United States Patent (19) 11 3,943,012 Tamai et al. (45) Mar. 9, 1976

54 MAGNETC RECORONG MEDUM 3,535,104 10/1970 Little et al...... 148/05

75 Inventors: Yasuo Tamai; Masashi Aonuma; 3,567,525 3.1197 Graham et al...... 751.5 AA Matsuaki Nakamura; Hiroshi 3,661556 3/1972 Jolley et al...... 751.5 AA Agawa; Goro Akashi, all of 3,821,025 6/1974 Akashi et al...... 117/235 Odawara, Japan Primary Examiner-Walter R. Satterfield 73) Assignee: Fuji Photo Film Co., Ltd., Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Minami-ashigara, Japan Zinn & Macpeak 22 Filed: Aug. 19, 1974 (57) ABSTRACT (21) Appl. No.: 498,337 A magnetic recording medium for high density record ing comprising a support having thereon a magnetic 30 Foreign Application Priority Data recording layer comprising a ferromagnetic metal Aug. 18, 1973 Japan...... 48-92721 powder of the Fe-Co-Cr-B system and having a coer cive force of about 700 to 500 oersteds in the oriented (52) U.S. Cl...... 148/105; 751.5 AA; 148/108; direction of the magnetic substance and a residual 427/132; 428/432 magnetic flux density of about 1500 gausses or more, (51) Int. Cl.'...... H01F 1/02 the residual magnetic flux density of which after stor 58) Field of Search...... 148/105, 108, 31.55; age for 160 hours under the conditions of a tempera 757.5 AA, 5 AB; 1171235, 236; 427/126, ture of 60°C and 90%RH is 85% or more of the initial 127, 132; 428/432 value thereof before storage under these conditions in a binder. The magnetic recording medium is especially (56) References Cited suitable for high density recording, having sufficient UNITED STATES PATENTS sensitivity and excellent resistance. 3,206,338 9/965 Miller et al...... I 48105 5 Claims, 2 Drawing Figures U.S. Patent March 9, 1976 3,943,012

FIG

WA X/ZX7\A 100 90 89 D 80 - Fe (%)

SAMPLE (#2)

80

70

NCOMPARATIVEN-- SAMPLE (#3) 60

50 — 00 60 200 FIG 2 PASSED TIME AT 60°C 90%R.H. (HR) 3,943,012 1. 2 from the mercury, for example, as disclosed in Japa MAGNETIC RECORDING MEDUM nese Patent Publication Nos. 5525/64 and 8123/65. VI. A salt of a ferromagnetic metal material is re BACKGROUND OF THE INVENTION duced in a solution thereof, for example, as disclosed in 1. Field of the Invention Japanese Patent Publication Nos. 20520/63, 26555/63, This invention relates to magnetic materials for mag 20116/68 and 41718/72, U.S. Patent Nos. 3,663,318 netic recording media, such as magnetic recording and 3,661556 and German Patent Application Laid media for high density recording containing these mag Open to Public Inspection OLS No. 2,132,430. netic materials. In particular, this invention relates to Investigations have revealed that a magnetic record the production of video tapes using ferromagnetic 10 ing medium having a ferromagnetic material prepared metal powder materials of a novel composition. by the above Method (VI) is relatively free from noise 2. Description of the Prior Art and has better surface characteristics, when used as a Ferromagnetic powder materials heretofore used in video tape, as compared with other tapes having other video tapes include y-Fe,0s, FeaQ, Co-containing y ferromagnetic materials prepared by other methods. FeO and CrO. 5 Accordingly, the ferromagnetic materials used in the The recording wavelengths in video tapes are far present invention are those prepared by Method (VI), shorter than those of other sound recording tapes, and and in particular, a borohydride compound or a deriva for example, it is necessary to record short waves of at tive thereof such as borane, borazane, borohydride, least up to a minimum wavelength of 6 u or so in a VTR sodium borohydride, potassium borohydride, dimethyl (video tape recorder) for television broadcast. The aminoborane or diethylaminoborane is used as the above-described conventional ferromagnetic materials reducing agent in Method (VI). are not as suitable for magnetic recording of recording Method (VI) wherein a salt of a ferromagnetic metal signals of a short wavelength (of about 10 u, or less). material is reduced in a solution thereof with a borohy That is, these ferromagnetic materials have insufficient dride compound or a derivative thereof has some de magnetic characteristics of coercive force (He) and 25 fects as described below. The powder obtained accord residual magnetic flux density for use in high density ing to this method are less resistant to moisture, partic recording. Miniaturization and simplification of re ularly when iron is present, and are gradually oxidized cording and reproducing mechanisms has occurred even at normal temperature, in an extreme case, result recently, and development of a small size VTR having ing in a loss of the magnetic characteristics thereof to a stationary head has been accelerated in this technical 30 become consequently a non-magnetic substance. Ac field in substitution for conventional rotary head type cording to this method, furthermore, since the surface VTR's. An especially important element in a stationary activity of the particles obtained is high, the particles head VTR is how to reduce the relative velocity be are highly active. This high activity is industrially disad tween the tape and the head. vantageous from the standpoint of the production More precisely, the minimum recording wavelength 35 thereof. Use of highly active powders in air is danger is desirably at most 2 u or less so as to avoid the high ous due to their explosive character. In addition, these speed conveyance of a video tape in a small size VTR. powders, when kneaded with a binder, tend to deterio Recently, extensive development of ferromagnetic rate the binder used, often resulting in a disadvantage powder materials having magnetic characteristics suit in dispersion and coating. A tape utilizing a magnetic able for high density recording has been carried out. 40 substance obtained in Method (VI) is defective in that, One of the subject materials is a ferromagnetic metal the rubbing of the tape against a video-head at a high powder. The powder is made of a metal or a metal relative speed often deteriorates the magnetic material alloy. This powder additionally includes an intermetal in the tape (presumably the material is oxidized). All of lic compound. Metals which are mainly used include these defects must necessarily be overcome in the de iron, cobalt and nickel, and other elements such as 45 velopment of magnetic recording media for high den chromium, manganese, rare earth elements and zinc sity recording. However, it has been extremely difficult are optionally added thereto. For preparation of these up to the present to solve all of these problems. For ferromagnetic materials the following methods are example, it is possible to manufacture magnetic materi known: als capable of having a high He and a high squareness I. A salt of a ferromagnetic metal and an organic acid 50 ratio, however, it is difficult to manufacture in Method is pyrolyzed and reduced with a reductive gas, for ex (VI) magnetic materials of a low He and a high square ample, as disclosed in Japanese Patent Publication Nos. ness ratio. 1412/66 and 3841 7/72. II. A needle-shaped oxyhydroxide, or a derivative SUMMARY OF THE INVENTION thereof containing other metals, or a needle-shaped 55 Accordingly, one object of this invention is to over iron oxide obtained from these oxyhydroxide sub come the defects in the prior art and to provide video stances is reduced, for example, as disclosed in Japa tapes having sufficient sensitivity and excellent weath nese Patent Publication Nos. 3862/60 and 39477/72 er-proof properties and being suitable for high density and British Patent No. 1,192,167. recording. III. A ferromagnetic metal is evaporated in an inert 60 Another object of this invention is provide magnetic gas, for example, as disclosed in Japanese Patent Publi recording media having improved magnetic character cation No. 27718/72 and Ohyo Butsuri (Applied Phys istics. ics), Vol. 40, No. 1, page 110 (1970). Still another object is to use moisture-proof and diffi IV. A metal carbonyl compound is decomposed, for cultly oxidizable magnetic powder materials in the example, as disclosed in U.S. Pat. Nos. 2,983,997 and 65 manufacture of video tapes. 3,228,882. More particularly, this invention provides magnetic V. A ferromagnetic metal is deposited by electrode recording, medium for high density recording compris position using a mercury electrode, and then separated ing a support having thereon a magnetic recording 3,943,012 3 4 layer comprising a ferromagnetic metal powder and cordingly, the Br/Hc value in relation to self-demagnet having a coercive force of about 700 to 1500 Oe in the ization is desirably about 2 or higher, more preferably oriented direction of the ferromagnetic powder, a 1.5 or higher. Thus, a preferable range for the Br/Hc is squareness ratio of about 0.70 to 0.93 and a residual 4.5 to 1.5, more preferably 3.8 to 2.0. magnetic flux density of about 1500 gausses or more, 5 It is desirable that the squareness ratio be ideally the residual magnetic flux density of which after stor 1.00. The squareness ratio can be increased by apply age for 160 hours under conditions of a temperature of ing a strong orienting magnetic field to the magnetic 60° C and 90%RH is 85% or more of the initial value layer which is not dried. However, application of an thereof before storage, in a binder. extremely strong orienting magnetic field to the mag 10 netic layer after coating with a magnetic coating solu BRIEF DESCRIPTION OF THE ACCOMPANYING tion containing the ferromagnetic metal powder results DRAWINGS in a degradation of the surface characteristics of the FIG. 1 shows a preferred composition range of the magnetic layer, the so-called orientation chap. Accord Fe-Co-Cr-ferromagnetic metal powder of this inven ingly, a squareness ratio higher than about 0.93 is in tion. 15 convenient, causing a degradation in sensitivity. FIG. 2 shows the variation in residual magnetic flux The magnetic recording medium of this invention has density for samples of the invention and comparative excellent weather-resistance. For example, the degree samples during weather resistance testing. of degradation of the residual magnetic flux density thereof is within 15% in a severe weather-resistance DETAILED DESCRIPTION OF THE INVENTION test in which the temperature is 60 C, the relative Those ferromagnetic metal powders of the humidity is 90%RH and the storage time is 160 hours. Fe-Co-Cr-B system are especially preferred for A residual magnetic flux density of 1500 gausses or attainment of the above objects of this invention. higher before the weather-resistance test is one requi Magnetic recording media require a high squareness site for magnetic recording media for obtaining a suffi ratio, a high He and a high residual magnetic flux den- 25 ciently high sensitivity, and the excellent weather sity for retention of sufficient sensitivity. However, an resistance thereof is more important. This is because extremely high He is inconvenient due to the necessity magnetic recording media with poor weather-resist for the use of a larger amount of electric current for ance have defects which are practically fatal in that not recording and the difficulty in erasure of signals. On only are the recording conditions varied due to deterio these grounds, the Hc is desirably about 1800 Oe or 30 ration of the medium with the lapse of time but also the less, more preferably 1500 Oe or less. On the other reduction in output in reproduction after recording is hand, a degradation of sensitivity due to an increase of great. self-demagnetization occurs when the He is too low. In The importance of a Br degradation within 15% of use of magnetic substances prepared in the above men the original value means not only do the magnetic re tioned Method (VI), a decrease in the squareness ratio 35 cording media of the present invention have excellent results from the decrease in the He, causing a further magnetic characteristics but also these characteristics decrease of sensitivity. From these results, the lower are essential for retaining as high as possible an output limit of Hic is found desirably to be about 700 Oe. In in recording short wavelengths. If the weather-resist this case, the lower limit of the squareness ratio is about ance is insufficient and the Br is degraded thereby (for O.70. 40 example, degraded to an extent of 25% or more), the In magnetic recording tapes utilizing ferromagnetic resultant reduction in output is unexpectedly high (for powder, the residual magnetic flux density (Br) thereof example, -3dB). This is considered a characteristic is generally high because of high saturation magnetiza feature of magnetic recording media utilizing a ferro tion of the magnetic powder itself. A higher residual magnetic metal powder. The abnormal reduction of magnetic flux density is preferable in recording long 45 output is similar to the loss resulting from the gap be wavelengths, causing an increase in output in such tween the surface of the recording medium and the recording. However, a higher residual magnetic flux recording and reproducing head. This is considered to density also causes a self-demagnetization, and there mean that the oxidation of magnetic powder in a mag fore, the output in recording short wavelengths is not netic layer is greater in the vicinity of the surface of the increased thereby. This means that the increase in re- 50 magnetic layer. sidual magnetic flux density must necessarily follow the In the magnetic recording media of the present in increase in coercive force (Ho) in magnetic recording vention, the magnetic layer is desirably thin because media suitable for recording short wavelengths. Vari the media are used in recording short wavelengths. ous kinds of tapes using various kinds of ferromagnetic More particularly, it is important that the thickness of powder were produced and tested. As a result, it has 55 the layer be about 8 pu or less, desirably 6 pu or less, been found that recording media with less self-demag more preferably 4.5 u or less. netization and sufficient magnetic characteristics of the The magnetic material which is used in the present ferromagnetic metal substance have a Br/Hc value of invention is an alloy of the ferromagnetic metals of about 5 or less, preferably 4.5 or less, more preferably iron, cobalt and chromium and boron. The boron con 3.8 or less, wherein the coercive force (Hc) is repre- 60 tent in the magnetic substance is about 2 to 10.5% by sented in oersteds (Oe) and the residual magnetic flux weight. (All percents are by weight hereinafter, unless density (Br) is represented in gausses (G). On the other otherwise specifically indicated.) The boron compo hand, loss in recording short wavelengths decreases nent is derived from the borohydride compound. The with a reduction in the thickness of the magnetic layer, proportion of the Fe-Co-Cr in the magnetic sub but in this case, when the Br is too low, the output in 65 stance exclusive of the boron is desirably as follows: recording long wavelengths is insufficient. Therefore, about 92 to 55%, preferably 89 to 65% Fe; about 5 to the Br is desirably at least about 1500 gausses or 40%, preferably 7 to 34%. Co; and about 0.2 to 9%, higher, more preferably 2000 gausses or higher. Ac preferably 0.5 to 5% Cr. If the iron content exceeds the 3,943,012 S 6 upper limit, the coercive force is reduced and the and/or Sn, Al, W, Mn, Cu, Zn, Ag, Pd, and/or Ti. These weather-resistance is degraded. On the contrary, if the metals are employed in aqueous solutions in the form iron content is smaller than the lower limit, the satura of chlorides, sulfates, nitrates, formates, acetates, pyro tion magnetization tends to be reduced and the cost of phosphates or sulfamates and the resulting salt solu production increases. If the cobalt content exceeds the 5 tions are reduced with borohydride compounds. upper limit, the saturation magnetization tends to be In the ferromagnetic powder materials of this inven reduced and the cost of product increases. In addition, tion, chromium forms an alloy with iron and cobalt, if the cobalt content is smaller than the lower limit, the and the proportion of the respective components pres coercive force is reduced and the weather-resistance is ent in the alloy formed is different in the central part of degraded. If the chromium content exceeds the upper O the particle from that in the vicinity of the surface of limit, the coercive force is reduced while the square the particle. This has been substantiated from analyti ness ratio is somewhat improved. In addition, if the cal results of particles wherein the ferromagnetic pow chromium content is smaller than the lower limit, the der particles are packed in a glass tube, hydrochloric weather-resistance is markedly degraded and the acid is gradually introduced into the tube and the solu squareness ratio also is reduced. The total amount of 5 tion flowing down the tube is successively analyzed. In cobalt and chromium is desirably about 10% or higher this analysis, the amount of chromium in the eluent is on the basis of the total of the ferromagnetic powder larger in the initial stage of the analysis than that in the substance including all of the metal components and latter stage of the analysis. Although it is not com the boron component. If the amount of cobalt and pletely clear since the particles are so fine, it was ob chromium is smaller than about 10%, the weather 20 served that the chromium concentration in the alloy in resistance is markedly degraded. It would not have the vicinity of the central part of the particle was about been predicted that boron would specifically serve to 80 to 50% of that in the vicinity of the surface part of improve the weather-resistance. The range of the re the particle. spective components of the magnetic materials of the The metal salt solution can contain, if desired, addi present invention falls within the shaded area in FIG. 1 25 tional additives such as chelating agents pH buffers attached hereto. and/or pH adjusting agents, in addition to the above It is well known to add chromium to ferromagnetic described components. metals for improving the weather-resistance thereof. These chelating agents are water-soluble and form a However, in preparing ferromagnetic metals actually complex ion with the hereinbefore described metal ions using a borohydride compound, the use of chromium 30 and include monocarboxylic acids such as formic acid, requires an extremely delicate control. That is, the acetic acid, propionic acid, butyric acid, valeric acid, magnetic characteristics of the magnetic material ob acrylic acid, trimethylacetic acid, benzoic acid or chlo tained abruptly varies, even with a slight change of the roacetic acid or the salts thereof (as pH buffers and amount of the added chromium. complex forming agents); dicarboxylic acids such as 35 oxalic acid, succinic acid, malonic acid, maleic acid, Accordingly, the He, squareness ratio (Sq) and satu itaconic acid or p-phthalic acid or the salts thereof and ration magnetization (Bm represented by gauss/cm) oxycarboxylic acids such as glycolic acid, lactic acid, were studied in relation to the sensitivity. As a result, it salicylic acid, tartaric acid or citric acid or the salts was found that, with respect to only the saturation thereof; The pH buffering agents are water-soluble and magnetization, the use of the data thereof after the 40 include boric acid, carbonic acid or sulfurous acid (as weather-resistance test shows the data approximated pH adjusting agents and pH buffers); and ph adjusting the sensitivity of the actual media. In the weather agents such as inorganic acids or organic acids, ammo resistance test effective for investigation of magnetic nium or alkali metal hydroxides. These additives can be substances, the magnetic material alone is desirably present in an amount of less than about 20% by weight, stored for 1 week in a relative humidity of 85%RH at 45 preferably less than about 12% by weight. 45 C. Various samples of the Fe-Co-Cr system were The above-described additives not only have their tested under these conditions and the sensitivity was individual function but in some instances have more determined. The test of the magnetic material alone than are function. For example, some compounds act under this condition corresponds to a test of the tape not only as a complex forming agent but also as a pH containing the substance under the conditions of 60°C, SO buffer. 90%RH for 160 hours. From the results of the various Further, to the reaction solution there can be added tapes tested the range of sufficient sensitivity and excel as desired a soluble protein together with a proteolytic lent weather-resistance is obtained, corresponding to enzyme, a carbohydrate together with a carbohydrate the shaded area of FIG. 1. decomposer, and an organic solvent, e.g., in an amount This range almost corresponds to that which satisfies 55 of less than about 12% by weight, preferably less than the following experimental formula: 6% by weight. Suitable soluble proteins include simple proteins 3 log He log Sq log Bn which decompose into chiefly amino acids upon hydro 500 -- 0.9 -- 5000 > 0.8 lysis, conjugated proteins comprising polypeptide 60 chains connected to other compounds, derived prote The formula shows the range capable of imparting a ins which have been modified by various physical, ther sensitivity higher than that of a standard chromium mal, photochemical or chemical procedures, etc. They dioxide tape by about +4dB in a non-bias recording of are all composed of macromolecules of polypeptides, 5MHz. comprising amino acids, having a molecular weight of The ferromagnetic metal powder materials which are 65 from about 10,000 to about 5,000,000. used in this invention are of the Fe-Co-Cr-B sys Simple proteins suited for the present invention in tem. These substances can optionally contain a small clude albumins such as egg albumin, blood serum albu amount of other additives such as rare earth elements min, lactoalbumin, etc., globulins such as serum globu 3,943,012 7 8 lin, lactoglobulin, myosin, edestin, ammandin, legumin, two molecules of D-galactose, D-glucose and D-fruc etc., glutelins such as glutenin, hordenin, oryzenin, etc., tose), etc. prolamins such as gliadin, hordein, zein, etc., albumin Polysaccharides which can be used for the present oids such as collagen, elastin, keratin, fibroin, etc., invention include dextrin (D-glucose), starch (D- histones such as thymus-histone, liver-histone, scom glucose), glycogen (D-glucose), cellulose (d-glucose), brone, etc., and protamines such as salmine, clupeine, inulin (fructose), mannan (mannose), araban (arabi strurine, iridine, etc. nose), Xylan (Xylose), dextran (D-glucose), galactan Conjugated proteins include chromoproteins, phos galactose), gum arabic (comprising galactose, glucu phoproteins, metalloproteins lipoproteins, glycopro ronic acid, hexose and methylpentose), etc. teins, nucleoproteins, etc. Examples of chromoproteins O As is clear from the above expalanations, suitable are hemoproteins such as hemoglobin, myoglobin, cy carbohydrates for the present invention are monosac tochrome, catalase, peroxydaze, etc., chlorophyll pro charides and polysaccharides comprising a multiplicity teins such as chlorophylin; carotinoid proteins such as of monosaccharides connected by glycoside linkages. rhodopsin, etc., flavoproteins such as flavin mononu Further, as the enzyme to decompose such a carbohy cleotide, flavin adeninedinucleotide, etc. Phosphopro 15 drate, a hydrolase such as a-amylase (diastase), g-amy teins include casein, hyderin, apoferritin, etc. Metallo lase (diastase), cellulase, lichenase, laminarinase, inu proteins include iron proteins such as ferritin, apoferri lase, a-glucosidase, g-glucosidase, o-galactosidase, tin, etc., copper proteins such as hemocyanine, etc., fg-mannosidase, etc., all of which are glycosidases, can zinc proteins; manganese proteins, etc. Lipoproteins be used. include thrombplastein, a-lipoprotein, a-lipoprotein, An inorganic acid such as hydrogen chloride, sulfuric lipobilitein, lipotenilin, etc., glucoproteins include mu acid, nitric acid, etc. can also be used to decompose cin, celluloplasmin, siderophilin, fibrin, prothrombin carbohydrates. collagen, enterokinase, haptoglobin, mucoid, etc., and Use of ultrasonic waves in the reduction is effective nucleoproteins include nucleic acids, deoxypentose to improve the characteristics of the resulting magnetic nucleoprotein, pentose-nucleoprotein, viruses, bacte 25 powder material. In addition, it also is effective to carry riophages, etc. out the reduction reaction in a magnetic field of several Derived proteins include gelatin modified protein, tens of Oe or more for the purpose of increasing the proteans, proteoses, peptones, polypeptides, metapro coercive force and the squareness ratio of the resulting teins, etc. magnetic materials. The strength of the magnetic field These proteins can be used individually or in combi 30 is preferably about 500 to 3000 Oe, and the stronger nation. the field the better. In the reduction reaction wherein a To decompose any of these proteins, proteases be borohydride compound is used as the reducing agent, longing to the hydrolase type, can be employed, includ the temperature in the reaction solution is desirably ing pepsin, trypsin, chymotrypsin, cathepsin, rennin, about 65°C or below, e.g., from about -10°C to about papain, promelin, ficin, thrombin, enteropeptidase, 35 65 C. Use of a temperature above 65° C deteriorates plasmin, mold protease, yeast protease, bacterium pro the character of the ferromagnetic powder obtained tease, etc. Such proteolytic enzymes can be used indi and use of a temperature less than -10°C results in a vidually or in combination. slow reaction rate and the solution tends to freeze. Carbohydrates comprise monosaccharides, oligosac The metal ion concentration desirably ranges from charides such as di-, tri- or tetrasaccharides and poly 40 about 0.002 to 2 moles/liter, more preferably 0.01 to saccharides. 0.5 mole/liter. Monosaccharides includes polyhydric alcohols con The concentration of the borohydride compound or taining aldehyde groups (aldoses) and those containing derivative thereof to be used as the reducing agent keto groups (ketoses). desirably ranges from about 0.0001 to 15 mol/liter, Oligosaccharides comprise dimers, trimers or tetra 45 preferably 0.0002 to 10 moles/liter, and the reducing mers of monosaccharides, each of which may be com agent/metal ion molar ratio desirably ranges from mon or different, through glycoside linkages. Polysac about 0.1:1 to 5:1, preferably 0.25:1 to 4:1. charides are polymers of mono- or oligosaccharides. The borohydride compound or the derivative thereof Suitable monosaccharides include glycol aldehydes is dissolved in water, methanol or a like solvent, prefer which is the aldose of a diose (CHO), a triose 50 ably water, when used, and it is preferred that hydrox (CHO) such as glyceraldehyde (aldose) or dihydrox ide ion be present in the solution. In this case, the yacetone (ketose), etc. a tetrose (CHO) such as amount of the hydroxide ion affects the weather-resist erythrose (aldose), erythrulose (ketose), etc., a pen ance of the formed magnetic material. More precisely, tose (CHO) such as ribose, xylose, arabinose (al when the concentration of the hydroxide ion is in the dose), arabinulose (ketose), xylulose (ketose), etc. a 55 range of about 0.001N to 0.6N, the weather-resistance hexose (CHOs) such as D-glucose, mannose, galac of the magnetic substance formed is high. Suitable tose (aldose), D-fructose, sorbose (ketose), and a hep alkaline materials which can be used to obtain this tose (CHO,) such as mannoheptose, which is an hydroxide concentration are water soluble, produce aldose, or heptulose which is a ketose. hydroxide ions in solution and are capable of generat Oligosaccharides, include disaccharides such as lac 60 ing a pH of higher than about 8. Preferred inorganic tose (comprising D-glucose and D-galactose), maltose hydroxides are the hydroxides of Group I and Group Il (comprising two moles of D-glucose), sucrose (com elements such as sodium hydroxide, potassium hydrox prising D-glucose and D-fructose), trehalose (compris ide, barium hydroxide and calcium hydroxide, and ing D-glucose); trisaccharides such as raffinose (com suitable examples of organic alkaline materials include prising D-glucose, D-fructose and D-galactose), gen 65 n-butylamine, isopropylamine, hydrazine, etc. tianose (comprising D-fructose and two molecules of Suitable reducing agents include borohydrides and D-glucose), mannotriose (the trimer of mannose), etc.; derivatives thereof such as borane, borazane, borohy and tetrasaccharides such as stachyose (comprising dride, sodium borohydride, potassium borohydride, 3,943,012 10 dimethylaminoborane, diethylaminoborane, etc. These 15206/68, 2889/69, 17947 fe9, 14020/70, 14500/70, reducing agents can be used individually or in combina 8573/72, 22063/72, 22064f72, 22068/72, 22069/72, tion. These compounds are compounds which contain 22070,72 and 22886/72, and U.S. Pat. Nos. 3, 144,352, boron and are water-soluble. Upon reaction hydrogen 3,419,420, 3,499,789 and 3,713,887, etc. and boron metal are produced. Suitable chromium salts Thermosetting resins are those having a molecular which can be present in the solution during reduction weight of about 200,000 or less in the form of a coating include chromium chloride, chronium sulfate, chro solution, and when heated, after being coated and mium nitrate, etc., chromates, dichromates, etc. dried, the molecular weight thereof becomes infinitely Observation has revealed that ferromagnetic pow large to condensation or addition reactions. Preferred ders obtained in the method of this invention as de O resins are those which neither soften nor melt below scribed above are granular, each having a particle size the decomposition point of the resin. Examples of pre of about 50 to 1000 A, and that several or several tens ferred resins are phenol resins, epoxy resins, polyure or more of the respective particles are linked together thane setting resins, urea resins, melamine resins, alkyd to form a string-like, rod-like or necklace-like form. resins, silicone resins, reactive acrylic resins, epoxy Heating the ferromagnetic powders obtained in the 15 polyamide resins, nitro cellulose-melamine resins, mix present invention for about 15 seconds to about 120 tures of a high molecular weight polyester resin and an hours, preferably 3 minutes to 24 hours, at a tempera isocyanate prepolymer, mixtures of a methacrylate ture of about 120° C to 450° C, preferably 150° C to copolymer and a diisocyanate prepolymer, mixtures of 37 () C, in a non-oxidizing atmosphere or in the pres a polyester-polyol and a polyisocyanate, urea-for ence of a slight amount of water or Og, further im maldehyde resins, mixtures of low molecular weight proves the magnetic characteristics of the powders glycol/high molecular weight dioli triphenylmethane obtained in the present invention. Suitable non-oxidiz triisocyanate, polyamine resins and mixtures thereof. ing atmospheres include inert gases such as helium, These resins are disclosed in Japanese Patent Publi neon, argon, krypton, xenon, etc., and gases such as cation Nos. 8103f64, 977.9/65, 7, 192/66, 8.016766, nitrogen, carbon monoxide, carbon dioxide, etc. 14275/66, 18179/67, 12081168, 28023/69, 14501170, Where oxygen is present a suitable oxygen concentra 24902F70, 13 103171, 22065/72, 22066/72, 22067f72, tion is less than about 50 mmHg, preferably less than 22072172, 22073/72, 28.045/72, 28048/72 and 20 mmHg, and a suitable amount of water is a relative 28922/72, and U.S. Pat. Nos. 3, 144,353, 3,320,090, humidity of less than 10%. 3,437,510, 3,597,273, 3,781,210 and 3,781,211, etc. The ferromagnetic materials obtained in the present One or more of these binders are used, and other invention contain a slight amount of boron. The boron additives can be added thereto. The proportion offer component is believed to result from the borohydride romagnetic powder material to binder is about 100 compound which is used as one of the starting materi parts by weight of the ferromagnetic substance to 10 to als. The boron content was found to range from about 200 parts by weight, preferably 25 to 120 parts by 2.0 to 10.5% by weight. weight, of the binder. The ferromagnetic powder materials obtained in this Suitable additives includes dispersing agents, lubri invention are used for the production of magnetic re cants and ahrasives. cording media in combination with various other mate Examples of dispersing agents are fatty acids rials. (RCOOH where R represents an alkyl group having Binders which can be used together with the ferro 40 about l l to 7 carbon atoms) such as caprylic acid, magnetic powder materials of the present invention capric acid, lauric acid, myristic acid, palmitic acid, include conventional thermoplastic resins and thermo Stearic acid, oleic acid, elaidic acid, linoleic acid, lino setting resins. These resins can be used individually or lenic acid, and stearolic acid, fatty acid esters or in the form of a mixture. (RCOOR where R and Ra each represents an alkyl Thermoplastic resins are those having a softening 45 group having about 1 to 12 carbon atoms) such as ethyl point of about 150°C or below, an average molecular caprylate and propyl laurate; metallic soaps of the weight of about 10,000 to 200,000, and a polymeriza above described fatty acids and alkali metals (such as tion degree of about 200 to 1,000 or so, and represen Li, Na, K) or alkaline earth metals (such as Mg, Ca, tative examples thereof are vinyl chloride-vinyl acetate Ba); and lecithins. In addition, higher alcohols having copolymers, vinyl chloride-vinylidene chloride copoly about 12 to 24 carbon atoms such as lauryl alcohol, mess, vinyl chloride-acrylonitrile copolymers, acrylate pentadecyl alcohol, cetyl alcohol, stearyl alcohol, acrylonitriie copolymers, acrylate-vinylidene chloride nonadecyl alcohol, etc., and the sulfates thereof can copolymers, acrylate-styrene copolymers, methacry also be used. The amount of the dispersing agent pres late-acrylonitrile copolymers, methacrylate-vinylidene ent is about l to 20 parts by weight on the basis of 100 chloride copolymers, methacrylate-styrene copoly 55 parts by weight of binder. mers, polyvinyl fluorides, vinylidene chloride-acryloni Examples of the lubricants which can be used are trile copolymers, butadiene-acrylonitrile copolymers, silicone oil, graphite, molybdenum disulfide, tungsten polyamide resins, polyvinyl butyral resins, cellulose disulfide, fatty acid esters of a monobasic fatty acid derivatives (such as cellulose acetate butyrate, cellu having about 12 to 16 carbon atoms and a monohydric lose diacetate, cellulose triacetate, cellulose propionate 6 alcohol having about 3 to 12 carbon atoms, and fatty and nitrocellulose), styrenebutadiene copolymers, acid esters of a monobasic fatty acid having about 17 or polyester resins, chlorovinyletheracrylate copolymers, more carbon atoms and a monohydric alcohol, the annin resins and various kinds of synthetic rubber type number of carbon atoms of the acid and the alcohol the Inoplastic resins. These resins can be used individu being about 15 to 28 in total. Suitable examples of fatty aily or in the form of a mixture thereof. These resins are 65 acid esters include ethyl caprylate, ethyl laurate, propyl disclosed in Japanese Patent Publication Nos. 6877/62, myristate, methyl palmitate, ethyl stearate, amyl stea 2528/ 64, 19282/64, 5349 f65. 20907 fe5, 94.63f66, rate, ethyl behenate, ethyl oleate, propy linolate, 14059 (56, 6985/66, 6428/67, 1 6 12 F67, 4623/68, methyl linolenate, etc. The amount of the lubricant 3,943,012 11 12 present is about 0.2 to 20 parts by weight on the basis of 100 parts by weight of the binder. These lubricants EXAMPLE 1. are disclosed in Japanese Patent Publication Nos. A direct current magnetic field of 500 Oe was ap 23889/68, 28647/67 and 81543/68, U.S. Pat. Nos. plied to 100 liters of an aqueous solution of ferrous 3,470,021, 3,492,235, 3,497.41 1, 3,523,086, 5 chloride, cobalt chloride and chromium alum, these 3,625,760, 3,630,772, 3,634,253, 3,647,539 and components being dissolved in a predetermined pro 3,687,725, IBM Technical Disclosure Bulletiz, Vol. 9, portion, and the solution was kept at 20°C. 20 liters of No. 7, page 779, December 1966, and ELEKTRONIK sodium borohydride solution were added to the above 1961, No. 12, page 380, etc. metal salt solution at a rate of l.2 liter/sec. The concen Examples of abrasives include conventional materials 10 tration of the metal salt was 0.2 mole?liter total, and the such as alumina, fused alumina, silicon carbide, chro concentration of the sodium borohydride solution was mium oxide, corundum, synthetic corundum, diamond, 2 moles/liter. This solution had a sodium hydroxide synthetic diamond, garnet and emery (main compo concentration of 0.06N. The reaction started simulta nents: corundum and magnetite). These abrasives have neously with the addition of the reducing agent, and an average particle size of about 0.05 to 5 u (diame 5 vigorous foaming was noticed. After the reaction, the ter), preferably 0, 1 to 2 u. The amount of the abrasive black precipitate obtained was fully washed with water present is 7 to 20 parts by weight on the basis of 100 and then with acetone. Afterwards, the precipitate was parts of binder. These abrasives are disclosed in Japa dried at 25 C in an atmosphere of a humidity of 30% nese Patent Application No. 26749/73, U.S Pat. Nos. or less. 3,007,807, 3,041,196, 3,293,066, 3,630,910 and 20 The analysis results of the metal components and the 3,687,725; British Pat. No. 1,145,349 and German Pat. boron in the respective samples prepared are shown in No. 853,21 1, etc. the following Table 1. The formation of the magnetic recording layer is carried out by dissolving the above described compo Table 1 (%) nents in an organic solvent and coating the resulting 25 Sample Fe Co Cr B coating solution on a support. The thickness of the A 74.0 17.3 2.3 6.4 B 65.7 26.3 1.8 6.2 support is suitably about 5 to 50 u, or so, preferably 10 C 83.9 7.5 1.9 6.7 to 40 u or so, and suitable examples of supports, are, D 90.3 13.9 0.0 5.8 for example, polyesters such as polyethylene tere phthalate, polyolefins such as polypropylene, cellulose 30 derivatives such as cellulose triacetate or cellulose The following Table 2 shows the saturation magneti diacetate and polycarbonates. zation (magnetic field: 2000 Oe) of these samples be Coating of the above-described magnetic recording fore and after weather-resistance testing. layer on a support can be carried out by various meth ods such as airdoctor coating, blade coating, air-knife 35 Table 2 (T) coating, squeeze coating, dip coating, reverse-roll coat Sample Initial Value After Weather-Resistance ing, transfer-roll coating, gravure coating, kiss coating, Testing A. 86SO 7800 cast coating and spray coating, and other means can B 8400 795.0 also be utilized therefor. These coating means are de C 92.90. 4240 scribed in detail Coating Engineering (pp. 253-277), 40 D 8700 4080 Asakura Publishing Co., March 20, 1971. A suitable coating composition concentration can range from (*stored for one week at 45C, 85%Rh) about 150 to 500 g, preferably 200 to 450 g, per kg of the solvent. Both Samples A and B of the present invention have Representative examples of organic solvents which 45 an original saturation magnetization value (before can be used in coating the magnetic recording layer on weather-resistance testing) somewhat lower than that a support are ketones such as acetone, methyl ethyl of the other Samples C and D, while after the weather ketone, methyl isobutyl ketone and cyclohexanone; resistance testing the Samples A and B show a satura alcohols such as methanol, ethanol, propanol and buta tion magnetization value far higher than that of the nol; esters such as methyl acetate, ethyl acetate, butyl 50 Samples C and D. acetate, ethyl lactate, glycol acetate monoethylether; Magnetic coating compositions of the following in ethers and glycol ethers such as diethyl ether, glycol gredients and these four samples were prepared. dimethylether, glycolmonoethylether dioxane and tet rahydrofuran; aromatic hydrocarbons such as benzene, 55 parts toluene, and xylene; chlorinated hydrocarbons such as Ferromagnetic Powder 300 methylene chloride, ethylene chloride, carbontetra (average particle size of about 0.25 u in length and 0.04 it chloride, chloroform, ethylene-chlorohydrin and di in width) chlorobenzene; and dimethylsulfoxide and dimethyl Polyester-polyol" 40 formamide. Cellulose Acetate Butyrate 25 60 Polyisocyanate Compound" 20 The present invention is explained in greater detail Chromium Sesquioxide 4 by reference to the following Examples and Compara (average particle size: about 0.1 ...) Soybean Lecithin 6 tive Examples. One skilled in the art can easily under Methyl Ethyl Ketone 400 stand that the components, proportion and operational Butyl Acetate 500 procedure as shown herein can be varied as long as 65 *Condensate of adipic acid and butanediol, having terminal hydroxy groups and a these are within the present invention. Accordingly, molecular weight of about 800 this invention is not to be interpreted as being limited **Desmodur l; trade name, produced by Bayer AG; 75 wt.% ethylacetate solution; to the illustrated Examples only. All parts and percents adduct 3 moies of toluenediisocyanate and mole of trimethyoi propane. are by weight unless otherwise specifically indicated. 3,943,012 13 14 Each of the resulting coating compositions was ap magnetic recording layer having a coercive force of plied to one surface of a polyethyleneterephthalate film about 700 to 1500 oersteds in the oriented direction of (thickness: 25 pu) in a magnetic field and heated and the ferromagnetic powder and a residual magnetic flux dried to form a layer having a thickness of 4.5 u. The density of about 1500 gausses or higher, the residual thus obtained magnetic web was treated with a super 5 magnetic flux density of which after storage for 160 calender and slit to form a video tape having a width of hours in an atomosphere of 60°C and 90% RH is 85% % inch. The magnetic characteristics of the tapes ob or higher of the initial value thereof before said storage, tained are shown in the following Table 3. and said ferromagnetic alloy powder comprising the Table 3 Sample Magnetic Hc Square- Residual Magnetic Flux Density" (G) Sensitivity** Substance (Oe) less Initial Walue After Weather- (dB) Ratio Resistance Testing No. 1 A 980 0.85 1900 1630 +.6 No. 2 B 07.0 0.86 1820 1660 +2.0 No. 3 C 720 0.82 2010 1305 -1.3 No. 4 D 970 0.85 1970 1070 0.0 'Stored for 160 hours at 60°C, 90%RH "After weather-resistance testing, non-bias recording of 5MHz, with No. 4 as standard. FIG. 1 shows a preferred composition range of the Fe-Co-Cr system of this invention. The preferred reaction product of reducing a mixed solution contain range is the shaded portion in FIG. 1. (This ternary ing Fe, Co and Cr ions with a borohydride compound figure only shows the three components of Fe, Co and reducing agent, said mixed solution containing metal Cr contained in the samples, and the boron component ions ranging from 0.01 to 0.5 mole/liter in concentra therein is not shown.) The respective Samples A, B, C 25 tion, such that said ferromagnetic alloy powder com and D are plotted in FIG. 1 with respect to their Fe prises about 65 to 89%. Fe, about 7 to 34% Co, and Co-Cr composition. about 0.5 to 5% Cr, said percentages being by weight. FIG. 2 shows the variation in residual magnetic flux 2. The magnetic recording medium claimed in claim density of Samples No. 2 (present invention) and No. 3 1, wherein the borohydride compound is in a solution (comparative sample) in weather-resistance testing. 30 having a hydroxide ion concentration of about 0.001N From the above results, it is apparent that the mag to 0.6N. netic recording tapes A and B of this invention have 3. The magnetic recording medium as claimed in more excellent weather-resistance than other conven claim 1, wherein Br/Hc of the ferromagnetic metal tional tapes. powder is about 1.5 to 4.5, in which He is the coercive While the invention has been described in detail and 35 force in oersteds and Br is the residual magnetic flux with reference to specific embodiments thereof, it will density in gausses. be apparent to one skilled in the art that various 4. The magnetic recording medium as claimed in changes and modifications can be made therein with claim 3, wherein the Br/Hc is 3.8 to 2.0. out departing from the spirit and scope thereof. 5. The magnetic recording medium as claimed in What is claimed is: 40 claim 1 wherein the proportion of the respective metal 1. A magnetic recording medium comprising a sup components is within the range of the cross-hatched port having thereon a magnetic recording layer com portion in FIG. 1. prising a binder and a ferromagnetic alloy powder, said k k k 45

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