JP2000063407A - Dispersion stabilizer for emulsion polymerization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare stable and relatively low-viscosity emulsions such as vinyl acetate-based emulsions, (meth)acrylate-based emulsions and styrene-butadiene- based emulsions. SOLUTION: An emulsion comprises (A) a polyvinyl alcohol-based polymer having mercapto groups with an average saponification degree (X) of 85 mol.% or more and (B) a polyvinyl alcohol-based polymer with an average saponification degree (Y) of 85 mol.% or less, wherein X minus Y is 5 mol.% or more and the weight ratio of solid contents of A/B is 100/0.1-100/50.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dispersion stabilizer for emulsion polymerization.

[0002]

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

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. That is, in applications where the emulsion is left unsatisfactory in stability, mechanical stability, chemical stability, freeze-thaw stability and pigment miscibility, and the emulsion viscosity is generally low, a high viscosity is required. 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, it is true that the stability during emulsion polymerization is high for styrene-based monomers, diene-based monomers, and (meth) acrylic acid ester-based monomers, which have relatively low radical reactivity, and Stability,
Although an emulsion excellent in chemical stability and the like can be obtained, one problem is that the viscosity of the emulsion polymerization system or the obtained emulsion is higher than that of the emulsifier system and may be limited depending on the application. .

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide PV
In producing an aqueous emulsion using A as an emulsion polymerization dispersant, not only vinyl acetate and vinyl chloride but also conventional P
A PVA-based emulsion that can be widely applied to ethylenically unsaturated monomers and diene-based monomers for which a stable aqueous emulsion was difficult to produce when VA was used as a dispersant, and that a relatively low-viscosity emulsion was obtained. It is to provide a dispersion stabilizer for emulsion polymerization.

[0006]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of the above circumstances, and as a result, (A) an average saponification degree (X) is a polyvinyl alcohol-based polymer having a mercapto group of 85 mol% or more. (A) / (B), which is composed of a polymer and a (B) polyvinyl alcohol-based polymer having an average saponification degree (Y) of 85 mol% or less and XY is 5 mol% or more.
Is a dispersion stabilizer for emulsion polymerization having a solid content weight ratio of 100 / 0.1 to 100/50, and particularly the dispersion stabilizer for emulsion polymerization described above, wherein (B) is a polyvinyl alcohol-based polymer having a mercapto group. The inventors have found that the emulsion has excellent emulsion polymerization stability and has a relatively low viscosity, and completed the present invention.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as the PVA-based polymer having a mercapto group, a PVA-based polymer having a mercapto group in the main chain of the polymer may be used. A PVA-based polymer having a mercapto group only at one end of a molecule is preferable because it is easy to handle because there is no risk of insolubilization because a disulfide bond may be formed by oxidation and insolubilization may occur. 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. Of these, vinyl acetate is preferable from the viewpoint of obtaining PVA.

It is also possible to copolymerize the vinyl ester-based monomer and the copolymerizable monomer in the coexistence.
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 compound, fumaric acid, maleic acid, itaconic acid, maleic anhydride, phthalic anhydride, trimetic acid anhydride or itaconic anhydride, and the like, 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 component (A) which constitutes the dispersion stabilizer for emulsion polymerization of the present invention is preferably a PVA polymer having a mercapto group having an average saponification degree (X) of 85 mol% or more, and more preferably. A PVA polymer having a mercapto group having an average saponification degree of 85 to 99.9 mol%, and more preferably an average saponification degree of 85 to 99.5 mol%. When the average degree of saponification is lower than 85 mol%, there is a problem that the emulsion viscosity obtained increases with the decrease in emulsion polymerization stability.

The component (B) which constitutes the dispersion stabilizer for emulsion polymerization of the present invention is P having an average degree of saponification (Y) of 85 mol% or less.
A VA polymer is preferable, and more preferably,
A PVA-based polymer having an average saponification degree of 65 to 80 mol%, and more preferably an average saponification degree of 68 to 80 mol%. When the average degree of saponification is higher than 85 mol%, there is a problem that the obtained emulsion viscosity becomes high. Further, it is preferable that (B) has a mercapto group because the effect of the present invention is further improved. Further, the difference between the average saponification degree (X) of (A) and the average saponification degree (Y) of (B), XY, must be 5 mol% or more, and preferably 8 mol% or more. Is. When XY is less than 5 mol%, the viscosity of the obtained emulsion cannot be lowered.

The dispersion stabilizer for emulsion polymerization of the present invention includes:
The solid content weight ratio of the components (A) and (B) is 100 /
It is necessary to be 0.1 to 100/50, preferably 100 / 0.5 to 100/40, and more preferably 100/1 to 100/20. When the amount of the component (B) is less than 0.1 based on 100 of the component (A), the viscosity of the obtained emulsion cannot be reduced. Also,
If the amount of component (B) is more than 50, there is a problem that stability during emulsion polymerization decreases.

P which is the component (A) and (B) of the present invention
Viscosity average degree of polymerization of VA polymer (hereinafter abbreviated as degree of polymerization)
May be selected according to various situations and is not particularly limited, but is preferably 3500 or less, more preferably 2000 or less, still more preferably 1500 or less. Polymerization degree is 35
When it is larger than 00, there is a problem that stability of emulsion polymerization is lowered and the viscosity of the obtained emulsion becomes very high, which is contrary to the object of the present invention.

The dispersion stabilizer for emulsion polymerization of the present invention is effective in emulsion polymerization of one or more radically polymerizable monomers selected from ethylenically unsaturated monomers and diene unsaturated monomers. used. 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 t-
Acrylic esters such as butyl, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-methacrylic acid
-Propyl, n-butyl methacrylate, methacrylic acid i
-Butyl, t-butyl methacrylate, 2-methacrylic acid
Methacrylic acid esters such as ethylhexyl, dodecyl methacrylate, octadecyl methacrylate, acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid and its sodium salt, an acrylamide-based unit amount Body, nitriles such as acrylonitrile and methacrylonitrile, allyl compounds such as allyl acetate and allyl chloride, styrene-based monomers such as styrene, α-methylstyrene, P-methylstyrene sulfonic acid and sodium and potassium salts thereof. Other examples include N-vinylpyrrolidone, and examples of the diene monomer include butadiene, isoprene, chloroprene, and the like. Among them, vinyl acetate, vinyl acetate / ethylene,
Vinyl acetate / (meth) acrylic acid ester, (meth) acrylic acid ester, (meth) acrylic acid ester / styrene, styrene / butadiene, styrene / butadiene /
It is particularly effective for each monomer system of (meth) acrylic acid ester.

When emulsion-polymerizing the above-mentioned monomer using the dispersion stabilizer for emulsion polymerization of the present invention, the method is not particularly limited, and a conventionally known emulsion-polymerization method is adopted. In the method of adding the monomers to the polymerization system, the method of adding all the monomers at once in an initial stage, adding a part of the monomers to start the polymerization, and then sequentially adding the remaining monomers And a method of intermittently adding, a method of previously emulsifying a monomer and an emulsion polymerization dispersion stabilizer aqueous solution, and adding the same. In addition, in the method of adding the dispersion stabilizer for emulsion polymerization, a method of adding the whole amount to the polymerization system before the initiation of the polymerization, and a part of the emulsion polymerization dispersion stabilizer is charged at the beginning of the polymerization to start the polymerization, and then the rest is sequentially added. Alternatively, a method of intermittently adding it to the polymerization system may be used.

The amount of the emulsion polymerization dispersion stabilizer used in the present invention is
The amount is 0.5 to 100 parts by weight, preferably 1 to 50 parts by weight, and more preferably 2 to 30 parts by weight, based on 100 parts by weight of the monomer. 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. Also, PVA
If the amount of the system polymer exceeds 100 parts by weight, there are problems such as an increase in the viscosity of the polymerization system, an increase in the viscosity of the obtained emulsion, and a decrease in the water resistance of the film. In addition, conventionally known nonionic properties,
Anionic, cationic, amphoteric surfactant, or
PVA polymer having a mercapto group at the terminal other than (A) or (B), PV having no mercapto group at the terminal
Water-soluble polymers such as A-based polymers and hydroxyethyl cellulose may be used in combination with the mercapto group-containing PVA-based polymers (A) and (B) of the present invention.

In the emulsion polymerization using the dispersion stabilizer for emulsion polymerization of the present invention, the initiator of the emulsion polymerization is bromic acid which generates a radical only by a redox reaction with the mercapto group of the PVA polymer having a mercapto group. In addition to potassium, water-soluble initiators such as potassium persulfate, ammonium persulfate, hydrogen peroxide and t-butyl hydroperoxide, and oil-soluble initiators such as azobisisobutyronitrile and benzoyl peroxide are used alone or in various reducing agents. Used in redox system in combination with. 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 emulsion polymerization using the emulsion polymerization dispersion stabilizer of the present invention, a chain transfer agent can be used. The chain transfer agent is not particularly limited as long as it causes chain transfer, but a compound having a mercapto group is preferable in terms of chain transfer efficiency. Examples of the compound having a mercapto group include alkyl mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan and t-dodecyl mercaptan, 2-mercaptoethanol and 3-mercaptopropionic acid. When a chain transfer agent is used, the amount of the emulsion used is usually limited to 5 parts by weight or less per 100 parts by weight of the monomer in consideration of film physical properties and the like. 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.

The feature of the present invention is that (meth) acrylic acid is difficult to obtain by emulsion polymerization using PVA as a dispersant, not to mention vinyl ester type monomers, and emulsion having good stability. By using the emulsion-polymerization dispersion stabilizer of the present invention even in an acrylic homopolymerization or copolymerization system such as ester, styrene-butadiene copolymerization system, methylmethacrylate-butadiene copolymerization system, etc., on a practical and industrial scale. A stable and relatively low viscosity emulsion is obtained.

The emulsion thus obtained is
It can be used for various purposes as it is or by adding conventionally known additives. For example, it is used for a wide range of applications such as paints, adhesives, fiber processing agents, paper processing agents, inorganic binders, cement admixtures and mortar primers. Furthermore, it can be effectively used as a so-called powder emulsion obtained by pulverizing the obtained emulsion by spray drying or the like.

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

[0021]

Example 1 A glass container equipped with a reflux condenser, a dropping funnel, a thermometer, a nitrogen blowing port, and a stirrer was charged with PVA having a mercapto group at the end (PVA-A1: polymerization degree 550, saponification degree 88). .3
mol%, mercapto group content 3.3 × 10 ⁻⁵ equivalent / g)
PVA having 5 parts and a mercapto group at the end (PVA-B
1: degree of polymerization 550, degree of saponification 77.0mol%, 2.3 × 10 ^-5 eq /g)0.3 parts mercapto group content, was charged with 90 parts of ion-exchanged water were completely dissolved at 95 ° C.. Then, after adjusting the pH to 4 with dilute sulfuric acid, 10 parts of methyl methacrylate, 10 parts of n-butyl acrylate, and 0.1 part of n-dodecyl mercaptan were added with stirring at 150 rpm, and the temperature was raised to 70 ° C. after nitrogen substitution. . Polymerization was started by adding 5 parts of 1% potassium persulfate, and a mixture of 40 parts of methyl methacrylate, 40 parts of n-butyl acrylate and 0.4 parts of n-dodecyl mercaptan was continuously added over 2 hours. . 3 hours after the start of the polymerization, the conversion reached 99.5% and the polymerization was completed. Solid content concentration 52.0
%, Viscosity 200 mPa. A stable methyl acrylate / n-butyl acrylate copolymer emulsion of s was obtained.

Comparative Example 1 A test was conducted in the same manner as in Example 1 except that PVA-B1 was not used. The emulsion obtained is
Solid content concentration 51.9%, viscosity 700 mPa.s. It was s.

Comparative Example 2 A test was conducted in the same manner as in Example 1 except that 3 parts of PVA-B1 was used. The obtained emulsion has a solid content concentration of 52.1% and a viscosity of 300 mPa.s. However, the blocked product was visually observed.

Example 2 A test was conducted in the same manner as in Example 1 except that 0.9 part of PVA-B1 was used. The obtained emulsion has a solid content concentration of 52.0% and a viscosity of 220 mPa.s. s, which was stable.

Example 3 A PVA having a mercapto group at its end (PVA-A) was used in a pressure-resistant autoclave equipped with a nitrogen blowing port and a thermometer.
2: 10% aqueous solution 10 having a degree of polymerization of 350, a degree of saponification of 88.5 mol% and a mercapto group content of 7.0 × 10 ⁻⁵ equivalent / g)
0 part, PVA having a mercapto group at the end (PVA-B
2: 1 part of a 10% aqueous solution having a degree of polymerization of 550, a degree of saponification of 70.5 mol% and a mercapto group content of 2.0 × 10 ⁻⁵ equivalent / g) was prepared and adjusted to pH = 4 with dilute sulfuric acid to prepare styrene 60.
Part, 1 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% t-butyl hydroperoxide was press-fitted to initiate polymerization. The internal pressure decreased from 4.5 Kg / cm ^{2 as the} polymerization progressed, and after 20 hours reached 0.3 Kg / cm ² , and the polymerization rate was determined to be 99.2%. Solid content concentration 51.6%, viscosity 550 mPa.s. A stable styrene-butadiene copolymer emulsion of s was obtained.

Comparative Example 3 The procedure of Example 3 was repeated except that PVA-B2 was not used. As a result, the solid content concentration was 51.5% and the viscosity was 3900 mPa.s. It was a styrene-butadiene copolymer emulsion of s.

Example 4 A PVA having a mercapto group at its end (PVA-3) was placed in a pressure resistant autoclave equipped with a nitrogen blowing port and a thermometer.
A: degree of polymerization 1500, degree of saponification 98.5 mol%, mercapto group content of 2.1 × 10 ^-5 5% aqueous solution of 10 eq / g)
0 part, PVA having a mercapto group at the end (PVA-3
B: degree of polymerization 1500, degree of saponification 79.5mol%, 5% aqueous solution of mercapto group content 1.1 × 10 ^-5 eq / g) 10
A portion was charged and the pH was adjusted to 3.5 with diluted sulfuric acid. 80 parts of vinyl acetate was added, the temperature was raised to 60 ° C., and the atmosphere was replaced with nitrogen. 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 54.5%, viscosity 800 mPa.s. A stable ethylene-vinyl acetate copolymer emulsion of s was obtained.

Comparative Example 4 Example 4 was repeated except that PVA-B3 was not used. As a result, the solid content concentration was 54.3% and the viscosity was 2500 mPa.s. It was an ethylene-vinyl acetate copolymer emulsion of s.

[0029]

As described above, when the emulsion polymerization dispersion stabilizer of the present invention is used, not only vinyl acetate type emulsions but also (meth) acrylic acid ester type or styrene-butadiene type emulsions are stable. And that the obtained emulsion has a relatively low viscosity.

Claims (2)

[Claims] 1. An average saponification degree (X) of (A) is 85 mol%.
The polyvinyl alcohol-based polymer having the above mercapto group and (B) the polyvinyl alcohol-based polymer having an average saponification degree (Y) of 85 mol% or less, and XY is 5
A dispersion stabilizer for emulsion polymerization, wherein the dispersion stabilizer is at least mol% and the solid content weight ratio of (A) / (B) is 100 / 0.1 to 100/50. 2. The dispersion stabilizer for emulsion polymerization according to claim 1, wherein (B) is a polyvinyl alcohol polymer having a mercapto group.