Method for softening rubber using limonene

Abstract

To provide a method for producing softened rubber in which, by contacting vulcanized rubber with a liquid containing limonene and water, the viscosity of the liquid used in the reaction is reduced and the cost of raw materials used in the reaction is lowered.SOLUTION: A method for producing softened rubber by contacting vulcanized rubber with a liquid containing limonene and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing softened rubber. [Background technology]

[0002] Patent Document 1 below describes a method for recycling vulcanized rubber, which comprises the steps of impregnating vulcanized rubber chips with an aromatic oil, granulating the treated material, irradiating the granules with microwaves under reduced pressure, and recovering the treated granules. The aromatic oil is said to contain one selected from the group consisting of d-limonene, linalool, myrcene, or a mixture thereof.

[0003] Patent Document 2 below describes a method for reusing vulcanized rubber without changing the physical properties of the elastomer by using two solvents, DMSO and d-limonene. It is said that by contacting test pieces taken from tires with purified d-limonene, the Shore hardness of the vulcanized rubber gradually decreases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 5,362,759 [Patent Document 2] U.S. Patent No. 6,872,754 Summary of the Invention [Problem to be solved by the invention]

[0005] As in Patent Document 1 or Patent Document 2, d-limonene is used in a technology for recycling vulcanized rubber. In the methods of Patent Document 1 and Patent Document 2, d-limonene is used alone or mixed with a liquid such as linalool, myrcene, or DMSO.

[0006] Purified compounds of d-limonene, linalool, myrcene, and DMSO are available. However, these compounds are expensive, and the cost of large-scale reactions increases. Furthermore, purified d-limonene has a strong odor, so environmental considerations are needed when large-scale reactions are performed.

[0007] An object of the present invention is to provide a method for producing softened rubber in which the amount of limonene used in the reaction is reduced by bringing a liquid containing limonene and water into contact with vulcanized rubber. [Means for solving the problem]

[0008] Limonene is a non-polar liquid, and water is a polar solvent, so limonene and water are immiscible. The present invention is based on the discovery that contacting vulcanized rubber with a suspended liquid containing limonene and water, rather than purified limonene alone, softens the vulcanized rubber.

[0009] The present invention solves the above-mentioned problems by providing a method for producing softened rubber, in which vulcanized rubber is brought into contact with a liquid containing limonene and water to produce softened rubber.

[0010] In the method for producing softened rubber, the liquid may have a pH of 8 or less.

[0011] In the method for producing softened rubber, the temperature at which the liquid is brought into contact with the vulcanized rubber can be 40° C. or lower.

[0012] In the method for producing softened rubber, the liquid is an emulsion, and the emulsion can contain water as a dispersion medium and limonene as a dispersoid.

[0013] In the method for producing softened rubber, the liquid may contain 50% by volume or more of water.

[0014] In the method for producing softened rubber, the concentration of limonene can be set to 1 to 3100 mM. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for producing softened rubber in which the amount of limonene used in the reaction is reduced by bringing a liquid containing limonene and water into contact with vulcanized rubber. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the method for producing softened rubber of the present invention will be described.

[0017] The present invention is a method for producing softened rubber, in which vulcanized rubber is brought into contact with a liquid containing limonene and water to produce softened rubber.

[0018] Examples of the vulcanized rubber include natural rubber (NR) and synthetic rubber. Natural rubber and synthetic rubber may be used alone or in combination. The synthetic rubber is not particularly limited, but may include one or more synthetic rubbers selected from the group consisting of isoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), and butadiene rubber (BR). Diene-based rubbers having double bonds in the polymer main chain are preferred. These natural and synthetic rubbers can be any known type. Vulcanized rubbers have reduced fluidity through a crosslinking reaction. Rubbers vulcanized with known crosslinking agents such as sulfur, metal oxides (e.g., magnesium), selenium, tellurium, or organic oxides can also be used.

[0019] The vulcanized rubber may be blended with additives such as fillers such as carbon black or calcium carbonate, known vulcanization accelerators, known antioxidants, known plasticizers, etc. Since vulcanized rubber blended with additives can also be softened, the target vulcanized rubber may be waste materials such as tires, shoe soles, and cushioning materials.

[0020] The shape of the vulcanized rubber to be treated is not particularly limited. Thin vulcanized rubber sheets with a thickness of less than 0.1 mm, such as rubber gloves, can be softened, as can thick vulcanized rubber sheets with a thickness of 1.0 mm or more. The upper limit of the rubber thickness is not particularly limited, but may be, for example, 12.0 mm or less, 7.0 mm or less, or 3.0 mm or less. The upper limit of the rubber thickness is also not particularly limited, but may be, for example, a value exceeding 0 mm. The shape of the vulcanized rubber is not limited to a film or sheet, and molded products having various shapes containing rubber as the main component, such as granular materials such as rubber chips and flat materials such as rubber mats, are also eligible. Note that when the vulcanized rubber is not in a sheet shape, for example, granular materials, the thickness can be considered to be the portion where the particles have the largest diameter.

[0021] Limonene is a monocyclic monoterpene that exists as a liquid at room temperature and pressure and is practically insoluble in water. Limonene includes d-limonene, l-limonene, and the racemic dipentene. Any of d-limonene, l-limonene, and the racemic dipentene can be used in the softened rubber manufacturing method.

[0022] The liquid contains water in addition to limonene. The liquid may be an emulsion in which the dispersion medium is water and the dispersoid is limonene. The water content is not limited, but may be, for example, 30% by volume or more, 50% by volume or more, 80% by volume or more, or 88% by volume or more. The upper limit of the water content is not limited, but may be, for example, 99.99% by volume or less. The upper limit of the water content may be 99.3% by volume or less, or 98.5% by volume or less. Water can be obtained inexpensively, so a liquid containing limonene can be easily prepared. Furthermore, by increasing the amount of water used, the amount of limonene used can be reduced, thereby allowing a liquid containing limonene to be obtained inexpensively. Furthermore, as described below, even if the limonene concentration is excessively high, the effect of softening vulcanized rubber tends to saturate. Reducing the amount of limonene and increasing the amount of water is cost-effective and reduces the viscosity of the liquid, making it easier to handle.

[0023] The concentration of limonene in the liquid is not particularly limited, but can be 1 to 3100 mM. The upper limit of the limonene concentration can be, for example, 1000 mM or less. The lower limit of the limonene concentration can be, for example, 45 mM or more. The lower limit of the limonene concentration can be, for example, 75 mM or more.

[0024] The pH of the liquid is not particularly limited, but can be, for example, pH 8 or less. The lower limit of the pH is not particularly limited, but can be, for example, pH 2 or more. The lower limit of the pH can be pH 6 or more. If the pH of the liquid is 6 to 8, in many cases the water can be used as is without adjusting the pH. Furthermore, by adjusting the pH to 6 or less, bacterial growth in the reaction liquid can be prevented.

[0025] The pH of the liquid can be adjusted with one or more organic acids selected from the group consisting of, for example, acetic acid, succinic acid, tartaric acid, and citric acid. The organic acids listed above are not strong acids or toxic substances, so they are easy to handle, and wastewater treatment is relatively easy and inexpensive, making them suitable for use. Alternatively, the pH of the liquid may be adjusted with an appropriate buffer solution, such as a phosphate (sodium) buffer solution or an acetate (sodium) buffer solution. Acetic acid is preferred because of its high antibacterial effect.

[0026] The temperature at which the vulcanized rubber and the liquid are brought into contact is not particularly limited, but can be 40°C or lower. The lower limit of the temperature is not particularly limited, but can be a temperature above 0°C. When the vulcanized rubber and the liquid are brought into contact, the liquid may be heated to adjust the temperature, or may be kept at room temperature without heating. Room temperature is preferable because it reduces the energy and labor required for heating. If the temperature is high, the limonene contained in the liquid becomes more likely to volatilize, making the reaction conditions more likely to change. Furthermore, if the temperature is high, the limonene becomes more likely to volatilize, making odor problems more pronounced.

[0027] The time for which the vulcanized rubber is in contact with the liquid is not particularly limited and can be changed depending on the degree of softening of the vulcanized rubber and the size of the vulcanized rubber. The time for which the vulcanized rubber is in contact with the liquid can be, for example, 1 to 240 hours, or 1 to 100 hours.

[0028] Although not essential, before contacting the vulcanized rubber with the unsaturated fatty acid, a pretreatment may be carried out in which the vulcanized rubber is contacted with an organic solvent such as ethanol or methanol, or with a surfactant.

[0029] According to the above-described method for producing softened rubber, a solid rubber that is softer than the vulcanized rubber before the production method is carried out can be obtained. The detailed mechanism by which the vulcanized rubber is softened by contacting the vulcanized rubber with a liquid containing limonene and water is unknown, but it is presumed that limonene has a higher affinity with the vulcanized rubber than water, and the limonene contained in the liquid gathers around the vulcanized rubber. Therefore, even if the concentration of limonene in the liquid is relatively low, the effect of softening the vulcanized rubber can be obtained. In fact, when the vulcanized rubber is contacted with a liquid containing water and limonene, the limonene becomes localized around the vulcanized rubber, and thus the rubber can be efficiently softened with a small amount of limonene. [Example]

[0030] The present invention will be described below by way of examples. The examples shown below are merely examples of the present invention, and the technical scope of the present invention is not limited to the examples exemplified below.

[0031] [Test Examples 1 to 9] A 1.0 mm thick test piece of vulcanized rubber was prepared by the following method, and the test piece was brought into contact with a liquid containing limonene having the following composition, and the physical properties of the rubber were examined by the following method.

[0032] [Rubber test piece] Dumbbell-shaped test pieces were cut from a 1.0 mm thick rubber sheet manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 test piece punch (Kobunshi Keiki Co., Ltd.). The rubber sheet contained, by mass, 35.2% polymer components, 45.4% calcium carbonate, 16.6% carbon black, and 2.8% organic and inorganic components as trace components. The polymer components were primarily natural rubber, with a small amount of SBR.

[0033] [Reaction solution composition] The test specimens were immersed in a liquid containing limonene at the concentrations listed in Table 1 below, or in water (control). The container containing the test specimen and reaction solution was shaken in a water bath set at 100 rpm at 35°C for 20 hours to maintain constant temperature. After shaking, the liquid was wiped off, and the test specimens were subjected to the following tensile test. The limonene used was a first-class reagent (d-limonene) manufactured by Wako Pure Chemical Industries, Ltd. (product number 124-03892), and deionized water was used. The reaction solution was prepared by mixing linalool and deionized water to the concentrations listed in Table 1 to form an emulsion. The emulsion did not contain an emulsifier, and the water and limonene separated upon standing. The emulsion was translucent in appearance.

[0034] [Tensile test] The test was carried out using the following test method. The tensile test was carried out by attaching a digital force gauge (ZTA-500N) manufactured by IMADA to an electric measuring stand (vertical type) (MX2-500N) manufactured by IMADA, attaching clamps to the stand and the digital force gauge, and holding the test piece with the clamps, under the following conditions: The tensile speed was 1 mm / sec. The clamp used was a knurled cam attachment (GP-15 / 30) manufactured by IMADA.

[0035] The dumbbell-shaped test specimens used in the tensile test were cut using a No. 7 test specimen punch as described above. The width of the wide portions at both ends of the test specimen was 6.0 mm, the length of the wide portions at both ends was 7.0 mm, and the width of the narrow portion connecting the wide portions at both ends was 2.0 mm, and the length of the narrow portion was 10.0 mm. The thickness of the test specimen was equal to the thickness of the rubber sheet. The boundary between the narrow portion and the wide portion was fixed with a clamp. The distance between the clamps at the start of the tensile test was 10.0 mm.

[0036] Breaking elongation, tensile strength, 200% modulus (M 200 ) and the volume expansion rate were calculated using the following formula.

[0037] Breaking elongation (%) = Distance between clamps when test piece breaks ÷ Distance between clamps before tensioning begins × 100

[0038] Tensile strength (MPa) = Load at break of test piece (N) ÷ Cross-sectional area of ​​test piece (m 2 ) x 1 / 10 6

[0039] M 200 (MPa) = Load (N) when the test piece is elongated by 200% ÷ Cross-sectional area of ​​the test piece (m 2 ) x 1 / 10 6

[0040] Volume expansion rate = length (mm) of rubber sheet after immersion in the liquid ÷ length (mm) of rubber sheet before immersion in the liquid The length of the rubber sheet is the length in the longitudinal direction of the dumbbell-shaped test piece.

[0041] The composition of the reaction solution and the results of the tensile test are shown in Table 1 below.

[0042] [Table 1]

[0043] [Test Examples 10 to 18] Dumbbell-shaped test pieces were cut from a 1.0 mm thick rubber sheet manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 test piece punch (Kobunshi Keiki Co., Ltd.). The rubber sheet contained, by mass, 35.2% polymer components, 45.4% calcium carbonate, 16.6% carbon black, and 2.8% organic and inorganic components as trace components. The polymer components were primarily natural rubber, with a small amount of SBR.

[0044] The test pieces were immersed in a liquid containing limonene at each concentration listed in Table 2 below, or in water (control), and the container containing the test piece and reaction liquid was shaken in a water bath set at 100 rpm at 35°C for 20 hours. The liquid used in Test Examples 10 to 18 and the control was maintained at pH 3 by adding 0.1 M acetate buffer (acetic acid / sodium acetate buffer). After immersion, tensile tests were carried out on each test piece in the same manner as above to measure the elongation at break, tensile strength, and 200% modulus (M 200 The results are shown in Table 2. The limonene used in the tests in Table 2 was the same as that used in Table 1.

[0045] [Table 2]

[0046] The results in Tables 1 and 2 show that softened rubber can be produced by contacting vulcanized rubber with a liquid containing limonene. Furthermore, Test Examples 10 to 18 show that lowering the pH of the reaction liquid facilitates the softening of rubber. Furthermore, it is clear that the rubber-softening effect tends to saturate as the concentration of limonene in the liquid increases.

[0047] In the limonene-containing liquids used in Test Examples 1 to 18, the less limonene contained in the liquid, the less limonene odor there was and the easier it was to handle. Furthermore, the less limonene contained in the liquid, the cheaper the cost required to prepare the liquid.

Claims

1. A method for producing softened rubber by contacting vulcanized rubber with a liquid containing limonene and water.

2. The method for producing softened rubber according to claim 1 , wherein the liquid has a pH of 8 or less.

3. 3. The method for producing softened rubber according to claim 1, wherein the temperature at which the vulcanized rubber is brought into contact with the liquid is 40°C or lower.

4. the liquid is an emulsion; 3. The method for producing softened rubber according to claim 1, wherein the emulsion contains water as a dispersion medium and limonene as a dispersoid.

5. 3. The method for producing softened rubber according to claim 1, wherein the liquid contains 50% by volume or more of water.

6. The method for producing softened rubber according to claim 1 or 2, wherein the concentration of limonene in the liquid is 1 to 3100 mM.

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