Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-10-19
2004-08-17
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S223000, C523S322000
Reexamination Certificate
active
06777488
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous dispersion of polyamide resin wherein polyamide resin particles are dispersed in an aqueous dispersion medium, and to a method of manufacture thereof.
BACKGROUND ART
Aqueous dispersions of polyamide resin can convey oil a resistance, solvent resistance, chemical resistance, abrasion resistance and gas blocking and adhesive properties and the like when used as a basis in the formation of coating films. Consequently, aqueous dispersions of polyamide resin are widely used in water-color inks, textile treatments, textile fillers, paper treatments, binders, lubricants, steel plate finishing agents, surface modifiers, hot melt adhesives and the like.
It is difficult to prepare a dispersion of polyamide in an aqueous dispersion medium by a direct process of emulsion polymerization in the aqueous dispersion medium because of its manufacturing process. Therefore, various methods have been proposed for manufacturing aqueous dispersions of polyamide resin by dispersion in an aqueous medium of polyamide resin formed by condensation polymerization or ring-opening polymerization. Possible methods of dispersing polyamide resin in an aqueous medium include reprecipitation and post-emulsification.
Reprecipitation is a method of dissolving polyamide resin in an organic solvent, reprecipitating the polyamide resin and replacing the organic solvent with an aqueous medium (see for example Japanese Patent Applications Laid-open No. S61-223059 and S63-186738).
The main problems with reprecipitation are the following. First, the polyamide resin particles obtained from reprecipitation are large in diameter, limiting the uses of the manufactured aqueous dispersion of polyamide resin. Second, polyamide resin particles often re-aggregate when the organic solvent is replaced with an aqueous medium, so the aqueous dispersion of polyamide resin obtained by reprecipitation is lacking in standing stability. Third, the inclusion of the step of replacing the organic solvent with an aqueous medium complicates the manufacturing process in the reprecipitation method.
In the post-emulsification method polyamide resin is dispersed in an aqueous medium as follows. In the first step, polyamide resin is dissolved in a non-water-soluble or slightly water-soluble organic solvent to prepare a polyamide resin solution. In the second step, the polyamide resin solution is mixed together with an emulsifier in an aqueous medium to prepare a mixture. In the third step, the mixture is agitation emulsified at high shear force in a specialized emulsifying apparatus. In the fourth step, the organic solvent is removed from the mixture, resulting in an aqueous dispersion of polyamide resin.
The main problems with post-emulsification are the following. First, because polyamide resin is not very soluble with respect to organic solvents, the post-emulsion method has low productivity and cannot be called economical. Second, because bubbling occurs during removal of the organic solvent in the post-emulsification method, a process is required to control bubbling, complicating the operation and making the method less economical. Third, the aqueous dispersion of polyamide resin obtained by post-emulsification inevitably contains residues of organic solvent and emulsifiers. Fourth, the post-emulsification method uses large quantities of organic solvent which could contaminate the work environment and cause environmental a pollution.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to resolve the various issues discussed above.
The aqueous dispersion of polyamide resin provided by the first aspect of the present invention contains dispersed polyamide resin particles, basic material and water, with the dispersed polyamide resin particles having a weight-average diameter of 0.1-10 &mgr;m and a ratio of end carboxyl groups to end amino groups being between 60/40 and 100/0, and with the amount of said basic material being 0.2-3.0 mol per mol of said end carboxyl groups.
Polyamide resin has carboxyl and/or amino groups on the ends. In general, carboxyl groups have a relatively low degree of electrolytic dissociation with respect to water. However, coexisting carboxyl groups with basic material promotes electrolytic dissociation of carboxyl groups in water solution (aqueous dispersion). Consequently, addition of basic material to the aforementioned aqueous dispersion of polyamide resin promotes electrolytic dissociation of end carboxyl groups on the dispersed polyamide resin particles, and improves dispersive power with respect to an aqueous dispersion medium.
The cause of aggregation of dispersed polyamide resin particles is attractive force acting on the particles. One such attractive force can be attributed to hydrogen bond. The aforementioned dispersed polyamide resin particles have relatively few amino groups in proportion to carboxyl groups. Consequently, with the aforementioned aqueous dispersion of polyamide resin there is relatively little hydrogen bonding force acting among the dispersed polyamide resin particles, and excessive aggregation of the dispersed polyamide resin particles is therefore prevented.
Thus, because excessive aggregation of the dispersed polyamide resin particles is controlled with the aforementioned aqueous dispersion of polyamide resin, standing stability is excellent.
An alkali metal hydroxide or amino compound is preferred as the basic material.
Examples of possible alkali metal hydroxide include sodium hydroxide and potassium hydroxide.
In the present invention, the term “amino compound” also includes ammonia.
The method of manufacturing an aqueous dispersion of polyamide resin provided by the second aspect of the present invention is characterized by the addition of polyamide resin to an aqueous dispersion medium containing 0.2-3.0 mol of basic material per mol of end carboxyl groups on the polyamide resin.
As mentioned already, electrolytic dissociation of carboxyl groups is promoted by the coexistence of basic material with polyamide resin, allowing for the prevention of excessive aggregation between polyamide resin particles. The aforementioned method of manufacturing an aqueous dispersion of polyamide resin employs an aqueous dispersion medium containing basic material, providing an aqueous dispersion of polyamide resin with small-diameter polyamide resin particles and excellent standing stability.
The amount of said basic material in the aforementioned aqueous dispersion medium should be in the range of 0.2-3.0 mol per mol of said end carboxyl groups. If the amount of said basic material falls below this range, aggregation of polyamide resin particles will not be sufficiently controlled, making it difficult to obtain an aqueous dispersion of polyamide resin. If the amount of said basic material exceeds this range, the resulting aqueous dispersion of polyamide resin will be impractical due to high alkalinity.
Preferably, the amount of said basic material should be 0.4-2.0 mol per mol of said end carboxyl groups. Particularly favorable results are obtained if the amount of said basic material is 0.6-1.5 mol.
The ratio of said end carboxyl groups to said end amino groups in the polyamide resin should be between 60/40 and 100/0.
As mentioned above, amino groups are one cause of aggregation of polyamide resin particles because of their susceptibility to hydrogen bonding. The polyamide resin used in the aforementioned method of manufacturing an aqueous dispersion of polyamide resin has a relatively small number of end amino groups in proportion to end carboxyl groups. Consequently, the aforementioned manufacturing method avoids excessive aggregation caused by end amino groups, and provides an aqueous dispersion of polyamide resin with excellent standing stability.
The polyamide resin used in the aforementioned method of manufacturing an aqueous dispersion of polyamide resin should have 50-3000 mmol of end carboxyl groups per kg of said polyamide resin. If the amount of end carboxyl groups falls below this range, it will be impossible t
Araki Eiichi
Manabe Hiroshi
Nakao Kaichiro
Sugihara Norihiro
Merchant & Gould P.C.
Niland Patrick D.
Sumitomo Seika Chemicals Co. Ltd.
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