Note: Descriptions are shown in the official language in which they were submitted.
~ 7053
1 This invention relates to n novel antioxidant for rubber,
and more particularly an antioxidant for rubber h~ving an
excellent antioxidizing effect upon deterioration of vulcanized
natural or synthetic rubber or the like by light, ozone or
oxygen, and deterioration thereof by dynamic fatigue, especially
heat deterioration, and having no staining effect by coloring
even when applied to white rubber and the like, and further
preventing effect for the blooming when unvulcanized, and also
no lowering effect for the peeling resistance between rubber `
and rubber.
Generally, vulcanized rubber products of natural or
synthetic rubber are deteriorated by light, ozone or oxygen,
and also by dynamic fatigue or heat, and cannot be used further
more. Even in the case of unvulcanized rubber, such disadvantages
are known that there appear deterioration phenomenon such as
gelation or increase in viscosity during the storage or in the
mastication step at the processingO .
To prevent such deterioration phenomena, various anti-
oxidants or stabilizers are used. Especially for prevention of
deterioration by heat~ the antioxidant containing 2,2,4~
trimethyl-1,2-dihydroquinoline polymers as a main component . -
(antioxidant RD) is mainly used
However, the commercially available antioxidant of 2,2,4-
trimethyl-1,2-dihydroquinoline polymers has such disadvantages ';
that a blooming phenomenon (appearance of bluish oil film on
the surface of unvulcanized rubber) appears on the rubber
aclmixed with the antioxidant, and a peeling resistance between
rubber and rubber is considerably lowered.
As a result of extensive studies to remove or improve
said disadvantages, and judging that, though 2,2,4-trimethyl-
1,2-dihydroquinoline polymers are usually prepared from
aniline and acetone according to the following formula: ~-
- 2 ~ ~
7~5~
1 ~ ~2CH3C0Ctl3 = ~ 3 CH3~ C
l ¦ n
J, Craig / J, Amer, Chem. Soc., 60, 1458(1938)l reports that~
in the production of 2,2,4-trimethyl-1,2-dihydroquinoline
poLymers by condensing aniline and acetone at 100C in the
presence of a trace of concentrated hydrochloric acid, diphenyl- Fw_
amine, 4-isopropyldiphenylamine, p-cumidine, p,p'-diamino-2~2'-
diphenylpropane and further high mo~lecular weight substances
are contained as impurities, the present inventors presumed~ ~;
that the commercially available antioxidant comprising 2,2,4-~
trimethyl-1,2-dihydroquinoline polymers is contaminated with a
considerable amount of said amine impurities, and found, as a
result of analysis of such commercially available antioxidant
by gas chromatography~ that the materials detected cover as
many as 10-13 kinds including dimer and trimer of 2,2~4-trimethyl-
1,2-dihydroquinoline. Furthermore, there are no great difer~
ences in the number of materials detected among several commercial~
ly available industrial products. And it is a surprising Eact
that a considerable amount of primary amines such as p,p'-diamino~ ,~
2,2-diphenylpropane is contained as amine impurities, and it has
been also found that 2,2,4-trimethyl-1,2-dihydroquinolines
having various degrees of polymerization are widely distributed.
The present inventors have studied the relations among-
the distribution of the degree of polymerization of commercially i~
available antioxidant of 2,2,4-trimethyl-1,2-dihydroquinoline r"
polymer, the content of amine impurity and the blooming phenome- `~`
non of unvulcanized rubber containing such antioxidant, and have
found, as the result, that there is an evident correlation a~ong
~U~ 3
I ~hese, and the blooming phenomenon is more rarely observed with
an increasing content of 2,294-trimethyl-1,2-dihydroquinoline
dimer and a decreasing content of the amine impurities.
In view of the foregoing facts, the present invention is
to provide an antioxidant for rubber containing 2,2,4-trimethyl-
1~2-dihydroquinoline polymers of the following general formula
as the main component:
~ CH3
(~herein n = an integer of 0 to 2), which comprises purified t
2,2,4-trimethyl-1,2-dihydroquinoline polymers having more than
50% by weight of a dimer component of n = 0, and not more than
20% by weight of amine impurities other than said polymers.
The antioxidant of the present invention comprising purified
2,2,4-trimethyl~1,2-dihydroquinoline polymers can be prepared
20 according to several known processes, for example, (1) by
rectifying ordinary 2,2,4-trimethyl-1,2-dihydroquinoline mono-
mer and polymerizing it in the presence of a trace amount of
concentrated hydrochloric acid or anhydrous aluminum chloride
at 90 ~ 5C~ or (2) by condensing aniline with acetone in the
plesence of a catalytic amount of iodine, hydrogen iodide9
hydrogen bromide, aromatic sulfonic acid, sulfanilic acid, etc. ~i~
The antioxidant for rubber comprising purified 2,294-
trimethyl-1,2-dihydroguinoline polymers thus prepared contain
the dimer thereof as the main component and a small amount of
30 the trimer and the tetramer thereof in addition, and a very
small amount of amine impurities. To attain the object of
the present invention, it i5 necessary tha-t more than 50% by
weight of dimer component and not more than 20% by weight,
preferably not more than 10% by weight9 of the amine impurities
are contained. 10 to 40% by weight of the trimer and 0 to 7% by
~ 7~ ~ 3
1 weight of the tetramer can be contained. ~-;
The antioxidant of the present invention will hardly bring
about a blooming phenomenon ~nd a decrease in physical proper
ties of rubber, and can be used in a larger arnount than the
conventional antioxidant so far used. Usually, not more than 5
parts by weight, preferably 0.5 to 3 parts by weight thereof
can be added per lO0 parts by weight of rubber. The present
antioxidant can prevent not only a decrease in peeling
resistance between rubber and rubber due to said blooming
phenomenon, but also is very effective against deterioration by
heat, or light, ozone or oxygen, and other dynamic fatigue~
Furthermore, staining by coloring is hardly observed when
applied to white rubber, etc., and a solubility in rubber is
excellent.
The antioxidant of the present invention can be effectively
used for natural rubber (NR), and various synthetic rubbers such
as styrene-butadiene rubber (SBR), polybutadiene rubber (BR),
polyisoprene rubber (IR), etc., and shows a particularly good
effect on NR and S~R where the decrease in peeling resistance
due to the blooming phenomenon is a problem.
The antioxidant of the present invention can be used
together with other antioxidants such as N-phenyl-N'-isopropyl- ~'
p-phenylenediamine, a high temperature reaction product of i;~
diphenylamine with acetone, etc., so long as the object of the
present invention is not interrupted.
The present invention will be discribed in detail referring ~;
to the following examples.
Blue blooming tests of unw lcanized rubber sheets were '
30 carried out in the present ExampleO
100 parts by weight of unvulcanized rubber was blended with
0.5 to 3 parts by weight of various antioxidants shown in Tablel
to prepare rubber sheets, and number of days until the blue
blooming phenomenon appears was determined by blowing the air r
to the sheets at room temperature of about 25 C by a forcing fan,
~ 7 ~j3
1 for example, electric fan.
Table 1
Antioxidant used
(Quantitative analysis by gas chromatgraphy: % by weight)
\ - ~ . _ _ ~
\ Species Examples Comparative Conventional
\ Examples Produc-t
Com- \ _ _ . __ _
pO S i t iOIl\ A B C D E F ~ H
. . _ _ _ . _ __ .... ,
Dimer 75 S2 6255 57 4640 35
10 Trimer19 32 2325 14 2518 17
Tetramer 2 4 7 5 5 13 6 6
Aimmpinrities 4 12 8 15 24 16 36 40
~A) Blooming phenomenon in unvulcanized rubber blended with
naturaL rubber: `~
Unvulcanized rubber blended with natural rubber was
obtained according to the following Table 1-A.
Table l-A
- Natural rubber (NR) 100 parts by weight . ~r
FEF carbon black 40 " ;~'~
Aroma oil 1~ t
Stearic acid 3
Zinc oxide 5 " ;~
Accelerator 0.5 " ~`;
(N-oxydiethylene-2-Benzothiazole r~
sulfenamide) ?"`
Sul~ur 3 L,
Antioxidant 0.5 - 3 " ,~
~Table 1, A - H)
Number of days until the appearances of the blooming phenomena
in the sheets of unvulcanized rubber blended with natural
rubber were given in Table l-B.
~.''
7~ 3
l Table l-B
~ . . _ __ :_ _ _. __ _ __.___ . . _ ~
\ Species
Amount added\ A B C D E F G H
\ _ . . _
by weight 19 lO 12 lO 5 6 5 4
l.0 " lO 6 7 6 4 4 3 2
2.0 " 7 4 5 4 l 2 l l
3.0 " 3 2 2 2 l l l
_ ~ _ _ . . _ ~ _ _
(B) Blooming phenomenon -in unvulcanized rubber blended with
styrene-butadiene rubber (SBR):
Unvulcanized rubber blended with SBR was ob-tained according
to the ollowing Tabel l-C. .`
Table l-C
SBR lO0 parts by weight -
ISAF carbon black 40 "
Aroma oil lO "
Stearic acid l "
~inc oxide 4
Accelerator 0.5
(N-cyclohexyl-2-benzothiazole
sulfenamide) '~
(Tetramethylthiuram monosulfide) 0.2 " j~,
Sulfur 2 " ^,:,
~ntioxidant 0.5 - 3 parts by weight ~;
(Table l, A - H~
Number of days until the appearances of the blooming phenomena
in the sheets of unvulcanized rubber blended with SBR were r
given in Table l-D.
~``,
1 Table_l-D
. .... _ . . __ .. .. ..
Species
added ~ A B C D E F G H
. _ _ . _ . . _ _ _ . . _
0.5 parts by weight 45 or 30 45 or 25 15 19 13 10
more more
1.0 " " " 25 14 21 15 7 13 7 5
2 0 " " " 12 6 6 7 2 4 2 2
3 0 4 3 3 3 1 2
It is seen from Tables l-B and l-D that the antioxidant of
the present invention was much improved in the blooming
phenomenon.
Example 2 !~
Peeling tests of unvulcani~ed rubber sheets subjected to
the blue blooming tests of Example 1 for a definite number of
days were carried out in the present Example.
That is, said unvulcanized sheets (thickness : 4mm) were
laminated, and pressingly vulcanized at 145C for 30 minutes ~:
20 to prepare test piecesO The test pieces (width : 2.5cm) were t~:`
subjected to 20 times repetitions of stretching at the dyn~nic
strain of about 200% and the tensile speed of lOOmm/min, and `~
the peeling resistance was measured at the tensile speed of
50mm/min (kg/2.5cm).
(A)Measurement of peeling resistance in the case of natural .~
rubber blending: ~;
Peeling resistances of the unvulcanized rubber sheets of
natural rubber in Table l-A were measured as described above, and the
results were given in Table 2-A.
7~3
1 Table 2-A
(Samples after ten days of the blooming test)
. . _ _ _ _ . ~, ..
A B C D E F G H
.... ~ . , __ __ _ _
0.5 parts by weight22 21 22 20 14 16 14 14
~.0 " ll ,. 22 14 16 15 7 9 7 6
2.0 " " " 15 11 13 10 2 2 2 2
30 ~ _ 9 3 ~ 4 2 2 2 2
_ _ __ . _
(B) Measurement of peeling resistance in the case of styrene-
butadiene rubber (SBR) blending:
Peeling resistances of the unvulcanized rubber sheets of
SBR in Table l-C were measured as described above, and the
results were given in Table 2-B.
Table-2-B
(Samples after ten days of the blooming test)
~ Species _ r~
~madudnet~ A B C D E F G H ~`
.. ~ .. , __ . ~ .~ ~ _ ~ _ ,.
0.5 parts by weight 23 23 23 23 18 20 15 13 v
1.0" " " 23 20 22 18 8 11 7 7
2.0" " " 13 10 12 9 2 2 2 2 ~:
3 0" " _ 5 2 4 2 2 2 2 2 6'.;,
~; "
Interfacial peeling took place at the laminated face, and
an influence of the blooming phenomenon upon the peeling
resistance was large. In the antioxidant of the present
invention, a considerable improvement in the peeling resistance
was observed.
Example 3
Antioxidizing tests by heat of vulcanized rubber blended ~A
with natural rubber were carried out in the present Example
_ g
7~3
1Unvulcanized rubbers blended with natural rubber in
Table l-B were used, but those containing only 1.0 part by
weight of the antioxidant were used.
The unvulcanized rubber blended with natural rubber was
vulcanized at 145C for 30 minutes, and the vulcc~nized products
~ere subjected to antioxidizing tests by heat in test tubes
heated at 100C. Percent changes in physical properties
after 48 hours were determined. The results were given in
Table 3.
Table 3
:
` -- ...... _ _ _ .. _ _ .... ,, ~:
T ~ A B C D E F G H ~ ~
,.... ~ __ .. .. _ . .
Before aging
Elongation (%)489 488 480 482 483482 485 480
~- Tensile strength 230 235 230 228231 229 234 230
(kg/cm~ _ _ _ _
After aging
Percent change(%) -19 -24 -21 -24 -29 -31 -30 -35
., ... _ ___~_ _ , _ _ _ _ ___
It is seen from the results in Table 3 that, in the anti-
oxidant especially A, the antioxidizing effect by heat was
considerably observed. ~
Example 4. j.
Flexing tests (dynamic fatigue) of vulcanized rubbers
blended with natural rubbers were carried out in the present
Example.
~nvulcanized rubbers blended with natural rubbers in
Table l-B were used, but those containing only 1.0 parts by F
weight of the antioxidant were used.
The unvulcanized rubber blended with natural rubber was
vulcanized in the same conditions as in Example 3 to prepare
test pieces, and 300 times repetitions per minute of defor-
mation were given to the test pieces by a de Mattia machine
determine a time until the appearances of cracks. The results r'
were given in Table 4.
- 10 -
1 Table 4
. - 1 .. _I _ ~
Te ~ A B C D E F G H
Flex~ng 12 0 11.0 11.0 ~ 8.5 8.5 7.0 505
res iS tance (hr) ~ ~ _
It is seen from the results in Table 4 that the antioxidant
of the present invention hacl the excellent flexing resistance.
Example 5
Ozone deterioration tests of vulcanized rubbers blended
with natural rubbers were carried out in the present Example,
Unvulcanized rubbers blended with natural rubbers in
Table l-B (those containing only 1.0 parts by weight o~ the
~ntio~idant were used, and vulcanized under the same conditions
as in Example 3 to prepare test pieces. The time until
appearances of visually determinable cracks were measured in
an ozone weather meter at the ozone concentration of 40 pphm,
a temperature of 40C and a static percent elongation of 20%. ~
The results were given in Table 5. ~7:
Table 5 k.
~, ~
,~ . _ ___ .. -__ . ____ . __ ____
T ~ A B C D E F G H j~
_ ._ ~ ~ .. . _ . ._ _ P.'
Time until 6 or 6 or 6 or 6 or 4 or 4 or 2 or 2 or L
- - - - ~ ]. es 5 le s s 1 e s s 1 e s s le s s 1 es s les s 1 es s lx ~
~r
It is seen from the results of Table 5 that the anti- ~
oxidant of the present invention had the excellent resistance ~Y
to the rubber deterioration by ozone.
30 Example 6
Staining tests of white rubber were carried in the present
Example.
White rubber given in Table 6-A was used. F
~ 7~;3
1 Table 6-A .-
Natural rubber 100 parts by weight
Titanium oxide 30 "
. Calcium carbonate 20 "
Ultramarine blue 0.3 "
Zinc white 5'O0 "
di-o-tolylquanidine 0.3 "
di-benzothizyl disulfite 0.6 "
Sulfur 1.5 "
10Unvulcarlized white rubber in said Table 6-A was contacted
with unvulcanized rubber blended with natural rubber in Table
; l-B (those containing only 1.0 part by weight of the anti~
oxidant), and vulcanized under the conditions of Example 3.
After being left standing for two days, coloring was -
e~fected by ultraviolet irradiation, and the degree of staining
white rubber was visually determined. The results were ..
given in Table 6-B.
Table_6-B r~.
. - _ ~ __ _ . . .
- 20 ~ les A B C D ~
.' . ......... ...... ~ ...... ..
Foulingness Almost Slight Almost Slight f
.. ___ colorless yellow colorless yellow !`
;;
. ... ___ .. __ ... _ _ j~,
E F G H
. . ._ - .......... .... .__ ..
. Yellow ~ellow Yellow Yellow
It is seen from the results of Table 6-B that the anti-
- 30 oxidant of the present invention had the excellent non-staining-
ness to white rubber.
.,
- 12 -
.
. i
