WO1995028512A1

WO1995028512A1 - Process for producing shiny mouldings which are galvanised or coated with a zinc alloy

Info

Publication number: WO1995028512A1
Application number: PCT/EP1995/001286
Authority: WO
Inventors: Ulrich Schröder; Klaus Glaser; Thomas Wehlage
Original assignee: Basf Aktiengesellschaft
Priority date: 1994-04-16
Filing date: 1995-04-07
Publication date: 1995-10-26
Also published as: DE4413251A1

Abstract

The production of shiny galvanised or zinc-alloy-coated mouldings by the electrolytic separation of zinc or a zinc alloy from aqueous-acid galvanic baths which contain as essential components one or more zinc salts and possibly salts of the other alloy metals, one or more conducting salts, one or more tensides and one or more gloss agents, in which the gloss agents used are compounds (I), in which R1 is C1 to C8 alkoxy, phenoxy, benzyloxy, amino, C1 to C6 alkyl amino or Di(C1 to C6) alkylamino, R2 is C1 to C4 alkyl, phenyl, benzyl or the substances under R1, and Ar is phenyl or naphthyl which may additionally be substituted by one to three C¿1? to C4 alkyl groups or C1 to C4 alkoxy groups, and the auxiliary gloss agents are compounds of the general formula (II) H-(OA?1)¿m-S-(A2O)n-H and/or (III) R?3-S-(A1O)¿m-H, in which R3 is C1 to C24 alkyl, A?1 and A2¿ are, mutually independently, an alkylene group or a mixture of alkylene groups with 2 or 3 C atoms and m and n are mutually independently an integer from 1 to 100.

Description

Process for the production of shiny galvanized or zinc alloyed molded parts

description

The present invention relates to an improved process for the production of shiny galvanized or zinc alloyed molded parts by electrolytic deposition of zinc or a zinc alloy from aqueous acidic galvanic baths. The invention further relates to brightener mixtures for this purpose.

In the galvanic deposition of zinc or zinc alloys on metallic substrates from aqueous-acidic solution, a glossy coating is often sought in order to give the galvanized object an advantageous decorative appearance, i.e. in addition to the corrosion-preventing effect, a decorative effect is often desired. In order to achieve the desired effects, it is essential that the galvanic baths contain certain auxiliaries, because otherwise the zinc coatings formed from acidic solution are usually matt and often also irregular. A group of such aids for acidic galvanic baths are, for example, conductive salts which are used to improve the conductivity of the baths, another group of aids are the so-called brighteners.

DE-A 29 48 261 (1) describes acidic galvanic zinc baths with and without ammonium salts which as aromatic brighteners see aromatic, carbonyl-containing compounds such as o-chlorobenzaldehyde, p-chlorobenzaldehyde, o-hydroxybenzaldehyde, aminobenzaldehyde, vertraaldehyde, benzylidene acetone , Coumarin, 3,4, 5, 6-tetrahydrobenzaldehyde, acetophenone, propiophenone, furfurylidine acetone, 3-methoxybenzalacetone, benzaldehyde, vanillin, hydroxybenzaldehyde, anisaldehyde, benzoic acid, sodium benzoate, sodium salicylate or 3-pyridic acid ) contain. To improve the properties of the electroplating baths, the use of polymeric, sulfur-containing compounds of the general formulas is used

RS- (AO) _n -H or S [(A0) _n -H] ₂

with R = alkyl up to 24 carbon atoms,

A = alkylene with 2 or 3 carbon atoms and n = 1 - 100 2 described in connection with the carbonyl-containing compounds mentioned. "^"

The most important representative of such brighteners for acid zinc baths is benzylidene acetone (benzal acetone). A serious disadvantage of benzylidene acetone and its homologues, however, is the fact that these compounds cause allergic reactions such as reddening of the skin and itching in many people who handle it.

DE-A 41 19 341 (2) recommends replacing gloss formers based on benzylidene acetone in aqueous-acidic, galvanic baths for the deposition of zinc or zinc alloys by certain other substances which achieve the effectiveness of the known gloss formers, however do not lead to health impairments in persons who handle these substances.

The disadvantage is that with brighteners, as described in (2), good results can only be obtained at relatively low temperatures below 30 ° C.

It was therefore an object of the present invention to provide brightener systems which can be handled without health risks and which permit the operation of galvanic zinc baths at higher temperatures which are more favorable in terms of application technology.

Accordingly, a process for the production of shiny zinc-coated or zinc alloy-coated molded parts by electrolytic deposition of zinc or a zinc alloy from aqueous-acidic galvanic baths, the essential components of which are one or more zinc salts and optionally salts of the other alloy metals, contain one or more conductive salts, one or more surfactants and one or more brighteners, characterized in that compounds of the general formula I

0

C — R ¹

Ar — CH: (I)

^* C — R ²

0 in R is C -. - to Cg-alkoxy, phenoxy, benzyloxy, amino, Ci to C _δ -AlkTLamino or di (C - to Ce ~) alkylamino,

R ² C- _; - bis- Cή-alkyl, phenyl, benzyl or the meanings listed under R ¹ and

Ar represents phenyl or naphthyl, which can additionally be substituted by one to three C 1 -C ₄ -alkyl groups or C-- to C ₄ -alkoxy groups,

and as auxiliary brighteners, compounds of the general formula II and / or III

H- (OA ^l ) _m -S- (A ² 0) _n -H (II)

R ³ -S- (A ¹ 0) _rr -H (III)

in which

R ³ denotes Ci to C ₂ <* - alkyl,

A ¹ and A ² each independently denote an alkylene group or a mixture of alkylene groups with 2 or 3 carbon atoms and

m and n each independently represent an integer from 1 to 100,

starts.

This makes it possible to operate baths at a temperature of 30 to 90 ° C, preferably 40 to 50 ° C.

Preferred radicals R ¹ are Ci to Cβ alkoxy groups such as n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl ,. n-heptyl, 2-ethylhexyl, octyl or especially methyl or ethyl based residues.

Preferred radicals R ² are C 1 -C ₄ -alkyl groups such as ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl or especially methyl and C-_ - To C _ß -alkoxy groups such as n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl or especially methyl or ethyl based Leftovers. The preferred radical Ar is the phenyl group, which can additionally be substituted by one or two methyl, ethyl, methoxy or ethoxy groups, but especially the unsubstituted phenyl group.

Very particularly preferred compounds I are methyl and ethyl 2-benzylidene-acetoacetate (R * = 0CH ₃ or OC ₂ H ₅ , R ² = CH ₃ , Ar = Ph) and dimethyl and diethyl 2-benzylidene-malonate (R. = R ² = OCH ₃ or OC ₂ H _b , Ar = Ph).

These substances are easily and inexpensively accessible by condensation from benzaldehyde and the corresponding acetoacetic or malonic ester. The preparation of methyl benzylidene-acetoacetate is described, for example, in J. Org. Chem. 1990, Vol. 55, pp. 319-324.

These compounds I are in the aqueous-acidic galvanic baths according to the invention in an amount of advantageously 0.01 g to 3 g per liter, preferably 0.05 to 1.5 g per liter, in particular 0.1 g to 0.7 g per liter.

It is of course possible to use mixtures of compounds I as brighteners and to use the brighteners according to formula I together with other known brighteners.

Preferred radicals R ³ are linear or branched C ₆ - to C _2] alkyl groups, especially Cs to C ₂ ^_ ~ o alkyl groups, for example n-octyl, 2-ethylhexyl, n-nonyl, iso-nonyl, n-decyl, n -Undecyl, n-dodecyl, n-tridecyl, iso-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl or eicoryl.

The alkylene groups A ¹ and A ² denote 1,2- or 1,3-propylene or preferably 1,2-ethylene.

The variables m and n each preferably represent an integer from 2 to 50, in particular 3 to 30.

In a preferred embodiment, compounds II are used as auxiliary brighteners in which the sum of m + n is a number from 2 to 40, in particular 4 to 32. A ¹ and A ² are preferably the same. 5

The auxiliary brighteners of the formulas II and III are advantageously used in the aqueous-acidic galvanic baths according to the invention in an amount of 0.1 to 80 g per liter, in particular 0.5 to 15 g per liter.

The aqueous-acidic galvanic baths according to the invention have the usual compositions with respect to the other components. They contain, for example, 50 to 150 g / 1 zinc chloride or the equivalent amount of zinc sulfate. If zinc alloys are to be deposited on metallic substances, for example with cobalt and / or nickel and / or iron, the baths generally additionally contain 1 to 30 g / 1 cobalt and / or nickel and / or iron sulfate or the equivalent Amount of another water-soluble cobalt and / or nickel and / or iron salt.

Another essential component of the baths are conductive salts. A suitable conductive salt is potassium chloride, which is usually present in amounts of 100 to 250 g / l in the aqueous acidic electroplating bath. Other conductive salts are, for example, ammonium chloride or sodium chloride, which are usually used in amounts of 10 to 150 g / l.

Another essential constituent of the aqueous acidic galvanic baths according to the invention are nonionic and anionic surfactants. Suitable nonionic surfactants are known for example from GB-PS 1 149 106. These are addition products of ethylene oxide with fatty alcohols, for example with C 6 -C ₈ -alcohols, or addition products of ethylene oxide with phenol or alkylphenols, in particular with nonylphenol. As a rule, 5 to 100 moles of ethylene oxide are added per mole of alcohol or phenol. Polyoxyalkylated naphthols can also be added.

Good solubilizers and auxiliary brighteners are also polyethylene glycols with molecular weights from 200 to 10,000.

Another useful component in the acidic zinc baths according to the invention can be poly (alkyleneimines). Poly (alkylene imines) can be used as such or they can be reacted with a cyclic carbonate consisting of carbon, hydrogen and oxygen atoms. A description of the preparation of examples of such reaction products can be found in US-A 2,824,857. 6

To improve the ductility and auxiliary brighteners as the aromatic sulphonic acids in ^{^} the US-A 2,824,857 mentioned as well as from DE-OS 23 26 300 the known condensation products of the benzene or naphthalene sulfonic acids with formaldehyde are useful.

Suitable anionic surfactants are known, for example, from US Pat. No. 3,787,296. These are mainly sulfated polyethers, which can be obtained, for example, by adding ethylene oxide to fatty alcohols, fatty amines, amides of Cζ to Cio-carboxylic acids and longer-chain fatty acids and subsequent sulfonation. Sulfonates of polyalkylene oxides or block copolymers of ethylene oxide and propylene oxide are also used as anionic surfactants.

Another group of anionic surfactants is from the

EP-B 115 020 known. This describes sulfonated and sulfated alkylphenol ethoxylates which, for example, have the general formula IV

in the R ⁴ C - to C ₂ o-alkyl, X and Y the groups -S0 ₃ H or -S0 ₃ Me, where Me is ammonium, alkali metal or an equivalent of alkaline earth metal or zinc, and P is a number from 5 to 50 mean, have.

In addition to the compounds of the formula IV, those sulfonated and sulfated products whose polyether chain contains 1 to 25 propylene oxide or butylene oxide units are also suitable as anionic surfactants.

DE-C 38 39 824 discloses anionic additives based on monobasic and polybasic ether sulfonic acids. These are by individual or combined sulfopropylation and / or sulfobutylation of the following hydroxyl-containing compounds

a) block polymers of ethylene oxide and / or glycidol with propylene oxide and / or butylene oxide, 7 b) one or polyhydric, mono-, saturated or unsaturated aliphatic alcohols, and or polyhydric tischefT ^*, alkylated or non-alkylated phenols or naphthols, einschließ¬ Lich ih-rer alkoxylates,

manufactured.

The advantage of the sulfonated and sulfated alkylphenol alkoxylates is that they have an extraordinarily high cloud point, so that the electrolytic deposition of the zinc not only in the temperature range from 20 to 30 ° C, but also at temperatures from 30 to 90 ° C , preferably in a range of 40 to 50 ° C, can be made. The nonionic and anionic surfactants act as auxiliary brighteners and at the same time are solubilizers for, for example, the compounds described in (2). Otherwise they are hardly soluble in water.

These suitable surfactants and also phenol-formaldehyde condensation products or naphthalenesulfonic acid / formaldehyde condensation products which can also be used as surfactants are usually present in amounts of 1 to 20 g / 1, preferably 2 to 15 g / 1, in the aqueous-acidic galvanic compositions according to the invention Bä¬ applied. A mixture of several surfactants can also be used.

In addition, alkali metal or ammonium benzoates such as, in particular, sodium benzoate, in amounts of 0.1 to 8 g / 1, preferably 1 to 4 g / 1, can advantageously be used as additional brighteners.

The pH of the aqueous-acidic galvanic baths according to the invention is generally 3 to 7, preferably 4 to 5. It is adjusted by adding acids, e.g. usual mineral acids such as sulfuric acid or hydrochloric acid.

Particularly advantageous results in the galvanizing are obtained if, in the aqueous acid baths according to the invention, the substances described with formulas I and II in an amount of 0.1 to 80 g / 1 as auxiliary brighteners simultaneously with methyl and ethyl esters of 2- Benzylidenacetoacetic acid or 2-benzylidenmalonic acid in a concentration of 0.02 to 2 g / 1, preferably 0.1 g to 0.7 g / 1, is used as a brightener. These combinations have proven particularly useful in ammonium salt-free, higher-temperature, aqueous-acidic galvanic zinc baths or zinc alloy baths. 8th

The present application also relates to aqueous acidic galvanic baclers for the electrolytic deposition of zinc or a zinc alloy as a glossy coating on moldings, the baths being an essential constituent of one or more zinc salts and optionally salts of the other alloy metals, one or more conductive salts or contain more surfactants and one or more brighteners, characterized by an effective content of a mixture of the compounds I and the compounds II and / or III.

The present application also relates to brightener mixtures for aqueous-acidic galvanic baths for the electrolytic deposition of zinc or a zinc alloy from the compounds I and the compounds II and / or III. These brightener mixtures advantageously consist of 0.01 to 3.0 parts by weight, preferably 0.05 to 1.5 parts by weight, in particular 0.1 to 0.7 parts by weight, of the compounds I and 0.1 to 80 parts by weight, preferably 0.5 to 15 parts by weight of the compounds II and / or III.

The process according to the invention galvanizes molded parts made of metals, mainly iron and steel, in order to protect them against corrosion and at the same time to give them a high gloss high-gloss and ductile zinc coatings which correspond in quality to the coatings which are obtainable using benzylidene acetone according to the prior art. The baths according to the invention can be handled without recognizable health risks such as triggering skin allergies.

Examples

The effectiveness of the mixtures of compounds I and II in aqueous acidic galvanic baths for electrolytic

Zinc deposition is demonstrated using two different baths.

Composition of the baths:

Zinc chloride 100 g / 1

Potassium chloride 200 g / 1

Boric acid 20 g / 1 commercial naphthalenesulfonic acid / formaldehyde condensation product 2 g / 1

Sodium benzoate 2 g / 1 commercial fatty alcohol polyethylene glycol ether "~ with 10 ethylene glycol units 1 g / 1 nonylphenol polyethylene glycol ether, sulfonated and sulfated, with 10 ethylene glycol units xg / i bath 1 x = 4

Bath 2 x = 10

Brighteners according to the invention according to the table

The pH of the baths was 4.8. The pH was adjusted with dilute hydrochloric acid. The galvanizing of brass or steel sheets took 10 minutes each. It was carried out in a 250 ml Hull cell with 1 or 2 amperes at the temperature indicated. Following the galvanizing, it was briefly immersed in 0.5% HNO ₃ and then blue chromated.

The quality of the zinc coatings obtained can be seen from the following table. The gloss and ductility of the galvanic coatings was assessed visually, the marks mean

bad, 2 = low, 3 = moderate, 4 = good and 5 = very good

It can be seen that the action of the compounds II used according to the invention in combination with aromatic esters I according to (2) is at least equivalent to the very good action of benzylidene acetone.

Table: Brightener in aqueous-acidic galvanic zinc baths

E.g. substance conc. Bath no. Temp. Result 1 No. [g / i] [° C] gloss ductility according to the invention:

1 benzylidene acetoacetic acid 0.1 1 23 4-5 5 methyl acid ester

H (OCH ₂ CH ₂ ) _n -S- (CH ₂ CH ₂ 0) _m H, n + m = 11 1.0

2 benzylidene acetoacetic acid - 0.2 2 40 4 5 acid ethyl ester

H (OCH ₂ CH ₇ ) _r; -S- (CH ₂ CH ₂ 0) _m H, n + m = 11 1.0

3 benzylidene acetoacetic acid - 0.2 2 45 4 5 methyl ester

H (OCH ₂ CH ₂ ) _n -S- (CH ₂ CH ₂ 0) _m H, n + m = 11 1.0

4 benzylideneacetoacetic acid - 0.2 2 40 3-4 5 methyl acid ester

H (OCH ₂ CH ₂ ) _n -S- (CH ₂ CH ₂ 0) _m H, n + m = 6 4.0

5 benzylidene acetoacetic acid - 0.2 2 40 3-4 5 methyl acid ester

H (OCH ₂ CH ₂ ) _n -S- (CH ₂ CH ₂ 0) _m H, n + m = 31 1.5

Claims

1. Process for the production of shiny galvanized or zinc alloy-coated molded parts by electrolytic deposition of zinc or a zinc alloy from aqueous-acidic galvanic baths, the essential components of which are one or more zinc salts and optionally salts of the other alloy metals or more conducting salts, one or more surfactants and one or more brightening agents, characterized in that compounds of the general formula I

0

II

C — R ¹

Ar — CH = C ⁽ I ⁾

^ C — R ²

0 in

R ^{1 is} Ci to Cβ alkoxy, phenoxy, benzyloxy, amino, Ci to Ce alkylamino or di (Ci * - to C _ß -) alkylamino,

R ² denotes Ci to C ₄ alkyl, phenyl, benzyl or the meanings listed under R ¹ and

Ar represents phenyl or naphthyl, which may additionally be substituted by one to three C 1 -C ₄ -alkyl groups or C 1 -C 4 -alkoxy groups,

and as auxiliary brighteners, compounds of the general formulas II and / or III

H- (OA ⁱ ) _m -S- (A ² θ) _n -H (II)

R -S- (A ¹ 0) _m -H (III)

in which

R ³ denotes Ci to C ₂ alkyl, A ^: and A ² each independently denote an alkylene group or a mixture of alkylene groups with 2 or 3 carbon atoms and

m and n each independently represent an integer of

1 to 100 means

starts.

2. A process for the production of shiny galvanized or zinc alloy-coated molded parts according to claim 1, characterized in that compounds I are used as brighteners in which

R ^{1 is} Ci to C ₈ alkoxy,

R ² Ci to C ₄ alkyl or C- _. - C ₆ alkoxy and

Ar represents phenyl, which can additionally be substituted by one or two methyl, ethyl, methoxy or ethoxy groups.

3. A process for the production of shiny galvanized or zinc alloy-coated moldings according to claim 1 or 2, characterized in that the compounds I are used in an amount of 0.01 g to 3 g per liter of the aqueous acidic galvanic bath.

4. A process for the production of shiny galvanized or zinc alloy-coated molded parts according to claims 1 to 3, characterized in that compounds II are used as auxiliary brighteners in which the sum of m + n is a number from 2 to 40 .

5. A process for the production of shiny galvanized or zinc alloy-coated moldings according to claims 1 to 4, characterized in that the compounds II and / or III in an amount of 0.1 to 80 g per liter of the aqueous acidic galvanic bath.

Process for the production of shiny galvanized or zinc alloy-coated molded parts according to claims 1 to 5, characterized in that alkali metal or ammonium benzoates are used as additional brighteners.

7. Use of a mixture of the compounds I and the compounds II and / or III according to claims 1 to 6 as brighteners and auxiliary brighteners in aqueous-acidic galvanic baths, the essential constituents of one or more zinc salts and optionally salts of contain other alloying metals, one or more conductive salts, one or more surfactants and one or more brighteners, for the electrolytic deposition of zinc or a zinc alloy as a shiny coating on molded parts.

8. Aqueous, acidic galvanic baths for the electrolytic deposition of zinc or a zinc alloy as a glossy coating on molded parts, the baths being essential components of one or more zinc salts and optionally salts of the other alloy metals, one or more conducting salts, one or more Contain surfactants and one or more gloss formers, characterized by an effective content of a mixture of the compounds I and the compounds II and / or III according to claims 1 to 6.

9. brightener mixtures for aqueous-acidic galvanic baths for the electrolytic deposition of zinc or a zinc alloy from the compounds I and the compounds II and / or III according to claims 1 to 6.

10. Brightener mixtures according to claim 9 from 0.01 to 3.0 parts by weight of the compounds I and 0.1 to 80 parts by weight of the compounds II and / or III.