JPS6254806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrially advantageous method for producing ultrafine polymer latex by emulsion polymerization.

Ultrafine particle polymer latex with a particle size of about 0.005 to 0.05μ differs from normal white opaque polymer latex with a particle size of about 0.05 to 0.4μ.
It is a semi-transparent or transparent viscous material that appears blue-white to reflected light and yellow-red to transmitted light, and is dense and transparent with a luster comparable to that of solvent-volatile solution-type polymers. It has become increasingly important in the latex industry because it has excellent physical properties and workability, such as being able to form a film with good viscosity and easily producing polymer latex with relatively high viscosity. There is.

Conventionally, the method for producing ultrafine particle polymer latex is to swell a carboxylic acid-modified acrylic polymer latex in an aqueous medium containing a small amount of a water-soluble solvent, and then stir it vigorously at high temperature to form polymer particles. There is a known method of finely dividing (DuPont Hydrosol), but
This method is difficult to operate, and it is possible to produce ultrafine polymer latex particles only within extremely limited ranges such as the amount of carboxylic acid monomer, degree of alkali neutralization, and molecular weight through copolymerization. There were restrictions.

On the other hand, as is well known, in normal emulsion polymerization, the number of particles of the polymer latex produced increases in proportion to the 0.6th power of the emulsifier concentration, and the particle size decreases with the emulsifier concentration, but when the particle size is 0.05 In order to produce a polymer latex with ultrafine particles of micron size or less, a very large amount of emulsifier is required, which is impractical. Additionally, as the particle size of the polymer latex decreases, the viscosity of the resulting polymer latex becomes significantly higher as the polymerization progresses and if the polymer concentration is high. It separates into layers and cannot be dispersed in the aqueous phase, making industrial production practically impossible.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an advantageous method for producing ultrafine polymer latex having a particle size of about 0.005 to 0.05 μm.

The present inventors have conducted intensive research to overcome the drawbacks of the conventional methods described above and to develop an industrially advantageous method for producing ultrafine particle polymer latex consisting of a wider range of arbitrary monomer components. As a result of repeated studies on the selection of suitable surfactants, the effects of various polymerization conditions, and methods for reducing the viscosity of the resulting polymer latex, we have developed an ultrafine particle polymer with low viscosity and high concentration without complicating polymerization operations such as stirring. The inventors discovered a method for easily producing latex and completed the present invention.

That is, the present invention consists of the following first and second steps, and is characterized in that an ionic electrolyte is added in an effective amount for reducing viscosity before the viscosity increases due to polymerization in the first or second step. It is.

First step: at least one hydrophilic monomer A selected from the group consisting of acrylic acid lower alkyl ester, methacrylic acid lower alkyl ester, and vinyl acetate, or a hydrophobic monomer copolymerizable with the monomer A 1 to 15 parts by weight of a monomer mixture consisting of monomer B and the at least one hydrophilic monomer A is added to a water-soluble polymerization initiator at a concentration of 1.0 x 10 ^-3 to 1.0 x 10 ^-2 mol/. 100% in an aqueous medium at a pH of 2 to 7 in the presence of an anionic surfactant and 1 to 8 parts by weight of an anionic surfactant.
A process of producing a primary polymer latex by emulsion polymerization in parts by weight.

Second step: A monomer C of the same type or different type as the monomer in the first step is added to the primary polymer latex obtained in the first step in the aqueous medium.
A step of polymerizing the monomer C using the polymer particles in the primary polymer latex as a nuclide by stirring while dropping 70 to 90 parts by weight per 100 parts by weight.

The polymerization initiator used in emulsion polymerization of polymerizable monomers in an aqueous medium is not particularly limited as long as it is water-soluble, and examples of polymerization initiators commonly used in this type of emulsion polymerization, such as A redox initiator consisting of a persulfate or a known reducing sulfoxy compound such as a persulfate, a thiosulfate, or a sulfite can be used. The amount added is determined by the concentration in the aqueous medium.
It is 1.0×10 ⁻³ to 1.0×10 ⁻² mol/.

Hereinafter, the configuration of the present invention will be explained in detail.

(1) In the present invention, first, a first stage polymerization step is carried out to produce a polymer latex having a particle size of 0.02 μm or less in an aqueous medium. In this case, an emulsifier is present in the aqueous medium. Examples of emulsifiers include those that have an emulsifying effect in the pH range of 2 to 7, such as alkyl sulfates such as lauryl sulfate, and alkylbenzene sulfones such as dodecylbenzenesulfonate. Anionic surfactants such as acid salts, dialkyl sulfosuccinates such as diethyl sulfosuccinate, and POE alkyl ether sulfate salts are suitable. These emulsifiers should be added in an amount of 1 part by weight per 100 parts by weight of the aqueous medium.
It is added in a proportion of 8 parts by weight, preferably 2 to 4 parts by weight. If the amount of emulsifier used is too large, the foaming properties of the produced polymer latex and the physical properties of the film will be adversely affected, so it is desirable that the amount of emulsifier used be as small as possible. However, if the amount of emulsifier is less than 1 part by weight, the particle size of the resulting polymer latex will be 0.1 μm or more, making it impossible to achieve the intended purpose.

The monomer used in this step may be any monomer as long as it is relatively hydrophilic, can be emulsified and dispersed in an aqueous medium, and forms a water-insoluble polymer through polymerization, but in general, vinyl acetate is used. , lower alkyl esters (eg, methyl ester, ethyl ester) of acrylic acid and methacrylic acid. Furthermore, a mixture of at least one of these hydrophilic monomers and a hydrophobic monomer copolymerizable therewith, such as styrene, butyl acrylate, acrylic acid, acrylonitrile, etc., can be used.

In this step, the above monomer or the above mixture is added in an amount of 1 to 15 parts by weight per 100 parts by weight of the aqueous medium and emulsified and dispersed. This amount is such that the amount of polymer in the polymer latex produced in this step is 15 to 1.5% by weight, preferably 12 to 2.5% by weight. If the amount of monomer added exceeds this range, the number of particles of the polymer latex produced decreases and the particle size increases, which is disadvantageous because a larger amount of emulsifier is required to obtain ultrafine polymer latex. It is. Further, temperature elevation is also undesirable since it becomes extremely difficult to control the polymerization reaction. On the other hand, if the amount is less than this range, it will be below the solubilization limit of the monomer and the number of produced polymer particles will decrease, which is disadvantageous.

Next, polymerization is performed after dispersing the monomer amount within the above range. In this case, the polymerization temperature is 50
A temperature of -90°C, preferably 60-70°C is employed, but even if the temperature is raised to 80°C or higher due to the heat of polymerization, it is sufficient as long as the temperature at the start of polymerization is 60-70°C. Also
The pH value is preferably on the acidic side of 2 to 7,
When the pH becomes alkaline, the polymer particles in the latex produced tend to become larger.

In this way, particle size of 0.02 μ or less, usually
A polymer latex with a polymer content of 15 to 1.5% by weight of ultrafine polymer particles of about 0.01 to 0.005 μm is obtained. This polymer latex is used as a polymerization nuclide in the next second stage polymerization step.

(2) Next, in the present invention, a polymerizable monomer that provides a water-insoluble polymer is continuously added dropwise to the polymer latex obtained in the first stage polymerization process. The polymerization process is carried out. The monomers added in this step are not limited to the same kind of hydrophilic monomers used in the first stage polymerization step, but also different kinds of monomers, such as hydrophobic monomers such as ethylene. , styrene, butadiene, and _C4 or higher alkyl esters of acrylic acid and methacrylic acid. The amount of the polymerizable monomer added in the second stage polymerization step is 70 to 90 parts by weight per 100 parts by weight of the aqueous medium, or such an amount that the polymer content in the resulting polymer latex is 35 to 48% by weight. The amount of water-soluble polymerization initiator in this step is 5.0×10 ^-3 to 5.0 in solution concentration.
×10 ^-4 /mol, preferably 1.0 × 10 ^-3 to 2.0 ×
10 ^-3 mol/. Note that the polymerization initiator is the first
Add the entire amount in advance in the polymerization process of the second stage, and
It is also possible to omit the addition of a step. The polymerization conditions in the second stage polymerization step are not as limited as those in the first stage polymerization, and can be carried out at any temperature (usually 50 to 90°C) and PH depending on the type of monomer, and may be acidic or alkaline, preferably is PH3～
It will be held at 9. The monomer is polymerized while being continuously added dropwise to prevent a significant temperature rise due to the heat of polymerization.

(3) Furthermore, in the present invention, an ionic electrolyte is added to the aqueous medium in either the first or second step. This is to suppress the increase in viscosity of the resulting polymer latex in order to facilitate stirring operations and enable industrial production. In this way, the ionic electrolyte used as a viscosity reducing agent must not contain salts such as heavy metals that cause significant PH value fluctuations, suppress or inhibit polymerization reactions, or precipitate water-soluble salts during double decomposition. Although a wide range of water-soluble organic and inorganic electrolytes can be used, the following types are generally preferred.

(a) Various phosphates, sulfates, chlorides, carbonates, consisting of alkali salts or ammonium salts such as potassium chloride and diammonium phosphate;
Acetates, persulfates, imidosulfates, sulfonates.

(b) Aqueous ammonia (28%), methyldiethylaminoalcohol, morpholine, sodium paratoluenesulfonate, etc.

In the present invention, it is necessary to limit the amount of such ionic electrolyte added within an appropriate range; if the amount added is too large or too small, the viscosity of the resulting polymer latex will become extremely high, which is disadvantageous. It is. In other words, if the amount is limited to an appropriate range, it is possible to effectively prevent the viscosity of the polymer latex from increasing during polymerization, regardless of its type. The amount of ionic electrolyte added that can effectively prevent viscosity increase varies depending on the polymerization conditions applied and the type of electrolyte, and cannot be determined unambiguously, but it is generally added to 100 parts by weight of the aqueous medium. The amount is 0.4 parts by weight or less, usually in the range of 0.2 to 0.3 parts by weight. A person skilled in the art can easily determine the preferable amount to be added through several preliminary experiments. Therefore, in the present invention, the amount of ionic electrolyte added that can effectively suppress the increase in viscosity of the polymer latex during the polymerization reaction is defined as the effective viscosity-lowering range amount.

The specific type of the ionic electrolyte actually used in the present invention is appropriately selected in relation to the polymerization conditions. When a basic salt such as sodium pyrophosphate or sodium imidobis sulfate or aqueous ammonia is applied and the PH of the polymerization system is adjusted to an alkaline side, ammonia water is applied and the PH of the polymerization system is adjusted to an acidic side. Para-toluenesulfonic acid and ammonium imidosulfate are effectively applied.

These ionic electrolytes are usually added to the reaction system in the form of an aqueous solution, but they can be added at any time before the viscosity starts to increase during the polymerization reaction, but they can be added at any time before the viscosity starts to increase during the polymerization reaction. In order to prevent destruction, it is preferable to add it before the start of polymerization in the first stage polymerization step. However, the first stage polymerization process needs to be carried out at an acidic pH, and aqueous ammonia, sodium pyrophosphate, etc., which make the pH of the polymerization system alkaline, must be added at 10g/dl after the start of the second stage polymerization process. It is preferable to add it to the reaction system while gradually dropping it as an aqueous solution having a concentration below the concentration. Aqueous ammonia, various amino alcohols, morpholine, etc. are relatively resistant to cohesive failure, and are volatile during the film forming process by drying the polymer latex, so they have desirable advantages in film formation.

The ultrafine particle polymer latex produced by the method of the present invention has the advantage of good permeability and surface wetting, and that the viscosity can be easily adjusted without the need for a thickener. It also has good film-forming properties, and the resulting film is dense and has excellent gloss, making it even more useful as a latex for floor polishing emulsions that do not require puffing, coating agents, leather finishing, paper processing, and textile processing. Can be used for

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 400 ml of distilled water in a 1000 ml four-neck separable flask equipped with a gas introduction tube, a reflux condenser, a composite glass electrode for PH measurement, and a stirring device (equipped with a half-moon stirring piece with a string length of 6 cm). 10 ml of methyl methacrylate as a monomer for the first stage polymerization step was emulsified and dispersed in a solution of 8 g of sodium lauryl sulfate dissolved in the solution, and potassium persulfate at a concentration of 1.0 x 10 ^-3 mol/in the system was used as a polymerization initiator. , while maintaining a constant stirring state (300 rpm), at a temperature of 60 to 70.
Polymerization was carried out under the conditions of .degree. C. and pH of 2 to 3. This first
The step polymerization process was completed in 8 minutes, yielding a transparent latex dispersion with a proteinaceous glow.

Next, 290 ml of methyl methacrylate was gradually added dropwise into this protein-colored polymer latex dispersion to prevent a significant temperature rise due to polymerization heat.
The second stage of polymerization was carried out using potassium persulfate at a system concentration of 1.0 x 10 ^-3 mol/ as an initiator. In this case, as the polymerization progresses, the viscosity of the system increases rapidly, making monomer dispersion and stirring operations difficult, and fluidity is lost, but immediately after the start of the second stage polymerization, 1.5-2ml ammonia water (28%)
When polymerization was carried out while maintaining the pH of the polymerization system at 8.7 to 9.0 by gradually adding it dropwise, the viscosity of the polymerization system did not increase significantly and the fluidity was maintained.
Dispersion and agitation of the monomers were good. Also,
A similar effect was obtained when 1 to 2 ml of methyldimethylamino alcohol or morpholine was added in addition to ammonia water.

The polymer latex thus obtained is a semi-transparent, slightly viscous colloidal dispersion that appears blue-white to reflected light and yellow-red to transmitted light; The transmittance was 31.0%.

(wavelength 800 mμ, sample thickness 1 cm). Also, the viscosity is B
Type rotational viscometer spindle No. 4 when rotation speed is 6 rpm
It was a non-Newtonian viscous material with a rather high viscosity of 36,600 centivoise and 8,626 centivoise at 60 rpm.

The viscosity of this somewhat highly viscous polymer latex is further reduced by the addition of an electrolyte. For example, when 1 ml of a sodium pyrophosphate aqueous solution with a concentration of 10 g/dl is added to 130 g of this polymer latex, the viscosity decreases significantly. However, it turned into a Newtonian viscous material with 420 centivoise, and when 3ml was added, it changed into a very low viscosity polymer latex with 43 centivoise.

The particle size of the polymer latex determined from an electron micrograph was 0.048μ.

Example 2 Using the same apparatus as in Example 1, a solution of 8.0 g of sodium lauryl sulfate and 0.7 g of sodium paratoluenesulfonate crystalline powder dissolved in 400 ml of distilled water was placed in a 1000 ml four-necked separable flask. 10 ml of methyl methacrylate was emulsified and dispersed as a monomer in the first stage polymerization step, and potassium persulfate at a concentration of 1.0 × 10 ^-3 mol/in the system was used as a polymerization initiator in the same manner as in Example 1 with constant stirring. keep the condition 60
Polymerization was carried out at ℃. The pH of the polymerization system was 5 to 6, and the first stage polymerization was completed in about 5 minutes, producing a transparent latex dispersion with a proteinaceous glow. Then, while continuously dropping 290 ml of methyl methacrylate,
When the second stage polymerization was carried out using 10 ^-3 mol/mol of potassium persulfate as a polymerization initiator, the viscosity of the system increased only slightly and there were no problems such as difficulty in stirring.
Polymerization was completed in minutes. The resulting polymer latex is translucent, blue-white, and has a light transmittance of 29%.B
The viscosity measured by a type viscometer is 6 to 6 on spindle No. 2.
It was a low viscosity polymer latex with 485 to 750 centivoise in the 60 rpm range. The pH of the latex produced was 3 to 4.

The particle size of the polymer latex determined from an electron micrograph was 0.055μ.

Example 3 Distilled water was prepared using the same equipment and method as in Example 1.
After emulsifying and dispersing 50 ml of methyl methacrylate in an aqueous solution of 8 g of sodium lauryl sulfate in 400 ml, adding 1.0812 g of potassium persulfate crystals, the pH of the polymerization system becomes 1.5 to 1.2. Next, 2 to 3 drops (1 ml or less) of 28% ammonia water are added with a pipette, and the pH becomes 7 to 8, and polymerization starts and the system changes from a milky state to a translucent state. Next, 250 ml of methyl methacrylate monomer is continuously added. Polymerization was continued while dropping, and the polymerization was completed approximately 27 minutes after the start.
A fluid polymer latex with a small increase in viscosity was obtained. The light transmittance of the produced polymer latex is 45% (800 mμ, 1 cm thickness) and the viscosity is 1840 to 3040.
It was centiboise.

The particle size of the primary particles determined from the electron micrograph is
It was 174±26 Å.

Example 4 Sodium lauryl sulfate was placed in a 1000 ml four-neck separable flask equipped with a gas inlet tube, a reflux condenser, a composite glass electrode for PH measurement, and a stirring device.
The composition ratio of ethyl acrylate and methyl methacrylate is 7: in 400 ml of distilled water in which 8.0 g and 0.50 g of diammonium phosphate, which acts as a viscosity reducing agent, are dissolved.
Disperse 10 ml of the mixed monomers from step 3 and mix with potassium persulfate as an initiator (concentration in the system: 1.0 x 10 ^-3 mol/) while maintaining constant stirring (300 rpm).
Polymerization was initiated at ℃ PH2-4. Next, copolymerization was carried out while dropping 290 ml of a mixed monomer consisting of ethyl acrylate and methyl methacrylate (composition ratio 7:3) to prevent a significant temperature increase due to heat of polymerization. Polymerization was completed within 60 minutes, and until the completion of polymerization, the viscosity of the polymerization system was low, and there were no problems such as difficulty in stirring, and a transparent ultrafine particle polymer latex was produced (light transmittance of 38% at 800 mμ). The viscosity of latex measured by a viscometer is determined by the spindle rotation speed.
It was 2248 centimeter voice at 60 rpm. The pH value of the polymer latex was 7.

30 ml of the obtained ethyl acrylate-methyl methacrylate copolymer latex was cast onto a 11 x 15 cm square glass plate and dried under natural ventilation at room temperature to form a transparent, glossy polymer latex film. did.

The particle size of the polymer latex determined from an electron micrograph was 0.041μ.

Comparative Example 1 Distilled water was prepared using the same equipment and method as in Example 1.
After emulsifying and dispersing 300 ml of styrene monomer in an aqueous solution of 12 g of sodium lauryl sulfate in 400 ml, the temperature was raised to 60°C while maintaining constant stirring using potassium persulfate at a concentration of 1.0 x 10 ^-3 mol/in the system as a polymerization initiator. Polymerization was carried out at ~70°C and pH 3-4. The resulting polymer latex was white and opaque, and the particle size determined from an electron micrograph was 0.09μ. In the case of emulsion polymerization of hydrophobic monomers such as styrene, the Smith-Ewart theory [J.chem.phys.,
16, 592 (1948)], and the number of particles is proportional to the 0.6th power of the emulsifier concentration, so if the particle size is 0.05μ
In order to produce the following ultrafine particle polymer latex, a large amount of sodium lauryl sulfate of 8% by weight (32 g) or more is required. In the case of other emulsifiers, even larger amounts of emulsifiers are required, but the use of such large amounts of emulsifiers significantly increases the foaming properties of the resulting polymer latex, and also adversely affects the intended use due to the side effects of the emulsifiers. It's inappropriate.

Comparative Example 2 0.75684g of potassium persulfate in Example 3
When 1.4055 g was used and when 1.4055 g was used, the viscosity of the polymerization system increased as the polymerization progressed, and the monomer layer being added separated onto the top of the highly viscous latex layer, making it impossible for the monomer to diffuse. The resulting polymer latex was highly viscous, ranging from 12,000 to 41,150 centipoise.

Claims (1)

[Claims] 1. Consisting of the following first and second steps, the first step
Alternatively, a method for producing an ultrafine particle polymer latex, characterized in that an ionic electrolyte is added in an amount effective for reducing the viscosity before the viscosity increases due to polymerization in the second step. First step: at least one hydrophilic monomer A selected from the group consisting of acrylic acid lower alkyl ester, methacrylic acid lower alkyl ester, and vinyl acetate, or a hydrophobic monomer copolymerizable with the monomer A 1 to 15 parts by weight of a monomer mixture consisting of monomer B and the at least one hydrophilic monomer A is added to initiate water-soluble polymerization at a concentration of 1.0 x 10 ^-3 to 1.0 x 10 ^-2 mol/. 100% in an aqueous medium at a pH of 2 to 7 in the presence of an anionic surfactant and 1 to 8 parts by weight of an anionic surfactant.
A process of producing a primary polymer latex by emulsion polymerization in parts by weight. Second step: A monomer C of the same type or different type as the monomer in the first step is added to the primary polymer latex obtained in the first step in the aqueous medium.
A step of polymerizing the monomer C using the polymer particles in the primary polymer latex as a nuclide by stirring while dropping 70 to 90 parts by weight per 100 parts by weight.