A composite material product activating the integral or selective metallisation by means of chemical plating of surfaces of three-dimensional matrices made of cross-linked resin obtained by 3D printing

Abstract

The invention relates to: A) A three-dimensional composite material product comprising: i) a three-dimensional matrix made of cross-linked resin obtained by 3D printing, having the desired shape of the final product; ii) particles of a metal salt, arranged inside said matrix and entirely or partially on one or more of said surfaces; iii) metal particles in the elemental state completely or partially arranged on at least one or more surfaces of said matrix wherein: in said products iii) the elemental metal is the reduced form of the metal salt, ii) and said particles are arranged completely on one or more surfaces other than those completely occupied by the metal salt particles, or are arranged partially on one or more of the same surfaces on which the metal salt particles are arranged; B) a metallised product obtained by depositing one or more metal layers on at least one surface or part thereof of the product A); C) the process of preparing the metallised product B).

Description

[0001] A composite material product activating the integral or selective metallisation by means of chemical plating of surfaces of three-dimensional matrices made of cross-linked resin obtained by 3D printing.

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a composite material product capable of triggering both complete and selective metallisation by chemical plating, of at least one surface of three-dimensional matrices made of cross-linked resin obtained by 3D printing, the related final metallised product, and the process for preparing the final metallised product, from the aforesaid product.

[0004] BACKGROUND ART

[0005] Additive manufacturing refers to the industrial process that, thanks to various technologies, manufactures components, semi-finished or finished products by superimposing layers of material. Additive manufacturing proceeds by addition: the material is added layer upon layer from the outer perimeter to the inner perimeter with the various fillings.

[0006] Additive manufacturing is thus the opposite of traditional manufacturing, whereby the product is made by removing material through milling or turning (Ian Gibson, David Rosen, Brent Stucker, Mahyar Khorasani, Additive Manufacturing Technologies, third edition, Springer Cham, 2020).

[0007] Additive manufacturing is also known as 3D printing because it produces objects from a digital design file, which is “printed” in three dimensions. 3D printing has been used in rapid prototyping since the mid-80s, but only in recent years has the reduction in the cost of machines, the possibility of producing larger objects in less time and with a greater range of materials / filaments made this type of technology also interesting in real industrial processes.

[0008] Today, additive manufacturing is used in rapid prototyping as it allows to reduce design costs by changing the digital file: an example is the production of components in aeronautics. It is also used to obtain highly-customised small batch products, to meet emergencies of lack of components for in-line production, to re-engineer parts to increase plant productivity. It is therefore widely used in the automotive industry, in the medical sector, in construction and as a substitute for injection moulding. The first step in additive manufacturing is the creation of a CAD, Computer Aided Design, drawing. 3D CAD works on the basis of volumes, and obtains the drawing by composing and intersecting the different blocks.

[0009] Once the design CAD file has been created, it is inserted and / or sent to the 3D printer: the software inside the printer decodes the design and divides it into layers; it then creates the path for the machine to follow during manufacturing.

[0010] The object can be printed using different technologies.

[0011] In Fused Deposition Modelling, better known by the acronym FDM, filaments of the selected material (plastic polymers such as PLA, ABS, Nylon, PET, PEEK) are collected on spools and connected to one or more extruders, nozzles, heated tips that fluidise the filaments and move according to the software coordinates: outer perimeter, inner perimeter, filling, all the details provided by the computer file. One or more extruders move layer by layer: when the layer is finished, the plane on which the object rests is lowered to begin the next one.

[0012] Once the last layer is finished, the printer switches off, the object is left to cool and then it is extracted, ready for use.

[0013] In stereolithography (SLA), on the other hand, the file is printed using lasers or light sources.

[0014] Specifically, in laser stereolithography, the “levels” of the object are created by means of a perforated plate inserted on the bottom of a tank filled with a liquid resin: a laser beam is projected and modulated to reconstruct the image of the first level of the section of the object, the plate is lowered and so does for each successive scan. When finished, the printed object is inserted in an ultraviolet light oven.

[0015] In DLP - Digital Light Processing stereolithography, a light source projected at a minimum distance from the resin is used instead of a laser to have greater resolution: in contact with light, the polymer hardens, layer upon layer.

[0016] In LCD - Liquid Crystal Display stereolithography, liquid crystal displays that are backlit by ultraviolet sources are used.

[0017] Laser Sintering or SLS - Selective Laser Sintering creates the object by solidifying (sintering) layers of powder through the laser. When finished, the piece is cleared from exceeding powder and placed in the oven as required. Additive manufacturing metallization processes, whether by electrolysis or by total or partial chemical plating, have long been known. However, they provide the best results especially in stereolithography in terms of both efficiency and process economy. The standard process to chemically deposit a metal layer on a non-conductive surface, such as that of a polymeric 3D print, involves the use of a palladium salt. Said salt is adsorbed and then reduced in situ on the surface itself, thus producing metal nanonuclei capable of catalysing the chemical reaction leading to the deposition of the metal of interest. This approach has been applied in the past on SLA and DLP prints, Bemasconi et al., J. Electrochem. Soc. 2017, 164(5), B3059-B3066. This basic approach, however, often results in reduced adhesion of the metal layer and uneven surface activation. Moreover, the process involves the use of a precious metal such as palladium, which is expensive and poorly available. Therefore, alternative approaches have been developed.

[0018] Li et al., ACS Appl. Mater. Interfaces 2021, 13, 22891-22901 disclose a hybrid 3D additive manufacturing (SLA) technology to produce high-performance electronic products for direct current (DC) and high-frequency domains, which involves the use of a new type of SLA resin containing a copper salt. The resin can be cross-linked by UV, selectively activated and metallised by chemical plating. Thus, the metal coating can be selectively applied according to specific patterns.

[0019] The resin, containing the copper salt, is prepared by dispersing the copper salt within the resin. The metal salt is activated by laser.

[0020] However, this type of technique entails a number of problems for both metal plating of entire surfaces and partial plating with specific patterns.

[0021] In the first case of deposition on the entire surface of the metal, the laser cannot activate parts with surfaces characterised by complex geometries. In the case of selective metal deposition, the salt activation by laser is in any case an expensive process, hardly applicable for an industrial process.

[0022] Lee et al, ACS Appl. Polym. Mater. 2021, 3, 4735-4745 describe a photo-cross- linkable resin incorporating zinc oxide nanoparticles in order to activate subsequent copper plating.

[0023] US10494721 discloses a process for metallising a three-dimensional structure obtained by 3D printing comprising: i) wetting said three-dimensional structure with an aqueous solution of a metal salt; ii) transferring the three-dimensional structure soaked in said salt into a solution containing a first reducing agent; iii) wetting the three-dimensional structure from the previous step in a metal plating bath comprising a coordination agent, a palladium or platinum salt, a buffer solution and a second reducing agent to obtain a metallised three- dimensional structure.

[0024] Although this process involves the reduction of metal salts that are part of the 3D structure, it does not allow for optimal complete or selective metallisation since the salts are added superficially onto the already formed 3D matrix.

[0025] SUMMARY OF THE INVENTION

[0026] The Applicant has now found that it is possible to overcome the drawbacks of metallisation processes by chemical plating of 3D-printed products with the process according to the present invention, which provides to necessarily use, as a processing intermediate, a three-dimensional composite material product comprising: i) a three-dimensional matrix made of cross-linked resin obtained by 3D printing, having the desired shape of the final product; ii) particles of a metal salt, arranged inside said matrix and entirely or partially on one or more of said surfaces; iii) metal particles in the elemental state completely or partially arranged on at least one or more surfaces of said matrix;

[0027] This product is characterised in that the elemental metal particles iii):

[0028] • are the elemental form of the metal salt ion ii) as they are obtained by reduction of said metal salt ii) and are arranged:

[0029] • completely on one or more surfaces other than those completely occupied by the metal salt particles, or

[0030] • partially on one or more of the same surfaces on which the metal salt particles are arranged. A further object of the invention is the final metallised product obtained from the above-described composite material product object of the invention onto which at least one metal layer has been entirely or partially applied on one or more surfaces of said product.

[0031] Finally, a further object of the invention is the process of preparing this product, which comprises the following steps: a) Mixing and grinding at least one metal salt in at least one UV-cross- linkable liquid resin mixture in a ceramic ball mill for a time between 110 and 130 minutes, preferably 120 minutes, gradually increasing the speed of the mill until the maximum speed of between 200 and 400 rpm, preferably 300 rpm, is reached; b) separating the balls by a sieve and obtaining a resin suspension in which the at least one metal salt is evenly dispersed; c) 3D printing the suspension obtained in the previous step to obtain a crosslinked resin-based product wherein metal salt particles are dispersed both superficially and internally; d) reducing the metal salt on at least one surface or part thereof with a reducing agent, preferably selected from sodium borohydride, sodium bi s(2-methoxy ethoxy) aluminium hydride, hydrazine, diisobutylaluminium hydride, more preferably sodium borohydride; e) At least one layer of metal is deposited by plating to obtain the metallised product.

[0032] The composite material product object of the invention substantially produces, compared to similar substrates of the prior art, the following technical effects:

[0033] • it has nucleation sites to trigger metal deposition by chemical plating;

[0034] • it creates a self-etching effect that causes an increase in roughness, promoting the adhesion of the metallised layer.

[0035] Thus, it is not necessary to activate the surface of the pre-printed material by energy- intensive processes, such as plasma treatments or the use of lasers, to prevent delamination of the metal layers. Compared to the process disclosed in US10494721, which involves the application of mineral salts already on the 3D-printed matrix and subsequent reduction with sodium borohydride, the process of the invention has the following advantages:

[0036] • the metal salts are already part of the three-dimensional structure, so delamination of the metal layer is more difficult, as they are not applied after the formation of the three-dimensional matrix by 3D printing, as is the case with the aforesaid prior Patent.

[0037] • it makes it possible to quantify the concentration of metal salts that are then completely or partially reduced on the surface.

[0038] A preferred schematic embodiments of steps d) and e) of the process of the invention to prepare the product obtained by 3D printing and completely metallised on at least one surface is shown in Figure 1.

[0039] In particular, the second rectangle is a cross-sectional view of the product according to the present invention, and the third block is the product completely metallised on at least one surface, a further object of the invention.

[0040] Figure 2 shows a preferred embodiment of steps d) and e) of the process according to the present invention in order to obtain the product obtained by 3D printing partially metallised on at least one surface.

[0041] DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 represents a preferred schematic embodiment of steps d) and e) of the process according to the present invention to obtain the product completely metallised on at least one surface.

[0043] Figure 2 represents a preferred schematic embodiment of steps d) and e) of the process according to the present invention to obtain the product obtained by 3D printing, partially metallised on at least one surface.

[0044] Figures 3 and 4 show the viscosity curves as a function of the shear stress for composite mixtures of cross-linkable resin containing NiCh and CuSCU respectively at the following concentrations: 0%, 7%, 10% e 13% Figure 5 shows the viscosity curves of the composite mixture of plant-origin crosslinkable resin containing 0% and 16% of FeNFU (SO4)2 respectively as a function of shear stress.

[0045] Figures 6a) and 6b) show the calibration curves of the composite mixtures of NiCh and CuSO4 at the following concentrations: 0%, 7%, 10% and 13% Figure 6c) shows the calibration curves of the composite mixtures containing 0 and 16% of FeNFU (SO4)2.

[0046] Figure 7a) represents a perspective view of the product 1 obtained by 3D printing from the composite mixture containing 7% by weight of NiCh, of the product 2 obtained after reduction from product 1, and finally of the product 3 obtained by applying a layer of NiP by chemical plating, from product 2. Figure 7b) represents a view from above of the product 3.

[0047] Figure 8 is an SEM image of the material 1 from Figure 7a) at 1000X magnification.

[0048] Figure 9a) is an SEM image at 5000X magnification of product 1, Figure 9b) is an SEM image at 5000X magnification of product 2, Figure 9c) is an SEM image at 5000X magnification of product 3, Figure 9d) is an SEM image at 5000X magnification of the cross-section of product 3.

[0049] Figures 10a), 10b) and 10c) are SEM images at 5000X magnification of metallised products obtained by 3D printing from composite mixtures containing 7%, 10% and 13% of NiCh by weight, respectively.

[0050] Figures Ila) and 11b) are the XRD diffractograms of the product obtained by 3D printing from the composite mixture containing 7% by weight of NiCh respectively as-printed and on which NiP was deposited by a plating bath.

[0051] Figure 12 is the EDS spectrogram of product 1 in Figure 7a)

[0052] Figure 13 is the EDS spectrogram of product 2 in Figure 7a)

[0053] Figure 14 is the EDS spectrogram of product 3 in Figure 7a).

[0054] Figure 15 is an SEM image at 10000X magnification of the mapping of Ni and Cl elements of product 1. Figure 16 is an SEM image at 10000X magnification of the mapping of Ni and Cl elements of product 2.

[0055] Figures 17a) 17b) are SEM images at 10000X magnification combined with the EDS analysis of product 1 and product 2 from Figure 7a).

[0056] Figure 18 shows the Vickers hardness results as a function of NiCh content.

[0057] Figure 19a) represents a side view of product 1 obtained by 3D printing from the composite mixture containing 7% by weight of CuSO4, product 2 obtained from the surface reduction of product 1 and product 3 obtained after depositing a layer of Cu on the surface of product 2 to which a layer of Cu was superficially applied by plating. Figure 19b) represents a perspective view of the product on which a layer of copper was deposited and obtained by 3D printing from the composite mixture containing 10% of CuSO4.

[0058] Figures 20a), 20b) and 20c) are SEM images at 5000X magnification of the product represented in Figure 19b) obtained by 3D printing from the composite mixture containing 10% by weight of CuSO4, respectively: as-printed, reduced and metallised superficially with a Cu layer by chemical plating. Figure 20d) is an SEM image of the cross-section of the metallised product in Figure 19b).

[0059] Figures 21a), 21b) and 21c) are SEM images at 5000X magnification of the 3D-printed product metallised by chemical plating using a composite mixture containing 7% by weight, 10% by weight and 13% by weight of the total weight of said composite mixture, respectively.

[0060] Figures 22a) and 22b) are the XRD diffractograms of the product obtained by 3D printing from the composite mixture containing 13% by weight of CuSO4of the total weight of the composite mixture of the product as-printed and of the product metallised with a layer of copper by chemical plating, respectively.

[0061] Figures 23a), 23b) and 23c) represent the EDS spectrograms of the product obtained by 3D printing from the composite mixture containing 10% by weight of CuSO4of the total weight of said mixture respectively: of the product as-printed, of the relative product submitted to surface reduction, and of the product superficially coated with a layer of copper applied by chemical plating. Figure 24 reproduces SEM mapping images at 10000X magnification of S, O and Cu elements of the 3D-printed product as-printed from the composite mixture containing 10% by weight of CuSCU

[0062] Figure 25 is an SEM mapping image at 10000X magnification of C, O, S and Cu elements of the 3D-printed product as-printed from the composite mixture containing 10% by weight of CuSCU.

[0063] Figure 26 reproduces SEM mapping images at 10000X magnification of S, O and Cu elements of the 3D-printed product as-printed from the composite mixture containing 13% by weight of CuSCU of the total weight of the composite mixture.

[0064] Figures 27a) and 27b) are SEM images at 10000X magnification of, respectively, a surface other than the top surface and of the top surface of the product obtained by 3D printing, as-printed from a composite mixture containing 13% by weight of CuSCU of the total weight of the composite mixture.

[0065] Figure 28 represents a schematic embodiment of step c) of the 3D printing process of the composite mixture containing a metal salt.

[0066] Figure 29 represents the hardness trend of the 3D-printed product obtained by 3D printing as a function of CuSCU concentration.

[0067] Figure 30a) shows a perspective view of a product obtained by 3D printing from a composite mixture of plant-origin resin containing 16% by weight of FeNH4(SO4)2 of the total weight of the composite mixture to which a layer of NiP was applied by chemical plating. Figures 30b), 30c) and 30d) are SEM images at 10000X magnification of the product obtained by 3D printing from the composite mixture containing 16% by weight of FeNH4(SO4)2 respectively: as-printed, submitted to reduction, and onto which a layer of NiP was applied superficially by chemical plating.

[0068] Figures 31a) and 31b) show the XRD diffractograms of the product obtained by 3D printing from the composite mixture containing 16% by weight of FeNH4(SO4)2 of the total weight of the composite mixture respectively: as-printed and of the relative product onto which a layer of NiP was applied by chemical plating. Figure 32 shows the graph of the hardness of the product obtained by 3D printing of the pure plant-origin cross-linkable resin and the one of the product obtained by 3D printing of the composite mixture containing 16% by weight of FeNH4(SO4)2 of the total weight of said mixture.

[0069] Figure 33a) shows from above the product obtained by 3D printing of a composite mixture containing 7% by weight of NiCh then coated with a layer of NiP applied by chemical plating, which in turn is coated with a layer of copper applied by electrolytic deposition, Figure 33b) shows an SEM image at 5000X magnification of the crosssection of the product shown in Figure 33a).

[0070] Figure 34 shows the EDS spectrogram of the product shown in Figure 33a).

[0071] Figures 35a), 35b) and 35c) represent a product (in the shape of an owl) obtained by 3D printing of a composite mixture containing 7% of NiCh coated respectively: with a layer of Cu, coated in turn with a layer of Ni, and finally coated with a layer of Au.

[0072] Figures 36a), 36b), 36c) and 36d) represent a view from above of a product obtained by 3D printing from a mixture of cross-linkable resin containing 10% by weight of copper sulphate of the total weight of the mixture, subsequently submitted to reduction on a portion of the surface by applying by ink-jet printing an aqueous solution of 10 g / 1 of sodium borohydride at pH=12 at the following Drop Spacing (DS): 10 pm, 15 pm, 20 pm and 30 pm, and then immersed in a plating bath to be partially coated with Cu.

[0073] Figures 37a), 37b), 37c) and 37d) represent SEM images at 1000X magnification of the products in Fig. 36a), 36b), 36c) and 36d).

[0074] Figure 38a) is a product obtained by 3D printing from a mixture of cross-linkable resin containing 13% by weight of copper sulphate of the total weight of the mixture, subsequently submitted to reduction on a portion of the surface by applying by ink-jet printing an aqueous solution of 10 g / 1 sodium borohydride at pH 12, with DS 20 pm and applying 3 layers of Cu by immersion in a plating bath. Figure 38b) is an SEM image at 2500 X magnification of the product in Figure 38a).

[0075] Figure 39 a) is a product obtained by 3D printing from a cross-linkable resin mixture containing 13% by weight of copper sulphate of the total weight of the mixture, subsequently submitted to reduction by applying by ink-jet printing, only on a portion of the surface according to a particular pattern, a 10 g / 1 aqueous solution of sodium borohydride at pH 12, with DS 20 pm and applying 3 layers of Cu by immersion in a plating bath, Figure 39b) represents a SEM image at 100 X magnification of a detail of the pattern reported in Figure 39a).

[0076] Figures 40a) and 40b) represent two products seen from above obtained by 3D printing from a cross-linkable resin mixture containing 13% by weight of copper sulphate of the total weight of the mixture which was subsequently submitted to reduction by inkjet printing only on a portion of the surface, according to a particular pattern, of an aqueous solution of 20 g / 1 of sodium borohydride at pH 13 with DS = 10 pm and 20 pm respectively, and subsequently metallised with a layer of copper by immersion in a plating bath for 50 minutes.

[0077] Figure 41a) is an SEM image at 100 X magnification of the product shown in Figure 40a), Figure 41b) is an SEM image at 2500 X magnification of the same detail shown in Figure 41a).

[0078] Figure 42 shows that the product in Figure 40a) conducts current in the metallised portions.

[0079] Figures 43a) and 43b) represent a perspective view and a view from above of a product obtained by 3D printing from a composite mixture containing 13% of copper sulphate.

[0080] Figure 44 represents a side view of the longest indentation of the product in Figure 43.

[0081] Figure 45a) represents the complex- shaped 3D-printed product shown in Figures 43 and 44 above, which was subsequently submitted to reduction by ink-jet printing only on a portion of the top surface and the 3 inclined surfaces according to a particular pattern of an aqueous solution of 20 g / 1 of sodium borohydride at pH 13, and then metallised with a layer of copper by immersion in a plating bath for 50 minutes with DS = 10 pm respectively, which shows that this product is not perfectly metallised in the areas indicated. Figures 45b), 45c) and 45 d) show that the product is conductive in every part of the pattern, after the non-conductive areas in Figure 45a) have been coated with electrolytic copper.

[0082] DETAILED DESCRIPTION OF THE INVENTION For the purposes of the present invention, the definition "comprising" does not exclude the presence of further components / steps in addition to those listed after this definition.

[0083] For the purposes of the present invention, the definitions "consisting of’ or "made up of instead exclude the presence of such components not expressly listed.

[0084] For the purposes of the present invention, 3D printing refers to stereolithography (SLA) and digital light projection (DLP) or liquid crystal display (LCD) techniques, all using similar light-curing resins.

[0085] Preferably, the matrix of the composite material product that is the object of the present invention is obtained by digital light projection (DLP) from a UV-cross-linkable liquid resin usually used for DLP, on the assumption that it does not dissolve salts.

[0086] For the purposes of the present invention, metals in their elemental state are defined as metals with oxidation number 0 and metal ions are defined as metals having an oxidation number greater than 0.

[0087] In the composite material product that is the object of the present invention, the metal salts ii) are preferably selected from: Ni salts, Cu salts, Fe salts, Pd salts, Pt salts, Au salts, Ag salts.

[0088] According to a particularly preferred embodiment, these salts are selected from NiCh • 6H2O, CUSO4• 5H2O, NH4Fe(SO4)2• 12H2O.

[0089] For the purposes of the present invention, the particles contained in the resin generally have a diameter of between a few hundred nanometres and a few microns, preferably between 300 nm and 2000 nm. This diameter is mainly limited by the conditions of use of the ball mill, which does not allow to obtain diameters smaller than a few hundred nanometres.

[0090] In the process of preparing the metallised product that is the object of the present invention, when the metallic salts are in hydrated form, prior to step a) they are submitted to dehydration at a temperature of between 140° and 230°C, preferably in a closed container with a glass lid to allow gradual evaporation of the water, the lid being subsequently removed until an anhydrous dry powder is obtained, whose dimensions are reduced by loading said powder into a powder crusher. Preferably, the content of the metal salts to be added in step a) of the process of the present invention is between 5 and 20%, more preferably between 7 and 16% by weight of the total weight of the composite mixture.

[0091] A composite mixture is defined as the liquid mixture containing the metal salt in addition to the cross-linkable resin.

[0092] Preferably in the process according to the present invention, step b) provides that the balls after sifting are loaded back into the mill together with other resin to recover any ground material remaining attached thereto, and the resulting mixture is further ground and sieved.

[0093] Preferably in the process that is the object of the present invention, when step d) is carried out on at least one complete surface, said at least one surface is immersed in an aqueous solution of sodium borohydride at a concentration of between 15 and 25 g / 1 for a time between 40 seconds and 90 seconds, preferably 60 seconds.

[0094] Preferably, in the process that is the object of the present invention when step d) is carried out partially on at least one surface, it comprises the following steps: dl) a sodium borohydride solution is prepared at concentrations between 8 and 25 g / 1, preferably between 10 g / 1 and 20 g / 1 at a pH of 12 to 13, and loaded into a cartridge to be used in a conventional inkjet printer such as piezo inkjet, thermal inkjet, aerosol jetting, etc; d2) the aqueous solution prepared in the above step dl) is applied by ink-jet printing onto a portion or according to a desired path.

[0095] For the purposes of the present invention, “chemical plating” or “electroless deposition” is the deposition of one or more metal coatings or metal alloys on even non-metal substrates by immersion in special chemical plating baths, i.e. aqueous or non-aqueous solutions without the input of external energy. In fact, chemical plating is a purely chemical process involving only oxidation-reduction reactions, without applying electrical currents and thus quite different from the so-called electrolytic plating or electroplating.

[0096] The chemical plating baths applied are of the conventional type, as we will analyse later. With the process of the invention, it is possible to apply a layer by chemical plating of a metal different from the one contained in the salts and consequently contained in the metal after chemical salt reduction.

[0097] With the process of the invention, it is possible to apply, by chemical plating, one or more layers, or alternatively a layer of a different metal can also be applied by electrolytic deposition on the first metal layer applied by chemical plating.

[0098] In the following description, some preferred embodiments are provided of the composite material product that is the object of the present invention and of the corresponding final product on which at least one metal layer has been deposited by chemical plating obtained by particularly preferred embodiments of the process according to the present invention.

[0099] METAL SELECTION AND PREPARATION.

[0100] In theory, any metal salt whose reduced form is capable of catalysing metal deposition by chemical plating can be used, including, for example, Ni, Cu, Fe, Pd, Pt, Au, Ag salts.

[0101] The reduced form of the salt may be different from the one deposited by chemical plating, (e.g. nickel chloride reduced to metal nickel is able to trigger the deposition of metal copper by means of chemical plating). The following examples are given: nickel chloride NiCh • 6H2O, which gives rise, by reduction, to metal nickel particles to catalyse the deposition of metal nickel by chemical plating; copper sulphate CuSCU • 5H2O which gives rise, by reduction, to particles to catalyse the deposition of copper by metal plating, iron (III) ammonium sulphate NH4Fe(SO4)2 • I2H2O which gives rise to metal iron particles to catalyse the deposition of metal nickel by chemical plating. The aforesaid salt is of particular interest because of its lack of toxicity, which makes the final product safer.

[0102] As pointed out above, salts cannot be used in their hydrated form. In fact, resin is an organic material, incompatible with water. If hydrated salts in particle form are mixed with resin, agglomeration of the particles, which precipitate (thus making it impossible to 3D print the material) is first observed. To remove this water, metal salt powders are heated, as outlined above, according to the following reaction patterns

[0103] NiCh • 6H2O + heat NiCh + 6 H2O

[0104] CuSO4• 5H2O + heat CuSO4+ 5 H2O

[0105] NH4Fe(SO4)2• 12H2O + heat NH4Fe(SO4)2+ 12 H2O

[0106] Therefore, according to a particularly preferred schematic, the dehydration temperature can be set at 220 °C because the aforesaid metal salts do not degrade. If other types of salts are used, the temperature must be selected precisely in order to avoid decomposition thereof while at the same time removing all hydration water. A glass cover is preferably placed at the beginning of this heating to avoid a very rapid dehydration reaction that can also change the structure of the metal salt. This lid is removed to achieve complete anhydrification of the powder. The powder size is reduced by using a powder crusher. In any case, the final particle size is not relevant, because the step that determines the final particle size is the grinding and mixing with resin in a ball mill or step a) of the process of the invention.

[0107] RESIN SELECTION AND COMPOSITE MATERIAL PREPARATION

[0108] As outlined above, any type of resin suitable in general for stereolithography and in particular for digital light projection (DLP) can be used for preparing the three- dimensional matrix of the composite product object of the present invention. The resins concerned are generally based on urethanes, acrylates or mixtures of these chemical species. The only limitation is the need to keep the metal salt particles in suspension; therefore, the resin should not solubilise the selected metal salt. Among the preferred ones we mention Anycubic UV 405 nm resin, in other words a liquid acrylate-based UV resin that is cross-linkable at 405 nm in 6-10 seconds, or the transparent plant-based resin ELEGOO, which comes from soya and is also crosslinkable at 405 nm, and which is preferably used with iron salts to create fully biodegradable products.

[0109] Preferably, nickel chloride and copper sulphate at the following concentrations are used for preparing the product object of the present invention: 7%, 10% and 13% by weight of the total weight of the mixture. Excessively low concentrations do not provide enough reduced metal to activate chemical deposition. Conversely, concentrations that are too high constitute a waste of metal salt.

[0110] When using ammonium iron sulphate, it is preferable to use a salt concentration of 16% of the total weight of the mixture. In this case, the concentration must be higher as iron sulphate contains less metal in molar terms than nickel chloride and copper sulphate.

[0111] Mixing and grinding in a ball mill must take place in an anhydrous environment and the balls must be added in 20 times the weight of the metal salt particles. For example, for a resin mixture containing 10% of nickel chloride, 5 g of nickel chloride, 45 g of resin and 100 g of balls are required.

[0112] The balls are arranged in a balanced manner inside the planetary ball mill after loading the salt particles and part of the resin, a rotation is gradually applied and speeded up until a rotational speed of 300 rpm is reached, after which this speed is maintained for 120 minutes. When finished, the remaining portion of the resin is added and the mill is kept rotating at 200 rpm. Then the balls are separated from the mixture using a small sieve.

[0113] The mixture is then weighed to calculate the mixing yield.

[0114] The following table shows the results obtained: Table 1.

[0115] The dispersions are stable for a reasonably long time (>10 h), which allows 3D printing by photo-polymerisation.

[0116] In addition, the viscosity of the composite mixture is measured. Excessive viscosities are detrimental to DLP printing. Figure 3 shows the viscosity curves of the Anycubic 405nm UV resin mixtures at the different NiCh concentrations shown in the aforesaid table as a function of shear stress. Figure 4 shows a similar graph of the mixture of the same resin at the same concentrations as those shown in the previous figure, but in which the metal salt is copper sulphate.

[0117] Figure 5 shows in a graph the measurement of viscosity as a function of shear stress for the composite mixture of cross-linkable UV resin of plant origin ELEGOO and ammonium iron sulphate in concentrations of 16% by weight of the total weight of the mixture.

[0118] It can be observed that all composite mixtures are non-Newtonian fluids, which means that the viscosity of these fluids changes as a function of the shear stress.

[0119] It can be noted that the different composite mixtures have a lower viscosity than pure resin at high shear stress values. The shear stresses at which the resin viscosity is lower than that of pure resin are 1000, 100 and 10,000 s' 'for nickel chloride, copper sulphate and Fe(III) ammonium sulphate, respectively.

[0120] It is worth noting that the viscosity values at low shear stresses are the most significant, because they are related to the low speed at which the printing plate moves while manufacturing the product.

[0121] For all the mixtures examined, an increase in viscosity is observed as the concentration of metal salts increases.

[0122] In general, all the mixtures analysed were within a reasonable viscosity limit to successfully produce 3D printed products.

[0123] Products can be obtained from the composite mixture using any type of stereolithographic-type 3D printer. In this specific example, a DLP -type 3D printer was used. This type of printer uses a screen capable of emitting UV radiation to crosslink the resin mixture and create the 3D printed product. The specific device which is used is the Photon S printer, manufactured by Anycubic. Before using the 3D printer, an important critical parameter must be determined: the required exposure time, i.e. the time required to obtain a cross-linked polymer layer with the desired thickness. An exposure time that is too long will result in a lower resolution of the sample, while an exposure time that is too short does not allow to obtain 3D printing. The right value is determined by creating calibration curves in a diagram showing the thickness of the resin layer cross-linked with UV in the DLP printer at different concentrations of metal salt particles as a function of cross-linking time.

[0124] The calibration curves at the different concentrations of the specific metal salt used are shown in Figure 6, where in particular graph a) shows those of the mixture containing nickel chloride, graph b) shows those of the mixture containing copper sulphate and graph c) shows the calibration curve of the mixture with iron (III) ammonium sulphate at 16% by weight of the total weight of the mixture.

[0125] It can be observed that, for the same cross-linking times, the thickness of the crosslinked layer decreases as the salt concentration within the composite mixture increases, but this also translates into the fact that longer exposure times are required for more concentrated composite mixtures.

[0126] It can be observed that composites containing copper sulphate are less sensitive to increasing particle concentrations of the metal salt than those containing nickel chloride.

[0127] Based on the above calibration curves a) and b), the following parameters were applied to print layers with a pitch of 50pm.

[0128] * of the layers following the base layer, which has significantly longer exposure times to allow not only for the polymer to cure, but also for the polymer to adhere to the printing plate where the 3D product is created. Table 2.

[0129] At the end of 3D printing, the product is removed with pliers. The cross-linked resin is cleaned with acetone and dried. The product is submitted to post-curing for 4 minutes in the presence of a UV source.

[0130] REDUCTION OF METAL SALT ON THE SURFACE

[0131] At the end of the 3D printing step, in other words of step c) of the process according to the present invention, the metal salt is reduced by a suitable reducing agent. The aim is to obtain metal nanoclusters. For this reason, the reducing agent should be strong enough to reduce the metal ion present in the salt to its elemental state.

[0132] So any reducing agent that meets the aforesaid requirements can be used, but the most suitable is sodium borohydride (due to its limited toxicity).

[0133] Specifically, the oxidation-reduction reactions involved when the composite material product coming from 3D printing, which contains one of the aforesaid salts i.e. nickel chloride, copper sulphate and iron (III) ammonium sulphate, is submitted to reduction with sodium borohydride, are the following:

[0134] Then, after the 3D printing process, the surface is activated by immersing the product in a 20 g / 1 solution of NaBHj for 1 minute without stirring the solution. Through this process, the surface of the product changes its colour due to the formation of metal particles. At the end of this operation, the product is washed with demineralised water and placed in a chemical plating bath. It is important to carry out the reduction step just before immersing it into the chemical plating bath, because some metals can form an oxide layer, which will passivate if the metal is left in the open air for some time, thus hindering subsequent plating. CHEMICAL PLATING

[0135] Any chemical plating process can be carried out on the composite material object of the present invention, with the assumption that the catalytically active particles of a suitable metal have been obtained by the reduction reaction described in the previous chapter. The only real limitation is the resin used to make the composite, which is normally characterised by a low glass transition temperature, potentially changing the mechanical properties and structural geometry of the 3D printed product. In the examples described herein, the plating temperature is 45°-50°C, preferably 45°C, well below the glass transition temperature of Anycubic resins (60-65°C). The compositions and electrolyte concentrations of the chemical plating bath for nickel and copper respectively are given in the following two tables:

[0136] Table 3.

[0137] Table 4. The bath deposition times depend on the final metal thickness required. In these examples, in order to deposit about 1 pm of metal, the deposition time is 20 minutes and 35 minutes for NiP and Cu respectively. During deposition, it is essential to keep stirring the bath to avoid hydrogen build-up creating unwanted bubbles on the surface. Upon completion of the aforesaid operations, the product is washed with demineralised water and dried in a nitrogen atmosphere.

[0138] RESULTS OF THE METALLISATION PROCESS

[0139] NiP deposition on NiCh-added material products

[0140] NiP deposition was successfully carried out on composite material products added with NiCh at 7, 10 and 13% by weight of the total weight of the composite.

[0141] In Figure 7, the resulting components are shown for the composite product with 7% by weight of NiCh.

[0142] In Figure 7a), element 1 is the product obtained by 3D printing with pure resin, element 2 is the composite material product placed in a sodium borohydride reducing bath for 1 minute and 3 is the product made of metallised composite material. Figure 7b) shows that the only surface that has not undergone metallisation is the top surface of the 3D print. This is caused by the lower concentration of nickel chloride due to the fact that this surface coincides with the lower base of the 3D print. At a concentration of 10% and 13% by weight, the entire surface of the composite is instead completely covered with NiP.

[0143] The composite material product at a concentration of 7% by weight of NiCh was submitted to SEM analysis and its three-dimensional structure obtained by 3D printing was observed (Figure 8). From this SEM image, it can be observed that the surface of the 3D-printed component has a wave structure. This trend is caused by the 3D printing process: at each step, part of the resin is cross-linked onto the pre-existing cross-linked polymer layer, which leads to the creation of the product. It can also be observed that each wave on the surface has a thickness of 50 pm, which is identical to the pitch size. This wave trend makes the surface rougher and thus more suitable for metallisation. SEM images of the non-reduced, reduced and metallised form with chemical plating are shown in Figures 9a), 9b), 9c) respectively. Figure 9d) instead shows the crosssection of the metallised composite material product. In these images, it can be noted that the surface of the composite product that has undergone reduction is rougher than the unreduced form. The reduction of nickel chloride causes an etching effect. The characteristics of the final product whose image is shown in Figure 9c) coincide with the typical morphology of a metal layer deposited by chemical plating, and it can be observed that with this type of metallisation, the polymer is completely covered by NiP.

[0144] In Figure 9d), the wavy structure can be observed and NiP appears uniformly deposited on the surface of the composite material product in which no gas bubbles are observed. Figure 10a) shows the SEM images of the metallised surface of the composite material product obtained from the composite mixture containing 7% by weight of nickel chloride. Figure 10b) shows the metallised surface obtained from the composite mixture containing 10 % by weight of nickel chloride, Figure lOd) represents the SEM image of the metallised surface of the composite material product metallised from the composite mixture containing 13 % by weight of nickel chloride.

[0145] From these images, it can be seen that all three metallised surfaces show a metal layer covering the entire surface of the composite material product.

[0146] The composite material product from 7% by weight was analysed by X-ray diffractometry and the respective diffractograms are shown in Figure 11.

[0147] In particular, Figure I la) shows the diffractogram of the non-reduced and consequently non-metallised composite material product. It can be noted from this diffractogram an amorphous phase consisting of the polymeric material, flanked by a crystalline phase consisting of the nickel chloride salt.

[0148] As highlighted in Figure 11b), after metal deposition the amorphous phase disappears, a high peak relative to nickel appears, while the peak relative to the metal salt disappears.

[0149] An EDS analysis was also carried out on the 7% by weight composite material product, whose spectrograms are respectively shown in Figure 12 for the 3D-printed product containing metal salts both internally and superficially, in Figure 13 for the reduced product and in Figure 14 for the metallised product.

[0150] In the spectrum of Figure 12, a very high peak of Cl is observed, compared to a lower concentration of Nickel. In Figure 13, after the complete reduction of surface nickel chloride, a considerable increase in Ni concentration can be observed, accompanied by a significant reduction in Cl. Finally, in the graph of Figure 14, post-metallisation, the carbon and oxygen peaks drop considerably which indicates that the polymer surface is completely coated with NiP, while the Cl peaks have definitely disappeared, the Nickel peaks have increased considerably compared to those in Figure 13, and the phosphorus peak appears for the first time.

[0151] Therefore, the EDS analysis also confirms the results shown by the XRD analysis. These results were also confirmed by percentage atomic analysis, producing the results shown in the table below.

[0152] Table 5.

[0153] The following Figures 15 and 16 show the mapping of Ni and Cl components for the non-reduced and reduced sample, respectively, at 10000X magnification. It can be observed that the components are more homogeneous in the reduced form and that the amount of Cl atoms is lower. However, a considerable amount of Cl atoms is still present due to the fact that the elemental mapping EDS partially penetrates the three- dimensional structure, highlighting the nickel chloride not affected by the reduction reaction.

[0154] In Figure 15, the metal salt particles can also be identified through combined EDS and SEM. An example of this can be found within the small circle. With this particular method, particles with an average diameter of ±4 pm are not ignored by the analysis. Figure 17 compares the morphology of the non-reduced surface against the activated one. The increase in roughness induced by the reduction process is evident. In fact, the reduced metal has a much smaller volume than metal salt. Thus, the process leaves cavities, only partially added with reduced metal, at the metal salt particles

[0155] Using EDS mapping, the amount of the components on the surface was calculated and the results are shown in the following table:

[0156] Table 6.

[0157] A Vickers hardness test was carried out on the non-reduced samples and the results are shown in Figure 18. It can be observed from the curve that the hardness of the composite decreases when the mass % of Nickel chloride increases. This could be explained by the fact that anhydrous nickel chloride absorbs ultraviolet light, interfering with the cross-linking process, during 3D printing.

[0158] This results in a reduction in the mechanical properties of the product. From the results reported and discussed above, it can be concluded that the product whose 3D-printed polymer matrix is obtained from a 7% by weight nickel chloride composite mixture is the optimal choice when the mechanical properties of the composite product are important.

[0159] Copper deposition on copper sulphate-added composite material products

[0160] Figure 19a) shows the printed product added with 7% by weight of copper sulphate (1), the same in reduced form (2) and finally the one (3) on which a layer of copper was deposited by chemical deposition. It can be seen that the amount of metal salt is not sufficient to fully activate and coat the product. Hence the decision to use composite material products added with 10 % by weight and 13 % by weight of copper sulphate, respectively, for further characterisation of these products.

[0161] Indeed, Figure 19b) shows that metallisation of the composite product added with 10 % by weight of copper sulphate results in complete coverage, which means that only composite products added with salt concentrations greater than 10 % by weight can be used for metallisation by chemical plating. SEM images of the composite material product as-printed a), the one in reduced form b) and the metallised one c) are respectively shown in Figure 20 at 5000X magnification. It can be observed that the composite material product as-printed and added with the copper sulphate particles has the same wavy structure as the one added with nickel chloride, a wavy structure imparted by the printing process.

[0162] Similarly to what has been observed for the nickel-chloride-added metal, the surface of this product becomes rougher (as shown in Figure 20b)), creating in this case as well an etching effect that favours the adhesion of the subsequent metal layer.

[0163] From Figure 20c) it can be noted that the metallisation process is complete, as there is a uniform layer with smaller metal grains than nickel grains. Furthermore, it can be observed that the coating is less uniform than the one obtained with NiP.

[0164] From Figure 20d), which represents a cross-section of the metallised composite product, it can be observed that hydrogen gas bubbles are absent in the coating. In this case, a thickness of approximately 1 micron is obtained, as expected based on the deposition time.

[0165] In Figure 21, the morphology of the copper deposit obtained on composite materials containing different concentrations of copper sulphate can be observed. It can be seen that the final metallic layer applied on composite material added with 13% by weight of copper sulphate is less uniform than the one obtained on material added with 10% by weight of copper sulphate. It can also be seen from Figure 21a) that the metallised product obtained from the composite material added with 7% by weight of copper sulphate is characterised by the presence of holes, which shows that the surface is not completely coated.

[0166] The XRD diffractograms shown in Figure 22 concern the composite product added with 13% by weight of copper sulphate, respectively, as-3D-printed (Figure 22a) and metallised (Figure 22b).

[0167] From the comparison of these diffractograms it can be noted that the copper sulphate peaks present in Figure 22a) are no longer present in Figure 22b), as they have been replaced by the metal copper peaks.

[0168] EDS analyses of the composite material product 10% by weight of copper sulphate before reduction, after reduction and after deposition of the copper layer are shown in Figures 23a), 23b) and 23c) respectively, and show behaviours similar to those observed in the corresponding products obtained from composite materials containing nickel chloride.

[0169] In fact, the S and O content decreases after reduction, where a large part of the sulphate is dissolved in the aqueous sodium borohydride solution. On the other hand, the second copper peak increases significantly due to the formation of elemental copper, formed on the surface as a result of reduction.

[0170] On the other hand, looking at the EDS spectrum of the metal deposition (Figure 23c)), it can be noted that the peak relating to copper has significantly increased compared to the one of the spectrum shown in Figure 22b), while all the peaks relating to the other components are completely negligible, thus demonstrating that the entire surface has been completely coated with copper.

[0171] The reported results are confirmed using atomic masses, whose values are given in the table below.

[0172] Table 7.

[0173] The elemental mapping of the sample as-is (as-printed) from 10 % by weight of CuSCU is shown in Figure 24. From this figure, the average particle diameter can be calculated. For example, when you look in the circle shown in the figure, you can spot a copper sulphate particle and observe that the diameter is approximately 1 pm. It can be observed that these particles are much smaller than those of nickel chloride. Finally, it can be observed that the elements are uniformly arranged on the regular surface of the product as-printed.

[0174] Figure 25 shows the combined mapping of SEM images with EDS spectra. It can be noted also in this figure that the particle size is slightly smaller than in NiCh (between 1 and 2 pm). The following table shows the elemental composition of the sample being analysed. T1

[0175] Table 8.

[0176] It can be observed that the amount of copper and sulphur is very similar, so it can be inferred that each copper atom corresponds to approximately one sulphur atom (as expected observing the stoichiometry of the copper sulphate salt).

[0177] This cannot be verified for oxygen, due to the fact that oxygen is also present in the cross-linked resin. In any case, this allows us to see that copper sulphate is present on the surface of the composite material product as-3D-printed.

[0178] Since no metal deposition by chemical plating with low metal salt content is observed at certain areas of the printed product, the morphology and composition at these areas were studied. In particular, it was observed that the top surface of the product, i.e. the one in contact with the printing plate, has difficulties from the point of view of metallisation. The analysis was carried out on the composite product as-printed and obtained from the 13% by weight mixture of copper sulphate. Figure 26 shows the elemental mapping of the upper surface. In this figure, the copper sulphate particles are identified by combining the elemental mapping.

[0179] Comparing this mapping with the side surface of the composite material product as- printed and obtained from the composite with 13% by weight of copper sulphate, a lower intensity is observed in the elemental EDS mapping on the top surface. Also when comparing the normalised atomic percentage, it can be seen that the concentration of copper is much lower on the top surface than on the other surfaces, as it can be seen in the following table.

[0180] Table 9.

[0181] When analysing the atomic concentration of the top surface compared to that of the other surfaces of the composite material product 13% by weight of copper sulphate, a lower atomic concentration of the elements forming copper sulphate is observed than on the top surface.

[0182] This is also confirmed by the SEM images at 10000X magnification in Figure 27. Comparing the figure on the right, where an SEM image of the side surface is shown, with the figure on the left, representing the top surface, a lower presence of copper sulphate particles can be observed in the latter. Furthermore, it can be observed that the surface structure of the two surfaces is also different.

[0183] This phenomenon is explained by Figure 28, where three-dimensional printing is schematically reproduced.

[0184] From this figure, one can clearly see the causes of this phenomenon, namely:

[0185] - the roughness of the side and bottom surfaces;

[0186] - the lowest probability for metal salt particles to reach the top surface due to gravity;

[0187] - the movement of the particles when lowering the building plate when printing the product.

[0188] When 3D printing the product, the side surfaces have a certain microscopic roughness that is created during the layering steps typical of 3D printing.

[0189] The bottom surface also shows some roughness, caused by the irregularities of the surface exposure to UV radiation.

[0190] Due to this roughness of the side and bottom surfaces, a larger contact area is formed between the 3D product and the liquid-state resin. So, in these cases, the probability of the metal salt being on the surface is higher than the probability of it being on the top surface, which, by the way, is completely smooth and planar precisely because it is in direct contact with the printing plate.

[0191] Secondly, metal salts have more possible ways of reaching the bottom and side surfaces unlike what happens on the top surface. Finally, the downward movement of the building plate during the cross-linking step causes the particles to be dragged towards the side surfaces, creating more product build-up on these surfaces.

[0192] Tests on the hardness of the 3D-printed product obtained from the composite mixtures with different concentrations of copper sulphate (7% by weight, 10% by weight and 13% by weight) are shown in Figure 29.

[0193] It can be observed that the hardness of the composite increases as the concentrations of copper sulphate increase. This can be explained by the fact that copper sulphate has a low absorption in UV light, with the result that it poorly affects the 3D printing process; therefore, the mechanical properties of the composite increase as the concentration of the metal salt alone increases. This shows that the product obtained from the composite material containing 13% by weight of the total weight of the composite allows to obtain a product with better mechanical properties than those containing 7 and 10% by weight of the total weight of the composite.

[0194] NiP deposition on products obtained from composite material added with NH4Fe(SO4)2

[0195] The process according to the present invention makes it possible to obtain a final metallised product with a metal or alloy (NiP) other than that contained in the metal salt (NH4Fe(SO4)2) added into the composite material and superficially reduced to elemental metal Fe.

[0196] The product obtained by 3D printing from a composite material containing 16% by weight of the total weight of the composite material is shown in Figure 30a). Its SEM characterisation, at 10000X magnification, is also shown in Figure 30b) for the as- printed, in Figure 30c) for the surface-reduced and in Figure 30d) for the NiP-coated. A test was also carried out to metallise a 3D product from composite material containing the aforesaid salt at 10% by weight of the total weight of the composite mixture, but at this concentration, metal deposition did not occur. In fact, the iron salt has an unfavourable stoichiometry compared to the previously used nickel and copper salts. Where they contain atomic 33% (NiCh) and atomic 16.66 % (CuSO4) of metal, iron ammonium sulphate contains only atomic 6.25 %.

[0197] Therefore, the concentration of this metal salt within the composite mixture must be maintained at a minimum of 16% by weight of the total weight of the mixture. Furthermore, by using said salt together with cross-linkable resins of plant origin such as those described above, it is possible to obtain a 3D-printed product capable of activating the chemical deposition of a metal on said product and completely biodegradable.

[0198] The XRD diffractogram of the product with the surface as it is (i.e. as-printed) is shown in Figure 31a) and the peak revealing the presence of the salt NH4Fe(SO4)2 can be noted.

[0199] After NiP deposition (Figure 31b)), one can see how the iron ammonium sulphate peaks decrease significantly, showing that this salt has almost completely disappeared at the surface, and that a peak of considerable intensity is present due to NiP deposition on the sample surface.

[0200] The results of the hardness tests carried out on the pure biodegradable resin product and on the product obtained by 3D printing from the composite material containing 16% by weight of iron ammonium sulphate salt are shown in Figure 32. From this Figure, it can be noted that the addition of the aforesaid salt substantially reduces the hardness of the composite material product as-printed. This is caused by reasons substantially similar to those given for the composite material product containing NiCh. However, it can be noted that the biodegradable resin used here has a higher hardness than the Anycubic base resin used in the preparation of composite materials containing nickel chloride and copper sulphate.

[0201] Salt concentrations greater than or equal to 16% in the composite material object of the invention are therefore the only option to obtain a complete NiP coating.

[0202] MULTILAYER DEPOSITION

[0203] Once the outer surface of the 3D print has been made conductive by a first metal layer, further metal layers can be added by means of electrolytic deposition.

[0204] For example, a copper layer was electrolytically deposited using a commercial copper electrolyte on a 3D-printed composite product containing 7% by weight of the total weight of nickel chloride and completely coated with a NiP layer (Figure 33a)).

[0205] The SEM image of the resulting sample is shown in Figure 33b) and from it one can see how the surface of the 3D-printed, completely NiP-coated product can in turn be coated with a thick layer of electrolytically deposited copper. Furthermore, from the EDS spectrum (Figure 34), one can observe only the presence of high intensity peaks of copper, while the other elements are negligible.

[0206] Multilayer metal deposition gives excellent results even on complex geometries.

[0207] As an example, Figure 35 shows the statue of an owl coated with a layer of copper (Fig.35a), then coated with a layer of nickel (Fig.35b) and finally coated with a layer of gold (Fig.35c). The first layer was applied by chemical plating of copper onto the product obtained by 3D printing and the subsequent layers by electrolytic deposition. This proves that with the technique described in the present invention, it is possible to apply several metal layers onto products obtained with complex geometry.

[0208] SELECTIVE METAL DEPOSITION BY CHEMICAL PLATING

[0209] Selective activation of flat surfaces

[0210] In the case of selective activation, an aqueous sodium borohydride solution was loaded into a 10 pL cartridge to be used in a piezoelectric drop-on-demand inkjet printer. Compared to the previously described non-selective reduction, the use of a jet technique entailed a number of additional problems which have been solved. The main one is that sodium borohydride is unstable in water, tending to develop hydrogen. In order to overcome this problem, the concentration of this reducing agent was halved (10 g / L instead of 20 g / L), the pH was taken to 12 by adding sodium hydroxide and the temperature was carefully controlled. In particular, the latter must be below 25°C. In order to check the influence of the printing parameters, a 10 g / L aqueous solution of sodium borohydride at pH 12 was ejected using the standard parameters for printing water-based inks onto a surface of an product obtained by 3D printing from a composite mixture containing 10% by weight of copper sulphate. Square patterns were printed with different drop spacing DS (10 pm, 15 pm, 20 pm and 30 pm).

[0211] Subsequently, a layer of copper was deposited on each of these samples by chemical plating.

[0212] The results of this test are shown in Figures 36a), 36b), 36c) and 36d) respectively. Figures 37a) for DS 10 pm, 37b) for DS 15 pm, 37c) for DS 20 pm and 37d) for DS 30 pm depict the SEM analysis of the different samples shown in Figure 36.

[0213] It can be seen from the SEM images that none of the samples have a continuous copper layer on the polymer. In Figure 37a), a discontinuous deposition is observed, in Figure 37b) and 37c), deposition is only observed in the grooves of the polymer roughness. Finally, it was confirmed that there is no metal deposit on the sample with a DS of 30pm.

[0214] From these results, it can be concluded that none of the samples gave optimal results in terms of metal deposition by chemical plating on an product obtained by 3D printing from a composite mixture containing 10% by weight of copper sulphate of the total weight of said composite mixture, because none of the samples has sufficient metal salt on the surface, which, once reduced, allows for the deposition of a metal layer by chemical plating.

[0215] Applying the aqueous solution by ink-jet printing at the aforesaid concentration, pH and temperature, it was therefore not possible to obtain significant results.

[0216] Using a sample obtained by printing from a composite mixture containing 13% of copper sulphate and the aqueous solution at the same pH, concentration and temperature as defined above with a DS of 20pm, 3 layers of reducing solution were then applied to the composite material sample and the results of this test are shown in Figures 38a) and 38b).

[0217] Although only some parts of the composite have been metallised, this is sufficient to make the composite sample conductive.

[0218] However, when trying to print a more complex pattern, the resulting reduced layer was not uniform and the deposited copper layer was not conductive. For example, a simple circuit was printed on a sample obtained by 3D printing and metallised by deposition by means of chemical plating for 30 minutes.

[0219] The resulting sample is shown in Figure 39a). From this image, it can be seen that even in this case the metal deposition is not uniform and shows some irregularities in certain parts of the metal layer. Connected to an electrical circuit to check conductivity, it was verified that it was conductive only in some areas.

[0220] From the result of this test, it was therefore concluded that it was necessary to increase the sodium borohydride concentration and use longer metal deposition times.

[0221] In fact, the SEM image at 100X magnification of the circuit showed that the copper layer did not completely cover the pattern, and therefore the circuit was not conductive. For this reason, it was decided to increase the concentration of sodium borohydride in water to 20 g / L, using a chemical plating metal deposition time of 50 minutes. The pH was raised to 13 with a DS of 10 and 20 pm.

[0222] The results of these tests are shown in Figure 40a) and 40b), which show that both samples are conductive.

[0223] In the SEM images shown in Figures 41a) and 41b), images are shown at different magnifications (100 - 150X) of only the reduced circuit with inkjet printing with DS of 10pm in Figure 40a). These images show that the circuit 40a) on which the metal was deposited is sufficiently uniform.

[0224] Figure 42 shows that circuit 40a) is capable of switching on a green light LED. Selective activation of inclined surfaces

[0225] The selective activation method described herein can also be applied to variously inclined surfaces. For example, a pattern was printed on the complex structure visible in Figures 43a) (structure in perspective view) and 43b) (view from above), using an aqueous solution of 20 g / L of sodium borohydride.

[0226] This complex structure was obtained by 3D printing from a composite mixture containing 13% by weight of copper sulphate of the total weight of said mixture.

[0227] ADS of 10pm was used for inkjet printing because of the indented structure. In Figure 44, it is possible to see how the DS changes as a function of changes in the orientation of the surface. The calculation of the DS (drop spacing) for the longest indentation is as follows:

[0228] So a DS of 14pm is sufficient for surface activation.

[0229] Metal deposition was successfully conducted, as shown in Figure 45. In it (Figure 45a)), it can be noted that even if the planar and inclined surfaces are conductive, the pattern as a whole is not conductive due to the disconnection at the edges.

[0230] This problem can be solved in two ways: either by increasing the number of printing passes through the reducing agent or by increasing the exposure time in the plating or electrolytic bath in order to deposit more metal and overcome interruptions. In the experimental test shown in Figure 45, the sample was immersed in a commercial electrolyte bath for 20 minutes at 40 mA / cm2. In Figures 45b), 45c) and 45d) it can be observed that the entire metallised surface is conductive.

Claims

Claims1. Three-dimensional composite material product comprising: i) a three-dimensional matrix made of cross-linked resin obtained by 3D printing, having the desired shape of the final product; ii) particles of a metal salt, arranged inside said matrix and entirely or partially on one or more of said surfaces; iii) metal particles in the elemental state completely or partially arranged on at least one or more surfaces of said matrix wherein:• said metal particles iii) are the reduced elemental form of the metal ion of the metal salt ii); and are arranged:• completely on one or more surfaces other than those completely occupied by the metal salt particles, or• partially on one or more of the same surfaces on which the metal salt particles are arranged.

2. Product according to claim 1, wherein said metal salts are selected from:• Ni salts• Cu salts• Fe salts• Pd salts• Pt salts• Au salts• Ag salts.

3. Product according to claim 1 or 2 of the three-dimensional cross-linked composite material according to claim 2 wherein said salts are selected from: NiCh • 6H2O, CuSO4• 5H2O, NH4Fe(SO4)2• 12H2O.

4. Product according to any one of claims 1-3, wherein said cross-linked resin matrix i) is obtained by stereolithography (SLA) from a UV-cross-linkable liquid resin commonly used for 3D printing by digital liquid projection DLP, said resin not being capable of dissolving the metal salt.

5. Three-dimensional metallised product obtained by applying a metal layer by chemical plating to one or more surfaces or parts thereof of the product according to any one of claims 1-4.

6. Product according to claim 5 wherein the metal layer applied by chemical plating is different from that contained in the metal salt.

7. Product according to any one of claims 5 or 6 containing one or more metal layers applied by electrolytic means on said at least one layer applied by chemical plating.

8. Process for preparing the metallised product according to any one of claims 5-7 comprising the following steps: a) Mixing and grinding at least one metal salt in at least one UV-cross-linkable liquid resin mixture in a ceramic ball mill for a time between 110 and 130 minutes, preferably 120 minutes, gradually increasing the speed of the mill until the maximum speed of between 200 and 400 rpm, preferably 300 rpm is reached; b) separating the balls by a sieve and obtaining a resin suspension in which the at least one metal salt is evenly dispersed; c) 3D printing the suspension obtained in the previous step to obtain a crosslinked resin-based product wherein metal salt particles are dispersed both superficially and internally; d) reducing the metal salt on at least one surface or part thereof with a reducing agent, preferably selected from sodium borohydride, sodium bi s(2-methoxy ethoxy) aluminium hydride, hydrazine, diisobutylaluminium hydride, more preferably sodium borohydride; e) depositing by chemical plating at least one layer of metal to obtain the metallised product.

9. Process according to claim 8, wherein, when the metal salts are in hydrated form, prior to step a) they are submitted to dehydration at a temperature of between 140° and 230°C, preferably in a closed container with a removable lid to allow gradual evaporation of the water, the lid being subsequently removed until an anhydrous dry powder is obtained, the size of which is reduced by loading said powder into a powder crusher.

10. Process according to any one of claims 8 or 9, wherein the content of the metal salts to be added in step a) is between 5 and 20 %, preferably between 7% and 16 % by weight of the total weight of the final mixture obtained.

11. Process according to any one of claims 8-10, wherein step b) provides that the balls after being separated from the mixture are loaded back into the mill together with other resin to recover any ground material remaining attached to them and the resulting mixture is further ground and sieved.

12. Process according to any one of claims 8-11, wherein, when step d) is carried out on at least one complete surface, said at least one surface is immersed in an aqueous solution of sodium borohydride at a concentration of between 8 and 25 g / 1 for a time between 40 seconds and 90 seconds, preferably 60 seconds.

13. Process according to any one of claims 8-11, wherein when step d) is carried out on at least one surface partially, it comprises the following steps: dl) a sodium borohydride solution is prepared at concentrations between 8 and 25 g / 1, preferably between 10 g / 1 and 20 g / 1, and loaded into a cartridge for use in a piezo ink-jet printer; d2) the aqueous solution prepared in the previous step dl) is applied by ink-jet printing to a portion or according to a desired path of at least one surface of said product, resulting in the selective reduction.

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