JPH0718121A - Short fiber-reinforced rubber composition - Google Patents

Abstract

PURPOSE:To obtain a rubber composition having improved physical properties such as workability and elastic modulus and useful for gum chafer, etc., by compounding a specific rubber component with short fibers and an unsaturated fatty acid containing conjugated dienoic acid in the molecule. CONSTITUTION:This rubber composition is produced by compounding (A) 100 pts.wt. of a rubber component composed of at least one kind of natural rubber or diene-type synthetic rubber with (B) >=2.5 pts.wt. of short fibers and (C) 0.1-10 pts.wt. of an unsaturated fatty acid having two or more C-C double bonds in the molecule and containing >=10wt.% (preferable >=25wt.%) of conjugated dienoic acid having one or more sets of conjugated double bonds in the molecule. The short fiber used as the component B is preferably composed of a thermoplastic polyamide and has an L/D ratio of >=8 and D of <=1mum (L is average length and D is average diameter of the fiber).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a short fiber reinforced rubber composition.

[0002]

2. Description of the Related Art In recent years, automobile tires have been required to have higher performance, and in recent years, in particular, fuel economy, riding comfort and maneuverability have been required to be highly compatible. For example, regarding the bead filler, by arranging a super-hard rubber in the bead filler, although improvement in fuel efficiency and maneuverability is recognized (Japanese Utility Model Publication No. 47-16084, French Patent No. 1260138, US Patent No. 4067373). No.), the ride comfort has to be sacrificed. Also, by increasing the elasticity of the belt coating rubber that affects the characteristics of the belt composite material, the durability and maneuverability of the belt can be greatly improved, but it is extremely inferior in terms of riding comfort and fuel efficiency. Therefore, it is not sufficient to satisfy various required characteristics.

On the other hand, in order to obtain a reinforced rubber composition having a high elastic modulus, it has been conventionally practiced to mix vulcanizable rubber with short fibers. For example, Japanese Patent Publication No. 1-17494 describes a reinforced rubber in which a rubber and a nylon fiber embedded therein are graft-bonded through an initial condensation product of a resol-type alkylphenol formaldehyde resin. However, in this method, since a resole-type alkylphenol resin having high reactivity to heat is used, it is difficult to control the graft bond between the nylon fiber and the rubber, and the usable rubber is limited. Only a small amount of reinforced rubber composition could be obtained.

In order to solve this problem, Japanese Patent Publication No. 3-21572 discloses that fine fibrous material of thermoplastic polyamide is dispersed in a synthetic rubber containing a tackifier and is synthesized with the polyamide at this interface. A method of graft-bonding with a rubber via a novolac type phenolic resin is described. In this method, a kneaded product of rubber, polyamide and resin is mixed with a resin curing agent and cured in the rubber. There were various problems.

Further, Japanese Examined Patent Publication No. 3-49932 describes that by kneading an aromatic polyamide pulp and a phenolic resin into rubber, short fiber reinforcement and resin reinforcement are carried out, and by these, a high elastic modulus can be obtained. There is. However, in this technology, the rubber molecules and the polyamide pulp short fibers are not directly bonded, so the reinforcement efficiency is low, and the short fibers themselves act as fracture nuclei in the rubber, which reduces the fatigue durability and creep properties of the rubber. In addition to the drawback of significantly reducing the pulp-like fibers, since the fibers are dispersed in the rubber using a kneading machine such as a Banbury mixer, the dispersion level is extremely low. However, when the amount is further increased, there is a drawback that kneading and extrusion become extremely difficult.

Further, in order to obtain a desired elastic modulus, it is conceivable to add a reinforcing agent such as carbon black or novolak type phenol resin to the short fiber compounded rubber, but carbon black or novolac type phenol resin is added. This greatly increases the viscosity of the rubber, making it extremely difficult to work in each process such as kneading, sheeting, heating, and extruding, and it is also difficult to arrange the short fibers in the desired direction. However, there is a drawback in that the effect of blending short fibers is greatly reduced.

Further, from the viewpoint of improving workability and workability of rubber, a conventional method is to add a softening agent such as oil or resin. When using, the viscosity is reduced by softening, the short fibers can be easily arranged in a desired direction, but like the conventional rubber, a decrease in elastic modulus due to the addition of a softening agent and deterioration of heat generation cannot be avoided, and therefore, It does not reach the desired physical properties.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to improve workability due to viscosity reduction during kneading and physical properties such as high elastic modulus.

[0009]

Means for Solving the Problems In reinforcing the rubber composition with short fibers, the present inventors have paid attention to the arrangement of short fibers and the viscosity of the rubber, and as a result of diligent study, as a result, short fiber reinforced rubber was obtained. By combining specific organic unsaturated fatty acids, short-fiber reinforcement alone has not been possible to achieve a large decrease in viscosity, and the accompanying improvement in short-fiber orientation (= anisotropy). With the addition of a softening agent, it was found that a high rubber elastic modulus could not be achieved at all and a large improvement in exothermicity was found, and the present invention was completed.

That is, the constitution of the present invention is as follows.
100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene-based synthetic rubber, 2.5 parts by weight or more of short fibers, and unsaturated fatty acid having two or more carbon-carbon double bonds in the molecule 0.1 To 10 parts by weight, and the unsaturated fatty acid contains 10% by weight or more of a conjugated diene-based acid having one or more sets of conjugated double bonds in the molecule. Composition.

Further, it is preferable that the unsaturated fatty acid contains 25% by weight or more of a conjugated diene acid. Further, it is preferable that the short fibers are made of thermoplastic polyamide. Also,
It is preferable that the short fibers have a ratio (L / D) of the average length L and the average diameter D of 8 or more and the average diameter D of 1 μm or less.

Further, in order to make the rubber composition after vulcanization harder, it is preferable to add a resin, and such a composition is suitable for applications such as imparting steering stability to a racing tire. Even if the amount of carbon black is relatively large and short fibers are added to the carbon black, since it is used in combination with a softening agent, inconvenience during kneading can be avoided.

Further, for example, when thermoplastic polyamide is used as the short fibers and novolac type phenol resin is used as the resin, the diene rubber and the short fibers form a graft bond through the resin to have a reinforcing effect. can get.

Further, 2% of the rubber composition obtained by orienting and vulcanizing the short fibers in a direction parallel to the orientation direction of the short fibers is used.
Preferably dynamic elastic modulus at strain (E _'P) and dynamic modulus at 2% strain in the perpendicular direction (E' ratio _{V) (E 'P / E} ' V) is at least 2.0.

The present invention will be described in detail below. Examples of the diene rubber that can be preferably used in the present invention include natural rubber (NR), synthetic isoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SB).
R), chloroprene rubber (CR), butyl rubber (II
R), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR) and ethylene-propylene rubber (EPDM).

In the present invention, the "conjugated diene acid" means at least one pair of carbon-carbon double bonds having a conjugated relationship in the molecule (for example, -CH = CH-CH = CH-).
The unsaturated monocarboxylic acid containing is shown.

The unsaturated fatty acid containing two or more carbon-carbon double bonds in the molecule containing 10% by weight or more of the conjugated diene-based acid (hereinafter, simply referred to as unsaturated fatty acid) naturally contains the conjugated diene-based acid. However, the other unsaturated fatty acids include two or more carbon-carbon double bonds, but differ in that they are in a non-conjugated relationship with each other. The unsaturated fatty acid has a molecular weight of 10 to 22 in terms of carbon number, and it is preferably within the range of fatty acids which are conventionally used vulcanization accelerators including conjugated diene acids.

The content of the conjugated diene-based acid in the unsaturated fatty acid must be 10% by weight or more, preferably 25% by weight or more, and 100% by weight, that is, the unsaturated fatty acids are all conjugated diene-based acids. Good. Conjugated diene acid content is 10
If it is less than wt%, a sufficient elastic modulus of the vulcanized rubber cannot be obtained,
The breaking strength improvement effect cannot be obtained.

The conjugated dienoic acids include 2,4-pentadienoic acid, 2,4-hexadienoic acid, 2,4-decadienoic acid,
2,4-dodecadienoic acid, 9,11-octadecadienoic acid, eriostearic acid, 9,11,13,15-octadecatetraenoic acid, 9,11,13-octadecatrienoic acid, and the like. Are used alone, in a mixture or in a form contained in the unsaturated fatty acid. Further, as a preferred example of the unsaturated fatty acid containing a conjugated diene-based acid, for example, dehydrated castor oil fatty acid obtained by dehydration reaction of castor oil is mentioned as substantially corresponding to the unsaturated fatty acid used in the present invention, The content of the conjugated diene-based acid can be changed depending on the dehydration method, and for example, those having a content of 35% by weight or 50% by weight can be obtained. In the case of this dehydrated castor oil fatty acid, the conjugated diene-based acid is mainly 9,11-octadecadienoic acid,
Other unsaturated fatty acids mainly include non-conjugated octadecadienoic acid. Examples of the non-conjugated unsaturated fatty acid also include linoleic acid and linolenic acid.

In the rubber composition of the present invention, the unsaturated fatty acid is contained in an amount of 0.1 to 10 parts by weight, preferably 100 parts by weight of the rubber.
0.1 to 5 parts by weight is blended. When the content is more than 10 parts by weight or less than 0.1 parts by weight, a sufficient elastic modulus of the rubber cannot be obtained, and when it is less than 0.1 parts by weight, the breaking strength improving effect cannot be obtained. Further, in the rubber composition of the present invention, it is more preferable to use, in addition to the unsaturated fatty acid, a conventionally used fatty acid represented by stearic acid.

As the thermoplastic polyamide, for example, a polyamide having a melting point of 190 to 235 ° C., preferably 190 to 225 ° C., more preferably 200 to 220 ° C. is used. For example, nylon 6, nylon 610, nylon 12, nylon 611.
, Nylon such as 612, and the like.
The amount of this polyamide, by further kneading the diene rubber to the polyamide reinforced rubber masterbatch,
It can be adjusted appropriately. Further, in the rubber composition of the present invention, the thermoplastic polyamide is contained in the form of short fibers.
From the viewpoint of physical properties and processing, it is necessary to consider the amount of polyamide as short fibers, and the amount of short fibers in the rubber composition is 2.5 to 100 parts by weight with respect to 100 parts by weight of the diene rubber in the composition. It is preferably 5 to 50 parts by weight. If it is less than 2.5 parts by weight, the effect of reinforcing short fibers does not appear in the physical properties of the rubber composition, and if it exceeds 100 parts by weight, kneading and extrusion become difficult in the production of the rubber composition, which is not preferable.

The short fibers in the rubber composition of the present invention are
It may be in some bonding state with the rubber molecule, but is preferably chemically bonded such as graft bonding.
This short fiber has a circular cross section and an average diameter D of 0.05.
~ 0.8 μm is preferable, and 90% by weight or more is 1 μm
It is preferable that the fiber length L is 10 m or less, and the fiber length L is 10 μm or more, and 90% by weight or more thereof is 1000 μm or less. When the fiber diameter is large, the stress concentration at the fiber end causes
The fatigue durability is lowered, and the larger the L / D of the fiber is, the more easily the fibers are oriented, and the more the anisotropy is increased.
Therefore, the ideal direction for short fibers is to reduce the diameter to L / D
It can be said that the direction is to increase. Therefore, L / D is 8
It is necessary that it is not less than 10 and preferably not less than 10.
The conventional short fiber is a method of cutting a spun fiber, and there is a limit in reducing the diameter, but the short fiber used in the present invention is melt-stretched in rubber, and therefore is extremely microfiber. Therefore, a great improvement in fatigue durability can be realized.

The amount of carbon black used in the present invention is 5 to 90 parts by weight, preferably 10 to 70 parts by weight, and more preferably 20 to 60 parts by weight, based on 100 parts by weight of the diene rubber. If the amount is less than 5 parts by weight, it is insufficient to uniformly disperse the phenolic resin in an amount necessary to give a reinforcing effect, while if it exceeds 90 parts by weight, the rubber becomes brittle and the durability of the rubber composition is reduced. It is not preferable because it is extremely deteriorated.

A tackifier having a tackifying effect on a diene rubber which is a masterbatch with the polyamide short fibers may be added to this system. Excellent compatibility with rubber,
A non-reactive or extremely low-reactive substance that does not substantially react with the diene rubber when heated can be used. For example, coumarone resin such as coumarone indene resin, non-reactive phenol formaldehyde resin such as non-reactive phenolic resin, alkylphenol acetylene resin, terpene / phenolic resin, polyterpene resin,
Examples thereof include hydrocarbon-based tackifying resins, petroleum-based hydrocarbon resins such as polybutene, rosin derivatives such as zinc resinate, and mixtures thereof.

Next, an example of the method for producing the rubber composition according to the present invention will be described. The materials and their amounts used here are as described above. A short fiber reinforced rubber masterbatch can be obtained by kneading a diene rubber, a thermoplastic polyamide, and optionally a tackifier at a temperature not lower than the melting point of the thermoplastic polyamide and not higher than 270 ° C, extruding, and then winding. However, it may then be rolled or stretched below the melting point of the thermoplastic polyamide.

Further, with respect to the obtained masterbatch (diene rubber reinforced by thermoplastic polyamide fibrous material by graft bonding), in order to adjust the polyamide fiber content in the composition to the desired amount, Rubber is added as appropriate, and it is filled with carbon black and the above-mentioned unsaturated fatty acids, sulfur normally used in the rubber industry, vulcanizing agents, vulcanization accelerators, antioxidants, silica other than carbon black, etc. A desired rubber composition can be obtained by appropriately adding an agent, a novolac type phenol resin, a process oil, and the like and kneading with a Banbury mixer.

Since the rubber composition of the present invention is excellent in high elastic modulus and low heat build-up, the blending amount of short fibers, carbon black, sulfur, accelerator, etc. should be adjusted appropriately to the desired elastic modulus. Therefore, it is suitably used as a tire material such as a bead filler, a gum chafer, a belt coating rubber, and a ply coating rubber. Further, since the rubber composition of the present invention is a unidirectional reinforcing material, it can be suitably used as a belt ply which is a skeleton material of a tire and a selective reinforcing material around beads.

[0028]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

In this example, the followings were used for the short fiber reinforced masterbatch and the novolac type oil-modified phenolic resin added in the resin curing agent. 1. Short fiber reinforced masterbatch UBE-FRR-NR HE0100 [trade name: Ube Industries, Ltd.] compounded natural rubber 100 parts by weight 6-nylon ¹⁾ 50 parts by weight tackifier ²⁾ 2 parts by weight 1) Melting point: 221 ° C , Molecular weight: 3 × 10 ⁴ 2) Non-reactive phenol / formaldehyde resin In this masterbatch, the blending amount of polyamide (6-nylon) is adjusted by kneading with other diene rubber in a Banbury mixer. It can be adjusted. In this example, 2 parts are added to 100 parts by weight of the rubber component.
(Comparative Example 10), 20, 50 parts by weight was used. 2. Novolac-type oil-modified phenolic resin added in the curing agent Synthetic examples are shown below.

[Synthesis Example 1] 200 g of a novolac-type phenolic resin (melting point 80 ° C.) modified with cashew oil, 150 g of water and 4 g of gum arabic in a 1 liter glass flask.
Was charged, and the content was heated to 95 ° C. with stirring. A solution prepared by dissolving 20 g of hexamethylenetetramine in 150 g of water was added thereto, and the reaction was carried out for 15 minutes while maintaining the liquid temperature at 95 ° C while stirring. Next, lower the contents to 30 ° C,
After adding 500 g of water, the solid-liquid was separated by filtration with a filter paper and washed with water to obtain resin particles. This resin was dried under reduced pressure (5 mmHg or less) at 35 ° C. for 24 hours to obtain resin A as novolac-type modified phenolic resin particles added in the resin curing agent.

Various rubber compositions were prepared according to the compounding contents shown on the label, and a sheet-like sample was prepared with a viscosity before kneading after kneading with an OOC Banbury and a 10-inch roll.
The dynamic elastic modulus E ′ and the dynamic loss coefficient tan δ at room temperature after vulcanization at 0 ° C. for 20 minutes were measured. Regarding the anisotropy, the dynamic elastic modulus at 2% strain (E ′ _P ) in the short fiber orientation direction and the dynamic elastic modulus at 2% strain (E ′ _{V in the} direction orthogonal to the short fiber orientation direction) _{ratio) (E 'P / E'} V) were compared by calculating the. Here, 'the _P in the parallel direction to the short fiber orientation direction, and E' E and _V shows a dynamic modulus at 2% strain in a direction perpendicular thereto.

Next, in order to examine the effect on the tire, FIG.
A tire of size 175 / 70R13 having a two-ply steel cord layer as a belt layer and a one-ply layer of 1500d / 2 PET fiber as a carcass layer as shown in FIG. In the trial pneumatic tire 10 held in a low position in the vicinity of, the compounding rubber shown in Table 1 was used as the rubber composition of the bead filler 14, and the orientation direction 16 of the short fibers was changed to the bead wire.
Create a tire parallel to 12 and roll resistance (R
P), maneuverability and riding comfort were evaluated (actual vehicle test). The results are shown in Table 2. The various evaluation methods are as follows.

(1) Viscosity of rubber ML ₁ +4 According to JIS K 6300-1974, preheating for 1 minute,
Measurement was carried out for 4 minutes at a temperature of 130 ° C.

(2) Dynamic elastic modulus E ', dynamic loss coefficient tan
δ Using a viscoelastic spectrometer (VES / F type) from Iwamoto Seisakusho, sample piece thickness 2mm, width 4.7mm, length 20m
It was measured at room temperature under the conditions of m, static strain of 3%, dynamic strain of 2% and frequency of 50 Hz.

(3) Maneuverability (cornering power (CP)
Index) A trial tire filled with an internal pressure of 2.0 kg / cm ² was installed on a drum with an outer diameter of 3000 mm, and after applying a load of 300 kgf, it was preliminarily run for 30 minutes at a speed of 30 km / h, and the internal pressure was maintained under no load. 2.0 kg
readjusted to / cm ² , apply 300 kgf load again, and continuously apply positive and negative slip angles up to ± 14 ° on the drum with the same diameter, and measure the cornering force (CF) at positive and negative angles. , Cornering power (CP)
I decided. CP (kg / deg) = {CF (1 °) ＋ CF (2 °) / 2 ＋ CF (3 °) / 3 ＋ CF
(4 °) / 4} / 4

(4) Rolling resistance index (RRC index) A trial tire filled with an internal pressure of 2.0 kg / cm ² was installed on a drum having an outer diameter of 1708 mm, and after applying a load of 300 kgf, the tire was 30 at a speed of 80 km / h. Preliminarily run for 1 minute, readjust the air pressure, 200km
After increasing the drum rotation speed to a speed of / h, the drum was coasted and calculated from the moment of inertia until the drum rotation speed decreased from 185 km / h to 20 km / h.

(Rolling resistance of tire) = [-ds / dt
(Id / Rd ² + It / Rt ² ) − (resistance of drum alone)] In the formula, Id is the moment of inertia of the drum, It is the moment of inertia of the tire, Rd is the drum radius, and Rt is the tire radius.

The rolling resistance value at 50 km / h obtained by the above equation was obtained as a representative value. The measurement was carried out in a room controlled at 24 ± 2 ° C. The indexing is expressed by rounding off the value below the decimal point of the following formula.

(Rolling resistance index) = [(representative value of test tire) / (representative value of control tire)] × 100 As a result, the smaller the rolling resistance index is, the better the fuel economy is.

(5) Actual Vehicle Experiment Each trial tire was mounted on a passenger vehicle, and a feeling test of steering stability and vibration riding comfort on a dry road surface was conducted by a professional driver. The evaluation was 10 for the control tire (tire using the rubber composition of Comparative Example 2).
In the relative evaluation by the point method, it was distinguished from the control as 0: not changed +2: somewhat good -2: slightly bad +4: good -4: bad. It should be noted that the + tire indicates that steering stability or vibration riding comfort is better than that of the control tire.

[0041]

[Table 1]

[0042]

[Table 2]

The following can be seen from Tables 1 and 2. In comparison with Example 1, if the average diameter of the short fibers is large, the decrease in the number of mixed fibers is unavoidable, and the anisotropy is decreased accordingly (Example 5). Therefore, it is preferable that D is small. Since the anisotropy is proportional to L / D, in the case of L / D = 6 (Example 6), the anisotropy is lower than that in L / D = 8. Therefore, the higher L / D is preferable.

When the short fibers are PVA (Example 7), since they do not undergo graft polymerization unlike polyamides, reinforcement due to adhesion with rubber molecules cannot be obtained, and E _p ′ and E _v ′ are reduced. Therefore, polyamide such as nylon is preferable.

At 15% of the dehydrated castor oil fatty acid diene (Example 8), although M _{1 + 4} decreased, E after vulcanization
_p ′ and E _v ′ are not enough. Therefore, a diene of 35% is preferable.

It is better to add stearic acid to E _p ′, E _v
'Is improved (Example 9). With 8% of diene (Comparative Example 8), E _p ′ and E _v ′ are lowered, which is inconvenient. The mixture of linoleic acid containing no dehydrated castor oil fatty acid (Comparative Example 9) has a low softening effect and insufficient E _p ′ and E _v ′, which is inconvenient. If the amount of the short fibers is less than 2.5 parts by weight (Comparative Example 10), anisotropy does not appear, which is inconvenient.
Further, the improvement is insufficient with only short fibers (Comparative Examples 1 to 4), and neither short fibers nor unsaturated fatty acids are contained (Comparative Examples 5 to 5).
It can be seen that 7) is not achieved due to both dry stability and riding comfort.

Compared with the comparative example, the rubber composition of the present invention satisfied an extremely high dynamic elastic modulus in the direction of orientation of the short fibers and an extremely low dynamic loss coefficient in the direction orthogonal to the orientation, and dehydrated castor oil fatty acid was added. As a result, the effect of improving the anisotropy appears. This indicates that when this rubber composition is used for a tire tread, a tire having a high elastic modulus but low loss characteristics, that is, excellent fuel economy can be obtained.

Further, as can be seen from Table 2, the tire using the rubber composition of the present invention as a bead filler rubber is excellent in low rolling resistance, that is, excellent in fuel economy, and further, a comparative example in which dehydrated castor oil fatty acid is not added. Compared to 5, it exhibited a surprisingly high level of both steering stability and vibration riding comfort at the same time.

EFFECTS OF THE INVENTION The rubber composition of the present invention is different from the conventional reinforcing means using only carbon black, phenol resin, etc., and exhibits the maximum characteristics by adding an organic fatty acid such as dehydrated castor oil fatty acid. Is. Therefore, in the tire member, not only the bead filler,
Suitable for gum chafer, belt coating rubber, bri coating rubber, etc., and also as a unidirectional reinforcing material, so it is also suitable as a selective reinforcing material for belts, plies, and bead peripheral parts that are the frame material of tires. Used for.

[Brief description of drawings]

FIG. 1 is a perspective view around a bead of a pneumatic tire according to an embodiment of the present invention.

[Explanation of symbols]

 10 Pneumatic tire 12 Bead wire 14 Bead filler 16 Orientation direction of short fibers (parallel to bead wire)

Claims (4)

[Claims] 1. 100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene-based synthetic rubber, 2.5 parts by weight or more of short fibers, and 2 or more carbon-carbon double bonds in the molecule. Having unsaturated fatty acids
0.1 to 10 parts by weight, wherein the unsaturated fatty acid contains 10% by weight or more of a conjugated diene-based acid having one or more conjugated double bonds in the molecule. Rubber composition. 2. The unsaturated fatty acid comprises a conjugated diene acid 25
The short fiber reinforced rubber composition according to claim 1, which is contained in an amount of not less than wt%. 3. The short fiber-reinforced rubber composition according to claim 1, wherein the short fibers are made of thermoplastic polyamide. 4. The short fiber according to claim 1, wherein the short fiber has a ratio (L / D) of an average length L and an average diameter D of 8 or more and an average diameter D of 1 μm or less. Fiber-reinforced rubber composition.