Pneumatic tire

Abstract

Provided is a pneumatic tire capable of excellently retaining high-speed durability even when a recycled PET resin is used for a carcass cord. In a pneumatic tire provided with a carcass layer 4, an organic fiber cord comprising a PET resin having a melting point of 240-260°C is used as a carcass cord constituting the carcass layer 4, and the PET resin contains a recycled PET resin.

Description

pneumatic tires

[0001] The present invention relates to a pneumatic tire having a carcass layer made of organic fiber cords.

[0002] In recent years, from the perspectives of resource conservation and environmental protection, numerous attempts have been made to reuse collected used PET bottles as recycled PET resin for clothing and industrial materials. The use of such renewable raw materials is also desired in the field of tires. It is known that organic fiber cords (PET cords) are used for the reinforcing cords that make up the carcass layer and belt reinforcing layer of tires, and the use of the aforementioned recycled PET resin as the resin material for these cords has been investigated (see, for example, Patent Documents 1 and 2). However, recycled PET resin contains small amounts of impurities (e.g., IPA (isophthalic acid) and DEG (diethylene glycol)), which makes it difficult to achieve desired tire performance (for example, Patent Documents 1 and 2 show that fiber cords made of recycled PET resin are twisted with fiber cords made of another resin to form a so-called hybrid cord). Therefore, even when recycled PET resin is used, it is necessary to fully ensure desired tire performance (e.g., durability).

[0003] Japanese Patent Publication No. 2022-533443 Japanese Patent Publication No. 2018-130974

[0004] An object of the present invention is to provide a pneumatic tire having a carcass layer made of organic fiber cords, which is capable of maintaining good high-speed durability even when recycled PET resin is used for the carcass cords.

[0005] In order to achieve the above object, the pneumatic tire of the present invention comprises a tread portion extending circumferentially of the tire to form an annular shape, a pair of sidewall portions arranged on either side of the tread portion, and a pair of bead portions arranged radially inward of the sidewall portions, and the pneumatic tire has at least one carcass layer mounted between the pair of bead portions, wherein the carcass cords constituting the carcass layer are organic fiber cords made of PET resin having a melting point of 240°C to 260°C, and the PET resin contains recycled PET resin.

[0006] In the present invention, organic fiber cords containing recycled PET resin are used as the carcass cords constituting the carcass layer, as described above. Since the melting point of the PET resin (PET resin containing recycled PET resin) constituting the organic fiber cords is in the range of 240°C to 260°C, good high-speed durability can be maintained even when recycled PET resin is used. Specifically, the inventors of the present invention found that the higher the content of impurities (components such as IPA and DEG contained in used PET bottles before decomposition) in recycled PET resin, the lower the melting point of the recycled PET resin (the melting point of the PET resin (mixture) as a whole containing recycled PET resin) tends to be, and that using such recycled PET resin (PET resin containing recycled PET resin) for carcass cords reduces durability. Therefore, by optimizing the melting point of the recycled PET resin (PET resin containing recycled PET resin) (setting it within the above-mentioned range), it became possible to ensure durability when recycled PET resin is used.

[0007] In the present invention, the melting point of PET resin refers to the melting point of a mixture of recycled PET resin and other PET resins (petroleum-derived), and refers to the temperature of the melting peak on a DSC curve obtained by measuring using a differential scanning calorimeter (DSC) in the temperature range of 25°C to 300°C at a heating rate of 10°C / min. When the proportion of recycled PET resin in the PET resin is 100%, the melting point is the melting point of the recycled PET resin alone measured as described above.

[0008] In the present invention, the coating rubber that coats the carcass cord has a nitrogen adsorption specific surface area NSA of 25 m per 100 parts by mass of the rubber component. 2 / g to 50m2 Preferably, the tire is made of a rubber composition containing 30 to 80 parts by mass of carbon black having a carbon black content of 1000 kJ / g. By using such a coated rubber, the carcass cord containing recycled PET resin can be appropriately reinforced, which is advantageous for maintaining good high-speed durability. In addition, the coated rubber can suppress heat generation, thereby reducing rolling resistance. The nitrogen adsorption specific surface area N2SA of carbon black is measured in accordance with JIS K6217-2.

[0009] In the present invention, the tensile strength of the carcass cord containing recycled PET resin is preferably 6.0 cN / dtex or more. By having such a tensile strength, it is possible to obtain performance (durability) equivalent to that of conventional petroleum-derived PET cords. The tensile strength is a value measured in accordance with JIS L1017.

[0010] In the present invention, the number of twists of the carcass cord is preferably 25 times / 100 mm to 50 times / 100 mm. By setting the number of twists in this range, even if the carcass cord contains recycled PET resin, the spring properties and rigidity of the cord can be improved, which is advantageous for maintaining good high-speed durability and load durability.

[0011] In the present invention, from the viewpoint of increasing the proportion of renewable raw materials in the tire, it is preferable that the proportion of recycled PET resin in the PET resin is 20% to 100%. Note that the "proportion" here refers to the proportion of the weight of recycled PET resin relative to the weight of PET resin (PET resin (mixture) containing recycled PET resin).

[0012] FIG. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention.

[0013] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0014] As shown in Figure 1, the pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 disposed on either side of the tread portion 1, and a pair of bead portions 3 disposed radially inward of the sidewall portions 2. In Figure 1, the symbol CL indicates the tire equator. Although not depicted in Figure 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction and form an annular shape, thereby constituting the basic toroidal structure of the pneumatic tire. The following explanation using Figure 1 will be based basically on the meridian cross-section shape shown, but each tire constituent member also extends in the tire circumferential direction and forms an annular shape.

[0015] A carcass layer 4 including a plurality of reinforcing cords (hereinafter referred to as carcass cords) extending in the tire radial direction is mounted between a pair of left and right bead portions 3. A bead core 5 is embedded in each bead portion, and a bead filler 6 having a generally triangular cross section is disposed on the outer periphery of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from the inner side to the outer side in the tire width direction. As a result, the bead core 5 and the bead filler 6 are enclosed by the main body portion of the carcass layer 4 (the portion extending from the tread portion 1 through each sidewall portion 2 to each bead portion 3) and the folded back portion (the portion folded back around the bead core 5 in each bead portion 3 and extending toward each sidewall portion 2).

[0016] Meanwhile, multiple belt layers 7 (two layers in the illustrated example) are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords (hereinafter referred to as belt cords) that are inclined with respect to the tire circumferential direction, and are arranged so that the belt cords cross each other between layers. In these belt layers 7, the inclination angle of the belt cords with respect to the tire circumferential direction is set in the range of 10° to 40°, for example. As the belt cords that make up the belt layers 7, for example, steel cords are preferably used.

[0017] Furthermore, a belt cover layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability. The belt cover layer 8 includes reinforcing cords (hereinafter referred to as cover cords) oriented in the tire circumferential direction. In the belt cover layer 8, the cover cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction. The belt cover layer 8 may include a full cover layer 8a that covers the entire width of the belt layer 7, and a pair of edge cover layers 8b that locally cover both ends of the belt layer 7 in the tire width direction, either alone or in combination (in the illustrated example, both the full cover layer 8a and the edge cover layer 8b are provided). The belt cover layer 8 may be formed, for example, by spirally winding a strip material in the tire circumferential direction, in which at least one cover cord is covered with a coating rubber. A jointless structure is particularly desirable.

[0018] The present invention mainly relates to the cords (carcass cords) that constitute the carcass layer 4 described above, and the basic structure of the tire and other tire constituent members are not limited to those described above.

[0019] In the present invention, the carcass cords constituting the carcass layer 4 are composed of organic fiber cords formed by twisting together filament bundles of organic fiber cords. These organic fiber cords are composed of PET resin (polyethylene terephthalate resin) having a melting point of 240°C to 260°C, preferably 248°C to 260°C, and the PET resin must contain recycled PET resin. The recycled PET resin is obtained by decomposing recovered used PET bottles through mechanical recycling (physical recycling method) or chemical recycling (chemical recycling method). Mechanical recycling (physical recycling method) involves crushing and cleaning used PET bottles, followed by melting at high temperatures, reducing pressure, filtering, and other processes to regenerate the PET resin. Chemical recycling (chemical recycling method) involves crushing and cleaning used PET bottles, followed by depolymerization to decompose and refine the raw materials or intermediate materials of PET resin, which are then repolymerized to produce new PET resin. Of these methods, recycled PET resin obtained by chemical recycling contains less impurities and has a melting point equivalent to that of petroleum-derived PET resin, and is therefore suitable for use in the present invention.

[0020] When using organic fiber cords containing recycled PET resin, the melting point of the PET resin (the melting point of the entire PET resin (mixture) containing recycled PET resin) is set to a range of 240°C to 260°C, thereby maintaining good high-speed durability even when recycled PET resin is used. If the melting point of the PET resin is below 240°C, the PET cord may melt due to temperature increases during high-speed driving, making it difficult to maintain good high-speed durability. The melting point of PET resin (single PET resin without recycled PET resin) is 260°C, and the melting point of the PET resin (mixture) of the present invention, which tends to have a lower melting point, does not exceed 260°C. The melting point of the PET resin (mixture) varies depending on the recycled PET resin content and purity. That is, the higher the recycled PET resin content, the lower the melting point of the PET resin (mixture) of the present invention tends to be. Furthermore, even if the content of recycled PET resin is the same, the melting point tends to decrease as the amount of impurities (components such as IPA and DEG) contained in the recycled PET resin increases.

[0021] In the present invention, from the viewpoint of increasing the proportion of renewable raw materials in tires, the proportion of recycled PET resin in the PET resin is preferably 20% to 100%, more preferably 50% to 100%, and even more preferably 70% to 100%. If the proportion of recycled PET resin in the PET resin is less than 20%, the impact of the recycled PET resin on durability is low, and durability can be maintained without applying the above-mentioned present invention.

[0022] The carcass cord of the present invention, which is made of a PET resin containing recycled PET resin as described above, preferably has a tensile strength of 6.0 cN / dtex or more, more preferably 6.2 cN / dtex to 7.5 cN / dtex. Having such a tensile strength is advantageous for obtaining performance (durability) equivalent to that of conventional petroleum-derived PET cords. If the tensile strength of the carcass cord is less than 6.0 cN / dtex, it is not possible to maintain good high-speed durability. The tensile strength of the carcass cord can be set appropriately depending on the degree of polymerization of the PET resin used as the raw material and the spinning conditions of the cord.

[0023] Furthermore, the twist number of the carcass cord is preferably 25 turns / 100 mm to 50 turns / 100 mm, more preferably 30 turns / 100 mm to 45 turns / 100 mm. By setting the twist number in this range, even carcass cords containing recycled PET resin can have good spring properties and rigidity, which is advantageous for maintaining good high-speed durability and load durability. If the twist number of the carcass cord is less than 25 turns / 100 mm, there is a risk that the spring properties will decrease and load durability will deteriorate. If the twist number of the carcass cord is more than 50 turns / 100 mm, there is a risk that the rigidity of the cord will decrease and high-speed durability will deteriorate.

[0024] In the carcass layer 4, the carcass cords are coated with a coating rubber. In this case, the rubber composition constituting the coating rubber preferably contains carbon black as a filler. More specifically, the carbon black blended in the rubber composition constituting the coating rubber preferably has a nitrogen adsorption specific surface area NSA of 25 m 2 / g to 50m 2 / g, more preferably 30m 2 / g~45m 2 / g. The amount of carbon black compounded is preferably 30 to 80 parts by mass, and more preferably 50 to 70 parts by mass, per 100 parts by mass of the rubber component that is the main component of the rubber composition that constitutes the coating rubber. By using such a coating rubber, the carcass cord containing recycled PET resin can be appropriately reinforced, which is advantageous for maintaining good high-speed durability. Furthermore, the coating rubber can suppress heat generation, thereby reducing rolling resistance.

[0025] The nitrogen adsorption specific surface area N2SA of the carbon black compounded in the coated rubber is 25 m 2 If the nitrogen adsorption specific surface area N2SA of the carbon black compounded in the coating rubber is less than 50 m / g, the reinforcing effect of the coating rubber cannot be obtained sufficiently, and the effect of maintaining durability is limited. 2If the carbon black content exceeds 30 parts by mass / g, the heat generation of the coating rubber increases, and the rolling resistance and durability may deteriorate. If the amount of carbon black is less than 30 parts by mass per 100 parts by mass of the rubber component, the reinforcing effect of the coating rubber is not sufficiently obtained, and the effect of maintaining durability is limited. If the amount of carbon black is more than 80 parts by mass per 100 parts by mass of the rubber component, the heat generation of the coating rubber increases, and the rolling resistance and durability may deteriorate.

[0026] The type of main rubber component in the rubber composition that constitutes the coating rubber is not particularly limited, and diene rubbers commonly used in tires (coating rubbers) such as natural rubber, styrene-butadiene rubber, butadiene rubber, etc. These diene rubbers can be used alone or in any blend.

[0027] The rubber composition constituting the coating rubber may contain fillers other than carbon black. Examples of other fillers include silica, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, and titanium oxide. The rubber composition constituting the coating rubber may also contain various additives commonly used in rubber compositions for tires, such as vulcanization or crosslinking agents, vulcanization accelerators, various oils, antioxidants, and plasticizers. These additives can be kneaded by a conventional method to form a rubber composition, which can then be used for vulcanization or crosslinking. The amounts of these additives may be conventional amounts, as long as they do not deviate from the objectives of the present invention. The rubber composition constituting the coating rubber can be produced by mixing the above-mentioned components using a conventional rubber kneading machine, such as a Banbury mixer, kneader, or roll.

[0028] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

[0029] Pneumatic tires (test tires) of Conventional Example 1, Comparative Example 1, and Examples 1 to 10 were manufactured, each having a tire size of 245 / 40R18 and the basic structure shown in FIG. 1 , with the carcass cords having the presence or absence of recycled PET resin, the proportion of recycled PET resin in the PET resin, tensile strength, melting point of the PET resin, number of twists, and type of coating rubber set as shown in Tables 1 and 2.

[0030] The "Melting Point" column in Tables 1 and 2 shows the melting point of the PET resin (petroleum-derived PET resin, a mixture of petroleum-derived PET resin and recycled PET resin, recycled PET resin) constituting the carcass cord used in each tire, measured using a Shimadzu Corporation differential scanning calorimeter (DSC) in the temperature range of 25°C to 300°C at a heating rate of 10°C / min. The melting point of the resulting DSC curve is shown as the temperature of the melting peak. The "Type of Coating Rubber" column in Tables 1 and 2 shows the number (A to D) of the four types of coating rubber (coating rubbers A to D) having the formulation shown in Table 3 that were used.

[0031] Conventional Example 1 is a case where no recycled PET resin was used, and only petroleum-derived PET resin was used. Examples 1 and 2 have the same recycled PET resin content of "100%," but the melting points differ due to the different impurity content of the recycled PET resin used in each example. Examples 1 and 10 have the same melting points despite different recycled PET resin content, which is also due to the different impurity content of the recycled PET resin used in each example.

[0032] These test tires were evaluated for high speed durability and rolling resistance by the following evaluation methods, and the results are shown in Tables 1 and 2.

[0033] High-Speed ​​Durability Each test tire was mounted on a wheel with a rim size of 18 x 7.0J, the internal pressure of the test tire was set to 220 kPa, and the tire was attached to an indoor drum testing machine (drum diameter: 1707 mm). The ambient temperature was set to 38±3°C, the load was set to 88% of the JATMA maximum load, and the running speed was accelerated from 120 km / h by 10 km / h every 20 minutes, and the running distance until tire failure occurred was measured. The evaluation results were expressed as an index, with Conventional Example 1 being set to 100. The higher the index value, the greater the running distance until failure occurred, and the better the high-speed durability.

[0034] Rolling Resistance Each test tire was mounted on a wheel with a rim size of 18 x 7.0J, the air pressure was set to 200 kPa, and the tire was mounted on an indoor drum testing machine (drum diameter 1707 mm). In accordance with JIS D4234, the tire was pressed against the drum with a load equivalent to 85% of the maximum load at that air pressure as specified in JATMA, and the rolling resistance was measured while the tire was traveling at a speed of 80 km / h. The evaluation results were expressed as an index, with the value of Conventional Example 1 being 100. The smaller the index, the lower the rolling resistance.

[0035]

[0036]

[0037]

[0038] The types of raw materials used in Table 3 are as follows: NR: Natural rubber, TSR20; SBR: Styrene butadiene rubber, manufactured by Nippon Zeon Co., Ltd., SBR1502; BR: Butadiene rubber, manufactured by Nippon Zeon Co., Ltd., Nipol 1220; CB1: Carbon black (GPF grade), manufactured by Tokai Carbon Co., Ltd., SEAST V (nitrogen adsorption specific surface area NSA: 35 m) 2 / g) CB2: Carbon black (HAF grade), manufactured by Cabot Japan Co., Ltd., Show Black N330 (nitrogen adsorption specific surface area NSA: 80 m 2 / g) Aroma oil: Extract No. 4 manufactured by Showa Shell Sekiyu K.K. Zinc oxide: Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd. Stearic acid: Beads stearic acid NY manufactured by Nippon Oil & Fats Co., Ltd. Sulfur: Myucron OT-20 manufactured by Shikoku Chemical Industry Co., Ltd. (sulfur content: 80 mass%) Vulcanization accelerator: NS-G manufactured by Sanshin Chemical Industry Co., Ltd.

[0039] As can be seen from Tables 1 and 2, the tires of Examples 1 to 10 maintained high-speed durability and rolling resistance equivalent to those of Conventional Example 1 (when using carcass cords that did not contain recycled PET resin). On the other hand, in Comparative Example 1, the high-speed durability deteriorated due to the low melting point of the PET resin containing recycled PET resin.

[0040] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt cover layer CL tire equator

Claims

1. A pneumatic tire comprising a circumferentially extending annular tread portion, a pair of sidewall portions disposed on either side of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, with at least one carcass layer mounted between the pair of bead portions, wherein the carcass cords constituting the carcass layer are organic fiber cords made of PET resin with a melting point of 240°C to 260°C, and the PET resin contains recycled PET resin.

2. The coating rubber covering the carcass cord has a nitrogen adsorption specific surface area N2SA of 25 m per 100 parts by mass of the rubber component. 2 / g to 50m 2 2. The pneumatic tire according to claim 1, characterized in that the pneumatic tire is made of a rubber composition containing 30 to 80 parts by mass of carbon black having a viscosity of 1 / g.

3. A pneumatic tire according to claim 1 or 2, characterized in that the carcass cord containing the recycled PET resin has a tensile strength of 6.0 cN / dtex or more.

4. A pneumatic tire according to any one of claims 1 to 3, characterized in that the number of twists of the carcass cords is 25 times / 100 mm to 50 times / 100 mm.

5. A pneumatic tire according to any one of claims 1 to 4, characterized in that the recycled PET resin accounts for 20% to 100% of the PET resin.

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