Classifications

• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/39—Organic or inorganic per-compounds
  • C11D3/3902—Organic or inorganic per-compounds combined with specific additives
  • C11D3/3937—Stabilising agents
  • C11D3/394—Organic compounds

Definitions

• the present invention relates to novel stabilizers for bleaching agents and to detergent compositions containing the same.
• Bleaching agents have long been used in laundry detergents to enhance the overall cleaning action thereof. Instability of bleaching agents in detergents is mediated principally by metal ion contamination in the detergent themselves, in the wash liquors and in the textiles and fabrics being cleaned.
• the hydrogen peroxide responsible for the bleaching action in detergent formulas containing a peroxide- based bleaching agent acts by dissociating into perhydroxyl ion:
• NTA nitrilotriacetic acid
• EDTA ethylenediaminetetraacetic acid
• ETMP ethylenediaminetetramethylenephosphonic acid
• PDTA propylenediaminetetraacetic acid
• HPDTA hydroxypropylenediaminetetraacetic acid
• hydroxyethanediphosphonic acid diethylenetriaminetetraacetic acid, diethylenetriaminetetramethylenephosphonic acid, hydroxyethylimino, diacetic acid, hydroxyethylethylenediaminetriacetic acid diethylenetriaminepentaacetic acid and also for example diethanolglycine, ethanolglycine, citric acid, glucoheptonic acid or tartaric acid, as found for example under the heading of Waschsch in Ullmann's Encyklopädie der ischen Chemie, 4th edition, volume 24, pages 63-160, in particular pages 91-96, Verlag Chemie, 4th edition, volume 24, pages 63-160,
• NTA makes a very good complexing agent and, in detergents, a fairly good builder for improving the whitening effect and for preventing deposits which cause incrustations and graying on the fabric.
• its performance as a bleach stabilizer is comparatively poor.
• EDTA turns out to be insufficiently biodegradable in conventional tests, as do PDTA, HPDTA and certain phosphonates which, furthermore, are frequently undesirable on account of their phosphorus content.
• France Patent Application No. 1,338,856, patented August 26, 1963 discloses perborate detergent compositions for washing laundry in boiling water.
• the detergent composition contains methyliminodiacetic acid in association with a water-soluble copper salt to enhance the whitening effects of the perborate bleaching agent. This association forms a metal buffer which maintains the amount of free copper present in the washing medium at a value corresponding to the maximum effect of the whitening efficiency of the perborate.
• the patent does not disclose alkyliminodiacetic acid for bleach stabilization in detergent compositions.
• substituted ammonium refers to an ammonium radical substituted with one or more alkyl groups having from 1 to 4 carbon atoms.
• stabilizers in accordance with the invention include, for example, methyliminodiacetic acid, ethyliminodiacetic acid, propyliminodiacetic acid and the like.
• Alkyliminodiacetic acids are available commercially but may be prepared cheaply and easily by the method for the preparation of methyliminodiacetic acid as described by G. J. Berchet in Organic Synthesis, Vol. 11, pages 397-398, which method is described in Example I below.
• Bleaching agents which may be stabilized in accordance with the invention are, in particular, hydrogen peroxide and derivatives thereof or available chlorine compounds.
• bleaching agent compounds which provide H 2 0 2 in water, sodium perborate hydrates, such as NaB0 2 .H 2 0 2 .3H 2 0 and NaB0 2 .H 2 0 2 , are of particular importance. However, it is also possible to use other H 2 0 2 -providing borates.
• peroxyhydrates such as peroxycarbonates, peroxyphosphonates, citrate perhydrates, urea-H 2 0 2 , or melamine-H 2 0 2 compounds and also by H 2 0 2 -providing peracid salts, for example caroates, perbenzoates or peroxyphthalates.
• customary water-soluble and/or water-insoluble stabilizers for peroxy compounds can be incorporated together with the former in amounts from 0.25 to 10% by weight, based on the peroxy compound.
• Suitable water-insoluble stabilizers are the magnesium silicates MgO:Si0 2 from 4:1 to 1:4, preferable from 2:1 to 1:2, in particular 1:1, in composition usually obtained by precipitation from aqueous solutions. In their place it is also possible to use other alkaline earth metals of corresponding composition.
• bleach activators in the detergent, advantageously in an amount from 5 to 30% by weight, based on the H 2 0 2 providing compound.
• Activators for peroxy-compounds which provide H 2 0 2 in water are certain N-acyl and O-acyl compounds, in particular acetyl, propionyl or benzyl compounds, which form organic peracids with H 2 0 2 and also carbonic and pyrocarbonic esters.
• Useful compounds are inter alia:
• N-diacylated and N,N'-tetraacylated amines e.g. N,N,N',N'-tetraacetyl-methylenediamine or - ethylenediamine, N,N-diacetylaniline and N,N-diacetyl-p-toluidine, and 1,3-diacylated hydantoins, alkyl-N-sulfonylcarboxamides, N-acylated cyclic hydrazides, acylated triazoles or urazoles, e.g. monoacetyl- maleohydrazide, O,N,N-trisubstituted hydroxylamines, e.g.
• glucose pentaacetate imidazolidine derivatives, such as 1,3-diformyl-4,5-diacetoxyimidazolidine, 1,3-diacetyl-4,5- diacetoxyimidazoline and 1,3-diacetyl-4,5-dipropionyloxyimidazolidine, acylated glycolurils,e.g. tetrapropionylglycoluril or diacetyldibenzoylglycoluril, dialkylated 2,5-diketopiperazines, e.g.
• the bleaching agents used can also be active chlorine compounds of the inorganic or organic type.
• Inorganic active chlorine compounds include alkali metal hypochlorites which can be used in particular in the form of their mixed salts and adducts on orthophosphates or condensed phosphates, for example on pyrophosphates and polyphosphates or on alkali metal silicates. If the detergent contains monopersulfates and chlorides, active chlorine will form in aqueous solution.
• Organic active chlorine compounds are in particular the N-chlorine compounds where one or two chlorine atoms are bonded to a nitrogen atom and where preferably the third valence of the nitrogen atom leads to a negative group, in particular to a CO or S0 2 group.
• These compounds include dichlorocyanuric and trichlorocyanuric acid and their salts, chlorinated alkylguanides or alkylbiguanides, chlorinated hydantoins and chlorinated melamines.
• Bleaching stabilizers of the invention may be used in detergent formulations in general in an amount from about 0.01 to 10% by weight, preferably from 0.05 to 6% by weight, most preferably 0.1 to 2.0% by weight, based on the total weight of the detergent formulations.
• the stabilizers according to the invention can also be used in detergent formulations together with other prior art constituents e.g. complexing agents, builders, co-builders, surfactants, whiteners, etc., in which case the general properties can be substantially improved in respect of sequestration, incrustation inhibition, grayness inhibition, primary washing action and bleaching action.
• other prior art constituents e.g. complexing agents, builders, co-builders, surfactants, whiteners, etc.
• Detergent formulations which, based on the total weight, contain from 0.01 to 10%, preferably from 0.05 to 6.0%, by weight of a compound in accordance with the invention generally contain as additional constituents, based on the total weight, from 6 to 25% by weight of surfactants, from 15 to 50% by weight of builders with or without cobuilders, from 5 to 35%, typically 15 to 20%, by weight of bleaching agents, with or without bleaching agent activators, and from 3 to 30% by weight of assistants, such as enzymes, foam regulants, corrosion inhibitors, optical brighteners, scents, dyes or formulation aids, e.g. sodium sulfate.
• surfactants from 15 to 50% by weight of builders with or without cobuilders, from 5 to 35%, typically 15 to 20%, by weight of bleaching agents, with or without bleaching agent activators, and from 3 to 30% by weight of assistants, such as enzymes, foam regulants, corrosion inhibitors, optical brighteners, scents, dyes or formulation aids, e.g
• Suitable surfactants are those which contain in the molecule one or more hydrophobic organic radicals and one or more water-solubilizing anionic, zwitterionic or nonionic groups.
• the hydrophobicradicals usually are aliphatic hydrocarbyl of 8 to 26, preferably 10 to 22, in particular 12 to 18, carbon atoms or aromatic alkyl having 6 to 18, preferably 8 to 16, aliphatic carbon atoms.
• Suitable synthetic anionic surfactants are in particular those of the sulfonate, sulfate or synthetic carboxylate type.
• Suitable surfactants of the sulfonate type are alkylbenzenesulfonates having 4 to 15 carbon atoms in the alkyl moiety, mixtures of alkene and hydroxyalkane-sulfonates and also disulfonates as obtained for example from monoolefins having a terminal or nonterminal double bond by sulfonation with gaseous sulfur trioxide and subsequent alkaline or acid hydrolysis of the sulfonation products.
• alkanesul- fonates obtainable from alkanes by sulfochlorination or sulfoxidation and subsequent hydrolysis or neutralization or by bisulfite addition onto olefins.
• surfactants of the sulfonate type are the esters of alpha-sulfo fatty acids, for example the alpha-sulfonic acids of hydrogenated methyl or ethyl esters of coconut, palm kernel or tallow fat acid.
• Suitable surfactants of the sulfate type are the sulfuric monoesters of primary alcohols, for example coconut fat alcohols, tallow fat alcohols or oleyl alcohol, and those of secondary alcohols. Also suitable are sulfated fatty acid alkanolamines, fatty acid monoglycerides or reaction products of from 1 to 4 moles of ethylene oxide with primary or secondary fatty alcohols or alkylphenols.
• anionic surfactants are the fatty acid esters or fatty amides of hydroxy- or aminocarboxylic or sulfonic acids, for example the fatty acid sarcosides, glycolates, lactates, taurides or isothionates.
• Anionic surfactants can be present in the form of their sodium, potassium and ammonium salts and also as soluble salts of organic bases, such as mono-, di-, or triethanolamine. Also possible are ordinary soaps, i.e. salts of natural fatty acids.
• Suitable nonionic surfactants are for example adducts of from 3 to 40, preferably 4 to 20, moles of ethylene oxide on 1 mole of fatty alcohol, alkylphenol, fatty acid, fatty amine, fatty acid amide or alkanesulfonamide. Of particular importance are the adducts of from 5 to 16 moles of ethylene oxide on coconut or tallow fat alcohols, on oleyl alcohol or on synthetic alcohols of 8 to 18, preferably 12 to 18, carbon atoms, and also on mono- or dialkylphenols of 6 to 14 carbon atoms in the alkyl(s).
• water-soluble nonionics it is also possible to use water-insoluble or incompletely water-soluble polyglycol ethers having 1 to 4 ethylene glycol ether radicals in the molecule, in particular if used together with water-soluble nonionic or anionic surfactants.
• nonionic surfactants are the water-soluble adducts of ethylene oxide on propylene glycol ether, alkylenediaminopolypropylene glycol and alkylpolypropylene glycol having 1 to 10 carbon atoms in the alkyl chain which contain from 20 to 250 ethylene glycol ether groups and from 10 to 100 propylene glycol ether groups and where the polypropylene glycol ether chain acts as a hydrophobic radical.
• nonionic surfactants of the amine oxide or sulfoxide type.
• the foaming power of surfactants can be enhanced or reduced by combining suitable types of surfactants. A reduction can also be obtained by adding nonsurfactant like organic substances.
• Suitable builder substances are for example: wash alkalis, such as sodium carbonate and sodium silicate, or complexing agents, such as phosphates, or ion exchangers, such as zeolites, and mixtures thereof.
• wash alkalis such as sodium carbonate and sodium silicate
• complexing agents such as phosphates, or ion exchangers, such as zeolites, and mixtures thereof.
• phosphates or ion exchangers, such as zeolites, and mixtures thereof.
• zeolites such as zeolites, and mixtures thereof.
• these builder substances have as their function to eliminate the hardness ions, which come partly from the water, partly from dirt or the textile material, and to support the surfactant action.
• the builder component may further contain cobuilders. In modern detergents, it is the function of cobuilders to undertake some of the functions of phosphates, e.g. sequestration, soil antiredeposition and primary and secondary washing action.
• the builder components may contain for example water-insoluble silicates as described for example in German Laid-Open Application DE-OS No. 2,412,837 and/or phosphates.
• a phosphate it is possible to use pyrophosphate, triphosphate, higher polyphosphates and metaphosphates.
• phosphorus-containing organic complexing agents such as alkanepolyphosphonic acids, amino- and hydroxy-alkanepolyphosphonic acids and phosphonocarboxylic acids, are suitable for use as further detergent ingredients.
• detergent additives are the following compounds: methanediphosphonic acid, propane-1,2,3-triphosphonic acid, butane-1,2,3,4-tetraphosphonic acid, polyvinylphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, 1-amino-1-phenyl-1,1-diphosphonic acid, aminotris- methylenetriphosphonic acid, methylamino- or ethylamino-bismethylenediphosphonic acid, ethylenediaminetetramethylenetetraphosphonic acid, diethylenetriaminopentamethylenepentaphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, phosphonoacetic and phosphonopropionic acid, copolymers of vinylphosphonic acid and acrylic and/or maleic acid and also partially or completely neutralized salts thereof.
• polycarboxylic acids are dicarboxylic acids of the general formula HOOC-(CH 2 ) m -COOH where m is 0-8, and also maleic acid, methylenemalonic acid, citraconic acid, mesaconic acid, itaconic acid, noncyclic polycarboxylic acids having 3 or more carboxyl groups in the molecule, e.g. tricarballylic acid, aconitic acid, ethylenetetracarboxylic acid, 1,1,3-propanetetracarboxylic acid, 1,1,3,3,5,5-pentanehexacar- boxylic acid, hexanehexacarboxylic acid, cyclic di- or polycarboxylic acids, e.g.
• cyclopentanetetracarboxylic acid cyclohexanehexacarboxylic acid, tetrahydrofurantetracarboxylic acid, phthalic acid, terephthalic acid, benzene-tricarboxylic, -tetracarboxylic or-pentacarboxylic acid and mellitic acid.
• hydroxymonocarboxylic and hydroxypolycarboxylic acids are glycollic acid, lactic acid, malic acid, tartronic acid, methyltartronic acid, gluconic acid, glyceric acid, citric acid, tartaric acid and salicylic acid.
• aminocarboxylic acids are glycine, glycylglycine, alanine, asparagine, glutamic acid, aminobenzoic acid, iminodiacetic acid, iminotriacetic acid, hydroxyethyliminodiacetic acid, ethylenediaminotetraacetic acid, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid and higher homologues which are preparable by polymerization of an N-aziridylcarboxylic acid derivative, for example of acetic acid, succinic acid or tricarballylic acid, and subsequent hydrolysis, or by condensation of polyamines having a molecular weight of from 500 to 10,000 with salts of chloroacetic or bromoacetic acid.
• Preferred cobuilder substances are polymeric carboxylic acids. These polymeric carboxylic acids shall include the carboxymethyl ethers of sugars, of starch and of cellulose.
• Particularly important polymeric carboxylic acids are for example the polymers of acrylic acid, maleic acid, itaconic acid, mesaconic acid, aconitic acid, methylenemalonic acid, citraconic acid and the like, the copolymers between the aforementioned carboxylic acids, for example a copolymer of acrylic acid and maleic acid in a ratio of 70:30 and having a molecular weight of 70,000, or copolymers thereof with ethylenically unsaturated compounds, such as ethylene, propylene, isobutylene, vinyl alcohol, vinyl methyl ether, furan, acrolein, vinyl acetate, acrylamide, acrylonitrile, methacrylic acid, crotonic acid and the like, e.g. the 1:1 copolymers of maleic anhydride and methyl vinyl ether having a molecular weight of 70,000 or the copolymers of maleic anhydride and ethylene and/or propylene and/or furan.
• the cobuilders may further contain soil antiredeposition agents which keep the dirt detached from the fiber in suspension in the liquor and thus inhibit graying.
• soil antiredeposition agents which keep the dirt detached from the fiber in suspension in the liquor and thus inhibit graying.
• water-soluble colloids usually of an organic nature, for example the water-soluble salts of polymeric carboxylic acids, glue, gelatin, salts of ethercarboxylic acids or ethersulfonic acids of starch and of cellulose or salts of acid sulfates of cellulose and of starch.
• Even water-soluble polyamides containing acid groups are suitable for this purpose.
• Polyvinylpyrrolidone is also usable.
• Suitable foam regulants in particular if surfactants of the sulfonate or sulfate type are used, are surface-active carboxybetaines of sulfobetaines and also the abovementioned nonionics of the alkylolamide type. Also suitable for this purpose are fatty alcohols or higher terminal diols.
• Reduced foaming which is desirable in particular for machine washing, is frequently obtained by combining various types of surfactants, for example sulfates and/or sulfonates, with nonionics and/or with soaps.
• surfactants for example sulfates and/or sulfonates
• soaps the foam inhibition increases with the degree of saturation and the number of carbon atoms of the fatty acid ester; soaps of saturated C 2o -C 24 -fatty acids, therefore, are particularly suitable for use as foam inhibitors.
• the nonsurfactant-like foam inhibitors include possibly chlorine-containing N-alkylated aminotrizines which are obtained by reacting 1 mole of cyanuric chloride with from 2 to 3 moles of a mono-and/or dialkylamine having 6 to 20, preferably 8 to 18, carbon atoms in the alkyl.
• a similar effect is possessed by propoxylated and/or butoxylated aminotriazines, for example products obtained by addition of from 5 to 10 moles of propylene oxide onto 1 mole of melamine and further addition of from 10 to 50 moles of butylene oxide onto this propylene oxide derivative.
• nonsurfactant-like foam inhibitors are water-insouble organic compounds, such as paraffins or haloparaffins having melting points below 100° C, aliphatic C 18 - to C 4 o-ketones and also aliphatic carboxylic esters which, in the acid or in the alcohol moiety, possibly even both these moieties, contain not less than 18 carbon atoms (for example triglycerides or fatty acid fatty alcohol esters); they can be used in particular in combinations of surfactants of the sulfate and/or sulfonate type with soaps for foam inhibition.
• water-insouble organic compounds such as paraffins or haloparaffins having melting points below 100° C, aliphatic C 18 - to C 4 o-ketones and also aliphatic carboxylic esters which, in the acid or in the alcohol moiety, possibly even both these moieties, contain not less than 18 carbon atoms (for example triglycerides or fatty acid fatty alcohol
• the detergents may contain optical brighteners for cotton, for polyamide, for polyacrylonitrile of for polyester fabrics.
• suitable optical brighteners are derivatives of diaminostilbene-disulfonic acid for cotton, derivatives of 1,3-diarylpyrazolines for polyamide, quaternary salts of 7-methoxy-2-benzimidazol-2'-ylbenzofuranor of derivatives from the class of the 7-[1',2',5'-triazol-1'yl]-3-[1 ",2",4"-triazol-1 "yl]-coumarins for polyacrylonitrile.
• Examples of brighteners suitable for polyester are products of the class of the substituted styryls, ethylenes, thiophenes, naphthalenedicarboxylic acids or derivatives thereof, stilbenes, coumarins and naphthalimides.
• assistants or formulation aids are the conventional substances known to those skilled in the art, for example solubilizers, such as xylenesulfonates or cumenesulfonates, standardizing agents, such as sodium sulfate, enzymes or scent oils.
• compositions of this invention may be formulated according to any of the various commercially desirable forms.
• the formulations of this invention may be provided in granular form, in liquid form, in tablet form, or in the form of flakes or powders.
• compositions of this invention are susceptible to variation and in most cases will vary depending upon such factors as the nature of the particular ingredients being utilized, the end use of which the composition is intended to be put, the relative costs of the ingredients, and the like.
• the preferred compositions of this invention are phosphorus-free although it may be desired to include therein reduced quantities of conventional phosphorus-containing materials such as sodium tripolyphosphate, tetrasodium pyrophosphate, salts of substituted methylene disphosphonic acids, long chain tertiary phosphine oxides, or the like.
• the invention is not to be limited to any particular method of mixing the stabilizer and the detergent.
• the stabilizer may be mechanically mixed in, crutched in the detergent in the form of a slurry, or dissolved in a solution of the detergent.
• the stabilizer may be admixed with the detergent in any of the forms in which the detergent is manufactured, as well as being added simultaneously or separately to an aqueous solution.
• the stabilizers of the invention are intended to be used with the detergent at the time of application as a cleansing agent.
• the hydrogen peroxide responsible for the bleaching action in sodium perborate based laundry detergents is decomposed catalytically by transition metal ions such as Mn" and Cu". This degradation can be prevented by complexing the metal ions.
• the peroxide stabilizing effect of stabilizers in accordance with the invention was tested by measuring the peroxide present before and after storage in a hot aqueous solution which contains copper or manganese ions.
• the efficiency of the bleaching action of a laundry detergent containing the stabilizers of the invention was measured by washing white poly-cotton fabric swatches previously stained with grape juice. The test was carried out using the following detergent formulation:
• the pH of the wash solution was 10.3. The swatches were then rinsed for 5 minutes in 25 °C water and air dried.
• the efficiency of the bleaching action was determined by measuring the brightness (AE) of the swatches and the percentage of soil removed from the swatches.
• the biodegradability of bleach stabilizers described hereinabove was determined using the Sturm C0 2 Evolution Test (J. Amer. Oil Chem. Soc., 50, 159(1973)).
• the Sturm Test measures the ultimate biodegradation of soluble organic materials.
• the term "ultimate biodegradation" is defined herein to indicate the complete mineralization of material to C0 2 , water, and inorganic salts.
• the C0 2 generated from the degradation of the stabilizer of the invention was trapped using a series of three barium hydroxide traps. The barium hydroxide reacted with the C0 2 to form barium carbonate and the amount of C0 2 evolved was determined by titrating the unreacted barium hydroxide with hydrochloric acid.
• test medium was a modified BOD (Biochemical Oxygen Demand) water which contains, per liter of distilled water, the following standard BOD reagent solutions:
• a stock solution of the test compound was prepared at a concentration of 1000 mg/I and the pH adjusted to 7.0 if the initial pH was outside of a 4.0-10.0 pH range.
• the inoculum was prepared by taking unacclimated sludge and homogenizing it for two minutes, at room temperature, using a Waring Blender at medium speed. The homogenized sample was transferred to a beaker and left to settle for 15-30 minutes. The supernatant was carefully decanted and 10 ml of this solution was added to each test flask. Immediately prior to the beginning of the test, the viability of the test organisms was determined. There must be at least 1 x 10 6 microorganisms per milliliter before this inoculum can be used. The inoculum was used the day it was prepared.
• test flask was charged with 980 ml of test medium and then purged for twenty-four hours using C0 2 free air. Following the removal of residual C0 2 , the test flasks were connected to a series of three barium hydroxide traps each containing 100 ml of 0.024 N barium hydroxide. Ten milliliters of the test sample stock solution was added to each flask followed by the addition of 10 ml of the inoculum prepared above.
• the head space of each flask was aerated with C0 2 free air at a flow rate of 50-100 cc/min for the duration of the test. Every 2-3 days the first barium hydroxide trap (nearest to the test flask) was titrated using 0.05N standardized HCI and the amount of C0 2 evolved was determined. The remaining two barium hydroxide traps were moved forward to positions one and two and a new barium hydroxide trap was placed in position three. The length of the test was typically 26-30 days.
• Each test also included a sample of glucose which was used as a control to guarantee the activity of the microorganisms.
• Each stabilizer tested was degraded as described hereinabove with the exception that AspDA was degraded using acclimated microorganisms.
• the microorganisms were acclimated in a bench scale semicontinuous activate sludge system. The initial activated sludge was adjusted to a suspended solids level of 2500-3000 mg/I. The activated sludge was exposed to increasing levels of test material over a five day period (4, 8, 12, 16, and 20 mg/I) and then maintained at 20 mg/I for an additional five days. The acclimated microorganisms were then treated as described above prior to the start of the Sturm test.

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• 1992
  • 1992-04-15 CA CA 2066126 patent/CA2066126A1/fr not_active Abandoned
  • 1992-04-15 AU AU14933/92A patent/AU1493392A/en not_active Abandoned
  • 1992-06-30 MX MX9203844A patent/MX9203844A/es unknown
  • 1992-07-06 JP JP20018292A patent/JPH05194996A/ja active Pending
  • 1992-07-29 EP EP19920250197 patent/EP0526959A3/en not_active Withdrawn

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