[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] European patent application 0 452 189 relates to a solid material for dry lubrication
of the contact between a first surface made of a first material and a second surface
made of ceramic material wherein it comprises at lease one rare-earth fluoride. From
this document is known a process for dry lubrication of the contact between two surfaces
one of which is made of ceramic material wherein it consists in interposing between
the two surfaces to be lubricated a layer of a lubricating material comprising at
least one rare-earth fluoride. This document does not disclose a film as lubricating
coating.
[0004] International application W0 00/53702 relates to an aqueous coating composition for
providing a dry film lubricant coating to a substrate, comprising 10-70% by weight
alkaline earth metal fluoride, 2-65% by weight of a silicon resin binder, and water,
wherein the silicon resin is an alkyl silicone resin emulsion in water and is used
primarily to hold the lubricating powders on the surface of the substrate.
[0005] European patent application 0 217 138 relates to a low friction support member comprising
a compacted body formed from an intercalated graphite powder, which is stable in air
and at an elevated temperature. The intercalated graphite is compressed uniaxially
such as in a mold or dye, or isostatically such as in a pressurized fluid to form
a compact body of the desired shape. This document does not relate to a solid film
lubricant system useful in coating a metal, ceramic or polymeric material wear surface.
[0006] French patent application 2 684 684 relates to self-lubricating dense articles, consisting
essentially of sintered rare-earth fluorides and exhibiting a fine-grained uniform
microstructure. These self-lubricating dense articles are obtained by a process consisting
of sintering, in a non-oxidizing and/or reducing atmosphere, a submicron and very
pure powder of rare-earth fluorides in the presence of a carbonaceous sintering additive.
These articles can be employed as self-supporting components or as insert components,
but they cannot be regarded as a solid film lubricant system useful in coating a metal,
ceramic or polymeric material wear surface.
[0007] U.S. patent 3,756,982 relates to a method of producing antifriction materials for
dry friction units, consisting of curing a mixture of polyphenylene oligomers in combination
with various fillers. Pulverulent fillers are added into a mixture of oligomers in
an alcohol, with which a fabric is then impregnated. The result of the impregnation
procedure is an impregnated fabric which is then dried at a temperature of 130 °C,
and the mass thus obtained is placed into cold compression molds, heated up to 180
°C, the compression mold is then closed and a pressure is built up therein with a
view towards obtaining an article of adjustable density. The resulting articles are
work pieces which can be finished to a required size on metal working machines. This
document does not relate to a solid film lubricant system useful in coating a metal,
ceramic or polymeric material wear surface.
[0008] U.S. patent 6,228,815 relates to solid lubricants containing bismuth sulfide for
use in friction linings for applications such as brake disk pads, brake drums and
clutch disks. The friction material matrix comprises at least one solid lubricant,
the solid lubricant containing bismuth sulfide and at least one binder system.
[0009] Japanese publication No. 04 004293 relates to a solid lubricant having good lubricating
characteristics by blending a graphite based solid lubricant with a graphite intercalation
compound and thermally treating. This document does not relate to a solid film lubricant
system useful in coating a metal, ceramic or polymeric material wear surface.
[0010] 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.
[0011] The AF coatings that are known from the prior art, for example from US patent No
5,554,020, can be considered to be suspensions of solid lubricants having a very small
particle size, such as MoS
2, graphite or PTFE in inorganic and organic binders and solvents, such as a matrix
resin selected from the group of polyimides, epoxy and polyaryl sulphon.
[0012] 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.
[0013] Another object of the present invention is to provide a solid lubricant system which
does not comprise any environmentally objectionable components.
[0014] 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.
[0015] Yet another object of the present invention is to provide a solid lubricant system
which covers a broad temperature range, which provides a contact pressure loading
capacity that exceeds the yield limit of most metals that are used in practice and
which moreover exhibits adequate protection against corrosion and scuffing.
[0016] Another object of the present invention is to provide matrices for use in solid lubricant
systems, which matrices have a glass transition temperature T
g of more than 300 °C, a matrix strength of more than 100 MPa at room temperature,
a high elasticity modulus and a high starting temperature (onset T) in the thermogravimetric
analysis.
[0017] According to the present invention, the solid lubricant system as referred to in
the introduction is characterized in that said i) 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 and that said ii) solid lubricant
components, being comprised of at least two ingredients selected from the group of
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.
[0018] The aforesaid objectives will be accomplished if two or more of the aforesaid solid
lubricants in combination with one or more of the aforesaid carriers are used in the
present solid lubricant system.
[0019] The preferred amount of carrier or binder is 20-90 wt.%, based on the total amount
of solid lubricant system.
[0020] According to the present invention, the boron modified phenol resins, such as bisphenol
A formaldehyde or bismaleimide resin, comprise decaborane or o-carborane series or
boron-containing allyl series in the molecule. Such boron modified resins attain in
uncured and uninforced condition at room temperature a strength of about 50 MPa to
about 120 MPa.
[0021] Polycarbosilanes (-SiR
2-CR
2-)
n or polysilanes (-SiR
2-SiR
2-)
n, wherein R is hydrogen, methyl, ethyl or phenyl group, and n is an integer of 3-200,
are preferred embodiments of a carrier.
[0022] Typical compounds for polybenzimidazole resins (PBI) are poly[(1,5-dihydrobenzo[1,2-d:4,5-d']diimidazole-2,6-idyl)-1,4-phenylene],
poly-2,2' (m-phenylene)-5,5'-bibenzimidazole or the commercially available poly-(2,2'-m-phenylene-5,5'-bibenzimidazole),
which compounds exhibit glass transition temperatures ranging from about 400 - 663
°C.
[0023] Polyphenylene benzobisoxazole (PBO) has an E-modulus of more than >300 GPa, in combination
with a strength value of >3000 MPa. The molecule of poly(6F-benzoxazole) (6F-PB) decomposes
at a temperature of about 650 °C. The glass transition temperature of poly(2,5-benzimidazolidyl-5,2-benzimidazolidyl-1,3-phenylene)
is higher than 703 °C. The elasticity modulus of poly-p-phenylene benzo-bisthiazole
(PBT) is about 340 GPa.
[0024] Poly-p-phenylene (PPP) is stable at temperatures of up to about 450 °C in the air
and up to about 550 °C in inert conditions. Another polymer according to the present
invention, which is used as a carrier or matrix, is poly-p-xylylene, which polymer
will melt at a temperature of about 395 - 425 °C, depending on the molecular weight.
[0025] Polymineral resins or "geopolymers" form binders with a base of alumino silicates.
Although the preparation thereof is described in great detail in US patent No 5,342,595,
the special use thereof in anti-friction coatings is not known therefrom. Polymineral
resins are classified into (-Si-O-Al-O)-type poly(sialate), (-Si-O-Al-O-Si-O)-type
poly(sialate-siloxy) and (-Si-O-Al-O-Si-O-Si-O)-type poly(sialate-disiloxy). An Si:Al
ratio of 1, 2 or 3 gives the polysialates ceramic properties, whilst an Si:Al ratio
of > 15 gives said polysialates polymeric properties. The aforesaid polymineral resins
are thermally stable at temperatures of up to 1200 °C.
[0026] Suitable solid lubricants 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.%.
[0031] The ii) solid lubricant components used in the present solid lubricant system have
a particle size < 5 µm.
[0032] 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.
[0033] Furthermore it can be noted that the graphite intercalation compounds and the graphite
inhibited compounds have an aspect ratio of at least 6:1.
[0034] 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.
[0035] 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. In certain
specific embodiments of the present invention talcum and/or vermiculite should be
prevented.
[0036] Suitable additives are selected from the group consisting of Na-, K- and NH
3-salts, of polyaspargic acid and N-alkyl morpholines, lecithin, sodium olefin copolymers,
ethylene diamine terminated polytetraalkylene glycol, succinimide, (bismuth (>C
6 alkylene dithiocarbamates) and bimethylene bis dibutyl dithiocarbamates, methylamino
acetic acid or its sodium salt, butylamino ethanol and urea, or 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 i) 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, and that said ii) solid lubricant components being comprised of
at least two ingredients selected from the group of 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.
2. A solid film lubricant system according to claim 1, characterized in that the amount of i) carrier is 20-90 wt.%, based on the total lubricant system.
3. A solid film lubricant system according to any of claims 1 and 2, characterized in that said ii) solid lubricant components are present in said system in an amount of less
than 70 wt.%.
4. A solid film lubricant system according to any one of the claims 1-3, characterized in that said ii) solid lubricant components have a particle size < 5 µm.
5. A solid film lubricant system according to claim 4, characterized in that said ii) solid lubricant components have a particle size in the range of 15-300 nm.
6. A solid film lubricant system according to any one of the claims 1-5, characterized in that said graphite intercalation compounds and said graphite inhibited compounds have
an aspect ratio of at least 6:1.
7. A solid film lubricant system according to any one of claims 1-6, characterized in that the group of Serpentine having a density of 2.2-2.6 g/cm2 is used as phyllosilicates.
8. A solid film lubricant system according to any one of the claims 1-7, characterized in that one or more compounds 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 are incorporated in said graphite intercalation compounds
and said graphite inhibited compounds in order to improve the anti-friction properties
of said graphite compounds.
9. A solid film lubricant system according to any one of the claims 1-8, 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.