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 Art

[0002] In the following Patent Document 1, aromatic oil is infiltrated into chips of vulcanized rubber, the treated material is granulated, and the granulated material is irradiated with microwaves under reduced pressure, and a method for recycling vulcanized rubber having a recovery step for the treated granulated material is described. The aromatic oil is said to contain one selected from the group consisting of d-limonene, linalool, myrcene, or a mixture thereof.

[0003] In the following Patent Document 2, a method for recycling vulcanized rubber using two solvents, DMSO and d-limonene, without changing the physical properties of the elastomer is described. And it is said that the Shore hardness of the vulcanized rubber gradually decreases by contacting a test piece collected from a tire with purified d-limonene.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As in Patent Document 1 or Patent Document 2, d-limonene is used in the 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] d-limonene, linalool, myrcene, and DMSO can be used as purified compounds. However, these compounds are expensive, and the cost increases even further when the reaction is scaled up. Furthermore, purified d-limonene has a strong odor, and consideration for the surrounding environment is necessary when the reaction is scaled up.

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

[0008] Limonene is a nonpolar liquid, while water is a polar solvent; therefore, limonene and water do not mix. This invention is based on the discovery that even a suspension of limonene and water, rather than purified limonene alone, can cause vulcanized rubber to soften when brought into contact with the vulcanized rubber.

[0009] The present invention solves the above problems by providing a method for producing softened rubber by contacting vulcanized rubber with a liquid containing limonene and water.

[0010] In the method for producing the softened rubber, the pH of the liquid can be reduced to 8 or less.

[0011] In the method for manufacturing the 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 the softened rubber described above, the liquid is an emulsion, and the emulsion can have water as the dispersion medium and limonene as the dispersed phase.

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

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

[0015] According to the present invention, a method for producing softened rubber is provided in which the amount of limonene used in the reaction is reduced by contacting the vulcanized rubber with a liquid containing limonene and water. [Modes for carrying out the invention]

[0016] The following describes embodiments for carrying out the method for manufacturing softened rubber according to the present invention.

[0017] The present invention relates to a method for producing softened rubber by contacting vulcanized rubber with a liquid containing limonene and water.

[0018] Examples of the vulcanized rubber include natural rubber (NR) or synthetic rubber. Natural rubber and synthetic rubber may be used individually or in combination. The synthetic rubber is not particularly limited, but examples 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 main chain of the polymer are preferred. Known natural rubbers or synthetic rubbers can be used. Vulcanized rubber is obtained by reducing its fluidity through a crosslinking reaction. Vulcanized rubber can be obtained by vulcanizing with known crosslinking agents such as sulfur, metal oxides such as magnesium, selenium, tellurium, or organic oxides.

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

[0020] The shape of the vulcanized rubber to be processed is not particularly limited. It is possible to soften a thin vulcanized rubber sheet with a thickness of less than 0.1 mm, such as a rubber glove, and it is also possible to soften a thick vulcanized rubber sheet with a thickness of 1.0 mm or more. The upper limit value of the rubber thickness is not particularly limited. For example, it may be 12.0 mm or less, 7.0 mm or less, or 3.0 mm or less. The upper limit value of the rubber thickness is not particularly limited, but for example, any value exceeding 0 mm may be used. The shape of the vulcanized rubber is not limited to a film shape or a sheet shape, and molded products having various shapes mainly composed of rubber, such as granular materials such as rubber chips and flat objects such as rubber mats, are targeted. In addition, when the shape of the vulcanized rubber is not sheet-like, for example, in the case of a granular material, the portion where the particle has the maximum diameter may be considered as the above-mentioned thickness.

[0021] The limonene is a monocyclic monoterpene, exists as a liquid at normal temperature and pressure, and is hardly soluble in water. Limonene includes d-limonene, l-limonene, and dipentene which is a racemic form. Any of d-limonene, l-limonene, and the racemic form can be used in the method for producing softened rubber.

[0022] In addition to limonene, the liquid contains water. The liquid may be an emulsion in which the dispersion medium is water and the dispersed substance is limonene. The water content is not limited, but for example, it may be 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 for example, it can be 99.99% by volume or less. The upper limit of the water content can be 99.3% by volume or less, or 98.5% by volume or less. Since water can be procured at a low cost, it is possible to easily prepare a liquid containing limonene. Also, if the amount of water used is increased, the amount of limonene used can be reduced, so a liquid containing limonene can be obtained at a low cost. Further, as will be described later, even if the concentration of limonene is excessively increased, the effect of softening the vulcanized rubber tends to saturate. Reducing the amount of limonene and increasing the amount of water is efficient in terms of cost, and the viscosity of the liquid decreases, making it easier to handle.

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

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

[0025] The pH of the liquid can be adjusted using, for example, one or more organic acids selected from the group consisting of acetic acid, succinic acid, tartaric acid, and citric acid. Such organic acids are suitable for use because they are not strong acids or hazardous substances, are easy to handle, allow for relatively easy disposal of waste liquid, and are inexpensive. In addition, the pH of the liquid may be adjusted using appropriate buffer solutions such as sodium phosphate buffer or sodium acetate buffer. Acetic acid is preferred because it has a high bacterial inhibitory 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 above 0°C. When bringing the vulcanized rubber and the liquid into contact, the liquid may be heated to adjust the temperature, or it may be at room temperature without heating. At room temperature is preferable because it eliminates the energy and labor required for heating. If the temperature is high, the limonene contained in the liquid becomes more volatile, and the reaction conditions tend to change. Also, if the temperature is high, the volatilization of limonene tends to become more pronounced, and odor problems tend to become more noticeable.

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

[0028] Although not mandatory, pretreatment may be performed before contacting the vulcanized rubber with the unsaturated fatty acid, such as contacting the vulcanized rubber with an organic solvent like ethanol or methanol, or contacting the vulcanized rubber with a surfactant.

[0029] According to the above method for manufacturing softened rubber, a softened solid rubber can be obtained compared to the vulcanized rubber before the manufacturing method is carried out. The detailed mechanism by which vulcanized rubber softens when it is brought into contact with a liquid containing limonene and water is unknown, but it is presumed that limonene has a higher affinity for vulcanized rubber than water, and the limonene contained in the liquid gathers around the vulcanized rubber, so even if the concentration of limonene in the liquid is relatively low, the effect of softening the vulcanized rubber can be obtained. Rather, when vulcanized rubber is brought into contact with a liquid containing water and limonene, the limonene becomes localized around the vulcanized rubber, so the rubber can be softened efficiently with a small amount of limonene. [Examples]

[0030] The present invention will be described below with reference to 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 shown.

[0031] [Test Examples 1 to 9] A 1.0 mm thick vulcanized rubber test specimen was prepared using the following method, and the physical properties of the rubber were investigated by contacting the test specimen with a liquid containing limonene having the following composition.

[0032] [Rubber test piece] A 1.0 mm thick rubber sheet manufactured by iteck co., ltd. was cut into dumbbell-shaped test pieces using a JIS K 6251 No. 7 test piece punching blade (Kyoko Keiki Co., Ltd.). The rubber sheet contains, by mass, 35.2% polymer components, 45.4% calcium carbonate, 16.6% carbon black, and 2.8% trace organic and inorganic substances. The polymer components are mainly natural rubber with a small amount of SBR.

[0033] [Composition of the reaction solution] The test specimens were immersed in liquids containing limonene at the concentrations listed in Table 1, or in water (control). The containers containing the test specimens and reaction solutions were then shaken in a water bath set to 100 rpm at 35°C for 20 hours to maintain a constant temperature. After shaking, the liquid was wiped off, and the test specimens were subjected to the following tensile tests. Limonene used was first-grade reagent (d-limonene) (product code 124-03892) manufactured by Wako Pure Chemical Industries, Ltd., and deionized water was used. The reaction solution was an emulsion prepared by mixing linalool and deionized water to the concentrations listed in Table 1. The emulsion did not contain any emulsifiers, and when the emulsion was allowed to stand, the water and limonene separated. The emulsion was semi-transparent in appearance.

[0034] [Tensile test] The following test method was used. For the tensile test, an IMADA Corporation digital force gauge (ZTA-500N) was attached to an IMADA Corporation electric measuring stand (vertical type) (MX2-500N). Clamps were attached to the stand and the digital force gauge, and the test specimen was held by the clamps. The tensile test was performed under the following conditions. The tensile speed was 1 mm / second. An IMADA Corporation knurled cam attachment (GP-15 / 30) was used as the clamp.

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

[0036] Elongation at break, tensile strength, 200% modulus (M) 200 The coefficients of volume expansion and volume expansion were calculated using the following formula.

[0037] Elongation at break (%) = Distance between clamps at the time of specimen fracture ÷ Distance between clamps before tension begins × 100

[0038] Tensile strength (MPa) = Load at the time of specimen fracture (N) ÷ Cross-sectional area of ​​specimen (m²) 2 ) × 1 / 10 6

[0039] M 200 (MPa) = Load (N) when the test specimen is stretched 200% ÷ Cross-sectional area (m²) of the test specimen 2 ) × 1 / 10 6

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

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

[0042] [Table 1]

[0043] [Test Examples 10 to 18] A 1.0 mm thick rubber sheet manufactured by iteck co., ltd. was cut into dumbbell-shaped test pieces using a JIS K 6251 No. 7 test piece punching blade (Kyoko Keiki Co., Ltd.). The rubber sheet contains, by mass, 35.2% polymer components, 45.4% calcium carbonate, 16.6% carbon black, and 2.8% trace organic and inorganic substances. The polymer components are mainly natural rubber with a small amount of SBR.

[0044] The test specimens were immersed in liquids containing limonene at the concentrations listed in Table 2 below, or in water (control). The containers containing the test specimens and reaction solutions were then shaken in a water bath set to 100 rpm at 35°C for 20 hours. The liquids used in Test Examples 10 to 18 and the control were adjusted to maintain a pH of 3 by adding 0.1 M acetate buffer (acetic acid / sodium acetate buffer). Tensile tests were performed on each immersion specimen using the same method as described above, and the elongation at break, tensile strength, and 200% modulus (M) were measured. 200 ) was determined. 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, from Test Examples 10 to 18, it can be seen that as the pH of the reaction solution decreases, the softening of the rubber is more easily promoted. In addition, it can be seen that as the concentration of limonene in the liquid increases, the effect of softening the rubber tends to saturate.

[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 lower the amount of limonene in the liquid, the lower the cost of preparing the liquid.

Claims

1. A method for producing softened rubber involves contacting vulcanized rubber with a liquid containing limonene and water to produce softened rubber. The aforementioned liquid contains water in an amount of 50% or more by volume. The vulcanized rubber is natural rubber (NR), synthetic rubber, or a mixture of the natural rubber and the synthetic rubber. The aforementioned synthetic rubber is 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). A method for manufacturing softened rubber, which involves localizing limonene around the vulcanized rubber to soften it.

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

3. The method for producing softened rubber according to claim 1 or 2, wherein the temperature at which the vulcanized rubber is brought into contact with the liquid is 40°C or lower.

4. The aforementioned liquid is an emulsion, The method for producing softened rubber according to claim 1 or 2, wherein the emulsion is a dispersion medium of water and the dispersed phase is limonene.

5. 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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