EP0337425B1

EP0337425B1 - Antirust additives for lubricants or greases based on perfluoropolyethers

Info

Publication number: EP0337425B1
Application number: EP89106508A
Authority: EP
Inventors: Ezio Strepparola; Piero Gavezotti; Costante Corti
Original assignee: Ausimont SpA
Current assignee: Solvay Specialty Polymers Italy SpA
Priority date: 1988-04-13
Filing date: 1989-04-12
Publication date: 1991-10-16
Anticipated expiration: 2009-04-12
Also published as: CA1316923C; IT1218217B; IT8820183A0; DE68900331D1; EP0337425A1; JPH0258600A; JP2922215B2

Description

The present invention relates to functionalized fluoropolyether compounds which impart antirust properties to lubricating oils and greases based on perfluoropolyethers.
It is known that the utilization of perfluoropolyethers as lubricants does not prevent the formation of rust on the surface of ferrous materials when moisture is present, even if said materials are covered with an oil film.
This is due to the high permeability to gases, vapours and, among these, also to water vapour, exhibited by perfluoropolyethers (PFPE).
PFPE utilizable also for formulating lubricating oils and greases are well-known on the market, for example, Fomblin^(R) (produced by Montedison), KRYTOX^(R) (produced by DuPont), DENNUM^(R) (produced by Daikin), and the like.
It is known that it is very difficult to add substances to said PFPE because a characteristic thereof is their absolute immiscibility with most of the chemical compounds. Consequently, in the case of PFPE lubricants, it is impossible to use the products usually added as antirust additives for mineral oils (which are the traditional lubricants) which form stable mixtures with each other.
The compounds according to the present invention represent a significant improvement in antirust protection as compared with the anticorrosive products described in EP-A-95825, 165649, 165650 and IT-A-20159 A/86.
In particular, the additives described in IT-A-20159 A/86, which have exhibited antirust properties, have the following structures:
wherein R_f = ―CF₂R_f′CF₂―, R_f′ being a perfluoropolyether chain having an average molecular weight of 2000 and belonging to class (I).
The additives of the above types 1 and 3, however, exhibit the drawback of being scarcely soluble in the lubricating perfluoropolyether which causes problems with respect to phase separation, while the additive of type 2, although showing an acceptable solubility at the beginning, results in a certain amount of formed ester compounds in the course of time, whereby the mixture becomes cloudy and tends to form an overfloating layer. i.e., the additive separates from the lubricant.
There is, thus, a need to have available compounds capable of imparting to the lubricants to which they are added not only excellent antirust properties but also a long "shelf-life" (solubility of the additive retained in the course of time), which is absolutely necessary for the marketing of a lubricant.
It has, surprisingly, been found that the above properties may be achieved if, as an additive, a perfluoropolyether having a sequence of one or more of the following units is used:

wherein the groups R′_f, which may be the same or different from each other, are H or fluoroalkyl radicals (preferably having 1 to 3 carbon atoms such as, for example, CF₃ and C₂F₅) and having at least one end group selected from:

(a): ―CFX-CN;
(b): ―CFX-CH₂-NR₁R₂, wherein R₁ and R₂, the same or different from each other, represent H, C₁₋₈-, preferably C₁₋₄-alkyl, C₇₋₁₁-, preferably C₇₋₉-alkylaryl and C₆₋₁₀-, preferably C₆₋₈-cycloalkyl, optionally substituted with one or more C₁₋₃-alkyl groups; R₁ and R₂ optionally containing one or more heteroatoms selected from O, N and S;

The other end group may be one of the above groups (a), (b) and (c) but may also represent a perfluoroalkyl radical with 1 to 3 carbon atoms, for example, CF₃ or C₂F₅.
Some of these compounds are already described in US-A-4085137 for the preparation of polymers and as anti-corrosion agents. These compounds are not within the scope of the invention as claimed.
Examples of the various generic groups mentioned above are:

C₁₋₈-alkyl:: Methyl, ethyl, n- and i-propyl, n-, i-, sek- and tert-butyl, pentyl, hexyl, heptyl and octyl; preferred are methyl and ethyl.
C₇₋₁₁-alkylaryl:: Benzyl, phenylethyl, naphtylmethyl.
C₆₋₁₀-cycloalkyl:: Cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl; preferred are cyclohexyl and cyclooctyl.
C₁₋₃-alkyl;: see C₁₋₈-alkyl.

When A in group (c) is a nitrogen atom, the group attached thereto preferably has the same meanings as the groups R₁ and R₂, particularly H, CH₃ and C₂H₅.
In particular, preferred antirust additives of the present invention belong to the following classes:

wherein at least one of the end groups T and T′ is selected from:

(a): ―CFX-CN;
(b): ―CFX-CH₂-NR₁R₂, R₁ and R₂ being defined as above;

_f

Generally, the additives of the present invention exhibit a solubility in the PFPE lubricant of at least 1% by weight based on the lubricant.
The amount of the above fluoropolyether antirust additives preferably ranges from 1% to 5% by weight, based on the total lubricant amount, even more preferred from 2% to 4% by weight.
If the lubricant to which the antirust additive is added is a grease based on perfluoropolyethers, it may be prepared as is described in EP-A-92825.
In particular, such a grease can be formulated by suspending polytetrafluoroethylene particles having, for example, a spherical morphology and being composed of aggregates having a size of from 1 to 200 µm, in a liquid perfluoropolyether such as Fomblin ^(R)Y or Fomblin^(R)Z.
Due to their intrinsic lubricating properties the compounds having end groups of types (b) and (c) indicated above can also be utilized as such.
Furthermore, it has been found that the additives having the above end groups (a), (b) and (c) can be used in combination with small amounts of fluoropolyether compounds having the same chain structure as the compounds of the present invention, for example structures (I) to (XI), but one or two end groups ―CFX-COOH, wherein X is F or CF₃. Generally, the latter compounds are employed in amounts ranging from 1/30 to 1/20 (about 3 to about 5%) of the weight of the additive characterized by end groups (a), (b) and/or (c).

The fluoropolyether precursors of the additives of the present invention may be prepared as follows:

Class (I):: According to the processes described in US-A-3242218;
Class (II):: According to US-A-3665041;
Classes (III) and (IV):: According to EP-A-148482;
Class (V):: According to US-A-4523039;
Class (VI):: According to EP-A-151877;
Class (VII):: According to US-A-3665041;
Class (VIII):: According to US-A-3250808;
Class (IX):: According to EP-A-148482;
Class (X):: According to the processes described in PCT application WO87/00538;
Class (XI):: According to the processes described in PCT application WO87/02992.

The above end groups can be introduced, for example, by the method described in US-A-3010874. In particular, the introduction of the end groups of type (a) may be effected by treating the corresponding derivatives with ester end groups ―CFX-COOR₃ (R₃ = CH₃, C₂H₅, C₆H₅) with anhydrous ammonia, preferably in a solvent such as, for example, ethyl ether, methanol or 1,1,2-trichlorotrifluoroethane, and subsequent treatment of the resulting amide with P₂O₅.
The introduction of end groups of types (b) and (c) may be effected by reacting the ester compounds indicated above with an amine of the formulae NHR₁R₂ or
to form the corresponding amides and by subsequent reduction of the latter with hydrides.
In the case of classes (II), (III), (V), (VII), (VIII), (IX) and (X), in which the starting perfluoropolyethers have only one functional end group, it is possible to obtain the corresponding bifunctionalized product by means of the process described in EP-A-224201.
The antirust properties of the lubricants according to the present invention have been evaluated by means of the following tests:

Antirust test in the fog chamber (method ASTM D.1748, modified)

Object

Determination of the antirust properties of oils on metals in high humidity conditions.

Summary of the method

Carbon steel plates (C15) (UNI), superficially treated as described below, were dipped into the oil, allowed to drip and hung in a fog chamber at 50°C and 100% relative humidity for a predetermined number of hours. The oil passes or does not pass the test on the basis of the number of rust stains visible on the surface of the plates.

Apparatus

The fog chamber consisted of a compressed-air-actuated sprayer (P = 3 atm.), connected with a water reservoir so as to saturate the environment with humidity; the temperature was adjusted to 50°C (see ASTM B.117, 287, 368).

Test conditions

The tests described below were carried out using partially demineralized water (pH = 5.5 to 7.5) and for the following periods of time:

(1): The plates were hung and allowed to drip for 16 hours;
(2): They were then placed into a fog chamber which was kept in operation for 8 hours;
(3): The fog chamber was kept out of operation for 12 hours;
(4): The fog chamber was turned on again and kept in operation for 8 hours;

Subsequently, the evaluation was made.

Preparation of the steel plates

The steel plates were cleaned and degreased by means of a cloth soaked with Delifrene^(R) 113 (trichlorotrifluoroethane); the surface was polished by means of emery paper (400 mesh and 600˝), washed with water and dried. The utilized plates had the following dimensions: 50 × 100 × 2 mm. (Note: polyethylene gloves must be used to handle the plates).

Evaluation of the tests (in analogy to method DIN 51802 (EMCOR) for bearings)

The results of the tests were expressed according to the following rating system:

(0): No traces of rust were observed;
(1): Very few corrosion points having a diameter below 1 mm;
(2): 30% of the surface were covered by small stains having a diameter below 2 mm;
(3): 60% of the surface were covered by small stains having a diameter below 3 mm;
(4): 100% of the surface were covered by large stains having a diameter of 4 to 5 mm but the polished surface is visible in some points;
(5): 100% of the surface were covered by large stains; the underlying surface is not visible.

In the evaluation, the rust stains appearing in the area up to 0.5 mm from the edges were not taken into consideration. With a rating of (0), the test was passed.
In the evaluation, two figures are given: The first figure refers to the state of the exposed face; The second figure refers to the non-exposed face (with respect to the sprayer).
The following examples merely serve to illustrate the invention and do not limit it in any way.

EXAMPLE 1

Lubricants consisting of perfluoropolyethers having perfluoroalkyl end groups (Fomblin^(R)Y25), characterized by a viscosity of 250 cSt (250 mm²/s) at 20°C, to which the compounds indicated in the following Table 1 had been added, were subjected to the accelerated corrosion test in a fog chamber according to the method described above.
Table 1 shows the weight percentage of the additive with respect to the perfluoropolyether and the results of the corrosion test, expressed by the ratings (figures) outlined above.

EXAMPLE 1A

Example 1 was repeated, using as lubricant perfluoropolyether Fomblin^(R)Y25 without additive. The result was a complete corrosion of the plate: 5-5.

EXAMPLE 1B

Example 1 was repeated, using as lubricant Fomblin^(R)Y25 to which the following mixture had been added:
CH₂=CH-CH₂OCH₂CF₂O(CF₂CF₂O)_m(CF₂O)_nCF₂CH₂OCH₂CH=CH₂
M.W. = 2000; 2%
HOOC-CF₂O(CF₂CF₂O)_m(CF₂O)_n-CF₂COOH
M.W. = 2000; 0.1%
This mixture was soluble in the perfluoropolyether but the result of the test was 3-2.

EXAMPLE 2

Lubricants consisting of perfluoropolyethers having perfluoroalkyl end groups (Fomblin^(R)Z25), characterized by a viscosity of 250 cSt (250 mm²/s) at 20°C to which the compounds reported in the following Table 2 had been added were subjected to the accelerated corrosion test of example 1.

Table 2 shows the results of said tests.

EXAMPLE 2A

Example 2 was repeated, using as lubricant perfluoropolyether Fomblin^(R)Z25 without additive. The result was a complete corrosion of the plate: 5-5.

EXAMPLE 2B

Example 2 was repeated, using as lubricant Fomblin^(R)Z25, to which the following mixture had been added:
CH₂=CH-CH₂OCH₂CF₂O(CF₂CF₂O)_m(CF₂O)_nCF₂CH₂OCH₂CH=CH₂
M.W. 2000; 2%
HOOC-CF₂O(CF₂CF₂O)_m(CF₂O)_n-CF₂COOH
M.W. 2000; 0.1%
The test revealed a rather good anticorrosive effect (2-0) but the additive was insoluble in this type of perfluoropolyether.

EXAMPLE 3

Subjected to the accelerated corrosion test of example 1 were the lubricants consisting of perfluoropolyethers having perfluoroalkyl end groups (Fomblin^(R)YR 140/13), characterized by a viscosity of 1400 cSt (1400 mm²/s) at 20°C to which the following mixture had been added:
The result of the corrosion test was 0-0.

EXAMPLE 3A

Example 3 was repeated, using as lubricant perfluoropolyether Fomblin^(R)YR 140/13 without additive. The result was a complete corrosion of the plate: 5-5.

EXAMPLE 3B

Example 3 was repeated, using as lubricant Fomblin^(R)YR 140/13, to which the following mixture had been added:
CH₂=CH-CH₂OCH₂CF₂O(CF₂CF₂O)_m(CF₂O)_nCF₂CH₂OCH₂CH₂=CH₂
M.W. = 2000; 2%
HOOC-CF₂O(CF₂CF₂O)_m(CF₂O)_n-CF₂COOH
M.W. = 2000; 0.1%
The test revealed a rather good anticorrosive effect (1-0) but the additive was insoluble in this type of perfluoropolyether.

Claims

1. Antirust additives for lubricants based on perfluoropolyethers, comprising one or more fluoropolyether compounds having one or more of the following units:

wherein R′_f is H or a fluoroalkyl radical,
and having at least one end group selected from:

(a) ―CFX-CN;

(b) ―CFX-CH₂-NR₁R₂, wherein R₁ and R₂, the same or different from each other, are C₁₋₈-alkyl, C₇₋₁₁-alkylaryl or C₆₋₁₀-cycloalkyl groups, optionally substituted by C₁₋₃-alkyl groups, R₁ and R₂ optionally containing heteroatoms selected from O, N and S;

wherein A = O, N or S and R is H or a C₁₋₃-alkyl group;
the radical X in (a), (b) and (c) representing F or CF₃;
whereas the other end group has the meanings given above for the first end group or is a perfluoroalkyl radical having 1 to 3 carbon atoms; provided that in the case of fluoropolyether compounds having only units (Cf₂Cf₂O) and (Cf₂O) and one end group (a) or (b) the other end group is a perfluoroalkyl radical having 1 to 3 carbon atoms.

2. Additives according to claim 1, comprising one or more of the following fluoropolyether compounds:

wherein at least one of the end groups T and T′ is selected from:

(a) ―CFX-CN;

(b) ―CFX-CH₂-NR₁R₂;

wherein X, R₁, R₂, A and R, are defined as in claim 1;
the other end group T or T′ can also be a perfluoroalkyl radical having 1 to 3 carbon atoms, and in the case of compound (I) has to be a perfluoroalkyl radical having 1 to 3 carbon atoms;
g, h, m, n, k, J, p, q, s, t, r, u, v, z, x, y are integers selected in a manner such that the average molecular weight of the polyoxyfluoroalkylene chain ranges from 600 to 6000; R_f is a fluoroalkylene radical; R′_f is H or a fluoroalkyl radical;
the oxyfluoroalkylene units are statistically distributed along the chain;
said additives having a solubility in the PFPE lubricant of at least 1% by weight based on the lubricant.

3. Additives according to claim 2, having a formula of type (I), end group of type (a) and an average molecular weight of about 2000.

4. Additives according to claim 2, having a formula of type (VII), end groups of type (c) and an average molecular weight of about 1000.

5. The use of fluoropolyether compounds having one or more of the following units as antirust additives for lubricants based on perfluoropolyethers;

(a) ―CFX-CN;

(b) ―CFX-CH₂-NR₁ R₂, wherein R₁ and R₂, the same or different from each other, are C₁₋₈-alkyl, C₇₋₁₁-alkylaryl or C₆₋₁₀-cycloalkyl groups, optionally substituted by C₁₋₃-alkyl groups, R₁ and R₂ optionally containing heteroatoms selected from O, N and S;

wherein A = O, N or S and R is H or a C₁₋₃-alkyl group;
the radical X in (a), (b) and (c) representing F or CF₃;
whereas the other end group has the meanings given above for the first end group or is a perfluoroalkyl radical having 1 to 3 carbon atoms.

6. The use according to claim 5, wherein one or more of the following fluoropolyether compounds are employed:

wherein at least one of the end groups T and T′ is selected from:

(a) ―CFX-CN;

(b) ―CFX-CH₂-NR₁R₂;

wherein X, R₁, R₂, A and R, are defined as in claim 1;
the other end group T or T′ can also be a perfluoroalkyl radical having 1 to 3 carbon atoms;
g, h, m, n, k, j, p, q, s, t, r, u, v, z, x, y are integers selected in a manner such that the average molecular weight of the polyoxyfluoroalkylene chain ranges from 600 to 6000; R_f is a fluoroalkylene radical; R′_f is H or a fluoroalkyl radical;
the oxyfluoroalkylene units are statistically distributed along the chain;
said additives having a solubility in the PFPE lubricant of at least 1% by weight based on the lubricant.

7. The use according to claim 6, wherein fluoropolyether compounds having a formula of type (I), end groups of type (a) and an average molecular weight of about 2000 are employed.

8. Lubricants based on perfluoropolyethers having antirust properties, which contain the additives as defined in any one of claims 1 to 7.

9. Lubricants according to claim 8, wherein the additives are present in an amount ranging from 1 to 5% by weight, particularly from 2 to 4% by weight, based on the total amount of lubricant.

10. Lubricants according to any one of claims 8 and 9, additionally comprising fluoropolyether compounds having the same chain structure as the additives of claims 1 to 7, except that they show one or two end groups of the formula ―CFX-COOH, wherein X is F or CF₃, said additional additives being present in an amount ranging from 1/30 to 1/20 of the weight of the additives of claims 1 to 7.