Pneumatic tires

Abstract

To provide a pneumatic tire capable of maintaining good high-speed durability even when recycled PET resin is used for the carcass cord. In a pneumatic tire having a carcass layer 4, an organic fiber cord made of PET resin having a melting point of 240° C. to 260° C. is used as a carcass cord constituting the carcass layer 4, and the PET resin contains recycled PET resin.

Description

[Technical field]

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

[0002] In recent years, from the viewpoint of resource conservation and environmental protection, many attempts have been proposed to reuse collected used PET bottles as recycled PET resin for clothing applications and industrial material applications. In the field of tires, the use of such renewable raw materials is also required. It is known that organic fiber cords (PET cords) are used for reinforcing cords that constitute the carcass layer and belt reinforcing layer among the constituent members of tires, and the use of the above-mentioned recycled PET resin as the resin material for these cords has been considered (see, for example, Patent Documents 1 and 2). However, recycled PET resin contains a small amount of impurities (IPA (isophthalic acid) and DEG (diethylene glycol) etc.), which makes it difficult to obtain desired tire performance (for example, Patent Documents 1 and 2 use a so-called hybrid cord by twisting a fiber cord made of recycled PET resin with a fiber cord made of another resin to obtain the desired performance). Therefore, even when recycled PET resin is used, it is required to sufficiently ensure the desired tire performance (for example, durability). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-533443 [Patent Document 2] JP 2018-130974 A Summary of the Invention [Problem to be solved by the invention]

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

[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 both sides of the tread portion, and a pair of bead portions arranged on the radially inward side of the sidewall portions, and the pneumatic tire has at least one carcass layer mounted between the pair of bead portions, wherein the carcass cord constituting the carcass layer is an organic fiber cord made of PET resin having a melting point of 240°C to 260°C, and the PET resin contains recycled PET resin. Effect of the Invention

[0006] In the present invention, as described above, an organic fiber cord containing recycled PET resin is used as the carcass cord constituting the carcass layer, and since the melting point of the PET resin is in the range of 240°C to 260°C, high-speed durability can be maintained well even if recycled PET resin is used. In detail, the inventor 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 the recycled PET resin, the lower the melting point of the recycled PET resin (melting point of the PET resin (mixture) containing recycled PET resin as a whole) tends to be, and durability of using such recycled PET resin (PET resin containing recycled PET resin) for the carcass cord decreases, and by optimizing (setting to the above-mentioned range) the melting point of the recycled PET resin (PET resin containing recycled PET resin), it is possible to ensure durability when using recycled PET resin.

[0007] In the present invention, the melting point of the PET resin is the melting point of a mixture of the recycled PET resin and other PET resins (derived from petroleum), and refers to the temperature of the melting peak of the DSC curve obtained by measuring the temperature range of 25°C to 300°C at a heating rate of 10°C / min using a differential scanning calorimeter (DSC). When the proportion of the 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 for coating the carcass cord has a nitrogen adsorption specific surface area N 2 SA is 25m 2 / g~50m 2 It is preferable that the rubber composition contains 30 to 80 parts by mass of carbon black having a nitrogen adsorption specific surface area of ​​1000 nm / g. By using such a covering rubber, the carcass cord containing recycled PET resin can be appropriately reinforced, which is advantageous for maintaining good high-speed durability. In addition, the covering rubber can suppress heat generation, thereby reducing rolling resistance. The nitrogen adsorption specific surface area N 2 SA shall be measured in accordance with JIS K6217-2.

[0009] In the present invention, the tensile strength of the carcass cord containing the 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 a conventional petroleum-derived PET cord. 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 springiness and rigidity of the cord can be improved, which is advantageous for maintaining high-speed durability and load durability at a good level.

[0011] In the present invention, from the viewpoint of increasing the ratio of renewable raw materials in tires, the ratio of recycled PET resin in PET resin is preferably 20% to 100%. Note that the "ratio" here refers to the ratio of the weight of recycled PET resin to the weight of PET resin (PET resin (mixture) containing recycled PET resin). [Brief description of the drawings]

[0012] [Figure 1] 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0014] As shown in Fig. 1, the pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the tire radially inward side of the sidewall portions 2. In Fig. 1, the symbol CL indicates the tire equator. Although not depicted in Fig. 1 because it is a meridian cross section, the tread portion 1, the sidewall portions 2, and the bead portions 3 each extend in the tire circumferential direction to form an annular shape, thereby forming a basic toroidal structure of a pneumatic tire. The following explanation using Fig. 1 is basically based on the meridian cross section shown in the figure, but each tire component extends in the tire circumferential direction to form 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 inside to the outside 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) inclined with respect to the tire circumferential direction, and the belt cords are arranged so as to 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 constituting the belt layers 7, for example, steel cords are preferably used.

[0017] Furthermore, a belt cover layer 8 is provided on the outer circumferential side of the belt layer 7 for the purpose of improving high-speed durability. The belt cover layer 8 includes a reinforcing cord (hereinafter referred to as a cover cord) oriented in the tire circumferential direction. In the belt cover layer 8, the cover cord is set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction. As the belt cover layer 8, a full cover layer 8a that covers the entire area in the width direction 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 can be provided 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 winding a strip material in which at least one cover cord is covered with a coating rubber in a spiral shape in the tire circumferential direction, and it is particularly preferable to have a jointless structure.

[0018] Since the present invention mainly relates to the cords (carcass cords) constituting the above-mentioned carcass layer 4, 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 cord constituting the carcass layer 4 is composed of an organic fiber cord in which filament bundles of organic fiber cords are twisted together. This organic fiber cord is 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 necessarily contains recycled PET resin. The recycled PET resin is PET resin (polyethylene terephthalate resin) obtained by decomposing collected used PET bottles by mechanical recycling (physical regeneration method) or chemical recycling (chemical regeneration method). Mechanical recycling (physical regeneration method) is a method in which used PET bottles are crushed and washed, and then melted at high temperature, decompressed, filtered, etc., to regenerate them as PET resin. Chemical recycling (chemical regeneration method) is a method in which used PET bottles are crushed and washed, and then depolymerized to decompose and refine them into raw materials or intermediate raw 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] In using the organic fiber cord containing recycled PET resin, the melting point of the PET resin (the melting point of the PET resin (mixture) containing recycled PET resin as a whole) is set in the range of 240°C to 260°C, so that high-speed durability can be maintained well even if recycled PET resin is used. If the melting point of the PET resin is less than 240°C, the PET melt phenomenon may occur during high-speed running, and high-speed durability cannot be maintained well. Since the melting point of the PET resin (single substance not containing recycled PET resin) is 260°C, the melting point of the PET resin (mixture) of the present invention containing recycled PET resin, 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 content of the recycled PET resin and the purity of the recycled PET resin. That is, the higher the content of the recycled PET resin, the lower the melting point of the PET resin (mixture) of the present invention tends to be. In addition, even if the content of the recycled PET resin is the same, the more impurities (components such as IPA and DEG) contained in the recycled PET resin, the lower the melting point tends to be.

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

[0022] The carcass cord of the present invention made of 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 a conventional petroleum-derived PET cord. If the tensile strength of the carcass cord is less than 6.0 cN / dtex, high-speed durability cannot be maintained well. The tensile strength of the carcass cord can be appropriately set depending on the degree of polymerization of the raw material PET resin and the spinning conditions of the cord.

[0023] The twist number of the carcass cord is preferably 25 times / 100mm to 50 times / 100mm, more preferably 30 times / 100mm to 45 times / 100mm. By setting the twist number in this range, even if the carcass cord contains recycled PET resin, the springiness and rigidity of the cord can be improved, which is advantageous for maintaining good high-speed durability and load durability. If the twist number of the carcass cord is less than 25 times / 100mm, there is a risk that the springiness will decrease and the load durability will deteriorate. If the twist number of the carcass cord is more than 50 times / 100mm, there is a risk that the rigidity of the cord will decrease and the high-speed durability will decrease.

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

[0025] The nitrogen adsorption specific surface area N of carbon black compounded in the coated rubber 2 SA is 25m 2 If the carbon black content is less than 1 / g, the reinforcing effect of the coating rubber is not sufficiently obtained, and the effect of maintaining durability is limited. 2 SA is 50m 2If 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] In the rubber composition constituting the coating rubber, the type of the main rubber component is not particularly limited, and for example, diene rubbers commonly used in tires (coating rubber), such as natural rubber, styrene-butadiene rubber, butadiene rubber, etc. These diene rubbers can be used alone or as any blend.

[0027] The rubber composition constituting the coating rubber can 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 can also contain various additives that are generally used in rubber compositions for tires, such as vulcanization or crosslinking agents, vulcanization accelerators, various oils, antioxidants, and plasticizers, and these additives can be kneaded in a general manner to form a rubber composition, which can be used for vulcanization or crosslinking. The amount of these additives to be added can be a conventional amount, as long as it does not go against the purpose of the present invention. The rubber composition constituting the coating rubber can be produced by mixing the above-mentioned components using a general rubber kneading machine, such as a Banbury mixer, a kneader, or a roll.

[0028] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. 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 cord 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 1-2 shows the melting point of the PET resin (petroleum-derived PET resin, mixture of petroleum-derived PET resin and recycled PET resin, recycled PET resin) that constitutes 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 "Type of Covering Rubber" column in Tables 1-2 shows the number (A to D) of the four types of covering rubber (covering rubbers A to D) with the composition shown in Table 3 that were used.

[0031] Conventional Example 1 is a case where no recycled PET resin is used, and only petroleum-derived PET resin is used. Examples 1 and 2 have the same percentage of recycled PET resin, "100%," but the percentage of impurities in the recycled PET resin used in each example is different, resulting in a difference in melting point. Also, Examples 1 and 10 have different percentages of recycled PET resin, but have the same melting point, which is also due to the different percentages of impurities in the recycled PET resin used in each example.

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

[0033] fast 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 220kPa, and the tire was attached to an indoor drum test machine (drum diameter: 1707mm). The ambient temperature was set to 38±3°C, the load was set to 88% of the maximum JATMA load, the running speed was accelerated from 120km / h by 10km / h every 20 minutes, and the running distance until the tire broke down was measured. The evaluation results were expressed as an index with Conventional Example 1 being 100. The higher the index value, the greater the running distance until the tire broke down, 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 test machine (drum diameter 1707 mm). In accordance with JIS D4234, a load equivalent to 85% of the maximum load at the relevant air pressure as stated in JATMA was applied to the drum and the tire was pressed against the drum. The rolling resistance was measured when the tire was driven at a speed of 80 km / h. The evaluation results were shown as an index with the value of Conventional Example 1 being 100. The smaller the index, the lower the rolling resistance.

[0035] [Table 1]

[0036] [Table 2]

[0037] [Table 3]

[0038] The types of raw materials used in Table 3 are shown below. NR: Natural rubber, natural rubber, TSR20 SBR: Styrene butadiene rubber, Zeon SBR1502 BR: Butadiene rubber, Zeon Nipol 1220 CB1: Carbon black (GPF grade), Tokai Carbon Co., Ltd., Seast V (nitrogen adsorption specific surface area N 2 SA:35m 2 / g) CB2: Carbon black (HAF grade), Cabot Japan Co., Ltd. Show Black N330 (nitrogen adsorption specific surface area N 2 SA:80m 2 / g) Aroma oil: Showa Shell Sekiyu Extract No. 4 Zinc oxide: 3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. Stearic acid: Beads Stearic Acid NY manufactured by Nippon Oil & Fats Co., Ltd. Sulfur: Shikoku Chemical Industry Co., Ltd., Myucron OT-20 (sulfur content: 80% by 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 a carcass cord that does not contain recycled PET resin). On the other hand, in Comparative Example 1, the melting point of the PET resin containing recycled PET resin is low, so the high-speed durability was deteriorated.

[0040] The present disclosure includes the following inventions. Invention [1] A pneumatic tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewall portions, and having at least one carcass layer mounted between the pair of bead portions, A pneumatic tire, wherein the carcass cord constituting the carcass layer is an organic fiber cord made of PET resin having a melting point of 240° C. to 260° C., and the PET resin contains recycled PET resin. Invention [2] The coating rubber for coating the carcass cord has a nitrogen adsorption specific surface area N 2 SA is 25m 2 / g~50m 2The pneumatic tire according to the invention [1] is made of a rubber composition containing 30 to 80 parts by mass of carbon black having a molecular weight of 1.0 to 1.0 / g. Invention [3] The pneumatic tire according to invention [1] or [2], wherein the carcass cord containing the recycled PET resin has a tensile strength of 6.0 cN / dtex or more. Invention [4] The pneumatic tire according to any one of inventions [1] to [3], characterized in that the number of twists of the carcass cord is 25 turns / 100 mm to 50 turns / 100 mm. Invention [5] The pneumatic tire according to any one of inventions [1] to [4], characterized in that the proportion of the recycled PET resin in the PET resin is 20% to 100%. [Explanation of symbols]

[0041] 1 Tread section 2 Sidewall 3 Bead section 4 Carcass layer 5 Bead Core 6 Bead Filler 7 Belt layer 8 Belt cover layer CL Tire Equator

Claims

1. A pneumatic tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the tire radially inward side of the sidewall portions, the pneumatic tire having at least one carcass layer mounted between the pair of bead portions, The carcass cord constituting the carcass layer is an organic fiber cord made of PET resin having a melting point of 240°C to 260°C, and the PET resin contains recycled PET resin.

2. The coating rubber for coating the carcass cord has a nitrogen adsorption specific surface area N 2 SA is 25m 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. 3. The pneumatic tire according to claim 1, wherein the carcass cord containing the recycled PET resin has a tensile strength of 6.0 cN / dtex or more.

4. 3. The pneumatic tire according to claim 1, wherein the number of twists of the carcass cord is 25 turns / 100 mm to 50 turns / 100 mm.

5. 3. The pneumatic tire according to claim 1, wherein the recycled PET resin accounts for 20% to 100% of the PET resin.

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