ES2551283B2 - Procedure for preparing starting materials for additive manufacturing - Google Patents

Abstract

Process for preparing starting materials for additive manufacturing of polymer base with the addition of nanostructured components, consisting of two sequential processes: surface mechanical coating of the biodegradable polymer matrix with nanoadditives by ball grinding, followed by extrusion melt mixing. # With this procedure, a nanocomposite filament of direct application is obtained as a starting material in additive manufacturing processes by means of melt deposition modeling.

Description

PROCEDURE FOR THE PREPARATION OF STARTING MATERIALS FOR ADDITIVE MANUFACTURING.

SECTOR OF THE TECHNIQUE

The described invention comprises both a process of manufacturing materials and some products developed by it. The process includes the surface coating by means of additive trimmings, with at least one of its dimensions in the nanometric order, of a polymer-based material and its subsequent melt mixing and extrusion. The application of this manufacturing process provides as a result a filament of material, useful for application in additive manufacturing machines as starting material

The invention can be framed within the field of materials research, more specifically in the area of nanomaterials, since the additives used are nanoadditive in accordance with what is expressed above. In the context of current research in materials for additive manufacturing, the present invention will procure materials with different properties that improve those of those that are conventionally used. What will be applicable in industrial manufacturing linked to the aeronautical and consumer goods sector, among other sectors.

STATE OF THE TECHNIQUE

The invention described herein consists of a process of manufacturing materials for additive manufacturing. The development of manufacturing techniques runs parallel to the need to find materials that are increasingly resistant, reliable and durable, while being economical, recyclable and environmentally friendly. In this sense, the manufacturing or additive synthesis 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 three-dimensional piece or complete element in a only 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 piece that is manufactured, of a thickness as much as

5 possible fine (Gibson, l .; Rosen, D. W .; Stucker, B. Additive manufacturing technologies: rapid prototyping to direct digital manufacturing; Springer, 2010).

By virtue of the above, and with the intention of finding materials with improved properties for additive manufacturing, the multiple possibilities of the nanotechnology field must be considered: in fact, the 10 macroscopic properties of materials are very variable on the nanometric scale and this makes it particularly interesting when it comes to improving the properties of conventional materials by creating new composite materials: the so-called nanocomposites or nanocomposites (Haghi, AK; Zaikov, GE Update on Nanofillers in Nanooomposites: From Introduction to 15 Application; Smithers Rapra, 2013 ). In particular, polymer-based nanooomposites are materials based on a polymer matrix that contains structures of different nature, with the particularity that these structures have at least one of their dimensions in the nanometric order (Raquez, J.-M. ~ al. Prog. Polym. Sci. 2013, 38, 1504), (Hussain, F., al. J. Compos. Maler. 20 2006, 40, 1511). The purpose of the inclusion of these structures is the improvement and optimization of the properties of the matrix, thus, the addition of nanoparticulate substances to polymeric matrices has the advantage of penetrating the manipulation of the properties of the manufactured objects, through knowledge and control of manufacturing processes and characterization of

25 materials, in a process of continuous feedback.

Among the main techniques of additive manufacturing, the most significant is the selective laser sintering, melt deposition modeling and stereolithography. It should be noted that the teninino "3D printing" has also become very popular when referring to additive manufacturing techniques . Selective laser sintering (SLS) is an additive manufacturing technique based on the production of parts or pieces from material in powdery material (Zheng, H., et al. Mater. Lett . 2006, 60, 1219), (Liu, FR, al. International Journal of Marine Tools and Manufacture 2013, 65, 22). The SLS process is based on the layer-to-layer merger of a 5-part pnlvo that is distributed homogeneously over the work area. The powder is fed to a chamber where a laser beam is focused on the corresponding bed, so that the material melts according to a pattern according to which a cross section of the piece is obtained. The dust surrounding this section is removed and reused in subsequent layers until the manufacture of

10 the same (Gibson, l .; Rosen, D. W .; Stucker, B. Additive manufacturing technologies: rapid prototyping to direct digital manufacturing; Springer, 2010).

Fused deposition modeling (Fused Deposition Modeling, FDM) is another technique in which a polymeric filament is passed through a micro-extruder to deposit it layer by layer, with solidification of 15 each, until completing the piece or part of designed piece (Gibson, l .; Rosen, D.

W.j Stucker, B. Additive manufacturing technologies: rapid prototyping to direct digital manufacturing; Springer, 2010). The filaments used are obtained by means of an extrusion process in which certain starting materials are used, usually in granulated form or pellet.

20 Stereolithography is a technique whereby a three-dimensional piece is generated by layer-to-layer deposition, in this case of a resin, in a photopolymerization process: a UV laser beam moves according to a computer-controlled pattern to perform the above deposition (Sánchez-Salcedo, S. et al. Chem. Eng. J. Amsterdam, Nelh. 2008, 137, 62).

25 Materials for additive manufacturing can be classified according to the methodology used for their preparation. Thus, among the various techniques described in the bibliography, it is worth highlighting the following, grouped by their physical or chemical character:

Chemical route

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Solution of precursors: The nanoadditives, functionalized or not as appropriate to favor dispersion (Raquez, J.-M., et al. Prog. Polym. Sci. 2013, 38, 1504), are introduced into solution together with the polymer ~ previously 5 solubilized, and the catalysts required in each case (Shameli, K., et al. Int. J.

Nanomed 2010, 5, 573), (Fortunali, E., al. J. Food Eng. 2013, 118, 117), (Pillai, SK, al. J. Appl. Polym. Sci. 2013, 129, 362) .

-

Emulsion polymerization: Starting from the polymer initiating monomer, the dispersion of nanoadditives is carried out in the solution containing said monomer and the catalysts required in each case to achieve in-situ polymerization (Ding, X., al. Maler Let! 2004, 58, 3126), (Ye, D., al.

J. Appl. Polym ScL 2012, 125, IE17), (Li, Q.-h., al. Trans. Nonferrous Me !. Soco China 2013, 23, 1421).

Physical way

15 -Extnlsión: A hot mixture of the precursors (nanoadditive and polymer matrix) is carried out in a device designed to homogenize and compress the mixture through a nozzle, so that a thread of the nanocomposite material is obtained. Said thread is usable in machines for additive manufacturing

(Jonoobi, M., e! Al. Compos. Sci. Technol. 2010, 70, 1742), (ViIlmow, T., al. 20 Polymer 2008, 49, 3500), (Eyholzer, c., Al. J. Polym. Environ. 2012, 20,1052).

-

Melt mixing: The nanoadditives are added to the hot polymer, at a temperature higher than the melting temperature (Iwatake, A., et al. Composites

Science and Technology 2008, 68, 2103), (Goodridge, R. D., al. Polym. Test.

2011, 30, 94). The procedure is similar to the previous one, although the material is not processed in a thread but rather as granulated material or pellet, which subsequently processed acquires utility in different additive manufacturing processes.

-

Others: Several sources of elaboration of nanocomposites are contemplated physically, not normally linked to extrusion, as a previous stage. Grinding

(Qian, Z., e! Al. Polym. Eng. Sci. 2012, 52, 1195) (Saleern, 1. Y .; Smyth, H. D. C.

AAPS PhannSciTech 2010, 11, 1642), (Takamatsu, H., et al. J. Ceram. Soco Jpn. 2006, 114, 332), mechanical mixing (Eyholzer, e., Et al. J. Polym. Environ. 2012 , 20, 1052), supercritical extraction (obtaining encapsulates and co-precipitates by solvent extraction by supercritical e02) (Montes, A., et al. The

5 Joumal of Supercritical Fluids 2012, 63, 92); they are other of the possibilities that the bibliography contemplates for the elaboration of nanocomposites.

Research in materials for additive manufacturing has had industrial concretion in the development of various patents referring to manufacturing processes themselves and for the preparation of the precursor materials involved. Specifically, for the preparation of polymeric nanocomposites containing graphene by solution of precursors (Gauthy, F., et al. Solvay SA, WIPO Patent, 2013, N "W02013127712 (Al)), elastomers additive with nano-clays by mechanical mixing (Ebrahimian, S ., et al. AlphaGary eorporation. USPTO, 2004, N "US6797760 (BI», polyamides additive with

15 phyllosilicates by extrusion (Presenz, U., Sutter, A. M. EMS-ehemie AG. USPTO Patent, 2005, N "US7442333 (B2», among others contemplated in the literature.

The present invention consists in the elaboration of a nano-additive biodegradable polymer wire, by means of the prior extrusion technique 20 mechanical coating of the polymer in a ball mill. The novelty of the proposed invention is to make a surface coating of the polymer with the nanoadditive, instead of pursuing the perfect mechanical or chemical mixing, in a way prior to extrusion. The dispersion is achieved by homogenization that the rotary spindle of the corresponding machine is capable

25 to confer on the hot mix of the nanoadditive coated polymer. In this way a simple elaboration process is achieved, not previously described.

DESCRIPTION OF THE INVENTION

Additive manufacturing is done following a manufacturing concept where processes

Conventional for obtaining parts for industrial and consumer use ~

based on different machining techniques that lead to manufacturing in

S

staggered processes, are overcome by obtaining pieces of form

automatic and in a single process faster and with less material.

However, the industrial scale implementation of these new processes of

production requires a research effort aimed at minimizing costs of

material and equipment, so that additive manufacturing processes result

10

more profitable than conventional. With the above and what is deducted from

state of the art described in the previous section, that aforementioned effort

Researcher in starting materials for additive manufacturing is justified. To the

problem of providing new materials for additive manufacturing that improve

the conventional ones, mainly pure polymers, intend to solve the

lS

present invention

In this regard, a procedure has been proposed to prepare materials for

heading for additive manufacturing by physical route, consisting of the coating

surface of polymeric granules by nanoadditives that improve some of their

mechanical, thermal, electrical and optical properties. In particular, and without

twenty

prejudice of the applicability of the procedure explained below, it has been

worked with biodegradable polymers. Biodegradable polymers add up to

This environmental advantage comes from renewable sources, not linked

to the consumption of fossil fuels. However, its mechanical properties are

poor and, in this regard, the inclusion of nanoaddives of diverse nature has

2S

proved to be of interest when it comes to improving these properties, and even

introduce electrical conductivity in an initially insulating material such as

the polymers, among other improvements.

In short, the object of the invention is to provide a solution to the problem.

of the development of new materials for additive manufacturing, contributing

30

nanocomposite materials and a procedure that allows greater simplification

technique than others applied, while the improvement of properties of materials of conventional use in additive manufacturing has been pursued by the inclusion of nanoadditives, following the elaboration procedure described below by the present invention.

5 A procedure for preparing starting materials for additive manufacturing has been devised for the purpose of the invention, consisting of a sequential two-stage process that is described in detail. First of all, a mechanical coating is carried out based on introducing into a suitable grinding equipment, specifically a planetary ball mill, the starting polymer in

10 granules phonoa and the corresponding nanoadditive together with an adequate load of moving elements, which seek contact between the granulated polymer and the nanoadditive. Secondly, the material thus prepared is subjected to melt mixing with extrusion to obtain a filament of nanocomposite material. achieving homogenization of the nanoadditive by dispersion through the matrix

15 polymeric.

The planetary ball mill is a team consisting of a turntable on which the grinding vessel is fixed, however allowing the rotation movement (hence the planetary designation: the turning mechanism of the grinding plate-glass assembly is similar to celestial kinematics). The equipment transmits 20 to the grinding vessel, or glass itself, an angular speed of rotation for a long period of time. The mobile elements introduced into the grinding vessel, balls at the time, are subjected to a random movement caused by the centrifugal force itself that the glass, by turning, confers on the balls and their own collisions. In this way, the polymer introduced as

The particulate matter of millimeter granulometry (pellets) is subjected to multiple collisions against the balls and walls of the grinding vessel, the surface coating being produced through this mechanism, since the nanoadditive has been introduced as a charge to the vessel.

As described previously, it is essential to determine the variables of operation to develop a final product with the best possible properties.

The extnlsión is a conventional process in the production of materials for additive manufacturing, so that the novelty in the present invention consists in coating pellets of polymeric material with the nanoadditive, by means of the grinding process described, as a previous step to the said melt mixing with extrusion.

5 Specifically, the milling operation variables will be the load and type of balls, material load (polymer and nanoadditive) to the vessel, coating time and angular speed of rotation of the mill plate.

A Y-Zr oxide grinding vessel, a ceramic with high impact and abrasion resistance and balls thereof has been used. In general, when it is desired to minimize the particle size of the grinding filler particles, balls of the smallest possible size should be used. Since the reduction of the pellets is not desired (and in addition it is not possible given its eminently plastic mechanical behavior) but only the surface coating with the nanoadditive, it has been decided to use the largest available balls. Specifically, 15 a set of 25 balls of 20 mm 0 has been used. Once the ball load is known and fixed, it is necessary to determine the recommended material load to the vessel. If polymer is loaded in excess, the freedom of collisions will be minimized and with eHo the degree of coating; otherwise, the defect of load will suppose the defonnación of the pellets by increasing the number of collisions. Following recommendations

20 equipment techniques polymer and nanoadditive loads should be between 65-180 g. Finally, an angular speed of the plate of excessive grinding entails, by increasing the number of collisions, the defonnación of the pellets reason why it must arrive at a relation of commitment of maximum angular speed for less time of process.

In the context of the present invention, the described process has been used and demonstrated its usefulness for the elaboration of different materials for additive manufacturing. Among others, PLAlPHA type biodegradable plastic pellets (Polylactic acidIPolyhydroxyalkanoate) and PLA have been coated with nanoadditives such as graphite sheets of nanometric thickness.

30 GNP, (from English Graphite Nano-Platelets) and functionalized nanoparticles of Ag, Au and other precious metals, to favor the excitation of nanoscale surface plasmons. Indeed, the interaction of plasmons, or quantized oscillations of plasma density of free electrons of metals, with photons or quanta of light gives rise to optical changes in the

5 polymeric materials by emission in a certain range of the visible spectrum.

The application of the coating process for the described materials has provided satisfactory results, according to what was observed by scanning electron microscopy and focused ion beam microscopy: they are observed

10 cross sections of pellets where the surface coating is verified by the absence of nanoadditives in the polymer core.

As part of the claim claimed in the present invention, it is desired to emphasize the elaboration of nanoadditioned PLAlPHA with GNP. It has been prepared by the described manufacturing process, by mechanical coating followed by melt mixing with extrusion, to obtain a filament of nanocomposite material with a homogeneous dispersion of the nanoadditive in the polymer matrix. This material has been applied in additive manufacturing, specifically through molten deposition modeling. The determination of technical properties has confined the non-degradation of the polymer at the working temperature of the aforementioned additive manufacturing machine. This fact, together with the measurement and verification of the mechanical properties, which have improved both the elastic and the plastic regime the properties of conventional pure PLA, make the PLAlPHA-GNP based filament a promising material for manufacturing by additive synthesis . The above is extended, from analogous sources, to other nanocomposites involving the same or other polymers and other nanoadditives, such as those mentioned with surface plasmonic behavior at the nanoscale including metal nanoparticles (silver, gold or other metals whose surface plasmons make possible the absorption of light with the necessary energy when it affects said 30 metals with nanoscale dimensions). To these last filaments

Nano-additives with metallic nanoparticles with the indicated plasmonic behavior will be called "plasmonic filaments".

EMBODIMENT OF THE INVENTION

The preparation of material referred to in the present invention may be carried out following the sequence that follows.

l. The weights corresponding to the polymer and nanoadditive load together with the balls in the quantities indicated in the description of the invention will be introduced into the grinding vessel. The nanoadditive load should be adjusted to

10 percentage by weight of polymer desired.

2.

Next, the grinding vessel should be fixed to the plate of the corresponding planetary ball mill and, if it is secured, set the conditions of angular plate speed and grinding time.

3.

After the grinding time, the balls must be separated from the

15 coated polymer after the previous step and collect the second as material prepared for extrusion melt mixing.

4. The loading of pellets is introduced into the loading hopper of an extruder whose spindle will rotate at a certain speed forcing the polymer to pass through the body divided into heated sections thereof. The extruder machine

20 concludes in a small diameter nozzle through which the polymer will flow forming a thread.

5. The thread of the fourth step must be cooled for solidification in a water bath arranged at the exit of the extrusion equipment. Finally, the filament thus formed is collected and coiled conveniently, being prepared for its

25 arrangement in additive manufacturing machines for molten deposition modeling.

An example of elaboration is as follows: 130 g of PLA together with 0.1% plp of GNP, placed next to 25 balls of 20 mm 0 of Y-Zr oxide in a commercial grinding glass of a ball mill Retsch planetarium model PMI00. This load is stirred in the mill for 15 min at 350 rpm achieving the coating

5 superlicial of PLA pellets by GNP. This material is injected into an extruder with a spindle speed of 50 rpm and heated sections with temperatures ranging from 160-180 OC, to obtain a constant diameter filament of 1.75 mm.

10 INDUSTRIAL APPLICATION

The invention includes a process for the preparation of filaments of nanocomposite materials for additive manufacturing as well as some of the described and claimed formulations. The object of industrial application itself is the filament. which is the starting material for machines

15 molten deposition modeling. FDM

Once the improvement of the mechanical properties has been demonstrated, with respect to conventional polymeric materials for additive manufacturing, by the materials developed from the process object of the present invention, the interest of this material will be linked to the development of the techniques

20 of additive manufacturing and its implementation on an industrial scale, as indicated in the prior art.

With a view to the implementation of the additive manufacturing process by FDM, the procedure for the manufacture of filaments must also be scaled in order to achieve a production of starting materials according to the

25 needs of an eventual company developed from the technologies described in the present invention.

Claims (8)

l. Process for preparing starting materials for additive manufacturing comprising the sequential realization of the following steps: a) Surface coating of polymer granules with nanoadditives, 5 through a mechanical procedure. b) Mixed in melt with subsequent extrusion. 2. Process for preparing starting materials for additive manufacturing, according to claim 1, characterized in that the coating The surface of the polymer granules with nanoadditives is carried out by introducing both components in a grinding equipment. 3. Process for preparing starting materials for additive manufacturing, according to claim 2, characterized in that the coating The surface of the polymer granules with nanoadditives is carried out by introducing both components into a planetary ball mill. 4. Process for preparing starting materials for additive manufacturing, according to claim 3, characterized in that the coating The surface of the polymer granules with nanoadditives is carried out on polymer masses between 65-180 g, in a Y-Zr oxide grinding vessel with 25 balls of the same material of 20 mm 0. 5. Procedure for preparing starting materials for manufacturing Additive according to claims 1 to 4, wherein the polymer granules are biodegradable polymers. 6. Procedure for manufacturing starting materials for manufacturing additive according to claim 5, wherein the polymer granules are of the type PLAIP HA or pure PLA. 7. Process for preparing starting materials for additive manufacturing, according to claims 1 to 4, wherein the nanoadditives used are graphite sheets of nanometric thickness (GNP).

5. Process for the preparation of starting materials for additive manufacturing, according to claims 1 to 4, wherein the nanoadditives used are functional nanoparticles of metals with nanoscale surface plasmonic behavior.

9. Process for the preparation of starting materials for additive manufacturing, according to claim 8, wherein the nanoadditives used are functional silver nanoparticles hoisted with surface plasmonic behavior at nanoscale.

10. Method for preparing starting materials for additive manufacturing, according to claim 8, wherein the nanoadditives used are functional gold nanoparticles hoisted with surface plasmonic behavior at nanoscale. 20 11. Nano-additive polymeric filaments made according to claims 8 to 10, which due to their surface plasmonic behavior at nanoscale are called "plasmonic filaments". 12. Use of the filaments, according to claim 11, in additive manufacturing by means of melt deposition modeling machines.