JP7250379B1 - Method for producing softened rubber - Google Patents

Abstract

A method for producing a softened vulcanized rubber by utilizing linalool without relying on the Fenton reaction caused by hydrogen peroxide and divalent iron ions is provided. A method for producing a softened rubber comprising contacting a vulcanized rubber with a liquid containing linalool to produce a softened rubber. The liquid may contain, in addition to linalool, unsaturated fatty acids having one or more double bonds. The unsaturated fatty acid may be one or more unsaturated fatty acids selected from the group consisting of linoleic acid, oleic acid, linolenic acid, and arachidonic acid. The liquid may have a pH of 7.5 or less. The liquid may contain water. The liquid may contain 50% by volume or more of water. The temperature at which the vulcanized rubber and the liquid are brought into contact may be room temperature. [Selection figure] None

Description

The present invention relates to a method for producing softened rubber.

Patent Literature 1 describes a method of decomposing vulcanized rubber to obtain liquid rubber using lipid peroxidation. Specifically, for 100 ml of a reaction solution containing 0.2 mM hydrogen peroxide, 1 mM ferrous sulfate, 5 mM linoleic acid, 15 mM buffer, and 0.01 mM nonionic surfactant, It is said that the rubber is decomposed by immersing 0.1 g of latex rubber gloves and stirring at 37° C. for 24 hours. After that, it is described that the reaction liquid obtained by decomposing the rubber is subjected to a predetermined treatment to recover the rubber component.

JP 2011-153272 A

The method of Patent Document 1 is said to cause a Fenton reaction between hydrogen peroxide and divalent iron ions derived from ferrous sulfate to produce hydroxyl radicals. Hydroxy radicals are said to act as initiators and give rise to lipid radicals. Lipid radicals are said to radicalize vulcanized rubber to produce vulcanized rubber radicals. Vulcanized rubber radicals are said to be oxidized and partly undergo β-cleavage. Also, it is said that the double bond site of the vulcanized rubber is decomposed by being attacked by lipid radicals and undergoing β-cleavage. That is, in the method of Document 1, hydrogen peroxide and divalent iron ions are essential for softening the rubber.

In the method of Patent Document 1, hydrogen peroxide, a salt containing divalent iron ions such as ferrous sulfate, linoleic acid, a buffer, and a nonionic surfactant are used for the purpose of causing the Fenton reaction. was used as a reaction solution, and the preparation of the reaction solution was complicated. It becomes more complicated, especially when performing a large-scale reaction.

In addition, linoleic acid has a high unit price, and the method of Patent Document 1 has a problem of increased cost.

The present invention provides a method for producing softened vulcanized rubber by utilizing linalool without relying on the Fenton reaction caused by hydrogen peroxide and divalent iron ions.

The above problem is solved by a method for producing a softened rubber in which a vulcanized rubber is brought into contact with a liquid containing linalool to produce a softened rubber.

In the method for producing a softened rubber described above, the liquid preferably contains an unsaturated fatty acid having one or more double bonds in addition to linalool.

In the method for producing softened rubber, the unsaturated fatty acid is preferably one or more unsaturated fatty acids selected from the group consisting of linoleic acid, oleic acid, linolenic acid, and arachidonic acid.

In the above method for producing a softened rubber, the liquid preferably has a pH of 7.5 or less.

In the above method for producing softened rubber, the liquid preferably contains water. The liquid preferably contains 50% by volume or more of water.

In the method for producing the softened rubber described above, the temperature at which the vulcanized rubber and the liquid are brought into contact is preferably normal temperature.

According to the present invention, it is possible to provide a method for producing softened vulcanized rubber by using linalool without using the Fenton reaction caused by hydrogen peroxide and divalent iron ions.

Hereinafter, the form for implementing the softened rubber of this invention is demonstrated.

The present invention is a method for producing softened rubber in which vulcanized rubber is brought into contact with a liquid containing linalool to produce softened rubber.

The method of contacting the vulcanized rubber with the linalool-containing liquid is not particularly limited as long as the vulcanized rubber and the linalool-containing liquid can be contacted. For example, the vulcanized rubber may be immersed in a liquid containing linalool, or the liquid containing linalool may be sprayed on the vulcanized rubber. In the case of immersion, contact may be made while shaking.

Natural rubber (NR) or synthetic rubber can be used as the vulcanized rubber. Natural rubber and synthetic rubber may be used alone or in combination. The synthetic rubber is not particularly limited, but isoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR) and butadiene rubber (BR). One or more synthetic rubbers selected from the group consisting of Known rubbers can be used as these natural rubbers or synthetic rubbers. A vulcanized rubber has a reduced fluidity due to a cross-linking reaction. Those vulcanized with known cross-linking agents such as metal oxides such as sulfur and magnesium, selenium, tellurium, or organic oxides can be used.

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

The shape of the vulcanized rubber to be treated is not particularly limited. For example, it can soften a thin vulcanized rubber sheet with a thickness of less than 0.1 mm, such as rubber gloves, and a thick vulcanized rubber sheet with a thickness of 1.0 mm or more. . Although the upper limit of the thickness of the rubber is not particularly limited, it may be, for example, 12.0 mm or less, 7.0 mm or less, or 3.0 mm or less. The shape of the vulcanized rubber is not limited to film-like or sheet-like, and can be molded articles having various shapes, such as granular materials such as rubber chips and flat materials such as rubber mats, having rubber as a main component. If the shape of the vulcanized rubber is not in the form of a sheet, for example, in the case of granules, the portion where the particles have the maximum diameter may be considered as the above thickness.

The linalool-containing liquid preferably contains water in addition to linalool. The water content is not limited, but may be, for example, 50% by volume or more, or 80% by volume or more. The upper limit of the water content is not limited, but can be, for example, 99.8% by volume or less. Since water can be procured inexpensively, it is possible to easily prepare a liquid containing linalool. Moreover, if the amount of water used is increased, the amount of linalool used can be reduced, so a liquid containing linalool can be obtained at low cost. Further, as will be described later, even if the concentration of linalool is excessively increased, the effect of softening the vulcanized rubber tends to be saturated. If the amount of linalool is reduced and water is increased, it is efficient in terms of cost, and if linalool and unsaturated fatty acids are used together, the liquid becomes less viscous and easier to handle.

The linalool-containing liquid may contain, in addition to linalool, unsaturated fatty acids having one or more double bonds. Examples of unsaturated fatty acids include one or more unsaturated fatty acids selected from the group consisting of linoleic acid, oleic acid, linolenic acid, and arachidonic acid.

Although the pH of the liquid containing linalool is not particularly limited, for example, it is preferably pH 7.5 or less, more preferably pH 5.5 or less, and even more preferably pH 3.5 or less. Although the lower limit of pH is not particularly limited, it can be, for example, pH 2.0 or higher. The softening of the rubber can be promoted by adjusting the pH of the liquid containing linalool.

The pH of the liquid containing linalool is not particularly limited, but can be adjusted by one or more organic acids selected from the group consisting of, for example, acetic acid, succinic acid, tartaric acid, and citric acid. Organic acids such as those described above are not strong acids or deleterious substances, are easy to handle, are relatively easy to treat waste liquids, and are inexpensive, so they can be preferably used. Among organic acids, acetic acid has an antibacterial effect and can suppress propagation of microorganisms. The use of acetic acid is preferable because it can suppress the growth of microorganisms in the liquid containing linalool and the resulting pH fluctuation of the reaction solution. In addition, the pH of the liquid containing linalool may be adjusted with an appropriate buffer such as phosphate (sodium) buffer or acetate (sodium) buffer.

As linalool, (R) form, (S) form, racemic form including both (R) form and (S) form can be used.

The concentration of linalool in the linalool-containing liquid or the total concentration of linalool and unsaturated fatty acids (hereinafter referred to as the concentration of linalool, etc.) is appropriately changed depending on the shape of the vulcanized rubber. That is, when the thickness of the vulcanized rubber is large, the concentration of linalool or the like contained in the liquid is increased. Conversely, when the thickness of the vulcanized rubber is small, the concentration of linalool or the like contained in the liquid is reduced. Even if the concentration of linalool or the like contained in the liquid is excessively increased, the effect of softening the vulcanized rubber tends to be saturated. In order to reduce costs, the concentration of linalool or the like in the liquid is preferably 700 mM or less, more preferably 540 mM or less, and more preferably 270 mM or less. The lower limit of linalool or the like in the liquid may be selected in consideration of the shape of the vulcanized rubber, as described above, and may be, for example, 5 mM or more, or 10 mM or more.

When the unsaturated fatty acid is blended with the liquid containing linalool, the concentration of the unsaturated fatty acid is not particularly limited, but for example, it is preferably 110% or less of the linalool concentration (mM), and the linalool concentration It is more preferably 60% or less of the linalool concentration (mM), more preferably 50% or less of the linalool concentration (mM), and more preferably 20% or less of the linalool concentration (mM). The lower limit of the unsaturated fatty acid is not particularly limited, but can be 0% or more, or 1% or more of the concentration (mM) of linalool.

Adding an unsaturated fatty acid to a liquid containing linalool tends to shorten the rubber softening time. If it is desired to soften the rubber in a short period of time, it is preferable to add unsaturated fatty acids.

Compared to unsaturated fatty acids, linalool has low viscosity, is easy to handle, is easy to adjust the concentration, and is low in cost. If these characteristics are important, the unsaturated fatty acid should be either not added or the content of the unsaturated fatty acid should be reduced.

Liquids containing linalool do not decompose vulcanizates by the Fenton reaction. Whether the Fenton reaction is used can be determined by whether or not the liquid containing linalool contains both divalent iron ions and hydrogen peroxide. When hydrogen peroxide is contained and divalent iron ions are contained as impurities in excess of the permissible concentration, it can be determined that the Fenton reaction is utilized. If it does not contain hydrogen peroxide, or if it does not contain iron, or if it contains only an allowable concentration of iron as an impurity, it can be determined that the Fenton reaction is not being used.

Since the rubber softening method described above does not utilize the Fenton reaction, in principle, it is not necessary to contain iron, which generates iron ions, and hydrogen peroxide. However, tap water or industrial water may contain 0 to 0.3 mg/L of iron as an impurity. The iron contained as an impurity may be used as it is without being removed. For example, as the solvent for the liquid, water that has undergone operations such as distillation, ion exchange, or ultrafiltration, or industrial water or tap water containing iron in the range of 0 to 0.3 mg/L can be used. . Note that divalent iron ions become trivalent iron ions when exposed to air. The iron content referred to herein is the sum of bivalent iron ions and trivalent iron ions.

The temperature at which the vulcanized rubber is brought into contact with the unsaturated fatty acid to soften the vulcanized rubber is not particularly limited. good too. Normal temperature is preferable because the energy and man-hours required for heating can be omitted.

The time for which the vulcanized rubber is brought into contact with the linalool-containing liquid is not particularly limited, but the effect of softening the rubber peaks out even if the contact is made for a long time. More preferably, the lower limit of the contact time is, for example, 10 hours or longer. More preferably, the upper limit of the contact time is, for example, 30 hours or less. When linalool and unsaturated fatty acids are used in combination, the reaction time may be, for example, 1 to 240 minutes.

Although not essential, pretreatment such as contacting the vulcanized rubber with an organic solvent such as ethanol or methanol or contacting the vulcanized rubber with a surfactant before contacting the vulcanized rubber with the unsaturated fatty acid. may be implemented.

According to the method for producing a softened rubber described above, it is possible to obtain a solid rubber that is softened compared to the vulcanized rubber before the production method is carried out. The detailed mechanism by which the vulcanized rubber is softened by bringing the vulcanized rubber into contact with a liquid containing linalool is unknown, but it is believed that the crosslinked structure of the vulcanized rubber is cleaved by a specific linalool. guessed.

The linalool-containing liquid may contain an organic solvent such as acetone, and a surfactant. By containing an organic solvent such as acetone and a surfactant, the softening of the vulcanized rubber can be accelerated and the time required for softening the vulcanized rubber can be shortened.

As the organic solvent, it is preferable to use a water-soluble organic solvent such as methanol, ethanol, or acetone. As the surfactant, an anionic surfactant such as ammonium lauryl sulfate can be preferably used. When adding an organic solvent and a surfactant, for example, the organic solvent can be adjusted to 1.30 to 4.1 M and the surfactant can be adjusted to 0.7 to 1.4 mM.

Examples of the present invention will be described below. The examples shown below are merely examples of the present invention, and the technical scope of the present invention is not limited to the illustrated examples.

[Test Examples 1 to 3]
A test piece of vulcanized rubber with a thickness of 1.0 mm is prepared by the following method, and the test piece is brought into contact with a liquid containing linalool having the following composition, and the physical properties of the rubber are examined by the following method. rice field.

[Rubber test piece]
Dumbbell-shaped specimens were cut out from rubber sheets having a thickness of 1.0 mm manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 specimen punching blade (Kobunshi Keiki Co., Ltd.). The above rubber sheet contains 35.2% polymer component, 45.4% calcium carbonate, 16.6% carbon black, and 2.0% organic matter and inorganic matter as minor components, based on mass. Contains 8%. The polymer component is mainly composed of natural rubber and contains a small amount of SBR.

[Composition of reaction solution]
The test piece was immersed in a liquid containing linalool at each concentration listed in Table 1 below, or water (control), and the test piece and reaction solution were placed in a container at 35°C for 20 hours at 100 rpm. was shaken in a water bath set to After shaking, the liquid was wiped off and the specimen was subjected to the following tensile test. As linalool, a first grade reagent (racemic form) manufactured by Wako Pure Chemical Industries, Ltd. was used, and as water, deionized water was used. A reaction solution was prepared by mixing linalool and deionized water at concentrations shown in Table 1. The liquid (reaction solution) containing linalool does not contain divalent iron ions and hydrogen peroxide.

[Tensile test]
It implemented by the following test methods. In the tensile test, a digital force gauge (ZTA-500N) manufactured by IMADA was attached to an electric test stand (vertical type) (MX2-500N) manufactured by IMADA, and a clamp was attached to the stand and the digital force gauge. A tensile test was performed under the following conditions while holding the test piece with a clamp. The tensile speed was set to 1 mm/sec. For the clamp, a knurled cam attachment (GP-15/30) manufactured by IMADA was used.

Dumbbell-shaped test pieces used in the tensile test were cut out with a No. 7 test piece punching blade as described above. The width of the wide portions at both ends of the test piece 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, The narrow portion has a length of 10.0 mm. The thickness of the test piece is equal to the thickness of the rubber sheet. A boundary line between the narrow portion and the wide portion was fixed with a clamp. The distance between the clamps at the beginning of the tensile test is 10.0 mm.

Elongation at break, tensile strength, and 300% modulus ( _M300 ) were determined by the following equations.

Elongation at break (%) = Distance between clamps when test piece breaks / Distance between clamps before starting tension x 100

Tensile strength (MPa) = load (N) at break of test piece / cross-sectional area of test piece (m ² ) × 1/10 ⁶

M ₃₀₀ (MPa) = load (N) when the test piece is stretched 300% / cross-sectional area of the test piece (m ² ) × 1/10 ⁶

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

[Test Examples 4 to 8]
Dumbbell-shaped specimens were cut out from rubber sheets having a thickness of 5.0 mm manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 specimen punching blade (Kobunshi Keiki Co., Ltd.). The composition of the rubber sheet is the same as that of the rubber sheet used in the test of Table 1, but the thickness is different. The test piece was immersed in a liquid containing linalool at each concentration listed in Table 2 below, or water (control), and the test piece and reaction solution were placed in a container at 35°C for 20 hours at 100 rpm. was shaken in a water bath set to For Test Examples 4, 5, and 8, reaction solutions were prepared by mixing linalool and deionized water so that the concentrations shown in Table 2 were obtained. For Test Example 6, the pH of an acetic acid solution (acetic acid concentration of 0.1 M) prepared by mixing acetic acid and deionized water was adjusted to pH 3.0 with a diluted sodium hydroxide solution, and the acetic acid solution (organic Acid solution) and linalool were mixed to prepare a reaction solution. For Test Example 7, the pH of a citric acid solution (0.1 M citric acid concentration) prepared by mixing citric acid and deionized water was adjusted to pH 5.0 with a diluted sodium hydroxide solution. An acid solution and linalool were mixed to prepare a reaction solution. The same linalool and water as above were used. The liquid (reaction solution) containing linalool does not contain divalent iron ions and hydrogen peroxide. Each test piece after immersion was subjected to a tensile test in the same manner as described above to determine elongation at break, tensile strength, and 300% modulus (M ₃₀₀ ). Table 2 shows the results.

From the results in Tables 1 and 2, it can be seen that a softened rubber can be produced by bringing vulcanized rubber into contact with a liquid containing linalool. Further, from Test Examples 6 to 8, it can be seen that softening of the rubber is accelerated when the pH of the reaction solution is lowered.

[Test Examples 9 to 14]
Dumbbell-shaped specimens were cut out from rubber sheets having a thickness of 1.0 mm manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 specimen punching blade (Kobunshi Keiki Co., Ltd.). The rubber sheet is the same as the rubber sheet used in the tests in Table 1. The test piece is immersed in a liquid containing each concentration of linalool and each concentration of linoleic acid shown in Table 3 below, or water (control), and a container containing the test piece and the reaction solution is °C with a water bath set at 100 rpm for 20 hours. The same linalool and water as above were used. The liquid (reaction solution) containing linalool does not contain divalent iron ions and hydrogen peroxide. As linoleic acid, a first grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used. Each reaction solution except for the control was prepared by mixing succinic acid and deionized water to prepare a succinic acid solution (0.1 M succinic acid concentration), which was adjusted to pH 3.0 with a diluted sodium hydroxide solution. The succinic acid solution (organic acid solution) and linalool were mixed to prepare a reaction solution. Each test piece after immersion was subjected to a tensile test in the same manner as described above to determine elongation at break, tensile strength, and 300% modulus (M ₃₀₀ ). Table 3 shows the results.

[Test Examples 15 and 16]
Dumbbell-shaped specimens were cut out from rubber sheets having a thickness of 5.0 mm manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 specimen punching blade (Kobunshi Keiki Co., Ltd.). The rubber sheet is the same as the rubber sheet used in the tests in Table 2 above. The test piece is immersed in a liquid containing each concentration of linalool and each concentration of linoleic acid shown in Table 4 below, or water (control), and a container containing the test piece and the reaction solution is °C with a water bath set at 100 rpm for 20 hours. The same linalool, linoleic acid, and water as above were used. The liquid (reaction solution) containing linalool does not contain divalent iron ions and hydrogen peroxide. As linoleic acid, a first grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used. The reaction solution for the test piece 15 was prepared by mixing tartaric acid and deionized water and adjusting the pH of a tartaric acid solution (tartaric acid concentration: 0.1 M) to pH 3.0 with a diluted sodium hydroxide solution. A liquid (organic acid liquid) and linalool were mixed to prepare a reaction liquid. Each test piece after immersion was subjected to a tensile test in the same manner as described above to determine elongation at break, tensile strength, and 300% modulus (M ₃₀₀ ). Table 4 shows the results.

As shown in Tables 3 and 4, it can be seen that a softened rubber can be obtained even if a part of linalool is replaced with linoleic acid.

[Test Examples 17 to 19]
Dumbbell-shaped specimens were cut out from rubber sheets having a thickness of 1.0 mm manufactured by Iteck Co., Ltd. using a JIS K 6251 No. 7 specimen punching blade (Kobunshi Keiki Co., Ltd.). The rubber sheet is the same as the rubber sheet used in the tests in Table 1. The test piece was immersed in a liquid containing linalool at the concentration shown in Table 5 below and each concentration of oleic acid, linolenic acid, or arachidonic acid, or water (control), and the test piece and the reaction solution was shaken in a water bath set at 100 rpm for 20 hours at 35°C. The same linalool and water as above were used. The liquid (reaction solution) containing linalool does not contain divalent iron ions and hydrogen peroxide. For oleic acid, linolenic acid, or arachidonic acid, first grade reagents manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. were used. Except for the control, each reaction solution was prepared by mixing acetic acid and deionized water (acetic acid concentration: 0.1 M), and the pH was adjusted to pH 3.0 with a diluted sodium hydroxide solution. A liquid (organic acid liquid) and linalool were mixed to prepare a reaction liquid. Each test piece after immersion was subjected to a tensile test in the same manner as described above to determine elongation at break, tensile strength, and 300% modulus (M ₃₀₀ ). Table 5 shows the results.

As shown in Table 5, it can be seen that a softened rubber can be obtained even if a part of linalool is replaced with oleic acid, linolenic acid, or arachidonic acid.

[Test Example 20]
A 1.0 mm-thick vulcanized rubber sheet containing EPDM as the main component was immersed in a liquid containing linoleic acid at a concentration shown in Table 6 or water (control) and immersed in a vortex mixer set at 100 rpm. After agitation, the vessel containing the specimen and reaction was shaken in a water bath set at 100 rpm at 50° C. for 3 hours. A reaction solution was prepared by mixing linoleic acid and deionized water. The physical properties of the rubber sheet were evaluated 3 hours after the start of immersion. For linoleic acid, the same reagent as above was used, and for water, deionized water was used. A liquid (reaction solution) containing linoleic acid does not contain divalent iron ions and hydrogen peroxide.

The physical properties of the rubber sheet were evaluated for tensile strength, elongation at break and 300% modulus in the same manner as above. Table 6 shows the results of physical property evaluation.

As shown in Table 6, it can be seen that the use of linoleic acid results in a softened rubber with a shorter reaction time.

The reaction liquids used in Test Examples 1 to 20 had a volume of 1 ml, and the amount of water contained in each reaction liquid was in the range of 80 to 99% by volume. Since most of the water contained in the reaction solution is water, it is easy to handle and the cost required for preparation of the reaction solution is low.

Claims (6)

A method for producing a softened rubber in which a vulcanized rubber is brought into contact with a liquid containing linalool to produce a softened rubber,
The method for producing a softened rubber , wherein the liquid contains 50% by volume or more of water . 2. The method for producing softened rubber according to claim 1, wherein the liquid contains an unsaturated fatty acid having one or more double bonds in addition to linalool. 3. The method for producing softened rubber according to claim 2, wherein the unsaturated fatty acid is one or more unsaturated fatty acids selected from the group consisting of linoleic acid, oleic acid, linolenic acid and arachidonic acid. The method for producing softened rubber according to claim 1 or 2, wherein the liquid has a pH of 7.5 or less. The method for producing softened rubber according to claim 1 or 2, wherein the liquid contains water. The method for producing softened rubber according to claim 1 or 2, wherein the temperature at which the vulcanized rubber and the liquid are brought into contact is normal temperature.