JP2000199181A - Short fibers for dispersing in rubber composition and power trnasmission belt using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce short fibers improved in dispersibility in rubber compositions, and a power transmission belt capable of prolonging the belt life, prolonging the time until generating a clack after beginning of its use by improving the dispersibility of the short fibers mixed in a compressed rubber part. SOLUTION: In the power transmission belt 1 obtained by laminating a compressed rubber layer 4 on a bonding rubber layer 3 embedding wires 2, a rubber composition dispersing 1-40 pts.wt. of short cotton fibers obtained by cutting a silver in twistless state which is obtained by orienting fibers at least including cotton fibers in longitudinal direction and carrying out a bonding process using a resorcinol formalin.latex solution, per 100 pts.wt. of the rubber is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short fiber for dispersing a rubber composition and a power transmission belt using the same, and more particularly, to a short fiber having improved dispersibility in a rubber composition and mixed into a compressed rubber portion. The present invention relates to a friction transmission type power transmission belt including a V-ribbed belt, a cut edge type V belt and the like, which can improve the dispersibility of short fibers and extend the crack generation time after running to extend the belt life.

[0002]

2. Description of the Related Art In a V-ribbed belt, a core wire is buried in a cushion rubber layer, a cover canvas is laminated on an upper portion of the cushion rubber layer as necessary, and a plurality of rib portions are provided below the cushion rubber layer. Provided. This V-ribbed belt is widely used in place of the V-belt for power transmission of auxiliary equipment such as an air compressor and an alternator of an automobile. Conventionally, in order to efficiently transmit the power of the belt, it is necessary to reduce the slip ratio between the belt and the pulley, and the belt tension is increased to reduce the slip ratio.

In this type of belt, a short fiber group such as cotton, nylon, vinylon, rayon, and aramid fibers is buried in a rib portion while maintaining the orientation to the belt width, so that a lateral pressure resistance of a friction transmission portion of the belt is improved. In addition, the wear resistance is improved by positively exposing a part of the buried short fibers to both side walls of the friction transmission portion.

Further, there has been proposed a power transmission belt which aims at a frictional performance of a rib portion and an effect of suppressing sound generation due to adhesion by intentionally protruding a part of embedded short fibers from a side surface of the belt.

[0005] Further, in order to further advance the effect of the belt, aramid fibers are used as the short fibers protruding from both side walls of the friction transmission portion. A transmission belt intended for improvement is disclosed, for example, in Japanese Patent Application Laid-Open No. 1-164839.

[0006]

However, when short fibers such as cotton, nylon, vinylon, and aramid fibers are kneaded in rubber, these short fibers may be aggregated and dispersed in the rubber. . In particular, when a spun cotton yarn constituting canvas, denim, or the like is used as a cut yarn, the cotton yarn is twisted. Otherwise, dispersibility may be lacking, and short fibers may agglomerate in the rubber to cause poor dispersion.

In general, the ribs of the power transmission belt are repeatedly subjected to compression fatigue. Therefore, when a large amount of short fibers are present in the rubber, crack nuclei are generated from the vicinity of the short fibers at an early stage. The result was a longevity.

The present invention has been made to solve the above problems, and in order to solve the above problems, the short fibers having improved dispersibility in a rubber composition and the dispersibility of short fibers mixed into a compressed rubber portion have been improved. It is an object of the present invention to provide a power transmission belt capable of extending the life of a belt by extending the time of occurrence of cracks after running by improving the running speed.

[0009]

That is, according to the first aspect of the present invention, there is provided a non-twisted state in which fibers containing at least cotton fibers are oriented in the longitudinal direction. After the sliver is bonded with a resorcinol-formalin-latex liquid, the cut short fibers are in the rubber composition dispersing short fibers, and are kneaded into rubber.
Good dispersion.

In the invention according to the second aspect of the present invention, the sliver in a non-twisted state is obtained by blending cotton fibers and chemical fibers, so that dispersion in rubber can be improved. The number of short fiber masses in the power transmission belt also decreased,
The crack generation time in the running test also becomes longer.

According to the invention as set forth in claim 3 of the present invention, in a power transmission belt in which an adhesive rubber layer embedded with a core wire and a compression rubber layer are laminated, fibers including at least cotton fibers are oriented in the longitudinal direction in the compression rubber portion. A power transmission using a rubber composition obtained by bonding a non-twisted sliver to a resorcinol / formalin / latex liquid and then dispersing the cut short fibers in 1 to 40 parts by weight with respect to 100 parts by weight of rubber. On the belt.

That is, in the power transmission belt of the present invention, a non-twisted shino having a thickness of 3 to 5 cm, in which a fiber containing at least a cotton fiber as a cotton sliver is oriented in a longitudinal direction in a compression rubber layer, is formed of resorcinol-formalin.・ Adhesion treatment with latex solution and use of cut short fibers improve dispersion in rubber, and also reduce lumps of short fibers and nuclei of cracks generated from them, Life can be extended.

In the invention according to claim 4 of the present application, the core wire is a power transmission belt which is a twisted yarn obtained by twisting a group of polyester fiber filaments having ethylene-2,6-naphthalate as a main constituent unit, and this core wire is used. As a result, belt slip during running is reduced and belt life is expected to be extended.

In the invention according to claim 5 of the present application, the power transmission belt has an adhesive rubber having a core buried along the belt longitudinal direction and a compressed rubber layer having at least one rib portion along the belt longitudinal direction. V-ribbed belt, which reduces the number of nuclei of cracks generated from lumps of short fibers in the rib portion, thereby extending the life of the belt.

[0015]

Next, a V-ribbed belt according to the present invention will be specifically described with reference to the accompanying drawings. FIG.
A V-ribbed belt 1 shown in FIG. 1 has a cord 2 made of a high-strength, low-elongation cord made of polyester fiber, aramid fiber, or glass fiber embedded in an adhesive rubber layer 3 and an elastic layer below the core. It has a certain compressed rubber layer 4. The compressed rubber layer 4 is provided with a plurality of rib portions 7 having a substantially triangular cross section extending in the longitudinal direction of the belt, and a rubber attached fabric 5 attached to the surface of the belt.

For the rib 7, hydrogenated nitrile rubber, ethylene-α-olefin elastomer, chloroprene rubber, natural rubber, CSM, ACSM, SBR are used.
The hydrogenated nitrile rubber has a hydrogenation rate of 80% or more, and preferably 90% or more in order to exhibit heat resistance and ozone resistance characteristics. A hydrogenated nitrile rubber having a hydrogenation rate of less than 80% has extremely low heat resistance and ozone resistance. In consideration of oil resistance and cold resistance, the amount of bound acrylonitrile is preferably in the range of 20 to 45%.

The above-mentioned ethylene-α-olefin elastomer refers to a rubber composed of ethylene-propylene rubber (EPR) or ethylene-propylene-diene monomer (EPDM). Examples of diene monomers include dicyclopentadiene, methylene norbornene, ethylidene norbornene, 1,4-hexadiene, cyclooctadiene, and the like.

A sliver, that is, a cotton fiber or a cotton fiber and a chemical fiber such as polyamide, polyester, rayon, vinylon, and aramid are used for the rib portion 30/70.
A non-twisted 3 to 5 cm thick Shino with a length of 70 to 30 blended and oriented in the longitudinal direction is prepared and placed in a tank containing a resorcinol / formalin / latex liquid (RFL liquid). After immersion, the fibers are passed through a drying oven set at a temperature of 100 to 250 ° C. for 30 to 600 seconds to perform an adhesive treatment, and then short fibers cut continuously to 1 to 50 mm are used. The sliver is not particularly limited, such as a card sliver, a comb sliver, and a drawing sliver.

The RFL solution is a mixture of an initial condensate of resorcinol and formalin and rubber latex. In this case, the molar ratio of resorcinol to formalin is 3/1.
It is preferable to reduce the thickness to 〜 in order to increase the adhesive strength. The initial condensate of resorcinol and formalin is adjusted by mixing it with rubber latex such that the resin content is 5 to 50 parts by weight per 100 parts by weight of rubber of rubber latex.

The rubber latex forming the rubber component 21 includes styrene-butadiene-vinylpyridine terpolymer (VP) and styrene-butadiene copolymer (SB).
R), chloroprene (CR), acrylonitrile butadiene copolymer (NBR), hydrogenated NBR (H-NB)
One or more blends of R), chlorosulfonated polyethylene (CSM), natural rubber and the like are used.

Of course, if a higher degree of adhesion between the short fibers and the rubber is required, it may be treated with an epoxy compound or an isocyanate compound before the RFL treatment.

The added amount of the staple fiber obtained from the sliver is 1 to 40 parts by weight based on 100 parts by weight of the rubber. If the amount is less than 1 part by weight, there is a disadvantage that the rubber of the rib 7 is liable to stick and is worn.
The dispersibility of short fibers decreases.

Of course, in addition to the short fibers obtained from the sliver, short fibers made of another polyamide such as nylon 6 or nylon 66, polyester, vinylon or aramid are mixed to improve the lateral pressure resistance of the rib 7. In addition, the short fibers can be projected on the surface of the rib 7 which comes into contact with the pulley, and the friction coefficient of this surface can be reduced to reduce noise during belt running. However, it goes without saying that the amount of addition is large for short fibers obtained from sliver.

In order for the aramid short fibers to sufficiently exhibit the above-mentioned effects, the fiber length of the aramid fibers should be 1 to 20.
mm, the amount of addition is 1 to 3 with respect to 100 parts by weight of rubber.
0 parts by weight. This aramid fiber has an aromatic ring in the molecular structure, for example, trade names Conex, Nomex,
Kevlar, Technora, Twaron and the like. Further, in order to improve the adhesion of the aramid short fiber to the rubber of the rib portion 7, the short fiber is subjected to an adhesive treatment with a treatment liquid selected from an epoxy compound and an isocyanate compound.

The cord 2 has a total denier of 4,000 to 8,000 obtained by twisting polyester fiber filaments having ethylene terephthalate or ethylene-2,6-naphthalate as a main constituent unit.
A bonded code of 0 is used. The upper twist coefficient of this cord is 1.0 to 4.0, and the lower twist coefficient is 1.0 to 4.0. If the total denier is less than 4,000, the modulus and strength of the cord become too low, and if it exceeds 8,000, the belt becomes thicker,
Flex fatigue becomes poor.

The ethylene-2,6-naphthalate used in the present invention is usually prepared by condensation polymerization of naphthalene-2,6-dicarboxylic acid or an ester-forming derivative thereof with ethylene glycol in the presence of a catalyst under appropriate conditions. To be synthesized. At this time, if one or more appropriate third components are added before the completion of the polymerization of ethylene-2,6-naphthalate, a copolymer polyester is synthesized. Of course, aramid fibers can also be used in addition to the above polyester fibers.

The bonding process of the core wire 2 is carried out by (1) impregnating the untreated cord into a tank containing a treatment liquid selected from an epoxy compound and an isocyanate compound and pre-dipping it; Drying by passing through a drying oven set to a temperature of 30 ° C. for 30 to 600 seconds.
Immerse in the tank containing the adhesive liquid consisting of L liquid, (4) 2
3 to the stretching heat setting processor set at 10-260 ° C
It is stretched for -1 to 3% through 0 to 600 seconds to obtain a stretched cord.

Examples of the epoxy compound include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol; reaction products of polyalkylene glycols such as polyethylene glycol with halogen-containing epoxy compounds such as epichlorohydrin; (4-hydroxyphenyl) dimethylmethane,
It is a reaction product with polyhydric phenols such as phenol-formaldehyde resin and resorcin-formaldehyde resin and halogen-containing epoxy compounds. This epoxy compound is used by being mixed with an organic solvent such as toluene and methyl ethyl ketone. Examples of the isocyanate compound include 4,4′-diphenylmethane diisocyanate, tolylene 2,4-diisocyanate, P-phenyl diisocyanate, and polyaryl polyisocyanate. This isocyanate compound is also used by being mixed with an organic solvent such as toluene and methyl ethyl ketone.

The RFL solution is obtained by mixing a latex with an initial condensate of resorcinol and formalin, and the latex used herein includes chloroprene, styrene / butadiene / vinylpyridine terpolymer, hydrogenated nitrile, NBR, etc. It is.

The cord subjected to the stretching heat setting treatment has a spinning pitch, that is, a core winding pitch of 1.0 to 1.0 mm.
By setting the thickness to 1.3 mm, a belt having a high modulus can be finished. If it is less than 1.0 mm, the cord runs over the adjacent cord and cannot be wound, while if it exceeds 1.3 mm, the modulus of the belt gradually decreases.

The cover canvas 5 is a cloth woven in a plain weave, a twill weave, a satin weave, or the like using a yarn made of cotton, polyamide, polyethylene terephthalate, and aramid fiber.

An example of a method for manufacturing the V-ribbed belt 1 is as follows. First, on the peripheral surface of the cylindrical forming drum,
After winding a plurality of cover canvases and a cushion rubber layer, a cord made of a rope is spirally spun on this, and a compressed rubber layer is sequentially wound thereon to obtain a laminate,
This is vulcanized to obtain a vulcanized sleeve. Next, the vulcanization sleeve is hung between the drive roll and the driven roll, and is run under a predetermined tension, and the rotated grinding wheel is moved so as to abut the running vulcanization sleeve to compress the vulcanization sleeve. A plurality of 3 to 100 groove portions are ground on the surface of the rubber layer at a time. The vulcanized sleeve obtained in this manner is removed from the drive roll and the driven roll, and the vulcanized sleeve is hung on another drive roll and the driven roll to travel, cut to a predetermined width by a cutter, and cut into individual pieces. Finish with a V-ribbed belt.

Further, in the present invention, in addition to the above-described V-ribbed belt, a V-belt 8 in which a rubber-attached canvas is attached only to the upper and lower surfaces of the belt as shown in FIG. The V-belt 8 has a core wire 2 embedded in an adhesive rubber layer 3 and a compression rubber layer 4 as an elastic body layer below the core wire 2. Cogs may be provided on the compressed rubber layer 4 at predetermined intervals along the longitudinal direction.

[0034]

The present invention will be described below in more detail with reference to specific examples. Example 1, Comparative Examples 1-2 The cotton sliver shown in Table 1 was immersed in the RFL solution shown in Table 2, and then heat-treated at 200 ° C for 2 minutes. The sliver treated with the RFL solution was used as short cotton fibers cut to a length of 6 mm in the longitudinal direction. As a comparative example, 10 ^S and 20 ^S cotton yarns shown in Table 1 were cut to a length of 6 mm, immersed in an RFL solution shown in Table 2, and then heat-treated at 200 ° C. for 2 minutes. Thereafter, the mixture shown in Table 3 was kneaded with a Banbury mixer, and then rolled with a calender to produce a rubber composite containing short fibers, and the physical properties of the rubber composite were evaluated.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

Further, in order to produce a V-ribbed belt, 1,000 denier ethylene-2,6-naphthalate fiber (PEN fiber) is used as a core wire in a 2 × 3 twist configuration, a first twist coefficient of 3.0, and a lower twist. An untreated cord of total denier 6,000 twisted with a coefficient of 3.0 was prepared.

Next, 90 g of toluene was used for each unprocessed code.
After pre-dip with an adhesive consisting of 10 g of PAPI (a polyisocyanate compound manufactured by Kasei Upjohn),
10-3 in a drying oven set at a temperature of about 180-190 ° C
It was dried by passing through for 00 seconds, then impregnated with an adhesive composed of the RFL solution shown in Table 2, and subjected to a hot stretch fixing treatment under the treatment conditions to obtain a treated cord.

The method for manufacturing the V-ribbed belt in this embodiment is as follows. First, after a single ply of a rubber-made canvas obtained by friction of chloroprene rubber was wound around a plain woven fabric composed of cotton threads of warp and weft in a cylindrical mold, an adhesive rubber sheet made of a chloroprene rubber composition shown in Table 3 was wound thereon. The above cord was spun thereon, and a rubber layer composed of the chloroprene rubber composition shown in Table 3 was wound around to complete the molding. 160 ° by a known method
C, vulcanized for 30 minutes to obtain a cylindrical vulcanized rubber sleeve.

The above-described vulcanized rubber sleeve was mounted on a driving roll and a driven roll of a polishing machine, and was rotated after applying tension. A polishing wheel having a 150-mesh diamond mounted on its surface was rotated at 1600 rpm, and this was brought into contact with a vulcanization sleeve to polish a rib portion. After the sleeve taken out of the polishing machine was set on the cutting machine, it was cut while rotating.

In the produced V-ribbed belt, the cords composed of the above-mentioned respective stretching and fixing cords are embedded in the cushion rubber layer, and one layer of cotton canvas with rubber is laminated on the upper side, and on the other side under the cushion rubber layer. There was a compression section and three ribs were in the longitudinal direction of the belt. This V-ribbed belt is a K-type 3-ribbed belt having a length of 1,100 mm according to the RMA standard, a rib pitch of 3.56 mm, and a rib height of 2.9.
mm, rib angle 40 °, and various belt thicknesses.

Here, the compressed rubber portion and the cushion rubber layer were prepared from the rubber compositions shown in Table 3, respectively, kneaded with a Banbury mixer, and then rolled with a calender. The compressed rubber portion contains the rubber composite containing short fibers described above, and is oriented in the belt width direction.

Next, the static and dynamic performance of the V-ribbed belt was evaluated. Table 4 shows the results.
In addition, the test method of a cord and a belt is as follows.

(1) TB ratio In accordance with JIS K6301, the tensile strength (TBa) of the rolled rubber in the direction parallel to the grain and the tensile strength (TBb) in the direction perpendicular thereto were measured, and the ratio (TBa / TBb) was determined. .

(2) Number of short fiber masses of φ1 mm or more in the belt In 20 V-ribbed belts, the number of short fiber masses of φ1 mm or more was counted, and the average number of short fiber masses per belt was calculated.

(3) Rib crack generation time A driving pulley (120 mm in diameter), a driven pulley (12 mm in diameter)
0 mm), and a belt was hung on a triaxial pulley composed of a tension pulley (diameter: 45 mm), and the tension pulley was pulled at 85 kgf to apply tension to the belt. The running conditions are as follows: the ambient temperature is 85 ° C., the rotation speed of the driving pulley is 4900 rpm, and the load of the driven pulley is 12 ps.
Using this running test machine, the time was measured until cracks occurred in the ribs.

[0048]

[Table 4]

As a result, the TB ratio of the example is higher than that of the comparative example, because the example has a good orientation of the short fibers in the parallel direction to the grain. In addition, it can be seen that the number of short fiber masses is smaller in the example and the crack generation time in the running test is longer.

Examples 2-3, Comparative Examples 3-4 As shown in Table 5, various slivers and filaments were
And then heat-treated at 200 ° C. for 2 minutes. The sliver to be used is a card sliver, a comb sliver, a drawing sliver, or the like. The sliver and the filament subjected to the RFL treatment were cut into a length of 6 mm in the longitudinal direction to obtain short fibers. Then, after kneading with the Banbury mixer from the composition shown in Table 6, it was rolled with a calender to produce a rubber composite containing short fibers, and the physical properties of the rubber composite were evaluated.

[0051]

[Table 5]

[0052]

[Table 6]

Further, in order to produce a V-ribbed belt, 1,000 denier ethylene-2,6-naphthalate fiber (PEN fiber) as in Example 1 was used as a core wire in a 2 × 3 ratio.
, A total denier of 6,000 untwisted cord was prepared by twisting with an upper twist coefficient of 3.0 and a lower twist coefficient of 3.0.

Next, 90 g of toluene was used for each unprocessed code.
After pre-dip with an adhesive consisting of 10 g of PAPI (a polyisocyanate compound manufactured by Kasei Upjohn),
10-3 in a drying oven set at a temperature of about 180-190 ° C
It was dried by passing through for 00 seconds, then impregnated with an adhesive composed of the RFL solution shown in Table 2, and subjected to a hot stretch fixing treatment under the treatment conditions to obtain a treated cord.

The manufacturing method of the V-ribbed belt in the present embodiment is the same as that of the first embodiment. First, a one-ply rubberized canvas in which a chloroprene rubber is frictionally applied to a plain woven fabric composed of cotton and warp and weft in a cylindrical mold is used. After winding, an adhesive rubber sheet made of the chloroprene rubber composition shown in Table 6 was wound, the above-mentioned cord was spinned thereon, and a rubber layer made of the chloroprene rubber composition shown in Table 6 was wound and completed. This can be done in a known manner
Vulcanization was performed at 60 ° C. for 30 minutes to obtain a cylindrical vulcanized rubber sleeve. A V-ribbed belt similar to that of Example 1 was produced from this sleeve.

Next, the static and dynamic performance of the V-ribbed belt was evaluated. Table 7 shows the results.
The physical properties of the rubber composite are as follows.

(4) Standard Deviation of TB According to JIS K6301, the tensile strength (TB) of the rolled rubber in the grain parallel direction was measured by n = 20, and the standard deviation was obtained.

(5) Deviation of Short Fiber Dispersion The rib portion of the rib belt is cut perpendicular to the belt back in the longitudinal direction of the belt, and the number of short cotton fibers (NC) and the number of short chemical fibers in a 1 mm square of the cut surface. (NS) was counted. This was repeated 10 times at different locations, and the ratio of short cotton fibers was calculated by the following formula, and the difference between the maximum value and the minimum value of the ratio was determined. RC (%) = NC / (NC + NS) · 100 Deviation of short fiber dispersion = RCmax−RCmin RC: Ratio of cotton short fiber RCmax: Maximum value of ratio of cotton short fiber RCmin: Minimum value of ratio of cotton short fiber

[0059]

[Table 7]

As a result, in this embodiment, the tensile strength (TB)
It can be seen that these fibers are more uniformly dispersed in rubber by using a sliver in which cotton fibers and other chemical fibers are blended, since the dispersion of short fibers and short fibers is small. Moreover, it can be seen that the V-ribbed belt using this rubber composite also has a small number of short fiber masses and a long crack generation time in a running test.

[0061]

As described above, among the short fibers dispersed in the rubber composition according to the present invention, a non-twisted sliver in which fibers containing at least cotton fibers are oriented in the longitudinal direction is used as a resorcinol-formalin. After the adhesive treatment with the latex solution, the cut short fibers are present in the short fibers for dispersing the rubber composition, and it can be seen that the kneading and dispersion in the rubber become good. In particular, when cotton fibers and chemical fibers are blended as a non-twisted sliver, the dispersion in rubber is further improved,
The V-ribbed belt using the rubber composite also has an effect that the number of short fiber masses is small and the crack generation time in a running test is long.

Further, in the power transmission belt of the present invention, a non-twisted sliver having a thickness of 3 to 5 cm in which at least fibers including cotton fibers are oriented in the longitudinal direction on the compression rubber layer is bonded with a resorcinol / formalin / latex liquid. After processing, the use of cut short fibers improves kneading and dispersion in rubber, and also reduces lumps of short fibers and nuclei of cracks that occur from this, prolonging belt life. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a sectional perspective view of a V-ribbed belt according to the present invention.

FIG. 2 is a vertical sectional view of a V-cut edge type V-belt according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 V-ribbed belt 2 core wire 3 adhesive rubber layer 4 compression rubber layer 5 canvas with rubber 7 rib

Claims (6)

[Claims] Claims 1. A short fiber which is dispersed in a rubber composition and is used in a non-twisted sliver in which fibers including at least cotton fibers are oriented in a longitudinal direction, after bonding treatment with a resorcinol-formalin latex liquid, Short fibers for dispersing a rubber composition, which are cut short fibers. 2. The short fiber for dispersing a rubber composition according to claim 1, wherein the non-twisted sliver is a blend of cotton fiber and chemical fiber. 3. A non-twisted sliver in which a power transmission belt in which an adhesive rubber layer embedded with a core wire and a compression rubber layer are laminated, wherein at least a fiber containing cotton fibers is oriented in a longitudinal direction in the compression rubber portion. A power transmission belt, characterized in that a rubber composition is used in which a rubber composition is prepared by adhering to a resorcinol-formalin-latex solution, and then dispersing the cut short fibers into 1 to 40 parts by weight with respect to 100 parts by weight of rubber. 4. The power transmission belt according to claim 3, wherein the non-twisted sliver is a blend of cotton fibers and chemical fibers. 5. The power transmission belt according to claim 3, wherein the core wire is a twisted yarn obtained by twisting a group of polyester fiber filaments having ethylene-2,6-naphthalate as a main constituent unit. 6. The power transmission belt according to claim 1, wherein the power transmission belt is a V-ribbed belt comprising an adhesive rubber having a core buried along the belt longitudinal direction and a compressed rubber layer having at least one rib portion along the belt longitudinal direction. Item 3. A power transmission belt according to Item 3.