U.S. patent application number 14/653517 was filed with the patent office on 2015-10-29 for surface sulfurization of a metal body by flame spray pyrolysis.
The applicant listed for this patent is COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN, MICHELIN RECHERCHE ET TECHNIQUE S.A.. Invention is credited to ANTONIO DELFINO, MILAN FEDURCO, ROBERT NIKOLAUS GRASS, JEAN PAUL MERALDI, WENDELIN JAN STARK.
Application Number | 20150307981 14/653517 |
Document ID | / |
Family ID | 47989136 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150307981 |
Kind Code |
A1 |
GRASS; ROBERT NIKOLAUS ; et
al. |
October 29, 2015 |
SURFACE SULFURIZATION OF A METAL BODY BY FLAME SPRAY PYROLYSIS
Abstract
The surface of a body, in particular a metal reinforcer, at
least the surface of which comprises a layer of metal referred to
as surface metal capable of forming sulphides, is sulfurized. The
metal can be chosen from copper, zinc and their alloys. The process
comprises at least one stage of flame spray pyrolysis (FSP) of a
sulphur-donating precursor, for example, thiophene, which generates
hydrogen sulphide in the flame. The metal bodies or reinforcers
thus treated can be directly adhesively bonded, without adhesion
primer or addition of metal salt, such as a cobalt salt, to
matrices of unsaturated rubber such as natural rubber.
Inventors: |
GRASS; ROBERT NIKOLAUS;
(Zurich, CH) ; FEDURCO; MILAN; (Clermont-Ferrand,
FR) ; DELFINO; ANTONIO; (Clermont-Ferrand, FR)
; MERALDI; JEAN PAUL; (Zurich, CH) ; STARK;
WENDELIN JAN; (Langenthal, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN
MICHELIN RECHERCHE ET TECHNIQUE S.A. |
Clermont-ferrand
Granges-Paccot |
|
FR
CH |
|
|
Family ID: |
47989136 |
Appl. No.: |
14/653517 |
Filed: |
December 16, 2013 |
PCT Filed: |
December 16, 2013 |
PCT NO: |
PCT/EP2013/076713 |
371 Date: |
June 18, 2015 |
Current U.S.
Class: |
427/446 |
Current CPC
Class: |
C23C 4/04 20130101; B60C
2009/0014 20130101; C23C 8/08 20130101; D07B 1/0666 20130101 |
International
Class: |
C23C 4/12 20060101
C23C004/12; C23C 4/04 20060101 C23C004/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2012 |
FR |
1262411 |
Claims
1.-15. (canceled)
16. A process for the surface sulfurization of a body, the surface
of which comprises a layer of metal capable of forming sulfides,
the process comprising the step of: conducting at least one stage
of flame spray pyrolysis of a sulfur precursor which generates
hydrogen sulfide in the flame.
17. The process according to claim 16, wherein the metal is
selected from the group consisting of aluminium, silver, cobalt,
copper, tin, iron, manganese, molybdenum, nickel, zinc and alloys
comprising at least one of these elements.
18. The process according to claim 17, wherein the metal is
selected from the group consisting of copper, zinc and alloys
comprising at least one of these elements.
19. The process according to claim 18, wherein the metal is
brass.
20. The process according to claim 16, wherein the sulfur precursor
is liquid.
21. The process according to claim 16, wherein the sulfur precursor
is sulfur or a sulfur-donating organic compound.
22. The process according to claim 21, wherein the sulphur-donating
organic compound comprises from 1 to 15 carbon atoms.
23. The process according to claim 22, wherein the sulfur-donating
organic compound is liquid and is selected from the group
consisting of monosulfide, disulfide or polysulfide compounds of
saturated or unsaturated aliphatic or cycloaliphatic type or
aromatic type.
24. The process according to claim 23, wherein the sulfur-donating
organic compound is selected from the group consisting of thiophene
and its derivatives, thiocarbonyl compounds, aliphatic or aromatic
thiols, aliphatic or aromatic organic disulfides, aliphatic or
aromatic organic polysulfides, acyclic or cyclic thioethers,
thioesters, and mixtures thereof.
25. The process according to claim 24, wherein the sulfur-donating
organic compound is selected from the group consisting of thiophene
and its derivatives, aliphatic or aromatic organic disulfides,
aliphatic or aromatic organic polysulfides, acyclic or cyclic
thioethers, and mixtures thereof.
26. The process according to claim 21, wherein the sulfur-donating
organic compound is a compound devoid of a nitrogen atom.
27. The process according to claim 26, wherein the sulfur-donating
organic compound is a compound devoid of an oxygen atom.
28. The process according to claim 27, wherein the sulfur-donating
organic compound is a compound consisting exclusively of carbon,
sulfur and hydrogen atoms.
29. The process according to claim 28, wherein the sulfur-donating
organic compound is thiophene or a thiophene derivative.
30. The process according to claim 16, wherein a surface
temperature of the metal during the sulfurization treatment is
between 50.degree. C. and 500.degree. C.
31. The process according to claim 30, wherein the surface
temperature is between 100.degree. C. and 350.degree. C.
32. The process according to claim 16, wherein the body is a wire,
a cord, a film or a plate.
Description
1. FIELD OF THE INVENTION
[0001] The present invention relates to processes for the surface
treatment of metals, in particular of metal bodies, which can be
used as reinforcers in metal/rubber composites intended in
particular for the manufacture of articles made of rubber, such as
tyres.
[0002] It relates more particularly to processes for the surface
sulphurization of these metals for the purpose of making it
possible for them to subsequently adhere to ethylenically
unsaturated polymers, such as natural rubber.
2. STATE OF THE ART
[0003] Composites of metal/rubber type, in particular for tyres,
are well known. They are generally composed of a matrix made of
unsaturated rubber, generally diene rubber, which can be
crosslinked with sulphur, comprising metal reinforcing elements (or
"reinforcers"), such as wires or cords made of carbon steel.
[0004] As they are subjected to very high stresses during the
running of the tyres, in particular to repeated actions of
compression, bending or variation in curvature, these composites
must, in a known way, satisfy a large number of sometimes
contradictory technical criteria, such as uniformity, flexibility,
endurance in bending and compression, tensile strength, wear
resistance and corrosion resistance, and must maintain this
performance at a very high level for as long as possible.
[0005] It is easily understood that the adhesive interphase between
the rubber and these reinforcers plays a dominating role in the
persistence of this performance.
[0006] The conventional process for connecting the rubber
compositions to carbon steel consists in coating the surface of the
steel with brass (copper/zinc alloy), the bonding between the steel
and the rubber matrix being provided by sulphurization of the brass
(formation of zinc and copper sulphides) during the subsequent
vulcanization (that is to say, three-dimensional crosslinking by
sulphur) of the rubber matrix. This sulphurization process is
reflected in particular by the in situ formation of metal clusters
at the surface of the brass known as "dendrites", around which it
is assumed that the rubber matrix will anchor (by mechanical and
chemical anchoring) during the vulcanization.
[0007] In addition, organic salts or complexes of cobalt are
generally incorporated in this rubber matrix as adhesion-promoting
additives. It is known that cobalt actively participates not only
in the process of vulcanization of the rubber but also in that of
dendritization of the brass by being incorporated in the dendrites
themselves (by formation of Cu--Zn--Co intermetallic sulphides),
according to complex mechanisms of redox reactions resulting, it is
assumed, in the corrosion of the brass, in the dissolution of the
metal and its redeposition in the form of these metal sulphide
dendrites (sulphur-comprising dendrites). Reference may be made for
further details to the RCT (Rubber Chemistry and Technology)
publication, Vol. 78, pp. 426-457, author W. Stephen Fulton,
entitled "Steel tire cord-rubber adhesion, including the
contribution of cobalt").
[0008] However, it is also known that the presence of these cobalt
compounds in rubber compositions renders the latter more sensitive
to oxidation and to aging, so much so that the adhesion between the
carbon steel and the rubber matrix is also liable to weaken over
time as a result of the gradual change in the sulphides formed,
under the effect of the various stresses encountered, in particular
mechanical and/or thermal stresses, it being possible for the above
decomposition process in addition to be accelerated in the presence
of moisture.
[0009] Their incorporation also significantly increases the cost of
the rubber compositions, not to mention that it is desirable in the
long run to eliminate cobalt from these compositions, due to recent
developments in European regulations, cobalt and cobalt salts being
regarded as relatively toxic to the environment.
[0010] For all the reasons set out above, manufacturers of
metal/rubber composites, in particular tyre manufacturers are on
the lookout for novel adhesive solutions in order to adhesively
bond metal reinforcers to rubber compositions, while overcoming, at
least in part, the abovementioned disadvantages.
3. BRIEF DESCRIPTION OF THE INVENTION
[0011] In point of fact, during their research studies, the
Applicant Companies have found a novel surface sulphurization
process which meets such an objective.
[0012] The present invention relates to a process for the surface
sulphurization of a body, the surface of which comprises a layer of
metal, referred to as surface metal, capable of forming sulphides,
characterized in that it comprises at least one stage of flame
spray pyrolysis of a sulphur precursor which generates hydrogen
sulphide in the flame.
[0013] The metal reinforcers treated with the process of the
invention exhibit the major advantage of being able to be
subsequently adhesively bonded directly, that is to say without
adhesion primer or addition of metal salt (in particular cobalt
salt), to matrices of unsaturated rubber such as natural
rubber.
[0014] The invention and its advantages will be easily understood
in the light of the detailed description and of the implementation
examples which follow, and also of the figures relating to these
examples, which represent or give a diagrammatic representation of:
[0015] a scheme illustrating the principle of the FSP process of
the invention and also an example of a device which can be used for
the implementation of this process (FIG. 1); [0016] a scheme
illustrating the surface condition of the metal M once treated by
FSP, with formation of dendrites of sulphur-comprising
nanoparticles at the surface of the metal (FIG. 2); [0017] a scheme
illustrating the anchoring of a rubber matrix around the dendrites
formed above by virtue of the FSP surface treatment (FIG. 3);
[0018] a reproduction of SEM photographs, taken at the surface of
wires made of brass-coated carbon steel after FSP treatment,
demonstrating the presence of nanoparticles or dendrites at the
surface of the treated wires (FIG. 4); [0019] a reproduction of an
SEM photograph, taken at the surface of a brass-coated steel plate
after two consecutive FSP stages, a first stage of deposition of
copper (Cu) and a second stage in accordance with the invention of
sulphurization of the surface copper by FSP, also demonstrating the
presence of very fine dendrites or nanoparticles at the surface of
the plate thus treated (FIG. 5).
4. DETAILED DESCRIPTION OF THE INVENTION
[0020] In the present description, unless expressly indicated
otherwise, the percentages (%) shown are % by weight.
[0021] Furthermore, any interval of values denoted by the
expression "between a and b" represents the range of values
extending from more than a to less than b (that is to say, limits a
and b excluded), whereas any interval of values denoted by the
expression "from a to b" means the range of values extending from a
up to b (that is to say, including the strict limits a and b).
[0022] The invention thus relates to a process for the surface
sulphurization of a body, whether it is metallic or nonmetallic, at
least the surface of which comprises, for all or part, a layer of
metal referred to as surface metal, this surface metal (hereinafter
denoted "M") being capable of forming sulphides.
[0023] This surface treatment has the essential characteristic of
comprising a stage of flame spray pyrolysis, abbreviated to "FSP",
of a sulphur-donating precursor which generates hydrogen sulphide
in the flame.
[0024] The gas (H.sub.2S) formed is propelled, sprayed by the flame
towards the surface of the body being treated, hence the name
assigned to this technology. By virtue of the strong oxidizing
power of the hydrogen sulphide with regard to the surface metal,
metal sulphides are thus formed.
[0025] The process of the invention is preferably employed for the
purpose of subsequently adhesively bonding the body thus treated to
an ethylenically unsaturated rubber, that is to say a vulcanizable
(crosslinking with sulphur) rubber, such as a diene elastomer.
[0026] Flame spray pyrolysis is a method well known today which has
been essentially developed for the synthesis of ultrafine powders
of simple or mixed oxides of various metals (e.g., SiO.sub.2,
Al.sub.2O.sub.3, B.sub.2O.sub.3, ZrO.sub.2, GeO.sub.2, WO.sub.3,
Nb.sub.2O.sub.5, SnO.sub.2, MgO, ZnO, Ce.sub.xZr.sub.(1-x)O.sub.2),
having controlled morphologies, and/or their deposition on various
substrates, this being the case starting from a great variety of
metal precursors, generally in the form of sprayable organic or
inorganic liquids which are preferably non-flammable; the liquids
sprayed into the flame, on being consumed, give off in particular
metal oxide nanoparticles which are sprayed by the flame itself
onto these various substrates.
[0027] The principle of this method has been recalled, for example,
in the recent publication (2011) by Johnson Matthey entitled "Flame
Spray Pyrolysis: a Unique Facility for the Production of
Nanopowders", Platinum Metals Rev., 2011, 55, (2), 149-151.
Numerous alternative FSP processes and reactors have also been
described, by way of examples, in the patents or patent
applications U.S. Pat. No. 5,958,361, WO 01/36332 or U.S. Pat. No.
6,887,566, WO 2004/005184 or U.S. Pat. No. 7,211,236, WO
2005/103900, WO 2007/028267 or U 8 182 573, WO 2008/049954 or U.S.
Pat. No. 8,231,369, US 2009/0123357, US 2009/0126604, US
2010/0055340 or WO 2011/020204.
[0028] However, to the knowledge of the Applicant Companies, the
FSP method had never been used to date for the in situ
sulphurization (that is to say, without requiring an external
contribution of metal) of metal surfaces, in particular of surfaces
based on copper, zinc or brass.
[0029] Metal M sulphides are understood to mean, in a known way,
compounds which can be denoted symbolically by M.sub.xS.sub.y (in
this general expression, depending on the applicable stoichiometry
and the nature of the metal, x and y, which are identical or
different, are nonzero integers identical to or different from 1)
or also can be denoted more simply as M.sub.xS (in this expression,
y being conventionally equal to 1, x is then an integer or decimal
number other than zero). It is obvious that this definition also
encompasses the cases where several different metals (M then
representing M1, M2, M3, and the like) are present at the surface
of the treated body, in the form of mixed sulphides (for example of
the M1.sub.x1M2.sub.x2M3.sub.x3S.sub.y type) of these various
metals.
[0030] Preferably, the surface metal M, by definition capable of
forming sulphides, is chosen from the group consisting of aluminium
(Al), silver (Ag), cobalt (Co), copper (Cu), tin (Sn), iron (Fe),
manganese (Mn), molybdenum (Mo), nickel (Ni), zinc (Zn) and the
metal alloys (for example binary, ternary or quaternary) comprising
at least one of these elements, these metal alloys consequently
being themselves capable of forming sulphides.
[0031] Preferably, the surface metal is chosen from the group
consisting of cobalt, copper, tin, iron, molybdenum, nickel, zinc
and the metal alloys comprising at least one of these elements.
[0032] More preferably still, the surface metal is chosen from the
group consisting of copper, zinc and the alloys comprising at least
one of these elements, that is to say alloys of Cu and/or Zn.
Mention will in particular be made, as metal elements which can
participate in the composition of such alloys, in addition to Cu
and/or Zn, of those chosen from the group consisting of cobalt,
tin, iron, molybdenum and nickel.
[0033] The surface metal is more particularly chosen from the group
consisting of copper, zinc and brass (Cu/Zn alloy), thus by
definition a metal capable of forming zinc sulphide (ZnS) or copper
sulphides (Cu.sub.xS, x here being an integer or decimal number
varying from 1.0 to 2.0).
[0034] The invention applies very particularly to brass, in
particular in the applications where the body treated by the
process of the invention is a metal reinforcer intended to adhere
subsequently to an unsaturated rubber matrix, such as natural
rubber, in order to form a metal/rubber composite, such as those
normally encountered in articles made of rubber, such as tyres.
[0035] "Sulphur precursor" or "sulphur-donating precursor", capable
of generating hydrogen sulphide (H.sub.2S) during its combustion in
the flame, is understood to mean, in the present patent
application, the product which is sprayed into the flame, whatever
the form or the presentation of this product.
[0036] It can be sulphur, a sulphur-comprising starting compound or
else a more complex product, for example a composition or a
solution, comprising sulphur in whatever form. It might be solid,
for example in the form of a powder, sprayed and melted directly in
the flame; it is preferably liquid at ambient temperature
(20.degree. C.). It can be organic or inorganic and monosulphide,
disulphide or polysulphide.
[0037] If a sulphur-comprising starting compound is used and if the
latter is not organic as such, it can advantageously be dissolved
or dispersed in an organic solvent (such as, for example, benzene,
cyclohexane, styrene or toluene) or an organic liquid, so as to
form a sulphur-donating precursor which can then be described as
organic. In the same way, if this sulphur-comprising starting
compound is not liquid (for example in the solid sulphur form), it
can advantageously be dispersed in an organic solvent or another
appropriate liquid so as to form a sulphur-donating precursor which
can be described as liquid.
[0038] The sulphur precursor is preferably an organic compound more
preferably comprising from 1 to 15 carbon atoms; it can be
monosulphide, disulphide or polysulphide, in particular of the
saturated or unsaturated aliphatic or cycloaliphatic type, or of
the aromatic type. More preferably still, it is an organic compound
which is liquid at ambient temperature, in particular of the
non-flammable type.
[0039] More preferably, the sulphur precursor is an organic
compound devoid of a nitrogen atom; more preferably still, it is
also devoid of an oxygen atom and very preferably the sulphur
precursor is an organic compound devoid of a heteroatom other than
sulphur. Thus, very preferably, the sulphur precursor is an organic
compound consisting exclusively of carbon, sulphur and hydrogen
atoms.
[0040] Mention may be made, among the numerous examples of liquid
organic compounds corresponding to the preferred definitions above,
of the compounds of formulae I to XXIV below, and their
derivatives, that is to say the compounds including, in their
chemical structure, the entities of formulae I to XXIV.
##STR00001## ##STR00002## ##STR00003##
[0041] More preferably still, the organic sulphur-donating
precursor is chosen from the group consisting of the following
compounds: [0042] thiophene (formula XIV) and its derivatives
(e.g., formula XIVa or XIVb); [0043] thiocarbonyl compounds (e.g.,
formulae XII, XXI, XXII, XXIII and XXIV); [0044] aliphatic or
aromatic thiols (e.g., formulae XV and XVI); [0045] aliphatic or
aromatic organic disulphides (e.g., formulae VI, VIII, XVII, XVIII,
XXIV); [0046] aliphatic or aromatic organic polysulphides (e.g.,
formulae XI and XXI); [0047] acyclic thioethers (e.g., formulae
XVI, XIX and XX) or cyclic thioethers, such as: [0048] thiiranes
(formula I) and its derivatives, [0049] thietane (formula II) and
its derivatives, [0050] thiolane (formula III) and its derivatives,
(e.g., formula Ma), [0051] thiane (formula IV) and its derivatives,
[0052] thiepane (formula V) and its derivatives, [0053] dithiolanes
(e.g., formula VII) and their derivatives, (e.g., formula VIIa),
[0054] trithiolane (formula VIII), and its derivatives, [0055]
dithianes (e.g., formula IX) and their derivatives, (e.g., formulae
IXa and IXb), [0056] trithianes (e.g., formula X) and their
derivatives, (e.g., formula Xa); [0057] thioesters (e.g., formula
XXIII); [0058] and the mixtures of such compounds.
[0059] More preferably still, this organic sulphur-donating
precursor is chosen from the group consisting of thiophene and its
derivatives, aliphatic or aromatic organic disulphides, aliphatic
or aromatic organic polysulphides, acyclic or cyclic thioethers,
and the mixtures of such compounds.
[0060] More particularly still, the sulphur-donating precursor is
thiophene or a thiophene derivative. This sulphur-comprising
organic compound, of formula C.sub.4H.sub.4S, which is volatile and
nonflammable, has here the direct function of sulphur donor; it can
also advantageously be used as organic solvent.
[0061] The FSP treatment can be carried out at any temperature, of
course lower than the melting point of the metal M. It might be
carried out at a temperature, in particular at a temperature close
to ambient temperature (23.degree. C.). However, in order to
optimize the duration and the effectiveness of the treatment, the
temperature of the surface metal, during the sulphurization, is
preferably between 50.degree. C. and 500.degree. C., more
preferably between 100.degree. C. and 350.degree. C.
[0062] The appended FIG. 1 illustrates, highly diagrammatically,
without observing a specific scale, the principle of the FSP (flame
spray pyrolysis) process of the invention and also an example of a
device (1) which can be used in the implementation of this
process.
[0063] The principle of the method is to inject a sulphur-donating
precursor (P) and then to comminute it in a flame using a
propellant and oxidizing gas; the combustion of the precursor (P)
in the flame (F) makes possible the formation of the targeted
entity (in this case, in accordance with the invention, hydrogen
sulphide H.sub.2S).
[0064] The device 1 of this example essentially comprises three
respective feeds: [0065] atomization means (10, 11), comprising at
least one capillary (10) and one nozzle (11) for feeding with fuel
or precursor (P), in this instance in a liquid form, the role of
which is to eject and comminute the precursor in the form of fine
droplets (12), the shape of the jet being dictated by the specific
atomization conditions; these atomization means (10, 11) are, of
course, preceded by a pump of appropriate proportions (in the
examples which follow, a gerotor rotary volumetric micropump, model
mzr-2905 from HNP Mikrosysteme GmbH), not represented in this
figure for simplicity; [0066] a feed of oxidation gas (13) (using a
pump not represented in the diagram) which ejects the oxidizing gas
into the outlet region of the feed nozzle (11), the role of which,
on the one hand, is to propel the droplets (12) into the flame (F)
and, on the other hand, to oxidize the precursor (P) in order to
convert it into hydrogen sulphide (H.sub.2S); [0067] finally, a
feed of support gas (ignition and combustion gas) (14), for example
a mixture of methane and oxygen, which feeds two small flames
(secondary flames) (15) for their part intended to ignite the
droplets (12) of precursor (P) for formation of the main flame
(F).
[0068] It is thus the flame (F) generated by the combustion gas
(14) and the oxidizing gas (13) which constitutes the FSP reactor,
a thermal reactor at very high temperature since the temperature
inside the flame (F), depending on the preferred operating
conditions given above, is greater than 500.degree. C., for example
between 600.degree. C. and 800.degree. C.
[0069] It is the combustion in the flame (F) of the
sulphur-comprising precursor (P) in the presence of oxygen (13)
which will generate the targeted hydrogen sulphide (16) and also
other gaseous entities depending on the specific nature of the
precursor used, these entities preferably being neutral or
reducing, as explained in more detail below.
[0070] A person skilled in the art will understand that the FSP
sulphurization treatment is in this instance carried out in an
atmosphere "depleted in oxygen" ("reducing flame" or "reducing
atmosphere" conditions), that is to say with the minimum of oxygen
necessary (the trend is towards incomplete combustion), without
which there will be no formation of hydrogen sulphide (and of other
gaseous reducing entities); preferably, the oxygen content of the
combustion chamber (measured immediately at the chamber outlet) is
less than 200 ppm, in particular within a range from 5 to 200 ppm,
preferably less than 100 ppm, in particular within a range from 10
to 100 ppm. The whole of the combustion chamber (in the examples
which follow, a simple fitted-out closed glove box) is thus swept
with a stream of inert gas, such as nitrogen. The height of the
main flame (F) is typically between 5 and 10 cm.
[0071] The flame is placed, as a function of the desired intensity
of the treatment, at a variable distance from the surface (17) of
the metal M to be treated, which distance a person skilled in the
art can easily define as a function of the specific conditions for
implementing the invention. This distance, denoted "d" in FIG. 1,
measured between the base of the flame (F) and the surface (17) of
the metal M, is preferably between 50 and 250 mm, in particular
between 60 and 180 mm.
[0072] It is the flame (F), by virtue of its kinetic energy, which
acts as propellant for the gas H.sub.2S (16) towards the surface
(17) of the metal M to be treated. In other words, in accordance
with the invention, a gas (H.sub.2S) is generated which is
projected and which chemically attacks the metal M with this
gas.
[0073] In this instance, which is a distinguishing feature of the
process of the invention, metal sulphides M.sub.xS are created by
erosion, without any external contribution of metal being
necessary, in contrast to the FSP techniques of the prior art
(synthesis of metal oxides) mentioned in the introduction to the
present account.
[0074] The duration of the treatment is typically from a few
seconds to a few minutes, preferably from a few seconds to a few
tens of seconds, depending of the specific conditions for
implementing the invention, according in particular to the nature
of the metal M, according to whether the body treated is stationary
or, on the contrary, is moving in front of the flame at a given
rate which can, for example, vary from a few tens of cm/min to
several tens of m/min.
[0075] The plants which can be used for the implementation of the
process of the invention are, of course, not limited to the
examples and embodiments described above.
[0076] Thus it is that, in order to treat large surface areas
and/or large amounts of parts, such as, for example, wires, cords,
films or plates, in particular at high speed, the plants used might
comprise a combination of several flames in line.
[0077] The invention also applies to the cases where other entities
formed in the flame (F) or another (at least one other) flame, in
particular nongaseous entities, such as, for example, particles of
metal or of metal oxide, contributed by precursors other than the
sulphur-donating precursor described above, will be sprayed,
simultaneously or nonsimultaneously, at the surface of the metal M
to be treated.
[0078] FIG. 2 represents, highly diagrammatically, the surface
condition of the metal M once it has been treated by FSP as
indicated above.
[0079] Subsequent to the chemical attack (erosion) by the gas
H.sub.2S, a highly specific roughness which may be described as
"nanoroughness" (by analogy with what is customarily referred to as
microroughness) is obtained: the surface (17) of the metal M has
been provided with a multitude of metal sulphide M.sub.xS
nanoparticles (in this case, Cu.sub.xS and ZnS in the case where M
is brass) of nanometric size, generally agglomerated in the form of
dendrites (18) themselves in nanometric size.
[0080] "Nanoparticles" are understood to mean, by definition,
particles, the size (diameter or greater dimension in the case of
anisometric particles) of which is greater than 1 nm (nanometre)
and less than 1 .mu.m (micrometre), in contrast in particular to
particles referred to as microparticles, the size of which is equal
to or greater than 1 .mu.m.
[0081] The nanoparticles described here can be provided in the
individual isolated state; usually, they are provided in the form
of agglomerates of such nanoparticles, also known as "dendrites".
Such agglomerates (clusters, packets) of nanoparticles are capable,
in a known way, of deagglomerating to give these nanoparticles
under the effect of an external force, for example under the action
of mechanical work. "Nanoparticles" should thus be understood as
meaning the indivisible assembly (i.e., which cannot be cut,
divided or split) which is produced in the formation, the synthesis
or the growth of the nanoparticles.
[0082] The nanoparticles as such (individual) have a mean size
(diameter or greater dimension in the case of anisometric
particles) which is preferably between 5 and 400 nm, more
preferably within a range from 10 to 200 nm, in particular within a
range from 10 to 100 nm (average calculated by number).
[0083] With regard to the agglomerates or dendrites of
nanoparticles, their mean size (diameter or greater dimension in
the case of anisometric dendrites) is preferably between 20 and 800
nm, more preferably within a range from 30 to 600 nm, in particular
within a range from 40 to 400 nm (average calculated by
number).
[0084] By virtue of FSP sulphurization treatment of the invention,
the aim of which, it should be remembered, is to cause the surface
metal to adhere firmly to a matrix of ethylenically unsaturated
(thus crosslinkable with sulphur) polymer, a body (in particular a
reinforcer, such as wire, cord, film or plate) having an at least
partially metallic (in particular brass-coated) surface is obtained
which can be described as "ready-for-use": at this stage, this body
or reinforcer is devoid of any polymer or rubber matrix at its
periphery; it is ready for use as it is, without any adhesion
primer or adhesion activator, such as a cobalt salt, as reinforcing
element of an unsaturated rubber or polymer matrix, such as natural
rubber.
[0085] FIG. 3 gives a diagrammatic representation of the anchoring
of a rubber matrix (19) around the dendrites (18) previously formed
by virtue of the FSP surface treatment, with an of course highly
simplified representation of the metal/rubber interphase, once the
surface (17) of the metal (M) has come into contact with the rubber
matrix (19) (for example a rubber composition based on a diene
elastomer, such as natural rubber) and once the assembly has been
subsequently vulcanized.
[0086] The presence of these nanoparticles and dendrites (18) of
metal sulphides M.sub.xS makes it possible to obtain a strong and
permanent adhesion between the metal M and the rubber, as is
demonstrated in particular in the implementational examples which
follow.
5. IMPLEMENTATIONAL EXAMPLES OF THE INVENTION
Test I
[0087] During a first test, a plate made of brass-coated (Cu/Zn:
60/40) carbon steel was subjected to an FSP treatment according to
the invention, carried out using the device represented
diagrammatically in FIG. 1 (closed glove box swept with a stream of
nitrogen) in an atmosphere depleted in oxygen (O.sub.2 content of
the combustion chamber, measured immediately at the chamber outlet,
of less than 100 ppm).
[0088] The plate, with a thickness equal to approximately 3 mm
(thickness of the brass layer of between 200 and 500 nm) was
immobile and was treated for a period of time of 5 s at a distance
"d" from the flame equal to approximately 70 mm.
[0089] The combustion chamber 1 was in this instance fed
continuously with approximately 5 ml/min of pure thiophene
(precursor P), 5 l/min of oxygen (oxidation gas 13) and a mixture
of methane and oxygen (support gas 14) (CH.sub.4: 1.2 l/min;
O.sub.2: 2.2 l/min). The height of the flame (F) was between 6 and
7 cm and the temperature inside the flame was equal to
approximately 700.degree. C.
[0090] In the present implementational example and for the various
operating conditions above, the combustion and the oxidation of the
precursor P (thiophene) resulted in a gas composition, measured
immediately at the chamber outlet by mass spectrometry (Pfeiffer
Quadstar 100), which was as follows: approximately 10 ppm of
H.sub.2S, 500 ppm of SO.sub.2, less than 100 ppm of O.sub.2, 1% of
H.sub.2O, 1% of H.sub.2 and 0.5% of CO.sub.2 (mol %).
[0091] It should be noted that, in other tests, the thiophene was
used in the state diluted (for example at 10% by weight) in an
organic solvent (for example a mixture of 1 part of THF per 2 parts
of 1,2-ethylhexanoic acid), this being done while keeping constant
the ratio of the volume of dispersing gas (5 l/min of O.sub.2) to
the volume of fuel (5 ml/min of thiophene or of thiophene
equivalent in the case of a dilution).
[0092] The plate made of brass-coated steel, thus treated by FSP,
was then, once cooled, sandwiched between two layers of a
conventional rubber composition for a passenger vehicle tyre belt
reinforcement, based on natural rubber, on carbon black and silica
as filler and on a vulcanization system (sulphur and sulphenamide
accelerator), this composition being devoid of cobalt salt.
[0093] The metal/rubber composite test specimen thus prepared was
then placed under a press and the combination was cured at
165.degree. C. for 30 min under a pressure of 20 bar.
[0094] After vulcanization of the rubber, excellent adhesive
bonding between the rubber matrix and the metal plate was obtained,
despite the absence of cobalt salt in the rubber matrix: this is
because, during peeling tests carried out both at ambient
temperature (23.degree. C.) and at high temperature (100.degree.
C.), it was found that the failure had occurred systematically in
the rubber matrix itself and not at the interface between metal and
rubber.
[0095] It is essential to note that, during comparative tests
carried out under the same conditions (no cobalt salt in the rubber
matrix) apart from the absence of the FSP treatment according to
the invention, it was found that the brass plate did not adhesively
bond to the rubber.
Test II
[0096] Other FSP treatments in accordance with the invention have
been carried out under the same flame conditions as above, this
time on wires made of brass-coated carbon steel (diameter of
approximately 0.30 mm) having high strength (for cords of
"Steelcord" type for tyres).
[0097] During the treatment, these wires progressed forward
continually, by virtue of a motorized robot, at a uniform speed (in
this case, in these examples, at 60 cm/min) and at a distance "d"
from the base of the flame which could vary automatically within a
broad range of values.
[0098] The appended FIG. 4 reproduces the three SEM photographs (5
kV; magnification 185 000) which were taken at the surface of the
wires thus treated. The surface (brass M) of the plate, during its
treatment, was located respectively at a distance "d" equal to 200
mm (FIG. 4A), 150 mm (FIG. 4B) and 100 mm (FIG. 4C) from the
flame.
[0099] With regard to these reproductions of FIG. 4, 1 cm is
equivalent to approximately 200 nm (nanometres). A more or less
marked surface nanoroughness, existing in the form of more or less
agglomerated nanoparticles, is visible on each of these three
photographs, for which nanoparticles it can be easily seen that the
size, typically from a few tens (FIG. 4A) to a few hundreds of nm
(maximum of approximately 400 nm in these examples) (FIGS. 4A and
4B), increases when the distance "d" decreases, that is to say when
the intensity of the FSP treatment increases.
[0100] The surface of the wires thus treated was analysed by EDS (5
kV). This EDS (Energy Dispersive Spectroscopy) technique makes it
possible, it should be remembered, to determine the % by weight of
each element present at the surface of the sample analysed. It has
been used to measure the degree of sulphurization of the surface
after the FSP treatment: for the three conditions above
(respectively FIGS. 4A, 4B and 4C), the sulphur content measured
was approximately 5.5%, 12% and 25% by weight respectively. The
analysis on an untreated control wire indicated the absence of
sulphur (at any rate, below the detection limit).
Test III
[0101] The appended FIG. 5 reproduces an SEM photograph (5
kV--magnification 100 000) taken at the surface of a plate made of
brass-coated carbon steel identical to that of Test I but which has
been subjected to a treatment in accordance with the invention this
time comprising 2 consecutive FSP stages: [0102] a first stage of
synthesis and deposition of copper nanoparticles, according to a
method of deposition (by external contribution of metal) known per
se, as described in the introduction to the present account; the
copper precursor consisted of a solution of copper ethylhexanoate
in an inorganic solvent (THF); then [0103] a second stage in
accordance with the invention of sulphurization of the surface thus
copper-coated beforehand, according to the FSP method (attacked by
H.sub.2S for formation of copper sulphides Cu.sub.xS) described in
Test I (same operating conditions). The plate, during its
treatment, was located at a distance "d" equal to approximately 70
mm from the flame.
[0104] In this reproduction of FIG. 5, 7 mm is approximately
equivalent to 200 nm. This photograph itself also very clearly
demonstrates the presence of a particularly fine surface
nanoroughness in the form of nanoparticles, agglomerated in the
form of dendrites; it can be easily seen that the mean size of
these nanoparticles, measured in the plane of the photograph, is
markedly less than 200 nm.
[0105] The presence of these dendrites (18) of metal sulphides
(Cu.sub.xS) makes it possible to obtain a strong and permanent
adhesion between the metal M and the rubber (19) by virtue of its
strong mechanical and chemical anchoring, as illustrated in FIG. 3
commented on above. Thus, cobalt salts or other metal salts can be
dispensed with as adhesion promoters in the rubber compositions
intended to be connected to brass-coated metal reinforcers.
[0106] The process of the invention exhibits numerous advantages:
[0107] the amount of sulphur (in the form of sulphur-comprising
nanoparticles and dendrites) deposited at the surface 17 of the
metal M (thus at the metal/rubber future interphase in rubber
reinforcing applications), and the size and the geometry of the
nanoparticles and dendrites of metal sulphides (18) can be easily
adjusted by the operating parameters of the FSP reactor; [0108]
this being the case without having to intervene with regard to the
formulation, in particular with regard to the vulcanization system,
of the rubber matrix intended to subsequently coat the metal;
[0109] large amounts of metal sulphides M.sub.xS, in particular
copper and/or zinc sulphides, can thus be deposited on the surface
of the metal M (in particular brass) without risk of otherwise
penalizing the rubber properties; [0110] nanoparticles of metal
(e.g. copper, zinc, cobalt) other than nanoparticles of metal
sulphides (M.sub.xS) can advantageously be added, incorporated in
the dendrites of sulphides for the purpose of further improving, if
need be, adhesive performance of the reinforcer.
* * * * *