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
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/1601—Process or apparatus
  • C23C18/1617—Purification and regeneration of coating baths
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31—Surface property or characteristic of web, sheet or block

Definitions

• This invention relates to a method for regenerating spent 'chromic acid etchant solutions. More particularly, this invensought to be deposited from solutions of their salts either by electroless plating methods or in vacuum volatization, etc.
• ABS acrylonitrile-butadiene-styrene
• Chemical etching involves a process of deglazing the surface'without seriously roughening it, in contrast to the result usually obtained when mechanical processing is employed.
• a low level degree of roughening is desirable since this facilitates the subsequent production of metal deposits of greater smoothness and brilliance in the finished article.
• Chemical etching of plastic substrates is generally well known in the art and many solutions useful for this purpose are described in the literature. In general these prior art solutions consist essentially of a formulation of sulfuric acid together with chromic acid and, in addition, phosphoric acid, if desired.
• the contacting of the surface of the plastic substrate in theetching operation may be done in any conventional way, as by dipping or spraying and is continued for a period of time sufficient to produce the desired effect.
• the degree of treatment or modification of the normally hydrophobic surface of the plastic can be regulated by varying the temperature and strength of the etching solution as well as the exposure time of the surface to the solution. With strong solutions at moderate temperatures the surface is rendered hydrophilic in about 0.5 to about 5 minutes. After the treatment', water is found to spread evenly over the plastic surface instead of gathering in drops as in the case with an untreated surface.
• a preferred etching composition consists of approximately 14 percent by weight of chromium trioxide 40 percent by weight of sulfuric acid (66Be. with the balance being water. Usually this solution is employed at approximately F. and the plastic substrate is immersed in or otherwise contacted with it for a period of from about 1 to about 10 minutes or more.
• chromicacid-sulfuric acid-water etching solution described above is generally satisfactory for converting the hydrophobic surface of plastic substrates, such as ABS (acrylonitrile-butadiene-styrene), polysulfones, polypropylenes, polystyrenes, epoxys, phenolics, polybenzimidazoles, polyphenylene oxides, acrylics and the like to a receptive hydrophilic surface, a number of problems present themselves in operating such systems commercially. Etching processes, known in the art using such etching solutions, suffer from the following disadvantages:
• Another object of this invention is to provide a method for regenerating chromic acid etchant solutions in such a way as to prolong substantially their life.
• Another object of this invention is to reduce the time spent by personnel in the hazardous operation of charging and dumping the etchant tanks.
• Anotherobject of this invention is to substantially reduce the cost of etching plastic substrates for reception of a metal film by the electroless plating method.
• chromic etchant solutions which have been used to etch plastic substrates can be regenerated by adding to the spent or partially depleted solutions with mixing, an alkali metal permanganate selected from the group consisting of sodium, potassium and lithium permanganate and mixtures thereof; if desired, the regenerated etching solution can then be reused, as is, after the sludge which fonns during the process has been allowed to settle to the bottom of the etching solution tank. This usually requires from about 6 to about 12 hours or more.
• the clear regenerated etching solution can be recovered by decantation after the settling period.
• the sludge can be removed from the regenerated solution by centrifugation, filtration or by any other convenient method. It has been found highly desirable to remove the sludge from the regenerated etchant bath since clogging ofthe air tubes in the etching tank and reduced agitation with concomitant reduction in efficiency and quality may result if this is not done. After regeneration, it may be desirable to adjust the concentration of the chromic acid, sulfuric acid or phosphoric acid and this can be done by adding the required amounts of these ingredients to the regenerated etching solution. Where an excess of water is present in the regenerated solution, it can be removed by evaporation.
• the regeneration process of this invention is conducted at temperatures ranging from about 60 F. to about 200 F. and, preferably, from about 130 F. to about 160 F.
• the quantity of the alkali metal permanganate added may be varied widely and, generally will be about 1.2 to about 1.7 times the stoichiometric requirement for converting all of the trivalent chromium in the etching solution to hexavalent chromium.
• the amount of the alkali metal permanganate added will be from about 0.10 to about lbs. per gallon of the spent or depleted etching solution being treated.
• the alkali metal permanganate compound may be added as a finely divided powder, any other convenient form can be utilized.
• the preferred alkali metal permanganate is potassium permanganate.
• Spent or depleted chromic acid etching solutions which can be regenerated by the process of this invention are solutions resulting from, for example, the etching of plastic substrates with etchants initially containing from about 1 to about 25 percent by weight of chromium trioxide in solution, at least about 30 percent by weight of an acid selected from the group consisting of sulfuric and phosphoric and combinations of the two, with the balance being water.
• the etchant solution has the following initial composition:
• ABS acrylonitrile-butadiene-styrene
• current practice involves subjecting some plastic substrates to a pretreatment by immersion in an adhesion promoter which is retained in the surface and facilitates subsequent oxidation by the chromic acid.
• polypropylene can be advantageously treated by immersing it in a bath containing emulsified linseed oil or turpentine for about 10 minutes at a temperature of about F. as described in Grunwald and DOttavio application Ser. No. 654,901, filed Jan. 14, 1967.
• Spent solutions resulting from the etching of such pretreated substrates can be regenerated by the process of this invention equally as well as spent solutions obtained in etching those plastic substrates which have not been subjected to surface pretreatment operations.
• EXAMPLE II A solution of the composition set forth below is utilized in etching ABS articles Ingredient Percent by Weight Chromium Trioxide 1.4 Sulfuric Acid 88.0 Water Balance
• the articles, which are subjected to etching in this example, are not pretreated in any manner.
• the above-mentioned solution is utilized to etch ABS articles at a temperature of 135 F. by immersion and after about 50 sq. ft. per gallon has been etched, the adhesion between the ABS and the subsequently deposited plated metal decreases to nearly 0 pounds per inch.
• the chromium trioxide content of the depleted solution is 0.14 percent.
• Potassium permanganate (about one-fourth inch size) is then added to the depleted etchant solution in amount of about 0.25 pounds per gallon of solution over a period of about 5 minutes with agitation. During the addition process, the temperature of the bath is maintained at about EXAMPLE III A chromic acid etching solution of the following composition is prepared:
• Regeneration of the depleted solution is accomplished by adding about 0.75 pound of crystalline potassium permanganate to each gallon of the depleted etchant at a temperature of 145 F. over a period of about 10 minutes with agitation yielding a regenerated etching solution having a chromium trioxide content of about 14 percent.
• the regenerated solution is again employed to etch ABS articles and the adhesion of metal plated on the etched surface is found to be as satisfactory as that resulting when the original solution was employed.
• etching solution which has been only partially depleted, for example, one in which only 5 percent or less of the chromium is present as trivalent chromium, can be efficiently regenerated by the process of this invention in a batchwise or continuous manner.
• One embodiment of this invention that is contemplated to enable a chromic acid etching solution to be used indefinitely for etching is a continuous etching process utilizing continuous regeneration of the etching solution. This process is conducted by contacting plastic substrates with a chromic acid etching solution containing from about 1 to about 25 percent by weight of chromium trioxide in solution, at least about 30 percent by weight of an acid selected from the group consisting of sulfuric and phosphoric and combinations of the two with the balance being water, at a temperature of about room temperature to about 200 F.
• an alkali metal permanganate selected from the group consisting of sodium, potassium and lithium permanganate and mixtures thereof in the amount of from about 0.10 to about 5 pounds per gallon at a temperature of from about 60 to about 200 F., to regenerate the etching solution, separating the sludge which forms during the regeneration operation by any convenient method, such as by decantation after the sludge has been allowed to settle and recycling the thus-regenerated etching solution back to the main body of the etching solution.
• sulfuric acid; chromium trioxide, or phosphoric acid may be added continuously, as required, to maintain the desired concentration of these two ingredients.
• the main body of the etching solution can be used to etch continuously until foreign impurities build up to such a point that the quality of the etch is affected.
• a continuous process of this type obviates the necessit for replacing the spent etching solution and for adde waste treatment processes to permit disposal of the spent solution.
• the contacting of the plastic surface may be done by any conventional method, such as by dipping or spraying.
• Recovered sludge which consists mainly of manganese oxide (MnO and MnO as well as some potassium sulfate, can be washed, dried and sent to an appropriate process for recovery of the manganese oxides.
• etching plastic substrates such as polypropylene
• chromic acid etching solutions were usually exhausted after treating no more than about 50 sq. ft. per gallon of solution.
• the etching solution can be utilized to treat a minimum of 300 sq. ft. of polypropylene per gallon.
• a process for continuous etching of plastic substrates which comprises contacting plastic substrates with a chromic acid etching solution containing from about 1 to about 25 percent by weight of chromium trioxide in solution, at least about 30 percent by weight of an acid selected from the group consisting of sulfuric and phosphoric and combinations of the two, with the balance being water, at a temperature of about room temperature to about 200 F.
• etching solution for a period of about 0.5 to about 30 minutes, continuously removing a portion of the etching solution from the main body of the etching solution, adding from about 0.10 to about 5 pounds per gallon of the etching solution of an alkali metal permanganate selected from the group consisting of sodium, potassium and lithium permanganate and mixtures thereof, at a temperature of from about 60 to about 200 F separating the sludge formed from the regenerated solution, and returning the said portion of the regenerated etchant solution to the main body of the etching solution.
• an alkali metal permanganate selected from the group consisting of sodium, potassium and lithium permanganate and mixtures thereof

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Chemically Coating (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• ing And Chemical Polishing (AREA)

Applications Claiming Priority (1)

Publications (1)

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Country Status (7)

Cited By (6)

Citations (2)

• 0
  • BE BE756045D patent/BE756045A/xx unknown
• 1969
  • 1969-09-12 US US861542A patent/US3650859A/en not_active Expired - Lifetime
• 1970
  • 1970-09-02 DE DE19702043576 patent/DE2043576A1/de active Pending
  • 1970-09-03 ES ES383605A patent/ES383605A1/es not_active Expired
  • 1970-09-09 NL NL7013291A patent/NL7013291A/xx unknown
  • 1970-09-11 FR FR7033039A patent/FR2061310A5/fr not_active Expired
  • 1970-09-14 GB GB4386070A patent/GB1305077A/en not_active Expired

Patent Citations (2)

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