WO1992004427A1 - Fluorinated lubricants - Google Patents

Abstract

The proposal concerns fluorinated lubricants based on perfluoropolyether oils (PFPE) which, compared to prior art PFPE oils, contain an increased proportion of short-chained oligomers with fewer than 8 perfluoroalkylene components. The proposal is also for mixtures of prior art PFPE oils with low-molecular perfluorinated fluids based on hexafluoro-propylene oxide oligomers as lubricants. The lubricants have an adequately low viscosity for processing without solvents and a relatively low vapour pressure.

Description

Fluorinated lubricants.

Fluorinated lubricants such as perfluoropolyether oils are used to lubricate plastic parts and gold contacts. In plastics, they are the only known lubricant that ensures permanent lubrication when applied once. In the case of telephone sets, for example, the dial must be lubricated in order to ensure a reproducible dialing process. This depends on the return time of the dial, which must remain constant even after 20 years of use of the telephone set. Plastic keyboards are also exposed to high levels of friction, which can lead to premature wear and thus inoperability of the keyboard without lubrication. The perfluoropolyether oils are chemically inert to plastics and do not creep because they do not form a continuous film on plastic surfaces. Another application is fluorinated lubricants for lubricating gold contacts in the connector strips of electronic devices, where they prevent premature wear with up to 10,000 connections.

Perfluoropolyether oils used as lubricants have, for example, a structure corresponding to the general structural formulas A to E.

AC ₃ F ₇ (-CFCF ₂ O) _n -C ₂ F ₅

B CF3- (OCFCF ₂ ) _m-1 - OCFCF ₂ - OCF ₂ - (OCF ₂ ) _n-1 - OCF ₃

C CF ₃ - (OCF ₂ CF ₂ ) _m-1 - OCF ₂ CF ₂ _ OCF ₂ - (OCF ₂ ) _n-1 - OCF ₃ DC ₃ F ₇ O - (CF ₂ CF ₂ CF ₂ O) _n - C ₂ F ₅

EC ₃ F ₇ O - (CFCF ₂ O) _p - (CF ₂ CF ₂ CF ₂ O) _q - (CF ₂ CF ₂ O) _r - (CF ₂ O) _s - C ₂ F ₅

CF ₃ where the indices n or the sum of the indices (p + q + r + s) a value of 8 to depending on the requirements of the lubricant

10 can accept. In the case of the lubricant of structure E with the mixed structural units, their order in the entire molecule is purely random, so that individual indices (p, q, r or s) can also be 0. An oil corresponding to structure A with n = 8 has a boiling point of min. 300 ° C and one

Viscosity from 40 to 45 mm ² s ^-1 at room temperature. Because of the high viscosity, it is not possible to apply the lubricant directly, for example by dipping or otherwise applying the desired and constant layer thickness. The lubricants cannot be applied even by vapor deposition (decomposition or thermal attack of low-temperature resistant plastics).

A known method for applying fluorinated lubricants A or B therefore uses 3 to 10% solutions in, for example, R113 (trifluorotrichloroethane). After immersing the part to be lubricated in the solution, a layer thickness corresponding to the viscosity of the solution is established on the part

(approx. 1 to 2 μm). The solvent itself can evaporate easily due to the low boiling point of 47 ° C. However, this effect, which is desired in principle, requires intensive cooling of the apparatus or of the exhaust air in order to retain the solvent in the apparatus. A complete retention of the solvent, which is environmentally harmful due to its climate impact and the damaging effect on the ozone layer, can only be achieved with great expenditure on equipment.

It is therefore an object of the present invention to provide a fluorinated lubricant which can be applied as far as possible without loss of evaporation, has no ozone-depleting potential, but nevertheless has a high lubricating capacity. This object is achieved according to the invention by a fluorinated lubricant with the general formula A, B, C, D or E corresponding components

AC ₃ F ₇ O - (CFCF ₂ O) _n - C ₂ F ₅

B CF ₃ - (OCFCF ₂ ) _m-1 - OCFCF ₂ - OCF ₂ - (OCF ₂ ) _n-1 - OCF ₃

C CF ₃ - (OCF ₂ CF ₂ ) _m-1 - OCF ₂ CF ₂ - OCF ₂ - (OCF ₂ ) _n-1 - OCF ₃

DC ₃ F ₇ O- (CF ₂ CF ₂ CF ₂ O) _n - C ₂ F ₆ EC ₃ F ₇ O- (CFCF ₂ O) _p - (CF ₂ CF ₂ CF ₂ O) _q - (CF ₂ CF ₂ O) _r - (CF ₂ O) _s - C ₂ F ₅

which is 2 to 10 percent by weight of longer-chain oligomers A, B, C, D or Emin greater than or equal to 8 or (p + q + r + s) greater than or equal to 8 and as remaining constituents at least one shorter-chain oligomer A, B, C, D or E (n <8 or (p + q + r + s) <8) or their monomers (n = 0 or p = q = r = s = 0).

Another way of producing a lubricant that meets the requirements is to use components of the general formula A, B, C, D and / or E specified above or mixtures of these components in proportions of 2 percent to 20 percent with compounds of the general formula F. to mix

FC ₃ F ₇ O - (CFCF ₂ O) _χ - CF - CF - (CCF ₂ CF) _y - OC ₃ F ₇ where x and y are independently 0, 1, 2 or 3.

Furthermore, a lubricant that meets the requirements can be produced by using components of the general formula A, B, C, D and / or E or mixtures of these components in proportions of 2 percent to 20 percent mixed with compounds of the general formula G,

GC ₃ F ₇ O - (CFCF ₂ O) _χ - CF - CF ₂ CF ₃ where x = 0, 1, 2 or 3.

Further refinements of the invention can be found in the subclaims.

In the lubricant according to the invention, the shorter-chain oligomers and the monomers, that is to say the compounds with the shortest possible chain length, serve as solvents for the longer-chain ones. For example, the "monomer" of compound A (n = 0) has a boiling point of approximately 45 ° C and compound A with n = 1 has a boiling point of approximately 95 ° C, each with a viscosity of 5 to 10 mm ² s ^-1 on.

Furthermore, the two shortest-chain compounds of the formula F with x, y = 0 or x = 1 and y = 0 have boiling points. 130ºC or 175ºC and compound G with x = 1 a boiling point of 72ºC, each with viscosities between 5 and

10 mm ² s ^-1 . Compared to compound A with n = 8 (40 - 45 mm ² s ^-1 ), this means a significantly reduced viscosity and thus easier and better processability.

The lubricant according to the invention can thus be used and applied in the same way as the previously known solution in R113, but has the advantage over this known method that the more volatile constituents evaporate more slowly by a factor of 3. This simplifies the process for applying the lubricant and enables it to be carried out in a continuous system. The more volatile components of the lubricant can easily be retained in the atmosphere prior to evaporation and used again in the process. All possible combinations of structures A and B have the desired lubricating effect, see above that a usable lubricant is not primarily dependent on the chain length of the oligomers contained, but only on the viscosity of the oligomer mixture. It is therefore not necessary to use a refined perfluoropolyether oil (PFPE oil). Rather, it is possible to use a natural oligomer mixture obtained in the production of the PFPE oils and thus to achieve further cost advantages. The lubricant is preferably applied to a part to be lubricated by immersing the part in the lubricant.

For price reasons, it makes sense to mix the recovered low-molecular components with higher-molecular components, which is cheaper in any case than using special raffinates. A higher boiling point (e.g. about 100 ° C and more) of the low molecular weight components facilitates recovery.

There are also advantages in systems which are integrated in the injection molding of plastics and in which some of the medium evaporates. Known systems have a volume of about 2 liters and are cooled to about 4 ° C, so that only the lubricant portion (including evaporable monomers) is effectively transferred. The total monomer losses thus reach their minimum.

If devices for applying the lubricant are integrated in injection molding systems, it may be necessary to remove the monomer components with boiling points from 130 to 180 ° C using a hot air blower and to recover them by condensation. This is particularly the case when using lubricants consisting of mixtures of known PFPE oils and compounds of the general formulas F and / or G. Here, too, it is not necessary to use constantly redistilled liquids of the form in F and / or G for mixing, rather it seems sensible for reasons of price to mix the low-molecular components recovered by condensation with higher-molecular ones. With correspondingly higher expenditure, lower-boiling components can also be recovered (for example, boiling point 40 to 100 ° C), if provided by

 Cost advantages of more volatile lubricants appear economical. Longer-chain oligomers with boiling points above 150ºC no longer pose a risk to the ozone layer. Components of the lubricant that boil less than 150ºC can be evaporated quickly with the help of the thin layers with the help of heating (a few minutes). Since these low-boiling fractions can also be completely recovered and reused, the relatively high ones

Lubricant costs also achieved a cost advantage over a process that previously worked with a high CFC (fluorocarbon) loss.

The lubricant according to the invention contains, inter alia, longer-chain oligomers with 8 to 10 intermediate members. That means, connections A, B, C, D or E with 8 small equals, m less than or equal to 10 resp. 8 small equal (p + q + r + s) small equal 10.

The proportion of these long-chain oligomers in the lubricant according to the invention is preferably between 3 and 5 percent by weight. In this ratio, one for processing or. the application of the lubricant to parts to be lubricated receive favorable viscosity.

One embodiment of the invention relates to a lubricant that contains only the chemically uniform PFPE oil A.

The invention is explained in more detail below on the basis of 10 exemplary embodiments.

Table 1 shows the compositions of 10 suitable lubricant mixtures, the constituents of which are identified by the trade names of Hoechst AG.

The low viscosities of the specified lubricants allow problem-free direct application to plastic parts or gold contacts to be lubricated, for example by immersion coating.

The evaporation behavior of the lubricants at 25ºC is documented in Table 2. The measured values are obtained by weighing a sample (5 g sample weight) after different time intervals.

Table 2: Evaporation rates (at 25ºC, weight in each case 5.0 g, weight determined at specified, time intervals)

The measured values show the broad field of application of the lubricants according to the invention. A suitable lubricant can be found for every application, and the selection can be made using the specified lubricant parameters.

Claims

Claims 1. Fluorinated lubricant with the general formulas A, B, C, D and / or E corresponding components

? AC ₃ F ₇ O - (CFCF ₂ O) _n - C ₂ F ₅ B CF ₃ - (OCFCF ₂ ) _m-1 - OCFCF ₂ - OCF ₂ - (OCF ₂ ) _n-1 - OCF ₃

₃

C CF ₃ - (OCF ₂ CF ₂ ) _m-1 - OCF ₂ CF ₂ - OCF ₂ - (OCF ₂ ) _n-1 - OCF ₃ DC ₃ F ₇ O- (CF ₂ CF ₂ CF ₂ O) _n -C ₂ F ₅ EC ₃ F ₇ O- (CFCF ₂ O) _p - (CF ₂ CF ₂ CF ₂ O) _q - (CF ₂ CF ₂ O) _r - (CF ₂ O) _s - C ₂ F ₅

which is 2 to 10 percent by weight of longer-chain oligomers A, B, C, D or E with n greater than 8 or (p + q + r + s) greater than or equal to 8 and as remaining constituents short-chain oligomers A, B, C, D or E or whose monomers (n = 0 or p = q = r = s = 0) contains. 2. Fluorinated lubricant consisting of I) 2 to 20 parts by weight of one or a mixture of several components which conform to the general structural formulas A, B, C, D or E, where n or the sum (p + q + r + s) is greater than or equal to 8 and II) Compounds of the general structure F and / or G in a proportion missing in total of 100 parts by weight

FC ₃ F ₇ O - (CFCF ₂ O) _χ - CF - CF - (OCF ₂ CF) _y - OC ₃ F ₇

GC ₃ F ₇ O - (CFCF ₂ O) _χ - CF - CF ₂ CF ₃ where x, y = 0, 1, 2 or means. 3. Lubricant according to claim 1 or 2, so that the lowest boiling constituents have an initial boiling point at 100 ° C. 4. Lubricant according to claim 1 or 2, so that the lowest boiling constituents have an initial boiling point at 150 °. 5. Lubricant according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that applies to the long-chain oligomers: 8 less than or less than 10 or 8 less than (p + q + r + s) less than 10. 6. Lubricant according to one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that it contains 3 to 5 percent by weight of longer-chain oligomers. 7. Lubricant according to one of claims 1 to 6, that the composition of the lubricant corresponds to a natural mixture of oligomers which is obtained in the production of the longer-chain oligomers. 8. Lubricant according to at least one of claims 1 to 7, d a d u r c h g e k e n n z e i c h n e t that it contains only monomers and oligomers of formula A.