COMPOSITIONS FOR USE IN FUSED FILAMENT 3D FABRICATION AND METHOD FOR MANUFACTURING SAME

Abstract

A method for forming a blended material for use as a deposition material in a fused filament fabrication (FFF) printer is provided. A semi-crystalline material and an amorphous material are physically mixed at an appropriate ratio. The mixed material is then heated to a temperature that is above the melting point of the semi-crystalline material and above the glass transition temperature of the amorphous material to form a blended material. The blended material is then extruded through an extruder die for use in the FFF printer.

Claims

1. A method for forming a blended material for use as a deposition material in an additive manufacturing system, the method comprising: providing a first amount of a semi-crystalline material and a second amount of an amorphous material; physically mixing the first amount of the semi-crystalline polyaryletherketone material and the second amount of the amorphous material which includes a polyarylsulfone, wherein the weight ratio of the first amount to the second amount is between 60:40 and 80:20, inclusive; melt blending using a screw extruder the mixed material at a temperature that is above the melting point of the semi-crystalline material and above the glass transition temperature of the amorphous material to form a blended material; and extruding the blended material into a strand through an extruder die.

2. The method of claim 1 wherein the screw extruder is a twin-screw extruder.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0011] FIG. 1 is a flowchart of a method of fabricating a blended extrudate of amorphous and semi-crystalline materials according to an aspect of the present invention.

[0012] FIG. 2 is a flowchart of a method of fabricating a filament roll from the blended extrudate which is suitable to be fed into a fused filament fabrication printer according to an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Printing with the blended material results in 3D objects having more desirable mechanical properties and chemical resistance than would be possible using an amorphous material alone. This results from the presence of the semi-crystalline material in the blend, which is characterized by significantly better chemical resistance and mechanical properties such as tensile strength.

[0014] In one embodiment, the blend is a mixture of polyphenylsulfone (PPSU), representing the amorphous polymer, and polyether ether ketone (PEEK) as the semi-crystalline material.

[0015] In some other embodiments, other amorphous materials, such as other polyarylsulfones (e.g., polyethersulfone (PESU), polysulfone (PSU), etc.) can be used in conjunction with PEEK to form a blended material in accordance with the present teachings and suitable for use in a fused filament fabrication process. Still further, other amorphous materials can be used in conjunction with PEEK or other semi-crystalline materials to form a blended material in accordance with the present teachings and suitable for use in a fused filament fabrication process. Such other amorphous materials include, for example and without limitation, polyetherimide (PEI), polyphenylene oxides (PPOs), acrylonitrile butadiene styrene (ABS), methyl methacrylate acrylonitrile butadiene styrene copolymer (ABSi), polystyrene (PS), and polycarbonate (PC).

[0016] In some other embodiments, polyaryletherketones (PAEKs) other than PEEK can be used as the semi-crystalline component of the blended material. In still further embodiments, other semi-crystalline thermoplastics, for example and without limitation, polyamide (PA), polybutylene terephthalate (PBT), poly(p-phenylene sulfide) (PPS) can be blended with appropriate amorphous thermoplastics to form a blended material in accordance with the present teachings. For example, some other suitable blended materials include PA (semi-crystalline) and PPO (amorphous), PBT (semi-crystalline) and PC (amorphous), and PPS (semi-crystalline) and PEI (amorphous).

[0017] In one exemplary embodiment, the weight ratio of semi-crystalline material to amorphous material in the blend is in a range of about 50:50 to about 95:05, inclusive, or about 50:50 to about 90:10, inclusive. Preferably, the weight ratio of semi-crystalline material to amorphous material in the blend is between 60:40 and 80:20, inclusive. In certain applications, however, the weight ratio of semi-crystalline material to amorphous material in the blend could be between 80:20 and 90:10, inclusive, or 80:20 or greater to obtain the most benefit of the superior properties of the semi-crystalline material so long as the blend viscosity is sufficiently high at the operating temperature to preserve its shape upon printing through the extrusion head of the fused filament fabrication printer. The ratio selected for any particular application may vary primarily as a function of the materials used and the properties desired for the printed object.

[0018] Since a semi-crystalline polymer by itself has a relatively high viscosity, it would be problematic if not impossible to extrude the material through an extrusion head of a fused filament fabrication printer. However, according to the present invention, the presence of an amorphous polymer in the blend exhibits the relatively more desirable rheological properties characteristic of an amorphous polymer. In other words, the amorphous polymer in the blend decreases the viscosity sufficiently to allow printing of the material through the fused filament fabrication printer.

[0019] In another embodiment, the blended material may include two or more semi-crystalline materials and/or two or more amorphous materials. In embodiments in which multiple semi-crystalline materials or multiple amorphous materials are used to form the blended material, the total amount of each type of material (semi-crystalline or amorphous) should fall within the ratio guidelines provided above.

[0020] In yet another embodiment, a solid non-polymer filler material having a higher melting temperature than both the amorphous material and semi-crystalline material can be added to the blend to improve mechanical properties of the 3D objects. The amount of the filler material by weight is up to about 60%, and more preferably between 5% and 20% of the total blend. The filler material can include chopped carbon fibers, chopped glass fibers, chopped aramid/Kevlar fibers. Preferably, the fibers are chopped in 1-3 mm in length and are suspended in the blend during its fabrication. In an exemplary embodiment, the chopped fibers are encapsulated or coated with resin.

[0021] Referring to FIG. 1, the blend is prepared as follows. The materials to be blended are typically provided in pellet or powder form. In step 100, the materials are dried in a dryer to remove moisture in order to prevent hydrolysis of polymer that can reduce polymer chain length resulting in poorer properties. In step 102, the dried materials in powder form are physically and thoroughly mixed in a mixing device. In step 104, the mixed semi-crystalline and amorphous materials are then fed to a hopper of an extruder. In one embodiment, a twin-screw extruder is used to melt blend the materials and then extrude the blended material into a strand.

[0022] In case a filler material is used, it can be added during step 102 or 104 or in step 114 as will be discussed later herein. In the extruder, the mixed materials are melted (step 106). In accordance with one embodiment, the melt blending is performed at a temperature that is: (a) above the glass transition temperature of the amorphous polymer materials, preferably at a temperature at which the polymer is fluid; (b) above the melting point of semi-crystalline polymer materials; and (c) below the polymer degradation temperature of all amorphous and semi-crystalline materials. In case more than one amorphous polymer material is used in the blend, the melt blending is performed at a temperature that is above the glass transition temperature of all the amorphous polymer materials, at which the polymers behave like a fluid. Likewise, in the case of more than one semi-crystalline polymer materials, the melt blending is performed at a temperature that is above the melting point of all the semi-crystalline polymer materials that are used in the blend.

[0023] It has been found that this methodology provides good dispersion of the components and enables good viscosity management (controlling viscosity so that it is in an appropriate range for extrusion) during 3D printing by FFF.

[0024] Table 1 below depicts the glass transition temperature (T.sub.g) or melting temperature (T.sub.m), and the melt processing temperature for several components used in forming blended materials in accordance with the present teachings.

TABLE-US-00001 TABLE 1 Glass Transition, Melting, and Melt Processing Temperature Glass Typical Melt Transition Melting Processing Temperature, Temperature, Temperature Material Type T.sub.g ( F.) T.sub.m ( F.) ( F.) PEEK Semi-Crystalline 650 670-700 PPSU Amorphous 428 650-750 PEI Amorphous 420 660-750 PESU Amorphous 437 650-725

[0025] In step 108, the melted material passes through a die of the twin-screw extruder and is extruded. In one embodiment, the resulting extrudate is typically formed into a strand, which is typically - inch in diameter. The melt processing temperature (i.e., the temperature of the material as it is extruded through an extrusion head of a fused filament fabrication printer), as provided in Table 1, will typically be near the temperature at which the materials are melt blended. For example, PEEK (semi-crystalline) and PPSU (amorphous), PEEK (semi-crystalline) and PEI (amorphous), and PEEK (semi-crystalline) and PESU (amorphous) can be melt blended at about 690 F. The melt processing temperature, as per Table 1, will be a similar temperature.

[0026] Of course, the melt processing temperature for the blended material will be dictated by the highest melting temperature or highest glass transition temperature of all the amorphous and semi-crystalline materials in the blend, whichever is higher. In the case of the PEEK/PPSU blend, the melting temperature of PEEK is higher than the glass transition temperature of the PPSU. Thus, the melt processing temperature of the blend during printing is in the range of 670-700 F. at the extrusion printhead of the FFF printer.

[0027] After extrusion, in step 110, the strand is cooled, such as in a water bath. In one embodiment, the size of the extrusion die is such that the strand is in a form of a filament having a diameter of 1-2 mm. The filament is then wound as a roll of filament, which can be fed directly into the FFF printer. Alternatively, in step 112, the strand is cut into small pellets for storage. In that case, the pellets will need to be reprocessed into a filament of 1-2 mm in diameter which is adapted for direct feeding into the FFF printer as illustrated in FIG. 2.

[0028] In step 114, the pellets containing the blended materials from step 112 are fed into a hopper of an extruder such as a single or twin-screw extruder. If the filler material is involved, it can be added in this step instead of step 102 or 104. In step 116, the blended pellets are melted in the extruder. Similar to step 106, the melting is performed at a temperature that is: (a) above the glass transition temperature of the amorphous polymer materials, preferably at a temperature at which the polymer is fluid; (b) above the melting point of semi-crystalline polymer materials; and (c) below the polymer degradation temperature of all amorphous and semi-crystalline materials. The temperature in the extruder for melting the PEEK (semi-crystalline) and PPSU (amorphous), PEEK (semi-crystalline) and PEI (amorphous), and PEEK (semi-crystalline) and PESU (amorphous) blend is about 690 F.

[0029] In step 118, the melted material passes through a die of the extruder and is extruded into a filament, which is typically 1 to 2 mm in diameter. After extrusion, in step 120, the filament is cooled, such as in a water bath and is rolled onto a roll as a final product in step 122, which is suitable to be fed directly into the FFF 3D printer.

[0030] To print a 3D object, the filament from the filament roll of the heat blended material is fed to the FFF printer. The filament being fed is then heated by a heater block of the FFF printer to a useable temperature which is above the melting point of the semi-crystalline material and above the glass transition temperature of the amorphous material. The FFF printer then deposits the heated material in a selected pattern layer by layer in accordance with a mathematical model of the 3D object in order to fabricate the 3D object.

[0031] As a consequence of the aforementioned desired temperature guidelines, those skilled in the art will appreciate that not all combinations of the aforementioned semi-crystalline thermoplastics and amorphous thermoplastics will be well suited to melt blending for forming the blended material. For example, the thermal transition temperatures should satisfy the aforementioned guidelines and the materials need to be miscible or otherwise compatible. Using this disclosure and readily available reference sources, it is within the capabilities of those skilled in the art to appropriately pair a semi-crystalline thermoplastic and an amorphous thermoplastic to create a blended material in accordance with the present invention.

[0032] The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many modifications, variations, and alternatives may be made by people of ordinary skill in this art without departing from the scope of the invention. Those familiar with the art may recognize other equivalents to the specific embodiments described herein. Accordingly, the scope of the invention is not limited to the foregoing specification.