JPS628441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrially advantageous method for producing ultrafine particle polymer latex. Ultrafine particle polymer latex with a particle diameter of about 0.005 to 0.05μ differs from ordinary polymer latex, which is white and opaque with a particle size of about 0.05 to 0.4μ, to be blue-white to reflected light and transparent to transmitted light. It has a transparent or semi-transparent viscosity that appears yellow-red, and it is possible to form a dense and transparent film with a gloss comparable to that of solvent-volatile solution-type polymers. It is becoming increasingly important in the latex industry because it has excellent physical properties and workability, such as the ability to easily obtain viscous polymer latex.

Conventionally, the method for producing ultrafine polymer latex is to divide alkali-swollen carboxylic acid-modified acrylic polymer latex into fine particles by stirring vigorously at high temperatures (DuPont Hydrosol). However, this method is complicated to operate, and the amount of carboxylic acid monomer, degree of alkali neutralization, and average molecular weight of the copolymer components must be kept within extremely limited ranges, making it difficult to manufacture. It came with major constraints.

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 ultrafine particles of micron size or less, a very large amount of emulsifier is required, which is impractical. Furthermore, as the particle size of the polymer latex becomes minute, the viscosity of the resulting polymer latex increases significantly as the polymer concentration progresses and the polymerization process becomes more difficult.
In particular, it seriously impedes stirring, and unpolymerized monomers separate into layers and cannot be dispersed in the aqueous phase, making industrial production practically impossible.

The present inventors have conducted extensive research to overcome the drawbacks of the conventional methods described above and to develop an industrially advantageous method for producing ultrafine polymer latex. As a result, the emulsion polymerization reaction can be carried out under specific conditions. At the same time, by adding a limited amount of ionic electrolyte as a viscosity reducing agent to the polymerization system, high quality ultrafine particle polymer latex can be produced without increasing the viscosity of the polymerization system. The present inventors have discovered that the following can be obtained, and have completed the present invention.

That is, the present invention provides lower alkyl acrylates, lower alkyl methacrylates,
and at least one hydrophilic monomer selected from the group consisting of vinyl acetate, or a monomer consisting of the hydrophilic monomer and a hydrophobic monomer copolymerizable with this hydrophilic monomer. A redox polymerization initiator consisting of a persulfate and a sulfoxy compound, a redox polymerization initiator consisting of a transition metal ion, an anionic surfactant, and a viscosity reducing agent consisting of an ionic electrolyte in an effective amount for reducing viscosity. In the presence of
This is a method for producing ultrafine particle polymer latex, which is characterized in that emulsion polymerization is carried out in an aqueous medium while maintaining the pH at least at 2 to 7 at the start of polymerization.

In the present invention, it is essential to suppress the increase in viscosity of the polymerization system in order to facilitate the stirring operation and enable industrial production, and the present inventors have conducted various studies on effective viscosity reduction methods. As a result, we discovered the surprising fact that when various ionic electrolytes were added in amounts within a limited narrow concentration range, the viscosity of ultrafine particle polymer latex was significantly reduced.

The ionic electrolyte used in the present invention is a water-soluble organic electrolyte excluding salts such as heavy metals that cause significant fluctuations in PH value, suppress or inhibit polymerization reactions, or precipitate water-insoluble salts during double decomposition. Although a wide range of inorganic electrolytes can be used, the following types are generally preferred:

(1) Potassium chloride, diammonium phosphate, etc.
Various phosphates, sulfates, hydrochlorides, carbonates, acetates, persulfates, imidosulfates, and sulfonates consisting of alkali salts or ammonium salts (2) Aqueous ammonia (28%), methyldiethylaminoalcohol, Morpholine, sodium paratoluenesulfonate, etc.

In the present invention, in order to prevent an increase in the viscosity of the polymer latex during polymerization, it is necessary to limit the amount of the ionic electrolyte added to an appropriate range depending on the component composition of the polymerization system. However, if the amount added is too large or too small, the viscosity of the resulting polymer latex will become extremely high, which is disadvantageous. In other words, by limiting the amount to an appropriate range, it is possible to effectively prevent the viscosity of the polymer latex from increasing during polymerization, regardless of its type. Therefore, the amount of ionic electrolyte added in the present invention is within a range that can effectively prevent such an increase in the viscosity of the polymer latex, and is defined as the "effective range for reducing viscosity."

The "effective range for reducing viscosity" of the electrolyte defined in the present invention varies depending on the type of electrolyte and the component composition of the polymerization system and cannot be unambiguously determined, but is generally 100 parts by weight of the aqueous medium. The specific viscosity-lowering effective range of the preferred ionic electrolyte can be easily determined by those skilled in the art through several preliminary experiments.

The polymerizable monomer used in the present invention is arbitrary as long as it has hydrophilicity and can be emulsified and dispersed in an aqueous medium, but generally lower alkyl esters of acrylic acid or methacrylic acid, such as methyl,
Ethyl is preferably applied, also vinyl acetate being suitable. Hydrophobic monomers such as styrene, butyl acrylate, and butadiene produce polymer latexes with relatively large particle sizes, but when used in the form of mixtures with the hydrophilic monomers mentioned above, copolymers with ultrafine particles are produced. Latex is produced and can be used as a polymerizable raw material in the present invention. In this case, the hydrophobic monomer is preferably used in a proportion of 50% by weight or less in the mixture with the hydrophilic monomer.

The polymerization initiator used in the method of the present invention is a redox initiator that is a combination of persulfate and a reducing sulfoxy compound such as thiosulfate or sulfite, and a trace amount (concentration in the polymerization system of 5.0×10 ^-6 to 5.0× 10 ^-4 mol/) transition metal ions are added as a redox polymerization accelerator. In this case, transition metals include copper ions, iron ions, cobalt ions, etc., but divalent copper ions are preferably used. The use of a redox initiator using such a transition metal ion as a redox polymerization accelerator not only significantly reduces the particle size of the resulting polymer latex, but also
This shows the effect that the amount of anionic surfactant used can be further reduced. The concentration of the redox initiator that is easy to implement is 5.0× in the polymerization system.
10 ^-4 to 7 x 10 ^-3 mol/, preferably 1.0 x 10 ^-3 to
The combination was in equimolar amounts of 5 x 10 ^-3 mol/.

The PH value of the polymerization system in the present invention is set under neutral to acidic conditions, that is, PH2 to 7, preferably PH3 to
Condition 5 is adopted. If the pH condition becomes alkaline, the polymer particle size in the produced latex will increase, which is not preferable. However, this PH condition is necessary at the start of polymerization, and after the polymerization has progressed to a certain extent and ultrafine particle polymers have been formed, this becomes a nuclide and the polymerization progresses, so there are no restrictions even on the alkaline side of PH10 or less. .

As the emulsifier in the present invention, it is necessary to use an anionic surfactant, but fatty acid soap,
Good results cannot be obtained when a strongly alkaline anionic surfactant such as rosinate soap and a nonionic surfactant such as polyoxyethylene nonylphenol are used. Examples of anionic surfactants suitable for the present invention include alkyl sulfates, alkylbenzene sulfonates, dialkyl sulfosuccinates, and the like.
These emulsifiers are used in an amount of 0.3 parts by weight per 100 parts by weight of the aqueous solvent.
It is used in a proportion of 4 parts by weight, preferably 0.5 to 2 parts by weight. If the amount of emulsifier is too large, the produced polymer latex will have significant foaming properties and its quality will deteriorate, so it is desirable that the amount is as small as possible.

However, if the amount of emulsifier is less than 0.2 parts by weight, the particle size of the resulting polymer latex will be large, for example 0.1 μm or more, which is not preferable.

The emulsion polymerization temperature in the present invention is 40 to 90°C, preferably 50 to 80°C, but it is preferable that the polymerization temperature is as low as possible during the polymerization initiation reaction. Further, in order to prevent temperature rise due to significant heat of polymerization, it is necessary to add the monomer continuously and gradually dropwise.

According to the present invention, in the presence of a viscosity reducing agent consisting of an anionic surfactant and an ionic electrolyte in an effective viscosity reducing amount, the pH at the start of polymerization is at least 2 to 2.
By carrying out emulsion polymerization in an aqueous medium at a temperature of 7.7, an ultrafine polymer latex having a particle size of approximately 0.005 to 0.05 μm can be obtained.

According to the prior art, as the particle size of the polymer latex becomes smaller and the concentration becomes higher, the viscosity of the polymerization system increases and stirring becomes difficult.

However, in the present invention, since the viscosity reducing agent consisting of an ionic electrolyte is used in an amount within the effective range for reducing the viscosity, the polymerization reaction can proceed while suppressing the increase in viscosity of the polymerization system, and the concentration of the produced polymer latex increases. However, stirring of the polymerization system does not become difficult, and formation of ultrafine particles of the polymer latex is promoted. This is extremely advantageous when implementing the present invention industrially.

In addition, in the present invention, the PH of the polymerization system is maintained at 2 to 7, that is, neutral to acidic, so the PH of the polymerization system is maintained at 2 to 7, that is, neutral to acidic.
becomes alkaline, thereby preventing the particle size of the polymer latex from increasing.

Furthermore, since the present invention uses an anionic surfactant as an emulsifier, emulsion polymerization is possible.

Furthermore, since the present invention can increase the concentration of the polymer latex as described above, it is possible to obtain a polymer latex within a practical concentration range.

As described above, the polymer latex obtained by the present invention is ultrafine particles with a particle size of about 0.005 to 0.05μ, so it is transparent or semitransparent, and has good permeability and "wetting".
It is possible to form a dense and transparent film with a gloss comparable to that of solvent-volatile solution-type polymers.

Therefore, it can be advantageously used as a glossy paint, an emulsion for floor polishing that does not require puffing, a coating agent, a finishing agent for leather, a latex for paper and textile processing, and the like.

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

Example 1 Sodium lauryl sulfate was dissolved at a ratio of 2.0 g per 100 ml of aqueous medium using a 1000 ml four-necked separable flask equipped with a gas introduction tube, a reflux condenser, a composite glass electrode for PH measurement, and a stirring device. Disperse 10 ml of methyl methacrylate in 400 ml of distilled water, and add copper sulfate (concentration in the system: 2.5 x 10 ^-5 mol/
) as an accelerator and a redox initiator consisting of equimolar amounts of potassium persulfate/sodium thiosulfate (concentration in the system: 1.0 x 10 ^-3 mol/) at 60°C and pH 2 to 4.
Polymerization was started. Next, polymerization was carried out while gradually dropping 290 ml of methyl methacrylate to prevent a significant temperature rise due to polymerization heat. As the polymerization progresses, the viscosity of the system increases, making stirring operations such as dispersing monomers difficult, but before the viscosity of the polymerization system begins to rise, add 3 to 4 ml of aqueous ammonia (28%) dropwise. When the pH of the system was maintained at 8.7 to 9.0, the viscosity of the polymerization system increased only slightly and the monomers were well dispersed and stirred. The resulting ultrafine particle polymer latex is a transparent, slightly viscous colloidal dispersion that appears blue-white to reflected light and yellow-red to transmitted light, and its light transmittance measured by a spectrophotometer is It was 55% (800mmμ 1cm thick).
The viscosity of the polymer latex is 660 centipoise when the spindle rotation speed is 6 rpm using a B-type rotational viscometer.
It was 600 centipoise at 60 rpm.

The particle size of the polymer latex was determined by spraying a polymer latex dispersion diluted to 10 ^-2 % or less onto a hydrophilized carbon support membrane, and using an electron microscope photograph at a magnification of 20,000 times after electron staining168 ±
It was 7 Å (0.0168 μ).

Example 2 In Example 1, ammonia water was added to adjust the pH.
Instead of maintaining the viscosity at 8.7 to 9.0 to suppress the increase in viscosity, if 5 ml of imidobis diammonium sulfate aqueous solution with a concentration of 10 g/dl was added to 400 ml of the aqueous medium as a viscosity reducing agent, the B-type viscosity of the produced polymer latex The viscosity measured by the meter is the spindle rotation speed.
It was 2600 centipoise at 60 rpm. When 10 ml of the above-mentioned viscosity reducing agent was added, the viscosity was significantly lowered until the polymerization was completed, and the viscosity was very low and maintained sufficient fluidity, but the viscosity increased over time and the product was left unused for more than a month. The liquid lost its fluidity and became paste-like. (The transparent state is maintained.) The appearance of the produced polymer latex is the same as in Example 1, and it is a transparent colloidal dispersion.
The light transmittance of μ was 50%. Moreover, the PH value of the polymer latex was 2.7 to 3.5.

Next, when 8 ml of a 10 g/dl aqueous solution of diammonium imidobis sulfate and trisodium imidobis sulfate, which is homologous to imidobis sulfate, is added, the pH value of the polymerization system is 8 to 9, and the viscosity of the produced polymer latex is
It was 2900 centipoise at 60 rpm.

Furthermore, instead of adding an aqueous solution of imidobis sulfate after the start of polymerization, adding 1.20 g of imidobis sulfate diammonium salt crystals before starting polymerization will not affect the polymerization rate and particle size. A transparent ultrafine particle polymer latex was produced without any inconvenience such as difficulty in stirring (800
(light transmittance of mμ 55%). The viscosity of the produced latex measured by a B-type viscometer was 1004 centipoise at 60 rpm, and the pH of the polymerization system was 3.0.

Example 3 Under the same polymerization method and polymerization conditions as in Example 1, 1.0% potassium chloride crystals were added as a viscosity reducing agent instead of adding aqueous ammonia to reduce the viscosity.
When polymerization was carried out with the addition of 50 g before the start of polymerization, there was only a slight increase in viscosity, there were no inconveniences such as difficulty in stirring, and the polymerization was completed in 25 minutes, resulting in a transparent product (transmittance of 58% at 800 mμ). ) A low viscosity ultrafine particle polymer latex was obtained. In this case, the viscosity at 60 rpm measured by a B-type viscometer was 514 centipoise. Similarly, when 1.50 g of potassium chloride crystals were added as a viscosity reducing agent before the polymerization started, the viscosity was lower than when 1 g of potassium chloride was added, and the polymerization was carried out with good stirring. However, the viscosity increased over time after the polymerization was completed, and when left for a long period of time, it became paste-like and lost fluidity.

Comparative Example 1 In Examples 1 to 3, when polymerization was carried out without using a viscosity reducing agent consisting of ammonia water or an ionic electrolyte, the viscosity of the polymerization system rapidly increased as the polymerization progressed, resulting in a high viscosity. When approximately 1/2 of the total amount of monomer is added, it becomes impossible to stir substantially uniformly, and the monomer that is being continuously added drops into a gel-like phase. Separation occurred on the upper part of the membrane, making polymerization impossible.

Example 4 For 100 ml of aqueous medium using a 1000 ml four-necked separable flask equipped with a gas introduction tube, a reflux condenser, a composite glass electrode for PH measurement, and a stirring device.
0.50g sodium lauryl sulfate (400ml water medium)
A mixture of ethyl acrylate and methyl methacrylate with a composition ratio of 7:3 was added to 400 ml of distilled water in which 2.0 g of ethyl acrylate and methyl methacrylate were dissolved and 0.125 g of diammonium phosphate (0.125 g in 400 ml of aqueous medium) as a viscosity reducing agent (0.50 g in 400 ml of aqueous medium) was dissolved. volume 50ml
Copper sulfate (concentration in the system 2.5×
Potassium persulfate with 10 ^-5 mol/) as accelerator
60 with a redox initiator consisting of an equimolar amount of sodium thiosulfate (concentration in the system: 1.0 x 10 ^-3 mol/).
Polymerization was initiated at ℃ and pH 2-4. Next, copolymerization was carried out while dropping 250 ml of a mixed monomer consisting of ethyl acrylate and methyl methacrylate (composition ratio 7:3) to prevent a significant rise in temperature due to polymerization heat. The polymerization was completed within 60 minutes, and the viscosity of the polymerization system was low until the completion of the polymerization, maintaining sufficient fluidity, and a transparent ultrafine particle polymer latex was produced without any inconveniences such as difficulty in stirring. (Light transmittance at 800 mμ: 40.5%) The viscosity measured by a B-type rotational viscometer was 77 centipoise at a spindle rotation speed of 60 rpm. The pH value of the 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 at room temperature under natural ventilation, producing a highly transparent and glossy latex film.

Comparative Example 2 In Example 4, when copolymerization was carried out without adding 0.50 g of diammonium phosphate crystals that acted as a viscosity reducing agent, the viscosity increased from about 20 minutes after the start of polymerization and all monomers were absorbed. When 150 ml, which is half the amount, was added dropwise, the monomers separated from the latex phase even when stirred at high speed, making it difficult to continue the polymerization and had to be discontinued. In this case, the viscosity of the latex produced is at a spindle rotation speed of 60 rpm.
It was gel-like with 8960 centipoise and 66000 centipoise at 6 rpm.

Comparative Example 3 In Example 1, when polyoxyethylene nonyl phenyl ether (added with 50 moles of ethylene oxide), a nonionic surfactant, was used as the emulsifier, the latex produced was white and opaque, and the particle size of the polymer latex produced was 2026±. It became quite large at 221 Å.

Comparative Example 4 In Examples 1 and 5, the amount of sodium lauryl sulfate used was 0.2 g per 100 ml of aqueous medium (400 ml of aqueous medium).
When 0.8 g/ml was used, the resulting polymer latex was white and opaque, and the particle size measured by electron microscopy was 706±58 Å.

Comparative Example 5 In Example 1, when the pH of the polymerization system was maintained at an alkaline level of 7 or less using aqueous ammonia or the like at the beginning of polymerization, the polymer latex produced became white and opaque from the early stage of polymerization, and the resulting polymer latex The particle size was 753±63 Å. Similarly, when a salt consisting of a weak acid and a strong base such as crystalline sodium pyrophosphate or sodium acetate was added as a viscosity reducing agent before the start of polymerization, the resulting latex became white and opaque. However, 10g/dl of these salts
When it was added as an aqueous solution with a concentration of about 100 mL after polymer particles were formed after polymerization had started, a transparent ultrafine particle-like polymer latex was produced and exhibited an effective viscosity-reducing effect.

Example 5 Copolymerization of methyl methacrylate and butyl acrylate at a composition ratio of 1:1 was carried out using the same method and polymerization conditions as in Example 4. As a result, there was no increase in viscosity, and the light transmittance was 16%, as measured by a rotational viscometer. A translucent copolymer latex with a viscosity of 135 centipoise was obtained.

Example 6 When vinyl acetate was polymerized using the same method and polymerization conditions as in Example 4, there was only a slight increase in the viscosity of the produced latex, and the viscosity measured by a B-type rotational viscometer at a spindle of 60 rpm was 172 centipoise and 800 mμ. An ultrafine polymer latex with a light transmittance of 39% was produced. The resulting polymer latex had film-forming properties at room temperature, and a relatively hard, transparent, and glossy film was formed by air drying.

Claims (1)

[Claims] 1 Consisting of a hydrophobic monomer copolymerizable with at least one hydrophilic monomer selected from the group consisting of acrylic acid lower alkyl ester, methacrylic acid lower alkyl ester, and vinyl acetate, and the hydrophilic monomer. A redox polymerization initiator consisting of a persulfate and a sulfoxy compound,
Redox polymerization accelerator consisting of transition metal ions,
In the presence of a viscosity reducing agent consisting of an anionic surfactant in an amount of 0.3 to 4 parts by weight per 100 parts by weight of the aqueous medium and an ionic electrolyte in an effective amount for reducing viscosity, the pH at the start of polymerization is at least 2 to 2. 7. A method for producing an ultra-particle polymer latex, which comprises carrying out emulsion polymerization in an aqueous medium while maintaining a temperature of 7.