Note: Descriptions are shown in the official language in which they were submitted.
~ ~1. 5126~
PROCESS FOR INCREASING THE ~TRENGTH OF THE
BOND BETWEEN RUBBER AND METALS
.. .. _ . ... . .
This invention relates tc a ~rocess for lncreasing
the bond strenath between rubber and metals wherein
cobalt phenolates are added to the rubber.
Many technical rubber articles such as
tyres, conveyor belts or high pressure tubes are provided
with reinforcing inserts of high carbon steel, frequently
ir. the form of steel cord.
To ensure high performance and long life of the
articles, a firm and durable bond between the metal and
rubber is necessary.
It is only possible to achieve this withou-t the
addition of an adhesive if the filaments of the steel
cord are plated with a thin layer of ~-brass, or some
other alloy containing zinc and copper as its main
constituents, or pure zinc.
The plated cord is directly incorporated by
vulcanization in the rubber mixture, which generally
contains additives to increase the strength of
the bond.
The most usual additives for improving the bonding
power, hereinafter referred to as "bonding agentsl', may
be divided into two groups according to their chemical
structure.
The first group includes all bonding agents which
; 25 only act as multicomponent systems. These all contain
highly active silicates.
The other components are resorcinol or resorcinol-
formaldehyde condensation products and formaldehyde-
releasing compounds such as hexamethylenetetramine,
30 etherified or esterified methylol melamines in various
degrees of etherification or esterification, and their
condensation products (German Auslegeschriften No.
1,301,475 and No~ 1,301,478).
Although these systems provide good bonding
35 Le A 20 688
.~
s
F - 2 -
characteristics, they occasionally produce vapours and
noxious odours in the process of vulcani~ation and they
considerably impair the facility with which the
substances can be processed in mixing machines, e.g.
on roller mixers, since resorcinol tends to undergo
sublimation, particularly at temperatures near its
melting pointu
The second group includes organometallic compounds,
especially cobalt compounds. Cobalt soaps in
particular, such as those also conventionally used as
desiccating agents in the lacquer industry, have been
used for some time~
Various cobalt salts, e.g. cobalt stearate, cobalt
linolate and cobalt naphthenate, are discribed in French
Patent No. 1,323,934. Organic boron compounds contain-
ing cobalt as d~scrihed US Patent No~ 3,296,242 are
also suitable. Copper, nickel, lead and zinc are
also suitable metals (see German Offenlegungsschrift ~o.
2,303,674 and ~S Patent No. 4,154,911).
There are marked differences between the effects
produced by the bonding agents of the first group and o~
the second group.
When organometallic compounds are added to the
rubber mixture, they generally improve the bond between
the metal and rubber after vulcanization and have a long
lasting effect in delaying corrosion of the metal
component.
Their main disadvantage, however, is that the strength
of the bond may be severely reduced, particularly under
conditions o high temperature vulcanization (180 to 240C);
reversion is also a serious problem.
Bonding agents belonging to the irst group provide a
rubber-metal bond which has better resistance to
reversion and the bonds are also relatively resis-
tant to the ef~ects o heat and mois~ure.
Le A 20 688
.. ~, . . , ~
%~
The bonding mixtures are therefore frequently mixed with
bonding agent combinations, using either individual components of
a bonding system or the whol.e bonding system (German Offenlegungs-
schriften No. 1~720~144 and 2~841~401)o
It would be deslrable to provide a bonding system which
shows little or no reversion after prolonged ageing by heat and is
subject to little or no loss of bond strength.
I~ has now surprisingly been found that the bond between
rubber and metals such as raw steel or steel plated with brass or
zinc may be substantially improved and good resistance to ageing
and reversion may be obtained by adding a phenolic cobalt
compound.
Accordingly, an aspect oE the present invention provides
a process for increasing the strength of the bond between rubber
and metal by the addition of a bond-increasing compound, followed
by vulcanization, wherein a compound corresponding to formula (-1)
or formula ( 2)
~3 ~ 2 Co . 2 H20 (1
K4 R5
or
2 ~2
~ C o - --O
X ~ (2)
R7 ~8 Rg Rlo
is added as the bond-increasing compound to the rubber in
quantities of 0.1 to 20 parts hy weight per 100 parts by weight of
rubber, the groups in the formulae having the following meaning:
Rl to Rl1 each denotes hydrogen, hydroxyl, Cl-Clg-alkyl,
Cs-C12-cycloalkyl, Cl-Cl~-alkylthio, C6-C14-aryl,
C6-C14-aryl-Cl-C4-alkyl, C~-Clg-alkoxy, Cs-Cl2-cycloalkoxy,
C6 C14-aryloxy, C6-Cl~-aryl-Cl-C4 alkyloxy or halogen, and X
denotes Cl-C4-alkylene, sulfur, dithio, oxygen or N-Cl-C4-alkyl.
The bond-increasing compound is added preferably from
0.3 to 10 parts by weight in particular from 0.5 to 5 parts by
weight, per 100 parts by weight of rubber.
These compounds do not manifest the disadvantages of the
above mentioned bonding agents containing metal.
Another aspect of the invention provides a rubber com-
position which comprises the compound of formula (1) or (2).
Still another aspect of the invention provides an
article comprising a reinforcing metal bonded to vulcanized rubber
which comprises the compound of formula tl) or (2).
An adclitional increase in the bond strength may be
~ .
obtained by adding a formaldehyde-releasing compound in quantities
of 0.01 to 10 phr, preferably 1 to 3 phr, to the rubber in addi-
tion to the compounds of formu]ae (1`1 and (2~.
In addition, resorcinol or its derivatives, such as,
for example, dimethoxybenzene, diacetoxybenzene, dibenzoyloxy-
benzene, dipropoxybenzene, dipropionyloxybenzene or di-(trimethyl-
silyloxy)-benzene, or sulphonic esters, phosphoric acid esters,
phosphorous acid esters, urethanes and carbonates or resorcinol
may be added to the rubber in quantities of from 0.01 to 10 parts
by weight, preferably from 0.5 to 5 parts hy weight, per 100 par-ts
by weight of rubber.
The resorcinol compound may be added to the rubber
separately or in combination with the formaldehyde-releasing com-
pound, or resorcinol precondensed with formaldehyde may be added
to the rubber in quantities of from 0.01 to 10 parts by weight,
preferably from 3 to 5 parts by weight, per 100 parts by weight of
rubber, the precondensate used containing 1 to 3 mol of formal-
dehyde per mol of resorcinol.
Silicates may also be added in the usual quantities.
The groups Rl to Rll in formulae (1) and (2) have the
following meaning and may be identical or different:
hydrogen, hydroxyl Cl-Clg-alkyl, Cs-C12-cycloalkyl,
Cl C16-alkylthio, C6-C14-aryl, C6-C14-aryl-Cl-C4-alkyl, Cl-C18-
alkoxy, Cs-C12-cycloalkoxy, C6-C14-aryloxy, C6-C14-ary]-Cl-C4-
alkyloxy, and halogen (Cl, Br or I, preEerably Cl).
In formula (1), the groups Rl, R2, R4 ancl Rs are prefer-
ably hyclrogen and R3 is preferably C6-C12-alkyl or C6-C14-aryl-Cl-
(:4-a:Lk,yl .
- 4a -
~ 5 --
F~
In formula 2 r the groups R6, R7, Rlo and Rll are
preferably hydrogen and the groups R8 and Rg preferably
Cl-C4~alkyl, benzyl or halogen or R6, R8~ Rg and Rll are
preferably Cl-C~-al~yl or halogen and the groups R7 and
Rlo are preferably hydrogen, Cl-C4-alkyl, phenyl or halogen.
X denotes Cl-C4--alkylene such as methylene, ethylidene,
propylidene or butylidene, or sulphur, dithio, oxygen
or N-Cl-C~ alkyl-
The compounds of formulae 1 and 2 may be present as
isomeric mixtures.
The groups Rl to Rll may have the following specificmeanings:
hydrcgen, methyl, ethyl, propyl, isopropyl, n-butyl,
sec.-butyl, isobutyl~ tert.-butyl, n-pentyl, isopentyl,
sec.-pentyl, neopentyl, n-hexyl, isohexyl, sec.hexyl,
cyclohexyl, n-heptyl, isoheptyl, tert.-heptyl, octyl,
2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyi,
tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,
methylcyclohexyl, cyclohexylmethyl, naphthyl~ anthracenyl,
naphthylmethyl, cycloheptyl, cyclooctyl, phenyl, benzyl
cyclononyl, cyclodecyl, cycloundecyl, and cyclododecyl.
The alkoxy and alkylthio groups may be the same as
those mentioned under the alkyl groups but with oxygen or
sulphur added.
The follo~ing compounds are mentioned as examples:
Compounds 2 to 43 may be present in the ortho-, meta-
or para-form or as mixtures of isomers.
Bis-(phenoxy)-cobalt dihydrate
Bis-(methyl-phenoxy)-cobalt dihydrate 2
30 Bis-(ethyl-phenoxy) cobalt dihydrate 3
Bis-~propyl-phenoxy)-cobalt-dihydrate 4
Bis-(isopropyl-phenoxy)-cobalt dihydrate 5
Bis-(butyl-phenoxy)-cobalt dihydrate 6
Bis-(pentyl-phenoxy)-cobalt dihydrate 7
~5
Le A 20 688
Bis-~tert.-butyl-phenoxy)-cobalt dihydrate 8
Bis-(isobutyl-phenoxy)-cobalt dihydrate 9
Bis-(secO-b~ltyl-phenGxy)-cobalt dihydrate 10
Bis-(hexyl-phenoxy)-cobalt dihydrate 11
Bis-(heptyl-phenoxy)-cobalt dihydrate 12
Bis-(octyl-phenoxy)-cobalt dihydrate 13
Bis-(2-ethylheptyl)-phenoxy cobalt dihydrate 14
Bis-(ncnyl-phenoxy)-cobalt dihydrate 15
Bis-(decyl phenoxy)-cobalt dihydrate 16
Bis-(undecyl-phenoxy)-cobalt dihydrate 17
Bis-(dodecyl-phenoxy)-cobalt dihydrate 18
Bis-(tridecyl-phenoxy)-cobalt dihydrate 19
Bis-(tetradecyl-phenoxy)-cobalt dihydrate 20
Bis~(pentadecyl-phenoxy)-cobalt dihydrate 21
Bis-(hexadecyl-phenoxy)-coablt dihydrate22
Bis-(heptadecyl-phenoxy)-cobalt dihydrate 23
Bis-(phenyl-phenoxy)-cobalt dihydrate 24
Bis-(benzyl-phenoxy)-cobalt dihydrate 25
Bis-(naphthyl-phenoxy)-cobalt dihydrate 26
Bis-(cyclohexyl-phenoxy)-cobalt dihydrate 27
Bis-(cycloheptyl-phenoxy)-cobalt dihydrate 28
Bis-(cyclononyl-phenoxy)-cobalt dihydrate 29
Bis-(cyclodecyi-phenoxy)-cobalt dihydrate 30
Bis-(cycloundecyl-phenoxy)-cobalt dihydrate 31
Bis-(cyclododecyl~phenoxy)-cobalt dihydrate 32
Bis-!phenoxylphenoxy)-cobalt dihydrate 33
Bis-(butyloxy-phenoxy)-cobalt dihydrate 34
Bis-(methoxy-phenoxy)-cobalt dihydrate 35
Bis-~decyloxy~phenoxy~-cobalt dihydrate36
Bis-(benzyloxy-phenoxy~-cobalt dihydrate37
Bis-(chloro-phenoxy)-cobalt dihydrate 38
Bis-(cyclohexyloxy-phenoxy)-cobalt dihydrate 39
Bis-(phenyl-thio-phenoxy)-cobalt dihydrate 40
,
Le ~ 20 6a8
~'
-- 7
Bis-(methylthio-phenoxy)-cobalt dihydrate 41
Bis-(butylthio-phenoxy)-cobalt dihydrate 42
Bi.s-(hydroxyphenoxy)-cobalt-dihydrate 43
(5,5'-Dimethyl-dlphenylmethane-2,2'-dihydroxy)-cobalt
dihydrate 44
(5,5'-Dichloro-diphenylmethane-2 r 2'-dihydroxy)-
cobalt dihydrate 45
(5,5',3,3'~tetramethyl diphenylmethane-2,2'-
dihydroxy)-cobalt dihydra-te 46
(5,5',3,3'-Tetramethyl-diphenyl-(l,l isobutane)-
2,2'-dihydroxy)-cobalt dihydrat~ 47
(5,5'-Dimethyl-diphenyloxy-2,2'-dihydroxy)-cobalt
dihydrate 48
(5,5'-Di-cyclohexyl-diphenylmethane-2,2'-dihydroxy)
cobalt dihydrate 49
Bis-l2-naphthoxy)-cobalt dihydrate 50
Bis-(2,4-di-tert.-butyl-phenoxy)-cobalt dihydrate 51
(5,5'-Di-nonyl-diphenyl-sulphide-2,2'-dihydroxy)-
cobalt dihydrate 52
3,3',5,5'-Tetramethyl-diphenylsulphide-2,2'-
dihydroxy)-cobalt dihydrate 53
3,3',5,5'-Tetramethyl-diphenyl-disulphide-2,2'-
dihydroxy)-cobalt dihydrate 54
Pyrocatechol-cobalt dihydrate 55
Bis-(3-nonyl-2-hydroxy-phenyl)-methane-cobalt
dihydrate 56
Bis-(4 nonyl-2-hydroxyphenyl)-me-thane-cobalt
dihydrate 57
3-Phenylpyrocatechol-cobalt dihydrate . 58
The products corresponding to formulae 1 and 2 are
prepared by mixing a cobalt salt of a suitable acid with
the required, optionally substituted, phenol in -the absence
of a solvent, and slowly heating the mixture. The tempera~
Le A 20 688
, - 8 -
ture of the mixture is raised slowly so that initially
only water is released from the water of crystallisation
of the cobalt salt, and as the temperature is further
raised to the region of 220 to 350C, preferably 220 to
270C, the acid, which is generally lower boiling, i.e.
more volatile than the aforesaid substituted or unsubstituted
phenol, is split off and displaced by the phenol in
the heat and the product of formula 1 or 2 is formed.
The acid may undergo decarboxylation under the reaction
conditions so that, instead of being split off as such,
it may be released in the ~orm o~ carbon dioxide and possibly
also ketones and other h~drocarbons. Suitable cobalt salts
for this process include cobalt fo mi~e, cobalt acetate,
cobalt propionate, cobalt butyrate, etc. The phenols used
in this process of preparation are those on which the products
shown in the Table are based. The components are generally
used in stoichiometric quantitiesr although a slight excess
of substitited phenol, up to 10~ by weisht, may be used to
accelerate the reaction, the excess being either distilled
off under vacuum after the reaction or left in the product
to reduce an otherwise high melting point. A certain excess
of substituted phenol is advisable also if partial dealkylation
of the substituted phenol is liable to occur under the reaction
conditions.
The products are generally obtained in the form of
dihydrates but may lose water of crystallisation under
prolonged heating in the upper temperature region
(~~' 270C).
The structure of the products was determined by
ESR and ESCA spectroscopy.
The products may be decomposed quantitatively by
water into the corresponding phenols and cobalt hydroxides.
The product may contain a certain quantity of unreacted cobalt
salt if the reaction has been incomplete.
he A 2~ 688
The products, even i~ they have varying particle
sizes, may be pxotected against hydrolysis by enveloping
them in the usual manner with water-repellent substances
such as, for example, paraffin oil, wax or water-repellent
polymers.
The synthesis of an isomeric mixture of o-, m- and
p-nonylphenoxy-Co-dihydrate is described below as an example
of the preparation of these products.
1155 g of nonyl phenol are mixed with 622.5 g of
commercial cobalt acetate and the mixture is slowly heated
with stirring. Water of crystallisation initially sep-
arates, and subsequently acetic acid, the reaction temperature
being raised to 250C. At this temperature, the reaction
mixture is stirred until a deep navy blue, completely
homogeneous liquid is obtained. The liquid is cooled to 200C,
excess nonyl phenol is drawn off under vacuum and the residue
is completely cooled down under vacuum. The product solidifies
at 110 to 115C.
By contrast, bisphenol-Co products linked by sulphur
bridges are readily prepared in aqueous or aqueous-alcoholic
solution from the corresponding bisphenol, a cobalt salt
and the appropriate quantity of sodium hydroxide solution.
The preparation of 3,3',5,5'-tetramethyl-diphenylsulphide- ¦
2,2~-dihydroxy-cobalt dihydrate is described below by way
of example.
A solution of 274 g of 3,3',5,5'-tetramethyl-2,2'-
dihydroxy-diphenylsulphide and 80 g of sodium hydroxide
in 600 ml o~ water was added dropwise to 249 g of cobalt
acetate.4 H20 in 800 ml of water at room temperature. The
reaction mixture was stirred for 2 hours, suction-
~iltered, washed and dried under vacuum. 351 g of productmelting above 300C were obtained.
Similar bisphenol sulphides and bisphenol disulphides
containing different substituents may be reacted in analogous
manner.
Le ~ 20 688
..... ~......... .
- 10 -
Formaldehyde-releasing compounds are understood to be
substances which are capable o~ splitting off ~ormaldehyde
when heated, e.g. to temperatures in the region of 40 to 200C,
in particular under conditions of vulcanizationJ optionally
in the presence of water. When methylol ethers or
methylol esters are used, condensation reactions may also
occur, accompanied by the liberation of alcohols-or acids.
These products will hereinafter brie~ly be referred to as
"~ormaldehyde-releasing compounds".
The following are examples of formaldehyde-releasing
compounds: trimeric methylene aminoacetonitrile, l,aza-
3,7-dioxabicyclo~3,3,0~ octane, oxazolidines, bis-(1,3-
oxazolidino)-methane, octahydro-1,3-benzoxazole t tetrahydro~
1,3-oxazine, dialkylaminomethylalkylether, and diallyl-
amino-methylalkylether (see e.g. selgian Patent No. 621,923),
e.g. 4~4-dimethyl-1,3-oxazolidine, bis-(~,4-dimethyl-1,3-
oxazolidino)-methane, N-n-butyl-5(6)-cyanooctahydro-1,3-
benzoxazole, 3-n-hutyl-tetrahydro-1,3-oxazine, diisopropyl-
aminomethyl-ethylether, diallyl-aminomethyl-ethyl ether,
he~a-(methoxymethyl)-melamine, N-methylolcarboxylic acid
amides, e.g. N-methylolacetamide, N-methylolbutyramide,
N-methylolacrylamide, N-methylolmethacrylamide, N-methylol-
succinimide and N-methylolmaleic acid imide.
The following are ~urther exarnples of formaldehyde-
releasing compounds: 1,8-di-(methyleneamino)-p-methane;
azomethines such as ~ dimethyl-benzyl-azomethine (see
US Patent No. 2,512,128) and cyclotrimethylenetriamines,
e.g. N,N',N"-trimethyl-cyclotrimethylenetriamine and
N,N',N"-triethyl-cyclotrimethylenetriamine; diaminomethane
3~ substituted on both nitrogen atoms, e.g. bis-tdi-tcyano-
methyl)-amin~ -methane and bis-(diallylamino)-methane;
imidazolines substituted on both nitrOgen atoms, such as
N,N'-diphenyl~imidazolidine or N,N'-dibenzyl-imidazolidine;
and heY~ahydropyrimidines substituted on both nitrogen atoms,
e.g. N,N'-di-n-hexyl-hexahydropyrimidine (see Belgian
Patent No~ 62~,519). J
Le ~ 20 688
r
Other formaldehyde-releasing compounds used according
to the invention include methylolmelamines such as hexa-
methylolmelamine in which all or part of the hydroxyl
groups may be etherified or es-terified. Hexamethylol-
melamine need not be used in its pure form but may be used
in the form of products having a somewhat lower forrnalde-
hyde content or containing higher molecular weight conden-
sation products. The hexamethylolmelamine may be prepared
by known methods, e.g. by the reaction of approximately
l mol of melamine with approximately 6 mol of aqueous
formaldehyde solution (see "Helvetica chimica acta", 24,
page 3lS ~, Swiss Patent No. 197,486 and ~ouben-Weyl,
"Methoden der organischen Chemie", Vol.8, page 242).
Instead of hexamethylolmelamine, its esters or ethers
may be used, as already mentioned above; these may be
regarded as masked methylol compounds. Both in the
present case and in the following cases described it is
suitable to use ethers or esters, in particular the lower
alkyl ethers such as, for example, methyl, ethyl, propyl,
2G butyl and allyl ethers; from 1 to 6 hydroxyl groups may
be etherified. Suitable esters include in particular
the lower aliphatic carboxylic acid esters such as acetates
and propionates. Methylol melamines may, of course, also
be used; these should not contain more than 5 and
preferably contain 3 to 5 methylol groups per mol,
and the methylol groups may be partly or completely ether-
ified or esterified. The compounds may be prepared by
known methods of reacting melamine with the desired quantity
of formaldehyde, optionally followed by etherification or
esterification of the methylol compounds obtained (see
Houben-Weyl, 'IMethoden der organischen Chemie", Vol.8,
page 358~. These processes generally do not yield
chemically uniform compounds but mixtures of various
methylol compounds, which are also suitable. What has
Le A ~O 688
- 12 -
been said o~ hexamethylolmelamine applies analogously
to the esters and ethers. The ~ollowiny are examples
of such compounds: pentamethylolmelamine acetate and
pentamethylolmelamine propionate.
Te-tramethylolhydrazodicarbonamide may also be used.
Its hydroxyl groups may optionally be partly or completely
etherified or esterified. Tetramethylolhydrazodicarbon-
amide, which is prepared by the reaction of hydrazodicar-
bonamide with 4 mol of formaldehyde (see Houben-Weyl,
"Methoden der organischen Chemie", Vol. 14/2, page 352)
is preferably used in its crystalline form. Instead of
using the pure compound (m.p. 149C), resinous condensation
products containing ~arying quantities of ~ormaldehyde
may be used. Tetramethylolhydrazodicarbonamide acetate
l~ and propionate are examples of its esters and ethers.
The ~ollowing compounds may alsG be used as formal-
dehyde-releasing compounds: tetramethylol-acetylene-
diurea, in which the hydroxyl groups may be completely or
partly etherified or esterified. Tetramethylol-acetylene-
diurea need not be used in its pure form but may be used
in the form of products having a somewhat lower proportion
of formaldehyde or containing higher molecular weight
condensation products. Tetramethylol-acetylene~diurea
may be prepared by known methods, e.g. as described in
Houben-Weyl~ "Makromolekulare Chemie", 2, page 353.
The following are examples of its esters and ethers:
tetramethylol-acetylene-diurea-tetramethylether, and
tetramethylol-acetylene-diurea-tetraacetate. Other suit-
able formaldehyde-releasing compounds include methylol
3~ compounds, in particular N-methylol compounds and their
derivatives, in which the hydroxyl groups are optionally
completely or partly etheri~ied or esteriEied, e.g. N9N'-
dimethylol-urea, dimethylol-urea-dimethylether, N,N'-
dimethylol-urone-dimethylether, methylene-bis-(methylol-
urea-methylether) and dimethylol-urea-di-n-butyl ether.
N-substil:uted l,3,5-dioxazines which May be substitut-
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- ~3 -
ed on the nitrogen atom by straight-chained or branch-chained,
saturated or unsaturated, substituted or unsubstituted
alkyl, cycloalkyl, aryl or aralkyl groups, and wherein the
substituent may also contain further dioxazine rings, are
also suitable. The following are examples of such com-
pounds: N-allyl-, N-butyl-l N-isobutyi-, N-cyclohexyl-,
N-phenyl-, N-(~ hydroxyethyl)- and ~-acetic acid-ethyl-
ester-1,3,5-dioxazine, and N,N'-ethylene-bis-(1,3,5-diox-
azine).
The dioxazines may be prepared by the known method of
reacting the corresponding amines with an excess of formal-
dehyde. The mixtures of compounds with condensation
products containing varying quantities of ~ormaldehyde such
as are obtained from such a method of preparation may be
1~ used insteaà of the pure compounds.
Paraformaldehyde and hexamethylenetetramine may also
be used. Exceptionally firm bonding has been obtained
with the following compounds: hexamethylolmelamine,
hexam~thylolmelamine-pentamethylether, mixtures of hexa-
~o methylGlmelamine-tetramethylether and trimethylether,
pentamethylolmelamine-trimethylether, tetramethylolhydrazo-
dicarbonamide, tetramethylol-acetylene-diurea, N,N'-dimeth-
ylol-urea, N-methylol-dicyandiamide, methyleneamino-
acetonitrilet N-allyl-dioxazine, N-phenyl-dioxazine, l-aza-
3,7-di-oxa-bicyclo~3,3~-octane and hexamethylenetetramine.
Rubber compositions containing the above combination of
bonding agents have excellent adherence to iron, cGpper,
brass, zinc, bronze, aluminium and other reinforcing
metals. Typical rubbers suitable for such mixtures o~
bonding agents are those of the diene type such as natural
rubber, polyisoprene, polybutadiene, s-tyrene-butadiene
copolymers, acrylonitrile-butadienerubber, chloroprene
rubber, EPDM and mixtures of these types of rubber.
The rubber mixtures should contain the usual con-
stituents such as reinforcing carbon blacks, inactiveLe A 20 68
2~$
- 14
and active fillers such as silicates and zinc oxides,
processing auxiliaries, sulphur and vulcanization accel-
erators.
Particularly suitable accelerators are the sulphen-
amides derived from 2-mercaptobenzothiazole, such as, for
example, N-cyclohexyl-thiobenzothiazole, N-morpholino-
thiobenzothiazole, and N,N-dicylohexyl-thiobenzothiazole.
Other accelerators may, of course, also be used, either
alone or in combination. Examples include thiurams,
mercaptobenzothiazole and dithiocarbonates.
Vulcanization retarders may also be added. The cobalt
compounds according to the invention themselves act as
accelerators and may therefore be used without additional
acceleratingcomponents ~see German Offenlegungsschrift
No. 2,736,680).
A suitable vulcanization temperature is chosen,
e.g. 120 to 220C, preferabiy 140 to 180C.
The advantages of the present invention for the
production of very high strength bonds with steel cables
or steel cords having an untreated, brass plated, zinc
plated or blank surface are illustrated by the Examples
which ~ollow.
The following compositions are used for the mixtures:
Mixture A
Natural rubber (RSS l) 60`parts by weight
Poly-cis-butadiene 40 " " "
Active silicate 15 " " "
Carbon black N 330 35 " " "
Zinc oxide 6 " " "
Stearic acid l part by weight
Phenyl~ -naphthylamine l " " "
Aromatic mineral oil plasticiser 4 parts by weight
Colop}lony 2
Sulphur 4 " " "
35 N,N-dicyclohexyl-thioben20thiazole 0.7 part by weight
~e A 20 688
__ I
26~L~
Mlxture B
Natural rubber (RSS 1)60 parts by weight
Poly-cis-butadiene 40 " " "
Carbon black N 33055 " " "
Zinc oxide 6 " " "
Stearic acid1 part by weight
Phenyl-~-naphthylamine1 " " "
Aromatic mineral oil plasticiser 4 parts by weight
Colophony 2 " " "
Sulphur 4 " " ~
N,N-dicyclohexyl-thiobenzothiazole 0.7 part by weight
Mixture C
Natural rubber (RSS 1)100 parts by weight
Carbon biack N 33055 " " "
Zinc oxide 6
Stearic acid1 part by weight
Phenyl-~ naphthylamirle
Aromatic mineral oil plasticiser 4 parts by weight
Colophony 2 " " "
Sulphur 4 " " "
N,N-dicy~ohexyl thiobenzothiazole 0.7 part by weight
Mixture D
Natural rubber (RSS 1)lOG parts by weight
Carbon black N 326 43 " " "
Carbon black N 539 20 " " ~
Colophony 3 " " "
Phenyl~ -naphthylamine1.5
Zinc oxide 10 " " "
Sulphur 7 " " "
N,N dicyclohexyl-thiobenzothiazole 0.7
Mixtures A, B and C are prepared on laboratory mixing
rollers at a roller temperature of 40C. In the case of
mixture D, the basic mixture free from sulphur compounds
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and accelerators is first mixed in a laboratory internal
mixer at 70C and sulphur, accelerator and optionally
bonding agent are subsequently added on laboratory mixing
rollers at a roller temperature of 60C.
Samples measuring 20 x 15 x 6 mm are prepared to
test for the bond strength by the T-test method ~see
Bayer-Mitteilungen fur die Gummi-Industrie, No. 29,
page 69).
Steel cords having blank, brass-plated or zinc-
pla~ed surface are used in a construction measuring
7 x 3 x 0.15mm.
Vulcanization of the test samples is carried out at
150C, corresponding to the tgo value. To test for the
resistance of the rubber-steel cord bond to reversion,
the samples are vulcanized at 180C for 45 minutes longer
than corresponds to the tgO-value. To test for ageing,
the samples are kept several days in a Geer furnace at
100C or exposed to superheated steam at 120C for several
hours.
The bonding values are determined at a test temperature
of 80C, using tensile testing apparatus at a draw-off
speed at the clamps of lOG mm/min. The values are given
in terms of the maximum force in N/20 mm required
to pull the cord out of the sample of rubber~ At least
4 test samples of the same construction are used for one
measurement and the average obtained from these individual
values is used for assessment.
Examp 1 e
The properties of the compounds claimed for bonding
brass-plated steel cord are illustrated in E~ample l.
Table 1: Some representative cobalt phenolates for
bonding brass plated steel cord (using vulcan-
izates of B type mixture; the cobalt content
is 0.5 parts by weight/lO0 parts by weight of
polymer)~
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Vulcaniza 15UC/t90 150C/t90 180C~45' 180C/45' 180C/45'
Ageing - 3 d H - 3 d HL 8 h steam
_ 417N~ 262N/ 363N/ 201N/
20 mm 20 mm 20 mm 2G mm
Cobalt
naphthen-
ate (com- - ~
parison 495 483 L08 102 '50
,. " ~, ,.
Compound
44 434 316 278 293
" "
Compound
47 440 323 ~15 416 166
Compound
49 414 423 308 25
r . __ _ _ . ._ _~_ _ . _ _ _
Table 1 shows thatJ with the test samples which have
been vulcanized according to the tgO-value, firm bonding is
generally obtained even without the use of bonding additives.
Substantially better bonding of the rubber to metal
is nevertheless obtained if a bonding agent is also added
to the mixture.
Under conditions of reversion and ageing, consider-
able weakening of the bond rapidly sets in when conven-
-tional cobalt~bonding agents are used~ In the case of
cobalt naphthenate, the residual bonding level is signif-
icantly lower after 45 minutes vulcanization at 180C than
in samples free from any bonding additive.
By contrast, the residual bonding values obtained
after vulcanization are substantially higher when the
bonding additives according to the invention are used.
Even when the test samples are stored for 8 hours in
superheated steam at 120C, the residual bonding strength,
for example in the case of compound 46, is still 166N~20 mm
whereas in the case of cobalt naphthenate virtually no bond
remains.
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The superiority of the group of compounds claimed
according to the invention over the cobalt bonding agents
used in the present state of the art becomes even clearer
when mixtures with high sulphur contents, such as are
conventionally used as bonding mixtures for the belt
inserts of radial tyres, and with high cobalt contents are
compared (Table 2)~ ~
Table 2: Comparison of bonding action of cobalt phenol-
ates with cobalt naphthenate in mixtures of
type D with high sulphur contents (cobalt
content: 0.5 parts by weight/100 par-ts by
weight NR).
Vulcaniz- 150C~tgo 150C/tgo 180C/45l 180C/45'
. _ . _
15Ageing - 5 d HL - 5 d HL
100C 100C
.
- 41lN/2Cmm 29lN/20mm 374N/20mm 239N/20mm
cobalt
naphthen-
ate (com-
parison) 463 " 444 " 58 " 88
Compound
469 " 42g " 314 " 287 "
Compound
416 " 365 " 274 " 289 "
Compound
18 458 " 398 " 303 " 18~ "
_ . .. _ _ . .. _ _
A similarly advantageous spectrum of activity is
found in mixtures containing highly active silicates
(Table 3).
Table3: The resistance to separation of some
cobalt phenolates in vulcanizates containing
highly active silicates (mixture type A)
(cobalt content: 0.5 parts by weight/lO0 parts
by weight of rubbe.r).
3S
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Vulcaniz- 150C/t90 180C/45' 180C/45'
atior,
Ageing - 3 d HL/100 C
-- -- ~ .....
Compound
52 392 N/20n~ 19~ N/2C n~ 207 N/20 mm
Compound
53 494 N/20n~; 306 N/20 mm 330 N/20 n~
Compound
54 427 N/20mm 301 N/20 mm 264 N/20 n~
.. _ ~ _ . ...... .. _
Example 2
In contrast to the bond obtained on brass plated
steel, the use of bonding additives in-the rubber mixture
is absolutely essential for articles containing zinc-
plated steel inserts.
; 15 The effectiveness of the bonding action varies
sharply with the vulcanization conditions.
Thus, for example, many con~ercially available
bonding agents produce a complete loss of adherence under
conditions of over vulcanization.
Table 4 shows that the compounds described do not
have this disadvantage. They maintain a high level of
bonding strength even when vulcanization is carried out
for 45 minutes at 180 C. The value obtained is fre-
quently higher by a factor of 3 - 4 than that obtainable
with cobalt naphthenate.
Table 4: Bonding on zinc-plated steel cord (0~5 parts
by weight of cobalt/100 parts by weight of
polymer)
'
t
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Bonding Cobal-t Mixture150 C 180 C/45'
Additive content t90
_ - D 55
Co naphthenate
(comparison) 0.5 B 343 N/20 47 N/20
mm mm
ComPcund 500.5 C 305
Compound 57O.S C 335
Compound 490.5 B 305 158
Compound 560.5 B 305 194
Compound 54005 D 313
Compound 150.5 D 375 160
Compound 250.5 D 311 131
Compound 180.5 D 339 128
Compound 510.3 D 106
. . , _ . _
Example 3
The compounds described provide good bonding values
even on raw steel (Table 5).
Table 5: Bonding on raw steel cord
(Cobalt contento 0.5 parts by weight/100 parts
by weight of polymer).
BondinsType of Bond strength under
additive mixture vulcanization
150C/tgo
Cobalt naph-
thenate
(comparison) D 62 N/20 mm
Compound 50 C 124
Compound 25 B 106
Compound 54 B 134
Compound 47 B 165
Compound 49 B 126
Compound 15 D 112
Compound 18 D 95
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Example 4
The following Example illustrates that vulcanizable
rubber mixtures containing both the cobalt naphthenates
mentioned above and formaldehyde donors based on methylol-
S melamine respond particularly favourably under conditions
of ageing in steam and hot air. ~i
In the laboratory experiment carried out by the
process described, the following results, for example,
were obtained for compound 47:
The vulcanized mixture without methylol compound
has a bonding value of 430 N/20 mm immediately after
vulcanization. This value falls to 369 N/20 mm after
3 days' ageing in hot air. In rubber mixtures which
in addition contain resorcinol and methylol compound as
bonding agents, the corresponding figures are: 423 N/20 mm
before ageing and 406 N/20 mm after ageing.
The differences become even more marked under condi-
tions of ageing in superheated steam at 120C. Vulcan-
izates free from methylol but containing cobalt have only
25% of their initial bonding value after 15 hours' ageing.
When the vulcanisates contain compound 47 as cobalt
component and a methylol-melamine mixture consisting
mainly of hexamethyiolmelamine pentamethylether, the
bonding value only falls to 75% of its initial value. ~-
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