METHOD FOR PRODUCING MASTERBATCH

Abstract

The present invention provides a method for producing a masterbatch and related products which enhance the dispersibility of fillers in rubber to improve the balance of tensile strength, rigidity, and fuel economy. Provided is a method for producing a masterbatch, including a step of mixing a rubber latex having a zeta potential of 100 to 20 mV with a filler dispersion having a zeta potential of 10 to 90 mV, and preparing a latex compound having a zeta potential of 20 to 0 mV.

Claims

1. A method for producing a masterbatch, the method comprising a step of mixing a rubber latex having a zeta potential of 100 to 20 mV with a filler dispersion having a zeta potential of 10 to 90 mV, and preparing a latex compound having a zeta potential of 20 to 0 mV.

2. The method for producing a masterbatch according to claim 1, wherein the filler is a microfibrillated natural fiber.

3. The method for producing a masterbatch according to claim 1, wherein the rubber latex is a diene rubber latex.

4. A masterbatch, produced by the method according to claim 1.

5. A rubber composition for tires, produced from the masterbatch according to claim 4.

6. A pneumatic tire, formed from the rubber composition according to claim 5.

Description

EXAMPLES

[0074] The present invention will be specifically described with reference to, but not limited to, examples.

[0075] The chemicals used in the examples and comparative examples are listed below.

[0076] Natural rubber latex: Hytex Latex (high ammonia type, solids concentration: 60% by mass) available from Nomura Trading Co., Ltd.

[0077] Microfibrillated natural fiber: biomass nanofiber (product name: BiNFi-s chitin, chitin nanofiber, solids content: 2% by mass, moisture content: 98% by mass, average fiber diameter: 10 to 50 nm, degree of polymerization: 300, specific surface area: 200 m.sup.2/g) available from Sugino Machine Limited

[0078] Natural rubber: TSR20

[0079] Polybutadiene rubber: BR150B (cis content: 97% by mass, ML.sub.1+4 (100 C.): 40) available from Ube Industries, Ltd.

[0080] Carbon black: SHOBLACK N550 (N.sub.2SA: 42 m.sup.2/g) available from Cabot Japan K.K.

[0081] Antioxidant: NOCRAC 6C (N-phenyl-N-(1,3-dimethyl-butyl)-p-phenylenediamine) (6PPD) available from Ouchi Shinko Chemical Industrial Co., Ltd.

[0082] Zinc oxide: zinc oxide #2 available from Mitsui Mining & Smelting Co., Ltd.

[0083] Stearic acid: stearic acid beads Tsubaki available from NOF Corporation

[0084] Sulfur: Seimi Sulfur (oil content: 10%) available from Nippon Kanryu Industry Co., Ltd.

[0085] Vulcanization accelerator: NOCCELER NS (N-tert-butyl-2-benzothiazolesulfenamide) (TBBS) available from Ouchi Shinko Chemical Industrial Co., Ltd.

<Preparation of Masterbatch>

Example 1

[0086] An amount of 1,000 g of pure water was added to 500 g of the microfibrillated natural fiber to obtain a 0.5% by mass (solids concentration) suspension of the microfibrillated natural fiber. The suspension was stirred for about five minutes using a high-speed homogenizer (T50 available from IKA Japan, rotational speed: 8,000 rpm) to give a homogeneous aqueous dispersion (viscosity: 7 to 8 mPa.Math.s).

[0087] The solids concentration (DRC) of the natural rubber latex was adjusted to 10% by mass, and then the aqueous dispersion prepared as above was added to the natural rubber latex such that the dry weight (solids content) of the microfibrillated natural fiber was 20 parts by mass per 100 parts by mass of the rubber solids in the natural rubber latex, followed by stirring and mixing at 25 C. for five minutes using a high-speed homogenizer (T50 available from IKA Japan, rotational speed: 8,000 rpm) to obtain a rubber latex dispersion. Next, a 1% by mass formic acid aqueous solution was added to the rubber latex dispersion with slow stirring at 25 C. for five minutes using an Eurostar (electronically controlled stirring device) (available from IKA Japan, rotational speed: 100 rpm) to adjust the zeta potential to 20 mV, thereby obtaining a latex compound as a coagulum. The coagulum was filtered and dried at 80 C. for six hours to obtain masterbatch 1.

[0088] The zeta potential was measured using the device under the conditions described below. [0089] Measurement device: zeta potential analyzer ELS-PT available from Otsuka Electronics Co., Ltd.

Measurement Conditions

[0090] A pH titrator was used. [0091] pH titration mode [0092] Solvent: water [0093] Temperature: 25 C. [0094] Dielectric constant: 78.22 [0095] Viscosity: 0.8663 cp [0096] Refractive index: 1.3312

[0097] The zeta potentials of the natural rubber latex (solids concentration: 10% by mass) and the aqueous dispersion of the microfibrillated natural fiber (solids concentration: 0.5% by mass) measured as above were as follows. [0098] Natural rubber latex (solids concentration: 10% by mass): 65 mV [0099] Aqueous dispersion of microfibrillated natural fiber (solids concentration: 0.5% by mass): 35 mV

[0100] The dispersibility of the microfibrillated natural fiber in the rubber in masterbatch 1 was observed with a scanning electron microscope (SEM), and it was confirmed that the microfibrillated natural fiber formed no aggregate and was finely dispersed in the rubber.

Example 2

[0101] Masterbatch 2 was prepared as in Example 1, except that a 1% by mass formic acid aqueous solution was added to the rubber latex dispersion with slow stirring at 25 C. for five minutes using an Eurostar (available from IKA Japan, rotational speed: 100 rpm) to adjust the zeta potential to 10 mV, thereby obtaining a latex compound as a coagulum.

[0102] The dispersibility of the microfibrillated natural fiber in the rubber in masterbatch 2 was observed with a scanning electron microscope (SEM), and it was confirmed that the microfibrillated natural fiber formed no aggregate and was finely dispersed in the rubber.

Comparative Example 1

[0103] An amount of 1,000 g of pure water was added to 500 g of the microfibrillated natural fiber to obtain a 0.5% by mass (solids concentration) suspension of the microfibrillated natural fiber. The suspension was stirred for about five minutes using a high-speed homogenizer (T50 available from IKA Japan, rotational speed: 8,000 rpm) to give a homogeneous aqueous dispersion (viscosity: 7 to 8 mPa.Math.s).

[0104] The solids concentration (DRC) of the natural rubber latex was adjusted to 10% by mass, and then the aqueous dispersion prepared as above was added to the natural rubber latex such that the dry weight (solids content) of the microfibrillated natural fiber was 20 parts by mass per 100 parts by mass of the solids in the natural rubber latex, followed by stirring and mixing at 25 C. for about five minutes using a high-speed homogenizer (T50 available from IKA Japan, rotational speed: 8,000 rpm) to obtain a rubber latex dispersion. Next, a 1% by mass formic acid aqueous solution was added to the rubber latex dispersion with slow stirring at 25 C. for five minutes using an Eurostar (available from IKA Japan, rotational speed: 100 rpm) to adjust the pH to 7 using a pH meter D51T (available from Horiba, Ltd.), thereby obtaining a latex compound as a coagulum (the zeta potential was also measured as in Example 1 and found to be 29 mV). The coagulum was filtered and dried at 80 C. for six hours to obtain comparative masterbatch 1.

[0105] The dispersibility of the microfibrillated natural fiber in the rubber in comparative masterbatch 1 was observed with a scanning electron microscope (SEM), and it was confirmed that the microfibrillated natural fiber formed slight aggregates and was not sufficiently finely dispersed in the rubber.

Comparative Example 2

[0106] Comparative masterbatch 2 was prepared as in Example 1, except that a 1% by mass formic acid aqueous solution was added to the rubber latex dispersion with slow stirring at 25 C. for five minutes using an Eurostar (available from IKA Japan, rotational speed: 100 rpm) to adjust the zeta potential to 30 mV, thereby obtaining a coagulum.

[0107] The dispersibility of the microfibrillated natural fiber in the rubber in comparative masterbatch 2 was observed with a scanning electron microscope (SEM), and it was confirmed that the microfibrillated natural fiber formed aggregates and was not finely dispersed in the rubber.

Comparative Example 3

[0108] Comparative masterbatch 3 was prepared as in Example 1, except that a 1% by mass formic acid aqueous solution was added to the rubber latex dispersion with slow stirring at 25 C. for five minutes using an Eurostar (available from IKA Japan, rotational speed: 100 rpm) to adjust the zeta potential to 20 mV, thereby obtaining a coagulum.

[0109] The dispersibility of the microfibrillated natural fiber in the rubber in comparative masterbatch 3 was observed with a scanning electron microscope (SEM), and it was confirmed that the microfibrillated natural fiber formed aggregates and was not finely dispersed in the rubber.

<Preparation of Vulcanized Rubber Composition>

Examples 11 and 12, and Comparative Examples 11 to 13

[0110] According to each of the formulations shown in Table 1, the chemicals other than the sulfur and the vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, the sulfur and the vulcanization accelerator were added to the kneaded mixture and kneaded together using an open roll mill to obtain an unvulcanized rubber composition. The unvulcanized rubber composition was press-vulcanized at 170 C. for 15 minutes to obtain a vulcanized rubber composition. The vulcanized rubber compositions prepared as above were evaluated as described below. Table 1 shows the results.

(Tensile Test)

[0111] A tensile test was performed using No. 3 dumbbell-shaped rubber specimens prepared from the vulcanized rubber compositions in accordance with JIS K 6251 Rubber, vulcanized or thermoplasticsDetermination of tensile stress-strain properties to determine the tensile strength at break (tensile strength: TB (MPa)) of the vulcanized rubber compositions.

[0112] The TB of each formulation example is expressed as an index (tensile strength index (TB index) ) using the equation below, with Comparative Example 11 set equal to 100. A higher TB index indicates a higher tensile strength and better durability.

(TB index)=(TB of each formulation example)/(TB of Comparative Example 11)100

(Viscoelastic Test)

[0113] The complex modulus E* (MPa) and loss tangent (tan ) in the tire circumferential direction of specimens cut out of the formulation examples (vulcanized rubber compositions) were measured using a viscoelastic spectrometer VES (available from Iwamoto Seisakusho Co., Ltd.) at a temperature of 70 C., a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 2%.

[0114] The E* and tan of each formulation example are expressed as indices (E* index, tan index) using the equations below, each with Comparative Example 11 set equal to 100. A higher E* index indicates higher rigidity and better handling stability. A higher tan index indicates better rolling resistance properties (fuel economy).

(E* index)=(E*of each formulation example)/(E* of Comparative Example 11)100

(tan index)=(tan of Comparative Example 11)/(tan of each formulation example)100

[0115] The term tire circumferential direction means the direction along which the vulcanized rubber composition was extruded.

(Balance Index)

[0116] An index of the balance of tire properties was calculated from the above indices using the equation below. A higher balance index indicates a better balance of tensile strength, rigidity, and fuel economy.

(Balance index)=(TB indexE* indextan index)/10,000

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 11 Example 11 Example 12 Example 12 Example 13 Formulation Masterbatch Comparative Masterbatch 1 Masterbatch 2 Comparative Comparative (parts by Masterbatch 1 (Example 1) (Example 2) Masterbatch 2 Masterbatch 3 mass) (Comparative (Comparative (Comparative Example 1) Example 2) Example 3) (Natural rubber solids: 30 30 30 30 30 100 parts by mass) (Microfibrillated natural fiber: 20 parts by mass) Adjusted zeta potential 29 20 10 30 20 [mV] Natural rubber 45 45 45 45 45 Polybutadiene rubber 30 30 30 30 30 Carbon black 40 40 40 40 40 Antioxidant 2 2 2 2 2 Zinc oxide 2 2 2 2 2 Stearic acid 2 2 2 2 2 Sulfur 2 2 2 2 2 Vulcanization 1 1 1 1 1 accelerator Evaluation TB index 100 109 110 99 95 E* index 100 105 104 100 97 tan index 100 120 118 99 96 Balance index 100 137 135 98 88

[0117] Table 1 demonstrates that the balance of tensile strength, rigidity, and fuel economy was improved in Examples 11 and 12 each using a masterbatch produced by a method including a step of mixing a rubber latex having a zeta potential of 100 to 20 mV with a filler dispersion having a zeta potential of 10 to 90 mV, and preparing a latex compound having a zeta potential of 20 to 0 mV, as compared to Comparative Example 11. In contrast, the balance of tensile strength, rigidity, and fuel economy was found to deteriorate in Comparative Examples 12 and 13 each using a masterbatch produced by adjusting the zeta potential of the latex compound to a value outside the range of 20 to 0 mV.