of a water soluble polymer in the composition making up the utility material. These are known in the art and can be used to control the stiffness, flexibility, tear strength, and other physical properties of the breather material, as well as to stabilize the foaming agent or surfactant, if present. The water soluble polymer functions as a thickener and prevents the water from running out. The water soluble polymer may be added to the composition already dissolved in water (e.g., if a non-aqueous binder is used) or in dried form (e.g., if an aqueous binder is used). The water soluble polymer may also function to stabilize the surfactant or foaming agent. In essence, the water soluble polymer helps to stabilize the composition until the binder is cured. Examples of water soluble polymers include, but are not limited to, polyethylene oxide, hydroxy ethyl cellulose, poly vinyl alcohol.

As will be recognized by those skilled in the art, there are many different types of water soluble polymers that may be used to achieve the intended purpose. BREATHER FORMS AND PART FABRICATION AND BREATHER APPLICATION METHODS

As discussed briefly above, a present invention end product breather material may be configured to comprise a flowable form that is pumpable and able to be dispensed using a spray technique or applied with a brush or other applicator, or a flexible, semirigid form, wherein the breather material is pre-formed, cut and later applied within a fiber lay-up. Each one of these forms is discussed more fully below.

With respect to the flowable and pumpable or sprayable form, the microspheres are mixed with a binder and any foaming agent in an appropriate ratio so as to achieve a flowable mixture that can be pumped and sprayed prior to the binder curing. The composition is pre-mixed and then agitated to activate the foaming agent. Bonding of the binder occurs during the drying stage and application of the breather material to the fiber lay-up (or components thereof, such as a release film).

Obviously, from the description here, the present invention contemplates several different compositions for forming a flowable microparticle-based breather material, as well as several different options for applying a flowable breather material. In one embodiment, the components of the breather material may be pre-mixed and then sprayed. Typically the binder used in this type of breather material will be a water-based or aqueous binder. In another embodiment, the components may again pre-mixed, but may then be hand spread, or spread with a brush or other applicator, onto the fiber lay-up. Water or non-water based binders may be used in this embodiment.

In still another embodiment, the constituents are not pre-mixed, but instead are brought together in a mixing chamber prior to being dispensed from the nozzle of a spray gun and being disposed on the fiber lay-up, or inter-air prior to being disposed on the fiber lay-up. For example, two separate spray devices or guns may be used, or a single spray device with multiple feeds may be used. Both water-based and non-water based binders are contemplated for use in such an embodiment. In yet another embodiment, the flowable breather may be formed by pre-coating a portion of the microparticles with an A side of a reactive component and a portion of the microp articles with a B side of a reactive component. These can be brought together with the A side reacting with the B side to adhere the microparticles together.

With a flowable composition, the breather material is formed by applying the composition to at least a portion of the mold surface and/or the fiber lay-up and allowed to dry (in the event of an aqueous binder) or cure (in the event of a non-aqueous binder). With respect to a semi-rigid sheet-like microparticle-based breather material, the constituents of the composition are preferably pre-mixed and allowed to dry or cure. The composition can be dried or cured within a mold to achieve a certain configuration, or the composition can be dispensed onto a large surface (e.g., a conveyor) and further formed into shape, cut, or otherwise processed. Thicknesses between 1/10^th and 3/10^th of an inch are preferred.

With either the flowable or semi-rigid form, once formed, the micro-particle- based breather material of the present invention can be used with any conventional or known vacuum bag and with any known vacuum bagging process to achieve the intended purpose of a breather and to form a composite article. Indeed, the breather may be adapted to perform its function relative to the mold surface, at least a portion of the fiber lay-up and/or one or more vacuum or resin injection ports. The breather may be caused to cover at least part of the fiber lay-up, or it may be caused to completely envelop the fiber lay-up (or any release films, etc. as known in the art). The breather may be disposed about the fiber lay-up and about the working surface of a mold or other structures, or mold surface. The breather may be applied directly to a surface of an impermeable layer or member (e.g., a vacuum bag or mold top). The breather may interact with various vacuum and/or resin injection ports to enable these to be selectively positioned and function as intended. The breather may be selectively applied in multiple or a plurality of layers about select locations.

FIG. 1 illustrates an exploded, cross-sectional side view of a vacuum bagging system 10 utilizing a breather 14 formed in accordance with the present invention. As illustrated in FIG. 1, an open mold 18 is provided having an upper surface 22. The mold 18 and upper surface 22 may also include contoured shapes 26 which may be protrusions or depressions, or any combination of the above as needed to form a composite part with the desired dimensions. A vacuum bag 30 is supplied in accordance with any known method.

A first release layer may be applied to the contoured surface 22 of the mold 18 prior to the lay-up of the fiber reinforcing members. The release layer may be any coating or film known in the art which will allow the finished composite article to readily release from the mold 18. The release layer may followed by a lay-up of pre-wetted fiber reinforcement material, or pre-pregs 34. The pre-preg may be laid up in a single thick layer, but more commonly a small number of thin pre-preg plies will be laid one on top of the other to form a first portion of the composite article known as the laminate 38.

An optional peel-ply 42 may be laid over the pre-preg plies to give the laminate a bondable finish to better adhere to the next sequence of pre-preg plies. The peel ply may in turn covered by a permeable release film 46 which is configured to not bond to the laminate, and to allow air to pass through to the next layer above.

As stated, a breather member 14 is provided. Similar to prior related breather materials, namely those made of fabric or cloth, the breather layer or member 14 of the present invention provides a continuous air path between the laminate and the vacuum bag for drawing the vacuum during consolidation and debulking. However, unlike prior relate breathers, the breather 14 of the present invention comprises a plurality of microparticles 16 dispersed within a binder (not shown) as discussed herein. The breather is shown as being sprayable using a spray applicator 70. The spray applicator 70 may be manipulated as desired to provide a breather 14 in all needed areas of the lay-up. This gives operators significant advantages over the use of prior related breathers in that they can simply deposit the flowable breather onto any needed surfaces.

In another aspect, the breather 14 maybe in the form of a pre-formed sheet, also comprising a plurality of microparticles. This sheet, although different in form, would function similar to prior related breathers wherein operators would strategically position the breather between the laminate and the vacuum bag by hand and cause is to interact with various components, such as vacuum ports.

The complete lay-up comprising the laminate, peel-ply, release film and breather layer is then covered by the vacuum bag 30. The periphery of the bag is clamped or sealed against the surfaces of the mold to form a sealed vacuum envelope surrounding the lay-up. An airtight seal between the vacuum bag and the open mold can be formed by any method well-known in the art, including the use of tacky tape such as chromium tape installed continuously around the periphery of the open mold. A vacuum source (not shown) is placed in pneumatic or fluid communication with the volume between the mold 18 and the vacuum bag 30 via the vacuum suction port 50. The vacuum source functions to create a negative pressure or vacuum environment within the sealed off volume. The drawing of the vacuum performs several functions. First, the vacuum bag 30 is firmly pressed against the pre-preg laminate 38 laid up on the open mold 18, thereby forming the materials to the shape of open mold 18. The vacuum also draws out any pockets of air which were left trapped between the layers of pre-preg material, consolidating the layers into a tighter laminate structure. After the consolidation/debulking step is completed, the vacuum bag 30, release film 42, and breather 14 are removed and the process repeated until the laminate composite part has been built up into its intended size. After the final group of pre-preg plies has been consolidated and debulked onto the layers beneath, the entire laminate assembly may be placed in an autoclave where a vacuum is continuously pulled while the composite part is heated to curing temperature.

The foregoing detailed description describes the invention with reference to specific exemplary embodiments. However, it will be appreciated that various modifications and changes can be made without departing from the scope of the present invention as set forth in the appended claims. The detailed description and accompanying drawings are to be regarded as merely illustrative, rather than as restrictive, and all such modifications or changes, if any, are intended to fall within the scope of the present invention as described and set forth herein.

More specifically, while illustrative exemplary embodiments of the invention have been described herein, the present invention is not limited to these embodiments, but includes any and all embodiments having modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the foregoing detailed description. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the foregoing detailed description or during the prosecution of the application, which examples are to be construed as nonexclusive. For example, in the present disclosure, the term "preferably" is non-exclusive where it is intended to mean "preferably, but not limited to." Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus-function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) "means for" or "step for" is expressly recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given above. What is claimed and desired to be secured by Letters Patent is:

Claims

1. A method for fabricating a composite article comprising: preparing a fiber lay-up about a working surface; providing a breather material operable with said fiber lay-up, said breather material comprising: a plurality of microparticles having a generally spherical shape; and a binder configured to adhere said plurality of microparticles together to form a plurality of voids that define a plurality of fluid passages; creating a sealed environment about said fiber lay-up; initiating a negative pressure to cause gasses to move through said plurality of voids in said breather; and curing said fiber lay-up to form said composite article.

2. The method of claim 1 , further comprising causing said breather material to be in fluid communication with one or more selectively positioned ports.

3. The method of claim 1 , wherein said breather comprises a flowable, pumpable formulation, and wherein said step of applying comprises applying said breather using a spray applicator.

4. The method of claim 1 , wherein said breather comprises a flexible, semi-rigid sheet, and wherein said applying comprises manually applying said breather.

5. The method of claim 1, wherein said breather further comprises a foaming agent adapted to facilitate formation and application of said breather as a flowable mixture.

6. The method of claim 1 , further comprising agitating said flowable mixture to activate said foaming agent.

7. The method of claim 1 , wherein said breather further comprises a water soluble polymer adapted to facilitate manipulation of various physical properties of said breather material.

8. The method of claim 1, wherein said microparticles are naturally occurring.

9. The method of claim 1, wherein said microparticles are synthetic in nature.

10. The method of claim 1, wherein said microparticles are generally spherical in shape to define one or more voids in said breather material upon being adhered together.

11. The method of claim 1 , wherein said microparticles comprise a hollow interior to enhance the thermal properties of said breather material.

12. The method of claim 1, wherein said microparticles comprise a size ranging between 100 and 1,000 microns in diameter.

13. The method of claim 1, wherein said binder comprises a degree of temperature resistance to permit evacuation of said gasses during said step of curing.

14. The method of claim 1, wherein said binder is selected from the group consisting of an aqueous and non-aqueous binder.

15. The method of claim 1, further comprising balancing an amount and type of said binder and an amount and size of said microparticles to control a porosity of said breather.

16. The method of claim 1, wherein said step of applying comprises applying said breather directly to at least a portion of a surface of an impermeable member.

17. The method of claim 1, wherein said step of applying comprises applying said breather directly to a surface of a composite prepreg.

18. The method of claim 1, further comprising forming a plurality of breather layers at select locations about said fiber lay-up.

19. A system for fabricating a composite article comprising: a working surface; a fiber lay-up supported about said working surface and comprising a plurality of fiber reinforcing members; an impermeable member adapted to facilitate formation of a negative pressure environment about said fiber lay-up and said working surface; a breather operable with said fiber lay-up and said working surface, said breather comprising: a plurality o f microp articles ; and a binder configured to adhere said plurality of microparticles together to form a plurality of voids that define a plurality of fluid passages, said breather facilitating evacuation of gasses and volatiles from said negative pressure environment during fabrication of said composite article,

20. A method for forming a breather material operable about a surface within a negative pressure environment to facilitate evacuation of gasses, said method comprising: obtaining a plurality of microparticles; obtaining a binder; interspersing and suspending said plurality of microparticles in said binder to form a flowable mixture; and curing said flowable mixture to cause said microparticles to adhere together to form said breather material.

21. The method of claim 20, further comprising: prior to said curing, applying, in wet form, said composition to a surface, wherein upon said curing said flowable mixture is caused to become a flexible, semi-rigid breather material; and subsequent said curing, processing said semi-rigid breather material to obtain a desired breather configuration.

22. The method of claim 20, wherein said step of interspersing comprises applying said flowable mixture to a surface prior to said step of curing.

23. The method of claim 20, wherein said step of interspersing comprises pre-mixing said microparticles and said binder prior to applying to a surface.

24. The method of claim 20, wherein said flowable mixture is pumpable, and applied to a surface using a spray applicator in a selective manner.

25. A breather material for facilitating the flow of gasses, said breather material comprising: a plurality of microparticles having a generally spherical shape; and a binder configured to adhere said plurality of microparticles together to form a plurality of voids that define a plurality of fluid passages, said breather being adapted to facilitate fluid flow within a negative pressure environment.