FR2735075A1 - Prodn. of metallic patina effect on plastic material - Google Patents

Abstract

Prodn. of metallic patina effect on a plastic component is claimed, in which (1) a layer of nickel is applied to the article; (2) the nickel-plated article is contacted with a chemical colourant soln. for nickel; and (3) the surface of the treated prod. is abraded by suitable abrasive agents.

Description

 The present invention relates to a method for imparting a patinated metallic appearance to a plastic part.

 For the production of various objects, plastics have many advantages which allow them to gradually supplant metals. Plastic parts are lighter and easier to manufacture, and are often more inert than metal parts in various reactive environments.

However, they have the defect of having poor aesthetic qualities.

 This drawback becomes of major importance when the manufactured object is intended for the packaging of luxury products. Thus, for example in the field of perfume bottles, glass bottle stoppers made of plastic material have the advantage of withstanding the alcoholic medium of the perfume but must be subjected to a decorative treatment so as not to harm the good presentation. from the bottle.

 Among the possible decorative treatments, it is common to metallize the pieces to give them the appearance of precious metals such as gold and silver.

However, the nuances obtained are few and are often limited to giving a matt or shiny appearance to the metallic coating.

 The object of the present invention is to propose new shades of metallic coatings on plastic parts, by giving an appearance of aged metal to these parts.

 There are aging or patina techniques applicable to metallic or metallized parts. They consist of applying a coat of paint or wax by hand to the part, then wiping each part with a cloth. These manual techniques are based on artisanal know-how and skill and are only suitable for the production of small series of parts.

 Another object of the invention is to propose a process for decorating plastic parts suitable for the production of parts in large series.

To this end, the subject of the invention is a method for imparting a patinated metallic appearance to a plastic part, according to which
(i) a layer of metallizable plastic is deposited on a layer of nickel,
(ii) the nickel-plated part is brought into contact with a chemical coloring solution for nickel, and
(iii) the surface of the colored part is degraded by abrasion using suitable abrasive agents.

 By "chemical coloring solution for nickel" is conventionally meant a solution which, when applied to nickel, is capable of forming on the surface of nickel a conversion layer whose color is different from that of nickel .

 - It appeared that the colored conversion layer formed on the surface of nickel in step (ii) on the nickel-plated part is relatively poorly adherent and part of this layer can be removed by abrasion.

However, probably due to the relative irregularity of the profile of the surface of the nickel coating deposited in step (i), the same quantity of material is not removed in all the areas of the surface of the part. Thus, the part abraded in step (iii) has a surface dotted with points, or relatively large areas, where the coloring persists, and which has the pitted appearance of aged metal, giving the effect of a patina.

 By “metallizable plastic material” is meant any plastic material capable of receiving a metal deposit on the surface by chemical or electrolytic means, after a possible preparatory treatment of said surface.

 Depending on the shape of the part, metallization by simply coating the part in a metal sheath may be possible, or else the surface must be primed to allow better surface adhesion of the deposited metal layer.

 The preferred plastics for implementing the process of the invention are chosen from acrylonitrile-butadiene-styrene copolymers, mixtures (or alloys) of polycarbonates and acrylonitrile-butadiene-styrene copolymers, charged polypropylenes, acetal resins and thermosetting polymers.

 The loaded polypropylenes can contain various fillers, in particular talc or mica. Their density can vary over a wide range, in particular from 1.2 to 2.

 The piece of plastic material treated can have any shape, depending on the use for which it is intended. A solid part can be obtained in particular by molding, preferably by injection molding.

 The method of the invention is advantageously applied to parts having a very uneven relief. Thus, areas of the part that are not accessible to abrasive agents keep their colored appearance, while the other more accessible areas more or less lose their color at the end of the surface degradation operation. The contrast effect obtained accentuates the illusion of a natural patina.

 Preferably, the surface nickel layer of the metallized part is deposited electrolytically. This technique has been the subject of numerous developments in the field of decorative nickel plating and makes it possible to provide certain nuances of gloss to the coating. These nuances actually come from the more or less regular surface finish of the coating. This surface condition having a certain influence on the ability of the colored conversion layer to be removed or not by abrasion, different aging qualities can be obtained depending on the shade of an electrolytic deposit of nickel.

 To be able to receive a galvanic deposit, the plastic part must be metallized beforehand, in particular by means of a layer of nickel deposited by chemical means.

 Preferably, the nickel deposition step (i) comprises the successive substeps of a) chemical deposition of a first nickel layer, b) electrolytic deposition of a second nickel layer, c) electrolytic deposition of a layer of copper, and d) electrolytic deposition of a third layer of nickel.

 The superimposition of metal layers, including an intermediate layer of copper, improves the ductility of the coating and thus its mechanical resistance, in particular its resistance to handling.

 Before the chemical deposition of a layer of nickel (a), it is preferable to subject the plastic part to a preliminary treatment with a solution containing a soluble palladium compound. This treatment initiates the surface, depositing palladium particles in the surface pores which will play a catalytic role during the chemical deposition process by reduction.

 The chemical deposition of nickel (a) provides a first layer of nickel, the thickness of which is advantageously from 0.1 to 0.3 μm.

 Preferably, this deposition is carried out in a conventional manner in a bath containing nickel chloride or nickel sulfate, in the presence of a reducing agent, in an alkaline medium, in particular at a pH of 8.5 to 9.5.

 The reducing agent is advantageously chosen from an alkali metal hypophosphite, in particular sodium, and a boron compound such as an alkali metal boranate or a borazane, in particular dimethylamineborane, diethylamine-borane or tripropylamineborane.

 A hypophosphite bath advantageously comprises approximately 20 to 30 g / l of nickel chloride or sulphate, 10 to 25 g / l of sodium hypophosphite, in the presence of ammonia.

 The first electrolytic deposition of nickel (b) is preferably carried out in a Watts-type bath comprising from 150 to 400 g / l of nickel sulfate, from 20 to 150 g / l of nickel chloride and from 15 to 60 g / 1 of boric acid, and having a pI <of 3 to 5.

 - The known variants of the Watts bath can also be used, such as the electrolyte any sulfate which contains sodium sulfate instead of nickel chloride.

For the deposit, advantageously, the bath is adjusted to a temperature of 40 to 75 "C and a cathodic current density of 1 to 10 is applied
A / dm2. The bath can be agitated by air circulation or by mechanical agitation.

 The nickel layer thus deposited preferably has a thickness of 2 to 3 μm.

 A relatively thick layer of copper is then deposited, still electrolytically, the thickness of which is advantageously from 10 to 30 μm.

 The deposition can be carried out in a conventional bath with copper sulphate, in particular at a rate of 200 to 250 g / l, and of sulfuric acid, in particular at a rate of 10 to 60 g / l.

 For the deposit, advantageously, the bath is adjusted to a temperature of 16 to 50 "C and a voltage of 1 to 4 V is applied, with a current density of 1 to 5 A / dm2, (which can be from 10 to 20 A / dm2 if the bath is agitated).

 The deposition of the surface layer or of the last nickel layer (d) can be carried out in the same type of bath as the deposition of the second nickel layer (b). The conditions for implementing the deposit are preferably such that the thickness of nickel deposited is 5 to 15 μm. The cathodic current density applied is advantageously from 3 to 8 A / dm2. The deposit obtained is usually dull.

 When the nickel metal tenellr is greater than 10-13 g / l, the deposit tends to be relatively brighter.

 In order to provide the nickel-plated surface with the desired gloss nuances, the bath may include leveling additives or brighteners.

Among the brightening additives, there are:
- primary gloss and lrs which lead to shiny deposits but which are not leveled. These brighteners usually contain the functional group
C = C - SO2 where the non-sulfur-carrying carbon atom can come from an unsubstituted aryl nucleus Oll, from an unsaturated chain, in particular vinyl or allyl, or from a heterocyclic compound, and the SO2 group is in the form sul fonic acid, sulfinic acid, sulfonamide or sulfonimide.

 These compounds are added in the form of water-soluble salts, in particular sodium and sometimes nickel.

 They are used preferably at a rate of 1.5 to 15 g / l.

 - secondary brighteners to produce deposits with a large shine.

et

A wide variety of such additives exists; they all have at least one unsaturated bond in the molecule, in particular in the following functional groups.

and

 Significant examples of brighteners are given in Dennis J., Such T., Nickel and chromium plating, 1972, Butterworth.

 Leveling agents have the ability to mask surface irregularities in the deposit. The best known is coumarin. Other useful compounds can be found in Lombino A., New semi-gloss nickel-plating process without coumarin, Galvano (F) N "495, 1979, p. 335-7, and in Handbook on electroplating, 22 ' ed. 1978, Canning.

 The nature and quantity of the agents used is determined as a function of the gloss and the surface condition desired.

 As a variant, the desired appearance can be imparted by carrying out, after the deposition of nickel, an operation of chemical brightening in an acid medium or of chemical satin-finishing, in a known manner.

 The remainder of the process of the invention consists in forming a colored surface layer on the nickel-plated part by bringing it into contact with a chemical coloring solution for nickel.

 This contacting can be carried out by any known means, in particular by dipping.

 The coloring solution can be of any type known for producing on nickel a colored conversion layer of various shades.

 Advantageously, a black coloring solution is used to give the piece, at the end of the process, the appearance of patinated or aged silver.

 In general, the conditions of the coloring treatment, for example the temperature, the pH of the solution or the duration of immersion in a dip treatment, are chosen so that the nickel-plated part is entirely, or only partially , covered with a colored conversion layer.

 An example of a solution which can be used is an aqueous solution comprising sodium thiosulphate, lead acetate and potassium acid tartrate (bitartrate).

The composition can be formulated as follows:
- Sodium thiosulfate 200 g / l
- Lead acetate 20 g / l - - Potassium acid tartrate 40 g / l
This bath can be used at room temperature and it is possible to obtain, depending on the immersion time, yellow, red, blue, green and gray shades.

Lead acetate can be replaced by copper acetate to obtain very specific shades.

 To obtain a black coloration, an aqueous solution comprising sodium thiosulfate can be used; a nickel salt, in particular nickel sulphate, nickel chloride or nickel nitrate; zinc sulfate; and a compound based on fluorinated ions, in particular sodium fluoroborate.

The solution can for example be formulated as follows
- sodium thiosulfate 15-36 g / l
- nickel sulfate 7.5-21 g / l
- zinc sulfate 3-12 g / l
- sodium fluoroborate 0.15-0.9g / l
This bath is preferably usable hot at a temperature of about 70 to 80 "C, by immersion for 1 to 5 minutes with gentle agitation.

 Staining solutions of this type are described in US Patent US-A-4,789,409.

 After the coloring step, the colored metallized part is subjected to a mechanical finishing treatment by abrasion, intended to remove from the surface of the part a certain amount of the colored surface layer.

 The abrasion can be carried out by any known means.

 Mechanical finishing devices, such as a rotating barrel or a vibrating bowl, where repeated contact and shock are caused between a workpiece and solid abrasive agents can be advantageously used.

 Abrasive agents are solids of various shapes, including spherical, cubic, cylindrical, conical, tetrahedral or parallelepipedic.

 The material which constitutes them can itself be variously chosen from plastics, plastics loaded with metallic particles, wood, glass and ceramics.

 The material, shape and size of the abrasive agents is chosen according to the shape and size of the parts treated, as well as the desired aging effect.

 Thus, to give a slightly aged appearance to the part, we will adjust the various parameters to obtain a high rate of abrasion. When the part has a very uneven relief, the shape and size of the abrasive agent will be adjusted so that it can reach as many elements of the relief as possible, including the least accessible parts.

 Conversely, to give a strong aging effect, we will try to limit the abrasion rate at least in certain places of the room. When said part has a very uneven relief, one can for example choose the shape and size of the abrasive agent so that the latter can only reach the projecting areas.

This creates a very advantageous contrast between the abraded areas and the non-abraded areas.

 After this step, the aged metallic part is finished and ready to be used. No further treatment such as the application of a varnish is necessary. The residual parts of the colored layer which are not removed by abrasion are sufficiently adherent so that the part can be handled without damage to its appearance.

 The use of mechanical finishing devices - of large capacity makes it possible to carry out the final stage of treatment on a large quantity of parts.

These devices constitute a productive and economic final workshop of a production line for mass production of parts, to obtain a competitive production cost.

 The following example illustrates the invention.

 A piece molded of acrylonitrilebutadiene-styrene copolymer, intended to serve as a perfume bottle stopper, is subjected to the following treatment.

1. Stripping
The purpose of this operation is to remove plastic particles from the surface of the part to create surface pores.

The cleaned part is immersed in a bath containing for 100 liters
36 kg of chromic acid,
60 1 deionized water,
and 20 l of sulfuric acid of density 1.84.

 The immersion time is 3 to 10 minutes in the bath at a temperature of 60 to 65 "C. For continuous use, the bath can be regenerated by reoxidation of trivalent chromium.

 The piece taken out of the bath is rinsed three times with water, the last rinse is colorless.

 2. Preparation c: analytical.

 I1 is to deposit in the pores generated in 1 of the palladium particles. The piece is immersed for 2 to 3 minutes at room temperature in a bath containing 75% by volume of deionized water and 25% by volume of pure hydrochloric acid.

 Then, the part immersed in an aqueous bath containing 25% by volume of pure hydrochloric acid and 4 t by volume of a solution sold under the name CATALYST 9F by the company SHIPLEY and which contains a soluble palladium compound. The immersion is maintained for 2 to 3 minutes at room temperature, then the part taken out of the bath is rinsed twice with deionized water.

 3. Deposit of chemical nickel.

The part is immersed in a bath with dimethylamine borane of the following formula nickel sulphate NiSO4, 6H20 25 g / l dimethylamine borane (CH3) 2NHBH3 1.5 g / l sodium pyrophosphate Na4P207, 10H20 50 g / l ammonia NH4OH (28% NH3) 45 ml / l
The pH of the bath is adjusted between 8 and 10, preferably between 8.5 and 9.5 periodically by adding ammonia.

 Immersion takes place for 5 to 7 minutes, between room temperature and 35 "C, after which the part is rinsed twice with deionized water.

 The deposited layer has a thickness of 0.1 to 0.3pu.

 4. Deposition of electrolytic nickel.

After being rinsed with water, the part is placed in a Watts type bath, the formula of which is the following nickel sulphate NiSO4, 6H20 280 g / l. nickel chloride NiCl2, 6H20 50 g / l boric acid H3B03 42 g / l
The pH of the bath is adjusted to about 4 and its temperature is 50 to 60 "C.

 By applying a current density of 1.1 to 1.3 A / dm2 for 8 to 13 minutes, a layer of nickel 2 to 3 μm thick is deposited.

 5. Deposition of electrolytic copper.

A bath of the following composition is used. copper sulphate CuSO4, 5H20 210 g / l. sulfuric acid H2SO4 53 g / l
The nickel-plated part rinsed with water is immersed in this bath at a temperature of 16 to 50 "C. By applying a current density of 1 to 5 A / dm2 for 20 minutes, a layer of copper is deposited from 10 to 30 um thick.

 6. Deposit of electrolytic nickel.

 A Watts type bath identical to that used in 4 is used, at the same temperature.

 By applying a cathodic current density of about 4 A / dm2 for 6 to 20 minutes, the thickness of nickel deposited is about 5 to 15 µm.

 7. Coloring of the surface.

The part is rinsed with water and then immersed in a solution of black coloring for nickel having the following composition
- sodium thiosulfate 27 g / l
- nickel sulphate NiSO4, 5H20 15 g / l
- zinc sulfate ZnSO4, HO 7.5g / l
- sodium fluoroborate 0.5g / l
(in aqueous solution)
The coloring bath is maintained under gentle stirring, at a temperature of approximately 70 to 80 C.

 Depending on the case, the immersion time can vary from 1 to 5 minutes.

 After one minute, the surface of the part is completely blackened. The latter is removed from the bath, rinsed with running water and dried with hot air.

- 8. Mechanical degradation
The blackened part is mechanically degraded in a vibrating bowl with ceramic alumina beads.

The duration of the operation is adjusted by visual estimation of the degradation as a function of the desired aging effect. The coin presents after degradation the appearance of old silver.

 Once fitted to a perfume bottle, the part is capable of undergoing daily use without noticeable degradation and resists satisfactorily the handling and contact with perfume solvents.

 The invention is not limited to the particular embodiment described in this example. The number and nature of the metal sub-layers placed between the plastic part and the surface nickel layer may vary depending on the characteristics sought for the final product.

 Likewise, the formulation of the electrolytic or chemical conversion baths can be modified in a conventional manner to obtain different shades.

 The method of the invention can also be implemented for other applications than perfume bottles, where it is desired to use a plastic part, thereby benefiting from the attractive appearance of the patinated metal.

Claims (10)

 1. Method for imparting a patinated metallic appearance to a plastic part, according to which  (i) a layer of metallizable plastic is deposited on a layer of nickel,  (ii) the nickel-plated part is brought into contact with a chemical coloring solution for nickel, and  (iii) the surface of the colored part is degraded by abrasion using suitable abrasive agents.  2. Method according to claim 1, in which the plastic material is chosen from acrylonitrile-butadiene-styrene copolymers, mixtures of polycarbonates and acrylonitrile-butadienestyrene copolymers, charged polypropylenes, acetal resins and thermosetting polymers.  3. Method according to claim 1 or 2, wherein the plastic part is a molded part.  4. Method according to any one of claims 1 to 3, wherein the nickel deposition step (i) comprises a sub-step of final deposition of a nickel layer by electrolytic means.  5. The method of claim 4, wherein said electrolytic deposition of nickel results in a surface nickel coating with a thickness of 5 to 15 µm.  6. Method according to any one of claims 1 to 5, wherein the solution used in step (ii) comprises sodium thiosulfate, lead or copper acetate, and potassium acid tartrate.  7. Method according to any one of claims 1 to 5, in which the solution used in step (ii) comprises sodium thiosulfate, a nickel salt, zinc sulfate and a compound based on fluoride ions. .  8. Method according to any one of claims 1 to 7, wherein step (ii) is carried out by immersion of the nickel-plated part in the chemical coloring solution.  9. Method according to any one of claims 1 to 8, in which the degradation of the surface of the colored part in step (iii) is carried out in a mechanical finishing apparatus, in particular a rotating barrel or a vibrating bowl, by stirring with abrasive agents.  10. Method according to any one of claims 1 to 9, in which the abrasive agents are objects of spherical, cubic, cylindrical, conical, tetrahedral or parallelepiped shape, of a material chosen from plastics, filled plastics metal particles, wood, glass and ceramics.