Dual-cure formulation for 3D printing

Abstract

The present invention relates to a dual-cure formulation for 3D printing, characterised in that it comprises, in percentage by weight: 15-50% of an acrylic resin; 20-60% of an epoxy resin; 10-60% of a coupling agent consisting of an acrylate or methacrylate monomer comprising at least one hydroxyl (-OH) group; 0.5-5% of a free-radical photoinitiator; and 0.5-5% of a thermal cationic initiator. This formulation allows the production, by 3D printing, of a first partially cured material that is capable of withstanding major deformations and can be transformed in a second curing step into a rigid material, characterised in that it has a high modulus of elasticity and high tensile strength.

Description

[0001] DESCRIPTION

[0002] DUAL CURING FORMULATION FOR 3D PRINTING

[0003] TECHNICAL SECTOR

[0004] The present invention belongs to the technical field of the chemical industry. In particular, it relates to a novel dual-curing formulation for 3D printing.

[0005] BACKGROUND OF THE INVENTION

[0006] Light-cured resins used in Additive Manufacturing (AM) have generated great interest in the scientific and industrial community, due to their versatility in terms of ease of generating geometries and structures without the need for a mold or other industrial tool.

[0007] However, the potential use of this technology in much of the manufacturing industry remains limited by the availability and versatility of currently available materials [MBA Tamez and I. Taha, Additive Manufacturing 37 (2021) 101748],

[0008] Although a wide variety of acrylic resins are used today in the formulation of these materials, they have notable limitations in terms of their mechanical performance, processing, and versatility. Parts processed from these materials do not guarantee good structural performance in applications requiring high strength and durability.

[0009] Regarding versatility, there are processing challenges, as current processes do not allow for modifying the geometry of the parts to achieve a specific geometry that meets the required structural demands. Furthermore, current processes require the use of supports which, while helpful in generating parts with complex geometries, can alter the geometry of the printed parts, creating problems when the goal is to manufacture complex parts with precise geometry.

[0010] The change in geometry of printed parts is associated with the mechanical properties of each type of resin. For example, rigid photocurable resins used in 3D printing do not show significant deformation after post-curing and behave as rigid materials, preventing substantial changes in the geometry of the parts due to their low strain. Conversely, flexible photocurable resins allow for substantial deformation, but they are not structurally strong, as they cannot withstand significant stress, unlike rigid resins.

[0011] Another limitation of this technology is related to the generation of large-sized elements, because large pieces can suffer swelling or contraction, causing internal stresses or deformations in the layer forming processes.

[0012] Another parameter to consider is the liquid state of the resin, as this plays a fundamental role in both processing and determining the final mechanical properties of the printed parts. The physical characteristics of the resin are intrinsically linked to its formulation, specifically the molecular weight of the base material, which directly affects the resin's viscosity—a crucial parameter for processing. Typically, resins with superior mechanical properties have larger constituent molecules [Z. Weng et al., Nature Communications 14 (2023) 1-9], which means they are more viscous. This correlation presents a double challenge in processing. On the one hand, resins with superior mechanical properties require longer processing times due to their higher molecular weight, highlighting the need for more complex configurations.Similarly, higher viscosity resins require longer processing times due to the redistribution of the resin across the entire printing area. Conversely, resins with lower viscosities, attributed to lower molecular weights, offer faster processing times. However, this accelerated processing comes at a cost. Resins with lower viscosities tend to exhibit inferior mechanical properties, making them susceptible to behaving as brittle or ductile materials with undesirable mechanical properties. This disadvantage limits their suitability for structural applications, as they may present deficiencies in terms of strength and durability. The balance between molecular weight, viscosity, processing time, and resulting mechanical properties confirms the challenge that exists in optimizing resin formulations for diverse applications [J. Zhao et al., Additive Manufacturing 41 (2021) 101962].

[0013] The dual-curing methodology addresses the ability to generate photocurable 3D printed parts. Initially, the reaction activation is considered in two stages: the first through the inclusion of a photoactivator and the second through a thermal activator. In the first stage, the part is generated in the 3D printer through photopolymerization, where residual groups of the same or another monomer or oligomer may be present, capable of being thermally activated to complete the reaction. To date, general studies have focused on enabling the processing of solid parts in 3D printing and subsequently achieving the desired mechanical properties through the reaction of the residual groups present in the matrix via a thermal reaction. However, the potential of the intermediate material with configurations designed to obtain different properties in each of its states has not yet been explored (Pagac, M. et al.)., Polymers, 2021, 13, 598 or Haohuan W. et al., Polymer, vol. 282, 2023, 126153).

[0014] The present invention addresses the challenges detailed above, offering a formulation that allows obtaining by 3D printing a first partially cured material, capable of withstanding large deformations, which can be transformed into a rigid material in a second curing stage, characterized by having a high modulus of elasticity and high tensile strength.

[0015] DESCRIPTION OF THE INVENTION

[0016] Thus, a first object of this invention is a dual-curing formulation for 3D printing, characterized in that it comprises, by weight percentage: a) Between 15% and 50%, preferably between 20% and 30%, of an acrylic resin; b) Between 20% and 60%, preferably between 40% and 60%, of an epoxy resin, preferably of the cycloaliphatic type; c) Between 10% and 60%, preferably between 20% and 50%, of a coupling agent, which may preferably consist of an acrylate or methacrylate monomer comprising at least one hydroxyl group (-OH) in its formulation, such as methacrylate or hydroxyethyl acrylate;d) Optionally, between 0% and 15%, preferably between 5% and 10%, of a crosslinking regulator, which may consist of a polyol comprising at least one hydroxyl group, the polyol being preferably liquid or of relatively low molecular weight (preferably between 200 and 600 g / mol, for example, 400 g / mol), thus ensuring that the viscosity of the formulation is low (usually between 15 and 30 cP at 30°C). Preferably, the polyol may be polyethylene glycol; e) Between 0.5% and 5%, preferably 2%, of a radical photoinitiator, understood as an initiator that generates free radicals upon exposure to UV light, such as phenylbis(2,4,6-trimethylbenzoyl)phosphine;f) Between 0.5% and 5%, preferably 2%, of a thermal cationic initiator, understood as an initiator capable of activating a cationic polymerization reaction by thermal activation, such as N-(p-methoxybenzyl)-N,N-dimethylanilinium hexafluoroantimonate; g) Optionally, between 0.1% and 5%, preferably 0.5%, of a thermal radical initiator, understood as an initiator capable of generating free radicals by thermal activation, such as 1,1-bis(tert-amylperoxycyclohexane).

[0017] This formulation can be used in 3D printing. Thus, the described formulation can be used in a 3D printing process characterized in that it comprises: a) a first UV curing stage in which a first material in an intermediate state is obtained (also referred to as intermediate material), understood as a material that has only been cured by UV radiation.This first stage is carried out up to a phase prior to the complete curing of the material, resulting in an intermediate material consisting of a ductile material, made up of an acrylic network, which is characterized by being able to withstand unit deformations greater than 100% and by having a modulus of elasticity that can be between 1 and 13 MPa, measured according to ISO 527-1 / -2; and b) a second thermal curing stage, in which the intermediate material obtained in the first stage is transformed, through the reaction of the epoxy resin monomers, into a cured or final material, which is more rigid, and this material is characterized by having a modulus of elasticity that can reach values ​​between 10 and 2000 MPa, measured according to ISO 527-1 / -2, and a tensile strength that can exceed 60 MPa, measured according to ISO 527-1 / -2.

[0018] In particular, the intermediate material obtained in the first curing stage allows its geometry to be modified and adapted to specific needs, adopting geometries that, currently, could only be obtained using supports. In addition to these advantages, the material in its intermediate state offers the benefit of being used to manufacture large parts, as it creates bonds between the pieces, capable of withstanding the deformations caused by expansion or contraction stresses during the printing process. This is because the entire surface is activated by epoxide groups present in the epoxy resin, which allows the formation of covalent bonds at the interface of the bonds.

[0019] DETAILED DESCRIPTION OF THE INVENTION

[0020] To complete the general description of the object of the invention, the physical and mechanical properties of the material obtained from two particular embodiments of the claimed formulation are detailed below, both in its intermediate state (where the acrylic and methacrylate groups are cured by UV radiation), and in its final state, after a thermal curing process.

[0021] In the first particular embodiment, the formulation comprises hydroxyethyl methacrylate, HEMA, as a coupling agent. In particular, the formulation of the first embodiment is characterized in that it comprises, by weight percentage: a) 19.01% of an acrylic resin; b) 28.51%, 38.02%, or 47.53% of hydroxyethyl methacrylate as a coupling agent; c) a cycloaliphatic epoxy resin, specifically 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, in percentages of 47.53%, 38.02%, or 28.51%.d) 2.57% of a radical photoinitiator consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; e) 1.90% of a thermal cationic initiator consisting of a 50% by weight solution of N-(p-methoxybenzyl)-N,N-dimethylanilinium hexafluoroantimonate as initiator and 5% by weight of triethanolamine as stabilizer, in propylene carbonate as solvent; and f) 0.48% of a thermal radical initiator, consisting of a 60% by weight solution of 1,1-bis(tert-amylperoxy)cyclohexane, preferably with a mixture of aliphatic hydrocarbons (such as, for example, aliphatic naphtha with CAS number 64741-65-7).

[0022] In the second particular embodiment, the formulation comprises hydroxyethyl acrylate (HEA) as a coupling agent and polyethylene glycol (PEG) with a molecular weight of 400 g / mol as a crosslinking regulator. Specifically, the formulation of the second embodiment is characterized in that it comprises, by weight percentage: a) 19.01% of an acrylic resin; b) 38.02% hydroxyethyl acrylate as a coupling agent; c) 0%, 4.75%, or 9.50% polyethylene glycol (PEG, 400 g / mol) as a crosslinking regulator; d) a cycloaliphatic epoxy resin, namely bis(3,4-epoxycyclohexylmethyl) adipate, in a percentage of 38.02%, 33.27%, or 28.52%. e) 2.57% of a radical photoinitiator consisting of phenylbis(2,4,6-thmethylbenzoyl)phosphine oxide;f) 1.90% of a thermal cationic initiator consisting of a 50% by weight solution of N-(p-methoxybenzyl)-N,N-dimethylanilinium hexafluoroantimonate as initiator and 5% by weight of triethanolamine as stabilizer, in propylene carbonate as solvent; and g) 0.48% of a thermal radical initiator, consisting of a 60% by weight solution of 1,1-bis(tert-amylperoxy)cyclohexane, preferably with a mixture of aliphatic hydrocarbons (such as, for example, aliphatic naphtha with CAS number 64741-65-7).

[0023] Tables 1 and 2 define the nomenclature of each formulation, indicating their compositions in weight percentages. Tables 3 and 4 define the properties of the intermediate and final materials obtained from a UV radiation curing process (in the case of the intermediate material), followed by a thermal curing process (in the case of the final material), for the formulation corresponding to the first embodiment (Table 3) and the formulation corresponding to the second embodiment (Table 4).

[0024] Dynamic single-cantilever tests were also performed, measuring the storage modulus (E'), loss modulus (E"), loss factor (Tan (E” / E')), and maximum loss factor (Maximum Tan (E” / E')). A 0.1% strain oscillation and a temperature ramp of 3°C / min were applied, with the storage modulus measured at 60°C and 25°C for the formulation described in Table 3 and Table 4, respectively, according to ISO 6721-10. The apparent viscosity was determined at 30°C using an IKA-Werke GmbH & Co. KG SP6'7 screw, according to ISO 2555-18. The depth of cure (Cd) was measured in micrometers (µm) following the procedure described in Jacobs, P., “Rapid prototyping & manufacturing: fundamentals of stereolithography”, Society of Manufacturing Engineers, 1992, using an intensity of 4.73 mW / cm 2for 35 seconds for the formulation defined in Table 3 and 10 seconds for the formulation described in Table 4.

[0025] Specifically, the properties shown in tables 3 and 4 are as follows:

[0026] Maximum tensile strength, measured according to ISO 527-1 / -2,

[0027] . Modulus of elasticity (E), measured in accordance with ISO 527-1 / -2,

[0028] . Unit strain, measured according to ISO 527-1 / -2,

[0029] Maximum shear stress, using custom-made tooling. The results are corroborated with pure shear tests.

[0030] Storage module (E'), measured in accordance with ISO 6721-10,

[0031] . Loss modulus (E”), measured in accordance with ISO 6721-10,

[0032] . Loss factor (Tan (E” / E')), measured in accordance with ISO 6721-10,

[0033] . Apparent viscosity, measured in accordance with ISO 2555-18,

[0034] . Curing depth or thickness (Cd), procedure based on Jacobs, P., “Rapid prototyping & manufacturing: fundamentals of stereolithography”, Society of Manufacturing Engineers, 1992.

[0035] Table 1: Nomenclature and composition of the first embodiment, where compositions are based on total weight percentages. RAC is defined as acrylic resin and AC as hydroxyethyl methacrylate. The code number in the nomenclature refers to the rounded percentages of acrylic resin (RAC) and coupling agent, hydroxyethyl methacrylate (AC).

[0036] Table 2: Nomenclature and composition of the second embodiment, where the compositions are based on total weight percentages. RAC is defined as acrylic resin, HEA as hydroxyethyl acrylate, and PEG as polyethylene glycol 400 g / mol. The code number in the nomenclature refers to the rounded percentages of acrylic resin (RAC), coupling agent, hydroxyethyl acrylate (HEA), and polyethylene glycol 400 g / mol (PEG).

[0037] Table 3: Characterization of the intermediate material (mi) and the final, fully cured material (cc) obtained from the formulation corresponding to the first realization, in the three variations of the percentage of coupling agent (AC30, AC40 and AC50), where RAC20 refers to 19.01% acrylic resin.

[0038] Table 4: Characterization of the intermediate material (mi) and fully cured material (cc) obtained from the formulation corresponding to the second realization, in the three variations of the percentage of polyethylene glycol (PEGO, PEG5 and

[0039] PEG10), where RAC20 refers to 19.01% acrylic resin and HEA40 to 38.02% hydroxyethyl acrylate.

[0040] BRIEF DESCRIPTION OF THE FIGURES To complement the description and in order to facilitate the understanding of the characteristics of the invention, a series of figures are included with this descriptive report in which, for illustrative and non-limiting purposes, the following has been represented:

[0041] Figure 1 shows a graph of tensile stress, maximum unit strain and modulus of elasticity (E) corresponding to the partially cured material obtained after the first curing stage (respectively, FIG. 1A, FIG. 1B and FIG. 1C) and a graph of tensile stress, maximum unit strain and modulus of elasticity (E) corresponding to the fully cured material obtained after the second curing stage (respectively, FIG. 1D, FIG. 1E and FIG. 1F);

[0042] Figure 2 shows the thermo-mechanical behavior of three analyzed formulations, displaying the loss factor (Tan(E” / E)), the storage modulus (E'), and the loss modulus (E”) (FIG. 2A, FIG. 2B, and FIG. 2C, respectively), and the infrared spectrum of each intermediate material in solution (Sol) obtained from the partial UV curing of each of the three formulations from the first embodiment (RAC20AC30, RAC20AC40, and RAC20AC50). Figure 2D shows the results corresponding to the fully cured material. In Figure 2D, the dark vertical bands correspond to the vibrations of the acrylic and methacrylate groups present in the formulation, and the more transparent band corresponds to the absorption band of the epoxy resin.

[0043] Figure 3 shows the apparent viscosity of each formulation (RAC20AC30, RAC20AC40 and RAC20AC50) at 30°C (FIG. 3A) and a Jacobs chart for each formulation (FIG. 3B1, FIG. 3B2 and FIG. 3B3, corresponding respectively to RAC20AC30, RAC20AC40 and RAC20AC50);

[0044] Figure 4 shows the differential scanning calorimetry (photo-DSC, in FIG. 4A and DSC, in FIG. 4B) of one of the tested formulations (RAC20AC40);

[0045] Figure 5 shows a TGA thermogram of each of the RAC20AC30, RAC20AC40 and RAC20AC50 formulations tested;

[0046] Figure 6 shows a printed mesh part obtained after a first curing stage (FIG. 6A1), a printed mesh part obtained after a second curing stage (FIG. 6A2), a printed mesh part obtained after a second curing stage with a load (FIG. 6A3), a flexible printed rectangle in the shape of a bottle cylinder obtained after a first curing stage (FIG. 6B1), a rigid cylinder obtained after a second curing stage (FIG. 6B2), the same rigid cylinder shown in FIG. 6B2 with a load (FIG. 6B3), three flexible rectangular parts obtained after the first curing stage (FIG. 6C1), and a rigid T-joint obtained after a second curing stage (FIG. 6C2 and FIG. 6C3). Figures 6D1, 6D2, and 6C3 also show...Figures 6D3 show a part that was formed in less than 8 minutes into a rectangular shape and was then reprocessed in a mold designed to adopt the geometry shown in Figure 6D. If the part had been printed in this shape using a conventional method, it would have taken more than an hour to print and would have required supports for shaping. Figures 6E1, 6E2, and 6E3 show a reprocessed part equivalent to the one shown in Figure 6D, but with a different configuration.

[0047] Figure 7 shows a graph of the tensile stress caused by a tensile test, maximum strain and modulus of elasticity (E) corresponding to the partially cured material (respectively, FIG. 7A, FIG. 7B and FIG. 7C) and a graph of the tensile stress, maximum strain and modulus of elasticity (E) corresponding to the fully cured material (respectively, FIG. 7D, FIG. 7E and FIG. 7F) obtained from each of the formulations corresponding to the second embodiment (RAC20HEA40PEG0, RAC20HEA40PEG5 and RAC20HEA40PEG0);

[0048] Figure 8 shows the thermal reaction kinetics of the tested formulations (FIG. 8A) and the Tg of the materials (FIG. 8B);

[0049] Figure 9 shows the loss factor (Tan(E” / E’)), the storage modulus (E’) and the loss modulus (E”) of each of the formulations, contrasting the PEG content (respectively, FIG. 9A, FIG. 9B and FIG. 9C);

[0050] Figure 10 shows the apparent viscosity in relation to the PEG content (FIG. 10A), while Figures FIG. 10B, FIG. 10C and FIG. 10D show the Jacobs charts for each of the formulations RAC20HEA40PEG0, RAC20HEA40PEG5 and RAC20HEA40PEG0;

[0051] Figure 11 shows two different pieces printed using the formulation with 5% by weight of PEG (respectively, FIG. 11A and FIG. 11B).

[0052] PREFERRED EMBODIMENT OF THE INVENTION

[0053] The tests carried out to demonstrate the mechanical properties of the claimed formulation are described below. In particular, the tests performed with the formulations corresponding to the first particular embodiment RAC20AC30, RAC20AC40, and RAC20AC50, as described above (see Table 3), based on the coupling agent HEMA and without a crosslinking regulator, are detailed.

[0054] The tests were carried out to demonstrate that a printed material obtained from the formulation that is the subject of the invention can withstand unit deformations greater than 100%, after a first curing stage, as well as transform into a rigid material capable of withstanding stresses at tensions greater than 60 MPa, after a second curing stage.

[0055] The main mechanical properties of the partially cured state of each formulation are detailed in Figure 1 (FIG. 1A, FIG. 1B, and FIG. 1C), which shows a tensile stress graph, as well as the maximum percentage of deformation reached by each formulation and its modulus of elasticity, respectively. The same test was performed with a fully cured material. The results are shown in FIG. 1D, FIG. 1E, and FIG. 1F.

[0056] The results also demonstrate that increasing the percentage of coupling agent (HEMA) in the formulations increases the maximum strength and modulus of elasticity of the intermediate material obtained after the first curing stage, while simultaneously decreasing its strain. Furthermore, in the case of the fully cured material, a slight variation in tensile strength was observed, showing that the lower the coupling agent content of the formulation, the higher its tensile strength, within a range of 65 to 90 MPa.

[0057] Figure 2 shows the thermo-mechanical behavior of each formulation, illustrating how the HEMA content affects the mechanical behavior of the materials at different temperatures. Figure 2D shows the decrease in acrylic groups during the first curing stage and the decrease in epoxy groups during the second curing stage, indicating the completion of the reaction after the thermal curing process, corresponding to the second curing stage.

[0058] Figure 3A shows the apparent viscosity for each formulation at 30°C. It is important to note that viscosity is a crucial parameter for 3D printing, where high-strength resins often have high molecular weights and densities, making processing difficult. Figures 3B1, 3B2, and 3B3 show the layer thickness achieved for different doses (Eo), where the dose is associated with the light intensity (4.73 mW / cm²). 2 with an LED wavelength of 385 nm) over different time periods. This comparative parameter is described by the Jacobs work curve in equation 1: where, Cd (pm) represents the depth or thickness of curing of the sample, E c is the critical energy and E is the maximum energy (mJ / cm²) 2 ) for the radiation of the light incident on the surface, and D p(pm) indicates the depth of light penetration. When plotting Cd as a function of E m Plotting ax on semi-logarithmic axes, a linear curve known as the Jacobs working curve is obtained. The determination of E c is performed at the point where this curve crosses the x-axis, while D p It is calculated from its slope. It is important to note that this curve is obtained using the least squares method, where each point is considered to determine the line on a logarithmic scale. The following equations were obtained for the formulations of the first realization:

[0059] RAC20AC30: C d = 203.68ln(E) - 715.58

[0060] RAC20AC40: C d = 224.32ln(E) - 803.35

[0061] RAC20AC50: C d = 93.213ln(E) - 300.14

[0062] And for the formulations of the second realization, the following were obtained:

[0063] RAC20PEG0: C d= 146.98ln(E) - 443.67

[0064] RAC20PEG5: C d = 126.03ln(E) - 267.54

[0065] RAC20PEG10: C d = 124.43ln(E) - 331.03

[0066] Figure 4 shows a differential scanning calorimetry (photo-DSC) analysis for the RAC20AC40 formulation (FIG. 4A) and a DSC analysis for the same formulation (FIG. 4B). The photo-DSC assay allows the study of the activation of the first reaction, which is very rapid and takes place at room temperature. The conventional DSC, performed subsequently, allows observation of the second reaction stage. The graphs show that the system has excellent latency and reactivity in each of the stages of the curing process. This is particularly interesting, as it indicates the start and end of each reaction and, furthermore, demonstrates the latency of each system, confirming that it is a doubly latent system. In both graphs, the curing process is marked by the peak in the process, which corresponds to the release of heat due to the chemical reaction.In the first case, the peak begins upon irradiation (activation is almost instantaneous), and the process ends when the signal returns to the horizontal baseline, indicating that all possible heat has been released and, therefore, all the acrylic groups have reacted. In the second case, a nearly horizontal baseline is also observed, along with a slightly wider but well-defined peak, corresponding to the heat release due to the reaction of the epoxy groups. This demonstrates that the first reaction is photolatent, as it is not activated (by the photoinitiator) until the system is properly irradiated with suitable light. The second reaction is thermally latent, meaning it requires sufficient heating to release the thermal initiator capable of activating the reaction of the epoxy component.In this latter case, the good latency is due to the fact that, once a certain temperature is exceeded, the reaction is activated quickly (the peak of the process is abrupt), but at lower temperatures the system is much more stable, the reaction is much slower, which allows for its safe storage.

[0067] The following describes a series of tests performed to compare the variation of the crosslinking regulator in the formulation of the invention. In particular, the tests carried out with the formulations corresponding to the second particular embodiment RAC20HEA40PEG0, RAC20HEA40PEG5, and RAC20HEA40PEG10, as described above (see Table 4), based on the coupling agent HEA and varying amounts of polyethylene glycol (PEG), are detailed.

[0068] The main mechanical properties of the partially cured state of each formulation are detailed in Figure 7, which shows a stress-strain curve for each formulation (FIG. 7A), the maximum percentage of strain reached by each formulation (FIG. 7B), and the modulus of elasticity for each (FIG. 7C). Figures 7D, 7E, and 7F show the same curves as those in FIG. 7A, 7B, and 7C, but for the formulations in their fully cured state. Figure 8A shows a thermogram analyzing the thermal reaction. As shown in the figure, the system has excellent latency, activating near 130°C and maintaining a single reaction peak, demonstrating the system's simplicity. The second thermogram shown in Figure 8A...8B shows the appearance of the glass transition temperature (Tg) in the differential scanning calorimetry (DSC) analysis.

[0069] Figure 9 shows the thermo-mechanical behavior of each formulation, contrasting the PEG content in each formulation. It can be observed that the maximum values ​​of Tan (FIG. 9A), as well as the storage modulus (FIG. 9B) and the loss modulus (FIG. 9C), decrease as the amount of PEG in each formulation increases.

[0070] Figure 11A1 shows a photograph of a partially cured mesh-like part. The good print resolution in the area below the main image is noteworthy. Figure 11A2 shows the same part fully cured. Figure 11A3 shows the thickness of the part. Figure 11B1 shows a part with a circular mesh in its partially cured state, where the resolution can be analyzed below the main image. Figure 11B2 demonstrates the ability to accommodate deformations in its partially cured state, while Figure 11B3 shows the fully cured part.

[0071] It is worth noting that the parts can be reshaped in a manner similar to the system shown in Figure 6. The printing capabilities (resolution and precision) and reprocessing are similar to those of formulations 1 through 3. Likewise, they are similar in terms of viscosity and mechanical properties in their partially cured state. It is after the thermal curing process that the differences between the formulations become apparent, demonstrating their ability to adapt to parts with varying mechanical requirements.

[0072] The tests carried out demonstrate the main advantages of the claimed formulation compared to other prior art alternatives. In this regard, most commercially available resins currently have an apparent viscosity greater than 100 cP at 30°C and do not guarantee high tensile strength. This means that currently available commercial resins also do not ensure high performance in parts subjected to considerable stress, limiting their use in the structural parts and components industry. The formulation of the invention overcomes these limitations.In particular, the claimed formulation offers the following advantages: (a) it has low viscosity; (b) it is capable of producing large parts that efficiently absorb the stresses caused by expansion and contraction; (c) it has high mechanical strength; (d) it is capable of undergoing post-processing and modifying its geometry after the printing process; (e) it can acquire new mechanical properties after heat treatment; (f) it has the ability to operate in modern systems, such as the high-performance CLIP printing technology, where viscosity plays a crucial role in relation to manufacturing processes and curing times; and (g) on ​​the other hand, meticulous control of the processing stages, especially through the combination of UV 3D printing and thermal curing, offers significant advantages by allowing greater precision in the geometry of the parts and an improvement in mechanical properties.This dual approach also opens the door to designing materials with different glass transition temperatures, allowing for rigid or ductile behavior depending on the specific application requirements. This flexibility is achieved by modifying various components, such as the coupling agent, epoxy resin, and crosslinking regulator, further expanding the range of applications and opening new opportunities in advanced materials design.

Claims

CLAIMS 1. Dual-cure formulation for 3D printing, characterized in that it comprises, in weight percentage: a) between 15% and 50% of an acrylic resin; b) between 20% and 60% of an epoxy resin; c) between 10% and 60% of a coupling agent consisting of an acrylate or methacrylate monomer comprising at least one hydroxyl group (-OH); d) between 0.5% and 5% of a radical photoinitiator; and e) between 0.5% and 5% of a thermal cationic initiator.

2. Formulation, according to claim 1, wherein the epoxy resin is a cycloaliphatic epoxy resin.

3. Formulation, according to claim 1 or 2, wherein the coupling agent is methacrylate or hydroxyethyl acrylate.

4. Formulation, according to any one of the preceding claims, wherein the formulation further comprises between 0.1% and 5% of a thermal radical initiator.

5. Formulation, according to any one of the preceding claims, wherein the formulation further comprises between 5% and 10% of a crosslinking regulator consisting of a polyol comprising at least one hydroxyl group.

6. Formulation, according to claim 5, wherein the polyol is polyethylene glycol.

7. Formulation, according to any one of claims 1 to 4, wherein the formulation comprises, in weight percent: a) 19.01% of an acrylic resin; b) 28.51%, 38.02% or 47.53% of hydroxyethyl methacrylate as a coupling agent; c) a cycloaliphatic epoxy resin consisting of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, in a percentage of 47.53%, a 38.02% or 28.51%; d) 2.57% of a radical photoinitiator consisting of phenylbis(2,4,6-thinmethylbenzoyl)phosphine oxide; e) 1.90% of a thermal cationic initiator consisting of a 50% by weight solution of N-(p-methoxybenzyl)-N,N-dimethylanilinium hexafluoroantimonate and 5% by weight of triethanolamine, in propylene carbonate as solvent; and f) 0.48% of a thermal radical initiator, consisting of a 60% by weight solution of 1,1-bis(tert-amylperoxy)cyclohexane.

8. Formulation, according to any one of claims 1 to 6, wherein the formulation comprises, in weight percent: a) 19.01% of an acrylic resin; b) 38.02% hydroxyethyl acrylate as a coupling agent; c) 0%, 4.75% or 9.50% 400 g / mol polyethylene glycol as a crosslinking regulator; d) a cycloaliphatic epoxy resin consisting of bis(3,4-epoxycyclohexylmethyl) adipate, in a percentage of 38.02%, 33.27%, or 28.52%; e) 2.57% of a radical photoinitiator consisting of phenylbis(2,4,6-trimethylbenzoylphosphine) oxide; f) 1.90% of a thermal cationic initiator consisting of a 50% by weight solution of N-(p-methoxybenzyl)-N,N-dimethylanilinium hexafluoroantimonate and 5% by weight of triethanolamine, in propylene carbonate as solvent; and g) 0.48% of a thermal radical initiator consisting of a 60% by weight solution of 1,1-bis(tert-amylperoxy)cyclohexane.

9. Intermediate material characterized in that it consists of a formulation according to any one of claims 1 to 8, subjected to a UV radiation curing stage, wherein said material exhibits unit deformations greater than 100% and an elastic modulus between 1 and 13 MPa.

10. Material characterized in that it consists of a formulation according to any one of claims 1 to 8, subjected to a UV radiation curing stage, followed by a thermal curing stage, wherein said material has a modulus of elasticity between 10 and 2000 MPa and a tensile strength greater than 60 MPa.

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