LIGHTWEIGHT REINFORCING MAT AND PULTRUSION PROCESS

Abstract: A bonded mat is provided for use in a variety of processes including pultrusion. The bonded mat comprises discrete, sized glass fibers randomly dispersed throughout the bonded mat, a coupling agent, and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions.

Description: LIGHTWEIGHT REINFORCING MAT AND PULTRUSION PROCESS BACKGROUND ART This invention is directed to bonded glass fiber mats and, more particularly, to bonded mats having randomly disposed discrete glass fibers. Pultrusion is a process for continuously foπning reinforced plastic materials having a consistent cross-sectional profile. The word "pultrusion" is a hybrid which combines the words "pull" and "extrusion." The product is literally pulled through a forming die. In its most usual form, pultrusion involves feeding a multiplicity of fiberglass rovings, with additional plies of glass mat of appropriate width, through an impregnation system which applies a resin, normally a thermosetting material such as a polyester to the reinforcement. The resin-impregnated reinforcement is then reshaped to the approximate shape of the pultrusion die. The die itself is heated. As the product is drawn from the die, the resin is either cured, or very nearly cured. The endless product so formed is then cut in appropriate lengths. Many variations of this general process have been developed as the technology has matured. Pultruded products are used in a wide variety of applications. In many places they have replaced metallic construction materials, particularly those used in highly corrosive environments. Structural beams, floor gratings, handrails, ladders, and many similar products are now made by pultrusion processes. Continuous filament glass fiber mats have been used in a variety of pultrusion products. Continuous filament mats, however, suffer from several limitations which can be problematic in pultrusion applications. For example, continuous glass fiber mats can vary in weight by up to fifteen percent from one section to the next. This lack of consistency is undesirable in pultruded products, where weight uniforrnity is a main concern. Secondly, due to the grouping of the continuous fibers into strands or bundles of fibers, the apparent density of the mat is relatively high. That is, the weight of the continuous filament mat is high relative to its thickness, which adds to the cost of such mats. An alternative to mats formed from continuous filament glass fibers are mats formed from discrete or chopped glass fibers. Discrete glass fibers are relatively short in length, typically a few inches (many mm) or less. Attempts have been made in the past to use discrete glass fiber mats in pultrusion products. However, such mats have been found to be mostly unacceptable because of lack of strength, conformability, i.e., the ability to be formed into complex shapes, compatibility with the matrix resin, or a combination of the above items. Also, most discrete fiber mats have insufficient dry and wet tensile strength to survive the pultrusion process. 5 Therefore, a need exists for a bonded glass fiber mat which is flexible enough to be formed into complex shapes, is compatible with the matrix resin, and is lightweight yet has sufficient strength properties such that it can be used satisfactorily in pultrusion products. DISCLOSURE OF INVENTION 10 The present invention meets that need by providing an improved glass fiber mat which is lightweight, can be formed into complex shapes and has sufficient strength properties such that it can be used acceptably in pultrusion applications. The bonded mat of the present invention has been found to occupy generally the same volume as prior art continuous filament mats which typically weigh twice as much. 15 Accordingly, the mat of the present invention will occupy generally the same volume in a pultruded product as would a continuous filament mat having twice the weight. Depending on the cross-section and stacking sequence, the pultruded part can have comparable sectional performance properties as the same section produced with continuous filament mats. Use of the mat of the present invention will also result in a pultruded product with 20 increased uniformity in part performance and weight. In accordance with a first aspect of the present invention, a bonded mat is provided which is adapted for use in pultrusion applications. The mat comprises discrete, sized glass fibers, a coupling agent, and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions. Preferably, the binder consists essentially of a 25 thermosetting acrylic resin. The glass fibers are preferably from about 0.5 inch (12.7 mm) to about 3.0 inches (76 mm) in length, most preferably about 1.5 inches (38 mm) in length. The glass fibers also preferably have a diameter from about 10 microns to about 30 microns, most preferably from 16 to 23 microns. The coupling agent is preferably a silane. It is also preferable for the bonded mat to have a nominal basis weight of 0.20 to 1.0 oz ft 2 (61.030 to 30305.152 g/m 2 ). The bonded mat of the present invention has an average thickness of between 0.040 and 0.060 inch per ounce (0.036 and 0.054 mm/g) of mat material when subjected to 20 psi (239 kPa) of pressure, which is typical of compaction pressures encountered during pultrusion processes. In accordance with a second aspect of the present invention, a process is provided for forming a bonded glass fiber mat which is adapted for use in pultrusion applications. The process is a modified papermalάng process, typically known as the "wet-laid" process. The process for forming the bonded glass fiber mat is as follows. Discrete or chopped, sized fibers of a particular diameter and length are dispersed in an aqueous slurry through a combination of mechanical agitation and chemical dispersants. This slurry, suitably diluted, is presented to a continuous fine mesh conveyor or forming wire through which most of the water drains leaving a randomly oriented, uniform, continuous layer or web of fibers. Excess water is removed from the mat, typically by vacuum extraction. The web is transferred to a second screen conveyor and saturated with a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions. The binder saturated web is then passed through an oven where the water is evaporated and the binder cured. The resulting continuous, dry mat is wound upon a spool or mandril for further processing. In accordance with a third aspect of the present invention, a pultrusion product is provided which comprises at least one layer of roving, at least one layer of veil, a resin, and a bonded mat. The bonded mat includes discrete, sized glass fibers, a coupling agent, and a binder consisting essentially of a compound selected from the group consisting of acrylic resins and styrene-polyester emulsions. The resin is preferably a styrene-based polyester or vinylester. In accordance with a fourth aspect of the present invention, a process is provided for forming a pultruded product. The process comprises the steps of: providing a layer of glass roving; providing first and second layers of bonded mat each comprising discrete, sized glass fibers, a coupling agent, and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions; locating the roving layer between the first and second bonded mats; providing first and second layers of veil; locating the roving layer and the first and second bonded mats between the first and second layers of veil; impregnating the layers of veil, the first and second bonded mats and the roving layer with a thermosetting resin; and, drawing the impregnated layers of veil, mat and roving through a heated pultrusion die to form a pultruded product. The step of impregnating the layers of veil, mat and roving generally occurs in a resin bath ahead of the die but may occur when the veil layers, the roving layer, and the first and second mats pass through an initial portion of the heated pultrusion die. Preferably, the thermosetting resin is a styrene-based polyester or vinylester. Accordingly, it is an object of the present invention to provide a bonded glass fiber mat which is flexible enough to be formed into complex shapes and is lightweight yet has sufficient strength properties such that it can be used satisfactorily in pultrusion products. It is a further object of the present invention to provide a bonded mat having randomly disposed discrete glass fibers. It is another object of the present invention to provide a process for forming a bonded mat for use in pultrusion applications and which includes randomly disposed discrete glass fibers. It is yet a further object of the present invention to provide an improved process for forming a pultruded product. These and other objects and advantages of the present invention will be apparent from the following description and the appended claims. MODES FOR CARRYING OUT THE INVENTION The bonded mat of the present invention is provided with discrete, sized glass fibers which are randomly dispersed throughout the bonded mat. "Discrete fibers" are non-continuous fibers which are relatively short in length, typically a few inches (many mm) or less. The fibers are preferably from about 0.5 inch (12.7 mm) to about 3.0 inches (76 mm) in length, most preferably about 1.5 inches (38 mm) in length. In addition, the glass fibers are preferably from about 10 microns to about 30 microns in diameter, most preferably 16 to 23 microns. The glass material is preferably E glass or S glass, but can be any other suitable glass product. It is also preferable for the bonded mat to have a nominal basis weight of 0.20 to 1.0 oz/ft 2 (61.030 to 305.152 g/m 2 ). The bonded mat also comprises a coupling agent, and a binder. The binder is selected from the group consisting of acrylic resins and styrene-polyester emulsions. In a preferred embodiment, the binder consists essentially of a thermosetting acrylic resin. In another preferred embodiment, the binder consists of a styrene/unsaturated polyester emulsion catalyzed with 1% BPO (benzoylperoxide). Most preferably, the binder is a thermosetting acrylic resin, an example of which is commercially available from Rohm and Haas Company under the product name "Experimental Resin HF-05." This binder consists of a polyacrylic acid, triethanolamine and a promoter for the esterification of the acid groups. This binder is preferred because it is both strong and virtually inert to styrene which, as will be discussed below, is present in many resins used during pultrusion. The coupling agent can be any compound which serves to increase the adhesion of the binder or matrix resin to the glass fibers. A preferred coupling agent is a silane, an example of which is commercially available from OSi Specialties, Inc. under the product name "A-174." The coupling agent is preferably from 0.1 to 0.04 weight percent of the final mat product. The coupling agent is preferably incorporated into the binder to insure that it is present at a specific level in the final mat rather than mixed with the glass fibers where it may be subject to being washed off during manufacture of the mat by white water and also to insure that the coupling agent does not interfere with fiber dispersion. In a preferred embodiment, the binder of the present invention contains about 1.4 solids weight percent of the silane coupling agent. Size is applied to alter the surface characteristics of the glass to, for example, impart lubricity to the glass. The size can be any suitable glass size composition. Typical ingredients of size compositions include lubricants such as tristearates, trioleates, polyvinyl pyrrolidone and mixtures thereof; film formers such as water soluble polymers; and coupling agents such as silanes. A preferred size composition contains a fatty acid amide, a silane, and a water soluble polymer and is compatible with the acrylic resin of the present invention. Glass fibers having such a size composition are commercially available from Owens-Corning Fiberglas Corporation under the product name "Wet Chopped Strands" with size number 685. The bonded mat can be formed by a variety of processes, including air-laid and wet-laid processes. The bonded mat is preferably formed by a wet-laid process. The wet laid process initially involves forming an aqueous dispersion or slurry of discrete, sized glass fibers in a mix tank with general chemical dispersion agents and agitation. The process water, "white water," used to disperse the fibers may, in addition to the dispersion agents, contain defoamers and viscosity modifiers. Examples of dispersion agents are quaternary ammonium compounds and amine compounds such as polyoxyethylated tallow amine. The total solids content of the slurry is preferably from about 0.5% to about 0.9%, and is most preferably about 0.7%. The aqueous dispersion is processed into a wet-laid mat by a modified papermaking process utilizing an inclined wire fourdrineer such as the "Delta Former," available from Valmet-Sandy Hill Corporation, or the "Hydroformer" available from Domes (a division of the Voith-Gruppe). Examples of other machines which can be used to produce the mat of the present invention include Rotoformers and variations thereof which .are available from Valmet-Sandy Hill Corporation, and the "Vertiformer," which is commercially available from the Black Clawson Company. The aqueous fiber dispersion or slurry is processed into a wet-laid mat in the following manner. The above-described diluted slurry is deposited onto the screen conveyor or forming wire of an inclined wire fourdrineer. The majority of the water drains through the forming wire leaving a randomly oriented fiber web which is further dewatered by a vacuum slot or like device. The wet web is transferred to a second screen conveyor and a binder and a coupling agent applied. The mat is impregnated with the coupling agent and binder in a conventional manner, such as by curtain coating, spraying, a twin wire dip bath, or a two roll padder. Water, excess binder, and excess coupling agent are removed by a vacuum device. Finally, the binder-impregnated glass fiber product is dried and cured in one or more ovens. A typical temperature range for drying is from about 425°F (218°C) to about 580°F (304°C). The dried and cured product is the finished glass fiber mat. The glass fiber mat may be used to form a pultruded product through a conventional pultrusion process. Typically, one or more layers of roving, one or more layers of a veil, and a resin are used in forming the pultruded product. The layers of roving provide the pultruded product with longitudinal strength and structural support. The rovings or yarns may be made from glass, graphite, boron or polyaramid fibers. Preferably, the roving is made from glass fibers. The bonded mat provides the pultruded product with transverse strength and structural support. The bonded mat of the instant invention offers the opportunity to introduce rovings in the transverse direction which rovings may be secured to the bonded mat by stitching. This arrangement allows the required amount of pultrusion die fillage to be met by adjusting the mat weight while the amount of transverse roving can be independently adjusted to meet the strength requirements of the pultruded product. The veil layers are used to provide a protective exterior layer which encases the glass fiber mats. Each veil layer comprises a fabric formed from glass or a thermoplastic material, such as a polyester. Inorganic veils such as glass veils made from E, C, or ECR glass are commercially available from the Owens-Corning Fiberglas Corporation. An organic veil comprising a spun lace polyester veil is commercially available from Precision Fabrics Group under the product name "Nexus." A spun-woven polyester veil is commercially available from Precision Fabrics Group under the product name "Reemay." The pultruded product may include the aforementioned layers stacked in order (from top to bottom) as follows: glass or thermoplastic veil, glass fiber mat, roving, glass fiber mat, roving, glass fiber mat, glass or thermoplastic veil. These layers are bound together with the resin. Examples of commercially available resin compounds are unsaturated polyesters, vinylesters, epoxies, and phenolic compounds. The resin is most commonly a styreneated polyester or vinylester. Any conventional pultrusion apparatus may be used to form the pultruded product of the present invention. For example, one such apparatus is disclosed in U.S. Patent 3,556,888 to Goldsworthy et al., the disclosure of which is hereby incorporated by reference. The pultruded product is formed in the following manner. First and second layers of glass roving, first and second layers of veil, and first and second layers of bonded mat are provided. The layers are arranged in order (from top to bottom) as follows: veil, glass fiber mat, roving, glass fiber mat, roving, glass fiber mat, veil. The combined layers are then impregnated with a thermosetting resin and drawn through a heated pultrusion die. Thereafter, the pultruded product is cured and cooled, resulting in a finished pultruded product. The bonded glass fiber mat of the present invention can also be used in other processes, such as a conventional reactive thermoplastic manufacturing process. In order that the invention may be more readily understood, reference is made to the following example, which is intended to illustrate the invention but not limit the scope thereof. Example A bonded mat having randomly dispersed glass fibers was formed in accordance with the present invention in the following manner. One hundred four (104) pounds (47.174 kg) of a silane coupling agent (commercially available from OSi Specialties Inc. under the product name "A-174") was hydrolyzed in 5800 pounds (2.6 metric tons) of water to which 3.6 pounds (1.633 kg) of glacial acetic acid had been added for a period of 30 minutes. Eight thousand nine hundred eleven (8911) pounds (4.0 metric tons) of a formaldehyde-free acrylic resin (commercially available from Rohm and Haas Company as "Experimental Resin HF-05") was added to that mixture. Twenty-five (25) pounds (11.3 kg) of a defoamer (commercially available from the Drew Industrial Division of Ashland Chemical, Inc. under the product name Drew L-139) was then added to the mixture together with a sufficient quantity of water to bring the total volume of the binder mixture to 15,000 pounds (6.8 metric tons). The total solids content of the mixture was 30.5 weight percent. Glass fibers generally having a diameter of 23 microns and a length of 1.5 inches (38 mm) were formed into a mat using a wet-laid process. The process or white water used in the wet-laid process contained approximately 10 ppm (parts per million) of a dispersion agent (commercially available from Rhone-Poulenc under the product name "Rhodameen VP532"); 15 ppm of a viscosity modifier (commercially available from American Cyanamid under the product name "Magnifloc 1885A"); and 5-10 ppm of defoamer (commercially available from Henkel under the product name "NXZ") and was pH controlled to about 8.0 by ammonia. The above binder was applied to the mat at approximately 10% solids. The resultant mat had a nominal 5.6 percent loss on ignition (LOI) which yields a 0.08 weight percent silane level on the mat. Three layers of nominal 1.0 oz/ft 2 (305.152 g/m 2 ) bonded mat produced in essentially the same manner as the mat set out above were compressed under 20 psi (239 Pa) of pressure and exhibited a total thickness of 0.139 inch (3.531 mm) which indicates an average thickness of 0.046 inch per ounce (0.041 mm/g) of material. Three layers of nominal 0.75 oz/ft 2 (228.864 g/m 2 ) bonded mat produced in essentially the same manner as the mat set out above were compressed under 20 psi (239 kPa) of pressure and exhibited a total thickness of 0.1063 inch (2.700 mm) which indicates an average thickness of 0.047 inch per ounce (0.042 mm/g) of material. Three layers of nominal 0.5 oz/ft 2 (152.576 g/m 2 ) bonded mat produced in essentially the same manner as the mat set out above were compressed under 20 psi (239 kPa) of pressure and exhibited a total thickness of 0.0775 inch (1.969 mm) which indicates an average thickness of 0.052 inch per ounce (0.047 mm/g) of material. The bonded mat had a nominal basis weight of 1.0 oz/ft 2 (305.152 g/m 2 ). The average tensile strength in the longitudinal direction of the mat was 35.8 lbs/2-inch (16.2 kg/51-mm) strip, and the average tensile strength in the cross-machine direction of the mat was 31.3 lbs/2-inch (14.2 kg/51-mm) strip. While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the processes and products disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.

Claims: CLAIMS 1. A bonded mat having sufficient strength for use in pultrusion products comprising discrete, sized glass fibers randomly dispersed throughout said bonded mat, a coupling agent, and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions. 2. The bonded mat of claim 1, wherein said binder consists essentially of an acrylic resin. 3. The bonded mat of claim 1, wherein said glass fibers are from about 0.5 inch (12.7 mm) to about 3.0 inches (76 mm) in length. 4. The bonded mat of claim 1, wherein said coupling agent is a silane. 5. The bonded mat of claim 1, wherein said glass fibers are from about 16 microns to about 23 microns in diameter. 6. The bonded mat of claim 1, wherein said bonded mat has a nominal basis weight of 0.20 to 1.0 oz/ft 2 (61.030 to 305.152 g/m 2 ). 7. A process for forming a bonded glass fiber mat comprising the steps of: a. dispersing discrete size-coated glass fibers and depositing said fibers substantially randomly onto a support; b. impregnating said layer of discrete glass fibers with a coupling agent and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions; c. removing any undesired excess of said binder and said coupling agent from the impregnated glass fibers; and, d. heating the impregnated glass fibers to remove volatile components therefrom and to cure said binder to form said glass fiber mat. 8. The process of claim 7, wherein said binder consists essentially of an acrylic resin. 9. The process of claim 7, wherein said coupling agent is a silane. 10. The process of claim 7, wherein said glass fibers are about 1.5 inches (38 mm) in length. 11. The process of claim 7, wherein said glass fibers are from about 16 microns to about 23 microns in diameter. 12. The process of claim 7, wherein said bonded glass fiber mat has a nominal basis weight of 0.20 to 1.0 oz/ft 2 (61.030 to 305.152 g/m 2 ). 13. A pultrusion product comprising a resin, and a bonded mat containing discrete, sized glass fibers, a coupling agent, and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions. 14. The pultrusion product of claim 13, wherein said binder consists essentially of an acrylic resin. 15. The pultrusion product of claim 13, wherein said coupling agent is a silane. 16. The pultrusion product of claim 13, wherein said resin is selected from the group consisting of styreneated polyesters, vinylesters, epoxies, and phenolic compounds. 17. The pultrusion product of claim 13, wherein said glass fibers are from about 16 microns to about 23 microns in diameter. 18. The pultrusion product of claim 13, wherein .said glass fibers are from about 0.5 inch (12.7 mm) to about 3.0 inches (76 mm) in length. 19. The pultrusion product of claim 13, wherein said bonded mat has a nominal basis weight of 0.20 to 1.0 oz/ft 2 (61.030 to 305.152 g/m 2 ). 20. A process for forming a pultruded product comprising the steps of: a. providing a continuous layer of glass roving; b. providing first and second bonded mats each comprising discrete, sized glass fibers, a coupling agent, and a binder selected from the group consisting of acrylic resins and styrene-polyester emulsions; c. locating said roving layer between said first and second bonded mats; d. providing first and second layers of veil; e. locating said roving layer and said first and second bonded mats between .said first and second layers of veil; f. impregnating said first and second layers of veil, said first and second bonded mats, and said layer of roving with a thermosetting resin; and, e. drawing the impregnated layers of veil, mat and roving through a heated pultrusion die to form a pultruded product. 21. The process of claim 20, wherein said binder consists essentially of an acrylic resin. 22. The process of claim 20, wherein said coupling agent is a silane. 23. The process of claim 20, wherein said step of impregnating said layers of veil, said layers of roving, and said mat occurs when said veil layers, said roving layers, and said mat pass through an initial portion of said heated pultrusion die. 24. The process of claim 20, wherein said thermosetting resin is selected from the group consisting of a styreneated polyesters, vinylesters, epoxies, and phenolic compounds. 25. The process of claim 20, wherein said glass fibers are from about 0.5 inch (12.7 mm) to about 3.0 inches (76 mm) in length. 26. The process of claim 20, wherein said glass fibers are from about 16 microns to about 23 microns in diameter. 27. The process of claim 20, wherein said bonded glass fiber mat has a nominal basis weight of 0.20 to 1.0 oz/ft 2 (61.030 to 305.152 g/m 2 ).

Inventors: BRANDON RALPH E, GAUCHEL JAMES V, HELWIG GREGORY S, BRANDON, RALPH, E., GAUCHEL, JAMES, V., HELWIG, GREGORY, S.
Applicants: OWENS CORNING FIBERGLASS CORP, OWENS-CORNING FIBERGLAS CORPORATION
Application year: 1995
Main classification: D04H1
IPC codes: B29C70, C08J5, D04H1