Lubricant For Textile Machinery

Abstract

A lubricating composition that is uniquely designed for the lubrication of textile machinery such as a circular knitting machine comprises a lubricating oil containing zinc oxide as an antiwear agent. The zinc oxide is incorporated in the lubricating oil composition by first preparing an additive concentrate wherein up to 10 weight percent of zinc oxide has been dispersed in a lubricating oil using as a dispersing agent zinc naphthenate, magnesium naphthenate or mixtures thereof. The lubricating composition also preferably contains an oiliness agent, an antioxidant and an extreme pressure agent. The zinc naphthenate or magnesium naphthenate not only serves to suspend the zinc oxide but also imparts scourability to the composition, thereby aiding in the removal of the lubricant from the textile processed by the textile machinery.

Description

BACKGROUND OF THE INVENTION

This invention relates to an improved lubricating composition that is uniquely designed for the lubrication of small machine parts that operate at high speeds where it is necessary that the parts must be protected against high rates of wear and frictional power losses must be minimized, and where the oil must not damage the material being handled by the machine. Thus, the lubricating composition is particularly useful for textile machinery and still more particularly for the lubrication of a circular knitting machine, e.g. one used in the manufacture of seamless stockings. The invention also concerns a lubricant additive concentrate that is adapted for formulation of a finished lubricant composition of the invention.

In the manufacture of certain textile goods such as stockings, circular knitting machines are used. A representative machine of this type has a knitting head which may be briefly described as follows: The knitting head has a cylinder of steel about 5 inches in diameter, the wall of the cylinder being about one-half inch in thickness and provided with a large number of vertical slots distributed around the periphery of the cylinder. Each of these slots, which is about 32nd of an inch thick, receives a needle that moves rapidly up and down in the slot during the knitting operation. The knitting head is lubricated with an automatic lubricating device which feeds measured amounts of lubricant onto the moving parts. This lubricant is not recirculated and some of it necessarily finds its way onto the textile being knitted and thus must be later washed out of the knitted product. Thus, the lubricant for the knitting machine must have adequate scourability so that it can be removed from the textile. Other properties of the lubricant that are desired include rust inhibition, low coefficient of friction, good oxidation resistance and good load-carrying capabilities. Adequate load-carrying and antiwear properties in the lubricant are needed because of the large number of moving surfaces that require lubrication. Friction losses must be low in order to reduce frictional heat and to reduce the tremendous power load encountered during the start-up of the machinery.

In the prior art, load-carrying and antiwear properties were imparted to lubricants for knitting machines by incorporating finely divided molybdenum disulfide into the lubricants. While this additive did provide adequate load-carrying and antiwear properties, it had the disadvantage of tending to settle out of the lubricant so that the lubricant supply had to be continuously agitated to prevent such settling. Furthermore, the molybdenum disulfide tended to stain the textiles.

In accordance with the present invention, zinc oxide is used as the antiwear and load-carrying agent because zinc oxide will not stain the textiles. Furthermore, in the present invention the zinc oxide is maintained in suspension in the lubricant by means of an eminently stable suspending agent and by means of a novel procedure for preparing the zinc oxide suspension. More particularly, the zinc oxide is first suspended as a concentrate in a lubricating oil with the aid of zinc napthenate, magnesium naphthenate or mixtures of the two and the concentrate is thereafter blended into the finished lubricating composition in the desired concentration. It is not possible to prepare a finished lubricant of this nature that will be satisfactory by simply dispersing zinc oxide in the mixture of other components of the finished lubricant because the zinc oxide will tend to settle out of the mixture. It is thus necessary to first prepare the described concentrate. In a preferred aspect of the invention the zinc oxide is first coated with a zinc salt of a lower fatty acid before preparing the concentrate.

The essential component of a textile machine lubricant of the present invention is a suspension of zinc oxide in a mineral lubricating oil. The zinc oxide is of microscopic particle size of the order of about 0.02 to 0.25 micron and has a surface area of from about 5 to 25 square meters per gram. Preferably, the zinc oxide is treated with a C.sub.2 to C.sub.4 carboxylic acid to form a zinc salt on its surface, e.g. zinc propionate as taught in U.S. Pat. No. 2,303,330, and thereby aid in the dispersion of the zinc oxide.

The amount of zinc oxide in the additive concentrate will range from about 0.1 to about 10 weight percent, preferably from about 0.5 to 5 weight percent. To maintain the zinc oxide in suspension in the concentrate as well as in the finished lubricant, there is employed in the concentrate from about 0.5 to about 50 weight percent, preferably from about 1 to about 30 weight percent, of either zinc naphthenate or magnesium naphthenate or mixtures thereof. These metal naphthenates are prepared from petroleum naphthenic acids. The preferred naphthenic acids are those having molecular weights of from about 200 to about 350 and neutralization numbers of from about 150 to 230. A convenient procedure for dispersing the zinc oxide in the concentrate is to place the zinc oxide, metal naphthenate and lubricating oil in a ball mill and run the ball mill for from about 1 to 2 hours.

To prepare the finished textile machine lubricating oil the zinc oxide concentrate and the other desired components of the lubricant are incorporated in the desired base stock by simple mixing. The finished composition will contain from about 0.5 to about 5 weight percent of the zinc oxide concentrate along with other desired components such as an antioxidant, e.g. a zinc dialkyl dithiophosphate, phenyl-alpha-naphthylamine tertiarybutyl paracresol, or the like, an oiliness agent such as oleic acid or zinc oleate, and an extreme pressure agent such as sulfurized sperm oil, tricresyl phosphate or the like. A particularly preferred composition will contain, in addition to the zinc oxide concentrate dispersion, from about 0.1 to about 2 weight percent of a zinc dialkyl dithiophosphate, from about 0.2 to 1.5 weight percent of oleic acid, and from about 1 to about 5 weight percent of sulfurized sperm oil. The zinc dialkyl dithiophosphate will comprise one or more oil-soluble dithiophosphates wherein the alkyl groups have from about three to 18 carbon atoms, e.g. a mixture obtained from mixed isopropanol and methyl isobutyl carbinol, a mixture of amyl alcohols and technical lauryl alcohol, etc. The sulfurized sperm oil can be one containing from about 5 to 35 weight percent sulfur, preferably 8 to 20 per cent sulfur.

The zinc naphthenate or magnesium naphthenate that is present in the finished composition not only keeps the zinc oxide in suspension, but also imparts washability or scourability, thus aiding in the removal of any of the lubricant that gets picked up by the textile being processed by the textile machine.

The lubricating oil constituting the base oil in the compositions of this invention can be any well refined mineral lubricating oil distillate. The oil is preferably obtained from a naphthenic or paraffinic base crude oil, e.g. a Mid-Continent oil. The viscosity of the oil can range from about 50 to 250 SUS at 100.degree. F. Usually the viscosity will be within the range of about 75 to 200 SUS at 100.degree. F.

The nature of this invention will be better understood when reference is made to the following examples.

EXAMPLE 1

A concentrate of a zinc oxide dispersion was prepared by mixing together 94 parts by weight of a solvent neutral mineral lubricating oil of 100 SUS viscosity at 100.degree. F., 5 parts by weight of zinc naphthenate derived from naphthenic acids of about 280 molecular weight, and one part by weight of zinc oxide. The zinc oxide had been surface-treated with propionic acid as described in U.S. Pat. No. 2,303,330. The zinc oxide had a mean particle size of 0.11 micron and a surface area of 10 square meters per gram. It analyzed 99.1% ZnO. The mixture was placed in a ball mill and the dispersion was prepared by running the ball mill for 2 hours at ambient temperature.

EXAMPLE 2

A finished lubricant suitable for the lubrication of a circular knitting machine was prepared by blending together the following components in the weight percentages indicated below:

Wt. % Base oil* 95 Zinc dialkyl dithiophosphate 0.5 Oleic acid 0.5 Sulfurized sperm oil 3.0 Zinc Oxide Concentrate of Example 1 1.0

the zinc dialkyl dithiophosphates mentioned above, were in the form of a 75 weight percent concentrate in lubricating oil of the zinc salts prepared from the dithiophosphoric acids obtained by reacting P.sub.2 S.sub.5 with 65 weight percent of isobutanol and 35 weight percent of mixed primary C.sub.5 alcohols. The sulfurized sperm oil had a sulfur content of about 12 percent by weight.

The finished lubricant had a viscosity of 139.6 SUS at 100.degree. F., a viscosity of 43.2 SUS at 210.degree. F., and a viscosity index of 115.7. It was found to be a very suitable lubricant for a circular knitting machine, and left no stains on seamless hosiery knit by the machine, after said hosiery had been washed by standard procedures.

An attempt to prepare a finished lubricant with the same components in the same proportions as above, but simply dispersing the zinc oxide into the mixture of other components was not successful, because the zinc oxide would not remain in suspension.

EXAMPLE 3

A concentrate similar to that described in Example 1 was prepared using 5 weight percent of zinc oxide and 5 weight percent of zinc naphthenate. The dispersion was prepared by blending the mixture for 2 hours in a ball mill filled with steel balls. A portion of the product was set aside and observed for settling tendencies. No zinc oxide settled out of the concentrate in a period of 18 hours. About one-half weight percent of zinc oxide settled out after 48 hours. When the concentrate was used to prepare a finished textile machine oil of the same nature as described in Example 1, i.e. an oil containing about 0.01 weight percent of zinc oxide, there was no settling of zinc oxide even after the composition had been allowed to stand for 1 year.

EXAMPLE 4

Example 3 was repeated using magnesium naphthenate in place of the zinc naphthenate. The resulting dispersion was about as stable as that of Example 2, i.e. no more than about 1/2 to 1 weight percent of zinc oxide settled out of the concentrate after 48 hours.

COMPARATIVE EXAMPLE A

Example 3 was repeated using 5 weight percent of zinc oxide and 5 weight percent, in respective individual preparations, of lead naphthenate, barium sulfonate, calcium sulfonate, and aluminum stearate. In none of these cases was a satisfactory stable concentrate obtained. In the case of lead naphthenate, there was 100 percent settling of the zinc oxide after 18 hours. In the case of both the barium sulfonate and the calcium sulfonate, there was 90 percent separation of zinc oxide by settling after 18 hours. The sulfonates employed were the barium and calcium salts of petroleum sulfonic acids of about 400 molecular weight.

COMPARATIVE TEST B

The finished oil composition of Example 2, the base composition (i.e. the finished lubricant of Example 2 without the added zinc oxide concentrate) and a lubricant of the same composition as that of Example 2 with the exception that the 0.01 weight percent of zinc oxide was replaced with an equal quantity of molybdenum sulfide, were each subjected to the well known 4-Ball Wear Test. The test was conducted as follows:

The test lubricant is placed in the cup of the machine and heated to 75.degree. C. The test cup contains three steel balls which are fixed in position by a screw cap. A fourth steel ball held in a chuck is pressed against the three lower balls with a force of 40 kilograms and is rotated at 1,200 r.p.m. for 1 hour. At the end of the test, the amount of wear is determined by measuring the diameter of the wear scar on each of the steel balls and averaging the results.

The results obtained in the 4-Ball Wear Test with each of the two blends as well as with the base oil are given in Table I which follows. It will be seen that the lubricant containing zinc oxide was more effective in reducing wear than was the lubricant containing the molybdenum disulfide.

TABLE I

Oil Blend 4-Ball Wear, mm. __________________________________________________________________________ Base Oil 0.658 Composition with Zinc Oxide 0.399 Composition with Molybdenum Disulfide 0.433 __________________________________________________________________________

It is to be understood that the examples presented herein are intended to be merely illustrative of the invention and not as limiting it in any manner.

Claims

What is claimed is:

1. A process for preparing a stable dispersion of zinc oxide of about 0.02 to 0.25 micron size in a liquid lubricating oil composition which comprises the following steps:

a. mixing together about 0.1 to 10 weight percent of zinc oxide, about 0.5 to 50 weight percent of zinc naphthenate or magnesium naphthenate or a mixture thereof, and about 40 to 99.4 weight percent of mineral lubricating oil, said weight percents being based on the resulting mixture;

b. grinding said mixture in a mill whereby a zinc oxide concentrate is obtained from which no more than about 1 weight percent of zinc oxide will settle within a period of 48 hours;

c. thereafter dispersing about 0.5 to 5 weight percent of said concentrate into a liquid lubricating oil composition.

2. Process as defined in claim 1 including the step of precoating said zinc oxide with the zinc salt of a C.sub.2 to C.sub.4 fatty acid.

3. Process as defined in claim 2 wherein said zinc salt is zinc propionate.