PNEUMATIC TIRE

Abstract

A pneumatic tire having a tread, wherein the ground contact surface of the tread is composed of at least two types of rubber compositions different in the thermal conductivity, and the following formulas (1) and (2) are satisfied:

1700≤(Dt.sup.2×π/4)/Wt≤2827.4  (1)

[(V+1.5×10.sup.7)/Wt]≤2.88×10.sup.5  (2)

where Wt (mm) is the cross-sectional width and Dt (mm) is the outer diameter of the tire when installed on a standardized rim and inflated to an internal pressure of 250 kPa, and V (mm.sup.3) is the virtual volume of the space occupied by the tire.

Claims

1. A pneumatic tire having a tread portion, wherein the tread portion has a ground-contacting surface made of at least two types of rubber compositions having different thermal conductivities, when the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm.sup.3), when the tire is installed on a standardized rim and the internal pressure is 250 kPa, the tire satisfies following (formula 1) and (formula 2):
1700≤(Dt.sup.2×π/4)/Wt≤2827.4  (formula 1)
[(V+1.5×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 2).

2. The pneumatic tire according to claim 1, wherein the following (formula 3) is satisfied:
1718≤(Dt.sup.2×π/4)/Wt≤2827.4  (formula 3).

3. The pneumatic tire according to claim 1, wherein the following (formula 4) is satisfied:
[(V+2.0×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 4).

4. The pneumatic tire according to claim 3, wherein the following (formula 5) is satisfied:
[(V+2.5×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 5).

5. The pneumatic tire according to claim 1, wherein, when the outer diameter of the tire is Dt (mm) and the cross-sectional height of the tire is Ht (mm) when the tire is installed on a standardized rim and the internal pressure is 250 kPa, (Dt−2×Ht) is 470 (mm) or more.

6. The pneumatic tire according to claim 1, which has an aspect ratio of 40% or more.

7. The pneumatic tire according to claim 6, which has an aspect ratio of 45% or more.

8. The pneumatic tire according to claim 7, which has an aspect ratio of 47.5% or more.

9. The pneumatic tire according to claim 8, which has an aspect ratio of 50% or more.

10. The pneumatic tire according to claim 1, wherein, when the thermal conductivity of the rubber composition with the highest thermal conductivity is Ka (W/m.Math.K), and the thermal conductivity of the rubber composition with the lowest thermal conductivity is Kb (W/m.Math.K), among the at least two types of rubber compositions having different thermal conductivities, the following (formula 6) is satisfied:
Ka−Kb>0.01  (formula 6).

11. The pneumatic tire according to claim 10, wherein the following (formula 7) is satisfied:
Ka−Kb>0.05  (formula 7).

12. The pneumatic tire according to claim 1, wherein when the thermal conductivity of the rubber composition with the highest thermal conductivity is Ka (W/m.Math.K), and the thermal conductivity of the rubber composition with the lowest thermal conductivity is Kb (W/m.Math.K), among the at least two types of rubber compositions having different thermal conductivities, in the tread portion, the ratio Sb (%) of the contact area of the contact portion formed from the rubber composition having the thermal conductivity of Kb to the total contact area is larger than the ratio Sa (%) of the contact area of the contact portion formed from the rubber composition having the thermal conductivity of Ka to the total contact area, and (Sb−Sa)×Wt<3.00×10.sup.4 is satisfied.

13. The pneumatic tire according to claim 12, wherein (Sb−Sa)×Wt<2.50×10.sup.4 is satisfied.

14. The pneumatic tire according to claim 1, wherein loss tangent (30° C. tan δ) measured under the conditions of 30° C., frequency of 10 Hz, initial strain of 5%, and dynamic strain of 1% for the rubber composition with the lowest thermal conductivity among the at least two types of rubber compositions having different thermal conductivities is 0.16 or less.

15. The pneumatic tire according to claim 14, wherein the 30° C. tan δ is 0.14 or less.

16. The pneumatic tire according to claim 1, wherein, when Td (mm) is the thickness of the tread portion, the following (formula 8) is satisfied:
30° C. tan δ×Td≥1.5  (formula 8).

17. The pneumatic tire according to claim 16, wherein the following (formula 9) is satisfied:
30° C. tan δ×Td≥1.8  (formula 9).

18. The pneumatic tire according to claim 1, wherein the tread portion has a plurality of circumferential grooves continuously extending in the tire circumferential direction, and the total cross-sectional area of the plurality of circumferential grooves is 10 to 30% of the cross-sectional area of the tread portion.

19. The pneumatic tire according to claim 1, wherein the tread portion has a plurality of lateral grooves extending in the tire axial direction, and the total volume of the plurality of lateral grooves is 2.0 to 5.0% of the volume of the tread portion.

20. The pneumatic tire according to claim 1, wherein Dt is less than 685 (mm), where Dt (mm) is the outer diameter of the tire when the tire is installed on a standardized rim and the internal pressure is 250 kPa.

21. The pneumatic tire according to claim 1, wherein the cross-sectional width Wt (mm) is less than 205 mm.

22. The pneumatic tire according claim 21, wherein the cross-sectional width Wt (mm) is less than 200 mm.

23. The pneumatic tire according to claim 1, which is a pneumatic tire for a passenger car.

Description

EXAMPLES

[0219] Hereinafter, the present invention will be described in more specific with reference to Examples. In the following description, two types of rubber compositions having different thermal conductivities were used as the rubber composition forming the tread portion (tread rubber composition).

[Experiment 1]

[0220] In this experiment, 175 size tires were prepared and evaluated.

1. Manufacture of Rubber Compositions for Treads

[0221] First, a rubber composition for tread was produced.

(1) Compounding Material

[0222] First, each compounding material shown below was prepared. [0223] (a) Rubber component [0224] (a-1) NR: TSR20 [0225] (a-2) BR: UBEPOL-BR150 manufactured by Ube Kosan Co., Ltd. (cis content: 97 mass %, trans amount: 2 mass %, vinyl bond amount: 1 mass %) [0226] (a-3) SBR: Europrene SOL R C2525 manufactured by Versalis (styrene content: 26% by mass, vinyl bond amount: 24% by mass) [0227] (b) Compounding Materials Other than Rubber Components [0228] (b-1) Carbon black-1: Seast F manufactured by Tokai Carbon Co., Ltd. [0229] (b-2) Carbon black-2: Ketjen Black EC300J manufactured by Ketjen Black International Co., Ltd [0230] (b-3) Silica: Ultrasil VN3 manufactured by Evonik Co., Ltd. [0231] (b-4) Silane coupling agent: Si363 manufactured by Degussa Co., Ltd. [0232] (b-5) Oil: Process oil A/OMIX manufactured by Sankyo Yuka Kogyo Co., Ltd. [0233] (b-6) Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. [0234] (b-7) Stearic acid: Stearic acid “TSUBAKI” manufactured by NOF CORPORATION [0235] (b-8) Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. [0236] (b-9) Anti-aging agent-1: Nocrac 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd. [0237] (b-10) Crosslinking agent and vulcanization accelerator [0238] Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. [0239] Vulcanization accelerator-1: Nocceler CZ-G (CBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-Cyclohexyl-2-benzothiazolyl sulphenamide) [0240] Vulcanization accelerator-2: Nocceler D (DPG) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (1,3-Diphenylguanidine)
(2) Production of Rubber Composition with Low Thermal Conductivity

[0241] First, using each compounding material described above, base kneading and finish kneading were performed with a composition of 50 parts by mass of NR, 40 parts by mass of BR, 10 parts by mass of SBR, 5 parts by mass of carbon black-1, 0.1 parts by mass of carbon black-2, 50 parts by mass of silica, 4 parts by mass of silane coupling agent, 15 parts by mass of oil, 1.5 parts by mass of wax, 2 parts by mass of stearic acid, 3 parts by mass of zinc oxide, 3 parts by mass of antioxidant, 1.5 parts by mass of sulfur, 1 part by mass of vulcanization accelerator 1, and 0.5 parts by mass of vulcanization accelerator-2, and a rubber composition with low thermal conductivity (Kb: 0.30 W/m.Math.K) was obtained. The loss tangent (30° C. tan δ) of this rubber composition was measured under the conditions of 30° C., a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1% using an Eplexor series manufactured by GABO, and it was 0.14.

(b) Production of Rubber Composition with High Thermal Conductivity

[0242] Next, using the same compounding materials, except that the amounts of carbon black-1, carbon black-2, and silica were increased as appropriate, base kneading and finish kneading were performed with the same compounding, and four types from A to D of rubber compositions with high conductivity were obtained. The specific thermal conductivity Ka of the rubber compositions A to D is 0.32 W/m.Math.K for the rubber composition A, 0.41 W/m.Math.K for the rubber composition B, and 0.54 W/m.Math.K for the rubber composition C, and 0.38 W/m.Math.K for rubber composition D.

2. Tire Manufacturing

[0243] Next, a rubber composition with low thermal conductivity and a rubber composition with high thermal conductivity are used to perform biaxial extrusion molding, so that a tread was obtained in which the difference of the region Sb of the rubber composition with low thermal conductivity and the region Sa of the rubber composition with high thermal conductivity (Sb−Sa) is the values shown in Tables 1 and 2. The resulting tread was pasted with other tire members to form an unvulcanized tire, and press vulcanized for 10 minutes at 170° C. to produce each test tire of size 175 type (Example 1-1 to Example 1-5 and Comparative Examples 1-3 to 1-5). The thickness Td of the tread portion was set to 13 mm (30° C. tan δ×Td=1.82).

[0244] In addition, two types of test tires (Comparative Example 1-1 and Comparative Example 1-2) were manufactured using treads formed from only one type of rubber composition.

[0245] In each test tire, the above-mentioned (L.sub.80/L.sub.0) was 0.5, the total cross-sectional area of the circumferential groove was 22% of the cross-sectional area of the tread portion, and the total volume of the lateral grooves including the lateral grooves having the groove width/groove depth of 0. 65 was set to 3.5% of the volume of the tread portion.

3. Parameter Calculation

[0246] After that, the outer diameter Dt (mm), the cross-sectional width Wt (mm), the cross-sectional height Ht (mm), and the aspect ratio (%) of each test tire were obtained, and the virtual volume V (mm3) was obtained. At the same time, (Ka−Kb) was determined. The results are shown in Tables 1 and 2.

[0247] Then, (Dt−2×Ht), (Dt.sup.2×π/4)/Wt, (V+1.5×10.sup.7)/Wt, (V+2.0×10.sup.7)/Wt, (V+2.5×10.sup.7)/Wt, and (Sb−Sa)×Wt were calculated. The results are shown in Tables 1 and 2.

5. Performance Evaluation Test

(1) Evaluation of Grip at High-Speed Running

[0248] Each test tire was installed on all wheels of the vehicle (domestic FF vehicle, displacement 2000cc), filled with air so that the internal pressure became 250 kPa, and then driven on the test course on the dry road surface at a speed of 100 km/h, and the lap time at that time was measured and evaluated. For the evaluation, the difference from the lap time of a separately prepared reference tire was obtained, and the time difference in Comparative Examples 1-5 was set to 100, indexed based on the following formula, and the grip during high-speed running was relatively evaluated. The larger value is, better grip during high-speed running.

Grip at high-speed running=[(lap time of test tire−lap time of reference tire)/(lap time of Comparative Example 1-5−lap time of reference tire)]×100

(2) Evaluation of Durability Performance

[0249] After installing each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000cc) and filling it with air so that the internal pressure became 250 kPa, a driving 10 laps at a speed of 50 km/h, followed by climbing onto the unevenness provided on the road surface at a speed of 80 km/h were repeated on the test course on a dry road surface in an overloaded state. Thereafter, the lap was performed again at a speed of 50 km/h and then the speed was gradually increased to measure the speed at the time when the driver felt an abnormality.

[0250] Next, the result in Comparative Example 1-5 was set to as 100, and the durability performance was relatively evaluated by indexing based on the following formula. The larger the value, the better the durability.

Durability=[(Result of test tire)/(Result of Comparative Example 1-5)]×100

(3) Comprehensive Evaluation

[0251] The evaluation results of (1) and (2) above were totaled to obtain a comprehensive evaluation.

(4) Evaluation Result

[0252] The results of each evaluation are shown in Tables 1 and 2. In Comparative Examples 1-1 and 1-2, since the values of (Ka−Kb) and (Sb−Sa) cannot be calculated, the related results are indicated by “-”.

TABLE-US-00001 TABLE 1 Example No. 1-1 1-2 1-3 1-4 1-5 SIZE 175/40R21 175/40R21 175/40R21 175/50R20 175/60R19 Rubber composition with A B C A A high thermal conductivity (Parameter) Dt(mm) 672 673 674 684 693 V(mm.sup.3) 23225099 23279803 23332669 29988186 34384955 Wt(mm) 177 176 175 182 177 Ht(mm) 69 71 70 87 106 Dt-2 × Ht(mm) 534 531 534 510 481 (Dt.sup.2 × π/4)/Wt 2004 2021 2039 2019 2131 (V + 1.5 × 10.sup.7)/Wt 215961 217499 219044 247188 279011 (V + 2.0 × 10.sup.7)/Wt 244210 245908 247615 274660 307260 (V + 2.5 × 10.sup.7)/Wt 272458 274317 276187 302133 335508 Aspect ratio (%) 39 40 40 48 59 Ka-Kb 0.02 0.11 0.24 0.02 0.02 Sb-Sa 94 92 88 94 94 (Sb-Sa) × Wt 16638 16192 15400 17108 16638 (Evaluation result) Grip at high speed 104 111 118 106 109 running Durability 112 114 117 109 105 Comprehensive evaluation 216 225 235 215 214

TABLE-US-00002 TABLE 2 Comparative example No. 1-1 1-2 1-3 1-4 1-5 SIZE 175/80R14 175/60R19 175/80R14 175/80R14 175/80R14 Rubber composition with — — A B C high thermal conductivity (Parameter) Dt(mm) 636 693 635 637 636 V(mm.sup.3) 38652508 34384955 38041064 38610099 38870883 Wt(mm) 177 177 175 176 178 Ht(mm) 141 105 140 142 140 Dt-2 × Ht(mm) 354 483 355 353 356 (Dt.sup.2 × π/4)/Wt 1795 2131 1810 1811 1785 (V + 1.5 × 10.sup.7)/Wt 303122 279011 303092 304603 302645 (V + 2.0 × 10.sup.7)/Wt 331370 307260 331663 333012 330735 (V + 2.5 × 10.sup.7)/Wt 359619 335508 360235 361421 358825 Aspect ratio (%) 79 59 80 80 79 Ka-Kb — — 0.02 0.11 0.24 Sb-Sa — — 94 92 88 (Sb-Sa) × Wt — — 16450 16192 15664 (Evaluation result) Grip at high speed 90 92 96 98 100 running Durability 89 92 94 96 100 Comprehensive evaluation 179 184 190 194 200

[Experiment 2]

[0253] In this experiment, 195 size tires were prepared and evaluated.

[0254] After manufacturing test tires of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-5 shown in Tables 3 and 4 in the same manner as in Experiment 1, each parameter was obtained. Then, similarly, a performance evaluation test was performed and evaluated. In this experiment, the result in Comparative Example 2-5 was set as 100 for evaluation. The results of each evaluation are shown in Tables 3 and 4.

TABLE-US-00003 TABLE 3 Example No. 2-1 2-2 2-3 2-4 2-5 SIZE 195/40R20 195/40R20 195/40R20 195/50R19 195/60R18 Rubber composition with A B C A A high thermal conductivity (Parameter) Dt(mm) 664 663 665 679 690 V(mm.sup.3) 28719183 28653292 28783303 35835871 42160723 Wt(mm) 200 201 199 200 201 Ht(mm) 79 77 78 99 116 Dt-2 × Ht(mm) 506 509 509 481 458 (Dt.sup.2 × π/4)/Wt 1731 1718 1745 1811 1860 (V + 1.5 × 10.sup.7)/Wt 218596 217181 220017 254179 284382 (V + 2.0 × 10.sup.7)/Wt 243596 242056 245142 279179 309257 (V + 2.5 × 10.sup.7)/Wt 268596 266932 270268 304179 334133 Aspect ratio (%) 39 39 39 49 58 Ka-Kb 0.02 0.11 0.24 0.02 0.02 Sb-Sa 94 92 88 94 94 (Sb-Sa) × Wt 18800 18492 17512 18800 18894 (Evaluation result) Grip at high speed 103 109 117 105 108 running Durability 111 113 117 110 106 Comprehensive evaluation 214 222 234 215 214

TABLE-US-00004 TABLE 4 Comparative example No. 2-1 2-2 2-3 2-4 2-5 SIZE 195/65R17 195/40R20 195/65R17 195/65R17 195/65R17 Rubber composition with — — A B C high thermal conductivity (Parameter) Dt(mm) 686 664 687 685 686 V(mm.sup.3) 44856521 28719183 44849025 44417998 45079688 Wt(mm) 201 200 200 200 202 Ht(mm) 126 77 127 128 127 Dt-2 × Ht(mm) 434 510 433 429 432 (Dt.sup.2 × π/4)/Wt 1839 1731 1853 1843 1830 (V + 1.5 × 10.sup.7)/Wt 297794 218596 299245 297090 297424 (V + 2.0 × 10.sup.7)/Wt 322669 243596 324245 322090 322177 (V + 2.5 × 10.sup.7)/Wt 347545 268596 349245 347090 346929 Aspect ratio (%) 63 39 64 63 63 Ka-Kb — — 0.02 0.11 0.24 Sb-Sa — — 94 92 88 (Sb-Sa) × Wt — — 18800 18400 17776 (Evaluation result) Grip at high-speed 91 93 97 98 100 running Durability 90 92 93 94 100 Comprehensive evaluation 181 185 190 192 200

[Experiment 3]

[0255] In this experiment, 225 size tires were prepared and evaluated.

[0256] After manufacturing test tires of Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-5 shown in Tables 5 and 6 in the same manner as in Experiment 1, each parameter was obtained. Then, similarly, a performance evaluation test was performed and evaluated. In this experiment, the result in Comparative Example 3-5 was set as 100 for evaluation. The results of each evaluation are shown in Tables 5 and 6.

TABLE-US-00005 TABLE 5 Example No. 3-1 3-2 3-3 3-4 3-5 SIZE 225/35R22 225/35R22 225/35R22 225/50R20 225/40R21 Rubber composition with A B C A A high thermal conductivity (Parameter) Dt(mm) 716 717 718 735 713 V(mm.sup.3) 36200312 36300653 36878037 51413226 40613053 Wt(mm) 230 229 231 232 231 Ht(mm) 80 79 81 114 91 Dt-2 × Ht(mm) 556 559 556 507 531 (Dt.sup.2 × π/4)/Wt 1751 1763 1753 1829 1728 (V + 1.5 × 10.sup.7)/Wt 222610 224020 224580 286264 240749 (V + 2.0 × 10.sup.7)/Wt 244349 245854 246225 307816 262394 (V + 2.5 × 10.sup.7)/Wt 266088 267688 267870 329367 284039 Aspect ratio (%) 34 35 34 49 39 Ka-Kb 0.02 0.11 0.24 0.02 0.02 Sb-Sa 94 92 88 94 94 (Sb-Sa) × Wt 21620 21068 20328 21808 21714 (Evaluation result) Grip at high speed 107 107 107 107 107 running Durability 110 112 116 107 105 Comprehensive evaluation 212 219 231 211 212

TABLE-US-00006 TABLE 6 Comparative example No. 3-1 3-2 3-3 3-4 3-5 SIZE 225/60R20 225/50R20 225/60R20 225/60R20 225/60R20 Rubber composition with — — A B C high thermal conductivity (Parameter) Dt(mm) 779 734 777 778 777 V(mm.sup.3) 63003628 51145556 62169986 61904251 61898502 Wt(mm) 230 232 229 227 228 Ht(mm) 136 114 134 135 136 Dt-2 × Ht(mm) 507 506 509 508 505 (Dt.sup.2 × π/4)/Wt 2072 1824 2071 2094 2080 (V + 1.5 × 10.sup.7)/Wt 339146 285110 336987 338785 337274 (V + 2.0 × 10.sup.7)/Wt 360885 306662 358821 360812 359204 (V + 2.5 × 10.sup.7)/Wt 382624 328214 380655 382838 381134 Aspect ratio (%) 59 49 59 59 59 Ka-Kb — — 0.02 0.11 0.24 Sb-Sa — — 94 92 88 (Sb-Sa) × Wt — — 21526 20884 20064 (Evaluation result) Grip at high speed 92 93 98 99 100 running Durability 89 91 92 95 100 Comprehensive evaluation 181 184 190 194 200

[Summary of Experiments 1 to 3]

[0257] From the results of Experiments 1 to 3 (Tables 1 to 6), it was found that, when the above (formula 1) and (formula 2) are satisfied in any size tire of 175 size, 195 size, and 225 size, a pneumatic tire with sufficiently improved grip performance and durability during high-speed running can be provided.

[0258] Then, it turns out that, by satisfying each of the requirements specified in claim 2 and thereafter, it is possible to provide a tire with further improved grip and durability at high-speed running.

[0259] On the other hand, it turns out that, when either (formula 1) or (formula 2) is not satisfied, the grip and durability during high-speed running cannot be sufficiently improved.

[Experiment 4]

[0260] Next, three types of tires (Examples 4-1 to 4-3) with no significant difference in the relationship between the virtual volume V and the cross-sectional width Wt were produced with the same formulation and evaluated in the same manner. Here, in addition to evaluation of grip and durability during high-speed running, fuel efficiency was also evaluated.

[0261] Specifically, each test tire was installed on all wheels of a vehicle (domestic FF vehicle, displacement 2000cc), and after filling air so that the internal pressure was 250 kPa, the tire was run on a dry road test course. After making 10 km laps at a speed of 100 km/h, the accelerator was released, and the distance from when the accelerator was turned off until the vehicle stopped was measured as the rolling resistance during high-speed running. The larger the value, the longer the distance from when the accelerator is released until the vehicle stops, and the smaller the rolling resistance in the steady state.

[0262] Next, taking the result in Example 4-3 as 100, it was indexed based on the following formula to evaluate fuel efficiency. The larger the value, the smaller the rolling resistance in the steady state and the better the fuel efficiency. The results of evaluation are shown in Table 7.

Low fuel consumption=[(measurement result of test tire)/(measurement result of Example 4-3)]×100

[0263] Then, as in Experiments 1 to 3, each evaluation result was totaled to obtain a comprehensive evaluation. The results of each evaluation are shown in Table 7.

TABLE-US-00007 TABLE 7 Example No. 4-1 4-2 4-3 SIZE 175/55R18 195/50R19 225/45R20 Rubber composition with D D D high thermal conductivity (Parameter) Dt(mm) 650 678 709 V(mm.sup.3) 30346008 35622714 43419514 Wt(mm) 181 200 226 Ht(mm) 97 98 100 Dt-2 × Ht(mm) 456 482 509 (Dt.sup.2 × π/4)/Wt 1833 1805 1747 (V + 1.5 × 10.sup.7)/Wt 250530 253114 258493 (V + 2.0 × 10.sup.7)/Wt 278155 278114 280617 (V + 2.5 × 10.sup.7)/Wt 305779 303114 302741 Aspect ratio (%) 53 49 44 Ka-Kb 0.08 0.08 0.08 Sb-Sa 90 90 90 (Sb-Sa) × Wt 16290 18000 20340 (Evaluation result) Grip at high-speed running 109 104 100 Durability 105 102 100 Fuel efficiency 110 105 100 Comprehensive evaluation 324 311 300

[0264] From Table 7, when there is no large difference in the relationship between the virtual volume V and the cross-sectional width Wt, as the cross-sectional width Wt becomes smaller as from less than 205 mm to less than 200 mm, and as the aspect ratio increases, it was found that all of the grip during high-speed running, durability and fuel efficiency were improved, and a remarkable effect was exhibited.

[0265] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equal range as the present invention.