^
- 1 -
Description
Title of Invention: TOOTHED BELT
Technical Field
[0001]
The present invention relates to a toothed belt
utilized for power transmission, conveyance and the like,
particularly to a toothed belt in which the whole or a
part of a belt body is formed from a thermoplastic
elastomer alloy.
Background Art
[0002]
The toothed belt is, different from flat belts and
V-belts to transmit the rotary force only by friction, a
belt capable of transmitting the rotation without
slipping by being brought into mesh with tooth profiles
provided on pulleys. Therefore, the toothed belt is
broadly utilized as high-load or synchronous power
transmission belts and precise conveyance belts.
[0003]
A toothed belt is usually constituted of a belt body,
and a tension member and the like provided as required.
The belt body is known to be formed from a thermoplastic
elastomer. For example, Japanese Patent Laid-Open No.
2004-224848 discloses a toothed belt whose toothed rubber
- 2 -
layer and back rubber layer are formed from urethane
elastomers. Japanese Patent Laid-Open No. 2004-347054
discloses a toothed belt equipped with a body part
composed of a thermoplastic polyurethane elastomer, cord
as a tension member, and a fabric covering a belt toothed
surface.
[0004]
However, if conventional toothed belts having a belt
body formed from a thermoplastic polyurethane elastomer
are used as high-load power transmission belts or the
like, the belt body abrades and cracks in an early stage,
and providing the belts with insufficient durability in
some cases.
Citation List
Patent Literature
[0005]
Patent Literature 1: Japanese Patent Laid-Open No. 2004-
224848
Patent Literature 2: Japanese Patent Laid-Open No. 2004-
347054
Summary of Invention
Technical Problem
[0006]
Therefore, it is an object of the present invention
to provide a toothed belt which does not cause abrasion.
damage, cracks, breakage, and the like on the belt body
in an early stage, and is thus remarkably excellent in
durability even if being used at a high load for power
transmission and the like.
Solution to Problem
[0007]
After intensive investigations to acheve the
objects, the present inventors have found that if a belt
body of a toothed belt is formed by using a thermoplastic
elastomer alloy obtained by blending a thermoplastic
polyurethane with an ethylene-propylene-diene
copolymerized rubber modified with an unsaturated
carboxylic acid or a derivative thereof (EPDM modified
with an unsaturated carboxylic acid or a derivative
thereof), which is crosslinked and utilized as an
industrial rubber product in many cases, and has not been
so much used as a modifier for other resins so far, the
toothed belt remarkably improved in abrasion resistance
and bending fatigue resistance and remarkably excellent
in durability can be obtained; and this finding has led
to the completion of the present invention.
[0008]
That is, the present invention provides a toothed
belt in which the whole or a part of a belt body is
formed from a thermoplastic elastomer alloy comprising a
thermoplastic polyurethane (A) and an ethylene-propylene^
- 4
diene copolymerized rubber (B) modified with an
unsaturated carboxylic acid or a derivative thereof (a
toothed belt having a belt body containing a part formed
from a thermoplastic elastomer alloy comprising a
thermoplastic polyurethane {A) and an ethylene-propylenediene
copolymerized rubber (B) modified with an
unsaturated carboxylic acid or a derivative thereof).
[0009]
In the toothed belt, the weight proportion [(B)/(A)]
of the ethylene-propylene-diene copolymerized rubber (B)
modified with an unsaturated carboxylic acid or a
derivative thereof to the thermoplastic polyurethane (A)
is preferably 0.1/99.9 to 30/70.
[0010]
The ethylene-propylene-diene copolymerized rubber
(B) modified with an unsaturated carboxylic acid or a
derivative thereof is preferably an ethylene-propylenediene
copolymer modified with maleic anhydride.
[0011]
At least the tooth part of the belt body is
preferably formed from the thermoplastic elastomer alloy.
[0012]
The thermoplastic elastomer alloy preferably has a
hardness (JIS K6253, durometer type A) of not less than
75.
[0013]
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In the present description, the hardness is a value
measured according to JIS K6253 (durometer type A).
Advantageous Effects of Invention
[0014]
The toothed belt according to the present invention,
since a belt body is formed from a specific thermoplastic
elastomer alloy, is excellent not only in abrasion
resistance but also in bending fatigue resistance, and
hardly causes abrasion, damage, cracks, breakage and the
like on the belt body in an early stage and is remarkably
excellent in durability, even if the belt is used at a
high load for a long time.
Brief Description of Drawings
[0015]
[Figure 1] Figure 1 is a perspective diagram
illustratively showing one example of the toothed belt
according to the present invention.
[Figure 2] Figure 2 is a schematic perspective diagram
illustratively showing one example of a method for
manufacturing the toothed belt according to the present
invention.
[Figure 3] Figure 3 is a SEM photograph of a pellet
cross-section of a thermoplastic elastomer alloy (an
alloy of an EPDM and an etheric TPU) obtained in
Comparative Example 4.
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[Figure 4] Figure 4 is a SEM photograph of a pellet
cross-section of a thermoplastic elastomer alloy (an
alloy of a maleic anhydride-modified EPDM and an etheric
TPU) obtained in Example 4.
[Figure 5] Figure 5 is an SEM photograph of a pellet
cross-section of a thermoplastic elastomer alloy (an
alloy of an EPDM and an esteric TPU) obtained in
Comparative Example 6.
[Figure 6] Figure 6 is an SEM photograph of a pellet
cross-section of a thermoplastic elastomer alloy (an
alloy of a maleic anhydride-modified EPDM and an esteric
TPU) obtained in Example 7.
Description of Embodiments
[0016]
[Toothed belt]
Figure 1 is a perspective diagram illustratively
shown by breaking a part of one example of the toothed
belt according to the present invention. In the example,
the toothed belt 1 is constituted of a belt body 2 and
cords (tension members) 3 embedded in the interior of the
belt body 2. The belt body 2 comprises a back part 2a
and a tooth part 2b; the surface (back surface) of the
back part 2a side is a flat surface; and on the surface
(toothed surface) of the tooth part 2b side, crosssectionally
trapezoidal tooth parts 2b extending in the
belt width direction and tooth bottom parts 2c are
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alternately formed at constant intervals in the belt
longitudinal direction. At a nearly central part in the
belt longitudinal direction of the tooth bottom part 2c,
a tooth groove part 2d corresponding to a shape of a mold
to embed the cords 3 in predetermined positions of the
belt body 2 is formed. Then, in the back part 2a of the
belt body 2, the plurality of cords 3 are embedded in the
belt longitudinal direction at predetermined intervals in
the belt width direction. The cord 3 is a member used to
suppress the elongation and provide a high strength in
applications requiring high-torque transmission.
[0017]
The cross-sectional shape of the tooth part 2b may
not be trapezoidal, and may be, for example, of an arc
shape (arc tooth profile) or the like, and can suitably
be selected according to applications and the like.
[0018]
The cords 3 are not especially limited, and usable
are, for example, steel cords, stainless steel cords,
aramid fiber cords, glass fiber cords and carbon fiber
cords.
[0019]
The toothed belt according to the present invention
may have, as required, components, parts, coating layers
and the like other than the above.
[0020]
In the toothed belt according to the present
invention, the whole or a part of the belt body 2 is
formed from a thermoplastic elastomer alloy comprising a
thermoplastic polyurethane (A), and an ethylenepropylene-
diene copolymerized rubber (B) modified with an
unsaturated carboxylic acid or a derivative thereof. The
belt body 2 may be constituted of one member, or may be
constituted of two or more members. In the present
invention, at least the tooth part 2b in the belt body 2
is preferably formed from the thermoplastic elastomer
alloy. Hereinafter, "ethylene-propylene-diene
copolymerized rubber modified with an unsaturated
carboxylic acid or a derivative thereof" is abbreviated
simply to "modified ethylene-propylene-diene
copolymerized rubber" or "modified EPDM" in some cases.
[0021]
[Thermoplastic polyurethane (A)]
In the present invention, as the thermoplastic
polyurethane (A), known thermoplastic polyurethanes (TPU)
can be used. The thermoplastic polyurethane (A) can be
used singly or in combinations of two or more. The
thermoplastic polyurethane is usually obtained by
reacting a polyisocyanate, a long-chain polyol and a
chain extender, and as required, other isocyanatereactive
compounds.
[0022]
w
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The polyisocyanate is not especially limited as long
as it is a compound having at least two isocyanate groups
in the molecule. The polyisocyanate includes, for
example, aliphatic polyisocyanates, alicyclic
polyisocyanates, aromatic polyisocyanates and araliphatic
(aromatic-aliphatic) polyisocyanates. The polyisocyanate
can be used singly or in combinations of two or more.
[0023]
Examples of the aliphatic polyisocyanate include
aliphatic diisocyanates such as 1,3-trimethylene
diisocyanate, 1,4-tetramethylene diisocyanate, 1,5-
pentamethylene diisocyanate, 1,6-hexamethylene
diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene
diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene
diisocyanate, 2-methyl-l,5-pentamethylene diisocyanate,
3-methyl-l,5-pentamethylene diisocyanate, 2,4,4-
trimethyl-1,6-hexamethylene diisocyanate and 2,2,4-
trimethyl-1,6-hexamethylene diisocyanate.
[0024]
Examples of the alicyclic polyisocyanate include
alicyclic diisocyanates such as 1,3-cyclopentane
diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-
cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-
trimethylcyclohexyl Isocyanate (isophorone diisocyanate),
4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-
cyclohexane diisocyanate, methyl-2,6-cyclohexane
diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-
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bis(isocyanatomethyl)cyclohexane and norbornane
diisocyanate.
[0025]
Examples of the aromatic polyisocyanate include
aromatic diisocyanates such as m-phenylene diisocyanate,
p-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-
tolylene diisocyanate, naphthylene 1,4-diisocyanate,
naphthylene 1,5-diisocyanate, 4,4'-diphenyl diisocyanate,
4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane
diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-
diphenyl ether diisocyanate, 2,2'-diphenylpropane-4,4'-
diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-
diisocyanate and 4,4'-diphenylpropane diisocyanate.
[0026]
Examples of the araliphatic polyisocyanate include
araliphatic diisocyanates such as 1,3-xylylene
diisocyanate, 1,4-xylylene diisocyanate, co,(JO'-
diisocyanato-1,4-diethylbenzene, 1,3-bis{1-isocyanato-lmethylethyl)
benzene, 1,4-bis(1-isocyanato-l-methylethyl)
benzene and 1,3-bis(a,a-dimethylisocyanatomethyl)benzene.
[0027]
As the polyisocyanate, suitably usable are 1,6-
hexamethylene diisocyanate, 4,4'-methylenebis{cyclohexyl
isocyanate), 1, 3-bis(isocyanatomethyl)cyclohexane, 1,4-
bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
4,4'-diphenylmethane diisocyanate, 1,3-xylylene
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diisocyanate, 1,4-xylylene diisocyanate, norbornane
diisocyanate and l,3-bis{a,adimethylisocyanatomethyl)
benzene.
[0028]
As the polyisocyanate, also usable are dimers,
trimers, reaction products or polymers of the above
exemplified aliphatic polyisocyanates, alicyclic
polyisocyanates, aromatic polyisocyanates and araliphatic
polyisocyanates (for example, a dimmer or a trimer of
diphenylmethane diisocyanate, reaction products of
trimethylolpropane and tolylene diisocyanate, reaction
products of trimethylolpropane and hexamethylene
diisocyanate, polymethylene polyphenyl isocyanates,
polyether polyisocyanates, polyester polyisocyanates and
the like) and the like.
[0029]
Examples of the long-chain polyol include polyether
polyols, polyester polyols, polycarbonate polyols,
polyolefin polyols and polyacryl polyols. The long-chain
polyol has a number-average molecular weight of usually
not less than 500, preferably 500 to 10,000, still more
preferably 600 to 6,000, and further still more
preferably 800 to 4,000. The long-chain polyol can be
used singly or in combinations of two or more.
[0030]
Examples of the polyether polyol include
polyalkylene ether glycols such as polyethylene ether
1§
- 12 -
glycols, polypropylene ether glycols and
polytetramethylene ether glycols (PTMG), and additionally
copolymers containing a plurality of alkylene oxides
(alkylene oxide-another alkylene oxide copolymer) as
monomer components, such as ethylene oxide-propylene
oxide copolymers. Among the polyether polyols,
especially preferable are polytetramethylene ether
glycols (PTMG).
[0031]
As the polyester polyol, usable are, for example,
polycondensates of a polyhydric alcohol and a polyvalent
carboxylic acid, ring-opened polymers of cyclic esters
(lactones), and reaction products of three components of
a polyhydric alcohol, a polyvalent carboxylic acid and a
cyclic ester (lactone). In the polycondensates of a
polyhydric alcohol and a polyvalent carboxylic acid, as
the polyhydric alcohol, usable are, for example, ethylene
glycol, diethylene glycol, propylene glycol, dipropylene
glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol,
2-methyl-l,3-propanediol, 1,5-pentanediol, neopentyl
glycol, 1,6-hexanediol, 3-methyl-l,5-pentanediol, 2,4-
diethyl-1,5-pentanediol, 1,9-nonanediol, 1,10-decanediol,
glycerol, trimethylolpropane, trimethylolethane,
cyclohexanediols (1,4-cyclohexanediol and the like),
cyclohexanedimethanols (1,4-cyclohexanedimethanol and the
like), bisphenols (bisphenol A and the like), and sugar
alcohols (xylitol, sorbitol and the like). On the other
- 13 -
hand, examples of the polyvalent carboxylic acid include
aliphatic dicarboxylic acids such as malonic acid, maleic
acid, succinic acid, glutaric acid, adipic acid, suberic
acid, azelaic acid, sebacic acid and dodecanedioic acid;
alicyclic dicarboxylic acids such as 1,4-
cyclohexanedicarboxylic acid; and aromatic dicarboxylic
acids such as terephthalic acid, isophthalic acid, orthophthalic
acid, 2,6-naphthalenedicarboxylic acid, paraphenylenedicarboxylic
acid and trimellitic acid. In the
ring-opened polymers of cyclic esters, examples of the
cyclic ester include propiolactone, |3-methyl-5-
valerolactone and s-caprolactone. In the reaction
products of three components, the above exemplified
polyhydric alcohols, polyvalent carboxylic acids and
cyclic esters and the like can be used. Among the
polyester polyols, preferable are adipate-based polyester
polyols [for example, C2-6 alkylene adipates such as
poly(ethylene adipate), poly(diethylene adipate),
poly(propylene adipate), poly(tetramethylene adipate),
poly(hexamethylene adipate) and poly(neopentylene
adipate)] which are polycondensates of adipic acid and a
polyhydric alcohol (for example, one or two or more of
alkane diols having 2 to 6 carbon atoms such as ethylene
glycol, 1,4-butanediol, neopentyl glycol and 1,6-
hexanediol) , caprolactone polyols obtained by ringopening
polymerization of s-caprolactone, polyester
polyols obtained by ring-opening polymerization of p-
14 -
methyl-8-valerolactone using a polyhydric alcohol such as
ethylene glycol, and the like.
[0032]
Examples of the polycarbonate polyol include
reaction products of a polyhydric alcohol and phosgene, a
chloroformate ester, a dialkyl carbonate or a diaryl
carbonate(a polyhydric alcohol and a compound selected
from the group consisting of phosgene, a chloroformate
ester, a dialkyl carbonate and a diaryl carbonate); and
ring-opened polymers of cyclic carbonate esters (alkylene
carbonates and the like). In the reaction products of a
polyhydric alcohol and phosgene, as the polyhydric
alcohol, specifically usable are the above exemplified
polyhydric alcohols (for example, ethylene glycol,
propylene glycol, 1,3-butanediol, 1,4-butanediol,
neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol and
1,9-nonanediol). In the ring-opened polymers of cyclic
carbonate esters, examples of the alkylene carbonate
include ethylene carbonate, trimethylene carbonate,
tetraraethylene carbonate and hexamethylene carbonate.
Here, the polycarbonate polyol suffices if being a
compound having carbonate bonds in the molecule and
having hydroxyl groups at the terminals, and may have
ester bonds together with the carbonate bonds. Typical
examples of the polycarbonate polyol include
poly(hexamethylene carbonate) diols, diols obtained by
ring-opening addition polymerization of a lactone to a
- 15 -
poly(hexamethylene carbonate) diol, and cocondensates of
a poly(hexamethylene carbonate) diol and a polyester diol
or a polyether diol.
[0033]
The polyolefin polyol is a polyol having an olefin
as a component of a skeleton (or a main chain) of a
polymer or a copolymer, and having at least two hydroxyl
groups in the molecule (particularly at the terminals).
The above olefin may be an olefin (for example, an aolefin
such as ethylene or propylene) having a carboncarbon
double bond at the terminal, may be an olefin (for
example, isobutene) having a carbon-carbon double bond at
a site other than the terminals, or further may be a
diene (for example, butadiene or isoprene), Typical
examples of the polyolefin polyol include substances
(compounds) obtained by modifying, with hydroxyl groups,
the terminals of butadiene- or isoprene-based polymers
such as butadiene homopolymers, isoprene homopolymers,
butadiene-styrene copolymers, butadiene-isoprene
copolymers, butadiene-acrylonitrile copolymers,
butadiene-2-ethylhexyl acrylate copolymers, butadiene-noctadecyl
acrylate copolymers.
[0034]
The polyacryl polyol is a polyol having a
(meth)acrylate as a component of a skeleton (or a main
chain) of a polymer or a copolymer, and having at least
two hydroxyl groups in the molecule (particularly at the
- 16 -
terminals). As the (meth)acrylate, suitably used are
alkyl (meth) acrylate esters [for example, Ci-20 alkyl
(meth)acrylate esters]. As the polyol, every material
other than materials cited here can be used.
[0035]
As the chain extender, usable are chain extenders
usually used in production of thermoplastic polyurethanes,
and the type thereof is not especially limited, and lowmolecular
weight polyols and polyamines and the like can
be used. The chain extender has a molecular weight of
usually less than 500, and preferably not more than 300.
The chain extender can be used singly or in combinations
of two or more.
[0036]
Typical examples of the chain extender include
polyols (particularly, diols) such as ethylene glycol,
propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-
butanediol, 1,5-pentanediol, 1,2-pentanediol, 2,3-
pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-
1,5-pentanediol, 1,4-cyclohexanediol and 1,4-
cyclohexanedimethanol, and polyamines (particularly,
diamines) such as hexamethylenediamine, 3,3'-dimethyl-
4,4'-diaminodicyclohexylmethane and 4,4'-methylenebis-2-
chloroaniline. Among these, diols are especially
preferable.
[0037]
- 17 -
As the thermoplastic polyurethane (A), preferable
are thermoplastic polyurethanes obtained by reacting a
polyisocyanate, a long-chain polyol and a chain extender
in the range of the ratio (NCO/isocyanate-reactive
groups), of the molar number of isocyanate groups of the
polyisocyanate and the molar number of isocyanatereactive
groups (hydroxyl group, amino group and the
like) of the long-chain polyol and the chain extender, of
0.9 to 1.3, especially 0.95 to 1.1, The proportion of
the long-chain polyol to the chain extender, [the former
/ the latter (molar ratio)], can suitably be selected in
the range of, for example, 0.1 to 1.0, and preferably 0.2
to 2, according to physical properties and the like of
the thermoplastic polyurethane. In the above reaction,
in order to promote the reaction, as required, a catalyst
such as a tertiary amine, an organometal compound or a
tin compound may be used.
[0038]
The thermoplastic polyurethane usually has a weightaverage
molecular weight Mw of 5,000 to 1,000,000.
The thermoplastic polyurethane has thermoplasticity,
though some exhibit no distinct melting point. The
thermoplastic polyurethane has thermoplasticity, and can
be molded by a common thermoplastic resin molding machine
such as extrusion, injection molding, heat press or the
like.
[0039]
- 18 -
The hardness of the thermoplastic polyurethane (A),
from the viewpoint of raising mechanical properties of
the thermoplastic elastomer alloy, is preferably not less
than 75 (for example, 75 to 96), more preferably not less
than 78 {for example, 78 to 96), still more preferably
not less than 89 (for example, 89 to 95), and especially
preferably not less than 91 (for example, 91 to 94).
From the viewpoint of letting the thermoplastic elastomer
alloy have reasonable flexibility and raising the bending
fatigue resistance, the thermoplastic polyurethane (A)
has a hardness in the range of, for example, 75 to 93,
and especially preferably 78 to 91 (particularly 78 to
88) .
[0040]
As the thermoplastic polyurethane (A), commercially
available products can be used. Examples of the
commercially available products include an adipate-based
TPU of 80 in hardness (an adipate-based TPU with a
hardness of 80, a hardness of 80), an adipate-based TPU
of 90 in hardness, a caprolactone-based TPU of 90 in
hardness, a PTMG-based TPU of 92 in hardness, and an
adipate-based TPU of 92 in hardness.
[0041]
[Modified ethylene-propylene-diene copolymerized
rubber (B)]
In the present invention, as the modified ethylenepropylene-
diene copolymerized rubber (B) (modified EPDM)
19 -
modified with an unsaturated carboxylic acid or a
derivative thereof, usable are known ethylene-propylenediene
copolymerized rubbers modified with an unsaturated
carboxylic acid or a derivative thereof. The modified
ethylene-propylene-diene copolymerized rubber (B)
modified with the unsaturated carboxylic acid or a
derivative thereof can be used singly or in combinations
of two or more.
[0042]
An ethylene-propylene-diene copolymer (EPDM) is a
copolymer of ethylene, propylene and a non-conjugated
diene. Examples of the diene include 5-ethylidene-2-
norbornene, dicyclopentadiene and 1,4-hexadiene. A
modified ethylene-propylene-diene copolymerized rubber
(modified EPDM) used in the present invention is obtained
by modifying an EPDM with, for example, an unsaturated
carboxylic acid or a derivative thereof (an ester, an
acid anhydride, or the like) or another functional group.
Examples of the unsaturated carboxylic acid or the
derivative thereof include acrylic acid, methacrylic acid,
glycidyl (meth)acrylate, maleate esters and maleic
anhydride, and the unsaturated carboxylic acid or the
derivative thereof may have a structure of an ester salt,
a metal salt thereof and the like. Miong these,
preferable are acrylic acid, methacrylic acid and maleic
anhydride, and especially preferable is maleic anhydride.
[0043]
1^
20 -
Modification of an EPDM can be carried out, for
example, by heating and kneading the EPDM and an
unsaturated carboxylic acid or a derivative thereof in
the presence of a graft polymerization initiator [for
example, a peroxide initiator such as l,3-bis(tbutylperoxyisopropyl)
benzene or dicumyl peroxide]. The
ratio of ethylene and propylene in an EPDM used as a raw
material is, from the viewpoint of properties thereof as
an elastomer, and the like, for example, the former / the
latter (weight ratio) = 10/90 to 95/5, and preferably
about 50/50 to 85/15. The content rate of a structural
unit derived (originated) from a diene component in an
EPDM is, for example, about 0.1 to 25 wt%, preferably
about 1 to 20 wt%, and more preferably about 2 to 10 wt%,
to the whole EPDM.
[0044]
The modification ratio with an unsaturated
carboxylic acid or a derivative thereof in the modified
ethylene-propylene-diene copolymerized rubber (B) is, as
a content rate of a structural unit derived (originated)
from the unsaturated carboxylic acid or the derivative
thereof, for example, about 0.1 to 20 wt%, preferably
about 0.5 to 10 wt%, and more preferably about 1 to 8 wt%j
with respect to a whole amount of the modified EPDM (the
whole modified EPDM). If the content rate is too low,
the improving effect of the abrasion resistance and the
bending fatigue resistance in blending with a
•p
21 -
thermoplastic polyurethane (A) is liable to become small.
By contrast, if the content rate is too high, the
function (property) as an elastomer becomes liable to
decrease.
[0045]
The modification of an EPDM may be carried out
independently for the EPDM before being blended with a
TPU, or may be carried out simultaneously in a stage of
blending a before-modification EPDM (EPDM before being
modified) with a TPU. An unreacted carboxylic acid or a
derivative thereof may be removed, or may be used as it
remains.
[0046]
The modified ethylene-propylene-diene copolymerized
rubber (B) has a melt flow rate (ASTM D1238, 280°C/2.16
kg) of, for example, 5 to 80 g/lO-min, and preferably 10
to 40 g/lO-min,
[0047]
As the modified ethylene-propylene-diene
copolymerized rubber (B), commercially available products
may be used. Examples of the commercially available
product include "Fusabond N416" by trade name (maleic
anhydride-modified EPDM, Du Pont K.K.).
[0048]
Note that a modified ethylene-propylene-diene
copolymerized rubber (B) may be crosslinked, or
uncrosslinked. Dynamic crosslinking, in which
- 22 -
crosslinking is carried out with thermoplasticity being
maintained, may be used.
[0049]
[Thermoplastic elastomer alloy]
In the present invention, the thermoplastic
elastomer alloy comprises the thermoplastic polyurethane
(A) and the ethylene-propylene-diene copolymerized rubber
(B) modified with an unsaturated carboxylic acid or a
derivative thereof. Toothed belts obtained from such a
thermoplastic elastomer alloy are excellent not only in
the abrasion resistance but also in the bending fatigue
resistance, and remarkably suppressed in damage such as
abrasion and cracks even if being continuously or
intermittently used at a high load for a long time, thus
exhibiting a remarkably elongated life.
[0050]
Observation by a scanning electron microscope (SEM)
of a molded article cross-section of the thermoplastic
elastomer alloy {a cross-section of a molded article
formed from the thermoplastic elastomer alloy) reveals
that the modified ethylene-propylene-diene copolymerized
rubber (B) is highly micro-dispersed in a matrix composed
of the thermoplastic polyurethane (A) (see Figures 4 and
6) . For example, according to a SEM photograph at a
magnification of 2,000 times, in a thermoplastic
elastomer alloy composed of a modified EPDM and an
etheric TPU, no particulate shape cannot be observed
iP5
- 23 -
though unevenness is slightly seen; and in a
thermoplastic elastomer alloy composed of a modified EPDM
and an esteric TPU, almost no unevenness is observed. By
contrast, in the case of using a non-modified EPDM in
place of the modified EPDM, the particle of EPDM can be
clearly observed; particularly in a thermoplastic
elastomer alloy composed of an EPDM and an esteric TPU,
it is clearly observed that spherical particles of the
EPDM are dispersed in a matrix of the esteric TPU. That
the dispersibility is remarkably improved in a
thermoplastic elastomer alloy composed of a modified EPDM
and a TPU (especially, an esteric TPU) is presumably
because a modified sites having a polarity in the
modified EPDM has an affinity for polar sites of the TPU.
[0051]
In the present invention, the weight proportion
[(B)/(A)] of an ethylene-propylene-diene copolymerized
rubber (B) modified with an unsaturated carboxylic acid
or a derivative thereof to a thermoplastic polyurethane
(A) is, but not limited to, preferably in the range of
0.1/99.9 to 30/70. The weight proportion [(B)/(A)] of
the (B) to the (A) is more preferably 1/99 to 25/75, and
still more preferably 3/97 to 22/78 (particularly
7.5/92.5 to 22/78). With the proportion less than
0.1/99.9, the improving effect of the abrasion resistance
and the bending fatigue resistance becomes small. By
contrast, with the proportion exceeding 30/70, the
p - 24 -
property (mechanical strength) intrinsic to TPU is liable
to decrease.
[0052]
In the thermoplastic elastomer alloy, in addition to
the above (A) and (B), as required, additives can be
blended. Examples of the additives include antioxidants,
ultraviolet absorbers, plasticizers, stabilizers, mold
lubricants, surfactants, antistatic agents, colorants
(pigments, dyes), flame retardants, foaming agents, slip
agents, bulking agents, crosslinking agents, waxes and
antiaging agents.
[0053]
In the thermoplastic elastomer alloy, the total
content of a thermoplastic polyurethane (A) and a
modified ethylene-propylene-diene copolymerized rubber
(B) is, for example, not less than 85 wt%, preferably not
less than 90 wt%, and still more preferably not less than
95 wt%.
[0054]
The hardness of the thermoplastic elastomer alloy is
preferably not less than 75 (for example, 75 to 95), more
preferably not less than 78 (for example, 78 to 95),
still more preferably not less than 89 (for example, 89
to 95), and especially preferably not less than 91 (for
example, 91 to 95). From the viewpoint of having a
reasonable flexibility and raising the bending fatigue
resistance, the hardness of the thermoplastic elastomer
D
- 25 -
alloy is, for example, in the range of 75 to 93, and
especially preferably in the range of 77 to 91
(particularly, 77 to 88). The hardness of the
thermoplastic elastomer alloy can be regulated by the
hardness of the thermoplastic polyurethane (A), the
weight proportion of the thermoplastic polyurethane (A)
to the modified ethylene-propylene-diene copolymerized
rubber (B), the kinds and amounts of additives and the
like.
[0055]
The breaking strength {JIS K7311) of the
thermoplastic elastomer alloy is, for example, 25 to 100
MPa, preferably 30 to 80 MPa, and more preferably 35 to
75 MPa; and the breaking elongation (JIS K7311) thereof
is, for example, 300 to 1,000%, preferably 350 to 800%,
and more preferably 400 to 700%.
[0056]
The thermoplastic elastomer alloy can be produced by
mixing the thermoplastic polyurethane (A), the modified
ethylene-propylene-diene copolymerized rubber (B), and
the additives used according to needs by the same method
as the case of preparing usual polymer alloys or polymer
blends. For example, the thermoplastic elastomer alloy
can be produced by pre-mixing the thermoplastic
polyurethane (A), the modified ethylene-propylene-diene
copolymerized rubber (B) , and the additives used
according to needs in predetermined proportions, and
26 -
thereafter, kneading the mixture under heating by using a
single-screw extruder, a twin-screw extruder, a mixing
roll, a Banbury mixer or the like. In the case of
carrying out heating and kneading using an extruder, the
alloy is subjected to melt extrusion, and may be cut into
a suitable length to thereby make a granule such as a
pellet. Besides the above method, the thermoplastic
elastomer alloy can be produced also by charging the
modified ethylene-propylene-diene copolymerized rubber
(B) and/or the additives during the production of the
thermoplastic polyurethane (A).
[0057]
The manufacture of the thermoplastic elastomer alloy
and the molding of the toothed belt may be carried out
simultaneously. This case can employ, for example, a
side feed system, a dry blend system or the like.
[0058]
[Manufacture of a toothed belt]
Since the thermoplastic elastomer alloy can be melt
molded and thermally processed, the toothed belt
according to the present invention can be manufactured by
utilizing an optional method such as extrusion, injection
molding, blow molding, calendering or casting.
[0059]
Figure 2 is a schematic perspective diagram
illustratively showing one example of a method for
manufacturing the toothed belt according to the present
27 -
invention. In the example, the thermoplastic elastomer
alloy is continuously melt extruded in a sheet form from
a front end die (T-die) by an extruder 4; while the melt
resin 20 (thermoplastic elastomer alloy) is poured, at
the vicinity of the die, into a cavity formed between the
surface of a forming mold roll 5 rotating and having on
the mold surface a convexoconcave shape conforming to a
toothed surface shape of the toothed belt 1 as an object
and a steel band 9; and cords 3 (steel cords or the like)
are drawn in to thereby form the belt. A press roll 6, a
roll 7 and a roll 8 are disposed in the vicinity of the
forming mold roll 5; and the steel band 9 is stretched
between each roll 6 to 8, and is made to turn together in
cooperation with the forming mold roll 5. The cords 3
are embedded in the melt resin by a pressure of the
forming mold roll 5 and the steel band 9 to thereby form
a long-sized toothed belt 1.
[0060]
An endless belt can be manufactured as follows from
the long-sized toothed belt thus obtained. That is, the
long-sized toothed belt obtained in the above is cut into
a necessary length by a certain-width finger (W)-shaped
blade; both ends of the cut belt are butted, and set in a
mold having a convexoconcave shape conforming to the belt
tooth profile on the surface; and the butted portion is
fused by hot press to form a joint to thereby make an
endless belt. Here, although the cords (steel cords or
- 28 -
the like) are divided at the cut portions, the resin
portions fuse and are united to thereby hold a strength
necessary as a belt. An endless belt may be a seamless
belt having no joint. The seamless belt having no joint ,
makes a further highly durable belt.
[0061]
The toothed belt according to the present invention
is excellent not only in abrasion resistance but also in
bending fatigue resistance, and hardly causes abrasion,
damage, cracks, breakage and the like, and is thus
remarkably excellent in durability and has an elongated
life, even if being continuously or intermittently used
at a high load for a long time.
Examples
[0062]
Hereinafter, the present invention will be described
more specifically by way of Examples and Comparative
Examples. The present invention is not any more limited
thereto.
[0063]
Materials used in Examples and the like are shown
below.
[0064]

TPU-1: an adipate-based TPU of 90 in hardness
TPU-2: a caprolactone-based TPU of 90 in hardness
- 29
TPU-3: a PTMG-based TPU of 92 in hardness
TPU-4: an adipate-based TPU of 92 in hardness
TPU-5: an adipate-based TPU of 80 in hardness
[0065]

MAH-EPDM: trade name "Fusabond N416" (a maleic anhydridemodified
ethylene-propylene-diene copolymerized rubber,
made by Du Pont K.K.)
[0066]

EPDM: trade name "EP21" (an ethylene-propylene-diene
copolymerized rubber, made by JSR Corp.)
[0067]
Example 1
100 parts by weight of TPU-1 and 10 parts by weight
of MAH-EPDM were kneaded using a twin-screw extruder
(made by Technovel Corp., trade name "KZW20TW-30"). The
extruder was set at a barrel temperature of 200°C (here,
a feeder portion temperature of 160°C) and a screw
rotation frequency of 300 rpm; and the resins were melt
kneaded, and passed through a pelletizer to thereby
fabricate a pellet. The obtained pellet was injection
molded using an injection molding machine (made by Nissei
Plastic Industrial Co., Ltd., trade name "NEX110-18E"} to
thereby fabricate test pieces [100 mm x 100 mm x 2 mm
^
- 30 -
thick (for abrasion test), 120 mm x 10 mm x 4 mm thick
(for Demattia flex test)].
[0068]
Comparative Example 1
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-1 alone as a raw material resin.
[0069]
Example 2
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-2 and 10 parts by weight of MAH-EPDM as raw
material resins.
[0070]
Comparative Example 2
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-2 alone as a raw material resin.
[0071]
Example 3
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-3 and 5 parts by weight of MAH-EPDM as raw
material resins.
[0072]
Example 4
^
- 31 -
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-3 and 10 parts by weight of MAH-EPDM as raw
material resins.
[0073]
Example 5
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-3 and 20 parts by weight of MAH-EPDM as raw
material resins.
[0074]
Comparative Example 3
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-3 alone as a raw material resin.
[0075]
Comparative Example 4
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-3 and 10 parts by weight of EPDM as raw
material resins.
[0076]
Example 6
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-4 and 5 parts by weight of MAH-EPDM as raw
material resins.
- 32 -
[0077]
Example 7
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-4 and 10 parts by weight of MAH-EPDM as raw
material resins.
[0078]
Example 8
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-4 and 20 parts by weight of MAH-EPDM as raw
material resins.
[0079]
Example 9
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-5 and 10 parts by weight of MAH-EPDM as raw
material resins.
[0080]
Comparative Example 5
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
weight of TPU-4 alone as a raw material resin.
[0081]
Comparative Example 6
A pellet and test pieces were fabricated by the same
operation as in Example 1, except for using 100 parts by
••ir
- 33 -
weight of TPU-4 and 10 parts by weight of EPDM as raw
material resins.
[0082]
Evaluation tests A

An abrasion loss (mg) after the rotation number of
1,000 times using a Taber abrasion tester using an
abrasion wheel H-22 at a load of 9.8 N was measured for
the test piece of 100 mm x 100 mm x 2 mm thick, according
to JIS K7311. The results are shown in Table 1.
[0083]

A Demattia flex test was carried out according to
JIS K6260. A notch of 0.5 mm in depth was cut across the
nearly entire length in the width direction of a middle
portion of the long side (a position of 60 mm from the
end in the longitudinal direction) on the strip test
piece of 120 mm x 10 mm x 4 mm thick, and the notched
test piece was provided for the test. The test was
carried out under the condition of a maximum distance
between chucks of 80 mm, a motion distance between the
chucks of 70 mm and a bending speed of 97 times/min, and
a bending number of times until the depth of a crack from
the notch of the test piece reached 3.5 mm was measured.
The results are shown in Table 1.
[0084]

- 34
A hardness was measured according to JIS K6253
(durometer type A). The pellet was injection molded by
an injection molding machine (made by Nissei Plastic
Industrial Co., Ltd., trade name "NEX110-18E") to thereby
fabricate test pieces of 100 mm x 100 mm x 2 mm thick;
three sheets thereof were stacked to thereby prepare a
test piece of 6 mm in thickness; and a measurement of a
hardness was carried out using the stacked test piece.
The results are shown in Table 1.
[0085]

A tensile test was carried out according to JIS
K7311, and a breaking strength (MPa) and a breaking
elongation (%) were determined. The results are shown in
Table 1.
[0086]

Cross-sections of the pellets obtained by a twinscrew
extruder were cut out by a freezing microtome, and
observed using a scanning electron microscope (made by
Hitachi High-Technologies Corp., trade name "S-4300") at
a magnification of 2,000 times. A SEM photograph of a
cross-section of the pellet obtained in Comparative
Example 4 is shown in Figure 3; a SEM photograph of a
cross-section of the pellet obtained in Example 4, in
Figure 4; a SEM photograph of a cross-section of the
pellet obtained in Comparative Example 6, in Figure 5;
- 35 -
and a SEM photograph of a cross-section of the pellet
obtained in Example 7, in Figure 6.
[0087]
From the evaluation results shown in Table 1, it is
clear that the molded articles formed from a
thermoplastic elastomer alloy used in the present
invention are remarkably better not only in the Taber
abrasion loss but also in the bending fatigue resistance
than the molded articles formed from a thermoplastic
polyurethane alone, and the molded articles formed from a
thermoplastic elastomer alloy composed of a thermoplastic
polyurethane and a non-modified ethylene-propylene-diene
copolymerized rubber. The case where a modified
ethylene-propylene-diene copolymerized rubber is added
can improve the abrasion resistance and the bending
fatigue resistance without spoiling the material property
of a thermoplastic polyurethane. Although even the case
where a non-modified ethylene-propylene-diene
copolymerized rubber is added exhibits an improving
affect in some degree of the bending fatigue resistance
in some cases, the cases of largely improving the
abrasion resistance and the bending fatigue resistance
are cases of a thermoplastic polyurethane alloyed with a
modified ethylene-propylene-diene copolymerized rubber.
From the results of the disperse state checking test, it
is clear that the disperse states are better in order of
an esteric TPU-EPDM < an etheric TPU-EPDM < an etheric
H
- 36
TPU-maleic anhydride-modified EPDM < an esteric TPUmaleic
anhydride-modified EPDM. The reason why the Taber
abrasion and the bending number of times are remarkably
improved is conceivably that a retardation effect of
crack extension of the microdispersion of the rubber
component having an energy absorbing effect changes
states from the severe progress of adhesion wearing of
TPU to the mild progress. This is because a combination
in which an elastomer component turns to a micro phase
separation structure in a form of not excessively
reacting with TPU was attained, in the present invention.
If a micro phase separation structure is made, the heat
generation of the alloy usually becomes large under the
dynamic fatigue condition, thereby causing inferior
durability. However, in the thermoplastic elastomer
alloy according to the present invention, an excessive
hardness change due to the alloying is suppressed and the
durability under a severe condition of being impressed
with a repeated load is remarkably improved. Nobody has
developed such properties and confirmed the effects, and
the properties and effects have been found by exhaustive
devices by the present inventors.
[0088]
- 37 -
[Table 1]
Table 1
TPU-1
TPU-2
TPU-3
TPU-4
TPU-5
MAH-EPDM
(Phr)
EPDM (phr)
Taber
Abrasion
Amount (mg)
Bending
Number Of
Times (times)
nsA
Hardness
Breaking
Strength
(MPa)
Breaking
Elongation
(%)
Example
1
100
10
9.3
400,000
90
-
-
Comp.
Ex.1
100
12.9
5,000
92
-
-
Example
2
100
10
6.3
18,000
87
-
-
Comp.
Ex.2
100
11.5
3,000
88
-
-
Example
3
100
5
8.1
8,000
92
-
-
Example
4
100
10
8.5
250,000
92
-
-
Example
5
100
20
8.5
170,000
90
-
-
Comp.
Ex.3
100
12.5
3,000
92
-
-
Comp.
Ex.4
100
10
12.4
40,000
91
-
-
Example
6
100
5
11
15,000
93
57
560
Example
7
100
10
6.8
330,000
93
47
510
Example
8
100
20
10.8
270,000
91
38
490
Comp.
Ex.5
100
16.4
5,000
95
52
520
Comp.
Ex.6
100
10
16.6
17,000
91
-
-
Example
9
100
10
7.4
1,800,000
79
-
-
!»gWJWBj»IKWpaW!BWIWW^^ simmmfmmmmwmmmm'm'^^'i^^^i^'mw^^^''' »fw*HP'yffl'W'ii0.12 (S/Z) ] were drawn in and
formed with the resin to thereby obtain a long-sized
toothed belt 1.
The obtained long-sized toothed belt was cut into a
necessary length by a certain-width finger (W)-shaped
blade; both ends of the cut belt were butted, and set in
a mold having on the surface a convexoconcave shape
conforming to the belt tooth profile; and the butted
portion was fused by hot press to form a joint to thereby
obtain an endless toothed belt [tooth profile: TIO
(trapezoidal tooth profile), tooth number: 120 teeth,
belt width: 25 mm, belt length: 1,200 mm]. In the
obtained tQothed belt, the count of the steel cord per 1
inch width is 15.
[0090]
f - 39
Comparative Example 7
An endless toothed belt was manufactured by the same
operation as in Example 10, except for using the pellet
{thermoplastic elastomer) obtained in Comparative Example
3.
[0091]
Evaluation test B

The endless toothed belts obtained in Example 10 and
Comparative Example 7 were subjected to a belt life test
using an overload running tester. The condition of the
running test is as follows. The test was finished at the
timepoint when the belt lost the rotary transmission
capability.
Layout: simple two-shafts
Pulley tooth number: 14 teeth
Rotation frequency: 2,300 rpm
Load torque: 5.88 N-m (0.6 kgf-m)
Initial tension: 216 N
As a result, the life (running time) of the toothed
belt of Example 10 was not less than 900 (running time
ratio: not less than 9 times) where the life (running
time) of the toothed belt of Comparative Example 7 was
taken to be 100.
From the above test results, it is conceivable that
the life of the toothed belt has a correlation with the
abrasion loss in the Taber abrasion test of a
- 40 -
thermoplastic elastomer (alloy) and the bending number of
times in the Demattia flex test thereof (Table 1).
Industrial Applicability
[0092]
The toothed belt according to the present invention
is excellent not only in abrasion resistance but also in
bending fatigue resistance, and hardly causes abrasion,
damage, cracks, breakage and the like on the belt body in
an early stage and is thus remarkably excellent in
durability, even if the belt is used at a high load for a
long time. Therefore, the belt can suitably be utilized
as belts for power transmission, conveyance and the like.
Reference Signs List
[0093]
1 TOOTHED BELT
2 BELT BODY
2a BACK PART
2b TOOTH PART
2c TOOTH BOTTOM PART
2d TOOTH GROOVE PART
3 CORD
4 EXTRUDER
5 FORMING MOLD ROLL
6 PRESS ROLL
7 ROLL
%'
- 41 -
8 ROLL
9 STEEL BAND
20 MELT RESIN (THERMOPLASTIC ELASTOMER ALLOY)

- 42
Claims
[Claim 1]
A toothed belt wherein the whole or a part of a belt
body is formed from a thermoplastic elastomer alloy
comprising a thermoplastic polyurethane (A) and an
ethylene-propylene-diene copolymerized rubber (B)
modified with an unsaturated carboxylic acid or a
derivative thereof.
[Claim 2]
The toothed belt according to claim 1, wherein a
weight proportion [{B)/{A)] of the ethylene-propylenediene
copolymerized rubber (B) modified with an
unsaturated carboxylic acid or a derivative thereof to
the thermoplastic polyurethane (A) is 0.1/99.9 to 30/70.
[Claim 3]
The toothed belt according to claim 1 or 2, wherein
the ethylene-propylene-diene copolymerized rubber (B)
modified with an unsaturated carboxylic acid or a
derivative thereof is an ethylene-propylene-diene
copolymer modified with maleic anhydride.
[Claim 4]
The toothed belt according to any one of claims 1 to
3, wherein at least a tooth part of the belt body is
formed from the thermoplastic elastomer alloy.
[Claim 5]
- 43 -
The toothed belt according to any one of claims 1 to
4, wherein the thermoplastic elastomer alloy has a
hardness (JIS K6253, durometer type A) of not less than
75.