JP6594754B2 - Natural rubber, method for producing natural rubber, rubber composition and tire - Google Patents

Description

  The present invention relates to natural rubber, a method for producing natural rubber, a rubber composition, and a tire.

In general, natural rubber is known as a rubber excellent in mechanical properties, and is widely used as a rubber component of rubber products such as tires. Such natural rubber can be obtained by collecting natural rubber latex from rubber tree such as para rubber tree and coagulating, washing and drying. Further, the obtained natural rubber is masticated, compounded with a compounding agent, molded, and vulcanized to produce a desired rubber product.
Here, the natural rubber latex contains non-rubber components such as proteins, lipids, carbohydrates and inorganic substances in addition to the rubber content of about 25 to 35% w / v (weight / volume). The natural rubber obtained by coagulation contains about 6% by mass of a non-rubber component. Although these non-rubber components have an anti-aging effect and a vulcanization acceleration effect, it is known that highly polar compounds such as proteins are components that deteriorate the exothermic properties of rubber compositions and vulcanized rubbers. Various technologies for reducing heat generation (lower hysteresis loss) of natural rubber have been studied.

  For example, in Japanese Patent Application Laid-Open No. 2008-184476 (Patent Document 1), a natural rubber latex is added without adding a compound having a quaternary ammonium salt structure in the molecule without coagulation, and moisture is removed and dried. , A method for producing solid natural rubber is disclosed, and it is taught that the rubber composition can be made to have a low hysteresis loss by using the natural rubber obtained by the method in the rubber composition. Furthermore, the result which improves also about the abrasion resistance of a rubber composition is shown.

JP 2008-184476 A

  However, due to recent demands for further energy savings, there is a need for technologies to further improve the fuel efficiency of tires. On the other hand, for resource saving requests, in order to extend the usable period of tires, A technique for further improving the wear resistance is also demanded. In order to meet these demands, a natural rubber having further lower hysteresis loss and wear resistance than the natural rubber described in Patent Document 1 is required. Need to develop.

Then, this invention makes it a subject to provide the natural rubber which further improved the low hysteresis loss property and abrasion resistance compared with the past, and its manufacturing method.
The present invention also provides a rubber composition containing such natural rubber and excellent in low hysteresis loss and wear resistance, and a tire excellent in fuel efficiency and wear resistance using the rubber composition. This is a further issue.

  The gist configuration of the present invention for solving the above problems is as follows.

The natural rubber of the present invention has a long chain branching index (LCB index) at 70 ° C. of 10.6 to 17.9 and a long chain branching index (LCB index) at 130 ° C. of 3.0 or less. It is characterized by that.
Such natural rubber of the present invention further improves low hysteresis loss and wear resistance compared to the conventional rubber.

［式中、γ₀：振幅、ｔ：時間、ω：角速度（単位：ｒａｄ／ｓ）］で表わされるシェアストレスτの式にフィッティングし、さらに、
上記式で求めたτを用いて、測定条件として、質量５ｇの試験片に対して、測定中の力を１５．６ｋＮで、温度７０℃、周波数１．６７Ｈｚ、歪０．５％で１分間置いた後、１０秒間かけて（すなわち、０．１Ｈｚ）、角速度ωを０．５０ｒａｄ／ｓとして、角度７１．５度、歪１０００％で、測定中の力を１５．６ｋＮとする条件下で、７０℃、８０℃、９０℃、１００℃、１１０℃、１２０℃、１３０℃と順次温度を上げながら、各温度で、下記式：

で表わされるＧ’_nを求め、Ｇ’₁／Ｇ’₅から７０℃と１３０℃における長鎖分岐指数（ＬＣＢ Ｉｎｄｅｘ）を求める（即ち、ＬＣＢ ｉｎｄｅｘ＝Ｇ’₁／Ｇ’₅）。 Here, in the present invention, the long chain branching index (LCB index) is the dynamic characteristic of the dissolved polymer, and the influence of the molecular weight distribution is removed from the behavior of the long chain branching (LCB) having an approximate characteristic and the molecular weight distribution. It is a more accurate index of long-chain branching, and can be measured by an LAOS (Large Amplitude Oscillation Shear) measurement method using an RPA2000 tester (manufactured by Alpha Technologies). For details on the LAOS measurement method for obtaining the LCB index, see “FT-Rheology, a Tool to Quantify Long Chain Branching (LCB) in Natural Rubber and its Effect on Mastication, Mixing Behavior and Final. Properties. ”(Henri G. Burhin, Alpha Technologies, UK 15 Rue du Culot B-1435 Hevillers, Belgium).
In the present invention, the shear stress signal obtained by the measurement in the LAOS mode is calculated by discrete Fourier transform using an RPA2000 type tester (manufactured by Alpha Technologies) to n = 1 to 9 (n is an integer). And the following formula:

Fitting to the equation of shear stress τ represented by [where γ ₀ : amplitude, t: time, ω: angular velocity (unit: rad / s)],
Using τ determined by the above formula, as a measurement condition, a force during measurement is 15.6 kN, a temperature of 70 ° C., a frequency of 1.67 Hz, and a strain of 0.5% for 1 minute with respect to a test piece of mass 5 g. After placing, for 10 seconds (that is, 0.1 Hz), the angular velocity ω is 0.50 rad / s, the angle is 71.5 degrees, the strain is 1000%, and the force during measurement is 15.6 kN. 70 ° C., 80 ° C., 90 ° C., 100 ° C., 110 ° C., 120 ° C., 130 ° C.

In represented by G 'look _n, G' ₁ / G _'5 long chain branching index at 70 ° C. and 130 ° C. (LCB Index) seek _{(i.e., LCB index = G' 1 /} G '5).

In a preferred example of the natural rubber of the present invention, the long chain branching index (LCB index) at 70 ° C. is 10.6 or more and 15.0 or less, and the long chain branching index (LCB index) at 130 ° C. is 2.0 or more and 3.0 or less.
In this case, the natural rubber has a sufficient resistance to cracking and is excellent in low hysteresis loss and wear resistance.

The natural rubber of the present invention preferably has a polymer gel content of 10% by mass or less.
In this case, the natural rubber has high crack resistance.

  In the present invention, the ratio of the polymer gel in the natural rubber is determined by swelling the natural rubber in toluene for 12 hours, treating it with a centrifuge at 35,000 rpm for 1.5 hours, and allowing the precipitated gel to stand for 48 hours. The amount of gel is weighed to obtain the amount of gel, which is calculated as a percentage based on the amount of natural rubber used.

In another preferred embodiment of the natural rubber of the present invention, the long chain branching index (LCB index) at 70 ° C. is 12.0 or more and 14.5 or less.
In this case, the wear resistance and crack resistance of natural rubber are particularly excellent.

In the method for producing natural rubber according to the present invention, the long chain branch index (LCB index) at 70 ° C. is 7.8 or more and the long chain branch index (LCB index) at 130 ° C. is 3.5 or less. It is characterized by adding laccase to a certain raw natural rubber.
According to the method for producing natural rubber of the present invention, natural rubber excellent in low hysteresis loss and wear resistance can be produced.

In a preferred embodiment of the method for producing natural rubber according to the present invention, the laccase is added to the natural rubber latex of the raw natural rubber or the chopped product of the natural rubber latex coagulum.
In this case, the low hysteresis loss property and wear resistance of natural rubber can be further improved.

In another preferred embodiment of the method for producing natural rubber of the present invention, the raw natural rubber is a raw natural rubber obtained from Para rubber tree variety PB330.
In this case, a natural rubber that is particularly excellent in low hysteresis loss and wear resistance can be produced.

Moreover, the natural rubber of the present invention is characterized by being produced by the above-described method for producing natural rubber.
The natural rubber produced by the above-described method for producing natural rubber further improves low hysteresis loss and wear resistance as compared with the conventional rubber.

The rubber composition of the present invention is characterized by containing the above natural rubber.
The rubber composition of the present invention containing the natural rubber is excellent in low hysteresis loss and wear resistance.

The tire of the present invention is characterized by using the above rubber composition.
The tire of the present invention using the rubber composition is excellent in low fuel consumption and wear resistance.

According to the present invention, it is possible to provide a natural rubber having further improved low hysteresis loss and wear resistance and a method for producing the same, as compared with the prior art.
In addition, according to the present invention, a rubber composition containing such natural rubber and excellent in low hysteresis loss and wear resistance, and a tire excellent in fuel efficiency and wear resistance using the rubber composition are provided. Can be provided.

<Natural rubber>
Below, the natural rubber of this invention is demonstrated in detail based on the embodiment.
The natural rubber of the present invention has a long chain branching index (LCB index) at 70 ° C. of 10.6 to 17.9 and a long chain branching index (LCB index) at 130 ° C. of 3.0 or less. It is characterized by that.

In general, the starting point of natural rubber branching can be divided into two types: strong bonds and weak bonds. Here, strong bonds are caused by covalent bonds and affect the long chain branching index (LCB index) at 130 ° C., while weak bonds are caused by hydrogen bonds and the like, and the long chain branching index at 70 ° C. ( LCB index).
And the branch of strong bond is not cut even at high temperature, which deteriorates the uptake of the filler during the kneading of the rubber composition, not only increases the viscosity of the unvulcanized rubber, but also deteriorates the dispersibility of the filler. Will lead to an increase in the hysteresis loss of the rubber composition, so it is preferable that the amount be smaller. Accordingly, in the natural rubber of the present invention, the long chain branching index (LCB index) at 130 ° C. is set to 3.0 or less from the viewpoint of low hysteresis loss.
On the other hand, branching of weak bonds is in a cut state during the kneading of the rubber composition, so that the contribution to the dispersibility of the filler is small, and after vulcanization, the rubber component (natural rubber) has a high molecular weight. However, since it leads to the improvement of the abrasion resistance of the rubber composition, the larger one is better. Therefore, in the natural rubber of the present invention, the long chain branching index (LCB index) at 70 ° C. is set to 10.6 or more from the viewpoint of wear resistance.
However, if too many weak bonds are branched, the polymer gel increases, leading to a decrease in crack resistance. Therefore, in the natural rubber of the present invention, the long chain branching index (LCB index) at 70 ° C. is set to 17.9 or less from the viewpoint of crack resistance.

  The natural rubber of the present invention has a long chain branching index (LCB index) at 70 ° C. of preferably 10.6 to 15.0, more preferably 12.0 to 14.5. Although the above-mentioned weak bond branching contributes to the improvement of the abrasion resistance of the rubber composition, when too many weak bond branches increase, the polymer gel increases, leading to a decrease in crack resistance. However, if the long chain branching index (LCB index) at 70 ° C. of natural rubber is 15.0 or less, sufficient crack resistance can be secured. Moreover, if the long chain branching index (LCB index) at 70 ° C. of natural rubber is 12.0 or more and 14.5 or less, the wear resistance and crack resistance of natural rubber can be highly compatible.

  Here, in the natural rubber of the present invention, the polymer gel is preferably 10% by mass or less, and more preferably 9% by mass or less. If the ratio of the polymer gel in the natural rubber is 10% by mass or less, the natural rubber has good crack resistance.

  The natural rubber of the present invention preferably has a long chain branching index (LCB index) at 130 ° C. of 2.0 or more and 3.0 or less. If the long chain branching index (LCB index) at 130 ° C. of natural rubber is 2.0 or more, a sufficient molecular weight can be obtained.

  Furthermore, the natural rubber of the present invention has a long chain branching index (LCB index) at 70 ° C. of 10.6 to 15.0 and a long chain branching index (LCB index) at 130 ° C. of 2. It is particularly preferably 0 or more and 3.0 or less. The long chain branching index (LCB index) at 70 ° C. is 10.6 to 15.0 and the long chain branching index (LCB index) at 130 ° C. is 2.0 to 3.0. While ensuring sufficient crack resistance of rubber, it is possible to achieve both high wear resistance and low hysteresis loss of natural rubber.

  The above-mentioned long chain branching index (LCB index) at 70 ° C. is 10.6 to 17.9 and the long chain branching index (LCB index) at 130 ° C. is 3.0 or less. The natural rubber of the present invention is selected as appropriate from the type of para rubber tree used as a raw material, mixed with the obtained natural rubber latex and its coagulum, appropriately selected for drying conditions, and as described later, a specific raw natural rubber It can be produced by adding laccase to.

<Production method of natural rubber>
Next, the manufacturing method of the natural rubber of this invention is demonstrated in detail based on the embodiment.
The method for producing natural rubber of the present invention can be suitably used for producing the natural rubber of the present invention described above.
The method for producing natural rubber according to the present invention comprises a raw material having a long chain branching index (LCB index) at 70 ° C. of 7.8 or more and a long chain branching index (LCB index) at 130 ° C. of 3.5 or less. It is characterized by adding laccase to natural rubber.

  As described above, there are strong bonds and weak bonds at the starting point of natural rubber branching, and it is considered that an optimal branching structure exists. The reason is not always clear, but long chain branching at 70 ° C. Long chain branching at 130 ° C. is achieved by adding laccase to raw natural rubber having an index (LCB index) of 7.8 or more and a long chain branching index (LCB index) at 130 ° C. of 3.5 or less. The index (LCB index) decreases, the long chain branching index (LCB index) at 70 ° C. increases, and the wear resistance can be improved while improving the low hysteresis loss property of natural rubber.

  The natural rubber (modified natural rubber) produced by the method for producing natural rubber of the present invention has a long chain branching index (LCB index) at 70 ° C. of 7.8 or more and a long chain branching index at 130 ° C. Although it will not specifically limit as long as it manufactures through the process of adding laccase to the raw material natural rubber whose (LCB index) is 3.5 or less, the manufactured natural rubber (modified natural rubber) is 70. The long chain branching index (LCB index) at 10 ° C. is preferably 10.6 or more, and the long chain branching index (LCB index) at 130 ° C. is preferably 3.0 or less.

In the natural rubber production method of the present invention, the laccase is preferably added to natural rubber latex or a natural rubber latex coagulated product. When laccase is added to the raw material natural rubber in the latex state, the effect of adding laccase is easily manifested, and when the raw natural rubber is a natural rubber latex coagulated product, By adding laccase to the laccase, the effect of adding laccase can be expressed with high efficiency, and in any case, the low hysteresis loss and wear resistance of natural rubber can be further improved. When the raw natural rubber is in a latex state, the long chain branching index (LCB index) at 70 ° C. and 130 ° C. of the raw natural rubber is measured in a state where the solidified product obtained by coagulating the latex is dried.
Here, examples of natural rubber latex include field latex and centrifugal concentrated latex.
On the other hand, the natural rubber latex coagulated product includes a coagulated product obtained by adding a coagulant to natural rubber latex, a natural rubber cup lamp obtained by leaving a cup from which natural rubber field latex is collected, a natural rubber Examples thereof include a coagulated product (skim natural rubber) obtained by adding a coagulant to a skim (serum) obtained when the field latex is centrifuged. Moreover, it is preferable that the length of one side is about 0.1-2 mm from the viewpoint of the acceleration | stimulation of the addition effect of a laccase, and a viewpoint of manufacture ease, as for the shredded material of natural rubber latex coagulum.

  In the method for producing natural rubber of the present invention, the raw natural rubber includes various forms of raw natural rubber obtained from Para rubber tree varieties PB330, PB260, RRIM921, etc., and the raw material obtained from Para rubber tree cultivar PB330. Natural rubber is particularly preferred. By using the raw natural rubber obtained from Para rubber tree cultivar PB330, it is possible to produce a natural rubber that is particularly excellent in low hysteresis loss and wear resistance.

  The laccase used in the method for producing natural rubber of the present invention is an enzyme classification EC 1.10.3 defined by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (IUB-MB). .2, a copper-containing enzyme that oxidizes phenolic compounds using molecular oxygen as an electron donor. The laccase may be derived from a plant, derived from bacteria, or derived from fungi (including filamentous fungi and yeast).

Molds from which laccase is derived include Aspergillus, Neurospora [eg, N. et al. N. Classa], Podospora, Botrytis, Colivia, Fomes, Lentinus, Pleurotus, Trametes, eg Trametes. T. vilosa and T. vilosa. T. versicolor], Rhizoctonia [e.g., R. R. solani], Coprinus [e.g. C.I. Cinereus, C. C. comatus, C.I. C. friesii, and C.I. C. plicatiris], Psatirrella [e.g. P. concelleana], Panaeolus [e.g. P. pionionauses], Myceliophthra [e.g. Thermophila], Citalidium [e.g., S. et al. S. thermophilum], Polyporus [e.g. Pincitus], Pynoporus [e.g. P. cinnabarinus], Plevia [eg. P. radita], or Coriolus [e.g., C.I. Strains of C. hirustus] and the like.
Examples of bacteria from which laccase is induced include Bacillus.
Examples of strains from which laccase is derived include Coprinus, Myceliophthra, Polyporus, Pycnoporus, Scytalidium, Rhizocnetopuricus Myceliophthra thermophila (Myceliophthra thermophila), Polyporus pincitus (Polyporus pinsitas), Pynoporus sinnabarinus, Citaridium thermophilum (Schitalidum) octonia solani), and the like.

  Also, European Patent Application Publication No. 765394, US Pat. No. 5,770,419, 6,008,029, 5,925,554, 6,184,015. Laccases described in No. 6,218,170, WO 92/01046, and JP-A No. 02-238885 are also preferably exemplified.

  Moreover, as a laccase, a commercially available thing can also be used preferably. Commercially available laccases include NS51001 [Polyporus pinsitas laccase], NS51002 (Myserioptora thermophila laccase), NS44192 [Myserioptra derived, syringaldazin (as mediator) formulation], NS81268 (Myserioptra) (Above, Novozymes A / S), 38429-1G (cat) (Trametes Versicolor) (Aldrich) and the like.

  The enzyme activity of the laccase is preferably 20 to 2000 (Unit / g), more preferably 40 to 1500 (Unit / g), from the viewpoint of obtaining excellent low hysteresis loss and wear resistance. . In the enzyme activity of laccase, 1 Unit is the amount of enzyme that oxidizes 1 mmol of syringaldazine and converts it to quinone in 1 minute. Here, the oxidation reaction of syringaldazine was carried out at 30 ° C. and pH 7.5 using 145 μl of 25 mM tris (hydroxymethyl) aminomethane as a buffer, and 15 μl laccase was added thereto, and 480 seconds later, 0.22 mM syringe was added. 18 μl of gardazine was added, and 60 seconds after adding syringaldazin, and then every 4.5 seconds at a total of 12 points (up to 109.5 seconds after addition), the reaction turned purple. The absorbance of the color of the laccase that changes color is measured over time at a wavelength of 540 nm, the change in absorbance is measured, and the amount of enzyme is calculated.

  The amount of the laccase added is from the viewpoint of low hysteresis loss and wear resistance of natural rubber, when adding laccase to raw natural rubber supplied as a rubber latex such as natural rubber latex. A range of 0.01 to 0.15 parts by mass with respect to 100 parts by mass of the rubber component is preferable, and when adding laccase to a raw material natural rubber supplied as a solid such as a coagulate of natural rubber latex, The range of 0.1-0.3 mass part is preferable with respect to 100 mass parts of rubber components in natural rubber.

  The amount of the laccase added unit is preferably 7 (Unit / g × phr) or more with respect to the rubber component in the raw natural rubber from the viewpoint of obtaining more excellent low hysteresis loss and wear resistance. (Unit / g × phr) or more is more preferable, 50 (Unit / g × phr) or more is more preferable, 80 (Unit / g × phr) or more is particularly preferable, It is preferably 5000 (Unit / g × phr) or less, more preferably 2500 (Unit / g × phr) or less, still more preferably 1500 (Unit / g × phr) or less, and 500 (Unit / G × phr) or less, more preferably 250 (Unit / g × phr) or less. Here, phr is an added unit amount (parts by mass) with respect to 100 parts by mass of the rubber component in the raw natural rubber.

The redox potential of the laccase is preferably 800 mV or less, more preferably 700 mV or less, and particularly preferably 600 mV or less. When the oxidation-reduction potential of laccase is 800 mV or less, the progress of the reaction of the non-rubber component becomes good, and it is easy to improve the low hysteresis loss and wear resistance of natural rubber. In addition, although the oxidation-reduction potential of laccase is so preferable that it is small, when considering availability, it is usually preferably 200 mV or more, more preferably 300 mV or more, and particularly preferably 400 mV or more.
Here, the oxidation-reduction potential of laccase is described in non-patent literature [Feng XU et al, Biochimica et Biophysica Acta 1292 (1996), p. 303-311, 2.2.2. It is the value measured based on the method described in Redox potential determinations].

  The laccase is preferably used alone, and it is preferable not to use a mediator. Here, the mediator is a low molecular weight compound having a property of promoting a catalytic effect on the oxidation-reduction reaction of laccase by being oxidized by laccase to generate radicals. Examples of the mediator include organic compounds having a phenol group such as 1-hydroxybenzotriazole, catechol, and 2,6-dimethoxyphenol. By not using a mediator, the oxidation-reduction reaction of the non-rubber component proceeds more effectively, and the low hysteresis loss and wear resistance of natural rubber are further improved.

Further, in the present invention, it is preferable to add a laccase substrate, and this is particularly effective when laccase is added to a material other than a raw material natural rubber in a latex state. Here, the substrate refers to a substance whose chemical reaction is promoted by laccase, that is, a substance whose redox reaction is promoted by the catalytic effect of laccase on the redox reaction. As such a substrate, a polar group-containing phenoxy compound containing a polar group is preferable.
Examples of the polar group include amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, hydroxyl group. Group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, tin-containing group, alkoxysilyl group, and the like. It may have. Among these, the polar group is preferably an amino group and a carboxyl group, and at least one of each of the amino group and the carboxyl group may be directly bonded to the aromatic ring, or may be directly bonded to the aromatic ring. At least one amino group and one carboxyl group may be bonded to one hydrocarbon group. In addition, at least one of an amino group and a carboxyl group may be directly bonded to the aromatic ring, and the other may be bonded to one hydrocarbon group directly bonded to the aromatic ring. The amino group and the carboxyl group may be present in at least one selected from the group consisting of peptide residues and protein residues.
Examples of the polar group-containing phenoxy compound containing the polar group include tyrosine, amido, 4-aminophenol, 4- (aminomethyl) phenol, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol, 4-triethoxysilylphenol, Examples include 4-[(2-triethoxysilyl) ethyl] phenol, and among these, tyrosine, a peptide containing tyrosine, a protein containing tyrosine, and amido are preferable.
In the present invention, the amount of the substrate added is preferably in the range of 0.01 to 5 parts by mass, more preferably in the range of 0.03 to 1 part by mass, with respect to 100 parts by mass of the rubber component in the raw natural rubber. A range of 0.05 to 0.3 parts by mass is particularly preferable. When the added amount of the substrate is within the above range, more excellent low hysteresis loss and wear resistance can be obtained.

  The laccase is added to raw natural rubber, for example, it may be added to those supplied in the form of a rubber latex such as natural rubber latex, or in the form of a solid such as a coagulated product of natural rubber latex. You may add to what is supplied. In addition, when adding to what is supplied with solid forms, such as a solidified material of natural rubber latex, it is preferable to add laccase after making a shredded product as mentioned above.

In addition, the modification of the raw natural rubber with laccase is preferably performed in the presence of water from the viewpoint of uniformly performing the modification reaction and obtaining better low hysteresis loss and wear resistance.
For example, when laccase is added to a raw natural rubber with water from the beginning, such as natural rubber latex, the modification is naturally performed in the presence of water.
When laccase is added to, for example, a raw material natural rubber supplied in a solid state without moisture, a supernatant obtained by centrifuging natural rubber field latex into the solid raw natural rubber (skim, serum) Is added, the reforming is performed in the presence of water, and water may be added.

When the laccase is added to the raw natural rubber supplied as a rubber latex such as natural rubber latex, the pH of the raw natural rubber (rubber latex) is preferably 6 to 11, and preferably 7 to 11. More preferred.
Moreover, when adding laccase to raw natural rubber supplied as a solid such as a coagulate of natural rubber latex, the raw natural rubber (solid) preferably has a pH of 3 to 11, preferably 3 to 7. It is more preferable.
In addition, what is necessary is just to use an acid or a base for adjustment of pH, and it is preferable to use weak bases, such as weak acids, such as carbonic acid, formic acid, and an acetic acid, and ammonia. Moreover, you may add other additives, such as surfactant, as needed.

When adding laccase to raw natural rubber supplied as a rubber latex such as natural rubber latex, for example, adjust the pH by adding the above acid or base for pH adjustment as necessary, and if necessary It is preferable to add the substrate and mix by stirring. The stirring time is preferably about 30 minutes to 3 hours, and more preferably 45 minutes to 2 hours. When stirring and mixing, a ball mill (vibration mill, rotary mill, etc.) or the like can be used.
Next, for example, the pH is adjusted to about 3 to 6, more preferably 3 to 5 using an acid such as formic acid, and the latex is coagulated to obtain a coagulated product. In this case, a solidified product may be obtained by coagulation using a polymer flocculant. In order to perform uniform drying, the obtained solidified product is preferably applied to a creper about 3 to 10 times and passed through a shredder to crumb. Thereafter, drying is preferably performed at a temperature of 90 to 150 ° C., more preferably 100 to 130 ° C., preferably 30 minutes to 5 hours, more preferably 1 to 4 hours to obtain a modified natural rubber. It is done.

  Moreover, when adding laccase to the raw material natural rubber supplied as solids such as a solidified product of natural rubber latex, for example, the length of one side of these solids is about 0.1 mm to 2 mm square, particularly about 1 mm square. In the process of producing natural rubber, for example, a skim (serum) obtained when centrifuging field latex is added, and the above acid or base for pH adjustment is added as necessary. It is preferable to adjust the pH by adding, and add a substrate if necessary, and mix by stirring. The stirring time is preferably about 30 minutes to 3 hours, more preferably 45 minutes to 2 hours. When stirring and mixing, a ball mill (vibration mill, rotary mill, etc.) can be used. After that, a modified natural rubber is obtained by performing a drying treatment as necessary.

  In the method for producing natural rubber according to the present invention, as described above, when laccase is added to raw natural rubber in a latex state, protease is added to natural rubber latex modified with the laccase, Proteins in rubber latex may be degraded.

Examples of the protease include the following.
From the viewpoint of classification according to the position of degradation, exopeptidase (type that cuts from the sequence end of the protein / peptide chain (approximately 1 to 2 amino acid residues)), endopeptidase (type that cuts the center of the protein / peptide chain sequence) For example).
In addition, from the viewpoint of classification by substrate, proteinases (proteinases that decompose proteins) and (narrowly defined) peptidases (peptidases, those that decompose synthetic peptides having a lower molecular weight) can be mentioned.
From the viewpoint of classification by catalytic mechanism, serine proteases such as chymotrypsin and subtilisin; aspartic proteases (acidic proteases) such as pepsin, cathepsin D and HIV protease; Metalloprotease such as thermolysin; Cysteine protease such as papain and caspase; and N-terminal threonine protease (N-terminal threonine protease known as proteasome) ) And glutamate protease (gl tamic protease), and the like.
In the present invention, endopeptidase is preferable from the viewpoint of the degradation position. Furthermore, a protease having a high activity at a pH of about 10.5 by adding ammonia, that is, an alkaline protease is preferable. From the viewpoint of suppressing the coagulation of natural rubber latex, the optimum temperature is 10 to 40 ° C., preferably room temperature. Proteases with high activity around (for example, 20 ° C.) are preferred.
As the protease, only one kind of those described above may be used, or a composition containing two or more kinds of those described above may be used. Furthermore, a protease may be included as a main component and an enzyme other than protease. Other than the above may be a main component and may contain a protease as a side active component.

  The amount of the protease added is preferably in the range of 0.05 to 1.0 part by weight, and 0.1 to 0.3 part by weight with respect to 100 parts by weight of the rubber component in the natural rubber latex modified with laccase. The range of is more preferable. By making the amount of protease added within the above range, the degradation due to the side activity of industrial enzymes is suppressed and the protein is selectively and appropriately decomposed, so that the processability of natural rubber is improved and the natural rubber is In the used pneumatic tire, the dispersibility of the filler such as carbon black with respect to natural rubber is improved, and as a result, the fuel efficiency of the pneumatic tire is improved.

The pH at the time of proteolysis when a protease is used is preferably in the alkaline region (for example, around pH 10.5), and the temperature is preferably from 10 to 40 ° C. from the viewpoint of suppressing coagulation of natural rubber latex. Further, it is more preferably around room temperature (for example, 20 ° C.). By making the pH at the time of decomposition alkaline, the destabilization of the lipid membrane due to the decomposition of the protein is suppressed, and as a result, the desired protein decomposition proceeds and coagulation of the natural rubber latex is suppressed. The
In addition, although the decomposition processing time by protease changes with the addition amount of protease, pH and temperature at the time of decomposition | disassembly, it is preferable that it is 1-48 hours, for example.

In the method for producing natural rubber of the present invention, as described above, a coagulated product obtained by coagulating a natural rubber latex modified with laccase, or a solid form natural rubber modified with laccase is washed. Or may be aged before drying. For example, it is preferably aged for 1 day or more in an environment of a relative humidity of 40 to 90% and a temperature of 10 to 70 ° C.
By aging the coagulated rubber or solid rubber in the above atmosphere for 1 day or longer, proteins etc. are appropriately decomposed by bacteria existing inside and outside the coagulated rubber or solid rubber, and obtained natural The processability of rubber is further improved, and the dispersibility of fillers such as carbon black in natural rubber is increased due to the appropriate decomposition of proteins, etc., improving the fuel efficiency of tires using the natural rubber To do.

  In the method for producing natural rubber according to the present invention, it is preferable to perform washing after each of the operations described above.

In the method for producing natural rubber according to the present invention, it is preferable to add an anti-aging agent to the coagulated rubber or solid rubber after washing and then dry it. Here, as a method for adding the anti-aging agent, for example, it may be sprayed on a solidified rubber or a solid form rubber, or a solidified rubber or a solid form rubber may be immersed in the anti-aging agent, An anti-aging agent may be kneaded into the solidified rubber or solid rubber.
By adding an anti-aging agent, it is possible to suppress the generation of radicals (free radicals) in the natural rubber, and it is possible to suppress an increase in branching of the natural rubber by suppressing the generation of radicals.
Here, the antioxidant is preferably an antioxidant or a hydrazide compound, more preferably a hydrazide compound, from the viewpoint of capturing radicals generated when the solidified rubber or solid rubber is dried.

  The hydrazide compound suppresses branching due to aldehyde-protein bonds and aldehyde-phospholipid bonds by capping aldehydes generated in the main chain by oxidation of natural rubber when natural rubber is dried. Therefore, an increase in branching during drying can be suppressed. The hydrazide compound is preferably a carboxylic acid hydrazide, and the carboxylic acid portion of the carboxylic acid hydrazide preferably has 1 to 20 carbon atoms, and the carboxylic acid portion is selected from an aliphatic carboxylic acid and an aromatic carboxylic acid. It is preferable to be derived from at least one selected from the above. As the hydrazide compound, either a cyclic hydrazide compound or an acyclic hydrazide compound may be used, but an acyclic hydrazide compound is preferred from the viewpoint of reactivity due to steric hindrance.

  As the hydrazide compound, an aliphatic carboxylic acid hydrazide having 2 to 20 carbon atoms is preferable, and an aliphatic carboxylic acid hydrazide having 2 to 6 carbon atoms is particularly preferable. Specific examples of these hydrazide compounds include adipic acid dihydrazide (ADH), sebacic acid hydrazide (SDH), dodecanediohydrazide (DDH), propionic acid hydrazide (PHZ), stearic acid hydrazide, palmitic acid hydrazide, lauric acid hydrazide ( Dodecanoic acid hydrazide), butyric acid hydrazide, pentanoic acid hydrazide, hexanoic acid hydrazide, heptanoic acid hydrazide, octanoic acid hydrazide, nonanoic acid hydrazide, decanoic acid hydrazide, propionic acid from the viewpoint of radical scavenging ability Hydrazide (PHZ) and stearic acid hydrazide are preferred.

The addition amount of the anti-aging agent is preferably in the range of 0.01 to 0.5 parts by mass, and 0.05 to 0.3 parts by mass with respect to 100 parts by mass of the rubber component in the solidified rubber or solid rubber. Is more preferable, and a range of 0.1 to 0.2 parts by mass is even more preferable. Depending on whether the anti-aging agent is added by spraying, dipping or kneading, it is preferable to appropriately select the addition amount of the anti-aging agent, but by making the addition amount of the anti-aging agent within the above range, at the time of drying An increase in the amount of branching of the rubber component is suppressed, and the processability of natural rubber can be improved.
The anti-aging agent is preferably sprayed and immersed in an aqueous solution from the viewpoint of suppressing variation in addition.

  In the method for producing natural rubber of the present invention, it is further preferable to dry using a normal dryer such as a vacuum dryer, an air dryer or a drum dryer. The drying temperature is preferably 90 to 150 ° C, more preferably 100 to 130 ° C, and the drying time is preferably 30 minutes to 5 hours, more preferably 1 to 4 hours.

<Rubber composition>
The rubber composition of the present invention comprises the above-mentioned natural rubber, that is, (1) a long chain branching index (LCB index) at 70 ° C. of 10.6 to 17.9 and a long chain branching index at 130 ° C. (LCB index) is a natural rubber characterized by 3.0 or less, or (2) long chain branching index (LCB index) at 70 ° C. is 7.8 or more and 130 ° C. It contains natural rubber produced by a method for producing natural rubber, characterized in that laccase is added to raw natural rubber having an index (LCB index) of 3.5 or less. Since the rubber composition of the present invention contains the natural rubber, it is excellent in low hysteresis loss and wear resistance. The rubber composition of the present invention may further contain a rubber component other than the natural rubber.

In the rubber composition of the present invention, the content of the above-mentioned natural rubber is preferably 5% by mass or more, more preferably 10% by mass or more in the rubber component. If 5% by mass or more of the rubber component is the natural rubber described above, the low hysteresis loss and the wear resistance of the rubber composition can be sufficiently improved.
In the rubber composition of the present invention, examples of other rubber components that can be used in combination with the natural rubber described above include ordinary natural rubber and diene synthetic rubber. Examples of the diene synthetic rubber include styrene- Examples include butadiene copolymer rubber (SBR), polybutadiene (BR), and polyisoprene (IR).

In addition to the natural rubber, the rubber composition of the present invention includes fillers such as carbon black and silica, anti-aging agents, silane coupling agents, vulcanization accelerators, vulcanization accelerators, vulcanizers, and the like. They can be appropriately selected and blended within a range that does not impair the object of the present invention. As these compounding agents, commercially available products can be suitably used.
The rubber composition of the present invention can be produced by blending a rubber component containing at least the natural rubber with various compounding agents appropriately selected as necessary, kneading, heating, extruding, and the like. .

<Tire>
The tire of the present invention is characterized by using the above-described rubber composition. Since the rubber composition of the present invention uses the rubber composition, the tire has excellent fuel efficiency (that is, low rolling resistance and excellent low hysteresis loss) and excellent wear resistance. Here, examples of the part of the tire using the rubber composition include a tread, a sidewall, a case member, and the like, and a tread is preferable.

  The tire of the present invention may be obtained by vulcanization after molding using an unvulcanized rubber composition depending on the type of tire to be applied, or a semi-crosslinked rubber composition (semi-half It may be obtained by molding using a vulcanized rubber and then further vulcanizing. The tire of the present invention is preferably a pneumatic tire, and as a gas filled in the pneumatic tire, an inert gas such as nitrogen, argon, helium, or the like other than normal or oxygen partial pressure adjusted air is used. Can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
As the raw natural rubber, field latex of Para rubber tree variety PB330 was used, and the field latex was adjusted to pH 10.5 with ammonia water.
Next, laccase [“NS81268 (product number)”, enzyme activity: 1000 (Unit / g), oxidation-reduction potential: 480 mV, manufactured by Novozymes A / S, Inc.] with respect to 100 parts by mass of the rubber component contained in the raw natural rubber. Was added and stirred for 1 hour to react.
Thereafter, diluted formic acid was added to the reaction solution to adjust the pH to 4.7, the latex was coagulated, and the obtained coagulated product was treated 5 times with a creper and passed through a shredder to crumb. Subsequently, it was dried for 2 hours under a temperature condition of 130 ° C. using a hot air dryer to obtain a natural rubber.

(Example 2)
Natural rubber was obtained in the same manner as in Example 1 except that the amount of laccase added was 0.05 parts by mass and the stirring time (reaction time) was overnight (12 hours).

(Example 3)
Naturally the same as in Example 1 except that propionate hydrazide (PHZ) is sprayed in an amount of 0.1 parts by mass with respect to 100 parts by mass of the rubber component contained in the raw natural rubber before drying the crushed coagulum. Got rubber.

Example 4
As raw material natural rubber, a cup lamp obtained by leaving a field latex of Para rubber tree varieties PB330 is prepared by chopping it into 1 mm squares. After adding 100 parts by weight of skim (serum) obtained by separation, the pH was adjusted to 4.7 with diluted formic acid, and laccase [“NS81268 (product number)”, enzyme activity: 1000 (Unit / g), redox potential : 480 mV, manufactured by Novozymes A / S] was added in an amount of 0.2 part by mass with respect to 100 parts by mass of the rubber component contained in the raw natural rubber, and the mixture was stirred for 1 hour to be reacted. Subsequently, it was dried for 2 hours under a temperature condition of 130 ° C. using a hot air dryer to obtain a natural rubber.

(Example 5)
Natural rubber was obtained in the same manner as in Example 4 except that the amount of laccase added was 0.05 parts by mass.

(Example 6)
Except for using as raw material natural rubber, latex obtained by mixing paraffin rubber field PB260 field latex and field RRIM921 field latex so that the mass ratio of the rubber component in the latex is 1: 1. Natural rubber was obtained in the same manner as in No. 2.

(Example 7)
As a raw natural rubber, dilute formic acid is added to a latex obtained by mixing a paraffin rubber field PB330 field latex and a field RRIM 921 field latex so that the mass ratio of rubber components in the latex is 1: 1. The pH was adjusted to 4.7 to coagulate the latex, and the resulting coagulated product was treated with a creper five times and crushed through a shredder.
Next, propionate hydrazide (PHZ) is sprayed on the crushed coagulum in an amount of 0.1 part by mass with respect to 100 parts by mass of the rubber component contained in the raw natural rubber, and then using a hot air dryer. Natural rubber was obtained by drying at 130 ° C. for 2 hours.

(Example 8)
A natural rubber was obtained in the same manner as in Example 2 except that a field latex of Para rubber tree cultivar PB260 was used as a raw natural rubber and dried at 115 ° C. for 6 hours.

Example 9
As the raw natural rubber, field latex of Para rubber tree variety PB330 was used, and the field latex was adjusted to pH 10.5 with ammonia water.
Next, laccase ["NS81268 (product number)", enzyme activity: 1000 (Unit / g), oxidation-reduction potential: 480 mV, manufactured by Novozymes A / S, Inc.] with respect to 100 parts by mass of the rubber component contained in the raw natural rubber. 0.1 parts by mass was added and reacted for 1 hour.
Furthermore, 0.2 parts by mass of protease [“Savinase 16L”, manufactured by Novozymes, Inc.] was added to 100 parts by mass of the rubber component contained in the raw natural rubber, and reacted for 1 hour.
Thereafter, diluted formic acid was added to the reaction solution to adjust the pH to 4.7 to coagulate the latex, and the obtained coagulated product was aged in an environment of 50 ° C. and 50% relative humidity for 10 days.
Further, the resulting aged product was treated five times with a creper and passed through a shredder to crumb. Subsequently, it was dried for 3.5 hours under a temperature condition of 130 ° C. using a warm air dryer to obtain a natural rubber.

(Example 10)
Natural rubber was obtained in the same manner as in Example 8 except that drying was performed at 110 ° C. for 8 hours.

(Example 11)
A natural rubber was obtained in the same manner as in Example 8 except that the stirring time (reaction time) was 1 hour and the drying was performed at 120 ° C. for 4 hours.

(Comparative Example 1)
A natural rubber was obtained in the same manner as in Example 1 except that laccase was not added.

(Comparative Example 2)
Natural rubber was obtained in the same manner as in Comparative Example 1 except that the coagulated product obtained by coagulating the latex was aged for 10 days in an environment of 50 ° C. and 50% relative humidity.

(Comparative Example 3)
Naturally the same as in Comparative Example 1 except that propionate hydrazide (PHZ) is sprayed in an amount of 0.1 parts by mass to 100 parts by mass of the rubber component contained in the raw natural rubber before drying the crumbly solid. Got rubber.

(Comparative Example 4)
A natural rubber was obtained in the same manner as in Example 9 except that laccase was not added.

(Comparative Example 5)
A natural rubber was obtained in the same manner as in Example 1 except that the amount of laccase added was 0.2 parts by mass.

(Comparative Example 6)
Natural rubber was obtained in the same manner as in Comparative Example 1 except that drying was performed at a temperature of 80 ° C. for 168 hours (7 days).

(Comparative Example 7)
Natural rubber was obtained in the same manner as in Comparative Example 1 except that field latex of Para rubber tree variety PB260 was used as the raw natural rubber.

(Comparative Example 8)
A natural rubber was obtained in the same manner as in Example 1 except that a field latex of Para rubber tree variety PB260 was used as the raw natural rubber.

(Comparative Example 9)
Natural rubber was obtained in the same manner as in Comparative Example 1 except that a field latex of Para rubber tree variety RRIM921 was used as the raw natural rubber.

(Comparative Example 10)
Comparative example, except that a latex obtained by mixing paraffin rubber field PB330 field latex and field RRIM 921 field latex so that the mass ratio of the rubber component in the latex is 1: 1 is used as the raw natural rubber. Natural rubber was obtained in the same manner as in 1.

  For the natural rubber obtained in the above Examples and Comparative Examples, the long chain branching index and the polymer gel ratio were measured by the following methods.

<Measurement of long chain branching index>
“RPA2000 Auto100” (manufactured by Alpha Technologies Co., Ltd.) was used as a test apparatus, and “Alpha Technologies PRA2000Auto type die D5051” was used as a die in the apparatus, and a sample 5 g was placed on “die D5051” at a temperature of 70 ° C. Then, after placing for 1 minute at a frequency of 1.67 Hz and a distortion of 0.5%, the shear stress signal obtained by measurement in the LAOS mode is calculated up to n = 9 by discrete Fourier transform, and the above-described equation is used. As a measurement condition, a test piece having a mass of 5 g was subjected to a measurement force of 15.6 kN, a temperature of 70 ° C., a frequency of 1.67 Hz, and a strain of 0.5% for 1 minute, and then for 10 seconds (ie, 0.1 Hz), the angular velocity ω is 0.50 rad / s, the angle is 71.5 degrees, the strain is 1000%, Under the condition that the force during the measurement was 15.6 kN, G ′ _n was obtained at each temperature while increasing the temperature sequentially from 70 ° C., 80 ° C., 90 ° C., 100 ° C., 110 ° C., 120 ° C., 130 ° C. G was determined _'1 / G' ₅ long chain branching index at 70 ° C. and 130 ℃ (LCB index) _{(i.e., LCB index = G '1 /} G' 5).
In addition, for those to which laccase was added, long-chain branching index of natural rubber obtained by drying (through coagulation, if necessary) without adding laccase (long-chain branching index of raw natural rubber) And after adding laccase (through coagulation, if necessary), the long chain branching index of the natural rubber obtained by drying (long chain branching index of the modified natural rubber) is measured. It was. When the raw natural rubber was in a latex state, the long-chain branching index of the raw natural rubber was measured in a state where the solidified product obtained by coagulating the latex was dried. The results are shown in Tables 1 and 2.

<Measurement of polymer gel ratio>
0.2 g of natural rubber obtained as described above was swollen in toluene overnight, treated with a centrifuge at 35000 rpm for 1.5 hours, and the precipitated gel was left to dry in a draft for 2 days and weighed. The amount of the polymer gel was determined, and the ratio of the polymer gel in the natural rubber was calculated. The results are shown in Tables 1 and 2.

<Preparation of rubber composition>
For 100 parts by mass of the natural rubber obtained as described above, 50 parts by mass of carbon black [N339, manufactured by Tokai Carbon Co., Ltd., trade name “SEAST 7KH”] and softener [manufactured by Sankyo Oil Chemical Co., Ltd., Product name "A / O mix"] 5 parts by weight, stearic acid 2 parts by weight, anti-aging agent 6C [N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, Ouchi Eshin 1 part by mass of “NOCRACK 6C” manufactured by Chemical Industry Co., Ltd., and vulcanization accelerator DZ [N, N′-dicyclohexyl-2-benzothiazylsulfenamide, “NOCSELER DZ” manufactured by Ouchi Shin Chemical Co., Ltd.] 9 parts by mass and 1 part by mass of sulfur were blended to prepare a rubber composition according to a conventional method.

<Evaluation of tire wear resistance>
A tire having a tire size of 11R22.5 was produced using the rubber composition prepared as described above as a tread member. The prepared tire is attached to the drive shaft of the truck, and the amount of wear (reduction in the groove of the tire) after traveling 10,000 km on a rough road is measured. expressed. The results are shown in Tables 1 and 2. The larger the index value, the smaller the amount of wear and the better the wear resistance of the tire.

<Evaluation of tire fuel efficiency>
The tire produced as described above was run on a drum at a speed of 80 km / h to measure the rolling resistance, and the index was displayed with the reciprocal of the rolling resistance of the tire of Comparative Example 1 being 100. The results are shown in Tables 1 and 2. The larger the index value, the smaller the rolling resistance and the better the fuel efficiency (low hysteresis loss) of the tire.

  From Table 1 and Table 2, it can be seen that the wear resistance and fuel efficiency of the tire can be improved by using the rubber composition containing the natural rubber of the example according to the present invention for the tire.

  The natural rubber of the present invention can be used, for example, in a rubber composition used for tires and the like. The rubber composition of the present invention can be used for tires and other rubber products. The tire of the present invention can be used as a tire for various vehicles.

Claims (3)

  A laccase is added to raw natural rubber having a long chain branching index (LCB index) at 70 ° C. of 7.8 or more and a long chain branching index (LCB index) at 130 ° C. of 3.5 or less. A method for producing natural rubber. The method for producing natural rubber according to claim 1 , wherein the laccase is added to a natural rubber latex of the raw natural rubber or a chopped product of a natural rubber latex coagulum. The method for producing natural rubber according to claim 1 , wherein the raw natural rubber is a raw natural rubber obtained from Para rubber tree variety PB330.