Note: Descriptions are shown in the official language in which they were submitted.
10~1874
....
SPECIFICATION
This invention relates to rubber compositions for use
in the production of improved vulcanized rubber products and,
more particularly, to rubber compositions containing benzoic
acid or monohydroxy benzoic acid.
In the past it has been known to adhere rubber to
metallic materials, such as steel cords, or flbrous materials,
~ r . ..
such as nylon cords, by plating a copper alloy, such as
bronze or brass, onto the surface of steel cords or by
treating the surface of nylon cords with a resorcinol formaldehyde
latex.
Such methods, however, have not proven entirely satisfactory,
particularly in the tire field where the development of high
speed and high powered automobiles has created a demand for
rubber products of improved adhesive strength.
Recently, rubber has been mixed with white carbon,
resorcinol and hexamethylenetetramine; the so-called "HRH"
type rubber to improve its adhesive characteristics. However,
it has been found that when "~RH" type rubber compositions
are mixed in Banbury or roll mixers, they give off fumes
owing to the sublimating property of resorcinol, causing
problems of environmental pollution and scorching during
processing.
It has also been known to use a primary condensate of
resorcinol and formalin instead of resorcinol in the "HRH"
rubber compositions to overcome these shortcomings of resorcinol;
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but this creates its own shortcomings, namely, a deterioration
in its vulcanizing characteristics as well as its adhesive
properties to metallic or fibrous materials.
Further, in OTR (Off The Road) tires and in tires for
trucks or buses used under conditions of high load, it is
important to have good cutting and chipping resistance
properties in the tire treads. Attempts have been made in
the past to improve these properties by selecting specific
diene-type polymers, for example, combinations of natural
rubber and a copolymer of styrene-butadiene, and mixing them
with carbon black or inorganic reinforcing fillers. The
improvements achieved by these methods, however, have not
always been sufficient, and if the amount of carbon black or
inorganic reinforcing filler is increased too much, the
processing ability of the rubber compositions during mixing
is affected, and the build-up of heat during use of the
resulting rubber goods is often increased.
Japanese Patent Publication No. 48-38615, for example,
discloses the addition of cyclopentadiene type resin into a
copolymer of styrene-butadiene to improve the cutting
resistance of the tire treads.
Also, it has been known to prevent scorching during the
processing of rubber by mixing aromatic carboxylic acids,
such as salicylic acid, into rubber. However, the aromatic
carboxylic acids tend to delay the vulcanization rate and,
therefore, they have been used only in an amount of from
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- 10708~
0.1 - 0.5 part by weight per 100 parts of rubber and never
more than 1 part at the most.
In accordance with the present invention, it has been
found that with the addition of benzoic acid or monohydroxy
benzoic a~id; i.e., ortho-hydroxy benzoic acid (so-called
salicyiic acid), meta-hydroxy benzoic acid or para-hydroxy
benzoic acid; to rubber in relatively large amounts, excellent
-. adhesion of the rubber to metallic or fibrous materials can
be achieved and that there is an excellent improvement in
the chipping resistance and the cutting resistance of the
tires produced therefrom.
According to this invention, benzoic acid or monohydroxy
benzoic acid is mixed with the rubber in an amount of from
more than 1 part and, preferably, from 1 to 20 parts by
weight per 100 parts of rubber.
If less than 1 part by weight is used, the results
cannot be achieved, and by using more than 20 parts by
weight, undesirable features such as delay in the vulcanization
rate and deterioration of the physical properties of the
resulting products may appear.
The preferable amounts of the agents of this invention
to be included depend on the kinds of rubber to be used, the
vulcanizing accelerators and vulcanization system. Usually,
however, where the main objective is to improve the adhesion
characteristics, 2-5 parts by weight is preferably used. On
the other hand, where the main objective is to improve the
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~070874
¦¦ cu~ting and he chipping resistance, 3-10 parts by weight
should be used.
The rubber to be used may be a diene-type rubber;
for example, natural rubber, polyisoprene rubber, polybutadiene
.. ..
rubber, styrene-butadiene copolymer rubber, acrylonitrile-
butadiene copolymer rubber, chloroprene rubber, or mixture
thereof, and a great many kinds of other rubber may be used.
. With respect to a vulcanization system, well known
sulfur-vulcanizing accelerator system, peroxide system,
and the others may be used.
The vulcanizing accelerator may be selected from a wide
variety of well known materials for this purpose; for example,
a sulphenamide type, such as N-oxydiethylene benzothiazole
sulphenamide; a thiazole type, such as 2-mercaptobenzothiazole;
or a thiuram type, such as tetramethyl thiuram disulfide.
Other ingredients, such as zinc oxide, stearic acid,
carbon black, or white carbon, can be used according to
their purposes, as is well known to those skilled in the
art.
With respect to the vulcanization temperature, the
temperature used is that conventionally used in a vulcanization
process.
Moreover, it has been found effective to mix in any of
the compounds capable of generating formalin when heated,
such as hexamethylenetetramine or hexamethylolmelamine.
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1C~70874
This invention will now be explained with reference to
the following examples. In these examples, the following
tests were conducted on the resulting vulcani.zed rubber
products.
Adhesion Test
Fabric was prepared by coating both faces of bronze-
plated or brass-plated steel cords which were set in parallel
and 3 mm apart, with the rubber composition (1 inch embedded)
followed by vulcanization at 145C for 45 minutes. The
pulling out test of the steel cords was conducted according
to ASTM D 2229.
Mooney Scorch Time (ts)
It was measured according to JIS K 6301 (measuring
temperature 125C).
Cutting Resistance (Falling Weight Impact Test)
It was evaluated by measuring depth of a cut caused by
dropping an edge of 12.98 kg made from steel onto the test
piece of the vulcanized rubber composition from 25 cm in
hei.ght. The data are shown as indexes corresponding to 100
- of Standard 1. The larger the number, the better the effect.
Chipping Resistance (By Means of Dynamic Chipping Tester)
The tester is operated so as to simulate chipping that
occurs during actual driving, and the resistance is evaluated
by measuring the loss in weight of the tire treads (volume
cc = loss in weight g/specific gravity) caused by driving
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1070874
a miniature tire of 15 cm in diameter, 4 cm in width and
about 750 g in weight with a lug pattern tread on a drum
having a sharp pro~ection made from steel, at a rotation
velocity of 120 times per minute for 3 hours.
The data are shown as indexes corresponding to 100 of
Standard 1, as in the cutting resistance, and the larger the
, _ number, the more advantageous the result.
EXAMPLES 1-4
Rubber compositions were prepared, as shown in Table 1,
by mixing the master batch ingredients in a Banbury mixer,
followed by mixing the master batch with the vulcanization
~ ingredients in a roll mixer. Vulcanized rubber products
; were then prepared from the compositions for use in the
various tests. Vulcanization took place for 45 minutes at
145C.
The results of the above tests performed on the vulcanized
rubber products of Examples 1-4 as well as the Standard and
Control samples are shown in Table 2.
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1070874
From Table 2, it is clear that the rubber compositions
of these examples have the following features in comparison
with known rubber compositions containing resorcinol, as
shown in the Control samples: the physical properties of
vulcanized rubber are almost equal, the adhesive strength in
brass-plated steel cords is almost equal or more, the adhesive
strength in zinc-plated steel cords is extremely higher, the
scorch is more retarded, the cutting resistance and the
chipping resistance are extremely higher, no fume is generated
durlng mixing operation at all, and it has not bloo~ed after
mlxlng .
The reason why the scorch time in Example 4 is shorter
than in Control 2 is that the addition amount of vulcanizing
accelerator, N-oxydiethylene-2-benzothiazole sulphenamide in
Example 4 is greater than in Control 2.
EXAMPLE 5
Mixing of the rubber composition, vulcanization and
testing were conducted in the same manner as set forth in
Examples 1-4, the ingredients of Example 5 being shown in
Table 3 and the test results in Table 4.
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1.070 87 4
TABLE 3
__ . _ _
Example Standard Control
_ _ 5 2 3
Master Batch:
natural rubber (RSS#l)100 100 100
zinc oxide No. 3 5 5 5
stearic acid 3 3 3
carbon black (HAF) 45 45 45
process oil 5 5 5
. .
resorcinol - - 3
p-hydroxybenzoic acid 3 - -
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Vulcanization System:
sulfur ! 4 , 4 4
N-oxydiethylene-2-
benzothiazole sulphenamide
TABLE 4
Example Standard Control
Physical Properties:
tensile strength (kg/cm2) 235 227 220
elongation (~) 400 390 490
300% tensile stress (kg/cm2)184 178 135
hardness (JIS A) 74 75 65
~- scorch time (t5) 24 min.12 min. 21 min.
Adhesive Strength (kg):
brass plated steel cord70 48 59
zinc plated steel cord23 14 15
fuming none none much
blooming none none much
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From Table 4, it is clear that the rubber composition
of this example has almost the same physical properties as
the known rubber composition and has the advantage of greater
adhesive strength to steel cord and no fume and no bloom,
which appear during mixing with resorcinol, and no bloom
after mixing.
EXAMPLES 6-8
_ Mixing of the rubber compositions was conducted in the
same manner as set forth in Examples 1-4, the ingredients
being shown in Table`5, and the obtained compositions were
vulcanized and tested as follows:
Vulcanization conditions for testing the physical
properties were conducted at 148C for 30 minutes.
Adhesive strength to nylon fiber: H-test by means of
ASTM D 2138 (Vulcanization condition 148C for 30 min.).
Other tests are the same as mentioned above.
The results of the tests performed on the vulcanized
rubber compositions of Examples 6-8 as well as the Standard
an~ Control amples are shown ln Table 6.
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10 70874
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From Table 6, it ls clear that the rubber compositions
of these examples have almost the same physical properties
as the known resorcinol containing composition, have longer
scorch tlme and have stronger adhesion to nylon cord, that
is, the same adhesive strength to both non-treated and RFL-
treated nylons as the known resorcinol compositions, and
much greater adhesive strength ln comparison with the Standard 3
_. composition (no resorcinol).
EXAMPLES 9-10
Mixing of the rubber compositions was conducted in the
same manner as set forth in Examples 1-4, the ingredients of
the compositions being shown in Table 7.
, The resulting rubber compositions were vulcanized at
148C for 30 minutes, and the test results are shown in
Table 8.
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From Table 8, it is clear that the rubber compositions
of these examples have more improved cutting resistance and
chipping resistance than the known rubber compositions.
- : :.. EXAMPLES 11-12
Mixing of the rubber compositions was conducted in the
same manner as set forth in Examples 9 and 10, and the
resulting rubber compositions were vulcanized and tested in
- lr _ . _.
the same manner as set forth in Examples 9 and 10.
The ingredients are shown in Table 9 and the test
results are shown in Table 10.
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From Table 10, it is clear that the rubber compositions
of these examples have more cutting resistance than the
known rubber compositions.
~ - EXAMPLES 13-14
~ixing of the rubber compositions was conducted in the
same manner as set forth in Examples 9 and 10, and the
................. resulting rubber compositions were vulcanized and tested in
the same manner as set forth in Examples 9 and 10.
. The ingredients are shown in Table 11 and the test
results are shown in Table 12.
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From Table 12, it is clear that the rubber compositions
of these examples have improved cutting resistance and
chipping resistance over known rubber compositions.
As is clear from the above description, the novel
S rubber compositions of this invention have been shown to
have excellent scorch stability., excellent adhesion to steel
. cords and nylon cords, and excellent chipping and cutting
resistance. Accordingly, they can be excellently used as
new adhesive agents for rubber and also as new agents for
improving cutting resistance and chipping resistance.
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