CATIONICALLY CHARGED COATING ON GLASS FIBERS

Abstract: A glass fiber having a cationically charged coating thereon, the coating including a functionalized cationic polymer crosslinkable by heat, in which the functionalized cationic polymer has been crosslinked by heat after being coated onto the glass fiber. Also provided is a fibrous filter including glass fibers having a cationically charged coating thereon, the coating including a functionalized cationic polymer crosslinkable by heat, in which the functionalized cationic polymer has been crosslinked by heat after being coated onto the glass fibers. Further provided is a method of preparing a fibrous filter. The method involves providing a fibrous filter which includes glass fibers, passing a solution of a functionalized cationic polymer crosslinkable by heat through a fibrous filter under conditions sufficient to substantially coat the fibers with the functionalized cationic polymer, and treating the resulting coated fibrous filter with heat at a temperature and for a time sufficient to crosslink the functionalized cationic polymer present on the glass fibers. By way of example, the functionalized cationic polymer may be an epichlorohydrin-functionalized polyamine or an epichlorohydrin-functionalized polyamido-amine.

Description: CATIONICALLY CHARGED COATING ON GLASS FIBERS Background of the Invention The present invention relates to filter materials. More particularly, the present invention relates to charge-modified filters. Charge-modified filters are known in the art. They typically consist of microporous membranes or involve the use of materials which are glass fibers, blends of glass fibers and cellulose fibers, or blends of cellulose fibers and siliceous particles. Charge modification generally is accomplished by coating the membrane or at least some of the fibers with a charge-modifying agent and a separate crosslinking agent in order to ensure the durability of the coating. While microporous membranes generally are capable of effective filtration, flow rates through the membrane typically are lower than for fibrous filters. Moreover, microporous membranes generally have higher back pressures during the filtration process than do fibrous filters. Accordingly, there is a need for fibrous filters having effective filtration capabilities for charged particles. There also is a need for fibrous filters composed of glass fibers, without a requirement for a precipitation step, a crosslinking agent, or the presence of cellulosic fibers or siliceous particles. Summary of the Invention The present invention addresses some of the difficulties and problems discussed above by providing a glass fiber having a cationically charged coating thereon. The coating includes a functionalized cationic polymer which has been crosslinked by heat. That is, the functionalized cationic polymer has been crosslinked by heat after being coated onto the glass fiber. By way of example only, the functionalized cationic polymer may be an epichlorohydrin-functionalized polyamine or an epichlorohydrin-functionalized polyamido- amine. The present invention further provides a fibrous filter which includes glass fibers having a cationically charged coating thereon. The coating includes a functionalized cationic polymer which has been crosslinked by heat; in other words, the functionalized cationic polymer has been crosslinked by heat after being coated onto the glass fibers. Again, the functionalized cationic polymer may be an epichlorohydrin-functionalized polyamine or an epichlorohydrin-functionalized polyamido-amine. The present invention also provides a method of preparing a fibrous filter. The method involves providing a fibrous filter which includes glass fibers, passing a solution of a functionalized cationic polymer crosslinkable by heat through the fibrous filter under conditions sufficient to substantially coat the fibers with the functionalized cationic polymer, and treating the resulting coated fibrous filter with heat at a temperature and for a time sufficient to crosslink the functionalized cationic polymer present on the glass fibers. The functionalized polymer may be an epichlorohydrin-functionalized polyamine or an epichlorohydrin-functionalized poiyamido-amine. The present invention provides a number of advantages over the materials known previously. First, the method of the present invention does not require the use of a separate or secondary precipitating or crosslinking agent. Second, the method of the present invention may be utilized in a continuous process on roll goods. Third, a cellulosic component is not required. Other advantages, of course, will be apparent to those having ordinary skill in the art. Detailed Description of the Invention As used herein, the terms "cationically charged" in reference to a coating on a glass fiber and "cationic" in reference to the functionalized polymer mean the presence in the respective coating and polymer of a plurality of positively charged groups. Thus, the terms "cationically charged" and "positively charged" are synonymous. Such positively charged groups typically will include a plurality of quaternary ammonium groups, but they are not necessarily limited thereto. The term "functionalized" is used herein to mean the presence in the cationic polymer of a plurality of functional groups, other than the cationic groups, which are capable of crosslinking when subjected to heat. Thus, the functional groups are thermally crosslinkable groups. Examples of such functional groups include epoxy, ethylenimino, and episulfido. These functional groups readily react with other groups typically present in the cationic polymer. Such other groups typically have at least one nucleophile and are exemplified by amino, hydroxy, and thiol groups. It may be noted that the reaction of a functional group with another group often generates still other groups which are capable of reacting with functional groups. For example, the reaction of an epoxy group with an amino group results in the formation of a β-hydroxyamino group. Thus, the term "functionalized cationic polymer" is meant to include any polymer which contains a plurality of positively charged groups and a plurality of functional groups which are capable of being crosslinked by the application of heat. Particularly useful examples of such polymers are epichlorohydrin-functionalized polyamines and epichlorohydrin-functionalized polyamido-amines. Both types of polymers are exemplified by the Kymene ® resins which are available from Hercules Inc., Wilmington, Delaware. Other suitable materials include cationically modified starches, such as RediBond, from National Starch. As used herein, the term "thermally crosslinked" means the coating of the functionalized cationic polymer has been heated at a temperature and for a time sufficient to crosslink the above-noted functional groups. Heating temperatures typically may vary from about 50°C to about 120°C. Heating times in general are a function of temperature and the type of functional groups present in the cationic polymer. For example, heating times may vary from less than a minute to about 60 minutes or more. The term "zeta potential" (also known as "electrokinetic potential") is used herein to mean the difference in potential between the immovable liquid layer attached to the surface of a solid phase and the movable part of the diffuse layer in the body of the liquid. The zeta potential may be calculated by methods known to those having ordinary skill in the art. See, by way of example, Robert J. Hunter, "Zeta Potential in Colloid Science," Academic Press, New York, 1981; note especially Chapter 3, "The Calculation of Zeta Potential," and Chapter 4, "Measurement of Electrokinetic Parameters." In the absence of sufficiently high concentrations of electrolytes, positively charged surfaces typically result in positive zeta potentials and negatively charged surfaces typically result in negative zeta potentials. As stated earlier, the present invention provides a glass fiber having a cationically charged coating thereon. The coating includes a functionalized cationic polymer crosslinkable by heat, in which the functionalized cationic polymer has been crosslinked by heat after being coated onto the glass fiber. Particularly useful examples of functionalized cationic polymers are epichlorohydrin- functionalized polyamines and epichlorohydrin-functionalized polyamido-amines. Both types of polymers are exemplified by the Kymene ® resins which are available from Hercules Inc., Wilmington, Delaware. Other suitable materials include cationically modified starches, such as RediBond, from National Starch. Desirably, the functionalized cationic polymer will be an epichlorohydrin-functionalized polyamine or an epichlorohydrin-functionalized poiyamido- amine. The present invention further provides a fibrous filter including glass fibers having a cationically charged coating thereon. The coating is the functionalized cationic polymer crosslinkable by heat described above. in general, the fibrous filter will contain at least about 50 percent by weight of glass fibers, based on the weight of all fibers present in the filter. In some embodiments, essentially 100 percent of the fibers will be glass fibers. When other fibers are present, however, they generally will be cellulosic fibers, fibers prepared from synthetic thermoplastic polymers, or mixtures thereof. Sources of cellulosic fibers include, by way of illustration only, woods, such as softwoods and hardwoods; straws and grasses, such as rice, esparto, wheat, rye, and sabai; canes and reeds, such as bagasse; bamboos; woody stalks, such as jute, flax, kenaf, and cannabis; bast, such as linen and ramie; leaves, such as abaca and sisal; and seeds, such as cotton and cotton linters. Softwoods and hardwoods are the more commonly used sources of cellulosic fibers; the fibers may be obtained by any of the commonly used pulping processes, such as mechanical, chemimechanical, semichemical, and chemical processes. Examples of softwoods include, by way of illustration only, longleaf pine, shortleaf pine, loblolly pine, slash pine, Southern pine, black spruce, white spruce, jack pine, balsam fir, douglas fir, western hemlock, redwood, and red cedar. Examples of hardwoods include, again by way of illustration only, aspen, birch, beech, oak, maple and gum. Examples of thermoplastic polymers include, by way of illustration only, end-capped polyacetals, such as poly(oxymethylene) or polyformaldehyde, poly(trichloroacetaldehyde), poly(n-valeraldehyde), poly(acetaldehyde), and poly(propionaldehyde); acrylic polymers, such as polyacrylamide, poly(acrylic acid), poly(methacrylic acid), poly(ethyl acrylate), and poly(methyl methacrylate); fluorocarbon polymers, such as poly(tetrafluoroethylene), per- fluorinated ethylene-propylene copolymers, ethylene-tetrafluoroethylene copolymers, poly(chlorotrifluoroethylene), ethylene-chlorotrifluoroethylene copolymers, poly(vinylidene fluoride), and poly(vinyl fluoride); polyamides, such as poly(6-aminocaproic acid) or poly(ε- caprolactam), poly(hexamethylene adipamide), poly(hexamethylene sebacamide), and poly(11-aminoundecanoic acid); polyaramides, such as poly(imino-1 ,3-phenylenei- minoisophthaloyl) or poly(m-phenylene isophthalamide); parylenes, such as poly-p-xylylene and poly(chloro-p-xylylene); polyaryl ethers, such as poly(oxy-2,6-dimethyl-1 ,4-phenylene) or poly(p-phenylene oxide); polyaryl sulfones, such as poly(oxy-1 ,4-phenylenesulfonyl-1 ,4- phenyleneoxy-1 ,4-phenylene-isopropylidene-1 ,4-phenylene) and poly(sulfonyl-1 ,4- phenyleneoxy-1 ,4-phenylenesulfonyl-4,4'-biphenylene); polycarbonates, such as poly- (bisphenol A) or poly(carbonyldioxy-1 ,4-phenyleneisopropylidene-1 ,4-phenylene); polyesters, such as poly(ethylene terephthalate), poly(tetramethylene terephthalate), and poly(cyclohexylene-1 ,4-dimethylene terephthalate) or poly(oxymethylene-1 ,4- cyclohexylenemethyleneoxyterephthaloyl); polyaryl sulfides, such as poly(p_-phenylene sulfide) or poly(thio-1 ,4-phenylene); polyimides, such as poly(pyromellitimido-1 ,4- phenylene); polyolefins, such as polyethylene, polypropylene, poly(l-butene), poly(2- butene), poly(l-pentene), poly(2-pentene), poly(3-methyl-1-pentene), and poly(4-methyl-1- pentene); vinyl polymers, such as poly(vinyl acetate), poly(vinylidene chloride), and poly(vinyl chloride); diene polymers, such as 1 ,2-poly-1 ,3-butadiene, 1 ,4-poly-1 ,3-butadiene, polyisoprene, and polychloroprene; polystyrenes; copolymers of the foregoing, such as acrylonitrile-butadiene-styrene (ABS) copolymers; and the like. When fibers other than glass fibers are present in the fibrous filter, they desirably will be cellulosic fibers, fibers prepared from thermoplastic polyolefins, or mixtures thereof. Examples of thermoplastic polyolefins include polyethylene, polypropylene, poly(l-butene), poly(2-butene), poly(1 -pentene), poly(2-pentene), poly(3-methyl-1 -pentene), poly(4-methyl- 1 -pentene), and the like. In addition, such term is meant to include blends of two or more polyolefins and random and block copolymers prepared from two or more different un- saturated monomers. Because of their commercial importance, the most desirable polyolefins are polyethylene and polypropylene. The present invention further provides a method of preparing a fibrous filter. The method involves passing a solution of a functionalized cationic polymer crosslinkable by heat through a fibrous filter which includes glass fibers under conditions sufficient to substantially coat the fibers with the functionalized cationic polymer, and treating the resulting coated fibrous filter with heat at a temperature and for a time sufficient to crosslink the functionalized cationic polymer present on the glass fibers. In general, the solution of the functionalized cationic polymer will be an aqueous solution containing from about 0.1 to about 10 percent by weight, based on the weight of the solution, of the functionalized cationic polymer. For example, the solution may contain from about 0.1 to about 5 percent by weight of the functionalized cationic polymer. As another example, the solution may contain from about 0.1 to about 1 percent by weight of the functionalized cationic polymer. In some embodiments, the aqueous solution of the functionalized cationic polymer may contain minor amounts of polar organic solvents which are soluble in or miscible with water. If present, such solvents generally will constitute less that 50 percent by volume of the liquid phase. For example, such solvents may constitute less than about 20 percent by volume of the liquid phase. Examples of such solvents include, by way of illustration only, lower alcohols, such as methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutanol, and f-butyl alcohol; ketones, such as acetone, methyl ethyl ketone, and diethyl ketone; dioxane; and N,N-dimethylformamide. Depending upon the functionalized cationic polymer, it may be either desirable or necessary to adjust the pH of the aqueous solution containing the polymer. For example, aqueous solutions of epichlorohydrin-functionalized polyamines or epichlorohydrin- functionalized polyamido-amines desirably have pH values which are basic or slightly acidic. For example, the pH of such solutions may be in a range of from about 6 to about 10. The pH is readily adjusted by means which are well known to those having ordinary skill in the art. For example, the pH may be adjusted by the addition to the polymer of a dilute solution of a mineral acid, such as hydrochloric acid or sulfuric acid, or an alkaline solution, such as a solution of sodium hydroxide, potassium hydroxide, or ammonium hydroxide. The solution of the functionalized cationic polymer may be passed through the fibrous filter by any means known to those having ordinary skill in the art. For example, the solution may be "pulled" through the filter by reducing the pressure on the side of the filter which is opposite the side against which the solution has been applied. Alternatively, the solution may be forced through the filter by the application of pressure. Once the fibers of the filter have been coated with the functionalized cationic polymer, the polymer is crosslinked by the application of heat at a temperature and for a time sufficient to crosslink the functional groups present in the polymer. Temperatures typically may vary from about 50°C to about 150°C. Heating times in general are a function of temperature and the type of functional groups present in the cationic polymer. For example, heating times may vary from about 1 to about 60 minutes or more. The present invention is further described by the examples which follow. Such examples, however, are not to be construed as limiting in any way either the spirit or the scope of the present invention. Example 1 An aqueous solution containing 0.4 percent by weight of an epichlorohydrin- functionalized poiyamido-amine (Kymene ® 450, Hercules Inc., Wilmington Delaware) was made by diluting 2 ml of stock Kymene ® 450 solution (20 percent by weight solids) with 100 ml of deionized water. The pH of the solution was about 6 and was used without further adjusting its pH, since the effective pH range for Kymene ® 450 is approximately 5 to 9. Twenty-five ml of this diluted Kymene ® 450 solution were poured onto a 90 mm diameter microfiber glass filter (Whatman Type GF/D, having a pore size of 2.7 micrometers, Whatman International Ltd., Maidstone, England) which in turn had been placed in a coarse fritted glass funnel. The funnel was mounted in a filter flask to which a vacuum was applied to draw the solution through the glass filter over a period of 20 seconds, thereby coating the fibers with the polymer. The filter was removed from the funnel and heated in an oven at 85°C for one hour to crosslink the polymer present on the fibers of the glass filter. After removal from the oven, the filter was washed with 500 ml of distilled, deionized water by the procedure used to coat the fibers. The washed, coated filter then was allowed to air dry. Filter capture efficiency was tested against 0.5 micrometer diameter polystyrene latex microparticles (with carboxylic acid functional groups which gave a surface titration value of 7.0 μeq/g) without surfactant (Bangs Laboratory, Inc., Fishers, Indiana) suspended in 100 ml of water at a concentration of 10 8 particles per ml. Two layers of 2-inch (about 5.1 -cm) diameter filter discs cut from the 90 mm disc were placed in a 2-inch (about 5.1 -cm) diameter Nalgene reusable filter holder (250 ml, Nalgene # 300-4000, Nalge Nunc International, Naperville, Illinois). The particle solution was passed through the filters by gravity. Greater than 99.9 percent of the particles were removed by filtering the solution through the coated glass filters which had a combined basis weight of 6 ounces per square yard or osy (about 203 grams per square meter or gsm). The Whatman glass filter had a zeta potential before being coated of -46 millivolts and a zeta potential after being coated of 16-36 millivolts. The zeta potentials of solid membranes were determined from measurements of the streaming potentials generated by the flow of a potassium chloride solution (10 mM in distilled water, at a pH of 4.7 and a temperature of 22°C) through several layers of membranes which were secured in a membrane holder on an Electro Kinetic Analyzer (EKA, Brookhaven Instruments Corporation, Hotlsville, New York). The testing procedures and calculation methods were published by D. Fairhurst and V. Ribitsch in "Particle Size Distribution II, Assessment and Characterization," Chapter 22, ACS Symposium Series 472, edited by Theodore Provder. Example 2 The procedure of Example 1 was repeated, except that the heating time for crosslinking the polymer present on the fibers of the filter was reduced from one hour to ten minutes. Filter capture efficiency was carried out as described in Example 1 with the same results. Example 3 The procedure of Example 2 was repeated, except that the heating temperature for crosslinking the polymer present on the fibers of the filter was increased to 100°C. Filter capture efficiency was carried out as described in Example 1 with the same results. Example 4 An aqueous solution containing 0.4 percent by weight of an epichlorohydrin- functionalized poiyamido-amine (Kymene ® 450, Hercules Inc., Wilmington Delaware) was prepared as described in Example 1. Twenty-five ml of this Kymene ® 450 solution were poured onto a 90 mm diameter microfiber glass filter (LB-5211-A-O, from Hollingsworth & Vose Company, East Walpole, Massachusetts, containing 3-7% acrylic resin binder and a 0.5 osy or about 17 gsm Reemay supporting scrim) which in turn had been placed in a coarse fritted glass funnel. The funnel was mounted in a filter flask to which a vacuum was applied to draw the solution through the glass filter over a period of 20 seconds, thereby coating the fibers with the polymer. The filter was removed from the funnel and heated in an oven at 85°C for one hour to crosslink the polymer present on the fibers of the glass filter. After removal from the oven, the filter was washed with 1 ,000 ml of distilled, deionized water by the procedure used to coat the fibers. The washed, coated filter then was allowed to air dry. A single layer of a 2-inch (about 5.1 -cm) diameter filter disc cut from the 90 mm disc was placed in a 2-inch (about 5.1 -cm) diameter Nalgene reusable filter holder as described in Example 1. One hundred ml of a 0.1 percent by weight sodium chloride solution was passed through the filters by gravity. After the saline solution washing, the filter capture efficiency was tested against 200 ml of the 0.5 micrometer diameter polystyrene latex microparticles without surfactant described in Example 1. The 200 ml (containing 10 8 particles per ml) of particle solution were prepared by mixing 100 ml of a 0.2 percent by weight sodium chloride solution with 100 ml of a 2 x 10 8 particles/ml particle solution. The resulting solution then was passed through the filter by gravity. Greater than 99.9 percent of the particles were removed by filtering the solution through the coated glass filter which had a basis weight of 2.2 osy (about 75 gsm). Example 5 The procedure of Example 4 was repeated, except that the microfiber glass filter employed was LA-8141-O-A, also from Hollingsworth & Vose Company, East Walpole, Massachusetts, and also containing 3-7% acrylic resin binder and a 0.5 osy or about 17 gsm Reemay supporting scrim. As in Example 4, greater than 99.9 percent of the particles were removed by filtering the solution through the coated glass filter; in this example, the coated glass filter had a basis weight of 2.5 osy (about 85 gsm). While the specification has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.

Claims: WHAT IS CLAIMED IS: 1. A glass fiber having a cationically charged coating thereon, the coating comprising: a functionalized cationic polymer which has been crosslinked by heat. 2. The glass fiber of claim 1 , in which the functionalized cationic polymer is an epichlorohydrin-functionalized polyamine. 3. The glass fiber of claim 2, in which the functionalized cationic polymer is an epichlorohydrin-functionalized poiyamido-amine. 4. A fibrous filter comprising glass fibers having a cationically charged coating thereon, the coating comprising: a functionalized cationic polymer which has been crosslinked by heat. 5. The fibrous filter of claim 4, in which the functionalized cationic polymer is an epichlorohydrin-functionalized polyamine. 6. The fibrous filter of claim 5, in which the functionalized cationic polymer is an epichlorohydrin-functionalized poiyamido-amine. 7. A method of preparing a fibrous filter, the method comprising: providing a fibrous filter which comprises glass fibers; passing a solution of a functionalized cationic polymer crosslinkable by heat through the fibrous under conditions sufficient to substantially coat the fibers with the functionalized cationic polymer; and treating the resulting coated fibrous filter with heat at a temperature and for a time sufficient to crosslink the functionalized cationic polymer present on the glass fibers. 8. The method of claim 7, in which the functionalized cationic polymer is an epichlorohydrin-functionalized polyamine. 9. The method of claim 8, in which the functionalized cationic polymer is an epichlorohydrin-functionalized poiyamido-amine.

Inventors: WEI NING, WEI, NING
Applicants: KIMBERLY CLARK CO, KIMBERLY-CLARK WORLDWIDE, INC.
Application year: 1999
Main classification: C03C25
IPC codes: B01D39, C03C25