Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
  • C23G1/20—Other heavy metals
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G5/00—Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/24—Cleaning or pickling metallic material with solutions or molten salts with neutral solutions

Definitions

• the present invention relates to a liquid composition, generally denoted for brevity hereinafter as a “bath” or more specifically as a “tinplate-cleaning bath”, that is used to clean the surface of tinplate (i.e., tin plated steel), especially in the form of » sheet, strip, and products made by shaping them, e.g., cans and other containers and the like.
• tinplate i.e., tin plated steel
• tinplate stock i.e., tin plated steel
• the present invention also relates to a process for cleaning tinplate stock.
• the present invention is excellently suited for cleaning "DI" tinplate cans that are fab ⁇ ricated by the drawing and ironing of tinplate sheet and strip.
• the present invention relates to a novel tinplate-cleaning bath and process that, when applied to the surface of tinplate, results in the removal of or ⁇ ganic materials (e.g., oil, lubricants, etc.) and inorganic materials (e.g., abrasives, etc.) and the generation of a surface condition that is well adapted for conversion treatment.
• this novel tinplate-cleaning bath and process are strongly resistant to the deposition of the sludge that is caused by the insolubilization of tin eluted by cleaning into the bath from the surface of the tinplate stock.
• the alkaline cleaning bath of Japanese Patent Publication Number Sho 59-2752 contains alkali metal silicate, alkali metal salt and alkali metal bicarbonate at ⁇ 1.5-fold (weight basis) of the amount of alkali metal silicate, and surfactant at ⁇ 5 0.4-fold (weight basis) of the amount of alkali metal silicate.
• This particular alkali component (known as builder) is specified in order to inhibit excessive dissolution of the tinplate surface due to line stoppage caused by problems in the degreasing line.
• the alkaline cleaning bath of Japanese Patent Application Laid Open Number Hei 3-59993 is intended to inhibit excess dissolution of the tinplate surface.
• This bath is an aqueous solution that contains 1.5 to 10 grams per liter (hereinafter often abbreviated "g L") of alkali metal or ammonium salt of orthophosphoric acid and 0.5 to 2 g/L of alkali metal nitrite. These two components are used in a molar ratio (former : latter) of 1 : 1 to 3.86 : 1.
• Bath pH is regulated to 9 to 11 with alkali metal carbonate.
• the alkaline cleaning bath of Japanese Patent Application Laid Open Number Hei 3-59994 is intended to inhibit excess disso ⁇ lution of the tinplate surface.
• This bath is an alkaline aqueous solution with pH 9 to 13 that contains surfactant, alkali metal or ammonium salt of orthophosphoric acid, and at least 0.005 g/L of at least 1 selection from the group comprising the alkaline earth metal oxides, hydroxides, chlorides, bromides, iodides, carbonates, nitrates, sulfates, and phosphates.
• This bath does not contain organic acid nor the salts of organic acids.
• Tinplate stock is typically cleaned by spraying.
• the equipment for treating the surface of tinplate DI can is generally known as a washer.
• the formed DI can is continuously treated — while inverted — with the cleaning bath and conver ⁇ sion bath.
• Existing washers are organized into 6 stations (preliminary cleaning, cleaning, water wash, conversion treatment, water wash, and de-ionized water wash), and all the steps are executed by spraying.
• the alkaline cleaning bath is sprayed onto a plural number of DI cans in the preliminary cleaning and cleaning steps, and is then recycled to a tank and returned to the spray.
• the alkaline cleaning bath of Japanese Patent Publication Number Sho 59-2752 initially has a good cleaning performance when actually used in a washer, but silicate salts gradually precipitate and sediment from this cleaning bath. A satisfactory cleaning operation is ultimately precluded because this precipitate — a solid generally known as sludge — clogs the pipe system and nozzles in the spray equipment
• Japanese Patent Application Laid Open Number Hei 3-59993 teaches that the presence of condensed phosphate salts in alkaline cleaning baths causes an increase in metal solubilization and a deterioration in corrosion resistance both for unpainted and painted tinplate stock. While the omission of condensed phosphate salts from this bath does result in the inhibition of tin dissolution, moderate amounts of dissolved tin still precipitate as, for example, tin phosphate. This results in the production of sludge thus the appearance of the same problem as outlined above.
• a tinplate-cleaning bath characteristically has a pH of 8 to 11 and comprises, preferably consists essentially of, or more preferably consists of: water; 0.5 to 10.0 g L of alkali builder comprising one or more selections from the alkali metal hydroxides, alkali metal and ammonium salts of inorganic phosphoric acid, alkali metal borates, alkali metal silicates, and alkali metal and ammonium carbonates; 0.05 to 1.0 g L of chelat- ing agent comprising one or more selections from the hydroxyalkyldiphosphonic acids, aminotrialkylphosphonic acids, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acids, and the alkali metal and ammonium salts of the preced ⁇ ing; and 0.05 to 2.0 g/L of surfactant
• the present invention was achieved based on this
• the tinplate-cleaning bath of the present invention produces only vanishingly small quant- ities of the sludge that forms from the tin eluting into the cleaning bath and the hard water components present in the water used to make up the bath.
• the cleaning bath of the present invention is excellently suited for cleaning DI cans.
• large numbers of DI cans may be continuously cleaned with the cleaning bath of the present invention — without the production of a hard water com- ponent/tin sludge — by conveying the tinplate-cleaning bath of the invention from a storage tank through a pipe system, then spraying the same from a nozzle onto the tin- plate stock to be cleaned, returning the bath to said storage tank, and subsequently re-spraying the bath.
• the tin ⁇ plate-cleaning process under consideration makes possible continuous and long-term cleaning without the production of the sludge that forms from tin eluting into the 5 cleaning bath and hard water components present in the water used to make up the bath.
• the tinplate-cleaning process of the present invention removes organic materials (e.g., oil, lubricants, etc.) and inorganic materials (e.g., abrasives, etc.) from the surface of tinplate stock (sheet, strip, and products therefrom such as can, etc.) and generates a surface condition that is strongly adapted for 10 conversion treatment.
• Sludge production is evaluated by the following procedure: Liquid is withdrawn into a transparent container from the storage tank for the alkaline cleaning bath, and the transparency of the sample is then evaluated with the unaided eye.
• the alkaline cleaning bath of the present inven ⁇ tion contains 0.05 to 10.0 g/L of an alkali builder comprising one or more selections from the alkali metal hydroxides, alkali metal and ammonium salts of inorganic phos ⁇ phoric acid, alkali metal borates, alkali metal silicates, and alkali metal and ammom ⁇ um carbonates.
• This component is designated as component A in the examples.
• the alkaline cleaning bath of the present invention also contains 0.05 to 1.0 g/L of compound(s) comprising one or more selections from the hydroxyalkyldiphos- phonic acids, aminotrialkylphosphonic acids, ethylenediaminetetraacetic acid, nitrilotri- acetic acid, condensed phosphoric acids, and the alkali metal and ammomum salts of these compounds.
• This component is designated as component B in the examples. so
• the alkaline cleaning bath of the present invention also contains 0.05 to 2.0
• g L of surfactant (designated as component C in the examples).
• Water is the balanc ⁇ ing component, and this water can be industrial-grade water or tapwater as well as ⁇ eionized, distilled, or other purified water.
• the tinplate-cleaning bath of the present invention should have a pH of 8 to 11.
• the alkali metal salts comprising the alkali builder consist of the potassium and sodium hydroxides, carbonates, borates, and inorganic phosphates. Examples are potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, po ⁇ tassium bicarbonate, borax, trisodium phosphate, and so forth. These may be used singly or in combinations of two or more selections.
• the particular alkali builder con ⁇ centration should be selected so as to provide a cleaning power (etching capacity) adapted to the surface condition of the tinplate stock.
• the alkali builder will generally be used at a concentration of from 0.5 to 10.0 g/L and is preferably used at a concentration of from 1.0 to 5.0 g L.
• the chelating agent (hydroxyalkyldiphosphonic acid, aminotrialkylphosphonic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, condensed phosphoric acid, and the alkali metal and ammomum salts of the preceding) is added in order to promote stable dispersion and or solubility of the tin ions released from the tinplate stock in the cleaning bath.
• tin ion accumulates in the bath during the continu- ous cleaning of tinplate stock, and this tin ion reacts with phosphoric acid, silicic acid, or carbonic acid to produce sludge.
• the listed compounds are believed to chelate the tin ions and thereby inhibit the production of sludge (tin phosphate, etc.) in the clean ⁇ ing bath.
• This inhibition of sludge production results in a substantial reduction in the work inputs for cleaning the pipe system and nozzles of the spray equipment
• the calcium and magnesium ions present as hard water components in tapwater do not accumulate in the cleaning bath and thus will not hamper the continuous process from this standpoint.
• hydroxyalkyldiphosphonic acid is exemplified by 1-hydroxyethyli- dene-l,l-diphosphonic acid, with the formula given below: H 3 O C O
• H H H H Aminotrialkylphosphonic acid is exemplified by aminotrimethylenephosphonic acid.
• Condensed phosphoric acid is exemplified by pyrophosphoric acid, tripolyphos- phoric acid, and tetrapolyphosphoric acid.
• Hydroxyalkyldiphosphonic acid, aminotrial ⁇ kylphosphonic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and con ⁇ densed phosphoric acid can be used in the cleaning bath in acid form or as the alkali metal salt or ammonium salt
• this component should be present at 0.05 to 1.0 g/L and preferably at 0.1 to 0.5 g/L. At less than 0.05 g/L, there will normally be a strong tendency for sludge to be produced in the cleaning bath because of an inad ⁇ equate chelating capacity. Quantities in excess of 1.0 g/L do not cause any particular problems, but are less economical due to the associated increase in costs.
• Ethylenediaminetetraacetic acid, nitrilotriacetic acid, and condensed phosphoric acids are refractory to wastewater treatment because they are only poorly sedimentable by slaked lime (calcium hydroxide).
• slaked lime calcium hydroxide
• the use of the hydroxyalkyldiphos ⁇ phonic acids and their metal (ammomum) salts is recommended, since these species are very sedimentable by slaked lime.
• the use of con ⁇ densed phosphoric acid-free cleaning agents has become correspondingly desirable.
• the effects of the present invention are not impaired by the supplemental addi ⁇ tion of another type of chelating agent, for example, an organic acid such as gluconic acid as well as the alkali metal and ammonium salts of such organic acids.
• a cleaning agent that leads readily to a wastewater that is free from phosphor ⁇ us and nitrogen will be particularly useful in regions where wastewater regulations are particularly stringent.
• the alkali builder for the present invention may be selected from the hydroxides, carbonates, and borates and the chelating agent may be selected from me hydroxyalkyldiphosphonic acids and aminotrialkylphosphonic ac- ids.
• the cleaning bath of the present invention can employ alkali salt concentrations as low as ⁇ 4 g L, which is lower than that reported in experimental examples of the prior art This reduction in the use quantity of alkali builder also makes possible a reduction in the quantity of wastewater treatment sludge produced during wastewater treatment
• the surfactant is selected from the anionic and nonionic surfactants.
• Nonionic surfactants are exemplified by hydrocarbon derivatives, abietic acid derivatives, ethox- ylated primary alcohols, and modified polyethoxylated alcohols.
• the surfactant can be used in the form of a single species or as a combination of two or more species. It should be present at a concentration of from 0.05 to 2.0 g/L and preferably at a concentration of from 0.2 to 1.0 g/L.
• the organic material on the sur ⁇ face of the tinplate stock will sometimes not be completely removed when the sur ⁇ factant is used at a concentration of less than 0.05 g/L.
• the use of more than 2.0 g L surfactant is not associated with any particular problems in terms of cleaning effects, but rather is economically undesirable due to the higher cost
• the cleaning bath should have a pH in the range of 8 to 11 and preferably in the range of 9 to 10. At a pH below 8, the etching capacity is diminished and it be ⁇ comes difficult if not impossible to obtain a good cleaning effect. Moreover, there is a strong tendency for sludge production to occur at a pH below 8. In contrast etching is undesirably strong at pH values above 11, resulting in a deterioration in appearance.
• the pH can be adjusted using the usual alkalis and acids, i.e., sodium hydroxide, po ⁇ tassium hydroxide, sulfuric acid, phosphoric acid, and the like, and no specific restriction exist in this regard.
• the cleaning bath of the present invention may be used at treatment tempera- tures ranging from ambient temperature to 80° C, but it is preferably heated generally to 40 to 60 ° C for use.
• the treatment time should be 2 to 60 seconds. A satisfactory cleaning effect is not usually obtained at below 2 seconds, while treatments in excess o ⁇ 60.:seconds do not usually result in any further improvement in cleaning effect.
• the treatment method may be either immersion or spray, but as discussed above the present invention produces particularly good effects when used with spray equipment.
• the metal ion is first dissociated from the chelate compound in the acidic pH range. Solid-liquid separation is then carried out by the addition of calcium hydroxide and polymer flocculent to give the wastewater treatment sludge. Since the cleaning bath of the present invention has a low alkali concentration, it generates only small quantities of sludge for disposal. Moreover, the wastewater treatment efficiency is also good because the hydroxyalkyl- diphosphonic acids and aminotrialkylphosphonic acids are highly sedimentable by calcium hydroxide and polymer flocculants.
• tin ions accumulate during the cleaning of tinplate stock, and it is estimated that the tin ion concentration in the cleaning bath is 0.01 to 0.1 g L when sludge is produced.
• the sludge produced by its precipitation is very sticky and adheres to the interior of the nozzles and pipe system and thus impedes the cleaning operation.
• This adhesion problem can be avoided by inhibiting dissolution of the tinplate surface in order to prevent an increase in tin ion concentration. How ⁇ ever, there are limitations on the application of this approach to large-scale cleaning runs.
• the present invention has therefore devised the use of a particular component, as described above, in addition to alkali builder and surfactant
• test material consisted of 1,000 uncleaned cans (66 mm diameter x 124 mm height) that had been fabricated by the drawing and ironing of tin-plated steel sheet. Cleaning was conducted in a conventional washer.
• Treatment agent PALFOS® K3482, registered brand name of Nihon Parkerizing Company, Limited concentration: 3 %, temperature: 60° C 4. Water wash (10 seconds, spray)
• the degreasing performance was evaluated based on the quantity of residual oil on the surface.
• the can was ultrasonically cleaned using carbon tetrachloride, and the oil fraction eluted into the carbon tetrachloride from the can surface was determined using an instrument for measuring the oil con ⁇ centration (POC-100 from Kabushiki Kaisha Shimadzu Seisakusho). This value is re ⁇ ported as the residual quantity of oil per unit surface of the can. Values ⁇ 2 mg/m 2 are generally considered excellent.
• the corrosion resistance was evaluated using the iron exposure value (IEV).
• IEV iron exposure value
• the IEV was measured based on United States Patent Number 4,332,646. Lower IEV values indicate a better corrosion resistance. Values ⁇ 150 are generally considered excellent.
• the can was first treated by process [2], and the surface of the can was then coated with an epoxy/urea can paint to a paint film thickness of 5 to 7 micrometers. After baking for 4 minutes at 215° C, the can was cut into 5 x 150 mm strips, and the test specimen was prepared by hot-press bonding with polyamide film. This was peeled using the 180° peel test method in order to evaluate the peel strength. Larger peel strength values indicate a better paint adherence. Values > 1.5 kgf/5 mm width are generally considered excellent.
• the wastewater treatability was evaluated as follows. The treatment bath was first diluted 1/10, which is equivalent to the degree of dilution in the wastewater treat ⁇ ment of process baths in actual operations, and the pH of the resulting bath was brought to 2.5 with sulfuric acid. Aqueous aluminum sulfate solution was then added to give 20 ppm as aluminum, and the pH was subsequently brought to 10 with calci ⁇ um hydroxide. 10 ppm of polymer flocculant was added and a solid-liquid separation was then carried out. The residual sludge (solids) was dried for 24 hours at 100" C, then cooled and weighed. The wastewater treatability was evaluated based on this weight, i.e., low quantities of sludge production are desirable.
• Example 1 Cleaning was conducted at 50° C for 30 seconds using cleaning bath 1. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 1. cleaning bath 1 sodium carbonate (A) sodium bicarbonate (A) sodium tripolyphosphate (B) nonylphenol/11 EO adduct (C) pH 9.6 (adjusted with sodium hydroxide)
• Cleaning was conducted at 50° C for 30 seconds using cleaning bath 2.
• the water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 2.
• cleaning bath 2 potassium carbonate (A) potassium bicarbonate (A) l-hydroxyethylidene-l,l-diphosphonic acid (B) higher alcohol/5 EO/10 PO adduct (C) pH 9.6 (adjusted with sodium hydroxide)
• Example 3 Cleaning was conducted at 50° C for 30 seconds using cleaning bath 3. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 3. cleaning bath 3 sodium carbonate sodium bicarbonate sodium ethylenediaminetetraacetate s higher alcohol/5 EO/10 PO adduct pH 10.0 (adjusted with sodium hydroxide)
• Example 4 Cleaning was conducted at 50° C for 60 seconds using cleaning bath 4. The water wettability, degreasing performance, corrosion resistance, and paint adherence o were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 4. cleaning bath 4 sodium carbonate (A) sodium bicarbonate (A) s l-hydroxyethylidene-l,l-diphosphonic acid (B) nonylphenol/11 EO adduct (C) pH 8.7 (adjusted with sulfuric acid)
• Example 5 Cleaning was conducted at 40° C for 15 seconds using cleaning bath 5. The o water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 5. cleaning bath 5 sodium hydroxide (A) 5 disodium hydrogen phosphate (A) l-hydroxyethylidene-l,l-diphosphonic acid (B) nonyl ⁇ henol/11 EO adduct (C) pH 10.5 (adjusted with sodium hydroxide)
• Example 6 o Cleaning was conducted at 60° C for 60 seconds using cleaning bath 6. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated lor cleaning bath 6. cleaning bath 6 sodium carbonate sodium bicarbonate sodium tripolyphosphate l-hydroxyethylidene-l,l-diphosphonic acid higher alcohol/5 EO/10 PO adduct pH 8.7 (adjusted with sulfuric acid)
• Example 7 Cleaning was conducted at 30° C for 60 seconds using cleaning bath 7. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 7. cleaning bath 7 sodium carbonate sodium bicarbonate borax
• Comparison Example 1 Cleaning was conducted at 50° C for 30 seconds using cleaning bath 8. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 8. cleaning bath 8 sodium carbonate (A) sodium bicarbonate (A) higher alcohol/5 EO/10 PO adduct (C) pH 9.6 (adjusted with sodium hydroxide) Comparison Example 2 Cleaning was conducted at 50° C for 30 seconds using cleaning bath 9. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 9. cleaning bath 9 potassium carbonate potassium bicarbonate
• Comparison Example 3 Cleaning was conducted at 60° C for 60 seconds using cleaning bath 10. The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for cleaning bath 10. cleaning bath 10 sodium metasilicate (A) sodium carbonate (A) higher alcohol 5 EO/10 PO adduct (C) pH 11.0 (adjusted with sodium hydroxide)
• Comparison Example 4 Cleaning was carried out for 30 seconds at 50° C using the 1% cleaning bath of a commercial cleaning agent for tinplate DI can that contained alkali builder and surfactant as effective components (FINE CLEANERTM 4361 A, registered brand name of Nihon Parkerizing Company, Limited). The water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for this cleaning bath.
• a commercial cleaning agent for tinplate DI can that contained alkali builder and surfactant as effective components (FINE CLEANERTM 4361 A, registered brand name of Nihon Parkerizing Company, Limited).
• the water wettability, degreasing performance, corrosion resistance, and paint adherence were evaluated. Sludge production and wastewater treatability were also evaluated for this cleaning bath.
• the present invention exhibits an excellent cleaning performance in the cleaning of tin- plated DI can as evaluated on the basis of the generally critical properties of water wettability, degreasing performance, corrosion resistance, and adherence. This clean ⁇ ing performance is equivalent to that afforded by the prior art However, the present invention is superior to the prior art with regard to sludge inhibition and wastewater treatability.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Detergent Compositions (AREA)

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• 1992
  • 1992-03-13 JP JP08948092A patent/JP3199824B2/ja not_active Expired - Fee Related
• 1993
  • 1993-03-11 WO PCT/US1993/001993 patent/WO1993018205A1/en active IP Right Grant
  • 1993-03-11 EP EP93907235A patent/EP0630427B1/de not_active Expired - Lifetime
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