[0001] 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 glycol or polyglycol base material. The
base material may be water-soluble or water-insoluble.
[0002] 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, downtime
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.
[0003] 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.
[0004] 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 glycol (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, and are electrically conductive,
which can be disadvantageous in some uses. Such solid lubricants over time cake the
equipment and thus form a barrier inhibiting the penetration of subsequent applications
of lubricant. Regular application is necessary in view of the fact that graphite/molybdenum
do not provide sufficient lubricity once the polyglycol base fluid has evaporated.
In some applications, polyglycol bases can also carry their own disadvantages, which
are mentioned more fully below.
[0005] 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
have a tendency to drip from machinery and require frequent re-application, increasing
downtime. In addition, aqueous dispersions exhibit "spitting" at raised temperatures,
which is undesirable.
[0006] 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. They are also extremely
expensive.
[0007] 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. 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), which, over time, require extensive cleaning (ultrasonic or dry-ice).
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.
[0008] The selection of the base material for the lubricant is of considerable importance.
The production of corrosive and/or 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, have been used as a base fluid.
However, it has been found that application of high molecular weight polyglycol-based
lubricants can be difficult, and a great care must be taken in order to avoid the
generation of dense smoke and fumes when the oven is first heated to working temperature
after re-application. Indeed, in some circumstances, it is practice to turn off the
building's fire alarm whilst this process is carried out.
[0009] Whilst there are several commercially available lubricants which are labelled as
"food grade", the majority of these products are listed as FDA H2 approved (
no 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 H1 approval (incidental contact with food). There are commercially available products
which are listed as FDA H1 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.
[0010] The base fluid must provide a suitable suspension of the lubricant material therein.
The inventors of the present invention have found that typical lubricant base fluids
which are suitable for use in food ovens are unsuitable or unsatisfactory in this
respect, particularly when the solid lubricant material is boron nitride.
[0011] 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.
[0012] The present invention solves or alleviates the problems of the prior art.
[0013] In a first aspect of the invention, there is provided a lubricant composition for
food ovens comprising boron nitride particles dispersed in a base material comprised
of propylene glycol, a polyglycol, or mixtures thereof.
[0014] In a first embodiment, the base material is comprised of a water-insoluble polyglycol.
[0015] In this embodiment, the lubricant composition may operate as a dry-film lubricant,
as a wet-film lubricant, or as both a dry-film and wet-film lubricant. Preferably
the lubricant composition is both a dry-film and wet-film lubricant.
[0016] 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.
[0017] Preferably the water-insoluble polyalkylene glycol is a polypropylene glycol. The
polypropylene glycol may be butyl terminated.
[0018] The viscosity of suitable polyglycols increases with the molecular weight of the
polyglycol (which in turn increases with the length of the polymerisation reaction
time). Preferably, the water-insoluble polyglycol has a viscosity at 40°C of from
50 to 400 cSt. More preferably, the water-insoluble polyglycol has a viscosity in
the range of 75 to 350 cSt at 40°C.
[0019] Preferred water-insoluble polyglycols are butanol-initiated (monol-initiated) propylene
oxide homo-polymers. Such compounds are obtained by the reaction between butanol and
propylene oxide only. The reaction is terminated when the desired molecular weight
of the polymer is attained. Preferred butanol-initiated propylene oxide homopolymers
have a viscosity of from 75 to 350 cSt at 40°C.
[0020] Preferred propylene glycols are selected from one or more of the Cognis
™ Breox range. Most preferred are the butanol-initiated propylene oxide homopolymers
marketed as the Cognis
™ Breox B-Range (for instance, those market under the trade names Breox B75, B125,
B225 and B335, wherein the "B number" corresponds approximately to the viscosity,
in centipoises, at 40°C), which are FDA compliant. Further preferred water-insoluble
polyalkylene glycols are those marketed under the trade name Emkarox VG by Uniquema
™.
[0021] In one embodiment, the polyglycol has a molecular weight of around 1200 to around
2800 amu. More preferably still the polyglycol has a molecular weight of around 1400
to 2500 amu. The most preferred polyalkylene glycols have molecular weights of 1403,
1710, 2117 and 2446. The viscosity of such materials is 75 cSt, 122 cSt, 224 cSt and
330 cSt, respectively. These viscosities are representative of the materials Breox
B75, B125, B225 and B335 respectively.
[0022] The flash point of the polyalkylene glycol component is typically from 211°C to 225°C.
[0023] The use of a base material having a relatively high boiling point enables the lubricant
to operate as a wet-film lubricant in cooler end-uses.
[0024] The lubricant composition comprises a suspension of boron nitride particles in said
base material. The boron nitride particles are preferably substantially evenly dispersed
in said base material.
[0025] In an embodiment, the lubricant composition may comprise, by weight of the composition,
between 1% and 20% boron nitride. Preferably the composition comprises between 2%
and 10% by weight boron nitride. More preferably, the composition comprises between
4% and 7.5% by weight boron nitride. Most preferably, the composition comprises approximately
5% by weight boron nitride.
[0026] The remainder of the composition may comprise the base, which may be present in an
amount of up to 99% by weight of the composition. The base is typically present in
an amount from 87.5 to 97.4% by weight of the composition, preferably from 90.0 to
95.0% by weight. More preferably the base is present in an amount.of approximately
93.5% by weight.
[0027] The lubricant composition may comprise additional components. For instance, the lubricant
composition may additionally comprise a suspending agent (also known as a rheology
modifier). Where present, the composition may comprise up to 5% by weight of the suspending
agent. Typically the composition comprises 0.1 to 3.0% by weight of the suspending
agent. Preferably the composition comprises approximately 0.5 to 2.0% by weight of
the suspending agent. Preferably the composition comprises approximately 1.0% by weight
of the suspending agent. A preferred inert suspending agent is hydrophilic fumed silica.
One such product is marketed as HDK
®-N20 hydrophilic fumed silica by Wacker Silicones (HDK
®-N20P, HDK
®-T30 or HDK
®-T40 could also be used).
[0028] The lubricant composition may further comprise a corrosion inhibitor and/or an extreme
pressure and anti-wear additive. Typically, the composition comprises between 0.01%
and 5.0% by weight of the corrosion inhibitor/anti-wear additive. Preferably the composition
comprises 0.1 and 2.0% of the corrosion inhibitor/anti-wear additive. More preferably
the corrosion inhibitor/anti-wear additive is present in an amount of from 0.1 to
0.5% by weight of the composition. Still more preferably the composition comprises
approximately 0.5% by weight of the corrosion inhibitor. A preferred corrosion inhibitor/anti-wear
additive comprises phosphoric acid, mono and dihexyl esters and compounds with alkylamines.
A particularly preferred corrosion inhibitor/extreme pressure anti-wear additive is
marketed under the trade name Irgalube
®349 by Ciba
® Speciality Chemicals.
[0029] The remainder of the composition preferably comprises the base. The base may consist
of the water-insoluble polyglycol.
[0030] In one embodiment, the lubricant composition comprises, by weight: from 2.0% to 10%
boron nitride particles; from 87.5% to 97.4% base; from 0.1 % to 0.5% corrosion inhibitor
and extreme pressure and anti-wear additive; and from 0.5% to 2.0% suspending agent.
[0031] In a preferred embodiment, the lubricant composition comprises, by weight, 5.0% boron
nitride particles; 93.5% base; 0.5% corrosion inhibitor and extreme pressure and anti-wear
additive; and 1.0 % inert suspending agent.
[0032] Typically the water-insoluble polyalkylene glycol will slowly depolymerise after
application and exposure to heat, and will evaporate at higher temperatures without
leaving carbonaceous residues or lacquers. The base fluid will remain for a sufficient
length of time such that it carries the boron nitride particles into the moving components
of the equipment, such as chain linkages and bearings.
[0033] Alternatively, the lubricant composition of the present invention can be used as
a highly effective wet-film lubricant, when used at temperatures below the temperature
at which the base material evaporates.
[0034] The particular choice of polyalkylene glycol component will depend on the end use/working
temperature of the oven. The desired level of lubricity, viscosity, etc. can be adjusted
by variation of the choice of polyalkylene glycol and level of boron nitride, in particular.
[0035] In another embodiment, the base material is comprised of propylene glycol, a water-soluble
polyglycol, or mixtures thereof. The lubricant is preferably a dry-film lubricant.
[0036] In this 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.
[0037] In a preferred embodiment, the water-soluble polyglycol is a poly(propylene)glycol
of Formula I:
[(C3H6)mOm-1](OH)2 (Formula I)
wherein: m is 1, 2, 3 or 4; or a mixture thereof.
[0038] 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.
[0039] In an embodiment, the base material is comprised of one or more water-soluble polyglycols
having a molecular weight of less than or equal to 250. In another embodiment, the
base material is comprised of one or more water-soluble polyglycols having a molecular
weight of less than or equal to 192. In another embodiment, the base material is comprised
of one or more water-soluble polyglycols having a molecular weight of less than or
equal to 134. In another embodiment, the base material is comprised of propylene glycol
or polyglycols having a molecular weight in the range of 76 to 250.
[0040] 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 butanol-initiated ethylene/propylene copolymers. More preferred
are those butanol-initiated ethylene/propylene copolymers which are FDA compliant
for use as food contact lubricants.
[0041] Typically the molecular weight of the preferred butanol-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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] The remainder of the composition preferably comprises the base. The base may consist
of the propylene glycol and/or the water-soluble polyglycol.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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 236°C; tripropylene glycol
- approximately 276°C. The particular choice of poly(glycol) component will depend
on the end use/working temperature of the oven.
[0052] A composition according to the present invention may consist essentially of boron
nitride and said base material. The composition may optionally further include, independently,
water, said corrosion inhibitor, said rheology modifier and/or said dispersing agent.
[0053] The boron nitride particles may be of any size suitable to operate as a lubricant
material. Preferred boron nitride particles have a diameter of less than around 15µm,
preferably less than 13 µm. In a preferred embodiment, the boron nitride particles
have a particle diameter range of 12 to 13µm. Such a material is available from GB
Advanced Ceramics of Ohio, under the trade name AC6004, which is NSF approved for
food contact. In another preferred embodiment, the boron nitride particles preferably
have an average diameter of less than 5 microns, more preferably less than 1 micron.
Preferably the boron nitride particles are hexagonal. Hexagonal boron nitride particles
are also commercially available from Acheson Colloids Company, of Michigan, USA.
[0054] The base material acts as a carrier for the boron nitride particles in the composition.
[0055] The base material is preferably non-toxic. The components of the composition, in
particular the corrosion inhibitor, dispersing agent and rheology modifier (where
present) are preferably approved by regulatory authorities (FDA) for use in circumstances
where incidental contact with food may occur. 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.
[0056] The present invention provides a lubricating composition which can operate at temperatures:up
to 2200°C.
[0057] 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. The oven will typically operate at a working
temperature of 260°C or more, and is typically a food-baking oven.
[0058] 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.
[0059] In another aspect of the invention, there is provided the use of at least one of
propylene glycol and a water-soluble polyglycol as a base material in a dry-film lubricant
composition.
[0060] 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.
[0061] The composition will generally be applied to the moving parts of said oven.
[0062] 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.
[0063] The term "glycol" as used herein describes an essentially aliphatic carbon chain
comprising two hydroxyl groups, for example propylene glycol (C
3H
6(OH)
2).
[0064] Glycols can be polymerised by dehydration. The resultant polymers and co-polymers
are typically referred to as "polyglycols" (or polyalkylene glycols), and include,
for example, dipropylene glycol or tripropylene glycol, polypropylene glycol and co-polymers
of ethylene glycol and propylene glycol.
[0065] 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.
[0066] In one embodiment, 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.
[0067] In another embodiment, the invention utilised polyglycols which are water-insoluble
in all proportions at 20°C. Such polyglycol based lubricants can be used as dry or
wet film lubricants. The water-insolubility of such compositions allows them to be
used in steam ovens and the like, where high levels of moisture are present. In addition,
the higher boiling point - when compared to the water-soluble glycols/polyglycols
- water insoluble polyglycols will de-polymerise and evaporate at higher temperatures
and thus provide extended time for the boron nitride to penetrate linkages. By correct
application, lacquers and deposits can also be avoided.
[0068] The lubricant compositions of the present invention are stable dispersions of boron
nitride in the base material. By careful selection of the base material and optionally
the suspending agent and other materials the inventors of the present invention have
provided stable dispersions of boron nitride particles. The lubricant compositions
of the present invention will not separate (i.e. the boron nitride will not separate
from the base material) for substantial periods of time - and considerably longer
than the lubricants of the prior art. For example, compositions prepared according
to the present invention do not separate for at least 4 months. Prior art compositions
for equivalent purposes typically separate into solid lubricant and base material
within a few days or I to 2 weeks at most.
[0069] The invention will now be further described with reference to the Examples and Figures
1 to 3, in which:
Figure 1 is graphical representation of the results of comparative testing of a composition
according to an embodiment of the present invention with known polyol ester and graphited
polyglycol lubricants;
Figure 2 is a photographic depiction of the results of weight loss testing at 280°C
with the lubricants used in Figure 1; and
Figure 3 is a graphical representation of the change in friction coefficient over
time of a composition according to an embodiment of the present invention.
Example 1
[0070] A dry-film lubricant composition according to the present invention and comprising
propylene glycol was made up to the specification shown in Table 1 below.
[0071] 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)1 |
10.0% |
water |
9.1% |
Water soluble food quality corrosion inhibitor2 |
0.5% |
Ciba™ Dispex™ N40 (food quality dispersant) |
0.3% |
Keltrol™ E (food quality rheology modifier and suspending agent) |
0.1 % |
monopropylene glycol (food quality) |
80.0% |
1 AC6004 GE Advanced Ceramics
2 Ciba™ Irgacor™ DSS G |
[0072] The lubricating composition of Example 1 was applied to the moving components of
a Mecatherm
™ 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.
[0073] 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 Rocol
™ Foodlube High Temperature Chain Fluid (Comparative lubricant 1 [CL1])and Kluber
™ 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.
[0074] 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.
[0075] 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.
[0076] By comparison, the dry-film lubricant of Example 1 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).
[0077] In operation, the base fluid in the lubricating composition of Example I 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.
[0078] In addition to the economic advantage provided by the present invention, the lubricant
is also clean and fume-free. CL 1 and CL2, in contrast, produced dense smoke/fumes
when the oven was first heated to working temperature.
Example 2
[0079] An alternative dry- or wet- film lubricant composition according to the present invention
was made up to the specification shown in Table 2 below.
Table 2
Component |
% by weight |
Butanol-initiated propylene oxide homo-polymer1 |
93.5 |
Boron nitride particles2 |
5.0 |
Corrosion inhibitor3 |
0.5 |
Hydrophobic fumed silica4 |
1.0 |
1base carrier fluid and lubricant with viscosity of 225 cSt at 40°C;
2 AC6004 GE Advanced Ceramics
3 Ciba® Specialities Irgalube® 349
4 Wacker Silicones HDK®-N20. |
[0080] In operation, the base fluid in the lubricating composition of the Example 2 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 base evaporates cleanly, producing no smoke or harmful vapours.
[0081] The results set out in Table 3 below compare the properties of boron nitride with
those of other competitive dry film lubricants and an oil-based wet film lubricant.
Table 3
|
Test Method |
Lubricant |
Falex Extreme Pressure Failure Load ASTM D3233 lbs |
Four Ball Weld Load ASTM D2783 Kgs |
Coefficient of Friction - Falex Mathod |
Continuous Operating Temperature (degC) |
Boron nitride - dry film |
4500 |
200 |
0.105 |
2200 |
Graphite - dry film |
1250 |
150 |
0.123 |
450 |
PTFE - dry film |
4250 |
200 |
0.094 |
260 |
Oil based lubricant |
750 |
125 |
0.159 |
230 |
Example 3
[0082] Further comparative testing was carried out on the composition of Example 2 using
the ball on reciprocating plate technique under the following conditions:
Ball and plate of ANSI standard steel No. E-52100;
Ball size 12mm
Reciprocating frequency 1Hz
Load applied 100 N
Temperature 280°C.
[0083] The results are shown in Figures 1 and 2. The graphited polyol lubricant, and the
polyol ester were Kluber YF100 and APV High Temperature Chain Oil, respectively.
[0084] After 236 minutes at 280°C, the weight loss of the plates was assessed.
[0085] Graphited polyglycol lubricant: -10mg - Figure 2A
[0086] Polyol ester lubricant: N/A due to severe oxidation/degradation - Figure 2B
Example 2: -6mg - Figure 2C
[0087] In terms of stability, the product of the present invention had not noticeably separated
after a period of 4 months. In comparison, CL1 separates in a matter of days, and
CL2 begins to show deposition within two weeks.
Example 4
[0088] The friction coefficient of the composition of Example 2 was assessed over time,
at 280°C and a 100N load. The results of the assessment are shown in Figure 3.
[0089] It is clear that the composition of Example 2 exhibits a steady friction coefficient
over a prolonged period of time. By comparison, friction becomes very high with the
graphited lubricant, and the polyol severely degrades at 280°C. At high temperature,
the wear rate of Example 2 is considerably less than that of the graphited lubricant
(the wear rate of the polyol lubricant could not be measured due to the formation
of deposits.
Example 5
[0090] Further wear testing was performed at ambient temperature, to assess the performance
of Example 2 as a wet-film lubricant. The tests were performed using a portable Reichert
Wear Tester having a hardened steel roller, a fixed roller bearing and a 3Kg applied
load.
[0091] Example 2 performed as well as perfluorinated polyether alternatives, and outperformed
all other currently available, leading brand lubricant products.
[0092] The present invention provides a food-safe lubricant material that is clean, energy
efficient, cost effective and decreases downtime and running costs. The lubricants
do not form carbonaceous deposits or lacquers, provide excellent lubrication performance
at a wide variety of temperatures, and can be manufactured in varying viscosities
to meet end needs.
[0093] The above-mentioned examples and specific description are not limiting on the scope
of the invention. For instance, the compositions of the present invention may be formulated
for administration as aerosols, or as greases (such as a No. 2 grease). It will therefore
be appreciated that the embodiments described above may be modified within the scope
of the appended claims.
1. A lubricant composition for food ovens comprising boron nitride particles dispersed
in a base material comprised of propylene glycol, a polyglycol, or a mixture thereof.
2. A lubricant according to claim 1, wherein the base material is comprised of one or
more water-insoluble polyglycol.
3. A lubricant according to claim 1 or 2, wherein the water-insoluble polyglycol is a
polypropylene glycol.
4. A lubricant according to any preceding claim, wherein the water-insoluble polyglycol
has a viscosity at 40°C of from 50 to 400 cSt.
5. A lubricant according to any preceding claim, wherein the water-insoluble polyglycol
is a butanol-initiated propylene oxide homo-polymer.
6. A lubricant according to any preceding claim comprising, by weight of the composition,
from 2% to 10% boron nitride.
7. A lubricant according to any preceding claim comprising, by weight of the composition,
from 87.5 to 97.4% of said base material.
8. A lubricant according to any preceding claim, comprising up to 5% by weight of a suspending
agent.
9. A lubricant according to claim 8, wherein the suspending agent is hydrophilic fumed
silica.
10. A lubricant according to any preceding claim, further comprising a corrosion inhibitor
and/or an extreme pressure and anti-wear additive.
11. A lubricant according to any preceding claim comprising, by weight: from 2.0% to 10%
boron nitride particles; from 87.5% to 97.4% base; from 0.1% to 0.5% corrosion inhibitor
and extreme pressure and anti-wear additive; and from 0.5% to 2.0% suspending agent.
12. A lubricant according to claim 1, wherein the base material is comprised of propylene
glycol, a water-soluble polyglycol, or a mixture thereof.
13. A lubricant according to claim 12, wherein the water-soluble polyglycol is a polypropylene
glycol of Formula I:
[(C3H6)mOm-1](OH)2 (Formula I)
wherein: m is 2, 3 or 4.
14. A lubricant according to claim 12 or 13, wherein the base material is comprised of
propylene glycol.
15. A lubricant according to claim 12, wherein the water-soluble polyglycol comprises
a co-polymer of ethylene glycol and propylene glycol.
16. A lubricant according to claim 15, wherein the co-polymer of ethylene glycol and propylene
glycol has a molecular weight of approximately 2000 or more.
17. A lubricant according to any of claims 12 to 16, wherein the composition comprises
between 1% and 30% by weight boron nitride.
18. A lubricant according to any of claims 12 to 17, further comprising one or more of
water, a corrosion inhibitor, a dispersing agent, and a rheology modifier.
19. A lubricant composition according to claim 1 or any of claims 12 to 18, 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.
20. The use of a lubricant composition comprising boron nitride for lubricating components
in an oven.