Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2002-04-03
2004-01-13
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C106S014150, C106S287340, C252S194000, C252S389300, C516S086000
Reexamination Certificate
active
06677389
ABSTRACT:
The present invention relates to a novel cationized silica dispersion prepared by dispersing dry processed silica and a cationic resin in a polar solvent. Specifically, the present invention relates to a cationized silica dispersion useful for producing a coating composition for providing a gas barrier property, a corrosion resistance, a hydrophilic property, a glossiness and a liquid absorbing property. More specifically, the present invention relates to a cationized silica dispersion which inhibits coagulated matters from being produced when mixed with a water soluble resin as a binder in order to produce a coating composition to make it possible to stably produce the coating composition.
A dispersion prepared by dispersing silica in a polar solvent has so far been known as a coating composition useful for providing a coated article with a gas barrier property, a corrosion property and other characteristics. For example, a gas barriering film comprising silica and a polyvinyl alcohol base polymer is proposed in Japanese Patent Application Laid-Open No. 233478/2000.
Further, a gas barrier coating agent comprising a water soluble high polymer and dry processed silica is proposed in Japanese Patent Application Laid-Open No. 192675/1999 as a coating composition useful for obtaining a smooth and highly transparent coating film. However, involved therein is the problem that when above dry processed silica is present in a dispersion in a high concentration, dispersion stability of silica is reduced, and a coating composition produced using such dispersion is difficult to form a coating layer which can provide a prescribed effect.
A dry processed silica dispersion having a high dispersion stability obtained by blending alkali such as sodium hydroxide with a dispersion in which dry processed silica is dispersed to a high degree is proposed in Japanese Patent Application Laid-Open No. 142827/1997 as a dispersion capable of solving the problem described above.
Further, various cationized silica dispersions having an improved dispersion stability obtained by treating dry processed silica dispersions with cationic resins having a cationic group such as a quaternary ammonium salt group.
In producing a coating composition, a water soluble resin such as cellulose derivatives, polyvinyl alcohol, polyvinyl alcohol derivatives, polyalcohols, starches or vinyl base copolymers is usually blended as a binder for providing the coating composition with a coating function. However, when a cationized silica dispersion obtained using dry processed silica as silica is mixed with these binders to produce a coating composition, caused is a phenomenon in which coagulated matters are produced in the resulting coating composition. In particular, in the cases of a cationized silica dispersion obtained using dry processed silica having a high specific surface area and/or a cationized silica dispersion in which dry processed silica is dispersed to a high degree, such coagulated matters as described above have tended to be produced in a large amount. If such coagulated matters are produced, the coating composition is notably reduced in transparency and stability, and this brings about the disadvantage that the product value of a coating layer formed from the above coating composition is markedly damaged. In addition thereto, such coating composition is not fixed in various physical properties and exerts an adverse effect on the coating conditions thereof, so that it is difficult to stably form a coating layer having fixed characteristics.
Accordingly, an object of the present invention is to provide a cationized silica dispersion which is less liable to produce coagulated matters in producing a coating composition by blending with a binder and which can produce a coating composition having a high transparency with good reproducibility, that is, a dispersion prepared by dispersing dry processed silica and a cationic resin in a polar solvent.
Intensive investigations repeated by the present inventors in order to achieve the object described above have resulted in obtaining the knowledges that when using dry processed silica as a silica source for a silica dispersion, obtained is a cationized silica dispersion having a very high concentration of silicic acid (hereinafter referred to merely as dissolved silicic acid) which is dissolved in the form of a silicic acid polymer and low molecular weight polysilicic acid as compared with a case where so-called wet processed silica such as precipitated silica, silica gel and colloidal silica and that when such cationized silica dispersion having a high concentration of dissolved silicic acid is used to produce a coating composition, coagulated matters are liable to be produced in the above coating composition.
Intensive investigations further repeated by the present inventors based on such knowledges have resulted in finding that a reduction in a concentration of dissolved silicic acid contained in the above cationized silica dispersion to a specific value makes it possible to obtain a cationized silica dispersion which does not produce coagulated matters in blending with a binder and which can produce a coating composition having stabilized physical properties with good reproducibility.
Thus, according to the present invention, provided is a cationized silica dispersion prepared by dispersing dry processed silica and a cationic resin in a polar solvent, wherein a concentration of dissolved silicic acid contained in the above dispersion at 25° C. is 200 ppm or less in terms of SiO
2
.
The dry processed silica used in the present invention is obtained by burning a silane base gas such as silicon tetrachloride in oxyhydrogen flame and is called “fumed silica”. In general, available is dry processed silica having a specific surface area falling in a range of 30 to 500 m
2
/g which is determined by a BET method, and it can suitably be used in the present invention.
In particular, use of dry processed silica having preferably a specific surface area falling in a range of 50 to 500 m
2
/g makes it possible to obtain a coating composition capable of forming a coating layer which is excellent in prescribed characteristics such as transparency.
The dry processed silica used in the present invention has preferably an average primary particle diameter falling in a range of 5 to 60 nm and an average coagulated particle diameter falling in a range of 10 to 1000 nm.
Dry processed silica having an average primary particle diameter of smaller than 5 nm is instable in the dispersion. On the other hand, if using dry processed silica having an average primary particle diameter of larger than 60 nm, the prescribed characteristics such as a transparency of the coating layer are likely to be reduced.
If using dry processed silica having an average coagulated particle diameter of smaller than 10 nm, a viscosity of the cationized silica dispersion is elevated too high, so that it is likely to be less liable to handle. On the other hand, if using dry processed silica having an average coagulated particle diameter of larger than 1000 nm, silica is likely to settle down to be susceptible to phase separation in the cationized silica dispersion or the coating composition. Further, a coating layer formed by the above coating composition is reduced in transparency.
A small amount of so-called wet processed silica such as precipitated silica, silica gel and colloidal silica and an inorganic matter such as silica, alumina, titania and calcium carbonate may be contained in the cationized silica dispersion of the present invention for the purpose of elevating the characteristics of the coating layer, for example, a gas barrier property, a corrosion property, a hydrophilic property, a glossiness and a liquid absorbing property.
In the cationized silica dispersion of the present invention, the dispersion having a light scattering index (hereinafter referred to merely as an n value) controlled to 2.0 or more is particularly excellent in a dispersibility of dry processed silica. Such dry processed silica dispe
Fukuda Kentaro
Fukunaga Kenji
Yamashita Hiroya
Lovering Richard D.
Tokuyama Corporation
Wenderoth , Lind & Ponack, L.L.P.
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