WO1996037579A1 - Lubricant composition for refrigerating compressors - Google Patents

Abstract

A lubricant composition for refrigerating compressors is described, which uses a refrigerant with a wear imprint, as measured by ASTM D4172, of less than 0.80 mm, a viscosity, as measured by AFNOR T60100, of 10-100 cst and with total HFC miscibility at a composition concentration of not more than 10 wt.%, characterised in that it contains at least 10-100 wt.% of one or more linear heptanoic acid ester with a neopolyol containing not more than 5 hydroxyl groups.

Description

 LUBRICATING COMPOSITION FOR REFRIGERATION COMPRESSORS

The present invention relates to lubricating compositions for refrigeration compressors with improved lubricating and anti-wear properties for the new chlorine-free fluorocarbon refrigerant gases.

The fact of favoring the lubricating and anti-wear properties of these compositions is particularly new since the current trend is rather to favor the miscibility of the lubricating compositions and of the refrigerant gases, which generally goes against lubricating performance. In fact, it has been found that many compressors easily seize up when the miscibility of the lubricating compositions and of the refrigerant gases had been chosen as the sole selection criterion for these lubricating compositions.

Compared to the specifications of manufacturers and users, the miscibility requirements are often lower in reality and depend very much on the compressor technology. In fact, most industrial refrigeration compressors are open or semi-hermetic systems which are equipped with oil separators, thus making it possible to avoid entrainment of the lubricating composition in the compressor. In such compressors, the lubrication and anti-wear properties must therefore be favored since it is not necessary for the lubricant composition and the refrigerant gases to be miscible.

Furthermore, even in the case of hermetic refrigeration compressors of small power, without separator, it has been found experimentally that too much miscibility of the lubricating composition in the refrigerant gas causes seizure of the parts in friction, particularly in the highly charged areas of the piston / liner type, and piston pin / big end. To select a good lubricating composition for refrigeration compressor, it is therefore essential to choose chemical structures allowing good lubrication of mechanical parts in friction such as piston-liner-connecting rod assemblies in reciprocating compressors or screw-cylinders or pallets. -stators or others for rotary compressors.

Currently, the most sought-after lubricating compositions for refrigeration compressors are obtained from esters of neopolyols, in particular reaction products of carboxylic acids with short branched chains comprising at most six carbon atoms and carboxylic acids with long chains linear or branched comprising more than eight carbon atoms with neopolyols such as neopentylglycol (NPG), trimethylolpropane (TMP), and mono, di and tri pentaerythritols (PE). These lubricating compositions described very widely in the patents of the technique aim to obtain an optimum of miscibility of the lubricating composition and of the refrigerant gas in the temperature and concentration ranges of lubricating composition imposed by the refrigerating installations. This optimum is most often targeted by excess to 30% by weight of lubricating composition.

In addition, it has been found experimentally that an optimum miscibility set between 5 and 10% is more than sufficient for the proper functioning of the compressor, particularly in small hermetic type systems.

The present invention therefore relates to a lubricating composition with improved lubrication and anti-wear properties, the viscosity of which is sufficient and does not drop suddenly by high miscibility with the refrigerant gases, thus causing binding of the friction parts, even in pressurized systems favoring such drops in viscosity. Unlike previous work, the lubricant composition is selected on the basis of lubrication, viscosity and anti-wear criteria, the viscosity having to be sufficient to avoid seizing of the friction parts and limiting their wear, miscibility being considered here as a secondary criterion. . The present invention therefore relates to a lubricating composition whose anti-wear characteristic corresponding to the diameter of the imprint measured in accordance with standard ASTM D4172 is less than 0.80 mm as in previous mixtures of mineral oil / R12, the viscosity measured at 40 ° C according to AFNOR T60100 standard is between 10 and 100 mm ² s- ¹ and whose miscibility is total for a concentration of said composition at 10% by weight in the hydrofluorocarbon refrigerant gases hereinafter called HFC is less than 10% by weight, characterized in that it consists of at least 10 to 100% by weight of at least one ester of linear heptanoic acid with a neopolyol, the number of hydroxyl groups of which is less than or equal to 5.

By convention, it is accepted that there is seizure of metallic surfaces in contact when the cavity diameter measured according to standard ASTM D4172 is greater than 0.8 mm.

Preferably, the neopolyols are chosen from the group consisting of neopentylglycol (NPG), trimethylolpropane (TMP), monopentaerythritol (mPE), taken alone or as a mixture. The presence of at least one ester of linear heptanoic acid constitutes the best compromise between the required lubrication characteristics (antiwear and viscosity) and the limit of miscibility allowed. However, it makes sense to have ranges of lubricants whose ISO viscosimetric grade varies from 10 to 100. To obtain them all, this ester of heptanoic acid must necessarily be present in mixture with other compounds.

Thus for the production of compositions according to the invention of ISO viscosimetric grades less than 32, the lubricating composition comprises 60 to 100% by weight of at least one ester of linear heptanoic acid with a neopolyol having at most 5 hydroxyl groups and 40 to 0% by weight of at least one linear pentanoic acid ester with a neopolyol comprising at most five hydroxyl groups, the neopolyols retained being able to be identical or different and the esters being able to be simple or mixed.

By simple ester is meant an ester obtained from a single neopolyol and a single carboxylic acid. By comparison, the mixed ester is obtained from a single neopolyol but from minus two carboxylic acids reacting with hydroxyl groups of the same neopolyol molecule.

In a first form of the invention, a composition of ISO viscosimetric grade less than or equal to 22 consists of 70 to 100% by weight of linear heptanoic acid ester with a neopolyol from the group consisting of neopentylglycol and monopentaerythritol taken alone or as a mixture and from 30 to 0% of linear pentanoic acid with monopentaerythritol. In a second embodiment of the invention, a composition of ISO viscosimetric grade between 22 and 32 is constituted by an ester of pentaerythri ol obtained for 40 to

20% by weight from a linear pentanoic acid and for 60 to

80% by weight from linear heptanoic acid, the esters can be simple or mixed.

The intermediate grades are obtained either from a single composition or by mixing the two preferred compositions.

For the composition of ISO viscosimetric grade composition greater than or equal to 32, a composition comprising from 75% to 100% of its weight is preferred a mixture of neopolyol ester comprising at most five hydroxyl groups consisting of 10 to 60% by weight of 'A linear heptanoic acid ester and 90 to 40% by weight of an isononanoic ester, the esters can be simple or mixed.

In a first preferred form of ISO viscosimetric grade greater than or equal to 32, the composition is a pentaerythritol ester obtained for 10 to 60% of its weight with a linear heptanoic acid and for 90 to 40% of its weight with an isononanoic acid.

The use of pentaerythritol isononanoate makes it possible to adjust the high viscosities more easily.

In a second preferred form of compositions of grade greater than or equal to 32, the composition of the invention comprises from 10 to 55% by weight of an ester obtained with a linear heptanoic acid, from 85 to 20% of an ester of isononanoic acid and from 5 to 25% of a linear pentanoic acid ester, the polyols used being from the group consisting of trimethylolpropane and monopentaerythritol, the esters can be simple or mixed.

However, it would not depart from the scope of the invention if, to improve the antiwear properties of the high grade compositions, were added to these said compositions, known conventional antiwear additives.

The compositions according to the invention can be used in all types of industrial or household compressors in the presence of the main hydrofluorocarbon refrigerant gases developed or under development as pure gases such as R134a, R152a, R 143a, R125, R32 etc. or in the form of mixtures such as R404A, R407c, R 410A, R507, etc.

The examples are given below by way of illustration but without limitation of the present invention.

EXAMPLE 1

The present example aims to show the influence of the chain length of the acid used in the formulation of

The ester and the influence of the number of hydroxyl groups of the polyol used on the antiwear properties of the said composition according to the invention.

Several simple esters obtained were thus prepared with:

either the same polyol, here trimethylolpropane or TMP, with linear monocarboxylic acids comprising 5 to 10 carbon atoms, hereinafter designated nC5, nC6, nC7, nC8, nC9, nCIO,

- or the same monocarboxylic acid, here linear heptanoic acid with 7 carbon atoms, nC7, with polyols comprising from two to 10 hydroxyl groups, neopentylglycol or NPG, trimethylolpropane or TMP, monopentaerythritol or mPE and dipentaerythritol or diPE.

The anti-wear properties of these compositions are measured according to standard ASTM D4172 also called the 4-ball test consisting in measuring the diameter of the wear imprint in mm, under the following test conditions:.

load: 40 daN (decanewton) speed: 1200 rpm Temperature C: 75 ° C Table I below gives the influence of the length of the carbon chain of the neopolyol esters on the imprint diameters "4 balls".

TABLE I

It is found that for the same polyol, the more the chain length of the linear acid increases the more the wear decreases. In particular, the composition of the nC5 TMP ester leads to obvious binding of the parts in contact. For the same monocarboxylic acid, the preferred acid of the invention, heptanoic acid or nC7, the more the number of hydroxyl groups increases the greater the wear imprint and the risk of seizure. It is deduced from these tests that the compositions which would comprise a lot of ester obtained from C5 acid or from diPE are very little lubricating.

EXAMPLE 2

The present example aims to show that the lubricant compositions according to the invention have sufficient miscibility in the refrigerant gases for an oil content of

10% at -30 ° C, good anti-wear characteristics and a viscosity corresponding to the desired grade.

Four lubricating compositions according to the invention were prepared according to techniques known to those skilled in the art, for ISO viscosimetric grades from 10 to 100. Their composition is given as well as their miscibilities and their anti-wear effect and their viscosity in Table 2 below.

The miscibilities were measured according to the DIN 51.351 method in sealed tubes, based on the visual determination of the demixing temperature of the lubricant / refrigerant gas mixtures.

The anti-wear properties and the viscosity were measured respectively by the "4-ball" wear method (ASTM D4172) as described in Example 1 and by the method described by AFNOR T60100 standard.

Table II below gives the characteristics of the lubricating compositions of ISO grades 10 to 100.

TABLE II

I

I00

I

* addition of 0.5% phosphorus antiwear additive - without additive: 1.10 mm

It can be seen that, for the whole range of viscosities required, it is possible to simultaneously obtain total miscibility with 10% of oil in the presence of the reference gases R 124a and R404A, and with good anti-wear properties.

(no seizure).

However, in high grade compositions, it is preferable to add an anti-wear additive.

Claims

Pî? VFNnτraττnM.ς - Lubricating composition for refrigerant, the wear imprint measured according to ASTM D4172 standard is less than 0.80 mm, viscosity measured by AFNOR T60100 standard between 10 and 100 mm ² s ^-1 and total miscibility for a concentration of the composition less than or equal to 10% by weight in HFCs characterized in that it consists of at least 10 to 100% by weight of at least one ester of linear heptanoic acid with a neopolyol the number of hydroxylated groups is less than or equal to 5. - Composition according to claim 1 characterized in that the neopolyols are chosen from the group consisting of neopentylglycol, trimethylolpropane and monopentaerythritol, taken alone or as a mixture. - Composition according to claim 1 characterized in that ISO viscosimetric grade less than 32, it consists of 60 to 100% by weight of at least one ester of linear heptanoic acid with a neopolyol having at most 5 hydroxyl groups and 40 to 0% by weight of at least one ester of linear pentanoic acid with a neopolyol comprising at most five hydroxyl groups. - Composition according to claims 2 and 3 characterized in that of viscosimetric grade less than or equal to 22, it consists of 70 to 100% by weight of linear heptanoic acid ester with a neopolyol from the group consisting of neopentylglycol and monopentaerythritol taken alone or in admixture and 30 to 0% of linear pentanoic acid with monopentaerythritol. - Composition according to claims 2 and 3 characterized in that, of ISO viscosimetric grade between 22 and 32, it consists of a pentaerythritol ester obtained for 40 to 20% by weight from linear pentanoic acid and for 60 to 80 % by weight from linear heptanoic acid. - Composition according to claim 1 characterized in that of viscosimetric grade greater than 32, it comprises from 75% to 100% of its weight a mixture of neopolyol ester comprising at most five hydroxyl groups consisting of 10 to 60% by weight of an ester of linear heptanoic acid and 90 to 40% by weight of an ester of isononanoic acid. - Composition according to claims 6 and 2 characterized in that it consists of a pentaerythritol ester obtained for 10 to 60% of its weight with a linear heptanoic acid and for 90 to 40% of its weight with an isononanoic acid. 8 - Composition according to claims 6 and 2 characterized in that it consists of 10 to 55% by weight of an ester obtained with a linear heptanoic acid, from 85 to 20% by weight of an ester of isononanoic acid and 5 to 25% by weight of a linear pentanoic acid ester, the polyols used being from the group consisting of trimethylolpropane and monopentaerythritol, the esters being able to be chosen simple or mixed. 9 - Use of the composition defined by claims 1 to 8 as a lubricant in all types of industrial or household compressors in the presence of all types of known hydrofluorocarbon refrigerants, or in development and more particularly hermetic or semi-hermetic compressors of the reciprocating or rotary type not fitted with an oil separator.