JPH08325311A - Production of aqueous emulsion - Google Patents

Abstract

PURPOSE: To obtain an aqueous emulsion having extremely good polymerization stability in practical and industrial scale even in the case of styrene, an acrylic acid ester and diene each having relatively small radical reactivity. CONSTITUTION: In carrying out emulsion polymerization of one or more kinds of monomers selected from an ethylenically saturated monomer and a diene- based monomer in the presence of a dispersant comprising a polyvinyl alcohol- based polymer having mercapto group, 0.01-5 pts.wt. chain transfer agent is added to 100 pts.wt. of the monomers and emulsion polymerization of the monomers is carried out.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an aqueous emulsion.

[0002]

2. Description of the Related Art Conventionally, ethylenically unsaturated monomers and diene monomers such as styrene-butadiene copolymer emulsions, (meth) acrylic acid ester type resin emulsions and vinyl ester type resin emulsions are used alone or as a copolymer. The synthetic resin emulsion obtained by polymerization is used in a wide variety of applications such as various adhesives, paints, binders, fiber processing agents, and mortar admixtures.

The above-mentioned synthetic resin emulsion is obtained by emulsion polymerization of an ethylenically unsaturated monomer and / or a diene monomer in the presence of a surfactant, polyvinyl alcohol (hereinafter referred to as PVA). Abbreviated) and hydroxyethyl cellulose and the like, which are roughly classified into two types when they are obtained by emulsion polymerization in the presence of a water-soluble polymer. The former has many problems resulting from the use of surfactants. In other words, in applications where the emulsion is left unresolved, mechanically stable, chemically stable, freeze-thaw stable, and pigment miscible is insufficient, and the viscosity of the emulsion is generally low. In many cases, the final physical properties are adversely affected because methods such as addition of a thickener and thickening of an alkali by copolymerization of an unsaturated acid must be taken, and migration of a surfactant occurs.

On the other hand, regarding the latter, in emulsion polymerization of vinyl acetate or vinyl chloride, an emulsion produced by using a PVA polymer as an emulsion dispersion stabilizer has mechanical stability,
It is excellent in dispersion stability such as chemical stability, freeze-thaw stability, and pigment miscibility, and has an advantage that an emulsion having a desired viscosity can be obtained by a polymerization formulation, and is widely put into practical use. However, in this case, the target is limited to vinyl acetate and vinyl chloride, which have high radical reactivity, and styrene-based monomers, diene-based monomers, and (meth) acrylic acid ester-based monomers, which have relatively low radical reactivity. With respect to the monomer, there is a problem that a stable emulsion cannot be obtained by emulsion polymerization using PVA as a dispersion stabilizer. To solve such problems, JP-A-60-1972229 proposes to use a PVA-based polymer having a mercapto group for these emulsion dispersion stabilizers. In this case, a commonly used initiator, for example, a redox initiator obtained by using potassium persulfate, ammonium persulfate, hydrogen peroxide alone or in combination with various reducing agents, etc. has a low grafting efficiency to the PVA-based polymer and sufficient practical use. However, there is a problem that it is difficult to secure a stable stability, and an initiator such as potassium bromate, which generates a radical only by a redox reaction with the mercapto group of the PVA-based polymer, shows an improvement in the polymerization stability. When the mercapto group in PVA was consumed, there was a problem that it became so-called Dead-End and it was difficult to control and complete the polymerization.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide PV
In producing an aqueous emulsion using A as a dispersant, not only vinyl acetate and vinyl chloride but also a stable aqueous emulsion was difficult to produce when using PVA as a dispersant. An object of the present invention is to provide a method for producing an aqueous emulsion that can be widely applied to system monomers.

[0006]

Means for Solving the Problems The present inventors have made earnest studies in view of the above circumstances, and as a result, in the presence of a dispersant composed of a polyvinyl alcohol-based polymer having a mercapto group, an ethylenically unsaturated monomer is present. Body and diene-based monomer, one or two or more kinds of monomers are emulsion polymerized by adding 0.01 to 5 parts of a chain transfer agent to 100 parts by weight of the monomer. The present invention has been completed by finding a method for producing an aqueous emulsion characterized by the following.

In the method for producing the aqueous emulsion of the present invention, the ethylenically unsaturated monomer unit and the diene unsaturated monomer unit are not particularly limited as long as they are radically polymerizable. The ethylenically unsaturated monomer, ethylene, propylene, olefins such as isobutene, vinyl chloride, vinylidene chloride, vinyl fluoride, halogenated olefins such as vinylidene fluoride, vinyl formate, vinyl acetate, vinyl propionate, Vinyl esters such as vinyl versatate and vinyl pivalate, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, acrylic acid Acrylic esters such as t-butyl, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate,
Methacrylic acid esters such as n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate and octadecyl methacrylate, Acrylamide,
Methacrylamide, N-methylol acrylamide,
N, N-dimethylacrylamide, acrylamide-2
-Acrylamido monomers of methylpropanesulfonic acid and its sodium salt, nitriles such as acrylonitrile and methacrylonitrile, allyl compounds such as allyl acetate and allyl chloride, styrene, α-methylstyrene, P
-Styrene-based monomers such as methylstyrene sulfonic acid and its sodium and potassium salts, and other N-vinylpyrrolidone and the like, and the diene-based monomers include
Butadiene, isoprene, chloroprene and the like. These monomers are used alone or in combination of two or more.

A PV having a mercapto group used as a dispersant in the method for producing an aqueous emulsion of the present invention.
As the A-based polymer, a PVA-based polymer having a mercapto group in the polymer main chain may be used, but this PVA-based polymer may be insolubilized by forming a disulfide bond due to oxidation of itself. Therefore, the PVA-based polymer having a mercapto group only at one end of the molecule is preferable because it is easy to handle without fear of insolubilization. The PVA-based polymer having a mercapto group only at one end is, for example, a polyvinyl ester-based polymer obtained by polymerizing a vinyl monomer mainly containing a vinyl ester-based monomer in the presence of thiolacetic acid. It can be prepared by saponification according to a conventional method. The vinyl ester-based monomer can be used as long as it can be radically polymerized, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, Examples thereof include vinyl pivalate. Vinyl acetate is preferred from the viewpoint of obtaining a PVA-based polymer suitable for the present invention.

It is also possible to co-polymerize the vinyl ester-based monomer and the copolymerizable monomer together.
For example, olefins such as ethylene, propylene, 1-butene and isobutene, acrylic acid, methyl acrylate,
Ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, t acrylate
-Butyl, 2-ethylhexyl acrylate, acrylic acid dodecyl, octadecyl acrylate, and other acrylic acid esters, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-methacrylate. Methacrylic acid esters such as butyl, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, methyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-
Butyl vinyl ether, i-butyl vinyl ether, t
-Vinyl ethers such as butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether, nitriles such as acrylonitrile and methacrylonitonyl, vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, allyl acetate and allyl chloride. Allyl compounds, fumaric acid, maleic acid, itaconic acid, maleic anhydride, phthalic anhydride, trimetic anhydride or itaconic anhydride, and other carboxyl group-containing compounds and their esters, ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid , 2-acrylamide-2-
Examples thereof include sulfonic acid group-containing compounds such as methylpropanesulfonic acid, vinylsilane compounds such as vinyltrimethoxysilane, isopropenyl acetate, 3-acrylamidopropyltrimethylammonium chloride, 3-methacrylamidopropyltrimethylammonium chloride and the like. The amount of the above monomer is preferably 5 mol% or less.

The viscosity average degree of polymerization (hereinafter abbreviated as the degree of polymerization) of the PVA polymer used in the method for producing the aqueous emulsion of the present invention may be selected according to various situations and is not particularly limited, but it is 3500. The following is preferable, and 1500 or less is more preferable. On the other hand, the toughness of the PVA polymer is
Although it cannot be generally stated because it depends on the type of other modifying groups, P
From the viewpoint of the water solubility of the VA polymer, it is 40 to 99.99.
The amount is preferably mol%, more preferably 50 to 99.9 mol%, still more preferably 60 to 99.5 mol%.

The chain transfer agent used in the method for producing the aqueous emulsion of the present invention is not particularly limited as long as chain transfer occurs, but a compound having a mercapto group is preferable in terms of chain transfer efficiency. As the compound having a mercapto group, a compound having a mercapto group having 50 or less carbon atoms is preferable, a compound having a mercapto group having 30 or less carbon atoms is more preferable, and a compound having a mercapto group having 20 or less carbon atoms is particularly preferable. N-
Octyl mercaptan, n-dodecyl mercaptan, t
-Alkyl mercaptans such as dodecyl mercaptan, 2
-Mercaptoethanol, 3-mercaptopropionic acid, etc. are mentioned.

The method for producing the aqueous emulsion of the present invention comprises:
In the presence of a dispersant composed of the PVA-based polymer, one or two or more monomers selected from ethylenically unsaturated monomers and diene-based monomers are emulsion-polymerized to obtain 100 It is characterized by adding 0.01 to 5 parts by weight of a chain transfer agent to emulsion polymerization.

In the method for producing an aqueous emulsion of the present invention, as an initiator for emulsion polymerization, potassium bromate, which generates radicals only by a redox reaction with a mercapto group of a PVA polymer having a mercapto group,
Potassium persulfate, ammonium persulfate, hydrogen peroxide, t
Water-soluble initiators such as butyl hydroperoxide and oil-soluble initiators such as azobisisobutyronitrile and benzoyl peroxide are used alone or in a redox system in combination with various reducing agents. The method of using these is not particularly limited, and a method of adding them all at once in the initial stage, a method of continuously adding them to the polymerization system, and the like can be used.

In the production method of the present invention, the PVA polymer is used in an amount of 0.5 to 1 with respect to 100 parts by weight of the monomer.
The amount is 00 parts by weight, preferably 1 to 50 parts by weight, more preferably 2 to 30 parts by weight. When the amount of PVA-based polymer is less than 0.5 parts by weight, polymerization stability is lowered and mechanical stability and chemical stability, which are characteristic of an aqueous emulsion containing PVA as a dispersant, and film strength are lowered. Happens.
When the PVA polymer exceeds 100 parts by weight, there are problems such as reaction heat removal due to increase in viscosity of the polymerization system and deterioration of film water resistance. The method of adding the PVA-based polymer is not particularly limited, and the method of adding all at once in the initial stage and the method of adding PV in the initial stage
There is a method of adding a part of the A-type polymer and continuously adding it to the polymerization system during the polymerization. In addition, conventionally known nonionic properties,
Anionic, cationic, amphoteric surfactant, or
A PVA-based polymer having no mercapto group at the terminal or a water-soluble polymer such as hydroxyethyl cellulose may be used in combination with the PVA-based polymer having a mercapto group of the present invention.

In the method for producing the aqueous emulsion of the present invention, as a method of adding the monomers, a method of adding them all at once to the polymerization system, a method of adding a part of the monomers initially and the rest during the polymerization are added. A method of continuously adding, a method of continuously adding a pre-emulsified monomer, water and a dispersant to a polymerization system, and the like,
Various methods are possible.

The addition amount of the chain transfer agent in the present invention is 0.01 to 5 parts by weight with respect to 100 parts by weight of the monomer. If the amount of the chain transfer agent is less than 0.01 part by weight, the effect of improving the polymerization stability is small and it is not practical. On the other hand, if it exceeds 5 parts by weight, the polymerization stability is lowered, and the molecular weight of the polymer forming the dispersoid is remarkably lowered, resulting in deterioration of various emulsion physical properties. The method of adding the chain transfer agent is preferably a method of continuously adding it to the polymerization system, specifically, a method of continuously adding the chain transfer agent alone or a continuous mixture of premixed monomers to be continuously added. There is a method of adding.

In the method for producing the aqueous emulsion of the present invention, the polymerization conditions or the polymerization method other than the above are not particularly limited, and various conventionally known emulsion polymerization methods can be adopted. A feature of the present invention is that not only vinyl ester-based monomers but also emulsions having good stability have been difficult to obtain by emulsion polymerization using PVA as a dispersant, such as (meth) acrylic acid ester. Acrylic homopolymerization or copolymerization system, styrene-butadiene copolymerization system,
Even in the methyl methacrylate-butadiene copolymer system, if the method for producing an aqueous emulsion of the present invention is adopted, a stable aqueous emulsion can be obtained on a practical and industrial scale.

The aqueous emulsion thus obtained is used for various purposes as it is or by adding conventionally known additives. For example, paints, adhesives, fiber processing agents, paper processing agents, inorganic binders, cement admixtures,
It is used in a wide range of applications such as mortar primers.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the examples, "part" and "%" mean weight basis.

[0020]

【Example】

Example 1 In a glass container equipped with a reflux condenser, a dropping funnel, a thermometer, a nitrogen blowing port, and a stirrer, PVA having a mercapto group at the end (PVA-1: degree of polymerization 550, degree of saponification 88.3 m).
ol%, mercapto group content 3.3 × 10 ^-5 equivalents / g) 5
And 90 parts of deionized water were charged and completely dissolved at 95 ° C. Then, after adjusting the pH to 4 with dilute sulfuric acid, 150
10 parts methylmethacrylate, n with stirring at rpm
-Butyl acrylate (10 parts) and n-dodecyl mercaptan (0.1 part) were added, and the temperature was raised to 70 ° C after purging with nitrogen.
Polymerization was started by adding 5 parts of 1% potassium persulfate, and further, over 2 hours, 40 parts of methyl methacrylate, 40 parts of n-butyl acrylate, 0.4 parts of n-dodecyl mercaptan.
A mixture of parts was added continuously. 3 hours after the start of the polymerization, the conversion reached 99.5% and the polymerization was completed. Solid content concentration 52.0%, viscosity 700 mPa.s. A stable methyl acrylate / n-butyl acrylate copolymer emulsion of s was obtained. The following tests were conducted using this emulsion. Table 2 shows the results.

Polymerization stability test: When the obtained emulsion was filtered through a 200-mesh wire net, 200-mesh-on was dried by a 105 ° C. drier, and 200-mesh-on dry solid content based on the total solid content before filtration. Ratio to pp
Calculated by m. -Microscopic observation The obtained emulsion was diluted and observed with a 400x phase contrast microscope.

Comparative Example 1 The same procedure as in Example 1 was repeated except that n-dodecyl mercaptan was not used, and the solid content concentration was 51.5%.
Viscosity 530 mPa.s A s methyl acrylate / n-butyl acrylate copolymer emulsion was obtained. The following tests were conducted using this emulsion. Table 2 shows the results.

Comparative Example 2 The same procedure as in Example 1 was carried out except that 10 parts of n-dodecyl mercaptan was used with respect to 100 parts of the monomer, and the solid content was 52.5% and the viscosity was 1200 mPa.s. A s methyl acrylate / n-butyl acrylate copolymer emulsion was obtained. Example 1 using this emulsion
The same test was performed. Table 2 shows the results.

Example 2 A PVA having a mercapto group at its end (PVA-2: PVA-2: in a pressure-resistant autoclave equipped with a nitrogen blowing port and a thermometer).
100 parts of a 4% aqueous solution having a degree of polymerization of 350, a saponification degree of 88.5 mol% and a mercapto group content of 7.0 × 10 ⁻⁵ equivalent / g) was charged, adjusted to pH = 4 with dilute sulfuric acid, and 60 parts of styrene,
One part of t-dodecyl mercaptan was charged. Next, after performing nitrogen substitution, 40 parts of butadiene was press-fitted with a pressure-resistant measuring device to raise the temperature to 70 ° C. Then, 10 parts of 2% ammonium persulfate was press-fitted to initiate polymerization. Internal pressure is 4.
Decreases with the progress of polymerization from 5 kg / cm ^2, after 20 hours was 99.2% when calculated 0.3 Kg / cm ^2, and the rate of polymerization. Solid content concentration 49.1%, viscosity 1
05 mPa. A styrene-butadiene copolymer emulsion of s was obtained. The same test as in Example 1 was conducted using the obtained emulsion. Table 2 shows the results.

Comparative Example 3 The procedure of Example 2 was repeated except that t-dodecyl mercaptan was not used, and the solid content was 48.5%.
Viscosity 75 mPa. A styrene-butadiene copolymer emulsion of s was obtained. The same test as in Example 1 was conducted using the obtained emulsion. Table 2 shows the results.

Example 3 A pressure-resistant autoclave equipped with a nitrogen blowing port and a thermometer was used, and PVA having a mercapto group at its end (PVA-3:
6.25% aqueous solution 8 having a degree of polymerization of 1500, a degree of saponification of 96.8 mol%, and a mercapto group content of 2.1 × 10 ⁻⁵ equivalent / g)
0 part was charged and the pH was adjusted to 3.5 with dilute sulfuric acid. Add 80 parts vinyl acetate and 0.1 parts n-dodecyl mercaptan,
The temperature was raised to 60 ° C. and nitrogen substitution was performed. Then, ethylene was press-fitted to 45 Kg / cm ^2, and 5 parts of a 5% Rongalit aqueous solution was added. A 0.4% aqueous hydrogen peroxide solution was continuously added to initiate polymerization. After 3 hours, the vinyl acetate concentration reached 1.0% and the polymerization was completed. Solid content concentration 55.0
%, Viscosity 1800 mPa.s. An ethylene-vinyl acetate copolymer emulsion of s was obtained. The same test as in Example 1 was carried out using this emulsion. Table 2 shows the results.

Comparative Example 4 The procedure of Example 3 was repeated except that n-dodecyl mercaptan was not used, and the solid content concentration was 54.6%.
Viscosity 1550 mPa. An ethylene-vinyl acetate copolymer emulsion of s was obtained. The same test as in Example 1 was carried out using this emulsion. Table 2 shows the results.

[0028]

[Table 1]

* Parts in the table are parts by weight per 100 parts by weight of monomer * PVA-1: degree of polymerization 550, degree of saponification 88.3 mol% mercapto group content 3.3 x 10 ^-5 equivalents / g * PVA- 2: degree of polymerization 350, degree of saponification 88.5 mol% mercapto group content 7.0 × 10 ^-5 equivalents / g * PVA-3: degree of polymerization 1500, degree of saponification 96.8 mol% mercapto group content 2.1 × 10 ^-5 equivalents / g

[0030]

[Table 2]

[0031]

INDUSTRIAL APPLICABILITY The method for producing an aqueous emulsion of the present invention has very good polymerization stability even in the case of styrene, acrylic ester, diene and the like having relatively small radical reactivity, and has a practical and industrial scale. Can be implemented in.

Claims (2)

[Claims] 1. In the presence of a dispersant comprising a polyvinyl alcohol-based polymer having a mercapto group, one or more monomers selected from ethylenically unsaturated monomers and diene-based monomers are added. Upon emulsion polymerization, the monomer 10
A method for producing an aqueous emulsion, which comprises adding 0.01 to 5 parts by weight of a chain transfer agent to 0 part by weight and performing emulsion polymerization. 2. The method for producing an aqueous emulsion according to claim 1, wherein the chain transfer agent is a compound having a mercapto group.