JP2018058975A - Method for producing natural rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a natural rubber that conveniently reduces an odor of natural rubber from cup lump as raw material, and does not cause the deterioration of physical properties such as thermal aging resistance.SOLUTION: A method for producing natural rubber includes a sheet-making step for making cup lump into a sheet to prepare a natural rubber sheet with a moisture percentage of 20% or less, and a drying step for drying the natural rubber sheet at 125°C or less.SELECTED DRAWING: None

Description

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

Natural rubber (NR) used in the rubber industry is a solidified sap (latex) collected from rubber trees called Hevea braziliansis cultivated in the tropics. As a method of solidifying, a method of solidifying with an acid such as formic acid and drying, a cup lamp obtained by natural coagulation in a latex collection cup in a rubber plantation, repeatedly pulverizing and washing, There is a method of manufacturing by pressing after drying.

Since it is produced by the method as described above, natural rubber contains a large amount of non-rubber components such as proteins, lipids and sugars in addition to the polyisoprene component. Therefore, these components rot during the storage period in the previous stage of drying, causing a bad odor. In particular, cup lamps contain a large amount of non-rubber components, and the storage period is long due to storage in farms, storage / transportation periods in processing plants, and odor problems are likely to occur. However, natural rubber made from cup lamps has been used in recent years for tire applications because of ease of production and cost. The decaying odor of natural rubber has become a problem not only in processing plants for natural rubber, but also in manufacturing factories for rubber products such as tires, and so on.

In order to solve the problem of natural rubber odor, proteolytic enzymes and surfactants are added to and reacted with natural rubber latex to reduce the odor by removing the protein that is one of the causes of spoilage. Rubber odor is reduced by adding inorganic salts and proteolytic enzymes to the serum that is generated when natural rubber is concentrated and purified from natural rubber latex. (For example, refer to Patent Document 2).

Patent Document 3 discloses a method of reducing odor by adding an antioxidant to natural rubber latex and further lowering the drying temperature. In addition, a method of reducing the odor component by immersing a coagulated product of natural rubber latex in an alkaline solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is also disclosed (for example, see Patent Documents 4 and 5).

Japanese Patent No. 3654934 Japanese Patent No. 3750100 Japanese Patent No. 531439 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 Documents 1 and 2, a method of removing protein from natural rubber latex or serum by proteolytic enzyme treatment. Is applicable only when liquid raw materials such as latex and serum are used, and odor cannot be reduced with respect to solid natural rubber such as cup lamps. Similarly, Patent Document 3 can be applied only when latex is used as a raw material, and odor cannot be reduced with respect to solid natural rubber such as a cup lamp. On the other hand, as disclosed in Patent Documents 4 and 5, the method of treating the solidified rubber with a strong alkaline solution such as an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide can reduce the odor. It was found that the rubber deteriorated during drying, and it was found impossible to achieve both odor reduction and natural rubber property maintenance.
As described above, there has not yet been a technique that can easily reduce the odor and maintain the physical properties of a cup lamp that can be obtained easily and inexpensively.

An object of the present invention is to solve the above-mentioned problems, and to provide a method for producing natural rubber that can easily reduce the odor of natural rubber using cup lamp as a raw material and that does not deteriorate physical properties such as heat aging resistance. .

The present invention is characterized in that it includes a sheet forming step of obtaining a sheeted natural rubber having a moisture content of 20% or less by sheeting a cup lamp, and a drying step of drying the sheeted natural rubber at 125 ° C. or lower. The present invention relates to a method for producing natural rubber.

The moisture content of the sheeted natural rubber is preferably 15% or less.

It is preferable that the manufacturing method further includes a base treatment step in which the sheeted natural rubber is brought into contact with a basic solution before the drying step.

The basic solution is preferably a solution containing at least one basic inorganic material selected from the group consisting of metal carbonates, metal bicarbonates, metal phosphates, and ammonia.

The basic solution is preferably a solution further containing a surfactant.

According to the present invention, there is provided a natural rubber comprising a sheet forming step of obtaining a sheeted natural rubber having a moisture content of 20% or less by sheeting a cup lamp, and a drying step of drying the sheeted natural rubber at 125 ° C. or lower. Since it is a manufacturing method, the odor of natural rubber made from cup lamps can be reduced easily and synergistically, and physical properties such as heat aging resistance can be maintained without deteriorating.

The method for producing natural rubber of the present invention comprises a sheeting step for obtaining a sheeted natural rubber having a moisture content of 20% or less by sheeting a cup lamp, and a drying step for drying the sheeted natural rubber at 125 ° C. or lower. Including. The production method of the present invention may include other steps such as a base treatment step, a pH adjustment step, and a washing step, which will be described later, as long as the above steps are included, and each step may be performed once. It may be repeated several times.

The odor of natural rubber is that non-rubber components of natural rubber, such as proteins, lipids and sugars, decay during storage or decompose during drying, resulting in the generation of lower fatty acids that cause odor. Is considered to be the cause. Therefore, by reducing the water content by making the cup lamp into a sheet, it is possible to suppress the rot during storage and suppress the generation of lower fatty acids which are odor-causing substances even when stored, and reduce the odor. It becomes possible to reduce. In addition to the reduction of the water content, it is considered that by making into a sheet, the wind passage during storage is improved and the progress of decay can be suppressed. Moreover, by making the drying temperature at the time of drying the sheeted natural rubber below a certain temperature, generation of lower fatty acids due to decomposition of non-rubber components can be suppressed, and odor can be reduced. Here, surprisingly, it is possible to produce a sheeted natural rubber having a low water content by forming a cup lamp into a sheet, and to dry the sheeted natural rubber at a certain temperature or less, thereby reducing odor. The inventors of the present invention have found for the first time that an effect (so-called synergistic effect) more than the sum of the effects of performing each of them alone can be obtained.
Furthermore, since only sheet formation and drying at a certain temperature or less are performed, physical properties such as heat aging resistance can be maintained without deteriorating.

The sheeting step is a step of obtaining a sheeted natural rubber having a moisture content of 20% or less by sheeting the cup lamp.

A cup lamp is provided for the sheet forming step in the present invention. A cup lamp is obtained by naturally coagulating natural rubber latex in a latex collection cup in a rubber plantation or the like. By solidifying natural rubber latex with an acid such as formic acid, drying it and solidifying it. It contains more non-rubber components such as proteins, lipids, sugars, etc. than polyisoprene components compared to other solid natural rubber such as latex coagulated rubber that is produced. Since the storage period is long due to the storage and transportation period, the material is liable to cause odor problems. In the present invention, even when a cup lamp that easily causes such odor problems is used as a rubber raw material, the odor can be easily reduced and maintained without degrading physical properties such as heat aging resistance. Natural rubber can be manufactured.
It should be noted that the natural rubber made into a sheet generally called “unsmoked sheet (USS)” or “ribbed smoked sheet (RSS)” is obtained by coagulating the collected natural rubber latex with an acid. Therefore, the sheeted natural rubber obtained by the sheeting step in the present invention for forming a cup lamp into a sheet is not applicable.

Moreover, the said cup lamp can be used for the said sheet forming process in shapes, such as a block shape and a granular form, for example. Specifically, the longest side is preferably provided in a block shape 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 moderately sized cup lamp can be obtained by crushing and / or cutting a large-sized cup lamp.

The cup lamp used for the sheet forming step is preferably used within 2 weeks after the natural rubber latex coagulates, more preferably within 1 week, and particularly preferably within 3 days. Thereby, the odor generation | occurrence | production by the rot at the time of storage can be prevented effectively.

In the sheet forming step, the method for forming the cup lamp into a sheet is not particularly limited as long as a sheet-like natural rubber is obtained, and it is possible to form a sheet by a method usually used when molding the rubber into a sheet. it can. Specifically, for example, a method of forming a sheet through a roll can be used.

The thickness of the sheeted natural rubber is preferably 3 cm or less. When the thickness of the sheeted natural rubber is such a thickness, the advantageous effects obtained by forming the sheet can be sufficiently obtained. The thickness is more preferably 2 cm or less. On the other hand, the lower limit of the thickness is not particularly limited, but is preferably 2 mm or more from the viewpoint of workability.

The moisture content of the sheeted natural rubber is 20% or less. When the moisture content of the sheeted natural rubber obtained by the sheeting step is within such a range, the progress of decay during storage can be suppressed, and the advantageous effects obtained by forming into a sheet can be sufficiently obtained. be able to. The moisture content is preferably 16% or less, and more preferably 15% or less. On the other hand, the lower limit of the moisture content is not particularly limited and is preferably as low as possible, but is preferably 3% or more, more preferably 5% or more, and even more preferably 10% or more from the viewpoint of the efficiency of adjusting the moisture content. .
The moisture content can be determined from the difference in weight before and after sufficiently drying the sheeted natural rubber, as will be described in the examples described later.

The moisture content of the sheeted natural rubber may not be 20% or less just by performing the sheeting process once depending on the state of the cup lamp used in the sheeting process. Can be reduced to 20% or less by repeating a plurality of times or appropriately drying the sheeted natural rubber obtained by the sheeting step. However, in this case, in the case of drying, it is preferably performed under the same conditions as in the drying step described later.
The moisture content of the sheeted natural rubber described above may be measured immediately after the sheeted natural rubber is obtained by the sheeting process or immediately after the drying or the like is performed.

In the production method of the present invention, since the sheet forming step is performed, even if the sheet is stored for a long time after the sheet forming step, the progress of decay is suppressed and the odor can be reduced. Thereafter, when the sheeted natural rubber is stored for a long period of time, the effects of the present invention will be exhibited more remarkably.

In the present invention, a drying process is performed in which the sheeted natural rubber having a moisture content of 20% or less obtained by the sheeting process is dried at 125 ° C. or less. That is, the said drying process is a process of drying the said sheet-like natural rubber at 125 degrees C or less.

The method for drying is not particularly limited, and can be carried out by a method usually used for drying natural rubber.

The drying temperature in the said drying process is 125 degrees C or less. By setting the drying temperature in such a range, generation of lower fatty acids due to decomposition of the non-rubber component can be suppressed, and odor can be reduced. The drying temperature is preferably 120 ° C. or lower, and more preferably 115 ° C. or lower. On the other hand, the lower limit of the drying temperature is not particularly limited, but the lower the temperature, the longer it takes to obtain the same dry state. From the viewpoint of efficiency and productivity, 75 ° C. or higher is required. Preferably, 80 degreeC or more is more preferable, and 100 degreeC or more is still more preferable.

The drying time in the drying step can be appropriately set according to the drying temperature, and is preferably as short as possible if moisture can be removed sufficiently (completely).

It is preferable that the manufacturing method further includes a base treatment step in which the sheeted natural rubber is brought into contact with a basic solution before the drying step. That is, after the sheet forming step, it is preferable to perform a base treatment step in which the sheeted natural rubber obtained by the sheet forming step is brought into contact with a basic solution. In the production method of the present invention, even when the sheeted natural rubber is stored by performing the sheeting step, it is possible to suppress the decay during storage and to suppress the generation of lower fatty acids that are odor-causing substances. Although it is possible to reduce odor, it is still impossible to completely suppress the generation of lower fatty acids. However, a small amount of low-fatty acid can be generated by contacting the sheeted natural rubber after storage with a basic solution. It is possible to further reduce odor by neutralizing and removing the lower fatty acids.
Note that when the sheeted natural rubber is brought into contact with the basic solution in the base treatment step, the sheeted natural rubber may be used as it is, or may be appropriately cut and reduced to an arbitrary size. Good.

In the basic treatment step, as a method of bringing the sheeted natural rubber into contact with the basic solution, for example, the basic solution is applied to the sheeted natural rubber, sprayed by spraying, showering, or the like. Although it can carry out by immersing in a basic solution, the method of immersing a sheet-like natural rubber in a basic solution from a viewpoint of a deodorizing effect and efficiency is preferable.

As a method of bringing the sheeted natural rubber into contact with the basic solution, when adopting a method of immersing the sheeted natural rubber in the basic solution, by leaving the sheeted natural rubber in the basic solution, However, it is preferable to perform stirring and / or microwave irradiation during the 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.

In the above base treatment step, the contact time (treatment time) between the sheeted natural rubber and the basic solution is not particularly limited, but is preferably 5 minutes or more, more preferably 10 minutes or more, still more preferably 30 minutes or more, 3 hours or more is particularly preferable. The effect of this invention is acquired more favorably by making it contact for 5 minutes or more. The upper limit of the contact time between the sheeted natural rubber and the basic solution depends on the pH and concentration of the basic solution, and is not particularly defined. However, from the viewpoint of productivity, it is preferably 48 hours or less, and 24 hours or less. More preferred is 16 hours or less.

Although it does not specifically limit as a contact temperature (treatment temperature) with a sheet-like natural rubber and a basic solution in the said base treatment process, For example, it is preferable to set it as 10-50 degreeC, and 15-35 degreeC is more preferable. Especially, room temperature (20-30 degreeC) is especially preferable.

The basic solution is preferably a solution containing at least one basic inorganic material selected from the group consisting of metal carbonates, metal bicarbonates, metal phosphates, and ammonia. By using such a basic solution as a basic solution to be brought into contact with the sheeted natural rubber, it is possible to further neutralize and remove the odor component, thereby further reducing the odor of the sheeted natural rubber. In addition, it is possible to maintain without deteriorating physical properties such as heat aging resistance.
Examples of the basic solution include an aqueous solution containing the basic inorganic material, an alcohol solution containing the basic inorganic material, and the like, and an aqueous solution containing the basic inorganic material is preferable.
The basic solution can be prepared by diluting and dissolving the basic inorganic substance with a solvent such as water or alcohol.

Examples of the metal carbonate include alkali metal carbonates such as lithium carbonate, sodium carbonate and potassium carbonate; alkaline earth metal carbonates such as magnesium carbonate, calcium carbonate and barium carbonate;
Examples of the metal hydrogen carbonate include alkali metal hydrogen carbonates such as lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate.
Examples of the metal phosphate include alkali metal phosphates such as sodium phosphate and sodium hydrogen phosphate.
These basic inorganic substances may be used alone or in combination of two or more.

Among these basic inorganic substances, metal carbonates, metal hydrogen carbonates, and ammonia are preferable, and alkali metal carbonates, alkali metal hydrogen carbonates, and ammonia are more preferable, and sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and carbonate are more preferable. Potassium hydrogen is more preferable, and sodium carbonate and sodium hydrogen carbonate are particularly preferable.

The concentration of the basic inorganic substance in the basic solution is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.5% by mass or more in 100% by mass of the basic solution. preferable. When it is 0.1% by mass or more, the odor component can be more sufficiently neutralized and removed. Further, the concentration is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5.0% by mass or less, and particularly preferably 3.0% by mass or less in 100% by mass of the basic solution. . When the amount is 20% by mass or less, the amount of decrease in the odor component increases according to the amount of the basic inorganic substance used, and the efficiency corresponding to the cost can be obtained. Further, the physical properties of rubber after treatment (heat aging resistance, etc.) can be maintained.

The basic solution preferably further contains a surfactant. That is, it is also one preferred embodiment of the present invention that the basic solution is a solution containing the basic inorganic substance and a surfactant.
Thus, by including a surfactant together with the basic inorganic material, it is easy to extract the odor-causing component inside the sheeted natural rubber, or to facilitate the penetration of the basic inorganic material into the sheeted natural rubber. It is possible to neutralize and remove odor components more efficiently.

As the surfactant, at least one selected from the group consisting of an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. Examples of the anionic surfactant include carboxylic acid-based, sulfonic acid-based, sulfate ester-based and phosphate ester-based anionic surfactants.
Examples of the nonionic surfactant include nonionic surfactants such as polyoxyalkylene ester, polyhydric alcohol fatty acid ester, glycolipid ester, and alkylpolyglycoside.
Examples of the amphoteric surfactants include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type. Among these, anionic surfactants are preferably used.
These surfactants may be used alone or in combination of two or more.

As the anionic surfactant, for example, alkyl sulfate ester salt, polyoxyethylene alkyl ether sulfate ester salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, and fatty acid salt can be preferably used. Examples of these salts include alkali metal salts (such as sodium salts), ammonium salts, amine salts (alkanolamine salts such as monoethanolamine, diethanolamine, and triethanolamine salts).
Among these, a polyoxyethylene alkyl ether sulfate ester salt is particularly preferable.

As the alkyl sulfate ester salt, higher alkyl sulfate ester salts (higher alcohol sulfate ester salts) are preferable, and alkali metal salts such as sodium salts are preferable. Moreover, 10-20 are preferable and, as for carbon number of the alkyl group in an alkyl sulfate ester salt, 10-16 are more preferable. Specific examples of the alkyl sulfate salts include sodium lauryl sulfate (sodium dodecyl sulfate), potassium lauryl sulfate, ammonium lauryl sulfate, triethanolamine lauryl sulfate, sodium myristyl sulfate, potassium myristyl sulfate, sodium cetyl sulfate, and potassium cetyl sulfate. Can be mentioned. Among these, sodium lauryl sulfate is preferable because it is excellent in the effect of reducing the amount of protein and the like.

As said polyoxyethylene alkyl ether sulfate ester salt, the polyoxyethylene alkyl ether sulfate ester salt which has a C10-C18 alkyl group is preferable, an amine salt and a sodium salt are more preferable, and a sodium salt is still more preferable. The carbon number is preferably 10-14. The average degree of polymerization of the oxyethylene group is preferably 1 to 10, more preferably 1 to 5. Specific examples of the polyoxyethylene alkyl ether sulfate ester salt include sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene myristyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate such as sodium polyoxyethylene oleyl ether sulfate, polyoxyethylene Examples thereof include ethylene alkyl ether sulfate triethanolamine. Of these, sodium polyoxyethylene lauryl ether sulfate is preferred because of its excellent effect of reducing the amount of protein and the like.

Examples of the alkylbenzene sulfonate include alkylbenzene sulfonates having an alkyl group having 3 to 20 carbon atoms, and alkali metal salts are preferred. Specific examples of the alkylbenzene sulfonate include dodecyl benzene sulfonic acid, pentadecyl benzene sulfonic acid, decyl benzene sulfonic acid, sodium salt of cetyl benzene sulfonic acid, potassium salt, ammonium salt, triethanolamine salt, calcium salt and the like. Can be mentioned. Among these, sodium dodecylbenzenesulfonate is preferable because it is excellent in the effect of reducing the amount of protein and the like.

Examples of the alkyl naphthalene sulfonate include sodium mono, di or triisopropyl naphthalene sulfonate, potassium mono, di or triisopropyl naphthalene sulfonate, sodium octyl naphthalene sulfonate, potassium octyl naphthalene sulfonate, sodium dodecyl naphthalene sulfonate. And alkali metal salts of alkyl naphthalene sulfonate such as potassium dodecyl naphthalene sulfonate. Of these, sodium alkylnaphthalene sulfonate is preferred because of its excellent effect of reducing the amount of protein and the like.

As the fatty acid salt, a higher fatty acid salt having 10 to 20 carbon atoms is suitable, and examples thereof include a sodium salt and a potassium salt. Specific examples of the fatty acid salt include oleic acid, stearic acid, octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, docosanoic acid, linoleic acid, 2-ethylhexanoic acid, and 2-octylundecanoic acid. And sodium salts such as mixed fatty acids derived from palm oil, palm oil, castor oil, palm kernel oil, beef tallow and the like, and potassium salts (such as castor oil potassium soap). Of these, potassium oleate soap is preferable because it is excellent in reducing the protein amount and the like.

The concentration of the surfactant in the basic solution is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and more preferably 0.05% by mass or more in 100% by mass of the basic solution. preferable. When it is 0.01% by mass or more, the odor component can be more sufficiently neutralized and removed. Moreover, as this density | concentration, 5 mass% or less is preferable in 100 mass% of said basic solutions, and 3 mass% or less is more preferable. When the amount is 5% by mass or less, the amount of decrease in odor components increases according to the amount of the surfactant used, and the efficiency corresponding to the cost can be obtained.

After the base treatment step for bringing the sheeted natural rubber into contact with the basic solution, it is preferable to carry out a step of washing the basic solution remaining on the surface of the resulting treated natural rubber.

If the basic solution remaining on the surface of the treated natural rubber (also referred to as “base-treated natural rubber”) obtained as a result of performing the base treatment step can be washed and removed, the method is as follows. Although not particularly limited, for example, a method of diluting the treated natural rubber with water and then centrifuging, a method of leaving the treated natural rubber in a water bath and floating it, discharging only the aqueous phase and taking out the natural rubber, etc. Can be mentioned.

The production method of the present invention may further include a pH adjustment step of adjusting the pH of the base-treated natural rubber obtained by the base treatment step to 2 to 7. That is, in the present invention, after the treatment with the basic solution, the washing step is performed as necessary, and the pH of the treated natural rubber obtained is further adjusted to 2 to 7 to remove the deodorized natural product. Rubber can also be obtained. Especially, as a range of pH adjusted, 3-6 are preferable and 4-6 are more preferable. By adjusting the pH of the base-treated natural rubber within such a range, the deodorizing effect can be maintained for a long time, and the deterioration of heat aging resistance can be further prevented.
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. Is a value measured using.
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. By extracting by the extraction method using waves, the substance (pH) of the natural rubber after the treatment can be known.

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 the deterioration of the heat aging resistance can be further 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 3 seconds or more, more preferably 10 seconds or more, further preferably 30 seconds or more, and more preferably 5 minutes or more. More preferred is 10 minutes or more, and most preferred is 30 minutes or more. If it is 3 seconds or more, the solution is sufficiently neutralized and the effects of the present invention can be obtained better. The upper limit of the contact time between the base-treated natural rubber and the acidic solution is not particularly specified because it depends on the pH and concentration of the acidic solution, but is preferably 48 hours or less, more preferably 24 hours or less in terms of productivity and work efficiency. Preferably, 10 hours or less is more preferable, and 5 hours or less is particularly preferable.

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, room temperature (20-30 degreeC) is especially preferable.

The acidic solution is preferably 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.
In addition, the said acidic solution can be prepared by diluting and melt | dissolving the acidic compound mentioned later with solvents, such as water and alcohol.

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. Of these, sulfuric acid, formic acid, and acetic acid are preferable as the acidic compound.

The concentration of the acidic compound in the acidic solution is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, in 100% by mass of the acidic solution. 0.0 mass% or more is particularly preferable. The concentration is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5.0% by mass or less, and particularly preferably 3.0% by mass or less in 100% by mass of the acidic solution. When the concentration of the acidic compound in the acidic solution is within the above range, better heat aging resistance can be obtained.

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. The method for performing the cleaning step is as described above.

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

Various chemicals used in Examples and Comparative Examples are shown below.
Na ₂ CO ₃ : Sodium carbonate (manufactured by Sigma-Aldrich)
E-27C: EMAL E-27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation

<Obtaining natural rubber samples>
A cup lamp made in a normal rubber plantation was obtained.

(Comparative Example 1)
The cup lamp obtained as described above was stored as it was for one month. It was 32% when the moisture content of the cup lamp before storage was measured by the following method.
The cup lamp stored for one month as described above was washed about 5 times with water and then dried at 135 ° C. for 2 hours to obtain a natural rubber sample.

(Measurement of moisture content)
1 g of a cup lamp was accurately weighed (weight before drying), cut into fine pieces, dried at 70 ° C. for 14 hours, and then the weight after drying was measured. And the moisture content was calculated | required by the following formula.
Moisture content (%) = {(weight before drying (g) −weight after drying (g)) / weight before drying (g)} × 100

(Comparative Example 2)
The cup lamp obtained as described above was passed through a roll to form a sheet having a thickness of 10 mm or less to prepare a sheeted natural rubber, which was stored at room temperature (20-30 ° C.) for 1 month. The moisture content of the sheeted natural rubber before storage was measured by the method described below and found to be 16%.
The sheeted natural rubber stored for one month as described above was washed about 5 times with water and then dried at 135 ° C. for 2 hours to obtain a natural rubber sample.

(Measurement of moisture content)
1 g of sheeted natural rubber was accurately weighed (weight before drying), finely cut and dried at 70 ° C. for 14 hours, and then the weight after drying was measured. And the moisture content was calculated | required by the following formula.
Moisture content (%) = {(weight before drying (g) −weight after drying (g)) / weight before drying (g)} × 100

(Comparative Example 3)
A natural rubber sample was obtained in the same manner as in Comparative Example 1 except that the cup lamp stored for one month was washed about 5 times with water and then dried at 115 ° C. for 2 hours.

Example 1
A natural rubber sample was obtained in the same manner as in Comparative Example 2 except that the sheeted natural rubber stored for 1 month was washed with water about 5 times and then dried at 115 ° C. for 2 hours.

(Comparative Example 4)
The cup lamp obtained as described above was passed through a roll to form a sheet having a thickness of 10 mm or less to prepare a sheeted natural rubber, which was stored at room temperature (20-30 ° C.) for 1 month. When the moisture content of the sheeted natural rubber before storage was measured in the same manner as in Comparative Example 2, it was 16%.
After washing the sheeted natural rubber stored for one month as described above with water about 5 times, 100 g of the sheeted natural rubber was added to 1 L of the aqueous solution prepared at the concentration shown in Table 1 for 6 hours at room temperature (20- (30 ° C). During the immersion, a weight or the like was appropriately placed so that the sheeted natural rubber did not float on the liquid surface of the aqueous solution, and the whole was set so as to sink into the aqueous solution. The sheeted natural rubber was taken out, washed with water, and dried at 135 ° C. for 2 hours to obtain a natural rubber sample.

(Comparative Example 5)
The cup lamp obtained as described above was stored as it was for one month. When the moisture content of the cup lamp before storage was measured in the same manner as in Comparative Example 1, it was 32%.
After the cup lamp stored for one month as described above was washed with water about 5 times, the cup lamp 100 g was added to 1 L of the aqueous solution prepared at the concentration shown in Table 1 for 6 hours at room temperature (20-30 ° C.). Soaked in. During the immersion, a weight or the like was appropriately placed so that the cup lamp did not float on the liquid surface of the aqueous solution, and the whole was placed in the aqueous solution. The cup lamp was taken out, washed with water, and then dried at 115 ° C. for 2 hours to obtain a natural rubber sample.

(Examples 2-3)
The cup lamp obtained as described above was passed through a roll to form a sheet having a thickness of 10 mm or less to prepare a sheeted natural rubber, which was stored at room temperature (20-30 ° C.) for 1 month. When the moisture content of the sheeted natural rubber before storage was measured in the same manner as in Comparative Example 2, it was as shown in Table 1.
After washing the sheeted natural rubber stored for one month as described above with water about 5 times, 100 g of the sheeted natural rubber was added to 1 L of the aqueous solution prepared at the concentration shown in Table 1 for 6 hours at room temperature (20- (30 ° C). During the immersion, a weight or the like was appropriately placed so that the sheeted natural rubber did not float on the liquid surface of the aqueous solution, and the whole was set so as to sink into the aqueous solution. The sheeted natural rubber was taken out, washed with water, and then dried at the drying temperature shown in Table 1 for 2 hours to obtain a natural rubber sample.

The natural rubber samples obtained in Comparative Examples 1 to 5 and Examples 1 to 3 were evaluated as follows. The results are shown in Table 1.

(Odor component analysis method)
The main causative substances of the natural rubber odor include lower fatty acids such as acetic acid, valeric acid, isovaleric acid, isovaleric aldehyde, butyric acid and their aldehydes.
Accordingly, the peak area ratio of the above components detected using Head-Space GCMS (manufactured by Shimadzu Corporation, product name “GCMS-QP2010 Ultra”, and “HS-20” manufactured by Shimadzu Corporation as the headspace sampler) is used. Was corrected with the olfactory threshold of each component, and the sum of all was used as the odor component index. And the odor component rate was evaluated by the following formula.
Odor component ratio (%) = (odor component index in natural rubber sample of each example / odor component index in natural rubber sample of Comparative Example 1) × 100

(Evaluation of deterioration characteristics of natural rubber)
The deterioration characteristics of the natural rubber samples were evaluated by the following formula to evaluate the Mooney viscosity retention after aging at 80 ° C. for 72 hours. A larger Mooney viscosity retention value indicates that the natural rubber sample is more excellent in deterioration characteristics (heat aging resistance). Specifically, if the Mooney viscosity retention is 60% or more, it can be said that the deterioration characteristics are sufficiently excellent, if it is 65% or more, it can be said that the deterioration characteristics are more excellent, and if it is 70% or more, further deterioration occurs. If it is 80% or more, it can be said that it is further excellent in deterioration characteristics, if it is 85% or more, it is particularly excellent in deterioration characteristics, and if it is 95% or more, it is particularly deteriorated. It can be said that it has excellent characteristics.
Mooney viscosity retention rate (Mw retention rate,%) = (Mooney viscosity after aging / Mooney viscosity before aging) × 100

From the results shown in Table 1, the natural rubber subjected to the treatment of the present invention (to obtain a sheeted natural rubber having a moisture content of 20% or less by drying into a sheet and to dry the sheeted natural rubber at 125 ° C. or lower) It can be seen that the heat resistance and aging resistance are excellent.
In particular, when a sheeted natural rubber having a moisture content of 20% or less is obtained by sheeting and the sheeted natural rubber is dried at 125 ° C. or less (Example 1), the sheet is converted to a sheet and the moisture content is 20% or less. The sheeted natural rubber was obtained, but when the sheeted natural rubber was dried at a temperature higher than 125 ° C. (Comparative Example 2), it was stored at a moisture content of more than 20% without being formed into a sheet and dried at 125 ° C. Compared with the case (Comparative Example 3), the odor component rate could be significantly reduced synergistically.
Furthermore, in Examples 2 to 3 in which the sheeted natural rubber was treated with an aqueous solution having a concentration as shown in Table 1, the odor component was greatly reduced as compared with Comparative Example 1 in which the treatment of the present invention was not performed. Was confirmed.

Claims (5)

Production of natural rubber, comprising a sheet forming step of obtaining a sheeted natural rubber having a moisture content of 20% or less by forming a cup lamp into a sheet, and a drying step of drying the sheeted natural rubber at 125 ° C. or lower Method. The method for producing natural rubber according to claim 1, wherein the moisture content of the sheeted natural rubber is 15% or less. The said manufacturing method is a manufacturing method of the natural rubber of Claim 1 or 2 further including the base treatment process which makes the said sheet-like natural rubber contact a basic solution before the said drying process. The natural rubber production according to claim 3, wherein the basic solution is a solution containing at least one basic inorganic substance selected from the group consisting of metal carbonates, metal hydrogen carbonates, metal phosphates, and ammonia. Method. The method for producing natural rubber according to claim 3 or 4, wherein the basic solution is a solution further containing a surfactant.