Ink composition for powder bed and inkjet head 3D printing

Abstract

The present invention relates to an ink composition containing a multifunctional adhesive suitable for a three-dimensional (3D) printer and the use thereof. The multifunctional adhesive of the present invention contains a compound with a catechol group and exhibits excellent adhesion to various materials (e.g. dry plaster powders, polymers, metals, ceramics, and composite materials). The use of the ink composition of the present invention containing the multifunctional adhesive enables the processing of various functional materials that were difficult to fabricate into a 3D structure. Therefore, it is highly likely that the ink composition of the present invention can effectively create a market for functional materials for a 3D printer and find new areas of application (e.g. automotive, medical, fashion, aviation/aerospace, construction, consumer electronics, entertainment, etc.).

Claims

1. An ink composition for three-dimensional (3D) printing, comprising: an adhesive; a solvent; a stabilizer; and a viscosity controlling agent, wherein the adhesive is a compound containing a catechol group, and wherein the ink composition contains the adhesive at 10 to 30% by volume, the solvent at 40 to 60% by volume, the stabilizer at 5 to 10% by volume, and the viscosity controlling agent at 20 to 40% by volume.

2. The ink composition of claim 1, wherein the ink composition has an Ohnesorge number (Oh) ranging from 0.1 to 1.0.

3. The ink composition of claim 1, wherein the adhesive is selected from a group consisting of a polydopamine, a chitosan-catechol, a hyaluronic acid-catechol, and an alginate-catechol.

4. The ink composition of claim 1, wherein the solvent is an alcohol-based solvent.

5. The ink composition of claim 1, wherein the stabilizer is anhydrous 2-ethylhexyl acrylate (2-EHA) or 2-methoxyethanol (2-ME).

6. The ink composition of claim 1, wherein the viscosity controlling agent is ethylhexanoic acid or 1,2-propanediol.

7. The ink composition of claim 1, wherein the ink composition further comprises an oxidizing agent or a dye.

8. The ink composition of claim 7, wherein the oxidizing agent is piperidine.

9. The ink composition of claim 7, wherein the dye is an organic or inorganic dye listed in the Colour Index International.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of a powder bed and inkjet head three-dimensional (3D) printing system. In the diagram, 1 denotes a box containing a material in a powder form, 2 denotes a device enabling the accumulation of the powder by adjusting the height of the powder with a piston, 3 denotes a device for supplying the material in a powder form, 4 denotes the material in a powder form, which is usually a dry plaster powder or a polymer, 5 denotes a device with a roller that evenly spreads the powder that has been supplied, 6 denotes a device for supplying a liquid adhesive, and 7 denote a special liquid adhesive.

(2) FIGS. 2 to 5 are results showing the binding effectiveness of a polydopamine Compared to conventional binders, a polydopamine can effectively enable the adhesion of TiO.sub.2 to a powder surface.

(3) FIGS. 6 to 8 are the results of centrifugation showing that a polydopamine can effectively cause the adhesion of TiO.sub.2 to a powder.

(4) FIG. 9 and FIG. 10 are experimental results respectively showing the stability of 3D-printed structures fabricated using an adhesive with or without a polydopamine.

MODES OF THE INVENTION

(5) Hereinafter, the present invention will be described in further detail with reference to exemplary embodiments. The exemplary embodiments are only for describing the present invention more specifically, and it will be clear to those skilled in the art that the gist and scope of the present invention are not limited to those exemplary embodiments

EXAMPLES

Example 1: Analysis of Polydopamine Adhesive Properties

(6) FIG. 1 is a simple schematic diagram describing the present invention and shows the applicability of the present invention to various materials, not like the conventional adhesives for a powder bed and inkjet head three-dimensional (3D) printing technique, the uses of which were restricted to limited material types. The adhesive normally refers to a spraying solution containing an adhesive in the form of an ink that can be sprayed through an inkjet head. Besides a liquid adhesive, the solution may contain an ink stabilizer, a solvent, a viscosity controlling agent, a dye, and the like. Each of the ingredients may be contained in a varying amount depending on use, but it is highly important that moisture is not contained in the composition and that the Ohnesorge number (Oh) is in the range of 0.1 to 1.0 for spraying and evaporation. The Ohnesorge number greater than 1.0 is not desirable, because in this case, the solution drops in the form of satellite drops, causing the phenomenon of a water drop bursting upon contacting a surface. In addition, when the Ohnesorge number is 0.1 or less, the high viscosity causes the spraying of the solution to become difficult and hinders the formation of water drops. Therefore, the Ohnesorge number within the range of 0.1 to 1.0 is very important for the uniform spraying of the solution. The Ohnesorge number can be calculated as follows:

(7) $\mathrm{Oh}=\frac{}{\sqrt{L}}=\frac{\sqrt{\mathrm{We}}}{\mathrm{Re}}\frac{\mathrm{viscous}\mathrm{forces}}{\sqrt{\mathrm{inertia}.Math.\mathrm{surface}\mathrm{tension}}}$

(8) In the above equation, is the viscosity coefficient, is the surface energy, is the density, L is the characteristic length scale, Re is the Reynolds number, and We is the Weber number [B. Derby and N. Reis, Inkjet Printing of Highly Loaded Particulate Suspensions, MRS Bulletin, pp. 815-818 (2003)]. The Ohnesorge number of each ingredient can be calculated using the above equation.

(9) The conventional powder bed and inkjet head 3D printing system took advantage of binding between a material in a powder form 4 and a special liquid adhesive 7 as a result of a particular reaction (i.e. a self-hydration reaction) therebetween (FIG. 1). As can be seen in FIG. 2, the present inventors have found that the mixing of a conventional binder (VisiJet PXL clear; 3D Systems, Inc., U.S.) and 250 mg of a powder (a dry plaster powder (CaSO.sub.4); 3D Systems, Inc. U.S.) resulted in a particular chemical reaction due to the water contained in the binder composition, which led to the deformation of a part of the powder surface into a rod-like shape. Such deformation is a result of a self-hydration reaction that occurred due to the binder composition and converted CaSO.sub.4 into recrystallized gypsum. In contrast, when a polydopamine (2 mg/ml; Sigma-Aldrich Co., U.S.) dissolved in ethanol was mixed with a powder, a deformation into a rod-like shape was not observed on the powder surface because of the lack of water (FIG. 3).

(10) To study if the polydopamine can have an adhesion property that is equal, similar, or superior to that of a conventional binder, the present inventors examined the roles of a binder and a polydopamine in the adhesion between a powder and TiO.sub.2 (2.5 mg). As shown in FIGS. 4 and 5, it could be observed that a polydopamine as well as a conventional binder enabled the adhesion of TiO.sub.2 to a powder surface.

Example 2: Analysis of Adhesion of Polydopamine Adhesive

(11) To study the functionality of a polydopamine as a general-purpose adhesive in more detail, the ingredients were mixed in the composition shown in the following Table 1 for 24 hours at room temperature. The precipitates obtained by the centrifugation of the liquid mixture were washed with ethanol 5 times. The mixture that had been washed was then centrifuged at 1,200 rpm and 2,000 rpm, and the precipitation status was observed.

(12) TABLE-US-00001 TABLE 1 Sample number Composition Mixing condition 1 (Ethanol + TiO.sub.2 + powder + Four ingredients are mixed dopamine) together 2 (Ethanol + powder + dopamine) + TiO.sub.2 is added after binding TiO.sub.2 dopamine to the powder 3 (Ethanol + TiO.sub.2 + powder + An oxidizing agent (piper- dopamine + piperidine) idine) is added to Sample 1 4 (Ethanol + powder + dopamine + TiO.sub.2 is added to Sample 2 piperidine) + TiO.sub.2 5 (Ethanol + TiO.sub.2 + powder) Ingredients are mixed in an absence of the dopamine adhesive

(13) Excellent Adhesion of Polydopamine

(14) More specifically, when the precipitation by centrifugation was performed at 1,200 rpm, the added dopamine (2 mg/ml; dissolved in ethanol) induced the stable adhesion of TiO.sub.2 (2.5 mg) to the powder (250 mg), leading to the formation of distinct precipitates. In contrast, in an absence of the dopamine adhesive, TiO.sub.2 did not adhere to the powder, and precipitates were not produced during centrifugation at 1,200 rpm (FIG. 6). When the precipitation was performed at a centrifugation speed of 2,000 rpm, the precipitates were obtained only when dopamine was added, and such precipitation occurred in a more stable manner in a sample containing dopamine as the sole additive than in a sample containing an oxidizing agent as well. Still, in an absence of the dopamine adhesive, TiO.sub.2 did not adhere to the powder, and any precipitate was not produced during centrifugation at 2,000 rpm (FIG. 7).

(15) In addition, the ingredients in parentheses in Samples 1 to 4 of Table 1 were first mixed and then were dried. The dried mixture was again added to ethanol and then was subjected to centrifugation. When the centrifugation was performed at 2,000 rpm, all of Samples 1 to 4 were well precipitated and could be separated with ease. Moreover, when the addition of TiO.sub.2 was performed after the drying of a mixture of other ingredients (i.e. Samples 2 and 4), the adhesion of TiO.sub.2 occurred successfully and precipitates were observed (FIG. 8). In contrast, Sample 5, which did not contain dopamine, still did not produce any precipitate.

Example 3: 3D Printing Using Polydopamine Adhesive

(16) To demonstrate the effectiveness of a polydopamine in 3D printing, the present inventors performed 3D printing in both absence (FIG. 9) and presence (FIG. 10) of a polydopamine, and studied the stability of the 3D-printed structures produced therethrough. The pristine forms thereof were fabricated successfully regardless of the presence or absence of a polydopamine. However, upon immersion in water (the second panels of FIGS. 9 and 10), the 3D-printed structure fabricated using an adhesive containing a polydopamine was more stable than the 3D-printed structure produced using an adhesive without a polydopamine. Moreover, when respectively shaken at 100 rpm in water, the 3D-printed structure fabricated using the adhesive with a polydopamine maintained its structure in a more stable manner (the third panels of FIGS. 9 and 10). The 3D-printed structure fabricated using the adhesive without a polydopamine (control) was completely destroyed in most areas after being shaken in water, and was not preserved even after being dried at room temperature (the fourth panel of FIG. 9). In contrast, the 3D-printed structure produced using the adhesive with a polydopamine and maintained with higher stability even after shaking in water was sustained even after drying at room temperature (the fourth panel of FIG. 10). Therefore, the present inventors substantially confirmed that an adhesive containing a polydopamine is effectively applicable to 3D printing.

(17) Detailed descriptions of specific parts of the context of the present invention have been provided above. However, it will be clear to those skilled in the art that such specific descriptions are merely exemplary and do not limit the scope of the present invention. Therefore, the actual scope of the present invention is determined by the appended claims and their equivalents.