JPS6261044B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for agglomerating rubbery polymer particles of rubber latex, which is industrially useful without generating almost any rubber particles and without significantly lowering the concentration of the rubbery polymer. The present invention provides a method for obtaining a rubber latex of high quality.

Conventionally, it is well known to add an acidic substance to a diene rubber latex to lower the pH of the latex, and then add a basic substance to obtain a rubber latex consisting of coagulated and enlarged rubber particles. For example, in the method described in Japanese Patent Publication No. 42-3112, an acidic substance is added to a rubber latex with a rubbery polymer concentration of 20% or more and a pH of 8.0 or more to raise the pH of the rubbery latex to 8.0 to 1.0, and to increase the rubbery polymer concentration. In this method, the particle size of the rubbery polymer particles is increased by adjusting the concentration of the latex to 20% or less and then adding a basic substance to make the pH of the latex 8.0 or higher. However, in this method, in general, in order to sufficiently agglomerate the rubber particles and enlarge them to a predetermined particle size, it is necessary to add a large amount of an acidic substance to sufficiently lower the pH of the latex. As a result, the mechanical stability of the latex deteriorated, and some rubber particles adhered to the stirrer and tank walls as rubber lumps. The production of rubber lumps not only impairs workability, but also impairs the appearance of the final product if it is mixed into the product. In order to avoid the formation of rubber lumps, it was necessary to lower the latex concentration or the acid concentration of the acidic aqueous solution to be added. As a result, the rubber concentration in the rubbery polymer latex decreases, which has the disadvantage of impairing productivity. Further, as a means for avoiding the formation of such rubber lumps, there is, for example, a method described in Japanese Patent Publication No. 49-43266. In this method, the PH of the rubber latex is always kept neutral or alkaline, and by adding acidic and alkaline substances to the latex alternately or simultaneously, the rubber latex particles are coagulated and enlarged without forming almost any rubber lumps. It is to let them do it. However, this method has the disadvantage that it is complicated to industrially maintain the pH at a predetermined value during aggregation, and that both acidic and alkaline substances must be added in larger quantities than when added alone. The present inventors focused on this problem, and as a result of intensive study, they found that lactic acid is preferable as a flocculant that has a strong flocculating effect and is difficult to form rubber lumps. By controlling the temperature of the polymer latex, the temperature when adding the lactic acid aqueous solution, the acid concentration, and the stirring strength of the system, it is possible to effectively agglomerate and enlarge the rubber particles with almost no rubber lumps. I discovered that it is possible to complete the

That is, in the present invention, an aqueous lactic acid solution is added to a conjugated diene rubber latex, the pH of the latex is lowered to below 7, and the temperature of the system is maintained at 30°C or higher to coagulate and enlarge the latex particles, and the acid concentration in the aqueous lactic acid solution is This is a latex aggregation method characterized by adding basic substances to latex while maintaining the content at 1.5 to 15%, and then adding a basic substance.

As the rubbery polymer latex, poly-1,
A latex containing a copolymer of butadiene and other copolymerizable monomers containing 50% by weight or more of 3-butadiene and 1,3-butadiene, and this type of polymer can be produced by a well-known method. Can be done. 1-
Monomers that can be copolymerized with 3-butadiene include:
Vinyl aromatic compounds such as styrene and α-methylstyrene; Vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; acrylic esters;
Examples include methacrylic acid ester. These polymers may be gel-free or may be those in which the gel content is further increased by using a crosslinking agent such as divinylbenzene. As the emulsifier used in the production of these polymers, any commonly used emulsifier such as potassium rosinate, sodium rosinate, and potassium oleate can be used. Furthermore, the pH of rubbery polymer latex is 7.0.
In the above, an emulsifier in a stable state is used. It is also possible to use a blend of rubbers produced by different methods in appropriate proportions. The average particle size of the rubbery polymer particles is preferably 0.4 μm or less, and may have a uniform particle size distribution or a suitable particle size distribution.

In order to effectively achieve the object of the present invention, first, lactic acid is added to the rubbery polymer latex,
It is necessary to lower the pH of the latex to a value lower than 7.0 to coagulate and enlarge the rubbery polymer particles. The acid concentration of the lactic acid aqueous solution to be added is 1.5 to 15% by weight, preferably 2 to 5% by weight.

If the acid concentration of the lactic acid aqueous solution is lower than 1.5% by weight, the solid content in the rubbery polymer latex will decrease, making it impossible to obtain a rubbery polymer latex with a high solids content concentration, which is the objective of the present invention. ,
If the acid concentration is 15% by weight or more, rubber lumps are likely to be formed, which is not preferable. Also, when performing this coagulation operation, the temperature of the rubbery polymer latex is
Must be kept above ℃. The temperature of the latex is 30
If the temperature is below 0.degree. C., rubber lumps are likely to occur, making it impossible to perform a stable aggregation operation. Similarly, the temperature of the lactic acid aqueous solution to be added is 30°C or higher, preferably 40°C or higher.
Must be kept at 80℃.

The preferred method for adding lactic acid is the usual continuous addition, but rather than dropping it dropwise from the top of the stirring tank where aggregation occurs, it is preferable to supply it from an internal pipe or the bottom of the stirring tank and bring it into direct contact with the rubbery polymer latex. It is preferable to do so. This is to prevent the surface of the latex from being disturbed and the formation of rubber lumps when lactic acid is dropped from the top of the stirring tank.

The pH of the rubbery polymer latex after adding lactic acid is an important factor because it has a great effect on the state of aggregation of the rubbery polymer. That is, the pH of the rubbery polymer latex needs to be 7.0 or less, preferably 2.5 to 6.0. If the pH of the latex is lower than 2.5, rubber lumps are likely to be formed, and if it is higher than 6.0, the coagulation and enlargement effect will be weak and undesirable. This is because when an acidic substance is added to a rubbery polymer latex, it is adsorbed to the rubbery polymer particles, neutralizes the electrostatically stabilized surfactant, and causes collision and fusion of these rubbery polymer particles. This is thought to be because the In order to perform more stable aggregation operation,
Anionic surfactants that are relatively stable against acids, such as sodium dodecylbenzene sulfonate and sodium sulfosuccinate diocle ester, can be added to the rubbery polymer latex as a dispersion stabilizer. These dispersion stabilizers may be added all at once before adding the lactic acid aqueous solution, or may be added to the lactic acid aqueous solution and added at the same time. The amount of such a dispersion stabilizer added is preferably about 0.005 to 0.2% by weight based on the solid content of the rubbery polymer latex. When this amount is 0.2% by weight or more, the effect of aggregating rubbery polymer particles by lactic acid is reduced, which is not preferable.

Although the rate at which the aqueous lactic acid solution is added can vary over a wide range, industrially it is preferable that the addition time be about 3 to 15 minutes. The vessel in which the rubbery polymer particles are agglomerated and enlarged may be any jacket or reaction vessel equipped with a stirrer. The strength of stirring when coagulating and enlarging the rubbery polymer particles using this reaction vessel has a great effect on the stability of the system, so it is necessary to select an appropriate stirring strength. The strength of stirring is determined by the diameter and rotational speed of the stirring blade, but if the stirring is too strong, a large number of rubber lumps will be formed, which is undesirable, and if the stirring is too weak, the surface fluidity of the rubbery polymer latex will be poor. This is sufficient to easily form a film-like rubber lump on the surface of the rubbery polymer latex. Furthermore, if it is extremely weak, the contact between the lactic acid and the rubbery polymer latex will be insufficient, and the rubbery polymer particles will not be sufficiently agglomerated and enlarged.
When using a stirring blade used in ordinary polymerization operations, a stirring strength within the range shown below will give good results.

N ³ D ² = 5 × 10 ³ ~ 5 × 10 ⁴ where D: Diameter of stirring blade (unit: m) N: Rotation speed of stirring blade (unit: rpm) However, D = 0.1 (m) ~ 3.0 (m) limited to the range of

In addition, as a method for coagulating and enlarging the rubbery polymer particles, a rubbery polymer latex is charged in advance using this reaction vessel, and after the temperature is maintained at 30°C or higher, an aqueous lactic acid solution is added to coagulate and enlarge the rubbery polymer particles. A batch method may be used, or a method may be used in which a rubbery polymer latex and an aqueous lactic acid solution are each continuously supplied to a reaction vessel to continuously obtain agglomerated and enlarged rubbery polymer latex from the upper part of the vessel.

The rubbery polymer latex, which has been coagulated and enlarged by adding an aqueous lactic acid solution as described above, is in an extremely unstable state as it is, and it is necessary to add a basic substance. Examples of the basic substance to be added include sodium hydroxide, potassium hydroxide, and sodium carbonate, and sodium hydroxide and potassium hydroxide are preferably used. It is preferable that these basic substances are diluted and added to a concentration of 2 to 10% by weight.
If it is added at a concentration of 10% by weight or more, rubber lumps are likely to occur, which is not preferable, and if the concentration is too low, the amount of liquid increases, which is not preferable. It is important to add these basic substances immediately after the addition of the lactic acid aqueous solution is completed, and it is necessary to add them within 30 seconds at the latest. If there is an interval of 30 seconds or more between the addition of the lactic acid aqueous solution and the addition of the basic substance, the rubber latex will be subjected to the stirring action in an unstable state, and rubber lumps will stick around the stirrer. Therefore, it is not desirable.

As mentioned above, in order to obtain a stable latex by adding a basic substance, it is desirable to maintain the final pH between 8 and 12. The rubbery polymer latex produced by the method of the present invention is further graft-polymerized by adding a vinyl aromatic monomer or a mixture of a vinyl aromatic monomer and at least one polymerizable vinyl monomer. , impact-resistant resin can be obtained.

The method of the present invention will be explained in detail below using examples.

Example 1 Equipped with an anchor-type stirring blade with a diameter of 0.36 m and a jacket
SBR with the following characteristics for 200 reaction vessels
Latex (SLB manufactured by Japan Synthetic Rubber Co., Ltd.)
I loaded 13.0Kg.

Solid content 23.3% Bound styrene 23% Mooney viscosity ML ₁₊₄ gel content None Emulsifier Mixed acid system When this latex was observed with an electron microscope, the average particle size was 0.05μ. The latex was heated with steam until the temperature of the latex reached 60° C. while stirring the reaction vessel at a rotation speed of 50 rpm. Meanwhile, an acid aqueous solution consisting of 1.68 kg of 50% lactic acid aqueous solution and 6.72 kg of deionized water was heated to a temperature of 75°C. When the temperature of the latex reached 60°C, this acid aqueous solution was continuously supplied to the reaction vessel through an internal tube. The feeding time was 7 minutes. The pH of the latex at this time was 4.2.

5% by weight immediately after addition of lactic acid aqueous solution
7.2 kg of a concentrated aqueous sodium hydroxide solution was added over 5 minutes. The latex thus obtained was cloudy and completely opaque. When this latex was observed under an electron microscope, the average particle size of the rubbery polymer particles was 0.43μ. The solid content concentration of the latex after flocculation was 20.8%. After the flocculation operation was completed, the latex was taken out from the reaction can and the inside of the reaction can was observed, and it was found that almost no rubber lumps were observed, and the next batch operation could be carried out without cleaning the inside.

Comparative Example 1 The same procedure as described in Example 1 was carried out except that stirring was continued for 1.5 minutes after the addition of the acid aqueous solution was completed and then addition of the sodium hydroxide aqueous solution was started. When the latex was extracted from the bottom of the reaction can and the inside of the reaction can was observed, a small amount of rubber lumps were found adhering to the inner wall, internal pipe, and stirring blade.

When these adhered rubber lumps were taken out and the weight after drying was measured, it was 0.25 kg (0.8% by weight based on the total rubber content).

Example 2 A first reaction can of No. 5 equipped with a jacket and a stirrer equipped with three paddle-shaped stirring blades with a diameter of 12 cm and two reaction cans equipped with a jacket and fan-turbine type stirring blades were installed in parallel. did. There are two supply nozzles at the bottom of the first reactor, one of which
The same rubbery polymer latex as in Example 1 was fed through the main nozzle using a pump at a rate of 500 c.c./min. The temperature of the rubber latex was adjusted to 60°C using steam heating from the jacket. An acid aqueous solution consisting of 2.8 kg of 50% lactic acid aqueous solution and 11.2 kg of deionized water was adjusted to a temperature of 75°C in advance. Three minutes after starting the supply of rubber latex, this acid aqueous solution was started to be supplied from the other supply nozzle at a rate of 33 c.c./min. After about 10 minutes, overflow started from the first reactor. This latex was completely cloudy. This latex was led to the supply nozzle at the bottom of the second reaction vessel, and a 5% by weight aqueous sodium chloride solution adjusted to 60°C was started to be supplied from the upper nozzle at a rate of 13 c.c./min. About 4 minutes later, overflow started from the upper part of the second reaction vessel.

After that, the same conditions were maintained for 2 hours, and about 65 latexes were obtained. The solid content concentration of this latex is 22%.
The pH was 9.8. When this latex was observed under an electron microscope, the average particle diameter of the rubbery polymer particles was found to be
It was 0.40μ.

After the flocculation operation was completed, the latex was extracted from the bottoms of the first and second reaction vessels, and when the inside of the reaction vessels was observed, it was found that almost no rubber lumps were formed, and it was possible to operate for a longer period of time. Ta.

Example 3 1300 g of butadiene monomer, 26 g of potassium rosinate, 2.6 g of n-dodecyl mercaptan, 1950 g of deionized water, and 2.6 g of potassium persulfate were placed in a stainless steel autoclave equipped with a stirrer under vacuum, and the temperature was 50 to 60. The polymerization reaction is carried out in the temperature range of ℃ until no pressure drop is observed.
Unreacted monomers were removed by steam stripping to obtain a synthetic rubber latex with a polymerization yield of 96.5% and a solid content of 40%. The properties of the obtained rubber latex were as usual.

PH: 11.3 Mooney viscosity: 125 Gel content: 86 1,000 g of this latex was charged into a jacketed reaction vessel equipped with an anchor-shaped stirring blade having a diameter of 8 cm. When this latex was observed with an electron microscope, its average particle size was 0.22μ. The temperature of the latex was raised to 50° C. while stirring while maintaining the rotation speed of the stirring blade of this reaction vessel at 120 rpm. Meanwhile, an acid aqueous solution consisting of 0.06 g of sodium dodecylbenzenesulfonate, 24 g of 50% lactic acid aqueous solution, and 276 g of deionized water was heated to 75°C. When the temperature of the latex reaches 50℃,
This acid aqueous solution was continuously supplied to the reaction vessel through an internal tube. The feeding time was 10 minutes. The pH of the latex at this time was 3.5. Immediately after the addition of this acid aqueous solution, add 5% by weight at a temperature of 50°C.
103g of aqueous sodium hydroxide solution adjusted to 100% was added over 5 minutes. When the obtained latex was observed under an electron microscope, the average particle diameter of the rubbery polymer particles was 0.36μ. The solid content concentration of the latex after flocculation is 28.5
It was %. After the flocculation operation, the latex was taken out from the reactor and the inside of the reactor was observed, and it was found that there was almost no adhesion of rubber lumps, and the next batch operation could be carried out without cleaning the inside.

Example 4 Equipped with an anchor-shaped stirring blade with a diameter of 0.20 m and a jacket
6 kg of the SBR latex used in Example 1 and 6 kg of the polybutadiene latex used in Example 3 were charged into 30 reaction vessels. The mixture was stirred and mixed by setting the rotation speed of the stirring blade to 80 rpm. The solid content in the latex at this time was 31.65%. This latex was a mixture of rubbery polymer particles with an average particle size of 0.05μ and rubbery polymer particles with an average particle size of 0.22μ. This latex was heated with steam until the temperature reached 60°C. Meanwhile, an acid aqueous solution consisting of 0.38 g of sodium dodecylbenzenesulfonate, 190 g of a 50% lactic acid aqueous solution, and 1710 g of deionized water was heated to a temperature of 75°C. When the temperature of the latex reaches 60℃,
This acid aqueous solution was continuously supplied to the reaction vessel through an internal tube. The feeding time was 5 minutes. The pH of the latex at this time was 4.6. Immediately after the addition of the acid aqueous solution was completed, 815 g of a 5% by weight aqueous sodium hydroxide solution was added over 5 minutes.
The latex thus obtained was cloudy and completely opaque. A chemical solution consisting of 42 g of glucose, 42 g of sodium pyrophosphate, 0.4 g of ferrous sulfate, and 1.05 kg of deionized water was added to this latex all at once. While maintaining the temperature of the latex at 60° C., monomers consisting of 3376 kg of styrene, 1.266 kg of acrylonitrile, and 17 g of tertiary dodecyl mercaptan were prepared and charged continuously at a constant speed for 4 hours. At the same time as monomer preparation, a mixed aqueous solution of a polymerization initiator and an emulsifier consisting of 17 g of cumene hydroperoxide, 170 g of potassium oleate, and 4640 g of deionized water was added at 5.5 g.
It was fed continuously at a constant speed. After the addition of the monomer mixture and the mixed aqueous solution of the polymerization initiator and emulsifier was completed, the graft reaction was continued at 60° C. for 1 hour.
Adding an antioxidant to the obtained polymer latex,
It was further coagulated with magnesium sulfate, filtered, washed with water, and dried. The obtained polymer was in the form of a white powder. The rubbery polymer content of the graft polymer is 34.1
It was %. Hard resin beads (polymerization composition of styrene and acrylonitrile of 73%: 27%) obtained by separate suspension polymerization were added to the obtained graft polymer powder.
%, intrinsic viscosity MEK 30°C, [η] = 0.50 dl/gr) and kneaded with a Henschel mixer to form a mixed powder with a rubbery polymer content of 15% by weight in the entire composition, This was extruded to obtain pellets. Test specimens were prepared using the pellets by injection molding, and various physical properties were evaluated in accordance with the ASTM method. Izotsu impact strength (1/2″×1/
2'') was 25.5 Kg/cm (notched), and the tensile strength (yield value) was 455 Kg/cm ² .

Comparative Example 2 Graft polymerization was carried out in the same manner as in Example 4 except that the agglomeration operation was not carried out, and various physical properties were measured using the obtained pellets in the same manner. 1/2″) is 7.5
Kg・cm/cm (with notch), tensile strength (yield value)
It was 490Kg/ ^cm2 .

Claims (1)

[Claims] 1 Add lactic acid aqueous solution to conjugated diene rubber latex, lower the pH of the latex to below 7, and raise the temperature of the system to 30°C to coagulate and enlarge the latex particles.
℃ or higher, and the acid concentration in the lactic acid aqueous solution
A method for aggregating latex, which is characterized in that it is added to latex while maintaining it at 1.5 to 15%, and then a basic substance is added.