Embedded 3D printing system

Abstract

The present invention relates to an embedded 3D printing system, and provides an ink composition that can be 3D printed using a DIW method. When printing using the DIW method, a printing matrix used includes fumed silica and silicone oil, such that that an ink composition with low viscosity can be stably printed, a structure is maintained even after printing is completed, and mechanical properties are enhanced.

Description

Embedded 3D Printing System

[0001] The present invention relates to an embedded 3D printing system.

[0002] Additive manufacturing, which enables the design and direct printing of three-dimensional (3D) objects, has revolutionized the research possibilities for industrial and advanced materials. In particular, 3D printing of polymers can be broadly divided into two types: extrusion molding using heat and photocuring using polymer resins with photocuring agents.

[0003] Additionally, there is potential for various functionalities using various types of nanomaterials, making them applicable to various industrial and engineering fields.

[0004] Direct ink write (DIW) is an extrusion-based 3D printing technology that enables the programmable assembly of 3D architectures. Unlike conventional lithography techniques such as laser-based polymerization or epitaxial assembly, it can be applied to a wide range of materials, both inorganic and organic.

[0005] The ink composition of the above DIW is easy to extrude, but it is necessary to use a viscoelastic ink that maintains its shape even after extrusion, but the development of such a viscoelastic ink is difficult.

[0006] In general, the ink composition used in DIW contains a high concentration of nanomaterials, and it is important that the ink composition passes through the nozzle of the 3D printer and achieves a support structure for the printed material itself after printing.

[0007] The higher the concentration of the above nanomaterial, the better the printing resolution can be obtained.

[0008] Accordingly, the ink composition used in DIW includes nanomaterials to impart viscoelastic properties, but if the concentration of the nanomaterials mixed is too low, the viscoelastic properties are insufficient, making it difficult to achieve a support structure after printing. In addition, if the concentration is too high, there are problems such as the nanomaterials being unevenly distributed within the ink composition, resulting in deterioration of the physical properties of the printed matter.

[0009] To solve the above problems, it is necessary to develop an ink composition and printing system suitable for 3D printing using the DIW method.

[0010] [Prior Art Literature]

[0011] [Patent Document]

[0012] (Patent Document 1) KR 10-2022-0129335 A1

[0013] An object of the present invention is to provide an embedded 3D printing system.

[0014] Another object of the present invention is to provide an ink composition that can be 3D printed using the DIW method, and to provide a 3D printing system that can stably print an ink composition having low viscosity, including fumed silica and silicone oil as a printing matrix used when printing using the DIW method, maintain a structure even after printing is completed, and enhance mechanical properties.

[0015] To achieve the above object, the present invention relates to an embedded 3D printing system, comprising: a viscoelastic ink composition; a printing matrix; and a DIW (Direct ink writing)-3D printer, wherein the ink composition may include a photocurable oligomer and nanoclay.

[0016] The above printing matrix may include fumed silica and silicone oil.

[0017] The above printing matrix can be uniformly dispersed with 1.5 to 3.5 wt% of fumed silica in silicone oil.

[0018] The ink composition may include an oligomer represented by the following chemical formula 1:

[0019] [Chemical Formula 1]

[0020]

[0021] [Chemical Formula 2]

[0022]

[0023] [Chemical Formula 3]

[0024]

[0025] [Chemical Formula 4]

[0026]

[0027] [Chemical Formula 5]

[0028]

[0029] [Chemical Formula 6]

[0030]

[0031] Here,

[0032] n is an integer from 1 to 100,

[0033] m is an integer from 1 to 50,

[0034] A, B, C and D are the same or different from each other and are repeating units each independently selected from the group consisting of compounds represented by chemical formulas 2 to 6,

[0035] a, b, c and d are the same or different and are each independently an integer from 1 to 30,

[0036] R1 and R2 are the same or different, and can each be independently selected from the group consisting of hydrogen, deuterium, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 30 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and a substituted or unsubstituted heteroaryl group having 1 to 30 carbon atoms.

[0037] The above nano clay is sepiolite, and the sepiolite is in the form of a single fiber, with an average length of 0.2 to 4 ㎛, a width of 10 to 30 nm, and an average thickness of 5 to 10 nm.

[0038] The ink composition may include a monomer and a photoinitiator.

[0039] The present invention provides an ink composition that can be 3D printed using the DIW method, and when printing using the DIW method, a printing matrix used includes fumed silica and silicone oil, so that the ink composition with low viscosity can be stably printed, maintain a structure even after printing is completed, and enhance mechanical properties.

[0040] Figure 1 is a photograph showing the dispersion stability of an ink composition according to one embodiment of the present invention.

[0041] Figure 2 is a schematic diagram of crevasse formation conditions according to the yield stress of a printing matrix according to one embodiment of the present invention, viscosity, shear stress measurement results, storage and loss modulus, storage elastic modulus, and loss elastic modulus.

[0042] Figure 3 shows the rheological properties of a printing matrix according to one embodiment of the present invention.

[0043] Figure 4 shows the rheological properties of a SEP composite resin composition according to one embodiment of the present invention.

[0044] FIG. 5 shows the results of measuring the storage and loss modulus of a supporter in a cyclic stress time sweep in a SEP nanocomposite resin composition according to one embodiment of the present invention.

[0045] Figure 6 shows the results of measuring the change in the fluid properties of a resin composition upon UV irradiation according to the content of SEP according to one embodiment of the present invention.

[0046] Figure 7 shows the results of measuring the mechanical properties of the elongation at break of a SEP nano composite resin composition according to one embodiment of the present invention.

[0047] Figure 8 shows the results of changes in tensile strength characteristics according to a 3D printing method according to one embodiment of the present invention.

[0048] Figure 9 shows the results of the fluid properties of a resin composition according to the manufacturing process depending on whether or not SEP is included according to one embodiment of the present invention.

[0049] Figure 10 is an SEM image of SEP powder according to one embodiment of the present invention.

[0050] Figure 11 is an SEM image of a fracture surface observed after applying tension to a sample printed using the DLP method according to one embodiment of the present invention.

[0051] Figure 12 is an SEM image of a fracture surface observed after applying tension to a sample printed using the DIW method according to one embodiment of the present invention.

[0052] FIG. 13 is a TEM image of directional SEP particles in a sample printed using the DIW method according to one embodiment of the present invention.

[0053] The present invention relates to an embedded 3D printing system comprising a viscoelastic ink composition; a printing matrix; and a DIW (Direct ink writing)-3D printer, wherein the ink composition comprises a photocurable oligomer and a nanoclay.

[0054] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0055] Among nanomaterials with excellent physical properties, nanoclay is particularly suitable for industrial use due to its low price. Mg8Si 12 O 30 Sepiolite (SEP), a hydrated magnesium silicate with a half-unit cell structure of (OH)4·12H2O, is one of the most widely used nanoclays as a reinforcing filler. A single SEP fiber is 0.2 to 4 μm long, 10 to 30 nm wide, and 5 to 10 nm thick. The SEP fiber has a needle-like or fiber-like shape composed of multiple blocks and tunnels oriented parallel to the fiber direction.

[0056] In general, ink compositions used in DIW contain nanomaterials to maintain their shape after extrusion. This is because the ink composition containing the nanomaterials has a higher concentration, which is advantageous in maintaining the shape of the output after passing through the nozzle, thereby achieving better printing resolution. In particular, in the case of an ink composition containing cellulose nanocrystals, cellulose nanocrystals, which are anisotropic building blocks, can become fillers of nanocomposites with shear-induced orientation during the extrusion process through the DIW nozzle. However, since the nanocomposite contains a high concentration of nanomaterials, the properties of the composite may be deteriorated due to slippage or non-uniformity of the nanomaterials. Therefore, it is necessary to derive an optimal concentration to improve sufficient viscoelastic properties and the mechanical properties of the printed 3D product in the DIW process.

[0057] As described above, when using the ink composition at a high concentration to improve the viscoelastic properties and mechanical properties of the output, nozzle clogging may occur.

[0058] Therefore, it is important to maximize the mechanical strength while maintaining a low ink composition concentration. DIW can improve mechanical properties by aligning nanomaterials during printing, but to align the nanomaterials as described above, the concentration of the nanomaterials must be low. However, if the concentration of the nanomaterials included in the ink composition is low, the viscoelastic properties are not sufficient. Therefore, a method to overcome the limitations of the DIW printing method by embedding liquid features in a soft printing matrix along a predefined omnidirectional printing path has been introduced in recent studies. However, the application of the above method requires consideration of the rheological properties and chemical interactions between the ink composition, which is the printing material, and the printing matrix.

[0059] The present invention seeks to provide an optimal embedded 3D printing system that takes into account the rheological properties and chemical interactions between the ink composition and the printing matrix.

[0060] Specifically, an embedded 3D printing system according to one embodiment of the present invention includes a viscoelastic ink composition; a printing matrix; and a DIW (Direct ink writing)-3D printer, wherein the ink composition may include a photocurable oligomer and nanoclay.

[0061] The present invention is characterized by using a viscoelastic ink composition containing a low concentration of nano-sized anisotropic nano clay using an embedded 3D printing system, and using a printing matrix containing fumed silica and silicone oil, and the output printed by the 3D printing system has increased physical properties due to alignment of the nano clay while passing through a printing nozzle, and thus, the mechanical properties can be significantly increased.

[0062] The above printing matrix includes fumed silica and silicone oil as described above, and 1.5 to 3.5 wt% of fumed silica can be uniformly dispersed in the silicone oil.

[0063] The above printing matrix must be able to maintain the printed shape by rapid recovery of the matrix when the printed output is injected. To exhibit the above characteristics, it is preferable that the storage modulus and loss modulus be equal, or that the storage modulus be higher than the loss modulus. However, if the difference between the storage modulus and loss modulus is too large, the problem of crevasses forming in the output may occur.

[0064] Accordingly, in order for the printed matter output by DIW to maintain its shape within the printing matrix, it is important that the storage modulus and loss modulus of the printing matrix exhibit appropriate values, and these storage modulus and loss modulus are affected by the content of fumed silica.

[0065] Accordingly, the fumed silica may be included in the silicone oil at 1.5 to 3.5 wt%, preferably 2 to 3 wt%, and more preferably 2.5 wt%, and within the above range, as the shear rate increases, it may exhibit shear thinning behavior. This is due to the interaction between the fumed silica included in the silicone oil and the silicone oil, which exhibits a Newtonian fluid due to its large specific surface area.

[0066] The ink composition may include a photocurable oligomer and nano clay.

[0067] The above nano clay is sepiolite, and the sepiolite is in the form of a single fiber, with an average length of 0.2 to 4 ㎛, a width of 10 to 30 nm, and an average thickness of 5 to 10 nm.

[0068] The ink composition of the present invention, since it includes the nanoclay, requires an appropriate balance of viscosity characteristics and yield characteristics. That is, the viscoelastic ink composition must always remain in a flowing state. Otherwise, even if problems do not occur in the embedded 3D printing method, printing may not occur in a DLP printing environment. However, since the viscoelastic ink composition needs to maintain the printed shape by increasing viscosity after printing, it needs to exhibit shear thinning behavior like the aforementioned printing matrix. To exhibit the shear thinning behavior described above, the ink composition may include nanoclay.

[0069] The above nano clay is included in an amount of 0.5 to 5 parts by weight, and may be included in an amount of 2 to 5 parts by weight, based on 100 parts by weight of the photocurable composition. Within the above range, the nano clay may exhibit shear thinning behavior due to the rotation of the nano clay within the composition being hindered. An ink composition not including nano clay or an ink composition including a low concentration of nano clay exhibits Newtonian fluid behavior, and an ink composition including nano clay within the above range exhibits a clear shear thinning behavior, and thus printing is possible using the DIW method.

[0070] The photocurable composition may be cured by UV irradiation, as described below, and may include a photocurable oligomer, a monomer, and a photoinitiator. Details are as described below.

[0071] The ink composition may include an oligomer represented by the following chemical formula 1:

[0072] [Chemical Formula 1]

[0073]

[0074] [Chemical Formula 2]

[0075]

[0076] [Chemical Formula 3]

[0077]

[0078] [Chemical Formula 4]

[0079]

[0080] [Chemical Formula 5]

[0081]

[0082] [Chemical Formula 6]

[0083]

[0084] Here,

[0085] n is an integer from 1 to 100,

[0086] m is an integer from 1 to 50,

[0087] A, B, C and D are the same or different from each other and are repeating units each independently selected from the group consisting of compounds represented by chemical formulas 2 to 6,

[0088] a, b, c and d are the same or different and are each independently an integer from 1 to 30,

[0089] R1 and R2 are the same or different, and can each be independently selected from the group consisting of hydrogen, deuterium, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 30 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and a substituted or unsubstituted heteroaryl group having 1 to 30 carbon atoms.

[0090] The above photocurable oligomer is characterized by including a urethane acrylate structure as a main chain, a photocurable functional group bonded to the urethane structure, and including a soft functional group and a hard functional group in the compound.

[0091] The output exhibits flexible properties due to the soft functional group included in the photocurable composition, and can also exhibit heat resistance due to the hard functional group.

[0092] That is, by combining a photocurable functional group with a photocurable oligomer and utilizing a soft functional group and a hard functional group, a flexible effect can be exhibited by utilizing a carbon skeleton having a soft property at room temperature, and heat-resistant properties can also be exhibited by utilizing a carbon skeleton having a hard property at room temperature.

[0093] The above A, B and D are the same or different from each other, and may be repeating units independently selected from compounds represented by chemical formula 2 or 3.

[0094] The above C may be a repeating unit selected from the group consisting of compounds represented by chemical formulas 4 to 6.

[0095] Specifically, the photocurable oligomer represented by the above chemical formula 1 can be manufactured by a method for synthesizing a urethane acrylate series. Basically, it proceeds through a stepwise polymerization reaction of a diol and a diisocyanate, and in order to prevent gelation of the material due to an increase in molecular weight during the polymerization process of the material, an acrylic monomer without a reaction site is used as a suspension. The monomer used in the synthesis of the oligomer of the present invention as an available acrylic monomer may be Isobornyl acrylate, Cyclic Trimethylolpropane Formal Acrylate, Lauryl acrylate, Lauryl methacrylate, 3,5,3-trimethelhexyl acrylate, Tetrahydrofurfuryl acrylate, Tetrahydrofurfuryl methacrylate, Benzyl methacrylate, etc.

[0096] More specifically, diol was pre-introduced into the monomer base used as the primary monomer to stabilize it, and then diisocyanate was added. As the urethane reaction progressed, heat of reaction was generated, the urethane chain lengthened, and the molecular weight increased.

[0097] As the molecular weight increases, the viscosity of the material may also increase. If the above-mentioned increase in molecular weight proceeds rapidly, the temperature rises rapidly, which also causes the urethane reaction to proceed more quickly, and as a result, the oligomer gels before reaching a sufficient molecular weight, making it unusable as a material. Therefore, in the present invention, in order to prevent this reaction, a solvent selected from the group consisting of Isobornyl acrylate, Cyclic Trimethylolpropane Formal Acrylate, Lauryl acrylate, Lauryl methacrylate, 3,5,3-trimethelhexyl acrylate, Tetrahydrofurfuryl acrylate, Tetrahydrofurfuryl methacrylate, Benzyl methacrylate, and mixtures thereof is used as a solvent for introducing the diol. The solvent does not participate in the reaction, and is used to control the reaction speed of the material and prevent a rapid increase in viscosity due to an increase in molecular weight. Additionally, the monomers used to synthesize the oligomer of the present invention must be free of functional groups capable of reactive urethane reactions, such as hydroxyl groups or urethane groups. Under the above conditions, the present invention can produce oligomers with excellent mass production and process stability.

[0098] In addition, the equivalent ratio of diol and diisocyanate was set to a state where the equivalent of diisocyanate was higher than that of diol, so that the oligomer terminal exists as an isocyanate group. A reaction catalyst including a Zn-based catalyst can be used during the reaction process. The catalyst may or may not be included. The catalyst is included to proceed the reaction more quickly, and the reaction can proceed even if it is not necessarily included, but even if it is included, the reaction can proceed with a very small amount added.

[0099] After the temperature increase was stopped due to the completion of the urethane reaction, 2-hydroxy acrylate and 2-hydroxy methacrylate were added dropwise to end-cap the ends of the oligomers.

[0100] The diols used for the preparation of the above oligomers are as follows:

[0101]

[0102] In addition, the diisocyanate for reacting with the above diol is as follows:

[0103]

[0104]

[0105] Additionally, monomers that may be included to terminate the urethane reaction or increase the molecular weight are as follows:

[0106]

[0107]

[0108] The compound represented by the above chemical formula 1 manufactured by the above manufacturing method can be selected from the group consisting of the following compounds:

[0109]

[0110]

[0111]

[0112]

[0113]

[0114] Here, p, p', p", q, q', q", r, s, t, u and v are integers from 1 to 100.

[0115] The photocurable oligomer may have a number average molecular weight (Mn) of 1,500 to 6,000, 1,500 to 5,500, or 1,600 to 5,000. The photocurable oligomer may have a weight average molecular weight (Mw) of 2,500 to 9,000, 3,000 to 8,500, or 3,500 to 8,000.

[0116] The above monomer is a reactive monomer, and may specifically be an acrylate monomer.

[0117] More specifically, the acrylate monomer may be cyclic trimethylolpropane formal acrylate (CTFA) and / or isobornyl acrylate (IBOA).

[0118] The photoinitiator may be BP, TPO, DCP, BPO, DPPO, etc., and preferably DPPO (2-hydroxy-2-methylpropiophenone) may be used. However, the present invention is not limited to the above examples, and any photoinitiator capable of producing a photocurable composition may be used without limitation.

[0119] In addition, a stabilizer may be included, and the stabilizer may be selected from the group consisting of tertiary amines such as diethylethanolamine and trihexylamine, hindered amines, organic phosphates, and hindered phenols, but is not limited to the above examples, and any stabilizer capable of producing a photocurable composition may be used without limitation.

[0120] In order to improve thermal and oxidation stability, storage stability, surface properties, flow properties, and process properties, the above additives may include conventional additives such as leveling agents, slip agents, or stabilizers.

[0121] A photocurable composition according to one embodiment of the present invention may contain 1 part by weight of a photoinitiator per 100 parts by weight of a UV resin. The UV resin may include a photocurable oligomer of the present invention and a monomer, and more specifically, may contain a compound represented by the following chemical formula 1, a compound represented by the following chemical formula 7, and a compound represented by the following chemical formula 8 in a weight ratio of 1:1:1 to 2:1:1.

[0122] With respect to 100 parts by weight of the above photocurable composition, the nano clay may be included in an amount of 0.5 to 5 parts by weight, and may be included in an amount of 2 to 5 parts by weight.

[0123] Manufacturing example

[0124] ingredient

[0125] Oligomer resins (GR30860, GR3060) were supplied by Graphy Co., Ltd. (Korea). Cyclic trimethylolpropane formal acrylate (CTFA) was purchased from Miwon Specialty Chemical Co. Ltd (Korea). Isobornyl acrylate (IBOA) was purchased from Evonik Industries AG (Germany). Bis(2,6-dichlorobenzoyl)-(4-propylphenyl)phosphine oxide (Irgacure 819) was purchased from BASF (Germany). SEP (Mg2H2Si3O9·xH2O) with a diameter of 10–30 nm and a length of 1–2 μm was purchased from Sigma-Aldrich (USA). Fumed silica was purchased from Sigma-Aldrich (USA), and silicone oil (KF-54) was purchased from Shinetsu (Japan).

[0126] The above oligomer resin (GR30860, GR3060) is represented by the following chemical formulas 9 and 10:

[0127] [Chemical Formula 9]

[0128]

[0129] [Chemical Formula 10]

[0130]

[0131] The analysis results for the oligomers of the above chemical formulas 9 and 10 are as follows.

[0132] [Oligomer of chemical formula 9]

[0133] Mn 4767 g / mole, Mw 7591 g / mole, PDI 1.59

[0134] [Oligomer of chemical formula 10]

[0135] Mn 2691 g / mole, Mw 3703 g / mole, PDI 1.38

[0136]

[0137] Preparation of the printing matrix

[0138] The printing matrix for embedded printing was prepared by dispersing fumed silica in silicone oil. The suspensions of silicone oil and fumed silica had fumed silica concentrations of 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, and 3.5 wt%, and the total mass of the suspensions was 40 g. To disperse the fumed silica in the silicone oil, an ultrasonic processor (VCS-130, Sonics & Materials Inc, USA) with a power of 130 W and a frequency of 20 kHz was used for ultrasonication at 70% amplitude for 180 s. The prepared silicone oil / fumed silica suspension was poured into a polystyrene petri dish.

[0139] Preparation of photocurable resin composition and SEP composite resin composition (ink composition)

[0140] The photocurable resin composition and the photocurable SEP composite resin composition are comprised of the component ratios as shown in Table 1 below. The photocurable oligomer resin (GR30860, GR3060) was heated in an oven at 60°C for 12 hours to ensure fluidity, and then 50 g of CTFA and 50 g of IBOA were mixed, and then SEP was added to the mixture under stirring. The mixture was ultrasonically treated at 750 W for 1 minute. Thereafter, 1 part by weight of a photoinitiator was added to the mixture based on 100 parts by weight of the total mixture, and degassed using a paste mixer to prepare an SEP composite resin composition.

[0141] As shown in Fig. 1, the SEP composite resin composition showed a very stable dispersion state even after 3 days of storage.

[0142] Composition Sample Printing Method Sepiolite (parts by weight) Sample Printing Method Sepiolite (parts by weight) UV Resin Photoinitiator 1001 DLP sep-0 DLP 0 EMB sep-0 Embedded DIW 0 DLP sep-0.5 0.5 EMB sep-0.5 0.5 DLP sep-11 EMB sep-11 DLP sep-22 EMB sep-22 DLP sep-33 EMB sep-33 DLP sep-55 EMB sep-55

[0143] (The total weight of UV resin is 225g, and sepiolite is included based on 100 parts by weight of the photocurable composition)

[0144] Sample preparation

[0145] SEP composite resin compositions were used to fabricate specimens using a DLP-type 3D printer (G PRINTER, Gooo3D, Korea), and tensile strength and DMA specimens were manufactured. The tensile strength specimens were printed according to ASTM D638-5, and the DMA specimens were printed in a size of 12.5 x 3 x 60 mm. A 405 nm UV LED was used as the light source.

[0146] In addition, the SEP composite resin composition was printed on the printing matrix using a DIW-3D printer. The 3D nozzle path was designed using commercially available Rhinoceros software (Rhinoceros 5.0, Robert McNeel & Associates, Seattle, WA, USA). The designed 3D nozzle path model was translated into G-code instructions for deposition using slicing software (Cura, Ultimaker, Geldermalsen, The Netherlands). The SEP composite resin composition in a 5 mL syringe was printed on the printing matrix. The nozzle was inserted into the bottom center of the printing matrix in a petri dish, and the G-code was transmitted to the printer using the host software. The SEP composite resin composition was extruded through a nozzle with an inner diameter of 250 μm. The applied pressure was 45 psi and the printing speed was 10 mm / s. The output was 2 mW / cm to stabilize the dimensions. 2 was exposed to UV at 120,000 mJ / cm using CureM U102H (Graphy Inc., Korea). 2 The printed output was post-cured by irradiating it with UV light for 5 minutes.

[0147] Specialization

[0148] The rheological properties of fumed-silica / silicone oil were measured using a rheometer (MCR 302, Anton Paar Ltd., Austria). The diameter of the disposable parallel plates was 50 mm, the experimental temperature was 25°C, the plate gap was 100 μm, the step-wise shear force was 300 Pa and 0.1 Pa, and the experimental time was 50 s for each step (total 350 s). The diameter of the disposable parallel plates was 25 mm, the experimental temperature was 25°C, the plate gap was 100 μm, and the shear rate was 0.1–100 rad / s. The shear rate for measuring the photorheological properties of the photocurable resin composition and the SEP composite resin composition was 0.01%, and the radian was 10 rad / s. A UV LED with a wavelength of 365 nm was used, and the intensity was 15 mW / cm. 2was performed. Vibration was applied for 30 seconds, and then UV was irradiated for 300 seconds. The degree of shrinkage of the material was measured at a shear force of 0.1 N. The tensile strength of the specimens was measured using a UTM (AllroundLine Z010, Zwick, Germany) to confirm the change according to the difference in SEP content and printing method. A crosshead speed of 5 mm / min was used during the measurement, and the mechanical properties were analyzed at room temperature (RT, ~20 ℃). Seven specimens were used for each composition to calculate the error range. To define the degree of SEP orientation in the SEP composite resin composition printed using the embedded printer from a morphological point of view, the specimens were observed using a TEM (JEM-2100F, JEOL Co., Japan). The TEM samples were sliced ​​using Spurr resin. To obtain TEM samples, 3D-printed specimens were impregnated with Spurr resin, maintained under vacuum conditions (-0.95 bar) for 24 h, and cured in an oven at 70°C for 24 h. The cured specimens were sliced ​​using an ultramicrotome (EM UC7, Leica, Germany). The sliced ​​specimens were loaded onto copper grids and carbon-coated for 30 s.

[0149] To investigate the effect of SEP on the fracture behavior of polymer composites, samples printed using an embedded 3D printing system were subjected to tensile tests, and the fracture surfaces were observed using a field-emission scanning electron microscope (FE-SEM, SUPRA 55VP, Carl Zeiss, Germany) at an accelerating voltage of 10 kV. Prior to FE-SEM measurements, each sample was coated with platinum (99.99% purity) by ion sputtering to remove electronic charges. Dynamic mechanical analysis (Q800, TA Instrument, USA) was performed at -30 to 120°C using a three-point bending method at a frequency of 1 Hz and a strain of 0.1%.

[0150] result

[0151] Rheological properties of the matrix

[0152] Unlike DIW, embedded printing utilizes a printing matrix to reliably print low-viscosity materials onto the matrix, ensuring that the material retains its shape even after printing. Figures 2a and 2b illustrate the importance of the rheological properties of the matrix in embedded printing.

[0153] According to the above figures 2a and 2b, immediately after the nozzle passes through, the crevasse formed during the printing process collapses at the bottom under hydrostatic pressure (ρgh, where ρ is density, g is gravity, and h is depth). If the yield stress of the printing matrix is ​​too high, the printing matrix does not recover quickly, and the ink composition fills the crevasse, changing the shape of the design.

[0154] Here, the rheological properties of the fumed silica / silicone oil suspension were examined by varying the concentration to determine the fumed silica concentration suitable for embedded printing. As the shear rate increased, the printing matrix including the fumed silica showed shear-thinning behavior. Figures 2c and d confirm that the shear-thinning behavior of the printing matrix became more evident as the concentration of the fumed silica increased. Fumed silica and silicone oil have excellent compatibility, and the nano-sized fumed silica has a high specific surface area, so it interacts well with silicone oil, which exhibits a Newtonian fluid. Therefore, it was confirmed that even when the fumed silica was included at 0.5 wt%, a rapid change in shear-thinning behavior occurred.

[0155] As the distance between the fumed silica particles and the silicone oil decreases, the yield stress and viscosity increase. This shear thinning behavior is due to the printing matrix's response to the deformation that occurs during the printing process through the nozzle. Therefore, it is important to find appropriate yield characteristics. The yield stress corresponds to the shear stress when the shear rate is 0. As shown in Figure 3, it was confirmed that the shear thinning behavior was observed and a stable response was observed between 1 and 10 Hz. Based on the above results, experiments were conducted under conditions of 1 Hz.

[0156] The yield stress characteristics of a printing matrix containing fumed silica / silicone oil are important because the elastic modulus changes rapidly as the shear stress applied to the printing matrix increases. To determine the yield stress of a printing matrix containing fumed silica / silicone oil, an oscillatory shear rheology test was performed at a frequency of 1 Hz. Figure 2e shows the changes in the elastic and viscous moduli of a printing matrix containing fumed silica / silicone oil according to changes in the fumed silica content. As the fumed silica content increased, the range of the elastic modulus and solid-dominated shear stress increased. The yield stress is determined by the changes in the storage modulus and the loss modulus, and is determined by the shear stress value when the storage modulus decreases. As the storage modulus and the loss modulus gradually decrease in the yield stress region, it can be confirmed that there is no abrupt change in the material shape at the yield point. The yield stress of the matrix increased as the fumed silica concentration increased.

[0157] Additionally, both the storage and loss moduli of the matrix increased, but this may be due to the increased difference in the storage and loss moduli as the fumed silica content increased. The closer the space between the fumed silica particles, the more the silicone oil is influenced by the silicone surface, which may increase the interaction. The shear modulus and viscosity of the printing matrix containing fumed silica / silicone oil may vary depending on the fumed silica content as well as the shear stress. As the printer nozzle passes through the matrix, the crevasses created in the matrix collapse. However, after the printing material is injected, the matrix must quickly recover to maintain the shape of the printed shape. Figure 2f shows the creep and recovery properties of the matrix at higher shear forces due to its low modulus. The printing matrix containing 2 wt% fumed silica / silicone oil had a storage modulus higher than the loss modulus at 0.5 Pa, but after the structure collapsed under a force of 300 Pa, it did not fully recover from the 0.5 Pa state. The printing matrix containing 2 wt% fumed silica / silicone oil had a loss modulus higher than its storage modulus. This result suggests that the printing matrix does not perfectly retain the material after printing. On the other hand, the matrix containing 2.5 wt% fumed silica exhibited a storage modulus slightly higher than its loss modulus when exposed to a shear force of 0.5 Pa after being subjected to a shear force of 300 Pa. This allows the injected print to be preserved. The printing matrices containing 3 wt% and 3.5 wt% fumed silica exhibited excellent recovery properties, but the large difference between the storage modulus and the loss modulus may lead to crevasses in the matrix. Based on the rheological properties, the printing matrix containing 2.5 wt% fumed silica is considered suitable for embedded printing.

[0158] Rheological properties of photocurable composite resins

[0159] A printing matrix containing 2.5 wt% fumed silica was used as the matrix of an embedded 3D printing system, and photocurable resin compositions containing different concentrations of SEP were used as printing ink compositions. The composite resin compositions containing nanomaterials exhibited shear thinning behavior. The rheological behavior of the photocurable resin compositions in silicone oil was confirmed using photocurable resin compositions containing various concentrations of SEP (Fig. 4b). The SEP composite resin compositions exhibited Newtonian fluid behavior when SEP was contained at 0, 0.5, and 1 wt%, and shear thinning behavior when SEP was contained at 2 wt% or more. This shear thinning occurs because the viscosity decreases and the yield stress is generated as the structure of the nanostructures composed in a stationary state collapses. The photocurable resin without SEP was rich in CTFA and IBOA and contained only oligomeric resins and some photoinitiators, so it exhibited Newtonian fluid behavior. When SEP is included at 0.5 and 1 part by weight, the two ends of the needle-shaped SEP do not interfere with each other, and no interference occurs regardless of the direction in which the SEP rotates. However, as the concentration increases, the movement of the SEP is impeded, resulting in a penetration threshold. When SEP is included at 5 parts by weight, an entangled penetration threshold is observed, resulting in a clear shear thinning behavior.

[0160] Figure 4d relates to the yield characteristics of the SEP composite resin composition. The yield characteristics of the printing matrix of the present invention are important for maintaining the shape of the printed material. However, the photocurable resin, the material to be printed, must always remain in a flowing state. Otherwise, even if problems occur in the embedded printing method, printing may not occur in the DLP printing environment.

[0161] However, since viscosity increases as the SEP content increases, yield characteristics must be checked. In the case of composite resin compositions containing 0, 0.5, and 1 part by weight of SEP, Newtonian fluid behavior was observed, and thus yield characteristics were insignificant. In the case of composite resin compositions containing 2 to 5 parts by weight of SEP, both the storage modulus and loss modulus increased as the SEP content increased.

[0162] In addition, as the SEP content increased, the difference between the storage modulus and the loss modulus narrowed. However, the loss modulus remained higher than the storage modulus in the shear force range within all ranges, and it was confirmed that the samples flowed when SEP was included below 5 wt%. Therefore, all samples are suitable for DLP and EMB3D 3D printing. The shear modulus and viscosity of the fumed silica / silicone oil matrix in Fig. 2e depend not only on the fumed silica content but also on the shear stress and time, so the shear modulus changed according to the SEP content, stress, and time, as shown in Figs. 4e and 5. As can be seen in Figs. 8 to 13, the photocurable printing material is always fluid. The storage modulus decreases at a shear force of 300 Pa but recovers at a shear force of 0.5 Pa. However, throughout the test, the material always maintained a loss modulus higher than the storage modulus.

[0163] Figure 6 shows the results of observing the change in storage modulus of a photocurable composite resin during the curing process. The resin was stabilized for 30 seconds and then exposed to UV light. Generally, photocurable compositions containing nanomaterials tend to cure slowly because the nanomaterials absorb UV light.

[0164] In DLP 3D printing, the reason why photocuring occurs during the printing process is important. The time it takes for UV light to irradiate a layer must be considered. If curing is delayed by SEP, different printing conditions must be applied to each sample. However, Figure 6 confirms that the storage modulus of all samples increased immediately after UV irradiation. Furthermore, the tendency for the material's storage modulus to increase increases with increasing SEP content. This phenomenon suggests that SEP has good compatibility with the resin and is effective in supporting the structure.

[0165] Mechanical property analysis of 3D printed samples

[0166] The present invention examined the difference in mechanical properties according to the printing method for a 3D printer composition including a nanomaterial with cultivability. The results of measuring the tensile strength after printing samples using the DLP method (isotropic) and the embedded method (anisotropic) are as shown in Figures 8a and 8b. The experimental results of the samples printed using the DLP method showed that the tensile strength and elastic modulus increased as the SEP content increased. When included at 5 parts by weight, the tensile strength increased from 20.7 MPa (control group, pure photocurable resin) to 25.6 MPa, and the elastic modulus increased from 210.9 MPa (control group, pure photocurable resin) to 346.4 MPa.

[0167] At the same time, the elongation at break of the specimen was maintained despite the increase in SEP load, as shown in FIGS. 8e and 8f and FIG. 7. The above experimental results may be due to the characteristics of the acrylate oligomer used in this experiment. The high-viscosity oligomers (GR30860, GR3060) included in the present invention and CTFA and IBOA used as viscosity diluting monomers can interact with SEP through electrical attraction and respond to structural reinforcement and deformation. If the mobility of molecular chains in the polymer matrix within the SEP composite resin composition is restricted, the strength increases but the elongation decreases.

[0168] The tensile strength and elastic modulus of the samples printed by the embedded method are as shown in Figs. 8c and 8d. When the composition containing 5 parts by weight of SEP was used, the tensile strength increased from 16.2 MPa (control, pure photocurable resin) to 27.2 MPa, and the elastic modulus increased from 123.6 MPa (control, pure photocurable resin) to 215.8 MPa. Simultaneously, as the content of SEP increased, the elongation at break of the specimens also increased, as shown in Figs. 8e and 8f and Fig. 7. The pure photocurable resin printed by the DLP method exhibited a higher tensile strength than the pure photocurable resin printed by the embedded method. This is due to the following phenomenon: since the process inevitably creates voids separated by gaps (55, 56) that reduce the mechanical properties of the substrate, the samples printed by the embedded method using pure photocurable resin have relatively lower physical properties than the samples printed by DLP. On the other hand, the strength does not increase consistently with increasing SEP content. As the SEP content increases to 0.5 and 1 part by weight in pure photocurable resin, the tensile strength increases with a slope similar to that of the samples printed by the DLP method. However, when included at 2 and 3 parts by weight, the tensile strength increases very rapidly. The above results are related to the rheological behavior of the photocurable resin including SEP. The rheological penetration threshold of the photocurable resin can be confirmed in Fig. 4b. Compositions containing 0.5 parts by weight and 1 part by weight of SEP and compositions not containing SEP exhibit Newtonian fluid behavior, while compositions containing 2 parts by weight or more of SEP exhibit shear thinning behavior. This shear thinning behavior coincides with an increase in tensile strength, and SEP aligns the shear thinning behavior to enhance tensile strength. In addition, embedded (anisotropic SEP) printing showed a greater increase in tensile strength compared to DLP (isotropic SEP) printing.

[0169] According to the above experimental results, the SEP nano composite resin composition of the present invention has improved mechanical properties due to the synergistic effect between the constituent components.

[0170] DMA was performed to measure the storage modulus of the photocurable resin composition and the SEP nanocomposite resin composition. The storage modulus curves of the cured pure resin and SEP nanocomposite resin are shown in Figure 9. The storage modulus significantly increased as the SEP content increased. The storage modulus of the photocured pure resin at 25°C was 194.9 MPa, but the storage modulus gradually increased as the SEP content increased. When the SEP content was 5 parts by weight, the storage modulus was 267.3 MPa. The tan δ values, which represent the ratio of the loss modulus to the storage modulus for the photocured pure resin and the SEP nanocomposite resin, are shown in Figure 9b. The maximum tan δ value of the photocured pure resin was confirmed at 65.1°C. It increased as the SEP content increased, and when the SEP content was 5 parts by weight, the maximum tan δ value was confirmed at 73.3°C. The storage modulus of the SEP nanocomposite resin in the glassy state is higher than that of the photocured pure resin, which means that the well-dispersed interfacial bonding mixed structure improves the mechanical properties of the composite resin.

[0171] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0172] The present invention relates to an embedded 3D printing system.

Claims

1. Viscoelastic ink composition; printing matrix; and Includes DIW (Direct ink writing)-3D printers, The above ink composition comprises a photocurable oligomer and nano clay. Embedded 3D printing system.

2. In paragraph 1, The above printing matrix contains fumed silica and silicone oil. Embedded 3D printing system.

3. In paragraph 2, The above printing matrix is ​​a silicone oil in which 1.5 to 3.5 wt% of fumed silica is uniformly dispersed. Embedded 3D printing system.

4. In paragraph 1, The above ink composition comprises an oligomer represented by the following chemical formula 1: Embedded 3D Printing Systems: [Chemical Formula 1] [Chemical formula 2] [Chemical Formula 3] [Chemical Formula 4] [Chemical Formula 5] [Chemical formula 6] Here, n is an integer from 1 to 100, m is an integer from 1 to 50, A, B, C and D are identical or different from each other and are repeating units each independently selected from the group consisting of compounds represented by chemical formulas 2 to 6, a, b, c and d are equal to or different from each other and are each independently an integer from 1 to 30, R1 and R2 are the same or different, and can each independently be selected from the group consisting of hydrogen, deuterium, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 30 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and a substituted or unsubstituted heteroaryl group having 1 to 30 carbon atoms.

5. In paragraph 1, The above nano clay is Sepiolite. Embedded 3D printing system.

6. In paragraph 5, The above sepiolite is in the form of a single fiber, with an average length of 0.2 to 4 ㎛, a width of 10 to 30 nm, and an average thickness of 5 to 10 nm. Embedded 3D printing system.

7. In paragraph 1, The above ink composition comprises a monomer and a photoinitiator. Embedded 3D printing system.

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