WO2011108660A1

WO2011108660A1 - Method for producing modified natural rubber

Info

Publication number: WO2011108660A1
Application number: PCT/JP2011/054944
Authority: WO
Inventors: 直生岩瀬; 今井　英幸; 明繁瀬尾; 河原　成元; 祥正山本; 圭一郎塩原
Original assignee: 豊田合成株式会社; 国立大学法人長岡技術科学大学
Priority date: 2010-03-05
Filing date: 2011-03-03
Publication date: 2011-09-09
Also published as: JPWO2011108660A1; JP5739867B2; CN102858805A

Abstract

Disclosed is a method for producing modified natural rubber, comprising an epoxidation step, a removal step, and a reduction and ring-opening step. In the epoxidation step, in a latex in which a plant-derived rubbery polymer having a plurality of unsaturated double bonds in the main chain is dispersed in water serving as a dispersion medium, an organic peracid is reacted with the rubbery polymer. In this manner, by the epoxidation of a part of the unsaturated double bonds in the rubbery polymer, an epoxidated rubbery polymer is obtained. In the removal step, organic peracid-derived substances generated from the organic peracid in the epoxidation step are removed from the latex, whereby the content of the organic peracid-derived substances in the latex is reduced to 35 parts by mass or less based on 100 parts by mass of the epoxidated rubbery polymer. In the reduction and ring-opening step, under the conditions of pH 7 to 8 and in the presence of an organic acid salt, a part or the whole of the remaining unsaturated double bonds in the epoxidated rubbery polymer in the latex are reduced, and also a part or the whole of the epoxy groups in the epoxidated rubbery polymer are ring-opened.

Description

Method for producing modified natural rubber

The present invention relates to a method for producing a modified natural rubber, and more particularly, to a method for producing a modified natural rubber capable of simplifying the production process after the epoxidation process.

Conventionally, rubber products have been put to practical use in various fields. Raw materials for rubber products are classified into plant-derived natural rubber and petroleum-derived synthetic rubber. Among synthetic rubbers, various synthetic rubbers excellent in oil resistance, weather resistance, gas permeability, cold resistance and the like have been put into practical use. For example, as a synthetic rubber excellent in weather resistance and ozone resistance, ethylene-propylene rubber (EPDM) can be mentioned. This type of synthetic rubber is used in applications such as automobile parts and insulators.

In recent years, there are concerns about the depletion of petroleum resources and global warming. For this reason, interest in plant-derived materials is increasing as an alternative material for petroleum-derived materials. Plant-derived materials are expected to suppress the consumption of limited petroleum resources and to suppress global warming because carbon dioxide is absorbed during the plant growth process.

Plant-derived natural rubber (rubber-like polymer) is collected from rubber trees as a polymer. Natural rubber is excellent in processability and strength. On the other hand, natural rubber is inferior in weather resistance and ozone resistance. For this reason, various modifications of natural rubber have been attempted for the purpose of improving rubber properties and imparting new rubber properties. Various modified natural rubbers have been developed for the purpose of improving the application range and convenience.

Patent Document 1 describes a modified nature in which unsaturated double bonds in the main chain are reduced to reduce unsaturated double bonds, and a part of the unsaturated double bonds are epoxidized and opened to give a hydroxyl group. A rubber is disclosed. The modified natural rubber disclosed in this document has excellent weather resistance and ozone resistance because unsaturated double bonds are reduced. Furthermore, the modified natural rubber disclosed in this document is excellent in cross-linking ability because it has a hydroxyl group. Such modified natural rubber is applied, for example, to automotive window frame parts such as weather strips and parts used around water such as water hoses.

JP 2008-308601 A

A modified natural rubber in which the unsaturated double bond in the main chain is reduced to reduce the unsaturated double bond, and a part of the unsaturated double bond is epoxidized and opened to give a hydroxyl group to the above rubber The following method is used as a method for producing from a polymer. First, in the epoxidation process, an organic peracid is added to a latex in which a rubber-like polymer is dispersed in water, and a part of the unsaturated double bond in the main chain of the rubber-like polymer is epoxidized to epoxidize it. A rubbery polymer is produced. Next, in the reduction / ring opening step, hydrogen is added to the epoxidized rubber-like polymer in the presence of a hydrogenation catalyst to open the epoxy group of the main chain and reduce the remaining unsaturated double bonds. To produce modified natural rubber. Then, the modified natural rubber in the reaction solution after the ring-opening / reducing step is solidified to be isolated and purified. Thus, a solid modified natural rubber is obtained.

In the reduction / ring-opening step, a large amount of the organic acid and the organic acid salt derived from the organic peracid added in the epoxidation step may be present in the reaction system. In this case, undesired side reactions such as cyclization and formation of crosslinks may be caused in the epoxidized rubber-like polymer, and rubber properties may be lost. Therefore, conventionally, after the epoxidation step, the epoxidized rubber-like polymer in the latex is solidified and isolated from the dispersion medium, whereby the epoxidized rubber-like polymer and the organic peracid-derived substance are combined. It was separated. And what re-dispersed the solidified epoxidized rubber-like polymer in the dispersion medium, or the thing melt | dissolved in the organic solvent was processed in the reduction | restoration and ring-opening process. As described above, in the conventional production method, it is necessary to perform both the isolation treatment and the redispersion treatment or the dissolution treatment of the epoxidized rubber-like polymer between the epoxidation step and the reduction / ring-opening step. For this reason, the manufacturing process was complicated.

An object of the present invention is to provide a method for producing a modified natural rubber capable of simplifying the production process.

In order to achieve the above object, according to the first aspect of the present invention, in a latex in which a plant-derived rubbery polymer having a plurality of unsaturated double bonds in the main chain is dispersed in water as a dispersion medium. An epoxidation step of obtaining an epoxidized rubber-like polymer by reacting an organic peracid with the rubber-like polymer and epoxidizing a part of the unsaturated double bond of the rubber-like polymer; The organic peracid-derived substance generated from the organic peracid in the polymerization step is removed from the latex, and the content of the organic peracid-derived substance in the latex is 35 masses per 100 parts by mass of the epoxidized rubber-like polymer. Part or all of unsaturated double bonds remaining in the epoxidized rubber-like polymer in the latex under the condition of pH 7-8 and in the presence of an organic acid salt. As well as the epoch Method for producing a modified natural rubber and a reduction and ring opening step for opening a part or all of the epoxy groups of the sheet of rubbery polymer is provided.

In the above modified natural rubber production method, in the removing step, it is preferable to replace a part of the dispersion medium in which the substance derived from the organic peracid in the latex is dissolved with a new dispersion medium.
In the method for producing a modified natural rubber, in the removing step, the latex after the epoxidation step is subjected to a centrifugal separation treatment, whereby the latex is mainly composed of an upper layer in which the epoxidized rubber-like polymer is dispersed, and is mainly organic. It is preferable to separate into a lower layer in which the peracid-derived substance is dissolved, and to remove the lower layer and add a new dispersion medium to the upper layer.

In the configuration of each invention described above, after the epoxidation step, the organic peracid-derived substance is removed from the latex to separate the epoxidized rubber-like polymer and the organic peracid-derived substance. In other words, as in the past, it is necessary to solidify and isolate and purify the epoxidized rubber-like polymer from the latex, and to redisperse the solidified epoxidized rubber-like polymer into a latex. do not do. Therefore, the isolation process and redispersion process of the epoxidized rubber-like polymer which were performed between the epoxidation process and the reduction / ring-opening process are omitted. Therefore, the manufacturing process after the epoxidation process can be simplified. Further, the epoxidation step and the reduction / ring-opening step can be continuously performed in the latex state without isolating and purifying the epoxidized rubber-like polymer from the latex. For this reason, the work efficiency at the time of manufacture improves.

In the above modified natural rubber production method, it is preferable to remove proteins in the latex together with the organic peracid-derived substance in the removing step.
Natural rubber latex collected from plants contains various proteins in addition to rubbery polymers. When a modified natural rubber is produced using a natural rubber latex mixed with such a protein as a raw material, the physical properties of the resulting modified natural rubber may become unstable or the quality may be lowered. Therefore, when producing a modified natural rubber using a natural rubber latex mixed with protein as a raw material, it is desirable to perform a deproteinization treatment to remove the protein.

According to the above configuration, in the removing step, the protein is also removed simultaneously with the removal of the organic peracid-derived substance. Thereby, even if it is a case where a deproteinization process is added during a series of manufacturing processes, it is not necessary to add the operation | work for isolate | separating a rubber component and a protein. Therefore, an increase in work amount can be minimized.

In the above modified natural rubber production method, in the reduction / ring-opening step, hydrogen atoms are added to the unsaturated double bond remaining in the epoxidized rubber-like polymer, and the epoxy group of the epoxidized rubber-like polymer is added. It is preferred to open the ring to form a hydroxyl group.

According to the present invention, the production process of the modified natural rubber can be simplified.

Hereinafter, an embodiment embodying a method for producing a modified natural rubber according to the present invention will be described in detail.
In the method for producing a modified natural rubber in the present embodiment, a plant-derived rubber-like polymer having a plurality of unsaturated double bonds in the main chain is used as a raw material. Then, the unsaturated double bond in the main chain is reduced to reduce the unsaturated double bond, and a part of the unsaturated double bond is epoxidized and opened to provide a modified natural rubber having a hydroxyl group. To manufacture. The method for producing a modified natural rubber in the present embodiment includes an epoxidation step, a removal step, and a reduction / ring-opening step. In the epoxidation step, a part of unsaturated double bonds of a plant-derived rubber-like polymer having a plurality of unsaturated double bonds in the main chain is epoxidized to obtain an epoxidized rubber-like polymer. In the removal step, the organic peracid-derived substance generated in the epoxidation step is removed. In the reduction / ring-opening step, part or all of the unsaturated double bond remaining in the epoxidized rubber-like polymer is reduced, and part or all of the epoxy group of the epoxidized rubber-like polymer is opened. The

<Raw material>
As a raw material, natural rubber latex containing a plant-derived rubber-like polymer having a plurality of (two or more) unsaturated double bonds in the main chain can be used. Specifically, a field latex obtained from a natural rubber tree and a processed product obtained by treating the field latex can be used. Examples of the treated product include latex in which field latex is concentrated to increase the rubbery polymer concentration, latex in which field latex is treated with ammonia, latex in which field latex is deproteinized, and a mixture thereof. Further, a solid rubber obtained by isolating and purifying a rubber-like polymer from natural rubber latex can also be used as a raw material.

Examples of the deproteinization treatment method include known methods described in JP-A Nos. 6-56902 and 2004-99696. In the deproteinization treatment, the nitrogen content in the natural rubber latex is preferably set to 0.1 parts by mass or less with respect to 100 parts by mass of the rubbery polymer, and more preferably set to 0.05 parts by mass or less. preferable.

<Epoxidation process>
In the epoxidation step, an organic peracid is reacted with the rubber-like polymer, and a part of the unsaturated double bond of the main chain of the rubber-like polymer is substituted with an epoxy group to obtain an epoxidized rubber-like polymer. It is a process. Specifically, first, a natural rubber latex or a solid rubber as a raw material is dispersed in water as a dispersion medium to prepare a reaction system latex. Here, in order to distinguish from natural rubber latex, latex used in the production process is described as reaction latex. At this time, in order to stabilize the dispersion state of the rubber-like polymer, it is preferable to add a surfactant to the dispersion medium.

Water as the dispersion medium may contain a small amount of components other than water, for example, a hydrophilic organic solvent. As the surfactant, anionic surfactant sodium dodecyl sulfate is preferably used, but is not limited to this, and anionic surfactants such as carboxylic acid, sulfonic acid, sulfate, and phosphate Agents, nonionic surfactants such as polyethylene glycol and polyhydric alcohols, cationic surfactants such as quaternary ammonium salts, amphoteric surfactants such as amino acids and betaines, plant-based biobased interfaces An activator or the like may be used.

Next, an organic peracid is reacted with the rubber-like polymer in the prepared reaction latex to perform epoxidation. Examples of organic peracids include perbenzoic acid, peracetic acid, performic acid, perphthalic acid, perpropionic acid, trifluoroperacetic acid, and perbutyric acid. These organic peracids may be added directly to the reaction system latex. As another method, a component capable of generating an organic peracid may be added to generate the organic peracid in the reaction system latex. For example, formic acid can be produced by sequentially adding formic acid and hydrogen peroxide. In order to produce peracetic acid, acetic anhydride and hydrogen peroxide may be added sequentially.

After a predetermined time has elapsed since the addition of the organic peracid, the reaction system latex is neutralized with a base such as an aqueous ammonia solution. By the neutralization reaction at this time, the organic peracid and the organic acid present in the reaction system latex are neutralized to produce an organic peracid and a salt of the organic acid. For example, when the organic peracid is peracetic acid and neutralization is performed using an aqueous ammonia solution, acetic acid is generated from the peracetic acid, and the reaction system latex containing acetic acid is neutralized. Is generated.

The epoxidation reaction is preferably performed so that the epoxidation rate of the product epoxidized rubber polymer is in the range of 1 to 25%. The epoxidation rate of the epoxidized rubber polymer is adjusted by changing the amount of organic peracid added and the processing time. The epoxidation rate of the epoxidized rubber polymer can be calculated by the following formula. In the formula, “number of double bonds of rubber polymer” (value before epoxidation) and “number of epoxy groups of epoxidized rubber polymer” can be obtained from the measurement result of 1H-NMR, for example. .

<Removal process>
A removal process is a process of removing the organic acid and organic acid salt which are the substances derived from an organic peracid from the reaction system latex after an epoxidation process, and reducing those density | concentrations. In the removal step, the total content of the organic acid derived from the organic peracid and the salt thereof in the reaction system latex is 35 parts by mass or less, preferably 30 parts by mass or less, more preferably 100 parts by mass of the epoxidized rubber polymer. Is reduced to 25 parts by mass or less.

As a method for removing the organic peracid-derived substance from the reaction latex, for example, a centrifugal separation process is used. Specifically, the reaction system latex can be separated into an upper layer and a lower layer (separation operation) by centrifuging the reaction system latex after the epoxidation step. The upper layer is a latex (cream) layer in which mainly an epoxidized rubber-like polymer is dispersed at a high concentration. The lower layer is a liquid layer in which a substance derived from an organic peracid is dissolved. For example, if the centrifugation treatment is performed for several tens of minutes at 5000 to 15000 G, the reaction system latex can be separated as described above.

Next, the upper layer is recovered and a dispersion medium is added to the upper layer (redispersion operation). The dispersion medium added in the redispersion operation may be the same as or different from the composition during the epoxidation step. By the separation operation and the redispersion operation, the dispersion medium in which the substance derived from the organic peracid in the reaction system latex is dissolved is replaced with a new dispersion medium. Thus, the concentration of the organic peracid-derived substance is reduced. In this case, it is preferable to repeat the separation operation and the redispersion operation twice or more according to the concentration of the organic peracid-derived substance in the reaction system latex after the redispersion operation.

In addition, when natural rubber latex that has not been subjected to deproteinization treatment is used as a raw material, the deproteinization treatment can be performed simultaneously in the removal step. Specifically, a protein denaturant is added to the reaction system latex before the centrifugation treatment to denature the protein in the reaction system latex. When centrifugation is performed in a state where the protein is denatured, the protein in the reaction system latex moves to a liquid lower layer in which a substance derived from organic peracid exists. For this reason, the protein which modified | denatured with the substance derived from an organic peracid can also be removed by isolate | separating an upper layer and a lower layer. Examples of protein denaturants include urea compounds (urea derivatives, urea double salts) represented by the following general formula (1), and sodium hypochlorite. Examples of urea compounds represented by the following general formula (1) include urea, methyl urea, ethyl urea, n-propyl urea, i-propyl urea, n-butyl urea, i-butyl urea, and n-pentyl urea. Can be mentioned. Of these, urea, methylurea, and ethylurea are particularly preferable.

RNHCONH ₂ (1)
(Wherein R represents H or an alkyl group having 1 to 5 carbon atoms)
When deproteinization treatment is performed, the nitrogen content in the reaction system latex is preferably set to 0.1 parts by mass or less with respect to 100 parts by mass of the epoxidized rubber-like polymer, and 0.05 parts by mass or less. It is more preferable to set.

<Reduction / ring opening process>
The reduction / ring-opening step reduces part or all of the unsaturated double bonds remaining in the epoxidized rubber-like polymer in the reaction system latex, and part or all of the epoxy groups of the epoxidized rubber-like polymer. Is a step of opening the ring. Known reduction methods and ring-opening methods carried out in the state of latex as reduction of unsaturated double bonds of epoxidized rubber-like polymer and ring-opening reaction of epoxy groups (hereinafter referred to as reduction / ring-opening reaction) Can be used.

In this case, it is necessary to adjust the pH during the reduction / ring-opening reaction within a predetermined range. In other words, if the pH during the reduction / ring-opening reaction is shifted to the acidic side or the basic side outside the range of 7-8, the cyclization of the epoxidized rubber-like polymer during the reduction / ring-opening reaction is excessively accelerated. Is done. Therefore, regardless of which method is employed, it is necessary to proceed the reduction / ring-opening reaction under the conditions of pH 7 to 8 and in the presence of an organic acid salt. The organic acid salt works as a buffer solution by dissolving in water which is a dispersion medium of the reaction system latex. For this reason, the organic acid salt can suppress a large change in pH during the reduction / ring-opening reaction.

Examples of organic acid salts include sodium salts, potassium salts, calcium salts, amine salts (primary to tertiary) of carboxylic acids such as benzoic acid, acetic acid, formic acid, phthalic acid, propionic acid, trifluoroacetic acid, and butyric acid, And ammonia salts. The organic acid salt may be an organic acid salt derived from an organic peracid that remains in the reaction latex without being removed during the removal step, or may be a newly added organic acid salt during the reduction / ring-opening reaction. There may be. The content of the organic acid salt during the reduction / ring-opening reaction is preferably 0.1 to 35 parts by mass and preferably 1.7 to 25 parts by mass with respect to 100 parts by mass of the epoxidized rubber polymer. More preferred.

Examples of the known reduction method and ring-opening method performed in the latex state described above include, for example, a method in which hydrogen is brought into contact with the epoxidized rubber-like polymer in the presence of a hydrogenation catalyst. Hereinafter, a case where a method of bringing hydrogen gas into contact with the epoxidized rubber-like polymer in the presence of a hydrogenation catalyst will be described as a reduction / ring-opening reaction.

First, a hydrogenation catalyst is added to the reaction system latex after the removal step, and the pH of the reaction system latex is adjusted to a range of 7-8. Here, when the organic peracid-derived organic acid salt is not contained in the reaction latex after the removing step, a predetermined amount of the organic acid salt is added to the reaction latex before adjusting the pH. After adjusting the pH, an organic acid salt may be added to the reaction system latex. In this case, the condition is that the pH of the reaction latex after the addition of the organic acid salt is maintained in the range of 7-8.

On the other hand, when the reaction system latex after the removal step contains an organic acid salt derived from an organic peracid, the pH of the reaction system latex is adjusted to the range of 7 to 8 after adding the hydrogenation catalyst. As the hydrogenation catalyst, a homogeneous catalyst and a heterogeneous catalyst can be used. Specific examples of the hydrogenation catalyst include metal catalysts such as nickel, ruthenium, platinum, palladium, and rhodium.

After adjusting the pH of the reaction system latex, hydrogen is supplied into the reaction system latex in an air atmosphere, an inert gas atmosphere such as argon or nitrogen, or a hydrogen atmosphere. In this case, hydrogen gas such as high-pressure hydrogen gas may be directly supplied, or hydrogen generated in the reaction system may be supplied by adding a component capable of generating hydrogen (hydrogen donor). Then, in the presence of the hydrogenation catalyst, hydrogen is brought into contact with the epoxidized rubber-like polymer in the reaction system latex at a predetermined temperature for a predetermined time.

As a result, a hydrogen atom is added to the unsaturated double bond remaining in the main chain of the epoxidized rubber-like polymer, and the unsaturated double bond is reduced. At the same time, the epoxy group of the main chain of the epoxidized rubber-like polymer is opened, and a hydrogen atom is added to an oxygen atom to form a hydroxyl group. This reduces the unsaturated double bond in the main chain to reduce the unsaturated double bond, and also epoxidizes and opens a part of the unsaturated double bond to give a hydroxyl group. Hereinafter, it is simply referred to as modified natural rubber).

In the reduction / ring-opening reaction, the hydrogenation rate of the modified natural rubber as a product is preferably 80% or more. The hydrogenation rate of the modified natural rubber can be adjusted by changing the treatment temperature and treatment time in the reduction / ring-opening reaction. The treatment temperature in the reduction / ring-opening reaction is preferably set in the range of 0 to 100 ° C, more preferably in the range of 40 to 80 ° C. When the treatment temperature is less than 0 ° C., it becomes difficult to sufficiently advance the reaction. If the treatment temperature exceeds 100 ° C., the molecular chain of the epoxidized rubber-like polymer may be broken, leading to a reduction in molecular weight.

The hydrogenation rate of the modified natural rubber can be calculated by the following formula. The “number of double bonds of rubber polymer” in the formula (number before epoxidation) and “remaining number of double bonds of modified natural rubber” can be obtained from, for example, the measurement result of 1H-NMR. it can.

<Recovery process>
The recovery step is a step of recovering the modified natural rubber in the reaction system latex. The modified natural rubber is recovered using a known method for recovering the rubber component from the latex in which the rubber component is dispersed. For example, by adding methanol to the reaction system latex, the modified natural rubber in the reaction system latex is condensed and precipitated. The modified natural rubber can be isolated by collecting the precipitate. At that time, it is preferable to remove the hydrogenation catalyst in the reaction system latex before adding methanol. As a method for removing the hydrogenation catalyst, for example, a method of adding a complexing agent such as dimethylglyoxime to the reaction system latex to precipitate and remove the hydrogenation catalyst can be mentioned.

Next, operational effects in the present embodiment will be described below.
(1) In the removal step after the epoxidation step, the organic peracid-derived substance is removed from the reaction system latex in the state of the latex in which the epoxidized rubber-like polymer is dispersed. Then, the reaction latex from which the organic peracid-derived substance has been removed is treated in a subsequent reduction / ring-opening step. Therefore, as in the past, it is necessary to solidify the epoxidized rubber-like polymer from the reaction system latex, isolate and purify, and re-disperse the solidified epoxidized rubber-like polymer to form a latex. And not. Therefore, the isolation process and redispersion process of the epoxidized rubber-like polymer which were performed between the epoxidation process and the reduction / ring-opening process are omitted. Therefore, the manufacturing process after the epoxidation process can be simplified. Also, without isolating and purifying the rubber component (rubber-like polymer or epoxidized rubber-like polymer) from the reaction system latex, the epoxidation step and the reduction / ring-opening step are continuously performed in the latex state. It can be carried out. For this reason, the working efficiency at the time of manufacture and the yield of the natural modified rubber which is the final product are improved.

(2) In the removal step, a part of the dispersion medium in which the substance derived from the organic peracid in the reaction latex is dissolved is replaced with a new dispersion medium. Thereby, the water-soluble impurities contained in the raw natural rubber latex can be removed together with the organic peracid-derived substance in the removal step.

(3) In the removal step, the protein present in the reaction latex is removed together with the organic peracid-derived substance. Therefore, it is not necessary to newly add a separation operation for separating the rubber component and the protein. Therefore, the increase in the work amount accompanying the addition of the deproteinization step can be minimized.

(4) The reduction / ring-opening reaction is performed under conditions of pH 7 to 8 and in the presence of an organic acid salt. Thereby, the cyclization of the epoxidized rubber-like polymer during the reduction / ring-opening reaction can be suppressed.

(5) When the molecular weight of the modified natural rubber decreases, the strength of the modified natural rubber also decreases. In that respect, according to the above embodiment, the treatment temperature during the reduction / ring-opening reaction is set in the range of 0 to 100 ° C., so that the epoxidized rubber-like polymer during the reduction / ring-opening reaction and The molecular weight reduction of the modified natural rubber obtained from the polymer can be suppressed. Therefore, the strength reduction of the modified natural rubber due to the low molecular weight of the modified natural rubber can also be suppressed.

The present embodiment may be modified as follows.
-You may abbreviate | omit the deproteinization process in the removal process. That is, apart from the removal step, for example, deproteinization treatment may be performed before the epoxidation step. Moreover, it is not necessary to perform the deproteinization process at all.

-In the said embodiment, although the neutralization process of the reaction system latex was performed in the epoxidation process, you may perform the neutralization process in a removal process or after a removal process.
-The manufacturing method of the modified natural rubber of the said embodiment can be applied to the modification method of natural rubber.

Next, the above embodiment will be described more specifically with reference to examples and comparative examples.
<Reaction system latex adjustment>
As a natural rubber latex of raw material, singleHA latex (rubber component concentration (rubber-like polymer concentration) 60.2% by mass, ammonia content 0.7% by mass, average particle size of rubber particles about 1 μm) manufactured by GOLDEN HOPE PLATATION used. And while diluting the said raw material latex using distilled water, sodium dodecyl sulfate (henceforth SDS) which is an anionic surfactant was added. Thus, a reaction latex having a rubber component concentration (rubber polymer concentration) of 10% by mass and an SDS concentration of 1% by mass was prepared.

<Epoxidation step and removal step (including deproteinization treatment)>
As a natural rubber epoxidation process, treatment with peracetic acid or performic acid is common. In this test, treatment with peracetic acid was adopted from the viewpoint of safety. However, even when the treatment with performic acid was adopted, the same result as in the above case could be obtained. Specific description will be given below.

To 100 g of the reaction system latex, 10 ml of peracetic acid was added dropwise at a rate of 1 ml / second. And reaction system latex and peracetic acid were made to react, shaking for 3 hours on 6 degreeC conditions. Thereafter, the reaction system latex was centrifuged (15 ° C., 10000 G, 30 minutes). Thereby, the reaction system latex was separated into a creamy upper layer and a liquid lower layer (separation operation). The upper creamy latex was recovered and a 1% by mass SDS aqueous solution was added to the upper layer. Thus, a reaction system latex having a rubber component concentration (epoxidized rubber-like polymer concentration) of 10% by mass was prepared again (redispersion operation).

Next, the reconstituted reaction system latex was neutralized using 28% aqueous ammonia. After neutralization, 0.1 part by mass of urea was added to 100 parts by mass of the rubber component in the reaction system latex. And it stirred at 25 degreeC for 2 hours, and modified | denatured the protein in reaction system latex. Thereafter, the separation operation and the redispersion operation were repeated a predetermined number of times. In the first separation operation and the redispersion operation after the neutralization treatment and protein denaturation treatment, the denatured protein was removed together with acetic acid and acetate, which are peracetic acid-derived substances. In total, in the second and subsequent redispersion operations, the reaction system latex was re-prepared so that the rubber component concentration (epoxidized rubber-like polymer concentration) was 30% by mass.

Here, the concentration of acetic acid and ammonium acetate present in the reaction system latex was quantified using 1H-NMR. Specifically, a known amount of an internal standard (standard substance) is added to the reaction system latex to be subjected to 1H-NMR, 1H-NMR measurement is performed, and a peak based on the internal standard in the obtained NMR spectrum; The peaks based on acetic acid and ammonium acetate were compared. And it confirmed that the total content of the acetic acid derived from peracetic acid and ammonium acetate in reaction system latex was 35 mass parts or less with respect to 100 mass parts of epoxidized rubber-like polymers.

<Reduction / ring opening process>
First, a predetermined amount of palladium chloride was dissolved in hydrochloric acid to prepare a hydrogenation catalyst. Next, the reaction system latex having a rubber component concentration (epoxidized rubber-like polymer concentration) of 30% by mass and an SDS concentration of 1% by mass obtained in the removing step was diluted with a 1% by mass SDS aqueous solution. Thus, the rubber component concentration (epoxidized rubber-like polymer concentration) in the reaction system latex was adjusted to a predetermined concentration. After dropping the hydrogenation catalyst into 100 ml of the reaction system latex, the pH of the reaction system latex was adjusted to a predetermined pH value using an aqueous sodium hydroxide solution. Thereafter, hydrogen gas was bubbled into the reaction system latex at a flow rate of 100 ml / min for 9 hours while sufficiently stirring at 70 ° C.

Subsequently, the temperature of the reaction system latex was cooled to 40 ° C., 4 ml of hydrogen peroxide was added, and the mixture was stirred for 1 hour. Further, 1 g of dimethylglyoxime was added and stirred for 48 hours. And reaction system latex was left still at 40 degreeC for 24 hours, and the hydrogenation catalyst was precipitated. Thereafter, the supernatant was separated by decantation. Methanol was added to the supernatant after separation to condense the rubber component. And the modified natural rubber was obtained by collect | recovering the deposits.

Tables 1 and 2 show the production methods of Examples and Comparative Examples, and modified natural rubbers obtained by the production methods, respectively. In each example, “the number of repetitions of separation operation and redispersion operation”, “concentration of rubber component in reaction system latex (epoxidized rubber-like polymer concentration) in reduction / ring-opening step”, and “reduction / ring-opening step” "Catalyst amount" and "pH during reduction / ring-opening process" are changed.

Further, Comparative Example 1 is an example in which the removal process is omitted. In Comparative Example 1, the reaction system latex subjected to the neutralization treatment was directly treated in the subsequent reduction / ring-opening step. Comparative Examples 2 and 3 are examples in which the pH during the reduction / ring-opening reaction was excluded from the range of 7-8. Comparative Example 4 is an example in which a reduction / ring-opening reaction was performed in the absence of an organic acid salt. In Comparative Example 4, a part of the production method was changed so that an organic acid salt was not generated during the production process. Specifically, in the epoxidation step, a separation latex and a redispersion operation were performed without performing a neutralization treatment, and a reaction system latex to be treated in the reduction / ring opening step was prepared. The pH of the reaction system latex was adjusted to 7 by repeating the separation operation and the redispersion operation and performing dilution treatment. In the reduction / ring-opening step, the reaction system latex of pH 7 is simply heated at 70 ° C. for 9 hours, and the addition of a hydrogenation catalyst, pH adjustment with an aqueous sodium hydroxide solution, and bubbling of hydrogen gas are not performed. It was.

As shown in Table 1, in each Example in which the removal step was performed after the epoxidation step, the concentration of acetic acid and its salt (ammonium acetate) was 1% by mass or less. From this result, it was confirmed that the epoxidized rubber-like polymer and acetic acid and salts thereof can be effectively separated even when the removing step of the present invention is adopted. In each Example, the modified natural rubber could be obtained without the epoxidized rubber-like polymer being cyclized in the subsequent reduction / ring-opening step.

As shown in Table 2, in Comparative Example 1 in which the reduction / ring-opening step was performed as it was following the epoxidation step, the epoxidized rubber-like polymer in the reaction system latex was condensed during the reduction / ring-opening reaction. Things became floating. As a result, the intended modified natural rubber could not be obtained. This is because the epoxidized rubber-like polymer in the reaction system latex was cyclized by a side reaction caused by a large amount of acetic acid and its salt.

Comparative Examples 2 and 3 are examples in which the pH during the reduction / ring-opening reaction was 9 and 6, respectively. Comparative Example 4 is an example in which a reduction / ring-opening reaction was performed in the absence of an organic acid salt. In these cases as well, as in Comparative Example 1, the epoxidized rubber-like polymer in the reaction system latex was cyclized, and the desired modified natural rubber could not be obtained. The results of Comparative Examples 1 to 3 show that, in order to suppress cyclization of the epoxidized rubber-like polymer during the reduction / ring-opening reaction, the pH is in the range of 7 to 8 and in the presence of the organic acid salt. This suggests that a reduction / ring-opening reaction is necessary.

<Analysis of modified natural rubber>
The hydrogenation rate of the modified natural rubber obtained by the production method of each example was calculated based on the measurement result using 1H-NMR. Further, a component having a particularly high molecular weight (hereinafter referred to as a high molecular weight component) contained in the resulting modified natural rubber was measured by the following method. Modified natural rubber finely chopped in toluene was added to a concentration of 0.1% by mass and immersed for one week. Then, the toluene solution was separated into a sol component soluble in toluene and a gel component unnecessary for toluene by centrifuging (15 ° C., 10,000 G, 30 minutes). A gel component unnecessary for toluene was recovered as a high molecular weight component, and this was dried at 50 ° C. for one week. The weight of the high molecular weight component after drying was measured, and the ratio of the high molecular weight component contained in the modified natural rubber was calculated from the ratio to the charged amount. Table 3 shows the hydrogenation rate of the modified natural rubber obtained by the production method of each example and the ratio of the high molecular weight component.

Reference Example 1 shown in Table 3 is an example in which modified natural rubber was produced using a conventional method. Regarding Reference Example 1, in particular, the removal step and the reduction / ring-opening step are different from those in each Example. In Reference Example 1, after the neutralization treatment in the epoxidation step, the epoxidized rubber-like polymer in the latex was coagulated and isolated from the dispersion medium. Then, the isolated epoxidized rubber-like polymer was dried and allowed to stand for another month to remove acetic acid and acetate. In the reduction / ring-opening step, the dried epoxidized rubber-like polymer was dissolved in p-xylene, and paratoluenesulfonyl hydrazide was added to the p-xylene solution. And reduction | restoration and ring-opening reaction were performed by recirculating | refluxing at 145 degreeC for 6 hours.

As shown in Table 3, the modified natural rubber obtained by the production method of each example was hydrogenated in the range of 30 to 90% hydrogenation rate. That is, the desired modified natural rubber was obtained. In addition, the proportion of epoxy groups in the modified natural rubber was measured using 1H-NMR. As a result, the number of epoxy groups was reduced to a level where measurement was impossible. From this, it can be inferred that almost all of the epoxy groups introduced in the epoxidation step were opened in the reduction / ring-opening step to form hydroxyl groups.

Further, the modified natural rubber obtained by the production method of each example contained a high molecular weight component in a proportion of 35% or more. On the other hand, the modified natural rubber obtained by the production method of Reference Example 1 did not contain the high molecular weight component as described above. The difference in the content of the high molecular weight component between each example and the reference example is considered to result from the difference in the treatment temperature during the reduction / ring-opening reaction.

That is, when the epoxidized rubber-like polymer and the modified natural rubber in the reaction system latex are exposed to high temperature conditions during the reduction / ring-opening reaction, the molecular chain is broken and the molecular weight is lowered. In the production method of Reference Example 1, the reduction / ring-opening reaction was performed at a relatively high temperature of 145 ° C. Such high temperature conditions promoted the reduction of the molecular weight of the epoxidized rubber-like polymer and the modified natural rubber during the reduction / ring-opening reaction, so that the finally obtained modified natural rubber has a high molecular weight component. It is thought that it did not remain. On the other hand, in the production method of each example, the reduction / ring-opening reaction was performed at a relatively low temperature of 70 ° C. As a result, the reduction of the molecular weight of the epoxidized rubber-like polymer and the modified natural rubber in the reduction / ring-opening reaction was suppressed, so that the high molecular weight component can remain in the finally obtained modified natural rubber. It is thought.

As shown in Table 3, the modified natural rubber obtained by the production method of each Example contained a high molecular weight component at a high ratio. From this, it can be said that the strength of the obtained modified natural rubber was high. Actually, the tensile strength (Tb) of the modified natural rubber obtained by the production methods of Example 5 and Reference Example 1 was measured. As a result, the measured values of the tensile strength of the modified natural rubber in Example 5 and Reference Example 1 were 3.99 MPa and 0.97 MPa, respectively. That is, according to the production method of each example, it was shown that a modified natural rubber having higher strength than the production method of the reference example can be obtained. As for the tensile strength (Tb) of the modified natural rubber, 4 phr of adipic acid hydrazide was added to the modified natural rubber obtained by the production method of Example 5 and Reference Example 1, and heated and pressed at 180 ° C. and 11 Mpa for 20 minutes. The sample was taken as a sample and measured according to ISO 37 (JIS K6251).

Claims

In a latex in which a plant-derived rubbery polymer having a plurality of unsaturated double bonds in the main chain is dispersed in water as a dispersion medium, the rubbery polymer is reacted with an organic peracid, An epoxidation step of obtaining an epoxidized rubber-like polymer by epoxidizing a part of the unsaturated double bond of the rubber-like polymer;
In the epoxidation step, the organic peracid-derived substance generated from the organic peracid is removed from the latex, and the content of the organic peracid-derived substance in the latex is 100 parts by mass of the epoxidized rubber-like polymer. Removing step to reduce to 35 parts by mass or less,
Reducing part or all of unsaturated double bonds remaining in the epoxidized rubber-like polymer in the latex under the conditions of pH 7 to 8 and in the presence of an organic acid salt, and the epoxidized rubber And a reduction / ring-opening step for opening a part or all of the epoxy groups of the polymer.
The method for producing a modified natural rubber according to claim 1, wherein in the removing step, a part of the dispersion medium in which the substance derived from the organic peracid in the latex is dissolved is replaced with a new dispersion medium.
In the removing step, the latex after the epoxidation step is subjected to a centrifugal separation treatment, whereby the latex is mainly composed of an upper layer in which the epoxidized rubber-like polymer is dispersed and a substance mainly derived from the organic peracid. The method for producing a modified natural rubber according to claim 1 or 2, wherein the method further comprises separating into a dissolved lower layer, further removing the lower layer, and adding a new dispersion medium to the upper layer. .
The method for producing a modified natural rubber according to any one of claims 1 to 3, wherein, in the removing step, proteins in the latex are removed together with the substance derived from the organic peracid.
In the reduction / ring-opening step, a hydrogen atom is added to the unsaturated double bond remaining in the epoxidized rubber-like polymer, and the epoxy group of the epoxidized rubber-like polymer is opened to form a hydroxyl group. The method for producing a modified natural rubber according to any one of claims 1 to 3, wherein: