Rubber composition and tire

Abstract

To provide a rubber composition having performance equal to that of a conventional wax by using a post industrial maricycle wax, and to provide a tire.SOLUTION: A rubber composition comprising: a post industrial recycled wax (A); and at least one rubber component (B) selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, wherein the rubber composition comprises 0.1 to 10 parts by mass of the post industrial recycled wax (A) per 100 parts by mass of the rubber component (B).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition containing post-industrial recycled wax, and a tire. [Background technology]

[0002] Natural rubber, synthetic rubber, and other rubbers age over time depending on the environment they are placed in, causing cracks and hardening, resulting in a loss of their original properties. External factors that cause rubber aging include oxygen, ozone, oxidizing substances, heat, light, radiation, metals, mechanical fatigue, etc., and it is believed that these, in combination with internal factors such as the composition of the rubber, cause aging. To prevent such rubber aging, various antioxidants such as amine-based, phenol-based, and wax-based antioxidants are used. These antioxidants are used alone or in combination depending on the intended use of the rubber composition.

[0003] Among wax-based antioxidants, paraffin wax and microcrystalline wax are widely used as the wax component in the antioxidant. Due to their blooming properties, paraffin wax and microcrystalline wax as antioxidants precipitate on the surface of the rubber composition over time, thereby protecting the rubber composition from the effects of external oxygen, ozone, oxidizing substances, etc.

[0004] Non-polar olefin waxes such as polyethylene wax and polypropylene wax are also used as wax-based antioxidants. Rubber compositions containing these waxes suppress the amount of wax bloom, making the rubber surface less susceptible to cracking and discoloration, and maintaining good appearance for a long period of time (Patent Document 1).

[0005] Meanwhile, with the need to achieve carbon neutrality and strengthen responses to the problems of marine plastic waste and climate change, promoting plastic recycling is becoming increasingly important. Recycled materials are generally classified into post-consumer recycled materials (hereinafter sometimes abbreviated as PCR) and post-industrial recycled materials (hereinafter sometimes abbreviated as PIR). PCR refers to materials collected or recycled after a product has been used and discarded by consumers, while PIR refers to materials collected or recycled from waste generated during the manufacturing process before the product reaches the consumer. Compared to PCR materials, PIR materials have less variation in quality due to degradation and other factors, making them more likely to produce stable products when used as recycled raw materials.

[0006] A method for producing wax from waste plastics (hereinafter sometimes abbreviated as waste plastics) (Patent Document 2) and a method for utilizing the wax (Patent Document 3) have been proposed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3917450 [Patent Document 2] Patent No. 5964825 [Patent Document 3] Patent No. 6880051 Summary of the Invention [Problem to be solved by the invention]

[0008] The recycled waxes proposed in Patent Documents 2 and 3 are made from waste plastics as raw materials, and because they contain impurities (PET, nylon, etc.) compared to virgin wax, their usage and applications are limited. In particular, when used in rubber compositions and tires, the degradation of mechanical properties and product deterioration due to the contamination of foreign matter is significant, making it difficult to use PCR materials.

[0009] Therefore, an object of the present invention is to provide a rubber composition and a tire using recycled wax produced from waste plastics, which have the same quality as those obtained when conventional virgin wax is used. [Means for solving the problem]

[0010] As a result of extensive research into solving the above-mentioned problems, the present inventors have discovered that by compounding a PIR wax obtained by thermally decomposing waste PIR plastics, particularly discarded polyethylene resins, into rubber compositions and tires, an anti-aging effect comparable to that obtained when virgin wax is compounded can be obtained, and further, better roll processability can be obtained than when virgin wax is compounded, thereby completing the present invention.

[0011] That is, the embodiments of the present invention are [1] to [4] shown below. [1] A rubber composition comprising a post-industrial recycled wax (A) and at least one rubber component (B) selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, wherein the post-industrial recycled wax (A) is contained in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the rubber component (B). [2] The rubber composition according to [1], wherein the post-industrial recycled wax (A) satisfies the following (i) to (iii): (i) The number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 500 or more and 8,000 or less. (ii) The ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (molecular weight distribution: Mw / Mn) measured by GPC is 1.0 or more and less than 4.0. (iii) The melting point (Tm) measured by differential scanning calorimetry (DSC) is 60°C or higher and 125°C or lower. [3] The rubber composition according to [1] or [2], wherein the post-industrial recycled wax (A) is a polyethylene wax. [4] A tire in which at least the surface layer of the tread portion and / or sidewall portion is made of the rubber composition according to any one of [1] to [3]. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a rubber composition and a tire made from PIR wax, which have an anti-aging effect comparable to that of a rubber component containing virgin wax, and which also have better roll processability than a rubber component containing virgin wax. Furthermore, this leads to a reduction in waste plastics, and is of great industrial value. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below.

[0014] A rubber composition according to one embodiment of the present invention comprises a post-industrial recycled wax (A) and at least one rubber component (B) selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, and contains 0.1 to 10 parts by mass of the post-industrial recycled wax (A) per 100 parts by mass of the rubber component (B).

[0015] The PIR wax (A) preferably has a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) of 500 to 8,000, more preferably 500 to 3,000. When the number average molecular weight (Mn) is within the above range, the blooming properties of the PIR wax (A) are optimized, and the anti-aging effect is maintained for a long period of time.

[0016] The PIR wax (A) preferably has a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (molecular weight distribution: Mw / Mn) measured by GPC of 1.0 or more and less than 4.0, more preferably 1.0 or more and less than 3.3. When the molecular weight distribution is within the above range, the blooming properties of the PIR wax (A) are optimized and the anti-aging effect is maintained for a long period of time.

[0017] The PIR wax (A) preferably has a melting point of 60° C. or higher and 125° C. or lower, more preferably 70° C. or higher and 115° C. If the melting point is within the above range, the PIR wax (A) melts and is appropriately dispersed in the rubber.

[0018] Next, a method for producing the PIR wax (A) will be described.

[0019] PIR wax (A) is produced by feeding waste PIR plastic into an extruder and thermally decomposing it in the extruder.

[0020] The waste plastic for PIR materials is preferably polyethylene resin, and examples of such waste plastics include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-high molecular weight polyethylene. A mixture of these waste plastics is also acceptable. The plastics are not limited to pellets or powder, but may also be in the form of films, sheets, bottles, fibers, pipes, injection-molded products, and other molded products, as well as their crushed parts. Examples of such waste plastics include used products, non-standard products, and discarded products. Of these, waste polyethylene generated during the extrusion lamination molding process is the most preferred. When the waste plastic is a rubber composition, it may be in a state where the components are melted and mixed together, or in a state where the components are physically mixed in the form of solids, such as pellets or scraps.

[0021] PIR waste plastics can be used as they are, with antioxidants added during manufacturing or when they are molded into products such as film.Furthermore, antioxidants can be added to prevent oxidative degradation during the thermal decomposition reaction, and the thermal decomposition reaction can also be carried out.

[0022] The extruder is not particularly limited, and examples thereof include a single-screw extruder, a co-rotating twin-screw extruder, a counter-rotating twin-screw extruder, a multi-screw extruder such as a four-screw or eight-screw extruder in which three or more screws are arranged in parallel in the cylinder of the extruder, and a tandem extruder in which two or more extruders are connected in series, an extruder in which the outlet of one extruder is connected to the inlet of the other extruder and arranged in an L-shape, an extruder in which the outlet of one extruder is connected to the side of the other extruder and arranged in a T-shape, etc. Furthermore, examples of the extruders constituting the tandem extruder include a single-screw extruder or a multi-screw extruder with two to eight screws, and two or more of these extruders can be combined to form a tandem extruder. Among these extruders, a co-rotating twin screw extruder, a 4- to 8-screw multi-screw extruder, or a tandem extruder is preferred because it can produce a PIR wax (A) of particularly stable quality and has excellent stability in torque and discharge rate during extrusion. These extruders are preferably equipped with a side feeder for adding a modifier.

[0023] The extruder is preferably equipped with a vacuum vent port to efficiently discharge pyrolyzed low-molecular-weight gas components outside the extruder. Furthermore, the ratio (L / D) of screw length (L) to screw diameter (D) is preferably 30 or more, particularly 40 or more, so that the pyrolysis of waste plastic can be efficiently carried out and PIR wax (A) of stable quality can be obtained.

[0024] The conditions for pyrolysis after feeding the waste plastic to the extruder should be adjusted appropriately depending on the molecular weight of the desired pyrolysis wax, but since pyrolysis can be carried out in a short time and the odor of the resulting pyrolysis wax can be easily suppressed, the cylinder temperature in the pyrolysis zone can be in the range of 330 to 480°C, more preferably 350 to 460°C, and particularly preferably 380 to 450°C. The residence time in the pyrolysis zone can be in the range of 0.5 to 60 minutes, more preferably 1 to 45 minutes, and particularly preferably 1.5 to 30 minutes.

[0025] In order to suppress the odor of the resulting PIR wax (A) and to facilitate control of the molecular weight and degree of modification, it is preferable to replace the atmosphere inside the extruder with an inert gas such as hydrogen, helium, argon, nitrogen, or carbon dioxide during pyrolysis, and nitrogen gas is particularly preferable. The wax extruded from the extruder can be pelletized by methods such as hot cutting, mist cutting, or underwater cutting, or by cooling on a steel belt and then cutting.

[0026] The PIR wax (A) can be used in any form such as pellets, powder, flakes, granules, grains, or paste.

[0027] In the present invention, the rubber component (B) is the main component of the rubber product and provides elasticity to the rubber product. The rubber component may be at least one selected from the group consisting of natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR).

[0028] Natural rubber (NR) generally used is natural rubber standardized by the Green Book (international quality packaging standard for various grades of natural rubber).

[0029] In addition, isoprene rubber (IR) has a specific gravity of 0.91 to 0.94 and a Mooney viscosity [ML 1+4 Isoprene rubber with a thermal expansion coefficient (TSC) (at 100°C) of 30 to 120 is generally used.

[0030] Styrene-butadiene rubber (SBR) has a specific gravity of 0.91 to 0.98 and a Mooney viscosity [ML 1+4 SBR having a viscosity index (100°C) of 20 to 120 is generally used.

[0031] Butadiene rubber (BR) has a specific gravity of 0.90 to 0.95 and a Mooney viscosity [ML 1+4(100°C)] of 20 to 120 is generally used.

[0032] The rubber component (B) may contain a rubber component other than the rubber components exemplified above. Examples of other rubber components include isoprene-isobutylene rubber (IIR), halogenated butyl rubber (X-IIR), and ethylene-propylene-diene rubber (EPDM).

[0033] The rubber component (B) may consist of one kind alone or a combination of two or more kinds. The rubber component (B) may also contain fibers or organic fillers within the range that does not impair the object of the present invention.

[0034] [Rubber composition] The rubber composition according to the present invention preferably contains the PIR wax (A) in an amount of usually 0.1 to 10 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component (B).

[0035] If the content of the PIR wax (A) is less than 0.1 parts by mass per 100 parts by mass of the rubber component, the absolute amount of wax that blooms onto the surface of the rubber product decreases, which may make the product more susceptible to cracking. On the other hand, if the content of the PIR wax (A) is more than 10 parts by mass per 100 parts by mass of the rubber component, the PIR wax (A) may bloom too much onto the surface of the rubber product, which may make the product more susceptible to discoloration.

[0036] The rubber composition can be produced by any known method, for example, by kneading the above components using a rubber kneading device such as an open roll or a Banbury mixer at 120 to 150°C for 5 to 10 minutes.

[0037] 〔tire〕 The tire according to the present invention is a tire in which at least the surface layer of the tread portion and / or the sidewall portion is obtained from the above rubber composition.

[0038] In the tire of the present invention, these portions are obtained from the above rubber composition, so that wax does not bloom on the surface, impairing the appearance, or causing cracks. The tire of the present invention is obtained by vulcanizing a green tire. At the green tire stage, at least the surface layer of the tread portion and / or sidewall portion is made of the above rubber composition. This green tire is placed in a mold vulcanizer and vulcanized, for example, at 140 to 180°C for 10 to 15 minutes to obtain a tire. [Example]

[0039] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these. (1) Evaluation method for PIR wax 1) GPC measurement Apparatus: HLC (registered trademark)-8321GPC / HT (detector: RI method) (manufactured by Tosoh Corporation) Columns: One column of (i) and three columns of (ii) below are used in series. (i) TSKgel® guardColumn H (HR) (30) HT (7.5 mm I.D.) x 7.5 cm (manufactured by Tosoh Corporation) x 1 (ii) TSKgel® GMH(HR)-H(20)HT (7.5 mm I.D.) x 30 cm (Tosoh Corporation) x 3 Eluent: 1,2,4-trichlorobenzene (containing 0.05 wt% BHT) (Purchased from Fujifilm Wako Pure Chemical Industries, Ltd.) Flow rate: 1.0mL / min Injection volume: 0.3mL Column temperature: 140℃ System temperature: 40°C Sample concentration: 1 mg / mL Calibration curve: quintic approximation curve using standard polystyrene manufactured by Tosoh Corporation. However, the molecular weight was converted to PE equivalent molecular weight using the Q factor.

[0040] 2) Melting point measurement Measured in accordance with JIS K7122 (2012).

[0041] The melting point of the PIR wax was measured by DSC7000X (manufactured by Hitachi High-Technologies Corporation) in accordance with the differential scanning calorimetry (DSC) method. Approximately 10 mg of the sample was sealed in an aluminum pan, heated from -20°C to 200°C at a rate of 10°C / min, and the endothermic peak of the obtained curve was determined as the melting point. Before this heating measurement, the sample was once heated to about 200°C, held for 5 minutes, and then cooled to -20°C at a rate of 20°C / min to unify the thermal history of the sample.

[0042] <Production Example of PIR Wax> [Production Example 1] As the extruder, a co-rotating twin-screw extruder with a screw diameter of 11 mm and a ratio of screw length L to screw diameter D (L / D) of 40 was used. As the waste plastic, polyethylene (number average molecular weight 15,000) of the used PIR material generated during the resin changeover in the extrusion lamination molding of low-density polyethylene (Tosoh Corporation's Petrothene (registered trademark) 205) was used. It was pulverized and volume-reduced to an average particle size of 10 mm or less by a pulverizer, and then fed from the main feeder of the extruder at a supply rate of 2 kg / hr together with a constant flow of nitrogen gas, and thermally decomposed by melt-kneading under the condition that the cylinder temperature in the thermal decomposition region of the extruder was heated to 450°C and the cooling region was heated to 200°C. Next, the melt-kneaded product was extruded onto a steel plate placed in a nitrogen atmosphere, cooled, and then pulverized to obtain powdery PIR wax. As a result of performing GPC measurement using the obtained PIR wax (A-1), the number average molecular weight (Mn) was 1,500, the molecular weight distribution (Mw / Mn) was 3.0, and the melting point (Tm) was 108°C.

[0043] [Production Example 2] PIR wax was obtained in the same manner as in Example 1, except that polyethylene (number average molecular weight 13,000) of the used PIR material, which was the end material of the laminated film of low-density polyethylene (Tosoh Corporation's Petrothene (registered trademark) 203), was used as the waste plastic. The analysis results of the obtained PIR wax (A-2) are shown in Table 1.

[0044] [Manufacturing Example 3] PIR wax was obtained in the same manner as in Example 1, except that the waste plastic used was polyethylene (number average molecular weight 13,000) from a used PIR material, which was a laminate film remnant of low-density polyethylene (Petrothene (registered trademark) 203 manufactured by Tosoh Corporation), and the feed rate was 120 g / hr. The analytical results of the obtained PIR wax (A-3) are shown in Table 1.

[0045] [Manufacturing Example 4] PCR wax was obtained in the same manner as in Example 1, except that the waste plastic used was polyethylene from PCR material (recovered from waste plastic containers and packaging, polypropylene (<0.5%) and polystyrene (<1.3%), containing trace amounts of other polymers (<0.03% polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene, polyamide, polyurethane)). The analytical results of the obtained PCR wax (B-1) are shown in Table 1.

[0046] [Manufacturing Example 5] PCR wax was obtained in the same manner as in Example 1, except that polyethylene of PCR material (recovered from waste beverage bottles, specific gravity 0.96, MFR (190°C, 10 minutes) 0.35) was used as the waste plastic. The analytical results of the obtained PCR wax (B-2) are shown in Table 1.

[0047] [Examples 1 to 3] In a Banbury mixer (1.7 liter capacity), 50 parts by mass of natural rubber (RRS#1) and 50 parts by mass of polybutadiene rubber (Nipol BR1220, manufactured by Zeon Corporation) were masticated for 30 seconds, followed by the addition of 1 part by mass of stearic acid (manufactured by New Japan Chemical Co., Ltd.), 50 parts by mass of carbon black (N550 Diablack E, manufactured by Mitsubishi Chemical Corporation), and 10 parts by mass of oil (KF96-100CS, manufactured by Shin-Etsu Chemical Co., Ltd.). After a total mixing time of 5 minutes, the mix was removed. The ram pressure and rotation speed were adjusted so that the compound temperature at the time of removal was 140°C to 150°C. After the obtained compound was cooled to room temperature, 2 parts by mass of an antioxidant (manufactured by Ouchi Shinko, product name 810NA), 3 parts by mass of zinc oxide (manufactured by Inoue Lime Industry), 1 part by mass of a vulcanization accelerator (manufactured by Ouchi Shinko, product name Noccela DM), 1 part by mass of paraffin wax (manufactured by Nippon Seiro, product name 155), 2 parts by mass of sulfur (manufactured by Tsurumi Chemical Industry) as a vulcanizing agent, and 2 parts by mass of PIR wax (A-1 to A-3) in Table 1 were added and kneaded for about 1 minute (the temperature at the time of removal was 110°C or less), and then sheeted using an 8-inch roll to obtain an unvulcanized rubber composition.

[0048] The rubber composition was then vulcanized using a steam heating press at a temperature of 150°C for 30 minutes to obtain a vulcanized rubber composition. The properties of the vulcanized rubber composition were measured using the following test methods. The results are shown in Table 2.

[0049] [Standard example] A vulcanized rubber composition was obtained in the same manner as in the Examples, except that a polyethylene wax (trade name: Sanwax (registered trademark)-171P, manufactured by Sanyo Chemical Industries, Ltd., physical properties of which are shown in Table 1) was used instead of the PIR wax used in the Examples. The evaluation results of the obtained vulcanized rubber composition are shown in Table 2.

[0050] [Comparative Examples 1 and 2] A vulcanized rubber composition was obtained in the same manner as in the Examples, except that the PCR waxes of Production Examples 4 and 5 (physical properties shown in Table 1) were used instead of the PIR wax used in the Examples. The evaluation results of the obtained vulcanized rubber composition are shown in Table 2.

[0051] [Ozone resistance test: JIS K 6301] The vulcanized rubber sheet was punched into the shape of a No. 1 dumbbell, and the rubber pieces were exposed to an ozone atmosphere (ozone concentration 100 pphm, temperature 40°C) at 50% elongation for 22 hours using an Ozone Weather Meter OSM-1V manufactured by Suga Test Instruments Co., Ltd., and the state of cracks was examined. The smaller and fewer the cracks on the surface of the rubber sheet, the better the ozone resistance. The results of the comparative example were used as the standard, and the following index was used for evaluation. (Evaluation indicators) ○: The size of the cracks is equal to or smaller than that of the standard example, and the number of cracks is less than twice as many.

[0052] ×: The cracks were larger than those of the standard sample and / or the number of cracks was twice or more.

[0053] [Roll processability] The processability of the unvulcanized rubber on the roll was evaluated as follows.

[0054] ⊚: The film is well wound around the roll and can be processed without any problems.

[0055] ○: The film is not wound around the roll well, but can be processed without any problems.

[0056] △: The winding onto the roll was poor, and processing was not possible unless a back roll with a high roll rotation speed was used.

[0057] ×: No wrapping around the roll at all, to the extent that processing is difficult.

[0058] [Rubber appearance evaluation: Whitening and discoloration test (indoor)] A vulcanized rubber sheet (145 x 145 x 2 mm) prepared by vulcanizing the rubber composition was hung in a constant temperature dry bath at 40°C and left for 45 days, after which it was removed and the surface of the rubber sheet was measured with a colorimeter (Minolta CM2002). L*(SCE) was used to evaluate whitening and discoloration. The smaller the L*(SCE) value, the darker the rubber surface and the better the appearance. Evaluation was performed using the following index, with the results of the comparative example as the standard. (Evaluation indicators) ◎: The value is 1.0 or more smaller than the standard example.

[0059] ○: The difference in value compared to the standard example is in the range of less than +0.5 to less than -1.0.

[0060] △: The difference in value compared to the standard example is in the range of +0.5 or more to less than +2.0.

[0061] ×: The value is +2.0 or more larger than the standard example. [Measurement of discoloration degree] After the ozone resistance test, the appearance of the test piece was evaluated visually.

[0062] ○: No change in surface color.

[0063] △: The surface is slightly discolored.

[0064] ×: The surface has turned brown or white.

[0065] [Table 1]

[0066] [Table 2] [Industrial Applicability]

[0067] PIR wax, produced by simply and efficiently pyrolyzing waste plastic from PIR materials, can reduce waste plastic and, when blended with rubber components, can provide excellent rubber compositions and tires.

Claims

1. The rubber composition contains a post-industrial recycled wax (A) and at least one rubber component (B) selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, and contains 0.1 to 10 parts by mass of the post-industrial recycled wax (A) per 100 parts by mass of the rubber component (B).

2. The rubber composition according to claim 1, wherein the post-industrial recycled wax (A) satisfies the following (i) to (iii): (i) The number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 500 or more and 8,000 or less. (ii) The ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (molecular weight distribution: Mw / Mn) measured by GPC is 1.0 or more and less than 4.

0. (iii) The melting point (Tm) measured by differential scanning calorimetry (DSC) is 60°C or higher and 125°C or lower.

3. The rubber composition according to claim 1, wherein the post-industrial recycled wax (A) is a polyethylene wax.

4. A tire in which at least the surface layer of the tread portion and / or sidewall portion is made of the rubber composition according to any one of claims 1 to 3.

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