JP2006257237A - Mastication method of natural rubber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mastication method of a natural rubber which simply and effectively reduces the odor generated on the mastication of the natural rubber irrespective of the kind of the natural rubber. <P>SOLUTION: In the mastication method of a natural rubber in a Banbury mixer, the temperature for allowing the natural rubber to fall from the Banbury mixer to be taken out is set at ≤145°C. Preferably, zinc white and/or carbon black is added to the natural rubber in an amount of ≤5 pts.mass based on 100 pts.mass natural rubber on the mastication. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for masticating natural rubber, and more particularly to a method for masticating natural rubber that can reduce the odor peculiar to natural rubber generated during mastication of natural rubber.

  In general, the natural rubber used in the rubber industry is obtained by coagulating and drying a sap of a rubber tree (natural rubber latex) called Hevea brasiliens cultivated in the tropics. The methods for producing this natural rubber are roughly classified into technical rubbers (TSR) and technical rubber (RSS).

  TSR is classified into advanced grade and lower grade. The high grade TSR is produced by coagulating fresh latex with acid, washing and pulverizing it with water, and drying it with hot air at around 120 ° C. In addition, the lower grade TSR washes and pulverizes cup lamps made by natural coagulation of latex in latex recovery cups of rubber trees, and slabs obtained by natural coagulation of latex collected by small-scale farmers. Further, it is manufactured by drying. On the other hand, RSS is obtained by coagulating latex with an acid, rolling it into a sheet form with a roll to make an unmade sheet (USS), and further smoking it.

  The natural rubber produced by these manufacturing methods is packed with polyethylene before shipment, coated with talc, or because the temperature of the rubber has already dropped to room temperature. It is small and does not cause a problem.

  By the way, in general, natural rubber has a higher molecular weight than synthetic rubber, so it is difficult to uniformly knead various compounding agents in a rubber product factory. The operation of kneading and lowering the rubber molecular weight to an appropriate size is required. This operation is called “scouring”.

  When kneading, heat is generated as the kneading is promoted, and the temperature of the kneaded rubber compound rises. For the purpose of avoiding problems such as rubber burning caused by the increase in temperature, natural rubber is usually added to a Banbury mixer, and then a peptizer (peptizer) is added in an amount of 0. It is added in the range of 1 part by mass or less and kneaded at about 150 to 180 ° C.

  However, since the temperature rise of the natural rubber kneaded product cannot be sufficiently suppressed only by the cooling efficiency of the Banbury mixer itself, usually, the process of dropping from the Banbury mixer to the under roll in one to three minutes and taking it out is performed several times. It is common to repeat the process in multiple stages.

  During such a mastication process, odor components conventionally contained in natural rubber are emitted, and non-rubber components are further oxidized and decomposed to emit new odors. If these odors leak into and out of the factory, they may develop into environmental problems.

  When the odor generated by mastication of natural rubber is supplemented and analyzed by GC-MS, lower fatty acids such as acetic acid and propionic acid, aldehydes, nitrogen cyclic compounds such as prazines and pyrroles, ammonia, etc. are detected. It is known.

  To combat this odor problem, various countermeasures have been taken so far, such as installing a deodorizing filter in the exhaust duct of the kneading equipment or spraying fragrance around the kneading equipment. Further, as a method for improving the natural rubber itself, that is, for reducing the odor of the natural rubber, for example, when producing natural rubber from natural latex, By contacting with one or more alkaline solutions selected from sodium oxide, potassium hydroxide, and calcium hydroxide, odors are reduced by changing volatile fatty acids, which are odorous components produced from non-rubber components by microorganisms, to non-volatile fatty acids. A natural rubber production method is known (Patent Document 1).

Further, in the natural rubber production process, by adding a specific odor reducing component to the latex before coagulation in a specific amount range with respect to 100 parts by mass of dry rubber, only volatile fatty acids contained in natural rubber can be obtained. In addition, it is known that odors can be more effectively reduced by suppressing generation of unique odor components due to decomposition of aldehydes, nitrogen cyclic compounds, ammonia, and the like (Patent Document 2).
JP-A-8-81504 (claims, etc.) Japanese Patent Laying-Open No. 2005-29590 (Claims etc.)

  However, the technique described in Patent Document 1 is to reduce the odor by changing the volatile fatty acid of the odor component produced from the non-rubber component by microorganisms to a non-volatile fatty acid, but the odor component of natural rubber is Not only volatile fatty acids but also aldehydes, nitrogen cyclic compounds, ammonia and the like are present, and this technology has not yet reduced the odor of natural rubber to a satisfactory level.

  In addition, the technique described in Patent Document 2 requires that a specific odor reducing component is added to the latex before coagulation in a specific amount range. Could not be applied.

  Accordingly, an object of the present invention is to provide a natural rubber mastication method that can easily and effectively reduce the odor generated during mastication of natural rubber regardless of the type of natural rubber, eliminating the above problems. is there.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by setting the extraction temperature when masticating natural rubber with a Banbury mixer to a predetermined temperature or lower, The present invention has been completed.

  That is, the natural rubber mastication method of the present invention is a natural rubber mastication method in which natural rubber is masticated by a Banbury mixer, and the natural rubber is dropped from the Banbury mixer and taken out. Is 145 ° C. or lower.

  In the present invention, it is preferable to add zinc white to the natural rubber during mastication, more preferably 5 parts by mass or less with respect to 100 parts by mass of the natural rubber. Moreover, it is also preferable to add carbon black to the natural rubber during mastication, more preferably 5 parts by mass or less with respect to 100 parts by mass of the natural rubber.

  ADVANTAGE OF THE INVENTION According to this invention, the odor which generate | occur | produces at the time of mastication of natural rubber can be reduced simply and effectively irrespective of the kind of natural rubber.

Hereinafter, embodiments of the present invention will be specifically described.
In the present invention, it is important to set the temperature when the natural rubber paste is dropped from the Banbury mixer to the under roll to 145 ° C. or lower. As a result of repeated experiments, the present inventor has found that the odor suddenly increases when this temperature exceeds 149 ° C. (see FIG. 1). It has been found that it is necessary to regulate the temperature to 145 ° C. or lower for proper odor reduction. This can also be understood from the fact that the loss of heat of natural rubber by DSC in the laboratory is drastically reduced from around 150 ° C. and volatiles are greatly generated (see FIG. 2). That is, it can be seen from FIG. 1 that the odor of mastication has an inflection point when the drop temperature is 145 to 150 ° C., and the difference between the natural rubber types is small at this time. Moreover, the curve of the graph shown in FIG. 1 is similar to the heating loss curve by the DSC analysis shown in FIG. 2, and this also shows that the odor can be reduced by regulating the drop temperature.

  The conditions of the Banbury mixer that can be used in the present invention can be the same as those employed in the conventional mastication process except for the above-mentioned drop temperature. For example, the conditions except for the volume of the rotor part of the Banbury mixer can be used. The fill factor representing the contrast filling rate can be set to 50 to 80%, and the rotational speed of the rotor can be set to 8 to 80 rpm.

  In the present invention, from the viewpoint of reducing odor, it is preferable to add zinc oxide and carbon black to the natural rubber at the same time, or more, at the time of mastication, and more preferably to 100 parts by mass of the natural rubber. However, it is added at 5 parts by mass or less. It is not preferable to add more than 5 parts by mass because it adversely affects the subsequent kneading.

  Furthermore, in the present invention, thiophenol, disulfide, and the like that are usually used as a peptizer (peptizer) can be appropriately added to natural rubber.

Next, the present invention will be described specifically and in detail based on examples and comparative examples.
[Examples 1 to 3 and Comparative Examples 1 and 2]
Natural rubber was masticated with a Banbury mixer according to the formulation shown in Table 1 below and the temperature at which the masticated material dropped from the Banbury mixer. The odor concentration during mastication was evaluated according to the following. These results are shown in FIG.

The odor concentration was evaluated by the following procedures 1) to 6).
1) Using a 3.7 liter Banbury mixer for a test room, mastication was performed for 3 minutes and 30 seconds under conditions of circulating water at 70 ° C. and a rotor rotation speed of 70 rpm.
2) Immediately after mastication, the ram was raised immediately, and the odor mixed air discharged from the rubber inlet was collected for about 2 liters for about 2 minutes in a sampling back with a pump.
3) A prescribed amount of odor mixed air collected in the sampling bag was sampled with a chemical syringe and injected into a 3 liter odor bag filled with clean air in advance (sample). The dilution rate is determined with an injection volume of ml and 3 liters. For example, if the injection volume is 1 ml, the dilution factor is 3000.
4) The odor was judged by the nose with an odor monitor of at least 3 people to see if the sample felt odor compared to clean air.
5) If a smell was felt, a sample with an increased dilution factor was prepared, and it was judged again whether or not the smell was felt by a monitor.
6) The dilution ratio at which no odor was felt was taken as the odor concentration.

１）ノクタイザーＳＫ（大内新興化学工業（株）製）
２）ＲＳＳ：ＲＩＢＢＥＤ ＳＭＯＫＥＤ ＳＨＥＥＴ（品番：ＲＳＳ＃４）
３）ＴＳＲ：ＴＥＣＨＮＩＣＡＬＬＹ ＳＰＥＣＩＦＩＥＤ ＲＵＢＢＥＲ（品番：ＳＭＲ＃２０）
４）ＴＳＲ：ＴＥＣＨＮＩＣＡＬＬＹ ＳＰＥＣＩＦＩＥＤ ＲＵＢＢＥＲ（品番：ＳＩＲ＃２０）

1) Noctizer SK (Ouchi Shinsei Chemical Co., Ltd.)
2) RSS: RIBBED SMOKED SHEEET (Part No .: RSS # 4)
3) TSR: TECHNICALLY SPECIFED RUBBER (Part No .: SMR # 20)
4) TSR: TECHNICALLY SPECIFED RUBBER (Part No .: SIR # 20)

  It can be seen from Table 1 and FIG. 3 that the odor can be reduced by regulating the kneading drop temperature to 145 ° C. or lower regardless of the type of natural rubber. Moreover, it turns out that the further effect is acquired by using together zinc white and carbon.

It is a graph which shows the relationship between the fall temperature of RSS and TSR, and an odor density | concentration. It is a graph which shows the relationship between drop temperature and weight loss rate. It is a graph showing the relationship between the fall temperature and odor temperature in Examples 1-3 and Comparative Examples 1,2.

Claims (5)

  In a natural rubber mastication method in which natural rubber is masticated with a Banbury mixer, the natural rubber is dropped from the Banbury mixer and the temperature of the natural rubber when taken out is 145 ° C. or less. The method of practicing.   The mastication method according to claim 1, wherein zinc white is added to the natural rubber during mastication.   The mastication method according to claim 2, wherein the zinc white is added at 5 parts by mass or less with respect to 100 parts by mass of the natural rubber.   The mastication method according to any one of claims 1 to 3, wherein carbon black is added to the natural rubber during mastication.   The mastication method according to claim 4, wherein the carbon black is added at 5 parts by mass or less with respect to 100 parts by mass of the natural rubber.

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