PROPYLENE BASED FILAMENT FOR 3D PRINTER

FIELD OF THE INVENTION

[0001] The present disclosure relates to a filament comprising an heterophasic propylene ethylene copolymer to be used in an extrusion-based 3D printer.

BACKGROUND OF THE INVENTION

[0002] An extrusion-based 3D printer is used to build a 3D model from a digital representation of the 3D model in a layer-by-layer manner by extruding a flowable modeling material. A filament of the modeling material is extruded through an extrusion tip carried by an extrusion head, and is deposited as a sequence of roads on a substrate in an x-y plane. The extruded modeling material fuses to previously deposited modeling material, and solidifies upon a drop in temperature. The position of the extrusion head relative to the substrate is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D model resembling the digital representation. Movement of the extrusion head with respect to the substrate is performed under computer control, in accordance with build data that represents the 3D model. The build data is obtained by initially slicing the digital representation of the 3D model into multiple horizontally sliced layers. Then, for each sliced layer, the host computer generates a build path for depositing roads of modeling material to form the 3D model.

[0003] In the printing process the filament clearly plays an important role, changing the material of the filament the final mechanical and aesthetic properties of the finished object change. Usually in the art filament of polylactic acid (PLA) or acrylonitrile, butadiene, styrene (ABS) polymer or polyamides are used.

[0004] One of the most important properties of a filament is constant diameter (usually 1.75 mm or 3 mm) otherwise it is not possible to finely tune the amount of material in the printed object. This property is not easily achieved and depends on the characteristics of the polymer.

[0005] Furthermore the filament, once prepared, has to be printable, i.e. it has to be possible to achieve a good adhesion with the plate and among the layers. [0006] Propylene based polymers have been proposed as polymers suitable for making filaments, however from the tests carried out by the applicant the propylene based filaments available on the market gave poor results in the print test.

[0007] Therefore there is the need for propylene based polymers that can be used as a filament in a 3D printer.

SUMMARY OF THE INVENTION

[0008] The applicant found a consumable filament for use in an extrusion-based additive manufacturing system comprising an heterophasic propylene ethylene copolymer having a xylene soluble content ranging from 15 wt to 50 wt and a melt flow rate MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 0.5 to 100 g/10 min.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is the front view of the sample used in the print tests of the examples. The measure are given in mm, the sample once completely printed is 5 mm thick. .

DETAILED DESCRIPTION OF THE INVENTION

[0010] The applicant found a consumable filament for use in an extrusion-based additive manufacturing system comprising an heterophasic propylene ethylene copolymer having a xylene soluble content ranging from 15 wt to 50 wt ; preferably from 20 wt to 40 wt more preferably from 22 wt to 35 wt and a melt flow rate MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 0.5 to 100 g/10 min;

preferably from 2.0 to 50.0 g/10 min; more preferably from 5.0 to 20.0 g/10 min.

[0011] The expression "heterophasic copolymer" as used in the instant invention indicates that the elastomeric propylene ethylene copolymer is (finely) dispersed in the matrix, i.e. in the propylene homo or copolymer. In other words the elastomeric propylene ethylene copolymer forms inclusions in the matrix. Thus the matrix contains (finely) dispersed inclusions being not part of the matrix and said inclusions contain the elastomeric propylene copolymer. The term "inclusion" according to this invention shall preferably indicate that the matrix and the inclusion form different phases within the heterophasic system, said inclusions are for instance visible by high resolution microscopy, like electron microscopy or scanning force microscopy.

[0012] Preferably the heterophasic propylene ethylene copolymer has an ethylene content ranging from 5 wt and 30 wt ; more preferably from 8 wt to 25 wt ; even more preferably from 10 wt% and 20 wt%.

[0013] The matrix of the heterophasic propylene ethylene content can be propylene homopolymer or propylene ethylene copolymer having an ethylene content up to 10 wt ; preferably up to 5 wt ; preferably the matrix is a propylene homopolymer.

[0014] The elastomeric phase is a propylene ethylene copolymer having an ethylene content ranging from 12 wt to 80 wt ; preferably from 30 wt to 70 wt .

[0015] Preferably the intrinsic viscosity of the fraction soluble in xylene at 25°C ranges from 2.0 to 6.0 dl/g; more preferably from 2.5 to 5.0 dl/g; even more preferably from 3.1 dl/g to 4.5 dl/g

[0016] The term copolymer means that the polymer is formed by only two monomers, propylene and ethylene.

[0017] The term xylene soluble or xylene soluble fraction it is intended to be the fraction soluble in xylene at 25°C measured according to the procedure reported in the examples section.

[0018] heterophasic propylene ethylene copolymer used in the present disclosure can be extruded in a filament having a constant diameter, the diameter of the filament being that of one used in the art such as 1.75 mm or 3 mm. Other possible diameters can also be used. The variation from the nominal diameter is +/- 0.05 mm preferably +/- 0.03 mm.

[0019] When amorphous polymeric materials, such as acrylonitrile-butadiene-styrene (ABS) resins and polycarbonate resins are used they have little or no ordered arrangements of their polymer chains in their solid states. This reduces the effects of curling and plastic deformation in the resulting 3D model or support structure.

[0020] Crystalline or semicrystalline polymer exhibits superior mechanical properties but due to the crystallinity when used for building 3D model they show undesirable shrinkage effects both when the extruded road is deposited to form a portion of a layer of a 3D model and when the road is cooled. The shrinkage effects renders the crystalline or semicrystalline polymers not usable for the building of 3D object in a an extrusion-based additive manufacturing process. [0021] The applicant found that heterophasic propylene ethylene copolymer of the present disclosure can be advantageously used for building a 3D model comprising semi crystalline polymers as shown by the amount of xylene soluble material.

[0022] The propylene ethylene copolymer of the present disclosure is available in the market. Examples of copolymers can be EP3080 or EP3307 sold by LyondellBasell,

[0023] The filament object of the present invention can additionally contain additives normally used in the art such as antioxidants, slipping agents, process stabilizers, antiacid and nucleants.

[0024] The filament can additionally contains fillers known in the art such as talc, calcium carbonate, wollastonite, glass fibers, glass spheres and carbon derived grades.

[0025] Furthermore the filament of the present invention can also contains wood powder, metallic powder marble powder and similar materials normally used for obtaining 3D object having particular aesthetic appearances or improved mechanics.

[0026] The following examples are given to illustrate and not to limit the present invention.

EXAMPLES

[0027] The data of the propylene polymer materials were obtained according to the following methods:

[0028] Xylene-soluble fraction at 25°C

[0029] The Xylene Soluble fraction was measured according to ISO 16152, 2005, but with the following deviations (between brackets is what is prescribed by the ISO 16152)

[0030] The solution volume is 250 ml (200 ml)

[0031] During the precipitation stage at 25°C for 30 min, the solution, for the final 10 minutes, is kept under agitation by a magnetic stirrer (30 min, without any stirring at all)

[0032] The final drying step is done under vacuum at 70°C (100 °C)

[0033] The content of said xylene-soluble fraction is expressed as a percentage of the original 2.5 grams and then, by difference (complementary to 100), the xylene unsoluble %

[0034] Ethylene (C2) content

[0035] ¹³ C NMR of propylene/ethylene copolymers

[0036] 1 ¹ 3 ^J C 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. [0037] The peak of the S 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 a 8 % wt/v concentration. Each spectrum was acquired with a

90° pulse, 15 seconds 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.

[0038] 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:

PPP = 100 Tpp/S PPE = 100 Tps/S EPE = 100 T ₈₈ /S

PEP = 100 S _pp /S PEE= 100 S _p8 /S EEE = 100 (0.25 S _y8 +0.5 S ₈₈ )/S

S = Τββ + Τβδ + Τδδ + S p + Sps + 0.25 Sys + 0.5 See

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

E% mol = 100 * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation:

100 * E% mol * MW _E

E% wt. =

E% mol * MW _{E +} P% mol * MW _P

[0039] where P% mol is the molar percentage of propylene content, while MW _E and MWp are the molecular weights of ethylene and propylene, respectively.

[0040] The product of reactivity ratio r _\ r ₂ was calculated according to Carman (C.J. Carman, R A. Harrington and C.E. Wilkes, Macromolecules, 1977; 10, 536) as: [0042] The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTpp (28.90-29.65 ppm) and the whole Tpp (29.80-28.37 ppm)

[0043] Melt flow rate (MFR)

[0044] The melt flow rate MFR of the polymer was determined according to ISO 1133 (230°C, 2.16 Kg).

[0045] The following polymers have been used

[0046] PPl

Propylene homopolymer having an MFR 6,5 and a fraction soluble in xylene at 25°C of < 4%

[0047] PP2

Commercial filament of diameter 1.75 mm sold under the tradename PP REPRAP BLACK FILAMENT German RepRap PP Filament 600g, a random propylene ethylene copolymer having an ethylene content of 3 wt an MFR of 2 dl/10 min and a fraction soluble in xylene at 25°C of 6.2 wt%.

[0048] PP3

[0049] Heterophasic propylene ethylene copolymer sold under the tradename HIFAX

EP3080 having an ethylene content of 18 wt , xylene soluble content of 32.0 wt an MFR of

7.5 g/10 min and intrinsic viscosity of xylene soluble fraction IV of 3.5 dl/g.

Polymers PPl and PP3 have been extruded to form a filament having 1.75 mm of diameter. In order to be able to extrude PPl 10 wt of talc has been added.

[0050] Print test

[0051] The printer was a 3D Rostock delta printer. The printer conditions are the followings:

Filament diameter mm 1,75 +0.03

Nozzle diameter mm 0,4

Temperature first layer °C 245

Temperature other layers °C 245

1

Layer high mm 0,2

Temperature plate °C 100

polybutene

Plate material. sheet

PB0300M

Infill 100%

printer speed mrn/min 3600

Speed first layer 60%

Speed other layers 100%

Speed infill mrn/min

4.000

[0052] The sample to be printed is reported in Fig 1. For each filament 5 printer tests have been carried out, the print has been stopped when one side of the object is detached from the plane and thus the print of the object was no longer possible . The results are reported on table 1

Table 1

[0053] * comparative

From table 1 clearly results that only PP3, that is the material according to the invention, can be used to fully print the sample.