Lubricant fluid for the cold-rolling of steel

Lubricant fluids for the cold-rolling of steel, comprising one or more organic carbonates of general formula (I) ##STR1## where R and R', which can be identical or different, represent a C.sub.6 -C.sub.30 linear or branched alkyl, cycloalkyl or cycloalkyl-alkyl radical, possibly mixed, in a quantity sufficient to provide the composition with the lubricant power necessary for the particular application, with a mineral oil base. These lubricant fluids can be conveniently used in the cold-rolling of any type of steel, either as whole oils or, after adding suitable quantities of emulsifiers, as oil concentrates for forming aqueous emulsions or microemulsions. In addition to possessing all the typical characteristics of rolling fluids, they are also able to minimize the formation of carbon residues and deposits in the subsequent annealing process.

This invention relates to the use of alkyl or cycloalkyl esters of carbonic 
acid in the preparation of lubricant fluids suitable for the cold-rolling 
of steel, and the resultant lubricant fluids containing such carbonic 
esters. 
The choice of the lubricant fluid in steel rolling, and in particular in 
cold rolling processes, has become extremely critical with the advent of 
high-speed rolling mills. There is more than one reason for feeding a 
lubricant fluid between the material to be rolled and the rolls which 
produce the plastic deformation (friction reduction, wear reduction, 
obtaining the required surface finish etc.), and in choosing the most 
suitable lubricant fluid the relative importance of these factors must be 
carefully evaluated on the basis of the process used, the material to be 
rolled and the required product. 
Of the lubricant fluids suitable for this particular process those 
currently most widely used are natural fats and synthetic fatty esters, 
either as such or preferably diluted in a mineral oil base. These 
lubricants are either used as such or, with the addition of suitable 
quantities of emulsifiers, are used to prepare aqueous emulsions of 
varying concentration. Aqueous emulsions are used when the main factor is 
the control of temperature, whereas whole oils are preferred when it is 
the lubricant effect which is the most important or when the presence of 
water can create particular corrosion problems. 
In selecting a suitable lubricant for the cold-rolling of steel another 
factor extremely important from the technical aspect must also be 
considered, namely that the lubricant must not stain the product. In this 
respect, if the required product is to have a shiny finish after 
cold-rolling or be subsequently coated, the lubricant used must after the 
high-temperature annealing leave no residues which can damage or ruin the 
appearance of the surface. The complete removal of the rolling oil before 
annealing using special cleaning or degreasing methods would be an obvious 
step, but this results in excessive production costs; in addition, if a 
strip with a too clean surface is annealed at high temperature, the 
adjacent turns of a coil can adhere to each other. 
In normal practice it is therefore sought to reduce this problem as much as 
possible by removing the excess lubricant by rubbing or with air jets, and 
then allowing the remaining lubricant to evaporate either during a pause 
in the process immediately before annealing, or during the initial stages 
of annealing. 
As complete lubricant removal is never obtained in this manner, it is clear 
why in the last twenty years various studies have been carried out 
directed to identifying and perfecting lubricant fluids suitable for the 
cold-rolling of steel which either solve or at least as far as possible 
reduce the problem of staining. Thus traditional animal or vegetable oil 
such as lard oil or palm oil, possibly mixed with mineral oil, has been 
superseded by a mixture of this latter with synthetic additives and in 
particular synthetic fatty esters, which have resulted in a reduction of 
the phenomenon. It has however now been found possible to prepare 
lubricant fluids suitable for the cold-rolling of steel which besides 
possessing all the typical characteristics of metal rolling fluids are 
also able to minimize the formation of carbon residues and deposits during 
subsequent annealing. 
These lubricant fluids, which represent a first aspect of the present 
invention, comprise one or more organic carbonates of general formula (I) 
##STR2## 
where R and R', which can be identical or different, represent a C.sub.6 
-C.sub.30 linear or branched alkyl, cycloalkyl or cycloalkyl-alkyl 
radical, possibly mixed, in a quantity sufficient to provide the 
composition with the lubricant power necessary for the particular 
application, with a mineral oil base. 
In practice, this "sufficient quantity", expressed as a weight percentage 
of the total weight of the composition, is generally greater than 5%, 
preferably greater than 10% and more preferably greater than 15%. 
The radicals R and R' indicated in formula (I) represent C.sub.6 -C.sub.30 
linear or branched alkyl, cycloalkyl or cycloalkyl-alkyl radicals, in 
which the radical carbon atom can be primary, secondary or tertiary. 
Preferably, R and R' represent C.sub.6 -C.sub.30 linear or branched alkyl 
radicals. More preferably, R and R' represent C.sub.10 -C.sub.20 linear or 
branched alkyl radicals. 
The esters of carbonic acid with higher aliphatic or cycloaliphatic 
alcohols of formula (I) are known compounds, and are easily prepared 
either by transesterification of lower alkyl carbonates such as 
dimethylcarbonate or diethylcarbonate with higher alcohols or mixtures of 
higher alcohols, in the presence of suitable transesterification 
catalysts, or by reacting the higher alcohol, or alcohol mixture, with 
phosgene at high temperature preferably in the presence of an organic or 
inorganic base. A lubricant effect of higher alcohol carbonic esters is 
known from U.S. Pat. No. 2,758,975, which claims a particular composition 
of organic carbonates and tricresylphosphate, and from European patent 
application No. 89,709, which relates to the use of organic carbonates in 
formulating lubricants for internal combustion engines and/or industrial 
machines. 
It has however now been found that the lubricant characteristics of these 
organic carbonates can also be used in the specific field of lubrication 
in the rolling of steel, which as stated differs considerably from 
conventional lubrication both because of the more complex objectives which 
are set and because of the type of deformation involved (plastic rather 
than only elastic). It has also been found that the thermal stability 
characteristics of the organic carbonates of formula (I) and their 
volatility are such as to make these compounds particularly suitable for 
their use in the cold rolling of steel. In particular, thermogravimetric 
analysis has shown that the organic carbonates of formula (I) have good 
thermal stability at the temperature peaks attainable during rolling 
(250.degree.-270.degree. C.) and are able to evaporate completely at 
temperatures much lower than the standard annealing temperatures (which 
are typically between 650.degree. and 730.degree. C.). 
These compounds also have the peculiar property of evaporating without 
excessive decomposition within a relatively narrow temperature range. 
A lubricant fluid consisting of one or more carbonates of formula (I) 
possibly mixed with a mineral oil base, which can be of paraffinic, 
aromatic or naphthenic type, can conveniently be used whole for the cold 
lubrication of any type of steel, from normal steels of low carbon content 
to stainless steels. Moreover, it can be used, upon addition thereto of 
appropriate quantities of emulsifying agents, as an oily concentrate for 
the formation of microemulsions, or of a minor proportion of such a 
concentrate in a greater proportion of water, in order to form stable 
emulsions. In preparing these emulsions or microemulsions, the preparation 
of which is conventional, it is preferable to use mixtures of one or more 
carbonates of formula (I) with a mineral oil base containing suitable 
emulsifiers in a quantity sufficient to allow the aqueous emulsion or 
microemulsion to be prepared at the required concentration. 
Suitable emulsifiers are all the normal ashless non-ionic or anionic 
surfactants such as polyoxyethylenic ethers and esters, and in particular 
ethoxylated alkylphenols such as those marketed by Hoechst under the name 
of Emulsogen.RTM. or Sapogenat.RTM., or those marketed by Huls under the 
name of Marlophen.RTM.. 
Preferably, the organic carbonate (of formula I) content of this oil 
concentrate is between 5 and 65%, and more preferably between 10 and 50%. 
If desired, the emulsions or microemulsions can also contain other 
conventional additives such as anticorrosion agents, antiwear agents etc., 
as known in this field. 
Generally the concentration of the oil phase in water varies between 1 and 
5% and is preferably around 2-3%. 
In particular, it is preferred to use the aqueous emulsion or microemulsion 
obtained in this manner for steel lubrication and rolling in four-high or 
tandem rolling mills, whereas the whole oil is preferred for cold rolling 
in reversible rolling mills of Sendzimir type. 
The following examples are provided merely for the purpose of describing 
some lubricant compositions representative of the present invention in 
greater detail, and are in no way to be considered as setting a limitation 
on the scope of the invention.

EXAMPLE 1 
Synthesis of Carbonic Esters of Formula (I) 
General Method 
The synthesis apparatus consists of a jacketed three-neck flask 
temperature-controlled by an externally circulating fluid, surmounted by a 
distillation column comprising perforated plates and a liquid dividing 
head, and fitted with a magnetic stirrer and thermometer. 
The low-boiling alcohol carbonate (dimethyl carbonate), an at least 
stoichiometric quantity of the higher alcohol or mixture of higher 
alcohols, i.e. double the moles of the lower alcohol carbonate, and 
preferably in excess over the stoichiometric, plus the transesterification 
catalyst in the form of an organic or inorganic compound of strongly basic 
character are placed in the flask. The reaction is conducted in an inert 
atmosphere, heating the reaction mixture to boiling point and removing as 
overheads the low-boiling alcohol which forms. In some cases the reaction 
was conducted in the presence of an inert solvent able to form a minimum 
azeotrope with the low-boiling alcohol so as to facilitate its removal by 
distillation. On termination of the reaction the catalyst can be removed 
(by washing with water, filtration or neutralization) and the reaction 
product can be recovered by distilling off the unwanted by-products and 
any unreacted higher alcohols in excess. 
In this manner, starting from the following mixtures of suitable higher 
alcohols, the corresponding mixtures of organic carbonates (I) are 
obtained, their molecular weights being indicated in parentheses: 
(A) a mixture of iso-decyl alcohols (342.6); 
(B) n-decyl alcohol (342.6); 
(C) a 50 wt % mixture of C.sub.14 -C.sub.15 branched alcohols (468); 
(D) a mixture of iso-tridecyl alcohols (50 wt %) and C.sub.12 -C.sub.15 
alcohols containing 40% of linear and 60% of branched (50 wt %) (430.2 
mean); 
(E) a mixture of C.sub.12 -C.sub.15 oxo-alcohols (442.0 means). 
EXAMPLE 2 
A formulation is prepared consisting of 30% of the carbonic ester of 
Example (1A) in low-viscosity paraffinic mineral oil for use as a whole 
oil for steel rolling on a reversible Sendzimir rolling mill. 
The lubricant power of this composition, evaluated by the Almen-Wieland 
machine test, was found to be 1850 kg, and the EP power evaluated by the 
four ball method according to ASTM D-2783 was 400 daN, with maximum 
no-seizure load of 80 daN. 
EXAMPLE 3 
A formulation is prepared consisting of 35% of the carbonic ester of 
Example (1B) in low-viscosity paraffinic mineral oil for use as a whole 
oil for steel rolling on a reversible Sendzimir rolling mill. 
The lubricant power of this composition, evaluated by the Almen-Wieland 
machine test, was found to be 1900 kg, and the EP power evaluated by the 
four ball method was 420 daN, with maximum no-seizure load of 90 daN. 
EXAMPLE 4 
A transparent microemulsion of 2-3% of an oil phase in water is prepared, 
the oil phase consisting of 35% of the carbonic ester of Example (1C), 45% 
of paraffinic mineral oil and 20% of anionic emulsifiers of the 
ethoxylated alkylphenol class. This formulation is conveniently used for 
the cold-rolling of steel on tandem rolling mills. The lubricant power of 
this emulsion, evaluated by the Almen-Wieland machine test, was found to 
be 2750 kg, and the EP power evaluated by the four ball method was 110 
daN, with maximum no-seizure load of 60 daN. The degree of cleanliness of 
the strips after rolling always exceeded 90% (Scotch test), and the carbon 
powder after annealing was an average of 2.5 mg/m.sup.2. 
EXAMPLE 5 
A milky emulsion of 2-3% of an oily phase in water is prepared, the oily 
phase consisting of 45% of the carbonic ester of Example (1D), 37% of 
paraffinic mineral oil and 18% of emulsifiers as in the preceding example. 
This formulation is conveniently used for the cold-rolling of steel on 
four-high rolling mills. The lubricant power of this emulsion, evaluated 
by the Almen-Wieland machine test, was found to be 1950 kg, and the EP 
power evaluated by the four ball method was 160 daN, with maximum 
no-seizure load of 75 daN. The degree of cleanliness of the strips after 
rolling always exceeded 90% (Scotch test), and the carbon powder after 
annealing was less than 4 mg/m.sup.2. 
The concentrated oil was subjected to thermogravimetric analysis before 
using the rolling mill to measure the oil weight loss as a function of 
temperature and thus determine both its evaporation rate and thermal 
stability. For this purpose, a small quantity of the oil placed in a 
platinum microcapsule connected to a balance is heated at a predetermined 
rate, then recording the weight variation as a function of temperature. 
During the experiment the first differential of the weight/temperature 
curve is calculated and recorded, to produce a curve which represents the 
evaporation rate of the substance. 
The thermogram for this oil is shown in FIG. 1a. This graph shows that the 
temperature at which the entire oil disappears (T.sub.a) is decidedly less 
than the steel annealing temperature (455.degree. C. as against the 
general annealing temperature of between 650.degree. and 730.degree. C.), 
and that the temperature at which maximum evaporation rate is attained 
(T.sub.b) is much higher than the temperature peaks reached during rolling 
(300.degree. C. as against the 250.degree.-270.degree. C. reached during 
cold-rolling), thus demonstrating the good thermal stability at working 
temperatures of the carbonic ester contained in the emulsion. 
EXAMPLE 6 
The thermal stability of the carbonate mixture of Example 1E is evaluated 
by thermogravimetric analysis using the procedure described in the 
preceding example. 
The relative thermogram is shown in FIG. 1b. It can again be seen that the 
T.sub.a (425.degree. C.) is much less than the annealing temperature and 
that the T.sub.b (310.degree. C.) is much higher than the temperature 
peaks reached in the cold rolling process. 
EXAMPLES 7-8 
Comparison 
The thermal stability of conventional rolling lubricants is evaluated by 
thermogravimetric analysis using the procedure described in Example 5. The 
specific lubricants used are of the natural fatty ester class, 
particularly lard oil, and the synthetic fatty ester class, particularly 
oleates. The relative thermograms are shown in FIGS. 2a and 2b 
respectively. 
It can be seen that the T.sub.b values are less in both cases (205.degree. 
and 220.degree. C.) than the temperature peaks reached in cold-rolling, 
which could imply partial decomposition of the lubricant during working. 
With regard to the T.sub.a values, for natural fatty esters (655.degree. 
C.) it is in fact within the annealing temperature range, which implies 
the possibility of considerable carbon deposits forming on the surface of 
the material during passage, whereas for synthetic fatty esters, although 
not higher (520.degree. C.) it is however fairly close to conventional 
annealing temperatures. 
By comparing FIGS. 1a and 1b with FIGS. 2a and 2b it can also be seen that 
in the case of the carbonic esters there is only one maximum on the 
differentiated rate curve and that this is very narrow, whereas in the 
case of the natural or synthetic fatty esters there are two and of greater 
width.