Patent Application
20110020648
The present invention relates to hollow polymer particles, and more particularly, to hollow polymer particles having a thin shell wall and high void ratio, colored hollow polymer particles and a simple production process thereof.
Hollow polymer particles are widely used as microcapsules in which various functional substances are contained within the particles. In addition, since these particles have unique light scattering properties attributable to internal pores, they are known to be useful as light scattering agents and light scattering assistants for imparting performance such as luster, opacity or whiteness in fields such as coatings and paints for paper, fibers or leather. Moreover, since the insides of these particles are hollow, they can be expected to demonstrate high bulk, weight reduction and heat insulating effects.
Several processes have been proposed for producing such hollow polymer particles. For example, a process has been proposed for obtaining hollow polymer particles by adding base to latex, containing polymer particles having at least a three-layer structure, comprising a core layer polymer composed of a copolymer of 20 to 60% by mass of a carboxyl group-containing monomer and 80 to 40% by mass of a monomer capable of copolymerizing there with, an intermediate layer polymer composed of a copolymer of 1 to 12% by mass of a carboxyl group-containing monomer and 99 to 88% by mass of a monomer capable of copolymerizing there with, and a surface layer copolymer composed of a polymer of a monomer not containing carboxyl groups, to make the pH of the latex to 8 or more, and adding acid to make the pH of the latex to 7 (see, for example, Patent Document 1).
In addition, a production process of hollow polymer particles is disclosed that uses a dynamic swelling method (see, for example, Patent Document 2). In this production process, by first absorbing a monomer such as divinylbenzene, a water-insoluble organic solvent such as toluene, and a liposoluble polymerization initiator into seed polymer particles such as polystyrene particles in a hydrophilic organic solvent, the seed polymer particles are swollen or dissolved. According to this procedure, the water-insoluble organic solvent dissolves the seed polymer particles, allowing the obtaining of liquid droplets containing a mixture of the seed polymer particles, monomer, water-insoluble organic solvent and liposoluble polymerization initiator. When heated in this state, the monomer in the liquid droplets polymerizes due to the presence of the liposoluble polymerization initiator, a first shell layer is formed composed of a polymer film of the monomer, and seed polymer particles dissolved in the water-insoluble organic solvent are present therein. By drying the particles obtained in this manner, the water-insoluble organic solvent of the core portion volatilizes, and hollow polymer particles are obtained having a second shell layer in which the seed polymer particles are adhered to the inside of a shell layer composed of the polymer film of the monomer.
However, in the process proposed in Patent Document 1, since polymer particles having a structure including at least three layers are produced in advance in order to obtain hollow polymer particles, the process is excessively complex. In addition, since it is also necessary to carry out acid treatment and post-treatment after treating the resulting particles with base, numerous steps and considerable time are required. Moreover, since hollow particles are produced using particles having a three-layer structure, it is difficult to increase the void ratio of the resulting hollow polymer particles.
In the process disclosed in Patent Document 2 as well, seed polymer particles are required as previously described to obtain hollow polymer particles, and since it is necessary to go through a plurality of steps including dispersing the seed polymer particles in a hydrophilic organic solvent followed by swelling the seed polymer particles by a dynamic swelling method and carrying out seed polymerization, numerous steps and considerable time are required. In addition, the void ratio of hollow polymer particles obtained with this process is low since the particles have a second shell layer formed from a seed polymer in the inside wall, the size of the resulting particles is only on the micrometer order, while nanosize particles cannot be obtained.
In this manner, since production processes of hollow polymer particles known in the prior art are typically required to go through a plurality of steps and have poor production efficiency, there are expectations for the development of a simple process. In addition, in terms of the application of hollow polymer particles, there are also expectations for improving the void ratio of hollow polymer particles produced.
Therefore, studies were conducted on a process for allowing the obtaining of hollow particles having a small number of steps, and for example, a process was disclosed by which fine particles are obtained in which a target component is enveloped in the hollow portion of hollow fine particles composed of a shell and hollow portion by adding a solution, in which a target component and polymerization initiator are uniformly dissolved in a monomer component, to water containing a dispersion stabilizer, stirring while heating, and carrying out suspension polymerization (see, for example, Patent Document 3). In this process, solvent-enveloped fine particles can be obtained if a specific organic solvent is used for the target component, and single-layer, hollow polymer fine particles can be obtained by then removing this solvent.
However, in the process proposed in Patent Document 3, although hollow polymer particles can be obtained without going through a plurality of steps, complexity of all steps of the polymerization itself cannot be avoided, such as the use of a dispersion stabilizer to disperse a solution of target component and polymerization initiator uniformly dissolved in a monomer component in water, and the use of a special dispersion method, such as a dispersion method that uses mechanical shear force using a homogenizer or membrane emulsification. In addition, the size of the droplets in the dispersion obtained from the above-mentioned dispersion method is not uniform but rather includes mixture of droplets having various different particle diameters, thus resulting in the problem of multiple dispersion in the particle size distribution of the ultimately obtained hollow polymer particles. Consequently, the obtaining of hollow particles having a uniform particle diameter is premised on improving the pretreatment steps, such as using a special emulsification method that uses porous glass (SPG).
All of the previously described hollow polymer particle production methods are completely unrelated to methods involving the induction of a hollow structure by a spontaneous organization process utilizing, for example, the polymerization activity of a polymerizable monomer molecular structure or physical changes in a growing polymer accompanying monomer polymerization, and obtain hollow particles by increasing the number of steps based on a processing technique. In the production of hollow polymer particles using a radical polymerization system, there are many aspects of this production that still rely on this method, and the development of a production process that conserves on energy and places a small burden on the environment has become a challenging topic.
In addition, a method has also been disclosed for obtaining hollow fine particles by carrying out a radial polymerization reaction at a water/oil interface in a W/O inverted emulsion medium by utilizing the temperature-dependent hydrophilic-hydrophobic changes of poly(N-isopropylacrylamide) (see, for example, Non-Patent Document 1). In this method, an aqueous solution in which N-isopropylacrylamide and tetraethylenepentamine have been dissolved is first emulsified in toluene in which a radical polymerization crosslinking agent in the form of divinylbenzene has been dissolved (oil layer) to form a W/O inverted emulsion. Subsequently, benzoyl peroxide is added to the oil phase to induce an oxidation-reduction reaction between the peroxide and the tetraethylenepentamine dissolved in water droplets at the water/oil interface, and the resulting radicals cause a polymerization reaction of the N-isopropylacrylamide in the water droplets. Since the poly(N-isopropylacrylamide) that grows in the water droplets is a temperature-sensitive polymer, if the reaction temperature is not less than the lower critical solution temperature of poly(N-isopropylacrylamide) (LCST, 32 to 34° C.), the poly(N-isopropylacrylamide) becomes hydrophobic and moves to the water/oil interface rather than the water droplets. At that interface, a copolymerization reaction proceeds with the divinylbenzene crosslinking agent dissolved in a large amount in the oil phase, resulting in the formation of a crosslinked polymer that is insoluble in both water and oil at the water/oil interface.
In the method described in Non-Patent Document 1, although the polymerization process itself allows the obtaining of hollow particles without having to go through a plurality of steps, due to the formation of a W/O inverted emulsion, the use of an emulsifier is required, and since it is also necessary to select a suitable type of emulsifier and amount used along with a suitable emulsification method and the like, it is necessary to carry out complex procedures in all steps. In addition, since a radical polymerization reaction proceeds at the water/oil interface of a W/O inverted emulsion in this method, even if the size of the water droplets is made to be uniform prior to initial polymerization, since the size of the water droplets becomes irregular overall during the entire polymerization process, particle diameter and film thickness of the hollow particles cannot controlled, and as a result, only comparatively large particles having a non-uniform diameter of 1 to 3 μm and having a large shell thickness of 100 nm can be obtained. Moreover, the radical polymerization of this method cannot be carried out at all at the water/oil interface in the absence of a heat-sensitive, water-soluble polymer as indicated by the lower critical solution temperature (LCST), thereby preventing the deployment of this method to a wide range of monomers. In addition, since this method uses a W/O inverted emulsion, the discharge of a large amount of organic solvent in the form of toluene cannot be avoided, thereby placing an extremely large burden on the environment.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H6-248012
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H8-020604
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2003-096108
[Non-Patent Document 1] Q. Sun, et al., Journal of American Chemical Society, Vol. 127, 2005, p. 8274-8275
With the foregoing in view, an object of the present invention is to provide hollow polymer particles and colored hollow polymer particles on the nanometer order having a high void ratio, and a simple and environmentally-friendly production process for producing these particles by using a pseudo-emulsion radical polymerization step without requiring the use of a dispersion stabilizer such as a surfactant or the like.
As a result of conducting extensive studies to solve the aforementioned problems, the inventors of the present invention found that by polymerizing a monomer group including a radial polymerizable water-soluble monomer (A) and a radical polymerizable water-insoluble monomer (B) in an aqueous medium, hollow polymer particles having a hydrophilic surface and high void ratio are formed accompanied by spontaneous formation of a polymer organization during progression of the polymerization reaction, thereby leading to completion of the present invention.
Namely, the present invention provides hollow polymer particles comprise a shell wall having for a main component thereof a copolymer obtained by polymerizing a monomer group (I) including a radical polymerizable water-soluble monomer (A) and a radical polymerizable water-insoluble monomer (B) and having a thickness of the shell wall of 5 to 80 nm, and provides a production process thereof.
In addition, the present invention provides colored hollow polymer particles comprise a shell wall having for main components thereof a copolymer (X), obtained by polymerizing a monomer group (I) including a radical polymerizable water-soluble monomer (A) and a radical polymerizable water-insoluble monomer (B), and a coloring compound (Y), and provides a production process thereof.
According to the present invention, hollow polymer particles can be obtained that have a high void ratio. These hollow polymer particles can be obtained by a simple and easily reproducible process in the form of the production process of the present invention including pseudo-emulsion radical polymerization of a radical polymerizable water-soluble monomer and a radical polymerizable water-insoluble monomer in an aqueous medium using a water-soluble polymerization initiator. Since the resulting hollow polymer particles have monodispersibility, the shell thickness thereof is thin at 5 to 80 nm and the surface thereof is hydrophilic, they exist stably in an aqueous medium. The hollow polymer particles are able to incorporate various functional molecules into the hollow portions thereof either during or after their production, thereby allowing the hollow polymer particles to have various functions based on the incorporated functional molecules. In particular, colored hollow polymer particles can also be obtained by physically bonding (adsorption) or chemically bonding a coloring compound.
Thus, the hollow polymer particles of the present invention can be applied in the fields of aqueous coatings, paints and the like as light scattering improvers and whitening pigments for imparting functions such as luster, opacity or whiteness to paper, fibers, leather and the like by using their unique light scattering properties attributable to internal pores. In addition, the hollow polymer particles of the present invention can also be applied to cosmetics by utilizing the light scattering, moisture absorption and oil absorption properties attributable to their hollow structure, and can also be used as an ink jet receiving layer. In addition, due to their hollow structure, the hollow polymer particles of the present invention can also be applied as heat insulating or soundproofing materials since they are able to inhibit the transmission of heat and sound, and can also be used as weight reduction agents since they are able to reduce weight for an equal volume. Moreover, the hollow polymer particles of the present invention can also be used as chemical substance retention agents containing various chemical substances therein, and can also be used as chemical substance sustained release agents and materials for drug delivery systems (DDS) capable of gradually releasing components contained therein in response to some form of stimulus such as temperature, pressure or pH.
The hollow polymer particle production process of the present invention does not require complex steps extending over a large number of stages, and uses a conventionally employed radical polymerization system, thereby making it possible to provide hollow polymer particles inexpensively for the various applications described above, while also facilitating structural design corresponding to each type of application.
The following provides a detailed explanation of the present invention.
The hollow polymer particles of the present invention use as essential raw materials thereof a radical polymerizable water-soluble monomer (A) and a radical polymerizable water-insoluble monomer (B), have a shell in the form of a polymer layer obtained by copolymerizing this group of monomers (I), and have a thin shell thickness of 5 to 80 nm The thickness of the shell composed of the polymer layer can be controlled to within the range of 5 to 80 nm by adjusting the types and usage proportions of the water-soluble monomer (A) and the water-insoluble monomer (B). Hollow polymer particles having a shell thickness of less than 5 nm or more than 80 nm are undesirable from the viewpoint of industrial application. This is because if the shell thickness is less than 5 nm, the shape stability of the hollow polymer particles becomes poor, while if the shell thickness exceeds 80 nm, the carrier function when loading a substance into the hollow portion of the hollow polymer particles decreases.
Even in the case of ordinary radical polymerization systems, if those properties originating in the characteristics of the monomers used as raw materials, including polymerization activity, physical changes in polymer segments during growth from monomers into polymer, the type of polymerization initiator and the polymerization medium, are effectively utilized, molecular self-assembly can be occur simultaneous to the polymerization reaction, thereby making it amply possible to induce a domain of a polymer organization.
In the present invention, the spontaneous formation of hollow polymer particles was completed by combining an aqueous polymerization initiator with a monomer group (I) including a radical polymerizable water-soluble monomer (A) and a radical polymerizable water-insoluble monomer (B), and radical polymerizing the combination thereof in a completely aqueous medium. Namely, in the case of copolymerizing two types of monomers having different polymerization activities and affinities for an aqueous medium, a phenomenon is utilized by which, instead of random polymerization, a segment of dense monomer unit 1 and a segment of dense monomer unit 2 are formed in the copolymer, and this is then able to function as an amphiphilic polymer.
When copolymerizing monomer group (I) including radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B) in an aqueous medium, the molar concentration of water-soluble monomer (A) is extremely low in comparison with that of water-insoluble monomer (B). If polymerization is carried out using a water-soluble initiator, water-soluble monomer (A) is polymerized preferentially and hydrophilic segments originating in monomer (A) are formed. However, when the hydrophilic segments of the terminal radical grow to a certain size, depletion interaction is strongly induced between droplets of water-insoluble monomer due to factors such as an increase in the degree of polymerization, and a phenomenon occurs in which hydrophilic segments are concentrated on the surfaces of the droplets as they grow. In other words, the periphery of the growing ends of the hydrophilic segments becomes embedded in water-insoluble monomer (B). Thus, an addition reaction of water-insoluble monomer (B) begins at the radical growing ends of the hydrophilic segments, and polymerization of water-insoluble monomer (B) proceeds rapidly. As a result, a copolymer is formed having two segments with mutually contrary properties. A copolymer having hydrophobic segments and hydrophilic segments formed in this manner functions as a so-called polymer surfactant, and during the course of the polymerization reaction, the copolymer spontaneously organizes into bimolecular membrane polymer organized particles (polymer vesicles) in which hydrophobic segments are sandwiched there between. As a result, the majority of the remaining water-insoluble monomer (B) polymerizes while being incorporated into the membrane of the polymer organized particles, ultimately yielding hollow polymer particles having a thin shell wall in which inner and outer surfaces are hydrophilic resembling a polymer vesicle structure. In the present invention, a polymerization process like that described above is defined as pseudo-emulsion polymerization.
Although hollow polymer particles obtained in the manner described above can be produced to have a mean particle diameter of 50 nm to 5 μm corresponding to the objective, hollow polymer particles having a mean particle diameter of 50 nm to 1 μm in particular can be easily produced from the viewpoint of enabling the polymer organization described above to be present in a stable manner due to the use of pseudo-emulsion polymerization for the production process. In addition, since the polymer organization which are spontaneously formed according to the types of water-soluble monomer (A), water-insoluble monomer (B) and water-soluble initiator, and the blending ratios thereof, serve as the base of the hollow polymer particles, the hollow polymer particle size distribution is monodispersed, thereby also capable of producing the hollow polymer particles having the variation coefficient of 0.1 or less.
In addition, the hollow polymer particles of the present invention can be obtained in which the thickness of the shell wall varies according to the particle diameter of the particles. For example, in the case of hollow polymer particles having a mean particle diameter of 50 nm to less than 300 nm, these particles can be produced to have a shell wall thickness of 5 nm to 30 nm, while in the case of hollow polymer particles having a mean particle diameter of 300 nm to less than 1 μm, particles can be produced in which the shell wall thickness is 5 nm to 80 nm. Although this shell wall thickness can be suitably selected to produce hollow polymer particles within the above ranges corresponding to the objective, in order to obtain a high void ratio and allow the shell wall to maintain adequate strength, hollow polymer particles having a mean particle diameter of 50 nm to less than 300 nm more preferably have a shell wall thickness of 5 nm to 15 nm, while hollow polymer particles having a mean particle diameter of 300 nm to less than 1 μm more preferably have a shell wall thickness of 10 to 40 nm. Furthermore, as well as the particle size, hollow polymer particles in which the shell wall thickness is uniform can also be obtained by spontaneous organization accompanying with the polymerization of monomer. Namely, not only the thicknesses of all shell of one particle are uniform, but also the shell thicknesses of all particles obtained under identical conditions are uniform. In the present invention, the mean value resulting from measurement of shell thickness at 30 locations of hollow polymer particles observed by SEM is taken to be the thickness of the shell wall.
Although there are no particular limitations on the radical polymerizable water-soluble monomer (A) used in the present invention, that dissolved at 1.0% by mass or more with respect to distilled water is preferable, while that able to be miscible voluntarily with distilled water is more preferable, and that having, for example, an amido group, amino group, oxyalyklene group, cyano group or acid anhydride group in the structure thereof can be used. For example, water-soluble monomer (A) having a carboxyl group, hydroxy group, sulfonate group or phosphate group and the like, as well as alkaline metal salts or ammonium salts thereof, can be used. More specifically, examples of water-soluble monomers having an amido group include acrylamide, N-substituted (meth)acrylamides or N,N-di-substituted (meth)acrylamides such as N-ethylacrylamide, N-ethylmethacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-n-propylacrylamide, N-n-propylmethacrylamide, N-cyclopropylacrylamide, N-cyclopropylmethacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylaminopropylacrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-isopropylacrylamide or N-methyl-N-n-propylacrylamide, N-hydroxyethylacrylamide, acryloylmorpholine, N-vinylpyrrolidone, diacetoneacrylamide and N,N′-methylenebisacrylamide. Examples of water-soluble monomers having an amino group include allylamine, N,N-dimethylaminoethylacrylate and dimethylamino-ethylmethacrylate. In addition, examples of water-soluble monomers having a carboxyl group include acrylic acid, methacrylic acid and maleic acid, while examples of water-soluble monomers having a hydroxy group include 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropylmethacrylate, 4-hydroxybutylacrylate and 1,4-dicyclohexanedimethanol monoacrylate. Examples of water-soluble monomers having a sulfonate group include styrene sulfonic acid, sodium styrene sulfonate, lithium styrene sulfonate, ammonium styrene sulfonate, styrene sulfonic acid ethyl ester, styrene sulfonic acid cyclohexyl ester and 2-acrylamide-2-methylpropane sulfonate. Moreover, a quaternary monomer may also be used that is obtained by converting to a quaternary form a monomer synthesized by reacting an organic amine with vinylpyridine or glycidyl methacrylate.
Those water-soluble monomers (A) having an amido group, amino group, carboxyl group or salt thereof, or sulfonic acid group or salt thereof in the structure thereof are preferable in terms of being superior in terms of ease of industrial acquisition, water solubility and ease of radical polymerization.
Moreover, N-substituted acrylamides and N,N-di-substituted acrylamides are considered to have surface activating action as a result of having a hydrophobic group and hydrophilic group in a single molecule thereof, and homopolymers thereof have the unique property of the degree of water solubility changing according to the degree of polymerization and temperature of the aqueous medium. As a result of having these properties, the previously described reaction mechanism can be easily achieved thereby facilitating production of the hollow polymer particles of the present invention.
In addition, the unique properties of homopolymers of N-substituted acrylamides and N,N-di-substituted acrylamides of having a lower critical solution temperature (LCST) in an aqueous solution, and causing the occurrence of coil-globule transition in the vicinity of this temperature, namely the polymer chain hydrating and becoming hydrophilic at low temperatures while contracting and becoming hydrophobic at high temperatures, also has an effect on the surface structure of the resulting hollow particle polymers, with the hollow polymer particles having a temperature-responsive layer such that the particle diameter of the hollow polymer particles becomes larger at low temperatures and becomes smaller at high temperatures bordering on the LCST.
The thickness of this temperature-responsive layer in an aqueous medium changes according to the ratio of moles used between radical polymerizable water-insoluble monomer (B) and radical polymerizable water-soluble monomer (A), and also differs according to the particle diameter of the resulting hollow polymer particles. For example, in the case of hollow polymer particles having a mean particle diameter of 50 nm to less than 300 nm, particles can be produced that have a thickness of the temperature-responsive layer of 5 to 100 nm, while in the case of hollow polymer particles having a mean particle diameter of 300 nm to less than 1 μm, particles can be produced in which the thickness of the temperature-responsive layer is 5 to 200 nm.
Although various monomers can be used for the radical polymerizable water-insoluble monomer (B) used in the present invention provided it has a group that is polymerizable with the aforementioned water-soluble monomer (A), the solubility thereof with respect to distilled water is preferably 0.5% by mass or less, and an acrylate or methacrylate is preferable due to its superior reactivity with the water-soluble monomer (A) and its ease of industrial acquisition.
Examples of acrylates include butyl acrylate, lauryl acrylate, cyclohexyl acrylate, phenyl acrylate, isobornyl acrylate, glycidyl acrylate, tert-butyl-α-trifluoromethyl acrylate, 1-adamantyl-α-trifluoromethyl acrylate, (3-methyl-3-oxcetanyl)methyl acrylate, acryloylpropyl trimethoxysilane, acryloylpropyl triethoxysilane, methyl acrylate and ethyl acrylate.
In addition, examples of methacrylates include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, stearyl methacrylate, glycidyl methacrylate, allyl methacrylate, 2,2,2-trifluoroethyl methacrylate, (3-methyl-3-oxcetanyl)methyl methacrylate, methacryloylpropyl trimethoxysilane and methacryloylpropyl triethoxysilane. These radical polymerizable water-insoluble monomers (B) can be used alone or two or more types can be used as a mixture. Unless specifically indicated otherwise, (meth)acrylates used in the following descriptions are used generically referring to acrylates alone, methacrylates alone and mixtures thereof.
Among the radical polymerizable water-insoluble monomers (B) described above, during the course of forming a copolymer or after having formed a copolymer with the previously described radical polymerizable water-soluble monomer (A), those having a cyclic ether structure such as glycidyl (meth)acrylate or oxcetanyl (meth)acrylate can be crosslinked within that copolymer or between molecules thereof, and since this crosslinking reaction is thought to contribute to enhanced strength of the copolymer forming the shell portion of the resulting hollow polymer particles as well as enhanced stability of the hollow polymer particles, such polymerizable water-insoluble monomers can be used particularly preferably.
Bifunctional di(meth)acrylates can also be used alone or as a combination of two or more types for the radical polymerizable water-insoluble monomer (B), examples of which include poly-ethylene di(meth)acrylates such as ethylene di(meth)acrylate, diethylene (meth)acrylate or triethylene di(meth)acrylate, poly-propylene di(meth)acrylates such as propylene di(meth)acrylate, dipropylene di(meth)acrylate or tripropylene di(meth)acrylate, and glycerol di(meth)acrylates. In the case of using these di(meth)acrylates, it is preferable to combine their use with a monofunctional (meth)acrylate previously described for the purpose of preventing aggregation of the resulting hollow particles, and in particular, the usage ratio of (meth)acrylate in the radical polymerizable water-insoluble monomer (B) in terms of a molar ratio is preferably 0.7 or more.
A compound other than a (meth)acrylate, such as a styrene compound, vinyl ester, vinyl ether or bisvinyl compound, can be used alone or as a combination of two or more types for the radical polymerizable water-insoluble monomer (B). At this time, it is preferable to combine their use with a (meth)acrylate in terms of easily obtaining the hollow polymer particles of the present invention, and in particular, the usage ratio of (meth)acrylate in the radical polymerizable water-insoluble monomer (B) in terms of a molar ratio is preferably 0.5 or more.
The aforementioned styrene compound is a compound having a styryl group, examples of which include styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene, o-, m- and p-chlorostyrene, p-ethylstyrene, p-tert-butoxystyrene, m-tert-butoxystyrene, p-acetoxystyrene, p-(1-ethoxyethoxy) styrene, p-methoxystyrene, styryltrimethoxysilane, styryltriethoxysilane, vinylnaphthalene, vinylbiphenyl, vinylanthracene and vinylpyrene.
Examples of the vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl monochloroacetate, vinyl pivalate and vinyl butyrate.
Examples of the vinyl ethers include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, allyl vinyl ether, cyclohexane dimethanol vinyl ether, 1,4-butanediol divinyl ether, nonanediol divinyl ether, cyclohexanediol divinyl ether, cyclohexane dimethanol divinyl ether, trimethylpropane trivinyl ether, pentaerythritol tetravinyl ether and phenyl vinyl ether.
Examples of the bisvinyl compounds include divinylbenzene, and these are preferably from the viewpoint of allowing the production of stable hollow particles due to the formation of a crosslinked structure within the shell of the hollow polymer particles.
Although the usage ratio between the radical polymerizable water-insoluble monomer (B) and the radical polymerizable water-soluble monomer (A) is selected according to mean particle diameter of the target hollow polymer particles, the thickness of the shell wall and the like, from the viewpoint of obtaining hollow polymer particles capable of stably existing in an aqueous medium and the stability of the hollow structure, the molar ratio of (B)/(A) of the radical polymerizable water-insoluble monomer (B) to the radical polymerizable water-soluble monomer (A) is preferably 3.5 to 12, and particularly preferably 3.5 to 10. Furthermore, in the production process of the present invention to be described later, when controlling the mean particle diameter of the hollow polymer particles or the thickness of the shell wall by adding the radical polymerizable water-insoluble monomer (B) after the polymerization has progressed and the hollow polymer particles have been formed to a certain extent instead of adding monomer group (I) all at once, stable hollow polymer particles can be obtained even if the above molar ratio exceeds 12.
The colored hollow polymer particles of the present invention are obtained by combining a coloring compound with the aforementioned hollow polymer particles, and are composed of a shell wall having for main components thereof a copolymer (X), obtained by polymerizing a monomer group (I) containing a radical polymerizable water-soluble monomer (A) and a radical polymerizable water-insoluble monomer (B), and a coloring compound (Y).
The radical polymerizable water-soluble monomer (A) and the radical polymerizable water-insoluble monomer (B) able to be used here are the same as those previously described, and preferable examples of those monomers are also the same.
Examples of the coloring compound (Y) that can be used include compounds having optical absorption in the visible light range (400 to 800 nm) as well as photochromic compounds having optical absorption in the visible light range as a result of a molecular structure change due to absorption of ultraviolet light, and compounds having photoemission in the visible light range.
In the colored hollow polymer particles of the present invention, the copolymer (X), obtained by polymerizing monomer group (I) containing radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B), and the coloring compound (Y) may be physically bonded or chemically bonded. Moreover, the coloring compound (Y) may be present as a single type or a plurality of types may simultaneously be present. In this case, those that are physically bonded and those that are chemically bonded may be present simultaneously.
Colored hollow polymer particles in which the copolymer (X) and the coloring compound (Y) are physically bonded refer to, for example, those in which copolymer (X) is contained within coloring compound (Y) in hollow polymer particles having a shell mainly composed of copolymer (X) by carrying out radical polymerization in the presence of the coloring compound (Y) in the production process of colored hollow polymer particles to be described later, followed by adsorbing onto the inner surface of the shell wall by removing the aqueous medium by drying and the like, or those in which coloring compound (Y), which has been dissolved in an aqueous medium, is adsorbed onto the surface of the hollow polymer particles in an aqueous medium removal step.
In addition, colored hollow polymer particles in which copolymer (X) and coloring compound (Y) are physically bonded include those in which the coloring compound (Y) having low water solubility is dissolved in radical polymerizable water-insoluble monomer (B) followed by carrying out radical polymerization to disperse the coloring compound (Y) within the shell of hollow polymer particles mainly composed of copolymer (X) in the production process of colored hollow polymer particles to be described later.
In addition, colored hollow polymer particles in which copolymer (X) and coloring compound (Y) are chemically bonded refer to, for example, those having a structure originating in coloring compound (Y) for the shell portion that composes the hollow polymer particles by combining the use of reactive groups present in the copolymer (X) with coloring compound (Y) having groups capable of chemically bonding therewith followed by chemical reaction of those groups. In this case, since coloring compound (Y) is present within the shell of the hollow polymer particles as a result of chemical bonding, stable colored hollow polymer particles can be obtained.
A water-soluble pigment or oil-soluble pigment and the like can be used for the coloring compound (Y) used in the present invention. There are no particular limitations on the water-soluble dye provided it is a dye that is soluble in an aqueous medium used in the production of the hollow polymer particles of the present invention to be described later, and various naturally-occurring and organically synthesized dyes can be used. Examples of such dyes that can be used include azo dye, anthraquinone dye, indigo dye, sulfide dye, diphenylmethane dye, triphenylmethane dye, acridine dye, xanthene dye, azine dye, oxazine dye, thiazine dye, azomethine dye, nitro dye, nitroso dye, thiazole dye, methine dye, polymethine dye, cyanine dye, porphyrin and phthalocyanine dye. In addition, compounds in the form of aqueous solutions by converting to sulfonic acid or sulfonic acid salt such as naphthalene sulfonic acid, sodium naphthalene sulfonate or sodium pyrene sulfonate can also be used preferably. These water-soluble dyes can be used alone or two or more types can be used in combination.
There are no particular limitations on the oil-soluble dye provided it is an oil-soluble dye that dissolves in the radical polymerizable water-insoluble monomer (B), and examples of such dyes that can be used include condensed polycyclic dyes such as monoazo-based, disazo-based, anthraquinone-based, perylene-based, quinophthalone-based or anthrapyridone-based dyes. Moreover, condensed polycyclic aromatic compounds and derivative molecules thereof, such as naphthalene, anthracene, tetracene, pentacene, phenanthrene, glycene, chrysene, triphenylene or pyrene, oligophenylenes and derivative molecules thereof such as biphenyl or terphenyl, and photochromic dyes in the form of azobenzene, spiropyrane, spirooxazine, fulgide and diarylethene can also be used preferably. These oil-soluble dyes can be used alone or two or more types can be used in combination.
The thickness of the shell wall of the colored hollow polymer particles of the present invention is preferably 5 to 80 nm. If the thickness is within this range, the resulting colored hollow polymer particles are stable in water and have a wide application range in the same manner as the previously described hollow polymer particles. In addition, the colored hollow polymer particles can also be used preferably even in the case of mixing with the aforementioned hollow polymer particles.
The hollow polymer particles and colored hollow polymer particles of the present invention can be easily obtained by emulsion polymerizing the monomer group (I) containing the radical polymerizable water-soluble monomer (A) and the radical polymerizable water-insoluble monomer (B) in an aqueous medium.
The following provides a detailed description of the production process of the present invention.
The production process of the present invention enables one-pot production of hollow polymer particles, or in other words, enables the production of hollow polymer particles in the same reaction vessel without requiring an isolation procedure, and includes pseudo-emulsion radical polymerization of the radical polymerizable water-soluble monomer (A) and the radical polymerizable water-insoluble monomer (B) in an aqueous medium using a water-soluble polymerization initiator.
Examples of aqueous media used for the pseudo-emulsion polymerization other than when using water alone include water and a lower alcohol such as methanol, ethanol or isopropanol, water and a polyvalent alcohol such as ethylene glycol, propylene glycol, butanediol, diethylene glycol or triethylene glycol, water and a ketone such as acetone or methyl ethyl ketone, and water and an ether such as tetrahydrofuran, either used alone or in the form of a mixed solvent including a mixture of a plurality of types thereof.
Although the blending ratio when using a mixed solvent can be suitably selected according to the purpose so that a water-soluble polymerization initiator described below and the radical polymerizable water-soluble monomer (A) are soluble, and the solubility of the radical polymerizable water-insoluble monomer (B) is within the range of 0.5% by mass or less, the ratio of water is preferably 50% by mass or more and particularly preferably 80% by mass or more to allow the water-soluble polymerization initiator to maintain a high efficiency of polymerization initiation.
Although there are no particular limitations on the water-soluble polymerization initiator and various such initiators can be used, persulfates or amino group-containing azo compounds are used preferably, examples of which include potassium persulfate (KPS), ammonium persulfate (APS), 2,2′-azobis(2-amidinopropane) dihydrochloride, 2,2′-azobis [2-(imidazolin-2-yl)propane]dihydrochloride, 2,2′-azobis [2-(2-imidazolin-2-yl)propane]dihydrochloride dihydrate, 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamide]dihydrochloride, 2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, 2,2′-azobis [2-(2-imidazolin-2-yl)propionamide], 2,2′--azobis[-methyl-N-(2-hydroxyethyl)propionamide], 2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide} and 2,2′-azobis(2-methylbutaneamidooxime)dihydrochloride tetrahydrate.
Although the ratio at which these water-soluble polymerization initiators are used may be suitably selected within a range of 0.1 to 5 parts by mass based on 100 parts by mass of the total amount of radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B), the ratio is more preferably selected within a range of 0.5 to 3 parts by mass for the purpose of increasing the efficiency of the polymerization reaction and inhibiting aggregation of the hollow polymer particles.
Although the target hollow polymer particles can be produced without using any surfactant or other dispersion stabilizer in the production of the hollow polymer particles of the present invention, various types of suitable dispersion stabilizers may be used as necessary. Although examples of dispersion stabilizers include anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants and organic suspension protective agents, the use of an anionic surfactant or cationic surfactant is particularly preferable since this allows the hollow polymer particles to be obtained efficiently.
Examples of anionic surfactants include rosinates such as potassium rosinate or sodium rosinate, sodium salts or potassium salts of fatty acids such as potassium oleate, potassium laurate, sodium laurate, sodium stearate or potassium stearate, sulfuric acid esters of aliphatic alcohols such as sodium lauryl sulfate, and alkylallyl sulfonates such as sodium dodecylbenzene sulfonate.
Examples of nonionic surfactants include alkyl esters, alkyl ethers and alkylphenyl ethers of polyethylene glycol.
Examples of cationic surfactants include alkyltrimethyl ammonium salt-based, dialkyldimethyl ammonium salt-based, alkyldimethylbenzyl ammonium salt-based and amine salt-based surfactants.
Examples of amphoteric surfactants include alkylamino fatty acid salts, alkylbetaines and alkyl amine oxides.
These dispersion stabilizers can be used alone or as a combination of two or more types as necessary. When using a dispersion stabilizer, an ionic surfactant or nonionic surfactant having a charge equal to the surface charge imparted to the hollow polymer particles by the water-soluble polymerization initiator is preferably used to prevent aggregation of the resulting hollow polymer particles.
Although the amount of dispersion stabilizer used may be suitably selected as necessary, if the concentration thereof in the initial stage of the reaction is excessively high, ordinary emulsion polymerization proceeds. Since this makes it difficult for the particles to have a hollow structure, the amount used is reduced during the initial stage and then added later accompanying formation of the particles.
In the production process of the present invention, although the reaction temperature of polymerization may be suitably set within a range of 35 to 90° C. in coordination with the polymerization initiation temperature of the water-soluble polymerization initiator used, the temperature is preferably set to a range of 40 to 85° C. and more preferably 60 to 80° C. from the viewpoint of increasing the initiation ability of the water-soluble polymerization initiator and inhibiting destabilization of the reaction system by preventing evaporation of the aqueous medium.
In the production process of the present invention, since the synthesis efficiency of the hollow polymer particles becomes poor if the concentration of the monomers during polymerization is excessively low, while aggregation occurs easily if excessively high, the monomer concentrations are preferably suitably selected within the range of 0.5 to 20% by mass according to the purpose, and preferably selected within the range of 1 to 10% by mass from the viewpoint of allowing hollow polymer particles of higher stability to be obtained more efficiently.
A one-pot radical polymerization production process of the prior art can be employed for the production process of the present invention, including carrying out polymerization using a water-soluble polymerization initiator in the state in which the entire amounts of the radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B) have been added to an aqueous medium in advance.
In addition, hollow polymer particles can also be synthesized in a one-pot production process by carrying out polymerization using a water-soluble polymerization initiator in the state in which the radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B) have been added in advance to an aqueous medium, and the further adding radical polymerizable water-insoluble monomer (B) once the polymerization reaction has progressed. In the case of using this post-addition method, the thickness of the shell walls of the hollow structure can be increased.
In addition, in the production process of these hollow polymer particles, colored hollow polymer particles of the present invention can be obtained by carrying out emulsion polymerization of a monomer group (I) containing radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B) using a water-soluble polymerization initiator in the state in which a coloring compound (Y) having high water solubility is dissolved in an aqueous medium.
In addition, colored hollow polymer particles of the present invention can also be obtained by carrying out polymerization of monomer group (I) containing radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B) using a water-soluble polymerization initiator after having first dissolved a coloring compound (Y) having low water solubility in the radical polymerizable water-insoluble monomer (B).
In these processes, although the amount of the coloring compound (Y) used may be suitably set within an arbitrary range according to the purpose provided it does not impair the progression of polymerization, the amount of coloring compound (Y) used in terms of the molar ratio based on monomer group (I) containing radical polymerizable water-soluble monomer (A) and radical polymerizable water-insoluble monomer (B) is preferably 3 mol % or less and particularly preferably 1 mol % or less.
In addition, colored hollow polymer particles can also be obtained by adding a coloring compound (Y) following production of hollow polymer particles. The amount of the coloring compound (Y) used at this time is such that the coloring compound (Y) can be used at an arbitrary ratio according to the purpose within a range that does not cause aggregation of the resulting hollow polymer particles. In the case of using an ionic coloring compound in particular, it is preferable to use that having a charge opposite that of the surface charge of the hollow polymer particles, namely a change attributable to functional groups contained in the water-soluble monomer (A) used as a raw material.
In addition, examples of methods for chemically bonding the copolymer (X) and coloring compound (Y) composing the shell of the colored hollow polymer particles include a method in which polymerization is carried out in combination with a radical polymerizable coloring compound, a method in which radical polymerizable functional groups are introduced in a coloring compound having reactive functional groups followed by polymerizing in combination with the resulting compound (Y′), and a method in which a coloring compound is chemically reacted with reactive groups in a copolymer composing hollow polymer particles after obtaining the hollow polymer particles.
Among these methods, the method in which a radical polymerizable coloring compound (Y′) is obtained by introducing radical polymerizable functional groups into a coloring compound having reactive functional groups is preferable in terms of general-purpose applicability and bonding reliability. Specific examples of this method include a method in which a coloring compound having an amino group, such as 7-amino-4-methyl coumarin, 7-amino-4-trifluoromethyl coumarin, aminofluorescein, aminonaphthalene, aminoanthracene, aminopyrene or aminobiphenyl, is reacted with a glycidyl (meth)acrylate or (meth)acrylic acid chloride and the like, and a method in which a coloring compound having a hydroxyl group, such as 7-hydroxy-4-methyl coumarin, 6-hydroxy-4-methyl coumarin, fluorescein, hydroxymethyl biphenyl or 2-(hydroxymethylanthracene) is reacted with (meth)acrylic acid chloride and the like.
A structure derived from a coloring compound can be introduced into the shell wall composing the hollow polymer particles by emulsion polymerization using the radical polymerizable coloring compound (Y′) obtained in the manner described above, the water-soluble monomer (A) and the water-insoluble monomer (B) according to a method as described above, thereby allowing the obtaining of colored hollow polymer particles. The water-soluble monomer (A) and water-insoluble monomer (B) used at this time may be the same or different from those reacted with the coloring compound. In addition, in the case the resulting radical polymerizable coloring compound (Y′) is water-soluble, the entire amount of the water-soluble monomer (A) used to obtain hollow polymer particles may be replaced with the radical polymerizable coloring compound (Y′). Moreover, in the case the radical polymerizable coloring compound (Y′) is water-insoluble, the entire amount of water-insoluble monomer (B) used to obtain hollow polymer particles may be replaced with the radical polymerizable coloring compound (Y′).
There are no particular limitations on the method by which the hollow polymer particles and colored hollow polymer particles obtained in the present invention are used, and they can be used as, for example, in the field of aqueous coatings and paints as light scattering improvers, white pigments or concealers and the like for imparting performance such as luster, opacity and whiteness to paper, fibers and leather. In addition, these hollow polymer particles can also be used as rewritable materials, anti-counterfeiting coatings or special applications paper by utilizing marking effects, coloring or decoloring effects and optical emission characteristics attributable to coloring components present in colored hollow polymer particles. Moreover, these hollow polymer particles can also be applied to cosmetics by utilizing the light scattering, moisture absorption and oil absorption properties attributable to their hollow structure, and can also be used as an ink jet receiving layer. In addition, due to their hollow structure, these hollow polymer particles can also be applied as heat insulating or soundproofing materials since they are able to inhibit the transmission of heat and sound, and can also be used as weight reduction agents since they are able to reduce weight for an equal volume. Moreover, these hollow polymer particles can also be used as chemical substance retention agents capable of containing various chemical substances therein, and can also be used as chemical substance sustained release agents and materials for drug delivery systems (DDS). In addition, hollow polymer particles containing a coloring component can be used as labeled, highly functional drug carriers and affinity beads. In using in applications such as these, the monodispersibility and thin shell walls of the hollow polymer particles of the present invention are considered to be effective in allowing the hollow polymer particles to efficiently and uniformly demonstrate various types of performance required by those applications, thereby giving them a high degree of usefulness.
Although the following examples and comparative examples are indicated for providing a more detailed explanation of the present invention, the present invention is naturally not limited in any way by these explanations.
The particle diameters of particles dispersed in water were measured according to a dynamic light scattering method using the FPAR-1000 particle size measuring system manufactured by Otsuka Electronics Co., Ltd.
The shape and hollowness of fine particles were confirmed by SEM observation using the VE-9800 three-dimensional real surface view microscope manufactured by Keyence Corp., and the thickness of the shells of hollow polymer particles was measured using SEM micrographs obtained with the S-800 field-emission scanning electron microscope manufactured by Hitachi, Ltd.
(Synthesis of Hollow Polymer Particles)
<Synthesis of Hollow Polymer Particles Composed of a Poly (NIPAM-co-GMA) Copolymer of N-Isopropylacrylamide (NIPAM) and Glycidyl Methacrylate (GMA)>
8.52 g of glycidyl methacrylate (Wako Pure Chemical Industries Ltd.) were added to 200 ml of an aqueous solution in which was dissolved 1.4 g of N-isopropylacrylamide (Kohjin Co., Ltd., abbreviated as NIPAM) followed by heating to 70° C. while stirring under nitrogen atmosphere. 20 ml of an aqueous solution in which was dissolved 0.1 g of potassium persulfate (KPS, Wako Pure Chemical Industries, Ltd.) were added to this mixture (GMA/NIPAM=4.8 mol/mol). A particle dispersion was obtained by stirring for 1 hour at the same temperature. This dispersion was then washed and purified by centrifugal separation. Identification of the purified particles was carried out by dynamic light scattering, SEM and 1H-NMR. When the particle diameter of the particles was measured by dynamic light scattering, a mono-dispersed particle size distribution was demonstrated (
<Synthesis of Hollow Polymer Particles Composed of Copolymers of Various Water-Soluble Monomers and Water-Insoluble Monomers>
Hollow polymer particles were obtained in the same manner as Example 1 with the exception of changing types and amounts of water-soluble monomer (A), water-insoluble monomer (B), water-soluble polymerization initiator and aqueous solution used in Example 1 to the substances and values shown in Table 1. The physical property values of the resulting polymers are summarized in Table 2. Furthermore, a surfactant in the form of sodium lauryl sulfate was used in Example 6, and was used by adding a prescribed amount to an aqueous solution of NIPAM and uniformly stirring.
<Synthesis of Poly(NIPAM-co-GMA) Hollow Polymer Particles by Two-Stage Addition of Water-Insoluble Monomer>
4.5 g of GMA were added to 200 ml of an aqueous solution in which was dissolved 0.7 g of NIPAM followed by heating to 70° C. while stirring under nitrogen atmosphere (GNA/NIPAM=5.1 mol/mol). 20 ml of an aqueous solution in which was dissolved 0.05 g of KPS were then added to this mixture. After stirring for 1 hour at the same temperature, 2.2 g of GMA were added (total GMA/NIPAM=7.6 mol/mol) followed by stirring for 1 hour at the same temperature to obtain a particle dispersion. After washing this dispersion by centrifugal separation, measurement of the particle diameter of the particles by dynamic light scattering revealed a mono-dispersed particle size distribution, and the mean particle diameter at 25° C. was 380 nm with a coefficient of variation of 0.03. Observation of the shape of these particles revealed mono-dispersed spherical particles. When the shape of the particles was observed after crushing the particles, the polymers were confirmed to be hollow polymer particles having a hollow center (
<Synthesis of Various Types of Hollow Polymer Particles by Two-Stage Addition of a Water-Insoluble Monomer>
Hollow polymer particles were obtained in the same manner as Example 27 with the exception of changing the types and amounts of the water-soluble monomer (A), water-insoluble monomer (B), polymerization initiator and aqueous solution used in Example 27 to each of the substances and values shown in Table 3. The physical property values of the resulting particles are summarized in Table 4.
(Synthesis of Colored Hollow Particles)
<Synthesis of Colored Hollow Polymer Particles Containing Rhodamine B>
1.4 g of NIPAM and 8.84 g of GMA were added to 200 ml of an aqueous solution containing 5 mg of rhodamine B (Wako Pure Chemical Industries, Ltd.) followed by heating to 70° C. while stirring under nitrogen atmosphere. 20 ml of an aqueous solution in which was dissolved 0.1 g of KPS were then added to this mixture (GMA/NIPAM=5.0 mol/mol, pigment/polymerizable monomer=1.3×10 mol/mol) followed by stirring for 1 hour at this temperature to obtain a particle dispersion. After washing this dispersion by centrifugal separation, measurement of the particle diameter of the particles by dynamic light scattering revealed a mean particle diameter at 25° C. of 670 nm. The mean particle diameter at 50° C. was 600 nm and the particles had a temperature-responsive layer of about 35 nm When the shape of these particles was observed after crushing, the particles were confirmed to be hollow polymer particles having a hollow center (
<Synthesis of Colored Hollow Polymer Particles Containing Pyrene>
A mixture of 13.1 mg of pyrene (Tokyo Chemical Industry Co., Ltd.) and 0.89 g of GMA was added to 20 ml of an aqueous solution containing 0.14 g of NIPAM followed by heating to 70° C. while stirring under nitrogen atmosphere. 10 mg of AIBA were added to this mixture (GMA/NIPAM=5.0 mol/mol, pigment/polymerizable monomer=8.6×10−3 mol/mol) followed by stirring for 1 hour at this temperature to obtain a dispersion of particles having a mean particle diameter of 380 nm and coefficient of variation of 0.06. After washing this dispersion by centrifugal separation and observing the shape of the fine particles after crushing, the particles were confirmed to be hollow polymer particles having a hollow center (
<Synthesis of Colored Hollow Polymer Particles Containing Spironaphthoxazine>
A mixture of 11.6 mg of spironaphthoxazine (SP-99, Nippon Kanko Shikiso Kenkyusho Co., Ltd.) and 0.87 g of GMA was added to 20 ml of an aqueous solution containing 0.14 g of NIPAM followed by heating to 70° C. while stirring under nitrogen atmosphere. 11 mg of AIBA were added to this mixture (GMA/NIPAM=4.8 mol/mol, pigment/polymerizable monomer=4.7×10−3 mol/mol) followed by stirring for 1.5 hours at the same temperature to obtain a dispersion of particles having a mean particle diameter of 280 nm and coefficient of variation of 0.05. When the shape of the fine particles was observed after crushing, the particles were confirmed to be hollow polymer particles having a hollow center, and the thickness of the shell wall of the particles was 10 nm. The resulting white hollow polymer particles turned blue when irradiated with ultraviolet light from a mercury lamp. The fine particles returned to a white color when blocked from the ultraviolet light, thereby confirming that these hollow polymer particles exhibit photochromic properties.
<Synthesis of Colored Hollow Polymer Particles Containing Aminopyrene Residues>
A mixture containing 0.013 g of a GMA derivative bound to aminopyrene and 0.87 g of GMA was added to 20 ml of an aqueous solution containing 0.14 g of NIPAM followed by heating to 70° C. while stirring in a nitrogen atmosphere. 11 mg of KPS were added to this mixture (GMA/NIPAM=5.0 mol/mol, radical polymerizable coloring compound/polymerizable monomer=6.0×10−3 mol/mol) followed by stirring for 1 hour at the same temperature to obtain a dispersion of particles having a mean particle diameter of 250 nm and coefficient of variation of 0.03. When the dispersion was washed by centrifugal separation, a white dispersion of fine particles was obtained, and this dispersion showed blue fluorescence emission when irradiated with ultraviolet light. When the shape of the fine particles after crushing was observed, the particles were confirmed to be hollow polymer particles having a hollow center, and the thickness of the shell wall was 10 nm.
The hollow polymer particles of the present invention can be applied in the fields of aqueous coatings, paints and the like as light scattering improvers and whitening pigments for imparting functions such as luster, opacity or whiteness to paper, fibers, leather and the like by utilizing the characteristic light scattering properties attributable to their internal pores. In addition, the hollow polymer particles of the present invention can also be applied to cosmetics by utilizing the light scattering, moisture absorption and oil absorption properties attributable to their hollow structure, and can also be used as an ink jet receiving layer. In addition, due to their hollow structure, the hollow polymer particles of the present invention can also be applied as heat insulating or soundproofing materials since they are able to inhibit the transmission of heat and sound, and can also be used as weight reduction agents since they are able to reduce weight for an equal volume. Moreover, the hollow polymer particles of the present invention can also be used as chemical substance retention agents capable of containing various chemical substances therein, and can also be used as chemical substance sustained release agents and materials for drug delivery systems (DDS) capable of gradually releasing components contained therein in response to some form of stimulus such as temperature, pressure or pH.
In addition, the hollow polymer particle production process of the present invention does not require complex steps extending over a large number of stages, and uses a conventionally employed radical polymerization system, thereby making it possible to provide hollow polymer particles inexpensively for the various applications described above, while also facilitating structural design corresponding to each type of application, thereby resulting in superior industrial usefulness.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-090764 | Mar 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/056884 | 3/29/2007 | WO | 00 | 10/13/2010 |
