POLYPROPYLENE FOR EXTRUSION ADDITIVE MANUFACTURING

Abstract

An extrusion-based additive manufacturing process for producing a 3D printed article, the process involving the steps of: (i) providing a build material in pellet form, containing a propylene polymer composition with specific weight percentages of heterophasic propylene copolymer, propylene homopolymer or copolymer, elastomeric block copolymer, elastomeric ethylene copolymer, glass material as filler, and a compatibilizer, the propylene polymer composition having MFR of at least 1.0 g/10 min; (ii) providing an additive-manufacturing system; (iii) at least partially fusing the build material within the system to create a fused build material; and (iv) extruding the fused build material to form the final 3D printed article.

Description

FIELD OF THE INVENTION

In general, the present disclosure relates to the field of chemistry. More specifically, the present disclosure relates to polymer chemistry. In particular, the present disclosure relates to an extrusion additive manufacturing process.

BACKGROUND OF THE INVENTION

Three-dimensional (3D) printing involves movement of an extrusion head with respect to a substrate under computer control, in accordance with build data that represent the 3D article. The build data are obtained by initially slicing the digital representation of the 3D article into multiple horizontally layers. For each layer, a host computer generates a build path to deposit strands of fused material, which form the 3D printed article as they cool.

The build material is molten and extruded through an extrusion die carried by an extrusion head. The build material is deposited as a sequence of layers, also called “roads” on a substrate in an x-y plane. The distance of the extrusion head relative to the substrate is incremented along the z-axis (perpendicular to the x-y plane). The process is repeated to form a 3D article resembling the digital representation. Alternatively, the substrate moves while the extrusion die is stationary. In some instances, a filament-free extrusion-based 3D printing process is commercially available from ARBURG GmbH & Co.KG.

In some instances, Fused Deposition Modeling (FDM) extrusion additive manufacturing process (or Fused Filament Fabrication (FFF)) is used with a 3D printer to feed the build material to the extrusion section in form of a filament.

In some instances, the build material is fed to the 3D printer in the form of a pellet or more than one pellets.

In some instances, filaments of polylactic acid (PLA) or acrylonitrile, butadiene, styrene (ABS) polymer or polyamides are used.

In some instances, polyolefins, like polypropylene, are processable with extrusion-based 3D printers.

In some instances, it is believed that warping results from material shrinkage while the 3D printed build material solidifies from the fused state, thereby causing the deformation of the printed object, like corners lift up and detach from the build plate. When plastics are printed, the plastics first expand and then contract as the plastics cool down. If material contracts too much, the print bends up from the build plate and yields deformed 3D printed objects.

SUMMARY OF THE INVENTION

In a general embodiment, the present disclosure provides extrusion-based additive manufacturing process to produce a 3D printed article comprising the steps of:

• • (i) providing a build material in the form of pellet comprising a propylene polymer composition comprising:
    • A) from 20 to 60 wt. % of a heterophasic propylene copolymer;
    • B) from 5 to 33 wt. % of a propylene homopolymer or copolymer, wherein the copolymer contains up to 5 wt. % of an alpha-olefin selected from the group consisting of ethylene, 1-butene, 1-hexene and 1-octene;
    • C) from 2 to 15 wt. % of an elastomeric block copolymer made from or containing styrene;
    • D) from 4 to 32 wt. % of an elastomeric ethylene copolymer;
    • E) from 5 to 50 wt. % of a glass material as filler; and
    • F) from 0.1 to 5 wt. % of a compatibilizer,
    • wherein the amounts of components A), B), C), D), E) and F) are referred to the total weight of A), B), C), D), E) and F) and wherein the melt flow rate MFR (ISO 1133-2:2011, 2.16 kg/230° C.) of the propylene polymer composition is at least 1.0 g/10 min.;
  • (ii) providing an additive-manufacturing system;
  • (iii) at least partially fusing the build material in the additive-manufacturing system to form a fused build material; and
  • (iv) extruding the at least partially fused build material to form the 3D printed article.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the top view of a specimen used for warpage test, including the naming of the corners and the length of the diagonal relevant for the measurement carried out.

FIG. 2 is the side view of the warpage measurement setup, including the naming of the corners and the warpage height relevant for the measurement carried out.

FIG. 3 is a chart depicting the surface quality (roughness) of polypropylene composition (I), determined from the side wall of a 3D printed cube.

FIG. 4 is a chart depicting the surface quality (roughness) of comparison material 1, determined from the side wall of a 3D printed cube.

FIG. 5 is a chart depicting the surface quality (roughness) of comparison material 2, determined from the side wall of a 3D printed cube.

DETAILED DESCRIPTION OF THE INVENTION

In some embodiments, the present disclosure provides an extrusion-based additive manufacturing process wherein the build material provided in step (i) comprises a propylene polymer composition comprising:

• • A) from 20 wt. % to 60 wt. %; alternatively, from 25 wt. % to 52 wt. %; alternatively from 31 wt. % to 46 wt. %, of a heterophasic propylene copolymer;
  • B) from 5 wt. % to 33 wt. %; alternatively from 8 wt. % to 23 wt. %; alternatively from 9 wt. % to 18 wt. %, of a propylene homopolymer or copolymer, wherein the copolymer contains up to 5 wt. % of an alpha-olefin selected from the group consisting of ethylene, 1-butene, 1-hexene and 1-octene;
  • C) from 2 wt. % to 15 wt. %; alternatively from 3 wt. % to 10 wt. %, of an elastomeric block copolymer made from or containing styrene;
  • D) from 4 wt. % to 32 wt. %; alternatively from 6 wt. % to 23 wt. %; alternatively from 8 wt. % to 18 wt. %, of an elastomeric ethylene copolymer;
  • E) from 5wt. % to 50 wt. %; alternatively from 10 wt. % to 35 wt. %; alternatively from 15 wt. % to 29 wt. %; alternatively from 18 wt. % to 28 wt. %, of a glass material as filler; and
  • F) from 0.1 wt. % to 5 wt. %; alternatively from 0.3 wt. % to 3 wt. %; alternatively from 0.5 wt. % to 2 wt. %, of a compatibilizer;
  • wherein the amounts of components A), B), C), D), E) and F) are referred to the total weight of A), B), C), D), E) and F) and wherein the melt flow rate MFR (ISO 1133-2:2011, 2.16 kg/230° C.) of the propylene polymer composition is at least 1.0 g/10 min.; alternatively from 3 g/10 min to 100 g/10 min.

Heterophasic Propylene Copolymer Component A

As used herein, the term “heterophasic propylene copolymer” refers to a copolymer wherein a rubber phase is (finely) dispersed in the matrix, that is, in a propylene homopolymer or copolymer. In some embodiments, the rubber phase forms inclusions in the matrix. In some embodiments, the matrix contains (finely) dispersed inclusions being not part of the matrix, wherein the inclusions contain the rubber phase. As used herein, the term “inclusion” refers to the matrix and the inclusion forming different phases within the heterophasic system. In some embodiments, the inclusions are visible by high-resolution microscopy. In some embodiments, the high-resolution microscopy is selected from the group consisting of electron microscopy and scanning force microscopy.

In some embodiments, the matrix of the heterophasic propylene ethylene content is a propylene homopolymer or a propylene/ethylene copolymer having an ethylene content up to 10 wt. %; alternatively up to 5 wt. %; and having a fraction soluble in xylene at 25° C. lower than 10 wt. %; alternatively lower than 5 wt. %; alternatively lower than 3 wt. %. In some embodiments, Component A) has a MFR (ASTM D 1238-13 230° C./2.16 kg, equivalent to ISO 1133) of 0.1-100 g/10 min, alternatively 1-60 g/10 min, alternatively 1.5-60 g/10 min. In some embodiments, the matrix is a propylene homopolymer.

In some embodiment, the rubber phase is: (i) a propylene/ethylene copolymer having an ethylene content ranging from 15 wt. % to 75 wt. %; alternatively from 20 wt. % to 65 wt. %. In some embodiment, the rubber phase is: (ii) an ethylene-C₄-C₈ alpha-olefin copolymer having an ethylene content ranging from 35 wt. % to 70 wt. %; alternatively from 43 wt. % to 65 wt. %. In some embodiments, the alpha-olefin is selected from the group consisting of 1-butene, 1-hexene and 1-octene. In some embodiments, the alpha-olefin is 1-butene. In some embodiments, the rubber phase is (iii) a mixture of the propylene/ethylene copolymer (i) and the ethylene/C₄-C₈ alpha-olefin copolymer (ii). In some embodiments, the rubber phase is a mixture of propylene/ethylene copolymer and ethylene/C₄-C₈ alpha-olefin copolymer.

In some embodiments, the matrix in the heterophasic propylene copolymer ranges from 30 wt. % to 70 wt. %; alternatively from 42 wt. % to 63 wt. %, referred to the total weight of the heterophasic copolymer and the remaining part, up to 100 wt. %, being the rubber phase. In some embodiments, the rubber phase is a mixture the rubber phase is a mixture comprising from 33 wt. % to 67 wt. % of a propylene/ethylene copolymer and 33 wt. % to 67 wt. % an ethylene/C₄-C₈ alpha-olefin copolymer, referred to the total weight of the rubber phase. In some embodiments, the matrix is a propylene homopolymer and the rubber phase is a mixture of propylene ethylene/copolymer and ethylene/C₄-C₈ alpha-olefin copolymer, preferably a mixture comprising from 33 wt. % to 67 wt. % of a propylene/ethylene copolymer and 33 wt. % to 67 wt. % an ethylene/C₄-C₈ alpha-olefin copolymer, referred to the total amount of the rubber phase.

Propylene Homopolymer or Copolymer Component B

In some embodiments, the propylene homopolymer or copolymer is a propylene homopolymer or propylene/ethylene copolymer having an ethylene content of up to 10 wt. %; alternatively up to 5 wt. %. In some embodiments, Component B) has a fraction soluble in xylene at 25° C. lower than 10 wt. %; alternatively lower than 5 wt. %; alternatively lower than 3 wt. %. In some embodiments, Component B) has a MFR (ASTM D 1238-13 230° C./2.16 Kg, equivalent to ISO 1133) of 10-3000 g/10 min., alternatively 100-2500 g/10 min., alternatively 500-2500 g/10 min. In some embodiments, component B) is a propylene homopolymer. In some embodiments, component B) is obtained by using metallocene-based catalysts.

In some embodiments, the component B) is a propylene homopolymer having a fraction soluble in xylene at 25° C. lower than 5 wt. %, alternatively lower than 3 wt. %.

Elastomeric Block Copolymer Made From or Containing Styrene C

In some embodiments, elastomeric block copolymer made from or containing styrene is selected from the group consisting styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-butadiene-styrene block copolymers (SBS), and styrene-isoprene-styrene block copolymers (SIS) containing from 5 wt. % to 30 wt. % of polystyrene and having a hardness (Shore A, ASTM D-2240-15) value equal to or lower than 70 points, alternatively equal to or lower than 55 points, alternatively equal to or lower than 50 points.

Elastomeric Ethylene Copolymer Component D

In some embodiments, the elastomeric ethylene copolymer has a hardness (Shore A, ASTM D-2240-15) value equal to or lower than 80 points, alternatively equal to or lower than 60 points, alternatively equal to or lower than 55 points. In some embodiments, the elastomeric ethylene copolymer has a MFR (ASTM D 1238-13 190° C./2.16 kg, equivalent to ISO 1133) of 0.5-20 g/10 min, alternatively 0.5-3 g/10 min, alternatively 0.9-1.5 g/10 min.

In some embodiments, the elastomeric ethylene copolymer is selected from copolymers of ethylene with a C₃-C₁₀ alpha-olefin containing at least 20 wt %, alternatively from 20 to 70 wt %, of C₃-C₁₀ alpha-olefin (¹³C-NMR analysis), based on the weight of the copolymer. In some embodiments, the elastomeric ethylene copolymer is obtained with metallocene or constrained geometry catalysis. In some embodiments, the elastomeric ethylene copolymer is commercially available. In some embodiments, the elastomeric ethylene copolymer has a molecular weight distribution (Mw/Mn measured via GPC) of from 1 to 3.

In some embodiments, the elastomeric ethylene copolymer Components (C) are:

• • (i) elastomeric copolymers of ethylene with 1-octene having from 20 wt % to 45 wt % of 1-octene (¹³C-NMR analysis), based on the total weight of the copolymer; or
  • (ii) elastomeric thermoplastic copolymers of ethylene with 1-butene having from 20 wt % to 40 wt % of 1-butene (¹³C-NMR analysis), based on the weight of the copolymer.

In some embodiments, the elastomeric copolymer of ethylene with 1-octene (i) has density of less than 0.89 g/ml (measured according to ASTM D-792). In some embodiments, the elastomeric thermoplastic copolymer of ethylene with 1-butene (ii) has density of less than 0.89 g/ml (measured according to ASTM D-792).

In some embodiments, the copolymer (ii) is an ethylene-butene-1 random copolymer rubber ENGAGE 7467 produced by The Dow Chemical Co. Ltd., having density of 0.862 g/cm³ according to method ASTM D 792-08, MFR of 1.2 g/10 min (ASTM D 1238-13 190° C./2.16 kg, equivalent to ISO 1133), hardness Shore A (ASTM D-2240-15) of 52.

Glass Material Component E

In some embodiments, the glass material filler component E) of the propylene polymer composition is made from, containing glass fibers, or chopped glass fibers, glass particles in the form of ground glass or milled glass fibers, or a mixture thereof. In some embodiments, the glass fibers' or chopped glass fibers' average length is from 10 μm to 20 mm. In some embodiments, the ground glass' or milled glass fibers' average particle size is in the range from 3 μm to 5 mm.

In some embodiments, the glass material filler component E) of the propylene polymer composition is made from or contains glass fibers or chopped glass fibers whose average length is from 10 μm to 400 μm, alternatively from 50 μm to 200 μm, glass particles in the form of ground glass or milled glass fibers whose average particle size is in the range from 3 μm to 100 μm, hollow glass bubbles whose average diameter is from 1 μm to 150 μm, or mixtures thereof.

Compatibilizer Component F

In some embodiments, the compatibilizer improves interfacial properties between glass material fillers and polymers. In some embodiments, the compatibilizer reduces the agglomeration tendency of filler particles, thereby improving their dispersion within the polymer matrix.

In some embodiments, the compatibilizer is selected from the group consisting of low molecular weight compounds having reactive polar groups for increasing the polarity of the polyolefin and which react with the functionalized coating or sizing of the fillers, thereby enhancing compatibility with the polymer. In some embodiments, the functionalized coatings of the fillers are silanes. In some embodiments, the silanes are selected from the group consisting of aminosilanes, epoxysilanes, amidosilanes and acrylosilanes. In some embodiments, the silane is an aminosilane.

In some embodiments, the compatibilizers are made from or containing a polymer modified (functionalized) with polar moieties and optionally a low molecular weight compound having reactive polar groups.

In some embodiments and in terms of structure, the modified polymers are graft or block copolymers. In some embodiments, the modified polymers contain groups deriving from polar compounds. In some embodiments, the polar compounds are selected from the group consisting of acid anhydrides, carboxylic acids, carboxylic acid derivatives, primary and secondary amines, hydroxyl compounds, oxazoline and epoxides, and ionic compounds.

In some embodiments, the polar compounds are selected from the group consisting of unsaturated cyclic anhydrides and their aliphatic diesters, and the diacid derivatives. In some embodiments, the polar compounds are selected from the group consisting of maleic anhydride, C₁-C₁₀ linear and branched dialkyl maleates, C₁-C₁₀ linear and branched dialkyl fumarates, itaconic anhydride, C₁-C₁₀ linear and branched itaconic acid dialkyl esters, maleic acid, fumaric acid, itaconic acid and mixtures thereof.

In some embodiments, the compatibilizer is a propylene polymer grafted with maleic anhydride.

Polymers A), B), C), D) and F) are different from each other.

In some embodiments, the propylene polymer composition further contains additives. In some embodiments, the additives are selected from the group consisting of antioxidants, slipping agents, process stabilizers, antiacid and nucleants.

In some embodiments, the propylene polymer composition further contains wood powder, metallic powder, marble powder and similar materials. In some embodiments, these components affect the aesthetic appearances or mechanics of the 3D printed object.

In some embodiments, step (iii) of the process of the present disclosure comprises at least partially fusing the build material at a temperature of from 120° C. to 300° C., alternatively 140° C. to 280° C., alternatively 160° C. to 240° C.

In some embodiments, in step (iv) the at least partially fused build material is extruded and deposited as a sequence of layers to obtain a 3D printed article. When using an extrusion-based 3D printer, extrusion is carried out through an extrusion die carried by an extrusion head.

In some embodiments, the control of the deposition rate varies by setting the throughput rate, the cross-sectional dimension of the die, and the rate of motion of the die head and/or of the article.

In some embodiments, the deposition is unidirectional or multidirectional or without orientation in case of the deposition of drops or beads.

In some embodiments, step (iv) comprises extruding the at least partially molten build material on a build plate. Articles printed with build material adhere for the timescale of the extrusion additive manufacturing process to a smooth or rough build plate, like a glass or metal surface. Adhesion to the build plate is optionally promoted using adhesive spray “Dimafix®” from Dima3D at a surface temperature higher than 70° C., alternatively higher than 90° C.

In some embodiments, the process comprises a further step (v) of removing the 3D printed article from the build plate, optionally but preferably at room temperature, like at 25° C.

The following examples are given to illustrate and not to limit the present disclosure.

EXAMPLES

The data of the propylene polymer materials were obtained according to the following methods:

Xylene-Soluble Fraction at 25° C.

The Xylene Soluble fraction was measured according to ISO 16152, 2005, but with the following deviations (the ISO 16152-specified conditions are within the parentheses).

The solution volume was 250 ml (200 ml).

During the precipitation stage at 25° C. for 30 min, the solution, for the final 10 minutes, was kept under agitation by a magnetic stirrer (30 min, without stirring).

The final drying step was done under vacuum at 70° C. (100° C.).

The content of the xylene-soluble fraction is expressed as a percentage of av original 2.5 grams sample and then, by difference (complementary to 100), the xylene insoluble %.

Ethylene (C2) Content

¹³C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cryoprobe, operating at 160.91 MHz in the Fourier transform mode at 120° C.

The peak of the SBB carbon (nomenclature according to “Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by ¹³C NMR. 3. Use of Reaction Probability Mode” C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) was used as internal reference at 29.9 ppm. The samples were dissolved in 1,1,2,2-tetrachloroethane-d2 at 120°° C. with an 8% wt/v concentration. Each spectrum was acquired with a 90° pulse, 15seconds of delay between pulses and CPD to remove ¹H-¹³C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

The assignments of the spectra, the evaluation of triad distribution and the composition were made according to Kakugo (“Carbon-13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with δ-titanium trichloride-diethylaluminum chloride” M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equations:

$\begin{array}{ccc}\mathrm{PPP}=100T_{\mathrm{\beta \beta }}/S& \mathrm{PPE}=100T_{\mathrm{\beta \delta }}/S& \mathrm{EPE}=100T_{\mathrm{\delta \delta }}/S\end{array}$ $\begin{array}{ccc}\mathrm{PEP}=100S_{\mathrm{\beta \beta }}/S& \mathrm{PEE}=100S_{\mathrm{\beta \delta }}/S& \mathrm{EEE}=100\left(0.25S_{\mathrm{\gamma \delta }}+0.5S_{\mathrm{\delta \delta }}\right)/S\end{array}$ $S=T_{\mathrm{\beta \beta }}+T_{\mathrm{\beta \delta }}+T_{\mathrm{\delta \delta }}+S_{\mathrm{\beta \beta }}+S_{\mathrm{\beta \delta }}+0.25S_{\mathrm{\gamma \delta }}+0.5S_{\mathrm{\delta \delta }}$

The molar percentage of ethylene content was evaluated using the following equation:

$E\%\mathrm{mol}=100*\left[\mathrm{PEP}+\mathrm{PEE}+\mathrm{EEE}\right]$

The weight percentage of ethylene content was evaluated using the following equation:

$E\%\mathrm{wt}.=\frac{100*E\%\mathrm{mol}*{\mathrm{MW}}_E}{E\%\mathrm{mol}*{\mathrm{MW}}_{E+}P\%\mathrm{mol}*{\mathrm{MW}}_P}$

where P % mol is the molar percentage of propylene content, while MWE and MWp are the molecular weights of ethylene and propylene, respectively.

The product of reactivity ratio r₁r₂ was calculated according to Carman (C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977; 10, 536) as:

$r_1{r}_2=1+\left(\frac{\mathrm{EEE}+\mathrm{PEE}}{\mathrm{PEP}}+1\right)-\left(\frac{P}{E}+1\right){\left(\frac{\mathrm{EEE}+\mathrm{PEE}}{\mathrm{PEP}}+1\right)}^{0.5}$

The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmT_ββ (28.90-29.65 ppm) and the whole T_ββ (29.80-28.37 ppm).

Melt Flow Rate (MFR)

The melt flow rate MFR of the polymer and the composition were determined according to ISO 1133-2:2011 (230° C., 2.16 kg).

Melt Temperature

The melting Temperatures were determined by differential scanning calorimetry (DSC). A sample, weighing (6±1) mg, was heated to (220±1)° C. at a rate of 10 K/min and kept at (220±1)° C. for 5 minutes in nitrogen stream. The sample was cooled at a rate of 10 K/min to (−30±1)° C. and then kept at this temperature for 10 min, thereby crystallizing the sample. Then, the sample was again fused at a temperature rise rate of 10 K/min up to (220±1)° C. The second melting scan was recorded. A thermogram was obtained. The temperatures corresponding to peaks were read. The differential scanning calorimeter used was DSC 6200 from Seiko. The data were evaluated with the software NETZSCH Proteus Thermal Analysis 6.1.0.

Mechanical Properties: Tensile Modulus, Tensile Strength, and Charpy Impact Strength

Tensile Modulus and tensile strength were measured with tensile specimens DIN EN ISO 527-2 5A according to the procedure DIN EN ISO 527:2012. The tensile test machine used was ZWICK Z005, load cell 2.5 kN, makroXtens extensiometer.

Charpy impact strength was measured with specimens DIN EN ISO 179-1/1eA according to the procedure DIN EN ISO 179-1. The impact test machine used was Zwick 5102.100/00 pendulum impact tester

The test specimens were injection molded or 3D printed.

Specimens for tensile tests according to DIN EN ISO 527-2 5A were prepared with 3D printing, namely:

• • i) unidirectional specimens, or
  • ii) multidirectional specimens.

Specimens for Charpy impact tests according to DIN EN ISO 179-1/1eA were prepared with 3D printing, namely:

• • i) unidirectional specimens, or
  • ii) multidirectional specimens.

For the unidirectional specimens i), the 3D printing was carried out with a filling pattern orientation at 0° or 90° relative to the stress (pulling/impact) direction, which corresponds with the length of the test specimens.

For the multidirectional specimens ii), each 3D printed layer was deposited with alternate filling pattern orientation at 0° and 90° as well as +45° and −45° relative to the stress direction.

The injection molded test specimens were cut from an injection molded plate of the polymer material, with the length of each test specimen oriented at 0° or 90° relative to the injection flow.

After determining the cross-sectional area, the tensile test specimens were clamped vertically and stretched to break.

The specific characteristics of the tensile tests were determined from the stress-strain diagrams obtained. The bone sized test specimens were subjected to testing at a pulling speed of up to 50 mm/min. The data were evaluated with the software TESTXPERT II V3.31. The results are listed as the mean of the tested specimen and the sample standard deviation.

After determining the cross-sectional area at the notch, the Charpy impact test specimens were fixed horizontally and impacted.

The specific characteristics of the impact test were determined from the dissipated energy. The results are listed as the mean of the tested specimen and the sample standard deviation.

Warpage

Warpage of printed objects was quantified by printing objects adapted from M. Spoerk et al. Macromol. Mater. Eng. 2017, 302, 1700143. as shown in FIG. 1 using a printing speed of 40 mm/s. The other printing conditions are reported in Table 3. The direction of the linear infill pattern was alternating +45° layer by layer, wherein +45° indicates that the infill strands were oriented in parallel to the diagonal between corner 1 and corner 3 (see FIGS. 1) and −45° indicates that the infill strands were oriented perpendicular to the infill strands of +45°. The first layer that adhered to the build plate had the infill orientation +45°.

After the print finished, the warpage specimens were removed from the build plate and tempered at (80±5)° C. in vacuum for (24÷1) hours.

After cooling the warpage specimen down, the warpage specimen was fixed to the ground at a horizontal distance of 2 mm from corner 1 with a 2 mm diameter rod as illustrated in FIG. 2.

The warpage height h, that is, the distance between the ground and the lower edge of corner 3 (FIG. 2) which was diagonal to the fixed corner 1, was measured for each warpage specimen.

Afterwards, corner 1 and corner 3 were fixed to the ground and the length of the diagonal d between the edges of corner 1 and corner 3 were measured.

The warpage (unit: %) was calculated using the following equation:

$\mathrm{Warpage}\left[\%\right]=\frac{\mathrm{warpage}\mathrm{heigth}h}{\mathrm{length}\mathrm{of}\mathrm{diagonal}d}·100\%$

Five specimens were printed and measured for each material composition. The results are listed as the mean of the tested specimen and the sample standard deviation.

Surface Quality

The surface quality was measured using a profilometer μSCAN SELECT from NANOFOCUS. The surface roughness was determined according to DIN EN ISO 4287:2010-07 quantified by the maximum height of the roughness profile R_z and the arithmetic mean deviation of the roughness profile R_a and according to DIN EN ISO 25178 quantified by the maximum height of the roughness profile S_z and the arithmetic mean deviation of the roughness profile S_a. The total measured surface area was 10×10 mm², using a sampling frequency of 300 Hz and a step width of 20 μm.

For each material, the surface of one side wall of a cube of edge length 50 mm was measured. The cube was printed using a printing speed of 40 mm/s. The other printing conditions are reported in Table 3.

The side wall was oriented perpendicular to the build plate.

Propylene Polymer Composition (1)

Propylene composition (1) was prepared by compounding the following materials: 37 wt. % of component A); 14 wt. % of component B); 5 wt. % of component C); 14 wt. % of component D); 26 wt. % of component E); 1 wt. % of component F); and 3 wt. % additives and pigments.

Component A) was HX CA 7201 heterophasic propylene copolymer, containing 52 wt. % of propylene homopolymer; 26 wt. % of ethylene 1-butene copolymer (55:45); and 22 wt. % of propylene ethylene copolymer (46:54), and having a MFR of 12 g/10 min (ASTM D 1238-13 230° C./2.16 Kg, equivalent to ISO 1133). HX CA 7201 heterophasic propylene copolymer was commercially available from LyondellBasell.

Component B) was MC MF650Y propylene homopolymer, having an MFR of 2000 g/10 min and a soluble xylene at 25° C. fraction lower than 5 wt. %. MC MF650Y propylene homopolymer was commercially available from LyondellBasell.

Component C) was KRATON G 1657 styrene-ethylene/butylene-styrene block copolymer, having a polystyrene content of 13 wt. % and a shore A (10 s) measured according to ASTM 2240 of 47. KRATON G 1657 styrene-ethylene/butylene-styrene block copolymer was commercially available from Kraton Polymers U.S. LLC (Houston, Texas).

Component D) was ENGAGE 7467, having density of 0.862 g/cm³ according to method ASTM D 792-08, MFR of 1.2 g/10 min (ASTM D 1238-13 190° C./2.16 kg, equivalent to ISO 1133), and hardness Shore A (ASTM D-2240-15) of 52. ENGAGE 7467 was commercially available from The Dow Chemical Co. Ltd.

Component E) was DS 2200-10P glass fibers, having a diameter of 10 μm. DS 2200-10P glass fibers were commercially available from Binani 3B The Fibreglass Company.

Component F) was Polybond 3200 maleic anhydride grafted polypropylene. Polybond 3200 maleic anhydride grafted polypropylene was commercially available from Crompton.

The compounding was carried out on a Leistritz twin-screw extruder with a screw diameter of 50 mm. The parameters used are summarized in Table 1 below.

TABLE 1
Parameters for compounding propylene polymer
composition (I) for further processing
Parameter              Value
TZone 1/° C.           180
TZone 2-9/° C.         200
TZone 10/° C.          210
Revolutions/Number/min 365
Feed Rate/kg/h         80

The resulting composition has a melt flow rate of 11 g/10 min (230° C./2.16 kg) and a melting point of 163° C.

Comparative Composition 1 (CM1)

Comparative composition 1 was MOPLEN 2000HEXP ethylene propylene copolymer, filled with 25% by weight with glass fibers having an average length lower than 200 μm. MOPLEN 2000HEXP ethylene propylene copolymer was commercially available from LyondellBasell. The resulting composition had a melt flow rate of 15 g/10 min (230° C./2.16 kg) and a melting point of 165° C.

Comparative Composition 2 (CM2)

Comparative composition 2 (CM2) was INNOFIL3D PPGF30 filament of diameter 2.85 mm. The filament was commercially available from BASF. Innofil3D polypropylene homopolymer was filled with 30% by weight of glass fibers, having a melt flow rate of 7 g/10 min. (230° C./2.16 kg) and a melting point of 166° C.

Filament Extrusion

The filament for 3D printing from the polypropylene composition (I) and the comparison material (CM 1) was produced from granules on a twin-screw extruder COLLIN TEACH-LINE™ ZK 25T with a round die (3.00 mm diameter;). The extruded polymer strand was withdrawn, water cooled and rolled up on printer coils. The parameters used are listed in Table 2 below.

TABLE 2
	propylene polymer composition (I):	CM1:
Parameter	Value	Value
TZone 1/° C.	190	180
TZone 2/° C.	190	180
TZone 3/° C.	180	170
TZone 4/° C.	175	160
Revolutions/Number/min	38	55
Feed Rate/kg/h	2.0	2.0
Output/mm/s	57	58

FFF (Fused Filament Fabrication) 3D Printing

All FFF printed parts were produced with an Ultimaker S5 FFF printer using 100% infill and a nozzle of 0.5 mm diameter leading to a line width of 0.48 mm. The layer thickness for the analysis of warpage and mechanical properties was 0.2 mm while, for surface quality analysis, the layer thickness was 0.1 mm. For surface quality analysis, a printing speed of 40 mm/s was used for the propylene polymer composition (I) and the comparison materials 1 and 2.

TABLE 3
	Polypropylene
Material	composition (I)	CM1	CM2
Build plate	glass + Dimafix	PP adhesive tape	PP adhesive tape
material		(“Scotch Extreme”)	(“Scotch Extreme”)
Nozzle	0.5	0.5	0.5
diameter [mm]
Line width	0.48	0.48	0.48
[mm]
Wall	1.44 (for surface	1.44 (for surface	1.44 (for surface
thickness	quality measurements)	quality measurements)	quality measurements)
[mm]	0.48 (for mechanical	0.48 (for mechanical	0.48 (for mechanical
	properties	properties	properties
	measurements)	measurements)	measurements)
Layer height	0.2 (0.1 for surface	0.2 (0.1 for surface	0.2 (0.1 for surface
[mm]	analysis)	analysis)	analysis)
Nozzle	220	240	240
temperature
1st layer [° C.]
Nozzle	220	240	240
temperature
other layers [° C.]
Build plate	100	100	30
temperature [° C.]
Infill [100]	100	100	100
Printer speed	40 (for surface quality	40 (for surface quality	40 (for surface quality
[mm/s]	measurements)	measurements)	measurements)
	25, 40, 100, or 150 (for	40 or 100 (for	40 or 100 (for
	mechanical properties	mechanical properties	mechanical properties
	measurements)	measurements)	measurements)
Infill pattern	lines	lines	lines
Printed build plate	no	no	no
adhesion
(Raft, Brim, etc.)

Injection Molding

Injection molding of plates for tensile specimen DIN EN ISO 527-2 5A was performed on an injection molding system DEMAG 160 at 220° C., injection speed of 11 mm/s, 90 bar, and 30 s of holding pressure. The mold temperature was 30° C. The tensile specimen DIN EN ISO 527-2 5A were milled from the plates in parallel) (0° or perpendicular) (90° relative to the injection flow.

Injection molding of plates for impact specimen DIN EN ISO 179-1/1eA was performed on an injection molding system KRAUSS MAFFEI 110 at 220° C., injection speed of 13 mm/s, 90 bar, and 15 s of holding pressure. The mold temperature was 40° C. The impact specimen DIN EN ISO 179-1/1eA were milled from the plates parallel) (0° or perpendicular) (90° relative to the injection flow.

Mechanical Characterization Test Results

The filament of propylene composition (I) used for producing sample was compared with injection-molded sample. The results of the tests are reported in Table 4.

TABLE 4
	Printing/
	injection
	orientation
	relative	Mechanical properties
		Printing	to stress	Tensile	Tensile	Impact
		speed	test	Modulus	strength	strength
Example	Process	[mm/s]	direction	[MPa]	[MPa]	[kJ/m2]
1	FFF	25	0°	2460 ± 50	29.4 ± 0.4	36.7 ± 1.0
	unidirectional
2	FFF	25	90°	1020 ± 50	15.3 ± 0.2	17.4 ± 1.0
	unidirectional
3	FFF	40	0°	2500 ± 40	30.3 ± 0.4	38.9 ± 0.7
	unidirectional
4	FFF	40	90°	1010 ± 30	18.3 ± 0.3	18.3 ± 0.9
	unidirectional
5	FFF	100	0°	2370 ± 30	29.2 ± 0.2	37.0 ± 1.2
	unidirectional
6	FFF	100	90°	940 ± 30	16.3 ± 0.2	17.2 ± 0.4
	unidirectional
7	FFF	150	0°	2280 ± 40	26.5 ± 0.3	34.7 ± 1.2
	unidirectional
8	FFF	150	90°	890 ± 30	16.1 ± 0.3	16.9 ± 0.4
	unidirectional
9	FFF	40	0 + 90°	1720 ± 50	21.5 ± 0.3	24.7 ± 0.7
	multidirectional
10	FFF	40	−45 + +45°	1530 ± 30	18.4 ± 0.3	29.1 ± 0.8
	multidirectional
CE1	Injection	n.a.	0°	2300 ± 20	26.7 ± 0.9	27.2 ± 0.9
	molding		90°	990 ± 120	16.3 ± 0.2	15.5 ± 0.8

The filament of CM1 used for producing sample was compared with injection-molded sample. The results of the tests are reported in Table 5.

TABLE 5
	Printing/
	injection
	orientation
	relative	Mechanical properties
		Printing	to stress	Tensile	Tensile	Impact
		speed	test	Modulus	strength	strength
Example	Process	[mm/s]	direction	[MPa]	[MPa]	[kJ/m2]
CE1_1	FFF	40	0°	2990 ± 40	29 ± 2	17.9 ± 1.0
	unidirectional
CE1_2	FFF	40	90°	1190 ± 130	17.6 ± 0.8	7.1 ± 1.7
	unidirectional
CE1_3	FFF	100	0°	2810 ± 100	26.2 ± 0.7	14.1 ± 0.7
	unidirectional
CE1_4	FFF	100	90°	970 ± 100	16.4 ± 0.5	5.5 ± 0.9
	unidirectional
CE1_5	FFF	40	0 + 90°	1990 ± 80	22.2 ± 0.7	9.1 ± 0.9
	multidirectional
CE1_6	FFF	40	−45 + +45°	1920 ± 90	20.9 ± 1.7	9.0 ± 1.1
	multidirectional
CE1_7	Injection	n.a.	0°	4200 ± 100	54 ± 3	16 ± 2
	molding		90°	2240 ± 40	30 ± 0.3	9 ± 2

The filament of CM2 used for producing sample was compared with injection-molded sample. The results of the tests are reported in Table 6.

TABLE 6
	Printing
	orientation
	relative	Mechanical properties
		Printing	to stress	Tensile	Tensile	Impact
		speed	test	Modulus	strength	strength
Example	Process	[mm/s]	direction	[MPa]	[MPa]	[kJ/m2]
CE2_1	FFF	40	0°	3760 ± 130	20 ± 3	5.7 ± 0.7
	unidirectional
CE2_2	FFF	40	90°	2500 ± 300	33.5 ± 0.7	4.2 ± 0.5
	unidirectional
CE2_3	FFF	100	0°	3590 ± 80	16.8 ± 1.4	4.1 ± 0.7
	unidirectional
CE2_4	FFF	100	90°	2300 ± 300	30.2 ± 0.7	3.1 ± 0.4
	unidirectional
CE2_5	FFF	40	0 + 90°	3000 ± 300	38 ± 9	4.7 ± 0.2
	multidirectional
CE2_6	FFF	40	−45 + +45°	2630 ± 160	37.8 ± 1.1	4.2 ± 0.3
	multidirectional
CE2_7	Injection	n.a.	0°	5100 ± 80	60.0 ± 1.0	7.0 ± 0.4
	molding		90°	3350 ± 40	45.6 ± 0.5	4.8 ± 0.3

Warpage Characterization Test Results

Tables 7 reports the test results for warpage tests.

TABLE 10
	Example	Material	Warpage [%]
	W1	Polypropylene composition (I)	2.0 ± 0.2
	W2	CM1	12.6 ± 0.4
	W3	CM2	23.1 ± 0.3

Surface Quality

Table 8 reports surface roughness. FIGS. 3 to 5 illustrated the surface roughness of the side wall of cubes printed with the three different materials.

TABLE 11
	Side wall
Example	Material	Rz [μm]	Ra [μm]	Sz [μm]	Sa [μm]
SQ1	Polypropylene	374	66	594	66
	composition (I)
SQ2	Comparison material	223	34	452	37
	1 (CM1):
	ethylene propylene
	copolymer with 25%
	by weight glass fibers
SQ3	Comparison material	161	25	288	27
	2 (CM2): BASF
	Innofil3D PP GF30

In some embodiments and to reduce roughness, 3D printed articles are finished and smoothed by mechanical or thermal postprocessing. It is believed that the reduced visibility of the layer-by-layer structure from printed parts of the polypropylene composition (I) is not affected by the process.

Claims

1. An extrusion-based additive manufacturing process to produce a 3D printed article comprising the steps of: (i) providing a build material in the form of pellet comprising a propylene polymer composition comprising: A) from 20 to 60 wt. % of a heterophasic propylene copolymer;B) from 5 to 33 wt. % of a propylene homopolymer or copolymer, wherein the copolymer contains up to 5 wt. % of an alpha-olefin selected from the group consisting of ethylene, 1-butene, 1-hexene and 1-octene;C) from 2 to 15 wt. % of an elastomeric block copolymer made from or containing styrene;D) from 4 to 32 wt. % of an elastomeric ethylene copolymer;E) from 5 to 50 wt. % of a glass material as filler; andF) from 0.1 to 5 wt. % of a compatibilizer,wherein the amounts of components A), B), C), D), E) and F) are referred to the total weight of A), B), C), D), E) and F) and wherein the melt flow rate MFR (ISO 1133-2:2011, 2.16 kg/230°° C.) of the propylene polymer composition is at least 1.0 g/10 min.;(ii) providing an additive-manufacturing system;(iii) at least partially fusing the build material in the additive-manufacturing system to form a fused build material; and(iv) extruding the at least partially fused build material to form the 3D printed article.

2. The extrusion-based additive manufacturing process according to claim 1, wherein the propylene polymer composition comprises: A) from 25 to 52 wt. % of a heterophasic propylene copolymer;B) from 8 to 23 wt. % of a propylene homopolymer or copolymer;C) from 3 to 10 wt. % of an elastomeric block copolymer made from or containing styrene;D) from 6 to 23 wt. % of an elastomeric ethylene copolymer;E) from 10 to 35 wt. % of a glass material as filler, andF) from 0.3 to 3 wt. % of a compatibilizer.

3. The extrusion-based additive manufacturing process according to claim 1, wherein component A) is a heterophasic propylene copolymer wherein a rubber phase is dispersed in the matrix, and wherein the matrix is a propylene homopolymer or propylene ethylene copolymer having an ethylene content of up to 10 wt. % and a fraction soluble in xylene at 25° C. lower than 10 wt. %; andthe rubber phase is: (i) a propylene/ethylene copolymer having an ethylene content ranging from 15 to 75 wt. %, or (ii) an ethylene/C4-C8 alpha-olefin copolymer having an ethylene content ranging from 35 to 70 wt. % by weight, or (iii) a combination thereof.

4. The extrusion-based additive manufacturing process according to claim 1, wherein component A) is a heterophasic propylene copolymer, wherein a rubber phase is dispersed in the matrix and wherein the amount of the matrix is in the range of from 30 to 70 wt. %, referred to the total weight of the heterophasic copolymer, and the remaining part, up to 100% by weight, is the rubber phase.

5. The extrusion-based additive manufacturing process according to claim 1, wherein component A) is a heterophasic propylene copolymer, wherein a rubber phase is dispersed in the matrix and wherein the rubber phase is a mixture comprising from 33 wt % to 67 wt % of a propylene/ethylene copolymer and 33 wt % to 67 wt % an ethylene/C4-C8 alpha-olefin copolymer, referred to the total amount of the rubber phase.

6. The extrusion-based additive manufacturing process according to claim 1, wherein component A) is a heterophasic propylene copolymer wherein a rubber phase is dispersed in the matrix, and wherein the matrix is a propylene homopolymer andthe rubber phase is a mixture of a propylene ethylene/copolymer and an ethylene/C4-C8 alpha olefin copolymer.

7. The extrusion-based additive manufacturing process according to claim 1, wherein component B) is a propylene homopolymer having a fraction soluble in xylene at 25° C. lower than 5 wt. %, alternatively lower than 3 wt %.

8. The extrusion-based additive manufacturing process according to claim 1, wherein component C) is selected from the group consisting of styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-butadiene-styrene block copolymers (SBS), and styrene-isoprene-styrene block copolymers (SIS) containing from 5 to 30 wt. % of polystyrene and having a hardness (Shore A, ASTM D-2240-15) value equal to or lower than 70 points.

9. The extrusion-based additive manufacturing process according to claim 1, wherein component D) has a hardness (Shore A, ASTM D-2240-15) value equal to or lower than 80 points.

10. The extrusion-based additive manufacturing process according to claim 1, wherein component D) is an elastomeric thermoplastic copolymer of ethylene with 1-butene containing from 20 to 40 wt. % 1-butene, and having density of less than 0.89 g/ml (measured according to ASTM D-792).

11. The extrusion-based additive manufacturing process according to claim 1, wherein component E) is made from or contains glass fibers or chopped glass fibers, glass particles in the form of ground glass or milled glass fibers, or a combination thereof.

12. The extrusion-based additive manufacturing process according to claim 1, wherein component E) is glass fibers or chopped glass fibers having an average length of from 10 μm to 20 mm.

13. The extrusion-based additive manufacturing process according to claim 1, wherein component E) is glass particles in the form of ground glass or milled glass fibers whose average particle size is in the range from 3 μm to 5 mm.

14. The extrusion-based additive manufacturing process according to claim 1, wherein component F) is a propylene polymer grafted with maleic anhydride.