Transmission belt

A transmission belt including a part formed by a vulcanized product of a rubber composition comprising 100 parts by weight of chloroprene rubber, 1 to 30 parts by weight of zinc powder and 0.5 to 10 parts by weight of 4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine, and having a high level of dynamic heat resistance and a long life.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a transmission belt. More particularly, it is a 
transmission belt having a part formed from vulcanized chloroprene rubber. 
2. Description of the Prior Art 
There is an increasing demand for a transmission belt exhibiting a high 
level of dynamic heat resistance and having a long life even at a high 
temperature. For example, a transmission belt installed in an automobile 
has come to be required to withstand a very high temperature to which it 
is exposed as a result of a reduction in size of the automobile. 
A V-belt, or polyribbed belt is generally required to be capable of 
withstanding lateral pressure, as it by virtue of a wedge effect transmits 
power from a driving pulley to a driven one. As the greater part of the 
lateral pressure bears on the bottom rubber layer of the belt, the layer 
is required to have a high modulus. The rubber which is used in a toothed, 
or plain belt is also required to have a sufficiently high modulus for 
withstanding any shearing force exerted by the pulleys. 
If a transmission belt is made by using rubber having a high modulus, 
however, a large amount of heat is usually generated in the belt when it 
is bent. This presents a serious problem particularly if the belt is 
exposed to a high temperature as hereinabove stated. Its temperature 
becomes so high that it suffers from heavy deterioration by heat during 
its travel and results in cracking and even breaking soon. 
It is known that the use of an appropriate aging inhibitor is important for 
improving the heat resistance of chloroprene rubber. It is known that 
p-(p-toluene-sulfonylamide)diphenylamine and p,p'-dioctyldiphenylamine 
are, for example, effective as aging inhibitors. None of these aging 
inhibitors, however, exhibits any appreciable effect in improving the 
dynamic heat resistance of chloroprene rubber, though they may improve its 
static heat resistance when used in combination with zinc white. 
A different method of improving the heat resistance of chloroprene rubber 
is proposed in the Japanese patent application laid open under No. S 
50-87437. The proposed method is characterized by vulcanizing a mixture of 
chloroprene rubber, phenyl-.alpha.-naphthylamine as an aging inhibitor, 
and a zinc powder. The rubber so vulcanized, however, still fails to 
exhibit any improved dynamic heat resistance, though it may have an 
improved static heat resistance. 
SUMMARY OF THE INVENTION 
Under these circumstances, it is an object of this invention to provide a 
transmission belt including a part formed from chloroprene rubber 
exhibiting an improved dynamic heat resistance, and having a long life 
even if exposed to a high temperature. 
This object is attained by a transmission belt having a part formed from a 
vulcanized product of a rubber composition consisting of 100 parts by 
weight of chloroprene rubber, 1 to 30 parts by weight of zinc powder and 
0.5 to 10 parts by weight of 
4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine. 
More specifically, the vulcanized product forms the bottom rubber layer of 
a transmission belt which is united with a bonding rubber layer in which 
tension members are embedded. It greatly improves the oxidation resistance 
and dynamic heat resistance of the bottom rubber layer and therefore the 
belt as a whole, and thereby renders the belt durable for a long period of 
time even in an environment in which a high temperature prevails. 
Other features and advantages of this invention will be apparent from the 
following description and the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION 
A polyribbed belt embodying this invention is shown in FIG. 1. It comprises 
a top surface layer 1 formed by one or more plies of rubber-coated canvas, 
a bottom rubber layer 5 having ribs 4, and a bonding rubber layer 3 
disposed between the top surface layer 1 and the bottom rubber layer 5 for 
joining them together. A plurality of tension members 2 are embedded in 
the bonding rubber layer 3. Each tension member 2 may, for example, 
comprise a cord of polyester, polyamide, carbon or glass fiber, or steel 
having a low degree of elongation. The bottom rubber layer 5 contains 
short fibers 6 which are distributed throughout it along its width to 
increase its resistance to lateral pressure. 
According to a salient feature of this invention, the bottom rubber layer 5 
is formed from a vulcanized product of a rubber composition consisting of 
100 parts by weight of chloroprene rubber, 1 to 30, preferably 3 to 15, 
parts by weight of zinc powder, and 0.5 to 10, preferably 1 to 5, parts by 
weight of 4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine having the 
formula: 
##STR1## 
The zinc powder may have a particle diameter of 0.1 to 10 microns. Its 
preferred particle diameter is in the range of 1 to 5 microns. 
The vulcanized product of the chloroprene rubber composition greatly 
improves the dynamic heat resistance of the lower rubber layer during the 
movement of the belt, as well as its oxidation resistance. Therefore, the 
belt exhibits a long life even if it may be exposed to a high temperature. 
If the composition contains only less than one part by weight of zinc 
powder for 100 parts by weight of chloroprene rubber, it does not produce 
any satisfactory improvement in the dynamic heat resistance of the belt. 
If it contains more than 30 parts by weight of zinc powder, its scorching 
takes place so rapidly that its processing is difficult. 
If the composition contains only less than 0.5 part by weight of 
4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine for 100 parts by weight 
of chloroprene rubber, it does not achieve any satisfactory improvement in 
the dynamic heat resistance of the belt irrespective of the use in 
combination of the zinc powder. If its proportion exceeds 10 parts by 
weight, it prevents the vulcanization of the rubber and the resulting belt 
is so low in lateral pressure and shearing force resistance as to break 
soon. 
Although the vulcanized product of the chloroprene rubber composition has 
been described as forming the bottom rubber layer of the belt, it can also 
be used to form its bonding rubber layer or the rubber coating the canvas 
forming its top surface layer. The same is the case with any corresponding 
part of a V-belt and any rubber coating the canvas forming the bottom 
surface layer of any such belt. In other words, the term "part" of a belt 
as herein used for defining the invention not only means its bottom rubber 
layer, but also covers any such other part as its bonding rubber layer. 
The term "part" further includes, for example, the rubber layer of a 
toothed belt in which tension members are embedded, the rubber coating the 
canvas covering its teeth, the rubber layer of a plain belt in which 
tension members are embedded, and the rubber coating the canvas covering 
its top and/or bottom surface. 
The chloroprene rubber composition which is used for making the belt of 
this invention may further contain not only any vulcanizing or reinforcing 
agent that an ordinary chloroprene rubber composition usually contains, 
but also other additives, such as a filler, a softener, a plasticizer, a 
vulcanizing accelerator, a coloring agent and a lubricant. Examples of 
these additives include carbon black and silica as the reinforcing agent, 
light and heavy calcium carbonate as the filler, aromatic, naphthenic and 
paraffinic oils as the softener, dioctyl phthalate or adipate as the 
plasticizer, di-o-tolylguanidine dicatechol borate and TMU as the 
vulcanizing accelerator, red oxide as the coloring agent, and stearic acid 
as the lubricant. 
A known or usual method can be employed for making the transmission belt of 
this invention. For example, chloroprene rubber and the necessary and 
desirable additives are kneaded together in a Banbury mixer, and the 
resulting mixture is rolled by calender rolls to form a rubber sheet in 
which short fibers are uniformly distributed and equally oriented. The 
sheet is cut to suit the mold width, and after any necessary canvas and 
tension members have been laid on the sheet so that the short fibers may 
be oriented along the belt width, the whole is placed in a vulcanizer and 
the rubber composition is vulcanized. Then, the vulcanized product is 
ground into the shape of a belt and cut to the desired width. 
The invention will now be described more specifically with reference to a 
few examples thereof, as well as comparative examples. It is to be 
understood that the following description is not intended for limiting the 
scope of this invention. 
EXAMPLES 
Various chloroprene rubber compositions were each prepared by kneading in a 
Banbury mixer the materials shown in TABLE 1. Each composition was rolled 
by calender rolls to form a sheet of unvulcanized rubber in which short 
nylon-66 fibers having a thickness of 2 D and a length of 6 mm were 
oriented in a direction corresponding to the width of a belt. The sheet 
was subjected to 30 minutes of vulcanization at 150.degree. C. to produce 
a sheet of vulcanized rubber. The properties thereof are shown in TABLE 1. 
A polyribbed belt having three ribs and having a length of 975 cm was made 
by using each unvulcanized rubber composition for its bottom rubber layer. 
Its dynamic heat resistance was examined by a traveling test. The 
traveling test was conducted by passing the belt around a driving pulley 
having a diameter of 120 mm, a driven pulley having a diameter of 120 mm 
and an idle pulley having a diameter of 45 mm, placing a load of 12 hp on 
the driven pulley and a set weight (tension) of 85 kgf on the idle pulley, 
and rotating the driving pulley at a speed of 4900 rpm to cause the belt 
to travel. The test was conducted in a place having a temperature of 
85.degree. C. The belt was kept traveling until its bottom rubber layer 
cracked, and the time which had passed before such cracking occurred was 
taken as a measure of the life of the belt. The temperature of the bottom 
rubber layer was measured at the end of the life of the belt. The results 
are shown in TABLE 1. 
In EXAMPLE 1, the chloroprene rubber composition contained not only 
4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine as an aging inhibitor, 
but also zinc powder, and the vulcanized product thereof formed the bottom 
rubber layer of a transmission belt according to this invention. The belt 
exhibited a high degree of dynamic heat resistance and a long life, while 
its bottom rubber layer was maintained at a low temperature. These results 
apparently confirm that the zinc powder enables the effective dissipation 
of heat from the traveling belt and thereby the high dynamic heat 
resistance of the belt according to this invention. 
In COMATIVE EXAMPLE 1, the bottom rubber layer of the belt was formed 
from the vulcanized product of a conventional chloroprene rubber 
composition containing p,p'-dioctyldiphenylamine as an aging inhibitor. 
The belt exhibited a low dynamic heat resistance and had, therefore, only 
a short life. 
In COMATIVE EXAMPLE 2, the composition did not contain any zinc powder, 
though it contained the same aging inhibitor as that which had been used 
in EXAMPLE 1. It yielded only a belt having a short life. Its bottom 
rubber layer had at the end of its life a temperature which was over 
10.degree. C. higher than that as measured in EXAMPLE 1. The same was true 
of the bottom rubber layer of the belt according to COMATIVE EXAMPLE 1. 
In COMATIVE EXAMPLE 3, the composition contained 
p,p'-dioctyldiphenylamine and zinc powder, and yielded a belt having a 
bottom rubber layer which showed at the end of its life even a temperature 
which was lower than that as measured in EXAMPLE 1. Its life was, however, 
not a great improvement over the results which had been obtained in 
COMATIVE EXAMPLES 1 and 2. 
In COMATIVE EXAMPLE 5, the composition contained 
4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine and zinc powder, but 
the use of too large a proportion of the former disabled the satisfactory 
vulcanization of the rubber. The traveling belt was heavily worn and broke 
very soon. These results confirm that the excellent results as achieved by 
the belt of this invention can be achieved only when an appropriate 
proportion of 4,4'-(.alpha.,.alpha.-dimethylbenzyl)diphenylamine is used 
with zinc powder. 
In COMATIVE EXAMPLES 6 and 7, conventional aging inhibitors were used 
with zinc powder, but neither of the belts showed any substantially 
improved life. 
No description is made of any other example or the results thereof, as they 
are obvious from TABLE 1. 
TABLE 1 
__________________________________________________________________________ 
Compara- 
Ex- Ex- tive Ex- 
ample 
Comparative Example 
ample 
Example 
ample 
Comparative Example 
1 1 2 3 2 4 3 5 6 7 8 
__________________________________________________________________________ 
Chloroprene rubber 
composition.sup.1 
Chloroprene rubber.sup.2 
100 100 100 100 100 100 100 100 100 100 100 
Stearic acid 1 1 1 1 1 1 1 1 1 1 1 
Magnesia 4 4 4 4 4 4 4 4 4 4 4 
Octamine.sup.3 -- 4 -- 4 -- -- -- -- 0.5 -- -- 
CD.sup. 4 4 -- 4 -- 4 4 10 15 -- -- -- 
PA.sup. 5 -- -- -- -- -- -- -- -- -- 4 -- 
810NA.sup. 6 -- -- -- -- -- -- -- -- -- -- 4 
Process oil 8 8 8 8 8 8 8 8 8 8 8 
HAF carbon 35 35 35 35 35 35 35 35 35 35 35 
Short polyamide fiber 
20 20 20 20 20 20 20 20 20 20 20 
Zinc white 5 5 5 5 5 5 5 5 5 5 5 
Zinc powder.sup.7 
5 -- -- 5 30 40 5 5 1 5 5 
Mooney scorch time of 
12'13" 
&gt;30' 
&gt;30' 
12'10" 
1'30" 
0'15" 12'15" 
13'00" 
&gt;30' 12'08" 
12'11" 
unvulcanized rubber.sup.8 
Properties of vulcanized rubber 
In parallel to grain direction: 
10% modulus (kg/cm.sup.2) 
56 54 55 55 54 50 21 8 55 54 55 
Stress of rupture (kg/cm.sup.2) 
110 92 103 115 102 95 92 41 101 104 101 
Elongation at rupture (%) 
280 260 230 270 240 270 370 510 260 250 260 
At right angles to grain direction: 
Hardness (deg.) 
86 86 85 86 86 86 85 79 86 85 86 
Stress at rupture (kg/cm.sup.2) 
105 100 103 105 106 104 100 42 101 107 101 
Elongation at rupture (%) 
288 270 272 291 289 291 360 472 275 282 275 
Tensile test after heat aging: 
Change in hardness (deg.) 
+6 +11 +10 +9 +6 +6 +5 +3 +8 +9 +8 
Change in stress at rupture (%) 
+5 +6 +1 +3 +10 .+-.0 +1 +1 +3 +3 +3 
Change in elongation at 
-44 -52 -50 -47 -46 -45 -41 -43 -46 -48 -46 
rupture (%) 
Dynamic heat resistance of traveling belt 
Life of bottom rubber 
643 251 246 325 660 Processing 
552.sup.9 
45.sup.9 
470 325 470 
layer which ended by cracking, impossible 
unless otherwise noted (hr) 
Temp. of bottom rubber 
114 125 126 113 110 115.sup.9 
116.sup.9 
118 114 118 
layer (.degree.C.) 
__________________________________________________________________________ 
Notes: 
.sup.1 Parts by weight. 
.sup.2 Neoprene GRT. 
.sup.3 p,p' dioctyldiphenylamine. 
.sup.4 4,4' (.alpha.,dimethylbenzyl)diphenylamine. 
.sup.5 Phenylnaphthylamine. 
.sup.6 Nisopropyl-Nphenyl-p-phenylenediamine. 
.sup.7 Zinc powder UF having a particle diameter of 1 to 5 .mu.m. 
.sup.8 JIS K 6300, MS 125.degree. C.