JPS60242517A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having an excellent squareness ratio, etc. by coating an aq. dispersion of a specific water insoluble polyester resin on a polyester film base body then forming a magnetic layer for which a binder contg. a specific polyester resin as one component is used on the coated film thereof. CONSTITUTION:The aq. dispersion of the polyester resin consisting essentially of the water insoluble polyester copolymer A consisting essentially of the condensate of the mixed dicarbon in which 0.5-15mol% in the entire dicarboxylic acid component is a dicarboxylic acid contg. sulfonate group and glycol, the water souble org. compd. B such as alcohol having 60-200 deg.C b.p. and water C and contg. A/B=100/20-5,000, B/C=100/500-10,000 by weight is coated on the surface of the polyester film consisting of polyethylene terephthalate, etc. and is drived. The magnetic layer consisting of the pulverous magnetic powder dispersed into the binder contg. the polyester resin formed by reaction with the mixed dicarboxylic acid which has >=0.1 reduced viscosity and in which 0.7- 7mol% in the entire dicarboxylic acid component is the dicarboxylic acid contg. sulfonate group as one component is formed on the coated film. The durability, etc. are thus improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a magnetic recording medium in which a magnetic layer is provided on a substrate via an undercoat layer. The object of the present invention is to provide a magnetic recording medium in which the adhesion of the magnetic layer to the substrate is improved by using an extremely good binder as one component.

<Relationship with prior art> Magnetic recording media are usually made by coating a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as polyester film and drying it. In response to improved performance, efforts are being made to increase the filling of magnetic powder.

However, when the packing density of the magnetic powder is increased, the adhesion of the magnetic layer to the substrate tends to deteriorate and the strength of the coating film tends to decrease. In order to improve this, a method has been adopted that improves the adhesion of the magnetic layer by applying an undercoat to the substrate and providing 6 layers of undercoat between the magnetic layer and the substrate. Although polyester resins are widely used as excellent undercoating agents, they are still not fully satisfactory. On the other hand, in order to obtain a high-performance magnetic recording medium, a high filling property, that is, a low porosity is required as well as a large r/Bm. According to the experimental results of the present inventors, the porosity of a magnetic tape made by combining magnetic powder and ordinary linear polyester is 0.
88 to 0.45, which does not satisfy the performance of a high-performance magnetic tape. In this case, it is possible to reduce the porosity by lengthening the crosstalk time, but the magnetic powder becomes even more finely divided and the sensitivity of the magnetic tape is reduced.

<Purpose of the Invention> In view of the above circumstances, the present inventors have developed a method to improve Br/Bm (squareness ratio, Br: residual magnetization, Bm:
With the aim of providing a high-performance magnetic recording medium with increased saturation magnetization) value, decreased porosity, and extremely good adhesion of the magnetic layer to the substrate, we have continued various research efforts and have developed polyester. A water-insoluble polyester copolymer whose main components are residues of a mixed dicarboxylic acid in which 0.5 to 15 mol % of the total dicarboxylic acid component is a dicarboxylic acid containing a sulfonic acid metal group and a residue of glycol on at least one side of the film. , (Bl water-soluble organic compound with a boiling point of 60 to 200 ° C and (C) water as the main components, and M+/(Bl = 100/20 to 5000, (Bl/(
c) A coating film is formed from an aqueous dispersion of polyester resin blended in a weight ratio of 100150 to 10000, and a CD+reduced viscosity of 0.1 or more is formed on one side of the coating film. , in a binder containing at least one component of a polyester resin containing residues of mixed dicarboxylic acids and glycol residues, in which 8 to 7.0 mol % of the total dicarboxylic acid components are dicarboxylic acids containing sulfonic acid metal bases. A magnetic recording medium having a porosity of 0.25 is coated with a magnetizable layer in which fine powder magnetic particles are uniformly dispersed and contained.
~0.88, Br/Bm*0.78=0.90, and
The present invention has been achieved by discovering that the magnetizable layer has such good adhesion that it does not peel off in any of the acupressure methods, beer bag methods, and solvent sliding methods.

<Configuration of the Invention> The polyester copolymer (Al is a sulfonic acid metal base-containing dicarboxylic acid 06
It is a substantially water-insoluble polyester copolymer obtained by reacting a mixed dicarboxylic acid of 5 to 15 mol% and 85 to 99.5 mol% of a dicarboxylic acid containing no sulfonic acid metal base with a polyol component. . Substantially water-insoluble means that the polyester copolymer does not dissipate in hot water even if the polyester copolymer is stirred in hot water at 80°C. excessive 80
The weight loss of the polyester copolymer after being stirred in °C hot water for 24 hours is 5% by weight or less.

The above-mentioned sulfonic acid metal base-containing dicarboxylic acids include:
Examples include metal salts of sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthacine-2,fudicarboxylic acid, and 5(4-sulfophenoxy]isophthalic acid, with 5-sulfophthalic acid being particularly preferred. These are sodium sulfoisophthalic acid and sodium sulfoterephthalic acid.These sulfonic acid metal base-containing dicarboxylic acid components are 0.5 to 15 mol%, preferably 2.0 to 10 mol%, based on the total dicarboxylic acid components. %.If it exceeds 15 mol%, the water dispersibility will improve, but the water resistance of the polyester copolymer will decrease significantly, and if it is less than 0.5 mol%, the water dispersibility will decrease significantly.Polyester copolymer The dispersibility of the polymer in water depends on the copolymer composition,
The amount of the sulfonic acid metal base-containing dicarboxylic acid is preferably small, as long as it does not impair the dispersibility in water, although it varies depending on the type and blending ratio of the water-soluble organic compound.

Dicarboxylic acids that do not contain sulfonic acid metal bases include:
Aromatic, aliphatic, and alicyclic dicarboxylic acids can be used.

Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, and 2,6-naphthalenedicarboxylic acid. It is preferable that these aromatic dicarboxylic acids account for 40 mol% or more of the total dicarboxylic acid components, and if it is less than 40 mol%, the mechanical strength and water resistance of the polyester copolymer will decrease. Aliphatic and alicyclic dicarboxylic acids include succinic acid, adipic acid, stem basic acid, 1,8-cyclobentanedicarboxylic acid, 112-
Examples include cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid. Addition of these non-aromatic dicarboxylic acid components may improve adhesive performance in some cases, but generally reduces the mechanical strength and water resistance of the polyester copolymer.

The polyol component to be reacted with the mixed dicarboxylic acid is an aliphatic glycol having 2 to 8 carbon atoms or an alicyclic glycol having 6 to 12 carbon atoms, and specifically, ethylene glycol/I/, 1 .2-Propylene glycol, 1,8-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanedimetatool, l,8-cyclohexanedimeta tool, 1,4-cyclohexane dimetatool, P-xylylene glycol, diethylene glycol, triethylene glycol, and the like. Examples of polyethers include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, an oxycarboxylic acid component such as P-oxyethoxybenzoic acid may be copolymerized.

Polyester copolymers are obtained by conventional melt polycondensation. In other words, there is a direct esterification method in which the above dicarboxylic acid component and glycol component are directly reacted, water is distilled off and esterified, and then polycondensation is performed, or the dimethyl ester of the above dicarboxylic acid component and the glycol component are reacted to form methyl alcohol. It can be obtained by a transesterification method, etc., which involves distilling off, transesterifying, and then polycondensing it. In addition, solution polycondensation, interfacial polycondensation, etc. may also be used, and the polyester copolymer of the present invention is not limited by the polycondensation method.

During melt polycondensation, antioxidants, slip agents, inorganic fine particles, antistatic agents, and the like can be added as appropriate.

To obtain the aqueous dispersion of the above polyester copolymer,
It is necessary to disperse it in water together with water-soluble organic compounds. For example, the above polyester copolymer and a water-soluble organic compound are mixed in advance at 50 to 200°C, and water is added to this mixture and dispersed by stirring, or conversely, the mixture is added to water and dispersed by stirring. Alternatively, there is a method in which a polyester copolymer, a water-soluble organic compound, and water are made to coexist and stirred at 40 to 120°C.

The water-soluble organic compound is an organic compound having a solubility in water of 20 g or more at 20°C, and specifically includes aliphatic and alicyclic alcohols, ethers, esters, and ketone compounds, such as methanol, ethanol, Improper tool, monohydric alcohols such as n-butanol,
These include glycols such as ethylene glycol and propylene gelylcol, glycol derivatives such as methyl cellosolve, ethyl cellosolve, and n-butyl cellosolve, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate, and ketones such as methyl ethyl ketone. These water-soluble organic compounds can be used alone or in combination of two or more. Among the above compounds, butyl cellosolve and ethyl cellosolve are preferred in terms of dispersibility in water and coatability on films.

The weight ratio of the above polyester copolymer, [B] water-soluble organic compound and (C1 water) is 1/(Bl=
100/20~500003)/C1=10015
It is important to satisfy 0 to 10,000. Contains less water-soluble organic compounds than polyester copolymer (A)
/(When Bl exceeds 100/20, the dispersibility of the aqueous dispersion decreases. In this case, dispersibility can be assisted by adding a surfactant, but the amount of surfactant If it is too large, the adhesion and water resistance will decrease.On the contrary, if it is less than (A+/(B)IQO0015000, or if (Bl/(cI) exceeds IQO150, the amount of water-soluble organic compounds in the aqueous dispersion will decrease. As a result, there is a risk of explosion due to the solvent during in-line coating, in which the aqueous dispersion of the polyester resin is applied to the melt-extruded unstretched film or stretched film, and then stretched, so it is necessary to take explosion-proof measures. CB+
/ When (C) is less than 100/10000, the surface tension of the aqueous dispersion increases, the wettability to the film decreases, and coating spots are likely to occur. In this case, the wettability can be improved by adding a surfactant, but if the amount of the surfactant is too large, the adhesiveness and water resistance will decrease as described above.

A slip agent, an antistatic agent, an anti-blocking agent, a crosslinking agent, etc. may be added to the above aqueous dispersion.

The polyester film to which the aqueous dispersion of the polyester copolymer (5) is applied is a melt-extruded unstretched film, a -axially stretched film, or a biaxially stretched film; in the case of an unstretched film or a stretched film, After applying an aqueous dispersion of polyester resin, the film is stretched to form a biaxially stretched film.

The amount of the aqueous dispersion applied to the polyester film is preferably 0.01 to 51/rrl of the polyester copolymer to the biaxially stretched film.

When the coating amount is less than o, o1y/i, the adhesiveness of the magnetic material layer provided on the polyester copolymer layer is insufficient. When the coating amount exceeds 511/m'', the mechanical strength of the polyester film decreases, and the copolymerized polyester resin in the recovered and recycled film increases, resulting in deterioration of the mechanical strength and heat resistance of the recycled film.

If the polyester film is subjected to a corona discharge treatment before being coated with the aqueous dispersion of the polyester resin described above, the coating properties of the aqueous dispersion will be good, and the adhesive strength between the polyester film and the polyester polymer coating will be improved. This is a preferred embodiment because it improves.

Furthermore, wettability and adhesion with the magnetic layer can be improved by subjecting the polyester copolymer layer to corona discharge treatment, corona discharge treatment under a nitrogen atmosphere, ultraviolet irradiation treatment, or the like.

Although various films have been proposed as base films for magnetic recording media, polyester films are preferred due to their superior mechanical properties, chemical resistance, and heat resistance.
Among these, polyethylene terephthalate film is excellent in terms of various properties.

The surface roughness of this polyethylene terephthalate film is very important for reducing noise and preventing signal dropouts in the production of magnetic recording media, and is referred to as center line average roughness (RA) (Surfcom 300A surface roughness meter (manufactured by Tokyo Seimitsu)). using
Needle diameter 1 μm, weight 0.07 g, measurement standard length 0.8 fl
, measured under the condition of cutoff 0.08111) is 0.05
It is preferable that the thickness be less than 0.05 μm, and if it exceeds 0.05 μm, noise and signal loss will occur, causing problems in use.

On the other hand, the dicarboxylic acid component of the copolyester resin used as a component of the binder in the magnetic layer in the present invention includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid; These include aromatic oxycarboxylic acids such as P-oxybenzoic acid and P-(hydroxyethoxy)benzoic acid, and aliphatic dicarboxylic acids such as conozylic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. It is preferable that the molar ratio of the aromatic dicarboxylic acid component to the aliphatic dicarboxylic acid component is 50,150 to 10,010, and that at least 30 moles of the aromatic dicarboxylic acid component is terephthalic acid. Small amounts of tri- and tetracarboxylic acid components such as trimellitic acid, trimesic acid, and pyromellitic acid may be used in combination.

The glycol component to be reacted with the above dicarboxylic acid includes ethylene glycol, propylene glycol, 1,3
-Propanediol, 1.4-butanediol, 1.5
-bentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, cyfropylene glycol, 2.2.4-trimethyl-1,3-bentanediol, 1.4-cyclohexane dimetatool, bisphenolic ethylene oxide Examples include adducts and propylene oxide adducts, ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Trimethylolethane, trimethylolpropane, glycerin,
Small amounts of tri- and tetraols such as pentaerythritol may also be used. Further, an oxycarboxylic acid component such as P-oxyethoxybenzoic acid may be copolymerized.

The dicarboxylic acid component containing a sulfonic acid metal base that characterizes the copolymerized polyester resin (D) includes 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid. The copolymerization amount of the dicarboxylic acid component containing these sulfonic acid metal bases is 0.3 to 7.0 mol%, preferably 1.0 to 5.0 mol%, based on the total dicarboxylic acid component. be. If the copolymerization amount is less than 0.3, the performance improvement will not be sufficient;
．． If the copolymerization amount exceeds 0 mol %, the solvent solubility of the copolymerized polyester will be poor and it will be impractical.

Copolymerized polyester resin (A) obtained in this way
, utilizing the terminal group of (D) to form a difunctional incyanate compound, e.g. 2.4 tolylene diisocyanate), 2.6
A polymer subjected to a chain extension reaction with tolylene diisocyanate, diphenylmethane diisocyanate, xylene diisocyanate, or inphorone diincyanate can be used. This method allows two types of copolymerized polyester resins to be combined to take advantage of their characteristics. In other words, the introduction of urethane groups improves adhesion to polyester films,
This is a preferred embodiment because it can increase the solvent solubility of the copolyester resin, improve the dispersibility of the magnetic powder, and improve the water resistance of the coating film.

Examples of the fine powder magnetic particles used in the present invention include -FeO, CrO, and the like having a spinel structure.

If the softening point of the copolyester resin (D) is low, depending on the application, there is a risk that the resin may soften due to the heat between it and the head, or that it may be damaged when the tape is wrapped. In such a case, it is desirable to mix a compound that is compatible with the copolyester resin within a range that does not impair the dispersibility of the fine powder magnetic particles, and that also reacts and crosslinks. The mixing amount is generally 2 to 100 parts by weight per 100 parts by weight of the copolyester resin.

Examples of such compounds include epoxy resins, incyanate compounds, and melamine resins.

Among these, isocyanate compounds are particularly preferred.

Plasticizers such as dibutyl phthalate and triphenyl phosphate, lubricants such as zinc stearate, soybean oil lecithin, and silicone oil, and various antistatic agents may be added to the magnetic recording medium of the present invention as necessary. can. In addition, if necessary, nitrocellulose, polyvinylidene chloride resin, vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, polymethyl methacrylate resin, vinylidene chloride-methyl methacrylate copolymer, polyurethane resin, An appropriate amount of a binder such as an epoxy resin may be used in combination.

<Examples> The present invention will be specifically explained below with reference to Examples. In the examples, parts simply indicate parts by weight.

The acupressure method for adhesion testing involves passing a magnetic tape between the index finger and middle finger, bending it at an angle of 1800 degrees between the thumb and index finger, and applying strong friction between the tapes with the magnetic layer on the outside. This was done by observing the state of peeling. In the beer pack method, an adhesive tape was pasted on the surface of the magnetic layer, and after uniformly adhering to the entire surface, the state was observed when it was instantly peeled off. In addition, the solvent sliding method was performed by observing the state when the surface of the magnetic layer was rubbed 10 times with gauze soaked in tetrahydrofuran. /tetrachloroethane (weight ratio 6/4') mixed solvent 25-dissolved and measured at 30°C.

The softening point was measured according to JIS2351.

The measured specific volume was measured by immersing the magnetizable layer in water, and the true specific volume was calculated from the specific volume of each component contained in the magnetizable layer using the following formula: True specific volume = 8 (0 pi) Σω1 ωi Blend weight of component i ρi Density of component i The smoothness of the magnetizable layer in the examples is good, somewhat good, and poor when the value on the gloss meter is 30 to 5o, 15 to 30.15 or less. The higher the number, the higher the gloss,
The higher the gloss, the higher the level of smoothness.

In the water resistance test in the examples, the magnetic layer was left in an atmosphere of 90% RH for 5 days at 50° C., and changes in appearance on the surface and opposite surface of the magnetic layer were visually judged.

Those in which the appearance did not change at all were rated as ○, those in which some lifting occurred were rated as ×, and those in the middle were rated as △.

Example 1 (1) Production of aqueous dispersion of polyester copolymer (4) 117 parts (49 mol%) of dimethyl terephthalate, 11 parts (49 mol%) of dimethyl isotumelate, 103% (50 mol%) of ethylene glycol ), 58 parts (50 mol%) of diethylene glycol, 0.08 part of zinc acetate, and 0.08 part of antimony trioxide in a reaction vessel at 40 to 220°C.
The temperature was raised to
9 parts (2 mol %) of sodium sulfoisophthalic acid was added and the mixture was subjected to an esterification reaction at 220 to 260°C for 1 hour, followed by a polycondensation reaction for 2 hours under reduced pressure (10 to 0.2 + s Hg) to obtain an average molecular weight. 18000, softening point 140
℃ obtained polyester copolymer. 300 parts of this polyester copolymer and 140 parts of n-butyl cellosolve were stirred in a container at 150 to 170°C for about 3 hours to obtain a homogeneous and viscous melt, and 560 parts of water was gradually added to the melt. After about 1 hour, a uniform pale white aqueous dispersion with a solid content concentration of 30% was obtained, which was further diluted by adding 4500 parts of water and 4500 parts of ethyl alcohol to obtain a coating liquid with a solid content concentration of 3%. Ta.

(2) Production of coated film Polyethylene tereftate is melt extruded at 280 to 300°C, cooled with a cooling roll at 15°C to obtain an unstretched film with a thickness of 130 microns, and this unstretched film is extruded at different circumferential speeds at 85°C. Stretched 3.5 times in the longitudinal direction between a pair of rolls, subjected to corona discharge treatment to this -axially stretched film, applied the above coating solution to the corona discharge treated surface using an air knife method, and dried with hot air at 70°C. Then, the film was stretched 3.5 times in the transverse direction at 98° C. using a tenter, and further heat-set at 200 to 210° C. to obtain a biaxially stretched coated polyester film having a thickness of 12 microns. (Undercoating process: inline) (3
) Copolymerized polyester resin for binder in magnetic layer (D)
175 parts of dimethyl terephthalate, 78 parts of dimethyl inphthalate, 161 parts of ethylene glycol, 145 parts of neopentyl glycol, 14 parts of dimethyl 5-sodium sulfoisofucrate, 8 parts, zinc acetate 0.17 parts,
0.02 parts of sodium acetate and 0.02 parts of antimony trioxide.
16 parts were added and transesterification reaction was carried out at 140 to 220°C for 3 hours. Next, 131 parts of sebacic acid was added and 210 parts of sebacic acid was added.
After reacting at ~250°C for 1 hour, the reaction system was depressurized to 1 to 5 mHg over 60 minutes, and further heated to 0.1 mHg at 250°C.
The polycondensation reaction was carried out for 60 minutes under reduced pressure of ~0.3% Hg. The obtained copolymerized polyester resin (D) has ηs p/
It was pale yellow and transparent with a softening point of C-0.63 and a softening point of 113°C. According to NMR (nuclear magnetic resonance) analysis, the composition was as follows: Terephthalic acid 45 mol% Isophthalic acid 20 Sebacic acid 32.5 5-Sodium sulfoisophthalic acid 2.5 Ethylene glycol 50 Neopentyl glycol 50 (4 ) Preparation and coating of magnetic paint 250 parts of Cr0z fine powder particles, 2 parts of dioctyl sulfonodium succinate, 4 parts of copolymerized polyester resin T fat (D) and 600 parts of cellosolve acetate were mixed for about 24 hours using a ball mill. 350 parts of copolyester resin (D) and 1,000 parts of methyl ethyl ketone were added to 400 parts of this mixture, and the mixture was mixed again for about 70 hours using a ball mill. After filtering and defoaming the resulting mixture, a doctor film with a gap of 30μ was placed on the biaxially stretched coated polyester film with a thickness of 12μ obtained in step (2) above.
It was applied using a blade and then placed in a parallel magnetic field of 1,000 oersted for about 1 second.

Next, the solution was left in a hot air dryer at 80° C. for 3 days to remove the solvent.

Example 2 In Example 1, part of the DEC in the composition of the primer was
A magnetic recording medium was obtained in the same manner as in Example 1 except that PEG was used as described in the table.

Examples 3 to 4' Same as Example 2 except that in Example 2, the undercoat of Example 2 was applied to the biaxially stretched film and dried (undercoating process: off-line), and the polyester binder composition was changed as shown in Table 1. and obtained a magnetic recording medium.

Comparative Example 1 A magnetic recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was not formed. Comparative Example 2 In Example 1, the undercoat, 5-sodium sulfoisophthalic acid, was completely replaced. A magnetic recording medium was obtained in the same manner as in Example 1 except that 20 mol% of the dicarboxylic acid was added.

Comparative Examples 3 to 4 Magnetic recording media were prepared in the same manner as in Example 3, except that the amount of 5-sodium sulfoisophthalic acid as a binder in the magnetic layer was changed to 0.1 and 10 mol% based on the total dicarboxylic acids. Obtained.

Comparative Example 5 A magnetic recording medium was obtained in the same manner as in Example 3 except that a vinyl chloride/vinyl acetate copolymer (manufactured by UCC Corporation, trade name: VAGH) was used as the binder in the magnetic layer.

Comparative Example 6 A magnetic recording medium was obtained in the same manner as in Comparative Example 5 using vinyl chloride/vinyl acetate copolymer (manufactured by UCC Corporation, trade name: VAGH) as a binder without undercoating.

Example 5 The copolymerized polyester resin obtained in Example 1 (3) was
It was dissolved in a mixture of methyl ethyl ketone and toluene (weight ratio 50150) to a concentration of 30%, heated to 40°C.
Diphenylmethane diisocyaner) (abbreviated as MDI) was added so that OH/NCO = 1.05, and 10
Dibutyltin dilaurate was then added in an amount of 0.1% based on MDI, the temperature was raised to 80°C, and a urethane reaction was carried out for 2 hours.

Furthermore, in (4) of Example 1, a magnetic paint was prepared using the above resin instead of the polyester resin, and a magnetic paint coated film was obtained in the same manner as in Example 1.

From Table 2, when there is no undercoat layer (Comparative Example 1) and the amount of 5-sodium sulfoisophthalic acid in the undercoat agent is 15
When the amount of 5-sodium sulfoisophthalic acid in the binder is 0.3 mol% or more (Comparative Example 2)
Comparative Example 3) and 7 mol% or more (Comparative Example 4), when the binder was changed to vinyl chloride/vinyl acetate other than the present invention (Comparative Example 5), and when the binder was changed to vinyl chloride/vinyl acetate without undercoating. It can be seen that the method of the present invention has extremely good adhesion, magnetic recording properties, and appearance (smoothness) as compared to the case (Comparative Example 6).

Procedural amendment (voluntary) June 14, 1980 Patent application dated May 16, 1980 (4) λ Name of invention magnetic recording medium & person making corrections Relationship to the case: Patent applicant 2-2-8 Dojimahama, Kita-ku, Osaka Detailed description of the invention in the specification & Contents of correction (1) Lines 3 to 4 of page 12 of the specification do.

(2) On page 12, line 5, ``Improve explosion-proof measures'' is corrected to ``request explosion-proof measures.''

(8) On page 16, line 4, "Polytetramethylene glycol" is corrected to "Polytetramethylene glycol."

(4) Change "-FeOsOrO etc." to "-FeOsOrO, etc." on page 17, line 18 of the same page to "/f-F e 901
s Or C1g, etc.”

(5) Page 19, line 17 [Reduced viscosity ηsp/C(a//r)J is defined as “reduced viscosity Correct 胛日70(dt/I)J.

(6) On page 20, line 6, "ωl゛ Mixed weight of component 1" is corrected to "ωl゛ Mixed weight of component 1."

I am corrected.

(9) On page 20, lines 14 and 15, "90% in the atmosphere" is corrected to "90% in the atmosphere."

do.

Claims (5)

[Claims] (1) At least one side of the polyester film is coated with sulfonic acid metal base-containing dicarboxylic acid containing 0.5 to 15 mol % of the total dicarboxylic acid components.The main components are residues of a mixed dicarboxylic acid and glycol residues. A coating film is formed from an aqueous dispersion of a water-insoluble polyester copolymer, a water-soluble organic compound with a boiling point of 60 to 200°C, and a polyester resin containing water as the main component and blended in a weight ratio of On one side of the coating film, ■) a mixture having a reduced viscosity of 0.1 or more and containing sulfonic acid metal base-containing dicarboxylic acid in an amount of 0.8 to 7.0 mol% of the total dicarboxylic acid component; It is characterized by a magnetizable layer in which fine powder magnetic particles are uniformly dispersed and contained in a binder containing at least one component of a polyester resin whose main components are dicarboxylic acid residues and glycol residues. magnetic recording media. (2) The magnetic recording medium according to claim W11, wherein the polyester film is a film made of polyethylene terephthalate. (3) Center line average roughness R of polyester film surface
3. The magnetic recording medium according to claim 1, wherein A) is 0.05 μm or less. (4) The magnetic recording medium according to any one of claims 1 to 3, wherein the water-insoluble polyester copolymer (Al is a polymer chain-extended with a diincyanate compound). (5) The magnetic recording medium according to claims 1 to 4, wherein the polyester resin) is a polymer chain-extended with a diincyanate compound.