JP2006213751A - Natural rubber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a natural rubber capable of saving work such as not necessarily requiring a mastication process, also not requiring to perform a viscosity adjustment by using a kneading machine, etc., such as a dry pre-breaker, etc., and without causing unevenness in its mastication quality, and a method for producing the same. <P>SOLUTION: This natural rubber is obtained by the coagulation treatment of natural rubber latex within 3.0-4.2 pH range by a coagulating acid and the natural rubber obtained by such method has a low molecular weight and not necessarily requires the mastication process, and also is obtained by adding a hydrazine compound or triazole compound as its viscosity stabilizer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to natural rubber and a method for producing the same, and more particularly to a natural rubber having a stable quality that can save labor in a mastication process in a tire factory as a natural rubber for tires and a method for producing the same. It is.

  In general, natural rubber is widely used in large quantities in the rubber industry and the tire industry because of its excellent physical properties. Conventionally, the following two methods are typical for the production process of natural rubber. In the ribbed smoked sheet (RSS) according to the international quality packaging standard for natural rubber grades (commonly known as the Green Book), the rubber component is solidified (USS) with acid etc. after collecting the natural rubber latex, Separated into rubber component (solid rubber), non-rubber component (natural rubber serum), and deposit, washed solid rubber with water, dehydrated, dried (smoked) for 5-7 days at about 60 ° C. Is doing. In the case of RSS as such a tire raw material, the molecular weight is conventionally high and the processability is inferior. In order to improve such problems, USS raw material natural rubber containing a viscosity stabilizer has been proposed (for example, see Patent Document 1). Conventionally, in such a constant viscosity natural rubber, a molecular weight is lowered by mixing a kneading agent in a dry prebreaker (hereinafter referred to as DPB) after drying.

  In addition, rubber materials for tires such as technically graded rubber (TSR) made of cup lamps (things that have been hardened naturally by formic acid in latex cups in advance) have a low molecular weight, but are naturally Since the solidified cup lamp is the main component, there is a large variation in quality, and foreign substances are easily mixed in, so that it is necessary to remove this in the manufacturing process.

For these reasons, the conventional natural rubber as a raw material for tires has not yet completely eliminated the mastication process at the tire factory. In RSS, it is difficult to reduce the viscosity until the mastication process in the tire factory is omitted, and it is necessary to remove foreign matter after the mastication process even in the case of a cup lamp, raw material TSR, or the like.
Therefore, the conventional molecular weight adjustment method is mainly a method for thermally and mechanically lowering the molecular weight, such as adjusting the temperature of a dryer and using DPB, and there is still a problem in processability as a rubber raw material for tires and the like. .

JP-A-8-67703

  The problem of the present invention is that the mastication step is not necessarily required, and it is possible to save labor in a tire factory such as no need to adjust the viscosity using a kneader such as a dry prebreaker, and the preservation of quality is good. An object of the present invention is to provide a natural rubber that does not vary and a method for producing the same.

The inventor of the present invention, when coagulating a natural rubber latex, further reduces the molecular weight of the natural rubber produced by lowering the pH value from the range of pH 4.4-5.0 at the time of coagulation of the rubber latex. And that natural rubber obtained by such adjustment does not necessarily require a mastication step and can be obtained as a low molecular weight, and even in such a pH environment, natural rubber latex or coagulated rubber It has been found that a sufficient effect is exhibited by adding a constant viscosity agent to the resin, and that a natural rubber having storability and uniformity in quality can be obtained, leading to the present invention.
That is, the present invention is characterized by having the following configuration or structure.

  (1) Natural rubber obtained by coagulating natural rubber latex with a coagulating acid in the range of pH 3.0 to 4.2.

(2) The natural rubber according to (1) above, wherein a hydrazine compound or a triazole compound is added as a constant viscosity agent.
(3) The natural rubber according to (2) above, wherein the hydrazide compound or triazole compound is added to the rubber latex before coagulation or is added by dipping or spraying on the rubber before drying.
(4) The natural rubber according to (2) or (3), wherein the hydrazine compound is represented by the following general formula.
General formula: R—CONHNH ₂ (wherein R represents an alkyl group having 1 to 30 carbon atoms and a cycloalkyl group having 3 to 30 carbon atoms)
(5) The natural of the above (2) or (3), wherein the triazole compound comprises at least one selected from 1,2,4-triazole and 4-amino-1,2,4-triazole. Rubber.

  (6) A method for producing natural rubber, in which a coagulating acid is added to natural rubber latex, the rubber latex is coagulated to a pH of 3.0 to 4.2, and dried.

  (7) The method for producing natural rubber according to the above (6), wherein the viscosity stabilizer is added to the rubber latex before coagulation, or is immersed or sprayed before drying.

  In the natural rubber of the present invention and the method for producing the same, the molecular weight of the natural rubber to be produced can be adjusted by adjusting the natural rubber latex to a pH of 3.0 to 4.2 when the rubber latex is coagulated. It can be obtained as a low molecular weight material that does not necessarily require tire milling and that can save labor in the tire factory. In addition, by adding a viscosity stabilizer before the drying step, quality storage stability and quality variation are improved, and this can be easily used as a rubber composition and a tire.

Embodiments of the present invention will be described below. In addition, the natural rubber of this invention and its manufacturing method are not limited to the following embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention.
The following two methods are typical for the production of natural rubber. That is, in the ribbed smoked sheet (RSS) according to the international quality packaging standard (commonly known as the Green Book) of natural rubber grade products, the rubber component is solidified (USS) with acid etc. after collecting the natural rubber latex. The solid rubber is separated from the water-soluble non-rubber component by a roll, and the solid rubber is dried (smoking) at about 60 ° C. for 5 to 7 days. In addition, in the technical rating rubber (TSR), after tapping, the rubber component of the natural rubber latex is naturally coagulated (cup lamp), the solid rubber is pulverized, washed with water, dehydrated, and then the solid rubber is heated to 110 ° C to 140 ° C. Dry with hot air for several hours at ℃.
The natural rubber of the present invention is based on such a production method and includes the following treatment steps as necessary.

The natural rubber of the present invention is obtained by coagulating natural rubber latex with a coagulating acid in the range of pH 3.0 to 4.2.
<Natural rubber latex>
The natural rubber latex is, for example, a fresh latex after tapping that is used within 3 hours after tapping from a natural rubber tree, and a stabilizer that is stabilized by ammonia treatment or the like after being added to the latex after tapping, preferably Examples include latex having a pH of about 7.0 and centrifuge latex obtained by centrifuging these latexes using a centrifuge (each used alone or in combination of two or more).

<Coagulation treatment of natural rubber latex>
For the coagulation treatment, the following treatment with a coagulating acid or the like is performed. The coagulating acid may be an organic acid or an inorganic acid, and examples thereof include formic acid, citric acid, phosphoric acid, sulfuric acid and the like, and the pH of the latex to be treated is in the range of 3.0 to 4.2. Add acid.
Compared with the conventional coagulation reaction at pH 4.7, when the pH of the treated latex is 4.2 or less, the rubber viscosity after drying, which will be described later, is secured to the extent that it can be processed as it is in a tire factory. it can. The natural rubber viscosity after drying is preferably 65 or less in Mooney viscosity (Mooney value ML _{1 + 4} at 100 ° C. in accordance with JIS K 6300-1994). On the other hand, if the pH of the treated latex is less than 3.0, the modulus, resilience, and adhesiveness of the rubber after coagulation are adversely affected, and desired rubber properties cannot be obtained. In addition, the coagulation time is shortened and solidifies during stirring. The coagulation aging time is selected according to the natural rubber raw material species.

<Clamation processing>
In the present invention, it is preferable to perform a crumb treatment before drying the solidified solidified product. The crumb treatment is not necessarily required, but is performed for uniform drying. For example, the crumb treatment can be performed through a creper process and / or a shredder process. As the creper process, for example, a creper sheet can be obtained by passing the coagulated material four times through Creper Model CRC 14/28 manufactured by SPHERE. Also, as the shredder process, for example, a Shredder Model CRC manufactured by SPHERE is used. The crumb can be obtained by charging this creper sheet on 14/28.

<Drying process>
The drying treatment of the solidified product is not limited to the following method, but can be performed using, for example, a bucket dryer or a belt dryer. Examples of the bucket dryer include a dryer used for normal TSR production, specifically, Single Box Dryer Model CRDS manufactured by SHARE. Moreover, as a belt-type dryer, the thing provided with the conveyor-type dryer, for example, a far infrared ray apparatus, or a microwave apparatus, is mentioned. The solidified product is dried until the moisture content of the natural rubber mixture is preferably 1.5% or less, more preferably 0.8% or less, from the viewpoint of kneading stability and material stability of the compounded rubber. It is desirable.

<Constant viscosity formulation>
In the present invention, the hydrazide compound or triazole compound as a viscosity stabilizer can be added to the natural rubber depending on whether it is added to the rubber latex before coagulation, or added to the rubber before drying by dipping or spraying. . Among these, it is preferable to add a viscosity stabilizer to the rubber latex before coagulation. As described above, the compounding before coagulation can suppress the increase in viscosity before the drying step and can suppress the increase in viscosity in the subsequent steps, and as a result, a homogeneous natural rubber raw material can always be obtained. Further, it is not necessary to use a kneader after drying.
The term "before coagulation" means that the rubber latex is in a coagulated state. For example, as long as the rubber latex is in a coagulated state, the viscosity stabilizer may be added to the rubber latex at the same time as the coagulating acid described above. Etc. may be added after addition. However, it is preferable that the coagulation treatment is started after the constant viscosity agent is preferably added to the rubber latex and aged for a predetermined time.
In addition, although it can also knead | mix and add to the rubber | gum after drying, since kneading machines, such as a dry prebreaker (DPB), are applied in this case, it cannot contribute to labor saving.

Examples of the viscosity stabilizer used in the present invention include hydrazide compounds and triazole compounds. These can be blended separately or together.
Specific examples of the hydrazide compound include hydrazide compounds represented by the following general formula (1).
General formula (1): R-CONHNH ₂
(However, R in the formula represents any of an alkyl group having 1 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, and an aryl group having 3 to 30 carbon atoms.)
Examples of the hydrazide compound represented by the above general formula include acetohydrazide, propionic acid hydrazide, butyl hydrazide, lauric acid hydrazide, palmitic acid hydrazide, stearic acid hydrazide, cyclopropyl hydrazide, cyclohexyl hydrazide, cycloheptyl hydrazide, and benzoic acid hydrazide. , O-, m-, p-tolyl hydrazide, p-methoxyphenyl hydrazide, 3,5-xylyl hydrazide, 1-naphthyl hydrazide.

Moreover, as a triazole compound, the triazole compound represented by following General formula (2) is preferable.
General formula (2): R—C ₂ H ₂ N ₃
However, R in General formula (2) shows a hydrogen group, a C1-C30 alkyl group, a C3-C30 cycloalkyl group, and an aryl group. Further, an amino group, mercapto group, hydroxyl group, carbonyl group, or benzo group may be added to the triazole skeleton.

  As specific triazole compounds, 1,2,4-triazole, 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, 3-mercapto-1,2,4- Triazole, 1,2,4-triazol-3-ol, 5-amino-3-mercapto-1,2,4-triazole, 5-amino-1,2,4-triazole, 1,2,4-triazole- Examples of the triazole compound include 3-carboxylic acid, benzotriazole, and 1-hydroxybenzotriazole (monohydrate).

The viscosity of the natural rubber to be produced can be adjusted according to the type of the above-mentioned compound. The hydrazide compound which has this can be mentioned. Examples of medium viscosity natural rubber include propionic acid hydrazide, acetohydrazide, butyl hydrazide, 1,2,4-triazole, 4-amino-1,2,4-triazole and the like. Examples of low-viscosity natural rubber include alkyl acid hydrazides having 12 or more carbon atoms in R, such as lauric hydrazide and palmitic hydrazide.
In the natural rubber of the present invention, one or more of such high viscosity, medium viscosity, and low viscosity viscosity stabilizers are appropriately selected, and the natural rubber has a Mooney viscosity of 80 or less, particularly 75 to It is preferable to be in the range of 40.

The above-mentioned viscosity stabilizer can be directly blended as it is before coagulation, and when it is added by dipping or spraying on the rubber before drying, the viscosity stabilizer is dissolved in a dispersion medium, a solvent or the like. It is preferable to mix them.
The dispersion medium can be used as an aqueous solution when the type of the viscosity stabilizer is aqueous, or as an emulsion when the type is oily.
The thickener emulsion can be obtained by a usual method using an emulsifier and, if necessary, an affinity agent. It is preferable that the concentration of the aqueous solution of the viscosity stabilizer is 20 to 80% by mass, and the concentration of the viscosity stabilizer emulsion is 3 to 50% by mass. If the concentration is too thin (the concentration is less than 20% by mass or less than 3% by mass), the amount of the viscosity stabilizer required to add a desired amount of the viscosity stabilizer becomes too large. If the concentration is too high (the above concentration exceeds 80% by mass or 50% by mass), the stability of the liquid may be impaired and the dispersibility of the chemical may be deteriorated.

  Moreover, the addition amount of the constant viscosity agent with respect to natural rubber (raw rubber) is 0.001 to 3 mass% with respect to the natural rubber (raw rubber) whole quantity, Preferably, it is 0.03 to 2.5 mass%. If the addition amount of the viscosity stabilizer is less than 0.001% by mass, the desired viscosity effect may not be exhibited. If the amount exceeds 3% by mass, it remains in the rubber composition, and the rubber The low exothermic property and durability of the composition may be lowered, and the dispersibility of carbon black and other compounding chemicals may be lowered.

  As an aspect of immersing the viscosity stabilizer, a method of immersing natural rubber (USS sheet, crumb, etc.) as it is in a viscosity stabilizer aqueous solution or a viscosity stabilizer emulsion in which each of the above viscosity stabilizer types is dissolved, a viscosity stabilizer aqueous solution or Examples include a method of immersing natural rubber (USS sheet, crumb, etc.) in a state where the viscosity stabilizer emulsion is stirred. In addition, although immersion time is fluctuate | varied with a natural rubber seed | species, a magnitude | size, etc., Preferably it is 10 second-80 minutes, More preferably, it is 30 second-60 minutes. In this immersion treatment, the desired effect can be exhibited in a short time. In addition, as an aspect of spraying the viscosity stabilizer, the aqueous solution of viscosity stabilizer or the emulsion of viscosity stabilizer dissolved in each of the above viscosity stabilizer types is sprayed uniformly on both sides of the USS sheet and crumb on the conveyor using a sprayer. Etc. In the present invention, a viscosity stabilizer can be added to natural rubber (raw rubber) in the above-described dipping mode or in the above-described spraying mode, and further, if necessary, this dipping and spraying mode. Can also be added in combination.

  The natural rubber of the present invention can be directly made into a rubber composition such as tire rubber without a mastication step. In addition to the natural rubber, various synthetic rubbers can be used for the rubber composition. It is preferable to use a gen synthetic rubber from the viewpoint of polymer compatibility (uniform dispersion). Examples of the gen-based synthetic rubber that can be used include at least one selected from isoprene rubber, styrene-butadiene copolymer rubber, butadiene rubber, and styrene-isoprene copolymer rubber, particularly from the viewpoint of heat resistance. Desirable is at least one selected from isoprene rubber, styrene-butadiene copolymer rubber, and butadiene rubber. In such a rubber composition, the content of the natural rubber obtained above is 5% by mass or more, preferably 10 to 70% by mass with respect to the total amount of all rubber components. When the content of the natural rubber is less than 5% by mass, the viscosity improving effect is lost when used for a tire member or the like.

In the natural rubber of the present invention configured as described above and the method for producing the natural rubber, the natural rubber latex is coagulated, and the natural latex produced by setting the pH at the time of coagulation of the rubber latex to be in the range of 3.0 to 4.2. Reduce the molecular weight of the rubber. For this reason, since the mastication process in a tire factory is not necessarily required, labor saving in a tire factory is attained. In addition, when a viscosity stabilizer is added in a relatively early step of the natural rubber production process, an increase in viscosity before the drying process can be suppressed, and an increase in viscosity in the subsequent process can be suppressed. A homogeneous natural rubber raw material will always be obtained.
The natural rubber obtained in the above treatment step of the present invention includes, as necessary, a filler, a reinforcing agent, a softening agent, a vulcanizing agent, a vulcanization accelerator, a vulcanization acceleration aid, an antiaging agent, and the like. These optional components can also be contained. Natural rubber is widely used in the rubber industry and the tire industry because of its excellent physical properties, and is particularly preferably used for tire rubber.

Hereinafter, the present invention will be described more specifically and in detail by examples and comparative examples, but the present invention is not limited to the following examples.
The following processes were appropriately selected to produce natural rubbers and rubber compositions of Examples and Comparative Examples. The selection process and the evaluation of Mooney viscosity are shown in Tables 1 and 2.

<Natural rubber latex>
A natural rubber latex (a rubber concentration (DRC) of 30%) added with 0.4% by mass of ammonia was used.
<Coagulation process>
To the rubber latex, the coagulating acid shown in Table 1 below was added to adjust the pH shown in Table 1, and the natural rubber latex was coagulated.
<Clamation process>
The solidified product was crushed by passing it through a crusher, a scraper 3 times and a shredder.
<Drying process>
It dried at 110 degreeC and 300 minutes with the bucket dryer.
<Powdering process>
Kneading with a dry prebreaker (DPB).

<Stage viscosity adding process>
A 50 mass% aqueous solution of propionic acid hydrazide was added at the following timing. In addition, the compounding quantity of the viscosity stabilizer in Table 2 is mass% with respect to natural rubber (raw rubber).
(Input before solidification)
A constant viscosity agent is added, and after stirring for 30 seconds, a coagulating acid is added. Then, it was left for 8 hours.
(After drying)
A predetermined amount of a constant viscosity agent was mixed with a dry prebreaker (DPB).

(Evaluation method of molecular weight)
The molecular weight is measured by a gel permeation chromatography method. The measuring apparatus includes a gel permeation chromatograph (HCL-8020) manufactured by Tosoh Corporation, the column includes GMHXL manufactured by Tosoh Corporation, and standard polystyrene manufactured by Tosoh Corporation for calibration. THF (primary) was used as the solvent, and 0.01 g sample / 30 cc THF was used as the solution.

(Measuring method of Mooney viscosity)
In accordance with JIS K 6300-1994, using an automatic Mooney viscometer SMV-202 manufactured by Shimadzu Corporation, Mooney viscosity at 100 ° C. immediately after production: ML _{1 + 4} (ORIGINAL) and this natural rubber in an oven at 60 ° C. Mooney viscosity at 100 ° C. after storage for 7 days in the medium: ML _{1 + 4} (AGED) was measured, and as a constant viscosity effect,
The Mooney viscosity difference was determined by ML _{1 + 4} (AGED) −ML _{1 + 4} (ORIGINAL) to evaluate the constant viscosity effect.

In the table, ◯ is the use process. Note (1) is the viscosity before mastication, and note (2) is the viscosity of the compounded rubber composition.
The content of the rubber composition is 50 parts by mass for each natural rubber, 50 parts by mass for isoprene rubber (N110), 5 parts by mass for aroma oil, 1 part by mass for stearic acid, 3 parts by mass for zinc white, and vulcanization acceleration. The agent (DZ: N, N-dicyclohexyl-2-benzothiasulfenamide) is 0.8 part by mass and sulfur is 1.2 parts by mass.

The natural rubber of the present invention and the production method thereof do not necessarily require a kneading process, and it is possible to save labor in a tire factory, such as no need to adjust the viscosity using a kneader such as a dry prebreaker. The quality does not vary, and the industrial applicability is high.

Claims (7)

A natural rubber obtained by coagulating natural rubber latex with a coagulating acid in the range of pH 3.0 to 4.2. The natural rubber according to claim 1, wherein a hydrazine compound or a triazole compound is added as a constant viscosity agent. 3. The natural rubber according to claim 2, wherein the hydrazide compound or triazole compound is added to the rubber latex before coagulation, or is immersed or sprayed on the rubber before drying. The natural rubber according to claim 2 or 3, wherein the hydrazine compound is represented by the following general formula.
General formula: R—CONHNH ₂ (wherein R represents an alkyl group having 1 to 30 carbon atoms and a cycloalkyl group having 3 to 30 carbon atoms) The natural rubber according to claim 2 or 3, wherein the triazole compound comprises at least one selected from 1,2,4-triazole and 4-amino-1,2,4-triazole. A method for producing natural rubber, comprising adding a coagulating acid to natural rubber latex, coagulating the rubber latex to a pH in the range of 3.0 to 4.2, and drying. The method for producing natural rubber according to claim 6, wherein the viscosity stabilizer is added to the rubber latex before coagulation, or is immersed or sprayed before drying.