Glass fiber bundles for mat applications and methods of making the same

Abstract

Dried bundles of chopped glass fibers that may be used in mat forming applications is provided. The chopped glass fiber bundles are formed of individual glass fibers positioned in a substantial parallel orientation. The dried chopped glass fiber bundles may be prepared by applying a size composition to attenuated glass fibers, splitting the fibers to obtain a desired bundle tex, chopping the wet glass bundles to a discrete length, and drying the wet glass bundles in a dielectric oven, a Cratec® oven, or a rotating tray oven. Alternatively, the dried chopped glass bundles may be prepared by sizing attenuated glass fibers, passing the sized fibers through a heat transfer chamber where air heated by a bushing is drawn into the heat transfer chamber to dry the glass fiber bundles, splitting the dried, sized glass fiber bundles to obtain a desired bundle tex, and chopping the dried bundles of glass fibers.

Description

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to non-woven fibrous mats, and more particularly, to dried bundles of chopped glass fibers that may be used as a replacement for glass forms conventionally utilized in mat forming applications, and even more particularly, to wet-laid mat forming applications. Methods of forming the dried bundles of chopped glass fibers are also provided.

BACKGROUND OF THE INVENTION

Typically, glass fibers are formed by drawing molten glass into filaments through a bushing or orifice plate and applying an aqueous sizing composition containing lubricants, coupling agents, and film-forming binder resins to the filaments. The sizing composition provides protection to the fibers from interfilament abrasion and promotes compatibility between the glass fibers and the matrix in which the glass fibers are to be used. After the sizing composition is applied, the wet fibers may be gathered into one or more strands, chopped, and collected. The chopped strands may contain hundreds or thousands of individual glass fibers. The collected chopped glass strands may then be packaged in their wet condition as wet chopped fiber strands (WUCS) or dried to form dry chopped fiber strands (DUCS).

Wet chopped fibers are conventionally used in wet-laid processes in which the wet chopped fibers are dispersed in a water slurry that contains surfactants, viscosity modifiers, defoaming agents, and/or other chemical agents. The slurry containing the slurry containing the fibers is deposited onto a moving screen where a substantial portion of the water is removed to form a web. A binder is then applied, and the resulting mat is dried to remove any remaining water and cure the binder. The formed non-woven mat is an assembly of dispersed, individual glass filaments.

Dried chopped strands are commonly used in dry-laid processes in which the dried strands are air blown onto a conveyor or screen and consolidated to form a mat. For example, dry chopped strands are suspended in air, collected as a loose web on a screen or perforated conveyor, and then consolidated to form a mat of randomly oriented bundles.

Fibrous mats formed by wet-laid and dry-laid processes are extremely suitable as reinforcements for many types of applications. In order for the final laminate to achieve acceptable mechanical performance, it must include a sufficient amount by weight of glass reinforcements. Although the bundles of fibers present in the dry-laid mats provide for a high glass content, manufacturing dry chopped strands is expensive because such strands are generally dried and packaged in separate steps before being chopped. Thus, it would be desirable to utilize a less expensive glass formation platform that would achieve the increased glass content in composites that require a high impact strength.

Bundles of dried chopped fibers have previously been manufactured. Some examples of the processes of forming these bundles of dried chopped fibers are described below.

U.S. Pat. No. 4,024,647 to Schaefer discloses a method and apparatus for drying and conveying chopped glass strands. Glass filaments are attenuated through orifices in a bushing and coated with a lubricant binder and/or size. The filaments are gathered into one or more strands and chopped. The wet, chopped fibers then falls onto a first vibratory conveyor. The vibrations of the first vibratory conveyor maintains the chopped strands in fiber bundles by keeping the bundles from adhering to each other. The chopped strands are then passed to a second vibratory conveyor and through a heating zone where the chopped strands are heated to reduce the moisture content to less than 0.1 percent by weight. Chopped strands of a desired length then pass through a foraminous portion of the second vibratory conveyor and into a collection package.

U.S. Pat. No. 5,055,119 to Flautt et al. describe an energy efficient process and apparatus for forming glass fiber bundles or strands. Glass fibers are formed from molten glass discharged from a heated bushing. The fibers are moved downwardly and a sizing is applied to the glass fibers by an applicator. To dry the glass fibers, air from around the bushing is passed beneath the bushing where it is heated by the heat of the bushing. The heated air is drawn into a chamber through which the glass fibers pass. The heat transfer contact causes the water or solvent in the sizing composition to be evaporated. The dried fibers are then gathered into a bundle. The bundles may subsequently be chopped.

U.S. Pat. No. 6,148,641 to Blough et al. describe a method and an apparatus for producing dried, chopped strands from a supply of continuous fiber strands. In the described method, chopped fiber strands are produced from one or more continuous strands by chopping the fiber strands in a chopping assembly, ejecting the chopped strands from an exit assembly into a transition chute directly into a drying chamber, collecting the chopped strands in the drying chamber, and at least partially drying the strands in the drying chamber.

In addition, chopped strand glass mats have been formed that contain glass bundles, such as is found in dry-laid processes, and individual fibers such as are found in wet-laid processes, by utilizing wet-laid processes. Some examples of these mats are set forth below.

U.S. Pat. Nos. 4,112,174 and 4,129,674 to Hannes et al. disclose glass mats that are formed of a web of monofilament fibers and elongated glass fiber bundles interspersed throughout the web in a randomly oriented pattern. The glass fiber bundles preferably contain from about 20-300 monofilaments. The fibrous mats are formed by wet-laid processes. To keep the glass fiber bundles in a bundle form in the slurry during the mat forming process, the bundles are coated with a water or other such liquid insoluble binder.

U.S. Pat. Nos. 4,200,487 and 4,242,404 to Bodoc et al. describe glass mats that include individual glass filaments and extended glass fiber elements. The extended glass fiber elements are formed from bundles of glass fibers that slide apart and become connected longitudinally when the slurry is agitated. It is asserted that the glass fiber elements contribute to high strength properties of the mat and that the individual filaments provide a uniform denseness necessary for the impregnation of asphalt in the manufacturing of roofing shingles. The mats are formed by a wet-laid process.

U.S. Pat. No. 6,767,851 and U.S. patent application Publication No. 2002/0092634 to Rokman et al. disclose non-woven mats in which at least 20% of the fibers are present as fiber bundles having about 5-450 fibers per bundle. In preferred embodiments, at least 85% of the fibers in the mats are in the form of bundles. The fibers are held in the bundles by a substantially non-water soluble sizing such as an epoxy resin or PVOH. The bundles may comprise at least 10% reinforcing fibers such as glass fibers. The mat may be made by a foam or water process.

Despite the existence of these dried chopped glass bundles and fiber bundle-containing mats, there remains a need in the art for a cost-effective and efficient process for increasing the glass fiber content resulting from the use of wet-laid glass mats.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide chopped glass fiber bundles that may be used as a replacement for conventional glass forms utilized in mat forming applications. The chopped glass fiber bundles are formed of a plurality of individual glass fibers positioned in a substantially parallel orientation to each other. The glass fibers used to form the chopped fiber bundles may be any type of glass fiber. Although reinforcing fibers such as natural fibers, mineral fibers, carbon fibers, ceramic fibers, and/or synthetic fibers may be present in the chopped glass fiber bundles, it is preferred that all of the fibers in the chopped glass fiber bundles are glass fibers. The fibers are at least partially coated with a size composition that includes one or more film forming agents (such as a polyurethane film former, a polyester film former, and/or an epoxy resin film former), at least one lubricant, and at least one silane coupling agent (such as an aminosilane or methacryloxy silane coupling agent). The size on the glass fibers maintains bundle integrity during the formation and subsequent processing of the glass fiber bundles and assists in filamentizing the chopped glass fiber bundles during subsequent processing steps in order to form a mat that gives an aesthetically pleasing look to the finished product.

It is also an object of the present invention to provide a method of forming chopped glass fiber bundles that may be used as a replacement for conventional glass forms utilized in mat forming applications. A size composition including one or more film forming agents (such as a polyurethane film former, a polyester film former, and/or an epoxy resin film former), at least one lubricant, and at least one silane coupling agent (such as an aminosilane or methacryloxy silane coupling agent) is applied to attenuated glass fibers in a conventional manner. The sized glass fibers may be split into glass fiber strands containing a predetermined number of individual glass fibers. It is desirable that the glass fiber bundles have a bundle tex of 20-200 g/km. The glass fiber strands may then be chopped into wet chopped glass fiber bundles and dried to consolidate or solidify the sizing composition. Preferably, the wet bundles of fibers are dried in an oven such as a conventional dielectric (RF) oven, a fluidized bed oven such as a Cratec® oven (available from Owens Corning), or a rotary tray thermal oven to form the chopped glass fiber bundles.

It is also an object of the present invention to provide a method of forming chopped glass fiber bundles that utilizes a heat transfer chamber to adiabatically dry the wet, sized glass fibers. A size composition including one or more film forming agents (such as a polyurethane film former, a polyester film former, and/or an epoxy resin film former), at least one lubricant, and at least one silane coupling agent (such as an aminosilane or methacryloxy silane coupling agent) is applied to glass fibers attenuated by a bushing. The sized glass fibers may then be passed through a heat transfer chamber where air heated by the bushing is drawn into said heat transfer chamber to substantially dry the sizing on the glass fibers. The dried glass fibers exiting the heat transfer chamber may be split into glass fiber strands that contain a preselected number of individual glass fibers. It is desirable that the glass fiber bundles have a bundle tex of 20-200 g/km. The glass strands may be gathered together into a single tow prior to chopping the glass strands into chopped glass fiber bundles. In one exemplary embodiment, the chopped fiber bundles are further dried in a conventional dielectric (RF) oven, a fluidized bed oven such as a Cratec® oven (available from Owens Corning), or a rotary tray thermal oven.

It is an advantage of the present invention that the chopped glass fiber bundles may be formed at a faster rate of speed than conventional air-laid processes. Increasing the rate of speed that the chopped glass fiber bundles can be produced permits for a higher throughput and additional product that can be sold to the customers.

It is another advantage of the present invention that the chopped glass fiber bundles can be formed with low manufacturing costs since the wet glass fibers do not have to be dried and chopped in separate steps.

It is yet another advantage of the present invention that the wet fibers utilized to form the chopped glass fiber bundles produce little or no fuzz in the final chopped strand mat.

The foregoing and other objects, features, and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description that follows. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a chopped strand bundle according to an exemplary embodiment of the present invention;

FIG. 2 is a flow diagram illustrating steps of an exemplary process for forming glass fiber bundles according to at least one embodiment of the present invention;

FIG. 3 is a schematic illustration of a processing ling for forming dried chopped strand bundles according to one exemplary embodiment of the present invention;

FIG. 4 is a schematic illustration of a processing line for forming dried chopped strand bundles according to at least one other exemplary embodiment of the invention;

FIG. 5 is a schematic illustration of a processing line for forming a chopped strand mat utilizing chopped strand bundles according to the present invention;

FIG. 6 is a graphical illustration of the laminate tensile strengths in the machine direction and the cross direction for conventional chopped strand mats and chopped strand mats utilizing dried chopped glass fiber bundles according to the instant invention;

FIG. 7 is a graphical illustration of the laminate tensile moduli in the machine direction and the cross direction for conventional chopped strand mats and chopped strand mats utilizing dried chopped glass fiber bundles according to the instant invention;

FIG. 8 is a graphical illustration of the laminate flexural strengths in the machine direction and the cross direction for conventional chopped strand mats and chopped strand mats utilizing dried chopped glass fiber bundles according to the instant invention;

FIG. 9 is a graphical illustration of the laminate flexural moduli in the machine direction and the cross direction for conventional chopped strand mats and chopped strand mats utilizing dried chopped glass fiber bundles according to the instant invention;

FIG. 10 is a graphical illustration of the tensile strength in the machine direction for laminates formed utilizing dried chopped glass fiber bundles according to the present invention;

FIG. 11 is a graphical illustration of the tensile strength in the cross-machine direction for laminates formed utilizing dried chopped glass fiber bundles according to the present invention;

FIG. 12 is a graphical illustration of IZOD notched impact strength of bulk molding compounds made with glass fibers sized with sizing compositions according to the present invention versus control at 0 degrees;

FIG. 13 is a graphical illustration of IZOD notched impact strength of bulk molding compounds made with glass fibers sized with sizing compositions according to the present invention versus control at 90 degrees.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references.

In the drawings, the thickness of the lines, layers, and regions may be exaggerated for clarity. It is to be noted that like numbers found throughout the figures denote like elements. The terms “top”, “bottom”, “side”, “upper”, “lower” and the like are used herein for the purpose of explanation only. It will be understood that when an element is referred to as being “on,” another element, it can be directly on or against the other element or intervening elements may be present. The terms “sizing”, “size”, “sizing composition”, and “size composition” may be interchangeably used herein. The terms “strand” and “bundle” may also be used interchangeably herein.

The present invention relates to chopped glass fiber bundles that may be used as a replacement for conventional glass forms utilized in mat forming applications and to a process for forming such chopped glass fiber bundles. An example of a chopped glass fiber bundle according to the present invention is depicted generally in FIG. 1. As shown in FIG. 1, the chopped glass fiber bundle 10 is formed of a plurality of individual glass fiber 12 having a diameter 16 and a length 14. The individual glass fibers 12 are positioned in a substantially parallel orientation to each other in a tight knit or “bundled” formation. As used herein, the phrase “substantially parallel” is meant to denote that the individual glass fibers 12 are parallel or nearly parallel to each other. The chopped glass fiber bundles according to the present invention may be used in the formation of chopped strand mats (CSM), in forming sheet molding compounds (SMC), in bulk molding compounds (BMC), in hand lay-up applications, and in spray-up applications. In addition, the chopped glass fiber bundles may be used to create preforms for use in resin transfer molding (RTM) or structural reaction injection molding (SRIM). In structural reaction injection molding, the dried chopped glass fiber bundles 10 are blown onto a screen to take the shape of the desired part, such as a truck bed or automobile door inner.

The glass fibers used to form the chopped fiber bundles may be any type of glass fiber, such as A-type glass fibers, C-type glass fibers, E-type glass fibers, S-type glass fibers, ECR-type glass fibers (e.g., Advantex® glass fibers commercially available from Owens Corning), wool glass fibers, or combinations thereof. In at least one preferred embodiment, the glass fibers are wet use chopped strand glass fibers (WUCS). Wet use chopped strand glass fibers may be formed by conventional processes known in the art. It is desirable that the wet use chopped strand glass fibers have a moisture content of from about 5 to about 30%, and even more desirably a moisture content of from about 5 to about 15%.

The use of other reinforcing fibers such as natural fibers, mineral fibers, carbon fibers, ceramic fibers, and/or synthetic fibers such as polyester, polyethylene, polyethylene terephthalate, polypropylene, and/or polyparaphenylene terephthalamide (sold commercially as Kevlar®) in the bundles of fibers 10 is considered to be within the purview of the invention. As used herein, the term “natural fiber” is meant to indicate plant fibers extracted from any part of a plant, including, but not limited to, the stem, seeds, leaves, roots, or bast. The inclusion of synthetic fibers in the fiber bundles gives a mat formed from the fiber bundles more flexibility or conformability to small radii. Further, the use of synthetic fibers may act as a mat binder in later processing to hold the chopped glass fiber bundles 10 together and form a chopped strand mat. However, it is preferred that all of the fibers in the bundles 10 are glass fibers.

In one exemplary embodiment, shown generally in FIG. 2, the process of forming the chopped glass fiber bundles 10 includes forming glass fibers (Step 20), applying a size composition to glass fibers (Step 22), splitting the fibers to obtain a desired bundle tex (Step 24), chopping wet fiber strands to a discrete length (Step 26), and drying the wet strands (Step 28) to form the chopped glass fiber bundles.

As shown in more detail in FIG. 3, glass fibers 12 may be formed by attenuating streams of a molten glass material (not shown) from a bushing or orifice 30. The attenuated glass fibers 12 may have diameters of about 8 to about 23 microns, preferably from 10-16 microns. After the glass fibers 12 are drawn from the bushing 30, an aqueous sizing composition is applied to the fibers 12. The sizing may be applied by conventional methods such as by the application roller 32 shown in FIG. 3 or by spraying the size directly onto the fibers (not shown). The size protects the glass fibers 12 from breakage during subsequent processing, helps to retard interfilament abrasion, and ensures the integrity of the strands of glass fibers, e.g., the interconnection of the glass filaments that form the strand.

In the present invention, the size on the glass fibers 12 also maintains bundle integrity during the formation and subsequent processing of the glass fiber bundles 10, such as in a wet-laid process to form a chopped strand mat (CSM). In this process, the glass fiber bundles 10 are added to a white water slurry and agitated. The slurry is then deposited onto a moving screen where a majority of the water is removed to form a web, a binder is applied, and the web is dried to remove the remaining water and cure the binder. Unlike conventional glass bundles, chopped glass fiber bundles 10 sized with the size composition described below remain in a bundle form or substantially in a bundle form in the white water slurry during the formation of the chopped strand mat. In at least one exemplary embodiment, the fibers 12 within the bundles 10 may be sized with the sizing composition so that a predetermined amount of fibers 12 disperse from the fiber bundles 10 in the slurry during agitation. The size composition on the glass fibers 12 also assists in filamentizing the bundles 10 during subsequent processing steps in order to form a mat that gives an aesthetically pleasing look to the finished product.

Another example of where the size on the glass fibers maintains bundle integrity during processing is in molding a sheet molding compound (SMC). In molding a sheet molding compound, a matched metal die is loaded (filled) with a sheet molding compound or bulk molding compound (BMC). It is desirable that the glass fiber bundles 10 have bundle integrity when the metal die closes and is heated so that the sheet molding compound (or BMC) can flow and fill the die to form the desired part. However, if the glass fiber bundles 10 disassociate into single fibers within the die before the flow is complete, the individual glass fibers form clumps and incompletely fill the die, thereby resulting in a defective part. On the other hand, after the sheet or bulk molding compound has flowed and the die has been filled, it is desirable that the glass fiber bundles 10 filamentize at that time to reduce the occurrence of or even prevent “telegraphing” or “fiber print”, which is the outline of the glass fiber bundles 10 at the part surface. Thus, the size on the glass fibers 12 also assists in filamentizing the chopped glass fiber bundles 10 during future processing steps (such as molding a chopped strand mat formed of the glass fiber bundles 10) to form an aesthetically pleasing final product.

The size composition applied to the glass fibers 12 includes one or more film forming agents (such as a polyurethane film former, a polyester film former, and/or an epoxy resin film former), at least one lubricant, and at least one silane coupling agent (such as an aminosilane or methacryloxy silane coupling agent). When needed, a weak acid such as acetic acid, boric acid, metaboric acid, succinic acid, citric acid, formic acid, and/or polyacrylic acids may be added to the size composition to assist in the hydrolysis of the silane coupling agent. The size composition may be applied to the glass fibers 12 with a Loss on Ignition (LOI) of from about 0.05 to about 2.0% on the dried fiber. LOI may be defined as the percentage of organic solid matter deposited on the glass fiber surfaces.

Film formers are agents which create improved adhesion between the glass fibers 12, which results in improved strand integrity. Suitable film formers for use in the present invention include polyurethane film formers, epoxy resin film formers, and unsaturated polyester resin film formers. Specific examples of film formers include, but are not limited to, polyurethane dispersions such as Neoxil 6158 (available from DSM); polyester dispersions such as Neoxil 2106 (available from DSM), Neoxil 9540 (available from DSM), and Neoxil PS 4759 (available from DSM); and epoxy resin dispersions such as PE-412 (available from AOC), NX 9620 (available from DSM), Neoxil 0151 (available from DSM), Neoxil 2762 (DSM), NX 1143 (available from DSM), AD 502 (available from AOC), Epi Rez 5520 (available from Hexion), Epi Rez 3952 (available from Hexion), Witcobond W-290 H (available from Chemtura), and Witcobond W-296 (available from Chemtura). The film former(s) may be present in the size composition from about 5 to about 95% by weight of the active solids of the size, preferably from about 40 to about 80% by weight of the active solids.

The size composition also includes one or more silane coupling agents. Silane coupling agents enhance the adhesion of the film forming agent(s) to the glass fibers 12 and to reduce the level of fuzz, or broken fiber filaments, during subsequent processing. Examples of silane coupling agents which may be used in the present size composition may be characterized by the functional groups amino, epoxy, vinyl, methacryloxy, ureido, isocyanato, and azamido. Suitable coupling agents for use in the size composition are available commercially, such as, for example, y-aminopropyltriethoxysilane (A-1100 available from General Electric) and methacryloxypropyltriethoxysilane (A-174 available from General Electric). The silane coupling agent may be present in the size composition in an amount of from about 5 to about 30% by weight of the active solids in the size composition, and even more preferably, in an amount of from about 10 to about 15% by weight of the active solids.

In addition, the size composition may include at least one lubricant to facilitate manufacturing. The lubricant may be present in the size composition in an amount of from about 0 to about 15% by weight of the active solids in the size composition. Preferably, the lubricant is present in an amount of from about 5 to about 10% by weight of the active solids. Although any suitable lubricant may be used, specific examples of lubricants suitable for use in the size composition include stearic ethanolamide, sold under the trade designation Lubesize K-12 (available from AOC); PEG 400 MO, a monooleate ester having about 400 ethylene oxide groups (available from Cognis); and Emery 6760 L, a polyethyleneimine polyamide salt (available from Cognis).

It has been discovered that certain families of chemistry in combination are especially effective in causing the chopped glass fiber bundles 10 to remain in a bundle form during subsequent processing. For example, urethane-based film forming dispersions in combination with aminosilanes, such as, for example, y-aminopropyltriethoxysilane (sold as A-1100 by General Electric) are effective in the size composition to keep the individual glass fibers 12 bundled together. Adding an additive such as a polyurethane-acrylic alloy to the urethane-based sizing composition has also been found to help maintain bundle integrity.

Additionally, epoxy-based film former dispersions in combination with epoxy curatives are effective sizing compositions for use in the present invention. In particular, an epoxy-based film former such as Epi-Rez 5520 and an epoxy curative such as DPC-6870 available from Resolution Performance Products forms an effective sizing composition, particularly in combination with a methacryloxy silane such as methacryloxypropyltriethoxysilane (commercially available as A-174 from General Electric).

Further, unsaturated polyester resin film formers have been found to be effective in forming a useful sizing composition. For example, an unsaturated polyester resin film former such as PE-412 (an unsaturated polyester in styrene that has been emulsified in water (AOC)) or Neoxil PS 4759 (available from DSM) are effective sizes for use in the present invention. Unsaturated polyester film formers may be used alone or in combination with a benzoyl peroxide curing catalyst such as Benox L-40LV (Norac Company, Inc.). The benzoyl peroxide curing catalyst catalyzes the cure (crosslinking) of the unsaturated polyester resin and renders the film surrounding the glass fibers water resistant.

The sizing composition may optionally contain conventional additives including antifoaming agents such as Drew L-139 (available from Drew Industries, a division of Ashland Chemical), antistatic agents such as Emerstat 6660A (available from Cognis), surfactants such as Surfynol 465 (available from Air Products), Triton X-100 (available from Cognis), and/or thickening agents. Additives may be present in the size composition from trace amounts (such as <about 0.1% by weight of the active solids) up to about 5% by weight of the active solids.

After the glass fibers 12 are treated with the sizing composition, they are gathered and split into fiber strands 36 having a specific, desired number of individual glass fibers 12. The splitter shoe 34 splits the attenuated, sized glass fibers into fiber strands 36. The glass fiber strands 36 may be passed through a second splitter shoe (not shown) prior to chopping the fiber strands 36. The specific number of individual glass fibers 12 present in the fiber strands 36 (and therefore the number of splits of the glass fibers 12) will vary depending on the particular application for the chopped glass fiber bundles 10. For example, assuming that a bushing has 4000 orifices for attenuating glass fibers, it would be necessary to split the attenuated glass fibers 40 ways to achieve a bundle of glass fibers that contain 100 fibers. The bundle tex of that particular bundle of glass fibers depends on the diameter of the glass fibers forming the bundle. In the example given above where the fiber bundles contain 100 individual glass fibers, if the fiber diameter of the glass fibers is 12 microns, the calculated bundle tex is 29. If the fiber diameter is 16 microns, the calculated bundle tex is 51 g/km. It is desirable that the glass fibers 12 are split into bundles of fibers that have a specific number of individual fibers to achieve a bundle tex of about 20 to about 200 g/km, preferably from about 30 to about 50 g/km.

The fiber strands 36 are passed from the gathering shoe 38 to a chopper 40/cot 60 combination where they are chopped into wet chopped glass fiber bundles 42 having a length of approximately about 0.125 to about 3 inches, and preferably about 0.25 to about 1.25 inches. The wet, chopped glass fiber bundles 42 may fall onto a conveyor 44 (such as a foraminous conveyor) for conveyance to a drying oven 46. Alternatively, the wet bundles of chopped glass fibers 42 may be collected in a container (not illustrated) for use at a later time.

The bundles of wet, sized chopped fibers 42 are then dried to consolidate or solidify the sizing composition. Preferably, the wet bundles of fibers 42 are dried in an oven 46 such as a conventional dielectric (RF) oven, a fluidized bed oven such as a Cratec® oven (available from Owens Corning), or a rotary tray thermal oven to form the chopped glass fiber bundles 10. The dried chopped glass fiber bundles 10 may then be collected in a collection container 48. In exemplary embodiments, greater than (or equal to) about 99% of the free water (i.e., water that is external to the chopped fiber bundles 42) is removed. It is desirable, however, that substantially all of the water is removed by the drying oven 46. It should be noted that the phrase “substantially all of the water” as it is used herein is meant to denote that all or nearly all of the free water from the fiber bundles 42 is removed.

In at least one exemplary embodiment, the wet bundles of glass fibers 42 are dried in a conventional dielectric (RF) oven. The dielectric oven includes spaced electrodes that produce alternating high-frequency electrical fields between successive oppositely charged electrodes. The wet bundles of glass fibers 42 pass between the electrodes and through the electrical fields where the high alternating frequency electrical fields act to excite the water molecules and raise their molecular energy to a level sufficient to cause the water within the wet chopped fiber bundles 42 to evaporate.

Dielectrically drying the bundles of wet glass fibers 42 enhances fiber-to-fiber cohesion and reduces bundle-to-bundle adhesion. The dielectric energy penetrates the wet bundles of chopped glass fibers 42 evenly and causes the water to quickly evaporate, helping to keep the wet glass bundles 42 separated from each other. Additionally, the dielectric oven permits the wet glass fiber bundles 42 to be dried with no active method of fiber agitation as is conventionally required to remove moisture from wet fibers. This lack of agitation reduces or eliminates the attrition or abrasion of fibers as is commonly seen in conventional fluidized bed and tray drying ovens due to the high air flow velocities within the ovens and the mechanical motion of the fibrous material in the beds. In addition, the lack of agitation greatly increases the ability of the dielectric oven to maintain the glass fibers in bundles and not filamentize the glass fiber strands as in aggressive conventional thermal processes.

In alternative embodiments, the wet chopped glass fiber bundles 42 may be dried in a fluidized bed oven such as a Cratec® oven or in a rotating tray oven. In both the Cratec® drying oven and rotating try oven, the wet chopped glass fiber bundles 42 are dried and the sizing composition on the fibers is solidified using a hot air flow having a controlled temperature. The dried fiber bundles 10 may then passed over screens to remove longs, fuzz balls, and other undesirable matter before the chopped glass fiber bundles 10 are collected. In addition, the high oven temperatures that are typically found in Cratece and rotating tray ovens allow the size to quickly cure to a very high level of cure which reduces occurrences of premature filamentization.

In a second embodiment of the present invention depicted generally in FIG. 4, glass fibers 12 are attenuated from a bushing 30. An aqueous sizing composition as described in detail above is applied to the attenuated glass fibers 12 to form wet sized glass fibers 50. The sizing may be applied by conventional methods such as by an external application roller 32 or by spraying the size directly onto the glass fibers 12 (not shown). It is considered to be within the purview of the invention to position a size applicator internally within the heat transfer chamber 52. The wet sized glass fibers 50 then enter the heat transfer chamber 52 and ambient air is drawn into the uppermost end 54 of the heat transfer chamber 52 from circumferentially around the bushing 30.

As shown in FIG. 4, the heat transfer chamber 52 extends beneath the size applicator 32 and is positioned with the uppermost end 54 of the heat transfer chamber 52 in a sufficiently close proximity to the bushing 30 so that the air being drawn into the uppermost end 54 of the heat transfer chamber 52 is heated by the extreme heat generated by the bushing 30. In addition, the heat transfer chamber 52 is essentially circumferentially disposed about the sized glass fibers 50 so that the heated air may evaporate any water or solvent present in the size composition on the wet glass fibers 50. The heat transfer chamber 52 extends downwardly from the size applicator 32 a distance that is sufficient to dry or substantially dry the wet sized glass fibers 50. In a preferred embodiment, the moisture content of the glass fibers 50 is less than about 0.05%. The wet glass fibers 50 travel through the heat transfer chamber 52 and exit the chamber 52 as dried glass fibers 56. Such an adiabatic process is described in detail in U.S. Pat. No.5,055,119 to Flautt et al., the content of which is hereby incorporated by reference in its entirety.

The dried sized glass fibers 56 are then gathered and split into dried fiber strands 58 having a specific, desired number of individual glass fibers 12. A splitter shoe 34 splits the dried sized glass fibers 56 into dried fiber strands 58, which may then be gathered by a gathering shoe 38 into a single tow 59 for chopping. It is to be appreciated that the splitter shoe 34 may be positioned internally (not illustrated) in the heat transfer chamber 52 to split the wet glass fibers 50 into fiber strands prior to exiting the heat transfer chamber 52. In this situation, the gathering shoe 38 may or may not be positioned within the heat transfer chamber 52. It is also to be appreciated that the splitter shoe 34 may be positioned between the size applicator 32 and the heat transfer chamber 52 to split the glass fibers 12 prior to entering the heat transfer chamber 52 (not shown).

The tow of combined glass fiber strands 59 may be chopped by a conventional cot 60 and cutter 40 combination to form the dried chopped fiber bundles 10. As described above, the dried chopped fiber bundles 10 may have a length of about 0.125 to about 3 inches, and preferably a length of about 0.25 to about 1.25 inches. In at least one preferred embodiment, the dried sized glass fibers 56 are split into dried bundles of fibers 58 with a bundle tex of from about 20 to about 200 g/km, and preferably from about 30 to about 50 g/km. The dried, chopped glass fiber bundles 10 may fall onto a collection container 48 for storage or placed onto a conveyor for an in-line formation of a chopped strand mat (embodiment is not illustrated). In an alternate embodiment, the dried, chopped fiber bundles 10 may be placed onto a conveyor (not shown) for conveyance to a conventional dielectric (RF) oven, a fluidized bed oven such as a Cratec® oven (available from Owens Corning), or a rotary tray thermal oven to further dry them.

In use, the dried chopped glass fiber bundles 10 may be used to form a chopped strand mat 84, as shown in FIG. 5. The dried chopped glass bundles 10 may be provided to a conveyor 62 by a storage container 60. The dried chopped glass fiber bundles 10 are placed into a mixing tank 64 that contains various surfactants, viscosity modifiers, defoaming agents, and/or other chemical agents with agitation to form a chopped glass fiber bundle slurry (not shown). The slurry may be passed through a machine chest 66 and a constant level chest 68 to further disperse any fibers selectively released from the chopped glass fiber bundles 10 by the size composition. The glass fiber bundle slurry may then be transferred from the constant level chest 68 to a head box 70 where the slurry is deposited onto a moving screen or foraminous conveyor 74 and a substantial portion of the water from the slurry is removed to form a web 72. The water may be removed from the web 72 by a conventional vacuum or air suction system (not illustrated in FIG. 5). A binder 76 is then applied to the web 72 by a binder applicator 78. The binder-coated web 80 is then passed through a drying oven 82 to remove any remaining water and cure the binder. The formed non-woven chopped strand mat 84 that emerges from the oven 82 includes randomly dispersed glass fiber bundles. The non-woven chopped strand mat 84 may be rolled onto a take-up roll 86 for storage for later use.

The binder may be an acrylic binder, a styrene acrylonitrile binder, a styrene butadiene rubber binder, a urea formaldehyde binder, or mixtures thereof. Preferably, the binder is a standard thermosetting acrylic binder formed of polyacrylic acid and at least one polyol (e.g., triethanolamine or glycerine). Examples of suitable acrylic binders for use in the present invention include a plasticized polyvinylacetate binder such as Vinamul 8831 (available from Celenese) and modified polyvinylacetates such as Duracet 637 and Duracet 675 (available from Franklin International). The binder may optionally contain conventional additives for the improvement of process and product performance such as dyes, oils, fillers, colorants, UV stabilizers, coupling agents (e.g., aminosilanes), lubricants, wetting agents, surfactants, and/or antistatic agents.

There are numerous advantages provided by the chopped glass fiber bundles 10 of the present invention. For instance, the chopped glass fiber bundles 10 may be formed at a significantly fast rate, especially when compared glass bundles formed by conventional air-laid processes. Increasing the rate of speed that the chopped glass fiber bundles can be produced permits for a higher throughput and additional product that can be sold to the customers. In addition, the chopped glass fiber bundles can be formed with low manufacturing costs since the fibers do not have to be dried and chopped in separate steps.

In addition, the chopped glass fiber bundles 10, when utilized in the formation of chopped strand mats in the wet process described above, provides for a mat that has a substantially uniform distribution of glass (aerial density) and is white in appearance. It is also advantageous that the wet fibers utilized to form the chopped glass fiber bundles produce little or no fuzz in the final chopped strand mat.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.

EXAMPLES

Example 1

Formation of Dry Chopped Glass Fiber Bundles

The sizing formulations set forth in Tables 1-4 were prepared in buckets as described generally below. To prepare the size compositions, approximately 90% of the water and, if present in the size composition, the acid(s) were added to a bucket. The silane coupling agent was added to the bucket and the mixture was agitated for a period of time to permit the silane to hydrolyze. After the hydrolyzation of the silane, the lubricant and film former were added to the mixture with agitation to form the size composition. The size composition was then diluted with the remaining water to achieve the target mix solids of approximately 4.5% mix solids.

TABLE 1
Polyurethane Size Composition A
Component of Size % by Weight of
Composition       Active Solids
W290H(a)          83.64
A-187(b)          1.12
A-1100(c)         4.68
A-100(d)          9.95
Lubesize K-12(e)  0.06
(a)polyurethane film forming dispersion (Cognis)
(b)epoxy curative (Resolution Performance Products)
(c)γ-aminopropyltriethoxysilane (General Electric)
(d)polyurethane-acrylic alloy (Cognis)
(e)stearic ethanolamide (AOC)

TABLE 2
Polyurethane Size Composition B
Component of Size % by Weight of
Composition       Active Solids
W296(a)           491.76
A-187(b)          6.79
A-1100(c)         25.86
PEG 400 MO(d)     2.21
(a)polyurethane film forming dispersion (Chemtura)
(b)epoxy curative (Resolution Performance Products)
(c)γ-aminopropyltriethoxysilane (General Electric)
(d)polyurethane-acrylic alloy (Cognis)
(e)monooleate ester (Cognis)

TABLE 3
Epoxy Size Composition A
Component of Size % by Weight of
Composition       Active Solids
ER 5520(a)        46.15
DPC-6870(b)       46.15
PEG 400 MO(c)     3.08
A-174(d)          4.62
(a)epoxy resin film forming dispersion in water (Resolution Performance Products)
(b)epoxy curative (Resolution Performance Products)
(c)monooleate ester (Cognis)
(d)methacryloxypropyltrimethoxysilane (General Electric)

TABLE 4
Epoxy Size Composition D
Component of Size % by Weight of
Composition       Active Solids
ER 3546(a)        47.20
DPC-6870(b)       47.20
PEG 400 MO(c)     0.88
A-174(d)          4.72
(a)epoxy resin film forming dispersion (Resolution Performance Products)
(b)epoxy curative (Resolution Performance Products)
(c)monooleate ester (Cognis)
(d)methacryloxypropyltrimethoxysilane (General Electric)

Each of the sizes were applied to E-glass in a conventional manner (such as a roll-type applicator as described above. The E-glass was attenuated to 13 μm glass filaments in a 75 lb/hr throughput bushing fitted with 2052 hole tip plate. The filaments were gathered and split 16 ways to achieve 128 filaments per glass fiber bundle and a bundle tex of about 43 g/km. The glass fiber bundles were then chopped with a mechanical cot-cutter combination to a length of approximately 1¼ inches and gathered into a plastic pan. The chopped glass fibers contained approximately 15% forming moisture. This moisture in chopped glass fiber bundles was removed in a dielectric oven (40 MHz, Radio Frequency Co.) to form dried chopped glass fiber bundles.

Example 2

Formation of Chopped Strand Mat Using Dried Chopped Glass Fiber Bundles

The dried chopped fiber bundles formed in accordance with the procedures set forth in Example 1 were used to form four chopped glass mats. The dried chopped fiber bundles (each containing a different size composition set forth in Tables 1-4) were suspended in 250 gallon mixing tanks in which the appropriate additives (surfactants, dispersants, and the like) were added with agitation to form chopped glass fiber bundle slurry slurries. The components of the white water slurry (other than water) are set forth in Table 5.

TABLE 5
White Water     Amount
Components      (ppm)
Drewfloc 270(a) 400-900
Surfynol 465(b) 50-200
Drew L-139(c)   5-25
Nalco 7330(d)   1-5
(a)anionic polyacrylamide (available from Drew Industries)
(b)nonionic surfactant (available from Air Products)
(c)antifoaming agent (available from Drew Industries)
(d)biocide (ONDEO Nalco)

The glass slurries were each deposited onto a moving chain where a majority of the water was removed by a vacuum to form a web. A plasticized polyvinylacetate mat binder was applied to the glass webs (Vinamul 8831 from Celenese) by a weir (curtain coater). The webs were then passed through a forced air oven at 450° F. for 30 seconds to remove the remaining water from the webs, cure the binder, and form the chopped glass mats. The basis weight of the mats were determined to be approximately 1 oZ/ft². It was also determined that the binder was present on the mats at 5.0% by weight. The mats were extremely white and visually showed excellent aerial density. In addition, the chopped glass mats displayed dry tensile strengths of 30 lb in the machine direction (MD) and 25 lb in the cross-machine direction (CD).

Laminates were prepared from the chopped glass mats with a polyester resin (AOC R937) and catalyzed with Attofina DDM9 catalyst (2-Butanone Peroxide). To facilitate comparison, the laminates containing the inventive chopped glass fiber bundles all had a 3 oz/ft² basis weight and substantially equivalent thicknesses. Simulating hand layup, the laminates were formed in a hydraulic press under nominal temperature (120° F.) and pressure for about 30 minutes. Pressure, at the low end of the press range was 10,000 lb for the 14 in² laminates, which translates to about 50 psi. The laminates underwent post-cure in an oven for 2 hours at 200 ° F. before mechanical testing.

The laminates containing the inventive chopped glass fiber bundles were tested for tensile strength and flexural strength. The tensile strength was determined according to the testing procedures set forth in ASTM D5083 and flexural strength was determined according to the testing procedures set forth in ASTM D790. The comparative mats are set forth in Table 6.

TABLE 6
Conventional
Mat   Description
M723A 1 oz/ft2 chopped strand mat from Owens
      Corning
M8643 1 oz/ft2 electrical-pultrusion grade continuous
      filament mat from Owens Corning
M8610 1 oz/ft2 general purpose continuous filament
      mat from Owens Corning

Mechanical testing of the laminates containing the inventive chopped glass fiber bundles revealed a nearly equivalent performance of the inventive laminates relative to a standard chopped strand mat (M723A) and surprisingly, M8643 and M8610, continuous filament mats (CFM). The results of the comparative testing is set forth in FIGS. 6-9.

Example 3

Formation of Dry Chopped Glass Fiber Bundles Utilizing a Heat Transfer Chamber

Each of the sizes set forth in Tables 1-4 were prepared and applied in a conventional manner to E-glass attenuated to 13 μm glass filaments in a 75 lb/hr throughput bushing fitted with 2052 hole tip plate. The sized fibers were split 16 ways to achieve 128 filaments per glass fiber bundle and passed through a heat transfer chamber where air heated by the extreme heat generated by the bushing was drawn into the heat transfer chamber to dry the glass fiber bundles. The dried glass fiber bundles had a bundle tex of about 43 g/km. The dried glass fiber bundles were gathered into one tow and chopped with a mechanical cot-cutter combination to a length of 1¼ inches. The chopped glass fibers were gathered into a plastic pan. The glass fibers contained 0% forming moisture.

Example 4

Formation of Chopped Strand Mat Using Dried Chopped Glass Fiber Bundles Formed Utilizing a Heat Transfer Chamber

The dried chopped fiber bundles formed in accordance with the procedures set forth in Example 3 were used to form four chopped glass mats. The dried chopped fiber bundles (each containing a different size composition set forth in Tables 1-4) were suspended in 250 gallon mixing tanks in which the appropriate additives (surfactants, dispersants, and the like) were added with agitation to form chopped glass fiber bundle slurry slurries. The components of the white water slurry (other than water) are set forth in Table 7.

TABLE 7
White Water     Amount
Components      (ppm)
Drewfloc 270(a) 400-900
Surfynol 465(b) 50-200
Drew L-139(c)   5-25
Nalco 7330(d)   1-5
(a)anionic polyacrylamide (available from Drew Industries)
(b)nonionic surfactant (available from Air Products)
(c)antifoaming agent (available from Drew Industries)
(d)biocide (ONDEO Nalco)

The glass slurries were each collected onto a moving chain where a majority of the water was removed by a vacuum to form a web. A plasticized polyvinylacetate mat binder was applied to the glass webs (Duracet 675 from Franklin International) by a weir (curtain coater). The webs were then passed through a forced air oven at 450 ° F. for 30 seconds to remove the remaining water from the webs, cure the binder, and form the chopped glass mats. The basis weight of the mats were determined to be approximately 1 oz/ft². It was also determined that the binder was present on the mats at 5.0% by weight. On visual observation, it was noted that the mats were extremely white and visually showed excellent aerial density. In addition, the chopped glass mats displayed dry tensile strengths of 32 lb in the machine direction (MD) and 27 lb in the cross-machine direction (CD).

Laminates were prepared from the chopped glass mats with a polyester resin (AOC R937) and catalyzed with Attofina DDM9 catalyst (2-Butanone Peroxide). To facilitate comparison, the laminates containing the inventive chopped glass fiber bundles were all 3 oZ/ft² basis weight and substantially equivalent thicknesses. Simulating hand layup, the laminates were formed in a hydraulic press under nominal temperature (120° F.) and pressure for about 30 minutes. Pressure, at the low end of the press range was 10,000 lb for the 14 in² laminates, which translates to about 50 psi. The laminates underwent post-cure in an oven for 2 hours at 200° F. before mechanical testing. Mechanical testing of the laminates containing the inventive chopped glass fiber bundles revealed a nearly equivalent performance of the laminates relative to a standard chopped strand mat (M723A) and, surprisingly, M8643 and M8610, continuous filament mats (CFM) (set forth in Table 6).

Example 5

Tensile Strength of Laminates from Chopped Strand Mats Using Dried Chopped Glass Fiber Bundles

Dried chopped fiber bundles formed in accordance with the procedures set forth in Example 3 were used to form four chopped glass mats as described above in Example 4. The dried chopped fiber bundles sized Polyurethane Size Composition A (Table 1) were suspended in 250 gallon mixing tanks in a white water slurry containing the components set forth in Table 7. The glass slurries were each collected onto a moving chain where a majority of the water was removed by a vacuum to form a web. A plasticized polyvinylacetate mat binder was applied to the glass webs (Duracet 675 or Duracet 637 from Franklin International) by a weir (curtain coater). The webs were then passed through a forced air oven at 450° F. for 30 seconds to remove the remaining water from the webs, cure the binder, and form the chopped glass mats.

Laminates were prepared from the chopped strand mats in accordance with the procedure described above in Example 4. The various samples tested (Samples 1-7) are set forth in Table 8. Samples 1 and 2 contained Duracet 637 as a binder and Samples 3 and 4 contained Duracet 675 as a binder. The laminates were tested for tensile strength in the machine direction (MD) and in the cross-machine direction (CD). The results are set forth in Tables 10 and 11. The results indicated that the laminates demonstrated a bias in the machine direction. This demonstration of bias is contrary to mats made in accordance with conventional air-laid processes, which show no or virtually no bias. A bias in the machine direction is an advantage to the laminates because the chopped strand mat will be naturally stronger in the direction that a customer will pull it off of the roll. As a result, larger rolls may be manufactured. In addition, the additional strength would enable a customer to pull the chopped strand mat off the roll at a faster rate of speed with a less likelihood that the mat would tear. The data also demonstrates superior strength for laminates formed with the chopped glass fiber bundles sized with Size Composition A compared to the controls.

TABLE 8
       Description of
Sample Chopped Strand Mat
1      6 plys of 0.5 oz/ft2
2      2 plys of 1.5 oz/ft2
3      6 plys of 0.5 oz/ft2
4      2 plys of 1.5 oz/ft2
5      M723A (3 plys of 1 oz/ft2) control
6      M723A-2 (6 plys of 0.5 oz/ft2) control
7      M723A-3 (2 plys of 1.5 oz/ft2) control

Example 6

Formation of Bulk Molding Compound Utilizing Various Sizing Compositions

one quarter inch (¼″) chopped glass fiber samples were made into bulk molding compound with the formulation set forth in Table 8.

TABLE 9
Bulk Molding Compound Formulation
                         pph
Component                (Parts Per Hundred)
Polyester Resin E-342(a) 60
Thermoplastic P-713(b)   40
tBPB(c)                  1.5
Calwhite II(d)           200
Zinc Stearate(e)         4
(a)unsaturated polyester resin (AOC)
(b)thermoplastic (AOC)
(c)tert-butylperbenzoate catalyst
(d)calcium carbonate (Cabot)
(e)mold release agent (Aldrich Chemical Co.)

The bulk molding compound formulation in Table 8 was prepared with various experimental glasses sized with the various sizing compositions at 20% by weight. The various experimental glass fibers are set forth below as Samples 1-10. The charge was placed into a 12 inch×18 inch tool and was molded at 10,000 psi at 265° F. for 5 minutes. The laminates were tested for resistance to notched impact strength according to ASTM D256 in the 0° and 90° direction. The results are set forth in Tables 12 and 13. The results indicated that the glass fibers sized with the experimental size composition demonstrated at least comparable performance to the control. The results were unexpected because an at least comparable impact strength was achieved by drying the glass fibers for a short period of time (30 minutes) as compared to conventional processes in which the glass is thermally dried for at least 20 hours.

Sample 1—Polyurethane Size Composition A (Table 1) was applied to glass fibers and dried for 6 hours a thermal oven at 265° F.

Sample 2—Polyurethane Size Composition A (Table 1) was applied to glass fibers and dried for 30 minutes in an RF oven followed by 1 hour in a thermal oven at 265° F.

Sample 3—Polyurethane Size Composition A (Table 1) was applied to glass fibers and dried for 30 minutes in an RF oven followed by 2 hours at in a thermal oven at 265° F.

Sample 4—Polyurethane Size Composition A (Table 1) was applied to glass fibers and dried for 30 minutes in an RF oven followed by 2 hours in a thermal oven at 265° F.

Sample 5—Polyurethane Size Composition A (Table 1) was applied to glass fibers and dried for 30 minutes in an RF oven followed by 2 hours in a thermal oven at 265° F.

Sample 6—Polyurethane Size Composition A (Table 1) was applied to glass fibers and dried for 30 minutes in an RF oven followed by 2 hours in a thermal oven at 265° F.

Sample 7—Polyurethane Size Composition B (Table 2) was applied to glass fibers and dried for 30 minutes in an RF oven; no post heating.

Sample 8—Epoxy Size Composition A (Table 3) was applied to glass fibers and dried for 30 minutes in an RF oven; no post heating.

Sample 9—Epoxy Size Composition A (Table 3) was applied to glass fibers and dried for 20 minutes in an RF oven; no post heating.

Sample 10—Polyurethane Size Composition B (Table 2) was applied to glass fibers and dried for 20 minutes in an RF oven; no post heating.

Sample 12—control bulk molding compound (BMC) dry use chopped strands (101C from Rio Claro, Brazil; Owens Corning).

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below.

Claims

1. A chopped glass fiber bundle for use in mat forming applications comprising:

a plurality of substantially parallel glass fibers positioned in a bundled orientation, said glass fibers being at least partially coated with a size composition that maintains said plurality of glass fibers in said bundled orientation during the formation and subsequent processing of glass fibers in said bundled orientation;

wherein said sizing composition includes: one or more film forming agents selected from the group consisting of a polyurethane film former, an unsaturated polyester film former and an epoxy resin film former; at least one silane coupling agent; and at least one lubricant.

2. The chopped glass fiber bundle of claim 1, wherein said plurality of glass fibers have a bundle tex of about 20 to about 200 g/km.

3. The chopped glass fiber bundle of claim 1, wherein said glass fibers are wet use chopped strand glass fibers.

4. The chopped glass fiber bundle of claim 1, wherein said film forming agent is a polyurethane film forming agent and said size composition further comprises a polyurethane-acrylic alloy.

5. The chopped glass fiber bundle of claim 1, wherein said film forming agent is an epoxy resin film former and said size composition further comprises an epoxy curative.

6. The chopped glass fiber bundle of claim 1, wherein said film forming agent is an unsaturated polyester film forming agent and said size composition further comprises a benzoyl peroxide curing catalyst.

7. The chopped glass fiber bundle of claim 1, wherein said one or more film forming agent is present in said size composition in an amount of from about 80 to about 95% by weight total solids, said at least one silane coupling agent is present in said size composition in an amount of from about 3 to about 15% by weight total solids, and said at least one lubricant is present in said size composition in an amount of from about 0.1 to about 2% by weight total solids.

8. The chopped glass fiber bundle of claim 1, wherein said at least one silane coupling agent is selected from the group consisting of an aminosilane coupling agent and a methacryloxy silane coupling agent.

9. The chopped glass fiber bundle of claim 1, wherein said size composition filamentizes said glass fibers in said bundled orientation during future processing to form an aesthetically pleasing final product.

10. A method of forming chopped glass fiber bundles comprising the steps of:

applying a size composition to a plurality of attenuated glass fibers, said size composition including: one or more film forming agents selected from the group consisting of a polyurethane film former, an unsaturated polyester film former and an epoxy resin film former; at least one silane coupling agent; and at least one lubricant;

splitting said plurality of glass fibers into glass fiber strands having a predetermined number of glass fibers therein;

chopping said glass fiber strands to form wet chopped glass fiber bundles, said wet chopped glass fiber bundles having a discrete length; and

drying said wet chopped glass fiber bundles in a drying oven selected from the group consisting of a dielectric oven, a fluidized bed oven and a rotating tray thermal oven to form chopped glass fiber bundles.

11. The method of forming chopped glass fiber bundles according to claim 10, wherein said predetermined number of glass fibers in said glass fiber strands is a number sufficient to provide a bundle tex of about 20 to about 200 g/km.

12. The method of forming chopped glass fiber bundles according to claim 10, further comprising the step of:

depositing said wet chopped glass fibers onto a conveyor prior to said drying step.

13. The method of forming chopped glass fiber bundles according to claim 10, wherein greater than or equal to about 99% of the water external to said wet chopped glass fiber bundles is removed in said drying oven.

14. The method of forming chopped glass fiber bundles according to claim 13, wherein said oven is said dielectric oven; and

wherein said drying step comprises: passing said wet chopped glass fiber bundles through successive oppositely charged electrodes positioned in said dielectric oven to cause water within said wet chopped fiber bundles to evaporate without agitating said wet chopped fiber bundles.

15. The method of forming chopped glass fiber bundles according to claim 13, wherein said wet chopped fiber bundles are dried in a fluidized bed and the sizing composition on said glass fibers is solidified using a hot air flow having a controlled temperature.

16. A method of forming chopped glass fiber bundles comprising the steps of:

applying a size composition to a plurality of glass fibers attenuated by a bushing, said size composition including: one or more film forming agents selected from the group consisting of a polyurethane film former, an unsaturated polyester film former and an epoxy resin film former; at least one silane coupling agent; and at least one lubricant;

passing said plurality of sized glass fibers through a heat transfer chamber where air heated by said bushing is drawn into said heat transfer chamber to substantially dry said plurality of sized glass fibers and form dried glass fibers;

splitting said dried glass fibers into glass fiber strands having a predetermined number of said dried glass fibers therein; and

chopping said glass fiber strands to form chopped glass fiber bundles, said chopped glass fiber bundles having a discrete length.

17. The method of forming chopped glass fiber bundles according to claim 16, further comprising the step of:

gathering said glass fiber strands into a single tow prior to chopping said glass fiber strands.

18. The method of forming chopped glass fiber bundles according to claim 16, wherein said predetermined number of glass fibers in said glass fiber strands is a number sufficient to provide a bundle tex of about 20 to about 200 g/km.

19. The method of forming chopped glass fiber bundles according to claim 16, further comprising the step of:

heating said chopped glass fiber bundles in a drying oven selected from the group consisting of a dielectric oven, a fluidized bed oven and a rotating tray thermal oven to further dry said chopped glass fiber bundles.

20. The method of forming chopped glass fiber bundles according to claim 16, wherein said splitting step occurs prior to said dried glass fibers exiting said heat transfer chamber.