JPH10139926A - Discoloration inhibitor for deproteinized natural rubber latex, deproteinized natural rubber latex, and method for storing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a discoloration inhibitor which can prevent the pinking of a deproteinized natural rubber latex occurring when the latex in the state containing a phenolic antioxidant is stored for a long term by using a specified compound such as a water-soluble dithiocarbamic acid derivative salt or a pyrosulfite. SOLUTION: This inhibitor comprises at least one member selected from among salts of water-soluble dithiocarbamic acid derivatives (e.g. sodium diethyldithiocarbamate), pyrosulfites (e.g. sodium pyrosulfite), cycloalkanethiols (e.g. cyclohexanethiol) and halogenated thiophenols (e.g. 4-bromothiophenol). A deproteinized natural rubber latex containing a phenolic antioxidant can be prevented from pinking by adding 0.005-15 pts.wt., desirably 0.01-10 pts.wt., more desirably 0.5-10 pts.wt., per 100 pts.wt. rubber component, above inhibitor thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an agent for preventing discoloration of a deproteinized natural rubber latex, a deproteinized natural rubber latex using the same, and a method for storing the deproteinized natural rubber latex.

[0002]

2. Description of the Related Art Natural rubber has been widely used from industrial rubber products such as automobile tires, belts and adhesives to household rubber products such as gloves. Such natural rubber is obtained as a latex containing non-rubber components such as proteins, lipids and ash, in addition to the rubber component. For this reason, a natural rubber product obtained by coagulating a rubber component from the latex, masticating the thus obtained raw rubber (crepe rubber or smoked sheet rubber), compounding a compounding agent, molding and vulcanizing is used. The non-rubber component is included as an impurity.

In recent years, it has been reported that the use of natural rubber products causes allergic symptoms, and it is presumed that the cause is caused by proteins in natural rubber. Thus, a deproteinized natural rubber latex from which proteins have been removed as much as possible has been developed (JP-A-6-56902). On the other hand, non-rubber components such as proteins, lipids, and ash have an effect of preventing rubber aging caused by heat, oxidation, ozone, and the like in natural rubber latex. For this reason, the deproteinized natural rubber latex has poor aging resistance, and it is necessary to add an antioxidant.

[0004] As antiaging agents for natural rubber latex, various types such as phenols, amines, organic phosphites and imidazoles are known. Among the agents, a phenolic antioxidant was found to be excellent in emulsification or dispersion stability in latex, and was most preferably used.

[0005]

However, the addition of such a phenolic anti-aging agent causes a new problem. In other words, natural rubber products composed of deproteinized natural rubber latex have the advantage of being excellent in colorless transparency, but when added with a phenolic antioxidant and stored for a long time, the entire white latex turns pink. There is a problem that a phenomenon (so-called pinking) occurs.

[0006] Since this discoloration does not occur in the latex of isoprene rubber (IR) having almost the same molecular structure as natural rubber, it is considered that this discoloration is different from the discoloration accompanying the normal progress of aging. It is presumed that one of the causes is that a magnesium ion (Mg ²⁺ ) of the above and phenol in the antioxidant form a chelate compound.

[0007] Natural rubber products obtained using white deproteinized natural rubber latex are colorless and transparent, whereas pinking-generated latex gives pink-colored natural rubber products. Therefore, the colorless transparency characteristic of the deproteinized natural rubber product is impaired. Therefore, it is required to prevent discoloration while preventing aging of the deproteinized natural rubber latex.

It is an object of the present invention to provide an agent for preventing discoloration of a deproteinized natural rubber latex. Another object of the present invention is to prevent the progress of aging during storage,
An object of the present invention is to provide a deproteinized natural rubber latex capable of preventing discoloration during storage caused by an anti-aging agent, and a storage method thereof.

[0009]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, found that a salt of a water-soluble dithiocarbamic acid derivative, a pyrosulfite, a cycloalkane, When at least one selected from the group consisting of thiol and halogenated thiophenol is blended, a new fact that discoloration of the deproteinized natural rubber latex can be prevented has been found, and the present invention has been completed.

That is, the discoloration inhibitor of the deproteinized natural rubber latex of the present invention comprises at least one selected from the group consisting of salts of water-soluble dithiocarbamic acid derivatives, pyrosulfites, cycloalkanethiols and halogenated thiophenols. It is characterized by the following. Such a discoloration inhibitor is added to the deproteinized natural rubber latex or added to the natural rubber latex before removing the protein, thereby preventing discoloration of the deproteinized natural rubber latex caused by the phenolic antioxidant. .

The deproteinized natural rubber latex of the present invention contains a phenolic antioxidant, and further contains the above anti-tarnish agent in an amount of 0.005 to 100 parts by weight of the latex rubber.
It is characterized by containing 15 parts by weight. According to such a deproteinized natural rubber latex, discoloration of the latex due to the incorporation of the phenolic antioxidant can be prevented, and a natural rubber product excellent in colorless and transparent can be provided.

The method for storing a deproteinized natural rubber latex of the present invention is characterized in that the above-mentioned discoloration inhibitor and a phenolic antioxidant are blended in a deproteinized natural rubber latex and stored. According to the storage method, aging of the deproteinized natural rubber latex due to the action of the phenolic antioxidant can be prevented, and discoloration due to the phenolic antioxidant can also be prevented by the action of the discoloration inhibitor.

[0013]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the salt of a water-soluble dithiocarbamic acid derivative, pyrosulfite, cycloalkanethiol and halogenated thiophenol are used in the form of a powder or in the form of an aqueous solution. Among them, from the viewpoint of easy dissolution in natural rubber latex,
It is preferable to use an aqueous solution containing the above compound in an amount of about 1 to 30% by weight.

The salt of the water-soluble dithiocarbamic acid derivative is a salt of dithiocarbamic acid and an alkali metal, and has a general formula:

[0015]

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(Wherein R ¹ and R ² are the same or different and each represent a hydrogen atom, an alkyl group or an aryl group;
Represents an alkali metal. ). As the groups R ¹ and R ² , in addition to a hydrogen atom, for example, methyl, ethyl, n-
Examples include an alkyl group such as propyl, isopropyl, n-butyl and t-butyl and an aryl group such as phenyl. Examples of the alkali metal represented by the group M include sodium and potassium.

Specific examples of the salt of the water-soluble dithiocarbamic acid derivative include, for example, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium dibutyldithiocarbamate, potassium diethyldithiocarbamate, sodium dithiocarbamate and the like. Examples of the pyrosulfite (diphosphonate) include salts of pyrosulfite with an alkali metal such as sodium pyrosulfite and potassium pyrosulfite.

Examples of the cycloalkanethiol include thiols having a cycloalkyl group having 5 to 8 carbon atoms, such as cyclopentanethiol, cyclohexanethiol, cycloheptanethiol, and cyclooctanethiol. Examples of the halogenated thiophenol include, for example, 4-bromothiophenol, pentachlorothiophenol, 1,3,5-triiodothiophenol, and the like, in which hydrogen on the benzene ring is substituted with a halogen atom such as chlorine, bromine, or iodine. Is raised.

The discoloration inhibitor is used after being subjected to the deproteinization treatment or before the deproteinization treatment, by being blended into the natural rubber latex. The deproteinized natural rubber latex of the present invention contains a phenolic antioxidant, and further contains the above discoloration inhibitor in an amount of 0.005 to 15 parts by weight, preferably 0.01 to 10 parts by weight, based on 100 parts by weight of the rubber component of the latex. Parts, more preferably 0.5 to 10 parts by weight, especially 1 to 5 parts by weight.

If the amount of the discoloration inhibitor is less than 0.005 parts by weight, the effect of preventing discoloration of the latex is undesirably reduced. On the other hand, even if the discoloration inhibitor is contained in an amount exceeding 15 parts by weight, the effect of preventing discoloration of the latex does not change. Conversely, the discoloration inhibitor acts as an excess component after molding, and the quality of the rubber product is reduced. May be adversely affected.

In the present invention, the natural rubber latex is
It means a field latex obtained from a natural rubber tree, and any commercially available ammonia-treated latex or fresh field latex can be used. In the present invention, the deproteinized natural rubber latex indicates a protein having a lower protein content than ordinary natural rubber latex, but generally, the protein in the raw rubber obtained from the deproteinized natural rubber latex has a nitrogen content of Indicates that the content is 0.05% by weight or less.

The deproteinized natural rubber latex of the present invention is obtained by using a natural rubber latex as a raw material, a conventionally known deproteinization treatment, for example, adding a protease to natural rubber latex to decompose a protein, and then adding a surfactant. In addition, it can be obtained by a process of repeatedly washing the latex to remove degraded proteins. The discoloration inhibitor may be incorporated into the latex at the time of deproteinizing natural rubber latex, or may be previously incorporated into natural rubber latex that has not been subjected to deproteinizing treatment.

The protease used for deproteinizing natural rubber latex is not particularly limited, and any of those derived from bacteria, those derived from filamentous fungi, those derived from yeast and the like can be used. It is preferred to use the following protease. As the surfactant used for deproteinizing natural rubber latex, for example, an anionic surfactant and / or a nonionic surfactant can be used.

As the anionic surfactant, for example, a carboxylic acid type, a sulfonic acid type, a sulfate ester type, a phosphate ester type and the like are suitably used. Examples of the carboxylic acid-based anionic surfactant include a fatty acid salt having 6 to 30 carbon atoms, a polyvalent carboxylate, a rosinate, a dimer acid salt, a polymer acid salt, and a tall oil fatty acid salt. A carboxylate having 10 to 20 carbon atoms is particularly preferably used. When the carbon number is 6 or less, dispersion and emulsification of non-rubber components such as proteins are insufficient, and when the carbon number is 30 or more, it is difficult to disperse in water. Examples of the sulfonic acid-based anionic surfactant include an alkylbenzene sulfonate, an alkyl sulfonate, an alkyl naphthalene sulfonate, a naphthalene sulfonate, and a diphenyl ether sulfonate. Examples of the sulfate-based anionic surfactant include alkyl sulfate salts,
Examples thereof include polyoxyalkylene alkyl sulfates, polyoxyalkylene alkyl phenyl ether sulfates, tristyrenated phenol sulfates, and polyoxyalkylenedistyrenated phenol sulfates. Examples of the phosphate-based anionic surfactant include an alkyl phosphate ester salt and a polyoxyalkylene phosphate ester salt.

Examples of the salt in the anionic surfactant exemplified above include metal salts (Na salt, K salt, Ca salt, Mg salt,
Zn salt, etc.), ammonia salt, amine salt (triethanolamine salt, etc.) and the like. As the nonionic surfactant, for example, polyoxyalkylene ether-based, polyoxyalkylene ester-based, polyhydric alcohol fatty acid ester-based, sugar fatty acid ester-based, and alkyl polyglycoside-based are preferably used.

Examples of the polyoxyalkylene ether-based nonionic surfactant include polyoxyalkylene alkyl ether, polyoxyalkylene alkyl phenyl ether, polyoxyalkylene polyol alkyl ether, polyoxyalkylene styrenated phenol ether, and polyoxyalkylene. Examples include range styrenated phenol ethers and polyoxyalkylene tristyrenated phenol ethers. Examples of the polyoxyalkylene ester-based nonionic surfactant include polyoxyalkylene fatty acid esters.
Examples of the polyhydric alcohol fatty acid ester nonionic surfactant include a fatty acid ester of a polyhydric alcohol having 2 to 12 carbon atoms or a fatty acid ester of a polyoxyalkylene polyhydric alcohol. Examples of nonionic surfactants of sugar fatty acid esters include sucrose, glucose,
Examples include maltose, fructose, and fatty acid esters of polysaccharides, and adducts of these polyalkylene oxides can also be used. Examples of the alkyl polyglycoside nonionic surfactant include alkyl glucoside, alkyl polyglucoside, polyoxyalkylene alkyl glucoside, polyoxyalkylene alkyl polyglucoside, and the like, and fatty acid esters thereof. Further, these polyalkylene oxide adducts can also be used.

The alkyl group in these surfactants includes, for example, those having 4 to 30 carbon atoms. Examples of the polyoxyalkylene group include those having an alkylene group having 2 to 4 carbon atoms, for example, those having an addition mole number of ethylene oxide of about 1 to 50 mol. In addition, examples of the fatty acid include a linear or branched saturated or unsaturated fatty acid having 4 to 30 carbon atoms.

In order to degrade the protein in the natural rubber latex with the protease, the protease is added to the field latex or the ammonia-treated latex by about 0.001.
What is necessary is just to add in the ratio of 10 to 10 weight%. The treatment time with the enzyme is not particularly limited, but the treatment is preferably performed for several minutes to about one week. Further, the latex may be stirred or may be allowed to stand. Temperature adjustment may be performed as needed. The temperature suitable for the treatment with the enzyme is 5 to 9
0 ° C., preferably 20 to 60 ° C. Processing temperature is 90
When the temperature exceeds ℃, the inactivation of the enzyme is accelerated.

As a method for washing the latex with a surfactant, for example, a method in which a surfactant is added to latex that has been treated with an enzyme and centrifuged is preferably used.
At that time, the surfactant is 0.001 to latex.
It is appropriate to add in the range of 10% by weight. Centrifugation may be performed once or several times. Further, instead of the centrifugal separation, a washing method of aggregating and separating latex particles can be employed.

In the above description, after the enzymatic decomposition, a surfactant is added to wash the latex. However, the enzyme and the surfactant may be added and treated at the same time. The phenolic antioxidant blended in the deproteinized natural rubber latex of the present invention is not particularly limited.
Di (t-butyl) -4-methylphenol, 4,4′-
Thiobis (6-t-butyl-3-phenol), 2,5
-Di (t-butyl) hydroquinone, styrene-phenol condensate and the like are known in the art.

The blending amount of the phenolic antioxidant is not particularly limited.
The amount is set in the range of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, more preferably 0.1 to 3 parts by weight with respect to 00 parts by weight. If the amount of the antioxidant is less than the above range, the rubber may be insufficiently prevented from aging. Conversely, if the compounding amount of the antioxidant exceeds the above range, the quality of the obtained rubber product may be adversely affected, and if the compounding amount is too large, the anti-tarnish of the present invention may cause pinking. May occur.

The method of blending the phenolic antioxidant with the latex is not particularly limited, but it is appropriate to add it as an o / w emulsion or suspension. The surfactant used to make the phenolic antioxidant into an o / w emulsion or suspension is not particularly limited, but usually includes the anionic surfactants and nonionic surfactants exemplified above. .

The phenolic antioxidant may be incorporated in the deproteinized natural rubber latex, or may be previously incorporated in the natural rubber latex that has not been subjected to deproteinization. In the deproteinized natural rubber latex of the present invention,
Suitably, the weight percentage of rubber solids is in the range of 58-62% by weight, preferably 59-61% by weight.

The method for storing a deproteinized natural rubber latex according to the present invention comprises mixing the above anti-tarnish agent and a phenolic antioxidant in a deproteinized natural rubber latex and storing the compound. The kind and amount of the phenolic antioxidant are the same as described above. The conditions for storing the deproteinized natural rubber latex are not particularly limited, but it is preferable to store in a light-shielded and sealed state in a temperature range of 20 to 30 ° C., which prevents the aging and discoloration of the latex more reliably. It is preferable from the viewpoint of doing.

[0035]

【Example】

Reference Example (Preparation of Deproteinized Natural Rubber Latex) Alkalase 2.0M manufactured by Novo Nordisk Bioindustry Co., Ltd. was used for the proteolytic enzyme, and solid rubber latex 6 manufactured by Soctech (Malaysia) was used for the natural rubber latex.
0.2% was used.

The above natural rubber latex (15 ml) was diluted with distilled water (200 ml) and stabilized with 0.12% sodium naphthenate. Next, sodium dihydrogen phosphate was added to the diluted natural rubber latex to adjust the pH to 9.2. The above alcalase 2.0M (0.78 g) was dispersed in 10 ml of distilled water, and then added to the diluted natural rubber latex. Further, after readjusting the pH to 9.2, 37
It was left at 24 ° C. for 24 hours.

A nonionic surfactant "Triton X-1" (manufactured by Toho Chemical Industry Co., Ltd.) at a concentration of 1% was added to the enzyme-treated latex at 11,000 rpm.
For 30 minutes. The creamy fraction thus obtained was redispersed in 200 ml of distilled water containing 1% Triton X-1 (supra) and centrifuged again. After repeating this operation three times, a creamy deproteinized natural rubber was obtained.

The nitrogen content of the deproteinized natural rubber thus obtained was 0.01% or less. The nitrogen content was determined by the RRIM test method (Rubber Research Institute).
ofMalaysia (1973). Determined by 'SMR Bulletin No.7'). Example 1 "Emulbin W" and "Tamol N" (both BASF
Antioxidants (2,6-di (t-butyl) -4-methylphenol, Nouchi Crack 200, trade name of Ouchi Shinko Chemical Co., Ltd.) )) To give an emulsion having a concentration of 20% by weight.

On the other hand, sodium diethyldithiocarbamate (trade name “NOCSELLER SD” of Ouchi Shinko Chemical Co., Ltd.)
C ") was adjusted to 20% by weight to prepare an aqueous solution (anti-discoloring agent). Water was added to the deproteinized natural rubber cream obtained in the above reference example so that the concentration of the rubber component became 60% by weight, to give a latex form. Next, the emulsion of the above-mentioned antioxidant was added so that the compounding amount of the phenolic antioxidant was 3 parts by weight based on 100 parts by weight of the rubber component of the latex.

Further, the amount of sodium diethyldithiocarbamate is 0.01 to 100 parts by weight of the rubber component.
The above discoloration inhibitor was added so as to be parts by weight to obtain a deproteinized natural rubber latex. Example 2 A deproteinized natural rubber latex was obtained in the same manner as in Example 1, except that the amount of sodium diethyldithiocarbamate was changed to 0.1 part by weight based on 100 parts by weight of the rubber component.

Example 3 A deproteinized natural rubber latex was obtained in the same manner as in Example 1, except that the amount of sodium diethyldithiocarbamate was changed to 1.0 part by weight based on 100 parts by weight of the rubber component. Example 4 Instead of an aqueous solution of sodium diethyldithiocarbamate, an aqueous solution of sodium dibutyldithiocarbamate (trade name “Noxeller TP” manufactured by Ouchi Shinko Chemical Co., Ltd.) (concentration: 20% by weight) was used as a discoloration inhibitor. The amount of sodium dibutyldithiocarbamate was adjusted to 100
A deproteinized natural rubber latex was obtained in the same manner as in Example 1 except that the amount was 1.0 part by weight based on the weight part.

Example 5 A deproteinized natural rubber latex was obtained in the same manner as in Example 1, except that the amount of sodium diethyldithiocarbamate was changed to 2.0 parts by weight based on 100 parts by weight of the rubber component. Example 6 A deproteinized natural rubber latex was obtained in the same manner as in Example 1, except that the amount of sodium diethyldithiocarbamate was 8.0 parts by weight based on 100 parts by weight of the rubber component.

Example 7: The amount of sodium diethyldithiocarbamate was changed to 10.0 parts by weight based on 100 parts by weight of rubber.
In the same manner as in Example 1, a deproteinized natural rubber latex was obtained. Comparative Example Water was added to the deproteinized natural rubber cream obtained in the above Reference Example so that the concentration of the rubber component became 60% by weight, to give a latex form. Next, an emulsion of the above antioxidant was added so that the compounding amount of the phenolic antioxidant was 3 parts by weight based on 100 parts by weight of the rubber content of the latex, to obtain a deproteinized natural rubber latex.

(Evaluation of Discoloration Prevention Effect) Examples 1 to 7
And the deproteinized natural rubber latex obtained in Comparative Example 2
The color of the latex was visually observed immediately after the discoloration inhibitor was added, 10 days after the addition, and 50 days after the addition, in a 5 ° C. environment. Table 1 shows the results.
Shown in If the color of the latex is white, it becomes colorless and transparent when it is made into a rubber product.

[0045]

[Table 1]

As is clear from Table 1, the latex of Comparative Example 1 which did not contain the discoloration inhibitor changed the color of the latex to pink when allowed to stand for 10 days. on the other hand,
In Examples 1 and 2, the degree of discoloration after 10 days and 50 days was very small. Further, in Examples 3 to 7, the latex could be kept white even after 50 days.

Example 8 As a discoloration inhibitor, an aqueous solution of sodium pyrosulfite (concentration: 20% by weight) was used instead of the aqueous solution of sodium diethyldithiocarbamate. A deproteinized natural rubber latex was obtained in the same manner as in Example 1 except that 2.0 parts by weight was used.

Example 9 Instead of the aqueous solution of sodium diethyldithiocarbamate, an aqueous solution of cyclohexanethiol (concentration: 20% by weight) was used as a discoloration inhibitor. A deproteinized natural rubber latex was obtained in the same manner as in Example 1 except that the amount was changed to 0 parts by weight.

Example 10 An aqueous solution of 4-bromothiophenol (concentration: 20% by weight) was used in place of the aqueous solution of sodium diethyldithiocarbamate as a discoloration inhibitor. Deproteinized natural rubber latex was obtained in the same manner as in Example 1 except that the amount was 2.0 parts by weight based on parts.

Example 11 An aqueous solution of pentachlorothiophenol (concentration: 20% by weight) was used in place of the aqueous solution of sodium diethyldithiocarbamate as a discoloration inhibitor, and the blending amount of pentachlorothiophenol was adjusted to 100 parts by weight of rubber. 2.0 for
A deproteinized natural rubber latex was obtained in the same manner as in Example 1 except that the amount was changed to parts by weight.

The deproteinized natural rubber latexes obtained in Examples 8 to 11 were evaluated for the effect of preventing discoloration in the same manner as described above. Table 2 shows the results.

[0052]

[Table 2]

As is clear from Table 2, in Examples 8 to 11 in which the discoloration inhibitor of the present invention was blended, the latex could be kept white even after 50 days.

[0054]

As described above, the present invention can prevent discoloration of the deproteinized natural rubber latex for a long time,
It is suitable for providing a deproteinized natural rubber product excellent in colorless transparency without discoloration.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 5/41 C08K 5/41 C08L 7/02 C08L 7/02 C09K 15/10 C09K 15/10 15/14 15/14 15 / 28 15/28

Claims (3)

[Claims] 1. A discoloration inhibitor for a deproteinized natural rubber latex comprising at least one selected from the group consisting of salts of water-soluble dithiocarbamic acid derivatives, pyrosulfites, cycloalkanethiols and halogenated thiophenols. 2. A latex having a rubber content of at least one selected from the group consisting of salts of water-soluble dithiocarbamic acid derivatives, pyrosulfites, cycloalkanethiols and halogenated thiophenols, which contains a phenolic antioxidant. A deproteinized natural rubber latex, which is contained in a ratio of 0.005 to 15 parts by weight with respect to parts by weight. 3. A deproteinized natural rubber latex comprising a phenolic antioxidant and a salt of a water-soluble dithiocarbamic acid derivative,
At least one selected from the group consisting of pyrosulfite, cycloalkanethiol and halogenated thiophenol
A method for storing a deproteinized natural rubber latex, which comprises storing a seed and a seed.