A solid film fubricant system useful in coating a metal, ceramic or polymeric material wear surface

Description

[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 MoS₂, 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.nH₂O, ZrO₂.nH₂O, Bi₂S₃, graphite intercalation compounds, graphite inhibited compounds, phyllosilicates and CeF₃.

[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 (-SiR₂-CR₂-)_n or polysilanes (-SiR₂-SiR₂-)_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.nH₂O, ZrO₂.nH₂O, Bi₂S₃, graphite intercalation compounds, graphite inhibited compounds, phyllosilicates and CeF₃.

[0027] Cerium fluoride (CeF₃) is a white crystal having a hexagonal crystal structure, it is characterized by high-pressure properties which surpass the properties of MoS₂ to a significant degree, because CeF₃ 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.nH₂O and ZrO₂.nH₂O as zirconium-containing compounds.

[0029] Unlike MoS₂, 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 FeCl₃, CuFeS₂, α-Fe₂PO₅, AsF₅, NiCl₂, CaF₂, BaF₂, LiF, AgCl, AgF, SbF₅, AlCl₃, CuCl₂, CoCl₂, MnCl₂, MoCl₅, SbCl₃, SbCl₅ 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 Si₄O₁₀-layers and octrahedral layers containing (Mg, Fe,) or Al. The aforesaid group includes kaolinite, chlorite, serpentine, biotite, muscovite, pyrophyllite/pirophillite AlSiO₂O₅OH (H_v ∼ 100 MPa) or ferripyrophyllite Fe³⁺₂Si₄(OH)₂O₁₀, marien glass CaSO₄ (high plastic deformation capacity, high µ), synthetic hillebrandite (Ca₂SiO₂.H₂), vermiculite Mg₃(Al,Si)₄O₁₀(OH)₂.4H₂O, meixnerite Mg₆Al₂(OH)₁₈.4(H₂O), ρ = 1,95 g/cm³, ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂26(H₂O)) [H_v < 1000 MPa], molybdenum hydroxide-hydrate [MoO₃.nH₂O], 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/cm² 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, Zn₃P₂O₅, zinc orthophosphate KH₂PO₄, AlPO₄ and Li₂OMgOP₂O₅, 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 NH₃-salts, of polyaspargic acid and N-alkyl morpholines, lecithin, sodium olefin copolymers, ethylene diamine terminated polytetraalkylene glycol, succinimide, (bismuth (>C₆ alkylene dithiocarbamates) and bimethylene bis dibutyl dithiocarbamates, methylamino acetic acid or its sodium salt, butylamino ethanol and urea, or mixtures thereof.

Claims

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.nH₂O, ZrO₂.nH₂O, Bi₂S₃, graphite intercalation compounds, graphite inhibited compounds, phyllosilicates and CeF₃.

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.