Foamable resin composition

Abstract

This disclosure provides a foamed resin composition. The foamed resin composition includes a polyurethane (meth)acrylate oligomer, a photoinitiator, thermally expandable microcapsules, and a photopolymerizable monomer.

Description

[Technical Field]

[0001] This disclosure relates to a resin composition for Continuous Liquid Interface Production (CLIP) 3D printing technology, and particularly to a foamed resin composition for continuous liquid interface production. [Previous Technology]

[0002] Continuous liquid interface 3D printing technology utilizes UV light projection onto a transparent resin tank at the bottom, causing the liquid photosensitive resin within to photocur and form a shape. The detailed steps are described in Tumblestone et al. (2015). Science, 347(6228), 1349–1352. Although the UV light used in continuous liquid interface 3D printing technology has a short wavelength and can provide fine resolution, the process efficiency still needs further improvement due to the need to print 3D objects layer by layer.

[0003] Carbon3D, in US11292186B2, discloses a foamed resin composition in which microcapsules are added to a resin raw material. This foamed resin composition is placed in a continuous liquid interface production machine and photocured to form an intermediate. The intermediate is then heated to thermocure and set its shape, during which the microcapsules mixed within it also expand due to the heat. This method allows for the initial printing of smaller intermediate products, which are then heated to expand and obtain larger final products, thereby increasing production speed.

[0004] Although the concept of adding microcapsules to dual-curing resins to accelerate production speed is disclosed in these documents, the viscosity of foamed resin compositions increases due to the fluid shear thickening effect after the resin raw materials are mixed with microcapsules. This may lead to lamination misalignment during the printing process, thus affecting the printing quality. This has not been reported in previous cases. Furthermore, the increased viscosity after adding microcapsules requires the addition of diluents to facilitate the printing of foamed resin compositions in 3D printing technology with continuous liquid interface production. Also, the considerations of how to ensure that the intermediate formed after printing / UV polymerization has the characteristics required to successfully complete foaming during the heating foaming process have not been further studied in the literature.

[0005] Based on the above reasons, it is necessary to develop a foaming resin composition that is suitable for continuous liquid interface production and takes into account both production efficiency and printing quality. At the same time, the intermediate of this foaming resin composition after UV polymerization also has the property of being suitable for heating and foaming. Therefore, after heating, the microcapsules mixed in the intermediate can fully expand, resulting in a final volume increase and full thermosetting. [Summary of the Invention]

[0006] This disclosure provides a foaming resin composition comprising: 20 to 90 parts by weight of a polyurethane (meth)acrylate oligomer, 0.1 to 10 parts by weight of a photoinitiator, 1 to 25 parts by weight of thermally expandable microcapsules, and 10 to 45 parts by weight of a photopolymerizable monomer, wherein the photopolymerizable monomer comprises the following compounds having formula (1), compounds having formula (2), compounds having formula (3), compounds having formula (4), compounds having formula (5), compounds having formula (6), or combinations thereof: Formula (1), wherein R1 is methyl, ethyl, tert-butyl, octadecyl, isodecyl, isodecyl, iso Nonyl, C3-C11 cycloalkyl, 2-methyl-2-adamantyl or substituted or unsubstituted aromatic group, R2 is hydrogen or methyl, or R1 is dodecyl or isooctyl and R2 is methyl; formula (2), wherein R3 is methyl and n is any integer from 3 to 12; formula (3), wherein Y is a branched C1-C8 alkyl group or a substituted or unsubstituted cycloalkyl group, R4 is hydrogen or methyl, or Y is a straight-chain C1-C8 alkyl group and R4 is methyl; formula (4), wherein i+j+k=15 and R5 is hydrogen or methyl; formula (5), wherein R6 is hydrogen or methyl; and formula (6), wherein R7 is hydrogen or methyl.

[0007] In some embodiments, the thermally expandable microcapsule has an alkane compound and a nitrile polymer shell encapsulating the alkane compound, wherein the alkane compound includes low-carbon alkanes, which are volatile liquids.

[0008] In some embodiments, the foamed resin composition further includes 0 to 70 parts by weight of curing agent.

[0009] In some embodiments, the weight ratio of polyurethane (meth)acrylate oligomer to photopolymerizable monomer in the foamed resin composition is 1.5:1 to 2.5:1, for example 1.5:1, 2:1 or 2.5:1.

[0010] In some embodiments, the C3-C11 cycloalkyl group includes cyclohexyl, and the substituted or unsubstituted aromatic group includes phenyl, benzyl, phenoxy or phenolic.

[0011] In some embodiments, compounds having formula (2) include polyethylene glycol (200) dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate or combinations thereof, and compounds having formula (3) include tricyclodecanedimethyl dimethacrylate, 1,4-butanediol dimethacrylate or combinations thereof.

[0012] In some embodiments, the viscosity of the foamed resin composition at 25 °C is 100 cps to 10000 cps.

[0013] In some embodiments, the photopolymerizable monomer with a viscosity of 50 cps or more is less than 45 parts by weight in the foamed resin composition, and the photopolymerizable monomer with a viscosity of 100 cps or more is less than 20 parts by weight in the foamed resin composition.

[0014] In some embodiments, the weight ratio of the compound having formula (1) to the compound having formula (2) or the compound having formula (3) is 1:1 to 12:1.

[0015] In some embodiments, the thermally expandable microcapsules account for 2 to 15 parts by weight in the foamed resin composition.

[0016] In some embodiments, the thermally expandable microcapsules account for 3 to 10 parts by weight in the foamed resin composition.

[0017] In some embodiments, the particle size of the thermally expanded microcapsules is from 5 µm to 100 µm.

[0018] In some embodiments, the polyurethane (meth)acrylate oligomer, photopolymerizable monomer and photoinitiator used may be those disclosed in US11,241,822, US9,598,606, US9,676,963 or US9,453,142.

[0019] In some embodiments, the molecular weight of the polyurethane (meth)acrylate oligomer is 30,000 Da to 40,000 Da.

[0020] In some embodiments, the curing agent includes 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane.

[0021] In some embodiments, the foamed resin composition as described in any of the above embodiments further includes fillers to add desired properties to the final product, such as: enhancing mechanical properties, changing surface properties, increasing / reducing weight, extending the durability / weather resistance of the final product, adding antifouling effects, and enhancing appearance. Specifically, fillers that strengthen the final product, such as rigid components like fiberglass, can be added; fillers that prevent slippage, such as rough particles like mortar, can be added; fillers that change the weight of the final product, such as adding metal powder to increase weight or adding hollow / lightweight particles to reduce weight, can be added; fillers that give the final product durability / weather resistance, such as adding UV-resistant agents to prevent yellowing and disintegration after prolonged sun exposure, can be added to achieve a mud-resistant effect, for example, adding anti-fouling powder to a foamed resin composition for printing, the anti-fouling powder can be silicone-based or fluorine-based; and various fillers that can give the final product the desired appearance, such as various colorants, can be added.

[0022] In some embodiments, the colorant may be a resin dye (color masterbatch), a thermochromic material, or a photochromic material (sunlight-changing ink).

[0023] This invention provides a foamed resin composition suitable for continuous liquid interface production, which involves adding thermally expandable capsules to an elastic dual-curing resin mixture. The elastic dual-curing resin can be a resin composition that combines UV polymerization and thermal curing stages. The thermally expandable microcapsules can be foamed particles with a hollow spherical structure, containing a nitrile polymer shell and alkane contents. The glass transition temperature (Tg) of the thermally expandable capsules is lower than the melting point temperature (Tm) and thermal decomposition temperature (Td) of the elastic dual-curing resin, ensuring that during the heating stage, when the shell of the thermally expandable capsule softens due to heat, the elastic dual-curing resin has neither melted nor decomposed.

[0024] In some embodiments, the outer shell of the thermally expandable microcapsules may also be colored to provide the desired visual effect for the resulting resin molded articles. In some embodiments, the thermally expandable microcapsules may be black, white, red, blue, yellow, or other desired colors.

[0025] In addition, under UV light irradiation, the photoinitiator absorbs light energy to generate free radicals, which in turn initiates the polymerization reaction of photopolymerizable monomers and polyurethane (meth)acrylate oligomers.

[0026] Photopolymerizable monomers may include compounds having the following chemical formula: R-Xa, where X is the reactive part and R is the non-reactive part. Specifically, X is a carbon-carbon double bond (-C=C-) group that reacts with the photoinitiator, while R is a residue part that does not react with the photoinitiator. When the photoinitiator is irradiated by UV light, it generates free radicals, which attack the carbon-carbon double bond group on the photopolymerizable monomer, thereby converting the double bond of the carbon-carbon double bond group into a single bond and π electrons. The photopolymerizable monomer forms an intermediate carbocation, which crosslinks with polyurethane (meth)acrylate oligomers to form a polymer network. In other words, the X part of the photopolymerizable monomer reacts with the polyurethane (meth)acrylate oligomer, while the R part of the photopolymerizable monomer does not participate in the chain-growth polymerization reaction during UV polymerization. Detailed steps are described in Konuray et al. (2018). Polymers, 10(2), 178.

[0027] In some embodiments, the photopolymerizable monomer includes a reactive portion (X) and a portion (R) that does not participate in the chain polymerization reaction. Specifically, X is a carbon-carbon double bond group used to interact with the photoinitiator, while R is a residue group that does not interact with the photoinitiator.

[0028] In some embodiments, the R portion of the photopolymerizable monomer with the chemical formula R-Xa is a steric hindrance residue portion; specifically, R exists in a bulky occupancy adjacent to a reactive site. The steric hindrance R group in the photopolymerizable monomer can create space when it bonds with a side group of the polymer backbone. This space can create reaction space for other types of photopolymerizable monomers. Specifically, it can act as a spacer when the photopolymerizable monomer is linked with a polyurethane (meth)acrylate oligomer, reducing entanglement of other long-chain photopolymerizable monomers and promoting a smooth reaction. In addition to its influence on the chain polymerization reaction, the steric residues also contribute to the overall properties of the intermediates after UV polymerization. Specifically, since the steric R groups restrict the chain mobility when they are bonded to the oligomer backbone, making it difficult for them to rotate or slide, the intermediates after UV polymerization tend to be in a rigid state and have higher mechanical strength.

[0029] In some embodiments, the photopolymerizable monomer with the chemical formula R-Xa contains a long-chain group, such as a long-chain alkyl group, for example, a C3-C30 alkyl group; preferably a C3-C20 alkyl group; more preferably a C3-C12 alkyl group. Photopolymerizable monomers with long-chain alkyl groups can provide a higher degree of rotational freedom for the polymer backbone, thus making the intermediate after UV polymerization more flexible and having better deformation ability.

[0030] In some embodiments, the photopolymerizable monomer with the chemical formula R-Xa also contains long chains with side reaction sites in the R portion. These side reaction sites can increase intermolecular interactions, causing adjacent polymer chains to form links. In some embodiments, the R portion is a long polyether chain, and the portion containing oxygen (O) is a side reaction site, which may form hydrogen bonds with molecules on adjacent polymer chains. Thus, in addition to the main reaction in the X portion, side reactions also occur in the R portion, thereby increasing the degree of polymerization crosslinking, making the interconnected network denser, and helping to enhance the flexibility of the intermediate after UV polymerization.

[0031] In some embodiments, the R portion of the photopolymerizable monomer with the chemical formula R-Xa is a small molecule group, which has a small spatial position and a low molecular weight. In other words, the number of reaction sites provided per unit weight of the small molecule photopolymerizable monomer is higher than that of the larger molecule photopolymerizable monomer. In this way, the crosslinking density can be increased. In some embodiments, the photopolymerizable monomer is, for example, methyl methacrylate (MMA), ethyl methacrylate (Ethyl methacrylate), or a combination thereof.

[0032] In some embodiments, the viscosity of the photopolymerizable monomer at 25 °C is 1 cps to 7000 cps.

[0033] In some embodiments, the foamed resin composition includes one or more of the above-mentioned photopolymerizable monomers with the chemical formula R-Xa.

Implementation Method

[0035] To make the description of this disclosure more detailed and complete, various forms of embodiments and illustrative descriptions of specific embodiments are provided below. The embodiments of this disclosure are not limited to one form, and embodiments can be combined or substituted with each other where advantageous. Other embodiments may also be added to this disclosure without further description or explanation.

[0036] This disclosure provides a foamed resin composition. The foamed resin composition includes a polyurethane (meth)acrylate oligomer (i.e., a polyurethane acrylate oligomer or a polyurethane methacrylate oligomer), a photoinitiator, thermally expandable microcapsules, and a photopolymerizable monomer. The foamed resin composition may further include a curing agent. This disclosure provides a foamed resin composition comprising 20 to 90 parts by weight of polyurethane (meth)acrylate oligomer, 0.1 to 10 parts by weight of photoinitiator, 1 to 25 parts by weight of thermally expandable microcapsules, 0 to 70 parts by weight of curing agent, and 10 to 45 parts by weight of photopolymerizable monomer. The photopolymerizable monomer may include a compound having the following chemical formula: R-Xa, wherein X is the reactive moiety, and R is the moiety that does not participate in the chain polymerization reaction. In some embodiments, the photopolymerizable monomer wherein X is the reactive moiety, and R is the moiety that does not participate in the chain polymerization reaction. The reactive monomer R-Xa has one to six reactive functional groups X and a group R that does not participate in the chain polymerization reaction, and the group R may have multiple reaction sites that can form hydrogen bonds, wherein R is selected from the group consisting of: small molecule groups, sterically hindered groups, side reaction site groups, and long chain groups.

[0037] First, polyurethane (meth)acrylate oligomers will be described. Polyurethane (meth)acrylate oligomers can be cured by crosslinking reactions and thus serve as structural supports in resin molded articles. In some embodiments, polyurethane (meth)acrylate oligomers may be obtained from commercial sources or prepared by known methods. For example, they may be prepared by the methods described in Velankar, Pazos, and Cooper, Journal of Applied Polymer Science 162, 1361 (1996), or by the methods disclosed in Carbon3D patents, such as those described in patent numbers US10,471,655, US10,350,823 or US 9,453,142, the entire contents of which are incorporated herein by reference. In some embodiments, preferred polyurethane (meth)acrylate oligomers comprise compounds having the following formula (7): Formula (7), where m is any integer from 500 to 700. In some embodiments, the preferred polyurethane (meth)acrylate oligomer has a molecular weight of 30,000 Da to 40,000 Da, such as 30,000 Da, 32,500 Da, 35,000 Da, 37,500 Da, or 40,000 Da, so that the viscosity of the foamed resin composition is not too high, but still has a sufficiently long main chain structure to provide structural support. In some embodiments, the polyurethane (meth)acrylate oligomer accounts for 20 to 90 parts by weight in the foamed resin composition, such as 20, 30, 40, 50, 60, 70, 80, or 90 parts by weight.

[0038] Next, the photopolymerizable monomers will be described. As described above, the photopolymerizable monomers disclosed herein can reduce the viscosity of foamed resin compositions to improve print quality. In some embodiments, the viscosity of the foamed resin composition at 25 °C is from 100 cps (or cP, centipoise) to 10,000 cps, preferably from 1,000 cps to 8,000 cps, and more preferably from 1,500 cps to 6,000 cps. In some embodiments, the viscosity of the foamed resin composition at 40 °C is preferably from 1,500 cps to 5,000 cps.

[0039] The photopolymerizable monomers disclosed herein can dilute the viscosity of foamed resin compositions to prevent excessively high viscosity from hindering printing when applied to 3D printing, thereby improving 3D printing quality. Suitable photopolymerizable monomers can be obtained from various commercial sources or prepared by known methods. For example, SR313A, SR399, SR340, SR423SN, CD406, CD590, SR506SN, SR252, SR259, SR295, SR508, SR540, SR214, SR9035, SR421, SR238, and SR602 from Sartoma Chemical Co., Ltd. can be used; and EM70, EM75, and EM90 from Chang Hsing Chemical Co., Ltd. can also be used. EM210, EM221, EM225, EM2380, EM2192, EM218, EM226, EM227, EM242, EM265, EM309, EM315, EM320, EM3205, EM2306, EM327, EM328, EM331; or LM-D300M, LM-20TA, LM-A022 and other products provided by Liangmao Technology. The viscosity of the photopolymerizable monomers at 25°C is 1~7000 cps. Preferably, photopolymerizable monomers with a viscosity of 50 cps or higher account for less than 45 parts by weight of the total formulation, and photopolymerizable monomers with a viscosity of 100 or higher account for less than 20 parts by weight of the total formulation. More preferably, photopolymerizable monomers with a viscosity of 50 cps or higher account for less than 20 parts by weight of the total formulation, and photopolymerizable monomers with a viscosity of 100 cps or higher account for less than 10 parts by weight of the total formulation.

[0040] Continuing with the explanation of photopolymerizable monomers. The photopolymerizable monomers disclosed herein can also adjust the degree, speed, and morphology of UV polymerization by selecting the type and ratio of monomers, so that the intermediate after UV polymerization has suitable properties. It can provide sufficient encapsulation force to the microcapsules during the subsequent thermosetting process to prevent the capsules from exploding, while also providing appropriate extensibility so that the microcapsules can fully expand during the formation of the intermediate in UV polymerization. Therefore, it helps to make the microcapsules expand as much as possible while maintaining the integrity of the microcapsules, improve the bulk foaming rate of thermally expanded microcapsules, and thus improve the efficiency and yield of 3D printing.

[0041] In some embodiments, the foamed resin composition comprises one or more photopolymerizable monomers with the chemical formula R-Xa. X is the reactive portion, and R is the portion that does not participate in the chain polymerization reaction. The reactive monomer R-Xa has one to six reactive functional groups X and groups R that do not participate in the chain polymerization reaction, and groups R may have multiple hydrogen-bonding reaction sites, wherein R is selected from the group consisting of: small molecule groups, sterically hindered groups, side-reactive site groups, and long-chain groups. Photopolymerizable monomers having small molecule groups, sterically hindered groups, and long-chain groups (e.g., long-chain alkyl groups) include compounds having formula (1), formula (4), formula (5), or formula (6); photopolymerizable monomers having side-reactive site groups include compounds having formula (2) or formula (3). The details are as follows: Formula (1), wherein R1 is a straight-chain or branched alkyl group (e.g., C1-C18 straight-chain or branched alkyl group, such as methyl, ethyl, tert-butyl, dodecyl, octadecyl, isodecyl, isooctyl, isononyl), a substituted or unsubstituted cycloalkyl group (e.g., C3-C11 cycloalkyl group (e.g., cyclohexyl), isobornyl, 2-methyl-2-adamantyl), or a substituted or unsubstituted aromatic group (e.g., phenyl, benzyl, phenoxy, phenolic), and R2 is hydrogen or an alkyl group (e.g., methyl). When the photopolymerizable monomer includes a small molecule group, R1 may be methyl or ethyl. When the photopolymerizable monomer includes a sterically hindered group, R1 may be tert-butyl, isobornyl, 2-methyl-2-adamantyl, cyclohexyl, phenyl, benzyl, phenoxy, or phenolic. When the photopolymerizable monomer includes a long-chain group, R1 may be dodecyl, octadecyl, isodecyl, isooctyl, or isononyl. Formula (2), wherein R3 is hydrogen or methyl, and n is any integer from 3 to 12, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. Formula (3), wherein Y is a straight-chain or branched alkyl group (e.g., C1-C8 straight-chain or branched alkyl group) or a substituted or unsubstituted cycloalkyl group, and R4 is hydrogen or methyl. Formula (4), wherein i+j+k=15, and R5 is hydrogen or methyl; Formula (5), wherein R6 is hydrogen or methyl; and Formula (6), wherein R7 is hydrogen or methyl. In some embodiments, the photopolymerizable monomer includes compounds having formula (1), compounds having formula (2), compounds having formula (3), compounds having formula (4), compounds having formula (5), compounds having formula (6), or combinations thereof.In some embodiments, the photopolymerizable monomer includes a compound having formula (1); at least one of a compound having formula (2) and a compound having formula (3); and at least one of a compound having formula (4) and a compound having formula (5), wherein the compound having formula (1) accounts for 0.1 to 25 parts by weight of the foaming resin composition, and at least one of the compound having formula (2) and the compound having formula (3) and at least one of the compound having formula (4) and the compound having formula (5) together account for 0.1 to 20 parts by weight of the foaming resin composition.

[0042] In some embodiments, the photopolymerizable monomer having the R part having a small molecule group includes: methyl methacrylate (MMA), ethyl methacrylate (Ethyl methacrylate), or a combination thereof.

[0043] In some embodiments, the photopolymerizable monomers of the R portion having steric hindrance include: tert-butyl acrylate, isobornyl acrylate (IBOA), 2-methyl-2-adamantyl acrylate, cyclohexyl methacrylate, benzyl methacrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol hexaacrylate, or combinations thereof.

[0044] In some embodiments, the photopolymerizable monomer having a long-chain alkyl R moiety includes: lauryl methacrylate (LMA), stearyl acrylate (SA), isodecyl acrylate (ISODA), isooctyl acrylate (IOA), isononyl acrylate (INAA), or combinations thereof.

[0045] In some embodiments, the photopolymerizable monomer having a long chain R portion containing a side reaction site includes: polyethylene glycol (200) diacrylate (PEG(200)DA), polyethylene glycol (400) diacrylate (PEG(400)DA), polyethylene glycol (600) diacrylate (PEG(600)DA), polyethylene glycol (200) dimethacrylate (PEG(200)DMA), polyethylene glycol (400) dimethacrylate (PEG(400)DMA), polyethylene glycol (600) dimethacrylate (PEG(600)DMA), PEG(600)DMA), or combinations thereof.

[0046] In some embodiments, the photopolymerizable monomer containing the side reaction site may include a compound having the following chemical formula: tricyclodecane dimethanol diacrylate, 1,4-butanediol dimethacrylate (BDMA), or a combination thereof.

[0047] In some embodiments, the photopolymerizable monomer accounts for 10 to 45 parts by weight in the foamed resin composition, for example, 10, 15, 20, 25, 30, 35, 40, or 45 parts by weight. In some embodiments, when the photopolymerizable monomer includes a compound having formula (1) and a compound having formula (2), the preferred weight ratio of the compound having formula (1) to the compound having formula (2) is 1:1 to 12:1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, or 12:1. In some embodiments, when the photopolymerizable monomer includes a compound having formula (1) and a compound having formula (3), the preferred weight ratio of the compound having formula (1) to the compound having formula (3) is 1:1 to 12:1, for example 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1 or 12:1.

[0048] Next, the thermally expandable microcapsules will be described. In the process of producing dual-curing resin mixture products using a continuous liquid interface, thermally expandable microcapsules are mixed with the base resin raw material to form a foamed resin composition. During the continuous liquid interface production printing process, the composition is photocured to form an intermediate containing the thermally expandable microcapsules. At this point, the thermally expandable microcapsules have not yet expanded due to heat. Subsequently, the intermediate is heated to thermally cure and set its shape, and at the same time, the microcapsules mixed in it also expand due to heat. During the heating process, the thermally expandable microcapsules expand due to heat, and at the same time, the intermediate is also thermally cured and set its shape. As the heating time progresses, the volume of the thermally expandable microcapsules gradually expands, and at the same time, the intermediate gradually thermally cures. Therefore, the final polyurethane (meth)acrylate oligomer product has a larger volume than the volume originally printed from the continuous liquid interface machine. In some embodiments, the expansion rate of the thermally expanding microcapsules is approximately equal to the thermal curing rate of the base resin material; in some embodiments, the expansion rate of the thermally expanding microcapsules is faster than the thermal curing rate of the base resin material; and in some embodiments, the expansion rate of the thermally expanding microcapsules is slower than the thermal curing rate of the base resin material.

[0049] Continuing with the description of thermally expandable microcapsules. In some embodiments, the thermally expandable microcapsules comprise a polymer shell and a volatile liquid encapsulated within the polymer shell. When the temperature exceeds the glass transition temperature of the polymer shell, the polymer shell softens, and the volatile liquid vaporizes, causing the polymer shell to expand outward. In some embodiments, the polymer shell comprises a heat-softened polymer, such as a shell composed of a nitrile polymer, particularly a shell comprising a copolymer of acrylonitrile and methacrylonitrile. In some embodiments, the volatile liquid encapsulated within the polymer shell is a low-carbon alkane, particularly a liquid alkane that vaporizes upon heating, such as isobutane, isopentane, isohexane, or other alkane that are liquid at room temperature but vaporize upon heating. In some embodiments, the thermally expandable microcapsules have approximately uniform shape and particle size, such that the pores formed in the final product after thermal expansion have a generally uniform shape and volume. In some embodiments, the preferred shape of the thermally expandable microcapsules is circular or elliptical. In some embodiments, the pre-foaming thermally expandable microcapsules preferably have a particle size of 5 µm to 100 µm, more preferably 10 µm to 50 µm, and most preferably 10 µm to 30 µm. In some embodiments, the thermally expandable microcapsules comprise 1 to 25 parts by weight of the foamed resin composition, for example, 1 part by weight, 5 parts by weight, 10 parts by weight, 15 parts by weight, 20 parts by weight, or 20 parts by weight. The expanded thermally expandable microcapsules retain a substantially intact shell after expansion, providing partial structural support for the resin molded article.

[0050] In some embodiments, the polymer shell of the thermally expandable microcapsules may include a colorant. In some embodiments, the colorant contained in the thermally expandable microcapsules may diffuse into the base resin after being formulated into the foamed resin composition of the present invention, giving the final molded resin article a saturated and rich color appearance. In some embodiments, the thermally expandable microcapsules containing colorants may be commercially available, or commercially available colorants may be mixed with colorant-free thermally expandable capsules to produce colorant-containing thermally expandable microcapsules.

[0051] In some embodiments, the thermally expanded microcapsules may be commercially available microcapsules or may be prepared by known methods. Commercially available sources include, but are not limited to, products from: Dongjin Semiconductor Chemical's UNICELL series, such as the UNICELL-DS series (e.g., D300L, D600, D900, D1100, D1300, D2500), G series (e.g., G, GP9, GP3, GP5), MS series (e.g., MS140DS / D, MS2002, MS4002, MS4600, MS180DY, MS190D, MS197D), PG series (e.g., PG-40, PG-42, PG-12, PG46, PG26, PG-18, PG-16); and Sekisui Chemicals' Micropearl series products, such as Micropearl... SP series (e.g., SP-210, SP-2095, SP-209, SP-208, SP-207, SP-206, SP-205, SP-204, SP-203), Micropearl EX series (e.g., EX-0055, EX-005, EX-00475, EX-0045), Micropearl EXH series (SP-0069, SP-0068, SP-0067, SP-0066, SP-0065, SP-0062, SP-006, SP-0058, SP-0055, SP-0049), Micropearl EZ series (e.g., EZ3P-020, EZ4P-030), Micropearl SLC series, Micropearl WS series (WS-606, WS-608, WS-302, WS-101); Matsumoto Oils & Fats Pharmaceutical Co., Ltd.'s Matsumoto Microsphere® products, such as the F series (e.g., F-30, F-36), FN series (e.g., FN-65, FN-100S), HF series, or MSH series (e.g., MSH890, MSH550, MSH380, MSH340, F-AC160D, HF-36D); AkzoNobel's Expancel® series products, such as the WE series (e.g., 921WE40), DE series (e.g., 920DE40), WUF series (e.g., 031WUF40, 007WUF40); Kureha Corporation's H series, S series, and other products.

[0052] Next, the photoinitiator will be described. The photoinitiator promotes the above-mentioned crosslinking reaction by absorbing light. In some embodiments, the photoinitiator includes diphenyl(2,4,6-trimethylbenzoyl)phosphine oxyde (TPO).

[0053] Continuing with the description of the foamed resin composition. In some embodiments, the foamed resin composition as described in any of the preceding embodiments further includes a curing agent to provide different curing mechanisms for the foamed resin composition, thereby producing the desired properties. In some embodiments, the curing agent includes 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (Dimethyldicykan, DMDC). In some embodiments, the curing agent accounts for 0 to 70 parts by weight in the foamed resin composition, for example, 0 parts by weight, 3 parts by weight, 5 parts by weight, 10 parts by weight, 30 parts by weight, 50 parts by weight, or 70 parts by weight.

[0054] Continuing with the description of the foamed resin composition. In some embodiments, the foamed resin composition as described in any of the preceding embodiments further includes a colorant, such that the 3D-printed resin molded article has the desired color. In some embodiments, the colorant includes any feasible colorant, such as white titanium dioxide or black carbon black. In some embodiments, the colorant may be a resin dye (masterbatch), a thermochromic material, or a photochromic material (sunlight-sensitive ink). In some embodiments, the colorant accounts for 0 to 10 parts by weight in the foamed resin composition. For example, 0 parts by weight, 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.5 parts by weight, 1 part by weight, 3 parts by weight, or 10 parts by weight.

[0055] Continuing with the description of the foamed resin composition. In some embodiments, the foamed resin composition further includes fillers that add desired properties to the final product. Examples include: glass fibers, glass microparticles, hollow glass beads, metal powders, UV-resistant agents, silicone-based antifouling powders, or fluorine-based antifouling powders.

[0056] Continuing with the description of the foamed resin composition. In some embodiments, the foamed resin composition described in any of the preceding embodiments further includes any feasible thermoplastic resin. In some embodiments, the types of thermoplastic resins are referenced in full in US Patent No. 9,453,142.

[0057] This disclosure also provides a resin molded article obtained by irradiation and heating of the aforementioned foamed resin composition. Irradiation (e.g., ultraviolet light) causes a photoinitiator to induce a crosslinking polymerization reaction between the polyurethane (meth)acrylate oligomer and the photopolymerizable monomer to form a curing intermediate. Heating (e.g., at 110°C) causes the thermally expandable microcapsules to expand, thereby expanding the aforementioned curing intermediate containing the cured polyurethane (meth)acrylate oligomer and the photopolymerizable monomer, to form a resin molded article with increased volume. In some embodiments, irradiation is performed before heating, and the photopolymerizable monomer has completely reacted with the polyurethane (meth)acrylate oligomer before heating. In some embodiments, the resulting resin molded article has a bulk foaming rate of about 110% to about 305% (the bulk foaming rate is the percentage increase in volume after expansion relative to the volume before expansion) compared to its volume before expansion (i.e., compared to the volume of the curing intermediate). In some embodiments, the resulting resin molded article includes a plurality of closed-cell structures, and these closed cells are substantially the same in shape and size and are distributed substantially uniformly within the resin molded article. The closed-cell structures contain gas, which gives the resin molded article insulating properties such as electrical insulation, thermal insulation, and sound insulation, and also provides shock absorption, compressibility, and ductility. Considering the aforementioned excellent properties of the resin molded article, this disclosure can be applied to various fields, such as applying the foamed resin composition of this disclosure to 3D printed insoles.

[0058] The foamed resin composition and resin molded articles disclosed herein will now be described with reference to only some embodiments. Therefore, the scope intended to be covered by the appended claims should not be limited by the following detailed embodiments.

[0059] In the experiment, the type of photopolymerizable monomer was used as an operational variable to reveal that the cross-linking polymerization of the photopolymerizable monomer in the polyurethane (meth)acrylate oligomer could result in a resin molded product with a good bulk foaming rate (i.e., except for the type of photopolymerizable monomer, the other controllable variables in Examples 1 to 4 were the same). The composition and concentration of the foamed resin composition in Examples 1 to 4 are shown in Table 1, and the experimental results are shown in Table 2. The polyurethane (meth)acrylate oligomer is, for example, the compound having the above formula (7), and the thermally expandable microcapsules are, for example, a copolymer of acrylonitrile and methacrylonitrile and isopentane encapsulated by the copolymer.

[0060] Table 1: Components and Concentrations (Concentration unit is parts by weight) polyurethane (Methyl)propane Acrylates TPO DMDC thermal expansion Slight swelling capsule MMA LMA IBOA PEG (200) DMA Example 1 70 1 5 5 20 0 0 0 Example 2 70 1 5 5 0 20 0 0 Example 3 70 1 5 5 0 0 20 0 Example 4 70 1 5 5 0 0 0 20

[0061] Table 2: Experimental Results Foaming rate (%) Example 1 245.55 Example 2 183.71 Example 3 245.55 Example 4 123.32

[0062] In Experiment 2, the good bulk foaming rate of the obtained resin molded product was revealed by the combination of different types of photopolymerizable monomers in the foamed resin composition and the concentration ratio of each component in the foamed resin composition. The components and concentrations of the foamed resin composition in Experiment 5 and Experiment 6 in Experiment 2 are shown in Table 3, and the experimental results are shown in Table 4. The polyurethane (meth)acrylate oligomer is, for example, the compound having the above formula (7), the colorant is, for example, the above white titanium dioxide, and the thermal expansion microcapsules are, for example, the above acrylonitrile and methacrylonitrile copolymer and isopentane encapsulated by the copolymer.

[0063] Table 3: Components and Concentrations (Concentration unit is parts by weight) polyurethane (Methyl)propane Acrylates LMA PEG (600) DMA IBOA DMDC TPO Pigment thermal expansion Slight swelling capsule Example 5 70 20 2 2 5 1 0.3 10 Example 6 70 15 15 0 5 1 0.3 10

[0064] Table 4: Experimental Results Foaming rate (%) Example 5 303.45 Example 6 178.70

[0065] The foamed resin composition disclosed herein has a moderate viscosity, which avoids a decline in print quality when applied to 3D printing. Furthermore, the foamed resin composition improves 3D printing yield and efficiency through a favorable foaming process.

[0066] This disclosure describes some embodiments in considerable detail. Other embodiments may also be possible. Therefore, the scope and spirit of the appended claims should not be limited to the embodiments described in this disclosure.

[0067] For those skilled in the art, modifications and alterations to this disclosure are permissible as long as they do not depart from the spirit and scope of this disclosure. If such modifications and alterations fall within the scope and spirit of the appended patent applications, they are considered to fall within the scope of this disclosure. [Simplified Explanation of the Diagram]

[0034] None [Biomaterial Storage]

[0069] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. A foaming resin composition, comprising: 20 to 90 parts by weight of a polyurethane (meth)acrylate oligomer; 0.1 to 10 parts by weight of a photoinitiator; 1 to 25 parts by weight of a thermally expandable microcapsule; and 10 to 45 parts by weight of a photopolymerizable monomer, wherein the polyurethane (meth)acrylate oligomer and the photopolymerizable monomer in the foamed resin composition are in a weight ratio of 1.5:1 to 2.5:1, the photopolymerizable monomer comprising the following compounds having formula (1), compounds having formula (2), compounds having formula (3), compounds having formula (4), compounds having formula (5), compounds having formula (6), or combinations thereof: Formula (1), wherein R1 is methyl, ethyl, tert-butyl, octadecyl, isodecyl, isononyl, C3-C11 cycloalkyl, 2-methyl-2-adamantyl or an aromatic group having a substituted or unsubstituted group, R2 is hydrogen or methyl, or R1 is dodecyl or isooctyl and R2 is methyl; Formula (2), wherein R3 is methyl, and n is any integer from 3 to 12; Formula (3), wherein Y is a branched C1-C8 alkyl group, or a substituted or unsubstituted cycloalkyl group, and R4 is hydrogen or methyl; or Y is a straight-chain C1-C8 alkyl group and R4 is methyl; Formula (4), wherein i+j+k=15, and R5 is hydrogen or methyl; Formula (5), wherein R6 is hydrogen or methyl; and Formula (6), wherein R7 is hydrogen or methyl.

2. The foamed resin composition as claimed in claim 1, wherein the thermally expandable microcapsule has an alkane compound and a nitrile polymer shell encapsulating the alkane compound, wherein the alkane compound includes a low-carbon alkane, which is a volatile liquid.

3. The foamed resin composition as claimed in claim 1 further comprises 0 to 70 parts by weight of a curing agent.

4. The foaming resin composition as claimed in claim 1, wherein the C3-C11 cycloalkyl group includes cyclohexyl, and the substituted or unsubstituted aromatic group includes phenyl, benzyl, phenoxy, or phenolic.

5. The foamed resin composition as claimed in claim 1, wherein the compound having formula (2) comprises polyethylene glycol (200) dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate or combinations thereof, and the compound having formula (3) comprises tricyclodecanedimethyl dimethacrylate, 1,4-butanediol dimethacrylate or combinations thereof.

6. The foamed resin composition as claimed in claim 1, wherein the foamed resin composition has a viscosity of 100 cps to 10000 cps at 25 °C.

7. The foamed resin composition as claimed in claim 2, wherein one particle size of the thermally expandable microcapsule is from 5 µm to 100 µm.

8. The foamed resin composition as claimed in claim 1, wherein a photopolymerizable monomer with a viscosity of 50 cps or more is present in less than 45 parts by weight in the foamed resin composition, and a photopolymerizable monomer with a viscosity of 100 cps or more is present in less than 20 parts by weight in the foamed resin composition.