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(11) | EP 4 283 013 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | FINISHING PROCESS OF A PRODUCT |
| (57) It is the object of the present invention a finishing method of a product obtained
by die-casting, stamping or turning a metal material. The method comprising the steps
of: (a) carrying out a roughing or grinding of the product using a coarse grain, equal to or less than P60; (b) washing the roughened or ground product; (c) carrying out a first step of painting the product so as to deposit on the product a first layer of an industrial resin-based paint suitable for giving the surface of the product a chrome-plating effect; (d) when the first layer of resin has at least partially dried, carrying out a second coating step to deposit a second layer of said industrial resin-based paint. |
[0001] The present invention relates to the production of manufactured products by die-casting, stamping, or turning of metal materials, and in particular to the treatments of the outer surface of the die-cast, stamped, or turned product, suitable for imparting special aesthetic effects to the article, such as for its use in the furniture industry.
[0002] One of the most popular treatments is chrome plating, that is the application of a coating of chrome that, in addition to its protective and hardening function, gives the product an aesthetic effect of luster that is particularly popular in modern furniture.
[0003] The most common chrome plating process is galvanic chrome plating, which involves immersing the part to be chrome plated in a series of baths. The main bath, where the part dwells the longest, is in electrolytic nickel solution. In fact, prior to the chromium metal plating, a layer of nickel is created on the part that unifies the metal surface as much as possible at the microscopic level. After a washing bath, immersion in the bath with electrolytic chromium solution takes place.
[0004] A particularly popular effect is satin (matte) chrome plating. The process of satin chrome plating is similar to that described above, except that, after nickel plating, matte nickel plating is performed using special oils; these oils create microbubbles evenly distributed over the surface of the part that give the characteristic matte appearance to the surface.
[0005] In the face of these valuable aesthetic and functional effects, chrome plating has the disadvantage of being unfortunately harmful to humans and the environment. Recently, improvements have been made to chromium plating processes to try to make them less hazardous, for example by replacing hexavalent chromium, which has been shown to be carcinogenic, with trivalent chromium. However, the problem of the harmfulness of chromium plating, not only for the workers who come into contact with the substances used the chromium plating treatment and for the environment into which these substances are discharged, but also for the people themselves who, during the life of the article, come into contact with the chromium plated surface, has been only partially alleviated.
[0006] The object of the present invention is to completely solve the problem of the harmfulness of chromium plating and thus to propose a method of surface finishing of a manufactured product capable of imparting an aesthetic effect similar to, if not better than, that imparted by chromium plating treatments, but environmentally friendly, or otherwise not based on the use of the hazardous or harmful substances used in chromium plating treatments.
[0007] This object is achieved by a surface finishing method according to claim 1. Dependent claims describe preferred or advantageous forms of implementation of the finishing method.
[0008] However, the features and advantages of the surface finishing method according to the invention will be evident from the description below of its preferred examples of implementation, given by way of illustration and not limitation, with reference to the attached figures, in which:
- Figure 1 is a block diagram of the surface finishing method according to the invention; and
- Figure 2 is a sectional view of a portion of an product made with the finishing method according to the invention.
[0009] In said drawings, 1 has been used to denote a finishing method of a product 100 obtained by means of die-casting, molding or turning a metal material.
[0012] The rough product may be obtained by means of a traditional die-casting, molding, or turning process 10.
[0014] While a traditional chrome plating process in galvanic bath requires a roughing or grinding with a medium or fine grain, e.g., equal to or greater than P180, the roughing or grinding of the proposed finishing method is coarse grain, e.g., equal to or less than P60.
[0015] After this roughing or grinding operation, the product undergoes a washing step 14. The washing step 14 may consist of or include degreasing and/or blowing of the artifact.
[0017] This first painting step 16 serves to deposit on the product a first layer of an industrial resin-based paint suitable for giving the surface of the product an effect similar to chrome plating.
[0018] When the first layer of paint has at least partially dried, a second painting step 20 is made to deposit a second layer of industrial resin-based paint.
[0019] Note that the two layers of paint allow for a coating having a thickness such that it will not show cracks or signs of wear over time.
[0023] For example, the thickness of the coating obtained by depositing the two layers of paint is similar to the thickness of traditional chrome plating.
[0024] However, such a thickness of the compressive coating layer may not be achieved in a single coating step, as drops or surface irregularities would be formed.
[0025] Furthermore, in an embodiment, the second layer of paint contains a matting paste suitable for giving the surface of the product a satin chrome effect.
[0026] For example, the matting paste is about 3 percent by weight of the amount of resin required for the second coating step.
[0027] Therefore, since the matting substance is useful only on the outermost layer of the coating, making a single coating step would result in unnecessary waste of matting paste.
[0028] In an embodiment, the second layer of paint also contains an antibacterial and/or antivirus additive.
[0029] In an embodiment, between the first painting step and the second painting step, the product is left to dry for about 20-30 minutes essentially at room temperature (drying step 18).
[0030] In one embodiment, the second coat of paint is applied before the first coat of paint has completely dried, so as to avoid unwanted shade changes.
[0031] Therefore, in an embodiment, drying between the first coat of paint and the second coat of paint takes place at room temperature and not in a drying oven, which would result in the first coat of paint drying completely, causing the above-mentioned shade variation between the first coat of paint and the second coat of paint.
[0032] In one form of realization, after the second painting step, the painted product is dried in an oven at a temperature below 100°C (drying step 22).
[0033] It is also an object of the present invention a product 100, such as a door or window handle, made of a die-cast, molded, or turned 102 metal material.
[0034] The metal material has an outer surface 102' roughened or ground with a coarse grain equal to or less than P60.
[0035] The rough or ground outer surface is coated with two layers of resin-based paint 104, 106 which give the product the chrome plating effect.
[0037] In an embodiment, the outermost layer of paint 106 contains an antibacterial and/or antivirus agent.
[0038] Note that coarse-grain roughing or grinding, as opposed to the usual medium- or fine-grain roughing or grinding, allows for the extraction of gases trapped in the product as a result of die casting. The gas extraction is preparatory to the subsequent painting step, as the gases, trying to escape from the product, may cause the solidified paint layer to crack. On the contrary, chromium plating in galvanic has a pore-closing effect, so gas extraction is not necessary.
[0039] Note that the effect given by coarse-grained roughing or grinding is softened by painting, so that the final effect, to the touch, is similar to that of a fine-grained rough-edged or ground product.
[0040] It should also be noted that if traditional chrome plating were applied to a coarse grain, the artifact would instead be extremely rough to the touch, also exhibiting pitting on the surface, compromising its durability as well as its aesthetics.
[0041] From what has been described, it is clear that the proposed surface finishing method and the resulting product may be considered environmentally friendly, as it does not require the use of the harmful substances used for chromium plating in acid, nickel, and chromium electroplating baths.
[0042] The product coated with the proposed finishing method has a longer service life than a product with traditional chrome plating, a similar aesthetic effect, even in the satin version, if not better.
[0043] The finish obtained by the proposed method is much more homogeneous, in terms of standardization, than the finish obtained by traditional chrome plating, where differences in aesthetics may occur even between one production batch and another. Furthermore, the proposed finishing method makes it possible to significantly reduce, almost to zero, the physiological rejection due to surface defects such as, for example, halos, shading or speckling, which are completely absent by employing the proposed finishing method.
[0044] Furthermore, artifacts made by the proposed method, unlike those chromed in the traditional way, may be remelted at the end of life without altering the starting metal material, as they are nickel-free.
[0045] To the embodiments of the surface finishing method according to the invention, a skilled person in the art, in order to meet contingent needs, may make modifications, adaptations, and substitutions of features with functionally equivalent ones, without departing from the scope of the following claims. Each of the features described as belonging to one possible form of embodiment may be realized independently of the other described forms of embodiment.
1. A finishing method for a product obtained by means of the die-casting, molding or
turning of a metal material, comprising the steps of:
a) carrying out a roughing or grinding of the product obtained by means of the die-casting, molding or turning, using a coarse grain, equal to or less than P60;
b) washing the roughened or ground product;
c) carrying out a first step of painting the product so as to deposit on the product a first layer of an industrial resin-based paint suitable for giving the surface of the product a chrome plating effect;
d) when the first layer of resin has at least partially dried, carrying out a second painting step to deposit a second layer of said industrial resin-based paint.
2. A method according to claim 1, wherein said second layer of industrial resin-based
paint further contains a matting paste suitable for giving the surface of the product
a satin chrome plating effect.
3. A method according to claim 1 or 2, wherein said second layer of industrial resin-based
paint further contains an antibacterial and/or antiviral additive.
4. A method according to any one of the preceding claims, wherein the metal material
is selected among: aluminum, zamak, brass, steel.
5. A method according to any one of the preceding claims, wherein between the first painting
step and the second painting step the product is left to dry for about 20-30 minutes,
substantially at room temperature.
6. A method according to any one of claims 2-5, wherein the matting paste is about 3%
by weight of the second layer of industrial resin-based paint.
7. A method according to any one of the preceding claims, wherein, after the second painting
step, the painted product is dried in an oven at a temperature below 100°C.
8. A method according to any one of the preceding claims, wherein the first layer of
industrial resin-based paint has a thickness between 15 and 30 pm.
9. A method according to any one of the preceding claims, wherein the second layer of
industrial resin-based paint has a thickness between 15 and 30 pm.
10. A product made of a die-cast, molded or turned metal material, wherein the metal material
has an external surface which is roughened or ground with a coarse grain equal to
or less than P60, and wherein said roughened or ground external surface is coated
with two layers of resin-based paint which give the product a chrome plating effect.
11. A product according to claim 10, wherein the outermost layer of paint contains a matting
paste.
12. A product according to claim 10 or 11, wherein the outermost layer of paint contains
an antibacterial and/or antiviral agent.