Note: Descriptions are shown in the official language in which they were submitted.
10`'~ ~7~:~
1 The present invention relates to a process for pro-
ducing vulcanizable acrylic rubber. ,
Conventional acrylic rubbers are stable to heat and
oilproof because of high polarity of their ester structure, but
are unvulcanizable with sulfur because they do not have any
unsaturated groups or double bonds in their polymer backbone.
Therefore, the conventional process for producing acrylic rubbers
is by copolymerizing acrylic esters with a suitable amount of a
cross-linking monomer which reacts with a vulcanizing agent such
as soaps, ethyltetramines and tetraethylpentamines, and curing
the copolymer with such a vulcanizing agent. Such monomers
include those which contain halogen such as ~-chloroethyl vinyl
ether and vinyl chloroacetate, and those which contain an
epoxy group such as allyl glycidyl ether, glycidyl acrylate and
glycidyl methacrylate.
Such conventional acrylic rubbers are, however, liable
to scorch during storage and have low resistance to cold and
poor processibility. Particularly, the acrylic rubbers produced
by use of liquid polyamine as a vulcanizing agent have undue
adhesiveness to a mixing roll, poor bin stability, high corrosive-
ness, and offensive odor and toxicity coming from the amine.
It is an object of this invention to provide a processof producing vulcanizable acrylic rubber which does nc~ have
such disadvantages.
According to the present invention, an acrylic ester
or esters are copolymerized with a malonic acid derivative
having an acti~e methylene group to produce acrylic rubber which
can be cured with vulcanizing agents in the thiuram series
~or cross-linking.
- 2
109~7~2
1 FIG. 1 is a graph showing the vulcanization curves
for ~n acrylic rubber produced according to this invention
and for the conventional acrylic rubber.
FTG. 2 is a similar graph for the acrylic rubbers pre-
pared in Example 9.
The malonic acid derivative having an active methylene
group utilized in the present invention has the following general
formula:
/ COORl
C 2 \ (1)
wherein Rl represents vinyl, allyl or methallyl group and X
represents COOR2 or cyano group.
First, if X represents COOR2 in the formula (1), the
malonic acid derivative has the following general formula:
~ COORl
2Q CH2 (2
COOR
wherein R2 represents methyl, ethyl or propyl group. Thus,
the derivatives are malonic acids with an active methylene
group having one of two acid radicals esterified with an
unsaturated alcohol such as allyl alcohol, and having the
other acid radical esterified with a saturated alcohol. Such
derivatives include allyl ethyl malonate and allyl methyl
malonate, for example.
10~7~2
1 A process for producing the former will be described
by way of example. A mixture of 1 mole of ethyl cyanoacetate,
1 mole of sulfuric acid and 1 mole of water is kept at 80C or
lower for about four hours under stirring. 1.5 mole of allyl
alcohol is added, the mixture being allowed to react with slow
stirring at room temperature for a~out 72 hours. The mixture
is then rinsed dehydrated and distilled under reduced pressure.
During distillation, ethyl cyanoacetate distills off first and
allyl ethyl malona~e distills off last. In this process, if
allyl cyanoacetate and ethyl alcohol are used as the starting
materials the reaction product contains only allyl cyano-
acetate and allyl ethyl malonate, containing no ethyl cyano-
acetate which has a bad effect on cross-linking.
Next, if X represents cyano group in the formula (1),
the malonic acid derivative has the following general formula:
~ COORl
2 (3)
CN
wherein Rl represents vinyl, allyl or methallyl group. The
malonic acid derivatives include esters of cyanoacetic acid
(that is, malonic acid mononitrile) having an active methylene
group with an unsaturated alcohol, such as allyl cyanoacetate
or methallyl cyanoacetate, and esters thereof with hydroxy-
ethyl acrylate or hydroxyethyl methacrylate.
Such malonic acid derivative having the general formula
~3) may be produced by the conventional processes, one of which
will be described by way of example. One part by weight of
p-toluene sulfonic acid as a catalyzer is added to a mixture
3-~
~0~7~Z "
1 of 100 parts of cyanoacetic acid, 100 parts of allyl alcohol,
50 parts of benzene and 50 parts of cyclohexane. The mixture
undergoes esterification at 70 - 80C for about 24 hours while
refluxing by means of a phase separator to remove water. After
reaction, it is cooled, rinsed, dehydrated and distilled to
remove the solvents. Thereafter it is further distilled under
reduced pressure of 10 mmHg. The derivative aimed at is
obtained by collecting the fraction at 110~ - 112C.
The acrylic esters used in this invention are
methylacrylate, ethylacrylate and butylacrylate.
In the copolymerization according to this invention,
the amount of the malonic acid derivative having the general
formula (2) or (3) is preferably 2 - 10% by weight, and more
preferably 2 - 6%, relative to the acrylic ester. If it were
less than 2~, the addition of malonic acid derivative would not
have a sufficient effect, whereas for more than 10~ the curing
rate would be much higher and the tensile strength would increase
owing to o~er-cure, but the hardness would increase, thus
resulting in lower elongation and elasticity.
The reaction temperature for copolymerization is
50 - 70C, and the reaction time is preferably 30 to 40 minutes.
As vulcanizing agents used for the acrylic rubber
produced according to the present invention, tetramethylthiuram
disulfide and tetraethylthiuram disulfide are preferable. Also,
tetramethylthiuram monosulfide or thiazole is preferably used
as a vulcanizing accelerator.
The acrylic rubbers produced according to the present
invention show much higher curing rate and mar~ed plateau
effect in comparison with the conventional acrylic rubber cured
with amines, as will be seen in FIG. 1 wherein (~) is the
10947~2
1 vulcanization curve for the acrylic rubber produced according
to this invention and (B) is the curve for conventional acrylic
rubber. The present acrylic rubbers also retain resistance
to heat, oil, ozone, weathering and bend-cracking which the
conventional acrylic rubber has. Furthermore, they have
additional advantages of better processibility with a mixing
roll, freedom from scorch during processing or storage, no
corrosiveness to a curing mold and easy adhesion to metal
inserts. Besides the present acrylic rubbers allow use of white
carbon in the silica or talc series as well as the conventional
carbon black as a reinforcing agent. This provides greater
flexibility for production of colored rubber.
The acrylic rubber produced according to the present
invention may be formed into rolls, seals, gaskets, "O" rings,
hoses and so on.
The following examples are included merely to aid in
the understanding of the present invention. Unless otherwise
stated, quantities are expressed as parts by weight.
Example 1
A~ In a flask were put 200 parts of water, 0.5 part of sodium
laurylsulfate and 2 parts of polyoxyethylene lauryl ether as
emulsifiers, 5 parts of allyl ethyl malonate, 0.05 part of
potassium persulfate as a polymerization initiator and 0.05
part of so~ium hydrogen biculfite as redox catalyst. The
mixture was heated to 50-70C while blowing ~itrogen gas there-
into and 95 parts of ethyl acrylate was added drop by drop,
taking 30 to 40 minutes, for emulsion polymerization to give
vulcanizable acrylic rubber.
B) To 100 parts of the acrylic rubber thus prepared in (A)
were added 50 parts of MEF (medium extrusion furnacel carbon,
~0947~2
1 1 part of stearic acid, 2.4 parts of tetramethylthiuram
disulfide and 3.3 parts of dibenzothiazolyl disulfide.
After kneading well in an open roll, the mixture was put
into a curing mold and heated at 170C for 10 minutes.
The rubber slab thus made was subjected to post cure at
150C for 16 hours. Table 1 summarizes the physical
- 6a -
~0~?~742
1 properties of the cured acrylic rubber in an
original test, an air heat a2ing test at 1~0C
for 70 hours and oil resist~nce tests, respectively.
Table 1
'~roperties Hardness Te~sile Elongation Volume
\ (in Hs) strength 2 percentage change
Eind of Tes ~ ~ (i = (i. ~) p rD:~=a~c
Ori~inal test 74 123 250
Air heat ag~ng 78 142 215
test at 150 C
for 70 hours
Oil resistance
test
with JIS N8.1 78 131 270
oil at 150 C
for 70 hours
with JIS ~8.3 1 69 118 310
oil at 150 C
f or 70 hours I I
~0 ~ I
(JIS is an abbreviation of the Japanese Industrial Standard.)
~xample 2
Except that 4 parts of allyl methyl malon'te
and 96 parts of ethyl acrylate were used7 the s~,me
mixi~g ratio and reaction conditions as in ~xample 1
were used to prepare ~ulcanizable acrylic rubber.
To 100 parts of the acrylic rubber were added 50
parts of white carbon, 1 part of stearic acid, ~.4 parts
of tetraethylthiuram disulfide and 3.3 parts of
dibenzothiazolyl disulfide After kneading~ the
mixture ~s pre-cured at 170C for 10 minutes and ~i?ost-eured
109~742
1 at 150C for 4 hours. ~able 2 shows the physical
properties of the cured acrylic rubber measured as in
Example 1.
Table 2
\ Properties Hardnessl ~ensile ~longation Volume
\ I (in Hs) strength 2 percentage change
\ I (in kg/cm ) (in ~) p(rcentage
Eind of ~es ~ I
~ ~ _
Original test lll 74 115 260
Air heat agOing I 79 1~5 270
test at 150 c I I
~or 70 hours I l
li
Oil resistance
test
with JIS Ng.1 78 ' 1 ~7 230 1 _o . 8
oil at 150 C
for 70 hours ¦
with JIS ~8~3 l 70 1 110 1 330 +11.7
oil at 150 c
for 70 hours
E~mple 3
Except that ~ parts o~ allyl ethyl malonate, 80
parts o~ ethyl acrylate and 15 parts of butyl acrylate
were used as monomers 7 the s~me mixing ratio and
reaction conditions as in Example 1 were used. ~he
acrylic rubber thus ma~e was cured in the same m.~nner as
20 in Example 1 except that the pos. cure time ~A~'as 7
hours. 'rable ~ shows the physical properties o~ the
cured acrylic rub`~er.
" 10~474Z
1 ~able 3
\ Properties Hardness Tensile Elongation Volume
\ (in Hs) strength 2 percentage change
\ (in k~/cm ) (in o/O) P(in o70) g
Eind of Tes ~
\ .,
Original test 65 109 300
Air heat ag~ng ¦ 74 121 240
test at 150 C I
for 70 hours
Oil resistance ¦
test
with JIS ~8.1 ¦ 76 118 250 +2.
oil at 150 C
for 70 hours
with JIS ~8.3 ~ 58 102 380 +19.3
oil at 150 C
for 70 hours i
_
Example 4
Except that 8 parts of all~l ethyl malonate and
92 parts of ethyl ac~late were used, the same mixin~
ratio and reaction conditions as in Example 1 were
used to produce vulcanizable acrylic rubber. It was then
cured as in Example 1 except that tetraethylthiuram
disulfide was used instead of tetramethylthiuram
di~ulfide. Table 4 shows the physical properties of
the cured acrylic rubber.
3o
~09~742
1 Table 4
\ Properties Hardnessl ~ensile Elongation Volume
\ (in Hs) strength 2 percentage change
\ (in kg/cm ) (in %) (ln %)
~ind of ~est\
\
Original test 79 152 180
Air heat ag~ng 84 168 150
test at 150 C
for 70 hours
Oil resistance
test
with JIS Ng.1 83 162 190 -0.9
oil at 150 C
for 70 hours
with JIS ~8 3 73~ 147 270 +11.8
oil at 150 C
for 70 hours
~xample 5
A) In a flask were put 200 parts of water, 0.5 part
of sodium laurylsulfate and 2 parts of polyoxyethylene
lauryl ether, 5 parts of allyl cyanoacetate, 0.05
part of potassium persulfate and 0.05 part of
sodium nydrogen bisulfite. The mixture was heated
to 50-70~C while blowing nitrogen gas thereinto and
95 parts of ethyl acrylate was added drop by drop,
taking 30 to 40 minutes, for emulsion polymerization
to give vulcanizable acrylic rubber.
3o
~) To 100 parts of the acrylic rubber thus prepared
~~ were added 50 parts of ME~ carbon, 1 part of ~tearic
'10!~7~2
1 acid~ 2 parts of tetramethylthiuram disulfide and
2 parts of dibenzothiazolyl disulfide. After
kneading well in an open roll, the mixture was put
into a curing mold and heated at 170~ for 10
minutes. The rubber slab thus made was subjected
to post cure at 150C for 16 hours. ~able 5 shows
the physical properties of the cured acrylic rubber.
~able 5
\ Properties Hardness Tensile Elongation Volume
\ (in Hs) strength 2 percentage change
\ (in kg/cm ) (in ,b) ~ercentage
Kind of ~est \
\ . .
Original test 73 145 260
Air heat ag~ng 79 142 226
test at 150 C
fo ~ ours
Oiltresistance
with JIS ~8'1 78 138 ~73 -0.9
oil at 150 C
for 70 hours
with JIS ~00.3 67122 ¦ 310 +12.1
oil at 150 C
for 70 hours
Y l
~.,
Example 6
Except that 7 p3rts of allyl cyanoacet~te, 15 -parts
of meth~l acrylate and 78 parts of ethyl acrylate ~ere
3~ used as monomers, the same mi~ing ratio and reaction
conditions as in ~xample 5 were used.
o 100 parts of the acrylic rubber thus ~repared
109~t742
1 were added 50 parts of white carbon as a reinforcing
agent, 1 part of stearic acid, 3 parts of tetraethylthiuram
disulfide and 3 p~rts of diben~othiazol~l disulfide.
The acrylic rubber was cured as in Example 5 except
that the post cure time was 4 hours.
Example 7
Except that ~ parts of allyl cyanoacetate, 10 parts
of acr~lonitrile and 85 parts of but~l acrylate were
used, the same mixing ratio and reaction conditions as
in Example 5 were used.
The acrylic rubber thus prepared was cured as in
Example 5 except that 1.5 parts of dibenzothiazolyl
disulfide were used and that the post cure time was 7
hours. Table 6 shows the physical properties of the
cured acrylic rubber.
Table 6
Propertiesl~Iardness Tensile ¦ Elongation Volume
\ (in Hs) strength 2 I percentage change
\ (in kg/cm ) (in ~) ~ercentage
Kind of ~est \ I
_
Original test 70 135 210
. .
Air heat ag~ng 75 162 1 206
test at 150 C
for 70 hours
Oil resistance ¦
test I '~
with JIS ~8~1 7 ~ 5 241 I +0.5
oil at 150 C
for 70 hours I ~ I
with JI~ ~8.3 61 112 25~ +1~.4
oil at 150 C
for 70 hours
10~742
1 EYample 8
Except that 7 parts of allyi cyanoacetate and 9~
parts of ethyl acrylate were used as monomers, the s~me
mixing ratio and reaction conditions as in ~xample 5
were used~
~ o .100 parts of the acrylic rubber thus prepared
were added 50 parts of MEF carbon, 1 part of stearic
acid, 2 parts of tetraethylthiuram disulfide and 2 parts
of dibenzothiazolyl disulfide. ~he acrylic rubber was
cured as in Example 5 except that the post cure time was
4 hours.
Example 9
~ he vulcaniza~le acrylic rubber prepared in step (A)
of Example 5 was cured at 170C by use of such vulcanizing
agent, accelerators and retarder as shown in Table 7.
Table 7
~est No. ¦ 1 2 1 3
Acrylic rubber 100100 ¦ 100
partsparts I parts
MEF carbon 5 1 50 1 50
Stearic acid
~etramethylthiuram 12 1 2 2
disulfide
Dibenzothia~olyl 12 ¦ 2 2
disulfide
~etramethylthiuram '0.5 1 - , 0
monosulfide l I ,
~-phenyl~ - 2
naphthylamine
(retarder)
~ .
109"7~Z
1 ~ig. 2 shows the vulcanization curves for these
three tests. This test results show that the acrylic
rubber produced according to the present invention has a
large advantage over the conventional acrylic rubber
that the rise or start of vulcanization is adjustable
by using a vulcanization accelerator or retarder.
