PNEUMATIC SAFETY TIRE

Abstract: The present invention provides a pneumatic safety tire comprising a pair of left and right bead cores, a carcass layer, a multi-layer belt portion, a tread portion, and a pair of side wall portions disposed at the left and right of said tread portion, wherein at least one sheet of a rubber-filament fiber composite formed from filament fibers and a rubber component is disposed at said side wall portions in a vicinity of said carcass layer. The safety tire of the present invention maintains the properties during ordinary use under the inflated condition at high levels, has a light weight, and shows remarkably improved properties during use under the run-flat condition.

Description: The present invention relates to a pneumatic safety tire which is reinforced at the side parts thereof and enables satisfactory use under the run-flat condition. As tires which are pneumatic and can be used under the run-flat condition (these tires are referred to as pneumatic safety tires) or tire wheels having the same property, there are known tires of an internal wheel type in which an annular internal wheel made of a metal or a synthetic resin is attached to a rim in the pneumatic chamber of the tire and tires of a side reinforced type in which portions of side walls from bead parts to shoulder areas are reinforced by layers made of relatively hard rubber having a crescent-shaped cross-section disposed at an inner side of a carcass (Structure I in Figure 2). Between tires of these two types, tires of the internal wheel type have been regarded as useful to some degree for vehicles for transportation of goods and military vehicles which are not particularly required to have a good riding quality, and tires of the side reinforced type have been regarded as useful to some degree for passenger cars which are loaded with a relatively light weight and are required to have a good riding quality. In a tire of the side reinforced type, the tire is reinforced by a relatively hard reinforcing rubber layer having a crescent-shaped cross-section disposed at the inner side of the side wall in such a manner that an end portion of the reinforcing rubber layer overlaps belt layers, with the carcass being between the belt layers and the reinforcing layer, and another end portion overlaps a rubber filler. When the tire is punctured during use and the contained air is lost, the weight is supported by the rigidity which is inherent to the side walls reinforced with the reinforcing rubber layer, and the vehicle can be driven in a specified distance under the run-flat condition although the speed of the vehicle must be somewhat decreased. As described above, various safety tires of the side reinforced type have heretofore been proposed. However, most of the proposed tires are used as ultra-low profile high performance tires, i.e. tires having a low aspect ratio and used for vehicles having a relatively small axle load, such as sports cars, but those tires do not show sufficient durability under the run-flat condition. The aspect ratio is expressed as {(height of a tire)/(width of a tire)}×100under the condition that the tire is attached to a rim, and an ultra-low profile tire is a tire having an aspect ratio less than 60%, such as 30 to 40%. However, as safety is required increasingly in recent years, safety tires are required also for general use tires for passenger cars which have an aspect ratio of 60% or more. Although a load applied to a tire is relatively small in the case of a general use tire for passenger cars, the load per one tire may be as large as 500 kgf in the case of larger passenger cars. In such a case, deformation of side walls under the condition of puncture is increased, and the side walls are completely buckled under a dynamic load which is formed by driving and is several times as large as that under the normal condition. The buckling repeatedly takes place during the driving. As a result, the bead part in the side wall is pushed up by a flange of the rim, and a covering rubber and a turned-up portion of the carcass which are squeezed between the curved flange and the rubber filler melt or fracture by heat. When this occurs, the tire cannot be used any more even after the part which caused the puncture has been repaired. As the result of intensive studies comparing ultra-low profile high performance tires and general use tires for passenger cars, the following differences have been found. a. Because general use tires for passenger cars have larger heights than those of ultra-low profile high performance tires, general use tires show larger deflection under load. b. Because general use passenger cars generally have larger weights than those of sports cars to which ultra-low profile high performance tires are attached, general use passenger cars cause larger load to the tires. Because of the characteristics a. and b. described above, the temperature within a tire is not very high when an ultra-low profile high performance safety tire is used under the run-flat condition. In contrast, the temperature within a tire reaches a temperature as high as or higher than 200°C when a general use size safety tire for passenger cars is used under the run-flat condition. Therefore, it must be considered well that the temperature within a tire during use is different depending on the type of the tire. On the other hand, decrease in weight of a tire is strongly required in order to decrease the fuel consumption of a vehicle. To decrease weight of a tire, thickness of a side wall of the tire tends to be decreased more. It is required that use under the run-flat condition, i.e. at the internal pressure of the tire of 0 kg/cm 2 , must be possible, and at the same time satisfactory properties during ordinary use under an inflated condition are naturally required. Attention is also drawn to the disclosure of US-A-4 067 372, which corresponds to the preamble of claim 1. The first object of the present invention is to provide a pneumatic safety tire having an aspect ratio less than 60% and, exhibiting a small deflection because of its small height and use thereof under a small applied weight, maintaining properties during ordinary use under an inflated condition at high levels, enabling decrease in the weighty, and showing remarkably improved properties under the run-flat condition in comparison with those of conventional safety tires having a rubber reinforcing layer. The second object of the present invention is to provide a pneumatic safety tire having an aspect ratio of 60% or more and, exhibiting a large deflection because of a large height, and use thereof under a large applied weight, maintaining properties during ordinary use under an inflated condition at high levels, enabling decrease in the weight, and showing remarkably improved properties under the run-flat condition in comparison with those of conventional safety tires having a rubber reinforcing layer. As the result of extensive studies conducted by the present inventors to solve the above problems, particularly on the relation between the side wall portion of a tire and the properties during use under the run-flat condition, it was found that the above objects can be achieved by a tire comprising the features of claim 1. A layer of a fiber reinforced component is prepared by covering specific filament fibers with rubber to form an integrated layer (a rubber-filament fiber composite) and disposed at the side wall in a vicinity of a carcass layer and other means as described in the following. An embodiment of the pneumatic safety tire of the present invention relates to a low profile safety tire which has an aspect ratio less than 60% and shows a small deflection because it has a small height and is used under a small applied load (referred to as an embodiment of the low profile tire). Another embodiment of the pneumatic safety tire of the present invention relates to a general use safety tire for passenger cars which has an aspect ratio of 60% or more and shows a large deflection because it has a large height and is used under a large applied load (referred to as an embodiment of the general use tire). With respect to both the embodiment of the low profile tire and the embodiment of the general use tire, a pneumatic safety tire (1) of the present invention comprises: a pair of left and right ring-shaped bead cores; a carcass layer formed from one or more plies in which a plurality of cords disposed parallel to each other are embedded in a covering rubber, both end portions of said carcass layer being folded over said bead cores and turned up such that said carcass layer is formed in an annular shape; a multi-layer belt portion disposed at an outer side of said carcass layer in a radial direction of the tire; an annular tread portion disposed at an outer side of said belt portion in the radial direction of the tire; a pair of side wall portions disposed at the left and right of said tread portion; and a rubber reinforcing layer having a crescent-shaped cross-section disposed at an inner side of said carcass layer; wherein at least one sheet of a rubber-filament fiber composite formed from a rubber component and a non-woven fabric as filament fiber having a weight per area of 10 to 300 g/m 2 , is disposed at said side wall portions in a vicinity of said carcass layer. Preferred embodiments of the low profile tire of the present invention provide: (2) A pneumatic safety tire described in (1), wherein an aspect ratio of said tire is less than 60%, and at least one sheet of said rubber-filament fiber composite is disposed at said side wall portions in a vicinity of said carcass layer; (3) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed at an inner side of said carcass layer; (4) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed both at an inner side of said carcass layer and between said side wall portions and an outer surface of said carcass layer; (5) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed between said side wall portions and an outer surface of said carcass layer, and a rubber reinforcing layer having a crescent-shaped cross-section is disposed at an inner side of said carcass layer; (6) A pneumatic safety tire described in (2), wherein said rubber-filament fiber composite is disposed at an inner surface of a rubber reinforcing layer having a crescent-shaped cross-section which is disposed at an inner side of said carcass layer; and (7) A pneumatic safety tire described in (2), wherein 4 to 50% by weight of said rubber-filament fiber composite is the filament fibers. Preferred embodiments of the general use tire of the present invention provide: (8) A pneumatic safety tire described in (1), wherein an aspect ratio of said tire is 60% or more, and at least one sheet of said rubber-filament fiber composite is disposed at said side wall portions in a vicinity of said carcass layer; (9) A pneumatic safety tire described in (8), wherein an aspect ratio of said tire is 60% or more, a rubber reinforcing layer having a crescent-shaped cross-section is disposed at an inner side of said carcass layer, and at least one sheet of said rubber-filament fiber composite is disposed at an inner side of said rubber reinforcing layer which is disposed at the inside of said carcass layer; (10) A pneumatic safety tire described in (9), wherein at least one down carcass layer is additionally disposed between said side wall portions and an outer surface of said carcass layer; (11) A pneumatic safety tire described in (9), wherein in addition to being disposed at the inner side of said rubber reinforcing layer, said rubber-filament fiber composite is also disposed between said side wall portions and an outer surface of said carcass layer; (12) A pneumatic safety tire described in (11), wherein at least one down carcass layer is disposed between the outer surface of said carcass layer and said rubber-filament fiber composite which is disposed at the outer side of said carcass layer in the radial direction of said tire; (13) A pneumatic safety tire described in (8), wherein an aspect ratio of said tire is 60% or more, a rubber reinforcing layer having a crescent-shaped cross-section is disposed at an inner side of said carcass layer, and at least one sheet of said rubber-filament fiber composite is disposed between said side wall portions and an outer surface of said carcass layer; (14) A pneumatic safety tire described in (13), wherein at least one down carcass layer is additionally disposed between the outer surface of said carcass layer and said rubber-filament fiber composite which is disposed at the outer side of said carcass layer in the radial direction of said tire; (15) A pneumatic safety tire described in (8), wherein 4 to 50% by weight of said rubber-filament fiber composite is the filament fibers, and the filament fibers are fibers which do not exhibit meltability when the tire is used under a run-flat condition; (16) A pneumatic safety tire described in (8), wherein said rubber-filament fiber composite is formed from a rubber and a non-woven fabric having a weight per area of 10 to 300 g/m 2 , and the filament fibers do not exhibit meltability when the tire is used under a run-flat condition; (17) A pneumatic safety tire described in (8), wherein the filament fibers in said rubber-filament fiber composite do not exhibit meltability at 270°C or lower; and (18) A pneumatic safety tire described in (17), wherein the filament fibers are at least one type of fibers. selected from the group consisting of polyester fibers, aramide fibers, polyimide fibers, carbon fibers, glass fibers, and steel fibers; (19) A pneumatic safety tire described in (1), wherein said rubber-filament fiber composite is formed from a rubber component and filaments having a diameter or a maximum cross-sectional dimension of 0.0001 to 0.1 mm and a length of 8 mm or more, and said rubber filament fiber composite has a thickness of 0.05 to 2.0 mm, is also provided. The invention will be further described with reference to the accompanying drawings, wherein: Figure 1 shows a schematic sectional view of a pneumatic safety tire as an example of the embodiment of the low profile tire, which does not however include a crescent-shaped reinforcing layer; Figures 2A through 2E show schematic representations each exhibiting a layout of various reinforcing components in a side part of a pneumatic safety tire used in an Example of the embodiment of the low profile tire of the present invention or in a Comparative Example, but wherein Figures 2A, 2B and 2D do not show embodiments of the invention; Figure 3 shows a schematic sectional view of a pneumatic safety tire as an example of the embodiment of the general use tire of the present invention; Figures 4A through 4F show schematic representations each exhibiting a layout of various reinforcing components in a side part of a pneumatic safety tire used in an Example of the embodiment of the general use tire of the present invention or in a Comparative Example, but wherein Figures 4A and 4E do not show embodiments of the invention; Figures 5A through 5D show other schematic representations each exhibiting a layout of various reinforcing components in a side part of a pneumatic safety tire used in an Example of the embodiment of the general use tire of the present invention or in a Comparative Example, but wherein Figure 5B does not show an embodiment of the invention. In the present invention, the filament fiber used in the rubber-filament fiber composite which is used as a layer of a fiber reinforcing component is not formed into twisted or woven bundles of a number of fibers like cord fabric for tire cords, and a non-woven fabric is used. As the process for producing a non-woven fabric, the carding process, the paper making process, the air lay process, the melt blow process, or the spun bond process can be used. A web is prepared by any one of these processes. As a process for binding fibers in any of the processes except for the melt blow process and a spun bond process, a heat melting process, a process using a binder, a water entanglement process in which fibers are tangled to each other by using a water stream, or a needle punch process in which fibers are tangled to each other by using needles may be used. Particularly, non-woven fabrics obtained by the water entanglement process in which fibers are tangled to each other by using a water stream, the needle punch process in which fibers are tangled to each other by using needles, the melt blow process, or the spun bond process are preferably used. In the present invention, the important fundamental requirements for the rubber-filament fiber composite are that the composite has a structure which allows the rubber to penetrate into parts between the fiber filaments and that the composite has a structure which allows the filament fiber and the rubber to form respective continuous layers in a relatively long distance and in a relatively wide range. For satisfying these requirements the diameter or the maximum cross-sectional dimension of the filament fiber is preferably in the range of 0.0001 to 0.1 mm, more preferably in the range of 0.0001 to 0.05 mm. The section of the filament fiber may have a circular shape or a shape other than a circle. The filament fiber may have a hollow structure. The length of the filament fiber is preferably 8 mm or more, more preferably 10 mm or more. When the length of the filament fiber is less than 8 mm, entanglement of filament fibers is not sufficient, and the strength required for a reinforcing layer.cannot be maintained. When the content of the filament fiber in the rubber-filament fiber composite is less than 4% by weight, uniformity cannot be maintained, and the rigidity required for a reinforcing layer cannot be exhibited. Thus, such a content is not preferable. When the content exceeds 50% by weight, the content of the continuous layer of the fiber in the rubber-filament fiber composite is excessively large, and durability of the rubber-filament fiber composite is decreased to cause decrease in durability of the tire. Thus, such a content is not preferable, either. When a non-woven fabric is used, it is preferable that the thickness be in the range of 0.05. to 2 .0 mm, more preferably 0.1 to 0.5 mm (measured under a pressure of 20 g/cm 2 ). The weight per area (the weight per 1 m 2 ) is in the range of 10 to 300 g, preferably in the range of 10 to 100 g. When the thickness of the non-woven fabric is less than 0.05 mm, maintaining uniformity of the non-woven fabric becomes difficult, and a composite prepared from the non-woven fabric and rubber has insufficient strength and rigidity. When the thickness exceeds 2.0 mm, thickness of a composite prepared from the non-woven fabric and rubber is increased to cause inferior uniformity and workability, and such a material is not preferable as a component of a tire. When the weight per area is less than 10 g/m 2 , uneven non-woven fabric is obtained because maintaining uniformity of the non-woven fabric itself becomes difficult, and a composite prepared from the non-woven fabric and rubber shows large random variations in strength, rigidity, and elongation at break after the composite is vulcanized. When the weight per area exceeds 300 g/m 2 , rubber tends not to penetrate into the space inside the non-woven fabric although the penetration may be different depending on fluidity of the rubber, and such a weight per area is not used from the standpoint of separation between the fabric and the rubber of the layer of the fiber reinforcing component which is the rubber-non-woven fabric composite when the composite is used as a component of a tire. As described above, the fiber reinforcing component is used in the pneumatic safety tire of the present invention. However, it is necessary that the light weight of the tire be kept unaffected by the use because decrease in fuel consumption can be expected by maintaining the light weight. In the embodiment of the low profile tire of the present invention, it is preferable that a fiber used as the filament fiber does not exhibit meltability under the run-flat condition for this pneumatic safety tire. The low profile safety tire shows small deflection because it has a small height and is used under a small applied load, and the temperature within the tire is not so high as that of a general use tire under the run-flat condition. Therefore, the melting point or the softening point of a selected filament fiber can be held lower than that of a filament fiber used for a general use safety tire. As for the material of the filament fiber, one or a plurality of fibers selected from natural macromolecular fibers, such as cotton, rayon, and cellulose; synthetic macromolecular fibers, such as aliphatic polyamide fibers, polyester fibers such as polyethylene terephthalate (PET) fibers, polyvinyl alcohol fibers, polyimide fibers, and aramide fibers; carbon fibers; glass fibers; and steel fibers may be used by themselves or in combination with any of the above fibers. Among these fibers, PET fibers are preferable because the necessary functions are sufficiently exhibited without melting or softening under the run-flat condition of the low profile safety tire and also because they are organic fibers and therefore light weight. A filament fiber having a multi-layer structure in which different materials are used in adjacent layers may also be used. Moreover, composite fibers having a core-shell structure in which different materials are used in an outer layer and in an inner layer, a radiate structure, a petal structure, or a layered structure may also be used. In the embodiment of the general use tire of the present invention, it is preferable that a fiber used as the filament fiber does not exhibit meltability under the run-flat condition for this pneumatic safety tire. When a composite which is applied to the embodiment of the low profile tire as a component for suppressing blow failure of a rubber material, deflection, and propagation of crack, such as a rubber-filament fiber composite using PET fiber, is used for the embodiment of the general use tire, it occasionally occurs that the PET fiber softens or melts and does not exhibit sufficient function because the temperature within the tire becomes higher. As for the material of the filament fiber used for the embodiment of the general use tire, a fiber selected from the group consisting of fibers which do not exhibit meltability at or below 270°C, such as aramide fibers, rayon fibers, oxidized acrylic fibers (formed by baking polyacrylonitrile fibers; precursors of carbon fiber), polyester fibers such as polyethylene naphthalate fibers, polyimide fibers, carbon fibers., glass fibers, and steel fibers, can be used. Among these fibers, aramide fibers, rayon fibers, and oxidized acrylic fibers are more. preferable. The fiber may be used singly or as a mixture of a plurality of fibers. A filament fiber having a multi-layer structure in which different materials are used in adjacent layers may also be used. Moreover, composite fibers having a core-shell structure in which different materials are used in an outer layer and in an inner layer, a radiate structure, a petal structure, or a layered structure may also be used. In the embodiment of the general use tire of the present invention, when a safety tire of a general use tire size is used under the run-flat condition, the temperature inside the tire becomes as high as or higher than, for example, 200°C because of a large deflection, and a fiber which softens or melts at 270°C or lower cannot exhibit sufficient functions. Therefore, a fiber which does not exhibit meltability at 270°C or lower is preferably used in the embodiment of the general use tire of the present invention. A fiber which does not exhibit meltability at 270°C or lower means a fiber having a melting point of 270°C or higher when the fiber is crystalline and a fiber which does not exhibit fluidity at 270°C or lower when the fiber is amorphous. When a tire is prepared by using the rubber-filament fiber composite comprising the fiber used in the present invention, heat generated by the tire is decreased because of the decreased deflection of the tire, and moreover an effect of suppressing formation of cracks into the disposed rubber reinforcing layer is exhibited. Thus, durability under the run-flat condition is enhanced. The rubber component used in the rubber-filament fiber composite is not particularly limited. Examples of the rubber component include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), and isoprene rubber (IR). Among these rubber components, natural rubber and butadiene rubber are preferable. To form a composite of the filament fiber and the rubber in the fiber reinforcing component layer used in the present invention, an unvulcanized rubber composition is applied to the fiber in advance while the components remain unvulcanized. Specifically, mixing in the preparation of a rubber sheet may be conducted by using any method generally used in the rubber industry, such as a method using a roll or a Banbury mixer. It is preferable from the standpoint of dispersion of the fiber that the filament fiber is added in small portions. When a non-woven fabric is used, an unvulcanized rubber composition of a sheet form is pressed to one or both faces of the non-woven fabric by using a press or a roll so that the air contained inside the non-woven fabric is sufficiently replaced with the unvulcanized rubber composition. When the fluidity of the unvulcanized rubber composition is not sufficient, it may be necessary that the unvulcanized rubber composition is pressed under an increased temperature condition within the range that vulcanization does not start substantially. In another method, the unvulcanized rubber is liquefied by using a solvent and applied to the non-woven fabric to provide the fabric with tackiness. The unvulcanized composite thus obtained is applied as the fiber reinforcing component to prepare a green tire, which is then vulcanized in a mold. In the formation of the composite, the fiber may be used without any adhesive treatment in advance when the adhesion to rubber is sufficient after vulcanization. However, when the adhesion is insufficient, the dipping heat set treatment may be applied to the filament fiber in a similar manner to that used for enhancement of adhesion between fiber codes for tires and rubber. Because of the above characteristics, the safety tire prepared by using a rubber-filament fiber composite shows a remarkably increased durability under the run-flat condition in comparison with conventional safety tires in which a rubber reinforcing layer having a crescent-shaped cross-section alone is disposed on the inner surface of the carcass layer. The above effects can be obtained independently of the place where the rubber-filament fiber composite is disposed. However, a more enhanced effect is obtained when the composite is disposed at an inner side of the carcass. The more enhanced effect is considered to arise because, when the composite is disposed at an outer side of the carcass, the effect of suppressing cracking to the disposed rubber reinforcing layer is decreased although the durability under the run-flat condition is enhanced by the effect of suppressing deflection. I. The embodiment of the low profile tire of the pneumatic safety tire of the present invention is described in the following with reference to Figures, Examples, and Comparative Examples. A schematic sectional view of this pneumatic safety tire is shown in Figure 1. A carcass layer 2 has a single ply in which cords are arranged to the radial directions of the tire 1, and both end portions of the carcass layer are folded over a pair of left and right bead wires 3a and 3b and turned up. A steel belt 4 having two layers is disposed in a ring shape at the upper side of the carcass layer 2 in a radial direction of the tire. A tread rubber 6 is disposed at the tread portion 5 of the tire at the upper side of the steel belt. Side wall rubbers 7a and 7b are disposed on the carcass layer at both sides of the tread rubber 6. In this example, layers of a fiber reinforcing component 8a and 8b are disposed on the inner surface of the carcass layer 2 at the side walls and extend from the side of bead fillers 9a and 9b to the vicinity of the end portion of the belt layer having the maximum width of all of the belt layers. In Structures II, III, IV, and V shown in Figures 2B to 2E, examples of the layout of reinforcing components in the tire side part of the pneumatic safety tire of the embodiment of the low profile tire of the present invention are shown. However, figures 2B and 2D do not have crescent-shaped rubber reinforcing layers. In Structure II, a layer of a fiber reinforced component 8 of the rubber-filament fiber composite is disposed on the inner surface of the carcass layer. In Structure III, a layer of a fiber reinforced component 8 is disposed between the side wall rubber 7 and the carcass layer 2, and a rubber reinforcing layer 10 which has a crescent-shaped cross-section and a smaller thickness than those used for the conventional tires (maximum thickness: 3 mm, Shore hardness: 80 degrees) is disposed on the inner surface of the carcass layer 2. In Structure IV, a layer of a fiber reinforced component 8 is disposed on both inner and outer surfaces of the carcass layer 2 at the side wall. In Structure V, a rubber reinforcing layer 10 which has a crescent-shaped cross-section and a smaller thickness than those used for the conventional tires (the maximum thickness: 3 mm, Shore hardness: 80 degrees) is disposed on the inner surface of the carcass layer 2, and a layer of a f iber reinforced component 8 is disposed on the inner surface of this rubber reinforcing layer. A layout of reinforcing components in a conventional tire is shown in Structure I of Figure 2A for comparison with the layouts of reinforcing components in the above. embodiments of the low profile tire. In Structure I, a conventional rubber reinforcing layer having a crescent-shaped cross-section (the maximum thickness: 7 mm, Shore hardness: 80 degrees) is disposed on the inner surface of the carcass 2 in place of the above layer of the fiber reinforced component. Methods of evaluation used in the following Examples and Comparative Examples are as follows: Durability under the run-flat condition A tire was attached to a rim and inflated to an internal pressure of 3.0 kg/cm 2 . After the tire was placed in a chamber at a room temperature of 38°C for 24 hours, the core of the valve was removed to decrease the internal pressure to 0 kg/cm 2 . Then, the drum driving test of the tire was conducted under the condition of an applied weight of 400 kg, a speed of 80 km/hour, and a room temperature of 38°C. Durability under the run-flat condition was obtained from the driving distance at the time that the fracture occurred. Durability under the run-flat condition in Examples 1 to 5 is shown as indices with reference to the value obtained in Comparative Example 1 which is set to 100. Durability under the inflated condition A tire was attached to a rim and inflated to an internal pressure of 3.0 kg/cm 2 . After the tire was placed in a chamber at a room temperature of 25°C for 24 hours, the internal pressure was adjusted again to 3.0 kg/cm 2 . Then, the tire was pressed to a drum rotating at a circumferential speed of 60 km/hour under an applied load which was twice the load specified by the Japanese Association of Tire Manufacturers, and the driving distance at the time that the fracture occurred was measured. To decide whether the tire can actually be used; the result was rated as × (cannot be used) when the driving distance was 20,000 km or less, and as ○ (can be used) when the driving distance exceeded 20,000 km. Examples 1 to 5 and Comparative Example 1 The rubber composition used for the rubber layer in the rubber-filament fiber composites and rubber reinforcing layers was prepared in accordance with the formulation shown in Table 1. Materials used for reinforcing components and layouts of reinforcing components are shown in Table 2. The carcass consisted of two carcass plies made with rayon cords which were made of ply-twisted fibers of 1840 decitex. Low profile tires of size 265/35ZR18 were obtained by using these components. Durability under the run-flat condition, durability under the inflated condition, and the weight (as an index of the light weight) of the tires were measured. The results are shown in Table 2. However, Examples 1, 2, 3 and 5 do not have crescent-shaped rubber reinforcing layers. Also, Example 5 does not use a non-woven fabric. parts by weight rubber component 100 natural rubber 25 BR01 75 carbon black (FEF) 55 spindle oil 2.5 zinc oxide 5 stearic acid 1 antioxidant ) 2 vulcanization accelerator ) 3.5 sulfur 6 Example 1 2 3 4 5 Comparative Example 1 reinforcing component reinforcing rubber layer used not used used not used used not used rubber-filament fiber composite thickness of the composite (mm) - 0.9 0.9 0.9 0.9 0.9 form of fiber - non-woven fabric non-woven fabric non-woven fabric non-woven fabric fiber type of fiber - PET PET PET PET PET length of fiber (mm) - 50 50 50 50 50 diameter of fiber (mm) - 0.02 0.02 0.02 0.02 0.02 weight per area of non-woven fabric (g/m 2 ) - 40 40 40 40 - thickness of non-woven fabric (mm) - 0.3 0.3 0.3 0. 3 - layout of reinforcing components (Figure 2) St I 2P st St II 2P st St III 2P st St IV 2P st St V 2P st St V 2P st durability under the run-flat condition (index) 100 110 100 160 160 160 durability under the inflated condition ○ ○ ○ ○ ○ ○ weight of tire (kg) 13.4 12.4 13.0 12.7 13.0 13.0 II. The embodiment of the general use tire of the pneumatic safety tire of the present invention is described in the following with reference to Figures, Examples, and Comparative Examples. A schematic sectional view of this pneumatic safety tire is shown in Figure 3. A carcass layer 2 has a single ply in which cords are arranged to the radial directions of the tire 1, and both end portions of the carcass layer are folded over a pair of left and right bead wires 3a and 3b and turned up. A steel belt 4 having two layers is disposed in a ring shape at the upper side of the carcass layer 2 in a radial direction of the tire. A tread rubber 6 is disposed at the tread portion 5 of the tire at the upper side of the steel belt. Side wall rubbers 7a and 7b are disposed on the carcass layer at both sides of the tread rubber 6. In this example, rubber reinforcing layers 10a and 10b having a crescent-shaped cross-section are disposed on the inner surface of the carcass layer 2 at the side wall, and layers of a fiber reinforced component 8a and 8b are disposed on the inner surface of the rubber reinforcing layers and extend from the side of bead fillers 9a and 9b to the vicinity of the end portion of the belt layer having the maximum width of all of the belt layers. In Structures VII, VIII, IX, XI, XII, XIV, and XV shown in Figures 4B, 4C, 4D, 4F, 5A, 5C, and 5D, examples of the layout of reinforcing components in the tire side part of the pneumatic safety tire of the embodiment of the general use tire of the present invention are shown. However, figures 4E and 5B do not have fiber reinforced components 8. In Structure VII, a reinforcing rubber layer 10 having a crescent-shaped cross-section (for example, maximum thickness: 11 mm, Shore hardness: 80 degrees) is disposed at an inner side of a carcass layer 2a having a 3P carcass structure which has 2 sheets of a turned-up carcass 2a and a single sheet of a down carcass 2b disposed on the outermost layer of the turned-up carcass. Moreover, a layer of a fiber reinforced component 8 of a rubber-filament fiber composite is disposed on the inner surface of the thus formed structure. Structure VIII has a 3P carcass structure and is similar to Structure VII except that a layer of a fiber reinforced component 8 is not disposed on the inner surface of the rubber reinforcing layer as is the case in Structure VII but is disposed at an outer side of the down carcass 2b. Structure IX has a 3P carcass structure and is similar to Structure VII except that a layer of a fiber reinforced component 8 is additionally disposed at an outer side of the down carcass 2b, i.e. that this structure has two layers of a fiber reinforced component. In Structure XI, a rubber reinforcing layer 10 having a crescent-shaped cross-section is disposed at an inner side of a carcass layer 2a having a 2P carcass structure which has a single sheet of a turned up carcass 2a and a single sheet of a carcass 2a having the end portion turned up to a tread portion. Moreover, a layer of a fiber reinforced component 8 of a rubber-filament fiber composite is disposed on the inner surface of the thus formed structure. Structure XII has a 2P carcass structure .and is similar to Structure XI except that a layer of a fiber reinforced component 8 is not disposed at an inner side of the rubber reinforcing layer as is the case in Structure XI but is disposed at an outer side of carcass 2a. Structure XIV has a 1P structure which has a single sheet of a carcass 2a having the end portion turned up to a tread portion. A reinforcing rubber layer 10 and a layer of a fiber reinforced component 8 are disposed at an inner side of the thus formed structure in a manner similar to that in Structure XI. Structure XV has a 1P carcass structure and is similar to Structure XIV except that a layer of a fiber reinforced component 8 is disposed at an outer side of the carcass 2a. Layouts of reinforcing components in conventional tires are shown in Structures VI, X, and XIII in Figures 4A, 4E, and 5B for comparison with the above layouts of reinforcing components of the present invention. Structures VI, X, and XIII are similar to Structures VII, XI, and XIV, respectively, of the embodiments of the general use tire of the present invention except that the layer of a fiber reinforced component 8 of the rubber-filament fiber composite is absent. Methods of evaluation used in the following Examples and Comparative Examples are as follows: Durability under the run-flat condition Durability under the run-flat condition was evaluated in accordance with the same method as that described in I, except that the applied weight was 570 kg and the speed was 89 km/hour. Values of the durability under the run-flat condition in Comparative Example 2 and Examples 1 to 6, in Examples 7 and 8, and in Examples 9 and 10 are shown as indices with reference to the values obtained in Comparative Example 1, 3, and 4, respectively, which are set to 100. Durability under the inflated condition Durability under the inflated condition was evaluated in accordance with the same method as that described in I. Examples 6 to 15 and Comparative Examples 2 to 5 The rubber composition used for the rubber layer in the rubber-filament fiber composites and rubber reinforcing layers was prepared in accordance with the formulation shown in Table 1. Materials used for reinforcing components and layouts of reinforcing components are shown in Tables 3 and 4. Rayon cords which were prepared by twisting' two ply-twisted fibers of 1840 decitex were used for the carcass. Ordinary passenger car tires of size 225/60R16 were obtained by using these components. Durability under the run-flat condition, durability under the inflated condition, and the weight (as an index of the light weight) of the tires were measured. The results are shown in Tables 3 and 4. However, Example 9 does not use a non-woven fabric. Example 6 7 Comparative Example 2 3 reinforcing component reinforcing rubber layer used used used used rubber-filament fiber composite thickness of the composite (mm) - 0.9 0.9 0.9 form of fiber - non-woven fabric non-woven fabric non-woven fabric type of fiber - PET aramide aramide length of fiber (mm) - 50 50 50 diameter of fiber (mm) - 0.02 0.02 0.02 weight per area of non-woven fabric (g/m 2 ) - 40 50 50 thickness of non-woven fabric (mm) - 0.3 0.3 0.3 layout of reinforcing components (Figure 4) St VI 3P st St VII 3P st St VII 3P st St VIII 3P st durability under the run-flat condition (index) 100 116 130 124 durability under the inflated condition ○ ○ ○ ○ weight of tire (kg) 15.4 15.4 15.7 15.7 Example 8 9 10 11 Comparative Example reinforcing component reinforcing rubber layer used used used used rubber-filament fiber composite thickness of the composite (mm) 0.9 0.9 0.9 0.9 form of fiber non-woven fabric fiber non-woven fabric non-woven fabric type of fiber aramide aramide aramide aramide length of fiber (mm) 50 50 50 50 diameter of fiber (mm) 0.02 0.02 0.02 0.02 weight per area of non-woven fabric (g/m 2 ) 50 - 50 50 thickness of non-woven fabric (mm) 0.3 - 0.3 0.3 layout of reinforcing components (Figure 4) St IX 3P st St VII 3P st St VII 3P st St VII 3P st durability under the run-flat condition (index) 140 130 126 126 durability under the inflated condition ○ ○ ○ ○ weight of tire (kg) 16 15.4 15.7 15.7 Example 12 13 14 15 Comparative Example 4 5 reinforcing component reinforcing rubber layer used used used used used used rubber-filament fiber composite thickness of the composite (mm) - 0.9 0.9 - 0.9 0.9 form of fiber - non-woven fabric non-woven fabric - non-woven fabric non-woven fabric type of fiber - aramide aramide - aramide aramide length of fiber (mm) - 50 50 - 50 50 diameter of fiber (mm) - 0.02 0.02 - 0.02 0.02 weight per area of non-woven fabric (g/m 2 ) - 50 50 - 50 50 thickness of non-woven fabric (mm) - 0.3 0.3 - 0.3 0.3 layout of reinforcing components (Figures 4 and 5) St X St XI St XII St XIII St XIV St XV 2P st 2P st 2P st 1P st 1P st 1P st durability under the run-flat condition (index) 100 120 115 100 130 120 durability under the inflated condition ○ ○ ○ ○ ○ ○ weight of tire (kg) 14.5 14.8 14.8 13.6 13.9 13.9 As shown in Tables 2, 3, and 4, it is understood that the pneumatic safety tire of the present invention realizes a light weight and shows a 'remarkably improved property under the run-flat condition while properties such as durability in ordinary use under the inflated condition are maintained at high levels. The safety tire having the layout of reinforcing components in' which the rubber reinforcing layer alone was used (without using the fiber composite) (Comparative Example 1) showed the property under the run-flat condition inferior to that of the pneumatic safety tires having the rubber-filament fiber composite alone (Examples 1, 3, and 5) and the pneumatic safety tires having both the rubber reinforcing layer and the rubber-filament fiber composite in combination (Examples 2 and 4). The safety tire having a layout of reinforcing components (a 3P structure) in which the rubber reinforcing layer alone was used (without using the fiber composite) (Comparative Example 2) and the safety tire having a layout of reinforcing components (a 3P structure) in which the rubber reinforcing layer and a rubber-filament 'fiber (PET) composite outside the scope of the embodiment of the general use tire of the present invention (Comparative Example 3) showed the property under the run-flat condition inferior to that of the pneumatic safety tires having the reinforcing rubber layer, the rubber-filament fiber composite, and the layout of these reinforcing components (a 3P structure) in accordance with the embodiment of the general use tire of the present invention (Examples 6 to 11). The safety tire having the layout of reinforcing components (a 2P structure) in which the rubber reinforcing layer alone was used (without using the fiber composite) (Comparative Example 4) showed the property under the run-flat condition inferior to that of the pneumatic safety tires having the reinforcing rubber layer, the rubber-filament fiber composite and the layout of these reinforcing components (a 2P structure) in accordance with the embodiment of the general use tire of the present invention (Examples 12 and 13). The safety tire having the layout of reinforcing components (a 1P structure) in which the rubber reinforcing layer alone was used (Comparative Example 5). showed the property under the run-flat condition inferior to that of the pneumatic safety tires having the layout of reinforcing components (a 1P structure) in accordance with the embodiment of the general use tire of the present invention (Examples 14 and 15). The safety tire of the present invention maintains the properties during ordinary use under the inflated condition at high levels, realizes a light weight; shows remarkably improved properties during use under the run-flat condition in comparison with those of conventional safety tires having a rubber reinforcing layer, and is used as an ultra-low profile high performance tire having an aspect ratio less than 60% and as a general use passenger car tire having an aspect ratio of 60% or more.

Claims: A pneumatic safety tire (1) comprising: a pair of left and right ring-shaped bead cores (3a, 3b); a carcass layer (2) formed from one or more plies in which a plurality of cords disposed parallel to each other are embedded in a covering rubber, both end portions of said carcass layer being folded over said bead cores (3a, 3b) and turned up such that said carcass layer is formed in an annular shape; a multi-layer belt portion (4) disposed at an outer side of said carcass layer (2) in a radial direction of the tire; an annular tread portion (5) disposed at an outer side of said belt portion (4) in the radial direction of the tire; a pair of side wall portions (7a, 7b) disposed at the left and right of said tread portion (5); characterized by a rubber reinforcing layer (10) having a crescent-shaped cross-section disposed at an inner side of said carcass layer (2); wherein at least one sheet of a rubber-filament fiber composite (8), formed from a rubber component and a non-woven fabric as filament fiber having a weight per area of 10 to 300 g/m 2 , is disposed at said side wall portions (7a, 7b) in a vicinity of said carcass layer (2). A pneumatic safety tire as claimed in Claim 1, characterized in that an aspect ratio of said tire is less than 60%. A pneumatic safety tire as claimed in Claim 2, characterized in that said rubber-filament fiber composite (8) is disposed at an inner side of said carcass layer (2). A pneumatic safety tire as claimed in Claim 2, characterized in that said rubber-filament fiber composite (8) is disposed both at an inner side of said carcass layer (2) and between said side wall portions (7) and an outer surface of said carcass layer. A pneumatic safety tire as claimed in Claim 2, characterized in that said rubber-filament fiber composite (8) is disposed between said side wall portions (7) and an outer surface of said carcass layer (2), and said rubber reinforcing layer (10) having a crescent-shaped cross-section is disposed at an inner side of said carcass layer. A pneumatic safety tire as claimed in Claim 2, characterized in that said rubber-filament fiber composite (8) is disposed at an inner surface of said rubber reinforcing layer (10) having a crescent-shaped cross-section which is disposed at an inner side of said carcass layer (2). A pneumatic safety tire as claimed in any of Claims 2 to 6, characterized in that 4 to 50% by weight of said rubber-filament fiber composite (8) is the filament fibers. A pneumatic safety tire as claimed in Claim 1, characterized in that an aspect ratio of said tire is 60% or more. A pneumatic safety tire as claimed in Claim 8, characterized in that said rubber reinforcing layer (10) having a crescent-shaped cross-section is disposed at an inner side of said carcass layer (2), and at least one sheet of said rubber-filament fiber composite (8) is disposed at an inner side of said rubber reinforcing layer which is disposed at the inside of said carcass layer. A pneumatic safety tire as claimed in Claim 9, characterized in that at least one down carcass layer (2b) is additionally disposed between said side wall portions (7) and an outer surface of said carcass layer (2a). A pneumatic safety tire as claimed in Claim 9, characterized in that in addition to being disposed at the inner side of said rubber reinforcing layer (10), said rubber-filament fiber composite (8) is also disposed between said side wall portions (7) and an outer surface of said carcass layer (2). A pneumatic safety tire as claimed in Claim 11, characterized in that at least one down carcass layer (2b) is disposed between the outer surface of said carcass layer (2a) and said rubber-filament fiber composite (8) which is disposed at the outer side of said carcass layer (2a) in the radial direction of said tire. A pneumatic safety tire as claimed in Claim 8, characterized in that said rubber reinforcing layer (10) having a crescent-shaped cross-section is disposed at an inner side of said carcass layer (2), and at least one sheet of said rubber-filament fiber composite (8) is disposed between said side wall portions (7) and an outer surface of said carcass layer. A pneumatic safety tire as claimed in Claim 13, characterized in that at least one down carcass layer (2b) is additionally disposed between the outer surface of said carcass layer (2a) and said rubber-filament fiber composite (8) which is disposed at the outer side of said carcass layer (2a) in the radial direction of said tire. A pneumatic safety tire as claimed in any of Claims 8 to 14, characterized in that 4 to 50% by weight of said rubber-filament fiber composite (8) is the filament fibers. A pneumatic safety tire as claimed in any of Claims 1 to 15, characterized in that the filament fibers do not exhibit meltability when the tire is used under a run-flat condition. A pneumatic safety tire as claimed in any of Claims 1 to 16, characterized in that the filament fibers in said rubber-filament fiber composite do not exhibit meltability at 270°C or lower. A pneumatic safety tire as claimed in Claim 17, characterized in that the filament fibers are at least one type of fibers selected from the group consisting of polyester fibers, aramide fibers, polyimide fibers, carbon fibers, glass fibers, and steel fibers. A pneumatic safety tire as claimed in any of Claims 1 to 18, characterized in that said rubber-filament fiber composite (8) is formed from a rubber component and filaments having a diameter or a maximum cross-sectional dimension of 0.0001 to 0.1 mm and a length of 8 mm or more, and said rubber-filament fiber composite has a thickness of 0.05 to 2.0 mm.

Inventors: ITO SHUNGO, KINOSHITA KATSUHIKO, KOBAYASHI KAZUOMI, MATSUO KENJI, NISHIKAWA TOMOHISA, ITO, SHUNGO, KINOSHITA, KATSUHIKO, KOBAYASHI, KAZUOMI, MATSUO, KENJI, NISHIKAWA, TOMOHISA
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1997
Main classification: B60C17
IPC codes: B60C9, B60C17, B60C15