WO2019197582A1

WO2019197582A1 - 3d printed article comprising polypropylene

Info

Publication number: WO2019197582A1
Application number: PCT/EP2019/059352
Authority: WO
Inventors: Dominique Olivier; Bernard Jacques
Original assignee: Total Research & Technology Feluy
Priority date: 2018-04-11
Filing date: 2019-04-11
Publication date: 2019-10-17

Abstract

The present invention relates to a 3D printed article comprising a 3D printable composition comprising at least 90.0 % by weight of a polypropylene, based on the total weight of the 3D printable composition; wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene, wherein the melting peak temperature (Tm) of the polypropylene is at most 10 °C higher than the onset melting temperature (T_{melt onset}) of the polypropylene; wherein the start melt temperature (T_{melt start}) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods; and wherein the polypropylene is a polypropylene random copolymer comprising at most 8.0 % by weight of comonomer content, relative to the total weight of the polypropylene random copolymer, as determined by ¹³C-NMR analysis. The present invention also relates to a process for preparing said 3D printed article and to the use of said 3D printed article.

Description

3D PRINTED ARTICLE COMPRISING POLYPROPYLENE

FIELD OF THE INVENTION

The invention relates to a 3D printed article made of polypropylene and to processes for producing said articles.

BACKGROUND OF THE INVENTION

Significant advances in three-dimensional (3D) printing technology over the past decade have transformed the potential ways in which products are designed, developed and manufactured. Interest in 3D printing has grown swiftly as application has progressed from rapid prototyping to the production of end-use products. 3D printing technology is increasingly used in the medical, aerospace, aviation, automotive, sports and electronics industries.

3D printing (technology) also referred to as additive manufacturing is the process of joining materials to make objects from Computer Aided Design (CAD) model data, usually layer upon layer. There are several additive manufacturing processes based on the physical state of starting material used. Selective laser sintering (SLS) is one of them and it commonly uses nylon or polyamide as starting materials.

Polypropylene is a polymer that exhibits excellent electrical insulation, chemical resistance, heat resistance and fatigue resistance, which together with its low price and excellent processing performance, makes it an attractive material to use in the field of 3D printing. However, polypropylene tends to exhibit poor toughness, and high shrinkage. In particular, when polypropylene is used in 3D printing, the product easily shrinks and warping occurs, and the product tends to be fragile.

There is a need in the art to overcome the drawbacks related to the use of polypropylene in 3D printing technology. It is the object underlying the present invention to provide 3D printed articles which have excellent plasticity, high elongation, low moisture absorption and durability. It is another object of the present invention to provide 3D printed articles which show improved nominal elongation at break.

SUMMARY OF THE INVENTION

The present inventors have now surprisingly found that one or more of the above objects can be achieved by using a polypropylene to manufacture 3D printed articles.

According to a first aspect of the invention, a 3D printed article is provided, the 3D printed article comprising a 3D printable composition comprising

at least 90.0 % by weight of a polypropylene, based on the total weight of the 3D printable composition; wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene,

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; and

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods.

Preferably, the 3D printed article comprises a 3D printable composition comprising

at least 90.0 % by weight of a polypropylene, based on the total weight of the 3D printable composition;

wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene,

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene;

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods; and wherein the polypropylene is a polypropylene random copolymer comprising at most 8.0 % by weight of comonomer content, relative to the total weight of the polypropylene random copolymer, as determined by ¹³C-NMR analysis.

According to a second aspect of the invention, a process for producing a 3D printed article is provided, the process comprising the steps of:

(a) providing a 3D printable composition comprising:

at least 90.0 % by weight of a polypropylene based on the total weight of the 3D printable composition;

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods; (b) 3D printing the composition issued from step (a) to form a 3D printed article.

Preferably the process for producing a 3D printed article, comprises the steps of:

(a) providing a 3D printable composition comprising:

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods; and

wherein the polypropylene is a polypropylene random copolymer comprising at most 8.0 % by weight of comonomer content, relative to the total weight of the polypropylene random copolymer, as determined by ¹³C-NMR analysis;

(b) 3D printing the composition issued from step (a) to form a 3D printed article.

According to a third aspect, the present invention also encompasses a 3D printed article obtainable by a process according to the second aspect of the invention.

According to a fourth aspect, the present invention also encompasses the use of a 3D printed article according to the first or third aspect of the invention for the automotive industry, the aerospace industry, the medical and dental industries, the electronic industry, the sports industry.

The present process allows getting 3D printed articles which have excellent plasticity, high elongation, low moisture absorption and durability. The present process allows getting 3D printed articles which show improved nominal elongation at break.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description.

The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent or other dependent claims as appropriate.

The present invention will now be further described. In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature or statement indicated as being preferred or advantageous may be combined with any otherfeatures or statements indicated as being preferred or advantageous. The reference figures quoted below refer to the attached drawings.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 represents an example of the ¹³C-NMR spectrum of metallocene-catalyzed polypropylene random copolymer containing about 5 % by weight of ethylene.

Figure 2 represents a graph showing the DSC profile of PP1 recorded during the cooling phase.

Figure 3 represents a graph showing the DSC profile of PP1 recorded during the second heating phase.

DETAILED DESCRIPTION OF THE INVENTION

Before the present articles, processes and uses encompassed by the invention are described, it is to be understood that this invention is not limited to particular articles, processes and uses described, as such articles, processes and uses may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present invention. When describing the articles, processes and uses of the invention, the terms used are to be construed in accordance with the following definitions, unless the context dictates otherwise.

As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, the term "a polypropylene" means one polypropylene or more than one polypropylene.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of, "consists" and "consists of.

The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1 .0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

Reference throughout this specification to“one embodiment” or“an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims and statements, any of the embodiments can be used in any combination.

As used herein,“3D printed article” refers to an object built by a 3D printing system. 3D printed articles according to the present invention include prototypes, ornamental and decorative objects, industrial pieces, prosthetic implants and medical devices, architectural reproductions, eyewear, and fashion articles.

As used herein,“3D printing”, or“three-dimensional (3D) printing” also referred to as additive manufacturing, rapid prototyping or solid freeform fabrication, is a process of making a three- dimensional solid object from a digital model. The basic principle of 3D printing resides on building a product layer by layer from a particular material.

Preferred statements (features) and embodiments of the articles, processes and uses of this invention are set herein below. Each statement and embodiment of the invention so defined may be combined with any other statement and/or embodiment, unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other features or statements indicated as being preferred or advantageous. Hereto, the present invention is in particular captured by any one or any combination of one or more of the below numbered aspects and embodiments, with any other statement and/or embodiment.

1 . A 3D printed article comprising a 3D printable composition comprising

wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene, wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; and

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods. A 3D printed article comprising a 3D printable composition comprising

The 3D printed article according to any one of statements 1 to 2, wherein the 3D printable composition comprises at least 90.0 % by weight of the polypropylene, preferably at least 93.0 % by weight; preferably at least 95.0 % by weight, preferably at least 95.5 % by weight, preferably at least 96.0 % by weight, preferably at least 96.5 % by weight, preferably at least 97.0 % by weight, preferably at least 97.5 % by weight, preferably at least 98.0 % by weight, more preferably at least 98.5 % by weight, more preferably at least 99.0 % by weight, more preferably at least 99.5 % by weight, based on the total weight of the 3D printable composition. The 3D printed article according to any one of statements 1 to 3, wherein the 3D printable composition comprises from 90.0 to 99.5 % by weight of the polypropylene, based on the total weight of the 3D printable composition; preferably from 92.0 to 99.5 % by weight, preferably 95.0 to 99.5 % by weight, preferably from 95.5 to 99.5 % by weight, preferably from 95.0 to 98.7 % by weight, preferably from 95.5 to 98.5 % by weight, preferably from 96.0 to 99.5 % by weight, preferably from 96.5 to 99.5 % by weight, preferably from 97.0 to 99.5 % by weight, more preferably from 97.5 to 99.0 % by weight, more preferably from 95.0 to 99.0 % by weight, more preferably from 95.5 to 99.0 % by weight, even more preferably from 97.0 to 98.5 % by weight of the total weight of the 3D printable composition. The 3D printed article according to any one of statements 1 to 4, wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene; preferably at least 23 °C higher; preferably at least 25 °C higher; preferably at least 27 °C higher; preferably at least 30 °C higher; preferably at least 33 °C higher, preferably at least 35 °C higher than the crystallization temperature (T_c) of the polypropylene.

The 3D printed article according to any one of statements 1 to 5, wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (T_meit onset) of the polypropylene; preferably at most 9 °C higher; preferably at most 8 °C higher; preferably at most 7 °C higher; preferably at most 6 °C higher; preferably at most 5 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene.

The 3D printed article according to any one of statements 1 to 6, wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene; preferably at most 59 °C lower; preferably at most 58 °C lower; preferably at most 57 °C lower; preferably at most 56 °C lower preferably at most 55 °C lower; preferably at most 54 °C lower; preferably at most 52 °C lower than the melting peak temperature (T_m) of the polypropylene.

The 3D printed article according to any one of statements 1 to 7, wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene; preferably at least 23 °C higher; preferably at least 25 °C higher; preferably at least 27 °C higher; preferably at least 30 °C higher; preferably at least 33 °C higher, preferably at least 35 °C higher than the crystallization temperature (T_c) of the polypropylene;

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; preferably at most 9 °C higher; preferably at most 8 °C higher; preferably at most 7 °C higher; preferably at most 6 °C higher; preferably at most 5 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; and

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene; preferably at most 59 °C lower; preferably at most 58 °C lower; preferably at most 57 °C lower; preferably at most 56 °C lower preferably at most 55 °C lower; preferably at most 54 °C; preferably at most 52 °C lower than the melting peak temperature (T_m) of the polypropylene.

The 3D printed article according to any one of statements 1 to 8, wherein the polypropylene is a metallocene-catalyzed polypropylene. 10. The 3D printed article according to any one of statements 1 to 9, wherein the polypropylene is a polypropylene random copolymer.

1 1 . The 3D printed article according to any one of statements 1 to 10, wherein the polypropylene is a random copolymer comprising a comonomer content at most 7.5 % by weight, relative to the total weight of the random copolymer, as determined by ¹³C-NMR analysis; preferably at most 7.0 % by weight; preferably at most 6.5 % by weight; preferably at most 6.0 % by weight; preferably at most 5.5 % by weight; preferably at most 4.5 % by weight; preferably at most 4.0 % by weight; preferably at most 3.5 % by weight.

12. The 3D printed article according to any one of statements 1 to 1 1 , wherein the polypropylene is a random copolymer comprising a comonomer content of at least 1.0 % by weight, relative to the total weight of the random copolymer, as determined by ¹³C-NMR analysis; preferably at least 1 .5 % by weight; preferably at least 2.0 % by weight.

13. The 3D printed article according to any one of statements 1 to 12, wherein the polypropylene is isotactic.

14. The 3D printed article according to any one of statements 1 to 13, wherein the polypropylene has a content of mmmm pentads of at least 60.0 % as determined by ¹³C-NMR analysis, preferably at least 65.0 %, preferably at least 70.0 %, preferably at least 75.0 %, preferably at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 95.0 %.

15. The 3D printed article according to any one of statements 1 to 14, wherein the polypropylene is a metallocene-catalyzed polypropylene random copolymer.

16. The 3D printed article according to any one of statements 1 to 15, wherein the comonomer is ethylene.

17. The 3D printed article according to any one of statements 1 to 16, wherein the polypropylene has a melt flow index of from 7.0 to 15.0 g/10 minutes, as determined according to ISO 1 133:2005, Method B, at 230 °C and under a load of 2.16 kg; preferably of from 7.5 to 15.0 g/10 min; preferably of from 8.0 to 13.5 g/10 min; preferably of from 8.5 to 13.0 g/10 min; preferably of from 9.0 to 12.5 g/10 min; preferably of from 9.5 to 12.0 g/10 min.

18. The 3D printed article according to any one of statements 1 to 17, wherein the polypropylene has a M_w/M_n of at most 6.0, preferably of at most 5.5; preferably of at most 5.0; preferably of at most 4.0; preferably of at most 3.8; preferably of at most 3.6; preferably of at most 3.2; preferably of at most 3.0, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight. 19. The 3D printed article according to any one of statements 1 to 18, wherein the polypropylene has a M_w/M_n of from 2.0 to 4.0; preferably of from 2.0 to 3.8; preferably of from 2.1 to 3.6; preferably of from 2.2 to 3.4, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight.

20. The 3D printed article according to any one of statements 1 to 19, wherein the polypropylene has a flexural modulus of at most 950 MPa as determined according to ISO 178:2011 ; preferably of at most 940 MPa; preferably of at most 930 MPa; preferably of at most 935 MPa; preferably of at most 920 MPa, preferably of at most 910 MPa.

21. The 3D printed article according to any one of statements 1 to 20, wherein the polypropylene has tensile modulus of at most 1300 MPa as determined according to ISO 527-2:93; preferably of at most 1250 MPa; preferably of at most 1200 MPa; preferably of at most 1 150 MPa; preferably of at most 1 100 MPa; preferably of at most 1000 MPa; preferably of at most 1050 MPa.

22. The 3D printed article according to any one of statements 1 to 21 , wherein the polypropylene has a nominal elongation at break of at least 300 % as determined according to ISO 527-2:93; preferably of at least 350 %; preferably of at least 400 %; preferably of at least 450 %; preferably of at least 500 %; preferably of at least 540 %.

23. The 3D printed article according to any one of statements 1 to 22, wherein the 3D printable composition further comprises at least one antioxidant.

24. The 3D printed article according to any one of statements 1 to 23, wherein the 3D printable composition further comprises from 300 to 2000 ppm by weight of at least one antioxidant; preferably comprises from 310 to 1500 ppm by weight; preferably comprises from 320 to 1400 ppm by weight; preferably comprises from 330 to 1300 ppm by weight; preferably comprises from 340 to 1200 ppm by weight; preferably comprises from 350 to 1 100 ppm by weight.

25. The 3D printed article according to any one of statements 1 to 24, wherein the 3D printable composition further comprises at least one antioxidant selected from the group comprising hindered phenols, hindered amine light stabilizers (HALS), hindered amine light stabilizers comprising sterically hindered phenol moieties, and combinations thereof.

26. The 3D printed article according to any one of statements 1 to 25, wherein the 3D printable composition further comprises two or more antioxidants.

27. The 3D printed article according to any one of statements 1 to 26, wherein the 3D printable composition further comprises an additive selected from the group consisting of 1 , 4, 5, 6, 7, 7-hexachlorobicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic acid, and isoleucine. The 3D printed article according to any one of statements 1 to 27, wherein the 3D printable composition further comprises from 0.05 to 0.1 % by weight of isoleucine based on the total weight of the 3D printable composition; preferably from 0.06 to 0.09 % by weight; preferably from 0.07 to 0.09 % by weight of isoleucine based on the total weight of the 3D printable composition.

The 3D printed article according to any one of statements 1 to 28, wherein the 3D printable composition further comprises from 0.10 to 0.40 % by weight of 1 , 4, 5, 6, 7, 7- hexachlorobicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic acid based on the total weight of the 3D printable composition; preferably from 0.1 1 to 0.39 % by weight; preferably from 0.12 to 0.38 % by weight, preferably from 0.13 to 0.37 % by weight; preferably from 0.14 to 0.36 % by weight, preferably from 0.15 to 0.35 % by weight of 1 , 4, 5, 6, 7, 7-hexachlorobicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic acid based on the total weight of the 3D printable composition. A process for producing a 3D printed article, the process comprising the steps of:

(a) providing a 3D printable composition comprising:

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (T_meit onset) of the polypropylene; and

wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods;

(b) 3D printing onto a substrate the composition issued from step (a) to form a 3D printed article according to any one of statements 1 to 27.

A process for producing a 3D printed article, the process comprising the steps of:

(a) providing a 3D printable composition comprising:

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; wherein the start melt temperature (T_meit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, as determined using differential scanning calorimetry as described in the specification under the Determination methods; and

32. The process according to any one of statements 30 or 31 , wherein the 3D printed article is an article according to any one of statements 1 to 29.

33. The process according to any one of statements 30 to 32, wherein the 3D printable composition is provided as a powder.

34. The process according to any one of statements 30 to 33, wherein the 3D printable composition is provided as a powder having a mean particle size D50 value within the range of from 65 pm to 80 pm.

35. The process according to any one of statements 30 to 34, wherein the 3D printable composition is first provided as pellets which are then ground into powder.

36. The process according to any one of statements 30 to 35, wherein the 3D printing is performed using laser sintering printing (SLS) or infrared multi jet fusion printing.

37. A 3D printed article obtainable by a process according to any one of statements 30 to 36.

38. Use of a 3D printed article according to any one of statements 1 to 29 and 37 for the automotive industry, the aerospace industry, the medical and dental industries, the electronic industry, the sports industry.

39. Use of a composition as defined in any one of statements 1 to 29 for the manufacture of an article by 3D printing process.

The present invention encompasses a 3D printed article comprising a 3D printable composition, wherein said 3D printable composition comprises

at least 90.0 % by weight of a polypropylene, preferably at least 91 .0 % by weight; preferably at least 92.0 % by weight, preferably at least 93.0 % by weight, preferably at least 94.0 % by weight, preferably at least 95.0 % by weight, preferably at least 96.0 % by weight, preferably at least 97.0 % by weight, preferably at least 98.0 % by weight, more preferably at least 98.5 % by weight, more preferably at least 99.0 % by weight, more preferably at least 99.5 % by weight, based on of the total weight of the 3D printable composition; and wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene, preferably at least 22 °C higher; preferably at least 24 °C higher; preferably at least 25 °C higher; preferably at least 29 °C higher; preferably at least 32 °C higher, preferably at least 34 °C higher than the crystallization temperature (T_c) of the polypropylene;

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (T_meit onset) of the polypropylene, preferably at most 9 °C higher; preferably at most 8 °C higher; preferably at most 7 °C higher; preferably at most 6 °C higher; preferably at most 5 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, preferably at most 59 °C lower; preferably at most 58 °C lower; preferably at most 57 °C lower; preferably at most 56 °C lower preferably at most 55 °C lower; preferably at most 54 °C; preferably at most 52 °C lower than the melting peak temperature (T_m) of the polypropylene; as determined using differential scanning calorimetry as described in the specification under the Determination methods;

and preferably wherein the polypropylene is a polypropylene random copolymer comprising at most 8.0 % by weight of comonomer content, relative to the total weight of the polypropylene random copolymer, as determined by ¹³C-NMR analysis; preferably at most 7.3 % by weight; preferably at most 6.3% by weight; preferably at most 5.3 % by weight; preferably at most 4.3 % by weight; preferably at most 3.3 % by weight of comonomer content.

The polypropylene

As used herein, the terms "polypropylene" and "propylene polymer" may be used synonymously. For the purposes of the present application, the term "polypropylene" is used to denote propylene homopolymer as well as propylene copolymers. If the propylene is a copolymer, the comonomer can be any alpha-olefin i.e. any C2 to C12 alpha-alkylene, other than propylene. The polypropylene can be atactic, isotactic or syndiotactic polypropylene, preferably the polypropylene is isotactic polypropylene.

In some embodiments, the polypropylene is characterized by a high isotacticity, for which the content of mmmm pentads is a measure. Preferably the content of mmmm pentads in said polypropylene is at least 60.0 %, preferably at least 65.0 %, preferably at least 70.0 %, preferably at least 75.0 %, preferably at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 % and most preferably of at least 95.0 %. The isotacticity may be determined by ¹³C-NMR analysis as described in the determination methods part.

In preferred embodiments, the polypropylene is a random copolymer. The one or more comonomers are preferably selected from the group consisting of ethylene and C4-C10 alpha- olefins, such as for example 1 -butene, 1 -pentene, 1 -hexene, 1 -octene, or 4-methyl-1 -pentene. Ethylene and 1 -butene are the preferred comonomers. Ethylene is the most preferred comonomer.

The term "random" indicates that the co-monomers of the propylene copolymer are randomly distributed within the propylene copolymer. The term random is understood according to IUPAC (Glossary of basic terms in polymer science; IUPAC recommendations 1996).

In some embodiments, the polypropylene random copolymer comprises up to 8.0 % by weight of one or more co-monomers, preferably up to 5.0 % by weight of one or more co-monomers, preferably up to 4.0 % by weight of one or more co-monomers. It is preferred that it comprises at least 1 .0 % by weight of one or more co-monomers, preferably at least 1 .5 % by weight, preferably at least 2.0 % by weight, relative to the total weight of said polypropylene. For the purposes of the present invention the comonomer content of the random copolymer is given relative to the total weight of the random copolymer and can be measured by Infrared Spectroscopy (IR) or by ¹³C- NMR. Preferably it is measured by ¹³C-NMR as described herein in the determination methods part. Preferably the one or more co-monomer is ethylene.

Preferably, said polypropylene, preferably said polypropylene random copolymer, may have a molecular weight distribution, defined as M_w/M_n, of at most 5.0; preferably at most 4.0; preferably at most 3.8; preferably at most 3.6; preferably of at most 3.2; preferably of at most 3.0. Preferably, said polypropylene, preferably a random copolymer, has an M_w/M_n of from 2.0 to 4.0; preferably of from 2.0 to 3.8; preferably of from 2.1 to 3.6; preferably of from 2.2 to 3.4. Molecular weights can be determined by size exclusion chromatography (SEC), frequently also referred to as gel permeation chromatography (GPC), as described in detail in the example section.

In some embodiment, the polypropylene for use in the 3D printable composition, preferably the polypropylene random copolymer, has a melt flow index determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and under a load of 2.16 kg of at most 15.0 g/10 min, preferably at most 14.0 g/10 min, preferably at most 13.0 g/10 min, preferably at most 12.0 g/10 min.

In some embodiment, the polypropylene for use in the 3D printable composition, preferably the polypropylene random copolymer, has a melt flow index determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and under a load of 2.16 kg of at least 3.0 g/10 min, preferably at least 5.0 g/10 min, preferably at least 7.0 g/10 min, preferably at least 8.0 g/10 min, preferably at least 9.0 g/10 min.

In some embodiment, the polypropylene for use in the 3D printable composition, preferably the polypropylene random copolymer, has a melt flow index determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and under a load of 2.16 kg of from 5.0 to 15.0 g/10 min, preferably from 7.0 to 15.0 g/10 min, preferably of from 7.0 to 14.0 g/10 min, preferably from 7.0 to 13.0 g/10 min, preferably from 8.0 to 12.0 g/10 min, preferably from 9.0 to 12.0 g/10 min.

The polypropylene can be produced by polymerizing propylene and one or more co-monomers, such as ethylene, in the presence of a catalyst system and optionally in the presence of hydrogen. The polypropylene can be produced in a single, double or multiple polymerization reactors.

As used herein, the term“catalyst” refers to a substance that causes a change in the rate of a polymerization reaction. In the present invention, it is especially applicable to catalysts suitable for the polymerization of propylene to polypropylene. In some embodiments, the catalyst can be a metallocene catalyst system.

In some embodiments, the polypropylene is prepared using a metallocene catalyst system. The term "metallocene catalysts" refers to compounds of Group IV transition metals of the Periodic Table such as titanium, zirconium, hafnium, etc., which have a coordinated structure with a metal compound and ligands composed of one or two groups of cyclopentadienyl, indenyl, fluorenyl or their derivatives. In some preferred embodiments, the metallocene catalyst system comprises a bridged metallocene component, a support and an activating agent.

In some embodiments, the metallocene component is a metallocene of the following general formula: (-R^a)(R^b)(R^c)MXiX2, wherein R^a, R^b, R^c, M, Xi, X₂ have the meaning given herein.

R^a is a bridge between R^b and R^c, i.e. R^a is chemically connected to R^b and R^c. In a preferred embodiment, R^a is selected from the group consisting of -(CR¹R²)_P-, -(SiR¹R²)_p-, -(GeR¹R²)_p-, - (NR¹)_P-, -(PR¹)_p-, -(N⁺R¹R²)_P- and -(P⁺R¹R²)_p-, and p is 1 or 2, and R¹ and R² are each independently selected from the group consisting of hydrogen, Ci-Cioalkyl, Cs-Cscycloalkyl, Ce- Ciearyl, Ci-ioalkylC6-i5aryl, or any two neighboring R (i.e. two neighboring R¹, two neighboring R², or R¹ with a neighboring R²) may form a cyclic saturated or non-saturated C4-C10 ring; each of said alkyl, cycloalkyl, aryl, alkylaryl optionally contains one or more heteroatoms from groups 14- 16; each R¹ and R² may in turn be substituted in the same way, for example by one or more halogen, such as fluoro, or chloro. Such heteroatom is preferably O, N or S, preferably O. Preferably R^a is -(CR¹R²)_P- or -(SiR¹R²)_p- with R¹, R² and p as defined above. Most preferably R^a is -(SiR¹R²)_p- with R¹, R² and p as defined above. Specific examples of R^a include Me₂C, ethanediyl (-CH₂-CH₂-), Ph₂C and Me₂Si.

M is a metal selected from Ti, Zr and Hf, preferably it is Zr.

X¹ and X² are each independently selected from the group consisting of halogen, hydrogen, C1- Cioalkyl, C₆-Cisaryl, Ci-ioalkylC6-i5aryl. Preferably X¹ and X² are halogen or methyl.

R^b and R^c are selected independently from one another and comprise a cyclopentadienyl ring, indenyl, tetrahydroindenyl orfluorenyl, each R^b and R^c being optionally substituted by one or more R^y. each R^y is independently selected from the group consisting of hydrogen, C1-C10 alkyl, C5-C7 cycloalkyl, C6-C15 aryl, alkylaryl with C1-C10 alkyl and C6-C15 aryl, or any two neighboring R may form a cyclic saturated or non-saturated C4-C10 ring; each of said alkyl, cycloalkyl, aryl, alkylaryl optionally contains one or more heteroatoms from groups 14-16; each R^y, may in turn be substituted, for example by one or more halogen, such as fluoro, or chloro. Such heteroatom is preferably O, N or S, preferably O.

In some preferred embodiments, R^b and R^c are both substituted cyclopentadienyl, or are independently from one another unsubstituted or substituted indenyl or tetrahydroindenyl, or R^b is a substituted cyclopentadienyl and R^c a substituted or unsubstituted fluorenyl. More preferably, R^b and R^c may both be the same and may be selected from the group consisting of substituted cyclopentadienyl, unsubstituted indenyl, substituted indenyl, unsubstituted tetrahydroindenyl and substituted tetrahydroindenyl.

Preferred examples of halogen are Cl, Br, and I. Preferred examples of Ci-Cioalkyl are methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, and tert-butyl. Preferred examples of Cs-Crcycloalkyl are cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl. Preferred examples of C₆-Cisaryl are phenyl and indenyl. Preferred examples of alkylaryl with Ci-Cioalkyl and C₆-Cisaryl are benzyl (- Chh-Ph), and -(CH2)2-Ph. By "unsubstituted" is meant that all positions on R^b resp. R^c, except for the one to which the bridge is attached, are occupied by hydrogen. By "substituted" is meant that, in addition to the position at which the bridge is attached, at least one other position on R^b and/or R^c is occupied by a substituent other than hydrogen, wherein each of the substituents may independently be selected from the group consisting of Ci-Cioalkyl, Cs-Czcycloalkyl, C₆-Cisaryl, and Ci-ioalkylC6-i5aryl, or any two neighboring substituents may form a cyclic saturated or non- saturated C₄-Cio ring; each of said alkyl, cycloalkyl, aryl, alkylaryl optionally contains one or more heteroatoms from groups 14-16; each substituent, may in turn be substituted, for example by one or more halogen, such as fluoro, or chloro. A substituted or unsubstituted cyclopentadienyl may for example be represented by the general formula CsR³R⁴R⁵R⁶. A substituted or unsubstituted indenyl may for example be represented by the general formula C₉R⁷R⁸R⁹R¹⁰R¹¹R¹²R¹³R¹⁴. A substituted or unsubstituted tetrahydroindenyl may for example be represented by the general formula C9H₄R¹⁵R¹⁶R¹⁷R¹⁸. A substituted or unsubstituted fluorenyl may for example be represented by the general formula Ci3R¹⁹R²⁰R²¹ R²²R²³R²⁴R²⁵R²⁶. Each of the substituents R³ to R²⁶ may independently be selected from the group consisting of hydrogen, C-i-C-ioalkyl, C5- C7cycloalkyl, C₆-Cisaryl, and Ci-ioalkylC6-i5aryl, or any two neighboring R may form a cyclic saturated or non-saturated C₄-C-io ring; each of said alkyl, cycloalkyl, aryl, alkylaryl optionally contains one or more heteroatoms from groups 14-16; each R³ to R²⁶, may in turn be substituted, for example by one or more halogen, such as fluoro, or chloro. Preferred metallocene components are those having C2-symmetry or those having Ci-symmetry. Most preferred are those having C2- symmetry. Particularly suitable metallocene components are those wherein R^b and R^c are the same and are substituted cyclopentadienyl, preferably wherein the cyclopentadienyl is substituted in the 2-position, the 3-position, or simultaneously the 2-position and the 3-position. Particularly suitable metallocene components are also those wherein R^b and R^c are the same and are selected from the group consisting of unsubstituted indenyl, unsubstituted tetrahydroindenyl, substituted indenyl and substituted tetrahydroindenyl. Particularly suitable metallocene components may also be those wherein R^b is a substituted cyclopentadienyl and R^c is a substituted or unsubstituted fluorenyl.

Non-limiting examples of particularly suitable metallocenes are:

methyl(cyclohexyl)silanediyl-bis[(2-methyl-4-(4-tert-butylphenyl)indenyl]zirconium dichloride; dimethylsilanediyl-bis(cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(2-methyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(3-methyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(2-tert-butyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(3-tert-butyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(2-tert-butyl-5-methyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(3-tert-butyl-5-methyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(2,4-dimethyl- cyclopentadienyl)zirconium dichloride; dimethylsilanediyl-bis(indenyl)zirconium dichloride; dimethylsilanediyl-bis(2-methyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(3-methyl- indenyl)zirconium dichloride; dimethylsilanediyl-bis(2-isopropyl-indenyl)zirconium; dimethylsilanediyl-bis(3-isopropyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(2-tert- butyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(3-tert-butyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(4,7-dimethyl-indenyl)zirconium dichloride; dimethylsilanediyl- bis(2,7-dimethyl-4-isoproyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(2-methyl-4,6- diisoproyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(tetrahydroindenyl)zirconium dichloride; dimethylsilanediyl-bis(benzindenyl)zirconium dichloride; dimethylsilanediyl-bis(2- methyl-4,5-benzindenyl)zirconium dichloride; dimethylsilanediyl-bis(2 -ethyl-4, 5- benzindenyl)zirconium dichloride; dimethylsilanediyl-bis(3,3'-2-methyl-benzindenyl)zirconium dichloride; dimethylsilanediyl-bis(4-phenyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(2- methyl-4-phenyl-indenyl)zirconium dichloride; dimethylsilanediyl-bis(2-ethyl-4-phenyl- indenyl)zirconium dichloride; dimethylsilanediyl-bis(2-methyl-4-isopropyl-indenyl)zirconium dichloride; dimethylsilanediylbis(2-methyl-4-[3',5'-dimethylphenyl]indenyl)zirconium dichloride; dimethylsilanediylbis(2-methyl-4-[4'-tert-butyl-phenyl]indenyl)zirconium dichloride; diethylsilanediylbis(2-methyl-4-[4'-lert-butylphenyl]indenyl)-zirconium dichloride; dimethylsilanediylbis(2-ethyl-4-[4'-tert-butylphenyl]indenyl)zirconium dichloride; dimethylsilanediylbis(2-propyl-4-[4'-tert-butylphenyl]indenyl)zirconium dichloride; dimethylsilanediylbis(2-isopropyl-4-[4'-tert-butylphenyl]indenyl)zirconium dichloride; dimethylsilanediylbis(2-n-butyl-4-[4'-tert-butylphenyl]indenyl)zirconium dichloride; dimethylsilanediylbis(2-hexyl-4-[4'-tert-butylphenyl]indenyl)zirconium dichloride; ethylene- bis(indenyl)zirconium dichloride; ethylene-bis(tetrahydroindenyl)zirconium dichloride; and isopropylidene-(3-tert-butyl-5-methyl-cyclopentadienyl)(fluorenyl) zirconium dichloride.

The preferred metallocene component to produce the inventive polypropylene are dimethylsilyl- bridged bis(indenyl)zirconium dichloride, and among them dimethylsilyl bridged- bis(indenyl)zirconium dichloride wherein indenyl is substituted, such as: methyl(cyclohexyl)silanediyl-bis[(2-methyl-4-(4-tert-butylphenyl)indenyl]zirconium dichloride, dimethylsilanediyl-bis(2-methyl-indenyl)zirconium dichloride; dimethylsilanediyl- bis(tetrahydroindenyl)zirconium dichloride; dimethylsilanediyl-bis(benzindenyl)zirconium dichloride; dimethylsilanediyl-bis(4-phenyl-indenyl)zirconium dichloride; and dimethylsilanediyl- bis(2-methyl-4-phenyl-indenyl)zirconium dichloride.

The metallocene catalyst may be supported according to any method known in the art. In the event it is supported, the support can be any organic or inorganic solid, particularly porous supports such as talc, inorganic oxides, clays and clay minerals, ion-exchanged layered compounds, diatomaceous earth compounds, zeolites or a resinous support material, such as a polyolefin, for example. Preferably, the support material is an inorganic oxide in its finely divided form. Suitable support materials include solid inorganic oxides, such as silica, alumina, magnesium oxide, titanium oxide, boron trioxide, calcium oxide, zinc oxide, barium oxide, thorium oxide, as well as mixed oxides of silica and one or more Group 2 or 13 metal oxides, such as silica-magnesia and silica-alumina mixed oxides. Silica, alumina, and mixed oxides of silica and one or more Group 2 or 13 metal oxides are preferred support materials. Preferred examples of such mixed oxides are the silica-aluminas. Most preferred is a silica compound. In a preferred embodiment, the metallocene catalyst is provided on a solid support, preferably a silica support. The silica may be in granular, agglomerated, fumed or other form._Preferably, the inorganic support may comprise silica and/or alumina, the silica can be titanated. The inorganic support may comprise from 10 to 100 % by weight of silica and/or preferably from 10 to 100 % by weight of alumina.

In some embodiments, alumoxane is used as an activating agent for the metallocene catalyst. As used herein, the term“alumoxane” and“aluminoxane” are used interchangeably, and refer to a substance, which is capable of activating the metallocene catalyst. In an embodiment, alumoxanes comprise oligomeric linear and/or cyclic alkyl alumoxanes. In a further embodiment, the alumoxane has formula (V) or (VI)

R^X-(AI(R^X)-0)_X-AIR^x ₂ for oligomeric, linear alumoxanes; or

(-AI(R^x)-0-)y for oligomeric, cyclic alumoxanes wherein x is 1 -40, and preferably 10-20; wherein y is 3-40, and preferably 3-20; and wherein each R^x is independently selected from a C-i-Csalkyl, and preferably is methyl. In a preferred embodiment, the alumoxane is methylalumoxane (MAO).

In a preferred embodiment, the metallocene catalyst is a supported metallocene-alumoxane catalyst comprising a metallocene and an alumoxane which are bound on a porous silica support.

The polymerization may be performed in the presence of a co-catalyst. One or more aluminumalkyl represented by the formula AIR^e _t can be used as additional co-catalyst, wherein each R^e is the same or different and is selected from halogens or from alkoxy or alkyl groups having from 1 to 12 carbon atoms and t is from 1 to 3. Non-limiting examples are Tri-Ethyl Aluminum (TEAL), Tri-Iso-Butyl Aluminum (TIBAL), Tri-Methyl Aluminum (TMA), and Methyl- Methyl-Ethyl Aluminum (MMEAL). Especially suitable are trialkylaluminums, the most preferred being triethylaluminum (TEAL), and triisobutylaluminum (TIBAL). The alkyl aluminium can be used in combination with a perfluoroborate e.g. [Ph3C][B(C6F₅)4] or [Me2NPhH][B(C6F₅)4]. For example, using a combination of [Ph3C][B(C6F₅)4]/TIBAL or of [Me2NPhH][B(C6F₅)4]/TIBAL.

The polymerization can be carried out according to known techniques in one or more polymerization reactors. The polymerization is preferably performed in liquid propylene at temperatures in the range from 20 °C to 100 °C. Preferably, temperatures are in the range from 60 °C to 80 °C. The pressure can vary from 5 to 50 bars, preferably from 5 to 40 bars.

The amount of co-monomer to be injected in said one or more polymerization reactors may be determined such as to obtain the required co-monomer content in the polypropylene.

Addition of hydrogen in the polymerization medium may be controlled to prepare said polypropylene. The amount of hydrogen added is determined to obtain the required melt flow index values.

The polymerization of propylene can for example be carried out in liquid propylene as reaction medium (bulk polymerization). It can also be carried out in diluents, such as hydrocarbon that is inert under polymerization condition (slurry polymerization). It can also be carried out in the gas phase. Those processes are well known to one skilled in the art. The slurry process can be carried out in a reactor suitable for such processes, such as continuously stirred tank reactors (CSTRs) or slurry loop reactors (in particular liquid full loop reactors). The pressure in the reactor can vary from 0.5 to 50 bars, preferably from 5 to 40 bars.

According to an embodiment, the polypropylene for use in the 3D printable composition is preferably a polypropylene random copolymer, said polypropylene having the following thermal properties:

the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene, the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene;

- the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene,

wherein the melting peak temperature (T_m), the crystallization temperature (T_c), the onset melting temperature (Tmeit onset) and the start melt temperature (Tmeit start) of the polypropylene are determined using differential scanning calorimetry as described in the specification under the Determination methods.

The skilled man in the art will be able to determine the relevant thermal properties, from the graph obtained from the differential scanning calorimetry (DSC) of the polypropylene, as described in the Determination methods.

In some preferred embodiment, the 3D printed article comprising a 3D printable composition, wherein said 3D printable composition comprises:

at least 90.0 % by weight of a polypropylene, preferably at least 91 .0 % by weight; preferably at least 92.0 % by weight, preferably at least 93.0 % by weight, preferably at least 94.0 % by weight, preferably at least 95.0 % by weight, preferably at least 96.0 % by weight, preferably at least 97.0 % by weight, preferably at least 98.0 % by weight, more preferably at least 98.5 % by weight, more preferably at least 99.0 % by weight, more preferably at least 99.5 % by weight, based on of the total weight of the 3D printable composition; and

wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene, preferably at least 22 °C higher; preferably at least 24 °C higher; preferably at least 25 °C higher; preferably at least 29 °C higher; preferably at least 32 °C higher, preferably at least 34 °C higher than the crystallization temperature (T_c) of the polypropylene;

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene, preferably at most 9 °C higher; preferably at most 8 °C higher; preferably at most 7 °C higher; preferably at most 6 °C higher; preferably at most 5 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, preferably at most 59 °C lower; preferably at most 58 °C lower; preferably at most 57 °C lower; preferably at most 56 °C lower preferably at most 55 °C lower; preferably at most 54 °C; preferably at most 52 °C lower than the melting peak temperature (T_m) of the polypropylene; as determined using differential scanning calorimetry as described in the specification under the Determination methods; and preferably wherein the polypropylene is a polypropylene random copolymer, preferably an isotactic polypropylene random copolymer, comprising at most 8.0 % by weight of comonomer, preferably at most 8.0 % of ethylene as comonomer, relative to the total weight of the polypropylene random copolymer, as determined by ¹³C-NMR analysis; preferably at most 7.0 % by weight; preferably at most 6.0 % by weight; preferably at most 5.0 % by weight; preferably at most 4.0 % by weight; preferably at most 3.0 % by weight of comonomer content,

preferably wherein the content of mmmm pentads in said isotactic polypropylene is at least 60.0 %, preferably at least 65.0 %, preferably at least 70.0 %, preferably at least 75.0 %, preferably at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 % and most preferably of at least 95.0 %, as determined by ¹³C-NMR analysis;

said polypropylene, preferably said polypropylene random copolymer, may have a molecular weight distribution, defined as M_w/M_n, of at most 5.0; preferably at most 4.0; preferably at most 3.8; preferably at most 3.6; preferably of at most 3.2; preferably of at most 3.0, for example from 2.0 to 4.0; preferably from 2.0 to 3.8; preferably from 2.1 to 3.6; preferably of from 2.2 to 3.4; and may have a melt flow index determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and under a load of 2.16 kg of at most 15.0 g/10 min, preferably at most 14.0 g/10 min, preferably at most 13.0 g/10 min, preferably at most 12.0 g/10 min, preferably at least 3.0 g/10 min, preferably at least 5.0 g/10 min, preferably at least 7.0 g/10 min, preferably at least 8.0 g/10 min, preferably at least 9.0 g/10 min, for example from 3.0 to 15.0 g/10 min, preferably from 5.0 to 15.0 g/10 min, preferably from 7.0 to 15.0 g/10 min, preferably of from 7.0 to 14.0 g/10 min, preferably from 7.0 to 13.0 g/10 min, preferably from 8.0 to 12.0 g/10 min, preferably from 9.0 to 12.0 g/10 min.

at least 90.0 % by weight of a polypropylene, preferably at least 91.0 % by weight; preferably at least 92.0 % by weight, preferably at least 93.0 % by weight, preferably at least 94.0 % by weight, preferably at least 95.0 % by weight, preferably at least 96.0 % by weight, preferably at least 97.0 % by weight, preferably at least 98.0 % by weight, more preferably at least 98.5 % by weight, more preferably at least 99.0 % by weight, more preferably at least 99.5 % by weight, based on of the total weight of the 3D printable composition; and

wherein the melting peak temperature (T_m) of the polypropylene is at least 20 °C higher than the crystallization temperature (T_c) of the polypropylene, preferably at least 22 °C higher; preferably at least 24 °C higher; preferably at least 25 °C higher; preferably at least 29 °C higher; preferably at least 32 °C higher, preferably at least 34 °C higher than the crystallization temperature (T_c) of the polypropylene; wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (T_meit onset) of the polypropylene, preferably at most 9 °C higher; preferably at most 8 °C higher; preferably at most 7 °C higher; preferably at most 6 °C higher; preferably at most 5 °C higher than the onset melting temperature (Tmeit onset) of the polypropylene; wherein the start melt temperature (Tmeit start) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, preferably at most 59 °C lower; preferably at most 58 °C lower; preferably at most 57 °C lower; preferably at most 56 °C lower preferably at most 55 °C lower; preferably at most 54 °C; preferably at most 52 °C lower than the melting peak temperature (T_m) of the polypropylene; as determined using differential scanning calorimetry as described in the specification under the Determination methods;

and wherein the polypropylene is an isotactic polypropylene random copolymer, comprising at most 8.0 % by weight of comonomer, preferably at most 8.0 % of ethylene as comonomer, relative to the total weight of the polypropylene random copolymer, as determined by ¹³C-NMR analysis; preferably at most 7.0 % by weight; preferably at most 6.0 % by weight; preferably at most 5.0 % by weight; preferably at most 4.0 % by weight; preferably at most 3.0 % by weight of comonomer content,

wherein the content of mmmm pentads in said isotactic polypropylene is at least 60.0 %, preferably at least 65.0 %, preferably at least 70.0 %, preferably at least 75.0 %, preferably at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 % and most preferably of at least 95.0 %, as determined by ¹³C-NMR analysis;

preferably wherein said isotactic polypropylene random copolymer has a molecular weight distribution, defined as M_w/M_n, of at most 5.0; preferably at most 4.0; preferably at most 3.8; preferably at most 3.6; preferably of at most 3.2; preferably of at most 3.0, for example from 2.0 to 4.0; preferably from 2.0 to 3.8; preferably from 2.1 to 3.6; preferably of from 2.2 to 3.4; and preferably wherein said isotactic polypropylene random copolymer has a melt flow index determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and under a load of 2.16 kg of at most 15.0 g/10 min, preferably at most 14.0 g/10 min, preferably at most 13.0 g/10 min, preferably at most 12.0 g/10 min, preferably at least 3.0 g/10 min, preferably at least 5.0 g/10 min, preferably at least 7.0 g/10 min, preferably at least 8.0 g/10 min, preferably at least 9.0 g/10 min, for example from 3.0 to 15.0 g/10 min, preferably from 5.0 to 15.0 g/10 min, preferably from 7.0 to 15.0 g/10 min, preferably of from 7.0 to 14.0 g/10 min, preferably from 7.0 to 13.0 g/10 min, preferably from 8.0 to 12.0 g/10 min, preferably from 9.0 to 12.0 g/10 min.

In some preferred embodiment, the 3D printed article comprising a 3D printable composition, wherein said 3D printable composition comprises: at least 90.0 % by weight of a polypropylene, preferably at least 91 .0 % by weight; preferably at least 92.0 % by weight, preferably at least 93.0 % by weight, preferably at least 94.0 % by weight, preferably at least 95.0 % by weight, preferably at least 96.0 % by weight, preferably at least 97.0 % by weight, preferably at least 98.0 % by weight, more preferably at least 98.5 % by weight, more preferably at least 99.0 % by weight, more preferably at least 99.5 % by weight, based on of the total weight of the 3D printable composition; and

said isotactic polypropylene random copolymer having a melt flow index determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and under a load of 2.16 kg of at most 15.0 g/10 min, preferably at most 14.0 g/10 min, preferably at most 13.0 g/10 min, preferably at most 12.0 g/10 min, preferably of at least 3.0 g/10 min and at most 15.0 g/10 min, preferably at least 5.0 g/10 min, preferably at least 7.0 g/10 min, preferably at least 8.0 g/10 min, preferably at least 9.0 g/10 min, for example from 3.0 to 15.0 g/10 min, preferably from 5.0 to 15.0 g/10 min, preferably from 7.0 to 15.0 g/10 min, preferably of from 7.0 to 14.0 g/10 min, preferably from 7.0 to 13.0 g/10 min, preferably from 8.0 to 12.0 g/10 min, preferably from 9.0 to 12.0 g/10 min; and

preferably wherein said isotactic polypropylene random copolymer has a molecular weight distribution, defined as M_w/M_n, of at most 5.0; preferably at most 4.0; preferably at most 3.8; preferably at most 3.6; preferably of at most 3.2; preferably of at most 3.0, for example from 2.0 to 4.0; preferably from 2.0 to 3.8; preferably from 2.1 to 3.6; preferably of from 2.2 to 3.4.

wherein the content of mmmm pentads in said isotactic polypropylene is of at least 60.0 %, preferably at least 65.0 %, preferably at least 70.0 %, preferably at least 75.0 %, preferably at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 % and most preferably of at least 95.0 %, as determined by ¹³C-NMR analysis;

said isotactic polypropylene random copolymer having a molecular weight distribution, defined as M_w/M_n, of at most 5.0; preferably at most 4.0; preferably at most 3.8; preferably at most 3.6; preferably of at most 3.2; preferably of at most 3.0, for example from 2.0 to 4.0; preferably from 2.0 to 3.8; preferably from 2.1 to 3.6; preferably of from 2.2 to 3.4.

at least 96.0 % by weight, preferably at least 97.0 % by weight, preferably at least 98.0 % by weight, more preferably at least 98.5 % by weight, more preferably at least 99.0 % by weight, more preferably at least 99.5 % by weight, based on of the total weight of the 3D printable composition; and

wherein the melting peak temperature (T_m) of the polypropylene is at most 10 °C higher than the onset melting temperature (T_{meit onset}) of the polypropylene, preferably at most 9 °C higher; preferably at most 8 °C higher; preferably at most 7 °C higher; preferably at most 6 °C higher; preferably at most 5 °C higher than the onset melting temperature (T_{meit onset}) of the polypropylene; wherein the start melt temperature (T_{meit start}) of the polypropylene is at most 60 °C lower than the melting peak temperature (T_m) of the polypropylene, preferably at most 59 °C lower; preferably at most 58 °C lower; preferably at most 57 °C lower; preferably at most 56 °C lower preferably at most 55 °C lower; preferably at most 54 °C; preferably at most 52 °C lower than the melting peak temperature (T_m) of the polypropylene; as determined using differential scanning calorimetry as described in the specification under the Determination methods;

wherein the content of mmmm pentads in said isotactic polypropylene is of at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 % and most preferably of at least 95.0 %, as determined by ¹³C-NMR analysis;

said isotactic polypropylene random copolymer having a molecular weight distribution, defined as M_w/M_n, of at most 4.0; preferably at most 3.8; preferably at most 3.6; preferably of at most 3.2; preferably of at most 3.0, for example from 2.0 to 4.0; preferably from 2.0 to 3.8; preferably from 2.1 to 3.6; preferably of from 2.2 to 3.4.

Optional additives

In some embodiments, the 3D printable composition further comprises at least one antioxidant. In some embodiments, the 3D printable composition comprises two or more antioxidants. Suitable antioxidants may be found in Zweifel, Hans, ISBN 354061690X, Springer-Verlag 1998. Preferred antioxidants for use in the 3D printable composition can be chosen among:

(i) hindered phenols,

(ii) hindered amine light stabilizers (HALS), (iii) hindered amine light stabilizers comprising steri cally hindered phenol moieties, and

(iv) mixtures of at least two antioxidants independently chosen from groups (i) to (iii).

Preferred hindered phenol antioxidants are lrganox®1010 and lrgafos®168, as shown below.

Irganox®1010: lrgafos®168:

Preferred hindered amine light stabilizers (HALS) include those comprising a 2, 2,6,6- tetramethylpiperidine moiety and derivatives thereof, including polymers containing them, such as polymethylsiloxane polymers.

Preferred hindered amine light stabilizers comprising steri cally hindered phenol moieties include for example, Tinuvin® 144; Tinuvin® 622 SF, Tinuvin® 770 DF; Cyasorb® UV 3853, Cyasorb® UV 3529, Cyasorb® UV 3346, as shown below.

Tinuvin® 144 Tinuvin® 622 SF

In some embodiments, the 3D printable composition further comprises from 300 to 2000 ppm by weight of at least one antioxidant; preferably comprises from 305 to 1800 ppm by weight; preferably comprises from 315 to 1600 ppm by weight; preferably comprises from 325 to 1500 ppm by weight; preferably comprises from 335 to 1400 ppm by weight; preferably comprises from 345 to 1200 ppm by weight. In some embodiments, the 3D printable composition further comprises an additive selected from the group consisting of 1 , 4, 5, 6, 7, 7-hexachlorobicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic acid (CAS No. 1 15-28-6) and isoleucine (CAS No. 73-32-5).

In some embodiments, the 3D printable composition further comprises from 0.05 to 0.1 % by weight of isoleucine based on the total weight of the 3D printable composition; preferably from 0.06 to 0.09 % by weight; preferably from 0.07 to 0.09 % by weight of isoleucine based on the total weight of the 3D printable composition.

In some embodiments, the 3D printable composition further comprises from 0.10 to 0.40 % by weight of 1 , 4, 5, 6, 7, 7-hexachlorobicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic acid based on the total weight of the 3D printable composition; preferably from 0.12 to 0.37 % by weight; preferably from 0.14 to 0.35 % by weight of 1 , 4, 5, 6, 7, 7-hexachlorobicyclo [2.2.1] hept-5-ene-2, 3- dicarboxylic acid based on the total weight of the 3D printable composition.

Preparing the 3D printable composition

Any process known in the art can be applied for preparing the 3D printable composition used in the invention.

The polypropylene and any other optional additives (for example antioxidant) may be mixed and/or blended either in dry form or in the melt.

According to one embodiment, the polypropylene and other optional additives are first dry mixed together to form an essentially homogeneous dry blend which is further supplied either simultaneously or in a sequence to a melt processing device to form a homogeneous melted blend.

According to another embodiment, the polypropylene and other optional additives are directly melt blended in a batch process such as with a Banbury, Haake or Brabender Internal mixer or in a continuous process, such as in an extruder e.g. a single or a twin screw extruder to form a homogeneous mixture while providing temperature conditions so as to melt the blend components and initiate chemical and physical interactions between the components. Particularly suitable melt processing device may be a co-rotating, twin screw extruder.

In one embodiment, the 3D printable composition is prepared by extrusion at a temperature ranging from 170 °C to 230 °C.

In a preferred embodiment, the residence time in the extruder is at most 30 minutes, more preferably at most 20 minutes, more preferably at most 10 minutes, more preferably at most 8 minutes, more preferably at most 5 minutes, for example at most 4 min, for example at most 3 min; for example at most 2 min. As used herein, the term“residence time” refers to the time wherein the mixture is present in the extruder, or is present in a series of extruders In an embodiment, the 3D printable composition is prepared by melt blending the components at a temperature ranging from 150 °C to 230 °C, for example from 150 °C to 200 °C, preferably for example from 150 °C to 180 °C.

After melt blending, according to one embodiment, the resulting blend is extruded directly through a die and pelletized.

In an embodiment, the resulting pellets are ground to a powder. Any method known in the art may be used to grind the pellets to a powder. Suitable grinding methods include cooling or chilling the pellets and then grinding them preferably with a mill; this process is also known as cryogenic grinding. Particularly suitable grinding method is cryogenic grinding using liquid nitrogen to cool or chill the pellets.

In an embodiment the powder has a mean particle size D50 of from 60 pm to 85 pm, preferably from 62 to 83 pm, more preferably from 65 to 80 pm.

In another embodiment, the 3D printable composition used in the invention may further comprise additives to impart desired physical properties, such as e.g. flow agent, dyes, fillers. These additives may be included in amounts effective to impart desired properties. The additives may be mixed with the resulting powder after the grinding step described herein.

In order to improve flow during the printing process, a flow agent can be added to the 3D printable composition according to the present invention. Preferably this flow agent is of substantially spherical shape. The flow agent can for instance be an inorganic powdered substance having a particle size of less than 20 pm, preferably less than 10 pm, selected from the group consisting of hydrated silicas, amorphous alumina, glassy silicas, glassy phosphates, glassy borates, glassy oxides, titania, talc, mica, fumed silicas, kaolin, attapulgite, calcium silicates, alumina, magnesium silicates and/or mixtures thereof. The flow agent is present only in an amount sufficient to cause the 3D printable composition to flow and level during the layer by layer process employed in the 3D printing process. It is preferred that the 3D printable composition according to the present invention comprises less than 5.0 % by weight of flow agent, more preferably from 0.05 to 2.0 % by weight of flow agent, particularly preferably from 0.05 to 1.0 % by weight of flow agent based on the total weight of the 3D printable composition.

Suitable dyes include azo dyes such as aniline blue, metal phthalocyanines such as copper or vanadium phtalocyanine and K2Fe(CN)6. The dyes may be added to the 3D printable composition in the form of a solution in a solvent that is compatible with polypropylene.

Three-dimensional printing (3D printing)

The present inventors have surprisingly found that the 3D printable composition may be used in the manufacture of 3D printed articles. The 3D printable composition may be employed as the build material that forms the three-dimensional article and structures. In some embodiments, the 3D printable composition is supplied to a three-dimensional printer in the form of a powder. Any of a variety of three-dimensional printer systems can be employed in the present invention. Particularly suitable printer systems are selective laser sintering and multi jet fusion processes. In these processes, the 3D printable composition can be generally supplied under the form of powder. Such powder may, for example, have a mean particle size D50 of from 60 pm to 85 pm, preferably from 62 to 83 pm, more preferably from 65 to 80 pm. The 3D printable composition under powder form can be generally included within a printer cartridge that is readily adapted for incorporation into the printer system.

Typically, the laser sintering process proceeds as follows: the part to be produced is represented by a 3D CAD (computer aided design) file (usually in .stl format), the file is sliced into discrete layers, each slice representing a cross-section of the part; a thin layer of powder is spread over the build area, and a computer-controlled laser scans over this area, heating and consolidating the powder particles in specified areas corresponding to a given cross-sectional slice of the CAD model. Between layers, the platform on which the part is built (“build platform”) is lowered by a small, predetermined increment (typically 0.1 mm) and another layer of powder is spread over the previously sintered layer. The process then repeats for all layers that encompass the part until the entire component or part has been fabricated. The powder in each layer that has not been consolidated by the laser remains in place to support the subsequent layers. Upon completion of the build, the parts and surrounding supporting material in the build chamber, collectively known as the“part cake”, are removed from the machine. Parts are removed from the part cake and the loose powder is either brushed off or bead-blasted. Unfused powder can be sieved and reused for subsequent builds.

Typically, the multi jet fusion process proceeds as follows: in a preliminary phase, one or more "Build-Units" are filled with the printing powder (usually a mixture of virgin and recycled powder from previous work); this is done by inserting each "Build-Unit" to be filled in the reserved space of the "Processing Station". The ratio of virgin/ recycled printing powder is programmed by the operator. The additional volume of powder to be injected into the "Build-Unit" is determined by means of a level probe. The filling is done automatically by suction from the feed tanks and the recycled powder drum. A full "Build-Unit" (mounted on a wheeled cart) is then inserted by the operator into the central space of the printing machine. The print job begins with the creation of a 15-20 mm thick primer, which is also used for calibrating IR lamps and fusion and finishing agent injection nozzles. Control parts are produced at the bottom of the "Build-Unit" during this calibration step. After calibration is complete, the printing process can begin. Once the print job is complete, the "Build-Unit" is extracted from the printer and reinserted into the "Processing Station" for rapid cooling of the printed powder, followed by automatic vacuuming of the unused powder. The present invention also encompasses a 3D printed article prepared using a process according to invention. The resulting article has a greater nominal elongation at break and is lighter as compared with those produced with commercially available polyamides.

The 3D articles are particularly useful for the automotive industry, the aerospace industry, the medical and dental industries, the electronic industry, the sports industry, orthopedic products.

The present invention can be further illustrated by the following examples, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLES

Unless otherwise indicated, all percentages in the following examples, as well as throughout the specification, are percentages by weight (wt.%).

Determination methods

The melt flow rate (MFR) of the polypropylene was determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C and a 2.16 kg load, using a die of 2.096 mm.

The melt flow rate of the 3D printable composition was determined according to ISO 1 133:2005 Method B, condition M, at a temperature of 230 °C under 2.16 kg load, using a die of 2.096 mm.

Density of the polypropylene was measured according to ISO 1 183:2004.

The molecular weight (M_n (number average molecular weight), M_w (weight average molecular weight) and molecular weight distributions D (M_w/M_n), and D’ (M_z/M_w) were determined by size exclusion chromatography (SEC) and in particular by IR-detected gel permeation chromatography (GPC) at high temperature (145 °C). Briefly, a GPC-IR5MCT from Polymer Char was used: 10 mg polymer sample was dissolved at 160 °C in 10 ml of trichlorobenzene stabilized with 1000 ppm by weight of butylhydroxytoluene (BHT) for 1 hour. Injection volume: about 400 pi, automatic sample preparation and injection temperature: 160 °C. Column temperature: 145 °C. Detector temperature: 160 °C. Column set: two Shodex AT-806MS (Showa Denko) and one Styragel HT6E (Waters), columns were used with a flow rate of 1 ml/min. Mobile Phase: trichlorobenzene stabilized with 1000 ppm by weight of butylhydroxytoluene (BHT) filtered through a 0.45 pm PTFE filter. Detector: Infrared detector (2800-3000 cm ¹) to measure the concentration, one narrow filter center based at 2928 cm ¹, and one narrow filter center based at 2959 cm ¹. Calibration: narrow standards of polystyrene (PS) (commercially available).

Calculation for polypropylene of molecular weight M, of each fraction i of eluted polymer is based on the Mark-Houwink relation log-io(Mpp) = log-io(Mps) - 0.25323 (cut off on the low molecular weight end at MPP = 1000). The molecular weight averages used in establishing molecular weight/property relationships are the number average (M_n), weight average (M_w) and z-average (M_z) molecular weight. These averages are defined by the following expressions and are determined form the calculated M,:

Here N, and W, are the number and weight, respectively, of molecules having molecular weight M,. The third representation in each case (farthest right) defines how one obtains these averages from SEC chromatograms hi is the height (from baseline) of the SEC curve at the i_th elution fraction and M, is the molecular weight of species eluting at this increment.

Co-monomer content of the polypropylene random copolymer: The percentage by weight of ethylene incorporated in the polypropylene random copolymer was determined using ¹³C-NMR.

The sample was prepared by dissolving a sufficient amount of polymer in 1 ,2,4-trichlorobenzene (TCB 99 % spectroscopic grade) at 130 °C and occasional agitation to homogenize the sample, followed by the addition of hexadeuterobenzene (ΰbϋb, spectroscopic grade) and a minor amount of hexamethyldisiloxane (HMDS, 99.5+ %), with HMDS serving as internal standard. To give an example, about 600 mg of polymer were dissolved in 2.0 ml of TCB, followed by addition of 0.5 ml of ΰbϋ_q and 2 to 3 drops of HMDS.

¹³C-NMR signal was recorded on a Bruker 500 MHz with a 10 mm probe using the conditions listed in Table 1.

Table 1

1³C{¹H}-NMR spectrum was obtained by Fourier Transform on 131 K points after a light Gaussian multiplication. Spectrum was phased, baseline corrected and chemical shift scale was referenced to the internal standard HMDS at 2.03 ppm. Chemical shifts of signals are peak picked and peaks are integrated shown in Figure 1 and in the following Table 2.

Table 2

Chemical shits are given at +/- 0.05 ppm.

The main peak A is indicative of 1 ,2 PP units.

Peak I is indicative of 1 ,3 PP units.

Peaks B, C, D, E, F, G, H are indicative of 2,1 PP units.

Peaks T, U, V, W, X, Y are indicative of ethylene incorporation in 1 ,2 PP unit

Peaks P, Q, R, S are indicative of ethylene incorporation after 2,1 PP unit

The_% by weight of the ethylene content is obtained by the following areas (A) combination

AC32,1 ⁼ (AB + Ac + AD + AE + AF + AG + AH)/7 + (0.5^*Ap + 0.5*AQ + 0.5^*As)/3

AC31,3 = A_| / 2

A_C2 EI 1,2 = (0.5^* A_T + A_Y)/2

AC2 E2 1,2 = (Au -Ai + A_x)/2 - A_v

AC2 E3 1,2 = ((Au -Ai + AT)*0.5 + (Ax - Av)^*0.5 + Av + Aw + Ac + Ag)/2 - Ac2 EI 1,2 -Ac2 E21,2

AC22,1 ⁼ (0.5^*Ap + 0.5*AQ + 0.5*AS + AR)/4

AC2 = (AC2 E1 1,2 + AC2 E21,2 + Ac2 E31,2 + Ac22,l)

AC3 = (Ac31,2 + AC32,1 + Ac31,3)

% (wt.) Ethylene (C2) = (28 ^* A_C2) / (28 ^* A_C2 + 42 ^* Acs) x 100

The term "tacticity" refers to the arrangement of pendant groups in a polymer. For example, a polymer is "atactic" when its pendant groups are arranged in a random fashion on both sides of the chain of the polymer. In contrast, a polymer is "isotactic" when all of its pendant groups are arranged on the same side of the chain and "syndiotactic" when its pendant groups alternate on opposite sides of the chain.

The tacticity was determined by ¹³C-NMR. The ¹³C-NMR analysis was performed at an operative frequency of 125 MHz using a 500 MHz Bruker NMR spectrometer with a high temperature 10 mm cryoprobe under conditions such that the signal intensity in the spectrum is directly proportional to the total number of contributing carbon atoms in the sample. Such conditions are well known to the skilled person and include for example sufficient relaxation time, etc. In practice, the intensity of a signal is obtained from its integral, i.e. the corresponding area. The data were acquired using proton decoupling, 240 scans per spectrum, a pulse repetition delay of 1 1 seconds and a spectral width of 26000 Hz at a temperature of 130 °C. The sample was prepared by dissolving a sufficient amount of polymer in 1 ,2,4-trichlorobenzene (TCB, 99 %, spectroscopic grade) at 130 °C and occasional agitation to homogenize the sample, followed by the addition of hexadeuterobenzene (Obϋb, spectroscopic grade) and a minor amount of hexamethyldisiloxane (HMDS, 99.5+ %), with HMDS serving as internal standard. To give an example, about 200 mg of polymer were dissolved in 2.0 ml. of TCB, followed by addition of 0.5 ml. of Obϋb and 2 to 3 drops of HMDS.

Following data acquisition, the chemical shifts were referenced to the signal of the internal standard HMDS, which was assigned a value of 2.03 ppm.

The isotacticity of a homopolymer is determined by ¹³C-NMR analysis on the total polymer. In the spectral region of the methyl groups the signals corresponding to the pentads mmmm, mmmr, mmrr and mrrm are assigned using published data. Only the pentads mmmm, mmmr, mmrr and mrrm are taken into consideration due to the weak intensity of the signals corresponding to the remaining pentads. For the signal relating to the mmrr pentad a correction is performed for its overlap with a methyl signal related to 2,1 -insertions. The percentage of mmmm pentads is then calculated according to

% mmmm = AREAmmmm / (AREAmmmm + AREAmmmr + AREAmmrr + AREAmrrm) ^* 100

The regiodefects content in the polypropylene is the percentage of 2,1 -insertions in the polypropylene. The determination of the percentage of 2,1 -insertions is detailed herein with respect to ethylene as co-monomer but can be applied with other co-monomers.

The determination of the percentage of 2,1 -insertions for a polypropylene random copolymer with ethylene as comonomer is determined by two contributions:

(i) the percentage of 2,1 -insertions as defined above for the propylene homopolymer, and

(ii) the percentage of 2,1 -insertions, wherein the 2,1 -inserted propylene neighbors an ethylene, thus the total percentage of 2,1 -insertions corresponds to the sum of these two contributions. The signals corresponding to the 2,1 -insertions are identified with the aid of published data. A first area, AREA1 , is defined as the average area of the signals corresponding to 2,1 -insertions. A second area, AREA2, is defined as the average area of the signals corresponding to 1 ,2- insertions. The assignment of the signals relating to the 1 ,2-insertions is well known to the skilled person and need not be explained further. The percentage of 2,1 -insertions is calculated according to

2,1 -insertions (in %) = AREA1 / (AREA1 + AREA2) ^* 100 with the percentage in 2,1 -insertions being given as the molar percentage of 2,1 -inserted propylene with respect to total propylene.

The assignments of the signal for case (ii) can be done either by using reference spectra or by referring to the published literature.

The 3D printable composition apparent bulk density was measured according to ISO 1068:1975 at 23 °C. A weighed test portion was filled into a measuring cylinder and densified by means of a specified vibration apparatus. The apparent bulk density was calculated from the weight and the measured volume after densification.

The apparent density of the 3D printable composition was measured according to ISO 61 :1976 at 23 °C. A portion of 60 g of material was dropped little by little into a measuring cylinder as evenly distributed as possible. A plunger with specified mass fitting to the measuring cylinder was slowly lowered until it was entirely supported by the material. After 1 min the volume of the material with the plunger resting upon it, was determined and the apparent density was calculated.

The mean particle size (D50) of the 3D printable composition powder after grinding was measured using ISO 13320:2009, with D50 being defined as the particle size for which fifty percent by volume of the particles has a size lower than the D50. A sample, dispersed at an adequate concentration in a suitable liquid or gas, was passed through the beam of a monochromatic light source, usually a laser. The light scattered by the particles, at various angles, was measured by multi-element detectors, and numerical values relating to the scattering pattern were recorded. These numerical scattering values were then transformed, using an appropriate optical model and mathematical procedure, to yield the proportion of the total volume of particles to a discrete number of size classes forming a volumetric particle size distribution (PSD). The laser diffraction technique for the determination of PSDs is based on the phenomenon that particles scatter light in all directions with an intensity pattern that is dependent on particle size. In addition to particle size, particle shape and the optical properties of the particulate material influence the scattering pattern.

The melting point temperature (T_m) of the 3D printable composition powder after grinding was measured using Differential Scanning Calorimetry (DSC) following ISO 1 1357-3:201 1 as described herein below. The crystallization point temperature (T_c) of the 3D printable composition powder after grinding was measured using Differential Scanning Calorimetry (DSC) following ISO 1 1357-3: 201 1 as described herein below. The start (T_meit start), onset (T_meit onset), peak (T_m) and stop (Tmeit stop) melt temperature, start (T_cryst start), onset (Tcryst onset), peak (T_c) and stop (Tcryst stop) crystallization temperatures of the polypropylene were analyzed by DSC (Differential Scanning Calorimetry) measurement as described herein below.

The“start melt temperature” or“start melting temperature” (Tmeit start ) is the temperature at which the melting starts. The“onset melt temperature” or“onset melting temperature” (T_meit onset) is the temperature at which the tangent drawn from the low temperature side of the melting peak intercepts the peak baseline on a heat flow versus temperature plot. The“melt temperature” (T_m) (also referred as“melting peak temperature”, or“melting point temperature”) is the temperature at which the highest differential heat flow is observed from the corrected heat flow and temperature data. The“stop melt temperature” (T_meit stop ) is the temperature at which the melting ends.

The“start crystallization temperature” (T_cryst start ) is the temperature at which the crystallization starts. The“crystallization onset temperature” (T_cryst onset) is the temperature at which the tangent drawn from the high temperature side of the crystallization peak intercepts the peak baseline on a heat flow versus temperature plot. The“crystallization temperature” (T_c) (also known as“peak crystallization temperature”) is the temperature at which the highest differential heat flow is observed from the corrected heat flow and temperature data. The stop crystallization temperature (T_{cryst sto} ) is the temperature at which the crystallization ends

The above mentioned temperatures were performed on a Q 2000 Differential Scanning Calorimeter (DSC) from TA Instruments. It was calibrated with Indium at 156.50 °C and using T zero mode. The measurements were conducted under nitrogen atmosphere in a closed cup. The sample size was 1 .870 mg. DSC was run according to ISO 1 1357-3:201 1 in a heat / cool / heat cycle with a scan rate of 20 °C/min (heating and cooling) in the temperature range of 30 °C to 220 °C, as described herein below.

The following heating profile was used:

Equilibrate at 40 °C

Heat at 20 °C/min to 220 °C (first heat)

Isothermal for 3 min

Cool down at 20 °C/min to 30 °C (first cool)

Isothermal for 2 min

Heat at 20 °C/min to 220 °C (second heat).

The exothermic peak of crystallization (first cool) was analyzed using the TA Universal Analysis software and the peak crystallization temperature (T_c) corresponding to 20 °C/min cooling rate was determined. The endothermic peak of melting (second heat) was also analyzed using the TA Universal Analysis software and the peak melting temperature (T_m) corresponding to 20 °C/min heating rate was determined.

The heat defection temperature (HDT) was determined according to ISO 75f method A or B. The test specimens having a dimension of 80 x 10 x 4 mm (length x width x thickness) were prepared by injection molding according to EN ISO 1873:2007. The test specimen was loaded in three- point bending in the flatwise direction. The stress used for testing was either 0.455 MPa or 1.82 MPa, and the temperature was increased at 2 °C/min until the specimen deflected 0.25 mm. The heat deflection temperature is the temperature at which a polymer sample deforms under a specified load.

The flexural modulus was determined according to ISO 178:2011 , method A at 23 °C. The test specimens having a dimension of 80 x 10 x 4 mm³ (length x width x thickness) were prepared by injection molding according to EN ISO 1873-2:2007. The length of the span between the supports was 64 mm, the test speed was 2 mm/min and the force was 0.5 N. the conditions are listed in Table 3.

Table 3

Tensile Modulus, Tensile stress at yield, Tensile strain at break, elongation and nominal elongation at break were measured at 23 °C according to ISO 527-2:93-1 B. The test specimens having a dimension of the 1 B type were prepared by injection molding according to EN ISO 1873- 2:2007. The length of the span between the supports was 64 mm, the test speeds were 1 mm/ min (between 0.05 and 0.25 % of strain corresponding to the module calculation), then speed was increased to 50 mm/min. The force was 5 N. The“dumbbell-shaped” test specimens were placed in the grips of a testing machine and subjected to controlled tension until they broke. An extensometer was used to measure specimen parameters.

Charpy impact strength (unnotched) was determined according to ISO 179-1 :1997 eU at 23 °C. The unnotched test specimens having a dimension of 80 x 10 x 4 mm³ (length x width x thickness) were prepared by injection molding according to EN ISO 1873-2:2007. The test speed was 2.9 m / s. The specimen was mounted horizontally and supported unclamped at both ends. The hammer was released and allowed to strike through the specimen. Impact energy was expressed in joules. Impact strength was calculated by dividing impact energy in joules by the area. Charpy Impact is a single point test that measures a materials resistance to impact from a swinging pendulum. Charpy impact is defined as the kinetic energy needed to initiate fracture and continue the fracture until the specimen is broken. The direction of the impact is flatwise.

Example 1

A 3D printable composition was prepared comprising a metallocene-catalyzed polypropylene random co-polymer (PP1 ), lrganox®1010 and lrgafos®168.

Polypropylene PP1 was produced in a loop reactor using a supported metallocene catalyst with dimethylsilanediyl-bis(2-methyl-4-phenyl-indenyl)zirconium dichloride as metallocene component supported on a silica which has been previously activated with MAO (i.e. the support was MAO/S1O2). The reaction conditions for preparing PP1 are given in Table 4.

Table 4

PP1 has a melt flow index of 10 g/10 min (ISO 1133, 230 °C, 2.16 kg), an ethylene content of 2.2 % by weight as determined by ¹³C-NMR, and a density of 0.902 g / cm³ (ISO 1 183). The % of mmmm pentads for PP1 was above 90.0%. The M_w/M_n of PP1 was 2.8, determined by gel permeation chromatography. The mechanical properties of PP1 are shown in Table 5.

Table 5

The start (T_meit start), onset (T_meit onset), peak (T_m) and stop (Tmeit stop) melt temperatures, start (T_cryst start), onset (Tcryst onset), peak (T_c) and stop (Tcryst stop) crystallization temperatures of PP1 were analyzed by DSC as described herein above. The resulting enthalpy curves (Figures 2 and 3) were analyzed. Table 6 shows the peak integration results of the DSC measurements.

Table 6. Thermal properties of PP1

Two commercially available polyamide based grades were used as comparative examples: Polyamide 1 1 (PA1 1 ) and Polyamide 12 (PA12).

PA1 1 is a commercial polyamide-based material for additive manufacturing, produced from castor oil. The mechanical properties of PA1 1 are shown in Table 7.

Table 7

PA12 is a commercial polyamide-based material for additive manufacturing. The mechanical properties of PA12 are shown in Table 8.

Table 8

A 3D printable composition was prepared by extruding the metallocene-catalyzed polypropylene random co-polymer PP1 in the presence of 400 ppm by weight of lrganox®1010 and 400 ppm by weight lrgafos®168 in a twin screw extruder to obtain pellets. Irganox®1010 is a commercial antioxidant (CAS number 6683-19-8), commercially available from BASF Corporation. lrgafos®168 is a commercial antioxidant (CAS number 31570-04-4), commercially available from Ciba.

The extrusion conditions were as follows:

Temperature profile: 210 °C,

- Screw speed: 100 rpm,

Throughput: 100 kg/ h,

67 mm twin screw extruder.

The thus obtained pellets underwent cryogenic grinding within liquid nitrogen to obtain a powder having a mean particle size of 70 pm, as measured using ISO 13320.

The resulting 3D printable composition has an apparent bulk density (powder pack density) of 0.33 g/cm³ as measured according to ISO 1068:1975 at 23 °C, and apparent density of 0.89 g/cm³ as measured according to ISO 61 :1976 at 23 °C. The melt flow rate of the 3D printable composition is 10 g/ 10 min, at 230 °C under a 2.16 kg load according to ISO 1 133:2005 standard test. Table 9 shows the thermal properties of the resulting 3D printable composition, while Table 10 shows its mechanical properties.

Table 9

Table 10

The resulting 3D printable composition has translucent color and is practically non-staining; it has excellent plasticity, high elongation, low moisture absorption and durability.

Once the powder had returned to room temperature, it was used for additive manufacturing in a process involving a selective laser sintering (SLS) printer. The SLS printing process was performed under the following conditions: • Work under inert atmosphere

• Preheating of powder 2 hours at 130 °C

• Energy density (ED): 14 to 21 mJ/mm² with Laser Power=13 W, scan speed=2.5 m/s, scan spacing=0.25 mm

• Layer thickness: 100 to 150 pm

• Recycling rate of powder: 80%

The 3D articles formed with the present 3D printable composition show a greater nominal elongation at break (7 to 127 % greater), than those printed with commercially available polyamide base grades such as PA1 1 and PA12. The 3D articles formed with the present 3D printable composition are lighter as compared with those produced with commercially available polyamides.

Claims

1. A 3D printed article comprising a 3D printable composition comprising

2. The 3D printed article according to claim 1 , wherein the polypropylene is a metallocene- catalyzed polypropylene.

3. The 3D printed article according to any one of claims 1 to 2, wherein the comonomer is ethylene.

4. The 3D printed article according to any one of claims 1 to 3, wherein the polypropylene has a melt flow index of from 7.0 to 15.0 g/10 min, as determined according to ISO 1133:2005, Method B, condition M, at 230 °C and under a load of 2.16 kg.

5. The 3D printed article according to any one of claims 1 to 4, wherein the polypropylene has an M_w/M_n of at most 4.0, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight.

6. The 3D printed article according to any one of claims 1 to 5, wherein the polypropylene is isotactic, preferably having a content of mmmm pentads of at least 60.0 %, preferably at least 70.0 %, preferably at least 80.0 %, more preferably at least 90.0 %, as determined by ¹³C- NMR analysis.

7. The 3D printed article according to any one of claims 1 to 6, wherein the 3D printable composition further comprises at least one antioxidant, preferably from 300 to 2000 ppm by weight of at least one antioxidant.

8. A process for producing a 3D printed article, the process comprising the steps of:

(a) providing a 3D printable composition comprising: at least 90.0 % by weight of a polypropylene based on the total weight of the 3D printable composition;

9. The process according to claim 8, wherein the 3D printed article is an article according to any one of claims 1 to 7.

10. The process according to any one of claims 8 to 9, wherein the 3D printable composition is provided as a powder.

1 1. The process according to any one of claims 8 to 10, wherein the 3D printable composition is provided as a powder having a mean particle size D50 value within the range of from 65 pm to 80 pm.

12. The process according to any one of claims 8 to 11 , wherein the 3D printable composition is first provided as pellets which are then ground into powder.

13. The process according to any one of claims 8 to 12, wherein the 3D printing is performed using laser sintering printing (SLS) or infrared multi jet fusion printing.

14. Use of a 3D printed article according to any one of claims 1 to 7 for the automotive industry, the aerospace industry, the medical and dental industries, the electronic industry, the sports industry.

15. Use of a composition as defined in any one of claims 1 to 7 for the manufacture of an article by 3D printing process.