JP4810568B2 - Modified natural rubber and method for producing the same - Google Patents

Description

The present invention relates to a modified natural rubber and a method for producing the same.

The modification of natural rubber is generally performed in a latex state stabilized with a surfactant because of cost, ease of handling, and the like, but in some cases, it is also performed in a solid rubber state or in a rubber solution. However, about 5% of non-rubber components such as proteins are present in ordinary natural rubber latex. Also, about 3% of non-rubber components are present in commercially available concentrated latex. Therefore, these non-rubber components, particularly proteins, inhibit the modification of natural rubber. For example, in the case of graft copolymerization, the graft ratio and graft efficiency are lowered, and a high modification effect and modification efficiency are obtained. There was a problem that it could not be obtained.

Therefore, deproteinization and high reforming efficiency are being studied. For example, in Patent Documents 1 and 2, deproteinized natural rubber is produced by a method of degrading protein by adding a proteolytic enzyme to latex or a method of repeatedly washing with a surfactant, and epoxidizing the deproteinized natural rubber Thus, a method for producing a modified natural rubber is disclosed. However, although these methods can reduce the protein to some extent, the phospholipid, which is one of the causes for inhibiting the modification of natural rubber, has not been sufficiently removed, and there is room for improvement. is there.
JP 2004-359773 A JP-A-2005-41960

An object of the present invention is to solve the above-mentioned problems and to provide a modified natural rubber having an excellent modifying effect and a method for producing a modified natural rubber having a high modifying efficiency.

The present invention relates to a modified natural rubber characterized by being modified by subjecting a natural rubber having a phosphorus content of 200 ppm or less to a graft copolymerization treatment of an organic compound having an unsaturated bond.

The present invention also relates to a modified natural rubber characterized in that a natural rubber having a phosphorus content of 200 ppm or less is modified by an addition reaction with an organic compound.

The present invention also relates to a modified natural rubber characterized in that a natural rubber having a phosphorus content of 200 ppm or less is modified by epoxidation treatment.

The natural rubber having a phosphorus content of 200 ppm or less is preferably obtained by saponifying natural rubber latex.

The modified natural rubber is preferably substantially free of phospholipids and has no peak due to phospholipid at -3 ppm to 1 ppm in ³¹ P NMR measurement of the chloroform extract.

The present invention is also characterized in that after the phosphorus compound is removed until the phosphorus content in the natural rubber latex is 200 ppm or less, an organic compound having an unsaturated bond is graft copolymerized with the obtained natural rubber. The present invention relates to a method for producing modified natural rubber.

The present invention also provides the production of the modified natural rubber, wherein the phosphorus compound is removed until the phosphorus content in the natural rubber latex is 200 ppm or less, and then the organic compound is subjected to an addition reaction with the obtained natural rubber. Regarding the method.

The present invention also relates to a method for producing the above-mentioned modified natural rubber, wherein the phosphorus compound is removed until the phosphorus content in the natural rubber latex is 200 ppm or less, and then the obtained natural rubber is epoxidized.

In the modified natural rubber production method, the phosphorus compound is preferably removed by saponifying natural rubber latex.

According to the present invention, a natural rubber in which a natural rubber latex is originally removed and a phosphorus compound (for example, phospholipid) originally contained in the natural rubber is removed as much as possible by a technique such as saponification treatment of natural rubber latex and washing treatment after saponification treatment. Modified rubber (for example, graft copolymerization treatment of an organic compound having an unsaturated bond, addition reaction with an organic compound, epoxidation treatment) has an excellent modification effect. In the case of copolymerization, a modified natural rubber having a high graft ratio can be obtained, and the natural rubber is modified with high modification efficiency (for example, high graft efficiency in the case of graft copolymerization). be able to.

The modified natural rubber of the present invention is obtained by modifying a natural rubber having a phosphorus content of 200 ppm or less. The phosphorus content in the natural rubber is 200 ppm or less, preferably 100 ppm or less. If it exceeds 200 ppm, the modification effect and modification efficiency (for example, graft efficiency in the case of graft copolymerization) in producing modified natural rubber from natural rubber tend to be reduced. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

The natural rubber is preferably substantially free of phospholipids. “Substantially no phospholipid is present” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

Natural rubber having a phosphorus content of 200 ppm or less can be produced, for example, by saponifying natural rubber latex with alkali and washing the agglomerated rubber. The collected natural rubber latex is saponified in a fresh state. After saponification, it is washed thoroughly with water to remove phospholipids that are non-rubber components on the surface of natural rubber latex particles. It is inferred that reforming can be performed at

The saponification treatment is performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a predetermined time. In addition, you may perform stirring etc. as needed. According to the method of the present invention, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed. In the present invention, alkali can be added to natural rubber latex for saponification, but by adding to natural rubber latex, there is an effect that saponification can be efficiently performed.

Natural rubber latex is collected as sap of heavy trees and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is thought to be based on the complex presence of various impurities. . In the present invention, raw latex produced by tapping a heavy tree or purified latex concentrated by centrifugation can be used. Furthermore, high ammonia latex to which ammonia is added by a conventional method may be used in order to prevent the progress of decay due to bacteria present in the raw rubber latex and to avoid coagulation of the latex. The rubber latex to be used for production of raw rubber is preferably within 10 days after being collected. This is because the gel content increases when the rubber latex is left for more than 10 days.

Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and amine compounds. From the viewpoint of the saponification effect and the influence on the stability of the latex, sodium hydroxide or hydroxide is particularly preferable. It is preferable to use potassium.

The amount of alkali added is not particularly limited, but the lower limit is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and the upper limit is 12 parts by mass or less with respect to 100 parts by mass of the solid content of natural rubber latex. Is preferably 5 parts by mass or less. If the amount of alkali added is less than 0.1 parts by mass, saponification may take time. Conversely, if the amount of alkali added exceeds 12 parts by mass, the natural rubber latex may be destabilized.

As the surfactant, at least one of an anionic surfactant, a nonionic surfactant and an amphoteric surfactant can be used. Among these, 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 ether, polyoxyalkylene ester, polyhydric alcohol fatty acid ester, sugar fatty acid ester, and alkyl polyglycoside. . Examples of amphoteric surfactants include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type.

The addition amount of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and the upper limit is preferably 6 parts by mass or less with respect to 100 parts by mass of the solid content of the natural rubber latex. 3 parts by mass or less is more preferable. If the addition amount of the surfactant is less than 0.01 parts by mass, the natural rubber latex may become unstable during the saponification treatment. On the other hand, if the amount of the surfactant added exceeds 6 parts by mass, the natural rubber latex is too stabilized and it may be difficult to coagulate.

The temperature of the saponification treatment can be appropriately set within the range where the saponification reaction with alkali can proceed at a sufficient reaction rate and the natural rubber latex does not cause alteration such as coagulation, but is usually 20 to 70 ° C. Preferably there is. Further, the treatment time is 3 to 48 hours in consideration of both sufficient treatment and productivity improvement, depending on the treatment temperature when the treatment is performed with natural rubber latex standing. Is preferred.

After completion of the saponification reaction, the agglomerated rubber is crushed and washed. Examples of the washing treatment include a method of diluting a rubber component with water and washing it, and then performing a centrifugal separation treatment to extract the rubber component. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by weight, preferably 10 to 30% by weight. Then, it may be centrifuged at 5000 to 10,000 rpm for 1 to 60 minutes. After completion of the washing treatment, a saponified natural rubber latex is obtained.

The modification of the natural rubber having a phosphorus content of 200 ppm or less can be performed, for example, by applying a method similar to a known modification method of the natural rubber latex to the saponified natural rubber latex.

Among the modified natural rubbers of the present invention, a modified natural rubber obtained by graft copolymerization with an organic compound having an unsaturated bond is added with an organic compound having an unsaturated bond to a saponified natural rubber latex, and an appropriate polymerization is started. It is obtained by adding an agent and reacting. Examples of the organic compound having an unsaturated bond include methacrylic acid, acrylic acid, methyl methacrylate, methyl acrylate, methacrylic acid such as 2-hydroxyethyl methacrylate, and derivatives thereof, acrylonitrol, vinyl acetate, styrene, acrylamide. And monomers capable of graft copolymerization such as vinyl pyrrolidone. When the organic compound having an unsaturated bond is added to the latex, an emulsifier is added to the latex in advance, or the organic compound having an unsaturated bond is emulsified and then added to the latex. The emulsifier is not particularly limited, but a nonionic surfactant is preferably used.

The amount of the organic compound having an unsaturated bond is usually 5 parts by mass or more, more preferably 10 parts by mass or more, and the upper limit is preferably 100 parts by mass or less, based on 100 parts by mass of natural rubber. Less than the mass part is more preferable. If the addition amount of the organic compound having an unsaturated bond is less than 5 parts by mass, the grafting amount of the organic compound having an unsaturated bond may be reduced, and the modification effect may be reduced. Conversely, when the amount of the organic compound having an unsaturated bond exceeds 100 parts by mass, the production of homopolymer increases and the graft efficiency may be lowered.

Examples of the polymerization initiator include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, 2,2-azobisisobutyrotitryl, and potassium persulfate. In particular, it is preferable to use a redox polymerization initiator in order to reduce the polymerization temperature. In such a redox polymerization initiator, examples of the reducing agent combined with the peroxide include tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ions, ascorbic acid, and the like. Examples of preferred combinations in the redox polymerization initiator include tert-butyl hydroperoxide and tetraethylenepentamine, hydrogen peroxide and Fe ²⁺ salt, K ₂ SO ₂ O ₈ and NaHSO _{3 and the} like. In addition, these may be used independently and may use 2 or more types together.

The addition amount of the polymerization initiator is preferably 0.3 mol% or more, more preferably 0.5 mol% or more, and the upper limit is preferably 10 mol% or less with respect to 100 mol of the organic compound having an unsaturated bond. 1 mol% or less is more preferable. A graft copolymer is obtained by charging these components into a reaction vessel and reacting at 30 to 80 ° C. for 2 to 10 hours. The natural rubber having a phosphorus content of 200 ppm or less may be in a latex state, or may be a rubber solution or a solid rubber.

The graft copolymer (modified natural rubber) obtained as described above has a high graft ratio (ratio of the weight of the graft polymerized monomer to the weight of the main chain polymer) and a high graft efficiency (the graft polymerized monomer with respect to the total polymerized weight of the monomer). Therefore, it is excellent in properties such as adhesiveness while maintaining strength, and can be suitably used for applications such as adhesives.

The addition reaction of the organic compound to the natural rubber having a phosphorus content of 200 ppm or less in the present invention is performed, for example, by adding an organic compound such as a thiol compound to a saponified natural rubber latex and adding the organic compound to the natural rubber. Is called. Examples of the thiol compound include ethyl mercaptan, 1-propanethiol, n-butyl mercaptan, 1-hexanethiol, 1-dodencanthiol, 1-octanethiol, benzenethiol, 1,2-ethanedithiol, 1,3- Propanedithiol, 1,4-butanethiol, 1,2-benzenethiol, 1,4-benzenethiol, 2-aminoethanethiol, 2-aminobenzenethiol, 4-aminobenzenethiol, mercaptoacetic acid, o-mercaptobenzoic acid Etc.

When adding the thiol compound to the latex, an emulsifier may be added to the latex in advance, or the thiol compound may be added to the latex after being emulsified with the emulsifier. Moreover, an organic peroxide can also be added as needed. The emulsifier is not particularly limited, but a nonionic surfactant is preferably used.

The addition amount of the thiol compound is usually preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 20 parts by mass or less, relative to 100 parts by mass of natural rubber. Part or less is more preferable. There exists a tendency for the effect by thiol compound addition to be small that the addition amount of a thiol compound is less than 0.1 mass part. Conversely, if the amount of thiol compound added exceeds 20 parts by mass, the processability of rubber may be deteriorated.

The addition reaction is preferably carried out with stirring. For example, the above components such as latex and thiol compound are charged in a reaction vessel, and irradiated with 500 to 1000 W microwave for 10 minutes to 1 hour, thereby saponifying natural rubber. A modified natural rubber in which a thiol compound is added to the molecule is obtained.
In addition, for example, the above-described components such as latex and thiol compound are charged into a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 24 hours, whereby a modified natural thiol compound is added to a saponified natural rubber molecule. Rubber is obtained.

The natural rubber having a phosphorus content of 200 ppm or less to be used may be in a latex state as in the grafting described above, and can be carried out with a rubber solution or a solid rubber. The organic compound adduct of the saponified natural rubber thus obtained has a high addition reaction rate (weight of added organic compound / weight of main chain polymer), and thus exhibits high reinforcement and is suitable for applications such as tire treads. Can be used.

The epoxidation treatment for the natural rubber having a phosphorus content of 200 ppm or less in the present invention is performed, for example, by adding an organic peracid to a saponification natural rubber latex and epoxidizing the natural rubber. Examples of the organic peracid include perbenzoic acid, peracetic acid, performic acid, perphthalic acid, perpropionic acid, trifluoroperacetic acid, perbutyric acid, and the like. These organic peracids may be added directly to the latex, but it is preferable to add two components that form the organic peracid to the latex so that the organic peracid produced reacts with the natural rubber in the latex. For example, when producing formic acid, formic acid and hydrogen peroxide may be added sequentially. In the case of peracetic acid, glacial acetic acid and hydrogen peroxide may be added sequentially to cause the reaction.

The amount of the organic peracid added is usually preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and the upper limit is preferably 70 parts by mass or less, and 60 parts by mass or less with respect to 100 parts by mass of natural rubber. More preferred. Also when adding 2 components which produce | generate an organic peracid, addition amount is adjusted so that the produced | generated organic peracid exists in this range. If the amount of the organic peracid added is less than 5 parts by mass, the modification effect may be reduced. On the other hand, if the amount of the organic peracid added exceeds 60 parts by mass, the physical properties may be greatly deteriorated due to side reactions.

Prior to adding these organic peracids or their reaction components to the latex, a nonionic emulsifier is added to the latex and the latex is kept at a neutral pH of about 5 to 7 and stabilized. Is preferred. The epoxidation reaction is usually performed by reacting at a temperature of 20 to 60 ° C. for 3 to 10 hours.

The natural rubber having a phosphorus content of 200 ppm or less to be used may be in a latex state as in the grafting described above, and can be carried out with a rubber solution or a solid rubber. The epoxidized product of natural rubber obtained as above has a high epoxidation rate (change rate of unsaturated bond to epoxy group), so it has excellent properties such as oil resistance and gas permeation resistance while maintaining strength. It can be suitably used for applications such as tire inner liners.

In addition to the modified natural rubber obtained by the present invention, if necessary, other rubber components such as diene rubber, fillers such as carbon black and silica, silane coupling agents, zinc oxide, stearic acid, vulcanizing agents A rubber composition applicable to the rubber industry such as tires can be produced by blending additives such as a vulcanization aid, a vulcanization accelerator, and an anti-aging agent.

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

First, various chemicals used in Production Examples, Examples, and Comparative Examples will be described.
Surfactant: Emal-E manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries
Nonionic emulsifiers: Emulgen 106, Emulgen 430, manufactured by Kao Corporation

Production Example 1
(Saponification process)
After adjusting the field latex obtained from the farm to a solid content concentration (DRC) of 30% (w / v), 10 g of Emal-E and 10 g of NaOH are added to 1000 g of natural rubber latex, and saponification reaction is performed at 70 ° C. for 24 hours. Went. Water was added to the obtained latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized and washed repeatedly with 1000 ml of water to obtain a saponified natural rubber latex.

Production Example 2
(Saponification process)
After adjusting the field latex obtained from the farm to a solid content concentration (DRC) of 30% (w / v), 10 g of Emal-E and 20 g of NaOH are added to 1000 g of natural rubber latex, and saponification reaction is performed at 70 ° C. for 48 hours. Went. Water was added to the obtained latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized and washed repeatedly with 1000 ml of water to obtain a saponified natural rubber latex.

Production Example 3
(Saponification process)
After adjusting the field latex obtained from the farm to a solid content concentration (DRC) of 30% (w / v), 10 g of Emal-E and 10 g of NaOH are added to 1000 g of natural rubber latex, and the saponification reaction is performed at room temperature for 24 hours. went. Water was added to the obtained latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized and washed repeatedly with 1000 ml of water to obtain a saponified natural rubber latex.

About each natural rubber of manufacture examples 1-3, phosphorus content etc. were measured by the method shown below.
-Measurement of phosphorus content The phosphorus content of raw rubber was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
· ³¹ P-NMR measurement NMR analyzer of phosphorus used (400MHz, AV400M, Bruker Japan Co., Ltd.), the measurement peak of 80% P atoms of the phosphoric acid aqueous solution as a reference point (0 ppm), and extracted from the raw rubber with chloroform purification of the ingredients were measured and dissolved in CDCl _3.

Example 1
(Production of graft copolymerized natural rubber)
Into a four-necked flask equipped with a stir bar, dropping funnel, nitrogen inlet tube and condenser, 600 g of the saponified natural rubber latex (solid content 25%) obtained in Production Example 1 is added and slowly stirred under a nitrogen atmosphere. Then, 0.92 g of a nonionic emulsifier (“Emulgen 430” manufactured by Kao Corporation) dissolved in 250 ml of distilled water was added all at once. Next, 91.6 g of methyl methacrylate was added and stirred vigorously for several seconds to mix each chemical well. Next, 1.43 g of a polymerization initiator tert-butyl hydroperoxide dissolved in 50 ml of distilled water and 15.0 g of tetraethylenepentamine were added and reacted at 30 ° C. for 3 hours. Since the latex after the reaction was coagulated, extraction with petroleum ether and extraction with a 2: 1 mixed solvent of acetone and methanol separated unreacted natural rubber, homopolymer and graft copolymer. . These were confirmed to be independent by FT-IR and NMR analyzers.

Examples 2-3
(Production of graft copolymerized natural rubber)
The same procedure as in Example 1, except that the saponification natural rubber latex obtained in Production Example 2 (solid content 25%) and the saponification natural rubber latex obtained in Production Example 3 were used, respectively. As a result, a graft copolymer was obtained.

Comparative Example 1
(Production of graft copolymerized natural rubber)
A graft copolymer was obtained in the same manner as in Example 1 except that HA type latex obtained from Guthrie (Malaysia) was used after being diluted to a solid content of 25%.

Comparative Example 2
(Production of graft copolymerized natural rubber)
A natural rubber latex (solid content 61%) obtained from Guthrie (Malecia) was diluted to a solid content of 30%, concentrated to a solid content of 60%, and diluted to a solid content of 25% and used again. Otherwise, a graft copolymer was obtained in the same manner as in Example 1.

About the graft copolymer obtained by each Example and the comparative example, the graft ratio and graft efficiency which evaluate a polymerization degree were calculated | required by following Formula.
Graft ratio = (weight of grafted monomer (g)) / (weight of main chain polymer (g)) × 100
Graft efficiency = (weight of grafted monomer (g)) / (total weight of monomer polymerization (g)) × 100

The obtained graft ratio and graft efficiency are shown in Table 1 together with the phosphorus content of each natural rubber used.

As shown in Table 1, the phosphorus content of the saponified natural rubber latex obtained in Production Examples 1 to 3 was 200 ppm or less. In Examples 1 to 3 using a saponified natural rubber latex, a higher graft ratio and graft efficiency were shown than in Comparative Examples 1 and 2 where no saponified natural rubber latex was used.
Moreover, in the ³¹ P NMR measurement of the extract extracted from the saponification-treated natural rubber latex obtained in Production Examples 1 to 3, no peak due to phospholipid was detected at -3 ppm to 1 ppm.

Example 4
(Manufacture of natural rubber added with organic compounds)
600 g of the saponified natural rubber latex (solid content 25%) obtained in Production Example 1 was charged into a three-necked flask equipped with a stirrer, a dropping funnel and a condenser. Subsequently, 5.4 g of a nonionic emulsifier (“Emulgen 106” manufactured by Kao Corporation) dissolved in 300 ml of distilled water was added with slow stirring. Next, 20 g of aminoethanethiol was added and stirred, followed by irradiation with microwaves at 500 W for 1 hour to carry out an addition reaction.

Examples 5-6
(Manufacture of natural rubber added with organic compounds)
Except for using the saponification-treated natural rubber latex (solid content 25%) obtained in Production Example 2 and the saponification-treated natural rubber latex (solid content 25%) obtained in Production Example 3, respectively, the procedure was the same as in Example 4. The aminoethanethiol was added.

Comparative Example 3
(Manufacture of natural rubber added with organic compounds)
Aminoethanethiol was added in the same manner as in Example 4 except that HA type latex obtained from Guthrie (Malaysia) was used after being diluted to a solid content of 25%.

Comparative Example 4
(Manufacture of natural rubber added with organic compounds)
A natural rubber latex (solid content 61%) obtained from Guthrie (Malecia) was diluted to a solid content of 30%, concentrated to a solid content of 60%, and diluted to a solid content of 25% and used again. Otherwise, aminoethanethiol was added in the same manner as in Example 4.

The addition reaction rate (weight of added organic compound [g] / weight of main chain polymer [g]) was measured.
The measured addition reaction rate is shown in Table 2 together with the phosphorus content of each natural rubber used.

As shown in Table 2, in Examples 4 to 6 using the saponified natural rubber latex, a higher addition reaction rate was shown compared to Comparative Examples 3 and 4 in which the saponified natural rubber latex was not used.

Example 7
(Manufacture of epoxidized natural rubber)
600 g of the saponified natural rubber latex (solid content 25%) obtained in Production Example 1 was charged into a three-necked flask equipped with a stirrer, a dropping funnel and a condenser. Subsequently, 5.4 g of a nonionic emulsifier (“Emulgen 106” manufactured by Kao Corporation) dissolved in 300 ml of distilled water was added with slow stirring. Next, acetic acid was added to adjust the pH to neutral, heated to 40 ° C., and 30.6 g of formic acid was added with stirring. Further, the mixture was heated to 50 ° C., 166.8 g of hydrogen peroxide (39% aqueous solution) was added in 20 minutes, and then reacted at room temperature for 5 hours to obtain an epoxidized rubber.

Examples 8-9
(Manufacture of epoxidized natural rubber)
Except for using the saponification-treated natural rubber latex (solid content 25%) obtained in Production Example 2 and the saponification-treated natural rubber latex (solid content 25%) obtained in Production Example 3, respectively, in the same manner as in Example 7. Thus, an epoxy rubber was obtained.

Comparative Example 5
(Manufacture of epoxidized natural rubber)
Epoxy rubber was obtained in the same manner as in Example 7 except that HA type latex obtained from Guthrie (Malaysia) was used after being diluted to a solid content of 25%.

Comparative Example 6
(Manufacture of epoxidized natural rubber)
After diluting a natural rubber latex (solid content 61%) obtained from Guthrie (Malecia) to a solid content of 30%, the solid content is concentrated to 60% and diluted to a solid content of 25%. In the same manner as in Example 7, an epoxy rubber was obtained.

The epoxidation rate of the epoxidized rubber obtained in each Example and Comparative Example was measured using FT-IR and ¹³ C-NMR. The measurement was carried out in Chemical Demonstration of the Randomness of Epoxidized Natural Rubber, Br. Polym. J. et al. 1984, 16, 134 (Davey et al.) And to compare the reaction rate, the epoxidation rate of the double bond after 3 hours was measured.
The measurement results of the epoxidation rate of the epoxidized rubber obtained in each Example and Comparative Example are shown in Table 3 together with the phosphorus content of each natural rubber used.

As shown in Table 3, in Examples 7 to 9 using the saponified natural rubber latex, a higher epoxidation rate was shown compared to Comparative Examples 5 and 6 in which the saponified natural rubber latex was not used.

Claims (10)

A modified natural rubber modified by subjecting a natural rubber having a phosphorus content of 200 ppm or less to a graft copolymerization treatment of at least one of methacrylic acid, acrylic acid, and derivatives thereof,
The natural rubber is obtained by saponifying the natural rubber latex with alkali, repeatedly washing the agglomerated rubber and washing away the phosphorus compound separated by saponification, thereby reducing the phosphorus content in the natural rubber latex to 200 ppm. A modified natural rubber, characterized in that: A modified natural rubber modified by subjecting a natural rubber having a phosphorus content of 200 ppm or less to an addition reaction with a thiol compound,
The natural rubber is obtained by saponifying the natural rubber latex with alkali, repeatedly washing the agglomerated rubber and washing away the phosphorus compound separated by saponification, thereby reducing the phosphorus content in the natural rubber latex to 200 ppm. A modified natural rubber, characterized in that: A modified natural rubber modified by epoxidizing a natural rubber having a phosphorus content of 200 ppm or less,
The natural rubber is obtained by saponifying the natural rubber latex with alkali, repeatedly washing the agglomerated rubber and washing away the phosphorus compound separated by saponification, thereby reducing the phosphorus content in the natural rubber latex to 200 ppm. A modified natural rubber, characterized in that: The modification according to claim 1, wherein in the graft copolymerization treatment, the addition amount of at least one of methacrylic acid, acrylic acid, and derivatives thereof is 5 to 100 parts by mass with respect to 100 parts by mass of natural rubber. Natural rubber. The modified natural rubber according to claim 2, wherein the addition amount of the thiol compound is 0.1 to 20 parts by mass with respect to 100 parts by mass of the natural rubber in the addition reaction. The modified natural rubber according to claim 3, wherein the amount of the organic peracid added in the epoxidation treatment is 5 to 70 parts by mass with respect to 100 parts by mass of the natural rubber. The modified natural rubber according to any one of claims 1 to 6, wherein a peak due to phospholipid does not exist at -3 ppm to 1 ppm and substantially no phospholipid exists in ³¹ P NMR measurement of the chloroform extract. The natural rubber latex is saponified with alkali, and the agglomerated rubber is washed repeatedly to remove the phosphorus compound until the phosphorus content in the natural rubber latex is 200 ppm or less . The method for producing a modified natural rubber according to claim 1 or 4 , wherein acrylic copolymer and at least one of these derivatives are graft copolymerized. Natural rubber latex is saponified with alkali, and the agglomerated rubber is repeatedly washed to remove the phosphorus compound until the phosphorus content in the natural rubber latex is 200 ppm or less, and then the thiol compound is added to the obtained natural rubber. 6. The process for producing a modified natural rubber according to claim 2, wherein an addition reaction is carried out. Natural rubber latex is saponified with alkali, and the agglomerated rubber is washed repeatedly to remove the phosphorus compound until the phosphorus content in the natural rubber latex is 200 ppm or less, and then the resulting natural rubber is epoxidized. The method for producing a modified natural rubber according to claim 3 or 6, wherein: