JP2016079272A - Method for treating natural rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating natural rubber reducing odor of the natural rubber with a solid shape, maintaining deodorization effects and hardly reducing physical properties such as thermal aging resistance.SOLUTION: There is provided a method for treating natural rubber including a base treatment process for contacting natural rubber with a solid shape without a deproteinizing treatment with a basic solution and a pH adjustment process for adjusting pH of a base treated natural rubber obtained by the base treatment process to 2 to 7.SELECTED DRAWING: None

Description

The present invention relates to a method for treating natural rubber.

Natural rubber is used in various fields including tires because of its excellent physical properties, particularly strength. Distribution of natural rubber includes solid rubber such as ribbed smoked sheet (RSS type) and technically rated rubber (TSR type) according to the international quality packaging standards (commonly known as Green Book) of natural rubber grades, It is done with latex that is shipped as it is. Among these, coagulated rubber is advantageous from the viewpoint of ease of transportation and storage, but has the following problems.

Usually, solid natural rubber is obtained by collecting rubber tree sap (natural rubber latex) called Hevea brasiliensis grown in the tropics in a rubber plantation, coagulating and drying. Here, the natural rubber latex has almost no odor immediately after collection, but there is a problem that the odor becomes stronger with time. This odor can be a problem not only during storage of coagulated rubber, during processing such as kneading, but also in products, and is a serious problem for industries involving natural rubber. This odor is not caused by natural rubber itself, but is thought to be caused by spoilage caused by bacteria such as proteins and lipids as impurities.

As a method for removing the impurities, a method for removing impurities from natural rubber latex by a method such as enzyme treatment or saponification to increase the purity is known (for example, see Patent Document 1).

On the other hand, the raw material of coagulated rubber that is inexpensive and easy to distribute, the field latex is naturally coagulated in the collection cup (cup lamp), the slab obtained by coagulating latex collected in the farm in a box shape, There are cases where there is a storage and distribution period of about one month or more before it is delivered to the factory after being harvested by a farmer and processed into TSS, etc., and during that time, considerable decay will occur.

Since a volatile organic acid can be considered as a causative substance of odor due to decay, a method of treating a solidified rubber with an alkaline solution is known as a method for reducing odor (see, for example, Patent Documents 2 and 3).

Japanese Patent No. 3806317 Japanese Patent No. 3573498 JP2013-249411A

As described above, various studies have been made to remove the odor of natural rubber. For example, as in Patent Document 1, high purity is achieved by removing impurities from natural rubber latex by enzyme treatment, saponification or the like. Although this method is effective for latex, it cannot cope with the state of coagulated rubber that occupies most of the natural rubber circulation. Moreover, there existed a problem that a process was complicated and cost and time required. On the other hand, as in Patent Documents 2 and 3, in the method of treating the coagulated rubber with an alkaline solution, the odor is reduced, but as a result of the study by the present inventors, the physical properties of the treated natural rubber, particularly the heat aging resistance, is improved. It turns out that there is a problem of being inferior. Also, it has been newly found that there is a problem that even if the treatment is performed once, the rot occurs again during storage and odor is generated.
As described above, there has not yet been a technique that can easily reduce the odor of solid natural rubber that can be easily obtained, maintain the deodorizing effect, and maintain the physical properties.

An object of the present invention is to solve the above-mentioned problems, to reduce the odor of solid natural rubber, to maintain a deodorizing effect, and to provide a method for treating natural rubber that does not deteriorate physical properties such as heat aging resistance. To do.

The present invention relates to a base treatment step in which solid natural rubber that has not been deproteinized is brought into contact with a basic solution, and pH adjustment to adjust the pH of the base-treated natural rubber obtained by the base treatment step to 2 to 7 And a process for treating natural rubber.

The above-mentioned pH is obtained by cutting the base-treated natural rubber into a size of 2 mm square or less on each side, immersing it in distilled water, extracting it at 90 ° C. for 15 minutes while irradiating with microwaves, and using the pH meter It is preferable that the measured value.

The pH adjustment step is preferably a step of adjusting the pH to 2 to 7 by bringing the base-treated natural rubber into contact with an acidic solution.

The basic solution is preferably alkaline electrolyzed water.

The basic solution is also preferably a 0.01-0.1N basic compound solution.

The pH adjustment step is preferably a step of adjusting the pH to 2 to 7 by immersing the base-treated natural rubber in acidic electrolyzed water.

It is preferable that the said base treatment process and / or the said pH adjustment process are performed by irradiating a microwave.

According to the present invention, the base treatment step in which a solid natural rubber that has not been deproteinized is brought into contact with a basic solution, and the pH of the base treatment natural rubber obtained by the base treatment step is adjusted to 2 to 7. Since the natural rubber treatment method includes a pH adjustment step, the odor of the solid natural rubber can be reduced and the deodorizing effect can be maintained without deteriorating physical properties such as heat aging resistance.

The natural rubber treatment method of the present invention comprises a base treatment step in which a solid natural rubber that has not been deproteinized is brought into contact with a basic solution, and the pH of the base treatment natural rubber obtained by the base treatment step is 2 to 2. PH adjustment step of adjusting to 7. The treatment method of the present invention may include other steps as long as the above steps are included, and each step may be performed once or a plurality of times.

The treatment method of the present invention includes a base treatment step in which solid natural rubber that has not been deproteinized is brought into contact with a basic solution.

The solid natural rubber treated in the present invention has not been deproteinized. That is, the solid natural rubber treated in the present invention is not particularly limited as long as it is a coagulated product obtained by coagulating natural rubber latex that has not been deproteinized. The deproteinization treatment represents, for example, a protein degradation treatment using a strong alkali such as sodium hydroxide or a proteolytic enzyme. Therefore, the solid natural rubber used in the present invention refers to such a protein. It is a coagulated product obtained by coagulating natural rubber latex not subjected to decomposition treatment. Examples of such solid natural rubber include latex coagulated rubber, cup lamp, tree lace, unfinished sheet (unsmoked sheet: USS), cup lamp solidified with field latex (slab), and processed as TSR. The later ones or a mixture of these may be mentioned. Among these, the solid natural rubber is at least one selected from the group consisting of a cup lamp, a blank sheet (unsmoked sheet: USS), and a cup lamp solidified with field latex (slab). Furthermore, it is also one of preferred embodiments of the present invention that the solid natural rubber is a cup lamp.

In the solid natural rubber, the nitrogen content is preferably 0.3% by mass or more, more preferably 0.35% by mass or more, and more preferably 0.4% by mass or more from the viewpoint that the deodorizing effect of the present invention appears remarkably. Further preferred. Since the solid natural rubber treated in the present invention has not been deproteinized, it contains at least 0.3% by mass of nitrogen. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

Natural rubber latex is collected as a sap of rubber tree such as Hevea tree and contains water, proteins, lipids, inorganic salts, etc. in addition to rubber, and the gel content in rubber is based on the complex presence of various impurities. It is considered. As natural rubber latex, raw latex (field latex) produced by tapping Hevea tree, concentrated latex concentrated by centrifugation or creaming method (refined latex, high ammonia latex added with ammonia by conventional method, zinc white and And LATD latex stabilized with TMTD and ammonia).

As the above-mentioned cup lamp, natural rubber latex is collected in a cup for collecting natural rubber, and it has a function of coagulating natural rubber latex in advance or natural rubber solidified naturally by fatty acids generated by decomposition of non-rubber components by microorganisms. The natural rubber etc. which put the chemical | medical agent which has it in the cup and forcibly solidified quickly are mentioned. The chemical having the function of coagulating the natural rubber latex is not particularly limited as long as it has such a function. For example, acids such as sulfuric acid, formic acid, hydrochloric acid and acetic acid, cations such as calcium ions and the like And organic solvents such as methanol and ethanol.

In addition, the shape of the solid natural rubber to be treated in the present invention is not particularly limited, and can be selected according to the rubber production method and application, such as a sheet shape, a block shape, and a granular shape. From the viewpoint of deodorizing effect and final drying efficiency, a sheet shape with a thickness of 3 cm or less is preferable, the thickness is more preferably 2 cm or less, further preferably 1 cm or less, and most preferably 5 mm or less. . In a form other than the sheet form, the longest side is preferably a block form having a length of 30 cm or less, more preferably 20 cm or less, still more preferably 10 cm or less, and particularly preferably 1 cm or less. The above-mentioned moderately large solid natural rubber can be obtained by crushing and / or cutting large-sized solid natural rubber. Further, it may be intentionally coagulated into a small shape from a cup lamp or latex.

The base treatment step is preferably performed within 2 weeks after the natural rubber latex coagulates, more preferably within 1 week, and particularly preferably within 3 days. As a result, it is possible to effectively prevent the generation of odor due to decay during storage. On the other hand, the treatment method of the present invention can exert an odor reducing effect even for solid natural rubber that has been stored for a long time after coagulation of natural rubber latex and has been rotted and a lot of odor has been generated.

In the base treatment step, the solid natural rubber is brought into contact with the basic solution. For example, the basic solution is applied to the solid natural rubber, sprayed by a spray, a shower, or the like. Although it can carry out by immersing natural rubber in a basic solution, the method of immersing solid natural rubber in a basic solution from a viewpoint of a deodorizing effect and efficiency is preferable.

As a method of bringing the solid natural rubber into contact with the basic solution, when adopting a method in which the solid natural rubber is immersed in the basic solution, the solid natural rubber is left in the basic solution. However, it is preferable to perform stirring and / or microwave irradiation at the time of immersion because the deodorizing effect is further promoted.
Thus, it is also one of the suitable embodiment of this invention that the said base treatment process is performed by irradiating a microwave.

The contact time between the solid natural rubber and the basic solution in the base treatment step is not particularly limited, but is preferably 5 minutes or more, more preferably 10 minutes or more, and particularly preferably 30 minutes or more. By bringing the solid natural rubber and the basic solution into contact with each other for 5 minutes or more, a deodorizing effect sufficient for human perception can be obtained. The upper limit of the contact time between the solid natural rubber and the basic solution depends on the pH and concentration of the basic solution, and is not particularly specified. However, it is 48 hours or less to prevent deterioration of the rubber. desirable.

Although it does not specifically limit as a contact temperature (processing temperature) of solid natural rubber and a basic solution in the said base treatment process, For example, it can be 10-50 degreeC. Preferably it is 15-35 degreeC. Especially, 20-35 degreeC is especially preferable.

As the basic solution, alkaline electrolyzed water is preferable. By using alkaline electrolyzed water as the basic solution, it is possible to remove odor components and sterilize microorganisms that cause odors to the inside of the solid natural rubber. The alkaline electrolyzed water is not particularly defined, but preferably has a pH of 9 or more and more preferably has a pH of 10 or more in terms of odor reduction efficiency. The upper limit of the pH is not particularly limited, but is preferably 13.5 or less. Alkaline electrolyzed water can be easily obtained by using a commercially available electrolytic water adjuster. In addition, when using alkaline electrolyzed water, it is not necessary to perform a step of washing with water after the treatment with the basic solution because impurities are less likely to remain than when using the basic compound solution described later. In addition, particularly excellent effects can be obtained in terms of the sustainability of the deodorizing effect and the heat aging resistance. The raw material for alkaline electrolyzed water may be ordinary tap water or saline.

The basic solution may be a 0.01-0.1N basic compound solution. If it is less than 0.01 N, the effect of removing odor may be insufficient, and if it exceeds 0.1 N, the physical properties of rubber after treatment may be deteriorated. More preferably, it is 0.02-0.08N as a density | concentration of a basic compound solution, More preferably, it is 0.02-0.06N.

Examples of the basic compound solution include an aqueous solution of a basic compound and an alcohol solution of a basic compound, but an aqueous solution of a basic compound is preferable.
The basic compound may be an inorganic substance or an organic substance, but a basic inorganic substance is preferable from the viewpoint of ease of treatment and deodorization efficiency.

Examples of the basic inorganic substance include metal hydroxides such as alkali metal hydroxides and alkaline earth metal hydroxides; metal carbonates such as alkali metal carbonates and alkaline earth metal carbonates; alkali metal hydrogen carbonates and the like Metal phosphates such as alkali metal phosphates; metal acetates such as alkali metal acetates; metal hydrides such as alkali metal hydrides; ammonia and the like.

Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
Examples of the alkaline earth metal hydroxide include magnesium hydroxide, calcium hydroxide, and barium hydroxide.
Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate.
Examples of the alkaline earth metal carbonate include magnesium carbonate, calcium carbonate, and barium carbonate.
Examples of the alkali metal hydrogen carbonate include lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate.
Examples of the alkali metal phosphate include sodium phosphate and sodium hydrogen phosphate.
Examples of the alkali metal acetate include sodium acetate and potassium acetate.
Examples of the alkali metal hydride include sodium hydride and potassium hydride.

Among these, as the basic inorganic substance, metal hydroxide, metal carbonate, metal hydrogen carbonate, metal phosphate, and ammonia are preferable, and alkali metal hydroxide, alkali metal carbonate, alkali metal hydrogen carbonate are preferable. Salt and ammonia are more preferable, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium hydrogen carbonate are more preferable, and sodium carbonate and sodium hydrogen carbonate are particularly preferable.
As said basic compound, these may be used independently and 2 or more types may be used together. For example, as a form in which two or more kinds are used in combination, a form using a mixture of sodium carbonate and sodium bicarbonate is particularly preferable.

After the base treatment step for bringing the solid natural rubber into contact with the basic solution, the base treatment is performed before the pH adjustment step for adjusting the pH of the base treatment natural rubber obtained by the base treatment step to 2 to 7. A step of washing the basic solution remaining on the surface of the natural rubber may be performed. In particular, when alkaline electrolyzed water is used as the basic solution, the washing step may or may not be performed because impurities are unlikely to remain, but when a basic compound solution is used as the basic solution, A washing step is preferably performed.

The washing step is not particularly limited as long as the basic solution remaining on the surface of the base-treated natural rubber can be washed and removed as a result of the base treatment step. Examples include a method of centrifuging after dilution with water, a method of leaving the base-treated natural rubber in a water bath and floating it, and discharging only the aqueous phase to take out the base-treated natural rubber.

The processing method of the natural rubber of this invention includes the pH adjustment process which adjusts the pH of the base processing natural rubber obtained by the said base processing process to 2-7. That is, in the present invention, after the treatment with the basic solution, the pH of the obtained base-treated natural rubber is adjusted to 2 to 7 to obtain a deodorized natural rubber. Especially, it is preferable to adjust to pH 3-6, and it is more preferable to adjust to pH 4-6. By adjusting the pH of the base-treated natural rubber within such a range, it is possible to maintain the deodorizing effect for a long period of time and to prevent a decrease in heat aging resistance.
The pH is determined by cutting the base-treated natural rubber to a size of 2 mm square or less and immersing it in distilled water and extracting it at 90 ° C. for 15 minutes while irradiating with microwaves. Specifically, it is measured by the method described in Examples described later.
Here, as for the above extraction, even if it is extracted for 1 hour with an ultrasonic cleaner or the like, the water-soluble component cannot be completely extracted from the inside of the rubber. It has been found by the present inventors that the substance (pH) of the natural rubber after the treatment can be known by extraction by an extraction method using waves.

In the pH adjustment step, the method for adjusting the pH of the base-treated natural rubber to 2 to 7 is not particularly limited. For example, the base-treated natural rubber is exposed to an acidic atmosphere or the base-treated natural rubber is exposed to an acidic compound and It can be carried out by applying an acidic solution, spraying an acidic compound and / or acidic solution on the base-treated natural rubber by spraying or showering, or immersing the base-treated natural rubber in the acidic solution. There is a method of contacting the base-treated natural rubber with the acid solution, such as applying an acid solution to the base-treated natural rubber, spraying the acid solution on the base-treated natural rubber, or immersing the base-treated natural rubber in the acid solution. preferable. That is, the pH adjustment step is a step of adjusting the pH to be 2 to 7 by bringing the base-treated natural rubber into contact with an acidic solution, which is also a preferred embodiment of the present invention. is there.
Among these, the method of immersing the base-treated natural rubber in an acidic solution is particularly preferable from the viewpoint of work efficiency. By performing this treatment, the deodorizing effect can be maintained for a long period of time, and further, the deterioration of heat aging resistance can be prevented.

As the acidic solution, it is preferable to use one having a pH adjusted to 6 or less. By bringing the base-treated natural rubber into contact with such an acidic solution, a long-lasting deodorizing effect and excellent heat aging resistance can be obtained. The upper limit of the pH of the acidic solution is more preferably 5 or less, and even more preferably 4.5 or less. Further, the lower limit is not particularly limited, and although it depends on the contact time, it is preferably 1 or more, more preferably 2 or more, because if the acidity is too strong, the rubber deteriorates or takes time and effort due to wastewater treatment.

As a method of adjusting the pH of the base-treated natural rubber to 2 to 7, when adopting a method of immersing the base-treated natural rubber in an acidic solution, by leaving the base-treated natural rubber in the acidic solution In addition, it is preferable to perform stirring and / or microwave irradiation during the immersion because the treatment efficiency is further improved.
Thus, it is also one of the preferred embodiments of the present invention that the pH adjustment step is performed by irradiating microwaves.

The contact time between the base-treated natural rubber and the acidic solution in the pH adjustment step is not particularly limited, but is preferably 5 minutes or more, more preferably 10 minutes or more, and particularly preferably 30 minutes or more. By contacting the base-treated natural rubber and the acidic solution for 5 minutes or longer, the deodorizing effect can be maintained for a sufficiently long period of time, and a sufficient heat resistance improving effect can be obtained. The upper limit of the contact time between the base-treated natural rubber and the acidic solution depends on the pH and concentration of the acidic solution and is not particularly defined, but is preferably 48 hours or less in terms of work efficiency.

The contact temperature (treatment temperature) between the base-treated natural rubber and the acidic solution in the pH adjustment step is not particularly limited, and can be, for example, 10 to 50 ° C. Preferably it is 15-35 degreeC. Especially, 20-35 degreeC is especially preferable.

As the acidic solution, acidic electrolyzed water is preferable. By using acidic electrolyzed water as the acidic solution, not only a particularly excellent deodorizing effect and heat resistance improving effect are obtained, but also the sustainability of the deodorizing effect is improved. The acidic electrolyzed water is not particularly defined, but preferably has a pH of 5 or less, more preferably has a pH of 4 or less, and still more preferably has a pH of 3 or less, from the viewpoint of odor reduction efficiency. The lower limit of the pH is not particularly limited, but is preferably 1 or more, more preferably 2 or more as described above. The acidic electrolyzed water can be easily obtained by using a commercially available electrolytic water adjuster. In addition, when acidic electrolyzed water is used, impurities are less likely to remain as compared with the case where an acidic compound solution described later is used, and thus there is an advantage that it is not necessary to perform a water washing step after the treatment with the acidic solution. is there. The raw material for the acidic electrolyzed water may be ordinary tap water or saline.
Thus, the pH adjustment step is a step of adjusting the pH to 2 to 7 by immersing the base-treated natural rubber in acidic electrolyzed water, which is also a preferred embodiment of the present invention. One.

The acidic solution may be an acidic compound solution. Examples of the acidic compound solution include an aqueous solution of an acidic compound, an alcohol solution of an acidic compound, and the like, and an aqueous solution of an acidic compound is preferable.

The acidic compound is not particularly limited, and inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, metaphosphoric acid, boric acid, boronic acid, sulfanilic acid, sulfamic acid; formic acid, acetic acid, glycolic acid, oxalic acid , Propionic acid, malonic acid, succinic acid, adipic acid, maleic acid, malic acid, tartaric acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, salicylic acid, methanesulfone Acid, itaconic acid, benzenesulfonic acid, toluenesulfonic acid, naphthalenedisulfonic acid, trifluoromethanesulfonic acid, styrenesulfonic acid, trifluoroacetic acid, barbituric acid, acrylic acid, methacrylic acid, cinnamic acid, 4-hydroxybenzoic acid, amino Benzoic acid, naphthalene disulfonic acid, hydroxy Organic acids such as benzene sulfonic acid, toluene sulfinic acid, benzene sulfinic acid, α-resorcinic acid, β-resorcinic acid, γ-resorcinic acid, gallic acid, phloroglicin, sulfosalicylic acid, ascorbic acid, erythorbic acid, bisphenolic acid, etc. Can be mentioned. As said acidic compound, you may use independently and may use 2 or more types together.

The concentration of the acidic compound solution is preferably 0.01 to 0.1N. If it is less than 0.01 N, the durability of the deodorizing effect and the effect of improving heat resistance may be insufficient, and if it exceeds 0.1 N, the physical properties of the rubber after treatment may be deteriorated. More preferably, it is 0.02-0.08N as a density | concentration of an acidic compound solution, More preferably, it is 0.02-0.04N.

You may perform the process of wash | cleaning the acidic solution which remains on the surface of the obtained deodorizing natural rubber after the pH adjustment process which adjusts the pH of the said base processing natural rubber to 2-7. In particular, when acidic electrolyzed water is used as the acidic solution, the washing step may or may not be performed because impurities are unlikely to remain, but when the acidic compound solution is used as the acidic solution, the washing step is not performed. It is preferred to do so. The method for performing the cleaning step is as described above.

A preferable embodiment of the present invention includes an embodiment in which alkaline electrolyzed water is used in the base treatment step and acidic electrolyzed water is used in the pH adjustment step. When producing electrolyzed water, alkaline electrolyzed water and acidic electrolyzed water can be produced at the same time without using a strong acid or strong base compound, and the produced electrolyzed water can be discarded without any special treatment. By using it, it is possible to perform an efficient and inexpensive process while considering the environment. Moreover, compared with the case where it processes using the aqueous solution of an acidic compound or a basic compound, it has a good affinity to natural rubber, the deodorizing effect is great, the effect is sustained, and the heat aging resistance tends to be excellent. Even when a relatively large solid rubber is processed, the deodorizing effect is exhibited.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

The solutions used in Examples and Comparative Examples are shown below.
Basic solution 1: alkaline electrolyzed water (pH 13.1, obtained by electrolyzing saline using an electrolyzer)
Basic solution 2: Sodium carbonate / sodium hydrogen carbonate mixed aqueous solution basic solution in which sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) and sodium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) are dissolved to a concentration of 0.05 N respectively. 3: 0.05N sodium hydroxide aqueous solution (sodium hydroxide is manufactured by Wako Pure Chemical Industries, Ltd.)
Acidic solution 1: acidic electrolyzed water (pH 2.5, produced simultaneously with basic solution 1)
Acidic solution 2: 0.02N formic acid aqueous solution (formic acid is manufactured by Wako Pure Chemical Industries, Ltd.)
Acidic solution 3: 1N hydrochloric acid solution (hydrochloric acid manufactured by Wako Pure Chemical Industries, Ltd.)

Table 1 shows the results of treating solid natural rubber as in the following examples and comparative examples and evaluating under the following conditions.

Example 1
The natural rubber latex collected by tapping was naturally coagulated in a cup, prepared as a cup lamp (nitrogen content: 0.48% by mass), and stored for 3 days. Thereafter, a large block-shaped cup lamp was pulverized, washed with water, dehydrated, and molded into a sheet shape having a thickness of 1 cm, and processed into a square sheet shape having a side of 30 cm. The sheet was immersed in the basic solution 1 for 4 hours at room temperature (25 to 32 ° C.), and the surface was simply washed with water, and then immersed in the acidic solution 1 for 4 hours at room temperature (25 to 32 ° C.). Thereafter, the rubber surface was washed with running water and dried in a vacuum dryer for 2 days.

(Example 2)
The cup lamp prepared in Example 1 was processed in the same manner as in Example 1 except that the cup lamp was stored in a storage room with a roof for 70 days.

(Example 3)
The cup lamp prepared in Example 1 was processed in the same manner as in Example 1 except that the cup lamp was stored in a storage room with a roof for 70 days, and was used in the form of a block (diameter of about 15 cm) without being pulverized.

Example 4
The same treatment as in Example 1 was conducted except that the basic solution 2 was used instead of the basic solution 1 and the acidic solution 2 was used instead of the acidic solution 1.

(Example 5)
The basic solution 3 was treated in the same manner as in Example 1 except that the basic solution 3 was used instead of the basic solution 1, and the acidic solution 2 was used instead of the acidic solution 1.

(Comparative Example 1)
The treatment was performed in the same manner as in Example 1 except that the treatment with the acidic solution 1 was not performed.

(Comparative Example 2)
The treatment was performed in the same manner as in Example 2 except that the treatment with the acidic solution 1 was not performed.

(Comparative Example 3)
A square sheet having a side of 30 cm was prepared in the same manner as in Example 1 without performing the treatment with the basic solution 1 and the treatment with the acidic solution 1.

(Comparative Example 4)
The treatment was performed in the same manner as in Example 5 except that the treatment with the acidic solution 2 was not performed.

(Comparative Example 5)
A square sheet having a thickness of 1 cm and a side of 30 cm, which has been finely cut to about 1 mm on a side, is subjected to a treatment with the basic solution 1. Was treated in the same manner as in Example 1 except that was not washed.

<PH of solid rubber>
5 g of the obtained rubber was cut so that the total of the three sides was 5 mm or less (about 1-2 mm × about 1-2 mm × about 1-2 mm), put in a 100 ml beaker, and 50 ml of distilled water at room temperature was added. The temperature was raised to 90 ° C. for 1 minute, and then irradiation with microwaves (300 W) was performed for 13 minutes (total 15 minutes) while maintaining the temperature at 90 ° C. Next, the immersion water was cooled with an ice bath to 25 ° C., and then the pH of the immersion water was measured using a pH meter.

<Odor sensory evaluation>
Sensory evaluation based on the following criteria was performed on the rubber before treatment, immediately after treatment, and after storage for 30 days after treatment.
Evaluation standard 6: Even if it is 1m away, it smells violently and unpleasantly. Even if it is 5: 1m away, the odor can be felt considerably. Feel close and feel odor 1: Feel close to about 10cm and feel a little odor 0: Don't feel much odor even if you close your nose

<Heat aging resistance>
Mooney viscosity ML _{(1 + 4)} of solid rubber before and after heat treatment (80 ° C., 18 hours) 130 ° C. was measured according to JIS K6300: 2001-1, and a heat aging index was calculated by the following formula (1). . If the Mooney viscosity before heat treatment is in the range of 50 to 70, particularly in the range of 50 to 65, the physical properties are good and there is no need for mastication, which is excellent. If it is too low, the rubber properties are poor. Moreover, the greater the heat aging index, the better the heat aging resistance.
Heat aging index (%) = (Mooney viscosity after treatment of deodorized natural rubber at 80 ° C. for 18 hours) / (Mooney viscosity of each solid natural rubber before treatment) × 100 (1)

From the results in Table 1, it can be seen that the solid natural rubber after coagulation subjected to the treatment of the present invention has reduced odor, sustained deodorizing effect, and excellent heat aging resistance. Moreover, in the Example which used electrolyzed water for the process, it was especially excellent in the sustainability of a deodorizing effect, and heat aging resistance (Comparison with Example 1 and Example 4, 5).

Claims (7)

A base treatment step in which solid natural rubber that has not been deproteinized is brought into contact with a basic solution, and a pH adjustment step in which the pH of the base-treated natural rubber obtained by the base treatment step is adjusted to 2 to 7. Processing method of natural rubber. The base-treated natural rubber is cut to a size of 2 mm square on each side, soaked in distilled water, extracted at 90 ° C. for 15 minutes while irradiating microwaves, and the soaked water is extracted using a pH meter. The processing method of the natural rubber according to claim 1, which is a value measured by The method for treating natural rubber according to claim 1 or 2, wherein the pH adjusting step is a step of adjusting the pH to 2 to 7 by bringing the base-treated natural rubber into contact with an acidic solution. The natural rubber treatment method according to claim 1, wherein the basic solution is alkaline electrolyzed water. The natural rubber treatment method according to claim 1, wherein the basic solution is a 0.01-0.1 N basic compound solution. The treatment of natural rubber according to any one of claims 1 to 5, wherein the pH adjustment step is a step of adjusting the pH to 2 to 7 by immersing the base-treated natural rubber in acidic electrolyzed water. Method. The method for treating natural rubber according to any one of claims 3 to 6, wherein the base treatment step and / or the pH adjustment step is performed by irradiation with microwaves.