Note: Descriptions are shown in the official language in which they were submitted.
~62~
This lnvention relates to a method of treating surfaces
and, more especially to a method of treating surfaces which are
suitable for bonding to polymers.
It is known that oxidic surfaces may be treated with
silanes containing mercapto groups in order to improve bonding
thereto of a sulphur-crosslinked rubber. Unfortunately, the use
of silanes containing mercapto groups has a drawback, which is
that -the oxidic surfaces pretreated with the silanes and mixed
with the rubber, show undesirable and uncontrollable reactivity
characterized by a premature vulcanisation. This premature ~ i
vulcanisation occurs is a short time, which complicates control- ;~
led, uniform processing of the rubber compositions.
Attempts have already been made to obviate these disad-
vantages by using silanes con-tainlng tetrasulphide groups, of
the general formula (Ro)3Si-R'-S4-R'-Si(oR)3 wherein R is an
alkyl radical and R' is an alkylene radical. Although this ~ -
procedure has resulted in an improvement in the processing
properties of the rubber compositions, it has the drawback that
the sulphur bridges containing silanes are difficu1t to produce -
in the pure form in which they have to be used. - -
According to the present invention there is provided
a method of treating a surface, which method comprises the steps
of applying to the surface an aqueous solution comprising from
O.Ol to 60% of a mercaptosilane of the general formula:
k 3-x ;~ ~i
in which R represents an alkyl or alkoxyalkyl radical having from
1 to 8 carbon atoms, R' represents a monovalent hydrocarbon
radical having from 1 to 4 carbon atoms, R" represents a divalent
'':' .' ~ . ,.
C.`,, ' ~ ~
f',-,~,.''
;297~
hydrocarbon radical having from 1 -to 10 carbon atoms, _ is
. -
0 or 1 and x is 0,1, 2 or 3, the radicals represented by Rbeing identical or different when x is grea-ter than l; oxidizing
the mercaptosilane; and drying the surface to obtain the desired
treated surface.
The radieal represented by R" may be linear or branched
and preferably has from 2 to 4 earbon atoms. This radieal option-
ally eontaining a hetero-atom.
Suitable solvents for the aqueous solution include
water alone and aqueous alcohols. In the ease of alcohols, it
is preferred to use those having from 1 to 4 carbon atoms.
Another water-immiscible or water-emulsifiable organic solvent
which has a dissolving effect upon the mercapto silane, may
also be used.
When alcohols or other organie solvents are used,
it is important that they be mlxed with water so that silanol
groups may form in the solution.
~ The eoncentration of the mercapto silane in the aqueous
solution is governed by the speeific surface of the material to
be treated. It may vary from 0.01% to 60~, the range from 0.1
to 10~ being preferred.
In one embodiment of the invention the mereaptosilane
is oxidized with oxygen in the presence of a catalyst, for
example iron or copper. In a preferred embodiment the solution
eomprises a mereaptosilane and an oxidizing agent eapable of
..'
oxidizing the mereaptosilane to a disulphide. , -
The eoneentration of the oxidizing agent is seleeted
in aeeordanee with the concentration of -the mercapto silane.
The oxidizing agent is preferably present in an excess relative
to the stoichiometrically necessary quantity. The stoichiome-
trieally neeessary quantity is~the quantity theoretieally requir-
ed for oxidizing mereaptans into disulphides. The preferred ~ -
range for _ "
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1C~62971
the excess of oxidizing agent is compri~ed between 10 and 50%
of the stoichiometrically necessary quantity.
In addit~on to atmospheric oxygen acting in conjunction
with a catalyst (for example Fe or Cu), suitable oxidizing
agents are hydrogen peroxide or o~idiæing agents of the type
described in Houben-Weyl "Methoden der Organishen Chemie",
4th Edition (1955), Vol. 9, pages 59 to 65. When applying the
solutions to the sur~aces to be treated, it is possible to work
in the acid or alkaline condition, depending upon the oxidizing
agent used or the mercapto sila~e used.
~ he surface which may be treated by the method according
to the invention may be oxidic or metallic. The~e include both
natural mineral oxidic surfaces and also surfaces of synthetically
produced products. ~hey also include surfaces of silica and
carbonate-containing minerals. Examples of materials which may
be subjected to surface pretreatment by the process according to ,~ `~
the invention include quartz, mica, asbestos, aluminium silicates,
kaollns, silica~, iron oxide, titanium o~ide, chalk, glass fibres,
iron~copper, zinc, aluminium and also alloy~ such as brass and
bronze~
.: . . .. . .
When treated by the method according to the invention ;~
the surfaces may be bonded to a polymer. Polymers, whose adhesion ~;
to the above-mentioned surfaces i~ improved by the pretreatment
according to the invention, include natural and synthetic rubbers,
polymerisation product~, such as PVC, and polycondensation and
polyaddition products, such as resol resins, furan resins, epoxide
resins or polyurethane resin~.
~ he treatment of the above-mentioned surface~ with the
solution according to the invention i9 preferably carried out
at a temperature below 30C in order to a~oid undesirable further
oxidation of the di~ulphlde bond. It is also advisable to use
freshly prepared solutio~s of mercapto silane and oxidizing age~t.
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~062~71 :
~he ~olution may be applied to the surfaces by any of
the standard coating technique~, for example dip-coating, spray-
coating or spread-coating. After the ~olution has been applied,
the material silanized in this way is ~ubjected to a dr~ing
process.
~XAMPIæ ~ '
~ .
Water-sized glass filaments were immersed for 1 minute
in a 0.5% aqueou3 alcoholic solution of -mercapto propyl triethoxy
silane containing 0.2% of hydrogen peroxide and having a pH-value
of about 8. ~he filaments were removed and le~t to drain a~d
then dried for 15 minutes at 130GC. ~he solution was examined
for mercaptan immediately before coating, the result being
negative. ~he sized gla~s filaments were then dipped into an
epoxide resin and processed into round glass fibre rein~orced
,: , ,
bars. ~he bars obtained were hardened for 17 hours at 130C.
~he flexural strength of the hardened bars was
determined in accordance with DIN 53432 after 72 hours storage
in boiling water.
~he results are set out in the following ~able:
,; . . .
Flexural ~trength of glass-fibre-rei~forced
epo~ide resin roundbars (kp/cm2)
Adhesion promoter without ¦ with
3torage in water
. _ _ ..
a) none 9,500 4,500
b) -aminoprop~l triethoxy
sila~e 9,600 7,600
c) oxidation produot of
HS-(CH2)3-Si(OC2H5)3 10,400 8,300 i
: , . , ~ .
~est~ a) and b) are comparison tests. ~he ~xample
shows that the oxidation of the mercapto silane i~ solution gives
products which show an improved adhesion-promoting effect, u r
: .
clthough ro mcroapto groups are preoc~t.
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