Method of manufacturing fuses and polymer blend used therein

Abstract

A method of fused filament fabrication (FFF) additive manufacturing comprising employing a thermoplastic blend consisting of a high density polyethylene and a second thermoplastic polymer, wherein the second polymer is a low density polyethylene (LDPE), a functionalized polyolefin, or a combination thereof, and the weight ratio of the amount of the high density polyethylene to the amount of the second thermoplastic polymer is 1.5 / 1 to 20 / 1. LDPE refers to polyethylene that has been polymerized under high pressure with free radicals. The method allows the additive manufactured article to retain the desired mechanical properties of HDPE without encountering the problems inherent to FFF printing of HDPE or use of solid fillers. In particular embodiments, the additive manufactured article has a continuous phase and the second thermoplastic polymer is present in a discontinuous phase within the additive manufactured article and the filament used to make the article.

Description

Technical Field

[0001] This invention relates to a method of additive manufacturing, for example, using filaments propelled and heated through a nozzle and deposited on a pressure plate, wherein thermoplastic polymer powder is melted and extruded (commonly referred to as filament fabrication). In particular, the invention enables the use of a thermoplastic polymer primarily composed of high-density polyethylene, which is unusable in additive manufacturing processes due to poor warpage and adhesion. Background Technology

[0002] Additive manufacturing of thermoplastic polymers (typically nylon) is well known. For example, fused filament fabrication (FFF) (often also known as plastic jet printing) has been used to form 3D parts by using thermoplastic filaments that are drawn into a nozzle, heated, melted, and then extruded, wherein the extruded filaments fuse together upon cooling (see, for example, U.S. Patent No. 5,121,329). Because this technique requires molten filaments and extrusion, the materials are limited to thermoplastic polymers (typically nylon) and complex equipment. Furthermore, this technique requires a support structure that is also extruded during the fabrication of complex parts, which must withstand the high temperatures required to form the parts while also being easily removable, for example by dissolving the support structure or by dissolving the layer between the support structure and the final article, as described in U.S. Patent No. 5,503,785.

[0003] Nylon or other polymers with polar groups must be used to ensure sufficient adhesion between the layers deposited during 3D printing of the part (lacking adhesion in the z-direction). Similarly, polymers exhibiting crystallization in specific directions, such as high-density polyethylene (HDPE), tend to warp and cannot be printed adequately. For these reasons, HDPE has not been successfully used for commercial FFF 3D printing. Blends of polymers with small amounts of HDPE have been reported to be printed, as described in WO2016080573. Likewise, high filler contents of solid fillers have been used to reduce the undesirable crystallization of HDPE (e.g., CN104629152A and CN105295175), but the filler content required for adequate printing always reduces the desired mechanical properties of such parts formed from HDPE.

[0004] It is desirable to provide a method for printing polymers containing HDPE that retains the desired properties of HDPE while avoiding one or more of the problems of 3D printing HDPE in existing technologies. Summary of the Invention

[0005] We have discovered an improved filament fabrication additive manufacturing method, the method comprising:

[0006] (i) Provides a thermoplastic blend consisting of high-density polyethylene (HDPE) and a second thermoplastic polymer (STP), wherein the second polymer is low-density polyethylene, a functionalized polyolefin, or a combination thereof, and the weight ratio of the amount of high-density polyethylene to the amount of the second thermoplastic polymer is from 1.5 / 1 to 20 / 1.

[0007] (ii) Heating and dispensing the thermoplastic blend through a nozzle to form an extrusion deposited on a substrate;

[0008] (iii) While dispensing the thermoplastic blend, moving the substrate, the nozzle, or a combination thereof to cause horizontal displacement between the substrate and the nozzle in a predetermined pattern, thereby forming an initial layer of material on the substrate; and

[0009] (iv) Repeat steps (ii) and (iii) to form a continuous layer of the material adhered to the initial layer, thereby forming an additively manufactured part.

[0010] A second aspect of the invention is an additively manufactured article comprising at least two layers of a plurality of extrudates, said extrudates being a blend of high-density polyethylene and a second thermoplastic polymer, wherein said second polymer is low-density polyethylene, a functionalized polyolefin, or a combination thereof, and the weight ratio of the amount of said high-density polyethylene to the amount of the second thermoplastic polymer is from 1.5 / 1 to 20 / 1.

[0011] A third aspect of the invention is a filament that can be used in additive manufacturing, comprising a filament composed of a thermoplastic blend, said thermoplastic blend being composed of high-density polyethylene and a second thermoplastic polymer, wherein said second thermoplastic polymer is low-density polyethylene, a functionalized polyolefin, or a combination thereof, and the weight ratio of the amount of said high-density polyethylene to the amount of the second thermoplastic polymer is from 1.5 / 1 to 20 / 1.

[0012] An improved additive manufacturing method can be used to form additively manufactured polymeric parts that possess the desired properties of high-density polyethylene (HDPE) while avoiding 3D printing problems associated with printing HDPE, such as warpage and lack of adhesion in the z-direction (height). This method is particularly suitable for producing thermoplastic parts using the FFF method, which are primarily composed of HDPE and do not contain additives, such as fillers, that are solid at the melting temperature or the 3D printing temperature used in FFF. Attached Figure Description

[0013] Figure 1 This is a side view of the additively manufactured article of the present invention, obtained by the method of the present invention.

[0014] Figure 2 This is an end view of the extruded material of the initial layer formed in the method of the present invention.

[0015] Figure 3 This is an end view of the final initial layer of the method of the present invention.

[0016] Figure 4 The photographs are of comparative examples of additively manufactured articles using HDPE alone and three examples of additively manufactured articles of the present invention using HDPE with a second thermoplastic polymer. Detailed Implementation

[0017] Additive manufacturing methods can utilize any suitable equipment and methods for manufacturing FFF parts, such as those known in the art (e.g., method steps of heating, dispensing, repeating, and removing), using pre-prepared filaments as described above, and then loading them into a known FFF printing device. The method can also melt the blended material at or before the nozzle and extrude the extrudate in a more conventional manner, while forming an additive material manufactured as follows.

[0018] Turning Figures 1 to 3 The method includes heating and dispensing a thermoplastic blend via a nozzle 100 attached to a nozzle assembly 110. During dispensing, the material forms an extrusion 120, which forms an initial layer 130 and a continuous layer 140 on a substrate 150. The nozzle assembly 110 is depicted as orthogonal to the substrate but can be configured at any angle available for forming the extrusion, whereby the extrusion 120 and the nozzle assembly 110 form an obtuse angle, wherein the extrusion 120 is parallel to the substrate. Additionally, the nozzle assembly 110 can be rotated about its longitudinal axis, for example, to reorient the shape of the opening in the nozzle 100 to produce an extrusion 120 with a different relationship to the substrate 150, such as... Figures 1 to 3 As shown in the image.

[0019] The relative movement of the base 150 and the nozzle assembly 110 is also shown, but it should be understood that the base 150, the nozzle assembly 110, or both can be moved to induce relative movement in any horizontal or vertical direction. Movement can be performed in a predetermined manner, which can be achieved by any known CAD / CAM methods and apparatus, such as those well known in the art and readily available robotic or computerized machine tool interfaces. Such pattern formation is described, for example, in U.S. Patent No. 5,121,329.

[0020] The extrudate 120 can be continuously dispensed or broken to form the initial layer 130 and the continuous layer 140. If a broken extrudate 120 is required, the nozzle can be constituted by a valve (not shown) for cutting off the material flow. This valve mechanism can be any suitable valve mechanism, such as any known electromechanical valve, which can be easily controlled by any CAD / CAM method combined with the pattern.

[0021] Because the material can be viscous, the substrate 150 can be a low surface energy fluoropolymer, such as Teflon. Alternatively, the substrate can have a release agent, such as those known in polyurethane reactive injection molding technology, or the substrate can have a sheet of paper or film of low energy material placed on the substrate before dispensing and forming the additively manufactured part.

[0022] More than one nozzle assembly 110 can be used to create composite or gradient structures within the additively manufactured part. Similarly, a second nozzle assembly 110 can be used to distribute a support structure, which can be later removed to allow for the formation of more complex geometries, as described in U.S. Patent No. 5,503,785. The support material can be any material that adds support and is easily removable, such as materials known in the art, for example, wax.

[0023] The method employs a thermoplastic blend composed of high-density polyethylene (HDPE) and a second thermoplastic polymer, wherein the second polymer is low-density polyethylene, a functionalized polyolefin, or a combination thereof. The weight ratio of HDPE to the second thermoplastic polymer is from 1.5 / 1 to 20 / 1.

[0024] HDPE can be any known HDPE, such as those commercially available. HDPE is generally understood in the art to be characterized by the catalysts used to produce them, such as Philips chromium catalysts, Ziegler catalysts, or metallocene catalysts. Compared to low-density polyethylene, HDPE has a slightly higher density and greater crystallinity, with very few or almost no branches, resulting in polymers with higher crystallinity compared to LDPE. HDPE is characterized by a higher strength-to-weight ratio compared to LDPE. Typically, the density of HDPE will be from about 9.4 to 9.65, and the melt index will be from about 0.1 to about 50, and preferably from about 0.25 to 40 (ASTM D1238). Exemplary commercially available HDPEs include (but are not limited to) DMDA-8007NT 7 (melt index 8.3, density 0.965), DMDC-8910NT 7 (melt index 10, density 0.943), DMDA-1210NT 7 (melt index 10, density 0.952), HDPE 17450N (melt index 17, density 0.950), DMDA-8920NT 7 (melt index 20, density 0.954), DMDA 8940NT 7 (melt index 44, density 0.951), DMDA-8950NT 7 (melt index 50, density 0.942), DMDA-8965-NT 7 (melt index 66, density 0.952), and DMDC-1210NT7 (melt index 10, density 0.952), all of which are available from The Dow Chemical Company. Other exemplary HDPEs may include HDPE HD6601.29 (melt index 5, density 0.948) and HDPE HD6733.17 (melt index 33, density 0.950), both available from Exxon Mobil; Alathon H5220 (melt index 20, density 0.952) and Alathon M4661 (melt index 6.1, density 0.946), both available from Lyondell Basel; Lutene H Me8000 (melt index 8.0, density 0.957), available from LG Chem; and HDPE CC254 (melt index 2.1, density 0.953), available from Sabic.

[0025] The second thermoplastic polymer (STP) used in conjunction with HDPE to form thermoplastic blends is low-density polyethylene (LDPE), functionalized polyolefins, or combinations thereof. LDPE refers to polyethylene that has undergone free radical polymerization under high pressure, resulting in significant branching, compared to HDPE and linear low-density polyethylene (LLDPE). Typically, LDPE has a density of about 0.91 to about 0.93 and a melt index of about 0.1 to 50, and more typically about 0.5 to 40. Possible suitable exemplary commercially available LDPEs include those available from Dow Chemical Company (Midland, Michigan), such as LDPE 150E (melt index 0.25, density 0.921), LDPE 421E (melt index 3.2, density 0.930), LDPE 780E (melt index 20, density 0.923), LDPE 722 (melt index 8, density 0.918), AGILITY 1021 (melt index 1.9, density 0.919), HP7023 from SABIC (melt index 7.0, density 0.932), Lupolen 1800S from LyondellBasell (melt index 20, density 0.917), and LDPE LD 102.LC from ExxonMobil (melt index 6.8, density 0.921). LD136.MN (melt index 2.0, density 0.912).

[0026] Functionalized polyolefins are polyolefins containing atoms other than carbon and hydrogen. For example, functionalized polyolefins can be modified with hydroxyl, amine, aldehyde, epoxide, ethoxylate, carboxylic acid, ester, anhydride, or combinations thereof. Generally, functionalized polyolefins contain functional groups, such as protonated (-COOH) or non-protonated (-COO-) acid groups or acid salts. Examples include ethylene / acrylic acid copolymers (e.g., under the trademark PRIMACOR). TM (Dow Chemical Company's trademark ("Dow")), NUCREL) TM (Trademark of DuPont and Company) and ESCOR TM (ESCOR is a trademark of Exxon Corporation) polymers sold by Exxon Corporation, ethylene / methacrylic acid copolymers (e.g., under the trademark NUCREL) TM Polymers for sale), maleic anhydride-modified polyolefins (e.g., under the trademark LICOCENE) TM (Trademark of Clariant AG Corporation), EPOLENE TM(EPOLENE is a trademark of Westlake Chemical Corporation) and MORPRIME TM (Polymers sold by Rohm and Hass Chemicals LLC, a trademark). Ethylene ester copolymers, such as those modified with vinyl acetate (ELVAX, DuPont, Wilmington, DE (“DuPont”), acrylate-modified (ELVALOY, available from DuPont) and AMPLIFY (Dow)). Similarly, subsequent ionomers of functionalized polyolefins are formed via neutralization with cations of metals such as Zn, Na, Mg, or K, an example of which is SURLYN, available from DuPont.

[0027] The weight ratio of HDPE and the second thermoplastic polymer in the thermoplastic blend is the same as that in the case where the majority of the thermoplastic blend is HDPE, such that the HDPE / thermoplastic polymer ratio is from 1.5 / 1 to 20 / 1. Preferably, the amount of HDPE / (STP) is from 2 / 1, 5 / 1, or 10 / 1 to 15 / 1. In one embodiment, it is preferred that the thermoplastic blend contains no other components.

[0028] In one embodiment, the thermoplastic blend is in granular form, which is subsequently heated and extruded during the additive manufacturing process. In another embodiment, the thermoplastic blend is in filament form. Each of these can be obtained by processes known in the art. When HDPE is used with a specific STP, the filament surprisingly achieves a microstructure that is believed to enable the formation of additively manufactured articles with the desired mechanical properties of HDPE, while allowing excellent z-axis adhesion and minimizing or eliminating warpage.

[0029] In one embodiment, HDPE is a continuous matrix, and STP is discontinuously dispersed within the continuous HDPE matrix in the filament or printed article (referred to herein as "grains"). Generally and desirably, the STP features are characterized on a scale substantially smaller than the diameter of the filament (e.g., the grain size is at least 5 or 10 times smaller than the diameter of the filament). Illustratively, STP grains are smaller than about 5 micrometers, and in some embodiments are submicron particles (e.g., smaller than about 1 micrometer) dispersed in the continuous HDPE phase. Grains can have any shape, but tend to be spherical. These features can be uniformly dispersed or have a concentration gradient. The STP grains and microstructure of the filament or manufactured article can be observed using microscopy techniques such as atomic force microscopy or scanning electron microscopy.

[0030] In one embodiment, the thermoplastic blend has one or more optional components, such as pigments, fillers, lubricants, slip agents, or flame retardants, provided that the majority of the blend is HDPE. Other components may include additives to improve one or more properties or functions, such as the compatibility of HDPE and STP or the mechanical properties of the final product. Nucleating agents, such as HPN-20E from Milliken, may also be added to further improve shrinkage characteristics. Internal lubricants or processing aids may include those such as Dynamar FX5911 (3M), Kynar PPA (Arkema), or Licolub H 12 or Licowax PE520 (Clariant). Thermoplastic blends may include inorganic particles, commonly referred to as fillers, as well as dyes and anti-caking / flow control agents (e.g., fumigated silica). The dyes can be inorganic dyes (e.g., carbon black or mixed metal oxide pigments) or organic dyes, such as inoaniline, oxoaniline, porphyrin derivatives, anthraquinone, styrene, oxabenzothium, and aromatic cyanine derivative compounds. The fillers can be any typical fillers used in plastics, such as calcium carbonate, silicates, or oxides (quartz, alumina, or titanium dioxide).

[0031] HDPE and STP typically have different melt temperatures, defined as the difference between the initial melt temperatures of the two polymers, determined by differential scanning calorimetry (DSC). Generally, the melt temperatures of HDPE and STP are within 20°C or 10°C of each other, but this is not always the case. For example, as an illustration, the optimal melt temperature for a given material may not be a single temperature, but rather a range of several degrees Celsius. It is desirable for STP to have a melt temperature lower than that of HDPE.

[0032] The method produces novel additively manufactured parts, wherein the parts consist of at least two layers of extrudate adhered together between the layers, wherein the STP is dispersed within HDPE at a scale smaller than the filament diameter or the extrusion nozzle opening used to form the extrudate, and the HDPE / STP weight ratio is 1.5 / 1 to 20 / 1. This scale is analogous to the scale described above regarding grains within the filament. In specific embodiments, the STP is dispersed within a continuous HDPE matrix, and the diameter (equivalent spherical diameter) of the STP grains is less than about 5 micrometers, and in some embodiments less than 1 micrometer.

[0033] Example

[0034] Material:

[0035] The materials used to produce additively manufactured articles are shown in Table 1.

[0036] Table 1

[0037]

[0038] MI = Melt Flow Index, MP = Melting Point; * It is now available from SK Chemicals;

[0039] HDPE DMDC 1250 and HDPE DMDA 8940NT-7 are used in their supplied condition. Blends of HDPE with LDPE, LLDPE, or PRIMACOR copolymers are formed by melt blending in a single-screw extruder to produce pellets. The pellets are then fed into the single-screw extruder to form filaments, which are heated to 190°C with the screw rotating at 10 rpm, extruding the polymer melt through a 1.8 mm nozzle to form filaments with substantially the same diameter. Other diameters can be produced depending on the size of the part to be manufactured and specific 3D printing capabilities, typically resulting in filament sizes in the range of approximately 10 mm (less than 0.5 mm).

[0040] Print:

[0041] The parts were printed on a MakerBot copier 2X, which was available from Stratasys Ltd, Minneapolis, MN (USA). Small, three-dimensional boxes (2cm × 2cm × 1mm) filled with infill were printed with a layer height of 0.2mm. The print bed temperature was 110°C, and the nozzle temperature was 210°C. The print results are shown in Table 2. Print quality was determined in part by measuring the corner gap height at the planar corners. If a part was not fully printed, it was because of significant deformation and gaps during printing, leading to further print failures. The results of the printed example and comparative example parts are shown in Table 2. Similarly, photographs of the prints of Comparative Example 3 and Examples 3 through 5 are shown in Table 2. Figure 4 As shown in the image.

[0042] Table 2

[0043]

[0044] From Table 2 and Figure 4 It is evident that using a small amount of the second thermoplastic polymer with HDPE resulted in HDPE printing without warping, voids, or other deformations.

Claims

1. An additive manufacturing method, (i) A thermoplastic blend comprising high-density polyethylene and a second thermoplastic polymer is provided, wherein the second polymer is low-density polyethylene, a functionalized polyolefin or a combination thereof, and the weight ratio of the amount of high-density polyethylene to the amount of the second thermoplastic polymer is from 1.5 / 1 to 20 / 1. (ii) Heating and dispensing the thermoplastic blend through a nozzle to form an extrusion deposited on a substrate; (iii) While dispensing the thermoplastic blend, move the substrate, the nozzle, or a combination thereof to cause horizontal displacement between the substrate and the nozzle in a predetermined pattern, thereby forming an initial layer of material on the substrate; as well as (iv) Repeat steps (ii) and (iii) to form a continuous layer of the material adhered to the initial layer, thereby forming an additively manufactured part.

2. The method of claim 1, wherein the method further comprises repeating step (iv) such that a plurality of successive layers adhere and stack to form the additively manufactured part.

3. The method according to claim 1, wherein the weight ratio of the amount of high-density polyethylene to the amount of the second thermoplastic polymer is 10 / 1 to 20 / 1.

4. The method of claim 3, wherein the high-density polyethylene has a melting temperature and the second thermoplastic polymer has a melting temperature, wherein the melting temperature of the high-density polyethylene is higher than the melting temperature of the second thermoplastic polymer.

5. The method of claim 4, wherein the high-density polyethylene has a melt index, and the second thermoplastic polymer has a melt index, and the melt index of the high-density polyethylene and the melt index of the second thermoplastic polymer have a melt index ratio of the high-density polyethylene to the second thermoplastic polymer of 0.1 to 5.

6. The method of claim 5, wherein the melt index ratio is 0.2 to 1.

7. The method of claim 1, wherein the second thermoplastic polymer is a functionalized polyolefin.

8. The method of claim 7, wherein the functionalized polyolefin is an ethylene / acrylic acid copolymer, an ethylene / methacrylic acid copolymer, a maleic anhydride-modified polyolefin, or a combination thereof.

9. The method of claim 1, wherein the high-density polyethylene and the second thermoplastic polymer are melted before being dispensed through the nozzle.

10. The method of claim 1, wherein the high-density polyethylene and the second thermoplastic polymer form a filament, the filament being drawn into the nozzle and melted within the nozzle.

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