JP3359545B2 - Multistage enlargement method of rubber latex - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a large particle rubber latex having a desired weight average particle diameter and a desired particle diameter distribution by an industrially simple method, and more particularly to a method for enlarging a rubber latex.

[0002]

2. Description of the Related Art ABS resins and ASA resins include vinyl cyanide monomers such as acrylonitrile, aromatic vinyl monomers such as styrene, and unsaturated carboxylate esters such as acrylate. It is a resin composition obtained by graft polymerizing a monomer mixture such as a polymer to a rubber-like polymer, and is widely used in various applications because of its characteristics such as high impact resistance, high surface gloss, and good fluidity. I have.

The properties of the ABS resin generally depend on the properties of the rubbery polymer, the dispersed particle size and particle size distribution in the matrix resin, the amount of the graft copolymerized on the rubbery polymer and the thickness of the graft layer. It is known to Therefore, in order to balance the impact resistance, the fluidity and the appearance of the resin molding on a high level, in addition to the properties of the rubber-like polymer, the amount of the graft copolymerized to the rubber-like polymer and the thickness of the graft layer, the rubber polymer It is extremely important to control the dispersed particle size and particle size distribution in the matrix resin according to each application.

The average particle size of the dispersed particles is from 150 to
The range of 400 nm is common. However, particle size 15
When an attempt was made to produce a rubber-like polymer latex of 0 to 400 nm by an emulsion polymerization method, it took a very long time and the productivity was low. Therefore, it has been attempted to produce a rubber-like polymer latex having a relatively small particle diameter of less than 150 nm in advance, and to increase the average particle diameter to 150 to 400 nm by some method. Tokiko 32-959
Japanese Patent Publication No. 2 and JP-B-33-4437 propose an enlargement by the freezing method. However, industrially, the equipment required for the enlargement process becomes enormous, and there are problems such as excessive cost. there were.

Japanese Patent Publication No. 37-10565, Japanese Patent Publication No. 41-982, and Japanese Patent Publication No. 60-19930 propose a method of enlarging a latex by applying a mechanical force such as a shear force. However, there are problems that coagulated products are easily generated, and it is difficult to stably obtain a rubber latex having the same particle diameter.

Further, Japanese Patent Publication No. 46-32056, Japanese Patent Publication No. 59-49937, and Japanese Patent Publication No. 62-6104
No. 4 proposes a method of increasing the size by adding an acidic substance or an acid anhydride. In these methods, the amount of coagulum generated is relatively small and is an industrially effective method.However, the obtained enlarged latex has a relatively narrow particle size distribution, and has a predetermined particle size distribution to be used as an ABS raw material. It is necessary to prepare a plurality of enlarged rubber latexes having different particle diameters in advance, and to latex blend these at a certain ratio. As a result, the manufacturing process is complicated, a large amount of capital investment is required, and there are many problems from an industrial point of view.

Japanese Patent Publication No. 46-35976 discloses a method of enlarging a latex obtained by mixing or mixing a latex obtained by polymerizing or copolymerizing a monomer having an acid group with a rubbery polymer latex. Although it has been proposed, there is a problem that a relatively large amount of a rubbery polymer that does not increase in size remains, and a desired particle size distribution cannot be obtained.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a large particle rubber latex having a desired average particle diameter and particle diameter distribution can be easily produced from a small particle diameter rubber latex without generating any undesirable coagulate. It is an object of the present invention to provide a method of manufacturing at low cost and with high productivity by a simple manufacturing process.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a first method for enlarging latex particles by adding an acid or an acid anhydride to a neutral or alkaline small particle rubber latex which is unstable in an acidic region. After the process, to the enlarged latex obtained in the previous enlargement step, neutral or alkaline small particle rubber latex which becomes unstable in the acidic region,
The present invention relates to a method for multistage enlargement of rubber latex, which comprises repeating a step of adding an acid or an acid anhydride to enlarge latex particles at least once, and finally adjusting the latex to neutral or alkaline.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The small particle rubber latex used in the present invention is neutral or alkaline (pH> 6), and becomes unstable when made acidic (pH ≦ 6). That is, the small particle rubber latex used in the present invention is:
In the acidic region, the rubber latex particles tend to agglomerate with each other, and as a result, the particle diameter increases or coagulates are generated. The average particle size of the latex particles of the small rubber latex is usually less than 150 nm.

The type of the emulsifier used in the small particle rubber latex is not particularly limited as long as the above-mentioned object is achieved, and examples thereof include sodium oleate, sodium stearate, sodium laurate, sodium mixed fatty acid, and potassium salts thereof. Fatty acid soaps such as salts and rosin acid soaps typified by abietic acid salts can be used. These can be used in combination.
When the small-particle latex is obtained by emulsion polymerization, the amount of the emulsifier used is preferably 0.5 to 5 parts by weight used in usual emulsion polymerization with respect to 100 parts by weight of the polymer (rubber).

Polymer (rubber) of small particle rubber latex
The composition is not particularly limited as long as it exhibits rubber-like properties at room temperature. For example, polybutadiene rubber, styrene-
Butadiene copolymer rubber (SBR), acrylonitrile-
Butadiene copolymer rubber (NBR), polybutyl acrylate rubber and the like can be used. These may be used alone or in combination.

[0013] The concentration of the small particle rubber latex has a great influence on the enlarged particle diameter and the amount of coagulated product. The higher the concentration, the larger the enlarged particle size, but the more undesired coagulates are generated. When the concentration is reduced, the opposite tendency occurs. Therefore, it is necessary to select an appropriate concentration according to the application and conditions, but if the concentration is too low, a large amount of acid or acid anhydride is required, and if the concentration is too high, a large amount of coagulated product is generated. A practically preferred range is 20
５０50% by weight.

As a method for obtaining the small particle rubber latex, emulsion polymerization is preferred because of easy production.
The initiator used in the emulsion polymerization is not particularly limited, and a “hot rubber” formulation using ordinary potassium persulfate,
So-called "using organic peroxides and reducing agents, catalysts"
Cold rubber “prescription” (redox prescription) and the like can be used.

In the present invention, a first enlargement is performed by adding an acid or an acid anhydride to such a small particle rubber latex.

The acid used at this time is not particularly limited. For example, hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid, oxalic acid, nitric acid, propionic acid, benzoic acid, formic acid, citric acid,
Lactic acid and maleic acid can be used. Among these, hydrochloric acid, sulfuric acid, acetic acid, and phosphoric acid are preferable in that the particle diameter can be easily adjusted.

The acid anhydride to be used at this time is not particularly limited as long as it is hydrolyzed to an acid in rubber latex, but acetic anhydride, maleic anhydride,
Carboxylic anhydrides such as propionic anhydride, benzoic anhydride, glutaric anhydride, valeric anhydride, isovaleric anhydride, succinic anhydride, citraconic anhydride, and itaconic anhydride are preferred, and the particle size is particularly easily adjusted. Preferred are acetic anhydride and maleic anhydride.

The amount of the acid or acid anhydride to be added is selected according to the desired enlarged particle size. When a large amount of acid or acid anhydride is used, a rubber latex having a large particle diameter is obtained, and when a small amount is used, a rubber latex having a small particle diameter is obtained. If the addition amount of the acid or the acid anhydride is too small, the pH is insufficiently reduced and the enlargement itself becomes difficult to progress, so the amount of the acid or the acid anhydride is appropriately changed according to the pH of the small particle rubber latex itself. I do. Although it depends on the type of acid or acid anhydride, it is generally necessary to add 0.1 parts by weight or more based on 100 parts by weight (solid content) of the small particle rubber latex.

The method of adding the acid or the acid anhydride is not particularly limited. However, in order to uniformly disperse the acid or the acid anhydride in the rubber latex, the acid or the acid anhydride is previously diluted (dissolved) with water.
Alternatively, it is preferable to disperse and use at an appropriate concentration (dispersion concentration). Enlargement is possible even when using a high concentration or the same acid or acid anhydride, but undesired coagulation tends to be generated in large quantities, while when the concentration is too low, coagulation hardly occurs. However, because the enlarged latex is diluted, its practical value is reduced. Therefore, depending on the type of acid or acid anhydride,
The concentration (dispersion concentration) is generally about 0.1 to 20% by weight, preferably about 0.5 to 10% by weight.

When an acid anhydride is used, an aqueous solution or dispersion of the acid anhydride may be added to the small particle rubber latex by any method, and may be added to the latex all at once or dropwise. . However, since it is necessary to uniformly diffuse the acid anhydride in the rubber latex, it is necessary to add the acid anhydride under appropriate stirring. If the stirring is not performed or the stirring is insufficient, the acid anhydride is not uniformly dispersed, so that a large amount of coagulated material is generated.

When an acid anhydride is used, the acid anhydride added to the small-particle rubber latex is gradually hydrolyzed according to the hydrolysis rate to become an acid to enlarge the small-particle rubber latex. . Therefore, an enlarging time corresponding to the hydrolysis rate of the acid anhydride is required, and the time is appropriately adjusted according to the type of the acid anhydride. Usually, more than tens of minutes are required. If the hypertrophy time is short, the hypertrophy progresses insufficiently,
The diameter of the enlarged particles becomes small, and small particles that do not enlarge tend to remain.

When an acid is used, an aqueous solution or aqueous dispersion of the acid is preferably added gradually to the small particle rubber latex by dropping or the like. When an acid is used, since the enlargement proceeds at the same time as the addition of the acid, the amount and time of dropping and the stirring of the latex are adjusted so as to prevent coagulation.

By the way, stirring during enlargement has almost no effect on the size of the enlarged particles, but when a strong shearing force is applied to the latex having a reduced pH, the growth rate of the particles is remarkably increased, and an undesired coagulated product is produced. Occurs in large quantities. Therefore, at the time of enlargement, adjustment is made so as to suppress the generation of coagulated material by weakening the stirring. In the case of using an acid anhydride, if it is added all at once and uniformly dispersed at the time of addition, since it is gradually hydrolyzed thereafter, the entire uniformity is maintained without any stirring at the time of enlargement. Therefore, it is preferable to use an acid anhydride rather than an acid.

Next, after the first enlargement is completed, the second
In the step of enlarging the latex, the second small particle rubber latex is added, and then an acid or an acid anhydride is added to enlarge the latex particles.

The second small particle rubber latex used in the second enlargement step is a rubber latex having the above-mentioned properties,
It may be the same as the first small particle rubber latex,
The polymer (rubber) composition may be different depending on the average particle diameter and the case. The addition amount of the second small particle rubber latex is arbitrarily selected according to a desired particle size distribution.

After the addition of the second small particle rubber latex,
The mixed latex is stabilized by making the pH neutral or alkaline. PH of the second small particle rubber latex
The pH of the mixed latex does not become neutral or alkaline depending on the amount added, and in this case, an alkaline substance is separately added to stabilize the mixed latex.

Although any alkaline substance may be used, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide (aqueous ammonia), sodium carbonate, potassium carbonate and the like, particularly preferably sodium hydroxide or hydroxide Potassium can be used. These can be used in the form of an aqueous solution, the concentration of which is selected depending on the type of the substance, and an aqueous solution of about 1 to 10% by weight is used. If it exceeds 10% by weight, a coagulated product is liable to be generated, and if it is less than 1% by weight, the latex becomes too thin and its practical value decreases.

Next, an aqueous solution or dispersion of an acid or an acid anhydride is again added to the mixed latex stabilized in the same manner as in the first enlargement step, whereby the latex particles in the mixed latex become enlarged. I do.

The enlargement at this time can be performed in exactly the same manner as the enlargement in the first enlargement step. The amount of acid or acid anhydride to be used can also be selected according to the target enlarged particle size, as in the first enlargement step. By the addition of the acid or the acid anhydride, not only the second small particle rubber latex but also the latex particles enlarged in the first enlargement step are further enlarged. Therefore, in order to control the particle size distribution to a desired value, it is necessary to adjust the amount of the second small particle rubber latex and the amount of the acid or acid anhydride added.

Thereafter, if necessary, the third and fourth enlargement steps can be repeated in the same manner as in the second enlargement step. The number of times the enlargement step is repeated can be appropriately selected so that a desired particle size and particle size distribution can be obtained.

As described above, when the enlarged latex obtained through the multi-stage enlargement process is finally adjusted to neutral or alkaline by using an alkaline substance, the latex is re-stabilized. As the alkaline substance used,
The aforementioned alkaline substances can be used.

In the present invention, by adjusting the amount and type of the small particle rubber latex to be added in each step of the enlargement process, the amount and type of the acid added, and the number of stages of the enlargement process, etc. Since a desired average particle size and particle size distribution can be obtained, rubber latex used in various fields can be produced.

In order to use the rubber latex enlarged according to the present invention for producing an ABS resin, it is preferable to produce the rubber latex such that the weight average particle size of the rubber latex is 150 to 400 nm. Less than 150 nm and 400 n
When it exceeds m, the impact resistance of the obtained resin is low, and the practical value is low.

[0034]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which should not be construed as limiting the scope of the invention.

The percentages and parts in the following examples are based on parts by weight unless otherwise specified. Also, the following examples,
The particle size distribution of the rubber latex in the comparative example was determined by placing an ultra-dilute rubber latex droplet on a copper mesh for a transmission electron microscope, staining this with osmium tetroxide, evaporating the water to dryness, and evaporating to dryness. After taking a photo with (magnification 2
(0000 times), and the size of 300 to 500 rubber particles was counted. The average particle size is a weight average.

[Production Example 1] Production of small particle rubber latex (A): In a 10-liter stainless steel autoclave equipped with a stirrer, 150 parts of deionized water (hereinafter simply referred to as water) and styrene 1 were used.
0 parts, 1.5 parts of potassium oleate, 1.5 parts of potassium rosinate, 0.1 part of potassium hydroxide, and 0.3 part of potassium persulfate.
0 parts were charged, the internal temperature was raised to 70 ° C., and polymerization was carried out for 10 hours. After removing the remaining butadiene monomer by steam distillation, the mixture was cooled to give an average particle size of 85 nm and a solid content of 40.1.
%, A rubber rubber latex (A) having a pH of 11.0 was obtained.

Production Example 2 Production of Small Particle Rubber Latex (B): In Production Example 1, 10 parts of styrene were changed to 5 parts of acrylonitrile.
Polymerization was carried out in the same manner except that 90 parts of butadiene was changed to 95 parts, and the average particle size was 80 nm, the solid content was 40.3%, and p
A small particle rubber latex (B) of H11.1 was obtained.

[Production Example 3] Production of small particle rubber latex (C): nitrogen-substituted 10
In a L glass reactor (with a stirrer), 200 parts of water, 0.03 part of sodium carbonate, 1.0 part of disodium polyoxyethylene nonyl phenyl ether phosphate, 0.3 part of Rongalite, ferrous sulfate heptahydrate 0.00005 part of salt and 0.00015 part of disodium ethylenediaminetetraacetate were charged and the temperature was raised to 75 ° C. To this, 100 parts of n-butyl acrylate, 0.9 part of allyl methacrylate, tert
-Butyl hydroperoxide 0.2 part, polyoxyethylene nonyl phenyl ether phosphate disodium 0.8
Part of the solution was added dropwise over 4 hours under a nitrogen flow, kept for 2 hours after the completion of the addition, cooled, and cooled to an average particle size of 85 n
m, a solid content of 32.8%, and a small particle rubber latex (C) having a pH of 7.1 were obtained.

Example 1 A small-sized rubber latex (A) (50 parts (solid content)) was charged into a 200-mm inner diameter 5 L glass reactor equipped with a stirrer having a diameter of 110 mm, and charged at 250 r.
Stirred at pm. To this was added 0.35 parts (actual amount) of acetic anhydride using a 5% aqueous solution in 1 minute below the latex liquid level, and stirring was continued for 2 minutes. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The average particle diameter of the first-stage enlarged rubber is 330 nm.
Met.

Thereafter, 50 parts by weight (solid content) of the small particle rubber latex (A) was further added, and the mixture was allowed to stand for 5 minutes, after which stirring was resumed (250 rpm). The pH of the mixed latex at that time was 7.5. To this, 0.25 parts (actual amount) of acetic anhydride was added below the liquid surface of the latex in 1 minute using a 5% aqueous solution, stirring was continued for 2 minutes, and then stirring was stopped and left for 30 minutes. 0.65 parts (actual amount) of potassium hydroxide is added as it is using a 5% aqueous solution, and stirring is restarted after 5 minutes to finally give a pH of 10.5, an average particle diameter of 290 nm, and a solid content of 35.0%. An enlarged latex was obtained.

When the coagulated product obtained by filtering the latex through gauze was dried, the amount of the coagulated product was as small as 0.01 part. Observation of the latex with a transmission electron microscope showed the particle size distribution shown in Table 1.

[0042]

[Table 1]

Example 2 In the same reactor as used in Example 1, 30 parts of a small particle rubber latex (B) (solid content)
Was stirred at 250 rpm. To this, 0.26 parts (actual amount) of acetic anhydride was added under the latex liquid level in 1 minute using a 5% aqueous solution, and stirring was continued for 2 minutes. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The average particle size of the first-stage enlarged rubber was 355 nm.

Thereafter, 40 parts by weight (solid content) of the small particle rubber latex (B) was further added, and the mixture was allowed to stand for 5 minutes, after which stirring was resumed (250 rpm). At that time, the pH of the mixed latex was 7.7. To this, 0.25 parts (actual amount) of acetic anhydride was added below the liquid surface of the latex in 1 minute using a 5% aqueous solution, stirring was continued for 2 minutes, and then stirring was stopped and left for 30 minutes.

Thereafter, 30 parts by weight (solid content) of the small particle rubber latex (B) and 0.15 part (actual amount) of potassium hydroxide using a 5% aqueous solution were added, and the mixture was allowed to stand for 5 minutes, after which stirring was resumed. (250 rpm). The pH of the mixed latex at that time was 7.3. To this, 0.13 part (actual amount) of a 5% aqueous solution of acetic anhydride was added under the latex liquid level in 1 minute, stirring was continued for 2 minutes, and then stirring was stopped and left for 30 minutes. Without stirring, 0.52 parts (actual amount) of a 5% aqueous solution of potassium hydroxide was added, and after 5 minutes, stirring was resumed, and finally pH 10.5, average particle size 290 nm,
An enlarged latex having a solid content of 34.1% was obtained.

When the coagulated product obtained by filtering the latex through gauze was dried, the amount of the coagulated product was as small as 0.06 parts. Observation of the latex with a transmission electron microscope showed the particle size distribution shown in Table 2.

[0047]

[Table 2]

Example 3 Into the same reactor used in Example 1, 50 parts of a small particle rubber latex (A) (solid content)
Was stirred at 250 rpm. To this, 0.33 parts (actual amount) of acetic anhydride was added under the latex liquid level over 2 minutes using a 5% aqueous solution. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The average particle diameter of this first-stage enlarged rubber is 290 n
m.

Thereafter, 50 parts (solid content) of the small particle rubber latex (A) and 0.10 part of sodium dodecylbenzenesulfonate were added, and the mixture was allowed to stand for 5 minutes and then restarted stirring (250 rpm). PH of the mixed latex at that time
Was 7.8. To this, 0.30 part (actual amount) of sulfuric acid was added under the latex liquid level in 10 minutes using a 2% aqueous solution, stirring was continued for 2 minutes, and then stirring was stopped. 0.70 parts (actual amount) of potassium hydroxide was added using a 5% aqueous solution, and after 5 minutes, stirring was resumed, and finally a hypertrophy having a pH of 11.0, an average particle diameter of 290 nm, and a solid content of 34.9% was obtained. A latex was obtained.

When the coagulated product obtained by filtering the latex through gauze was dried, the amount of the coagulated product was as small as 0.05 part. Observation of the latex with a transmission electron microscope showed the particle size distribution shown in Table 3.

[0051]

[Table 3]

Example 4 In the same reactor used in Example 1, 50 parts (solid content) of small particle rubber latex (B)
Was stirred at 250 rpm. To this was added 0.29 parts (actual amount) of acetic anhydride using a 5% aqueous solution in 1 minute below the latex liquid level, and stirring was continued for 2 minutes. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The average particle diameter of the first-stage enlarged rubber was 210 nm.

Thereafter, 50 parts by weight (solid content) of the small particle rubber latex (B) was further added, and the mixture was allowed to stand for 5 minutes and then the stirring was restarted (250 rpm). The pH of the mixed latex at that time was 8.1. To this, 0.32 parts (actual amount) of acetic anhydride was added below the liquid surface of the latex in 1 minute using a 5% aqueous solution, stirring was continued for 2 minutes, and then stirring was stopped and left for 30 minutes. 0.67 parts (actual amount) of potassium hydroxide is added as it is using a 5% aqueous solution, and stirring is restarted after 5 minutes to finally give a pH of 10.5, an average particle diameter of 250 nm, and a solid content of 34.3%. An enlarged latex was obtained.

When the coagulated product obtained by filtering the latex through gauze was dried, the amount of the coagulated product was as small as 0.07 part. Further, when the latex was observed with a transmission electron microscope, the particle size distribution shown in Table 4 was shown.

[0055]

[Table 4]

Example 5 In the same reactor as used in Example 1, 40 parts of small particle rubber latex (C) (solid content)
Was stirred at 250 rpm. To this, using a 5% aqueous solution, 0.28 parts (actual amount) of acetic anhydride was added under the latex surface over 2 minutes. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The average particle diameter of the first-stage enlarged rubber is 260 n.
m.

Thereafter, 50 parts (solid content) of the small particle rubber latex (C) was further added, and the mixture was left for 5 minutes, and the stirring was resumed (250 rpm). The pH of the mixed latex at that time was 6.1. To this, 0.14 parts (actual amount) of acetic anhydride was added under the latex liquid level in 2 minutes using a 5% aqueous solution, stirring was continued for 2 minutes, and then stirring was stopped. 5
0.46 parts (actual amount) of potassium hydroxide was added using a 5% aqueous solution, and after 5 minutes, stirring was restarted to finally enlarge the mixture to have a pH of 7.3, an average particle size of 270 nm, and a solid content of 28.4%. Latex was obtained.

When the coagulated product obtained by filtering the latex with gauze was dried, the amount of the coagulated portion t was as small as 0.01 part. In addition, when the latex was observed with a transmission electron microscope, the particle size distribution shown in Table 5 was shown.

[0059]

[Table 5]

Comparative Example 1 In this comparative example, small-particle rubber latex was used at once and acetic anhydride was added in two portions. First, the same reactor as used in Example 1 was charged with 100 parts (solid content) of the small particle rubber latex (A) and stirred at 250 rpm. to this,
Using a 5% aqueous solution, 0.35 parts (actual amount) of acetic anhydride was added below the latex surface in 1 minute, and stirring was continued for 2 minutes. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The first-stage enlarged rubber had an average particle diameter of 180 nm and a pH of 7.5.

Further, 0.25 parts (actual amount) of acetic anhydride was added under the latex liquid level in 1 minute using a 5% aqueous solution, and stirring was continued for 2 minutes. Then, stirring was stopped and left for 30 minutes. did. 0.65 parts (actual amount) of potassium hydroxide was added as it was using a 5% aqueous solution, and stirring was restarted after 5 minutes to finally give a pH of 10.5, an average particle diameter of 230 nm, and a solid content of 3%.
An enlarged latex of 3.1% was obtained.

When the coagulated product obtained by filtering the latex through gauze was dried, it was found that 1.30 parts of the coagulated product had been generated. Observation of the latex with a transmission electron microscope showed the particle size distribution shown in Table 6.

[0063]

[Table 6]

[Comparative Example 2] In this comparative example, acetic anhydride was added all at once, and the small-particle rubber latex was used twice. First, 50 parts (solid content) of small particle rubber latex (A) were placed in the same reactor used in Example 1.
Was stirred at 250 rpm. To this, 0.60 part (actual amount) of acetic anhydride was added under the latex liquid level in 1 minute using a 5% aqueous solution, and stirring was continued for 2 minutes. Thereafter, stirring was stopped and the mixture was left for 30 minutes. The average particle diameter of the first-stage enlarged rubber was 400 nm.

Thereafter, 50 parts of the small particle rubber latex (A) was further added, and the mixture was left for 5 minutes, and the stirring was resumed (25 parts).
0 rpm). At that time, the pH of the mixed latex was 6.
It was 4. Stir for 2 minutes and then stop stirring for 3 minutes.
Left for 0 minutes. 0.65 parts (actual amount) of potassium hydroxide is added as it is using a 5% aqueous solution, and stirring is resumed after 5 minutes to finally give a pH of 10.2, an average particle diameter of 320 nm, and a solid content of 32.4%. An enlarged latex was obtained.

When the coagulated product obtained by filtering the latex with gauze was dried, it was found that 2.11 parts of the coagulated product had been generated. When the latex was observed with a transmission electron microscope, the particle size distribution shown in Table 7 was shown.

[0067]

[Table 7]

[0068]

According to the present invention, a large particle rubber latex having a desired average particle diameter and a particle diameter distribution can be easily produced from a small particle diameter rubber latex with almost no undesirable coagulation. It can be manufactured inexpensively with high productivity by the process.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08C 1/065 C08F 6/18

Claims (2)

(57) [Claims] Claims: 1. A first step of enlarging a latex particle by adding an acid or an acid anhydride to a neutral or alkaline small particle rubber latex which is unstable in an acidic region to enlarge the latex particles. Add a neutral or alkaline small particle rubber latex that is unstable in the acidic region to the enlarged latex obtained in the process, and then add an acid or acid anhydride to enlarge the latex particles. A method for multistage enlargement of rubber latex, wherein the latex is adjusted to neutral or alkaline after repeating at least once. 2. The method according to claim 1, wherein the weight average particle diameter of the latex particles finally obtained is 150 to 400 nm.