; ~045Z64
.,.
~ The present invention is related to a rubber composition
.
which has excellent adhesive properties with a reinforcing
material. The present invention also provides for the prepara-
tion of a composite vulcanized product of the rubber and the
:
reinforcing material.
:. -
Heretofore, for adhesion between a rubber and a metallic
:
material such as a steel cord or between a rubber and a fibrousmaterial such as nylon cord, the metallic material has been plated
with a zinc or a copper alloy such as brass and bronze and to
~ 10 treat the fibrous material such as nylon cord with a resorcinol- ; ;~
- formaldehyde latex. Further to improve adhesive properties of the
rubber, certain additives such as a cobalt salt of organic acid
such as cobalt naphthenate, cobalt stearate, and cobalt octylate
have been incorporated in the rubber. However, the adhesive
. ,, ~
l J system has the disadvantages that the adhesive properties greatly
.
decrease with excess time or temperature of heat treatment in a
vulcanization and the moisture resistance of adhesion is low.
`~ To improve adhesion, it has also been proposed to add an alkyl-
~, phenol resin to allow for the decrease of adhesive property caused
-s 20 by the vulcanization. However in such case an improvement of ~ -
~;` moisture resistance is not to be expected and the vulcanization
is disadvantageously slow.
~ .
The present invention provides a rubber composition
which has high adhesive properties with a reinforcing material
and high moisture resistance of adhesive properties and has
. .. .
sufficient vulcanization characteristics.
The object of the invention can be attained by providing
.~
-~ a rubber composition which comprises more than 0.5 wt. part of
,~ a cobalt salt of organic acid, more than 0.5 wt. part of mono-
~ 30 hydroxybenzoic acid component and 100 wt. parts of a ~ubber.
-~ Typical rubbers used in the composition of the present
invention include natural rubber and synthetic rubbers such as
::
.. , -- 1 --
,
~- ~045Z64
styrene-butadiene rubber, polybutadiene rubber, polyisoprene
rubber, chloroprene rubber and nitrile rubber. Natural rubber
is mainly used for the manufacture of tires. Typical cobalt
salts of organic acids include cobalt salts of organic acids
having carbon atoms of 6 - 30 such as cobalt naphthenate, cobalt
î stearate, cobalt octylate, cobalt-octoate, cobalt-oleate, cobalt-
resinate, cobalt-linoleate, and cobalt-tallate.
The monohydroxybenzoic acid component may be provided
by monohydroxybenzoic acid and derivatives thereof which form
monohydroxybenzoic acid or a salt thereof in the rubber composition.
Typical derivatives include alkyl monohydroxybenzoates. It is
preferable to use paramonohydroxybenoic acid. However, a
desirable effect cannot be obtained by using small amount of
;~ orthomonohydroxybenzoic acid. It is desirable to combine 0.5 -
10 wt. parts, preferably 1 - 6 wt. parts, of a cobalt salt of
~,!, organic acid and 0.5 - 10 wt. parts, preferably 1 - 6 wt. parts
;~ of monohydroxybenzoic acid with 100 wt. parts of a rubber. When
the content of the cobalt salt of organic acid and the content
of the monohydroxybenzoic acid are less than the lower limit,
they are not effective whereas when they are more than the upper
limit the physical properties of the rubber composition are
adversely affected although the increase of the content does
, not effectively affect the characteristic advantages of the
t invention. With the combination of the cobalt salt of the organic
acid and the monohydroxybenzoic acid with the rubber, it is possi-
ble to provide a rubber composition which has excellent adhesive
i properties with a metallic material by a vulcanization wherein a
cure rate (a vulcanization speed) of unvulcanized rubber composi-
tion is not delayed and the adhesive properties are maintained even
with excess vulcanization.
It is possible to improve the adhesive properties with
a fibrous material and the moisture resistance of the adhesion
-- 2 --
, . . ~-. .
~ 104S~69~
before or after the vulcani~ation by further combining more
than 0.5 wt. part, preferably 0.5 - 10 wt. parts based on 100
parts of the rubber of at least one of an alkylphenol type
resin and cresol-formaldehyde type resin, with the above-mention-
ed rubber composition (I). The resulting rubber composition will
be referred as the rubber composition (II). When a content of
the alkylphenol type resin or cresol-formaldehyde type resin
r; is less than the lower limit, the aforesaid effect is not achieved
- whereas when it is more than the upper limit, physical properties
of the rubber composition (II) are adversely affected though
the increase of the content does not effectively affected to the
above-mentioned characteristic advantages. The alkyphenol
type resins include t-butylphenol-formaldehyde resin, p-octyl-
;~ phenol-formaldehyde resin, and modified phenol resins such as
.
cashew oil modified phenol resin, dicyclopentadiene modifed
phenol resin. The cresol-formaldehyde type resins include o-
` cresol-formaldehyde resin and p-cresol-formaldehyde resin.
,
The rubber c~mposition of the present invention can be
' prepared by blending said components to the rubber by the conven-
s 20 tional blending method. It is usual to add a suitable vulcani-
;~ zing agent, a filler, a reinforcing material or other additives
together with said additives or separately before the vulcaniza-
tion, as described in the prior art. The conditions of the
present invention can be considered to be in accordance with
~' the prior art such as Encyclopedia of Polymer Science and Tech-
nology Vol. 12 Pages 161-353 on rubbers; ibid Vol. 14 Pages 42 -
64 on tires and tire cord; ibid Vol. 8 Pages 184 - 185 on tire
cord dip; ibid Vol. 14 Pages 740 - 756 on Vulcanization; and
Rubber Chemistry and Technology 46 (4) Pages 981 - 998 on rubber-
to-textile and rubber-to-steel cord adhesion.
The present invention will be further illustrated by
way of the following Examples.
` -:
- ~ : . .. -. .
lV45Z64
Examples l - 7, Standard Example l; and Comparative Example 1:
The compositions in Table l were blended as follows.
The test results of the rubber compositions of Examples 1 - 7;
Standard Example l; and Comparative Example l are stated in
: Table 2.
. .
: Preparation and Vulcanization of Rubber composition:
., ~ _ . .... _
The components of each master batch was blended by
a Blambury's mixer and a vulcanizing agent was blended to the
.-: master batch by a roller mill to prepare each rubber composition.
. ~
The vulcanization of the rubber composition was
~; carried out at 145C for 45 minutes.
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-- 6 --
~045Z64
Examples 8 - 14: Standard Example 2: Comparative Example 2:
; The compositions stated in Table 3 were blended as :
follows;
The test results of the rubber compositions of Examples 8-14:
: Standard
~ Example 2 and Comparative Example 2 are stated in Table 4.
Preparation and Vulcanization of Rubber composition:
.
` The components of each master batch was blended by a : :
. , .
.f Blambury's mixer and a vulcanizing agent was blended to the : :
, 10 master batch by a roller mill to prepare each rubber composition. :~
The vulcanization of the rubber composition was carried out at -:
`~ 145C for 45 minutes.
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1045264
*4: RFL treatment: resorcino-formaldehyde latex treatment
*5: Kevlar(Aramid fiber) cord: a trademark of duPont Co.
*6: The test piece being similar to that of adhesion test
waspreparedinunvulcanized condition by pressing in
` a mold as follows.
Rubber composition was filled in a mold of ASTM D 2229
wherein brass-plated steel cords were disposed in
parallel with each gap of 12.5 cm and were embedded
for 1 inch. The rubber composition was molded by a
I 10 press at the room temperature.
The test piece was kept in 100% of relative humidity
for 10 days and then it was vulcanized at 145C for
45 min
, i
The pull-out test was carried out.
*7: The rubber composition was filled in a mold of ASTM D
' 2229 wherein brass-plated steel cords were disposed
~ in parallel with each gap of 12.5 cm and were embedded
;, for 1 inch. The rubber composition was molded by a
,. ~ .
press at the room temperature. It was vulcanized at
~, 20 145C for 45 min. and then the test piece was kept
`^'q in 100% of relative humidity for 10 days. The pull-
,
out test was carried out.
.
The tests of adhesive strength
Mooneyscorch time (t5)
- Rheometer vulcanization degree T95 were carried out
as follows.
Adhesive strength test
1) Adhesive strength to metal material
Steel cords plated with brass or zinc were arranged
, 30 in parallel with each gap of 12.5 mm. ~ach rubber composition
, was coated from both side of the steel cords to form each fabrica-
ted product in which each cord was embedded for 1 inch and the
'
:~ - 10 -
1~ 5264
~ fabricated product was vulcanized under condition of 145C - 45 mm.;
.
160C-20 min.; or 160C - 60 min..
- The pull-out test was carried out in accordance with
, ASTM D 2229.
`~ 2) Adhesive strength to fibrous material
.
- The adhesive strength to nylon cord or Kevlar (a
trademark)(or Aramid, (atrademark) fiber) cord was measured in
accordance with H test of ASTM D 2138. (under a vulcanization at
.,
; 148C for 30 min.)
~ . .
Mooney scorch time: (t )
- 5-
- In accordance with Japanese Industrial Standard K 6301,
it was measured at 125C.
, . :
Rheometer vulcanization degree T95:
-~ In order to measure suitable vulcanizing time by a
Rheometer manufactured by Monsanto Co., Ltd., the time for reaching
to 95% torque of the maximum torque was shown as T95.
As will be seen from the results shown in Table 2, the
rubber compositions (I) of the invention have cure rates (vulcani-
. . i .
' zation speeds) faster than that of the Standard Example, superior
' 20 adhesive strength under appropriate vulcanization at 145C for
:.
45 min., to those of Standard Example 1 and Comparative Example 1
and remarkably superior adhesive strength under excess vulcaniza-
tion at 160C for 60 min. to those of Standard Example 1 and
Comparative Example 1. The fact was clearly found from the result
of rubber adhesion on the surface of steel cord pulled out (rubber
coverage).
The other characteristics of the rubber compositions
of the invention are superior to those of the Standard Examples and
the Comparative Examples. Moreover, in processability, the rubber
compositions of the invention are easily mixed without excessive
stickness on the surface of a mill roll comparing with those
of the Comparative Examples. From the results of Table 4, it will
-- 1 1 --
~........................................................................ .
lV~5~64
be seen that the rubber compositions (II) which contain the
alkylphenol type resin or the cresol-formaldehyde type resin
have remarkably superior adhesive properties comparing with those
of Standard Example 2 and Comparative Example 2 through the physi-
cal properties of the vulcanized products are similar. Thus,
the rubber compositions (II) of the present invention have excellent
adhesive property to nylon cord and Kevlar (a trademark) cord
which are treated with resorcinol-formaldehyde latex and steel
cord plated with zinc. In particular, the rubber compositions (II)
of the present invention have excellent moisture resistance in the
adhesion to the brass plated steel cord even though the unvulcan-
` ized or vulcanized rubber samples are exposed under high humidity
comparing with those of the Standard Example and the Comparative
. Example. These characteristics are very important in the case
of preparation of rubber-wire composites under high humidity,
and can be attained by the rubber composition of the present
invention. As stated above, the rubber compositions (I) of the
present invention have excellent adhesive properties to a wire
material in both cases of appropriate vulcanization and excess
vulcanization without delaying the vulcanization, and they can
be used as an adhesive rubber composition. The rubber composi- - `
~ tions (II) of the present invention have excellent adhesive
-~ properties to the nylon cord, Kevlar (a trademark) cord and the
zinc plated or brass plated steel cord with high heat resistance
in excess vulcanization and without a delay of vulcanization.
With regard to the adhesion to the brass plated steel
` cord, the rubber compositions (II) have excellent moisture
resistance so that they can be used, for composites or rubber-
fibrous material or metallic material such as in the belt and
carcass of tires and in the cores of belt conveyors as adhesive
rubber compositions.
- 12 -
.
. . :
