MULTIFILAMENT REINFORCING ARTICLE

Abstract: A multifilament reinforcing article which comprises fibers coated and impregnated with at least a partially cured, a moisture reduced residue derived from an aqueous chemical coating composition in which the major polymeric component is an elastomeric polymer. The coated and impregnated fibers are bound with a polymeric film-forming binder in the form of a tape, wire or other shape retaining arrangement in which the fibers are substantially parallel.

Description: MULTIFILAMENT REINFORCING ARTICLE BACKGROUND OF THE INVENTION Many coatings and treatments for glass and other fibers have been developed over the years for use in varying applications of such fibers, for example for use with polymers where the coated fibers are incorporated into, encapsulated or surrounded by the polymer. Coatings and chemically treated fiber bundles are described in U.S. Patents 4,663,231; 4,762,750 and 4,762,751, among others. One such use for such coated fibers is as reinforcement or support in applications requiring high tensile strength, such as in the ' reinforcement of fiber optic cables and storage tanks for liquids. SUMMARY OF THE INVENTION This invention provides multifilament reinforcing articles made from coated strands of sized fibers which are bound together in the form of tape, wire or other easily handled shape so as to enable them to be placed easily and economically around the item to be reinforced to provide tensile reinforcement. The tensile strength of the reinforcing article is approximately the sum of the tensile strengths of the individual fibers, providing a great deal of strength in a relatively small, convenient package. These reinforcing articles are preferably made from glass fibers which are sized in the conventional manner and coated and impregnated usually as flexible bundles of fibers with an aqueous, at least partially cured elastomeric coating, and then bound in the desired shape by the use of a chemical binder. The binder is preferably an elastomeric polyurethane. DETAILED DESCRIPTION OF THE INVENTION The invention is particularly applicable to high modulus, low elongation fibers, i.e., fibers having a modulus of elongation of at least 7 x 10° psi and an elongation at break of at most 5 percent, so that while other fibers are suitable for use in this invention, glass fibers are the most preferred. Suitable glass fibers may be made from formulations such as D-glass, S-glass or others, though the most commonly used is E-glass; typical formulations of such glass fibers are disclosed in The Manufacturing Technology of Continuous Glass Fibres. Library of Congress number 72-97429, by K. L. Loewenstein, Elsevier Scientific Publishing, 1973, at page 29. Immediately after formation, the fibers are treated with a sizing material which serves to protect them from interfilament abrasion and from abrasion by contact with guide rods and other processing apparatus. While the many sizes known in the art may be used on the fibers to be employed in this invention, non-starch sizes are preferred. The multifilament reinforcing articles of the invention are provided by processing the sized and then coated bundles of fibers to form an elongated, substantially shape-retaining configuration, such as a tape, a product in the shape of wire or cable or other suitable shape, with the use of a chemical binder to hold the fibers in the desired shape. Any method known to those skilled in the art can be used to form such articles, for example, processing a plurality of coated glass fiber strands with a binder between calendaring rollers or in a suitable die. The term "tape" as used herein means a predominantly non-metallic, relatively narrow fabric or flexible strip or band. The term "wire" as used herein means a predominantly non-metallic, relatively rounded and flexible, thread, slender rod or cable. Neither definition requires that the article be adhesive or restrict it from so being. As used herein, the term "size and sizing" refer to the aqueous composition applied to the fibers immediately after formation. The term "coating" refers to the aqueous composition applied secondarily, after the sizing. The term "binder" refers to the chemical added to the coated strands just before they are fed into a die or calendaring machine to be made into tape, wire, or the like. The aqueous sizing composition is commonly applied by sprayers, rollers, belts, or the like. The sized glass fibers generally have between about 0.05 and 5 percent of sizing composition based on the weight of the glass fiber. Examples of the sizing composition and the manner of application of the size and coating to the sized glass fibers, as well as the types of fibers used, can be found in U.S. Patents 4,663,231; 4,762,750 and 4,762,751. An example of a suitable non-starch sizing is disclosed in U.S. Patent 4,390,647. The aqueous sizing composition usually comprises a hydrophilic reducing agent such as a coupling agent and a protectant which can be a glass fiber lubricant or a glass fiber film former. This aqueous sizing may include silane coupling agents, lubricants, antifoams, antistatic agents, emulsifierε, bactericides or any other ingredient(s) known in the art to be useful in sizing fibers, though preferably not starch, in addition to water. The sized glass fibers may be gathered into bundles comprising a plurality of individual fibers, generally from 200 to more than 3000. The bundles are usually wound onto a forming package and the sizing is dried at room temperature or by oven heating prior to coating. The sized fibers for use in the present invention are then coated and impregnated with a moisture-reduced residue of an aqueous coating composition which contains, as the major polymeric component, one or more elastomeric polymers and which is at least partially cured. Among the elastomeric polymers useful in the aforesaid coating composition are polyurethanes, silicones, fluororubbers, polysulfide polymers, polyethers, interpolymers of ethylene with one or more polar comonomers and acrylic polymers. The compositions are made at least partially curable by inclusion of functional groups in at least one of the elastomeric polymers present which makes that polymer self-crosslinking as is the case when a polyurethane or an ethylene-acrylic acid copolymer is used. Alternatively, there may be included in the composition a separate crosslinking agent such as a melamine-formaldehyde or phenol-formaldehyde resin, or an epoxy resin. The composition may also include optional components such as plasticizer, microcrystalline wax, etc. Examples of such coating compositions are described in U.S. Patents 4,663,231; 4,762,750 and 4,762,751, and U.S. patent application nos. 07/900,034, filed June 17, 1992 and 07/934,133, filed August 21, 1992. These coatings are all aqueous when applied, i.e., have components which are water dispersible, soluble or emulsifiable. The preferred compositions for use in the invention include compositions comprising: (a) Interpolymers of ethylene with one or more polar comonomers, along with crosslinking resinous material and a diene-containing elastomer in an amount sufficient to effect partial curing of the coating. Such compositions and specific examples of the aforesaid components are described in U.S. Patent 4,663,231. (b) Coating compositions containing an elastomeric polymer such as an ethylene-containing interpolymer or a polyurethane as described in U.S. Patent 4,762,750. The coating further has a crosslinking material which may be self crosslinkable or crosslinkable with the polymer. (c) Compositions described in U.S. Patent 4,762,751 which comprise a polyurethane and a non-sulfur vulcanizing crosslinking material. The polyurethane may be internally softened, internally plasticized or unplasticized and unsoftened. When the polyurethane is unsoftened or unplasticized, a softening agent is used. (d) Compositions described in U.S. patent application no. 07/900,034 which are aqueous coating compositions containing a self- crosslinking acrylic polymer and a crosslinkable ethylene-acrylic acid copolymer which are present in ranges of between about 30 and 90 weight percent and about 5 and 30 weight percent respectively, before dilution with water. The amount of water in the composition is an amount to provide the composition with between 10 and 50 percent solids before drying. The coating may also include an elastomeric curable polymer such as a polyurethane. The coating may also include a microcrystalline wax which may be oxidized and/or a water soluble dye in an amount sufficient to impart a color to the residue on the fibers. The predominant component, besides water, is the acrylic polymer emulsion of acrylic homopolymers and copolymers including copolytners with acrylamide and methylol acrylamide. The acrylic emulsion is preferably of the self-crosslinking type and preferably anionic or non-ionic. Though the acrylic emulsion is self-crosslinking, if a faster crosslinking rate is desired or less than optimal conditions exist, a catalyst may be added to speed the reaction rate. The reactive acrylic monomers include acrylamide and methylol acrylamide which crosslink upon the addition of heat to yield the acrylic polymer and water. The acrylic is characterized by the temperature at which the torsional modulus of an air dried film is 300 kg/cm 2 , referred to as T300, and which is a relative measure of stiffness. A T300 of about 22°C is considered soft while higher numbers indicate more stiff acrylics. The acrylics which may be used in the practice of this invention have a T300 which may range from about -50 to about +35. The use of a low T300 acrylic will result in a relatively less stiff product which may also be somewhat tacky. The addition of a polyurethane can reduce this tackiness yet also detracts from stiffness. Examples of self-crosslinking acrylic emulsions are the family of Rhoplex® emulsions commercially available from the Rohm & Haas Company. A specific example is Rhoplex® TR-407 which is anionic and has a T300 of +30, is milky white in appearance, has 45.5 percent solids, a Brookfield LVF viscosity at 25°C of 30 cps (#1 spindle, 60 RPM), a pH of 3.5, and a density of 8.9 lb/gal. Another example is Rhoplex® HA-8 which is nonionic, has a T300 of -14, is milky white in appearance, has 45,5 percent solids, a Brookfield LVF viscosity of 550 cps (#3 spindle, 60 RPM), a pH of 3.0, and a density of 8.7 lb/gal. Among the preferred ethylene-acrylic acid (EAA) copolymers which are employed in the compositions described in U.S. Patent application no. 07/900,034 are copolymers having a molecular weight of about from 5,000 to 10,000, a hardness (shore D) of from about 42 to 48, a vicat softening point of about 104 to 115, a melt index of from about 300 to 1300 g/10 min. and a density of about 0.96 gm/cc at 25°C. Specific examples of such copolymer dispersions are Michem® Prime 4990 or Michem® Prime 4983HS available from Michelman Inc. of Cincinnati, Ohio, which are white in color and have a total solids content of approximately 20 to 38 percent, a Brookfield viscosity of about 100 to 600, and a surface tension of about 44 to 49 dynes/cm, and weigh about 8.22 lbs/gal. The dispersible polymer in the two Michem® Prime formulations are Primacor® 5990 and 5980, respectively. (e) Aqueous compositions containing at least one polyurethane and at least 15 weight percent on a non-aqueous basis of one or more high boiling point plasticizers as described in U.S. patent application no. 07/934,133. The polyurethane component is an elastomeric curable polyurethane or polyurethane-urea type polymer. These materials generally have a glass transition temperature of around 0°C or less. Suitable polyurethane polymers are described in U.S. Patents 4,143,091; 4,208,494; 4,208,495; 4,066,591 and 4,762,751. The preferred polyurethane is that sold as Witcobond® W-290H, which is milky white in appearance, aliphatic in type with a 65 percent solids level and with a particle size of around 5 microns, a pH at 25°C (77°F) of 7.5, a viscosity as measured by Brookfield LVF in cps of 200 and surface tension of 42 dynes/cm. The film properties of the 290H material, when cured with 6.5 parts of epoxy resin dispersion like Witcobond® XW for 100 parts of urethane latex, are: 4500 psi tensile strength, 720 percent elongation and moduli of 250 psi at 100%, 540 psi at 300% and 1550 psi at 500%. The amount of polyurethane can range from about 45 to about 80 weight percent of the non-aqueous portion of the impregnating coating composition. Also present in these aqueous coating composition is a plasticizer having a sufficiently high boiling point such that it will not become volatile during the impregnation of the bundles of fiber, e.g., plasticizers with boiling points above 225°C (437 β F) at a pressure of 10 millimeters of mercury (mmHg). Examples of such plasticizers are Santicizer® 160 produced by Monsanto Corporation which is a clear oily liquid having a boiling point of 240°C (464°F) at 10 mmHg a specific gravity of 1.12, diisononyl phthalate (DINP) (sold as PX-109 by Aristech Chemical Corporation),and the mixed hexyl, octyl and decyl ester of 1,2,4-Benzenetricarboxylic acid sold as PX-336 by Aristech Chemical Corp. The aqueous coating compositions used to coat and impregnate the fibers may be prepared by adding the components to the appropriate amount of water with any emulsifiers or other additives such as flame retardants, dye or wax. The bundle of fibers or strand is coated, for example, by dipping in a bath, or other conventional methods such as those described in U.S. Patent 4,663,231. The coated strand may be partially dried in air at room temperature or alternatively in a furnace or oven to speed the curing process. Preferably, the drying is conducted at a temperature in the range of about 400 β F to 600°F (204°C to 315°C) for a time of about 10 to about 60 seconds or any equivalent time/temperature relationship to accomplish a similar degree of moisture reduction and curing. The strand may be "opened up" just before entering the secondary treating composition bath by passing it over a bar or other spreading device which acts to separate the individual fibers from one another. This spreading of the fibers from one another results in a more thorough impregnation of the strand with the coating. The amount of the coating on the strand is defined as the dip pick-up or DPU, which is the coated strand weight minus the uncoated strand weight, then divided by the uncoated strand weight. Multiplying the resultant figure by 100 results in %DPU. The DPU of the coated bundles or strands is in a range of about 5 to about 20% for a single pass through the coating bath and drying step. The strands may ultimately have a greater amount of coating than 20% by passing them through the bath a number of times. The binder which holds the coated glass fiber strands together as a reinforcing article such as tape or wire is an epoxy resin, polyester, ethylene-acrylic acid copolymer, acrylic polymer, polyurethane, polyolefin, pol (vinyl alcohol), poly(vinyl chloride), poly(vinyl acetate), ethylene-vinyl acetate copolymer or any other polymeric film-forming material known in the art which is compatible with the ingredients of the particular coating used. The binder may be aqueous but is not required to be so. The choice of binder is usually dictated by the composition of the coating, i.e. the binder must be compatible with the coating. If a strand coated predominately with polyurethane is to be used, for example, the binder is preferably a polyurethane and in most cases the same or a similar polyurethane can be employed. The various polyurethanes described above can be utilized and the preferred polyurethane for use as the binder is that sold as Witcobond® W-290H, also described above. Among the other polymeric film-forming binder materials for use in making the reinforcing article are ethylene vinyl acetate copolymers described in U.S. Patent 4,663,231. A suitable ethylene-vinyl acetate copolymer is that commercially available from Air Products and Chemicals, Inc. in an emulsion form under the trade designation Airflex® 410 vinyl acetate/ethylene copolymer emulsion. Ethylene-acrylic acid copolymers and other acrylic polymers also have been described above and may be employed as the chemical binder. The coated fibers may be made into a tape by any method known to those skilled in the art, such as that shown in U.S. Patent 3,755,061. One method is, for example, to combine a plurality of sized, coated glass fiber strands between calendaring rollers with the addition of the binder. This may be done, for example, at a temperature of about 350°F to 600°F (177°C to 315 β C). The time for the binder and strands to be between the rollers is short. What is required is a contact time at the temperature such that the binder cures to some degree in contact with the strands. The strands and binder can be further cured by heat treating if desired. Another method of producing tape intended to be encompassed by this invention, is to combine the sized glass fibers with the coating and then feed the coated, sized glass fibers immediately into the calendaring rollers. By going directly from the step of coating the fibers to producing tape, storage of coated fibers and any possible damage to the coated fibers in winding, transport, and storage can be eliminated. In this method, either a binder is added directly to the coating bath, or an excess of one of the regular coating components which meets the above definition of a binder is added to the coating bath. The coated fibers may be made into the shape of wire in a similar way but instead of calendaring rollers the strands are brought together through a die of the desired diameter where they are coated with binder. The strands then pass through an oven at the above temperature and then through yet another die while still hot. The wire configuration is considerably stiffer than the tape configuration. Other configurations can be used so long as they are sufficiently shape-retaining to provide bound fibers in a substantially parallel arrangement and permit easy handling compared to flexible bundles of filaments. The tape, wire or other shaped article made in accordance with the invention may be used to reinforce objects by applying it to the object. A tape configuration may be placed around, for example, a fiber optic cable, either by bending it around the cable with the seam on one side or by bending it around the cable in a spiral or helix configuration. The wire configuration may be wound around the outside of objects to be reinforced, for example, storage tanks for liquids. The wire, tape or other configuration makes the fibers easy to handle and allows rapid application to the object to be reinforced. The following is an example of the practice of this invention: glass fibers were produced and sized with an aqueous sizing in which the non-volatile portion contained 48 parts by weight of a polyoxyalkylene polyol available under the trade designation Pluracol® V-10, 9.1 parts by weight of a silane coupling agent available under the trade designation A-1108 from the Union Carbide Corporation, and 4.5 parts by weight of a polyamine lubricant commercially available under the trade designation Emery® 6717, which had been treated with acetic acid. An alternative sizing is shown in U.S. Patent No. 4,762,751 at column 16, lines 19-48. The sized fibers were dipped into an aqueous coating bath and dried in order to coat them. The coating bath contained polyurethane polymer (Witco W-290H), butyl benzyl phthalate (Sanitizer 160), polyoxyethylene sorbitan monolaurate (Tween 21), aqueous dispersion of polyurethane polymer (Baybond XW 110), aqueous epoxy dispersion (Witco XW), the composition and preparation of which are described in U.S. Patent 4,762,751 at column 16, line 60 to column 17 line 8, except that about 138 grams of a microcrystalline wax (Polymekon SPPW-40 microcrystalline wax, which is a hydrocarbon water dispersion with a 40 percent solids) was added. The impregnated coated fiber bundles were passed through an oven to reduce the moisture content and cure the impregnating coating. The temperature of the oven was in the range of about 490°F (254°C) to 530°F (277°C) and the line speed was around 200 to 250 feet per minute (60 to 76 meters/min) through the oven. The coated fibers were made into a tape configuration by feeding the coated, dried fiber strands into a bath of Witcobond® 290-H polyurethane binder in a simple dip arrangement. The strands were separated from each other in the bath in order to provide more complete wet out. The strands were guided together to form a 0.75 inch (19 mm) wide band. The binder covered strands next entered a thermal calendaring machine which was held at a temperature of about 480°F (249°C). The heated contact drum dried and cured the binder to form a finished tape which was produced at a speed of about 18 feet per minute. The tape released cleanly from the Teflon® coated calendar belt and drum and did not require the use of a release paper. The tape was air cooled and then wound on spools. The final product was 0.75 inches (19 mm) wide by 0.02 inches (0.5 mm) thick, though tape of other dimensions may of course be produced. The tape exhibited excellent tensile strength, and was easily applied to optical cables as reinforcement. An alternative means of producing tape is by using a commercially available slashing (coating) machine such as the Callaway Slasher Model 51 produced by the West Point Foundry and Machine Company of West Point, Georgia. This machine can coat the strands and align them before winding them around four 18 inch (45.7 cm) diameter heated drums, giving a contact time between the tape and drum of about 15 seconds per drum. The first two drums are Teflon® coated and the second two are stainless steel. The tape travels approximately 3/4 of the way around each drum sequentially in a manner such that both sides of the tape contact a drum, and it is then wound on a spool.

Claims: THEREFORE, WE CLAIM: 1. A multifilament reinforcing article comprising sized fibers, coated and impregnated with an at least partially cured chemical coating composition in which the major polymeric component is an elastomeric polymer, and bound together in an elongated, substantially parallel and shape retaining arrangement by a polymeric film-forming chemical binder. 2. The multifilament reinforcing article of claim 1 which is in the configuration of tape. 3. The multifilament reinforcing article of claim 1 which is in the configuration of wire. 4. The multifilament reinforcing article of claim 1 in which said coating composition comprises an interpolymer of ethylene with one or more polar comonomers. 5. The multifilament reinforcing article of claim 1 in which said coating composition comprises a polyurethane. 6. The multifilament reinforcing article of claim 1 in which said coating composition comprises a self-crosslinking acrylic polymer. 7. The multifilament reinforcing article of claim 1 in which said coating composition comprises an ethylene-acrylic acid copolymer. 8. The multifilament reinforcing article of claim 1 in which said polymeric, firm-forming binder is a polyurethane. 9. The multifilament reinforcing article of claim 1 wherein said chemical coating composition incorporates said binder. 10. The multifilament reinforcing article of claim 1 wherein said coating composition and said binder each comprises substantially the same polyurethane.

Inventors: GIRGIS MIKHAIL M, RAU ROBERT B, GIRGIS, MIKHAIL, M., RAU, ROBERT, B.
Applicants: PPG INDUSTRIES INC, PPG INDUSTRIES, INC.
Application year: 1993
Main classification: D02G3
IPC codes: D02G3