Magnetic recording medium containing ferromagnetic particles with specified crystallite sizes and wherein the ratio of chlorine to iron at the surface is within a specified range

A magnetic recording medium is disclosed, which comprises a non-magnetic support having thereon a magnetic layer comprising ferromagnetic fine particles and a binder containing a vinyl chloride polymer, wherein the crystalline size of the ferromagnetic fine particles is from 350 to 500 angstrom, the content of the vinyl chloride polymer is from 20 to 50% by weight based on the amount of the total binder, and an integrated intensity ratio .alpha. of the Cl-2P spectrum to the Fe-2P (3/2) spectrum at the surface of the magnetic layer measured by an X-ray photoelectron spectroscopy is 1.80/1>.alpha.>0.50/1.

FIELD OF THE INVENTION 
The present invention relates to a magnetic recording medium comprising a 
non-magnetic support having thereon a magnetic layer composed of 
ferromagnetic particles dispersed in a binder, and more particularly to a 
magnetic recording medium having excellent running property and 
durability, and causing less fast sticking on the surface of a magnetic 
head by rubbing the head surface with the magnetic layer during running of 
the magnetic recording medium. 
BACKGROUND OF THE INVENTION 
In general, a magnetic recording medium comprising a non-magnetic support 
having formed thereon a magnetic layer composed of ferromagnetic particles 
dispersed in a binder is used as magnetic recording media such as audio 
tapes, video tapes, computer tapes, etc. 
In response to the recent demand for high density recording in magnetic 
recording media, it has been practiced to reduce the particle sizes of 
ferromagnetic fine particles, improve the dispersibility of ferromagnetic 
fine particles, improve the surface property of a magnetic layer, and 
improve the packing density of ferromagnetic fine particles. 
For example, in order to improve the dispersibility of ferromagnetic fine 
particles, dispersing agents are used for preparing magnetic coating 
positions, and also it is recently proposed to improve the dispersibility 
of ferromagnetic fine particles by using a polyurethane resin containing a 
metal sulfonate and a vinyl chloride resin as a binder, namely by 
introducing polar groups into the binder, as described in JP-A-61-123017 
(the term "JP-A" as used herein means as "unexamined published Japanese 
patent application"). 
Also, it is known to improve the surface property of the magnetic layer by 
increasing the temperature or pressure for a calendar treatment of a 
magnetic recording medium, and also improve the surface property of a 
magnetic recording medium by grinding the surface of the magnetic layer by 
a grinding tool, as described in JP-A-63-98834. 
Furthermore, it is proposed to polish the surface of the magnetic layer by 
a polishing tape for providing a magnetic recording medium causing less 
clogging of a magnetic head and less occurrence of dropout in 
JP-A-63-259830. 
It has been found that by the aforesaid improvements, the number of readily 
releasable particle components such as ferromagnetic particles from the 
surface of the magnetic layer is reduced to greatly decrease the 
occurrence of dropout and clogging of a magnetic head. 
However, although the occurrence of dropout and clogging of magnetic head 
is reduced, fast sticking on magnetic head (i.e., components of a magnetic 
layer are locally fast-stuck on the surface of a video head during running 
of a magnetic recording tape to reduce the output) occurs and the 
phenomenon is particularly severe when the crystallite sizes of 
ferromagnetic fine particles are from 350 to 500 angstrom. 
That is, a magnetic recording medium having improved electromagnetic 
conversion characteristics for high density recording generally tends to 
reduce the running property and durability thereof. In particular, the 
occurrence of the fast sticking phenomenon on magnetic head tends to 
become severe in a magnetic recording medium for high density recording. 
In other words, it has been found that even by employing the aforesaid 
improving methods, a magnetic recording medium having improved running 
characteristics without causing fast sticking on magnetic head can not be 
obtained. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a magnetic recording 
medium having an improved surface property of the magnetic layer, an 
improved packing density of ferromagnetic fine particles, and greatly 
excellent electromagnetic conversion characteristics by highly dispersing 
the ferromagnetic fine particles in a binder, without causing dropout and 
clogging of magnetic head and further without causing fast sticking on 
magnetic head. 
Other objects and effects of the present invention will be apparent from 
the following description. 
As the result of various investigations, the inventors have discovered that 
the aforesaid object can be attained by the present invention as set forth 
hereinbelow. 
According to the present invention, there is provided a magnetic recording 
medium comprising a non-magnetic support having thereon a magnetic layer 
comprising ferromagnetic fine particles and a binder containing a vinyl 
chloride polymer, wherein the crystallite size of the ferromagnetic 
particles is from 350 to 500 angstrom, the content of the vinyl chloride 
polymer is from 20 to 50% by weight based on the amount of the total 
binder, and an integrated intensity ratio, which is denoted by .alpha., of 
the Cl-2P spectrum to the Fe-2P (3/2) spectrum at the surface of the 
magnetic layer measured by an X-ray photoelectron spectroscopy is 1.80/1 
&gt;.alpha.&gt;0.50/1. 
The content of the vinyl chloride polymer is preferably from 25 to 45% by 
weight based on the amount of the total binder. The integrated intensity 
ratio .alpha. of Cl-2P spectrum to the Fe-2P (3/2) spectrum at the surface 
of the magnetic layer measured by an X-ray photoelectron spectroscopy is 
preferably 0.80/1 &gt;.alpha.&gt;0.51/1. 
In a preferred embodiment of the present invention, the vinyl chloride 
polymer contains at least one epoxy ring and at least one polar group 
selected from the group consisting of --SO.sub.3 M, --OSO.sub.3 M, 
--PO.sub.3 M.sub.2, --OPO.sub.3 M, and --CO.sub.2 M in the molecule 
(wherein M represents a hydrogen atom, an alkali metal, or ammonium). 
DETAILED DESCRIPTION OF THE INVENTION 
As the result of various investigations, the present inventors have 
discovered that the substance fast stuck on the surface of a magnetic head 
during running of a magnetic recording medium is ferromagnetic particles 
and it has been clarified that fast sticking on magnetic head is caused as 
follows. That is, the insufficiency of a binder at the surface of a 
magnetic layer causes an exposed portion of ferromagnetic fine particles 
without being sufficiently covered by the binder and such fine particles 
are fast stuck locally on the surface of the magnetic head during running 
of the magnetic recording medium. 
The present inventors have also found a method of determining the ratio of 
a vinyl chloride polymer as a binder component to ferromagnetic fine 
particles at the surface of a magnetic layer by using an X-ray 
photoelectron spectroscopy. The present inventors have thus discovered 
that the occurrence of fast sticking on magnetic head has a close relation 
to the ratio of the vinyl chloride polymer as a binder component to 
ferromagnetic fine particles at the surface of the magnetic layer not to 
the ratio thereof in the whole magnetic layer, and the possibility of the 
occurrence of fast sticking on magnetic head is determined by the ratio of 
the vinyl chloride polymer as a binder component to the ferromagnetic fine 
particles at the surface of the magnetic layer. Also, it has been found 
that the ratio of the vinyl chloride polymer as a binder component to 
ferromagnetic fine particles at the surface of the magnetic layer can be 
controlled regardless of the ratio of the binder to the ferromagnetic fine 
particles in the whole magnetic layer. 
That is, when the integrated intensity ratio .alpha. of the Cl-2P spectrum 
to the Fe-2P(3/2) spectrum at the surface of a magnetic layer 
(corresponding to the ratio of a vinyl chloride polymer as a binder 
component to ferromagnetic fine particles at the surface of the magnetic 
layer) of a magnetic recording medium measured by an X-ray photoelectron 
spectroscopy is not lower than 0.50/1, the ferromagnetic fine particles in 
the surface of the magnetic layer are not exposed even when the binder at 
the surface of the magnetic layer is scraped off by a magnetic head during 
running of the magnetic recording medium, thereby fast sticking on 
magnetic head during running of the magnetic recording medium does not 
occur. 
Also, when the integrated intensity ratio .alpha. of the Cl-2P spectrum to 
the Fe-2P(3/2) spectrum at the surface of the magnetic layer measured by 
an X-ray photoelectron spectroscopy is higher than 1.80/1, the magnetic 
recording medium itself adheres to a cylinder of a video tape recorder 
during running thereof to give undesirable influences. 
The Cl-2P spectrum and Fe-2P (3/2) spectrum mean 2P spectrum of Cl and 2P 
(3/2) spectrum of Fe as measured by X-ray photoelectron spectroscopy, 
respectively. With respect to the X-ray photoelectron spectroscopy, 
reference can be made to Thomas A. Carlson, Photoelectron and Auger 
Spectroscopy, p.3, PLENUM PRESS (1975). 
The integrated ratio .alpha. of the magnetic recording medium of the 
present invention can be controlled by various factors such as the 
crystallite size of the ferromagnetic fine particles, the content of vinyl 
chloride in the binder, the stress of kneading which can be controlled by 
the amount of solvents used in the kneading step, and the surface abrading 
treatment of the magnetic recording medium. In the present invention the 
value .alpha. is controlled to fall within the above mentioned range by 
suitably selecting these conditions. 
Examples of the ferromagnetic fine particles for use in the present 
invention include ferromagnetic alloy fine particles, ferromagnetic iron 
oxide fine particles, Co-doped ferromagnetic iron oxide fine particles, 
barium ferrite fine particles, etc. The effect of the present invention is 
particularly remarkable in the case of using ferromagnetic alloy fine 
particles for the magnetic recording medium. This is because that since 
the magnetic recording medium using such ferromagnetic alloy fine 
particles is excellent in the surface property of the magnetic layer and 
also the recording wavelength for the magnetic recording medium is short, 
the magnetic recording medium is more sensitive to the reduction of output 
by fast sticking on magnetic head. 
The ferromagnetic alloy fine particles contain at least 75% by weight of 
metal component and at least 80% by weight of the metal component is a 
ferromagnetic metal such as Fe, Co, Ni, Fe-Ni, Co-Ni, and Fe-Co-Ni. 
The acicular ratio (long axis/short axis) of the ferromagnetic alloy fine 
particles, ferromagnetic iron oxide fine particles, Co-doped ferromagnetic 
iron oxide fine particles or ferromagnetic chromium dioxide particles is 
generally from about 2/1 to 20/1, and preferably 5/1 or higher. The 
average particles length (in the long axis) of these ferromagnetic fine 
particles is generally about from 0.2 to 2.0 .mu.m. 
Also, the effect of the present invention is particularly remarkable when 
the crystallite size of the ferromagnetic fine particles is from 350 to 
500 angstrom. The crystallite size referred herein is determined by an 
X-ray diffraction. In the present invention, however, when the crystallite 
size is larger than the aforesaid size, the running property and 
durability of the magnetic recording medium are effectively improved by 
using the technique of the present invention, and when the crystallite 
size is in the above range, the aforesaid properties are effectively 
improved. 
The vinyl chloride polymer which can be used as a binder component for the 
magnetic recording medium of the present invention is a polymer containing 
vinyl chloride as a main monomer component, and examples thereof include a 
vinyl chloride/vinyl acetate copolymer, a vinyl chloride/vinyl propionate 
copolymer, a vinyl chloride/vinyl alcohol/maleic acid copolymer, a vinyl 
chloride/vinyl alcohol/acrylic acid copolymer, a vinyl chloride/vinylidene 
chloride copolymer, and a vinyl chloride/acrylonitrile copolymer. 
The content of vinyl chloride in the vinyl chloride copolymer is preferably 
from 70 to 95 wt% based on the amount of the vinyl chloride copolymer. 
The binder for use in this invention may further contain other resin in 
addition to the aforesaid polymer or copolymer. Examples of such a resin 
include an ethylene/vinyl acetate copolymer, cellulose derivatives (e.g., 
a nitrocellulose resin), an acrylic resin, a polyvinyl acetal resin, a 
polyvinyl butyral resin, an epoxy resin, a phenoxy resin, and a 
polyurethane resin. 
In the aforesaid vinyl chloride polymers, vinyl chloride polymers such as a 
vinyl chloride/vinyl acetate copolymer, a vinyl chloride/vinyl propionate 
copolymer and a vinylidene chloride/vinyl acetate copolymer, which contain 
at least one epoxy ring and at least one polar group selected from 
--SO.sub.3 M, --OSO.sub.3 M, --PO.sub.3 M.sub.2, --OPO.sub.3 M.sub.2, and 
--CO.sub.2 M (wherein M represents a hydrogen atom, an alkali metal, or 
ammonium) in the molecule are preferred. In these polar groups, --SO.sub.3 
M and --CO.sub.2 M are preferred and --SO.sub.3 M is more preferred. 
The content of the polar group is about from 1.times.10.sup.-7 to 
1.times.10.sup.-3 equivalent, and preferably from 1.times.10.sup.-5 to 
1.times.10.sup.-4 equivalent per gram of the polymer. If the content 
thereof outside the aforesaid range, the dispersibility of ferromagnetic 
fine particles tends to be reduced and also the electromagnetic conversion 
characteristics tend to be reduced. The polymer may contain one or more 
kind of such polar groups. 
Also, if the polymer further contains a hydroxy group, the dispersibility 
of ferromagnetic fine particles is more improved. The content of the 
hydroxyl group is preferably from 1.times.10.sup.-4 to 1.5.times.10.sup.-3 
equivalent per gram of the polymer. 
The content of the epoxy ring is preferably from 1.times.10.sup.-4 to 
1.times.10.sup.-2 mole, and more preferably from 5.times.10.sup.-4 to 
5.times.10.sup.-3 mole per gram of the polymer. 
The weight average molecular weight of the vinyl chloride polymer is 
preferably from 20,000 to 100,000, and more preferably from 30,000 to 
80,000. If the weight average molecular weight is outside the aforesaid 
range, the dispersibility of ferromagnetic fine particles tends to be 
reduced. The above polymers can be used alone or in combination thereof. 
The binder may be subjected to a curing treatment by adding known 
isocyanate crosslinking agents (e.g., tolylene diisocyanate, tri-addition 
product of triethylolpropane). Furthermore, an acrylic acid ester oligomer 
and monomer may be added to the binder and may be cured by irradiation. 
Other resins can be added to the above binder component. Examples of such 
resins include cellulose derivatives such as nitrocellulose resins, 
ethylene/vinyl acetate copolymers, acrylic resins, polyvinyl acetal 
resins, polyvinyl butyral resins, epoxy resins, phenoxy resins, and 
polyurethane resins. 
In the present invention, polyurethane resins are preferably used with the 
vinyl chloride polymer, and polyester polyurethane resins, polyether 
polyurethane resins and polycarbonate polyurethane resins are particularly 
preferred. The polyurethane resins can be produced by reacting a polyol, a 
polyisocyanate and a branched crosslinking agent, and if desired a 
chain-extender, in a conventional manner. 
Examples of polyols include polyether polyols, polyester polyols, 
polycarbonate polyols, and polycaprolactone diols. Representative 
polyether polyols are polyalkylene glycols such as polyethylene glycol, 
polypropylene glycol and polytetramethylene glycol. Polyester polyols can 
be produced, for example, by polycondensation of a dihydric alcohol such 
as glycols (e.g., ethylene glycol, propylene glycol, butanediol, 
1,6-hexanediol and cyclohexanedimethanol) and a dibasic acid, (e.g., 
adipic acid, azelaic acid, sebacic acid, fumaric acid, itaconic acid, 
phthalic acid, isophthalic acid and terephthalic acid), open-chain 
polymerization of lactones (e.g., caprolactones), and the like. Preferred 
polycarbonate polyols include those having a molecular weight of 300 to 
20,000 and a hydroxyl value of 20 to 300 which are synthesized, for 
example, by condensation or ester interchange reaction of phosgene, a 
chloroformate, a dialkyl carbonate or a diaryl carbonate with a polyhydric 
alcohol represented by formula (I): 
EQU HO--R.sup.1 --OH (I) 
wherein R.sup.1 represents --(CH.sub.2).sub.n --(n=3 to 14), 
##STR1## 
and polycarbonate polyester polyols having a molecular weight of 400 to 
30,000 and a hydroxyl valve of 5 to 300 which are synthesized by 
condensation of the above polycarbonate polyols with a dibasic carboxyl 
acid represented by formula (II): 
EQU HOOC--R.sup.2 --COOH (II) 
wherein R.sup.2 represents an alkylene group having 3 to 6 carbon atoms, 
1,4-phenylene group, 1,3-phenylene group, 1,2-phenylene group, 
1,4-cyclohexylene group, 1,3-cyclohexylene group, or 1,2-cyclohexylene 
group. Polyesterether polyols and polyesters may be compounded together 
with the above polyols in an amount of 90% by weight or less based on the 
weight of the polyols. 
Polyisocyanates which are reacted with the polyols are not particularly 
limited, and those conventionally used for the production of polyurethane 
resins can be used, such as hexamethylene diisocyanate, tolylene 
diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 
1,4-xylylene diisocyanate, cyclohexane diisocyanate, toluidine 
diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 
4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene 
diisocyanate, 1,5-naphthylene diisocyanate, 4,4-diphenylmethane 
diisocyanate, 3,3-dimethylphenylene diisocyanate, and dicyclohexylmethane 
diisocyanate. 
For the branched crosslinking agent, there may be mentioned polyhydric 
alcohols having three or more functional groups, such as 
trimethylolpropane, glycerol, hexanetriol, triethanolamine, diglycerol, 
pentaerythritol, sorbitol, dipentaerythritol, ethylene oxide or propylene 
oxide adducts of the above compounds, and propylene oxide adducts of 
ethylenediamine. Of the branched crosslinking agents, those having three 
hydroxyl groups per molecule are preferred, such as trimethylolpropane and 
glycerol. The amount of the branched crosslinking agent is generally from 
0.1 to 1 mmol per 1 g of polyurethane resins. If the amount is more than 1 
mmol/g, solubility of the resulting polyurethane resins is reduced. If it 
is less than 0.1 mmol/g, properties of the resins are deteriorated with 
respect to dispersibility, durability and calendering contamination. 
While the above-mentioned polyhydric alcohols may function as a chain 
extender, aliphatic polyamines, alicyclic polyamines and aromatic 
polyamines may also be used for the purpose. 
In the binder as described above, conventional isocyanate type crosslinking 
agents may be added as a binder component to cure the binder. The 
isocyanate type crosslinking agents used in the present invention are 
polyisocyanate compounds having two or more isocyanate groups, such as 
isocyanates (e.g., tolylene diisocyanate, 4,4'-diphenylmethane 
diisocyanate, hexamethylene diisocynate, xylylene diisocyanate, 
naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone 
diisocyanate, triphenylmethane diisocyanate, reaction products of these 
isocyanates and polyols (e.g., an adduct of three mol of tolylene 
diisocyanate and one mol of trimethylolpropane), and polyisocyanates 
produced by condensation of these isocyanates. These polyisocyanate 
compounds are commercially available under the trade marks, Coronate L, 
Coronate HL, Coronate H, Coronate EH, Coronate 2014, Coronate 2030, 
Coronate 2031, Coronate 2036, Coronate 3015, Coronate 3040, Coronate 3041, 
Millionate MR, Millionate MTL, Daltosec 1350, Daltosec 2170 and Daltosec 
2280 (produced by Nippon Polyurethane Co., Ltd.), Takenate D102, Takenate 
D110N, Takenate D200 and Takenate D202 (produced by Takeda Pharmaceutical 
Industries Co., Ltd.), Sumidur N75 (produced by Sumitomo Bayer Co., Ltd.), 
Desmodur L, Desmodur IL, Desmodur N and Desmodur HL (produced by Bayer 
A.G.), and Barnok D850 and Barnok D802 (produced by DAINIPPON INK AND 
CHEMICAL INC). Acrylic ester oligomers and acrylic ester monomers may also 
be added as a binder component to make the binder curable by irradiation. 
A preferred binder used in the present invention comprises a vinyl chloride 
polymer, a polyurethane resin, and a curing agent such as the isocyanate 
type crosslinking agents, wherein the vinyl chloride polymer, the 
polyurethane resin and the curing agent are contained in amounts of 20 to 
50 parts by weight, 20 to 50 parts by weight and 10 to 40 parts by weight, 
respectively, based on 100 parts by weight of the total amount of the 
three components. 
The content of the total binders in the magnetic layer of the magnetic 
recording medium of the present invention is generally from 10 to 100 
parts by weight, and preferably from 20 to 40 parts by weight, per 100 
parts by weight of the ferromagnetic fine particles in the layer. 
A preferred method of producing the magnetic recording medium of this 
invention using the aforesaid ferromagnetic fine particles, the binder, 
etc., is described below in detail. 
Since ferromagnetic fine particles are in a secondary aggregated state due 
to their own magnetism, it is preferred to mechanically pulverize the 
aggregated particles. The introduction of the pulverizing step can shorten 
the time for the succeeding kneading step. 
The pulverizing step can be conducted using a simple mill (manufactured by 
Shinto Kogyo Co., Ltd.), a sand mill (manufactured by Matsumoto Chuzo 
Kogyo Co., Ltd.), a sand grinder, a double roll mill, a triple roll mill, 
an open kneader, a pressure kneader, a continuous kneader, a Henschel 
mixer, etc. It is preferred that the pulverizing step is conducted using 
the same apparatus as that used in the succeeding kneading step since a 
transfer step of the pulverized ferromagnetic particles can be omitted. 
In a kneading step, the aforesaid binder, the ferromagnetic particles and a 
solvent are first kneaded by the aforesaid roll mill or kneader, and then 
they are dispersed. At the dispersing step, a sand mill, a ball mill, an 
attritor, a Henschel mixer, etc., can be used. The binder may be added as 
a solution dissolved in the solvent or may be added separately from the 
solvent. 
The magnetic coating composition in this invention may further contain a 
lubricant. Examples of the lubricant include fatty acid having from 12 to 
24 carbon atoms, fatty acid esters (e.g., various monoesters, sorbitan 
fatty acid esters, glycerol fatty acid esters, polybasic acid esters, 
etc.), fatty acid amides, metallic soaps, higher aliphatic alcohols, 
monoalkyl phosphates, dialkyl phosphates, trialkyl phosphates, paraffins, 
silicone oils, fatty acid-denatured silicone compounds, fluorine oils, 
esters having a perfluoroalkyl group, silicone compounds having a 
perfluoroalkyl group, animal oils, vegetable oils, mineral oils, higher 
aliphatic amines, and inorganic fine particles (e.g., graphite, silica, 
molybdenum disulfide, tungsten disulfide). Among these lubricants, fatty 
acids having from 14 to 22 carbon atoms, fatty acid amides having from 14 
to 22 carbon atoms, fatty acid esters having from 22 to 36 carbon atoms, 
esters having a perfluoroalkyl group having 6 or more carbon atoms, and 
silicone compounds having a perfluoroalkyl group having 6 or more carbon 
atoms are preferred. 
Furthermore, the magnetic coating composition in this invention may further 
contain additives such as abrasive, dispersing agents, antistatic agents, 
rust preventives, etc. 
There is no particular restriction on the abrasive for use in this 
invention if the Moh's hardness of the abrasive is at least 5, and 
preferably at least 8. Examples of the abrasive having a Moh's hardness of 
at least 5 include Al.sub.2 O.sub.3 (Moh's hardness: 9), TiO (Moh's 
hardness 6), TiO.sub.2 (Moh's hardness: 6), SiO.sub.2 (Moh's hardness: 7), 
SnO.sub.2 (Moh's hardness: 6.5), Cr.sub.2 O.sub.3 (Moh's hardness: 9), and 
.alpha.-Fe.sub.2 O.sub.3 (Moh's hardness: 5.5). They can be used singly or 
as a mixture thereof. Abrasive having a Moh's hardness of at least 8 are 
particularly preferred in this invention. When an abrasive having a Moh's 
hardness of lower than 5 is used, the abrasive is liable to drop off from 
the magnetic layer to reduce the running durability of the magnetic 
recording medium. 
The content of the abrasive is generally in the range of from 0.1 to 20 
parts by weight, and preferably in the range of from 1 to 10 parts by 
weight, per 100 parts by weight of the ferromagnetic fine particles. 
As the antistatic agent, carbon black, particularly that having a mean 
grain size of from 10 to 300 nm, is preferably used in the present 
invention. 
Examples of an organic solvent which is used for preparing the magnetic 
coating composition by kneading and dispersing the above-described mixture 
and for coating the coating composition include ketones such as acetone, 
methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.; esters 
such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, 
glycol acetate monoethyl ether, etc.; ethers such as ethyl ether, glycol 
dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, etc.; 
aromatic hydrocarbons such as benzene, toluene, xylene, etc; and 
chlorinated hydrocarbons such as methylene chloride, ethylene chloride, 
carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, 
etc. 
The magnetic recording medium of the present invention may be subjected to 
a surface treatment such as calendaring treatment after drying, and may 
further be subjected to a surface abrading treatment. The abrading 
treatment can be carried out by using a single-edged razor blade, an 
abrasive tape, a fixed blade, a diamond wheel, a rotary blade or the like. 
It is preferred that the abrasion be done by moving an abrasive tape or a 
rotary blade in a direction opposite to the direction to which the 
magnetic layer proceeds. When an abrasive tape is used, it is preferably 
moved at a speed of 1 to 3 cm/min with respect to the magnetic layer. 
Examples of the material for the support on which the magnetic coating 
composition is coated include polyesters such as polyethylene 
terephthalate, polyethylene 2,6-naphthalate, etc.; polyolefins such as 
polyethylene, polypropylene, etc.; cellulose derivatives such as cellulose 
triacetate, etc.; plastics such as polycarbonate, polyimide, polyamide 
imide, etc.; as well as, according to uses, non-magnetic metals such as 
aluminum, copper, tin, zinc, non-magnetic alloys of these metals, etc.; 
and plastics vapor-deposited with a metal such as aluminum. 
The thickness of the support is generally from 3 to 100 .mu.m, preferably 
from 3 to 20 .mu.m, for magnetic recording tapes, and generally from 20 to 
100 .mu.m for magnetic recording disks. 
The form of the support may be films, tapes, sheets, disks, cards, drums, 
etc., and various materials are selectively used according to the form of 
support. 
Furthermore, in this invention a backing layer may be formed on the 
opposite surface of the support for static prevention, for preventing the 
occurrence of wow and flutter, for improving the strength of the magnetic 
recording medium, and for matting the back surface of the support. 
In this invention, since ferromagnetic fine particles of the crystallite 
size of from 350 to 500 angstrom are used, a vinyl chloride polymer is 
used as a main component of the binder of the magnetic layer, and the 
integrated intensity ratio .alpha. of the Cl-2P spectrum to the Fe-2P(3/2) 
spectrum at the surface of the magnetic layer measured by an X-ray 
photoelectron spectroscopy is 1.80/1 &gt;.alpha.&gt;0.50/1, the occurrence of 
fast sticking on magnetic head and the occurrence of adhering on a 
cylinder are remarkably prevented. This is because the vinyl chloride 
polymer which is the main binder component for ensuring the durability of 
the magnetic recording medium firmly covers the ferromagnetic fine 
particles at the surface of the magnetic layer. 
That is, the occurrence of fast sticking on magnetic head is caused by 
ferromagnetic fine particles uncovered by a binder and, on the other hand, 
if the amount of a binder at or in the surface of a magnetic layer is too 
large, the excessive binder increases the tackiness of the surface of the 
magnetic layer to cause the phenomenon of adhering the magnetic recording 
medium onto the cylinder of a video tape recorder. 
In this invention, by controlling the integrated intensity ratio .alpha. of 
the Cl-2P spectrum based on the vinyl chloride polymer to the Fe-2P(3/2) 
spectrum based on the ferromagnetic fine particles at the surface of the 
magnetic layer as the aforesaid range, the vinyl chloride polymer properly 
cover the ferromagnetic fine particles at the surface of the magnetic 
layer, whereby the requirement of not causing fast sticking on magnetic 
head while 50 pass running and the requirement of not causing adhering on 
a cylinder, which conflict with each other, are simultaneously satisfied. 
The following examples are intended to illustrate the present invention 
practically but not to limit it in any way. In addition, all parts in 
these examples are by weight.

EXAMPLE 1 
In an open kneader were pulverized 100 parts of ferromagnetic alloy fine 
particles (composition: Fe 94%, Zn 4%, and Ni 2%, Hc: 1,500 Oe, 
crystallite size: 350 .ANG.) for 10 minutes, and the ferromagnetic alloy 
fine particles were mixed and kneaded with 12 parts (46% by weight to the 
total binder of a compound (SO.sub.3 Na=6 .times.10.sup.-5 eq/g, epoxy 
equivalent =10.sup.-3 eq/g, molecular weight =50,000) formed by adding a 
sodium salt of hydroxyethyl sulfonate to a copolymer of vinyl 
chloride/vinyl acetate/glycidyl methacrylate (86/9/5 by weight ratio) and 
40 parts of methyl ethyl ketone for 60 minutes. 
Then, to the kneaded mixture were added 8 parts (as solid component) of a 
SO.sub.3 Na-containing urethane resin (UR 8200, trade name, made by Toyobo 
Co., Ltd.), 5 parts of a lubricant (Al.sub.2 O.sub.3, grain size 0.3 
.mu.m), 2 parts of carbon black (particle size 40 m.mu.), and 200 parts of 
a methyl ethyl ketone/toluene mixture (1/1 by weight ratio) followed by 
dispersing for 120 minutes using a sand mill. 
To the dispersion was further added 6 parts (as solid content) of 
polyisocyanate (Coronate 3041, trade name, made by Nippon Polyurethane 
Co., Ltd.), 1 part of stearic acid, 2 parts of butyl stearate, and 50 
parts of methyl ethyl ketone and after stirring and mixing them for 20 
minutes, and mixture was filtered using a filter having a mean pore size 
of 1 .mu.m to provide a magnetic coating composition. 
The coating composition thus prepared was coated on the surface of a 
polyethylene terephthalate film support having a thickness of 10 .mu.m at 
a dry thickness of 3.5 .mu.m using a reverse roll. 
The non-magnetic support having the coated layer of the magnetic coating 
composition was subjected to a magnetic orientation by magnets of 3,000 
gauss while the coated layer of the magnetic coating composition was in 
undried state. Then, after drying the coated layer, the magnetic recording 
medium was subjected to a super calendar treatment, slit to 8 mm width, 
and polished by an abrasive tape (as disclosed in JP-A-63-259830) to 
provide an 8 mm video tape. 
EXAMPLE 2 
By following the same procedure as Example 1 except that 60 parts of methyl 
ethyl ketone was used at kneading the magnetic coating composition, an 8 
mm video tape was prepared. 
EXAMPLE 3 
By following the same procedure as Example 1 except that a copolymer of 
vinyl chloride/vinyl acetate/glycidyl methacrylate (86/9/5 by weight 
ratio) was used in place of the copolymer in Example 1, an 8 mm video tape 
was prepared. 
EXAMPLE 4 
By following the same procedure as Example 2 except that a copolymer of 
vinyl chloride/vinyl acetate/glycidyl methacrylate (86/9/5 by weight 
ratio) was used in place of the copolymer in Example 1, an 8 mm video tape 
was prepared. 
EXAMPLE 5 
By following the same procedure as Example 2 except that Co-doped 
.alpha.-iron oxide fine particles (Hc: 900 Oe, crystallite size 480 
angstrom) were used as the ferromagnetic fine particles, a 1/2 inch video 
tape was prepared. 
COMATIVE EXAMPLE 1 
By following the same procedure as Example 1 except that 30 parts of methyl 
ethyl ketone was used at kneading the magnetic coating composition, an 8 
mm video tape was prepared. 
COMATIVE EXAMPLE 2 
By following the same procedure as Example 1 except that 80 parts of methyl 
ethyl ketone was used at kneading the magnetic coating composition, an 8 
mm video tape was prepared. 
COMATIVE EXAMPLE 3 
By following the same procedure as Example 1 except that 30 parts of methyl 
ethyl ketone was used at kneading the magnetic coating composition, an 8 
mm video tape was prepared. 
EXAMPLE 6 
By following the same procedure as Example 3 except that 6 parts (24% by 
weight to the total binder) of the vinyl chloride copolymer was used in 
place of 12 parts of the copolymer, 12 parts of the SO.sub.3 Na-containing 
polyurethane resin was used in place of 8 parts of the resin, and 8 parts 
of polyisocyanate was used in place of 6 parts thereof, an 8 mm video tape 
was prepared. 
COMATIVE EXAMPLE 4 
By following the same procedure as Comparative Example 2 except that 4 
parts (15% by weight to the total binder) of the vinyl chloride copolymer 
was used in place of 12 parts of the copolymer, 12 parts of the SO.sub.3 
Na-containing polyurethane resin was used in place of 8 parts of the 
resin, and 10 parts of polyisocyanate was used in place of 6 parts 
thereof, an 8 mm video tape was prepared. 
COMATIVE EXAMPLE 5 
By following the same procedure as Example 1 except that 14 parts (55% by 
weight to the total binder) of the vinyl chloride copolymer was used in 
place of 12 parts of the copolymer, 7 parts of the SO.sub.3 Na-containing 
polyurethane resin was used in place of 8 parts of the resin, and 5 parts 
of polyisocyanate was used in place of 6 parts of polyisocyanate, an 8 mm 
video tape was prepared. 
The evaluation results of each of the video tapes thus prepared are shown 
in Table 1 below. 
TABLE 1 
______________________________________ 
Fast Sticking 
Adhering to 
Sample .alpha. on Head Cylinder 
______________________________________ 
Example 1 0.51/1 A A 
Example 2 0.75/1 A A 
Example 3 0.98/1 B A 
Example 4 1,24/1 B A 
Example 5 1.52/1 B A 
Comparative 
0.43/1 C A 
Example 1 
Comparative 
1.81/1 A C 
Example 2 
Comparative 
0.49/1 C A 
Example 3 
Example 6 0.65/1 C A 
Comparative 
0.59/1 C A 
Example 4 
Comparative 
0.62/1 A C 
Example 5 
______________________________________ 
.alpha.: An integrated intensity ratio of Cl2P spectrum to Fe2P(3/2) 
spectrum measured by an Xray photoelectron spectroscopy 
The test results shown in the above table were evaluated as follows. 
Evaluation Method of Fast Sticking on Head 
Each of the video tapes thus prepared was loaded on a VTR (FUJIX-8 trade 
name, made by Fuji Photo Film Co., Ltd.), and the tape of the whole length 
(120 minutes running) was run repeatedly at 50 passes under the condition 
of 20.degree. C., 10%RH and the reduction of output was determined. 
The surface of the magnetic head after running was observed by an optical 
microscope, whereby the occurrence of fast sticking on the surface was 
determined. 
The video tape in Example 5 was slit to a 1/2 inch width and the same test 
as above was performed using a VTR for S-VHS (AG 6200, trade name, made by 
Matsushita Electric Industrial Co., Ltd.). 
The grades of the evaluations are as follows. 
A: Neither fast sticking on head nor reduction of output were observed. 
B: Fast sticking on head was observed but the output was not reduced. 
C: Fast sticking on head was observed and the output was reduced. 
Evaluation of Adhering to Cylinder 
Each of the video tapes thus prepared was loaded on a VTR (FUJIX-8, trade 
name, made by Fuji Photo Film Co., Ltd.), and after storing it for 24 
hours under the condition of 40.degree. C., 80%RH, the running state of 
each tape was determined. Also, the sample in Example 5 was slit to a 1/2 
inch width and the running state was determined using a VTR for S-VHS (AG 
6200, trade name, made by Matsushita Electric Industrial Co., Ltd.). 
The grades of the evaluations are as follows. 
A: No abnormality was observed in running. 
C: Tape adhered to a cylinder to stop running. 
Measurement Method of .alpha. 
An X-ray photoelectron spectrometer (PHI-560, trade name, made by 
Perkin-Elmar Co.) was used. An Mg anode was used as the X-ray source and 
the measurement was conducted at 300 W. First, after washing away the 
lubricant of the video tape with n-hexane, the video tape was mounted on 
the X-ray photoelectron spectrometer. The distance between the X-ray 
source and the sample video tape was 1 cm. 
After degassing the sample under vacuum for 5 minutes, the Cl-2P spectrum 
and the Fe-2P(3/2) spectrum were measured by integrating them for 10 
minutes. The pass energy was kept at a constant value of 100 eV. 
The integrated intensity ratio .alpha. of the Cl-2P spectrum to the 
Fe-2P(3/2) spectrum measured was determined by calculation. 
As is clear from the result shown in Table 1, each of the samples in 
Examples 1 to 6, wherein 1.80/1 &gt;.alpha.&gt;0.51/1 which is the range of this 
invention, fast sticking on head does not occur or even if it occurs, the 
output is not reduced and also no abnormal running is observed due to 
adhering to a cylinder. 
On the other hand, when the value .alpha. is outside the aforesaid range 
defined in this invention, that is, when the value .alpha. is 1.81/1 as in 
Comparative Example 2, fast sticking on head occurs and when the value 
.alpha. is 0.43/1 as in Comparative Example 1, adhering to a cylinder 
occurs. 
When the content of the vinyl chloride copolymer which is the main binder 
component is from 20 to 50% by weight of the total binder and the value 
.alpha. is within the aforesaid range defined in this invention, neither 
fast sticking on head nor adhering to cylinder occur. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.