Food-grade Lubricating Grease and Method for Preparing Same

Abstract

Disclosed is food-grade lubricating grease and a method for preparing the same, belonging to the technical field of lubricating grease. The food-grade lubricating grease is prepared from the following components in percentage by mass: 75% to 85% of food-grade white oil, 6% to 16% of stearic acid, 2.0% to 3.0% of benzoic acid, 4.7% to 8.7% of aluminum isopropoxide, 1.0% to 1.5% of water and 1.0% to 7.0% of nano-PTFE, and has good extreme-pressure, abrasion-resistant and friction-reduction properties, a last non-seizure load (P.sub.B) reaching 411.6 N, a sintering load (P.sub.D) reaching 1,960 N, and a friction coefficient reduced by 18.5%. The lubricating grease can be used for a food production industry and in household food appliances, the service life of a device and the service life of the food-grade lubricating grease are effectively prolonged, and meanwhile, food security is guaranteed to a certain degree.

Claims

1. A method for preparing food-grade lubricating grease, wherein the food-grade lubricating grease comprises the following components in percentage by mass: 75% to 85% of food-grade white oil, 6% to 16% of stearic acid, 2.0% to 3.0% of benzoic acid, 5% to 8.7% of aluminum isopropoxide, 1.0% to 1.5% of water and 1.0% to 7.0% of nano-PTFE; and the method comprises the following steps: (1) mixing the food-grade white oil and the aluminum isopropoxide with the benzoic acid, and performing heating to completely dissolve the mixture to obtain a mixture; (2) adding the stearic acid into the dissolved mixture in step (1), and dissolving the stearic acid through stirring to obtain a corresponding product system A; (3) adding water into the product system A obtained in step (2) for saponification, performing dewatering after the saponification is completed, then, adding the food-grade white oil, and raising the temperature for refining to obtain a product system B; (4) adding the food-grade white oil into the product system B obtained in step (3) after temperature raising refining, and performing grinding after cooling to obtain food-grade lubricating grease base grease; and (5) mixing the food-grade lubricating grease base grease obtained in step (4) with food-grade nano-PTFE through stirring, and then, performing ultrasonic treatment and grinding to obtain the food-grade lubricating grease.

2. The method for preparing food-grade lubricating grease according to claim 1, wherein the food-grade lubricating grease comprises the following components in percentage by mass: 78% to 82% of food-grade white oil, 10% to 12% of stearic acid, 2.0% to 3.0% of benzoic acid, 6.5% to 7.0% of aluminum isopropoxide, 1.0% to 1.5% of water and 5.0% to 7.0% of nano-PTFE.

3. The method for preparing food-grade lubricating grease according to claim 1, wherein the food-grade white oil in step (1) has a kinematic viscosity of 28.8 cst to 33.5 cst at 40° C.

4. The method for preparing food-grade lubricating grease according to claim 1, wherein the heating in step (1) is performed at 95° C. to 110° C. for 30 min to 40 min.

5. The method for preparing food-grade lubricating grease according to claim 1, wherein the saponification in step (3) is performed at 110° C. to 115° C. for 20 min to 40 min.

6. The method for preparing food-grade lubricating grease according to claim 1, wherein the temperature raising refining is performed at 200° C. to 210° C. for 20 min to 40 min.

7. The method for preparing food-grade lubricating grease according to claim 1, wherein an amount of the food-grade white oil in step (1) accounts for 50% to 55% of a total amount of use of the food-grade white oil, an amount of the food-grade white oil in step (3) accounts for 20% to 25% of the total amount of use of the food-grade white oil, and an amount of the food-grade white oil in step (4) accounts for 25% to 30% of the total amount of use of the food-grade white oil.

8. The method for preparing food-grade lubricating grease according to claim 1, wherein an amount of the food-grade white oil in step (1) accounts for 50% of a total amount of use of the food-grade white oil, an amount of the food-grade white oil in step (3) accounts for 25% of the total amount of use of the food-grade white oil, and an amount of the food-grade white oil in step (4) accounts for 25% of the total amount of use of the food-grade white oil.

9. The method for preparing food-grade lubricating grease according to claim 1, wherein the mass percentage of the food-grade nano-PTFE in step (5) is 7%.

10. Food-grade lubricating grease prepared by the method for preparing food-grade lubricating grease according to claim 1.

Description

BRIEF DESCRIPTION OF FIGURES

[0040] FIG. 1 is a photo of food-grade lubricating grease prepared according to Example 1.

[0041] FIG. 2 is a schematic diagram of MS-10A four-ball friction used in Example 7.

[0042] FIG. 3 is a schematic diagram of MFT-5000 friction and abrasion testers used in Example 7.

[0043] FIG. 4 is a schematic diagram of a friction-reduction principle of food-grade nano-PTFE.

DETAILED DESCRIPTION

[0044] The disclosure will be further illustrated with reference to specific examples. It should be understood that these examples are only used for illustrating the disclosure and are not intended to limit the scope of the disclosure. Additionally, it should be understood that those skilled in the art can make various changes or modifications on the disclosure after reading the disclosure, and these equivalent forms all fall within the scope of the appended claims.

[0045] Raw materials used in examples and comparative examples of the disclosure are as shown in the following table, but are not limited to the materials manufactured by the listed manufacturers.

TABLE-US-00001 TABLE 1 Raw Materials Raw material Manufacturer Food-grade white oil MOROKE Stearic acid Sinopharm Chemical Reagent Co., Ltd. Benzoic acid Sinopharm Chemical Reagent Co., Ltd. Aluminum isopropoxide Shanghai Macklin Biochemical Co., Ltd. Nano-PTFE DuPont Co. America

EXAMPLE 1

[0046] (1) Firstly, 400 g of food-grade white oil, 66.9 g of aluminum isopropoxide and 23.5 g of benzoic acid were added into a reaction kettle. Heating was performed to control a temperature in a range between 95° C. and 100° C. Stirring was performed to completely dissolve the mixture.

[0047] (2) Then, 109.5 g of stearic acid was added into the dissolved mixture in step (1). Stirring was performed for 30 min to enable the stearic acid to sufficiently dissolve and react.

[0048] (3) Then, 11.8 g of water was sprayed in a linear manner into a product obtained in step (2). Saponification was performed at a temperature of 110° C. to 115° C. for 30 min. The temperature was raised to 160° C. to perform dewatering for 20 min, so that moisture in floccules after saponification was evaporated until the floccules after saponification were scattered to present a blocky state. Then, 200 g of food-grade white oil was added into the floccules. The temperature was raised to 200° C. to 210° C. for high-temperature refining for 30 min.

[0049] (4) Finally, 200 g of food-grade white oil was added into a product obtained in step (3) after temperature raising refining. Rapid cooling was performed. After stirring cooling, grinding was performed by using an S65 three-roller grinder for 3 times. Food-grade lubricating grease base grease was obtained.

[0050] (5) 100 g of the food-grade lubricating grease base grease and food-grade nano-PTFE with the mass percentage of 7.0% were taken, put into a flask and uniformly stirred for 10 min, and were then vibrated in an ultrasonic cleaner for 10 min. Grinding was performed through a three-roller grinder for three times to obtain the food-grade lubricating grease containing a 7.0% food-grade nano-PTFE additive.

[0051] FIG. 1 is a photo of food-grade lubricating grease prepared according to this example. From FIG. 1, it can be seen that the prepared food-grade lubricating grease is pure white with no other impurities and no special odor, and the prepared food-grade lubricating grease has good viscosity, hardness, etc.

EXAMPLE 2

[0052] (1) to (4) were the same as steps (1) to (4) in Example 1.

[0053] (5) 100 g of the food-grade lubricating grease base grease and food-grade nano-PTFE with the mass percentage of 1.0% were taken, put into a flask and uniformly stirred for 10 min, and were then vibrated in an ultrasonic cleaner for 10 min. Grinding was performed through a three-roller grinder for three times to obtain the food-grade lubricating grease containing a 1.0% food-grade nano-PTFE additive.

EXAMPLE 3

[0054] (1) to (4) were the same as steps (1) to (4) in Example 1.

[0055] (5) 100 g of the food-grade lubricating grease base grease and food-grade nano-PTFE with the mass percentage of 3.0% were taken, put into a flask and uniformly stirred for 10 min, and were then vibrated in an ultrasonic cleaner for 10 min. Grinding was performed through a three-roller grinder for three times to obtain the food-grade lubricating grease containing a 3.0% food-grade nano-PTFE additive.

EXAMPLE 4

[0056] (1) to (4) were the same as steps (1) to (4) in Example 1.

[0057] (5) 100 g of the food-grade lubricating grease base grease and food-grade nano-PTFE with the mass percentage of 5.0% were taken, put into a flask and uniformly stirred for 10 min, and were then vibrated in an ultrasonic cleaner for 10 min. Grinding was performed through a three-roller grinder for three times to obtain the food-grade lubricating grease containing a 5.0% food-grade nano-PTFE additive.

EXAMPLE 5

[0058] (1) Firstly, 375 g of food-grade white oil, 66.9 g of aluminum isopropoxide and 23.5 g of benzoic acid were added into a reaction kettle. Heating was performed to control a temperature in a range between 95° C. and 100° C. Stirring was performed to completely dissolve the mixture.

[0059] (2) Then, 109.5 g of stearic acid was added into the dissolved mixture in step (1). Stirring was performed for 30 min to enable the stearic acid to sufficiently dissolve and react.

[0060] (3) Then, 11.8 g of water was sprayed in a linear manner into a product obtained in step (2). Saponification was performed at a temperature of 110° C. to 115° C. for 30 min. The temperature was raised to 160° C. to perform dewatering for 20 min, so that moisture in floccules after saponification was evaporated until the floccules after saponification were scattered to present a blocky state. Then, 187.5 g of food-grade white oil was added into the floccules. The temperature was raised to 200° C. to 210° C. for high-temperature refining for 30 min.

[0061] (4) Finally, 187.5 g of food-grade white oil was added into a product obtained in step (3) after temperature raising refining. Rapid cooling was performed. After stirring cooling, grinding was performed by using an S65 three-roller grinder for 3 times. Food-grade lubricating grease base grease was obtained.

[0062] (5) 100 g of the food-grade lubricating grease base grease and food-grade nano-PTFE with the mass percentage of 7.0% were taken, put into a flask and uniformly stirred for 10 min, and were then vibrated in an ultrasonic cleaner for 10 min. Grinding was performed through a three-roller grinder for three times to obtain the food-grade lubricating grease containing a 7.0% food-grade nano-PTFE additive.

EXAMPLE 6

[0063] (1) Firstly, 425 g of food-grade white oil, 66.9 g of aluminum isopropoxide and 23.5 g of benzoic acid were added into a reaction kettle. Heating was performed to control a temperature in a range between 95° C. and 100° C. Stirring was performed to completely dissolve the mixture.

[0064] (2) Then, 109.5 g of stearic acid was added into the dissolved mixture in step (1). Stirring was performed for 30 min to enable the stearic acid to sufficiently dissolve and react.

[0065] (3) Then, 11.8 g of water was sprayed in a linear manner into a product obtained in step (2). Saponification was performed at the temperature of 110° C. to 115° C. for 30 min. The temperature was raised to 160° C. to perform dewatering for 20 min, so that moisture in floccules after saponification was evaporated until the floccules after saponification were scattered to present a blocky state. Then, 212.5 g of food-grade white oil was added into the floccules. The temperature was raised to 200° C. to 210° C. for high-temperature refining for 30 min.

[0066] (4) Finally, 212.5 g of food-grade white oil was added into a product obtained in step (3) after temperature raising refining. Rapid cooling was performed. After stirring cooling, grinding was performed by using an S65 three-roller grinder for 3 times. Food-grade lubricating grease base grease was obtained.

[0067] (5) 100 g of the food-grade lubricating grease base grease and food-grade nano-PTFE with the mass percentage of 7.0% were taken, put into a flask and uniformly stirred for 10 min, and were then vibrated in an ultrasonic cleaner for 10 min. Grinding was performed through a three-roller grinder for three times to obtain the food-grade lubricating grease containing a 7.0% food-grade nano-PTFE additive.

Comparative Example 1

[0068] The aluminum isopropoxide in step (1) in Example 1 was replaced with trimeric aluminum. Other preparation methods were the same as those in Example 1.

[0069] When a thickening agent was changed into the trimeric aluminum, a color of the prepared lubricating grease would change, and the security could not be guaranteed. The trimeric aluminum was an oil solvent, and was mostly prepared from industrial oil, so its color was mostly tan. Additionally, the industrial oil might cause certain contamination on the food-grade white oil, so that the security could not be guaranteed. Therefore, by comparison, the color and security of the food-grade lubricating grease prepared in Example 1 were better than those in Comparative example 1.

Comparative Example 2

[0070] (1) Firstly, 400 g of food-grade white oil, 109.5 g of stearic acid and 23.5 g of benzoic acid were added into a reaction kettle. Heating was performed to control a temperature in a range between 95° C. and 100° C. Stirring was performed to completely dissolve the mixture.

[0071] (2) Then, 66.9 g of aluminum isopropoxide was added into the dissolved mixture in step (1). Stirring was performed for 30 min to enable the aluminum isopropoxide to sufficiently dissolve and react.

[0072] (3) to (5) were the same as steps (3) to (5) in Example 1. Food-grade lubricating grease containing a 7.0% food-grade nano-PTFE additive was obtained.

Comparative Example 3

[0073] An operation of adding white oil in three times in steps (1), (3) and (4) in Example 1 was replaced with an operation of adding 800 g of white oil in step (1) but adding no white oil in steps (3) and (4), and other preparation methods and processes were the same as those in Example 1.

EXAMPLE 7 PROPERTY TEST

[0074] Physical and Chemical Property Test

[0075] Physical and chemical property characterization is performed on the lubricating grease prepared in Example 1, Example 5, Example 6, Comparative example 2 and Comparative example 3 by utilizing an SYP4100-I lubricating grease penetration tester (Shanghai Jingxi Instrument Manufacturing Co., Ltd.), an SYD-4929 lubricating grease dropping point tester (Shanghai Changji Geological instrument Co., Ltd.) and an SYD-0324 lubricating grease steel mesh oil separation tester (Shanghai Jingxi Instrument Manufacturing Co., Ltd.). The results are as shown in Table 2.

TABLE-US-00002 TABLE 2 Physical and chemical properties Steel mesh oil separation ¼ penetration, Dropping Items (100° C., 30 h)/% 0.1 mm point/° C. Example 1 1.92 65 >300 Example 5 1.85 63 >300 Example 6 2.21 70 260 Comparative 1.98 75 285 example 2 Comparative 1.86 82 232 example 3

[0076] From Table 2, it can be seen that when the amount of the food-grade white oil is changed from 80% in Example 1 into 75% in Example 5, the hardness of the prepared food-grade lubricating grease is higher, that is, the penetration is lower, the viscosity is poorer than that under the condition of 80% amount, and the lubricating grease is inconvenient to bring and suck into a friction gap. When the amount of the food-grade white oil is changed from 80% in Example 1 into 85% in Example 6, the prepared food-grade lubricating grease is thin, the penetration is higher, the still standing oil separation is much, the properties are poorer than that under the condition of 80% amount, and this lubricating grease is not applicable to high-temperature or steaming and boiling work conditions. The dropping point of the lubricating grease prepared in Comparative example 2 is lower than that in Example 1, the penetration and the steel mesh oil separation indexes are higher than those in Example 1, and the properties are relatively poorer. In Comparative example 3, the while oil was added in one step, and rapid cooling is not performed after high-temperature refining is completed, so that its physical and chemical properties are relatively poorer, its penetration is higher, the lubricating grease is softer, and its dropping point is relatively lower. On the whole, the lubricating grease prepared in Example 1 has better properties, realize complete saponification, and is more applicable to high-temperature or steaming and boiling work conditions of food machinery. Therefore, the influence of food-grade nano-PTFE of different contents on the extreme-pressure, friction-reduction and abrasion-resistant properties of the lubricating grease will be investigated hereafter based on Example 1.

[0077] Extreme-Pressure Property Test and Friction and Abrasion Property Test

[0078] Extreme-pressure property tests were performed on a food-grade lubricating grease test specimen by using an MS-10A four-ball friction tester (Xiamen Tenkey Automation Co., Ltd.). A schematic diagram of a device in the tests is as shown in FIG. 2. In the whole test process, an upper steel ball was pressed down to be in contact with three steel balls (GCr15, diameter: 12.7 mm, and Rockwell hardness: 64 to 66 HRC) fixed at a lower portion. According to the Standard SH/T 0202-94, all the tests were performed under the test conditions that the rotating speed was 1,770 r/min, the time was 10 s, the temperature was 20° C., the last non-seizure load (P.sub.B) was locked to 68 Nm in the test, the sintering load (P.sub.D) was locked to 100 Nm in the test. The steel balls were subjected to ultrasonic cleaning by petroleum ether for 10 min before and after each test.

[0079] The food-grade lubricating grease in the above examples was subjected to friction and abrasion property test by using MFT-5000 friction and abrasion testers (Rtec instruments). A schematic diagram of the MFT-5000 friction and abrasion testers (Rtec instruments) is as shown in FIG. 3. The steel balls used in the tests were made of GCr15, and friction disks used in the tests were made of 45 steel. Test parameters such as load, rotating speed and time were set before the tests.

[0080] The test results of the above examples are as shown in Table 3.

TABLE-US-00003 TABLE 3 Results of extreme-pressure property and friction tests Content Last non- Sintering Friction of nano- seizure load load coefficient Items PTFE (P.sub.B) (N) (P.sub.D) (N) (COF) Base grease in .sup. 0% 333.2 1234.8 0.119 Example 1 Lubricating grease 7.0% 411.6 1960.0 0.097 in Example 1 Lubricating grease 1.0% 352.8 1568.0 0.159 in Example 2 Lubricating grease 3.0% 392.0 1960.0 0.116 in Example 3 Lubricating grease 5.0% 392.0 1568.0 0.066 in Example 4

[0081] From Table 3, it can be seen that when the food-grade nano-PTFE is used as a food-grade lubricating grease base grease additive, and a concentration of the food-grade nano-PTFE is respectively increased from 0.0% to 7.0%, the last non-seizure load (P.sub.B) and the sintering load (P.sub.D) are obviously increased. In a process of testing the extreme-pressure by using the four-ball friction and abrasion tester, with the continuous increase of the exerted load, the lubricating form between friction pairs accordingly change. Under a low-load work condition, the lubricating form between the friction pairs mainly relies on the lubrication of full-membrane fluid formed through lubricating grease flowing. Along with the load increase, the lubricating form is transited from full-membrane fluid lubrication to elastic fluid dynamic lubrication, mixed lubrication and boundary lubrication. A value of the last non-seizure load (P.sub.B) represents a bearing capacity of a boundary membrane, and is mainly related to adsorption properties (physical adsorption or chemical adsorption) of the additive. A value of the sintering load (P.sub.D) is a maximum value of a bearing capacity of a chemical membrane, and is mainly related to a chemical reaction and an additive concentration. Therefore, when the food-grade nano-PTFE is added into the food-grade lubricating grease base grease to be used as an additive, the last non-seizure load (P.sub.B) of the food-grade lubricating grease can be obviously increased. Compared with that of the food-grade lubricating grease base grease, the P.sub.B can be improved by 24% by the 7.0% food-grade nano-PTFE. The result show that the PTFE has good adsorption properties, and can increase the bearing capacity of the boundary membrane through an adsorption effect. When concentrations of the added food-grade nano-PTFE are 3.0% and 7.0%, a value of P.sub.D of the food-grade lubricating grease test specimen is optimum (1,960 N, g=9.8 m/s.sup.2). When a concentration of the added food-grade nano-PTFE is 5.0%, a value of P.sub.D of is slightly decreased, and this may be caused by weak chemical reactivity at the nano-PTFE content of 5.0%. Any one reaction has certain reversibility, and in a lubricating process, ingredients of the food-grade lubricating grease may take a certain chemical reaction, so when the content of the nano-PTFE is 5.0%, the chemical reactivity cooperativity between them are weak. However, on the whole, when the content of the nano-PTFE is 5.0%, the value of P.sub.D is better than that of the base grease. Compared with that of the base grease, the value of P.sub.D can be improved by 59% through 3.0% food-grade nano-PTFE and 7.0% food-grade nano-PTFE. This shows that the bearing capacity of a chemical reaction membrane at this moment is best.

[0082] From Table 3, it can be known that the friction-reduction and abrasion-resistant properties of the food-grade lubricating grease can be improved by adding the food-grade nano-PTFE. By adding the food-grade nano-PTFE, the friction coefficient of the food-grade lubricating grease can be reduced. Due to an agglomeration phenomenon of nano-particles, the friction coefficient may fluctuate to a certain degree. Therefore, more is not better. A friction-reduction mechanism of the nano-PTFE is mainly achieved through obstruction on the direct contact of the friction pairs by the boundary membrane generated through the adsorption effect, and its principle diagram is shown in FIG. 4. For achieving the comprehensive effect of the extreme-pressure property and the wear-resistant property, Example 1 can be used as an optimum recipe for the food-grade lubricating grease.

[0083] Although the exemplary examples of the disclosure have been disclosed above, they are not intended to limit the disclosure. Those skilled in the art may make various changes and modifications without departing from the scope and spirit of the disclosure. Therefore, the protection scope of the disclosure should be determined by the claims.