Rubber composition and tires

Abstract

Heavy-duty tires, such as those for trucks and buses, require high fracture strength that is unaffected by road conditions. Meanwhile, from an environmental perspective, there is a growing demand for improved fuel efficiency in automobiles. [Solution] The above problem was solved by a rubber composition characterized by (A) blending 1 to 40 parts by mass of polypropylene resin with (B) a difference (Tic-Tec) between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), measured by a DSC (differential scanning calorimeter) in accordance with JIS K7121:2012, of 4 to 11°C, per 100 parts by mass of rubber component.

Description

Technical Field

[0001] The present invention relates to a rubber composition and a tire using the same, and more particularly to a rubber composition having excellent fracture physical properties and low heat build-up properties, and a tire using the same.

Background Art

[0002] Heavy-duty tires such as truck and bus tires are required to have high fracture physical properties that are not affected by road surface conditions. On the other hand, from the perspective of the global environment, the demand for lower fuel consumption in automobiles is increasing, and the development of tires with good rolling resistance is desired.

[0003] As a conventional technique that has the problem of providing a tire having good fracture physical properties and low heat build-up, for example, in Patent Document 1 below, a diene rubber, a filler, and an acid-modified polypropylene-based polymer are contained, and the melting point of the acid-modified polypropylene-based polymer is 136 to 155 ° C, and the content of the acid-modified polypropylene-based polymer is 1 to 30 parts by mass with respect to 100 parts by mass of the diene rubber. The diene rubber includes natural rubber, butadiene rubber, and aromatic vinyl-conjugated diene copolymer rubber, and the content of the natural rubber is 15 to 80% by mass with respect to the diene rubber. A rubber composition is disclosed. Further, in Patent Document 2 below, 2 to 75 parts by weight of high-density polyethylene (35 to 70% by weight of which has a crosslinkable portion) is blended with respect to 100 parts by weight of a rubber component, and kneaded at a temperature higher than the melting point of the blended resin. A rubber composition is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a rubber composition that has excellent fracture properties and low heat generation, and a tire using the same. [Means for solving the problem]

[0006] As a result of diligent research, the inventors discovered that the above problems could be solved by blending a specific amount of a particular polypropylene resin with the rubber component, and thus completed the present invention.

[0007] In other words, the present invention provides a rubber composition characterized by (A) blending 1 to 40 parts by mass of polypropylene resin with (B) a difference (Tic-Tec) between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), measured by a DSC (differential scanning calorimeter) in accordance with JIS K7121:2012, of 4 to 11°C, to 100 parts by mass of rubber component. [Effects of the Invention]

[0008] The rubber composition of the present invention is (A) 100 parts by mass of rubber component, and (B) 1 to 40 parts by mass of polypropylene resin having a difference (Tic-Tec) between the extracorporeal crystallization start temperature (Tic) and the extracorporeal crystallization end temperature (Tec), measured by a DSC (Differential Scanning Calorimeter) in accordance with JIS K7121:2012, which is 4 to 11°C. Therefore, it is possible to provide a rubber composition and a tire using the same that have excellent fracture properties and low heat generation.

[0009] The (B) polypropylene resin used in this invention has a narrow crystallization temperature range (Tic-Tec) of 4 to 11°C, which makes it difficult for crystals to grow during the cooling process after the rubber is vulcanized. This suppresses the formation of foreign matter in the (B) polypropylene resin, resulting in improved fracture properties and reduced heat generation. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram illustrates the extracellular crystallization start temperature (Tic) and extracellular crystallization end temperature (Tec). [Modes for carrying out the invention]

[0011] The present invention will be described in more detail below. (A) Rubber component The rubber component used in the present invention is preferably a diene rubber, and more preferably isoprene rubber accounting for 30 parts by mass or more, and particularly preferably 50 parts by mass or more, when the total is 100 parts by mass. (A) Including isoprene rubber in the rubber component significantly improves the breaking properties when polypropylene resin is blended. Examples of isoprene rubber include natural rubber (NR) and synthetic isoprene rubber (IR). Examples of diene rubbers other than isoprene rubber include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and acrylonitrile-butadiene copolymer rubber (NBR). The molecular weight and microstructure of the rubber component are not particularly limited and may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or epoxidized. The weight-average molecular weight (Mw) of the diene rubber is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000. In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are standard polystyrene equivalent values ​​obtained by gel permeation chromatography (GPC) measurement.

[0012] (B) Polypropylene resin The polypropylene resin (B) used in the present invention is characterized in that the difference between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), measured by a DSC (differential scanning calorimeter) in accordance with JIS K7121:2012 (Tic-Tec), is 4 to 11°C. The aforementioned Tic and Tec are publicly known and described in JIS K7121:2012. As shown in Figure 1, the extrapolation crystallization start temperature (Tic) is the temperature at the intersection of a straight line extending from the high-temperature baseline to the low-temperature side and a tangent line drawn at the point where the slope is maximum on the high-temperature side of the crystallization peak curve. The extrapolation crystallization end temperature (Tec) is the temperature at the intersection of a straight line extending from the low-temperature baseline to the high-temperature side and a tangent line drawn at the point where the slope is maximum on the low-temperature side of the crystallization peak curve. Tpc is the crystallization peak temperature, which is the temperature at the top of the crystallization peak. The rubber composition of the present invention may have a sea-island structure in which (B) polypropylene resin exists as island phases within (A) rubber component. Due to the presence of a sea-island structure, (A) rubber component and (B) polypropylene resin are miscible, and an interface phase with an intermediate elastic modulus is formed between (A) rubber component and (B) polypropylene resin. The interface layer formed between (A) rubber component and (B) polypropylene resin follows deformation, and (B) polypropylene resin behaves like a filler, thus exhibiting stress, which is an advantage. The polypropylene resin (B) used in this invention has a difference between the extracorporeal crystallization start temperature (Tic) and the extracorporeal crystallization end temperature (Tec) (Tic-Tec) of 4 to 11°C. Because the crystallization temperature range is narrow, crystal growth is difficult during the cooling process after the rubber is vulcanized. This suppresses the formation of foreign matter in the polypropylene resin (B), resulting in improved fracture properties and reduced heat generation.

[0013] From the viewpoint of further improving the effects of the present invention, (B) the polypropylene resin preferably satisfies the following embodiments. (1) The difference (Tic-Tec) is preferably 4 to 9°C, and more preferably 4 to 8°C. Breakage properties are particularly improved within this range. (2) The melt mass flow rate (MFR) measured at 230 °C and a load of 2.16 kg is preferably 2 to 30 g / 10 min, more preferably 2 to 27 g / 10 min, and particularly preferably 4 to 25 g / 10 min. Within the above range, the effect of excellent mixing processability is also achieved. The melt mass flow rate (MFR) is measured at a temperature of 230 °C and a load of 2.16 kg in accordance with JIS K 7210-1:2014. (3) The melting point is preferably 125 to 150 °C, more preferably 125 to 145 °C, and particularly preferably 125 to 140 °C. Within the above range, the effect of improving the dispersibility of the polypropylene resin is also achieved. The melting point is measured using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min in accordance with JIS K 7121:2012. (4) The load deflection temperature at a load of 0.45 MPa measured in accordance with JIS K7191-2:2015 is preferably 65 to 90 °C, more preferably 70 to 90 °C, and particularly preferably 75 to 90 °C. Within the above range, the effect that tanδ(60 °C), which is an index of heat generation during tire running, becomes small is achieved. The more the forms of (1) to (4) are satisfied, the more preferable it is because the effects of the present invention are improved.

[0014] (B) Polypropylene resin used in the present invention can satisfy 4 to 11 °C, which is the difference (Tic - Tec) between the supplementary crystallization start temperature (Tic) and the supplementary crystallization end temperature (Tec), by being produced using a metallocene catalyst. Further, (B) polypropylene resin produced using the metallocene catalyst used in the present invention can utilize commercially available products. For example, Wintec WMX03 manufactured by Japan Polypropylene Corporation (Tic = 103.9 °C, Tec = 96.2 °C, difference (Tic - Tec) = 7.6 °C, Tpc = 101.3 °C, MFR = 25 g / 10 min, melting point = 130 °C, heat deflection temperature = 65 °C), WFX6 (Tic = 92.0 °C, Tec = 82.8 °C, difference (Tic - Tec) = 9.2 °C, Tpc = 88.4 °C, MFR = 2 g / 10 min, melting point = 126 °C, heat deflection temperature = 70 °C), WSX03A (Tic = 92.3 °C, Tec = 84.7 °C, difference (Tic - Tec) = 6.9 °C, Tpc = 88.8 °C, MFR = 25 g / 10 min, melting point = 125 °C, heat deflection temperature = 70 °C), WFW4M (Tic = 105.3 °C, Tec = 95.3 °C, difference (Tic - Tec) = 10.0 °C, Tpc = 119.2 °C, MFR = 7 g / 10 min, melting point = 135 °C, heat deflection temperature = 80 °C), WMG03UX (Tic = 122.4 °C, Tec = 113.0 °C, difference (Tic - Tec) = 9.3 °C, Tpc = 119.2 °C, MFR = 30 g / 10 min, melting point = 140 °C, heat deflection temperature = 90 °C), etc. can be mentioned.

[0015] As the type of (B) polypropylene resin, from the viewpoint of improving the effects of the present invention, random polypropylenes such as propylene - ethylene random copolymer, propylene - 1 - butene random copolymer, propylene - ethylene - 1 - butene random copolymer, etc. are preferable. (B) Polypropylene resin used in the present invention can arbitrarily adopt comonomers other than the above as long as it can satisfy the above difference (Tic - Tec) of the present invention.

[0016] (Carbon black) The rubber composition of the present invention may contain carbon black. The carbon black used in the present invention has a nitrogen adsorption specific surface area (N2SA) of 20-300 m², which is desirable for improving the effects of the present invention. 2 It is preferable that the value be / g, and 40-150m 2 It is even more preferable that it be / g. The nitrogen adsorption specific surface area (N2SA) was determined in accordance with JIS K6217-2.

[0017] (silica) The rubber composition of the present invention may contain silica. From the viewpoint of improving the effects of the present invention, the silica used has a nitrogen adsorption specific surface area (N2SA) of 20 to 300 m². 2 It is preferable that the value be / g, and 80-250m 2 It is even more preferable that the amount is / g. Silica may be silica derived from biomass materials such as rice husks.

[0018] (Ratio of rubber composition) The rubber composition of the present invention is characterized by comprising (A) 100 parts by mass of rubber component and (B) 1 to 40 parts by mass of polypropylene resin. If the amount of (B) polypropylene resin is less than 1 part by mass, the amount is too small to achieve the effects of the present invention, and conversely, if it exceeds 40 parts by mass, the elongation at break decreases. In the rubber composition of the present invention, the amount of (B) polypropylene resin blended is preferably 1 to 40 parts by mass, and more preferably 4 to 40 parts by mass, per 100 parts by mass of (A) rubber component.

[0019] In the rubber composition of the present invention, the amount of (C) carbon black and / or silica blended is preferably 5 to 150 parts by mass, more preferably 10 to 140 parts by mass, and even more preferably 20 to 130 parts by mass, per 100 parts by mass of (A) rubber component. Specifically, in the rubber composition of the present invention, the amount of carbon black blended is preferably 5 to 150 parts by mass, 10 to 140 parts by mass, and more preferably 20 to 130 parts by mass, per 100 parts by mass of rubber component (A). The amount of silica blended is preferably 5 to 150 parts by mass, 10 to 140 parts by mass, and more preferably 20 to 130 parts by mass, per 100 parts by mass of rubber component (A).

[0020] (Other ingredients) In addition to the components mentioned above, the rubber composition of the present invention may contain various additives commonly used in rubber compositions, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; various fillers such as clay, talc, calcium carbonate, and aluminum hydroxide; antioxidants; plasticizers; resins; curing agents; silane coupling agents; and processing aids. These additives can be mixed in a conventional manner to form a composition which can then be used for vulcanization or crosslinking. The amounts of these additives can also be conventional amounts, as long as they do not contradict the purpose of the present invention.

[0021] The rubber composition of the present invention can be manufactured by a compounding step of blending the (A) rubber component and the (B) polypropylene resin, and a kneading step of kneading the resulting mixture under conditions above the melting point of the (B) polypropylene resin. Alternatively, a vulcanization step may be performed after the kneading step under conditions above the melting point of the (B) polypropylene resin. The kneading and vulcanization can be carried out according to known conditions and using known equipment.

[0022] The rubber composition of the present invention has excellent fracture properties and low heat generation, making it preferable for use in tire treads, and more preferably for use in the treads of heavy-duty tires. Furthermore, the tire of the present invention is preferably a pneumatic tire and can be filled with air, an inert gas such as nitrogen, and other gases. [Examples]

[0023] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0024] (Preparation of various polypropylene resins) The following materials were used as random polypropylene (r-PP). r-PP A: Manufactured by Nippon Polypropylene Co., Ltd. Novatec MG05ES r-PP B: Manufactured by Sun Allomer Co., Ltd. Sun Allomer PM731V r-PP C: Manufactured by Sun Allomer Co., Ltd. Sun Allomer PM931M r-PP D: Sun Allomer PM940M, manufactured by Sun Allomer Co., Ltd. r-PP E: Manufactured by Nippon Polypropylene Co., Ltd. Wintech WMX03 r-PP F: Manufactured by Nippon Polypropylene Co., Ltd. Wintech WFX6 r-PP G: Manufactured by Nippon Polypropylene Co., Ltd. Wintech WSX03A r-PP H: Manufactured by Nippon Polypropylene Co., Ltd. Wintech WFW4M r-PP I: Manufactured by Nippon Polypropylene Co., Ltd. Wintech WMG03UX The physical properties of the various random polypropylenes mentioned above were measured as follows. The results are shown in Table 1 below.

[0025] [Table 1]

[0026] Standard Examples 1-6, Examples 1-19, and Comparative Examples 1-12 (1) Mixing of rubber composition In the formulations (parts by mass) shown in Tables 2-6, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were mixed in a Banbury mixer at 80°C for 5 minutes. The temperature reached at that time was 150°C. Next, the vulcanization system was added using a roll and mixed to obtain the rubber composition. (2) Preparation of vulcanized rubber test specimens for evaluation Each of the obtained rubber compositions (unvulcanized) was press-vulcanized at 148°C for 60 minutes to produce tires (tire size = 245 / 70R19.5). The produced tires were allowed to cool naturally, and the intermediate layer inside the tire tread was cut out to a thickness of 2 mm to obtain vulcanized rubber test pieces (10 cm × 10 cm × 2 mm). (3) Breaking strength / Breaking elongation (2) The vulcanized rubber test specimens obtained in (2) were punched out as JIS No. 3 dumbbell test specimens (2 mm thick) in accordance with JIS K 6251:2023, and tested at room temperature at a tensile speed of 500 mm / min to measure the breaking strength [MPa] and breaking elongation [%]. The results obtained are shown in the "Breaking Strength" and "Breaking Elongation" columns as an index with the values ​​of standard examples 1 to 6 set to 100. A larger index indicates better breaking strength. An index of 105 or higher indicates that sufficient effect has been achieved. (4) Pyrokinetics: tanδ (60℃) For the vulcanized rubber test pieces obtained in (2), the loss tangent tanδ(60°C) at a temperature of 60°C was measured using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) under conditions of initial strain of 10%, amplitude of ±2%, and frequency of 20Hz, and the heat generation was evaluated. The values ​​for Standard Examples 1 to 6 are shown in the "Heat Generation" column as an index with a base value of 100. Smaller indices indicate lower heat generation, which is preferable. An index of 110 or less indicates sufficiently low heat generation. (5) Meltmass Florate (MFR) (B) The melt mass flow rate (MFR) of polypropylene resin was measured in accordance with JIS K 7210-1:2014 at a temperature of 230°C and a load of 2.16 kg. (6) Melting point (B) The melting point (Tm) of polypropylene resin was measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min in accordance with JIS K 7121:2012. The melting point was defined as the temperature at the peak of the melting. (7) Temperature of deflection under load (B) The temperature of deflection under load of the polypropylene resin was measured at a load of 0.45 MPa in accordance with JIS K 7191-2:2015.

[0027] Regarding the results for breaking strength, elongation at break, and heat generation, Examples 1-13 and Comparative Examples 1-6 were compared with Standard Example 1, Examples 14-15 and Comparative Examples 7-8 were compared with Standard Example 2, Example 16 and Comparative Example 9 were compared with Standard Example 3, Example 17 and Comparative Example 10 were compared with Standard Example 4, Example 18 and Comparative Example 11 were compared with Standard Example 5, and Example 19 and Comparative Example 12 were compared with Standard Example 6.

[0028] The results are shown in Tables 2-6.

[0029] [Table 2]

[0030] [Table 3]

[0031] [Table 4]

[0032] [Table 5]

[0033] [Table 6]

[0034] • NR:SIR20 • BR: Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., number average molecular weight = 1.8 × 10⁻⁶ 5 ) • Carbon Black (CB): Manufactured by Cabot Japan, product name Show Black N339, CTAB specific surface area = 90 m² 2 / g • Silica: Zeosil 1085GR manufactured by Solvay Japan, Nitrogen adsorption specific surface area (N2SA) = 90m² 2 / g, CTAB specific surface area=80m2 / g • Silane coupling agent: Si69 manufactured by Evonik Degussa, bis(3-triethoxysilylpropyl)tetrasulfide • Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. • Stearic acid: Stearic acid YR manufactured by NOF Corporation • Anti-aging agent: SANTOFLEX 6PPD manufactured by Flexis • Sulfur: Sulfur processed by Karuizawa Refinery Co., Ltd. • Vulcanization accelerator: Sancella NS-G, manufactured by Sanshin Chemical Industry Co., Ltd. From the results in the tables above, it can be seen that each example is characterized by (A) blending 1 to 40 parts by mass of polypropylene resin with (B) a difference (Tic-Tec) between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), measured by DSC (Differential Scanning Calorimeter) in accordance with JIS K7121:2012, to 100 parts by mass of rubber component, thereby providing a rubber composition with excellent fracture properties and low heat generation. In contrast, in Comparative Examples 1-4, the difference (Tic-Tec) exceeded the upper limit defined in the present invention, so neither the fracture properties nor the heat generation properties improved. In Comparative Example 5, the amount of (B) polypropylene resin blended was below the lower limit specified in the present invention, so neither the fracture properties nor the heat generation properties improved. In Comparative Example 6, the amount of (B) polypropylene resin blended exceeded the upper limit specified in the present invention, so neither the fracture properties nor the heat generation properties improved. Comparative Examples 7-12 failed to simultaneously improve fracture properties and heat generation because the difference (Tic-Tec) exceeded the upper limit defined in the present invention.

[0035] The present invention encompasses the following embodiments. Embodiment 1: A rubber composition characterized by (A) blending 1 to 40 parts by mass of polypropylene resin with respect to 100 parts by mass of rubber component, and (B) having a difference (Tic-Tec) between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), measured by a DSC (differential scanning calorimeter) in accordance with JIS K7121:2012, of 4 to 11°C. Embodiment 2: The rubber composition according to Embodiment 1, characterized in that the (B) polypropylene resin is a resin polymerized using a metallocene catalyst. Embodiment 3: The rubber composition according to Embodiment 1 or 2, characterized in that the melt mass flow rate (MFR) of the polypropylene resin (B) measured at 230°C and a load of 2.16 kg is 2 to 30 g / 10 min. Embodiment 4: The rubber composition according to any one of Embodiments 1 to 3, characterized in that the (B) polypropylene resin is random polypropylene having a melting point of 125 to 150°C. Embodiment 5: The rubber composition according to any one of Embodiments 1 to 4, characterized in that the load deflection temperature of the (B) polypropylene resin at a load of 0.45 MPa, as measured in accordance with JIS K7191:2015, is 65 to 90°C. Embodiment 6: The rubber composition according to any one of Embodiments 1 to 5, characterized in that isoprene-based rubber accounts for 30 parts by mass or more of 100 parts by mass of the rubber component (A). Embodiment 7: The rubber composition according to any one of Embodiments 1 to 6, characterized in that 5 to 150 parts by mass of (C) carbon black and / or silica are further added to 100 parts by mass of the rubber component (A). Embodiment 8: A tire using the rubber composition described in any of Embodiments 1 to 7.

Claims

1. A rubber composition characterized by comprising (A) 100 parts by mass of rubber component, (B) 1 to 40 parts by mass of polypropylene resin having a difference (Tic-Tec) between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), measured by DSC (Differential Scanning Calorimeter) in accordance with JIS K7121:2012, between the extrapolation crystallization start temperature (Tic) and the extrapolation crystallization end temperature (Tec), which is 4 to 11°C, 5 to 150 parts by mass of carbon black having a nitrogen adsorption specific surface area (N₂SA) of 20 to 300 m² / g, and 5 to 150 parts by mass of silica having a nitrogen adsorption specific surface area (N₂SA) of 20 to 300 m² / g.

2. The rubber composition according to claim 1, characterized in that the (B) polypropylene resin is a resin polymerized using a metallocene catalyst.

3. The rubber composition according to claim 1, characterized in that the melt mass flour (MFR) of the polypropylene resin (B) measured at 230°C and a load of 2.16 kg is 2 to 30 g / 10 min.

4. The rubber composition according to claim 1, characterized in that the (B) polypropylene resin is random polypropylene having a melting point of 125 to 150°C.

5. The rubber composition according to claim 1, characterized in that the load deflection temperature of the (B) polypropylene resin at a load of 0.45 MPa, measured in accordance with JIS K7191:2015, is 65 to 90°C.

6. The rubber composition according to claim 1, characterized in that isoprene-based rubber accounts for 30 parts by mass or more of 100 parts by mass of the rubber component (A).

7. A tire using the rubber composition described in claim 1.

8. A heavy-duty tire using the rubber composition described in Claim 1 for the tread.

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