JPS63241045A - Rubber composition for tire bead filler - Google Patents

Abstract

PURPOSE:To obtain the title rubber composition excellent in durability, vibration-damping comfortableness of drive, steering stability, processability, etc., by mixing a natural rubber-based rubber component with reinforcing carbon black, sulfur and a metal acrylate at a specified weight ratio. CONSTITUTION:100pts.wt. natural rubber or blend rubber (A) prepared by mixing natural rubber with 50% or below synthetic diene rubber (e.g., polyisoprene rubber) is mixed with 50-100pts.wt. reinforcing carbon black (B), 1-10pts.wt. sulfur (C) and 1-15pts.wt. metal acrylate (D) to obtain the purpose rubber composition for tire bead fillers. As component B, carbon black having an iodine absorption of 40-150mg/g and a dibutyl phthalate absorption of 0.5-1.3cc/g is desirable. As component D, aluminum acrylate or zinc acrylate especially excellent in a function of prolonging a fatigue life is desirable.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a rubber composition for bead filler of pneumatic tires, and more specifically, it relates to a rubber composition for use as a bead filler for pneumatic tires, and more specifically, it relates to a rubber composition for use in bead fillers of pneumatic tires. The present invention relates to a rubber composition suitable for a tire bead filler with excellent properties.

(Prior Art) Since the bead filler rubber of pneumatic tires, especially radial tires, has a great influence on tire durability, handling stability, riding comfort, etc., various studies have been made so far. For example, Japanese Utility Model Publication No. 47-16084, French Patent No. 126013, and U.S. Patent No. 40673
Specification No. 73 and the like discloses that the motion performance and the like are improved by applying super hard material or rubber to the bead filler.

However, these conventional techniques give little consideration to durability. For this reason, as a technology that takes durability into consideration, for example, Japanese Patent Application Laid-Open No. 55-54337 discloses a bead composition containing a diene rubber such as natural rubber, a novolac type phenol resin, a resin curing agent, and carbon black. It is disclosed for use in fillers.

Furthermore, JP-A-55-151053 discloses that short fibrous syndiotactic-1,2-polybutadiene is block polymerized to cis-1,4-polybutadiene in order to improve both durability and transport performance. A rubber composition for bead filler has been proposed which contains a graft polymerized polymer, a thermosetting resin, and a curing agent as main components.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional technology in which a thermosetting resin and a resin curing agent are blended into a rubber composition for bead filler in order to increase the elastic modulus of rubber, hex. As described in Rubber Chemistry and Technology 1, Vol. 49, No. 4, 1976, pp. 1040-1059, the use of methylenetetramine causes a decrease in the strength of the polyethylene terephthalate fiber cord due to the amine. However, there was a problem in that it adversely affected the durability of the tire. On the other hand, when hexamethoxymethylolmelamine is used instead of hexamethylenetetramine as a curing agent for such thermosetting phenolic resins, it is possible to prevent the strength from decreasing due to amine decomposition of polyethylene terephthalate, but when processing such as kneading and extrusion, Due to the curing reaction of the resin, there were problems in obtaining uniform quality and in processability.

Another method to increase the elastic modulus is to mix carbon black into a large pot, but this method significantly deteriorates the flow characteristics of the rubber, and conventional rubber industrial processing equipment is not suitable for Banbury rolls, extrusion, etc. There are many restrictions on processing, and it has been difficult to obtain a desired high elastic modulus rubber.

Furthermore, high elastic modulus rubber can be obtained by incorporating a large amount of sulfur as a crosslinking agent in the rubber polymer, but in this case, the flexural durability required for the bead filler is significantly reduced, making it impractical. There aren't many.

As explained above, in the prior art, it has been impossible to obtain a rubber composition for tire bead filler that is satisfactory in all aspects such as driving performance, durability, and processability.

Therefore, an object of the present invention is to provide a rubber composition for tire bead filler that can solve the above-mentioned problems and exhibit excellent effects in all aspects of durability, vibration riding comfort, handling stability, and processability. It is in.

(Means for Solving the Problems) As a result of intensive studies to solve the above problems, the present inventors have found that natural rubber alone or blended rubber with synthetic diene rubber can be used as a filler in rubber compositions for tire bead fillers. Besides prescribed amounts of reinforcing carbon black and sulfur,
The present inventors have discovered that a vulcanized rubber with high elasticity, high elongation, and high durability and fatigue properties can be obtained by blending a predetermined amount of a metal salt of acrylic acid, and have completed the present invention.

That is, in the present invention, for 100 parts by weight of natural rubber alone or blended rubber containing up to 50% of synthetic diene rubber,
50 to 100 parts by weight of reinforcing carbon black and 1 part by weight of sulfur
The present invention relates to a rubber composition for a tire bead filler, which contains 1 part by weight of 1 to 15 parts by weight of an acrylic acid metal salt.

The rubber component used in the present invention is natural rubber alone or a blended rubber with synthetic diene rubber. Examples of such synthetic diene rubber include polyisoprene rubber, high cis-polybutadiene rubber, and medium vinyl-containing rubber with a vinyl content of 35 to 55%. Polybutadiene rubber, high vinyl content polybutadiene rubber with a vinyl content of 70% or more, syndiotactic-1,2
- Polybutadiene rubber containing polybutadiene, emulsion polymerized styrene-butadiene rubber, solution polymerized styrene-butadiene rubber, and modified rubbers of these diene rubbers, such as carboxylated styrene-butadiene rubber, epoxidized natural rubber, and the like.

Next, the reinforcing carbon black used in the present invention preferably has an iodine adsorption amount of 40 to 150 mg/g and a dibutyl phthalate absorption amount of 0.5 to 1.3 CG/g. Further, as the metal salt of acrylic acid, those in which the metal is aluminum or zinc are particularly preferable.

In addition, in the rubber composition of the present invention, a vulcanization accelerator, a vulcanization accelerating aid, an anti-aging agent, a softener, etc. are appropriately blended.

(Function) Blending acrylic acid metal salts into rubber components is described in US Pat. No. 4.191.671 and British Patent No. 2.04.
No. 2,553, each of which is vulcanized with peroxide and is not intended for use as a bead filler rubber for tires, and therefore does not achieve the effects of the present invention. It wasn't something. On the other hand, JP-A-60-147451 discloses that an elastic modulus equivalent to that of a sulfur-curable natural rubber composition containing a large amount of carbon black can be achieved by blending zinc dimethacrylate into the rubber composition. It is stated that by being able to obtain a rubber composition with a reduced amount of carbon black, elongation at break and resilience can be improved in such a rubber composition, making it suitable for use in tires. However, the simple addition of zinc dimethacrylate resulted in high elasticity but decreased elongation at break and poor fatigue durability.

In contrast, the purpose of the present invention is to improve the durability and fatigue performance of tires without impairing their motion performance and vibration riding comfort. It is desirable that the dynamic loss coefficient (tan δ) be 0.19 or more from this point of view.

In order to satisfy such requirements, the metal acrylate used in the present invention may be selected from, for example, aluminum acrylate, zinc acrylate, nickel acrylate, cobalt acrylate, lead acrylate, iron acrylate, manganese acrylate, and barium acrylate. , calcium acrylate or magnesium acrylate.

Furthermore, it is desirable that the change in elongation at break and elastic modulus of vulcanized rubber due to temperature be small, so from this point of view, aluminum acrylate, zinc acrylate, calcium acrylate, or magnesium acrylate is preferable, and aluminum acrylate is more preferable. and zinc acrylate. Furthermore, aluminum acrylate is particularly preferred from the viewpoint of increasing fatigue life.

Although the mechanism by which adding acrylic acid metal salts increases fatigue life while maintaining high elastic modulus is unknown, it is presumed that acrylic acid metal salts have a mitigating effect on microscopic stress concentration. .

Next, we will specifically examine the temperature and dynamic loss coefficient ja when aluminum acrylate is added as an additive in different amounts.
The relationship between n and dynamic elasticity E' is shown in FIG.

According to FIG. 1, tan δ does not change even if the amount added is changed, but E' increases as the amount added increases, indicating the effect of increasing elasticity. In addition, the elongation at break and modulus also increase accordingly. However, the effect of increasing elasticity reaches its limit when the number of parts by weight added is 15 parts by weight, and even if more than 15 parts by weight are added, the effect of increasing elasticity is small. Moreover, if the amount of acrylic acid metal salt exceeds 15 parts by weight, the rubber breaking strength decreases and the cookness increases during heating, resulting in a decrease in workability. Therefore, in the present invention, the amount of the acrylic acid metal salt is within the range of 1 part by weight to 15 parts by weight, at which the effect of increasing elasticity begins to be exhibited.

Here, the loss coefficient tan δ and the dynamic elastic modulus E' are measured using a viscoelastic spectrometer (VES-
F type), specimen thickness 2+nm, width 4.7mm
, length 20I]ll111 Measured under conditions of temperature 25° C., dynamic strain 1%, frequency 50Hz, and initial strain 1%.

Next, it is effective that the reinforcing carbon black used in the present invention has an iodine adsorption amount of 40 to 150 mg/g and a dibutyl phthalate absorption amount of 0.5 to 1.3 cc/g. If it is less than this range, the effect of improving the elastic modulus will be poor, while if it exceeds this range, the dispersibility of carbon black will decrease, resulting in worsening fatigue life, or the Muni viscosity of unvulcanized rubber will become too high, resulting in poor workability. This is because.

The amount of reinforcing carbon black specified in the present invention, together with the amount of sulfur, defines the range in which the elasticity of the tire bead filler should be ensured, and if the amount of carbon black is less than 50 parts by weight, Elasticity will be insufficient, and if it exceeds 100 parts by weight, durability will be insufficient.

Next, FIG. 2 shows the effect of improving the durability and fatigue performance, that is, the number of cycles at break, by adding aluminum acrylate to natural rubber alone or to a blend rubber with styrene-butadiene copolymer rubber. From this Figure 2, it can be seen that blending styrene-butadiene copolymer rubber tends to reduce the durability and fatigue performance, and that the limit for the blending type of styrene-butadiene copolymer rubber is 50 parts by weight. .

In other words, a blend larger than this is not preferable because it has little effect on improving the durability and fatigue performance of the rubber composition.

The number of repetitions at breakage was determined using a cyclic fatigue testing machine manufactured by Sam Electronics Machinery Co., Ltd., and the thickness of the specimen was 2+11111. Shape JIS
-3, measured under the conditions of an initial static load of 30 kg/cm2, a dynamic repeated load of 20 kg/cm2, and an ambient temperature of 27°C.

As explained above, in the rubber composition of the present invention,
A high modulus of elasticity of the bead filler rubber has been achieved, which reduces heat generation and improves fatigue resistance. Also, the deterioration of polyethylene terephthalate fiber carcass cords is small.
Furthermore, it has a disadvantageous effect on workability to obtain uniform quality, and is economically advantageous. Therefore, it can sufficiently contribute to improving the tire's durability performance, handling stability, and vibration riding comfort.

(Example) The present invention will be explained based on examples.

Table 1 below shows the blending ratio (parts by weight) of the rubber compositions for bead fillers of Examples and Comparative Examples, as well as the elongation at break, modulus, dynamic modulus (E'), and
The graph shows the dynamic loss coefficient (tan δ) and the number of rupture cycles. The methods for measuring these physical properties were as follows: dynamic modulus of elasticity (E'), dynamic loss coefficient (tan δ), and number of cycles at break were measured in the same manner as described above, and elongation at break and modulus were measured in accordance with JIS K6301. .

For example, in Example 1, 100 parts by weight of natural rubber was placed in a Banbury mixer, then stearic acid, zinc white, carbon black, and aluminum acrylate were added and mixed, and finally, a usual vulcanization accelerator and sulfur were added. and mixed.

Similar blending methods were followed in other Examples and Comparative Examples.

Next, the effectiveness of the rubber composition for bead filler in tires was evaluated. Specifically, as shown in FIG. 3, a tire size 185/70SR14 is provided with two ply steel cord layers as the belt layer 2 and one ply 1500 denier/2 polyethylene terephthalate fiber cord layer as the carcass layer 3. In Tire 1, high-speed running performance, handling stability, ride comfort vibration, and durability were evaluated using a rubber composition having the compounding ratio shown in Table 1 as the rubber of bead filler 5.

The evaluation test method is as follows.

(b) High-speed running performance test The tires were assembled on a 5J rim, filled with an internal pressure of 2.1 kg/am2, pressed onto a metal drum with a diameter of 1.7 m with a load of 390 kg, and run at a speed of 80 km/hour for 2 hours. After a preliminary run, the vehicle was left for 3 hours. Then 121 km/
If you have sex for 30 minutes at the same speed and complete the race without any abnormalities, the following 8
The speed was increased in km/hour in 30 minute increments, and the speed at the time the failure occurred and the running time at that speed were measured.

(b) Steering stability test Tires with the normal internal pressure and normal load according to JIS D 4230 were run on a drum with a diameter of 2.5 m, and the cornering force was measured by changing the slip angle, and the cornering force per slip angle was measured. The cornering power was expressed as an index, and Comparative Example 1 was used as a control. The larger the index, the better the tire response to the steering angle.

In addition, the maximum cornering force increases the slip angle (
The value at which the cornering force reached the maximum was expressed as an index using Comparative Example 1 as a control.

The larger the index, the better the tire's ability to grip the road surface at large steering angles.

(c) Ride comfort vibration test One iron protrusion (height 9
．． A tire with a regular internal pressure and a regular load was run on a drum with a diameter of 5 mm), and the tire fixed axle load variation force when passing over a protrusion was determined and expressed as an index using Comparative Example 1 as a control. The larger the index, the smaller the axial force when riding over a bump, indicating better riding comfort.

(d) Special durability drum test The tire was mounted on a drum with a diameter of 1.7 m under conditions of overload and excessive internal pressure such that the strain energy concentrated at the folded end of the carcass was approximately four times that of the normal driving of the actual vehicle. 60km after crimping
The vehicle was run at a speed of /hour, and durability was evaluated based on the distance traveled until failure occurred at the folded end of the carcass ply. still,
If the vehicle traveled up to 30,000 km, the vehicle passed the test.

Also, under these conditions, 20. A carcass ply cord was taken from a tire that had been driven OOOkm, and the strength of the cord in the area adjacent to the bead filler was measured, and the results were expressed as an index using Comparative Example 1 as a control. The larger the index, the smaller the deterioration of the code due to the durability test.

The results obtained in each of the above tests, particularly in Comparative Examples 1 and 2 and Example 2, are also listed in Table 2 below. In addition, as a result of the above test, the dynamic loss coefficient (tan δ), the ratio of dynamic elastic modulus (E') to tan δ (E'/lan δ), handling stability, vibration ride comfort, and durability. The relationship between
When we investigated all the rubber compositions shown in the table, we found that
The relationship shown in FIG. 4 was obtained.

As is clear from the test results shown in Table 2, the rubber composition of the present invention of Example 2 has better high-speed running performance, handling stability, durability, and cord strength than the rubber compositions of Comparative Examples 1 and 2. It was excellent in terms of.

Furthermore, from Fig. 4, tan δ and E'/
It has been found that lan δ needs to be within a predetermined range. That is, tan δ is preferably within the range of 0.19 to 0°35. If tan δ is smaller than 0.19, the vibration damping properties will be poor and the ride quality vibration will deteriorate; It was confirmed that if it exceeds 35, the heat generation property of the bead portion increases and the durability decreases. Also, E'/lan δ is 13X10"
It is preferably within the range of ~21×10”dyn/cm2, and E
'/lan δ is less than 13 XlO"dyn/am2, the tire response to steering angle is small;
It has been found that if it exceeds 8d\n/am2, the frictional force between the tires and the road surface decreases when the steering angle is large, which can be dangerous.

(Effects of the Invention) As explained above, the rubber composition for tire bead filler of the present invention exhibits excellent effects in all aspects of durability, vibration riding comfort, and handling stability, and also Since it does not contain a thermosetting resin, curing agent, or large excess of carbon black or sulfur, unlike a rubber composition, it can exhibit excellent effects in terms of processability.

[Brief explanation of the drawing]

Figure 1 shows the temperature and dynamic loss coefficient tan when aluminum acrylate according to the present invention is added in varying amounts.
A graph showing the relationship between δ and dynamic elastic modulus E', Figure 2 shows the blend ratio ( 3 is a partial side sectional view of the tire used in the example, and FIG. 4 is a graph showing the relationship between tan δ and E'/lan δ It is a graph showing the range of excellent handling stability, vibration riding comfort, and durability in relation to the following. l... Tire 2... Belt layer 3... Carcass layer 4... Sidewall part... Bead filler 6... Bead wire patent applicant Bridgestone Corporation $y chart temperature (°C) 2nd Figure tanδ

Claims (1)

[Scope of Claims] 1. 50 to 100 parts by weight of reinforcing carbon black, 1 to 10 parts by weight of sulfur, and acrylic acid to 100 parts by weight of natural rubber alone or a blended rubber containing up to 50% of synthetic diene rubber. A rubber composition for a tire bead filler, which contains 1 to 15 parts by weight of a metal salt. 2. The reinforcing carbon black is 40 to 150 mg/
The tire bead filler according to claim 1, which has an iodine adsorption amount of 0.5 to 1.3 cc/g and a dibutyl phthalate absorption amount of 0.5 to 1.3 cc/g, and wherein the metal in the acrylic acid metal salt is aluminum or zinc. Rubber composition for use.