BACKGROUND

Field of the disclosure

Ihe present disclosure is directed to lubricant compositions and more specifically to lubricant compositions comprising aqueous graphite dispersions utilizing polymeric dispersants.

Introduction

Hot forging is an industrial process where a metal workpiece is placed in a die and is deformed under pressure. The energy applied to the metal workpiece to plastically deform it is converted into heat. Repeated forging of workpieces and generation of heat raises the temperature of the of the die. A lubricant is used during forging at the interface between workpiece and die to reduce friction and to ensure the workpiece can be removed from the die. Good lubrication can improve the workpiece deformation, favor accurate filling of the die cavities, reduce tool wear at those points with free flow movement and high specific pressures, and reduce the forging force. Such features will lessen the stresses induced in the forging tool and prevent direct tool to w'orkpiece contact, which contributes to longer tool life and betterquality control.

In recent years, the lubricant of choice for hot forging has been a water-based lubricant. Water based lubricants typically include water as a carrier and a lubricating particle such as graphite. Water based lubricants adhere the graphite to the die to form a solid coating on the die as the water evaporates. Water based lubricants are advantaged relative to oil-based lubricants as oil-based lubricants tend to run off the die surface and be squeezed out of the work piece/die interface under pressure. Water based lubricants are not without disadvantages though. Graphite dispersions in water are not stable and require continuous agitation otherwise flocculation and sedimentation occur. Flocculation and sedimentation occurring in lubricant holding tanks can result in an incorrect amount of graphite being applied to the die thereby decreasing the useful life of the die. Flocculation and sedimentation can also result in clogged pipes and spray nozzles intended to apply the lubricant to the forging die. Ideally, a graphite dispersion will resist sedimentation for extended periods of time. One measurement of waterbased lubricants examines if the lubricant can maintain 80% dispersion of the graphite after 24 hours with the sediment remaining in a dispersible form (“Sedimentation Test”).

There have been attempts at decreasing the flocculation and sedimentation of waterbased graphite dispersions using dispersants. The theoretical explanation for the efficacy of different dispersants on graphite is not agreed upon. For example, United States Patent Application Publication number US20090305052A1 (“the ‘052 publication”) discloses stable aqueous graphite dispersion with high solids content. The ‘052 publication achieves a higher solid loading content in its aqueous graphite dispersion by utilizing a dispersant such as lignosulfonic acids which comprise aromatic ring/phenyl groups and ionic sulfonate groups.

Chinese patent application publication number CN111925697 A (“the ‘697 publication”) provides a graphene and water-soluble polymer dispersant composite material that can be dispersed in water to form a membrane. The ‘697 publication explains that an enhanced aqueous graphene dispersion can be obtained by the inclusion of water-soluble polymer dispersant containing an aromatic ring structure and ionic sulfonate groups because the dispersant improves the compatibility between the surface inert graphene and the water- soluble polymer due to pi- pi interaction between the dispersant and the graphene.

In view of the importance for dispersants used with graphitic materials to comprise aromatic structures and ionic sulfonate groups as demonstrated by the prior art, it would be surprising to discover a dispersant that is able to pass the Sedimentation Test while not comprising aromatic or ionic sulfonate moieties.

SUMMARY OF THE DISCLOSURE

The present disclosure provides dispersants that can pass the Sedimentation Test but do not comprise aromatic structures or ionic sulfonate moieties. The inventor of the present application has discovered that lubricant compositions comprising non-ionic polymeric dispersants comprising monomeric structural units derived from acrylic acid and monomeric structural units derived from 2-acrylamido-2-methylpropane sulfonic acid are able to pass the Sedimentation Test. Such a result is surprising in that despite the prior art’s suggestions that phenyl or aromatic ring structures are a necessary component to achieve compatibilization between the dispersants and the graphite thus stabilizing the dispersion, the dispersants of the present application do not have such structures. Further, the dispersants of the present invention do not comprise ionic sulfonate moieties yet are still able to pass the Sedimentation Test.

The present disclosure is particularly useful for the formation of lubricants utilizing graphite.

According to a first feature of the present disclosure, a lubricant composition comprises water, graphite, a thickener, and a polymeric dispersant comprising monomeric structural units derived from acrylic acid and monomeric structural units derived from 2-acrylamido-2- methylpropane sulfonic acid. According to a second feature of the present disclosure, the lubricant composition comprises 20 wt% to 60 wt% water based on a total weight of the lubricant composition.

According to a third feature of the present disclosure, the lubricant composition comprises 10 wt% to 60 wt% of graphite based on a total weight of the lubricant composition.

According to a fourth feature of the present disclosure, the graphite has a D90 particle diameter of from 0.5 pm to 5.0 pm.

According to a fifth feature of the present disclosure, the polymeric dispersant has a weight average molecular weight of 3,000 g/mol to 6,000 g/mol as measured according to gel permeation chromatography.

According to a sixth feature of the present disclosure, the lubricant composition comprises 0.01 wt% to 1.0 wt% of the dispersant based on a total weight of the lubricant composition.

According to a seventh feature of the present disclosure, the polymeric dispersant comprises 20 wt% to 30 wt% of monomeric structural units derived from 2-acrylamido-2- methylpropane sulfonic acid based on a total weight of the polymeric dispersant.

According to an eighth feature of the present disclosure, the polymeric dispersant has a weight average molecular weight of 4,000 g/mol to 5,000 g/mol as measured according to gel permeation chromatography

According to a ninth feature of the present disclosure, the polymeric dispersant comprises monomeric structural units derived from N-tert-butylacrylamide.

According to a tenth feature of the present disclosure, the polymeric dispersant comprises 1 wt% to 30 wt% of the monomeric structural units derived from N-tert- butylacrylamide based on a total weight of the polymeric dispersant.

DETAILED DESCRIPTION

As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

All ranges include endpoints unless otherwise stated. As used herein, the term weight percent (“wt%”) designates the percentage by weight a component is of a total weight of the polymeric composition unless otherwise specified.

As used herein, Chemical Abstract. Services registration numbers (“CAS#”) refer to the unique numeric identifier as most recently assigned as of the priority date of this document to a chemical compound by the Chemical Abstracts Service.

Lubricant composition

The present disclosure is directed to a lubricant composition. The lubricant composition comprises water, graphite, a thickener, and a polymeric dispersant comprising monomeric structural units derived from acrylic acid and monomeric structural units derived from 2- acrj'lamido-2-methylpropane sulfonic acid. The lubricant composition may comprise 20 wt% to 60 wt% water based on a total weight of the lubricant composition. For example, the lubricant composition comprises 20 wt% or greater, or 25 wt% or greater, or 30 wt% or greater, or 35 wt% or greater, or 40 wt% or greater, or 45 wt.% or greater, or 50 wt% or greater, or 55 wt% or greater, while at the same time, 60 wt% or less, or 55 wt% or less, or 50 wt% or less, or 45 wt% or less, or 40 wt% or less, or 35 wt% or less, or 30 wt% or less, or 25 wt% or less of water based on a total weight of the lubricant composition. The lubricant composition may comprise one or more other additives designed to alter a property of characteristic of the lubricant composition.

Thickener

The thickener is included in the lubricant composition to aid in the application and retention of the lubricant composition on surfaces. The thickener may comprise a polysaccharide such as agar, sodium alginate, rhamsam gum, locust bean gum, carrageenan, gum arabic, neem gum, gum chatti, caranna, galactomannan, gum tragacanth, karava gum, guar gum, welan gum, beta-glucan, cellulose, chicle gum, kino gum, dammar gum, glucomannan, acacia gum, cassia gum, mastic gum, spruce gum, pysllium seed husks, gellan gum, xanthan gum, diutan gum, fenugreek gum, ghatti gum, methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, karava gum, konjac gum, pectin and combinations thereof. Additionally or alternatively, the thickener may also include other viscosity modifying components such as polyethylene glycol, polyacrylic acid, polyethyleneimine, polyvinyl alcohol, polyacrylamides, carboxyvinyl polymers, poly(vinylpyrrolidinone) and copolymers, polyoxypropylene and combinations thereof. The lubricant composition may comprise 0. 1 wt% to 5.0 wt% thickener based on a total weight of the lubricant composition. For example, the lubricant composition may comprises 0.1 wt% or greater, or 0.2 wt% or greater, or 0.4 wt% or greater, or 0.6 wt% or greater, or 0.8 wt% or greater, or 1.0 wt% or greater, or 1.5 wt% or greater, or 2.0 wt% or greater, or 2.5 wt% or greater, or 3.0 wt% or greater, or 3.5 wt% or greater, or 4.0 wt% or greater, or 4.5 wt% or greater, while at the same time, 5.0 wt% or less, or 4.5 wt% or less, or 4.0 wt% or less, or 3.5 wt% or less, or 3.0 wt.% or less, or 2.5 wt% or less, or 2.0 wt% or less, or 1.5 wt.% or less, or 1.0 wt% or less, or 0.5 wt% or less of the thickener based on the total weight of the lubricant composition.

Graphite

The lubricant composition comprises graphite. The graphite may have spherical shape, a plate like shape, an oblong shape and/or an irregular shape. The particles of the graphite may have a D90 of from 0.5 microns (“pm”) to 10 pm. As used herein, the term “D90” means that 90% of the graphite particles have a diameter or longest length dimension smaller than the indicated value and 10% of the particles have a diameter or longest length dimension greater than the indicated value. The graphite may have a D90 particle size of 0.5 pm or greater, or 1.0 pm or greater, or 1.5 pm or greater, or 2.0 pm or greater, or 2.5 pm or greater, or 3.0 pm or greater, or 3.5 pm or greater, or 4.0 pm or greater, or 4.5 pm or greater, or 5.0 pm or greater, or 5.5 pm or greater, or 6.0 pm or greater, or 6.5 pm or greater, or 7.0 pm or greater, or 7.5 pm or greater, or 8.0 pm or greater, or 8.5 pm or greater, or 9.0 pm or greater, or 9.5 pm or greater, while at the same time, 10 pm or less, or 9.5 pm or less, or 9.0 pm or less, or 8.5 pm or less, or 8.0 pm or less, or 7.5 pm or less, or 7.0 pm or less, or 6.5 pm or less, or 6.0 pm or less, or 5.5 pm or less, or 5.0 pm or less, or 4.5 pm or less, or 4.0 pm or less, or 3.5 pm or less, or 3.0 pm or less, or 2.5 pm or less, or 2.0 pm or less, or 1.5 pm or less, or 1.0 pm or less. The D90 particle size of the graphite is determined using a Malvern Mastersizer™ laser diffraction particle size analyzer.

The lubricant composition comprises 10 wt% to 60 wt% of graphite based on a total weight of the lubricant composition. For example, the lubricant composition comprises 10 wt% or greater, or 15 wt% or greater, or 20 wt% or greater, or 25 wt% or greater, or 30 wt% or greater, or 35 wt% or greater, or 40 wt% or greater, or 45 wt% or greater, or 50 wt% or greater, or 55 wt% or greater, while at the same time, 60 wt% or less, or 55 wt% or less, or 50 wt% or less, or 45 wt.% or less, or 40 wt% or less, or 35 wt.% or less, or 30 wt% or less, or 25 wt.% or less, or 20 wt% or less, or 15 wt% or less of graphite based on a total weight of the lubricant composition.

Dispersant

The lubricant composition comprises the dispersant. The dispersant is a poly carboxyl ate dispersant comprising monomeric structural units derived from acrylic acid and monomeric structural units derived from 2-acrylamido-2-methylpropane sulfonic acid. The dispersant is a polymer. As used herein, the term “polymer” means a macromolecular compound comprising a plurality of monomers of the same or different type which are bonded together, and includes homopolymers and interpolymers. As used herein, the term “interpolymer” means a polymer comprising at least two different monomer types bonded together. Interpolymer includes copolymers (usually employed to refer to polymers prepared from two different monomer types), and polymers prepared from more than two different monomer types (e.g., terpolymers (three different monomer types) and quaterpolymers (four different monomer types)). The dispersant may comprise monomeric structural units derived from acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, N-tert-butylacrylamide, other monomer precursors and combinations thereof. The dispersant may be free of sulfonate ionic groups or moieties.

The dispersant may comprise from 40 wt% to 80 wt% of monomeric structural units derived from acrylic acid based on the total weight of the dispersant. For example, the dispersant may comprise 40 wt% or greater, or 45 wt% or greater, or 50 wt% or greater, or 55 wt% or greater, or 60 wt% or greater, or 65 wt% or greater, or 70 wt% or greater, or 75 wt% or greater, while at the same time, 80 wt% or less, or 75 wt% or less, or 70 wt% or less, or 65 wt% or less, or 60 wt% or less, or 55 wt% or less, or 50 wt% or less, or 45 wt% or less of monomeric structural units derived from acrylic acid based on the total weight of the dispersant.

The dispersant may comprise from 10 wt% to 40 wt% of monomeric structural units derived from 2-acrylamido-2-methylpropane sulfonic acid based on the total weight of the dispersant. For example, the dispersant may comprise 10 wt% or greater, or 15 wt% or greater, or 20 wt% or greater, or 25 wt% or greater, or 30 wt% or greater, or 35 wt% or greater, while at the same time, 40 wt% or less, or 35 wt% or less, or 30 wt% or less, or 25 wt% or less, or 20 wt% or less, or 15 wt% or less of monomeric structural units derived from 2-acryIamido-2- methylpropane sulfonic acid based on the total weight of the dispersant.

The dispersant, may comprise from 1 wt% to 30 wt% of monomeric structural units derived from N-tert-butylacrydamide based on the total weight of the dispersant. For example, the dispersant may comprise 1 wt% or greater, or 5 wt% or greater, or 10 wt% or greater, or 15 wt% or greater, or 20 wt% or greater, or 25 wt% or greater, while at the same time, 30 wt% or less, or 25 wl% or less, or 20 wt% or less, or 15 wt% or less, or 10 wt% or less, or 5 wt% or less of monomeric structural units derived from N-tert-butylacrylamide based on the total weight of the dispersant.

The dispersant may comprise from 40 wt% to 80 wt% of monomeric structural units derived from acrylic acid, from 10 wt% to 40 wt% of monomeric structural units derived from 2-acrylamido-2-methylpropane sulfonic acid, and 0 wt% to 30 wt% of monomeric structural units derived from N-tert-butylacrylamide based on the total weight of the dispersant. The dispersant may comprise any value within the v/t% ranges identified above for each monomeric structural unit. The dispersant may be end capped with poly(phthalaldehyde), Xylene, other end capping agents and combinations thereof.

The dispersant may have a weight average molecular weight of 3,000 grams per mole (“g/mol”) to 6,000 g/mol as measured according to gel penneation chromatography. For example, the weight average molecular weight of the dispersant may be 3,000 g/mol or greater, or 3,500 g/mol or greater, or 4,000 g/mol or greater, or 4,500 g/mol or greater, or 5,000 g/mol or greater, or 5,500 g/mol or greater, while at the same time, 6,000 g/mol or less, or 5,500 g/mol or less, or 5,000 g/mol or less, or 4,500 g/mol or less, or 4,000 g/mol or less, or 3,500 g/mol or less as measured according to gel permeation chromatography.

The dispersant may be suspended in a suspension agent such as water. In such a case, the amount of dispersant in the suspension agent is referred to as the solids content and is expressed as a weight, percent of the dispersant, based on the total weight, of the combined dispersant and suspension agent. The solids content may be from 20 wt% to 60 wt% based on a total weight of the combined dispersant and suspension agent. For example, the solids content may be 20 wt% or greater, or 25 wt% or greater, or 30 wt% or greater, or 35 wt% or greater, or 40 wt% or greater, or 45 wt% or greater, or 50 wt% or greater, or 55 wt% or greater, while at the same time, 60 wt% or less, or 55 wt% or less, or 50 wt% or less, or 45 wt% or less, or 40 wt% or less, or 35 wt% or less, or 30 wt% or less, or 25 wt% or less based on the total weight, of combined dispersant and suspension agent.

The lubricant composition may comprise 0.1 wt% to 5.0 wt% dispersant based on a total weight of the lubricant composition. For example, the lubricant composition comprises 0.1 wt% or greater, or 0.2 wt% or greater, or 0.3 wt.% or greater, or 0.4 wt% or greater, or 0.5 wt% or greater, or 0.6 wt% or greater, or 0.7 wt% or greater, or 0.8 wt% or greater, or 0.9 wt% or greater, or 1.0 wt% or greater, or 1.5 wt% or greater, or 2.0 wt% or greater, or 2.5 wt% or greater, or 3.0 wt% or greater, or 3.5 wt% or greater, or 4.0 wt% or greater, or 4.5 wt% or greater, while at the same time, 5.0 wt% or less, or 4.5 wt% or less, or 4.0 wt% or less, or 3.5 wt% or less, or 3.0 wt% or less, or 2.5 wt% or less, or 2.0 wt% or less, or 1.5 wt% or less, or 1.0 wt% or less, or 0.9 wt% or less, or 0.8 wt% or less, or 0.7 wt% or less, or 0.6 wt% or less, or 0.5 wt% or less, or 0.4 wt% or less, or 0.3 wt% or less, or 0.2 wt% or less of the dispersant based on the total weight of the lubricant composition.

Examples

Materials

The following materials were used in the examples.

Graphite is a powder of graphite particles having a D90 of 5.0 pm and is commercially available from Molygraph Lubricants, Mumbai, India.

Thickener is xanthan gum commercially available from Loba Chemie Mumbai, India.

Dispersant 1 is a solution of an alkylammonium salt of a polycarboxylic acid sold under the tradename ANTI-TERRA'''' ³ and is commercially available from BYK-Chemie GmbH,

Wesel, Germany.

Dispersant 2 is a 97 wt% actives powder having Structure (I), a CAS# of 9084-06-4 and is available from The Dow Chemical Company, Midland Michigan. Structure (I)

Dispersant. 3 is pure sodium dodecyl sulfate having a CAS# of 151-21 -3 and is available from Loba Chemie Mumbai, India.

Dispersant 4 is a homopolymer of monomeric structure units derived from acrylic acid that is end capped with poly(phthalaldehyde), has a weight average molecular weight of 2000 g/mol, has a 47-49 wt% solids content and is available from The Dow Chemical Company, Midland Michigan.

Dispersant 5 is a copolymer of approximately 75 wt% to 80 wt% of monomeric structural units derived from acrylic acid and 20 wt% to 25 wt% of monomeric structural units derived from 2-aciylamido-2-methylpropane sulfonic acid. Dispersant 5 has a weight average molecular weight of 4500 g/mol, is end capped with poly(phthalaldehyde) and has a solids content of 40 wt% to 45 wt% based on the total weight of the dispersant. Dispersant 5 is available from The Dow Chemical Company, Midland Michigan.

Dispersant 6 is a terpolymer of approximately 60 wt% to 70 wt% of monomeric structural units derived from acrylic acid, 25 wt% to 30 wt% of monomeric structural units derived from 2-acrylamido-2-methylpropane sulfonic acid and 5 wt% to 10 wt% of monomeric structural units derived from N-tert-butylacrylamide. Dispersant 6 has a weight average molecular weight of 4500 g/mol, is end capped with poly(phthalaldehyde) and a solids content of 40 wt% to 45 wt% based on the total weight of the dispersant. Dispersant 6 is available from The Dow Chemical Company, Midland Michigan.

Dispersant 7 is a terpolymer of approximately 55 wt% to 65 wt% of monomeric structural units derived from acrylic acid, 15 wt% to 25 wt% of monomeric structural units derived from 2-acrylamido-2-methylpropane sulfonic acid and 15 wt% to 25 wt% of monomeric structural units derived from N-tert-butylacrylamide. Dispersant 7 has a weight average molecular weight of 5000 g/mol and a solids content of 40 wt% to 50 wt% based on the total weight of the dispersant. Dispersant 7 is available from The Dow Chemical Company, Midland Michigan.

Sample Preparation

The examples w-ere prepared by first combining the thickener, the dispersant and a portion of the water and then mixing the solution for 1 minute using a stirrer. Next, the graphite powder was added slowly to the solution and mixed until a paste was formed. Next, the graphite paste was diluted with the remaining water and mixed using an overhead stirrer to form a dispersion having the composition listed in the Table 1. The diluted paste was then added to a 100 milliliter (“ml”) volumetric flask and filled to the 100 ml line.

Test Method

Sedimentation Test: The Sedimentation Test determines what percentage of the dispersion remains dispersed after a predetermined period of time. The 100 ml volumetric flask is filled to the 100 ml mark with the example and the flask is left undisturbed for the indicated period of time. The amount of example remaining dispersed is measured by visually observing the phase separation interface between a clear or hazy water phase and a dispersed graphite phase. The phase separation is determined by examining at what ml demarcation the graphite dispersion phase and water phase is at after an identified period of time, dividing by the initial 100 ml and multiplying by 100. For example, if the interface of the graphite dispersion phase and the water phase is at 95 ml, then 95% of the dispersion resisted phase separation. An example is considered to have passed the Sedimentation Test, if 80% of the example remains in the graphite dispersion phase after 24 hours (i.e., 1 day).

Results

Table 1 below provides the composition of each comparative example (“CE”) and each inventive example (“IE”) in weight percents of components while Table 2 provides the performance data of each IE and CE. The data of Table 2 provides the percent of the example remaining in the graphite dispersion phase. Hie entry “nm” indicates that a particular time interval was not measured.

Table 1

As can be seen from Tables 1 and 2, IE1-IE6 drastically outperform CE1-CE10 in terms of producing a lubricant composition that passes the Sedimentation Test as indicated by IE1 - IE6 all maintaining greater than 80% graphite dispersion after 24 hours. CE1 and CE2 demonstrate a baseline for the stability that can be expected from an aqueous graphite dispersion when no dispersants are included. CE4, CE7 and CE8 all demonstrate that the inclusion of certain dispersants can have no effect on dispersion stability or actually decrease the stability of graphite in water relative to dispersions having no dispersant as evidenced by lower percentages of retained graphite dispersion phases of CE4, CE7 and CE8 relative to CE1 and CE2. CE3, CE5, CE6, CE9 and CE10 all exhibit better dispersion stability than the control samples CEl and CE2, but fail to achieve the stability desired by the Sedimentation Test.

Unlike CE1-CE10, each of IE1-IE6 is able to maintain 80% or greater of the graphite dispersion phase after 24 hour of testing and therefore pass the Sedimentation Test. Such a result is surprising because despite the variety of types of dispersants tested, the polymeric dispersants which are free of phenyl or aromatic ring structures perform the best despite the suggestion to the contrary by the prior art. Even more surprising is that despite Dispersant 2 (i.e. CE5 and CE6) including multiple aromatic structures and ionic sulfonate moieties, the dispersants of IE1-IE6 exhibit better performance than CE2 without aromatic or ionic sulfonate moieties.