FIELD

The present disclosure relates to methods of preparing bearings, bearing surfaces, and bearing components comprising a coating or layer of a thermoplastic hot melt pressure sensitive adhesive capable of bonding to diverse materials including those with low surface energy such as fluoropolymers used to reduce friction in bearings. The adhesive comprises polydopamine polymers having catechol-amine functionalities incorporated into an adhesive system that allows bonding between substrates (surfaces of articles) including metallic materials and low surface energy materials (e.g., fluoropolymers or their composites such as polyimide fluoropolymer composites). The disclosure also relates to the application of core-shell colloidal polymeric materials that function as hot-melt pressure sensitive adhesives (e.g., for interfacial bonding of materials including fluoropolymers and/or composites comprising fluoropolymers) in methods of making bearing and bearing components.

BACKGROUND

Bearings may have tribological components that provide surface(s) (tribological surfaces) with suitable friction control (i.e., increased or reduced friction), lubrication, and wear resistance made from, for example, metals (e.g., babbit) and polymeric materials (e.g., fluoropolymers). Such tribological components comprise a tribological material, for example, in the form of a polymeric coating or film, and may further comprise a substrate that acts as a structural support (e.g., structural metal or structural polymer support/backing). The substrate may provide strength, rigidity, and/or allow the tribological material, particularly polymer-based tribological materials, to be held/formed into an appropriate shape, such as a cylinder thereby providing an appropriately configured surface with suitable levels of friction, lubrication, and/or wear resistance. Where such components comprise two materials such as a metallic substrate and polymeric tribological material, they must be bonded in a manner that withstands the thermal, mechanical and wear (abrasive) conditions inherent to the circumstances in which the bearing is employed. The metal-polymer, metal-metal, or polymer-polymer interlayer that provides such bonding is often a critical part of providing the appropriate load bearing and tribological characteristics. In some cases, tribological materials have been impregnated into sintered materials such as sintered bronze etc., however, such bonding techniques are not compatible with all substrates and tribological materials, and are inefficient, particularly where the substrate and or tribological material is a low surface energy material such as a fluoropolymer. Accordingly, there is a need for adhesives that allow bonding between bearing substrates and tribological materials such as fluoropolymers used in mechanical bearings to reduce friction.

A close look at the naturally occurring phenomena exhibited by mussels, which adhere to the surface of metallic and non-metallic substrates, reveals the possibility of leveraging their biological mechanism of adhesion to promote the effective coupling of metallic and organic functional groups in difficult and non-compatible systems. One aspect of the present disclosure, which is inspired by natural phenomena, is directed to pressure sensitive macromolecular adhesive polymers having catechol-amine functionalities that can bind low surface energy materials, such as fluoropolymer, as an adhesive system. Such systems could allow bonding between diverse substrates including metallic substrates and low energy polyolefins or fluoropolymers or their composites including those used in tribological applications.

SUMMARY

This disclosure describes, among other things, novel methods of forming adhesive interfaces using hot-melt dopamine-based thermoplastic polymers (polydopamine polymers) that bond together mechanical bearing elements such as those providing support (e.g., substrates providing structural support) for a tribological material and tribological materials used in bearings (e.g., polyolefins and fluorinated polymers such as fluorinated polyolefins such as PTFE). Polydopamine polymers may be prepared by an in situ polymerization reaction of dopamine in the presence of one or more carboxylic acid(s). The polymerization reaction may be conducted in the presence of materials (e.g., in the form of particles, tubes, sheets or films) onto which dopamine-based polymers can be deposited and/or grafted, depending on the nature of the materials, forming a partial or complete layer on the surface(s) of the materials.

One aspect of this disclosure is directed to a method of preparing a dopamine-based thermoplastic polymer, the method comprising contacting dopamine and/or dopamine analogs with one or more carboxylic acids in the presence of a redox initiator (such as elemental oxygen) that oxidizes all or part of the dopamine or dopamine analogs to quinol or semiquinones. The reaction may be carried out in a basic aqueous buffer solution (such as a tris-(hydroxymethyl)aminomethane buffered solution) optionally comprising a water miscible organic solvent such as an alcohol or ketone; the reaction forming a polymer comprising polymerized monomers of dopamine quinone, semiquinone, semiquinone ester, quinol, and/or quinol esters of the dopamine and/or dopamine analogs. Another aspect of this disclosure relates to the product formed by such a process.

A portion of this disclosure is directed to core-shell particles having a shell of dopamine-based thermoplastic polymer and their application to a surface of a tribological material to be used as an interface with a bearing material in the formation of a bearing component. The core-shell particles are produced by the introduction of particles into a reaction mixture in which the polymerization of dopamine and/or dopamine analogs occurs, where the particles function as a core upon which a shell layer of dopamine-based thermoplastic polymer becomes deposited (the polydopamine polymer forms a shell on the particle which serves as a core). Thermoplastic shell layers of polydopamine polymers can be formed upon a variety of core materials including, but not limited to, inorganic materials (e.g., metal or metalloid oxides) or core polymers (also referred to as core polymeric materials, e.g., either non-fluorinated or fluorinated thermoset plastics, or non-fluorinated or non-fluorinated thermoplastics). Core polymers include, but are not limited to, materials such as vinylidene fluoride polymers or copolymers, vinyl chloride copolymers, and polytetrafluoroethylene (PTFE) in the form of sheets or particles. Solution-phase polymerization of dopamine in the presence of one or more types of core particles can result in the formation of a suspension (e.g., colloidal suspension) of core particles with a shell layer of dopamine-derived polymer deposited, partially grafted, or fully grafted on the particles' surfaces. The composite core-shell polymer particles may be designed to function as hot-melt pressure sensitive adhesive compositions for coupling bearing interfaces or surfaces including, among other things, low surface energy polymeric substrates such as PTFE and/or polyolefin with high surface energy metallic surfaces.

The core of a core-shell particle may constitute about 45% to about 90% of the total weight of the core-shell particle, and the shell about 10% to about 55% of the total weight of the particle on a dry weight basis. Dopamine and/or dopamine analogs may constitute up to about 70% (e.g. from 20%-35%, 35%-50%, 50%-60%, or 60%-70%) of the weight of the shell on a dry weight basis.

The disclosure also describes core-shell particles and suspensions of core-shell particles comprising a core and a shell, wherein: a) the core is comprised of about 45 percent to about 100 percent of core polymer material on a dry weight basis; and b) the shell is comprised of about 10 to about 55 percent on a dry weight basis of dopamine monomers polymerized with one or more carboxylic acids and/or one or more carboxylic acid anhydrides to form a shell polymer; wherein the core-shell polymeric particles are thermoplastic and display hot-melt pressure sensitive adhesive properties. From 0 to 100 percent of the polymer forming the shell may be grafted (covalently bound) to the polymer forming the core (e.g., covalently bound to the backbone of the core polymer material).

An aspect of the disclosure is directed to core-shell particles having a core particle that is comprised of a) about 90 to about 95 percent of one or more polymerized olefins (e.g., vinyl monomers and/or fluorinated olefin monomers such as in a PTFE core particle) on a dry weight basis, and b) up to about 10 percent of divinyl, trivinyl or tetravinyl monomers (e.g., allyl methacrylate, ethylene glycol dimethacrylate or trimethylolpropane trimethylate), or a mixture thereof, on a dry weight basis; and a shell that comprises about 10 to about 55 percent on a dry weight basis of dopamine monomers polymerized with one or more carboxylic acids and/or one or more carboxylic acid anhydrides to form a shell polymer; wherein the core-shell polymeric particles are thermoplastic and display hot-melt pressure sensitive adhesive properties. From 0 to 100 percent (e.g., from 0 to 10, from 10 to 30, from 30 to 60, from 60 to 80 or from 80 to 100 percent) of the polymer forming the shell may be grafted (covalently bound) to the polymer forming the core (e.g., covalently bound to the backbone of the core polymer material).

Another aspect of the disclosure is directed to core-shell particles having a core particle that is comprised of a) about 70 to about 100 percent of one or more polymerized olefins (e.g., vinyl monomers and/or fluorinated olefin monomers such as in a PTFE core particle) on a dry weight basis, and b) up to about 30 percent of divinyl, trivinyl or tetravinyl monomers (e.g., allyl methacrylate, ethylene glycol dimethacrylate or trimethylopropane trimethylate), or a mixture thereof, on a dry weight basis; and a shell that comprises about 10 to about 55 percent on a dry weight basis of dopamine monomers polymerized with one or more carboxylic acids and/or one or more carboxylic acid anhydrides to form a shell polymer; wherein the core-shell polymeric particles are thermoplastic and display hot-melt pressure sensitive adhesive properties. From 0 to 100 percent (e.g., from 0 to 10, from 10 to 30, from 30 to 60, from 60 to 80 or from 80 to 100 percent) of the polymer forming the shell may be grafted (covalently bound) to the polymer forming the core (e.g., covalently bound to the backbone of the core polymer material).

The core particle may comprise a polymeric material (a “core polymer”) that comprises, consists essentially of, or consists of a thermoplastic particle, such as a thermoplastic fluoropolymer (e.g., polytetrafluoroethylene (PTFE)) particle. In such embodiments, the core polymer material may have a glass transition temperature ranging from −103° C. to 200° C. (e.g., −103° C. to −50° C., −50° C. to 0° C., 0° C. to 50° C., 50° C. to 100° C., 100° C. to 150° C., or 150° C. to 200° C.).

The shell may comprise dopamine HCl monomers polymerized with (in the presence of) one or more carboxylic acids and/or one or more carboxylic acid anhydrides to form a shell polymer. The shell polymer of a core-shell particle may also comprise a polydopamine polymer that is a copolymer or heteropolymer comprising dopamine analogue.

The polydopamine polymers forming the shell may be partially or fully grafted onto the core or core polymer thereby forming covalent attachments between the core and shell of the core-shell polymeric particles.

The particle size distribution of the core-shell polymeric particles may be bimodal or multimodal. In an embodiment the distribution is bimodal and the diameter measurement of the core-shell polymeric particles has a peak in the range of 0.01 μm to 0.5 μm, and a peak in the range of 0.5 μm to 1.0 μm.

This disclosure also describes hot-melt pressure sensitive adhesive coatings comprising core-shell polymeric particles. Such pressure sensitive adhesives comprising core-shell particles can function to join the surfaces of various materials such as metals and low surface energy polymers (e.g., PTFE, expanded-PTFE, FEP or expanded-FEP) under mechanically abrasive environments at temperatures ranging from ambient (about 20° C.) to 360° C. (e.g., from 200° C. to 300° C., from 230° C. to 330° C., or from 300° C. to 350° C.), and/or pressures ranging from sub-atmospheric (e.g., 0.1 Pa (or less)) to 22 MPa (e.g., less than 0.1 Pa, 0.1 Pa to 100 Pa, 100 Pa to 100,000 Pa, 0.1 MPa to 1 MPa, or 1 MPa to 22 MPa), where “Pa” is a Pascal and MPa is a mega Pascal.

Also described herein are methods of making polydopamine polymers (e.g., esterified polydopamine polymers) and the use of such polymers as primers and/or adhesives between diverse materials including polymers (thermoset and/or thermoplastic polymers), metals, glasses, ceramics, metal oxides, metalloid oxides and the like. The polydopamine polymers and core-shell particles comprising a shell of polydopamine polymer find particular application as an adhesive in demanding applications including, but not limited to, the manufacture of bearings and tribological materials where plastic/polymeric components (e.g., fluoropolymer and perfluoropolymers) need to be secured to other materials including metals or metal alloys). The polydopamine polymers and core-shell particles comprising a shell of polydopamine polymer may also be used to secure plastics and polymers to metals and other surfaces in applications such as wire/conductive surface insulation (e.g., polyimide-fluoropolymer composites).

A portion of this disclosure is directed to mechanical bearings comprising: a substrate bonded to a tribological material by an adhesive comprising hot-melt pressure-sensitive core-shell polymeric particles; wherein the hot-melt pressure-sensitive core-shell polymeric particles comprise a core and a shell; wherein the adhesive is comprised of up to about 95% by weight of the core-shell polymeric particles based on the weight of the adhesive; and whereina. the core comprises a polymeric particle comprised of one or more polymers or the core is an inorganic particle comprised of one or more non-metallic inorganic materials,b. the shell comprises a thermoplastic polydopamine polymer comprised of dopamine and/or dopamine analog monomers polymerized with one or more carboxylic acids, andc. 0 to 100 percent (e.g., from 5%-10%, from 10%-25%, from 25%-50%, from 50%-75% or 75%-100%) of the shell polydopamine polymer is grafted onto the core.

A portion of this disclosure is directed to methods associated with the use of thermoplastic polydopamine polymers and core-shell particles having a shell of such particles as adhesives in the preparation of mechanical bearings. Accordingly, the disclosure provides methods of forming mechanical bearings or bearing components comprising a substrate bonded to a tribological material by an adhesive comprising hot-melt pressure-sensitive core-shell polymeric particles, the method comprising applying a composition comprising the core-shell particle to all or part of the substrate and/or tribological material and contacting the substrate with the tribological material at a point where the composition has been applied. The disclosure also provides methods of preparing adhesive tribological materials, comprising applying a composition comprising core-shell particles (e.g., an aqueous composition) to all or part of the tribological material and optionally heating the tribological material. Methods of coating all or part of a bearing's substrate or a tribological material with an adhesive comprising hot-melt pressure-sensitive core-shell polymeric particles are also disclosed and provided for.

