Patent Description:
A power transmission belt using a cord made of carbon fibers has been known. For example, <CIT> discloses a toothed belt in which a cord made of carbon fibers is embedded in a belt body made of rubber. <CIT> also discloses a power transmission belt according to the preamble of claim <NUM>.

The present invention is directed to a power transmission belt according to claim <NUM>.

An embodiment will be described in detail below with reference to the drawings.

<FIG> and <FIG> illustrate a toothed belt B of an embodiment. The toothed belt B of the embodiment is an engagement power transmission belt and is advantageously used for high load transmission of machine tools, printing machines, textile machines, and injection machines, for example. The toothed belt B of the embodiment has a belt length of, for example, <NUM> or more to <NUM> or less. The toothed belt B of the embodiment has a belt width of, for example, <NUM> or more to <NUM> or less. The toothed belt B of the embodiment has a (maximum) belt thickness of, for example, <NUM> or more to <NUM> or less.

The toothed belt B of the embodiment includes an elastomer-made endless toothed belt body <NUM> made of polyurethane resin. The toothed belt body <NUM> includes a flat band portion <NUM> having a horizontally elongated rectangular cross-section and a plurality of teeth <NUM> provided on the inner periphery of the flat band portion <NUM> so as to be integral therewith. The teeth <NUM> are provided at a constant pitch in a belt length direction.

Examples of the tooth profile of the each tooth <NUM> in the side view include an arc tooth profile of the super torque synchronous (STS) belts in which both sides of the tooth are bowed outward in the form of an arc and a trapezoidal tooth profile. The number of teeth <NUM> is, for example, <NUM> or more to <NUM> or less. The teeth <NUM> each have a width (the maximum dimension in the belt length direction) of, for example, <NUM> or more to <NUM> or less. The teeth <NUM> each have a height of, for example, <NUM> or more to <NUM> or less. The teeth <NUM> are arranged at a pitch of, for example <NUM> or more to <NUM> or less.

The polyurethane resin forming the toothed belt body <NUM> is obtained by heating, pressurizing, and curing an urethan composition which is obtained by blending a curing agent, a plasticizer, and the like to a urethan prepolymer.

The urethan prepolymer is a relatively low molecular weight urethan compound which is obtained by a reaction between an isocyanate component and a polyol component and having a plurality of NCO groups at its terminals. Examples of the isocyanate component include tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Examples of the polyol component include poly tetramethylene ether glycol (PTMG). The urethan prepolymer may be composed of a single urethan prepolymer or a plurality of urethan compounds blended.

Examples of the curing agent include amine compounds such as <NUM>,<NUM>-phenylene diamine, <NUM>,<NUM>-diamino toluene, <NUM>,<NUM>-naphthalene diamine, <NUM>,<NUM>'-diamino diphenylmethane, and <NUM>,<NUM>'-dichloro-<NUM>,<NUM>'-diamino diphenylmethane (MOCA). The curing agent suitably contains one kind or two or more kinds of them. The amine compound serving as a curing agent is suitably blended to have an α value (NH<NUM> group/NCO group) of <NUM> or more to <NUM> or less. The α value is a ratio of the amount of NH<NUM> groups by mole in the curing agent to the amount of NCO groups by mole in the urethan prepolymer.

Examples of the plasticizer include: dialkyl phthalates such as dibutylphthalate (DBP) and dioctyl phthalate (DOP); dialkyl adipates such as dioctyl adipate (DOA); and dialkyl sebacate such as dioctyl sebacate (DOS). The plasticizer suitably contains one kind or two or more kinds of them. The plasticizer is blended at <NUM> parts by mass or more to <NUM> parts by mass or less relative to <NUM> parts by mass of the urethan prepolymer.

Example of the other compound ingredients include a colorant, an antifoaming agent, and a stabilizer.

The polyurethane resin forming the toothed belt body <NUM> has a hardness of, for example, <NUM>° or more to <NUM>° or less. The hardness of the polyurethane resin is measured in accordance with JIS K <NUM>: <NUM>.

The toothed belt B of the embodiment includes a cord <NUM> made of carbon fibers and embedded in the flat band portion <NUM> of the toothed belt body <NUM>. The cord <NUM> has an outer diameter of suitably <NUM> or more to <NUM> or less, more suitably <NUM> or more to <NUM> or less, in terms of obtaining excellent durability in high load transmission.

The carbon fibers forming the cord <NUM> are suitably PAN-based carbon fibers, in terms of obtaining excellent durability in high load transmission. The carbon fibers each have a filament diameter of suitably <NUM> or more to <NUM> or less, more suitably <NUM> or more to <NUM> or less.

The total number of filaments of the carbon fibers forming the cord <NUM> is suitably <NUM> (<NUM>) or more to <NUM> (<NUM>) or less, more suitably <NUM> (<NUM>) or more to <NUM> (<NUM>), yet more suitably <NUM> (<NUM>), in terms of obtaining excellent durability in high load transmission. The carbon fibers forming the cord <NUM> have a fiber fineness of suitably <NUM> tex or more to <NUM> tex or less, more suitably <NUM> tex or more to <NUM> tex or less, yet more suitably <NUM> tex, in terms of the same.

The cord <NUM> is suitably a twisted yarn, in terms of obtaining excellent durability in high load transmission. The twisted yarn forming the cord <NUM> includes a single twist yarn, a plied yarn, and a lang's lay. The cord <NUM> of the twisted yarn is suitably a single twist yarn obtained by twisting a filament bundle of the carbon fibers in one direction. The number of twists of the cord <NUM> of the single twist yarn is suitably <NUM>/<NUM> or more to <NUM>/<NUM> or less, more suitably <NUM>/<NUM> or more to <NUM>/<NUM> or less, in terms of the same. For the cord <NUM> of the single twist yarn, either an S-twist yarn or a Z-twist yarn may be used, or both of them may be used.

The cord <NUM> is provided to form a helical pattern with a pitch in the belt width direction. The cord <NUM> may be made of two yarns of the S-twist yarn and the Z-twist yarn arranged in a double helix form. The cords <NUM> are disposed to extend in parallel with each other at intervals in the belt width direction, and the number of cords <NUM> per <NUM> belt width of the cord <NUM> is suitably <NUM>/<NUM> or more to <NUM>/<NUM> or less, more suitably <NUM>/<NUM> or more to <NUM>/<NUM> or less, in terms of obtaining excellent durability in high load transmission.

The cord <NUM> has been suitably subjected to adhesion treatment such as immersing it in a liquid adhesive agent and then drying before molding.

The toothed belt B of the embodiment further includes unwoven fabric <NUM> embedded along the belt length direction on the inner peripheral side of the toothed belt body <NUM> from the position at which the cord <NUM> is embedded in the belt thickness direction. The unwoven fabric <NUM> may be made of a single sheet or a plurality of sheets.

The unwoven fabric <NUM> contains polyurethane resin forming the toothed belt body <NUM>, and provided to form a layer in a side view. Portions of the unwoven fabric <NUM> corresponding to the respective teeth <NUM> extend inside the teeth <NUM> so as to bulge toward inner periphery in a side view and expand thickly in the belt thickness direction. Portions of the unwoven fabric <NUM> corresponding to the portions between the teeth <NUM> are in contact with the cords <NUM> and are compressed in the belt thickness direction to be thin.

Examples of the fiber material forming the unwoven fabric <NUM> include nylon fibers, polyester fibers, aramid fibers, polyketone fibers, and carbon fibers. The unwoven fabric <NUM> may be made of a single kind of fibers, or a mixture of a plurality of kinds of fibers.

The unwoven fabric <NUM> has been suitably subjected to adhesion treatment such as immersing it in a liquid adhesive agent and then drying before molding.

In the toothed belt B according to the embodiment, the belt tension T<NUM> per <NUM> belt width at <NUM>% of a belt extension rate is <NUM> N/mm or more. The belt tension T<NUM> is suitably <NUM> N/mm or more, more suitably <NUM> N/mm or more, in terms of obtaining excellent durability in high load transmission. The belt tension T<NUM> is suitably <NUM> N/mm or less, more suitably <NUM> N/mm or less, in terms of avoiding impairing of flex fatigue resistance due to increase in flexural rigidity.

The belt tension T<NUM> and the belt tension T<NUM> are determined as follows.

In a <NUM> atmosphere, the toothed belt B according to the embodiment is wrapped around a pair of flat pulleys <NUM> with a pulley diameter of <NUM> in a belt tensile tester <NUM> such that a belt backface comes into contact with the flat pulleys <NUM>, as shown in <FIG>.

Then, one of the flat pulleys <NUM> is separated from the other flat pulley <NUM> at a speed of <NUM>/min. At this time, the relationship between displacement between the flat pulleys <NUM> in pair and the tension detected via either one of the flat pulleys <NUM> in pair is recorded.

Then, the displacement between the flat pulleys <NUM> in pair is doubled to calculate the amount of extension of the belt, which is then divided by the belt length of the toothed belt B according to the embodiment under a no-load condition. Thus, the displacement between flat pulleys <NUM> in pair is converted into the belt extension rate. Further, the tension detected is divided by <NUM> to calculate the belt tension, which is then divided by the belt width of the toothed belt B according to the embodiment. Thus, the tension detected is converted into the belt tension per <NUM> belt width.

Then, zero-point amendment is performed based on the relationship between the belt extension rate and the belt tension so that the point at which the belt tension per <NUM> belt width reaches 50N is a starting point, and the belt tension T<NUM> and the belt tension T<NUM> are determined.

In the toothed belt B according to the embodiment, the ratio of the belt tension T<NUM> to the belt tension T<NUM> (the belt tension T<NUM>/the belt tension T<NUM>) is <NUM> or more. The belt tension T<NUM>/the belt tension T<NUM> is suitably <NUM> or more, more suitably <NUM> or more, in terms of obtaining excellent durability in high load transmission. The belt tension T<NUM>/the belt tension T<NUM> is suitably <NUM> or less, more suitably <NUM> or less, yet more suitably <NUM> or less, in terms of practical use.

In the toothed belt B according to the embodiment with such a configuration, the belt tension T<NUM> is <NUM> N/mm or more, the belt tension T<NUM> is <NUM> N/mm or more, and the ratio of the belt tension T<NUM> to the belt tension T<NUM> is <NUM> or more. Accordingly, excellent durability in high load transmission can be obtained. This is presumably because the belt tension T<NUM> is <NUM> N/mm or more and the belt tension T<NUM> is <NUM> N/mm or more, which provide excellent dimensional stability in use under wide range of high loads, and the belt tension T<NUM>/the belt tension T<NUM> is <NUM> or more, which suppresses excessive tension even if the belt extension rate increases due to thermal expansion of pulleys, for example, thereby suppressing progress of wearing.

Next, a method for forming the toothed belt B of the embodiment will be described.

First, as shown in <FIG>, a cylindrical inner mold <NUM> is covered with the unwoven fabric <NUM>, and the cord <NUM> is then spirally wound around it. At this time, on the outer periphery of the inner mold <NUM>, recesses <NUM> with cross sectional shapes corresponding to the respective teeth <NUM> extending axially are provided at a constant pitch at intervals in a circumferential direction, and ridges <NUM> extending axially between the recesses <NUM> are formed. Then, the unwoven fabric <NUM> and the cord <NUM> are provided to be supported with the ridges <NUM>.

Then, as shown in <FIG>, the inner mold <NUM> is housed in a cylindrical outer mold <NUM>. At this time, a cavity C for molding the toothed belt body is formed between the inner mold <NUM> and the outer mold <NUM>.

Subsequently, as shown in <FIG>, a liquid urethan composition obtained by blending a compound ingredient into a urethan prepolymer is injected and charged into the closed cavity C. At this time, a toothed belt body <NUM> of polyurethane resin is formed by the urethan composition flowing and cured. Further, the teeth <NUM> are formed in the recesses <NUM>. The cord <NUM> is adhered and embedded in the toothed belt body <NUM>. The urethan composition is impregnated into the unwoven fabric <NUM> and then cured, and the unwoven fabric <NUM> is adhered to and embedded in the toothed belt body <NUM>. In this way, the toothed belt body <NUM>, the cord <NUM>, and the unwoven fabric <NUM> are integrated to form a cylindrical belt slab S.

Finally, the belt slab S is demolded from the inner mold <NUM> and the outer mold <NUM>, and cut into round slices, whereby the toothed belt B according to the embodiment is obtained.

In the embodiment described above, the toothed belt B is made of the toothed belt body <NUM>, the cord <NUM>, and the unwoven fabric <NUM>, but is not limited thereto. A reinforcing fabric may be provided on the teeth face on the inner periphery side of the toothed belt body and/or the backface on the outer periphery side of the toothed belt body.

In the embodiment, the toothed belt B includes a toothed belt body made of polyurethane resin, but is not particularly limited thereto. The toothed belt body may be formed of a crosslinking rubber composition.

In the embodiment, the toothed belt B is shown as a power transmission belt, but the power transmission belt is not particularly limited thereto and may be a flat belt, a V-belt, a V-ribbed belt, or the like.

Toothed belts of Example and Comparative Examples <NUM> to <NUM> were prepared. Constituents of each belt will also be shown in Table <NUM>.

A STS toothed belt with the same configuration as in the embodiment was prepared as Example.

The toothed belt of Example had a belt length of <NUM>, a belt width of <NUM>, and a belt thickness (at maximum) of <NUM>. The teeth were S8M defined in ISO <NUM>: <NUM> (E).

As the urethan composition for forming a toothed belt body, one obtained by blending <NUM> parts by mass of <NUM>,<NUM>'-dichloro-<NUM>,<NUM>'-diamino diphenylmethane as a curing agent and <NUM> parts by mass of dioctyl phthalate as a plasticizer to <NUM> parts by mass of urethan prepolymer was used. A polyurethane resin which forms the toothed belt body had a hardness of <NUM>°, measured based on JIS K7312.

As a cord, a single twist yarn obtained by twisting a filament bundle of carbon fibers (Tenax-J UTS50 F22, manufactured by TEIJIN LIMITED, <NUM>, <NUM> tex, a filament diameter: <NUM>) each with the number of filaments of <NUM> in one direction and with the number of twists per <NUM> length of <NUM>/<NUM> was used. For the cord of single twist yarn, a S-twist yarn and a Z-twist yarn were provided, and were subjected to adhesion treatment of immersing them in an adhesive and drying. The S-twist yarn and the Z-twist yarn which form a single twist yarn for the cord are arranged alternately in the belt width direction to form a double helix pattern. The number of cords per <NUM> of the belt width was eight. The cord had an outer diameter of <NUM>.

As unwoven fabric, one made of nylon fibers and formed by needle punching without pressurization was used. The unwoven fabric was not subjected to adhesion treatment.

In the toothed belt of Example, the belt tension T<NUM> was <NUM> N/mm, and the belt tension T<NUM> was <NUM> N/mm. Thus, the belt tension T<NUM>/the belt tension T<NUM> was <NUM>.

A toothed belt with the same configuration as in Example except that the number of cords per <NUM> belt width was <NUM> was prepared as Comparative Example <NUM>.

In the toothed belt of Comparative Example <NUM>, the belt tension T<NUM> was <NUM> N/mm, and the belt tension T<NUM> was <NUM> N/mm. Thus, the belt tension T<NUM>/the belt tension T<NUM> was <NUM>.

A toothed belt with the same configuration as in Example except that the number of twists of the cord per <NUM> length was <NUM>/<NUM> and the number of cords per <NUM> belt width was <NUM> was prepared as Comparative Example <NUM>. The cord had an outer diameter of <NUM>.

A toothed belt with the same configuration as in Example except that the number of twists of the cord per <NUM> length was <NUM>/<NUM> was prepared as Comparative Example <NUM>. The cord had an outer diameter of <NUM>.

<FIG> shows a layout of pulleys in the belt running tester <NUM> used in a high load durability test. The belt running tester <NUM> includes a drive pulley <NUM> with <NUM> teeth and a driven pulley <NUM> with <NUM> teeth, provided on the right side of the drive pulley <NUM>. The driven pulley <NUM> is provided to be movable to the left or right side, and is configured to be applied with an axial load and a load torque.

In a <NUM> atmosphere, each of the toothed belts B of Example and Comparative Examples <NUM> to <NUM> was wrapped around the drive pulley <NUM> and the driven pulley <NUM>, applied with a fixed axial load (SW) of 608N to apply tension to the toothed belt B, and applied with a load torque of <NUM> N·m. In this state, the drive pulley <NUM> was rotated at the number of revolutions of <NUM> rpm. Then, the time until the toothed belt B was broken was measured, and the time was used as a high load durability life.

Table <NUM> shows the test results. As can be seen, durability in high load transmission in Example was significantly higher than that in each of Comparative Examples <NUM> to <NUM>.

Claim 1:
A power transmission belt (B) including a belt body (<NUM>) made of an elastomer, and a cord (<NUM>) made of carbon fibers and provided to be embedded in the belt body (<NUM>) and to form a helical pattern having a pitch in a belt width direction,
wherein
the carbon fibers forming the cord (<NUM>) are PAN-based carbon fibers,
the carbon fibers have a filament diameter of <NUM> or more to <NUM> or less, characterized in that
a total number of filaments of the carbon fibers forming the cord (<NUM>) is <NUM>,
the cord (<NUM>) is a single twist yarn obtained by twisting a filament bundle of the carbon fibers in one direction,
the number of twists of the cord (<NUM>) of the single twist yarn per <NUM> length is <NUM>/<NUM>,
the number of cords (<NUM>) per <NUM> belt width is <NUM>/<NUM> or more to <NUM>/<NUM> or less, and
a belt tension T<NUM> per <NUM> belt width at <NUM>% of a belt extension rate is <NUM> N/mm or more, a belt tension T<NUM> per <NUM> belt width at <NUM>% of the belt extension rate is <NUM> N/mm or more, and a ratio of the belt tension T<NUM> to the belt tension T<NUM> is greater than at least <NUM>, each of the belt tension T<NUM> and the belt tension T<NUM> being obtained by: wrapping, in a <NUM> atmosphere, the power transmission belt (B) around a pair of flat pulleys (<NUM>) with a pulley diameter of <NUM> in a belt tensile tester such that a belt back face comes into contact with the flat pulleys (<NUM>); recording a relationship between displacement between the pair of flat pulleys (<NUM>) and a tension detected via either one of the pair of flat pulleys (<NUM>) under a condition that one of the flat pulleys (<NUM>) is separated from another one of the flat pulleys (<NUM>) at a speed of <NUM>/min; doubling the displacement between the pair of flat pulleys (<NUM>), to calculate a belt extension amount, and dividing the belt extension amount by a belt length of the power transmission belt (B) under a no-load condition, to convert the displacement between the pair of flat pulleys (<NUM>) into a belt extension rate; meanwhile dividing the detected tension by <NUM>, to calculate a belt tension, and dividing the belt tension by a belt width of the power transmission belt (B), to convert the detected tension into a belt tension per <NUM> belt width; and performing zero-point amendment based on a relationship between the belt extension rate and the belt tension so that a point at which the belt tension per <NUM> belt width reaches 50N is a starting point.