JP2001316523A - Natural rubber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a natural rubber having suppressed gelling tendency without lowering the molecular weight of natural rubber and giving a rubber composition having excellent processability and physical properties and provide a method for the production of the natural rubber. SOLUTION: The natural rubber is produced by adding at least one kind of compound selected from specific benzoic acids, naphthoic acids, dicarboxylic acids and aromatic polycarboxylic acid derivatives to a natural rubber latex. There is further disclosed a method for the production of the natural rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a natural rubber and a method for producing the same, and more particularly, to a natural rubber and a rubber composition which exhibit a small change in viscosity during storage and transportation, and which have good processability and physical properties of a rubber composition. It relates to the manufacturing method.

[0002]

2. Description of the Related Art Generally, natural rubber is produced in tropical countries such as Thailand, Malaysia and Indonesia. Natural rubber is widely and widely used in the rubber and tire industries because of its excellent physical properties. Natural rubber immediately after its production has a Mooney viscosity of 60.
Mooney viscosity rises to around 90-100 in several months when stored and transported to Japan (gelation)
(This is called storage hardening).

[0003] As a cause of storage hardening of natural rubber, it is said that a heterogeneous bond (aldehyde group or the like) in the isoprene chain reacts with a protein or amino acid in natural rubber to cause cross-linking and gelation (refer to literatures and the like). The mechanism is not clearly understood.) The gelation (increase in the amount of gel) in natural rubber deteriorates processability. In general, the natural rubber preferably has a large molecular weight, and a decrease in the molecular weight adversely affects the physical properties of the natural rubber. The molecular weight and the amount of the gel greatly depend on the conditions of coagulation of rubber from natural rubber latex and drying conditions after washing with water. Typical drying methods in the process of producing natural rubber include the following two drying conditions.
That is, in the case of the ribbed smoke sheet (RSS) according to the international quality packaging standard (commonly called Green Book) of various grades of natural rubber, smoking is performed at about 60 ° C. for 5 to 7 days. In the case of technical grade rubber (TSR), hot air drying is performed at about 120 ° C. for several hours.

However, there is a problem that the gelation is promoted under the drying conditions at the time of manufacturing the RSS.
There is a problem in that the molecular weight is reduced under the drying conditions during R production. Further, during storage of both RSS and TSR, viscosity increases due to gelation (storage hardening or the like), so that a mastication step of raw rubber (natural rubber) is indispensable in the processing step. Generally, the meaning of mastication is to impart sufficient plasticity by applying mechanical shearing force to raw rubber. This mastication facilitates the mixing and kneading operation (operation of uniformly kneading the various compounding agents into the raw rubber) by facilitating the dispersion of various compounding agents such as a vulcanizing agent and a filler, and is also a post-process. In rolling, extrusion, etc., stabilize dimensions, clean skin, make it difficult to scorch, etc.
It plays a role in facilitating these tasks.

[0005] In this mastication, the molecular weight is reduced due to molecular cutting of the raw rubber by simple mechanical mastication such as a roll machine or a closed kneader, and the rubber is plasticized. Kneading requires a great deal of power, labor and time. Therefore, it is generally well known that a mastication accelerator (peptizer) is used in the mastication step of raw rubber. However, the use of this mastication accelerator promotes plasticization and lowers the viscosity of the rubber, but at the same time, cuts the molecular chains and vulcanizes the rubber. There is an issue in that Further, British Patent No. 147064 describes that adding a constant viscosity agent to natural rubber is effective, and further discloses that a hydrazide compound having 8 to 30 carbon atoms is effective as a constant viscosity agent. Have been. However, the above publication does not mention how the physical properties after vulcanization change. Further, when a hydrazide compound having a large number of carbon atoms is added as described above, there is a problem that a decrease in vulcanization properties such as an increase in hysteresis loss is observed.

As described above, in the conventional technology, in the processing of natural rubber, the use of rubber having a high molecular weight and a small gel amount is a trade-off and is incompatible at present. More recently, the Malaysian Rubber Research Institute (RRM) has treated natural rubber latex with hydroxylamine sulfate (NH ₂ OH.H ₂ SO ₄ ) at about 0.08 to 0.30% by weight to prevent the storage hardening. As natural rubber with constant viscosity. Further, a type (SMR-GP) in which the same hydroxylamine sulfate is mixed with a solution of natural rubber after drying has been developed. However, natural viscosity natural rubber using hydroxylamine sulfate is
(1) Hydroxylamine sulfate is difficult to use in Japan because it is designated as a deleterious substance. (2) Viscosity increase is observed in the initial stage of storage. (3) In severe conditions (in an oven at about 60 ° C.) There are problems that the viscosity effect is low, (4) poor compatibility with rubber and poor dispersibility, and (5) the decomposition temperature is low, and the effect cannot be sufficiently obtained by kneading at a high temperature.

On the other hand, a document (BCSekhar, J. et al.) Showing the results of screening for additives for natural rubber having a constant viscosity effect.
PolymerScience, Vol. XLVIII, 133 (1960)) describes semicarbazide (NH ₂ NHCONH ₂ ). Examples of additives for natural rubber that are likely to have a viscosity effect include hydroxylamine, semicarbazide, and dimedone (1,1). -Dimethylcyclohexane-3,5-dione). However, it has been confirmed that although the amount of each compound is less than the lower limit, although there is variation, the constant viscosity effect is basically low from the beginning or the viscosity increases from a certain period. Possible causes include (1) a certain amount is required to block aldehyde groups and the like which are considered to cause gelation, and (2) sufficient dispersibility cannot be obtained due to the addition of a small amount.

In Japanese Patent Application Laid-Open Nos. 10-265611 and 11-209406, a specific compound having a carboxyl group is added at the time of mastication of natural rubber without lowering the molecular weight. Although reducing the gelation is described, the effect of adding these compounds during the production of natural rubber is not described.

[0009]

SUMMARY OF THE INVENTION Under the above circumstances, the present invention solves the problem of the drying conditions in the conventional natural rubber production process, that is, the problem of the drying conditions in the production of RSS or TSR. It is an object of the present invention to provide a natural rubber capable of suppressing gelation and preventing a decrease in molecular weight and having good processability and physical properties, and a method for producing the same.

[0010]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned conventional problems, the present inventors have found that a specific compound having a carboxyl group is added, particularly at the stage of producing natural rubber from latex. Thereby, the formation of a gel in natural rubber is suppressed even after long-term storage without lowering the molecular weight, and the processability and physical properties of a rubber composition obtained from the natural rubber composition can be improved. And completed the present invention.

That is, the present invention relates to benzoic acids represented by the following general formula (I), naphthoic acids represented by the following general formula (II), dicarboxylic acids represented by the following general formula (III) and An object of the present invention is to provide a natural rubber obtained by adding at least one compound selected from aromatic polycarboxylic acid derivatives represented by the formula (IV) to a natural rubber latex. Also, the present invention provides a method for producing a benzoic acid represented by the following general formula (I), a naphthoic acid represented by the following general formula (II), after collecting natural rubber latex and before drying the natural rubber latex, The following general formula (I
(II) a natural rubber latex comprising adding at least one compound selected from dicarboxylic acids represented by the following general formula (IV) and an aromatic polycarboxylic acid derivative represented by the following general formula (IV) to a natural rubber latex: It also provides a manufacturing method.

[0012]

Embedded image [In the formula (I), R ¹ and R ² each independently represent halogen, hydrogen, an alkyl group having 1 to 4 carbon atoms, —NH ₂ ,
OH, -SH, -NO _2, benzoyl group, 1 to 4 carbon atoms
And may be the same or different. ]

[0013]

Embedded image [In the formula (II), R ³ and R ⁴ are each independently hydrogen, —NH ₂ or —OH. HOOC-R ⁵ —COOH (III) wherein, in the formula (III), R ⁵ is a phenylene group, an alkenylene group having 2 to 4 carbon atoms, or — (CH ₂ ) _n — (where n is 1 To 14).

[0014]

Embedded image [In the formula (IV), m and k are each an integer of 1 to 3, and p is 1
Where m + k + p = 6 and m ≧ 2,
Some or all of the carboxyl groups may be dehydrated in the molecule. X is oxygen, NR ⁸ (R ⁸ is hydrogen or an alkyl group having 1 to 24 carbon atoms) or —O (R ⁹ O) _q (R ⁹
Is an alkylene group having 1 to 4 carbon atoms, and q is an integer of 1 to 5).
R ⁶ is an alkyl group having 1 to 24 carbon atoms, 2 to 24 carbon atoms.
An alkenyl group or an aryl group having 6 to 24 carbon atoms, R ⁷
Is hydrogen, -OH, an alkyl group, an alkenyl group or an aryl group, R ^6, R ⁷ are both a part or all of hydrogen may be substituted with halogen. ]

[0015]

DETAILED DESCRIPTION OF THE INVENTION In the general formula (I), the halogen -Br, -Cl etc., -CH ₃ as an alkyl group having 1 to 4 carbon _{atoms, -C 2 H 5, -CH 2} CH 2
Examples of the alkoxyl group having 1 to 4 carbon atoms such as CH ₃ and —CH (CH ₃ ) ₂ include —OCH ₃ and —OC ₂ H ₅ groups. The benzoic acids represented by the general formula (I) used in the present invention include, for example, benzoic acid, p-toluic acid, pt-butylbenzoic acid, anthranilic acid, p-aminobenzoic acid, p-nitrobenzoic acid Acid, o-benzoylbenzoic acid, salicylic acid, thiosalicylic acid, and the like;
In particular, p-toluic acid and pt-butylbenzoic acid are preferred because the effects of the present invention are large, the cost is low, and there is no sublimability.

The naphthoic acids represented by the general formula (II) used in the present invention include, for example, α-naphthoic acid,
β-naphthoic acid, β-oxynaphthoic acid and the like. In the general formula (III), R ⁵ is

Embedded image And the like. Examples of the dicarboxylic acids represented by the general formula (III) include phthalic acid, terephthalic acid,
Examples include isophthalic acid, fumaric acid, adipic acid, maleic acid, citraconic acid, sebacic acid, dodecane diacid, and the like. Particularly, since the effects of the present invention are large, the cost is low, and there is no sublimation, phthalic acid, terephthalic acid, etc. Acids, isophthalic acid, fumaric acid, adipic acid are preferred.

In the aromatic polycarboxylic acid derivative represented by the general formula (IV), X is oxygen or -O (R ⁹ O)
It is preferably _q . R ⁶ is preferably an alkyl group having 1 to 22 carbon atoms. As the aromatic polycarboxylic acid derivative, for example, a derivative of any of phthalic acid, trimellitic acid, pyromellitic acid and anhydride thereof is preferable. Specifically, monostearyl phthalate,
Monodecyl phthalate, monooctylamide phthalate, polyoxyethylene lauryl phthalate, monodecyl trimellitate, monostearyl trimellitate, monostearyl pyromellitic acid, distearyl pyromellitic acid, etc., in particular, reducing the amount of gel Polyoxyalkylene alkyl phthalate is preferred because of its excellent effect and plasticization effect and low cost, and polyoxyethylene lauryl phthalate is particularly preferred.

In the production method of the present invention, the compound is added by (1) adding the compound into an emulsion and adding it to natural rubber latex, and (2) collecting a natural rubber latex cup lamp. (3) adding the compound to the natural rubber after the dehydration step of the natural rubber latex, and adding the compound to the natural rubber after the dehydration step of the natural rubber latex; and (4) adding the compound to the natural rubber. It is preferable to have a step of mixing after addition to the latex. In the natural rubber and the method for producing the same according to the present invention, at least one kind selected from the above (I) to (IV) is added at the stage of producing the natural rubber. It is preferable to mix 0.01 to 20 parts by weight with respect to parts by weight. If the amount is less than 0.01 part by weight, the effect of the present invention of reducing the gel amount without reducing the molecular weight cannot be obtained. On the other hand, if it exceeds 20 parts by weight, not only the effect corresponding to the increased amount cannot be obtained, but also a bad influence on the breaking characteristics of the vulcanized rubber. The above-mentioned compounding amount varies in the above-mentioned compounding range depending on the kind and grade of the natural rubber to be used, but from the viewpoint of cost and handling, more preferably 0.5 to 8 parts by weight, especially 0.2 to 5 parts by weight. Parts by weight are desirable.

The natural rubber composition obtained as described above can be obtained by entanglement of molecular chains in natural rubber, and between functional groups in isoprene chains of natural rubber or such functional groups and non-rubber in natural rubber. Since gel formation due to the reaction with the components is suppressed, the mastication time for reducing the molecular weight of the natural rubber can be shortened, or the mastication step can be omitted altogether. In the present invention, when performing mastication,
Examples of the mastication machine to be used include, for example, a roll machine, a closed kneader, a Gordon plasticizer and the like, but the mastication in the present invention is usually performed under significantly milder conditions compared to the mastication conditions of natural rubber. For example, when the mastication start temperature is 60 to 85 ° C., the mastication time is 50 to 90 seconds in the conventional method, whereas it is about 30 seconds or less in the present invention. Can be reduced without substantially reducing the molecular weight, and the processability can be improved.

When the natural rubber obtained in the present invention is processed, it can be blended with other synthetic rubbers if desired. Various compounding agents, such as antioxidants, antioxidants, vulcanization accelerators, and sulfur, can be appropriately compounded. Further, the obtained natural rubber composition can be suitably used for rubber products such as pneumatic tires, conveyor belts, belts, hoses and the like.

[0021]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited by these examples. [Various Measurement Methods] The properties and physical properties of various samples were evaluated according to the following methods. (1) Gel amount 0.2 g of a rubber piece was dissolved in toluene first grade (60 cc),
The gel content was separated by a centrifugation method, and after drying it, the amount of gel was measured and shown as a percentage (%). (2) Mooney viscosity of natural rubber In order to examine whether or not the viscosity is constant, each natural rubber is allowed to stand at room temperature and maintained in a curing-accelerated state.
The change with time of Mooney viscosity (measured at 100 ° C.) was measured according to 300 and expressed as an index. The smaller the value, the lower the viscosity. (3) Mooney viscosity of rubber composition According to JIS K6300, Mooney viscosity (130
(Measured in ° C.) was measured and expressed as an index. The smaller the value, the lower the viscosity.

Examples 1 to 16 and Comparative Examples 1 to 5 At the stage of producing natural rubber from latex,
A natural rubber (an unsmoked sheet) produced by adding a predetermined amount (shown in parts by weight based on 100 parts by weight of a rubber component) of various additive compounds under the processing conditions shown in the table was used on day 0.
After standing at room temperature for 30 days and 60 days, the gel amount and Mooney viscosity (100 ° C.) were measured. The results are shown in Table 1. Also,
About each said natural rubber, after masticating on predetermined conditions as shown in Table 1, with respect to 100 weight part of natural rubbers,
50 parts by weight of carbon black, 2 parts by weight of stearic acid,
2 parts by weight of zinc white, N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine [Nocrack 6C,
Trademark: Ouchi Shinko Chemical Co., Ltd.] 1 part by weight, N-tert
-Butyl 1-2 benzothiazolesulfenamide [Noxeller NSP, trademark; Ouchi Shinko Chemical Co., Ltd.] 1.5
Parts by weight and 1.5 parts by weight of sulfur were blended to prepare a rubber composition. The Mooney viscosity (130 ° C.) of this rubber composition was measured by the method described above. The results are shown in Table 1.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[Note] * 1: Type of additive compound I-1; p-toluic acid I-2; pt-butylbenzoic acid II-1; α-naphthoic acid III-1; terephthalic acid III-2; Adipic acid IV-1; monostearyl phthalate IV-2; phthalic acid mono (polyoxyethylene lauryl) ester V-1; 2-ethylhexanoic acid hydrazide (comparative example) V-2; benzoic acid hydrazide (comparative example) * 2: Timing of addition (1) The added compound is made into an emulsion and added to the natural rubber latex. (2) Addition (mixing) of the added compound before the drying step of the natural rubber latex. (3) The additive compound is added and penetrated into the natural rubber after the step of dehydrating the natural rubber latex. * 3: Mastication conditions No mastication. The mastication start temperature is 80 ° C., and mastication is performed for 30 seconds. The mastication start temperature is 80 ° C., and mastication is performed for 60 seconds (usually mastication conditions for natural rubber).

In the above table, Examples 3 to 9 are examples in which the type of the specific compound added in the present invention is changed, and Examples 1, 2 and 9 are examples in which the addition time of the specific compound is changed. It is. In Examples 9 to 11, the same natural rubber was used, but the mastication conditions were changed. Comparing these Examples with Comparative Examples 1 to 5, it can be seen that the natural rubber to which the specific compound of the present invention is added has a very effective suppression of the increase in the gelling amount and Mooney viscosity due to aging. . Further, Examples 12 to
No. 16 is a specific compound in which phthalic acid mono (polyoxyethylene lauryl) ester is used and the amount thereof is changed. Particularly, the amount is 0.01 to 20 parts by weight with respect to 100 parts by weight of natural rubber. It can be seen that the effect of the present invention is great in the case of parts by weight.

As described in detail above, when natural rubber is produced by the method of the present invention, gelation can be reduced without lowering the molecular weight. Therefore, there is little change in viscosity during storage or transportation. Further, the processability and physical properties of the rubber composition obtained from the natural rubber of the present invention are good.

Claims (10)

[Claims] 1. A benzoic acid represented by the following general formula (I), a naphthoic acid represented by the following general formula (II), a dicarboxylic acid represented by the following general formula (III) and the following general formula (IV) A natural rubber obtained by adding at least one compound selected from aromatic polycarboxylic acid derivatives represented by the formula to natural rubber latex. Embedded image [In the formula (I), R ¹ and R ² each independently represent halogen, hydrogen, an alkyl group having 1 to 4 carbon atoms, —NH ₂ ,
OH, -SH, -NO _2, benzoyl group, 1 to 4 carbon atoms
And may be the same or different. [Chemical formula 2] [In formula (II), R ³ and R ⁴ are each independently hydrogen, —NH ₂ or —OH. ] During ^{HOOC-R 5 -COOH ··· (III} ) [Formula (III), R ⁵ is a phenylene group, an alkenylene group having 2 to 4 carbon atoms, or _{- (CH 2) n - (} n is 1 to 14
Is an integer. )] Embedded image [In the formula (IV), m and k are each an integer of 1 to 3, and p is 1
Where m + k + p = 6 and m ≧ 2,
Some or all of the carboxyl groups may be dehydrated in the molecule. X is oxygen, NR ⁸ (R ⁸ is H or an alkyl group having 1 to 24 carbon atoms) or —O (R ⁹ O) _q (R ⁹ is an alkylene group having 1 to 4 carbon atoms; integer). R
⁶ is an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms or an aryl group having 6 to 24 carbon atoms,
⁷ is a hydrogen, -OH, an alkyl group, an alkenyl group or an aryl group, R ^6, R ⁷ are both a part or all of hydrogen may be substituted with halogen. ] 2. The natural rubber according to claim 1, wherein the benzoic acid represented by the general formula (I) is p-toluic acid and / or pt-butylbenzoic acid. 3. The dicarboxylic acid represented by the general formula (III) is at least one selected from phthalic acid, terephthalic acid, isophthalic acid, fumaric acid and adipic acid. 2. The natural rubber according to 1. 4. The aromatic polycarboxylic acid derivative represented by the general formula (IV) is at least one derivative selected from phthalic acid, trimellitic acid, pyromellitic acid and anhydride of pyromellitic acid. The natural rubber according to claim 1, wherein 5. The natural rubber according to claim 1, wherein the compound is added in an amount of 0.01 to 20 parts by weight based on 100 parts by weight of the natural rubber component. 6. After the natural rubber latex is collected and before the natural rubber latex is dried, the following general formula (I):
Of benzoic acids represented by the following general formula (II), dicarboxylic acids represented by the following general formula (III) and aromatic polycarboxylic acid derivatives represented by the following general formula (IV) At least one compound selected from among
A method for producing natural rubber, which is added to natural rubber latex. Embedded image [In the formula (I), R ¹ and R ² are each independently halogen, hydrogen, an alkyl group having 1 to 4 carbon atoms, —NH ₂ , —
OH, -SH, -NO _2, benzoyl group, 1 to 4 carbon atoms
And may be the same or different. [Chemical formula 5] [In the formula (II), R ³ and R ⁴ are each independently hydrogen, —NH ₂ or —OH. ] During ^{HOOC-R 5 -COOH ··· (III} ) [Formula (III), R ⁵ is a phenylene group, an alkenylene group having 2 to 4 carbon atoms, or _{- (CH 2) n - (} n is 1 to 14
Is an integer. )] [In the formula (IV), m and k are each an integer of 1 to 3, and p is 1
Where m + k + p = 6 and m ≧ 2,
Some or all of the carboxyl groups may be dehydrated in the molecule. X is oxygen, NR ⁸ (R ⁸ is hydrogen or an alkyl group having 1 to 24 carbon atoms) or —O (R ⁹ O) _q (R ⁹
Is an alkylene group having 1 to 4 carbon atoms, and q is an integer of 1 to 5).
R ⁶ is an alkyl group having 1 to 24 carbon atoms, 2 to 24 carbon atoms.
An alkenyl group or an aryl group having 6 to 24 carbon atoms, R ⁷
Is hydrogen, -OH, an alkyl group, an alkenyl group or an aryl group, R ^6, R ⁷ are both a part or all of hydrogen may be substituted with halogen. ] 7. The method for producing natural rubber according to claim 6, wherein the compound is made into an emulsion and added to natural rubber latex. 8. The method for producing natural rubber according to claim 6, wherein the compound is added after the cup lamp of the natural rubber latex is collected and before the drying step of the natural rubber latex. . 9. The method for producing natural rubber according to claim 6, further comprising a step of adding and permeating the compound into natural rubber after the step of dehydrating the natural rubber latex. 10. The method for producing natural rubber according to claim 6, further comprising a step of mixing the compound after adding the compound to natural rubber latex.