TWI892589B - Foaming, dual-curing, and additive manufacturing method and additive manufactured resin elastomer obtained therefrom - Google Patents

Abstract

The present disclosure provides a method of additive manufacturing foamed dual-curing resin and the additive manufactured resin elastomer may formed therefrom. The method includes the following operations. Resin providing process: a foamed dual-cure resin composition suitable for additive manufacturing in continuous liquid interface production is provided. Additive manufacturing process: the foamed dual-curing resin composition is placed in a printer for continuous liquid interface production, and a digital UV light source is used to irradiate the foamed dual-curing resin composition, such that a portion of the foamed dual-curing resin composition that is irradiated photopolymerizes to form a grid structure which is an intermediate having a three-dimensional grid. Foaming procedure: the intermediate having the three-dimensional grid is placed in a heated environment to perform foaming, and the intermediate is thermally cured to further enhance the performance, thereby forming the additive manufactured resin elastomer.

Description

Foaming type dual-curing additive manufacturing method and additive manufacturing resin elastomer obtained therefrom

This disclosure relates to a method for additive manufacturing of a foamed dual-cure resin and an additively manufactured resin elastomer formed by this method. In particular, it relates to an additive manufacturing method for a foamed dual-cure resin for use in continuous liquid interface production (CLIP) 3D printing technology and the resulting additively manufactured resin elastomer.

Continuous Liquid Interface Production (CLIP) 3D printing technology uses UV light to project onto a transparent resin feed tank. Upon exposure to the UV light, the liquid dual-cure resin composition within the tank undergoes crosslinking and polymerization, forming a three-dimensional structure. This three-dimensional structure is then heated, causing the closed-type polyurethanes in the dual-cure resin composition to deblock and rearrange, ultimately curing the product. Details about the CLIP technology can be found on the Carbon3D website at https://www.carbon3d.com/carbon-dls-technology. While the continuous liquid interface design allows for the creation of more delicate and precise structures than conventional layer-by-layer 3D printing, the placement of the liquid dual-cure resin composition within the resin tank also limits the size of printed objects. Therefore, Carbon3D has developed a foaming resin composition that first prints a smaller 3D structure using CLIP technology, then heat-cures and foams it during the heating process. This ultimately results in a finished product that is not limited by the resin tank size in the CLIP printer.

The expandable resin composition developed by Carbon3D utilizes physical foaming of microcapsules. This involves mixing expanding particles, which consist of a thermoplastic resin shell and a low-alkane content, with a base resin (also known as a dual-cure resin composition) to form the foamable dual-cure resin composition. When the foamable dual-cure resin composition is printed in a CLIP printer, the microcapsules and the base resin are exposed to UV light. As the base resin undergoes crosslinking and polymerization, forming a three-dimensional structure, the microcapsules embedded within it become embedded within the solid portion of the structure. Because microcapsules expand when their low-alkanes vaporize upon heating, their thermoplastic resin shell softens and expands to still enclose the vaporized alkanes. Compared to the more mature chemical foaming process, it is more environmentally friendly and does not have the drawbacks of other physical foaming processes, such as those involving supercritical fluids, which require expensive equipment and carry potential safety risks.

However, while Carbon3D's patent application US11292186B2 discloses an additive manufacturing technology for creating low-density three-dimensional objects using a foaming resin composition, it does not further explore how to control the process to achieve a uniformly foamed final product when heat-expandable microspheres are added to the dual-cure resin. Patent Publication No. WO2023078844A1 proposes a shoe midsole that combines the dual shock-absorbing effects of a foam material and a three-dimensional network structure. However, the technology employed here relies on achieving the desired cushioning effect through the spatial geometry of the three-dimensional network and the expansion ratio of the foaming agent. It does not specify the physical foaming technology used, nor does it address the specific foaming process or foaming uniformity. Therefore, the relevant literature does not clearly teach how to manufacture an additively manufactured resin elastomer that simultaneously possesses an additively manufactured three-dimensional network structure and foamed material properties within the solid structure of the lattice structure to ensure that the resulting additively manufactured resin elastomer maintains the integrity of the additively manufactured three-dimensional network during the foaming process.

This disclosure provides a method for additive manufacturing of a foamable dual-cure resin. The method includes the following steps: performing a resin provision process, including providing a foamable dual-cure resin composition, wherein the foamable dual-cure resin composition includes a base resin and thermally expandable microcapsules. The additive manufacturing process includes placing a foamed dual-cure resin composition in a continuous liquid interface production (LIIP) printer, causing a base resin irradiated with ultraviolet light to undergo photopolymerization to form a solid portion, thereby defining a plurality of lattice structures, wherein: the lattice structures collectively constitute a three-dimensional network, and the three-dimensional network constitutes an intermediate body; and thermally expandable microcapsules in the foamed dual-cure resin composition are embedded in the solid portion within the lattice structure of the intermediate body as the base resin in the foamed dual-cure resin composition photopolymerizes. The foaming process involves removing the intermediate from a continuous liquid interface printing machine and placing it in a heated environment. Thermally expandable microcapsules embedded in the solid portion of the lattice structure expand as a result of the heat, thereby enlarging the three-dimensional network of the intermediate due to the expansion of the thermally expandable microcapsules. The overall volume of the intermediate expands accordingly, completing the final foaming. The intermediate is then heated in the heated environment to achieve thermal curing, ultimately forming an additive manufacturing resin elastomer. In some embodiments, the lattice structure includes a solid portion and spaces enclosed by the solid portion.

In some embodiments, the resin providing process provides a foamable dual-cure resin composition with minimal settling based on Stokes' law, such as a resin formulation having the following characteristics: a small density difference between the thermally expandable microcapsules and the base resin, an appropriate base resin viscosity, and an appropriate particle size. Stokes' law is as follows:

In some embodiments, the density difference between the base resin and the thermally expandable microcapsules in the foamable dual-cure resin composition is less than 1 g/mL and greater than or equal to 0 g/mL.

In some embodiments, the thermally expandable microcapsules do not react to UV light exposure during the additive manufacturing process.

In some embodiments, the foaming process includes a temperature ramping process and a constant temperature process. The temperature ramping process includes increasing the temperature from room temperature to 90°C to 220°C at a rate of 1°C to 3.5°C per minute. The constant temperature process includes continuing heating at the final temperature reached during the temperature ramping process for 1 to 5 hours after the temperature ramping process is completed.

In some embodiments, the foaming process includes sequentially performing a first temperature-raising process, a first temperature-holding process, a second temperature-raising process, and a second temperature-holding process. The first temperature-raising process involves heating from room temperature to a first temperature of 100°C to 120°C over 0.75 to 1.25 hours. The first temperature-holding process involves continuously heating at the first temperature for 3.5 to 4.5 hours. The second temperature-raising process involves heating from the first temperature to a second temperature of 130°C to 150°C over 20 to 40 minutes. When the second temperature is reached, the second temperature-holding process is performed. The second temperature-holding process involves continuously heating at the second temperature for 5 to 15 minutes.

In some embodiments, the foaming process is performed under standard atmospheric pressure.

In some embodiments, the foaming process includes ultraviolet light polymerization of the polymer network formed in the intermediate, which further generates polymer bonding due to the action of thermal energy, thereby enhancing the mechanical properties of the polymer network.

The present disclosure also provides an additively manufactured resin elastomer produced by the aforementioned method for additively manufacturing a foamed dual-cure resin. The elastomer comprises a three-dimensional network formed by additive manufacturing, the three-dimensional network comprising an interconnected lattice structure, each of the lattice structures comprising a spatial arrangement of a basic geometric shape formed by a solid portion, and the three-dimensional network formed by the lattice structure constituting the solid portion of the additively manufactured resin elastomer. The solid portion has a plurality of foamed pores within it. The absolute values of the density gradients of the additively manufactured resin elastomer in a first direction, a second direction, and a third direction are each less than 50 kg/( ^m³ *cm), and the first, second, and third directions are mutually perpendicular.

In some embodiments, each of the foamed pores is a closed-cell pore.

In some embodiments, the foamed pores cause the volume of the additively manufactured resin elastomer to expand by 100% to 350% compared to its pre-foamed state.

1~15: Position

100:Method

101~103: Steps

201: Digital UV Light Source

202: Digital UV light irradiation range

2021: Digital UV light focused irradiation area

2022: Digital UV light with no focused irradiation area

205: Foaming dual-cure resin composition

206: Resin Raw Material Tank

207: Carrier Platform

C:Intermediate

D: Pull-up direction

L: Grid structure

S, S’, S”: entity part

B: Thermal expansion microcapsules

F _in : resistance

F _out : impulse

When reading the drawings in this disclosure, it is recommended that you understand the various aspects of this disclosure from the following. Please note that, in accordance with standard industry practice, the dimensions of various features may not be drawn to scale. Furthermore, for clarity of discussion, the dimensions of various features may be arbitrarily increased or decreased. Furthermore, for simplicity, conventional structures and components may be shown in the drawings in a simplified, schematic manner.

Figure 1 is a flow chart of a method for additive manufacturing of foamed dual-cure resins according to some embodiments of the present disclosure.

Figure 2 is a schematic diagram illustrating the UV irradiation step in a continuous liquid interface printing machine according to some embodiments of the present disclosure, wherein a resin raw material tank is subjected to UV irradiation, causing the base resin in the resin raw material tank to undergo photopolymerization to form an intermediate.

FIG3 is a schematic diagram illustrating the UV irradiation step in a continuous liquid interface printing machine according to some embodiments of the present disclosure, wherein a resin raw material tank is subjected to UV irradiation, causing the base resin in the resin raw material tank to undergo photopolymerization to form an intermediate. FIG3 is presented in black and white and corresponds to an enlarged schematic diagram of the dashed box in FIG2.

Figures 4A and 4B are schematic diagrams illustrating the thermal curing of the intermediate and the expansion of the volume of the thermally expandable capsule therein during the foaming process according to some embodiments of the present disclosure.

Figures 5A and 5B are schematic diagrams illustrating the thermal curing of the intermediate and the expansion of the volume of the thermally expandable capsule therein during the foaming process according to some embodiments of the present disclosure.

FIG6 is a schematic diagram of an additively manufactured resin elastomer formed according to some embodiments of the present disclosure. The left side of the figure shows an additively manufactured resin elastomer obtained by additively manufacturing a foamed dual-cure resin. The right side of the figure shows an additively manufactured resin elastomer obtained by additively manufacturing a non-foamed dual-cure resin.

FIG7 is a schematic diagram of an additively manufactured resin elastomer formed according to some embodiments of the present disclosure. The left figure illustrates an example of a failure to properly control the foaming process, resulting in excessive foaming of thermal expansion microcapsules and destruction of the three-dimensional network of the additively manufactured resin elastomer. The right figure illustrates an additively manufactured resin elastomer obtained when the foaming process is properly controlled.

FIG8 is a schematic diagram of an additively manufactured resin elastomer formed according to some embodiments of the present disclosure, wherein the additively manufactured resin elastomer includes multiple portions distributed continuously from one side to an opposite side.

FIG9 is a graph showing the average density variation of various portions of an additively manufactured resin elastomer formed according to some embodiments of the present disclosure.

To make the description of this disclosure more detailed and complete, the following description provides illustrative examples of implementations. This description does not limit the implementation of this disclosure to a single form. The implementations of this disclosure may be combined or substituted with each other where beneficial, and additional implementations may be included without further explanation.

Spatially relative terms, such as above and below, may be used throughout this disclosure to describe the relationship of one element to another element in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, the device may be oriented in other ways (e.g., rotated 90 degrees or in other orientations), and therefore the spatially relative terms throughout this disclosure should be interpreted accordingly. Throughout this disclosure, unless otherwise specified, identical element numbers across different figures refer to identical or similar elements formed from identical or similar materials using identical or similar methods.

The terms "approximately," "approximately," "close to," "substantially," or "substantially" used in this disclosure include the values and features described and the range of deviations therefrom as understood by one of ordinary skill in the art. For example, to account for errors in values and features, these terms may refer to values within one or more standard deviations of the values described (e.g., within ±30%, ±20%, ±15%, ±10%, or ±5%), or to the deviations encompassed by the features described in practical operation (e.g., the statement "substantially parallel" may mean practically close to parallelism rather than ideally perfectly parallelism).

The present disclosure provides a method for additive manufacturing of a foamed dual-cure resin, as shown in method 100 in FIG. When reading method 100 in FIG. 1 , reference may be made to FIG. 2 through FIG. 9 . Specifically, method 100 includes steps 101 through 103 . Step 101: A resin provision process includes providing a foamable dual-cure resin composition suitable for continuous liquid interface additive manufacturing. This resin composition can be purchased from Carbon3D or Chenhong Electronic Materials (e.g., the foamable resin composition disclosed in Chenhong Electronic Materials' patent application entitled "Foamable Resin Composition and Resin Molded Article"). Alternatively, a commercially available non-foamable dual-cure resin and a thermal expansion capsule can be purchased separately and mixed. The difference between the density of the non-foamable dual-cure resin and the density of the thermal expansion capsule is less than 1 g/mL. The foamed dual-cure resin composition can be used in the method disclosed herein to produce an additive manufacturing resin elastomer (shown on the left in FIG. 6 ) having a larger volume than an unfoamed dual-cure resin composition (shown on the right in FIG. 6 ). Step 102: The additive manufacturing process includes pouring the liquid foamed dual-cure resin composition from the resin providing process of step 101 into a resin raw material tank in a continuous liquid interface production printing machine and irradiating it with a digital UV light source. This causes the irradiated resin composition to partially undergo photopolymerization, defining a lattice structure and forming an intermediate body having a three-dimensional network. The thermally expandable microcapsules mixed in the resin composition polymerize under UV light and become embedded in the solid portion of the lattice structure of the intermediate body. During this process, the thermally expandable microcapsules are unresponsive to UV light. Step 103: Foaming. This involves causing the thermally expandable microcapsules embedded in the solid portion of the three-dimensional structure of the intermediate body to expand due to heat. The thermal energy further strengthens the lattice structure of the intermediate body formed by photopolymerization. After step 103, the additively manufactured resin elastomer can achieve a high volume expansion ratio, and the lattice structure additively manufactured in step 102 is not destroyed due to the foaming process. In other words, the lattice structure in the additively manufactured resin elastomer is intact, and the solid structure formed by the solidification of the resin composition has a spatial arrangement with a basic geometric shape that is substantially the same as the configuration of the corresponding lattice structure in the intermediate body before heating. Furthermore, step 103 allows the solid structure formed by curing the resin composition, after being polymerized by UV light (step 102), to undergo further thermal curing. As a result, the mechanical properties of the additively manufactured resin elastomer are significantly improved, such as improved compressive strength, torsional stiffness, shear strength, impact resistance, tensile strength, elongation at break, and (trouser) tear strength. Method 100 is described in detail below based on implementations.

In step 101, when the resin is provided using a commercially available foamable dual-cure resin composition, since the foamable dual-cure resin composition comprises a liquid base resin and thermally expandable microcapsules suspended therein, before the foamable dual-cure resin composition is poured into the resin raw material tank, it is first stirred to evenly distribute the thermally expandable microcapsules throughout the liquid foamable dual-cure resin composition. This is because, while commercially available foamable dual-cure resin compositions are designed to take into account the effects of shelf life and storage environment before shipment, prolonged storage can still cause the thermally expandable microcapsules to sink or float, resulting in uneven suspension distribution of the microcapsules within the liquid base resin. Stirring should be sufficient to ensure the microcapsules are evenly suspended within the liquid base resin. Excessive stirring is not necessary to prevent shear thickening of the fluid, which could increase the overall viscosity and affect the printing quality during additive manufacturing (step 102). In step 101, when the resin is provided by purchasing a commercially available non-foaming dual-cure resin composition and a thermal expansion capsule separately and mixing the two, in addition to selecting a thermal expansion capsule with a density close to that of the base resin, it is also important to select a thermal expansion capsule product with a relatively uniform particle size distribution (PSD). Furthermore, when purchasing the base resin and thermally expandable microcapsules separately and mixing them together, the thermally expandable microcapsule particles should be moistened with a small amount of photopolymerizable monomer before adding them to the base resin. This prevents the dry thermally expandable microcapsule particles from clumping together during addition to the liquid base resin, making them difficult to evenly disperse. The photopolymerizable monomer can be the one described in the aforementioned patent application "Foamable Resin Composition and Resin Molded Article," or other monomers capable of participating in UV photopolymerization reactions.

Continuing with step 101, the foamable dual-cure resin composition 205 includes a base resin and thermally expandable microcapsules. The base resin composition may include polyurethane (meth)acrylate and a photoinitiator. Examples include EPU40, EPU41, EPU44, and EPU46 produced by Carbon3D. Their chemical compositions are disclosed in the patents filed and other references cited therein, such as US Pat. No. 10471655, US Pat. No. 10259171, US Pat. No. 10975193, and US Pat. No. 10350823. The difference in density between the base resin and the thermally expandable microcapsules is less than 1 g/mL and greater than or equal to 0 g/mL. Preferably, it is less than 0.5 g/mL. More preferably, it is less than 0.3 g/mL. When the density difference between the base resin and the thermal expansion microcapsule is within the aforementioned range, it is possible to avoid significant sedimentation differences between the base resin and the thermal expansion microcapsule in the foamed dual-cure resin composition 205. When the additive manufacturing process of step 102 is subsequently performed, the thermal expansion microcapsule can be evenly distributed when embedded in the solid part of the grid structure. The additive manufacturing resin elastomer formed by foaming these evenly distributed thermally expandable microcapsules in step 103 can also achieve uniform expansion in all dimensions. That is, the expansion effect is substantially the same in all X-Y-Z directions, resulting in the final additive manufacturing resin elastomer having the desired density uniformity and density variation. In some embodiments, the density of the base resin and the density of the thermally expandable microcapsules are each independently between 0.4 g/mL and 1.8 g/mL, for example, 0.4 g/mL, 0.8 g/mL, 1.0 g/mL, 1.1 g/mL, 1.2 g/mL, 1.5 g/mL, or 1.8 g/mL.

The description of step 101 continues. In some embodiments, the particle size of the thermally expandable microcapsules is preferably 10 μm to 30 μm, such as 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm. This prevents the thermally expandable microcapsules from settling too quickly or too slowly in the foamable dual-cure resin composition 205, thereby helping to improve the uniformity of the distribution of the thermally expandable microcapsules in the foamable dual-cure resin composition 205. In some embodiments, the viscosity of the foamable dual-cure resin composition 205 at approximately 25°C, as measured by a viscometer, is preferably between 100 cP and 10,000 cP, such as 100 cP, 500 cP, 1,000 cP, 3,000 cP, 4,000 cP, 5,000 cP, 5,500 cP, 6,000 cP, 7,000 cP, 8,000 cP, or 10,000 cP. More preferably, it is between 100 cP and 5,500 cP. This prevents the thermal expansion microcapsules from settling too quickly or too slowly in the foamable dual-cure resin composition 205, thereby helping to improve the uniformity of the distribution of the thermal expansion microcapsules in the foamable dual-cure resin composition 205.

In step 102, the digital UV light source 201 focuses the desired crosslinking region within the digital UV light irradiation range 202 to irradiate the liquid foamable dual-cure resin composition 205 in the resin raw material tank 206, causing the base resin therein to undergo a crosslinking reaction to form an intermediate C. The digital UV light source 201 can convert a digital signal into a light focusing region with a corresponding pattern via a device (not shown) based on digital light processing (DLP) technology. This allows the foamable dual-cure resin composition 205 irradiated by the digital UV light source 201 to be polymerized into the desired three-dimensional structure as required. The device using digital light processing technology can be a 3D printer manufactured by Carbon3D, such as the Carbon 3D printer, including models such as the M1, M2, M3, and L1. It can also be a printer from another brand designed based on the same or similar principles. Specifically, a digital UV light source 201 is positioned below the resin material tank 206. The tank 206 has a transparent bottom, allowing light from the digital UV light source 201 to penetrate the bottom and illuminate the foamable dual-cure resin composition contained within. The light emitted by the digital UV light source 201 is focused onto a specific portion of the resin material tank according to the irradiation area and irradiation time specified by the digital light signal. This causes the base resin in the digital UV light focused irradiation area 2021 to absorb the UV radiation energy and undergo photopolymerization, transforming from a liquid to a solid state. The area not irradiated by the digital UV light source 201 is referred to as the digital UV light unfocused irradiation area 2022. Since the foaming dual-curing resin composition 205 includes a liquid base resin and thermally expandable microcapsules evenly suspended therein, and the thermally expandable microcapsules therein do not react to UV light irradiation, when the liquid base resin polymerizes to form a solid state due to UV light irradiation, the thermally expandable microcapsules B originally mixed therein are embedded in the cured base resin, as shown in FIG5A . As the foamed dual-cure resin composition 205 loaded into the resin raw material tank 206 is additively manufactured in the 3D printing machine to form an intermediate body C having a three-dimensional network, the base resin in the foamed dual-cure resin composition 205 forms the solid portion S of the lattice structure L within the three-dimensional network, while the thermally expandable microcapsules in the foamed dual-cure resin composition 205 remain embedded in the solid portion S of the lattice structure L in their original state (not shown in FIG. 3 ).

Continuing with step 102, in some embodiments, the digital UV light focused irradiation area 2021 is located near the bottom of the resin material tank 206. More specifically, the digital UV light source 201 is focused on a plane parallel to the bottom of the resin material tank 206. In other words, the digital UV light focused irradiation area 2021 is entirely located on the same plane. For example, the digital UV light source 201 is focused on a plane parallel to the bottom of the resin material tank 206, forming a desired pattern in the digital UV light focused irradiation area 2021, as shown in Figure 3 of the accompanying drawings. In some embodiments, after the foaming dual-cure resin composition 205 is poured into the resin raw material tank 206, the carrier platform 207 is set near the bottom of the resin raw material tank 206, and the digital UV light source 201 is focused on the plane of the carrier platform 207 facing the resin raw material tank 206, and a digital UV light focused irradiation area 2021 with a desired pattern is formed on the plane, so that a solid part S' of the photopolymerized solid grid structure L is formed on the carrier platform 207. Since the UV light source is focused only on one plane, after the solid part S' is formed on the plane of the carrier platform 207 facing the bottom of the resin raw material tank, the 3D printing machine will move the carrier platform in the pulling direction D according to the predetermined printing process, so that the photopolymerized solid part S' leaves the original focusing plane. Then, the digital UV light source 201 will radiate focused UV light again according to the digital signal, forming a new solid part S' in the direction opposite to the pulling direction D of the solid part S'. The solid part S' formed before the carrier platform is pulled and the carrier The new solid portion S" formed after the platform is stretched is polymerized by subjecting the liquid foaming dual-cure resin composition 205 to focused UV light irradiation. Therefore, the solid portion S' before stretching and the new solid portion S" added after stretching are continuous and have no obvious boundary. In addition, since the foaming dual-cure resin composition 205 includes a base resin and thermal expansion microcapsules, and the thermal expansion microcapsules are uniformly suspended in the base resin, when the base resin in the foaming dual-cure resin composition 205 is irradiated with focused UV light and undergoes photopolymerization, the base resin in the foaming dual-cure resin composition 205 is polymerized. At the same time, the thermally expandable microcapsules originally uniformly suspended therein are also embedded in the solid portion S formed by the base resin. That is, after the intermediate body C is formed, the thermally expandable microcapsules are evenly dispersed in the solid portion S of the three-dimensional grid structure. These thermally expandable microcapsules uniformly distributed in the solid portion S of the three-dimensional grid structure exist in their original form. The so-called original form means that these microcapsules retain the same form as before step 102 after step 102. In other words, the thermally expandable microcapsules remain in the original form. During step 102, no changes occur, especially no changes due to thermal expansion. After the aforementioned 3D printing machine completes the intermediate body C with a three-dimensional network by digital UV printing according to a predetermined additive manufacturing process, the foaming process of step 103 is then carried out, including: removing the intermediate body C from the 3D printing machine and placing it in a heated environment, so that the thermal expansion microcapsules embedded in the solid part S of its grid structure L expand due to heat, so that the three-dimensional network of the intermediate body is enlarged by the expansion of the microcapsules, so that the overall volume expands accordingly and finally completes the foaming, for example As shown in the black and white schematic diagrams of Figures 4A and 4B, the volume changes before and after the foaming process are shown, respectively. The intermediate before foaming in Figure 4A and the final product after foaming in Figure 4B are shown on the same scale. Under the action of the heat energy of the foaming process, the intermediate also completes the thermal curing, that is, the polymer network formed by UV photopolymerization also produces a denser polymer bond due to the action of heat energy, further strengthening the mechanical strength of the solid part of the grid structure formed by the base resin, and finally forming an additive manufacturing resin elastomer. In some embodiments, the thermal curing and expansion step in the foaming process of step 103 includes a temperature increase process, wherein the temperature increase process includes slowly increasing the temperature at a rate of 1°C to 3.5°C per minute. In some embodiments, the temperature increase process includes slowly increasing the temperature from room temperature to a temperature between 90°C and 220°C. In some embodiments, the thermal curing and expansion step includes a constant temperature process, wherein the constant temperature process includes heating at a constant temperature between 90°C and 220°C. In some embodiments, the constant temperature process is performed for 1 to 5 hours. In some embodiments, the temperature may be increased at a rate of 1°C per minute. The intermediate C is heated at a rate of 1°C to 3.5°C. For example, the temperature may be slowly increased by 1°C, 1.2°C, 1.4°C, 1.5°C, 1.6°C, 1.8°C, 2°C, 2.5°C, 3°C or 3.5°C per minute. In some embodiments, the constant temperature process comprises heating the intermediate C at a constant temperature of 90°C to 220°C, such as 90°C, 110°C, 115°C, 125°C, 150°C, 165°C, 170°C, 190°C or 220°C, preferably 100°C to 170°C, more preferably 105°C to 150°C. ℃. In some embodiments, the constant temperature process is preferably performed for 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours. In some embodiments, the foaming process in step 103 includes a temperature increase process and a constant temperature process, and the constant temperature process is performed after the temperature increase process. In some embodiments, the final temperature increased from room temperature in the temperature increase process is equal to the temperature used in the constant temperature process. In some embodiments, room temperature includes 20℃ to 30℃, for example, 20℃, 22.5℃, 25℃, 27.5℃, or 30℃.

Continuing with step 103, in some embodiments, the thermal curing and expansion step in the foaming process of step 103 includes multiple stages of heating and holding temperature processes. For example, the process may include a first heating process, followed by a first holding temperature process, and after a period of time during the first holding temperature process, a second heating process, followed by a second holding temperature process. In some embodiments, the foaming process in step 103 includes a first heating process in which the intermediate C is heated from room temperature to 110°C over 1 hour, followed by a first temperature-fixing process in which the intermediate C is heated at 110°C for 4 hours. After the first heating process and the first temperature-fixing process, a second heating process is performed, in which the temperature is raised from 110°C to 140°C over 30 minutes. Once the temperature reaches 140°C, a second temperature-fixing process is performed, in which the intermediate C is heated at 140°C for 10 minutes. In some embodiments, the intermediate C is heated at a rate of 1°C to 3.5°C per minute. Preferably, the temperature is increased at a rate of 1°C to 2°C per minute; more preferably, the temperature is increased slowly at a rate of 1°C to 1.6°C per minute. In some embodiments, the second temperature-raising process has a gentler temperature-raising curve than the first temperature-raising process, that is, the temperature is raised at a smaller temperature increase per minute in the second temperature-raising process. In some embodiments, the first constant-temperature process lasts longer than the second constant-temperature process.

The description of step 103 continues. The aforementioned constant temperature process and/or elevated temperature process helps coordinate the expansion rate of the thermal expansion microcapsules with the thermal curing rate of the surrounding base resin, allowing the intermediate C to achieve complete foaming as much as possible. Complete foaming refers to the full expansion of the thermal expansion microcapsules embedded within the solid portion S of the lattice structure L of the three-dimensional network of the intermediate C. Specifically, the lower alkane liquid encapsulated within the thermal expansion microcapsules is fully converted into gas. The volume change caused by the liquid-to-gas conversion causes the outer shell of the thermal expansion microcapsules to expand outward, resulting in a plurality of pores embedded in the solid portion S. When the expansion rate of the thermal expansion microcapsules matches the curing rate of the base resin (which, after UV photopolymerization, will form the solid portion S of the lattice structure L), the shell of the thermal expansion microcapsules remains intact when the thermal expansion microcapsules are fully expanded. That is, after the foaming process in step 103 is completed, the solid portion S of the lattice structure L of the foamed additive manufacturing resin elastomer is embedded with closed-cell pores, and these closed-cell pores also have a substantially intact shell of the thermal expansion microcapsules. During the foaming process, the thermal environment of the intermediate body C should be properly controlled to ensure that the expansion rate of the thermal expansion microcapsules matches the curing rate of the base resin. In some embodiments, step 103 includes a heating process followed by a constant temperature process. During the heating process, the base resin of the solid portion S of the grid structure L of the intermediate body C is gradually cured by heat, while the thermally expandable microcapsules embedded in the solid portion S expand and foam due to the heat. The subsequent constant temperature process allows the thermal curing of the base resin to fully react. Furthermore, in embodiments in which step 103 includes a heating process and a constant temperature process, the thermally expandable microcapsules begin to expand and foam during the heating process. That is, the temperature at the end of the heating process (which also coincides with the beginning of the constant temperature process) is higher than the foaming starting temperature of the thermally expandable microcapsules. In another embodiment, step 103 includes multiple heating and holding temperature processes. For example, a first heating and holding temperature process is performed first, followed by a second heating and holding temperature process. During the first heating process, the base resin of the solid portion S of the lattice structure L of the intermediate body C is uniformly cured throughout the entire body C (e.g., both on the surface and within the body) due to the gradual heating process. Furthermore, the subsequent first holding temperature process allows the base resin to fully react and complete the thermal curing. However, neither the first heating nor the first holding temperature process reaches the initial temperature for foaming of the thermally expandable microcapsules. After the first heating process and the first temperature-holding process are completed, the second heating process is carried out. During this process, the intermediate body is further heated to a temperature that allows the microcapsules to foam. A second temperature-holding process is then carried out. During the second temperature-holding process, any thermally expandable microcapsules embedded in the solid portion S that have not yet completed expansion and foaming during the second heating process will complete their foaming during the second temperature-holding process.

Continuing with step 103, as shown in FIG. 5B , in a hot environment, the thermally expandable microcapsule, due to the heat conversion of the encapsulated lower alkane liquid into gas, increases in volume caused by this liquid-to-gas conversion, providing an outward expansion force F _out for the shell of the thermally expandable microcapsule. Simultaneously, the base resin also solidifies in the hot environment, thereby providing a resistance F _in to the outward expansion of the shell of the thermally expandable microcapsule. When step 103 includes a heating process followed by a constant temperature process, the rate of thermal curing of the base resin roughly matches the rate of expansion and foaming of the thermally expanding microcapsules. Therefore, during the heating process, the impulse force F _out remains approximately equal to the resistance force F _in . During the subsequent constant temperature process, the thermally expanding microcapsules have substantially completed foaming and no longer expand. Furthermore, the base resin does not substantially expand or contract during the thermal curing process. Therefore, the relative force between the impulse force F _out and the resistance force F _in no longer occurs during the constant temperature process. When step 103 includes multiple heating and holding temperature processes, for example, a first heating process, a first holding temperature process, a second heating process, and a second holding temperature process are sequentially performed, because neither the first heating process nor the first holding temperature process reaches the foaming start temperature of the thermal expansion microcapsules, only the base resin undergoes a thermal curing reaction during the first heating and holding temperature processes. The thermal expansion microcapsules begin foaming during the second heating and holding temperature processes. The embodiment in which step 103 includes multiple heating and holding temperature processes is further described in detail. The first heating process uses a gentle temperature increase to uniformly heat the intermediate C, avoiding uneven heating inside and outside the intermediate, which could lead to varying degrees of thermal curing. This is because as the thermal curing reaction begins, new crosslinks are formed in the intermediate C, gradually transitioning it from the green stage to the mature stage. Due to the different heat conduction characteristics of these two stages, improper control of the heating rate during the first heating process can lead to suboptimal thermal curing of the intermediate C. After the first heating process concludes, heating is continued for a period of time at the final temperature reached during the first heating process, allowing the first temperature-fixing process to proceed. During the first temperature-fixing process, the intermediate C continues to thermally cure until it uniformly approaches the mature stage. Because the base resin of the solid portion S of the grid structure L of the intermediate body C does not substantially expand or shrink during the thermal curing process, and the operating environment during the first heating process and the first temperature-stabilizing process have not yet reached the temperature at which the thermally expandable microcapsules begin to foam, the opposing forces of the impulse force F _out and the resistance force F _in are not generated during these processes. After the first heating process and the first temperature-stabilizing process are completed, the second heating process is then carried out. During this stage, the heat environment is gradually raised to a temperature at which the thermally expandable microcapsules embedded in the base resin can begin to foam. Because intermediate C has already reached the mature stage of polymer polymerization after the first heating and first constant-temperature processes, it already possesses a significant number of thermosetting bonds before the second heating process begins. This means that before the second heating process begins, the solid portion S of the lattice structure L of intermediate C, which contains the thermally expandable microcapsules, possesses stronger mechanical properties than it did right after being produced by the 3D printer. This means that when the second heating process begins, the base resin provides more resistance to the thermally expandable microcapsules. Because the outward expansion force _Fout of the thermally expandable microcapsules and the resistance Fin provided by the base resin to the outward expansion of the microcapsule _shell are in a relative relationship, even in implementations that include multiple heating and constant-temperature processes, the force _Fout and resistance _Fin are maintained approximately equal. That is, throughout the entire expansion and foaming process, the outward expansion force _Fout never exceeds the resistance _Fin provided by the mechanical strength of the base resin. Therefore, the intermediate C is protected from lattice damage during the foaming process. Finally, a second constant-temperature process is performed to ensure that any remaining thermally expandable microcapsules are fully foamed and that the intermediate C is fully cured.

Through the aforementioned process arrangement, the intermediate body C produced by the 3D printing machine can expand uniformly, achieving an increase in volume while maintaining a lattice that is roughly the same as before foaming, as shown in Figure 6 (right: unfoamed additive manufacturing resin elastomer; left: foamed additive manufacturing resin elastomer obtained in step 103). In contrast, when the foaming process is not properly controlled, the base resin's curing rate may be too far ahead of the thermal expansion capsule's expansion rate, resulting in the thermal expansion capsule's outward expansion impulse _Fout being insufficient to overcome the resistance to the thermal expansion capsule's expansion caused by the base resin curing. This prevents the thermal expansion capsule from expanding smoothly, which in turn results in the inefficient expansion of the intermediate C. Alternatively, the base resin's curing rate may lag too far behind the thermal expansion capsule's expansion rate, resulting in the thermal expansion capsule's outward expansion impulse _Fout being greater than the resistance _Fin caused by the base resin curing. , the base resin solidified during the expansion process of the thermal expansion microcapsule is insufficient to counteract the resistance force _F in to the expansion of the thermal expansion microcapsule. As a result, the shell of the thermal expansion microcapsule cannot withstand the impact of the outward expansion force F _{out of} the thermal expansion microcapsule, resulting in rupture. The volatile liquid contained in the thermal expansion microcapsule is unable to form complete closed pores during the process of converting to gas, resulting in a cracked lattice structure of the resulting additively manufactured resin elastomer, as shown on the left of Figure 7. The additively manufactured resin elastomer formed after step 103 has a high volume expansion ratio (e.g., the volume of the additively manufactured resin elastomer is approximately 100% to approximately 350% of the volume of the intermediate body C). Furthermore, the pores embedded in the solid portion S of the three-dimensional network of the additively manufactured resin elastomer are closed pores. The thermally expandable microcapsules constituting the pores retain a substantially intact outer shell after foaming. The spatial arrangement of the basic geometric shape formed by the solid portion S forms a lattice structure L. The lattice structure L is intact and substantially maintains the same shape as before step 103, without deformation due to heating, as shown on the right side of FIG. 7 .

The present disclosure also provides an additive manufacturing resin elastomer formed by the above method. The features of the foamed dual-cure resin composition 205 used to form the additive manufacturing resin elastomer can be found above. The additively manufactured resin elastomer comprises a solid portion S formed by cross-linked macromolecules contained in a base resin, and pores embedded in the solid portion, formed by the expansion of thermally expandable microcapsules. The solid portion S forms a spatially arranged grid structure L with a basic geometric shape. Multiple interconnected grid structures L form a three-dimensional network. Because the pores are closed pores formed by the largely intact outer shell of the thermally expandable microcapsules, they are generally circular, e.g., elliptical, or oval. The three-dimensional network is formed by additive manufacturing, and the specific steps involved can be found in the description of step 102 above. The overall density of the additively manufactured resin elastomer is 100 kg/m ³ to 1000 kg/m ³ , for example, 100 kg/m ³ , 500 kg/m ³ , 600 kg/m ³ , 700 kg/m ³ , 800 kg/m ³ , 900 kg/m ³ or 1000 kg/m ³ . In some embodiments, the additively manufactured resin elastomer includes a plurality of sections continuously distributed from one side to an opposite side (in some embodiments, the direction extending from the one side to the opposite side is substantially parallel to the pulling direction D described above), and the difference between the density of each of the sections and the average density of the additively manufactured resin elastomer is less than 80 kg/m ³ and greater than or equal to 0 kg/m ^3. In other words, the density of the three-dimensional network in the additively manufactured resin elastomer is sufficiently uniform. In some embodiments, the absolute value of the density gradient in the additive manufacturing resin elastomer is less than 50 kg/(m ³ *cm) and greater than or equal to 0 kg/(m ³ *cm). The density gradient refers to the density variation per centimeter in the distance from one side of the additive manufacturing resin elastomer to the opposite side. In other words, the density variation of the base resin in the additive manufacturing resin elastomer is sufficiently subtle without excessive variation. In some embodiments, the standard deviation of the density in the additive manufacturing resin elastomer is less than 32 kg/m ³ and greater than or equal to 0 kg/m ³ , thereby ensuring sufficient density uniformity and good mechanical properties.

Continuing with the additive manufacturing resin elastomer, after the additive manufacturing resin elastomer undergoes a dual curing process of photopolymerization in step 102 and thermal curing in step 103, the components in the original foamed dual-cure resin composition are fully cross-linked, giving the final additive manufacturing resin elastomer excellent mechanical properties, such as compressive strength, torsional stiffness, shear strength, impact resistance, tensile strength, elongation at break, and (trouser) tear strength. For example, the additively manufactured resin elastomer has a tensile strength of 3 MPa to 17 MPa, such as 3 MPa, 5 MPa, 7 MPa, 9 MPa, 11 MPa, 13 MPa, 15 MPa, or 17 MPa; an elongation at break of 120% to 340%, such as 120%, 140%, 180%, 220%, 260%, 300%, or 340%; and a (trouser-shaped) tear strength of 2 N/mm to 9 N/mm, such as 2 N/mm, 3 N/mm, 4 N/mm, 5 N/mm, 6 N/mm, 7 N/mm, 8 N/mm, or 9 N/mm.

Continuing with the description of the additively manufactured resin elastomer, in some embodiments, the additively manufactured resin elastomer may have the shape of a shoe midsole, as shown in FIG8 . In these embodiments, when forming the midsole C, the printing direction (relative to the pulling direction D) is substantially parallel to the direction from the toe to the heel. In these embodiments, the three-dimensional network in the additively manufactured resin elastomer has a first density at the toe portion, a second density at the heel portion, and a third density midway between the toe and heel portions, with the first density being greater than the second density, and both the first and second densities being greater than the third density.

The density distribution and variations of the sole shown in Figure 8 are described in detail below. However, it should be understood that the following specific embodiments are provided to help those skilled in the art better understand the present disclosure and are not intended to limit the scope of the present disclosure.

The average density of the shoe sole shown in Figure 8 is approximately 817.14 kg/m ³ . Referring to Tables 1 and 2, the shoe sole shown in Figure 8 is divided into 15 equal sections from the heel to the toe, and these sections are sequentially referred to as Positions 1 to 15. The density at Positions 1 to 15 and the difference between each position and the average density are measured, as shown in Table 1. The density variation between each of Positions 1 to 15 and its neighboring positions (e.g., Position 1 to Position 2, Position 2 to Position 3, and so on) is shown by the density gradient in Table 2. Figure 9 is a waterfall plot of the density of the shoe sole shown in Figure 8 as it increases and decreases with position, where the x-axis sequentially indicates each position and the difference between the corresponding density and the average density, and the y-axis is in kg/m ³ . The three-dimensional network in the shoe sole shown in Figure 8 has sufficient uniformity as described above.

Next, Examples 1-1 through 1-5 in Table 3, Examples 2-1 through 2-5 in Table 4, and Examples 3-1 through 3-5 in Table 5 illustrate that the additively manufactured resin elastomers formed using the methods of this disclosure exhibit excellent bulk expansion ratio, tensile strength, elongation at break, and (trouser-shaped) tear strength. Regarding the foamable dual-cure resin composition formulas used in these examples, Tables 3, 4, and 5 all utilize foamable dual-cure resin compositions produced by Chenhong Electronic Materials, but different models are selected based on the performance requirements of different products. Examples 1-1 through 1-5 in Table 3 all use the same foamable dual-cure resin composition. However, during the foaming process, the temperature rise from room temperature to the desired target temperature, the time required for temperature rise, and the rate of temperature rise may vary. Furthermore, the temperature and time of temperature hold during the temperature hold process may also vary. See Table 3 for details. Examples 2-1 through 2-5 in Table 4 all use the same foamable dual-cure resin composition. However, during the foaming process, the temperature rise from room temperature to the desired target temperature, the time required for temperature rise, and the rate of temperature rise may vary. Furthermore, the temperature and time of temperature hold during the temperature hold process may also vary. See Table 4 for details. Examples 3-1 through 3-5 in Table 5 all use the same foamable dual-cure resin composition. However, during the foaming process, the heating time and rate from room temperature to the desired temperature may vary. Furthermore, the settling temperature and settling time may also vary. See Table 5 for details.

Next, the comparative examples in Table 6 illustrate that when the methods disclosed herein are not used to form an additively manufactured resin elastomer, the foamed article may experience uneven foaming, resulting in a shape different from that before foaming, or may even explode due to excessive foaming. In Comparative Examples 1 through 6 in Table 6, the solidified bodies formed by the additive manufacturing process are 30cm*30cm*30cm cubes. The solidified bodies are foamed sequentially under heating conditions 1, 2, and 3 as shown in Table 6. Because the comparative examples were not foamed using the foaming process disclosed herein (e.g., a process without a slow temperature increase), the foamed articles in Comparative Examples 1 and 2 deform and fail to retain their pre-foaming cubic shape. The foam molded products in Comparative Examples 3 to 6 even experienced structural explosions (as shown on the left of Figure 7).

The additively manufactured resin elastomer formed by the disclosed method has a high volume expansion ratio, and the foaming process does not cause deformation of the three-dimensional network originally defined by the additive manufacturing process. In other words, the lattice structure in the final additively manufactured resin elastomer is intact and can maintain substantially the same shape as before foaming. After foaming, the final additively manufactured resin elastomer has a sufficiently uniform density, and the solid portion of the three-dimensional network of the additively manufactured resin elastomer is fully cured to achieve the expected mechanical properties of the three-dimensional network, such as perfect compressive strength, torsional stiffness, shear strength, impact resistance, tensile strength, elongation at break, and (trouser) tear strength.

This disclosure describes certain embodiments in considerable detail, but other embodiments may also be possible. Therefore, the description of the embodiments contained in this disclosure should not be construed as limiting the scope and spirit of the appended patent applications. Those skilled in the art will recognize that modifications and variations of this disclosure may occur without departing from the scope and spirit of this disclosure. This disclosure is intended to cover such modifications and variations as long as they fall within the scope and spirit of the appended patent applications.

100:Method

101~103: Steps

Claims (9)

A method for additive manufacturing of a foamable dual-cure resin comprises: Performing a resin provision process, including providing a foamable dual-cure resin composition, wherein the foamable dual-cure resin composition comprises a base resin and a thermally expandable microcapsule, wherein a component of the base resin comprises polyurethane (meth)acrylate, and a density difference between the base resin and the thermally expandable microcapsule in the foamable dual-cure resin composition is less than 1 g/mL and greater than or equal to 0 g/mL; An additive manufacturing process is performed, including placing the foamed dual-cure resin composition in a continuous liquid interface printing machine, causing the base resin to undergo a photopolymerization reaction after exposure to ultraviolet light to form a solid portion, thereby defining a plurality of lattice structures, wherein: the lattice structures collectively form a three-dimensional network, and the three-dimensional network forms an intermediate body; and the thermally expandable microcapsules in the foamed dual-cure resin composition are embedded in the solid portion of the lattice structures in the intermediate body as the base resin in the foamed dual-cure resin composition undergoes the photopolymerization reaction; and A foaming process is performed, including removing the intermediate from the continuous liquid interface printing machine and placing it in a hot environment. The thermally expandable microcapsules embedded in the solid portion of the grid structure expand due to the heat, thereby enlarging the three-dimensional network of the intermediate due to the expansion of the thermally expandable microcapsules. The entire volume of the intermediate also expands accordingly until a final foaming is completed. The intermediate is uniformly heated in the hot environment to complete a thermal curing, ultimately forming an additive manufacturing resin elastomer. The method for additive manufacturing of a foamable dual-cure resin as described in claim 1, wherein the foamable dual-cure resin composition has a viscosity of 100 cP to 10,000 cP at 25°C. The method for additive manufacturing of a foamed dual-cure resin as described in claim 1, wherein during the additive manufacturing process, the thermally expandable microcapsule does not react to the irradiation of the ultraviolet light. A method for additive manufacturing of a foamable dual-cure resin as described in claim 1, wherein the foaming process includes a heating process and a constant temperature process, the heating process includes heating from a room temperature to 90°C to 220°C at a rate of 1°C to 3.5°C per minute, and the constant temperature process includes continuing heating at a final temperature reached by the heating process for 1 hour to 5 hours after the heating process is completed. A method for additive manufacturing of a foamable dual-cure resin as described in claim 1, wherein the foaming process includes a first heating process, a first constant temperature process, a second heating process, and a second constant temperature process, wherein the first heating process is heating from room temperature to a first temperature of 100°C to 120°C for 0.75 hours to 1.25 hours, the first constant temperature process is continuously heating at the first temperature for 3.5 hours to 4.5 hours, the second heating process is heating from the first temperature to a second temperature of 130°C to 150°C for 20 minutes to 40 minutes, the second constant temperature process is performed when the second temperature is reached, and the second constant temperature process is continuously heating at the second temperature for 5 minutes to 15 minutes. The method for additive manufacturing of a foamed dual-cure resin as described in claim 1, wherein the foaming process is performed under standard atmospheric pressure. An additive manufacturing resin elastomer produced by the method for additive manufacturing of a foamed dual-cure resin as described in claim 1, comprising: a three-dimensional network formed by additive manufacturing, the three-dimensional network consisting of interconnected grid structures, each of the grid structures comprising a spatial arrangement of a basic geometric shape formed by the solid portion, and the three-dimensional network formed by the grid structures constituting the solid portion of the additive manufacturing resin elastomer; and a plurality of foamed pores within the solid portion, wherein an absolute value of a density gradient of the additive manufacturing resin elastomer in a first direction, an absolute value of a density gradient in a second direction, and an absolute value of a density gradient in a third direction are each less than 50 kg/(m ³ *cm), and the first direction, the second direction and the third direction are perpendicular to each other. The additively manufactured resin elastomer as described in claim 7, wherein each of the foamed pores is a closed pore. The additively manufactured resin elastomer as described in claim 7, wherein the foamed pores cause a volume of the additively manufactured resin elastomer to expand by 100% to 350% compared to before foaming.