ES2786098A1 - ABS-based thermoplastic material for 3D printing by extrusion of filaments and molten pellets (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

ABS-based thermoplastic material for 3D printing by extrusion of filaments and molten pellets. The invention provides starting materials for polymer-based additive manufacturing whose 3D printing by filament or molten pellets is carried out without the need to heat the 3D printing platform. With the proposed procedure, a thermoplastic polymeric filament or pellet is obtained with direct application in additive manufacturing processes by modeling by deposition of molten material. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

ABS-based thermoplastic material for 3D printing by extrusion of filaments and molten pellets

Technical sector

The invention falls within the materials production sector. In the context of additive manufacturing, the present invention will seek materials with different properties that improve those of those that are conventionally used, which will be applicable in industrial manufacturing linked to the naval, aeronautical and consumer goods sectors, among other sectors. .

Background of the invention

Additive manufacturing comprises a series of industrial manufacturing techniques where the fundamental principle is to elaborate, from a model generated by computer-aided design (3D-CAD), a complete three-dimensional part or element in a single process. The basis on which additive manufacturing is based is the layer-by-layer growth of the material: each layer constitutes a cross section of the part being manufactured, as thin as possible (Gibson, l .; Rosen, DW; Stucker, B. Additive manufacturing technologies: rapid prototyping to direct digital manufacturing; Springer, 2010). This invention is framed by the need to find new resistant, reliable, durable and inexpensive materials for use in additive manufacturing processes.

Among the main techniques of additive manufacturing (also commonly called 3D printing), it is worth highlighting the modeling by fused deposition (MDF or FDM of English Fused Deposition Modeling). In this technique, a typically polymeric filament is passed through a head at a temperature above its melting point (or glass transition temperature for amorphous polymers). This process causes the polymer to flow with a certain viscosity and allow it to be extruded through a nozzle of known diameter. Another variant of the same technique consists in using polymeric pellets as the starting material, instead of using the polymeric material in the form of a filament. In both cases, once the material has been deposited, it cools and solidifies, forming a layer of uniform thickness. This process of fusion and extrusion of the filament or pellets is repeated sequentially layer by layer, until the part or part of the designed part is completed (Gibson, I .; Rosen, DW; Stucker, B. Additive manufacturing technologies: rapid prototyping to direct digital manufacturing ; Springer, 2010).

One of the limitations of FDM is that currently not all materials can be printed using this technique. The vast majority of commercial materials that can be used today are of the thermoplastic polymer type, or failing that, they constitute the matrix of the material (Ligon, SC; Liska, R .; Stampfl, J .; Gurr, M .; Mülhaupt, R. Polymers for 3D Printing and Customized Additive Manufacturing. Chemical Reviews. 2017). These materials have in common a characteristic creep index, typically in the range of 180-260 ° C, which allows the material to pass through a die and solidify once it has been deposited. In addition, for a correct impression, the temperature of the platform on which the material is built must be at a certain temperature above ambient temperature. The filaments used are previously obtained by an extrusion process in which certain starting materials are used, usually in granular or pellet form. Except for polyacid lactic (PLA) filaments, all other thermoplastic materials used in FDM with good mechanical properties (for example, a tensile strength above 25 MPa) require heating the printing platform to temperatures of at least 90-100 ° C, so that good adhesion of the first layer is achieved and warping problems are avoided (Nazan MA; Ramli FR; Alkahari MR; Abdullah MA; Sudin MN An exploration of polymer adhesion on 3D printer bed; IOP Conference Series: Materials Science and Engineering, 2017).

In this context, the present invention consists in the elaboration of a processed material in the form of pellets or filaments suitable for use in FDM by mixing two different polymers by extrusion. The new product has the advantage that it can be printed in FDM without the need to increase the temperature of the platform above room temperature. In this way, it is possible to speed up the printing process while eliminating energy costs.

Explanation of the invention

Unlike classical manufacturing processes, additive manufacturing is done by adding material layer by layer to obtain parts for industrial and consumer use. Additively manufactured parts are manufactured automatically and in a single process faster and with less material waste than in conventional subtractive manufacturing processes. The industrial-scale implementation of these new production processes benefits from reduced energy costs, so that additive manufacturing processes are more profitable than conventional ones. The invention described here aims to solve the problem of the need to raise the temperature of the 3D printing platform above the ambient temperature. This is something that is currently done with very few materials, for example, with polylactic acid (PLA), but it is not usual for other polymers, for example, those produced by polymerization of acrylonitrile, butadiene and styrene (ABS), widely used .

In this sense, a new material is proposed by melt mixing of two thermoplastic materials inside an extruder. In particular, it has worked with polyurethane-based thermoplastic elastomeric polymers (TPU). TPU polymers do not require heating of the build platform for proper first layer adhesion. However, their mechanical properties are poor, compared to other polymeric materials used in engineering such as ABS and require a much lower printing speed, due to their melt viscoelastic behavior. Due to this, it is proposed to develop a mixture with a controlled composition so that a positive synergy is generated and good characteristic properties of these materials can be obtained.

Ultimately, the objective of the invention is to provide a solution to the problem of energy cost and downtime that involves raising the temperature of the printing platform (approximately 90 ° C when it is required to print ABS base materials in additive manufacturing), providing a new material that allows greater technical simplification than others applied, while the improvement of properties of materials of conventional use in additive manufacturing has been pursued.

For this, a procedure has been devised to manufacture parts with a majority content of ABS, so that it provides good mechanical properties. The process has two stages: First, the two polymers are mixed in the form of pellets inside an extruder (single screw or twin screw), in a known proportion from which a polymeric filament with a constant diameter or pellets resulting from the mixture of the two starting polymers. This filament or pellets is subsequently introduced into an FDM printer, where the only requirement is that the printer head reaches the temperature of the material, not being necessary, as it normally is, to raise the temperature of the printing platform above the ambient temperature.

The applicability of the new material is evident when printing a desired object previously loaded in the printer in .gcode format keeping the platform at room temperature. If different elements are printed, including tensile or impact specimens in accordance with ISO 527 standards that can be subsequently tested to evaluate the mechanical properties of the new material. As observed by different microscopic and spectroscopic techniques (atomic force microscopy and Raman spectroscopy), it is observed that the printed objects have a spatial distribution of the two polymers on a submicron scale, that is, no macro or microseparation of phases is appreciated. This is clearly indicative of a good mix and affinity between the two components of the polymer mix, caused by supramolecular interactions due to a similar nature of the materials. These results can be extrapolated to other polymer blends based on polyethylene (PE), polypropylene (PP), polymethylmethacrylate (PMMA), polymethyl acrylate (PMA), polystyrene (PS), polyethylene terephthalate (PET), polyamide (PA), polycarbonate (PC), polyetheretherketone (PEEK), polysulfone (PSU), polyimide (Pl) or other thermoplastic polymers according to the set of standards iSo / TC 61 / SC 9 in general instead of ABS or combined with ABS; In addition, these blends can include copolymers or derivatives such as ASA (Acrylonitrile-sterner-acrylate), which are derivatives of PS and PMA. Likewise, thermoplastic elastomers based on polyester-ether (TPE), styrene-butadiene (TPS), polyamide (TPA), with vulcanized rubber mixture (TPV) or any thermoplastic elastomer according to ISO 18064: 2014 can be used instead made of TPU or combined with TPU, as well as materials that include nano-additives of any characteristic. The mixing process can also be carried out in a twin screw extruder instead of a single screw extruder.

The new material proposed in this patent may be carried out through the following steps developed here:

1. Take the polymeric starting material previously dried according to the manufacturer in the form of pellets. The process can be carried out on scales ranging from tens of grams to kilograms or higher industrial productions. This mixture is introduced into the feed of an extruder (single or double screw) previously cleaned and purged. The extruder is an equipment that consists of one or two endless screws (single screw or double screw, respectively) that rotate at a constant speed. Inside, one or more zones are controlled at a certain temperature, equal to or higher than the melting temperature of the material to be extruded, so that it flows inside. In the case of blends, the ratio in the feed should be adjusted to the desired final percentage by weight of polymer.

2. The extrusion of this polymer or polymer mixture is carried out at a temperature higher than its melting temperature. The combination of these parameters causes the flow of the material inside it at a shear rate that generates a perfect mixture of the components introduced into the feed.

3. The output material of the single screw extruder will be a filament with a homogeneous composition and a nominal diameter of 1.75 mm, suitable for use in conventional 3D printers of the FDM type.

4. The filament obtained and properly wound will be placed in the feeding area of a 3D printer that works by means of polymeric extrusion for its correct 3D printing. In case the 3D printer works with pellets instead of filament, the material obtained in the extruder must be correctly pelletized. In either case, the temperature of the print head will rise above its melting point (Tm) for crystalline polymeric materials or 100 ° C above its glass transition temperature (Tg) in the case of amorphous polymers. This temperature will coincide with that of the extruder.

5. The temperature of the platform may rise at any temperature. However, this is not necessary, as the introduced material is capable of satisfactorily adhering to the printing platform without any need to increase the temperature above room temperature.

6. A 3D printing digital file (.gcode format) is chosen, loaded into the printer and manufactured.

7. It is verified by visual inspection that the impression has been satisfactory. For a more rigorous study, an optical profilometer or digital microscope can be used.

Preferred embodiment of the invention

An example of elaboration is as follows: 70g of ABS (previously dried in an oven at least 4h at 60 ° C) together with 30g of TPU in the form of pellets are introduced into the feed of a previously cleaned single screw extruder whose temperature has been previously raised to 230 ° C. The mixture is extruded at 45 rpm and a filament with a controlled diameter of 1.75 mm is obtained. The first 40 cm of filament obtained are discarded to avoid impurities in the material. One of the ends of this filament is introduced into the head of an FDM type printer whose temperature has previously been raised to 230 ° C for correct printing. The platform temperature remains the same as room temperature. A default print speed of 30mm / s and a layer height of 0.2mm are set. The first 5 centimeters of material are purged and then a model previously loaded in digital format is printed (.gcode type file). It is observed that the printed part meets the required quality standards, similar to those of a pure ABS type part.

Industrial application

The invention describes a new material that can be processed into pellets or filaments for use in additive manufacturing processes. This material comes from polymeric materials available in large quantities, so its industrial application is expected to be direct, in both small and large format melt deposition modeling equipment.

The problem with most of the materials that can be used in FDM is that the first layer exhibits poor adhesion to the printing platform unless the temperature of said platform is raised above a threshold temperature, typically 90 °. C for ABS-based polymers. Once a good adhesion of the first layer has been demonstrated on the platform of an FDM printer, it is shown that the mechanical properties of this new material are satisfactory for a large number of industrial applications. The materials developed according to the present invention will be linked to additive manufacturing techniques and their implementation on an industrial scale, as indicated in the state of the art.

With a view to said implementation of the additive manufacturing process by FDM, also the procedure for the elaboration of filaments or pellets should be scaled up to the object of to achieve a production of starting materials according to the needs of a possible company developed from the technologies described in the present invention.

Claims (8)

1. Material for additive manufacturing by extrusion of filaments or molten pellets without heating the printing platform that consists of a mixture composed of a thermoplastic elastomer and a thermoplastic polymer. 2. Material for additive manufacturing by extrusion of filaments or molten pellets without the need for heating the printing platform, according to claim 1, characterized in that the thermoplastic polymer is based on PE, PP, PMMA, PMA, PS, PET, PA , PC, PEEK, PSU, Pl, or a copolymer derived from these such as ASA or ABS, or a mixture thereof. 3. Material for additive manufacturing by extrusion of filaments or melted pellets without the need for heating the printing platform, according to claim 1, characterized in that the thermoplastic elastomer is selected from the set formed by TPE, TPS, TPA, TPV, TPU or combination thereof. 4. Material for additive manufacturing by extrusion of filaments or molten pellets without the need for heating the printing platform, according to claims 2 and 3, characterized in that the content of the thermoplastic elastomer is at least 21% by weight. 5. Material for additive manufacturing by extrusion of filaments or molten pellets without the need for heating the printing platform, according to claims 2 and 3, characterized in that the content of the thermoplastic elastomer is at least 30% by weight. 6. Material for additive manufacturing by extrusion of filaments or molten pellets without the need for heating the printing platform, according to claim 4, composed of 70% ABS and 30% TPU by weight. 7. Procedure for obtaining a material for additive manufacturing by extrusion of filaments or molten pellets without the need for heating the printing platform, which consists of placing the starting components of the material, according to claims 1 to 6, in a previously heated extruder at a temperature above 180 ° C to obtain a filament with controlled diameter. 8. Use of the material for additive manufacturing without the need for heating the printing platform, according to claims 1 to 6, which consists of introducing the filament obtained according to the procedure described in claim 6 in the head of an FDM type printer whose printing temperature it is higher than the melting temperature Tm for (semi) crystalline polymers or Tg 100 ° C for amorphous polymers.