EP1799881A2

EP1799881A2 - Non-galvanically applied nickel alloy

Info

Publication number: EP1799881A2
Application number: EP05784829A
Authority: EP
Inventors: Doris Bialkowski; Alfons Holländer
Original assignee: AHC Oberflaechenechnik GmbH
Current assignee: Aalberts Surface Technologies GmbH Kerpen
Priority date: 2004-09-28
Filing date: 2005-09-26
Publication date: 2007-06-27
Also published as: US20080196625A1; WO2006035397A3; WO2006035397A2; DE102004047423C5; DE102004047423B3

Abstract

The invention relates to a lead-free nickel phosphorous dispersion alloy on a metallic substrate surface, which may be obtained by non-galvanic deposition in an electrolyte, comprising 4 to 7 g/l nickel ions, 15 to 40 g/l hypophospite, at least one stabiliser, 5 to 400 mg/l of an alkylaryloxydialkylbenzylammonium chloride or a partially-fluorinated betain, 50 to 60 g/l of a complexing agent A, containing a carboxylic acid, 5 to 40 g/l of a complexing agent B containing a carboxylic acid different from A, 4 to 10 g/l dispersed particles, different from the nickel/phosphorus alloy composition and no boric acid or borates and objects coated therewith.

Description

Externally powered nickel alloy

The present invention relates to a lead-free, chemically, without external current produced nickel alloy with inclusions and articles coated therewith

The chemical nickel-plating of metal surfaces is a widely used method on an industrial scale for the corrosion and wear protection of metals

In general, a distinction is made between an electrolytic and an electroless deposition for the production of a nickel layer

Electrolytic deposition - also known as electrodeposition or coating - is a deposition reaction on the surface to be coated, which is forced by the introduced current

In electroless deposition - also known as chemical deposition or coating - the layer formation is based on an autocatalytic process, which is largely determined by the electrochemical potentials of the reactants involved

An electrolytic process for producing a nickel layer is known, for example, from EP 0 218 645 A1, in which a galvanic bath is used which, in addition to a cationic surfactant from the group of the alkylaryloxydialkylbenzylammonium chlorides, necessarily contains boric acid or borates. The layers thus obtainable have the disadvantage of Therefore, this method is not suitable for geo metric complex components (for example, carburetor housing, fuel rail for Emzitzsysteme etc) in which a uniform layer structure is crucial in all areas

Also, such geometrically complex components can not be coated without the use of inner anodes inside. The use of inner anodes has the disadvantage of extremely difficult positioning, small diameter holes (less than 2 mm) can not be coated using an inner anode using such methods Thus, off-line processes have become of greater industrial importance in the production of functional (ie, not exclusively decorative) nickel or nickel alloy layers. In order to achieve improved corrosion protection, it has proven necessary to achieve a nickel / phosphorus alloy by adding suitable compounds to the aqueous electrolyte.

Pure nickel and phosphine-containing electrolytes for chemical nickel plating also need stabilizers to prevent spontaneous decomposition. A stabilization sufficient for the industrial application has hitherto been achieved predominantly by the addition of lead compounds. Previously added stabilizers, such as molybdenum, cadmium or tin compounds, show a reduced mode of action compared to lead.

In addition, the addition of lead and cadmium is no longer responsible for environmental reasons; Against this background, it is understandable that, for example, the automotive industry is no longer allowed to use lead-containing components in view of the current EU end-of-life vehicle regulations.

An example of such a generally lead-containing bath for electroless nickel deposition is described in the patent DE 34 21 646 C2. There, in addition to a metal salt of the abovementioned type, a special sulfonium betaine is used as additional stabilizer.

According to WO 02/34964, an electrolyte which contains no lead-containing stabilizer but a combination of an antimony compound and a bismuth compound is used to produce a lead-free nickel alloy by means of an electroless method. This specially adapted electrolyte is not suitable for the production of dispersion layers, in particular not of PTFE-containing nickel layers.

However, such a compelling combination of antimony and bismuthions in the electrolyte is not universally suitable for the stabilization of electrolytes for the production of dispersion coatings. In particular, the preparation of PTFE-containing dispersion electrolytes with a combination of an antimony and a bismuth compound show insufficient stability of the electrolyte. The disadvantage is the overstabilization of the bath after a short time.

However, such nickel dispersion layers are being used more and more in highly stressed components such as, for example, parts of locks, valves, rotary unions, valve anchors, movable pistons, complex geometric fuel-carrying parts in the automotive industry. This is the deposition of a metal layer by an electroless process with simultaneous incorporation of solids that are dispersed in the electrolyte.

Depending on the intended use, these solids are lubricants (for example, PTFE, graphite, spherical aluminum oxide, encapsulated MoS _2, etc.) or hard materials (diamond, corundum, cubic BN, etc.).

A major problem in the production of these layers is the uniform incorporation of the solids in the metal matrix. Non-uniform dispersion layers lead to premature or undesired local wear, which can present a considerable safety risk depending on the field of application (for example hydraulic cylinders in the aircraft industry).

One possibility for producing such an IMlydispersion layer is described in US Pat. No. 4,997,686 A1. It is a process for electroless nickel plating, in which an electrolyte is used which, in addition to the nickel cations and phosphinate anions, contains a mixture of a nonionic surfactant with a cationic, anionic or amphoteric surfactant.

The addition of this surfactant combination in the hypophosphite electrolyte has the disadvantage that the service life of the electrolyte drastically shortened, for example, when incorporating finely divided PTFE. This life reduction is i.a. attributable to the formation of orthophosphite or nickel phosphite crystals and the formation of degradation products of the added surfactant mixture. Depending on the experimental conditions, decomposition of the bath can also be observed.

In addition, the surface texture is uneven, which promotes the early wear of these dispersion layers. Furthermore, these nickel dispersion layers are prepared using conventional nickel / phosphorus electrolytes containing as stabilizer either lead or a combination of tin with cadmium.

Therefore, in recent years there have been increasing efforts not to use emulsifiers or surface-active substances in hypophosphite-containing electrolytes for the electroless nickel plating of PTFE-containing dispersion layers.

US Pat. No. 6,273,943 discloses an electrolyte for electroless deposition of a nickel / PTFE dispersion layer which comprises a quaternary perfluoroalkylammonium halide and a lead compound as stabilizer. In addition to the decisive disadvantage of the mandatory use of lead, perfluorooctylsulfonyl (PFOS), an extremely toxic and bioaccumulative compound, is produced as an intermediate in the preparation of perfluoroalkylammonium halides.

The object of the present invention is to provide a lead-free nickel / phosphorus dispersion coating on a metallic substrate surface, which enables a uniform layer structure (especially at the edges, recesses and undercuts) even on geometrically complex components with the functional inclusions. The aim is to ensure the most uniform possible incorporation of the particles into the nickel alloy matrix.

This coating should be particularly suitable for geometrically complex components that are highly resilient mechanically and on friction and also have low tolerances. Finally, these nickel alloy layers should be obtainable by electroless deposition in an electrolyte, which is characterized by comparatively long service lives.

This object is achieved by a present on a metallic substrate surface, lead-free nickel / phosphorus dispersion alloy, available by electroless deposition in an electrolyte, the

• 4 to 7 g / l nickel ions;

• 15 to 40 g / l hypophospit;

• at least one stabilizer; "5 to 400 mg / l of an alkylaryloxydialkylbenzylammonium chloride or a partially fluorinated betaine;

• 50 to 60 g / l of a carboxylic acid-containing complexing agent A;

5 to 40 g / l of a complexing agent B other than A (for example or preferably dicarboxylic acid); 3 to 10 g / l dispersed particles, which differ from the composition nickel /

Distinguish phosphorus alloy; and

Contains no boric acid or borates, the details referring to the overall composition of the electrolyte.

It should be noted that the electrolyte also contains no cadmium. With the lead-free nickel / phosphorus dispersion alloy according to the invention, it is now possible to provide geometrically complex components, such as carburetor housings, fuel distributors for injection systems, etc., with a uniform layer structure of a coating which is highly resistant to abrasion, in particular at the edges, Recesses and undercuts.

These components have a finished coating of a tolerance of + 3 microns with a total layer thickness of 10 - 12 microns.

Depending on the particles used, it is possible to achieve a surface roughness or functional surface quality tailored to the corresponding application purpose.

By virtue of the components necessarily present in the electrolyte in accordance with the main claim for producing the coating according to the invention, uniform incorporation of the particles into the nickel alloy matrix is ensured. In this case, different particle shapes, such as e.g. Agglomerates, individual particles or particles of different geometry to be homogeneously distributed, which is easy to map using a metallographic Quer¬.

Finally, the service life of the electrolyte used for electroless deposition of a dispersion layer according to the invention with embedded silicon carbide particles can be a service life of up to 10 MTO (metal turn over, ie metal throughput based on the electrolyte used in Itr.).

The term "metallic substrate surface" is also understood as meaning plastic surfaces which are first activated by means of processes known to the person skilled in the art and subsequently nickel-plated.

Particularly preferred are metallized plastic surfaces which are produced using mechanical microstructuring and are disclosed, for example, in WO 2004/092436 A2 and WO 2004/092256 A1.

A usual layer thickness of this nickel / phosphorus dispersion alloy between 3 and 30 μm is sufficient to increase the wear resistance, to improve sliding and friction properties and to provide the non-stick properties. Depending on the type of particles used, however, it is also possible to produce force-transmitting functional layers.

A preferred embodiment of the nickel / phosphorus dispersion alloy according to the invention is achieved if the constituents nickel, phosphorus and particles are distributed uniformly in the alloy layer. The term "uniformly" here and in the following means an alloy and function-typical distribution of the corresponding components in the nickel matrix. This uniform distribution achieves a uniform microstructure in the alloy, so that the mechanical and functional properties of this layer are constant even in narrow tolerance ranges.

Complexing agents A used are the carboxylic and dicarboxylic acids known for preparing customary nickel / phosphorus electrolytes.

As complexing agent A, lactic acid and malonic acid are particularly preferably used; as complexing agent B, preferably succinic acid.

A simple example of an alkylaryloxydialkylbenzylammonium chloride is benzalkonium chloride of the formula

or the formula

can be used, in which X represents a chlorine atom. Such compounds are spielsweise marketed in 1622 by the company. Clariant under the trade name Hyamine ^®.

Further, simple examples of Alkylaryloxydialkylbenzylammoniumchloride are benzalkonium koniumchloride (N-alkyl-N, N-dimethyl-N-benzylammonium chloride with a C ₁₂ -, C ₄ - or C ₁₆ -alkyl) and Methyldodecylbenzyltrimethylammoniumchlorid. Benzalkonium be marketed under the trade name hyamine ^® 3500 by the company. Clariant

As a possible partially fluorinated betaine for example, such compounds can be expended under the trade name FLUOWET ^® CA. By the company Clariant sold ver¬. In a preferred embodiment of the invention, the electrolyte contains as stabilizer at least 10 mg / l antimony and at most 1, 5 mg / l bismuth ions. However, this antimony and bismuth additive is not mandatory - for example, only stabilizers based on tin (II) compounds can be used. Particularly preferably, the electrolyte contains as stabilizer 10-150 mg / l antimony and

0.01 - 1.5 mg / l of bismuths.

Due to the choice of stabilizers according to this embodiment, it is possible to achieve very high long-term stability of the electrolyte. For an electrolyte with SiC as a particle, this choice makes it possible to achieve service lives of up to 10 MTO (metal turn over, ie metal throughput based on the electrolyte used in Itr.) And for an electrolyte for producing a nickel-phosphorus-PTFE dispersion alloy Lifespan of 3 MTO and above can be achieved.

According to another embodiment of the present invention, the electrolyte additionally contains a nonionic surfactant. Particularly preferably, the nonionic surfactant is selected from the group of partially fluorinated or non-fluorinated surfactants. The term "partially fluorinated surfactants" means all surface-active substances which have no perfluorinated radicals.

The term "non-fluorinated surfactants" is understood as meaning all surface-active substances which have no fluorine atom.

In this way, an improved (ie more uniform) nickel-phosphorus dispersion layer can be obtained, since the use of an additional nonionic surfactant contributes to preventing undesired agglomeration in the electrolyte and at the same time contributing thereto, which does not To keep soluble components of the electrolyte in Schwe¬ be.

Thus, this embodiment also ensures a longer service life of the electrolyte.

The dispersed particles may in a preferred embodiment of the present invention be selected from the group of silicon carbide, corundum, diamond, cubic boron nitride, spherical alumina and tetraboron carbide, particular preference being given to non-metallic particles having a hardness greater than 1000 HV , The nickel-phosphorus dispersion alloys obtained according to this preferred embodiment are particularly suitable for imparting abrasion resistance, wear protection and increased friction to the coated substrates to ensure frictional connections or the desired surface structure. In this way For example, functional properties can be imparted to the substrate that are tailored to the needs of its use. Thus, in a nickel-phosphorus dispersion layer with incorporated silicon carbide particles, rough surface structures with typical functional embeddings are achieved which achieve friction coefficients of μ = 0.50 and above in frictional connections (for comparison: in dry steel contact, the coefficients of friction are only μ = 0.15 ).

In another, likewise preferred embodiment, the particles have friction-reducing properties and are selected from the group of polytetrafluoroethylene, molybdenum sulfide, molybdenum disulfide, hexagonal boron nitride, tin sulfide and graphite.

The nickel-phosphorus dispersion layers obtainable according to this embodiment are also to be selected according to the functional requirement of the resulting device. Thus, excellent friction-reducing properties are achieved by the incorporation of PTFE particles in the nickel phosphorus matrix. However, it is only through the special composition of the electrolyte according to the present invention that it is possible to provide a lead- and cadmium-free system which also ensures sufficient stability and good surface qualities for the production of nickel-phosphorus-PTFE alloys. Due to the complex interaction of all the components involved with regard to the stability of the electrolyte and good deposition rates, it has hitherto not been known to provide polytetrafluoroethylene-containing electrolytes which did not rely on lead- or cadmium-containing stabilizers.

Another advantage of the embodiment of the invention is the absence of perfluorinated cationic or nonionic surfactants. Perfluorinated cationic and nonionic surfactants have hitherto been used predominantly for polytetrafluoroethylene-containing electrolytes since these alone were suitable for imparting the charge required for migration and co-deposition to the PTFE particles. However, the preparation of these fluorinated cationic and nonionic surfactants proceeds via a toxic intermediate ("perfluorooctylsulfonyl") with bioaccumulation potential, so that these have been withdrawn from the program by the manufacturers worldwide. This development has led to the search for new methods in order to continue to produce PTFE-containing nickel phosphorus dispersion alloys, without having to use the no longer available fluorine-containing cationic surfactants. However, precisely this application is given with a nickel-phosphorus-PTFE dispersion alloy of the present invention in a manner which takes into account all the environmental and health policy conditions.

The nickel-phosphorous dispersion alloys according to the present invention can be used as a wear-resistant surface, in particular in the automotive industry and in the machine industry. nenbau, particularly preferred as lock parts for door closing system and functional components for fuel dosing or as a surface in the automotive industry with improved sliding friction properties, especially for parts of locks, Ven¬ valves, rotary joints, valve anchors, movable pistons, and other movable parts in the Automotive industry and used in mechanical engineering.

The individual process steps for producing a chemically produced nickel alloy by electroless metal deposition in an aqueous electrolyte are known in principle. This is especially true for the choice of suitable compounds for the nickel cations and phosphinations. In addition, it is also known to those skilled in the art which additives, stabilizers, complexing agents or other additives are still required for a corresponding nickel alloy.

However, these parameters are not critical to the application of the method of the invention. For this reason, this basic knowledge is not dealt with in detail, but rather the textbook "Introduction to Electroplating" by Bernhard Gaida, E. Leuze Verlag, is referred to.

In the process according to the invention, the proportion of nickel cations in the electrolyte can be between 4 and 7 g / l, based on the sum of the constituents nickel and phosphorus present in the aqueous electrolyte.

The proportion of phosphination can be in the electrolyte between 15 to 40 g / l, based on the weight ratio of phosphorus to the sum of the in the aqueous

Electrolytes contained components nickel and phosphorus.

The proportion of Alkylaryloxydialkylbenzylammoniumchlorid in the electrolyte can be between 0.01 and 0.4 wt .-%, in particular between 0.1 and 0.2 wt .-%, based on the sum of the components contained in the aqueous electrolyte nickel and

Phosphorus.

The sum of the proportions of the components previously described in the electrolyte is usually 100% by weight. The following examples serve to illustrate the invention:

Test Methods

The service life (in MTO = metal turn-over) is determined by wet-chemical titration on murexite indicator as consumption in g / l nickel.

The value is calculated from the amount of nickel ions that can be added to the finished electrolyte without having to exchange the electrolyte. It is based on the total amount of nickel in the electrolyte bath.

The uniform distribution of the PTFE particles is determined by a metallographic cross section of the coated steel sheets. It is characterized by the determination of the percentage of the distribution of the particles incorporated in the nickel / phosphorus matrix.

Example 1 (comparative example)

500 ml of demineralized water are placed in a 1 l beaker and the following compounds are added with stirring:

30 g / l nickel sulfate (NiSO ₄ X 6H ₂ O) 35 g / l sodium phosphinate (NaH ₂ PO ₂ XH ₂ O) 30 g / l malonic acid 30 g / l succinic acid 0.5 mg / 1 bismuth methanesulfonate (Bi (OS (O ) ₂ CH ₃ ) ₃ )

1.5 g / l antimony chloride 10 ml / l borofluoric acid (50%) 100 mg / l allyl thiourea

370 mg / l cationic perfluorinated fluorosurfactant "FT 754" of the company. 3M 7 g / l PTFE dispersion Zonyl ^® 3807 from the company. DuPont

15 mg / 1 nonionic surfactant "FSN-100" from DuPont

The pH is then adjusted to 4.3 by addition of a 25% strength aqueous ammonia solution and the solution is made up to 1000 ml by addition of demineralized water.

After heating to 88 ^° C., 1 mm thick steel plates of the alloy St 37 with the dimensions 50 * 50 mm are suspended in the bath for 60 minutes after usual pretreatment (degreasing, rinsing, activating, rinsing). Thereafter, the sheet is rinsed and dried. The achieved layer thickness is 5 μm.

The results of the service life of the electrolyte and the PTFE distribution in the dispersion layer are determined according to the test methods described above and are given in Table I.

Example 2 (according to the invention):

Comparative Example 1 is repeated, but with the following electrolyte composition:

25 g / l nickel sulphate (NiSO ₄ x6H ₂ O)

35 g / l sodium phosphinate (NaH ₂ PO ₂ XH ₂ O)

35 g / l lactic acid (synthetic)

30 g / l succinic acid 0.5 mg / 1 bismuth tartrate

1.5 g / l antimony chloride

0.5 mg / l potassium o-ethyl dithiocarbonate

195 mg / l Hyamine ^® 1622 by the company. Lonza

7 g / l PTFE dispersion Zonyl ^® 3807 from the company. DuPont 15 mg / l nonionic surfactant "FSN-100" of the company. DuPont

The pH of the electrolyte is adjusted to 4.5 by addition of a 25% aqueous ammonia solution. The achieved layer thickness is 5 μm.

Example 3 (according to the invention):

25 g / l nickel sulphate (NiSO ₄ x 6H ₂ O)

35 g / l sodium phosphinate (NaH ₂ PO ₂ XH ₂ O) 35 g / l lactic acid (synthetic)

30 g / l succinic acid

0.5 mg / l bismuth tartrate

1.5 g / l antimony chloride

0.5 mg / l potassium ethyl xanthate 725 mg / l Fluowet ^® CA Fa.Clariant

7 g / l PTFE dispersion Zonyl ^® 3807 from the company. DuPont

15 mg / l nonionic surfactant "FSN-100" from DuPont

The achieved layer thickness is 5 μm. Example 4 (according to the invention):

30 g / l nickel sulphate (NiSO ₄ x 6H ₂ O)

40 g / l sodium phosphinate (NaH ₂ PO ₂ XH ₂ O)

40 g / l lactic acid (synthetic)

5 g / l succinic acid

8 g / l malic acid

1 g / L citric acid

10 g / l sodium acetate

5 g / l ammonium sulfate

75 ppm Sn as stannous sulfate

725 mg / l Fluowet ^® CA Fa.Clariant

7 g / l PTFE dispersion Zonyl ^® 3807 from the company. DuPont

15 mg / l nonionic surfactant "FSN-100" from DuPont

The achieved layer thickness is 5.5 μm.

Table I

The electrolyte behavior "not stable" essentially means a foreign nucleation in the electrolyte during the layer formation process.

The electrolyte behavior "less stable" means a foreign nucleation in the electrolyte after one hour during the film formation process.

The electrolyte behavior "stable" does not signify any formation of foreign nucleation in the electrolyte during the layer formation process Table I shows markedly improved properties of the nickel alloy dispersion layers of the invention over those of the prior art.

Claims

Claims 1. On a metallic substrate surface, lead-free nickel phosphorous dispersion alloy obtainable by electroless deposition in an electrolyte containing: • 4 to 7 g / l nickel ions • 15 to 40 g / l hypophosphite; • at least one stabilizer • 5 to 400 mg / l of an alkylaryloxy dialkylbenzylammonium chloride or a partially fluorinated betaine • 50 to 60 g / l of a carboxylic acid-containing complexing agent A • 5 to 40 g / l of a carboxylic acid-containing complexing agent B other than A. • 4 up to 10 g / l dispersed particles, which differ from the composition nickel / phosphorus alloy; and • contains no boric acid or borates, the details relating to the total composition of the electrolyte.2) Nickel alloy according to claim 1, characterized in that the electrolyte as stabilizer at least 10 mg / 1 antimony and at most 1, 5 mg / l bismuth ions contains.3) Nickel alloy according to claim 2, characterized in that the electrolyte contains as stabilizer 10 - 150 mg / l antimony and 0.01 - 1, 5 mg / l bismuth ions.4) Nickel alloy according to one of the preceding claims, characterized in that the electrolyte additionally contains a nonionic surfactant.5) Nickel alloy according to claim 4, characterized in that the nonionic surfactant is selected from the group of partially fluorinated or nonfluorinated surfactants.6) Nickel alloy according to one of the preceding claims, characterized in that the particles are selected from the group of silicon carbide, corundum, diamond, cubic boron nitride, spherical Atumi aluminum oxide and tetrabor carbide.7) Nickel alloy according to one of the preceding claims, characterized in that the particles are non-metallic and have a hardness of more than

Have 1,000 HV.

8) Nickel alloy according to one of claims 1 to 6, characterized in that the particles have friction-reducing properties and are selected from the group of polytetrafluoroethylene, molybdenum sulfide, Molybdändisulf id, hexagonal boron nitride, tin sulfide and graphite.

9) Use of a nickel alloy according to any one of the preceding claims as a wear-resistant surface, in particular in the automotive industry and in mechanical engineering, particularly preferably as lock parts for door closing system and functional components for fuel dosing or as a surface in the automotive industry with improved sliding friction properties, in particular for parts of locks , Valves, rotary joints, valve anchors, movable pistons, and other moving parts in the automotive and engineering industries.