JPS6144892B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a deterioration inhibitor for rubber, specifically, general formula (A) (In the formula, R ₁ and R ₂ represent hydrogen or a lower alkyl group having 1 to 4 carbon atoms.) A compound consisting of diphenylamine (hereinafter sometimes referred to as DPA) or a derivative thereof, and N-phenyl- N'-tolyl-para-phenylenediamine, N-tolyl-N'-alkyl-para-phenylenediamine (alkyl group has 3 carbon atoms)
~8) Or natural rubber or a composition formed by mixing with N.N'-ditolyl-para-phenylenediamine, which significantly improves thermal aging and flex cracking during aging of rubber vulcanizates at high temperatures. This invention relates to anti-deterioration agents for synthetic rubber. Originally, natural rubber or synthetic rubber vulcanizates deteriorate due to factors such as oxygen, heat, ozone, and repeated mechanical fatigue, such as stickiness, hardening, and breakage when cut, making them unusable. These factors rarely act alone, and often two or more factors combine to deteriorate the properties of the rubber vulcanizate. In response to these deterioration phenomena, various deterioration inhibitors have been developed. However, none of the deterioration inhibitors used today is effective against all deterioration factors, and therefore two or three types of deterioration inhibitors are usually used in combination to take advantage of the strengths of each. It is. For example, 67% by weight of phenyl-β-naphthylamine ["Nonflex D" (trade name)] and N-N'-diphenyl-para-phenylenediamine [hereinafter sometimes referred to as "Nonflex H" (trade name)].
A mixed composition with 33% by weight [hereinafter referred to as "Nonflex P" (trade name)] is one of the typical deterioration inhibitors that prevents heat aging and flex cracking. As a result of the functional analysis of Nonflex P, which is a typical mixed composition, the present inventors found that
It has been discovered that a mixed composition of diphenylamine or its derivative and a para-phenylenediamine derivative is more effective than this in preventing heat aging and flex cracking of rubber vulcanizates. We have arrived at the present invention. In other words, diphenylamine has traditionally been considered to have a relatively excellent anti-thermal aging effect, but due to its strong sublimation properties, it lacks sustainability and its anti-thermal anti-aging effect deteriorates due to oxidative deterioration at high temperatures or long-term deterioration at low temperatures. is difficult to obtain, and therefore it is rarely used as a deterioration inhibitor for rubber. Therefore, as a result of research on diphenylamine, the present inventors found that
It was discovered that diphenylamine significantly suppresses the mechanical repeated fatigue of rubber vulcanizates, especially the growth of cracks caused by repeated bending.Furthermore, in order to suppress the sublimation property, which is a drawback of diphenylamine, a reaction product obtained by reacting diphenylamine with a lower olefin. The substance has less sublimation, so it not only has a long-lasting effect and has an anti-thermal aging effect, but also
It has also been found that the effect of preventing crack growth due to repeated bending is not lost at all compared to diphenylamine. In addition, the inventors are N.
As a result of analyzing the oxidation mechanism of N'-diphenyl-para-phenylenediamine, it was found that diphenylamine or its derivatives act as a regenerating agent for the former, further improving the antioxidant effect, and the sublimation property of diphenylamine It was confirmed that this can be suppressed by mixing with N.N'-diphenyl-para-phenylenediamine. Moreover, it has been found that the flex crack preventing effect of diphenylamine or its derivatives is not lost even when used in combination with N.N'-diphenyl-para-phenylenediamine. Furthermore, it was discovered that similar effects can be obtained with other para-phenylenediamine derivatives, leading to the completion of the present invention. The mixing ratio of the mixed composition used in the present invention, that is, diphenylamine or its derivative, and the para-phenylenediamine derivative is 90 to 30% by weight of the former and 10 to 70% by weight of the latter, preferably 80 to 70% by weight of the former. 50% by weight, and the latter is 20 to 50% by weight, and only with such a mixing amount can the effects of the present invention, which will be described later, be exhibited. The above mixed composition includes not only natural rubber but also styrene and butadiene copolymer rubber (SBR), polybutadiene rubber (BR), and polyisoprene rubber (IR).
It also has excellent heat aging and flex crack prevention effects on synthetic rubbers such as synthetic rubbers, and since vulcanization has no effect on these rubbers, scorch is not used during storage of rubber compounds at rubber factories. You can work safely during the machining process without worrying about it. Therefore, the present invention provides a compound represented by the above general formula (A) and the above N-phenyl-N'-tolyl-para-phenylenediamine, N-tolyl-N'-alkyl-para-phenylenediamine ( Alkyl group having 3 to 8 carbon atoms) or N・N'-ditolyl-para-
By using a mixed composition with phenylenediamine as an additive in rubber compounding, excellent heat aging prevention effects and flex crack prevention effects can be obtained. The amount of the mixed composition of the present invention added to the rubber is 0.5 to 5 parts by weight, preferably 0.7 to 3 parts by weight, per 100 parts by weight of the rubber. Note that the above para-phenylenediamine derivatives can not only be used as a single substance in a mixture with the compound represented by the general formula (A), but also any two or more of the above para-phenylenediamine derivatives can be used as a mixture. It is also possible to use the compound represented by the general formula (A) in combination with the compound represented by the general formula (A), and similar heat aging prevention effects and flex crack prevention effects can be obtained. Next, a method for producing the compound of general formula (A) used in the present invention will be illustrated. (a) Production of 4,4'-dimethyl-diphenylamine: 107 g of para-toluidine and 100 g of para-toluidine hydrochloride are reacted under pressure at 280°C for 6 hours, neutralized with sodium hydroxide, and distilled under reduced pressure to obtain 4.・59 g of 4'-dimethyl-diphenylamine (hereinafter referred to as product A) (melting point 76-78
°C) was obtained. (B) Production of 4,4'-diethyl-diphenylamine; 121 g of para-ethylaniline and 110 g of para-ethylaniline hydrochloride were reacted in the same manner as in (a) to produce 4,4'-diethyl-diphenylamine (hereinafter referred to as the product). 63g (referred to as substance B) (melting point 34-36
°C) obtained. (c) Production of 4,4'-di-tert-butyl-diphenylamine: 169 g of isobutylene is introduced and absorbed into 255 g of diphenylamine and 24 g of anhydrous aminium chloride at 125-130°C. When the reactant is washed with dilute hydrochloric acid, water, and sodium carbonate water and made neutral, it is distilled under reduced pressure.
201 g of 4,4'-di-tert-butyl-diphenylamine (hereinafter referred to as product C) (melting point 102
~106°C) was obtained. The mixture shown in Table 1 obtained by mixing the products A, B, and C obtained by the methods (a), (b), and (c) above with the para-phenylenediamine derivatives shown below, respectively. Heat aging tests and bending tests were conducted on samples in which the composition was blended with natural rubber and synthetic rubber in the same manner as general rubber compounding agents and vulcanized. As a result, excellent heat aging prevention effects and bending The crack prevention effect was recognized. Examples of para-phenylenediamine derivatives include (i) N.N'-ditolyl-para-phenylenediamine (DT-PPDA) (ii) N-phenyl-N'-tolyl-para-phenylenediamine (PT- PPDA) (iii) N-tolyl-N'-isopropyl-para-phenylenediamine (TIP-PPDA) (iv) N-tolyl-N'-1-ethyl-3-methylpentyl-para-phenylenediamine (TEMP
−PPDA).

[Table] Next, the anti-deterioration agent for rubber of the present invention will be specifically explained with reference to Examples. Example 1 A mixed composition as shown in Table 1 was prepared, and ingredients were added in the proportions shown in Table-2. That is, natural rubber and compounding agents were kneaded using an 8-inch roll at 50 to 60°C by a generally known method. The resulting mixture was press-vulcanized at 140°C for 20 minutes to prepare a sample. Heat aging was carried out in accordance with JIS K-6301 at 100° C. for 48 hours using a test tube heat aging tester.
The bending test was conducted in accordance with JIS K-6301, and scratches with an original length of 2 mm were
I read the number of bends until it reached 15mm. These results are shown in Table-2. Example 2 Compounding agents were blended into styrene-butadiene copolymer rubber (SBR) in the proportions shown in Table 3. That is, the mixture was kneaded in the same manner as in Example 1. The resulting mixture was press-vulcanized at 160°C for 15 minutes to prepare a sample. Heat aging was carried out in the same manner as in Example 1. The bending test was performed in the same manner as in Example 1, in which the maximum distance between the grips was 75 mm and the minimum distance was 31 mm.
The reciprocating motion was made such that These results are shown in Table-3. In the above Examples 1 and 2, DPA, DT-
A comparison was made using PPDA and dioctylated diphenylamine (octylated DPA). Here, the rate of change in 200% modulus, tensile strength, and elongation after heat aging is as follows: Rate of change = Value after heat aging - Value before heat aging / Value before heat aging ×
100(%), and the change in hardness was determined using the formula: change = value after heat aging - value before heat aging.

【table】

【table】

【table】

[Table] Heat aging resistance is determined by comparing each physical property before and after heat aging, and the rate of change or hardness of each physical property is expressed as a change value. Then, those with a small rate of change or change are judged to have excellent heat resistance. However, in the case of rubber products, particular emphasis is placed on the rate of change in tensile strength and elongation, and these rates of change are required to be as small as possible. and,
If the value is 2 to 3%, it can be judged that there is an anti-thermal aging effect, and if it is 10%, it is judged to have a significant effect, so the industrial value is very high. No.1, No.2, No.3, No.8 in Table-2,
The rate of change in tensile strength and elongation of No. 9 is shown in Figure 1, and No. 1, No. 2, and
The tensile strength and elongation change rates of No. 3, No. 10, and No. 11 are shown in Figure 2. It can be seen from FIGS. 1 and 2 that by mixing DPA and DT-PPDA, which do not have very good heat aging resistance, a more remarkable heat aging resistance can be obtained than both. Also, in that mixing ratio, DPA:DT
The maximum point is found near the -PPDA ratio of 2:1, and it can be seen that particularly excellent effects can be obtained with this mixing ratio. Furthermore, as shown in other examples in Tables 2 and 3, this combined effect is demonstrated by combining other lower alkylated diphenylamines with DT-PPDA or other
It can be seen that similar effects can be obtained when mixed with PPDA-based compounds. Next, we examined the effect of preventing crack growth due to repeated bending (hereinafter referred to as flex crack growth resistance), and found that diphenylamine had a particularly excellent effect, but paraphenylenediamine compounds did not have a very good effect. Not shown. This is shown in Table-
This is also clear from the comparative examples in Table 2 and Table 3. In this flex crack growth resistance, the above two
Mixing these materials has excellent resistance to flex crack growth.
It must be considered that the addition amount of DPA will be reduced and the flex crack growth resistance will be significantly reduced. However, in the mixture of the present invention, its flex crack growth resistance shows an effect comparable to that of using DPA alone. Here, when dioctylated diphenylamine is used as a typical example of higher alkylated diphenylamine that is generally used as a heat aging inhibitor for rubber, it has better heat aging resistance than DPA due to its low volatility, but it has a higher resistance to flex cracking. It can be seen that the growth rate is quite poor. The mixture of the present invention exhibits remarkable effects not only in flex crack growth resistance but also in heat aging resistance, compared to higher alkylated diphenylamines. As explained above, the anti-deterioration agent for rubber of the present invention exhibits various excellent effects as described below. (i) Since diphenylamine represented by the general formula (A) or its lower alkyl derivative is mixed with para-phenylene diamine, the volatility of diphenylamines can be suppressed by para-phenylene diamines, and flex crack growth resistance is achieved. It has now become possible to use diphenylamine or its lower alkyl derivatives, which have excellent properties but are rarely used due to their volatility. (ii) Conventionally, in order to alkylate diphenylamine to lower its volatility so that it can be used alone, diphenylamines generally have 8 or 9 carbon atoms.
However, in the present invention, lower alkylation with 1 to 4 carbon atoms is used, so the volatility is suppressed to some extent and the flex crack growth resistance is poor. Crack growth is not lost. (iii) Para-phenylene diamines have poor flex crack growth resistance when used alone and are used exclusively as anti-ozonation inhibitors, and when used in combination with diphenylamine, the proportion of diphenylamine is reduced, resulting in poor flex crack growth resistance. Although it is expected that the growth property will be lowered, when the two are mixed as in the present invention, a flex crack growth resistance substantially equivalent to that of diphenylamine can be obtained. (iv) Diphenylamine or its lower alkyl derivative acts as a regenerant for para-phenylenediamine, and exhibits better heat aging resistance than when each is used alone.

[Brief explanation of the drawing]

Figures 1 and 2 are comparison diagrams of the rate of change in tensile strength and elongation before and after heat aging in Examples and Comparative Examples. Figure 1 shows an example of natural rubber compounding, and Figure 2 shows a synthetic rubber compounding example. Give an example.

Claims (1)

[Claims] 1 General formula (A) (wherein R ₁ and R ₂ represent hydrogen or a lower alkyl group having 1 to 4 carbon atoms) 90 to 30% by weight of a compound consisting of diphenylamine or a derivative thereof represented by the formula:
N'-tolyl-para-phenylenediamine, N-
Tolyl-N'-alkyl-para-phenylenediamine (alkyl group has 3 to 8 carbon atoms) or N.
10 of N'-ditolyl-para-phenylenediamine
A deterioration inhibitor for rubber consisting of a composition mixed with ~70% by weight.