JP2006213754A - Method of controlling viscosity increase of natural rubber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of controlling the viscosity increase of natural rubber by using an additive which is safely handled and exhibits an excellent and lasting effect of stabilizing viscosity. <P>SOLUTION: The method of controlling the viscosity increase of natural rubber comprises adding a triazol compound expressed by formula (1): R-C<SB>2</SB>H<SB>2</SB>N<SB>3</SB>to natural rubber to control the increase in viscosity of natural rubber. In formula (1), R represents a hydrogen group, a 1-30C alkyl group, a 3-30C cycloalkyl group or an aryl group; an amino group, mercapto group, hydroxide group, carbonyl group and benzo group may be added to the triazol skeleton. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for suppressing the increase in viscosity of natural rubber, and more particularly, to a method for suppressing the increase in viscosity of natural rubber, in which an additive having a constant viscosity effect is contained in natural rubber.

  In general, natural rubber is produced in tropical countries such as Thailand, Malaysia, and Indonesia. The viscosity is as low as 60 to 70 immediately after production, but the viscosity is 90 to several months after being stored and transported in Japan. It rises (gels) to near 100 (this is called storage hardening). The cause of natural rubber storage and curing is that heterogeneous bonds (such as aldehyde groups) in the isoprene chain are cross-linked and gelled by reacting with proteins and amino acids in the natural rubber. Not clearly understood).

In order to prevent this storage curing, the Malaysian Rubber Research Institute (RRM) treats natural rubber latex with 0.08% to 0.30% of hydroxylamine sulfate (NH ₂ OH · H ₂ SO ₄ ) to maintain the natural viscosity. It is made of rubber. In addition, a type (SMR-GP) in which the solution is mixed with natural rubber after drying using the same hydroxylamine sulfate has been developed.

However, the constant viscosity natural rubber using hydroxylamine sulfate has the following problems.
(1) Hydroxylamine sulfate is difficult to use in Japan because it is a deleterious substance.
(2) An increase in viscosity is observed at the initial storage.
(3) The constant viscosity effect is low in a harsh state (in an oven at about 60 ° C.).
(4) There is concern that the compatibility with rubber is poor and the dispersibility is poor.
(5) The decomposition temperature is low, and the effect cannot be sufficiently obtained by kneading at a high temperature.

On the other hand, Non-Patent Document 1 showing the results of screening for additives for natural rubber having a constant viscosity effect describes semicarbazide (NH ₂ NHCONH ₂ ). Hydroxylamine, semicarbazide, and dimedone (1,1-dimethylcyclohexane-3,5-dione) are disclosed as additives for natural rubber that are likely to have a constant viscosity effect.

However, it has been confirmed that although the amount of each compound is less than the lower limit, there is variation, but basically the constant viscosity effect is low from the beginning or the viscosity increases from a certain period. There are two possible causes for this.
a) When sufficient dispersibility cannot be obtained due to addition of a small amount.
b) A certain amount is necessary to block aldehyde groups and the like that are supposed to cause gelation.

In order to solve such a problem, as a specific compound having a hydrazide group (—CONHNH ₂ ) has a constant viscosity effect, a method for suppressing the increase in viscosity of natural rubber using this as an additive has been proposed (for example, (See Patent Document 1). It can be handled safely, has a large constant viscosity effect, and can maintain the constant viscosity effect over a long period of time. However, what has a further constant viscosity effect is still expected.
JP-A-6-256570 (B. C. Sekhar, J. Polymer Science, Vol. XL VIII, 133 (1960))

  An object of the present invention is to solve the above-mentioned conventional problems, and uses an additive that can be handled safely, has an excellent constant viscosity effect, and maintains the constant viscosity effect over a long period of time. An object of the present invention is to provide a method for suppressing the increase in viscosity of natural rubber.

As a result of intensive studies to solve the above-mentioned conventional problems, the present inventors have found that a triazole compound having a specific triazole group (R—C ₂ H ₂ N ₃ ) has a constant viscosity effect. The inventors have found that by using an additive, the increase in the viscosity of natural rubber is suppressed, and the present invention has been completed.
That is, the method for suppressing the increase in viscosity of natural rubber according to the present invention is characterized by having the following configuration or structure.

(1) A method for suppressing the increase in the viscosity of natural rubber, wherein a triazole compound represented by the following formula (1) is added to the natural rubber to suppress an increase in the viscosity of the natural rubber.
_{R-C 2 H 2 N 3} ···· (1)
(In the formula (1), R represents a hydrogen group, an alkyl group having 1 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, or an aryl group. In addition, an amino group, mercapto group, or hydroxyl group is added to the triazole skeleton. , A carbonyl group or a benzo group may be added.)
(2) The method for suppressing the increase in viscosity of natural rubber according to (1), wherein the amount of the triazole compound added is 0.001 part by mass or more with respect to 100 parts by mass of natural rubber.

  In the method for suppressing the increase in viscosity of natural rubber according to the present invention, when the above-mentioned specific triazole compound is added to the natural rubber, the heterogeneous bonding reaction (aldehyde group etc.) in the isoprene chain is blocked, and the gel with the protein in the natural rubber Inhibits chemical reaction and suppresses viscosity increase. As shown also in the below-mentioned Example, in the rubber composition manufactured by this invention, the viscosity rise of a natural rubber is suppressed over the long term after 20 days.

Embodiments of the present invention will be described below. The method for suppressing the increase in viscosity of the natural rubber according to the present invention is not limited to the following embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.
The method for suppressing the increase in viscosity of natural rubber according to the present invention is to suppress the increase in the viscosity of natural rubber by adding a triazole compound represented by the following formula (1) to the natural rubber.
_{R-C 2 H 2 N 3} ···· (1)
However, R in Formula (1) shows a hydrogen group, a C1-C30 alkyl group, a C3-C30 cycloalkyl group, and an aryl group. Further, an amino group, mercapto group, hydroxyl group, carbonyl group, or benzo group may be added to the triazole skeleton.

As specific triazole compounds, 1,2,4-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, 3-mercapto-1,2,4- Triazole, 1,2,4-triazol-3-ol, 5-amino-3-mercapto-1,2,4-triazole, 5-amino-1,2,4-triazole, 1,2,4-triazole- Examples of the triazole compound include 3-carboxylic acid, benzotriazole, and 1-hydroxybenzotriazole (monohydrate).
Such a triazole compound can be handled safely, and when used in natural rubber, as will be apparent from the examples described later, exhibits a constant viscosity effect from the point of addition, and the The constant viscosity effect is sustained. As an aspect used for natural rubber, for example, there is a method of adding to the natural rubber produced in order to prevent storage curing or the like, or a method of adding at the stage of the rubber paste.

  In the method for suppressing the increase in viscosity of natural rubber of the present invention, the triazole compound represented by the above formula (1) is 0.001 part by mass or more with respect to 100 parts by mass of natural rubber. If the content of the triazole compound is less than 0.001 part by mass, the constant viscosity effect cannot be achieved. The content of the triazole compound varies slightly depending on the type of natural rubber used (produced) and the type of triazole compound used. A preferable range is 0.01 to 3.0 parts by mass.

Next, the present invention will be described more specifically and in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
(Examples 1 to 5, Comparative Examples 1 to 3) Table 1 below shows the results of measuring changes in Mooney viscosity over time for Examples and Comparative Examples in which additives and their contents were changed.

In addition, the preparation method of the rubber composition (paste rubber) containing the additive for natural rubber used in Examples 1-5 and Comparative Examples 1-3 and the measuring method of Mooney viscosity are as follows.
Examples 1 and 2
1. 100 parts by weight of natural rubber (RSS # 4) and 0.08 parts by weight of a peptizer, masticated rubbers were mixed with 0.05 parts by weight of 1,2,4-triazole and 0.1 parts by weight, respectively. Got.
[Examples 3, 4, and 5]
In the same manner as in Examples 1 and 2, 0.05 part by mass, 0.1 part by mass, and 0.2 part by mass of 4-amino-1,2,4-triazole were mixed to obtain a kneaded rubber.

[Comparative Examples 1 and 2]
The mixture was masticated with only 100 parts by mass of natural rubber (RSS # 4) and 0.08 parts by mass of a capping agent to obtain a masticated rubber (Comparative Example 1). Natural rubber (RSS # 4) 100 parts by mass and peptizer 0.08 parts by mass were further mixed with 0.07 parts by mass of the current hydroxylamine sulfate to obtain a kneaded rubber (Comparative Example 2).
[Comparative Example 3]
In the same manner as in Examples 1 and _2, 0.04 parts by mass of semicarbazide (NH ₂ —CONHNH ₂ ) was mixed to obtain a rubber paste.

[Method for measuring Mooney viscosity]
In order to examine whether or not the viscosity is constant, the kneaded rubbers of Examples 1 to 5 and Comparative Examples 1 to 3 are left in a 60 ° C. oven to be in a curing accelerated state, and the Mooney viscosity (measured at 60 ° C.) changes with time. Was measured.

  As is apparent from Table 1 above, Examples 1 to 5 have less Mooney viscosity change over time as compared with Comparative Examples 1 to 3, and have a constant viscosity effect over a long period after 20 days. In particular, Comparative Examples 2 and 3 are conventional natural rubber additives that are considered to have the above-described constant viscosity effect, but the additives (Examples 1 to 5) in the present invention are superior to these. You can see that

  The method for suppressing the increase in viscosity of natural rubber of the present invention inhibits the gelation reaction in natural rubber and suppresses the increase in viscosity over a long period of time, and prevents storage hardening when applied to the produced natural rubber. In addition, when it is applied at the stage of the kneaded rubber, it is a highly industrially applicable method that exhibits a constant viscosity effect from the point of addition.

Claims (2)

A method for suppressing an increase in the viscosity of natural rubber, wherein a triazole compound represented by the following formula (1) is added to the natural rubber to suppress an increase in the viscosity of the natural rubber.
_{R-C 2 H 2 N 3} ···· (1)
(In the formula (1), R represents a hydrogen group, an alkyl group having 1 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, or an aryl group. In addition, an amino group, mercapto group, or hydroxyl group is added to the triazole skeleton. , A carbonyl group or a benzo group may be added.) The method for suppressing the increase in viscosity of natural rubber according to claim 1, wherein the amount of the triazole compound added is 0.001 part by mass or more with respect to 100 parts by mass of natural rubber.