[0001] A solid film lubricant system useful in coating a metal, ceramic or polymeric material
wear surface.
[0002] The present invention relates to a solid film lubricant system useful in coating
a metal, ceramic or polymeric material wear surface, comprising
i) a carrier,
ii) solid lubricant components,
iii) additives.
[0003] The lubricant system referred to in the introduction is also known as so-called AF
coatings (anti-friction coatings), which coatings, being high-grade solid or dry lubricants,
generally provide maintenance-free, permanent lubrication, and they are capable of
meeting extreme requirements which the usual liquid or consistent lubricants cannot
meet. For anti-friction coatings it is not necessary to build up a hydrodynamically
carrying film via the hydrodynamically acting speed for separating the base member
and the counter member, so that parts which only reach low speeds upon being subjected
to high loads or which make oscillating movements have an active separating solid
film present between the surfaces from the moment the movement starts. AF coatings
are used in the case of extreme operating conditions, for example high temperatures
and pressures or no access for liquid lubricants. The AF coatings referred to in the
introduction exhibit excellent properties also in the field of corrosion protection,
in combination with reduction of wear, pressure loading capacity and resistance against
environmental influences. In combination with the addition of corrosion protection
additives it is possible to substitute the known coatings on metal, which are hazardous
to the environment and which generally have a base of chromium, nickel or cadmium.
Such coatings, which mainly contain Cr(VI), function to obtain the required lubricating
properties after galvanising, passivating and greasing. In addition to that, lead-containing
compounds and other heavy metal compounds are frequently used, which is dubious, however,
in view of the carcinogenic properties of said components. The lubricant systems referred
to in the present introduction are used for dry, durable lubrication of connecting
materials, such as nuts, washers and bolts, hinges, lock parts, such as catches, pins,
housings and handles, magnetos, bearings, bushes, shafts and the like, with a constant
coefficient of friction, a wide temperature range and a contact pressure loading capacity
which exceeds the yield limit of most metallic materials. Ageing or resinification
does not occur in the present lubricant system. Moreover, the effect of the present
lubricant system is retained even after a prolonged period of rest. Another aspect
of the present lubricant system is the fact that it provides a long-lasting corrosion
protection film exhibiting an excellent adhesion, even in the case of extreme deformation
of the workpiece, without exhibiting any signs of flaking. In addition, the present
lubricant system is insensitive to dust, dirt, moisture and chemical influences, it
is radiation-proof and easy to apply to pre-treated surfaces of workpieces.
[0004] The AF coatings that are known from the prior art, for example from US patent No
5,482,637, can be considered to be suspensions of solid lubricants having a very small
particle size, such as MoS
2, LiF
3, CaF
6, WS
2, graphite or BN in inorganic and organic binders and solvents, such as a matrix resin
selected from the group of alkyd polyester, epoxy and vinyl butyryl, with the suspension
further containing an active amount of moisturiser, defoaming agent and surfactant,
such as xanthane.
[0005] The object of the present invention is to provide a lubricant system which enables
the preparation of tailor-made AF coatings for industrial application through careful
selection of the suitable solid lubricant components.
[0006] Another object of the present invention is to provide a solid lubricant system which
does not comprise any environmentally objectionable components.
[0007] Another object of the present invention is to provide the lubricant system which
does not require the use of Cr(VI)-containing precoatings in order to obtain the lubricating
properties aimed at.
[0008] Yet another object of the present invention is to provide a solid lubricant system
which covers a broad temperature range, which provides a pressure loading capacity
that exceeds the yield limit of the metals that are used in practice and which moreover
exhibits adequate protection against corrosion.
[0009] Another object of the present invention is to provide a group of additives for use
in solid lubricant systems, which additives lead to a stable suspension not exhibiting
any or low sedimentation and/or phase separation and if, no coagulation of the solid
particles whilst keeping it uncured for a long time, both during storage and during
transport.
[0010] According to the present invention, the solid lubricant system as referred to in
the introduction is characterized in that said iii) additives are selected from the
group consisting of Na-, K- and NH
3-salt, of polyaspargic acid and N-alkyl morpholines, polyanilines, lecithine, sodium
olefin copolymers, ethylene diamine terminated polytetraalkylene glycol, succinimide,
bismuthtris (>C
6 alkylenedithio carbamates) and bi-methylenebisdibutyldithio carbamates, methylamino
acetic acid or its sodium salt, butylamino ethanol and urea, or mixtures thereof.
[0011] The aforesaid objectives will be accomplished if one or more of the aforesaid additives
are used in the present solid lubricant system.
[0012] The preferred amount of carrier or binder is less than 10 wt.%, preferably less than
3 wt.%, based on the total amount of solid lubricant system.
[0013] Polyanilines (poly-p-phenylene amine imine, Pani) comprise amine and imine groups.
Polyaniline is to be regarded as a benzene rings and chinon groups conjugated polymer,
chinoide-imine structures and benzeneamine groups respectively. Pani becomes electrically
conductive by paratoluene sulphonic acid. The maximum temperature of application is
220 °C, wherein, however, a temperature of about 260 °C is allowable during a short
period of time. Experimental data have shown that ≤ 20 wt.% polyaniline particles
having a dimension of < 500 nm will shift the corrosion potential with a value of
+ 800 mV, which shift is in particular favourable for anticorrosion objectives. It
is preferred to disperse 3-10 wt.% electrically conductive polyanilines having a average
particle size of about 20-30 nm in the present lubricant system. In the group of polyanilines
several oxidation steps are possible which determine the amount of N-H-bindings, as
well as the ratio of benzene rings and chinon groups, on which several reversible
redox reactions are based. Therefore, several compounds can be mentioned like leucomeraldine
(completely reduced Pani), emeraldine-base (a partially oxidized Pani) and pernigraline
base (a completely oxidized Pani). These compounds can be converted in each other
by proton delivery, reaction of amine groups with radicals, respectively, and the
salts thereof can be formed.
[0014] In particular lecithin-based compounds, such as commercially available technical
lecithin consists of lecithin (more than 60%), the remainder being soybean oil, or
sodium olefin copolymers, viz. anionic dispersing agents for aqueous systems, are
added as additives to the present lubricant system.
[0015] The use of PIB-succinimide (mono-, bis- en trisuccinimide) or salts of polyaspargic
acid is in particular desirable if graphite compounds are used as solid lubricant
components. Moreover, ethylene diamine grafted polytetralkene glycol is suitable for
use as an anti-sedimentation and dispersing agent. In addition (bismuth (>C
6 alkylene dithiocarbamates) and bimethylene bis dibutyl dithiocarbamates can be used
as molybdenum or zinc salts.
[0016] The group of N-alkylmorpholines is in particular suitable for use as an anti-corrosion
agent in water-based solid lubricant systems. In addition to that, said group exhibits
very good properties under extreme pressure conditions, stabilizing the pH-value as
a buffer. From a toxicologic point of view, the alkyl derivatives with a base of CH
3 and C
6H
13 are preferred, because such compounds are quickly biodegradable and exhibit a favourable
toxicity. In addition to that, polymers of polyaspargic acid are suitable on account
of their biodegradability, in combination with a low toxicity value. Moreover, polymers
of polyaspargic acid surprisingly have multifunctional properties, because polyaspargic
acid is dipolar, on account of the COOH and C=O groups, and adsorbs on surfaces, so
that said molecule has multifunctional anti-wear and high-pressure properties. In
addition, polyaspargic acid has a dispersing effect and prohibits coagulation on the
solid lubricant components of the present lubricant system, whilst also having a favourable
influence as regards the prevention of calcification. The molecule can be considered
to be strongly anionic and functions as a strong regulator or stabiliser. According
to the present invention, all types of D-, L- and DL-polyaspargic acid, preferably
L-polyaspargic acid, with potassium, sodium or lithium, as well as ammonium, having
a molecular weight of 1000 - 10.000 g/mol are suitable.
[0017] Suitable solid lubricant components are: Zr(OH)
4, Zr(OH)
4.nH
2O, ZrO
2.nH
2O, Bi
2S
3, graphite intercalation compounds, graphite inhibited compounds, phyllosilicates
and CeF
3, or a combination thereof
[0018] Cerium fluoride (CeF
3) is a white crystal having a hexagonal crystal structure, it is characterized by
high-pressure properties which surpass the properties of MoS
2 to a significant degree, because CeF
3 is thermally stable in air conditions above 600 °C and because it is resistant against
oxidation.
[0019] Zirconium hydroxide (Zr(OH)
4) exhibits a high degree of stability also in high-temperature air conditions, in
particular temperatures of up to about 650 °C, with zirconium hydroxide being insoluble
in water. It is also possible to use Zr(OH)
4. nH
2O and ZrO
2.nH
2O as zirconium-containing compounds.
[0020] Unlike MoS
2, which is known from the prior art, pure graphite does not have any intrinsic lubricating
properties, in spite of the fact that it has a hexagonal structure, because the binding
forces between the C-layers are too strong. Consequently, the graphite lattice requires
a specific gaseous substance, such as water vapour or a gas, for shifting the graphite
lamellae relative to each other, which substance is introduced between the layers
or "intercalated" and which increases the spacing between the individual layers. When
said intercalated substances are removed through the application of a vacuum or high
temperatures, the coefficient of friction of graphite compounds increases to a value
higher than 0.5. This actually explains the tribological sensitivity of graphite to
air humidity and water vapour. According to the present invention, in order to reduce
this mechanism to a minimum, one or more compounds selected from the group consisting
of FeCl
3, CuFeS
2, α-Fe
2PO
5, AsF
5, NiCl
2, CaF
2, BaF
2, LiF, AgCl, AgF, SbF
5, AlCl
3, CuCl
2, CoCl
2, MnCl
2, MoCl
5, SbCl
3, SbCl
5 and hydrated compounds thereof are used in graphite in order to improve the anti-friction
properties of the graphite compounds.
[0021] It is in particular preferred in the present lubricant system if said ii) solid lubricant
components are present in said system in an amount of less than 70 wt.%.
[0022] The ii) solid lubricant components used in the present solid lubricant system have
a particle size < 5 µm.
[0023] In a special embodiment it is desirable for said ii) solid lubricant components to
have a particle size in the range of 25-300 nm.
[0024] Furthermore it can be noted that the graphite intercalation compounds and the graphite
inhibited compounds have an aspect ratio of at least 6:1.
[0025] Suitable ii) solid lubricant components as used in the present lubricant system furthermore
include phyllosilicates, which compounds can be defined as so-called layered silicate
compounds, which are characterized by tetrahedral Si
4O
10-layers and octrahedral layers containing (Mg, Fe,) or Al. The aforesaid group includes
kaolinite, chlorite, serpentine, biotite, muscovite, pyrophyllite/pirophillite AlSiO
2O
5OH (H
v ∼ 100 MPa) or ferripyrophyllite Fe
3+2Si
4(OH)
2O
10, marien glass CaSO
4 (high plastic deformation capacity, high µ), synthetic hillebrandite (Ca
2SiO
2.H
2), vermiculite Mg
3(Al, Si)
4O
10(OH)
2.4H
2O, meixnerite Mg
6Al
2(OH)
18.4(H
2O), ρ = 1,95 g/cm
3, ettringite (Ca
6Al
2(SO
4)
3(OH)
1226(H
2O)) [H
v < 1000 MPa], molybdenum hydroxide-hydrate [MoO
3.nH
2O], wherein n = 1/3, 1/2, 1 or 2 (ilsemannite, H
v∼ 4600 MPa), trihydrated alumina(ATH), aluminium trihydroxide as Al(OH)
3, α-Al(OH)
3 bayerite, β-Al(OH)
3 nordstrandite, doyleite, γ-Al(OH)
3, gibbsite, hydragillite, alumina, monohydrated or oxohydroxide (Al(OOH) as γ-(Al(OOH)
boehmite and α-(Al(OOH) diaspore, with especially the group of Serpentine having a
density of 2.2-2.6 g/cm
2 being preferred. The following hydrates/hydroxides can be mentioned as ii) solid
lubricant components belonging to the group of Serpentine:
a. Antigorite (Mg,Fe)3Si2O5(OH)4,
b. Clinochrysotile Mg3Si2O5(OH)4 (monoclinical),
c. Lizardite Mg3Si2O5(OH)4 (trigonal and hexagonal),
d. Orthochrysotile Mg3Si2O5(OH)4 (orthorhombic),
e. Parachrysotile (Mg,Fe)3Si2O5(OH)4 (orthorhombic), and
f. Talcum Mg3Si4O10(OH)2.
[0026] In order to protect the graphite intercalation compounds and the graphite inhibited
compounds against oxidation, [CS]-surface complexes, Zn
3P
2O
5, zinc orthophosphate KH
2PO
4, AlPO
4 and Li
2OMgOP
2O
5, or a mixture thereof, are added to the present solid lubricant system.
[0027] A suitable carrier is selected from the group of polymineral resins, aniline resins,
phosphor and boron modified phenol resins, polyaniline resins, from polyazoles, as
polybenzimidazole, polypyrrolone, polyimidazolepyrrolone, poly-p-phenylene, poly-p-xylene,
poly-m-phenylene isophthalamide, polyphenylene benzoxazole, polyphenylene benzothiazole,
poly-tris(N-pyrrolyl) boron resins, polycarbosilanes and polysilanes as well as the
mixtures thereof.
1. A solid film lubricant system useful in coating a metal, ceramic or polymeric material
wear surface, comprising
i) a carrier,
ii) solid lubricant components,
iii) additives,
characterized in that said iii) additives are selected from the group consisting of Na-, K- and NH
3-salts, of polyaspargic acid and N-alkyl morpholines, polyanilines, lecithin, sodium
olefin copolymers, ethylene diamine terminated polytetraalkylene glycol, succinimide,
(bismuthtris (>C
6 alkylene dithiocarbamates) and bimethylene bis dibutyl dithiocarbamates, methylamino
acetic acid or its sodium salt, butylamino ethanol and urea, or mixtures thereof.
2. A solid film lubricant system according to claim 1, characterized in that the amount of said iii) additives is less than 10 wt.%, based on the total system.
3. A solid film lubricant system according to claim 1, characterized in that the amount of said iii) additives is less than 3 wt.%, based on the total system.
4. A solid film lubricant system according to any one of the preceding claims, characterized in that said ii) solid lubricant components are comprised of an ingredient selected from
the group of Zr(OH)4, Zr(OH)4.nH2O, ZrO2.nH2O, Bi2S3, graphite intercalation compounds, graphite inhibited compounds, phyllosilicates
and CeF3, or a combination thereof.
5. A solid film lubricant system according to claim 4, characterized in that said ii) solid lubricant components are present in said system in an amount of less
than 70 wt.%.
6. A solid film lubricant system according to any one of the claims 4-5, characterized in that said ii) solid lubricant components have a particle size < 5 µm.
7. A solid film lubricant system according to claim 6, characterized in that said ii) solid lubricant components have a particle size in the range of 15-300 nm.
8. A solid film lubricant system according to any one of the claims 4-7, characterized in that said graphite intercalation compounds and said graphite inhibited compounds have
an aspect ratio of at least 6:1.
9. A solid film lubricant system according to claim 4, characterized in that as phyllosilicates the group of Serpentine having a density of 2.2-2.6 g/cm2 is used.
10. A solid film lubricant system according to any one of the claims 4-9, characterized in that in said graphite intercalation compounds and said graphite inhibited compounds one
or more compounds are incorporated, selected from the group consisting of FeCl3, CuFeS2, α-Fe2PO5, AsF5, NiCl2, CaF2, BaF2, LiF, AgCl, AgF, SbF5, AlCl3, CuCl2, CoCl2, MnCl2, MoCl5, SbCl3, SbCl5, and hydrated compounds thereof in order to improve the anti-friction properties
of said graphite compounds.
11. A solid film lubricant system according to any one of the claims 4-10, characterized in that said graphite intercalation compounds and said graphite inhibited compounds are protected
against oxidation by adding thereto [CS]-surface complexes, Zn3P2O5, zinc ortho phosphate, KH2PO4, AlPO4 and Li2OMgOP2O5, or a mixture thereof.