Abstract:
A method is provided for plating a non-metal substrate (S), allowing a plated part to be obtained. The method includes steps of: (a) providing a non-metal substrate (S) having a surface ( 11 ); (b) forming a bonding layer (C 1 ) on the surface ( 11 ); (c) forming at least one reinforcement layer (C 2 ) on the bonding layer (C 1 ); (d) forming a varnish layer (C 4 ) above the reinforcement layer (C 2 ); and performing a drying step to dry the varnish layer, wherein the varnish layer is exposed to ultraviolet radiation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to the field of methods for plating parts and in particular non-metal substrates. Different manners are known to plate a non-metal substrate. 
         [0002]    In particular, dry processes are known using plasma or flame spray. Vacuum plating methods are also known such as PVD for example. However, these methods have the disadvantage of being relatively costly due to the energy required and the conditions under which they must be performed. Additionally, they are difficult to apply at industrial level. 
         [0003]    Plating methods are also known via electrolytic route whereby a layer of chromium is deposited. 
         [0004]    One advantage of this type of method is the obtaining of plated parts having a metal appearance. These parts are particularly used in the motor vehicle industry. 
         [0005]    However, chromium and in particular hexavalent chromium used for plating has the drawback of being toxic for the environment. Hexavalent chromium requires closed circuit treatment facilities for waste water to reduce the impact on the environment. The cost involved for the production of plated parts is therefore high. Trivalent chromium is also a toxic chemical product. Trivalent chromium raises the same problems as hexavalent chromium. 
         [0006]    A further disadvantage of the use of chromium is that the production thereof gives rise to a high rejection rate of produced parts. This high rejection rate therefore increases production costs of the parts. 
       SUBJECT AND SUMMARY OF THE INVENTION 
       [0007]    It is one objective of the invention to propose a method which overcomes the aforementioned shortcomings. 
         [0008]    For this purpose, the invention concerns a method for plating a non-metal substrate allowing a chromium-free plated part to be obtained, wherein:
       a non-metal substrate is provided having a surface;   a bonding layer is formed on said surface;   at least one reinforcement layer is formed on the bonding layer;   a step to dry the varnish layer is conducted whereby the varnish layer is exposed to ultraviolet radiation.       
 
         [0013]    With this method at least one varnish layer is formed above the reinforcement layer. 
         [0014]    Advantageously, at least one nickel layer is formed on the reinforcement layer and said at least one varnish layer is formed on the nickel layer. 
         [0015]    According to one embodiment of the method, the metal appearance is imparted by the presence of at least one nickel layer that is deposited on the reinforcement layer. 
         [0016]    This dispenses with the use of chromium. In other words plated part obtained by implementing the method is chromium-free. 
         [0017]    The varnish layer is deposited on the reinforcement layer or on the nickel layer to protect the reinforcement layer or the nickel layer and the underlying layers against the risk of corrosion and impacts derived from the environment in which the part is used. 
         [0018]    In addition, the varnish layer may comprise several varnish layers obtained by successive deposits of varnish layers. 
         [0019]    Also when the depositing step is completed, it will be understood that the varnish layer covers the reinforcement layer or the nickel layer for the purpose of improving the resistance of the part to impacts and corrosion. 
         [0020]    The part obtained by implementing the method therefore has a metal appearance whilst being robust. 
         [0021]    According to the invention, the deposited varnish is dried by a device emitting ultraviolet radiation to allow cross-linking of the varnish. The drying step is therefore a cross-linking step. 
         [0022]    Also, the drying step by means of ultraviolet radiation is preferably performed over a range of 150 nm to 400 nm. 
         [0023]    Preferably the drying step is conducted at a temperature lower than 60° C. 
         [0024]    It will be understood that the drying step with ultraviolet radiation uses an operating temperature lower than more conventional thermal drying temperatures for which the temperature is above 120° C. The non-metal substrate is therefore subjected to a lower temperature range thereby reducing the risk of degradation of said non-metal substrate. 
         [0025]    Furthermore, in another embodiment, the drying step of the varnish layer is conducted using a device which pulses hot air onto the varnish layer at temperatures lower than 120° C. Therefore in the same manner as for ultraviolet drying, the use of hot air at temperatures below 120° C. reduces the risk of deteriorating the non-metal substrate. 
         [0026]    Preferably, the varnish layer is transparent or coloured. Therefore by means of the invention, a transparent varnish layer allows the exposing of the natural colour of the reinforcement layer or of the nickel layer underlying the varnish layer. Also, the varnish layer may be tinted to obtain a coloured plated part. The part therefore adapts to the aesthetic environment in which said part is to be integrated. 
         [0027]    Preferably, the varnish layer is an electrolytic varnish layer. It will be understood that the varnish layer is deposited via chemical route. The parts are arranged so that they are immersed in an electrolytic bath via which the varnish is deposited on the reinforcement layer or on the nickel layer. 
         [0028]    Preferably, according to one non-limiting embodiment, the varnish layer comprises a succession of varnish layers. It will be understood that the varnish layer thus obtained has a transparency or tint which varies in relation to the number and thickness of the successive varnish layers. 
         [0029]    According to one preferred but nonexclusive embodiment, the non-metal substrate consists of acrylonitrile butadiene styrene. 
         [0030]    The non-metal substrate is a copolymer of acrylonitrile, butadiene and styrene. It has the advantage of displaying strong physical and chemical properties such as rigidity, impact resistance, heat resistance. 
         [0031]    According to another embodiment, the non-metal substrate consists of a polyamide or polypropylene. 
         [0032]    It will be understood that the non-metal substrate is made of a polyamide homopolymer. Furthermore, polyamides have good mechanical strength. 
         [0033]    Advantageously, the non-metal substrate can consist of a copolymer comprising acrylonitrile butadiene styrene associated with a polycarbonate. This polymer mixture has better impact resistance at low temperature than acrylonitrile butadiene styrene or a polycarbonate alone. 
         [0034]    According to another non-limiting embodiment, the non-metal substrate comprises a polymer of polypropylene type. The non-metal substrate therefore has good resistance to fatigue and has the advantage of being recyclable. 
         [0035]    Advantageously, the bonding layer is obtained by successively carrying out chemical attack on the surface of the non-metal substrate, activation of said chemically attacked surface and the depositing of a first nickel or copper layer on the activated surface. 
         [0036]    The surface therefore first undergoes chemical attack e.g. with an acid for a non-metal substrate comprising acrylonitrile butadiene styrene, or with a base for a substrate comprising a polyamide. Certain roughness of said surface is thus obtained. The subsequent activation step is conducted by depositing a catalyst compatible with the material of said surface. In this manner the depositing of a bonding layer is obtained on the activated surface to improve the adhesion of the reinforcement layer. 
         [0037]    Preferably, the reinforcement layer comprises at least one copper layer. 
         [0038]    Advantageously, the nickel layer comprises a layer of microporous or micro-fissured nickel. 
         [0039]    One advantage of the microporous or micro-fissured layer is that of obtaining a part having better corrosion resistance. Furthermore, the nickel layer can be subdivided into three successive layers of semi-shiny nickel, shiny nickel and microporous nickel. 
         [0040]    Having regard to the foregoing, it will be understood that the plated part obtained by implementing the method is advantageously chromium-free. 
         [0041]    The invention also concerns a plated part able to be obtained by applying the plating method of the invention. 
         [0042]    Advantageously, the plated part of the invention is free of chromium. Also, it preferably successively comprises a non-metal substrate having a surface, a first layer arranged of copper, or nickel deposited on the surface, a copper layer arranged on the first layer, at least one second layer of nickel arranged on the copper layer, and a varnish layer arranged on the second nickel layer. 
         [0043]    As a result, the second nickel layer imparts the metallic appearance whilst the varnish layer arranged on the second nickel layer provides protection for the plated part against corrosion and various attacks by the environment in which the plated part is used. 
         [0044]    Finally, the invention concerns a method to modify a plated part wherein a plated part is provided comprising a non-metal substrate successively having a bonding layer, a reinforcement layer, a nickel layer and a chromium layer. 
         [0045]    The chromium layer is removed and a varnish layer is deposited on the nickel layer. 
         [0046]    The removal of the chromium layer is performed by immersing the plated part in an electrolytic bath for a predetermined time. 
         [0047]    Preferably the nickel layer comprises a layer of microporous or micro-fissured nickel. 
         [0048]    Advantageously, the bonding layer is a nickel layer. 
         [0049]    Advantageously, the reinforcement layer is a copper layer. 
         [0050]    One advantage of this modification method is that existing parts can be chromium-deplated to improve their environmental impact whilst maintaining their metal appearance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0051]    The invention will be better understood on reading the following description of embodiments of the invention given solely as non-limiting examples, with reference to the appended drawings in which: 
           [0052]      FIG. 1  schematically illustrates a plated part according to the invention that is chromium-free and comprises a non-metal substrate and different successive layers arranged on the non-metal substrate; 
           [0053]      FIG. 2  illustrates the different steps of the plating method according to the invention, allowing a chromium-free plated part to be obtained; and 
           [0054]      FIG. 3  schematically illustrates the modification method according to the invention whereby an existing plated part is chromium deplated. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]      FIG. 1  schematically illustrates a plated part  10  free of chromium conforming to the invention. This part comprises a non-metal substrate S on which layers C 1  to C 4  will be deposited. The non-metal substrate S has a surface  11 . 
         [0056]    In this example, the non-metal substrate S is a part in plastic material. In this example, the substrate consists of ABS (Acrylonitrile Butadiene Styrene) which has good mechanical strength and corrosion resistance. In one variant, a copolymer is used comprising acrylonitrile butadiene styrene and a polycarbonate. 
         [0057]    In addition, in another example, the metal substrate can composed of a polyamide. 
         [0058]    In another variant, the non-metal substrate S comprises polypropylene. 
         [0059]    In  FIG. 2 , a first step S 100  is the step at which the substrate S in plastic material receives chemical treatment on its surface  11  to obtain roughness of said surface  11 . 
         [0060]    In this example, the chemical attack of the surface  11  of a part containing an acrylonitrile butadiene styrene polymer is conducted by immersing the parts in a bath comprising sulphuric acid which oxidises the butadiene present on the surface of the substrate S. 
         [0061]    Also, the bath is thermostat-controlled at a temperature of 65° C. oscillating around plus or minus 5° C. After a certain immersion time the surface has become roughened. 
         [0062]    Next at step S 102  the attacked surface  11  of said substrate S is activated for the depositing thereupon of a catalyst containing tin and palladium. 
         [0063]    In one embodiment in which the part comprises a polymer of polyamide type, the part is immersed in a bath containing a solvated base and thermostat-controlled at a temperature of 40° C. plus or minus 5° C. Similarly, roughness of the surface  11  is obtained. In this embodiment step S 102  to activate the surface of said substrate S is performed by depositing a palladium catalyst on the surface  11  of the previously activated surface S. 
         [0064]    According to  FIG. 2 , a step S 104  to deposit a bonding layer is carried out. It can be seen in  FIG. 1  that a first layer C 1  is deposited on the surface  11  of the non-metal substrate S. 
         [0065]    The first layer C 1  is a bonding layer which comprises a nickel layer or copper layer. In this example, the bonding layer C 1  is obtained by immersing the non-metal substrate S having an activated surface in a nickel bath. The bonding layer C 1  preferably has a thickness of between 0.15 micrometre and 0.25 micrometre. 
         [0066]    Said nickel is catalysed by the palladium and tin in the example in which the non-metal substrate comprises acrylonitrile. 
         [0067]    In one embodiment in which the non-metal substrate comprises a polyamide, the nickel is catalysed by palladium. 
         [0068]    A depositing step S 106  to deposit a reinforcement layer C 2  is conducted to reinforce the bonding layer C 1  and to obtain a homogeneous metallic layer. In this example said reinforcement layer C 2  is composed of copper. 
         [0069]    This deposition step S 106  of the reinforcement layer allows the depositing of said layer C 2  by immersing the non-metal substrate S in a copper bath. Therefore the reinforcement layer C 2  is deposited on the bonding layer C 1 . 
         [0070]    The reinforcement layer C 2  has a thickness of between 0.45 micrometre and 0.55 micrometre. 
         [0071]    In another embodiment, said reinforcement layer C 2  is composed of nickel. In the same manner, the reinforcement layer C 2  is deposited on the bonding layer C 1 . 
         [0072]    The next step is a depositing step S 108  to deposit a layer of nickel C 3  on the reinforcement layer C 2 . 
         [0073]    In this example, the nickel layer C 3  has a thickness of between 10 micrometres and 20 micrometres. 
         [0074]    The nickel layer C 3  is subdivided into three layers of nickel:
       a semi-shiny nickel layer;   a shiny nickel layer; and   a microporous nickel layer.       
 
         [0078]    A depositing step S 110  is subsequently performed to deposit a varnish layer C 4  on the nickel layer C 3 . The varnish layer C 4  is preferably deposited by immersing the plated part in a bath containing said varnish. 
         [0079]    A drying step S 112  follows comprising a step to crosslink the varnish layer C 4  using an ultraviolet radiation device comprising a group of ultraviolet lamps which expose the plated part comprising the varnish layer C 4  to ultraviolet radiation for a predetermined time so that the varnish layer is completely dried. 
         [0080]    A plated part is thus obtained that is chromium-free comprising the non-metal substrate S in polyamide or acrylonitrile butadiene styrene, the bonding layer C 1  comprising nickel, the reinforcement layer C 2  comprising copper, the nickel layer C 3  comprising three types of nickel, and the varnish layer C 4 . 
         [0081]    With reference to  FIG. 3  an embodiment will now be described of the modification method of the invention. 
         [0082]    The method starts with a chromium-plated part  100  comprising a non-metal substrate S, a bonding layer C 1  deposited on the surface of the non-metal substrate S, a reinforcement layer C 2  deposited on the bonding layer C 1 , the nickel layer C 3  deposited on the reinforcement layer C 2  and a chromium layer C 4 ′. 
         [0083]    According to the method, the chromium-plated part comprising the chromium layer C 4 ′ is immersed in a bath in which the chromium layer will be removed, to obtain a part  102  comprising the non-metal substrate S, the bonding layer C 1 , the reinforcement layer C 2  and the nickel layer C 3 . 
         [0084]    The effect of this step is therefore to remove the chromium layer. A varnish layer C 4  is then deposited on the nickel layer C 3  which becomes the top layer of the part from which the chromium layer C 4 ′ has been removed. 
         [0085]    The varnish layer C 4  deposited on the nickel layer is subjected to the drying step S 112  to fix the varnish layer C 4  on said nickel layer C 3 . 
         [0086]    This leads to obtaining a chromium-free plated part  104 .