USE OF POLYAMIDE DISPERSION FOR FILTER CARTRIDGES

Abstract: An apparatus for filtering fluids such as air, oil, and water includes a filter (13) adhesively attached to a structural supports (16, 17) by means of an aqueous dispersion of polyamide resin (14, 15). The dispersion (14, 15) is applied between the filter (13) and structure supports (16, 17) and then dried under ambient conditions or in an oven to solidify the resin (14, 15) and fixedly bond the filter (13) to the structural supports (14, 15).

Description: USE OF POLYAMIDE DISPERSION FOR FILTER CARTRIDGES CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority to Provisional Application Serial No. 60/042,193 filed March 31, 1997. BACKGROUND 1. Field of the Invention The present invention relates to filters and particularly to the use of adhesives for making filter cartridges. 2. Background of the Art Filters are generally used to remove paniculate impurities from fluids circulated through machinery. For example, automotive vehicles generally employ filters to remove paniculate impurities from the intake air and the motor oil. Dry cleaning equipment uses filters to remove dirt and lint from the cleaning solvent. Such filters are often provided in the form of replaceable cartridges. Typically, such filters comprise corrugated or pleated filter paper which is adhesively bonded to a support. For example the filter can be configured into a generally cylindrical shape with fluid being pumped radially through the filter. The cartridge is generally sealed with end caps. Adhesives are used to affix the filter paper to the end caps and/or cylindrical supports within the cartridge. Generally, a polyvinyl chloride (PVC) based adhesive such as plastisol is used. For example, the plastisol is applied to the end caps, the filter paper is placed into the end cap, and the plastisol is cured in an oven. A radially sealed air filter has been disclosed wherein the filter has a metal end cap affixed over the front end of corrugated filtering material within the filter, the metal end cap having a radially extending portion and inner and outer axially extending portions with one of the axially extending portions being longer than the other. Plastisol is used to bond the metal end cap to the end face of the corrugated filtering material and a seal of vulcanized rubber having a hardness of 35 to 40 durometer is bonded to the outside surface of the end cap. The opposite end of the filter is closed with a circular metal pan bonded thereto with plastisol. A loop is pivoted on the circular metal pan to facilitate withdrawing the filter from filter housing after the filter has been used for a prescribed period of time or has become clogged. An annular filter pack of longitudinally folded filter paper has been disclosed which has a plurality of longitudinally spaced bands of adhesive resin disposed around the inside periphery so as to accurately position the inside folds and dimensionally stabilize the filter pack. The filter pack is incorporated into filter cartridges which may be used to filter a variety of fluids. The PVC based plastisol adhesive systems are under scrutiny for potential health hazard because of the chlorine content. Accordingly, it would be advantageous to have an alternative non-P VC based adhesive for use in fixing filters to end caps or other supports in filter cartridges and the like. SUMMARY An apparatus is provided herein for filtering fluids. The apparatus includes a housing, a filter for separating particulate matter from a fluid, and a support for securing the filter within the housing. The filter can be, for example, porous paper which can be corrugated or pleated. The filter is adhesively bonded to the support by means of an aqueous dispersion of polyamide which can be applied to the support and/or filter paper and dried under ambient conditions or in an oven to solidify the resin. The polyamide is preferably derived from a fatty acid containing from about 8 to about 24 carbon atoms. The dispersion can optionally include surfactants and thickeners. The aqueous dispersion of polyamide advantageously avoids the use of chlorine containing resins while providing an easily used adhesive for securing the filter within a cartridge. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a filter cartridge. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The method of the present invention employs an aqueous polyamide dispersion as the adhesive for fixing filters to end caps or other support structures in filter cartridges for air, oil, water or other fluids. The polyamide dispersion is particularly useful for air filter cartridges such as those used in automobiles. The polyamide dispersion can be thickened with appropriate thickeners (discussed below) to meet process requirements. Note that all quantities appearing hereinafter shall be understood to be modified by the term "about" except in the Examples and unless indicated otherwise. Components of a suitable filter cartridge for use in the present invention are illustrated in FIG. 1. Referring now to FIG. 1, an exemplary automobile air filter cartridge 10 includes inner and outer cylindrical mesh supports 11 and 12, respectively, which are concentrically mounted between two end plates 16 and 17. A pleated porous filter 13, such as those usually fabricated from paper, is mounted within the annular space between the inner and outer mesh supports 11 and 12, and is adhesively bonded to the end plates 16 and 17 by adhesive layers 14 and 15. The adhesive is an aqueous polyamide dispersion which is applied to the end plates 16, 17 and/or the filter 13, and which can be cured by drying (i.e. evaporation of the water and any residual solvents in the dispersion) under ambient conditions or in an oven under mild heat of, for example, from 50°C to 100°C. It will be appreciated that there exist numerous types of polyamide resins which can be employed to form aqueous dispersions for use in to the present invention. A preferred polyamide resin dispersion is available under the designation Macromelt 6211 from Henkel Corporation, which can be prepared in accordance with the procedures set forth below. The terms "polyamide resin" or "resin" as employed herein are intended to include compositions comprising individual, chemically distinct polymerized fatty acid polyamide resins as well as blends thereof. Polyamide resins can be obtained commercially or can be prepared by generally well known methods. The polyamide resin has a minimum softening point of 90 °C, and a preferred softening point ranging of from 120°C to 200 °C. The term "polymerized fatty acid" is intended to be generic in nature and to refer to polymerized acids obtained from fatty acids. The term "fatty acids" refers to saturated, ethylenically unsaturated and acetylenically unsaturated, naturally occurring and synthetic monobasic aliphatic carboxylic acids which contain from 8 to 24 carbon atoms. While specific references are made in this application to polymerized fatty acid polyamide resins which are obtained from C18 fatty acids, it will be appreciated that the methods described herein can likewise be employed with other polymerized fatty acid polyamides. The preferred starting acids for the preparation of the polymerized fatty acids used in this invention are oleic and linoleic acids, due to their ready availability and relative ease of polymerization. Mixtures of oleic and linoleic acids are found in tall oil fatty acids, which are a convenient commercial source of these acids. Fatty acids can be polymerized using various well known catalytic and noncatalytic polymerization methods. A typical composition of the polymerized C18 tall oil fatty acids which are used as the starting materials for the polyamide resins used herein is: C 18 monobasic acids (monomer) 0- 15% by wt. C36 dibasic acids (dimer) 60-95% by wt. C54 (or higher) trimer acid or polybasic acids 0.2-35% by wt. In preparing polymerized fatty acid polyamide resins for use in the present invention, it is preferable that the starting polymerized fatty acid contains as high a percentage as possible of the dimer (C36 dibasic) acid, e.g. at least 90% by wt., in order to obtain optimum physical properties in the final product. In addition to the polymerized fatty acids, a wide variety of dicarboxylic acids can be used to prepare polymerized fatty acid polyamide resins, including aliphatic, cycloaliphatic, and aromatic dicarboxylic acids. Representative of such acids (which may contain from 2 to 22 carbon atoms) are oxalic, glutaric, malonic, adipic, succinic, suberic, sebacic, azelaic, pimelic, terephthalic, isophthalic, dodecanedioic and phthalic acids, naphthalene dicarboxylic acids, and 1,4-or 1,3-cyclohexane dicarboxylic acids. Preferred dicarboxylic acids employed in the invention are straight chain aliphatic diacids having at least 6 carbon atoms and more preferably 6 to 22 carbon atoms such as azelaic, sebacic, and dodecanedioic dicarboxylic acids. It should be understood that use of the corresponding acid anhydrides, esters, and acid chlorides of these acids is included in the term "dicarboxylic acid". These acids and anhydrides are readily available from commercial sources and methods for their preparation are well known. Monocarboxylic acids may be added to control molecular weight. Preferred monocarboxylic acids are linear and have 2 to 22 carbon atoms. Most preferred are stearic, tall oil fatty and oleic acids. The diamines used in the preparation of the polymerized fatty acid polyamide resins employed in the present invention may be one or more of the known aliphatic, cycloaliphatic or aromatic diamines having from 2 to 20 carbon atoms. Preferred are the alkylene diamines, such as ethylene diamine, 1,3-diaminopropane, 1,4-diaminobutane, terephthalyl diamine, known as p-xylene diamine, 1,6-hexamethylene diamine, bis-(4-cyclohexylamine)methane, 2,2-bis-(4-cyclohexylamine)propane, polyglycol diamines, isophorone diamine, isophthalyl diamine, known as m-xylene diamine, cyclohexanebis(methylamines), l,4'-bis-(2-aminoethyl)benzene, dimer diamine, polyether diamines, methyl pentamethylene diamine, and piperazine. These diamine compounds are all prepared by well known methods and many are commercially available. Particularly preferred are the straight chain aliphatic diamines of 2 to 20 carbons atoms, especially ethylene diamine and hexamethylene diamine, and cycloaliphatic diamines, especially 4,4'-methylenebis(cyclohexylamine) and piperazine. In certain embodiments, the polyamide is prepared from reactants which are further comprised of a polyoxyalkylenediamine. The polyoxyalkylenediamine reactant comprises one or more amino-compounds where the amino-compound comprises both amine groups and an essentially water-soluble polyether chain. The polyoxyalkyleneamine reactant is soluble or at least partially soluble in water. Examples of useful polyoxyalkylenediamines have the structural formula: H 2 N-CH(R 2 )CH 2 -O-R 1 -CH 2 CH(R 2 )-NH 2 wherein: R 1 represents a polyoxyalkylene chain having the structural formula: (O-CH 2 -CH 2 -) a -(O-CH 2 -CH(R 3 )) b wherein: R 3 is a monovalent organic radical selected from the group consisting of Cl to C4 aliphatic hydrocarbons, 'a' designates a number of ethoxy groups (O-CH 2 -CH 2 ), 'b' designates a number of monosubstituted ethoxy groups (O-CH 2 -CH(R 3 )), the sum of 'a' and 'b' is equal to or greater than 10 but less than or equal to 300, provided that for any values of a and b the sequence of ethoxy and monosubstituted ethoxy groups within a polyoxyalkylene chain may be completely random and/or there may be blocks of ethoxy and/or monosubstituted ethoxy groups, and R 2 designates hydrogen or a monovalent organic radical selected from the group consisting of Cl to C4 aliphatic hydrocarbons. The techniques to prepare suitable polyoxyalkyleneamines are known in the art, and include reacting an initiator containing two hydroxyl groups with ethylene oxide and/or monosubstituted ethylene oxide followed by conversion of the resulting terminal hydroxyl groups to amines. Illustrative of the polyoxyalkyleneamine reactants employed in the invention are the Jeffamine™ brand of polyoxyalkyleneamines available from Huntsman Corporation, Houston, Texas. These polyoxyalkyleneamines are prepared from reactions of bifunctional initiators with ethylene oxide and propylene oxide followed by conversion of terminal hydroxyl groups to amines. The most preferred polyoxyalkyleneamines are the Jeffamine™ D-series polyoxyalkyleneamines from Huntsman Chemical Company which have approximate number average molecular weight between 600 and 6,000. It is desirable to use as the polymerized fatty acid polyamide a material which is the result of as complete an amidation reaction as possible between the starting polymerized fatty acid and the diamine. Those skilled in the art will recognize that the degree of completion of the amidation process can be determined by evaluating the acid number and the amine number of the final polymer. Ideally, the acid functionality of the polyamide resin employed should be zero (0). However, it is often difficult, if not impossible, to reach complete reaction, and this value should be two or less, preferably no greater than 1. The polyamide should have a relatively low amine number, typically less than 40, more typically from 2 to 20. The preferred polyamides have amine numbers ranging from 6 to 12, preferably from 7 to 10. The number of free acid groups and free amine groups present in the polymerized fatty acid polyamide resin are directly related to the relative amount of the polymeric fatty acids, dicarboxylic acids and diamines involved in the polymerization reaction and the degree of completion of the reaction. For the above reasons, approximately stoichiometric amounts (typically with a slight excess of amine groups, e.g. a ratio of total amine to total acid groups of from 1.02: 1 to 1.1 : 1, more typically from 1.04:1 to 1.08: 1) of the polymerized fatty acids plus the dicarboxylic acids and the diamines based on the total number of available acid and amine groups should be used to prepare the polyamide resins for this invention and the reaction conditions should be selected to ensure completion or substantial completion of the amidation reaction. The reaction conditions required for the amidation reaction are generally well known in the art, with the reaction being generally conducted at temperatures from 100°C to 300°C for from 1 to 8 hours. The use of acid catalysts, such as phosphoric acid, and vacuum can be used, especially in the latter part of the reaction, to yield a more complete amidation reaction. Examples of useful polyamide resins include those disclosed in, for example, U.S. Patent Nos. 3,377,303, 4,777,238, and 5,154,760, the disclosures of which are incorporated herein by reference thereto. Generally, the polyamide resins most useful herein will have a moderate molecular weight, i.e. a molecular weight less than that of high polyamide polymers such as the nylons, but greater than polyamide oligomers, e.g. the aminopolyamides that are used as epoxy curing agents. Preferred polyamides typically have a weight average molecular weight of greater than 35,000, more typically greater than 40,000, but less than 200,000, more typically less than 150,000, and more typically from 50,000 to 100,000. Preferred polyamides will also have a polydispersity (defined as weight average molecular weight divided by number average molecular weight) of less than 4, more typically less than 3.5, even more typically less than 3.0, and typically between 1.5 and 3.0. more typically between 2.0 to 2.8. The molecular weights of the polyamide can be determined by size exclusion chromatography as set forth in more detail below. The first step of the process of this invention is the formation of a solution of a polyamide resin in an organic solvent. The organic solvent will typically have a Hildebrand solubility parameter of from 9 to 12, more typically from 10 to 11.5, and most typically from 10.5 to 11.0. The organic solvent should be miscible with water or at least slightly soluble therein. Examples of useful solvents include oxygenated hydrocarbons such as ketones (e.g. acetone, methyl ethyl ketone, and cyclohexanone), esters (e.g. methyl acetate and ethyl acetate), ethers (e.g. ethylene glycol monoethyl ether, 1,4-dioxane and tetrahydrofuran), and heterocyclics, e.g. N-methyl 2-pyrrolidone. Preferred examples of organic solvents are the medium chain (e.g. C 3 - C 5 alkanols) including n-propanol, isopropanol, n-butanol, and iso-butanol. Preferred solvents form a low boiling azeotrope with water to facilitate removal of the solvent from dispersion by distillation thereof. Preferred solvents also have a boiling point at atmospheric pressure of at least 100°C to allow heating, without pressurizing, of the solution of polyamide to a temperature below the softening point (e.g. by the ball and ring procedure of ASTM E28-67) of the polyamide. This heating reduces the viscosity of the solution of polyamide which facilitates mixing of the solution with the other ingredients of the dispersion. The organic solvent is typically employed in an amount that is just sufficient to dissolve all of the polyamide to be dispersed and to provide a fluid viscosity at a temperature at about the atmospheric boiling point of water, e.g. at 90°C to 100°C. Typically, the weight ratio of polyamide resin solids to solvent will be from 1 :2 to 5: 1, more typically from 1:1 to 3:1, and most typically from 1.5:1 to 2.5:1. A surfactant is also used in the preparation of the dispersion and it is typically dissolved in the solution of polyamide and organic solvent, but it can be present in a pre- mix with the polyamide and/or solvent. The surfactant is typically used in an amount of from 0.15 to 20%, more typically from 1% to 15% and even more typically from 5% to 10% by weight of the polyamide resin solids. The surfactant is typically a nonionic surfactant, but an anionic surfactant can be used along with the nonionic surfactant. When an anionic surfactant is used with a nonionic surfactant, the weight ratio of nonionic surfactant to anionic surfactant typically ranges from 20 : 1 to 1 : 1 , more typically from 9 : 1 to 1 : 1 , and even more typically from 4:1 to 2 : 1. Nonionic surfactants are compounds which contain a hydrophobic group and a nonionic hydrophilic group, typically a polyoxyethylene group. Examples of non-ionic surfactants include alkylphenoxypolyethoxyethanols having alkyl groups of from 7 to 18 carbon atoms and from 6 to 60 oxyethylene units, such as heptylphenoxypolyethoxyethanols, methyloctylphenoxypolyethoxyethanols, and the like; polyethoxyethanol derivatives of methylene-linked alkyl phenols; sulfur-containing agents such as those made by condensing from 6 to 60 (more typically from 20 to 50) moles of ethylene oxide with nonyl mercaptan, dodecyl mercaptan, and the like, or with alkylthiophenols wherein the alkyl groups contain from 6 to 16 carbon atoms; ethylene oxide derivatives of long-chained carboxylic acids, such as lauric acid, myristic acid, palmitic acid, oleic acid, and the like, or mixtures of acids such as those found in tall oil containing from 6 to 60 oxyethylene units per molecule; analogous ethylene oxide condensates of long-chained alcohols such as octyl, decyl, lauryl, or cetyl alcohols, analogous ethylene oxide condensates of long-chained secondary alcohols such as mixtures of Cll to C15 secondary alcohols; ethylene oxide derivative of etherified or esterified polyhydroxy compounds having a hydrophobic hydrocarbon chain, such as sorbitan monostearate containing from 6 to 60 oxyethylene units; also, ethylene oxide condensates of long-chain or branched chain amines, such as dodecyl amine, hexadecyl amine, and octadecyl amine, containing from 6 to 60 oxyethylene units; block copolymers of ethylene oxide sections combined with one or more hydrophobic propylene oxide sections. Preferred surfactants are the ethoxylated fatty alcohols having from 20 to 50 repeating oxyethylene units and an alkyl group of from 10 to 18 carbon atoms. Anionic surfactants are compounds which contain a hydrophobic group and an anionic group, typically a carboxylate, sulfonate, sulfate, or phosphate group. Typical examples of anionic surfactants are alkylbenzenesulfonates, alkanesulfonates, olefin sulfonates, alkylether sulfonates, glycerol ether sulfonates, -methyl ester sulfonates, sulfofatty acids, alkylsulfates, e.g. lauryl sulfate, fatty alcohol ether sulfates, glycerol ether sulfates, hydroxy mixed ether sulfates, monoglyceride (ether) sulfates, fatty acid amide (ether) sulfates, mono- and dialkyl sulfosuccinates, mono- and dialkyl sulfosuccinamates, sulfotriglycerides, amide soaps, ether carboxylic acids and salts thereof, fatty acid isethionates, fatty acid sarcosinates, fatty acid taurides, acyl lactylates, acyl tartrates, acyl glutamates, acyl aspar- tates, alkyl oligoglucoside sulfates, protein fatty acid condensates (particularly wheat- based vegetable products) alkyl (ether) phosphates, and alkaryl (ether) phosphates. Preferred anionic surfactants are phosphate esters of ethoxylated alkanols or alkylphenols. A particularly preferred class of anionic surfactants are mixtures of compounds of the formulas (I) R-O-(CH 2 CH 2 O) n -PO 3 M 2 and (II) (R-O-(CH 2 CH 2 O) n ) 2 PO 2 M where n is a number from 1 to 40, R is an alkyl or aralkyl group and M is hydrogen, ammonia or an alkali metal. Preferably R is a C 4 to C 12 alkylphenyl and n is from 5 to 15. A particularly preferred representative of this preferred class of anionic surfactants is commercially available as Rhodafac RE-610 from Rhone-Poulenc, Cranberry New Jersey, which is believed to be a 4: 1 mixture of compounds of formulas I and II, respectively, wherein R is nonylphenyl and n averages 9. The solution of polyamide in organic solvent also can contain an inorganic alkaline material in an amount sufficient to cause the solution to form an oil-in-water dispersion. Typically said inorganic alkaline material is present in said solution in an amount sufficient to cause said solution to exhibit a pH of at least 10, more typically at least 11, and even more typically at least 12, prior to the addition of water to the dispersion to form an oil-in- water dispersion. Examples of inorganic alkaline materials include high solids aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, soda ash, and the like. Typically the aqueous solution of inorganic alkaline material is added to a solution of the polyamide and surfactant in organic solvent with mixing. The alkaline material can, however, be pre-mixed with any of the other materials. The preferred inorganic alkaline material is sodium hydroxide and the amount of sodium hydroxide will typically be greater than 0.75% of the weight of the polyamide, more typically at least 0.80%, even more typically 0.90%, and preferably at least 1.0% by weight of the polyamide. Water which contains an acid is then added, with mixing, to the mixture in an amount sufficient to form an oil-in-water dispersion. The aqueous acid is typically at room temperature when added to form the oil-in-water dispersion. The temperature of the resulting mixture is thus typically well below the softening temperature of the polyamide resin, more typically more than 50°C below the softening point of the polyamide resin, e.g. the temperature of the resulting mixture is typically from 60 °C to 85 °C. The aqueous acid is typically added slowly to form the oil-in-water dispersion, typically at a rate of 1 part to 5 parts by weight of aqueous acid per 100 parts by weight of polyamide resin solids per minute. The mixture is typically heated during the addition of the aqueous acid to maintain the resulting mixture at an elevated temperature, i.e. the resulting mixture will typically be at a temperature of from 60 °C to 85 °C during the addition of aqueous acid. The elevated temperature will typically be more than 50 °C below the softening point of the polyamide resin. The total amount of aqueous acid added will be sufficient to provide a mixture having a weight ratio of water to polyamide resin solids typically in the range from 1 : 1 to 5: 1, more typically from 1 :1 to 3 : 1 , and most typically from 1.5: 1 to 2.85:1. Of course, if the distillation of the organic solvent will remove a portion of the water, e.g. as an azeotrope with the organic solvent, then the amount of water added should be adjusted to obtain a dispersion having the desired amount of water after distillation. The aqueous acid can be characterized as dilute. The concentration of the acid in the water should be sufficiently low so that the pH of the oil-in-water dispersion prior to removal of the organic solvent will be sufficiently high to form an oil-in-water dispersion without coagulation of the polyamide therefrom. The concentration of the acid in the water should be sufficiently low so that the pH of the oil-in-water dispersion prior to removal of the organic solvent will be at least 9, and more typically at least 9.5, and preferably at least 10.0. The acid can be any acid that is compatible with the dispersion. Examples include mineral acids, such as hydrochloric acid, sulfuric acid and phosphoric acid, and organic acids such as carboxylic acids and sulfonic acids. Preferred acids are the lower alkyl monocarboxylic acids such as acetic acid and propionic acid, and the lower alkylene dicarboxylic acids such as oxalic acid. The preferred acid is acetic acid and the amount of acetic acid used to partially neutralize the inorganic alkaline material will typically be greater than 0.5% to 1% of the weight of the polyamide, with a mole ratio of inorganic alkaline material to acid of from 1.25: 1 to 3: 1, more typically from 1.5: 1 to 2.5:1. The mixing used to form the dispersion need not be high shear mixing. Thus, there is typically no need to use conventional homogenizers or dispersers to obtain a dispersion of the desired particle size. Typically, the mixing is low to moderate shear mixing such as that provided by a propeller agitator operated at low to moderate rpm, e.g. a simple paddle mixer of 5 to 10 cm diameter operating at 350 to 450 rpm. The organic solvent is then essentially completely removed from the resulting oil-in- water dispersion by distillation thereof. The distillation will typically be a conventional fractional distillation, at atmospheric or reduced pressure, to retain the majority by weight of the water in the dispersion. The distillation should be effective to remove essentially all of the organic solvent, e.g. less than 2%, more typically less than 1%, by weight of residual organic solvent will remain in the dispersion. Removal of amounts less than 1% by weight is generally not necessary or efficient so that the amount of residual solvent will typically range from 0.5% to 0.95%. After distillation, the product oil-in-water dispersion is cooled. The pH of the dispersion can then be neutralized to an essentially neutral pH, e.g. typically a pH of 4 to 8.5, more typically from 6.0 to 8.0, with an acidic material, e.g. a mineral acid such as hydrochloric acid or sulfuric acid, or an organic acid such as acetic acid or propionic acid. The resulting dispersion will typically have a volume average particle size of from 0.01 to 20 micrometers, more typically from 0.01 to 5 micrometers, and even more typically from 0.05 to 1 micrometer. It has been found that the use of an anionic surfactant with a nonionic surfactant tends to produce a dispersion having a smaller average particle size than the use of a nonionic or an anionic surfactant alone, e.g. from 0.05 to 0.1 micrometers. It has also been found that the process of this invention will have little or no effect on the molecular weight of the polyamide, i.e. there will be essentially no hydrolysis of the polyamide during the process of dispersing the polyamide. The amount of coagulum that is formed can be measured by passing the dispersion through a 60 mesh (250 micrometer) screen. The polyamide is considered to have coagulated from the dispersion if the amount of material collected is greater than 2% by weight of the dispersion. The polyamide aqueous dispersions of this invention can contain various additives in addition to the above-noted materials, such as water-soluble alkali metal salts of polymeric organic acids and protective colloids such as lignin derivatives, proteins, water-soluble cellulose derivatives, starch, alginic acid, and long chain alcohols and lecithin. The amount of such additives employed can vary in amounts from 0% to 5% by weight, based on the weight of the polyamide resin. The aqueous dispersion may also contain a thickener. The amount of thickener can be adjusted to obtain a dispersion having a viscosity as desired. The thickener will typically be one of two types, i.e. a water-soluble gum or an associative thickener. Water-soluble gums are described in Encyclopedia of Polymer Science and Engineering, vol. 7, pp. 589- 613 (John Wiley & Sons, Inc. N.Y..N.Y. 1987), the disclosure of which is incorporated by reference. These materials are high molecular weight polymers, typically polysaccharides, which are soluble in water and thicken by polymer chain entanglement. Examples of such polymers include hydroxyethylcellulose and carboxymethylcellulose. Synthetic polymers that also thicken by chain entanglement are also available. Examples include the alkali swellable acrylic polymers, e.g. copolymers of low alkyl (e.g. methyl, ethyl or butyl) acrylate esters with acrylic or methacrylic acid. These polymers typically thicken water at a neutral or alkaline pH, e.g. a pH greater than 6. The thickener will preferably be an associative thickener. Associative thickeners are so called because the mechanism by which they thicken may involve hydrophobic associations between the hydrophobic species in the thickener molecules and other hydrophobic surfaces, either on other thickener molecules, or on molecules in the system to be thickened. The different types of associative thickeners include, but are not limited to, hydrophobically-modified polyurethanes, hydrophobically-modified polyethers, hydrophobically-modified alkali soluble emulsions, hydrophobically modified hydroxyethyl cellulose or other products, and hydrophobically modified polyacrylamides. The molecular weight and HLB of these associative thickeners, which usually are water soluble or dispersible polymers, is chosen to be sufficiently high to impart desired rheological properties to an aqueous composition containing the thickener. Typically, the polymer has a structure such that a solution containing up to 2-3 weight percent of this polymer will exhibit a viscosity of at least 5,000, preferably at least 15,000, and most preferably at least 20,000 centipoises (as measured on a Brookfield viscometer with a number 3 spindle at 10 RPM at 25 °C). Examples of associative thickeners are disclosed in U.S. Patent No. 5,425,806 (Doolan et al.), the disclosure of which is incorporated herein by reference. Precise levels of the thickener in the dispersion will vary depending upon the nature and efficiency of the thickener and the viscosity desired of the dispersion, but will generally vary between 0.1% and 10%, based on the total weight of the system to be thickened, more typically from 0.1% to 5%. The viscosity of the dispersions without added thickener will typically be in the range of 10 to 100 centipoise. The amount of thickener will typically be sufficient to impart to the dispersion a viscosity greater than 100 centipoise, e.g. from 150 centipoise to 5,000 centipoise. Among the associative thickeners, two chemical types are preferred, i.e. urethane thickeners and polyether thickeners. The urethane thickeners useful in the invention are urethane-functional compounds having at least two hydrophobic segments separated by at least one hydrophilic segment. These segments allow the polymer to act as an associative thickener for an oil-in-water emulsion. Examples of such compounds are found in U.S. Patent No. 4,079,028, (Emmons et al.), the disclosure of which is incorporated herein by reference. Typically, the polymers have at least three low molecular weight hydrophobic groups at least two of which are terminal (external) hydrophobic groups. Many of the polymers also contain one or more internal hydrophobic groups. The hydrophobic groups typically together contain a total of at least 20 carbon atoms and are typically linked through hydrophilic (water-soluble) groups containing polyether segments of at least 1,500, preferably at least 3,000, molecular weight each so that the polymers readily solubilize in water, either by self-solubilization or through interaction with a known solubilizing agent such as a water miscible alcohol or surfactant. The molecular weight of the polyurethanes is typically of the order of 10,000 to 200,000. The polyether thickeners a polyether-functional compounds having at least two hydrophobic segments separated by at least one hydrophilic segment. These segments allow the polymer to act as an associative thickener for an oil-in-water emulsion. Examples of such compounds are found in U.S. Serial No. 07/787,905, filed November 7, 1991, and U.S. Serial No. 08/236,328, filed May 9, 1994, the entire disclosures of which are incorporated herein by reference. This latter application discloses compounds having the formula (I): R 1 -(O-A) a -B 1 -R 2 -(B 2 -R 3 ) d -(B 3 -(A , -O) b . r (A'-B 4 ) r R 4 -(B 5 -R 5 ) e ) n -B 6 -(A"O) c -R 6 wherein: R 1 and R 6 are monovalent hydrophobic groups independently selected from the group consisting of an aliphatic group, a substituted aliphatic group, an aromatic group, and a substituted aromatic group; R 2 and R 4 are independently selected from the group consisting of aliphatic, substituted aliphatic, aromatic, or substituted aromatic radicals, each radical being divalent or trivalent; R 3 and R 5 are independently selected from hydrogen, lower alkyl and lower aralkyl; B 1 , B 2 , B 3 , B 4 , B 5 , and B 6 are linking groups independently selected from the group consisting of an oxygen atom (to form the ether linkage -O-), a carboxylate group (to form an ester linkage R 2 -C(O)-O- and/or R 4 -C(O)-O-), an amino group (to form the amine linkage R 2 -N(R)- and or R 4 -N(R)-, wherein R is hydrogen, lower alkyl, lower aralkyl, or lower acyl), and an amido group (to form the amide linkage R 2 -N(R)-C(O)- and/or R 4 - N(R)-C(O)-, wherein R is hydrogen, lower alkyl, lower aralkyl, or lower acyl); each of a, b, c, d, e, f, and n are integers, wherein each of a and c are independently any integer from greater than 20 to 200; b is any integer from greater than 20 to 450; d, e, and fare zero or 1; and n is any integer from 1 to 5; and each of A, A', and A" is independently an ethylene, 1,2-propylene, 1,2-butylene unit or combinations thereof. In preferred compounds, each of R 1 and R 6 is independently an aliphatic, substituted aliphatic, aromatic, or substituted aromatic radical having from 4 to 50 carbon atoms; each of B 1 - B 6 is an oxygen atom; R 2 and R 4 are both either propanetriyl or meta-xylyl; d and e are either (i) both zero (e.g. when R 2 and R 4 are both meta-xylyl) or (ii) both 1 and R 3 and R 5 are hydrogen, methyl or benzyl (e.g. when R 2 and R 4 are both propanetriyl); f is zero; each of A, A', and A" are ethylene, n is 1, b is from 50 to 450, more preferably from 90 to 450, and the values of a and c independently range from 50 to 150. The polyamide dispersion may likewise contain other materials such as viscosity modifiers, plasticizers, dyes, pigments and the like. The dispersion will typically be free of amino acid stabilizers such as those disclosed in U.S. Patent No. 5,407,985, discussed above. The aqueous dispersions may be used in, for example, overprint varnishes and aqueous inks, as well as in structural and laminating adhesives. The following examples will serve to further illustrate the preparation of the preferred polyamide resin and dispersion made therefrom, but should not be construed to limit the invention, unless expressly set forth in the appended claims. All parts, percentages, and ratios are by weight unless otherwise indicated in context. As used herein, the term "major amount" shall mean at least 50% by weight and the term "minor amount" shall mean less than 50% by weight. EXAMPLES Test Methods Determination of Molecular Weight and Molecular Weight Distribution(MWD) of Polyamide Dispersions by SEC Sample Preparation: Weigh approximately 60 mg of the sample into a disposable scintillation vial. Add 5 mis of the solvent mixture (tetrahydrofuran/methanol 75/25 with 0.5% triethylamine) using a graduated disposable 5 mis pipette. Upon dissolution, filter about 1 ml of solution through a 0.5 micron metal fit into an autosampler vial. Molecular weight calibration and calculation: The SEC column was calibrated with a dozen of narrow MWD polystyrene standards ranging from a molecular weight of 1,000 Daltons to a molecular weight of 2,000,000 Daltons. The molecular weight averages of the sample were calculated from the detector response and retention time against this calibration curve via PE Nelson SEC software. Chromatographic conditions: Instrument: Spectra-Physics IsoChrom LC pump + Perkin Elmer Autosampler Column: Jordi DVB Linear Mobile Phase: THF/MeOH 75/25 with 0.5% TEA Flow Rate: 1.0 ml/min. Injection Volume: 100 microliters Detector: Erma DRI @ 35 Deg. C. Example 1 A polyamide resin is prepared in a resin kettle from a mixture of dibasic acids and diamines as follows. The dibasic acid mixture is 54 eq.% dimer acid, available from Henkel Corp. as VERSADYME 288 and having a minimum dimer content of about 90% by weight, and 46 eq.% of azelaic acid. The diamine mixture is 24.5 eq.% ethylenediamine and 74.5 eq.% piperazine. The ratio of total amine equivalents to total acid equivalents is about 0.95: 1, respectively. The mixture, which also contains 0.022 parts by weight of phosphoric acid catalyst per hundred parts by weight of dimer acid and 0.0005 parts by weight of an anti-foam per hundred parts by weight of dimer acid, is heated to 225 °C under nitrogen sparge over a period of about 1.5 to 2 hours. After about 1.5 hours at 225 °C, a vacuum of about 40 mm of Hg is applied for about one hour. Vacuum is then broken and the mixture is discharged from the resin kettle. A dispersion of the polyamide resin is prepared as follows. Composition Parts Solid polyamide resin 26.50 Surfactant (Trycol 6969, 70% wt. active, Henkel Corp.) 2.65 isobutanol (flammable solvent, bp = 108 ° C) 13.26 50% sodium hydroxide solution 0.53 aqueous solution of acetic acid (0.33 %) 79.09 defoamer (Foamaster VF, Henkel Corp.) 0.04 (less azeotrope of 50:50 isobutanol-water mix) (-26.50) ethylene glycol 3.00 10% acetic acid solution 1.43 100.00 Procedure: Charge solid polyamide resin, surfactant, and isobutanol to the reactor. (The Trycol 6969 surfactant is a 70% solids 30 mole ethoxylate of nonylphenol and has an HLB of about 17.1). Start gentle agitation, heat to 100°C, and hold for 15 minutes. Cool to 85 °C. Charge sodium hydroxide solution and mix for 15 minutes. Charge aqueous solution of acetic acid (0.33% in water) to reactor at 1.32 parts/minutes while allowing the temperature in the reactor to drop to 70° C to 75° C. Charge defoamer, heat to reflux and remove azeotrope. Cool to 40 °C and charge ethylene glycol. Adjust the pH of the dispersion to 7.0 - 7.5 with acetic acid. Cool to 25°C to 30°C and discharge dispersion. Example 2 Example 1 can be repeated, but with the use of an acid component that is 60.5 eq.% dimer acid, 0.5 eq.% stearic acid, and 39 eq.% azelaic acid, and an amine component that is 55 eq.% of piperazine, 25 eq.% ethylenediamine, and 20 eq.% of an N-alkyl 1,3- propylenediamine, wherein the alkyl group corresponds to tall oil fatty acid in chain length and chain length distribution. Example 3 A dispersion of the polyamide resin of Example 1 is prepared as follows. Composition Parts Solid polyamide resin 25.50 Surfactant (Trycol 6969, 70% wt. active, Henkel Corp.) 2.36 isopropanol 12.75 50% sodium hydroxide solution 0.96 aqueous solution of acetic acid (0.33 %) 76.11 defoamer (Foamaster VF, Henkel Corp.) 0.05 (less azeotrope of 50 : 50 isobutanol-water mix) (-25.50) ethylene glycol 2.89 10% acetic acid solution 4.93 100.00 Procedure: Charge solid polyamide resin, surfactant, and isopropanol to the reactor. (The Trycol 6969 surfactant is a 70% solids 30 mole ethoxylate of nonylphenol and has an HLB of about 17.1). Start gentle agitation, heat to reflux (about 85 °C) and hold for 15 minutes. Cool to 75 °C. Charge sodium hydroxide solution and mix for 15 minutes. Charge aqueous solution of acetic acid (0.33% in water) to reactor at 1.32 parts/minutes at 70°C. Charge defoamer, heat to reflux and remove azeotrope. Cool to 40 °C and charge ethylene glycol. Adjust the pH of the dispersion to 7.0 - 7.5 with acetic acid. Cool to 25 °C to 30 °C and discharge dispersion. Filter through a 60 mesh screen. Example 4 A dispersion of the polyamide resin of Example 2 is prepared as follows. Composition Parts Solid polyamide resin 25.50 Surfactant (Trycol 6969, 70% wt. active, Henkel Corp.) 2.36 isopropanol 12.75 50% sodium hydroxide solution 0.96 aqueous solution of acetic acid (0.33%) 76.11 defoamer (Foamaster VF, Henkel Corp.) 0.05 (less azeotrope of 50:50 isobutanol-water mix) (-25.50) ethylene glycol 2.89 10% acetic acid solution 4.93 100.00 Procedure: Charge solid polyamide resin, surfactant, and isopropanol to the reactor. (The Trycol 6969 surfactant is a 70% solids 30 mole ethoxylate of nonylphenol and has an HLB of about 17.1). Start gentle agitation, heat to reflux (about 85°C) and hold for 15 minutes. Cool to 75 °C. Charge sodium hydroxide solution and mix for 15 minutes. Charge aqueous solution of acetic acid (0.33% in water) to reactor at 1.32 parts/minutes at 70°C. Charge defoamer, heat to reflux and remove azeotrope. Cool to 40 °C and charge ethylene glycol. Adjust the pH of the dispersion to 7.0 - 7.5 with acetic acid. Cool to 25 °C to 30 °C and discharge dispersion. Filter through a 60 mesh screen. Example 5 A dispersion of MACROMELT 6211 (TM polyamide dispersion available from Henkel Corp., Elgin, IL) was used to bond a filter media component to a filter metal end cap. After drying, the filter media pleats remained stiff and the metal end cap was bonded in place. It will be understood that various modifications may be made to the embodiments described herein. Accordingly, the above description should not be construed as limiting, but merely as exemplifications of the preferred embodiments. Those skilled in the art will envision many variations within the scope and spirit of the claims appended hereto.

Claims: WHAT IS CLAIMED IS 1 An apparatus for filtering a fluid, which comprises a) a housing, b) a filtering means for separating particulate matter from a fluid, c) support means for securing the filtering means within said housing, wherein said filtering means is adhesively bonded to said support means by an aqueous dispersion of polyamide 2 The apparatus of claim 1 wherein the support means comprises at least one end cap 3 The apparatus of claim 1 wherein the filtering means comprises at least one porous sheet 4 The apparatus of claim 1 wherein the filtering means comprises at least one sheet of pleated filter paper 5 The apparatus of claim 1 wherein the polyamide is comprised of a polymerized fatty acid 6 The apparatus of claim 1 wherein the polyamide is comprised of a polymerized fatty acid derived from carboxylic acids which contain from about 8 to about 24 carbon atoms 7 The apparatus of claim 1 wherein the polyamide is comprised of a polymerized fatty acid derived from carboxylic acids which contain about 18 carbon atoms The apparatus of claim 1 wherein the fluid to be filtered is oil 9. The apparatus of claim 1 wherein the aqueous dispersion of polyamide includes a surfactant. 10. The apparatus of claim 9 wherein the surfactant is present in the amount of from about 0.15% to about 20% by weight of the polyamide resin solids. 11. The apparatus of claim 9 wherein the surfactant is non-ionic. 12. The apparatus of claim 9 wherein in the surfactant is an ethoxylated alkylphenol having from about 20 to about 50 repeating ethyleneoxy units and an alkyl group of from about 7 to about 18 carbon atoms and 13. The apparatus of claim 1 wherein the pH of the dispersion is from about 4 to about 8.5. 14. The apparatus of claim 1 wherein the dispersion has a volume average particle size of less than about 20 micrometers. 15. The apparatus of claim 1 wherein the dispersion includes a thickener. 16. The apparatus of claim 15 wherein the thickener is an associative thickener selected from the group consisting of hydrophobically modified polyurethanes, hydrophobically modified polyethers, hydrophobically modified alkali soluble emulsions, hydrophobically modified hydroxyethyl celluloses, and hydrophobically modified polyacrylamides. 17. The apparatus of claim 1 wherein the dispersion has a viscosity of from about 150 centipoise to about 5,000 centipoise. 18. A method for mounting a filter to a structural support of a filter cartridge comprising the steps of a) adhesively bonding the filter to the structural support with an aqueous polyamide resin dispersion; and b) drying the aqueous polyamide resin dispersion. 19. The method of claim 18 wherein the aqueous polyamide dispersion is made by dissolving a polyamide in an organic solvent to form a solution of said polyamide in said solvent, said polyamide and said organic solvent being at a temperature below the softening point of said polyamide during said dissolving, said solution further comprising a surfactant, and wherein said polyamide has a weight average molecular weight greater than about 35,000, adding sufficient water to said solution with mixing to form an oil-in- water dispersion, the temperature of said solution and said water being below the softening point of said polyamide during said adding, and removing at least a major amount of said organic solvent from said oil- in-water dispersion. 20. The method of claim 19 wherein the organic solvent is selected from the group consisting of acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, ethylene glycol monomethyl ether, 1, 4-dioxanone, tetrahydrofuran and N-methyl- 2-pyrrolidone. 21. The method of claim 19 wherein the organic solvent is selected from the group consisting of n-propanol, isopropanol, n-butanol and iso-butanol. 22. The method of claim 19 wherein the surfactant is an ethoxylated alkylphenol having from about 20 to about 50 repeating ethyleneoxy units and an alkyl group of from about 7 to about 18 carbon atoms. 23. The method of claim 19 wherein the step of removing at least a major amount of the organic solvent from the oil-in-water dispersion is accomplished by distillation of said dispersion. 24. The method of claim 18 wherein the filter cartridge is an oil filtration cartridge for an automotive vehicle. 25. An apparatus for filtering fluid prepared in accordance with the method of claim 18.

Inventors: HEINRICH DWIGHT D, HEUCHER REIMAR, MILLER MARY SUE, HEINRICH, DWIGHT, D., HEUCHER, REIMAR, MILLER, MARY, SUE
Applicants: HEINRICH DWIGHT D, HENKEL CORP, HEUCHER REIMAR, MILLER MARY SUE, HEINRICH, DWIGHT, D., HENKEL CORPORATION, HEUCHER, REIMAR, MILLER, MARY, SUE
Application year: 1998
Main classification: C09J101
IPC codes: B01D29