JP2003268006A - Method for aggregation expanding rubber latex particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for expanding rubber latex, keeping a solid content concentration in a practical range without causing occurrence of a solidified material and adhesion to an apparatus and enabling industrial production in large-sized apparatus. <P>SOLUTION: An acidic substance is added to a small particle-diameter rubber latex emulsified by a surfactant having an alkali metal salt of a carboxylic acid as a hydrophilic group and having <0.2 μ number-average particle diameter of rubber particles in the latex. Thereby, liquid property of the latex is acidified and rubber particles in the latex are aggregation expanded to stably provide the rubber particles-containing latex having 0.2-0.6 μ number-average particle diameter. When obtaining the rubber particles-containing latex, an alkali metal salt of an inorganic acid and/or an alkali metal salt of a ≤4C saturated aliphatic carboxylic acid is previously added to the rubber latex having the small particle diameter. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coagulating and expanding rubber latex particles by adding an acidic substance. The present invention relates to a method for stably coagulating and enlarging rubber latex particles by adding a specific substance to latex and thereby preventing generation of aggregates and adhesion to a device. [0002] Conventionally, polybutadiene and styrene-
As a method of producing a rubber latex having a large particle diameter of a diene polymer such as a butadiene copolymer, a rubber latex having a small particle diameter is produced by emulsion polymerization, and then an acid substance such as 1% sulfuric acid is added to enlarge the latex particles. (Japanese Patent Publication No. 42-3112, Japanese Patent Publication No. 55-112)
19246, etc.). [0003] In the case of such particle enlargement, the formation of coagulates and the accompanying adhesion to equipment are not preferable in terms of production and / or quality, and techniques for suppressing these are very useful. In order to suppress the formation of coagulates and the accompanying adhesion to the equipment, it is desirable to reduce the concentration of the acidic substance, but as a result, the solid content of the rubber latex is reduced, which significantly impairs productivity. . On the other hand, if the concentration of the acidic substance is increased with an emphasis on productivity, a large amount of coagulated material is generated, which is not suitable for industrial production. For this reason, various methods of enlarging particles while suppressing the generation of coagulates have been devised,
For example, a method using lactic acid as an acidic substance [Japanese Unexamined Patent Publication No.
167704 (Japanese Patent Publication No. 62-61044)
Alternatively, a method has been proposed in which phosphoric acid is showered or atomized and added to the latex liquid surface (Japanese Patent Application Laid-Open No. 57-212201 (JP-B-2-9601)).
It was still insufficient to solve problems such as generation of coagulated material and adhesion to equipment while maintaining a relatively high solid content concentration. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned problems (formation of coagulated material and adhesion to an apparatus) and to maintain a solid content concentration in a practical range. An object of the present invention is to provide a new method for enlarging rubber latex which enables industrial production with a large-sized apparatus. Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above-mentioned problems, and as a result, by adding a specific substance to latex before the enlargement step, an acidic substance was added. The present inventors have found that the efficiency at the time of hypertrophy is improved and these problems are solved, and arrived at the present invention. That is, the present invention relates to a method of emulsifying a surfactant having an alkali metal salt of a carboxylic acid as a hydrophilic group,
And the number average particle diameter of the rubber particles in the latex is 0.2μ
An acidic substance is added to a rubber latex having a small particle diameter that is less than the number average particle diameter of 0.2 to 0.6 by coagulating and enlarging the rubber particles in the latex by making the liquid property of the latex acidic.
When obtaining a rubber particle-containing latex of μ under a stable condition, an alkali metal salt of an inorganic acid and / or an alkali metal salt of a saturated aliphatic carboxylic acid having 4 or less carbon atoms are added to the small particle size rubber latex in advance. It is intended to provide a method for coagulating and enlarging rubber latex particles characterized by the following. Hereinafter, the method of the present invention will be described in detail. The small particle size rubber latex having a number average particle size of less than 0.2 μm used in the present invention is an aqueous dispersion of a polymer having rubber elasticity, and is a diene such as polybutadiene, acrylonitrile-butadiene rubber, and styrene-butadiene rubber. Rubber, ethylene rubber such as polybutyl acrylate, ethylene-propylene rubber, ethylene-propylene rubber such as ethylene-propylene-nonconjugated diene rubber obtained by introducing a non-conjugated diene component such as ethylidene norbornene and dicyclopentadiene. And the like. Of these, diene rubber is particularly preferable. If the number average particle diameter of the rubber latex is 0.2 μm or more, it is difficult to enlarge the latex with a small particle diameter stably even if the present invention is applied. Further, from the viewpoint of industrial production, the lower limit is preferably 0.05 μ. Note that the range of the number average particle size is 0.1.
It is particularly preferred that the thickness be from 0.5 to 0.15 μm. [0008] The number average particle size of 0.2 μ
As the rubber latex having a small particle diameter of less than 1, it is essential to use a rubber latex emulsified with a surfactant having an alkali metal salt of a carboxylic acid as a hydrophilic group. In the case of a latex using a surfactant other than such a surfactant, it is difficult to coagulate and enlarge the rubber latex. Examples of the surfactant having an alkali metal salt of a carboxylic acid as a hydrophilic group include potassium laurate, sodium oleate, potassium stearate, mixed fatty acid potassium, sodium rosinate, disproportionated potassium rosinate, and the like. Alternatively, a mixture of two or more types can be used. The amount of the surfactant used is not particularly limited, but may be 1.0 to 5.0 parts by weight per 100 parts by weight of the monomer from the viewpoint of the polymerization stability of the rubber latex and the efficiency of the subsequent aggregation and enlargement treatment. preferable. The rubber latex having a small particle diameter to be subjected to coagulation enlargement can be obtained by a known emulsion polymerization method using the above-mentioned surfactant as an emulsifier. At that time, ordinary polymerization initiators, molecular weight regulators, basic substances and the like can be used. For example, as a polymerization initiator, a redox system in which a persulfate such as potassium persulfate, sodium persulfate, or ammonium persulfate, or an organic peroxide such as t-butylhydroxyperoxide or cumenehydroxyperoxide and a reducing agent component are combined. And the like, and examples of the molecular weight modifier include mercaptans (t-dodecyl mercaptan, n-dodecyl mercaptan, etc.), terpinolene, α-methylstyrene dimer, and the like.
Further, examples of the basic substance include sodium hydroxide, potassium hydroxide, ammonium hydroxide, and the like, and each may be used alone or in combination of two or more. The amount of these polymerization aids is not limited, but is generally 0.1 to 1.0 polymerization initiator per 100 parts by weight of the monomer.
Parts by weight, 0 to 1.0 parts by weight of a molecular weight modifier and 0.02 to 1.0 parts by weight of a basic substance. Also, monomers,
The method of adding the surfactant and the polymerization aid is not particularly limited, and any method such as initial batch addition and continuous or sequential addition of the monomer and / or the surfactant can be applied.
Furthermore, there is no particular limitation on the polymerization temperature,
A range of 80 ° C. is preferred. In addition, the small particle size rubber latex to be subjected to coagulation enlargement can be obtained by the above emulsion polymerization, but as another method, a separately polymerized solid rubbery polymer, for example, using a homogenizer or the like, It can also be obtained by emulsifying with the above-mentioned surfactant. The above-described rubber latex having a small particle diameter is coagulated and enlarged by contact with an acidic substance. Examples of such an acidic substance include mineral acids such as sulfuric acid, hydrochloric acid, and phosphoric acid;
Sodium hydrogen sulfate, acid salts such as sodium dihydrogen phosphate, and oxalic acid, citric acid, acetic acid, organic acids such as formic acid or acid anhydrides such as acetic anhydride can be used,
Although a mixture of two or more of these can be used, phosphoric acid or acetic anhydride is preferred. The amount of the acidic substance used is an amount necessary for making the small particle size rubber latex acidic (pH 7 or less). However, the particle size of the rubber latex to be enlarged, the type and amount of the emulsifier, and the intended enlarged rubber latex Is appropriately adjusted depending on the particle size of the particles. The acidic substance is basically diluted with deionized water and added as an aqueous solution. Further, the concentration is not limited at all, but in order to prevent the solid concentration of the rubber latex after coagulation enlargement from extremely lowering and to prevent generation of agglomerates and adhesion to equipment, 0.5 to 10%.
% By weight, and particularly preferably in the range of 1.0 to 7.0% by weight. An important point of the present invention is that an alkali metal salt of an inorganic acid and / or an alkali metal salt of a saturated aliphatic carboxylic acid having 4 or less carbon atoms are added to the small particle size rubber latex before enlarging with an acidic substance. Is added in advance. By performing this processing in advance, it is possible to suppress and prevent the generation of coagulated material and adhesion to the device. Examples of the alkali metal salt of an inorganic acid used in the pretreatment include sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium phosphate, potassium phosphate and the like. Examples of the alkali metal salt of a saturated aliphatic carboxylic acid having 4 or less carbon atoms include sodium oxalate, potassium oxalate, sodium citrate,
Examples thereof include potassium citrate, sodium acetate, and potassium acetate. A mixture of two or more of these can be used, but sodium sulfate or potassium sulfate, or sodium acetate or potassium acetate is preferable. The amount of the alkali metal salt of an inorganic acid and / or the alkali metal salt of a saturated aliphatic carboxylic acid having 4 or less carbon atoms is not particularly limited, but a rubber rubber latex having a small particle diameter to be enlarged (solid content) 0.01 to 1.
0 parts by weight is preferred. If the added amount is less than 0.01 part by weight, no improvement effect is exhibited, and if it is 1.0 part by weight or more, the effect is obtained, but the quality is unfavorably deteriorated. The form of the substance added to the rubber latex having a small particle diameter is preferably an aqueous solution, but the concentration thereof is not particularly limited, and is preferably in the range of 1.0 to 7.0% by weight. Further, the addition of the substance to the rubber latex having a small particle diameter to be enlarged is essential before the enlargement is performed, and it is preferable that the substance is added immediately before the enlargement is performed. It is possible to add after the completion of polymerization if it is obtained by adding it, or after its preparation if it is obtained by post-emulsification, or at the time of transfer or after transfer when storing them in a tank. The substance may be added as a polymerization aid before or during the start of polymerization, and may be used at this time. However, the addition at this time prevents the generation of aggregates and the adhesion to equipment during enlargement due to acidic substances. No effect is exhibited, and the effect is exhibited only when added to the latex in which rubber particle formation is substantially completed. In the present invention, before adding the acidic substance, a surfactant having an acidic and good surface activity may be previously added to the rubber latex, if necessary. By adding an acidic surfactant having good surface activity in advance, it becomes easy to control the particle diameter of the latex during coagulation and enlargement. Examples of the surfactant having acidic and good surface activity include sodium alkylbenzenesulfonate, sodium alkylnaphthalenesulfonate, potassium alkyldiphenylethersulfonate, sodium lauryl sulfate and the like. The amount of addition can be appropriately adjusted depending on the concentration of an acidic substance used for coagulation enlargement, the type of rubber latex, the concentration of solid content, and the like. A preferable addition amount is 0.2 parts by weight or less per 100 parts by weight of the rubber latex (solid content). If the amount is too large, the effect in the subsequent coagulation and enlargement step is reduced, and there is a tendency that enlarged particles having a target particle diameter cannot be obtained. After the coagulation enlargement, a basic substance is added to the rubber latex to adjust the pH of the rubber latex to 8 or more.
It is preferably 8 to 11 from the viewpoint of maintaining the mechanical stability of the coagulated enlarged latex and the stability at the time of graft polymerization using the rubber latex. Examples of the basic substance include sodium hydroxide and potassium hydroxide, and one or more of these can be used. There is no limitation on the method of adding the basic substance, and a method of injecting into a rubber latex liquid using an insert tube or the like used for the supply of an acidic substance after coagulation and enlargement, outside a stirring tank (tank, etc.) And a method of adding it in the form of a shower or a droplet to the liquid surface of the rubber latex in a flow-through tubular device having a stationary element. In addition, there is no restriction | limiting in particular about the stirring conditions at the time of addition of a basic substance. The agglomerated and enlarged rubber latex obtained by the method of the present invention is, as with the conventionally used large particle size rubber latex, styrene or styrene as a rubber component when producing a rubber reinforced resin such as an ABS resin. It can be used for graft polymerization using acrylonitrile or the like. Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples. Parts and% are based on weight. Reference Example 1 (Production of rubber latex having a small particle diameter) In a 100-liter pressure vessel, 95 parts of 1,3-butadiene, 5 parts of styrene, 0.5 part of n-dodecylmercaptan, and 0.1 part of potassium persulfate. 3 parts, 2.5 parts of sodium rosinate, 0.1 part of sodium hydroxide and 170 parts of deionized water were charged and reacted at 70 ° C. for 15 hours.
The reaction was terminated by cooling. The resulting latex had a solid content of 37%, a pH of 11, a number average particle size of 0.1 μm, and a gel content (toluene insoluble portion when immersed at 30 ° C. for 48 hours using toluene as a solvent and then filtered through a 100 mesh wire netting. Amount) was 85%. [Reference Example 2] (Production of small particle size rubber latex / addition of sodium sulfate after polymerization) In a 100 liter pressure vessel, 1,3-butadiene 95 was added.
Parts, styrene 5 parts, n-dodecyl mercaptan 0.5
Parts, potassium persulfate 0.3 parts, sodium rosinate 2.
5 parts, sodium hydroxide 0.1 part and deionized water 17
0 parts were charged, reacted at 70 ° C. for 15 hours, and then cooled,
5 parts of a 4% aqueous solution of sodium sulfate was added and mixed for 30 minutes. The latex obtained has a solid content of 36.
%, PH 11, number average particle diameter 0.1 μ, gel content (after immersion at 30 ° C. for 48 hours using toluene as a solvent,
Amount of toluene insoluble part when filtered through 100 mesh wire mesh)
85%. Example 1 100 parts of the small particle size rubber latex (solid content) obtained in Reference Example 1 was charged into a 100-liter stirring tank, and 5 parts of a 4% aqueous sodium sulfate solution was added. Mix for 30 minutes. While stirring the rotation speed of the stirring blade at 50 rpm (peripheral speed 0.3 m / sec),
30 parts of a 3% phosphoric acid aqueous solution was continuously supplied to one portion of the rubber latex liquid near the stirring blade through the insert tube for 30 minutes. 10% 10 minutes after supply of phosphoric acid is completed
7 parts of an aqueous potassium hydroxide solution was dropped from the upper portion of the stirring tank over 5 minutes. As a result, the obtained rubber latex had a solid content of 33% and a number average particle size of 0.45 μm, and the coagulated product formed at that time was 0.05% (the amount of residue on the mesh when filtered through a 100 mesh wire mesh). there were. After the bloat treatment,
When the inside of the stirring tank was observed, no adhesion to the tank wall and the stirring blade was observed, and the next enlargement treatment could be performed without washing the inside. In addition, the result in an Example and a comparative example was collectively shown in Table 1. Example 2 Using the small particle size rubber latex added with sodium sulfate obtained in Reference Example 2, 4%
The enlargement treatment was performed in the same manner as in Example 1 except that the operation of adding the aqueous sodium sulfate solution whose concentration was adjusted was not performed. As a result, the obtained rubber latex has a solid content of 33.
%, The number average particle diameter was 0.44 μm, and the coagulated product formed at that time was 0.03%. When the inside of the stirred tank was observed after the enlargement treatment, no adhesion was observed as in Example 1, and the next enlargement treatment could be performed without washing the inside. Example 3 0.3 parts of a 10% strength aqueous solution of sodium dodecylbenzenesulfonate was added to the small particle size rubber latex obtained in Reference Example 1 together with 5 parts of a 4% strength aqueous sodium sulfate solution. Add and mix for 30 minutes. The rotation speed of the stirring blade is 50 rpm (peripheral speed 0.3 m /
While stirring for 30 seconds, 30 parts of a 3% phosphoric acid aqueous solution was continuously supplied to one portion of the rubber latex liquid near the stirring blade through the insert tube for 30 minutes. Ten minutes after the supply of the phosphoric acid was completed, 7 parts of a 10% aqueous potassium hydroxide solution was dropped from the upper portion of the stirring tank over 5 minutes. As a result, the obtained rubber latex had a solid content of 33% and a number average particle size of 0.3.
7μ, 0.02% of coagulated product. When the inside of the stirred tank was observed after the enlargement treatment, no adhesion was observed as in Example 1, and the next enlargement treatment could be performed without washing the inside. Example 4 A thickening treatment was carried out in the same manner as in Example 1 except that sodium acetate was used instead of sodium sulfate as a salt to be added to the small particle size rubber latex. As a result, the obtained rubber latex had a solid content of 33% and a number average particle size of 0.45 μm, and the formed coagulate was 0.03%. When the inside of the stirred tank was observed after the enlargement treatment, no adhesion was observed as in Example 1, and the next enlargement treatment could be performed without washing the inside. Comparative Example 1 Using the small particle size rubber latex of Reference Example 1, an enlargement treatment was performed in the same manner as in Example 1 except that the addition operation of an inorganic or organic alkali metal salt was not performed. As a result, the obtained rubber latex had a solid content of 33% and a number average particle size of 0.42 μm, but the coagulated matter was as large as 0.7%. Observation of the inside of the stirring tank after the enlargement treatment revealed that the adhesion to the tank wall and the stirring blades was large, and it was necessary to wash the inside to perform the next enlargement treatment. [Comparative Example 2] The enlargement treatment was performed in the same manner as in Comparative Example 1 except that the concentration of the aqueous phosphoric acid solution added at the time of enlargement was 1%, the amount added was 90 parts, and the addition time was 90 minutes. went. As a result, the formed coagulated material was relatively small at 0.1%, and the number average particle diameter of the obtained rubber latex was 0.44 μm. However, the solid content was as low as 27%, and industrial productivity was low. Latex which hindered the surface. [Reference Example 3] In the production of the rubber latex having a small particle diameter described in Reference Example 1, the same operation was carried out except that the emulsifier used was changed to sodium dodecylbenzenesulfonate. A rubber latex with a small particle diameter having a number average particle diameter of 0.1 μm and a gel content of 86% was obtained. Comparative Example 3 An enlargement treatment was performed in the same manner as in Example 1 except that the rubber latex having a small particle diameter obtained in Reference Example 3 was used. As a result, the number average particle diameter of the obtained rubber latex was 0.11 μm, and the rubber latex was hardly enlarged. Reference Example 4 (Production of rubber latex of small particle diameter / addition of sodium sulfate at the start of polymerization) 1,3-butadiene 95 was placed in a 100-liter pressure vessel.
Parts, styrene 5 parts, n-dodecyl mercaptan 0.5
Parts, potassium persulfate 0.3 parts, sodium rosinate 2.
5 parts, sodium hydroxide 0.1 part, sodium sulfate 0.
Charge 2 parts and 170 parts of deionized water,
After reacting for an hour, the reaction was terminated by cooling. The latex obtained had a solid content of 37%, a pH of 11, a number average particle size of 0.1 μm, and a gel content (toluene was determined using toluene as a solvent.
After immersion for 48 hours at 0 ° C., the amount of toluene-insoluble parts when filtered through a 100-mesh wire gauze was 84%. Comparative Example 4 An enlargement treatment was performed in the same manner as in Comparative Example 1, except that the small particle size rubber latex to which sodium sulfate obtained in Reference Example 4 was added before the start of polymerization was used. As a result, the obtained rubber latex has a solid content of 3
Although the number average particle diameter was 3% and the number average particle diameter was 0.45 μm, the coagulated matter was as large as 0.35%. When the inside of the stirring tank was observed after the enlargement treatment, adhesion to the tank wall and the stirring blades was observed in a large amount, and it was necessary to wash the inside to perform the next enlargement treatment. [Table 1] According to the method for enlarging the rubber according to the present invention, it is possible to enlarge the rubber latex particles almost without producing any coagulated material, and to efficiently supply the rubber latex optimal for producing ABS resin. It is possible to do.

Claims (1)

Claims: 1. A small particle size emulsified with a surfactant having an alkali metal salt of a carboxylic acid as a hydrophilic group, and wherein the number average particle size of rubber particles in a latex is less than 0.2μ. An acidic substance is added to the rubber latex, and the liquid property of the latex is made acidic to coagulate and enlarge the rubber particles in the latex to obtain a rubber particle-containing latex having a number average particle diameter of 0.2 to 0.6 μm in a stable manner. A method of coagulating and enlarging rubber latex particles, which comprises adding an alkali metal salt of an inorganic acid and / or an alkali metal salt of a saturated aliphatic carboxylic acid having 4 or less carbon atoms to the small particle size rubber latex in advance. .