U.S. patent application number 12/675104 was filed with the patent office on 2011-07-21 for method for reducing friction.
This patent application is currently assigned to NEDERLANDSE ORGANISATIE VOOR TOEGEPAST- NATUURWETENSCHAPPELIJK ONDERZOEK TNO. Invention is credited to Hermanus Bernardus Maria Lenting, Aafke Tessa Ten Cate, Kjeld Jacobus Cornelis Van Bommel, Emile Van Der Heide.
Application Number | 20110177987 12/675104 |
Document ID | / |
Family ID | 39110887 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110177987 |
Kind Code |
A1 |
Lenting; Hermanus Bernardus Maria ;
et al. |
July 21, 2011 |
METHOD FOR REDUCING FRICTION
Abstract
The invention is directed to a method for reducing friction
between at least two bodies. The method of the invention comprises
providing a surface of at least one of said at least two solid
bodies with a covalently bound coating, wherein said surface is to
be contacted with another one of said at least two solid bodies,
and wherein said coating comprising at least one polymer; and
providing a liquid onto said coating.
Inventors: |
Lenting; Hermanus Bernardus
Maria; (Oldenzaal, NL) ; Van Bommel; Kjeld Jacobus
Cornelis; (Eindhoven, NL) ; Van Der Heide; Emile;
(Helmond, NL) ; Ten Cate; Aafke Tessa;
('s-Hertogenbosch, NL) |
Assignee: |
NEDERLANDSE ORGANISATIE VOOR
TOEGEPAST- NATUURWETENSCHAPPELIJK ONDERZOEK TNO
Delft
NL
|
Family ID: |
39110887 |
Appl. No.: |
12/675104 |
Filed: |
August 27, 2008 |
PCT Filed: |
August 27, 2008 |
PCT NO: |
PCT/NL2008/050569 |
371 Date: |
May 14, 2010 |
Current U.S.
Class: |
508/204 |
Current CPC
Class: |
C10M 2217/028 20130101;
C10N 2030/06 20130101; C10M 2217/046 20130101; C10N 2050/025
20200501; C10M 2205/026 20130101; C10M 2209/105 20130101; C10M
2205/024 20130101; C10M 2209/104 20130101; C10M 2209/084 20130101;
C03C 2217/75 20130101; C10M 2209/12 20130101; D06M 15/53 20130101;
D06M 2400/01 20130101; C10M 2205/04 20130101; C10M 2209/062
20130101; C10M 2229/02 20130101; D06M 23/005 20130101; D06M 15/263
20130101; C03C 2217/76 20130101; C10M 2205/022 20130101; C10M
2213/06 20130101; C10M 107/00 20130101; C03C 17/3405 20130101; D06M
2200/40 20130101; C10M 2209/107 20130101; C10M 2209/104 20130101;
C10M 2215/04 20130101 |
Class at
Publication: |
508/204 |
International
Class: |
C10M 139/00 20060101
C10M139/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2007 |
EP |
07115000.7 |
Claims
1. Method for reducing friction between at least two solid bodies,
comprising providing a surface of at least one of said at least two
solid bodies with a covalently bound coating, wherein said surface
is to be contacted with another one of said at least two solid
bodies, and wherein said coating comprising at least one polymer;
and providing a liquid onto said coating.
2. Method according to claim 1, wherein said coating and said
liquid are both hydrophilic.
3. Method according to claim 1, wherein said polymer is selected
from the group consisting of polyoxazoline, polyethylene glycol,
polyvinylalcohol, polyvinylpyrrolidone, polyacrylamide,
poly(meth)acrylic acid, polyethylene oxide-co-polypropylene oxide
block copolymers, poly(vinylether), poly(N,N-dialkylacrylamide),
polyelectrolytes, polyacyl alkylene imine,
polyhydroxyalkylacrylates, polyols, polysaccharides, polypeptides,
polyionic polymers, polyethyleneimine,
polyvinylbenzyltrimethylammonium, polyaniline, sulphonated
polyaniline, polypyrrole, polypyridinium, polythiophene-acetic
acids, polystyrenesulphonic acids, polymers of zwitterionic
molecules, and mixtures and copolymers thereof.
4. Method according to claim 1, wherein said coating comprises a
poly(acrylic acid) or a derivative thereof.
5. Method according to claim 1, wherein said coating comprises a
polyethylene glycol.
6. Method according to claim 1, wherein said coating comprising a
polyethylene glycol with a number average molecular weight of at
least 5 000 g/mol.
7. Method according to claim 1, wherein said coating is of
hydrophobic nature.
8. Method according to claim 1, wherein said polymer is selected
from the group consisting of polysiloxanes, fluoropolymers,
polystyrene, polyoxypropylene, polyvinylacetate, polyoxybutylene,
(hydrogenated) polyisoprene or polybutadiene, polyvinylchloride,
polyalkylacrylate, polyalkylmethacrylate, polyacrylonitrile,
polypropylene, polyethylene, polytetrahydrofuran,
polymethacrylates, polyacrylates, polysulphones, polyvinylethers,
polypropylene oxide), and mixtures and copolymers thereof.
9. Method according to claim 1, wherein said coating comprises at
least two polymers layers.
10. Method according to claim 1, wherein said coating has a
thickness of 1 .mu.m or less.
11. Method according to claim 1, wherein said liquid is water or an
aqueous medium.
12. Method according to claim 7, wherein said liquid is an organic
compound.
13. Method according to claim 7, wherein said liquid is a silicone
fluid.
14. Method according to claim 1, wherein the amount of liquid is in
the range of 0.05-10 g per gram of dry coating.
15. Method according to claim 1, wherein said at least two solid
bodies are of the same material or of different material.
16. Method according to claim 1, wherein said at least two solid
bodies comprise one of more materials selected from the group
consisting of plastics, metals, alloys, glass, textiles, metal
oxide, ceramics, wood, living tissue (skin), mucosal membranes, and
combinations thereof.
17. Method according to claim 1, wherein said polymer and said
liquid are selected from the group consisting of poly(acrylic acid)
polymer or derivatives thereof and water or an aqueous medium,
poly(acrylic acid) polymer or derivatives thereof and silicone oil,
poly(acrylic acid) polymer or derivatives thereof and
C.sub.6-C.sub.20 alkane, polyethylene glycol or derivatives thereof
and water or an aqueous medium, polyethylene glycol or derivatives
thereof and silicone oil, polyethylene glycol or derivatives
thereof and C.sub.6-C.sub.20 alkane, polysiloxane or derivatives
thereof and water or an aqueous medium, polysiloxane or derivatives
thereof and silicone oil, polysiloxane or derivatives thereof and
C.sub.6-C.sub.20 alkane, polyolefin or derivatives thereof and
water or an aqueous medium, polyolefin or derivatives thereof and
silicone oil, polyolefin or derivatives thereof and
C.sub.6-C.sub.20 alkane.
18. Method according to claim 17, wherein said coating comprises at
least two layers, wherein a first layer comprises poly(acrylic
acid) polymer or a derivative thereof and a second layer on top of
said first layer comprises the polymer as defined in claim 17.
19. Method according to claim 1, wherein said coating has a
thickness of 500 nm or less.
20. Method according to claim 1, wherein said coating has a
thickness of 100 nm or less.
21. Method according to claim 1, wherein the amount of liquid is in
the range of 0.1-5 g per gram of dry coating.
22. Method according to claim 1, wherein the amount of liquid is in
the range of 0.2-1 gram of dry coating.
Description
[0001] The invention is directed to a method for reducing friction
between at least two bodies.
[0002] When two bodies slide against each other, the resistance
against this sliding is termed friction. Friction is thus the force
that resists motion when the surface of one object comes into
contact with the surface of another. The level of friction, or the
calculated friction coefficient upon measurement, depends on the
operational conditions, the interacting surfaces of both objects
and the environment. Friction can be a serious nuisance in devices
that continuously move, since it constitutes a dissipation of
energy. Most of this energy loss appears as heat, while a small
proportion induces loss of material, from the sliding surfaces, and
this eventually leads to further waste, namely, to the wearing out
of the whole mechanism.
[0003] In order to lower the friction between interacting surfaces
of different objects to acceptable values lubricants are
conventionally applied. There is considerable interest in
developing new kinds of lubricants that produce low friction and
maintain this property for long periods of times, thereby reducing
maintenance expenses.
[0004] Conventional lubricants prevent contact of parts in relative
motion, and thereby reduce friction and wear. Typically, oils that
are derived from crude petroleum are used as lubricants. It is
often desirable to add various additive chemical to lubricating
oils. Such additives include viscosity-index improvers, pour-point
depressants, antioxidants, anti-wear and friction-reducing
additives, and dispersants. Normally, lubricants contain about 90%
base oil and less than 10% additives.
[0005] Lubricants do not necessarily have to be liquid. Non-liquid
lubricants include grease, powders (such as dry graphite,
polytetrafluorethylene (PTFE), molybdenum disulphide, talc, and
boron nitride), PTFE tape, air cushion and others.
[0006] Although lubricants in general considerably lower the amount
of friction, they do not always provide the desired level of
friction reduction, even in the presence of additives. Accordingly,
lubricant failure can occur. There is thus still a need in the art
for methods that allow reducing friction between solid objects to a
higher level and to novel types of lubricants.
[0007] Object of the invention is to fulfil this need and to
provide a method by which the friction between two or more solid
bodies can be reduced, which at the same time prevents, or at least
minimises, wear.
[0008] It was found that this object can be met by using a specific
combination of a polymeric coating with a liquid.
[0009] Accordingly, in a first aspect the invention is directed to
a method for reducing friction between at least two solid bodies,
comprising [0010] providing a surface of at least one of said at
least two solid bodies with a covalently bound coating, wherein
said surface is to be contacted with another one of said at least
two solid bodies, and wherein said coating comprising at least one
polymer; and [0011] providing a liquid onto said coating.
[0012] The inventors surprisingly found that the coating and the
liquid work synergistically in lowering the friction between the
two bodies when they are in moving contact with each other, i.e.
the combination of the coating and the liquid yields a lower
friction between two different objects than one would expect based
on the sum of the friction lowering effects of the coating or the
liquid alone.
[0013] The coating can bind to the surface of at least one solid
body in a durable way. Accordingly, the lowered friction
coefficient and desirable friction conditions can be maintained for
a prolonged period of time.
[0014] Once the coating has been applied to the surface of at least
one solid body the lowered friction characteristics can be induced
in a durable way at any desired time by addition of the liquid.
Additionally, the friction characteristics may be reversed by
removing the liquid (e.g. by evaporation, solvent extraction, etc.)
at any desired time.
[0015] A coating can comprise different polymers which can interact
with different liquids. Accordingly, a coating can be tailored to
fit existing fluid environments (e.g. biomedical environment) to
reduce friction.
[0016] Preferably, the coating has a strong chemical and/or
physical interaction with the liquid. Without wishing to be bound
by theory, it is believed that the combination of the coating and
the liquid provides a low viscous, yet somewhat immobilised layer
that improves lubricity.
[0017] The coating comprises a polymer. Preferably, this polymer is
an organic polymer. The polymer can suitably be a homopolymer or a
copolymer, such as a block copolymer. Mixtures or blends of
polymers and/or copolymers can also be used in the coating. The
polymer can be of hydrophilic or hydrophobic nature. Preferably, a
hydrophobic coating is combined with a hydrophobic liquid and a
hydrophilic coating is combined with a hydrophilic liquid. As an
example, when a more hydrophobic liquid is used, such as an oil or
certain hydrocarbons or silicone oil, the polymer preferably has a
hydrophobic nature. A large variety of suitable polymers can be
used.
[0018] In order to covalently bind to the surface of the solid
body, the polymer of the invention can have at least one functional
group. Suitable functional groups can for instance be chosen from
the group consisting of acids, acyl halogens, acrylates, alcohols,
aldehydes, alkenes, alkynes, amines, azides, carboxylics, cyanides,
epoxides, halogens, imines, isocyanates, ketones, silanes, thiols,
vinyls, and vinylethers.
[0019] Examples of suitable hydrophobic polymers include
polysiloxane, perfluoropolyether and other fluoropolymers,
polystyrene, polyoxypropylene, polyvinylacetate, polyoxybutylene,
(hydrogenated) polyisoprene or polybutadiene, polyvinylchloride,
polyalkylacrylates, polyalkylmethacrylates, polyacrylonitrile,
polypropylene, polyethylene, polytetrahydrofuran (PTHF),
polymethacrylates, polyacrylates, polysulphones, polyvinylethers,
and poly(propyleneoxide), and copolymers thereof.
[0020] Examples of suitable hydrophilic polymers include
polyoxazoline, polyethylene glycol, polyvinylalcohol,
polyvinylpyrrolidone, polyacrylamide, poly(meth)acrylic acid,
polyethylene oxide-co-polypropylene oxide block copolymers,
poly(vinylether), poly(N,N-dialkylacrylamide), polyacyl alkylene
imine, polyhydroxyalkylacrylates such as (homo)polymers of
hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate, and
hydroxypropyl acrylate, polyols, and copolymeric mixtures of two or
more of the above-mentioned polymers, natural polymers such as
polysaccharides and polypeptides, and copolymers thereof, and
optionally polyionic molecules such as polyallylammonium,
polyethyleneimine, polyvinylbenzyltrimethylammonium, polyaniline,
sulphonated polyaniline, polypyrrole, and polypyridinium,
polythiophene-acetic acids, polystyrenesulphonic acids, polymers
and copolymers of zwitterionic molecules, and polyelectrolytes.
[0021] Covalent binding of the polymer to the surface of the body
may be realised as described in WO-A-2007/021180, which is hereby
incorporated by reference. Thus, conventional wet-chemical
techniques as well as techniques such as chemical vapour deposition
(CVD), plasma deposition, plasma assisted grafting, or plasma
polymerisation can be used.
[0022] In a preferred embodiment the polymer is attached to the
surface of the body by a wet-chemical technique. The polymer
material suitably comprises a relatively high concentration of
pendant reactive moieties per monomer, such as at least 0.3 pendant
reactive moieties per monomer, preferably at least 0.5 pendant
reactive moieties per monomer, even more preferably at least one
pendant reactive moiety per monomer. The pendant reactive moieties
are preferably carboxyl moieties. Furthermore, the surface of the
body to which the polymer is to be applied is preferably
functionalised with amine groups. Even more preferably, the
polymeric material is a poly(acrylic acid) polymer or a derivative
thereof, and the surface of the body to which the polymer is to be
applied is functionalised with 3-aminopropyltrialkoxysilane.
[0023] It was found that the liquid can be retained better by the
coating, when the coating comprises more than one polymer layer.
The different polymer layers may be covalently bound to each other
or not. The different polymer layers may comprise different or the
same polymers.
[0024] Advantageously, the coating can have a thickness of less
than 1 .mu.m. Preferably, the coating has a thickness of less than
100 nm. Hence, in accordance with the invention a very small amount
of coating material suffices for obtaining a satisfactory reduction
in friction. In addition, it was found that relatively thin layers
attach better to the surface of the solid body. Moreover, the
advantage of having a thin film is that the solid body maintains
its characteristic properties and only the surface properties are
altered. Normally, the thickness of the coating is not less than 5
nm.
[0025] In a preferred embodiment a poly(acrylic acid) polymer (or a
derivative thereof), covalently linked to the surface, is modified
by reaction with either a hydrophobic or a hydrophilic polymer
containing either primary or secondary amine moieties. As an
example, but not limited thereto, an amino-functionalised
polyethylene glycol may be used for this purpose. In this way, a
coating comprising two polymer layers is created. In another
embodiment, post-modification of coated polymer layer(s) can be
realised.
[0026] Preferably, the coating comprises poly(acrylic acid) polymer
(PAA) or a derivative thereof. Such coatings give a remarkable
reduction in friction when combined with water as liquid. It was
found that in this combination the water is retained by the coating
very well due to the strong absorptive properties of the
poly(acrylic acid) polymer. The surface of the body with the
combination of the coating and water does not moisten its user, nor
does it feel wet when applying limiting amounts of water. These two
characteristics--remaining wet without feeling wet--make this
combination very attractive.
[0027] In the case of a hydrophilic polymer, the number average
molecular weight of the polymer in the coating can suitably be at
least 2 000 g/mol, preferably at least 5 000 g/mol, more preferably
in the range of 10 000-2 000 000 g/mol. In the case of a
hydrophobic polymer, the number average molecular weight of the
polymer in the coating can suitably be at least 500 g/mol,
preferably in the range of 2 000-50 000 g/mol, more preferably in
the range of 5 000-10 000 g/mol.
[0028] The liquid is preferably hydrophobic or hydrophilic. The
liquid can be a lubricant. Examples of liquids suitable in the
method of the invention include water, aqueous media, organic
fluids, silicone fluids, miscible combinations thereof or solutions
comprising these liquids.
[0029] Examples of preferred combinations of polymer and liquid,
which lead to significant reduction of friction include
poly(acrylic acid) polymer (and/or one or more derivatives thereof)
and water or an aqueous medium, poly(acrylic acid) polymer (and/or
one or more derivatives thereof) and silicone oil, poly(acrylic
acid) polymer (and/or one or more derivatives thereof) and
C.sub.6-C.sub.20 alkane, polyethylene glycol (and/or one or more
derivatives thereof) and water or an aqueous medium, polyethylene
glycol (and/or one or more derivatives thereof) and silicone oil,
polyethylene glycol (and/or one or more derivatives thereof) and
C.sub.6-C.sub.20 alkane, polysiloxane (and/or one or more
derivatives thereof) and water or an aqueous medium, polysiloxane
(and/or one or more derivatives thereof) and silicone oil,
polysiloxane (and/or one or more derivatives thereof) and
C.sub.6-C.sub.20 alkane, polyolefin (and/or one or more derivatives
thereof) and water or an aqueous medium, polyolefin (and/or one or
more derivatives thereof) and silicone oil, polyolefin (and/or one
or more derivatives thereof) and C.sub.6-C.sub.20 alkane. Suitable
C.sub.6-C.sub.20 alkanes include octane, nonan, decane, undecane,
dodecane, tetradecane, hexadecane, and octadecane. Suitable
polyolefins include polyethylene and polypropylene.
[0030] Particularly preferred combinations of polymer and liquid
are PAA (and/or one or more derivatives thereof) with water (or an
aqueous medium), polyethylene glycol (and/or one or more
derivatives thereof) with water (or an aqueous medium),
polyethylene glycol (and/or one or more derivatives thereof) with
silicone oil, polysiloxane (and/or one or more derivatives thereof)
with silicone oil, polysiloxane (and/or one or more derivatives
thereof) with dodecane, polyethylene (and/or one or more
derivatives thereof) with silicone oil, and polyethylene (and/or
one or more derivatives thereof) with dodecane.
[0031] Good results have been obtained when the polyethylene glycol
(and/or one or more derivatives thereof), the polysiloxane (and/or
one or more derivatives thereof), or the polyolefin (and/or one or
more derivatives thereof) is provided on top of a layer of PAA
(and/or one or more derivatives thereof).
[0032] Thus, in a preferred embodiment the following combinations
of coating and liquid are applied: a coating comprising a layer of
polyethylene glycol (and/or one or more derivatives thereof) on top
of a layer of poly(acrylic acid) polymer (and/or one or more
derivatives thereof) and water or an aqueous medium; a coating
comprising a layer of polyethylene glycol (and/or one or more
derivatives thereof) on top of a layer of poly(acrylic acid)
polymer (and/or one or more derivatives thereof) and silicone oil;
a coating comprising a layer of polyethylene glycol (and/or one or
more derivatives thereof) on top of a layer of poly(acrylic acid)
polymer (and/or one or more derivatives thereof) and
C.sub.6-C.sub.20 alkane; a coating comprising a layer of
polysiloxane (and/or one or more derivatives thereof) on top of a
layer of poly(acrylic acid) polymer (and/or one or more derivatives
thereof) and water or an aqueous medium; a coating comprising a
layer of polysiloxane (and/or one or more derivatives thereof) on
top of a layer of poly(acrylic acid) polymer (and/or one or more
derivatives thereof) and silicone oil; a coating comprising a layer
of polysiloxane (and/or one or more derivatives thereof) on top of
a layer of poly(acrylic acid) polymer (and/or one or more
derivatives thereof) and C.sub.6-C.sub.20 alkane; a coating
comprising a layer of polyolefin (and/or one or more derivatives
thereof) on top of a layer of poly(acrylic acid) polymer (and/or
one or more derivatives thereof) and water or an aqueous medium; a
coating comprising a layer of polyolefin (and/or one or more
derivatives thereof) on top of a layer of poly(acrylic acid)
polymer (and/or one or more derivatives thereof) and silicone oil;
and a coating comprising a layer of polyolefin (and/or one or more
derivatives thereof) on top of a layer of poly(acrylic acid)
polymer (and/or one or more derivatives thereof) and
C.sub.6-C.sub.20 alkane.
[0033] The amount of liquid to be combined with the coating of the
invention can vary. It is preferred to use an amount which more or
less equals the maximum loading capacity of the coating with the
respective liquid. Usually, the amount of liquid combined with the
coating will be in the range of 0.05-10 g per gram of dry coating,
preferably 0.1-5 g per gram of dry coating more preferably 0.2-1 g
per gram of dry coating.
[0034] The at least two solid bodies can be of the same or
different material. Suitably, the at least two solid bodies
comprise one or more materials selected from the group consisting
of plastics, metals, alloys, glass, textiles, metal oxide,
ceramics, wood, living tissue (skin) and mucosal membranes.
Excellent results have been obtained using two solid bodies made of
coated glass and silicone rubber, respectively, and two solid
bodies made of coated textiles and silicone rubber,
respectively.
[0035] The surface of one or more of the at least two solid bodies
may be surface modified in order to covalently bind the polymer to
the solid body through a suitable linker molecule. Typically, the
surface of the bodies can be modified with organic compounds which
can suitably be chosen from the group consisting of acids, acyl
halogens, acrylates, alcohols, aldehydes, alkenes, alkynes, amines,
azides, carboxylics, cyanides, epoxides, halogens, imines,
isocyanates, ketones, silanes, thiols, vinyl, and vinylethers.
Suitable linker molecules include aminopropyltrialkoxysilane,
aminopropyltrichlorosilane and heterofunctional silane-based
coupling agents.
[0036] The method of the invention can for instance be used in
sportswear to reduce friction between textiles and skin, for ski
runs with artificial snow to reduce friction between the artificial
snow and the ski equipment, blankets and garments like pyamas for
decubitus patients to reduce friction with the skin, catheters,
guide wires, endoscopes and other medical devices to reduce
friction with the living tissue as well as for other
applications.
EXAMPLES
Example 1
[0037] In this Example, a method of modifying a glass surface by
covalent bonding thereto of, subsequently, an
aminopropyltrimethoxysilane linker and a poly(acrylic acid) polymer
is described.
[0038] Pre-cleaned glass substrates were submerged in a fresh
coating solution of 5% 3-aminopropyltrimethoxysilane in
isopropylalcohol and sonicated for 20 min in an ultrasonic bath.
The substrates were thoroughly washed (3.times.) with water
followed by drying for 1 hour in an oven at 60.degree. C. The thus
functionalised substrates were dipped in a solution of poly(acrylic
acid) polymer (Mw 1 080 000; Mn 135 000) in water (0.5 wt. %) and
dried in an oven at 100.degree. C. under reduced pressure (<100
mbar) for 4 hours. The substrates were thoroughly washed (3.times.)
with water to remove physisorbed and not chemically bonded
poly(acrylic acid) polymer. Contact angle measurements of water on
the coating surface showed an advancing contact angle of 70-80
degrees, whereas that of the pre-cleaned glass substrate was found
to be in between 20 and 40 degrees depending on the cleaning
method.
Example 2
[0039] In this Example, a method of modifying a glass surface by
covalent bonding thereto of, subsequently, an
aminopropyltrimethoxysilane linker, a poly(acrylic acid) polymer
and amino functionalised polyethylene glycol (PEG 5 000; Mw 5 400;
Mn 5 000) is described.
[0040] Using the poly(acrylic acid) polymer modified glass
substrate prepared as described in Example 1, the glass substrate
was further dipped in a solution of 1% of monofunctionalised
amino-PEG 5 000 in water and dried in an oven at 120.degree. C.
under reduced pressure (<100 mbar) for 1 hour. The substrates
were thoroughly washed (3.times.) with water to remove physisorbed
and not chemically bonded PEG 5 000. Contact angle measurements of
water on the coating surface showed an advancing contact angle of
less than 20 degrees.
Example 3
[0041] In this Example a tribological assessment is done using the
coated glass surfaces from Examples 1 and 2.
[0042] Tribological assessment was done using a reciprocating
pin-on-plate test setup. This configuration was realised on the
commercially available tribometer PLINT TE67, for which a dedicated
glass support unit was constructed.
Operational Conditions:
[0043] All experiments were done at room temperature and in air.
The humidity and the temperature of the laboratory varied between
20-40% RH and 19-22.degree. C. respectively. Following the FIFA
08/05-01 test method "Determination of Skin/Surface Friction", in
which Silicon Skin L7350 is selected as best skin substitute, this
Silicone rubber is used for the tribological assessment.
Other Conditions:
[0044] Track length was set to 40 mm for all experiments. Ten
strokes were done per experiment (five from left to right and five
from right to left). The maximum velocity during the track was 1,
10 or 62 mm/s. The normal load was applied by the mass of the
specimen holder or by an additional dead weight to a resulting
normal force of 29 and 98 kPa respectively.
[0045] Tests were performed both with and without demineralised
water as liquid. The first condition is referred to as with water,
the second as dry conditions. The results are shown in FIGS. 1 and
2 for the dry condition and FIGS. 3 and 4 for the "with water"
condition. The used term glass means the pre-cleaned glass
substrate without coating whereas the terms +PAA and +PEG stands
for the glass substrate with a coating of PAA (Example 1) and PAA
plus a layer of PEG 5000 (Example 2) respectively.
[0046] The coefficient of friction is calculated based on the
friction force measured and normal force applied: .mu.=Fw/Fn
[0047] FIG. 1 shows the maximum coefficient of friction, fmax, as a
function of the sliding velocity and plate surface, at 98 kPa
contact pressure and at dry condition.
[0048] FIG. 2 shows the maximum coefficient of friction, fmax, as a
function of the sliding velocity and plate surface, at 29 kPa
contact pressure and at dry condition.
[0049] FIG. 3 shows the maximum coefficient of friction, fmax, as a
function of the sliding velocity and plate surface, at 98 kPa
contact pressure in the presence of water.
[0050] FIG. 4 shows the maximum coefficient of friction, fmax, as a
function of the sliding velocity and plate surface, at 29 kPa
contact pressure in the presence of water.
[0051] From the FIGS. 1-4 it can be observed that in the absence of
liquid the calculated maximum coefficients of friction are all
above 0.7 no matter the diverse circumstances. In the presence of
water, the calculated maximal coefficients of friction are somewhat
lower for the glass substrates without coating, as may be expected
upon addition of water, although water is not known to be an
effective lubricant as such. However, for glass substrates with
either PAA or PEG coating, the calculated coefficients are
substantially lower; an unexpected large reduction is observed.
These results show a large synergistic performance of the coating
polymer in cooperation with the liquid. Especially in the situation
wherein a normal pressure of 29 kPa is applied, a maximal
synergistic performance is obtained, no matter the maximum velocity
during the track.
Example 4
[0052] In this Example a tribological assessment is done using the
coated glass surfaces from Example 2.
[0053] Tribological assessment is done in parallel as described in
Example 3 using different liquids, i.e. water, silicone oil and
dodecane.
[0054] The maximum velocity during the track was 10 mm/s. The
normal load was applied by the mass of the specimen holder
resulting in a normal force of 29 kPa.
[0055] The results are shown in FIG. 5. Again, a coating as such
has no (major) influence on the obtained coefficient of friction.
Addition of a liquid alone often has, but not in the situation with
silicone oil, a certain reduction of the coefficient of friction.
However, the combination of the coating with the liquid results in
a synergistic reduction of the coefficient of friction. This
clearly shows that the observed reduction in the coefficient of
friction cannot be explained by the presence of the liquid as such,
neither by the presence of the coating as such, but is due to the
specific combination of the coating and the liquid lubricants which
results in a reduction in a synergistic way.
Example 5
[0056] In this Example a commercial available amino-containing
silicone polymer is integrated in the coating on top of the
poly(acrylic acid) polymer on glass substrate. The PAA-coated glass
substrate is covered with toluene solution containing the
amino-containing silicone polymer Wacker 1650 whereafter the
toluene is evaporated by heating at 120.degree. C. under N.sub.2
flow. Subsequently, the coated glass substrate is washed with
toluene and water at room temperature respectively whereafter dried
at 60.degree. C.
[0057] Tribological assessment is done in parallel as described in
Example 3 using different liquids, i.e. water, silicone oil and
dodecane.
[0058] The maximum velocity during the track was 10 mm/s. The
normal load was applied by the mass of the specimen holder
resulting in a normal force of 29 kPa.
[0059] As in Example 4, different lubricants are tested for
synergistic impact on coefficient of friction. As can be observed
in FIG. 6, use of silicone polymer as coating will lead to
reduction of coefficient of friction no matter the nature of
lubricant used. Whereas the use of water and dodecane as lubricant
will lead to friction reduction using uncoated glass substrate, a
synergistic effect is observed with the PAA-silicone polymer coated
glass substrate. Using silicone oil as lubricant, this synergistic
effect on friction reduction is also observed whereas the impact on
bare glass substrate is nil.
Example 6
[0060] In this Example glass substrate is coated with poly(acrylic
acid) and subsequent with either amino-functionalised polyethylene
(PE) or octadecylamine. Preparation of the PE top layer is realised
according the procedure described in example 5 for silicone top
layer except that the toluene solution is heated to prevent
precipitation of the poorly soluble PE polymer. Construction of the
octadecane top layer requires tetrahydrofuran (THF) instead of
toluene. The PAA modified glass substrate is dipped in octadecane
containing THF whereafter the substrate is heated.
[0061] Tribological assessment is done as described in Example
5.
[0062] In FIG. 7 the obtained coefficients of friction are shown
using water as liquid. Coefficients of friction from PE coated
glass substrate using silicone oil and dodecane as liquids are also
given.
[0063] As can been noted, coating of glass with PE top layer
results in obtained coefficients of friction which are
substantially reduced compared with that of the glass substrate
without coating: a synergistic impact of the combination of coating
with liquid is again shown since the friction reduction of uncoated
glass is substantial higher. This synergistic effect is optimally
shown in the situation of PE coating and silicone oil liquid:
without coating the application of silicone oil as liquid shows no
reduction of coefficient of friction at all, while with coating, a
substantial reduction is observed.
* * * * *