Foaming resin composition and resin molded article

Abstract

The invention provides a foaming type resin composition. The foaming type resin composition comprises a polyurethane (methyl) acrylate oligomer, a photoinitiator, a thermal expansion microcapsule and a photopolymerization monomer. The foaming type resin composition is moderate in viscosity, and printing quality reduction caused when the foaming type resin composition is applied to 3D printing can be avoided. In addition, the foaming type resin composition can improve the 3D printing yield and efficiency through a good foaming process.

Description

Technical Field

[0001] The present invention relates to a resin composition for continuous liquid interface production (CLIP) 3D printing technology, and more particularly to a foaming resin composition and a resin molded product for CLIP. Background Art

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

[0003] Carbon3D, in US11292186B2, proposes a foamable resin composition incorporating microcapsules into a resin feedstock. This foamable resin composition is placed in a continuous liquid interface fabrication machine, where it is photocured to form an intermediate. The intermediate is then heated to cure and solidify, simultaneously expanding the microcapsules mixed within. This approach allows for the initial printing of a smaller intermediate product, which is then heated and expanded to create a larger final product, thereby increasing production speed.

[0004] Although these documents disclose the concept of adding microcapsules to dual-cure resins to speed up production, the shear thickening effect of the fluid after the resin raw materials are mixed with the microcapsules increases the viscosity of the foamable resin composition. This can lead to misalignment of the layers during printing, thus affecting print quality. This has not been reported in previous cases. The literature also does not further explore the considerations of how to ensure that the intermediate formed after printing / UV polymerization has the properties required for successful foaming during the heating and foaming process in response to the increased viscosity after the addition of microcapsules.

[0005] For the reasons stated above, it is necessary to develop a foamable resin composition suitable for continuous liquid interface manufacturing that balances production efficiency and printing quality. Furthermore, the intermediate of this foamable resin composition after UV polymerization also has properties suitable for thermal foaming. Therefore, after heating, the microcapsules mixed therein can fully expand, resulting in a larger final volume and sufficient thermal curing to fix the shape. Summary of the Invention

[0006] The present invention provides a foamable 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. The photopolymerizable monomer comprises at least one compound having a chemical formula of R-Xa, having a reactive functional group X and a non-reactive group R, wherein the non-reactive group R is selected from the group consisting of a small molecule group, a highly sterically hindered group, a multi-reactive site group, and a long-chain group. In some embodiments, X is an alkenyl group. In some embodiments, a is 1 to 6. In some embodiments, the photopolymerizable monomer having a formula greater than 1 accounts for 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight. In some embodiments, the photopolymerizable monomer having a formula greater than 2 accounts for 0 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 1 to 2 parts by weight. In some embodiments, the foamable resin composition includes at least one compound of the chemical formula R-Xa, wherein a is 1, 2, and 3. In some embodiments, the foamable resin composition includes at least one compound of R-Xa, wherein 0.1 to 20 parts by weight are compounds with a>1, and wherein 0.1 to 25 parts by weight are compounds with a=1.

[0007] In some embodiments, the thermally expandable microcapsules comprise an alkane compound and a nitrile polymer shell encapsulating the alkane compound.

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

[0009] In some embodiments, the weight ratio of the polyurethane (meth)acrylate oligomer to the photopolymerizable monomer in the foamable 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 photopolymerizable monomer includes a compound having formula (1), a compound having formula (2), a compound having formula (3), a compound having formula (4), a compound having formula (5), a compound having formula (6), or a combination thereof:

[0011] wherein R1 is a linear or branched C1-C18 alkyl group, a substituted or unsubstituted cycloalkyl group, or a substituted or unsubstituted aromatic group, and R2 is hydrogen or methyl;

[0012] wherein R3 is hydrogen or methyl, and n is any integer from 3 to 12;

[0013] wherein Y is a linear or branched C1-C8 alkylene group, or a substituted or unsubstituted cycloalkylene group, and R4 is hydrogen or methyl;

[0014] wherein i+j+k=15, and R5 is hydrogen or methyl;

[0015] wherein R6 is hydrogen or methyl; and

[0016] Wherein R7 is hydrogen or methyl.

[0017] In some embodiments, R1 is methyl, ethyl, tert-butyl, dodecyl, octadecyl, isodecyl, isooctyl, isononyl, cyclohexyl, isobornyl, 2-methyl-2-adamantyl, phenyl, benzyl, phenoxy, or phenol.

[0018] In some embodiments, the compound having formula (2) includes polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate, polyethylene glycol (200) dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate, or a combination thereof, and the compound having formula (3) includes tricyclodecane dimethanol diacrylate, 1,4-butanediol dimethacrylate, or a combination thereof.

[0019] In some embodiments, the viscosity of the foamable resin composition at 25° C. is 100 cps to 10,000 cps.

[0020] In some embodiments, the photopolymerizable monomer having a chemical formula of R-Xa with a≥2 accounts for 0.1 to 20 parts by weight of the foamable resin composition.

[0021] In some embodiments, the photopolymerizable monomer having a viscosity of 50 cps or more is less than 45 parts by weight in the foamable resin composition, and the photopolymerizable monomer having a viscosity of 100 cps or more is less than 20 parts by weight in the foamable resin composition.

[0022] In some embodiments, the weight ratio of the compound of formula (1) to the compound of formula (2) or to the compound of formula (3) is 1:1 to 12:1.

[0023] In some embodiments, the thermally expandable microcapsules account for 2 to 15 parts by weight of the foamable resin composition.

[0024] In some embodiments, the thermally expandable microcapsules account for 3 to 10 parts by weight of the foamable resin composition.

[0025] In some embodiments, the particle size of the thermally expandable microcapsules is 5 μm to 100 μm.

[0026] In some embodiments, the polyurethane (meth)acrylate oligomer, photopolymerizable monomer, and photoinitiator used may be those disclosed in US Pat. No. 11,241,822, US Pat. No. 9,598,606, US Pat. No. 9,676,963, or US Pat. No. 9,453,142.

[0027] In some embodiments, the molecular weight of the polyurethane (meth)acrylate oligomer is 30,000 Da to 40,000 Da.

[0028] In some embodiments, the curing agent includes 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane.

[0029] In some embodiments, the foamable resin composition described in any of the above embodiments further includes a filler to impart desired properties to the final product, such as enhancing mechanical properties, modifying surface properties, increasing / reducing weight, extending durability / weather resistance, adding antifouling effects, and enhancing appearance. Specifically, fillers may be added to strengthen the final product, such as hard components such as glass fiber; fillers may be added to make the final product non-slip, such as rough particles such as mortar; fillers may be added to change the weight of the final product, such as metal powder to increase weight or hollow / lightweight particles to reduce weight; fillers may be added to impart durability / weather resistance to the final product, such as UV inhibitors to prevent yellowing and disintegration of the final product over time; antifouling agents may be added to impart mud resistance to the final product, such as by adding antifouling powder to the foamable resin composition for printing; the antifouling powder may be silicone-based or fluorine-based; and various fillers may be added to impart desired appearance to the final product, such as various pigments.

[0030] In some embodiments, the colorant may be a resin dye (masterbatch), a thermochromic material, or a photochromic material (heliochromic ink).

[0031] The present invention provides a foamable resin composition suitable for continuous liquid interface fabrication, comprising thermally expandable capsules added to an elastic dual-cure resin mixture. The elastic dual-cure resin can be a resin composition that undergoes both UV polymerization and thermal curing. The thermally expandable microcapsules can be hollow spherical foam particles having a nitrile polymer shell and an alkane content. The glass transition temperature (Tg) of the thermally expandable capsules is lower than the melting point (Tm) of the elastic dual-cure resin and lower than its thermal decomposition temperature (Td). This ensures that during the heating phase, when the shell of the thermally expandable capsules softens due to heat, the elastic dual-cure resin remains neither melted nor decomposed.

[0032] In some embodiments, the shell of the thermally expandable microcapsules may also have a color to provide a desired visual effect for the resulting resin molded article. In some embodiments, the thermally expandable microcapsules may be black, white, red, blue, yellow, or other desired colors.

[0033] Furthermore, under UV light irradiation, the photoinitiator absorbs light energy to generate free radicals, which in turn initiate the polymerization reaction of the photopolymerizable monomer and the polyurethane (meth)acrylate oligomer.

[0034] Photopolymerizable monomers may include compounds having the following chemical formula: R-Xa, where X is a reactive moiety and R is a non-reactive moiety that does not participate in the chain polymerization reaction. Specifically, X is a carbon-carbon double bond (-C=C-) group that reacts with the photoinitiator, while R is a residue that does not react with the photoinitiator. When the photoinitiator is exposed to UV light, free radicals are generated. These free radicals attack the carbon-carbon double bond groups on the photopolymerizable monomer, 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 the polyurethane (meth)acrylate oligomer through the carbocation to form a polymer network. In other words, the X moiety of the photopolymerizable monomer reacts with the polyurethane (meth)acrylate oligomer, while the R moiety of the photopolymerizable monomer does not participate in the chain-growth polymerization during the UV polymerization process. The detailed steps are as described in Konuray et al. (2018). Polymers, 10(2), 178.

[0035] In some embodiments, the photopolymerizable monomer wherein X is a reactive moiety and R is a moiety that does not participate in the chain polymerization reaction, specifically, X is a carbon-carbon double bond group that reacts with a photoinitiator, and R is a residue group that does not react with the photoinitiator.

[0036] In some embodiments, the R moiety in the photopolymerizable monomer of the formula R-Xa is a steric hindrance residue. Specifically, R represents a bulky occupancy near a reactive site. The sterically hindering R group creates space when bonding to a pendant group on the polymer backbone. This space creates reactive space for other types of photopolymerizable monomers. Specifically, it acts as a spacer when the photopolymerizable monomer is chained with a polyurethane (meth)acrylate oligomer, reducing entanglement between other long-chain photopolymerizable monomers and promoting a smooth reaction. In addition to its impact on chain polymerization, the sterically hindering R group also contributes to the overall performance of the UV-polymerized intermediate. Specifically, because the sterically hindering R group restricts chain mobility when bonded to the oligomer backbone, making it difficult for the chain to rotate or slide, the UV-polymerized intermediate tends to be rigid and possesses higher mechanical strength.

[0037] In some embodiments, the photopolymerizable monomer of the formula R-Xa comprises a long-chain group, such as a long-chain alkyl group, for example, a C3-C30 alkyl group, preferably a C3-C20 alkyl group, and more preferably a C3-C12 alkyl group. Photopolymerizable monomers with long-chain alkyl groups can provide the polymer backbone with greater rotational freedom, thereby making the intermediate after UV polymerization more flexible and having better deformability.

[0038] In some embodiments, the photopolymerizable monomer of the formula R-Xa includes a long chain of side reaction sites in the R portion. These side reaction sites can enhance intermolecular interactions, allowing adjacent polymer chains to form links. In some embodiments, the R portion is a long polyether chain, wherein the oxygen (O) moiety serves as a side reaction site, potentially forming hydrogen bonds with molecules on adjacent polymer chains. Furthermore, in addition to the primary reaction occurring in the X portion, side reactions also occur in the R portion, thereby increasing the degree of crosslinking and creating a denser interconnected network, thereby enhancing the flexibility of the UV-polymerized intermediate.

[0039] In some embodiments, the photopolymerizable monomer of the formula R-Xa, wherein the R portion is a small molecular group, has a small spatial position and a low molecular weight. In other words, a small molecular photopolymerizable monomer can provide more reactive sites per unit weight than a larger molecular photopolymerizable monomer, thereby increasing the crosslinking density. In some embodiments, the photopolymerizable monomer is, for example, methyl methacrylate (MMA), ethyl methacrylate (Ethyl methacrylate), or a combination thereof.

[0040] In some embodiments, the viscosity of the photopolymerizable monomer at 25° C. is 1 cps to 7000 cps.

[0041] In some embodiments, the foamable resin composition includes one or more of the photopolymerizable monomers of the above chemical formula R-Xa. DETAILED DESCRIPTION

[0042] To provide a more detailed and complete description of the present invention, the following provides illustrative descriptions of various aspects and specific embodiments of the present invention. The embodiments of the present invention are not limited to a single form, and the embodiments may be combined or interchanged with each other where beneficial. Other embodiments may also be appended to the present invention without further description or explanation.

[0043] The present invention provides a foamable resin composition. The foamable resin composition includes a polyurethane (meth) acrylate oligomer (i.e., a polyurethane acrylate oligomer or a polyurethane methacrylate oligomer), a photoinitiator, a thermally expandable microcapsule, and a photopolymerizable monomer. The foamable resin composition may further include a curing agent. The present invention provides a foamable resin composition, including 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, 0 to 70 parts by weight of a curing agent, and 10 to 45 parts by weight of a photopolymerizable monomer. The photopolymerizable monomer may include a compound having the following chemical formula: R-Xa, wherein X is a reactive portion and R is a portion that does not participate in the chain polymerization reaction. In some embodiments, the photopolymerizable monomer is a portion wherein X is a reactive portion and R is a portion that does not participate in the chain polymerization reaction. The reactive monomer R-Xa has any integer of 1 to 6 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: a small molecule group, a group with steric hindrance, a side reaction site group, and a long chain group.

[0044] First, the polyurethane (meth) acrylate oligomer is described. The polyurethane (meth) acrylate oligomers can be cured by cross-linking reactions with each other, and thus serve as structural supports in resin molded products. In some embodiments, the polyurethane (meth) acrylate oligomer can be obtained from commercial sources or prepared by known methods. For example, it can be prepared by the method described in Velankar, Pazos, and Cooper, Journal of Applied Polymer Science 162, 1361 (1996), or by the method disclosed in Carbon3D patents, such as those described in patent numbers US10,471,655, US10,350,823 or US9,453,142, which are incorporated herein by reference in their entirety. In some embodiments, preferred polyurethane (meth) acrylate oligomers include the following compounds having formula (7):

[0045] Formula (7),

[0046] wherein m is any integer from 500 to 700. In some embodiments, the molecular weight of the polyurethane (meth)acrylate oligomer is preferably 30,000 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 foamable resin composition is not too high while still having 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 of the foamable resin composition, such as 20 parts by weight, 30 parts by weight, 40 parts by weight, 50 parts by weight, 60 parts by weight, 70 parts by weight, 80 parts by weight, or 90 parts by weight.

[0047] Next, the photopolymerizable monomer will be described. As described above, the photopolymerizable monomer of the present invention can reduce the viscosity of the foamable resin composition to improve printing quality. In some embodiments, the viscosity of the foamable resin composition at 25°C is 100 cps (or cP, centipoise) to 10,000 cps, preferably 1,000 cps to 8,000 cps, and more preferably 1,500 cps to 6,000 cps. In some embodiments, the viscosity of the foamable resin composition at 40°C is preferably 1,500 cps to 5,000 cps.

[0048] The photopolymerizable monomers of the present invention can reduce the viscosity of the foamable resin composition, thereby preventing excessive viscosity from hindering printing when used in 3D printing, thereby improving 3D printing quality. Suitable photopolymerizable monomers are available from various commercial sources or can be prepared using known methods. For example, SR313A, SR399, SR340, SR423SN, CD406, CD590, SR506SN, SR252, SR259, SR295, SR508, SR540, SR214, SR9035, SR421, SR238, and SR602 from Sartomer can be selected; and EM70, EM75, EM90, EM210, EM221, EM225, EM2380, EM2192, EM218, EM226, EM227, EM242, EM265, EM309, EM315, EM320, EM3205, EM2306, EM327, EM328, and EM331 from Changxing Chemical can also be selected; LM-D300M, LM-20TA, and LM-A022 from Liangmao Technology can also be used. The viscosity of the photopolymerizable monomer at 25° C. is 1 to 7000 cps. Preferably, the photopolymerizable monomer having a viscosity of 50 cps or higher accounts for less than 45 parts by weight of the total formulation, and the photopolymerizable monomer having a viscosity of 100 cps or higher accounts for less than 20 parts by weight of the total formulation. More preferably, the photopolymerizable monomer having a viscosity of 50 cps or higher accounts for less than 20 parts by weight of the total formulation, and the photopolymerizable monomer having a viscosity of 100 cps or higher accounts for less than 10 parts by weight of the total formulation.

[0049] Continuing with the description of the photopolymerizable monomer, the photopolymerizable monomer of the present invention can also adjust the degree of crosslinking, speed, and type of UV polymerization by selecting the type and ratio of the monomer, so that the intermediate after UV polymerization has appropriate properties. It can provide sufficient coating force for the microcapsules during the subsequent thermal curing process to prevent the capsules from exploding, while also providing appropriate ductility to enable the microcapsules to fully expand during the UV polymerization process to form the intermediate. This helps to expand the microcapsules as fully as possible while maintaining their integrity, improves the volume expansion rate of the thermally expandable microcapsules, and thus enhances 3D printing efficiency and productivity.

[0050] In some embodiments, the foamable resin composition includes one or more photopolymerizable monomers of the chemical formula R-Xa. Wherein X is a reactive portion, and R is a portion that does not participate in the chain polymerization reaction. Wherein, the reactive monomer R-Xa has a reactive functional group X of any integer from 1 to 6 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 the following: a small molecule group, a group with steric hindrance, a side reaction site group, and a long chain group. Wherein, the photopolymerizable monomers having a small molecule group, a steric hindrance group, and a long chain group (such as a long chain alkyl) include the following compounds having formula (1), formula (4), formula (5), or formula (6); wherein the photopolymerizable monomers having a side reaction site group include the following compounds having formula (2) or formula (3). Detailed description is as follows:

[0051] Wherein R1 is a linear or branched alkyl group (e.g., a C1-C18 linear or branched alkyl group, such as methyl, ethyl, t-butyl, dodecyl, octadecyl, isodecyl, isooctyl, or isononyl), a substituted or unsubstituted cycloalkyl group (e.g., a C3-C11 cycloalkyl group (e.g., cyclohexyl), isobornyl, or 2-methyl-2-adamantyl), or a substituted or unsubstituted aromatic group (e.g., phenyl, benzyl, phenoxy, or phenol), and R2 is hydrogen or an alkyl group (e.g., methyl). When the photopolymerizable monomer includes a small molecular weight group, R1 can be methyl or ethyl. When the photopolymerizable monomer includes a sterically hindering group, R1 can be t-butyl, isobornyl, 2-methyl-2-adamantyl, cyclohexyl, phenyl, benzyl, phenoxy, or phenol. When the photopolymerizable monomer includes a long-chain group, R1 can be dodecyl, octadecyl, isodecyl, isooctyl, or isononyl.

[0052] 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.

[0053] wherein Y is a linear or branched alkylene group (eg, a C1-C8 linear or branched alkylene group) or a substituted or unsubstituted cycloalkylene group, and R4 is hydrogen or methyl.

[0054] wherein i+j+k=15, and R5 is hydrogen or methyl.

[0055] Wherein R6 is hydrogen or methyl.

[0056] Wherein R7 is hydrogen or methyl.

[0057] In some embodiments, the photopolymerizable monomer comprises a compound having formula (1), a compound having formula (2), a compound having formula (3), a compound having formula (4), a compound having formula (5), a compound having formula (6), or a combination thereof. In some embodiments, the photopolymerizable monomer comprises 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 foamable 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 foamable resin composition.

[0058] In some embodiments, the photopolymerizable monomer having a small molecular group R portion includes methyl methacrylate (MMA), ethyl methacrylate (MMA), or a combination thereof.

[0059] In some embodiments, the photopolymerizable monomer having a steric hindrance R moiety includes tert-butyl acrylate, isobornyl acrylate (IBOA), 2-Methyl-2-adamantyl acrylate, cyclohexyl methacrylate, benzyl methacrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, dipentaerythritol hexaacrylate, or a combination thereof.

[0060] In some embodiments, the photopolymerizable monomer having an R portion with a long chain alkyl group includes: lauryl methacrylate (LMA), stearyl acrylate (SA), isodecyl acrylate (ISODA), isooctyl acrylate (IOA), isononyl acrylate (INAA), or a combination thereof.

[0061] 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), or a combination thereof.

[0062] In some embodiments, the photopolymerizable monomer containing a side reaction site may include a compound having the following chemical formula: tricyclodecane dimethanol diacrylate, 1,4-butanediol dimethacrylate (BDMA), or a combination thereof.

[0063] In some embodiments, the photopolymerizable monomer accounts for 10 parts by weight to 45 parts by weight in the foamable resin composition, for example, 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, or 45 parts by weight. In some embodiments, when the photopolymerizable monomer includes a compound having formula (1) and a compound having formula (2), a 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.

[0064] Next, let's discuss the thermally expandable microcapsules. During the continuous liquid interface process for manufacturing dual-cure resin mixture products, the thermally expandable microcapsules are mixed with a base resin raw material to form a foamed resin composition. During the continuous liquid interface printing process, the thermally expandable microcapsules are photocured to form an intermediate containing the thermally expandable microcapsules. At this point, the thermally expandable microcapsules have not yet expanded. Subsequently, the intermediate is heated to thermally cure and solidify, simultaneously causing the microcapsules mixed therein to expand. During the heating process, the thermally expandable microcapsules expand while the intermediate is also thermally cured and solidified. As the heating time progresses, the thermally expandable microcapsules gradually expand in volume while the intermediate is also thermally cured. As a result, the resulting polyurethane (meth)acrylate oligomer product has a larger volume than the original volume printed from the continuous liquid interface machine. In some embodiments, the thermally expandable microcapsules expand at a rate approximately equal to the thermal curing rate of the base resin raw material; in some embodiments, the thermally expandable microcapsules expand at a rate faster than the thermal curing rate of the base resin raw material; and in some embodiments, the thermally expandable microcapsules expand at a rate slower than the thermal curing rate of the base resin raw material.

[0065] Continuing to explain the thermally expandable microcapsules. In some embodiments, the thermally expandable microcapsules include a polymer shell and a volatile liquid encapsulated in the polymer shell. When the temperature is greater than the glass transition temperature of the polymer shell, the polymer shell softens, and the volatile liquid increases in pressure due to vaporization, causing the polymer shell to expand outward. In some embodiments, the polymer shell includes a high molecular weight polymer that softens when heated, for example, it can be a shell composed of a nitrile polymer, in particular, a shell comprising a copolymer component of acrylonitrile and methacrylonitrile. In some embodiments, the volatile liquid encapsulated in the polymer shell is a low-carbon alkane, in particular a liquid alkane that evaporates into a gas when heated, for example, including isobutane, isopentane, isohexane, or other alkanes that are liquid at room temperature but can evaporate into a gas when heated. In some embodiments, the shape and particle size of the thermally expandable microcapsules are approximately uniform, so that the pores formed in the final product after thermal expansion have a roughly uniform shape and volume. In some embodiments, the shape of the preferred thermally expandable microcapsules is round or oval. In some embodiments, the thermally expandable microcapsules before foaming 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 account for 1 to 25 parts by weight of the foamable 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. After expansion, the thermally expandable microcapsules retain a substantially intact shell, which provides partial structural support for the resin molded article.

[0066] 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 can be dispersed into the base resin after being formulated into the foamable resin composition of the present invention, thereby imparting a saturated, rich color to the resulting resin molded article. In some embodiments, the colorant-containing thermally expandable microcapsules can be purchased from commercial sources, or commercially available colorants can be mixed with colorant-free thermally expandable microcapsules to produce custom colorant-containing thermally expandable microcapsules.

[0067] In some embodiments, the thermally expandable microcapsules can be purchased from commercial sources or prepared by known methods. Available commercial sources include, but are not limited to: UNICELL series products from Dongjin Semiconductor Chemical, such as 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); Micropearl series products from Sekisui Chemical, 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 Oil & Fat Pharmaceutical Co., Ltd. Products, such as F series (for example: F-30, F-36), FN series (for example: FN-65, FN-100S), HF series or MSH series (for example: MSH890, MSH550, MSH380, MSH340, F-AC160D, HF-36D); AkzoNobel's Series products, such as: WE series (for example: 921WE40), DE series (for example: 920DE40), WUF series (for example: 031WUF40, 007WUF40); Kureha Corporation's H series, S series and other products.

[0068] Next, the photoinitiator is described. The photoinitiator promotes the crosslinking reaction by absorbing light. In some embodiments, the photoinitiator includes diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide (TPO).

[0069] The foamable resin composition is further described. In some embodiments, the foamable resin composition as described in any of the above embodiments further includes a curing agent to provide the foamable resin composition with different curing mechanisms and produce desired properties. In some embodiments, the curing agent includes 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (DMDC). In some embodiments, the curing agent accounts for 0 to 70 parts by weight in the foamable resin composition, for example, 0, 3, 5, 10, 30, 50 or 70 parts by weight.

[0070] Continue to explain the foamable resin composition. In some embodiments, the foamable resin composition as described in any of the above embodiments further includes a colorant so that the resin molded product obtained by 3D printing 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 can be a resin colorant (masterbatch), a thermochromic material, a photochromic material (daylight-changing ink). In some embodiments, the colorant accounts for 0 to 10 parts by weight in the foamable 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.

[0071] Continuing with the foamable resin composition, in some embodiments, the foamable resin composition also includes a filler to enhance desired properties of the final product. Examples include glass fiber, glass particles, hollow glass beads, metal powder, UV inhibitors, silicone-based antifouling powder, or fluorine-based antifouling powder.

[0072] Continuing with the description of the foamable resin composition, in some embodiments, the foamable resin composition described in any of the above embodiments further comprises any feasible thermoplastic resin. In some embodiments, the types of thermoplastic resins are cited in their entirety from US Pat. No. 9,453,142.

[0073] The present invention also provides a resin molded article, obtained by irradiating and heating the aforementioned foamable resin composition. Irradiation (e.g., ultraviolet light) causes a photoinitiator to induce a cross-linking polymerization reaction between a polyurethane (meth)acrylate oligomer and a photopolymerizable monomer, thereby forming a cured intermediate. Heating (e.g., to 110° C.) causes the thermally expandable microcapsules to expand, thereby expanding the cured intermediate containing the cured polyurethane (meth)acrylate oligomer and the photopolymerizable monomer, to form a resin molded article with an increased volume. In some embodiments, irradiation is performed before heating, and the photopolymerizable monomer has already completely reacted with the polyurethane (meth)acrylate oligomer during irradiation before heating. In some embodiments, the resulting resin molded article has a volume expansion ratio (volume expansion ratio is the percentage of volume increase after expansion to volume before expansion) of about 110% to about 305% compared to its volume before expansion (i.e., compared to the volume of the cured intermediate). In some embodiments, the resulting resin molded article includes multiple closed-cell structures, and these closed-cell structures have approximately the same shape and size and are roughly evenly distributed throughout the resin molded article. The closed-cell structures contain gas, which imparts insulation properties such as electrical, thermal, and sound insulation to the resin molded article, and also provides shock absorption, compressibility, and ductility. Taking into account the aforementioned favorable properties of the resin molded article, the present invention can be applied in a variety of fields, such as using the foamed resin composition of the present invention in 3D-printed insoles.

[0074] The following describes the foamable resin composition and resin molded article of the present invention based on only some examples. Therefore, the following detailed examples should not limit the scope of the appended claims.

[0075] In the experiment, the type of photopolymerizable monomer was used as an operational variable to reveal that cross-linking the photopolymerizable monomer in the polyurethane (meth)acrylate oligomer can result in a resin molded article having a good volume expansion ratio (i.e., Examples 1 to 4 have the same controllable variables except for the type of photopolymerizable monomer). The components and concentrations of the foamable resin compositions 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 formula (7) described above, and the thermally expandable microcapsules are, for example, the acrylonitrile and methacrylonitrile copolymer described above and isopentane encapsulated by the copolymer.

[0076] Table 1: Components and concentrations (concentration units are parts by weight)

[0077]

[0078] Table 2: Experimental results

[0079]

[0080] In Experiment 2, the combination of different types of photopolymerizable monomers in the foamable resin composition and the concentration ratio of each component in the foamable resin composition revealed that the resulting resin molded article had a good volume expansion ratio. The components and concentrations of the foamable resin compositions in Experiments 5 and 6 of 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 formula (7), the colorant is, for example, the white titanium dioxide, and the thermally expandable microcapsules are, for example, the copolymer of acrylonitrile and methacrylonitrile and isopentane encapsulated by the copolymer.

[0081] Table 3: Components and concentrations (concentration units are parts by weight)

[0082]

[0083]

[0084] Table 4: Experimental results

[0085]

[0086] The foamable resin composition of the present invention has a moderate viscosity, which prevents degradation of print quality when used in 3D printing. Furthermore, the foamable resin composition improves 3D printing productivity and efficiency through a well-optimized foaming process.

[0087] The present invention has been described in considerable detail with reference to certain embodiments. Other embodiments are possible. Therefore, the scope and spirit of the appended claims should not be limited to the embodiments described herein.

[0088] It is common knowledge in the art that modifications and variations may be made to the present invention without departing from the spirit and scope of the present invention. If such modifications and variations fall within the scope and spirit of the appended claims, such modifications and variations shall be within the scope of the present invention.

Claims

1. A foamable resin composition, characterized in that: include: 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 photopolymerizable monomer comprises at least one compound having a chemical formula R-Xa, having a reactive functional group X and a non-reactive group R, wherein the non-reactive group R is selected from the group consisting of a small molecule group, a high steric hindrance group, a multi-reactive site group, and a long chain group. 2 . The foamable resin composition according to claim 1 , wherein the thermally expandable microcapsule comprises an alkane compound and a nitrile polymer shell encapsulating the alkane compound. 3 . The foamable resin composition according to claim 1 , further comprising 0 to 70 parts by weight of a curing agent. 4 . The foamable resin composition according to claim 1 , wherein a weight ratio of the polyurethane (meth)acrylate oligomer to the photopolymerizable monomer in the foamable resin composition is 1.5:1 to 2.5:

1.

5. The foamable resin composition according to claim 1, wherein the photopolymerizable monomer comprises a compound having formula (1), a compound having formula (2), a compound having formula (3), a compound having formula (4), a compound having formula (5), a compound having formula (6), or a combination thereof: wherein R1 is a linear or branched C1-C18 alkyl group, a substituted or unsubstituted cycloalkyl group, or a substituted or unsubstituted aromatic group, and R2 is hydrogen or methyl; wherein R3 is hydrogen or methyl, and n is any integer from 3 to 12; wherein Y is a linear or branched C1-C8 alkylene group, or a substituted or unsubstituted cycloalkylene group, and R4 is hydrogen or methyl; wherein i+j+k=15, and R5 is hydrogen or methyl; wherein R6 is hydrogen or methyl; and Wherein R7 is hydrogen or methyl.

6. The foamable resin composition according to claim 5, wherein R1 is methyl, ethyl, tert-butyl, dodecyl, octadecyl, isodecyl, isooctyl, isononyl, cyclohexyl, isobornyl, 2-methyl-2-adamantyl, phenyl, benzyl, phenoxy or phenol.

7. The foamable resin composition according to claim 5, wherein the compound having formula (2) comprises polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate, polyethylene glycol (200) dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (600) dimethacrylate or a combination thereof, and the compound having formula (3) comprises tricyclodecane dimethanol diacrylate, 1,4-butanediol dimethacrylate or a combination thereof. 8 . The foamable resin composition according to claim 1 , wherein a viscosity of the foamable resin composition at 25° C. is 100 cps to 10,000 cps. 9 . The foamable resin composition according to claim 2 , wherein the particle size of the thermally expandable microcapsules is 5 μm to 100 μm. 10 . The expandable resin composition according to claim 1 , wherein the photopolymerizable monomer having the chemical formula R—Xa with a≧2 accounts for 0.1 to 20 parts by weight of the expandable resin composition.

11. The foamable resin composition according to claim 1, wherein the photopolymerizable monomer having a viscosity of 50 cps or more accounts for less than 45 parts by weight of the foamable resin composition, and the photopolymerizable monomer having a viscosity of 100 cps or more accounts for less than 20 parts by weight of the foamable resin composition.

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