JPS63167417A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent dispersibility of magnetic powder and electromagnetic conversion characteristic and durability of the magnetic recording medium by incorporating a specific copolymer into a binder of a magnetic coating compd. CONSTITUTION:The graft copolymer obtd. by graft copolymn. of a vinyl chloride/vinylidene chloride copolymer and at least one kind selected from polyester oligomer and polycarbonate oligomer is incorporated into the binder of the magnetic recording medium coated with the magnetic coating compd. prepd. by dispersing ferromagnetic powder into a binder on a base. This binder exhibits excellent coated film characteristics in mechanical characteristics such as adhesiveness and toughness at low to high temp. and does not cause solvent shock and phase sepn. at all. Additional improvement in adsorptivity on the magnetic powder and the hardening characteristics of the coated film is permitted by incorporating a -COOH group and -OH group further into the molecules of the resin binder.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to an improved magnetic recording medium, and more particularly, to improved dispersibility of magnetic powder, electromagnetic conversion characteristics, and durability of the magnetic recording medium. The present invention relates to a magnetic recording medium with excellent properties.

(Prior Art) Magnetic recording media, such as tapes and disks for audio, video, or computers, are made by coating a magnetic coating consisting of magnetic powder, a resin binder, a solvent, and various additives on a support such as polyester. The recording layer is formed by uniformly coating the recording layer. At this time, the binder used has good dispersibility of the magnetic powder, which gives the magnetic recording medium excellent electromagnetic conversion properties, and also allows the magnetic layer to come into intense sliding contact with the magnetic head, etc. during recording and reproducing. It is necessary to select a material that can improve the wear resistance of the magnetic recording medium and the durability of the magnetic recording medium.

Therefore, various attempts have been made to improve the binder that binds the magnetic powder to the support, including vinyl chloride-vinyl acetate-vinyl alcohol copolymer, which has relatively good properties as described above, and various plasticizers. A combination of these has been proposed.

(Problems to be Solved by the Invention) By the way, although such a binder improves the dispersibility of the magnetic powder and the durability of the magnetic layer, it is not sufficient.
In particular, when used in magnetic recording media that require even better dispersibility and durability of magnetic powder, such as video magnetic tapes that require high-density recording, it has sufficiently satisfactory electromagnetic conversion characteristics and durability. I couldn't get it.

In addition, hexagonal ferrite magnetic powder, which is excellent as a high-density recording medium, has a powder surface chemical property that is similar to that of conventional Co-γ-F.
Since it is different from E 203, there is a problem in that it is more difficult to obtain good dispersibility, electromagnetic conversion characteristics, and durability.

The present invention was made to solve these problems, and provides a magnetic recording medium that enables uniform dispersion of magnetic powder, especially hexagonal ferrite powder, and has excellent electromagnetic conversion characteristics and durability. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) The magnetic recording medium of the present invention is a magnetic recording medium in which a magnetic paint in which ferromagnetic powder is dispersed in a binder is coated on a support. The binder is characterized in that it contains a graft copolymer obtained by graft copolymerizing a vinyl chloride-vinylidene chloride copolymer and at least one selected from polyester oligomers and polycarbonate oligomers.

The graft copolymer used in the present invention is vinyl chloride-
It is obtained by, for example, radical graft copolymerization of a vinylidene chloride copolymer and at least one selected from polyester oligomers and polycarbonate oligomers, and has a molecular weight of 5,000 to 100,000.
It is preferably about 10,000 to 3
It is 0000. When the molecule l is less than 5,000, the resin becomes brittle and it becomes difficult to form a strong coating;
When it exceeds 0, the solubility decreases, making it difficult to dissolve in solvents during the preparation of magnetic paints, making them impractical. The ratio of the monomers constituting this graft copolymer is such that the amount of vinyl chloride is 20 to 90% by weight, the amount of vinylidene chloride is 5 to 60% by weight, and the content of the resin selected from polyester and polycanibonate is 1% by weight. If the vinyl chloride content is preferably in the range of ~40% by weight, or if the vinylidene chloride content is less than 5% by weight, the strength as a coating film will be poor, When the vinyl chloride content exceeds 90% by weight or when the vinylidene chloride content exceeds 60% by weight, the coating film has poor flexibility and a desirable medium cannot be obtained.
If the content of the resin selected from polyester and polycarbonate is less than 1% by weight, the adsorption of the resin to the magnetic powder will be insufficient and the dispersibility will be poor, and if it exceeds 40% by weight, the viscosity of the paint will increase significantly during the coating stage. A good coating film cannot be obtained.

In addition, this graft copolymer is preferably synthesized so as to contain at least one of -COOH and -OH groups in the molecule, which further improves the adsorption of the resin to magnetic powder and the coating film curing properties. do.

Vinyl chloride, one of the starting materials for the graft copolymer
The vinylidene chloride copolymer has an average molecular weight of 500 to 5oo
oo level can be used.

In addition, among the polyester oligomer and polycarbonate oligomer that are the other starting materials, the polyester is an organic dibasic acid such as phthalic acid, adipic acid, trimerized lyluic acid, maleic acid, 1,3-butanediol, 1
．． 4-butanediol, 1,5-pentanediol, 1
Diols such as , 6-hexanediol, 1,10-decanediol; Glycols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol; It is synthesized by reaction with one or more polyols selected from alcohols. Polycarbonate is made by linking polyols with carbonate bonds, and includes, for example, the above-mentioned polyols or phenols having two or more 10 groups in the molecule, and phosgene, chloroformic acid ester, dialkyl carbonate, etc. Alternatively, it can be obtained by a condensation reaction with diallyl carbonate or the like. The polyester oligomer or polycarbonate oligomer preferably has an average molecular weight in the range of 700 to 40,000.
As the binder used in the present invention, for example, polyurethane resin, polyester resin, polyamide resin, acrylic resin, epoxy resin, phenoxy resin, melamine resin, vinyl butyral resin, vinyl Other resin components such as alcohol resins or copolymer resins thereof may be used in combination. In this case, the content of the graft copolymer is preferably 1% by weight or more, and more preferably 51% by weight or more. % or more. When the content of the graft copolymer is less than 1% by weight,
The effect of improving the dispersibility of magnetic powder is significantly reduced.

The method for manufacturing the magnetic recording medium of the present invention includes, for example, preparing a magnetic paint by kneading magnetic powder, a binder, and an additive with a solvent, applying this magnetic paint onto a support, and then performing orientation treatment and drying treatment. A commonly used method of manufacturing a magnetic recording medium by forming a magnetic layer by performing the above steps can be applied.

The mixing ratio of the ferromagnetic powder and the binder in the present invention is 5 to 400 parts by weight, preferably 6 to 200 parts by weight, per 100 parts by weight of the ferromagnetic powder. If the binder is too large, the recording density of the magnetic recording medium will be reduced, and if the binder is too small, the strength of the magnetic layer will be poor, resulting in undesirable situations such as decreased durability and powder falling off.

As a support, for example, polyethylene terephthalate,
Any support that is commonly used as a support for magnetic recording media, such as a film made of polyolefin sulfide or the like, may be used.

The magnetic powder used in the present invention is acicular or fine particle Co-γ-Fe with high coercive force suitable for high-density recording.
203, other ferromagnetic metal magnetic powders, and hexagonal ferromagnetic powders suitable for perpendicular magnetic recording.

Among these, hexagonal ferromagnetic powder is particularly suitable for use in the present invention. .

This hexagonal ferromagnetic powder includes Co, Co-Cr, C
o -Mn, Mn -AA, etc., may be fine powders of metals that form hexagonal crystals by themselves, but in particular, those with the general formula: AO
-n (Fe203) (wherein A represents any one element selected from the group of Ba, Sr, Pb, and Ca, n represents a number of 5 to 6, and part of Fe is Ti, Co, Zn, In, Mn, Cu
, Ge, Nb, Sn, or other transition metals. ) Hexagonal ferrites are suitable.

Among them, Ba ferrite is particularly preferred. Fine powder of such hexagonal ferrite is a single crystal of a regular hexagonal plate, and its axis of easy magnetization is in a direction perpendicular to the plate surface. (Unexamined Japanese Patent Publication No. 56-67904
(see Japanese Patent Laid-Open No. 155022/1983).

In addition, additives such as 40 parts by weight or less of a dispersant, 40 parts by weight or less of a lubricant, 400 parts or less of a hardening agent, and 40 parts by weight or less of an abrasive material may be added to the magnetic paint as needed per 100 parts by weight of the magnetic powder. May be added.

Dispersants include, for example, lecithin, lubricants include, for example, higher fatty acids, fatty acid esters, etc., curing agents include, for example, bifunctional or higher-functional isocyanate compounds, and abrasives include, For example, Cr
203, AJ220g, α-Fe203, and the like.

(Function) In the magnetic recording medium of the present invention, a binder obtained by graft polymerizing at least one resin selected from polyester and polycarbonate to a vinyl chloride-vinylidene chloride copolymer is used as a binder. Compared to binders, it exhibits superior coating film properties in terms of mechanical properties such as adhesion and toughness from low to high temperatures, and does not cause solvent shock or phase separation at all.Furthermore, the resin binder has -COOH groups in its molecules. , - By including the needle groups, it is possible to further improve the adsorption to magnetic powder and the coating film curing properties.

(Example) Next, examples of the present invention will be described.

Example 1 First, a polyester oligomer (average molecular weight 800) made from adipic acid and 1,4-butanediol,
Vinyl chloride-vinylidene chloride copolymer (average molecular i 8
000) to synthesize a vinyl chloride-vinylidene chloride-polyester graft copolymer (vinyl chloride 55% by weight, vinylidene chloride 25% by weight, polyester 20% by weight, average molecular weight 10,000).

After sufficiently mixing and dispersing the following composition using this graft copolymer in a ball mill, 5 parts by weight of trifunctional incyanate Coronate C-3041 (manufactured by Nippon Polyurethane Co., Ltd., trade name) was added as a curing agent. A magnetic paint was prepared by mixing and stirring until uniform. The obtained magnetic paint was applied to a polyester film using a reverse roll coater, and then the surface was smoothed using a super calendar to produce a magnetic recording medium with a magnetic layer thickness of 2 μm.

CO-containing 7-Fe2O3 magnetic powder 100ffl
Part i Vinyl chloride-vinylidene chloride-polyester graft copolymer 1Q 11 Polyurethane resin N-230410n (manufactured by Nippon Polyurethane Co., Ltd.) Carbon black (average particle size 70 μIn) 5++ Lecithin 4 rt Butyl stearate i 71α-AI20
! 5tt Methyl ethyl ketone 80 Tunotluene
gQ nFor this magnetic recording medium, the surface gloss 1 of the coating film, the output C, C/N ((1
8; relative value) Still durability was measured using a 1/2 inch VHS type VTR. The results are shown in Table 1.

Examples 2 to 6 Saturation magnetization as magnetic powder: 60 emu/g, coercive force: 850
Co-Ti substituted Ba-ferrite powder with an average particle size of 0.08 μm was used, and the same amount of vinyl chloride-vinylidene chloride-polyester graft copolymer used in Example 1 was used as a paint and binder. Paints with different composition ratios,
In addition, a paint using a vinyl chloride-vinylidene chloride-polyester graft copolymer containing -COOII group or -OH group and having a composition shown in Table 1 synthesized in the same manner as in Example 1 was used. Magnetic recording media were prepared under the same conditions as in Example 1, except that they were synthesized using the same coating method and dried while being passed through a perpendicular magnetic field during the formation of the magnetic coating. Furthermore, each characteristic was measured in the same manner as in Example 1 using these magnetic recording media. The results are shown in Table 1.

(Left below) Example 7 Polycarbonate oligomer made from diphenyl carbonate and bisphenol A (average molecular weight 900)
Vinyl chloride-vinylidene chloride-polycarbonate graft copolymer synthesized using 55% by weight of vinyl chloride
A magnetic recording medium was produced under the same conditions as in Example 1, except that 25% by weight of vinylidene chloride, 20% by weight of polycarbonate, and an average molecular weight of 10,000 were used, and each characteristic was measured. The results are shown in Table 2.

Examples 8 to 12 Using the same copolymer as the vinyl chloride-vinylidene chloride-polycarbonate graft copolymer used in Example 7 or a copolymer not synthesized in a similar manner, the formulations shown in Table 2 were prepared. A magnetic recording medium was produced under the same conditions as in Example 2 except for the amount and the content of -COOH groups and -OH groups, and each characteristic was measured. The results are shown in Table 2.

Comparative Example 1 A magnetic recording medium was produced under the same conditions as in Example 1, except for using a vinyl chloride-vinyl acetate copolymer (65% by weight of vinyl chloride, 35% by weight of vinyl acetate, -containing needle group), and each characteristic was was measured. The results are shown in Table 2.

Comparative Example 2 A magnetic recording medium was produced under the same conditions as in Example 2, except that the vinyl chloride-vinyl acetate copolymer used in Comparative Example 1 was used, and each characteristic was measured. The results are shown in Table 2.

(The following is a blank space) [Effects of the Invention] As explained above, according to the magnetic recording medium of the present invention, a vinyl chloride-vinylidene chloride copolymer and at least one selected from polyester oligomers and polycarbonate oligomers are used as resin binders. By using the graft copolymer, the dispersibility of magnetic powder is improved,
This improves the output characteristics (/N), enables high-density recording, and improves durability.

Applicant: Toshiba Corporation Patent Attorney Satoshi Suyama - Volunteer to write procedural amendments) May 27, 1985 2. Title of the invention: Magnetic recording medium 3. Person making the amendment. Relationship with the case. Patent applicant: For Kanagawa Prefecture. Toshiba Corporation 4, 72 Horiyo-cho, Saiwai-ku, Saki-shi (307), Agent 2-1 Kanda Tamachi, Chiyoda-ku, Tokyo 101 1ii 1. Name of the invention Magnetic recording medium 2. Scope of claims (1) A magnetic recording medium formed by coating a support with a magnetic paint in which ferromagnetic powder is dispersed in a binder, in which the binder comprises a vinyl chloride-vinylidene chloride copolymer, a polyester oligomer, and a polycarbonate oligomer. A magnetic recording medium comprising a graft copolymer obtained by graft copolymerization with at least one selected from the following.

(2) The magnetic recording medium according to claim 1, wherein the graft copolymer contains at least one of -COOHW and 1014 bases in the molecule.

(3) The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is hexagonal ferrite.

3. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to an improved magnetic recording medium, and more specifically to the dispersibility of magnetic powder, the electromagnetic conversion characteristics and durability of the magnetic recording medium. The present invention relates to a magnetic recording medium with excellent properties.

(Prior Art) Magnetic recording media, such as tapes and disks for audio, video, or computers, are made by coating a magnetic coating consisting of magnetic powder, a resin binder, a solvent, and various additives on a support such as polyester. The recording layer is formed by uniformly coating the recording layer. At this time, the binder used has good dispersibility of the magnetic powder, which gives the magnetic recording medium excellent 11a conversion characteristics, and improves the wear resistance of the magnetic layer, which comes into intense sliding contact with magnetic heads, etc. during recording and reproduction. However, it is necessary to select a material that can improve the durability of the magnetic recording medium.

For this reason, various attempts have been made to improve the binder that binds the magnetic powder to the support, and the above-mentioned vinyl chloride-pinyruhynyl acetate alcohol copolymer, which has relatively good properties, and various plasticizers have been tried. A combination of these methods has been proposed.

(Problems to be Solved by the Invention) By the way, although such a binder improves the dispersibility of the magnetic powder and the durability of the magnetic layer, it is not sufficient.
In particular, when used in magnetic recording media that require even better dispersibility and durability of magnetic powder, such as video magnetic tapes that require high-density recording, it has sufficiently satisfactory electromagnetic conversion characteristics and durability. I couldn't get it.

In addition, hexagonal ferrite magnetic powder, which is excellent as a high-density recording medium, has a powder surface chemical property that is similar to that of conventional Co-γ-F.
Because it is different from ez Ox, it has good dispersibility! There was a problem in that it was extremely difficult to obtain good la conversion characteristics and durability.

The present invention was made to solve these problems, and it enables uniform dispersion of magnetic powder, especially hexagonal ferrite powder, and provides a magnetic recording medium with excellent m-magnetic conversion characteristics and durability. The purpose is to provide.

[Structure of the Invention] (Means for Solving the Problems) The magnetic recording medium of the present invention is also a magnetic recording medium in which a magnetic paint in which ferromagnetic powder is dispersed in a binder is coated on a support. , the binder contains a graft copolymer obtained by graft copolymerizing a vinyl chloride-vinylidene chloride copolymer and at least one selected from polyester oligomers and polycarbonate oligomers.

The graft copolymer used in the present invention is vinyl chloride-
It can be obtained, for example, by radical graft copolymerization of a vinylidene chloride copolymer and at least one selected from polyester oligomers and polycarbonate oligomers.

At this time, in the reaction system, a reaction is mainly observed in which the above oligomer is bonded as a side chain to the vinyl chloride-vinylidene chloride copolymer which is the main chain. It does not matter at all if a bonding reaction occurs. The molecular weight of the graft copolymer is preferably about 5,000 to 100,000,
Particularly preferably 10,000 to 30,000. molecule】
If it is less than 5,000, the resin becomes brittle and it becomes difficult to form a strong coating film, and if it exceeds 100,000, the solubility decreases and it becomes poorly soluble in solvents when preparing magnetic paints, making it impractical. The ratio of the monomers constituting this graft copolymer is as follows: the amount of vinyl chloride is 20 to 90% by weight, the amount of vinylidene chloride is 5 to 601@%, and the content of the resin selected from polyester and polycarbonate is 1 to 4% by weight.
The range is preferably 0.0111%. When the vinyl chloride content is 20 ili weight% unmixed, or when the vinylidene chloride content is 5 weight% unmixed, the strength as a coating film is poor, and the vinyl chloride content is 90111%.
or if the nylidene chloride content exceeds 6011
If the percentage can be determined, the flexibility of the coating film is poor and a desirable medium cannot be obtained. In addition, the content of resin selected from polyester and polycarbonate is 1 liter.
If i is less than 1%, adsorption of the resin to the magnetic powder will be insufficient and the dispersibility will be poor, and if it exceeds 40%, the viscosity of the paint will increase significantly in the coating stage, making it impossible to obtain a good coating film.

In addition, this graft copolymer is preferably synthesized so as to contain at least one of -COOH and -OH groups in the molecule, which further improves the adsorption of the resin to magnetic powder and the coating film curing properties. do.

Vinyl chloride, one of the starting materials for the graft copolymer
The nylidene chloride copolymer has an average molecular weight of 500 to 500.
00 or so can be used.

In addition, among the polyester oligomer and polycarbonate oligomer that are the other starting materials, the polyester is composed of an organic dibasic acid such as phthalic acid, adipic acid, dimerized sulfuric acid, maleic acid, 1,3-butanediol, 1
, 4-butanediol, 1.5-bentanediol, 1
．． Diols such as 6-hexanediol and 1,10-decanediol; glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol; polyhydric alcohols such as nitrimethylolethane, trimethylolpropane, hexanetriol, glycerin, and pentaerythritol It is synthesized by reaction with one or more polyols selected from the following. Furthermore, polycarbonate is made by linking polyols with carbonate bonds, such as the above-mentioned polyols or two or more -
It is obtained by a condensation reaction between a phenol having an OH group and phosgene, chloroformic acid ester, dialkyl carbonate, diallyl carbonate, or the like. The polyester oligomer or polycarbonate oligomer preferably has an average molecular weight in the range of 1,700 to 400,003.

As the binder used in the present invention, for example, polyurethane 5II11 may be added to the above-mentioned graft copolymer as necessary.
, polyester resin, polyamide resin, acrylic resin,
Other resin components such as epoxy resins, phenoxy resins, melamine resins, vinyl butyral resins, vinyl alcohol resins, or combination resins thereof may be used in combination.

In this case, the content of the graft copolymer is 1!1ff
i% or more, more preferably 5I%
lf! i% or more. The content of the graft copolymer is I
If it is less than tffi%, the effect of improving the dispersibility of the magnetic powder is significantly reduced.

The method for manufacturing the magnetic recording medium of the present invention includes, for example, preparing a magnetic paint by kneading magnetic powder, a binder, and an additive with a solvent, applying this magnetic paint onto a support, and then performing orientation treatment and drying treatment. A commonly used method of manufacturing a magnetic recording medium by forming a magnetic layer by performing the above steps can be applied.

The mixing ratio of the ferromagnetic powder and the binder in the present invention is 100% of the ferromagnetic powder! The binder is used in an amount of 5 to 400 parts by weight, preferably 6 to 200 parts by weight. If the amount of binder is too large, the recording density of the magnetic recording medium will be reduced, and if it is too small, the strength of the magnetic layer will be poor, resulting in undesirable situations such as decreased durability and powder falling off.

As a support, for example, polyethylene terephthalate,
Any support that is commonly used as a support for magnetic recording media, such as a film made of polyolefin sulfide or the like, may be used.

The magnetic powder used in the present invention includes acicular or fine particle CO-γ-FI with high coercive force suitable for high-density recording.
Examples include O3 and other ferromagnetic metal magnetic powders, and hexagonal ferromagnetic powders suitable for perpendicular magnetic recording. Among these, hexagonal ferromagnetic powder is particularly suitable for use in the present invention.

This hexagonal ferromagnetic powder is Co1Co-Cr.

Fine powder of a metal that forms a hexagonal crystal by itself such as Co-Hn or Mn-A1 may be used, but in particular, it has the general formula: AQ・n(Fe20s>(wherein, A is B
Represents any one element selected from the group of a5Sr1Pb%Ca, n represents a number from 5 to 6, and a part of Fe is 1, Co, Zn, InlHn%Cu, Ge,
Nb.

It may be substituted with a transition metal such as Sn. ) Hexagonal ferrites are suitable. Among them, 8a ferrite is particularly preferred. Such fine powder of hexagonal ferrite is a single crystal of a regular hexagonal plate, and its axis of easy magnetization is in a direction perpendicular to the plate surface. (see Japanese Patent Application Laid-Open No. 155022/1983).

In addition, magnetic powder 100111 is added to the magnetic paint as necessary.
% of dispersant, 40 parts of dispersant, 40 parts of lubricant, 40,000 parts of curing agent, and 40 parts of abrasive. ! Additives such as up to 1 m part may be added.

Dispersants include, for example, lecithin, lubricants include, for example, higher fatty acids, fatty acid esters, etc., curing agents include, for example, bifunctional or higher-functional isocyanate compounds, and abrasives include, For example, C
Examples include r2O3, A1203, α-Fez 03, and the like.

(Function) In the magnetic recording medium of the present invention, a binder obtained by graft polymerizing at least one resin selected from polyester and polycarbonate to a vinyl chloride-vinylidene chloride copolymer is used as a binder. Compared to binders, it exhibits superior coating film properties in terms of mechanical properties such as adhesion and toughness from low to high temperatures, and does not cause solvent shock or phase separation at all. Furthermore, by including a -COOH group and -OH at 7% in the molecule of the resin binder, it becomes possible to greatly improve the adsorption to magnetic powder and the coating film curing properties.

(Example) Next, examples of the present invention will be described.

Example 1 First, a polyester oligomer (average molecular weight 800) made from adipic acid and 1,4-butanediol,
Vinyl chloride-chloride and nylidene copolymer (average molecular weight 518
00G) to synthesize a vinyl chloride-vinylidene chloride-polyester graft copolymer (vinyl chloride 55% by weight, vinylidene chloride 25% by weight, polyester 20% by weight, average molecular ffi 10000). After sufficiently mixing and dispersing the composition below using this graft copolymer in a ball mill, 51 parts of trifunctional isocyanate Coronate C-3041 (manufactured by Nippon Polyurethane Co., Ltd., trade name) was added as a curing agent, and the mixture was uniformly dispersed. A magnetic paint was prepared by mixing and stirring until the mixture was mixed and stirred. The obtained magnetic paint was applied to a polyester film using a reverse roll coater, and then the surface was smoothed using a super calendar to produce a magnetic recording medium with a magnetic layer thickness of 2 μm.

CO-containing 7-Fe 203 magnetic powder 100 weight 1
Part vinyl chloride-vinylidene chloride-polyester graft copolymer 10 Polyurethane resin N-23041On (manufactured by Nippon Polyurethane Co., Ltd.) Carbon black (average particle size 70 μm5) 5# lecithin 4 Butyl stearate 1 α-A1203
5n methyl ethyl ketone
80〃Toluene 8
0 Regarding this magnetic recording medium, the surface gloss of its coating film,
The output C, C/H (db; relative (i), and still durability using a 1/2 inch VHS type VTR were measured. The results are shown in Table 1.

Examples 2 to 6 Saturation magnetization as magnetic powder: 60 emu/g, coercive force: 850
0e.

The same vinyl chloride as used in Example 1 was used, using substituted 8a-ferrite powder with an average particle size of 008 μl.
Paints using the same amount of vinylidene chloride-polyester graft copolymer and polyurethane resin, paints with different binder composition ratios, and -COOH groups synthesized by the same method as in Example 1 and having the composition shown in Table 1. Alternatively, a paint using a -OH group-containing vinyl chloride-vinylidene chloride-polyester graft copolymer was synthesized by the same paint-forming method as in Example 1, and when forming a magnetic coating film, it was vertical! Magnetic recording media were manufactured under the same conditions as in Example 1, except that drying was performed while passing through the medium for 1 s. Furthermore, each characteristic was measured in the same manner as in Example 1 using these magnetic recording media.

The results are shown in Table 1.

(Margin below) 1st table ratio 2: Glossiness was measured at an incident angle of 60° and a reflection angle of ω°.

Shows the time until.

Example 7 Polycarbonate oligomer made from diphenyl carbonate and bisphenol 8 (average molecular m900)
Vinyl chloride-vinylidene chloride-polycarbonate graft copolymer synthesized using
A magnetic recording medium was produced under the same conditions as in Example 1, except that 25% by weight of nylidene chloride, 20% by weight of polycarbonate, and an average molecular weight of +oooo) were used, and each characteristic was measured. The results are shown in Table 2.

Examples 8 to 12 Using the same copolymer as the vinyl chloride-vinylidene chloride-polycarbonate graft copolymer used in Example 7 or a copolymer synthesized in a similar manner, formulation I shown in Table 2 was prepared. A magnetic recording medium was produced under the same conditions as in Example 2 except for the contents of -COOH group and -011 group, and each characteristic was measured. The results are shown in Table 2.

Comparative Example 1 A magnetic recording medium was produced under the same conditions as in Example 1, except for using a vinyl chloride-vinyl acetate copolymer (65% by weight of vinyl chloride, 35% by weight of vinyl acetate, -OH group content). Characteristics were measured. The results are shown in Table 2.

Comparative Example 2 A magnetic recording medium was produced under the same conditions as in Example 2, except that the vinyl chloride-vinyl acetate copolymer used in Comparative Example 1 was used, and each characteristic was measured. The results are shown in Table 2.

(Margin below) Table 2 Book 1: KOH value.

Umbrella 2: Glossiness was measured at an incident angle of 6o0 and a reflection angle of 60@.

-3, 4: Measured at 5 random times using a Sendust head with a gap of 0.25 μm.

Umbrella 5 Nistil durability is 172 inch VHS type,
This shows the time it takes for the output to drop by 3 dB during still shooting with a VTR.

[Effects of the Invention] As explained above, according to the magnetic recording medium of the present invention, a graft copolymer of a vinyl chloride-vinylidene chloride copolymer and at least one selected from polyester oligomers and polycarbonate oligomers is used as a resin binder. By using coalescence, the dispersibility of magnetic powder is improved,
This improves output characteristics and C/N, enables high-density recording, and improves durability.

Applicant Toshiba Corporation Patent Attorney Satoshi Suyama - Procedural amendment (voluntary) November 16, 1985 1, Case indication Patent application No. 6”l-311905 2,
Name of the invention Magnetic recording medium 3, Relationship with the amended person case Patent applicant 72 Horiyo-cho, Saiwai-ku, Yozaki-shi, Kanagawa (307) Toshiba Corporation °40 Agent Kandata, Chiyoda-ku, Tokyo 101 Town 2-chome-1 Detailed description of the invention in the specification attached to the written amendment submitted on May 27, 1986.

6. Correction details [Carbon black (average particle size 70 μm $)” on page 12 line 11 of the statement box was changed to [Carbon black (average particle size 70 μm $)
m) Correct it as J.

that's all

Claims (3)

[Claims] (1) A magnetic recording medium formed by coating a support with a magnetic paint in which ferromagnetic powder is dispersed in a binder, in which the binder comprises a vinyl chloride-vinylidene chloride copolymer, a polyester oligomer, and a polycarbonate oligomer. A magnetic recording medium comprising a graft copolymer obtained by graft copolymerization with at least one selected from the following. (2) The magnetic recording medium according to claim 1, wherein the graft copolymer contains at least one of a -COOH group and an -OH group in the molecule. (3) The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is hexagonal ferrite.