Note: Descriptions are shown in the official language in which they were submitted.
1~)68846
1 ELASTOMERIC MATERIALS REINFORCED
` WITH SMALL DIAMETER GLASS FIBERS
Background of the Invention
The invention herein relates to fiber reinforced
elastomeric materials. More particularly, it relates to
rubber and rubber-like natural and synthetic elastomeric
compositions reinforced with very small diameter glass
fibers. The elastomeric materials reinforced in accordance
with the present invention find use in various heated and
moulded rubber products, such as gaskets, tire treads, sheet
packings and the like.
It has heretofore been well known to use certain
types of glass fibers as reinforcement for various plastic
`~ and rubber compounds. For instance, a number of patents
` which describe various rubber compounds to be used for sheet
packing mention that the rubber can be reinforced by any of
a variety of fibrous materials, such as asbestos and glass
fiber. Also, various patents describe the use of strands or ~ -
bundles of continuous glass fiber filaments for reinforcement
of tires. In addition, the use of woven glass matts,
fabrics and yarns for reinforcement of elastomers has been
described. Heretofore, however, the short glass fibers of
small diameter which comprise loose or "bulk" fiber or blown
thermal insulating wool have not been considered suitable
for reinforcement purposes for elastomers.
; Similarly, there are few references to the use of
fine diameter fibers as elastomer reinforcements. U.S.
Patent No. 3,556,844 shows continuous strand of glass fiber
of 0.0001 to 0.0015 inch (2.5 to 38 microns) but does not
deal with the use of short fibers.
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While common reinforcing grades of short glass
fibers have been successfully used to reinforce various
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1068~46
1 types of thermoplastic and thermosetting resins, their use for
elastomer reinforcement has been less widespread and considerably
less successful. Such short "reinforcing" fibers are commonly
considered to be the coarse "D" through "U" grades, which have
fiber diameters of 0.0002 to 0.001 inch (5.1 to 25.4 microns).
While the exact reasons for the relatively unsatisfactory per-
formance of "reinforcing" glass fibers in elastomers are not
precisely known, it has been observed that there is a significant
deterioration in properties with the use of ordinary glass fiber
in the compounds. While certain properties, such as elongation,
` would be expected to be reduced because the inelastic glass
` fibers inhibit the stretching of the elastomer, it would normallybe expected that such reduction and elongation would also be
accompanied by a corresponding increase in tensile strength.
Observations, however, have shown that such increase in tensile
;~ strength is not achieved in most cases, and where there is an
increase it is not of a magnitude which would indicate that the ~
short coarse glass fibers were in fact providing a satisfactory `
~: level of reinforcement. In short, therefore, the conventional
short coarse "reinforcing" glass fibers have been found not to
provide adequate reinforcement for elastomers as compared to
materials such as asbestos fiber. Neither can they be considered ;
to be functioning as fillers, for unlike conventional fillers
; such as carbon black the fibers cause serious deterioration in ;
properties such as elongation without a concomitant increase in -~
other properties.
In addition, there is believed to be a surface area
factor involved in the adhesion of glass fiber to elastomers.
For example, a unit weight of grade "B" glass fiber has
approximately 80% more surface area than an equivalent
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~068846
1 unit weight of grade "D" fiber, and the disparity increases
rapidly as larger fiber diameter grades are considered.
Various fiber lengths and diameters have been
suggested for reinforcement of plastics. However, plastics
and elastomers are of significantly different physical and
chemical nature, and therefore, as noted above, teachings
relating to plastics reinforcement have not normally been
applicable to elastomer reinforcement. See, for instance,
ASTM Special Technical Publication No. 184 (1956), Dannis,
Rubber Age, pp 35-44 (July, 1975); and Rondeau, Machine Design,
pp 154-163 (July 21, 1966).
Brief Summary of the Invention
The invention herein resides in the unexpected and
surprising discovery that elastomers can be combined with
very fine short glass fibers to produce reinforced elastomeric
compositions having properties equivalent to or better than
- the properties of equivalent elastomeric materials reinforced
with asbestos fibers, and significantly better than the
properties of elastomeric materials reinforced with the
conventional large diameter "reinforcing" glass fibers. In
addition, such compositions can be much more readily formed
and used than prior art compositions containing continuous
strand or woven fabrics and the like long-fiber-containing
materials. Therefore, included within the scope of the
present invention is an elastomeric composition comprising a
., .
natural or synthetic rubber matrix reinforced by 5 to 150
phr, preferably 5 to 50 phr, of fine short glass fibers, the
glass fibers having diameters in the range of from 0.5 to
3.8 microns and lengths of about 3 to 50 mm (about 0.12 to
2.0 inches). (As used herein, "phr" is defined to stand for
parts by ~eight of the specified component per 100 parts by
.
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iO68846
1 weight of the natural or synthetic rubber matrix.) The
glass fibers may be in the form of loose fibers but it is
more convenient to mix the fibers in the form of glass wool
with the elastomer and then let the wool fibers be broken
down during milling of the wool into the elastomer.
Also included within the scope of the present
` invention is the discovery that the fine diameter short
`` glass fibers create a synergistic effect when incorporatedinto elastomeric materials along with carbon black. The
resultant products are found to be very strong, particularly
when compared to similar products reinforced with conventional
large diameter glass fibers and/or asbestos fibers.
Detailed Description and Preferred Embodiments
The gist of the present invention lies in the
discovery that very fine diameter short glass fibers, which
~; have heretofore been considered merely as insulation fibers
without any significant reinforcing value, can be incorporated
into elastomeric compounds and provide significant and
improved reinforcement to the synthetic and/or natural
rubber matrix. This good reinforcing effect is even the
more surprising when considered against the prior art back-
ground that has shown conventional short coarse glass fibers
or continuous or similar long glass fibers normally used as
reinforcements to have very little if any reinforcing effect
and indeed to be greatly inferior to fibers such as asbestos
fibers in reinforcing elastomers.
The elastomeric natural and synthetic rubbers and
rubber-like materials which can be reinforced by the fine
t diameter fibers of the present invention include natural
rubbers, styrene-butadiene (SBR) rubbers, butyl rubbers,
ethylene-propylene (EP) rubbers, synthetic polyisoprene
rubbers, polybutadiene rubbers, acrylonitrile-butadiene
.
1068846
I (nitrile) rubbers, polychloroprene (neoprene) rubbers, fluoro-
elastomer rubbers, and ethylene-propylene-diene (EPDM) rubbers.
All of these families of synthetic or natural rubbers and rubber-
like materials are well known and their various properties and
chemical compositions are widely published; see e.g., The Vanderbilt
Rubber Handbook (Winspear, ed.; 1968). While the reinforcing
effect of the fine diameter short glass fibers of the present
invention will be somewhat different in each of the various
natural or synthetic rubbers, a significant reinforcing effect
0 will be found with all.
The "fine diameter short glass fibers" as utilized in
the present invention are those glass fibers having diameters in
the range of 0.5 to 3.8 microns (0.00002 through 0.00015 inches)
and lengths of about 3 to S0 mm (about 0.12 to 2.0 inches).
These are normally referred to as being MA through B diameter
fibers, with B being the largest diameter fibers. The B diameter
fibers (2.5 to 3.8 microns; 0.00010 to 0.00015 inch) are preferred,
for they are the most readily fabricated and are also usually the
most economical. The individual lengths and distribution of
lengths will largely be determined by the type of process from
which the fiber is formed. The fibers may be present as individual
loose or bulk fibers or may be present as "wool." In the various
glass wools the fibers are massed together in bulky lightweight
` batts, which range in density from 0.5 to 5 pounds per cubic
foot (0.008 to 0.08 g/cm3) and a thickness of from about 3/8
inch up to about 6 inches (0.95 to 15.2 cm). Such batts are
normally considered to be solely insulating materials and -
are used as such in the trade. A part of the present invention,
however, is the discovery that such batts can be used directly ~-
for reinforcing of elastomeric materials. While in the wool
batts the fiber lengths may be somewhat greater than 50 mm ~ -
1~68846
l (2.0 inches) in the original batt, milling of the batt into
the elastomer will break down essentially all fibers into
lengths within the aforesaid 3 mm to 50 mm (0.12 to 2.0
inches) range.
The particular chemical composition of the glass
used to form the fibers is not critical to the present
invention. Various types of compositions, including the
well known "A", "C" and/or "E" glasses may be used. Ordinarily
the glass will have no additives, coatings, binding agents
; lO or similar materials on its surface. In order to promote a
more thorough bonding of the glass fiber surface to the
elastomeric material it is therefore preferred to add a
coupling agent, preferably a silane type, to the glass, in
the amount of from 0.25% to 3%, preferably 0.5% to 1.0% by
weight of glass fiber. Various organos;lanes are well known
~ .
` as coupling agents in the glass fiber art and their structure
:~ and use need not be detailed here. Typical of those which
have been found satisfactory are gamma-methacryloxypro-
pyltrimethoxysilane, and gamma-mercaptopropyltrimethoxysilane;
` 20 the first is particularly useful for coupling to elastomers
~ which have been cured with peroxides and the latter for
: coupling with elastomers which have been cured with sulfur.
. The glass fiber in the present invention will be
present in the elastomeric matrix in a concentration of from
5 to 150 phr, perferably 5 to 50 phr.
It has also been found that the use of the fine ~-
diameter short glass fibers in the present invention produces
a significantly superior product when carbon black is also
present in the mixture w1th the elastomer in glass fiber.
As will be noted below, very marked improvement ;n properties,
particularly the strength properties, are found by the -
synergistic combination of the fine diameter short glass
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1068846
1 fiber and the carbon black. A variety of different types of
carbon blacks can be used. Nomenclature and typical physical
properties for standard carbon blacks will be found in ASTM
Specifications Nos. D-1765 and D-2516. Excellent products
have been made using "FEF" type carbon blacks with typical
particle sizes in the range of 40 to 48 nanometers.
The carbon black will be present as 5 to 75 phr,
preferably 5 to 35 phr.
The compositions and articles of this invention
can be readily fabricated using conventional rubber milling
devices. Excellent sample have been made using a Banbury
milling machine. The rubber is placed in the machine in the
conventional manner and the glass fiber may be added in any
convenient manner. One which has been found entirely satisfactory
is to simply add the glass as batts of glass wool. The
carbon black may be added by direct mixing in the rubber
mill. The silanes can be applied to the glass directly, as
by roller coating or spraying, or simply added directly to
the mixture of materials in the rubber mill.
The following data and examples will illustrate
the superiority of the present invention over conventional
glass fiber and reinforced fiber elastomers. In each case
the "chopped strands" were conventional chopped strands of
reinforcing glass fiber having a nominal length of 1/4 inch
(6.3 mm) and a fiber diameter of approximately 13 microns
(classed as K fiber). Runs utilizing chopped strands are
designated by the letter "CS". The fine diameter fibers for
comparison were in the forln of glass wool and were fibers of
2.5 to 3.8 microns diameter (classed as B fiber). Milling
of the wool into the elastomer breaks down the fiber lengths
to lengths comparable to the nominal length of the comparison
"chopped strand." Runs utilizing the glass wool are
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1068846
designated by the initials "BW" signifying "B glass wool".
- Other notations are defined below. Carbon black where used
was a typical type FEF carbon black. Except where noted the
rubber used was a conventional styrene-butadiene (SBR)
rubber. The various chopped strands normally had conventional
glass sizings including silanes present on their surfaces.
The "B wool" fine diameter short fibers used had nothing on -
their surfaces other than the aforementioned gamma-mercaptopro-
pyltrimetho~wsilane, except where noted. Compositions were
formed in a laboratory Banbury mixer under standard rubber
milling conditions. Propert;es were measured according to
; the follow;ng standard tests:
Shore "A" hardness A5TM D-2240
Elongation ASTM D-412 (Die C)
' Tensile strength ASTM D-412 (Die C)
- ` Tensile modulus
at 100% elongation ASTM D-412 (Die C)
at 300% elongation ASTM D-412 (Die C)
Tear strength ASTM D-624 (Die B)
Modulus of compression was determined by forming
:;~ cylinders of the materials to be tested 1-1/8 inch (28.6 mm)
... .
in diameter and 1/2 inch (12.7 mm) thick from strips 5/8
inch (15.9 mm) wide and 1/32 inch (0.8 mm) thick. The -
cylinders were vulcanized for 15 minutes in the presence`of
~- 90 ps;g steam (308F; 153C). The fiber orientation was
~` axial in the cylinders. The cylinder samples were then
compressed in an Instron test machine at the rate of 0.2
inch (5.1 mm) per minute. The modulus of compression for
each was then taken as the initial shape of a plotted curve
of compressive force versus time.
` ~ Table I below illustrates direct comparisons
between SBR rubber (1) filled wlth chopped strand glass
fiber and ~2) reinforced with the B wool of the present
invention. The run designated "BW-O" is a run in which the
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1068846
1 fine diameter short glass fibers were used without any
silane so as to provide a direct comparison between the dry
B wool and the chopped strands.
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1068~346
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1068846
1 Table II below illustrates the effect of silane on
the various properties. Isolated here are runs BW-0 and BW-l
which are identical except for the presence of the silane:
TABLE II
Run No. BW-0 BW-l % Change
Silane, wt.% of glass None 2 ---
Shore hardness 42 43 + 2
Elongation, X 485 410 -15
Tensile strength, psi 231 359 ~55
Tensile modulus, psi
at 100% elDngation 157 199 ~27
at 300% elongation 278 320 +15
Tear strength, lb/in
lo across grain 58.4 75.4 ~29
with grain 52.8 53.7 + 2
Table III below compares the chopped strand (runs
CS-2 and CS-4) and the B wool (runs BW-2 and BW-4) with commercial
glass beads (Type 3000, Potter Industries, Carlstadt, N.J.;
runs labelled "GB") as fillers:
TABLE III `~
Run No. CS-2 CS-4 GB-l GB-2 BW-2 BW-4 i -
~ Chopped glass strand, phr 25 25 --- --- --- ---
-` -44 glass beads, phr --- --- 25 25 --- ---
"B" glass wool, phr --- --- --- --- 25 25
~ Carbon black, phr --- 25 --- 25 --- 25
; 20 Shore hardness 48 59 43 59 51 61
Elongation, % 342 633 438 547 253 559
: Tensile strength, psi
longitudinal 142 1361 241 1894 565 2241
; transverse --- --- 255 1815 360 1771
Tensile modulus, psi
at 100% elongation 144 150 128 263 435 790 `
at 300% elongation 144 408 202 751 --- 1008
Tear strength, lb/in
;~ across grain 42.2 66.0 48.1 127.7 102.1 173.7
-~ with grain 27.6 66.6 48.5 123.4 68.5 154.7
Table IY below is a similar comparison to that of `
Table III but compares the chopped strand and B wool to conven-
tional asbestos fiber reinforcements, all at 25 phr. The
- -
three types of asbestos fibers used were grades 3T, 5K, and ~ -
7T. "AF" designates the asbestos fiber runs.
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1068846
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1068846
Table V below illustrates the superiority of thefine diameter glass fibers over chopped strand in a variety
of different rubber matrices.
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1~68846
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1068846
1 Table VI below illustrates high loadings of fine
diameter glass fiber in a nitrile rubber matrix. While
properties are satisfactory over the entire concentration
range of 5 to 150 phr glass fibers, it is difficult to
incorporate more than 50 phr of fiber into a rubber matrix.
Since quite satisfactory properties are obtained at 50 phr
or less, as shown above, the preferred fiber concentration
is 5 to 50 phr.
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1~68~346
1 From all of the above data it will be immediately
evident that the elastomeric materials reinforced with the
fine diameter short glass fibers of the present invention
are much superior to similar compositions containing equivalent
amounts of chopped strand glass fibers of much coarser
`"reinforcing" diameter, or conventional glass bead fillers.
The fine diameter fibers of this invention provide reinforcement
equal to or better than that of conventional asbestos fibers.
This is particularly surprising in view of the fact that the
prior art has not heretofore considered fine short glass
fibers to have any reinforcing properties whatsoever.
It will also be noted from the above data that
when carbon black is present, significant increases are
found in strength properties.
The use of fine diameter short glass fibers also
overcomes many of the problems associated with the formation
of elastomeric materials reinforced with continuous glass
` filaments or woven glass fabrics. Milling or compounding of
compositions cannot be done with fabric reinforcement, for
the milling destroys the integrity of the fabric. Similarly,
` milling also breaks up the continuous filaments, substantially
reducing their reinforcement value. Even if the elastomeric
composition is made up using the continuous filaments or
fabric without milling, subsequent cutting of the composition
into such articles as gaskets reduces the reinforcing nature
~; of the filaments or fabric. The short fine diameter fiberreinforced elastomeric compositions of the invention, however,
can be milled, molded and cut with no significant degredation
in reinforcement.
It has been found that longer cure times for the
rubbers are needed when using the glass wool of the present
invention, as compared to the cure times for asbestos fiber
. . . . . . . .
. . .
1~68846
1 reinforced elastomers. This is believed to be due to the
fact that asbestos fiber has a somewhat catalytic effect on
the elastomer and hastens the cure, whereas the glass fiber
has no such effect~ Consequently, a longer cure time at the
same temperature is required for the glass fiber re;nforced
material. Alternatively, higher cure temperatures may be
used for the same length of time. It should be noted that
cure times and temperature with the glass fibers are equivalent
to those required with unfilled rubber; the asbestos fibers
effectively accelerate the normal cure cycle.
`
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