US 9,311,949 B2  3  4  salt of a carboxyl group and an alkali metal salt of a hydroxyl  group to a water-based magnetic liquid comprising magnetic  particles dispersed in an acidic water-based solvent to cause  the magnetic particles to aggregate in the water-based mag› netic liquid; and  collecting the aggregated magnetic particles to obtain the  magnetic powder.  In an embodiment, a compound the protic compound of  which is of weaker acidity than acid contained in the acidic  water-based solvent is employed as the alkali metal salt com- pound.  In an embodiment, the alkali metal salt compound that has  been adhered to a surface of the magnetic particles converts  into a protic compound, resulting in the aggregation of the  magnetic particles in the water-based magnetic liquid.  In an embodiment, the alkali metal salt compound is an  aromatic compound having the substituent.  In an embodiment, the alkali metal salt compound is  selected from the group consisting of an alkali metal salt  compound of cinnamic acid and an alkali metal salt com- pound of dihydroxynaphthalene.  A further aspect of the present invention relates to mag› netic powder manufactured by the above manufacturing  method.  A still further aspect of the present invention relates to a  method of manufacturing a magnetic recording medium,  which comprises:  manufacturing magnetic powder by the above manufactur› ing method;  dispersing the magnetic powder that has been manufac- tured together with an organic solvent and a binder to prepare  a magnetic coating material; and  forming a magnetic layer with the magnetic coating mate› rial that has been prepared.  A still further aspect of the present invention relates to a  magnetic recording medium manufactured by the above  manufacturing method.  The present invention can provide a magnetic recording  medium in which microparticulate magnetic powder is dis› persed to a high degree, affording good electromagnetic char› acteristics.  Further, since dispersion of the microparticulate magnetic  powder is facilitated, the dispersion load on the magnetic  particles in the manufacturing process can be greatly reduced.  Other exemplary embodiments and advantages of the  present invention may be ascertained by reviewing the  present disclosure.  Unless otherwise stated, a reference to a compound or  component includes the compound or component by itself, as  well as in combination with other compounds or components,  such as mixtures of compounds.  As used herein, the singular forms "a," "an," and "the"  include the plural reference unless the context clearly dictates  otherwise.  Except where otherwise indicated, all numbers expressing  quantities of ingredients, reaction conditions, and so forth  used in the specification and claims are to be understood as  being modified in all instances by the term "about." Accord› ingly, unless indicated to the contrary, the numerical param› eters set forth in the following specification and attached  claims are approximations that may vary depending upon the  desired properties sought to be obtained by the present inven› tion. At the very least, and not to be considered as an attempt  The above "water-based magnetic liquid" refers to a liquid  in which magnetic particles are in a state of dispersion, with› out precipitation or aggregation, to a degree where separation  of the solid phase and liquid phase cannot be determined  visually. One embodiment (referred to as the "first embodi- ment", hereinafter), can be obtained by simultaneously or  sequentially admixing the water-based solvent, magnetic par› ticles (also referred to as the "starting material magnetic  particles", hereinafter), and an acid component. From the  perspective of suitability to the formation of a high-density  recording-use magnetic recording medium, the starting mate› rial magnetic particles desirably have an average primary  particle size of equal to or less than 35 nm.  Preparation of Water-Based Magnetic Liquid  The method of manufacturing magnetic powder of the  present invention will be described more specifically below.  In the magnetic recording medium, the fact that the mag- netic particles are present in the form of microparticles in the  magnetic layer relates to enhancing electromagnetic charac› teristics. Thus, to enhance electromagnetic characteristics, it  is desirable for microparticulate magnetic particles to be  present in the magnetic layer in a highly dispersed state. To  that end, in the magnetic layer-forming coating liquid, it is  desirable to disperse the microparticulate magnetic particles  to a high degree. Through the above steps in the present  invention, despite aggregating in the water-based magnetic  liquid, it is possible to obtain a magnetic powder comprised of  magnetic particles that can be readily dispersed to a high  degree in an organic solvent-based magnetic layer-forming  coating liquid. Accordingly, by subjecting the microparticu› late magnetic powder to the above steps, it is possible to  obtain magnetic powder that is capable of forming a magnetic  layer in which a microparticulate magnetic powder is dis› persed to a high degree.  The present invention further provides the magnetic pow› der obtained by the above method.  collecting the aggregated magnetic particles to obtain the  magnetic powder.  adding an alkali metal salt compound comprising a sub› stituent selected from the group consisting of an alkali metal  salt of a carboxyl group and an alkali metal salt of a hydroxyl  group to a water-based magnetic liquid comprising magnetic  particles dispersed in an acidic water-based solvent to cause  the magnetic particles to aggregate in the water-based mag- netic liquid; and  An aspect of the present invention relates to a method of  manufacturing magnetic powder, which comprises:  The following preferred specific embodiments are, there› fore, to be construed as merely illustrative, and non-limiting  to the remainder of the disclosure in any way whatsoever. In  this regard, no attempt is made to show structural details of  the present invention in more detail than is necessary for  fundamental understanding of the present invention; the  description making apparent to those skilled in the art how  several forms of the present invention may be embodied in  practice.  Additionally, the recitation of numerical ranges within this  specification is considered to be a disclosure of all numerical  values and ranges within that range. For example, if a range is  from about 1 to about 50, it is deemed to include, for example,  1, 7, 34, 46.1, 23.7, or any other value or range within the  range.  to limit the application of the doctrine of equivalents to the  scope of the claims, each numerical parameter should be  construed in light of the number of significant digits and  ordinary rounding conventions.  DETAILED DESCRIPTION OF THE  EMBODIMENTS 