AQUEOUS EMULSION OF ACRYLIC ACID COPOLYMER

Abstract: Copolymerisation is carried out in the presence of a radical polymerisation initiator, of an aqueous mixture of, by weight: (a) 60 - 99.8% of an acrylic acid fluoroalkyl ester deriva­ tive up to 90% of which may be replaced by an acrylic acid alkyl ester and up to 99% of which may be replaced by a radical poly­ merisable vinyl monomer; (b) 0.1 - 20% of an acrylic acid derivative, (c) 0.1 - 20% of a polyfunctional monomer causing inter­ nal cross-linking of the copolymer and (d) optionally 0.001 - 10% of a vinyl monomer having a sulfonic acid group. The resultant emulsion contains copolymer particles of size 0.03 to 2 µm and a specific gravity of 0.9 to 1.5, and it has excellent stability and can be dispersed in a buffer solution or physiological saline solution.

Description: This invention relates to an aqueous emulsion of a synthetic resin or copolymer and more particularly to such emulsion which can be prepared with excellent polymerization stability and whose particles have excellent dispersion stability in an aqueous medium, particularly a buffer solution, physiological saline, or an aqueous solution containing a high polymer solute. The copolymer is generally referred to herein as a "resin". Typically employed aqueous resin emulsions have been prepared by emulsion polymerizatlon of a water sparingly soluble radical-polymerizable monomer, such as styrene, in the presence of an emulsifying agent and a water-soluble radical polymerization initiator. The emulsifying agent used is generally effective for ensuring polymerization stability in emulsion polymerization and for obtaining an aqueous resin emulsion having a small particle size and dispersion stability. The mechanism of the emulsifying agent to increase dispersion stability of the resulting emulsion has not been fully elucidated, but it is thought that an adsorption-desorption equilibrium is established in the emulsion between a part of the emulsifying agent adsorbed onto emulsion particles and the rest of the emulsifying agent present in the emulsion in a free state, and dispersion stability of the emulsion can thus be realized. Therefore, when an aqueous emulsion containing an emulsifying agent is dispersed in a buffer solution or physiological saline, the aforesaid adsorption-desorption equilibrium of the emulsifying agent in the resin emulsion is disturbed, and, as a result, stability of the resin emulsion is reduced, which readily leads to agglomeration or sedimentation of resin particles. In addition, since a polystyrene emulsion comprises hydrophobic resin particles, agglomeration of resin particles readily occurs when it is dispersed in a buffer solution or physiological saline containing an organic solute. There is known a process of obtaining an aqueous resin emulsion in which a methacrylic ester is emulsion copolymerized with hydrophilic methacrylic acid, 2-hydroxyethyl methacrylate and a polyfunctional monomer for internal cross-linking in the presence of a water-soluble radical polymerization initiator and an emulsifying agent, as disclosed in Polymer, Vol. 19, pp. 867-871 (Aug., 1978). However, the emulsion obtained by this process also contains an emulsifying agent, and, therefore, involves the same problem as mentioned above. Further, the above described emulsion has a tendency that resin particles are readily agglomerated especially upon dispersing in a buffer solution, etc., presumably because the copolymer particles have a hydroxyl group. For eliminating the above described problem, there has been proposed a process of obtaining an acrylic ester emulsion in the absence of an emulsifying agent as disclosed by Kagaku Gijutsu Kenkyusho Report, Vol. 75, No. 8, p. 341 (1980). However, the resin emulsion obtained by this process is still unsatisfactory in terms of dispersion stability, and, in particular, easily undergoes agglomeration under mechanical shear stresses. The present invention is intended to overcome the above described disadvantages. An object of this invention is to provide an aqueous resin emulsion comprising an acrylic ester derivative and an acrylic acid derivative as monomer components, which shows excellent polymerization stability in emulsion polymerization for the preparation thereof without the aid of an emulsifying agent and whose resin particles have a narrow and uniform size distribution and retain a stably dispersed state in an aqueous medium, which, therefore, can suitably be used in an aqueous medium in a stably dispersed state. Accordingly, the present invention provides an aqueous emulsion of a copolymer which has a particle size of from 0.03 to 2 µm, a specific gravity of 0.9 to 1 .5 and a glass transition temperature of at least 0°C, which is obtained by emulsion copolymerizing in an aqueous medium a monomer mixture comprising: (a) from 60 to 99.8% by weight of an acrylic acid fluoroalkyl ester derivative represented by the general formula: wherein R¹ represents a hydrogen atom or a lower alkyl group, R² represents the group (CH₂ ) m or the group , wherein m represents 0 or an integer of from 1 to 12 and x + y is an integer of from 1 to 11, n represents 0 or an integer of from 1 to 12, and R³ represents a hydrogen atom or an acetyl group, and A independently represents a hydrogen atom, a fluorine atom or CF₃, and this ester derivative (I) may be replaced by an amount (a¹) not more than 90% by weight, based on the total of the derivatives (I) and (III), of an acrylic acid alkyl ester derivative of the general formula: wherein R⁶ represents a hydrogen atom or a lower alkyl group and R⁷ represents an alkyl group having from 1 to 8 carbon atoms; and the ester derivative (I) may be replaced by an amount (a²) up to 99% by weight, based on the total of the derivative (I) and the following monomer, of radical copolymerizable vinyl monomer other than the acrylic acid alkyl ester derivative of formula (III), the acrylic acid derivatives of formula (II) below, an optional vinyl monomer having a sulfonic acid group (d) or the polyfunctional monomer (c) below for the internal crosslinking; (b) from 0.1 to 20% by weight of an acrylic acid derivative represented by the general formula: wherein R⁴ represents a hydrogen atom, a lower alkyl group or a carboxyl group, and R⁵ represents a hydrogen atom, or a lower alkyl group and -CH₂COOH when R⁴ represents a hydrogen atom, and (c) from 0.1 to 20% by weight of a polyfunctional monomer for internal cross-linking. (d) from 0.001 to 10% by weight of a vinyl monomer having a sulfonic group. The acrylic acid fluoroalkyl ester derivative represented by formula (I) preferably is a compound represented by one of formula (I-a) to (I-d): wherein R¹, m, n and R³ are as defined above. In the above formulae (I) and (I-a) to (I-d), R¹ preferably represents a hydrogen atom or a methyl group. Specific examples of particularly preferred acrylic acid fluoroalkyl ester derivatives are: CH₂=C(CH₃)COOCH₂CF₃ CH₂=C(CH₃)COOCH₂(CF₂)₂H CH₂=C(CH₃)COOCH₂(CF₂)₄H CH₂=C(CH₃)COO(CH₂)₂(CF₂)₈F In the present invention, an emulsion copolymer of the acrylic acid fluoroalkyl ester derivative (I) having excellent dispersion stability in an aqueous medium can be obtained by emulsion copolymerizing the ester derivative (I) with an acrylic acid derivative of the formula (II) and a polyfunctional monomer for internal cross-linking. According to this invention, a monomer mixture comprising these monomer components at a prescribed proportion can be emulsion-copolymerized in a stable state unaccompanied by agglomeration of resin particles without using any emulsifying agent, to thereby obtain an aqueous resin emulsion which remains stably dispersed in an aqueous medium and is free fron stains or imbibition (swelling). In formula (II) representing the acrylic acid derivative used in the present invention, R⁴ preferably represents a hydrogen atom or a methyl group, and R⁵ preferably represents a hydrogen atom or a methyl group. Specific examples of preferred acrylic acid derivatives include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, a monoalkyl maleic acid, a monoalkyl fumaric acid and a monoalkyl itaconic acid. Of these, acrylic acid, methacrylic acid and itaconic acid and mixtures thereof are particularly preferred. The polyfunctional monomer for internal cross-linking is particularly effective to render resin particles non-swelling thereby ensuring dispersion stability of resin particles in an aqueous medium. Such a polyfunctional monomer preferably includes a poly(meth)acrylate (that is, polyacrylate and polymethacrylate) of an aliphatic polyhydric alcohol. Specific examples are ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, triethylene glycol diacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate and tetramethylolmethane tetraacrylate. In addition, e.g. divinylbenzene, N,N'-methylenebisacrylamide may also be used as polyfunctional monomer for internal cross-linking. The monomer mixture which can be used for emulsion polymerization in the present invention comprises (a) from 60 to 99.8% by weight, and preferably from 70 to 95% by weight, of an acrylic acid fluoroalkyl ester derivative, (b) from 0.1 to 20% by weight, and preferably from 1 to 15% by weight, of an acrylic acid derivative, and (c) from 0.1 to 20% by weight, and preferably from 1 to 10% by weight, of a polyfunctional monomer for internal cross-linking. The acrylic acid derivative as component (b) is a monomer essentially required for achieving polymerization stability in emulsion copolymerization of the acrylic acid fluoroalkyl ester derivative as component (a) and stability of the resulting emulsion. It is required for effective manifestation of these effects that the acrylic acid derivative be present in the monomer mixture in an amount of at least 0.1% by weight. It should be noted, however, that use of this monomer component in excess results, rather, in reduction of polymerization stability and stability of the resulting emulsion. Hence, the upper limit of the acrylic acid derivative is 20% by weight. The polyfunctional monomer for internal crosslinking as component (c) is also a monomer necessary to achieve stable progress of polymerization and to maintain a stable dispersed state of the resulting resin particles as well as to make the resin particles non-swelling. This monomer component must be used in an amount of at least 0.1% by weight in the monomer mixture. Too large an amount of this monomer component unfavorably impairs polymerization stability and stability of the resulting emulsion. For the purpose of further improving polymerization stability in the emulsion copolymerization of the above-described monomer mixture and aqueous dispersion stability of the resin particles, a part of the aforesaid acrylic acid fluoroalkyl ester derivative can be replaced by an acrylic acid alkyl ester derivative represented by formula (III): wherein R⁶ represents a hydrogen atom or a lower alkyl group, and preferably a hydrogen atom or a methyl group; and R⁷ represents an alkyl group having from 1 to 8 carbon atoms. The amount of the above-described monomer component of formula (III) should be not more than 90% by weight based on the mixture of the acrylic acid fluoroalkyl ester derivative (I) and the acrylic acid alkyl ester derivative (III). Amounts exceeding 90% by weight rather deteriorate polymerization stability and also reduce aqueous dispersion stability of the resulting resin particles. A lower limit of the effective amount of the monomer component (III) is not particularly restricted, but is usually 1% by weight based on the mixture of (I) and (III). A preferred amount of the acrylic acid alkyl ester derivative (III) ranges from 10 to 90% by weight on the same basis. Further, the resin emulsion of this invention may additionally contain a vinyl monomer having a sulfonic acid group for the purpose of further improving polymerization stability in emulsion copolymerization for the preparation of the resin emulsion, and improving stability of the resulting emulsion. The vinyl monomer having a sulfonic acid group which can be used in the present invention includes alkylenesulfonic acids or alkali metal salts thereof, e.g., sodium ethylenesulfonate; sulfoalkyl acrylates or alkali metal or ammonium salts thereof represented by formula (IV): wherein R⁸ represents a hydrogen atom or a lower alkyl group, and preferably a hydrogen atom or a methyl group; R⁹ represents an alkylene group having from 1 to 6 carbon atoms, and preferably from 1 to 3 carbon atoms; and M represents a hydrogen atom, an alkali metal, or ammonium, e.g., sulfopropyl (meth)acrylate; styrenesulfonic acid, derivatives thereof or alkali metal or ammonium salts thereof represented by formula (V): wherein R¹⁰ represents a hydrogen atom or a lower alkyl group, and preferably a hydrogen atom or a methyl group; R¹¹ represents a hydrogen atom or a lower alkyl group; and M is as defined above, e.g., sodium styrenesulfonate; 2-acrylamidoalkanesulfonic acids, derivatives thereof or alkali metal or ammonium salts thereof represented by formula (VI): wherein R¹² represents a hydrogen atom or a lower alkyl group, and preferably a hydrogen atom or a methyl group; R¹³ represents an alkylene group having from 1 to 6 carbon atoms, and preferably from 3 to 4 carbon atoms; and M is as defined above, e.g., 2-acrylamido-2-meythlpropanesulfonic acid. The above described vinyl monomer having a sulfonic acid group is desirable for improving polymerization stability in emulsion copolymerization for the preparation of the aqueous resin emulsion of this invention and stability of the resulting emulsion. For effective manifestation of these effects, this monomer component is preferably used in an amount of from 0.001 to 10% by weight based on the total monomer mixture. Too large an amount of this vinyl monomer rather reduces polymerization stability and stability of the resulting emulsion. Furthermore, a part of the aforesaid acrylic acid fluoroalkyl ester derivative of formula (I) may be replaced with a radical copolymerizable vinyl monomer other than the aforesaid acrylic acid derivatives, the vinyl monomers having a sulfonic acid group, or the polyfunctional monomer for internal cross-linking. Such a radical copolymerizable vinyl monomer to be used as a monomer component includes, for example, hydrophobic monomers, homopolymers of which are water-insoluble. Specific examples of such hydrophobic monomers are α-olefins or halogen-substituted α-olefins, e.g., ethylene, propylene, vinyl chloride; alkenylbenzenes, e.g., styrene, methylstyrene, ethylstyrene, vinyltoluene, chlorostyrene; conjugated diolefins, e.g., butadiene, isoprene; (meth)acrylonitrile vinylacetate; and vinyl propionate. Preferred among them are alkenylbenzenes In addition, hydrophilic monomers, homopolymers of which are water-soluble or water-swelling can also be used as the radical copolymerizable vinyl monomer. Specific examples of such hydrophilic vinyl monomers include hydroxyalkyl (meth)acrylates, e.g., hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; (meth)acrylamide;and glycidyl (meth)acrylate. These hydrophilic monomers are particularly effective to introduce a functional group into the resulting resin particles, and are preferably used in combination with the aforesaid hydrophobic vinyl monomers. In the present invention, the acrylic acid fluoroalkyl ester derivative of formula (I) is an essential monomer component in order to maintain stable dispersibility in an aqueous medium also in the cases when a reactive functional group is introduced to emulsion particles or the emulsion is added to a solution containing a high polymeric solute. On the contrary, the above described radical copolymerizable vinyl monomer, when used in a large amount, reduces not only polymerization stability in emulsion copolymerization but also aqueous dispersion stability of the resulting resin particles. Therefore, the acrylic acid fluoroalkyl ester derivatives (I) should be used in an amount of at least 1% by weight based on the total amount of the acrylic acid fluoroalkyl ester derivative (I) and the aforesaid radical copolymerizable vinyl monomer. In other words, the above-described radical copolymerizable vinyl monomer is used in an amount not exceeding 99% by weight, and preferably not exceeding 97% by weight, based on the total weight of the radical copolymerizable vinyl monomer and the acrylic acid fluoroalkyl ester derivative (I), and, of the radical copolymerizable vinyl monomers, the hydrophilic monomer is used in an amount of not more than 30% by weight on the same basis. The lower limit of the radical copolymerizable vinyl monomer is not particularly restricted and is appropriately selected depending on the particular purpose. Usually, the lower limit is 1% by weight based on the mixture of the acrylic acid fluoroalkyl ester derivative (I) and the radical copolymerizable vinyl monomer. In a preferred embodiment of the present invention, a monomer mixture for preparing the aqueous resin emulsion comprises (a) from 60 to 99.8% by weight, and preferably from 70 to 95% by weight, of an acrylic acid fluoroalkyl ester derivative of formula (I), (b) from 0.1 to 20% by weight, and preferably from 1 to 15% by weight, of an acrylic acid derivative of formula (II), and (c) from 0.1 to 20% by weight, and preferably from 1 to 10% by weight, of a polyfunctional monomer for internal cross-linking. The above described monomer mixture may further contain an acrylic acid alkyl ester derivative represented by formula (III) wherein R⁶ and R⁷ are as defined above, up to 90% of the acrylic acid fluoroalkyl ester derivative of formula (I). In another preferred embodiment of the present invention, a monomer mixture for preparing the aqueous resin emulsion comprises (a) from 60 to 99.8% by weight, and preferably at least 65% by weight, of an acrylic acid fluoroalkyl ester derivative of formula (I), (b) from 0.1 to 20% by weight, and preferably from 0.5 to 15% by weight, of an acrylic acid derivative of formula (II), (c) from 0.1 to 20% by weight, and preferably from 0.5 to 15% by weight, of a polyfunctional monomer for internal cross-linking, and (d) from 0.001 to 10% by weight, and preferably from 0.01 to 5% by weight, of a vinyl monomer having a sulfonic acid group. The above described monomer mixture may further contain a radical copolymerizable vinyl monomer other than the components (b), (c) or (d) as a part of the component (a). Though depending on the intended use of the aqueous resin emulsion, the specific kind of each of the above described monomers constituting the monomer mixture can be selected so that the resulting copolymer may have a glass transition point of at least 0°C, and preferably at least room temperature. This is because when the glass transition point of the resin particles is lower than 0°C, the resin particles tend to be easily fused or agglomerated among themselves to thereby reduce dispersion stability. In the present invention, the above-described monomer mixture is emulsion copolymerized in an aqueous medium in the presence of a water-soluble radical polymerization initiator in a usual manner, to thereby obtain an aqueous resin emulsion of a water-insoluble acrylic acid fluoroalkyl ester copolymer. In carrying out the emulsion copolymerization, it is preferred not to use an emulsifying agent because, as described before, if an emulsifying agent is present in the resulting aqueous emulsion in a free state or in a state adsorbed onto the resin particles, various adverse influences are exerted especially upon use of the emulsion. According to the present invention, a monomer mixture having the above-described composition can be stably copolymerized without aid of an emulsifying agent, and the dispersion state of the resulting resin emulsion can be stably maintained. However, as described above, use of an emulsifying agent is not excluded as long as agglomeration or sedimentation of emulsion particles does not occur when the resulting emulsion is dispersed in a buffer solution or physiological saline. An emulsifying agent may indeed be used depending on the particular end use as far as it does not produce any adverse influences. In carrying out emulsion copolymerization to make an emulsion of the invention, a concentration of a monomer mixture in an aqueous medium is related to an average particle size of resin particles of the resulting emulsion, but is usually in the range of from 0.1 to 40% by weight. A polymerization initiator to be used is a water-soluble radical polymerization initiator. Preferred but not limiting examples of such polymerization initiator include persulfates, e.g., potassium persulfate, sodium persulfate, ammonium persulfate; and redox type polymerization initiators composed of the above-described persulfates and thiosulfates, e.g., sodium thiosulfate, potassium thiosulfate, sodium hydrogenthiosulfate, or sulfites, e.g., sodium sulfite, potassium sulfite, sodium hydrogenthiosulfite. These polymerization initiators are preferably used in amounts of from 0.01 to 1% by weight. The atmosphere of polymerization is also not particularly limited, but an oxygen-free inert gas atmosphere is preferably used. The polymerization temperature is not also particularly limited, but usually ranges from 20° to 100°C, and preferably from 40 to 90°C. The resin particles of the aqueous emulsion of the present invention should have an average particle size falling within a range of from 0.03 to 2 µm, preferably from 0.05 to 2 µm, and more preferably from 0.1 to 1 µm. If the resin particle size is too small, it will create a difficulty in recovering the spent emulsion. On the other hand, too large a particle size makes it difficult to maintain a stable dispersion state of the emulsion. The resin particles of the resin emulsion preferably have a specific gravity within a range of from 0.9 to 1.5, and more preferably from 0.9 to 1.3. If the specific gravity is smaller than 0.9, the resin particles are floated on the surface of the emulsion medium to deteriorate the dispersion stability. On the other hand, resin particles having a specific gravity of greater than 1.5 are sedimented in the emulsion medium to readily cause agglomeration. As described above, according to the present invention, emulsion copolymerization of an acrylic acid fluoroalkyl ester derivative can be performed while ensurin polymerization stability without using an emulsifying agent. The copolymer particles thus formed have a narrow and uniform size distribution and are free from swelling or stains. Further, the resulting emulsion retains its stable dispersed state even when dispersed in a buffer solution or physiological saline and, therefore, can advantageously be used in applications requiring dispersion stability of resin particles in an aqueous medium. In particular, since the resin particles in the aqueous resin emulsion according to the present invention contain the acrylic acid fluoroalkyl ester derivative, they can maintain a stable dispersibility in an aqueous medium even when a reactive functional group is introduced to the resin particles or the emulsion is mixed with a solution containing a high polymeric solute. The present invention will now be illustrated in greater detail with reference to the following examples and comparative examples. EXAMPLE 1 Sixty grams of a monomer mixture comprising 91.3 wt% of 2,2,2-trifluoroethyl methacrylate, 5.0 wt% of acrylic acid and 3.7 wt% of triethylene glycol dimethacrylate was added to 330 g of distilled water. To the mixture was added a polymerization initiator aqueous solution comprising 0.3 g of potassium persulfate and 10 ml of water at a temperature of 75°C under a nitrogen stream, followed by stirring at 120 rpm for 7 hours to effect polymerization to a degree of polymerization of 99.7%. There was obtained an aqueous emulsion containing resin particles having an average particle size of 0.36 µm. The polymerization proceeded very stably with no agglomeration. Determination of an agglomerate was carried out by cooling the produced resin emulsion to 30°C, filtering the emulsion using a filter cloth, drying the filter cake left on the filter cloth, and measuring the weight of the cake. COMPARATIVE EXAMPLE 1 A monomer mixture containing an excessive amount of methacrylic acid as shown in Table 1 was emulsion copolymerized in the same manner as described in Example 1. The results obtained are shown in Table 1. EXAMPLE 2 A monomer mixture comprising 18.9 wt% of 1H,1H, 5H-octafluoropentyl methacrylate, 36.2 wt% of methyl acrylate, 36.2 wt% of isobutyl methacrylate, 5.0 wt% of acrylic acid and 3.7 wt% of triethylene glycol dimethacrylate was emulsion copolymerized in the same manner as described in Example 1. The results obtained are shown in Table 1. EXAMPLES 3 TO 8 A monomer mixture having the composition shown in Table 1 was emulsion copolymerized in the same manner as in Example 1. The results obtained are shown in Table 1. COMPARATIVE EXAMPLES 2 TO 4 A monomer mixture containing no acrylic acid or polyfunctional monomer for internal crosslinking as shown in Table 1 was emulsion copolymerized in the same manner as in Example 1. The results obtained are shown in Table 1. COMPARATIVE EXAMPLES 5 AND 6 A monomer mixture containing an excessive amount of a methacrylic ester or a polyfunctional monomer for internal crosslinking as shown in Table 1 was emulsion copolymerized in the same manner as in Example 1. The results obtained are shown in Table 1. COMPARATIVE EXAMPLE 7 A monomer mixture containing styrene as a monomer component as shown in Table 1 was emulsion copolymerized in the same manner as in Example 1. The results obtained are shown in Table 1. In Table 1 below, the abbreviations used for the mononers have the following meanings: The manner of determining the polymerization stability and the dispersion stability are described below. EXAMPLE 9 Sixty grams of a monomer mixture comprising 5.0 wt% of acrylic acid, 0.1 wt% of sodium styrenesulfonate, 10.0 wt% of 1H,1H,5H-octafluoropentyl methacrylate, 40.0 wt% of methyl methacrylate, 40.0 wt% of isobutyl methacrylate and 4.9 wt% of triethylene glycol dimethacrylate was added to 330 g of distilled water. To the mixture was added a polymerization initiator aqueous solution comprising 0.12 g of potassium persulfate and 10 ml of water at a temperature of 75°C under a nitrogen stream, followed by stirring at 120 rpm for 7 hours to effect polymerization to a degree of polymerization of 99.9%. There was obtained an aqueous emulsion containing resin particles having an average particle size of 0.30 µm. The polymerization proceeded very stably with no agglomeration. Determination of an agglomerate was carried out in the same manner as in Example 1. The mono-dispersibility, stability in a high polymer solution, heat stability and modification stability of the resulting emulsion were evaluated by the methods hereinafter described, and the results obtained are shown in Table 3. EXAMPLES 10 TO 18 A monomer mixture having the composition shown in Table 2 was emulsion copolymerized to a degree of polymerization of 95% or more in the same manner as described in Example 9. The properties of the resulting resin aqueous emulsion were determined in the same manner as in Example 9, and the results obtained are shown in Table 3. EXAMPLE 19 A monomer mixture containing no vinyl monomer having a vinyl group as shown in Table 2 was emulsion copolymerized in the same manner as in Example 9 to obtain a resin aqueous emulsion. The properties of the resulting resin aqueous emulsion were determined in the same manner as in Example 9, and the results obtained are shown in Table 3. COMPARATIVE EXAMPLES 8 to 10 A monomer mixture containing no acrylic acid derivative, vinyl monomer having a vinyl group or a monomer for internal crosslinking as shown in Table 2 was emulsion copolymerized in the same manner as in Example 9 to obtain a resin aqueous emulsion. The properties of the resulting resin aqueous emulsion were determined in the same manner as in Example 9, and the results obtained are shown in Table 3. COMPARATIVE EXAMPLES 11 to 13 A monomer mixture containing an excess of an acrylic acid derivative, a vinyl monomer having a sulfonate group or a monomer for internal crosslinking as shown in Table 2 was emulsion copolymerized in the same manner as in Example 9 to obtain a resin aqueous emulsion. The properties of the resulting emulsion were determined in the same manner as in Example 9, and the results obtained are shown in Table 3. Methods for evaluating various properties of the aqueous resin emulsion are as follows. Mono-Dispersibility: Mono-dispersibility was determined in accordance with the following formula: (Standard Deviation)/(Average Particle Size) x 100 (%) Polymerization Stability: Polymerization stability was judged "good" when an agglomerate was observed only in a slight trace amount after completion of the polymerization, or otherwise designated as "agglomeration" (no gelation but agglomeration in an amount more than the trace amount) or "gelation" (agglomeration in an amount more than 90% of solid content). Dispersion Stability: The emulsion was centrifuged, and the solid was washed with distilled water and then redispersed in distilled water. After adjusting to a pH of 7.0 with a 0.001 N sodium hydroxide aqueous solution, 1 ml of the resulting emulsion having a solid content of 5 wt% was dispersed in 10 ml of a 1 M calcium chloride aqueous solution (pH 7.0). The dispersion was judged to have good dispersion stability when the resin particles remained stably dispersed one day after the dispersing, or was judged to have undergone "agglomeration" when agglomeration of resin particles was observed within one day from the dispersing. Stability in High Polymer Solution: One milliliter of the same emulsion having a solid content of 5 wt% and a PH of 8.0 as prepared above was dispersed in 10 ml of a 0.25 wt% polyethyleneimine aqueous solution (pH 8.0). The stability in a high polymer solution was judged "good" when the resin particles remained stably dispersed one day after the dispersing, or designated as "agglomeration" when agglomeration of particles was observed within one day from the dispersing. Heat Stability: One milliliter of the same emulsion having a solid content of 5 wt% and a pH of 8.0 as prepared above was dispersed in 10 ml of a 0.1M tris buffer solution (pH 8.0), and the dispersion was allowed to stand at a temperature of 60°C. The emulsion was judged to have "good" heat stability when the resin particles remained stably dispersed over a period of 1 month or more, or was judged to have undergone "agglomeration" when swelling of resins to agglomeration was observed within one month from the dispersing. Modification Stability: Emulsion particles were aminated using a water-soluble carbodiimide and hexamethylenediamine. The resulting aminated particles were dispersed in a boric acid buffer solution (pH 8.2) containing 0.85% sodium chloride. The modification stability was designated as "good" when the resin particles remained stably dispersed over a period of 1 month or more, or designated as "agglomeration" when agglomeration of particles was observed within one month after the dispersing. In Table 2 below, the abbreviations used in addition to those used in Table 1 have the following meanings:

Claims: An aqueous emulsion of a copolymer which has a particle size of from 0.03 to 2 µm, a specific gravity of 0.9 to 1 .5 and a glass transition temperature of at least 0°C, which is obtained by emulsion copolymerizing in an aqueous medium a monomer mixture comprising: (a) from 60 to 99.8% by weight of an acrylic acid fluoroalkyl ester derivative represented by the general formula: wherein R¹ represents a hydrogen atom or a lower alkyl group R² represents the group (CH₂ ) m or the group , wherein m represents 0 or an integer of from 1 to 12 and x + y is an integer of from 1 to 11, n represents 0 or an integer of from 1 to 12, and R³ represents a hydrogen atom or an acetyl group, and A independently represents a hydrogen atom, a fluorine atom or CF₃; and this ester derivative (I) may be replaced by an amount (a¹) not more than 90% by weight, based on the total of the derivatives (I) and (III), of an acrylic acid alkyl ester derivative of the general formula: wherein R⁶ represents a hydrogen atom or a lower alkyl group and R⁷ represents an alkyl group having from 1 to 8 carbon atoms; and ester derivative (I) may be replaced by an amount (a²) up to 99% by weight, based on the total of the derivative (I) and the following monomer, of a radical copolymerizable vinyl monomer other than the acrylic acid alkyl ester derivative of formula (III), the acrylic acid derivatives represented by formula (II) below, an optional vinyl monomer having a sulfonic acid group (d) or the polyfunctional monomer mentioned at (c) below for the internal cross-linking; (b) from 0.1 to 20% by weight of an acrylic acid derivative represented by the general formula: wherein R⁴ represents a hydrogen atom, a lower alkyl group or a carboxyl group, R⁵ represents a hydrogen atom or a lower alkyl group and -CH₂ COOH when R⁴ represents a hydrogen atom, (c) from 0.1 to 20% by weight of a polyfunctional monomer for internal cross-linking; and optionally (d) from 0.001 to 10% by weight of a vinyl monomer having a sulfonic group. An aqueous emulsion as claimed in Claim 1, wherein the copolymer particle size is from 0.05 to 2µm. An aqueous emulsion as claimed in Claim 2, wherein the particle size is from 0.1 to 1µm. An aqueous emulsion as claimed in Claim 1, 2 or 3, wherein the acrylic acid fluoroalkyl ester derivative represented by formula (I) is represented by one of the formulae: wherein R¹ , m, n and R³ are as defined in Claim 1. An aqueous emulsion as claimed in Claim 4, wherein the acrylic acid fluoroalkyl ester derivative is CH₂=C(CH₃)COOCH₂CF₃, CH₂=C(CH₃)COOCH₂(CF₂)₂H, CH₂=C(CH₃)COOCH₂(CF₂)₄H or CH₂=C(CH₃)COO(CH₂)₂(CF₂)₈F. An aqueous emulsion as claimed in any preceding claim, wherein the monomer mixture contains from 70 to 95% by weight of the acrylic acid fluoroalkyl ester derivative (a). An aqueous emulsion as claimed in any preceding claim, wherein the acrylic acid derivative (b) is acrylic acid, methacrylic acid, itaconic acid or a mixture thereof. An aqueous emulsion as claimed in any preceding claim, wherein the monomer mixture contains from 1 to 15% by weight of the acrylic acid derivative (b). An aqueous emulsion as claimed in any preceding claim, wherein the polyfunctional monomer (c) is a polyacrylate and/or polymethacrylate of an aliphatic polyhydric alcohol. An aqueous emulsion as claimed in any preceding claim, wherein the monomer mixture contains from 1 to 10% by weight of the polyfunctional monomer(c). An aqueous emulsion as claimed in any preceding claim, wherein the acrylic acid fluoroalkyl ester derivative (a) is present in the monomer mixture in an amount of from 60 to 99.8% by weight and 0.001 to 10% by weight of (d) is present. An aqueous emulsion as claimed in Claim 11, wherein the vinyl monomer having a sulfonic acid group is an alkylenesulfonic acid or an alkali metal salt thereof, a sulfoalkyl acrylate or an alkali metal or ammonium salt thereof represented by formula (IV) wherein R⁸ represents a hydrogen atom or a lower alkyl group, R⁹ represents a C1-6 alkylene group, and M represents a hydrogen atom, an alkali metal or ammonium; styrenesulfonic acid, a derivative thereof or an alkali metal or ammonium salt thereof represented by formula (V) wherein R¹⁰ and R¹¹ each represents a hydrogen atom or a lower alkyl group and M represents a hydrogen atom, an alkali metal or ammonium; a 2-acrylamidoalkanesulfonic acid, a derivative thereof, or an alkali metal or ammonium salt thereof represented by formula (VI) wherein R¹² represents a hydrogen atom or a lower alkyl group, R¹³ represents a C1-6 alkylene group, and M represents a hydrogen atom, an alkali metal or ammonium. An aqueous emulsion as claimed in Claim 11 or 12, wherein the monomer mixture contains component (a) in an amount of at least 65% by weight, and component (d) in an amount of from 0.01 to 5% by weight. An aqueous emulsion as claimed in Claim 13, wherein the monomer mixture contains component (b) in an amount of from 0.5 to 15% by weight, and component (c) in an amount of from 0.5 to 15% by weight. An aqueous emulsion as claimed in any preceding claim, wherein said radical copolymerizable vinyl monomer comprises a hydrophobic monomer and up to 30% by weight of a hydrophilic monomer based on a mixture of the acrylic acid fluoroalkyl ester derivative represented by formula (I), hydrophobic vinyl monomer and hydrophilic vinyl monomer.

Inventors: KAWASAKI, TAKASHI, C/O NITTO ELECTRIC IND. CO.LTD., KIHARA, YASUO, C/O NITTO ELECTRIC IND. CO.LTD., MORI, KENJIRO, C/O NITTO ELECTRIC IND. CO.LTD., USHIYAMA, KEIICHI, C/O NITTO ELECTRIC IND. CO.LTD.
Applicants: NITTO DENKO CORPORATION
Application year: 1985
Main classification: C08F220
IPC codes: C08F220, C08F2, C08F20, C08F12