JPS591549A - Vulcanized rubber - Google Patents

Abstract

PURPOSE:To reduce dissipation factor without lowering dynamic storage elastic modulus, by swelling a vulcanized rubber contg. reinforcing carbon black and exhibiting high dynamic hysteresis loss with an extender oil mainly composed of low-molecular hydrocarbon. CONSTITUTION:30-70pts.wt. reinforcing carbon black is blended with 100pts.wt. raw rubber such as natural rubber or polyisoprene rubber. Then the rubber is vulcanized and impregnated with an extender oil mainly composed of low- molecular hydrocarbon to swell the rubber at a degree of swelling of 2-10wt%, thus obtaining the desired vulcanized rubber. By swelling the vulcanized rubber with the extender oil, neighboring carbon aggregates in the rubber are slightly separated from one another, whereby dynamic hysteresis loss is reduced. Hence, when used for tire tread rubber part, the rolling resistance of tire can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to vulcanized rubber, and more specifically, the dynamic storage modulus, that is, the deformation characteristics of vulcanized rubber, can be improved by swelling vulcanized rubber containing reinforcing carbon black with extension oil. This invention relates to a vulcanized rubber that has a significantly reduced loss factor without significantly decreasing it.

In recent years, there has been a need to reduce dynamic hysteresis losses in vulcanized rubber used in the tread portion of pneumatic tires in conjunction with the desire to develop low rolling resistance tires.

The vulcanized rubber of this tread part is related to wear resistance, exercise performance, etc., so a large amount of highly reinforcing carbon black (15 to 30 vot% of the vulcanized rubber) is used as a filler. Therefore, there is a problem in that the energy loss from the vulcanized rubber of the tread portion is large during dynamic conditions, and rolling resistance cannot be reduced.

Recently, there has been a strong demand for tires with significantly reduced rolling resistance, and efforts are being made to reduce the amount of reinforcing carbon black to meet this demand, but tires still do not have sufficiently low rolling resistance performance. In this case, there also arises a problem in the reinforcing properties of the vulcanized rubber.

Further, even if transfer resistance is significantly reduced, it is not preferable if other characteristics such as exercise performance are impaired.

Note that the energy loss characteristic of vulcanized rubber corresponding to transfer resistance has a frequency of around 10 to 20 Hz and an ambient temperature of 30 to 60° C., and the lower the dynamic strain value, the lower the transfer resistance. In addition, the evaluation of maneuverability, especially steering stability, is performed using the storage modulus (G') of vulcanized rubber, and if the storage modulus decreases within 40% at a dynamic strain of 5 inches, then Otherwise, the steering stability will not be impaired.

The present invention aims to significantly reduce the loss coefficient of vulcanized rubber containing reinforcing carbon black and having high dynamic hysteresis loss without significantly reducing the storage modulus, and is applied to tire trend sections. This greatly contributes to reducing the rolling resistance of tires.

The present inventors have conducted research to reduce dynamic hysteresis loss without significantly changing the various performances required of the vulcanized rubber in the tread, and have developed a vulcanized rubber containing carbon black, which has particularly strong reinforcing properties. We investigated the mechanism by which hysteresis loss occurs in sulfur rubber.

The mechanism by which this hysteresis loss occurs, which has been shown in various literature, is that vulcanized rubber f! The hysteresis loss was thought to be caused by the raw rubber, which is the main compounding agent, and the hysteresis loss caused by carbon black, but the present inventors have investigated the mechanism by which this occurs in detail. It was found that the following new mechanism is the main factor in practical vulcanized rubber for tread parts. In other words, dynamic strain condition 1 to 10% frequency condition 1 is applied to vulcanized rubber containing carbon black, which has strong reinforcing properties.
Dynamic hysteresis loss when applying dynamic deformation around ~3011z is mainly caused by energy consumption due to solid friction between carbon aggregates formed by aggregation of carbon black particles, and this friction causes hysteresis loss. It has become clear that this will occur. Furthermore, even if the carbon black content is reduced within a practical range, carbon aggregates may still be dispersed adjacent to each other on a microscopic scale, and mixing methods normally used in the rubber industry cannot completely remove the carbon aggregates. It is difficult to disperse it evenly. For these reasons, it has been difficult to reduce solid friction caused by mutual movement between carbon aggregates and hysteresis loss caused by this. After shredding, we conducted research on how far the distance between carbon aggregates should be to reduce the hysteresis loss caused by this, and found that the average size of carbon aggregates was 300.
Data was obtained inferring that dynamic hystericine loss would be reduced if the distance between the carbon aggregates was made very small compared to the case of 0A). People,
Solid friction can be evaluated by measuring the dynamic strain dependence of dynamic viscoelasticity (Rubber Chemistry and Technology, 51(3), pp. 437-52 (1978))
.

Based on the above viewpoint, the present inventors swelled the vulcanized rubber with extension oil, thereby causing the adjacent carbon aggregates in the vulcanized rubber to be slightly separated, thereby allowing the vulcanized rubber to achieve the above objective. This discovery led to the present invention.

That is, the gist of the present invention is that vulcanized rubber containing 50 to 70 parts by weight of reinforcing carbon black per 100 parts by weight of raw rubber is treated with an extender oil containing 2 to 10 parts by weight of reinforcing carbon black based on 100 parts by weight of raw rubber. Vulcanized rubber characterized by being swollen.

In the present invention, the extender oil that swells the vulcanized rubber includes all extender oils that are mainly composed of low-molecular hydrocarbons and are generally used in rubber compositions, and may be aromatic, paraffinic, or naphthenic. I don't mind. The swelling amount of vulcanized rubber is
It is necessary to have a weight ratio of 2 to 10. If the weight ratio is less than 2 weight ratio, the tackiness value will not substantially change and no effect will be obtained. On the other hand, when swelling exceeds 10% by weight, the loss coefficient (tan δ), which is a measure of hysteresis loss, decreases significantly, but the storage modulus (G') value changes significantly, and the unswollen vulcanized rubber It does not show properties similar to that of the conventional one, so the balance of various physical properties must be re-balanced.

The present invention does not aim at drastically changing the characteristics of tires in this way, but rather, it aims at achieving practical changes without significantly changing the characteristics of tread rubber required for vulcanized rubber used in tire treads. The purpose is to reduce energy loss characteristics.

In the present invention, the vulcanized rubber can be swollen by attaching extender oil to the vulcanized rubber and impregnating it, or by impregnating the adjacent rubber with extender oil before vulcanization and then migrating it to a predetermined level after vulcanization. There are two methods: a method of swelling the rubber to a weight ratio of

The raw material rubber used for the vulcanized rubber of the present invention is not particularly limited, but examples include natural rubber, polyisoprene rubber, styrene-butadiene copolymer comb, diene-based synthetic rubber such as polybutadiene rubber, and halogenated butyl rubber. Examples include combinations of at least one or more selected from the following.

In addition, in the vulcanized rubber of the present invention, it is desirable that the carbon black be contained in an amount of 30 to 70 parts by weight per 100 parts by weight of the raw material rubber, and the amount of iodine adsorption is 65 to 140 parts by weight.
mg/g1 dibutyl phthalate oil absorption is 85 cc/1
It is preferable that the weight is in the range of 00g or more.

In the present invention, other compounding agents which are commonly incorporated into tire tread rubber in the rubber industry, such as zinc oxide, stearic acid, anti-aging agent, carbon black, extender oil, and vulcanization accelerator, may be blended in appropriate amounts.

The present invention will be specifically described below based on Examples and Comparative Examples. The formulations in Table 1 are parts by weight.

Examples 1 to 2 and Comparative Examples 1 to 6 Rubber compositions having the formulations shown in Table 1 were mixed by a mechanical mixing method to prepare rubber compositions. This rubber composition was heated to 148°C.
After press vulcanization for 30 minutes, a vulcanized rubber sheet with a thickness of 2 mm was prepared and used as a sample for measuring viscoelastic properties.

Table 1 *1: Nippon Zeon Co., Ltd., *2: N-phenyl-N'-impropyl-p-phenylenediamine, *3: N-oxydiethylene-2-penzolyl sulfenamide, thus obtained The vulcanized rubber is an unswollen vulcanized rubber (Comparative Example 1). This vulcanized rubber was mixed with paraffin oil at 1.5% by weight (Comparative Example 2) and 5.5% by weight (Example 1).
, 16.2% by weight (Comparative Example 3), respectively. In this swelling method, the weight of the desired swelling oil is calculated in advance, and this is applied uniformly to both sides of the rubber sheet and left for about one week. After the vulcanized rubber was swollen, the dependence of the viscoelastic value on dynamic strain was measured using a viscoelastic spectrometer (manufactured by Oiki Seisakusho). The exact swelling weight percentage (%) was determined from the ratio of the sample weights before and after swelling before measurement. The measurement conditions were 30°C and 60°C, and a frequency of 20Hz.

Select 0.2%, 0.5%, 1%, 2%, 5% and 10% as the dynamic strain, and select the storage modulus (G') and loss coefficient (j
anδ) was measured.

For comparison, tan δ and G' of a swollen vulcanized rubber (Comparative Example 1) were measured and are shown in FIGS. 1 and 2. Comparative Example 2, which was swollen with 1.5% by weight of paraffinic oil, had the same characteristics as the unswollen vulcanized rubber of Comparative Example 1 (solid lines in Figures 1 and 2) and G' and t.
It was found that both anδ did not change significantly and the effect was small. Comparative Example 6, which swelled by 16.2% by weight, was tan
Although δ is significantly reduced, G' is also reduced by more than 40%, and in practical terms, it is necessary to rebalance various other physical properties. On the other hand, as shown in Figures 1 and 2, Example 1 (dotted chain line in Figures 1 and 2), which was swollen by 5.5% by weight with paraffin oil, was compared with Comparative Example 1. The tan δ was significantly reduced, and the reduction in G/ was also within an acceptable range.

4.5% by weight of aroma oil in the same manner as in Example 1
Swollen vulcanized rubber (Example 2 - dashed lines in Figures 1 and 2)
The tan δ and G' were measured and shown in FIGS. 1 and 2.

Example 1, which was swollen by 5.5% by weight with paraffinic oil, had a higher G′ at 50°C and 60°C than Comparative Example 1, which was not swollen.
The values are almost the same, and various mechanical properties do not change significantly, but the value of tan δ decreases significantly over a wide dynamic strain range. Therefore, in Example 1, the dynamic energy loss is significant. It can be seen that this has been reduced.

In Example 2, which was swollen by 4.5 weight coefficient with aromatic oil, as in Example 1, G' did not change sharply and the jan δ value decreased.

As is clear from the dynamic strain dependence of the viscoelastic properties in Figures 1 and 2, the dynamic strain dependence of G' and tanδ becomes flat due to swelling or temperature rise. This means that the solid friction between the carbon aggregates is reduced, and it is estimated that the distance between the carbon aggregates is actually slightly larger.

As explained above, the vulcanized rubber of the present invention, in which the vulcanized rubber containing carbon black is swollen by 2 to 10% by weight with extender oil, has a significantly reduced loss coefficient without significantly reducing its storage modulus. Therefore, it is suitably used in the tire tread portion and contributes to reducing the rolling resistance of the tire.

[Brief explanation of drawings]

Figure 1 shows the storage modulus (G
') and dynamic strain (%), and Figure 2 shows the loss coefficient (tan δ) of Examples 1 to 2 and Comparative Example 1.
Graph showing the relationship between dynamic strain (C%) and dynamic strain (C%). Note that the solid line indicates Comparative Example 1, the dashed line indicates Example 1, and the broken line indicates Example 2. Patent Applicant Yokohama Rubber Co., Ltd. Agent Patent Attorney Tatsuo Ito Agent Patent Attorney Tetsuya Ito (,9) Table 4

Claims (1)

[Claims] 1. A vulcanized rubber containing 30 to 70 parts by weight of reinforcing carbon black based on 100 parts by weight of raw rubber was swollen by 2 to 10 parts by weight with an extender oil whose main component is a low molecular weight hydrocarbon. Characteristic vulcanized rubber.