Background Of The Invention
Government regulations and consumer preferences continue
to compel a reduction in the acceptable noise levels produced from the tires of
passenger vehicles. One source of road noise is resonance within the air chamber
enclosed by the innermost surface of the tire and the rim. One type of effort to
reduce tire noise is damping the sound from the air vibration in the air chamber,
which efforts have focused mainly on altering the innermost surface of the tire
adjacent the tire carcass. Shortcomings in these previous efforts, as well as new
stricter regulations regarding noise reduction, have provided a need for further
improvements to the tire to reduce sound transmission due to vibrations within the
Summary Of The Invention
The present invention is directed to a pneumatic tire according
to claim 1.
Dependent claims refer to preferred embodiments of the
Brief Description of the Drawings
The invention will be more readily understood with respect
to the accompanying drawings wherein:
Description of the Invention
- FIG. 1 is a cross-sectional view of one embodiment of a tire having a foamed
structure according to the present invention;
- FIG. 2 is a cross-sectional view of another embodiment of a tire having a foamed
structure according to the present invention;
- FIG. 3 is a cross-sectional view of another embodiment of a tire having a foamed
structure according to the present invention;
- FIG. 4 is a perspective view of another embodiment of a tire having multiple
foamed structures according to the present invention;
- FIG. 5 is an enlarged view of a photograph showing a plurality of foamed projections
in a tire having a foamed structure;
- FIG. 6 is a graph showing the noise level generated during testing of a tire
according to the invention.
In accordance with the present invention, there is provided
a pneumatic tire comprising two spaced inextensible beads; a ground contacting tread
portion; a pair of individual sidewalls extending radially inward from the axial
outer edges of said tread portion to join the respective beads, the axial outer
edges of the tread portion defining a tread width; a supporting carcass for the
tread portion and sidewalls; and at least one foamed structure disposed radially
inwardly of the carcass and exposed to the inner cavity of the tire, the foamed
structure comprising a co-vulcanized foamed rubber composition having a density
ranging from 0.1 to 1 g/cm3.
The integral foamed structure can be disposed in various
inner portions of the tire. For example it can extend from bead to bead for protection
of both the tread and sidewall portions of the tire or it can simply be selectively
and locally disposed on the inner surface of the tire.
The foamed structure is preferably co-vulcanized with the
tire in order to be integral with the dynamic tire construction. It is preferably
built as a solid unvulcanized layer containing a heat activatable blowing agent
onto the inner portion of the green, unvulcanized tire over a building form and
then shaped, molded and heated under pressure to simultaneously co-vulcanize therewith.
The pressure is generally supplied by a shaping bladder positioned within the tire
to press and shape it outwardly against a mold. In one aspect of the invention,
the foamed structure is formed by heat activating the blowing agent during the vulcanization
process to simultaneously expand said adherent solid layer. Typical vulcanization
temperatures range from 90°C to 200°C. Thus, the foamed structure can
be formed substantially simultaneously with the co-vulcanization step in order to
enhance the integral tire construction. The foamed structure itself is therefore
integral with the tire construction, instead of being a simple laminate that is
glued or otherwise attached to a previously cured tire.
The integral foamed structure of the tire is of such a
gauge as to not occupy any substantial inner portion of the inflated tire. Generally,
its thickness ranges from 1 to 80 and preferably 10 to 50 percent of the total tire
thickness, depending somewhat upon the tire size and intended use of the tire with
its structured volume being less than 25 percent, preferably less than 10 percent,
of the encompassed volume of air in the pneumatic tire. Thus, a typical thickness
is in the range of 10 to 30 percent of the total tire thickness for an ordinary
passenger pneumatic tire with its volume being less than 10 percent of the encompassed
volume of air in the pneumatic tire.
In order to obtain an adequate noise dampening effect by
the foamed structure in the tire, the foamed structure has a density or density
and porosity in ranges suitable to dampen noise.
In one embodiment, the foamed structure has a density ranging
from 0.1 to 1 g/cm3. This density is for the foamed, fully loaded compound,
including elastomers and additives such as carbon black, silica, zinc oxide, curatives
and oils. In another embodiment, the foamed structure has a density ranging from
0.2 to 0.9 g/cm3. In another embodiment, the foamed structure has a density
ranging from 0.2 to 0.8 g/cm3. In another embodiment, the foamed structure
has a density ranging from 0.25 g/cm3 to 0.7 g/cm3.
In one embodiment, the foamed structure has a porosity
ranging from 20 to 80 percent by volume. In another embodiment, the foamed structure
has a porosity ranging from 30 to 70 percent by volume. As defined in the present
invention, porosity is the fraction of the total volume of the foamed structure
not occupied by the rubber compound. In other words, the porosity is the volume
fraction of the foamed structure occupied by void space in the pores and cells formed
by the foaming agent.
The foamed structure is preferably foamed with a blowing
agent. The blowing agents used in the practice of this invention for the manufacture
of the pneumatic tire may be those which liberate gases upon heating.
Representative examples of such agents are those which liberate gases such as nitrogen
or carbon dioxide and cause the formation of the integral closed cell internal layer.
Usually agents which liberate nitrogen are preferred. Such blowing agents are compounds
which give off gases upon being triggered by the vulcanization temperatures, representative
of which are nitro, sulfonyl and azo compounds such as dinitrosopentamethylene tetramine,
N,N'-dimethyl-N,N'-dinitrosophthalamide, azodicarbonamide, sulfonyl hydrazides such
as benzenesulfonyl hydrazide, toluenesulfonyl hydrazide and p,p'-oxy-bis-(benzenenesulfonyl)hydrazide
and sulfonyl semicarbazides such as p-toluene sulfonyl semicarbazide and p,p'-oxy-bis-(benzenesulfonyl
semicarbazide). Carbon dioxide may be given off by compounds such as ammonium bicarbonate
and sodium bicarbonate.
In order to obtain the desired density and porosity in
the foamed structure, the amount of blowing agent may vary. In one embodiment, the
amount of blowing agent used in the rubber composition of the foamed structure ranges
from 5 to 25 phr. In another embodiment, the amount of blowing agent ranges from
10 to 25 phr.
The vulcanized rubber tire and the co-vulcanized integral
foamed structure can be of various cured or vulcanized rubbers such as natural rubber
and synthetic rubber and their mixtures or blends. For example, they can be rubbery
styrene-butadiene copolymers, butadiene-acrylonitrile copolymers, cis-1,4-polyisoprene,
polybutadiene, isoprene-butadiene copolymers, butyl rubber, halogenated butyl rubber
such as chloro or bromo butyl rubber, ethylene-propylene copolymers, ethylene-propylene-diene
terpolymers and polyurethane elastomers. Typically the various polymers are cured
or vulcanized by normal curing methods and recipes such as with sulfur, or with
peroxides in the case of the ethylene-propylene copolymers, or with primary diamines
in the case of polyurethane elastomers. The sulfur cured or vulcanized natural rubber
and synthetic rubbery polymers are preferred such as styrene-butadiene rubber, cis-1,4-polyisoprene,
polybutadiene, butyl rubber, chlorobutyl rubber, and bromobutyl rubber.
It is readily understood by those having skill in the art
that the rubber compositions used in the integral foamed structure would be compounded
by methods generally known in the rubber compounding art, such as mixing the various
sulfur-vulcanizable constituent rubbers with various commonly used additive materials
such as, for example, curing aids, such as sulfur, activators, retarders and accelerators,
processing additives, such as oils, resins including tackifying resins, silicas,
and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants
and antiozonants, peptizing agents and reinforcing materials such as, for example,
carbon black. As known to those skilled in the art, depending on the intended use
of the sulfur vulcanizable and sulfur vulcanized material (rubbers), the additives
mentioned above are selected and commonly used in conventional amounts.
The rubber compound may contain various conventional rubber
additives. Typical additions of carbon black comprise 20 to 200 parts by weight
per 100 parts by weight of diene rubber (phr), preferably 50 to 100 phr.
A number of commercially available carbon blacks may be
used. Included in the list of carbon blacks are those known under the ASTM designations
N299, S315, N326, N330, M332, N339, N343, N347, N351, N358, N375, N539, N550 and
N582. Processing aids may be present and can include, for example, aromatic, naphthenic,
and/or paraffinic processing oils. Typical amounts of tackifying resins, such as
phenolic tackifiers, range from 1 to 3 phr. Silica, if used, may be used in an amount
of 5 to 80 phr, often with a silica coupling agent. Representative silicas may be,
for example, hydrated amorphous silicas. Typical amounts of antioxidants comprise
1 to 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine
and polymerized 1,2-dihydro-2,2,4-trimethylquinoline. Typical amounts of antiozonants
comprise 1 to 5 phr. Representative antiozonants may be, for example, those disclosed
Vanderbilt Rubber Handbook (1990), Pages 363 through 367
. Typical amounts of fatty acids, if used, which can include stearic acid
comprise 0.5 to 3 phr. Typical amounts of zinc oxide comprise 1 to 10 phr. Typical
amounts of waxes comprise 1 to 5 phr. Typical amounts of peptizers comprise 0.1
to 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl
The vulcanization is conducted in the presence of a sulfur
vulcanizing agent. Examples of suitable sulfur vulcanizing agents include elemental
sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, an amine
disulfide, polymeric polysulfide or sulfur olefin adducts. Preferably, the sulfur
vulcanizing agent is elemental sulfur. As known to those skilled in the art, sulfur
vulcanizing agents are used in an amount ranging from 0.5 to 5 phr, or even, in
some circumstances, up to 8 phr, with a range of from 3 to 5 being preferred.
Accelerators are used to control the time and/or temperature
required for vulcanization and to improve the properties of the vulcanizate. In
one embodiment, a single accelerator system may be used, i.e., primary accelerator.
Conventionally, a primary accelerator is used in amounts ranging from 0.5 to 2.5
phr. In another embodiment, combinations of two or more accelerators which is generally
used in the larger amount (0.5 to 2.0 phr), and a secondary accelerator which is
generally used in smaller amounts (0.05 to 0.50 phr) in order to activate and to
improve the properties of the vulcanizate. In addition, delayed action accelerators
may be used which are not affected by normal processing temperatures but produce
satisfactory cures at ordinary vulcanization temperatures. Suitable types of accelerators
that may be used in the present invention are amines, disulfides, guanidines, thioureas,
thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the
primary accelerator is a sulfenamide. If a second accelerator is used, the secondary
accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.
The tire can be built, shaped, molded and cured by various
methods, which will be readily apparent to those having skill in such art. As noted
previously herein, the foamed structure is preferably co-vulcanized with the tire
in order to be integral with the dynamic tire construction. It is built as a solid
unvulcanized layer containing the heat activatable blowing agent onto the inner
portion of the green, unvulcanized tire over a building form and then shaped, molded
and heated under pressure to simultaneously co-vulcanize therewith. The pressure
is generally supplied by a shaping bladder positioned within the tire to press and
shape it outwardly against a mold. The foamed structure is formed by heat activating
said blowing agent during the vulcanization process to simultaneously expand said
adherent solid layer. Typical vulcanization temperatures range from 90°C to
200°C. Thus, the foamed structure is formed substantially simultaneously with
the co-vulcanization step in order to enhance the integral tire construction. To
do this, an unshaped and unvulcanized tire is built around a tire building drum
by first building over the drum an inner layer of rubber composition comprising
the blowing agent and optionally a non-foamed innerliner. Over this initial layer
of rubber the remainder of the tire is built including the lay-up of the rubberized
fabric plies, bead portions, sidewall and tread. The fabricated tire is then removed
from the building form and shaped, molded and vulcanized in the tire.
The inner layer of especially compounded rubber expands
as the blowing agent is heat activated during the vulcanization process to form
the foamed structure. However, this expansion is suppressed during the tire molding
by the presence of the shaping bladder which presses against the interior of the
tire owing to the significant pressure of the bladder. The pressure in the bladder
is maintained higher than the pressure of the blowing agent being released in the
foamed structure. Once the pressure in the bladder is released, the foamed structure
is free to expand to its final conformation, which may include open and/or closed
In one embodiment, the foamed structure includes a plurality
of foamed projections. In one embodiment, the foamed projections result from a pattern
impression in the foamed structure made by the patterned bladder used during molding.
As is known in the art, tire bladders may have a textured, or patterned, surface
to allow venting of gases during tire molding, as taught for example in
. Surprisingly and unexpectedly, use of such a patterned bladder during
molding to produce the tire having the foamed structure results in a foamed structure
having a plurality of foamed projections resulting from the impressed pattern of
the bladder. The foamed projection may in part resemble an inverse of the bladder
surface texture or pattern, as the pattern has been impressed into the rubber compound.
These foamed projections may assist in the dampening of noise in the tire.
The foamed structure having a plurality of foamed projections
may also be obtained by methods other than use of a patterned bladder. In one embodiment,
the solid unvulcanized layer containing the blowing agent may be pre-shaped to include
surface features that subsequent to molding will form foamed projections. In one
embodiment, the solid unvulcanized layer may be made as disclosed for example in
to impart a series of parallel raised ridges to one side of the sheet.
The sheet is then placed on the tire building drum as previously described herein,
with the raised ridges placed so as to be exposed to the bladder during cure. The
raised ridges may form expanded, foamed projections upon release of the bladder
pressure after tire molding.
Referring now to the drawings it is shown that a pneumatic
rubber tire can be prepared by building an unshaped and unvulcanized basic tire
10 containing what are to become the customary tread portion 13, sidewalls 11 and
carcass 12, which typically contains plies (not shown) to back and reinforce the
tread and sidewall portions, and particularly a foamed structure 18 which contains
for instance a heat activatable blowing agent. The green tire is then placed in
a mold where it is shaped, molded and heated under pressure to simultaneously co-vulcanize
the tire and foamed structure and also activate the blowing agent.
FIG. 1 depicts in cross-section one embodiment of a tire
10 in accordance with the present invention. Tire 10 includes a carcass 12 having
a tread 13 disposed on the outermost surface, which tread 13 is the portion of the
tire 10 that contacts the ground during operation of the tire 10. As is known in
the art, the carcass 12 may include one or more plies of cords (not shown) and the
carcass wraps the bead portions 15 of the tire. A foamed structure 18 is disposed
inside the carcass 12 with innermost surface 19 facing the air chamber 20, with
the foamed structure 18 extending circumferentially and from bead 15 to bead 15.
In the embodiment shown in FIG. 1, the foamed structure 18 may serve as an innerliner
to prevent air migration from the air chamber 20 through the tire 10. In an alternative
embodiment as shown in FIG. 2, the tire 10 includes innerliner layer 16 disposed
adjacent the carcass 12 and foamed structure 18 disposed adjacent innerliner layer
16 and forming the innermost surface 19, with the foamed structure 18 extending
circumferentially and from bead 15 to bead 15. In another alternative embodiment
as shown in FIG. 3, the tire 10 includes innerliner layer 16 disposed adjacent the
carcass 12 and foamed structure 18 disposed adjacent innerliner layer 16 and forming
the innermost surface 19, with foamed structure 18 extending circumferentially and
axially over less than the full width of the tread 13. In the embodiments shown
in FIGS. 2 and 3, innerliner 16 is made of a non-foamed rubber and serves to prevent
the air inside the air chamber 20 from escaping, thereby maintaining the air tightness
of the tire 10.
Thus, in one embodiment the foamed structure may extend
circumferentially about the inside of the tire and axially from bead to bead. In
another embodiment, the foamed structure may extend circumferentially about the
inside of the tire and only partially across the width of the tire. In one embodiment,
the foamed structure may extend axially no more than 50 percent of the tread width.
In another embodiment, the foamed structure may extend axially in a range of from
10 percent to 50 percent, alternately 20 to 40 percent of the tread width. In another
embodiment, the foamed structure may be substantially centered axially on the axial
centerline of the tire. In another embodiment, multiple circumferential foamed structures
may be used, disposed so as to equalize the load on the tire and maintain dynamic
In another embodiment, the foamed structure may include
a plurality of substantially equally and circumferentially spaced foamed structures
disposed about the circumference of the tire. In this embodiment as shown in Fig.
4, foamed structures 118 may extend partially across the radius of the tire 110.
Strips of nonfoamed compound (not shown) may be disposed between the foamed strips
118. In another embodiment, the foamed structures may extend bead to bead.
The practice of this invention is further illustrated by
reference to the following examples which are intended to be representative rather
than restrictive of the scope of the invention. Unless otherwise indicated, all
parts and percentages are by weight.
In this example, the effect of varying amounts of blowing
agent on the physical characteristics of a rubber compound is illustrated. A series
of rubber compounds were prepared following the recipes shown in Table 1, with amounts
given in parts by weight per 100 parts by weight of elastomer (phr). The compounds
were then cured at 170°C for 10 minutes. Porosity has been calculated from
the density of the resulting compounds measured using the ASTM D297(2), DIN 53479
method. The results are shown in Table 2.
1Bromobutyl 2222 from Exxon Chemical
2Corax N660 from Degussa
3Flexon 641 from Exxon Chemical
4Koresin resin from Strucktol
5SP1068 from Schenectady International
6MBTS Vulkacit DM/C from Bayer
7Celogen OT from Crompton Corporation
Porosity, vol %
In this example, co-vulcanization of a porous structure
on the inner surface of a tire is illustrated. A foamable rubber compound designated
as Sample 6 was prepared having the composition shown in Table 3. Dual strips of
the Sample 6 green rubber compound were then stitched circumferentially onto the
inner surface of a 215/45R17 green tire followed by cure in a bladder-type tire
mold for 20 min at 170°C. The bladder surface was of the "patio" texture type
as is known in the art. After cure and release of the bladder pressure, it was observed
that the rubber strip had foamed and the areas of the rubber strip impressed by
the bladder design had formed into a plurality of foamed projections extending radially
away from the inner surface of the tire. FIG. 5 shows the inner surface of the tire
A with dual foamed structures B. As seen in FIG. 5, the bladder impressed a patio
pattern (A) on the inner surface of the tire during cure. Upon release of the bladder
pressure, the strip of foamable compound (B) expanded with projections (C) resulting
from the impressed bladder pattern.
*All components identified as in Table 1.
In this example, the noise characteristic of a tire having
a co-vulcanized foamed structure with a plurality of foamed projections is illustrated.
A test tire with a foamable rubber strip was made using the compound of Sample 6,
and a control tire was made with an innerliner using the compound of Sample 1. The
tire of the invention was made using a single 5 cm by 180 cm strip of green Sample
6 rubber compound stitched circumferentially onto the inner surface of a 215/45R17
green tire followed by cure in a bladder-type tire mold for 20 min at 170°C.
The tires were tested for tire force transmissibility by measuring the force generated
at the hub for a unit force hammer impact on the tread surface. Typically, for a
tire the response of force transmissibility vs frequency shows two distinct peaks,
the so-called first vertical resonance at 90 Hz and the tire cavity resonance at
220 Hz. The response curve is shown in FIG. 6. Surprisingly and unexpectedly, the
tire with the foamed structure with Sample 6 showed an approximately 15 dB decrease
in the tire cavity resonance peak as compared with the control tire.