JPS6142936B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a short fiber-reinforced rubber, and more specifically, by incorporating microorganic short fibers whose amorphous portion has a glass transition temperature of lower than 30°C or higher than 120°C, the present invention provides high elastic modulus and crack growth resistance. This invention relates to a microorganic short fiber reinforced rubber composition which has extremely excellent cut resistance and impact resilience. A generally known method for increasing the modulus of elasticity of rubber is to increase the amount of carbon black.
However, when trying to increase the elastic modulus of rubber by using a reinforcing filler such as carbon black, there was a drawback that the hysteresis loss of the rubber increased accordingly. In addition to the above, as a method of increasing the elastic modulus of rubber,
It is also a well-known fact that short fibers such as nylon, vinylon, and polyester are blended into rubber.
However, although such short fiber-reinforced rubber has high reinforcing properties, large shear stress is applied to the ends of the short fibers, which causes the rubber to break, and furthermore, this kind of short fibers does not have sufficient rubber adhesion. For,
The above-mentioned fractured parts tend to grow along the surface of the short fibers, and as a result, the adhesive surface is destroyed, causing large creep, and the failure life of the rubber is extremely short when repeated elongation is applied. had. In order to solve these drawbacks, JP-A-55-
As described in Publication No. 23150, short fibers are micronized to reduce the stress applied to each short fiber to prevent creep, and to improve the inherent high reinforcing properties, crack growth resistance, and resistance of short fiber reinforced rubber. Rubber compositions that also have cuttability have been proposed. On the other hand, in response to the recent social demand for resource and energy conservation, research and development of automobiles with low gasoline consumption is not only focused on engine improvements, but also on the so-called low fuel consumption model, with the aim of reducing power loss derived from tires. is urgently needed. By the way, it is generally known that reducing the rolling resistance of tires can contribute to saving gasoline consumption in automobiles, and the quality of the rubber is a major factor that influences the rolling resistance of tires.
There are types and physical properties. That is, it is possible to reduce rolling resistance by using a material with a low glass transition temperature or a material with low hysteresis loss. However, the micro short fibers described in the above-mentioned Japanese Patent Application Laid-open No. 55-23150 etc. are syndiotactic.
Since it is a short fiber of an organic polymer consisting of 1,2-polybutadiene, the maximum hysteresis loss associated with the glass transition temperature (30 to 40°C) of the amorphous portion of the tire when running under normal usage conditions. It is difficult to reduce hysteresis loss because it is within the range of 30°C to 120°C, which is the exothermic temperature of In terms of fuel efficiency tires, the downside was rather significant. In view of the current situation, the present inventors have developed a rubber composition with a high modulus of elasticity, excellent cut resistance and crack growth resistance, and greatly improved hysteresis loss, which is extremely useful for use in fuel-efficient tires. As a result of intensive research in order to provide this invention, it was discovered that the desired rubber composition could be obtained by blending a specific amount of carbon black and a specific amount of specific microorganic short fibers into rubber, leading to the achievement of the present invention. . That is, the present invention applies natural rubber, synthetic polyisoprene rubber, butyl rubber, halogenated butyl rubber,
At least one rubber selected from polybutadiene rubber, sterene-butadiene copolymer rubber, ethylene-propylene-diene ternary copolymer rubber, and acrylonitrile-butadiene copolymer rubber
A composition containing 10 to 100 parts by weight of carbon black and 3 to 30 parts by weight of micro organic short fibers per 100 parts by weight, wherein the micro organic short fibers have a glass transition temperature of an amorphous portion of 30°C or higher. lower or higher than 120℃, the melting point of its crystal part is 160℃ or higher, and the average short fiber length is 0.8~30
µm, an average short fiber diameter of 0.02 to 0.8 μm, and a ratio of average short fiber length to average short fiber diameter of 8 to 400.Regarding a micro organic short fiber reinforced rubber composition. It is something. In the present invention, microorganic short fibers are defined as having a glass transition temperature of the amorphous portion lower than 30°C or higher than 120°C, and an average short fiber length of 0.8 to 30°C.
μm, the average short fiber diameter is 0.02 to 0.8 μm, the ratio of the average short fiber length to the average short fiber diameter is 8 to 400, and the melting point of the crystal part is 160°C or higher, such as polyvinylidene chloride. , polyvinylidene fluoride, poly-p-tert-butylstyrene, p
-chlorostyrene, dichlorostyrene, poly-α
-methylstyrene, poly-2-methylstyrene,
Poly-2,5-dimethylstyrene, poly-trimethylstyrene, poly-p-phenylstyrene, poly-o-vinylbenzyl alcohol, poly-p-
Vinylbenzyl alcohol, isotactic
Polypropylene, poly-4-methyl-1-pentene, poly-vinylnaphthalene, poly-oxymethylene, poly-bisphenol A carbonate,
It is a short fiber made of 1,4-poly-2,3-dimethylbutadiene, etc. Here, the glass transition temperature of the amorphous portion is lower than 30℃ or 120℃.
The reason why it is set higher than ℃ is because the heat generation temperature of tires when running under normal usage conditions is within the range of 30℃ to 120℃, so short fibers with the glass transition temperature of the amorphous part within this range This is because, in the normal case, the hysteresis loss becomes large. Also, the glass transition temperature of rubber is approximately -50℃.
Therefore, considering the affinity with rubber, micro organic short fibers with a glass transition temperature lower than 30°C are more preferable. In addition, the average short fiber length of the above micro organic short fibers is
The reason why the average short fiber diameter is 0.8 to 30 μm, the average short fiber diameter is 0.02 to 0.8 μm, and the ratio of the average short fiber length to the average short fiber diameter is 8 to 400 is as follows. Average short fiber length is 0.8μ
If it is less than 30 μm, the crack growth resistance of the resulting rubber composition will not be sufficiently improved, and if it exceeds 30 μm, workability such as kneading with a Banbury mixer will be significantly reduced, which is not preferable. If the average short fiber diameter is less than 0.02 μm, the micro short fibers will be cut and become too short during kneading or sheeting with rolls, and if it exceeds 0.8 μm, the stress per surface area of the short fibers will increase and the rubber This is not preferable because there is a risk that the adhesive surface with the rubber composition will be destroyed, and as a result, the resulting rubber composition will creep significantly or the bending resistance curve will drop. If the ratio of the average short fiber length to the average short fiber diameter is less than 8, the original characteristics of short fiber reinforcement, such as high reinforcing properties, cut resistance, and crack growth resistance, will decrease significantly, and if it exceeds 400, the short fiber This is not preferable because the stress applied during operation is greater than the strength, and the short fibers are likely to be cut. In addition, it is necessary that the melting point of the crystal part of the micro organic short fibers is 160℃ or higher.
This is true not only during tire running, but also during tire manufacturing, where temperatures can reach over 100 degrees Celsius.At this time, the short microfibers melt and harden again, changing their morphology and producing the desired reinforcing effect. This is because there is a risk of not being able to do so. Microorganic short fibers are 3 parts per 100 parts by weight of rubber.
~30 parts by weight is blended, but in this case, two or more types of the above-mentioned micro organic short fibers may be blended. If the amount is less than 3 parts by weight, little effect can be expected and is not preferred, while if it exceeds 30 parts by weight, the workability will be significantly reduced, which is not preferred. Furthermore, microorganic short fibers can be produced, for example, in the following manner. Taking isotactic polypropylene as an example, polymerized powdered isotactic polypropylene is swollen and crushed in n-hexane at 60°C to form a slurry, and then
It is ejected from a nozzle at a pressure of 110Kg/cm ² to produce micro short fibers. This is again dispersed in n-hexane, mixed with polymer cement, stirred, and then subjected to a normal rubber drying process to form a masterbatch.
At this time, the length, diameter, and length/diameter ratio of the microorganic short fibers obtained can be changed by controlling the solvent used for swelling, the temperature at that time, the pressure at the time of jetting from the nozzle, etc. is possible. In addition, microorganic short fibers are used as a masterbatch because it is relatively easy to uniformly disperse short fibers in rubber, but short fibers are directly mixed into rubber together with commonly used compounding agents such as carbon black. It is also possible to do so. Although the case of isotactic polypropylene has been described here, other microorganic short fibers can also be obtained in the same manner by swelling them with a relatively poor solvent and crushing them into a slurry form. good solvent and poor solvent
Of course, it is also possible to adjust the composition to a suitable composition by mixing solvents. In the present invention, it is necessary to mix 10 to 100 parts by weight of carbon black with respect to 100 parts by weight of rubber. If the amount is less than 10 parts by weight, the strength at break of the resulting rubber composition will decrease, which is undesirable, and if it exceeds 100 parts by weight, the workability will drop significantly, which is not preferred. In the present invention, in addition to the microorganic short fibers and carbon black mentioned above, compounding agents such as a vulcanizing agent, an accelerator, an accelerating aid, a filler such as silica, and a softening agent may be added within the usual amount. It can be blended. The rubber composition of the present invention having the above structure has a high modulus of elasticity and excellent cut resistance, and is more resistant to cracking than conventional rubber compositions reinforced with short fibers such as nylon, vinylon, and polyester. The growth properties are significantly improved, so the creep is significantly reduced, and the rebound properties are further improved compared to conventional microorganic short fibers, i.e., hysteresis and
This product was able to significantly reduce loss and is extremely useful for use in industrial products such as tires, conveyor belts, and hoses. Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. Examples 1 to 19, Comparative Examples 1 to 28 100 parts by weight of synthetic polyisopropylene rubber, 40 parts by weight of HAF carbon black, 5 parts by weight of aroma oil, 2 parts by weight of stearic acid, and 37 parts by weight shown in Table 1. Each type of micro organic short fiber
A rubber composition compounded at a ratio of 10 parts by weight was heated to a rubber temperature.
After kneading for 5 minutes at 155°C in a Banbury mixer (50 rpm), 4 parts by weight of zinc white, 0.5 parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide and 2 parts by weight of sulfur were added. Thirty-seven types of rubber compositions were created. These rubber compositions were evaluated for average impact resilience and short fiber work history, and the results are shown in Table 1. The evaluation method is as follows. (Average impact resilience) Impact resilience was evaluated at 30°C, 60°C, 90°C and 120°C in accordance with BS903 Part 19, and the value is the average value. However, if the materials of the short microfibers are different, the elastic modulus will not necessarily be the same even if the blending amount is the same, so it is difficult to clearly express the effects of the present invention by simply comparing each rubber composition. be. Therefore synthetic polyisoprene rubber
5 parts by weight of aroma oil per 100 parts by weight, 2
Parts by weight of stearic acid, 1 part by weight of zinc white, 0.5
parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide, 2 parts by weight of sulfur
Several types of rubber compositions containing varying amounts of HAF carbon black were prepared, and
The elastic modulus and rebound resilience were measured at 120°C, and a master curve was created by plotting the elastic modulus on the horizontal axis and the rebound resilience on the vertical axis at each temperature. From these master curves, read the rebound resiliency of the rubber composition reinforced only with carbon black, which corresponds to the elastic modulus of the micro short fiber reinforced rubber composition to be evaluated, and take this rebound resiliency as 100 to determine the elastic modulus of the rubber composition to be evaluated at a certain temperature. The rebound elasticity of the micro short fiber reinforced rubber composition was measured. The higher the value, the better. (Work history of short fibers) The average length and diameter of the microorganic short fibers in the raw rubber are measured in advance, and then, after creating a rubber composition as described above, the average length and diameter of the microorganic short fibers are measured. The average diameter was determined, and if these values were 85% or more of the average length and average diameter of the raw rubber, it was indicated as ○, and when it did not reach 85%, it was indicated as ×. The average diameter and average length of the short microorganic fibers were determined as follows: Raw rubber (or rubber composition) containing the short microorganic fibers was measured with a capillary rheometer at L/D = 4, 100. After extruding at 20 sec ^-1 at 150° C., it is vulcanized in a vulcanization can at 4 Kg/cm ² and 150° C. for 1 hour. Ultrathin sections were cut from this vulcanizate in directions perpendicular and parallel to the extrusion direction, and the diameter and length of the short microfibers were measured using an electron microscope. The average diameter and average length were determined using the following formula. =Σniri/Σni =Σnili
/Σni where: Average diameter: Average length ri: Short fiber diameter li: Short fiber length ni: Number of short fibers with diameter ri or length li Σni: 300

【table】

[Table] As is clear from Table 1, the glass transition temperature is
The rubber composition of the present invention, which contains microorganic short fibers with a melting point of lower than 30°C or higher than 120°C and 160°C or higher, has high rebound resilience without the microorganic short fibers being exposed to work history. It is clear that this is a significant improvement. Examples 10 to 12, Comparative Examples 29 to 34 Isotactic polypropylene in various forms as shown in Table 2 as microorganic short fibers was added to 100 parts by weight of synthetic polyisoprene rubber.
Nine types of rubber compositions were prepared by blending 10 parts by weight of the rubber composition with the other ingredients being the same as in Example 1. Roll workability for these compositions,
The results of evaluating the crack growth resistance, cut resistance, and working history of short fibers in the same manner as in Example 1 were evaluated in the second example.
Shown in the table. The evaluation method is as follows. (Roll workability) The presence or absence of a roll bag during kneading with a 10-inch roll was evaluated. (Crack growth resistance) A 2 mm wide crack was made in the center of a 5 cm wide and 2 mm thick vulcanized rubber sheet, and a 50% strain was applied with vibrations of 300 cycles/min. The time was measured. Since this value is greatly affected by the elastic modulus of the rubber, it was evaluated according to the evaluation method of the average rebound resilience in Example 1, that is, the value of the rubber composition reinforced only with carbon black having the same elastic modulus was set as 100. , showed the value of the microorganic short fiber reinforced rubber composition to be evaluated. The higher the value, the better. (Cut resistance) A blade with an angle of 45° can be cut with 120 joules of energy.
It was made to collide with a vulcanized rubber composition having a thickness of 8 cm at a speed of 0.894 m/sec, and the depth of the scratch at that time was determined. The evaluation was made in the same way as in the case of the crack growth resistance described above, in comparison with a rubber composition reinforced only with carbon black. The higher the value, the better.

[Table] As is clear from Table 2, the rubber composition of the present invention has excellent crack growth resistance and cut resistance, and has good workability. Examples 13 to 15, Comparative Examples 35 to 37 Rubber compositions having the formulations shown in Table 3 were prepared and evaluated in the same manner as in Example 10 for roll workability, crack growth resistance, and cut resistance. The results are shown in Table 3.

【table】

[Table] As is clear from Table 3, the rubber composition of the present invention has good workability and extremely excellent crack growth resistance and cut resistance.

Claims (1)

[Scope of Claims] 1 Natural rubber, synthetic polyisoprene rubber, butyl rubber, halogenated butyl rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, ethylene-propylene-diene ternary copolymer rubber, and acrylonitrile-butadiene copolymer A composition in which 10 to 100 parts by weight of carbon black and 3 to 30 parts by weight of microorganic short fibers are blended with 100 parts by weight of at least one kind of rubber selected from rubber, wherein the microorganic short fibers are The glass transition temperature of the amorphous part is lower than 30℃ or
Higher than 120℃, the melting point of the crystal part is 160℃
℃ or higher, an average short fiber length of 0.8 to 30 μm, an average short fiber diameter of 0.02 to 0.8 μm, and a ratio of the average short fiber length to the average short fiber diameter of 8 to 400. microorganic short fiber reinforced rubber composition. 2 Micro organic short fibers are polyvinylidene chloride,
Poly-vinylidene fluoride, poly-p-tert-butylstyrene, p-chlorostyrene, dichlorostyrene, poly-α-methylstyrene, poly-2-methylstyrene, poly-2,5-dimethylstyrene,
polytrimethylstyrene, poly-p-phenylstyrene, poly-o-vinylbenzyl alcohol,
Poly-p-vinylbenzyl alcohol, isotactic polypropylene, poly-4-methyl-
1-pentene, poly-vinylnaphthalene, poly-
The microorganic short fiber reinforced rubber composition according to claim 1, which comprises oxymethylene, poly-bisphenol A carbonate, and 1,4-poly-2,3-dimethylbutadiene.