JP4815117B2 - Coagulation of natural rubber latex - Google Patents

Description

  The present invention relates to a method for coagulating natural rubber latex. More particularly, the present invention relates to a method for continuously coagulating natural rubber latex.

  Coagulation of natural rubber latex is currently performed by the following method. Fresh natural rubber latex is put into a coagulation tank, diluted with an approximately equal amount of serum water, formic acid is added to adjust the pH of the latex to 4.5 to 5.5, and then left as it is. The crumb solidified after standing for about 9 hours is separated on the liquid surface. Although it may stir instead of leaving still, even in that case, solidification requires 3 to 4 hours. In either case, the solidified crumb becomes a thick mat. This is pulled out of the coagulation tank and subjected to dehydration, fragmentation and washing. Although the operation of each coagulation tank is a batch system, it is devised so that the subsequent steps of dehydration, fragmentation and water washing can be performed continuously by installing the coagulation tanks in parallel and switching them. However, the current natural rubber latex coagulation method has many problems from the industrial viewpoint as follows: (1) Coagulation rate is slow, (2) Therefore, batch operation is unavoidable. No, (3) Since the solidified crumb is a thick mat, it requires a lot of power and labor in the subsequent dehydration, fragmentation and water washing processes, and it costs a lot of money. (4) The solidified crumb is thick Because it is mat-like, it is difficult to remove impurities contained in the crumb, so the content of impurities is large. (5) It takes a lot of energy and time to dry the crushed crumb. (6) Equipment costs are high. (7) There is a problem of pollution in wastewater containing formic acid and residual rubber particles.

  An object of the present invention is to provide a coagulation method having a high coagulation rate, capable of continuous operation, and low operating cost and equipment cost in order to solve the above-mentioned problems of the natural rubber latex coagulation method.

  Another object of the present invention is to provide an innovative continuous solidification method and a solidification process for solving these problems.

  Still another object of the present invention is to provide a continuous coagulation method for natural rubber latex.

  Still other objects and advantages of the present invention will become apparent from the following description.

In accordance with the present invention, the above objects and advantages of the present invention include: (1) acid, and (2) (i) nitric acid, sulfuric acid, natural rubber latex, either fresh natural rubber latex or ammonia-added natural rubber latex . Porous coagulum obtained by adding at least one salt selected from the group consisting of calcium salt or ammonium salt of carbonic acid, phosphoric acid, hydrochloric acid and formic acid and / or (ii) a polymer flocculant with stirring. This is achieved by a natural rubber latex coagulation method characterized in that a slurry is produced.

  ADVANTAGE OF THE INVENTION According to this invention, the coagulation method which can coagulate | curing natural rubber latex rapidly and can give the natural rubber which is easy to post-process after coagulation | solidification and has few impurity contents is provided.

  The coagulation method of emulsion polymerization SBR performs instantaneous continuous coagulation by adding sodium chloride and sulfuric acid to SBR latex. The resulting coagulated rubber becomes a porous crumb slurry to facilitate subsequent washing and drying. Natural rubber latex has a high molecular weight, the latex particle protective film component is different from synthetic rubber latex, and contains non-rubber components with high adhesion. Even if added, solidification does not go well. As a result of intensive studies, the present inventor has devised a method and process capable of coagulating natural rubber latex quickly, preferably by continuous operation, by using a specific coagulation system suitable for coagulating natural rubber latex. I found it. This overcomes the problems associated with the conventional natural rubber latex coagulation process, and can dramatically increase productivity. That is, it was found that by using the solidification system in the present invention, solidification occurs quickly, the crumb to be produced is in the form of a porous slurry and can be obtained in a form that is easy to dry, and the serum is also transparent.

  The natural rubber latex used in the present invention may be either fresh natural rubber latex or ammonia-added natural rubber latex.

  As described above, the coagulation system used in the present invention comprises (1) an acid and (2) a specific salt and / or polymer flocculant.

  Either an organic acid or an inorganic acid can be used as the acid. As the organic acid, for example, formic acid and acetic acid are preferable, and as the inorganic acid, for example, sulfuric acid, hydrochloric acid, carbonic acid and the like are preferable. These acids are used alone or in combination of two or more.

  Specific salts are the calcium or ammonium salts of the respective acids of nitric acid, sulfuric acid, carbonic acid, phosphoric acid, hydrochloric acid and formic acid. These salts are used alone or in combination of two or more.

  As the polymer flocculant, any of anionic, cationic, and nonionic polymer flocculants can be used. Examples of the anionic polymer flocculant include sodium alginate, CMC-Na, sodium polyacrylate, acrylamide-sodium acrylate copolymer, polyacrylamide partial hydrolyzate, and the like.

  Examples of the cationic polymer flocculant include water-soluble aniline resin hydrochloride, polyethyleneimine, polyamine, polydiallyldimethylammonium chloride, chitosan, hexamethylenediamine-epichlorohydrin condensate, polyvinyl imidazoline, polyalkylamino (meth) acrylate, poly Examples include acrylamide Mannich modified products. Examples of nonionic polymer flocculants include starch, guar gum, gelatin, polyacrylamide, and polyethylene oxide.

  In the above coagulation system, the amount of acid added is adjusted so that the coagulation pH is preferably 3.0 to 6.5, more preferably 3.5 to 5.5, and the salt in the total mixture The concentration is preferably 0.5 to 3.0% by weight, more preferably 1.0 to 2.0% by weight. The polymer flocculant is preferably used in an amount of 0.001 to 1.0 part by weight, more preferably 0.01 to 0.75 part by weight, based on 100 parts by weight of the rubber component in the latex.

  As a procedure of operation, a specific salt and / or polymer flocculant is added to natural rubber latex in advance and mixed uniformly, and then an acid may be added to coagulate, or an acid is added to natural rubber latex in advance. Then, a specific salt and / or polymer flocculant may be added to solidify. Of course, a specific salt and / or polymer flocculant and acid may be added simultaneously to the natural rubber latex. Either method can be rapidly solidified to obtain a porous crumb slurry having a large surface area suitable for washing and drying.

  In developing laboratory results into continuous operations suitable for industrial production, systems with phase changes such as solidification operations often face many difficulties. A typical example of the continuous operation coagulation process is emulsion polymerization SBR, but even if this system is applied to the coagulation of natural rubber, the crumb discharged from the coagulation tank becomes a large mass due to the inherent stickiness of natural rubber. Thus, it is impossible to obtain a crumb slurry in a good dispersion state as in the case of emulsion polymerization SBR.

  For this reason, when applying the newly found coagulation system suitable for natural rubber latex to industrial production, we have investigated a continuous operation coagulation process based on a completely new concept. As a result, a coagulated crumb slurry having a large surface area that can be easily dehydrated, washed and dried can be supplied to the subsequent process, and the natural rubber coagulation and finishing processes can be continuously performed.

  The continuous coagulation process basically comprises a first stage apparatus used for uniform mixing of the supplied chemical solution for coagulation and a second stage apparatus for completing the coagulation. The purpose of the first stage apparatus is to uniformly mix the chemical solution and natural rubber latex, and to start creaming and aggregation of the latex. Although stirring with a stirrer is generally performed, a line mix, a static mixer, or the like may be used. The second-stage apparatus needs a capacity for securing a residence time for completing the coagulation, and it is necessary to stir the liquid to promote the coagulation. However, a two-stage apparatus is not necessarily required, and creaming, agglomeration, and solidification can be performed in one apparatus (coagulation tank). The main points of the continuous solidification process are two points: a solidification operation that does not make the solidified crumb into a large mass, and discharge from the solidification tank in a shape that is favorable for the subsequent process. We were able to solve this problem by devising the solidification operation conditions and the solidification tank structure.

  FIG. 1 shows an operation when the solid matter concentration (crumb slurry concentration) in the coagulation tank is low (for example, 20% by weight or less). Here, the latex, acid, and polymer flocculant are creamed in a cream tank with a stirrer. The cream supplied to the coagulation tank becomes a porous crumb slurry as the coagulation progresses. This is overflowed from the coagulation tank and supplied to the dehydrator. The obtained solidified product is porous and has a shape that can be easily dehydrated and washed. Although FIG. 1 shows a form in which forced flow by circulating serum water is used for liquid stirring in the coagulation tank, a form using a stirrer may be used. Further, the procedure is illustrated as mixing latex and acid in a cream tank and further adding a polymer flocculant thereto, but this is an example of the procedure, and the order of addition is not limited.

  FIG. 2 shows an operation when the solid matter concentration (crumb slurry concentration) in the coagulation tank is high (for example, when it exceeds 10% by weight). In this case, a kneader is used. Latex, acid and polymer flocculant are uniformly mixed in a kneader and coagulation proceeds at the same time. The coagulum becomes a fine crumb or an appropriately sized porous block and is supplied to a dehydrator. The size of the block can be adjusted by the structure and operating conditions of the kneader. FIG. 2 also shows that the procedure is to combine latex and acid together, and then add together with the polymer flocculant to the kneader, but this is also an example of the procedure, and the order of addition is not limited. .

  In these continuous coagulation methods, the serum water and rinsing water used for washing after solid-liquid separation of crumb are circulated for liquid flow in the coagulation tank, solid content adjustment of latex, and dilution of acid, polymer flocculant and salt. It is also possible to use it.

  Although there is no restriction | limiting in particular in solid content concentration (Dry Rubber Content (DRC), weight%) of the natural rubber latex to be used, Preferably it is about 1-60 weight%, More preferably, DRC is about 5-40 weight%. The coagulation temperature is not particularly limited, but generally a temperature from room temperature to about 80 ° C. is preferable.

  EXAMPLES The present invention will be described below with reference to examples, but these examples do not limit the present invention.

The latex and chemicals used in the experiment are as follows.
FL-latex
Latex (FL-latex) adjusted to pH 10-11 by adding ammonia to natural rubber fresh latex (DSC about 30% by weight)
Floerger
Cationic polymer (0.025% (w / v) aqueous solution) (dimethylaminoethyl acrylate / acrylamide copolymer)
Water Fracculent
Anionic polymer (0.025% (w / v) aqueous solution) (sodium acrylate / acrylamide copolymer)
Formic acid 5% (w / v) aqueous solution phr indicates the number of parts per 100 parts of rubber.

Examples 1-6 and Comparative Examples 1-3
An example of the salt / acid coagulation method is shown.

  An amount corresponding to a concentration of 1% (w / v) was added to FL-latex (adjusted to 10% by weight of DRC) and mixed well, and 50 ml of this was prepared. To this, 2 ml of the acid shown in Table 1 adjusted to 5% (w / v) was added dropwise with stirring. The solidification time was remarkably shortened and a crumb-like solid content having a large surface area that was easy to wash was obtained.

The results are shown in Table 1. A crumb with a large surface area that was easy to clean was obtained.
As a comparative example, coagulation examples of formic acid or sulfuric acid and sodium chloride are also shown. Both were found to have a slow solidification rate.

Examples 7-10
The polymer flocculant shown in Table 2 was added to FL-latex (adjusted to DRC 10 wt%) showing an example of the polymer flocculant / acid coagulation method, and sufficiently stirred and mixed. To 20 ml, 0.2 ml of the acid shown in Table 2 was added dropwise with stirring. The acid concentration was adjusted to 1% for sulfuric acid and 5% for formic acid. The polymer flocculant also shortened the coagulation time.

  The results are shown in Table 2. A crumb with a large surface area that was easy to clean was obtained.

Examples 11-14
Examples of acid / salt coagulation and acid / polymer coagulation are shown.

  The acid shown in Table 3 was added to 50 ml of FL-latex (adjusted to DRC 10% by weight) to adjust the pH to 4.5 to 5.5. While stirring the latex solution, the polymer flocculant or salt shown in Table 3 was continuously added. The added polymer flocculant or salt aqueous solution was 10 ml at a 5% concentration. Table 3 summarizes the time until solidification and the state of serum water. A crumb with a large surface area that was easy to clean was obtained.

  It was found that there was no difference in the order of addition.

Examples 15 to 23 and Comparative Examples 4 to 9
The example which confirmed the effect of inorganic salt is shown.
The following (A) was dropped into the following (B) while stirring, and the coagulation time was measured. At the same time, the transparency of serum water after coagulation was observed.
(A) Latex: 5 ml of an inorganic salt shown in Table 4 added to 5 ml of FL-latex 100 ml (DRC 30 wt%) and adjusted to a predetermined DRC was used)
(B) Formic acid (5% concentration): 20 ml
The results are shown in Table 4. In Examples 15 to 23, crumbs having a large surface area that were easily washed were obtained.

Examples 24-29
The example which confirmed the effect of the polymer flocculent is shown.

The following (A) was dropped into the following (B) while stirring, and the coagulation time was measured. At the same time, the transparency of serum water after coagulation was observed.
(A) Latex: 5 ml (using FL-latex (DRC 30 wt%) prepared by adding 0.025 phr of the polymer flocculant shown in Table 5 and adjusting a predetermined DRC)
(B) Formic acid (5% concentration): 20 ml
The results are shown in Table 5. In Examples 24-29, crumbs with a large surface area that could be easily washed were obtained.

Examples 30-35
The example which confirmed the effect of stirring is shown.

  50 parts by weight of 0.025% (w / v) Floerger aqueous solution was added to 100 parts by weight of FL-latex (DRC 30% by weight) to adjust to a predetermined DRC shown in Table 6. 5% (w / v) formic acid was added with stirring or non-stirring so that the serum pH after coagulation was 4.5-5.5. The effect of stirring was confirmed. The results are shown in Table 6.

Examples 36-41
The example which confirmed the effect of stirring is shown.

  5% (w / v) formic acid was added to 100 parts by weight of FL-latex (DRC 30% by weight). The amount of formic acid was adjusted so that the pH of the serum after coagulation was 4.5 to 4.5, and water was added so as to obtain a predetermined DRC. To this, 50 parts of 0.025% (w / v) Floerger aqueous solution was added with stirring or without stirring. The effect of stirring was confirmed even in this coagulation operation.

  The results are shown in Table 7.

Examples 42-47
The example which confirmed the effect of stirring is shown.

  In advance, an aqueous solution in which Floerger and formic acid were dissolved was prepared. This aqueous solution and FL-latex (DRC 30% by weight) were mixed at a ratio to give a predetermined crumb concentration, and a solidification experiment was conducted with and without stirring. The Floerger concentration and formic acid concentration of the aqueous solution to be prepared differ depending on the crumb concentration. With respect to Floeger, with respect to formic acid, the serum after the coagulation is maintained so that the ratio of FL-latex amount (DRC 30 wt%) and Floeger amount (0.025% (w / v) aqueous solution) is kept at 1: 0.5. The aqueous solution was prepared by adjusting the amount of each so that the pH of the solution became 4.5 to 5.5. Agitation was confirmed to be effective in promoting solidification. The crumb concentration is the amount of Dry Rubber in the mixture of this aqueous solution and FL-latex (DRC 30% by weight).

  The results are shown in Table 8.

Explanatory drawing of this invention method suitable to implement when solid content concentration is low. Explanatory drawing of this invention method suitable to implement when solid content concentration is high.

Claims (3)

To any natural rubber latex fresh natural rubber latex or ammonia added natural rubber latex, (1) acid, and (2) (i) nitric acid, sulfuric acid, carbonic acid, phosphoric acid, calcium salt of respective acid of hydrochloric acid and formic acid Or at least one salt selected from the group consisting of ammonium salts and / or (ii) a polymer coagulant with stirring to form a porous coagulated rubber, and a method for coagulating natural rubber latex . To the continuous flow of natural rubber latex, (1) acid and (2) the above-mentioned salt (i) and / or polymer flocculant (ii) are added with stirring to float the porous agglomerated rubber on the continuous flow. The coagulation method according to claim 1, wherein The solidification method according to any one of claims 1 to 2, wherein the stirring is performed by a stirrer or by forced flow of a continuous flow.

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