Disclosed is a process for making a granular detergent composition comprising the steps of: (a) granulating a detersive material comprising a detergent surfactant and a builder; and (b) coating an inorganic aqueous solution on the granules substantially to coat the granules.

The present invention relates to a process for preparing a detergent composition having improved solubility and improved physical properties.
There is a current trend for commercially available granular detergent compositions that have higher bulk densities as well as higher active ingredient content. Such granular detergent compositions offer greater convenience to the consumer and reduce the amount of packaging materials which will ultimately be disposed of.
In view of manufacturing of the compositions, a main concern over the years is to provide granular detergent compositions that exhibit good solubility in various wash water conditions, particularly in cold water, as well as good physical properties such as preferable bulk density and improved flowability. Recently, this concern has become important in the field with the proliferation of higher density xe2x80x9ccompactxe2x80x9d detergents, e.g., granular detergent compositions having bulk densities of 600 g/l or higher. Poor solubility of granular detergent compositions may cause, for example, clumps of granules that appear as solid white masses remaining in the washing machine and/or on washed clothes. In particular, such clumps of granules tend to occur in cold wash water conditions and/or when the order of addition to the washing machine is laundry detergent first, clothes second, and water last.
Various approaches to improving the solubility of detergent compositions have previously been taken by detergent manufacturers. One approach is to spray nonionic surfactant over the surfaces of spray-dried detergent beads. The nonionic surfactant is used as a binder between spray-dried detergent beads and Zeolite generally used for coating the detergent beads. As Zeolite is dried particles, Zeolite tends to use for separating detergent particles as well as provides good solubility of detergent composition. See, U.S. Pat. No. 5,565,422, Del Greco et al., issued Oct. 27, 1996, disclosing a process for making a granular detergent composition comprising the step of spraying a nonionic surfactant onto spray-dried detergent granules. Such detergent provides improved solubility and flowability.
However, such particles of granular detergent compositions, each of which is coated by nonionic surfactants, tend to stick together, resulting in the formation of large particles. The stickiness of nonionic surfactant may be caused by premature dissolution. For example, when the granular detergent compositions coated by nonionic surfactants are exposed to humidity or contacted with water, the nonionic surfactants start to dissolve first, changing their form to that of a gel-like substance, and finally becoming sticky. The sticky, gel-like formation of the nonionic surfactants on the surface of granular detergent particles tends to perform masking/covering of the detergent particles to prevent dissolution of detergent particles, particularly to prevent the dissolution of detergent slurry located inside of the granular particles. In addition, the stickiness tends to proceed agglomeration of the particles, resulting in increased caking of the granular detergent composition during the remainder of processing, after preparing granules, and in storage.
It would therefore be desirable to improve gel solubility of granular detergent compositions, e.g., prevent gel forming during processing and in storage, as well as maintaining physical properties such as good free flowability and providing low density granules.
Based on the foregoing, there is a need for a process which provides a granular detergent composition having improved solubility and improved physical properties. None of the existing art provides all of the advantages and benefits of the present invention.
The present invention is directed to process for making a granular detergent composition comprising the steps of:
(a) granulating a detersive material comprising a detergent surfactant and a builder; and
(b) coating an inorganic aqueous solution on the granules to substantially coat the granules.
These and other features, aspects, and advantages of the present invention will become better understood from a reading of the following description, and appended claims.
While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed that the present invention will be better understood from the following description.
All percentages, ratios, and levels of ingredients referred to herein are based on the actually total amount of the composition, unless otherwise indicated.
All measurements referred to herein are made at 25xc2x0 C. unless otherwise specified.
All publications, patent applications, and issued patents mentioned herein are hereby incorporated in their entirety by reference. Citation of any reference is not an admission regarding any determination as to its availability as prior art to the claimed invention.
Herein, xe2x80x9ccomprisingxe2x80x9d means that other steps and other ingredients which do not affect the end result can be added. This term encompasses the terms xe2x80x9cconsisting ofxe2x80x9d and xe2x80x9cconsisting essentially of.xe2x80x9d
Herein, xe2x80x9cmixturesxe2x80x9d is meant to include a simple combination of materials and any compounds that may result from their combination.
Herein, xe2x80x9ccold waterxe2x80x9d means water which has at a temperature of below 30xc2x0 C.
Herein, xe2x80x9cdensityxe2x80x9d means bulk density unless specifically stated otherwise.
All ingredients such as detersive surfactants and builders useful herein may be categorized or described by their benefit or their postulated mode of action. However, it is to be understood that the ingredients useful herein can, in some instances, provide more than one benefit or operate via more than one mode of action. Therefore, classifications herein are made for the sake of convenience and are not intended to limit an ingredient to the particularly stated application or applications listed.
The present invention is directed to a process for preparing a granular detergent composition comprising the steps of: granulating a detersive material comprising a detergent surfactant and a builder; and coating an inorganic aqueous solution on the granules to substantially coat the granules.
The granular detergent composition prepared by the process of the present invention provides improved solubility of detergent compositions, e.g., by coating of the aqueous inorganic that prevents gel-like formation of particulate granules in the remainder of processing, after preparing granules, and in storage. The improved solubility can be detected by evidence of increased solubility of the surfactants in the washing solution, by the decreased amount of granular detergent left on laundered clothes, and/or by substantially no caking in the stored package.
The composition prepared by the process herein can also provide good physical properties such as free flowability and high density to the granules. Improved free flowability can provide no caking and no lumps in product so as to be easy to use, e.g., to scoop and measure the detergent. The composition prepared by the present invention can provide increased bulk density, particularly increasing 50 to 70 g/l more (the range of conventional compact detergent is about 600 to 800 g/l), resulting in producing more a compact detergent product to the consumer. The composition which is more compact but has no caking and good solubility can make use of the detergent easier for the consumers.
It is believed that surfactants, particularly nonionic surfactants, contained in detersive materials, which change the form to gel when exposed to humidity or when contacted with water, tend to permeate coming out of the granules. In addition, the surfactant which coats the detergent beads may perform as well (binding detergent particles by gelled surfactants). The surfactant turned to gel-like formation makes each particulate stick together to form large agglomerates. Furthermore, such gelled surfactants may mask the each particulate, e.g., substantially cover the detersive material, resulting in preventing dissolution of the detersive material. It is also believed that inorganic aqueous solutions used in the process of the present invention have good water solubility, therefore tending to smoothly dissolve when exposed to humidity and facilitating dissolution of the composition.
A. Granulating Step
The first step for preparing granular detergent composition of the present invention is granulating a detersive material comprising a detergent surfactant and a builder. Any known processes conventionally used for preparing granules, various means and equipment are available. Preferably, the detersive material is applied by the form of an aqueous slurry. Herein, xe2x80x9cslurryxe2x80x9d refers to a mixture of a detergent surfactant and a builder, which is not substantially solid form. The slurry can also include other ingredients such as brighteners and buffers.
Spray-drying for slurry mixtures, preferably for aqueous slurry mixtures to form spray-dried granules, is preferable. More preferably, spray-drying in relatively tall spray drying towers is useful. Preferably, the spray drying process useful herein includes dispersing an aqueous slurry or mixture under high pressure through nozzles down a spray drying tower through which hot gases are counter-currently flowing up the tower. This step can be carried out in conventional spray drying equipment such as the aforementioned towers as well as other spray drying apparatus. The spray-dried granules, that are subsequently used as part of the overall process then can be compacted by a compacting machine. The aqueous slurry used comprises the anionic surfactant, the builder, and no more than about 1.0%, preferably about 0%, by weight of nonionic surfactant. The amount of nonionic surfactant in the aqueous slurry is based on limitations concerning environmental and safety concerns (plume opacity, auto-oxidation) and limitations concerning the physical properties of the slurry used during the spray drying process.
Spray-dried granules from a tower also can be densified further by loading a liquid such as water or a nonionic surfactant into the pores of the granules and/or subjecting them to one or more high speed mixer/densifiers. A suitable high speed mixer/densifier for this process is a device marketed under the tradename xe2x80x9cLxc3x6dige CB 30xe2x80x9d or xe2x80x9cLxc3x6dige CB 30 Recyclerxe2x80x9d which comprises a static cylindrical mixing drum having a central rotating shaft with mixing/cutting blades mounted thereon. In use, the ingredients for the composition are introduced into the drum and the shaft/blade assembly is rotated at speeds in the range of 100-2500 rpm to provide thorough mixing/densification. See U.S. Pat. No. 5,149,455, Jacobs et al, issued Sep. 22, 1992, and U.S. Pat. No. 5,565,422, Del Greco et al, issued Oct. 15, 1996. Other such apparatus includes the devices marketed under the tradename xe2x80x9cShugi Granulatorxe2x80x9d and under the tradename xe2x80x9cDrais K-TTP 80xe2x80x9d.
Another process step which can be used to further densify spray-dried granules involves treating the spray-dried granules in a moderate speed mixer/densifier. Equipment such as that marketed under the tradename xe2x80x9cLxc3x6dige KMxe2x80x9d (Series 300 or 600) or xe2x80x9cLxc3x6dige Ploughsharexe2x80x9d mixer/densifiers are suitable for this process step. Such equipment is typically operated at 40-160 rpm. The residence time of the detergent ingredients in the moderate speed mixer/densifier is from about 0.1 to 12 minutes conveniently measured by dividing the steady state mixer/densifier weight by the throughput (e.g., Kg/hr). Other useful equipment includes the device which is available under the tradename xe2x80x9cDrais K-T 160.xe2x80x9d This process step which employs a moderate speed mixer/densifier (e.g., Lxc3x6dige KM) can be used by itself or sequentially with the aforementioned high speed mixer/densifier (e.g., Lxc3x6dige CB) to achieve the desired density. Other types of granules manufacturing apparatus useful herein include the apparatus disclosed in U.S. Pat. No. 2,306,898, G. L. Heller, issued Dec. 29, 1942.
While it may be more suitable to use the high speed mixer/densifier followed by the low speed mixer/densifier, the reverse sequential mixer/densifier configuration also can be used. One or a combination of various parameters including residence times in the mixer/densifiers, operating temperatures of the equipment, temperature and/or composition of the granules, the use of adjunct ingredients such as liquid binders and flow aids, can be used to optimize densification of the spray-dried granules in the process of the invention. By way of example, see the processes in U.S. Pat. No. 5,133,924, Appel et al, issued Jul. 28, 1992; U.S. Pat. No. 4,637,891, Delwel et al, issued Jan. 20, 1987; U.S. Pat. No. 4,726,908, Kruse et al, issued Feb. 23, 1988; and, U.S. Pat. 5,160,657, Bortolotti et al, issued Nov. 3, 1992.
In those situations in which particularly heat sensitive or highly volatile detergent ingredients are to be incorporated into the final detergent composition, processes which do not include spray drying towers are preferred. The formulator can eliminate the spray-drying step by feeding, in either a continuous or batch mode, starting detergent ingredients directly into mixing equipment that is commercially available. One particularly preferred embodiment involves charging a surfactant paste and an anhydrous material into a high speed mixer/densifier (e.g., Lxc3x6dige CB) followed by a moderate speed mixer/densifier (e.g., Lxc3x6dige KM) to form high density detergent agglomerates. See U.S. Pat. No. 5,366,652, Capeci et al, issued Nov. 22, 1994 and U.S. Pat. No. 5,486,303, Capeci et al, issued Jan. 23, 1996. Optionally, the liquid/solids ratio of the starting detergent ingredients in such a process can be selected to obtain high density agglomerates that are more free flowing and crisp. See U.S. Pat. No. 5,565,137, Capeci et al, issued Oct. 15, 1996.
Optionally, the process may include one or more recycle streams of undersized particles produced by the process which are fed back to the mixer/densifiers for further agglomeration or build-up. The oversized particles produced by this process can be sent to grinding apparatus and then fed back to the mixing/densifying equipment. These additional recycle process steps facilitate build-up agglomeration of the starting detergent ingredients resulting in a finished composition having a uniform distribution of the desired particle size (400-700 microns) and density ( greater than 550 g/l). See U.S. Pat. No. 5,516,448, Capeci et al, issued May 14, 1996 and U.S. Pat. No. 5,489,392, Capeci et al, issued Feb. 6, 1996. Other suitable processes which do not call for the use of spray-drying towers are described by U.S. Pat. No. 4,828,721, Bollier et al, issued May 9, 1989; U.S. Pat. No. 5,108,646, Beerse et al, issued Apr. 28, 1992; and, U.S. Pat. No. 5,178,798, Jolicoeur, issued Jan. 12, 1993.
In yet another embodiment a high density detergent composition using a fluidized bed mixer. In this process, the various ingredients of the finished composition are combined in an aqueous slurry (typically 80% solids content) and sprayed into a fluidized bed to provide the finished detergent granules. Prior to the fluidized bed, this process can optionally include the step of mixing the slurry using the aforementioned Lxc3x6dige CB mixer/densifier or a xe2x80x9cFlexomix 160xe2x80x9d mixer/densifier, available from Shugi. Fluidized bed or moving beds of the type available under the tradename xe2x80x9cEscher Wyssxe2x80x9d can be used in such processes.
Another suitable process which can be used herein involves feeding a liquid acid precursor of an anionic surfactant, an alkaline inorganic material (e.g., sodium carbonate) and optionally other detergent ingredients into a high speed mixer/densifier so as to form particles containing a partially or totally neutralized anionic surfactant salt and the other starting detergent ingredients. Optionally, the contents in the high speed mixer/densifier can be sent to a moderate speed mixer/densifier (e.g., Lxc3x6dige KM) for further mixing resulting in the finished high density detergent composition. See U.S. Pat. No. 5,164,108, Appel et al, issued Nov. 17, 1992.
Optionally, high density detergent compositions according to the invention can be produced by blending conventional or densified spray-dried detergent granules with detergent agglomerates in various proportions (e.g., a 60:40 weight ratio of granules to agglomerates) produced by one or a combination of the processes discussed herein. See U.S. Pat. No. 5,569,645, Dinniwell et al, issued Oct. 29, 1996. Additional adjunct ingredients such as enzymes, perfumes, brighteners and the like can be sprayed or admixed with the agglomerates, granules or mixtures thereof produced by the processes discussed herein.
(1) Detergent Surfactant
The granular detergent compositions produced by the process of the present invention useful herein comprise from about 5% to about 80%, more preferably from about 10% to about 70%, most preferably from about 15% to about 40%, by weight of the composition, of detergent surfactant.
The detergent surfactant can be selected from the group consisting of anionic surfactants, nonionic surfactants, zwitterionic surfactants, ampholytic surfactants, cationic surfactants, and mixtures thereof; more preferably anionic surfactants, nonionic surfactants and mixtures thereof.
More specifically, the granular detergent compositions of the present invention comprise from about 5% to about 80% of anionic surfactant, preferably from about 10% to about 70%, most preferably 15% to about 40% by weight.
Water-soluble salts of the higher fatty acids, i.e., soaps, are useful anionic surfactants in the compositions herein. Such salts include alkali metal soaps such as the sodium, potassium, ammonium, and alkylolammonium salts of higher fatty acids containing from about 8 to about 24 carbon atoms, and preferably from about 12 to about 18 carbon atoms. Soaps can be made by direct saponification of fats and oils or by the neutralization of free fatty acids. Particularly useful are the sodium and potassium salts of the mixtures of fatty acids derived from coconut oil and tallow, i.e., sodium or potassium tallow and coconut soap.
Useful anionic surfactants also include the water-soluble salts, preferably the alkali metal, ammonium and alkylolammonium salts, of organic sulfuric reaction products having in their molecular structure an alkyl group containing from about 10 to about 20 carbon atoms and a sulfonic acid or sulfuric acid ester group. (Included in the term xe2x80x9calkylxe2x80x9d is the alkyl portion of acyl groups.) Examples of this group of synthetic surfactants are the sodium and potassium alkyl sulfates, especially those obtained by sulfating the higher alcohols (C12-18 carbon atoms) such as those produced by reducing the glycerides of tallow or coconut oil; and the sodium and potassium alkylbenzene sulfonates in which the alkyl group contains from about 10 to about 16 carbon atoms, in straight chain or branched chain configuration. See U.S. Pat. No. 2,220,099 and 2,477,383. Especially valuable are linear straight chain alkylbenzene sulfonates in which the average number of carbon atoms in the alkyl group is from about 11 to 14, abbreviated as C11-14 LAS.
Especially preferred are mixtures of C11-16 (preferably C11-13) linear alkylbenzene sulfonates and C12-18 (preferably C14-16) alkyl sulfates. These are preferably present in a weight ratio of between 4:1 and 1:4, preferably about 3:1 to 1:3, alkylbenzene sulfonate:alkyl sulfate. Sodium salts of the above are preferred.
Other anionic surfactants useful herein are the sodium alkyl glyceryl ether sulfonates and water-soluble salts of esters of alpha-sulfonated fatty acids. Examples of these anionic surfactants are set forth in U.S. Pat. No. 5,565,422, Del Greco, issued Oct. 15, 1996.
The granular detergent compositions of the present invention useful herein may also comprise nonionic surfactant. Depending on the nonionic surfactant, the nonionic surfactant can be incorporated into the composition as an integral part of the spray dried granule and/or via the spraying step of the process herein. A portion of the nonionic surfactant can also be incorporated after mixing and/or grinding the granules.
Water-soluble nonionic surfactants are used in the instant detergent compositions. Such nonionic materials include compounds produced by the condensation of alkylene oxide groups (hydrophilic in nature) with an organic hydrophobic compound, which may be aliphatic or alkyl aromatic in nature. The length of the polyoxyalkylene group which is condensed with any particular hydrophobic group can be readily adjusted to yield a water-soluble compound having the desired degree of balance between hydrophilic and hydrophobic elements.
Suitable nonionic surfactants include the polyethylene oxide condensates of alkyl phenols, e.g., the condensation products of alkyl phenols having an alkyl group containing from about 6 to 15 carbon atoms, in either a straight chain or branched chain configuration, with from about 3 to 80 moles of ethylene oxide per mole of alkyl phenol.
Included are the water-soluble and water-dispersible condensation products of aliphatic alcohols containing from 8 to 22 carbon atoms, in either straight chain or branched configuration, with from 3 to 12 moles of ethylene oxide per mole of alcohol.
Semi-polar nonionic surfactants include water-soluble amine oxides containing one alkyl moiety of from abut 10 to 18 carbon atoms and two moieties selected from the group of alkyl and hydroxyalkyl moieties of from about 1 to about 3 carbon atoms; water-soluble phosphine oxides containing one alkyl moiety of about 10 to 18 carbon atoms and two moieties selected from the group consisting of alkyl groups and hydroxyalkyl groups containing from about 1 to 3 carbon atoms; and water-soluble sulfoxides containing one alkyl moiety of from about 10 to 18 carbon atoms and a moiety selected from the group consisting of alkyl and hydroxyalkyl moieties of from about 1 to 3 carbon atoms.
Preferred nonionic surfactants are of the formula R1(OC2H4)OH, wherein R1 is a C10-16 alkyl group or a C8-12 alkyl phenyl group, and n is from 3 to about 80.
Particularly preferred are condensation products of alcohols with from about 5 to about 20 moles of ethylene oxide per mole of alcohol, e.g., C12-13 alcohol condensed with about 6.5 moles of ethylene oxide per mole of alcohol.
In a preferred embodiment, the nonionic surfactant is an ethoxylated surfactant derived from the reaction of a monohydroxy alcohol or alkylphenol containing from about 8 to about 20 carbon atoms, excluding cyclic carbon atoms, with from about 6 to about 15 moles of ethylene oxide per mole of alcohol or alkyl phenol on an average basis.
A particularly preferred ethoxylated nonionic surfactant is derived from a straight chain fatty alcohol containing from about 16 to about 20 carbon atoms (C16-20 alcohol), preferably a C18 alcohol, condensed with an average of from about 6 to about 15 moles, preferably from about 7 to about 12 moles, and most preferably from about 7 to about 9 moles of ethylene oxide per mole of alcohol. Preferably the ethoxylated nonionic surfactant so derived has a narrow ethoxylate distribution relative to the average.
The ethoxylated nonionic surfactant can optionally contain propylene oxide in an amount up to about 15% by weight of the surfactant and retain the advantages hereinafter described. Preferred surfactants of the invention can be prepared by the processes described in U.S. Pat. No. 4,223,163, Builloty, issued Sep. 16, 1980.
A highly preferred composition contains the ethoxylated monohydroxyalcohol or alkyl phenol and additionally comprises a polyoxyethylene, polyoxypropylene block polymeric compound; the ethoxylated monohydroxy alcohol or alkyl phenol nonionic surfactant comprising from about 20% to about 80%, preferably from about 30% to about 70%, of the total surfactant composition by weight.
Suitable block polyoxyethylene-polyoxypropylene polymeric compounds that meet the requirements described hereinbefore include those based on ethylene glycol, propylene glycol, glycerol, trimethylolpropane and ethylenediamine as the initiator reactive hydrogen compound. Polymeric compounds made from a sequential ethoxylation and propoxylation of initiator compounds with a single reactive hydrogen atom, such as C12-18 aliphatic alcohols, do not provide satisfactory suds control in the detergent compositions of the invention. Certain of the block polymer surfactant compounds designated PLURONIC and TETRONIC by the BASF-Wyandotte Corp., Wyandotte, Mich., are suitable in the surfactant compositions of the invention.
A particularly preferred embodiment contains from about 40% to about 70% of a polyoxypropylene, polyoxyethylene block polymer blend comprising about 75%, by weight of the blend, of a reverse block co-polymer of polyoxyethylene and polyoxypropylene containing 17 moles of ethylene oxide and 44 moles of propylene oxide; and about 25%, by weight of the blend, of a block co-polymer of polyoxyethylene and polyoxypropylene, initiated with tri-methylol propane, containing 99 moles of propylene oxide and 24 moles of ethylene oxide per mole of trimethylol propane.
Because of the relatively high polyoxypropylene content, e.g., up to about 90% of the block polyoxyethylene-polyoxypropylene polymeric compounds of the invention and particularly when the polyoxypropylene chains are in the terminal position, the compounds are suitable for use in the surfactant compositions of the invention and have relatively low cloud points. Cloud points of 1% solutions in water are typically below about 32 degC and preferably from about 15 degC to about 30 degC for optimum control of sudsing throughout a full range of water temperatures and water hardnesses.
In addition, the anionic and nonionic surfactants required in the detergent compositions of the invention herein, the detergent compositions may also contain surfactants selected from the group of ampholytic, zwitterinoic, cationic surfactants and mixtures thereof.
Ampholytic surfactants include derivatives of aliphatic or aliphatic derivatives of heterocyclic secondary and tertiary amines in which the aliphatic moiety can be straight chain or branched and wherein one of the aliphatic substituents contains from about 8 to 18 carbon atoms and at least one aliphatic substituent contains an anionic water-solubilizing group.
Zwitterionic surfactants include derivatives of aliphatic, quaternary, ammonium, phosphonium, and sulfonium compounds in which one of the aliphatic substituents contains from about 8 to 18 carbon atoms.
Cationic surfactants can also be included in the present detergent granules. Cationic surfactants comprise a wide variety of compounds characterized by one or more organic hydrophobic groups in the cation and generally by a quaternary nitrogen associated with an acid radical.
Pentavalent nitrogen ring compounds are also considered quaternary nitrogen compounds. Halides, methyl sulfate and hydroxide are suitable.
Tertiary amines can have characteristics similar to cationic surfactants at washing solution pH values less than about 8.5. A more complete disclosure of these and other cationic surfactants useful herein can be found in U.S. Pat. No. 4,228,044, Cambre, issued Oct. 14, 1980.
Cationic surfactants are often used in detergent compositions to provide fabric softening and/or antistatic benefits. Antistatic agents which provide some softening benefit and which are preferred herein are the quaternary ammonium salts described in U.S. Pat. No. 3,936,537, Baskerville, Jr. et al., issued Feb. 3, 1976. Useful cationic surfactants also include those described in U.S. Pat. No. 4,222,905, Cockrell, issued Sep. 16, 1980, and in U.S. Pat. No. 4,239,659, Murphy, issued Dec. 16, 1980.
(2) Builders
Builders are typically employed to sequester hardness ions and to help adjust the pH of the laundering liquid. Such builders present in the compositions up to about 85%, preferably from about 5% to about 50%, most preferably from about 10% to about 30% to provide their builder and pH-controlling functions. The builders herein include any of the conventional inorganic and organic water-soluble builder salts.
Such builders include water-soluble salts of phosphates, e.g., such as tripolyphosphates, pyrophosphates, orthophosphates, higher polyphosphates, other carbonates, silicates, and organic polycarboxylates. Specific preferred examples of inorganic phosphate builders include sodium and potassium tripolyphosphates and pyrophosphates.
Nonphosphorus-containing material may also be selected. Specific examples of nonphosphorus, inorganic detergent builder ingredients include water-soluble bicarbonate, and silicate salts. The alkali metal, e.g., sodium and potassium, bicarbonates, and silicates are particularly useful herein.
Aluminosilicate ion exchange materials useful in the practice of this invention are commercially available. The aluminosilicates useful in this invention can be crystalline or amorphous in structure and can be naturally-occurring aluminosilicates or synthetically derived. A method for producing aluminosilicate ion exchange materials is discussed in Krummel et al, U.S. Pat. No. 3,985,669, issued Oct. 12, 1976. Preferred synthetic crystalline aluminosilicate ion exchange materials useful herein are available under the designations Zeolite A, Zeolite B, and Zeolite X. In an especially preferred embodiment, the crystalline aluminosilicate ion exchange material in Zeolite A and has the formula Na12[(AlO2)12(SiO2)12]xH2O wherein x is from about 20 to about 30, especially about 27. Other preferred builder include a mixture of a water-insoluble aluminosilicate builder such as zeolite A or of a layered silicate (e.g., SKS-6), and a water-soluble carboxylate chelating agent such as citric acid. Still other preferred builder include a mixture of a water-insoluble aluminosilicate builder such as zeolite A, and a watersoluble carboxylate chelating agent such as citric acid. Preferred builder systems for use in liquid detergent compositions of the present invention are soaps and polycarboxylates.
Water-soluble, organic builders are also useful herein. For example, the alkali metal, polycarboxylates are useful in the present compositions. Specific examples of the polycarboxylate builder salts include sodium and potassium, salts of ethylenediaminetetraacetic acid, nitrilotriacetic acid, oxydisuccinic acid, mellitic acid, benzene polycarboxylic acid, polyacrylic acid, and polymaleic acid. Other desirable polycarboxylate builders are the builders set forth in Diehl, U.S. Pat. No. 3,308,067, Examples of such materials include the water-soluble salts of homo- and co-polymers of aliphatic carboxylic acids such as maleic acid, itaconic acid, mesaconic acid, fumaric acid, aconitic acid, citraconic acid, and methylenemalonic acid.
Other suitable polymeric polycarboxylates are the polyacetal carboxylates described in Crutchfield et al, U.S. Pat. No. 4,144,226, issued Mar. 13, 1979, and U.S. Pat. No. 4,246,495, issued Mar. 27, 1979. These polyacetal carboxylates can be prepared by bringing together under polymerization conditions an ester of glyoxylic acid and a polymerization initiator. The resulting polyacetal carboxylate ester is then attached to chemically stable end groups to stabilize the polyacetal carboxylate against rapid depolymerization in alkaline solution, converted to the corresponding salt, and added to a surfactant.
The compositions herein preferably contain little (e.g., less than 10%, preferably less than 5%, by weight) or no phosphate builder materials. The presence of higher levels of tripolyphosphate improves solubility of the compositions to the point where hydrophobic amorphous silicate provides little or no additional improvements. However, sodium pyrophosphate reduces solubility so that the benefit provided by the hydrophobic amorphous silicate is greater in granular compositions containing pyrophosphate.
B. Coating Step
The second step for making a granular detergent composition of the present invention is applying an inorganic aqueous solution on the granules to substantially coat the granule obtained by the first step of the process.
Without being bound by theory, it is believed that surfactants, particularly nonionic surfactants, contained in detersive materials, tend to change to gel-like formation when exposed to humidity or when contacted with water in the washing solution. If the nonionic surfactant becomes gel-like, it may permeate coming out of the granule particles during processing of detergent compositions. If such gelled nonionic surfactants are coated to detesive material granular, the coating of gelled nonionic surfactants may perform as well (coating/masking the particles). Such gel-like formation which turns to a hard coating and covers the detersive material, may inhibit preventing the dissolution of the detersive material.
In another case, the gel-like formation makes the particles stick together to form large agglomerates. Such large agglomeration may also make difficulty of the dissolution of detergent particles.
It is believed that the inorganic aqueous solutions used in the present invention do not become gel-like when exposed to humidity, are not sticky and have good dissolution/dispersion property, therefore tending to smoothly dissolve when exposed in humidity, and overall facilitating dissolution the composition.
Preferably, the inorganic aqueous solution is applied by spraying on the surface of the granules prepared by the granulating step. The concentration of the inorganic solution is from about 0.5% to about 95%, preferably from 1.0% to about 50%.
Preferably, the inorganic aqueous solution is prepared by mixing one or more ingredients selected from the group consisting of sodium carbonate, sodium sulfate, potassium carbonate, potassium sulfate, sodium silicate, sodium hydroxide, potassium hydroxide, and mixtures thereof. The ingredient useful herein could be used as the builder described above.
The inorganic aqueous solution useful herein is applied in an amount of from about 0.5% to about 6.0% by the total weight of detergent components, preferably from about 1.0% to about 4.5%. The temperature of inorganic aqueous solution during coating step is from about 10xc2x0 C. to about 100xc2x0 C., preferably from about 30xc2x0 C. to about 70xc2x0 C.
The process for preparing a granular detergent composition may further comprise the step of applying a shell to the surface of the inorganic coated detergent granules. Herein, xe2x80x9cshellxe2x80x9d means a material which covers the granules of detersive material to preventing agglomeration of the particles. The detergent granules covered by shell can provide increased bulk density and reduced friction between particles; thus, the volume of the product can be reduced, providing a more compact product to the consumer. Preferably, the concentration of the shell is from about 2% to about 15%, preferably from about 3.0% to about 7.0%. The shell useful herein is selected from the group consisting of fine inorganic materials having a mean particle size less than about 5 xcexcm, a micronized crystalline layered silicate (SKS-6 avairable from Hoechst Inc.,), a micronized carbonate, a micronized sodium sulphate, aluminosilicate (Zeolite), magnesium silicate, calcium silicate, and clay, preferably Zeolite.
It is believed that the adding the shell into inorganic aqueous solution or over the coating of inorganic solution tends to provide improved flowability. Preferably, the ratio of the inorganic aqueous solution to the shell is from about 0.2 to about 7.0.
Other Ingredients
Bleaching agents and activators additionally useful herein are described in U.S. Pat. No. 4,412,934, Chung et al., issued Nov. 1, 1983; U.S. Pat. No. 4,483,781, Hartman, issued Nov. 20, 1984; U.S. Pat. No. 4,634,551, Burns et al, issued Jan. 6, 1987; and U.S. Pat. No. 4,909,953, Sadlowski et al, issued Mar. 20, 1990. Chelating agents are described in U.S. Pat. No. 4,663,071, Bush et al. Suds modifiers are also optional ingredients and are described in U.S. Pat. 3,933,672, Bartoletta et al., issued Jan. 20, 1976; and U.S. Pat. No. 4,136,045, Gault et al., issued Jan. 23, 1979. Suitable smectite clays for use herein are described in U.S. Pat. No. 4,762,645, Tucker et al, issued Aug. 9, 1988. Suitable additional detergency builders for use herein are enumerated in U.S. Pat. No. 3,936,537, Baskerville, Jr. et al., issued Feb. 3, 1976, and in U.S. Pat. No. 4,663,071, Bush et al, issued May 5, 1987.
Other ingredients suitable for inclusion in a granular detergent composition can be added to the present compositions. These include bleach activators, suds boosters or suds suppressors, anti-tarnish and anticorrosion agents, soil suspending agents, soil release agents, germicides, pH adjusting agents, non-builder alkalinity sources, enzymes, enzyme-stabilizing agents and perfumes. Such ingredients are described in the Baskerville, Jr""s U.S. Patent referred to the above.

Process for preparing a granular detergent composition


The present invention relates to a system and a method for detecting and monitoring the distance between a patient and a reference point on an inflatable air mattress and for controlling the air supply to that mattress in relation to such distance. The patient distance sensing system includes a rigid support frame such as a bed frame, an inflatable air mattress positioned atop the bed frame with the upper surface of the inflatable air mattress forming a patient support surface, an air supply operable to provide controlled variations in air supply, and a series of patient distance sensing devices. Such devices including a heterodyning proximation detector, a force responsive distance sensing device, and a light responsive sensing device. Each device is operable to act separately or cooperatively in maintaining a therapeutically beneficial patient support surface through variable control of the delivery of inflation pressure to the air mattress. The heterodyning proximation detector is further operable to initiate inflation by way of a through space sensing of an approaching patient. The present invention further provides a preferred method for regulating the inflation of a therapeutic air mattress through operation of the described patient distance sensing system.

The present invention relates generally to monitoring and controlling therapeutic beds and mattress systems. More particularly, the invention relates to a system and methods for detecting and monitoring the distance between a patient and a reference point on a mattress and for controlling the mattress in relation to such distance.
For years those who suffer from limited mobility due to age, disease or immobilizing physical condition have sought relief from decubitus ulcers, cramping and discomfort as a result of being bedridden for long periods of time. A wide range of therapeutic supports for bedridden patients, such as inflatable mattresses, mattress overlays and mattress replacements, have been made commercially available in the United States. One such support is commercially available from Kinetic Concepts, Inc. (of San Antonio, Tex.) under the xe2x80x9cTheraKairxe2x80x9d designation, as a mattress which provides pulsating action through inflatable support cushions as described in U.S. Pat. No. 5,267,364.
Therapeutic mattresses are often designed to reduce xe2x80x9cinterface pressures,xe2x80x9d which are the pressures that are exerted by a mattress on skin of the patient (or vice versa) while the patient is lying on the mattress. Given time, elevated interface pressures can reduce local blood circulation around the skin and, as a result, may contribute to bedsores and other complications. With inflatable mattresses, as the inflation air pressure decreases, a patient""s susceptibility to encountering elevated interface pressures also tends to decrease, thereby reducing the likelihood that the patient will develop bedsores.
A problem with deflation, however, is the increased risk of xe2x80x9cbottoming-outxe2x80x9d, which is a widely known effect where the upper surface of an air mattress converges and comes into direct contact with the lower surface. Bottoming out can negate much of the benefit of an air mattress by increasing the patient""s pressures at the point of bottoming-out and, therefore, increase the risk of bedsores. Abrupt bottoming-out, such as when the patient is initially positioned on the mattress, could increase the risk of further injury to an already frail, bedridden patient. There has been a long felt need to have an inflatable mattress which self-adjusts the air pressure in inflatable cushions for optimal therapeutic purposes while significantly diminishing the risks of bottoming-out.
Some concepts of regulating air supply within a mattress for the prevention of bedsores and some concepts for the mitigation of bottoming-out effects are known. For example, U.S. Pat. No. 4,694,520 describes methods for detecting inadequate inflation while the patient is situated on the mattress. By contrast, the present invention detects the patient not only when positioned on the bed but also before the patient is even placed on the bed, thereby preventing the risks of rapid bottoming-out by xe2x80x9cpre-inflatingxe2x80x9d.
U.S. Pat. No. 4,873,737 provides for the detection of mattress thickness to supply a mean air pressure while the patient is situated thereon.
U.S. Pat. Nos. 4,745,647 and 4,768,249 provide force activated sensors to detect whether a patient has bottomed-out on a mattress but does not contemplate detecting the patient as the patient nears the bed.
U.S. Pat. No. 4,542,547 provides for mattress inflation through the detection of reflected and pulsed light while the present invention, by contrast, detects diffuse light.
It is an object of the present invention to enhance patient care and to overcome the obstacles and inadequacies of the prior art.
The present invention includes features and/or components that have been invented or selected for their individual and combined benefits and superior performance as an apparatus and a method for minimizing patient interface pressures by sensing patient distance and, if necessary, adjusting that distance to some predetermined or calculated level to optimize the therapeutic effects of the patient""s mattress. The system is a combination of components and methods that together have new and novel features. Each of the individual components work in association with the others and are optimally mated for performances.
The present invention circumvents current laborious requirements of manually adjusting a mattress for optimal therapeutic inflation or allowing a patient to be filly positioned on the bed before sensing means are activated. The present invention offers a unique xe2x80x9chands-freexe2x80x9d approach to controlling a mattress""s air supply while a patient is lying thereon. Through the use of a heterodyning proximation detector similar benefits are achieved even before a patient lies upon the mattress. With such benefits there is less need for extra personnel and training costs to operate a mattress""s air supply system. In addition, the present invention further reduces any risks for rapidly bottoming-out as a patient is initially placed on a mattress. Accordingly, the heterodyning proximation detector detects a patient as the patient nears a mattress and allows for air supply in the mattress to be increased before the patient is ever positioned atop the mattress.
The heterodyning proximation detector is an improved version of a somewhat obscure musical instrument that had been developed in the United States during the 1920s called a xe2x80x9cThereminxe2x80x9d. The present invention improves on the musical instrument""s ability to sense a human""s natural reactance, or electrical characteristics, and applies this improvement to therapeutically regulating an air mattress. The heterodyning proximation detector is effectively an antenna referenced to a conducting plate with a large surface area that variably responds to the dielectric constants of different materials. The heterodyning proximation detector may also be used to control air supply while the patient is on the mattress along with, or separately from, a force-responsive distance sensing apparatus or a light-responsive distance sensing apparatus, thus reducing the risks for gradual bottoming-out as well.
Aspects of the present invention feature a force-responsive distance sensing apparatus for continuously determining how high the patient is being supported on the mattress in real-time while the patient is on the mattress. The depth that the patient sinks into the mattress is used for controlling air supply to the mattress. The patient""s height (or depth) distance is represented as variations in height of a compliant, force transmitting member that is placed relative to the mattress. Thus, a change in height of the patient generates a change of force applied to a force sensitive component coupled to the force transmitting member.
Other aspects of the present invention relate to a light-responsive distance sensing apparatus using either visible light or infrared radiation. The mattress upon which the patient rests may be physically divided into sections, such as independently inflatable air-cells, or logically divided into sections, where no physical barrier isolates the air inside the mattress. A section, logical or physical, of the mattress""s initial shape becomes deformed in response to a patient being set atop the air mattress. A light emitter and light detector are situated in a fashion such that a deformation in the mattress shape reduces the amount of light that reaches the detector from the emitter, thereby generating a control signal to adjust the air pressure within the mattress accordingly. The preferred embodiments contain certain elements which include, but are not limited to:
a frame for supporting a mattress;
a therapeutic mattress set upon the frame where both frame and mattress cooperate in tandem to define a therapeutic bed;
a controlled air supply for selectively inflating one or multiple air cells upon receiving data relating directly or indirectly to the height of the patient relative to the bottom of the air mattress.
In one preferred embodiment, a heterodyning proximation detector is significantly influenced by the reactance of certain objects within a known distance of the detector. Such an embodiment depends on the electrical signature left by the particular dielectric constant of that object and the field pattern of the heterodyning proximation detector. In particular, the heterodyning proximation detector is either a conducting plate or wire referenced to a ground plane that is responsive to a body""s natural reactance and, thus, functions as an antenna. The antenna is variably connected to a tank circuit having a capacitor and a variable inductor. A frequency oscillator is operatively connected to the tank circuit as well. Thus, as a body nears the antenna, the body""s reactance changes the electrical fields induced into the antenna, resulting in a change in the natural frequency of the oscillator. Accordingly, the frequency signal ultimately generated by the heterodyning proximation detector is used by control circuitry to create a signal which, in turn, controls a blower or regulating valve. The blower is then connected to at least one of the air cells or sections that comprise the mattress. Another embodiment of the apparatus contemplates an array of air cells each with a heterodyning proximation detector and a blower or regulating valve that is responsive to the individual reactance signatures emitted by particular segments of the body.
One embodiment includes a force-responsive distance sensing apparatus. The force-responsive distance sensing apparatus comprises a force transmitting member and a force sensing element, which might be a force-sensitive resistor, piezoelectric crystal, or the like, coupled with the force transmitting member. In operation, the force-responsive distance sensing apparatus is placed relative to the mattress so that it is responsive in real-time to the compressive forces that are continuously generated by the patient when the patient is on the mattress. When a patient lying on the mattress has compressed it to the point of bottoming, the force transmitting member is subjected to the maximum amount of loading that is exerted by the patient on the mattress, whereas an uncompressed, fully inflated mattress signifies minimum or no loading on the force transmitting member. In turn, a force sensing element that is coupled to the force transmitting member detects a range of height distance in real-time as a variable range of compression exerted thereon by the force transmitting member. However, compression of the force transmitting member is not necessarily linearly scaled between the maximum and minimum distances of the patient relative to frame; e.g., compressive forces from the force transmitting member might not be generated until the mattress thickness is compressed to some predetermined ratio of the original thickness.
Ultimately, a resulting signal from the force sensing element that is related to the compressive forces exerted on the element of the force transmitting member is sent to a controller and compared to a preset calibrating signal. The signal is then converted into a control signal which is sent to a blower or regulating valve. The controller might also be set to work with a microprocessor to store and compare various voltage values.
One embodiment includes a light-responsive distance sensing apparatus. The light-responsive distance sensing apparatus comprises a deformable container, inflatable chamber, or the like, having a sealed inner surface that is constructed of light diffusing material. A light emitter and a light detector are attached to the air cell at different locations. In operation, as a patient is set atop the air mattress, the initial shape of the air cell becomes deformed due to the compressive forces exerted by the patient thereon. Thus, any deformation of the container""s inner surface between the light emitter and light detector would scatter light so that, ultimately, less light would be received and detected by the light detector than what light was initially emitted when the air cell was not subject to compressive forces. The resulting output signal from the light detector is sent to a controller and compared to a calibrated reference signal. The controller may then emit a control signal that indicates a significant disparity in the air supply within that air cell or mattress section to a blower or regulating valve to increase air supply.
One particular embodiment provides a therapeutic mattress for controlled support of a patient, the mattress comprising at least one inflatable chamber having a first translucent portion for the introduction thereto of light energy and a second translucent portion for the passage therethrough of light energy; a source of light energy adapted to introduce light energy through the first translucent portion into the interior of the inflatable chamber; and a receiver of light energy adapted to receive light energy through the second translucent portion from the interior of the inflatable chamber, the receiver being adapted to generate a signal indicative of the quantity of light so received. The first and second translucent portions are preferably disposed on opposing sides of the inflatable chamber. The inflatable chamber also has one or more pouches to secure the source and/or the receiver to the chamber. Preferably, the pouch also has a releasable closing to facilitate insertion and removal of the source and/or receiver. The pouch optionally also has an opaque portion to conceal the source and/or receiver secured within the pouch and a reflective portion to facilitate the transfer of light energy through the chamber. Cushioning material, such as foam, plastic, or cloth batting, is optionally disposed within the inflatable chamber to provide extra support cushioning to the patient. The chamber optionally also includes an air permeable portion to facilitate a gradual flow of air out of the chamber, and a water permeable portion to draw moisture away from the patient.
Another embodiment provides a therapeutic mattress for controlled support of a patient, the mattress comprising a plurality of inflatable chambers each having a light-scattering inner surface; a first of the inflatable chambers having a first light emitter and a first light detector; a second of the inflatable chambers having a second light emitter and a second light detector; and first and second pouches adjacent opposite sides of each of the first and second inflatable chambers. The first light emitter is disposed within the first pouch of the first chamber and is adapted to introduce light energy, preferably infrared light, into the interior of the first chamber. The first light detector is disposed within the second pouch of the first chamber and is adapted to receive light energy from the interior of the first chamber and generate a signal indicative of the quantity of light energy received. The second light emitter is disposed within the first pouch of the second chamber and is adapted to introduce light energy into the interior of the second chamber. The second light detector is disposed within the second pouch of the second chamber and is adapted to receive light energy from the interior of the second chamber and generate a signal indicative of the quantity of light energy received. Furthermore, the mattress is provided with a source of pressurized fluid in communication with the first and second inflatable chambers, the source being adapted to control inflation of the first chamber according to the signal generated by the first light detector, the source being further adapted to control inflation of the second chamber according to the signal generated by the second light detector. Inflation of the first and second inflatable chambers is controlled to minimize interface pressures between the therapeutic mattress and a patient lying on the mattress while simultaneously maintaining sufficient air pressure to prevent the inflatable chambers form bottoming out.
Other embodiments may include other distance sensing mechanisms either alone or in combination with the heterodyning proximation detector, force-responsive distance sensing apparatus or the light-responsive distance sensing apparatus, adapted to assist in controlling and monitoring the air supply of the mattress.
The invention may take the form of a method for regulating inflation within a mattress assembly or overlay. Such a method can be used to better accommodate a wide range of patient body sizes. The preferred method includes the following steps:
1. deflating the mattress and measuring and storing the height distance from a heterodyning proximation detector to a patient while the mattress is deflated;
2. initiating inflation of the mattress as the patient nears the heterodyning proximation detector;
3. placing the patient on the mattress and continuing to increase the air supply of the mattress until fully inflated.
4. measuring and storing the output signal or signals from the heterodyning proximation detector, force-responsive distance sensing apparatus, light-responsive distance sensing apparatus, or any combination of these while the mattress is fully inflated with a patient on top of the mattress;
5. calibrating the optimal height distance for that particular patient using the stored signals from the deflated and fully inflated positions;
6. monitoring and controlling air supply to the mattress based on the determined optimal height distance using the heterodyning proximation detector, force-responsive distance sensing apparatus, light-responsive distance sensing apparatus, or any combination of these.
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings. The drawings constitute part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

System and methods for mattress control in relation to patient distance


A method of coating a substrate is provided. A metallic layer comprising at least about 8% nickel is deposited by thermal spraying on a substrate. The metallic layer has an average density greater than about 80%. A slurry layer comprising from about 10% to about 90% aluminum or alloy thereof is deposited on the metallic layer. Heating to a temperature in excess of 500xc2x0 C. (932xc2x0 F.) results in the formation of an intermetallic layer of NiAl. The resulting coating is particularly suited for protecting the surfaces of incinerators or other combustion chambers.

The present invention relates to the field of protective coatings, specifically, to the method of depositing a multilayer coating having improved properties, which can be easily applied and repaired.
Modern waste incinerators burn waste to avoid the need to store waste in landfills, and to produce energy. The walls of incinerator combustion chambers (combustion zones or incinerator areas) are subject to extremely harsh conditions, including exposure to extreme heat, noxious gases, and corrosive chemical compounds which are the by-products of combustion.
Incinerators burn, for example, garbage, biomass and biological waste. Combustion of these materials produces CO2 and H2O vapor, plus acid gases, HCl, NOx (where NOx is any of a series of oxides or nitrogen) and SOx (where SOx is SO2 or SO3). Combustion of plastics, such as polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyvinylidene chloride (PV2C), etc., can produces free halides and hydrogen halide gases. All of these are highly corrosive.
In addition to the combustion of incinerator waste, impure fuels are used as the combustion means in incinerators of all types. Such fuels include, for example, high sulfur coal, lignite, plant matter and asphalt and tar products such as orimulsion. These fuels also produce acidic gases such as NOx and SOx, which can cause corrosion and oxidation of the incinerator surface in the combustion zone.
Molten ash is produced by complex low melting point salts. This molten ash rapidly attacks steel.
All of these products of waste combustion create an extremely harsh environment, causing extensive corrosion and oxidation of exposed incinerator surfaces. It has been found that in some cases an uncoated carbon steel surface lasts only approximately 12 months in this environment.
Accordingly, there exists a significant need to protect surfaces, exposed to such a corrosive and oxidizing environment, such as those found in an incinerator.
The need to protect the exposed surfaces of incinerators from corrosion and oxidation in modern waste management plants must be balanced with the goal of extracting energy from the combustion process. The steam generated from the utilization of the heat of combustion can be used for home heating, industrial use, or to produce power via turbine driven generators. Thus, modern waste management plants are referred to as xe2x80x9cwaste-to-energyxe2x80x9d plants.
Corrosion can be controlled by decreasing the heat acting on the incinerator walls by using, for example, refractory coatings, or by cooling the incinerator walls with water. However, this loss of heat results in a proportional loss of energy. If cooling is used as the means of corrosion prevention, the water-to-energy transformation is detrimentally compromised.
The combustion zone of an incinerator is typically formed from steel. Some incinerator combustion zones are formed from steel tubes. The life of an incinerator is measured in wall thickness, expressed in millimeters (mm) or mils (thousandths of an inch), lost per year as the steel is corroded and oxidized. Absent any protective coating on the steel surface, corrosion and oxidation occur rapidly.
Various solutions have been proposed to address the corrosion and oxidation problems faced by incinerators operators, each having its drawbacks:
(a) Nickel Based Superalloy Tubes.
One proposed solution to the problem of corrosion and oxidation in incinerators is to fabricate an entire incinerator from specially formulated nickel based superalloys. The proposed nickel based superalloys usually contain significant percentages of Cr and Mo, and are extremely expensive.
In addition to the prohibitive cost of using such superalloys, this solution does not address the need to provide corrosion and oxidation protection to preexisting facilities, short of rebuilding the entire facility.
While nickel based superalloys display effective corrosion resistance, they may still need to be replaced, in time. Moreover, if there is wall failure in a nickel based superalloy structure, there exists no simple, effective and cost effective method of repairing the wall.
(b) Composite or Coextruded Tubes.
Composite or coextruded tubes are produced by coextrusion of two component tubes metallurgically bonded together during the coextrusion process.
Composite tubes are high in cost. In addition, where the two components of a composite tube differ in their coefficient of thermal expansion, cracking can occur due to temperature changes.
Repair of composite tubes is difficult, and may require total replacement of the tubes.
(c) Weld Overlay of Steel Tubes with Nickel Alloy.
One proposed solution to the problems of corrosion and oxidation of incinerator walls is welding nickel alloy overlays over damaged portions of steel or steel tubes. This process is expensive, and requires welding equipment.
Weld overlays cannot conform to irregularly shaped surfaces, such as where two adjacent incinerator tubes are joined. Weld overlays leave gaps where tube surfaces can still be attacked.
In addition, the process of welding is highly stressful on the underlying structure. The welding process can thus further damage or crack previously damaged or weakened tubes.
(d) Thermal Spraying Techniques.
Thermal spray coating processes are often employed in order to protect surfaces which are exposed to extremely hostile conditions, such as environments exposed to high temperatures or noxious substances. Thermal spray coating processes are used in a variety of industries. A benefit of thermal spray coating is that an inexpensive base metal, such as carbon steel, can be treated on its surface, creating new surface properties that are far superior to that of the base metal. In this way, thermal spray coatings save costs associated with fabrication of entire structures from prohibitively expensive superalloys.
Currently, thermal spray coating processes exist which must be performed under tightly controlled conditions, such as at a manufacturing plant or laboratory, and must invariably be applied under ideal conditions. Accordingly, these known thermal spray coating processes are often applied to surfaces in controlled booths or cabins using robotic techniques. In some cases inert shrouding is used or even vacuum chambers. These coating processes are performed on discrete, pre-assembled component parts. The use of controlled conditions reduces the number of variables that effect the quality of the coating. Because these spray coating processes must be performed under ideal conditions, they are not practical where a thermal spray coating must be applied to an existing surface in situ.
Thermal spray coating processes fall under the following general categories, listed from lowest cost, least dense, and lowest perceived quality coating, to highest cost, most dense and highest quality coating:
(1) Combustion powder/wire (xe2x80x9cFlame sprayingxe2x80x9d). Combustion flame spraying employs compressed air or oxygen, mixed with one of a variety of fuels (e.g., acetylene, propylene, propane, hydrogen), to both melt and propel the molten metal particles. Generally, the process yields low density coatings. Combustion flame spraying uses either powder, wire or rod as the feedstock material and has found widespread usage around the world for its relative simplicity and cost effectiveness. Combustion flame spraying provides for a thermal coating having a density range of approximately 85-90%.
(2) Arc wire. Arc wire spraying involves two current-carrying electrically conductive wires fed into a common arc point at which melting occurs. A high-velocity air jet blowing from behind the moving wires strips away the molten metal which continuously forms as the wires are melted by the electric arc. Arc wire spraying provides for a thermal coating having a density range of approximately 80-95%.
(3) Plasma spray. A plasma gun operates on direct current, which sustains a stable non-transferred electric arc between a cathode and an annular anode. A plasma gas is introduced at the back of the plasma gun interior, the gas exiting out of the front of the anode nozzle. The electric arc from the cathode to the anode completes the circuit, forming an exiting plasma flame. The powder to be processed is introduced at this hottest part of the flame. Plasma spray is used to form deposits of greater than 50 micrometers of a wide range of industrial materials, including nickel and ferrous alloys, refractory ceramics, such as aluminum oxide and zirconia-based ceramics. Plasma spraying provides for a thermal coating having a density range of approximately 90-95%.
(4) High Velocity Oxyfuel Spraying (HVOF). This technique is based on special torch designs, in which a compressed flame undergoes free-expansion upon exiting the torch nozzle, thereby experiencing dramatic gas acceleration, to supersonic speeds. By properly injecting the feedstock powder from the rear of the torch, and concentrically with the flame, the particles are also subjected to velocities so high that they will achieve supersonic values. Upon impact onto the substrate, the particles spread out very thinly, and bond well to the substrate and to all other splats in its vicinity, yielding a well adhered, dense coating. HVOF spraying provides for a thermal coating having a density range of approximately greater than 95%.
(5) Shrouded HVOF. HVOF spraying carried out with a gaseous and/or mechanical or physical barrier placed around the spraying process designed to reduce the ingress of air into the system and so reduce oxidation of the of the particles being sprayed. Gas and particle velocity are significantly increased within the reduced pressure chamber. This yields a higher density deposit. Shrouded HVOF spraying provides for a thermal coating having a density range of approximately greater than 95%.
Proceeding from thermal spray processes (1) through (5) listed above, as the velocity of the molten particles increases, the cost of the process doubles or triples. Thus, while it would be ideal to always employ the highest velocity and highest density coating, it is not always practicable. Extremely dense coatings can be very stressed, as they have strong interconnected bonding. Cohesive forces within the particles of the coating can be greater than adhesive forces holding the coating to a substrate, and the coating may de-bond, i.e., pull away from a substrate.
Moreover, the highest quality processes, plasma spray and HVOF, produce coatings with the expected quality only when performed under tightly controlled conditions, such as at a manufacturing plant or in the laboratory, as discussed herein.
Another factor impacting thermal spray coating quality is the geometry of the substrate. High powered thermal spray processes, such as plasma spray or HVOF, produce high quality, dense coatings only when the thermal spray stream impacts the surface of the substrate at a substantially perpendicular angle. Such deposition angles are normally not possible in incinerators, which have irregularly shaped surfaces at fillets, heat exchangers, or welded areas around incinerator tubes.
In addition to fabrication issues, access to the surfaces of the inner walls of incinerators is greatly limited by space constraints. The equipment necessary for applying thermal spray coating is cumbersome, and difficult to position inside the plenum of an incinerator. The upper reaches of the walls of an incinerator can only be reached by being positioned on scaffolding. Most high-powered thermal spray coating equipment is too dangerous to be used in such a manner. In addition, high-powered thermal spray coating equipment produces vibrations. These vibrations could be hazardous if such equipment were employed in an enclosed or difficult to reach space.
A coating process which could be easily repaired, would be extremely useful in any situation where a metal is being exposed to a highly corrosive environment to which it is difficult to gain access.
While highly protective, thermal spray coatings do show signs of corrosion and erosion after exposure to harsh conditions. There presently exists no routine and cost effective method of repairing damaged or worn thermal spray coatings, short of stripping the damaged coating and re-applying a completely new coating to a surface. This process is expensive and time consuming. In addition, an operating facility where a new thermal spray coating must be applied may have to be shut down for an extended period of time during the re-application process.
An ideal thermal spray coating deposit has a density which approaches the density of a solid metal structure having the same composition as the composition being thermally sprayed. Thus, density of a coating, as used in the thermal spray coating arts and the herein specification, refers to the ratio of the measured density of the coating to the absolute density of a perfectly solid material of the same composition, expressed as a percentage.
A significant and inescapable drawback of thermal spray coating processes is the formation of porosity or voids in the coating, leading inevitably to coating densities below 100% (i.e., coating densities which are less than the density of the corresponding solid material of the same composition). Porosity is the largest source of coating failure.
As droplets or particles from the thermal spray coating process, known as xe2x80x9csplats,xe2x80x9d impact a substrate, the splats form layers. Pores or voids form between these layers, or between individual splats.
Porosity can originate from, inter alia, any of the following events in the coating process: material shrinkage on cooling from the liquid state; trapped, unmelted or partially melted particles, which form voids between adjacent to particles; voids that remain unfilled by the splats; poor intra-splat cohesion; and, separation of splats.
Notably, pores can form interconnected channels which reach directly from a coating""s outer surface to the underlying substrate, allowing corroding or oxidizing gas molecules, for example, to attack the base metal. Porosity can thus destroy a coating""s desired corrosion resistance.
Accordingly, there is a need for a thermal spray coating process which solves the problems of porosity associated with known spray coating processes. There is also a need for a thermal spray coating process which results in a coating having enhanced corrosion and oxidation resistance.
Aluminide coatings comprise one group of protective coatings which provide corrosion and oxidation resistance. Aluminide coatings are based on intermetallic compounds formed when nickel, in a nickel-based superalloy, for example, reacts with aluminum deposited at a substrate""s surface to form an aluminum-rich phase such as nickel aluminide (NiAl). NiAl has exceptional corrosion-resistant properties, and is stable and non-reactive. Accordingly, NiAl is desirable as a coating for any surface in a harsh environment.
Accordingly, it is an object of the invention to provide a coating on a substrate which can form an improved protective aluminide layer.
It is also an object of the invention to provide a coating which can be easily repaired.
The present invention generally provides a method of applying a coating to a substrate, which meets the needs outlined above. A metallic layer is deposited onto the substrate by thermal spraying. The metallic layer comprises at least about 8% nickel by weight. The deposited metallic layer has an average density of greater than about 80%. A slurry layer is deposited onto the metallic layer. The slurry layer comprises one or more diffusable aluminum-containing metallic pigments, and one or more inorganic liquid binders. The slurry layer comprises from about 10% to about 90% aluminum and/or aluminum alloy by weight.
The invention is also directed to a multilayer coating on a substrate, deposited according to the above-described process.
According to another embodiment, a method of repairing a nickel-containing metallic layer which has been deposited by thermal spraying is provided. The metallic layer comprises at least about 8% nickel by weight. The deposited metallic layer has an average density of greater than about 80%. A slurry layer is deposited onto the metallic layer. The slurry layer comprises one or more diffusable aluminum-containing metallic pigments, and one or more inorganic liquid binders. The slurry layer comprises from about 10% to about 90% aluminum and/or aluminum alloy by weight.
The method of the invention generally comprises first depositing onto a substrate, by thermal spray coating, a metallic layer comprising at least about 8% nickel (Ni) by weight. The metallic layer is deposited to a predetermined thickness which is effective to coat the substrate. The metallic layer may be deposited by any known thermal spray coating technique. The least expensive and uncomplicated thermal spray coating processes, such as combustion wire spraying (flame spraying), are preferred.
A slurry layer is then formed on the metallic layer by any suitable method including spraying, rolling or brush painting a slurry layer onto the metallic layer. The slurry layer comprises an inorganic liquid binder, and an aluminum-containing metallic pigment. The slurry provides an additional coating on the thermal spray deposited metallic layer, and soaks into and fills the pores present in the thermally sprayed metallic layer.
The coating of the invention may be applied to a surface which is subject to a high temperature environment, such as the surface inside a waste incinerator. Where the coating provided is applied to an incinerator surface subject to temperatures below approximately 450xc2x0 C. (842xc2x0 F.), the coating functions to reduce corrosion and oxidation of the underlying substrate. At temperatures below about 450xc2x0 C. (842xc2x0 F.), the metallic layer and slurry layer remain intact as distinct layers on the substrate.
At temperatures greater than approximately 450-500xc2x0 C. (842-932xc2x0 F.), aluminum from the slurry diffuses into the metallic layer, reacting with the Ni in the metallic layer, and forming an intermetallic layer composed of NiAl at the surface of the metallic layer. As described herein, NiAl possesses highly desirable properties, and provides additional protection for the substrate at high temperatures.
The method of the present invention is generally applicable to any surface which will be subjected to extreme temperatures or corrosive substances. The present invention provides a relatively simple to apply and cost-effective method, which provides for a coating can be easily repaired in situ.
It is desirable that the metallic layer have a high density, and thus a low porosity. However, one of the favorable features of the invention is that the metallic layer can be deposited using the least expensive, and lower density, thermal spray coating processes, such as flame spraying and arc wire. The more expensive thermal spray coating processes such as plasma spraying and HVOF, need not be employed, because the present invention provides for a solution to the problem of porosity in thermal spray coatings.
The coating method of the present invention may be applied to any substrate which would benefit from protection from adverse temperature, chemical or environmental conditions. In particular, the substrate may take the form of a wall such as the interior wall of an incinerator exposed to extreme heat and combustion products, known as the xe2x80x9cfireside wall.xe2x80x9d It should be appreciated that the process of the present invention can be applied to, and is useful on, any substrate that will be exposed to a similar harsh environment.
The thermal spray-deposited layer should be comprised of at least about 8% Ni by weight. It is contemplated that those skilled in the art would appreciate the existing nickel-containing thermal spray coatings which can be utilized as the metallic layer. Corrosion resistant superalloy coatings containing Ni are particularly suitable materials to be used for forming the metallic layer, so long as the selected alloys have a Ni content of at least about 8% Ni by weight.
According to a preferred embodiment of the present invention, the metallic layer also comprises at least about 12% chromium by weight. Chromium is known to have desirable corrosion and oxidation resistant properties, and has been incorporated into the formulation of various superalloys.
Acceptable superalloy thermal spray coatings include, for example, the following commercially available superalloys:
The above-listed superalloys are available under the indicated trade names, and other trade names. Other superalloys containing at least about 8% Ni by weight and at least about 12% Cr by weight are known to those skilled in the art, and may be selected for the practice of the present invention.
Thermal spray coatings have been combined with slurry mixtures to form abradable seals. These seals are applied to turbomachinery to maintain clearances between spinning blades and surrounding structure. For example, U.S. Pat. No. 5,024,884 to Otfinoski discloses such an abradable seal. An abradable seal must fragment and disappear when contacted by rotating parts which are spinning at high speeds. Thus, a thermal spray coating layer, if used for an abradable seal, must have a density when deposited of approximately between 12-40%, as described in Otfinoski and the abradable seal patents cited therein. At that density, the abradable seal will fragment and degrade when contacted.
Unlike an abradable seal, the metallic layer of the present invention must not fragment or disappear, even under extremely harsh conditions. Accordingly, the metallic layer of the present invention should be deposited to an average density generally greater than about 80%, corresponding to a porosity of no greater than about 20%, in order to perform effectively as a barrier to corrosion and oxidation. Abradable seals cannot be used as effective coating to prevent corrosion or oxidation.
One advantage of the present invention is that, once the metallic layer is deposited by thermal spraying, no special treatment, such as sanding or buffing, need be performed to prepare the metallic layer. The metallic layer may remain substantially rough, without having a detrimental effect on the coating process described herein. The metallic layer is deposited by thermal spraying until a preselected thickness has been deposited. The metallic layer should be deposited to a thickness in the range of about 150-1600 xcexcm.
The selected thickness for the metallic layer will vary depending on the thermal spray process and equipment chosen for depositing the metallic layer. For combustion flame spraying, the metallic layer should be deposited to a thickness of about 200-600 xcexcm, for example. The selected thickness will also depend on the ultimate use and environment of the substrate.
Once the metallic layer is properly deposited, a slurry layer is deposited over the metallic layer, by either spraying, rolling, brush painting, or any similar method. Another significant advantage of the present invention, is that the step of depositing the slurry layer can be performed in a simple and economical manner, using inexpensive tools. The slurry layer need not be deposited with exacting precision. Thus, the process of the present invention can be easily practiced in spaces which are difficult or uncomfortable to reach, such as the interior of an incinerator. The slurry layer is also easily applied to irregularly shaped surfaces, such as fillets or welded areas around incinerator tubes.
The slurry layer comprises an inorganic liquid binder and a metallic pigment. The inorganic liquid binder which should not be fugitive or decompose under the harsh conditions to which it will be exposed. Binders which are appropriate for use as components of the slurry layer include, but are not limited to, the following:
(1) acid phosphate/dichromates or acid phosphate/molybdates;
(2) acid phosphates, such as the acid phosphates exemplified by U.S. Pat. No. 5,478,413 to Mosser et al., the entire disclosure of which is incorporated herein by reference;
(3) alkali silicates;
(4) lithium polysilicates;
(5) quaternary silicates;
(6) colloidal silica;
(7) alkyl silicates;
(8) siloxanes.
Examples of acid phosphate/dichromate or acid phosphate/molybdate types of slurries are provided in U.S. Pat. No. 3,248,251 to Allen, described above, the entire disclosure of which is incorporated herein by reference. Allen describes coating compositions consisting essentially of a slurry of solid inorganic particulate pigment material (such as aluminum) in an aqueous acidic bonding solution containing dissolved metal chromate, dichromate or molybdate, and phosphate. These xe2x80x9cAllenxe2x80x9d coatings have been and still are successfully used to provide high quality coatings which protect ferrous metal alloy surfaces from oxidation and corrosion, particularly at high temperatures.
Alkali silicates are solutions of sodium and potassium silicates with various M2O/SiO2 ratios where M is sodium or potassium. These solutions are alkaline and can air set and air cure, often without heating.
Lithium polysilicates are similar to alkali silicates, but behave more like colloidal silica. These binders will also cure in air.
Quaternary silicates have the formula R4N+SiO3xe2x88x92, where R is typically a short chain alkyl group. These binders set or cure to SiO2 coatings.
Alkyl silicates such as tetraethyl orthosilicate can be used. These are tetraethoxysilanes which hydrolyze to form hydrated silicas.
Siloxanes (silicones) may also be used as binders. The organic portion of the siloxane chain decomposes at varying temperatures above about 200xc2x0 C., leaving SiO2 xe2x80x9cbackbonesxe2x80x9d.
Each of the above-listed binders possesses the characteristics necessary for proper performance in the present invention. Each binder allows entrained pigments to diffuse into the metallic layer when the temperature reaches about 500xc2x0 C. (932xc2x0 F.).
The metallic pigment comprises aluminum, typically in a powder form. Atomized aluminum powder is commonly used as a component in slurries. Particle size is not critical to the performance of the aluminum powder as used in the disclosed invention.
Aluminum alloy powders can also be used. An example of an aluminum alloy is an 88/12 aluminum/silicon (eutectic) powder. Additions of silicon (elemental) are desirable up to about 20% of the aluminum content. By xe2x80x9caluminum-containing metallic pigmentsxe2x80x9d is meant a metallic pigment which comprises aluminum and/or an aluminum alloy.
The amount of aluminum as the metallic pigment in the slurry layer, in either powder form or as an aluminum alloy, may range from about 10% to about 90% by weight of the total slurry layer content (weight of the metallic pigment plus the weight of the inorganic liquid binder), and is preferably in the range of about 40% to about 80% by weight. The range is more preferably from about 55% to about 70%, most preferably from about 58% to about 62%.
The thickness of the slurry layer can be adjusted to accommodate slurries having varying amounts of aluminum. In the case of slurries having a lower concentration of aluminum (for example 10% aluminum), a thicker slurry layer would be required to provide an adequately protective coating, and to provide an amount of aluminum necessary for forming an intermetallic layer of NiAl at higher temperatures, as described. The thickness of the slurry layer should preferably be at least 25 microns (1 mil), more preferably from about 50 to about 200 microns (2-8 mils), most preferably from about 75 to about 150 microns (3-6 mils).
The aluminum in the slurry layer should be diffusable, that is, capable of diffusing into the pores of the metallic layer and reacting with the Ni of the metallic layer at high temperatures, for example, at temperatures greater than approximately 500xc2x0 C. (932xc2x0 F.), in order to form an intermetallic layer of NiAl.
Examples of slurries suitable for use in the present invention containing aluminum powder include: the various slurries prepared according to U.S. Pat. No. 3,248,251 to Allen, particularly examples 2, 3, 7, 9, 10,12, and 14 thereof; the slurries described in U.S. Pat. No. 3,869,293 (Brumbaugh), which contain an Al/Mg metallic pigment; the slurries of U.S. Pat. Nos. 4,537,632 and 4,606,967, which contain spherical aluminum powder; and the slurries of U.S. Pat. No. 4,617,056 (Mosser et al.), U.S. Pat. No. 4,659,613 (Mosser et al.) and U.S. Pat. No. 4,863,516 (Mosser et al.), all containing atomized and/or flake aluminum compositions. The disclosures of the aforementioned patents are all incorporated herein by reference in their entireties.
It is also contemplated that a chromate-free slurry can form the slurry layer of the present invention. Suitable chromate-free slurries are described in U.S. Pat. No. 5,478,413 (Mosser et al.), U.S. Pat. No. 5,652,064 (Mosser et al.) and U.S. Pat. No. 5,803,990 (Mosser et al.), the entire disclosures of which are incorporated herein by reference.
The slurry layer is deposited over the rough porous thermal-sprayed metallic layer. Part of the binder liquid is absorbed into the pores of the metallic layer. The binder will form a phosphate or a silica once the slurry layer is deposited onto the metallic layer, depending on the formulation of the binder used. Both phosphates and silicas bond to oxidized metal surfaces, which are normally found in thermal spray coatings. The cured slurry coating creates a smooth surface layer further decreasing reaction and fouling.
It is well known in the art that aluminum-containing slurries such as those described in U.S. Pat. No. 3,248,251 to Allen, can be cured by heating, causing the slurries to lose water. The cured slurry is typically water-insoluble. Aluminum-containing slurries can be cured by heating to temperatures of about 300-350xc2x0 C. (572-662xc2x0 F.) for about 1 hour; 250xc2x0 C. (482xc2x0 F.) for about 4 hours; or, 190xc2x0 C. (374xc2x0 F.) for about 20 hours. As noted herein, slurries containing alkali silicates and lithium polysilicates can air set, without the need for heat curing.
However, it is not a requirement of the present invention that the slurry layer must be cured by a separate heating step. The slurry layer of the invention will typically be deposited in an environment subjected to extreme heat, such as the combustion zone of an incinerator. It is desirable that the slurry layer be deposited in a low humidity environment to keep the slurry from rewetting during the deposition process. Once the slurry layer is deposited, the incinerator can be placed into operation, and the high temperature of the incinerator operation will rapidly cure the slurry.
Due to the porosity of thermal spray coatings, described above, the deposited metallic layer acts as a sponge, which absorbs the slurry layer into the pores. Thus, aluminum from the slurry flows into and fills the pores of the metallic layer. This creates a coating which does not suffer from the porosity problems ordinarily associated with the application of thermal spray coatings.
Significantly, the composition formed by the process of the present invention provides a remarkable coating when used in a high temperature environment. At higher temperatures, above approximately 500xc2x0 C. (932xc2x0 F.), it is believed that aluminum from the slurry will begin diffusing into the thermal spray coating, forming a diffusion (intermetallic) layer of NiAl.
The NiAl intermetallic phase will form when the aluminum in the slurry layer diffuses into the nickel in the metallic layer. The NiAl structure may be hypostoichiometric or hyperstoichiometric, but will retain the NiAl structure. As noted, aluminides such as NiAl are resistant to high temperature degradation and therefore are preferred as protective coatings.
The NiAl diffusion layer formed at high temperatures has exceptional corrosion-resistant properties. It is continuous, is stable, non-reactive and has a very high melting point. The NiAl alloy formed is extremely hard and thermodynamically stable, which is an important advantage in a harsh environment. In addition, the NiAl diffusion layer resists oxidation and hot corrosion forming an adherent protective scale. As discussed below, it has been found that the NiAl will not be wet by flying molten ash.
The process of the present invention is described herein by a coating applied to fireside wall in an incinerator. However, it should be appreciated that the process is not so limited in its application, but may find use in any industry where surfaces may be exposed to extreme temperatures and noxious substances.
The process of the present invention may also be used to repair a previously deposited thermal spray coating layer. If a thermal spray coating layer meeting the requirements of the metallic layer of the present invention has been previously deposited onto a substrate, a slurry layer as described herein can be deposited over the previously deposited layer. This provides for the formation of the improved multilayer coating of the invention.
If a previously deposited thermal spray coating shows signs of damage, such as cracking or disbonding, the coating can be repaired by depositing additional thermal spray coating only to the damaged areas. A slurry layer can then be deposited on top of the repaired thermal spray coating. Thus, it is not necessary to completely recoat an entire incinerator, as had been previously required when using thermal spray coating techniques alone. According to this embodiment of the invention, a previously deposited thermal spray coating metallic layer can be repaired in an easy and cost effective manner, never before appreciated.

Method for coating and protecting a substrate


An intravascular catheter of the invention has an improved distal tip with an expanded portion which has exterior transverse dimensions greater than an unexpanded portion proximally adjacent to the expanded portion. In one presently preferred embodiment the catheter has an inflatable balloon with a distal skirt which is secured to the unexpanded portion of the distal tip so as to provide an even exterior surface thereto.

This invention generally relates to intravascular catheters, particularly catheters for use in percutaneous transluminal coronary angioplasty (PCTA) or stent delivery.
In a typical PTCA procedure a dilatation balloon catheter is advanced over a guidewire to a desired location within the patient""s coronary anatomy where the balloon of the dilatation catheter is properly positioned within the stenosis to be dilated. The balloon is then inflated to a predetermined size with radiopaque liquid at relatively high pressures (generally 8-18 atmospheres) to dilate the stenosed region of the diseased artery. One or more inflations may be needed to effectively dilate the stenosis. The catheter may then be withdrawn from the stenosis or advanced further into the patient""s coronary anatomy to dilate additional stenoses.
The distal tip of an intravascular catheter may be constructed to have non-traumatic characteristics to minimize damage when passing through a body lumen. A typical non-traumatic tip is formed from a short tubular member made of relatively soft polymeric material which is secured to the distal tip of the tubular distal extremity of the catheter. However, this construction does not always eliminate injury to the luminal lining. For example, the leading edge of the distal skirt of the balloon which extends radially outward can cause intimal injury even though it may be somewhat tapered. Moreover, securing a distal lip made from softer material or otherwise designed to collapse so as to avoid intimal injury, complicates the manufacturing procedure and increases its costs.
What has been needed and heretofore unavailable is a simple, inexpensive method for forming a nontraumatic distal tip. The present invention satisfies this and other needs.
This invention is directed to a distal tip construction for intraluminal catheters which has an improved non-traumatic characteristics and which is simple and inexpensive to produce.
The catheter of the invention generally has an elongated shaft with a proximal end, a distal end, a guidewire lumen extending through at least the distal portion of the catheter and a port in the distal end in fluid communication with the guidewire lumen. The elongated catheter has a tubular distal extremity which defines the guidewire lumen and which has an expanded portion with outer dimensions greater than a proximally adjacent unexpanded portion. Preferably, the tubular distal extremity tapers in the direction distal to the expanded portion to a smaller outer diameter at the distal end thereof which defines the port therein.
In one presently preferred embodiments of the invention, the catheter is a dilatation catheter having a balloon on a distal shaft section with an inner tubular member extending through and distal to the balloon which defines the guidewire lumen. The portion of the inner tubular member extending distal to the balloon is expanded in accordance with the present invention with the distal skirt of the balloon secured to an unexpanded portion of the inner tubular member proximally adjacent to the expanded portion. The distal skirt of the balloon is preferably sealingly bonded to the exterior of the unexpanded portion of the inner tubular member in a suitable manner such as by fusion or adhesive bonding. The expanded portion of the inner tubular member which extends distal to the distal skirt of the balloon preferably has outer dimensions which are essentially the same as or slightly larger than the outer dimensions of the distal skirt of the balloon so as to present a non-traumatic exterior to the interior of the body lumen in which the catheter is advanced.
The distal tubular extremity may be formed by placing it within a molding surface, such as a sheath, with interior dimensions the same as the desired dimensions of the expanded portion of the distal tubular extremity. The interior of the distal tubular extremity is then subjected to fluid pressure and the exterior to heat which causes the heated portion to soften or melt thereby expanding to the interior dimensions of the molding surface. The proximal portion of the distal tubular extremity, which is not to be expanded, may be supported exteriorly and not subjected to elevated temperatures so that it does not expand. The part of the distal tubular extremity distal to the expanded portion is likewise not expanded in a similar manner during the manufacturing procedure.
The expanded portion of the tubular distal extremity of the catheter ranges in length from about 0.1 to about 1.0 cm, preferably about 0.2 to about 0.5 cm. The overall length of the tubular distal extremity of the catheter which extends distal to the distal balloon skirt in the aforesaid presently preferred embodiment ranges from about 0.2 to about 1.5 cm, preferably about 0.3 to about 0.7 cm. The inner diameter or dimensions of the guidewire lumen extending through the expanded portion ranges from about 0.018 to about 0.035 inch (0.46-0.89 mm), preferably about 0.021 to about 0.025 inches (0.53-0.64 mm). The inner transverse dimensions of the guidewire lumen proximal to the expanded portion for a 3 mm balloon is about 0.013 to about 0.023 inches (0.33-0.58 mm), preferably about 0.016 to about 0.019 inch (0.41-0.48 mm) for a 0.014 inch (0.36 mm) guidewire. The guidewire lumen distal to the expanded portion is preferably tapered from the inner diameter of the expanded portion to transverse dimension slightly greater than the transverse dimensions of the guidewire to be passed therethrough. The wall thickness of the tubular distal extremity will vary depending upon the polymeric material from which the tubular member is made. The wall thickness of the expanded portion will usually be less than the unexpanded portion due to the expansion thereof by blowing unless the wall thickness of the portion to be expanded is initially greater than the portion which is not to be expanded.
The present invention provides an improved non-traumatic distal tip for intravascular catheters, which has gradual distal transitions in both profile and stiffness. This is particularly advantageous in balloon dilatation catheters where the distal skirt of the balloon can be secured to the unexpanded portion of the distal tubular extremity of the catheter proximal to the expanded portion so as to present a distal tip with a smooth, uniform exterior.
These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings.

Intravascular catheter with expanded distal tip