Abstract
A 3D printing process for manufacturing an article, which is a powder bed fusion additive manufacturing process, the process comprising the steps of: (i) provision of a first layer comprising a printing material, said printing material comprising polypropylene in non-nucleated and/or alpha-nucleated form; (ii) the optional provision of a second layer to at least a portion of the first layer; (iii) application of heat to at least a portion of the layer or layers; and (iv) optionally repeating steps (i) to (iii) one or more times; wherein the first layer or the second layer comprises a beta nucleating agent, and wherein the temperature of the printing material is between the melting temperature and the crystallisation temperature of the printing material. Also described is an ink for 3D printing, wherein the 3D printing process is a powder bed fusion additive manufacturing process, the ink comprising a beta nucleating agent, the use of the ink and an article obtained by the process.
Claims
1. A 3D printing process for manufacturing an article, which is a powder bed fusion additive manufacturing process, the process comprising the steps of: (i) provision of a first layer comprising a printing material, said printing material comprising polypropylene in non-nucleated and/or alpha-nucleated form; (ii) the optional provision of a second layer to at least a portion of the first layer; (iii) application of heat to at least a portion of the layer or layers; and (iv) optionally repeating steps (i) to (iii) one or more times; wherein the first layer or the second layer comprises a beta nucleating agent, and wherein the temperature of the printing material is between the melting temperature and the crystallisation temperature of the printing material.
2. The 3D printing process of claim 1, further comprising an absorber.
3. The 3D printing process of claim 1, wherein the application of heat to the second layer comprises the application of heat from a first or a second heat source; optionally wherein the first heat source is selected from: an IR lamp; one or more resistors; or combinations thereof and/or wherein the second heat source is selected from: a laser; an electromagnetic beam; one or more resistors; or combinations thereof.
4. The 3D printing process of claim 1, wherein the second layer is present and comprises the beta nucleating agent and an absorber; and optionally wherein the application of heat to the second layer is from a first heat source.
5. The 3D printing process of claim 1, wherein the second layer is present and comprises the beta nucleating agent; and optionally wherein the application of heat is to at least a portion of the second layer from a second heat source.
6. The 3D printing process of claim 1, wherein the first layer additionally comprises the beta nucleating agent; the second layer is present and comprises an absorber; and optionally wherein the application of heat to the second layer is from a first heat source.
7. The 3D printing process of claim 1, wherein the first layer additionally comprises the beta nucleating agent; the second layer is absent; and optionally wherein the application of heat is to at least the portion of the first layer from a second heat source.
8. The 3D printing process of claim 1, wherein the first and/or second layer comprises regions of beta nucleating agent or alpha nucleating agent selectively deposited onto the printing material.
9. The 3D printing process of claim 8, wherein the selective deposition of the beta and/or alpha nucleating agents is selected from a method comprising the formation of regions comprising beta and/or alpha nucleating agent by the selective deposition of layers which comprise the nucleating agents; and/or from a method comprising the formation of regions comprising beta and/or alpha nucleating agent by the selective deposition of beta and/or alpha nucleating agent within one or more layers which also comprise regions where the beta and/or alpha nucleating agent are absent.
10. The 3D printing process of claim 1, wherein the second layer is provided directly adjacent the first layer.
11. The 3D printing process of claim 1, wherein the second layer is applied via a print-head and/or wherein the second layer is provided as an ink.
12. The 3D printing process of claim 11, wherein the volume of ink deposited in a specific area of the first layer is controlled by controlling printhead drop size or spatial coverage of drops.
13. The 3D printing process of claim 1, further comprising the additional step of recycling unmelted printing material, wherein this additional step comprises cooling the printing material.
14. The 3D printing process of claim 1, further comprising the step of preparing the printing material, wherein the beta nucleating agent is dispersed throughout the polypropylene in non-nucleated and/or alpha-nucleated form by melt extrusion.
15. The 3D printing process of claim 1, wherein the temperature of the printing material is in the range of 100° C. to 140° C., the process further comprising a step of removing the article from the printing material and optionally cooling the article.
16. The 3D printing process of claim 1, wherein the printing material further comprises one or more additives selected from: a non-propylene polymer; a compatibilizer; a stabiliser; an acid scavenger; an oxygen scavenger; a moisture scavenger; a pigment; a colourant; a fragrance; a flame retardant; an antimicrobial, antifungal or antifouling agent; an antistatic agent; a magnetic agent; an electromagnetic shielding agent; a radio-opaque agent; a conductive agent; a cross-linking agent; a foaming agent; a flow aid; a reinforcing filler; a plasticiser; or combinations thereof.
17. An ink for 3D printing, wherein the 3D printing process is a powder bed fusion additive manufacturing process, the ink comprising a beta nucleating agent and optionally polypropylene.
18. The ink of claim 17, wherein the beta nucleating agent is provided as particles and/or the ink is selected from a liquid; or a solid in the form of a powder, granules, or pellets, or combinations thereof.
19. The ink of claim 18, wherein the ink comprises a solvent selected from an oleophobic liquid, such as water and/or an oleophilic liquid, such as a hydrocarbon.
20. The ink of claim 17, further comprising at least one additive selected from: an absorber; a stabiliser; an acid scavenger; a reinforcing filler; a compatibilizer; an oxygen scavenger; a moisture scavenger; a pigment; a colourant; a dispersant; a plasticiser; a fragrance; an alpha-nucleating agent; a flame retardant; an antimicrobial, antifungal or antifouling agent; an antistatic agent; a magnetic agent; an electromagnetic shielding agent; a radio-opaque agent; a conductive agent; a cross-linking agent; a foaming agent; an adjuvant to any of the above; or combinations thereof.
21. An article obtainable by the process according to claim 1.
Description
DESCRIPTION OF FIGURES
[0110] FIG. 1 is a schematic representation of a high speed sintering, Selective Absorption Fusion™, multi jet fusion process involving ink jet inks.
[0111] FIG. 2 is a schematic representation of a 3D process according to the invention.
[0112] FIG. 3 is a schematic representation of a 3D process according to the invention.
[0113] FIG. 4 is a schematic representation of a 3D process according to the invention.
[0114] FIG. 5 is a schematic representation of a 3D process according to the invention.
[0115] FIG. 6 illustrates a typical high speed sintering, Selective Absorption Fusion™, multi jet fusion or laser sintering processing window, whereby the polymer powder is held between its melting and crystallisation temperatures.
[0116] FIG. 7 shows experimental data for the effect of WBGII (Ca.sub.xLa.sub.1-x(LIG1).sub.m(LIG2).sub.n) rare earth metal complex beta nucleating agent on the elongation at break (%) and charpy impact strength (kJ/m2) of an injection moulded polypropylene copolymer (far left) and injection moulded polypropylene copolymers containing long chain branching without (A) and with (B) beta nucleating agent (J. Cao et al. Polymer Testing 55 (2016) 318-327).
[0117] FIG. 8 shows a comparison between Example 1 of Table 1 (top) and Comparative Example 2 of Table 1 (bottom) following a Tensile test performed according to ISO 527; ASTM D638; or equivalent method.
[0118] FIG. 9(a) shows experimental data from Table 1 for tensile specimens prepared by powder bed fusion using polypropylene A (Comparative Example 2 and Example 1) in the presence (right) and absence (left) of calcium tetrahydrophthalate beta nucleating agent, the data comparing elongation break (EaB).
[0119] FIG. 9(b) shows experimental data from Table 2 for tensile specimens prepared by powder bed fusion using polypropylene B (Comparative Example 3, and Example 6) in the presence (right) and absence (left) of calcium tetrahydrophthalate beta nucleating agent, the data comparing elongation break (EaB).
[0120] FIG. 10 illustrates the difference in melting point of beta-nucleated polypropylene and non-nucleated or alpha-nucleated polypropylene.
[0121] FIG. 11 is a schematic representation according to the invention, whereby a lower melting beta-nucleated polypropylene is introduced in the previously sintered layer, such that said layer will re-melt more readily upon exposure to heat energy.
[0122] FIG. 12(a) is an image of larger spherulites in an injection moulded non-nucleated polypropylene copolymer (J. Cao et al. Polymer Testing 55 (2016) 318-327).
[0123] FIG. 12(b) is an image of smaller spherulites in an injection moulded beta-nucleated polypropylene copolymer (J. Cao et al. Polymer Testing 55 (2016) 318-327).
[0124] FIG. 13 is a cross-sectional image of a laser sintered nylon 12 powder showing nucleation at boundaries between powder particles (H. Zarringhalam et al. Materials Science and Engineering: A 435-436 (2006) 172-180).
[0125] FIG. 14 is an image of the particle size distribution of a dispersion of quinacridone pigment E3B dispersed in an isoparaffinic solvent suitable for the formulation of an ink. Mean volume particle size is approximately 170 nm.
DETAILED DESCRIPTION
[0126] As shown in FIG. 1, high speed sintering, Selective Absorption Fusion™, multi jet fusion employs an infrared absorbing ink to sinter a polymer powder where the ink is deposited. The polymer powder is held between its melting and crystallisation temperatures ΔT (see FIG. 6) and the infrared absorbing ink allows printed sections to be melted and consolidated whilst the surrounding powder bed remains un-sintered. The final printed article can then be removed. The ink-jet ink of the high speed sintering, Selective Absorption Fusion™, multi jet fusion process represents an effective vehicle to introduce functionality and produce enhanced properties within an additive manufactured part, for instance polymer formulation is performed in-situ during the high speed sintering, Selective Absorption Fusion™, multi jet fusion manufacturing process.
[0127] FIG. 2 is a schematic representation of a 3D printing process. In step (i) a first layer of printing material 1 comprising polypropylene in non-nucleated and/or alpha-nucleated form is added to the build platform (or stage) 3. The polypropylene is provided in the form of a powder 5. In step (ii) a second layer 11 is applied in the form of an ink to at least a portion of the first layer 1. The ink comprises a beta nucleating agent and an absorber, and the ink is applied via a print-head 7 (for example, a thermal or piezoelectric print-head). In step (iii), the entire build platform 3 is irradiated with IR radiation 13 using an IR lamp 15, which selectively melts the printing material coated with the ink. This leaves behind unmelted polypropylene powder 17 and, after cooling, a region of solidified beta-polypropylene 18.
[0128] FIG. 3 is a schematic representation of a 3D printing process. In step (i) a first layer of printing material 5 comprising polypropylene in non-nucleated and/or alpha-nucleated form is added to the build platform 3. In step (ii) a second layer is applied in the form of an ink 11 to the first layer. The ink comprises a beta nucleating agent and is applied via a print-head (for example, a thermal or piezoelectric print-head). In step (iii), a specific region of the second layer is irradiated using a laser 27, such that a laser beam 29 selectively melts the printing material in a specific region. This leaves behind unmelted polypropylene powder 17 and, after cooling, a region of solidified beta-polypropylene 18.
[0129] FIG. 4 is a schematic representation of a 3D printing process. In step (i) a first layer of printing material 21 comprising polypropylene in non-nucleated and/or alpha-nucleated form is added to the build platform. A beta nucleating agent has been dispersed in the printing material 21. In step (ii) a second layer is applied in the form of an ink 23 to at least a portion of the first layer. The ink comprises an absorber and is applied via a print-head 7 (for example, a thermal or piezoelectric print-head). In step (iii), the entire build platform is irradiated with IR radiation 13 using an IR lamp 15, which selectively melts the printing material coated with the ink. This leaves behind unmelted polypropylene powder 25 and, after cooling, a region of solidified beta-polypropylene 18.
[0130] FIG. 5 is a schematic representation of a 3D printing process. In step (i) a first layer of printing material 21 comprising polypropylene in non-nucleated and/or alpha-nucleated form is added to the build platform 3. A beta nucleating agent has been dispersed in the printing material 21. In step (ii), a specific region of the first layer is irradiated using a laser beam 29 from a laser 27, which selectively melts the printing material in this specific region. This leaves behind unmelted polypropylene powder 25 and, after cooling, a region of solidified beta-polypropylene 18.
[0131] FIG. 6 illustrates a typical high speed sintering, Selective Absorption Fusion™, multi jet fusion or laser sintering processing window, whereby the polymer powder is held between its melting and crystallisation temperatures.
[0132] FIG. 7 shows experimental data for the effect of WBGII (Ca.sub.xLa.sub.1-x(LIG1).sub.m(LIG2).sub.n) rare earth metal complex beta nucleating agent on the elongation at break (%) and charpy impact strength (kJ/m2) of an injection moulded polypropylene copolymer (far left) and injection moulded polypropylene copolymers containing long chain branching without (A) and with (B) beta nucleating agent (J. Cao et al. Polymer Testing 55 (2016) 318-327).
[0133] As can be seen from FIG. 8 beta nucleation significantly increases ductility, which results in necking and increased elongation at break. For instance, with FIG. 8 AA without beta nucleating agent had an average elongation at break of 32.9%, whereas BB with beta nucleating agent had an average elongation at break of 68.6%.
[0134] As detailed above, FIG. 10 shows the difference in melting point of beta-nucleated polypropylene and non-nucleated or alpha-nucleated polypropylene. The 3D printing processes allow for the introduction of a lower secondary melting point, resulting in production of beta-nucleated polypropylene only in printed regions of a printed article, resulting in enhanced physical and mechanical properties. Introduction of a lower melting beta-nucleated polypropylene will result in the layer re-melting more readily upon exposure to energy from a heat source (see FIG. 11), resulting in improved consolidation and increased mechanical properties.
EXAMPLES
[0135] The invention will now be described with reference to the following non-limiting examples.
TABLE-US-00001 TABLE 1 Polypropylene Material A The β-nucleator used in the examples listed in Table 1 is calcium tetrahydrophthalate. β Ultimate Notched HDT nucleator Active Tensile Elongation Izod Flexural @ 0.45 MPa/ level in ink Ink Cooling Strength at Break Impact Modulus @ 1.8 MPa Example (wt %) Carrier of parts (MPa) (%) kJ/m.sup.2 (MPa) (° C.) Comparative 0 Water No 30 20 3.5 Not 100/60 Example 1 based tested Comparative 0 Mineral No 26.2 32.9 3.8 672 .sup. 111/58.1 Example 2 Oil base Example 1 0.9 Mineral No 26.5 68.6 4.2 700 113.4/59.7 Oil base Example 2 0.6 Mineral No 26.4 50.3 Not Not Not Oil base tested tested tested Example 3 0.6 Mineral No 26.1 60.3 Not Not Not Oil base tested tested tested Example 4 0.6 Mineral Yes 24.7 75.8 Not Not Not Oil base tested tested tested Example 5 1.8 Mineral No 28.7 61.0 Not 593 Not Oil base Tested tested
[0136] Table 1 and FIGS. 8 and 9(a) show the difference in tensile strength, elongation at break, notched Izod Impact, Flexural Modulus and Heat Deflection Temperature results between 3D printed articles according to the invention (Examples 1-5) and 3D printed articles not of the invention (Comparative Examples 1 and 2). Comparative Example 1 relates to a water-based ink containing carbon black infrared absorber prepared using high speed sintering/HP multi jet fusion, and Example 2 relates to a corresponding example employing an ink with a mineral oil base. As can be seen from the data, from incorporation of a beta nucleating agent, there is a noticeable increase in the percentage of elongation at break. For both the comparative examples and examples of the invention testing was performed as follows: tensile testing performed using type 1 specimens according to ASTM D638 or equivalent, notched Izod impact tests performed using Izod test method A and 3.2 mm specimens according to ASTM D256 or equivalent, heat deflection temperature (HDT) testing performed according to ASTM D648 or equivalent, flexural testing performed according to ASTM D790 or equivalent.
TABLE-US-00002 TABLE 2 Polypropylene Material B The β-nucleator used in the examples listed in Table 2 is calcium tetrahydrophthalate. β Ultimate Notched HDT nucleator Active Tensile Elongation Izod Flexural @ 0.45 MPa/ level in ink Ink Cooling Strength at Break Impact Modulus @ 1.8 MPa Example (wt %) Carrier of parts (MPa) (%) kJ/m.sup.2 (MPa) (° C.) Comparative 0 Mineral No 22 96 Not Not Not Example 3 Oil base tested tested tested Example 6 0.6 Mineral No 20.3 161 Not Not Not Oil base tested tested tested
[0137] Table 2 and FIG. 9(b) show the difference in tensile strength and elongation at break results between 3D printed articles according to the invention (Example 6) and 3D printed articles not of the invention (Comparative Example 3). Comparative Example 3 relates to a mineral oil based ink containing carbon black infrared absorber. As can be seen from the data, from incorporation of a beta nucleating agent, there is a noticeable increase in the percentage of elongation at break. For both the comparative examples and examples of the invention testing was performed as follows: tensile testing performed using Type 1 specimens according to ASTM D638 or equivalent.
[0138] FIG. 12(a) is an image of larger spherulites in an injection moulded non-nucleated polypropylene copolymer (J. Cao et al. Polymer Testing 55 (2016) 318-327).
[0139] FIG. 12(b) is an image of smaller spherulites in an injection moulded beta-nucleated polypropylene copolymer (J. Cao et al. Polymer Testing 55 (2016) 318-327).
[0140] FIG. 13 is a cross-sectional image of a laser sintered nylon 12 powder showing nucleation at boundaries between powder particles (H. Zarringhalam et al. Materials Science and Engineering: A 435-436 (2006) 172-180).
[0141] FIG. 14 is an image of the particle size distribution of a dispersion of quinacridone pigment E3B dispersed in an isoparaffinic solvent suitable for the formulation of an ink. Mean volume particle size is approximately 170 nm.
[0142] It would be appreciated that the process and apparatus of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.
