Composite materials and their applications, and 3D printing methods

Abstract

Provided are a composite material and applications thereof, and a 3D printing method. The composite material comprises a photoinitiator, a thermal curing agent, and a short-cut fiber reinforced epoxy resin, and the epoxy resin comprises an acrylate; wherein the operation time of the composite material is greater than 24 hours; and wherein the gel time of a surface layer of the composite material is 1-5 seconds after triggering the photoinitiator to react with the acrylate.

Description

Technical Field

[0001] This application relates to a composite material and its applications, as well as a 3D printing method. Background Technology

[0002] Material extrusion 3D printing technology typically uses thermoplastic polymers (such as thermoplastic resins) as 3D printing materials. However, the performance of structures printed from thermoplastic polymers is limited and cannot meet the requirements of certain applications. Therefore, expanding the range of materials available for 3D printing technology is a problem that needs to be addressed. Summary of the Invention

[0003] This application provides a composite material and its application, as well as a 3D printing method. The various aspects involved in this application are described below.

[0004] In a first aspect, a composite material is provided, the composite material comprising: a photoinitiator, a thermosetting agent, and a short-fiber reinforced epoxy resin, wherein the epoxy resin comprises an acrylate; wherein the working time of the composite material is greater than 24 hours; wherein, after triggering the reaction between the photoinitiator and the acrylate, the gel time of the surface layer of the composite material is 1 to 5 seconds.

[0005] In some implementations, the epoxy resin comprises 100 parts by weight, the thermosetting agent comprises 35 to 90 parts by weight, the chopped fibers comprises 5 to 225 parts by weight, the photoinitiator comprises 2 to 9 parts by weight, and the acrylate comprises 15 to 55 parts by weight.

[0006] In some implementations, the curing agent includes anhydride-based curing agents.

[0007] In some implementations, the epoxy resin is selected from at least one or a mixture of glycidyl ether epoxy resins, aliphatic epoxy resins, and glycidyl ester epoxy resins.

[0008] In some implementations, the aspect ratio of the chopped fibers is <20.

[0009] In some implementations, the chopped fibers are selected from at least one or a mixture of carbon fibers, glass fibers, and carbon nanotubes.

[0010] In some implementations, the photoinitiator is selected from at least one or a mixture of cationic photoinitiators and free radical photoinitiators.

[0011] In some implementations, the free radical photoinitiator is selected from at least one or a mixture of TPO and BAPO.

[0012] In some implementations, the composite material further includes one or more of a wetting and dispersing agent, an antioxidant, a polymerization inhibitor, and a latent thermal catalyst.

[0013] In some implementations, the thickness of the surface layer is less than or equal to 0.5 mm.

[0014] In some implementations, the gelation time is 1 to 3 seconds.

[0015] In a second aspect, a 3D printing method is provided, comprising: during the 3D printing process, using an extrusion device to extrude a composite material as described in the first aspect or any implementation thereof; irradiating the composite material with a light source to trigger a reaction between the photoinitiator and the acrylate, thereby causing the surface of the composite material to gel; and using a heat source to heat and trigger a reaction between the thermosetting agent and the epoxy resin, thereby causing the composite material to cure.

[0016] Thirdly, the composite material described in the first aspect or any implementation thereof is provided as an application of extrusion-based 3D printing material. Detailed Implementation

[0017] Material extrusion 3D printing technology typically uses thermoplastic polymers (such as thermoplastic resins) as 3D printing materials. However, thermosetting polymers (such as thermosetting resins) are also a large class of polymer materials, and thermosetting polymer-based fiber-reinforced composites generally achieve higher mechanical properties than thermoplastic polymer-based fiber-reinforced composites. Therefore, applying thermosetting polymers to material extrusion 3D printing technology will greatly expand the range of materials available for this technology.

[0018] To expand the material system of 3D printing materials, this application proposes a novel thermosetting resin-based chopped fiber reinforced composite material. The composition and properties of the composite material proposed in this application are described below.

[0019] The composite material provided in this application includes a photoinitiator, a thermosetting agent, and a short-fiber reinforced epoxy resin. This composite material can be used as a 3D printing material, particularly in extrusion-based 3D printing technologies.

[0020] The composite material provided in this application has an extremely long working time (e.g., greater than 24 hours, or 2-7 days). Working time refers to the time after all components of the composite material are mixed, during which it can remain in a workable state. A workable state means that the composite material has not significantly cured, and its viscosity remains appropriately low, allowing it to be extruded from the nozzle. For example, a photothermal hybrid thermosetting composite material will cure under the action of a thermosetting agent and a photoinitiator, resulting in a gradual increase in viscosity. However, at lower temperatures, the thermosetting agent will not significantly cure; under sealed, light-free conditions, the photoinitiator will not initiate significant curing, allowing the material to maintain a relatively long workable time. Even under lower temperatures and light-free conditions, resin materials with added thermosetting agents and photoinitiators will cure slowly, and the degree of slowness determines how long an extrusion operation can be performed.

[0021] Furthermore, the composite material provided in this application will gel instantaneously after the reaction between the photoinitiator and the acrylate in the epoxy resin is triggered (e.g., triggered by a light source). The gel time of the composite material mentioned here can refer to the gel time of the surface layer of the composite material (e.g., a thin layer with a surface thickness of less than or equal to 0.5 mm). In other words, the composite material provided in this application, while achieving short-cut fiber reinforced epoxy resin, has the characteristics of ultra-long operating time and externally triggered instantaneous surface gelation.

[0022] In some embodiments, the epoxy resin mentioned above may be selected from at least one or a mixture of glycidyl ether epoxy resins, aliphatic epoxy resins, and glycidyl ester epoxy resins. Different types of epoxy resins can be selected for different application requirements.

[0023] For example, epoxy resins can include glycidyl ether epoxy resins, such as bisphenol A type, hydrogenated bisphenol A type, and phenolic epoxy resins. Glycidyl ethers possess excellent rigidity, high strength, and high heat resistance due to their benzene ring structure. Glycidyl ether epoxy resins are mainly used in high-performance applications such as aerospace.

[0024] For example, epoxy resins can include aliphatic epoxy resins, such as epoxidized polybutadiene. Aliphatic epoxy resins provide flexibility and low-temperature performance due to their flexible long-chain molecular structure. Aliphatic epoxy resins are mainly used in applications requiring good flexibility and low-temperature adaptability, such as 3D printing of automotive shock absorber components and cryogenic seals.

[0025] For example, epoxy resins can include glycidyl ester epoxy resins. Glycidyl esters offer high light transmittance, therefore glycidyl ester epoxy resins are mainly used in printing optical devices where high light transmittance is required.

[0026] Among the three types of epoxy resins mentioned above, resins with different epoxy values ​​can be used to meet different application requirements. For example, for high toughness requirements, low epoxy value (0.18–0.22) resins can be selected; for comprehensive performance applications, medium epoxy value (0.23–0.45) resins can be selected; and for high temperature and high strength requirements, high epoxy value (0.45–0.54) resins can be selected.

[0027] In some embodiments, the chopped fibers mentioned above may refer to fibers with an aspect ratio <20. These chopped fibers may be selected from at least one or a mixture of carbon fibers, glass fibers, and carbon nanotubes. The addition range of these chopped fibers can be from 5 vol% to 50 vol% to address application requirements with varying performance, cost, and process adaptability.

[0028] Among various thermosetting agents for epoxy resins, anhydride-based curing agents are the most capable of providing both ultra-long working times and instantaneous gelation. The reaction rate between anhydrides and epoxy resins at room temperature is extremely slow, allowing the viscosity of the composite material to remain essentially unchanged for 24 hours or even weeks. Furthermore, anhydride-based curing agents offer advantages such as low cost and long pot life. However, if anhydride-based curing agents are used in a "latent curing agent + heat-triggered instantaneous curing" method, a strong accelerator needs to be added to the composite material. While adding an accelerator can significantly accelerate the curing reaction, it usually also causes the polymer to solidify significantly at low temperatures, thus shortening the working time. Moreover, even with the addition of a large amount of accelerator, a purely thermosetting process generally cannot achieve instantaneous gelation within 10 seconds.

[0029] Therefore, to increase the operating time, this application employs a photo / thermal dual-initiation system, namely, a "photo-triggered gel initiation + thermally triggered accelerated curing" approach. Thus, a photoinitiator is added to the composite material provided in this application, thereby forming a photo-thermal hybrid epoxy resin. This photoinitiator can be selected from at least one or a mixture of cationic photoinitiators and free radical photoinitiators. Cationic photoinitiators can be activated by cations (such as H+). + Chain ring-opening polymerization of epoxy resins catalyzed by ions such as iumonium (N, N, N) can be promoted by free radical photoinitiators, which can facilitate the chain addition polymerization of acrylates by providing free radicals (R·).

[0030] Optionally, the free radical photoinitiator can be selected from at least one or a mixture of TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide) and BAPO. For example, the free radical photoinitiator can include TPO. TPO has strong absorption near 380 nm, high matching degree with ultraviolet light source, high cleavage quantum yield and reactivity, and almost no absorption in the visible light region, having little impact on the working time. TPO has almost no absorption in the visible light region (>400 nm), does not initiate reaction under room temperature and light-protected conditions, and synergistically extends the working time (up to several days) with the low reactivity of the anhydride curing agent. Anhydride curing requires high temperature promotion, and the photocuring of TPO only triggers the acrylate portion, without affecting the slow reaction of the anhydride, avoiding accidental gelation. As another example, the free radical photoinitiator can include BAPO. BAPO, as a deep initiator, can ensure efficient deep curing in the presence of short-cut fibers. Alternatively, the free radical photoinitiator can include both TPO and BAPO mentioned above, so that the composite material combines the advantages of both.

[0031] The composite material provided in this application embodiment can utilize photo-triggered instantaneous gelation on the surface of the composite material, thereby inhibiting flow. After 3D printing, thermal triggering can be used to accelerate the reaction between the thermosetting agent (such as anhydride curing agent) and epoxy resin, thereby achieving final curing to form a high-performance short-cut fiber reinforced epoxy resin structural component. To achieve the above mechanism, this application embodiment adapts and adjusts the epoxy resin system by introducing acrylate groups: that is, grafting acrylate double bonds into the epoxy resin (such as using glycidyl methacrylate modification), so that the photoinitiator (such as TPO) can initiate rapid cross-linking of free radicals to form an initial network that inhibits flow. For example, ultraviolet light can be used to irradiate the surface of the composite material, instantly decomposing the onium salt to generate a super-strong Lewis acid (such as H+). + These protons violently attack the epoxy groups, initiating cationic ring-opening polymerization and forming a surface cross-linked network (gel) within 1–5 seconds, thereby inhibiting flow. Photocuring is primarily limited to thin surface layers (<0.5 mm), and the bulk properties of the component (deep curing, final Tg, mechanical strength) can be achieved through thermal triggering. For example, the anhydride curing agent and epoxy resin can be heated within a temperature range of 80–120°C to construct a complete, highly cross-linked three-dimensional network, ensuring the final mechanical properties of the structural component.

[0032] In some embodiments, the composite material provided in this application may further include a wetting and dispersing agent, such as BYK-163, to achieve stable dispersion of short-cut fibers through steric hindrance and charge regulation.

[0033] In some embodiments, the composite material provided in this application may further include an antioxidant / polymerization inhibitor to extend shelf life and prevent acrylate self-polymerization. The antioxidant may be provided in two stages to protect the composite material.

[0034] Phase 1: Protecting acrylates during processing and storage. The double bonds (C=C) of acrylates are highly reactive at room temperature, reacting with oxygen in the air to form peroxide radicals, thus initiating prepolymerization. This leads to increased system viscosity, shortened operating time, and even gelation during storage. In this phase, antioxidants (especially chain-terminating antioxidants like BHT) primarily act as "polymerization inhibitors," preferentially reacting with oxygen or early-formed free radicals, sacrificing themselves to protect the stability of the acrylate double bonds and ensure an exceptionally long operating time (>240 hours).

[0035] Phase Two: Protecting the Epoxy Resin During Thermosetting and Service Life. The oxidation of epoxy resin is a relatively slow process, but heat is its greatest enemy. During thermosetting (e.g., 120℃) and long-term high-temperature service, weak links (such as tertiary hydrocarbons) in the epoxy resin main chain are attacked by oxygen, resulting in chain degradation, main chain breakage, molecular weight reduction, brittleness, pulverization, and severe loss of mechanical strength (strength, modulus). The primary antioxidant (BHT) extinguishes alkyl free radicals (R·) generated during epoxy degradation, interrupting the chain reaction, while the secondary antioxidant (1076) decomposes hydroperoxides (ROOH) generated during degradation, preventing the formation of new free radicals and inhibiting the initiation of the chain reaction from its source.

[0036] Antioxidants can be selected from at least one or more of BHT and 1076. For example, antioxidants can be added in the following mass ratio: BHT:1076 = 1:1. BHT (primary antioxidant / polymerization inhibitor): protects acrylates at room temperature and epoxy resins at high temperatures, acting as the system's "first line of defense." 1076 (auxiliary antioxidant): provides long-term protection to the epoxy resin network by decomposing hydroperoxides, preventing thermo-oxidative aging, while also reducing the burden on BHT and extending its shelf life.

[0037] In some embodiments, the composite material provided in this application may further include a latent thermal catalyst. When using anhydride curing agents, incomplete curing and post-curing thermosetting failure may occur without a catalyst system. This is because the cross-linked network formed by photocuring hinders anhydride diffusion, leading to poor deep curing (bubbles, delamination). A latent catalyst can extend the working time (up to 7 days) and improve the final curing efficiency. For example, adding 0.3% zinc acetylacetonate can shorten the thermosetting time to 120°C / 2 hours with a gradual exothermic effect.

[0038] In some embodiments, the composite material provided in this application may also include a leveling agent (such as BYK-333 and / or BYK-UV 3510). The leveling agent can make the extruded material flow more smoothly and reduce surface roughness.

[0039] In some embodiments, the composite material provided in this application may also include a toughening agent (such as CTBN rubber).

[0040] In some embodiments, the composite material provided in this application may further include a coupling agent (such as KH-560). The coupling agent can improve the interfacial bonding between inorganic and organic materials, thereby enhancing the interlaminar shear strength, moisture resistance, and durability of the final material.

[0041] In some embodiments, the composite material provided in this application may further include fumed silica. Fumed silica can prevent the high-density chopped glass fibers (such as S-GF) in the composite material from settling and stratifying during storage.

[0042] In the composite material provided in this application embodiment, the epoxy resin can be 100 parts by weight, the thermosetting agent can be 35-90 parts by weight, the chopped fiber can be 5-225 parts by weight, the photoinitiator can be 2-9 parts by weight, and the acrylate can be 15-55 parts by weight.

[0043] Optionally, the composite material includes a wetting and dispersing agent, and the wetting and dispersing agent is present in parts by weight of 0.3 to 6 parts.

[0044] Optionally, the composite material includes a latent thermal catalyst, and the latent thermal catalyst is present in 0.1 to 2 parts by weight.

[0045] Optionally, the composite material includes an antioxidant, and the antioxidant is present in parts by weight of 0.1 to 1 part.

[0046] Optionally, the composite material includes a toughening agent, and the toughening agent is present in 6 to 12 parts by weight.

[0047] Optionally, the composite material includes a leveling agent, and the leveling agent is present in parts by weight of 0.4 to 1 part.

[0048] Optionally, the composite material includes a coupling agent, and the coupling agent is present in parts by weight of 1 to 3 parts.

[0049] Optionally, the composite material includes fumed silica, and the fumed silica is present in 1 to 2 parts by weight.

[0050] Optionally, the composite material includes nanoclay. Nanoclay can be used to modulate the rheological properties of the composite material. The amount of nanoclay added ranges from 1% to 10%.

[0051] Several more specific examples are given below.

[0052] Example 1 In Example 1, two acrylates, TPGDA and HDDA, were selected. In the presence of photoinitiators TPO and BAPO, UV irradiation causes the acrylates and photoinitiators to react and rapidly crosslink, quickly suppressing any flow of the extruded material and fixing the shape of the printed layer. Both TPGDA and HDDA are key reactive diluents and crosslinking agents in UV curing systems. TPGDA effectively reduces system viscosity and provides good flexibility after curing; HDDA, on the other hand, is characterized by its high reactivity and excellent adhesion, providing a high crosslinking density, resulting in a cured coating with better hardness, abrasion resistance, and chemical resistance.

[0053] Example 2 Example 3 This application also provides a 3D printing method. The 3D printing method includes: during the 3D printing process, extrudeing a composite material as described in any of the preceding embodiments using an extrusion device (or extrusion head). Then, irradiating the composite material with a light source (such as an ultraviolet light source) to trigger a reaction between a photoinitiator (such as TPO and / or BAPO) and acrylate, causing the surface of the composite material to gel instantaneously. Then, the composite material can be heated using a heat source to trigger a reaction between a thermosetting agent and epoxy resin, causing the composite material to cure. This step can be performed after 3D printing is complete, and the temperature of the heat source can be controlled, for example, between 80 and 120°C.

[0054] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A composite material, characterized in that, The composite material comprises: a photoinitiator, a thermosetting agent, and a short-fiber reinforced epoxy resin, wherein the epoxy resin comprises acrylate. The operating time of the composite material is greater than 24 hours; In this process, after the photoinitiator reacts with the acrylate, the gelation time of the surface layer of the composite material is 1 to 5 seconds.

2. The composite material according to claim 1, characterized in that, The epoxy resin comprises 100 parts by weight, the thermosetting agent comprises 35-90 parts by weight, the chopped fibers comprises 5-225 parts by weight, the photoinitiator comprises 2-9 parts by weight, and the acrylate comprises 15-55 parts by weight.

3. The composite material according to claim 1 or 2, characterized in that, The curing agent includes anhydride-based curing agents.

4. The composite material according to claim 1 or 2, characterized in that, The epoxy resin is selected from at least one or a mixture of glycidyl ether epoxy resins, aliphatic epoxy resins, and glycidyl ester epoxy resins.

5. The composite material according to claim 1 or 2, characterized in that, The aspect ratio of the chopped fibers is <20.

6. The composite material according to claim 1 or 2, characterized in that, The chopped fibers are selected from at least one or a mixture of carbon fibers, glass fibers, and carbon nanotubes.

7. The composite material according to claim 1 or 2, characterized in that, The photoinitiator is selected from at least one or a mixture of cationic photoinitiators and free radical photoinitiators.

8. The composite material according to claim 7, characterized in that, The free radical photoinitiator is selected from at least one or a mixture of TPO and BAPO.

9. The composite material according to claim 1 or 2, characterized in that, The composite material also includes one or more of the following: wetting and dispersing agents, antioxidants, polymerization inhibitors, and latent thermal catalysts.

10. The composite material according to claim 1 or 2, characterized in that, The thickness of the surface layer is less than or equal to 0.5 mm.

11. The composite material according to claim 1 or 2, characterized in that, The gelation time is 1 to 3 seconds.

12. A 3D printing method, characterized in that, include: During the 3D printing process, the composite material as described in any one of claims 1 to 11 is extruded using an extrusion device; The composite material is irradiated with a light source to trigger a reaction between the photoinitiator in the composite material and the acrylate, resulting in a gel on the surface of the composite material. The composite material is cured by using a heat source to trigger the reaction between the thermosetting agent and the epoxy resin.

13. The application of the composite material according to any one of claims 1 to 11 as an extrusion-based 3D printing material.

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