EP1029117B1 - Method for separating layers from articles - Google Patents

Description

• Wasserstoffperoxid
• mindestens eine Base
• mindestens eine Säure und/oder ein Salz einer Säure.

The present invention relates to a method for stripping bodies, provided with a hard material layer composed of a Ti compound in an alkaline solution

• hydrogen peroxide
• at least one base
• at least one acid and / or a salt of an acid.

DD 228 977 describes a process for stripping TiN layers, in particular for stripping on nickel substrates applied TiN layers. Thereby, the ones to be treated Parts for approx. 3 minutes at a temperature of approx. 70 ° C up to 80 ° C in a hydrogen peroxide solution with a content of 35 Ma% peroxide introduced, then rinsed in water, dried and then mulled. For stripping TiAlN layers this method is unsuitable because the Badly dissolves TiAlN in a hydrogen peroxide solution.

According to GB 2 127 042, titanium nitride hard material layers on stainless steel substrates in aqueous nitric acid decoated at temperatures above 70 ° C. The stripping time for a 1 µm thick layer, at 70 ° C, about 50 hours. This extremely long stripping time is very disadvantageous.

A process for the stripping of hard material layers various metal substrates is known from US 4,746,369. The acidic decoating bath consists of hydrogen peroxide as an oxidizer and a phosphoric acid or nitric acid together. There are also various surface-active substances to use. The very low pH of the solution of less than 0.5 is for use on high speed steel substrates - HSS (High Speed Steel) - very disadvantageous.

According to DE 41 10 595, hard material layers are proposed of tool surfaces in a stabilized by complexing agents Perform hydrogen peroxide solution, using as a complexing agent Potassium sodium tartrate tetrahydrate or sodium gluconate is used. On the one hand, this results in TiAlN layers not decoated at a satisfactory speed, on the other hand, the stabilizers used result in only one limited stabilizing effect.

DE 41 01 843 describes a process for the stripping of Hard material coated objects are known, wherein the objects with a solution containing tetra sodium diphosphate and hydrogen peroxide. Typical are the hydrogen peroxide concentrations from 8 to 12% that relatively high tetra sodium diphosphate concentration from 8 to 12%, the high process temperature, at boiling temperature, and the high pH from 8 to 12. The solution is about half of the initial volume evaporated - what at the high temperatures takes place relatively quickly - phosphating can already occur stripped surface occur. Titanium nitride and / or titanium nitride / carbide hard material layers.

DE 43 39 502 describes processes specific to layer material for stripping metal substrates, especially of Tungsten carbide substrates, known which hard material layers either from TiN, from TiCN or from TiAlN, or else from Layer systems made of TiN / TiAlN.

An alkaline solution with hydrogen peroxide, at least a base and at least one salt of mono- and Dicarboxylic acids used.

The solution bath settles, depending on the layer to be removed and while protecting the substrates, layer-specific a variety of components together.

From Patent Abstract of Japan, vol. 017, no 468 (C-1102), 26. August 1993 it is known to decoat TiN using a aqueous solution of 1 - 20% by weight of one or more species hydrocarbonate-like alkali salts of organic acids, 2 - 15 % By weight alkali salt of ethyldiamine acetic acid and 0.1-0.5% by weight Alkali hydroxide, 0.05-0.5% by weight alkali salt of thioglycolic acid and 3-7% by weight hydrogen peroxide.

Starting from the last-mentioned method, it is the task of the present one Invention to propose a method by means of which Industrial TiAlN layers of high-speed steel substrates can be stripped

definitions: 1) high-speed steel:

High-speed steel is characterized by high carbon concentrations, up to 1.5%, and additions of strong carbide-forming elements such as chrome, molybdenum and tungsten Vanadium. Up to 12% cobalt is in some of the more complex ones Varieties included.

High-speed steel is so called because of its high hardness in high speed applications (see D.T. Llewellyn, Steel: Metallurgy and Application, Butterworth-Heihemann Ltd., Oxford 1992, p. 174).

2) phosphate:

A salt of a phosphoric acid, diphosphoric acid, Triphosphoric acid etc. understood. For example, is the phosphate "Calcium phosphate" a salt of phosphoric acid, "disodium dihydrogen phosphate" a salt of diphosphoric acid, further "penta-sodium triphosphate" a salt of triphosphoric acid Etc.

3) Phosphonate:

Phosphonate is a salt of a phosphonic acid, in particular an organic phosphonic acid, i.e. one Phosphonic acid with organic substituents understood.

The above-mentioned task is solved in that for the stripping of HSS substrates from a layer of TiAlN, at least a substance from the group of phosphates, phosphonates and phosphonic acids is used.

The advantage is additionally obtained that by means of this Solution, as is known, TiN and TiCN continue to be solved, additionally but, according to the invention, TiAlN.

In contrast to TiN and TiCN, TiAlN dissolves in hydrogen peroxide solutions not even at elevated temperatures. Will the pH of the hydrogen peroxide solution by metering one Base, as raised by NaOH, to the alkaline range with pH ≥ 7, then - according to the invention - in addition to those mentioned TiN and TiCN layers also dissolved TiAlN layers. It it was recognized that this is also the case at low process temperatures the case is.

• Als Phosphat wird di-Natriumdihydrogenpyrophosphat, Na₂H₂P₂O₇ und/oder penta-Natriumtriphosphat (Na₅P₃O₁₀) bevorzugt eingesetzt;
• Als Phosphon-Säure wird bevorzugterweise Aminotri(methylenphosphonsäure) und/oder 1-Hydroxyethan (1,1-diphosphonsäure) eingesetzt. Dabei werden diese Phosphonsäuren als solche direkt in die Lösung eingebracht. Dies gilt generell für den Einsatz von Phosphonaten, Phosphaten und Phosphonsäuren. Dabei hat es sich mindestens vorläufig gezeigt, dass der Einsatz der 1-Hydroxyethan(1,1-diphosphonsäure) besonders geeigneter ist.
• Die Prozesstemperatur des Lösungsbades wird, gegebenenfalls durch Heizen und/oder Kühlen, auf 20°C bis 80°C gehalten (die Bereichsgrenzen sind eingeschlossen);
• Die Peroxidkonzentration wird zwischen 5 und 50 Gew.% gewählt (die Bereichsgrenzen sind eingeschlossen);
• Die Konzentration von Phosphat und/oder Phosphonat und/oder Phosphon-Säure wird zwischen 0,1 und 10 Gew.% gewählt (die Bereichsgrenzen sind eingeschlossen);
• Es können auch grössere Lösungsbadvolumina, z.B. ≥ 50 l oder gar ≥ 100 1, stabil betrieben werden;
• Die Lösung besteht vorzugsweise aus destilliertem Wasser, Wasserstoffperoxid, der erwähnten Base, beispielsweise NaOH, und den erwähnten Phosphaten und/oder Phosphonaten und/oder Phosphon-Säuren, mindestens in weitaus überwiegendem Anteil.

The following specific procedures are preferably used alternatively or in combination:

• Disodium dihydrogen pyrophosphate, Na ₂ H ₂ P ₂ O ₇ and / or penta sodium triphosphate (Na ₅ P ₃ O ₁₀ ) is preferably used as the phosphate;
• Aminotri (methylenephosphonic acid) and / or 1-hydroxyethane (1,1-diphosphonic acid) is preferably used as the phosphonic acid. These phosphonic acids are introduced directly into the solution as such. This generally applies to the use of phosphonates, phosphates and phosphonic acids. It has been shown, at least for the time being, that the use of 1-hydroxyethane (1,1-diphosphonic acid) is particularly suitable.
• The process temperature of the solution bath is kept at 20 ° C. to 80 ° C., optionally by heating and / or cooling (the range limits are included);
• The peroxide concentration is chosen between 5 and 50% by weight (the range limits are included);
• The concentration of phosphate and / or phosphonate and / or phosphonic acid is selected between 0.1 and 10% by weight (the range limits are included);
• Larger solution bath volumes, for example ≥ 50 l or even ≥ 100 1, can also be operated stably;
• The solution preferably consists of distilled water, hydrogen peroxide, the base mentioned, for example NaOH, and the aforementioned phosphates and / or phosphonates and / or phosphonic acids, at least in a predominant proportion.

This creates a layer-specific and complex solution composition bypassed and created the opportunity each of the hard material layers mentioned - according to the invention also TiAlN - to coat HSS substrates with the same solution. In addition, the very large expenditure on equipment is eliminated, which must be operated when an alkaline hydrogen peroxide bath with a pH of 8 to 12 in the boiling temperature range is operated. Also eliminated thanks to the deep Process temperatures at which the solution bath according to the invention is operable, the risk of phosphating, which, at high Process temperatures in the boiling temperature range, thanks to fast Evaporation exists.

This is for economic and large-scale industrial decoating given the possibility of stripping baths according to the invention with large volumes e.g. of over 50 l or even over 100 l stable to operate. Large quantities of hard-coated HSS substrates, such as tools, can be stripped within a few hours.

The advantage of alkaline hydrogen peroxide is the high process reliability with regard to corrosion of HSS material. In alkaline HSS behaves very noble in the media. So there is also then there is no risk of corrosion for the HSS substrate if longer Stripping times would have to be used.

The problem of the instability of alkaline hydrogen peroxide solutions, by auto-oxidizing the hydrogen peroxide takes place, which is catalyzed by metal ions, the are released into the solution during the stripping process, which in turn leads to overheating and boiling over of the decoating bath leads by the addition of at least one phosphate and / or phosphonates and / or at least one Phosphonic acid dissolved as a stabilizer. It will be added by this addition accelerates the stripping. With this addition the bath stability is improved so that the decoating bath Stably operated even at elevated temperatures could be. For maintaining the bath temperature can heating and / or cooling may be provided, if necessary the bath temperature is regulated to a setpoint, with heating and / or cooling as an actuator.

The difference in effect of phosphates and / or phosphonates and / or of phosphonic acid in the solution used:

When using phosphate alone, the bath life is relative low, is usually between 1 and 3 batches what Of course, in certain cases it is quite sufficient. This relatively short bath life is due to the limited Stability of polyphosphates. The stability of polyphosphates is only moderate in alkaline solutions, in acidic solutions bad. The polyphosphates are converted into orthophosphates by hydrolysis transferred for the stabilization of the peroxide solutions are far less effective.

The situation is different for organic phosphonates and Phosphonic acids. Compared to inorganic polyphosphates have phosphonates and phosphonic acids very good hydrolytic Stability. This is due to the very high stability of the C-P bonds attributed to the phosphonates and phosphonic acids. In addition to the increased stabilizing effect, increasing the Bath service life, cause phosphonates and phosphonic acids a further acceleration of the stripping reaction.

Example I:

• 125 l Wasserstoffperoxid, 17,5 Gew.%
• 1,25 kg Na₅P₃O₁₀
• 500 g NaOH

The following solution was used as the stripping bath:

• 125 l hydrogen peroxide, 17.5% by weight
• 1.25 kg Na ₅ P ₃ O ₁₀
• 500 g NaOH

The bath was heated to 60 ° C and 500 pieces of 12 mm HSS end mills, coated with a TiAlN layer in the solution brought in. The tools were complete after 3 hours decoated and the bath temperature was stable at 60 ± 2 ° C remained.

Example II:

• 125 l Wasserstoffperoxid, 17,5 Gew.%
• 0,2 mol/l Aminotri-(methylenphosphonsäure)ATMP
• 0,4 mol/l NaOH

The following decoating solution was used:

• 125 l hydrogen peroxide, 17.5% by weight
• 0.2 mol / l aminotri- (methylenephosphonic acid) ATMP
• 0.4 mol / l NaOH

The temperature of the stripping solution was controlled by heating / cooling kept constant at about 60 ° C, and 500 Piece of 12mm HSS end mill, coated with a TiAlN layer, introduced into the solution. After three hours they were Tools completely stripped and the bath temperature was remained stable at 60 ± 2 ° C. Several of the mentioned could Batches can be stripped in the same solution.

Compared to the use of polyphosphates according to Example I the belt life could be extended by a factor of 2 to 4 become.

Example III

• 125 l Wasserstoffperoxid, 17,5 Gew.%
• 2 Gew.% 1-Hydroxyethan(1,1-diphosphonsäure)HEDP
• 0,4 mol/l NaOH

The following decoating solution was used:

• 125 l hydrogen peroxide, 17.5% by weight
• 2% by weight 1-hydroxyethane (1,1-diphosphonic acid) HEDP
• 0.4 mol / l NaOH

Operated and loaded according to Example II resulted, however with shorter stripping times, the same results as according to example II.

The advantage of the present invention is that it remains simple Solution composition, the simple process management and the short stripping time. At solution temperatures well below the boiling point can already be within can be stripped within a few hours. Regarding corrosion HSS substrates have a high level of security: Because the stripping solution alkaline, there is no corrosion of HSS instead of.

Another major advantage is that in the same operation, i.e. with the same decoating solution, a large number HSS substrates, e.g. mixed with TiN, TiCN and / or TiAlN layers, can be stripped, e.g. by high volumes of solution, e.g. over 50 l or even over 100 l, can be operated stably with little effort.

Claims (12)

1. Process for decoating substrates fitted with a hard material layer of a Ti compound, in an alkaline solution comprising

   hydrogen peroxide

   at least one base

   at least one acid and/or a salt of an acid,

   characterised in that for decoating high speed steel substrates with at least one layer of TiAIN, the said acid and/or said salt contains a substance from the group consisting of phosphates, phosphonates, phosphonic acids.
2. Process according to claim 1, characterised in that phosphonate is introduced into the solution as such and/or by the introduction of an organic phosphonic acid.
3. Process according to claim 1 or claim 2, characterised in that aminotri-(methylene phosphonic acid) and/or preferably 1-hydroxyethane (1,1-diphosphonic acid) is used as a phosphonic acid.
4. Process according to any of claims 1 to 3, characterised in that disodium dihydrogenpyrophosphate and/or Na₂H₂P₂O₇ and/or pentasodium triphosphate (Na₅P₃O₁₀) is used as a phosphate.
5. Process according to one of claims 1 or 2, characterised in that the solution temperature is held between 20°C and 80°C, both limits included.
6. Process according to any of claims 1 to 3, characterised in that the hydrogen peroxide concentration is between 5 and 50 w.%, both limits included.
7. Process according to any of claims 1 to 4, characterised in that the concentration of phosphate and/or phosphonate and/or phosphonic acid is held between 0.1 and 10 w.%, both limits included.
8. Process according to any of claims 1 to 7, characterised in that a solution volume of at least 50 l is used, preferably at least 100 l.
9. Decoating process according to any of claims 1 to 8, characterised in that as well as at least one TiAlN layer, at the same time a TiN layer and/or a TiCN layer is removed.
10. Process according to any of claims 1 to 9, where the substrates are tools.
11. Process according to claim 10, where the tools are cutting or forming tools.
12. Process according to claim 11, where the tools are milling cutters, indexable inserts or embossing dies.