UV-CURABLE SUPERABSORBENT COATINGS

Abstract: Articles coated with a water-resistant coating that absorbs water to provide the water-resistant effect, and desorbs water when the coating is dried, and a method of providing water resistance and corrosion resistance to articles prepared with such coatings. The coating is formed by applying a composition comprising a non- aqueous solution of a water-swellable polymer and a liquid UV-curable resin onto the surfaces of the article, and curing to form a coating comprising the superabsorbent polymer by exposing to an ultraviolet (UV) light source.

Description: UV-CURABLE SUPERABSORBENT COATINGS TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION The present invention relates to a high strength superabsorbent coating capable of rapidly absorbing water, which is suitable for coating a variety of articles requiring a water-resistant surface, including, but not limited to, reinforced or molded products, as well as reinforcing materials used in the manufacture of such products. More specifically, the coating is formed from a non-aqueous composition comprising a water-swellable polymer powder and a liquid UV-curable resin. The coating composition may further include a viscosity-modifying agent. The inventive concept also relates to articles coated with the superabsorbent coating composition, including reinforced and molded products and fibrous reinforcing materials; as well as methods of applying such coatings. The coating of this invention demonstrates a high level of water absorption, and provides an excellent spreading and coating ability when applied to a substrate. BACKGROUND OF THE INVENTION Deterioration caused by the invasion of moisture beneath the exposed surfaces of articles used in outdoor environments is a well-known problem. This deterioration includes oxidative deterioration caused by reaction of water with the surfaces of reinforcing fibers used in these articles, as well as water-induced corrosion, h marine environments, for example, the problems associated with waterlogging are particularly compounded by the salinity of the environment. The presence of salt in such aqueous environments hastens the oxidative decomposition. In non-saline environments, for example in environments having high atmospheric humidity, water-resistant coatings are necessary to protect the structures and equipment surfaces from moisture-induced decomposition. Articles affected by the deterioration described above include items having a surface exposed to high moisture or humidity. Examples of such articles include reinforced rods and cables, such as fiber optic or telecommunications cables. These telecommunications cables are often used in situations where they are buried underground or submerged in water over long periods. As such, protection f om water damage is critical to the structural integrity of these cables and to the success of the functions they are intended to perform. A telecommunications cable, for example, may include a core comprising a glass rod that acts as a stiffening or reinforcing member. This rod contributes to the rigidity of the cable. When water penetrates to contact the core element of the cable, corrosion or chemical deterioration of the cable infrastructure may result. In order to combat the problems associated with this waterlogging damage, several strategies have been devised in an attempt to provide water resistance to cables and other reinforced articles, and to protect their sensitive inner surfaces from contact with water or water vapor present in the surrounding environment. These techniques for making water- repellent articles have included wrapping the articles in a protective sheathing material; or sealing the surface to be protected. Sealing techniques may include chemically manipulating the surface layer of the article to render it resistant to water-absorption, or applying a repellent coating. The technique of covering the surface with a protective sheathing material is conventional. It includes for example, using a wrap or tape made of an impervious polymer with water-blocking ability, or treating the wrapping material with an emulsion or solution of a water-blocking polymer. The sheathing process does not require application of a chemical compound or treatment to the surface of the article; rather the protection is derived only from the coverage by the sheathing material. Coatings used to repel water traditionally have been composed of substances that are both insoluble and impenetrable to water, and therefore presented a physical barrier to encroaching moisture. Such barrier coatings have included materials such as greases or gels. In the case of cables, for example, these coatings are applied by extrusion under pressure. There are however, certain drawbacks associated with this type of coating. Greases or gels are difficult to handle because of their slipperiness, and they contribute an unpleasant feel to the coated article. This is an important factor to be considered in the manufacturing process, particularly because it affects the ease of handling of the cable during splicing operations. Greases and gels also undergo changes in viscosity at low or high temperatures. These viscosity changes may affect the freeze/thaw performance and therefore the stability of the coating. Poor performance in these respects therefore affects the stable performance of the cables. More recently, greaseless, water-resistant dry coatings have been devised which, of themselves, have some degree of water-absorbing capacity. This ability to absorb water allows the coating to absorb the moisture contacting the article, while preventing direct contact with the sensitive surfaces. The absorbent component in these dry waterblocking coatings is a dry, granulated superabsorbent polymer that swells and absorbs upon contact with water. The superabsorbent polymers are usually characterized in terms of their swell rate, swell capacity and gel strength. Traditional uses for these dry superabsorbent polymers have primarily included personal hygiene product articles, food packaging articles and chemical spill cleanup compositions, however recent experimentation has included using these dry polymers to form coatings for other articles such as reinforced cables. For example, United States Patent 5,689,601 to Hager discloses a dry waterblocking coating for reinforcing fiber articles using a powdered or granulated water-soluble dry blocking ingredient encased in one or more thin layers of a sheathing polymer. This casing restricts the degree of water absorption that can be achieved by the granular polymer, and accordingly the swell capacity of this coating is limited. Generally, either dry or fluid coatings for reinforced fibers, strands and articles, such as cables that are made from these fibrous materials, are applied to the surface of the fibrous material and then cured before further processing, if any, occurs. The means of applying coatings, in general, differs depending on whether a fluid coating is used or whether a solid particulate coating is being applied. In the case of dry coatings, the coating process using granulated water-blocking agents involves several time-consuming and labor-intensive steps that are directly related to the use of a granulated or powdered polymer. These steps include the need for one or more treatments with a binding resin, and one or more applications of powdered resin at powder-coating stations using apparatus such as a fluidized bed. Alternatively, fluid coatings containing an absorbent polymer may be used. A drawback of aqueous coatings is the time required to set and cure the coating after it is applied. Conventional coating processes which require heating, for example in ovens, or air-drying, require additional processing time. This results in increased processing costs. There exists in the art then, a need for a waterblocking coating composition for application to reinforced articles or reinforcing materials, which possesses high capacity for water absorption and a concurrent, rapid swell rate. Moreover, it is desired that such a coating be capable of curing quickly and effectively, without a costly and time-consuming process. SUMMARY OF THE INVENTION It has now surprisingly been discovered that a highly absorbent waterblocking coating having an excellent water swelling capacity and a rapid swell rate can be formed from a non-aqueous coating composition comprising a non-aqueous liquid UV-curable resin and a water-swellable polymer. The coatings containing this water-swellable polymer are capable of substantially instantaneous water absorption when exposed to aqueous environments. In one aspect, this invention includes a method of providing water resistance to the surface of an article comprising: a) preparing a non-aqueous liquid coating composition comprising a water- swellable polymer and a UV curable resin; b) applying the non-aqueous liquid coating composition to the surface of the article to form a coated surface; and c) exposing the coated surface to UV light and curing the non-aqueous liquid coating to form a water-absorbing, water-resistant coating layer comprising a water-swellable polymer on the surface of the article. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The composition of this invention is suitable for forming a water-swellable coating on the surface of articles or materials requiring surfaces that are resistant to water, and therefore protects the material underlying the surfaces that are treated with the coating. The term "article", as it is used herein, is specifically intended to include any product or material having a surface that requires a water-resistant coating to protect the underlying structure from deterioration caused by exposure to moisture. Such articles include molded composite articles, laminates, sheets, reinforcing fiber materials known in the art, and products made using one or more of these fiber materials, either collectively or dispersed within a matrix of any type. The term also includes articles manufactured using reinforced fiber products, such as structural materials or equipment. As water contacts the coated surface of the article to be protected, the coating of the invention absorbs water and swells in volume. By absorbing the water, the coating effectively wicks away the moisture and thus prevents it from contacting the inner surfaces of the protected article. As a result, the sensitive inner surfaces remain dry and are protected from waterlogging deterioration. The coatings of this invention uniquely achieve water resistance protection by absorbing water to prevent moisture penetration beneath the coating layer. The water-swellable polymer used in the coatings of this invention may be selected from any such polymer capable of forming a non-aqueous solution for use in the coating mixture, and which, upon cure, has a swell capacity and swell rate that enables absorption of water followed by desorption without loss of the polymer itself when the coating is dried. Preferably, such a polymer is in powdered or particulate form. The water-swellable polymer for use in the present invention may, for example, be selected from the group of polymers possessing the required ability to absorb and desorb quantities of water. The coatings comprising the highly absorbent water swellable polymer of the present invention would absorb significantly higher quantities of water, demonstrating swell rates of up to 75% of the dry weight or more. A desirable content of water-swellable polymer in the coating composition is in the range of from 5-70% weight. Preferably, the amount of the water-swellable polymer is from about 44% by weight to about 70% by weight based on the total weight of the composition. An example of a suitable water- swellable polymer is a polyacrylate powder commercially available under the trade name "AP80HS", from Emerging Technologies Inc. The UV-curable resin that is included in the coating composition of the present invention is suitably a liquid, non-aqueous resin that is capable of curing rapidly and effectively upon exposure to ultraviolet light. Such liquid, non-aqueous resins may be selected from UV-curable epoxides, polyethers, polyesters, polyurethanes, acrylates, and combinations thereof. Preferably, the UV-curable resin is a solvent-free polyacrylate resin that is typically liquid at room temperature. While the resin should be a liquid, its viscosity will, however, vary as a function of temperature. Preferably, the UV-curable resin is a liquid at or above ambient temperature. An example of such a resin is a polyacrylate sold under the trade name "500 VINCH" by Zeon Technologies Inc. The UN-curable resin may be included in the coating composition at a concentration of from about 30% by weight to about 95% by weight, based on the total weight of the composition. Preferably, the concentration of UV-curable resin is from about 35% by weight to about 56% by weight. The compositions used to form the coatings of the present invention further comprises one or more photoinitiators, which initiate cross-linking of the UV-curable resin during the curing process. Examples of photoinitiators include 'TRGACURE 651" or 'TRGACURE 819" which are phenyl ketone photoinitiators available commercially from Ciba Specialty chemicals. Depending on the commercial formulation of the UV- curable resin that is selected, the photoinitiator may be included in the formulation. For example, 500 VLNCH UV-curable resin is sold as a combined formulation containing a UV-curable polyacrylate and one or more photoinitiators. The coating composition may also include one or more additives conventionally known for use in surface coating materials. For example, colorants, viscosity modifying agents, surface-active agents, and lubricants may be added to the formulation. The amount of any such additives may readily be selected according to the desired effect of the additive in the composition. The coating compositions may be formed by combining the water-swellable polymer powder with the liquid UV-curable resin and the photoinitiator. Preferably, the ingredients may be combined at room temperature; however, the resin may be pre-heated before it is combined with the other ingredients. For example, the resin may be heated to a temperature ranging from room temperature up to about 150°F (66°C) before mixing. The mixture may be blended by any suitable means. In one preferred embodiment, a blend of 50% by weight of a water-swellable polymer powder, such as a polyacrylate powder, is combined with 50% of a liquid UV-curable resin, such as acrylate resin. The coatings formed from this combination were observed to provide maximum water-swell capacity. The coating composition of the invention may be applied to fibers, rovings, rods, cables and any other articles in need of water-blocking protection. The coating composition may be applied to coat these articles by conventional means, including flooding, dipping, spraying any other known means. Where the articles to be protected is a reinforcing strand or roving, the composition may suitably be applied by means including, but not limited to, dip-draw immersion followed by passage through a stripper die. Where the coating composition is to be applied to a reinforcing strand or roving, the strand or roving may be first sized with an appropriate sizing composition that is compatible with the ingredients in the coating composition. The step of sizing before applying the coating is preferred because it reduces mechanical abrasion, which can cause breakage of the fiber filaments in the strand or roving, and fuzz build-up on processing machinery. The water resistant properties of the coatings of the present invention are obtained by curing the non-aqueous composition, after it has been applied on the surface of the article, by exposure to ultraviolet (UN) light. Curing by exposure to UV light permits fast, efficient formation of the coating without the need for equipment such as ovens, which consume larger amounts of energy, and which may require longer curing times. During the curing process, crosslinking occurs between the polymer chains, thereby allowing the coating containing the polymers to form a hardened layer, which protects the underlying coated article by absorbing water as it contacts the coated surface. Suitably, at least one layer of the coating composition is applied to one or more surfaces of the article to form a coated surface. The coated surface is then exposed to UV radiation at a wavelength of from about 200 to about 450 nanometers. The frequency of radiation is selected based on the curing requirements for the UV-curable resin. For example, where 500 VLΝCH polyacrylate is used, a preferred frequency for curing the coating is about 350 nanometers. The UV radiation may be supplied by any suitable UV light source that provides radiation of the desired frequency. For example, a light box sold under the brand name "FUSION" may be used. When the coatings of the invention are applied to the surfaces of reinforcing fiber strands and cured, they demonstrate a swell capacity of up to about 75 % the initial dry weight of the water-swellable polymer. Preferably, the swell capacity for this type of application is from about 40% up to about 60% by weight, based on the initial dry weight of the water-swellable polymer. Glass fiber reinforced articles comprising the water resistant coating herein described may be used in applications where exposure to water or water vapor is likely, and where the formation of a durable, resilient, flexible coating with good waterproofing properties is desired. The following examples are representative of, but are in no way limiting as to the scope of this invention. EXAMPLES Exemplary coating compositions were prepared by combining a water-swellable polyacrylate polymer powder, AP80HS, and 500 VLNCH polyacrylate, a non-aqueous liquid UV curable resin, in various proportions. The polymer powder and UV-curable resin were combined and blended to form a homogenous dispersion. The strands of "ADVANTEX R25H" or "TYPE-E" glass strand, which are pre-sized glass rovings commercially available from Owens Corning, were passed through a bath containing the coating composition to impregnate the strands. After impregnating, the strands were passed through a stripper die of desired orifice size to control the amount of coating composition deposited on the surface of the strand. The coated strand was then cured by exposure to UV light for a period of from about 0.1 second to about 5 seconds as it was passed through an array of UV ovens. The wavelength of the ultraviolet light in the UV ovens was about 365 nanometers. Example 1 In this example, a coating composition for UV curing was formulated by mixing a blend of a superabsorbent polyacrylate and a UV-acrylate in the proportions listed below: 95% weight of 500 VLNCH UV acrylate made by Zeon Technologies; and 5% weight of AP 80HS supplied by Emerging Technologies. Example 2 In this coating composition, the same ingredients were combined as follows: 86% weight of 500 VINCH UV acrylate; and 14% weight of AP 80HS. Example 3 An exemplary coating composition was developed according to the following formulation: 75.7% weight of 500 VLNCH UV acrylate; and 24.3% weight of AP 80HS. Example 4 In this example, a coating composition for UV curing was formulated by the following formulation: 64.9% weight of 500 VLNCH UV; and 35.1% weight of AP 80HS. Example 5 In this coating composition, the ingredients were combined as follows: 56% weight of 500 VINCH UV acrylate; and 44 o / 0 weight of AP 80HS. Example 6 In this coating composition, the ingredients were combined as follows: 45% weight of 500 VINCH UV acrylate; and 45% weight of AP 80HS. Example 7 In this coating composition, the ingredients were combined as follows: 50% weight of 500 VINCH UV acrylate; and 50% weight of AP 80HS. Example 8 In this coating composition, the ingredients were combined as follows: 30% weight of 500 VINCH UV acrylate; and 70% weight of AP 80HS. Example 9 The coatings of Examples 1 - 8 were investigated to determine their swell capacity in water when applied to reinforcing fiber materials. Strands of ADVANTEX R25H and TYPE-E glass reinforcing fibers were coated with the coating composition of each of Examples 1 - 8. The glass was sized with an aminosilane before the coating was applied. For each sample, the swell capacity, determined as the percentage swell over time calculated based on the total weight of coating and fiber, was measured. The results obtained are included in Table 1 : TABLE 1 Superabsorbent polyacrylate, Emerging Technologies Inc. UV acrylate, by Zeon Technologies Inc. Swell capacity was measured as the percentage change in weight of the coated strand after 1 minute. The observed results indicate that a significant amount of water absorption could be achieved, for example where the proportions of either the superabsorbent polymer or the UV curable polymer are in a concentration of from about 30% by weight to about 70% by weight, respectively. Having described and exemplified the invention, it should be appreciated that the following claims are not to be so limited but are to be afforded a scope commensurate with the wording of each element of the claim and equivalents thereof.

Claims: WHAT IS CLAIMED IS: 1. An article coated at least in part with a coating formed by curing a composition comprising a water-swellable polymer and a liquid UV-curable resin by exposure to UN light. 2. An article according to claim 1, wherein the coating absorbs water to provide a water-resistant effect and desorbs water when the coating is dried. 3. An article according to claim 1, wherein the water-swellable polymer, after curing, absorbs up to about 75% of its dry weight in water when immersed in an aqueous environment. 4. An article according to claim 1 , wherein the water-swellable polymer comprises a polyacrylate polymer. 5. An article according to claim 1, wherein the liquid UV-curable resin comprises an acrylate resin. 6. An article according to claim 1, which is a reinforced fiber material. 7. An article according to claim 6, further comprising an aminosilane sizing beneath the coating. 8. An article according to claim 1, which is a composite article. 9. An article according to claim 1, selected from the group consisting of tapes, mats, fabrics, rovings, fibrous strands, laminates, sheets, rods and cables. 10. An article according to claim 1, selected from the group consisting of molded articles, woven fabrics, scrims, wood and paper products, and construction materials. 11. A non-aqueous coating composition suitable for forming a coating that absorbs and desorbs water, comprising a water-swellable polymer and a liquid UV-curable resin. 12. The non-aqueous coating composition of claim 11, wherein the water-swellable polymer is a powdered polyacrylate. 13. The non-aqueous coating composition of claim 11 , wherein the liquid UV-curable resin is an acrylate. 14. The non-aqueous coating composition of claim 11, further comprising a photoinitiator. 15. The non-aqueous coating composition of claim 11 , wherein the proportion of water-swellable polymer in the composition is from about 30% by weight to about 70% by weight, and the proportion of the UV-curable resin in the composition is from about 30%) by weight to about 70% by weight. 16. A method of providing water resistance to the surface of an article comprising: a) preparing a non-aqueous liquid coating composition comprising a water- swellable polymer and a liquid UV curable resin; b) applying the non-aqueous liquid coating composition to the surface of the article to form a coated surface; and c) exposing the coated surface to UV light and curing the non-aqueous liquid coating composition to form a water-absorbing, water-resistant coating layer on the surface of the article. 17. The method of claim 16, wherein the step of applying the non-aqueous liquid coating composition to the surface of the article comprises contacting the non-aqueous liquid coatmg composition with the surface of the article to form a layer of non-aqueous liquid coating over the entire surface of the article. 18. The method of claim 16, wherein the UV light is of a wavelength of from about 200 nanometers to about 450 nanometers. 19. A reinforcing fiber material formed according to the method of claim 16. 20. A reinforcing fiber according to claim 19, which is sized with an aminosilane before the coating is applied. 21. A composite article formed according to the method of claim 16. 22. A reinforced fiber product formed according to the method of claim 16. 23. An article having at least one surface covered by a water-resistant UV-curable coating comprising: a silane; a water-swellable polymer; and a liquid UV curable resin.

Inventors: CARTER CURTIS, CARTER, CURTIS
Applicants: CARTER CURTIS, OWENS CORNING FIBERGLASS CORP, CARTER, CURTIS, OWENS CORNING
Application year: 2001
Main classification: C09D151
IPC codes: C08F265, C08F290, C09D5, C09D133, C09D151, D06M13, D06M15, D21H19, D21H25