METHOD FOR PRODUCING STRUCTURES FIELD OF THE INVENTION

The present invention relates to the field of methods for producing structures and layered structures for its use as a mould or as a mould part in polymer moulding processes or sheet metal stamping processes.

BACKGROUND

There are several process to obtain structures that might be used as mould, tie or tool parts. For example, patent application W020070133A1 discloses the production of a counterform comprising an inorganic material such as a ceramic material generated by additive 3D printing and coated by spraying graphite. Said counterform is used as a mould to produce a metallic alloy form or structure by densification (by pressure sintering). In order to produce the final ceramic mould, a highly energy consuming sintering process is required. In addition, once created, a ceramic mould is difficult to post process or repair.

There are several documents that describe the formation of moulds that comprise layers of different materials. For example, GB360743A describes a mould formed by spraying a metallic coating on a permanent form. US 2006/0097423 A1 describes a mould including a unitary metallic structure having a foam core. In addition, US 2006/0097423 A1 describes that the mould is generated by spray deposition of metallic layers over a foam model. However, those methods might lead to layered structures wherein the layers can separate or crack under temperature changes. In addition, the core layers of the structures obtained from the previous methods are permanent.

Therefore, there is a clear need for new structures, such as those for moulds or tool parts, with improved features and quality and for new cost-effective production methods of said structures with a reduced production time.

BRIEF DESCRIPTION OF THE INVENTION

The authors of the present invention have developed a method for producing a structure suitable to be used as a mould, a machined layered structure obtainable by the method, a structure obtained by the method of the invention, the use of the machined layered structure and the use of the structure as a mould or as a mould part, preferably for polymer moulding processes or sheet metal stamping processes. The method of the present invention allows the production of a more robust layered structure with less defects, for example, the number of cracks on the upper layer is reduced in the layered structure of the invention. In addition, the authors of the present invention have observed that the layers of the layered structure of the invention keep joined together even under significant changes of temperature. Furthermore, the method of the invention is cost-effective and lead to the production of structures with complicated and detailed shapes. In addition, the method of the invention allows a reduction of the fabrication time and leads to lightweight robust structures.

Therefore, a first aspect of the invention is directed to a method for producing a structure, said method comprising the following steps: i) additive manufacturing (AM) a polymeric structure; wherein the polymeric structure comprises a water soluble polymer; ii) coating at least part of the polymeric structure obtained in step (i) with a first composition comprising zinc to generate a first layered structure; iii) coating the first layered structure with a second composition comprising at least a metal element to generate a second layered structure; wherein the second composition has the same or lower thermal expansion coefficient than the first composition; and iv) machining the second layered structure to generate a machined layered structure; v) removing the polymeric structure from the second layered structure of step (iii) or from the machined layered structure of step (iv) to obtain a structure; and vi) optionally, adding at least one reinforcing layer to the structure obtained in step (v).

In a second aspect, the present invention is directed to a machined layered structure obtained by a method comprising: i) additive manufacturing (AM) a polymeric structure; wherein the polymeric structure comprises a water soluble polymer; ii) coating at least part of the polymeric structure obtained in step (i) with a first composition comprising zinc to generate a first layered structure; iii) coating the first layered structure with a second composition comprising at least a metal element; wherein the second composition has the same or lower thermal expansion coefficient than the first composition; and iv) machining the second layered structureto generate a machined layered structure; and wherein the machined layered structure comprises:

- a polymeric structure comprising a water soluble polymer;

- a first coating layer covering at least part of the surface of the polymeric structure, said first coating layer comprising a first composition comprising zinc;

- a second coating layer on top of the first coating layer, wherein said second layer comprises a second composition comprising at least one metal element, and said second coating layer having the same or lower thermal expansion coefficient than the first coating layer. In another aspect, the present invention is directed to a structure obtained by the method of the invention, wherein said structure comprises:

- at least a first layer of a first composition comprising zinc;

- a second layer on top of the first layer, wherein said second layer comprises a second composition comprising at least one metal element, and said second layer having the same or lower thermal expansion coefficient than the first layer; and

- optionally a reinforcing layer.

In another aspect, the present invention is directed to the use of the machined layered structure of the invention as a mould or as a mould part.

In another aspect, the present invention is directed to the use of the structure of the invention as a mould or as a mould part.

A further aspect relates to a mould for polymers comprising the machined layered structure or the structure of the invention.

FIGURES

Figure 1 : Layered structure obtained according to step (ii) of the process of the invention after having applied a Zn coating layer onto a polymer substrate.

Figure 2: Layered structure obtained according to step (iii) of the process of the invention after having applied a coating layer of an AI5Mg alloy onto the coating layer of Zn.

Figure 3: Structure obtained according to step (v) the process of the invention after removal of the polymer substrate. Figure 4: Steps of the process according to the invention. Left to right: 1) soluble polymer; 2) soluble polymer + Zn coating layer; 3) soluble polymer + Zn coating layer + AI5Mg coating layer; 4) soluble polymer + Zn coating layer + AI5Mg coating layer + steel layer + milling; 5) soluble polymer + Zn coating layer + AI5Mg coating layer + steel layer + milling + polishing.

Figure 5: Steps of a process according to the invention: (a) water soluble polymer + Zn coating layer + AI5Mg coating layer + Invar36; (b) polymer removal; c) milling of the final shape.

Figure 6: Structure resulting from a process where a coating layer of AI5Mg is applied onto a polymer substrate.

Figure 7: Structure resulting from a process where a coating layer of AI5Si is applied onto a polymer substrate.

Figure 8: Structure resulting from a process where a coating layer of AI5Mg is applied onto a steel substrate.

Figure 9. Polymeric structure with metal coating (left: aluminum, center: zinc/aluminium, right: no coating).

DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. As used herein, the singular forms “a” “an” and “the” include plural reference unless the context clearly dictates otherwise.

Method

As defined above, a first aspect of the invention is directed to a method for producing a structure comprising the following steps: i) additive manufacturing (AM) a polymeric structure; wherein the polymeric structure comprises a water soluble polymer; ii) coating at least part of the polymeric structure obtained in step (i) with a first composition comprising zinc to generate a first layered structure; iii) coating the first layered structure with a second composition comprising at least a metal element to generate a second layered structure; wherein the second composition has the same or lower thermal expansion coefficient than the first composition; and iv) machining the second layered structure to generate a machined layered structure; v) removing the polymeric structure from the second layered structure of step (iii) or from the machined layered structure of step (iv) to obtain a structure; and vi) optionally, adding at least one reinforcing layer to the structure obtained in step (v).

Step (i)

The step (i) of the method of the invention is directed to additive manufacturing (AM) a polymeric structure; wherein the polymeric structure comprises a water-soluble polymer.

In the context of the present invention, the expression “additive manufacturing” is the process of creating a structure by building it one layer at a time; preferably by a layer by layer method.

In an embodiment, the additive manufacturing (AM) step is performed by printing; preferably by 3D printing; more preferably by Fused Filament Fabrication (FFF) 3D printing.

In an embodiment, the additive manufacturing (AM) step is performed by printing at an infill printing density of the polymeric printed structure below 100 %; preferably below 99%; more preferably below 95%.

In a particular embodiment, the infill printing density of the polymeric printed structure is between 99% and 60%; preferably between 92% and 65%; more preferably between 95% and 70%.

In the context of the present invention, the “infill printing density” defines the amount of polymeric material used on the printed material as known in the art of additive manufacturing (AM).

The authors of the present invention have found that a printed polymeric structure with a reduced density is more suitable for the adhesion of a subsequent coating. In addition, material consumption and printing time is reduced.

In the context of the present invention, the expression “water-soluble polymer” is understood as known in the art, i.e. as a polymer that might be dissolved or disperse in an aqueous solution; preferably in water.

In an embodiment, the water-soluble polymer of step (i) is selected from polysaccharide polymers, acrylic polymers, ethylene glycol polymers, sulfonic acid polymers, vinyl alcohol polymers, their derivatives and mixtures thereof.

In the context of the present invention, the term “polysaccharide polymers” is understood as polymers comprising chains of saccharide units, such as monosaccharide or disaccharide units, preferably joined by glyosidic bonds. Non-limiting examples of “polysaccharide polymers” are dextran, pullulan, and cellulose derivatives such as hydro propyl methylcellulose (HPMC).

In the context of the present invention, the term “acrylic polymers” is understood as polymers obtained from derivatives of acrylic and methacrylic acids such as poly(acrylic acid) (PAA) and poly(methylacrylic acid) (PMAA).

In a particular embodiment, the water-soluble polymer of step (i) is selected from dextran, pullulan, hydro propyl methylcellulose (HPMC), poly(acrylic acid) (PAA), poly(methylacrylic acid) (PMAA), poly(ethylene glycol) (PEG), poly(styrenesulfonic acid), poly (vinyl alcohol), polybutene diol vinyl alcohol (BVOH) and mixtures thereof. More preferably, the water- soluble polymer is poly(vinyl alcohol).

In a particular embodiment, the polymeric structure consist of a water-soluble polymer as the ones defined above.

Step (7)

The step (ii) of the method of the invention is directed to coating at least part of the polymeric structure obtained in step (i) with a first composition comprising zinc to generate a first layered structure comprising a layer of a first composition comprising zinc.

In a particular embodiment, step (ii) comprises coating all the surface of the polymeric structure obtained in step (i) to generate a first layered structure.

In an embodiment, the first composition consist of metallic zinc or of an alloy comprising zinc.

In another embodiment, the first composition comprises zinc and at least an additional metal selected from the list consisting of Au, Ag, Pt, Na, Cu, V, Cr, Mn, Cd, Al, Fe, Ni, Ti, Co and mixtures thereof; preferably Al, Fe, Ni, Ti, Co and mixtures thereof; more preferably Al, Fe, Ni, and mixtures thereof; much more preferably Al.

In a particular embodiment, the first composition is an alloy comprising at least 30 wt.% of Zn of the total weight of the alloy; preferably at least a 40 wt.%; more preferably at least 50 wt.%; even more preferably at least a 60 wt.%; even much more preferably at least 70 wt.%.

In another particular embodiment, the first composition is an alloy comprising zinc and aluminum, wherein the zinc is present in more than 50 wt% and the aluminum is present in less than 50 wt%. In another particular embodiment, the first composition is an alloy consisting of zinc and aluminum, wherein the zinc is present in more than 50 wt% and the aluminum is present in less than 50 wt%.

More preferably, the alloy comprises 51-80 wt% of zinc and 20-49 wt% of aluminum, more preferably the alloy comprises 60-75 wt% of zinc and 25-40 wt% of aluminum. In a more preferred embodiment, the alloy consists of 51-80 wt% of zinc and 20-49 wt% of aluminum, more preferably the alloy consists of 60-75 wt% of zinc and 25-40 wt% of aluminum.

In another particular embodiment, the first composition is an alloy comprising zinc and iron, wherein the zinc is present in more than 75 wt% and the iron is present in less than 25 wt%. In another particular embodiment, the first composition is an alloy consisting of zinc and iron, wherein the zinc is present in more than 75 wt% and the iron is present in less than 25 wt%.

In another particular embodiment, the first composition is an alloy comprising zinc and nickel, wherein the zinc is present in more than 75 wt% and the nickel is present in less than 25 wt%. In another particular embodiment, the first composition is an alloy consisting of zinc and nickel, wherein the zinc is present in more than 75 wt% and the nickel is present in less than 25 wt%.

In another particular embodiment, the first composition is an alloy comprising zinc, aluminum, iron and nickel, wherein the aluminum is present in less than 50 wt%, the iron is present in less than 25 wt%, the nickel is present in less than 25 wt%, the remaining being zinc. In another particular embodiment, the first composition is an alloy comprising 40-60 wt% of zinc, 10-20 wt% of aluminum, 5-10 wt% of iron and 5-10 wt% of nickel. In another particular embodiment, the first composition is an alloy consisting of 40-60 wt% of zinc, 10-20 wt% of aluminum, 5-10 wt% of iron and 5-10 wt% of nickel.

The authors of the present invention have observed that a higher weight % of zinc in the first composition leads to a better adhesion of the coating to the polymeric structure and to less cracks in the layered structure.

In a particular embodiment, the coating of step (ii) is performed by spray coating at room temperature (i.e. between 10 and 35 °C). In an embodiment, the first composition comprising zinc is a composition comprising zinc particles; particularly further comprising aluminum and/or additives such as rosin.

In a particular embodiment, the coating of step (ii) is performed by spray coating; more preferably by spray coating melted zinc or a melted alloy comprising zinc. In particular, the spray coating may be performed by any technology known in the art; preferably by arc or plasma spray techniques. In a particular embodiment, the coating of step (ii) is performed at a temperature of less than 600°C; preferably of less than 550°C; more preferably of between 200 and 500 °C; more preferably between 250 and 450°C. In a particular embodiment, the coating of step (ii) is performed at about the melting temperature of Zn; preferably at about 420°C.

In a particular embodiment, the first layered structure obtained in step (ii) comprises a polymeric structure and at least a first composition coating layer; preferably the first composition coating layer has a thickness of at least 0.01 microns; preferably at least 1 microns; more preferably of at least 0.1 mm; even more preferably of at least 1 mm; even more preferably at least 1 cm.

In a particular embodiment, the layered structure obtained in step (ii) comprises a polymeric structure and at least a first composition coating layer; preferably the first composition coating layer has a thickness of between 0.1 micron and 100 mm; preferably of between 1 and 80 mm; more preferably between 1.5 and 50 mm; even much more preferably between 2 and 50 mm.

The thickness will depend on the geometry of the structure to be manufactured. It shall be the minimum possible, provided that a coating equal to or greater than the final geometry of the product or structure is ensured over the entire surface.

In a particular embodiment, the coating step (ii) is repeated at least 2 times; preferably at least 3 times; more preferably at least 5 times; even more preferably at least 10 times.

In a particular embodiment, the coating step (ii) is repeated between 1 and 20 times; preferably between 2 and 10 times; more preferably is repeated between 3 and 5 times.

Step (iii)

The coating step (ii) further comprises a second coating step; particularly, coating the first layered structure with a second composition; wherein the thermal expansion coefficient of the second composition is the same or lower that the thermal expansion coefficient of the first composition.

This second composition comprises at least a metal element.

In an embodiment, the coating with the second composition is performed after the coating of the first composition.

In an embodiment, the second composition comprises at least a metal element; preferably the metal is selected from the list consisting of Au, Ag, Pt, Na, Cu, V, Cr, Mn, Cd, Al, Fe, Zn, Ni, Ti, Co, Si and mixtures thereof; preferably Al, Fe, Zn, Ni, Ti, Co, Si and mixtures thereof; more preferably Al Fe, Zn, Ni, and mixtures thereof; much more preferably the second composition comprises Al.

In an embodiment, the second composition consist of at least a metal selected from the list consisting of Au, Ag, Pt, Na, Cu, V, Cr, Mn, Cd, Al, Fe, Zn, Ni, Ti, Co and mixtures thereof; preferably Al, Fe, Zn, Ni, Ti, Co and mixtures thereof; more preferably Al, Fe, Zn, Ni, and mixtures thereof; much more preferably the second composition consists of Al.

In another embodiment, the second composition is a preceramic material or a mixture of preceramic materials, a metal or an alloy. In a particular embodiment, the second composition is a preceramic material or a mixture of preceramic materials.

In an embodiment, the preceramic material or mixture of preceramic materials comprise Al or Si; preferably Si. In a more particular embodiment, the preceramic material is a preceramic polymer.

In the context of the present invention, the term “preceramic material” is understood as a material that under appropriate conditions (for example under a heating step at temperatures over 500°C, over 600°C or over 900°C and optionally in the absence of oxygen such as in an inert atmosphere) is converted into a ceramic compound. In another embodiment, the second composition is a metal or an alloy; preferably the second composition is an alloy comprising Al, Mg, Si, Fe, Zn, Ni, Ti, Co or a mixture thereof; preferably comprising Al, Mg, Si, Fe, Zn, Ni or a mixture thereof.

In another embodiment, the second composition is a metal; preferably is Al, Fe, Zn, Ni, Ti or Co; preferably is Al, Fe, Zn or Ni; more preferably is Al.

In another preferred embodiment, the second composition is an alloy comprising Al and a metal selected from Mg and Si. More preferably, the alloy comprises at least 90 wt% of Al and less than 10 wt% of Mg or Si.

In another embodiment, the second composition is steel, invar or aluminum; preferably is invar or aluminum.

In another embodiment, the second layered structure of step (iii) comprises a first coating layer and a second coating layer; wherein the first coating layer comprises the first composition and the second coating layer comprises the second composition.

In an embodiment, the step (iii) of the method of the invention comprises at least a further coating step; preferably a third coating step with a third composition.

In another embodiment, the second layered structure of step (iii) comprises an additional layer; preferably a third coating layer. In another embodiment, the third composition is a preceramic material or a mixture of preceramic materials, a metal or an alloy. More preferably, the third composition is an iron alloy or a nickel-iron alloy. Even more preferably, the third composition is steel or invar, particularly invar36®, provided that the third composition is different from the second composition.

In a more particular embodiment, if the second composition and/or third composition is a preceramic material or a mixture of preceramic materials, the method of the present invention comprises a further step of heating at a temperature of at least 500°C, preferably at least 600°C; more preferably at least 900°C the resulting layered structure. In an even more particular embodiment the heating step is performed under air or under an inert atmosphere such as N2.

In a particular embodiment, the value of the thermal expansion coefficient of the first coating layer is the same or higher than the value of the thermal expansion coefficient of the second coating layer of the second layered structure obtained in step (iii). In a particular embodiment, the value of the thermal expansion coefficient of the second coating layer is the same or higher than the value of the thermal expansion coefficient of the third coating layer of the layered structure obtained in step (iii).

In the context of the present invention, the expression “thermal expansion coefficient” refers to the linear change in size of a material per degree change in temperature measured at a constant pressure as known in the art, for example, the linear thermal expansion coefficient of Zn is 30*1 O ^{6 0} C ¹ (m/m°C).

In a particular embodiment, the thermal expansion coefficient of the first composition is between 10* 10 ⁶ and 45 * 10 ⁶ m/m°C; preferably between 15* 10 ⁶ and 35 * 10 ⁶ (m/m°C).

In an embodiment, the first and second compositions are the same or different compositions; preferably different; more preferably are metals or alloys.

Step (iv)

The step (iv) of the method of the invention is directed to machining the second layered structure of step (iii) to generate a machined layered structure.

In an embodiment, the machining step (iv) is performed by a technique selected from milling, stamping, bending, punching, turning, pressing, sparkling, grinding, polishing and any combination of techniques thereof; preferably from milling, turning, pressing, sparkling, grinding, polishing and any combination of techniques thereof.

In an embodiment, the machining step (iv) is performed by a stamping step followed by a polishing step of the surface of the layered structure.

In the context of the present invention, the term “milling” is understood as the process of machining using rotary cutters to remove material by advancing a cutter into a material as known in the art. In an embodiment, the milling step might be done by a bed mill, a box mill, a c-frame mill, a floor mill, a gantry mill, a horizontal boring mill, a jig borer mill, a knee mill, a planer-style mill, a ram-type mill or a turret mill.

In an embodiment, the stamping step is a metal stamping process.

The machining step (iv) is performed on the second layered structure comprising a polymeric structure coated with a first composition comprising zinc and with a second composition comprising at least a metal element resulting from step (iii).

In a particular embodiment, the method of the invention comprises an additional machining step after step (v) of removing the polymeric structure and/or after the optional step (vi). In an embodiment, a machining step is performed on the structure obtained in step (v) or on the structure obtained in step (vi) of the method of the invention.

In an embodiment, the second layered structure of step (iii), the machined layered structure of step (iv) and/or the structure of any of steps (v) or (vi) has a complex shape. In a particular embodiment, the machined layered structure of step (iv) or the structure of steps (v) or (vi) comprises two sides wherein one side is concave (a hollow side) and the other side is convex. The shape of the machined layered structure of step (iv) or of the structure of any of steps (v) or (vi) may be formed as consequence of the shape of the polymeric structure of step (i) and/or one or more machining step(s).

The authors of the present invention have found that by using an additive manufacturing technique for creating the polymeric structure of step (i), the second layered structure of step (iii), the machined layered structure of step (iv) and/or the structure of any of steps (v) or (vi) having complex shapes are obtained.

Step (v)

The step (v) of the method of the present invention is directed to removing the polymeric structure from the second layered structure of step (iii) or from the machined layered structure of step (iv) to obtain a structure; preferably to obtain a structure comprising a first layer comprising zinc and a second layer comprising at least a metal element.

In a particular embodiment, the removal step (v) of the method of the present invention is performed by dissolving said polymeric structure in an aqueous solution.

In a more particular embodiment, the aqueous solution comprises a basic compound; preferably a hydroxide; more preferably KOH or NaOH; even more preferably NaOH.

In a particular embodiment, the removal step (v) of the method of the present invention is performed at a temperature of at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 °C; preferably at a temperature of between 10 and 99°C; preferably of between 30 and 95 °C; more preferably of between 40 and 80°C; even more preferably of between 50 and 70°C.

In a particular embodiment, the removal step (v) of the method of the present invention is performed at atmospheric pressure or at a pressure higher than 1 atm.

In a particular embodiment, the removal step (v) of the method of the present invention is performed under mixing; preferably under mechanical mixing. In a particular embodiment, the removal step (v) of the method of the present invention is performed until the complete dissolution of the polymer structure.

In a particular embodiment, the structure resulting from step (v) comprises at least one first layer comprising zinc and at least one second layer comprising a metal element; preferably at least one first layer consisting of the first composition comprising zinc and at least one second layer consisting of the second composition comprising a metal element; more preferably at least one first layer consisting of zinc or of a zinc alloy and at least one second layer comprising a metal element.

In a particular embodiment, the structure resulting from step (v) comprises several layers having the same or different composition; preferably comprising at least one layer consisting of zinc or of a zinc alloy.

In a more particular embodiment, the structure resulting from step (v) comprises at least one layer comprising zinc or a zinc alloy and at least one layer comprising a second composition comprising at least a metal element.

Step (vi)

The step (vi) of the method of the present invention is directed to optionally, adding at least one reinforcing layer to the structure obtained in step (v).

In an embodiment, the structure obtained in step (v) comprises a first layer comprising zinc and a second layer comprising at least a metal element. In a more particular embodiment, the reinforcing layer is added to the structure obtained in step (v) to obtain a structure comprising a reinforcing layer being in contact to the first layer comprising zinc (i.e. coating at least part of the first layer).

In step (vi) a structure is obtained, particularly wherein said structure comprises at least one reinforcing layer; wherein the reinforcing layer is in contact with the first, second or third layer; preferably with the first layer; more preferably wherein the first layer is on top of the reinforcing layer.

In a particular embodiment, the at least reinforcing layer comprises cement or a polymeric material; preferably the at least reinforcing layer consist of concrete or of a polymer; preferably concrete or a thermostable polymer. In a particular embodiment, the cement is hydraulic or non-hydraulic cement. In a particular embodiment, the polymeric material comprises a polymeric composite material comprising reinforcing additives such as silicates.

In a particular embodiment, the polymeric material consist of a polymeric composite material comprising reinforcing additives such as silicates.

In a particular embodiment, the polymeric material comprises a polymer selected from the group consisting of nylon, polypropylene, polystyrene, fluoropolymer, polyurethane, epoxy resins, their derivatives and combinations thereof; preferably polyurethane, epoxy resins, their derivatives and combinations thereof; more preferably the polymeric material is a polyurethane foam.

In a particular embodiment, the polymeric material consist of a polymer selected from the group consisting of nylon, polypropylene, polystyrene, fluoropolymer, polyurethane, epoxy resins, their derivatives and combinations thereof; preferably polyurethane, epoxy resins, their derivatives and combinations thereof; more preferably the polymeric material is a polyurethane foam.

In an embodiment, the addition of at least one reinforcing layer to the structure obtained in step (v) is done by any technique known in the art; preferably by spraying methods; more preferably by arc or plasma spraying methods.

In a particular embodiment, if the structure comprises a hollow side, the addition of at least one reinforcing layer to the structure obtained in step (v) is done by the following steps:

(a) filling said hollow side completely or partially by a precursor or precursor mixture of the reinforcing layer of step (vi) and

(b) optionally drying and/or curing the precursor or precursor mixture of step (a).

In a particular embodiment, if the structure comprises two sides wherein one side is concave and the other side one is convex, the addition of at least one reinforcing layer to the structure obtained in step (v) is done by the following steps:

(a) filling said concave side completely or partially by a precursor or precursor mixture of the reinforcing layer of step (vi) and

(b) optionally drying and /or curing the precursor or precursor mixture of step (a). In an embodiment, the filling of the concave side is performed by pouring a mixture comprising a precursor or a precursor mixture of the reinforcing layer; preferably wherein the precursor or precursor mixture comprises a polymeric precursor or a cement precursor.

In a particular embodiment, the concave side of the structure is formed by the first layer comprising zinc.

Machined layered structure

A further aspect of the present invention is directed to a machined layered structure obtained by a method comprising: i) additive manufacturing (AM) a polymeric structure; wherein the polymeric structure comprises a water soluble polymer; ii) coating at least part of the polymeric structure obtained in step (i) with a first composition comprising zinc to generate a first layered structure; iii) coating the first layered structure with a second composition comprising at least a metal element to generate a second layered structure; wherein the second composition has the same or lower thermal expansion coefficient than the first composition; and iv) machining the second layered structure to generate a machined layered structure; and wherein the machined layered structure comprises:

- a polymeric structure comprising a water soluble polymer;

- a first layer coating at least part of the surface of the polymeric structure, said first layer comprising a first composition comprising zinc;

- a second layer on top of the first layer, wherein said second layer comprises a second composition comprising at least one metal element, and said second layer having the same or lower thermal expansion coefficient than the first layer.

Steps (i), (ii), (iii) and (iv) of the method for obtaining the machined layered structure of the invention have the same characteristics as steps (i), (ii), (iii) and (iv) of the method of the invention described above in any of their particular embodiments.

Alternatively, another aspect of the present invention is directed to a machined layered structure comprising:

- a polymeric structure comprising a water soluble polymer; - a first layer coating at least part of the surface of the polymeric structure, said first layer comprising a first composition comprising zinc;

- a second layer on top of the first layer, wherein said second layer comprises a second composition comprising at least one metal element, and said second layer having the same or lower thermal expansion coefficient than the first layer.

In an embodiment the first layer is coating completely the surface of the polymeric structure.

In an embodiment, the water-soluble polymer is selected from polysaccharide polymers, acrylic polymers, ethylene glycol polymers, sulfonic acid polymers, vinyl alcohol polymers, their derivatives and mixtures thereof.

In a particular embodiment, the water-soluble polymer is selected from dextran, pullulan, hydro propyl methylcellulose (HPMC), poly(acrylic acid) (PAA), poly(methylacrylic acid) (PMAA), poly(ethylene glycol) (PEG), poly(styrenesulfonic acid), poly (vinyl alcohol), polybutene diol vinyl alcohol (BVOH) and mixtures thereof. More preferably, the water- soluble polymer is poly(vinyl alcohol).

In a particular embodiment, the polymeric structure consist of a water-soluble polymer, such as the ones defined above.

In an embodiment, the first layer covers all the surface of the polymeric structure, preferably the first layer forms a continuous coating; more preferably forms a continuous homogeneous coating.

In an embodiment, the first composition comprising zinc of the first layer consists of zinc or of an alloy comprising zinc.

In an embodiment, the first composition further comprises at least a metal selected from the list consisting of Au, Ag, Pt, Na, Cu, V, Cr, Mn, Cd, Al, Fe, Ni, Ti, Co and mixtures thereof; preferably Al, Fe, Ni, Ti, Co and mixtures thereof; more preferably Al Fe, Zn, Ni, and mixtures thereof; much more preferably Al.

In a particular embodiment, the first composition is an alloy comprising at least 30 wt.% of Zn of the total weight of the alloy; preferably at least a 40 wt.%; more preferably at least 50 wt.%; even more preferably at least a 60 wt.%; even much more preferably at least 70 wt.%.

In another particular embodiment, the first composition is an alloy comprising zinc and aluminum, wherein the zinc is present in more than 50 wt% and the aluminum is present in less than 50 wt%. In another particular embodiment, the first composition is an alloy consisting of zinc and aluminum, wherein the zinc is present in more than 50 wt% and the aluminum is present in less than 50 wt%. More preferably, the alloy comprises 51-80 wt% of zinc and 20-49 wt% of aluminum, more preferably the alloy comprises 60-75 wt% of zinc and 25-40 wt% of aluminum. In a more preferred embodiment, the alloy consists of 51-80 wt% of zinc and 20-49 wt% of aluminum, more preferably the alloy consists of 60-75 wt% of zinc and 25-40 wt% of aluminum.

In another particular embodiment, the first composition is an alloy comprising zinc and iron, wherein the zinc is present in more than 75 wt% and the iron is present in less than 25 wt%. In another particular embodiment, the first composition is an alloy consisting of zinc and iron, wherein the zinc is present in more than 75 wt% and the iron is present in less than 25 wt%.

In another particular embodiment, the first composition is an alloy comprising zinc and nickel, wherein the zinc is present in more than 75 wt% and the nickel is present in less than 25 wt%. In another particular embodiment, the first composition is an alloy consisting of zinc and nickel, wherein the zinc is present in more than 75 wt% and the nickel is present in less than 25 wt%.

In another particular embodiment, the first composition is an alloy comprising zinc, aluminum, iron and nickel, wherein the aluminum is present in less than 50 wt%, the iron is present in less than 25 wt%, the nickel is present in less than 25 wt%, the remaining being zinc.

In another particular embodiment, the first composition is an alloy comprising 40-60 wt% of zinc, 10-20 wt% of aluminum, 5-10 wt% of iron and 5-10 wt% of nickel. In another particular embodiment, the first composition is an alloy consisting of 40-60 wt% of zinc, 10-20 wt% of aluminum, 5-10 wt% of iron and 5-10 wt% of nickel.

In an embodiment, the first and/or second layer have a thickness of at least 0.01 microns; preferably at least 1 micron; more preferably of at least 0.1 mm; even more preferably of at least 1 mm; more preferably at least 1 cm. In a particular embodiment, the second layer coats partially or completely the surface of the first layer; preferably coats completely the surface of the first layer. In an embodiment, the second layer comprises a second composition comprising at least one metal element, and said second layer has the same or lower thermal expansion coefficient than the first layer of the machined layered structure.

In another embodiment, the second layer is a preceramic material or a mixture of preceramic materials, ceramic material(s), a metal or an alloy. In a particular embodiment, the second composition is a preceramic material, a mixture of preceramic materials or ceramic material(s).

In an embodiment, the preceramic material, a mixture of preceramic materials or ceramic material(s) comprise Al or Si; preferably Si. In a more particular embodiment, the preceramic material is a preceramic polymer. In an even more particular embodiment, the ceramic material(s) comprise S1O ₂ , SiN, or AI ₂ O ₃ .

In an embodiment, the second composition comprises at least a metal element selected from the list consisting of Au, Ag, Pt, Na, Cu, V, Cr, Mn, Cd, Al, Fe, Zn, Ni, Ti, Co and mixtures thereof; preferably Al, Fe, Zn, Ni, Ti, Co and mixtures thereof; more preferably Al Fe, Zn, Ni, and mixtures thereof; much more preferably Al.

In an embodiment, the second composition consist of at least a metal selected from the list consisting of Au, Ag, Pt, Na, Cu, V, Cr, Mn, Cd, Al, Fe, Zn, Ni, Ti, Co and mixtures thereof; preferably Al, Mg, Si, Fe, Zn, Ni, Ti, Co and mixtures thereof; more preferably Al, Mg, Si, Fe, Zn, Ni, and mixtures thereof; much more preferably Al.

In a particular embodiment, the second layer or the second composition consist of a metal or a metal alloy; preferably of a metal alloy; more preferably of a metal alloy comprising Al, Mg, Si, Fe, Zn, Ni, Ti, Co or a mixture thereof.

In another preferred embodiment, the second layer or composition is an alloy comprising Al and a metal selected from Mg and Si. More preferably, the alloy comprises at least 90 wt% of Al and less than 10 wt% of Mg or Si.

In a particular embodiment, the machined layered structure comprises at least an additional layer; preferably a third layer on top of the second layer. In another embodiment, the third layer is a preceramic material or a mixture of preceramic materials, ceramic material(s), a metal or an alloy.

In a particular embodiment, the machined layered structure comprises: - a polymeric structure consisting of a water soluble polymer; wherein said water soluble polymer is selected from polysaccharide polymers, acrylic polymers, ethylene glycol polymers, sulfonic acid polymers, vinyl alcohol polymers, their derivatives and mixtures thereof;

- a first layer coating the surface of the polymeric structure, said first layer consisting of zinc;

- a second layer on top of the first layer, wherein said second layer consists of a metal alloy comprising Al, Mg, Si, Fe, Zn and/or Ni, preferably Al; and said second layer having the same or lower thermal expansion coefficient than the first layer; and

- optionally a third layer on top of the second layer.

Structure comprising zinc

An aspect of the present invention is directed to a structure obtained by the method of the invention, wherein said structure comprises:

- a first layer comprising a first composition comprising zinc;

- a second layer on top of the first layer, wherein said second layer comprises a second composition comprising at least one metal element, and said second layer having the same or lower thermal expansion coefficient than the first layer; and

- optionally at least one reinforcing layer.

Alternatively, another aspect of the present invention is directed to a structure comprising:

- a first layer comprising a first composition comprising zinc;

- a second layer on top of the first layer, wherein said second layer comprises a second composition comprising at least one metal element, and said second layer having the same or lower thermal expansion coefficient than the first layer; and

- optionally at least one reinforcing layer.

In an embodiment, the structure comprises a third layer on top of the second layer.

The characteristics and embodiment of the first layer, of the second layer and of the third layer of the structure are the same as the ones of the machined layered structure described above in any of the particular embodiments mentioned. In an embodiment, the at least one reinforcing layer is below the first layer. In an embodiment, the first layer is on top of said at least one reinforcing layer; preferably the first layer coats partially or completely the surface of the reinforcing layer; preferably it coats completely the surface of the reinforcing layer.

In a particular embodiment, the reinforcing layer comprises cement or a polymeric material; preferably the at least reinforcing layer consist of concrete or of a polymer; preferably concrete or a thermostable polymer.

In a particular embodiment, the polymeric material comprises a polymeric composite material comprising reinforcing additives such as silicates.

In a particular embodiment, the polymeric material consist of a polymeric composite material comprising reinforcing additives such as silicates.

In a particular embodiment, the polymeric material comprises a polymer selected from the group consisting of nylon, polypropylene, polystyrene, fluoropolymer, polyurethane, epoxy resins, their derivatives and combinations thereof; preferably polyurethane, epoxy resins, their derivatives and combinations thereof; more preferably the polymeric material is a polyurethane foam.

In a particular embodiment, the polymeric material consist of a polymer selected from the group consisting of nylon, polypropylene, polystyrene, fluoropolymer, polyurethane, epoxy resins, their derivatives and combinations thereof; preferably polyurethane, epoxy resins, their derivatives and combinations thereof; more preferably the polymeric material is a polyurethane foam.

In a more particular embodiment, the reinforcing layer has a thickness of at least 1 mm; preferably of at least 2 mm; more preferably of at least 10 mm; more preferably of at least 1 cm.

In a particular embodiment, the structure comprises:

- a reinforcing layer;

- a first layer on top of said reinforcing layer; wherein said first layer consist of zinc; and

- a second layer on top of the first layer, wherein said second layer consists of a metal or metal alloy comprising Al, Mg, Si, Fe, Zn and/or Ni, and said second layer having the same or lower thermal expansion coefficient than the first layer. All the characteristics described for structure, layered structure or the machined layered structure of the method of the present invention in the particular embodiments can be applied to the structure, layered structure or the machined layered structure of the invention.

Mould

In another aspect, the present invention is directed a mould comprising the machined layered structure of the invention or the structure of the invention in any of their particular embodiments; preferably consisting of the machined layered structure or the structure of the invention in any of its particular embodiments.

Uses

In another aspect, the present invention is directed to the use of the machined layered structure of the invention in any of its particular embodiments as a mould or as a mould part; preferably for moulding polymers.

An alternative aspect of the invention is directed to a method for moulding comprising a mould comprising the machined layered structure of the invention in any of its particular embodiments; preferably a method for moulding polymers.

In another aspect, the present invention is directed to the use of the structure of the invention in any of its particular embodiments as a mould or as a mould part; preferably for moulding polymers.

An alternative aspect of the invention is directed to a method for moulding comprising a mould comprising the structure of the invention in any of its particular embodiments; preferably a method for moulding polymers.

As used herein, the terms "about" or “around” means a slight variation of the value specified, preferably within 10 percent of the value specified. Nevertheless, the term "about" or the term “around” can mean a higher tolerance of variation depending on for instance the experimental technique used. Said variations of a specified value are understood by the skilled person and are within the context of the present invention. Further, to provide a more concise description, some of the quantitative expressions given herein are not qualified with the term “about". It is understood that, whether the term “about" is used explicitly or not, every quantity given herein is meant to refer to the actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including equivalents and approximation due to the experimental and/or measurement conditions for such given value.

All the features described in this specification (including the claims, description and drawings) and/or all the steps of the described method can be combined in any possible combination, with the exception of combinations of such mutually exclusive features and/or steps.

The invention will be further illustrated by means of examples which should not be interpreted as limiting the scope of the claims. EXAMPLES

The invention is illustrated by means of the following examples which in no case limit the scope of the invention.

EXAMPLE 1 : Method to prepare a structure with two layers.

In this example, a structure (for example a mould or tool) was produced following the multi- step process described below:

Step 1: A polymeric structure was made by Fused Filament Fabrication (FFF) 3D printing of polyvinyl alcohol (PVA). A printing density below 100% was used.

Results showed that the use of a printing density of below 100% increased the adhesion of the metal composition to the polymeric core in the subsequent steps. Step 2: A first coating of zinc was sprayed on top of the polymeric structure by arc or plasma spraying method to generate a first layered structure (see figure 1). This process was done either manually or with a robot. The zinc was melted when sprayed.

Step 3: A second coating of an aluminum alloy (AI5Mg, an alloy containing 95 wt% of Al and 5 wt% of Mg) was sprayed by the same method that the one described on step 2 to obtain a second layered structure. The authors have observed that when the thermal expansion coefficient of the second coating is equal or lower than that of the preceding layer no debonding or delamination of the coatings are observed.

Step 4. The layered structure was machined to obtain the desired shape (see figure 2). Step 5: The internal core was removed by immersing the layered structure in water to obtain a structure (see figure 3).

Example 2. Method to prepare a structure with three layers

The same procedure as example 1 was followed to prepare a structure having an additional coating layer.

Step 1: a polymeric structure was made by Fused Filament Fabrication (FFF) 3D printing of polyvinyl alcohol.

Step 2: A first coating of zinc was sprayed on top of the polymeric structure by arc or plasma spraying method to generate a first layered structure. This process was done either manually or with a robot. The zinc was melted when sprayed.

Step 3: A second coating of an aluminum alloy (AI5Mg, containing 95 wt% of Al and 5 wt% of Mg) was sprayed by the same method that the one described on step 2 to obtain a second layered structure.

Step 4: A third layer of steel was sprayed by the same method that the one described on step 2 to obtain a third layered structure having three coating layers.

Step 5. The layered structure was milling and polishing.

Step 6: The internal core was removed by immersing the layered structure in water to obtain a structure.

Figure 4 shows the different structures obtained after each step: 1) soluble polymer; 2) soluble polymer coated with Zn; 3) soluble polymer coated with a first layer of Zn and a second layer of AI5Mg; 4) soluble polymer coated with a first layer of Zn, a second layer of AI5Mg and a third layer of steel after being milled; 5) soluble polymer coated with a first layer of Zn, a second layer of AI5Mg and a third layer of steel after being polished.

Example 3. Method to prepare a structure with three layers

A similar procedure as described in example 2 was followed but substituting steel in the third layer with a coating of invar36®. The process of milling was done after having removed the soluble polymer (see figure 5).

In all the examples, a robust layered structure was obtained with almost no defects and wherein the layered structure kept joined together even under significant changes of temperature.

Example 4 (comparative). Method to prepare a structure having a non-Zn coating layer on a polymeric structure.

For comparative purposes, structures were prepared by directly spraying a coating composition of an aluminum alloy (AI5Mg, an alloy containing 95 wt% of Al and 5 wt% of Mg, or AI5Si, an alloy containing 95 wt% of Al and 5 wt% of Si) onto a soluble polymer substrate.

A polymer degradation was observed in both cases due to high temperature exposure along with a high temperature thermal expansion gradient (see figures 6 and 7). Thus, this process is not feasible and confirms that a coating layer comprising Zn is required to firstly coat the polymer substrate.

Example 5 (comparative): Method to prepare a structure wherein a coating layer having a higher thermal expansion coefficient is added on a substrate.

For comparative purposes, a structure was prepared by adding a coating composition of AI5Mg on a steel substrate.

A lack of bounding was observed due to the fact that the thermal expansion coefficient of the AI5Mg is higher than the steel (see figure 8). It confirms that is not feasible to add a coating layer having a higher thermal expansion coefficient over a layer having less thermal expansion coefficient.

Example 6: Comparative Experiment

Machined layered structures have been obtained by the following combination of steps, wherein each step is as described above on Example 1: steps 1 and 4, obtaining a uncoated machined polymeric structure; steps 1, 2 (coating with aluminum) and 4, obtaining a machined layered structure coated with aluminum; and steps 1 , 2 (coating with zinc), 3 (coating with aluminum) and 4 obtaining a machined layered polymeric structure coated with a first layer of zinc and with a second layer of aluminum. Figure 9 shows the machined layered structures obtained. More particularly, Figure 9 shows a hydrosoluble thermoplastic polymeric structure coated with aluminum (left), coated with- a first layer of zinc and a second layer of aluminum (center) and a similar structure but without a coating (right). Figure 9 shows that the layered product coated with a first layer of zinc has no cracks or less cracks than when coating with Al.