Note: Descriptions are shown in the official language in which they were submitted.
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Description
Spike and pneumatic vehicle tyre
[0001] The invention relates to a spike for anchoring in a
spike hole of a tread of a pneumatic vehicle tire, having at
least a base and a spike pin anchored therein, wherein the
spike is at least partially ensheathed with at least one
vulcanized rubber mixture and/or with a thermoplastic
vulcanizate. The invention also relates to a pneumatic vehicle
tire having a tread with spikes of this kind.
[0002] In general, pneumatic vehicle tires with spikes
composed of steel, aluminum or plastics are already known and
in use. The spikes frequently consist of a spike pin with a
free end protruding from the tread, and a base at the opposite
end from this free end that has a greater area than that of
the spike pin.
[0003] RU 2 148 498 Cl discloses that the spike pin, apart
from the free end projecting out of the tread, is accommodated
entirely within and surrounded by a polymer body. In this case,
the polymer is used to reduce the weight of the spike and forms
the base mentioned in the lower portion at the opposite end
from the free end of the spike pin. Once produced, the entire
spike is integrated into the pneumatic vehicle tire in the
region of the tread.
[0004] It is also known that the spikes can be produced from
a rubber material. Such a solution is apparent, for example,
from JP H08300911 A or from JP 6239112, from EP 0 383 401 Al
or from DE 697 17 544 T2, wherein, according to the content of
disclosure of said documents, fiber materials for
strengthening purposes and for improving the transmission of
force are additionally embedded into the rubber. This has not
been found to be successful in practice because the fiber
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materials do not exhibit sufficient wear resistance to be able
to perform a force-transmitting function of a pin over the
service life of a pneumatic vehicle tire. The pins are normally
produced from cemented carbide.
[0005] Another variant of spikes is known from DE 10 2015 223
091 Al. In the case of these, the spike pin and/or the base
that are generally formed from a cemented carbide and/or
aluminum are at least partly integrated into a rubber sheath
of a rubber material. This is intended to achieve reduced spike
wear and road wear coupled with reduced component weight. The
rubber sheath absorbs a certain proportion of the impact
energy.
[0006] DE 10 2015 223 091 Al discloses that the Shore A
hardness of the rubber material ensheathing the spike may be
equal to or different than that of the surrounding tread
material, with the tread of a typical winter tire having a
Shore A hardness of less than 60. Hardness values for the
rubber sheath are unspecified. The rubber mixture used for the
sheath of the spike may be a mixture that differs from the
tread mixture. The spikes and the rubber sheath may have a
wide variety of different shapes and positions.
[0007] Proceeding from this prior art, it is an object of the
invention to further improve spikes for pneumatic vehicle tires
of the type specified at the outset with regard to lateral
side forces, traction and braking on ice.
[0008] The object is achieved in accordance with the invention
in that, in the case of the spikes of the type specified at
the outset, the vulcanized rubber mixture and/or the
thermoplastic vulcanizate has a Shore A hardness to DIN ISO
7619-1 of 63 to 78 at room temperature.
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[0009] Surprisingly, an optimum with regard to grip
properties on icy terrain has been found for Shore A hardness.
It has always been assumed to date that maximum Shore A
hardness with otherwise identical vulcanizate properties is
advantageous for an improvement in the spike with regard to
grip properties on icy terrain and also the other desired
properties, such as spike wear and road wear. It seems that a
certain degree of mobility/yielding of the material
surrounding the spike by virtue of a specific Shore A hardness
is advantageous for the properties.
[0010] Particularly good lateral side forces on ice and
greatly improved traction and improved braking on ice are
achieved when the vulcanized rubber mixture and/or the
thermoplastic vulcanizate of the sheath has a Shore A hardness
to DIN ISO 7619-1 of 63 to 78 at room temperature.
[0011] According to the invention, the spike is at least
partly ensheathed with at least one vulcanized rubber mixture
and/or at least one thermoplastic vulcanizate. Thermoplastic
vulcanizates are understood here to mean blends of
thermoplastics and crosslinked elastomers that show
elastomeric behavior in the range of customary use
temperatures, but can be thermoplastically processed at higher
temperatures. Thermoplastic vulcanizate (TPVs) are also
referred to as elastomer alloys.
[0012] It is preferable when the thermoplastic(s) of the
thermoplastic vulcanizate is/are selected from the group
consisting of polyurethane, polypropylene, polystyrene,
polyamide and acrylonitrile-butadiene-styrene copolymer. These
thermoplastics impart an advantageous hardness to the
thermoplastic vulcanizate.
[0013] The elastomer of the thermoplastic vulcanizate is
preferably based on a rubber mixture comprising, as rubber(s),
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at least one of the rubbers selected from the group consisting
of natural rubber (NR), synthetic polyisoprene (IR),
polybutadiene (BR), styrene-butadiene rubber (SBR) and
nitrile-butadiene rubber (NBR). These are rubbers that also
find use in rubber mixtures of treads, which assists good
bonding of the spike body to the rubber material of the tread.
[0014] In a preferred development of the invention, the spike
is at least partly ensheathed with a vulcanized rubber mixture.
In this way, the spike body can be matched in an excellent
manner to the surrounding material of the tread of the
pneumatic vehicle tire.
[0015] The vulcanized rubber mixture preferably comprises at
least a diene rubber, a filler, a plasticizer and crosslinking
reagents. With these ingredients, the ensheathing material can
be adjusted to the hardness of the invention.
[0016] Diene rubbers are rubbers which are formed by
polymerization or copolymerization of dienes and/or
cycloalkenes and thus have C=C double bonds either in the main
chain or in the side groups.
[0017] The diene rubber is preferably selected from the group
consisting of natural polyisoprene (NR), synthetic
polyisoprene (IR), butadiene rubber (BR), solution-polymerized
styrene-butadiene rubber (SSBR) and emulsion-polymerized
styrene-butadiene rubber (ESBR).
[0018] The rubber mixture more preferably contains 40 to 80
phr of natural polyisoprene (NR) and/or synthetic polyisoprene
(IR) and 20 to 60 phr of butadiene rubber (BR).
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[0019] The unit "phr" (parts per hundred parts of rubber by
weight) used in this document is the standard unit of quantity
for mixture recipes in the rubber industry. The dosage of the
parts by weight of the individual substances is always based
here on 100 parts by weight of the total mass of all rubbers
present in the mixture. The mass of all rubbers present in the
mixture adds up to 100.
[0020] The rubber mixture may comprise different fillers,
such as carbon blacks, silicas, aluminosilicates, chalk,
starch, fibers, carbon nanotubes, graphite, graphenes,
magnesium oxide, titanium dioxide or rubber gels, in customary
amounts of up to 250 phr, where the fillers may be used in
combination.
[0021] If carbon black is used in the rubber mixture, the
types used are preferably those having a CTAB surface area (to
ASTM D 3765) of more than 30 m2/g. These can be mixed in in a
simple manner and ensure low buildup of heat.
[0022] If silicas are present in the mixture, they may be the
silicas that are customary for tire rubber mixtures. It is
particularly preferable when a finely divided, precipitated
silica is used, having a CTAB surface area (to ASTM D 3765) of
30 to 350 m2/g, preferably of 110 to 250 m2/g. Silicas used
may be either conventional silicas, such as those of the VN3
type (trade name) from Evonik, or highly dispersible silicas
known as HD silicas (e.g. Ultrasil 7000 from Evonik).
[0023] If the rubber mixture contains silica or other polar
fillers, silane coupling agents may be added to the mixture
for improvement of processability and for binding of the polar
filler to the rubber. The silane coupling agents react with
the surface silanol groups of the silica or other polar groups
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during the mixing of the rubber/the rubber mixture (in situ)
or in the context of a pretreatment (premodification) even
before addition of the filler to the rubber. Silane coupling
agents that may be used here include any silane coupling agents
known to those skilled in the art for use in rubber mixtures.
Such coupling agents known from the prior art are bifunctional
organosilanes having at least one alkoxy, cycloalkoxy or
phenoxy group as a leaving group on the silicon atom and
having, as another functionality, a group that, after cleavage
if necessary, can enter into a chemical reaction with the
double bonds of the polymer. The latter group may for example
be the following chemical groups: -SCN, -SH, -NH2 or -Sx- (with
x = 2-8). Silane coupling agents that may be used include, for
example, 3-mercaptopropyltriethoxysilane, 3-
thiocyanatopropyltrimethoxysilane or 3,3'-
bis(triethoxysilylpropyl) polysulfides having 2 to 8 sulfur
atoms, for example 3,3'-bis(triethoxysilylpropyl) tetrasulfide
(TESPT), the corresponding disulfide, or else mixtures of the
sulfides having 1 to 8 sulfur atoms with different contents of
the various sulfides. The silane coupling agents may also be
added here as a mixture with industrial carbon black, for
example TESPT to carbon black (trade name: X505 from Evonik).
Blocked mercaptosilanes as known for example from WO 99/09036
may also be used as a silane coupling agent. It is also possible
to use silanes as described in WO 2008/083241 Al, WO
2008/083242 Al, WO 2008/083243 Al and WO 2008/083244 Al. It is
possible to use, for example, silanes which are sold under the
NXT name in a number of variants by Momentive, USA, or those
that are sold under the VP Si 363 name by Evonik Industries.
Also usable are "silated core polysulfides" (SCPs,
polysulfides with a silylated core), which are described, for
example, in US 20080161477 Al and EP 2 114 961 Bl.
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[0024] The plasticizers include plasticizer oils or
plasticizer resins. Processing auxiliaries, which are
understood to mean oils and other viscosity-lowering
substances. These processing auxiliaries may, for example, be
plasticizer oils or plasticizer resins.
[0025] Plasticizer oils are, for example, aromatic,
naphthenic or paraffinic mineral oil plasticizers, for example
MES (mild extraction solvate) or TDAE (treated distillate
aromatic extract), natural oils, for example rapeseed oil, or
rubber-to-liquid oils (RTL) or biomass-to-liquid oils (BTL) or
liquid polymers (such as liquid BR), the average molecular
weight of which (determined by GPC = gel permeation
chromatography, using a method based on BS ISO 11344:2004) is
in the range from 500 to 20 000 g/mol. The plasticizer resins
include, for example, hydrocarbon resins.
[0026] The crosslinking agents present in the rubber mixture
include all substances known to those skilled in the art.
Preference is given to sulfur and/or sulfur donors, which are
added to the rubber mixture in the last mixing step in the
amounts commonly used by the person skilled in the art (0.4 to
8 phr).
[0027] The rubber mixture may additionally comprise
vulcanization-influencing substances such as vulcanization
accelerators, vulcanization retardants and vulcanization
activators in customary amounts. These are added in order to
control the time required and/or the temperature required for
vulcanization and to improve the vulcanizate properties. The
vulcanization accelerator may, for example, be selected from
the following groups of accelerators: thiazole accelerators,
for example 2-mercaptobenzothiazole, sulfenamide accelerators,
for example benzothiazy1-2-cyclohexylsulfenamide (CBS) and
benzothiazy1-2-dicyclohexylsulfenamide (DCBS),
guanidine
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accelerators, for example N,N'-diphenylguanidine (DPG),
dithiocarbamate accelerators, for example zinc
dibenzyldithiocarbamate, disulfides, thiophosphates. The
accelerators can also be used in combination with one another,
which can give rise to synergistic effects.
[0028] It is also possible to use further network-forming
systems, for example Vulkuren , Duralink or Perkalink , or
systems as described in WO 2010/049261 A2 in the rubberizing
mixture.
[0029] As well as the substances already mentioned, the rubber
mixture for the ensheathing of the spikes may comprise
customary additives in customary proportions by weight. These
additives include aging stabilizers, for example N-phenyl-N'-
(1,3-dimethylbuty1)-p-phenylenediamine (6PPD), N-isopropyl-
N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-trimethy1-1,2-
dihydroquinoline (TMQ) and other substances as known, for
example, from J. Schnetger, Lexikon der Kautschuktechnik
[Lexicon of Rubber Technology], 2nd edition, Hilthig Buch
Verlag, Heidelberg, 1991, p. 42-48, activators, for example
zinc oxide and fatty acids (e.g. stearic acid), waxes,
tackifying resins, for example hydrocarbon resins and rosin,
bonding systems, for example those based on resorcinol and
formaldehyde, and masticating aids, for example 2,2'-
dibenzamidodiphenyl disulfide (DBD).
[0030] In an advantageous development of the invention, the
Shore A hardness of the vulcanized rubber mixture for the
ensheathing of the spikes is adjusted via the level of filling
with filler and/or the degree of crosslinking and/or the
plasticizer content. With the aid of these measures, it is
possible to adjust the Shore A hardness in a simple manner
without needing to alter other mixing admixtures. Particular
preference is given to adjusting the Shore A hardness via the
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plasticizer content, since other vulcanization and vulcanizate
properties are then affected to a very minor degree.
[0031] In a further advantageous development of the
invention, the vulcanized rubber mixture for the ensheathing
of the spikes corresponds to the mixture of the surrounding
tread in terms of the diene rubbers present. In this way,
incompatibility between the rubber mixtures is avoided.
[0032] It has additionally been found to be advantageous when
the vulcanized rubber mixture has reduced rolling resistance,
i.e. contributes to reduced rolling resistance in driving
operation. This gives a low energy loss.
[0033] The rubber mixture may preferably have reduced rolling
resistance in that it comprises silica as filler.
[0034] The rolling resistance of the silica-containing rubber
mixture can be reduced further when it comprises at least one
silane coupling agent. This serves to bind the filler to the
rubber.
[0035] Spikes for pneumatic vehicle tires may be different in
terms of their shape. For instance, DE 10 20015 223 091 Al
discloses some possible shapes of spikes, spike pins and spike
bases.
[0036] According to the invention, the spike is at least
partly ensheathed with at least one vulcanized rubber mixture
and/or at least one thermoplastic vulcanizate. It is
accordingly possible to use multiple different rubber mixtures
and/or thermoplastic vulcanizates in different places on a
spike.
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[0037] The spike may firstly be fully ensheathed by the
vulcanized rubber mixture and/or the thermoplastic
vulcanizate. In this way, it is possible to produce a spike in
a simple manner, for example, by insert molding with an
unvulcanized rubber mixture, followed by vulcanization. The
insert molding can be effected from various positions, for
example from the base or from the spike pin.
[0038] Secondly, it is also possible that only the spike pin
and/or the base is/are at least partly ensheathed by the
vulcanized rubber mixture and/or the thermoplastic
vulcanizate. It is advantageous when that part that is the
main part responsible for the anchoring of the spike in the
rubber material of the tread, namely the base flange, has a
sheath made of the vulcanized rubber mixture and/or the
thermoplastic vulcanizate.
[0039] This sheath with the vulcanized rubber mixture and/or
the thermoplastic vulcanizate may have various external forms,
such that these, at least in sections, have a circular
cylindrical, conical, irregular, polygon or conical and/or
fitted outer shape. Undercuts or fitted portions improve the
adhesion of the spike in the tread of the pneumatic vehicle
tire.
[0040] The spikes of the invention are produced by methods
known to those skilled in the art. For example, a spike made
of a cemented carbide and/or aluminum can be clamped in a
device for holding the spike and then subjected to at least
partial insert molding with an unvulcanized rubber mixture
and/or a thermoplastic vulcanizate. It is optionally possible
to apply an adhesion promoter to the regions of the spike that
are ensheathed. This is followed by vulcanization. A spike
thus produced is typically introduced and/or bonded into the
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outer surface of a ready-vulcanized pneumatic vehicle tire
with the aid of spiking robots. Adhesives used are, for
example, reactive adhesives or hotmelt adhesive for rubber-
rubber or rubber-metal adhesion.
[0041] The invention further relates to a pneumatic vehicle
tire having a tread with spikes executed in accordance with
the invention.
[0042] Further features, advantages and details of the
invention will now be described in detail with reference to
the drawing, which illustrates a working example, and the table
below. Fig. 1 shows a detailed side-on cross-sectional view of
a spiked pneumatic vehicle tire in contact with a surface
beneath.
[0043] Figure 1 shows a detailed side-on cross-sectional view
of a spiked pneumatic vehicle tire 1 rolling on a surface 12
beneath and having a multitude of individual spikes 3 along
its circumference. Each of the spikes 3 has been inserted into
the profiled tread 2 of the pneumatic vehicle tire 1, with
only a free end 5 of a spike pin 4 of the spike 3 protruding
out of the tread 2 of the pneumatic vehicle tire 1. The spike
pin 4 in the present case consists of a cemented carbide, which
may be tungsten carbide for example, which is possible here
without any problem because the spike 3 as a whole is
surrounded by a rubber sheath 7 pressed into a corresponding
recess 11 of the tread 2. On that side of the spike 3 opposite
the free end 5 of the spike pin 4, said spike has a base 6
with a surface area 8, the projected area or cross-sectional
area of which is greater than that of the spike pin 4. The
base 6 of the spike 3, viewed in axial direction, merges into
a pedestal 9 which serves firstly as adhesion surface for the
rubber sheath 7 and secondly for connection to the spike pin
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4. The spike pin 4 is inserted or pressed into the pedestal 9,
or is bonded to the pedestal 9 by means of a cohesive bond.
[0044] Table 1 specifies example rubber mixtures for the
ensheathing 7 of spikes 3. Comparative mixtures are labeled V;
mixtures for inventive spikes 3 are labeled E. The mixtures
are altered in terms of their Shore A hardness by varying the
plasticizer content.
[0045] The mixtures were produced under standard conditions
with production of a base mixture and subsequently of the
finished mixture in a tangential laboratory mixer.
[0046] All mixtures were used to produce test specimens by
optimal vulcanization under pressure at 160 C, and these test
specimens were used to determine the material properties
typical for the rubber industry by the test methods specified
hereinafter.
0 Shore A hardness at room temperature to DIN ISO 7619-1
0 Resilience at room temperature to DIN ISO 4662
[0047] In addition, the mixtures from table 1 were used for
insert molding of spikes 3 according to figure 1 in the region
of the spike pin 4 and at the pedestal 9 to the base 6, namely
at the base of the flange, with the rubber mixtures, which
were vulcanized and bonded into a 205/55 R 16 pneumatic vehicle
tire 1 with the aid of a spike robot, followed by autoclaving.
[0048] These tires were used to conduct objective braking and
traction tests, and tests of the lateral side force on ice
according to the following test descriptions:
[0049] Braking: ABS braking tests and evaluation of average
delay in a defined speed range.
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[0050] Traction: Acceleration with traction control system
(ASR) and evaluation of average acceleration within a defined
speed range.
[0051] Lateral guiding: Rapid steering from a straight line
at a constant defined speed, measurement of transverse
acceleration in a constant time interval after commencement of
steering.
[0052] The behavior of mixture 1(V) was set at 100%. Values
greater than one hundred mean an improvement in the
corresponding property.
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Table 1
Constituents Unit 1(V) 2(E) 3(V)
Polyisoprene phr 60 60 60
Polybutadiene phr 40 40 40
N121 carbon black phr 8 8 8
Silicaa) phr 103 103 103
Plasticizer phr 6 25 58
Vulcanization activators phr 10 10 10
and aging stabilizers
Processing auxiliaries phr 2 2 2
(calcium soaps and fatty
acid amides)
Silane coupling agentb) phr - - -
Accelerator phr 4.1 4.1 4.1
Sulfur phr 1.8 1.8 1.8
Properties
Shore A hardness at RT Shore A 83 73 56
Resilience at RT % 37 36 35
Tire properties
Traction and braking on % 100 106 102
ice
Lateral side forces on ice % 100 103 100
a) Ultrasil VN3 from Evonik
b) Blocked mercaptosilane, NXT silane from Momentive
[0053] It is apparent from table 1 that the tires with spikes
ensheathed with a mixture having a Shore A hardness of 73 are
notable for a distinct improvement in traction and braking
characteristics on ice and also for improved lateral side
forces on ice. Given equal damping (equal resilience), tires
having spikes ensheathed with a harder (1(V)) or softer mixture
(3(V)) do not show any such improvement in properties. It has
also been found that the tires with the spikes of the invention
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have a distinct improvement in noise characteristics and
improved driving performance on ice.
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List of reference numerals
1 Pneumatic vehicle tire
2 Tread
3 Spike
4 Spike pin
Free end (tip)
6 Base
7 Rubber sheath
8 Surface of the base
9 Pedestal
11Recess (in the tread), spike hole
12 Surface beneath tire
