KR20030042893A - Tread rubber for truck and bus tire - Google Patents

Abstract

PURPOSE: A rubber composition for truck and bus tire treads which can form bubbles inside the treads to retard the growth of cracks generated by outside impact and to improve chip-cut resistance is provided. CONSTITUTION: The rubber composition for truck and bus tire treads comprises an independent spherical bubble having an average diameter of 10 to 200 micrometers. The rubber is foamed in the foaming ratio of 2 to 30% and comprises a foaming agent alone or together with foaming aids. The rubber composition preferably comprises 100 parts by weight of a base rubber containing a natural rubber alone or together with butadiene rubber or with styrene-butadiene copolymer, 30 to 55 parts by weight of carbon black, 5 to 30 parts by weight of silica and less than 8 parts by weight of a silane coupling agent.

Description

Tread rubber for truck and bus tire

The present invention relates to a tread rubber of a truck bus tire, and more particularly, to a tread rubber of a truck bus tire including a spherical independent bubble therein to slow down its growth rate when a crack occurs.

Chip cut performance is an important factor for truck bus tires driving in bad tracks.In order to improve this, a small amount of silica is used to increase the hardness of the rubber composition while increasing the tensile elongation and viscosity to suppress the initial crack formation due to the high hardness. In addition, the technology of lowering crack growth rate by increasing elongation and viscosity is very early technology and has been applied in many tire companies.

However, even though these technologies have improved the chip cut performance to some extent, they are not sufficient. Accordingly, Japanese tire makers have improved the chip cut performance by mixing and modifying natural or synthetic resins. As driving conditions become more severe, further improvement is required.

Therefore, the inventors of the present invention, while exploring other methods to improve the chip-cut performance of the truck bus tire tread, forming bubbles in the tread can slow down the growth rate even if cracks are generated by external impact. In view of the fact that the chip cut performance can be improved, a foaming agent and a foaming aid were introduced into the rubber composition to adjust other compositions, and as a result, it was found that the chip cut performance could be improved.

Accordingly, it is an object of the present invention to provide a tread rubber of a truck bus tire that has a spherical independent bubble inside to foam at a constant foaming rate, thereby slowing its growth when a crack occurs, thereby improving chip cut performance.

Tread rubber of the truck bus tie of the present invention for achieving the above object is characterized in that it comprises a spherical independent bubble having an average diameter of 10 ~ 200㎛.

1 is a reference view for formulating the growth rate of cracks generated in the tread portion by an external impact,

FIG. 2 is a reference view for explaining a decrease in crack growth rate when a spherical independent bubble is formed in a tread portion.

3 is a schematic diagram of an apparatus used to test chip cut resistance in an embodiment of the present invention.

* Detailed description of the main symbols in the drawings *

1-test tire 2-axis of rotation

3-Drive motor 4-Tread section

5-Support Body 6-Hydraulic Cylinder

7-Hydraulic Actuator 8-Support Frame

9-rotary roller 10-body

11-through hole 12-fitting groove

13-spacer 14-projection

15-fixing hole 16-cover

17-Bolt 18-Groove

The present invention will be described in more detail as follows.

It is well known that the crack growth rate generated by the external impact is in inverse proportion to the radius of the circle contacting the crack tip. If the radius of the circle in contact with the end of the crack is small, the stress is concentrated in the portion will increase the growth rate of the crack (see Fig. 1). The load on the crack tip is calculated by the following equation.

(Equation 1)

σ _t = σ + 2σ (l + r) ^1/2

In the above equation, σ _t is the stress applied to the region A in FIG. 1, σ is the stress applied to the solid body, l is the depth of the crack, and r is the radius of the circle contacting the end of the crack.

In the present invention, a spherical independent bubble is introduced into the rubber to lower the growth rate of the crack generated by the external impact (see Fig. 2).

When the edge of the growing crack meets the spherical free bubbles inside, the radius of the spherical free bubbles (r ₁ ) is much larger than the radius of the circle (r ₀ ) in contact with the crack ends. It becomes small.

It is preferable that the size of the spherical free bubbles is in the range of 10 to 200 μm. When the average diameter of the spherical free bubbles is less than 10 μm, the crack growth rate is not slowed down since the diameter of the spherical free bubbles is smaller than 10 μm. It becomes impossible. On the other hand, when the average diameter of the spherical independent bubble is larger than 200 mu m, it is not preferable because the wear resistance worsens.

The size of the spherical independent bubble can be measured by cutting the rubber of the tread part with a sharp razor and observing the cut plane at 100 times using VMS (Video Microscope).

In order to form such spherical independent bubbles in the tread rubber, a method including a foaming agent or a foaming aid in a conventional tread rubber composition can be used.

Examples of blowing agents that can be used include dinitrosopentamethylenetetraamine (DPT), azodicarbonamide (ADCA), dinitrosopentamstyrenetetraamine and benzenesulfonylhydride derivatives, and oxybenzenesulfonyl hydride (OBSH). Oxybenzenesulfonyl hydride is preferred in view of manufacturing processability.

As the foaming aid, auxiliary agents usually used in the production of foam products such as urea, zinc stearate, zinc benzenesulfinate and zinc gas can be used.

Foaming agents and foaming aids may be used other than the above.

When a tread rubber is prepared including such a foaming agent or a foaming aid, the foaming ratio of the tread portion is suitably 2 to 30%, preferably 5 to 25%.

The foaming rate (As) is expressed as As = (ρ ₀ / ρ ₁ -1) × 100 (%), where ρ ₁ is the density of the Balfort Red rubber and ρ ₀ is the density of the tread rubber without bubbles. .

If the foaming rate is less than 2%, the growing crack ends are less likely to meet the spherical free bubbles, and thus the crack growth rate cannot be slowed down. On the other hand, if the foaming rate exceeds 30%, the probability that the end of the growing crack meets the spherical free bubbles increases, but the tensile strength is greatly reduced, which adversely affects durability.

On the other hand, forming a spherical independent bubble in the tread portion of the heavy-duty truck bus tire as described above may result in a decrease in hardness and modulus to increase the amount of deformation under the same load, resulting in high heat generation and thus a separation. In order to improve this, it is possible to maintain the hardness and modulus of rubber including spherical free bubbles by increasing the amount of reinforcing agent in the rubber composition for forming the tread rubber in comparison with the conventional rubber. However, when the reinforcing agent is increased, the carbon black is increased to increase the heat generation due to interfacial friction. Therefore, in order to increase the hardness, it is preferable to increase the hardness and modulus by using the silica and the coupling agent. Separation can be improved by suppressing the chemical bond between the silica and the rubber by the coupling agent.

Preferred reinforcing agent in the tread rubber is 30 to 55 parts by weight of carbon black, 5 to 30 parts by weight of silica, and silane coupling agent within 8 parts by weight of silica based on 100 parts by weight of the raw rubber, but is not limited thereto.

On the other hand, as the raw material rubber for forming the tread rubber, natural rubber generally used for the tread rubber of truck bus tires is preferable. However, in order to improve abrasion resistance, polybutadiene rubber having a cis content of 90% or more can be added within 30% by weight. In addition, styrene-butadiene copolymer rubber may be added within 30% by weight to improve chip cut performance.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

In the following examples, the average diameter of the spherical free bubbles was measured by cutting the rubber of the tread part with a sharp razor and observing the cut plane 100 times using VMS (Video MicroScope).

And the wear resistance is 5kgf. The amount of wear for 5 minutes under the condition of 40% slip ratio is shown as an index.

Chip cut performance was tested using the equipment introduced in Patent Application No. 2000-73983 as shown in FIG. 3 and the performance was expressed in an index.

The exothermic characteristics were expressed as an index by measuring the temperature rise using an MTS tester.

Example 1

The following Table 1 illustrates the result of adding a foaming agent to form a spherical bubble having a certain bubble size in the tread portion, and further increase the carbon black.

Comparison 1 T1 T2 T3 Compounding agent Natural rubber 100 100 100 100 Carbon black: N220 50 55 55 55 Silica 5 5 5 5 Zinc oxide 3 3 3 3 Stearic acid 1.5 1.5 1.5 1.5 Anti-aging 2 2 2 2 Vulcanizer 1.5 1.5 1.5 1.5 blowing agent 0 One 4 8 Vulcanization accelerator 1 One One One One Carbon black Co., Ltd. made by Korea Carbon, Silica: Rhodia Cofranze Zeosil 175 Anti-aging agent: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine foaming agent: Oxybenzenesulfonyl hydride (OBSH) Vulcanization accelerator 1: TBBS (N-tert-butyl-2-benzothiazolesulfenamide) Bubble size (㎛) - 12 56 212 Foaming rate (%) - 3 12 35 Hardness (Shore A) 62 61 58 55 300% modulus 130 140 120 105 Wear resistance 100 99 97 90 Chip cut performance 100 98 103 86 Fever Index 100 95 94 87

As a result of increasing the carbon black and introducing the blowing agent from the results of Table 1, the foaming agent 1 part by weight (T1) has a small foaming rate and bubble size does not show a large difference from Comparative Example 1, exothermic performance according to the carbon black increase Only the disadvantageous results were shown, and when the foaming agent 8 parts by weight is used, it can be seen that the bubble size and the foaming rate are too large to have an adverse result in all performance.

Example 2

Table 2 shows an example in which the silane coupling agent and the foaming aid are introduced into the most preferable T2 of the rubber of Table 1 above.

Comparison 1 T2 T4 T5 T6 Compounding agent Natural rubber 100 100 100 100 100 Carbon black: N220 50 55 50 50 50 Silica 5 5 10 10 10 Silane coupling agent 0 0 0.5 0.5 0.5 Zinc oxide 3 3 3 3 3 Stearic acid 1.5 1.5 1.5 1.5 1.5 Anti-aging 2 2 2 2 2 Vulcanizer 1.5 1.5 1.5 1.5 1.5 blowing agent 0 4 4 4 4 Foaming aid 0 0 One 3 6 Vulcanization accelerator 1 One One One One One Vulcanization accelerator 2 0 0 0.2 0.2 0.2 Carbon Black Co., Ltd. made by Korea Carbon, Silica: Zeosil 175 Silane Coupling Agent: Made by Degussa, Si-69 (bis (3-triethoxysilylpropyl) -tetrasulfide) Aging inhibitor: N- ( 1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine foaming agent: oxybenzenesulfonylhydride (OBSH), foaming aid: urea vulcanization accelerator 1: TBBS (N-tert-butyl-2-benzothia Solsulfenamide) vulcanization accelerator 2: DPG (N, N'-diphenylguanidine) Bubble size (㎛) - 86 67 102 189 Foaming rate (%) - 15 12 16 37 Hardness (Shore A) 62 58 63 61 57 300% modulus 130 120 132 125 107 Wear resistance 100 97 102 101 92 Chip cut performance 100 103 101 102 93 Fever Index 100 94 98 97 92

From the results of Table 2, when the silica was increased and the silane coupling agent and the foaming aid were introduced, 1 part by weight of the foaming aid showed the same level of foaming as in Comparative Example 1, and the foaming rate was 6 parts by weight of the foaming aid. It can be seen that it is too big and has an adverse effect on all performance.

Example 3

30 parts by weight of silica and 30 parts by weight of carbon black were set, and the result of increasing the amount of the silane coupling agent from 3.3 parts by weight to 8 parts by weight of the amount of silica is shown in Table 3 below.

Comparison 1 T2 T5 T7 T8 T9 Compounding agent Natural rubber 100 100 100 100 100 100 Carbon black: N220 50 55 50 30 30 30 Silica 5 5 10 30 30 30 Silane coupling agent 0 0 0.5 1.0 1.5 2.4 Zinc oxide 3 3 3 3 3 3 Stearic acid 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging 2 2 2 2 2 2 Vulcanizer 1.5 1.5 1.5 1.5 1.5 1.5 blowing agent 0 4 4 4 4 4 Foaming aid 0 0 3 3 3 3 Vulcanization accelerator 1 One One One One One One Vulcanization accelerator 2 0 0 0.2 0.6 0.6 0.6 Carbon Black Co., Ltd. made by Korea Carbon, Silica: Zeosil 175 Silane Coupling Agent: Made by Degussa, Si-69 (bis (3-triethoxysilylpropyl) -tetrasulfide)) Anti-aging agent: N -(1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine foaming agent: oxybenzenesulfonylhydride (OBSH), foaming aid: urea vulcanization accelerator 1: TBBS (N-tert-butyl-2- Benzothiazolesulfenamide) vulcanization accelerator 2: DPG (N, N'-diphenylguanidine) Bubble size (㎛) - 86 71 74 97 134 Foaming rate (%) - 15 14 14 20 21 Hardness (Shore A) 62 58 61 63 64 64 300% modulus 130 120 125 101 120 135 Wear resistance 100 97 101 88 92 95 Chip cut performance 100 103 102 107 116 103 Fever Index 100 94 97 102 108 111

As a result of increasing the amount of the silane coupling agent, the results of Table 3 indicate that the wear resistance and the heat generation performance are good, but the chip cut resistance is the highest when the silane coupling agent is added at 5 parts by weight of silica. have.

Example 4

Examples of changing the ratio of carbon black and silica to 50:10, 40:20, and 30:30 are shown in Table 4 below.

Comparison 1 T2 T5 T8 T10 Compounding agent Natural rubber 100 100 100 100 100 Carbon black: N220 50 55 50 30 40 Silica 5 5 10 30 20 Silane coupling agent 0 0 0.5 1.5 1.0 Zinc oxide 3 3 3 3 3 Stearic acid 1.5 1.5 1.5 1.5 1.5 Anti-aging 2 2 2 2 2 Vulcanizer 1.5 1.5 1.5 1.5 1.5 blowing agent - 4 4 4 4 Foaming aid - - 3 3 3 Vulcanization accelerator 1 One One One One One Vulcanization accelerator 2 0 0 0.2 0.6 0.4 Carbon Black Co., Ltd. made by Korea Carbon, Silica: Zeosil 175 Silane Coupling Agent: Made by Degussa, Si-69 (bis (3-triethoxysilylpropyl) -tetrasulfide)) Anti-aging agent: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine foaming agent: oxybenzenesulfonylhydride (OBSH), foaming aid: urea vulcanization accelerator 1: TBBS (N-tert-butyl-2-benzo Thiazole sulfenamide) vulcanization accelerator 2: DPG (N, N'- diphenylguanidine) Bubble size (㎛) - 86 71 97 83 Foaming rate (%) - 15 14 20 16 Hardness (Shore A) 62 58 61 64 62 300% modulus 130 120 125 120 123 Wear resistance 100 97 101 92 95 Chip cut performance 100 103 102 116 104 Fever Index 100 94 97 108 102

From the results of Table 4, when the ratio of carbon black and silica is added to the same level of carbon black and silica, the wear resistance becomes slightly disadvantageous, but the exothermic performance and chip cut performance are the best. Able to know.

Example 5

Butadiene rubber and styrene-butadiene copolymer are shown in Table 5 as an example of the introduction of the raw material rubber.

From the results of Table 5, butadiene rubber was introduced, but the wear resistance was good, but the chip cut performance was remarkably deteriorated.The introduction of the styrene-butadiene copolymer significantly improved the chip cut performance, but the heat generation performance was detrimental. It can be seen that the results are shown. As a result of introducing butadiene rubber and styrene-butadiene copolymer at the same time, the heat generation was equivalent and the wear resistance and chip cut performance were good.

As described in detail above, according to the present invention, the tread rubber including the spherical independent bubble in the rubber may improve chip cut performance by slowing the growth rate of cracks generated in the tread portion by external impact.

Claims (6)

Tread rubber for truck bus tires containing spherical free bubbles having an average diameter of 10 to 200 µm. The tread rubber of a truckbus tire according to claim 1, wherein the tread rubber is foamed at a foaming rate of 2 to 30%. The tread rubber of a truckbus tire according to claim 1, wherein the tread rubber comprises a foaming agent alone or a mixture with a foaming aid. The tread rubber according to claim 1, wherein the tread rubber comprises 30 to 55 parts by weight of carbon black and 5 to 30 parts by weight of silica with respect to 100 parts by weight of the raw rubber. The tread rubber of a truckbus tire according to claim 1 or 4, wherein the tread rubber contains a silane coupling agent within 8 parts by weight of silica. The tread rubber of a truck bus tie according to claim 1, wherein the tread rubber is made of natural rubber alone or mixed rubber of natural rubber with butadiene rubber or styrene-butadiene copolymer.