JPH0533445B2 - - Google Patents

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 one side of a substrate via an undercoat layer, and a back coat layer is provided on the other side. By using a binder with extremely good dispersibility as one component for the lubricant in the back coat layer, the adhesion of the magnetic layer to the substrate is improved, and the other side lowers the coefficient of friction without reducing the S/N ratio. The present invention relates to a magnetic recording medium with improved running durability. <Relationship with Prior Art> Generally, in magnetic storage tapes for audio, video, or computers, the surface of the base film is finished to be smooth in order to improve the magnetic recording sensitivity of the tape. However, such a smooth magnetic recording tape is not wound in an orderly manner during winding and unwinding, and tends to wind randomly. If such magnetic tape is used, the running performance will deteriorate due to tension fluctuations, and the output will fluctuate.
The tape is also easily deformed and damaged. On the other hand, in response to higher performance magnetic recording, efforts are being made to increase the amount of magnetic powder packed. 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. In order to improve this, conventional methods have been adopted 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 primers, they are not completely satisfactory. On the other hand, in order to obtain a high-performance magnetic recording medium, a large Br/Bm value (squareness ratio, Br: residual magnetization,
Bm: saturation magnetization) and high filling properties, 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 lengthening the kneading time, but as the magnetic powder becomes more finely divided, the sensitivity of the magnetic tape will be adversely reduced. <Objective of the Invention> In view of the above circumstances, the present invention provides a magnetic storage medium which has good running properties, extremely good adhesion of the magnetic layer to the base film, and has a high packing density of magnetic powder in the magnetic layer. The purpose is to provide. <Structure of the Invention> The present invention provides at least one surface of a polyester film containing (A) residues of a mixed dicarboxylic acid in which 0.5 to 15 mol% of the total dicarboxylic acid components are dicarboxylic acids containing sulfonic acid metal bases and residues of glycol. Water-insoluble polyester copolymer mainly composed of (B) boiling point 60~
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 A polyester resin whose main components are residues of a mixed dicarboxylic acid in which 0.3 to 7.0 mol% is a dicarboxylic acid containing a sulfonic acid metal group and a residue of glycol.
A magnetizable layer containing fine powder particles uniformly dispersed in a binder containing at least one component of (D) is coated, and at least one component of polyester resin (D) is coated on the side surface of the diamagnetic layer of the polyester film. A magnetic recording medium has a coating film formed from a paint containing a lubricant dispersed in a binder, and the adhesion of the magnetic layer to the base film is extremely good, and the packing density of magnetic powder in the magnetic layer is They found that it has high performance and excellent running performance. The polyester copolymer (A) contained in the aqueous dispersion of the present invention is a mixture of 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 dicarboxylic acid with a polyol component. Substantially water-insoluble means that even if the polyester copolymer is stirred in hot water at 80°C, the polyester copolymer will not dissipate in the 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 sulfonic acid metal group-containing dicarboxylic acids 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 group-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 a polyester copolymer in water varies depending on the copolymer composition, the type of water-soluble organic compound, the blending ratio, etc., but the dicarboxylic acid containing a sulfonic acid metal base does not impair the dispersibility in water. As far as possible, a small amount is preferable. 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 aliphatic dicarboxylic acids include succinic acid, adibic acid, sebacic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid,
1,,3-cyclohexanedicarboxylic acid, 1,4
- Examples include 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 above 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, 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 polyether include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.
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 the polyester copolymer, water-soluble organic compound, and water are mixed together. There is a method in which they are allowed to coexist and stirred at 40 to 120°C. The above-mentioned water-soluble organic compound is an organic compound having a solubility in water of 1 of 20 g or more at 20°C, and specifically includes aliphatic and alicyclic alcohols, ethers,
Ester and ketone compounds, such as monohydric alcohols such as methanol, ethanol, isopropanol, and n-butanol, glycols such as ethylene glycol and propylene glycol, glycol derivatives such as methyl cellosolve, ethyl cellosolve, and n-butyl cellosolve, dioxane,
These include ethers such as 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 blending ratio of the above (A) polyester copolymer, (B) water-soluble organic compound, and (C) water is (A)/(B) = 100/20 to 5000 (B)/(C) = 100/50 It is important to satisfy ~10000. Compared to polyester copolymers, (A)/(B) has less water-soluble organic compounds.
When the ratio 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 (B)/(C) exceeds 100/50, the amount of water-soluble organic compounds in the aqueous dispersion increases and melt extrusion is difficult. During so-called in-line coating, in which an aqueous dispersion of the polyester resin is applied to an unstretched film or a uniaxially stretched film and then stretched, there is a risk of explosion due to the solvent, which requires explosion-proof measures. Since the cost is high, it is necessary to consider compound recovery. (B)／(C)
When the ratio is less than 100/10000, the surface tension of the aqueous dispersion increases, the wettability of 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, crosslinking 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 will decrease, and the amount of copolymerized polyester resin in the recovered and recycled film will increase, resulting in a decline in 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, the wettability and adhesion of the film surface can be improved by subjecting the polyester copolymer layer to a corona discharge treatment, a corona discharge treatment under a nitrogen atmosphere, an ultraviolet irradiation treatment, or the like. On the other hand, the dicarboxylic acid component of the copolymerized polyester resin (D) used as a component of the binder of the magnetic layer and the back coat layer in the present invention includes aromatic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1.5-naphthalic acid. dicarboxylic acid,
P-oxybenzoic acid, P-(hydroxyethoxy)
There are aromatic oxycarboxylic acids such as benzoic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid, but the molar ratio of the aromatic dicarboxylic acid component and the aliphatic dicarboxylic acid component The ratio is 50/50 to 100/0,
Moreover, it is desirable 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-1,3pepentanediol, 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, bifunctional isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenyl A polymer subjected to a chain extension reaction with methane diisocyanate, xylene isocyanate, or isophorone diisocyanate can be used. This method allows two types of copolymerized polyester resins to be combined to take advantage of their characteristics. In other words, 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, and improve the dispersibility of magnetic powder and 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. Furthermore, the lubricants used in the present invention include tungsten disulfide, molybdenum disulfide, boron nitride, SiO ₂ , CaCO ₃ , Al ₂ O ₃ , Fe ₂ O ₃ ,
Examples include TiO ₂ and BaSO ₄ . Among the above, SiO ₂ ,
CaCO ₃ , TiO ₂ and BaSO ₄ are preferred, and CaCO ₃ and BaSO ₄ are particularly preferred. When using these lubricants, particular attention must be paid to their size and hardness. Average particle size as size: 0.02~
It is preferably 0.5μ, particularly preferably 0.02 to 0.5μ. The hardness is preferably 2.5 or higher on the Mohs scale. The amount of these lubricants used is 0.1 by weight relative to the binder.
~4.0, preferably 0.1-2.5, particularly preferably 0.5
~1.5. Components other than polyester resin (D) used as binders for the magnetic layer and back coat layer include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, and acrylic acid ester. -Acrylonitrile copolymer, acrylic ester-
Acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-
Acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene copolymer, polyamide resin, Polyvinyl butyral, cellulose resin (cellulose acetate butyrate, nitrocellulose, cellulose diacetate, cellulose propionate, etc.), styrene, butadiene copolymer, chlorovinyl ether-acrylic acid ester copolymer, amino resin, phenolic resin , epoxy resin, polyurethane, hardening resin,
Examples include urea resins, melamine resins, alkyd resins, acrylic reactive resins, polyisocyanates, and polyaminones. The magnetic recording medium of the present invention may optionally contain plasticizers such as dibutyl phthalate and triphenyl phosphate, zinc stearate, soybean oil lecithin,
Lubricants such as silicone oil and various antistatic agents can also be added. When 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 lubricant particles, and which 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, isocyanate compounds, and melamine resins.
Among these, isocyanate compounds are particularly preferred. Various films have been proposed as the base film for magnetic storage media, but polyester film is superior in terms of mechanical properties, chemical resistance, heat resistance, etc. Among them, polyethylene terephthalate film is superior in terms of various properties. It is excellent. The surface roughness of the undercoat coated side and the anti-coat side of this polyester film is very important for reducing noise and preventing signal dropouts in the production of magnetic recording media, and the centerline average roughness ( _RA ) (Surfcom
Using a 300A type surface roughness meter (manufactured by Tokyo Seimitsu), measure the needle diameter.
(measured under the conditions of 1 μm, weight of 0.07 g, measurement reference length of 0.8 mm, and cutoff of 0.08 mm) is preferably 0.05 μm or less; if it exceeds 0.05 μm, noise and signal loss will occur, causing problems in use. In addition, the surface roughness of the coating film in which the lubricant is dispersed is very important in order to reduce noise and prevent signal loss when used as a magnetic tape, since the unevenness of the coating surface is transferred to the magnetic layer. Roughness (R _A ) (Using a Surfcom 300A surface roughness meter (manufactured by Tokyo Seimitsu), needle diameter 1 μm, weight 0.07 g, measurement reference length 0.8 mm,
(measured under the condition of cutoff 0.08 mm) is preferably 0.03 μm or less; if it exceeds 0.03 μm, noise and signal loss will occur, causing problems in use. Additives such as carbon black powder and graphite can be added to the coating film of the magnetic recording film of the present invention in which a lubricant is dispersed for antistatic purposes. <Effects of the Invention> As described above, when the magnetic recording medium obtained by the present invention is used for magnetic recording, the base of the magnetic layer has excellent adhesion to the film, and in the magnetic layer,
The magnetic powder has a high packing density, a low coefficient of friction during running, and excellent running durability. <Examples> The present invention will be specifically explained below using examples. In the examples, parts simply indicate parts by weight. In the adhesion test (beer bag method), an adhesive tape was pasted on the surface of the magnetic layer, the adhesive tape was adhered uniformly to the entire surface, and then the state was observed when it was instantly peeled off. The portion where the magnetic layer remains accounts for 95% or more of the total area ◎,
50-95% is indicated by ◯, 10-50% is indicated by △, and 10% or less is indicated by ×. The running durability test was 100 on a VHS video deck.
The coefficient of dynamic friction (at a running speed of 3.3 m/sec) on the coating film side in which the lubricant was dispersed was measured for the tape that was run repeatedly and the virgin tape that was not run. The reduced viscosity ηsp/C (dl/g) was measured at 30°C by dissolving 0.01 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. It was calculated from the specific volume of each contained component using the following formula: True specific volume = Σ(wi/pi)/Σwi wi blended weight of component i pi density of component i The smoothness of the magnetizable layer was visually determined. 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 0.2 mmHg) for 2 hours. 300 parts of this polyester copolymer and 140 parts of n-butyl cellosolve were mixed in a container at 150 parts
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 4500 parts of water and 4500 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 280-300℃, 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, and this uniaxially stretched film was subjected to corona discharge treatment, and then 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. (3) Production of copolymerized polyester resin (D) Add dimethyl terephthalate 175 to a reaction vessel equipped with a thermometer, stirrer, and partial reflux condenser.
parts, dimethyl isophthalate 78 parts, ethylene glycol 161 parts, neobentyl 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 copolymerized polyester resin (D) thus obtained was pale yellow and transparent with ηsp/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 Sepacic 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 copolymerized polyester resin (D) and 600 parts of cellosol 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 12μ thick biaxially stretched coated polyester film 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. (5) Method for forming a coating film with lubricant dispersed Copolymerized polyester resin (D) 50 parts Vinyl chloride vinyl acetate copolymer (manufactured by UCC, trade name
VAGH) 5 parts Nitrocellulose 10 parts Polyisocyanate 15 parts (manufactured by Nippon Polyurethane Co., Ltd., trade name Coronate L) A mixture of 70 parts of CaCO ₃ (average particle size 0.05μ) was kneaded and dispersed, and the mixture obtained in (2) above was applied. The coating film was dried to a thickness of 1 μm on a biaxially stretched coated polyester film having a thickness of 12 μm. Example 2 A magnetic tape 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 and 5 A magnetic tape was obtained in the same manner as in Example 2 except that the binder copolymer composition of the magnetic layer was changed. Example 4 A magnetic tape was obtained in the same manner as in Example 2 except that the composition of the back coat layer was changed. Comparative Examples 1 to 3 In Example 1, no undercoat was used, pentasodium sulfoisophthalic acid was deleted from the binder copolymer composition of the magnetic layer, or no back coat was used, respectively.
Otherwise, a magnetic tape was obtained in the same manner as in Example 1. Comparative example 4 Undercoat pentasodium sulfoisophthalate
A magnetic tape was obtained in the same manner as in Example 1 except that the amount was changed to 20 mol%. Comparative Example 5 A magnetic tape was obtained in the same manner as in Example 1 except that 10 mol% of pentasodium sulfoisophthalic acid was used in the magnetic layer binder. Comparative Example 6 A magnetic tape was obtained in the same manner as in Example 1 except that the polyester resin in the back coat layer was omitted. Comparative Example 7 A magnetic tape was obtained in Example 1 without using a back coat, but by changing the binder of the magnetic layer to VAGH (vinyl chloride-vinyl acetate copolymer). Comparative Example 8 A magnetic tape was obtained in Example 1 except that the binder of the magnetic layer was changed to VAGH without an undercoat or back coat. From Table 2, it can be seen that the method of the present invention provides magnetic tapes with higher performance than the comparative example.

【table】

【table】

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 polymerization ratio of 10,000, and on one side of the coating film (D) the reduced viscosity is 0.1 or more, and the total dicarboxylic acid component is A polyester resin whose main components are residues of a mixed dicarboxylic acid in which 0.3 to 7.0 mol% is a dicarboxylic acid containing a sulfonic acid metal group and a residue of glycol.
A magnetizable layer containing fine powder particles uniformly dispersed in a binder containing at least one component of (D) is coated, and at least one layer of polyester resin (D) is coated on the side surface of the diamagnetic layer of the polyester film. A magnetic recording medium on which a coating film is formed from a coating material in which a lubricant is dispersed in a binder component. 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 (R _A ) 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 centerline average roughness ( _RA ) of the surface of the coating film in which the lubricant is dispersed is 0.03 μm or less. 5. 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. 6. The magnetic storage medium according to claims 1 to 4, wherein the polyester resin (D) is a polymer chain-extended with a diisocyanate compound.