CA1042278A - Method of producing a magnetic recording material - Google Patents

Abstract

TITLE OF THE INVENTION
A method of producing a magnetic recording material ABSTRACT OF THE DISCLOSURE
The method of producing a magnetic recording material comprises heating, pressing and thus transferring a magnetic stripe to a support member, the heating and pressing treatment being carried out, followed by a magnetic annealing treatment, in a magnetic field in a direction wherein a magnetic recording is to be carried out.

Description

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.. ` 10 BACKGROUND OF ~H~ INVEMTIO~
'~his invention rela-tes to a method of producing a mar,netic recording material and more particularly~ it is con-cerned with a method for raising the sensitivit~ of a magnetic .. recording material.
~ he magnetic annealing effect to raise the sensi-tiv-ity of a magnetic recording material has hitherto been known . as menti.oned in "Theory and Application of ~errites" complied - by T. '~akei, Chapter 2, page 24 to 27, Japanese Patent Publica-;` tions 5927/1961 and 18282/1961 and it is mentioned in -the last publication that a magnetic tape is prepared using ferrite par-,~. ticles containing 0.2 to 35 atomic ~b of cobalt and subjected to magnetic annealing at a temperature ran6e of 50 to 300 a within ... .
which the tape is not deteriorated, whereby the sensitivit;y in ~:
. the magnetic annealin~,r cirection is raised to 1.5 or more times.i hi~,rher than that in a direction vertical thereto. It is also ;. known that a magnel~ic tape suffers from deformation upon expo- ~.
ure to a high temperature and is not useful substan-,ially as a magnetic recording medium, since the support OI the magnetic `: tape consists of a relatively heat resistant matarial such as c~ I I u I ~s~
~` 3~ polyethylene terephthalate, polyethylene naphthalate, cllu'oec ~;~. . , ~
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.: ` ' 4~Z~3 1 ace-tate or polyvinyl chloride, but has a small thickness.
~herefore~ the magnetic annealing is ordinarily carried out within a considerably'low temperatur0 range, but resulting in fast moderation and deterioration. ~hu~ thi~ method has no practical use.
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S~MMARY OF ~HE INVEN~ION
It i~ an ob~ect of the invention to provide a magnet-ic recording material having lastingly an excellent sensitivity.
;' It is another object of the invention to provide a ' 10 method Qf magnetic annealing in a static magnetic field.
'" ! It is a ~urther obaect of the invention to provide a ... i - - .
'I magnsbic recording material o~ magnetic recording layer transfer type having a high sensitivity.
I

~ he'above described objects can be accomplished by a method of producing a magnetic recording material which comprises heatingt pressing and thus transferring a magnetic stripe to a support member ~uch as card, the heating and pressing being car-ried out, followed ~ a magnetic annealing treatment, in a magnet- ''-; ia ~ield in a dirèction wherein a magnetic recording is carried out. .' DE~AIIæD DESCRIP~ION 0~ q~IE INVEN~ION
In the production of a magnetic card, it is known .. . .
that a thermoplastic magnetic layer or magnetic layer having ; ' a heat-fusible adhesive layer, these magnetic layers each being ' ' provided on a temporary support such as polyethylene terephthalate, is superinposed on a support such as paper or polyvinyl chloride, then heated and transferred. During the same time, the conditions of heating and pressing, depending on uses thereof, arè ordinarily '` within ranges of 50 to 300 C ancl 3 to 300 Kg/cm2 respectively and, thereafter, the magnetic card is cooled'to room temperature . ' ' .
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1 for a period of 5 minutes to 3 hours.
It is now found that the magnetic annealing effect ... .
:. is very large in such magnetic cards, since they are formed by - heating and pressing at a considerable temperature and pressure :~
and then annealing gradually for a long period of time to give ~ a magnetic recording material. .
.; In the method of producing a magnetic recording mate~
. rial according to the invention, the magnetic annealing is car-ried out at a higher temperature and higher pressure than employ-. 10 ed in the prior art when a magnetic layer is formed on a temporary .
;~ support and then transferred to a real support or when the forming ~ i~ effected after transferred, whereby the sensitivity can be ` .
.~ raised in a direction in which magnetic recording is to be carried ; out. ~he feature of the method of the invention consists in using ., , . : ..... ..
a spe¢ified ferromagnetic ~errite fine powder and effecting the heating and cooling in a magnetic field under pressure so as to .
obtain an excellent magnetic recording material.
Since the method of the invention is carried out under -~ pres~ed state in comparison ~ith the magnetic annealing using a :~
magnetic field and heat only, the residual magnetic flux density oan be markedly increased and stabilized, and a magnetic record-ing material can be subjected to magnetic annealing without de-.
formation, thus obtaining a very smooth, desirable magnetic card.
.. If necessary, an unusual form, for example, having a rugged sur- :
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~;; face can be obtained. ~here is little deformation of a magnetic ` recording material becau~e of pressing according to the invention ,, .
~: and, therefore, the heating can be carried out up to a higher i temperature than in the prior art, so that the magnetic annealing effect may further be enhanced. ~his is effective, in particular, ~
for magnetic ~heets. .~ -.. Examples of the magnetic fine powder suitable for the ` practice of the invention are cobalt doped maghemite (~-Fe203)~

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i,'~ ~ ,.` , , ~ 8 1 cobalt doped magnetite (~e~04) and cobalt doped berthollide ~erric oxide (FeOx : 1.33~ x ~1.50) with a grain size of not more than 10 microns. Ordinarily cobalt is contained in a quantity of 0~2 - 35 atomic %. In addition to cobalt in these ferromagnetic materials, manganese~ chromium, nickel and zinc can be in incorporated as a third component in a quantity of .. . ~
about 0.1 to 20 atomic %O
~ ~he magnetic recording layer o~ the present invention i can be combined with the above described magnetic fine powder and various materials to prepare recording mediaO
Binder materials which can be used in combination . . .
with the ~erromagnetic material o~ the present invention include thermoplasti¢ or thermoseW ing resins known in the art.
~ hermoplastic re~i~s are those with a softening temper-ature not higher than about 150 C, an average molecular weight ; . .
o~ ~rom about 10~000 to 200~000 and with a degree o~ polymeriza-tion of from about 300 to 1,000, including, e.g., vinyl chloride~
;~i . ....
vinyl a¢etate ¢opolymers, vinyl chloride/vinylidene chloride copolymers, vinyl chloride/acrylonitrile copolymers, acrylic acid ester/a¢rylonitrile copolymers, acrylic acid ester/vinylidene chloride copolymers, acrylic acid e~ter/styrene copolymers, methacrylic acid ester/acrylonitrile copolymers, methacrylic ; acid ester/vinylidene chloride copolymers, methacrylic acid ester/styrene copolymers~urethane elastomers, polyvinylidene ~luoride, vinylidene chioride/acrylonitrile copolymers, butadi-~.... .
ene/acryloni-trile copolymers, polyamides, poly(vinylbutyral), ; cellulose derivatives ~uch as cellulo~e acetate butyrate, cellu-;~ lose diacetate, cellulose triacetate, cellulose propionate, nitrocellulo~e, etc., styrene/butadiene copolymers, polyester resins, chlorovinyIether/acrylic acid ester copolymers, amino ; resins, various synthetic rubber based thermoplastic resins, and mixture~ thereof.
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1 Use of thése resi~s is described in the following Japane~e Patent Publication Nos. 6877~1962, 12528/1964, 19282/ ~i-1964, 5349/1965, 20907~1965, 9463/1966~ 14059/1966, 16985/1966, 6428/1967, 11621/1967, 4623/1968, 15206/1968, 2889/1969, 17947/
:
1969, 18232/1969, 1~020/1970, 14500/1970, 18573/1972~ 22063/1972, 22064/1972, 22068~19?2, 22069/1972 22070/1972 and 27886/1972, and U.S. Patent Nos. 3,144,352~ 3,419,420~ 3,4999789 and 3,713,887, etc.
Suitable thermose~ting re~ins which can be used are ;.. - ~,,: .
; 10 those which have a mole¢ular weight not greater than about 200,000 when present in the coating mixture, and which form a s network with an in~inite molecular weight through a condensation or addition reac~ion. Further those which do not soften or melt until thermal decomposi~ion are preferred. Specific examples are phenol re~ins, epoxy resins, curable polyurethane resins, melamine re~ins, urea resins, alkyd resins, silicone resins, reactive acrylic resins, epoxy-polyamide resins, mixtures of a hi~h molecular welght polyester resin with an isocyanate prepolymer, mixtures o~ methacrylic acid ester copolymers with diisocyanate prepolymers~ mixtures o~ polyester polyols with .
polyisocyanates, urea-formaldehyde resins, low molecular weight ~`
` glycol/high mole¢ular weight diol-triphenylmethane triisocyanate ", ~ i: mixture~ polyamide resin~, and mixtures thereof.
Use o~ these resins is described in the followin~
Japanese Patent Publication Nos. 8103/1964, 9779/1965, 7192/
1966, 8016/1966, 14275/1966, 18179/1967, 12081/19687 28023/1969, 14501/1970~ 24902/1970, 13103/1971, 22065/1972, 22066/1972, 22067/
1972, 22072/1972, 22073/1972, 28045/1972, 28048/1972,and 28922/1972, and U.S. Patent No~. 3,144,353, 3,320.090, ~,437,510, 3,597,273, -~
3,781,210 and 3,781,211, etc.
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~hese resin binders can be utilized individually or in combination, and fur~her additive~ can be employed. ~he mixing i"' ~ , , -..

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1 ratio between the ferromagnetic powder and the binder is from about 100 : 10 to 100 : 200 by weight, preferably 100 : 25 to 100 : 120 by weight.
~ ypical additives are a dispersing agent, a lubricat-ing agent, and an abrasive. Dispersing agents include caprylic acid, caproic acid, lauric acid, myristic acid, palmitic acid, ~tearic acid, olei¢ acid9 elaidic acid, linoleic acid, linolenic acid, stearolic acid, all of which have from about 12 to 18 car-bon atom~ with ~he general formula R1COOH (in which R1 represents an alkyl group having about 11 to 17 carbon atoms); a fatty acid ester with the general formula R2COOR3 wherein R2 and R3 each represent~ an alkyl group of having 1 ~o about 12 carbon atoms including ethyl acetate, butyl acetate, ethyl propionate, methyl butyrate, ethyl caprylate, propyl laurate 9 etc.; a metal soap ¢omprising an alkali metal (e.g., sodium, potassium, etc.) or an ` alkaline earth metal (e.g., magnesium, calcium, ètc.) salt of the above-cibed fatty acid; leci-thin, etc. ~urther, a higher alcohol having about 12 to 24 carbon atoms ~uch as lauryl alcohol, penta-deoyl alaohol, cetyl alcohol, stearyl alcohol, nonadecyl alcohol, etc. and bhe ~ulfuric acid ester thereof can be employed. Such a dispersing agent can be incorporated in an amount of from about , 1 to 20 part~ by wei~ht per 100 parts by weight of the binder.
` ~ Suitable lubricant~ include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a fatty acid ester oompri~ing a monocarboxylic fatty acid having about 12 to 16 carbon atoms and a monohydric alcohol having about 3 to 12 car-`; bon atoms~ a fatty acid ester comprising a monocarboxylic acid with more than about 17 carbon atoms and a monohydric alcohol ~; which will form an ester having about 15 to 28 total carbon ~
atoms. Suitable fatty acid esters include ethyl caprylate, : .
` ethyl laurate, propyl myristate, methyl palmitate, ethyl stea-.
; rate, amyl stearate, ethyl behenate, ethyl oleate, propyl ``` - 6 .,.` ' :,~.
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1 linolate, methyl linolenate, etc. Such a lubricant can be used at from about 0.2 to 20 parts by weight per 100 parts by weight of the binder. Descriptions as to the lubricant can be found in Japanese Patent Publication No. 23889/1968, and Japanese Pa-tent Publication Nos. 24041/1973 and 18482/1973, U. S. Patent Nos.
3,470,021, 3,492,235, 3,497,411, 3,523,086, 3,625,760, 3,630,772, 3,634,253, 3,647,539 and 3,687,725, B M Technical Disclosure --Bulletin Vol. 9, No. 7, Page 779, December 1966, and ELEKTRONIK
1961, No. 12, Page 380, etc.
As to the abrasive, those conventionally used abrasives can be used including alumina, fused alumina, silicon carbide, chrome oxide, c~rundum, synthetic corundum, diamond, synthetic diamond, garnet, emery (main ingredient; corundum and magnetite~, etc. A preferable size of such an abrasive ranges from about 0.1 to 2 microns in average. The abrasive can be present in an amount of from about 1 to 20 parts by weight per 100 parts by weight of the binder. Descriptions of abrasives can be found in Japanese Patent Publication No. 28642/1977, U.S. Patent Nos.
; 3,007,807, 3,041,196, 3,293,066, 3,630,910,and 3,687,725, British Patent No. 1,145,349 and German Patent No. 853,211. :
A magnetic recording layer can be formed by dissolving `
;; or dispersing the above described components in a suitable organicsolvent system and coating the resulting mixture on a substrate. -. . .
The substrate can have a thickness of about 5 to 50 microns, more preferably from 10 to 40 microns, and examples include a polyester such as poly(ethylene terephthalate), a polyolefin such as polypropylene, a cellulose derivative such r as cellulose triacetate, cellulose diacetate e-t., a polycarbonate, : ,:
etc.
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`~ 30 Suitable methods of coa-ting a magnetic recording layer ;; on a subs-trate include various coa-ting techniques such as air `
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~`~! doctor coating, blade coating, air knife coating, squee~e coating, , ~ .- , .,`'' ~'~ :".

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1 impregnation coating, reverse roll coating, transfer roll coat-ing, gravure coating~ kiss coating~ cast coating or spray coat-ing. Other method~ can be used and all o~ these methods are . . . ~ .
explained in detail in Coating Engineerin~, p.253-277, Asakura Shoten9 March 20, 1971.
Organic solvents which can be used for coating include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, pro-panol, butanol, etc~; esters such as methyl acetate, ethyl ace-tate, butyl acetate ethyl lactate, glycol acetate monoethylether, ... .
etc.; ethers and glycol ethers such as diethyl ether, glycoldimethylether, glycol monoethylether, dioxane, tetrahydrofuran, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, etc.; chlorinat~ed hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, ethylene chlorohydrin, chloroform, dichlorobenzene, etc., dimethyl sulfoxide, and dimethylformamide. A suitable concentration o~ the ferromagnet-ic powder in the coa-ting composition can ran~e from about 150 to 500 g, preferably 200 to 450 g per kg of solvent.
; 20 Example~ o~ the real or permanent suppor-t which can be used are resin sheebs or plates such as of polyvinyl chloride, polycarbonate, polyacrylonitrile, polystyrene, ABS resin, glass .
; fiber-reinforoed polyesters, etc.; metal sheet~ or plates such as of aluminum~ oopper~ stainle~ ~teel~ etc.; and glass ~heets or plate~.
As to the conditions for makin~ a magnetic card? the : heating temperature i~ ordinarily 50 to 300 C, preferably 120 to 180 C and the pressure is ordinarily 3 to 300 Kg/cm2, pref-erably 30 to 100 Kg/cm2. It is desirable to carry out the `: 30 magnetic annealing as ~lowly as possible, but the annealing ~ time iR ordinarily 5 minutes to 3 hours. However, the object ., ~ .
~ ~ o~ the invention can ~ubstantially be achieved in a annealing .~, .. : .
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1 time of about 10 to 60 minutes~ ~he strength of a magnetic field used is 100 to 3,000 gauss. Where the content of cobal-t is less, a relatively weak magnetic field, for example, having a strength of 100 to 200 gauss is sufficient, bu-t, where -the content of cobalt is more, a strength of 1,500 to 2,000 gauss is required.
.,; . .. -~ he present invention will be fur-ther illustrated in greater debail in the following examples and comparative ex-amples~ It will be self-evident to those skilled in the art that the ratios, ingredients in the following formulations, ~ and the order of operations can be modified within the scope of ; the present invention. ~herefore, the present invention is not ~ to be interpreted as being limited to the following examples~ `~
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All parts, percents and the like are by weight, unless otherwise indicated.
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i Example 1 -100 parts of a magnetic material of Co-corltaining magnebite (Co content = 2.5 atomic %, grain size = 0.8 x 0.2 ~), 45 parts of vinyl chloride/vinylidene chloride copolymer (weigh-t .. ..
ratio - 83/17, degree of polymerization = 420) and 200 parts of a mixtu~ of mebhyl e~h~l ~eton~/toluene (1/1~ we~e adequa-ke~y dispersed with 1 part of lecithin in a ball mill and coated onto a surface lubricant-coated temporary support of polyeth~lene terephthalate of 20 ~ to give a thickness of 12,~ on dry base.
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~he magnetic layer thus provided on the temporary support was thermalIy transferred to a support of polyvinyl chloride of 0.7 m/m in thickness and then pressed at 150 C under 50 Kg/cm2 -~
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for 15 minutes, whiIe simultaneously a DC magne~ic field of 1,000 gauss was applied in the recording direction of the card, and the card was magnetic annealed at a rate of 5 C/min to ambient temperature (23 a). ~he coercivity Hc for the record-ing direction was 650 oersteds, the maximum remanence magnetization 9 -- :
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1 ~r max was 1,200 gauss and the squareness ratio Br/Bm was 0.~4.
~ en a card was prepared ~rom the same coated sheet in the absence of -the ma~netic field, on the other hand, the magnetic properties thereof were Hc 620 oersteds, Br max 910 gauss and Br/Bm 0.64. ~he effec-t of the present invention is apparent from that the value o~ Br max was increased by about 32 ~o. ~urthermore, the re~ultant magnetic card was very smooth in spite of that it was exposed to the high temperature.
Similarly other magnetic cards were prepared in an analogous manner to described above bu-t varying the heating temperature, pressure and time (Sample Nos. 3 to 7).
~ he thus obtained results are summarized in ~able 1, in which Sample No. 2 is given for comparison.
~able Sample Temper~ pres- ~ime Magnetic Anneal- Xc Br ~r/Bm No. ature sure ~ield i~ ~eed max (a) (K~2? (min.) (Gaussl (C/min.) ~? ~
; ! 1. 150 5 15 1,000 5 6501, 200 0.84

2 . * 1 5050 15 - 620 910 0.64

3- 100 200 5 1,000 5 6541,180 0.83 `
~. 100 20 24 1,00023 6551,200 0.84 ; 5. 130 16 13 1~000 18 653 1,190 0.84 6- 180 25 8 1,000 32 660 1,210 0.84 7. 210 23 12 1,000 15 655 1,210 0.83 ; * Sample for comparison Example 2 100 parts of a magnetic material of Co and Mn doped berthollide ferric oxide (~eOx, X = 1.42) (Co content = 9 atomic , Mn content = 3 atomic ~, grain size = 0.07 ~ x 0.07 ~), 40 ': !
~, 30 parts of vinyl chloride/vinyl acetate copolymer (copolymerization ;
:...................................................................... .
ra~io = 80/20, degree of polymerization = 350), 5 pa~ts of a plasticizer of dioctyl phthalate, 1 part of lecithin and 200 ~`
parts of a mi};tUre of methyl ethyl ketone/methyl isobutyl ketone/
;` toluene were su~iciently ball milled to prepare a coating liquid -.:
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1 and then coated onto a surface lubricant-coated temporar~ support of polyethylene terephthalate of 20 ~ to give a thickness of 12 on dr~ base. ~he coated sheet was ~lit in a width of 9.5 mJm.
; ~he magnetic layer was thermally transferred to a ~upport of polyvinyl chloride of 0~7 m/m in thickness and then pressed at 120 C under 100 Kg/cm2 for 10 minutes, while simultaneously an AC magnetic field of 1~500 gauss was applied. ~hen the magnetic card was treated in a similar manner to that described in Example he coercivity Hc for the recording direction was 1,100 .
; 10 oersteds, the maximum-remanence magnetization was 900 gauss and .... . .
the squareness ratio Br/~m was 0.86.
` When a card was prepared from the same coated sheet . "
in the absence of the magnetic field, on the other hand, the magnetic properties thereof were Hc 900 oersteds, Br max 700 gauss and Br/Bm 0.67. Furthermore, the resultant magnetic card ... ..
had a very excellent surface property in spite of t~at it was exposed to the high temperature.
Example 3 , i~ 100 parrbs of a magnetic material of Co-containing ~-~e203 (Co conbent , 10 atomic ~ grain size (average) = 0.5 ~ x '` 0.08 ~)~ 30 parts of cellulose nitrate (RS1/2), 250 parts of a `~
~;` mixture of butyl acetate/ethyl acetate (1/1) and 10 parts of tri-phenyl phosphate were sufficiently ball milled to prepare a coat-... .
ing liquid and then coated onto a surface lubrican-t-coated tempo-rary support of polyethylene terephthalate o~ 20 ~ to give a -thick-ness of 12 ~ on dry base. ~he thus coated sheet was slit in a ~` width of 6.5 m/m. ~he magnetic layer was thermally transferred ~ to a support of polyvinyl chloride of 0.7 m/m in thickness and ; further pressed at 1~0 C under 150 Kg/cm2 ~or 15 minutes, while ~ .:
Il 30 simul-taneously a DC magnetic field of 2,000 gauss was applied, ; and the card was magnetic annealed to ambient temperature (23 C) at a rate of 10 C/min while holding the pressure. Measurement .
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4Z~8 1 of the magnetic properties of the resulting magnetic card gave .. . a coercivity Hc of 1,400 oersteds, maximum remanence ma~netiza-tion of 1,100 gauss and squareness ratio of 0.87.
i When a card was prepared from the same coated sheet in the absence of the magnetic field, on the other hand, the magnetic properties measured were Hc 1,000 oersteds, Br max 870 gauss and Br/Bm 0.68. ~he effect of the present invention is apparent from that the value of Br max was increased by about 27 ~. ~he resul-tant magnetic card had no probelm as a magnetic card in spite of , .
. 10 that it was treated at a high temperature under a pressure.
... .Where no pressure was applied in the procedures of Ex-amples 1 to 3, the thermal transfer of the magnetic la~er could ;~
.~ not be carried out and the deformation of the card was too marked ~ to use it as a magnetic card. .
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Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of producing a magnetic recording material which comprises:
a ferromagnetic fine powder containing 0.2 to 35 atomic % of cobalt, said ferromagnetic fine powder being selected from the group consisting of cobalt doped maghemite, cobalt doped magnetite and cobalt doped berthollide ferric oxide, said process comprising transferring a magnetic stripe to a support member by heating and pressing said magnetic stripe,and treating said stripe by a magnetic annealing treatment in a magnetic field in a direction wherein a magnetic recording is to be carried, said heating being carried out at a temperature of from 50 to 300°C and said magnetic field has a strength of from 100 to 3,000 gause.

2. A method as claimed in claim 1 wherein said magnetic annealing treatment is carried out during the transferring.

3. A method as claimed in claim 1 wherein said magnetic annealing treatment is carried out after the transferring.

4. A method as claimed in claim 1 wherein said pressing is carried out under a pressure of from 3 to 300 Kg/cm2.

5. A method as claimed in claim 2 wherein said magnetic annealing treatment is carried out in a period of 5 minutes to 3 hours.

6. A method as claimed in claim 3 wherein said magnetic annealing treatment is carried out in a period of 5 minutes to 3 hours.

7. A method as claimed in claim 1 wherein said ferro-magnetic fine powder contains, in addition, 0.1 to 20 atomic %
of a third component.

8. A method as claimed in claim 7 wherein said third component is selected from the group consisting of manganese, chromium, nickel and zinc.