JP5420891B2 - Manufacturing method of natural rubber masterbatch - Google Patents

Description

  The present invention relates to a method for producing a natural rubber wet masterbatch using natural rubber latex and carbon black, and a rubber composition using the same.

As a method for producing rubber having superior dispersibility and processability than conventional, as shown in Patent Document 1, natural rubber latex and a filler slurry such as carbon black are mixed, and a mixture of natural rubber and filler by a coagulant. A method for producing a so-called wet masterbatch is known, in which the solidified product is separated from water. This method has an advantage that the dispersibility and processability of the carbon black with respect to the rubber component are superior to a so-called dry masterbatch using a kneading roll or the like.
Patent Registration No. 2633913

  By the way, it is known that in an elastomer such as natural rubber in which carbon black is dispersed, the reinforcing effect increases as the particle size of the carbon black decreases. However, how to disperse the carbon black in the masterbatch when changing the particle size of the rubber particles in the natural rubber latex and the particle size of the carbon black in the carbon black slurry when manufacturing the wet masterbatch. It is unclear how it affects the properties such as processability, low heat build-up and fatigue resistance of the rubber composition using it.

  Therefore, in the present invention, in view of the above problems, by adjusting the particle size of the rubber particles in the natural rubber latex and the particle size of the carbon black in the carbon black slurry, the carbon black is excellent in dispersibility and blended into the rubber composition. Sometimes, it aims at providing the manufacturing method of the natural rubber masterbatch which can improve workability, low heat build-up, and fatigue resistance.

  As a result of intensive studies by the present inventors to solve the above-mentioned problems, a slurry in which carbon black is dispersed in water while maintaining a constant relationship with the particle size of the rubber particles in the natural rubber latex (hereinafter referred to as “the slurry”) By making the carbon black particle size in the carbon black slurry below a certain particle size, the dispersibility of the carbon black particles in the masterbatch is greatly improved, and the rubber composition using such a masterbatch is processed. The present invention has been completed by finding that characteristics such as heat resistance, low heat build-up and fatigue resistance are improved.

That is, the method for producing a natural rubber masterbatch according to the present invention comprises mixing a natural rubber latex and a slurry in which carbon black is dispersed in water, and coagulating and mixing the mixture of natural rubber and carbon black from the resulting mixture. A method for producing a masterbatch including a step of separating, wherein 90% by volume particle size (D90 _CB ) of carbon black in the slurry is 10 μm or less, and 90% by volume particle size of rubber particles in the rubber latex. _{(D90 NR)} ratio of 90 volume% particle size of the carbon black in the slurry for _(D90 CB / D90 _NR) is characterized in that 0.1 to 20.

The coagulated product (masterbatch) obtained by the above process has high dispersibility of carbon black, and when blended in a rubber composition, it becomes possible to improve processability, low heat buildup, fatigue resistance, and the like. . _{Incidentally, D90} CB / D90 _NR is more preferably 0.5 to 10.

  In order to adjust the particle size of the rubber particles in the natural rubber latex and the particle size of the carbon black in the slurry to the above ranges, it is preferable to perform a dispersion treatment on the natural rubber latex and / or the carbon black slurry. Thereby, the particles can be appropriately miniaturized while dispersing the rubber particles and the carbon black particles in the aqueous phase.

  As described above, the rubber composition using the natural rubber masterbatch obtained according to the present invention is excellent in processability, fatigue resistance and low heat build-up, so that it is used for tires such as tire dread rubber and sidewall rubber. It can be suitably used for various rubber compositions including rubber compositions.

  In the present invention, in a method for producing a masterbatch comprising a step of mixing natural rubber latex and carbon black slurry, and coagulating / separating the mixture of natural rubber and carbon black, 90% by volume particle size of carbon black in the slurry In this master batch, the ratio of the 90% by volume particle size of carbon black in the slurry to the 90% by volume particle size of rubber particles in the rubber latex was 0.1-20. The processability, low heat build-up and fatigue resistance of the rubber composition using can be improved.

  Hereinafter, embodiments of the present invention will be described. In the present invention, before the natural rubber latex and the carbon black slurry are mixed, the natural rubber latex and the carbon black slurry are subjected to a dispersion treatment as necessary. The dispersion treatment can be performed using a high shear (rotor / stator) mixer, a homogenizer, a colloid mill, or the like. These devices can make particles finer by increasing the number of rotations or extending the processing time.

  The carbon black slurry is obtained by mixing carbon black and water, forming the appearance slurry using the dispersion processing apparatus, and then continuing the treatment to atomize the carbon black agglomerated particles. The concentration of carbon black in the slurry is preferably 1% by weight to 20% by weight, and more preferably 3% by weight to 15% by weight. As the carbon black, SAF, ISAF, HAF, FEF, GPF and the like known for rubber compounding can be used, but are not limited thereto. Further, a dispersing agent (for example, Kao-made Demol N) may be added to the carbon black slurry. About natural rubber latex, a rubber particle can be atomized more by performing a dispersion process as needed.

  After mixing the carbon black slurry and the natural rubber latex with an appropriate stirring device, the mixture of natural rubber and carbon black is coagulated and separated using a coagulant such as an acid such as formic acid or a metal salt such as aluminum sulfate. In this case, if a stirring device that can give a strong impact to the mixed solution such as a high shear (rotor / stator) mixer or a homogenizer used in the dispersion processing device is used, the mixture is solidified without using a coagulant. be able to. Of course, a coagulant may be used at this time.

  The coagulated product obtained as described above is finally subjected to a drying treatment to evaporate moisture contained therein, whereby a natural rubber master batch is finally obtained.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, unless this invention exceeds the summary, it is not limited to these Examples.

  In this example, natural rubber (NR) latex and carbon black (CB) slurry were subjected to dispersion treatment under various conditions, and then both were mixed and the mixture of natural rubber and carbon black was coagulated with formic acid. A master batch was prepared.

Predetermined other components were added to the prepared master batch to prepare a rubber composition, and each rubber composition was subjected to an evaluation test of dispersibility, workability, fatigue resistance, and heat generation (Examples 1 to 3, Reference Examples 1 to 3 and Comparative Examples 1 to 7). The details are described below.

[Production of natural rubber masterbatch]
As the carbon black slurry, SAF grade carbon black (Tokai Carbon Seast 9 (N110)) is used as carbon black, and this is measured so that a predetermined amount of water (the content of carbon black in the slurry is 25% by weight). ), And dispersion treatment was carried out using a robot mix (high shear mixer) manufactured by PRIMIX.

  As the natural rubber latex, concentrated latex (Rubber concentration: DRC (Dry Rubber Content) 60%) manufactured by Resitex Corporation was used. The natural rubber latex was adjusted to have a DRC of 25%, and this was dispersed as necessary. The natural rubber is not limited to this, and field latex or the like can be used.

  The volume average diameter (MV) and 90 volume% particle diameter (D90) of the carbon black particles in the prepared carbon black slurry and the rubber particles in the natural rubber latex were measured. For the measurement, a particle size distribution meter (SALD-2200) manufactured by Shimadzu Corporation was used. The refractive index of carbon black particles was measured as 2.00-0.10i, and the refractive index of natural rubber particles was measured as 1.60-0.10i.

  Various carbon black slurries and natural rubber latexes having different MV and D90 were produced by changing the dispersion treatment conditions, and these were combined to produce a natural rubber master batch.

  Specifically, 1000 parts by weight of carbon black slurry (of which 50 parts by weight of carbon black) is added to 400 parts by weight of natural rubber latex (of which 100 parts by weight of rubber component). Mixing was performed using a tabletop quick homomixer (LR-1) (11300 rpm × 2 min).

  While stirring the liquid mixture thus obtained, 0.1 g of formic acid (0.1% by weight with respect to 100 parts by weight of the rubber component) was added as a coagulant to coagulate the mixture of natural rubber and carbon black. A natural rubber masterbatch was obtained by drying the coagulated product (120 ° C. × 120 min).

  A rubber composition was prepared using 13 kinds of natural rubber master batches obtained under different dispersion treatment conditions. The composition of the rubber composition is 1 part by weight of stearic acid (manufactured by Nippon Oil & Fats), 1 part by weight of anti-aging agent (6PPD made by Monsanto), 150 parts by weight of natural rubber masterbatch (of which 100 parts by weight of rubber component), zinc white 3 parts by weight (Mitsui Kinzoku No. 1), 1 part by weight of wax (manufactured by Nippon Seiwa), 2 parts by weight of sulfur (manufactured by Tsurumi Chemical Co., Ltd.), and 1 part by weight of accelerator (CBS made by Sanshin Chemical) .

[Evaluation test]
Each rubber composition was evaluated for dispersibility, workability, fatigue resistance, and heat generation. The vulcanization conditions for the rubber composition were 150 ° C. × 30 min.
(1) Dispersibility Measured according to ASTM D2663-69 (Method B).
(2) Fatigue resistance Measured according to JIS K6270 and displayed as an index with the characteristic value of Comparative Example 1 in Table 1 described later as 100. The larger the index, the better the fatigue resistance.
(3) Exothermic property Measured according to JIS K6265, and displayed as an index with the characteristic value of Comparative Example 1 in Table 1 described later as 100. The smaller the index, the lower the heat generation temperature and the lower the heat generation.
(4) Workability Measured according to JIS K6300-1 and displayed as an index with the characteristic value of Comparative Example 1 in Table 1 described later as 100. A smaller index indicates a lower Mooney viscosity and better processability.
(5) Dispersibility of carbon black in masterbatch (Phillips method)
Apart from the dispersibility of carbon black in the rubber composition according to ASTM D2663-69 (Method B), the dispersibility of the carbon black in the masterbatch (Phillips method) was evaluated. The dispersibility by the Philips method was evaluated using a dispersator (manufactured by Tech Pro) from the X value of the RCB method. It shows that it is excellent in the dispersibility, so that this value is large.

[Evaluation results]
Table 1 shows the dispersion treatment conditions of the natural rubber latex and the carbon black slurry, and the measurement results of the properties of the rubber composition.

表１よりカーボンブラックスラリー中のカーボンブラックのＤ９０_ＣＢ＞１０μｍでは凝集塊（アグロメレート）がまだかなり残存し、物性の大きな改良効果は見られない。

From Table 1, when D90 _CB > 10 μm of the carbon black in the carbon black slurry, agglomerates (agglomerates) still remain and no significant improvement in physical properties is observed.

On the other hand, physical properties (dispersibility, workability, fatigue resistance, and heat generation) are greatly improved in Examples 1 to 3 . This is thought to be due to the fact that the aggregates (agglomerates) are reduced and the natural rubber particles and the carbon black particles are in a relatively close range, so that they are easily mixed uniformly by interaction. (Refer to the evaluation results of dispersibility in Examples 1 to 3 ).

Even when D90 _CB <10 μm, when D90 _CB / D90 _NR exceeds 20, no significant improvement effect of physical properties is observed (Comparative Example 3). Further, it is technically difficult to make D90 _CB / D90 _NR less than 0.1, and D90 _CB / D90 _NR is 0. 0 in consideration of productivity and physical properties of the obtained rubber composition. It is preferable to set it as 5-10.

Claims (4)

A method for producing a masterbatch comprising a step of mixing a natural rubber latex and a slurry in which carbon black is dispersed in water, and coagulating / separating a mixture of natural rubber and carbon black from the obtained mixed solution, The 90 volume% particle size of the carbon black in the slurry is 1 μm or less, and the ratio of the 90 volume% particle diameter of the carbon black in the slurry to the 90 volume% particle diameter of the rubber particles in the rubber latex is 0.00. method for producing a natural rubber master batch, which is a 1-1. The method for producing a natural rubber masterbatch according to claim 1, wherein the natural rubber latex and / or the slurry is subjected to a dispersion treatment. A natural rubber masterbatch produced by the method according to claim 1 or 2. A rubber composition using the natural rubber masterbatch according to claim 3.