Power transmission belt manufacture

A power transmission belt manufacture wherein a modified rubber blend is utilized as at least one portion of the belt, with the blend including a silane coupling agent, silica and carbon black. The blend is advantageously adapted for use as the cushion rubber embedding the load-carrying cords of the belt. The invention comprehends the use of the blend further as at least one of the compression and tension sections of the belt, as desired. The modified rubber blend is advantageously utilized in power transmission belts having widely varying configurations and characteristics.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to power transmission belts and in particular to a 
rubber compound for use in at least one section of the belt. 
2. Description of the Background Art 
A number of applications of rubber compounds using silicas and silicates 
are known. Illustratively, silicas and silicates are utilized in rubber 
compounds for use as shoe soles and heels wherein the silicas provide 
stiffness, abrasion resistance, flex resistance, and nonmarking 
characteristics. Processing rolls utilized in the manufacture of steel, 
paper and textiles utilize rubber blends having silica therein for 
toughness and nonmarking characteristics. Off-road tire treads and 
conveyor belt covers have utilized silica blended rubber to provide 
cutting and chipping resistance. Skim stocks for tire and belt cords have 
utilized silicas for adhesion characteristics, and automotive engine 
mounts have used silicas in the rubber blends for heat resistance. Bumper 
strips and impact-absorbing devices have used silicas for stiffness, 
adhesion and desired coloration. Garden hose and cable jackets have 
utilized silica blended rubber for extrusion, abrasion resistance, and 
color characteristics. 
In connection with the use of silica in the tire blends, increased silica 
content has been found to lead to a higher index of friction to provide 
improved stopping distance and starting traction characteristics. One 
disadvantage in the use of silica in tires has been the relatively high 
tread wear. In an attempt to reduce such wear, silane coupling agents have 
been utilized in the formulations. 
In power transmission belts, it has been conventional to utilize rubber 
blends having carbon black in substantial proportion. However, such belts 
have not proven completely satisfactory because of relatively short life. 
The need for improvement in durability and reliability of power 
transmission belts utilizing rubber blends as a component of one or more 
sections thereof has been manifest. A number of problems have arisen in 
the use of the conventional carbon black blend rubber belts. 
Illustratively, cracking has occurred in the adhesion surfaces between the 
load-carrying cords and the embedding rubber layer known as the cushion 
layer. This problem has been particularly vexatious relative to the 
adhesion surfaces adjacent the lower part of the load-carrying cords. 
Another problem has arisen in the prior art belts in the cracking in the 
border layers between the cushion rubber layer embedding the load cords, 
and the compression rubber layer inwardly thereof. 
The problem has been aggravated where the belts have been utilized in 
environments where the temperature of the belt rises 40 to 90 degrees 
Centigrade as a result of the heat generated in the running operation. 
While the use of ISAF and SAF carbon black have, to some extent, improved 
the reinforcement of the belt rubber, such reinforcement has not proven 
fully satisfactory. The need for not only improved cushion rubber 
strength, but also increased adhesiveness relative to the load-carrying 
cords and the adjacent belt section materials, has been manifest and 
continuing. No one heretofore has found a fully satisfactory solution to 
this vexatious problem. 
SUMMARY OF THE INVENTION 
The present invention comprehends the provision of a modified rubber blend 
for use as the embedding material of the load-carrying section of a power 
transmission belt wherein the blend comprises about 100 parts by weight 
rubber, about 0.1 to 5.0 phr (per hundred parts rubber) of silane coupling 
agent, about 10 to 60 phr silica, and about 2 to 60 phr carbon black. 
The invention comprehends the use of the modified rubber blend additionally 
or alternatively as one or both of the compression section and tension 
section portions of the belt. 
The use of the modified rubber blend has unexpectedly been found to provide 
substantially improved durability and life of power transmission belts 
avoiding the problems of the prior art discussed above.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is concerned with power transmission belts, such as 
belt 10, adapted to transmit power between a driver pulley 11 and a driven 
pulley 12 as a result of the belt being trained about the pulleys. Belt 10 
may be in the form of any of a wide range of different belts, such as 
those illustrated in sectional views, FIGS. 3-7. Illustratively, referring 
to the V-belt 10a of FIG. 3, the belt includes a load-carrying section 13 
defined by a plurality of load carrying cords 14 which extend 
longitudinally of the belt, i.e. in the direction about the pulleys 11 and 
12, as seen in FIG. 1. The cords are embedded in a body of rubber 15 which 
is conventionally referred to as the cushion layer. The cushion layer is 
disposed outwardly of the inner compression section 16 of the belt and 
inwardly of the outer tension section 17 of the belt. In the embodiment of 
FIG. 3, belt 10a is provided with a plurality of distributed short fibers 
18 extending transversely across the compression section. As will be 
obvious to those skilled in the art, the fibers may be utilized in the 
tension section additionally or alternatively. Belt 10a is further 
provided with a covering fabric 19 on the tenion section 17 and a cover 
fabric 20 on the bottom of the compression section 16, leaving the sides 
of the V-belt uncovered so as to define a raw edge belt. Belt 10b 
illustrated in FIG. 4 is similar to belt 10a except that the fabric 21 is 
caused to extend about the entire belt so as to define a wrapped belt. 
FIG. 4 illustrates the use of a compression section 16b omitting the 
reinforcing fibers 18 therefrom. Belt 10b utilizes a load-carrying section 
13 similar to that of belt 10a. 
More specifically, as shown in FIG. 2, the load-carrying cords 14 are 
embedded in spaced relationship to each other within the cushion rubber 
15. As is well known in the art, the cords may be wound in helical fashion 
lengthwise of the belts in providing the desired distribution thereof, as 
illustrated in FIG. 2. The present invention is concerned with the use of 
an improved modified rubber blend as the cushion rubber 15 so as to have 
improved association with the load-carrying cords 14 as well as with the 
adjacent compression and tension sections of the belt. 
More specifically, the present invention comprehends the provision of the 
rubber 15 as a modified rubber blend preferably including about 100 parts 
by weight rubber, about 0.1 to 5.1 phr of silane coupling agent, about 10 
to 60 phr silica, and about 2 to 60 phr carbon black. 
The invention comprehends a preferable formulation of the rubber blend as 
one wherein the rubber is about 100 parts by weight, the silane agent is 
about 0.3 to 2.0 phr, the silica is about 20 to 45 phr, and the carbon 
black is about 10 to 40 phr. 
It has been found desirable to maintain the silane coupling agent at at 
least about 0.1 phr to provide the desired reinforcing effect. Further, it 
has been found that it is desirable to maintain the silane coupling agent 
at no greater than about 5.0 phr to maintain the reasonable scorch time 
particularly in the case of such a belt formulated of chloroprene rubber. 
It has further been found desirable to maintain the silica phr as at least 
about 10 phr so as to provide the desired adhesive and tear strength 
characteristics. It has been found desirable to maintain the silica phr no 
greater than about 60 phr so as to limit the viscosity characteristics of 
the blend. 
The term "rubber" as used herein includes any of the conventionally known 
rubbers, including natural rubber, chloroprene rubber, styrene butadiene 
rubber, etc. 
The term "silane coupling agent" as employed herein includes Vinyl-Tris 
(.beta.-Methoxy Ethoxy) Silane, .gamma.-Glysidoxypropyltrimethoxy Silane, 
N-.beta.-(Aminoethyl).gamma.-Aminopropyltrimethoxy Silane, 
.gamma.-Mercaptopropyltrimethoxy Silane, Bis-(3-[Triethoxisilyl]Propyl-) 
Tetrasulfane, etc. The Bis-(3-[Triethoxisilyl]Propyl-) Tetrasulfane or 
.gamma.-Mercaptopropyltrimethoxy Silane coupling agents have been found to 
be particularly advantageously adapted for use in the cushion rubber 
blend. 
The invention comprehends the use of a titanium coupling agent in lieu of 
the silane coupling agent. 
As is well known to those skilled in the art, the rubber blends utilized in 
such power transmission belts may further include additives, such as 
softeners, antioxidents, processing agents, tackifiers, accelerators, and 
sulphurs. Illustratively, these additives may comprise stearic 
acidmagnesium oxide, zinc oxide, and 2-mercapto imidazoline. The blends 
may be produced by conventional mixing procedures, such as using Calender 
rolls, Banbury mixers, etc. In specific examples, the blends were mixed in 
a Banbury mixer and vulcanized under conventional vulcanizing conditions 
of approximately 150.degree. C. for 20 minutes. 
EXAMPLE I 
100 phr chloroprene rubber was blended with 2 phr stearic acid, 4 phr 
magnesium oxide, 2 phr antioxidant, 5 phr process oil, 10 phr HAF carbon 
black, 40 phr silica, 1 phr .gamma.-mercaptopropyltrimethoxy silane, 5 phr 
zinc oxide, and 0.3 phr 2-mercapto imidazoline. 
The physical properties of the vulcanized blend were as follows: 
______________________________________ 
Hardness (JIS-A) 74 at 25.degree. C. 
25% Modulus (kg/cm.sup.2) 
14.8 at 25.degree. C. 
50% Modulus (kg/cm.sup.2) 
19.2 at 25.degree. C. 
Tensile Strength (kg/cm.sup.2) 
202 at 25.degree. C. 
Elongation (%) 520 at 25.degree. C. 
Tear Strength (JIS-A) 80 at 25.degree. C. 
Hardness (JIS-A) 73 at 90.degree. C. 
25% Modulus (kg/cm.sup.2) 
14.4 (-3) 
50% Modulus (kg/cm.sup.2) 
19.0 (-1) 
Tear Strength (JIS-A) 51.0 (-36) 
______________________________________ 
Note: 
Numerals in parentheses indicate Rate of Change 
Adhesion of the blend to the load-carrying cords and to the adjacent 
compression and tension sections was found to be excellent. The cord 
utilized in the belt construction was a polyester cord which was 
RFL-treated and having a characteristic of 1100D/2.times.3. The adhesive 
characteristic as measured by the force required to tear the cord out of 
the cushion rubber was as follows: 
Adhesive Force (kg/cm) at 25.degree. C.: 29.5 
Adhesive Force (kg/cm) at 90.degree. C.: 20.1 
The adhesive force of conventional load-carrying section utilizing carbon 
black has been normally less than approximately 10 kg/cm at 90.degree. C., 
such low tear strength being a substantial contributing factor to early 
failure of the prior art belts. The prior art belts further had a 
relatively low adhesive force of approximately 17.3 kg/cm at 25.degree. C. 
so that the improved blend formulation may be seen to provide improved 
characteristics at room temperatures as well as at elevated temperatures 
as occur in the belt during operation. 
EXAMPLE II 
A similar blend having a slightly modified formulation is prepared as 
follows: 
100 phr chloroprene rubber was blended with 2 phr stearic acid, 4 phr 
magnesium oxide, 2 phr antioxidant, 5 phr process oil, 25 phr HAF carbon 
black, 30 phr silica, 0.7 .gamma.-mercaptopropyltrimethoxy silane, 5 phr 
zinc oxide, and 0.3 phr 2-mercapto imidazoline. 
The physical characteristics of this improved blend are as follows: 
______________________________________ 
Hardness (JIS-A) 76 at 25.degree. C. 
25% Modulus (kg/cm.sup.2) 
17.0 at 25.degree. C. 
50% Modulus (kg/cm.sup.2) 
21.9 at 25.degree. C. 
Tensile Strength (kg/cm.sup.2) 
199 at 25.degree. C. 
Elongation (%) 455 at 25.degree. C. 
Tear Strength (JIS-A) 65 at 25.degree. C. 
Hardness (JIS-A) 75 at 90.degree. C. 
25% Modulus (kg/cm.sup.2) 
16.3 (-3) 
50% Modulus (kg/cm.sup.2) 
21.5 (-2) 
Tear Strength (JIS-A) 43 (-34 
______________________________________ 
Note: 
Numerals in parentheses indicate Rate of Change 
The adhesive force characteristics of this blend are as follows: 
Adhesive Force (kg/cm) at 25.degree. C.: 27.2 
Adhesive Force (kg/cm) at 90.degree. C.: 17.7 
The two example blends described above were utilized in a raw edge V-belt, 
such as V-belt 10a of FIG. 3, having a total strength of 1015 mm and 
having a height of 9.0 mm and maximum width of 12.5 mm. These belts were 
trained over suitable pulleys 11 and 12 and run with the following 
results: 
______________________________________ 
Reference Exam- 
ple (Carbon 
Example Example 
Black Only) 
I II 
______________________________________ 
Time duration until 
48 230 248 
cracking appears (Hrs) 
Time duration until belt- 
256 1120 1298 
life is over (Hrs) 
______________________________________ 
The pulley size was 60 mm diameter and the running speed waas 3600 rpm 
under a load of 50 kg. The substantial improvement in crack resistance and 
belt life over the prior art belt utilizing carbon black only shows a 
dramatic and totally unexpected improvement. Not only does the invention 
provide substantially improved belt life, but further tends to show 
further improved results at running temperatures. 
Referring to FIG. 5, a banded belt 10c is shown to comprise a belt 
utilizing the improved blend as the cushion rubber portion 13 in each of a 
plurality of V-elements 27 maintained in side-by-side relationship by a 
band 22. As shown, the band may be provided with a covering fabric 23. 
Another form of belt is illustrated in FIG. 6 to comprise a belt 10d 
wherein the compression section 16d is provided with a plurality of 
V-shaped grooves 24 to define a plurality of side-by-side triangular ribs 
25 as the innermost portion of the compression section. 
Still another form of belt generally designated 16e is illustrated in FIG. 
7 to comprise a belt having a plurality of transversely extending grooves 
26 inwardly of the cushion section 13. The different belt configurations 
illustrated in FIGS. 3-7 are exemplary only, it being understood that any 
suitable belt configuration, both raw edge and wrapped, etc. may be 
utilized with the invention. Further more specifically, the invention 
comprehends that the improved modified rubber blend be utilized 
alternatively or additionally as the tension and compression section 
material, as desired. 
Thus, while the invention is advantageously adapted in providing high 
T-peel test characteristics providing improved bonding of the cushion 
rubber to the load-carrying cords and to the adjacent tension and 
compression sections, the additional characteristics of the modified 
rubber blend haave been found unexpectedly to also be advantageously 
adapted for use as the tension and compression sections themselves. 
The invention provides an improved modified rubber blend for use in power 
transmission belts which maintains a high strength and adhesion 
characteristic at elevated belt-running temperatures providing extended 
belt life and durability. The increase in these parameters is unexpectedly 
great and the blend of the present invention provides a novel and simple 
solution to the vexatious problem of cracking and short useful life of the 
prior art power transmission belt utilizing carbon black in the absence of 
the silica and silane coupling ingredient. 
Having described our invention as related to the embodiments set out 
herein, it is our intention that the invention be not limited by any of 
the details of the description, unless otherwise specified, but rather, be 
constructed broadly within its spirit and scope as set out in the appended 
claims.