MIXTURES, ARTICLES HAVING LOW COEFFICIENTS OF FRICTION, METHODS OF MAKING THESE, AND METHODS OF USING THESE

Abstract

The present disclosure provides for mixtures, methods for making mixtures, articles, methods for making articles, and methods of using articles. In an aspect, the articles have superior tribological properties owing to combinations of polytetrafluoroethylene and an irradiated fluoropolymer described herein.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 62/400,679, having the title “MIXTURES, ARTICLES HAVING LOW COEFFICIENTS OF FRICTION, METHODS OF MAKING THESE, AND METHODS OF THESE”, filed on Sep. 28, 2016, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Solid lubrication is necessary in many industries, where friction and wear can cause the breakdown of parts and equipment. Bearings, bushings, and other high cycle and high friction sliding components can degrade over time. Solid lubricants made from polyfluorotetraethylene (PTFE) are commonly used to reduce friction in such parts. However, improvements in friction and wear properties are needed to improve the life of these types of components.

SUMMARY

Embodiments of the present disclosure provide for articles comprising mixtures derived from an irradiated fluoropolymer and a matrix and the like. In an aspect, the article, among others, comprises a mixture derived from an irradiated fluoropolymer and a matrix.

In another aspect, the article, among others, comprises: a mixture derived from an irradiated fluoropolymer and a matrix, wherein the matrix is chosen from polyamide (PA), poly amide imide (PAI), polypropylene, polyphenylene sulfide (PPS), polysulphone (PSU), polyether sulphone (PES), a precursor thereof, a derivative thereof, a homopolymer thereof, a monomer thereof, a copolymer thereof, a terpolymer thereof, and a combination thereof, wherein the article has a coefficient of friction of about 0.1 to 0.25, wherein the article has a wear rate of about 1×10⁻⁸ mm³/Nm or less, and wherein the irradiated fluoropolymer is a powder and the matrix is a powder.

In another aspect, the article is a bearing, a joint, a piston, a bushing, a socket, a seal, or a gasket, among others, that comprises: a mixture derived from an irradiated fluoropolymer and a matrix, wherein the article has a coefficient of friction of about 0.1 to 0.25, wherein the article has a wear rate of about 1×10⁻⁸ mm³/Nm or less.

Other articles, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional articles, methods, features and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.

DETAILED DESCRIPTION

As used herein, UHMWPE refers to Ultra High Molecular Weight Polyethylene.

As used herein, PEEK refers to poly(aryl-ether-ether-ketone).

As used herein, PTFE refers to polytetrafluoroethylene.

Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit (unless the context clearly dictates otherwise), between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of chemistry, tribology, and the like, which are within the skill of the art. Such techniques are explained fully in the literature.

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the compositions and compounds disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C., and pressure is in atmosphere. Standard temperature and pressure are defined as 25° C. and 1 atmosphere.

Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible.

It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a support” includes a plurality of supports. In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings unless a contrary intention is apparent.

Discussion

Embodiments of the present disclosure provide for mixtures, methods for making mixtures, articles, methods for making articles, and methods of using articles. Embodiments of the present disclosure relate to articles having superior tribological properties.

In an aspect, the article can be used in many different applications including, but not limited to, mechanical parts (e.g., bearing, joints, pistons, bushings, sockets, seals, gaskets, etc.), structures having load bearing surfaces, sporting equipment, machine parts and equipment, and the like.

In aspect, embodiments of the present disclosure can have a low coefficient of friction (e.g., about 0.1 to 0.25) and/or very low wear (e.g., about 1×10⁻⁷ mm³/Nm or less). In addition, embodiments of the present disclosure provide for articles that are resistant to chemicals, have a high strength, are biocompatible, are water resistant, and/or have high thermal resistance (e.g., withstand extreme temperatures).

In an exemplary embodiment, the mixture includes a fluoropolymer (e.g., an irradiated fluoropolymer and/or un-irradiated fluoropolymer) and a matrix. In an exemplary embodiment, the mixture includes the fluoropolymer powder and one or more matrix powders. In an exemplary embodiment, the mixture is a powder. In an embodiment, the powder can be sieved through a 325-mesh that allows a maximum particle size of about 44 micrometers, with a mean particle diameter of about 1 to 15 micrometers or about 5 micrometers. Although some embodiments are described as powders, an embodiment of the present disclosure contemplates using non-powders as one or both of the irradiated fluoropolymer and/or the matrix.

In an embodiment, the fluoropolymer (e.g., an irradiated fluoropolymer and/or un-irradiated fluoropolymer) can be about 5 to 95 weight % of the mixture. In an embodiment, the matrix component is about 5 to 95 weight % of the mixture.

Embodiments of the matrix can be made of polymers that have one or more of the following characteristics: inert, corrosion resistant, high melting point, high strength, or a combination thereof. In particular, embodiments of the matrix can be made of polymers such as, but not limited to, polyimide (PI), polyetheretherketone (PEEK), polyamide (PA), poly amide imide (PAI),polypropylene, polyphenylene sulfide (PPS), polysulphone (PSU), polyether sulphone (PES), precursors thereof, derivatives thereof, homopolymers thereof, monomers thereof, copolymers thereof, terpolymers thereof, or combinations thereof. In an embodiment, the matrix is PI. In an embodiment, the matrix is Nylon (e.g., Nylon 6). In an embodiment, the filler is a powder.

In an embodiment, the irradiated fluoropolymer can be formed by irradiating a fluoropolymer using an electron beam for an appropriate time frame (e.g., seconds to minutes to hours, or more). Although not intending to be bound by theory, the irradiation breaks polymer bonds thereby fragmenting the polymer into smaller portions and produces an increase in the number of carboxylic acid groups. The increase in the concentration of carboxylic acid groups causes the material to have a higher surface energy, which increases the wettability of the material.

Embodiments of fluoropolymers disclosed below can refer to either the irradiated fluoropolymer or un-irradiated fluoropolymer. For each of the fluoropolymers mentioned herein, each can be irradiated to form irradiated fluoropolymers. For clarity, the fluoropolymers below are not referred to as irradiated fluoropolymers, but irradiated fluoropolymers are intended to be included as well. As a result, embodiments of the fluoropolymers described below include both un-irradiated fluoropolymer and irradiated fluoropolymer, where the fluoropolymers can be irradiated to form the irradiated fluoropolymer.

In an embodiment, an individual fluoropolymer can be used alone; mixtures or blends of two or more different kinds of fluoropolymers can be used as well. Fluoropolymers useful in the practice of this disclosure can be prepared from at least one unsaturated fluorinated monomer (fluoromonomer). A fluoromonomer suitable for use herein preferably contains about 35 wt % or more fluorine, and preferably about 50 wt % or more fluorine, and can be an olefinic monomer with at least one fluorine or fluoroalkyl group or fluoroalkoxy group attached to a doubly-bonded carbon. In one embodiment, a fluoromonomer suitable for use herein is tetrafluoroethylene (TFE).

In one embodiment, the fluoropolymer can include polytetrafluoroethylene (PTFE), which refers to (a) polymerized tetrafluoroethylene by itself without any significant comonomer present, i.e. a homopolymer of TFE, and (b) modified PTFE, which is a copolymer of TFE with such small concentrations of comonomer that the melting point of the resultant polymer is not substantially reduced below that of PTFE (reduced, for example, by about 8% or less, about 4% or less, about 2% or less, or about 1% or less). Modified PTFE contains a small amount of comonomer modifier that improves film forming capability during baking (fusing). Comonomers useful for such purpose typically are those that introduce bulky side groups into the molecule, and specific examples of such monomers are described below. The concentration of such comonomer is preferably less than 1 wt %, and more preferably less than 0.5 wt %, based on the total weight of the TFE and comonomer present in the PTFE. A minimum amount of at least about 0.05 wt % comonomer is preferably used to have a significant beneficial effect on processability. The presence of the comonomer is believed to cause a lowering of the average molecular weight.

In an embodiment, the mixture can be made by mixing the fluoropolymer (e.g., irradiated fluoropolymer) and the matrix using a fluid energy mill, in which high-speed rotation subjects the mixture to intensive particulate collisions, producing increasingly smaller particles. The fluoropolymer powder and the matrix powder can be premixed and sent through the feed funnel of the mill to create excellent particle dispersion. After grinding, the resulting powder mixture can be formed into an article of manufacture having a desired shape using techniques such as extruded film casting, blown film, fiber spinning, stock shape extrusion, pipe and tubing extrusion, thermoforming, compression molding, sintering, or the like, accomplished using suitable forming equipment.

In other embodiments, materials produced by shaping operations, including melt processing and forming, compression molding or sintering, may be machined into final shapes or dimensions. In still other implementations, the surfaces of the parts may be finished by polishing or other operations.

In an embodiment, the mixture can be made by mixing the fluoropolymer and the matrix in a variety of polar organic liquids, which are useful in creating the particle dispersion and precursor slurry from which the present composite powder material and composite body are produced. Suitable liquids include, but are not limited to, lower alcohols, such as methanol, ethanol, isopropanol (IPA), n-butanol, and tent-butanol, or a combination thereof.

The fluoropolymer and the matrix can be added sequentially (in either order) or concurrently to the alcohol, or premixed and then added to the alcohol. In an embodiment, the mixture in the alcohol can be mixed using sonication (e.g., exposure to a source of ultrasonic energy produced by an ultrasonic horn). Preferably, the intensity and time of the exposure is sufficient to cause the particles to become substantially fully dispersed in the polar organic liquid. Alternatively, the energy may be supplied by any other suitable high-energy mixing technique, including without limitation, high vortex or high shear mixing. After mixing, the alcohol is allowed to evaporate off of the mixture for a period of time (e.g., evaporated in a fume hood until dry). In an embodiment, the dried mixture powder is compression molded and heated to a temperature of about 300 to 450° C. or about 370 to 390° C. in an atmosphere of laboratory air for about 1 to 5 hours or about 3 hours. The compression mold can be designed to produce a desired article. After the compression mold and heating process, the article is cooled.

Tribological Testing

The wear resistance and coefficient of friction data shown herein can be obtained using samples produced in accordance with the following procedure or a similar procedure.

The samples are cut to size (˜0.25×0.25×0.5″) using a laboratory numerically controlled milling machine. The machined samples are then polished on a polishing wheel. The samples are left to dry in laboratory air for 3-10 hours. The finished samples are then measured using digital calipers and weighed; a density of each sample is calculated from these measurements.

The sample is slid against a 304 stainless steel counter sample for use with a ˜250 N normal load, 2 in/s sliding velocity and 1 inch reciprocating stroke. The sliding tests are interrupted periodically so the sample can be weighed. Prescribed sliding cycles are 1000, then 10,000, then 100,000 then 1,000,000 to a total of 1,111,100 sliding cycles. A steady state wear rate is determined as the wear rate once the material runs in. “Running in” is a time towards the beginning of testing where a transfer film is being developed and a slightly higher mass loss rate is observed. It is observed that after the initial run-in, the wear rate is relatively constant.

Wear measurements are made using two methods: a mass loss method and a direct height loss measurement. For a mass loss measurement, a sample is massed both before and after sliding occurs. Based on the change in mass and the density of the material, a volume loss and wear rate is obtained. A displacement based measurement is complementary to the mass based measurement. A linear variable differential transformer (LVDT) monitors a height change of the sample, which can be equated to a volume and wear rate measurements. It should also be noted that more ideal counter materials and material finishes can generate lower wear rates.

Although not intending to be bound by theory, it appears that the combination of the irradiated fluoropolymer and matrix produces a synergistic effect on reducing the steady state wear rate. Although not intending to be bound by theory, the superior tribological properties of the articles may be the result of reactions occurring between the components.

In an embodiment, articles made in accordance with the foregoing process can be used in low friction applications. The types of articles can vary greatly and include articles where reduced friction is advantageous. In general, an embodiment of the article can have one or more sliding surfaces or surfaces in contact with another structures surface. The articles can have a variety of shapes and cross sections. In an embodiment, the shape of the article can be a simple three dimensional geometrical shape (e.g., sphere, polyhedron, and the like) or a complex three dimensional geometrical shape (e.g., irregular shapes). In general, the article can have a cross-sectional shape including, but not limited to, a polygon, a curved cross-section, irregular, and combinations thereof.

Embodiments of the articles can be used in many structures, parts, and components in the in the automotive, industrial, aerospace industries, and sporting equipment industries, to name but a few industries where articles having superior tribology characteristics are advantageous. The article can be used in many different applications including, but not limited to, mechanical parts (e.g., a bearing, a joint, a piston, a bushing, a socket, a seal, and a gasket), structures having load bearing surfaces, sporting equipment, machine parts and equipment, and the like.

As mentioned above, the mixture can be formed into articles. In an embodiment, the articles can be used in many structures, parts, and components in the in the automotive, industrial, aerospace industries, and sporting equipment industries, to name but a few industries where articles having superior tribology characteristics are advantageous. In an embodiment, the article can be used in many different applications including, but not limited to, mechanical parts (e.g., bearing, joins pistons, etc.), structures having load bearing surfaces, sporting equipment, machine parts and equipment, and the like. In particular, the article can include a bearing, bushing, socket, and other high cycle and high friction components.

In an embodiment including the irradiated fluoropolymer the coefficient of friction can be about 0.01 to 0.5 and the steady state wear rate can be about 1×10⁻⁷ mm³/Nm or less, about 1×10⁻⁸ mm³/Nm or less, or about 1×10⁻⁷ mm³/Nm to 1×10⁻⁹ mm³/Nm.

In an embodiment including the un-irradiated fluoropolymer the coefficient of friction can be about 0.1 to 0.25 and the wear rate can be about 1×10⁻⁸ mm³/Nm or less, about 1×10⁻⁸ mm³/Nm or less, or about 1×10⁻⁸ mm³/Nm to about 1×10⁻⁹ mm³/Nm or less.

It should also be noted that the coefficient of friction and wear characteristics of articles of the present disclosure can be designed for a particular application. Thus, embodiments of the present disclosure can provide articles that can satisfy many different requirements for different industries and for particular components.

EXAMPLES

Now having described the embodiments of the present disclosure, in general, the following Examples describe some additional embodiments of the present disclosure. While embodiments of present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit embodiments of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure.

Example 1

Example 1 refers to a mixture including PTFE and polyimide. Details regarding Example 1 are herein, including a summary describing the sample composition, counterface information, sample dimensions, testing environment, testing parameters, initial wear rate, steady state wear rate, total wear rate and average friction coefficients.

SAMPLE: PTFE 7C and 20 weight percent, Polyimide_UF1
PTFE 7C-80 weight percent
Counterface: 304L stainless steel lapped
Density of sample: 1.9 mg/mm³

Test Parameters

Environment: Lab Air

Reciprocating length: 25.4 mm

Sliding speed: 50.8 mm/s

Average Normal Force: 266.6 N

Results

Initial wear rate: 6.2×10⁻⁶ mm³ /Nm at 1000 cycles

Best wear rate: 1.1×10⁻⁸ mm³/Nm at 1000000 cycles

Total wear rate: 2.9×10⁻⁸ mm³/Nm at 1111000 cycles

Uncertainty in total wear rate: 1.1×10⁻⁹ mm³/Nm

Average friction coefficient: 0.20

Volume lost: 0.61 mm³

Example 2

Example 2 refers to a mixture including PTFE and nylon. Details regarding Example 2 are herein, including a summary describing the sample composition, counterface information, sample dimensions, testing environment, testing parameters, initial wear rate, steady state wear rate, total wear rate and average friction coefficients.

SAMPLE: Nylon Shamrock PTFE

Nylon 6—80 weight percent, Shamrock PTFE—20 weight percent (NanoFLON P51A Sub-micron PTFE)
Counterface: 304 stainless steel lapped
Density of sample: 1.2 mg/mm³

Test Parameters

Environment: Lab Air

Reciprocating length: 25.4 mm

Sliding speed: 50.8 mm/s

Average Normal Force: 265.9 N

Results

Initial wear rate: 6.2×10⁻⁶mm³/Nm at 1000 cycles

Best wear rate: 1.3×10⁻⁷ mm³/Nm at 1000000 cycles

Total wear rate: 1.8×10⁻⁷ mm³/Nm at 1111000 cycles

Uncertainty in total wear rate: 2.1×10⁻⁹ mm³/Nm

Average friction coefficient: 0.25

Volume lost: 2.93 mm³

Example 3

Example 3 refers to a mixture including PEEK and PTFE. Details regarding Example 3 are herein, including a summary describing the sample composition, counterface information, sample dimensions, testing environment, testing parameters, initial wear rate, steady state wear rate, total wear rate and average friction coefficients.

SAMPLE: PEEK PTFE 1 Sample 1

PEEK—80 weight percent, Shamrock PTFE—20 weight percent (NanoFLON P51A Sub-micron PTFE)
Counterface: 304 stainless steel lapped
Density of sample: 1.4 mg/mm³

Test Parameters

Environment: Lab Air

Reciprocating length: 25.4 mm

Sliding speed: 50.8 mm/s

Average Normal Force: 274.6 N

Results

Initial wear rate: 1.5×10⁻⁶ mm³/Nm at 1000 cycles

Best wear rate: 2.4×10⁻⁷ mm³/Nm at 1000000 cycles

Total wear rate: 2.5×10⁻⁷ mm³/Nm at 1111000 cycles

Uncertainty in total wear rate: 2.1×10⁻⁹ mm³/Nm

Average friction coefficient: 0.12

Volume lost: 3.96 mm³

Example 4

Example 4 refers to a mixture including UHMWPE and PTFE. Details regarding Example 4 are herein, including a summary describing the sample composition, counterface information, sample dimensions, testing environment, testing parameters, initial wear rate, steady state wear rate, total wear rate and average friction coefficients. SAMPLE: UHMWPE PTFE 1

UHMWPE—80 weight percent, Shamrock PTFE—20 weight percent
Counterface: 304 stainless steel lapped
Density of sample: 1 mg/mm³

Test Parameters

Environment: Lab Air

Reciprocating length: 25.4 mm

Sliding speed: 50.8 mm/s

Average Normal Force: 266.3 N

Results

Initial wear rate: 1.5×10⁻⁶ mm³/Nm at 1000 cycles

Best wear rate: 2.2×10⁻⁸ mm³/Nm at 100000 cycles

Total wear rate: 2.8×10⁻⁸ mm³/Nm at 1111000 cycles

Uncertainty in total wear rate: 2.0×10⁻⁹ mm³/Nm

Average friction coefficient: 0.16

Volume lost: 0.453 mm³

It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt % to about 5 wt %, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. In an embodiment, the term “about” can include traditional rounding according to measuring technique and the numerical value. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

Many variations and modifications may be made to the above-described embodiments. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

1. An article, comprising:

a mixture derived from an irradiated fluoropolymer and a matrix, wherein the matrix is chosen from polyamide (PA), poly amide imide (PAI), polypropylene, polyphenylene sulfide (PPS), polysulphone (PSU), polyether sulphone (PES), a precursor thereof, a derivative thereof, a homopolymer thereof, a monomer thereof, a copolymer thereof, a terpolymer thereof, and a combination thereof, wherein the article has a coefficient of friction of about 0.1 to 0.25, wherein the article has a wear rate of about 1×10−8 mm3/Nm or less, and wherein the irradiated fluoropolymer is a powder and the matrix is a powder.

2. An article, comprising:

a mixture derived from an irradiated fluoropolymer and a matrix.

3. The article of claim 2, wherein the matrix is selected from the group consisting of:

polyetheretherketone (PEEK), polyimide (PI), polyamide (PA), poly amide imide (PAI), polypropylene, polyphenylene sulfide (PPS), polysulphone (PSU), polyether sulphone (PES), a precursor thereof, a derivative thereof, a homopolymer thereof, a monomer thereof, a copolymer thereof, a terpolymer thereof, and a combination thereof.

4. The article of claim 2, wherein the irradiated fluoropolymer is a powder and the matrix is a powder.

5. The article of claim 2, wherein the article has a coefficient of friction of about 0.01 to 0.5.

6. The article of claim 2, wherein the article has a wear rate of about 1×10−7 mm3/Nm or less.

7. The article of claim 2, wherein the article is a solid lubricant or a coating.

8. The article of claim 2, wherein the mixture further comprises at least one un-irradiated fluoropolymer.

9. The article of claim 8, wherein one of the irradiated fluoropolymer includes at least one irradiated polytetrafluoroethylene.

10. The article of claim 8, wherein one of the at least one fluoropolymers is tetrafluoroethylene.

11. The article of claim 8, wherein the irradiated fluoropolymer is comprised of 50 wt % or more fluorine.

12. The article of claim 1, wherein the article is selected from the group consisting of: a bearing, a joint, a piston, a bushing, a socket, a seal, and a gasket.

13. An article, comprising:

a mixture derived from an irradiated fluoropolymer and a matrix, wherein the article is selected from the group consisting of: a bearing, a joint, a piston, a bushing, a socket, a seal, and a gasket, wherein the article has a coefficient of friction of about 0.1 to 0.25, wherein the article has a wear rate of about 1×10−8 mm3/Nm or less.