JPH06263806A - Dispersant aid for emulsion polymerization - Google Patents

Abstract

PURPOSE:To improve the flowability of an aqueous emulsion by using a dispersant aid comprising a PVA polymer having a mercapto group in the molecule to polymerize a radical-polymerizable ethylenically unsaturated monomer by emulsion polymerization. CONSTITUTION:A given amount of water is introduced into a polymerizer along with 0.1-20 pts.wt. dispersant comprising various surfactants, etc., and 0.1-20 pts.wt. dispersant aid comprising PVA polymer having a mercapto group in the molecule. The mixture is heated to dissolve the solid ingredients. An acid is added thereto to adjust the pH to 6 or lower. After the atmosphere in the polymerizer is replaced with N2, 100 pts.wt. radical-polymerizable ethylenically unsaturated monomer, e.g. vinyl acetate, is introduced into the polymerizer and heated to a polymerization temp. A polymerization initiator, e.g. K2O2, is then added to initiate polymerization. After a given time, the reaction is ceased to obtain an aqueous emulsion having excellent flowability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion aid for emulsion polymerization of radically polymerizable ethylenically unsaturated monomers, and more specifically, it improves the structural viscosity of an aqueous emulsion obtained by emulsion polymerization to a relatively high level. The present invention relates to the production of an aqueous emulsion having high viscosity and having viscosity characteristics similar to Newtonian and having excellent fluidity.

[0002]

2. Description of the Related Art Conventionally, an aqueous emulsion is produced by an emulsion polymerization method using a radical-polymerizable ethylenically unsaturated monomer in an aqueous medium and various surfactants and protective colloids as dispersion stabilizers. Often. in this case,
For emulsion polymerization of vinyl ester-based monomers and vinyl halide-based monomers having relatively high radical reactivity, water-soluble polymers such as polyvinyl alcohol and hydroxyethyl cellulose can be used as protective colloids to obtain stable aqueous emulsions. .

However, for monomers having relatively low radical reactivity such as (meth) acrylic acid ester-based, styrene-based, diene-based, and monomers, stable aqueous solutions are obtained when the above water-soluble polymer is used as a protective colloid. Since it is difficult to obtain an emulsion, an emulsion polymerization method using various kinds of surfactants as dispersion stabilizers for emulsion polymerization has been adopted.

In the case of an aqueous emulsion of a polymer of a (meth) acrylic ester type, a styrene type or a diene type monomer obtained by using a surfactant as a dispersion stabilizer, a carboxyl group modification or a reactive surfactant is used. By doing so, although mechanical stability was improved to some extent, it was not possible to produce a highly viscous aqueous emulsion having a flow characteristic similar to Newtonian.

Further, when polyvinyl alcohol is used as a dispersion stabilizer in a protective colloid, it is known that polyvinyl alcohol is chemically adsorbed (grafted) on dispersoid particles of an aqueous emulsion, and therefore various polyvinyl alcohols are used. Compared to the case where the dispersoid particles are stabilized by physical adsorption using a surfactant, the mechanical stability is improved, the interaction between the dispersoid particles is changed, and even when the aqueous emulsion has a high viscosity. It is known to exhibit Newtonian-like flow properties.

In the case of a vinyl acetate-based polymer emulsion obtained by emulsion polymerization of polyvinyl alcohol as a protective colloid, the amount of polyvinyl alcohol used is reduced to improve the water resistance. There is a demand for effective grafting of alcohol onto the surface of dispersoid particles.

Further, recently, a coating machine having a large shear rate,
For example, in the field of paper adhesion, corrugator machines, roll coaters, cartoning machines, pick-up rolls, etc. are often used for the purpose of improving work efficiency, and water-based aqueous solutions produced using conventional surfactants as dispersion stabilizers. The emulsion is too thixotropic,
The "dripping" of the aqueous emulsion from the coating machine, scattering, foaming, and non-uniformity of the coating amount often cause work problems, and it is strongly demanded to improve the fluidity of such aqueous emulsion. Has been done.

[0008]

DISCLOSURE OF THE INVENTION The present invention improves the structural viscosity of an aqueous emulsion produced by using a surfactant as an emulsion polymerization dispersion stabilizer during emulsion polymerization of an ethylenically unsaturated monomer to improve the high viscosity. The present invention aims to provide an aqueous emulsion having Newtonian structural viscosity. In addition, the present invention is a vinyl acetate polymer emulsion produced by an emulsion polymerization method using polyvinyl alcohol (unmodified) as a protective colloid. It is intended to improve the structural viscosity of the prepared aqueous emulsion.

[0009]

Under the circumstances described above, the present invention performs emulsion polymerization of a radically polymerizable ethylenically unsaturated monomer in an aqueous medium in order to solve the above problems. In doing so, various surfactants as the main dispersion stabilizer, unmodified polyvinyl alcohol, and polyvinyl alcohol obtained by randomly copolymerizing various copolymerization components are used,
A polyvinyl emulsion polymer having a mercapto group in the molecule is used in combination as a dispersion stabilizing aid, and an aqueous emulsion produced by adding a polymerization initiator to this emulsion polymerization system shows a Newtonian-like structural viscosity even with high viscosity, It was found that the liquidity was improved.

The main dispersion stabilizer used in the emulsion polymerization of the present invention, that is, various surfactants, unmodified polyvinyl alcohol, and polyvinyl alcohol obtained by randomly copolymerizing various copolymerization components are used in the following amounts: Depending on the type of ethylenically unsaturated monomer, it is 0.1 to 20 parts by weight, preferably 0.2 to 10 parts by weight, relative to 100 parts by weight of the monomer.
Parts by weight, particularly preferably 1 to 8 parts by weight.

The amount of the polyvinyl alcohol polymer having a mercapto group in the molecule, which is used as a dispersion stabilizer in the emulsion polymerization of the present invention, is 0.1 to 100 parts by weight of the monomer. 20 parts by weight, preferably 0.2-
The amount is 10 parts by weight, more preferably 0.5 to 8 parts by weight, still more preferably 1 to 5 parts by weight.

The "polyvinyl alcohol polymer having a mercapto group in the molecule" used in the present invention is effective as long as it is a polymer having a mercapto group in the molecule of a polyvinyl alcohol molecule. However, when there is a risk of insolubilization due to the formation of a disulfide bond due to the oxidation of polyvinyl alcohol itself, a polymer having a mercapto group only at one end of the polyvinyl alcohol molecule is preferable because there is no concern of insolubilization.

As described above, the polyvinyl alcohol polymer having a mercapto group only at one end of the molecule is obtained by polymerizing a vinyl ester monomer-based vinyl monomer in the presence of thiol acid, and using the obtained polyvinyl ester in a conventional method. It is obtained by saponification with. The method for producing a polyvinyl alcohol having a mercapto group will be described in detail. Examples of the thiol acid used here include an organic thiol acid having a -COSH group in the molecule. There are thiol acetic acid, thiol propionic acid, thiol valeric acid, and the like. Among them, thiol acetic acid is the most preferable because it has good decomposability.

As the vinyl ester copolymerized with thiol acid, any vinyl ester capable of radical polymerization can be used. Examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, vinyl laurate, vinyl stearate, and the like. Among them, vinyl acetate is the most polymerizable and preferred.

It is also possible to copolymerize the vinyl ester with a monomer copolymerizable therewith. For example, ethylene, propylene, isobutylene, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, or a salt thereof or an alkyl ester thereof, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl- (3-acrylamide-3 -Dimethylpropyl) -ammonium chloride, ethyl vinyl ether, butyl vinyl ether, N-vinyl pyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate, sodium allyl sulfonate. Etc.

Polymerization of vinyl monomers mainly composed of vinyl esters such as vinyl acetate in the presence of thiol acid is carried out by a bulk polymerization method, a solution polymerization method, using a radical polymerization initiator.
Although any method such as a pearl polymerization method or an emulsion polymerization method can be used, a solution polymerization method using methanol as a solvent is industrially most advantageous.

The amount and method of addition of the thiol acid present during the polymerization to the polymerization system are not particularly limited and should be appropriately determined according to the physical properties of the intended polyvinyl ester polymer. As the polymerization method, a known method such as a batch method, a semi-continuous method, or a continuous method can be adopted.

As the radical polymerization initiator, known radical polymerization initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, and carbonate carbonate can be used, but 2,2'-azobisisobutyro Azo initiators such as nitrile are preferable because they are easy to handle. Radiation, electron beam, etc. can also be used.

The polymerization temperature is preferably an appropriate temperature depending on the type of initiator used, but is usually 30 to 90.
It is selected from the range of ° C. After polymerizing for a predetermined time, unpolymerized vinyl esters are removed by a usual method to obtain a polyvinyl ester polymer having a thiol ester group at the terminal.

The polyvinyl ester polymer thus obtained is saponified by a conventional method, but it is usually advantageous to carry out the polymer as an alcohol solution, especially a methanol solution. As the alcohol, not only an anhydride but also a small amount of a water-containing alcohol may be used according to the purpose, and an organic solvent such as methyl acetate or ethyl acetate may be optionally contained. The saponification temperature is usually selected from the range of 10 to 70 ° C.

As the saponification catalyst, alkaline catalysts such as sodium hydroxide, potassium hydroxide, sodium methylate and potassium methylate are preferable, and the amount of the catalyst used is appropriately determined depending on the degree of saponification and the water content. It is desirable that the ester unit is used in a molar ratio of 0.001 or more, preferably 0.002 or more.
On the other hand, if the amount of alkali is too large, it becomes difficult to remove the residual alkali from the polymer, and the polymer is colored, which is not preferable, and the molar ratio is preferably 0.2 or less. When a component that consumes alkali by reacting with an alkali catalyst such as a carboxyl group or its ester group in the polyvinyl ester-based polymer is copolymerized,
It is necessary to use the amount of the alkali catalyst added to that amount.

By this saponification reaction, the thiol ester at the end of the polyvinyl ester polymer having a thiol ester group at the end and the vinyl ester bond at the main chain are saponified, and the polymer end becomes a mercapto group and the main chain becomes a vinyl alcohol. However, the degree of saponification of the vinyl ester unit in the main chain can be changed according to the purpose of use. The polymer precipitated after the saponification reaction is usually purified by a known method such as washing with methanol, and the impurities such as the residual alkali and the alkali metal salt of acetic acid are removed and dried to obtain a white powder.

The method for producing a polyvinyl alcohol-based polymer having a mercapto group at the terminal used in the present invention has been described above. The degree of polymerization of this polyvinyl alcohol-based polymer is preferably 3500 or less. The degree of saponification differs depending on the types of other modifying groups and cannot be uniquely stated, but it is preferably 70 mol% or more from the viewpoint of water solubility.

The polyvinyl alcohol-based polymer having a mercapto group in the molecule of the present invention is added to the polymerization system all at once when emulsion-polymerizing a radically polymerizable ethylenically unsaturated monomer in an aqueous medium. Alternatively, it may be added in small amounts continuously. Also, using water as a medium,
Various surfactants and non-denatured polyvinyl alcohol, dispersion stabilizers for emulsion polymerization such as polyvinyl alcohol randomly copolymerized with various vinyl copolymerization components, polymerization initiators, and polyvinyl alcohol-based compounds having a mercapto group in the molecule. A usual emulsion polymerization method in which the ethylenically unsaturated monomer is added all at once or continuously in the presence of the copolymer, and the mixture is heated and stirred can also be carried out. When adding the unsaturated monomer to the emulsion polymerization system, a method of continuously adding a mixture of the monomers previously mixed and emulsified in a dispersion stabilizer aqueous solution can also be carried out.

As the polymerization initiator, potassium persulfate, ammonium persulfate, hydrogen peroxide and the like which are usually used in emulsion polymerization can be used, and a redox system in which these are combined with various reducing agents is also possible. Furthermore, the polyvinyl alcohol-based polymer having a mercapto group in the molecule as a fluidity modifier of the aqueous emulsion of the present invention, the mercapto group and the above polymerization initiator or the oxidation of potassium bromate or the like having no self-initiating ability. Since the radicals are generated by the redox reaction with the agent, the polyvinyl alcohol polymer is effectively chemically adsorbed to the polymer composed of the ethylenically unsaturated monomer.

When the polyvinyl alcohol polymer having a mercapto group in the molecule is added to the emulsion polymerization system, the polymerization system is preferably acidic. This is because the radically active mercapto group, which exhibits extremely active reactivity in radical polymerization, has a large rate of ionic addition to and disappearance from the double bond of the monomer under basic conditions, which significantly reduces the polymerization efficiency. Although depending on the type of ethylenically unsaturated monomer, it is desirable to carry out all the operations at pH 6 or lower, preferably pH 4 or lower.

The radically polymerizable ethylenically unsaturated monomers in the present invention include olefins such as ethylene, propylene and isobutylene; halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride and vinylidene fluoride; vinyl formate. , Vinyl acetate, vinyl propionate, vinyl versatate, etc .; acrylic acid, methacrylic acid and their esters, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) 2-ethylhexyl acrylate, dodecyl (meth) acrylate,
2-Hydroxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate and quaternary compounds thereof; acrylamide monomers of (meth) acrylamide, acrylamido-2-methylpropanesulfonic acid and its sodium salt; styrene, α -Styrene-based monomers such as methylstyrene, P-styrenesulfonic acid and its sodium and potassium salts; diene-based monomers such as butadiene, isoprene and chloroprene; N-vinylpyrrolidone and the like. Copolymerization can be carried out.

The feature of the present invention is to use, as the dispersoid particles, a polymer of (meth) acrylic acid ester-based, diene-based, or styrene-based monomer, which has hitherto been able to obtain only various surfactant-based aqueous emulsions. Not only aqueous emulsions, but stable aqueous emulsions were obtained even when water-soluble polymers such as polyvinyl alcohol were used as protective colloids. Polymers of vinyl ester-based or halogenated olefin-based monomers were used as dispersoids. Even in the case of particles as an aqueous emulsion, during the emulsion polymerization thereof, the presence of a polyvinyl alcohol-based polymer having a mercapto group in the molecule effectively makes the polyvinyl alcohol-based polymer on the dispersoid particle surface. , Influences the interaction between dispersoid particles of aqueous emulsion by efficiently and chemically adsorbing, Is capable of imparting Newtonian similar properties even at a relatively high viscosity to improve the structural viscosity of the come aqueous emulsion. Therefore, the dispersion stabilizing aid of the present invention can be radically polymerized and can be widely applied to the production of polymer aqueous emulsions of many ethylenically unsaturated monomers which have been conventionally produced by emulsion polymerization.

[0029]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following examples, "part"
And "%" means "part by weight" and "% by weight", respectively.
Means

Example 1 400 g of ion-exchanged water and a nonionic surfactant (trade name: Nonipol 200, manufactured by Sanyo Kasei Co., Ltd.) in a 1 liter glass container equipped with a nitrogen blowing port, a thermometer and a dropping funnel.
Polyoxyethylene (20) nonyl phenyl ether)
16 g, PVA having a mercapto group at the end (PVA-
SH-1; polymerization degree 520, saponification degree 88.3 mol%) 4
After adding g and heating and dissolving, pH was adjusted to 4.0 with dilute sulfuric acid.

Thereafter, the temperature was raised to 70 ° C., and then 40 g of methyl methacrylate (MMA) and n-butyl acrylate (n-
40 g of BA) was added to initiate polymerization. After 30 minutes, 160 g of methyl methacrylate and 16 n-butyl acrylate
0 g was added continuously over 2 hours. The polymerization rate reached 99.5% in 3 hours, and the polymerization was completed. After cooling, the solid content concentration was measured by the polymerization method. Also, using a BM type viscometer,
The viscosity was measured under a temperature condition of 0 ° C. The structural viscosity index was calculated by the following formula. Structural viscosity index = -log (viscosity at 60 rpm) / (6r
Viscosity of pm) The results are shown in Table 1. Cp in Table 1 means the unit of viscosity, centipoise.

Comparative Example 1 PVA having a mercapto group at the terminal in Example 1
Emulsion polymerization was performed under the same conditions as in Example 1 except that (PVA-SH-1) was not used. The results are shown in Table 1. Comparative Example 2 PVA having a mercapto group at the end in Example 1
Instead of (PVA-SH-1), unmodified PVA (PVA
-205, degree of polymerization 550, degree of saponification 88.5 mol%,
Emulsion polymerization was performed under the same conditions as in Example 1 except that Kuraray Co., Ltd. was used. The results are shown in Table 1.

Example 2 400 g of water, an anionic surfactant (trade name: Sandet BL, manufactured by Sanyo Kasei Co., Ltd., alkyl diphenyl ether disulfonic acid) was placed in a 1 liter pressure-resistant glass autoclave equipped with a nitrogen inlet and a thermometer. Sodium) 12
g and a PVA having a mercapto group at the end (PVA-SH
-2, polymerization degree 310, saponification degree 98.0 mol%) 8 g was charged and dissolved by heating, and then diluted sulfuric acid was added to adjust the pH to 4.0.
Adjusted to. After nitrogen substitution, styrene (St) 24
0 g and 160 g of butadiene (BD) were charged from a pressure resistance meter, the temperature was raised to 70 ° C., and then 60 g of a 2% aqueous solution of potassium persulfate was injected to initiate polymerization. Internal pressure is 4.5 Kg
/ Cm ² decreases with the progress of polymerization, and after 20 hours, it becomes 0.4 Kg / cm ² , and the polymerization rate was determined to be 9
It was 8.9%. After cooling, the solid content concentration, viscosity, and structural viscosity index were determined in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 PVA having a mercapto group at the end in Example 2
Example 2 except that (PVA-SH-2) was not used.
Emulsion polymerization was performed under the same conditions as in. The results are shown in Table 1. Comparative Example 4 PVA having a mercapto group at the end in Example 2
Instead of (PVA-SH-2), unmodified PVA (PVA-
Emulsion polymerization was carried out under the same conditions as in Example 2 except that 103, a degree of polymerization of 310, and a degree of saponification of 98.0 mol% were used. The results are shown in Table 1.

Example 3 400 g of water, unmodified PVA (PVA-217, degree of polymerization 1700, degree of saponification 88.2 mol%, Kuraray Co., Ltd.) was placed in a 1 liter glass container equipped with a nitrogen inlet and a thermometer. 20 g, PVA having a mercapto group at the end (PV
A-SH-1) (4 g) was added, the mixture was heated and dissolved, and the pH was adjusted to 4.5 with dilute sulfuric acid. After nitrogen substitution, vinyl acetate 40
0 g was charged, the temperature was raised to 60 ° C., and the reaction was initiated with 0.5% aqueous hydrogen peroxide and 2.0% tartaric acid redox polymerization initiator. The polymerization rate reached 99.1% in 3 hours, and the polymerization was completed. After cooling, the solid content concentration, viscosity and structural viscosity index were determined in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 5 PVA having a mercapto group at the terminal in Example 3
Example 3 except that (PVA-SH-1) was not used.
The emulsion polymerization was carried out under the same conditions as in. The results are shown in Table 1. Comparative Example 6 In Example 1, the nonionic emulsifier (Nonipol 20
0) and PVA having a mercapto group at the end (PVA-
When emulsion polymerization was carried out using unmodified PVA (PVA217) instead of SH-1), emulsion particles were added during continuous addition of methyl methacrylate (MMA) and n-butyl acrylate (n-BA). Solidified and no emulsion was obtained.

[0037]

[Table 1] In the column of polymerization stability in Table 1, it means ◯ (good polymerization stability), Δ (somewhat poor polymerization stability), and × (poor because coarse particles were generated).

[0038]

As is clear from the results of Table 1, a polyvinyl alcohol polymer having a mercapto group in the molecule is excellent as a dispersion stabilizing aid for emulsion polymerization of radically polymerizable ethylenically unsaturated monomers. Therefore, it is possible to improve the structural viscosity of the aqueous emulsion so as to impart Newtonian-like properties even at a relatively high viscosity.

Claims (1)

[Claims] 1. A dispersion stabilizing aid for emulsion polymerization of a radically polymerizable ethylenically unsaturated monomer comprising a polyvinyl alcohol-based polymer having a mercapto group in the molecule.