Patent Description:
Polyurea grease has gained widespread attention for its high temperature stability and low noise characteristics attributed to its unique organic type of thickener as compared to traditional metal-based soap grease such as lithium-based grease. Lithium based grease currently has more than <NUM>% of grease market share, however, is under threat due to the rapid growth of electric vehicles that is expected to tighten the lithium supply. Polyurea grease despite its potential to replace lithium grease, on the other hand, is facing the challenges and difficulties in its manufacturing that is traditionally made in situ at high temperature often in excess of <NUM> by reacting isocyanates such as MDI and TDI with amines in the presence of base oils.

The pre-form thickener approach by first forming polyurea thickener and then reacting the said thickener with base oils to achieve the polyurea grease is highly attractive to many as it takes awaythe difficulties in managing the toxic and hazardous nature of the isocyanate and amine raw materials. The first prior art disclosed a continuous reaction screw (<CIT>) has failed to yield the thickener that is able to achieve desired grease matters with consistency and workability.

<CIT> employs high shear continuous mixer through in-situ mixing of isocyanates and amines and the use of liquid to produce master batch and subsequent recovery of dry powder with broad particle size distribution.

The spray drying at moderate pressure (<CIT>) employed a large excess of solvent that deems to be impractical for commercial operation and the recovered dry powder, (poly)urea particles to the total weight of the solvents of from <NUM>:<NUM> to <NUM>:<NUM>. This and other solvent based prior art compositions do not define the particle size distribution that has direct impact to the structural stability of the grease.

<CIT> disclosed an encapsulated approach wherein the powder was made via high pressure impingement device. Clogging in the impingement device was noted in the absenceof liquid diluent. However, in the presence of diluent oils, the powder resulted in porous and sponge like powder, and again with broad particle size distribution.

The presence of liquid diluent, such as solvent and base oils, limits its practicability for large scale and broad commercial production. Large particle size and broad distribution has direct and immediate impact to the subsequent grease making process and ultimate grease product performance resulting in lower thickener yield and reduced high temperature and structural stabilities. The foregoing highlights the difficulties and challenges in the making of polyurea preform thickener.

<CIT> discloses a method for preparing a grease, comprising preparing a first mixture comprised of a lubricating base oil and at least one amine, and a second mixture comprised of a lubricating base oil and at least one isocyanate, and mixing the two mixtures together under high pressure and high flow rate impingement conditions to thereby have the at least one amine and at least one isocyanate react and have the reaction product dispersed throughout the lubricating base oil, with the reaction and dispersion occurring nearly simultaneously.

There is a need for a non-metallic grease with soap like structures, that exhibits high temperature stability, low noise characteristic, good mechanical and oxidation properties and high-shear stability. Accordingly, one object of this invention is to develop a commercial viable and energy saving process in the making a novel preform polyurea thickener composition with well-defined particle sizes characteristics unique in the art and with the consistency and reliability/performance not previously attainable.

In view of the foregoing and to overcome the problems associated with the prior art, there is described a method of making a urea containing powder that comprises injecting at least one liquid amine and at least one liquid isocyanate simultaneously into a mixing chamber. The mixture chamber comprises at least one high pressure impingement mixing device, which is used to mix the amine and isocyanate at a high pressure, such as at least <NUM>,<NUM> MPa (<NUM> psi) for a time to form a first urea containing powder with substantially no unreacted isocyanates. Mixing time of mixing in the impingement device is typically less than <NUM> seconds such as <NUM> to <NUM> seconds, and results in a powder having an average particle size (D50) represented as D1, and molecular weight distribution (D90-D50) represented as DD <NUM>.

The method further comprises feeding the first urea containing powder into a sizing device to form a second urea containing powder with an average particle size (D50) represented as D2, wherein D2 is less than D1, and particle size distribution (D90-D50) represented as DD2, wherein DD2 is less than DD1.

The described method produces a urea containing powder composition with a stoichiometric mole ratio of isocyanates and amine functionalities.

In one embodiment, the method described herein further comprises at least one shear thickening step to form a thickened polyurea containing master batch. In this embodiment, the shear thickening step comprises a continuous shear driven process that includes mixing dry powder comprising the urea containing powder with at least one base oil, wherein the dry powder and base oil are mixed in a weight ratio ranging from <NUM>/<NUM> to <NUM>/<NUM>.

In yet another embodiment, the method described herein further comprises forming a polyurea grease by gelling under heat, such as a temperature ranges from <NUM> to <NUM> for the first or second urea containing powder, or from ambient to <NUM> for the urea containing master batch, in the presence of an oil to form a gelled product and milling the gelled product to produce a polyurea grease with a smooth consistency and texture. The resulting grease has been shown to have excellent heat stability, as evidenced by a dropping point at least <NUM>.

Aside from the subject matter discussed above, the present disclosure includes a number of other features such as those explained hereinafter. Both the foregoing description and the following description are exemplary only.

The accompanying figures are incorporated in and constitute a part of this specification.

As used herein, an "impingement device" also known as an "impingement mixer" refers to a mixing device which causes high velocity streams of multiple liquids to impinge in a small chamber. The impinging jet configuration typically causes turbulent flow which mixes the precursors, i.e., amine and isocyanate liquids, as they flow out of the chamber.

As used herein, the term "dropping point" of a grease is an indication of the heat resistance of the grease and is the temperature at which it passes from a semi-solid to a liquid state under specific test conditions. It is dependent on the type of thickener used and the cohesiveness of the oil and thickener of a grease.

As used here in, "gel or gelling" or any version thereof, means the formation of thicken material between the base oils with the first and second urea containing powders.

As used herein, "high temperature stability" means having a dropping point of at least <NUM>, such as at least <NUM>, and even at least <NUM>.

As used herein, "structural stability" means having an NLG grease grade change from <NUM> strokes to <NUM>,<NUM> strokes to less than one NLGI grade, a worked penetration (Pw) number of less than <NUM>.

As used herein, "base oil (Group I, II, III, IV and V)" refers to without limitation, naphthenic oils, synthetic naphthenic oils such as alkyl benzene, diphenyl either, biphenyl, and alkylated naphthalene. These oils are preferred due to their inherent high stability and solvency resulting in higher grease yield (less thickener dosage).

As used herein, the phrase, "super fine," such as used to describe a polyurea thickener powder, means a D50 size, determined via laser light scattering, ranging from <NUM>-<NUM> micron, such as <NUM>-<NUM> micron, even <NUM>-<NUM> micron, and particle size distribution (D90-D50) to <NUM> micron, such as <NUM> micron, or even <NUM> micron.

As used herein, "smooth consistency" means free of discernible or measurable lumps or other irregularities.

As used herein, "residence time" means the time the amines and isocyanate spend in the mixing chamber prior to exiting the chamber.

As used herein, "ultra-high pressure", as used with regard to the mixing chamber(s) and device(s) herein, means a pressure more than <NUM>,<NUM> MPa (<NUM>,<NUM> psi), more than <NUM>,<NUM> MPa (<NUM>,<NUM> psi), and up to <NUM>,<NUM> MPa (<NUM>,<NUM> psi). Ranges for these specific endpoints are also included within this definition, such as a pressure ranging from <NUM>,<NUM> MPa (<NUM>,<NUM> psi) to <NUM>,<NUM> MPa (<NUM>,<NUM> psi), and any range in between.

As used herein, the "NLGI consistency number" (sometimes called "NLGI grade") expresses a measure of the relative hardness of a grease used for lubrication, as specified by the standard classification of lubricating grease established by the National Lubricating Grease Institute (NLGI). NLGI numbers range from <NUM>-<NUM> and reflect an increased hardness with increasing numbers. For example, an NLGI number of <NUM> defines a semi-fluid while a grease having an NLGI number of <NUM> is very hard. A grease having an NLGI number of <NUM> is considered a "normal" grease while a grease having an NLGI number of <NUM> is considered very firm.

As used herein, "penetration" is the depth measured in tens of millimeter when a cone of a specific weight into the grease according to ASTM D217.

As used herein, "Delta P100,<NUM>" is the worked penetration (Pw) number change from <NUM> strokes to <NUM>,<NUM> strokes.

Disclosed herein is a novel process of making urea containing powder(s), also referred to herein as a "polyurea grease thickener composition" in pure and super fine powder form. In one embodiment, the urea containing powder described herein can be made in the absence of any solvent or base oils. It also can be made using negligible amounts of solvents or base oils. In both cases, the disclosed powder has well-defined particle size that effectively yields a polyurea grease with consistency and workability, as well as excellent high temperature and structural stability. The disclosed urea containing powders achieve the performance required for the grease by incorporating, without limitation, all necessary components such as various base oils and additives known to the industry.

Thus, according to a first embodiment described herein, and with reference to <FIG>, a ultra-high pressure mixing device <NUM> simultaneously receives at least one amine (<NUM> - Feed A) and at least one isocyanate (<NUM> - Feed I) under ultra-pressure. In an embodiment, feeds A (<NUM>) and I (<NUM>) are supplied to the mixing chamber via fixed or variable pumps to deliver stoichiometric equivalence to ensure complete formation of urea functionalities. These feeds are typically in liquid form and introduced into a mixing chamber <NUM> comprising one or multiple impingement devices at a temperature ranging from ambient to <NUM>, such as from <NUM> to <NUM> that are sufficient to maintain the feeds in liquid form and a back pressure of least <NUM>,<NUM> MPa (<NUM>,<NUM> psi), or <NUM>,<NUM> MPa (<NUM>,<NUM> psi), up to <NUM>,<NUM> MPa (<NUM>,<NUM> psi).

In one embodiment, the impingement devices described and used herein have a pore size, dimension, and geometry from flat to textured, necessary to achieve a residence time less than <NUM> seconds, such as less than <NUM> seconds or even less than <NUM> seconds. In another embodiment, the residence time is further determined by the feed temperature as well as the ultra high pressure applied to the impingement devices. The resulting urea containing powder is formed in the mixing chamber having a first particle size D1 (D50, determined via laser light scattering) and particle size distribution DD1 (D90-D50), which is subsequently fed <NUM> to a sizing (milling/grinding) device <NUM> that yields the powder <NUM> with an even narrower and well defined average particle size D2 (D50, determined via laser light scattering) within <NUM>-<NUM> micron, such as <NUM>-<NUM> micron, even <NUM>-<NUM> micron and particle size distribution (D90-D50) to <NUM> micron, such as <NUM> micron, or even to <NUM> micron. As mentioned, in various embodiments, the urea containing powder described herein can be made in the absence of any solvent or base oils, can be made using negligible amounts of solvents or base oils, or can be made using a predefined amount of base oil(s) or solvent(s).

According to a second embodiment disclosed herein, and with reference to <FIG>, there is disclosed a continuous shear driven process <NUM>, for instance but without limitation, a shear driven device <NUM>, such as a twin screw extruder by co-feeding a polyurea ("PU") thickener powder, as made according to the first embodiment, such as described with reference to <FIG>, and at least one solvent or base oil. In one embodiment, the powder made according to the first embodiment is continuously feed into a shear driven device <NUM>. In this second embodiment, the polyurea powder is mixed with appropriate base oils in a weight ratio from <NUM>/<NUM> to <NUM>/<NUM> to form a thickened polyurea master batch <NUM>. The thickened polyurea master batch <NUM> can be made into various forms, including but not limited to noodles, pallets, or in paste forms with average particle size (D50) within <NUM>-<NUM> micron, such as <NUM>-<NUM> micron, or even <NUM>-<NUM> micron.

According to the third embodiment disclosed herein, and with reference to <FIG>, a polyurea master batch made via the second embodiment <NUM> is further treated with at least one finishing device <NUM>, such as an appropriate mixing/grinding devices including, but not limited to, high speed mixer, pin, or ball mills, or any other appropriate devices such as homogenizer known to the art to produce a polyurea grease <NUM>. The method described herein to make the polyurea grease is performed under thermal conditions that are substantially lower than known prior art methods, such as from ambient temperature up to <NUM>, such as up to <NUM>, or even up to <NUM>.

In addition, the resulting polyurea grease <NUM> has a smooth fiber texture with excellent high temperature and structural stability. According to the various embodiments disclosed herein, polyurea grease has structural and thermal stability as evidenced by a dropping point up to <NUM> and above, such as from <NUM> and above, or even from <NUM>.

As described herein, in one embodiment the method of making a polyurea containing powder includes injecting liquid amines (Feed A) and liquid isocyanate (Feed I), together referred to as "liquid precursors", under ultra-pressure and temperature conditions simultaneously into a mixing chamber comprising one or more impingement devices.

The temperature conditions are high enough to maintain liquid states for the feeds as the liquids are fed through one or more impingement devices and back pressure conditions are sufficiently high, such as more than <NUM>,<NUM> MPa (<NUM>,<NUM> psi), such as <NUM>,<NUM> MPa (<NUM>,<NUM> psi), up to <NUM>,<NUM> MPa (<NUM>,<NUM> psi).

The overall residence time of the liquid precursors within the mixing chamber is determined, but not limited by the chamber design, pressure, and temperature. In various embodiment, the residence time is within <NUM> seconds, such as within <NUM> seconds, or even within <NUM> seconds, and in some cases instantaneous. Residence time also varies with the nature of the precursors, such as functionalities and molecular weight of isocyanate and amines used. For example, for certain aromatic isocyanates, such as methylene diphenyl diisocyanate (MDI) and aliphatic amines, the residence time is less than <NUM> seconds, less than <NUM> seconds, less than <NUM> seconds, less than <NUM> seconds, or even less than <NUM> seconds, or even shorter. Failures to control residence time could result in clogging wherein the introduction of solvent or oils would become necessary, thus fundamentally change the integrity/morphology/composition of the polyurea thickener from dry powder to paste or spongy/wet powders.

According to the present invention, the polyurea powder made after the ultra-high pressure mixing chamber can be used in the subsequent grease conversion. It is contemplated however, to further optimize the grease yield so it is highly desirable to be fed through the sizing chamber that results in well-defined average particle size (D50) within <NUM>-<NUM> micron, such as <NUM>-<NUM> micron, such as <NUM>-<NUM> micron and particle size distribution (D90-D50) to <NUM> micron, such as <NUM> micron, or even to <NUM> micron.

In one embodiment, the sizing device is carried out in continuous and batch process via size reduction techniques such as air or mechanical impact mills, including but not limited to, air classification, air jet, pin or ball mill or hammer/screen mill from ambient to temperature up to <NUM>.

According to an aspect of the present disclosure, the polyurea thickener may be exemplified as isocyanates being methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI), respectively as follows:
<CHM>
<CHM>.

The amines (R1 and R2) represent chemicals with amine functionalities that are aliphatic, alicyclic, aromatic amines, primary or secondary, linear or branched, mono or diamine, alcohol or alkoxy containing amines, or other amine derivatives, and mixtures thereof.

Examples of such amines, without limitation, include fatty amine such as lauryl, stearyl, or tallow amines, cyclohexyl and dicyclohexyl amine, benzylamine, aniline, diamine such as ethylene diamine and alike, mono or polyetheramine such as Jeffamine M or D and the alike.

The chemistry and molar ratio of amines vary as desired to achieve the rheological and performance required by the grease. In one embodiment, as exemplified by a diurea composition where MDI and mono amines such as fatty amine and cycloalkyl amine are used, the molar ratio of which varies from <NUM>/<NUM> to <NUM>/<NUM>. In others embodiments, amines such as mono and diamine or amines with other functionalities, The mixing chamber should be adjusted accordingly to accommodate the desired molar ratio of isocyanate (<FIG>, <NUM> - Feed I) to overall amines (FIG. <NUM>, <NUM> - Feed A) so the urea formation is fully achieved.

In another embodiment, alkanolamine such as ethanolamine or similar, or other functionalized amine that would allow a slight excess of isocyanates and provide alcohol functionalities to the resulting polyurea thickener can be used.

In yet another embodiment the selection of amine derivates and when a mixture of amine used, for instance, the aromatic amine is chosen over the aliphatic amine and the ratio of which will impact the resulting grease performance.

Isocyanates such as MDI (methylene diphenylene diisocyanate) and TDI (toluene di-isocyanate) are the two most popular choices in the grease industry. Others are certainly possible such as polymeric and isomeric MDI alternatives.

According to one aspect of the present disclosure, the polyurea thickener master batch shown in <FIG> is prepared using a continuous shear driven device, such as twin-screw extruder by co-feeding the super fine powder (from the first embodiment, <FIG>) and the base oils of choice in a weight ratio from <NUM>/<NUM> to <NUM>/<NUM> through the twin screw extruder. The extruder used is designed to provide from mild to the maximum shear, and thus further control the thickener particle size. By controlling the through flow of the powder/base oil mixture through a close clearance between the screw and wall clearance, the operator has another variable to adjust and provide both maximum milling effect and resulting properties in the polyurea master batch. The resulting master batch can be in in noodles, pallets, or in paste forms with average particle size (D50) within <NUM>-<NUM> micron, such as <NUM>-<NUM> micron, or even <NUM>-<NUM> micron.

In one embodiment, the continuous shear driven device as described is able to provide the preform polyurea thickener in various forms, such as noodle, extrudate, or paste forms with even small particle sizes with a significant decrease in the severity of process conditions, e.g., temperatures needed for grease conversion, while eliminating the need for subsequent milling.

In one embodiment, when a harder grease is desired, base oils can be used in amounts of up to <NUM>%. When added in these amounts to a twin-screw extruder, a polyurea grease having a NLGI grade <NUM> and above is formed. To make a softer grease, base oils can be used in an amount of more than <NUM>%. In doing so, the twin screw extruder yields polyurea grease having NLGI grade <NUM> and higher.

In one embodiment besides twin-screw extruder, alternative shear driven mixing device such rotor stator mixer, internal mixer such as Banbury mixer, extruder, or homogenizer, with the ordinary skill of the art, deems applicable to facilitate the shear thickening aspect in the use of polyurea powder.

In one embodiment the type of base oils used in making master batch can be paraffinic or naphthenic (Group I/II/III) or any type of synthetic base oils (Group IV and V) without limitation, or naphthenic oils, synthetic naphthenic oils such as alkyl benzene, diphenyl either, biphenyl, and alkylated naphthalene are preferred due to its inherent high stability and solvency resulting in higher grease yield (less thickener dosage).

In one embodiment, the super fine polyurea thickener powder prepared according to the first embodiment (<FIG>) is gelled in the presence of base oil, such as a hydrocarbon base oil, at a temperature of <NUM> to <NUM>, such as <NUM>-<NUM>, or even at range of <NUM> to <NUM>. Gelling can be done in an ordinary grease kettle at an effective dosage from <NUM>-<NUM>% based on the content of the urea containing composition from the first and second powder till thicken in less than <NUM>-<NUM> hours. Upon thickening, and typically within <NUM> minutes thereafter, the heat to the kettle is turned off. The remaining oil and additives such as antioxidant, extreme pressure or anti-wear, rust preventives, pour point depressant, tackifier, polymer, or other additives are added as it cools and milled to consistency to its final/desired grease. The present disclosure allows NLGI No. <NUM> polyurea grease to be made with urea thickener dosage from <NUM>-<NUM>%.

In another embodiment, as shown and described in <FIG>, a final grease is made. For example, a polyurea master batch made according to the second embodiment (as shown and described in <FIG>) with appropriate mixing/grinding devices is used to make a final grease. The appropriate mixing/grinding devices contemplated herein include, but are not limited to, high speed mixer, air or mechanical mill, ordinary grease kettle, contactor, and homogenizer or any other appropriate wet dispersion devices.

As shown in <FIG>, a polyurea grease with smooth fiber texture and excellent high temperature and structural stability can be made using a much simpler process than described in the prior art. For example, the grease can be made under thermal conditions ranging from ambient temperature to <NUM>, such as up to <NUM>, or even <NUM>. In addition, the grease can be formed without the grinding and milling steps often required in current commercial processes.

The disclosed polyurea containing greases, the related embodiments thereof, including the polyurea containing powders and master batch made from the powder, and methods of making the same, may be used in applications that require stability under extreme lubrication conditions, such as high temperatures, high speeds and/or high loads. A non-metallic grease made according to principles of the present disclosure exhibit improved properties in the form of high temperature stability, low noise characteristic, good mechanical and oxidation properties, and high-shear stability. Accordingly, a non-metallic grease made according to principles of the present disclosure made be used for applications such as sealedfor-life bearings, ball bearing, electric motors applications, and the like.

The features and advantages of the present disclosure are more fully shown by the following examples which are provided for purposes of illustration and are not to be construed as limiting the invention in any way.

The following examples disclose methods of making polyurea containing dry powders, master batch compositions containing the dry powders, and greases made from the dry powders.

In this example, a <NUM> to <NUM> mole mixture of tallow and cyclohexyl amine and isocyanate was co-fed without solvent or base oil through variable ratio pump into a ultrahigh pressure mixing chamber with chamber dimensions such as orifice size and chamber length sufficient enough to accommodate residence time ranging from greater than <NUM> seconds up to <NUM> seconds and a pressure of <NUM>,<NUM> MPa (<NUM>,<NUM> psi). The resulting super-fine, dry powder had an averaged particle size (D50) of <NUM> micron without a trace of unreacted isocyanates. It was subsequently fed to a continuous sizing device yielding an averaged particle size of <NUM> micron.

In this example, a <NUM> to <NUM> mole ratio of tallow and cyclohexyl amine and isocyanate were co-fed via ultrahigh pressure mixing chamber at a pressure of <NUM>,<NUM> MPa (<NUM>,<NUM> psi) according to example <NUM>.

Tallow and cyclohexyl amine and isocyanate were co-fed by mole ratio via ultrahigh pressure mixing chamber at a pressure of <NUM>,<NUM> MPa (<NUM>,<NUM> psi) according to examples <NUM> and <NUM>.

In these examples varying amine ratio and functionalities such as tallow and cyclohexyl amine (example <NUM> and example <NUM> with alkylated naphthalene ("AN23") base oil added), dicyclohexyl amine (example <NUM>), ethanol amine (example <NUM>), Jeffamine D (examples <NUM> and <NUM>), at a pressure of <NUM>,<NUM> MPa (<NUM>,<NUM> psi).

The first and second urea powders exemplified by all the above examples (<NUM>-<NUM>) gelled readily within <NUM>/<NUM> hours and the grease formation is complete within <NUM>-<NUM> hours of heating during which a smooth grease is formed with excellent grease consistency and workability and excellent structural and high temperature stability with high dropping point more than <NUM> (see Table <NUM>). The second urea powder after sizing further improve the workability and consistency of the grease (reduced number of milling) and increase the yield of the thickener.

Comparative Example A was made in a procedure given in example <NUM> with <NUM>% of an alkylated naphthalene through a commercially available impingement device. Comparative Example B was made via a solvent (THF, tetrahydrofuran) process. In Comparative Example A the impingement device continually clogged during processing. Even after cleaning and clearing the clog, the device would continuously clog. In both comparative examples the resulting urea powders did not gel at <NUM> within two hours. Furthermore, upon extended heating, the grease formed had poor consistency, which required multiple milling steps.

The first urea powder (example <NUM>) and alkylated naphthalene (<NUM> cSt@100C) were fed into a twin screw extruder in a <NUM>/<NUM> and <NUM>/<NUM> volume ratio respectively at to <NUM> to <NUM> (<NUM> to <NUM> pounds) per hour. The resulting polyurea masterbatch was in paste forms that can be further cut into pallets/extrudates (Example <NUM>, see Table <NUM>) and in thick grease form (Example <NUM>). In the subsequent grease conversion, additional AN23 base oil was used to give a final <NUM>% yield resulting in polyurea grease with reduced process time/temperature and even less milling and superior structural/mechanical stability.

Claim 1:
A method of making a urea containing powder, comprising:
injecting at least one liquid amine and at least one liquid isocyanate simultaneously into a mixing chamber, said mixture chamber comprising at least one high pressure impingement mixing device;
mixing the at least one amine and the at least one isocyanate in the at least one high pressure impingement mixing device at a pressure of at least <NUM>,<NUM> MPa (<NUM> psi) for a time sufficient to form a first urea containing powder with substantially no unreacted isocyanates, said time is less than <NUM> seconds, wherein the first urea containing powder has an average particle size,(D50, determined via laser light scattering) represented as D1, and particle size distribution (D90-D50, determined via laser light scattering) represented as DD1;
feeding the first urea containing powder into a sizing device to form a second urea containing powder with an average particle size (D50, determined via laser light scattering) represented as D2, wherein D2 is less than D1, and particle size distribution (D90-D50, determined via laser light scattering) represented as DD2, wherein DD2 is less than DD1,
wherein the second urea containing powder composition has a stoichiometric mole ratio of isocyanates and amine functionalities.