JPH0323087B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aqueous resin emulsion that is used in a state in which resin particles are stably dispersed in an aqueous medium. Specifically, the present invention relates to an aqueous resin emulsion that is used in a state in which resin particles are stably dispersed in an aqueous medium. The present invention relates to an aqueous acrylic acid alkyl ester resin emulsion that maintains a stable dispersion state and exhibits excellent dispersion stability, especially when dispersed in buffer solutions, physiological saline, aqueous solutions containing polymeric solutes, etc. A typical conventional aqueous resin emulsion is produced by emulsion copolymerization of a sparingly water-soluble radically polymerizable monomer such as styrene in the presence of an emulsifier and a water-soluble radical polymerization initiator. Here, the emulsifier ensures polymerization stability during emulsion copolymerization and also contributes to stabilizing the resulting aqueous resin emulsion. The stabilizing effect of this emulsion is not necessarily clear, but in general, a part of the emulsifier is adsorbed to the emulsion particles, and the rest exists in the emulsion in a free state. An adsorption-desorption equilibrium exists between the emulsifier adsorbed on these resin particles and the free emulsifier,
As a result of such equilibrium, emulsion stabilization is said to be achieved. Therefore, when an aqueous emulsion containing an emulsifier is dispersed in a buffer solution or physiological saline, the adsorption/desorption equilibrium of the emulsifier in the resin emulsion is disrupted, resulting in a decrease in the stability of the resin emulsion. damaged, resin particles tend to aggregate or settle.
Furthermore, since the resin particles of polystyrene emulsion are hydrophobic, they easily aggregate when dispersed in a buffer solution or physiological saline containing an organic solute. In addition, using a water-soluble radical polymerization initiator, methacrylic acid ester can be converted into hydrophilic methacrylic acid, 2-
A method of obtaining an aqueous resin emulsion by emulsion copolymerization with hydroxyethyl methacrylate and a polyfunctional monomer for internal crosslinking in the presence of an emulsifier is already known;
August, 867-871 (1978), emulsions obtained by this method also contain emulsifiers and therefore have the same problems as above, and furthermore, since the resulting copolymer particles have hydroxyl groups, it is especially difficult to use buffer solutions. There is a tendency for the resin particles to easily aggregate when dispersed in a liquid. To this end, in recent years a method has been proposed to obtain an acrylic ester emulsion in the absence of an emulsifier (Kagaku Technological Research Institute Report Vol. 75, No. 8, 341).
(1980), resin emulsions produced by this method also do not have sufficient dispersion stability and, in particular, easily aggregate under mechanical shear stress. The present invention has been made to solve the above-mentioned problems, and has excellent polymerization stability during emulsion polymerization without particularly using an emulsifier in its production, and the resulting resin particles can be produced in an aqueous medium. An aqueous resin emulsion containing an acrylic acid ester derivative and an acrylic acid derivative as main monomer components, which maintains a stable dispersion state and can therefore be suitably used in a state in which resin particles are stably dispersed in an aqueous medium. Regarding. The aqueous resin emulsion according to the present invention for use in a state in which resin particles are stably dispersed in an aqueous medium has the following formula: (a) General formula CH ₂ = CR ¹ COOR ² (wherein R ¹ represents hydrogen or a lower alkyl group) , R ² represents an alkyl group having 1 to 8 carbon atoms.) 30 to 98.8% by weight of an acrylic acid alkyl ester derivative represented by (b) the general formula R ³ CH=CR ⁴ COOH (wherein R ³ is hydrogen , represents a lower alkyl group or a carboxyl group, R ⁴ represents hydrogen or a lower alkyl group, and when R ³ is hydrogen or a lower alkyl group, R ⁴ may be a carbo-lower alkoxy group.) Acrylic acid derivative 0.1-30% by weight, (c) Vinyl monomer having sulfonic acid group 0.1-20%
(d) 1 to 20% by weight of polyfunctional internal crosslinking monomer, and (e) Acrylonitrile or methacrylonitrile 40% by weight.
% by weight or less, contains resin particles obtained by emulsion copolymerizing a monomer mixture ^consisting of It is characterized by having a content of ~60×10 ⁻⁶ mol/m ² . In the present invention, the acrylic acid alkyl ester derivative has the general formula CH ₂ = CR ¹ COOR ² (wherein R ¹ represents hydrogen or a lower alkyl group, preferably hydrogen or a methyl group, and R ² has a carbon number of 1).
~8 alkyl group is shown. ), for example, methyl (meth)acrylate,
Examples include ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, and octyl (meth)acrylate. In the present invention, in order to obtain an emulsion copolymer emulsion of an acrylic ester derivative having excellent dispersion stability in an aqueous medium, in addition to the acrylic ester derivative, an acrylic ester having a carboxyl group is added as a monomer component. A vinyl monomer having an acid derivative and a sulfonic acid group is used, as well as a polyfunctional internal crosslinking monomer. By emulsion copolymerizing a mixture of such monomer components at a predetermined ratio, the emulsion copolymerization is carried out stably without the generation of aggregates, and the dispersion state is stably maintained in an aqueous medium, such as Tris buffer. It is possible to obtain an aqueous resin emulsion that is stable over time, non-staining, and non-swellable even when maintained at an alkaline pH of 8.0. The above acrylic acid derivative has the general formula R ³ CH=CR ⁴ COOH (wherein R ³ represents hydrogen, a lower alkyl group or a carboxyl group, preferably hydrogen or a methyl group, and R ⁴ represents hydrogen or a lower alkyl group, preferably (represents hydrogen or a methyl group, and when R ³ is hydrogen or a lower alkyl group, R ⁴ may be a carbo-lower alkoxy group), for example, (meth)acrylic acid, itaconic acid, croton. acid, maleic acid, fumaric acid, monoalkyl maleic acid, morealkyl fumaric acid,
Preferred examples include monoalkyl itaconic acid, and in particular, one or a mixture of two or more of (meth)acrylic acid and itaconic acid is preferably used. Next, in the present invention, the vinyl monomer having a sulfonic acid group includes vinyl sulfonic acid, its metal salt or ammonium salt, and the general formula CH ₂ = CH ⁵ COOR ⁶ SO ₃ M (wherein R ⁵ is hydrogen or Represents a lower alkyl group, preferably hydrogen or a methyl group, R ⁶ has 1 carbon number
-6 alkylene group, preferably an alkylene group having 2 to 3 carbon atoms, and M represents hydrogen, an alkali metal or ammonium. ), such as sulfopropyl (meth)acrylate and its alkyl metal salts, with the general formula (However, R ⁷ represents hydrogen or a lower alkyl group, preferably hydrogen or a methyl group, and M is the same as above.) Styrene sulfonic acid, its derivatives,
These alkyl metal salts, such as sodium styrene sulfonate, have the general formula CH ₂ = CR ⁸ CONH-R ⁹ -SO ₃ M (where R ⁸ represents hydrogen or a lower alkyl group, preferably hydrogen or a methyl group, and R ⁹ is carbon number 1
-6 alkylene group, preferably an alkylene group having 3 to 4 carbon atoms, and M is the same as above. ) 2-acrylamidoalkanesulfonic acid, derivatives thereof and alkyl metal salts thereof,
For example, 2-acrylamido-2-methylpropanesulfonic acid and the like are used. The internal crosslinking polyfunctional monomer is particularly effective in non-swelling the resin particles and increasing the dispersion stability of the resulting resin particles in an aqueous medium. As such a polyfunctional internal crosslinking monomer, for example, poly(meth)acrylate of aliphatic polyhydric alcohol is preferably used. Specific examples include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, triethylene glycol diacrylate, trimethylolpropane trimethacrylate, and trimethylol. Propane triacrylate, tetramethylolmethanetetraacrylate, etc. are preferably used. Further, divinylbenzene, N-N'-methylenebisacrylamide, etc. can also be used as the polyfunctional internal crosslinking monomer. In producing the aqueous resin emulsion according to the present invention, the monomer composition for emulsion copolymerization is 30 to 98.8% by weight of an acrylic acid alkyl ester derivative;
Preferably 50-98% by weight, acrylic acid derivative 0.1
~30% by weight, preferably 0.5-20% by weight, vinyl monomers with sulfonic acid groups 0.1-20% by weight, preferably 0.5-15% by weight, polyfunctional monomers for internal crosslinking 1-20% by weight , preferably 1 to 15% by weight. Both the acrylic acid derivative and the vinyl monomer having a sulfonic acid group are essential monomers for the polymerization stability during emulsion copolymerization of acrylic acid alkyl ester and the stability of the resulting emulsion, and these effects In order to effectively express these, at least 0.1% by weight of each is required in the monomer composition. However, when used in excess as a copolymerization monomer component, the polymerization stability and the stability of the resulting emulsion are adversely affected, so they are used in the ranges of 30% by weight and 20% by weight or less, respectively. In addition, as described above, the internal crosslinking polyfunctional monomer is used to stably proceed the polymerization, maintain a stable dispersion state of the resulting resin particles, and make the resin particles non-swellable. It is a necessary monomer, and at least 1% by weight is required in the monomer composition. However, it is not preferable to use too much because it will actually impair polymerization stability and emulsion stability. Furthermore, in the present invention, (meth)acrylonitrile is used as a monomer component in order to further enhance the polymerization stability of the monomer mixture during emulsion copolymerization and the water dispersion stability of the resulting resin particles. The preferred amount to be used is up to 40% by weight based on the monomer composition; if it is used in an amount larger than this, the polymerization stability may be adversely affected, and the resulting resin particles may have poor water dispersion stability. become. The lower limit of the effective amount is not particularly limited, but is usually 1% by weight based on the monomer composition. A particularly preferable usage amount is 5 to
It is in the range of 20% by weight. Furthermore, although it depends on the use of the resulting aqueous resin emulsion, the specific types of individual monomers are selected so that the glass transition point of the resulting copolymer is 0° C. or higher, preferably room temperature or higher. . This is because when the glass transition point of the resin particles is lower than 0° C., mutual fusion and aggregation of the resin particles tend to occur, and the dispersion stability of the emulsion tends to decrease. In the present invention, a water-insoluble acrylic ester copolymer is obtained by emulsion copolymerizing each of the monomers described above in an aqueous medium using a water-soluble radical polymerization initiator in a conventional manner. An aqueous emulsion of a polymer resin can be obtained, but the emulsifier is free in the aqueous emulsion obtained.
Alternatively, when it is present in a state adsorbed to resin particles, as mentioned above, various harmful effects may appear especially during its use, so it is preferable not to use an emulsifier during emulsion copolymerization. The monomer composition according to the present invention is characterized in that stable copolymerization can be carried out without particularly using an emulsifier, and the dispersion state of the resulting resin emulsion can be stably maintained. However, as mentioned above, even when dispersed in a buffer solution or physiological saline, it is possible to use an emulsifier as long as emulsion particles do not aggregate or settle. If necessary, an emulsifier may be used if it does not cause any harmful effects. In addition, in the emulsion copolymerization according to the present invention, the concentration of the monomer component mixture in the aqueous medium is related to the average particle size of the resin particles in the resulting emulsion, but is usually in the range of 0.1 to 40% by weight. . As the polymerization initiator, a water-soluble radical polymerization initiator is used. Usually, persulfates such as potassium persulfate, sodium persulfate, ammonium persulfate, these persulfates and thiosulfates such as sodium thiosulfate, potassium thiosulfate, sodium hydrogen thiosulfate, etc., or sodium sulfite, potassium sulfite. A redox polymerization initiator with a sulfite salt such as , sodium bisulfite, etc. is preferably used, but is not limited thereto. The amount of these polymerization initiators to be used is based on the monomer mixture.
A range of 0.01 to 1% by weight is preferred. The atmosphere for polymerization is also not particularly limited, but preferably an inert gas atmosphere excluding oxygen is used. In addition, the polymerization temperature is not particularly limited, but is usually 20 to 100°C,
Preferably it is in the range of 50 to 90°C. In the resin aqueous emulsion according to the present invention,
The average particle size of the resin particles needs to be in the range of 0.05 μm to 2 μm, preferably in the range of 0.1 to 1 μm. If the particle size is too small, it will be difficult to recover it after use, while if the particle size is too large, it will be difficult to maintain a stable dispersion state. . Further, the specific gravity of the resin particles is preferably in the range of 0.9 to 1.3. When the specific gravity is less than 0.9,
Resin particles float on the surface of the emulsion aqueous medium,
This is because the dispersion stability becomes poor, and on the other hand, when it is larger than 1.3, the resin particles tend to settle in the emulsion aqueous medium and tend to cause aggregation as well. Furthermore, in the present invention, it is necessary that the resin particles have carboxyl groups at a density in the range of 0.7×10 ⁻⁶ to 60×10 ⁻⁶ mol/m ² . When the carboxyl group possessed by the resin particles is less than 0.7×10 ^-6 mol/m ² , water dispersion stability is insufficient;
This is because when the amount is more than 60×10 ⁻⁶ mol/m ² , the resin particles tend to have swelling properties especially in an alkaline aqueous solution, resulting in poor water dispersibility. As described above, according to the present invention, it is possible to perform emulsion copolymerization of an acrylic acid alkyl ester derivative while ensuring polymerization stability without using an emulsifier, and to obtain copolymer particles obtained. is non-swellable and non-staining, and not only maintains its dispersion state stably in aqueous media, but also maintains a stable dispersion state when dispersed in buffer solutions and physiological saline. Therefore, the aqueous resin emulsion according to the present invention can be suitably used in applications where resin particles are required to remain stably dispersed in an aqueous medium. The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. Example 1 38.3% by weight of methyl methacrylate, 38.3% by weight of isobutyl methacrylate, 5% by weight of acrylic acid, sulfopropyl acrylate sodium salt
60 g of a monomer mixture consisting of 0.5% by weight, 3.7% by weight of triethylene glycol dimethacrylate, and 14.2% by weight of methacrylonitrile were added to 330g of distilled water, and an aqueous polymerization initiator solution containing 0.3g of potassium persulfate dissolved in 10ml of water was added to 75% of a polymerization initiator solution. C. under a nitrogen stream and polymerized for 6 hours while stirring at 120 ppm to obtain an aqueous emulsion of resin particles with a polymerization rate of 98.8% and an average particle size of 0.28 .mu.m. The polymerization was very stable and there were no aggregates. Centrifuge this emulsion and remove the resin at 0.01N.
After making it into an acid form with hydrochloric acid, it was washed with distilled water and dispersed in distilled water. This emulsion was subjected to conductivity titration with a 0.05N aqueous potassium hydroxide solution to determine the amount of carboxyl groups. Separately, the particle size of the emulsion particles was measured using an electron microscope, and the amount of carboxyl groups possessed by the resin particles was determined from these measurements, and was found to be 4.4×10 ⁻⁶ mol/m ² . In addition, the emulsion obtained above was centrifuged, washed with distilled water, and then redispersed in distilled water.
When 1ml of a resin emulsion with a solid content of 5% adjusted to pH 7.0 with a 0.01N sodium hydroxide aqueous solution was dispersed in 10ml of a 1M calcium chloride aqueous solution (PH7.0), a stable dispersion state was maintained even after one month. Was. In the following, when 1 ml of such an emulsion is dispersed in 10 ml of a 1M calcium chloride aqueous solution, the dispersibility is considered to be good if the dispersion remains stable even after one month, and the resin particles are dispersed within a few hours. The dispersibility is considered to be poor when the particles coagulate and settle. Examples 2 to 8 Emulsion copolymerization was carried out in the same manner as in Example 1 using monomer mixtures having the compositions shown in the table. The results are shown in the table. Comparative Examples 1 and 2 As shown in the table, emulsion copolymerization was carried out in the same manner as in Example 1 using a monomer mixture that did not contain acrylic acid. The results are shown in the table. Comparative Example 3 As shown in the table, using a monomer mixture that does not contain sulfopropyl acrylate sodium salt,
Emulsion copolymerization was carried out in the same manner as in Example 1. The results are shown in the table. Comparative Examples 4 and 5 As shown in the table, emulsion copolymerization was carried out in the same manner as in Example 1 using a monomer mixture containing an excessive amount of acrylonitrile or sulfopropyl acrylate sodium salt. The results are shown in the table. Comparative Examples 6 to 8 As shown in the table, emulsion copolymerization was carried out in the same manner as in Example 1 using a monomer mixture containing styrene or 2-hydroxyethyl methacrylate. The results are shown in the table. Comparative Example 9 As shown in the table, emulsion copolymerization was carried out in the same manner as in Example 1, using a monomer mixture containing styrene as a monomer component instead of (meth)acrylic acid ester.
The results are shown in the table. In addition, in the table, the abbreviations indicating monomers have the following meanings. MMA Methyl methacrylate IBMA Isobutyl methacrylate St Styrene HEMA 2-Hydroxyethyl methacrylate SP Sulfopropyl acrylate sodium salt

【table】

[Table] SSS Sodium styrene sulfonate AMPS 2-acrylamido-2-methylpropanesulfonic acid TGM Triethylene glycol dimethacrylate PGM Polyethylene glycol dimethacrylate AA Acrylic acid MAA Methacrylic acid AN Acrylonitrile MAN Methacrylonitrile

Claims (1)

[Claims] 1 (a) General formula CH ₂ = CR ¹ COOR ² (wherein R ¹ represents hydrogen or a lower alkyl group, and R ² represents an alkyl group having 1 to 8 carbon atoms). 30 to 98.8% by weight of the represented acrylic acid alkyl ester derivative, (b) General formula R ³ CH=CR ₄ COOH (However, R ³ represents hydrogen, a lower alkyl group, or a carboxyl group, and R ⁴ represents hydrogen or a lower alkyl group. and when R ³ is hydrogen or a lower alkyl group, R ⁴ may be a carbo-lower alkoxy group.) 0.1 to 30% by weight of an acrylic acid derivative represented by Monomer 0.1~20
(d) 1 to 20% by weight of polyfunctional internal crosslinking monomer, and (e) Acrylonitrile or methacrylonitrile 40% by weight.
% by weight or less, contains resin particles obtained by emulsion copolymerizing a monomer mixture consisting ^of An aqueous resin emulsion for use in a state in which resin particles are stably dispersed in an aqueous medium, characterized in that the resin particles have a content of ⁶ to 60×10 ^-6 mol/m ² .