Compositions: coating or plastic – Coating or plastic compositions – Polishes
Reexamination Certificate
2002-03-19
2004-07-20
Turner, Archene (Department: 1775)
Compositions: coating or plastic
Coating or plastic compositions
Polishes
C106S481000, C106S482000, C516S111000, C516S201000, C516S097000, C516S097000, C516S923000
Reexamination Certificate
active
06764539
ABSTRACT:
The present invention relates to an aqueous hardenable composition with high storage stability (sedimentation resistance) containing foliar secondary silica particles and an organic polymer and a process for its production.
The present inventors previously proposed an aqueous hardenable composition containing mutually independent scaly silica particles having a laminated structure, consisting essentially of foliar secondary silica particles, each formed by a parallel face-to-face alignment of a plurality of flaky primary silica particles which are overlaid one on another, and a film-forming organic polymer (for example, Japanese Patent Application JP11-351182).
The secondary silica particles having a laminated structure in the hardenable composition were developed by the present inventors for the first time, and when incorporated in an organic coating in the form of an aqueous emulsion of an organic polymer such as an acrylic resin, an epoxy resin or a urethane resin to give an aqueous hardenable composition, they can impart excellent properties such as water resistance, acid resistance, alkali resistance and weather resistance to the resulting film by virtue of their unique shape and physical properties. In addition, because these particles themselves essentially have an excellent film-forming property, they overlie one on another orientationally in a coating film and therefore can impart a high level of hardness and strong adhesion to the substrate to the coating film.
However, unfortunately, the aqueous hardenable composition containing these foliar secondary silica particles and organic polymer particles sometimes separates during long-term stationary storage in storage vessels, sedimenting the foliar secondary silica particles as a concentrate. Especially, the sedimentation is remarkable when the viscosity of the hardenable composition is low.
The aqueous hardenable composition is useful as a coating composition for outer walls of structures such as buildings and bridges, a floor polish composition for floors of commercial facilities such as supermarkets, department stores and hotels. For commercial use as a coating on outer walls of structures or floors of large commercial facilities as described above, the hardenable composition is usually stored, shipped and supplied in vessels of 100 L to 200 L like metal drums. If the foliar secondary silica particles sediment at the bottom of such a large vessel as a metal drum while it is stored in a warehouse and/or shipped by sea, the vessel has to be shaken again to disperse the particles again. However, it is very tough for painters at the site of coating to shake up or stir up the silica particles in such a vessel to disperse them uniformly in the composition again. After all, such containers as large as metal drums are fairly heavy and can not be handled like containers for household use of several hundreds of milliliters to several liters which are easy to shake in one or two hands.
Thus, there is a strong demand among users of the hardenable composition for high storage stability that keeps the composition in a highly dispersed state during storage and shipping by preventing sedimentation of the foliar secondary silica particles as a concentrate. However, as a matter of fact, it is not easy to impart and realize such storage stability.
Obviously, it is known to those skilled in the art that particles are unlikely to sediment in a slurry when they are pulverized to smaller sizes. However, if the foliar secondary silica particles in the present invention are just mechanically pulverized by force to smaller sizes, the problem that the scaly silica suffers damage to the delicate laminated structure characteristic of the foliar secondary silica particles each composed of a parallel face-to-face alignment of a plurality of flaky primary silica particles arises. With such foliar secondary silica particles having a damaged laminated structure, storage stability may be imparted, but at the expense of part or all of the intrinsic film-forming property which is the most important characteristic. Therefore, the hardenable composition loses much of its advantage.
Even if an aqueous slurry of tertiary agglomerated particles of scaly silica (ternary particles of scaly silica in the form of porous three-dimensional disorderly agglomerates of foliar secondary silica particles, each of which is composed of a parallel face-to-face alignment of a plurality of flaky primary silica particles) is supplied to a wet system pulverizing apparatus (disintegrator) repeatedly by circulating (recycling) the aqueous slurry through the pulverizer as many as ten or twenty times in an attempt to disintegrate the tertiary silica particles into foliar secondary silica particles as disclosed in Japanese Patent Application JP11-351182 and Japanese Patent Application JP2000-206264, the tertiary particles just disintegrate insufficiently to foliar secondary silica particles with particle sizes of about 0.5 &mgr;m at the best (according to laser diffraction/light scattering particle size distribution analysis) which retain their laminated structure. Thus, it has been difficult to completely prevent sedimentation during stationary storage. It is presumed that an aqueous slurry containing foliar secondary silica particles having an average particle size smaller than the above-mentioned value is not likely to be obtained consistently by repetitious feeding into a pulverizer because when the particle size are reduced to a certain level, the disintegrated foliar secondary silica particles start to agglomerate again to avoid further disintegration.
The object of the present invention is to provide an aqueous hardenable composition with high storage stability (sedimentation resistance) containing foliar secondary silica particles and an organic polymer and a process for its production.
Namely, the present invention provides:
(1) A process for producing a hardenable composition with high storage stability containing scaly silica particles which consist essentially of foliar secondary silica particles and have a laminated structure, said process comprising:
(i) a step of subjecting a silica sol, a silica hydrogel or hydrous silicic acid to hydrothermal treatment in the presence of an alkali metal salt to form tertiary agglomerated particles of the scaly silica in the form of porous three-dimensional disorderly agglomerates of foliar secondary silica particles, each secondary particle being formed by a parallel face-to-face alignment of a plurality of flaky primary particles which are overlaid one on another, and
(ii) a step of disintegrating and dispersing the tertiary agglomerated particles of silica in an organic polymer in the form of an aqueous emulsion by a wet method.
(2) A process for producing a hardenable composition with high storage stability containing scaly silica particles which consist essentially of foliar secondary silica particles and have a laminated structure, said process comprising:
(i) a step of subjecting a silica sol, a silica hydrogel or hydrous silicic acid to hydrothermal treatment in the presence of an alkali metal salt to form tertiary agglomerated particles of the scaly silica in the form of porous three-dimensional disorderly agglomerates of foliar secondary silica particles, each secondary particle being formed by a parallel face-to-face alignment of a plurality of flaky primary particles which are overlaid one on another,
(ii) a step of disintegrating and dispersing the tertiary agglomerated particles of silica to foliar secondary silica particles by a wet method, and
(iii) a step of disintegrating and dispersing the foliar secondary silica particles in an organic polymer in the form of an aqueous emulsion by a wet method.
(3) A hardenable composition with high storage stability having scaly silica particles having a laminated structure consisting essentially of foliar secondary silica particles each of which is formed by a parallel face-to-face alignment of a plurality of flaky primary particles which are overlaid one on another, and fine
Fujii Atsunari
Inoue Masaki
Ono Eiichi
Sasaki Takayoshi
Terase Kunihiko
Asahi Glass Company Limited
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Turner Archene
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