Fluorine-containing polyether and lubricant comprising the same

Abstract: A fluorine-containing polyether of the formula: R f ¹COOR f ² (I) or R f ²OCO-R′ f ¹-COOR f ² (II) wherein R f ¹ and R′ f ¹ are a group containing a perfluoroalkyl polyether group, and R f ² is a fluorine-containing alkyl group or a fluorine-containing ether group, can be used as a lubricant which has good properties such as lubricity and durability.

Description: The present invention relates to a novel fluorine-containing polyether and a lubricant comprising the same fluorine-containing polyether. A perfluoropolyether is a fluorine-containing oil which has non-flammability and good durability. However, perfluoropolyethers have a weak affinity to the surface of a material such as metal or glass. When it is thinly spread, for example, on a metal surface and used as a lubricant, durability is very poor because of migration. To solve this problem, a fluorine-containing polyether which has, at an end of the molecule, -COOH, -CH₂OH or -COOR wherein R is -CH₃ or has been developed. However, such fluorine-containing polyethers have defects in that those containing a carboxyl group must be carefully treated and properties such as lubricity or durability are insufficient. JP-A-6215295 discloses fluorine-containing polyethers of this type which contain no fluorine in the terminal ester group. An object of the present invention is to provide a fluorine-containing polyether which can be easily treated and has good properties such as lubricity and durability. The invention is directed to a fluorine-containing polyether of the formula: R f ¹COOR f ² (I) or R f ²OCO-R' f ¹-COOR f ² (II) therein the R f ¹ and R' f ¹ groups contain a perfluoroalkyl polyether group having at least one repeating unit selected from a repeating unit of the formula: -C₃F₆O- (a) a repeating unit of the formula: -C₂F₄O- (b) and a repeating unit of the formula: -CF₂O- (c) provided that at least one of the repeating units (a) or (b) is contained and the total number of the repeating units (a), (b) and (c) is at least three and R f ² is a fluorine-containing alkyl group or a residue containing fluorine as well as an ether group. The repeating unit: -C₃F₆O- includes -CF₂CF₂CF₂O- and -CF(CF₃)CF₂O-. The repeating unit: -C₂F₄O- is usually -CF₂CF₂O-. The R f ¹ group is, for example, F(CF₂CF₂CF₂O) m CF₂CF₂- wherein m is 2 to 200. The R' f ¹ group is, for example, -CF₂CF₂O(CF₂CF₂CF₂O) n (CF₂)₄(OCF₂CF₂CF₂) n OCF₂CF₂- wherein each of n is 2 to 200. The R f ² group is, for example, C a F 2a+1 C b H 2b - (A) wherein a is an integer of 1 to 10 and b is 1 or 2, H(C₂F₄) d CH₂- (B) wherein d is an integer of 1 to 5, or F(C₃F₆O) l (C₂F₄O) m (CF₂O) n CF₂CH₂- (C) wherein l, m and n are 0 or a positive integer provided that at least one of l and m is not 0 and l + m + n is not smaller than 3. In the fluorine-containing ether group (C), the order of each repeating unit may not be the same as described above and is arbitrary in the molecule. Specific examples of the fluorine-containing polyethers according to the present invention are F(CF₂CF₂CF₂O) p CF₂CF₂COOCH₂CF₂CF₃ (1) wherein p is 2 to 200, preferably 25 on the average, [HCF₂CF₂CH₂OCOCF₂CF₂O-(CF₂CF₂CF₂O) m -CF₂CF₂]₂- (2) wherein m is 2 to 200, preferably 20 on the average, and F(CF₂CF₂CF₂O) q CF₂CF₂COOCH₂CF₂CF₂(OCF₂CF₂CF₂) r F (3) wherein q is 2 to 200, preferably 20 on the average and r is 2 to 200, preferably 20 on the average. The fluorine-containing polyether according to the present invention can be prepared by reacting a fluorine-containing compound of the formula: R f ¹-COOH, R f ¹-COF, or HOOC-R' f ¹-COOH wherein R f ¹ and R' f ¹ are the same as described above, with a fluorine-containing alcohol of the formula: R f ²OH wherein R f ² is the same as described above. A catalyst such as an acid (e.g. sulfuric acid) is preferably used in the reaction. The reaction is usually carried out at a temperature of 50 to 150°C for 1 to 10 hours. The fluorine-containing polyether according to the present invention can be used as a lubricant for materials such as a metal, a glass, a silica gel and graphite. It is particularly useful as the lubricant for a thin film magnetic tape or a thin film magnetic disc. A solution of the lubricant is preferably prepared to apply the lubricant on the surfaces of various materials. Specific examples of the solvent are fluorine-containing solvents, for example, trichlorotrifluoroethane (e.g. Daiflon S-3 manufactured by Daikin Industries, Ltd.), Cl(CF₂CFCl)₂Cl and N(C₃F₇)₃. The solvent may be used in an amount of 200 to 2000 parts by weight per part by weight of the lubricant. Then, the solution of the lubricant is applied on a surface of a substrate such as a magnetic tape or a magnetic disc by dipping or spraying, and heated to form a lubricant film. The solvent is evaporated by heating. The heating may be usually carried out at a temperature of about 80°C. The lubricant film may be formed to have a thickness of 0.002 to 0.01 µm. The reason why the lubricant according to the present invention has good properties such as lubricity and durability is not clearly known. It is assumed that since the metal, glass, silica gel and graphite have many hydroxyl groups on their surfaces, the fluorine-containing polyether is adsorbed on their surfaces because of transesterification between the fluorine-containing polyether and a hydroxyl group. When the fluorine-containing polyether has sufficiently higher acidity than that of a hydroxyl group of the surface, the fluorine-containing alcohol moiety of the fluorine-containing polyether quickly transesterificates with the hydroxyl group of the surface. The transesterification is achieved in the heating process to evaporate the solvent. The transesterification is completed by the frictional heat during use. The present invention is illustrated by following Examples. Example 1 In a 200 ml three-neck flask, the fluorine-containing carboxylic acid: F(CF₂CF₂CF₂O) p CF₂CF₂COOH wherein p is 25 on the average (200 g, 57 mmol) and then pentafluoropropanol (20 g, 130 mmol) were added and stirred. Then, concentrated sulfuric acid (0.5 ml) was added and the reaction was carried out at 90°C for 5 hours while stirring. The completion of the reaction was confirmed by disappearance of the absorption peak at 1780 cm⁻¹ for the carboxylic acid and appearance of the absorption peak at 1820 cm⁻¹ for the ester linkage in IR analysis. After the completion of the reaction, the reaction product was washed with water (100 ml) and a lower phase was separated. Silica gel (30 g) was added to the lower phase to remove the unreacted carboxylic acid. The reaction product was filtrated through a filter having a pore diameter of 0.2 µm to obtain the fluorine-containing polyether: F(CF₂CF₂CF₂O) p CF₂CF₂COOCH₂CF₂CF₃ wherein p is 25 on the average. Yield: 300 g (78%). The IR chart of the resultant fluorine-containing polyether is shown in the Figure. Example 2 To the fluorine-containing carboxylic acid: F(CF₂CF₂CF₂O) q CF₂CF₂COOH wherein q is 20 on the average (20 g), the fluorine-containing alcohol: F(CF₂CF₂CF₂O) r CF₂CF₂CH₂OH wherein r is 15 on the average (15 g) was added and stirred. Then, concentrated sulfuric acid (2 ml) was added and the reaction was carried out at 150°C for 10 hours while stirring. The completion of the reaction was confirmed by disappearance of the absorption peak at 1780 cm⁻¹ for the carboxylic acid and appearance of the absorption peak at 1820 cm⁻¹ for the ester linkage in IR analysis. After the completion of the reaction, the reaction product was washed with water (50 ml) three times and a lower phase was separated. Silica gel (100 g) was added to the lower phase to remove the unreacted carboxylic acid. The reaction product was filtrated through a filter having a pore diameter of 0.2 µm to obtain the fluorine-containing polyether: F(CF₂CF₂CF₂O) q CF₂CF₂COOCH₂CF₂CF₂(OCF₂CF₂CF₂) r F wherein q is 20 and r is 15 on the average. Yield: 24 g (64%). Example 3 A two patch type hard disc having an uppermost carbon layer was dipped in a 0.1% by weight solution of the fluorine-containing polyether: F(CF₂CF₂CF₂O) p CF₂CF₂COOCH₂CF₂CF₃ wherein p is 25 on the average prepared in Example 1 in trichlorotrifluoroethane. The disc was removed from the solution and heated at 80°C for one hour in an oven. The resultant lubricant film had a thickness of 0.01 µm. The durability of the hard disc was tested by using a CSS Tester. After 20,000 times, the µ value (friction coefficient) was not more than 0.5. Comparative Example A hard disc was treated in the same manner as in Example 3 but using the perfluoropolyether oil: F(CF₂CF₂CF₂O) p CF₂CF₃ wherein p is 25 on the average instead of the fluorine-containing polyether. The resultant lubricant film had a thickness of 0.01 µm. After 1,100 times, the µ value exceeded 0.5.

Claims: A fluorine-containing polyether of the formula: R f ¹COOR f ² (I) or R f ²OCO-R' f ¹-COOR f ² (II) wherein the R f ¹ and R' f ¹ groups contains a perfluoroalkyl polyether group having at least one repeating unit selected from a repeating unit of the formula: -C₃F₆O- (a) a repeating unit of the formula: -C₂F₄O- (b) and a repeating unit of the formula: -CF₂O- (c) provided that at least one of the repeating units (a) or (b) is contained and the total number of the repeating units (a), (b) and (c) is at least three and R f ² is a fluorine-containing alkyl group or a residue containing fluorine as well as an ether group. The fluorine-containing polyether according to claim 1, wherein the R f ² group is C a F 2a+1 C b H 2b - (A) wherein a is an integer of 1 to 10 and b is 1 or 2, H(C₂F₄) d CH₂- (B) wherein d is an integer of 1 to 5, or F(C₃F₆O) l (C₂F₄O) m (CF₂O) n CF₂CH₂- (C) wherein l, m and n are 0 or a positive integer provided that at least one of l and m is not 0 and l + m + n is not smaller than three. The fluorine-containing polyether according to claim 1, wherein the R f ¹ group is F(CF₂CF₂CF₂O) p CF₂CF₂- wherein p is an integer of 2 to 200, and the R f ² group is -CH₂CF₂CF₃. The fluorine-containing polyether according to claim 1, wherein the the R f ¹ group is F(CF₂CF₂CF₂O) q CF₂CF₂- wherein q is an integer of 2 to 200, and the R f ² group is -CH₂CF₂CF₂(OCF₂CF₂CF₂) r F wherein r is an integer of 2 to 200. A lubricant comprising the fluorine-containing polyether according to claim 1.

Inventors: MISUGI YOSHIHIKO, TOHZUKA TAKASHI, YAMAMOTO IKUO, MISUGI, YOSHIHIKO, TOHZUKA, TAKASHI, YAMAMOTO, IKUO
Applicants: DAIKIN IND LTD, DAIKIN INDUSTRIES, LIMITED
Application year: 1989
Main classification: C08G65
IPC codes: C10M107, C08G65, G11B5, C07C69, C10N30