KR20180019871A - Grease composition with improved highest-pressure resistance and small friction force - Google Patents

Abstract

The present invention relates to a grease composition having improved highest-pressure resistance and low friction force at the same time. Specifically, the present invention relates to a grease composition having improved highest-pressure resistance and low friction force at the same time. The composition includes a base oil component including polyalphaolefin (PAO) synthetic base oil and alpha olefin ester-based copolymer base oil, a molybdenum dialkyldithiocarbamate (MoDTC) which provides abrasion resistance to the base oil, a mixture of zinc dithiophosphate (ZnDTP) and molybdenum dialkyldithiophosphate (MoDTP), and calcium sulfonate as a thickener for providing highest-pressure resistance and low friction force to the base oil.

Description

[0001] The present invention relates to a grease composition having improved both extreme pressure and low friction performance,

The present invention relates to a grease composition having simultaneously improved extreme pressure performance and low friction performance.

Grease is a semi-solid lubricant used to optimize the lubrication of mechanical components systems such as bearings and gears, which are key components in automotive and industrial applications. Typically, grease consists of base oil, thickener and additives.

Base oil is a component included to minimize viscosity change of grease with temperature. As the base oil, ester base oils, silicone base oils, or fluorine base oils are available. However, since the use of such base oils is limited due to problems such as high price, synthetic base oils of polyalphaolefin (PAO) .

Thickener is a component that determines the main properties such as heat resistance and water resistance of grease. Typically, the thickener is classified into a soap-type thickener such as barium, lithium, calcium, sodium or aluminum and a non-metal soap-type thickener such as silica gel, benton, urea or the like. The soap thickener includes a metal salt of a fatty acid, typically lithium 12-hydroxystearate. However, the metal component contained in the soap-based thickener acts as a catalyst causing oxidation and corrosion, which causes deterioration of the oxidation stability and thermal stability of the grease, has a limitation in application to high-load lubrication conditions, has low abrasion resistance It is pointed out that there are problems such as losing.

In addition, since the physical properties of grease can be greatly changed by the choice of additives, it is also important to select suitable additives such as anti-friction agents, antioxidants, and corrosion inhibitors.

Various studies have been made on the above-mentioned grease compositions containing additives such as PAO base oil, lithium thickener and viscosity adjuster. [0005] However, most of the grease compositions have limitations in maintaining excellent extreme pressure performance and friction performance at the same time under various temperature environments.

In order to improve the performance of the vehicle, parts using new technology are applied to various parts. Development of materials that can withstand the operating environment due to the miniaturization, integration and high output development of these parts is also essential. Particularly, in the case of a rack-type gear (R-MDPS) part which is applied to improve fuel efficiency as an automobile part, a ball screw part is required to have low friction performance for smooth rotation of balls, Extreme pressure performance is required. However, since the low friction performance and the extreme pressure performance of the grease are opposite to each other, it is very difficult to develop a grease that maintains both low friction performance and extreme pressure performance at a high level.

Korean Patent Registration No. 10-0513625 entitled "Grease Composition for Actuator" Korean Patent Registration No. 10-0135414 entitled "Grease composition for ball joint" Korean Patent Laid-Open Publication No. 10-2014-0054557 "Noise Reducing Grease Composition for Noise Reduction & Korean Patent Registration No. 10-1438916 entitled "Grease composition having excellent lubrication performance at low temperature &

It is an object of the present invention to provide a grease composition having an effect of simultaneously improving extreme pressure performance and low friction performance.

In order to provide a grease composition which simultaneously improves extreme pressure performance and low friction performance by optimal combination of base oil, thickener and anti-friction agent,

Wherein the base flow path comprises a polyalphaolefin (PAO) synthetic base oil and an alpha olefin-ester based copolymer base oil at a weight ratio of 1: 0.15 to 1: 1.9; The thickener includes calcium sulfonate, and the friction rubbing agent includes a mixture of molybdenum dialkyldithiocarbamate (MoDTC), molybdenum dialkyldithiophosphate (MoDTP), and zinc dithiophosphate (ZnDTP) And the like.

If conventional grease containing polyalphaolefin (PAO) synthetic oil is applied to the ball screw portion of a rack-type gear (R-MDPS) part of an automobile, the friction performance can be satisfactorily satisfactory, If the load is large, it may cause the vehicle noise problem due to screw surface damage.

However, the grease provided by the present invention is excellent in both the extreme pressure performance and the low friction performance, thereby minimizing damage to the surface of the ball screw.

1 is a schematic view of a rack-type gear (R-MDPS) part of an automobile. FIG. 1 is attached to explain that there is a problem of noise generation when the surface of a ball screw which is loaded during operation is damaged.

The present invention relates to a grease composition having an effect of simultaneously improving extreme pressure performance and low friction performance.

The grease composition of the present invention essentially includes (1) base oil, (2) thickener and (3) friction agent, and other usual grease additives may be included. Each component constituting the grease composition of the present invention will be described in more detail as follows.

(1) Base oil

The grease composition of the present invention is characterized by including a polyalphaolefin (PAO) synthetic base oil having excellent thermal properties as base oil and an alpha olefin-ester based copolymer base oil having excellent oil film characteristics.

The base oil contained in the grease composition of the present invention is preferably used at a temperature of 40 ° C of 150 to 250 cSt through appropriate blending of a polyalphaolefin (PAO) synthetic base oil and an alpha olefin-ester based copolymer. If the kinematic viscosity of the base oil is less than 150 cSt, it may cause dura- tion noise due to friction characteristics applied to the ball screw part of the rack-type gear (R-MDPS) parts. If it exceeds 250 cSt, It can show a tendency to be inferior in sex. In order to maintain the kinematic viscosity of the base oil in the above range, it is preferable to maintain the weight ratio of the polyalphaolefin (PAO) synthetic base oil and the alpha olefin-ester based copolymer base oil in the range of 1: 0.15 to 1: 1.9.

The polyalphaolefin (PAO) synthetic base oil is conventionally used in the art, and can have a viscosity at 40 DEG C of 150 to 250 cSt.

The alpha olefin-ester based copolymer base oil is prepared by copolymerizing an alpha olefin monomer with an ethylenically unsaturated carboxylic acid or a derivative thereof. In the oil field, There has been no application in the field of grease .

However, in the present invention, by using the above-mentioned alpha-olefin-ester copolymer as a base oil in a predetermined content ratio in a PAO synthetic base oil, extreme pressure performance and low friction performance are obtained by using the inherent film properties of the copolymer and excellent resistance properties to shearing At the same time, it has become possible to provide excellent grease compositions.

As the monomer constituting the above-mentioned alpha-olefin-ester-based copolymer base oil, alpha-olefins may be alpha-olefins having 6 to 18 carbon atoms. Specific examples thereof include 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, -Heptadecene, 1-octadecene, and the like. As the other monomers constituting the alpha-olefin-ester-based copolymer base oil, the ethylenically unsaturated carboxylic acid may be acrylic acid, methylacrylate, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, , Or substituted equivalents thereof. The alpha-olefin-ester copolymer used in the present invention may be prepared by copolymerizing the alpha olefin monomer with an ethylenically unsaturated carboxylic acid or a derivative thereof in a molar ratio of 1: 3 to 3: 1.

The alpha olefin-ester copolymer may further contain a vinyl compound as a monomer. The vinyl compound may be specifically N-vinyl-formamide, N-vinyl acetamide, N-vinyl propionamide, N-vinyl hydroxyacetoamide, vinyl pyridine, N-vinyl imidazole, N-vinyl pyrrolidinone, N-vinylcaprolactam, and the like.

The grease composition of the present invention contains 27.6 to 50.6% by weight of a PAO synthetic base oil and 10 to 33% by weight of an alpha olefin-ester based copolymer base oil as a base oil component.

If the amount of the PAO synthesizer oil contained in the grease composition of the present invention is less than 27.6 wt%, the solubility of the additive may be lowered and the friction and extreme pressure characteristics may be deteriorated. When the content of the PAO synthesizer is more than 50 wt%, the alpha olefin- The content of base oil is small, so it has little effect on friction and load-bearing performance. If the content of the alpha-olefin-ester-based copolymer base oil contained in the grease composition of the present invention is less than 10% by weight, the effect of addition is insufficient and the solubility characteristics of the lubricant containing an excess amount exceeding 33% The effect of improving the extreme pressure and low friction characteristics may be low.

(2) thickener

The grease composition of the present invention comprises calcium sulfonate as a thickener. The calcium sulfonate has an excellent effect of improving the extreme pressure performance as compared with the conventional lithium soap thickener or urea thickener as a conventional thickener.

In the grease composition of the present invention, the calcium sulfonate thickener may be contained in the range of 13 to 40% by weight. If the content of the calcium sulfonate thickener is less than 13% by weight, it may be difficult to provide excellent grease at the same time as the extreme pressure performance and the low friction performance, and if the content exceeds 40% by weight, the extreme pressure is maintained, The friction performance may not be satisfied.

(3) Anti friction agent

The grease composition of the present invention comprises a mixture of molybdenum dialkyldithiocarbamate (MoDTC), molybdenum dialkyldithiophosphate (MoDTP) and zinc dithiophosphate (ZnDTP) as anti-friction agents. The anti-friction agent component is used as an anti-friction agent in the art as an organic molybdenum compound or an organic zinc compound, respectively.

However, the present invention is characterized by mixing MoDTC, MoDTP, and ZnDTP, which are known as anti-friction agents, as essential components, thereby improving the friction performance and improving the extreme pressure performance.

On the other hand, although calcium carbonate (CaCO ₃ ) is generally used as an extreme pressure additive for increasing the load-carrying property in the preparation of a grease composition, calcium carbonate can improve the load-bearing property but has an effect of improving the low- I can not expect it at all. In view of the above-mentioned facts, the present invention has the effect of simultaneously improving the extreme pressure performance and the low friction performance by the mixed use of MoDTC, MoDTP and ZnDTP.

In the present invention, MoDTC, MoDTP, and ZnDTP may be mixed in a weight ratio of 1: 0.2 to 1.6: 0.3 to 0.7. In the case of MoDTC, the coefficient of friction is low at high temperature but little at room temperature. In case of MoDTP, the coefficient of friction is low at low temperature, but the coefficient of friction is increased at high temperature. Considering that the operating environment condition of the general steering apparatus is -40 to 130 ° C., when the mixing ratio of MoDTP, MoDTC and ZnDTP is appropriately adjusted as suggested by the present invention, extreme pressure performance and low temperature performance in the entire temperature range from low temperature to high temperature The friction performance can be improved.

It is preferable that the grease composition of the present invention contains molybdenum dialkyldithiocarbamate (MoDTC) in the range of 1.0 to 3.0 wt%. If the content of MoDTC is less than 1.0 wt%, the coefficient of friction can be increased at high temperature, If it is used in an excess amount exceeding the weight%, there may be a problem that the friction coefficient is increased at a low temperature.

In addition, the grease composition of the present invention preferably contains molybdenum dialkyldithiophosphate (MoDTP) in the range of 0.8 to 2.8 wt%. If the content of MoDTP is less than 0.8 wt%, the problem that the friction coefficient increases at low temperatures , And when it exceeds 2.8% by weight, the coefficient of friction may rise at a high temperature.

If the content of ZnDTP is less than 0.8% by weight, the additive effect may be insignificant. When the content of ZnDTP is more than 1.5% by weight, the content of zinc dithiophosphate (ZnDTP) Sludge may occur during deterioration.

(4) Additives

The grease composition of the present invention may contain an antioxidant, a corrosion inhibitor, and the like as conventional additives, and may further include a rust inhibitor, a metal deactivator, and the like, if necessary.

The antioxidant may be selected from antioxidants, ozone deterioration inhibitors and antioxidants which are usually added to rubber, plastic, lubricating oil and the like. In the present invention, there is no particular limitation on the selection of the antioxidant, and the amount of the antioxidant to be used can also be appropriately adjusted within the range of the content of the additive level normally used. Specific examples of such an antioxidant are as follows. Phenyl-1-naphthylamine, phenyl-2-naphthylamine, diphenyl-p-phenylenediamine, dipyridylamine, phenothiazine, N-methylphenothiazine, P-phenylenediamine, N, N'-di-sec-butyl-p-phenylene Amine-based compounds such as diamines; Phenol-based compounds such as 2,6-di (tert-butyl) phenol; These organometallic compounds and the like can be used.

The corrosion inhibitor is also a commonly used component. The present invention does not have any particular limitation on the selection of the corrosion inhibitor, and the amount of the corrosion inhibitor can also be appropriately adjusted within the range of the content of the commonly used additive level. Specific examples of such a corrosion inhibitor are as follows. Ammonium salts of organic sulfonic acids; An organic sulfonic acid salt or an organic carboxylic acid salt of an alkaline earth metal; Hydroxy fatty acids such as oleoyl chalcogen; Mercapto fatty acids such as 1-mercaptostearic acid; Imidazoles such as thiazolidine 2- (decyldithio) -benzoimidazo zole, benzoimidazole; Phosphoric acid esters such as trisnonyl phenyl phosphite; Thiocarboxylic acid esters such as diarylthiopropionate and the like can be used. Nitrite and the like can also be used.

The total amount of the additive described above can be included in the content of 0.1 to 10% by weight in the whole composition of the grease.

The present invention will now be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention.

[Example]

Examples 1 to 6 and Comparative Examples 1 and 2: Preparation of grease

The composition and the composition ratio as shown in Tables 2 to 5 below were combined to prepare a grease composition.

[Ingredients Used]

(1) Base oil

  (a) PAO: a polyalphaolefin synthetic base oil (EXXON MOBIL, SPECTRASYN ULTRA) having a kinetic viscosity at 150 캜 of 150 cSt,

  (b) VM: alpha-olefin-maleate copolymer synthetic base oil (Lubrizol, VL1200H) having kinetic viscosity at 40 DEG C of 600 cSt,

  (c) ESTER: A polyester synthetic base oil (EXXON MOBIL, ESTEREX TM111) having a kinematic viscosity at 40 DEG C of 124 cSt,

  (d) OSP: An oil-soluble polyalkylene glycol synthetic base oil (DOW, OSP-150) having kinetic viscosity at 150 캜 of 150 cSt,

(2) Increasing agent:

   (a) Ca-sulfo: calcium sulfonate thickener

   (b) UREA: urea-based thickener, diurea

   (c) Li-soap: Lithium soap thickener

 (3) Anti friction agent

   (a) MoDTC: molybdenum dialkyldithiocarbamate

   (b) MoDTP: molybdenum dialkyldithiophosphate

   (c) ZnDTP: zinc dithiophosphate

(4) Antioxidants: amine-based antioxidants of amine phosphates

The properties of the greases were measured by the evaluation conditions shown in Table 1 below, and the results are summarized in Tables 2 to 5 below.

Evaluation items Evaluation standard Evaluation condition Remarks SRV Coefficient of friction ASTMD 5707 80 ° C x 300N x 50Hz x 1000um

Extreme pressure
(N) ASTM D5706 50 ° C x 50 ~ 2000N x 50Hz x 1000um (100N increments from 100N after 50N Break-in) 4-BALL Wear amount
(mm) ASTM D2266 75 DEG C x 1200 rpm x 400 N x 1 hr

Extreme pressure
(N) ASTM D2596 25 ° C x 1770rpm x Load step x 10s per load
(The detailed load is indicated in the standard) Rolling coefficient of friction - 80 占 폚 x 30N (under load) x 1 to 500 mm / s ²

division Example One 2 3 4 5 6


Furtherance
(weight%
Base oil PAO 50.6 27.6 35.6 43.6 35.6 35.6 VM 10 33 25 17 25 25 PAO: VM
(Weight ratio) 1: 0.2 1: 1.2 1: 0.7 1: 0.4 1: 0.7 1: 0.7 Thickener Ca-sulfo 34 34 34 34 34 34
Friction agent MoDTC 3 3 3 3 1.5 2 MoDTP 0.8 0.8 0.8 0.8 2.3 1.8 ZnDTP One One One One One One MoDTC: MoDTP: ZnDTP (weight ratio) 1: 0.27: 0.33 1: 0.27: 0.33 1: 0.27: 0.33 1: 0.27: 0.33 1: 1.53: 0.67 1: 0.9: 0.5 Amine antioxidant 0.6 0.6 0.6 0.6 0.6 0.6
evaluation
result
SRV friction
Coefficient 80 ℃ 0.053 0.061 0.042 0.053 0.052 0.054 25 ℃ 0.053 0.061 0.042 0.053 0.051 0.051 Extreme pressure (N) 1400 1500 1600 2000 1500 1300 4-BALL Wear amount (mm) 0.46 0.47 0.44 0.42 0.43 0.46 Extreme pressure (N) 620 800 800 800 620 620 Rolling coefficient of friction 0.038 0.043 0.03 0.034 0.041 0.052

Table 2 shows that the grease compositions of Examples 1 to 6 having the composition and composition ratio as proposed by the present invention have a high extreme pressure property and a low friction coefficient and wear amount.

division Comparative Example One 2 3 4 5 Furtherance
(weight% Base oil PAO 55.6 20.6 50.6 50.6 60.6 VM 5 40 - - - ESTER - - - 10 - OSP - - 10 - - Thickener Ca-sulfo 34 34 34 34 34 Friction agent MoDTC 3 3 3 3 3 MoDTP 0.8 0.8 0.8 0.8 0.8 ZnDTP One One One One One Amine antioxidant 0.6 0.6 0.6 0.6 0.6 evaluation
result SRV friction
Coefficient 80 ℃ 0.108 0.073 0.09 0.067 0.093 25 ℃ 0.108 0.073 0.09 0.067 0.093 Extreme pressure (N) 700 1200 1000 800 800 4-BALL Wear amount (mm) 0.65 0.51 0.57 0.54 0.62 Extreme pressure (N) 500 620 620 500 500 Rolling coefficient of friction 0.065 0.065 0.058 0.051 0.061

Table 3 is intended to compare extreme pressure performance and low friction characteristics according to the composition and content ratio of base oil. It can be confirmed that the extreme pressure property is relatively low as compared with the grease composition of Table 2, and the friction coefficient and wear amount have high values. That is, when the composition of the base oil proposed by the present invention can not be satisfied, it can be understood that a grease excellent in extreme pressure performance and low friction performance can not be obtained at the same time.

division Comparative Example 6 7 8 9 Furtherance
(weight% Base oil PAO 35.6 35.6 35.6 35.6 VM 25 25 25 25 Thickener Ca-sulfo 34 34 34 34 Friction agent MoDTC 3.8 0 0.5 One MoDTP 0 3.8 3.3 2.8 ZnDTP One One One 0 Amine antioxidant 0.6 0.6 0.6 0.6 Evaluation results SRV friction
Coefficient 80 ℃ 0.062 0.11 0.092 0.053 25 ℃ 0.10 0.054 0.053 0.051 Extreme pressure (N) 1200 1100 1100 1200 4-BALL Wear amount (mm) 0.57 0.56 0.053 0.043 Extreme pressure (N) 620 500 500 620 Rolling coefficient of friction 0.062 0.09 0.091 0.051

Table 4 is prepared to compare extreme pressure performance and low friction characteristics according to composition ratios of MiDTC, MoDTP, and ZnDTP included in the anti-friction agent. In contrast to the grease composition shown in Table 2, the grease composition which does not satisfy the composition ratios of MiDTC, MoDTP and ZnDTP as the friction agent, while satisfying the range of the composition and content of the base oil and the thickener proposed by the present invention, Is relatively low, it can be confirmed that the friction coefficient and the wear amount have a high value. That is, when the composition of the anti-friction agent proposed by the present invention can not be satisfied, it can be understood that excellent grease can not be obtained at the same time as the extreme pressure performance and the low friction performance.

division Comparative Example 10 11 12 13 14 Furtherance
(weight% Base oil PAO 80 66.6 45.1 60.6 43.9 VM - - 17 - 17.5 OSP - 10 - - - Thickener Ca-sulfo - - 34 34 34 UREA 15.5 - - - - Li-soap - 18 - - - Friction agent MoDTC - 3 - 3 3 MoDTP - 0.8 0.8 0.8 - ZnDTP One One - One One CaCO ₃ 2.5 - 2.5 - - Amine antioxidant One 0.6 0.6 0.6 0.6 evaluation
result SRV friction
Coefficient 80 ℃ 0.089 0.11 0.084 0.093 0.063 25 ℃ 0.089 0.11 0.084 0.093 0.12 Extreme pressure (N) 700 600 1300 800 - 4-BALL Wear amount (mm) 0.57 0.62 0.63 0.62 - Extreme pressure (N) 620 400 620 500 - Rolling coefficient of friction 0.053 0.054 0.058 0.061 0.063

division Comparative Example 15 16 17 18 Furtherance
(weight% Base oil PAO 44.2 60.63 53.47 35.1 VM 19.4 23.97 21.13 14.5 Thickener Ca-sulfo 34 10 20 45 Friction agent MoDTC - 3 3 3 MoDTP 0.8 0.8 0.8 0.8 ZnDTP One One One One Amine antioxidant 0.6 0.6 0.6 0.6 evaluation
result SRV friction
Coefficient 80 ℃ 0.11 0.71 0.051 0.087 25 ℃ 0.05 0.71 0.051 0.087 Extreme pressure (N) - 1200 1800 1400 4-BALL Wear amount (mm) - 0.62 0.48 0.64 Extreme pressure (N) - 620 800 800 Rolling coefficient of friction 0.12 - - -

Claims (8)

A grease composition comprising a base oil, a thickener and an anti-friction agent,
Wherein said base flow path comprises a polyalphaolefin (PAO) synthetic base oil and an alpha olefin-ester based copolymer base oil at a weight ratio of 1: 0.15 to 1: 1.9,
The thickener includes calcium sulfonate,
Characterized in that the anti-friction agent comprises a mixture of molybdenum dialkyldithiocarbamate (MoDTC), molybdenum dialkyldithiophosphate (MoDTP) and zinc dithiophosphate (ZnDTP). A grease composition with improved performance simultaneously.
The method according to claim 1,
Wherein the base oil has a viscosity at 40 DEG C of from 1,500 to 2,500 cSt, wherein the extreme pressure and low friction performance are simultaneously improved.
The method according to claim 1,
Wherein the alpha olefin-ester based copolymer base oil is prepared by copolymerizing an alpha olefin monomer and an ethylenically unsaturated carboxylic acid or a derivative thereof, wherein the extreme pressure and low friction performance are improved at the same time.
The method of claim 3,
Wherein the alpha olefin-ester based copolymer base oil is prepared by copolymerizing alpha-olefin monomer having 6 to 18 carbon atoms with maleic anhydride in a molar ratio of 1: 3 to 3: 1. .
5. The method of claim 4,
Wherein the alpha olefin-ester based copolymer base oil is produced by further copolymerizing a vinyl base compound to improve extreme pressure and low friction performance.
The method according to claim 1,
Wherein the weight ratio of the molybdenum dialkyldithiocarbamate (MoDTC): molybdenum dialkyldithiophosphate (MoDTP): zinc dithiophosphate (ZnDTP) contained in the abrasive agent is from 1: 0.2 to 1.6: 0.3 to 0.7 By weight. The grease composition according to claim 1, wherein the grease composition is a grease composition.
The method according to claim 1,
27.6 to 50.6% by weight of polyalphaolefin (PAO) synthetic base oil,
10 to 33% by weight of an alpha olefin-ester based copolymer base oil,
13 to 40% by weight of a calcium sulfonate thickener,
1.0 to 3.0% by weight of molybdenum dialkyldithiocarbamate (MoDTC)
0.8 to 2.8% by weight of molybdenum dialkyldithiophosphate (MoDTP), and
0.8 to 1.5% by weight of zinc dithiophosphate (ZnDTP)
Wherein the grease composition has improved extreme pressure and low friction performance.
The method of claim 1, wherein
Wherein the lubricating composition is applied to a ball screw portion of a rack-type gear (R-MDPS) part of an automobile.

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