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The present invention relates to the field of lubricating products for the hosiery and knitwear machinery sector.

In particular, the present invention concerns a lubricating product specifically for use on circular textile machinery for hosiery.

The sector of circular textile machinery for hosiery is a very specific sector, which requires exceptionally high quality standards: manufacturers are required to meticulously check all products before placing them on the market. The problem of waste caused by small imperfections is very important in this field, and therefore proper functioning of the machinery must be guaranteed at all times.

In circular machinery for hosiery, the needles having the function of knitting the yarns to obtain the textiles are subject to considerable inertial forces resulting from the high accelerations and decelerations they sustain in their reciprocating motion guided by a series of cams.

The reciprocating motion of each single needle enables a yarn to be hooked and carried under the knitting bed. This forms the loop that is released during the next rotation to create a row of stitches.

More conventional circular machines use around 400 needles and needle jacks, mounted on a cylinder of limited size (3.75 or 4 inches in diameter), and are provided with an electronic control system of the needles and their needle jacks. The needles can have a thickness of 0.3 mm and tolerances of a few hundredths of mm.

Given the complexity of these machines, the precision required to synchronize the movements of their needles at average speeds of 700 rpm is evident.

For these reasons, the needles constantly undergo substantial wear. Likewise, also the mechanical elements that form the needle control members, such as the working cylinders, are subject to heavy rubbing, which causes friction and leads to rapid wear.

Moreover, the high operating speeds reached by these circular machines cause, when operating at full speed, a considerable increase in temperature, which is damaging for the electronic components, and consequently energy must be wasted to activate specific cooling systems.

Currently, to attempt to reduce the aforesaid problems, there are used in these machines, and in particular in their internal linkages, lubricants adapted to substantially reduce friction between mutually moving metal parts and to minimize wear thereon.

This lubrication is carried out in an "oil bath": the lubricant is distributed on the head of the cylinders and in general on all the cylinders continuously and constantly, so as to fill the empty spaces between cylinders, needles and needle jacks. This lubrication system helps to reach higher production speeds and to significantly reduce friction of the moving members.

The most widely used lubricants for these purposes are mineral oils, obtained from oil refining, mixed with stabilizing additives with antioxidant and antiwear function.

These oils have some limits and disadvantages.

As stated above, one of the potentially problematic factors in circular machines for producing hosiery that operate at high speeds is the high temperature produced by these machines. An increase in the temperature promotes the phenomenon of oxidation after the oil molecules come into contact with the oxygen. The oil becomes more viscous and acids and sludges develop, compromising the efficiency of the machine, attacking the electrical and electronic components (control boards, wires, cables, gaskets etc.) and dissolving painted parts, with the risk of soiling the fabric and the hosiery being produced with a consequent increase in production waste. A significant parameter for measuring the performance of these oils for industrial application specifically for hosiery knitting machines is the viscosity index VI, linked to the ratio between the two viscosity values measured at two different temperatures (40° and 100°). In particular, a high viscosity index indicates a smaller variation in viscosity as the temperature increases; a high value of this index indicates that this oil tends to remain stable at high temperatures.

Industrial mineral oils found on the market, and which are conventionally used on circular machinery for hosiery, are characterized by viscosity index values close to or below 110.

This makes it necessary to add relatively high percentages of additives to the mineral oils, which is economically disadvantageous.

In the table set down below, various mineral oils currently widely used in circular hosiery machinery are listed and compared, classified according to their viscosity grade.

Conventional oils do not guarantee a significant decrease of the operating temperature of circular machines, which can reach up to 60°C: it is therefore essential to provide these machines with specific cooling systems, and to install cooling systems in the rooms housing the machinery.

Mineral oils deriving from oil refining are also difficult to dispose of and require specific and complex systems for removing processing waste and dye baths.

Moreover, notwithstanding the addition of specific additives, conventional mineral oils are still subject to a certain degree of oxidation and to the formation of lacquers or sludges, which makes it necessary to perform extraordinary maintenance, with unplanned downtimes and costs for loss of production.

Also known in the sector are products for the lubrication of synthetic textile yarns, but these have a very different composition compared to lubricants used on the linkages of circular machinery.

Oils for textile yarns are generally composed of:

esters of fatty acids and mineral oils (slack waxes and heavy gas oils) used as lubricating substance;

- phosphonate substances used as antistatic products to prevent the yarns from becoming electrostatically charged in contact with the metal parts of the textile machinery;

rubbers or resins used as anti-splash agents and binders to allow cohesion between the fibers of the textile yarn and prevent splashing;

- alcohols of fatty substances in high percentages used as emulsifiers to improve the washability of the oil during dyeing operations; water up to 3%, useful for improving the appearance of the product and increasing its transparency.

After being applied directly to the synthetic yarn, these products allow this yarn to run on the metal parts of the textile machinery (yarn guides, rollers, ceramic pulleys) at high speed without creating problems of electrostatic charge or friction.

An oil with these properties is known from the document DE19953326, which discloses a biodegradable lubricating oil for yarns.

However, these formulations would be damaging and extremely problematic to use on circular machinery:

- mineral oils (such as slack waxes and gas oils) would swell the gaskets, the O-rings used in the couplings of the compressed air lines, the sheaths of electrical wires, etc.;

- as anti-splash products are glues, they would promote adhesion between mechanical parts, a factor that must be avoided at all costs to enable smooth movement of the needles, needle jacks and various linkages;

- the presence of water (with large quantities of emulsifier) would cause oxidation of metal parts and of lubricating substances and oils, leading to the formation of lacquers, sludges and high density gels.

Moreover, oils for synthetic yarns must have high viscosity, in order to be well-absorbed by the textile fibers and to prevent splashing during the processing steps. On the contrary, a fluid and low viscosity oil must be used on circular machinery, to facilitate the smooth movement of the mechanical parts of the various kinematic mechanisms.

Therefore, it is not possible to use an oil that is normally used to lubricate the textile fibers also to lubricate the mechanical parts of circular hosiery machinery.

The main object of the present invention is to provide a new lubricating product specific for circular textile machinery for producing hosiery that overcomes the aforesaid problems, and therefore performs well from the point of view of lubrication of the linkages and mechanisms of the machine, with a reduction of wear and friction thereon, has a low viscosity, is not subject to oxidation, ensures low operating temperatures of the machinery, is easily washable, biodegradable and therefore easy to dispose of.

These and other objects are achieved with the lubricating product according to the main independent claim.

Further preferred formulations of the lubricating product according to the invention will be apparent from the remaining dependent claims.

The present invention also relates to a process for obtaining a lubricating product for circular textile machinery for hosiery.

With respect to products known in the art, the lubricating product of the invention allows high performances in the global output of the machine to be obtained.

The high lubricating power of the product disclosed in the present invention considerably reduces the friction and wear to which all the components of textile machinery for hosiery that operate with very high rotation speeds are normally subject.

Advantageously, the operating temperatures of the machinery decrease considerably with the use of this lubricating product: tests carried out showed a decrease of up to 10° C.

By way of example, in Figs, 1a, 1b and 2a, 2b show, with two thermographic images 1a and 2a two related histograms 1b and 2b of the temperatures, the performances of a circular textile machine for hosiery respectively lubricated with a conventional oil and with a lubricating product according to the present invention.

Comparative tests were carried out on a MATEC SC46 machine, and the temperature of the weaving room at the time in which the two measurements were taken was 25-26°C, shaded from the sun's rays.

The histogram of the temperatures of Fig. 1b, relating to the machine lubricated with the conventional oil, shows that the most frequent mean temperature is 59.3 °C, while the maximum temperature reached on the operating cylinder is 73.9 °C. The histogram of the temperatures of Fig. 2b relating to the machine lubricated with the lubricating product of the present invention, shows that the most frequent mean temperature drops below 50 °C, while the maximum temperature reached on the operating cylinder never exceeds 64.3 °C.

A decrease of the temperatures advantageously leads to a considerable saving of energy, both for the textile machine (a consumption per machine of up to 15% in kilowatt/hour less), but also for the whole processing plant. As a consequence, the systems for cooling the rooms are less overloaded. A further test was carried out, comparing a conventional oil and the lubricating product according to the invention in relation to electricity consumptions detected in 24 hours on the same textile machine.

This time the experiment was carried out on a MATEC Hf2.7 machine, and the electricity consumptions measured in W/h are indicated in the comparison table.

Even more advantageously, the lubricating product claimed has features of washability that satisfy the standards of modern dyeing processes, with less stress for the fibers and a better quality finish: its ability to emulsify with water thus facilitates elimination of residues from the textile fibers during washing.

This also leads to less waste of products with imperfections, resulting in a saving of money.

The additives used, albeit in minimum percentages, also offer considerable oxidation resistance to the base of esters to which they are mixed, preventing the formation of lacquers or sludges: this advantage was surprising, in view of the fact that esters have never been used as lubricant for mechanical parts in the textile sector, above all in damp environments like hosiery factories, due to their tendency to form lacquers.

Even more advantageously, the lubricating product according to the invention has optimal properties of biodegradability (>90%): this feature is important above all in the final steps to dispose of the dye baths with which the hosiery is treated, with a low environmental impact in the treatment process in biological purification plants.

Tests carried out show that the lubricating product according to the invention has a decidedly higher viscosity index compared to the conventional oils normally used on circular machinery, i.e. always in the range from 170 to 185. These value prove how the product according to the invention is advantageously very stable when the operating temperature varies, maintaining a controlled viscosity at all times, even at high temperatures, without the risk of dispersal and leakage of oil due to excessive fluidity.

According to the invention, the lubricating product, in its most general formula, comprises a mixture composed of:

- at least one ester having the following structural formula

wherein linear or branc nctional groups, with R from C ₃ to C ₆ and R' from C ₁₂ to Ci ₈ , are bonded to the ester functional group; - at least one alcohol ethoxylate.

These esters have chemical-physical characteristics in common: they have a viscosity at 20 °C between 15 and 40 mm ² /sec, a viscosity at 40 °C variable between 5 and 25 mm ² /sec; they have a neutralization number less than 1 mg KOH/g of oil and a iodine number less than 2 mg I ₂ /IOO g of substance.

Said at least one ester is chosen from 2-ethylhexyl stearate, 2- ethylhexyl palmitate, 2-ethylhexyl cocoate, 2-ethylhexyl laurate, isobutyl laurate, isotridecyl stearate, isopropyl palmitate, or a mixture thereof.

Preferably, the ester chosen is 2-ethylhexyl stearate (CAS N. 22047-49- 0), an ester with a molecular formula C26H52O2 obtained chemically from the esterification of stearic acid with 2-ethylhexyl alcohol.

Said at least one alcohol ethoxylate advantageously performs the function of pH regulator, antioxidant and anticorrosion and antirust of the metal surface of the machinery, as well as improving the washability of the lubricating product.

Examples of alcohol ethoxylates that can be used are alcohol C12-15 ethoxylate (CAS N. 68131-39-5) or 2-(2-dodecyloxyethoxy) ethanol (CAS N. 3055-93-4), or a mixture thereof. An example of mixture of alcohol ethoxylates provides for the following composition expressed in percentage in weight with respect to the total: 70% of alcohol C12-15 ethoxylate (CAS N. 68131-39-5) and 30% of 2-[2-( dodecyloxy)ethoxy] ethanol (CAS N. 3055-93-4).

In a preferred composition of the lubricating product according to the invention coconut amide is added.

The coconut amide has antioxidant function and inhibits degradation processes of the ester base: its particles tend to incorporate and sequester water, thus making the lubricant more transparent (pure esters have a turbid appearance, somewhat unappealing for the textile industry, which pays great attention to problems of stains on fabrics).

Some examples of mixtures according to possible embodiments of the invention, expressed in percentage in weight with respect to the total, are set down below.

Example 1 :

- 2-ethylhexyl stearate ester in commercial mixture of esters deriving from fatty acids C16-C18 (CAS N. 91031-48-0) at the rate of 97%, manufactured by the company Chimica Porlezza s.r.l;

- a mixture of alcohol ethoxylates at the rate of 2.5%; - coconut amide at the rate of 0.5%.

The chemical-physical characteristics of the lubricating product thus formulated are illustrated in the table below, which indicates values obtained by tests carried out according to the current regulations on this subject.

From the table it can be seen how the kinematic viscosity value at 40°C is much lower compared to the values found in the conventionally used mineral oils indicated above.

Example 2:

- isotridecyl stearate (CAS N. 31565-37-4) at the rate of 75%;

- 2-ethylhexyl palmitate (CAS N. 29806-73-3) at the rate of 15-29%;

- a mixture of alcohols ethoxylates at the rate of 1-10%;

- coconut amide at the rate of 0-1 %.

Example 3:

- isopropyl palmitate (CAS N. 142-91-6) at the rate of 30-40 %;

- 2-ethylhexyl palmitate (CAS N. 29806-73-3) at the rate of 30-40%;

- isotridecyl stearate (CAS N. 31565-37-4) at the rate of 10-20%;

- a mixture of alcohol ethoxylates at the rate of 1-10%;

- coconut amide at the rate of 0-1 %. A process to obtain a lubricating product for circular textile machinery for hosiery according to the invention comprises the following steps:

- to provide at least one ester having the following structural formula

and composed of the ester functional group and of linear or branched hydrocarbon functional groups, with R from C3 to C-| ₆ and R' from C12 to C ₁₈ ;

- to provide at least one alcohol ethoxylate;

- to provide coconut amide;

- to pour said ester, said alcohol and said coconut amide into a mixer.

Moreover, the process also comprises the step of treating said at least one alcohol with a process of washing with water to remove the polyglycols present before adding it into said mixer.