DE4434049A1 - Heterocyclic cpds. used in aq. soln. for compacting anodised layers - Google Patents

Abstract

The heterocyclic cpds. are used in aq. soln. at a total concn. of 0.05-1 g/l for compacting the anodised layer on anodised metals. The cpds. contain at least 4 N atoms, 2 of which are in the 1,3 position in a 5 or 6-membered N-C heterocycle. Also claimed is a process for compacting anodised layers by treating metal parts for 15 s - 15 minutes, pref. 1-5 minutes, with an aq. soln. as above, pref. by dipping or spraying.

Description

The invention is in the field of corrosion protection zender and / or decorative coatings on metals by anodic Oxidation. It relates to a new process for compacting the electrochemically produced porous anodizing layers for further Improve their properties.

The electrochemical anodic oxidation of metals in suitable Electrolytes is a widely used process for the formation of corrosion-protective and / or decorative coatings for this suitable metals. These procedures are, for example, in Ull mann’s Encyclopedia of Industrial Chemistry, 5th Edition, Vol. 9 (1987), pp. 174-176 briefly characterized. Accordingly, Titan, Ma Magnesium and aluminum and their alloys can be anodized, whereby the anodization of aluminum and its alloys technically is of the greatest importance. The electrolytically generated anodizing layer ten protect the aluminum surfaces from the influences of the white and other corrosive media. Furthermore, anodizing layers applied to obtain a harder surface and to achieve increased wear resistance of the aluminum chen. By the inherent color of the anodizing layers or by ab  sorptive or electrolytic coloring can be de achieve corative effects. The aluminum is anodized in an acidic electrolyte, with sulfuric acid being the most widely used is spreading. Other suitable electrolytes are phosphoric acid, Oxalic acid and chromic acid. The properties of the anodizing layers can be selected by the choice of the electrolyte, its temperature how the current density and the anodizing time vary within wide limits ieren. The anodization is usually carried out with direct current or with an alternating current superimposed direct current.

The fresh anodizing layers can be dipped in solutions a suitable dye or by an AC treatment in a metal salt containing, preferably in a tin containing Electrolytes can be colored afterwards. Alternatively to after Colored anodizing layers can be used for slow coloring receive so-called color anodization processes, for which one example as the anodization in solutions of organic acids, such as esp special sulfophthalic acid or sulfanilic acid, if appropriate in each case mixed with sulfuric acid.

These anodically generated protective layers, the structure of which we know scientific studies are available (R. Kniep, P. Lamparter and S. Steeb: "Structure of Anodic Oxide Coatings on Aluminum" Angew. Chem. Adv. Mater 101 (7), pp. 975-977 (1989)), are often referred to as Denoted "oxide layers". The above investigation has shown, however, that these layers are vitreous and tetra contains coordinated aluminum. Coordinate octahedral aluminum as in the aluminum oxides was not found. There forth in this patent application the more general term "Anodi sierschichten "instead of the misleading term" Oxidschich ten "is used.  

However, these layers do not yet meet all of the requirements look at the corrosion protection as it is still a porous structure exhibit. For this reason it is necessary to use the anodizer layers to condense. This compression is often hot or boiling water, alternatively with steam, and referred to as "sealing". This closes the pores and thus the corrosion protection increased considerably. About this ver extensive literature exists. Example Wise may be mentioned: S. Wernick, R. Pinner and P.G. Sheasby: "The Surface Treatment and Finishing of Aluminum and its Alloys "(Vol. 2, 5th Edition, Chapter 11: "Sealing Anodic Oxide Coatings"), ASM International (Metals Park, Ohio, USA) and Finishing Publications LTD (Teddington, Middlesex, England) 1987.

When compacting the anodizing layers are not only the pores are closed, but it forms on the whole Surface a more or less strong velvety covering, the so-called called sealing topping. This be made of hydrated aluminum oxide standing surface is visually disturbing, reduces the adhesive strength in the bonding of such aluminum parts and promotes later Ver dirt and corrosion. Since the subsequent removal of this Sealing linings by hand, mechanically or chemically maneuverable, chemical additives are added to the sealing bath to prevent the formation of this sealing topping. According to the DE C-26 50 989 are additions of cyclic polycarboxylic acids with 4 up to 6 carboxyl groups in the molecule, especially the cyclohexane hexa carboxylic acid, suitable. According to DE-A-38 20 650 can also be correct phosphonic acids, for example the 1-phosphonopropane Use 1,2,3-tricarboxylic acid.

When using water other than the sealingbe mentioned contains no further additives for an ef  fective compression high temperatures (at least 90 ° C) and rela tiv long treatment times in the order of about 1 hour required. The compression process is very energy consuming dig and because of its duration can be a bottleneck for the production area represent speed. Therefore, additives were already used for Compression bath wanted to support the compression process, so that this at lower temperatures (so-called cold compression or cold sealing) and / or with shorter treatment times. As additives that compress in the temperature range below Enabling 90 ° C have been proposed, for example: nickel salon ze, especially fluorides, some of which are used in practice , nitrosyl pentacyanoferrate, complex fluorides of titanium and Zirconium and chromates or chromic acid, optionally in ver binding with other additives. As an alternative to an actual Chen compression was the hydrophobization of the oxide layer by means of long-chain carboxylic acids or waxes recommended as well as the treatment with acrylamides that are to be polymerized in the pore space. Further information can be found in the above-mentioned literature from S. Wernick et al. be removed. Accordingly, are already nitrogen-containing heterocyclic organic compounds as agents for consolidation. Called who for example (US-A-3 257 244) compounds with pyridine, Quinoline and quinazoline rings as well as mononuclear carbocyclic Nitrogen compounds with an unsubstituted amino group, the at a temperature between about 70 ° C (160 ° F) and the boil point to be used. In particular, the following can be used: nicotine amide, ethylene quinolinium iodide, 1-ethyl-2,6-dimethylquinoliumium did, 6,8-dichloro-2,4- (1H, 3H) -quinazolinedione, m-tolylurea and Ethyl p-aminobenzoate. These suggestions could be put into practice don't enforce.

Processes for cold compression under Ver use of nickel fluoride. Because of the toxic properties of  Nickel salts and fluorides, however, become an expensive measure as a result required for wastewater treatment.

There is therefore still a need for alternative compression anodized surfaces that allow production speed due to shorter compaction times to increase and / or the energy required for the compression to reduce casting effort. The object of the invention is such a method and suitable additives are available deliver.

In a first aspect, the invention relates to the use of a or more heterocyclic compounds with at least 4 sticks atoms in the molecule, with 2 nitrogen atoms in the 1,3 position in a 5- or 6-membered nitrogen-carbon heterocycle are bound in aqueous solution with a total concentration in Range 0.05 to 1 g / l for compacting the anodizing layers anodically metals.

A first group of suitable connections is characterized by this net that it has the atomic structure of the purine.

The phrase "atomic structure of purine" is to be understood as that the compounds suitable for the use according to the invention represent a heterocyclic two-ring system in which the ring atoms are bound together in the same order as in Purine. The ring atoms can have different substituents wear, which are defined in more detail below. Depending on the absence or Presence of substituents and depending on whether substituents are bonded to the ring atoms via single or double bonds, are the ring atoms with their neighbors with single or double bin  connected so that the usual valence rules are observed the.

The heterocyclic compounds are preferably selected from Compounds with an atomic linkage according to the general formula (I)

where the substituents can have the meanings

R¹ = H, O or NH₂,
R², R⁴, R⁵, R⁷ independently of one another = H, CH₃ or not existing,
R³, R⁶ independently of one another = H or O,

and the bonds within the ring system and between ring atoms and substituents R depending on the nature of the substituents R single or Can be double bonds. O is through double bond, H, NH₂ and CH₃ are bound by single bonds.

Examples of such compounds are, in addition to the purine itself, adenine, Guanine, xanthine, hypoxanthine and the preferred urine re as well as more preferred compounds those who made are selected from compounds with an atomic linkage according to the general formula (II)

where R² is H or CH₃, R⁵, R⁶ and R⁷ are the above have given meanings and the bonds between those to the Substituents R⁵, R⁶ or R⁷ bound atoms and their neighbor atoms depending on the nature of these substituents single or double can be, with such compounds being preferred, in which R⁵ = CH₃ and R⁶ = O mean.

Examples of compounds of general formula (11), the particular ders are preferred, are caffeine with R², R⁵ and R⁷ = CH₃ and R⁶ = O, theobromine with R² and R⁵ = CH₃, R⁶ = O and R⁷ = H and Theo phylline with R² = H, R⁵ = CH₃, R⁶ = O and R⁷ = CH₃.

Another usable group of compounds is ge indicates that it has the atomic structure of pteridine, that is consists of two condensed heterocyclic six-membered rings of each of which carries two nitrogen atoms. Examples of such a connection are, in addition to the less preferred pteridine, pterine itself, Leucopterin, xanthopterin and folic acid.

Other suitable connections can be made by the six-atom ring of the above compounds with splits the atomic structure of purine in such a way that the five-atom ring is preserved and carries a side chain that has at least two Contains nitrogen atoms. An example of this is the allantoin, which can be obtained by oxidative degradation of the six-ring of uric acid  is. Derivatives thereof which have the same C-N skeleton can if you find other suitable connections of the general NEN formula (I) degrades oxidatively.

It applies in each case that individual compounds or mixtures ver Different connections can be used, provided they are the preferred bath conditions (pH in the range from 6 to 11, temperature 25 to 35 ° C) in the desired concentrate range between 0.05 and 1 g / l are soluble.

A reduction in treatment time and / or an improvement in Treatment results can be achieved if the aqueous Lö solutions of the heterocyclic ver bonds other additives are added. As such further Additives are preferred:

• 1. Cations of alkaline earth metals, especially magnesium and / or Calcium, rare earth metals, metals of the second subgroup, especially zinc, and / or the third main group of Peri odensystems, especially aluminum. These metal ions can used individually or in a mixture, the preferred amounts in the range 0.001 to 0.1 g / l, in particular 0.005 to 0.01 g / l. The cations of are particularly preferred Aluminum and / or magnesium. If the term "Katio nen "is used, it means that the Me talle can be present as (hydrated) cations, but also in the form of compounds or polyatomic cations or Anions in which the metal atoms are attached to more electronegative partners are bound and therefore themselves a formal positive charge carry. For example, aluminum as an aluminate anion or be present as an anionic sulfato or fluorocomplex. To the Use salts that are suitable under the conditions of  Sealing baths are soluble in the concentration range mentioned.
• 2. Free and / or complex bound fluoride in amounts of each 0.05 to 1 g / l, preferably 0.08 to 0.15 g / l. Free fluoride is preferably used as an alkali metal fluoride, in particular as Sodium fluoride used, but can also be used as hydrofluoric acid or be used in the form of acidic fluorides such as KHF₂. Complexes Fluorides are, for example, the alkali metal salts or Acids of the anions tetrafluoroborate, hexafluorosilicate, hexa fluorotitanate and hexafluorozirconate. Hexafluorosilicate is considered complex bound fluoride preferred.
• 3. One or more of the following components:
  10 to 2000 ppm alkali or ammonium salts of saturated or unsaturated monocarboxylic acids with 8 to 22 carbon atoms,
  0.01 to 1000 ppm anionic, cationic or nonionic surfactants, preferably nonionic surfactants and in particular ethoxylation products of fatty amines, for example cocosamine,
  1 to 1000, preferably 10 to 100 ppm, homo- or copolymers of acrylic acid and / or methacrylic acid and / or maleic acid, which can additionally carry phosphonic acid groups and preferably have an average molar mass in the range from 200 to 2000, preferably 400 to 800.

For the use according to the invention, it is recommended that the aqueous solution of the heterocyclic compounds a pH in Range from 6 to 11, preferably 8.5 to 10.5 and the Temperature of the solution preferably 25 to 35 ° C and in particular 28  is up to 30 ° C. The adjustment of the pH and if necessary its adjustment during the operation of the sealing bath can be done with Alkali metal lye or preferably with ammonia.

In a second aspect, the invention relates to a method for Densification of the anodizing layers of anodized metals, thereby characterized in that the metal parts for 5 seconds to 15 minutes, preferably 1 to 5 minutes with an aqueous solution after a or more of claims 1 to 10 are brought into contact, preferably by immersion in the solution or by spraying with the solution. Shorter treatment times worsen the condition success of the action, not essential during longer treatment times Chen advantage.

This treatment step according to the invention can be considered as a pre-compression, since this improves the layer properties compared to an undensified anodizing layer, but the technical requirements for the properties of the anodizing layers discussed below are generally not yet achieved. It is therefore preferred to follow this precompression - without or preferably with an intermediate rinsing with water, in particular with deionized water - a final compression by treatment with steam or by immersion in a conventional hot compression bath at a temperature between 80 and 100 ° C to let. Hot compression baths, such as those currently used in technology, are suitable for this. For example, the commercial hot sealing bath P3-almecoseal-SL ^R (Henkel KGaA, Düsseldorf) is suitable for this purpose, which is operated at a temperature of 96 ° C. or above and a pH value of 5.8 to 8.2 (speedseal). The required final compression time in such a hot compression bath is between 10 and 20 minutes, whereby times above 15 minutes are generally not necessary.

Accordingly, the method according to the invention is preferred as a preliminary method seal used before conventional hot compression. This requires one compared to the current state of the art additional treatment level, but has the advantage that the Total treatment time reduced despite additional step, so that the Productivity is increased per unit of time. Further reduced the shortened batch times in the downstream hot compression bath the amount of energy required per batch, the mainly due to the evaporation losses during the treatment duration is caused. The method according to the invention is there more economical in operation than the conventional one Hot compaction, in which the treatment time of a batch in hot compression bath is about an hour. In contrast, shortened the entire compression according to the inventive method time after anodizing to less than half.

After the accelerated and energy-saving Ver compacted anodizing layers can be produced, which in their layer properties do not match the conventionally produced ones stand. Of the practical cold compression processes under Ver The use of nickel salt solutions differs according to the invention moderate method in that the test values for the layer quality after a total of about 25 minutes seal time have assumed values that are the same for the other cold compaction only after a waiting period of at least 24 hours be preserved. As test parameters for the layer quality are technically in particular the removal of acid in chromic acid, the appearance conductance and the loss factor are important. This quality The key figures for the layers are based on standard test methods  checks that are given in the sample section.

The compression method according to the invention is preferably used for anodized aluminum or anodized aluminum alloys set. However, it can also be applied to the anodizing layers more anodizable metals such as titanium and magne Use sium or their alloys. It is for both undyed anodizing layers, usable as well for those who using conventional methods such as an integral staining, an adsorptive staining using organic color substances, a reactive coloring with formation of inorganic Color pigments, using an electrochemical coloring metal salts, especially tin salts, or an interfe border coloring were colored. With adsorptively colored anodi The process according to the invention has further layers partly that due to the shortened compression time and the low Temperature in the first compression step that with conventional Hot compression possible bleeding of the dye is reduced.

Examples

Aluminum sheets of the type Al 99.5 were conventionally anodized (direct current / sulfuric acid, one hour, layer thickness 20 µm) and, if necessary, colored electrochemically or with organic immersion colors. The plates were then immersed for 1 to 10 minutes at 28 to 30 ° C. in the compression solutions or comparative solutions according to the invention in accordance with the table. This was followed by a 2 to 10 second rinse with deionized water. Subsequently, the pre-compressed sheets for 10 to 15, maximum 20 minutes in a conventional commercial hot compression bath (P3almecoseal ^R SL, Henkel KGaA, Düsseldorf) were finally sealed at about 96 ° C. Details are given in the table.

To check the compaction quality, practical quality tests of the layers were carried out immediately after the final compaction:
The admittance Y₂₀ was determined according to the German standard DIN 50949 with an Anotest YD 8.1 measuring device from Fischer. The measuring system consists of two electrodes, one of which is conductively connected to the base material of the sample. The second electrode is immersed in an electrolyte cell that can be placed on the layer to be examined. This cell is designed as a rubber ring with an inner diameter of 13 mm and a thickness of approximately 5 mm, the ring surface of which is self-adhesive. The measuring area is 1.33 cm². A potassium sulfate solution (35 g / l) in deionized water is used as the electrolyte. The apparent conductance readable on the measuring device is converted to a measuring temperature of 25 ° C and a layer thickness of 20 µm according to the specifications of DIN 50949. The values obtained, which should be in the range between approximately 10 and approximately 20 μS, are entered in the table.

With the same measuring device, the Ver pleasure factor d determined according to the operating instructions. As a loss factor d is the ratio of active and reactive power, which in of the measuring cell at one (prescribed by the standard with 1 kHz) Measuring frequency is implemented. The loss factor can just as well than the ratio of the ohmic to the capacitive cell resistance can be specified. This method has the advantage of being largely un depending on the layer thickness, the measuring surface and the applied To be current density. It should range between about 0.45 and about 0.75. The values obtained are shown in the table carry.

As a parameter, the open-pored and therefore poorly compressed Layers, the residual reflection after staining with color fabric measured according to the German standard DIN 50946. Here was the measuring surface with the help of a self-adhesive measuring cell of the limited Anotest device described above. The test area with an acid solution (25 ml / l sulfuric acid, 10 g / l KF) wetted. After exactly one minute, the acid solution is washed off and dried the test area. Then the test area is included Dye solution (5 g / l Sanodal blue) wetted, which one minute leaves for a long time. After rinsing under running water, the Measuring cell removed. The stained test area is rubbed off attach loosely using a mild powder cleaner freed from the dye. After drying the surface, a relative reflection measurement made by the measuring head of a Light reflection measuring device (Micro Color from Dr. Lange) once an undyed part of the surface and the second on the indicated colored measuring surface is placed. The remaining reflection in% becomes hold by taking the quotient from the measured value of the colored area area divided by the measured value of the undyed area with a hundred multiplied. Residual reflection values between 85 and 100% testify to  good compaction quality, while values below 85% than not apply acceptable. The compression quality is higher the higher forth are the values of the residual reflection. The values found are in of the table.

For selected samples, the acid rejection was also measured based on ISO 3210. For this purpose, the test plate is weighed to the nearest 0.1 mg and then immersed for 15 minutes at 38 ° C in an acid solution containing 35 ml of 85% phosphoric acid and 20 g of chromium (VI) oxide per liter. At the end of the test period, the sample is rinsed with deionized water and dried in a drying cabinet at 60 ° C. for 15 minutes. The sample is then weighed again. The difference in weight between the first and the second measurement is calculated and divided by the size of the surface in dm². Weight loss is expressed in mg / dm² and should not exceed 30 mg / dm². Determined values are contained in the table. Furthermore, the optical appearance of the densified layers, which were generally colored with P₃-almecolor ^R ST2 tin (II), was assessed. Uniform, non-stained or iridescent layers on which no fingerprints are visible (referred to in the table as "fingerprints") are referred to as "good".

The pH of the pre-compression baths was adjusted with ammonia. The final compression was carried out with a commercially available hot compression bath (P3almecoseal ^R SL, Henkel KGaA). The respective treatment time is given in the table. The temperature of the bath was 96 ° C. and the pH, unless otherwise stated, was 5.8.

In the table below mean:

Al sulfate: Al₂ (SO₄) ₃ · 18H₂O
Araphene: nonionic surfactant, adduct of 12 moles of ethylene oxide with coconut amine
Prisorine: mixture of isostearic acid and isomers
Mg sulfate: MgSO₄ · 7H₂O
Ni sulfate: NiSO₄ · 6H₂O
Na tungstate: Na₂WO₄ · 2H₂O
Belclene: Belclene® 200, polymaleic acid (Ciba Geigy)

Claims (13)

1. Use of one or more heterocyclic compounds with at least 4 nitrogen atoms in the molecule, whereby 2 stick atoms in the 1,3 position in a 5- or 6-membered stick Substance-carbon heterotycle are involved in aqueous Solution with a total concentration in the range 0.05 to 1 g / l for compacting the anodizing layers of anodized metals. 2. Use according to claim 1, characterized in that the heterocyclic compounds have the atomic structure of the purine and are selected from compounds having an atomic linkage according to the general formula (I) where the substituents can have the meanings
R¹ = H, O or NH₂,
R², R⁴, R⁵, R⁷ independently of one another = H, CH₃ or not before,
R³, R⁶ independently of one another = H or O,
and the bonds within the ring system and between ring atoms and substituents R, depending on the nature of the substituents R, can be single or double bonds. 3. Use according to claim 2, characterized in that the heterocyclic compounds are selected from compounds having an atomic linkage according to the general formula (II) where R² is H or CH₃, R⁵, R⁶ and R⁷ have the meanings given in claim 1 and the bonds between the atoms bonded to the substituents R⁵, R⁶ or R⁷ and their neighboring atoms can be single or double bonds, depending on the nature of these substituents, such compounds are given before, in which R⁵ = CH₃ and R⁶ = 0. 4. Use according to one or both of claims 2 and 3, since characterized in that the heterocyclic compounds are selected from uric acid, caffeine, theobromine, theophylline or combinations thereof. 5. Use according to claim 1, characterized in that the heterocyclic compounds on the atomic structure of pteridine point and are preferably selected from Pterin, Leucopte rin, xanthopter and folic acid. 6. Use according to claim 1, characterized in that the heterocyclic compounds are selected from allantoin and derivatives derived therefrom while maintaining the C-N framework.   7. Use according to one or more of claims 1 to 6, since characterized in that the aqueous solution of the heterocycli compounds additionally cations of alkaline earth metals, Rare earth metals and / or metals of the second subgroup and / or the third main group of the periodic table in quantities from 0.001 to 0.1 g / l, preferably 0.005 to 0.01 g / l contains, the cations of aluminum and / or magnesium are preferred. 8. Use according to one or more of claims 1 to 7, because characterized in that the aqueous solution of the heterocycli connections are also free and / or complexly bound Fluoride in amounts of 0.05 to 1 g / l each, preferably Contains 0.08 to 0.15 g / l, with fluoride bound as a complex Hexafluorosilicate is preferred. 9. Use according to one or more of claims 1 to 8, characterized in that the aqueous solution of the heterocyclic compounds additionally contains one or more of the following components:
10 to 2000 ppm alkali or ammonium salts of saturated or unsaturated monocarboxylic acids with 8 to 22 carbon atoms,
0.01 to 1000 ppm anionic, cationic or nonionic surfactants, preferably nonionic surfactants and in particular ethoxylation products of fatty amines,
1 to 1000, preferably 10 to 100 ppm, homo- or copolymers of acrylic acid and / or metacrylic acid and / or maleic acid, which can additionally carry phosphonic acid groups and preferably have an average molecular weight in the range from 200 to 2000, in particular 400 to 800. 10. Use according to one or more of claims 1 to 9, because characterized in that the aqueous solution of the heterocycli compounds have a pH in the range from 6 to 11 preferably has 8.5 to 10.5 and the temperature of the solution preferably 25 to 35 ° C 'and in particular 28 to 30 ° C be wearing. 11. Method for densifying the anodized layers Metals, characterized in that the metal parts for 5 Se customers up to 15 minutes, preferably 1 to 5 minutes with one aqueous solution according to one or more of claims 1 to 10 be brought into contact, preferably by immersion in the solution or by spraying it with the solution. 12. Method for densifying the anodized layers Metals, characterized in that according to the method Claim 11, preferably after an intermediate rinse with what water, especially with demineralized water, a final compression by treatment with steam or by immersion in a Hot compression bath with a temperature between 80 and 100 ° C for a time between 10 and 20 minutes, preferably between 10 and 15 minutes. 13. The method according to claim 11 or 12, characterized in that the anodizing layers are anodizing layers Titanium, magnesium or in particular aluminum or in each case their Alloys.