JPS62104848A - Short fiber-containing rubber composition - Google Patents

Abstract

PURPOSE:The titled rubber composition, obtained by blending a hydrogenated nitrile rubber as a matrix with a given amount of aromatic polyamide short fibers and capable of producing V-shaped transmission belts having improved lateral pressure and heat aging resistance. CONSTITUTION:A short fiber-containing rubber composition obtained by blending (A) 100pts.wt. hydrogenated nitrile rubber having <=98%, preferably >=80% hydrogenation ratio and <=60 Mooney viscosity with (B) 0.5-5pts.wt. sulfur and 0.5-5pts.wt. crosslinking accelerator, e.g. di-o-tolylguanidine, (C) 5-50pts.wt. preferably <=20pts.wt. phenolic resin and >=0.3pts.wt. (5-10wt% based on the phenolic resin) curing agent for the phenolic resin, preferably hexamethylenetetramine and (D) <=13vol%, expressed in terms of volume fraction, aromatic polyamide short fibers having preferably 1-10mm, particularly 3-6mm fiber length and kneading the resultant mixture.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a short fiber-containing rubber composition, and more particularly, to belts, particularly for use in automobiles in order to have excellent lateral pressure resistance and heat aging resistance. The present invention relates to a rubber composition containing short fibers suitable for manufacturing a V-belt for a continuously variable transmission.

(Prior Art) Type 1 transmission belts are used in a wide range of fields, but in recent years there has been a demand for rubber V-belts that can be used in continuously variable transmissions for automobiles. For continuously variable transmissions for automobiles■
Metal belts have long been known as belts, but metal belts must be used in lubricating oil, whereas rubber V-belts do not require this, and are inexpensive to manufacture. This is also because maintenance management is easy.

Generally, as shown in the figure, a rubber V-belt for a transmission has a holding elastic layer 3 laminated with an adhesive elastic layer 2 in which a cord 1 is embedded, and short fibers are layered on this holding elastic layer. The belt is oriented in the width direction and is further laminated with canvas 4 on the bottom of the belt. In this way, short fibers are made into a composite rubber, imparting anisotropy and ensuring the belt's lateral pressure resistance. There is.

However, V-belts for continuously variable transmissions in automobiles are required to have an extremely high torque transmission ability, and conventional rubber V-belts cannot be used under such high loads. . For example, when transmitting the maximum torque of a 1000 cc engine with a V-belt, the V-belt should be 20
It must withstand side pressure reaching up to around 4 to 5 kg/aa, but conventional standard V-belts usually have a pressure of 4 to 5 kg.
It is designed to be used with a side pressure of 10kg/cf or less, especially for high-load V-belts.
The limit is around fl. As described above, the reason why the conventional rubber V-belt can be used only under relatively low loads is that under large lateral pressure, the belt easily buckles and deforms and generates heat, leading to premature failure of the belt.

The elastic modulus in the fiber orientation direction (longitudinal elastic modulus) of the short fiber-containing vulcanized rubber used in such conventional rubber V-belts is, for example, the dynamic elastic modulus E' at 100° C. in a viscoelasticity test.

Normally, it is about 1 to 2 x 109 dyne/cm", and even if it is high, it is 3 to 4 x 10'dyne/cm".
On the other hand, V for continuously variable transmissions of automobiles
When using a rubber V-belt under a high load like a belt, as mentioned above, the rubber V-belt needs to withstand a side pressure of about 20 kg/ad, and for that purpose, the holding elastic layer must be 6 x 109 dyne/cm. It is required to have a longitudinal elastic modulus of `` or more.

Furthermore, conventionally, chloroprene rubber has been used as a matrix rubber in rubber power transmission belts, but in order to increase the elastic modulus of this matrix rubber, a large amount of reinforcing carbon black is blended, while process oil and plasticizers are added. If the amount of oil blended is kept to a small amount, the viscosity of the unvulcanized rubber will increase, resulting in frequent fiber breakage during kneading of short fibers and scorch during kneading and sheeting. Furthermore,
Due to the large amount of carbon black blended, the vulcanized rubber properties are also poor in flexibility, tensile elongation at break, tear resistance, etc.

On the other hand, various short fibers have been known for forming rubber composites. For example, aromatic polyamide short fibers have excellent elastic modulus, strength, heat resistance, etc., and are difficult to cut when kneaded with rubber.
It is often used as a reinforcing material. However, even with such short aromatic polyamide fibers, when a large amount is blended into the matrix rubber, the longitudinal elastic modulus can be increased;
At the same time, the transverse modulus of elasticity also increases, resulting in a decrease in the tensile elongation at break in the transverse direction, which causes cracks to occur from the bottom when the belt runs, causing the belt to break in a short period of time and to be easily cut.

(Objective of the Invention) As a result of intensive research to solve the above-mentioned problems with the conventional rubber V-belt, the present inventors used hydrogenated nitrile rubber as a matrix rubber, and mixed a predetermined amount of aromatic polyamide short fibers therein. The present inventors have discovered that by vulcanizing an unvulcanized rubber composition made from the above, it is possible to produce a V-shaped power transmission belt with excellent lateral pressure resistance and heat aging resistance. It is something that

Therefore, the present invention is suitable for producing a vulcanizate having excellent side pressure resistance and heat aging resistance, particularly for producing a high-load rubber V-belt that can be applied to continuously variable transmissions of automobiles. It is an object of the present invention to provide a short fiber-containing hydrogenated nitrile rubber composition that can be used.

(Structure of the Invention) The short fiber-containing rubber composition according to the present invention has a hydrogenation rate of 98
% or less, Mooney viscosity (ML+, 4,100'C)
With respect to 100 parts by weight of hydrogenated nitrile rubber having a molecular weight of 60% or less, 5 parts by weight or more of a phenolic resin, an appropriate amount of a phenol curing agent, and a volume fraction of 13% by volume or more, together with an appropriate amount of sulfur and a crosslinking accelerator. It is characterized by containing aromatic polyamide short fibers.

Hydrogenated nitrile rubber is made by hydrogenating the double bonds in nitrile rubber to make recombination reactions based on double bonds less likely to occur, thereby maintaining the excellent oil resistance of conventional nitrile rubber and improving heat aging resistance. This is a rubber with improved properties. The hydrogenated nitrile rubber used in the present invention needs to have a hydrogenation rate of 98% or less. Similar to conventional nitrile rubber, in the present invention, hydrogenated nitrile rubber containing short fibers is vulcanized with sulfur, so it is necessary that at least unhydrogenated double bonds remain in the nitrile rubber. This is because. but,
If the hydrogenation rate is too low, the heat aging resistance will be insufficient, so the hydrogenation rate is preferably 80% or more.

Furthermore, in the present invention, it is necessary that the hydrogenated nitrile rubber has a Mooney viscosity (ML, . . . , ioo° C.) of 60 or less. When the Mooney viscosity exceeds 60, the short fibers are frequently cut during fiber kneading, which not only impairs the effect of short fibers on improving the lateral pressure resistance of the rubber, but also reduces the scorch time and reduces the scorch time during kneading. This is because scorching of the rubber occurs during sheeting, resulting in insufficient processing safety.

The short fiber-containing hydrogenated nitrile rubber composition according to the present invention comprises:
With respect to 100 parts by weight of the hydrogenated nitrile rubber as described above, 5 parts by weight or more of a phenol resin, an appropriate amount of a curing agent for the phenol resin, and a volume fraction of 13% by volume, along with an appropriate amount of sulfur and a crosslinking accelerator. Contains the following aromatic polyamide short fibers.

Sulfur as a vulcanizing agent is usually blended in an amount of 0.5 to 5 parts by weight per 100 parts by weight of hydrogenated nitrile rubber. Further, the crosslinking accelerator may be used in an appropriate amount, but it is usually hydrogenated nitrile rubber 100%! It is blended in a range of 0.5 to 5 parts by weight based on if# parts. The crosslinking accelerator is not particularly limited, but for example, diorthotolylguanidine (DT)
Guanidine series such as dibenzothiazyl disulfide (D
Thiazole type such as M), sulfenamide type such as N-cyclohexyl-2-benzothiazylsulfenamide (CZ), tetramethylthiuram monosulfide (TS)
, thiuram type such as tetramethylthiuram disulfide (TT), etc. can be used.

The phenolic resin is crosslinked and cured with a curing agent in the hydrogenated nitrile rubber to reinforce the hydrogenated nitrile rubber as a matrix rubber. When the amount of phenol resin blended is less than 5 parts by weight with respect to 100 parts by weight of hydrogenated nitrile rubber, the reinforcing effect is not sufficient. However, if too much is added, not only will processability deteriorate, such as scorch, but the resulting vulcanized rubber will have poor heat aging resistance, so the amount is usually 50 parts by weight or less, preferably 20 parts by weight. below. The phenol resin may be a phenol resin modified with resorcinol, cresol, cashew, melamine, or the like.

The curing agent for the phenol resin is not particularly limited, but for example, hexamine (hexamethylenetetramine) is suitable. The curing agent is usually blended in an amount of 5 to 10% by weight of the phenol resin. In the present invention, the amount is usually 0.3 parts by weight or more per 100 parts by weight of hydrogenated nitrile rubber.

The hydrogenated nitrile rubber composition according to the present invention contains short aromatic polyamide fibers in a volume fraction of 13% by volume or less. Various short fibers are known as rubber reinforcing materials, but as mentioned above, the required 6 x 109 dyne/
In order to obtain a longitudinal elastic modulus of cm2 or more, aromatic polyamide staple fibers are used in the present invention. Such aromatic polyamide short fibers can be produced by hand as, for example, Kepler manufactured by DuPont or HM=50 manufactured by Kijin ■.

Generally, in order to increase the elastic modulus of a rubber composite containing short fibers, the aspect ratio of the short fibers should be increased and the elastic modulus should be increased, and the volume fraction of the short fibers, i.e., the blending amount, should be increased. On the other hand, for rubber, it is known that increasing the matrix elastic modulus is effective.

In the present invention, when the above-mentioned short fibers are too short, the aspect ratio is small, resulting in poor reinforcing properties.On the other hand, when the short fibers are too long, the fibers become intertwined with each other when mixed with rubber, and the fibers are mixed into the rubber. Dispersion becomes non-uniform and fiber breakage occurs. Therefore, in the present invention, the short fibers used preferably have a fiber length of about 1 to 10 mm, particularly preferably 3 to 6 mm.

On the other hand, as mentioned above, when such short fibers are blended in a large amount, they increase the transverse modulus as well as the longitudinal elastic modulus, so the tensile elongation at break in the transverse direction decreases, and cracks occur from the bottom when the belt runs. The belt will be destroyed in a short period of time due to cutting. Therefore, in the present invention, it is blended in a volume fraction of 13% by volume or less.

According to such a composition, the viscosity during kneading is kept low, so cutting of short fibers is suppressed and the short fibers are uniformly dispersed. Therefore, by kneading such a composition with a mixing roll and rolling it into a sheet,
Short fibers can be easily oriented in the rolling direction.

Therefore, by cutting the above-mentioned sheet to an appropriate length, stacking the sheets with the adhesive elastic layer in which the cord is embedded, with the width direction of the sheet set as the longitudinal direction of the V-belt, and vulcanizing the short fibers. A V-belt whose orientation direction (grain direction) is perpendicular to the longitudinal direction (running direction) of the V-belt can be obtained.

(Effects of the Invention) As described above, according to the rubber composition containing short fibers according to the present invention, the viscosity during kneading is low, so that scorch of the rubber is suppressed, cutting of short fibers is suppressed, and short fibers are suppressed. Fibers are evenly distributed. Furthermore, it can be vulcanized with sulfur in the same way as ordinary nitrile rubber.

Therefore, by rolling and forming such a rubber composition into a sheet, short fibers can be easily oriented in the rolling direction, and since the blending amount of short fibers is adjusted, using such a sheet, it is possible to easily orient the short fibers in the rolling direction. With the width direction set as the longitudinal direction of the V-belt, the sheets are laminated with adhesive elastic layers in which cords are embedded, and vulcanized. When manufacturing a V-belt that runs perpendicular to the
The belt has an unexpectedly large modulus of elasticity in the grain direction, and has excellent lateral pressure resistance, as well as properties in the anti-grain direction, such as elongation, bending fatigue resistance, and elongation fatigue resistance. It's also excellent. For example, a vulcanized sheet obtained by rolling the rubber composition according to the present invention into a sheet and vulcanizing the sheet has a longitudinal elastic modulus (dynamic elastic modulus E') of 6 x 10' at 100°C.
dyne/cm" or more. A V-belt having such a holding elastic layer has an extremely large transmittable torque and a long life during running, so it is particularly suitable for continuously variable transmissions for automobiles used under high loads. Suitable for machine V-belts.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way.

Examples The formulations shown in Table 1 were kneaded with a mixing roll to obtain the matrix unvulcanized rubber shown in Table 2, which was vulcanized according to a conventional method to obtain the matrix vulcanized rubber shown in Table 2. Ta. Table 2 shows the physical properties of these unvulcanized rubbers and vulcanized rubbers.

In addition to the above formulations shown in Table 1, 1.5d (fiber length 6mm) aromatic polyamide short fibers (Kevlar) were blended, and similarly kneaded with a mixing roll and formed into a sheet. Vulcanization was performed under the same conditions as above. Table 3 shows the physical properties of the short fiber-containing hydrogenated nitrile rubber vulcanizate thus obtained.

Examples 1 and 2 and Comparative Examples 3 to 6 are examples in which hydrogenated nitrile rubber with a hydrogenation rate of approximately 90% is used as the matrix rubber, and Comparative Examples 7 and 8 are examples in which chloroprene rubber is used as the matrix rubber. This is an example.

Examples and comparative examples according to the present invention will be described.

(1) Characteristics of matrix unvulcanized rubber and vulcanized rubber First, Comparative Examples 5 and 7 were intended to increase the elastic modulus of the matrix rubber by blending a large amount of reinforcing carbon black. Compared to Examples 1 and 2 of the present invention, they exhibit almost the same elastic modulus E', but because of their high Mooney viscosity, the scorch time is short and the workability is poor. In Comparative Examples 6 and 8, by blending a large amount of short fibers,
This is intended to increase the elastic modulus of the short fiber-containing rubber vulcanizate, and although processing safety is somewhat satisfied, the elastic modulus is lower than in Examples 1 and 2. Furthermore, Comparative Example 8 showed significant heat aging. Comparative Example 3 does not contain phenolic resin, so its elastic modulus is low. Comparative Example 4 has a high Mooney viscosity.

(2) Characteristics of vulcanized rubber containing short fibers Among the vulcanizates of rubber containing short fibers, in Comparative Examples 4.5 and 7, the short fibers were broken during rolling and kneading due to the high Mooney viscosity of the unvulcanized rubber. As a result, the elastic modulus in the grain direction is small. In Comparative Examples 6 and 8, the amount of short fibers was too large, so the elongation in the anti-grain direction was small.

In contrast to these comparative examples, according to the examples of the present invention, since the blending amount of short fibers was within a predetermined range, the elastic modulus in the anti-grain direction was small, and as a result, bending heat generation was small. 5. Extension fatigue life is also shortened.

(3) Manufacture of V-belt and evaluation of its physical properties After kneading the short fiber-containing hydrogenated nitrile rubber composition described above, it is rolled into a sheet, and as described above, the grain direction is perpendicular to the direction of belt travel according to a conventional method. A variable speed V-belt with cogs was manufactured. The adhesive elastic layer of the belt has a dynamic elastic modulus of 4
High hardness rubber of 10" dyne/cm2 and JIS A hardness of 82 was used.

Table 3 shows the transmittable torque at low speeds, defined as the maximum torque of the belt that can be transmitted with 3% slip or less, and the life index at high speeds. It is recognized that the transmissible torque at low speeds is almost correlated with the longitudinal elastic modulus of the short fiber-containing vulcanized rubber, and Comparative Examples 6 and 8 have large longitudinal elastic modulus, but the blended amount of short fibers is too large. However, since the elongation is small, cracks occur early and the lifespan is short.

On the other hand, according to the V-belt having the holding elastic layer made of the rubber composition according to the present invention, the transmittable torque is 5.
kg-m or more, and has a long running life.

Comparative Example 3 has a rather small longitudinal elastic modulus, poor lateral pressure resistance, and short running life. In addition to the reasons for Comparative Example 3, Comparative Example 4 has a high Mooney viscosity and short fibers are cut during kneading, so that it is even worse than Comparative Example 3 in both transmittable torque and running life.

Comparative Examples 5 and 7 had a small longitudinal elastic modulus, a significantly short elongation fatigue life in the anti-grain direction direction, and a short running life.

[Brief explanation of drawings]

The drawing is a cross-sectional perspective view showing an example of a rubber V-belt for a transmission. DESCRIPTION OF SYMBOLS 1... Cord, 2... Adhesive elastic layer, 3... Holding elastic layer, 4... Canvas.

Claims (1)

[Claims] (1) Hydrogenation rate 98% or less, Mooney viscosity (ML_1
___+_4, 100°C) 60 or less per 100 parts by weight of hydrogenated nitrile rubber, along with an appropriate amount of sulfur and a crosslinking accelerator, 5 parts by weight or more of a phenolic resin, an appropriate amount of a phenolic resin curing agent, and a volume fraction. A short fiber-containing rubber composition, characterized in that it contains 13% by volume or less of aromatic polyamide short fibers.