WO2021214664A1

WO2021214664A1 - Particles including polytetrafluoroethylene and process for making a three-dimensional article

Info

Publication number: WO2021214664A1
Application number: PCT/IB2021/053263
Authority: WO
Inventors: Fee ZENTIS; Karoline Anna OSTROWSKI; Harald Kaspar; Klaus Hintzer; Andreas M. GELDMACHER
Original assignee: 3M Innovative Properties Company
Priority date: 2020-04-21
Filing date: 2021-04-20
Publication date: 2021-10-28

Abstract

Particles of a polytetrafluoroethylene for use in additive manufacturing. The polytetrafluoroethylene includes first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether. The second polymerized units are present in an amount not more than one percent by weight based on the total weight of the first polymerized units and the second polymerized units. The particles have a melt flow index of at least 0.5 gram/10 minutes (372 ˚C/5 kg) and a melting point of at least 316 ˚C, measured after the first melting and crystallization of the particles. The polytetrafluoroethylene may have a core and a shell, in which the shell has a greater amount of the second polymerized units than the core. A process for making a three-dimensional article using the particles, a three-dimensional article made by the process, and use of the particles for selective laser sintering are also disclosed.

Description

PARTICLES INCLUDING POLYTETRAFLUOROETHYLENE AND PROCESS FOR MAKING

A THREE-DIMENSIONAL ARTICLE

Cross-Reference to Related Application

This application claims priority to U.S. Provisional Application No. 63/013,313, filed April 21, 2020, the disclosure of which is incorporated by reference in its entirety herein.

Background

Polytetrafluoroethenes (PTFEs, also often referred to as polytetrafluoroethylenes) have found wide application due to their high chemical inertness, low friction properties, non-stick properties, high melting points and thus high service temperatures and thermal stability. These properties have made PTFEs a material of choice for making protective coatings; sealing materials like valves, washers, and O- rings; implants; insulators; membranes; films; and gaskets for use in household applications, architecture, and the medical, chemical, aircraft, and automotive industries.

According to international industry standards tetrafluoroethene (TFE) homopolymers and copolymers with up to one percent by weight of other perfluorinated monomers can be called PTFE (see, for example, DIN EN ISO 12086-1). Furthermore, to qualify as PTFE, the polymers have a melting point within the range of 327 +/-10 °C.

To have mechanical properties suitable for making shaped articles, the PTFE polymers typically have a high molecular weight (e.g., at least 10⁶ g/mole). However, PTFE polymers at such high molecular weight also have a very high melt viscosity and a melt flow index (MFI) of less than 0.1 gram per 10 minutes at 372 °C using a 5 kg load (MFI 372/5 of 0 g /10 min). Fluoropolymers with an MFI (372/5) of less than 0.1 gram per 10 minutes are considered not melt-processable. They cannot be processed from the melt by ordinary melt-processing techniques such as melt extrusion or injection molding. Therefore, to make shaped articles from PTFE special processing techniques (e.g., ram extrusion or cold compression molding and sintering) are typically used. Typically, PTFE’s are processed by preparing blocks, which are then sintered to fuse the polymer particles. The sintered billets are then skived or machined into shaped articles. These techniques may lead to inhomogeneous products containing cavities as a result of imperfect fusion of the PTFE particles during sintering. Furthermore, machining and skiving methods are economically inefficient because they produce considerable amounts PTFE waste.

Melt-processable fluoropolymers include copolymers of relatively high amounts of perfluoro alkyl vinyl ethers (PAVEs) with TFE. Typical amounts of copolymers range from one to five mole percent, which corresponds to 1.7 to 8.4 weight % in case of perfluoro methyl vinyl ether (PMVE) - the smallest of the perfluoro alkyl vinyl ethers. These types of fluoropolymers are referred to in the art as “PFAs”. PFAs have a molecular weight of 1 to 5 x 10⁵ g/mol and a melting point between 300 °C and 315 °C (Modem Fluoropolymers, John Schiers, Wiley& Sons New York, 1998, pp 223 to 232). PFAs are melt-processable with sufficient mechanical properties to make shaped articles. However, due to their lower melting point they have a lower service temperature and thermal stability than PTFEs.

In a different field, the technology of sintering polymer powders under a laser beam is used for the manufacture of objects in three dimensions. In the process, a layer of polymer powder is deposited on a horizontal plate held in a chamber heated to a temperature lying between the crystallization temperature Tc and the melting point Tm of the powder. The laser sinters powder particles at various points of the powder layer according to a geometry corresponding to the object, for example, using a computer which has the shape of the object in its memory and which reconstructs it in the form of slices. The horizontal plate is subsequently lowered by a value corresponding to the thickness of a layer of powder (e.g., between 0.05 mm and 2 mm and generally of the order of 0.1 mm), and then a new layer of powder is deposited and the laser sinters powder particles according to a geometry corresponding to this new slice of the object. The procedure is repeated until the complete object has been manufactured. A block of powder consisting of polymer powder and melt is obtained within which the object is present, with the parts that have not been sintered remaining in a powder form. Subsequently, the combination is cooled, and the object solidifies as its temperature falls below the crystallization temperature Tc. After cooling, the object is separated from the powder, which can be recycled and used in another sintering operation.

In Int. Pat. Appl. Pub. No. WO 2007/133912 (Audenaert et al.) selective laser sintering (SLS) of certain thermoplastic fluoropolymers (PVDF and PCTF) are described. In CN103709737, published April 9, 2014, and CN 105711104, published June 29, 2016, methods for SLS are described where the use of PTFE is mentioned. CN106009430, published October 12, 2016, a polytetrafluoroethylene powder material for SLS is described, which includes inter alia 100 parts of polytetrafluoroethylene and 30 parts of high-density polyethylene. The 3D-printing of aqueous PTFE-dispersions in the presence of UV- curable acrylates has been described in U.S. Pat. Appl. Pub. No. 2019/0022928 (Bartow et al.) and Int.

Pat. Appl. Pub. No. WO 2019/006266 (Bartow et al.).

Summary

While the 3D-printing of aqueous PTFE-dispersions in the presence of UV-curable acrylates is useful, it requires extra processing steps (e.g., evaporating solvents and burning off the acrylate binder). Selective laser sintering of fluoropolymer-powders is presently restricted to traditional melt-processable thermoplastics such as PFA and PVDF. The present disclosure provides particles of PTFE useful, for example, for SLS applications. Compared to PFA, the melting point of these particles can be at least 10 °C to 20 °C higher, which allows for higher service temperatures and parts with higher thermal stability.

In general, particles with a high MFI show good fusion properties and fuse into a dense, solid layer. However, such particles are prone to poor resolution. Using particles with a low MFI in a SLS process results in good dimensional resolution of parts but with densities much lower than expected for a solid part. While typical PTFE particles, which have an MFI of less than 0.1 gram per 10 minutes (372 °C / 5 kg), will not fuse into a solid part, the particles of the present disclosure have a MFI of at least 0.5 gram/10 minutes (372 °C/5 kg), which allows for particle fusion. Typically, and advantageously, the particles of the present disclosure can be formed into a solid three-dimensional part with good resolution and with a density within 50% of the density of a solid PTFE part.

In one aspect, the present disclosure provides particles of a polytetrafluoroethylene for use in additive manufacturing. The polytetrafluoroethylene includes first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether. The second polymerized units are present in an amount not more than one percent by weight based on the total weight of the first polymerized units and the second polymerized units. The particles have a melt flow index of at least 0.5 gram/10 minutes (372 °C/5 kg) and a melting point of at least 316 °C, measured after the first melting and crystallization of the particles.

In another aspect, the present disclosure provides particles of a polytetrafluoroethylene for use in additive manufacturing. The polytetrafluoroethylene has a core and a shell and includes first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether. The second polymerized units are present in an amount not more than one percent by weight based on the total weight of the first polymerized units and the second polymerized units in the core and the shell combined, and the shell has a greater amount of the second polymerized units than the core. The particles have a melt flow index of at least 0.5 gram/10 minutes (372 °C/5 kg) and a melting point of at least 316 °C, measured after the first melting and crystallization of the particles.

In another aspect, the present disclosure provides a process for making a three-dimensional article. The process includes subjecting the particles described herein to additive manufacturing, in some embodiments, selective laser sintering.

In another aspect, the present disclosure provides a process for making a three-dimensional article. The process includes providing a layer of the particles described herein in a confined region and selectively treating an area of the layer of the particles by irradiation with a laser beam to fuse at least some of the particles.

In another aspect, the present disclosure provides a three-dimensional article made by such a process.

In another aspect, the present disclosure provides the use of the particles described herein for additive manufacturing, in some embodiments, selective laser sintering.

In this application, terms such as "a", "an" and "the" are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terms "a", "an", and "the" are used interchangeably with the term "at least one". The phrases "at least one of' and "comprises at least one of' followed by a list refers to any one of the items in the list and any combination of two or more items in the list. All numerical ranges are inclusive of their endpoints and integral and non-integral values between the endpoints unless otherwise stated (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

Additive manufacturing, also known as “3D printing”, refers to a process to create a three- dimensional object by sequential deposition of materials in defined areas, typically by generating successive layers of material. The object is typically produced under computer control from a 3D model or other electronic data source by an additive printing device typically referred to as a 3D printer.

"Alkyl group" and the prefix "alk-" are inclusive of both straight chain and branched chain groups and of cyclic groups having up to 30 carbons (in some embodiments, up to 20, 15, 12, 10, 8, 7, 6, or 5 carbons) unless otherwise specified. Cyclic groups can be monocyclic or polycyclic and, in some embodiments, have from 3 to 10 ring carbon atoms.

The term "perfhioroalkyl group" includes linear, branched, and/or cyclic alkyl groups in which all C-H bonds are replaced by C-F bonds.

The phrase "interrupted by one or more -O- groups", for example, with regard to an alkyl or alkylene, or arylalkylene refers to having part of the alkyl or alkylene on both sides of the one or more - O- groups. An example of an alkylene that is interrupted with one -O- group is -CH2-CH2-O-CH2-CH2-.

The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments. It is to be understood, therefore, that the following description should not be read in a manner that would unduly limit the scope of this disclosure.

Brief Description of the Drawings

FIG. 1 illustrates an embodiment of a system for carrying out the process of the present disclosure;

FIG. 2 illustrates another embodiment of a system for carrying out the process of the present disclosure;

FIG. 3 is a schematic illustration of an embodiment of the process of the present disclosure; and

FIG. 4 is a photograph of the article made in Example 2.

Detailed Description

The polytetrafluoroethylene useful for the particles and processes of the present disclosure includes first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether. In some embodiments, the second divalent units are represented by formula

. In this formula Rf is a linear or branched perfluoroalkyl group having from 1 to 8 carbon atoms and optionally interrupted by one or more -O- groups, z is 0, 1 or

2, each n is independently from 1 to 4, and m is 0 or 1. In some embodiments, n is 1, 3, or 4, or from 1 to

3, or from 2 to 3, or from 2 to 4. In some embodiments, n is 1 or 3. In some embodiments, n is 1. When z is 2, the n in the two C_nF2_n groups may be independently selected. However, within a C_nF2_n group, a person skilled in the art would understand that n is not independently selected. C_nF2_n may be linear or branched. In some embodiments, C_nF2_n is branched, for example, -CF2-CF(CF3)-. In some embodiments, C_nF2_n can be written as (CF2)_n, which refers to a linear perfluoroalkylene group. In these cases, the divalent units of this formula are represented by formula

is a linear or branched perfluoroalkyl group having from 1 to 8 (or 1 to 6) carbon atoms that is optionally interrupted by up to 4, 3, or 2 -O- groups. In some embodiments, Rf is a perfluoroalkyl group having from 1 to 4 carbon atoms optionally interrupted by one -O- group. In some embodiments, z is 0, m is 0, and Rf is a linear or branched perfluoroalkyl group having from 1 to 4 carbon atoms. In some embodiments, Rf is a branched perfluoroalkyl group having from 3 to 6 or 3 to 4 carbon atoms. An example of a useful perfluoroalkyl vinyl ether (PAVE) from which these divalent units in which m and z are 0 are derived is perfluoroisopropyl vinyl ether (CF2=CFOCF(CF3)2), also called iso-PPVE. Other useful PAVEs include perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoro-n-propyl vinyl ether. In some embodiments, z is 0, m is 1, and Rf is a linear or branched perfluoroalkyl group having from 1 to 4 carbon atoms. Examples of useful perfluoroalkyl allyl ethers PAAEs include perfluoromethyl allyl ether, perfluoroethyl allyl ether, and perfluoro-n-propyl allyl ether.

In some embodiments, at least one of z is 1 or 2, or Rf is interrupted by one or more -O- groups. PTFEs having the second divalent units in which m is 0 or 1, and at least one of z is 1 or 2, or Rf is interrupted by one or more -O- groups and a melting point of greater than 316 °C are reported to have an MFI of at least 0.6 gram/10 minutes (372 °C/5 kg) and good mechanical properties (see EP 2409998, published January 25, 2012). Divalent units represented by formulas

which m is 0, and at least one of z is 1 or 2, or Rf is interrupted by one or more -O- groups, typically arise from perfluoroalkoxyalkyl vinyl ethers. Suitable perfluoroalkoxyalkyl vinyl ethers (PAOVE) include those represented by formula CF₂=CF[0(CF₂)_n]_zORf and CF2=CF(OC_nF2_n)_zORf, in which n, z, and Rf are as defined above in any of their embodiments. Examples of suitable perfluoroalkoxyalkyl vinyl ethers include CF₂=CFOCF₂OCF₃, CF2=CFOCF₂OCF₂CF3, CF2=CFOCF₂CF₂OCF3, CF₂=CFOCF2CF2CF₂OCF3 CF₂=CF0CF₂CF₂CF₂CF₂0CF3, CF₂=CF0CF₂CF₂0CF₂CF3, CF₂=CF0CF₂CF₂CF₂0CF₂CF3, CF₂=CF0CF₂CF₂CF₂CF₂0CF₂CF3, CF₂=CF0CF₂CF₂0CF₂0CF3, CF₂=CF0CF₂CF₂0CF₂CF₂0CF3, CF₂=CF0CF₂CF₂0CF₂CF₂CF₂0CF₃, CF₂=CF0CF₂CF₂0CF₂CF₂CF₂CF₂0CF₃, CF₂=CF0CF₂CF₂0CF₂CF₂CF₂CF₂CF₂0CF₃, CF₂=CF0CF₂CF₂(0CF₂)₃0CF₃, CF₂=CF0CF₂CF₂(0CF₂)₄0CF₃, CF₂=CF0CF₂CF₂0CF₂0CF₂0CF₃, CF₂=CF0CF₂CF₂0CF₂CF₂CF₃

CF₂=CF0CF₂CF₂0CF₂CF₂0CF₂CF₂CF3, CF₂=CF0CF₂CF(CF3)-0-C₃F₇ (PPVE-2), CF₂=CF(0CF₂CF(CF₃))₂-0-C₃F₇ (PPVE-3), and CF₂= CF(0CF₂CF(CF₃))₃-0-C₃F₇ (PPVE-4). In some embodiments, the perfluoroalkoxyalkyl vinyl ether is selected from CF2=CF0CF20CF3, CF₂=CFOCF₂OCF₂CF3, CF₂=CFOCF₂CF₂OCF3, CF₂=CF0CF₂CF₂CF₂0CF3, CF₂=CF0CF₂CF₂CF₂CF₂0CF3, CF₂=CF0CF₂CF₂CF₂0CF₂CF3, CF₂=CF0CF₂CF₂CF₂CF₂0CF₂CF3, CF₂=CF0CF₂CF₂0CF₂0CF3, CF₂=CF0CF₂CF₂0CF₂CF₂CF₂0CF3, CF₂=CF0CF₂CF₂0CF₂CF₂CF₂CF₂0CF3, CF₂=CF0CF₂CF₂0CF₂CF₂CF₂CF₂CF₂0CF3, CF₂=CF0CF₂CF2(0CF2)30CF3, CF2=CFOCF₂CF2(OCF2)₄OCF3, CF₂=CF0CF₂CF₂0CF₂0CF₂0CF3, and combinations thereof. Many of these perfluoroalkoxyalkyl vinyl ethers can be prepared according to the methods described in U.S. Pat. Nos. 6,255,536 (Worm et al.) and 6,294,627 (Worm et ak). In some embodiments, the PAOVE is perfluoro-3-methoxy-n-propyl vinyl ether.

The divalent units represented by formula

derived from at least one perfluoroalkoxyalkyl allyl ether. Suitable perfluoroalkoxyalkyl allyl ethers include those represented by formula CF2=CFCF2(OC_nF2_n)_zORf, in which n, z, and Rf are as defined above in any of their embodiments. Examples of suitable perfluoroalkoxyalkyl allyl ethers include CF₂=CFCF₂0CF₂CF₂0CF₃, CF₂=CFCF₂0CF₂CF₂CF₂0CF₃, CF₂=CFCF₂OCF₂OCF_3, CF₂=CFCF₂0CF₂0CF₂CF₃, CF₂=CFCF₂0CF₂CF₂CF₂CF₂0CF₃, CF₂=CFCF₂0CF₂CF₂0CF₂CF₃, CF₂=CFCF₂0CF₂CF₂CF₂0CF₂CF₃, CF₂=CFCF₂0CF₂CF₂CF₂CF₂0CF₂CF₃, CF₂=CFCF₂0CF₂CF₂0CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₂CF₂CF₂0CF₃, CF₂=CFCF₂0CF₂CF₂(0CF₂)₃0CF₃, CF₂=CFCF₂0CF₂CF₂(0CF₂)₄0CF₃, CF₂=CFCF₂0CF₂CF₂0CF₂0CF₂0CF₃, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₃, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂0CF₂CF₂CF₃, CF₂=CFCF₂0CF₂CF(CF3)-0-C3F₇ (PPAE-2), and CF₂=CFCF₂(0CF₂CF(CF3))₂-0-C₃F₇. In some embodiments, the perfluoroalkoxyalkyl allyl ether is selected from CF2=CFCF20CF2CF20CF3, CF₂=CFCF₂0CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂0CF3_, CF₂=CFCF₂0CF₂0CF₂CF3, CF₂=CFCF₂0CF₂CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF3, CF₂=CFCF₂0CF₂CF₂CF₂0CF₂CF3, CF₂=CFCF₂0CF₂CF₂CF₂CF₂0CF₂CF3, CF₂=CFCF₂0CF₂CF₂0CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF₂CF₂CF₂0CF3, CF₂=CFCF₂0CF₂CF₂(0CF₂)30CF3, CF₂=CFCF₂OCF₂CF₂(OCF₂)₄OCF3, CF₂=CFCF₂0CF₂CF₂0CF₂0CF₂0CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂CF3, CF₂=CFCF₂0CF₂CF₂0CF₂CF₂0CF₂CF₂CF₃, and combinations thereof. Many of these perfluoroalkoxyalkyl allyl ethers can be prepared, for example, according to the methods described in U.S. Pat. Nos. 5,891,965 (Worm et ah), 6,255,535 (Schulz et ah), and U.S. Pat. No. 4,349,650 (Krespan).

In some embodiments, the fluorinated vinyl ether or the fluorinated allyl ether forming the second polymerized units is perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, perfluoro-3-methoxy-n- propyl vinyl ether, perfluoro-3-methoxy-n-propyl allyl ether, perfluoromethyl allyl ether, perfluoropropyl allyl ether, or a combination thereof. In some embodiments, at least some of the second polymerized units in the PTFEs described herein are derived from a fluorinated bisolefm compound represented by the following formula:

CY2=CX-(CF₂)a-(0-CF2-CF(Z)-)_b-0-(CF2)c-(0-CF(Z)-CF₂)d-(0)e-(CF(A))f-CX=CY2, wherein a is an integer selected from 0, 1, and 2; b is an integer selected from 0, 1, and 2; c is an integer selected from 0, 1, 2, 3, 4, 5, 6, 7, and 8; d is an integer selected from 0, 1, and 2; e is 0 or 1; f is an integer selected from 0, 1, 2, 3, 4, 5, and 6; Z is independently selected from F and CF₃; A is F or a perfluorinated alkyl group; X is independently H or F; and Y is independently selected from H, F, and CF₃. In some embodiments, the fluorinated bisolefm compound is perfluorinated, meaning that X and Y are independently selected from F and CF₃. Examples of useful fluorinated bisolefm compounds include: CF₂=CF-0-(CF₂)₂-0-CF=CF₂, CF₂=CF-0-(CF₂)₃-0-CF=CF₂,

CF₂=CF-0-(CF₂)₄-0-CF=CF₂, CF₂=CF-0-(CF₂)₅-0-CF=CF₂, CF₂=CF-0-(CF₂)₆-0-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)₂-0-CF=CF₂, CF₂=CF- CF₂-0-(CF₂)₃-0-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)₄-0-CF=CF₂,

CF₂=CF-CF₂-0-(CF₂)5-0-CF=CF₂, CF₂=CF- CF₂-0-(CF₂)6-0-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)₂-0-CF₂-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)3-0-CF₂-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)₄-0-CF₂-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)₅-0-CF₂-CF=CF₂, CF₂=CF-CF₂-0-(CF₂)6-0-CF₂-CF=CF₂, CF₂=CF-0-CF₂CF₂-CH=CH₂, CF₂=CF-(0CF₂CF(CF3))-0-CF₂CF₂-CH=CH₂, CF₂=CF-(0CF₂CF(CF3))₂-0-CF₂CF₂-CH=CH₂,

CF₂=CF CF₂-0-CF₂CF₂-CH=CH₂, CF₂=CF CF₂-(OCF₂CF(CF3))-0-CF₂CF₂-CH=CH₂, CF₂=CFCF₂-(0CF₂CF(CF3))₂-0-CF₂CF₂-CH=CH₂, CF₂=CF-CF₂-CH=CH₂, CF₂=CF-0-(CF2)_C-0-CF2-CF2-CH=CH₂ wherein c is an integer selected from 2 to 6, CF₂=CFCF2-0-(CF2)_C-0-CF2-CF2-CH=CH₂ wherein c is an integer selected from 2 to 6, CF₂=CF-(0CF₂CF(CF₃))_b-0-CF(CF₃)-CH=CH₂ wherein b is 0, 1, or 2, CF₂=CF-CF₂-(0CF₂CF(CF₃))_b-0-CF(CF₃)-CH=CH₂ wherein b is 0, 1, or 2,

CH₂=CH-(CF₂)_n-0-CH=CH₂ wherein n is an integer from 1-10, and

CF₂=CF-(CF₂)_a-(0-CF₂CF(CF₃))_b-0-(CF₂)_c-(0CF(CF₃)CF₂)_f-0-CF=CF₂ wherein a is 0 or 1, b is 0, 1, or 2, c is 1, 2, 3, 4, 5, or 6, and f is 0, 1, or 2. In some embodiments, the fluorinated bisolefm compound is CF₂=CF-0-(CF₂)_n-0-CF=CF₂ where n is an integer from 2-6; CF₂=CF-(CF₂)_a-0-(CF₂)_n-0-(CF₂)_b-CF=CF₂ where n is an integer from 2-6 and a and b are 0 or 1 ; or a perfluorinated compound comprising a perfluorinated vinyl ether and a perfluorinated allyl ether.

The amount of the second polymerized units in the PTFEs described herein is not more than 1.0 % by weight, in some embodiments, not more than 0.95%, 0.9%, 0.8%, or 0.75% by weight based on the total weight of first polymerized units and the second polymerized units. In some embodiments, the amount of the second polymerized units in the PTFEs described herein is at least 0.1 % by weight, in some embodiments, at least 0.11%, 0.12%, or 0.13% by weight based on the total weight of first polymerized units and the second polymerized units. Combinations of different second polymerized units may be present in the PTFE; however, the total amounts of the second polymerized units is not more than 1.0 % by weight or any of the amounts listed above.

In some embodiments, the particles of the present disclosure are core-shell particles. Advantageously, the core-shell PTFE particles described herein for SLS, for example, combine the ability to produce parts with high resolution and high density by combining polymers with different flow characteristics within one particle.

A core-shell particle of the present disclosure comprises a core of one composition, which comprises the first polymerized units and optionally the second polymerized units, and a shell of a different composition, which comprises the first polymerized units and a higher amount of the second polymerized units than in the core. The core may contain only the first polymerized units. In some embodiments, the core comprises the second polymerized units in not more than 0.3, 0.2, or 0.1 percent by weight, based on the total weight of the first polymerized units and the second polymerized units. In some embodiments, the amount of the second polymerized units in the core is at least 0.05 % by weight, in some embodiments, at least 0.1% by weight based on the total weight of first polymerized units and the second polymerized units. In some embodiments, the core comprises polymerized units of another perfluorinated olefin (e.g., hexafluoropropylene) in not more than 0.3, 0.2, or 0.1 percent by weight, based on the total weight of the polymerized units. In some embodiments, the amount of the polymerized units of another perfluorinated olefin in the core is at least 0.05 % by weight, in some embodiments, at least 0.1% by weight based on the total weight of first polymerized units and the second polymerized units. In some embodiments, the PTFE core is at least 50% or at least 60% by weight of the core-shell particle.

The shell comprises the first polymerized units and the second polymerized units. In some embodiments, the shell comprises the second polymerized units in not more than five, four, three, or two percent by weight, based on the total weight of the first polymerized units and the second polymerized units. In some embodiments, the shell comprises the second polymerized units in a range from one percent to five percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

Typically, the core has an average diameter of at least 10 nm, 25 nm, 40 nm, or at least 50 nm and up to 100 nm, 125 nm, 150 nm, or 200 nm. The shell may have a variety of useful thicknesses. In some embodiments, the shell has a thickness of at least 1 nm, 2 nm, or 5 nm and at up to 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, or 200 nm. In some embodiments, the shell has a thickness in a range from 1 nm to 50 nm.

The PTFE particles disclosed herein have a melting point of at least 316 °C, 317 °C, 319 °C, 320 °C or at least 321 °C. The melting point is measured by differential scanning calorimetry (DSC) and is taken as the second melting point after a first heating and cooling cycle. Typically, the particles have a melting point in a range from 321 °C and 329 °C. Polymers with a very high content of TFE-units tend to have different melting points when being molten for the first time and after being molten for the first time, in which case the melting point tends to be somewhat lower. However, once the material has been molten the melting point remains constant. In the case of core-shell particles, the particles may or may not have two different melting points after the first heating and cooling cycle. In these instances, the core-shell particles have at least one melting point of at least 316 °C, 317 °C, 319 °C, 320 °C or at least 321 °C. Typically, the particles have at least one melting point in a range from 321 °C and 329 °C. The determination of the melting point by DSC is described in the Examples, below.

The PTFE particles disclosed herein have an MFI (372 °C/5 kg) of at least 0.5 g/10 min. In some embodiments, the PTFE particles have an MFI (372 °C/5 kg) of at least 0.6, 1, 4, 5, or 10 g/10 min. In some embodiments, the PTFE particles have an MFI (372 °C/5 kg) up to about 25 or 30 g/10 min. Outside this range the polymers may be too brittle to have a measurable tensile strength and/or elongation. For the core-shell particles, the polymeric compositions of both the core and shell both contribute to the overall MFI. The determination of the MFI has been described, for example, in DIN EN ISO 1133.

In the case of core-shell particles, the core polymer can have an MFI different from the shell. The MFI of the core can be determined by stopping the polymerization after the core is made and measuring the MFI. Similarly, the shell polymer can be made separately from the core polymer and evaluated by chemical and property analyses. In some embodiments, the core has an MFI (372 °C/5 kg) of at least 0.1 g/10 min. In some embodiments, the core has an MFI (372 °C/5 kg) of at least or up to 0.5, 1, or 2 g/10 min. In these embodiments, the core is considered melt-processable.

The PTFE particles disclosed herein can be made using techniques known in the art, for example, by aqueous emulsion polymerization with or without fluorinated emulsifiers, followed by coagulation of the latex, agglomeration, and typically washing and drying to obtain the particles. Polymerization details can be found, for example, in see EP 2409998, published January 25, 2012.

Adjusting, for example, the concentration and activity of the initiator, the concentration of each of the reactive monomers, the temperature, the concentration of any chain transfer agent, and the solvent using techniques known in the art can control the molecular weight of the fluoropolymer. In some embodiments, the PTFE particles of the present disclosure have a weight average molecular weight greater than 750,000 g/mol or greater than 1,000,000 g/mol. Molecular weight of a fluoropolymer relates to its melt flow index.

Core-shell particles according to some embodiments of the present disclosure can be made by aqueous emulsion polymerization in one step or multiple steps, for example. The monomer composition may be changed during the polymerization process, resulting in a core-shell structure in which the core contains the first polymerized units and optionally the second polymerized units, and the shell contains the first polymerized units and a greater amount of second polymerized units than the core. More details regarding such a process can be found in U.S. Pat. No. 7,019,083 (Grootaert et ah). In some embodiments, the core-shell particles are prepared in a two-step polymerization, carried out in the same reactor. In some embodiments, seed particles having a core different composition from the shell are used. The core can be used to seed the polymerization of the polymer component forming the shell. Polymerization of TFE using seed particles is described, for example, in U.S. Pat. Nos. 4,391,940 (Kuhls et al.) and 6,956,078 (Cavanaugh).

Fluoropolymer particles produced with a fluorinated emulsifier typically have an average diameter, as determined by dynamic light scattering techniques, in range of about 10 nanometers (nm) to about 300 nm, and in some embodiments in range of about 50 nm to about 200 nm. If desired, the emulsifiers can be removed or recycled from the fluoropolymer latex as described in U.S. Pat. Nos. 5,442,097 to Obermeier et al., 6,613,941 to Felix et al., 6,794,550 to Hintzer et al., 6,706,193 to Burkard et al. and 7,018,541 to Hintzer et al. In some embodiments, the polymerization process may be conducted with no emulsifier (e.g., no fluorinated emulsifier). Polymer particles produced without an emulsifier typically have an average diameter, as determined by dynamic light scattering techniques, in a range of about 40 nm to about 500 nm, typically in range of about 100 nm and about 400 nm. The fluoropolymer particles obtained from the aqueous emulsion polymerization process are called primary particles.

Dispersions of fluoropolymer particles may be treated by anion exchange (e.g., to remove the emulsifiers) if desired. Methods of removing the emulsifiers from the dispersions by anion-exchange and addition of non-ionic emulsifiers or stabilizers are disclosed, for example, in EP 2409998, published January 25, 2012. The fluoropolymer content in the dispersions may be increased by upconcentration, for example.

Primary particles obtained from aqueous emulsion polymerization may be coagulated or agglomerated together forming secondary particles having an average diameter of at least 1 micrometer, in some embodiments, at least 2, 5, 10, 20, or 30 micrometers. In some embodiments, particles of the present disclosure (e.g., in the form of secondary particles) have a particle size (dsn) in a range from 1 micrometer to 100 micrometers, 5 to 90 micrometers, 1 micrometer to 80 micrometers, 5 to 80 micrometers, 1 micrometer to 65 micrometers, or 1 micrometer to 60 micrometers. The dso value is a median value, indicating that 50% of the particles are smaller and 50% of the particles are larger than this value. Particle sizes can be determined by laser diffraction using the method described in the Examples, below.

Coagulating a fluoropolymer latex may be carried out, for example, by stirring at high shear rates. Alternatively, or additionally, any coagulant which is commonly used for coagulation of a fluoropolymer latex may be used, and it may, for example, be a water soluble salt (e.g., calcium chloride, magnesium chloride, aluminum chloride or aluminum nitrate), an acid (e.g., nitric acid, oxalic acid, hydrochloric acid or sulfuric acid), or a water-soluble organic liquid (e.g., alcohol or acetone). Further coagulants include an ammonium carbonate, a polyvalent organic salt, and a cationic emulsifier. Combinations and sequences of coagulants may also be used. The amount of the coagulant to be added may be in range of 0.001 to 20 parts by mass, for example, in a range of 0.01 to 10 parts by mass per 100 parts by mass of the fluoropolymer latex. The coagulated particles can be collected by fdtration and washed with water (e.g., ion exchanged water, pure water, or ultrapure water).

Particles of the present disclosure may also be obtained by spray-drying the aqueous dispersion of the fluoropolymer. Spray-drying is described, for example, in US. Pat. Nos. 3,953,412 (Saito et al.) and 6,518,349 (Felix et al.). The particle size distribution obtained by spray-drying can be controlled by the gas pressure in the nozzle at a given flow rate. Different nozzles may be used, including, for example, two-fluid nozzles, single-fluid nozzles, and rotary atomizers. Higher pressure leads to overall smaller particles than lower pressure. The solid content of the dispersion used in the spray drying influences the bulk density of the resulting powder. Higher concentrated dispersions will lead to higher bulk densities. Spray-drying may typically lead to predominantly spherical particles or substantially spherical particles. Predominantly means that the majority (i.e., more than 50% or more than 75% of the particles are spherical or substantially spherical). Substantially spherical means the particles are not exactly spherical but their geometric shape can be best approximated by a sphere, as compared to, for example, a cuboid. Particles obtained by spray-drying typically have on average a sphericity of at least 0.8. Sphericity is a ratio of the length of longest axis of the particles (first axis) to the length of longest axis perpendicular to the first axis and can be determined by scanning electron microscopy (SEM).

Particles of the present disclosure may also be obtained by a process comprising freeze- granulation. For freeze-granulation an aqueous fluoropolymer dispersion is fed through a nozzle or atomiser similar to spray drying but the resulting droplets are instantaneously frozen, for example, by exposing them to liquid nitrogen. The dispersing medium (i.e., water) is removed, for example, by sublimation to yield a powder. Particles obtained by freeze-granulation were found to have an even greater sphericity than particles obtained by spray-drying, for example having a sphericity of 0.90 or greater.

The particles obtained by spray-drying or freeze-granulation may be passed though one or more sieve or air classifier or a combination thereof for removing particles of a certain diameter range.

In some embodiments, particles obtained by spray-drying or freeze-granulation, which are substantially unsintered, may be subjected to a thermal treatment at a temperature lower than the melting temperature of the particles, thereby forming a powder comprising at least partially sintered particles of PTFE. In some embodiments, the at least partially sintered particles are subjected to a further thermal treatment at a temperature greater than the melting temperature of the particles, thereby forming a powder comprising at least partially sintered particles. In some embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or even at least 99% of the surface of each particle is (thermally) sintered. In some embodiments, 100% of the surface of each particle for use herein is (thermally) sintered.

The particles of the present disclosure may also be prepared by milling of solid PTFE compositions, for example, the “secondary particles” described above. The milled particles by may be passed though one or more sieve or air classifier or a combination thereof for removing particles of a certain diameter range. Milling can be carried out as is generally known in the art of making fluoropolymer powders as described, for example, in U.S. Pat. Appl. Pub. No 2006/0142514 (Chandler et ah), using, for example, milling equipment, sieves and air classifiers described therein. Sieves may be used to control the particle population, for example, by removing particles of a certain diameters. Air classifiers may be used in addition or as alternative to remove small particles. This way the smallest and largest particles sizes of the powders can be controlled. Contrary to the spray-drying method, the particles sizes of the starting fluoropolymer composition get reduced by milling.

The milling and sieving steps may be repeated until particles have the appropriate particle size distribution. Appropriate particle size distributions may also be obtained by blending (dry-blending) particles of known particle size distributions in appropriate amounts. Typically, the powders obtained by milling are less spherical than powders obtained by spray-drying or freeze-granulation and may have an average sphericity of less than 0.8, or less than 0.7.

Aqueous polymerization using the initiators described above will typically provide fluoropolymers with polar end groups; (see, e.g., Logothetis, Prog. Polym. Sci., Vol. 14, pp. 257-258 (1989)). Particles of the present disclosure may be subjected to a fluorination treatment to remove thermally unstable end groups (e.g., -CONH2, - COF, and -COOH groups). Fluorination is typically conducted so as to reduce the total number of those end groups to less than 100 per 10⁶ carbon atoms in the polymer backbone. Suitable fluorination methods are described for example in U.S. Pat. No.

4,743,658 (Imbalzano) and Great Britain Patent GB1210794, published October 28, 1970. A stationary bed of agglomerate may also be fluorinated as described in U.S. Pat. No. 6,693,164 (Blong). The amount of end groups can be determined by IR spectroscopy as described, for example, in EP 226 668 Al, published July 1, 1987.

In some embodiments, the particles of the present disclosure have a substantially monomodal size distribution of the particles. In some embodiments, the particles of the present disclosure have a multimodal size distribution. It may be useful to combine particles of the present disclosure having different MFIs, melting points, or second divalent units.

In some embodiments, the particles of the present disclosure further comprise inorganic particles mixed with the particles comprising polytetrafluoroethylene. In some embodiments, the inorganic particles comprise at least one of a metal, a non-oxide ceramic, an oxide ceramic, carbon, or a pigment. Examples of suitable metallic inorganic particles include aluminum, nickel, platinum, and gold.

Examples of suitable non-oxide ceramics include boron nitride, silicon carbide, silicon nitride, and titanium diboride. Ceramic microspheres (e.g., glass bubbles) such as those described in U.S. Pat. Appl. Pub. No. 2019/0344496 (Bartow et al.) may be useful. Examples of suitable oxide ceramics include aluminum (III) oxide, silicon oxides, and boron oxides. Suitable carbons include graphene, graphite, and carbon black. The carbon fdler can be, for example, carbon fibers, carbon nanotubes, platelet nanofibers, graphene nanoribbons, or a mixture thereof. In the case of carbon fibers, these can be any of the high- strength carbon fiber compositions known in the art. Examples of suitable pigments include carbon black, titanium dioxide, and pigment blue 60, 15.1, and 15.4. Inorganic particles may be selected such that they absorb at the wavelength of the laser to a greater extent than the particle of PTFE.

In some embodiments, the inorganic particles include microwave-absorbing particles. The microwave-absorbing material can comprise at least one of carbon nanotubes, carbon black, buckyballs, graphene, superparamagnetic nanoparticles, magnetic nanoparticles, metallic nanowires, semiconducting nanowires (e.g., silicon, gallium nitride, and indium phosphide nanowires), and quantum dots.

A variety of sizes of the inorganic particles may be useful. In some embodiments, the inorganic filler has at least one dimension up to 100 micrometers. Since the inorganic particles may have different shapes that are not symmetrical, in some embodiments, the largest dimension is up to 100 micrometers. The smallest dimension of the inorganic particles may be up to one nanometer (nm) or at least one nm. In some embodiments, the inorganic particles have at least one dimension (in some embodiments, the largest dimension) up to 50 micrometers, 20 micrometers, or 10 micrometers.

The inorganic particles may be blended (e.g., dry blended) with the PTFE particles. In some embodiments, the PFTE particles are coated with the inorganic particles. The inorganic particles may be present in an amount of at least 0.1 percent or 0.2 percent by weight, based on the total weight of PTFE particles and inorganic particles. The inorganic particles may be present in an amount up to 5, 10, 15, or 20 percent by weight, based on the total weight of PTFE particles and inorganic particles.

Other additives may be used with the particles of the present disclosure in any of the embodiments described above. Examples of other additives that may be useful, depending on the intended use of the three-dimensional article, include preservatives, mixing agents, colorants (e.g., pigments or dyes), dispersants, floating or anti-setting agents, flow or processing agents, wetting agents, anti-ozonant, odor scavengers, acid neutralizer, antistatic agent, and adhesion promoters (e.g., a coupling agent described above).

Inorganic particles including carbon black, graphite, silicon oxides, and aluminum oxides may be useful as flow agents. In some embodiments, particles of the present disclosure are essentially free of such flow agents. In some embodiments, the flow agent comprises silica nanoparticles. In some embodiments, the flow agent is present, for example, in an amount of at least 0.5 %, 1%, or 2% percent by weight, based on the total weight of the particles. “Essentially free” means containing no or only trace amounts, such as impurities, for example, up to 0.1 % by weight or up to 100 ppm and includes being free of such flow agents.

In some embodiments, particles of the present disclosure comprise at least 60%, 75%, 90%, or at least 95% by weight of particles comprising a PTFE (percentages are based on the total weight of the powder, which is 100% by weight). In some embodiments, the particles consist essentially of particles comprising a PTFE, by which is meant that the particles may contain trace amounts of impurities such as residues from the polymer production or work up processes, and such trace amounts are less than 5% by weight or less than 1% by weight, based on the total weight of the particles.

The particles of the present disclosure can be used for producing a three-dimensional fluoropolymer article, in particular by additive manufacturing, for example, by selective laser sintering (SLS). Processes for manufacturing three-dimensional articles, and in particular by SLS are known in the art. In some embodiments, the process of the present disclosure includes providing a layer of the particles of the present disclosure and selectively treating an area of the layer of the particles by irradiation with a laser beam to fuse at least some of the particles. The layer may be applied to a confined region. The laser may be any suitable laser operating at an infrared (IR), visible, and/or ultraviolet (UV) output wavelength. Examples of suitable lasers include gas lasers, excimer lasers, solid state lasers, and chemical lasers.

In some embodiments, the process of the present disclosure includes providing multiple layers of the particles and selectively treating areas of the multiple layer of the particles by irradiation with a laser beam to fuse at least some of the particles to generate a three-dimensional article comprising the fused particles. Typically, the article is built up layer-by-layer and a new layer of particles is added to the particle bed after each building step. Processing of the particles can be carried out in commercial additive processing devices including commercial SLS devices or 3D-printers.

The three-dimensional articles can be made, for example, from computer-aided design (CAD) models in a layer-by-layer manner. Movement of the laser with respect to the particle layer is performed under computer control, in accordance with build data that represents the three-dimensional article. The build data is obtained by initially slicing the CAD model of the three-dimensional article into multiple horizontally sliced layers. Then, for each sliced layer, the host computer generates for irradiating the particles to form the three-dimensional article. The process can be repeated as many times as necessary to form a three-dimensional article resembling the CAD model.

In some embodiments, a (e.g., non-transitory) machine-readable medium is employed in the process of making a three-dimensional article of the present disclosure. Data is typically stored on the machine-readable medium. The data represents a three-dimensional model of an article, which can be accessed by at least one computer processor interfacing with additive manufacturing equipment (e.g., a 3D printer, a manufacturing device, etc.). The data is used to cause the additive manufacturing equipment to create the three-dimensional article.

Data representing an article may be generated using computer modeling such as computer aided design (CAD) data. Image data representing the three-dimensional article design can be exported in STL format, or in any other suitable computer processable format, to the additive manufacturing equipment. Scanning methods to scan a three-dimensional object may also be employed to create the data representing the article. One exemplary technique for acquiring the data is digital scanning. Any other suitable scanning technique may be used for scanning an article, including X-ray radiography, laser scanning, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound imaging. Other possible scanning methods are described, e.g., in U.S. Patent Application Publication No. 2007/0031791 (Cinader, Jr., et al.). The initial digital data set, which may include both raw data from scanning operations and data representing articles derived from the raw data, can be processed to segment an article design from any surrounding structures (e.g., a support for the article).

Often, machine-readable media are provided as part of a computing device. The computing device may have one or more processors, volatile memory (RAM), a device for reading machine-readable media, and input/output devices, such as a display, a keyboard, and a pointing device. Further, a computing device may also include other software, firmware, or combinations thereof, such as an operating system and other application software. A computing device may be, for example, a workstation, a laptop, a personal digital assistant (PDA), a server, a mainframe or any other general- purpose or application-specific computing device. A computing device may read executable software instructions from a computer-readable medium (such as a hard drive, a CD-ROM, or a computer memory), or may receive instructions from another source logically connected to computer, such as another networked computer.

In some embodiments, the process for making a three-dimensional article of the present disclosure comprises retrieving, from a (e.g., non-transitory) machine-readable medium, data representing a model of a desired three-dimensional article. The process further includes executing, by one or more processors interfacing with a manufacturing device, manufacturing instructions using the data; and generating, by the manufacturing device, the three-dimensional article.

FIG. 1 illustrates an embodiment of a system 2000 for carrying out some embodiments of the process according to the present disclosure. The system 2000 comprises a display 2062 that displays a model 2061 of a three-dimensional article; and one or more processors 2063 that, in response to the 3D model 2061 selected by a user, cause a manufacturing device 2065 to create the three-dimensional article 2017. Often, an input device 2064 (e.g., keyboard and/or mouse) is employed with the display 2062 and the at least one processor 2063, particularly for the user to select the model 2061.

Referring to FIG. 2, a processor 2163 (or more than one processor) is in communication with each of a machine-readable medium 2171 (e.g., a non-transitory medium), a manufacturing device 2165, and optionally a display 2162 for viewing by a user. The manufacturing device 2165 is configured to make one or more articles 2117 based on instructions from the processor 2163 providing data representing a model of the article 2117 from the machine -readable medium 2171.

An example of an SLS device 65 is shown in FIG. 3 and is described in the Examples, below.

The three-dimensional object prepared by the process according to the present disclosure may be an article useful in a variety of industries, for example, the aerospace, apparel, architecture, automotive, business machines products, chemical, consumer, defense, dental, electronics, educational institutions, heavy equipment, jewelry, medical, semi-con, and toys industries. Some Embodiments of the Disclosure

In a first embodiment, the present disclosure provides particles comprising a polytetrafluoroethylene for additive manufacturing, the polytetrafluoroethylene comprising first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether, wherein the second polymerized units are present in an amount not more than one percent by weight based on the total weight of the first polymerized units and the second polymerized units, the particles having a melt flow index of at least 0.5 gram/10 minutes (372 °C/5 kg) and a melting point of at least 316 °C, measured after the first melting and crystallization of the particles.

In a second embodiment, the present disclosure provides the particles of the first embodiment, wherein the particles are core-shell particles, wherein the shell comprises the second polymerized units in not more than five percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

In a third embodiment, the present disclosure provides the particles of the second embodiment, wherein the core comprises the second polymerized units in not more than 0.2 percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

In a fourth embodiment, the present disclosure provides particles comprising a polytetrafluoroethylene for additive manufacturing, the polytetrafluoroethylene having a core and a shell and comprising first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether, wherein the second polymerized units are present in an amount not more than one percent by weight based on the total weight of the first polymerized units and the second polymerized units in the core and the shell combined, and wherein the shell has a greater amount of the second polymerized units than the core, the particles having a melt flow index of at least 0.5 gram/10 minutes (372 °C/5 kg) and a melting point of at least 316 °C, measured after the first melting and crystallization of the particles.

In a fifth embodiment, the present disclosure provides the particles of the fourth embodiment, wherein the shell comprises the second polymerized units in not more than five percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

In a sixth embodiment, the present disclosure provides the particles of the fourth or fifth embodiment, wherein the core comprises the second polymerized units in not more than 0.2 percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

In a seventh embodiment, the present disclosure provides the particles of any one of the second to sixth embodiment, wherein the core contributes at least 50 percent by weight, based on the total weight of the particles

In an eighth embodiment, the present disclosure provides the particles of any one of the second to seventh embodiments, wherein the core has a melt flow index of at least 0.1 gram / 10 minutes. In a ninth embodiment, the present disclosure provides the particles of any one of the second to eighth embodiments, wherein the shell comprises the second polymerized units in greater than one percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

In a tenth embodiment, the present disclosure provides the particles of any one of the first to ninth embodiments, wherein the second polymerized units are independently represented by formula

wherein Rf is a linear or branched perfluoroalkyl group having from 1 to 8 carbon atoms and optionally interrupted by one or more -O- groups, z is 0, 1, or 2, each n is independently 1, 2, 3, or 4, and m is 0 or 1.

In an eleventh embodiment, the present disclosure provides the particles of the tenth embodiment, wherein at least one of z is 1 or 2, or Rf is interrupted by one or more -O- groups.

In a twelfth embodiment, the present disclosure provides the particles of the tenth or eleventh embodiment, where the second polymerized units comprise polymerized units of the fluorinated allyl ether, and wherein m is 1.

In a thirteenth embodiment, the present disclosure provides the particles of any one of the first to eleventh embodiments, wherein the fluorinated vinyl ether or the fluorinated allyl ether is perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, perfluoro-3-methoxy-n-propyl vinyl ether, perfluoro-3-methoxy- n-propyl allyl ether, perfluoromethyl allyl ether, perfluoropropyl allyl ether, or a combination thereof.

In a fourteenth embodiment, the present disclosure provides the particles of any one of the first to thirteenth embodiments, wherein the particles have a melt flow index of at least 1 gram/10 minutes (372 °C/5 kg).

In a fifteenth embodiment, the present disclosure provides the particles of any one of the first to thirteenth embodiments, wherein the particles have a melt flow index of at least 5 grams/10 minutes (372 °C/5 kg).

In a sixteenth embodiment, the present disclosure provides the particles of any one of the first to fifteenth embodiments, having a melting point of at least 320 °C, measured after the first melting and crystallization of the particles.

In a seventeenth embodiment, the present disclosure provides the particles of any one of the first to sixteenth embodiments, having a particle size (dsn) in a range from 1 micrometer to 100 micrometers, or in a range from 1 micrometer to 80 micrometers. In an eighteenth embodiment, the present disclosure provides the particles of any one of the first to seventeenth embodiments, further comprising inorganic particles mixed with the particles comprising polytetrafluoroethylene .

In a nineteenth embodiment, the present disclosure provides the particles of any one of the first to eighteenth embodiments, further comprising inorganic particles coating the particles comprising polytetrafluoroethylene .

In a twentieth embodiment, the present disclosure provides the particles of the eighteenth or nineteenth embodiment, wherein the inorganic particles comprise at least one of metals, non-oxide ceramics, oxide ceramics, carbon, or a pigment.

In a twenty-first embodiment, the present disclosure provides the particles of any one of the eighteenth to twentieth embodiments, wherein the inorganic particles are present in an amount up to 20 percent by weight, based on the total weight of the particles.

In a twenty-second embodiment, the present disclosure provides a process for making a three- dimensional article, the process comprising subjecting the particles of any one of the first to twenty-first embodiments to additive manufacturing.

In a twenty-third embodiment, the present disclosure provides the process of the twenty-second embodiment, wherein additive manufacturing comprises selective laser sintering.

In a twenty-fourth embodiment, the present disclosure provides the process of the twenty-second or twenty-third embodiments, the process comprising: providing a layer of the particles of any one of the first to twenty-first embodiments; and selectively treating an area of the layer of the particles by irradiation with a laser beam to fuse at least some of the particles.

In a twenty-fifth embodiment, the present disclosure provides the process of the twenty-fourth embodiment, further comprising: providing multiple layers of the particles; and selectively treating areas of the multiple layer of the particles by irradiation with a laser beam to fuse at least some of the particles to generate a three-dimensional article comprising the fused particles.

In a twenty-sixth embodiment, the present disclosure provides the process of any one of the twenty-second to twenty-fifth embodiments, the process further comprising: retrieving, from a non-transitory machine readable medium, data representing a model of the three-dimensional article; and executing, by one or more processors interfacing with a manufacturing device, manufacturing instructions using the data.

In a twenty-seventh embodiment, the present disclosure provides the process of the twenty-sixth embodiment, further comprising generating, by the manufacturing device, the three-dimensional article. In a twenty-eighth embodiment, the present disclosure provides a three-dimensional article prepared by the process of any one of twenty-second to twenty-seventh embodiments.

In a twenty-ninth embodiment, the present disclosure provides the use of the particles of any one of the first to twenty-first embodiments for additive manufacturing.

In a thirtieth embodiment, the present disclosure provides the use of the particles of any one of the first to twenty-first embodiments for selective laser sintering.

EXAMPLES

The following specific, but non-limiting, examples will serve to illustrate the present disclosure. Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods. These abbreviations are used in the following examples: °C = degrees Celsius, cm = centimeters, mm = millimeters, pm = micrometers, rpm = revolutions per minute, wt. % = weight percent, L = liters, min = minutes, s = seconds, g = grams, kg = kilograms, mbar = millibar, MPa = megapascals, nm = nanometers, W = watts.

Evaluation of the PTFE particles Melting Point

The PTFE Examples were coagulated and dried. The melting point (T_m) was determined on the dry powder in accordance with ASTM D 793-01 and ASTM E 1356-98 by a differential scanning calorimetry (DSC Q2000, TA Instruments, New Castle, DE) under a nitrogen flow. The first heat cycle started at -85 °C and was ramped to 350 °C at a 10 °C/minute. The cooling cycle started at 350 °C and was cooled to -85 °C at 10 °C /min. The second heat cycle started at -85 °C and was ramped to 350 °C at a 10 °C/minute. A DSC thermogram was obtained from the second heat of a heat/cool/heat cycle to determine T_m.

Particle Size

The latex particle size determination was conducted by means of dynamic light scattering with a Malvern Zetasizer Nano S (Malvern, Worcestershire, UK) following a similar procedure to that described in DIN ISO 13321:2004-10. The reported average particle size diameter is the d50. Before the measurements, the PTFE latex as yielded from the polymerization was diluted with 0.01 mol/L NaCl solution. The measurement temperature was 25 °C in all cases. Average Particle Size and Particle Size Distribution of Secondary Particles

The particle size distributions of the secondary particles were determined by laser diffraction method according to Test Method ISO 13320 using a Sympatec Helos measurement device (HELOS-R Series, from Sympatec GmbH, Clausthal-Zellerfeld, Germany). The sample size of particles measured was 2 mL. The measurement range was from 0.4 pm to 175 pm.

Vinyl and allyl ether comonomer content

Thin fdms of approximately 0.1 mm thickness were prepared by molding the polymer at 360 °C using a heated plate press. These fdms were then scanned in a nitrogen atmosphere using a FT-IR spectrometer (Nicolet DX 510, ThermoFisher Scientific, Waltham, MA). The OMNIC software (ThermoFisher Scientific) was used for data analysis. Herein the CF₂=CF-CF₂-0-CF₂-CF₂-CF₃ (MA-3) content, reported in units of weight%, was determined from an infrared band at 999 1/cm and was calculated as 1.24 ^c the ratio (factor determined by means of solid-state NMR) of the 999 1/cm absorbance to the absorbance of the reference peak located at 2365 1/cm. The CF₂=CF-0-CF₂-CF₂-CF₃ (PPVE) content, reported in units of weight%, was determined from an infrared band at 993 1/cm and was calculated as 0.95 ^c the ratio of the 993 1/cm absorbance to the absorbance of the reference peak located at 2365 1/cm. The CF₂=CF-0-CF₃ (PMVE) content, reported in units of weight%, was determined from an infrared band at 889 1/cm and was calculated as 1 1.2 the ratio of the 889 1/cm absorbance to the absorbance of the reference peak located at 2365 1/cm.

Solid Content

The solid content of the PTFE particle dispersions was determined gravimetrically according to DIN EN ISO 12086-2:2006-05. A correction for non-volatile inorganic salts was not carried out. The solid content of the polymer dispersions was taken as polymer content.

Melt-flow index (MFI)

The MFI, reported in g/10 min, of the PTFE particles was measured according to DIN EN ISO 1133-1:2012-03 at a support weight of 5.0 kg. The MFI was obtained with a standardized extrusion die of 2.1 mm diameter and a length of 8.0 mm. Unless otherwise noted, a temperature of 372 °C was applied.

Preparation of Nanosilica particles for use in the Examples

A mixture of 100 grams of colloidal silica (16.06 wt.% solids in water; 5 nm size), 7.54 grams of isoctyltrimethoxy silane, 0.81 grams of methyltrimethoxysilane and 112.5 grams of an 80:20 wt/wt. % solvent blend of ethanol methanol were added to a 500 ml 3-neck round bottom flask (Ace Glass, Vineland, N.J.). The flask containing the mixture was placed in an oil bath set at 80 °C with stirring for 4 hours to prepare hydrophobically modified nanosilica particles. The hydrophobically modified nanosilica particles are transferred to a crystallizing dish and dried in a convection oven at 150 °C for 2 hours.

Example 1

An oxygen-free 40-L kettle was charged with 27 kg deionized water, 390 g of a 30 wt. % aqueous solution of CF₃-0-(CF₂)₃-0-CHF-CF₂-C00NH₄ ⁺, prepared as described for “Compound 1” in U.S. Pat. App. Pub. No. 2007 / 0015937, 100 g PPVE and 200 mbar ethane (at 25 °C). Then the reactor was heated to 75 °C, and TFE was charged until a pressure of 10 bar (1 MPa) was reached. The polymerization was initiated by feeding 3.0 g ammonium persulfate (APS) (dissolved in 50 g deionized water). TFE was constantly fed at 10 bar (1 MPa) pressure. After 5.6 kg total TFE, 280 g PPVE was fed into the reactor, and an additional 1 g of APS was added. After 7.0 kg total TFE, the polymerization was stopped. The latex had a solid content of 21 wt% and a particle size (dsn) of 172 nm.

The PTFE particles were coagulated by 10% oxalic acid. The resulting secondary particles had a dso of 2.5 pm and d9o of 5.5pm. The d9o value indicates that 90% of the particles are smaller than this value. The coagulated, dried polymer had an PPVE content of 0.8 wt%, an MFI (372 °C, 5 kg) of 18 g/10 min, and a melting point of 323 °C, measured after the first melting and crystallization.

Example 2

The PTFE particles of Example 1 were combined with 2 wt. % of the nanosilica described above as a flow agent. The resulting particles were used to prepare articles by selective laser sintering on a custom-made lab scale SLS platform 70 shown in FIG. 3.

PTFE particles were fed from chamber 10, and a layer 20 of the particles was spread by a motorized spreader bar 30.

Selective laser sintering was carried out using a CCE-laser 40 reflected off scanning mirror 50.

The laser had a laser power of 27W and a speed of 3000 mm/s, and 8 passes were used to fuse some of the particles to form article 17. The article 17 of Example 2 had an outer dimension of 30x30mm and a thickness of 3 mm and is shown in the photograph of FIG. 4.

This disclosure is not limited to the above-described embodiments but is to be controlled by the limitations set forth in the following claims and any equivalents thereof. This disclosure may be suitably practiced in the absence of any element not specifically disclosed herein.

Claims

What is claimed is:

1. Particles comprising a polytetrafluoroethylene for additive manufacturing, the polytetrafluoroethylene comprising first polymerized units of tetrafluoroethylene and second polymerized units of at least one of a fluorinated vinyl ether or a fluorinated allyl ether, wherein the second polymerized units are present in an amount not more than one percent by weight based on the total weight of the first polymerized units and the second polymerized units, the particles having a melt flow index of at least 0.5 gram/10 minutes (372 °C/5 kg) and a melting point of at least 316 °C, measured after the first melting and crystallization of the particles.

2. Particles of claim 1, wherein the second polymerized units are independently represented by formula

3. Particles of claim 2, wherein at least one of z is 1 or 2, or Rf is interrupted by one or more -O- groups.

4. Particles of claim 2 or 3, where the second polymerized units comprise polymerized units of the fluorinated allyl ether, and wherein m is 1.

5. Particles of any one of claims 1 to 3, wherein the fluorinated vinyl ether or the fluorinated allyl ether is perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, perfluoro-3-methoxy-n-propyl vinyl ether, perfluoro-3-methoxy-n-propyl allyl ether, perfluoromethyl allyl ether, perfluoropropyl allyl ether, or a combination thereof.

6. Particles of any one of claims 1 to 5, wherein the polytetrafluoroethylene has a core and a shell, wherein the shell has a greater amount of the second polymerized units than the core.

7. Particles of claim 6, wherein the shell comprises the second polymerized units in not more than five percent by weight, based on the total weight of the first polymerized units and the second polymerized units, and wherein the core comprises the second polymerized units in not more than 0.2 percent by weight, based on the total weight of the first polymerized units and the second polymerized units.

8. Particles of any one of claims 1 to 7, having a melt flow index of at least 1 gram/10 minutes (372 °C/5 kg).

9. Particles of any one of claims 1 to 8, having a melting point of at least 320 °C, measured after the first melting and crystallization of the particles.

10. Particles of any one of claims 1 to 9, having a particle size (dsn) in a range from 1 micrometer to 100 micrometers.

11. A process for making a three-dimensional article, the process comprising subjecting the particles of any one of claims 1 to 10 to additive manufacturing.

12. A process for making a three-dimensional article, the process comprising: providing a layer of the particles of any one of claims 1 to 10; and selectively treating an area of the layer of the particles by irradiation with a laser beam to fuse at least some of the particles.

13. The process of claim 11 or 12, further comprising: retrieving, from a non-transitory machine readable medium, data representing a model of the three-dimensional article; executing, by one or more processors interfacing with a manufacturing device, manufacturing instructions using the data; and generating, by the manufacturing device, the three-dimensional article.

14. A three-dimensional article prepared by the process of any one of claims 11 to 13.

15. Use of the particles of any one of claims 1 to 10 for selective laser sintering.