JPH0510731B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a magnetic recording medium, and more specifically to a coated type magnetic recording tape in which curling is prevented by heat treatment during manufacturing. BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes and magnetic sheets are widely used in the audio field for recording sound and the video field for recording images. Among the magnetic recording media used in these various fields, thin-film magnetic recording media made by vapor-depositing ferromagnetic metals are often used due to their high recording density; however, they are easily scratched on the surface. However, since the durability is insufficient, coating type magnetic recording media containing a binder resin in the magnetic layer are also often used. This coated type magnetic recording medium is produced by coating a magnetic coating mainly consisting of magnetic powder, a binder resin, and a solvent on a support such as a polyester film.
A magnetic layer is formed by drying, which is then usually calendered to smooth the surface of the magnetic layer.
However, after manufacturing, for example, a magnetic recording tape is curved toward the magnetic layer, causing so-called curling (cutting). If this curl occurs, for example, when this magnetic recording tape is used as a video tape, it may lack running stability on a video deck, or winding irregularities may occur when it is wound onto a reel. These tend to cause the edges of the tape to break, ie, so-called edge folds, and also cause problems in recording and reproducing video images. In addition, when the tape curls, the entire surface of the tape does not come into good contact with the head, which affects the electromagnetic characteristics of the video tape, i.e. jitter, which indicates image flickering, and chroma S/S, which indicates color noise.
N etc. gets worse. There are various causes of curling in the magnetic recording medium. For example, the ratio of the thickness of the support to the magnetic layer, the nature and amount of the binder resin contained in the magnetic layer, the curing speed if it is curable, the solvent used in the coating material that forms the magnetic layer, etc. Examples include the amount of this solvent remaining in the binder. Among these causes, the thicker the magnetic layer is, the harder the binder resin is,
The faster the curing speed is, the more easily the coated magnetic layer shrinks than the support, such as a polyester film, and the more affinity the solvent has for the support, such as a polyester film, the easier this film will be to stretch. As a result, the magnetic recording tape will curl a lot. In order to prevent such curling of magnetic recording media, a so-called back coat, in which a coating layer made of a resin film is provided on the back side of a support, has conventionally been used. This is because shrinkage during the formation of the magnetic layer is offset by a back coat layer that shrinks in the same way from the opposite side of the support, thereby preventing the resulting tape from curling as a whole. However, for example, when forming a 2.5μ magnetic layer on a 10μ polyester film, the back coat layer is usually 1μ or less, and this thickness may not be able to offset the shrinkage of the magnetic layer. . In particular, trends in magnetic recording technology in recent years include, for example, the use of compact cassettes in the audio tape field is transitioning to the use of microcassettes, and in the video field there is a shift from the current VHS and β formats to 8 mm video and electronic cameras. For example, the thickness of magnetic tape tends to become thinner, and for this purpose, the magnetic layer needs to have a higher recording density. The trend is to use highly ferromagnetic metal powder to exhibit the desired electromagnetic properties with a thin magnetic layer, and to thin the polyester film used as the support, for example, from the current approximately 10μ to approximately 7μ. For this reason, the thickness of the back coat layer cannot be increased, and the fact is that curling of the finished magnetic recording tape is even more likely to occur as the support becomes thinner. For this reason, it has been desired to develop a good method for preventing curling in coated magnetic recording media. OBJECT OF THE INVENTION An object of the present invention is to provide a method for preventing curling during the manufacture of coated magnetic recording media. Structure of the Invention In order to achieve the above object, the present inventor conducted extensive research and found that, for example, the curl of a magnetic recording tape formed by coating a magnetic layer on a polyester film is
The inventors have discovered that by heating this tape, particularly by heating the polyester film, the support film can be more effectively shrunk, thereby preventing the magnetic recording tape from curling. From this, the method for manufacturing a magnetic recording medium of the present invention includes a calendering step, and then a magnetic recording medium having a magnetic layer containing ferromagnetic powder and a binder resin on a support. It is characterized by having a heating step of heating at least the latter of the layer side and the opposite side by bringing a heating roll at a temperature higher than the calendering temperature and 90° C. or higher into contact with the layer side and the opposite side. The magnetic recording medium manufactured according to the present invention has a first
As shown in the figure, a magnetic layer is coated on the support,
The magnetic layer is then subjected to calender treatment, usually at a temperature of 85° C. or lower, to smooth the surface of the magnetic layer. In this way, a base film for heat treatment is completed. Thereafter, the base film for heat treatment is heat treated and then a back coat layer is provided on the support, or conversely, a back coat layer is first provided and then heat treated. In this heat treatment, heated rolls are brought into contact with each other. For example, as shown in FIG. 2, a method of bringing the base film 4 for heat treatment into contact with heated heat rolls 1, 2, and 3 may be mentioned. A heat roll may be brought into contact with the magnetic layer, but
A method in which a heat roll is brought into contact with at least the opposite side of the magnetic layer, that is, the back surface of the support or, if there is a back coat layer, is preferred because heat can be transferred well to the support. A method that can directly supply heat is preferred. When using a heat roll in this way, the temperature applied to the heat roll is 90℃.
The temperature is preferably ~150°C, and the contact time of the base film for heat treatment at this time is determined by its conveyance speed.
In the case of ~100 cm, preferably 5 ~ 200 m/min is exemplified. To form the above-mentioned magnetic layer, a paint containing ferromagnetic powder, a binder resin, and a solvent as described below and additives as described later is used, and this paint is applied and dried by the coating method described below. The back coat layer is used to suppress curling on the magnetic layer side of the support.
Contains resin as a main component, and additives and other lubricants that roughen the surface to reduce friction when the magnetic recording medium is used as a tape and is rubbed against, for example, the guide roll of a video deck. Contains auxiliary agents such as agents. These back coating resins and auxiliary agents are those described below, and any of these paints are applied by the coating method described below. These magnetic layers and back coat layers are coated on both sides of the support, which will be described later, and the thickness ratio between these layers and the support varies depending on the resin used for each layer, but usually The back coat layer is often used in the range of 0.5μ to 1.0μ and the support in the range of 12μ to 16μ. The ferromagnetic powder that can be used for the above magnetic layer is γ-
Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Co-coated γ-Fe ₂ O ₃ ,
Oxide magnetic powder such as Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ ,
Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-Zn
alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy,
Examples include various ferromagnetic powders such as metal magnetic powders containing Fe, Ni, and Co as main components, such as Fe-Al alloy and Fe-Al-Cu alloy. The binder resin that can be used in the magnetic layer includes thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and mixtures thereof. Thermoplastic resins used as binder resins have a softening temperature of 150℃ or less and an average molecular weight of 10,000~
200,000, with a degree of polymerization of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer,
Methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer , polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic ester copolymer, amino resin, various synthetic rubber-based thermoplastic resins, and mixtures thereof. These resins are disclosed in Japanese Patent Publications No. 37-6877 and No. 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-
No. 20907, No. 41-9463, No. 41-14059, No. 41-
No. 16985, No. 42-6428, No. 42-11621, No. 43-
No. 4623, No. 43-15206, No. 44-2889, No. 44-
No. 17947, No. 44-18232, No. 45-14020, No. 45
-14500, 47-18573, 47-22063, 47-22063, 47-18573, 47-22063,
No. 47-22064, No. 47-22068, No. 47-22069,
Publications No. 47-22070 and No. 48-27886, U.S. Patent No. 3144352, U.S. Patent No. 3419420, U.S. Patent No. 3499789,
It is described in the specification of the same No. 3713887. As the thermosetting resin or reactive resin, one is used that has a molecular weight of 200,000 or less in the state of a coating liquid and becomes insolubilized by a reaction such as condensation or addition after coating and drying. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenolic resin, epoxy resin, polyurethane curable resin, urea resin,
Melamine resin, alkyd resin, silicone resin,
Acrylic reaction resin, vinyl chloride-vinyl acetate resin, mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of high molecular weight polyester resin and isocyanate prepolymer, urea formaldehyde resin, mixture of polyester polyol and isocyanate, polyamide resin, These include mixtures of low molecular weight glycols, high molecular weight diols, triphenylmethane triisocyanate, and mixtures thereof. These resins are listed in Special Publication No. 39-8103 and No. 40-9779.
No. 41-7192, No. 41-8016, No. 41-14275,
No. 42-18179, No. 43-12081, No. 44-28023,
No. 45-14501, No. 45-24902, No. 46-13103,
No. 47-22067, No. 47-22072, No. 47-22073,
Publications No. 47-28045, No. 47-28048, No. 47-28922, U.S. Patent No. 3144353, U.S. Patent No. 3320090
No. 3437510, No. 3597273, No. 3597273, No. 3437510, No. 3597273, No.
It is described in each specification of No. 3781210 and No. 3781211. Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, polyester acrylic type,
Polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., and polyfunctional monomers include ether acrylic type, urethane acrylic type, phosphate ester acrylic type, karyl type, hydrocarbon type, etc. Among these, phenoxy resins, epoxy resins and polyurethane resins are preferred for use with ferromagnetic metal powder. Phenoxy resin is suitable as a dispersion medium for metal magnetic powder because
For example, high molecular weight polyhydroxy ether made from bisphenol A and epichlorohydrin. To explain, this material is chemically stable and does not easily decompose even with metallic magnetic powder. Furthermore, since it has a high concentration of hydroxyl groups along the main chain, it has excellent dispersibility of magnetic powder and excellent crosslinking properties. In addition, when it is included as a binder in a magnetic layer, it can provide appropriate softness, and the liquid phase does not change suddenly to a solid phase even with a slight temperature change, so the mechanical properties of the surface do not change. It is possible to provide a magnetic layer with excellent surface properties. It is particularly preferable to use phenoxy resin in combination with polyurethane. Usable phenoxy resins include the following, which are desirable in terms of storage stability and abrasion resistance. STX-04 (manufactured by Toto Kasei Co., Ltd.: hydrogenated type) STX-05 (manufactured by Toto Kasei Co., Ltd.: co-bonded type) PKHH (manufactured by UCC Co., Ltd.) Also, the following epoxy resins are mentioned. Araldite 6084 (Ciba Geigy: Bisphenol A type, average molecular weight 1740-2050) Araldite 6099 (Ciba Geigy: Bisfilm A type, average molecular weight 4800-8000) ECN-1273 (Ciba Geigy: Novolak type average molecular weight 1080) Ebicoat 834 (manufactured by Ciel: Bisphenol A)
Type, average molecular weight 470) Epicote 1004 (manufactured by Ciel: Bisphenol A)
type, average molecular weight 1600) Epicote 1007 (manufactured by Ciel: Bisphenol A)
type, average molecular weight 2900) EP-4080 (manufactured by Asahi Denka Co., Ltd.: Hydrogenated bisphenol A
Type) EPV-6 (manufactured by Asahi Denka Co., Ltd.: urethane modified) The above phenoxy resin and epoxy resin may be used alone or in combination. The following polyurethane resins can be used. Acrethane (manufactured by Fujikura Kasei Co., Ltd.: Acrylic urethane) PS-706 (manufactured by Mitsui Nisso Urethane Co., Ltd.: hard type) PS-815 (manufactured by Mitsui Nisso Urethane Co., Ltd.: hard type) MAU-2010 (manufactured by Dainichiseika Co., Ltd.) N -3022 (manufactured by Nippon Polyurethane Co., Ltd.) DN-3985 (manufactured by Nippon Polyurethane Co., Ltd.) Estan 5701 (manufactured by Gutsutoritsuchi Co., Ltd.) PANDEX 78-8 (manufactured by Dainippon Ink Co., Ltd.) Furthermore, to improve the durability of the magnetic recording medium according to the present invention Various hardening agents can be contained in the magnetic layer etc., for example, isocyanate can be contained. Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), and combinations of these isocyanates with active hydrogen compounds. There are adducts, etc.
The average molecular weight is preferably in the range of 100 to 3000. Specifically, the product names Sumidyur T80, Sumidyur 44S, Sumidyur PF, Sumidyur L, Desmodyur T65, Sumidyur 15, Sumidyur R, Sumidyur RF, Sumidyur IL, manufactured by Sumitomo Bayer Urethane Co., Ltd.
Same SL; Trade name: Takenate 300S, manufactured by Takeda Pharmaceutical Co., Ltd.
500; Product name “NDI” manufactured by Mitsui Nisso Urethane Co., Ltd.
"TODI"; Product name: Desmodyur T100, Millionate MR, MT, Coronate L, manufactured by Nippon Polyurethane Co., Ltd.; Product name: PAPI-, manufactured by Kasei Atupjiyun Co., Ltd.
135: TD165, TD 80, TD 100, Isocyanate
Products such as 125M and 1431 are listed. On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TMDI), and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred. Specifically, for example, Sumidyur N, Desmodyur Z4273, manufactured by Sumitomo Bayer Urethane Co., Ltd.
Asahi Kasei product name Duuranate 50M, 24A−
There are products such as 100, 24A-90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd., and TMDI manufactured by Hyurus Co., Ltd.Also, among aliphatic isocyanates, alicyclic isocyanates include, for example, methylcyclohexane-2,4- Diisocyanate 4,4-methylenebis(cyclohexyl isocyanate) Examples include isophorone diisocyanate and adducts of active hydrogen compounds thereof. Specifically, the product name IPDI manufactured by Hyurus Chemical Co., Ltd.
There are products such as PDI-T1890, PDI-T1890, PDI-H-2921, and PDI-B1065. Examples of the adduct of the above-mentioned isocyanate and an active hydrogen compound include an adduct of a diisocyanate and a trivalent polyol. Polyisocyanates can also be used as curing agents, including, for example, a pentamer of diisocyanate, a decarboxylation compound of 3 moles of diisocyanate and water, and the like. Examples of these include an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, a pentamer of tolylene diisocyanate, and 3 moles of tolylene diisocyanate. and 2 moles of hexamethylene diisocyanate, and these can be easily obtained industrially. Among these isocyanates, it is preferable to use aromatic isocyanates and aliphatic isocyanates in combination, for example, from the viewpoint of film properties of the magnetic layer. In order to create the magnetic recording medium of the present invention using these isocyanates, a magnetic paint is prepared by mixing and dispersing the binder resin exemplified above and various additives as necessary, which will be described later, in an organic solvent. The above-mentioned isocyanate (preferably aromatic isocyanate and aliphatic isocyanate) is added to the mixture, and the mixture is coated onto a support such as a polyester film, and dried if necessary. In this case, the amount of isocyanate added is 5
~35% by weight is preferred. If it is less than 5% by weight, the coating film tends to be insufficiently cured, and if it is more than 35% by weight, the coating film becomes too hard, which is not preferable. The magnetic paint may contain additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent other than the carbon black, if necessary. For example, other dispersants that may be used in combination include lecithin; caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid,
Fatty acids having 8 to 18 carbon atoms such as elaidic acid, linoleic acid, and linolenic acid (R-COOH, where R is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); Alkali metals (Li,
Na, K, etc.) or alkaline earth metals (Mg, Ca, etc.)
Examples include metal soaps made of Ba, etc.). In addition, higher alcohols having 12 or more carbon atoms, sulfuric esters, etc. can also be used. Moreover, commercially available general surfactants can also be used.
These dispersants may be used alone or in combination of two or more. In addition, as lubricants, silicone oil, graphite,
Molybdenum disulfide, tungsten disulfide, and fatty acid esters (waxes) having 21 to 23 carbon atoms made of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the magnetic powder. In addition, commonly used abrasives include fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main ingredients are corundum and magnetite), titanium dioxide, etc. .
These abrasives have an average particle diameter of 0.05 to 5 .mu.m, particularly preferably 0.1 to 1 .mu.m. These abrasives are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic powder. Also,
Antistatic agents include graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide
Conductive powder such as antimony oxide compounds; Natural surfactants such as saponin; Nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts, pyridine, and other complexes Cationic surfactants such as rings, phosphoniums, or sulfoniums; anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, and phosphoric ester groups; Examples include amphoteric activators such as sulfuric acid or phosphoric acid ester. In addition to these, as a preferable antistatic agent, it is effective to incorporate carbon black into the magnetic layer. Examples of such carbon black include Conductex 975 (specific surface area 270 m ² /g, particle size 46 mμ), Cabot Vulcan XC-72 (specific surface area 257 m ² /
g, particle size 18 mμ), etc. can be used. Carbon black is also used to adjust the running of the tape by detecting the difference in light transmittance between the tape part with the magnetic layer and the leader tape part, as in some types of video tapes. As carbon black, Columbia Carbon Co.'s Raven 2000 (specific surface area 180 m ² /g, particle size 19 m
μ), 2100, 1170, 1000, #100 manufactured by Mitsubishi Kasei Corporation,
#75, #44, #40, #35, #30, etc. are available. The mixing ratio of the carbon black to the binder is 5 to 35% by weight, preferably 10 to 25% by weight. Examples of the resin for the back coat layer include polyurethane, nitrocellulose, and polyisocyanate. Additives contained in this back coat layer include surface roughening agents such as CaCO ₃ , carbon black, and TiO ₂ , lubricants such as stearic acid, myristic acid, butyl stearate, butyl palmitate, and carbon black. There are antistatic agents. Solvents to be blended in the above magnetic paints and back coat paints or diluting solvents during application of these paints include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, Esters such as ethylene glycol monoacetate; ethylene glycol dimethyl ether, diethylene glycol monoethyl ether,
Ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene can be used. Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Al, Zn, glass, BN,
Ceramics such as Si carbide, porcelain, and earthenware can also be used. The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
30 μm to 10 in the case of disks and cards.
mm, and in the case of a drum shape, it is used in a cylindrical shape, and its shape is determined depending on the recorder used. An intermediate layer for improving adhesion may be provided between the support and the magnetic layer, or between the support and the back coat layer, and an overcoat layer may be provided on the magnetic layer. Coating methods for forming a magnetic layer by coating the magnetic paint and back coat paint on the support include air doctor coating, blade coating,
Air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, etc. can be used, but are not limited to these. Effects of the Invention As explained above, according to the present invention, after calendering is performed during the production of a coated magnetic recording medium, at least the latter of the magnetic layer and the opposite side is heated to a temperature higher than the calendering temperature and 90°C. Since a heat treatment step is provided in which the support is heated by contacting it with a heating roll having a temperature of .degree. C. or higher, the support curled toward the magnetic layer shrinks and the curl is corrected. especially the thickness
In the case of a thin support of around 10 μm, curling tends to occur, but this can also be well corrected. This prevents the lack of running stability caused by curling of the magnetic recording medium, the uneven winding on the reel, and the bending of edges, making it easier to handle, and preventing excessive force from being applied to the magnetic layer, thereby improving its durability. can be maintained.
Furthermore, as a result of being able to prevent the magnetic recording medium from curling in this way, it is possible to improve the electromagnetic conversion characteristics, ie, jitter, chroma S/N, envelope, etc., when it is used as a video tape, for example. In this way, it is possible to provide a magnetic recording medium that can meet the recent demands for miniaturization and higher density in the audio and video fields. Examples Next, examples of the present invention will be described, but the present invention is not limited thereto. Example 1 Co-coated γ-Fe ₂ O ₃ 65 parts by weight Vinyl chloride vinyl acetate copolymer (VMCH, manufactured by Union Carbide) 12 parts by weight Polyurethane (N-2304, manufactured by Nippon Polyurethane) 14 parts by weight Lecithin 2 parts by weight 50 parts by weight Methyl ethyl ketone 45 parts by weight Toluene 45 parts by weight Cyclohexanone 110 parts by weight The above formulation was mixed in a ball mill for 72 hours.
After dispersion, 5 parts by weight of polyisocyanate is added and mixed uniformly to prepare a magnetic paint. This paint is applied to one side of a 12 μm thick polyethylene terephthalate film using a wire bar coater under a magnetic field of 2000 Gauss to a dry film thickness of 5 μm, and then dried. The material thus obtained is subjected to supercalender treatment at a surface temperature of approximately 80°C to produce a base film for heat treatment. Next, this base film for heat treatment was individually transferred to heat rolls (40 cm in diameter) with surface temperatures of 120°C, 130°C, and 140°C, and the polyethylene terephthalate film was conveyed at a speed of 100 on the side opposite to the paint application side.
A heat-treated base film was obtained by contacting at a speed of m/min. After this, each of these heat-treated base films was coated with 45 parts by weight of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) 240 parts by weight of CaCO ₃ 240 parts by weight of nitrocellulose (RS1/2, manufactured by Daicel Chemical Co., Ltd.) 35 parts by weight of polyurethane (as described above) ) 20 parts by weight of methyl ethyl ketone 240 parts by weight of cyclohexanone A mixture of 240 parts by weight of cyclohexanone was kneaded and dispersed for 72 hours using a ball mill, filtered through a 1 μ filter, and the filtrate was mixed with a polyfunctional isocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.). ) 10 parts by weight is applied to the side of the polyethylene terephthalate in contact with the heat roll using a wire bar coater and dried. In this way, a heat-treated base film with a back coat layer was obtained. The curvature (1/m) of a tape slit to a width of 12.65 mm was measured for each of the heat-treated base films with a back coat layer, and the brightness C/N (dB) was also measured. The results are shown in Figure 3 A and B. Note that the point on the lowest temperature side in the figure is a point where only calendering is performed and there is no heating step of the present invention. In addition, for magnetic tapes on which a back coat layer was provided without being heat treated with the above heat roll, the back coat layer was brought into contact with a heat roll with a surface temperature of 100°C under the same conditions as above, and as a reference example, a back coat layer was also prepared. Figure 4 shows the measurement results of the curvature and brightness C/N of magnetic tapes in which the magnetic layer side was brought into contact with heat rolls at surface temperatures of 110°C, 120°C, and 130°C under the same conditions as above. Shown in A and B. In FIG. 4, □ indicates the back coat layer in contact with the heat roll (a line), and Γ (small circles) indicates the magnetic layer in contact with the heat roll (b line). From these results, when a back coat layer is provided after heat treatment, the curvature becomes 0 and curl disappears at a treatment temperature of 140℃;
It can also be seen that curling is significantly reduced compared to those that were not heat-treated. Furthermore, it can be seen that even when a back coat layer is provided without heat treatment and the heat treatment is performed from above the back coat layer, the effect of preventing curling is significantly greater than when this heat treatment is performed from the magnetic layer side. Furthermore, it can be seen that since the brightness C/N does not deteriorate even after heat treatment, problems such as roughening of the surface of the magnetic layer do not occur. Example 2 A magnetic paint was prepared by milling the composition of the magnetic paint 1 in Table 1 (parts by weight are shown; the same applies hereinafter) using a ball mill for 72 hours. on one side
The coating was applied to a dry film thickness of 5 μm under a 2000 Gauss magnetic field. This was treated with a super calender at 80°C to smooth the surface to prepare a base film for heat treatment. Next, this film was transferred to a heat roll with a surface temperature of 140°C at a speed of 100.
The polyethylene terephthalate film side was brought into contact at m/min. Next, 50 parts by weight of Graphite, 50 parts by weight of polyurethane (Estan 5701, manufactured by Gutduritsu), and 300 parts by weight of methyl ethyl ketone were kneaded and dispersed for 72 hours using a ball mill.
Back coating paint 1 prepared by filtering through a 1μ filter and adding 10 parts by weight of a polyfunctional isocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) to the filtrate was applied to the polyethylene terephthalate film side using a wire bar coater to coat the dried coating film. but
This example 2 was coated and dried to a thickness of 1 μm.
created a magnetic tape. The curvature of this magnetic tape was measured in the same manner as above, and the results are shown in Table 2.

【table】

[Table] In Table 1, the materials used for each component are as follows. Iron oxide: Co-coated γ-Fe ₂ O ₃ Polyurethane: N-2304 (manufactured by Nippon Polyurethane Co., Ltd.) Phenoxy resin: PKHH (manufactured by Union Carbide Co., Ltd.) Nitrocellulose: RS1/2 (manufactured by Daicel Chemical Co., Ltd.) Salt/vinyl acetate: VMCH (manufactured by Union Carbide) Polyisocyanate: Coronate L (manufactured by Nippon Polyurethane)

[Table] Comparative Example 1 Comparative Example 1 was prepared in the same manner as in Example 2 except that the heat treatment was not performed.
A magnetic tape was obtained, and its curvature was measured in the same manner as in Example 1. The results are shown in Table 3.

[Table] Examples 3 to 7 Same as Example 2 except that instead of using magnetic paint 1 having the composition in Table 1, magnetic paints having the compositions 2 to 6 in Table 1 were used. By operating the magnetic tapes of Examples 3 to 7, respectively. The curvatures of these magnetic tapes were also measured in the same manner as in Example 1, and the results are shown in Table 2. Comparative Examples 2 to 6 Magnetic tapes of Comparative Examples 2 to 6 were prepared in the same manner as in Examples 3 to 7, except that the heat treatment was not performed, and the curvature of each of these was the same as in Example 1. The results measured in Table 3 are shown in ~. Example 8 In Example 2, instead of using back coat paint 1, the following composition was used as back coat paint 1.
A magnetic tape of Example 8 was prepared in the same manner as in Example 2 except that back coat paint 2 prepared in the same manner as in Example 1 was used, and its curvature was also measured in the same manner as in Example 1. The results are shown in Table 2. Compound of back coat paint 2 Carbon black 3% by weight Polyurethane (Estan 5701, manufactured by Nippon Polyurethane Co., Ltd.) 50% by weight Methyl ethyl ketone 300% by weight Examples 9 to 13 In Example 8, instead of using magnetic paint 1 in Table 1, each The procedure was the same as in Example 8 except that magnetic paints 2 to 6 were used, and Examples 9 to 13 were obtained, respectively.
Magnetic tapes were prepared and their curvatures were measured in the same manner as in Example 1. The results are shown in Table 2. Comparative Examples 7 to 12 Comparative Examples 7 to 12 were prepared in the same manner as in Examples 8 to 13, except that the heat treatment was not performed.
Magnetic tapes were prepared and their curvatures were measured in the same manner as in Example 1. The results are shown in Table 3. Example 14 In Example 2, a paint prepared using the formulation of magnetic paint 7 in Table 4 in the same manner as in Example 2 was used, a polyethylene terephthalate film of 10 μm was used as a support, and the dry film thickness of the magnetic paint was
Example 2 except that the coating was applied to a thickness of 3 μm.
A magnetic tape of Example 14 was prepared in the same manner as in Example 1, and its curvature was measured in the same manner as in Example 1, and the results are shown in Table 5. The metal powder in Table 4 has a specific surface area of 49 m ² /g, Hc = 1505, σs =
136 emu/g was used, and the other ingredients were the same as those in Table 1.

【table】

【table】

Claims (1)

[Claims] 1. A method for manufacturing a magnetic recording medium having a magnetic layer containing ferromagnetic powder and a binder resin on a support, including a calendering step, followed by calendering on at least the latter of the magnetic layer side and the opposite side. 1. A method for manufacturing a magnetic recording medium, comprising a heating step of heating by contacting with a heating roll having a temperature of 90° C. or higher.