JPH0256731B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Field of Application> The present invention relates to a magnetic recording medium in which a magnetic layer is provided on a substrate via an undercoat layer, and its purpose is to use a binder having extremely good dispersibility with respect to magnetic powder as one component. 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. <Relationship with prior art> Magnetic recording media are usually made by applying a magnetic coating 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 magnetic powder is increased,
Adhesion of the magnetic layer to the substrate tends to deteriorate and the strength of the coating film tends to decrease. To improve this, conventional methods have been used to improve the adhesion of the magnetic layer by applying an undercoat to the substrate and providing an undercoat layer between the magnetic layer and the substrate. Although polyester resins are widely used as excellent undercoating agents, they are not yet fully satisfactory. On the other hand, in order to obtain a high-performance magnetic recording medium, high Br/Bm and high filling property, ie, low porosity, are required. 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 0.38 to 0.45, which does not satisfy the performance as a high-performance magnetic tape. In this case, it is possible to reduce the porosity by increasing the kneading time, but the magnetic powder becomes even more finely divided, and the sensitivity of the magnetic tape is conversely reduced. <Purpose of the Invention> In view of these circumstances, the present inventors have found that while using ordinary magnetic powder, the Br/Bm (squareness ratio, Br: residual magnetization, Bm: saturation magnetization) value increases, and the porosity increases. With the aim of providing a high-performance magnetic recording medium in which the adhesion of the magnetic layer to the substrate is reduced and the adhesion of the magnetic layer to the substrate is extremely good, various researches have been carried out, and it has been found that (A) all-dicarboxylic acid is added to at least one side of the polyester film. A water-insoluble polyester copolymer whose main components are residues of a mixed dicarboxylic acid in which 0.5 to 15 mol% of the components are dicarboxylic acids containing sulfonic acid metal groups and residues of glycol, (B) water-soluble with a boiling point of 60 to 200 °C The main components are organic organic compounds and (C) water, and (A)/(B)=100/20~5000, (B)/(C)=100/50~
A coating film is formed from an aqueous dispersion of polyester resin blended at a weight ratio of 10,000, and on one side of the coated film (D) the reduced viscosity is 0.1 or more, and the total dicarboxylic acid component is Finely powdered magnetic particles are uniformly dispersed in a binder containing at least one component of a polyester resin whose main components are a residue of a mixed dicarboxylic acid in which 0.3 to 7.0 mol% is a sulfonic acid metal group-containing dicarboxylic acid and a residue of glycol. A magnetic recording medium characterized by being coated with a dispersed and contained magnetizable layer has a porosity of 0.25 to 0.38, a Br/Bm value of 0.78 to 0.90, and can be applied by any of the acupressure method, peel back method, and solvent sliding method. The present invention was achieved by discovering that the magnetizable layer has such good adhesion that it does not peel off even in the above cases. <Structure of the Invention> The polyester copolymer (A) contained in the aqueous dispersion of the present invention contains 0.5 to 15 mol % of a dicarboxylic acid containing a sulfonic acid metal base and 85 to 99.5 mol % of a dicarboxylic acid containing no sulfonic acid metal base. It is a substantially water-insoluble polyester copolymer obtained by reacting a mixed dicarboxylic acid 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, and specifically, the polyester copolymer does not dissipate in hot water. The weight loss of the polyester copolymer after being stirred in 80°C hot water for 24 hours is 5% by weight or less. Examples of the above-mentioned dicarboxylic acids containing sulfonic acid metal groups include metals such as sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and 5[4-sulfophenoxy]isophthalic acid. salt was given,
Particularly preferred are 5-sodium sulfoisophthalic acid and sodium sulfoterephthalic acid. These sulfonic acid metal base-containing dicarboxylic acid components are 0.5 to 15 mol% of the total dicarboxylic acid components.
The content is preferably 2.0 to 10 mol%. 15
If it exceeds mol%, the dispersibility in water will improve, but the water resistance of the polyester copolymer will decrease significantly.
Moreover, if it is less than 0.5 mol%, the dispersibility in water will be significantly reduced. The dispersibility of the polyester copolymer in water varies depending on the copolymer composition, the type and blending ratio of the water-soluble organic compound, etc., but the above dicarboxylic acid containing a sulfonic acid metal group can be used as long as it does not impair the dispersibility in water. , a small amount is preferred. As the dicarboxylic acid containing no sulfonic acid metal base, aromatic, aliphatic, and alicyclic dicarboxylic acids can be used. Aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid,
Examples include 2,6-naphthalene dicarboxylic 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, sebacic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid,
1,3-cyclohexanedicarboxylic acid, 1,4-
Examples include cyclohexanedicarboxylic acid.
When these non-aromatic dicarboxylic acid components are added,
Although adhesive performance may be improved in some cases, it 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 aliphatic glycol having 6 to 12 carbon atoms, and specifically, ethylene glycol, 1,2-
Propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol These include methanol, P-xylylene glycol, diethylene glycol, triethylene glycol, and the like. Examples of polyethers include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Also, P
- An oxycarboxylic acid component such as 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, etc. can be added as appropriate. In order to obtain the aqueous dispersion of the polyester copolymer described above, it is necessary to disperse it in water together with a water-soluble organic compound. 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. method, or by coexisting a polyester copolymer, a water-soluble organic compound, and water.
There is a method of stirring at 120℃. 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. For example, monohydric alcohols such as methanol, ethanol, isopropanol, and n-butanol; glycols such as ethylene glycol and propylene glycol;
These include 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 (A) polyester copolymer, (B) water-soluble organic compound and (C) water is (A)/(B)=100/20~5000 (B)/(C)=100/ It is important to satisfy the range of 50 to 10,000. When the amount of the water-soluble organic compound is small relative to the polyester copolymer and the ratio (A)/(B) exceeds 100/20, the dispersibility of the aqueous dispersion decreases. In this case, dispersibility can be assisted by adding a surfactant, but if the amount of surfactant is too large, adhesiveness and water resistance will decrease. Conversely, if (A)/(B) is less than 100/5000, or
When (B)/(C) exceeds 100/50, the amount of water-soluble organic compounds in the aqueous dispersion increases, and the aqueous dispersion of the above polyester resin is applied to a melt-extruded unstretched film or a uniaxially stretched film. There is a risk of explosion due to the solvent during post-stretching, so-called in-line coating, and therefore it is necessary to take explosion-proof measures.Furthermore, it is necessary to take into account recovery of the compound because it causes environmental pollution and increases costs. (B)/(C) is 100/1000
When it is less than 0, 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. The above aqueous dispersion includes slip agents, antistatic agents,
Anti-blocking agents, cross-linking agents, etc. may be added. The polyester film to which the aqueous dispersion of polyester copolymer (A) is applied is a melt-extruded unstretched film, a uniaxially stretched film, or a biaxially stretched film. After coating an aqueous resin dispersion, it is stretched to form a biaxially stretched film. The amount of the aqueous dispersion applied to the polyester film is preferably 0.01 to 5 g/m ² of the polyester copolymer based on the film after biaxial stretching. If the coating amount is less than 0.01 g/m ² , the adhesiveness of the magnetic material layer provided on the polyester copolymer layer will be insufficient. If the coating amount exceeds 5 g/m ² , the mechanical strength of the polyester film decreases, and the amount of 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 corona discharge treatment before applying the aqueous dispersion of the polyester resin mentioned above, the applicability of the aqueous dispersion will be improved and the adhesive strength between the polyester film and the polyester copolymer coating will be improved. This is a preferred embodiment because it improves the performance. 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. Various films have been proposed as base films for magnetic recording media, but polyester films are superior in terms of mechanical properties, chemical resistance, heat resistance, etc. Among them, polyethylene terephthalate films are superior in terms of various properties. It is excellent. The surface roughness _of this polyethylene terephthalate film is extremely important for reducing noise and preventing signal dropouts in the production of magnetic recording media. (manufactured by), needle diameter 1 μm, weight 0.07 g,
Measured under the conditions of a measurement standard length of 0.8 mm and a cutoff of 0.08 mm) is preferably 0.05 μm or less, and if it exceeds 0.05 μm, noise and signal loss will occur, causing problems in use. On the other hand, copolyester resin (D) used as a component of the binder in the magnetic layer in the present invention
The dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid, and aromatic oxycarboxylic acids such as P-oxybenzoic acid and P-(hydroxyethoxy)benzoic acid. , aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid.
It is desirable that the molar ratio of the aromatic dicarboxylic acid component to the aliphatic dicarboxylic acid component is 50/50 to 100/0, and that at least 30 mol % 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 components to be reacted with the dicarboxylic acid include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,
6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct and propylene oxide adduct of bisphenol A , ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Small amounts of tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination. 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 dicarboxylic acid components containing these sulfonic acid metal bases is 0.3 to 7.0 mol%, preferably 1.0% by mole based on the total dicarboxylic acid components.
~5.0 mol%. If the copolymerization amount is less than 0.3, the performance improvement will not be sufficient;
If the amount of copolymerization exceeds the above, the solvent solubility of the copolymerized polyester will be poor and it will be impractical. Using the terminal groups of the copolymerized polyester resins (A) and (D) thus obtained, difunctional isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and A polymer subjected to a chain extension reaction with enylmethane diisocyanate, xylene diisocyanate, or isophorone diisocyanate can be used. This method allows two types of copolymerized polyester resins to be combined to take advantage of their characteristics. That is, this is a preferred embodiment because the introduction of urethane groups can improve the adhesion to polyester films, increase the solvent solubility of the copolymerized polyester resin, improve the dispersion of magnetic powder, and improve the water resistance of the coating film. Examples of the fine powder magnetic particles used in the present invention include γ-Fe ₂ O ₃ and CrO ₂ having a spinel structure. If the copolymerized polyester resin (D) has a low softening point, depending on the application, there is a risk that it will soften due to the intense heat between it and the head, or that it will block when wrapped with tape. In such a case,
It is desirable to mix a compound which is compatible with the copolyester resin within a range that does not impair the dispersibility of the fine powder magnetic particles, and which reacts and crosslinks. The mixing amount is generally based on copolymerized polyester resin.
The amount is 2 to 100 parts by weight per 100 parts by weight. Examples of such compounds include epoxy resins, isocyanate compounds, and melamine resins.
Among these, isocyanate compounds are particularly preferred. The magnetic recording medium of the present invention may optionally contain plasticizers such as diptylphthalate and triphenyl phosphate, zinc stearate, soybean oil lecithin,
Lubricants such as silicone oil and various antistatic agents can also be added. 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 using 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 180 degrees between the thumb and index finger, and applying strong friction between the tapes with the magnetic layer on the outside to peel off the magnetic layer. The peel-back method was performed by attaching an adhesive tape to the surface of the magnetic layer, uniformly adhering it to the entire surface, and then peeling it off instantly to observe the state. The solvent sliding method was carried out by rubbing the surface of the magnetic layer 10 times with gauze soaked in tetrahydrofuran and observing the condition. The ring element viscosity ηsp/C (dl/g) was measured at 30°C by dissolving 0.10 g of polyester resin in 25 ml of a mixed solvent of phenol/tetrachloroethane (weight ratio 6/4). The softening point was measured according to JIS2351. The porosity was determined from the following formula: Porosity = Measured specific volume - True specific volume / Measured specific volume The measured specific volume was obtained by immersing the magnetizable layer in water, and the true specific volume was determined by immersing the magnetizable layer in water. Calculated from the specific volume of each component contained using the following formula: True specific volume = Σ(Wi/Pi)/ΣWi Mixed weight of Wi component i Density of Pi component i Smoothness of the magnetizable layer in the example Good, somewhat good,
Defective values are 30-50, 15-30,
15 or less; the larger the number, the greater the photo selection, and the larger the photo selection, the better the 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 evaluated with the naked eye. 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 between were rated as △. Example 1 (1) Production of aqueous dispersion of polyester copolymer (A) 117 parts of dimethyl terephthalate (49 mol%),
Dimethyl isophthalate 117 parts (49 mol%), ethylene glycol 103 parts (50 mol%), diethylene glycol 58 parts (50 mol%), zinc acetate 0.08
40 parts and 0.08 parts of antimony trioxide in a reaction vessel.
The temperature was raised to ~220°C to carry out the transesterification reaction for 3 hours, and then 9 parts (2 mol%) of 5-sodium sulfoisophthalic acid was added and the mixture was heated at 220 to 260°C for 1 hour.
The esterification reaction was carried out for a period of time, and further under reduced pressure (10~
A polyester copolymer having an average molecular weight of 18,000 and a softening point of 140°C was obtained by carrying out a polycondensation reaction at a temperature of 0.2 mmHg) for 2 hours. 300 parts of this polyester copolymer and 140 parts of n-butyl cellosolve were mixed in a container with 150 parts of
Stir at ~170℃ for about 3 hours to obtain a homogeneous and viscous melt. 560 parts of water is gradually added to this melt, and after about 1 hour, a uniform pale white solid content is obtained.
A 30% aqueous dispersion was obtained, which was further diluted with 4,500 parts of water and 4,500 parts of ethyl alcohol to obtain a coating solution with a solid content concentration of 3%. (2) Manufacture of coated film Polyethylene terephthalate is melt-extruded at 280 to 300℃, cooled with a cooling roll at 15℃, and the thickness
An unstretched film of 130 microns was obtained, and this unstretched film was stretched 3.5 times in the longitudinal direction between a pair of rolls at different circumferential speeds at 85°C. This uniaxially stretched film was subjected to corona discharge treatment, and the film was stretched to the corona discharge treated surface. Apply the above coating liquid using an air knife method,
It was dried with hot air at 70°C, then 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 with a thickness of 12 microns. (Undercoating process: in-line) (3) Production of copolymerized polyester resin (D) for binder in magnetic layer Dimethyl terephthalate 175 was placed in a reaction vessel equipped with a thermometer, stirrer, and partial reflux condenser.
parts, dimethyl isophthalate 78 parts, ethylene glycol 161 parts, neopentyl glycol 145 parts
parts, 14.8 parts of dimethyl 5-sodium sulfoisophthalate, 0.17 parts of zinc acetate, sodium acetate
Add 0.02 parts and 0.16 parts of antimony trioxide.
The transesterification reaction was carried out at 140-220°C for 3 hours. Next, add 131 parts of sebacic acid and add 210 to 250 parts.
After reacting at ℃ for 1 hour, the reaction system was depressurized to 1 to 5 mmHg over 60 minutes, and further reduced to 0.1 mmHg at 250℃.
The polycondensation reaction was carried out for 60 minutes under reduced pressure of ~0.3 mmHg. The obtained copolymerized polyester resin (D) had ηsp/C-0.63, a softening point of 113°C, and was pale yellow and transparent. 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) Magnetic paint. Preparation and coating 250 parts of CrO ₂ fine powder particles, 2 parts of dioctyl sulfonodium succinate, 48 parts of copolyester resin (D) and 600 parts of cellosolve acetate
The mixture was mixed using a ball mill for about 24 hours. 400 parts of this mixture and 350 parts of copolyester resin (D)
and 1,000 parts of methyl ethyl ketone were added thereto and mixed again using a ball mill for about 70 hours. After filtering and defoaming the resulting mixture, a doctor film with a gap of 30μ was applied onto 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 1000 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 A magnetic recording medium was obtained in the same manner as in Example 1 except that part of the DEG in the composition of the undercoat was changed to PEG as shown in Table 1. Examples 3 to 4 Example 2 was applied to the biaxially stretched film in Example 2.
A magnetic recording medium was obtained in the same manner as in Example 2, except that the undercoating agent was applied and dried (undercoating step: off-line), and the polyester binder composition was changed as shown in Table 1. 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 A magnetic recording medium was obtained in the same manner as in Example 1 except that 5-sodium sulfoisophthalic acid as an undercoat was added in an amount of 20 mol % based on the total dicarboxylic acids. Comparative Examples 3 to 4 Magnetic recording media were obtained 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. . Comparative Example 5 In Example 3, the binder in the magnetic layer was vinyl chloride/vinyl acetate copolymer (manufactured by UCC, trade name
A magnetic recording medium was obtained in the same manner as in Example 3 except that the magnetic recording medium was changed to VAGH). Comparative Example 6 Vinyl chloride/vinyl acetate copolymer (manufactured by UCC, trade name: VAGH) as a binder without undercoating
A magnetic recording medium was obtained in the same manner as in Comparative Example 5. Example 5 Copolymerized polyester resin D obtained in Example 1 (3)
was dissolved in a mixture of methyl ethyl ketone and toluene (weight ratio 50/50) to a concentration of 30%, heated, and mixed with diphenylmethane diisocyanate (MDI) so that OH/NCO = 1.05 at 40°C. ) and after 10 min dibutyltin dilaurate was added to MDI.
0.1% of the solution was added, the temperature was raised to 80°C, and the urethanization reaction was carried out for 2 hours. Further, in (4) of Example 1, a magnetic paint was prepared using the above resin instead of polyester resin D, and a magnetic paint coated film was obtained in the same manner as in Example 1. Table 2 shows that when there is no undercoat layer (Comparative Example 1) and when the amount of 5-sodium sulfoisophthalic acid in the undercoat is 15 mol% or more (Comparative Example 2), the amount of 5-sodium sulfoisophthalic acid in the binder is
In the case of 0.3 mol% or less (Comparative Example 3) and 7 mol%
In the above case (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 (Comparative Example 6) In comparison, it can be seen that the method of the present invention has extremely good adhesion, magnetic recording properties, and appearance (smoothness).

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Claims (1)

[Claims] 1. (A) on at least one side of the polyester film
A water-insoluble polyester copolymer whose main components are residues of mixed dicarboxylic acid and glycol, in which 0.5 to 15 mol% of the total dicarboxylic acid components are dicarboxylic acids containing sulfonic acid metal bases, (B) boiling point 60 to 200 ℃
water-soluble organic compound and (C) water as main components, and (A)/(B)=100/20~5000, (B)/(C)=100/50~
A coating film is formed from an aqueous dispersion of polyester resin blended at a weight ratio of 10,000, and on one side of the coated film (D) the reduced viscosity is 0.1 or more, and the total dicarboxylic acid component is Finely powdered magnetic particles are uniformly dispersed in a binder containing at least one component of a polyester resin whose main components are a residue of a mixed dicarboxylic acid in which 0.3 to 7.0 mol% is a sulfonic acid metal group-containing dicarboxylic acid and a residue of glycol. A magnetic recording medium characterized in that it is coated with a dispersed and contained magnetizable layer. 2. The magnetic recording medium according to claim 1, wherein the polyester film is a film made of polyethylene terephthalate. 3 Claim 1 in which the center line average roughness (RA) of the polyester film surface is 0.05 μm or less
A magnetic recording medium according to items 1 to 2. 4. The magnetic recording medium according to claims 1 to 3, wherein the water-insoluble polyester copolymer (A) is a polymer chain-extended with a diisocyanate compound. 5. The magnetic recording medium according to claims 1 to 4, wherein the polyester resin (D) is a polymer chain-extended with a diisocyanate compound.