JPS62256220A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic conversion characteristic and running durability of a recording medium by radiating radiations to a magnetic layer contg. >=1 kinds of a specific PVC compd. and polyurethane compd. and polishing agent. CONSTITUTION:The following binder and the polishing agent (e.g.: alpha-Al2O3) having 0.1-1.0 average primary particle size and >=6 Mohs' hardness are incorporated into the magnetic layer contg. pulverized ferromagnetic powder, more preferably ferromagnetic alloy powder having >=30m/g BET specific surface area and further are irradiated with the radiations: The binder includes (A) the compd. (e.g.: vinyl chloride compolymer acrylate) which contains respectively >=1 polar groups and carbon-carbon unsatd. bonds within the molecule and has 1-30 acid value when the polar groups are a CO2H group, and (B) the polyurethane compd. contg. respectively>=1 CO2H groups and carbon-carbon unsatd. bonds within the molecule, more preferably polyurethan (meth)acrylate. >=1 Kinds of A and B are incorporated into the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as video tapes, audio tapes, computer tapes, and floppy disks.

[Prior art]

Magnetic recording media that are currently widely used include thermoplastic resins such as vinyl chloride-vinylidene chloride resin, vinyl chloride vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, acrylonitrile butadiene resin, etc. as a binder. There is a method of using these materials alone or in combination, but this method has the disadvantage that the abrasion resistance of the magnetic layer is poor and the running path of the magnetic tape is contaminated.

Also known are a method using a thermosetting resin such as a melamine resin or a urea resin, or a method in which a crosslinkable binder such as an isocyanate compound or a compound having an epoxy ring is added to the thermoplastic resin through a chemical reaction. However, when the above-mentioned crosslinking binder is used, (1) there is a problem in the storage stability of the liquid in which magnetic particles are dispersed, and the uniformity of the physical properties of the magnetic coating liquid and, by extension, the homogeneity of the magnetic recording medium cannot be maintained; 2) A heat treatment step is essential for curing the coating film after coating and drying, and it has disadvantages such as requiring a long time.

In order to prevent these drawbacks, methods for producing magnetic recording media using acrylic acid ester oligomers and monomers as binders and curing them by radiation irradiation after drying have been proposed in Japanese Patent Publication No. 4712423, Japanese Patent Application Laid-Open No. 47-13639,
It is disclosed in various publications such as JP-A-47-15104, JP-A-50-77433, and JP-A-56-25231. However, with the manufacturing method disclosed in the above patent publication, a magnetic recording medium having high electromagnetic conversion characteristics and durability could not be obtained.

[Problems to be solved by the present invention]

In recent years, there has been a demand for higher image quality in magnetic recording media.

For this purpose, it is necessary to bring the surface of the magnetic layer into closer contact with the video head and audio head, which improves the smoothness of the surface of the magnetic recording medium.
It is important to further dramatically improve the dispersibility of ferromagnetic fine powder. On the other hand, the smoother the surface of the magnetic layer, the greater the friction in the running system within the video tape recorder, the higher the running tension, and the more severe running durability is required of the magnetic recording medium. For this reason, conventional manufacturing methods for magnetic recording media have not been able to provide magnetic recording media that have the smoothness of the surface of the magnetic layer, the dispersibility of the ferromagnetic fine powder, and the running durability.

In particular, in recent years, magnetic tapes have been required to have thinner supports for longer recording times, and in the case of video tapes, for example, video tapes have become more versatile, requiring harsh usage conditions. ing. Another disadvantage is that when recording and reproducing for a long time, the video head and audio head get dirty, which deteriorates the electromagnetic conversion characteristics. Therefore, there has been a demand for technological development that simultaneously imparts durability and electromagnetic conversion characteristics to the magnetic layer that satisfy these requirements.

The present inventors have developed conventional techniques such as a method using a thermoplastic resin or a thermosetting resin, a method of adding a crosslinkable binder by the above-mentioned chemical reaction, and a method of using a hardenable binder by radiation crosslinking. The present invention was achieved as a result of intensive research to improve the drawbacks.

Therefore, the objects of the present invention are to provide characteristics that could not be achieved with conventional magnetic recording media, namely: 1) excellent electromagnetic conversion characteristics; 2)
The ferromagnetic fine powder has excellent dispersibility, 3) the magnetic coating liquid has good storage stability and uniform performance, 4) it has excellent running durability, and 5) the heat treatment process for curing the coating film is According to the present invention, it is an attempt to provide an unnecessary magnetic recording medium.
In particular, durability can be improved.

[Means for solving problems]

In terms of the above, in a magnetic recording medium mainly consisting of a non-magnetic support and a magnetic layer containing fine ferromagnetic powder, the magnetic layer has the following (A) and (B) (A) polar groups and carbon-carbon Each molecule contains one or more unsaturated bonds, and when the polar group is a C02H group, the acid value is 1 to 3o,
Polyvinyl chloride compound (B) Cot One or more compounds from the compound group of polyurethane compounds each containing one or more H groups and one or more carbon-carbon unsaturated bonds in the molecule and an average of -
Next particle 0.1-1. It has been found that the problem can be solved by a magnetic recording medium characterized by containing an abrasive having a hardness of 0 μm and a Mohs hardness of 6 or more, and further being irradiated with radiation.

That is, in the present invention, by irradiating the magnetic layer containing one or more of the compound groups (A) and (B) as a binder and further containing a specific abrasive, the synergistic effect of the two compounds is achieved. As a result, a magnetic recording medium which achieves all of the above-mentioned advantages and particularly has extremely excellent running durability can be obtained.

The polyvinyl chloride compound (A) containing one or more polar groups and one or more carbon-carbon unsaturated bonds in the molecule used in the present invention includes CO2H, OH,
, SO3HlS 03 N a , 0P03H1OP
A vinyl chloride polymer containing at least one group such as O:l Na group and a carbon-carbon unsaturated bond, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl propionate copolymer, These are copolymers such as vinylidene chloride-vinyl acetate copolymers. A preferred polar group is a CO2H1OH group, more preferably a Co2H1OH group.
, is an H group. When the polar group is coz H group, coz
The H group content is preferably about 1 to 30 in terms of acid value, more preferably 3 to 20, and most preferably 5 to 30.
It is 15. If it is outside this range, the dispersibility of the ferromagnetic fine powder will be poor and the electromagnetic conversion characteristics will also be significantly reduced. The average content of carbon-carbon unsaturated bonds is 1.5 to 20 per molecule, preferably 2 to 15. The molecular weight is 5°000 to 50,000, preferably 10.0
00-30.000. Outside this range, curing properties may be poor or durability may be poor.

These compounds are based on polyvinyl chloride polymers such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, Vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinylidene chloride-vinyl acetate-maleic acid Copolymers - Vinyl chloride copolymers such as vinylidene chloride-vinyl propionate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-acrylic acid copolymers, vinyl chloride-vinyl acetate-acrylic acid-vinyl alcohol copolymers, etc. A combination or a copolymer thereof may be saponified and used.

The carbon-carbon unsaturated bond can be introduced by modifying a part of the hydroxyl group or carboxyl group of these copolymers, or a part of the hydroxyl group generated by saponification. can.

For example, a compound having an epoxy ring and a carbon-carbon unsaturated bond such as glycidyl acrylate is reacted with a part of the hydroxyl group of the base polymer, or a part of the hydroxyl group or carboxyl group of the copolymer is reacted with a polyfunctional isocyanate. (For example, 2. 3-) lylene diisocyanate, 2. 6-) lylene diisocyanate,
1.3-xylylene diisocyanate, (1), 4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3.3-dimethylphenylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3. 3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate,
isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpropane, etc.), and the remaining NGO group is converted into a (meth)acryloyl group (hereinafter acryloyl group and methacryloyl group are collectively referred to as ( (referred to as meth)acryloyl group), such as (meth)acrylic acid, 2-hydroxyethyl (meth)
Obtained by a method of reacting with acrylate, hydroxyalkyl (meth)acrylates such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, (meth)acrylamide, N-methylol (meth)acrylamide, etc. Can be done.

Furthermore, examples of methods for introducing polar groups include the following methods. A part of the hydroxyl group or carboxyl group of the above base copolymer,
Alternatively, a part of the hydroxyl group generated by saponification is reacted with one NCO group of a polyfunctional isocyanate, and the remaining NGO group is converted into Co, H group, 5OiNa group, OP
It can be obtained by reacting with a hydroxyl group compound containing an O3N a group or the like. It is also possible to introduce the polar group simultaneously with the (meth)acryloyl group. Alternatively, a compound having both a polar group and a (meth)acryloyl group may be used. The method of introducing these groups is not limited to the above-mentioned method.

The cellulose-based (meth)acrylate used in the present invention is preferably a resin in which an OH group is modified into a (meth)acryloyl group, such as cellulose nitrate, cellulose acetate butyrate, cellulose acenate propionate, or cellulose diacetate. . A preferable range is 50 to 400, more preferably 80 to 200 in terms of the degree of polymerization of cellulose. Outside this range, the viscosity of the magnetic coating liquid increases and the dispersibility deteriorates, which is not preferable.

In addition, from the viewpoint of safety, cellulose acetate propionate and cellulose acetate butyrate are preferred as the base cellulose.

These (meth)acrylate compounds of celluloses can be produced by, for example, reacting celluloses with polyisocyanates, and then reacting them with an active hydrogen compound having the above-mentioned (meth)acryloyl group, such as 2-hydroxyethyl acrylate. It can be obtained by (meth)acryloylization of [.

Urethane compounds containing one or more CO groups and one or more carbon-carbon unsaturated bonds in the molecule used in the present invention (
As B), the main chain skeleton may be polyester, polyether, or polyester ether, and specific examples of dibasic acids used in these are oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid. acid,
Dodecanedioic acid, maleic acid, fumaric acid, itaconic acid, trimethyladipic acid, hexahydrophthalic acid, tetrahydrophthalic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, and the like can be used. Examples of dihydric alcohols include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol 1, octamethylene glycol, diethylene glycol, triethylene glycol 1, tetraethylene glycol, and 2,2-dimethylpropane. -1,3-diol, 2,2-diethylpropane-1,3-diol, cyclohexane-1,3
-diol, cyclohexane-1,4-diol, cyclohexane-1,4-dimetatool, cyclohexane-
1,3-dimetatool, 2,2-bis(4-hydroxyethoxy-cyclohexyl)propane, 2,2-bis(
4-hydroxyethoxy-phenyl)propane, 2゜2
-bis(4-hydroxyethoxyethoxy-phenyl)
Propane etc. can be used. It is also possible to use a lactone-based polyester skeleton such as γ-butyrolactone, δ-valerolactone, and ε-caprolactone. Isoyanates that form urethane bonds include:
2. 4-) Lylene diisocyanate, 2.6-) Lylene diisocyanate, 1,3-xylylene diisocyanate, ■, 4-xylylene diisocyanate, 1゜5-
Naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3-
Dimethylphenylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3,3-dimethyl-4,
Polyvalent isocyanates such as 4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpropane can be used. Further, the dibasic acid,
A part of the dihydric alcohol may be replaced with trihydric or higher acid and alcohol. C02H group and carbon-carbon double bond,
Preferably, the (meth)acryloyl group may be located at the terminal or side chain of the polyurethane. The method for introducing these groups is as follows: 1) Incorporate one or more of trivalent or higher acid, alcohol, or isocyanate into the urethane skeleton, and add these groups to the urethane that has CO2H groups, OH groups, or NGO groups remaining in the side chains. 2) reacting a urethane having an isocyanate group at the terminal with an active hydrogen compound having at least one C02H group, one or more (meth)acryloyl group, and one or more OH group, respectively. It can be obtained by, for example, causing The acid value of the urethane compound used in the present invention is preferably 1 to 30, more preferably 3 to 20, and still more preferably 5 to 15. The molecular weight is 1,000 to 100°000, preferably 2,000 to 50,000, particularly preferably 3,000.
~30,000. If the acid value is out of this range, the dispersibility of the ferromagnetic fine powder will be poor, leading to a decrease in electromagnetic conversion characteristics and deterioration in durability. Moreover, the average content of (meth)acryloyl groups is 1.5 to 10 per molecule, preferably 2 to 8.

When the molecular weight is less than 1000, the magnetic layer of the obtained magnetic recording medium becomes too strong, which tends to cause cracks when bent, and the magnetic recording medium tends to curl due to curing shrinkage after irradiation with radiation. . On the other hand, the molecular weight is 10
If it exceeds 0,000, the solubility of urethane (meth)acrylate in solvents tends to be poor, which not only makes handling inconvenient, but also deteriorates the dispersibility of the magnetic material and requires a large amount of energy for curing. Undesirable.

Furthermore, vinyl monomers can be added to the present invention. Vinyl monomers include compounds that can be polymerized by radiation irradiation and have one or more carbon-carbon unsaturated bonds in the molecule, such as (meth)acrylic esters, (meth)acrylamides, allyl Compound,
Examples include vinyl ethers, vinyl esters, vinyl heterocyclic compounds, N-vinyl compounds, styrenes, acrylic acid, methacrylic acid, crotonic acids, itaconic acids, and olefins. Among these, preferred are the following compounds containing two or more methacryloyl groups. Specifically, diethylene glycol di(meth)acrylate, 1-lyethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate,
(meth) of polyethylene glycols such as acrylates
Acrylates, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(
meth)acrylate, dipentaerythritol hexa(
meth)acrylate, tris(β-(meth)acryloyloxyethyl)isocyanurate, bis(β-(meth)
(acryloyloxyethyl) isocyanurate, or polyisocyanate (2,4-)lylene diisocyanate, 2,6-)lylene diisocyanate, 1,3-
Xylylene diisocyanate 1.4-xylylene diisocyanate, 1.5-naphthalene diisocyanate, m
-phenylene diisocyanate, p-phenylene diisocyanate, 3,3-dimethylphenylene diisocyanate, 4,4-diphenylmethane isocyanate, 3.
3-dimethyl = 4.4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpropane) and hydroxy (meth)acrylate compound (2-hydroxyethyl (meth) Acrylate, 2
-hydroxypropyl (meth)acrylate, etc.), and other difunctional or higher functional poly(meth)acrylates. These 1,000 sums are 1
It may be a species, or two or more kinds may be used.

The preferred composition ratio of the compound represented by (A) and the compound represented by (B) is 20 to 90 parts by weight/8.
0 to 10 parts by weight, particularly preferably 30 to 80 parts/70 to
There are 20 copies. If the ratio of the compound represented by (A) is less than this ratio or the ratio of the compound represented by (B) is less than this ratio, durability cannot be obtained. Further, the amount of the vinyl monomer added is preferably 50 parts by weight or less based on the total parts by weight of the compounds represented by (A) and (B).

If the ratio exceeds this ratio, the radiation dose required for polymerization becomes large, which is not desirable, and the magnetic recording medium may deteriorate or its durability may not be sufficiently improved.

The abrasive used in the present invention may have a Mohs hardness of 6 or more, preferably 8 or more.

Moreover, the particle size is 0. 1 to 1.0μ is preferable.

Examples of abrasives include magnesium oxide (Mohs hardness 6), quartz (Mohs hardness 7), titanium oxide (Mohs hardness 7), Crz 03 (Mohs hardness 8-9), α
Aj! 203 (Mohs hardness: 9), 5iC (Mohs hardness: 9 to 10), etc. If the particle size is larger than the above range, the amount of wear on the head will increase, making it impossible to use it for a long time. On the other hand, if the Mohs hardness is less than 6 or the particle size is smaller than the above range, there will be no effect and the electromagnetic conversion characteristics will be poor.

Further, the amount of the abrasive added is preferably 0.5 to 20 parts by weight, more preferably 1 to 1 l to 100 parts by weight of the magnetic material.
0 parts by weight, even more preferably 3 to 5 parts by weight. If the amount added is larger than this, the amount of head wear will increase,
It cannot be used for a long time, and on the other hand, if it is less than this, the electromagnetic conversion characteristics will be poor (there is one direction).

As the ferromagnetic fine powder used in the present invention, ferromagnetic iron oxide fine powder, Co-doped ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, ferromagnetic alloy powder, barium ferrite, etc. can be used. The acicular ratio of ferromagnetic iron oxide and chromium dioxide is about 2/1 to 20/1, preferably 5/1 or more, and the average length is 0. A range of approximately 2 to 2.0 μm is effective.

The ferromagnetic alloy powder has a metal content of 75 wL% or more, and 80 wt% or more of the metal content is a ferromagnetic metal (i.e., Fe, Co,
Ni, ,Fe-Ni, ,Co-Ni, ,Fe-Co-N
1) is a particle with a major axis of about 1.0 μm or less. Particularly effective in the present invention is a fine particle ferromagnetic alloy powder having an ET specific surface area of 30 m/g or more, preferably 45 m/g or more, since it is difficult to disperse the ferromagnetic fine powder.

Organic solvents used for dispersion and application of magnetic coating liquid include acetone, methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid glycol monoethyl ether; ethyl ether, glycol dimethyl ether, glycol monoethyl ether,
Ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, and tetracarbonized carbon;
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, and dichlorobenzene can be selected and used.

Further, additives such as a lubricant, an abrasive, a dispersant, an antistatic agent, and a rust preventive may be added to the magnetic coating liquid of the present invention. In particular, lubricants include saturated and unsaturated higher fatty acids with 12 or more carbon atoms, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, fluorine compounds, etc., and these are used when preparing magnetic coating liquids. It may be added, or it may be dissolved in an organic solvent after drying or irradiation with radiation, or applied directly to the surface of the magnetic layer, or
May be sprayed.

Materials for the support to which the magnetic coating liquid is applied include polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, and plastics such as polycarbonate, polyimide, and polyamideimide. In addition, non-magnetic metals such as aluminum, copper, tin, zinc, or non-magnetic alloys containing these metals, and plastics on which metals such as aluminum are vapor-deposited may also be used, depending on the purpose.

In addition, the forms of non-magnetic supports include films, tapes, sheets,
It may be a disk, card, drum, etc., and various materials are selected depending on the form as necessary.

In addition, the support of the present invention has a so-called bank surface on the side opposite to the side on which the magnetic layer is provided for the purpose of preventing static electricity, preventing transfer, preventing wow and flutter, improving the strength of magnetic recording media, and making the back surface matte. A back coat may be provided.

In the present invention, it is preferable to irradiate radiation after applying a magnetic paint and performing calender treatment, but it is also possible to perform calender treatment after irradiation. Alternatively, it is also possible to irradiate one more time.

The radiation irradiated to the magnetic layer of the present invention includes electron beam, γ
Although rays, β rays, ultraviolet rays, etc. can be used, electron beams are preferable. As the electron beam accelerator, a scanning method, double scanning method, curtain beam method, broad beam curtain method, etc. can be adopted. As for the electron beam, the accelerating voltage is 100 to 100 OKV, preferably 150 to 300 KV, and the absorbed dose is 1 to 20 M.
rad, preferably 3 to 15 Mrad. Accelerating voltage is 1. If it is less than oOKV, the amount of energy transmitted is insufficient, and if it exceeds 1.000 KV, the efficiency of energy used for polymerization decreases, making it uneconomical.

If the absorbed dose is less than I Mrad, the curing reaction will be insufficient and the strength of the magnetic layer will not be obtained, and if it is more than 20 Mrad, the energy efficiency used for curing will decrease and the irradiated object will generate heat. This is particularly undesirable since the plastic support is deformed.

〔Example〕

The present invention will be explained in more detail below using Examples and Comparative Examples. In the following Examples and Comparative Examples, all "parts" represent 1 part by weight.

Example 1 A magnetic coating liquid having the following composition was kneaded in a ball mill for 50 hours.

Fe-Ni alloy powder (13000, BET surface
Product: 48 rrr/g, Ni, 8 wt% Part: Activated mixture composition: Vinyl chloride copolymer system acrylate: 60 parts (acid value: 1
3. Molecular weight 20,000, average acryloyl group content 2
．． 8 parts/molecule) Urethane acrylate 40 parts (acid value 10, molecular weight 10,000, average acryloyl group content 3 parts/molecule) Stearic acid 4 parts Butyl stearate 4 parts Abrasive (as listed in the attached table) 16 parts Carbon black
10 parts methyl ethyl ketone
After dispersing 800 parts, it was coated on a polyethylene terephthalate support with a thickness of 10 μm using a doctor blade so that the dry film was 3 μm, oriented using a cobalt magnet, and the solvent was dried (100°C for 1 minute). Calendar treatment was performed. Next, the tape was irradiated with an electron beam at an accelerating voltage of 16'5 KV and a beam current of 6 mA to give an absorbed dose of 7 Mrad, and then slit into 1/2 inch width to prepare video magnetic tape samples Nos. 1 to 6.

The results are shown in the attached table.

Example 2 Video magnetic tape sample No. 7 was prepared in the same manner as in Example 1 except that only the binder composition was changed as shown below.

(Binder composition) PVC copolymer acrylate 60 parts (acid value 0
．． 5, molecular weight 10,000) 40 parts of urethane acrylate (acid value 12, molecular weight 15,000, average acryloyl group content M
3 molecules/molecule) The results are shown in the attached table.

Evaluation method: Measurement of acid value. Dissolve 1 g of the sample in tetrahydrofuran and titrate it with an ethyl alcohol-water (9515 V/V%) solution of potassium hydroxide using phenolfucrene as an indicator.
The number of times of potassium hydroxide required was defined as the acid value.

Head wear: Head abrasion was measured after running a videotape for 100 hours. A value of 5μ or less is practical.

Still durability: A constant video signal is recorded on a videotape (each sample) using a VHS video tape recorder (manufactured by Matsushita Electric Industrial Co., Ltd., NV8200), and the time until the reproduced still image loses its sharpness is measured. (Experiment at 5℃
(performed at 80% RH). S/N: Using the video tape recorder mentioned above, we recorded a gray signal with a 50% increase in cents, and measured the noise with a Shibaku 925C S/N meter, and expressed it as a relative value when sample No. 013 was taken as OdB. .

(Effects of the invention) The magnetic recording medium of the invention exhibits good electromagnetic conversion characteristics,
It is also clear that the running durability is particularly excellent.

Claims (4)

[Claims] (1) In a magnetic recording medium mainly consisting of a non-magnetic support and a magnetic layer containing fine ferromagnetic powder, the magnetic layer
The following (A) and (B) (A) Polyvinyl chloride containing one or more polar groups and one or more carbon-carbon unsaturated bonds in the molecule, and having an acid value of 1 to 30 when the polar group is a CO_2H group. Compound (B) One or more compounds from the group of polyurethane compounds each containing one or more CO_2H groups and one or more carbon-carbon unsaturated bonds in the molecule, and an average primary particle size of 0.1 to 1.0μ and 1. A magnetic recording medium comprising an abrasive having a Mohs hardness of 6 or more, and further irradiated with radiation. (2) The polyvinyl chloride compound (A) has C as a polar group.
The magnetic recording medium according to claim 1, which contains an O_2H group. (3) The magnetic recording medium according to claim 1, wherein the polyurethane compound (B) is a polyurethane (meth)acrylate having an acid value of 1 to 30. (4) The ferromagnetic fine powder has a BET specific surface area of 30 m^2/g
The magnetic recording medium according to claim 1, which is the above ferromagnetic alloy powder.