JPS6359382B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, the rubber reinforcing cords are individually connected one by one.
The present invention relates to a rubber-cord composite coated with highly reinforcing rubber containing short fibers and having excellent fatigue durability. Conventionally, rubber compositions with high modulus have been used as coating rubber for rubber reinforcing cords. This is because if the modulus of the cord and the coating rubber differ too much, a large stress concentration will occur near the interface, and the rubber will break from there. For this reason, methods have been used such as using highly reinforcing carbon black, increasing the amount of sulfur, using reinforcing materials such as short fibers and novolak resin, or a combination of these methods. However, if the modulus is increased too much, the fatigue resistance of the rubber itself decreases, and if repeated shear strain is applied between the cords, the cords will fatigue and break. Furthermore, when short fibers are used, they may inhibit the adhesion between the coating rubber and the cord, or they may provide nuclei for crack growth, resulting in a significant reduction in reinforcing properties. Summer. Such issues are particularly important with respect to tires. Under these circumstances, the wear resistance of tire treads has recently been rapidly improved, and tread retreading has become common practice, so it is necessary to significantly improve the fatigue resistance performance of tires. However, a fully satisfactory coating rubber for this purpose has not yet been developed. In order to solve the above-mentioned drawbacks, the present applicant filed a patent application filed in 1983-
As described in the specification of No. 58635, A. Fatigue fracture that occurs between the cord and rubber occurs due to stress concentration when the difference between the modulus of the cord and the modulus of the rubber is large.B. If the height is too high, the cords will not be able to withstand the repeated shear strain between the cords and will break.In order to solve the phenomenon of A and B, each cord should be coated independently with high modulus rubber. If a material with a relatively low modulus is used to form a cord-reinforcing rubber layer between the cords of each of the obtained cords, the stress concentration between the cords and the rubber will not be so large, and the repeated shear strain between the cords will be reduced. Syndiotactic has discovered that it can provide sufficiently high fatigue resistance performance even when used as a rubber composition that coats each cord independently.
It was proposed that a rubber composition containing 1,2-polybutadiene short fibers should be used. However, in the syndiotactic polybutadiene short fibers, the maximum hysteresis loss associated with the glass transition temperature (30 to 40°C) of the amorphous portion is 30 to 120°C, which is the heat generation temperature of the tire when running under normal usage conditions. ℃ range, it is difficult to reduce hysteresis loss.
This is not very desirable in terms of heat generation, and if this drawback could be resolved, fatigue durability could be further improved significantly. In view of the current situation, the present inventors filed a patent application in 1983-
The present inventors have discovered that a rubber-cord composite with significantly improved fatigue durability can be obtained by using the microorganic short fiber reinforced rubber composition proposed in the specification of No. 85064, thereby achieving the present invention. In other words, the present invention uses one rubber reinforcing cord,
Natural rubber, synthetic polyisoprene rubber, styrene
One or more rubbers selected from the group consisting of butadiene copolymer rubber and polybutadiene rubber, and 10 to 100 parts by weight of carbon black and 3 to 30 parts by weight of microorganism per 100 parts by weight of this rubber. A rubber composition mainly composed of short fibers, wherein the microorganic short fibers have a glass transition temperature of lower than 30°C or higher than 120°C in the amorphous part and a melting point of 160°C or higher in the crystal part. Yes Average short fiber length 0.8-30μm, average short fiber diameter
The present invention relates to a rubber-cord composite coated with a rubber composition comprising microorganic short fibers having a 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. 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 120°C.
30 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,
For example, polyvinylidene chloride, polyvinylidene 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, polyvinylenaphthalene, polyoxymethylene, polybisphenol A carbonate, 1,4-poly-
It is a short fiber made of 2,3-dimethylbutadiene or the like. Here, the reason why the glass transition temperature of the amorphous portion is lower than 30℃ or higher than 120℃ is because the heat generation temperature of the tire when running under normal usage conditions is within the range of 30℃ to 120℃. Therefore, short fibers whose amorphous portion has a glass transition temperature within this range usually have a large hysteresis loss. Also, since the glass transition temperature of rubber is around -50℃,
Considering the affinity with rubber, microorganic short fibers having 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. If the average short fiber length is less than 0.8 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 preferred. 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 have a large degree of creep and its bending resistance will decrease. 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, the melting point of the crystal part of the microorganic short fibers must be 160℃ or higher, which is necessary not only during tire running but also during tire manufacturing, which can reach over 100 degrees. This is because if the short microfibers melt and harden again, their morphology will change and there is a risk that the desired reinforcing effect cannot be expected. Further, it is more preferable that the maximum diameter of the microorganic short fibers is 10 μm or less, and if microorganic short fibers with a diameter exceeding 10 μm are present, they will become fracture nuclei and the rubber will be easily destroyed. 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, hardly any effect can be expected, which is undesirable, and if it exceeds 30 parts by weight, 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 110 kg/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. Of course, it is also possible to mix a good solvent and a poor solvent and adjust the composition to a suitable composition. 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 be reduced, which is undesirable, and if it exceeds 100 parts by weight, the workability will be significantly reduced, which is not preferred. The cords used in the present invention are rubber reinforcing cords, such as cords made of organic fibers such as nylon, polyester, rayon, and Kevlar;
Glass fiber cord, steel cord, etc. are used. In the present invention, such a cord is coated with a rubber composition mainly composed of rubber as a first component and short fibers as a second component. Alternatively, the cord is stretched through a coated rubber at a high temperature of, for example, 120 to 130°C, and the cord coated with the coated rubber is pulled out through a hole in a hot plate die. If the coating thickness of the rubber-cord composite thus obtained is thinner than 10 μm, the stress distribution referred to in the present invention will not be achieved sufficiently, and if it is thicker than 1 mm, the actual coating thickness will vary and the cord - The thickness of the relatively soft rubber layer filling between the cords is reduced, resulting in early fatigue as a rubber-cord reinforcement, which is undesirable, so it is usually set to 10 μm to 1.0 mm. In addition to the aforementioned microorganic short fibers and carbon black, the rubber composition that coats the cord contains conventional compounding agents used in the rubber industry, such as accelerators, accelerators, fillers such as silica, and softeners. It can be blended within the range of blending amount. As described above, the rubber composition used in the rubber-cord composite of the present invention is one in which a specific amount of carbon black is blended with rubber together with novel microorganic short fibers, and it has particularly high rebound resilience and generates little heat. Therefore, the rubber cord composite of the present invention using such a rubber composition has the advantage of significantly improved fatigue durability, and is suitably used as a reinforcing material for industrial products such as tires, conveyor belts, and hoses. The present invention will be explained in detail below using Examples and Comparative Examples. Examples 1 to 9, Comparative Examples 1 to 28 For 100 parts by weight of blend rubber of 80 parts by weight of synthetic polyisoprene rubber and 20 parts by weight of polybutadiene rubber, 40 parts by weight of HAF carbon black, 3 parts by weight of aroma oil, 2 parts by weight stearic acid,
A rubber composition containing 1 part by weight of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 10 parts by weight of each of the 37 types of micro organic short fibers shown in Table 1 was heated to a rubber temperature of 155. After kneading for 5 minutes in a Banbury mixer (50 rpm) at ℃, 4 parts by weight of zinc white, 0.6 parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide,
Thirty-seven rubber compositions were prepared by blending 0.2 parts by weight of dibenzothiazyl disulfide and 2.5 parts by weight of sulfur. These rubber compositions were evaluated for average rebound, work history, and fatigue durability. The results are shown in Table 1. The evaluation method is as follows. (Average impact resilience) The 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 80
3 parts by weight of aroma oil, 2 parts by weight of stearic acid, 1 part by weight of 2,
2,4-trimethyl-1,2-dihydroquinoline polymer, 4 parts by weight of zinc white, 0.6 parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide, 0.2 parts by weight of dibenzothiazyl disulfide, and Several types of rubber compositions were prepared by blending HAF carbon black with 2.5 parts by weight of sulfur, and the elastic modulus and repellency at 30°C, 60°C, 90°C and 120°C were measured. In,
A master curve was created by taking the elastic modulus on the horizontal axis and the repulsion elasticity on the vertical axis. 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. The impact elasticity of the micro short fiber reinforced rubber composition was determined as follows. The higher the value, the better. (Work history of short fibers) The average length and average diameter of the micro organic short fibers in the raw rubber are measured in advance, and then, after creating a rubber composition as described above, the average length and average diameter of the micro organic short fibers are measured. The diameter was determined, and if these values were 85% or more of the average length and average diameter of the raw rubber, they were marked as ○, and if they did not reach 85%, they were marked as ×. (Fatigue durability) The unvulcanized rubber composition was dissolved in 5 times the amount of rubber solvent to make rubber paste, and it was applied to a 1260 denier two-stranded 6 nylon fiber cord with a diameter of 0.61 mm using the dip method.
A rubber cord composite was created by coating to a thickness of 35 μm. Create a sample as shown in Figure 1 using a rubber cord composite, attach it to the sample holder shown in Figure 2, fix the cord 1 and the sample holder, and
5% repeated constant strain stress is applied at a frequency of 600 times/min.
The number of times it takes for cord 1 to come off was measured five times for each sample, and the average was calculated using a rubber composition that did not contain any microorganic short fibers and was reinforced only with carbon black, similar to the evaluation method for average repellency. case
Expressed as an index of 100. The higher the value, the better. Incidentally, the average diameter and average length of the microorganic short fibers were determined as follows. After extruding raw rubber (or rubber composition) containing microorganic short fibers using a capillary rheometer under conditions of L/D = 4, 100°C, and 20 sec ^-1 , it is extruded at 4 kg/cm ² using a vulcanizing iron. , vulcanize at 150°C for 1 hour. Ultrathin sections were cut from this vulcanizate in the direction perpendicular to the extrusion direction and in the average 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: Diameter of short fibers li: Length of short fibers ni: Number of short fibers with diameter of ri or length of li Σni: 300

【table】

[Table] As is clear from Table 1, the rubber cord composite of the present invention has significantly improved fatigue durability. Examples 10 to 12, Comparative Examples 29 to 34 Synthesis of isotactic polypropylene in various forms as shown in Table 2 as microorganic short fibers Blended rubber 100 with 80 parts by weight of polyisoprene rubber and 20 parts by weight of polybutadiene rubber
Nine types of rubber compositions were prepared by blending 10 parts by weight with respect to the other parts by weight, and the other ingredients were the same as in Example 1. These compositions were evaluated for roll workability, work history, and fatigue durability. The results are shown in Table 2. Regarding roll workability, we evaluated the presence or absence of roll baggies when kneading with 10-inch rolls.
Work history and fatigue durability were evaluated in the same manner as in Example 1.

[Table] As is clear from Table 2, the rubber-cord composite of the present invention has good workability and significantly improved fatigue durability. Examples 13 to 16, Comparative Examples 35 to 38 Rubber compositions having the formulations shown in Table 3 were prepared,
Roll workability and fatigue durability were evaluated in the same manner as in Example 10. Next, a rubber-cord (steel cord) composite coated to a thickness of 35 μm using the dip method using these rubber compositions was embedded in ordinary rubber, and a rubberized cord layer obtained was used as a carcass to form a carcass of size 1000R20. A tire is made, the tread and shoulder parts are removed along the carcass line, and the tire is run on a drum at a speed of 60 km/hr and a JIS 160% load until the tire fails. It was expressed as an index and evaluated as the durability of the drum. Combine the results and the third
Shown in the table.

【table】

[Table] As is clear from Table 3, it can be seen that the rubber-cord composite of the present invention has significantly improved fatigue durability. Examples 17-21 80 parts by weight of synthetic polyisoprene rubber, styrene
Blend rubber 100 consisting of 10 parts by weight of butadiene copolymer rubber and 10 parts by weight of polybutadiene rubber
10 parts by weight of isotactic polypropylene staple fiber (used in Example 11),
40 parts by weight of ISAF carbon black, 5 parts by weight of aroma oil, 1.5 parts by weight of 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 2 parts by weight of stearic acid, 4 parts by weight of zinc white, A rubber composition was prepared by blending 0.2 parts by weight of dibenzothiazyl disulfide, 0.7 parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide, and 2.5 parts by weight of sulfur. A rubber-cord composite was created by coating a steel cord. At this time, the coating thickness was varied from 8 to 1200 μm. The obtained rubber
Using the cord composite, the durability of the drum was expressed as an index in the same manner as in Example 13, with Example 16 set as 100. The results are shown in Table 4.

[Table] From Table 4, it can be seen that the rubber-cord composites with a coating thickness of 10 to 1000 μm have particularly markedly improved drum durability.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a sample for testing the fatigue durability of a rubber-cord composite, and FIG. 2 is a perspective view of a sample holder used for the fatigue durability test. 1...Rubber-cord composite, 2...Rubber.

Claims (1)

[Scope of Claims] 1. One rubber reinforcing cord is made of one or more rubbers selected from the group consisting of natural rubber, synthetic polyisoprene rubber, styrene-butadiene copolymer rubber, and polybutadiene rubber. , this rubber
A rubber composition containing 10 to 100 parts by weight of carbon black and 3 to 30 parts by weight of microorganic short fibers as main components per 100 parts by weight, wherein the microorganic short fibers have a glass transition of their amorphous portion. The temperature is lower than 30℃ or higher than 120℃, the melting point of the crystal part is 160℃ or higher, the average short fiber length is 0.8 to 30 μm, the average short fiber diameter is 0.02 to 0.8 μm, and the average short fiber length and average short Ratio to fiber diameter is 8~
A rubber cord composite characterized in that it is coated with a rubber composition consisting of microorganic staple fibers having a composition of 400. 2. The thickness of the rubber composition coated on the cord is 10 μm.
The rubber-cord composite according to claim 1, which has a thickness of 1.0 mm. 3 Micro organic short fibers include polyvinylidene chloride, polyvinylidene 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, polyvinylnaphthalene, polyoxymethylene, poly-bisphenol A carbonate,
The rubber according to claim 1 or 2, which is 1,4-poly-2,3-dimethylbutadiene.
code complex.