Masterbatch Manufacturing Method and Tire Manufacturing Method

Abstract

A masterbatch manufacturing method comprises an operation in which at least a filler slurry and a natural rubber latex are mixed to prepare a liquid mixture, and an operation in which a coagulant is added to the liquid mixture so as to cause pH to be not less than 5.0 but less than 8.0.

Claims

1. A masterbatch manufacturing method, comprising: an operation in which at least a filler slurry and a natural rubber latex are mixed to prepare a liquid mixture; and an operation in which a coagulant is added to the liquid mixture so as to cause pH to be not less than 5.0 but less than 8.0.

2. The masterbatch manufacturing method according to claim 1 wherein the filler slurry comprises carbon black.

3. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the coagulant is added to the liquid mixture, the coagulant is added to the liquid mixture so as to cause pH to be not less than 5.1.

4. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the coagulant is added to the liquid mixture, the coagulant is added to the liquid mixture so as to cause pH to be less than 7.8.

5. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the coagulant is added to the liquid mixture, the coagulant is added to the liquid mixture so as to cause pH to be less than 7.6.

6. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the coagulant is added to the liquid mixture, the coagulant is added to the liquid mixture so as to cause pH to be less than 7.4.

7. The masterbatch manufacturing method according to claim 1 wherein the coagulant is acid.

8. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the liquid mixture is prepared, the filler slurry and the natural rubber latex are combined so as to cause there to be not less than 10 parts by mass but not greater than 100 parts by mass of filler in the filler slurry per 100 parts by mass of dry rubber content in the natural rubber latex.

9. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the liquid mixture is prepared, the filler slurry and the natural rubber latex are combined so as to cause there to be not less than 20 parts by mass but not greater than 90 parts by mass of filler in the filler slurry per 100 parts by mass of dry rubber content in the natural rubber latex.

10. The masterbatch manufacturing method according to claim 1 wherein, at the operation in which the liquid mixture is prepared, the filler slurry and the natural rubber latex are combined so as to cause there to be not less than 30 parts by mass but not greater than 80 parts by mass of filler in the filler slurry per 100 parts by mass of dry rubber content in the natural rubber latex.

11. The masterbatch manufacturing method according to claim 1 further comprising: an operation in which an extruder is used to dewater a coagulum obtained by coagulation of the liquid mixture.

12. A tire manufacturing method comprising: an operation in which a masterbatch is prepared by the masterbatch manufacturing method according to claim 1; an operation in which the masterbatch is used to prepare a rubber composition; and an operation in which the rubber composition is used to prepare an unvulcanized tire.

13. The tire manufacturing method according to claim 12 wherein the operation in which the rubber composition is prepared comprises kneading at least the masterbatch and a compounding ingredient to prepare a rubber mixture, and kneading at least the rubber mixture and sulfur to obtain the rubber composition.

Description

WORKING EXAMPLES

[0064] Working examples in accordance with the present invention are described below. Hereinbelow, note that masterbatch is sometimes referred to as “MB”.

[0065] The raw materials and reagents that were used at the Working Examples are indicated below. [0066] Concentrated natural rubber latex (dry rubber content=31.2%; Mw=232,000) Manufactured by Golden Hope [0067] Carbon black “SEAST 9” manufactured by Tokai Carbon Co., Ltd.

Preparation of Masterbatch at the Various Examples

[0068] Water was added to concentrated natural rubber latex manufactured by Golden Hope to prepare a dilute natural rubber latex having a dry rubber content of 0.5 mass %, and a natural rubber latex having a dry rubber content of 25 mass %. Carbon black was added to this dilute natural rubber latex, and an agitator (Flashblend) manufactured by Silverson was used to carry out agitation at 3600 rpm for 30 minutes to prepare a carbon black slurry (hereinafter, this operation is sometimes referred to as “Operation (I)”). The natural rubber latex having the dry rubber content of 25 mass % was added to this carbon black slurry in accordance with TABLE 1 (that is, natural rubber latex was added to carbon black slurry so as to produce the blended amounts in TABLE 1), and a mixer (SMV-20 Supermixer) manufactured by Kawata Co., Ltd., was used to carry out agitation as this was heated in accordance with the conditions shown in TABLE 1 (hereinafter, this operation is sometimes referred to as “Operation (II)”). Next, as the liquid mixture was made to undergo agitation, coagulant—more specifically, a 10 mass % aqueous solution (pH 1.2) of formic acid—was added to the liquid mixture in a quantity sufficient to cause the pH to be value shown in TABLE 1 (hereinafter, this operation is sometimes referred to as “Operation (III)”). The coagulum formed as a result hereof was separated from the coagulation liquid (i.e., waste liquid). A squeezer-type single-screw dewatering extruder (Model V-02 screw press manufactured by Suehiro EPM Corporation) was used to dewater the coagulum at 200° C. That is, after the coagulum was made to undergo compaction by the squeezer-type single-screw dewatering extruder, it was plasticized as it was made to undergo drying at 200° C. Masterbatch was obtained as a result of such procedure.

Loss in Weight Due to Heating

[0069] As an index of the efficiency with which water was content was reduced, loss in weight due to heating of the coagulum following dewatering, i.e., loss in weight due to heating of the masterbatch, was evaluated. More specifically, an MX-50 heating-and-drying-type moisture analyzer manufactured by A&D Company, Limited, was used to measure the loss in weight due to heating of masterbatch in accordance with JIS K 6238-2. In other words, the volatile component was measured in accordance with JIS K 6238-2. The lower the loss in weight due to heating the lower the water content of the coagulum following dewatering, i.e., the water content of the masterbatch.

Loss in weight due to heating={(mass of MB before heating−mass of MB after heating)/(mass of MB before heating)}×100

Clogging of Inlet Port

[0070] Whether clogging occurred at the inlet port when a squeezer-type single-screw dewatering extruder was operated for 20 minutes was recorded.

TABLE-US-00001 TABLE 1 Comparative Working Working Comparative Comparative Working Example 1 Example 1 Example 2 Example 2 Example 3 Example 3 Blended amount Component blended in MB Carbon black 50 50 50 50 40 40 Natural rubber (dry rubber content) 100 100 100 100 100 100 Various conditions at Operation (II) and Operation (III) Agitation time (minutes) while carrying out heating at Operation (II) 30 30 30 30 30 30 Heating temperature (° C.) at Operation (II) 150 150 150 150 150 150 pH of coagulation liquid following addition of acid at Operation (III) 4.2 5.2 6.9 8.5 4.0 5.1 Agitator vane circumferential speed (m/s) at Operation (II) 9 9 9 9 9 9 Amount of heat at Operation (II) 47 47 47 47 47 47 Evaluation Loss in weight due to heating (%) 2.5 0.4 0.4 — 3.2 0.4 Clogging of inlet port No No No Yes No No Working Comparative Comparative Working Working Comparative Example 4 Example 4 Example 5 Example 5 Example 6 Example 6 Blended amount Component blended in MB Carbon black 40 40 30 30 30 30 Natural rubber (dry rubber content) 100 100 100 100 100 100 Various conditions at Operation (II) and Operation (III) Agitation time (minutes) while carrying out heating at Operation (II) 30 30 30 30 30 30 Heating temperature (° C.) at Operation (II) 150 150 150 150 150 150 pH of coagulation liquid following addition of acid at Operation (III) 7.2 8.6 4.3 5.4 7.2 8.5 Agitator vane circumferential speed (m/s) at Operation (II) 9 9 9 9 9 9 Amount of heat at Operation (II) 47 47 47 47 47 47 Evaluation Loss in weight due to heating (%) 0.3 — 4.0 0.5 0.3 — Clogging of inlet port No Yes No No No Yes

[0071] Supplemental explanation is given regarding TABLE 1.

[0072] “Heating temperature at Operation (II)” is the heating temperature, i.e., the temperature at the end of agitation at Operation (II).

[0073] “Amount of heat at Operation (II)” is the amount of heat per unit time and per unit mass which is imparted to the liquid mixture as a result of heating at Operation (II). The amount of this heat was calculated using the following formula.

Amount of heat=(temperature at end of agitation [K]−temperature at start of agitation [K])×specific heat [J/kg.Math.K]/agitation time [sec]

[0074] Note that where “−” is entered for the loss in weight due to heating, this indicates that measurement was not carried out.

[0075] At Comparative Example 1, where coagulant was added in sufficient quantity to cause pH to be 4.2, the loss in weight due to heating was 2.5%. On the other hand, at Working Example 1, where coagulant was added in sufficient quantity to cause pH to be 5.2, the loss in weight due to heating was a mere 0.4%. And at Working Example 2 as well, where coagulant was added in sufficient quantity to cause pH to be 6.9, the loss in weight due to heating was a mere 0.4%. At Comparative Example 2, where coagulant was added in sufficient quantity to cause pH to be 8.5, there was occurrence of clogging at the inlet port. This is thought to be due to the fact that tackiness of the coagulum prepared at Comparative Example 2 was greater than that of the other examples (i.e., Comparative Example 1, Working Example 1, and Working Example 2).

[0076] Loss in weight due to heating was less at Working Examples 3 and 4, where coagulant was added in sufficient quantity to cause pH to be 5.1 and 7.2, than at Comparative Example 3, where coagulant was added in sufficient quantity to cause pH to be 4.0. At Comparative Example 4, where coagulant was added in sufficient quantity to cause pH to be 8.6, there was occurrence of clogging at the inlet port. This is thought to be due to the fact that tackiness of the coagulum prepared at Comparative Example 4 was greater than that of the other examples (i.e., Comparative Example 3, Working Example 3, and Working Example 4).

[0077] Loss in weight due to heating was less at Working Examples 5 and 6, where coagulant was added in sufficient quantity to cause pH to be 5.4 and 7.2, than at Comparative Example 5, where coagulant was added in sufficient quantity to cause pH to be 4.3. At Comparative Example 6, where coagulant was added in sufficient quantity to cause pH to be 8.5, there was occurrence of clogging at the inlet port. This is thought to be due to the fact that tackiness of the coagulum prepared at Comparative Example 6 was greater than that of the other examples (i.e., Comparative Example 5, Working Example 5, and Working Example 6).