JP5219235B2 - Natural rubber mastication method - Google Patents

Description

  The present invention relates to a natural rubber mastication method, and more particularly to a natural rubber mastication method capable of improving the efficiency of mastication of natural rubber without deteriorating the performance of products, particularly tires.

  In general, natural rubber has a higher molecular weight than synthetic rubber, so it is difficult to uniformly knead various compounding agents in a rubber product factory. Therefore, natural rubber is kneaded with a small amount of a kneading accelerator. However, an operation for lowering the rubber molecular weight to an appropriate size is required. This operation is called “scouring”.

  When kneading, heat is generated as the kneading is promoted, and the temperature of the kneaded rubber compound rises. For the purpose of avoiding problems such as rubber burning caused by the increase in temperature, a peptizer (peptizer) is usually added after natural rubber is charged into a Banbury mixer.

  However, since the temperature rise of the natural rubber kneaded product cannot be sufficiently suppressed only by the cooling efficiency of the Banbury mixer itself, the process of dropping from the Banbury mixer to the under roller in one to three minutes and taking it out is usually performed several times. It is common to repeat the process in multiple stages.

After such mastication is completed, carbon black, a vulcanizing agent, oil or the like is added to the raw natural rubber and kneaded with a Banbury mixer or the like. Various kneading methods are known for this kneading. In general mixing and kneading procedures, as a first step, non-pro kneading is performed in which a raw rubber and a rubber compounding agent excluding a vulcanizing agent are kneaded by a Banbury mixer. After being discharged from the Banbury mixer and sufficiently cooled, the kneaded rubber is transferred to the Banbury mixer, and a rubber compounding agent containing a vulcanizing agent is added and further kneading is performed. Here, non-pro kneading is intended to sufficiently disperse carbon black and the like, and pro kneading is mainly intended to sufficiently disperse vulcanizing agent and the like. (Patent Document 1).
JP 10-1119036 A

  For truck and bus radial tires (TBR) and construction vehicle radial tires (OR), high-reinforcing carbon black is applied to improve the wear resistance of the tread rubber. This increased the productivity from the refining process to the extrusion process.

  In order to keep the viscosity of the professional kneaded rubber low, it has been known that a large amount of carbon black is added in the kneading process, for example, 10 to 20 parts by mass with respect to 100 parts by mass of the rubber, thereby reducing the kneading process. However, since the performance of the tire, particularly the wear resistance, cannot be ensured, it has not been put to practical use.

  Accordingly, an object of the present invention is to provide a natural rubber mastication method capable of solving the above-mentioned problems and improving the natural rubber mastication efficiency without causing deterioration of product performance.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by adding a small amount of carbon black when kneading natural rubber with a Banbury mixer. It came to complete.

  That is, the natural rubber mastication method of the present invention is a natural rubber mastication method in which a raw rubber containing natural rubber as a main rubber component is masticated with a Banbury mixer, and carbon black is added to the raw rubber during mastication. 5 to 10 parts by mass with respect to 100 parts by mass of the raw rubber, and in the first step of kneading, the carbon black is added after masticating only the raw rubber for 30 to 45 seconds. To do.

  In the present invention, the time for the first step of mastication is preferably 1.2 to 1.5 times the time required when carbon black is not added, and the energy required for mastication is not added with carbon black It is preferable to make it 1.2 to 1.5 times the energy required sometimes. Moreover, in this invention, a mastication process can be comprised suitably from 2 processes.

  According to the present invention, it is possible to improve the efficiency of mastication of natural rubber without causing deterioration of product performance, particularly tire wear resistance.

Hereinafter, embodiments of the present invention will be specifically described.
In the present invention, in a natural rubber mastication process in which a raw rubber containing natural rubber as a main rubber component is masticated by a Banbury mixer, carbon black is added to the raw rubber at 100 mass parts of the raw rubber during mastication. It is important to add 10 parts by mass.

  The present invention is particularly suitable for kneading, in which natural rubber is compounded in a large amount like TBR and OR, and an increase in the number of mastication steps is inevitable, and the efficiency of such mastication is improved. Therefore, the raw rubber has natural rubber as a main rubber component. Preferred examples of other rubber components that can be blended include polybutadiene rubber, polyisoprene rubber, EPDM rubber, halogenated butyl rubber, butyl rubber, acrylonitrile-butadiene rubber, acrylonitrile-styrene-butadiene rubber, and the like. Moreover, thiophenol, a disulfide, etc. which are normally used as a peptizer (peptizer) can be suitably added to raw rubber.

  Also, by adding 5 to 10 parts by mass of carbon black to 100 parts by mass of the raw material rubber and kneading, the kneaded product is obtained without impairing the performance of the tire as a product, particularly the wear resistance. As a result, the total number of mastication steps can be reduced. Here, if the amount of carbon black added is less than 5 parts by mass, the effect of reducing the viscosity of the kneaded product is small. On the other hand, if it exceeds 10 parts by mass, the performance of the tire as a product, particularly the wear resistance, cannot be ensured.

  In the present invention, the time required for the first step of mastication is preferably 1.2 to 1.5 times the time required when carbon black is not added, that is, the time of the first step of conventional mastication, In particular, it is about 1.5 times. As a result, the performance of the tire as a product, particularly the wear resistance, can be ensured satisfactorily. Particularly preferably, carbon black is added for about 15 seconds after mastication of only the raw rubber for 30 to 45 seconds in the first step of mastication, and then mastication is further performed for 30 to 45 seconds. At this time, the energy required for mastication is preferably 1.2 to 1.5 times the energy required when carbon black is not added, that is, the energy required for conventional mastication. Thereby, in this invention, the number of processes of the conventional mastication can be reduced, without impairing the performance of a product tire, Preferably it can carry out in two processes.

  Among the various conditions of the Banbury mixer that can be used in the present invention, the fill factor representing the substantial contrast ratio excluding the volume of the rotor portion of the Banbury mixer is 50 to 80%, the rotational speed of the rotor is 8 to 80 rpm, and the temperature is The temperature may be 150 to 180 ° C., and these conditions are not particularly limited.

Next, the present invention will be described specifically and in detail based on examples and comparative examples.
Example In the first step of kneading with a Banbury mixer, first, mastication of only natural rubber as a raw rubber was performed for 45 seconds, then carbon black was added over about 15 seconds, and then masticated for another 30 to 45 seconds. Other than having performed, practiced according to the ordinary method. At this time, the energy required for mastication was 1.5 times the energy required for conventional mastication without adding carbon black.

  Next, the kneaded product was dropped from the Banbury mixer onto the under roller, taken out, and the second mastication was performed for 60 seconds in accordance with a conventional method to obtain a final kneaded product.

Comparative Example In the first step of mastication with a Banbury mixer, mastication was carried out in the same manner as in Example except that mastication was carried out for 60 seconds without adding carbon black and this mastication was carried out three times in total. It was. Note that the energy required for mastication in the examples is 1.5 times the energy required for mastication in this comparative example.

  The kneaded products obtained in the examples and comparative examples were subjected to non-pro kneading in which a rubber compounding agent excluding the vulcanizing agent was kneaded with a Banbury mixer according to a conventional method, and then the non-pro kneaded materials were discharged from the Banbury mixer and cooled sufficiently. After that, the cooled non-pro kneaded product was transferred to a Banbury mixer, and a rubber compounding agent containing a vulcanizing agent was added and further kneading was performed.

FIG. 1 shows the relationship between the molecular weight of the kneaded materials of Examples and Comparative Examples and the viscosity of the subsequent kneaded products. Moreover, the carbon black dispersibility, viscosity, productivity, and abrasion resistance of the pro-kneaded products obtained in Examples and Comparative Examples were evaluated as follows.
(1) Carbon black dispersibility The X value of the RCB method measured using DISPERGRADER manufactured by Tech Pro, USA was used as an index. The greater the value, the better the dispersibility.
(2) Viscosity According to JIS K6300, Mooney viscosity ML _{1 + 4} was measured by preheating for 1 minute and measuring for 4 minutes.
(3) Productivity Productivity was evaluated based on the processing time per ton of raw rubber.
(4) Abrasion resistance A tire was produced using a pro-kneaded product as a tread rubber, and the produced tire was mounted on an actual vehicle and traveled on an actual vehicle. .
The obtained results are shown in Table 1 below.

  From FIG. 1, it can be seen that the example is superior in the viscosity reducing effect as compared with the comparative example. Moreover, it can be seen from Table 1 that productivity is improved without impairing wear resistance in the examples.

It is a graph which shows the relationship between the molecular weight of kneaded material, and the viscosity of subsequent professional kneaded material.

Claims (4)

In a natural rubber mastication method in which a raw rubber containing natural rubber as a main rubber component is masticated with a Banbury mixer, 5 to 10 parts by mass of carbon black is added to the raw rubber at 100 parts by mass during the mastication. And, in the first step of mastication, the carbon black is added after mastication of only the raw rubber for 30 to 45 seconds .   The method for masticating natural rubber according to claim 1, wherein the time of the first step of mastication is 1.2 to 1.5 times the time required when carbon black is not added.   The method for masticating natural rubber according to claim 1 or 2, wherein the energy required for mastication is 1.2 to 1.5 times the energy required when carbon black is not added. The natural rubber mastication method according to any one of claims 1 to 3 , wherein the mastication step comprises two steps.

Images