Process for producing acicular goethite particles and acicular magnetic iron oxide particles

Disclosed herein are a process for producing acicular goethite particles comprising the steps of: blowing an oxygen-containing gas into a ferrous salt reaction solution containing colloidal ferrous hydroxide or iron-containing colloidal precipitates which is obtained by reacting an aqueous ferrous salt solution with less than one equivalent of an aqueous alkali hydroxide solution and/or an aqueous alkali carbonate solution based on Fe.sup.2 + in said aqueous ferrous salt solution so as to oxidize said colloidal ferrous hydroxide or iron-containing colloidal precipitates and to produce acicular goethite nucleus particles, adding to the resultant aqueous ferrous salt reaction solution containing said acicular goethite nucleus particles not less than one equivalent of an aqueous alkali carbonate solution based on Fe.sup.2 + in said aqueous ferrous salt reaction solution, and blowing an oxygen-containing gas into the mixed aqueous ferrous salt reaction solution so as to grow said goethite nucleus particles; and a process for producing acicular magnetic iron oxide particles by reducing the acicular goethite particles obtained in the above process to produce acicular magnetite particles, and if necessary, oxidizing the acicular magnetite particles to obtain acicular maghemite particles, and if necessary, modifying the acicular magnetite or maghemite particles with Co or Co and Fe.sup.2 +.

BACKGROUND OF THE INVENTION 
The present invention relates to acicular goethite particles and acicular 
magnetic iron oxide particles which have a uniform particle size 
distribution, are substantially free of dendrites, and have a large aspect 
ratio (major axial diameter/minor axial diameter) and an excellent 
coercive force distribution. 
With progressing miniatirization and weight-reduction of magnetic recording 
and reproducing apparatuses in recent years, the necessity for a recording 
medium having a higher performance such as a magnetic tape and a magnetic 
disk has been increasing more and more. In other words, a magnetic 
recording medium is required to have a higher recording density, higher 
sensitivity and higher output characteristic. The magnetic characteristics 
of magnetic particles which are demanded in order to satisfy the 
above-mentioned requirements for the magnetic recording medium, are a high 
coercive force and an excellent dispersibility. In order to improve the 
sensitivity and the output of a magnetic recording medium, the magnetic 
particles must have as high a coercive force as possible. this fact is 
described in, for example, DEVELOPMENT OF MAGNETIC MATERIALS AND TECHNIQUE 
OF IMPROVING THE DISPERSION PROPERTY OF MAGNETIC POWDER (1982), published 
by K. K. Sogo Gijutsu Kaihatsu Center, p. 310: "Since the improvement of 
magnetic tapes has been directed toward a higher sensitivity and a higher 
output, it is an important point to enhance the coercive force of acicular 
.gamma.-Fe.sub.2 O.sub.3 particles, . . . " 
In order to improve the recording density of a magnetic recording medium, 
the magnetic recording medium must have a high coercive force and a large 
residual magnetization (Br), as described in the said DEVELOPMENT OF 
MAGNETIC MATERIALS AND TECHNIQUE OF IMPROVING THE DISPERSION PROPERTY OF 
MAGNETIC POWDER. p. 312: "The condition for high-density recording in a 
coating-type tape is that it is possible to keep the high output 
characteristics with respect to a short-wavelength signal at a low noise 
level. For this purpose, it is necessary that both the coercive force (Hc) 
and the residual magnetization (Br) are large, and that the thickness of 
the coating film is thin". It is therefore necessary that the magnetic 
particles have a high coercive force and they are excellent in 
dispersibility in the vehicle, and orientation property and packing 
density in the coating film. 
In order to enhance the output of a magnetic recording medium, it is 
required to have a small switching field distribution (hereinunder 
referred to as "S.F.D.") and hence, the magnetic particles are required to 
have a small width of coercive force distribution. This fact is described 
in Japanese Patent Application LaidOpen (KOKAI) No. 63-26821 (1988): "FIG. 
1 is a graph showing the relationship between the S.F.D. of the 
above-described magnetic disk and the recording and reproducing output. . 
. . The relationship between the S.F.D. and the recording and reproducing 
output is linear, as is clear from FIG. 1. It indicates that the recording 
and reproducing output is enhanced by using ferromagnetic powder having a 
small S.F.D. That is, in order to obtain a large output, an S.F.D. of not 
more than 0.6 is necessary. 
As well known, the coercive force of magnetic iron oxide particles depend 
upon the configurational anisotropy, crystalline anisotropy, strain 
anisotropy, exchange anisotropy, or the interaction thereof. 
Acicular magnetite particles and acicular maghemite particles which are 
used as magnetic iron oxide particles at present show a relatively high 
coercive force by utilizing the anisotropy derived from their shapes, 
namely, by increasing the aspect ratio (major axial diameter/minor axial 
diameter). 
The known acicular magnetic particles are obtained by reducing as a 
starting material goethite particles or hematite particle obtained by 
heat-treating the goethite particle at 280.degree. to 450.degree. C. in a 
reducing gas such as hydrogen, to form magnetite particles, or by further 
oxidizing the thus-obtained magnetite particles at 200.degree. to 
400.degree. C. in air to form maghemite particles. 
The known acicular magnetic iron oxide particles modified with Co or Co and 
Fe are obtained by dispersing acicular magnetite particles or acicular 
maghemite particles as the precursor particles in an alkaline suspension 
containing cobalt hydroxide or an alkaline suspension containing cobalt 
hydroxide and ferrous hydroxide so that 0.1 to 15.0 atomic% of Co based on 
Fe of the precursor particles is contained, and heat-treating the 
resultant dispersion. 
The residual magnetization (Br) in a magnetic recording medium depends upon 
the dispersibility of the magnetic particle in the vehicle, and the 
orientation property and packing density of the magnetic particles in the 
coated film, and in order to improve these properties, the magnetic 
particles to be dispersed in the vehicle are required to have as large an 
aspect ratio (major axial diameter/minor axial diameter) as possible, a 
uniform particle size distribution and no inclusion of dendrites. 
As described above, magnetic iron oxide particles which have a 
substantially uniform particle size distribution, which are substantially 
free of dendtritess and which have a large aspect ratio (major axial 
diameter/minor axial diameter) are now in the strongest demand. In order 
to obtain magnetic iron oxide particles provided with these properties, it 
is necessary that as the starting material goethite particles have a 
substantially uniform particle size, are substantially free of dendrites 
and have a large aspect ratio (major axial diameter/minor axial diameter). 
e.g. an aspect ratio of not less than 20. 
As a method of producing goethite particles which are the starting 
material, the following methods are conventionally known: (1) a method of 
producing acicular goethite particles by oxidizing a suspension containing 
colloidal ferrous hydroxide which is obtained by adding not less than one 
equivalent of an aqueous alkali hydroxide solution to a ferrous salt 
solution, at a temperature of not more than 80.degree. C. and pH of not 
less than 11 by blowing an oxygen-containing gas into the suspension 
(Japanese Patent Publication No. 39-5610 (1964)); (2) a method of 
producing spindle-shaped goethite particles by oxidizing a suspension 
containing FeCO.sub.3 which is obtained by reacting an aqueous ferrous 
salt solution with an aqueous alkali carbonate solution, by blowing an 
oxygen-containing gas into the suspension (Japanese Patent Application 
Laid-Open (KOKAI) No. 50-80999 (1975)); and (3) a method of producing 
acicular goethite nucleus particles by oxidizing an aqueous ferrous salt 
solution containing a colloidal ferrous hydroxide or an iron carbonate 
which are respectively obtained by adding not more than one equivalent of 
an aqueous alkali hydroxide solution or an aqueous alkali carbonate 
solution to an aqueous ferrous salt solution, by blowing an 
oxygen-containing gas into the suspension, and then growing the goethite 
nucleus particles by adding to the thus-obtained aqueous ferrous salt 
solution containing the goethite nucleus particles not less than one 
equivalent of an aqueous alkali hydroxide solution based on Fe.sup.2 + in 
the aqueous ferrous salt solution and blowing an oxygen-containing gas 
into the resultant aqueous ferrous salt solution for oxidization (Japanese 
Patent Publication No. 59 -48766 (1984), Japanese Patent Application 
Laid-Open (KOKAI) Nos. 59-128293 (1984), 59-128294 (1984), 59-128295 
(1984) and 60-21818 (1985)). 
Although acicular magnetic iron oxide particles which have a uniform 
particle size distribution, which are substantially free of dendtritess, 
and which have a large aspect ratio. (major axial diameter/minor axial 
diameter) and excellent coercive force distribution are now in the 
strongest demand, the particles obtained by the method (1) of producing as 
a starting material goethite particles contain dendrites and cannot be 
said to have a uniform particle size distribution in-spite of the large 
aspect ratio (major axial diameter/minor axial diameter), particularly, an 
aspect ratio of not less than 10. 
According to the method (2), although spindle-shaped particles having a 
uniform particle size distribution and being free of dendrites are 
produced, the aspect ratio (major axial diameter/minor axial diameter) 
thereof is not more than about 7. That is, the method (2) is defective in 
that it is difficult to produce particles having a large aspect ratio 
(major axial diameter/minor axial diameter). This phenomenon tends to be 
more prominent as the major axial diameter of the particles become 
smaller. Various attempts have been made to increase the aspect ratio 
(major axial diameter/minor axial diameter) of spindle-shaped goethite 
particles, but the actual aspect ratio (major axial diameter/minor axial 
diameter) obtained has been not more than about 17 to 18, which cannot be 
said satisfactory. 
The object of the method (3) is to improve the properties such as particle 
size, aspect ratio (major axial diameter/minor axial diameter) and the 
presence or absence of dendrites of the acicular goethite particles 
produced by the method (1) or (2), but goethite particles produced by the 
method (3) can not be said to satisfy the demand for various properties 
have not been obtained yet. 
Therefore, acicular magnetic iron oxide particles produced from as the 
starting material these goethite particles cannot be said to have a 
uniform particle size distribution, to be free of dendrites and to have a 
large aspect ratio (major axial diameter/minor axial diameter). 
Accordingly, it is an object of the present invention to provide acicular 
goethite particles and acicular magnetic iron oxide particles which have a 
uniform particle size distribution, which are substantially free of 
dendrites, and which have a large aspect ratio (major axial diameter/minor 
axial diameter) and excellent coercive force distribution. 
As a result of studies undertaken by the present inventors, it has been 
found that by blowing an oxygen-containing gas into a ferrous salt 
reaction solution containing colloidal ferrous hydroxide or 
iron-containing colloidal precipitates which is obtained by reacting an 
aqueous ferrous salt solution with less than one equivalent of an aqueous 
alkali hydroxide solution and/or an aqueous alkali carbonate solution 
based on Fe.sup.2 + in the aqueous ferrous salt solution so as to oxidize 
the colloidal ferrous hydroxide or iron-containing colloidal precipitates 
and to produce acicular goethite nucleus particles, adding to the 
resultant aqueous ferrous salt reaction solution containing the acicular 
goethite nucleus particles not less than one equivalent of an aqueous 
alkali carbonate solution based on Fe.sup.2 + in the aqueous ferrous salt 
reaction solution, and blowing an oxygen-containing gas into the mixed 
aqueous ferrous salt reaction solution so as to grow the goethite nucleus 
particles, the thus-obtained acicular goethite particles have a uniform 
particle size distribution, are substantially free of dendrites, and have 
a large aspect ratio (major axial diameter/minor axial diameter) and 
excellent coercive force distribution. On the basis of this finding, the 
present invention has been achieved. 
SUMMARY OF THE INVENTION 
In a first aspect of the present invention, there is provided a process for 
producing acicular goethite particles comprising the steps of: blowing an 
oxygen-containing gas into a ferrous salt reaction solution containing 
colloidal ferrous hydroxide or iron-containing colloidal precipitates 
which is obtained by reacting an aqueous ferrous salt solution with less 
than one equivalent of an aqueous alkali hydroxide solution and/or an 
aqueous alkali carbonate solution based on Fe2 +in the aqueous ferrous 
salt solution so as to oxidize the colloidal ferrous hydroxide or 
iron-containing colloidal precipitates and to produce acicular goethite 
nucleus particles; adding to the resultant aqueous ferrous salt reaction 
solution containing the acicular goethite nucleus particles not less than 
one equivalent of an aqueous alkali carbonate solution based on Fe.sup.2 + 
in the aqueous ferrous salt reaction solution; and blowing an 
oxygen-containing gas into the mixed aqueous ferrous salt reaction 
solution so as to grow the acicular goethite nucleus particles. 
In a second aspect of the present invention, there is provided a process 
for producing acicular magnetic iron oxide particles comprising the steps 
of: blowing an oxygen-containing gas into a ferrous salt reaction solution 
containing colloidal ferrous hydroxide or iron-containing colloidal 
precipitates which is obtained by reacting an aqueous ferrous salt 
solution with less than one equivalent of an aqueous alkali hydroxide 
solution and/or an aqueous alkali carbonate solution based on Fe.sup.2 + 
in the aqueous ferrous salt solution so as to oxidize the colloidal 
ferrous hydroxide or iron-containing colloidal precipitates and to produce 
acicular goethite nucleus particles; adding to the resultant aqueous 
ferrous salt reaction solution containing the acicular goethite nucleus 
particles not less than one equivalent of an aqueous alkali carbonate 
solution based on Fe.sup.2 + in the aqueous ferrous salt reaction 
solution; blowing an oxygen-containing gas into the mixed aqueous ferrous 
salt reaction solution so as to grow the acicular goethite nucleus 
particles; and heat-treating in a reducing gas the thus-obtained acicular 
goethite particles or acicular hematite particles obtained by 
heat-treating the thus obtained acicular goethite particles at 300.degree. 
to 700.degree. C., thereby obtaining acicular magnetite particles; and, if 
necessary, oxidizing the acicular magnetite particles, thereby obtaining 
acicular maghemite particles. 
In a third aspect of the present invention, there is provided a process for 
producing acicular magnetic iron oxide particles comprising the steps of: 
blowing an oxygen-containing gas into a ferrous salt reaction solution 
containing colloidal ferrous hydroxide or iron-containing colloidal 
precipitates which is obtained by reacting an aqueous ferrous salt 
solution with less than one equivalent of an aqueous alkali hydroxide 
solution and/or an aqueous alkali carbonate solution based on Fe.sup.2 + 
in the aqueous ferrous salt solution so as to oxidize the colloidal 
ferrous hydroxide or iron-containing colloidal precipitates and to produce 
acicular goethite nucleus particles; adding to the resultant aqueous 
ferrous salt reaction solution containing the acicular goethite nucleus 
particles not less than one equivalent of an aqueous alkali carbonate 
solution based on Fe.sup.2 + in the aqueous ferrous salt reaction 
solution; blowing an oxygen-containing gas into the mixed aqueous ferrous 
salt reaction solution so as to grow the acicular goethite nucleus 
particles; heat-treating in a reducing gas the thus obtained acicular 
goethite particles or acicular hematite particles obtained by 
heat-treating the thus-obtained acicular goethite particles at 300.degree. 
to 700.degree. C., thereby obtaining acicular magnetite particles; if 
necessary, further oxidizing the thus-obtained acicular magnetite 
particles, thereby obtaining acicular maghemite particles; dispersing the 
acicular magnetite particles or acicular maghemite particles as precursor 
particles in an alkaline suspension containing cobalt hydroxide or cobalt 
hydroxide and ferrous hydroxide so that the Co content in the suspension 
is 0.1 to 15.0 atomic % based on Fe of the precursor particles; and 
heat-treating the resultant aqueous dispersion, thereby producing acicular 
magnetite particles or acicular maghemite particles modified with Co or Co 
and Fe.sup.2 +.

DETAILED DESCRIPTION OF THE INVENTION 
As an aqueous ferrous salt solution used in the present invention, an 
aqueous ferrous sulfate solution and an aqueous ferrous chloride solution 
may be used. 
As an aqueous alkali hydroxide solution used for the reaction for producing 
acicular goethite nucleus particles in the present invention, an aqueous 
sodium hydroxide solution and an aqueous potassium hydroxide solution are 
usable. As an aqueous alkali carbonate solution, an aqueous sodium 
carbonate solution, an aqueous potassium carbonate solution and an aqueous 
ammonium carbonate solution are usable. 
The amount of aqueous alkali hydroxide solution and]or aqueous alkali 
carbonate solution used in the present invention is less than one 
equivalent based on Fe.sup.2 + in the aqueous ferrous salt solution. If it 
is not less than one equivalent, the goethite particles obtained have 
non-uniform particle size distribution and include dendrites and granular 
magnetite particles. 
The amount of existent acicular goethite nucleus particles in the present 
invention is 10 to 90 mol % based on the total amount of goethite 
particles produced. If it is less than 10 mol %, it is difficult to obtain 
objective acicular goethite particles. If it exceeds 90 mol %, since the 
ratio of iron carbonate to the acicular goethite nucleus particles is 
decreased,the reaction becomes non-uniform and, hence, the particle size 
distribution of the goethite particles obtained becomes non-uniform. 
As the aqueous alkali carbonate solution used for growing the acicular 
goethite nucleus particles, the same alkali carbonate as that used for the 
reaction for producing acicular goethite nucleus particles is usable. 
The amount of aqueous alkali carbonate solution used is not less than one 
equivalent based on Fe.sup.2 + in the residual aqueous ferrous salt 
solution. If it is less than one equivalent, the goethite particles 
obtained have non-uniform particle size distribution and include dendrites 
and spherical magnetite particles. 
In the present invention, oxidization is carried out by blowing an 
oxygen-containing gas such as air into a liquid under mechanical stirring, 
if necessary. 
The reaction temperature for producing goethite nucleus particles, the 
oxidization temperature and the reaction temperature for growing goethite 
nucleus particles in the present invention are not higher than 80.degree. 
C., which is the temperature for generally producing goethite particles, 
preferably 30.degree. to 60 .degree. C. If the temperature is higher than 
80.degree. C., granular magnetite particles are included in the acicular 
goethite particles. 
Before the addition of the aqueous alkali carbonate solution, the thus 
obtained aqueous ferrous salt reaction solution containing the acicular 
goethite nucleus particles may be treated by any one of the following 
steps. 
(1) To heat-treat the thus-obtained aqueous ferrous salt reaction solution 
containing the acicular goethite nucleus particles at a temperature of 
,not less than 75.degree. C., preferably 80.degree. to 95 .degree. C. for 
not less than 0.5 hrs, preferably 1 to 2 hrs; and to cool the resultant 
aqueous ferrous salt reaction solution containing .the acicular goethite 
nucleus particles to a temperature of less than 60.degree. C., preferably 
30.degree. to 55.degree. C. 
(2) To maintain the thus-obtained aqueous ferrous salt reaction solution 
containing the acicular goethite nucleus particles at a temperature of 
less than 60.degree. C., preferably 40.degree. to 55 .degree. C. in a 
non-oxidizing atmosphere for not less than 1 hr, preferably 2 to 5 hrs. 
(3) To heat-treat the thus-obtained aqueous ferrous salt reaction solution 
containing the acicular goethite nucleus particles at a temperature of not 
less than 75.degree. C., preferably 80.degree. to 95 .degree. C. for not 
less than 0.5 hrs, preferably 1 to 2 hrs; to cool the resultant aqueous 
ferrous salt reaction solution containing the acicular goethite nucleus 
particles to the temperature of less than 60.degree. C., preferably 30 to 
55.degree. C.; and to maintain the thus-obtained aqueous ferrous salt 
reaction solution containing the acicular goethite nucleus particles at a 
temperature of less than 60.degree. C., preferably 40.degree. to 50 
.degree. C. in non-oxidizing atmosphere for not less than 1 hrs, 
preferably 2 to 5 hrs. 
The magnetic iron oxide particles obtained through the above mentioned step 
(1), (2) or (3) have the following experior advantages as compared with 
those obtained by the basic process of the present invention without using 
the above-mentioned steps. 
By the step (1), an orientation and squareness of the magnetic iron oxide 
particles obtained are further improved. 
By the step (2), an S.F.D of the magnetic iron oxide particles obtained is 
further improved. 
By the step (3), an orientation, a squareness and an S.F.D. of the magnetic 
iron oxide particles obtained are further improved. 
The same reaction column may be used for both the reaction for producing 
goethite nucleus particles and the reaction for growing the goethite 
nucleus particles. It is also possible to obtain the objective goethite 
particles by using different reaction columns for these reactions. 
It is possible in the present invention to add elements, for example, Co, 
Ni, Zn, Al, Si and P other than Fe, which are conventionally added in the 
process for producing goethite particles in order to improve various 
properties of magnetic particles. In this case, the same advantages are 
produced. 
The acicular goethite particles are heat-treated at 300.degree. to 
700.degree. C. so as to obtain acicular hematite particles. 
The acicular goethite particles or acicular hematite particles are reduced 
at 280.degree. to 450 .degree. C. in a reducing gas such as hydrogen. 
The oxidization in the present invention is carried out at 200.degree. to 
500.degree. C. by an ordinary method. 
Co-modification (Co-coating) of the magnetic iron oxide particles in the 
present invention is carried out by an ordinary method. For example, the 
Co-modification is carried out by dispersing the precursor particles in an 
alkaline suspension containing cobalt hydroxide or cobalt hydroxide and 
ferrous hydroxide and heat-treating the dispersion at a temperature of 
50.degree. to 100 .degree. C., as described in, e.g., Japanese Patent 
Publication Nos. 52-24237 (1977), 52-24238 (1977), 52-36751 (1977) and 
52-36863 (1977). 
The cobalt hydroxide in the present invention is obtained by reacting an 
water-soluble cobalt salt such as cobalt sulfide and cobalt chloride with 
an aqueous alkali hydroxide solution such as an aqueous sodium hydroxide 
solution and an aqueous potassium hydroxide solution. 
The ferrous hydroxide in the present invention is obtained by reacting a 
water-soluble ferrous salt such as ferrous sulfide and ferrous chloride 
with an aqueous alkali hydroxide solution such as an aqueous sodium 
hydroxide solution and an aqueous potassium hydroxide solution. 
If the temperature is lower than 50.degree. C., it is difficult to produce 
magnetite particles or maghemite particles modified (coated) with Co or Co 
and Fe.sup.2 +, and even if they are produced, a very long time for the 
Co-modification is required. 
Since the modification arises in the form of a hydroxides of cobalt and 
ferrous, the modification is carried out under a non-oxidizing atmosphere 
in order to suppress an oxidization of cobalt and ferrous. The 
non-oxidizing atmosphere is preferably in the stream of an inert gas such 
as N.sub.2 and argon. 
The amount of water-soluble cobalt salt used for Co-modification in the 
present invention is 0.1 to 15.0 atomic % calculated as Co based on Fe of 
the precursor particles. If it is less than 0.1 atomic %, the coercive 
force of the acicular magnetite or maghemite particles produced is 
improved sufficiently. On the other hand, if it is more than 15.0 atomic 
%, the coercive force distribution of the acicular magnetite or maghemite 
particles produced is not improved sufficiently. In consideration of the 
coercive force and the coercive force distribution of the acicular 
magnetite particles or maghemite particles, the amount of water-soluble 
cobalt salt added is preferably 2.0 to 13.0 atomic %. 
Almost the whole amount of water-soluble cobalt salt added is utilized for 
the modification of the surfaces of the magnetic iron oxide particles. 
According to the present invention, when 1 an oxygen-containing gas is 
blown into a ferrous salt reaction solution containing colloidal ferrous 
hydroxide or iron-containing colloidal precipitates which is obtained by 
reacting an aqueous ferrous salt solution with less than one equivalent of 
an aqueous alkali hydroxide solution and/or an aqueous alkali carbonate 
solution based on Fe.sup.2 + in the aqueous ferrous salt solution so as to 
oxidize the colloidal ferrous hydroxide or iron-containing colloidal 
precipitates and to produce acicular goethite nucleus particles; 2 not 
less than one equivalent of an aqueous alkali carbonate solution based on 
Fe.sup.2 + in the aqueous ferrous salt reaction solution is then added to 
the aqueous ferrous salt reaction solution containing the acicular 
goethite nucleus particles; and 3 an oxygen-containing gas is finally 
blown into the mixed aqueous ferrous salt reaction solution so as to grow 
the acicular goethite nucleus particles in the neutral region (pH of 9 to 
10), it is possible to obtain acicular goethite particles which have a 
uniform particle size, which are free of dendrites and which have a large 
aspect ratio (major axial diameter/minor axial diameter), in particular, 
an aspect ratio of not less than 20, and also it is possible to obtain 
acicular magnetic iron oxide particles from the acicular goethite 
particles as a starting material, which have a uniform particle size 
distribution, which are substantially free of dendrites and which have a 
large aspect ratio (major axial diameter/minor axial diameter). These 
acicular magnetic iron oxide particles having these properties are also 
excellent in the coercive force distribution. 
In contrast, in the case of using an aqueous alkali hydroxide solution in 
place of an aqueous alkali carbonate solution for the reaction for growing 
the goethite nucleus particles, or in the case of using not less than one 
equivalent of an aqueous alkali hydroxide solution or an aqueous alkali 
carbonate solution, it is very difficult to obtain the objective acicular 
goethite particles which have a uniform particle size distribution, which 
are free of dendrites and which have a large aspect ratio (major axial 
diameter/minor axial diameter). 
The thus-obtained acicular goethite particles according to the present 
invention have a major axial diameter of not less than 0.1 .mu.m, 
preferably 0.15 to 0.4 .mu.m, an aspect ratio (major axial diameter/minor 
axial diameter) of not less than 20, preferably 22 to 35, and a particle 
size distribution (a geometric standerd deviation (.sigma.g) of not less 
than 0.6, preferably 0.7 to 0.9. 
The acicular magnetite particles according to the present invention have a 
major axial diameter of not less than 0.1 .mu.m, preferably 0.12 to 0.4 
.mu.m, an aspect ratio (major axial diameter/minor axial diameter) of not 
less than 6.5, preferably 6.7 to 9.0, a particle size distribution 
(geometric standard deviation (.sigma.g)) of not less than 0.6, preferably 
0.62 to 0.80. 
The acicular maghemite particles according to the present invention have a 
major axial diameter of not less than 0.1 pro, preferably 0.12 to 0.4 
.mu.m, an aspect ratio (major axial diameter/minor axial diameter) of not 
less than 6.5, preferably 6.6 to 8.0, a particle size distribution 
(geometric standard deviation (.sigma.g)) of not less than 0.6, preferably 
0.62 to 0.80. 
The acicular magnetite particles modified with Co or Co and Fe.sup.2 + 
according to the present invention have a major axial diameter of not less 
than 0.1 .mu.m, preferably 0.12 to 0.4 .mu.m, an aspect ratio (major axial 
diameter/minor axial diameter) of not less than 5.5, preferably 5.8 to 
7.5, a particle size distribution (geometric standard deviation 
(.sigma.g)) of not less than 0.55, preferably 0.59 to 0.75, and contain 
0.1 to 15 atomic % of Co based on Fe of the precursor particles and 0 to 
20 atomic % of coated Fe.sup.2 + based on Fe of the precursor particles. 
The acicular maghemite particles modified with Co or Co and Fe.sup.2 + 
according to the present invention have a major axial diameter of not less 
than 0.1 .mu.m, preferably 0.11 to 0.4 .mu.m, an aspect ratio (major axial 
diameter/minor axial diameter) of not less than 5.5, preferably 5.6 to 
7.5, a particle size distribution (geometric standard deviation 
(.sigma.g)) of not less than 0.55, preferably 0.58 to 0.75, and contain 
0.1 to 15.0 atomic % of Co based on Fe of the precursor particles and 0 to 
20 atomic % of coated Fe.sup.2 + based on Fe of the precursor particles. 
According to the process for producing acicular goethite particles, it is 
possible to obtain acicular goethite particles which have a uniform 
particle size, which are substantially free of dendrites and which have a 
large aspect ratio (major axial diameter/minor axial diameter). 
The magnetic iron oxide particles obtained from the acicular goethite 
particles as a raw material in accordance with the present invention also 
have a uniform particle size, are substantially free of dendrites, and 
have a large aspect ratio (major axial diameter/minor axial diameter) and 
excellent coercive force distribution, so that they are suitable as 
magnetic particles for high-density, high-sensitivity and high-output 
recording. 
EXAMPLES 
The present invention will be explained in more detail while referring to 
the following non-limitative examples. 
The major axial diameter and the aspect ratio (major axial diameter/minor 
axial diameter) in each of the following examples and comparative examples 
are expressed by the average values of the values obtained by measuring in 
the electron micrographs. 
The particle size distribution is expressed by the geometric standard 
deviation (.sigma.g). the major axial diameters of 350 particles were 
measured from electron micrographs (x 120,000) and the actual major axial 
diameters were calculated from the measured values. A cumulative mount (%) 
obtained from the number of the particles belonging to each regular 
interval of the particle diameter was plotted in a logarithmicro-normal 
probability paper with particle diameter (.mu.m) as abscissa and 
cumulative amount (%) as ordinate in accordance with a statistical method 
from the actual particle diameter and the number of the particles. A 
particle diameter (DS.sub.50) when the cumulative amount is 50% and a 
particle diameter (D.sub.84.13) when the cumulative amount is 84,13%, were 
read out of the obtained log-nomal distribution graph. The geometric 
standard deviation (.sigma.g) was found by dividing the particle diameter 
(D.sub.50) by the particle diameter (D.sub.84,13) [.sigma.g=D.sub.50 
/D.sub.84,13 ]. 
The magnetic characteristics and the coating film properties of the 
magnetic iron oxide particles were measured by using a "sample vibrating 
type magnetometer VSM-3S-15" (produced by Toei Kogyo K. K.) and applying 
an external magnetic field up to 5 KOe in case of acicular magnetite 
particles and acicular maghemite particles, or an external magnetic field 
up to 10 KOe in case of acicular magnetic iron oxide particles modified 
with Co or Co and Fe.sup.2 +. 
A sheet-like sample obtained by a method shown in later-described Example 
79 was used for measuring the squareness and the S.F.D. of the coating 
film. The S.F.D. was measured by using a differentiation circuit of the 
above-described magnetometer to obtain the differentiation curve of the 
demagnetizing curve of the magnetism hysteresis curve, measuring a 
half-width value of the curve and dividing the half-width value by the 
coercive force. 
PRODUCTION OF ACICULAR GOETHITE TICLES 
Examples 1 to 8 
Comparative Example 1 to 6 
Example 1 
12.8 l of an aqueous ferrous sulfide solution containing 1.50 mol/l of 
Fe.sup.2 + and 30.2 l of 0.44-N aqueous NaOH solution (the content of NaOH 
corresponds to 0.35 equivalent based on Fe.sup.2 + in the aqueous ferrous 
sulfide solution) were mixed to produce at 38.degree. C. at pH 6.7 an 
aqueous ferrous sulfide solution containing Fe(OH).sub.2. 
Air was blown into the aqueous ferrous sulfide solution containing 
Fe(OH).sub.2 at a rate of 130 l per minute at 40.degree. C. for 3.0 hours, 
thereby producing goethite nucleus particles. A part of the reaction 
solution was extracted, filtered out, washed with water and dried by an 
ordinary method. The electron micrograph (x 30000) of the particles 
obtained is shown in FIG. 1. 
To the aqueous ferrous sulfide solution containing the goethite nucleus 
particles (the mount of existent goethite nucleus particles corresponds to 
35 mol % based on the amount of goethite particles produced) were added 
7.0 l of 5.4-N aqueous Na.sub.2 CO.sub.3 solution (the content of Na.sub.2 
CO.sub.3 corresponds to 1.5 equivalents based on Fe.sup.2 + in the 
residual aqueous ferrous sulfide solution). Air was blown into the 
resultant solution at a rate of 130 l per minute at 42.degree. C. at pH 
9.4 for 4 hours, thereby producing goethite particles. The goethite 
particles produced were filtered out, washed with water and dried by an 
ordinary method. 
The goethite particles produced were acicular particles having a uniform 
particle size distribution (geometric standerd deviation (.sigma.g) of 
0.801), including no dendrites and having an average major axial diameter 
of 0.33 .mu.m and an aspect ratio (major axial diameter/minor axial 
diameter) of 25, as shown in the electron micrograph (x 30000) in FIG. 2. 
Examples 2 to 8 
Goethite particles were produced in the same way as in Example 1 except for 
varying the kind, Fe.sup.2 + content and amount of aqueous ferrous salt 
solution used, the kind, concentration and mount of aqueous alkaline 
solution used, the kind and amount of additional element, and the reaction 
temperature in the process for producing goethite nucleus particles; and 
the kind, concentration and amount of aqueous alkaline solution used, the 
kind and amount of additional element and the reaction temperature in the 
process for growing the goethite nucleus particles. 
The main conditions for production and the properties of the goethite 
particles obtained are shown in Tables 1 and 2. 
Any of the acicular goethite particles obtained in Examples 2 to 8 had a 
uniform particle size distribution and no inclusion of dendrites. 
Examples 9 and 10 
Goethite particles were produced in the same way as in Example 1 except for 
inserting the following steps before the addition of the aqueous alkali 
carbonate solution. 
The thus-obtained aqueous ferrous sulfide solution containing the goethite 
nucleus particles was heat-treated under the condition shown in Table 1 
and the cooled to 45 .degree. C. 
Examples 11 to 13 
Goethite particles were produced in the same way as in Example 1 except for 
inserting the following step before the addition of the aqueous alkali 
carbonate solution. 
The thus-obtained aqueous ferrous sulfide solution containing the goethite 
nucleus particles was maintained under the condition shown in Table 1. 
Example 14 
Goethite particles were produced in the same way as in Example 1 except for 
inserting the following steps before the addition of the aqueous alkali 
carbonate solution. 
The thus-obtained aqueous ferrous sulfide solution containing the goethite 
nucleus particles was heat-treated at a temperature of 90 .degree. C. for 
1 hrs, cooled to a temperature of 45 .degree. C. and maintained at the 
same temperature for 2 hrs in the stream of N.sub.2 gas. 
The main condition for production and properties of the goethite particles 
obtained in Examples 9 to 14 are shown in Tables 1 and 2. 
Any of the acicular goethite particles obtained in Examples 9 to 14 had a 
uniform particle size distribution and no inclusion of dendrites. 
Comparative Example 1 
Goethite particles were produced in the same way as in Example 1 except for 
using 7.0 l of 5.4-N aqueous NaOH solution (the content of NaOH 
corresponds to 1.5 equivalents based on Fe.sup.2 + in the residual aqueous 
ferrous sulfide solution) in place of 7.0 l of 5.4-N aqueous Na.sub.2 
CO.sub.3 solution. 
The particle size distribution of the acicular goethite particles obtained 
was non-uniform as expressed by a geometric standerd deviation (.sigma.g) 
of 0.511 and dendrites were included therein, as shown in the electron 
micrograph (x 30000) in FIG. 3. 
Comparative Example 2 
Goethite particles were produced in the same way as in Example I except for 
using 30.2 l of 0.44-N aqueous Na.sub.2 CO.sub.3 solution (the content of 
Na.sub.2 CO.sub.3 corresponds to 0.35 equivalent based on Fe.sup.2 + in 
the aqueous ferrous sulfide solution) in place of 30.2 l of 0.44-N aqueous 
NaOH solution, and 7.0 l of 5.4-N aqueous NaOH solution (the content of 
NaOH corresponds to 1.5 equivalents based on Fe.sup.2 + in the residual 
aqueous ferrous sulfide solution) in place of 7.0 l of 5.4-N aqueous 
Na.sub.2 CO.sub.3 solution. 
The particle size distribution of the acicular goethite particles obtained 
was non-uniform as expressed by a geometric standerd deviation (.sigma.g) 
of 0.516 and dendrites were included therein, as shown in the electron 
micrograph (x 30000) in FIG. 4. 
Comparative Example 3 
7.5 l of an aqueous ferrous sulfide solution containing 1.0 mol/l of 
Fe.sup.2 + and 24.2 l of 1.3-N aqueous Na.sub.2 CO.sub.3 solution (the 
content of Na.sub.2 CO.sub.3 corresponds to 2.1 equivalents based on 
Fe.sup.2 + in the aqueous ferrous sulfide solution) were mixed to produce 
FeCO.sub.3 at 42.degree. C. at pH 9.9. Air was blown into the aqueous 
solution containing FeCO.sub.3 at a rate of 100 l per minute at 45.degree. 
C. for 5 hours, thereby producing spindle-shaped goethite particles. 
To the aqueous solution containing the spindle-shaped goethite particles 
were added 8.3 l of an aqueous ferrous sulfide solution containing 1.8 
mol/l of Fe.sup.2 + and 10 l of 13-N aqueous NaOH solution (the content of 
NaOH corresponds to 4.4 equivalents based on Fe.sup.2 + in the aqueous 
ferrous sulfide solution added), and the resultant solution were stirred 
and mixed (the amount of spindle-shaped goethite particles corresponds to 
33 mol % of the amount of goethite particles produced). Air was blown into 
the resultant mixed solution at a rate of 150 l per minute at 50.degree. 
C. for 3 hours. 
The goethite particles produced were filtered out, washed with water and 
dried by an ordinary method. 
The goethite particles produced had a uniform particle size distribution 
(geometric standerd deviation (.sigma.g) of 0.841) and included no 
dendrites, but they had a small aspect ratio (major axial diameter/minor 
axial diameter) and took a strip shape, as shown in the electron 
micrograph (x 30000) in FIG. 5. 
Comparative Example 4 
12.8 l of an aqueous ferrous sulfide solution containing 1.3 mol/l of 
Fe.sup.2 + and 30.2 l of 2.4-N aqueous NaOH solution (the content of NaOH 
corresponds to 2.2 equivalents based on Fe.sup.2 + in the aqueous ferrous 
sulfide solution) were mixed to produce Fe(OH).sub.2 at 40.degree. C. at 
pH 13.2. Air was blown into the aqueous solution containing Fe(OH).sub.2 
at rate of 130 l per minute at 45.degree. C. for 15 hours, thereby 
producing acicular goethite particles. The goethite particles produced 
were filtered out and washed with water by an ordinary method. 
To 27.5 l of the aqueous solution containing 586 g of the acicular goethite 
particles were added 12.5 l of an aqueous ferrous sulfide solution 
containing 1.0 mol/l of Fe.sup.2 + and 10 l of 3.8-N aqueous Na.sub.2 
CO.sub.3 solution (the content of Na.sub.2 CO.sub.3 corresponds to 1.5 
equivalents based on Fe.sup.2 + in the aqueous ferrous sulfide solution 
added), and the resultant solution were stirred and mixed (the mount of 
acicular goethite particles corresponds to 35 mol % of the mount of 
goethite particles produced). Air was blown into the resultant mixed 
solution at a rate of 130 l per minute at 42.degree. C. for 4 hours. 
The goethite particles produced were filtered out, washed with water and 
dried by an ordinary method. 
The particle size distribution of the goethite particles obtained was 
non-uniform as expressed by a geometric standerd deviation (.sigma.g) of 
0.512, dendrites were included therein and the aspect ratio (major axial 
diameter/minor axial diameter) was as small as 10. 
Comparative Example 5 
10 l of an aqueous ferrous sulfide solution containing 1.5 mol/l of 
Fe.sup.2 + and 33 l of 1-N aqueous NaOH solution (the content of NaOH 
corresponds to 2.3 equivalents based on Fe.sup.2 + in the aqueous ferrous 
sulfide solution) were mixed to produce colloidal Fe(OH).sub.2 at 
38.degree. C. at pH 13. Air was blown into the suspension containing the 
colloidal Fe(OH).sub.2 at a rate of 13 l per minute at 42.degree. C. for 
15 hours, thereby producing acicular goethite particles. The goethite 
particles produced were filtered out, washed with water and dried by an 
ordinary method. 
The particle size distribution of the goethite particles obtained was 
non-uniform as expressed by a geometric standerd deviation (.sigma.g) of 
0.510 and dendrites were included therein, as shown in the electron 
micrograph (x 30000) in FIG. 6. 
Comparative Example 6 
10 l of an aqueous ferrous sulfide solution containing 1.5 mol/l of 
Fe.sup.2 + and 33 l of 1.8-N aqueous solution Na.sub.2 CO.sub.3 (the 
content of Na.sub.2 CO.sub.3 corresponds to 2.0 equivalents based on 
Fe.sup.2 + in the aqueous ferrous sulfide solution) were mixed to produce 
FeCO.sub.3 at 45.degree. C. at pH 9.8. Air was blown into the aqueous 
solution containing FeCO.sub.3 at a rate of 100 l per minute at 50.degree. 
C. for 5 hours, thereby producing goethite particles. The goethite 
particles produced were filtered out, washed with water and dried by an 
ordinary method. 
The goethite particles obtained were spindle-shape (a geometric standerd 
deviation (.sigma.g) of 0.829) and the aspect ratio (major axial 
diameter/minor axial diameter) was as small as 7, as shown in the electron 
micrograph (x 30000) in FIG. 7. 
PRODUCTION OF ACICULAR MAGNETITE TICLES 
Examples 15 to 28 
Comparative Examples 7 to 12 
Example 15 
5.3 Kg of the paste of the acicular goethite particles (corresponding to 
about 1.6 Kg of acicular goethite particles) obtained in Example 1 were 
suspended in 28 l of water. The pH of the suspension was 8.0. Thereafter, 
240 ml of an aqueous solution containing 24 g of sodium hexametaphosphate 
(corresponding to 1.15 wt % calculated as PO.sub.3 based on the acicular 
goethite particles) was added to the suspension, and the resultant mixture 
was stirred for 30 minutes. The resultant suspension was filtered and 
dried to obtain acicular goethite particles with the surfaces coated with 
a P compound. The thus-obtained acicular goethite particles coated with a 
P compound were heat-treated in air at 320.degree. C., thereby obtaining 
acicular hematite particles coated (modified) with a P compound. 
1000 g of the thus-obtained acicular hematite particles coated with a P 
compound were charged into a retort reducing vessel, and H.sub.2 gas was 
blown into the particles at a rate of 2 l per minute while rotating the 
vessel to reduce them at 360.degree. C., thereby obtaining acicular 
magnetite particles coated with a P compound. 
It was observed through an electron microscope that the acicular magnetite 
particles coated with a P compound had an average major axial diameter of 
0.25 .mu.m and an aspect ratio (major axial diameter/minor axial diameter) 
of 7.5, and that the particle size distribution was uniform as expressed 
by a geometric standard deviation (.sigma..sub.g) of 0.67 and no dendrites 
were included. When the magnetic characteristics were measured, a coercive 
force (Hc) was 400 Oe and a saturation magnetization (.sigma..sub.s) was 
82.7 emu/g. 
Examples 16 to 28, Comparative Examples 7 to 12 
Acicular magnetite particles were obtained in the same way as in Example 15 
except for varying the kind of the starting material and the heating 
temperature for the heat-treatment in air. The main conditions for 
production and the properties of the acicular magnetite particles obtained 
are shown in Table 3. 
As a result of observation through an electron microscope, any of the 
acicular magnetite particles obtained in Examples 16 to 28 proved to have 
a uniform particle size distribution and no inclusion of dendrites. 
PRODUCTION OF ACICULAR MAGHEMITE TICLES 
Examples 29 to 42 
Comparative Examples 13 to 18 
Example 29 
300 g of the acicular magnetite particles coated with a P compound obtained 
in Example 15 were oxidized in air at 300.degree. C. for 60 minutes to 
obtain acicular maghemite particles coated with a P compound. 
It was observed through an electron microscope that the acicular maghemite 
particles coated with a P compound had an average major axial diameter of 
0.24 .mu.m and an aspect ratio (major axial diameter/minor axial diameter) 
of 7.4, and that the particle size distribution was uniform as expressed 
by a geometric standard deviation (.sigma.g) of 0.66 and no dendrites were 
included. When the magnetic characteristics were measured, a coercive 
force (Hc) was 371 Oe and a saturation magnetization (.sigma..sub.s) was 
72.2 emu/g. 
Examples 30 to 42, Comparative Examples 13 to 18 
Acicular maghemite particles were obtained in the same way as in Example 29 
except for varying the kind of acicular magnetite particles. The main 
conditions for production and the properties of the maghemite particles 
obtained are shown in Table 4. As a result of observation through an 
electron microscope, any of the acicular maghemite particles obtained in 
Examples 30 to 42 proved to have a uniform particle size distribution and 
no inclusion of dendrites. 
PRODUCTION OF ACICULAR CO-MODIFIDED MAGNETITE TICLES 
Examples 43 to 60 
Comparative Examples 19 to 24 
Example 43 
100 g of the acicular magnetite particles coated with a P compound obtained 
in Example 15 were charged into 1.0 l of water with 0.085 mol of cobalt 
and 0.179 tool of ferrous iron dissolved therein by using cobalt sulfate 
and ferrous sulfate while preventing the inclusion of air as much as 
possible, and dispersed until the dispersion became a fine slurry. Into 
the dispersion, 102 ml of 18-N aqueous NaOH solution was poured and water 
was further added so as to form 1.3 l of a dispersion in which the 
hydroxyl concentration was 1.0 mol/l. The temperature of the dispersion 
was raised to 100.degree. C. and it was stirred for 5 hours. Thereafter, 
the slurry was taken out, washed with water, filtered out and dried at 
60.degree. C. to obtain acicular Co-modified magnetite particles. 
As a result of observation through an electron microscope, it was proved 
that the acicular maghemite particles obtained had the same configuration 
and the particle size as the precursor particles, namely, the acicular 
magnetite particles coated with a P compound, an average major axial 
diameter of 0.23 .mu.m and an aspect ratio (major axial diameter/minor 
axial diameter) of 6.7. The particle size distribution thereof was uniform 
as expressed by a geometric standard deviation (.sigma.g) of 0.62. When 
the magnetic characteristics were measured, a coercive force (Hc) was 825 
Oe and a saturation magnetization as was 84.6 emu/g. 
Examples 44 to 60, Comparative Examples 19 to 24 
Acicular magnetite particles modified by Co or Co and Fe.sup.2 + were 
obtained in the same way as in Example 43 except for varying the kind of 
precursor particles and the amounts of Co added and Fe.sup.2 + added under 
conditions that the amount of precursor magnetite particles was 100 g and 
the whole volume of the dispersion was 1.3 l. 
The main conditions for production and the properties of the particles 
obtained are shown in Table 5. 
PRODUCTION OF ACICULAR CO-MODIFIDE MAGHEMITE TICLES 
Examples 61 to 78 
Comparative Examples 25 to 30 
Example 61 
100 g of acicular maghemite particles with the surfaces coated with a P 
compound obtained in Example 29 were charged into 1.0 l of water with 
0.085 mol of cobalt and 0.179 mol of ferrous iron dissolved therein by 
using cobalt sulfate and ferrous sulfate while preventing the inclusion of 
air as much as possible, and dispersed until the dispersion became a fine 
slurry. Into the dispersion, 102 ml of 18-N aqueous NaOH solution was 
poured and water was further added so as to form 1.3 l of dispersion in 
which the hydroxyl concentration was 1.0 mol/l. The temperature of the 
dispersion was raised to 100.degree. C. and it was stirred for 5 hours. 
Thereafter, the slurry was taken out, washed with water, filtered out and 
dried at 60.degree. C. to obtain acicular Co-modified maghemite particles. 
As a result of observation through an electron microscope, it was proved 
that the particles obtained had the same configuration and the particle 
size as the precursor particles, namely, the acicular maghemite particles 
with the surfaces coated with a P compound, an average major axial 
diameter of 0.22 .mu.m and an aspect ratio (major axial diameter/minor 
axial diameter) of 6.6. The particle size distribution thereof was uniform 
as expressed by a geometric standard deviation (.sigma.g) of 0.63. When 
the magnetic characteristics were measured, a coercive force (Hc) was 790 
Oe and a saturated magnetization (.sigma..sub.s) was 77.0 emu/g. 
Examples 62 to 78, Comparative Examples 25 to 30 
Acicular maghemite particles modified by Co or Co and Fe.sup.2 + were 
obtained in the same way as in Example 61 except for varying the kind of 
the precursor particles, the amounts of Co added, Fe(II) added and NaOH 
added and the treating temperature and time under conditions that the 
mount of precursor acicular maghemite particles .was 100 g and the whole 
volume of the dispersion was 1.3 l 
The main conditions for production and the properties of the particles 
obtained are shown in Table 6. 
PRODUCTION OF MAGNETIC TAPE 
Examples 79 to 142 
Comparative Examples 31 to 54 
Example 79 
A magnetic tape was produced in the following manner. A magnetic coating 
was prepared by charging the acicular magnetic iron oxide particles coated 
with a P compound obtained in Example 15, the resin and the solvents 
described below into a 140-cc glass bottle in the following ratio, and 
mixing and dispersing the above materials by a paint conditioner for 2 
hours. The magnetic coating was applied to a polyethylene terephthalate 
film (25 .mu.m in thickness) to a thickness of 40 .mu.m by an applicator, 
and the film was then oriented and dried in a magnetic field of 1450 
Gauss. 
______________________________________ 
Glass beads of 1.5 mm in diameter 
100 g 
Acicular magnetite particles 
15 g 
Toluene 5.6 g 
Phosphate ester (GAFAC RE-610, produced 
0.6 g 
by Toho Chemical Industrial Co., Ltd.) 
Lecithin 0.6 g 
Vinyl chloride-vinyl acetate 
3.75 g 
copolymer (Vinilite VAGH, 
produced by Union Carbide) 
Butadiene acrylonitrile 0.75 g 
rubber (Hycar 1432 J, produced by 
Japan Geon Co., Ltd.) 
Mixed solution of Methyl isobutyl ketone, 
40.5 g 
methyl ethyl ketone and toluene (3:1:1) 
______________________________________ 
The magnetic tape produced had an S.F.D. of 0.44, a coercive force (Hc) of 
369 Oe, a residual flux density (Br) of 1630 Gauss and a squareness 
(Br/Bm) of 0.82. 
Examples 80 to 142, Comparative Example 31 to 54 
Magnetic tapes were produced in the same way as in Example 79 except for 
varying the kind of magnetic particles. The acicular maghemite particles 
were oriented in a magnetic field of 1450 Gauss and the acicular 
Co-modified magnetic iron oxide particles were oriented in a magnetic 
field of 1900 Gauss. The properties of the magnetic tapes obtained are 
shown in Tables 7 to 10. 
TABLE 1 
__________________________________________________________________________ 
Production of goethite nucleus particles 
Aqueous alkaline solution 
Amount Additional 
Aqueous ferrous salt solution CO.sub.3 Fe or 
element 
Fe.sup.2+ 2OH/Fe Amount Reaction 
content 
Amount Concentration 
(equivalent 
M/Fe pH for 
temperature 
Examples 
Kind (mol/l) 
(l) Kind (N) (l) 
ratio) 
Kind 
(mol %) 
mixing 
(.degree.C.) 
__________________________________________________________________________ 
Example 1 
FeSO.sub.4 
1.5 12.8 NaOH 0.44 30.2 
0.35 -- -- 6.7 40 
Example 2 
FeSO.sub.4 
0.71 38.0 NaOH 6.6 5.0 
0.61 P 0.80 7.2 42 
Example 3 
FeCl.sub.2 
1.5 12.8 KOH 0.54 30.2 
0.42 -- -- 6.8 40 
Example 4 
FeSO.sub.4 
1.5 12.8 Na.sub.2 CO.sub.3 
0.36 30.2 
0.28 -- -- 6.6 36 
Example 5 
FeSO.sub.4 
0.54 38.0 NaOH 4.4 5.0 
0.54 P 0.90 7.2 40 
Zn 2.0 
Example 6 
FeCl.sub.2 
1.5 12.8 NaOH 0.51 30.2 
0.40 Ni 0.5 6.8 40 
Example 7 
FeSO.sub.4 
1.5 12.8 KOH 0.40 30.2 
0.31 Zn 1.5 6.6 40 
Example 8 
FeSO.sub.4 
1.5 12.8 NaOH 0.51 30.2 
0.40 -- -- 6.7 40 
Example 9 
FeSO.sub.4 
1.5 12.8 NaOH 0.60 32.0 
0.50 -- -- 7.2 40 
Example 10 
FeSO.sub.4 
1.5 12.8 NaOH 0.54 32.0 
0.45 -- 0.28 7.0 35 
Example 11 
FeSO.sub.4 
0.54 38.0 NaOH 4.4 4.7 
0.50 -- 0.28 7.3 40 
Example 12 
FeSO.sub.4 
1.5 12.8 NaOH 0.54 39.1 
0.55 -- 0.28 7.3 45 
Example 13 
FeCl.sub.2 
0.77 25.0 KOH 0.66 23.3 
0.40 -- 0.28 7.1 40 
Example 14 
FeSO.sub.4 
1.5 12.8 NaOH 0.54 35.5 
0.50 -- 0.28 7.2 40 
__________________________________________________________________________ 
Heat-treatment Aging-treatment 
Temperature 
Time Temperature 
Time 
Examples 
(.degree.C.) 
(hr) 
Atmosphere 
(.degree.C.) 
(hr) 
Atmosphere 
__________________________________________________________________________ 
Example 1 
-- -- -- -- -- -- 
Example 2 
-- -- -- -- -- -- 
Example 3 
-- -- -- -- -- -- 
Example 4 
-- -- -- -- -- -- 
Example 5 
-- -- -- -- -- -- 
Example 6 
-- -- -- -- -- -- 
Example 7 
-- -- -- -- -- -- 
Example 8 
-- -- -- -- -- -- 
Example 9 
80 1 Air -- -- N.sub.2 
Example 10 
80 1.5 
Air -- -- N.sub.2 
Example 11 
-- -- -- 45 2 N.sub.2 
Example 12 
-- -- -- 40 3 N.sub.2 
Example 13 
-- -- -- 45 2 N.sub.2 
Example 14 
90 1 N.sub.2 
45 2 N.sub.2 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Growth of goethite nucleus particles Goethite particles 
Aqueous alkaline solution Aspect ra- 
Amount Additional tio (major 
Goethite Con- CO.sub.3 /Fe 
element Reaction 
Major 
axial di- Particle 
nucleus centra- 
(equiv- Amount tempera- 
axial di- 
ameter/mi size 
particles tion alent M/Fe ture ameter 
nor axial distri- 
Examples 
(mol %) 
Kind (N) (l) 
ratio) 
Kind 
(mol %) 
pH 
(.degree.C.) 
(.mu.m 
diameter) 
Shape 
bution 
__________________________________________________________________________ 
Example 1 
35 Na.sub.2 CO.sub.3 
5.4 7 1.5 -- -- 9.4 
42 0.33 25 Acicular 
0.801 
Example 2 
61 Na.sub.2 CO.sub.3 
5.3 7 1.5 -- -- 9.5 
42 0.30 28 " 0.810 
Example 3 
42 K.sub.2 CO.sub.3 
4.2 7 1.3 Co 2.0 9.4 
45 0.36 25 " 0.795 
Example 4 
28 Na.sub.2 CO.sub.3 
5.9 7 1.5 -- -- 9.6 
45 0.27 22 " 0.804 
Example 5 
54 Na.sub.2 CO.sub.3 
4.8 7 1.5 -- -- 9.4 
42 0.20 25 " 0.792 
Example 6 
40 K.sub.2 CO.sub.3 
5.0 7 1.5 -- -- 9.5 
42 0.35 23 " 0.790 
Example 7 
31 Na.sub.2 CO.sub.3 
5.8 7 1.5 -- -- 9.6 
50 0.32 23 " 0.787 
Example 8 
40 Na.sub.2 CO.sub.3 
5.6 7 1.7 Al 1.0 9.4 
45 0.35 20 " 0.791 
Example 9 
50 Na.sub.2 CO.sub.3 
4.7 7 1.7 -- -- 9.6 
45 0.37 32 " 0.792 
Example 10 
45 Na.sub.2 CO.sub.3 
4.8 7 1.6 -- -- 9.5 
48 0.25 24 " 0.800 
Example 11 
50 Na.sub.2 CO.sub.3 
4.4 7 1.5 -- -- 9.4 
42 0.30 29 " 0.830 
Example 12 
55 Na.sub.2 CO.sub.3 
3.7 7 1.5 -- -- 9.4 
40 0.22 25 " 0.842 
Example 13 
40 K.sub.2 CO.sub.3 
5.3 7 1.6 -- -- 9.5 
40 0.36 32 " 0.825 
Example 14 
50 Na.sub.2 CO.sub.3 
4.7 7 1.7 -- -- 9.6 
44 0.31 30 " 0.836 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Acicular 
goethite 
particles Heating 
Examples & 
(Example No. & 
Coating with P compound 
temperature 
Reducing 
Comparative 
Comparative Amount 
in air temperature 
Examples 
Example No.) 
Kind (wt %) 
(.degree.C.) 
(.degree.C.) 
__________________________________________________________________________ 
Example 15 
Example 1 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 16 
Example 2 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 17 
Example 3 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 18 
Example 4 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 19 
Example 5 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 20 
Example 6 
Sodium 1.15 650 360 
hexameta- 
phosphate 
Example 21 
Example 7 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 22 
Example 8 
Sodium 1.15 320 360 
hexameta- 
phosphate 
Example 23 
Example 9 
Sodium 1.15 660 360 
hexameta- 
phosphate 
Example 24 
Example 10 
Sodium 1.15 660 360 
hexameta- 
phosphate 
Example 25 
Example 11 
Sodium 1.15 660 360 
hexameta- 
phosphate 
Example 26 
Example 12 
Sodium 1.15 660 360 
hexameta- 
phosphate 
Example 27 
Example 13 
Sodium 1.15 660 360 
hexameta- 
phosphate 
Example 28 
Example 14 
Sodium 1.15 660 360 
hexameta- 
phosphate 
Comparative 
Comparative 
Sodium 1.15 320 360 
Example 7 
Example 1 
hexameta- 
phosphate 
Comparative 
Comparative 
Sodium 1.15 320 360 
Example 8 
Example 2 
hexameta- 
phosphate 
Comparative 
Comparative 
Sodium 1.15 320 360 
Example 9 
Example 3 
hexameta- 
phosphate 
Comparative 
Comparative 
Sodium 1.15 650 360 
Example 10 
Example 4 
hexameta- 
phosphate 
Comparative 
Comparative 
Sodium 1.15 320 360 
Example 11 
Example 5 
hexameta- 
phosphate 
Comparative 
Comparative 
Sodium 1.15 320 360 
Example 12 
Example 6 
hexameta- 
phosphate 
__________________________________________________________________________ 
Acicular magnetite particles 
Aspect ratio Saturation 
Examples & 
Major axial 
(major axial Coercive force 
magnetization 
Comparative 
diameter 
diameter/minor 
Particle size 
Hc .sigma..sub.s 
Examples 
(.mu.m) 
axial diameter) 
distribution 
(Oe) (emu/g) 
__________________________________________________________________________ 
Example 15 
0.25 7.5 0.67 400 82.7 
Example 16 
0.20 7.7 0.65 383 79.5 
Example 17 
0.24 7.4 0.66 510 79.0 
Example 18 
0.17 6.8 0.63 375 82.1 
Example 19 
0.13 7.0 0.63 358 78.9 
Example 20 
0.29 6.9 0.65 420 82.0 
Example 21 
0.24 7.0 0.64 399 81.4 
Example 22 
0.27 6.7 0.66 408 81.3 
Example 23 
0.30 8.0 0.67 406 82.7 
Example 24 
0.14 7.2 0.68 350 79.2 
Example 25 
0.20 7.8 0.73 380 80.5 
Example 26 
0.17 7.4 0.75 361 82.5 
Example 27 
0.28 7.6 0.72 410 78.6 
Example 28 
0.22 7.9 0.74 378 81.0 
Comparative 
0.16 5.6 0.42 346 82.0 
Example 7 
Comparative 
0.15 5.7 0.41 340 82.1 
Example 8 
Comparative 
0.22 5.0 0.58 352 82.4 
Example 9 
Comparative 
0.23 5.3 0.44 383 82.5 
Example 10 
Comparative 
0.25 5.2 0.43 387 82.5 
Example 11 
Comparative 
0.14 4.9 0.50 333 82.2 
Example 12 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
Acicular 
magnetite 
Acicular maghemite particles 
particles Aspect ratio Saturation 
Examples & 
(Example No. & 
Major axial 
(major axial Coercive force 
magnetization 
Comparative 
Comparative 
diameter 
diameter/minor 
Particle size 
Hc .sigma..sub.s 
Examples 
Example No.) 
(.mu.m) 
axial diameter) 
distribution 
(Oe) (emu/g) 
__________________________________________________________________________ 
Example 29 
Example 15 
0.24 7.4 0.66 371 72.2 
Example 30 
Example 16 
0.19 7.6 0.65 353 69.3 
Example 31 
Example 17 
0.22 7.2 0.65 395 68.8 
Example 32 
Example 18 
0.16 6.7 0.62 348 71.8 
Example 33 
Example 19 
0.13 7.0 0.63 330 68.1 
Example 34 
Example 20 
0.28 6.8 0.64 394 70.9 
Example 35 
Example 21 
0.24 7.0 0.63 370 71.0 
Example 36 
Example 22 
0.25 6.6 0.65 352 71.0 
Example 37 
Example 23 
0.29 7.8 0.67 380 71.5 
Example 38 
Example 24 
0.14 7.1 0.68 338 70.3 
Example 39 
Example 25 
0.18 7.7 0.74 360 71.2 
Example 40 
Example 26 
0.16 7.2 0.77 342 71.8 
Example 41 
Example 27 
0.27 7.5 0.73 391 70.1 
Example 42 
Example 28 
0.21 7.7 0.75 362 71.6 
Comparative 
Comparative 
0.15 5.5 0.41 316 72.0 
Example 13 
Example 7 
Comparative 
Comparative 
0.15 5.6 0.40 310 72.0 
Example 14 
Example 8 
Comparative 
Comparative 
0.21 4.8 0.57 324 73.1 
Example 15 
Example 9 
Comparative 
Comparative 
0.22 5.2 0.44 351 72.5 
Example 16 
Example 10 
Comparative 
Comparative 
0.23 5.0 0.42 348 73.3 
Example 17 
Example 11 
Comparative 
Comparative 
0.13 4.7 0.49 307 71.8 
Example 18 
Example 12 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Production of acicular magnetite particles modified 
with Co or Co and Fe.sup.2+ 
Precursor Amount 
particles of sodium 
Examples & 
(Example No. & 
Amount of Co 
Amount of 
hydroxide 
Comparative 
Comparative 
added Fe.sup.2+ added 
added 
Temperature 
Examples 
Example No.) 
(mol) (mol) (ml) (.degree.C.) 
__________________________________________________________________________ 
Example 43 
Example 15 
0.085 0.179 102 100 
Example 44 
Example 15 
0.0509 0.179 98 100 
Example 45 
Example 15 
0.0509 0.179 170 100 
Example 46 
Example 15 
0.0509 0.1074 
162 100 
Example 47 
Example 15 
0.0509 -- 150 100 
Example 48 
Example 16 
0.085 0.179 102 100 
Example 49 
Example 17 
0.085 0.179 102 100 
Example 50 
Example 18 
0.085 0.179 102 100 
Example 51 
Example 19 
0.085 0.179 102 100 
Example 52 
Example 20 
0.085 0.179 102 100 
Example 53 
Example 21 
0.085 0.179 102 100 
Example 54 
Example 22 
0.085 0.179 102 100 
Example 55 
Example 23 
0.085 0.179 102 100 
Example 56 
Example 24 
0.085 0.179 102 100 
Example 57 
Example 25 
0.085 0.179 102 100 
Example 58 
Example 26 
0.085 0.179 102 100 
Example 59 
Example 27 
0.085 0.179 102 100 
Example 60 
Example 28 
0.085 0.179 102 100 
Comparative 
Comparative 
0.085 0.179 102 100 
Example 19 
Example 7 
Comparative 
Comparative 
0.085 0.179 102 100 
Example 20 
Example 8 
Comparative 
Comparative 
0.085 0.179 102 100 
Example 21 
Example 9 
Comparative 
Comparative 
0.085 0.179 102 100 
Example 22 
Example 10 
Comparative 
Comparative 
0.085 0.179 102 100 
Example 23 
Example 11 
Comparative 
Comparative 
0.085 0.179 102 100 
Example 24 
Example 12 
__________________________________________________________________________ 
Acicular magnetite particles modified with Co or Co and Fe.sup.2+ 
Aspect ratio Saturation 
Examples & 
Major axial 
(major axial Coercive 
magnetization 
Comparative 
diameter 
diameter/minor 
Particle size 
force Hc 
.sigma..sub.s 
Examples 
(.mu.m) 
axial diameter) 
distribution 
(Oe) (emu/g) 
__________________________________________________________________________ 
Example 43 
0.23 6.7 0.62 825 84.6 
Example 44 
0.23 6.8 0.63 730 85.2 
Example 45 
0.23 6.8 0.63 762 85.4 
Example 46 
0.22 6.9 0.64 725 84.5 
Example 47 
0.22 7.1 0.65 680 80.7 
Example 48 
0.18 6.7 0.61 835 81.6 
Example 49 
0.23 6.6 0.63 945 82.0 
Example 50 
0.15 5.8 0.59 840 84.0 
Example 51 
0.12 5.8 0.60 850 81.3 
Example 52 
0.26 6.2 0.61 805 84.2 
Example 53 
0.22 6.2 0.60 810 83.7 
Example 54 
0.25 6.1 0.60 805 83.5 
Example 55 
0.29 7.2 0.66 851 85.3 
Example 56 
0.14 6.2 0.65 750 81.5 
Example 57 
0.18 7.0 0.72 785 83.2 
Example 58 
0.16 6.4 0.74 790 84.0 
Example 59 
0.27 6.9 0.73 848 84.4 
Example 60 
0.20 7.1 0.72 812 82.5 
Comparative 
0.14 4.8 0.39 810 84.1 
Example 19 
Comparative 
0.12 5.0 0.38 820 83.9 
Example 20 
Comparative 
0.20 4.3 0.54 790 84.6 
Example 21 
Comparative 
0.20 4.6 0.42 805 84.5 
Example 22 
Comparative 
0.23 4.5 0.40 795 84.7 
Example 23 
Comparative 
0.13 4.0 0.47 820 84.0 
Example 24 
__________________________________________________________________________ 
TABLE 6 
__________________________________________________________________________ 
Production of acicular maghemite particles 
Acicular maghemite particles 
Precursor 
modified with CO or CO and Fe.sup.2+ 
with CO or CO and Fe.sup.2+ 
particles Amount Aspect ratio Saturation 
(Example 
Amount 
Amount 
of Major 
(major axial 
Particle 
Coercive 
magneti- 
Examples & 
No. & of Co 
of Fe.sup.2+ 
sodium 
Temper- 
axial 
diameter/- 
size force 
zation 
Comparative 
Comparative 
added 
added 
hydroxide 
ature 
diameter 
minor axial 
distri- 
Hc .sigma..sub.s 
Examples 
Example No.) 
(mol) 
(mol) 
added (ml) 
(.degree.C.) 
(.mu.m) 
diameter) 
bution 
(Oe) (emu/g) 
__________________________________________________________________________ 
Example 61 
Example 29 
0.085 
0.179 
102 100 0.22 6.6 0.63 790 77.0 
Example 62 
Example 29 
0.0509 
0.179 
98 100 0.22 6.7 0.63 705 77.5 
Example 63 
Example 29 
0.0509 
0.179 
170 100 0.22 6.6 0.64 735 77.8 
Example 64 
Example 29 
0.0509 
0.1074 
162 100 0.21 6.8 0.64 696 76.8 
Example 65 
Example 29 
0.0509 
-- 150 100 0.21 7.0 0.65 653 70.0 
Example 66 
Example 30 
0.085 
0.179 
102 100 0.18 6.6 0.62 808 74.5 
Example 67 
Example 31 
0.085 
0.179 
102 100 0.20 6.4 0.62 839 74.0 
Example 68 
Example 32 
0.085 
0.179 
102 100 0.15 5.6 0.58 806 76.4 
Example 69 
Example 33 
0.085 
0.179 
102 100 0.11 5.7 0.60 825 73.0 
Example 70 
Example 34 
0.085 
0.179 
102 100 0.26 6.1 0.60 780 75.3 
Example 71 
Example 35 
0.085 
0.179 
102 100 0.22 6.0 0.60 786 76.0 
Example 72 
Example 36 
0.085 
0.179 
102 100 0.23 6.9 0.62 775 76.3 
Example 73 
Example 37 
0.085 
0.179 
102 100 0.27 7.0 0.67 820 78.5 
Example 74 
Example 38 
0.095 
0.179 
102 100 0.13 6.0 0.66 731 74.7 
Example 75 
Example 39 
0.085 
0.179 
102 100 0.16 6.5 0.73 756 77.2 
Example 76 
Example 40 
0.085 
0.179 
102 100 0.15 6,4 0.77 763 75.1 
Example 77 
Example 41 
0.085 
0.179 
102 100 0.26 6.9 0.74 821 79.0 
Example 78 
Example 42 
0.085 
0.179 
102 100 0.19 6.8 0.74 785 76.2 
Comparative 
Comparative 
0.085 
0.179 
102 100 0.14 4.6 0.38 782 76.8 
Example 25 
Example 13 
Comparative 
Comparative 
0.085 
0.179 
102 100 0.13 4.8 0.37 785 77.3 
Example 26 
Example 14 
Comparative 
Comparative 
0.085 
0.179 
102 100 0.19 4.1 0.54 760 78.3 
Example 27 
Example 15 
Comparative 
Comparative 
0.085 
0.179 
102 100 0.20 4.5 0.41 779 77.2 
Example 28 
Example 16 
Comparative 
Comparative 
0.085 
0.179 
102 100 0.21 4.4 0.38 768 78.0 
Example 29 
Example 17 
Comparative 
Comparative 
0.085 
0.179 
102 100 0.12 3.9 0.46 795 76.5 
Example 30 
Example 18 
__________________________________________________________________________ 
TABLE 7 
__________________________________________________________________________ 
Tape properties 
Magnetic Particles Coercive 
Residual flux 
Examples & (Example No. & Squareness 
force 
density Br 
Comparative Examples 
Comparative Example No.) 
S.F.D. 
(Br/Bm) 
He (Oe) 
(Gauss) 
Orientation 
__________________________________________________________________________ 
Example 79 Example 15 0.44 
0.82 369 1630 2.13 
Example 80 Example 16 0.47 
0.80 355 1520 1.98 
Example 81 Example 17 0.43 
0.83 470 1500 2.32 
Example 82 Example 18 0.50 
0.79 349 1610 2.08 
Example 83 Example 19 0.52 
0.77 331 1480 1.78 
Example 84 Example 20 0.42 
0.84 393 1600 2.45 
Example 85 Example 21 0.44 
0.82 370 1560 2.23 
Example 86 Example 22 0.41 
0.78 378 1550 1.98 
Example 87 Example 23 0.45 
0.85 380 1640 2.81 
Example 88 Example 24 0.52 
0.79 339 1580 2.36 
Example 89 Example 25 0.41 
0.80 361 1590 2.15 
Example 90 Example 26 0.42 
0.79 345 1620 2.01 
Example 91 Example 27 0.41 
0.83 391 1640 2.42 
Example 92 Example 28 0.40 
0.82 367 1680 2.68 
Comparative Example 31 
Comparative Example 7 
0.62 
0.69 318 1350 1.82 
Comparative Example 32 
Comparative Example 8 
0.65 
0.69 312 1330 1.78 
Comparative Example 33 
Comparative Example 9 
0.56 
0.70 325 1350 1.81 
Comparative Example 34 
Comparative Example 10 
0.59 
0.70 351 1360 1.85 
Comparative Example 35 
Comparative Example 11 
0.60 
0.72 358 1400 1.92 
Comparative Example 36 
Comparative Example 12 
0.67 
0.68 306 1310 1.61 
__________________________________________________________________________ 
TABLE 8 
__________________________________________________________________________ 
Tape properties 
Magnetic Particles Coercive 
Residual flux 
Examples & (Example No. & Squareness 
force 
density Br 
Comparative Examples 
Comparative Example No.) 
S.F.D. 
(Br/Bm) 
He (Oe) 
(Gauss) 
Orientation 
__________________________________________________________________________ 
Example 93 Example 29 0.35 
0.84 345 1350 2.40 
Example 94 Example 30 0.38 
0.82 336 1280 2.28 
Example 95 Example 31 0.33 
0.86 370 1220 2.55 
Example 96 Example 32 0.41 
0.81 314 1310 2.31 
Example 97 Example 33 0.42 
0.79 305 1230 2.05 
Example 98 Example 34 0.32 
0.86 361 1290 2.72 
Example 99 Example 35 0.33 
0.84 358 1290 2.58 
Example 100 Example 36 0.31 
0.80 320 1300 2.21 
Example 101 Example 37 0.33 
0.87 358 1390 3.07 
Example 102 Example 38 0.42 
0.81 317 1250 2.55 
Example 103 Example 39 0.31 
0.83 335 1280 2.47 
Example 104 Example 40 0.32 
0.82 321 1300 2.31 
Example 105 Example 41 0.30 
0.86 367 1330 2.77 
Example 106 Example 42 0.30 
0.84 338 1350 2.89 
Comparative Example 37 
Comparative Example 13 
0.53 
0.71 288 1150 2.01 
Comparative Example 38 
Comparative Example 14 
0.55 
0.71 283 1140 1.98 
Comparative Example 39 
Comparative Example 15 
0.48 
0.72 297 1190 2.20 
Comparative Example 40 
Comparative Example 16 
0.49 
0.72 321 1200 2.15 
Comparative Example 41 
Comparative Example 17 
0.49 
0.74 330 1210 2.32 
Comparative Example 42 
Comparative Example 18 
0.58 
0.70 275 1130 1.95 
__________________________________________________________________________ 
TABLE 9 
__________________________________________________________________________ 
Tape properties 
Magnetic Particles Coercive 
Residual flux 
Examples & (Example No. & Squareness 
force 
density Br 
Comparative Examples 
Comparative Example No.) 
S.F.D. 
(Br/Bm) 
He (Oe) 
(Gauss) 
Orientation 
__________________________________________________________________________ 
Example 107 Example 43 0.47 
0.82 855 1630 2.00 
Example 108 Example 44 0.44 
0.82 762 1640 2.06 
Example 109 Example 45 0.42 
0.83 790 1670 2.10 
Example 110 Example 46 0.39 
0.84 750 1670 2.14 
Example 111 Example 47 0.38 
0.85 701 1620 2.15 
Example 112 Example 48 0.50 
0.80 856 1530 1.81 
Example 113 Example 49 0.45 
0.82 995 1580 2.28 
Example 114 Example 50 0.52 
0.80 862 1580 2.00 
Example 115 Example 51 0.55 
0.76 865 1450 1.72 
Example 116 Example 52 0.45 
0.85 835 1680 2.38 
Example 117 Example 53 0.46 
0.82 826 1610 2.15 
Example 118 Example 54 0.44 
0.79 823 1650 1.89 
Example 119 Example 55 0.47 
0.85 879 1680 2.78 
Example 120 Example 56 0.53 
0.80 782 1600 2.30 
Example 121 Example 57 0.41 
0.81 809 1620 2.07 
Example 122 Example 58 0.42 
0.79 821 1680 1.96 
Example 123 Example 59 0.41 
0.83 871 1690 2.25 
Example 124 Example 60 0.41 
0.82 840 1720 2.59 
Comparative Example 43 
Comparative Example 19 
0.65 
0.69 825 1360 1.75 
Comparative Example 44 
Comparative Example 20 
0.67 
0.70 837 1380 1.69 
Comparative Example 45 
Comparative Example 21 
0.62 
0.71 804 1410 1.70 
Comparative Example 46 
Comparative Example 22 
0.62 
0.70 820 1390 1.72 
Comparative Example 47 
Comparative Example 23 
0.49 
0.73 812 1450 1.85 
Comparative Example 48 
Comparative Example 24 
0.70 
0.67 833 1320 1.58 
__________________________________________________________________________ 
TABLE 10 
__________________________________________________________________________ 
Tape properties 
Magnetic Particles Coercive 
Residual flux 
Examples & (Example No. & Squareness 
force 
density Br 
Comparative Examples 
Comparative Example No.) 
S.F.D. 
(Br/Bm) 
He (Oe) 
(Gauss) 
Orientation 
__________________________________________________________________________ 
Example 125 Example 61 0.39 
0.83 816 1500 2.25 
Example 126 Example 62 0.36 
0.84 732 1530 2.27 
Example 127 Example 63 0.35 
0.85 766 1550 2.29 
Example 128 Example 64 0.32 
0.86 726 1550 2.33 
Example 129 Example 65 0.30 
0.87 684 1430 2.35 
Example 130 Example 66 0.41 
0.83 829 1450 2.10 
Example 131 Example 67 0.37 
0.86 880 1500 2.45 
Example 132 Example 68 0.43 
0.81 826 1450 2.20 
Example 133 Example 69 0.45 
0.80 843 1370 2.00 
Example 134 Example 70 0.36 
0.85 807 1500 2.61 
Example 135 Example 71 0.36 
0.85 810 1520 2.42 
Example 136 Example 72 0.34 
0.81 794 1440 2.11 
Example 137 Example 73 0.34 
0.87 841 1620 3.00 
Example 138 Example 74 0.41 
0.82 750 1400 2.46 
Example 139 Example 76 0.31 
0.83 768 1410 2.38 
Example 140 Example 76 0.31 
0.82 785 1420 2.25 
Example 141 Example 77 0.30 
0.86 845 1520 2.70 
Example 142 Example 78 0.30 
0.84 800 1550 2.82 
Comparative Example 49 
Comparative Example 25 
0.57 
0.70 798 1270 1.98 
Comparative Example 50 
Comparative Example 26 
0.58 
0.71 801 1295 1.90 
Comparative Example 51 
Comparative Example 27 
0.53 
0.73 778 1350 2.05 
Comparative Example 52 
Comparative Example 28 
0.52 
0.71 793 1290 2.10 
Comparative Example 53 
Comparative Example 29 
0.51 
0.74 788 1360 2.16 
Comparative Example 54 
Comparative Example 30 
0.60 
0.69 809 1240 1.89 
__________________________________________________________________________