GB2434153A

GB2434153A - Boron nitride dry-film lubricant compositions

Info

Publication number: GB2434153A
Application number: GB0600816A
Authority: GB
Inventors: Richard Hutchinson; Steven Ian Reid
Original assignee: L & S Fluids Ltd
Current assignee: L & S Fluids Ltd
Priority date: 2006-01-16
Filing date: 2006-01-16
Publication date: 2007-07-18
Also published as: EP1808478A1; GB2434154A; DK1808478T3; GB0700678D0; ES2336502T3; GB0600816D0; EP1808478B1; PL1808478T3; DE602007003234D1; PT1808478E; ATE449151T1

Abstract

A dry film lubricant composition is provided, comprising boron nitride particles dispersed in a propylene glycol or water-soluble polyglycol base. The lubricant composition does not produce harmful vapours and forms a clean lubricating film capable of operation up to 2200{C, thus making it particularly suitable for lubricating ovens, particularly baking ovens. Also disclosed is the use of a lubricant composition comprising boron nitride for lubricating components in an oven; and the use of propylene glycol and water-soluble polyglycol as base materials in dry-film lubricant compositions.

Description

Lubricant Compositions The present invention relates to lubricant

compositions. More particularly, this invention relates to dry-film lubricant compositions for high temperature applications. More particularly still, this invention relates to boron nitride-containing lubricants, in which the boron nitride is dispersed in a water-soluble glycol or polyglycol base.

A number of different lubricants currently exist for use in high temperature environments, typically at temperatures over 260 C, and potentially up to 2000 C, such as on conveyor chains and bearings subjected to high temperatures in, for example, bakery ovens, kilns and paint stoving ovens. When selecting a lubricant for such uses, extreme pressure performance, operating temperature range, coefficient of friction and even the colour of the film are all relevant considerations. In addition, when working at high temperatures, particularly in baking ovens, safety is of paramount importance; the lubricant should not, of course, be flammable, nor should it produce toxic vapours. Furthermore, down-time for the machinery should be kept to a minimum, for economic reasons, and thus the lubricant should be easy to apply, not leave behind deposits or require cleaning, and it must maintain its lubricity for as long as possible.

Such known products include synthetic ester-based formulations: liquid lubricants enhanced with chemical additives to improve wear resistance and protect them from thermal degradation. Such compositions are generally limited to maximum operating temperatures of approximately 260 C, and their use will eventually lead to the formation of lacquers, gums and carbon deposits on the equipment being lubricated, which necessitates periodic cleaning (which, in turn, necessitates periodic shut-down of the equipment). In addition, being liquid products, synthetic ester-based formulations have a tendency to attract dust and dirt, which adheres to the lubricant film and, over time, will contribute to abrasive wear.

Another known lubricant for high-temperature use comprises a polyglycol-borne solid lubricant, typically graphite and/or molybdenum, dispersed in a high molecular weight, water-insoluble polypropylene glycols (typically having molecular weights of greater than 250). These fluids are designed to deposit a dry film of the solid lubricant; the polyglycol fluid acts, initially, as a conventional fluid lubricant, but depolymerises at a high-temperature and evaporates, thereby avoiding the formation of lacquers, and also avoiding gummy or carbon deposits.

Following the evaporation of the polyglycol, a dry film of lubricating solids remains on the lubricated surfaces, which has little tendency to attract dust and dirt. Both graphite and molybdenum provide good load carrying capacity, and can withstand temperatures of up to approximately 450 C and 350 C, respectively.

However, both are black in colour (which makes colouring difficult), and are electrically conductive, which can be disadvantageous in some uses. Polyglycol bases also carry their own disadvantages, which are mentioned more fully below.

Graphite and molybdenum can also be dispersed in water, in place of the polyglycol. However, aqueous dispersions tend to be very low viscosity fluids and accordingly drip from machinery and require frequent re-application, increasing downtime. In addition, aqueous dispersions exhibit "spitting" at raised temperatures, which is undesirable.

A further known class of lubricants are the polytetrafluoroethylene (PTFE) greases/dispersions. PTFE greases are dispersions of PTFE in perfluorinated polyether fluids (PFPE). PTFE is also used to enhance conventional ester-based lubricants, and is supplied as a dry film lubricant deposited in a similar manner to graphite and molybdenum. However, when supplied in ester fluids, the same problems occur as mentioned above. In addition, PTFE and PFPE lubricants cannot be recommended for continuous use above 260 C due to thermal degradation and emission of corrosive and toxic fumes.

Boron nitride particles are also used as the basis of various commercially available lubricant compositions, including lubricants for high temperature applications. Boron nitride is commercially available in various forms, either as a concentrate (in water, alcohol, oil or polyalphaolefin), for dilution with preferred base materials, or as a finished lubricant. Boron nitride can withstand extremely high temperatures and high loads, it is also non-reactive, thermally conductive, electrically insulating, and is white in appearance (enabling ease of colouring).

However, at present, there are no commercially available boron nitride based lubricants for baking ovens. Oil dispersions and those in polyalphaolefin are unacceptable due to carbonaceous deposit formation at high temperatures (i.e. over 260 C). Furthermore, alcohol dispersions give rise to flammable vapours in use and are also unsuitable. Water-based (i.e. aqueous) dispersions are disadvantageous, as discussed above. In addition, dispersing agents present in such compositions are generally not approved for food grade use.

The selection of the base material for the lubricant is of considerable importance. The production of corrosive andlor toxic fumes from a lubricant is a significant problem in all circumstances, and particularly in baking ovens. Baking ovens must not, of course, produce toxic fumes during baking, and enforced downtime to enable re-lubrication is undesirable, for economic reasons. In addition, baking ovens are often located in small premises where it is impractical to install the necessary ventilation equipment to remove any fumes which are produced during the lubricating process. As mentioned above, polyglycols, in particular polypropylene glycol, are commonly used as a base fluid. However, it has been found that high molecular weight polyglycol-based lubricants generate dense smoke and fumes when the oven is first heated to working temperature after re-application. Indeed, it some circumstances, it is practice to turn off the building's fire alarm whilst this process is carried out.

Whilst there are several commercially available lubricants which are labelled as "food grade", the majority of these products are listed as FDA H2 approved ( possibility of contact with food). As these products may clearly come into contact with food, or with food preparation surfaces, it is clearly desirable to have at least FDA Hi approval (incidental contact with food). There are commercially available products which are listed as FDA Hi approved, but these products, as discussed above, are based on synthetic esters, medicinal quality white oils, polyalphaolefins, or a combination of these, all of which form deposits when used at high temperatures in excess of 260 C.

Thus, there is a continuing need to provide an improved lubricant composition, particularly one comprised of food quality components and being suitable for use at high temperatures in baking or cooking ovens. The present invention solves or alleviates the problems of the prior art.

In a first aspect of the invention, there is provided a dry-film lubricant composition for food ovens comprising boron nitride particles dispersed in a base material comprised of propylene glycol, a water-soluble polyglycol, or mixtures thereof.

The base material is preferably non-toxic. More preferably, the base material is approved by the regulatory authorities for use where incidental contact with food may occur. In particular, the base material preferably has FDA approval for use as a lubricant where incidental contact with food may occur.

In one embodiment, the water-soluble polyglycol has a molecular weight of less than or equal to 250. In a more preferred embodiment, the water-soluble polyglycol has a molecular weight of less than or equal to 192. In a still more preferred embodiment, water-soluble polyglycol preferably has a molecular weight of less than or equal to 134.

In a preferred embodiment, the water-soluble polyglycol is a poly(propylene)glycol of Formula I: [(C3 H6)mOm..i1(OH)2 (Formula I) wherein: m is 1, 2, 3 or 4; or a mixture thereof.

More preferably the base material is comprised of propylene glycol (Mwt: 76), dipropylene glycol (Mwt: 134) tripropylene glycol (Mwt: 192), tetrapropylene glycol (Mwt: 250), or a mixture thereof. Most preferably, the base material is propylene glycol.

In another embodiment, the water-soluble polyglycol consists of one or more water-soluble copolymers of ethylene and propylene glycol. Preferred copolymers of ethylene and propylene glycol are monol-initiated ethylene/propylene copolymers. More preferred are those monol-initiated ethylene/propylene copolymers which are FDA compliant for use as food contact lubricants.

Typically the molecular weight of the preferred monol-initiated ethylene/propylene copolymers are greater than or equal to 2000. Such polyglycols include those sold under the trade names Cognis Breox 50A, 140, Breox FGL 150, 220, 320, 460, 680, 1000, and Uniqema Emkarox VG 132 W. The boron nitride particles preferably have an average diameter of less than microns, more preferably less than 1 micron. Boron nitride particles having average diameters of greater than five microns can, in some circumstances, lead to friction and abrasion damage. Preferably the boron nitride particles are hexagonal.

The lubricant composition may comprise, by weight of the composition, between 1% and 30% boron nitride. Preferably the composition comprises between 5% and 25% by weight boron nitride. More preferably, the composition comprises between 7.5% and 15% by weight boron nitride. Most preferably, the composition comprises approximately 10% by weight boron nitride.

The lubricant composition may further comprise water. The composition typically comprises between 0% and 50% by weight water. Preferably, however, the composition comprises between 0% and 40% by weight water. More preferably, the composition comprises between 0% and 20% by weight water.

More preferably still, the composition comprises between 0% and 15% by weight water. Most preferably, the composition comprises between 0% and 10% by weight water.

The lubricant composition may further comprise a corrosion inhibitor.

Typically, the composition comprises between 0.01% and 5% by weight of the corrosion inhibitor. More preferably the composition comprises 0.1 and 2% of the corrosion inhibitor. Still more preferably the composition comprises approximately 0.5% by weight of the corrosion inhibitor.

The lubricant composition may further comprise a dispersing agent. The composition may comprise between 0.1% and 0.5%, preferably approximately 0.3%, by weight of the dispersing agent.

The lubricant composition may further comprise a rheology modifier (also known as a suspending agent). Where present, the composition may comprise up to 1% by weight of the rheology modifier. Preferably the composition comprises approximately 0.1% by weight of the rheology modifier.

The remainder of the composition preferably comprises the base. The base may consist of the propylene glycol andlor the water-soluble polyglycol.

The components of the composition, in particular the corrosion inhibitor, dispersing agent and rheology modifier are preferably approved by regulatory authorities (FDA) for use in circumstances where incidental contact with food may occur.

In one embodiment, the lubricant composition comprises, by weight: from 5% to 15% boron nitride particles; from 5% to 45% water; from 0.1% to 1.0% corrosion inhibitor; from 0.1% to 0.5% dispersing agent; from 0% to 1% rheology modifier; and from 40% to 90% of said propylene glycol, water-soluble polyglycol or mixtures thereof. Preferably said propylene glycol, water-soluble polyglycol, or mixtures thereof is one or more of propylene glycol, dipropylene glycol or tripropylene glycol.

In one embodiment, the lubricant composition comprises, by weight, 10% boron nitride particles; 40% water; 0.5% corrosion inhibitors; and 49.5% of said propylene glycol or water-soluble polyglycol or mixture thereof. This composition may further comprise 0.2% dispersing agent and 0.5% rheology modifier, in place of the equivalent weight of said glycol. Preferably said propylene glycol, water-soluble polyglycol, or mixtures thereof is one or more of propylene glycol, dipropylene glycol or tripropylene glycol.

In a preferred embodiment, the lubricant composition comprises, by weight, 10.0% boron nitride particles; 9.1% water; 0.5% corrosion inhibitor; 0.3% dispersing agent; 0.1% rheology modifier; and 80.0% of one or more of propylene glycol, dipropylene glycol or tripropylene glycol.

In one embodiment, the composition consists essentially of boron nitride and said base material, and optionally further includes, independently, water, said corrosion inhibitor, said rheology modifier and/or said dispersing agent.

The present invention provides a lubricating composition which can operate at temperatures up to 2200 C.

In another aspect of the invention, there is provided the use of a lubricant composition comprising boron nitride for lubricating components in a baking oven. The components may be moving parts of said baking ovens.

In another aspect of the invention, there is provided the use of monopropylene glycol or a water-soluble polyglycol in a dry-film lubricant composition.

In another aspect of the invention, there is provided a method of lubricating a baking oven, the method comprising the steps of applying a composition according to the invention to a baking oven.

The composition will generally be applied to the moving parts of said oven.

After the application step, the method may include the further step of heating said lubricant composition to a temperature at which the (poly)glycol component evaporates. In this manner, the boron nitride lubricant composition forms a thin dry film on the lubricated components, and leaves behind no form of dirty residue.

The boiling point of the (poly)glycol component is preferably less than around 280 C. More preferably, the boiling point is between approximately 187 C to 276 C. The boiling point of the preferred poly(glycol) components are as follows: propylene glycol -approximately 187 C; dipropylene glycol -approximately 23 6 C; tripropylene glycol -approximately 276 C. The particular choice of poly(glycol) component will depend on the end use/working temperature of the oven.

The base material acts as a carrier for the boron nitride particles in the composition.

The term "glycol" as used herein describes an essentially aliphatic carbon chain comprising two hydroxyl groups, for example propylene glycol (C3H6(OH)2).

Glycols can be polymerised by dehydration. The resultant polymers and co-polymers are typically referred to as "polyglycols", and include, for example, dipropylene glycol or tripropylene glycol, and co-polymers of ethylene glycol and propylene glycol.

The solubility of a propylene and higher alkylene glycols decreases as the molecular weight of the molecule increases. Thus, propylene glycol is more water soluble than, for example, tetrapropylene glycol.

The present invention utilises polyglycols which are water-soluble in all proportions at 20 C. The propylene glycol and water-soluble polyglycols in the composition of the present invention evaporate on heating and do not produce smoke or toxic vapours.

In another aspect of the invention, there is provided a dry-film lubricant composition for food ovens, as described above, in which the base material comprised of propylene glycol, water-soluble polyglycol, or mixture thereof is replaced with a base material comprised of one or more water-insoluble propylene glycols.

Preferably the water insoluble propylene glycol is a (butyl terminated) propylene glycol.

Preferably, the (butyl terminated) propylene glycol is a monol-initiated propylene oxide homopolymer. Preferred (butyl terminated) propylene glycols are selected from one or more of the CognisTM Breox range. Most preferred are the monol-initiated propylene oxide homopolymers marketed under the trade names Breox B 75, B125, B225 and B335 products, which are FDA compliant (wherein the "B number" corresponds approximately to the viscosity, in centipoises, at 40 C). Further preferred water-insoluble polyglycols are those marketed under the trade name Emkarox VG.

The invention will now be further described with reference to the

examples.

A dry-film lubricant composition according to the present invention was made up to the specification shown in Table 1 below.

The composition had the appearance of a white viscous fluid. Solids content was 10 wt%. Viscosity at 20 C: thixotropic. The composition was also odourless and had a pH of 7.5.

Table 1

Component % by weight boron nitride particles (pharmaceutical grade <5 micron) 10.0% vater 9.1% Nater soluble food quality corrosion inhibitor* 0.5% Ciba1M DispexTM N40 (food quality dispersant) 03% KeItrolTM E (food aualitv rheolociv modifier and susendinci 0.1% agent) monopropylene glycol (food quality) 80.0% * Typically Ciba TMIrgacorTM DSS G Boron nitride powder was sourced from Precision Ceramics, Birmingham, UK (PCIDL -300 Boron Nitride). Sub-micron hexagonal boron nitride particles are also commercially available from Acheson Colloids Company, of Michigan, USA.

This lubricating composition was applied to the moving components of a MecathermTM baking oven, which had been switched off. The oven was then run up to working temperature (around 280 C to 300 C), prior to the introduction of steam. Re-application of lubricant was carried out as and when necessary -determined by the operators of the oven. Typically the operator will become aware that the lubricating film is breaking down by the audible sound of metal-metal contact between the moving parts within the oven.

Two commercially available baking oven lubricants were tested in the same manner. Re-application was carried out as and when necessary. The tested products were RocolTM Foodlube High Temperature Chain Fluid (Comparative lubricant 1 [CL1]) and KiuberTM YF100 (CL2). CL1 is a food, grade dry-film lubricant comprising talc particles in a polyalkylene glycol base fluid. It has an off-white appearance, and as a dry-film can operate at temperatures up to 550 C.

CL2 is a graphite based lubricant, using a water-insoluble polypropylene glycol as a base fluid.

In comparative testing, it was found that, after the initial weekly maintenance of the oven (in which around 7.5 litres of lubricant was applied), CL2 must be re-applied (5.0 litres each time) approximately once every 48 hours, each re-application involving an oven downtime of approximately 3 hours. Thus, over the course of a week, the use of CL2 led to a downtime of approximately 6 hours, and used around 17.5 litres of lubricant.

Lubricant CL1 was applied to ovens at double the dosage rate of the composition of the present invention in order to achieve "silencing" of the chains and conveyors (i.e. 15 litres of CL1 per application). Re-application of CL1 was necessary after approximately 24 hours. On heating, smoke was produced, although to a lesser extent than CL2.

By comparison, the dry-film lubricant of the present invention was applied during the weekly maintenance period (7.5 litres lubricant applied) and did not need any further re-application until the next weekly maintenance. Over the course of a year, the downtime could therefore be reduced by 288 hours or more.

It was found that re-application of the dry-film lubricant of the present invention was necessary once per week (a total of 6 hours downtime per week).

In operation, the base fluid in the lubricating composition of the present invention volatilises completely on heating to the working temperature, leaving behind a dry, white-coloured film of boron nitride, which is completely free from gums, resins and carbon residues. The (poly)glycol component evaporates cleanly, producing no smoke or harmful vapours. CL2 generated dense smoke when the oven was heated to working temperature, and CL1 was observed to leave behind a varnish-like deposit at high operating temperature.

In addition to the economic advantage provided by the present invention, the lubricant is also clean and fume-free. CL I and CL2, in contrast, produced dense smoke/fumes when the oven was first heated to working temperature.

It will be appreciated that the embodiments described above may be modified within the scope of the appended claims.

Claims

Claims 1. A dry-film lubricant composition for food ovens comprising

boron nitride particles dispersed in a base material comprised of propylene glycol, a water-soluble polyglycol, or a mixture thereof.

2. A lubricant according to claim 1, wherein the water-soluble polyglycol is a polypropylene glycol of Formula I: I(C3 H6)mOm..i] (OH')2 (Formula I) wherein: m is 2, 3 or 4.

3. A lubricant composition according to claim 1 or 2, wherein the base material is comprised of propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, or mixtures thereof.

4. A lubricant composition according to any preceding claim, wherein the base material is comprised of propylene glycol.

5. A lubricant composition according to any preceding claim, wherein the base material is comprised of dipropylene glycol.

6. A lubricant composition according to any preceding claim, wherein the base material is comprised of tripropylene glycol.

7. A lubricant composition according to claim 1 or 2, wherein the base material is comprised of one or more water-soluble polyglycols having a molecular weight of less than or equal to 250.

8. A lubricant composition according to claim 1 or 2, wherein the base material is comprised of one or more water-soluble polyglycols having a molecular weight of less than or equal to 192.

9. A lubricant composition according to claim 1 or 2, wherein the base material is comprised of one or more water-soluble polyglycols having a molecular weight of less than or equal to 134.

10. A lubricant composition according to claim 1 or 2, wherein the base material is comprised of propylene glycol or polyglycols having a molecular weight in the range of 76 to 250.

11. A lubricant composition according to claim 1, wherein the water-soluble polyglycol comprises a co-polymer of ethylene glycol and propylene glycol.

12. A lubricant composition according to claim 11, wherein the co-polymer of ethylene glycol and propylene glycol has a molecular weight of approximately 2000 or more.

13. A lubricant composition according to any preceding claim, wherein the boron nitride particles have a diameter of less than five microns.

14. A lubricant composition according to any preceding claim, wherein the composition comprises between 1% and 30% by weight boron nitride.

15. A lubricant composition according to any preceding claim, wherein the composition comprises between 5% and 25% by weight boron nitride.

16. A lubricant composition according to any preceding claim, wherein the composition comprises between 7.5% and 15% by weight boron nitride.

17. A lubricant composition according to any preceding claim, wherein the composition comprises approximately 10% by weight boron nitride.

18. A lubricant composition according to any preceding claim, further comprising water.

19. A lubricant composition according to claim 18, wherein the composition comprises up to 40% by weight water.

20. A lubricant composition according to claim 18, wherein the composition comprises up to 10% by weight water.

21. A lubricant composition according to any preceding claim, further comprising a corrosion inhibitor.

22. A lubricant composition according to claim 21, wherein the composition comprises between 0.0 1% and 5%, by weight of the corrosion inhibitor.

23. A lubricant composition according to claim 21, wherein the composition comprises between 0.1 and 2% by weight of the corrosion inhibitor.

24. A lubricant composition according to claim 21, wherein the composition comprises approximately 0.5% by weight of the corrosion inhibitor.

25. A lubricant composition according to any preceding claim, further comprising a dispersing agent.

26. A lubricant composition according to claim 25, wherein the composition comprises between 0.1 to 0.5 % by weight of the dispersing agent.

27. A lubricant composition according to claim 25, wherein the composition comprises approximately 0.2% by weight of the dispersing agent.

28. A lubricant composition according to any preceding claim, further comprising a rheology modifier.

29. A lubricant composition according to claim 28, wherein the composition comprises between from 0 to 1% of the rheology modifier.

30. A lubricant composition according to any one of claims 14 to 29, wherein the remainder of the composition comprises said propylene glycol, water-soluble polyglycol, or mixtures thereof.

31. A lubricant composition according to any preceding claim, comprising, by weight, from 5% to 15% boron nitride particles; from 5% to 45% water; from 0.1% to 1.0% corrosion inhibitor; from 0.1% to 0.5% dispersing agent; from 0% to 1% rheology modifier; and from 40% to 90% of said propylene glycol, water-soluble polyglycol, or mixtures thereof.

32. A lubricant composition according to any preceding claim comprising, by weight, 10.0% boron nitride particles; 9.1% water; 0.5% corrosion inhibitor; 0.3% dispersing agent; 0.1% rheology modifier; and 80.0% propylene glycol, dipropylene glycol, tripropylene glycol or mixtures thereof.

33. A lubricant composition according to any of claims 1 to 31 comprising, by weight, 10% boron nitride particles; 40% water; 0.5% corrosion inhibitor; and 49.5% propylene glycol, dipropylene glycol, tripropylene glycol or a mixture thereof.

34. The use of a lubricant composition comprising boron nitride for lubricating components in an oven.

35. The use according to claim 34, wherein the oven operates at a working temperature of 260 C or more.

36. The use according to claim 34 or 35, wherein the oven is a food-baking oven.

37. The use according to claim 34, 35 or 36, wherein the components are moving parts of said oven.

38. The use of at least one of propylene glycol and a water-soluble polyglycol as a base material in a dry-film lubricant composition.

39. The use according to claim 34, 35, 36, 37 or 38, wherein the lubricant accords to any of claims 1 to 33.

40. A method of lubricating an oven, the method comprising the steps of applying a composition according to any of claims 1 to 33 to components of said oven.

41. A method according to claim 40, wherein said components are moving parts of said oven.

42. A method according to claim 40 or 41, further comprising the step of, after said application step, heating said lubricant composition to a temperature at which said propylene glycol or water-soluble polyglycol evaporates.

43. A method according to claim 42, wherein said temperature is 260 C or higher.

44. A lubricant composition substantially herein described, with reference to

the examples.