JP2011025798A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which is made compatible in the reduction of the weight of a tire and an improvement of the durability of a belt by reducing the weight of the tire and suppressing the occurrence of belt edge separation and a fatigue failure of a code. <P>SOLUTION: A first belt layer 5a that is a first layer of the belt and a second belt layer 5b that is a second layer are formed by embedding bundles of nonwoven monofilament codes 6 into coating rubber 8. Each bundle includes eight to twelve nonwoven monofilament codes 6 with filament diameters of 0.15 to 0.22 mm, and the bundles are arranged along a belt width axis. An interval "w" between the monofilament code bundles along the belt width axis ranges from 0.4 to 1.2 mm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pneumatic tire (hereinafter, also simply referred to as “tire”), and more particularly, a pneumatic tire that achieves both durability and light weight by improving a belt cord, and more particularly, a pneumatic tire suitable for a passenger car. Regarding tires.

  In recent years, there has been an increasing demand for reducing the weight of tires in order to improve the fuel efficiency of automobiles. When considering weight reduction in a belt portion using a conventional twisted steel cord, assuming that a certain level of tensile strength is ensured, the steel belt layer can only be thinned.

  From such a viewpoint, a technique for using a metal monofilament as a cord for a belt without twisting has been developed, and various proposals have been made so far. For example, in Patent Document 1, for the purpose of improving fuel consumption and riding comfort, a bundle of three or four metal wires (monofilaments) arranged side by side in the width direction of the belt without being twisted is embedded in rubber as a unit. A pneumatic radial tire having a belt formed as described above has been proposed. Further, in Patent Document 2, in order to respond to the need for weight reduction of tires and to solve problems such as a decrease in durability due to breakage of metal wires, the belt layer is made of a metal monofilament in the belt ply width direction. A pneumatic radial tire composed of three belt plies arranged side by side and embedded in a coated rubber is disclosed.

  Further, Patent Document 3 discloses a second belt layer as a second layer in order to obtain a pneumatic radial tire that suppresses belt end separation and achieves both improvement in belt durability and reduction in tire weight. A technique is disclosed in which the gauge between the monofilaments of the first belt layer and the second belt layer at the end is 1.3 to 3.0 times the gauge at the center of the tire. Furthermore, in Patent Document 4, a monofilament cord having a filament diameter of 0.18 to 0.26 mm is applied to two belt layers as a unit, and a bundle of 5 to 7 is used as a unit. A pneumatic tire is disclosed in which the gauge of the rubber layer between the monofilament cords of the first belt layer and the second belt layer at the end is 1.3 to 3.0 times the gauge at the tire center.

JP-A-11-208210 (Claims etc.) JP 2001-334810 A (Claims etc.) JP 2005-349999 A (Claims etc.) JP 2007-302203 A (Claims etc.)

  As proposed so far, by applying a monofilament cord to the belt, even when the gauge between the cord centers is designed together, the rubber gauge between the layers can be secured, and the interlayer gauge is designed together By doing so, it is possible to reduce the weight of the tire, but on the other hand, there are the following problems. First, since the cord interval in the tire radial direction is close, there is a problem that cracks from adjacent cords are likely to progress. Next, since the amount of steel cord used in the belt surface is large, the interlaminar shear strain increases. As a result of such problems, belt edge separation (BES) is more likely to occur in belts using monofilament cords than in the case of using ordinary twist cords. Although the occurrence of BES is suppressed by increasing the gauge of the coating rubber, it naturally increases the weight, which is contrary to the intended weight reduction of the tire.

  According to the technique described in Patent Document 3 above, in a tire using a monofilament cord between belts, distortion at the belt end is suppressed by increasing the gauge of the belt-to-belt rubber at the belt end that is the starting point of the BES. Thus, it is possible to improve the BES resistance. Further, according to the technique described in Patent Document 4, in addition to reducing the tire weight by applying a monofilament cord to the belt, in addition to optimizing the gauge of the rubber layer between the cords, the filament diameter of the cord and the cord By limiting the number to a predetermined range, it becomes possible to more effectively suppress the occurrence of BES, and as a result, a pneumatic tire that achieves both high weight reduction of tire weight and improvement of belt durability. It is possible to realize. However, if the treat gauge is made thinner for the purpose of further weight reduction, in the prior art, the shear strain between layers increases, and it may be difficult to ensure BES resistance. Therefore, in order to realize further weight reduction, a technique for improving the code arrangement condition and reliably obtaining BES resistance is required.

  In addition, buckling occurs on the inner surface of the tire when the figure 8 turns. At this time, if the buckling strain is large, there is a concern about fatigue failure of the steel cord. In particular, as the treat gauge of the belt becomes thinner, the out-of-plane rigidity decreases, and the buckling distortion increases. Therefore, when reducing the weight of the tire, a design that suppresses belt buckling distortion is necessary in order to suppress fatigue failure of the steel cord.

  Accordingly, the object of the present invention is to eliminate the problems in the prior art described above and reduce the tire weight while suppressing the occurrence of belt edge separation and the fatigue failure of the cord, thereby reducing the weight of the tire and the durability of the belt. The object of the present invention is to provide a pneumatic tire that balances the above with a higher degree.

  Although it is possible to reduce the tire weight by applying the monofilament cord to the belt, there is a concern about the influence on the belt durability (BES property and cord fatigue property). As a result of diligent study, the present inventors have constrained the belt diameter and the number of cords to a predetermined range, and the distance in the belt width direction between monofilament cord bundles, that is, the cord interval, is within a predetermined range. It has been found that the occurrence of belt edge separation and the fatigue failure of steel cords can be more effectively suppressed.

That is, according to the present invention, a carcass composed of at least one radial carcass layer straddling a pair of left and right bead cores in a toroid shape, and a grounding portion is disposed on the outer side in the tire radial direction of the crown region of the carcass. In a pneumatic tire comprising: a tread portion; and a belt composed of at least two belt layers that are disposed between the tread portion and the crown region of the carcass to form a reinforcing portion.
A bundle of 8 to 12 monofilament cords having a filament diameter of 0.15 to 0.22 mm is formed on both the first belt layer of the first layer and the second belt layer of the second layer. The unit is characterized in that it is juxtaposed in the belt width direction and embedded in the coating rubber, and the belt width direction distance between the monofilament cord bundles is in the range of 0.4 to 1.2 mm. is there.

  In the present invention, the distance between the monofilament cords of the first belt layer and the second belt layer at the end portion of the second belt layer is such that the distance between the monofilament cords of the first belt layer and the second belt layer in the tire central portion is The distance is 1.3 to 4.0 times the distance, and the distance between the cord centers of the monofilament cords of the first belt layer and the second belt layer in the center of the tire is in the range of 0.60 to 1.10 mm. It is preferable that it exists in.

  Further, an inter-belt rubber is disposed between the first belt layer and the second belt layer at the end of the second belt layer, and the elastic modulus of the inter-belt rubber is 1.02 to the elastic modulus of the coating rubber. It is preferably 2.0 times. In this case, tan δ (25 ° C.) of the rubber between belts is preferably 0.20 or less, and more preferably, tan δ (25 ° C.) of the rubber between belts is tan δ (25 ° C.) of the coating rubber. It is 0.85-0.98 times. Further, it is preferable that 0.5 to 3.0 parts by mass of bismaleimide is blended with the rubber between belts with respect to 100 parts by mass of the rubber component.

  According to the present invention, the filament diameter and the number of cords of the monofilament cord are limited to a predetermined range, and the belt width direction distance between the monofilament cord bundles, that is, the cord interval is regulated to a predetermined range, thereby generating belt edge separation and The fatigue failure of the steel cord can be more effectively suppressed. As a result, while reducing the weight of the tire, the occurrence of belt edge separation and the fatigue breakage of the cord are suppressed, and a pneumatic tire that achieves both a high level of tire lightness and belt durability is realized. Became possible.

1 is a half sectional view showing a pneumatic tire according to a preferred example of the present invention. FIG. 4 is an enlarged partial cross-sectional view showing the vicinity of an end of a belt.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
FIG. 1 shows a pneumatic tire according to an embodiment of the present invention. The illustrated tire includes a tread portion 1 that is disposed in a crown region of the carcass and forms a ground contact portion, and a pair of sidewall portions 2 that extend continuously inward in the tire radial direction on both sides of the tread portion 1; A bead portion 3 is provided on the inner peripheral side of each sidewall portion 2.

  The tread portion 1, the sidewall portion 2, and the bead portion 3 are reinforced by a carcass 4 including a single radial carcass layer extending in a toroid shape from one bead portion 3 to the other bead portion 3. The tread portion 1 has at least two layers disposed in the tire radial direction outside of the crown region of the carcass 4, which will be described in detail below, and in the illustrated example, two layers of the first belt layer 5a and the second belt layer 5b. It is reinforced by a belt consisting of Here, the radial carcass layer of the carcass 4 may be a plurality of layers, and an organic fiber cord extending in a direction substantially orthogonal to the tire circumferential direction, for example, an angle of 70 to 90 ° can be suitably used.

  In FIG. 2, the cross section of the width direction of the belt edge part in the tire of this invention is expanded and shown. As shown in the figure, in the present invention, the first belt layer 5a of the first layer and the second belt layer 5b of the second layer are both monofilament cords 6 having a filament diameter of 0.15 to 0.22 mm. 8 to 12, in the illustrated example, the unit is a bundle of 8 bundles, and is juxtaposed in the belt width direction and embedded in the coating rubber 8. By using a monofilament cord having a small filament diameter of 0.15 to 0.22 mm to ensure belt foldability, the number of bundles is set to 8 to 12 to ensure rigidity. Here, if the filament diameter is less than 0.15 mm, the total belt strength is insufficient, and the buckling wavelength when the figure 8 is turned is shortened, resulting in a large surface distortion and belt folding. Results inferior to. On the other hand, if it exceeds 0.22 mm, the surface distortion becomes large, and the result is also inferior in belt foldability. Further, when the driving distance is increased and the cord interval is reduced, the steel amount increases and the tire weight increases.

  In the present invention, the distance in the belt width direction between the monofilament cord bundles, that is, the cord interval needs to be in the range of 0.4 to 1.2 mm. When the cord interval is less than 0.4 mm, the crack between the cord and the cord tends to be connected, and the BES property is deteriorated. On the other hand, if the cord interval exceeds 1.2 mm, cracks easily develop in the cord direction.

In the present invention, the distance H _E between the monofilament cord 6 between the first belt layer 5a and the second belt layer 5b in the second belt layer 5b ends, the first belt layer 5a in the tire center portion and the second belt layer 5b distance _{H C} between monofilament cord 6 with, it is preferable to 1.3 to 4.0 times. Distance H _E between the monofilament cord 6 in the second belt layer 5b ends, if it is 1.3 times less than the distance H _C between the monofilament cord 6 in the tire center portion, suppression of the belt end separation is no longer sufficient. On the other hand, when it exceeds 4.0 times the inter-cord distance H _C in the tire center portion, weight of the tire is not sufficient.

Further, the cord center distance h _C of the monofilament cord 6 between the first belt layer 5a and the second belt layer 5b in the center of the tire is preferably 0.60 to 1.10 mm, more preferably 0.70. It is in the range of 1.00 mm, especially 0.80 to 0.98 mm. If the distance h _C between the cord centers in the tire central portion is less than 0.6 mm, the belt buckling distortion increases and there is a concern about the occurrence of fatigue failure. On the other hand, if it exceeds 1.10 mm, the tire mass will increase.

Here, the distance H _E between the monofilament cord 6 between the first belt layer 5a and the second belt layer 5b at the belt ends, as shown, a first belt layer 5a in the second belt layer 5b ends the By arranging the inter-belt rubber 7 between the two belt layers 5b, it can be adjusted appropriately. In other words, by applying a thick gauge inter-belt rubber at the belt end to a monofilament cord coated with a thin gauge, the effect of suppressing the progress of cracks can be obtained, and both weight reduction of the tire and belt durability can be achieved. it can.

  The elastic modulus of the inter-belt rubber 7 is preferably 1.02 to 2.0 times, particularly 1.1 to 1.8 times that of the belt coating rubber 8. When the elastic modulus is within the range of the elastic modulus, the distortion at the belt end is satisfactorily suppressed, and the weight reduction of the tire and the durability of the belt can be achieved at a high level.

  Further, the tangent loss tan δ (25 ° C.) of the inter-belt rubber 7 is preferably 0.20 or less, and in particular, 0.85 to 0.98 times the tan δ (25 ° C.) of the belt coating rubber 8. By using such a low-loss rubber as the belt-to-belt rubber 7, distortion at the belt end is suppressed and an increase in tire temperature is suppressed.

（式中、Ｒは炭素数６〜１８の芳香族基、または炭素数７〜２４のアルキル芳香族基を表し、ｘおよびｙは０〜３のいずれかの整数をそれぞれ独立に表す）で表されるビスマレイミドを好適に用いることができる。具体的には例えば、Ｎ，Ｎ’−１，２−フェニレンビスマレイミド、Ｎ，Ｎ’−１，３−フェニレンビスマレイミド、Ｎ，Ｎ’−１，４−フェニレンビスマレイミド、Ｎ，Ｎ’−（４，４’−ジフェニルメタン）ビスマレイミド、２，２−ビス［４−（４−マレイミドフェノキシ）フェニル］プロパン、ビス（３−エチル−５−メチル−４−マレイミドフェニル］メタン等を例示することができ、特に好ましく
は、Ｎ，Ｎ’−（４，４’−ジフェニルメタン）ビスマレイミドであり、ゴム配合中に、これらを１種以上含むことができる。 Furthermore, in this invention, it is preferable to mix | blend 0.5-3.0 mass parts with bismaleimide with respect to 100 mass parts of rubber components in the rubber | gum 7 between belts. Thereby, the tangent loss tan δ (25 ° C.) can be kept low while improving the elastic modulus. As bismaleimide, the following general formula (1),

(Wherein R represents an aromatic group having 6 to 18 carbon atoms or an alkyl aromatic group having 7 to 24 carbon atoms, and x and y each independently represents an integer of 0 to 3) The bismaleimide prepared can be preferably used. Specifically, for example, N, N′-1,2-phenylenebismaleimide, N, N′-1,3-phenylenebismaleimide, N, N′-1,4-phenylenebismaleimide, N, N′- Illustrate (4,4′-diphenylmethane) bismaleimide, 2,2-bis [4- (4-maleimidophenoxy) phenyl] propane, bis (3-ethyl-5-methyl-4-maleimidophenyl] methane, etc. Particularly preferred is N, N ′-(4,4′-diphenylmethane) bismaleimide, and one or more of these can be included in the rubber compounding.

  The present invention relates to an improvement in the belt structure of a tire, and the structure and material of other members constituting the tire are not particularly limited, and a known structure and material can be adopted. . For example, the first belt layer 5a and the second belt layer 5b constituting the belt have a cord driving angle of preferably 10 ° to 30 ° with respect to the tire circumferential direction, and are arranged so as to cross each other.

Hereinafter, the present invention will be described in more detail with reference to examples.
A pneumatic tire having a structure including a two-layer steel belt was produced according to the conditions shown in the following table. The tire size was 185 / 70R14, and the driving angles of the monofilament cords 6 of the first belt layer 5a and the second belt layer 5b were + 22 ° and −22 °, respectively, with respect to the tire circumferential direction. Moreover, as rubber compounding of the rubber 7 between belts, natural rubber 100 mass parts, carbon black (N330) 50 mass parts, cobalt salt (cobalt naphthenate) 1.0 mass part, zinc oxide 10 mass parts, vulcanization accelerator (N, N′-dicyclohexyl-2-benzothiazolylsulfenamide, manufactured by Ouchi Shinsei Chemical Industry Co., Ltd., Noxeller DZ) 1.0 part by mass, sulfur 6.0 parts by mass, bismaleimide (N, N ′ -(4,4'-diphenylmethane bismaleimide)) What consists of 2.0 mass parts was used. The elastic modulus of the inter-belt rubber 7 was 1.2 times that of the belt coating rubber 8. Further, the tan δ (25 ° C.) of the inter-belt rubber 7 was 0.15, which was 0.90 times the tan δ (25 ° C.) of the belt coating rubber 8.

  The tires of the respective examples and comparative examples obtained were evaluated for the degree of weight increase (weight difference) with reference to Comparative Example 1. Further, the BES property and the cord fatigue property were evaluated according to the following. The results are also shown in the table below.

(Evaluation of BES properties)
Each test tire is mounted on a regular rim prescribed by JATMA, loaded with twice the normal load, filled with 210 kPa of internal pressure, traveled for 20,000 km, the tire was dissected, and the belt layer The length (separation length) of the crack generated at the end was measured. The crack length of each test tire was indicated by an index with the crack length of the tire of Comparative Example 1 as 100. The smaller the index value, the better the BES property.

(Evaluation of cord fatigue)
A vehicle equipped with an autopilot capable of running a figure 8 by assembling each test tire on a regular rim prescribed by JATMA, applying a load 1.05 times the normal load, filling an internal pressure of 100 kPa Then, after running the figure 8 turning test course at a turning acceleration of 0.7 G, a speed of 25 km / h and 300 laps, the tires were dissected and evaluated for belt breakage. The cord breakage rate of each test tire was shown as an index with the tire of Comparative Example 1 as 100. The smaller the index value, the better the cord fatigue.

＊１）軽量性（重量減が大きいほど良好） ◎：−２００ｇ以上、○：−１００ｇ以上−２００ｇ未満、△：＋０ｇ以上−１００ｇ未満、×：＋０ｇ未満
＊２）ＢＥＳ性（ＢＥＳ性の指数が小さいほど良好）◎：８０以下、○：８０を超え１００以下、△：１００を超え１２０以下、×：１２０を超える
＊３）疲労性（疲労性の指数が小さいほど良好）◎：７０以下、○：７０を超え１００以下、△：１００を超え１３０以下、×：１３０を超える
＊４）総合評価 ◎：（性能大幅改良）軽量性、ＢＥＳ性および疲労性がすべて◎，○：（性能改良）×がなく、◎を２つ含むか、または◎１つであとは○，△：（性能同等）○または△のみ，×：（性能悪化）×がある

* 1) Light weight (The better the weight loss, the better) ◎: -200g or more, ○: -100g or more but less than -200g, △: + 0g or more but less than -100g, X: less than + 0g * 2) BES property (BES property index) ): 80 or less, ◯: more than 80 and 100 or less, Δ: more than 100 and 120 or less, x: more than 120 * 3) Fatigue (the smaller the fatigue index, the better) ◎: 70 or less , ○: More than 70 and less than or equal to 100, Δ: More than 100 and less than or equal to 130, ×: More than 130 * 4) Overall evaluation ◎: (Performance greatly improved) ◎, ○: (Performance) (Improved) No x, 2 included ◎, or ◎ 1 means ○, △: (Equivalent performance) ○ or △ only, X: (Performance deteriorated) ×

  As shown in the above table, in each of the tires of each example in which a monofilament cord is applied to each of the two belt layers, the filament diameter and the number of cords of the cord are limited to a predetermined range, and the cord interval is regulated to a predetermined range. It was confirmed that all of the lightness, BES property and cord fatigue were improved as compared with Comparative Example 1 using a conventional twisted cord. On the other hand, although the tires of Comparative Examples 2 to 7 that use a monofilament cord but do not satisfy the cord conditions according to the present invention are improved to the same or better in terms of lightness and fatigue, It was insufficient.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass 5a 1st belt layer 5b 2nd belt layer 6 Monofilament cord 7 Belt rubber 8 Belt coating rubber

Claims (6)

A carcass composed of at least one radial carcass layer straddling a pair of left and right bead cores in a toroidal shape, a tread portion disposed on the outer side in the tire radial direction of the crown region of the carcass and forming a ground contact portion; and the tread In a pneumatic tire comprising: a belt composed of at least two belt layers, which is disposed between a portion and a crown region of the carcass to form a reinforcing portion,
A bundle of 8 to 12 monofilament cords having a filament diameter of 0.15 to 0.22 mm is formed on both the first belt layer of the first layer and the second belt layer of the second layer. Pneumatic, characterized in that the unit is juxtaposed in the belt width direction and embedded in the coating rubber, and the belt width direction distance between the monofilament cord bundles is in the range of 0.4 to 1.2 mm tire.   The distance between the monofilament cords of the first belt layer and the second belt layer at the end portion of the second belt layer is 1.3 of the distance between the monofilament cords of the first belt layer and the second belt layer at the center of the tire. The distance between cord centers of the monofilament cords of the first belt layer and the second belt layer in the center of the tire is in the range of 0.60 to 1.10 mm. The described pneumatic tire.   The inter-belt rubber is disposed between the first belt layer and the second belt layer at the end of the second belt layer, and the elastic modulus of the inter-belt rubber is 1.02 to 2. The pneumatic tire according to claim 1 or 2, wherein the pneumatic tire is 0 times.   The pneumatic tire according to claim 3, wherein tan δ (25 ° C) of the inter-belt rubber is 0.20 or less.   The pneumatic tire according to claim 3 or 4, wherein tan δ (25 ° C) of the inter-belt rubber is 0.85 to 0.98 times the tan δ (25 ° C) of the coating rubber.   The pneumatic tire according to any one of claims 3 to 5, wherein bismaleimide is blended in the rubber between the belts in an amount of 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the rubber component.

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