JP2010248388A - Modified natural rubber and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modified natural rubber which has excellent weather resistance and is modified to retain rubber characteristics, and to provide manufacturing method thereof. <P>SOLUTION: An epoxy group is introduced into a part of an unsaturated double bond of a main chain of a rubber polymer which consists of at least one of natural rubber or deproteinized natural rubber to form an epoxidated rubber polymer. Then, while carrying out hydrogenation of the unsaturated double bond which remains in the main chain of the epoxidated rubber polymer, a part of or whole epoxy group is made open to form a hydroxy group, thereby forming a hydrogenated rubber polymer in which the unsaturated double bond of the main chain is decreased to be less than 20%. After that, crosslinking is formed on the basis of the epoxy group and hydroxy group as a starting point to obtain the modified natural rubber. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a modified natural rubber which is excellent in weather resistance and modified so as to retain rubber properties, and a method for producing the same.

  Conventionally, rubber products have been put to practical use in various fields. The raw materials for these rubber products are classified into plant-derived natural rubber and petroleum-derived synthetic rubber. Of these, various types of synthetic rubbers having excellent properties such as oil resistance, weather resistance, gas permeability, and cold resistance 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, and the rubber is used in various applications such as automobile parts and insulators.

  On the other hand, in recent years, interest in plant-derived materials has increased due to concerns over the depletion of petroleum resources and global warming. This plant-derived material can suppress the consumption of limited petroleum resources and can also contribute to the suppression of global warming because the plant absorbs carbon dioxide that causes global warming during the growth process. It is expected.

  Here, natural rubber collected as a polymer from a rubber tree has excellent properties such as processability and strength, and is therefore used in various applications. However, since the main chain contains an unsaturated double bond, the weather resistance and ozone resistance are inferior, and there is a problem that it is difficult to apply to parts exposed to sunlight with a short product life. Therefore, development of a material that can improve the properties of such natural rubber and can be used as a substitute for the synthetic rubber is desired. To date, as a means for improving the properties of such natural rubber, a method of reducing unsaturated double bonds in the main chain by hydrogenation has been proposed (see, for example, Patent Document 1).

JP-A-61-28507

  By the way, when hydrogenation is performed on natural rubber, although unsaturated double bonds are reduced and weather resistance is improved, crystallization is advanced and rubber properties such as rubber elasticity may be lost. In addition, there is a disadvantage that it is difficult to form a crosslink due to a decrease in unsaturated double bonds.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a modified natural rubber modified so as to have excellent weather resistance and to retain rubber properties, and a method for producing the same.

  In order to achieve the above object, the invention described in claim 1 is a modified natural rubber, wherein the main chain of the rubbery polymer comprising at least one of natural rubber and deproteinized natural rubber is unsaturated. Crosslinking starting from a hydroxyl group in which the epoxy group introduced into the unsaturated double bond of the main chain of the rubber-like polymer has been opened, and the double bond has been reduced to less than 20% by epoxidation and hydrogenation The gist is to have a structure.

  According to the above configuration, since the unsaturated double bond in the main chain of the rubber-like polymer is reduced to less than 20%, ultraviolet rays, oxygen in the air, ozone, and the like act on the unsaturated double bond. It is possible to effectively suppress deterioration due to this, and to improve weather resistance and ozone resistance.

  Here, in order to improve the weather resistance in this way, it is desirable to reduce the unsaturated double bond of the rubber-like polymer to nearly 0%. However, if the unsaturated double bond is almost completely eliminated only by hydrogenation, crystallization proceeds and rubber properties such as rubber elasticity are lost, so that such a polymer may not be applicable to rubber products. .

  In this regard, the inventors of the present invention have made crystallization by performing hydrogenation by introducing an epoxy group or a hydroxyl group obtained by opening the epoxy group into an unsaturated double bond of the main chain of the rubber-like polymer. It has been found that the rubber properties can be maintained by this.

  Therefore, the modified natural rubber has a crosslinked structure starting from a hydroxyl group in which an epoxy group introduced into an unsaturated double bond of the main chain of the rubber-like polymer is opened. As a result, it is possible to obtain a modified natural rubber which is excellent in weather resistance and modified so as to retain rubber characteristics, and as a raw material for parts requiring rubber characteristics, weather resistance, and ozone resistance, the above modification Natural rubber can be used.

  The invention according to claim 2 is a method for producing a modified natural rubber, wherein a part of the unsaturated double bond in the main chain of the rubber-like polymer comprising at least one of natural rubber and deproteinized natural rubber is used. An epoxidation step of introducing an epoxy group to form an epoxidized rubber-like polymer, hydrogenating unsaturated double bonds remaining in the main chain of the epoxidized rubber-like polymer, and a part of the epoxy group or The hydrogenation step of forming a hydrogenated rubber-like polymer in which the unsaturated double bonds of the main chain are reduced to less than 20% by opening the whole to form hydroxyl groups, and the epoxy group and the hydroxyl group And a crosslinking step of forming a modified natural rubber by forming a crosslinking starting from the starting point.

  According to the above production method, a modified natural rubber in which the unsaturated double bond of the main chain is reduced to less than 20% is obtained, so that ultraviolet rays, oxygen in the air, ozone, etc. Deterioration due to action can be effectively suppressed, and a modified natural rubber excellent in weather resistance and ozone resistance can be produced.

  In the above production method, an epoxy group is previously introduced into a part of the unsaturated double bond of the main chain of the rubber-like polymer, and then the epoxy group is opened by hydrogenation to form a hydroxyl group. Yes. Therefore, even when the unsaturated double bond of the main chain of the rubber-like polymer is reduced by hydrogenation to improve weather resistance, the rubber-like polymer after hydrogenation (hydrogenated rubber-like polymer) Crystallization can be suppressed. In addition, since an epoxy group and a hydroxyl group are introduced into the main chain of the rubber-like polymer, it is possible to form a bridge starting from the epoxy group and the hydroxyl group in the subsequent crosslinking step. Therefore, according to the above production method, it becomes possible to produce a modified natural rubber which is excellent in weather resistance and modified so as to retain rubber characteristics. It can also be used as a raw material for parts that require properties, weather resistance, and ozone resistance.

  In the case of introducing an epoxy group after hydrogenation to the unsaturated double bond of the main chain of the rubber-like polymer, all of the unsaturated double bonds in the relatively long part of the main chain are hydrogenated. , The epoxy group may not be introduced into the part. For this reason, the hydrogenated rubber-like polymer is partially crystallized, and there is a possibility that the rubber characteristics cannot be sufficiently maintained.

  In this respect, according to the above production method, since hydrogenation is performed after the introduction of the epoxy group, the epoxy group (hydroxyl group) is introduced relatively evenly, and the crystallization of the hydrogenated rubber-like polymer is performed. It can be effectively suppressed.

  Here, in the hydrogenated rubber-like polymer, in order to sufficiently secure the starting point necessary for the subsequent cross-linking formation and sufficiently obtain the effect of suppressing crystallization, the epoxidation rate is 1% in the epoxidation step. It is desirable to form an epoxidized rubber-like polymer as described above. On the other hand, when the epoxidation rate of the epoxidized rubber-like polymer is higher than 25%, the inventors have found that the yield of the hydrogenated rubber-like polymer is reduced in the subsequent hydrogenation step. ing. In addition, as this cause, it is mentioned that a rubber-like polymer becomes low molecular weight in the same process.

  Therefore, as described in claim 3, by setting the epoxidation rate of the epoxidized rubber-like polymer to 1 to 25%, a modified natural rubber excellent in rubber characteristics, weather resistance, and ozone resistance can be obtained. It becomes possible to manufacture efficiently.

  Further, as described in claim 4, in the crosslinking step, crosslinking can be formed by using at least one crosslinking agent selected from dihydrazide, dicarboxylic acid, diamine, and diisocyanate.

  According to the present invention, the unsaturated double bond in the main chain of the rubber-like polymer is reduced to less than 20%, so that ultraviolet rays, oxygen in the air, ozone, etc. act on the unsaturated double bond. It is possible to effectively suppress deterioration due to this, and to improve weather resistance and ozone resistance. In addition, an epoxy group is previously introduced into a part of the unsaturated double bond of the main chain of the rubber-like polymer to form an epoxidized rubber-like polymer, and then the epoxy group is opened by hydrogenation to form a hydroxyl group. Since it is introduced, it is possible to suppress crystallization of the hydrogenated rubber-like polymer even when the unsaturated double bond of the main chain is reduced by hydrogenation. As a result, it is possible to produce a modified natural rubber which is excellent in weather resistance and ozone resistance and modified so as to maintain rubber characteristics.

Hereinafter, the modified natural rubber and the method for producing the same according to the present invention will be described in more detail.
(Raw material latex)
As the natural rubber latex used as a raw material for obtaining the modified natural rubber in the present invention, a latex obtained from a natural rubber tree and a product obtained by treating the latex can be used. For example, fresh field latex or Commercially available ammonia-treated latex or the like can be used.

In the present invention, a rubbery polymer in which the above natural rubber latex or the deproteinized natural rubber shown below is mixed in an arbitrary ratio can be used.
(Deproteinization of natural rubber)
The method for deproteinizing the natural rubber latex is not particularly limited, but a method of degrading the protein by adding a proteolytic enzyme or the like to the latex (JP-A-6-56902), repeatedly washing with a surfactant such as soap And a method using urea (Japanese Patent Application Laid-Open No. 2004-99696) can be used. Among these, for example, the method using urea previously proposed by the present inventors is a urea-based compound represented by the following general formula (1) in a natural rubber latex stabilized by adding an appropriate surfactant. A method of obtaining a deproteinized natural rubber latex by adding a protein denaturant selected from the group consisting of (urea derivative, urea double salt) and NaClO, denatures and removes the protein in the latex, and then washing with a surfactant It is.
RNHCONH ₂ (1)
(R in the formula represents H or an alkyl group having 1 to 5 carbon atoms)
As the surfactant to be used here, sodium dodecyl sulfate, which is an anionic surfactant, is preferably used, but is not limited thereto and can be appropriately changed. Specifically, anionic surfactants such as carboxylic acid, sulfonic acid, sulfate ester and phosphate ester, nonionic surfactants such as polyethylene glycol and polyhydric alcohols, quaternary Various surfactants such as cationic surfactants such as ammonium salts, amphoteric surfactants such as amino acids and betaines, and bio-based surfactants derived from plants can be used.

  Examples of the urea derivative represented by the general formula (1) include urea, methylurea, ethylurea, n-propylurea, i-propylurea, n-butylurea, i-butylurea, n-pentylurea, and the like. However, preferred urea derivatives include urea, methylurea, and ethylurea.

The deproteinization of the natural rubber latex is preferably performed so that the nitrogen content of the natural rubber particles is 0.1% by weight or less, preferably 0.05% by weight or less.
(Epoxidation)
The introduction (epoxidation) of an epoxy group into the unsaturated double bond (double bond) of the main chain of the rubber-like polymer is caused by reacting the rubber-like polymer with an organic peracid, This is done by substituting an unsaturated double bond of the main chain with an epoxy group. Specifically, an organic peracid is added to a latex of a rubber-like polymer stabilized with a surfactant, and the reaction is allowed to proceed for a predetermined time. Such epoxidation can be performed in a latex state, or by dissolving solid rubber or rubber in a suitable organic solvent. As for the surfactant used here, various surfactants can be used as in the case of deproteinization of the natural rubber.

  Examples of the organic peracid used for epoxidation 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 natural rubber latex, but a component capable of forming an organic peracid may be added to generate the organic peracid in the 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.

  The epoxidation rate of the epoxidized rubbery polymer obtained by epoxidation is desirably 1 to 25%. In addition, this epoxidation rate shows the ratio substituted by the epoxy group among the double bonds in the rubber-like polymer before epoxidation.

(Hydrogenation)
Hydrogenation of the epoxidized rubber-like polymer obtained by the above epoxidation involves dissolving the epoxidized rubber-like polymer in an inert organic solvent, and hydrogen in an inert gas or hydrogen atmosphere such as nitrogen or argon. It is carried out by adding an addition catalyst and supplying high-pressure hydrogen or adding a reducing agent. Inert means that it does not react with any participant in the hydrogenation reaction. Examples of the inert organic solvent include aliphatic hydrocarbons such as pentane, hexane, heptane, and octane, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, and cyclohexane, benzene, toluene, xylene, and ethylbenzene. Various types such as aromatic hydrocarbons can be used.

  As the hydrogenation catalyst, a homogeneous catalyst and a heterogeneous catalyst generally used for hydrogenation of carbon-carbon double bonds can be used. Specifically, a catalyst in which a metal such as nickel, ruthenium, platinum, palladium, or rhodium is supported on a simple substance such as carbon, silica, or alumina can be used. In the presence of such a catalyst, hydrogenation is performed by bringing a high-pressure hydrogen gas and a rubber-like polymer into contact with each other at a predetermined temperature for a predetermined time.

  As the reducing agent, a reducing agent such as p-toluenesulfonyl hydrazide can be used. Specifically, a reducing agent having a molar amount of about 4 times the molar amount of the monomer unit of the rubber-like polymer is added to the reaction system containing the rubber-like polymer and sufficiently stirred. Hydrogenation is carried out at reflux for 2-12 hours at temperature. In addition, you may implement such reaction by the continuous method other than the batch type mentioned above.

  By such hydrogenation, the unsaturated double bond (double bond) remaining in the main chain of the epoxidized rubber-like polymer is hydrogenated and the epoxy group in the epoxidized rubber-like polymer is opened. A hydrogenated rubber-like polymer having a hydroxyl group formed (hereinafter referred to as “hydrogenated product”) is obtained.

  In addition, it is preferable that the hydrogenation rate in the said hydrogenated material is 80% or more. This hydrogenation rate indicates the ratio of double bonds that have decreased due to the epoxidation and hydrogenation reaction among the double bonds in the rubber-like polymer before epoxidation. It can be calculated by measuring the number of remaining double bonds. That is, the ratio of double bonds remaining in the hydrogenated product obtained by hydrogenation is preferably reduced to less than 20%.

(Crosslinking)
The hydrogenated product is crosslinked by mixing the hydrogenated product and a crosslinking agent and then performing hot pressing. The crosslinking agent used here may be any one that reacts with a hydroxyl group, such as dihydrazides such as adipic acid dihydrazide and propionic acid dihydrazide, alkylhydrazines such as isopropylhydrazine sulfate, 4-amino-1,2 and 1, Use widely such as triazoles such as 1,4-triazole, diisocyanate compounds such as diphenylmethane diisocyanate, imide compounds such as bismaleimide, dicarboxylic acids such as phthalic anhydride, and diamines such as hexamethylenediamine carbamate. Can do. These crosslinking agents can be used alone or in combination. Of these, adipic acid dihydrazide is preferably used.

  Specifically, about 4 parts by weight of a crosslinking agent is added to 100 parts by weight of rubber of the hydrogenated product, and these hydrogenated product and the crosslinking agent are mixed. In addition, a normal kneading apparatus, for example, a rubber mill, a Banbury mixer, a pressure kneader, a twin screw extruder, or the like can be used for this mixing. Thereafter, using a press molding machine, the formation of cross-linking is completed by holding for a predetermined time at a predetermined temperature of about 180 ° C. to obtain a molded product (modified natural rubber).

  Next, the modified natural rubber and the method for producing the same according to the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these and may be changed as appropriate. it can.

<Evaluation method>
In this example, the following various evaluation methods were applied.
(Calculation of epoxidation rate)
The epoxidation rate of the epoxidized rubbery polymer was calculated by the following formula based on the measurement result using ¹ H-NMR.

(Calculation of hydrogenation rate)
The hydrogenation rate (hydrogenation rate) of the hydrogenated product was calculated according to the following formula based on the measurement results using ¹ H-NMR.

(Calculation of hydroxyl group ratio)
About the ratio of the hydroxyl group in a hydrogenated substance, it computed by following Formula based on the measurement result using < ¹ > H-NMR.

(Yield calculation)
The yield of the hydrogenated product was calculated by the following formula.

(Crosslinking)
Toluene was added so that the concentration of the sample for evaluation was 0.1% by weight, and the solution was allowed to stand at room temperature for 24 hours. Thereafter, the undissolved components obtained by filtering the solution were dried and weighed, and the gel fraction was calculated by the following formula. The gel fraction after hot pressing calculated in this way was higher than “0” and increased as compared to before hot pressing, and was judged as “crosslinkable”.

(Crosslink density)
After toluene was added so that the concentration of the sample for evaluation was 1% by weight, the solution was allowed to stand at room temperature for 72 hours to recover undissolved components. Then, after removing toluene adhering to the surface of the sample, the sample was weighed, and the crosslinking density was calculated by the following Flory-Rhener equation.

(Weatherability)
In accordance with JIS K6259, the elapsed time until cracking occurred in the sample for evaluation was measured under the conditions of a temperature of 40 ° C., an ozone concentration of 50 pphm, and a 5% elongation.

(crystalline)
In DSC measurement (−80 ° C. to 150 ° C., 10 ° C./min) using a differential scanning calorimeter, a sample having an endothermic peak derived from crystallization in the vicinity of 128 ° C. was judged as “with crystallinity”.

<Preparation of sample for evaluation>
Example 1
(Example 1: Deproteinization of natural rubber)
As the natural rubber latex, singleHA latex (rubber content concentration 60.2% by weight, ammonia content 0.7% by weight, average particle size of rubber particles of about 1 μm) manufactured by GOLDEN HOPE PLANTATION was used. After diluting the latex so that the rubber content is 30% by weight, 1.0 part by weight of sodium dodecyl sulfate as an anionic surfactant is added to 100 parts by weight of the latex solution to stabilize the latex. Made it. Next, 0.1 part by weight of urea was added to 100 parts by weight of the rubber content of the latex, followed by stirring at 25 ° C. for 2 hours for protein separation treatment. Thereafter, centrifugation was performed at 9000 rpm for 30 minutes at 15 ° C., and the upper cream was collected. The recovered cream was dispersed in a 1% by weight aqueous solution of sodium dodecyl sulfate so that the rubber content was 30% by weight, and the second centrifugation treatment was performed in the same manner as described above. Further, after the third centrifugation, the recovered cream was dispersed in a 1% by weight aqueous solution of sodium dodecyl sulfate to obtain a deproteinized natural rubber latex. In this example, only this deproteinized natural rubber latex was used as the rubbery polymer. The nitrogen content of the deproteinized natural rubber latex was 0.02% by weight.

(Example 1: Epoxidation) Epoxidation Step 4 ml of peracetic acid was added at a rate of 1 ml / sec to 100 g of rubber-like polymer latex added so that the rubber concentration was 10% by weight and sodium dodecyl sulfate was 1% by weight. It was dripped. Then, after making it react for 6 hours shaking on 6 degreeC conditions, the reaction solution was neutralized with 25% ammonia water. The sample was then condensed with methanol and the resulting precipitate was collected. Further, the precipitate was dissolved in toluene and then condensed again with methanol. By repeating these operations three times, an epoxidized rubber-like polymer was obtained as a precipitate. About the epoxidized rubber-like polymer obtained in this way, the epoxidation rate was computed according to the evaluation method mentioned above.

(Example 1: Hydrogenation) Hydrogenation step The above epoxidized rubber-like polymer was dissolved in p-xylene so that the rubber concentration was 1% by weight under nitrogen substitution, and then p-toluenesulfonyl hydrazide was added. Added and stirred well. The addition amount of this p-toluenesulfonyl hydrazide was made into 4 times the molar amount of the monomer unit of an epoxidized rubber-like polymer. The molar amount of the monomer unit is calculated by calculating the average molecular weight of the monomer unit in consideration of the epoxidation rate of the epoxidized rubber-like polymer, and the total weight of the epoxidized rubber-like polymer is calculated by the calculated average molecular weight. Determined by dividing. Subsequently, after making it react for 2 hours, making it recirculate | reflux at 135 degreeC, reaction was stopped by cooling at room temperature. Thereafter, the sample was condensed with methanol, and the resulting precipitate was collected. Furthermore, after this precipitate was dissolved in toluene, it was condensed again with methanol. By repeating these operations three times, a hydrogenated product was obtained as a precipitate.

The hydrogenation rate, hydroxyl ratio, and yield of the hydrogenated product thus obtained were calculated according to the evaluation methods described above. In addition, although the ratio of the epoxy group in this hydrogenated product was also measured using ¹ H-NMR, it was reduced to a level where measurement was impossible. Thereby, it was guessed that the epoxy group introduced by the previous process (epoxidation process) was ring-opened by hydrogenation to generate a hydroxyl group.

(Example 1: Crosslinking) Crosslinking Step After dissolving the hydrogenated product in toluene, 4 parts by weight of adipic acid dihydrazide (manufactured by Otsuka Chemical Co., Ltd.) as a crosslinking agent with respect to 100 parts by weight of the rubber content of the hydrogenated product. Was added and mixed. Thereafter, the sample was condensed with methanol, and the resulting precipitate was collected. The gel fraction of the sample thus obtained was calculated according to the evaluation method described above, and this was used as the gel fraction “before hot pressing”.

  Next, the sample is set on a press molding machine and held at 180 ° C. and 10 MPa for 20 minutes to form a cross-link starting from a hydroxyl group and press molding to form a molded product (modified) Natural rubber). A part of the modified natural rubber thus obtained was collected as an evaluation sample. The gel fraction of this evaluation sample was calculated according to the evaluation method described above, and this was used as the gel fraction “after hot pressing”. Further, the weather resistance (ozone resistance) of this sample for evaluation was evaluated according to the evaluation method described above.

(Examples 2 to 8)
In Example 1, an evaluation sample was prepared in the same manner as in Example 1, except that the amount of peracetic acid added in epoxidation and the reaction time in hydrogenation were changed to the conditions shown in Table 1, respectively.

  In addition, about the sample for evaluation concerning Example 2, the crosslinking density was computed according to the evaluation method (crosslinking density) mentioned above. Moreover, about the sample for evaluation concerning Example 4, crystallinity was also evaluated according to the evaluation method (crystallinity) mentioned above.

Example 9
Evaluation was made by using a “27-50 (trade name)” manufactured by Rubber Research Institute of Malaysia as an epoxidized natural rubber having an epoxidation rate of 25%, and performing hydrogenation and crosslinking reaction under the conditions described in Table 1. A sample was used.

(Comparative Example 1)
Using a deproteinized natural rubber prepared in the same manner as in Example 1, a sample subjected to a crosslinking reaction in the same manner as in Example 1 was used as an evaluation sample for judging the crosslinking property. Moreover, the sample for evaluation for evaluating a weather resistance (ozone resistance) what carried out the crosslinking reaction using peroxide (Nippon Yushi Co., Ltd. perbutyl P) using the said deproteinized natural rubber, did.

(Comparative Example 2)
A deproteinized natural rubber prepared in the same manner as in Example 1 was epoxidized under the conditions shown in Table 1, and then subjected to a crosslinking reaction in the same manner as in Example 1 as an evaluation sample.

(Comparative Example 3)
In Example 1, epoxidation and hydrogenation were respectively performed under the conditions shown in Table 1, and then a crosslinking reaction was performed in the same manner as in Example 1 as an evaluation sample.

(Comparative Example 4)
Epoxidation and hydrogenation were performed under the conditions shown in Table 1 using “27-50 (trade name)” manufactured by Rubber Research Institute of Malaysia as an epoxidized natural rubber having an epoxidation rate of 50%.

(Comparative Examples 5 and 6)
Using a deproteinized natural rubber prepared in the same manner as in Example 1, each rubber-like polymer obtained by hydrogenation under the conditions shown in Table 1 was used as an evaluation sample for judging crystallinity. In addition, about the crystallinity of these comparative examples 5 and 6, as shown in Table 2, the presence or absence of crystallinity was judged by performing DSC measurement on the conditions of -100 degreeC-150 degreeC (10 degreeC / min). .

(Examples 1-2 to 9-2)
In Example 1-2, the hydrogenated product prepared in the same manner as in Example 1 was used, and the crosslinking reaction was performed using the three crosslinking agents described in Table 3, respectively. A sample for evaluation was used. Similarly, in Examples 2-2 to 9-2, the hydrogenated products prepared in the same manner as in Examples 2 to 9 were used, respectively, and the crosslinking reaction was performed using the three kinds of crosslinking agents described in Table 3. This was used as an evaluation sample for judging the crosslinkability.

(Comparative Example 1-2)
In Comparative Example 1-2, the deproteinized natural rubber prepared in the same manner as in Comparative Example 1 was used, and the crosslinkability of each of the three cross-linking agents described in Table 3 was used to determine the crosslinkability. It was set as the sample for evaluation for.

(Comparative Example 2-2)
Using the epoxidized rubber-like polymer produced in the same manner as in Comparative Example 2 and using the three cross-linking agents listed in Table 3, each of which undergoes a cross-linking reaction, an evaluation sample for judging cross-linkability, did.

(Comparative Example 3-2)
Samples for evaluation for determining the crosslinkability were prepared by performing a crosslinking reaction using the three kinds of crosslinking agents shown in Table 3 using the hydrogenated product prepared in the same manner as in Comparative Example 3.

<Evaluation result 1>
The results of evaluating Examples 1 to 9 and Comparative Examples 1 to 6 are shown in Tables 1 and 2.
In addition, "-" of Table 1 and Table 2 represents not performing each reaction and evaluation.

上記表１に示す結果により、以下のことが分かる。

The results shown in Table 1 above show the following.

  As shown in “Yield” in Table 1, the yield of hydrogenated product decreased as the epoxidation rate increased. That is, the yield of the hydrogenated product in Example 9 in which the epoxidation rate was 25% was 4%, and the yield of the hydrogenated product in Comparative Example 4 in which the epoxidation rate was 50% was 0%. Thereby, when forming an epoxidized rubber-like polymer, it turned out that it is desirable to epoxidize a rubber-like polymer so that the epoxidation rate may be 25% or less.

As shown in “Crosslinkability” in Table 1, Examples 1 to 9 in which Comparative Example 1 was subjected to epoxidation and hydrogenation reaction, whereas the gel fraction after hot pressing was 0% And about the comparative example 3, the gel fraction after a hot press rose. Thereby, it was shown that the bridge | crosslinking was formed starting from the hydroxyl group in a hydrogenated material. In addition, as shown in Table 1, since the crosslinking density after the hot press in Example 2 was calculated as 1.3 × 10 ⁻⁴ (mol / cm ³ ), it can be confirmed that the crosslinking was formed. .

  Moreover, also about the comparative example 2 which performed only epoxidation, the gel fraction after a hot press was rising. Thereby, it was shown that the bridge | crosslinking was formed on the basis of the epoxy group contained in an epoxidized rubber-like polymer.

上記表２に示す結果により、以下のことが分かる。

From the results shown in Table 2, the following can be understood.

  As shown in “Weather resistance” in Table 2, for Comparative Examples 1 to 3 in which the hydrogenation rate was less than 80%, the time until cracking occurred in each evaluation sample was 2 to 8 hours. On the other hand, in Examples 1 to 9 in which the hydrogenation rate was 80% or more, the time until cracking occurred in each evaluation sample was 180 hours. This confirmed that the weather resistance (ozone resistance) of these examples was improved.

  As shown in “Crystallinity” in Table 2, for Comparative Example 6 (hydrogenation rate 97%) in which only hydrogenation was performed, a result of “crystalline” was obtained, whereas epoxidation was performed. About Example 4 which performed hydrogenation after having performed, although the hydrogenation rate was as high as 98.7%, the result of amorphous (crystallinity: nothing) was obtained. Thus, it was confirmed that the rubber properties of Example 4 were maintained while the hydrogenation rate was high and the crystallization did not proceed. In addition, about the comparative example 5 whose hydrogenation rate is 93%, the result that it was amorphous (crystallinity: nothing) was obtained, and the weather resistance from the result of other experiments by the inventors, etc. It has been found that when the hydrogenation rate is increased to about 95% or more in order to improve, crystallization proceeds and rubber properties such as rubber elasticity are lost.

<Evaluation result 2>
Table 3 shows the results of evaluating Examples 1-2 to 9-2 and Comparative Examples 1-2 to 3-2.

上記表３に示すように、架橋剤として無水フタル酸、ジアミン（ヘキサメチレンジアミンカーバメート）、ジイソシアネートのいずれを使用した場合であっても、エポキシ化及び水素添加を行った実施例１−２〜９−２及び比較例３−２について、熱プレス後におけるゲル分率が熱プレス前に比較して上昇した。これにより、水素添加物中の水酸基を起点として架橋が形成されたことが示された。なお、同表３に示す熱プレス前のゲル分率は、架橋剤としてアジピン酸ジヒドラジドを使用した場合（表１）における熱プレス前のゲル分率（０％）と比較して高く算出された。これは、無水フタル酸、ジアミン又はジイソシアネートを架橋剤として使用した場合には、水素添加物と架橋剤とを混合した時点において、ある程度架橋が形成されたことが原因であると推察される。

As shown in Table 3 above, Examples 1-2 to 9 in which epoxidation and hydrogenation were performed even when any of phthalic anhydride, diamine (hexamethylenediamine carbamate), and diisocyanate were used as a crosslinking agent. -2 and Comparative Example 3-2, the gel fraction after hot pressing increased as compared to before hot pressing. Thereby, it was shown that the bridge | crosslinking was formed starting from the hydroxyl group in a hydrogenated material. The gel fraction before hot pressing shown in Table 3 was calculated higher than the gel fraction before hot pressing (0%) when adipic acid dihydrazide was used as a crosslinking agent (Table 1). . When phthalic anhydride, diamine, or diisocyanate is used as a crosslinking agent, this is presumed to be due to the fact that some crosslinking was formed when the hydrogenated product and the crosslinking agent were mixed.

  Moreover, also about the comparative example 2-2 which performed only epoxidation, the gel fraction after a hot press was rising. This indicated that cross-linking was formed based on the epoxy group contained in the epoxidized rubber-like polymer.

According to the embodiment described in detail above, the following effects can be obtained.
(1) Since the double bond of the main chain of the rubber-like polymer (modified natural rubber) in this example is reduced to less than 20%, ultraviolet rays, oxygen in the air, ozone, etc. become double bonds. Accordingly, it is possible to effectively suppress deterioration due to the action, and to improve the weather resistance and ozone resistance of the modified natural rubber.

  (2) In this example, after introducing an epoxy group into a part of the double bond of the main chain of the rubber-like polymer in the epoxidation step, the epoxy group is opened in the hydrogenation step to form a hydroxyl group. I have to. Therefore, even if the double bond of the main chain of the rubber-like polymer is reduced by hydrogenation in order to improve the weather resistance, the crystallization of the formed hydrogenated rubber-like polymer is suppressed. Can do.

  (3) In addition, since hydrogenated rubber-like polymer is formed by hydrogenation after introducing an epoxy group, compared with rubber-like polymer formed by epoxidation after hydrogenation. The epoxy group (hydroxyl group) is uniformly introduced into the main chain of the hydrogenated rubber-like polymer. Therefore, crystallization of the hydrogenated rubber-like polymer, and thus crystallization of the modified natural rubber can be effectively suppressed.

  (4) Furthermore, since a hydroxyl group is introduced into the main chain of the hydrogenated rubber-like polymer formed in the hydrogenation step, in the subsequent crosslinking step, crosslinking starting from the hydroxyl group can be formed. Accordingly, it is possible to produce a modified natural rubber which is excellent in weather resistance and modified so as to maintain rubber characteristics.

  (5) Since the epoxidation rate of the epoxidized rubber-like polymer obtained in the epoxidation step is 1 to 25%, a modified natural rubber excellent in rubber characteristics and weather resistance can be produced efficiently.

  (6) The modified natural rubber obtained in this example can be used as a raw material for parts that require rubber characteristics and weather resistance.

Claims (4)

The unsaturated double bond in the main chain of the rubber-like polymer comprising at least one of natural rubber and deproteinized natural rubber has been reduced to less than 20% by epoxidation and hydrogenation,
A modified natural rubber characterized by having a crosslinked structure starting from a hydroxyl group in which an epoxy group introduced into an unsaturated double bond of the main chain of the rubber-like polymer is opened. An epoxidation step of forming an epoxidized rubber-like polymer by introducing an epoxy group into a part of the unsaturated double bond of the main chain of the rubber-like polymer comprising at least one of natural rubber and deproteinized natural rubber;
The unsaturated double bonds remaining in the main chain of the epoxidized rubber-like polymer are hydrogenated and part or all of the epoxy groups are opened to form hydroxyl groups, thereby forming unsaturated double bonds in the main chain. A hydrogenation step to form a hydrogenated rubbery polymer with bonds reduced to less than 20%;
And a crosslinking step of obtaining a modified natural rubber by forming a bridge starting from the epoxy group and the hydroxyl group. The method for producing a modified natural rubber according to claim 2,
The method for producing a modified natural rubber, wherein the epoxidized rubber-like polymer formed in the epoxidation step has an epoxidation rate of 1 to 25%. In the method for producing a modified natural rubber according to claim 2 or 3,
The method for producing a modified natural rubber, wherein the crosslinking step forms a crosslinking by using at least one crosslinking agent selected from dihydrazide, dicarboxylic acid, diamine, and diisocyanate.