JPS60121515A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which excels in the wear resistance with drop of powder and has no adhesion between a back-coat layer and a magnetic layer when these layers has a contact with each other, by using the benzoguanamine resin powder which is contained into the back-coat layer. CONSTITUTION:A back-coat layer is obtained by coating the dispersion suspension obtained by scattering the benzoguanamine resin powder into a solvent to a matter to be coated and adhering the resin powder to said matter by a reaction group of the resin, etc. or made of at least the binder resin and the benzoguanamine resin powder. The benzoguanamine resin is used in the form of powder having preferably the maximum grain size of <=2.0mum. The back-coat layer containing the benzoguanamine resin powder can improve its adhering power and has high drape performance to the binder resin to secure more intensive adhesion within the back-coat layer. Thus the resin powder is never dropped even in case a guide pole rubs the back-coat layer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium, and particularly to a magnetic tape having a magnetic layer on the surface of a support and a bank coat layer on the back surface thereof, and to improve the runnability and runnability of the bank coat layer. Concerning products with improved durability.

BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields. Among these, for example, regarding magnetic tape in the video field, when recording and playing back images, the cassette is loaded into the video deck, and the tape is attached to a guide pole or guide roller. While being guided and traveling, the magnetic head rubs and scans the magnetic head. In order to record images on magnetic tape or reproduce them in this way, in order to improve the sensitivity, especially the output in the high frequency range, the sliding condition of the magnetic tape against the magnetic head should not fluctuate. The surface of the magnetic layer is finished smooth. However, when this magnetic tape is run on a videoden, the front and back sides of the magnetic tape are rubbed by the guide poles and guide rolls, so the magnetic layer on the front side has good susceptibility to the guide poles and guide rolls. If the sliding part of the back side of the magnetic tape that is rubbed against these surfaces is not good, excessive tension will be applied to the running magnetic tape, and this will cause the magnetic layer to rub against the magnetic head excessively. Therefore, not only damage to the magnetic layer and peeling of magnetic powder in the magnetic layer occur, but also
The strength of the winding tension on the magnetic tape fluctuates, causing fluctuations in the spinal pressure, resulting in uneven running of the tape when it is reused. When these things happen, skew, jitter,
Images such as S/N or electromagnetic characteristics deteriorate. Therefore, a bank coat layer is provided on the back side of the magnetic tape.

As mentioned above, this bank coat layer has been devised to improve its sliding properties on guide poles and guide rolls, and one of these devises includes incorporating an inorganic powder into the resin layer. This is done by roughening the surface of the bank coat layer to reduce the contact area with gaitol and the like, thereby reducing the coefficient of friction. For example, JP-A-57-130234, JP-A-58 -161135
No. 1, JP-A-57-53825, JP-A-58-
No. 2415 all show examples using amorphous powder, and many of these also show those with limited particle sizes.

However, even those using these inorganic powders not only do not provide sufficient slipperiness, but also the bonding force of the particles to the binder to resist when the bank coat layer containing them is rubbed is insufficient. Easy to fall,
Particularly when large particles are mixed in, powder fall-off is more likely to occur, and when the magnetic layer and bank coat layer come into contact when the magnetic tape is wound, the protrusions on the back coat layer may damage the magnetic layer. The unevenness is also transferred to the magnetic layer, and when the magnetic layer is scanned to reproduce an image, it may impair electromagnetic characteristics such as chroma S/N, which indicates the degree of color noise in the image.

This is because, in general, inorganic powders not only have a wide variety of particle shapes and are not constant, but also have a wide distribution of particle sizes. In general, when the particle shape is spherical, the particles tend to be arranged regularly, and if these particles are arranged regularly on the surface of the back coat layer, when the bank coat layer contacts, for example, a guide pole, these particles will make point contact, reducing the coefficient of friction. In addition, when the particle size distribution of the particles is narrow, even if the average particle size is the same, particularly large particles will not be mixed in, but this is difficult to expect in the case of inorganic powder. Therefore, when inorganic particles are used, it is desirable to use particles with a relatively large particle size in order to make the surface of the back coat layer slippery. Ra is 0.010~0.0
26 μm, it is difficult to reduce the dynamic friction coefficient μ to 0.36 or less. Moreover, the center line maximum roughness Rm of cut off 0.08 mm is relatively high compared to spherical particles, which causes problems such as damaging the magnetic layer as described above. In the case of a back coat layer using inorganic powder, Ra is 0.017.
If μ is set to 0.37, Ra becomes 0.029 or more, and neither of the above target values can be satisfied at the same time. In this way, if the back coat layer cannot achieve the above target values of Ra and μ,
The above-mentioned chroma S/N may not be improved, and sufficient running performance of the magnetic tape cannot be obtained, and it is not possible to sufficiently prevent inorganic powder from falling off, abrasion, etc. Furthermore, when the magnetic tape is wound, interlayer adhesion may occur between the magnetic layer and the back coat layer that are in contact with each other.

In particular, recently, video equipment such as VH3 video movies and β movies have become smaller and more dense, making them easier to carry. As video recording is increasingly being carried out under various circumstances, it is hoped that magnetic tape will also be compatible with these conditions. In other words, the miniaturization and higher density of video equipment has made the path of the magnetic tape more complex, increasing the chances of the tape coming into contact with guide poles, guide rolls, etc., and increasing the frequency of friction, resulting in further improvements in running performance. There is a demand for improved wear resistance and durability to prevent powder falling off, etc.
For this purpose, it has been desired to realize the target values of Ra and μ.

In general, inorganic powders such as carbon blank, titanium oxide, and calcium carbonate have relatively good dispersibility in organic solvents among inorganic powders, but this is still insufficient, and the particles of these dispersions may aggregate. Also, if these dispersions are stored for a long period of time, the particles have a large specific gravity, and most of them, except for carbon blank, have a specific gravity of 2 to 4, so they may settle. There's a problem.

As mentioned above, conventional bank coat layers have problems associated with the use of inorganic powder, and improvements have been desired.

OBJECTS OF THE INVENTION The first object of the present invention is to provide a bank coat layer with excellent abrasion resistance so that the powder contained in the layer does not fall off, and to prevent glabella adhesion between the bank coat layer and the magnetic layer when they come into contact with each other. An object of the present invention is to provide a magnetic recording medium having a back coat layer having a unique back coat layer.

The second object of the present invention is to avoid increasing the surface roughness.
The object of the present invention is to provide a magnetic recording medium having a back coat layer that can have a small coefficient of dynamic friction, for example, l1a-0.010 to 0.026, and can have μ of 0.36 or less.

A third object of the present invention is to provide a magnetic recording medium having a back coat layer formed by coating with a coating liquid having dispersion stability.

Structure of the Invention The above object is achieved by using benzoguanamine resin powder as the powder contained in the bank coat layer.

Since this benzoguanamine-based resin is an organic substance, it is compatible with the binder, and therefore has a strong bonding force with the binder, so that it can increase the resistance when rubbed. This not only improves abrasion resistance and durability, but also improves the dispersion stability of the coating liquid used to form the bank coat layer, as it has good wettability with organic solvents and is less likely to settle due to its low specific gravity. . In addition, as a result of experiments, it is easy to disperse the particles using a ball mill, and the dispersed particles can be easily made into primary particles, and the variation in the particle size distribution of the particles can also be reduced, so the Ra does not need to be much larger than that of the above-mentioned inorganic powder. , friction coefficient μ
can be made smaller. As described above, the benzoguanamine resin powder has excellent properties not found in the above-mentioned inorganic powder, and the important point of the present invention lies in the novel use of this in place of the above-mentioned inorganic powder. Various functions can be effectively demonstrated.

From this, the magnetic recording medium of the present invention has a magnetic layer on one side of a support and a back coat layer on the other side of the support, in which the back coat layer is made of benzoguanamine-based resin. It is characterized by containing powder.

The bank coat layer in the present invention is formed by applying a dispersion suspension obtained by dispersing benzoguanamine resin powder in a solvent to an object to be coated, and coating the resin powder with the reactive groups of the resin powder. It is composed of something fixed to the coating body, or it is composed of at least a binder resin and benzoguanamine resin powder.

An example of benzoguanamine-based resin used in the present invention is a resin whose basic structure is derived from a compound having the following structure and formaldehyde through a condensation reaction, etc.
In addition to these, benzoguanamine resins manufactured from similar compounds having similar properties to the benzoguanamine resins described below are also included.

(2) This benzoguanamine resin is used in the form of powder, but the particles in the binder are preferably spherical for the reasons mentioned above. A mixture of different particles may be used.

The maximum particle size of the above penzigamine resin powder is 2.0 μm.
The following are preferable, and more preferably the average particle size is 0.
．． 02-Q, 5p, m. In this case, it is preferable for the particle size distribution to have little variation for the reasons mentioned above. However, particles with a wide particle size distribution may also be used, or two or more types of particle groups with different particle size distributions may be mixed and used.

A specific example of the benzoguanamine resin powder is Eposter S (manufactured by Nippon Shokubai Kagaku@).

If the bank coat layer contains a benzoguanamine resin, the strength of the resin will be weakened, which is undesirable, and if it is too small, the Ra value of the surface of the bank coat layer cannot be achieved. From this, it is appropriate to add 2 to 20% by weight of the binder resin.

The bank coat layer may further contain additives such as inorganic powders, which will be described later. A back coat layer made of a mixture of these components is formed by coating a dispersion described later on a support described later by a method described later, and the formed bank coat layer has an Ra of 0.010 to 0. 0
The thickness is preferably 26 μm, particularly 0.010 to 0.015 μm. Moreover, it is preferable that μ in this case be 0.36 or less.

Examples of inorganic powders used with the benzoguanamine resin powder include carbon blank, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Ftrd05, cruzi, kaolin, calcium sulfate, and boron nitride. , zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably having a function as a car pump.

The binder resin that can be used in the back coat layer includes thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and mixtures thereof.

The thermoplastic resin used as the binder resin has a softening temperature of 150°C or less and an average molecular weight of 10,000 to 20
0,000, 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 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 copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

These resins are disclosed in Japanese Patent Publications Nos. 37-6877 and 39-1.
No. 2528, No. 39-19282, No. 40-5349
No. 40-20907, No. 41-9463, No. 4
Nos. 1 to 14059, No. 41-16985, No. 42-6
No. 428, No. 42-11621, No. 43-4623, No. 43-15206, No. 44-2889, No. 44
-17947, 44-18232, 45-14
No. 020, No. 45-14500, No. 47-18573
No. 47-22063, No. 47-22064, No. 47-22068, No. 47-22069, No. 47-
22070, U.S. Patent No. 4B-27886, U.S. Patent No. 3.144.352, U.S. Pat.
It is stated in the specification of the No.

The thermosetting resin or reactive resin used is one that has a molecular weight of 200,000 or less in the state of a coating solution 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, phenol resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, vinyl chloride-vinyl acetate resin, meccrylate copolymer. and diisocyanate prepolymers, mixtures of high molecular weight polyester resins and isocyanate prepolymers, urea formaldehyde resins, mixtures of polyester polyols and isocyanate-1, polycarbonate-type polyurethanes, polyamide resins, low molecular weight glycols, high molecular weight diols, and triphenyl esters. mixtures of Kuntriisocyanates and mixtures thereof.

These resins are disclosed in Japanese Patent Publications Nos. 39-8103 and 40-97.
79 tatami volume No. 41-7192, No. 41-8016, No. 4
No. 1-14275, No. 42-18179, No. 43-1
No. 2081, No. 44-28023, No. 45-1450
No. 1, No. 45-24902, No. 46-13103,
No. 47-22067, No. 47-22072, No. 47
-22073, 47-28045, 47-28
No. 048, No. 47-28922, No. 58-4051,
Japanese Unexamined Patent Publication Nos. 57-31919 and 58-60430, Japanese Patent Application Nos. 151964-1980 and 58-1206
No. 97, No. 5B-120698, U.S. Patent No. 3
, No. 144.353, No. 3 320.090, No. 3,437.5'IO, No. 3, 597, 273
No. 3,781,210, No. 3.781,21
It is stated in each specification of No. 1.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, maleic anhydride type, urethane acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., or as a multifunctional upper layer, ether acrylic type, urethane acrylic type, phosphate ester acrylic type , aryl type, hydrocarbon type, etc.

Usable phenoxy resins include the following, which are desirable in terms of storage stability and abrasion resistance.

STX-04 (manufactured by Tobu Kasei Co., Ltd.: hydrogenated type) STX-05 (
(manufactured by Tobu Kasei Co., Ltd.: co-bonded type) PKHH (manufactured by UCC Co., Ltd.) Also, examples of epoxy resins include the following.

Araldite 6084 (Ciba Geigy: Bisphenol Δ type, average molecular weight 1740-2050) Araldite 6099 (Ciba Geigy: Bisfilm A type, average molecular weight 4800-8000) HCN-1273
(Manufactured by Ciba Geigy - Novolak type average molecular weight 1080
) Epicote 834 (manufactured by Shell: bisphenol A type,
Average molecular weight @410) Epicote 1004 (Shell Co., Ltd. 51: Bisphenol A type, average molecular weight 1600) Epicote 1007 (Shell Co., Ltd.: Bisphenol A
type, average molecular weight 2900) BP-4080 (manufactured by Layaseika Co., Ltd.: hydrogenated bisphenol A type) EPV-6 (manufactured by Layaseika Co., Ltd.: urethane modified) The above phenoxy resin and polyethylene resin are each used alone. It's fine, or you can use them together.

The following polyurethane resins can be used.

Acretan (Niacryl urethane manufactured by Fujikura Kasei Co., Ltd.) PS-
706 (Mitsui Nisso Urethane Co., Ltd.'s Nihard Type) PS-815 (Mitsui Nisso Urethane Co., Ltd.'s Nihard Type) MAD-2010 (Dainichiseika Chemical Co., Ltd. li!riN-302
2 (manufactured by Nippon Polyurethane Co., Ltd.) DN-3985 (manufactured by Nippon Polyurethane Co., Ltd.) Nissan 5701 (manufactured by Guttrich Co., Ltd.) PANDEX 78-8 (manufactured by Dainippon Ink Co., Ltd.) Furthermore, durability of the back coat layer of the magnetic recording medium according to the present invention In order to improve the hardening properties, the bank coat layer can contain various curing agents, such as isocyanate.

Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TO!), 4,4-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), mexylylene diisocyanate (MXDI), and combinations of these isocyanates with active hydrogen compounds. There are adducts, etc., and those having an average molecular weight in the range of 100 to 3,000 are suitable.

Specifically, Sumidur T80, Sumidur 44S, PP, L, Desmodur T65, 15, R1 RF, IL, and S manufactured by Bayer Urethane La4.
L; Trade name: Takenate 300S, manufactured by Takeda Pharmaceutical Co., Ltd., 5
00; Made by Mitsui Nisso Urethane Co., Ltd. Product name: rNDI J, [T
ODIJ; Product name: Desmodur T100, Millionate MR, Same Elbow, Coronate, manufactured by Nippon Polyurethane Co., Ltd.
Product name PAPI-135 manufactured by Kasei Upshun Co., Ltd.: T[
Products include 1165, 80, 100, Isonate 125M, and 1431.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (TM
DI) and adducts of these isocyanates and 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, Sumidur N1 Desmodur Z4273 manufactured by Sumidur Urethane Co., Ltd., Deeranate 50M, 24A-100, and 24 manufactured by Asahi Kasei Co., Ltd.
A-90CX, manufactured by Nippon Polyurethane Co., Ltd. (product name: Corone)
IIL, Hüls product name T? There are products such as IDI.In addition, examples of alicyclic isocyanates among aliphatic incyanates include methylcyclohexane-2,
4-diisocyanate (structural formula) (structural formula) Examples include isoborone diisocyanate and adducts of its active hydrogen compounds.

Specifically, product names IPDI and PDI manufactured by Huls Chemical Co., Ltd.
There are products such as -T1890, 11-2921, and 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. There is a pentamer consisting of 2 moles of hexamethylene diisocyanate, etc., which can be easily obtained industrially.

Of these isocyanates, for example, it is preferable to use aromatic isocyanates and aliphatic isocyanates together in view of the film properties of the bank coat layer.

In order to form the back coat layer of the magnetic recording medium of the present invention using these isocyanates, the binder resin shown in the above example □ and various additives described later as necessary are mixed and dispersed in an organic solvent to form a paint. The above-mentioned isocyanate (preferably an aromatic isocyanate and an aliphatic isocyanate) is added thereto and then applied onto a support such as a polyester film, and dried if necessary.

In this case, the amount of isocyanate added is preferably 5 to 15% by weight based on the binder. If it is less than 5% by weight, the coating film tends to be insufficiently cured, and if it is more than 15% by weight, the coating film becomes too hard, which is not preferable.

The above coating material may contain additives such as a dispersant, a lubricant, and an antistatic agent, if necessary. For example, dispersants include lecithin; fatty acids (R -COO) R represented by I is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms);
Alkali metals of the above fatty acids (Lt, Na, K, etc.)
Alternatively, metal soaps made of alkaline earth metals (MB, Ca, Ba, etc.) can be mentioned. In addition, the number of carbon atoms is 1
It is also possible to use two or more higher alcohols, and even sulfuric esters. 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 a lubricant, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, carbon atom number 12
Fatty acid esters (kola) having 21 to 23 carbon atoms made of a monobasic fatty acid and a monohydric alcohol as shown in Steps 6 to 6 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 benzoguanamine resin powder.

As scratch and antistatic agents, carbon black, graphite, tin oxide, antimony oxide compounds, and titanium oxide are used.
Conductive powders such as tin oxide-antimony oxide compounds;
Natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts,
Cationic surfactants such as pyridine and other heterocycles, phosphoniums or sulfonims; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid j-ster groups; amino acids, amino acids, etc. Examples include amphoteric activators such as smartphone acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above back coat paint or diluting solvents when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol. Ester cheeks such as monoacetate; ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane,
Ethers such as tetrahydrofuran; aromatic hydrocarbons such as henzene, toluene, and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polyamide and polycarbonate, metals such as Aj and Zn, glass, and BN. , Si carbide, ceramics such as porcelain, earthenware, etc. can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
In the case of a disk or card shape, the thickness is about 30 μm to 10+++ m, and in the case of a drum shape, it is cylindrical, and the shape is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the back coat layer.

Coating methods for forming a bank coat layer by applying the bank coat paint on the support include air doctor coat, blade coat, air knife coat, squeeze two 1-1 impregnation coat, reverse roll coat, and transfer roll coat. , gravure coat, kiss coat, cast coat, spray coat, etc. can be used, but are not limited to these.

The magnetic layer of the magnetic recording medium according to the present invention includes a binder resin, a dispersant, an antistatic agent, and a lubricant (0.2 to 100 parts by weight per 100 parts by weight of magnetic powder) used in the back coat layer.
20 parts by weight) etc. can be used. In addition, as magnetic powder, r
-Fe203, Go containing r-Fe20B, Co coated r-
Fe20B, Pe304, Co-containing Fa304. , ,
Oxide magnetic powder such as CrO2, Fe, Ni, C0%F
e-Nl-Co alloy, Fe-Mn-Zn alloy, Fe-N
j-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-G
o-Nj-P alloy, Co-Ni alloy etc. Fes, Nx,
Examples include various ferromagnetic powders such as metal magnetic powders containing Go as a main component. Abrasives can also be used in this magnetic layer, such as commonly used fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (seed components are corundum and magnetite). ), titanium dioxide, etc. are used.

These abrasives have an average particle size 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. The coating solvent and coating method for this magnetic layer are the same as those for the Hasokuko-1 layer described above.

Effects of the Invention As described above, the present invention contains benzoguanamine-based resin powder in the hack coat layer, so it is possible to improve the adhesion force within the layer. For example, when used together with a binder resin, Since it has good conformability and is firmly fixed within the layer, it is possible to reduce the amount of powder falling off even when the back coat layer is rubbed against, for example, a guide pole.

Further, benzoguanamine resin powder can be formed into spherical particles and its particle size distribution can have less variation, so when it is contained in a bank coat layer, Ra can be reduced and its friction coefficient μ can be reduced. This makes it possible to improve the slipperiness of the bank coat layer so that the magnetic tape can be wound evenly, and when the magnetic tape is wound, there is no unevenness on the magnetic layer that can cause trouble due to the unevenness of the back coat layer. The chroma S/N is not affected by this, and the surface of the magnetic layer is less likely to be damaged.

In addition, benzoguanamine resin powder is used as binder resin,
Since it has good dispersibility in organic solvents, it can improve the dispersion stability in the coating liquid, and can also contribute to improving productivity and saving energy.

EXAMPLES Next, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 A magnetic layer was previously coated on a polyethylene terecrate support as follows.

130 g of iron-based metal magnetic powder was added and mixed with 6 g of alumina into a solution of 4 g of phenoxy resin dissolved in 250 g of cyclohexanone, and the mixture was dispersed in a sand mill for 4 hours.

Next, 10 g of polyurethane and 0.0 g of butyl stearate.
05g, myristicin MO, 1g to cyclohexanone 1
A solution of 0 g and 100 g of tetrahydrofuran dissolved in a mixed solvent was mixed with the above dispersion, and further dispersed in a sand mill for 1 hour. To this dispersion, 3 g of Coronate as a hardening agent was added and mixed with stirring to prepare a paint. This coating material was applied onto a base film of polyethylene terephthalate under an orienting magnetic field, further dried, and the dried material was calendered.

Next, the composition of Example 1 shown in Table 1 was milled in a ball mill for 5 minutes.
A coating solution was prepared by kneading for hours. This coating solution was coated on the back surface of the support with a reverse roll and dried to form a back coat layer with a dry film thickness of 0.7 μm, which was then slit into 1/2 width to produce the magnetic tape of Example 1.

Example 2 A magnetic tape of Example 2 was prepared in the same manner as in Example 1 except that the composition of Example 2 in Table 1 was used instead of the composition of Example 1.

Comparative Example 1 In Example 1, the composition of Comparative Example 1 was used instead of the composition of Example 1 in Table 1, and this was
A magnetic tape of Comparative Example 1 was prepared in the same manner as in Example 1 except that the coating solution was prepared by kneading for 0 hours.

Comparative Example 2 A magnetic tape of Comparative Example 2 was prepared in the same manner as Comparative Example 1 except that the composition of Comparative Example 2 was used instead of the composition of Comparative Example 1 in Table 1. .

In Table 1, the numbers for the compositions indicate parts by weight; the polyester is Vylon 300 (manufactured by Toyobo ■), the nitrocellulose is Seltsuba (manufactured by Asahi Kasei ■), the polyisocyanate is Coronate (manufactured by Nippon Polyurethane ■), and the polyisocyanate is Coronate (manufactured by Nippon Polyurethane ■). The calcium is Homocal D (manufactured by Shiraishi Kogyo ■) with an average particle size of 0.3 μm, and the benzoguanamine resin is Nippon Shokubai Kagaku 1 m! l! Product Masterpiece Poster S (Average particle size 0.3
μm). In the table, the blending amounts of calcium carbonate and Epostor S differ in terms of weight, but in terms of volume, the former has a specific gravity of 2.
7.1 has a specific gravity of 1.2, so both are equal.

(Margins below this page) Table 1 Tests were conducted for each item shown in Table 2 for Examples 1 and 2 and Comparative Examples 1 and 2, and the results are shown in the corresponding columns of Table 2.

Here, the wear condition is the video deck (equipment name NV620).
0), each of the above magnetic tapes was passed 100 times, and the degree of abrasion of the bank coat layer was observed using an optical microscope.

If there was powder falling off, scratches would be visible on the surface of the bank coat layer, so it was evaluated based on whether this was more or less.

Tape damage was evaluated by visually observing the surface of the back coat layer of the magnetic tape that had been passed through the video deck 100 times, and evaluating whether there were many or few scratches. When abnormal tension is applied to the magnetic tape, large scratches occur on the bank coat layer (.

For cinching, the tape was run and wound using the above-mentioned video tape, and the winding appearance was evaluated as good if it was wound in an orderly manner, and bad if the tape-wrapped side surface was not flat and disordered.

Adhesion was tested by winding a 1/2 inch wide magnetic tape with a pressure of 1 kg in the same way as in the cinch test above, leaving it at 45°C and 80% relative humidity for 24 hours, then leaving it at room temperature for another 24 hours, then unwinding it. Those where there was resistance when pulling apart were evaluated as yes, and those where there was no were evaluated as none.

The coefficient of dynamic friction was measured using a rotating drum type surface property measuring device manufactured by Shinto Kagaku Co., Ltd. with a 4fi diameter Rondo at a load of 30 g and a rotation speed of 66.9 rpm.

The surface roughness was measured using a three-dimensional roughness measuring device 3E-3 manufactured by Koita Research Institute.
Measured using RK.

Table 2 From the results in Table 2, the bank coat layers of the magnetic tapes of the examples of the present invention are comparative examples (Example 1 and Comparative Example 1, Example 2 and Comparative Example 2) in which the surface roughness Ra and Rmax correspond to each other. It can be seen that the surface roughness and friction coefficient are both lower than those of the corresponding comparative examples. Note that when the tape of this example was wound, there were no scratches on the magnetic layer, and the chroma S/N of this magnetic layer was also good.

In addition, Figure 9 shows the results of a dispersion test in which the compositions of Example 1 and Comparative Example 1 in Table 1 were kneaded and dispersed in a ball mill. The size of the dispersed particles was evaluated by microscopic observation on a five-point scale (5 being the best and 1 being the worst).

As a result, it can be seen that the dispersibility of this example (curve a) is far superior to that of the corresponding comparative example (curve b).

[Brief explanation of drawings]

The figure is a graph showing the results of a dispersibility test of a coating liquid for a single layer of Hasokuko-1 for magnetic recording media of the present invention. Procedures on December 6, 1982? City official letter (spontaneous) February 22, 1980 Director of the Japan Patent Office Kazuo Wakasugi 1, Indication of the case 1982 Patent Application No. 229035 2, Name of the invention Magnetic recording medium 3, Person making the amendment Case and Relationship: Patent applicant 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo (227) Roku Konishi Photo Industry Co., Ltd. Representative Keio Ide 4, Agent 5 Date of amendment order Voluntary 6 Number of inventions increased by amendment None 7. Target of amendment: "Detailed description of the invention column in the specification" 8. Contents of amendment (1) In the 10th line of page 2 of the specification, the words "...have been finished. However" , “...
・It is finished. The magnetic layer is designed to have improved runnability and durability with respect to magnetic heads, guide rollers, and the like. But,” he corrected. (2) On page 16, lines 10 and 11 of the specification, "Bisfilm A type" is corrected to "Bisphenol A type." (3) On page 16, line 14 of the specification, ``Epicor 1-834 J'' is corrected to ``Epicor 834''. (In Book 41, page 26, line 19, the phrase "same as the case of a layer" is replaced with "same as the case of a layer." (5) In the 8th line of page 29 of the specification, the phrase ``1/2 width'' is corrected to ``1/2 inch width.'' ( 6) In the 6th line from the bottom of page 31 of the specification, the phrase ``as shown in the corresponding column of Table 2'' is replaced with ``as shown in the corresponding column of Table 2.'' Examples 3 to 4 Example 1.2 In each case, magnetic tapes of Example 3.4 were prepared in the same manner except that the composition of the paint for each magnetic layer was changed to the following composition, and these were also evaluated in the same manner as in Example 1.2. Similarly, favorable results were obtained. Iron-based metal magnetic powder 130 g Phenoxy resin 14 g Alumina 6 g Polyurethane 10 g Coronate L 3 g Butyl stearate 0.05 g Myristin @ 0.1 g Cyclohexanone 260 g Tetrahydrofuran 100 g Example 5~ 6 Magnetic tapes of Examples 5 and 6 were prepared in the same manner as in Examples 1. and -21, except that the composition of the coating material of the magnetic layer was changed to the following composition, and these tapes were also prepared in the same manner as in Example 1. The same evaluation as in 2 was conducted, and the same favorable results were obtained. Co-coated γ-Fe203 130 g Vinyl chloride vinyl acetate copolymer 15 g Alumina 6 g Polyurecne 25 g Coronate L 10 g Butyl stearate 0.05 g Myristic acid 0.1 g Cyclohexanone 260 g Tetrahydrofuran 100 g Correct.

Claims (1)

[Claims] (1) A magnetic recording medium having a magnetic layer on one side of a support and a back coat layer on the other side of the support, characterized in that the back coat layer contains benzoguanamine resin powder. magnetic recording medium.